DIFFUSION OF CYCLOHEXANE AND ALKYLCYCLOHEXANES IN SILICALITE

The diffusion of cyclohexane and several alkylcyclohexanes in silicali te was studied using a simultaneous thermal analyzer. This apparatus a llowed for the determination of heats of sorption and diffusion coeffi cients. Zero length chromatography was also used to determine diffusiv ities of some of the adsorbates. The trend in diffusion rates observed was trans-1,4-dimethylcyclohexane >> methylcyclohexane > cyclohexane > ethylcyclohexane, cis-1,4-dimethylcyclohexane. This is in qualitativ e agreement with the previous results of Chon and Park. A comprehensiv e interpretation of the experimental results was developed, using the basic qualitative arguments of transition state theory. The fast diffu sion of trans-1,4-dimethylcyclohexane is associated with a relatively low energy barrier for channel crossing. The transition entropy for di ffusion appears to be the reason for the more rapid diffusion of methy lcyclohexane relative to cyclohexane.