COMPOSITE SORPTION OF PURE VAPORS ON POLYOLEFINS, CARBON, AND MINERALS

A general composite sorption isotherm is developed to predict experime ntal isotherms of the types I, II, and III. The isotherm, based on het erogeneous chemical thermodynamic equilibrium considerations, is used to represent single vapor sorption isotherm data at high concentration s. Sorbents investigated include polybutylene, low-density polyethylen e, isopolypropylene, polytetrafluoroethylene, polyvinyl chloride, gran ular activated carbon, graphon, cabosil, Iceland spar, and quartz. Sor bates include ethane, n-butane, n-pentane, n-hexane, n-octane, trichlo roethylene, tetrachloroethylene, methyl bromide, dichloromethane, viny l chloride, benzene, ethanol, and ethyl ethanoate. The isotherm has tw o terms with two parameters each. One term represents the absorption o f individual vapor molecules, or monolayer adsorption. The second term represents the absorption of vapor molecule clusters, or multilayer a dsorption. Contributions of terms 1 and 2 to overall sorption are gene rally predominant at relatively low and high sorbate concentrations, r espectively. In contrast with the classic concept of infinite sorption for the BET isotherm, composite isotherm term 2 sorption capacity is finite.