Innovative breakthrough in sustainable chemical production

Carbon capture and utilization (CCU) technologies are crucial for addressing climate change while ensuring economic viability. MES has emerged as a promising approach for CO₂ reduction to biofuels and platform chemicals. However, the industrial adoption of MES has been hindered by low-value products like acetate or methane and high electric power demand.

In a new study recently published on 26 July 2023, in the journal Environmental Science and Ecotechnology, researchers from University of Girona conducted a study that focused on electrically efficient MES cells with low ohmic resistance (15.7 mΩ m²). Through a fed-batch mode, alternating high CO₂ and hydrogen (H₂) availability, they successfully promoted the production of acetic acid and ethanol. Chain elongation resulted in the selective (78% on a carbon basis) production of butyric acid, a valuable chemical used in pharmaceuticals, farming, perfumes, and the chemical industry. At an applied current of 1.0 or 1.5 mA cm⁻², the study achieved an impressive average production rate of 14.5 g m⁻² d⁻¹ of butyric acid. The key player in the chain elongation process was identified as Megasphaera sp. Inoculating a second cell with the enriched community replicated the butyric acid production rate, but with an 82% reduction in the lag phase. Butyric acid was successfully upgraded to butanol, a valuable biofuel compatible with existing gasoline infrastructure and used as a precursor in pharmaceutical and chemical industries for acrylate and methacrylate production. Solventogenic butanol production was triggered at a pH below 4.8 by interrupting CO₂ supply and maintaining specific pH and hydrogen partial pressure conditions. The MES cell design proved highly efficient, with average cell voltages of 2.6–2.8 V and an electric energy requirement of 34.6 kWh_el kg⁻¹ of butyric acid produced. Despite some limitations due to O₂ and H₂ crossover through the membrane, the study identified optimal operating conditions for energy-efficient butyric acid production from CO₂.

Highlights

•      Low-resistance bioelectro-cells were operated galvanostatically in fed-batch mode.

•      Alternating high pCO₂ and pH₂ promoted bioelectro-CO₂ conversion to butyric acid.

•      A rate of 14.4 g m⁻² d⁻¹ and 78% selectivity were achieved by consuming 35 kWh kg⁻¹.

•      Megasphaera sp. carried out chain elongation at the cathode.

•      Keeping pH₂ > 1.7 atm and pH < 4.8 promoted butanol production in absence of CO₂.

In conclusion, this study showcases the potential of bioelectrochemical conversion of CO₂ to butyric acid and its subsequent upgrade to butanol in microbial electrolysis cells. The process holds promise for sustainable and economically viable production of valuable chemicals from CO₂. Further research and development are crucial to optimize the process for large-scale applications, and with continued advancements, this technology can revolutionize chemical production while mitigating climate change impact.

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References

DOI

10.1016/j.ese.2023.100303

Funding information

The Spanish Ministry of 478 Innovation and Science (PID2021-126240OB-I00). The European Union’s Horizon 2020 research Marie Skłodowska-Curie grant agreement, project ATMESPHERE (101029266), The Spanish Government (FPU20/01362), The ICREA Academia award, The Research Training grant from the Catalan Government (2021 FISDU 00132), The Catalan Government (2021 SGR01352 and 2021 SGR01142).

About Environmental Science and Ecotechnology

Environmental Science and Ecotechnology (ISSN 2666-4984) is an international, peer-reviewed, and open-access journal published by Elsevier. The journal publishes significant views and research across the full spectrum of ecology and environmental sciences, such as climate change, sustainability, biodiversity conservation, environment & health, green catalysis/processing for pollution control, and AI-driven environmental engineering. The latest impact factor of ESE is 12.6, according to the Journal Citation Report^TM 2022.