An engineering analysis for the continuous reactor behavior of α-chymotrypsin-immobilized thermosensitive gel cylinders

Abstract

In this study, α-chymotrypsin was immobilized via physical entrapment within thermally reversible isopropylacrylamide–hydroxyethylmethacrylate copolymer gel cylinders. The enzyme-containing gel cylinders were prepared by a redox polymerization procedure and characterized by electron microscopy and equilibrium swelling studies in the hydrolysis medium. The performance of the thermosensitive enzyme–gel system was investigated in a continuous stirred reactor operated at steady-state conditions. The results indicated that the observed hydrolysis rate of the synthetic substrate (i.e. benzoyl- l-tyrosine ethyl ester) could be controlled by the thermosensitive properties of the carrier matrix. The maximum value of the observed hydrolysis rate was obtained at 30°C with the enzyme–gel system in the continuous reactor while the free enzyme exhibited maximum activity at 40°C in the batch one. A mathematical model was proposed to explain the kinetic behavior of the thermally reversible enzyme–gel cylinders. By the application of model, the effective diffusion coefficient of substrate within the gel matrix was calculated for different reaction temperatures. Thiele modulus and effectiveness factor values for the enzyme–gel system were also estimated. A sudden increase in the Thiele modulus of the enzyme–gel system at the lower critical solution temperature of the gel matrix (i.e. 35°C) was first shown, experimentally. The effectiveness factors determined at different reaction temperatures indicated that the overall hydrolysis rate was controlled by the mass transfer resistance within the gel matrix.