Thermodynamic modeling of binary and ternary adsorption on silica gel

Abstract

AbstractQualitative and quantitative characterization and prediction of multicomponent adsorption equilibria are essential for design of environmental remediation processes such as soil vapor extraction, bioventing, and thermal desorption. Single component, binary‐ and ternary‐mixture isotherms on silica gel were measured by the frontal analysis chromatography technique. Binary organic mixtures were composed of environmentally relevant VOCs, hexane/benzene (nonpolar/nonpolar), and hexane/trichloroethylene (nonpolar/slightly‐polar). Water binaries were water with hexane, benzene, or trichloethylene. Organic mixtures exhibited enhanced adsorption, where the adsorbed amount for each component was increased due to the second component. Water/hexane and water/benzene mixtures showed noncompetitive adsorption, where water adsorbed onto polar sites and n‐hexane or benzene adsorbed onto nonpolar sites. Competition for polar adsorption sites was observed for the trichloroethylene adsorption in water. Adsorption data of n‐hexane/benzene/water showed that n‐hexane and water were independently adsorbing onto different adsorption sites. Furthermore, n‐hexane and benzene with water showed the same adsorption behavior as without water. For the mixture of n‐hexane/trichloroethylene/water, only the amount of water adsorbed was reduced compared to the pure species adsorption of water. The adsorption equilibria of n‐hexane and trichloroethylene were not influenced in comparison to their pure species isotherms. Mixture isotherms were modeled with IAST, MSAM, and RAST. The nonideal adsorbed phase was characterized using activity coefficients.