Study of intracrystalline diffusion in zeolites. Communication 3. Kinetics of adsorption of trans-2-butene by NaA and NaMgA zeolites

Abstract

1. For the trans-2-butene-NaA zeolite system, the rate of adsorption is determined by the intracrystalline diffusion. The effect of transfer in the transport pores and the final rate of dissipation of the heat of adsorption can be neglected. The effective intracrystal-line diffusion coefficient at 303°K is equal to 0.8·10−16 m2/sec. 2. In adsorption of trans-2-butene by Na8Mg2A zeolite with a stepwise change in the pressure of the adsorbate, the kinetic curves are satisfactorily described by an internal diffusion equation for the kinetics of isothermal adsorption. The effective intracrystalline diffusion coefficients are a function of the degree of filling of the adsorbent and increase from 2.5·10−16 to 32·10−16 m2/sec with an increase in the filling from 0.44 to 1.93 mmoles/g. The self-diffusion coefficients calculated with the Darken equation also increase slightly with an increase in the filling (2.3−3.7·10−16 m2/sec). 3. The significant differences between the calculated and experimental curves in adsorption of trans-2-butene by microcrystalline NaA zeolite in the case of very convex adsorption isotherms could be caused by the effect of heat effects on the intracrystalline diffusion coefficient.