Integrated microsphere-packed bed enzymatic membrane reactor for enhanced bioconversion efficiency and stability: A proof-of-concept study

Fabricating high-performance enzyme reactors is requested for achieving efficient and stable bioconversions, but remains challenging, because few of them can possess high enzyme loading, sufficient mixing, and efficient mass transfer at the same time. Herein, we propose to develop a novel enzymatic packed bed membrane reactor (EPBMR) by integrating the advantages of both packed bed reactor (PBR) and enzymatic membrane reactor (EMR). A prototype study is conducted with the simplified enzyme-loaded microsphere-ultrafiltration EMR model (Mic-UF EMR). Invertase and dextranase are used in this work to produce glucose and oligodextran by hydrolysis of sucrose and dextran, respectively. Specifically, the use of microspheres can enlarge the contact area between enzymes and substrates and mitigate membrane fouling induced by free enzymes. Thus, Free&Mic-UF EMR (with both free and immobilized enzymes) exhibits a higher sucrose conversion rate (84%) than the EMR with free invertase (34%) and a negligible decline in sucrose conversion for 36 h continuous operation. Membrane fouling is ameliorated by alkaline cleaning and implementation of covalent bonding strategy. In addition, commercial resins with larger sizes are employed to replace konjac glucomannan microspheres (KGM) which reduce the pressure drop of EMR. Finally, by selecting the UF membrane with proper molecular weight cut-off (MWCO), the dextranase-based Mic-UF EMR system successfully produces oligodextran with desired molecular weight (Mw) and narrow Mw distribution. The outcome of this work not only offers a novel enzyme reactor construction strategy but also provides guidance for regulating the performance of EMR.