The MTO and DTO processes as greener alternatives to produce olefins: A review of kinetic models and reactor design

Considering the relevant role towards decarbonization of the MTO (methanol-to-olefins) and DTO (dimethyl ether-to-olefins) processes, this review summarizes their main advances, with special attention to kinetics models and reactor design. The DTO process is an alternative to the MTO, whose importance lies in the good perspectives of DME (dimethyl ether) one-stage synthesis from CO2 and syngas derived from biomass (thermodynamically favored compared to that of methanol synthesis). Furthermore, DME is generally more reactive than methanol, and the DTO process produces less water and is less exothermic than MTO. Due to the big similarities between mechanisms and kinetic models for both processes, the development of the DTO process will be based on the vast actual knowledge on the MTO process after five decades of studies: from the initial pioneer tests of Mobil with a HZSM-5 catalyst to the recent technological improvement in the industrial units with HSAPO-34 catalysts. HZSM-5 zeolite has shown the most promising catalytic performance for the DTO process, with high activity, selectivity and stability. Most of the proposed lump-based kinetic models for the DTO process have used the knowledge on the methanol-to-hydrocarbon chemistry and some examples have described important features of the process, as the consideration of deactivation kinetics and the quantification of the water effect on the extent of the reaction steps and deactivation. The reactor design and operation configuration of MTO and DTO processes are still determined by the catalyst deactivation and continuous regeneration is required. The main advances on the design of the dual reactor-regenerator system considering the distribution of activity or content of coke are also summarized herein.