Vapor permeation properties of an NaY-type zeolite membrane for normal and branched hexanes

An FAU-type zeolite contains pores which are larger than those of an MFI-type zeolite. Thus, membranes that are synthesized from these zeolites behave differently in terms of the separation of hydrocarbon vapors. This study describes an investigation of the vapor permeation of single-component 3-methylpentane (MP) and 2,2-dimethylbutane (DMB), as well as equimolar binary mixtures of n-hexane (n-C-6), benzene, and branched hexanes, through an NaY-type zeolite membrane, as a function of the permeation temperature. For the single-component systems, the permeances were in the order of n-C-6 much greater than MP > DMB; which are in good agreement with the extent of chain branching (i.e., molecular width). Adsorption isotherms for single-component n-C-6, MP, and DMB were fundamentally the same. Thus, the permeation of these components is based on differences in diffusion rates in the zeolitic channels. For the case of binary systems of n-C-6/MP and n-C-6/DMB, however, the presence of branched hexanes led to a significant decrease in the permeance to n-C-6, whereas the presence of n-C-6 had only a small effect on branched hexane permeation. The separation factors for the mixtures were close to unity, while the ideal separation factors were higher than 10. This suggests that a single-file transport mechanism prevailed.