Thermally integrated microreactor for Sabatier reaction: Study of air-cooled and inert-diluted counter-current operation strategies

CO2 methanation is the catalytic reduction of CO2 to methane, which is accompanied by side reactions that produce CO. Being an equilibrium-limited exothermic reaction, thermal management is essential for good reactor performance. We analyze efficient thermal coupling by transferring the heat of reaction from outlet to the inlet stream in a single thermally-integrated microreactor with counter-current flow. We use CFD simulations to compare two modes of heat removal, viz. external cooling and feed dilution, over a wide range of operating conditions. In one mode of operation, undiluted feed is processed with external cooling using air in counter flow (air-cooled reactor) and in the other, diluted reactant mixtures in alternate channels exchange heat counter-currently as the reaction proceeds (counter-current reactor). Depending on the inlet temperature, a favorable temperature profile that improves conversion to methane forms in each reactor. For the base case, 67 % CO2 conversion is obtained, with CH4 selectivity of 88 % and 91 % in air-cooled and counter-current reactors, respectively. Counter-current reactor shows autothermal operation with feed at ambient temperature while air-cooled reactor gives good performance at higher inlet temperatures. It is possible to attain high selectivity to methane through appropriate choice of operating conditions.