Researchers use efficient microbial electrosynthesis cells to convert CO2 to butyric acid; upgrade to butanol
Researchers from University of Girona (Spain) successfully used electrically efficient microbial electrosynthesis cells (MES) to convert CO2 to butyric acid. In an open-access paper published in the journal Environmental Science and Ecotechnology, they reported operating the low ohmic resistance (15.7 mΩ m2) cells in a batch-fed mode, alternating high CO2 and hydrogen (H2) availability to promote 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 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.
Romans-Casas et al.
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 kWhel 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.
This study showcases the potential of bioelectrochemical conversion of CO2 to butyric acid and its subsequent upgrade to butanol in microbial electrolysis cells.
Further research and development are needed to optimize the process for large-scale applications.
Meritxell Romans-Casas, Laura Feliu-Paradeda, Michele Tedesco, Hubertus V.M. Hamelers, Lluis Bañeras, M. Dolors Balaguer, Sebastià Puig, Paolo Dessì (2023) “Selective butyric acid production from CO2 and its upgrade to butanol in microbial electrosynthesis cells,” Environmental Science and Ecotechnology, Volume 17, doi: 10.1016/j.ese.2023.100303