Physical aging in carbon molecular sieve membranes

Xu, Liren; Rungta, Meha; Hessler, John C.; Qiu, Wulin; Brayden, Mark; Martinez, Marcos; Barbay, Gregory A.; Koros, William J.

doi:10.1016/j.carbon.2014.08.051

Cited by 114 publications

(74 citation statements)

References 57 publications

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“…Recent studies found that the separation performance of amorphous CMS films derived from glassy polymer precursors showed time dependence and exhibited somewhat similar physical aging phenomenon to that seen in glassy polymers [38]. Unlike simple glassy polymers, glassy carbons do not have well-defined glass transitions.…”

Section: Physical Aging Study Of Pure Gases Permeation On Four Cms Mamentioning

confidence: 95%

“…When temperature dropped below 100 o C, typically after three hours, the CMS dense films were unloaded from the furnace and loaded into permeation or sorption systems [38]. After each pyrolysis, the quartz plate and quartz tube were rinsed with ϭϮ acetone and baked at 800 o C with 500 scc/min air flow to burn out residue which could influence subsequent runs.…”

Section: ) Soak For 2 Hours At 550 °Cmentioning

confidence: 99%

“…Stage cut, referred to as the percentage of feed permeating through the membrane, was controlled by a needle valve and set to be lower than 1% to avoid concentration polarization. Permeate composition was analyzed using a gas chromatograph, as described earlier [38]. Mixture gas tests were conducted at 35 o C and 50 psia.…”

Section: Permeation Measurementsmentioning

confidence: 99%

“…The permeability and selectivity for CO 2 / CH 4 and O 2 /N 2 for CMS films derived from all four polymers were studied by storing the as-ϮϮ made samples under vacuum for about a month. Vacuum storage is the most rigorous aging mode based on prior studies [38], and Figure 6 shows the time dependence of gas permeability and selectivity. Clearly, the permeability for the four gases of the four CMS films showed a decreasing trend and the selectivity showed an increasing trend with aging time.…”

Section: Physical Aging Study Of Pure Gases Permeation On Four Cms Mamentioning

confidence: 99%

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Carbon molecular sieve membrane structure–property relationships for four novel 6FDA based polyimide precursors

Sanders

Kulkarni

et al. 2015

Journal of Membrane Science

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Section: Physical Aging Study Of Pure Gases Permeation On Four Cms Mamentioning

confidence: 95%

Section: ) Soak For 2 Hours At 550 °Cmentioning

confidence: 99%

Section: Permeation Measurementsmentioning

confidence: 99%

Section: Physical Aging Study Of Pure Gases Permeation On Four Cms Mamentioning

confidence: 99%

See 2 more Smart Citations

Carbon molecular sieve membrane structure–property relationships for four novel 6FDA based polyimide precursors

Sanders

Kulkarni

et al. 2015

Journal of Membrane Science

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129

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“…36,37 It is worth noting that Pinnau et al and Koros et al have shown that physical aging in microporous materials such as poly(1-trimethylsilyl-1-propyne) (PTMSP) and carbon molecular sieve (CMS) membranes can largely be mitigated by keeping the membranes under active penetrant pressure (actively testing the membranes for extended periods of time rather than periodic testing with long-term storage at ambient conditions). 37,38 The penetrant molecules likely act as "proppants" and physically hinder compaction or aging of the structure. 37,38 Alternatively, there has been increasing interest in intentionally removing excess free volume from membranes to bring their free volume closer to their equilibrium or aged state.…”

Section: Macromoleculesmentioning

confidence: 99%

Effect of Nonsolvent Treatments on the Microstructure of PIM-1

Jue¹,

McKay²,

McCool

et al. 2015

Macromolecules

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The combination of appreciable swelling at unit activity sorption, weak polymer−penetrant interactions, and high vapor pressure allows methanol to be effective at restoring free volume to glassy polymers compared to similar organics. Polymers of intrinsic microporosity (PIMs) are often soaked in methanol and then dried before permeation and sorption analysis to improve reproducibility and eliminate processing history. Here, surface area, pore volume, thermogravimetric analysis, sorption, and diffusion data are used to demonstrate the effectiveness of methanol treatments at removing nonsolvent-induced changes to PIM-1, specifically using dimethylformamide (DMF) as a candidate conditioning molecule. DMF clearly plasticizes PIM-1 while methanol does not. In addition, diethyl ether-conditioned PIM-1 showed marked increases in surface area and free volume higher than that found from methanol conditioning. Strongly plasticizing nonsolvents with low vapor pressures can be used as conditioning agents that promote polymer relaxations, accelerate chain packing, and remove additional nonequilibrium free volume. ■ INTRODUCTIONMicroporous polymeric materials have attracted significant interest for a variety of potential molecular separation applications due to their combination of synthetic tunability and unusually facile processability in the case of linear polymers. The most well-studied linear microporous polymer, PIM-1 (polymer of intrinsic microporosity 1, shown in Figure 1), has a characteristic spirocenter between cyclopentane rings that hinders efficient chain packing. These 90°bends in the polymer chain impart "intrinsic" microporosity and high free volume that is uncommon for amorphous, solution processable polymers. As a result, PIM materials have high permeabilities with moderate selectivities that helped redefine the Robeson upper bounds for many of the commonly studied gas pairs. 1 As polymers are cooled below their glass transition temperature (T g ), they retain excess free volume between the chains due to nonequilibrium packing defects. The concentration and nature of these free volume elements have been successfully used to describe the sorption, diffusion, and permeation of guest molecules through glassy polymers. 2−4 However, high free volume glassy polymers such as PIMs are particularly susceptible to aging and conditioningthe loss of permeability and concomitant gain in selectivity with time. After membrane formation, PIM-1 naturally begins to lose some of its excess free volume due to slow relaxations of the polymer chains toward their equilibrium packing. Lau et al. have shown that the CO 2 permeability of PIM-1 decreases by 62% over a period of eight months storage at ambient conditions. 5 However, not all of the free volume was lost, and there remained intrinsic microporosity to the polymers even after a year under ambient storage. 6 Moreover, PIMs are unusual linear polymers because they do not exhibit a measurable T g before decomposition. 7 As a result, near-T g annealing techniques used to alt...

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Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties

2017

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Membrane-based separations can reduce the energy consumption and the CO footprint of large-scale fluid separations, which are traditionally practiced by energy-intensive thermally driven processes. Here, a new type of membrane structure based on nanoporous carbon is reported, which, according to this study, is best referred to as carbon/carbon mixed-matrix (CCMM) membranes. The CCMM membranes are formed by high-temperature (up to 900 °C) pyrolysis of polyimide precursor hollow-fiber membranes. Unprecedentedly high permselectivities are seen in CCMM membranes for CO /CH , N /CH , He/CH , and H /CH separations. Analysis of permeation data suggests that the ultrahigh selectivities result from substantially increased sorption selectivities, which is hypothetically owing to the formation of ultraselective micropores that selectively exclude the bulkier CH molecules. With tunable sorption selectivities, the CCMM membranes outperform flexible polymer membranes and traditional rigid molecular-sieve membranes. The capability to increase sorption selectivities is a powerful tool to leverage diffusion selectivities, and has opened the door to many challenging and economically important fluid separations that require ultrafine differentiation of closely sized molecules.

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Physical aging in carbon molecular sieve membranes

Cited by 114 publications

References 57 publications

Carbon molecular sieve membrane structure–property relationships for four novel 6FDA based polyimide precursors

Carbon molecular sieve membrane structure–property relationships for four novel 6FDA based polyimide precursors

Effect of Nonsolvent Treatments on the Microstructure of PIM-1

Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties

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