Continuous enzymatic carboligation of benzaldehyde and acetaldehyde in an enzyme ultrafiltration membrane reactor and laminar flow microreactors

The synthesis of (S)-2-hydroxypropiophenone ((S)-2-HPP) from benzaldehyde and acetaldehyde catalyzed by benzoylformate decarboxylase (BFD) from Pseudomonas putida was studied in an enzyme ultrafiltration membrane reactor (UFMR) and in three different microreactors (MRs). The aim was to compare the volume productivity (QP) as well as biocatalyst productivity number (BPN) of these two continuous reactor systems. Influence of geometry, surface roughness of the microchannel walls, and inner mixing in the microreactors on conversion were also tested. In all used microreactors full conversion of benzaldehyde was achieved at residence times longer than 4 min. This was not the case in the UFMR where BFD was “soluble” immobilized because of the enzyme instability under the working conditions. The microreactor with inner mixing (micromixers) showed higher conversion at residence times shorter than 2 min (higher flow rates); while at longer residence times there were no significant differences between the different microreactor types. The biocatalyst productivity numbers of the microreactors were higher in comparison to the UFMR. The highest BPN was achieved in a microreactor with smooth surface microchannel walls (1.55 g g−1) at residence time of 5 min while the highest BPN in the UFMR (0.21 g g−1) was achieved at residence time of 30 min and 48 min of processing time.