ARGON POROSIMETRY OF SELECTED MOLECULAR-SIEVES - EXPERIMENTS AND EXAMINATION OF THE ADAPTED HORVATH-KAWAZOE MODEL

The calculated micropore size of various molecular sieves has been examined using static argon porosimetry and a simple model for adsorption. The molecular sieves used in this study are Na-Y, ZSM-5, AlPO4-5, AlPO4-11 and VPI-5. Since zeolites and aluminophosphates have different interactions with argon, a lumped parameter for adsorptive interactions was found to be critical to the evaluation of micropore size using an area-averaged cylindrical pore model. The parameter of choice is the magnetic susceptibility of the adsorbent oxide ion. For Na-Y and ZSM-5, a magnetic susceptibility of chi = -1.3 . 10(-29) cm(3) shows good results. With a value of chi = -1.9 10(-29) cm(3) the calculated pore sizes of AlPO4-5 and AlPO4-11 are in good accord with the values from X-ray diffraction studies. For VPI-5, which has a larger pore, the monolayer cylindrical pore model is more adequate, but it requires inclusion of an adjustable factor to compensate for adsorbate-adsorbate interactions.