An investigation was made of the vapor permeation of single-component 3-methylpentane and 2,2-dimethylbutane (table 19), as well as of equimolar binary mixtures of n-hexane (n-C6), benzene and branched hexanes, through an NaY-type membrane, as a function of temperature. For the single-component systems, the permeances were in the order: n-C6 >> methylpentane > dimethylbutane; in good agreement with the extent of chain-branching (molecular width). The adsorption isotherms for single-component n-C6, methylpentane and dimethylbutane were essentially the same. Thus the permeation of these components was based upon differences in the diffusion rates in the zeolitic channels. In the case of binary systems of n-C6/methylpentane and n-C6/ dimethylbutane, the presence of branched hexanes led to a significant decrease in the permeance to n-C6, whereas the presence of n-C6 had only a small effect upon branched hexane permeation. The separation factors for the mixtures were close to unity, while the ideal separation factors were greater than 10. This suggested that a single-file transport mechanism prevailed.

Vapor Permeation Properties of an NaY-Type Zeolite Membrane for Normal and Branched Hexanes. B.H.Jeong, Y.Hasegawa, K.I.Sotowa, K.Kusakabe, S.Morooka: Industrial and Engineering Chemistry Research, 2002, 41[7], 1768-73