Insights into the adsorption performance and separation mechanisms for CO2 and CO on NaX and CaA zeolites by experiments and simulation

Adsorption and recovery of CO2 from industrial gases are of great environmental significance in the field of environmental protection with reducing greenhouse gas emissions and increasing CO concentration. A comprehensive investigation with thermodynamics and kinetics experiments of CO2 and CO on NaX and CaA zeolites were studied and the separation mechanism explained by molecular simulation methods. The experiments show that the NaX zeolites have significant differences on CO2 and CO adsorption amounts leading the high CO2/CO selectivity, while the CaA zeolites exhibit separation stability under various partial pressures of mixed gas, which is supported by the standard deviation results. The theoretical simulations verify the above-mentioned experimental phenomena and provide a visual mechanism explanation for adsorption selectivity from the aspect of systematic interaction between cations and gas molecules. Compared with NaX, the same number and homogeneous distributions of Ca2+ and Na+ in the CaA provide stable separation performance. The strong electrostatic interactions between divalent Ca2+ and gas molecules especially CO make differences in the order of adsorption capacity and adsorption heat. Deeper insights into the cations-gas adsorption complexes revealed that the significant differences in the types of adsorption complexes for CO and CO2 in NaX contribute to the improvement of the adsorption selectivity.