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1. 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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2. 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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3. 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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4. Synthesis and Performance of Aromatic Polyamide Ionenes as Gas Separation Membranes

   https://doi.org/10.3390/membranes10030051  

   O’Harra, Kathryn E.; Kammakakam, Irshad; Noll, Danielle M.; Turflinger, Erika M.; Dennis, Grayson P.; Jackson, Enrique M.; Bara, Jason E. (March 2020, Membranes)

   null (Ed.)

   Here, we report the synthesis and thermophysical properties of seven primarily aromatic, imidazolium-based polyamide ionenes. The effects of varied para-, meta-, and ortho-connectivity, and spacing of ionic and amide functional groups, on structural and thermophysical properties were analyzed. Suitable, robust derivatives were cast into thin films, neat, or with stoichiometric equivalents of the ionic liquid (IL) 1-benzy-3-methylimidazolium bistriflimide ([Bnmim][Tf2N]), and the gas transport properties of these membranes were measured. Pure gas permeabilities and permselectivities for N2, CH4, and CO2 are reported. Consistent para-connectivity in the backbone was shown to yield the highest CO2 permeability and suitability for casting as a very thin, flexible film. Derivatives containing terephthalamide segments exhibited the highest CO2/CH4 and CO2/N2 selectivities, yet CO2 permeability decreased with further deviation from consistent para-linkages. 

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5. Temperature Effect of CO2 Reduction Electrocatalysis on Copper: Potential Dependency of Activation Energy

   https://doi.org/10.1115/1.4046552  

   Zong, Yixu; Chakthranont, Pongkarn; Suntivich, Jin (November 2020, Journal of Electrochemical Energy Conversion and Storage)

   Abstract The electrochemical CO2 reduction reaction (CO2RR) has gathered widespread attention in the past decade as an enabling component to energy and fuel sustainability. Copper (Cu) is one of the few electrocatalysts that can convert CO2 to higher-order hydrocarbons. We report the CO2RR on polycrystalline Cu from 5 °C to 45 °C as a function of electrochemical potential. Our result shows that selectivity shifts toward CH4 at low temperature and H2 at high temperature at the potential values between −0.95 V and −1.25 V versus reversible hydrogen electrode (RHE). We analyze the activation energy for each product and discuss the possible underlying mechanism based on their potential dependence. The activation barrier of CH4 empirically obeys the Butler–Volmer equation, while C2H4 and CO show a non-trivial trend. Our result suggests that the CH4 production proceeds via a classical electrochemical pathway, likely the proton-coupled electron transfer of surface-saturated COad, while C2H4 is limited by a more complex process, likely involving surface adsorbates. Our measurement is consistent with the view that the adsorbate–adsorbate interaction dictates the C2+ selectivity. 

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