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Carbon molecular sieve (CMS) hollow fibers are a special class of rigid, molecular sieving membranes with unique scalability and excellent separation properties for challenging gas-pairs. These high-performing membranes are subject to moderate productivity losses and selectivity gains over time via a phenomenon typically referred to as physical aging. This article considers the role of slit bypass...
Carbon molecular sieve (CMS) membranes are a special class of nanoporous membranes with angstrom-level molecular discrimination properties, which make them appealing for separating a wide spectrum of gas-pairs. The mechanism of pyrolysis by which a polymer coil is transformed into these rigid sieves is complex; however, we present a framework that can explain this transformation. Representative polymer...
Characterization techniques beyond microscopy, scattering and spectroscopy approaches are needed to understand and improve sub-angstrom discrimination between penetrants in carbon molecular sieve (CMS) membranes. Here we use a method based on molecular scale gas diffusion probes to understand relevant membrane properties at the required level of detail. We further use this method to consider hypotheses...
Temperature dependences of gas transport and sorption properties on four previously isothermally studied 6FDA based carbon molecular sieve (CMS) membranes: 6FDA/DETDA, 6FDA:BPDA(1:1)/DETDA, 6FDA/DETDA:DABA(3:2) and 6FDA/1,5-ND:ODA(1:1), were examined over the temperature range from 35 °C to 50 °C. The permeability, sorption and diffusivity of these materials are reported, and activation energies of...
Understanding the relationship between carbon molecular sieve (CMS) pore structure and corresponding gas separation performance enables optimization for a given gas separation application. The final pyrolysis temperature and starting polymer precursor are the two critical parameters in controlling CMS performance. This study considers structure and performance changes of CMS derived from a commercially...
This paper considers physical aging in carbon molecular sieve (CMS) membranes. Moreover, the performance of stabilized membranes under practical operating conditions is discussed. Physical aging has been studied extensively in glassy polymers, but aging in CMS membranes has previously focused primarily on adsorption: either chemisorption of oxygen, or physical adsorption of water and organics in the...
In this study, a novel pre-pyrolysis treatment is developed to restrict the morphology collapse in asymmetric carbon molecular sieve (CMS) hollow fiber membranes. The technique is referred as V-treatment, due to the use of a sol–gel crosslinking reaction between an organic-alkoxy silane (vinyltrimethoxysilane) and moisture. The V-treatment technique enables restricting the microscale morphology collapse...
A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N2/CH4 permeation tests. The effects of final pyrolysis temperature on N2/CH4 separation are reported. The separation performance...
Development of dense film carbon molecular sieve (CMS) membranes for ethylene/ethane (C 2 H 4 /C 2 H 6 ) separation is reported. A commercial polyimide, Matrimid®, was pyrolyzed under vacuum and inert argon atmosphere, and the resultant CMS films were characterized using pure C 2 H 4 and C 2 H 6 permeation at 35°C, 50psia feed pressure...
Previously, a pyrolysis method was developed to control separation performance of carbon molecular sieve (CMS) membranes by doping with trace oxygen. This method involved oxygen exposure during pyrolysis to tune the selective pore windows. During the development, it was observed that oxygen concentration in inert gas, rather than the total amount of oxygen exposed controls performance. In this study,...
Polymer precursor and processing method have a significant effect on the separation performance of carbon molecular sieve (CMS) membranes. The authors previously developed a polymer processing method involving oxygen exposure during pyrolysis using synthesized polyimide, 6FDA/BPDA-DAM. The objectives of this work were (i) to demonstrate the generality of the oxygen doping method with a commercially...
Sub-micron sized carbon molecular sieve (CMS) materials were produced via ball milling for subsequent use in hybrid material formation. A detailed analysis of the effects of the milling process in the presence of different milling environments is reported. The milling process apparently alters the molecular scale structure and properties of the carbon material. Three cases: unmilled, air milled and...
A significant extension of an earlier analysis of molecular sieving carbons formed from polymeric precursors is reported for separation of important gas pairs including O 2 /N 2 , CO 2 /CH 4 and C 3 H 6 /C 3 H 8 . Previously, it was shown that changing the time or temperature of the pyrolysis protocol for a commercially available polyimide...
Carbon molecular sieving membranes are chemically robust materials with tailorable gas transport properties for O 2 /N 2 , CO 2 /CH 4 and C 3 H 6 /C 3 H 8 separations. Such carbon materials were formed in this study by the pyrolysis of polyimide precursors. The final pyrolysis temperature was varied to alter the carbon structure, which...
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