http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Multilayer adsorption equilibria of volatile organic compound mixtures and water on silica gel
xvi, 191 leaves : illustrations ; 28 cm.
This study characterized how properties of the organic sorbates and water affect adsorption onto silica gel, and focused on modeling of binary and ternary mixture isotherms of these sorbates. Single component adsorption equilibria of three volatile organic compounds, n-hexane, benzene, trichloroethylene, and water, adsorption equilibria of these organic compounds in the presence of water, and binary mixtures of hexane-benzene (non-polar/non-polar) and hexane-trichloroethylene (non-polar/polar) both with and without water were examined. Using adsorption isotherms of single compounds, isotherms of binary and ternary mixtures were modeled. Adsorption isotherms of the single adsorbate systems were measured with the frontal analysis chromatography technique. They were BET-type II isotherms, which indicated minelayer followed by multilayer adsorption. The BET-analysis showed an increasing uptake at the minelayer with increasing polarity of the compounds. However adsorbent-adsorbate interactions of the organic sorbates were dominated by Van der Waals interactions and that Of water by hydrogen bonds, respectively. The adsorption equilibria of binary and ternary mixtures were measured using the same technique. Water adsorbed onto polar sites when coadsorbing with n-hexane or benzene, which were adsorbing onto nonpolar sites. The numbers of moles adsorbed were predicted with the two-site adsorption model. Competition for polar adsorption sites was observed for the adsorption of trichloroethylene in the presence of water, which was modeled with the real adsorbed solution theory (RAST). The adsorbed phase activity coefficients were above unity, indicating intermolecular interactions dominating the adsorbed phase properties. The presence of a second organic increased the uptake of the first organic sorbate in all experiments. Adsorbate-adsorbate interactions in the adsorbed phase were stronger for the nonpolar/polar than for the nonpolar/nonpolar mixture. The mixture isotherms of n-hexane/benzene and n-hexane/trichloroethylene could be modeled with the multistage adsorption model (MSAM) and the real adsorbed solution theory (RAST), respectively. The adsorbed phase activity coefficients were less than unity, indicating adsorbed phase interactions due to surface heterogeneity. Analysis of the ternary adsorption data of n-hexane/benzene/water showed that n-hexane and water were independently adsorbing onto different adsorption sites. For the ternary mixture of n-hexane/trichloroethylene/water, only the amount of water was reduced compared to the pure species adsorption of water.
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Includes bibliographical references (leaves 158-168).