Developing the rate equations for two enzymatic Ping-Pong reactions in series: Application to the bio-synthesis of Bis(2-ethylhexyl) azelate

Abstract

In this work, the rate equations of two simultaneous bisubstrate Ping-Pong in series reactions have been developed for the first time. To obtain these equations, the approximation to the stationary state has been applied and, for the total balance of enzyme, all the intermediate complexes of the two reactions, which are present simultaneously in the reaction medium, have been taken into account. To check the kinetic equations obtained, the synthesis of bis(2-ethylhexyl) azelate by transesterification from diethyl azelate and 2-ethylhexanol, in the presence of the immobilized lipase Novozym@ 435, has been used as reaction model. The reaction has been carried out in solvent-free conditions in a batch reactor. A design model of the reactor has also been developed and solved by applying a numerical method. The model equations have been implemented in user’s software in Visual Basic for Applications. In that software a routine, based on a very well-known procedure to minimize the sum of the square errors, has also been implemented. By using this software, the model parameters have been determined by fitting the experimental data to the model. A high determination coefficient was obtained, which validated both the kinetic equations and the reactor’s design model.