Adsorption of toluene-heptane mixtures on silica gels and carbon blacks

Abstract

1. Adsorption isotherms were determined for toluene adsorbed from its solutions in heptane on silica gels of various porous structures. The thickness of a unimolecular adsorbed layer of toluene is 3.7 A; toluene molecules are oriented in the flat position with respect to the silica gel surface. 2. Reduction in the pore size of silica gel from 104 to 30 A, which increases the adsorption potential, increases also the extent to which toluene is adsorbed at low concentrations and brings about a shift in the maximum of the isotherm in the direction of lower concentrations for more finely porous samples. 3. The preferential “adsorption of aromatic and unsaturated hydrocarbons on silica gel from their solutions in saturated hydrocarbons is associated with two factors: the magnitude of the interaction between the aromatic nuclei and the hydroxyls of silicic acid, and the effect of substituents, which increase the total area occupied by the molecule on the silica gel surface and weaken adsorption on an acidic surface. 4. Oil a carbon black with an acidic surface toluene is adsorbed positively over the whole range of concentrations from its solutions in heptane, but it is adsorbed more weakly than on silica gel. The graphitization of carbon black-greatly reduces the adsorption of toluene, and the adsorption becomes negative at high toluene concentrations.