Kinetics of coke formation in the dimethyl ether-to-olefins process over SAPO-34 catalyst

Abstract A kinetic of coke formation during dimethyl ether (DME) conversion to light olefins over SAPO-34 was studied by the use of a thermogravimetry (TG) reactor. Coke formation experiments were conducted at the heating rate from 4 K/min to 10 K/min and DME partial pressure between 40.53 kPa and 101.325 kPa. The effects of reaction temperature, DME partial pressure and coke content of catalyst on coking rate were investigated. The results showed that high reaction temperature and DME partial pressure led to high coking rate. The coking rate increased with coke content during the early stage of the DME to olefins (DTO) reaction, indicating that the coking reaction was autocatalytic reaction. A mechanism was proposed for the coke formation and a kinetic equation was established to correlate the rate of coke formation with DME partial pressure, reaction temperature and coke content of catalyst. The activation energies of coke formation and adsorption of DME onto the active sites of catalyst surface in DTO reaction were found to be 99 kJ/mol and 49 kJ/mol, respectively.