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1. Synthesis and Performance of 6FDA-Based Polyimide-Ionenes and Composites with Ionic Liquids as Gas Separation Membranes

   https://doi.org/10.3390/membranes9070079  

   O’Harra, Kathryn; Kammakakam, Irshad; Devriese, Emily; Noll, Danielle; Bara, Jason; Jackson, Enrique (July 2019, Membranes)

   null (Ed.)

   Three new isomeric 6FDA-based polyimide-ionenes, with imidazolium moieties and varying regiochemistry (para-, meta-, and ortho- connectivity), and composites with three different ionic liquids (ILs) have been developed as gas separation membranes. The structural-property relationships and gas separation behaviors of the newly developed 6FDA polyimide-ionene + IL composites have been extensively studied. All the 6FDA-based polyimide-ionenes exhibited good compatibility with the ILs and produced homogeneous hybrid membranes with the high thermal stability of ~380 °C. Particularly, [6FDA I4A pXy][Tf2N] ionene + IL hybrids having [C4mim][Tf2N] and [Bnmim][Tf2N] ILs offered mechanically stable matrixes with high CO2 affinity. The permeability of CO2 was increased by factors of 2 and 3 for C4mim and Bnmim hybrids (2.15 to 6.32 barrers), respectively, compared to the neat [6FDA I4A pXy][Tf2N] without sacrificing their permselectivity for CO2/CH4 and CO2/N2 gas pairs. 

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2. Carbon Molecular Sieve-derived POC/Mixed-Matrix Membranes for Gas Separation

   kowey, Isha; Rownaghi, Ali (May 2023, North American Membrane Society 2023)

   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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3. Gas Permeation and Separation Characteristics of Microporous TpHz COF Membranes Synthesized by Substrate-Assisted Interfacial Polymerization

   https://doi.org/10.1021/acs.iecr.3c04303  

   Lopez-Cazares, Jose Edgardo; Kim, Kyungtae; Lin, Jerry_Y S; Jin, Kailong (February 2024, Industrial & Engineering Chemistry Research)

   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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4. Porous Organic Cages-Stabilized Carbon Molecular Sieve for Efficient Gas Separation

   Sharif, Usman; Kowey, Isha; Rownaghi, Ali (November 2023, 2023 AIChE Annual Meeting)

   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. 

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5. Effect of the annealing temperature of polybenzimidazole membranes in high pressure and high temperature H2/CO2 gas separations

   https://doi.org/10.1016/j.memsci.2023.121619  

   Perez, Edson V.; Ferraris, John P.; Balkus, Kenneth J.; Musselman, Inga H. (July 2023, Journal of Membrane Science)

   The effect of the annealing temperature of polybenzimidazole (PBI) membranes on H2/CO2 gas separations was investigated. Membranes annealed from 250 ◦C to 400 ◦C were tested for gas permeation with pure H2, CO2, and N2 gases and a H2:CO2 (1:1) mixture at 35 ◦C, 100 ◦C, 200 ◦C, and 300 ◦C and at pressures up to 45 bar. Gas permeation data show that permeability and selectivity of the membranes is significantly impacted by the annealing temperature, the presence of adsorbed water, and remaining casting solvent (DMAc). At a testing temperature of 35 ◦C, ideal H2/CO2 selectivities of 50, 49, and 66 with pure H2 permeabilities of 1.5, 0.8, and 1.5 Barrer were obtained for membranes annealed at 250 ◦C, 300 ◦C, and 400 ◦C, respectively. At this temperature, high gas mixture H2/CO2 selectivities of 41, 73, and 47 with H2 permeabilities of 1.03, 0.26, and 0.50 Barrer were also obtained for these membranes. At testing temperatures of 300 ◦C, both the ideal and gas mixture H2/ CO2 selectivities dropped to 44, 28, and 30 (ideal, H2 = 45, 45, 44 Barrer) and to 19, 22, and 23 (mixture, H2 = 41, 43, and 44 Barrer) for membranes annealed at 250 ◦C, 300 ◦C, and 400 ◦C, respectively. As water was removed from the membranes at temperatures greater than 100 ◦C during permeation cycles, where the testing temperature was increased from 35 ◦C to 300 ◦C, the permselectivity properties of the membranes annealed at 400 ◦C became more reproducible. Permeabilities at 35 ◦C from a second permeability cycle increased, but H2/ CO2 selectivities decreased to 21 for gas mixtures (H2 = 1.4 Barrer) and to 34 for pure gases (H2 = 2.2 Barrer). The results suggest that high annealing temperatures may induce changes in the configuration and conformation of the polymer chains, imparting distinctive permselectivity properties to the membranes. Activation energies of permeability for H2, CO2, and N2 from pure gases and H2:CO2 mixtures correlated with these changes as well. 

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