(376n) A Scalable Method to Prepare Zeolitic-Imidazolate Framework ZIF-8 Membranes on Polymer Hollow Fibers for Propylene/Propane Separation

Separation of olefin/paraffin mixtures (e.g., ethylene/ethane and propylene/propane), is one of the most challenging separations due to the similarity of their physicochemical properties. Currently, propylene/propane separation is typically achieved through energy-intensive cryogenic distillation process. Although energy-efficient membrane-based separation processes have received significant attention, however, there are no commercially available membranes for olefin/paraffin separations mainly due to the limitations of current membrane materials and lack of cost-effective and simple processing methods to fabricate membrane with large area^1-3.

A sub-class of metal-organic frameworks (MOFs), zeolitic-imidazolate frameworks (ZIFs) with zeolite topologies are crystalline nanoporous materials with well-defined aperture sizes (< 5 Å). ZIFs, which are composed of divalent metal ions (typically Zn²⁺ and Co²⁺) and imidazole-based ligands⁴, have been extensively studied especially for gas separation applications. ZIF-8 in particular is a promising membrane material for high resolution propylene/propane separation because the effective pore size of ZIF-8 (~ 4 Å) ⁵ lies in between the size of propylene and propane molecules. Although ZIF-8 membranes (mostly planar configurations) synthesized either by in-situ or seeded growth method showed excellent propylene/propane separation performances, scaling-up and commercialization of the membranes requires them to be fabricated on a cheap and scalable support (i.e., hollow fiber or tubular support). Polymeric hollow fibers have been utilized as substrates, but only a few of the resulting ZIF-8 membranes showed promising propylene/propane separation performances.^6-9

Herein, we would like to present a simple and scalable method to synthesize well intergrown ZIF-8 membranes on polymeric hollow fibers. The method is based on substrates modification followed by solvothermal reaction in linker solution. High-quality ZIF-8 seed layers prepared from the solvothermal reaction are secondarily grown to form high quality ZIF-8 membranes. The resulting ZIF-8 membranes are tested for propylene/propane separation. In this work, the effects of different synthesis parameters on the microstructures of ZIF-8 membranes will be discussed. Finally, the gas separation performances of ZIF-8 membranes especially propylene/propane separation will be presented.

References and Notes

1 Koros, William J. and Fleming, G.K. (1993) “Membrane-based gas separation”, Journal of Membrane Science, 83, pp l-39

2 Baker RW., (2002) “Future Directions of Membrane Gas Separation Technology” Industrial & Engineering Chemistry Research., 41 (6), pp 1393-1411

3 Tanaka, K., Taguchi, A., Hao, JQ, Kita, H., and Okamoto, K., (1996) “Permeation and separation properties of polyimide membranes to olefins and paraffins”, Journal of Membrane Science, 121, pp 197-207

4 Park KS, Ni Z, Côté AP, et al., (2006) “Exceptional chemical and thermal stability of zeolitic imidazolate frameworks”, Proceedings of the National Academy of Sciences, 103 (27), pp 10186-10191

5 Zhang C, Lively RP, Zhang K, Johnson JR, Karvan O, Koros WJ., (2012) “Unexpected Molecular Sieving Properties of Zeolitic Imidazolate Framework-8”, The Journal of Physical Chemistry Letters., 3 (16), pp 2130-2134.

6 Andrew J. Brown, Nicholas A. Brunelli, Kiwon Eum, Fereshteh Rashidi, J. R. Johnson, William J. Koros, Christopher W. Jones, Sankar Nair, (2014) “Interfacial microfluidic processing of metal-organic framework hollow fiber membranes”, Science, 345, 6192, pp 72-75

7 FernandoCacho-Bailo, SilviaCatalán-Aguirre, MirenEtxeberría-Benavides, Oğuz Karvan, VictorSebastian, CarlosTéllez, JoaquínCoronas (2015) “Metal-organic framework membranes on the inner-side of a polymeric hollow fiber by microfluidic synthesis”, Journal of membrane science, 476, pp 277-285

8 Kiwon Eum, Chen Ma, Ali Rownaghi, Christopher W. Jones, and Sankar Nair (2016) “ZIF‑8 Membranes via Interfacial Microfluidic Processing in Polymeric Hollow Fibers: Efficient Propylene Separation at Elevated Pressures”, ACS Applied materials and interfaces, 8, pp 25337 – 25342

9 Anne M. Marti, Wasala Wickramanayake, Ganpat Dahe, Ali Sekizkardes, Tracy L. Bank, David P. Hopkinson, and Surendar R. Venna (2017) “Continuous Flow Processing of ZIF‑8 Membranes on Polymeric Porous Hollow Fiber Supports for CO2 Capture”, ACS Applied materials and interfaces, 9, pp 5678-5682