Kinetic modeling of dynamic changing active sites in a Mars-van Krevelen type reaction: Ethylene oxychlorination on K-doped CuCl2/Al2O3

Hongfei Ma,Erling S Sollund,Wei Zhang,Endre Fenes,Yanying Qi,Yalan Wang,Kumar R Rout,Terje Fuglerud,Marco Piccinini,De Chen

doi:10.1016/j.cej.2020.128013

Abstract

A kinetic model was developed by taking into account the dynamic nature of the active sites in Mars–van Krevelen type catalytic reactions to predict the evolution of the reactant and product composition in the gas phase and the CuCl2 concentration in the solid catalyst. The kinetic model at the steady-state of ethylene oxychlorination was obtained by combining transient experiments of the two half-reactions in the redox cycle, namely CuCl2 reduced to CuCl by ethylene and CuCl oxidation by oxygen on the K-promoted CuCl2/γ-Al2O3 catalyst. The dynamic transitions between CuCl2 and CuCl of the active sites during the reactions are also modeled, and the contributions of two active sites, namely Cu coordination numbers of 4 and 3 in CuCl2 were distinguished and included in the kinetic model. The kinetic models describe well the transient response of the reduction and oxidation steps as well as the reaction at the steady-state at different reaction conditions. Moreover, by combining the reactor modeling through a steady-state approach, the spatial-time resolved CuCl2 profile and the C2H4 reaction rate can be well predicted in comparison with the experimental results. The approach of both transient and steady-state kinetic modeling and simulation is supposed to have general relevance for a better understanding of Mars–van Krevelen type reactions.

Highlights

The oxidation reaction is one of the most common and significant catalytic processes in the field of heterogeneous catalysis [1,2]
It is evident that K promotion favors the CuCl2 oxidation state, which dominates along the catalyst bed, the Kinetic study of ethylene oxychlorination, a vital process involved in vinyl chloride monomer (VCM) production, was performed at 483–513 K, atmospheric pressure on the K-doped CuCl2/γ-Al2O3 catalyst
A new approach for kinetic modeling of the Mars–van Krevelen (MvK)-type process was developed taking into account the dynamic changing characters of the active sites in the redox cycle

Summary

Introduction

The oxidation reaction is one of the most common and significant catalytic processes in the field of heterogeneous catalysis [1,2]. [3,4,5,6], a better understanding of the mechanism in the process can fur therly improve the catalytic performance, which is closely related to costs and profits. In the view of industrial, many commercial catalytic processes are related to redox reactions, like NH3-SCR, NO oxidation, ethylene oxychlorination, etc. All these reactions involve redox cycles where both reactants and catalysts undergo electron-transfer reactions through reduction and oxidation. The redox catalytic cycles can be simplified as Eqs. (1) and (2):

Methods

Results

Conclusion