Mass transfer in pervaporation of active fermentation broth with a composite PDMS membrane

The pervaporation behavior and mass transfer coefficients of active fermentation broth as well as concerned ethanol mixtures were experimentally investigated. Ethanol was produced by Saccharomyces cerevisiae and recovered by pervaporation using a composite polydimethylsiloxane (PDMS) membrane prepared in the laboratory. The overall transfer coefficients across the membrane were nearly invariable when recovering ethanol from fermentation broth under the constant operating condition, which was 1.93 x 10(-6) m/s on average for flow rate of 100 L/h, downstream pressure of 5 mmHg and cell concentration of 5 g/L at 35 degrees C in contrast with 1.34 x 10(-6) m/s for an aqueous ethanol solution under similar conditions. Ethanol fluxes and selectivities for fermentation broth were all higher than those for aqueous ethanol solution at the same feed concentration. According to the resistance-in-series model, the boundary layer transfer coefficient of fermentation broth was nearly three times as much as the value with the model solution on the assumption that diffusive transfer coefficients in the same membrane remained invariable at a constant temperature. Overall transfer coefficient increased slightly with active cell concentration for fermentation broth but decreased with solid concentration for inactive cell suspension. Active fermentation broth gave the highest transfer coefficients among the feeds involved during pervaporation using the composite PDMS membrane. (C) 2004 Elsevier B.V. All rights reserved.