Thermodynamic modeling of binary and ternary adsorption on silica gel

Qualitative and quantitative characterization and prediction of multicompon ent adsorption equilibria are essential for design of environmental remedia tion processes such as soil vapor extraction, bioventing, and thermal desor ption. Single component, binary and ternary-mixture isotherms on silica gel were measured by the frontal analysis chromatography technique. Binary org anic mixtures were composed of environmentally relevant VOCs, hexane/benzen e (nonpolar/nonpolar), and hexane/trichloroethylene (nonpolar/slightly-pola r). Water binaries were water- with hexane, benzene or trichloethylene. Org anic mixtures exhibited enhanced adsorption where the adsorbed amount for e ach component was increased due to the second component. Water/hexane and w ater/benzene mixtures showed noncompetitive adsorption, where water adsorbe d onto polar sites and n-hexane or benzene adsorbed onto nonpolar sites. Co mpetition for polar adsorption sires 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 adsorpt ion behavior as without water For the mixture of n-hexane/trichloroethylene /water, only tire amount of water adsorbed was reduced compared to the pure species adsorption of water. The adsorption equilibria of n-hexane and tri chloroethylene were not influences in comparison to their pure species isot herms Mixture isotherms were modeled with LAST, MSAM, and RAST. The nonidea l adsorbed phase was characterized using activity coefficients.