Perpignan, France
Perpignan, France

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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.

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.

A novel solar-driven thermogravimeter has been developed for on-sun kinetic analysis of solid-gas thermochemical reactions at high temperature in controlled atmosphere. The proposed concept includes a cavity-type solar receiver and a separate tubular reaction chamber that aims at ensuring a reliable reaction temperature measurement during thermochemical processing while enabling on-line gas analysis. Other features include high temperature and heating rate capabilities (1600°C, up to 150Kmin-1), controlled atmosphere including reduced pressure or vacuum conditions or different flowing gas atmospheres, and precise measurement of mass variations (resolution of 10-5g over the whole range, capacity 220g). Since the available incident solar power absorbed by the reactor was determined by the size of the parabolic dish concentrator (about 1kW), a thermal analysis was performed to design properly the cavity size for reaching the desired temperature level. Limestone calcination and ZnO thermal reduction were successfully performed to validate the set-up reliability. The temperature- and pressure-dependent drift was determined and corrected using the mass variation observed during the heating period of the reactant. The device was finally operated to investigate the kinetics of ZnO and SnO2 solar thermal dissociation. © 2014 Elsevier Ltd.

Energy and Fuels | Year: 2011

The solar thermochemical splitting of CO 2 and H 2O with ceria and Zr-doped ceria for CO and H 2 production is considered. The two-step process is composed of the thermal reduction of the ceria-based compound followed by the oxidation of the nonstoichiometric ceria with CO 2/H 2O to generate CO/H 2, respectively. As a reference, the reactivity of pure undoped ceria was first characterized during successive thermochemical cycles using a thermobalance. Then, Zr 0.25Ce 0.75O 2 was synthesized using different soft chemical synthesis routes to evaluate the influence of the powder morphology on the reactivity during the reduction and the oxidation steps. The reduction yield of ceria was significantly improved by doping with Zr as well as the CO/H 2 production yields, but the kinetic rates of the oxidation step for doped ceria were lower than for pure ceria. CO and H 2 production of 241 and 432 μmol/g, respectively, have been measured. A kinetic analysis of the CO 2-splitting step allowed one to estimate the activation energy that ranged between 83 and 103 kJ/mol depending on the synthesis route of Zr 0.25Ce 0.75O 2. The powder morphology played an important role on the materials cyclability. In contrast to pure ceria, Zr-doped ceria showed possible deactivation when cycling at 1400 °C, and the influence of the synthesis route on the thermal stability was evidenced. The thermally resistant powders with porous morphology ensured stable reactivity during cycling. The Zr-doped ceria synthesized via pechini process produced the largest amounts of CO/H 2 during successive cycles. © 2011 American Chemical Society.

Abanades S.,CNRS PROMES | Villafan-Vidales I.,CNRS PROMES
International Journal of Energy Research | Year: 2013

The solar-driven dissociation of CO2 by thermochemical looping via Fe3O4/FeO redox reactions is considered. The process recycles and upgrades CO2 to ultimately produce chemical synthetic fuels from high-temperature solar heat and abundant feedstock as only inputs. The two-step process encompasses the endothermic reduction of Fe3O4 to FeO and O2 using concentrated solar energy as the high-temperature source for reaction enthalpy and the nonsolar exothermic oxidation of FeO with CO2 to generate CO. The resulting Fe3O4 is then recycled to the first step and carbon monoxide can be further processed to syngas and serve as the building block to synthesise various synfuels by catalytic processes. This study examines the thermodynamics and kinetics of the pertinent reactions. The high-temperature thermal reduction of Fe3O4 is realised above the oxide melting point by using concentrated solar thermal power. The reactivity of the synthesised FeO-rich material with CO2 at moderate temperature is then investigated by thermogravimetry. FeO conversion higher than 90% can be achieved with reaction rates depending on temperature, particle size and CO2 concentration. The solar-produced nonstoichiometric FeO is more reactive with CO2 than commercial pure FeO. Activation energies of 57 and 68kJ/mol are derived from a kinetic analysis of the CO2-splitting reaction in the range of 600°C to 800°C with solar and commercial FeO, respectively. © 2012 John Wiley & Sons, Ltd.

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.

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.

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.

The thermochemical CO 2 splitting via cerium-based mixed oxides is considered. This process targets the recycling and upgrading of CO 2 emissions for the production of solar fuels. The CO 2 reduction is achieved by thermochemical looping using ceria-zirconia solid solutions as oxygen carriers: (1) the mixed oxide is first reduced by thermal activation for releasing some oxygen from its lattice, (2) the reduced oxide is then oxidized with CO 2 for producing carbon monoxide and the initial metal oxide that is recycled to the first step. Reactive cerium-based mixed oxides were first synthesized as nanopowders by different soft chemical routes. Their reactivity was then investigated experimentally by thermogravimetry analysis to demonstrate that the produced nanoparticles react efficiently with CO 2. The two-step process consisting of thermal activation and CO 2-splitting reaction was able to produce CO repeatedly. The influence of the synthesis method, the Zr content in Zr xCe 1-xO 2, and the temperature of the CO 2 reduction reaction was investigated. The material was reduced at 1400 °C in flowing Ar and the CO 2 reduction was performed below this temperature (typically in the range of 700-1200 °C). Both the CO production and the material cyclability were improved when decreasing the Zr content, although the reduction extent was lessened. The Ce 0.75Zr 0.25O 2 and Ce 0.9Zr 0.1O 2 redox catalysts withstood repeated cycles without any noticeable sintering and reactivity losses. The most reactive material was the powder synthesized via the Pechini method (242 μmol CO/g at 1000 °C). © 2012 Elsevier Ltd. All rights reserved.

Journal of Physical Chemistry C | Year: 2012

Ceria has emerged as an attractive candidate for solar thermochemical hydrogen production; however, the necessary temperatures for CeO 2 reduction to Ce 2O 3 are too high for conventional solar concentrating systems, while the reduction to nonstoichiometric CeO 2δ below 1500°C shows restricted chemical yield. Doping ceria with another metal can improve the reactivity at lower temperatures. This study focuses on the doping of ceria with different metals such as tantalum or trivalent lanthanides (La, Sm, and Gd) to form binary oxides and on the doping of ceria-zirconia solid solutions to form ternary oxides. Ceria materials doped with tantalum show a high reducibility, but the structural evolution during thermal treatment leads to the formation of a secondary phase that hinders the water dissociation reaction. Besides, the doping with trivalent lanthanides results in an improved thermal stability during consecutive cycles, while the hydrogen production is unchanged compared to ceria. Concerning ternary oxides, the addition of 1% gadolinium to ceria-zirconia solid solutions results in the production of 338.2μmol (7.58 mL) of hydrogen per gram during one cycle with the O 2-releasing step at 1400°C and the H 2-generation step at 1050°C. This production is higher than the one observed for undoped ceria-zirconia. The addition of lanthanum enhances the thermal stability of ceria-zirconia solid solution, thus leading to stable reactivity during repeated cycles. © 2012 American Chemical Society.

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