Hyperaging Tuning of a Carbon Molecular‐Sieve Hollow Fiber Membrane with Extraordinary Gas‐Separation Performance and Stability

Abstract

This study reports 6FDA:BPDA-DAM polyimidederived hollowf iber carbon molecular-sieve (CMS) membranes for hydrogen and ethylene separation. Since H 2 /C 2 H 4 selectivity is the lowest among H 2 /(C 1 -C 3 )h ydrocarbons,a n optimizedC MS fiber for this gas pair is useful for removing hydrogen from all-cracked gas mixtures.Aprocess we term hyperaging provides highly selective CMS fiber membranes by tuning CMS ultramicropores to favor H 2 over larger molecules to give aH 2 /C 2 H 4 selectivity of over 250. Hyperaging conditions and ah yperaging mechanism are discussed in terms of an expedited physical aging process,w hich is largely controlled by the hyperaging temperature.F or the specific CMS material considered here,ahyperaging temperature beyond 90 8 8Cbut less than 250 8 8Cworks best. Hyperaging also stabilizes CMS materials against physical aging and stabilizes the performance of H 2 separation over extended periods.This work opens ad oor in the development of CMS materials for the separation of small molecules from large molecules.

Isomer‐Tailored Carbon Molecular Sieve Membranes with High Gas Separation Performance

“…Although the CO 2 /CH 4 selectivity was lower, the CO 2 permeability of aCMS‐800 membrane (∼4000 Barrers) is still much higher than those even from a cross‐linkable copolyimide, 6FDA‐mPDA : DABA(3 : 2), and Tröger base‐containing polyimide . Note that the conventional 6FDA 1 : sBPDA 1 : aBPDA 0 /DAM 2 copolyimide has been successfully spun into hollow fiber for gas separation, the 6FDA 2 : sBPDA 1 : aBPDA 0 /DAM 3 and 6FDA 2 : sBPDA 0.5 : aBPDA 0.5 /DAM 3 might also be easily made into hollow fibers, for developing outstanding high permeable CMS fibers in scale‐up for industrial application. The long‐term gas separation performance will be investigated with CMS hollow fiber.…”

“…Gas separation performance of CMS membranes is affected by factors including pyrolysis temperature, atmosphere, and the precursor polymer's chemical structure, etc . For 6FDA‐based polyimides, especially the 6FDA‐BPDA/DAM (BPDA=3,3′,4,4′‐biphenyl dianhydride; DAM=diaminomesitylene) copolyimide‐derived CMS membranes show an unusually attractive balance between gas selectivity and permeability properties . The precursor copolyimide's structure can be tailored and optimized by varying the monomer ratio and/or monomer structure, based on specific CMS membrane requirements.…”

Key Features of Polyimide‐Derived Carbon Molecular Sieves

“…The WAXD pattern of CMS‐550 is different from that of the CMS‐675 and CMS‐800 shown in Figure 4 a. The CMS‐675 and CMS‐800 samples show similar patterns containing a main amorphous peak and an additional smaller peak, which is a typical WAXD patterns of CMS materials [2e, j] . The 2 θ value of the main peak is 24.0° for CMS‐675 and 24.8° for CMS‐800, and the small peak at 44° remains unchanged.…”

Shape‐Selective Ultramicroporous Carbon Membranes for Sub‐0.1 nm Organic Liquid Separation

“…For the sharp discrimination of alkanes, the ultramicropores within CMS need to be similarly sized with the target molecules, and a rigid and confined structure needs to be provided for shape selectivity. Various parameters, including polymeric precursor, [ 36 , 37 ] pyrolysis conditions, [ 38 , 39 , 40 ] and pre‐/post‐treatment, [ 41 , 42 , 43 , 44 , 45 ] enable the fine tuning of pore size and structure of CMS. For example, higher pyrolysis temperature leads to tighter structure or smaller ultramicropore size.…”

“…[ 39 , 40 ] Meanwhile, post‐pyrolysis heat‐treatment process called “hyperaging” facilitates tightening and widening of ultramicropores when the CMS membranes are treated at below 250 and above 250 °C, respectively. 45 In this study, we sought to match the pore size distribution of carbon molecular sieve membranes to the size of hexane isomers by choosing the fluorinated polyimides as polymeric precursors followed by pyrolysis at 500 °C. Carbon molecular sieve membranes derived from 6FDA (4,4’‐(hexafluoroisopropylidene)diphthalic anhydride) based polyimides were reported to show higher permeability for several light hydrocarbon gas molecules compared to that of the other precursors such as commercial polyimides (Matrimid®, Kapton, Torlon, P84), polybenzimidazole (PBI), and polymers with intrinsic microporosity (PIMs).…”