Diffusion coefficients were measured for the diffusion of cyclohexane and alkylcyclohexanes ranging from methyl- to pentylcyclohexane in ZSM-5-type zeolites by using flat plate-like crystallites. The up-take curves of cyclohexanes by the samples are considered to represent mainly the diffusion of cyclohexanes into the straight channels. The diffusion coefficient of cyclohexane at 377K was 4.8 x 10−13cm2/s and they were 9.9 x 10−13, 2.3 x 10−13, 2.6 x 10−13, 3.8 x 10−13 and 5.4 x 10−13cm2/s for methyl-, ethyl-, n-propyl, n-butyl-, and n-pentylcyclohexane, respectively. The diffusion coefficients of monosubstituted n-alkylcyclohexane went through a minimum at ethylcyclohexane and increased steadily as the chain lengthened. The length of the ethylcyclohexane molecule was comparable to the intersection space, and the sharp decrease in diffusion coefficient was interpreted in terms of the cage effect. The diffusion coefficient of t-1,4-dimethylcyclohexane was two orders of magnitude larger than that of ethylcyclohexane although they had about the same molecular length and kinetic diameter. This was attributed to the methyl-methyl interaction resulting in a favorable orientation for diffusion through the intersection space.

Diffusion of Cyclohexanes in ZSM-5 Zeolites. H.Chon, D.H.Park: Journal of Catalysis, 1988, 114[1], 1-7