A MEMBRANE BIOREACTOR FOR BIOTRANSFORMATIONS OF HYDROPHOBIC MOLECULES

The Membrane Bioreactor for Biotransformations (MBB) is based on the a queous/organic two-phase system, and uses a tubular silicone rubber me mbrane to separate the two liquid phases. This avoids the key problem associated with direct contact two-phase processes, specifically, prod uct emulsification. The baker's yeast mediated reduction of geraniol t o citronellol was used as a model biotransformation to demonstrate MBB operation. Values for the overall mass transfer coefficient were dete rmined for geraniol, (2.0 x 10(-5) mS-?), and for citronellol, (2.1 x 10(-5) ms(-1)) diffusion across the silicone rubber membrane. Using th ese values, and the specific activity of the biocatalyst (5 nmols(-1)g biomass(-1)), a suitable membrane surface area: biomass ratio was det ermined as 2.4 x 10(-3) m(2)g biomass(-1). The bioreactor was operated at this surface area: biomass ratio and achieved a product accumulati on rate 90-95% that of a conventional direct contact two-phase system. The slight reduction in product accumulation rate was shown not to be due to mass transfer limitations with respect to reactant delivery or product extraction. (C) 1998 John Wiley & Sons, Inc.