Effect of Immobilization Site and Membrane Materials on Multiphasic Enantiocatalytic Enzyme Membrane Reactors

In this experimental work the optical resolution of racemic naproxen methyl ester with crude lipase immobilized in a membrane reactor was studied. The multiphasic enantiocatalytic enzyme membrane reactor consisted of an organic phase which dissolved the naproxen methyl ester, a lipase-loaded membrane, and an aqueous phase which extracted the reaction product. Lipase preferentially converted the (S)-naproxen methyl ester to (S)-naproxen acid that was simultaneously separated by membrane. The effect of immobilization site and membrane type on the performance of enzyme membrane reactor was studied. Capillary polyamide membrane with 10 kDa NMWCO (Nominal Molecular Weight Cut-off) and polysulfone membrane with 30 kDa NMWCO were applied, with lipase loaded in the sponge layer or on the thin layer of membranes. With different immobilization site and membrane type, the enzyme membrane reactors showed different productivity and enantioselectivity resulting from the different amount of immobilized enzyme and different microenvironment of hydrolysis reaction. Higher amount of immobilized enzyme led to higher productivity and generally higher enantioslectivity of membrane reactor. It seems that the location of organic/aqueous interface on membrane, which plays an important role on multiphasic enzyme membrane reactor, was influenced by immobilization site and membrane type and thus affected the productivity and enantioselectivity. As high as 90% of enantioexcess was obtained by polyamide membrane, and a lower one with polysulfone membrane. Briefly, the sponge layer of polyamide membrane is the preferable immobilization site for its higher productivity than the thin layer of membranes, and for its higher enantioselectivity than polysulfone membrane. As comparison with the unstable hydrolysis activity of free lipase in stirred tank reactor, a stable lipase activity can be obtained with lipase-immobilized membrane reactor, no matter whether using polyamide membrane or polysulfone membrane.