Adsorption of isobutene on partially hydrophobized aerosil

Abstract

The adsorption isotherms of isobutene on a hydrophobic silica, Aerosil R972, have been measured, and the isosteric and integral heats of adsorption and the integral entropy of adsorption have been calculated. A comparative study has been made of partial dehydroxylation by heating and by methylation. In the former, the heat of adsorption at low coverage decreases by 2.5 kcal mol^–1, while the quantity adsorbed on the monolayer remains constant. In the latter, the heat of adsorption remains constant, while the quantity adsorbed on the monolayer decreases, and is proportional to the part of the surface that is free of methyl groups and contains hydroxyl groups. A model that represents the methylated groups of the surface of Aerosil R972 is proposed, and it is suggested that the adsorption of isobutene takes place in the region where there are hydroxyl groups.