Adsorption of mixed vapors on solids. II. Cab-O-Sil

Abstract

The adsorption isotherms for ethanol-cyclohexane, ethanol-benzene, and benzene-cyclohexane vapor mixtures on Cab-O-Sil at 20, 30, and 40°C were measured at constant total pressure. The adsorption isotherms for the pure components were also obtained. The amounts of the pure vapors adsorbed on Cab-O-Sil followed the order ethanol > benzene > cyclohexane. Isosteric heats of adsorption and BET cross sectional areas were calculated for the pure adsorbates on Cab-O-Sil. The data indicated that the three adsorbates do not form close-packed monolayers on the Cab-O-Sil surface. The binary vapor adsorption isotherms were compared to the pure component isotherms. In several instances, the amounts of the components adsorbed from the mixtures were greater than from the pure states. For the Cab-O-Sil systems, selective adsorption of ethanol occurred from ethanol-cyclohexane and ethanol-benzene mixtures; benzene was selectively adsorbed from benzene-cyclohexane mixtures. The temperature dependence of the selectivity for the systems studied followed no consistent trend. Comparison of the binary vapor adsorption isotherms with the analogous solution adsorption isotherms indicated that selectivity is generally higher in adsorption from solution. The experimental binary vapor adsorption isotherms were compared to those calculated from the pure vapor adsorption isotherms using the ideal adsorbed solution model. It was found that the adsorbed solutions were ideal or slightly nonideal for all three mixtures on Cab-O-Sil. It was concluded that the ideal adsorbed solution model is a useful one for predicting binary vapor adsorption equilibria.