Oxidative coupling of biogas to ethylene over a trilobe-shaped Mn-Na2WO4/α-Al2O3 catalyst in a single-pellet reactor

The oxidative coupling of methane (OCM), which offers a direct route for converting methane into higher-value ethylene. Despite the development of selective catalyst formulations, kinetic and reactor design studies have been hampered by a lack of data for truly isothermal, relevant. Because of exothermicity issues, the temperature of a fixed-bed reactor filled with Mn-Na2WO4/SiO2 catalysts show a sudden temperature run-away accompanied with a drastic loss of selectivity. The objective of this study is to measure catalyst activity under relevant reaction conditions of pressure (3 bar), biogas composition (no dilution) and contact time, while keeping the process as isothermal as possible. To this aim, we have synthesized and shaped a trilobed Mn-Na2WO4/α-Al2O3 catalyst, which may be used as is at industrial scale, and measured its performance in a single-pellet reactor. We found that the presence of CO2 does not degrade catalyst performance, even on long run, which should enable the use of a CO2-rich stream such as biogas. Actually, higher methane conversions have been obtained in the presence of CO2, likely due to a possible contribution of methane dry reforming reaction. We also noticed a slow catalyst activation over the first 100 hours while selectivity was kept constant.