Single-Component and Binary-Mixture Adsorption of Volatile Organic Contaminants on Silica Gel

Abstract

Qualitative and quantitative characterization and prediction of multicomponent adsorption equilibria are essential for design of remediation processes such as soil vapor extraction, bioventing, and thermal desorption. The effects of physical properties of volatile organic components (VOCs) on adsorption equilibria were investigated by measuring single-component and binary-mixture adsorption isotherms on a polar adsorbent, silica gel, employing the frontal analysis chromatography technique. The binary mixtures were n-hexane/benzene (nonpolar/nonpolar), n-hexane/trichloroethylene (nonpolar/slightly polar), and chloroform/chlorobenzene (polar/polar). The adsorption isotherms for the single components were BET type II isotherms, indicating physical multilayer adsorption. The monolayer uptake increased with the increasing polarity of the components. The adsorption isotherms of the binary mixtures of n-hexane/benzene and n-hexane/trichloroethylene were BET-type II. For the chloroform/chlorobenzene mixture BET type III isotherms were observed. The coadsorption of the second adsorbate increased the uptake of the other adsorbate in all cases. Potential theory, the ideal adsorbed solution theory (IAS), and the multispace adsorbed solution model (MSAM) were used for the prediction of binary component isotherms from pure component isotherm data. Key words: Multicomponent adsorption equilibria; volatile organic contaminants; silica gel