The role of water on postcombustion CO₂ capture by vacuum swing adsorption: bed layering and purge to feed ratio

The influence of water vapor on the adsorption of CO₂ in carbon capture by vacuum swing adsorption (VSA) was described. VSA experiments with single and multilayered columns using alumina and zeolite 13X were conducted to understand the migration of water. The penetration depth of water in the column could be controlled by maintaining the purge-to-feed ratio above a critical value. At high water content in the feed (>4%), employment of a water adsorbing prelayer was essential to prevent failure of the carbon capture process. A simple axial working capacity model predicts the penetration depth of water in the column for a given feed temperature and adsorption isotherm, and the layering ratio can be selected accordingly. Although water is detrimental to CO₂ capture with polar adsorbents, long-term recovery of CO₂ is still possible by appropriate layering and ensuring an adequate purge-to-feed ratio.