The apparent diffusivity for the binary liquid systems benzene-cumene and cyclohexane-cumene in H-mordenite crystals at 25OC to 44OC was increased by an order of magnitude or more after the zeolite was acid-leached to increase the silica-alumina mole ratio from the range of 14 to 18 to the range of 70 to 89. The calculated diffusivities, which range from to 10-'6 cmZ/s, decrease with approach to sorption equilibrium and may be markedly reduced under some circumstances by adsorption of molecules from the bulk liquid, causing blockage of pores.Comparison of sorption capacities as a function of silica-alumina ratio as reported by various investigators indicates that considerable differences exist in the properties of acid-leached mordenites of the same silica-alumina ratio but of different origins.
SCOPEH-mordenite and acid-leached mordenites have remarkable catalytic activities for acid-catalyzed reactions, but the rate and selectivity of these reactions can be profoundly affected by the rate of counterdiffusion of product and reactant molecules inside the fine pore structure of these zeolites. Acid leaching removes alumina from the silica-alumina matrix and opens up the pores of mordenites, thereby increasing the rate of diffusion. However, leaching also reduces the concenbation of acid sites, thereby presumably decreasing the intrinsic reactivity of the catalyst. The two effects act in opposite directions on the apparent reactivity of the mordenite under diffusionlimiting conditions. A principle objective of this work was to determine quantitatively the effect of acid leaching on diffusivity in mordenites. Diffusion measurements were made by observing the rate of disappearance of a hydrocarbon species A by adsorption from a dilute solution of A in B into mordenite crystals previously saturated with B-termed here adsorption measurements; or by observing the rate of appearance of B from saturated mordenite into bulk liquid consisting initially of pure A-termed here desorption measurements.Sorption capacities for benzene or cumene vapors were also determined as a function of silica-alumina ratio and compared to previous reports on sorption of these and other hydrocarbons. Sorption capacities are of interest in themselves in connection with adsorption processes, and they also provide some insight into the nature of the fine pore structure.