Synthetic natural gas production via pressurized integrated carbon capture and in-situ methanation of Ni-Na2CO3/γ-Al2O3 dual function material

Integrated CO2 Capture and in-situ Methanation (ICCM) via dual function material (DFM) is a novel technology to produce synthetic natural gas while avoiding CO2 emissions from different sources and utilizing hydrogen from intermittent renewable energy. This study validated the feasibility of Pressurized ICCM (PICCM) by investigating into the effects of reactant partial pressures (CO2 or H2) and operational pressure (total pressure) on cyclic carbon capture and in-situ methanation of a model DFM composed of Na2CO3 adsorbent, Ni catalytic metal and gamma-Al2O3 support. It is found that increasing CO2 partial pressure or operational pressure exhibited a rapid increase in reaction kinetics and an improvement in adsorbent component conversion. Increasing H2 partial pressure or operational pressure promoted absorbed CO2 conversion, reaction kinetics and CH4 selectivity for insitu hydrogenation. The mechanism study on in-situ methanation at elevated H2 pressures showed that hydrogen dissociation on Ni-sites initialized DFM's in-situ hydrogenation, which significantly increased with H2 partial pressure. The amount of effective basic sites in DFM that could be hydrogenated into CH4 under mild conditions increased with H2 concentration. In-situ hydrogenation followed a stepwise hydrogenation regime. The rate of in-situ hydrogenation was jointly-controlled by hydrogen spillover and COsad hydrogenation towards CH4 at low H2 concentration; while at high H2 concentration, COsad hydrogenation was significantly promoted, leaving hydrogen spillover and/or the first-step hydrogenation to be the rate-limiting step. Furthermore, the gamma-Al2O3 support and the activate hydrogen spillover played important roles in the improvement of reaction kinetics and CH4 selectivity for in-situ hydrogenation.