Double sodium salt-promoted mesoporous MgO sorbent with high CO2 sorption capacity at intermediate temperatures under dry and wet conditions

Abstract

Mesoporous MgO·Na2CO3·NaNO3 composites were prepared using supercritical drying of methanol for CO2 capture in power plants at an intermediate temperature range between 250 and 450°C. The effects of the molar ratio of salt, temperature, and gas composition on the CO2 sorption were investigated under dry and wet conditions in order to clarify the sorption mechanisms and roles of NaNO3 and Na2CO3. The composites exhibited excellent sorption capacities of 56.0wt.% at 325°C in pure CO2 and 50.8wt.% at 275°C in a wet gas mixtures (10% CO2, 2.5% H2O, and balanced N2). The CO2 sorption mechanism was dominated through the formation of MgCO3 and Na2Mg(CO3)2 with Na2CO3 working as a CO2 carrier, while NaNO3 functioned as a reaction promoter. Under wet conditions, the formation of Mg(OH)2 resulted in fast sorption rates and high capacities even at low CO2 concentrations in the gas feedstock. One phase (liquid) condition of NaNO3 and water vapor during a sorption and regeneration cycle resulted in a high stability of the sorbent. The working capacity in a 14 cycle test under N2 regeneration (10min) at 450°C was 31.8wt.% at 325°C in pure dry CO2 and 29.4wt.% at 275°C with a wet CO2 mixture.