(30a) Technology Performance and Economical Feasibility of Bioethanol Production in Pervaporation Membrane Bioreactor with Mechanical Vapor Compression

A pervaporation membrane bioreactor with mechanical vapor compression was developed for bioethanol production. During the experiments of ethanol fermentation-pervaporation process, ethanol could be removed in situ from the broth and ethanol production could be enhanced with ethanol inhibition relieved. The yeast cell could continuously grow for long time with cell density of 38 g/L obtained. The byproducts accumulation in the broth led to the culture deterioration of the fermentation and became the main inhibitor against the cell growth. At the end of the fermentation process, over 80 g/L of the byproducts were determined in the broth and this concentration could indeed inhibit ethanol fermentation. Increasing the pH could decrease the concentration of the undissociated weak acids in the broth and improve the fermentation. During the pervaporation process, the total flux of the polydimethylsiloxane (PDMS) membrane was in the range of 350 g m^-2 h^-1 and 600 g m^-2 h^-1. At the downstream of the membrane, part of the permeate vapor under the vacuum condition before the inlet of the vacuum pump was condensed at the first condenser by the running water at the room temperature and the non-condensed vapor enriched with ethanol was compressed to the atmospheric pressure and pumped into the second condenser by the vacuum pump. The vapor in the second condenser was easily condensed into a liquid by air at room temperature since the pressure was increased. Ethanol concentration of over 50wt% could be obtained in the second condenser, which could enhance the process separation factor. Energy integration could be achieved by the use of mechanical vapor compression heat pump and the Coefficient Of Performance (COP) of the heat pump could reach 7-9. Improved separation factor and energy integration increased the energy efficiency of the pervaporation process. The cost of ethanol produced in the pervaporation membrane bioreactor was lower, compared with that in the traditional batch fermentation or coupled process with cold trap condensation.