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Nzihou A.,French National Center for Scientific Research | Flamant G.,CNRS PROMES | Stanmore B.,University of Queensland
Energy | Year: 2012

Biomass represents a renewable source for transport fuels when processed by gasification, followed by catalytic conversion of the syngas to liquids. The efficiency of biomass gasification can be improved by supplying process heat from concentrated solar systems, which can attain the required temperature of 900 °C. Various chemical routes and contacting configurations are reviewed. The challenges related to biomass-based processes are discussed. Heat and material balances are then deduced. The area of land required for growing biomass can be reduced using the application of thermal solar to one half of that needed for a standard gasification system. If hydrogen is generated by solar means in order to reduce carbon dioxide emissions to zero, the figure becomes one third. Examples of the land requirements for three different biomass materials are presented. © 2012 Elsevier Ltd.

Green | Year: 2011

Solar thermochemical processes efficiently convert high-temperature solar heat into storable and transportable chemical fuels. In such processes, thermal energy is provided by concentrated solar energy and the source of hydrogen differs as a function of the investigated routes. In a transition period, carbonaceous feedstocks, such as fossil fuels, biomass, or carbon-containing wastes, can be solarupgraded and transformed into valuable hydrogen fuel via cracking, reforming, and gasification processes. In the long term, H 2O-splitting via thermochemical cycles based on metal oxide redox reactions can be considered to produce renewable H2 that can be directly used in fuel cells or further processed to synthetic liquid fuels. The most promising different hydrogen production pathways are described by focussing on the existing state-of-the-art and on the latest technological advances in the field. Copyright © 2011 De Gruyter.

Industrial and Engineering Chemistry Research | Year: 2012

This study addresses the thermochemical production of CO and H 2 as high-value solar fuels from CO 2 and H 2O using reactive Zn nanoparticles. A two-step thermochemical cycle was considered: Zn-rich nanopowder was first synthesized from solar thermal ZnO dissociation in a high-temperature solar chemical reactor and the reduced material was then used as an oxygen carrier during theCO 2 andH 2Oreduction reactions. The kinetics ofCO 2 andH 2Oreduction was investigated by thermogravimetry to demonstrate that the solar-produced nanoparticles react efficiently with CO 2 andH 2O. Zn started to react from 513 K and almost complete Zn conversion (reaction extent over 95%) was achieved at 633-773 K in less than 5 min, thus confirming that the active Zn-rich nanopowder exhibits rapid fuel production kinetics during H 2O and CO 2 dissociation. The reaction mechanism was best described by a nucleation and growth model with an activation energy of 43 kJ/mol and an oxidant order of 0.8. The high reactivity of zinc was attributed to the specific solar synthesis route involving ZnO thermal dissociation and condensation of Zn vapor as nanoparticles. © 2011 American Chemical Society.

International Journal of Hydrogen Energy | Year: 2011

This study addresses the solar thermochemical production of hydrogen from water-splitting cycles using ceria-zirconia solid solutions prepared via soft chemistry methods. The effect of zirconium doping on the catalytic activity of ceria for hydrogen production was studied using thermogravimetric analysis. The influence of the zirconium content between 10% and 50% on the redox properties of the Ce1-δZrδO2 material was investigated. The higher the amount of zirconium, the higher the reduction yields. The reduction yield at 1400 °C in inert atmosphere was 9% for 10% Zr, 16% for 25% Zr, and 28% for 50% Zr. However, increasing the Zr content did not automatically lead to the highest amount of hydrogen produced during cycling. Indeed, the powder with 25% Zr produced 334 and 298 μmol H 2/g at 1050 °C during the first and the second cycle, respectively. In contrast, the powder with 50% Zr yielded 468 and 266 μmol H2/g during the two successive cycles. Moderate Zr contents thus favored H2 production during repeated cycles without any significant reactivity losses. A kinetic study of the reduction and the hydrolysis steps was proposed. The activation energies for the thermal reduction and the hydrolysis of Ce0.75Zr0.25O2 were 221 kJ/mol and 51 kJ/mol, respectively. Finally, the use of a template molecule during synthesis was considered, which improved the reduction yield markedly (up to 52%) but strong sintering phenomena limited the hydrogen production and the material cyclability. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

International Journal of Hydrogen Energy | Year: 2012

The thermochemical dissociation of CO 2 and H 2O from reactive SnO nanopowders is studied via thermogravimetry analysis. SnO is first produced by solar thermal dissociation of SnO 2 using concentrated solar radiation as the high-temperature energy source. The process targets the production of CO and H 2 in separate reactions using SnO as the oxygen carrier and the syngas can be further processed to various synthetic liquid fuels. The global process thus converts and upgrades H 2O and captured CO 2 feedstock into solar chemical fuels from high-temperature solar heat only, since the intermediate oxide is not consumed but recycled in the overall process. The objective of the study was the kinetic characterization of the H 2O and CO 2 reduction reactions using reactive SnO nanopowders synthesized in a high-temperature solar chemical reactor. SnO conversion up to 88% was measured during H 2O reduction at 973 K and an activation energy of 51 ± 7 kJ/mol was identified in the temperature range of 798-923 K. Regarding CO 2 reduction, a higher temperature was required to reach similar SnO conversion (88% at 1073 K) and the activation energy was found to be 88 ± 7 kJ/mol in the range of 973-1173 K with a CO 2 reaction order of 0.96. The SnO conversion and the reaction rate were improved when increasing the temperature or the reacting gas mole fraction. Using active SnO nanopowders thus allowed for efficient and rapid fuel production kinetics from H 2O and CO 2. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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