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.