Hemachand Jaladi1, Amit Katiyar1, Vadim V. Guliants2, and Neville G. Pinto3. (1) University of Cincinnati, 420,Riddle Road, #2A, Cincinnati, OH 45220, (2) Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, (3) Chemical & Materials Engineering, University of Cincinnati, P.O. Box 210012, Cincinnati, OH 45221-0012
Lipases are ubiquitous enzymes that exhibit high levels of catalytic efficiency and high chemical-, regio- and stereo-selectivity selectivities. However, the uses of free lipases in biocatalytic transformations are complicated by their limited stability and the need to recover costly enzyme from the batch reaction process. Enzyme stability and recovery from the reaction products may be improved significantly via enzyme immobilization onto porous supports. However, this is frequently at the expense of reduced mass-transfer rates and decreased biocatalytic efficiency. Ordered mesoporous silicas are currently being investigated as promising, novel hosts for enzyme immobilization. In this study we investigated the effects mass- transfer and kinetic parameters on biocatalytic activity of Burkholderia Cepacia (BC) lipase immobilized onto ordered mesoporous SBA-15 silicas. BC lipase was immobilized by physical adsorption from solution onto SBA-15 silicas of two pore sizes (55 Å and 240 Å). A colorimetric assay of p-nitrophenyl acetate hydrolysis was employed to determine catalytic activity. Michaelis-Menten rate constants (Km and Vmax) of the immobilized and free lipase were compared. Mass transfer effects were investigated by determining the effective substrate diffusivity (Deff), as a function of pore size of the SBA-15 host and enzyme loading. It was observed that for kinetic resolution processes plug flow reactors are preferred over batch reactors. Since lipases have found wide use in kinetic resolution of achiral molecules, it is desirable to investigate their performance in a continuous flow reactor. A mathematical model was developed to predict optimal operating parameters for immobilized BC lipase in a packed-bed reactor, and used to predict overall conversion in the reactor as a function of mass-transfer rate, intrinsic reaction rate, particle size, enzyme loading and liquid mean residence time. The model predictions are in good agreement with experimentally observed biocatalytic activity of BC lipase immobilized onto SBA-15, as a function of both the pore size and enzyme loading.