Simulation-based optimization of cycle timing for CO2 capture and hydrogenation with dual function catalyst

Abstract

CO2 methanation could play a significant role in the future energy system. The excess of renewable electric energy can be transformed into storable methane to balance the energy demand when required. Moreover, the CO2 methanation can be performed alternating steps of CO2 storage and reduction, avoiding expensive CO2 purification steps. In this work, we will use a previously developed and validated model to optimize by simulation the CO2 adsorption and hydrogenation cycles timing (tCO2/tH2). The performance of the catalyst is quantified by the CO2 conversion (XCO2, %), H2 conversion (XH2, %) and CH4 production (YCH4, mmol g−1 cycle−1). Long adsorption and hydrogenation times result in high CH4 productions per cycle, however, low CO2 and H2 conversion. Therefore, adsorption times close to the catalyst saturation (tCO2=60 s) and moderate hydrogenation times are preferable. To better select the optimal hydrogenation time, a new catalytic parameter is set, the average formation rate of CH4 (r¯CH4, μmol g−1 s−1). The optimal hydrogenation time is set at 120 s. In addition to having a high average formation rate of CH4, tCO2/tH2= 60/120 cycle timing would allow to work with three identical beds in parallel, one in adsorption mode and two in regenerating mode. With the optimum cycle timing of 60/120 the production of CH4 results in 148 μmol g−1 cycle−1 (1.2 μmol CH4 g−1 s−1) and a CO2 and H2 conversion of 25% and 43%, respectively