INTEGRATION OF PERVAPORATION AND CONTINUOUS BUTANOL FERMENTATION WITH IMMOBILIZED CELLS .1. EXPERIMENTAL RESULTS

In alcoholic fermentations substrate conversion is limited by product inhibition, but it can be increased by in situ product recovery. In this study pervaporation was used for in situ alcohol recovery in continuous isopropanol-butanol-ethanol fermentations with immobilized cells. The fermentation was performed in a stirred tank reactor and in a fluidized bed reactor, and the product was recovered by means of a laboratory-built pervaporation module. In the integrated process the substrate consumption could be increased by a factor of four by comparison with continuous fermentations without product recovery. Experiments with a commercially available pilot plant plate-and-frame pervaporation module are described for the separation of alcohols from aqueous mixtures and the dehydration of alcohol-water mixtures. This module was also coupled to continuous butanol fermentations; however, sterilization of the module was troublesome, and it was frequently plugged by microbial cells. Apart from these problems, which further development is expected to resolve, pervaporation is a promising method for in situ product recovery.