Peroxygenase-Driven Ethylbenzene Hydroxylation in a Rotating Bed Reactor

The ability of unspecific peroxygenase (UPO) to hydroxylate a wide range of substrates with just H2O2 as a cosubstrate has attracted a great deal of attention in biocatalytic research. The enzyme's intrinsic limitation to be inactivated by excess amounts of the oxidative cosubstrate has been tackled with in or ex situ hydrogen peroxide (H2O2) provision strategies. In this paper, we present the application of the covalently immobilized UPO mutant PaDa-I in a rotating bed reactor for the hydroxylation of ethylbenzene in a two-liquid-phase system. By monitoring product formation in the organic phase and H2O2 concentration in the aqueous phase, the multiphasic reaction was optimized. Over 58 h, up to 414 mM (R)-1-phenylethanol was accumulated in the organic phase, corresponding to a productivity of 436 mg L–1 h–1 and a selectivity for the alcohol product over the overoxidated ketone product of 62%. It was found that the overoxidation of (R)-1-phenylethanol to acetophenone resulted in part from the H2O2 concentration in the aqueous phase but mainly from the concentration of the target alcohol. Therefore, a repetitive batch was performed over five times for 13 h with similar product concentrations and formation rates as in the conventional approach but a considerably higher selectivity of 79%.