Liquid phase sorption and diffusion of branched and cyclic hydrocarbons insilicalite

Sorption and diffusion of several singly branched, doubly branched and cycl ic C-6 and C-7 hydrocarbons (2-methylpentane, 3-methylpentane, 3,3 dimethyl butane, 2,2-dimethylbutane, 2,4-dimethylpentane, cyclohexane, cyclohexene, n-hexane and 2 methyl-l-hexene) in large silicalite crystals, with n-hexane as the carrier, have been studied by liquid chromatography and by liquid Z LC measurements. The equilibrium data show mildly endothermic exchange ener gies and rather low equilibrium constants. Both the absolute values of the equilibrium constants and the exchange energies are consistent with vapor p hase data. The kinetic data are more surprising, yielding exchange diffusiv ities which are larger by several orders of magnitude relative to the value s derived from (single component) vapor phase measurements at low sorbate l oading. The diffusivity values derived from the chromatographic and ZLC mea surements are self-consistent. A tentative explanation involving expansion of the silicalite lattice under saturation conditions, is suggested, to exp lain these observations. (C) 1998 Elsevier Science B.V. All rights reserved .