Inclusion of fluorine compounds in faujasite I. The physical state of the occluded molecules

Abstract

An account has been given of the intracrystalline sorption of SF 6 , CF 4 , C 2 F 6 , C 3 F 8 , n - C 4 F 10 , C 2 F 4 Cl 2 , perfluoromethyl cyclo hexane, perfluorodimethyl cyclo hexane and perfluoro cyclo butene in crystals of a synthetic near-faujasite. The inclusion of all these molecules except perfluoro cyclo butene was reversible. In the region of capillary condensation in interparticle spaces, hysteresis not associated with inclusion, was observed. Perfluoro cyclo butene underwent a chemical reaction within the zeolite. The equilibrium isotherms have been analyzed, and it has been shown that if the quotient p (l — θ ) / θ is plotted against θ , curves of characteristic form are obtained for all the fluoro-compounds so examined. Reference to previous studies of hydrocarbon inclusion and of zeolitic water in faujasite showed this behaviour to be general for these materials. It can be interpreted for small θ in terms of configurational entropy changes associated with an observed exothermal molecule-molecule interaction (part II) and with changes in heats of inclusion due to these interactions. It appears to be determined, for larger values of θ , either by decrease in vibrational entropy of the included molecules, associated with higher binding energy (Barrer & Sutherland 1956) or by loss of rotational entropy due to closer packing, or to both effects simultaneously.