HEXANE AND BENZENE ADSORPTION BY ALUMINOPHOSPHATES AND SSZ-24 - THE EFFECT OF PORE-SIZE AND MOLECULAR-SIEVE COMPOSITION

The heat and entropy of benzene and hexane adsorption for AlPO4-11, AlPO4-5, AlPO4-31, VPI-5, and SSZ-24 have been determined from adsorption isotherms. As the pore diameter decreases, the heat of adsorption and entropy change increase. This reflects increased zeolite-hydrocarbon interaction and more highly ordered systems as the size of the hydrocarbon approaches the zeolite pore size. The measured Delta H agrees well with calculated values that were determined by the molecular mechanics program PCK6. The relative size of Henry's constants are largely influenced by Delta H for VPI-5 and AlPO4-5; however, for AlPO4-11 and AlPO4-31, Delta S plays a large role. When the adsorption parameters of AlPO4-5 were compared to those for isostructural SSZ-24, differences in benzene adsorption were observed, reflecting different surface compositions.