Selection and optimisation of a zeolite/catalyst mixture for sorption-enhanced CO2 methanation (SEM) process

Abstract

The sorption-enhanced methanation (SEM) process has emerged as a promising technology to produce high quality synthetic natural gas (SNG) from renewable sources under milder conditions than conventional methanation technologies. During the SEM process developed in this paper, an H2O adsorbent is combined with a Rhodium-based catalyst to remove the H2O generated during the CO2 methanation reaction, shifting the equilibrium towards CH4 formation. In this work, several commercial zeolites (3A, 4A, 5A and 13X) were studied as H2O adsorbents under SEM conditions. Based on the study performed, zeolite 4A demonstrated to be the most suitable zeolite which, combined with the proposed catalyst, allowed maximising the production and purity of the obtained CH4. The influence of gas space velocity, H2/CO2 ratio in the feed gas, zeolite/catalyst proportion and cyclic stability were analysed and optimized to maximise CH4 production. When the process was run under SEM conditions using zeolite 4A as sorbent at 275 °C and a gas space velocity of 230 Nml/h·gcat, the CH4 content increased from 10.6 vol% in conventional methanation up to 85 vol% in the SEM conditions. Thus, the enhanced performance of the SEM process was demonstrated.