Advances in reforming and partial oxidation of hydrocarbons for hydrogen production and fuel cell applications

One of the most attractive routes for the production of hydrogen or syngas for use in fuel cell applications is the reforming and partial oxidation of hydrocarbons. The use of hydrocarbons in high temperature fuel cells is achieved through either external or internal reforming. Reforming and partial oxidation catalysis to convert hydrocarbons to hydrogen rich syngas plays an important role in fuel processing technology. The current research in the area of reforming and partial oxidation of methane, methanol and ethanol includes catalysts for reforming and oxidation, methods of catalyst synthesis, and the effective utilization of fuel for both external and internal reforming processes. In this paper the recent progress in these areas of research is reviewed along with the reforming of liquid hydrocarbons, from this an overview of the current best performing catalysts for the reforming and partial oxidizing of hydrocarbons for hydrogen production is summarized

Catalytic and electrocatalytic oxidation of ethanol over a La0.6Sr0.4Co0.8Fe0.2O3 perovskite-type catalyst

The catalytic and electrocatalytic behavior of the perovskite-type La0.6Sr0.4Co0.8Fe0.2O3 catalyst was investigated during ethanol oxidation. Experiments were carried out at atmospheric pressure in a fully yttria-stabilized zirconia (YSZ) continuously stirred tank reactor (CSTR) in the temperature range between 300 and 750 degreesC and fuel-rich reactant mixtures (P-O2 = 2 kPa, P-ethanol = 13.5 kPa). It was round that oxygen-nitrogen streams saturated with ethanol (at room temperature and atmospheric pressure) lead mainly to the formation of formaldehyde and acetaldehyde. For the aforementioned reaction conditions, gas-phase oxidation becomes predominant at temperatures higher than 650 degreesC and in combination with heterogeneous phenomena leads to 100% ethanol conversion and high acetaldehyde yields (75%) at about 750 degreesC. The electrochemical supply of oxygen anions mainly affects the formation rates of CO and CO,. Due to the high operating temperatures, direct electrocatalysis and homogeneous reactions, more than NEMCA (Lambda (max) = 3), affect the overall kinetic behavior. (C) 2000 Elsevier Science B.V. All rights reserved

Performance of a SOFC Powered with External Ethanol Steam Reforming

In the present study, a solid oxide fuel cell (SOFC) system was considered being fed by the equilibrium products of the steam reforming of ethanol. The thermodynamic analysis of ethanol steam reforming was undertaken at total pressure of 1 bar in the temperature range between 800-1200 K assuming different steam/ethanol molar feed ratios in the range of 1-5. The possibility of carbon deposition in the equilibrium mixture was examined and all conditions of SOFC operation were selected appropriately so that this deposition to be thermodynamically impossible. The equilibrium mixture of reforming obtainable in each case was mathematically calculated using the method of the direct minimization of Gibbs free energy. The distribution of the molar fraction of the species in thermodynamic equilibrium was obtained in the examined range of conditions, and optimum conditions of SOFC operation were recognized in terms of its thermodynamic efficiency for generation of electrical power

Thermodynamic and economic analysis of a steam reformer-solid oxide fuel cell system fed by natural gas and ethanol

In the present work, ethanol and methane are compared as candidate fuels for solid oxide fuel cells (SOFCs). The thermodynamic analysis of both alternatives was undertaken considering that a SOFC stack operates by being fed by the equilibrium products of the steam reforming of each raw fuel. The comparison was made at atmospheric total pressure assuming low reforming factors (steam/fuel feed ratios) and SOFC operation in the temperature range of 800 to 1200 K. All operation conditions have been selected so that carbon deposition in the SOFC anode is thermodynamically impossible. Results were obtained in terms of the maximum theoretical electromotive force and the thermodynamic efficiency of total energy conversion. It was found that both fuels exhibit similar thermodynamic behavior when fed in a SOFC stack, and some qualitative advantages with respect to ethanol are discussed

Exergy analysis of an ethanol fuelled proton exchange membrane (PEM) fuel cell system for automobile applications

An integrated ethanol fuelled proton exchange membrane fuel cell (PEMFC) power system was investigated following a second law exergy analysis. The system was assumed to have the typical design for automobile applications and was comprised of a vaporizer/mixer, a steam reformer, a CO-shift reactor, a CO-remover (PROX) reactor, a PEMFC and a burner. The exergy analysis was applied for different PEMFC power and voltage outputs assuming the ethanol steam reforming at about 600 K and the CO-shift reaction at about 400 K. A detailed parametric analysis of the plant is presented and operation guidelines are suggested for effective performance. In every case, the exergy analysis method is proved to allow an accurate allocation of the deficiencies of the subsystems of the plant and serves as a unique tool for essential technical improvements. © 2005 Elsevier B.V. All rights reserved

Electrochemical Promotion of Pt During the Oxidation of Ethanol

The reaction of ethanol oxidation has been examined over a Pt polycrystalline film deposited on an yttria stabilized zirconia (YSZ) electrochemical reactor. Experiments were carried out at 325 degrees C at atmospheric total pressure and under open and closed circuit conditions. It was found that the electrochemically-induced change in the catalytic rate of ethanol consumption is four orders of magnitude higher than the rate of ion transport through the solid electrolyte. The galvanostatic transient behavior of the consumption rates of ethanol and oxygen and of the formation rates of carbon dioxide and acetaldehyde have been also recorded

Electrochemically promoted catalysis: The case of ethanol oxidation over Pt

Ethanol oxidation was investigated over polycrystalline Pt films deposited on 8 mol% Y2O3-stabilized-ZrO2 (YSZ) in the temperature range of 300-350degreesC. It was found that electrochemical supply of oxygen anions (O2-) to the Pt catalyst results in significant changes both in the rate of ethanol consumption and in the yield of acetaldehyde. Electrochemical supply of O2- anions induces an enhancement of the reaction rate that was found typically 10(3)-10(4) times larger than the Faradaic rate of O2- supply and an almost seven-fold increase in the reaction yield to acetaldehyde. In the range of the applied currents, it was found that the catalytic activation energies of ethanol consumption and acetaldehyde formation can be lowered by 70 and 80%, respectively, with respect to the regular (open-circuit) values. The observed behavior is discussed and explained on the basis of the theory of NEMCA. (C) 2002 Elsevier Science (USA)

Energy and exergy analysis of a solid oxide fuel cell plant fueled by ethanol and methane

The method of exergy analysis is presented for a SOFC power plant involving external steam reforming and fueled by ethanol and methane. The optimal operation parameters of the integrated SOFC plant are specified after minimizing the existing energy and exergy losses. A comparison of methane and ethanol as appropriate fuels for a SOFC-based power plant is provided in terms of exergetic efficiency assuming the minimum allowable (for carbon-free operation) reforming factors for both cases. Then, a parametric analysis provides guidelines for practical design. It is concluded that the exergy calculations pinpoint the losses accurately and that the exergy analysis gives a better insight of the system's process

High temperature electrochemical oxidation of ethanol over perovskite-type oxides

Ethanol oxidation was investigated in a solid electrolyte electrochemical reactor using a perovskite-type oxide La0.6Sr0.2Co0.8Fe0.2O3 as anode. Experiments were conducted between 300-750 degreesC at atmospheric pressure in an ytrria-stabilized-zirconia continuous stirred tank reactor using fuel-rich reactant mixtures

Exergetic potential of fuels: The case of a SOFC-based power plant

The method of exergy analysis is presented for a SOFC power plant involving external steam reforming and fed by methane and ethanol. The optimal operation parameters of the integrated SOFC plant are specified after minimizing the existing energy and exergy losses. A comparison of methane and ethanol as appropriate fuels for a SOFC-based power plant is provided in terms of exergetic efficiency assuming the minimum allowable (for carbon-free operation) reforming factors for both cases. Then, a parametric analysis provides guidelines for practical design. It is concluded that the exergy calculations pinpoint the losses accurately and that the exergy analysis gives a better insight into the system's process