Cl. Cavalcante et Dm. Ruthven, ADSORPTION OF BRANCHED AND CYCLIC PARAFFINS IN SILICALITE .2. KINETICS, Industrial & engineering chemistry research, 34(1), 1995, pp. 185-191
Intracrystalline diffusivities in silicalite have been measured by the
gravimetric sorption uptake method for several branched and cyclic Cg
paraffins (2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-
dimethylbutane, methylcyclopentane, and cyclohexane). The zero-length
column (ZLC) method was also used to check and validate some of the re
sults. Branching and cyclization of saturated hydrocarbon structures l
ead to significant changes in critical molecular diameter and hence to
differences in kinetic behavior. The following general trend was obse
rved for the diffusivities: linear > single-branched > double (ternary
C)-branched > cyclic paraffins > double (quaternary C)-branched. Ster
ic hindrance was most pronounced for compounds with a quaternary carbo
n atom, such as 2,2-dimethylbutane. The kinetic data conform well to a
one-dimensional (slab) diffusion model, reflecting the anisotropic di
ffusion behavior characteristic of the silicalite/ZSM-5 structure.