Continuous ethanol fermentation in a closed‐circulating system using an immobilized cell coupled with PDMS membrane pervaporation

BACKGROUND: A closed‐circulating system for ethanol fermentation was constructed by coupling a cell‐immobilized bed fermentor with pervaporation using a composite PDMS membrane. A continuous fermentation experiment was carried out for about 250 h in the system at 28 °C. RESULTS: The cell density in the immobilized bed was up to 1.76 × 10¹⁰ cells g^?1 gel. The ethanol concentration in the broth was maintained at about 43 g L^?1. The glucose utilization and ethanol productivity were 23.26 g L^?1 h^?1 and 9.6 g L^?1 h^?1, respectively. The total flux and the ethanol flux through the membrane pervaporation unit varied in the range 300–690 g m^?2 h^?1 and 61–190 g m^?2 h^?1, respectively. The average ethanol concentration in the permeate was 23.1% (wt%). The carbon recovery efficiency was 86.8% (wt%), determined by calculating the carbon balance kinetics. The effect of ethanol concentration in the broth on the ethanol productivity was analyzed by modeling product formation kinetics of the system. CONCLUSIONS: Compared with the traditional free cell fermentation system and packed bed fermentation system, the closed‐circulating system has the promising features of higher glucose utilization and ethanol productivity, and cleaner production. Copyright © 2010 Society of Chemical Industry