AIR-BUBBLING, HOLLOW-FIBER REACTOR WITH CELL BLEEDING AND CROSS-FLOW FILTRATION

Continuous asymmetric reduction of dyhydrooxoisophorone (DOIP) to 4‐hydroxy‐2,2,6‐trimethylcyclo‐hexanone (4‐HTMCH) was achieved by a thermophilic bacterium Bacillus stearothermophilus NK86‐0151. Three reactors were used: an air‐bubbling hollow‐fiber reactor with cell bleeding and cross‐flow filtration, an air‐lift reactor, and a CSTR with PAA immobilized cells. The maximum cell concentration of 11.1 g dry wt L−1 was obtained in an air‐bubbling hollow‐fiber reactor, while in the other reactors the cell densities were between 3.5 and 4.1 g dry wt L−1 The optimum bleed ratio was 0.1 at the dilution rate 0.3 h−1 in the hollow‐fiber reactor. The highest viable cell concentration was maintained in the dilution range of 0.4–0.7 h−1 by a combination of proper cell bleeding and cross‐flow filtration. The maximum volumetric productivity of 4‐HTMCH reached 826 mg L−1 h−1 at the dilution rate 0.54 h−1. This value was 4 and 2 times higher than those in the air‐lift reactor and CSTR, respectively. The increasing viable cell concentration increased the volumetric productivity of 4‐HTMCH. A cell free product solution was continuously obtained by cross‐flow filtration. Copyright © 1990 John Wiley & Sons, Inc.