A covered particle deactivation model and an expanded Dunford mechanism for the kinetic analysis of the immobilized SBP/phenol/hydrogen peroxide system

Abstract

Abstract An expanded version of the Dunford mechanism, which extends the initial peroxidase cycle to the reaction products, was developed and applied to the kinetic analysis of the immobilized soybean peroxidase/phenol/hydrogen peroxide system. At the same time, an enzyme deactivation model, based on the gradual covering of the catalytic particles by the products originated during the reaction (radicals and end-products, oligomers/polymers), was proposed. From the reaction mechanism and deactivation model, the kinetic equations for phenol, dimeric compounds and hydrogen peroxide were obtained and applied to the design of a batch reactor. In order to check the mechanism, an immobilized derivative of the enzyme on PG-glutaraldehyde, which retains 74% of the free enzyme activity and which was characterized in a previous work, was used. In a batch reactor, and without adding protective agents, several series of experiments were carried out, and the influence of operational variables on the conversion was studied. Phenol removal percentages of more than 90% were obtained in some of the tested situations. Using a method for initial rate estimation, three of the model parameters were calculated. In order to determine the remaining parameters, half of the experimental data series and a program for error minimization, based on the Simplex algorithm of Nelder and Mead, were used. A good fitting between the data and the model was obtained, and the typical deviation was 3.27%. Using the data from the remaining series, which had not been used for determining the parameters, the model was checked and even better agreement, with 2.72% typical deviation, was obtained, which confirms the validity of the proposed model.