A novel reactor concept for the enzymatic reduction of poorly soluble ketones

Reductions of poorly soluble ketones often suffer from low total turnover numbers conferring to the coenzyme and large volumes which are needed for the conversion. The novel emulsion membrane reactor overcomes these limitations. From an emulsion consisting of an organic substrate and an aqueous buffer phase, the aqueous phase is separated selectively by using a hydrophilic ultrafiltration membrane and fed to a subsequent enzyme membrane reactor. The product outflow is recirculated to the emulsion stirred vessel and, due to the partition coefficients, the aqueous phase is recharged with substrate while the product is extracted. This new reactor concept will be compared to the classical enzyme membrane reactor. The latter was operated under the same conditions over a period of 4 months at a space-time yield of 21.2 g l(-1) day(-1). As a model system the enantioselective reduction of 2-octanone to (S)-2-octanol (ee > 99.5%) is used, carried out by a carbonyl reductase from Candida parapsilosis. NADH is regenerated by formate dehydrogenase from Candida boidinii. In comparison to the classical enzyme membrane reactor the total turnover number could be increased by a factor 9 using the novel emulsion membrane reactor. (C) 1998 Elsevier Science B.V.