Faujasites, sorption benzene

Highly selective sorption of aromatic compounds from paraffin-containing solutions has been reported for the faujasites NaX, NaY, and HY under equilibrium conditions (2). Thus, benzene is preferentially adsorbed relative to n-hexane or n-decane, p-xylene relative to n-octane, and naphthalene relative to n-decane. The measured separation factors in these systems are so large (K>700) that essentially only one species exclusively occupies the internal volume of the zeolites. 

Figure 2. Arrhenius plot showing comparison of NMR and sorption diffusivities for benzene and o-xylene in NaX zeolite crystals. NMR data from (1) Germanus et al. (19) and (2) Karger and Ruthven (10). Uptake (corrected diffusivity) and tracer exchange data of Goddard (11-13) (50 pm and 100 pm NaX, 250 pm faujasite). ZLC data of Eic (15,16).

For deeply dealuminated samples, sorption isotherms of hydrocarbons are available (ref.26,61). Samples prepared by Method B with 6 and 8 A1/UC show a near rectilinear adsorption isotherm for hexane, butane and benzene. It was concluded that in these samples mesopores having radii in the range from 1.5 to 1.9 nm, typical of hydrothermally dealuminated samples were absent. These results do, however, not imply that the faujasite raicropore system is intact (ref.61). 

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