ANOMALOUS PATTERNS OF SORPTION UPTAKE CURVES OBSERVED IN THE SYSTEM P-ETHYLTOLUENE H-ZSM-5/

Uptake curves of p-ethyltoluene sorbed in large H-ZSM-5 crystals exhib it marked deviations from the second Pick law behaviour. The deviation s in the initial part of uptake curves indicate an additional mass tra nsport resistance at the crystal surface. On the basis of electron mic roprobe analysis, the aluminum concentration profile has been found to be parabolic with its minimum at the crystal centre. In the later sta ge of the uptake, a diffusion-immobilization process has been indicate d, perceptible only in long term sorption measurements performed under constant pressure conditions. For temperatures above 333 K the immobi lization process seems to be affected by chemical conversion of p-ethy ltoluene to the corresponding meta-isomer which has been detected in c rystals by an a posteriori FTIR analysis.