Bioethanol Production via Syngas Fermentation of Clostridium Ljungdahlii in a Hollow Fiber Membrane Supported Bioreactor

Abstract

Ethanol production via syngas fermentation obtained from lignocellulose gasification provides a method to completely utilize all the carbon content from lignocellulosic feedstock. A low mass transfer rate of less soluble gas CO and H2 to liquid has been considered as the major bottleneck of the overall process; thus, microporous membrane was proposed as a gas diffuser to improve gas-to-liquid mass transfer. In this study, a liquid batch of syngas fermentation employing Clostridium ljungdahlii with continuous gas supply was carried out with the configuration of a bioreactor connected to the microporous hydrophobic polypropylene hollow fiber membrane (HFM) as a gas diffuser. Liquid recirculation between the fermentation vessel and membrane module was applied to enhance the gas-liquid contact as well as cell-recycle. Fermentation performance with and without HFM was compared and evaluated by cell growth, CO utilization, ethanol yield, and productivity. A higher ethanol yield, 0.22 mol/mol, was achieved by the system of HFM-supported bioreactor with higher ethanol titter of 1.09 g/L and ethanol to acetate molar ratio of 1.43 mol/mol. The obtained result indicates HMF-supported bioreactor is the best fermentation system compared to STR without the membrane.

Keywords

• ethanol, Clostridium ljungdahlii, hollow fiber membrane, mass transfer, syngas fermentation