Concentration of fermented ethanol by pervaporation using silicalite membranes coated with silicone rubber

In order to stabilize the production of highly concentrated ethanol, a coupled fermentation/pervaporation process using ethanol permselective silicalite membranes coated with silicone rubber was studied. In case of the silicalite membrane without coating, the membrane flux and the ethanol concentration in the permeate decreased with the fermentation time. The completely recovered ethanol fermentation was 30% (w/w). This behavior partly resulted from the adsorption of succinic acid produced during the fermentation to the membrane. It was effective to coat a naked silicalite membrane with the silicone rubber in the production of concentrated fermented ethanol of constant concentration by pervaporation. During the fermentation, the ethanol concentration in the permeate was almost constant, about 70% (w/w) when the silicalite membrane coated with the silicone rubber was used. Even in the case of the fermentation/pervaporation using the coated silicalite membrane, the flux greatly decreased. It is suggested that the glycerol produced during the fermentation, which is not adsorbed by the membranes, might have affected the pervaporation fluxes.