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    Solar Carbo-Thermal and Methano-Thermal Reduction of MgO and ZnO for Metallic Powder and Syngas Production by Green Extractive Metallurgy
    (2022-01-01) ;
    Abanades, Stéphane
    The solar carbo-thermal and methano-thermal reduction of both MgO and ZnO were performed in a flexible solar reactor operated at low pressure through both batch and continuous operations. The pyro-metallurgical process is an attractive sustainable pathway to convert and store concentrated solar energy into high-value metal commodities and fuels. Substituting fossil fuel combustion with solar energy when providing high-temperature process heat is a relevant option for green extractive metallurgy. In this study, a thermodynamic equilibrium analysis was first performed to compare the thermochemical reduction of MgO and ZnO with solid carbon or gaseous methane, and to determine the product distribution as a function of the operating conditions. The carbo-thermal and methano-thermal reduction of the MgO and ZnO volatile oxides was then experimentally assessed and compared using a directly irradiated cavity-type solar reactor under different operating conditions, varying the type of carbon-based reducing agent (either solid carbon or methane), temperature (in the range 765–1167<sup>◦</sup>C for ZnO and 991–1550<sup>◦</sup>C for MgO), total pressure (including both reduced 0.10–0.15 bar and atmospheric ~0.90 bar pressures), and processing mode (batch and continuous operations). The carbo-thermal and methano-thermal reduction reactions yielded gaseous metal species (Mg and Zn) which were recovered at the reactor outlet as fine and reactive metal powders. Reducing the total pressure favored the conversion of both MgO and ZnO and increased the yields of Mg and Zn. However, a decrease in the total pressure also promoted CO<inf>2</inf> production because of a shortened gas residence time, especially in the case of ZnO reduction, whereas CO<inf>2</inf> formation was negligible in the case of MgO reduction, whatever the conditions. Continuous reactant co-feeding (corresponding to the mixture of metal oxide and carbon or methane) was also performed during the solar reactor operation, revealing an increase in both gas production yields and reaction extent while increasing the reactant feeding rate. The type of carbon reducer influenced the reaction extent, since a higher conversion of both MgO and ZnO was reached when using carbon with a highly available specific surface area for the reactions. The continuous solar process yielded high-purity magnesium and zinc content in the solar-produced metallic powders, thus confirming the reliability, flexibility, and robustness of the solar reactor and demonstrating a promising solar metallurgical process for the clean conversion of both metal oxides and concentrated solar light to value-added chemicals.
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    Continuous solar-driven gasification of oil palm agricultural bio waste for high-quality syngas production
    (2022-12-01) ;
    Abanades, Stéphane
    Empty fruit bunch (EFB) from oil palm is a solid agricultural bio-waste obtained from the edible oil process. Continuous solar-driven gasification of EFB offers a bright carbon–neutral avenue to convert both EFB bio-waste and renewable solar energy into sustainable and clean syngas. High-temperature concentrated solar heat is used to provide the reaction enthalpy, and therefore biomass waste feedstock is entirely dedicated to produce hydrogen and carbon monoxide (syngas). Solar energy is stored as a high-quality syngas and can be easily transported as a convertible and dispatchable chemical form. In this study, the performance of continuous steam gasification of EFB, fully powered by concentrated solar heat, was experimentally investigated in a solar gasification reactor. Experiments were carried out with continuous EFB biomass injection to evaluate the influence of temperature (1100–1300 °C) and biomass feeding rate (0.5–1.8 g/min). As a result, syngas yields and reactor performance were substantially enhanced by rising the EFB feeding rate and gasification temperature. An optimal EFB biomass feeding rate enabling maximum gasification performance was found to be 1.4 g/min at 1300 °C and 1.0 g/min at 1200 °C. Carbon conversion approaching 97%, energy upgrade factor of 1.38, and solar-to-fuel energy conversion efficiency up to 20% were demonstrated. Finally, the maximum syngas yield was found to be 81.1 mmol/g<inf>dry biomass</inf> at 1300 °C (with H<inf>2</inf> and CO as the main constituents), closely approaching the maximum theoretical expected value reached at thermodynamic equilibrium (85.2 mmol/g<inf>dry biomass</inf>). Combining concentrated solar energy and biomass waste gasification was shown to be a promising and sustainable pathway toward waste valorization into carbon–neutral solar fuels.
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    Comprehensive analysis of on-sun catalytic reforming of methane with a hydroxyapatite-supported nickel catalyst in a tubular solar reactor
    (2026-07-22) ;
    Kulporm, Ratikorn
    ;
    O-Thong, Sompong
    ;
    Pham Minh, Doan
    ;
    Abanades, Stéphane
    Methane reforming offers a suitable pathway for greenhouse gas utilization, but its implementation is hindered by catalyst deactivation due to carbon deposition and thermal sintering. This study shows that hydroxyapatite serves as a stable catalytic support for solar-driven dry, steam, and dual reforming. The influence of oxidizer type and concentration (H<inf>2</inf>O, CO<inf>2</inf>, H<inf>2</inf>O/CO<inf>2</inf> mixture) is experimentally investigated at 800 °C in a tubular solar reactor. A hydroxyapatite-supported nickel catalyst (Ni/HA) achieves methane conversion exceeding 95% with 95% H<inf>2</inf> and 96% CO selectivity. An excess of oxidant (oxidant/CH<inf>4</inf> mole ratio of 1.2-1.5) is recommended to promote CH<inf>4</inf> conversion, improve solar reactor performance, and prevent carbon formation and catalyst deactivation. Through sequential on-sun experimental runs, energy upgrade factor above 1.5 and solar-to-fuel efficiency over 20% are attained, demonstrating high catalytic performance stabilized by the metal dispersion on the support. Dual reforming exhibits the highest syngas yield and performance, with minimized carbon formation and H<inf>2</inf>/CO ratio approaching 2.0. Catalyst characterization (XRD, FTIR, SEM, TEM/EDX) confirms high thermal/chemical stability of Ni/HA under solar heating conditions. These results demonstrate compatibility of Ni/HA catalyst with solar methane reforming, providing a high-efficiency sustainable system for converting greenhouse gases into syngas.
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    Solar chemical looping gasification of biomass with the ZnO/Zn redox system for syngas and zinc production in a continuously-fed solar reactor
    (2018-03-01) ;
    Abanades, Stéphane
    ;
    Rodat, Sylvain
    The high-temperature solar-driven chemical looping gasification of lignocellulosic biomass with ZnO/Zn redox pair was investigated as a novel process producing both syngas and metallic zinc. A lab-scale solar reactor (1.5 kW) was operated for continuous combined biomass gasification and ZnO carbo-thermal reduction using solar energy as the source of high-temperature process heat. Experiments were performed at temperatures ranging from 1050 °C to 1300 °C with biomass/ZnO molar ratios from 0.5 to 1, using beech wood as a biomass feedstock. The objective of this study was to unveil the advantages and reliability of the combined process involving biomass pyro-gasification with solid ZnO as an oxidizing agent under continuous process operation for co-production of syngas and metallic Zn. The influence of temperature and reactant molar ratio on syngas production was highlighted and compared to the case of a pyrolysis process without any oxidant. Moreover, the chemical conversion of ZnO to Zn obtained by this endothermic step was also addressed, confirming pure Zn production with low recombination in the collected solid products. The evolved H<inf>2</inf> increased significantly, CO production also tended to increase slightly, while CO<inf>2</inf> and CH<inf>4</inf> decreased when increasing the temperature. The syngas yield of the combined gasification/carbo-thermal reduction (up to ∼8 mol<inf>syngas</inf>/mol<inf>biomass</inf> for a biomass/ZnO molar ratio of 0.75 at 1250 °C) was much higher in comparison with pyrolysis. The calorific value of the feedstock was solar up-graded through syngas and Zn production in the case of the biomass gasification using ZnO, whereas pyrolysis was not energetically efficient because of the energy content still remaining in the produced char. The optimal biomass/ZnO molar ratio was evidenced at 0.75 yielding maximum syngas production. The energy upgrade factor of the feedstock by the solar power input and the solar-to-fuel energy conversion efficiency were 1.17 and 19.8% respectively for a molar ratio of 0.75 at 1250 °C.
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    An overview of solar decarbonization processes, reacting oxide materials, and thermochemical reactors for hydrogen and syngas production
    (2020-09-30) ;
    Abanades, Stéphane
    Solar decarbonization processes are related to the different thermochemical conversion pathways of hydrocarbon feedstocks for solar fuels production using concentrated solar energy as the external source of high-temperature process heat. The main investigated routes aim to convert gaseous and solid feedstocks (methane, coal, biomass …) into hydrogen and syngas via solar cracking/pyrolysis, reforming/gasification, and two-step chemical looping processes using metal oxides as oxygen carriers, further associated with thermochemical H<inf>2</inf>O/CO<inf>2</inf> splitting cycles. They can also be combined with metallurgical processes for production of energy-intensive metals via solar carbothermal reduction of metal oxides. Syngas can be further converted to liquid fuels while the produced metals can be used as energy storage media or commodities. Overall, such solar-driven processes allow for improvements of conversion yields, elimination of fossil fuel or partial feedstock combustion as heat source and associated CO<inf>2</inf> emissions, and storage of intermittent solar energy in storable and dispatchable chemical fuels, thereby outperforming the conventional processes. The different solar thermochemical pathways for hydrogen and syngas production from gaseous and solid carbonaceous feedstocks are presented, along with their possible combination with chemical looping or metallurgical processes. The considered routes encompass the cracking/pyrolysis (producing solid carbon and hydrogen) and the reforming/gasification (producing syngas). They are further extended to chemical looping processes involving redox materials as well as metallurgical processes when metal production is targeted. This review provides a broad overview of the solar decarbonization pathways based on solid or gaseous hydrocarbons for their conversion into clean hydrogen, syngas or metals. The involved metal oxides and oxygen carrier materials as well as the solar reactors developed to operate each decarbonization route are further described.