Permeation of binary mixtures of benzene and saturated C4–C7 hydrocarbons through an FAU-type zeolite membrane

The permeation and separation properties through an FAU-type zeolite membrane for mixtures of benzene and saturated C4–C7 hydrocarbons were investigated at a permeation temperature of 373 K. The data related to permeation were cited from previous papers, and the new data on adsorption were obtained for such binary mixtures with and without benzene. The high benzene/cyclohexane separation factor can be attributed to the high adsorption selectivity in favor of benzene and the blockage against cyclohexane. The proposed model is as follows: For the feed of single-component benzene or cyclohexane, the adsorption of benzene is higher than that of cyclohexane, while the diffusivity of benzene is lower than that of cyclohexane. As a result, permeance to cyclohexane is higher than that to benzene. For the case of the feed consisting of an equimolar mixture of benzene and cyclohexane, the adsorption of benzene is smaller than that for the case of a single-component feed. Meanwhile, cyclohexane molecules are expelled from the adsorption sites by benzene, and the benzene/cyclohexane selectivity for adsorption reaches a value of approximately 19. The benzene molecules which are moving toward the permeate side frequently block the windows, and the diffusivity of cyclohexane through the windows is greatly retarded. The small separation factors for mixtures of saturated C6 hydrocarbons can be explained based on a single-file diffusion mechanism.