Multi-factor study of the effects of a trace amount of water vapor on low concentration CO2 capture by 5A zeolite particles

Water vapor is ubiquitous and affects the performance of an adsorbent. In this work, a grand-canonical Monte Carlo method (GCMC) combining with dispersion-corrected density functional theory (DC-DFT) calculation is adopted to investigate the effect of a trace amount of water vapor on low concentration CO2 capture in 5A zeolite particles. The force field parameters for the interactions among CO2, water, and 5A zeolite are obtained via DC-DFT calculations. The effects of the charges of water molecules on the CO2 and N2 adsorption amounts and the selectivity of the CO2/(N2 + O2) gas mixture under different trace amounts of water vapor ranging from 0.05 ppm to 5 ppm are studied. The results show that the presence of the water vapor in 5A zeolite particles increases or decreases the CO2 adsorption amount, which is strongly determined by the trace amount of water. Specifically, when the water vapor concentration is less than 0.1 ppm, the CO2 adsorption amount is increased by 0.7–53.4%, whereas when the water vapor concentration is greater than 0.3 ppm, the amount of adsorbed CO2 decreases, with the reduction proportional to the amount of trace water. However, the N2 adsorption amount and the selectivity of the CO2/(N2 + O2) gas mixture decrease with an increasing amount of trace water. This indicates that the electrostatic interactions induced by the water molecules are the dominant factor influencing the CO2 and N2 adsorption amount and the selectivity of the CO2/(N2 + O2) gas mixture. Therefore, to achieve the desired adsorption performance, a trace amount of water vapor (<0.1 ppm) is recommended for CO2 adsorption, whereas low trace amounts of water vapor (<0.1 ppm) are also recommended for the selectivity of the CO2/(N2 + O2) gas mixture in the 5A zeolite particle.