Diffusion of some n-paraffins in zeolite A

Abstract

A study has been made of the sorption kinetics of n-C₄H₁₀, n-C₆H₁₄ and n-C₉H₂₀ at each of three temperatures in four samples of Linde Sieve A with 30.55, 32.54, 34.10 and 35.48 % of Na⁺ replaced by Ca²⁺. Over the earlier stages good straight lines were obtained when the fractional uptake was plotted against time^½. The kinetics have been analysed in terms of the slopes k of these lines. The coefficients k/A(A= surface area) are independent of state of sub-division and distributions of shape and size of crystallites. They therefore characterise the sortion kinetics. Their dependences upon chain length of paraffin, amounts sorbed, temperature and % exchange of Na⁺ by Ca²⁺ have been evaluated. From k diffusion coefficients have been estimated and their dependence and that of the activation energies for diffusion upon the paraffin, and the extent of exchange have been found. The intrinsic mobility coefficient of n-C₄H₁₀ has been derived and found to decrease with the amount sorbed.