Diffusion of hydrocarbons in 13X zeolite

The kinetics of sorption of four representative hydrocarbons in 13X zeolite crystals have been investigated at temperatures within the range 409 to 513°K and pressures 0.1 to 100 torr. Extensive diffusivity data are presented showing the dependence on sorbate concentration and temperature. The form of the concentration dependence of the diffusivity for these systems is very similar to that of the small monatomic and diatomic molecules in 5A zeolite. This similarity is understandable, since the key factor which determines the diffusion behavior is the relative size of diffusing molecule and sieve window. For these hydrocarbons in the 13X sieve, as for the monatomic and diatomic gases in 5A, the critical diameters of the diffusing molecules are all appreciably smaller than the free diameter of the windows.