Diffusion in 5A zeolite. Study of the effect of crystal size

Abstract

The kinetics of sorption of CF₄ and n-C₄H₁₀ have been investigated in different size fractions of two different 5A zeolites with different Ca²⁺ contents. The results show that in the larger crystals the uptake rate is controlled entirely by intracrystalline diffusion while, in the small crystals, rates are controlled by the combined effects of external heat transfer and intracrystalline diffusion. Diffusivities are independent of crystal size but there are larger differences between the different zeolite samples. For both CF₄ and n-C₄H₁₀, diffusion in commercial Linde 5A crystals is very much slower than in the laboratory synthesized zeolite samples. Corrected diffusivities for butane in the fastest diffusing zeolite sample are within an order of magnitude of the values estimated from n.m.r. relaxation measurements.