Catalytic Oxygen Carriers and Process Systems for Oxidative Coupling of Methane Using the Chemical Looping Technology

Abstract

Directly upgrading natural gas is limited by the stability of its primary component, methane, and process economics. Since the 1980s, oxidative coupling of methane (OCM) has shown potential to produce ethylene and ethane (C2s). The typical OCM approach catalytically converts methane to C2 products using molecular oxygen, reducing process efficiency. To overcome this, chemical looping OCM converts methane to hydrocarbons via intermediate oxygen carriers rather than gaseous cofed oxidants. The chemical looping approach for OCM has been studied mechanistically for the first time with a Mn–Mg-based catalytic oxygen carrier (COC). The COC delivered stable performance in a fixed bed for 100 cycles for more than 50 h with a 63.2% C2 selectivity and 23.2% yield. These experimental results and original process simulations of an OCM chemical looping system for C2 or liquid fuel production with electricity cogeneration present a direct method for methane utilization.

Chemical looping beyond combustion – a perspective

“…225,228 Experiments with doped-Mg 6 MnO 8 and Mn/Na 2 WO 4 /SiO 2 , a catalyst previously shown to attain single pass C 2+ product yields of B25% in co-feed mode, 229,230 gave C 2+ product yields of 23.2% and 25%, respectively under a chemical looping mode. [231][232][233][234] In these studies, the selectivity toward the coupling reaction was high, but the H 2 molecules formed through the dehydrogenation reaction of ethane competed with CH 4 molecules for reacting with activated oxygen on the surface of the catalyst, resulting in a decreasing rate of CH 4 activation and consequently lower C 2+ yields than expected. 222 Hence, improving the activity of the redox catalysts without negatively affecting their selectivity is one important task.…”

Near 100% ethene selectivity achieved by tailoring dual active sites to isolate dehydrogenation and oxidation

“…Herein, strategically tailoring dual Ni active sites is proposed by utilizing the acid sites, three-dimensional pore structure, and supercages of HY zeolite to anchor Ni 2+ Lewis acid sites (LAS) and confine NiO clusters to isolate dehydrogenation and oxidation by lattice oxygen, respectively 2,[32][33][34][35][36] . As a result, this strategy avoids consecutive oxidation and achieves near 100% C 2 H 4 selectivity at a wider range of conversion compared with those reported in the previous work [37][38][39][40] .…”

Catalyst screening for the oxidative coupling of methane: from isothermal to adiabatic operation via microkinetic simulations

“…It should be mentioned that all the simulated scenarios refer to co-feed operation, where both CH4 and O2 are simultaneously fed to the reactor. This means that molecular oxygen from the gas phase is required for methane activation and that the catalysts do not undergo any cyclic operation in reduction−oxidation reactor modes 44 . The model output is a set of key performance indicators for catalyst and scenario .…”