High hexanol production from syngas by Clostridium carboxidivorans P7 through in situ hexanol recovery by adsorption

Hexanol production via gas fermentation using acetogens has emerged as a promising alternative to fossil fuel-derived hexanol. However, product inhibition significantly limits hexanol accumulation without in situ removal. This study aimed to enhance hexanol production by employing in situ adsorption during CO fermentation with Clostridium carboxidivorans P7. Among four tested adsorbents (L-493, SD-2, GSP-25, and activated carbon), activated carbon (AC) demonstrated superior performance, achieving 8.40 g/L hexanol production while maintaining effective product removal through its high adsorption capacity. Process optimization through initial pH adjustment and reduced AC loading shortened the acidogenesis phase, further increasing hexanol production to 9.82 g/L. To reduce carbon loss from CO2 generation during CO metabolism, H2 was co-supplied with CO (70:30 ratio) as an additional electron donor, promoting alcohol production and enabling CO2 reutilization. This strategy achieved a hexanol titer of 11.93 g/L while reducing the CO2 evolution/CO consumption ratio by 16.9–18.7 % compared to CO-only fermentation. These findings demonstrate that adsorption-assisted gas fermentation with CO/H2 co-utilization represents a promising strategy for sustainable hexanol production with reduced carbon emissions.