Green Methanol Production Process from Indirect CO2 Conversion: RWGS Reactor versus RWGS Membrane Reactor

Abstract

Herein, two different scenarios for indirect CO2 conversion process to produce methanol via reverse water gas shift (RWGS) reaction were investigated and compared. In the first scenario, CO2 is converted to synthesis gas over Fe2O3/Cr2O3/CuO catalyst in a RWGS reactor and then after passing a condenser to eliminate water, as an inhibitor of methanol synthesis catalyst, the product is sent to the methanol production reactor. While in the second, although the process is totally as the same as the previous one, a water permselective membrane was applied in the RWGS reactor. In this scenario, the produced water during the RWGS reaction is separated by the membrane; therefore, the free of water product no longer needed a separator before the methanol synthesis reactor. Both processes were numerically modeled and differential evolution (DE) method was employed to optimize the processes in order to achieve high methanol productivity. Also, the methanol production reactor from these two scenarios were compared with the conventional route (CR), in which methanol is produced from coal and natural gas. The results indicate that, in addition to water removal in the RWGS membrane reactor, a higher CO2 conversion and CO yield and subsequently a more proper synthesis gas composition are obtained. More importantly, methanol production rate increases 13 ton/day (% 4.15 increase) and 109 ton/day (% 50.23 increase) in this scenario compared to the first scenario and CR. Also lower water is produced (17% reduction) in the methanol synthesis reactor of the second scenario respect to the first one.