SORPTION OF N-PENTANE, 2-METHYLBUTANE AND CYCLOPENTANE IN MICROPOROUSALPO4-5

Sorption isotherms for n-pentane, 2-methylbutane and cyclopentane in t he aluminophosphate molecular sieve AlPO4-5 are reported at 303, 313, 323 and 333K. The sorption data were fitted into Langmuir, Sips and Du binin-Radushkevich isotherms. The heats of sorption at zero coverage d etermined from the data in the Henry region are in the order 2-methylb utane >cyclopentane >n-pentane. Free energy and entropy changes and he ats of sorption for these sorbates at various sorption coverages were also determined from the sorption data. The heat of sorption for n-pen tane varies only marginally with sorption coverage. However, the heats of sorption for 2-methylbutane and cyclopentane increase significantl y with the coverage indicating an increase in sorbate-sorbate interact ions. The dependence of thermodynamic properties like the free energy of sorption (Delta G) and the entropy change (Delta S) for 2-methylbut ane and cyclopentane on coverage show a sharp decrease and increase at sorption coverages 0.1-0.2 mmol g(-1) suggesting the rearrangement of molecular packing in the sorbed phase. These observations have been e xplained in terms of molecular interactions between the AlPO4-5 channe ls and sorbate molecules. (C) 1997 Elsevier Science B.V.