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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