PERMEATION OF AROMATIC HYDROCARBON VAPORS THROUGH SILICALITE-ZEOLITE MEMBRANES

Vapor permeances of pure aromatics through silicalite zeolite membrane s follow the relative order m-xylene > p-xylene > benzene approximate to toluene > ethylbenzene approximate to o-xylene near 380 K with perm eance ratios as high as 20. This trend does not follow the size order of the kinetic diameters, and therefore the kinetic diameter is not th e determining factor for the permeation. Activation energies for the a romatics varied from 13 to 57 kJ/mol. In binary and ternary mixtures, the faster permeating compounds were slowed to rates similar to slower permeating molecules, and thus no separation was obtained for any mix ture. These findings are consistent with single file transport, where all molecules have equal chances of entering the pores, but they canno t pass each other in the narrow channels and the slowest species deter mines the permeation rates.