Biotransformation in a microreactor: New method for production of hexanal

In this study, enzymatic oxidation of hexanol to hexanal (green note fragrance) using NAD(+) dependent commercial alcohol dehydrogenase from S. cerevisiae was conducted in continuously operated tubular microreactors with internal volumes of 6 and 13 mu L and in a tubular microreactor with a volume of 2 mu L that was equipped with internal micromixers. Flow profiles in microchannel were observed in experiments in which the aqueous phase was stained brilliant blue and the hexane was kept colourless. The effects of enzyme and coenzyme inlet concentrations and flow ratios of the immiscible phases on the conversion of hexanol and the volumetric productivity of hexanal were analyzed. Significant improvement in the conversion of hexanol when compared to the classical macroscale process was obtained for c (i,hexanol) = 5.5 mmol/L, c (i,NAD+) = 0.55 mmol/L, and gamma (i,ADH) = 0.092 g/L. In the 6 mu L microreactor 11.78% conversion of hexanol was attained after 72 sec, while in the macroscale process 5.3% conversion of hexanol was reached after 180 sec.