The cumene oxidation and cumene hydroperoxide decomposition in the presence of Zn, Cd or Hg 2-ethylhexanoate: Kinetic model and analysis of its sensitivity

Abstract

A general kinetic model for industrially significant cumene oxidation and cumene hydroperoxide decomposition in the presence of Zn, Cd or Hg 2-ethylhexanoate as catalyst was developed. The model was based on the mass action law, in the form of a stiff system of nonlinear differential equations describing the rates of change in the concentrations of all species in the reaction mixture during the processes. Physically substantiated values of the unknown coefficients of the model (the coefficients of the temperature dependencies of the reaction rate constants) were found as a result of solving the inverse problem. It was done by minimizing the average relative error (using the method of direct search of the zero order) between the data calculated as a result of the numerical solving of the model by the implicit BDF method and the experimental data. The analysis of model sensitivity to changes of its coefficients has been carried out. Through this analysis, the original model is reduced to a simplified form, more convenient for studying the kinetic regularities and the mechanism of the considered chemical processes. The modification of the original model involved in exception from its equations of the terms containing the coefficients that were found as a result of solving the inverse problem, for which change the model is insensitive. A total of 39 terms were excepted out of 179. Thus, a possible mechanism for the cumene oxidation and cumene hydroperoxide decomposition in the presence of Zn, Cd or Hg 2-ethylhexanoate has been substantiated. The developed model was used to study the catalytic activity and thermal stability of Zn, Cd and Hg 2-ethylhexanoates in cumene oxidation and cumene hydroperoxide decomposition. Computational experiments have shown that the catalytic activity of Zn, Cd and Hg 2-ethylhexanoates in cumene oxidation and cumene hydroperoxide decomposition is caused by formation of intermediate adducts ROOH⋅Cat, which turn to be an additional source of free radicals due to their lower thermal stability compared to the original catalyst and cumene hydroperoxide. This phenomenon can be used for practical purposes to increase the rate of cumene hydroperoxide accumulation during cumene oxidation. The kinetic model presented in the article, can be a starting point (model object) for the development of kinetic models of oxidation processes of other aromatic hydrocarbons, catalyzed by nontransition metals due to the formation of intermediate adducts.