Covalently coupled nanoparticles in capillary pores as enzyme carrier and as turbulence promoter to facilitate enzymatic polymerizations in flow-through enzyme-membrane reactors

Abstract

Enzyme–membrane reactors (EMR) with enzyme covalently immobilized on the pore walls are interesting alternatives for continuous processes, especially for polymerizations. However, the effective mass transfer in the pores is critical, and the synthesis of the high-molecular weight inulin from sucrose using fructosyltransferase (FTF) immobilized in the pores of track-etched membranes had been very much limited by a fast enzyme deactivation via aggregation with the product along with extensive pore blocking of the membranes. In this work, EMR had been prepared by covalent immobilization of FTF onto amino-functionalized track-etched poly(ethylene terephthalate) (PET) membranes with nominal pore diameters of 400, 1000 or 3000 nm, and in all cases the loss of enzyme activity was fast, and the extent of pore blocking was increasing with decreasing pore diameter. Experiments at varied cross-flow velocity with the FTF covalently immobilized on the surface of an epoxy-reactive non-porous film suggested that the rate of FTF deactivation could be much reduced by increasing mass transfer efficiency. Consequently, FTF–EMR with pore diameters of 1000 nm had been operated using regular backpulsing during flow-through or with dispersed inert nanoparticles (diameter 110 nm) in the feed solution flowing through the pores. For both variants, a significant performance improvement had been obtained. Finally, a novel nanoparticle composite membrane had been prepared via the covalent immobilization of epoxy-reactive nanoparticles (diameter 200–230 nm) on the pore walls of the track-etched membranes. Spacing between the particles had been achieved by using a mixture of reactive and inert nanoparticles and suited reaction and washing conditions. The FTF–EMR based on the novel nanoparticle composite membranes had a much higher productivity (prolongation of EMR operation time and more formation of inulin) as compared with all the other membranes or variants investigated in this study. Also a much lower pore-blocking tendency had been observed. This improved performance had been explained by the two functions of the nanoparticles in the membrane — turbulence promoter and support providing increased surface area for covalent enzyme immobilization.