Microwave Heating Applied to Pyrolysis

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 materialsPeer reviewe

Carbon Xerogels: The Bespoke Nanoporous Carbons

This chapter focuses on the main features of resorcinol-formaldehyde–based carbon xerogels. The first part of the chapter discusses ways of synthesizing these materials and the different variables involved. Then a review of the ways in which the meso- and macroporosity of organic xerogels can be controlled by adjusting the synthesis conditions is undertaken. Special attention is paid to the pH and components of the precursor solution and how these variables are interrelated with each other. The formation of the microporosity during the carbonization or activation processes that give rise to the carbon xerogels is also briefly discussed. Besides the fact that the porosity of these materials can be tailored during the synthesis, another notable characteristic is that, compared with most porous carbons, they possess a relatively high electrical conductivity, which make them ideal materials for use as electrodes in energy storage devices. Their use in supercapacitors and in lithium ion batteries is addressed in the last part of the chapter

Designing Nanostructured Carbon Xerogels

The syntesis of nanostructure carbon xerogels, the properties of carbon gels and the applications of carbon xerogels are reviewedPeer reviewe

Application of infiltrated LSCM-GDC oxide anode in direct carbon/coal fuel cells

The authors would like to thank the European project ‘Efficient conversion of coal to electricity- Direct Coal Fuel Cells’, funded by the Research Fund for Coal & Steel (RFC-PR-10007).Hybrid direct carbon/coal fuel cells (HDCFCs) utilise an anode based upon a molten carbonate salt with an oxide conducting solid electrolyte for direct carbon/coal conversion. They can be fuelled by a wide range of carbon sources, and offer higher potential chemical to electrical energy conversion efficiency and have the potential to decrease CO2 emissions compared to coal-fired power plants. In this study, the application of (La, Sr)(Cr, Mn)O3 (LSCM) and (Gd, Ce)O2 (GDC) oxide anodes was explored in a HDCFC system running with two different carbon fuels, an organic xerogel and a raw bituminous coal. The electrochemical performance of the HDCFC based on a 1–2 mm thick 8 mol% yttria stabilised zirconia (YSZ) electrolyte and the GDC–LSCM anode fabricated by wet impregnation procedures was characterized and discussed. The infiltrated oxide anode showed a significantly higher performance than the conventional Ni–YSZ anode, without suffering from impurity formation under HDCFC operation conditions. Total polarisation resistance (Rp) reached 0.8–0.9 Ω cm2 from DCFC with an oxide anode on xerogel and bituminous coal at 750 °C, with open circuit voltage (OCV) values in the range 1.1–1.2 V on both carbon forms. These indicated the potential application of LSCM–GDC oxide anode in HDCFCs. The chemical compatibility of LSCM/GDC with carbon/carbonate investigation revealed the emergence of an A2BO4 type oxide in place of an ABO3 perovskite structure in the LSCM in a reducing environment, due to Li attack as a result of intimate contact between the LSCM and Li2CO3, with GDC being stable under identical conditions. Such reaction between LSCM and Li2CO3 was not observed on a LSCM–YSZ pellet treated with Li–K carbonate in 5% H2/Ar at 700 °C, nor on a GDC–LSCM anode after HDCFC operation. The HDCFC durability tests of GDC–LSCM oxide on a xerogel and on raw bituminous coal were performed under potentiostatic operation at 0.7 V at 750 °C. The degradation mechanisms were addressed, especially on raw coal.PostprintPeer reviewe

Microondas para aplicaciones tecnológicas

Cuadernillo didáctico y de divulgación científica presentado en la Semana de la Ciencia y la Tecnología.Peer reviewe

Role of coal characteristics in the electrochemical behaviour of hybrid direct carbon fuel cells

There is a growing interest in Hybrid Direct Carbon Fuel Cells (HDCFCs) now considered as one of the most efficient options for the generation of clean energy from mineral coals. In this work, two different hard coals (bituminous and anthracite) have been modified via carbonisation and oxidation and their electrochemical behaviour has been compared in an electrolyte supported HDCFC. A new insight into the HDCFC reaction mechanism is presented, providing an exhaustive analysis taking into account not only the evolution of the properties of the coals upon treatment but also other relevant parameters such as the effect of the cell preparation step or the interaction of the coal with the other cell components. The results show that the carbon content, the carbonaceous structure and the reactivity of the coals are key characteristics for optimal electrochemical behaviour. The plasticity of bituminous coals, an important parameter overlooked in previous works, can help to extend the area for electrochemical reactions beyond the current collector/anode interface. The reaction mechanism proposed shows that additional gas phase electrochemical reactions are an important contribution during the early stages of the electrochemical testing and that the direct electrochemical oxidation of solid carbon is the dominant reaction at longer times.PostprintPeer reviewe

Optimization of the process variables in the microwave-induced synthesis of carbon xerogels

Carbon xerogels (CX) can be synthesized by microwave-assisted heating. The transfer of this technology to an industrial scale passes through the optimization of the variables that affect the process. The effect of the main operational variables, i.e., initial volume of the precursor, gelation and ageing time and temperature of the synthesis, on the final porous properties of CX has been evaluated. It was found that the development of porosity in the CX synthesised in the microwave oven is hardly influenced by the increase in the initial volume of the precursor solution. This suggests that it is feasible to scale up the production of these materials by means of microwave heating. Furthermore, the consumption of energy does not increase in proportion to the volume of xerogel synthesized. Thus, the process is energy efficient, saves a considerable amount of time and requires only a single device to carry it out. These advantages, along with the fact that a temperature variation of 10 C is not determinative in the xerogels' final properties, indicate that CX could be produced on a large scale in a cost effective way. © 2013 Springer Science+Business Media New York.Financial support from the Ministerio de Economía y Competitividad of Spain MINECO (under Projects MAT2011-23733 and IPT-2012-0689-420000) is greatly acknowledged. NRR is also grateful to MINECO for her predoctoral research grant.Peer Reviewe

Simultaneous adjustment of the main chemical variables to fine-tune the porosity of carbon xerogels

The objective of this study was to assess the effect of the resorcinol-formaldehyde molar ratio of precursor solutions with pH values ranging from 5.0 to 7.0 and dilution ratios between 5 and 10 upon the final porous properties of carbon xerogels synthesized by microwave heating, using an optimal design of response surface methodology. It was found that when the resorcinol-formaldehyde molar ratio was decreased the microporosity was enhanced as the addition reaction was favored. Hence, the micropore volume of carbon xerogels not only depends on the conditions used during carbonization, but also on the synthesis conditions. Mesoporosity was also increased when the resorcinol-formaldehyde molar ratio decreased while macroporosity was only influenced by the initial pH of the precursor solutions. The simultaneous variations of the three chemical variables allowed an exhaustive control of the final porous properties of carbon xerogels, which exhibited pore sizes and pore volumes that could not be obtained by modifying just the pH and the dilution ratio. © 2014 Elsevier Ltd. All rights reserved.Financial support from the Ministerio de Economía y Competitividad of Spain MINECO (under Projects MAT2011-23733 and IPT-2012-0689-420000) is greatly acknowledged. NRR is also grateful to MINECO for her predoctoral research grant.Peer Reviewe

A visual validation of the combined effect of pH and dilution on the porosity of carbon xerogels

The hypothesis about the formation of the porous structure of carbon xerogels when the pH and the dilution ratio of the precursor solution are simultaneously modified has been validated by means of scanning electron microscope analysis. The morphology of the carbon xerogels showed that the size and number of the clusters produced during the sol–gel reaction is not only influenced by the pH but also by the dilution ratio. As with a decrease in the pH value, an increase in the dilution ratio caused the formation of a small number of large clusters, leading to materials with large pores. However, depending on the values selected the effect of the pH and dilution ratio was enhanced or diminished by the effect of the other. Hence, an appropriate adjustment of these two variables allowed microporous, micro-mesoporous and micro-macroporous materials to be obtained with pore volumes that could not be achieved by modifying the pH or the dilution ratio separately.Financial support from the Ministerio de Economía y Competitividad of Spain MINECO (under Projects MAT2011-23733 and IPT-2012-0689-420000, (BES-2012-052676)) is greatly acknowledged. NRR is also grateful to MINECO for her predoctoral research grant.Peer reviewe

Comparative study of durability of hybrid direct carbon fuel cells with anthracite coal and bituminous coal

The author would like to acknowledge the funding support of “Efficient Conversion of Coal to Electricity-Direct Coal Fuel Cell” with the grant number “RFCR-CT-2011-00004” from the Research Fund for Coal & Steel of the European commission. CJ acknowledges the Royal Society of Edinburgh for a RSE BP Hutton Prize in Energy Innovation.Direct carbon fuel cells offer the opportunity of generating energy from coal at high efficiency as an alternative to the procedure of conventional power plants. In this study, raw anthracite coal and raw bituminous coal were investigated in a hybrid direct carbon fuel cell (HDCFC), which was a combination of a solid oxide fuel cell and a molten carbonate fuel cell. Mechanical mixing was confirmed to be an efficient method of mixing coal with carbonate. The coal samples had different properties, for example, carbon content, hydrogen content, volatile matter and impurities. The results showed that the maximum power density obtained by the cell with anthracite coal was similar to that obtained by the cell with bituminous coal. It was found that the total power output from coal in HDCFCs mostly depended on the carbon content, while volatile matter, hydrogen content, moisture, etc. had an effect on the short-term durability. HDCFCs were kept operating for more than 120 h with 1.6 g coal. This study demonstrates that energy can be generated efficiently by employing anthracite and bituminous coal in hybrid direct carbon fuel cells.PostprintPeer reviewe