(459e) Zeolitic-Imidazolate Framework ZIF-8 Membranes on Ceramic Tubular Supports for Scalable High-Resolution Propylene/Propane Separation

Zeolite-imidazole frameworks (ZIFs) have been extensively studied as a new membrane material for gas separations due to their robust synthesis protocols, chemical and thermal stability, and well-defined ultra-micropores (~ 2 to 5 Å).^{1, 2} ZIFs are comprised of metal centers (Zn, Co, and Cd) and bridging imidazole-based ligands. ZIF-8, composed of zinc nodes and 2-methylimidazole linkers, has been shown very promising for propylene/propane separations since its effective aperture size lies in between propylene (~ 4 Å) and propane (~ 4.2 Å).³ In fact, some of the polycrystalline ZIF-8 membranes synthesized by various methods have been reported to exhibit impressive propylene/propane separation factors up to 200.^{4, 5} These highly propylene-selective ZIF-8 membranes were supported mostly on alumina disks or occasionally on hollow fibers (polymer or ceramic).

For their large-scale industrial applications, however, the productivities of ZIF-8 membranes must be significantly improved.⁶ One way to increase the membrane productivity is to increase membrane area per volume. As such, current disk supports are not desirable. Though hollow fiber supports (either polymer or ceramic) are most desirable, they are unlikely to be used for large-scale applications in near future. This is because ceramic hollow fibers are highly fragile while polymer hollow fibers require much more development. While hollow fiber supports are transformative, ceramic tubular supports are readily available for large-scale applications. For example, ceramic tubular supports have been used for commercial polycrystalline zeolite membranes.⁷ Though ZIF-8 membranes on ceramic tubular supports were reported, none of those membranes showed promising propylene/propane separation capabilities.^{8, 9}

Here, we would like to present polycrystalline ZIF-8 membrane supported on alumina tubes showing high propylene/propane separation performances. The tubular membranes were synthesized using our microwave seeding and secondary growth method. The effects of the synthesis parameters on the microstructures of tubular ZIF-8 membranes will be presented. Finally, the propylene/propane separation performances of ZIF-8 membranes supported on alumina tubes will be discussed.

References and Notes:

(1) Park, S.; Kang, W. R.; Kwon, H. T.; Kim, S.; Seo, M.; Bang, J.; Lee, S. h.; Jeong, H. K.; Lee, J. S., The polymeric upper bound for N2/NF3 separation and beyond; ZIF-8 containing mixed matrix membranes. J. Membr. Sci. 2015, 486, 29-39.

(2) Chen Zhang, R. P. L., Ke Zhang, Justin R. Johnson, Oguz Karvan, William J. Koros, Unexpected molecular sieving properties of zeolitic imidazolate framework-8. The journal of physical chemistry letters 2012, 3, (16), 2130-2134.

(3) Li, K.; Olson, D. H.; Seidel, J.; Emge, T. J.; Gong, H.; Zeng, H.; Li, J., Zeolitic imidazolate frameworks for kinetic separation of propane and propene. J. Am. Chem. Soc. 2009, 131, (30), 10368-9.

(4) Lee, M. J.; Kwon, H. T.; Jeong, H. K., Defect-dependent stability of highly propylene-selective zeolitic-imidazolate framework ZIF-8 membranes. J. Membr. Sci. 2017, 529, 105-113.

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

(6) Baker, R. W., Future directions of membrane gas separation technology. Ind. Eng. Chem. Res. 2002, 41, (6), 1393-1411.

(7) Kosinov, N.; Gascon, J.; Kapteijn, F.; Hensen, E. J., Recent developments in zeolite membranes for gas separation. J. Membr. Sci. 2016, 499, 65-79.

(8) Hara, N.; Yoshimune, M.; Negishi, H.; Haraya, K.; Hara, S.; Yamaguchi, T., Diffusive separation of propylene/propane with ZIF-8 membranes. J. Membr. Sci. 2014, 450, 215-223.

(9) Zhang, X.; Liu, Y.; Kong, L.; Liu, H.; Qiu, J.; Han, W.; Weng, L.-T.; Yeung, K. L.; Zhu, W., A simple and scalable method for preparing low-defect ZIF-8 tubular membranes. J. Mater. Chem. A 2013, 1, (36), 10635.