(619d) Diffusive Separation of Propylene/Propane With ZIF-8 Membranes

Metal-organic frameworks (MOFs) have been recognized as a new candidate for gas and vapor separation. Among several varieties of MOFs, ZIF-8 is one of the most common materials for separation membranes. ZIF-8 is composed of zinc atoms and 2-methyl imidazole as ligands, forming the sodalite structure with large cavities, 1.16 nm in diameter, which are connected with a small pore aperture of 0.34 nm diameter [1]. Recently, several reports have focused on the potential of ZIF-8 for propylene/propane separation on the basis of their difference of diffusivity [2].

The most common preparation methods of ZIF-8 membranes are the in situ growth method and the secondary growth method. Pan et al. reported the separation of propylene/propane mixture, in which the ZIF-8 membrane is prepared by the secondary growth method with a separation factor of up to 50 for propylene/propane binary mixture [3]. Kwon et al. reported the preparation of ZIF-8 membranes using microwave-assisted seeding and secondary growth with the separation factor of up to 40 for propylene/propane binary mixture [4].

To improve the propylene/propane separation properties, diffusivity and solubility separation factors should be separately investigated from the single-component permeation measurements. In this study, we clarified the contribution of diffusive separation for propylene/propane with ZIF-8 membrane based on the analysis of diffusivity and solubility obtained from the membrane permeation properties. Permeation properties were studied using the single-component gas permeation properties, and superior separation properties for propylene/propane were achieved for ZIF-8 membranes with uniform selective layer. Permeability, diffusivity, solubility, and their dependencies on temperature were studied, and the contribution of diffusivity on propylene/propane separation is thoroughly discussed.

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[2] K. H. Li, D. H. Olson, J. Seidel, T. J. Emge, H. W. Gong, H. P. Zeng and J. Li, Zeolitic Imidazolate Frameworks for Kinetic Separation of Propane and Propene, J. Am. Chem. Soc. 131 (2009) 10368-10369., C. Zhang, R. P. Lively, K. Zhang, J. R. Johnson, O. Karvan and W. J. Koros, Unexpected Molecular Sieving Properties of Zeolitic Imidazolate Framework-8, J. Phys. Chem. Lett. 3 (2012) 2130-2134.

[3] Y. C. Pan, T. Li, G. Lestari and Z. P. Lai, Effective separation of propylene/propane binary mixtures by ZIF-8 membranes, J. Membr. Sci. 390 (2012) 93-98.

[4] H. T. Kwon and H. K. Jeong, Highly propylene-selective supported zeolite-imidazolate framework (ZIF-8) membranes synthesized by rapid microwave-assisted seeding and secondary growth, Chem. Commun. 49 (2013) 3854-3856.