Study on the consecutive reaction kinetics of synthesis of di(2‐ethylhexyl) terephthalate under nonisothermal conditions

Abstract Since more information concerning kinetic parameters can be obtained from a nonisothermal reaction, it was selected to investigate the consecutive esterification kinetics of terephthalic acid with 2‐ethylhexanol in the presence of tetrabutyl titanate catalyst. This is an equilibrium reaction that is carried out in industry to completion by removing the water formed. It results in an automatic rise in the esterifying temperature, from 453 to 519 K. Research shows that the first step of esterification carried out in a heterogeneous system has a slow reaction rate, but the second step of esterification in a homogeneous system has a relatively fast reaction rate. Based on the quasi‐homogeneous assumption, first the differential method is presented to deal with nonisothermal reaction data. Arrhenius equations of the two steps are established by using this method. It was found that the apparent activation energy of the first step of esterification was about 55 kJ/mol higher than that of the second step. The ratio (K) of reaction rate constants of the two steps decreases gradually with the increase in the reaction temperature. An equation of K vs. temperature is also derived from Arrhenius equations. Subsequently, integral expressions of components' concentrations are used to simulate experimental results of the nonisothermal reaction as well as a three‐stage isothermal reaction. The obtained simulations show that the determined kinetic equations and the parameters are reasonable. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 577–584, 2006