Enantioselective, continuous (R)- and (S)-2-butanol synthesis: achieving high space-time yields with recombinant E. coli cells in a micro-aqueous, solvent-free reaction system.

•Biocatalytic, stereoselective 2-butanone reduction in continuous micro-aqueous system.•High conversions (>95%) and ee (>96%) achieved for (R)-2-butanol.•Extremely high space-time yields were obtained.•System was successfully transferred to a (S)-selective catalyst.