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Membrane-based separations offer the potential for the lowest energy demand requirements of all separation options. Among all nanoporous membranes, the carbon molecular sieves (CMS), metal-organic frameworks (MOFs), and mixed-matrix membranes (MMMs) with angstrom level molecular discrimination properties makes them appealing for separating a wide spectrum of gas-pairs. Here we present results of gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the iridization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C2H6, C2H4, C3H8, C3H6 adsorption capacities reached to 42.61, 2.56, 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO2, CH4, CO, N2 and H2 adsorption capacities of 1.48, 0.84, 0.33, 0.11, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane were formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary H2/CO2, CH4/CO2 and C3H6/C3H8 feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes.
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Gas Permeation and Separation Characteristics of Microporous TpHz COF Membranes Synthesized by Substrate-Assisted Interfacial Polymerization
Microporous two-dimensional covalent organic framework (2D COF) membranes offer promise for gas separation applications, but their gas transport mechanism remains unclear. In this study, a TpHz 2D COF membrane supported on a macroporous nylon substrate is prepared by substrate-assisted interfacial polymerization under mild conditions. The formation of a continuous and dense thin (∼300 nm thick) TpHz layer is confirmed by scanning electron microscopy and Fourier transform infrared spectroscopy. Characterization by X-ray diffraction, grazing incidence wide-angle X-ray scattering, and N2 porosimetry qualitatively reveals the microstructures of the supported TpHz membranes, i.e., they comprise partially oriented 2D COF lamellar crystallites with moderate crystallinity in an eclipsed (AA) stacking geometry, centering the effective membrane pore size distribution at ∼1.1 nm. Single gas permeation data show that the transport of common molecular gases, including H2, He, CH4, N2, and CO2, through the synthesized TpHz membranes follows the Knudsen transport mechanism, where single gas permeance decreases with an increasing molecular weight and permeation temperature. Binary gas separation results show that in the equimolar CO2/N2 mixture, the presence of the CO2 surface flow slightly hinders the N2 flow at room temperature due to the reduced membrane channel size by the adsorbed CO2 gas layer on TpHz’s pore wall. In contrast, permeation of the equimolar CH4/N2 binary mixture does not exhibit a discernible surface flow of both gases due to their much lower gas uptake on TpHz, and their transport mechanism follows Knudsen-like behavior.
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- Award ID(s):
- 2216843
- PAR ID:
- 10544616
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- Industrial & Engineering Chemistry Research
- Volume:
- 63
- Issue:
- 8
- ISSN:
- 0888-5885
- Page Range / eLocation ID:
- 3684 to 3694
- Subject(s) / Keyword(s):
- Covalent organic frameworks Membranes Gas Separation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Here we present results of gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the thermal and chemical imidization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C3H8, C3H6, CO2, and H2) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C3H8, C3H6 adsorption capacities reached 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO2, CH4, CO, N2 and H2 adsorption capacities of 1.48, 0.84, 0.33, 0.11, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane was formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary H2/CO2, CH4/CO2 and C3H6/C3H8 feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.iecr.3c04303
