Microporous volume and external surface of Y zeolites accessible to p-xylene and m-xylene

Isothermal adsorption of p-xylene and m-xylene on NaY, KY and BaY zeolites was studied by thermogravimetry at 25 degrees C. Adsorption isotherms showed type H-4 hysteresis associated with a xylenes adsorption process activated by the pressure. Experimental data were analysed with the t-method to distinguish the amounts of xylene adsorbed in the alpha-cages and on the external surface of crystallites. Results were compared with those previously achieved by calorimetry. Whatever may be the isomer and the Y zeolite, the adsorption capacity of alpha-cages at 25 degrees C is equal to 3.5 molecule alpha(-1). At saturation, the amount of xylenes adsorbed on the external surface represents 13% of the total amount adsorbed on the zeolites and is twice as great for m-xylene than for p-xylene. The adsorption process on the external surface differs from that in alpha-cages by a low adsorption energy and a high adsorption rate. (C) 1997 Elsevier Science B.V.