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Impact of biowaste reducers on continuous solar-driven hematite reduction for carbon–neutral co-production of iron and syngas
(2026-09-15)
Chuayboon, Srirat
;
Abanades, Stéphane
Green iron production using bio-reducers and solar energy offers a promising alternative pathway towards carbon–neutral metallurgy. However, the types of raw bio-reducers play an important role in hematite reduction performance. An experimental investigation of continuous hematite reduction with seven agricultural biowastes was conducted in a solar reactor to unravel the impact of bio-reducer types and shapes (pellets and particles) on conversion performance and efficiency at 900–1200 °C. As a result, the most promising biowaste reducers were betel nut, palm oil empty fruit bunch, and beech wood due to their high volatile and carbon content, followed by bagasse, coconut fiber, and particle board. Conversely, rice husk was found to be inappropriate because of low gasification activity due to high ash content. No significant impact of reactant shape between particles and pellets was observed, pointing out that the reactor can accommodate various biomass feedstocks. The syngas yield varied in the range of 23.2–56.9 mmol/g<inf>dry_biomass</inf>, and simultaneous high-purity iron production was confirmed by XRD and SEM/EDS. High process efficiency was demonstrated with maximum carbon conversion of 83.1%, oxygen conversion of 100%, and energy upgrade factor up to 1.00. The solar-to-fuel energy efficiency reached 13.2% at 1200 °C, highlighting the remarkable conversion performance of waste biomass and solar energy to clean syngas fuel and renewable iron.
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Green iron and syngas production via continuous solar-driven agricultural waste biomass gasification combined with iron(III) oxide reduction
(2024-10-15)
Chuayboon, Srirat
;
Abanades, Stéphane
The production of renewable synthetic fuels and chemicals from solar energy and agricultural waste biomass is considered. Solar thermochemical conversion processes offer a promising pathway to a sustainable fuel economy and green chemical industry. This study investigates the continuous solar-driven gasification of agricultural biomass (betel nut waste) combined with iron oxide (Fe<inf>2</inf>O<inf>3</inf>) reduction to produce carbon-neutral syngas and green metallic iron in a single process. A thermodynamic analysis of the system was initially conducted to predict the distribution of equilibrium products. Then, on-sun continuous processing was experimentally carried out under different operating conditions, including betel/Fe<inf>2</inf>O<inf>3</inf> molar ratios (0.56–1.5) and temperatures (900–1200 °C) to evaluate the process feasibility and reliability. As a result, solar gasification of betel nut waste combined with Fe<inf>2</inf>O<inf>3</inf> reduction performed exceptionally well with continuous reactant particles feeding, demonstrating a feasible pathway for producing green iron and high-quality syngas. The maximum syngas yield reached 63.3 mmol/g<inf>dry_betel</inf>, approaching its theoretical value, and high-purity Fe was simultaneously produced. The process demonstrated high efficiency, with maximum carbon conversion approaching 98 %, energy upgrade factor up to 1.26, and solar-to-fuel energy conversion efficiency up to 14.4 %, highlighting remarkable conversion performance of biomass and solar energy to chemicals.
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Solar metallurgical process for high-purity Zn and syngas production using carbon or biomass feedstock in a flexible thermochemical reactor
(2023-05-05)
Chuayboon, Srirat
;
Abanades, Stéphane
Co-production of high-purity Zn and syngas via carbothermal reduction of ZnO was performed in a directly-irradiated concentrated solar reactor, thereby converting and storing intermittent sunlight into high-value chemical fuels and commodities. On-sun experiments were carried out by varying operating parameters including solid carbonaceous feedstocks (either solid carbon or beech wood biomass) in batch and continuous modes at 950–1350 °C, demonstrating solar reactor flexibility and robustness. Decreasing pressure (150–400 hPa) promoted both ZnO reduction rate and net ZnO conversion above 78%, thus enhancing Zn production yield. Nevertheless, CO selectivity decreased because of rising CO<inf>2</inf> due to the residence time decrease. A remarkable increase in gas production rates/yields, CO selectivity, and reaction extent was highlighted when increasing temperature during continuous pellets reactant injection. Furthermore, utilizing wood biomass as a sustainable green reducer was proved to be an attractive choice to produce both metallic Zn and high-quality syngas in a single process consisting of biomass gasification with solid ZnO. Zn content exceeding 90 wt% was demonstrated for both batch and continuous tests, unveiling high reactor performance for the metallurgical process. The energy content of the feedstock was upgraded by the solar power input (maximum energy upgrade factor up to 1.2), and the maximum solar-to-fuel energy conversion efficiency up to ∼ 6% was achieved with continuous reactant injection. The high-purity Zn can be further used to produce fuel via CO<inf>2</inf>-splitting in a complete and fast reaction.
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Solar metallurgy for sustainable Zn and Mg production in a vacuum reactor using concentrated sunlight
(2020-09-01)
Chuayboon, Srirat
;
Abanades, Stéphane
Solar carbothermal reduction of volatile metal oxides represents a promising pyro-metallurgical pathway for the sustainable conversion of both metal oxides and sunlight into metal commodities and fuels in a single process. Nevertheless, there are several scientific challenges in discovering suitable metal oxides candidates for the ease of oxygen extraction from metal oxides to enhance the reaction extent and in designing reactors for the efficient absorption of incident solar radiation to minimize losses. In this study, ZnO and MgO were considered as volatile metal oxides candidates, and their reaction behaviors were studied and compared through gas species production rate, metal oxides conversion, and yield. A solar reactor prototype was developed to facilitate solar carbothermal reduction of ZnO and MgO with different reducing agents comprising activated charcoal and carbon black. The process was operated in a batch operation mode under vacuum and atmospheric pressures to demonstrate the flexibility and reliability of this system for co-production of metals (Zn/Mg) and CO. As a result, decreasing total pressure enhanced conversion of ZnO and MgO, leading to increased Zn and Mg. However, in the case of ZnO, CO yield decreased with decreasing total pressure at the expense of favored CO<inf>2</inf> as a result of the decrease of residence time. In contrast, CO<inf>2</inf> formation was negligible in the case of MgO, and CO yield thus increased with decreasing pressure. Using activated charcoal as the reducing agent exhibited better conversion of both ZnO and MgO than carbon black thanks to the higher available specific surface area for chemical reactions. MgO and ZnO conversion above 97% and 78%, respectively, and high-purity Mg and Zn content were accomplished, as evidenced by the recovered products at the reactor outlet and filter containing pure metal. In addition, Mg product exhibited strong oxidation reactivity with air, thus requiring inert atmosphere for the handling of Mg-rich powders to avoid direct exposure to air.
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Clean magnesium production using concentrated solar heat in a high-temperature cavity-type thermochemical reactor
(2019-09-20)
Chuayboon, Srirat
;
Abanades, Stéphane
The synthesis of magnesium from the corresponding oxide via a solar carbo-thermal and methano-thermal reduction process using high-temperature concentrated solar heat was investigated. The reduction of magnesium oxide (MgO) was experimentally demonstrated in a directly-irradiated prototype solar reactor at reduced pressure and temperature up to ∼1650 °C. The solar reactor was successfully operated with a variety of reducing agents (carbon and CH<inf>4</inf>) in batch and continuous modes under atmospheric and low pressure conditions (0.1–0.9 bar), thus representing the first process demonstration of MgO carbothermal reduction with continuous reactant injection in vacuum condition. A parametric study regarding operating pressure, carbon feedstock type, and C/MgO molar ratio was conducted to emphasize their effect on products yield (Mg and CO) and solar reactor performance. MgO conversion, reduction rate, and CO yield increased with decreasing pressure, in agreement with thermodynamic analysis. Utilizing activated charcoal as reducing agent showed the highest MgO conversion and CO yield. High MgO conversion over 99% was demonstrated with maximal CO yield up to 24.59 mmol/g<inf>MgO</inf>, closely approaching theoretical maximum value (24.81 mmol/g<inf>MgO</inf>). Employing methane as a reducing agent was also shown to be an alternative option to produce Mg, although methane cracking occurred simultaneously at the elevated reaction temperature. Mg recovery in the outlet products was identified as one of the most critical process challenges because of the pyrophoric property of the produced nanopowder and its strong oxidation reactivity with air.

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