| Ethanol is the product of fermentation industry which has now the longesthistory and biggest yield in the world. As the substitute of the fossil fuels, ethanol hasexcitated more investigations on the advanced cleanly ethanol fermentation.Continuous fermentation-pervaporation technology with high efficiency and low costcan be achieved only if superior membranes are available. Due to it's selectivity toethanol and nontoxicity to microorganism, the composite polydimethylsiloxane(PDMS) membrane can be used to construct a continuous fermentation-pervaporation system. The product inhibition was lowered even avoided, becausethe coupling of the fermentation and pervaporation processes reduced the ethanolconcentration in the broth. Then the long-term system can run steadily and get ahigher ethanol production rate.The glucose was continuously fermented with the microorganism ofThermopHilic Alcohol Active Dry Yeast (TH-AADY). The membrane bioreactor wassteadily running for 269 hours. During the period, the cell, glucose and ethanolconcentrations were keeping steady. Due to the continuous pervaporation, the ethanolconcentration in the broth were successfully controlled between 35～45g/L. In thephase of fermentation coupled with pervaporation, the yeast concentration was heldat 20～25g/L. The ethanol production rate reached 3.4 g/(Lh), which was 4.5 times ofthe conventional batch fermentation, and the ethanol formation ratio of 0.46 wereachieved, corresponding to a conversion efficiency of 91%. The pervaporationmodule consistently produced a permeate of 28.2～16.5%(w%), while the overallpermeation flux and the ethanol flux reached 1226～707g/(m~2h) and 293～117g/(m~2h),respectively, corresponding to selectivity of 8.5-4.9. The starchy saccharide was used as the only carbon source of the continuousfermentation and pervaporation system. The membrane bioreactor was running for166 hours continuously, and the ethanol concentration in the broth reduced quickly,due to the pervaporation. The yeast concentration was increased and long-termedholding above 15g/L after the product inhibition was reduced. The average ethanolproduction rate was 1.37g/(Lh), and the ethanol formation ratio of 0.44 was reached,corresponding to a conversion efficiency of 86.2%. The two-stage condensation wasadopted in the pervaporation module. In the first stage(0℃), a permeate of 12.76～3.48%(w%) was produced and in the second stage(-30℃), a permeate of69.17～36.47%(w%) was reached for the ethanol solution first concentrating. Theoverall permeation flux and the ethanol flux reached 1105.3～599.3g/(m~2h) and371.5～91.6g/(m~2h), respectively, corresponding to selectivity of 8.1～6.5.The composite PDMS membrane prepared in the laboratory represented stableflux and selectivity in the pervaporation of fermentation broth. Fluxes and selectivityresulting from fermentation broth were higher than those characterized with modelsolution under similar situation. Compared with those of the nummular membranedevice, the fermentation and pervaporation parameter of the rectangle membranedevice were higher, which showed the achievement of enlarging the fermentation-pervaporation coupling system. And this is important to enlarge the continuousfermentation to a large scale.The coproduct inhibition was more obvious after the product inhibition wasreduced by the pervaporation. In the continuous fermentation of the starchysaccharide, the growth and metabolism of yeast became stagnated due to theinhibition. How to solve the coproduct inhibition and maintain the liveliness of themicroorganism will decide if the continuous fermentation and pervaporation systemcould bring about industrialization. Besides improving the ferment entironment, weneed choose microorganism which is more suitable to our system. Also we can usethe advanced gene technic to optimize the fermentation capability of themicroorganism.
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