Equilibrium and Hysteresis Formation of Water Vapor Adsorption on Microporous Adsorbents: Effect of Adsorbent Properties and Temperature

Abstract

Water vapor has been one of the vital problems in purification of volatile organic compounds. In this study, the adsorption-desorption equilibrium of water vapor were conducted at 298, 308, 318 and 328K on three adsorbents: hypercrosslinked polymeric adsorbents (HPA), activated carbon fiber (ACF) and granular activated carbon (GAC). The obtained isotherms were type V and the adsorption capacity at the same condition was as follows: GAC>ACF>HPA. Cluster Formation Induced Micro-pore Filling (CIMF) model was adopted to fit the adsorption isotherms and the fitting parameters showed that adsorption capacities of water vapor on micropores and functional groups had a negative logarithmic linear relationship with temperature. The existence of functional groups could weaken the negative influence of temperature on the water adsorption performance, while the influence of temperature had negligible relationship with microporous volume. The hysteresis loops at different temperatures on three adsorbents had similar shape, the size of which were also as follows: GAC>ACF>HPA. They mainly occurred in micropore adsorption, but their size had positive relationships with both functional groups and microporous volume. The hysteresis became smaller along with the increase of temperature, closely related with the stability of water clusters. In conclusion, temperature, functional groups and porous structure played crucial roles for water vapor adsorption and the formation of hysteresis.