Adsorption of benzene and methyl-substituted benzenes at the vapor/water interface. 3. Finite binary-component VHOC adsorption

Isothermal measurements (285.2, 291.2, and 298.2 K) of equilibrium aqueous solution surface tension (pressure) as a function of partial vapor-phase volatile hydrophobic organic compound (VHOC) pressure for benzene/methylbenzene, benzene/1,2-dimethylbenzene, benzene/1,3-dimethylbenzene, benzene/1,4-dimethylbenzene, and benzene/1,3,5-trimethylbenzene binary mixture pairs were made employing pendant drop tensiometry and gas chromatographic analysis. Surface pressure isotherms were developed at atmospheric pressure at three intermediate constant mole ratios for each compound pair and experimental temperature, from zero to near/at total VHOC (i.e., solute) saturated vapor pressure. Cot-responding single-solute surface pressure isotherms were also measured. Analyses indicate that vapor-phase/interface-phase binary VHOC equilibrium is well described by ideal mixing equations applied to single-component surface pressure and relative interface excess isotherms. The interface phase was found to be enriched with respect to the larger molecular size components (i.e., methyl-substituted benzenes) for a given vapor-phase composition, in a manner very similar to vaporphase/organic liquid-phase partitioning.