Oxidative Coupling of Methane: Opportunities for Microkinetic Model‐Assisted Process Implementations

Abstract

Oxidative coupling of methane is a low‐cost alternative for ethylene production. However, its high exothermicity, complex reaction network, and low selectivity to C2 products require more in‐depth analysis for economically viable process implementation. Microkinetic modeling enables assessment of operating conditions and catalyst properties on the overall performance via elementary gas‐phase and catalytic reactions. The know‐how to reproduce and interpret experimental kinetic data, especially the role of highly reactive intermediate species, is crucial for correct reaction network determination. Once the catalyst descriptors, physical catalyst properties, and operating conditions are determined and optimized, next catalyst generations can be developed tailored to the process implementation.

Oxidative Coupling of Methane for Ethylene Production: Reviewing Kinetic Modelling Approaches, Thermodynamics and Catalysts

“…Based on the evaluated scientific papers, seven different main subject streams have been identified: (1) modelling of the OCM process, embracing phenomenological and empirical mathematical descriptions of reactors and respective chemical kinetics [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], but also involving theoretical analyses of mechanistic models [23][24][25][26][27][28][29]; (2) economic evaluation of actual OCM commercial implementations, involving the analysis of capital and operational costs [30][31][32][33][34][35]; (3) assessment of environmental impacts, mainly involving the analysis of CO 2 emissions [31]; (4) development of new and/or improved catalysts for the production of ethylene from OCM reactions [27,; (5) development of alternative processes for CH 4 conversion into ethylene and/or other products, including, for instance, the non-oxidative coupling of methane [74][75][76]; (6) investigation of downstream purification strategies [77][78][79], concerning mainly the separation of products from the OCM reactor output stream; and finally, (7) the design, optimisation and development of OCM reactors for ethylene production, including the analysis of distinct reactor concepts (such as chemical looping…”

Advances in catalytic conversion of methane and carbon dioxide to highly valuable products

“…In the presence of oxygen, solid oxide catalysts can form active surface oxygen species that selectively abstract one hydrogen from methane to release free methyl radicals(CH 3 ·)in the gas phase, which subsequently couples to form ethane. The reaction is followed by the dehydrogenation of ethane to form ethylene or by the irreversible formation of oxidation products (CO or CO 2 ) . Furthermore, it was reported that electrophilic lattice oxygen species and the facile filling of surface lattice oxygen vacancies by gas‐phase oxygen are key factors to design efficient catalysts for the oxidative coupling of methane .…”

“…Methane is the most stable hydrocarbon due to its strong C‐H bond (434 kJ/mol) and thus its activation needs a high temperature. There are various techniques to convert methane to more valuable chemicals and fuels, which can be classified into three types of routes: (1) reforming to produce syngas including steam reforming (Equation ), dry reforming (Equation ), and partial oxidation (Equation ); (2) oxidative coupling (Equation and Equation ); and (3) conversion to oxygenates such as methanol (Equation ).…”

“…As shown in Table , one can see that multi‐component catalysts with alkali metal oxide are more effective than mono‐component ones. Comparing with conversional O 2 ‐OCM whose maximum C 2 yield ranges from 16% to 27% with selectivity 72%‐82%, CO 2 ‐OCM exhibits a lower maximum C 2 yield (6%) but comparable selectivity . Furthermore, to achieve higher methane conversion at low temperatures, nonconventional catalytic systems have also been reported, such as catalytic reactions in an electric field, catalytic reactions with discharge, and photocatalytic reactions …”

Research progress on methane conversion coupling photocatalysis and thermocatalysis

“…Methane as the main component of natural gas and a predominant hydrocarbon feedstock can be used to produce ethyne, chloromethane, carbon black, and so on, which becomes a relatively inexpensive and alternative energy resource to crude oil. [1][2][3][4][5][6] The abundant production and reserves of natural gas are beneficial to producing the valueadded chemicals, but also cause the problem of global warming. 5,[7][8][9][10] Therefore, the efficient conversion of methane is highly desired from aspects of the environmental protection and high-efficacy utilization of fossil fuel.…”