(705e) One-Step Fabrication of Highly Propylene-Selective Asymmetric Mixed-Matrix Membranes with in-Situ ZIF-8 Filler Formation

Separation of propylene from propane is one of the most energy-intensive separation processes due to the similarities in their physico-chemical properties[1]. Zeolitic-imidazolate framework-8 (ZIF-8), consisting of a zinc center tetrahedrally coordinated with 2-methylimidazolate linkers, is one of the most promising molecular sieve materials for propylene/propane separation. Recently, our group developed a scalable mixed-matrix membranes fabrication strategy using in-situ Zif-8 formation approach, named PMMOF[2]. The PMMOF enables formation of MMMs not only with much improved gas separation performances[2] but also in a scalable geometry (i.e., asymmetric hollow fibers with submicron thick selective MMM skin layers)[3]. However, the PMMOF suffers from two major challenges: 1) multi-steps involved that are relatively complicated and 2) limited choice of polymer matrices (i.e., polyimide-based polymers).

In this presentation, we plan to present a novel second-generation one-step ZIF-8-based asymmetric MMM fabrication strategy, addressing the challenges of the first-generation PMMOF process. The new process, termed “PIMOF”, enable rapid formation of high ZIF-8 loaded asymmetric MMMs. The as-prepared MMMs showed unprecedentedly high C₃H₆/C₃H₈ (C3) separation performance as compared to other propylene-selective MMMs reported so far with the C₃H₆ permeance of ~ 7.5 GPU and C₃H₆/C₃H₈ separation factor of ~ 107. It is worthy of noting that our MMMs exhibit comparable C3 separation performances even with polycrystalline ZIF-8 membranes. The unexpectedly high C3 performance of the membranes was attributed to 1) the uniform distribution of the extremely small ZIF-8 nanoparticles (~ 5-10 nm), 2) unusually high ZIF-8 nanofiller loading in the selective skin layers (> 50 wt%), and 3) improved molecular sieving properties of the ZIF-8 nanofillers resulting from the hindered linker flexibility upon confined filler formation.

Reference:

1. Sholl, D.S. and R.P. Lively, Seven chemical separations to change the world. Nature, 2016. 532(7600): p. 435-437.
2. Park, S., M.R. Abdul Hamid, and H.-K. Jeong, Highly Propylene-Selective Mixed-Matrix Membranes by in Situ Metal–Organic Framework Formation Using a Polymer-Modification Strategy. ACS Applied Materials & Interfaces, 2019. 11(29): p. 25949-25957.
3. Park, S. and H.-K. Jeong, Transforming polymer hollow fiber membrane modules to mixed-matrix hollow fiber membrane modules for propylene/propane separation. Journal of Membrane Science, 2020. 612: p. 118429.