Kinetic Modeling of Oxychlorination Reaction
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Polyvinyl chloride is a widely produced plastic polymer due to its various applications and relatively low cost. Oxychlorination of ethylene to 1,2-dichloroethane is an important step in the production of vinyl chloride monomer, which is the monomer of polyvinyl chloride. The oxychlorination reaction is commonly catalyzed by cupric chloride supported on gamma-alumina. However, in previous studies, promotion of the neat catalyst with alkali metals or rare earth metals have shown to have advantageous effects on the stability, selectivity and activity of the catalyst. A challenge with the oxychlorination is that the catalyst undergoes oxidation state changes, which complicates the formulation of a comprehensive kinetic description of the reaction pathway. Transient techniques are advantageous in order to extract information about the intrinsic kinetics, which is important for the optimization of the oxychlorination catalyst. A kinetic model was developed and used to solve the spatial-time change in the Cu(II) concentration. The model was applied for two different catalysts; a neat cupric chloride catalyst and a K promoted catalyst, and validated against experimental data. It was found that the model provided a good description of the reaction, both in the transient and in the steady-state case and holds for a wide range of conditions. The reactor model predicted the spatial-time Cu(II) profile well based on comparison with experimental data. An important finding in this study was that two types of active sites needed to be considered in the development of the kinetic model. Consequently, the reaction rates were separated into two parts. In addition, the change in the coordination number of Cu throughout the reaction was introduced in the rate expressions, making it possible to account for the state change of Cu.