MCAT

Abstract: Vivimos en una sociedad que demanda cantidades importantes de agua para su uso en numerosas actividades, por lo que la extracción de caudales de su ámbito natural de circulación es algo natural. En este libro se analizan los nuevos tratamientos y tecnologías que actualmente se llevan a cabo para el tratamiento en el ciclo del agua.

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Abstract: Microwave heating can be used to promote heterogeneous reactions with carbon materials, mainly because of the heating mechanism involved in microwave radiation and the phenomenon known as microplasmas. This work presents photographic evidence of plasma formation when different carbon materials are subjected to microwave heating. Two different kinds of plasmas were observed: ball lightning and arc discharge plasmas. The intensity of the plasmas in the less ordered carbon was significantly higher at the beginning of the process. © 2010 Elsevier Ltd. All rights reserved.

Abstract: Symmetric supercapacitors (SSC) and asymmetric supercapacitors (ASC) that use carbon xerogels with different porous textures as negative electrode and manganese oxide as positive electrode were investigated. The electrochemical performance of symmetric supercapacitors with carbon xerogel electrodes was mainly influenced by the textural characteristics of the carbon, pore size distribution being the property that has the strongest influence on the capacitance performance. The asymmetric supercapacitor showed an excellent capacitance performance (i.e. 213 F g�1) when a chemical activated carbon xerogel with a high SBET (i.e. 2360 m2 g�1) was used as negative electrode and high performing oxide-based manganese as positive electrode, thereby demonstrating that carbon xerogels and manganese oxide have potential applications in supercapacitor devices.

Abstract: The decomposition and CO2 reforming of methane, respectively, are promising alternatives to industrial steam methane reforming. In recent years, research has been focused on the development of catalysts that can operate without getting deactivated by carbon deposition, where, in particular, carbon catalysts have shown positive results. In this work, the role of carbon materials in heterogeneous catalysis is assessed and publications on methane decomposition and CO2 reforming of methane over carbon materials are reviewed. The influence of textural properties (BET surface area and micropore volume, etc.) and oxygen surface groups on the catalytic activity of carbon materials are discussed. In addition, this review examines how activated carbon and carbon black catalysts, which are the most commonly used carbon catalysts, are deactivated. Characteristics of the carbon deposits from methane are discussed and the influence of the reactivity to CO2 of fresh carbon and carbonaceous deposits for high and steady conversion during CO2 reforming of CH4 are also considered. © 2011 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences.

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Abstract: Resorcinol-formaldehyde carbon xerogels with several initial pH were synthesized using two different heating methods (conventional and microwave heating). The effect of the pH of the precursor solution and the method of synthesis employed on the textural and chemical properties of the final materials was evaluated. It was found that both methods produce tailored carbon xerogels depending on the initial pH and that the pores of the carbon xerogels become larger as the initial pH decreases. High pHs result in exclusively microporous carbon xerogels, while a decrease in the amount of NaOH added, i.e. lower pH, causes the materials to evolve firstly into micro-mesoporous samples and then into micro-macroporous carbon xerogels. The main difference between the two heating methods studied, apart from the duration of the synthesis (i.e. approximately 5 h for the microwave-assisted synthesis as opposed to several days by conventional methods) lies in the meso-macroporosity of the resulting materials, since microwave radiation produces mainly mesoporous carbon xerogels with a specific mesopore size over a wider range of pH than conventional synthesis. For example, the pH range for mesoporous MW samples is 4.5-6.5 while equivalent samples that are conventionally synthesized require an initial pH of between 5.8 and 6.5. This work also illustrates a simple and precise method for determining the gelation point (tg ) of different pH resorcinol-formaldehyde mixtures, based on varying the energy consumed by the microwave device during the synthesis of organic gels, without the need for other more complicated techniques. © 2011 Elsevier Inc. All rights reserved.

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Abstract: Carbon materials are, in general, very good absorbents of microwaves, i.e., they are easily heated by microwave radiation. This characteristic allows them to be transformed by microwave heating, giving rise to new carbons with tailored properties, to be used as microwave receptors, in order to heat other materials indirectly, or to act as a catalyst and microwave receptor in different heterogeneous reactions. In recent years, the number of processes that combine the use of carbons and microwave heating instead of other methods based on conventional heating has increased. In this paper some of the microwave-assisted processes in which carbon materials are produced, transformed or used in thermal treatments (generally, as microwave absorbers and catalysts) are reviewed and the main achievements of this technique are compared with those obtained by means of conventional (non microwave-assisted) methods in similar conditions. © 2009 Elsevier B.V. All rights reserved.

Abstract: A regenerated activated carbon used as catalyst support in the synthesis of vinyl acetate has been tested as a low-cost adsorbent for the removal of dyes. After a thorough textural characterization of the regenerated activated carbon, its adsorption isotherms and kinetics were determined using methylene blue as model compound at different initial concentrations. Both Langmuir and Freundlich isotherm models were developed and then compared. It was found that the equilibrium data were best represented by the Langmuir isotherm model. The kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models, and it was found that the best fitting corresponded to the pseudo-second-order kinetic model. The results showed that this novel adsorbent had a high adsorption capacity, making it suitable for use in the treatment of methylene blue enriched wastewater. © 2009 Elsevier B.V. All rights reserved.

Abstract: A series of carbon-based nickel (Ni) catalysts was prepared in order to investigate the effect of the preparation method on the dispersion of Ni and its final catalytic activity in the dry reforming of methane, i.e. CH4 + CO2 = 2H2 + 2CO. Three parameters were studied: (i) the influence of the surface chemistry of the carbon used as support; (ii) the method of drying (conventional vs. microwave drying); and, (iii) the temperature of the reduction stage. In order to study the role of the surface chemistry of the commercial activated carbon used as support, the active carbon was tested as received and oxidized. Although a better Ni dispersion was achieved over the oxidized support, the conversions were much lower. It was also found that microwave drying offers various advantages over conventional drying, the main one being that less time is required to prepare the catalyst. Two reduction temperatures were used (300 and 500 °C), being found that it is necessary to adjust this parameter to prevent the Ni particles from sintering. © 2010 Elsevier B.V.All rights reserved.

Abstract: The thermal valorization of glycerol to produce synthesis gas has been investigated under conventional and microwave heating systems. Different processes (pyrolysis, steam reforming and dry reforming) are compared, using a commercial activated carbon as catalyst. The reforming processes that employ oxidizing agents (CO2 or H2O) were found to promote higher glycerol conversions than mere thermal decomposition. Steam reforming generates the lowest gas fraction and the highest amounts of hydrogen and syngas, while the opposite occurs in the dry reforming experiments. Microwave processing produced higher gas yields with large syngas content than conventional heating processes in all cases. The use of carbon-based catalysts appears to be highly suitable for producing synthesis gas with a H2/CO ratio close to 1, minimum CO2 emissions being an additional advantage. © 2010 Elsevier B.V. All rights reserved.

Abstract: Activated carbon xerogels, with selected characteristics, were doped with Ni, using different methods, and tested for hydrogen storage. The results obtained show that the amount of nickel incorporated, the Ni-carbon interaction and the nickel particle size distribution depend more on the doping method used than on the textural properties of the carbon support. The amount of nickel incorporated by strong electrostatic adsorption is lower than that incorporated by dry impregnation. However, the strong electrostatic adsorption method produces Ni-doped carbon xerogels with a high Ni-carbon interaction and a narrower Ni particle size distribution. The influence of Ni on H2 storage capacity depends on the operating conditions and the doping conditions used. Thus, at -196 °C and 40 bar, storage capacity seems to be mainly influenced by the textural properties of carbon support while, at 25 °C and 200 bar, the spillover effect plays a significant role, being the interaction between the support and Ni particles key factor in the storage process. The best Ni-doped carbon xerogels obtained in this work exhibit hydrogen storage capacities of 6 wt.% and 31.8 g l-1 at -196 °C and 40 bar. © 2010 Elsevier Ltd. All rights reserved.

Abstract: After being subjected to conventional thermal treatment, a carbon-based spent catalyst from vinyl acetate synthesis has been proved to be a good precursor for the production of ZnO/activated carbon composites. Such composites can be used as photocatalysts for the removal of pollutants from wastewaters. Different operating temperatures were found to influence the properties of the final composites. As the temperature rises, the surface area of the activated carbon that is acting as catalyst support increases due to the decomposition of the organic deposits that are blocking the porous structure. XRD was used to evaluate the transformation of zinc acetate to zinc oxide after thermal treatment, showing higher crystal sizes with the rise in temperature. Both the adsorption capacity and the yield of the resulting composites were calculated and SEM-EDX analysis was used to evaluate the changes in surface morphology. © 2009 Taiwan Institute of Chemical Engineers.

Abstract: In this work the catalytic activity of heterogeneous mixtures of an activated carbon, FY5, and an in-lab prepared Ni/Al2O3 in the CO2 reforming of CH4 reaction was investigated. Initially, the reaction was carried out over FY5 and Ni/Al2O 3 separately. Under the operating conditions employed, the CO 2 and CH4 conversions obtained over FY5 were negligible, whereas they were high and steady over Ni/Al2O3. In the latter case, it was found that the spinel NiAl2O4 was formed due to the interaction between the reduced Ni and the support during heating under a N2 atmosphere. The reaction was also carried out over different mixtures of FY5 + Ni/Al2O3. The experimental conversions thus attained were higher than the conversions calculated by adding the weighted individual conversions (mixtures law). Therefore, a synergetic effect exists between the carbonaceous fraction and the metal-based fraction. This effect was found to increase with temperature. Differences between the experimental and theoretical CO2 conversion were also observed to increase when the proportion of FY5 in the mixture was increased, whereas in the case of CH4 conversion, the increase depended on the proportion of Ni/Al2O3 added. It was also observed that, when a heterogeneous mixture FY5 + Ni/Al2O3 was used as catalyst for the CO2 reforming of methane, the decomposition of CH4 occurred preferentially over the Ni-based fraction and that CO2 tended to gasify both the initial carbonaceous fraction and the carbon deposits from methane. © 2010 Elsevier B.V.

Abstract: In this work, various carbon materials were studied as catalysts/microwave receptors for the CO2 reforming of the CH4 reaction. Carbon materials with a different textural development (metallurgical coke, activated carbons, re-activated carbon) were selected as catalysts in order to determine the role of porosity and pore size in dry reforming. Microporosity was found to be necessary for a good performance of the carbon catalysts. An activated carbon and an oxidized activated carbon were compared in order to evaluate the influence of oxygen surface groups on the catalytic activity of carbons for the dry reforming reaction. Oxidized carbons were found to be bad catalysts, especially under microwave heating. The importance of CO2 reactivity for carbon materials to be able to act as acceptable catalysts was also established. © 2010 Elsevier Ltd. All rights reserved.

Abstract: In-lab synthesized Ni-doped carbon xerogels were used as a carbon support to study the possibility to improve the electrochemical behavior of AB 5-type alloy electrodes for nickel/metal hydride rechargeable batteries. The carbons used for this work were synthesized by polymerization of resorcinol and formaldehyde. These carbon supports were mixed with an AB 5-type alloy. For the electrochemical characterization of the electrodes, charge and discharge techniques, a high rate of discharge, and electrochemical impedance spectroscopy were used. Results show that this kind of carbon could be used as a support for hydrogen storage electrodes with good electrochemical behavior and kinetic response. © 2010 American Chemical Society.

Abstract: Resorcinol-formaldehyde carbon xerogels were prepared by means of two different synthesis methods: conventional (C) and microwave heating (MW). The influence of the heating method and the pH of the precursor solution on the textural and chemical properties of the carbon xerogels was investigated. It was found that by modifying the initial pH, it is possible to control the porosity of carbon xerogels independent of the heating method used. The electrochemical performance of a selection of synthesized carbon xerogels as electrode materials in electric double-layer capacitors was studied by cyclic voltammetry and charge/discharge experiments in an acidic medium (1 M H2 SO 4). The electrochemical performance of the carbon xerogels was compared to that of an activated carbon commercialized for this application (Norit Super DLC-50), and it can be seen that the carbon xerogels display similar specific capacitances to those of the commercial carbon. Moreover, carbon xerogels have a good cycle durability after 18?000 galvanostatic cycles, with a drop in specific capacitance of around 10%. This excellent cycle durability, together with the attractive properties of carbon xerogels and the saving of time and energy achieved with microwave-assisted synthesis, would make resorcinol-formaldehyde carbon xerogels promising materials for applications of an electric double-layer capacitor (EDLC). © 2010 American Chemical Society.

Abstract: The spent catalyst from vinyl acetate synthesis contains large quantity of zinc. The present study attempts to leach zinc using a mixture of ammonia, ammonium carbonate and water solution, after microwave treatment. The effect of important parameters such as leaching time, liquid/solid ratio and the ammonia concentration was investigated and the process conditions were optimized using surface response methodology (RSM) based on central composite design (CCD). The optimum condition for leaching of zinc from spent catalyst was identified to be a leaching time of 2.50 h, a liquid/solid ratio of 6 and ammonia concentration 5.37 mol/L. A maximum of 97% of zinc was recovered under the optimum experimental conditions. The proposed model equation using RSM has shown good agreement with the experimental data, with a correlation coefficient (R2) of 0.95. The samples were characterized before and after leaching using X-ray diffraction (XRD), nitrogen adsorption and scanning electron microscope (SEM). © 2009 Elsevier B.V. All rights reserved.

Abstract: The dry reforming of coke oven gases (COG) over an activated carbon used as catalyst has been studied in order to produce a syngas suitable for methanol synthesis. The primary aim of this work was to study the influence of the high amount of hydrogen present in the COG on the process of dry reforming, as well as the influence of other operation conditions, such us temperature and volumetric hourly space velocity (VHSV). It was found that the reverse water gas shift (RWGS) reaction takes place due to the hydrogen present in the COG, and that its influence on the process increases as the temperature decreases. This situation may give rise to the consumption of the hydrogen present in the COG, and the consequent formation of a syngas which is inappropriate for the synthesis of methanol. This reaction can be avoided by working at high temperatures (about 1000 °C) in order to produce a syngas that is suitable for methanol synthesis. It was also found that the RWGS reaction is favoured by an increase in the VHSV. In addition, the active carbon FY5 was proven to be an adequate catalyst for the production of syngas from COG. © 2009 Elsevier Ltd. All rights reserved.

Abstract: Activated carbon xerogels, with selected characteristics, were doped with Ni, using different methods, and tested for hydrogen storage. The results obtained show that the amount of nickel incorporated, the Ni-carbon interaction and the nickel particle size distribution depend more on the doping method used than on the textural properties of the carbon support. The amount of nickel incorporated by strong electrostatic adsorption is lower than that incorporated by dry impregnation. However, the strong electrostatic adsorption method produces Ni-doped carbon xerogels with a high Ni-carbon interaction and a narrower Ni particle size distribution. The influence of Ni on H2 storage capacity depends on the operating conditions and the doping conditions used. Thus, at -196 °C and 40 bar, storage capacity seems to be mainly influenced by the textural properties of carbon support while, at 25 °C and 200 bar, the spillover effect plays a significant role, being the interaction between the support and Ni particles key factor in the storage process. The best Ni-doped carbon xerogels obtained in this work exhibit hydrogen storage capacities of 6 wt.% and 31.8 g l-1 at -196 °C and 40 bar. © 2010 Elsevier Ltd. All rights reserved.

Abstract: Carbon xerogels synthesized with a fixed resorcinol/sodium carbonate molar ratio (R/C) were physically activated using CO2. The effect of activation temperature and activation time on the final properties of the activated carbon xerogels was evaluated. The specific surface area increases from �600 m2 g-1 to 2000 m2 g-1 and more by increasing the temperature and duration of the activation step. A comparison between physical activation with CO2 and chemical activation with hydroxides was also performed: it was found that both processes produce an increase of the micropore volume and specific surface area without altering the mesoporosity developed during the synthesis. However, chemical activation can lead to the development of the narrow microporosity mainly whereas, in physical activation, the widening of the narrow micropores takes place whatever the process conditions. © 2010 Elsevier Ltd. All rights reserved.

Abstract: A simple and precise method for determining the point of gelation in microwave-assisted synthesis of organic gels is reported. This method provide a relevant information in the carbon gels field, as it can be applied to stop the gelation process at the precise instant for using the material in further processes where it is necessary to have the material with a specific viscosity (i.e., point of gelation). © 2010 Elsevier Ltd. All rights reserved.

Abstract: The mechanism of reaction between NO and two models of carbonaceous materials with active sites was investigated at the UB3LYP/6-31 + G(d) and UM06-2X theory levels. The small model is the anthracene radical and the large one is also a monoradical built with ten benzene rings. The mechanistic routes found with both models lead to a satisfactory justification of the experimental data and showed the important role of the temperature and the oxygen and nitrogen surface complexes, generated in the carbonaceous material at intermediate steps of the mechanism, in the global process. The computational results presented in this work revealed that, at low temperatures, the high Gibbs energy barrier that appears after N2 release from the (NO)2 dimer, initially chemisorbed on the char surface, prevents the subsequent evolution of the system with the result that CO2 emission does not take place. On the other hand, at high temperatures, the mean energy available to the reactants may be sufficient to overcome this energy barrier giving rise to the formation of N2 and CO2 as reduction products. The N2 may come from two sources depending on the approach of the NO molecule at different points of the reaction coordinate. The best description of the carbonaceous surface through a larger model confirms the absence of N2O release in the reduction of nitric oxide on carbon surfaces. © 2009 Springer-Verlag.

Abstract: Increasing awareness of the influence of greenhouse gases on global climate change has led to recent efforts to develop strategies for the reduction of carbon dioxide (CO2) emissions. The strategy that is receiving the most attention involves the capture of CO2 from large point sources, such as fossil fuel-fired power plants, and long-term storage underground or in the ocean. CO2 capture can be achieved either by post or pre-combustion capture at ambient or high pressure respectively. Aqueous solutions of amines have long been used by industry as absorbents for acid gas (CO2,H2S) removal, but have a large number of short comings. As an alternative, adsorption is one of the more promising technologies for capturing CO2 from flue gases, potentially avoiding the shortcomings of aqueous amine systems. In this paper the development of solid adsorbents for post-combustion capture will be described. The generation and testing of a range of adsorbents for post-combustion capture of CO2 at ambient pressure has demonstrated the need for chemical type adsorbents. A range of chemical type adsorbents have been generated by two methods: Modification of the surface chemistry of both low cost carbons and mesoporous silica by impregnation with a basic nitrogen-containing polymers (i.e., polyethylenimine).Generation of a range of high nitrogen content carbon matrix adsorbents by carbonisation and subsequent thermal or chemical activation of a range of nitrogen compounds. CO2 adsorption capacities at equilibrium and under dynamic conditions using a simulated flue gas will be described at different temperatures and gas residence times. Regeneration using simulated temperature, pressure swing cycles and steam stripping and the effect of the processes on the lifetime of the adsorbent will be discussed. © 2009 Elsevier Ltd. All rights reserved.

Abstract: The effect of nickel distribution and content in Ni-doped carbon nanospheres on hydrogen storage capacity under conditions of moderate temperature and pressure was studied. It was found that the nickel distribution, obtained by using different doping techniques and conditions, has a noticeable influence on hydrogen storage capacity. The samples with the most homogeneous nickel distribution, obtained by pre-oxidising the carbon nanospheres, displayed the highest storage capacity. In addition, storage capacity is influenced by the amount of nickel. It was found a higher storage capacity in samples containing 5 wt.% of Ni. This is due to the greater interactions between the nickel and the support that produce a higher activation of the solid through a spillover effect. © 2009 International Association for Hydrogen Energy.

Abstract: In this work a series of carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The materials used were different types of commercial carbons: carbon fibers, carbon cloths, nanotubes, superactivated carbons, and synthetic carbons (carbon nanospheres and carbon xerogels). Their textural properties (i.e., surface area, pore size distribution, etc.) were related to their hydrogen adsorption capacities. These H2 storage capacities were evaluated by various methods (i.e., volumetric and gravimetric) at different temperatures and pressures. The differences between both methods at various operating conditions were evaluated and related to the textural properties of the carbon-based adsorbents. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. Furthermore, hydrogen storage capacity seems to be proportional to surface area, especially at 77 K. The micropore size distribution and the presence of narrow micropores also notably influence the H2 storage capacity of carbons. In contrast, morphological or structural characteristics have no influence on gravimetric storage capacity. If synthetic materials are used, the textural properties of carbon materials can be tailored for hydrogen storage. However, a larger pore volume would be needed in order to increase storage capacity. It seems very difficult approach to attain the DOE and EU targets only by physical adsorption on carbon materials. Chemical modification of carbons would seem to be a promising alternative approach in order to increase the capacities. © 2008 International Association for Hydrogen Energy.

Abstract: The pyrolysis of glycerol was carried out over carbonaceous catalysts to produce synthesis gas (up to 81 vol.%). The catalytic effect of two activated carbons was tested and compared with quartz glass chips as packing materials in a fixed-bed reactor. The main advantage of using a carbonaceous catalyst seems to be its higher selectivity toward hydrogen, resulting in a synthesis gas with a greater H2/CO ratio. The influence of the heating method (electrical furnace and microwave oven) and temperature (from 400 to 900 °C) on the pyrolysis of glycerol over a selected activated carbon was also studied. As a result, an elevated gas fraction with a higher H2 + CO composition was obtained under microwave heating, even at low temperatures. This proves that microwave heating could be used to upgrade the industrial surplus generated from bio-diesel production. © 2009 Elsevier B.V. All rights reserved.

Abstract: The possibility to improve the electrochemical behaviour of AB5-alloy commercial electrodes was studied using different carbons as support, such as carbon blacks and a selection of commercial and in-lab synthesised carbon nanotubes. The carbons selected for this work present different morphologies (i.e., spherical and tubular). Furthermore, they also present a variation of the porous structure and subsequent surface area, which are also going to influence their further electrochemical behaviour. Carbon samples were texturally characterised by the adsorption-desorption of N2 and CO2 at 77 and 273 K, respectively. The carbon structure was analysed by XRD, Raman, TEM, and the chemistry of the samples was also characterised by elemental analysis. The charge and discharge techniques, cyclic voltammetry, rate capability and linear polarisation were used for the electrochemical characterisation of the electrodes studied. The electrochemical behaviour of all the samples was related to their morphological, textural and chemical properties. The results show that there is a clear influence of the nature of the carbon support on the hydriding/dehydriding reaction of the alloy, and in the case of active carbons the kinetics decreases with the increase of the surface area of the carbon support. © 2008 Elsevier Ltd. All rights reserved.

Abstract: Adsorption is considered to be one of the more promising technologies for capturing CO2 from flue gases. The efficient adsorption of CO2 at low partial pressures, associated with post-combustion capture, require chemical type adsorbents containing basic amine functional groups. It has been demonstrated that amine polymers, for example polyethylenimine (PEI), immobilised on various porous substrates, silica, zeolites and fly ash, are effective adsorbents for CO2. When considering the use of adsorption for large scale CO2 capture, the ease of regeneration and the lifetime of the adsorbents are critical factors in determining their efficiency, cost and therefore feasibility for use. In this paper two approaches, thermal swing adsorption (TSA) cycles over a range of temperatures and time in an atmosphere of CO2 and thermally assisted pressure swing desorption, are explored for the regeneration of the PEI based adsorbents. The reactions occurring during the TSA regeneration of PEI based adsorbents in an atmosphere of CO2, especially the formation of a thermostable complex between PEI and CO2 above 130 °C are described. Identification of the complex by FTIR, XPS and 13C NMR as a urea linkage will be described. Overall, the results from this research have implications for the selection of regeneration strategies of all amine based CO2 adsorbents. © 2009 Elsevier Ltd. All rights reserved.

Abstract: The characteristics of carbonaceous materials deposited in fuel rich ethylene-oxygen mixtures on three types of palladium: foil, sputtered film, and nanopowder, are reported. It was found that the form of palladium has a dramatic influence on the morphology of the deposited carbon. In particular, on sputtered film and powder, tight 'weaves' of sub-micron filaments formed quickly. In contrast, on foils under identical conditions, the dominant morphology is carbon thin films with basal planes oriented parallel to the substrate surface. Temperature, gas flow rate, reactant flow ratio (C2H4:O2), and residence time (position) were found to influence both growth rate and type for all three forms of Pd. X-ray diffraction, high resolution transmission electron microscopy, temperature-programmed oxidation, and Raman spectroscopy were used to assess the crystallinity of the as-deposited carbon, and it was determined that transmission electron microscopy and X-ray diffraction were the most reliable methods for determining crystallinity. The dependence of growth on reactor position, and the fact that no growth was observed in the absence of oxygen support the postulate that the carbon deposition proceeds by combustion generated radical species. © 2009 Elsevier Ltd. All rights reserved.

Abstract: The present work gathers a general review of the properties, advantages and disadvantages of the principal electrode materials used in electrochemical capacitors (also called supercapacitors). The choice of these materials has an enormous influence on the final characteristics of the electrochemical device. Among the available electrode materials for their application in supercapacitors, carbonbased porous materials, transition metal oxides and conductive polymers are included. Each of these families of materials presents some advantages and drawbacks, so, in many occasions, a single material is not used for the preparation of the electrodes. The trend is directed to the use of hybrid electrodes, namely, those made of materials of different nature to combine the beneficial aspects and to offset the limitations of each material separately.

Abstract: This work deals with the catalytic decomposition of carbon-containing gases (ethylene) over nickel catalysts to grow graphitic capsules at relatively low temperatures (853 K). The influence of different experimental conditions, such as catalyst size, reactant flow ratio (C2H4:O2), gas flow rate and temperature, is studied. The size of the nickel particles determines the type of structures; while nano-sized nickel particles favor the growth of nanofilaments, graphitic capsules occur over nickel microparticles. The use of reducing and oxidizing environments in the growth of graphitic structures over microparticles are compared, the latter being more appropriate for growing nanofilaments. Below 853 K, no graphitic structures are formed. Moreover, a new model is proposed for the encapsulation of the catalyst metal particles by graphite layers. © 2009 Elsevier B.V.

Abstract: Chemical activation of carbon xerogels synthesized with different resorcinol/sodium carbonate molar ratios (R/C) was performed using alkaline hydroxides (KOH and NaOH). The effect of R/C and the type and amount of alkaline hydroxide on the final properties of the activated carbon xerogels were evaluated. It was found that, in general, both hydroxides produce an increase in microporosity regardless of the R/C value chosen, without altering the meso/macroporosity developed during the synthesis. KOH develops the microporosity of micro-mesoporous carbon xerogels more efficiently than NaOH, and for samples of large pore size (micro-macroporous samples), a similar textural development was observed for both hydroxides. However, when NaOH is used as activating agent, it is more difficult to eliminate residual Na from the activated carbon xerogels. © 2009 Springer Science+Business Media, LLC.

Abstract: Binary CuO/ZnO and ternary CuO/ZnO/Al2O3 catalysts have been rapidly synthesized in a multimode microwave oven by the homogeneous precipitation of aurichalcite and hydrotalcite-like precursors using urea hydrolysis. For purposes of comparison, the same catalysts were prepared under conventional heating. The corresponding metal nitrates were mixed with various amounts of urea to yield different urea/(ΣM+) molar ratios. The precipitation proceeded stepwise, copper being the first metal to be hydrolyzed. It was found that the higher the urea content, the higher the alkalinization of the solution, an effect which favored the precipitation of Zn (II) (the most pH dependent metal), and in turn, the synthesis of aurichalcite and hydrotalcite-like precursors. Microwave-synthesized catalysts presented similar characteristics to those obtained under conventional heating, but in considerably reduced aging times. Microwave radiation proved to be more efficient than conventional heating under harsh conditions of precipitation, i.e., lower molar ratios of urea with respect to the metal cations in the solution. © 2009 Elsevier B.V. All rights reserved.

Abstract: The expanded graphite (BOCHEMIE a.s., Czech Republic) was tested as the material for anodes of lithium secondary batteries. The irreversible charge was lowered and the cyclability improved if the material was annealed in CO 2. The specific capacity approached theoretical value corresponding to the composition LiC6. © 2008 Springer-Verlag.

Abstract: Nanofilamentous carbon was grown on a carbon foam by catalytic chemical vapour deposition (CVD) using the decomposition of ethylene/hydrogen mixtures over Ni. The carbon foam was obtained from a coal by a two-stage thermal process, with the first stage taking place at a temperature within the plastic region of the precursor coal. The extent of porosity and the pore size of the foam were mainly influenced by the pressure reached in the reactor during the first stage. In the CVD process, 700 °C was the optimum temperature for obtaining good yields of nanofilaments. A low ethylene/hydrogen ratio (1/4) in the reactive gas gave rise to almost only short and thin carbon nanostructures. A higher proportion of C2H4 (4/1, C2H4/H2) gave better yields of nanofilaments, with good proportions of higher-length and higher-diameter (up to around 0.5 μm) structures. Among the carbon forms produced, transmission electron microscopy revealed the predominance of fishbone-type nanofibres, with some bamboo-like nanotubes being also observed. © 2008 Elsevier Ltd. All rights reserved.

Abstract: Two approaches, thermal swing desorption over a range of temperatures and time in an atmosphere of CO2 and using nitrogen as a stripping gas at elevated temperatures, are explored for the regeneration of the polyethylenimine based adsorbents. Thermal swing regeneration was demonstrated to give good cyclic regeneration capacities (2 mmol g-1). However, further reaction of the regenerable carbamate ion to form urea linkages, significantly reduces cyclic capacity and therefore the lifetime of the adsorbent. Regeneration of this secondary reaction product at elevated temperatures was attempted in a nitrogen atmosphere, and whilst recovering some of the original capacity did not fully regenerate the adsorbent. Adsorbent regeneration with nitrogen as a stripping gas was used as an alternative regeneration method, the results of which suggest that steam stripping may be a potential method for adsorbent regeneration. Crown Copyright © 2008.

Abstract: In this work a series of solid sorbents were synthesized by immobilizing liquid amines on the surface of a mesoporous alumina. The samples were chemically characterized and BET surface areas calculated from the N2 adsorption isotherms at 77 K. The CO2 capture performance of the sorbents and their thermal stability was studied by thermogravimetric methods. The effect of amine loading on the CO2 capture performance of the prepared sorbents was also evaluated. Analysis of TG-DTG curves showed that thermal stabilization of the amines is significantly improved by immobilizing them on an inorganic support. Temperature-programmed CO2 adsorption tests from 298 K up to 373 K at atmospheric pressure, proved to be a useful technique for assessing the capacity of sorbents for CO2 capture. Alumina impregnated with diethylenetriamine presented the highest CO2 adsorption capacities throughout the tested temperature range. © 2008 Springer Science+Business Media, LLC.

Abstract: The aim of this work was to study the microwave-assisted pyrolysis of CH4 over an activated carbon, which acted as both microwave receptor and catalyst, and the influence of using different CH4/N2 ratios on the conversion of CH4 to H2. In order to compare the results obtained in the microwave oven, the pyrolysis was also carried out under conventional heating (electric furnace, EF). The effects of N2, which enhanced significantly CH4 conversion, differed depending on the heating device used. Under EF heating, N2 seemed to have an effect similar to distribute the CH4 molecules within the activated carbon bed. Under microwave heating (MW), the N2, as well as distributing the CH4 molecules, favoured the generation of energetic microplasmas, leading to higher conversions. The prevalence of one role over the other depended on the CH4/N2 ratio, the appearance of energetic microplasmas being favoured with high percentages of N2. Consequently, CH4 conversion was higher at low CH4/N2 ratios. Additionally, the formation of carbon nanofibres in experiments where a combination of N2 and MW heating was used is also reported. © 2008 Elsevier B.V. All rights reserved.

Abstract: The hydrophobic-hydrophilic character of a series of microporous activated carbons was explored as a key factor in competitive adsorption of a non-polar compound from liquid phase. The selectivity of the carbon surface towards naphthalene was explored by performing the adsorption isotherms in water, cyclohexane and heptane. Solvent polarity and adsorbent hydrophobic character were found to strongly influence the adsorption capacity of naphthalene. In aqueous media, despite the non-polar character of the adsorbate, surface acidity lowered adsorption capacity. This is attributed to the competition of water from the adsorption sites, via H-bonding with surface functionalities and the formation of hydration clusters that reduce the accessibility and affinity of naphthalene to the inner pore structure. In organic media the uptake decreased due to competition of the hydrophobic solvent for the active sites of the carbon and to solvation effects. This competitive effect of the solvent is minimized in oxidized carbons as opposed to the trend obtained in aqueous solutions. The results confirmed that although adsorption of naphthalene strongly depends on the narrow microporosity of the adsorbent, competitive adsorption of the solvent for the active sites becomes important. © 2008 Springer Science+Business Media, LLC.

Abstract: The microwave-assisted dry reforming of methane over an activated carbon, which acted as catalyst and microwave receptor, was investigated. As a preliminary study, the CO2 reforming of CH4 was carried out using conventional heating and microwave heating in order to compare both heating devices. Higher conversions of CH4 and CO2 were achieved by microwave heating. Under microwave heating, various operating variables were studied in order to determine the best conditions for performing dry reforming with high conversions and the most suitable H2/CO ratio. Thus, the dry reforming reaction was studied at different temperatures. An optimum range of working temperatures (between 700 °C and 800 °C) was established. In this range of temperatures, the dry reforming reaction is believed to take place as a combination of CH4 decomposition and CO2 gasification. Carbonaceous deposits from CH4 decomposition are gasified by CO2 and, as a result, active centres for the dry reforming reaction are constantly regenerated. The effect of the proportion of CO2 fed in on the CH4 and CO2 conversions was also investigated. Small increases in the percentage of CO2 fed in gave rise to large increases in both conversions, but especially in the case of CH4. The volumetric hourly space velocity was also studied. It was found that the lower the space velocity, the higher the conversions obtained. © 2008 International Association for Hydrogen Energy.

Abstract: Microwave drying was used to prepare resorcinol-formaldehyde aqueous gels, without performing any pretreatment, and to see whether it was possible to use this drying option to obtain porous carbon xerogels with controlled textural properties. By using microwave drying, the process for obtaining carbon gels is greatly simplified, textural properties are controlled likewise with other drying methods, but the time involved in the process is significantly reduced and no pretreatment is necessary. Therefore, microwave drying could help to simplify the carbon xerogels synthesis and reduce the associated costs. © 2008 Elsevier B.V. All rights reserved.

Abstract: In classic carbon supports is very difficult to control pore size, pore size distribution, and surface chemical properties at the same time. In this work microporous carbons derived from furfuryl alcohol are used as support to prepare Ni-doped carbon materials. The N2 flow rate used during the carbonisation process of the precursor influences on the size of the nanospheres obtained but not in their textural properties. Microporous carbon nanospheres have been synthesised with a narrow pore size distribution centred in 5.5 �. The surface chemistry of these materials can be easily modified by different treatments without detriment of the pore structure of the doped carbon nanospheres. © 2007 Elsevier B.V. All rights reserved.

Abstract: The aim of this work was to study the growth of nanofilaments on two carbon-based materials (i.e. an activated carbon and carbon fibres) from microwave-assisted decomposition of CH4. It was found that the nature of grown nanofilaments differed depending on the carbon support, probably due to the presence of diverse metals which catalyze the nanofilaments growth. Besides, it was also studied the influence of the composition of the in-flow gases on the growth of nanofilaments. Thus, tests with pure CH4 and different CH4/N2 mixtures were carried out, the yield in nanofilaments being higher when mixtures were fed in. No nanofilaments were found after analogous tests carried out under conventional heating, therefore it can be stated that microwave heating is a promising technology for growing nanofilaments. © 2007 Elsevier B.V. All rights reserved.

Abstract: Resorcinol-formaldehyde xerogels synthesised with different resorcinol/sodium carbonate molar ratios were chemically activated either after drying or after drying and pyrolysis, using potassium hydroxide. It was found that organic (i.e. dried) and carbon (i.e. pyrolysed) xerogels behave differently when subjected to chemical activation. In the case of carbon xerogels, the increase in the microporosity takes place without any significant modification to the meso/macroporosity formed during the synthesis step, leading to micro-mesoporous or micro-macroporous materials with a larger micropore volume. Furthermore, control of the microporosity is possible because its development depends on the amount of KOH used. However, when organic xerogels are activated, mainly microporous materials with BET specific surface areas of up to 2000 m2 g-1 are obtained, there hardly remaining any of the meso/macroporosity formed during the gel synthesis. Thus, the combination of different synthesis conditions and chemical activation with potassium hydroxide allows the textural properties of carbon xerogels to be tailored at both micropore and meso/macropore levels. © 2008 Elsevier Inc. All rights reserved.

Abstract: This paper assesses the feasibility of producing syngas from sewage sludge via two pyrolysis processes: microwave-induced pyrolysis (MWP) and conventional pyrolysis (CP). The changes in the composition of the produced gas as a function of the pyrolysis treatment and the initial moisture content of the sludge were evaluated. It was found that MWP produced a gas with a higher concentration of syngas than CP, reaching values of up to 94 vol%. Moreover, this gas showed a CO2 and CH4 concentration around 50% and 70%, respectively, lower than that obtained in the gas from CP. With respect to the effect of moisture on gas composition, this was more pronounced in CP than in MWP. Thus, the presence of moisture increases the concentration of H2 and CO2 and decreases that of CO, especially when CP was used. In order to elucidate the behaviour of CO2 during the pyrolysis, the CO2 gasification kinetics of the char obtained from the pyrolysis were investigated. It was established that in microwave heating the gasification reaction is much more favoured than in conventional heating. Therefore, the low concentration of CO2 and the high concentration of CO in the microwave pyrolysis gas could be due to the self-gasification of the residue by the CO2 produced during the devolatilization of the sewage sludge in the pyrolysis process. © 2007 Elsevier Ltd. All rights reserved.

Abstract: Textural properties of carbon gels can be controlled by varying the synthesis and drying process conditions. In this work, the influence of the initial pH and the drying method on the final properties of carbon gels, synthesized using methanol as a solvent, was evaluated. Furthermore, the use of microwaves as a drying method for the synthesis of carbon xerogels was assessed. In the light of the results obtained, in order to synthesize monolithic and microporous carbon gels in a short period of time, the use of a multimode microwave oven is proposed. The use of pH 7 also leads to shorter gelation times and more consistent monoliths. Furthermore, the multimode microwave drying can produce homogeneous microporosity and surface areas of up to 1341 m2 g-1, in a very short time (i.e., only 6 min is required for the drying step). © 2007 Elsevier B.V. All rights reserved.

Abstract: This work deals with the conventional and microwave-assisted pyrolysis of coffee hulls in order to determine the influence of the pyrolysis method on the characteristics of the pyrolysis products. The high syngas content obtained in microwave heating (73 vol %) is thought to be a result of the fact that self-gasification of the char with CO2 and the catalytic decomposition of CH4 are favoured in microwave. Individual reactions were also studied in both heating methods. The conversions were greater for microwave than for conventional heating. In the case of methane decomposition, CH4 conversion experiences a significant drop due to the formation of coke deposits which reduce catalytic activity. However, when a CH 4/CO2 mixture was used, this problem was minimized since the CO2 partly removed the carbon deposits formed, providing an "in situ" route for catalyst regeneration. Results reported in this paper have serve as starting point for the development of a new process for conversion of biogas into syngas.

Abstract: In this work a series of commercial carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. The highest H2 storage capacity at 298 K and 90 bar was 0.5 wt%, while at 77 K and atmospheric pressure it was 2.9 wt%. It is also showed that, in order to predict the hydrogen storage capacity of carbon material both at cryogenic and ambient temperature, the only use of BET surface area or total micropore volume obtained from N2 adsorption isotherm may be insufficient, the characterization of the narrow microporosity is needed due to its high contribution to hydrogen adsorption capacity. The process involved in hydrogen storage in pure carbon materials seems to be physisorption. Morphological or structural characteristics have no influence, at least on gravimetric storage capacity. © 2008 Springer Science+Business Media, LLC.

Abstract: Ignition tests were carried out on blends of three coals of different rank - subbituminous, high volatile and low volatile bituminous - in two entrained flow reactors. The ignition temperatures were determined from the gas evolution profiles (CO, CO2, NO, O2), while the mechanism of ignition was elucidated from these profiles and corroborated by high-speed video recording. Under the experimental conditions of high carbon loading, clear interactive effects were observed for all the blends. Ignition of the lower rank coals (subbituminous, high volatile bituminous) enhanced the ignition of the higher rank coal (low volatile bituminous) in the blends. The ignition temperatures of the blends of the low rank coals (subbituminous-high volatile bituminous) were additive. However, for the rest of the blends the ignition temperatures were always closer to the lower rank coal in the blend. © 2007 Elsevier Ltd. All rights reserved.

Abstract: Pellets of coffee hulls were pyrolyzed at different temperatures using microwave and electrical heating. A comparison of the gas composition obtained by both methods suggests that the different mechanisms of heating that take place in the microwave, in comparison to conventional heating, give rise to the formation of "microplasmas", which induce self-gasification of the char that is being formed. This hypothesis was corroborated by subjecting the char to reaction with CO2 at different temperatures using both methods of heating. The results showed that, whereas the transition in the reaction mechanism controlling the Boudouard reaction (i.e., chemical or diffusional control) takes place at about 800 °C in conventional heating, in the case of microwave heating the temperature is much lower and the reaction never proceeds under pure chemical control, the differences between microwave and conventional heating being quite significant even at low temperatures. © 2007 American Chemical Society.

Abstract: The mechanism of reactive adsorption of dibenzothiophene (DBT) on a series of modified carbons derived from the recycled PET was investigated. The influence of the oxygen functionalities of the adsorbent on the DBT adsorption capacity was explored. The results revealed that adsorption of DBT on activated carbons is governed by two types of contributions: physisorption on the microporous network of the carbons and chemisorption. Introduction of surface acidic groups enhanced the performance of the carbons as a result of their specific interactions with DBT. The nature of the acidic groups is a decisive factor in the selectivity of the reactive adsorption process. © 2007 Elsevier B.V. All rights reserved.

Abstract: The aim of this work was to investigate the role of porous and chemical heterogeneities of activated carbons in the adsorption of naphthalene from aqueous media. A commercially available activated carbon was used as the adsorbent, and its surface heterogeneity was systematically altered by heat treatment at 450 and 850 °C, obtaining a series of carbons with various oxygen contents and similar surface functionalities. The results confirmed that the adsorption of naphthalene depends strongly on the pore size distribution of the adsorbent, particularly narrow microporosity. Moreover, oxygen functionalities reduced the accessibility and affinity of naphthalene to the inner pore structure via formation of hydration clusters. Consequently, the hydrophobic/hydrophilic character of the adsorbent is important, since it dominates the competitive adsorption of water. Adsorbents with a high non-polar character (i.e., low oxygen content) have proven to be more efficient for naphthalene adsorption. © 2007 Elsevier B.V. All rights reserved.

Abstract: Adsorption is considered to be one of the more promising technologies for the capture of CO2 from flue gases. In general, nitrogen enrichment is reported to be effective in enhancing the specific adsorbent-adsorbate interaction for CO2. Nitrogen enriched carbons were produced from urea-formaldehyde and melamine-formaldehyde resins polymerised in the presence of K2CO3 as a chemical activation agent, with activation undertaken over a range of temperatures. CO2 adsorption capacity was determined to be dependent upon both textural properties and more importantly nitrogen functionality. Adsorbents capable of capturing above 8 wt.% CO2 at 25 °C were produced from the chemical activation of urea-formaldehyde resin at 500 °C. Chemical activation seems to produce more effective adsorbents than CO2 activation. © 2006 Elsevier Ltd. All rights reserved.

Abstract: The aim of this work was to correlate the textural and chemical features of carbonaceous adsorbents with the adsorption capacity of naphthalene from aqueous phase, at the concentration in which this compound is usually found in wastewater from coke ovens. The study reveals that the adsorption capacity in different carbon materials depends not only on the textural characteristics of the material but also on the functionalities of the activated carbons. The micropores of the adsorbents, particularly those of narrower diameter, were found to be active sites for the retention of naphthalene. In contrast, the modification of the surface chemistry of the carbon materials led to a decrease in the adsorption capacities. Dispersive forces play an important role, and adsorbents with a higher non-polar character have proven to be more efficient for the naphthalene adsorption. This behaviour has been linked to the presence of specific interactions between the basal planes and the polyaromatic structure of the naphthalene molecule. © 2006 Elsevier Ltd. All rights reserved.

Abstract: The determination of an accurate pore size distribution of activated carbons is still a complex issue and several methods and adsorbates are currently used to this purpose. In this work, different methods have been applied to characterize the microporosity of activated carbons with different burn-off degrees. A deep analysis of the N2 and CO2 adsorption data of the samples has been done. The results of the different methods applied to the gas adsorption isotherms have been compared and their predictions discussed, in order to throw some light on the characterization of microporous materials. © 2007 Elsevier B.V. All rights reserved.

Abstract: In the present work, the mechanisms involved in NO-char heterogeneous reduction have been studied using a synthetic coal char (SC char) as carbon source. Another synthetic char (SN char) without nitrogen in its composition has also been employed in these studies. Isothermal reduction tests at different temperatures have been carried out. Two temperature regimes were considered: low temperature (T < 250 °C) where NO chemisorption takes place and high temperature (T > 250 °C) where NO-C reaction occurs. Step response experiments combining consecutive reaction stages with NO and 15NO were performed in order to determine the role of nitrogen surface complexes, C(N), in the reduction process. The results revealed N2 and CO2 to be the main reduction products under the experimental conditions employed in this work. NO chemisorption at lower temperatures results in N2 emission and surface complexes (mainly oxygenated) formation, while char gasification by NO involves a direct NO attack on the char surface to form surface complexes. As a consequence of desorption of these complexes new sites of reaction are created. © 2006 Elsevier Ltd. All rights reserved.

Abstract: The aim of this paper is to study the reforming of CH4 with CO2 using as a catalyst a rich potassium char obtained from biomass pyrolysis. The reaction was carried out at 800 °C by means of two different methods of heating, microwave and electrical heating (MWH and EH, respectively). In addition, the individual reactions proposed for the dry reforming of methane, that is, (i) the decomposition of CH4 to form hydrogen and carbon and (ii) the dissociative adsorption of CO2 followed by reduction to give CO, were also studied with both heating methods at the same temperature. The results showed that MWH produces hot spots (microplasmas located inside the catalyst bed) that favor heterogeneous catalytic reactions. Thus, it was found that the conversion of CH4 and CO2 in the individual reactions was greater for MWH than for EH. An examination of the CH4 decomposition reaction proved the formation of coke deposits, which reduced catalytic activity and CH4 conversion. When a CH4/CO2 mixture was used, this problem was minimized since the CO2 partly removed the carbon deposits formed, thereby prolonging the activity of the catalyst. This gasification reaction, catalyzed by the high level of K contained in the char, provides an "in situ" route for catalyst regeneration. The results indicated that the presence of CO2 increased the conversion of CH4 to H2, the values being higher in MWH than in EH. Both heating methods produced an outlet gas composed mainly of syngas (CO + H2) and practically free of CO2 and CH4 (especially in the case of MWH). In addition, the study of the exhausted catalysts by scanning electron microscopy revealed the presence of significant amounts of carbon nanofibers on the char surface, but only in the case of MWH, these nanofibers being more abundant in the dry reforming reaction than in the single CH4 decomposition. © 2007 American Chemical Society.

Abstract: This paper describes the conventional and microwave-assisted pyrolysis of coffee hulls at 500, 800 and 1000 °C. The influence of the pyrolysis method and temperature on the product yields and on the characteristics of the pyrolysis products is discussed. It was found that the pyrolysis of this particular residue gives rise to a larger yield of the gas fraction compared to the other fractions, even at relatively low temperatures. A comparison of microwave-assisted pyrolysis and conventional pyrolysis showed that microwave treatment produces more gas and less oil than conventional pyrolysis. In addition, the gas from the microwave has much higher H2 and syngas (H2 + CO) contents (up to 40 and 72 vol.%, respectively) than those obtained by conventional pyrolysis (up to 30 and 53 vol.%, respectively), in an electric furnace, at similar temperatures. From the pyrolysis fraction yields and their higher heating values it was found that the energy distribution in the pyrolysis products decreases as follows: gas > solid > oil. Moreover, the energy accumulated in the gas increases with the pyrolysis temperature. By contrast, the energy accumulated in the char decreases with the temperature. This effect is enhanced when microwave pyrolysis is used. © 2006 Elsevier B.V. All rights reserved.

Abstract: The success of CO2 capture with solid sorbents is dependent on the development of a low cost sorbent with high CO2 selectivity and adsorption capacity. Immobilised amines are expected to offer the benefits of liquid amines in the typical absorption process, with the added advantages that solids are easy to handle and that they do not give rise to corrosion problems. In this work, different alkylamines were evaluated as a potential source of basic sites for CO2 capture, and a commercial activated carbon was used as a preliminary support in order to study the effect of the impregnation. The amine coating increased the basicity and nitrogen content of the carbon. However, it drastically reduced the microporous volume of the activated carbon, which is chiefly responsible for CO2 physisorption, thus decreasing the capacity of raw carbon at room temperature. © 2007 Elsevier Ltd. All rights reserved.

Abstract: The purpose of this work was to explore the application of microwaves for the regeneration of activated carbons spent with salicylic acid, a metabolite of a common analgesic frequently found in wastewater from the pharmaceutical industry. The exhausted carbon was treated in a quartz reactor by microwave irradiation at 2450 MHz at different temperatures and atmospheres, the regeneration efficiency being highly dependent on the operating conditions. Quantitative desorption of the pollutant was achieved at high temperature and oxidizing atmosphere, with regeneration efficiencies as high as 99% after six cycles. The stripping efficiency was superior to 95% at high temperatures and decreased at 450 °C. The incomplete desorption of the adsorbate at low temperature was further confirmed by the changes in the porosity observed by N2 and CO2 adsorption isotherms. Hence, micropores remain blocked which results in a reduction in loading capacities in successive cycles. © 2007 Elsevier Ltd. All rights reserved.

Abstract: The aim of this work was to combine microwave heating with the use of low-cost granular activated carbon as a catalyst for the production of CO2-free hydrogen by methane decomposition in a fixed bed quartz-tube flow reactor. In order to compare the results achieved, conventional heating was also applied to the catalytic decomposition reaction of methane over the activated carbon. It was found that methane conversions were higher under microwave conditions than with conventional heating when the temperature measured was lower than or equal to 800 {ring operator} C. However, when the temperature was increased, the difference between the conversions under microwave and conventional heating was reduced. The influence of volumetric hourly space velocity (VHSV) on the conversion tests using both microwave and conventional heating was also studied. In general, there is a substantial initial conversion, which declines sharply during the first stages of the reaction but tends to stabilise with time. An increase in the VHSV has a negative effect on CH4 conversion, and even more so in the case of microwave heating. Nevertheless, the conversions obtained in the microwave device at the beginning of the experiments are, in general, better than the conversions reported in other works which also use a carbonaceous-based catalyst. Additionally, the formation of carbon nanofibres in one of the microwave experiments is also reported. © 2007 International Association for Hydrogen Energy.

Abstract:

Abstract: Carbon nanofibres, obtained at industrial scale by chemical vapour deposition, were subjected to oxidative treatments under CO2 and air at different temperatures. The experiments were performed in electric and microwave furnaces, both at bench scale. The effect of the different treatments on the fibre content (i.e., depuration degree), surface chemistry, porous structure and graphitic properties, of the product obtained in the industrial reactor, were evaluated. The results obtained show that microwave treatments were less selective regarding the depuration process, but this process presents advantages like the low time consuming, besides the increase of the oxidation degree and the graphitic properties of the final sample.

Abstract: The present work explores an alternative method to the one generally employed for the pyrolysis of sewage sludge. This method consists in carrying out the pyrolysis of a wet sewage sludge as it is produced in the water treatment plant, i.e. with a typical moisture content of between 70 and 80 wt%, without subjecting it to any previous thermal drying process. In order to maximize gas production, the treatment is carried out at elevated temperatures (i.e. 1000 °C) using long gas residence times and high heating rates. Under these conditions the natural moisture of the sludge is converted during the process into steam, which gives rise to the partial gasification of the sludge and the reforming of the organic vapours at an early stage. In addition, homogeneous reactions between non-condensable gases are also favoured, especially in the water gas shift reaction. In order to establish the most favourable conditions for the production of a hydrogen rich fuel gas, the influence of the moisture content, heating rate and soaking time on the process was studied. It was found that subjecting the vapours to long residence times at high temperature combined with high heating rates and, above all, the presence of water in the raw sewage sludge, give rise to a process that combines both pyrolysis and gasification. As a result of this process, not only is a higher gaseous fraction produced but also gases of a much higher hydrogen content than in the pyrolysis of dry sludge. © 2006 Elsevier B.V. All rights reserved.

Abstract: The present study was aimed to investigate different methods of activation of carbon nanofibres, CNF, in order to determine the beneficial effect on the hydrogen sorption capacities of increasing the surface area. Two activation systems were used: physical activation with CO2 and chemical activation with KOH. A range of potential adsorbents were thus prepared by varying the temperature and time of activation. The structure of the CNF proved more suitable to activation by KOH than by CO2, with the former yielding higher surface area carbons (up to 1000 m2 g-1). The increased surface area, however, did not correspond directly with a proportional increase in hydrogen adsorption capacity. Although high surface areas are important for hydrogen storage by adsorption on solids, it would appear that it is essential that not only the physical, but also the chemical, properties of the adsorbents have to be considered in the quest for carbon based materials, with high hydrogen storage capacities. © 2005 Elsevier Ltd. All rights reserved.

Abstract: The modification of activated carbon fibres prepared from a commercial textile acrylic fibre into materials with monolithic shape using phenolic resin as binder was studied. The molecular sieving properties for the gas separations CO2/CH4 and O2/N2 were evaluated from the gas uptake volume and selectivity at 100 s contact time taken from the kinetic adsorption curves of the individual gases. The pseudo-first order rate constant was also determined by the application of the LDF model. The samples produced show high CO2 and O2 rates of adsorption, in the range 3-35 � 10-3 s-1, and in most cases null or very low adsorption of CH4 and N2 which make them very promising samples to use in PSA systems, or similar. Although the selectivity was very high, the adsorption capacity was low in certain cases. However, the gas uptake in two samples reached 23 cm3 g-1 for CO 2 and 5 cm3 g-1 for O2, which can be considered very good. The materials were heat-treated using a microwave furnace, which is a novel and more economic method, when compared with conventional furnaces, to improve the molecular sieves properties. © 2005 Elsevier Ltd. All rights reserved.

Abstract: For ecological reasons, there is an increasing demand for recycling polyethylene terephthalate (PET) wastes in developed countries. Although one potential application might be its utilisation for the production of activated carbons, the behaviour of these wastes when subjected to different heat treatments and activation processes is still not very well known. In the present work, samples with different degrees of burn-off were prepared by pyrolysis in an inert atmosphere and subsequent CO2 activation at high temperatures. The derived changes in the textural and structural properties of the residual solids were studied by helium picnometry, N2 and CO2 adsorption isotherms, powder XRD, Raman spectroscopy and XPS. The study reveals that CO2 activation of PET wastes develops a carbonaceous matrix with micropores. Helium measurements showed that the mass density of the activated samples increased as the degree of burn-off increased. Characterisation studies revealed that the structural changes derived from pyrolysis and further CO2 activation mostly involved a progressive decrease in the number of structural units.

Abstract: The oxidative adsorption of methyl mercaptan on nitrogen-enriched bituminous activated carbon was analyzed. Investigations show that mercaptans were highly volatile organic compounds responsible for disagreeable odors. It was found that the surface chemistry of bituminuous coal-based activated carbon changed with the high degree of aromatization. The results show an increased capacity of methyl mercaptan (MM) removal and an increase in the oxidizing power of materials on which MM oxidized to methyl methane thiosulfonate.

Abstract: GC-MS was used to determine the main components of high temperature oils obtained from the microwave pyrolysis of sewage sludge under different conditions. The effect of a multimode and a singlemode microwave oven and graphite and char as microwave absorbers on the pyrolysis process was investigated. The pyrolysis of sewage sludge was rapid with both absorbers, temperatures of up to 1000 °C being reached within a few minutes. Although the qualitative composition of the pyrolysis oils was the same for both microwave ovens and absorbers, certain quantitative differences were observed. For example, the use of graphite instead of char produced more cracking in the large aliphatic chains, a higher proportion of 1-alkenes than alkanes and an increase in the proportion of monoaromatics. The multimode microwave oven also favoured cracking and dehydrogenation reactions to a greater extent than the singlemode microwave oven. Compared with the electrical furnace, microwave-assisted heating required shorter times for pyrolysis. Moreover, the microwave pyrolysis oils were more aliphatic and oxygenated and did not contain environmentally harmful compounds such as heavy PAHs. Conversely, the pyrolysis of the sludge at high temperatures using conventional methods gave rise to an oil rich in PAHs including compounds such as benzo[e] and benzo[a]pyrene and benzo[ghi]perylene with 5 or 6 aromatic rings. © 2004 Elsevier B.V. All rights reserved.

Abstract: Model compounds, with a controlled heteroatoms content and well-defined functionalities, were used to study the release of nitrogen compounds from char combustion. In the present work, the mechanisms involved in NO-char heterogeneous reduction were studied with a synthetic coal (SC) char as carbon source. Another synthetic char (SN) without any nitrogen in its composition was also employed in these studies. Temperature programmed reduction (TPR) tests with a gas mixture of 400 ppm NO in argon and with isotopically labelled nitric oxide, 15NO (500 ppm 15NO in argon), were carried out. The gases produced were quantitatively determined by means of MS and FTIR analysers. Under the conditions of this work the main products of the NO-C reaction were found to be N2 and CO2. The main path of reaction involves the formation of surface nitrogen compounds that afterwards react with nitrogen from the reactive gas to form N2. It was observed that fuel-N also participates in the overall heterogeneous reduction reaction, although to a lesser extent. © 2005 Elsevier Ltd. All rights reserved.

Abstract: Adsorption is considered to be one of the more promising technologies for capturing CO2 from flue gases. For post-combustion capture, the success of such an approach is however dependent on the development of an adsorbent that can operate competitively at relatively high temperatures. In this work, low cost carbon materials derived from fly ash, are presented as effective CO2 sorbents through impregnation these with organic bases, for example, polyethylenimine aided by polyethylene glycol. The results show that for samples derived from a fly ash carbon concentrate, the CO2 adsorption capacities were relatively high (up to 4.5 wt%) especially at high temperatures (75 °C), where commercial active carbons relying on physi-sorption have low capacities. The addition of PEG improves the adsorption capacity and reduces the time taken for the sample to reach the equilibrium. No CO2 seems to remain after desorption, suggesting that the process is fully reversible. © 2005 Elsevier Ltd. All rights reserved.

Abstract: Carbon foams were obtained from a bituminous coal with good plasticity properties by a two-stage thermal process under different pressure and temperature conditions. The first stage was a controlled carbonisation treatment under pressure at 450 and 500 °C. In the second stage the carbonisation product was baked at 1100 °C. The foams produced display a macroporous texture with pressure and temperature determining the mean pore size and the amount of pores. The pressure increase reduces the pore size, while the increasing temperature increases the pore volume. © 2005 Elsevier Ltd. All rights reserved.

Abstract: In this work, simultaneous thermogravimetric-mass spectrometric (TG-MS) analysis was used to study the release of various nitrogen compounds during pyrolysis of different-rank coals. The influence of coal rank on the evolution of volatile compounds was also considered. In addition, a series of coal chars with different burn-off degrees were obtained in a bench-scale fluidized bed reactor, using the same parent coal. The evolution of gaseous compounds arising from the thermal treatment of the partially burned chars was studied in the TG-MS system. It was found that the different chemical structures of the chars exerted some influence on the evolution of the gaseous compounds during the devolatilization process. In addition, devolatilization tests were conducted in a bench-scale fluidized bed reactor. During these tests, special attention was given to the formation of N2O. Copyright © 2005 by Begell House, Inc.

Abstract: Coal blends are now widely used by the power generation industry and the general characteristics are well known. Attention is still directed to the emission of NOx, which is subject to more stringent regulation, and to the amount of carbon in ash. The latter is increased when low NOx burners are employed, which is the norm now. It is also increased as a result of additional air staging when over-fire air is added in furnaces, especially tangential fired systems. Such a furnace is studied here. Two approaches can be employed for prediction of NOx and unburned carbon. The first approach uses global models such as the 'slice' model which requires the combustor reaction conditions as an input but which has a detailed coal combustion mechanism. The second involves a computational fluid dynamic model that in principle can give detailed information about all aspects of combustion, but usually is restricted in the detail of the combustion model because of the heavy computational demands. The slice model approach can be seen to be complimentary to the CFD approach since the NOx and carbon burnout is computed using the slice model as a post-processor to the CFD model computation. The slice model that has been used previously by our group is applied to a commercial tangentially fired combustor operated in Spain and using a range of Spanish coals and imported coals, some of which are fired as blends. The computed results are compared with experimental measurements, and the accuracy of the approach assessed. The CFD model applied to this case is one of the commercial codes modified to use a number of coal combustion sub-models developed by our group. In particular it can use two independent streams of coal and as such it can be used for the combustion of coal blends. The results show that both model approaches can give good predictions of the NOx and carbon in ash despite the fact that certain parts of the coal combustion models are not exactly the same. However, if a detailed insight into the combustor behaviour is required then the CFD model must be used. © 2005 Elsevier Ltd. All rights reserved.

Abstract: A series of coals were blended and several aspects of the resultant blends were studied. This included determination of the grindability of the samples by means of the Hardgrove Grindability Index and temperature programmed combustion tests, which were carried out in a thermogravimetric analyzer coupled to a quadrupole mass spectrometer. Special attention was paid to the combustibility parameters and the NO emissions during blend combustion. It was found that while some coal blends present interaction between the individual coals, others do not. This behavior was assumed to be due to the differences in coal structure and functional groups composition. Copyright © 2005 by Begell House, Inc.

Abstract: An experimental study to determine the temperature and mechanism of coal ignition was carried out by using an entrained flow reactor (EFR) at relatively high coal feed rates (0.5 g min-1). Seven coals ranging in rank from subbituminous to semianthracite, were tested and the evolved gases (O 2, CO, CO2, NO) were measured continuously. The ignition temperature was evaluated from the gas evolution profiles, and it was found to be inversely correlated to the reactivity of the coal, as reflected by the increasing values of the ignition temperature in the sequence: subbituminous, high volatile bituminous, low volatile bituminous and semianthracite coals. The mechanism of ignition varied from a heterogeneous mechanism for subbituminous, low volatile bituminous and semianthracite coals, to a homogeneous mechanism for high volatile bituminous coals. A thermogravimetric analyser (TGA) was also used to evaluate coal ignition behaviour. Both methods, TGA and EFR, were in agreement as regards the mechanism of coal ignition. From the SEM micrographs of the coal particles retrieved from the cyclone, it was possible to observe the external appearance of the particles before, during and after ignition. The micrographs confirmed the mechanism deduced from the gas profiles. © 2005 Elsevier Ltd. All rights reserved.

Abstract: In this work, the CO2 capture capacity of a series of activated carbons derived from recycled polyethylene terephtalate (PET) was tested, facing two problems at the same time: minimising plastic waste and developing an adsorbent for CO2 capture. The PET raw material, obtained from post-consumer soft-drink bottles, was chemically activated with KOH. In addition, a series of nitrogen-enriched activated carbons was obtained by mixing the raw material with different nitrogen compounds (i.e., acridine, carbazole and urea). The influence of temperature on the CO2 capture capacity of the adsorbents was evaluated in a thermogravimetric system. The CO 2 uptake was also related to the chemical and textural characteristics of the samples. © 2005 Elsevier B.V. All rights reserved.

Abstract: Perhydrous coals are characterized by a high hydrogen content and exhibit a modified composition and physico-chemical properties in comparison with normal coals. These modifications affect the behaviour of perhydrous coals during pyrolysis and, therefore, may have an influence on the subsequent combustion process. In this work the combustibility behaviour of a series of perhydrous coals was evaluated in order to study the effect of hydrogen enrichment during the thermal treatment of the coals in an oxidant atmosphere. To this end temperature programmed combustion tests for the coals, and air isothermal (500°C) reactivity tests for their chars, were carried out in a thermogravimetric analyser. A clear relationship between the combustion behaviour of the perhydrous coals, and the aromatic to aliphatic hydrogen ratio was found. © 2005 Akadémiai Kiadó, Budapest.

Abstract: NOx emissions from sewage sludge combustion are a concern, because of the usually high nitrogen content of this fuel. The interactions during co-combustion in a fluidized-bed reactor of sewage sludge and a bituminous coal were evaluated, in relation to the nitrogen evolution during the combustion process. The nitrogen stable isotope measurements provide novel results regarding the tracing of nitrogen during combustion. Our preliminary results show that the co-combustion chars retain more nitrogen than expected, with the additional nitrogen being mainly derived from the sludge. Additional measurements are planned on the resultant co-combustion gases, to aid source apportionment of the NOx arising from coal/sewage interactions. © 2005 American Chemical Society.

Abstract: The regeneration of activated carbons used for the decontamination of water and wastewater polluted with organic compounds related to the pharmaceutical industry, has been studied in this work. To this end, the pyrolysis of exhausted activated carbons was performed in a quartz reactor. The influence of the pyrolysis of saturated activated carbons on their adsorptive capacities and porous structure was evaluated. Textural characterisation of the samples was carried out by helium density, and N2 and CO2 adsorption isotherms, at -196 and 0 °C, respectively. Consecutive cycles of pyrolysis of activated carbons exhausted with phenol and salicylic acid, generated a widening of the microporosity, and a decrease in the apparent BET surface areas. The adsorptive capacities for phenol retention after a series of adsorption/pyrolysis cycles were found to decrease drastically. In contrast, consecutive cycles gave higher salicylic acid adsorptive capacities, as compared to phenol. The DTG pyrolysis profiles of the samples saturated with salicylic acid appeared at lower temperatures than those of phenol, which showed two peaks, while those exhausted with salicylic acid only showed one. These results provide evidence of the different adsorption mechanisms of these two pollutants. © 2005 Elsevier B.V. All rights reserved.

Abstract: The nitrogen enrichment of active carbons is reported to be effective in enhancing the specific adsorbate-adsorbent interactions for CO2. In this work, nitrogen-enriched carbons were prepared by co-pyrolysis of sugar and a series of nitrogen compounds with different nitrogen functionalities. The results show that although the amount of nitrogen incorporated to the final adsorbent is important, the N-functionality seems to be more relevant for increasing CO2 uptake. Thus, the adsorbent obtained from urea co-pyrolysis presents the highest nitrogen content but the lowest CO2 adsorption capacity. However, the adsorbent obtained from carbazole co-pyrolysis, despite the lower amount of N incorporated, shows high CO 2 uptake, up to 9 wt.%, probably because the presence of more basic functionalities as determined by XPS analysis. © 2004 Elsevier B.V. All rights reserved.

Abstract: A novel method for sewage sludge treatment based on subjecting the wet sludge to high temperature thermal treatment in a microwave is being investigated at INCAR. Under the appropriate operating conditions, drying, pyrolysis and gasification of the sewage sludge take place, giving rise to a gas with a high CO and H2 content and an oil with a low PAH content. Moreover, due to the high temperatures that can be attained during the process it is possible to obtain a solid residue which is partially vitrified. Unlike other methods aimed at maximizing the porous texture of the solid residue in order to produce adsorbents, the aim of the method proposed in this work is to obtain a solid residue with minimal porous textural development, where the heavy metals present in the residue are occluded in a glassy-like matrix. The advantages of this technique are a substantial volume reduction with respect to the initial sludge and a solid residue that is more resistant to the leaching of organic substances and heavy metals than the char obtained by conventional pyrolysis. © 2005 Elsevier B.V. All rights reserved.

Abstract: The influence of polymerization with formaldehyde on the thermal reactivity of a low-temperature coal tar pitch has been investigated. The mechanism and extent of the polymerization depends on the catalyst used, the greatest extent of polymerization being achieved under basic catalytic conditions. After the polymerization treatment, samples were carbonized ar 420 °C and the products were characterized by optical microscopy. According to the results, polymerization with formaldehyde increases the reactivity of the pitch, giving rise to increased carbonization yields and leading to the formation of the mesophase with milder conditions. The polymerization process also affects the morphology of the resultant anisotropic material, giving rise to the formation of irregularly shaped mesophase particles and reducing the optical texture size of the anisotropic domains, giving mosaic texture, especially when basic catalysis is used. © 2005 American Chemical Society.

Abstract: The effect of different heating mechanisms on the porous network of activated carbons (AC) previously exhausted with phenol has been studied. To this end, thermal treatment of the exhausted AC was performed using two experimental devices: a single mode microwave device operating at 2450 MHz and a conventional electric furnace. By employing microwave energy, the regeneration time was considerably shortened compared to conventional thermal heating. Moreover, microwave heating preserved the porous structure of the regenerated AC more efficiently than treatment in a conventional device. In both cases successive regeneration cycles reduced the microporosity of the activated carbons. However, conventional heating shifted the micropore size distribution to pores of narrower sizes. The apparent BET surface areas were also reduced significantly over the regeneration cycles. A loss of the adsorptive capacity of the carbon material was observed after six adsorption-desorption cycles in both systems. The phenol adsorption capacities decreased to a greater extent in the samples regenerated in the electric furnace. © 2005 Elsevier Inc. All rights reserved.

Abstract: The microwave heating was used for introducing molecular sieve properties into activated carbon fibers (ACF). Acrylic textile fibers used as precursors for the production of the ACF and were manufactured from acrylonitrile (90 wt.%) and vinyl acetate (10 wt.%). During microwave treatment the carbon bed reached temperatures of 800-1000 °C after two min. heating. The results show that microwave heating could be a useful alternative to more commonly used methods for introducing molecular sieve properties into activated carbon adsorbents. One of the advantages of the microwave method is that, in the microwave furnace the carbon bed is uniformly heated throughout.

Abstract: Polyethyleneterephthalate (PET) has become one of the major post-consumer plastic wastes. PET products present a problem of considerable concern due to the huge amount of solid waste produced. The disposal of this waste, together with its low bio- and photo-degradability represents a serious challenge for industrial countries all over the world. Pyrolysis could provide an alternative and economically viable route for processing PET waste due to the potential uses of different by-products: energy from the pyrolysis gases (58% yield in this work), recovery of terephthalic acid and other subproducts (20%), and a solid residue (22%), which has shown a high textural development after activation. The pyrolysis of PET waste was performed in a quartz reactor (i.d. 35mm) under an inert atmosphere. Further activation was carried out at a temperature of 925°C, with a flow rate of 10mlmin-1 of CO2. A series of carbon materials with different burn-off degrees was obtained. Textural characterisation of the samples was carried out by performing N2 adsorption isotherms at -196°C. Changes in the morphological and structural properties of chars were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The carbons obtained were isotropic and highly microporous materials with apparent BET surface areas of up to 2500m2g -1. The suitability of the samples for hydrogen storage was studied by performing H2 adsorption measurements in the 0-1bar pressure range. Adsorption-desorption experiments showed that reversible physisorption takes place in all the samples. The hydrogen adsorption capacities of the activated PET waste compare favourably well with those attained with high-value carbon materials. © 2004 Elsevier B.V. All rights reserved.

Abstract: Understanding the ignition behaviour of coal is of utmost importance for the design of boilers and control of the combustion process. In recent years there has been an increasing utilisation of coal blends for combustion, but information on the possible interactive effects during ignition of the individual components is scarce. In this work the ignition behaviour of a series of coal blends, made up from three coals of different rank, sub-bituminous, high volatile and low volatile bituminous, was studied. To this end a thermogravimetric analyser linked to a mass spectrometer for evolved gas analysis was used. Different ignition behaviour was observed for the coals studied; the sub-bituminous and low volatile bituminous coals ignited heterogeneously, while homogeneous ignition occurred for the high volatile bituminous coal. In the case of blends of the low and high volatile bituminous coals, different mechanisms of ignition were observed depending on the blends composition.

Abstract: This paper explores the use of microwave energy for sewage sludge drying. Four sewage sludges and two microwave devices -a multimode microwave cavity oven (MC) and a single-mode microwave cavity oven (SMC)-were used. On comparing the results of microwave drying with those of conventional drying with hot air, it was found that the use of microwaves saved considerable time and energy. Thus, with the MC microwave oven only 5 minutes was needed to achieve less than 1 wt% moisture content whereas 8 min was required with the SMC and 55 min with conventional drying. The reduction in volume obtained during the drying process was also assessed, the values reached being between 65-90 %. The composition of the sludge was studied by IRTF and elemental analysis. The dried sludges showed a high oxygen content distributed among compounds with C=O and C-O-C groups and a high aliphatic hydrogen content.

Abstract: Four wet sewage sludges from different waste water treatment plants were dried and pyrolyzed (in a single process) at laboratory scale, using a multimode-microwave oven. The gases obtained from these pyrolysis experiments were analyzed and compared with those from a more conventional pyrolysis employing an electrical furnace. The results help to explain the complex mechanisms that take place during the pyrolysis of sewage sludge. This process produces a considerable amount of gases with potential value as fuels due to the fact that they have relatively high calorific values. Upon comparing the two pyrolysis processes, it was found that microwave pyrolysis takes a much shorter time than when using the electrical furnace. It was also found, that while microwave pyrolysis gives rise to a gas with a high content (up to 62%) of CO and H2 (synthesis gas), conventional pyrolysis generates a gas with an elevated proportion (ca. 25%) of hydrocarbons of high calorific value. © 2003 Elsevier B.V. All rights reserved.

Abstract: Coal pyrolysis is the initial, accompanying reaction of a number of coal conversion processes such as hydrogenation, combustion and gasification. However, because of the inherent complexity of coal composition, it is difficult to describe coal pyrolysis clearly. Single model compounds have been used before in order to provide additional insight into the complex processes that occur in the pyrolysis of coal. Yet the picture obtained is a simplified one and certain important aspects such as coal structure, interactions between different surface groups and cross-links are omitted. The approach used in this work involves the preparation of a synthetic coal, SC, with a known structure by curing a mixture of single, well-defined model compounds. By means of chemical characterisation, the SC was shown to contain the macroscopic features of a high volatile coal (proximate and ultimate analyses). FTIR characterisation revealed the presence of functional groups similar to those of coal in the structure of the SC. Temperature-programmed pyrolysis tests were performed in a thermobalance linked to a mass spectrometer and a Fourier transform infrared analyser (TG/MS/FTIR). The thermal behaviour of the synthetic coal (i.e., rate of mass loss and the evolution profiles of gaseous compounds during pyrolysis tests) is very similar to that of the high volatile bituminous coal which was used as a reference material. The great advantage of using SC lies in the fact that its composition and structure can be accurately determined and employed in subsequent applications in basic and mechanistic studies. © 2003 Elsevier B.V. All rights reserved.

Abstract: Knowledge of the amount and distribution of active sites in carbons is of paramount importance for a better understanding of the kinetics involved in heterogeneous gas solid reactions. In this work a commercial active carbon, CM, was treated at several temperatures in order to obtain a series of samples with different textural and structural properties. The results showed that the loss of reactivity of the samples, determined by thermogravimetric analysis, is related not only to the lower surface area but also to the decrease in the amount of active sites due to a higher structural ordering.

Abstract: The formation of mesophase from a low temperature coal tar pitch using formaldehyde as a promoter for polymerization, was studied. The types and contents of anisotropic material in the semi-coke were evaluated by optical microscopy. Samples were embedded in an epoxy resin, left overnight, cut and polished for the examination of particle cross-sections. The results show that the polymerization of a low temperature coal tar pitch with formaldehyde promotes the reaction of the phenolic compounds to form β-resins, and decreases the coalescence tendency of the mesophase.

Abstract: Vapour grown carbon nanofibres (VGCNFs) produced at industrial scale were subjected to different treatments in N2, air and CO2 atmospheres. The effect of these treatments on the homogeneity of the industrial product was investigated by means of TG analysis. Temperature programmed oxidation (TPO) experiments were performed to obtain DTG profiles. The DTG curves were deconvoluted into a mixture of Gaussian-Lorentzian curves, so that the contribution of each peak could be evaluated and assigned to phases of different reactivity. It was found that treatments in air are more selective in removing the most reactive phase (which has a higher content of amorphous carbon) at low burn-off, while at an elevated burn-off degree CO2 treatments result in a greater enrichment of the product in the less reactive phase (which has a higher content of fibre). This behaviour is attributed to the presence of a certain amount of iron in the industrially produced materials and its catalytic effect on the oxidative reactions. The effect of the treatments on the porous texture, surface chemistry and graphite-like character of the samples was also investigated. © 2004 Elsevier B.V. All rights reserved.

Abstract: This paper studies the chemical composition of several supercritical gas (SCG) extracts and its influence on the thermal behaviour under carbonisation conditions. The extracts were obtained from a Spanish lignite (Mequinenza), a low-quality coal from the point of view of energy applications. The lignite was treated with toluene, ethanol (EtOH) and tetrahydrofuran (THF) as solvents under different supercritical temperature and pressure conditions. The extracts display high aliphatic nature and enhanced concentrations of oxygen functional groups, aided by the contribution of hydrogenation and oxygen incorporation reactions occurring in the SCG extraction with EtOH and THF. Thiophenic compounds are also present in great concentrations derived from the exceptionally high organic sulphur content of the parent coal. The carbonisation of the extracts renders anisotropic material with fine mosaic texture, as a consequence of the significant thermal reactivity inferred by the aliphatic and oxygenated groups. The size of the mosaic increases with the temperature of the SCG extraction and varies with the supercritical solvent in the order: toluene<EtOH<THF. © 2004 Elsevier B.V. All rights reserved.

Abstract: Thermal treatment of activated carbon fibres (ACF) has been carried out using a microwave device, instead of a conventional furnace. The results show that microwave treatment affects the porosity of the ACFs, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACFs with the production of pyrone groups, detected by FTIR. As a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained. © 2004 Elsevier Ltd. All rights reserved.

Abstract: Poly(ethylene) terephthalate (PET), has become one of the major post-consumer plastic waste. In this work special attention was paid to minimising PET residues and to obtain a high value carbon material. Pyrolysis and subsequent activation of PET from post-consumer soft-drink bottles was performed. Activation was carried out at 925°C under CO2 atmosphere to different burn-off degrees. Textural characterisation of the samples was carried out by performing N2 adsorption isotherms at -196°C. The obtained carbons materials were mainly microporous, presenting low meso and macroporosity, and apparent BET surface areas of upto 2500m 2g-1. The capacity of these materials for phenol adsorption and PAHs removal from aqueous solutions was measured and compared with that attained with commercial active carbons. Preliminary tests also showed high hydrogen uptake values, as good as the results obtained with high-tech carbon materials. © 2004 Elsevier B.V. All rights reserved.

Abstract: Knowledge of surface properties is essential for understanding the reaction mechanisms involved in several coal conversion processes. However, due to the complexity and heterogeneity of coal this is rather difficult and the use of known model compounds could be a valuable tool. Single model compounds have been widely used, but they give a quite simplified picture. In this work a mixture of model compounds in a phenol-formaldehyde matrix was cured in order to create cross-linked structures. The obtained synthetic coal was pyrolysed in a fixed bed reactor, under helium atmosphere. The surface composition of the chars was evaluated by XPS, adsorption gravimetry of water vapour, temperature-programmed desorption and potentiometric titration. Texture was characterised by N 2 and CO2 adsorption isotherms at 77 and 273 K, respectively, and immersion calorimetry in benzene. The results obtained from the different techniques were contrasted in order to give an overview of the surface properties (chemical and physical) of the samples studied. Chars obtained under the same operating conditions from a high volatile bituminous coal were used as a reference. © 2004 Elsevier Ltd. All rights reserved.

Abstract: Bituminous coal-based activated carbon was modified by impregnation with melamine and heat treatment at 850 °C. Another sample was impregnated with melamine and urea and heat treated at 650 and 850 °C. Chemical and physical properties of the materials were determined using Boehm titration, thermal analysis, sorption of nitrogen and SEM with EDX. Then the H2S breakthrough capacity tests were carried out and the sorption capacity was calculated. The results revealed that carbons modified with nitrogen-containing species and heat-treated at 850 °C have a hydrogen sulfide removal capacity exceeding more then 10 times the capacity of unmodified sample. H2S on the surface of these materials is oxidized to sulfuric acid and elemental sulfur and stored in the pore system. New carbons are hypothesized to act as catalytic reactors promoting two different pathways of hydrogen sulfide oxidation in two different locations. In small micropores, where water is present, hydrogen sulfide dissociate to HS- ions and those ions are oxidized to sulfur radicals and sulfur dioxide leading to the formation of sulfuric acid. In larger pores with incorporated nitrogen, basic sites promote dissociation and formation of sulfur polymers, which are resistant to further oxidation. © 2003 Elsevier Ltd. All rights reserved.

Abstract: Poly(ethyleneterephthalate), PET, is nowadays one of the polymers more widely used. However, due to its big production, it accounts for a large part of the wastes generated and it becomes necessary to minimise them. The PET incineration with energy recovery is the most common way to eliminate these residues. Further research is needed in order to find alternative processes to recycling PET. In this work, it is shown that the post-consumer PET is an interesting source of carbonaceous materials that develop a well controlled microporosity, giving the possibility of application in several fields.

Abstract: The nature of basic sites on carbon surfaces is a controversial issue within Carbon Science. Traditionally, oxygen-containing groups like: γ pyrone-type, chromene, diketone or quinone groups, on the one hand, and delocalized �-electrons of the basal planes, on the other, are assumed to have a basic nature. However, there is no consensus about neither the strength as bases of these sites, nor the extent of their contribution to the overall carbon basicity. Researchers are divided between those that support basic-oxygen-containing groups as main responsible of carbon basicity and those that attribute the overall basicity of a carbon to the delocalized �-electrons of the basal planes. In this work we will discuss the virtues and drawbacks of the different hypotheses about basic carbon sites in view of experimental and theoretical results. © 2004 Elsevier Ltd. All rights reserved.

Abstract: Thermal regeneration of activated carbons (AC) was carried out at 1123 K and under N2 atmosphere. Experiments have been carried out using a single mode microwave device operating at 2450 MHz and a conventional electric furnace (EF) so as to compare the effect of the different heating mechanisms on the adsorptive capacities of the regenerated AC. The adsorbents were saturated with phenol in columns. Adsorptive capacities after subsequent regeneration cycles were evaluated from the breakthrough curves. Additionally, a complete textural and chemical characterization of the regenerated samples was also carried out in order to study the influence of the subsequent regeneration cycles on the texture and the adsorptive capacities of the AC. Textural characterization of the regenerated samples was carried out by means of N 2 adsorption isotherms at 77 K. © 2004 Elsevier Ltd. All rights reserved.

Abstract: A mixture of carbon compounds was pyrolysed under an inert atmosphere at different temperatures in a fixed bed reactor. The resultant chars were characterised in terms of texture and thermal behaviour. Textural characterisation of the chars was carried out by N2 and CO2 adsorption isotherms at -196 and 0 °C, respectively. Char isothermal reactivity in air at 500 °C, and in CO2 at 1000 °C, was performed in a thermogravimetric analyser (TGA). Temperature-programmed combustion tests under 20% oxygen in argon were also performed in the TGA linked to a mass spectrometer (TGA/MS). The results showed that char textural properties do not always relate well to their reactivity. Not only do physical properties (e.g. surface area, porosity) but also chemical properties (e.g. active sites concentration and distribution) play an important role in the reaction of carbonaceous material and oxidant. On the other hand, in terms of chemical composition the chars obtained from the mixture of carbon compounds were very similar to the chars produced under the same experimental conditions by a high volatile bituminous coal. The fact that carbon compounds are well known makes it easier to obtain knowledge about the functional groups present in synthetic char, and to study the mechanisms of heterogeneous reactions such as the reduction of NO with carbon. © 2003 Elsevier Ltd. All rights reserved.

Abstract: The increasing environmental concern caused by the use of fossil fuels and the concomitant need for improved combustion efficiency is leading to the development of new coal cleaning and utilisation processes. However, the benefits achieved by the removal of most mineral matter from coal either by physical or chemical methods can be annulled if poor coal combustibility characteristics are attained. In this work a high volatile bituminous coal with 6% ash content was subjected to chemical demineralisation via hydrofluoric and nitric acid leaching, the ash content of the clean coal was reduced to 0.3%. The original and treated coals were devolatilised in a drop tube furnace and the structure and morphology of the resultant chars was analysed by optical and scanning electron microscopies. The reactivity characteristics of the chars were studied by isothermal combustion tests in air at different temperatures in a thermogravimetric system. Comparison of the combustion behaviour and pollutant emissions of both coals was conducted in a drop tube furnace operating at 1000 °C. The results of this work indicate that the char obtained from the chemically treated coal presents very different structure, morphology and reactivity behaviour than the char from the original coal. The changes induced by the chemical treatment increased the combustion efficiency determined in the drop tube furnace, in fact higher burnout levels were obtained for the demineralised coal. © 2003 Elsevier Ltd. All rights reserved.

Abstract: The pyrolysis of sewage sludge was studied in a microwave oven using graphite as microwave absorber. The pyrolysis temperature ranged from 800 to 1000°C depending on the type of sewage sludge. A conventional electrical furnace was also employed in order to compare the results obtained with both methods. The pyrolysis oils were trapped in a series of condensers and their characteristics such as elemental analysis and calorific value were determined and compared with those of the initial sludge. The oil composition was analyzed by GC-MS. The oils from the microwave oven had n-alkanes and 1-alkenes, aromatic compounds, ranging from benzene derivatives to polycyclic aromatic hydrocarbons (PAHs), nitrogenated compounds, long chain aliphatic carboxylic acids, ketones and esters and also monoterpenes and steroids. The oil from the electric oven was composed basically of PAHs such as naphthalene, acenapthylene, phenanthrene, fluoranthene, benzo[a]anthracene, benzofluoranthenes, benzopyrenes, indenepyrene, benzo[ghi]perylene, and anthanthrene. In contrast, these compounds were not produced in the case of microwave-assisted pyrolysis. © 2003 Elsevier B.V. All rights reserved.

Abstract: Herein we report results from quantum chemical calculations on a large series of pyrone-like model compounds which are relevant for carbon basicity. In consonance with previous work (Carbon 1999, 37, 1002), pyrone-like functionalities at the edge of graphene layers are predicted to exhibit a broad range of pKa values (4-13) depending on the relative position of the ketone and etheric rings. The thermodynamic stability of pyrones is discussed in terms of reaction energies calculated for selected isodesmic processes which give insight into the role of the adjacent basal plane, the relative abundance of polycyclic pyrone-like structures, and so forth. In addition, we show that hypothetical redox processes involving pyrone-like structures have estimated electrochemical potentials which lie in the range of those observed in many carbons. Finally, the ability of pyrone-like model compounds to provide a global view of the chemical and electrochemical properties of basic carbon surfaces is discussed.

Abstract: The effect of curing temperature on smokeless fuel briquettes has been studied by Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS), and temperature programmed decomposition (TPD). These techniques help to predict the final properties of these briquettes which were prepared with a low-rank coal, sawdust, and olive stone as biomasses and humates as binder. The best mechanical properties are reached with both the mildest thermal curing at 95°C and the cocarbonized at 600°C of Maria coal (M2) and sawdust (S) due to the fibrous texture of sawdust. The temperature of curing causes the release of a certain amount of oxygenate structures and the decrease of the mechanical resistance.

Abstract: The present work reports a theoretical study of the infrared spectra of chemical structures that are suitable to the description of the surface chemistry of carbon materials. Prior to any consideration, the computational approach was tested and adapted by comparing the predicted IR spectra to those obtained experimentally for various reference compounds. Several models were considered, subsequently accounting for the most relevant functional groups that have been postulated to decorate the edges of graphene layers on carbon materials (i.e., anhydrides, carboxyls, lactones, phenolic, quinones, and pyrones). For each of the previous functional groups, different structures involving a different number of fused rings were considered. This strategy allowed us to establish the effect of conjugation on the shift of the IR frequencies corresponding to a given functional group. Cooperative effects between different functional groups (phenol-carboxyl, phenol-lactone, and so on) were another aspect that revealed itself to be an interesting issue when assigning frequencies in the IR spectra of highly oxidized carbon materials. Thus, it was found that the frequencies of the C=O bonds present in acid functional groups were systematically lowered when phenolic groups were close enough to establish hydrogen bonds. Special attention was also paid to the elucidation of the origin of the 1600-cm-1 band of carbons. It was found that, in the case of acid carbons, this band can be assigned to C=C stretching of carbon rings decorated mainly with phenolic groups. Cyclic ethers in basic carbons would also promote absorption in the 1600-cm-1 region of the IR spectrum. Finally, the predicted assignments are employed to interpret the IR spectra obtained experimentally for several activated carbons.

Abstract: Perhydrous coals are characterised by high H/C atomic ratios and so their chemical structure is substantially modified with respect to that of conventional coals. As a result, perhydrous coals show different physico-chemical properties to common coals (i.e. higher volatile matter content, enhancement of oil/tar potential, relatively lower porosity and higher fluidity during carbonisation). However, there is little information about thermal behaviour during the pyrolysis of this type of coal. In this work, six perhydrous coals (H/C ratio between 0.83 and 1.07) were pyrolysed and analysed by simultaneous thermogravimetry/mass spectrometry. The results of this work have revealed the influence of high H/C values on the thermal behaviour of the coals studied. During pyrolysis the perhydrous coals exhibit very well defined, symmetrical peaks in the mass loss rate profiles, while normal coals usually show a broader peak. The shape of such curves suggests that in perhydrous coals fragmentation processes prevailed over condensation reactions. The high hydrogen content of perhydrous coals may stabilise the free radicals formed during heat treatment, increasing the production of light components. © 2003 Elsevier Science B.V. All rights reserved.

Abstract: Coal blending is becoming of increasing importance in power stations firing pulverised coal as a result of increasing competition, stricter emission legislation and is an attractive way of improving plant economic and combustion performance. Presently, the two general methods used by power station operators to assess or predict the performance of an unknown coal blend to be fired in power station boilers are by the use of experimental large scale rig tests or correlation indices derived from experience of firing other coal blends in the power station environment. The first is expensive and the second is of doubtful accuracy in some cases. This paper evaluates the application of mathematical modelling of the combustion of a series of binary coal blends in the test situation of a drop tube reactor to predict the NO emissions and degree of char burnout. Its applicability to low NOx burners used in power stations is discussed and it is concluded that present mathematical coal combustion models are not developed sufficiently to enable an adequate description of the binary blends and the physical and chemical processes, which may include interactions, during combustion of the blend. This means that accurate predictions cannot be made. © 2001 Elsevier Science Ltd. All rights reserved.

Abstract: Emissions of nitrogen oxides during coal combustion are a major environmental problem. The chemically bound nitrogen in fuel accounts for up to 80% of total NOx emissions. In this respect, fundamental studies are needed to clarify the mechanisms and to identify the different species that are precursors in the formation of the NOx. Mass spectrometry (MS) has been used for decades as a successful technique in evolved gas analysis. However, MS is normally used to identify typical volatile compounds formed during coal pyrolysis (i.e. H2, CH4, CO, CO2 and H2O) but very few works on the detection by MS of nitrogen compounds during coal devolatilisation can be found. In this work, the possibility of detecting different nitrogen compounds by means of thermogravimetric-MS during the temperature-programmed pyrolysis of coal was evaluated. Interferences in the N-compounds MS signals were determined. The use of model compounds provided additional information on the MS response factors of the volatile compounds produced. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: This paper describes a new method for pyrolyzing sewage sludge using a microwave furnace. It was found that if just the raw wet sludge is treated in the microwave, only drying of the sample takes place. However, if the sludge is mixed with a small amount of a suitable microwave absorber (such as the char produced in the pyrolysis itself) temperatures of up to 900°C can be achieved, so that pyrolysis takes place rather than drying. Microwave treatments were also compared with those carried out in a conventional electric furnace, as well as the characteristics of their respective carbonaceous solid residues. © 2002 Elsevier Science Ltd. All rights reserved.

Abstract: The active surface area (ASA) values determined by gravimetric, temperature programmed desorption (TPD), and oxygen chemisorption isotherms (OCI) methods were compared. An activated carbon was treated using different temperatures and vacuum to obtain several samples with different textural properties. The gravimetric and TPD methods were carried out in a thermogravimetric analyzer (TGA) and a volumetric apparatus was used for OCI. Results showed that the gravimetric method yielded the highest ASA values.

Abstract: Polymer waste nowadays accounts for a large part of municipal solid waste and so poses a problem of considerable concern for the environment. In this study, it is reported that poly(ethylene terephthalate) pyrolysis is a valuable process with no residual solids, as all the products obtained are of potential use, i.e., energy from the gases produced (58%), terephthalic acid (approximately 20%), and a solid black residue (22%) which, when activated, shows interesting properties, making it useful as an adsorbent. Pyrolysis of raw PET was performed under nitrogen atmosphere, and ulterior activation was achieved at 925°C, with a flow rate of 10 mL min-1 of CO2, up to different burn-off degrees. Textural characterisation of the samples was carried out by measuring apparent density (mercury at 0.1 MPa), mercury porosimetry, and N2 and CO2 adsorption isotherms, at -196 and 0°C, respectively. The active carbons obtained were mainly microporous, with BET apparent surface areas of up to 2468 m2g-1.

Abstract: The aim of this work was to determine the influence that an advanced demineralisation procedure has on the combustion characteristics of coal. A high-volatile bituminous coal with 6.2% ash content was treated in a mixture of hydrofluoric and fluorosilicic acids (HF/H2SiF6). Nitric acid was used either as a pretreatment, or as a washing stage after HF/H2SiF6 demineralisation, with an ash content as low as 0.3% being attained in the latter case. The structural changes produced by the chemical treatment were evaluated by comparison of the FTIR spectra of the raw and treated coal samples. The devolatilisation and combustibility behaviour of the samples was studied by using a thermobalance coupled to a mass spectrometer (TGA-MS) for evolved gas analysis. The combustibility characteristics of the cleaned samples were clearly improved, there being a decrease in SO2 emissions. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: Nitrogen oxides are one of the major environmental problems arising from fossil fuel combustion. Coal char is relatively rich in nitrogen, and so this is an important source of nitrogen oxides during coal combustion. However, due to its carbonaceous nature, char can also reduce NO through heterogeneous reduction. The objectives of this work were on one hand to compare NO emissions from coal combustion in two different types of equipment and on the other hand to study the influence of char surface chemistry on NO reduction. A series of combustion tests were carried out in two different scale devices: a thermogravimetric analyzer coupled to a mass spectrometer and an FTIR (TG-MS-FTIR) and a fluidized bed reactor with an on line battery of analyzers. The TG-MS-FTIR system was also used to perform a specific study on NO heterogeneous reduction reactions using chars with different surface chemistry. According to the results obtained, it can be said that the TG-MS-FTIR system provides valuable information about NO heterogeneous reduction and it can give good trends of the behavior in other combustion equipments (i.e., fluidized bed combustors). It has been also pointed out that NO-char interaction depends to a large extent on temperature. n the low-temperature range (<800 °C), NO heterogeneous reduction seems to be controlled by the evolution of surface complexes. In the high-temperature range (>800 °C), a different mechanism is involved in NO heterogeneous reduction the nature of the carbon matrix being a key factor.

Abstract: In carbon materials, active surface sites only represent a fraction of the total surface area, called active surface area (ASA). Knowledge of the nature and concentration of the active sites is of paramount importance for a better understanding of the kinetics involved in heterogeneous gas-solid reactions. However, although ASA reveals interesting information about the sample, there is a need for a reliable and standardised method for its estimation. The aim of this work is to compare ASA determination by the usual methods (i.e., gravimetry, TPD) with another method, which is based on pressure measurements in order to perform an oxygen chemisorption isotherm (OCI). The results showed that the OCI method seems to be a valuable and alternative method for ASA determination, as it avoids the main potential source of errors inherent in the usual methods.

Abstract: The purpose of this work was to study the formation of mesophase spherules from a low-temperature coal tar pitch under carbonization conditions. For comparison, the carbonization of a high-temperature coal tar pitch and a petroleum pitch were also considered. Different operating conditions during the carbonization process were used in an attempt to cover different degrees of mesophase formation and development for each pitch. The parent pitches and the semicokes thus obtained were analyzed by elemental analysis, optical microscopy, and Fourier transform infrared spectroscopy (FT-IR). More significantly, the samples were subjected to thermal decomposition under well-controlled operating conditions from room temperature to 850°C in a thermogravimetric analyzer (TG). The use of a mass spectrometer linked to the TG (TG-MS) provides additional data about the devolatilization process, yielding information about the evolution of different volatile products and about possible chemical reactions occurring during thermal decomposition. Thus an insight into the process of mesophase formation is obtained. The results from FT-IR, elemental analysis, and the TG-MS tests were compared with the different extents of mesophase formation, checked by optical microscopy. According to the results, several stages can be distinguished as temperature increases in the carbonization process of the pitches. In the low-temperature coal tar pitch, the devolatilization of light components, especially phenols, accounts for the most significant weight loss. Moreover, cross-linking contributes greatly to the formation and development of mesophase, resulting in the predominance of bulk mesophase in a relatively short time in the case of the low-temperature coal tar pitch.

Abstract: Combustion profiles determined by TGA and experiments in a laminar entrained flow reactor (EFR) were used in this work to assess the relative combustion reactivities of different rank coals and their binary coal blends. The combustion behaviour of coal blends in TGA was greatly influenced by coal rank and the proportion of each component in the blend. Higher volatile coals exerted more influence in the low-temperature region and less reactive coals in the char combustion zone. The results in the EFR indicated that coal blends burnout and NO emissions show additivity in the case of similar nature coals. When one of the components was a high-rank coal, the burnout of the blend exhibited, in some cases, positive synergistic effects, while a clear deviation from linearity was found in NO emissions. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 °C) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: The pyrolysis of a sewage sludge, produced by a Spanish urban wastewater treatment plant, was carried out in a laboratory furnace. Pyrolysis conditions, like heating rate and final pyrolysis temperature, were varied so that their influence on the characteristics of the resulting gases, liquids and solid residues could be studied. It was found that increasing the pyrolysis temperature decreases the solid fraction yield and increases the gas fraction yield while that of the liquid fraction remains almost constant. Furthermore, the effect of the heating rate was found to be important only at low final pyrolysis temperatures. Independently of the pyrolysis conditions, all the solid products obtained were of a basic nature and highly macroporous, the meso- and micro-pore volumes being relatively low. Both oils and gases produced in the pyrolysis showed relatively high overall heating values, comparable to some conventional fuels, revealing the potential application of these products as fuel. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: A laboratory-scale study was performed in order to investigate the effects that the addition of petroleum coke has on the texture and reactivity of the resultant metallurgical cokes. It was observed that the addition of petroleum coke to coking blends causes a reduction in the micropore volume and reactivity of metallurgical cokes. A relation between these two parameters was found, suggesting that the decrease in reactivity is a consequence of the decrease in surface area undergone by the metallurgical cokes obtained with petroleum coke addition. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: Pyrolysis is currently being considered as an alternative method of treating sewage sludge. It yields residual oils and gases, which can be used as fuels, and a solid which can either be burned or physically activated with air or CO2. The aim of this work was to study the influence of different pyrolysis conditions (e.g. temperature and heating rate) on the reactivity in air and in CO2 of carbonaceous materials obtained from these types of residues. An anaerobic sewage sludge produced in a Spanish urban waste water treatment plant, containing 5 wt.% moisture after air-drying, was pyrolyzed in an electrical laboratory furnace under different pyrolysis conditions. Non-isothermal reactivities (up to 1100°C) in air and in CO2 of the carbonaceous materials obtained after pyrolysis were performed in a thermobalance. The TG and DTG curves obtained from these experiments are discussed. © 2001 Elsevier Science B.V.

Abstract: Thermal treatment of activated carbon fibres (ACF) in a flow of N2 gas has been carried out using a microwave device operating at 2450 MHz and with a power input of 1000 W, instead of a conventional furnace, and the samples were analysed by means of low temperature N2 adsorption, elemental analysis and determination of points of zero charge. The results show that microwave treatment for periods between 5 and 30 min affects the porosity of the ACF, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACF. During microwave treatment surface groups are completely eliminated, whereas oxygen and nitrogen atoms bonded within the pseudo-graphitic layer planes are retained. On re-exposure to air the surface groups only reform to a very limited extent and as a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained. © 2001 Elsevier Science B.V. All rights reserved.

Abstract: Knowledge of the coal devolatilisation rate is of great importance because it exerts a marked effect on the overall combustion behaviour. Different approaches can be used to obtain the kinetics of the complex devolatilisation process. The simplest are empirical and employ globaland kinetics, where the Arrhenius expression is used to correlate rates of mass loss with temperature. In this study a high volatile bituminous coal was devolatilised at four different heating rates in a thermogravimetric analyser (TG) linked to a mass spectrometer (MS). As a first approach, the Arrhenius kinetic parameters (k and A) were calculated from the experimental results, assuming a single step process. Another approach is the distributed-activation energy model, which is more complex due to the assumption that devolatilisation occurs through several first-order reactions, which occur simultaneously. Recent advances in the understanding of coal structure have led to more fundamental approaches for modelling devolatilisation behaviour, such as network models. These are based on a physico-chemical description of coal structure. In the present study the FG-DVC (Functional Group-Depolymerisation, Vaporisation and Crosslinking) computer code was used as the network model and the FG-DVC predicted evolution of volatile compounds was compared with the experimental results. In addition, the predicted rate of mass loss from the FG-DVC model was used to obtain a third devolatilisation kinetic approach. The three methods were compared and discussed, with the experimental results as a reference. © 2001 Elsevier Science B.V.

Abstract: Ab initio calculations predict that pyrone-like structures (see picture) have large thermodynamic basicities similar to those of the proton sponges, such as 1,8-bis(dimethylamino)naphthalene. These compounds could, therefore, be novel types of oxygen-based organic superbases and show a clear structure- activity relationship between their unusual basicity and the resonance stabilization achieved by their protonated forms.

Abstract: This study was designed to determine the value of microcalorimetry as a probe of acid/base sites on carbon surfaces. Calorimetric studies of ammonia adsorption on acid and ammonia pretreated activated carbon (BDH) samples demonstrated that the technique does titrate acid sites (at equilibrium) according to their relative strengths. However, only in conjunction with other techniques, including Boehm titration, point of zero charge (PZC) and temperature programmed desorption (TPD) is it possible to determine the probable identity of the acid sites present on a given carbon. Collective consideration of the data from all techniques suggests that ammonia pretreatments create a surface whose chemistry is completely different from that of the original carbon. Not only are new acidic sites created, but a high concentration of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreatment temperature.

Abstract: The surface chemistry of two active carbons was modified using a microwave device as a heat source. When microwave treatments are conducted in a nitrogen flow, most oxygen-containing groups are removed from the surface of the carbons. This in turn gives rise to a significant increase in the pH of the carbons. Microwave treatment is less time-consuming than conventional heating. Only a few minutes are required to transform an acidic carbon into a basic carbon with a relatively low oxygen content. On the other hand, microwave-treated carbons undergo re-oxidation, to a greater or lesser extent, upon atmospheric exposure. It was observed that atmospheric re-oxidation of microwave-treated carbons tends to restore more acidic groups when the treatment is carried out on an acidic precursor than when the carbon is of a basic character. Nevertheless, carbons exposed to the atmosphere for up to 2 months still showed higher pHs than those of the corresponding precursors.

Abstract: Simultaneous thermogravimetry-mass spectrometry was used to study the pyrolysis behaviour of an anthracite and three bituminous coals of different volatile matter content. This system was optimized by using calcium oxalate as a reference for calibration. A normalization method that permitted a semiquantitative comparison between the volatile species of the coals was also developed. The instantaneous evolution of the volatile compounds was studied by means of temperature-programmed pyrolysis experiments. The peaks varied in shape, temperature and size, and showed a marked dependence on coal rank. This can be attributed to the varying amounts of the different functional groups in the coals studied. Special attention was paid to the nitric oxide released during pyrolysis, together with its precursor species.

Abstract: The results presented in this work are part of a more extensive research programme aimed at assessing the impact of coal porous structure on density based process evaluation and modelling. The coal samples used were obtained from two different density-based cleaning processes, a Vorsyl dense medium separator for treating an anthracite (TW) with a size fraction of 0.5-8.0 mm and a spiral concentrator for treating a bituminous coal (DH) with a size of less than 2 mm. Textural characterisation of the samples was carried out by measuring true (helium) and apparent (mercury) densities and mercury porosimetry up to a maximum pressure of 200 MPa. Adsorption isotherms in CO2 at 273 K were also determined for both coal series. In the case of the bituminous coal series a linear relationship between porosity and ash level was found. This may have important implications if coal porosity and/or textural parameters need to be incorporated into new density-based simulation models.

Abstract: The contribution to carbon basicity of pyrone-type structures is examined in this work by carrying out ab initio calculations on various cluster models. The different basic sites in a bicyclic pyrone structure are studied at the MP2/6-311+G(2d,2p)�MP2/6-31G(d) level of theory, rendering a reaction energy of -84.2 kcal/mol when a proton transfer takes place from H3O+ to the carbonylic oxygen in pyrones. The interpretation of the theoretical results confirms that resonance stabilization is a crucial factor controlling the basic character of pyrone-type structures. Various effects, like the modification of the etheric position, the relative position of non-neighboring oxygen atoms, and the presence of an adjacent basal plane, are also taken into account. Due to the increase of resonance stabilization observed in large cluster models, a broad spectrum of base strength covered by pyrone-type structures is predicted. The reaction energies of these pyrone-type structures with H3O+ are a few kilocalories per mole more exoergic than that of quinoline, an illustrative organic base. These results support the outstanding role played by pyrone-type structures in carbon basicity.

Abstract: The emission of sulfur oxides during the combustion of coal is one of the causes, among other air pollution problems, of acid rain. The contribution of coal as the mainstay of power production will be determined by whether its environmental performance is equal or superior to other supply options. In this context, desulfurization of coal before combustion by biological methods was studied Four Spanish high-sulfur content coals of different rank were inoculated with bacteria isolated from mine-drainage waters and with naturally occurring bacteria inherent in the coals to be treated. Higher levels of desulfurization were obtained in the case of the samples treated with their own accompanying bacteria and when aeration was increased. All the samples were amenable to the biodepyritization processes. However, it is of little value to achieve large sulfur reductions if a decrease in coal combustion performance is obtained in the process. For this reason, a comparison was made between the combustibility characteristics of the original coals and those of the biodesulfurized samples. Results indicated that combustibility was not substantially modified by the overall biological treatment. The benefits of reduced sulfur emissions into the atmosphere ought to be taken into account as part of the general evaluation of the processes. The emission of sulfur oxides during the combustion of coal is one of the causes, among other air pollution problems, of acid rain. The contribution of coal as the mainstay of power production will be determined by whether its environmental performance is equal or superior to other supply options. In this context, desulfurization of coal before combustion by biological methods was studied. Four Spanish high-sulfur content coals of different rank were inoculated with bacteria isolated from mine-drainage waters and with naturally occurring bacteria inherent in the coals to be treated. Higher levels of desulfurization were obtained in the case of the samples treated with their own accompanying bacteria and when aeration was increased. All the samples were amenable to the biodepyritization processes. However, it is of little value to achieve large sulfur reductions if a decrease in coal combustion performance is obtained in the process. For this reason, a comparison was made between the combustibility characteristics of the original coals and those of the biodesulfurized samples. Results indicated that combustibility was not substantially modified by the overall biological treatment. The benefits of reduced sulfur emissions into the atmosphere ought to be taken into account as part of the general evaluation of the processes.

Abstract: Two commercial activated carbons were subjected to thermal treatment in a N2 atmosphere using a microwave multimode resonant cavity and a conventional electric tube furnace as heat sources. The temperature of the carbon bed during the microwave treatment was monitored using an infrared pyrometer and an Inconel sheltered type-K thermocouple. A comparison between both methods of measuring temperature was made. When similar treatment temperatures are used, both techniques produce similar changes in the textural and chemical properties of the activated carbons. However, microwave treatment is much less time-consuming than conventional heating. Microwave treatment in an inert environment seems to be an efficient and attractive way of removing oxygenated functionalities from carbon surfaces and of increasing the hydrophobicity and basicity of carbons.

Abstract: NO is the primary product of the oxidation of char nitrogen, and in some combustion processes the NO can be reduced on the char surface to give N2O and/or N2. In this study a range of bituminous coals (low, medium and high volatile matter content) were pyrolysed in a fixed bed reactor at various heating rates. Textural characterisation was carried out by measuring true (He) and apparent (Hg) densities and N2 (-196°C) and CO2 (0°C) adsorption isotherms. Pore volume distributions and surface areas were obtained for the chars studied. A thermogravimetric analyser coupled to a quadrupole mass spectrometer (TG-MS) was used to study the combustion behaviour of the samples and the nitrogen compounds evolved during temperature-programmed combustion. Results are discussed in terms of the influence of both textural properties and reactivity on NO emissions and on the heterogeneous reduction of NO.

Abstract: Previous experimental work with several carbons revealed the presence of various basic sites of different strength. The work reported here argues that this controversy is mainly due to an important lack of information. In particular, it is shown that the assumption about the weak basic character of the pyrone-like structures must be seriously reconsidered.

Abstract: Certain aspects of the Nippon Steel Corp. (NSC) based test for measuring metallurgical coke reactivity were studied at the Spanish National Coal Institute (INCAR). It was found that some highly reactive cokes do not follow the correlation between the coke reactivity index (CRI) and the coke strength after reaction (CSR) observed in most metallurgical cokes. It was proved that the temperature of the furnace at the beginning of the NSC test is irrelevant to the subsequent determination of CRI and CSR. By starting the test with a hot furnace, the total operation time and energy consumption can be reduced. In addition, a good correlation was found between the NSC test and a simpler and more economical test: the ECE-INCAR reactivity test.

Abstract: Grinding of a high volatile bituminous coal was performed in three comminution devices: Raymond Mill (RM), Rolls Crusher (RC) and Ball Mill (BM). The pulverised samples were sieved to obtain four particle size fractions, and temperature-programmed combustion (TPC) was used for the evaluation of their combustion behaviour. In addition, three coals of different hardness and rank were mixed in various proportions in order to compare the combustibility characteristics of the binary coal blends with those of the individual coals. The effect of coal blending on grindability was also studied. It was found that grindability was non-additive especially when coals of very different Hardgrove Grindability Index (HGI) were blended. The combustion studies also suggested that there exists an interaction between individual coals when they are burnt as a blend. Copyright (C) 1999 Elsevier Science S.A. Grinding of a high volatile bituminous coal was performed in three comminution devices: Raymond Mill (RM), Rolls Crusher (RC) and Ball Mill (BM). The pulverized samples were sieved to obtain four particle size fractions, and temperature-programmed combustion (TPC) was used for the evaluation of their combustion behaviour. In addition, three coals of different hardness and rank were mixed in various proportions in order to compare the combustibility characteristics of the binary coal blends with those of the individual coals. The effect of coal blending on grindability was also studied. It was found that grindability was non-additive especially when coals of very different Hardgrove Grindability Index (HGI) were blended. The combustion studies also suggested that there exists an interaction between individual coals when they are burnt as a blend.

Abstract: Coal combustion computational fluid dynamic (CFD) models are a powerful predictive tool in combustion research. In existing coal combustion CFD models, the process is described by three kinetic rates: coal devolatilization, volatile combustion and char combustion. A general, representative devolatilization rate for coal is a matter of some contention, and measured rates depend upon the type of experimental system employed in their determination. Thus the reported rates vary considerably, causing difficulties in the choice of rate expression for CFD modelling applications. In this investigation, a laminar flow CFD model of a drop-tube furnace was used to assess the influence of global devolatilization rates on overall combustion behaviour, and in particular, NOx emissions. The rates chosen include some of the common expressions employed by researchers in the field. Analysis, and comparison of the modelling results with those of the experimental, indicated that a single-step devolatilization rate can give satisfactory profiles. This rate can be calculated from the tar release rate using a network model such as FG-DVC (functional group, depolymerization, vaporization and cross-linking), together with the nitrogen partitioning between gas and char during pyrolysis. The use of these single-step models result in good predictions of NOx, and the inclusion of soot/NOx interactions can improve the model significantly to give an excellent agreement with experimental results.

Abstract: At present the primary difficulty with employing carbon for the purposes of NOx removal is the lack of selectivity. Carbon generally reacts as readily with oxygen as with NO. Thus, carbons in lean-burn exhausts (O2/NO&gt;100) generally `burn' rather than selectively removing NO. Here we report on microcalorimetric studies which show that high temperature (950 °C) hydrogen-treated carbons will adsorb NO at room temperature, but will not adsorb significant quantities of oxygen. In contrast, the same activated carbon treated at high temperature in nitrogen will strongly adsorb both species. The selective nature of the hydrogen-treated material and the less-selective nature of the nitrogen-treated material is fully consistent with an earlier model of carbon surface chemistry which highlights the contrast in the character and concentration of active surface species created by each of these treatments.

Abstract: In heterogeneous gas-solid reactions knowledge of the nature and concentration of active sites is important for an understanding of the kinetics involved in such reactions. Variations in the reactivity of chars have been associated with differences in the amounts of active surface area (ASA). Although procedures for measuring textural properties are well established, ASA is determined through a variety of techniques. In this study a low volatile bituminous coal was pyrolysed at various heating rates and soaking times in order to obtain chars with different properties. Total surface areas were obtained from gas adsorption isotherms in N2 at -196°C and in CO2 at 0°C. Total pore volume was calculated by measuring true (He) and apparent (Hg) densities. ASA was evaluated by using gravimetric and volumetric methods, and the results are discussed in terms of relating char reactivity in oxygen, with ASA values.

Abstract: The addition of petroleum coke to a typical industrial coal blend used in the production of metallurgical coke was studied. Cokes were produced at semi-industrial scale at the INCAR coking plant, using petroleum coke of different particle size distribution as an additive. Special attention was paid to changes caused in the textural properties (porosity, pore size distribution, fissures at the interface between metallurgical coke and petroleum coke) which have been found to be responsible for variations in the metallurgical coke quality parameters (e.g., mechanical strength and reactivity towards CO2). Variation in porosity was found to depend on particle size and the proportion of the additive. The decrease in the microporosity (i.e., pore radius &lt; 3.7 nm) of the metallurgical cokes observed when petroleum coke is added to the coal blend, is postulated to be one of the main factors responsible for the decrease in the reactivity of these cokes. The variation of the mechanical strength indices can be explained by the changes in porosity and the quality of the interfaces between petroleum coke and metallurgical coke. © 1998 Elsevier Science B.V. All rights reserved.

Abstract: The surface chemistry of two active carbons was modified by heating them using a microwave device as a heat source. When microwave treatments are conducted in a nitrogen flow, most oxygen-containing groups are removed from the surface of the carbons. This in turn gives rise to an increase in the pH of the carbon. Microwave treatment is less time-consuming than conventional heating. Thus, only a few minutes are required to transform an acidic carbon into a basic one with a relatively low oxygen content.

Abstract: Char nitrogen is considered as a key factor in NOX emissions during coal combustion. Coal char plays a role not only in the formation of NO but also in its reduction on the char surface. The textural properties of chars, therefore, and the nature and concentration of active sites are important in these heterogeneous reduction reactions. In this study a low volatile bituminous coal was pyrolysed at different heating rates in order to obtain chars with different textural properties. The results seemed to show a relationship between char texture and NO reduction on the char surface. The nature of active sites involved in the heterogeneous reduction of NO is another matter of concern. In this work the role of oxygen surface complexes was studied through chemical modification of char surface.

Abstract: Textural properties are usually considered as the most important properties of activated carbons, however many applications of these materials are conditioned by their chemical characteristics. The understanding of surface chemistry of activated carbons is being of increasing interest among manufactures, consumers and researchers of activated carbons. Despite of that, some aspects concerning surface chemistry of carbons are not well known. This work gives a global view about the importance, the characterization and the methods of modification of surface chemistry of activated carbons.

Abstract: The contribution to carbon basicity of �-cation interactions in aromatic systems has been investigated in this work by carrying out ab initio calculations on various cluster models. According to various levels of theory, the mono-, bi-, and tridentate H3O+-benzene complexes present a binding enthalpy in the gas phase of about -28 kcal/mol showing intermolecular contact through unconventional hydrogen bonding between H3O+ and the �-cloud of benzene. The interaction energies calculated for other cluster models (pyrene-benzene-H3O+, coronene-H3O+, and a C54H18-H3O+ cluster) indicate that the size of the basal plane has a slight influence on the strength of this �-cation interaction, whereas the presence of the �-� contacts reinforces the electrostatic interaction with the H3O+ cation. These theoretical results support experimental data on the ability of the basal planes to contribute to carbon basicity and suggest that �-cation interactions may play an important role in the surface chemistry of carbon materials.

Abstract: Microcalorimetry was employed to study the surface chemistry of activated carbon. The chemistry of active sites was found to be a function of the pretreatment procedure. Following treatment at high temperature (950°C) in nitrogen, the carbon adsorbed a great deal of oxygen at 25°C with a remarkably high heat of adsorption (approx. 125 kcal/gmol O2), whereas after treatment at high temperature in hydrogen the same carbon adsorbed virtually no oxygen at 25°C. It was found, however, that the hydrogen treated carbon did adsorb oxygen at an elevated temperature (150°C). Changes in the character of oxygen interaction with the carbon surface can be related to the nature of unsaturated sites on the carbon surface. Specifically, after treatment in nitrogen the surface contains a high concentration of highly unsaturated ('dangling') carbon atoms which interact rapidly and strongly with oxygen. All these sites are removed by the hydrogen treatment leaving only partially unsaturated sites, which only interact with oxygen at elevated temperature.

Abstract: In this paper, the use of calorimetric techniques to characterize different carbon materials is reviewed. The focus of the review is on the use of calorimetric techniques to assess chemical properties of carbons (e.g. nature of surface groups, hydrophobic/hydrophilic character, acidic/basic behavior, etc.), and a small section is dedicated to the application of calorimetry in determining the physical properties of carbons (e.g. surface areas, pore size distribution, etc.). The following techniques are described: immersion and flow-adsorption calorimetry and gas-adsorption microcalorimetry. Several representative examples of the use of calorimetry techniques to evaluate both physical and chemical properties are presented. It is demonstrated that calorimetry has provided unique insights into the structure and chemistry of active sites on the surface of various carbons.

Abstract: Activated carbon was modified by thermal treatment in order to obtain carbon samples with a very different surface chemistry and similar textural properties. The distribution of oxygen-containing surface groups in these carbons was assessed. The difference between the point of zero charge and the isoelectric point (pHPZC - pHIEP) showed the same trend as the difference between the oxygen content on the external surface, determined by XPS, and that in the bulk, obtained by chemical analysis (%Osurface - %Obulk). Thus, pHPZC - pHIEP can be used as a parameter for indicating the radial distribution of oxygen-containing groups in carbons. Carbon samples were loaded with molybdenum, using the procedure of incipient-wetness impregnation. Hydrophilicity conferred by the oxygen functionalities to the carbon substrates promotes the formation of small, well dispersed crystals of the metal precursor on the support. Results seem to indicate that oxygen-containing surface groups work as anchorage centres for molybdenum complexes. The activated catalyst prepared with the most acidic carbon showed a higher amount of molybdenum than in the case of the other carbon supports. This may be due to the presence of metal sulphides that are bound to the oxygen groups of the support. © 1998 Elsevier Science B.V. All rights reserved.

Abstract: One calcined and five green petroleum cokes were subjected, in a thermobalance, to controlled thermal treatment up to 1000°C in an N2 atmosphere and then reacted with CO2 at this temperature. Based on the DTG curves, the volatile matter released during the pyrolysis stage was divided into five intervals (&lt;150, 150-400, 400-500, 500-750 and 750-1000°C). Relevant information can be obtained from the amount of volatile matter released in these intervals. In particular, it was found that the amount of volatile matter released in the 400-500°C interval can be related to the modifications observed in the fluidity of coal/PC blends which in turn affects the properties of metallurgical cokes obtained from these blends. Petroleum coke reactivity parameters were also obtained. A good correlation was found between the reactivity at 20% of conversion (R20) and the optical texture index (OTI) calculated from the quantitative analysis of anisotropic components in the cokes. In contrast with the relevance of the information obtained from the volatile matter released during the thermal treatment of the petroleum cokes, the reactivity of petroleum cokes was found to have little influence on the reactivity of metallurgical cokes prepared from coal/PC blends. © 1998 Elsevier Science B.V. All rights reserved.

Abstract: Further insight into important aspects of the chemical surface properties of activated carbons is provided by rationalizing the differences in O2 adsorption and desorption behavior of hydrogen- and nitrogen-treated activated carbons. The effects of heat treatment on the electrochemical behavior of these carbons were also instrumental in elucidating the nature and the distribution of carbon active sites. Activated carbon surfaces stabilized with hydrogen at 950 °C adsorb very little O2 at room temperature but the graphene layers are terminated with many free carbon active sites because significant O2 adsorption does take place at 150 °C. Furthermore, the low-coverage differential heats of adsorption on sites accessible at 150 °C were lower than those on sites accessible at 25 °C. The role of these free carbon sites in determining the basicity of activated carbon was also addressed. On the basis of the important finding that the point of zero charge exhibits a maximum at intermediate heat-treatment temperature, it is proposed that - in addition to the delocalized basal-plane � electrons-the localized � electrons at graphene edge (e.g., inplane divalent sigma pairs) act as Lewis bases that interact with protons in aqueous solution.

Abstract: Activated carbons with various degrees of oxidation were prepared by treatment with concentrated nitric acid at various temperatures. Selective removal of the oxygen complexes by heating under nitrogen flow at 573, 773 and 1073 K was also considered. The samples were characterised through temperature-programmed desorption (TPD), Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques. FTIR and XPS techniques were found to be very useful for relating the shape of CO2 desorption profiles during pyrolysis with the nature of the functional groups desorbed. Three steps in TPD profiles were observed: (i) the desorption of carboxylic acid groups in the form of CO2 in the lower temperature range, 400-623 K; (ii) the decomposition of lactone groups created during HNO3 treatment and, to some extent, originated during heating rearrangements, in the temperature range 623-823 K; and (iii) the elimination of the more stable ether groups upon treatment at temperatures above 823 K. The combination of these three techniques (TPD, FTIR and XPS) gives a reasonable picture of the surface chemistry of the oxidised activated carbons. © 1997 Elsevier Science B.V.

Abstract: The adsorption of model aromatic compounds (aniline and nitrobenzene) on chemically tailored activated carbons has been systematically investigated. Adsorption experiments at controlled solution pH conditions confirmed that both electrostatic and dispersive adsorbate/adsorbent interactions can have a significant influence on the equilibrium uptakes of ionic and nonionic adsorbate species. For aniline (a weak electrolyte), maximum uptakes were found on oxidized carbon surfaces at solution pH near the adsorbate's point of zero charge (pHPZC). In contrast, nondissociating nitrobenzene uptakes were enhanced on heat-treated surfaces with graphene layers unperturbed by electron-withdrawing functional groups, particularly at solution pH � pHPZC. A theoretical model that can successfully account for the observed trends is hereby proposed as a much needed predictor of the experimental conditions and adsorbent surface chemical properties that will maximize the uptake of aromatic compounds by activated carbons. © 1997 Elsevier Science Ltd.

Abstract: The relevance of petroleum coke activity during the plastic stage in cocarbonization with a low-volatile bituminous coal was assessed by establishing differences in lowering of Gieseler maximum fluidity of the blend (bituminous coal and petroleum coke) and in metallurgical coke quality. Differences in fluidity of the blend were well correlated with parameters used in petroleum coke characterization such as hydrogen donor ability, the volatile matter released between 400 and 500 °C, and the ratio of methyl and methylene groups in aromatic clusters. The metallurgical cokes were produced in a laboratory oven from blends of petroleum coke-bituminous coal and, then, characterized in terms of abrasion strength and reactivity to CO2. There is a clear relation between the chemical activity of petroleum coke in cocarbonization systems with coal and improvements in metallurgical coke quality. The ability of petroleum coke to interact with coal during the plastic stage contributes to good bonding between components as evidenced by the quantitative study of interfaces by optical microscopy.

Abstract: Differences between the surface chemical properties of hydrogen- and nitrogen-treated samples of an activated carbon were quantified using several complementary techniques. Calorimetric studies conducted at 303 K revealed that the sample treated in N2 at 1223 K adsorbs a great deal of oxygen with unusually high differential heats. In fact, both the quantity and the heat of adsorption increased when the treatment temperature was raised from 773 to 1223 K. In contrast, samples treated in H2 adsorbed less and less O2 as the temperature of treatment was raised; after treatment at 1223 K, virtually no C-2 adsorption occurred. At the same time the H/C ratio in the H2-treated samples decreased with increasing treatment temperature. Point of zero charge measurements revealed that only H2 treatments at high temperature (&gt; 1073 K) create basic (hydrophobic) surfaces which are stable after prolonged air exposure. These findings are consistent with the notion that the removal of oxygen in the form of CO and CO2 during high-temperature N2 treatment leaves unsaturated carbon atoms at crystallite edges; these sites are very active for subsequent oxygen adsorption. In contrast, high-temperature Ha treatment accomplishes three tasks: (a) it also removes surface oxygen; (b) it stabilizes some of the (re)active sites by forming stable C-H bonds; (c) it gasifies the most reactive unsaturated carbon atoms. The relative contributions of these three effects depend on the temperature of H2 treatment. The carbon surface resulting from high-temperature H2 treatment is stable against subsequent Oz adsorption in ambient conditions.

Abstract: It is often assumed that green petroleum coke behaves as an inert material in cocarbonization with coking coal blends and has no active behavior on the important thermoplastic properties of the coal blend. This paper investigates that assumption. The objective of this study is to clarify effects arising when different petroleum cokes are added to a single coal or an industrial blend. The effects studied include changes during the pyrolysis stages of the cocarbonization, using a bituminous coal. This was done to study if petroleum coke is totally inert at the plastic stage of a given coal or there is an influence at the plastic stage. A further aim is to show how conventional and nonconventional techniques for petroleum coke characterization relate to its activity with the plastic stage of coal. A range of six petroleum cokes was used. The petroleum cokes were studied in terms of (a) optical texture, (b) FTIR spectroscopy, (c) hydrogen donor ability, (d) thermogravimetric analysis of the pyrolysis stage, (e) free-swelling index, and (f) thermoplastic properties of blends made up of a bituminous coal and petroleum coke. Evidence for a significant activity of some petroleum cokes was assessed using the above techniques, which can be considered as nonconventional in petroleum coke characterization. A good correlation among the parameters obtained from the above techniques/methods was found, indicating that the presence of unreacted and partially carbonized material, the hydrogen donor ability, the relative proportion of methyl and methylene groups, the amount of volatile matter released at a temperature range between 400 and 500°C, the temperature of maximum volatile matter evolution and, finally, the agglomeration degree of petroleum cokes can be considered as important factors in the plastic properties of cocarbonization systems with coking coals.

Abstract: The effects of coal preheating on the quality, textural and surface properties of the coke were assessed in comparison with the conventional wet charging system using a Spanish hvb coal. Coal was flash dried and preheated in a 2 t h-1 Precarbon pilot plant. Carbonization tests on the wet and preheated coals were carried out in a semi-industrial scale oven of 6 tonne capacity. Because textural and surface properties have an important effect on coke quality, an exhaustive characterization of the resultant cokes was made. Cokes were characterized by using microscopic image analysis, mercury porosimetry, density measurements, optical and scanning electron microscopy (SEM) of surfaces. Mechanical strength and reactivity towards CO2 were also studied. Surface areas were determined by N2 adsorption at 77 K. using the Brunauer-Emmett-Teller (BET) equation and CO2 adsorption at 273 K using the Dubinin-Radushkevich (DR) equation. Coal preheating improved coke mechanical strength considerably but at the same time increased the reactivity of the cokes. The higher reactivity could be due to the increase in microporosity and CO2 surface area.

Abstract: It is demonstrated that stable basic carbons, which will not adsorb oxygen in ambient laboratory conditions, can be created via a relatively low-temperature process. These highly basic carbons are created by treating mixtures of carbons and platinum (in the form of particles supported on a high surface area material) in hydrogen at 500°C, or even at lower temperatures in some cases. In the absence of platinum, creation of highly basic and stable surfaces with the same starting material requires hydrogen treatments at far higher temperatures (ca. 900°C). Evidence is presented to support the hypothesis that the role played by platinum (or any noble metal) is to produce atomic hydrogen, which spills over onto the carbon surface. This atomic hydrogen hydrogasifies the most reactive, unsaturated carbon atoms at far lower temperatures than molecular hydrogen, thus leading to surface stabilization at relatively low temperatures. © 1996 American Chemical Society.

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Abstract: The influence of coal preheating on the properties of the resultant cokes has been studied using a wide range of coking coals which were carbonized, wet and after preheating, at the INCAR Coking Test Plant operating on a semi-industrial scale. Coke mechanical strength improved by using the preheating process rather than wet charging, except for some cokes produced from coals with a content of volatile matter between 19.5 and 25 wt% db. The most significant differences between cokes from preheated and wet coals were observed in terms of microporosity. Increase in microporosity as a consequence of preheating is accompanied by an increase in coke reactivity. As regards the optical texture of cokes, a slight increase in the total anisotropy and the size of mosaic features was observed. © 1993.

Abstract: The relationship between the textural properties and reactivity in metallurgical cokes, obtained from different rank coals using wet and preheating techniques, was studied. Cokes from preheated coals exhibit a higher reactivity than those obtained from wet ones. This may be related to the higher microporosity and CO2 surface area. © 1993.

Abstract: Commissioning of the most widely accepted coke reactivity test, NSC, has been carried out at the Spanish National Coal Institute (INCAR). A study was made of the repeatability of the test and some factors shortening the test procedure,using different cokes produced from a wide range of coals at the INCAR Coking Test Plant. A correlation between the NSC test values and those obtained from the CEE test was obtained. The CEE test is quicker, cheaper and easier to perform than the NSC one.

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Abstract: the MW pyrolysis as an original thermochemical process of materials is presented. This chapter comprises a general overview of the thermochemical and quantifying aspects of the pyrolysis process, including current application togethe with a compilation of the most frequently used materials.

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Abstract: Adsorption is one of the more promising technologies for capturing CO2 from flue gases. Amine polymers, e.g., polyethylenimine (PEI), immobilized on variable porous substrates, silica, zeolites and fly ash, are effective adsorbents for CO2. Two approaches, thermal swing desorption over a range of temperatures and time in an atmosphere of CO2 and thermally assisted pressure swing desorption, are explored for the regeneration of the PEI based adsorbents. The advantages and disadvantages, for example irreversible carbamate formation, are described for both regeneration techniques with conclusions drawn to their feasibility and influence on adsorbent lifetime. This is an abstract of a paper presented at the 231th ACS National Meeting (Atlanta, GA 3/26-30/2006).

Abstract: Two different approaches of developing CO2 adsorbents were presented. Firstly, the modification of the surface chemistry of low cost carbons (carbon concentrates from pulverized fuel ash) by impregnation with nitrogen containing polymers, i.e., polyethylenimine. Additionally, a range of high nitrogen content carbons were developed by carbonization and subsequent activation of a range of materials (polyacrylonitrile, glucose-N compounds mixtures, melamine, and urea/melamine-formaldehyde resins). The results of both approaches for developing CO2 adsorbents were discussed comparing both the adsorption capacity vs. temperature and ease of regeneration of the different adsorbents. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8/22-26/2004).

Abstract: Two different approaches of developing CO2 adsorbents were compared, i.e., by impregnating amines upon activated carbon concentrates from fly ash (PFA)-derived unburned carbon concentrates (PFA_ACC) and through the carbonization and subsequent activation of mixtures of sugar and nitrogen containing compounds. For the PFA__ACC, tetra-ethylene-penta-amine-acrylonitrile was a stronger CO2 adsorption enhancing amine than di-ethanolamine or poly-ethylenimine. Of the N-compounds mixed with the sugars, urea yielded the highest nitrogen content in the resulting carbons. However, carbazole, despite yielding the lowest nitrogen content, engendered the highest adsorption capacity both in terms of the overall amount of CO2 adsorbed by the sorbents and also the mass of CO2 adsorbed per square meter of their surface area. This indicated that it is not just the amount of nitrogen in the adsorbent, but also the nitrogen functionality that has a strong influence upon the performance of the carbons.