Use of magnetic nanoparticles to enhance bioethanol production in syngas fermentation

•Nanoparticles were tested to enhance syngas fermentation by mass transfer improvement.•CoFe2O4@SiO2–CH3 nanoparticles showed better enhancement of syngas fermentation.•The reusability of CoFe2O4@SiO2–CH3 nanoparticles can improve economic feasibility. The effect of two types of nanoparticles on the enhancement of bioethanol production in syngas fermentation by Clostridium ljungdahlii was examined. Methyl-functionalized silica and methyl-functionalized cobalt ferrite–silica (CoFe2O4@SiO2–CH3) nanoparticles were used to improve syngas–water mass transfer. Of these, CoFe2O4@SiO2–CH3 nanoparticles showed better enhancement of syngas mass transfer. The nanoparticles were recovered using a magnet and reused five times to evaluate reusability, and it was confirmed that their capability for mass transfer enhancement was maintained. Both types of nanoparticles were applied to syngas fermentation, and production of biomass, ethanol, and acetic acid was enhanced. CoFe2O4@SiO2–CH3 nanoparticles were more efficient for the productivity of syngas fermentation due to improved syngas mass transfer. The biomass, ethanol, and acetic acid production compared to a control were increased by 227.6%, 213.5%, and 59.6%, respectively by addition of CoFe2O4@SiO2–CH3 nanoparticles. The reusability of the nanoparticles was confirmed by reuse of recovered nanoparticles for fermentation.