Sustainable production of pure hexanoic acid from CO₂ using microbial electrosynthesis with in-situ product recovery

Abstract

Carbon dioxide utilization is a key strategy for sustainable chemical production and climate change mitigation. Microbial electrosynthesis (MES) offers a promising approach to convert CO₂ into organic acids and multi‑carbon compounds, but its industrial application requires improved product recovery methods. In this study, we developed an integrated MES-sorption-distillation system for the recovery of pure hexanoic acid. Adsorption experiments identified conditions for C6-selective capture from C2–C6 carboxylate mixtures typically produced from MES. Subsequent desorption using CO₂ expanded methanol enriched hexanoic acid concentration by 13-fold compared to the aqueous feed, achieving 67 % recovery in a single pass, but 100 % overall, since recirculation of unrecovered carboxylates back to the MES reactor is proposed. This recirculation will enhance chain elongation, eliminate loss of unrecovered carboxylates, and reduce the need for external pH control during MES. Distillation of the desorbed mixture led to streams of pure products and reusable solvent, without losses. Notably, 87 % of the total energy demand for product formation is attributed to the MES stage, where electrical energy is directly supplied as electrons to drive microbial production. Thus, MES with the proposed recovery method enables pure hexanoic acid production with minimal losses of materials or energy and potentially allows the system to operate in a carbon-negative manner.