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 o C to 50 o C. The permeability, sorption and diffusivity of these materials are reported, and activation energies of permeation and diffusion as well as heats of sorption for gases CO 2 , CH 4 , O 2 , and N 2 of these materials are compared. Permselectivity of these materials at 35 o C was probed for three gas pairs: CO 2 /CH 4 , O 2 /N 2 , and N 2 /CH 4 , and results show that diffusion selectivity is the dominant factor in providing permselectivity. Diffusion selectivity can be factored further into an energetic selectivity and an entropic selectivity. The temperature dependence of both energetic and entropic selectivity and their contributions to overall diffusion selectivity are discussed in detail in this study. All four CMS membranes showed larger than unity entropic selectivity discriminations. 6FDA/DETDA derived CMS membrane, with the most compact structure, showed the largest entropic selectivity for CO 2 /CH 4 , O 2 /N 2 , and N 2 /CH 4 as about 7.40, 4.24, and 2.17 respectively.
A previously reported polyimide, 6FDA/DETDA:DABA(3:2), was pyrolyzed under different protocols to produce carbon molecular sieve (CMS) dense film membranes for separation of important gas pairs, including pure gases CO 2 /CH 4 , O 2 /N 2 and mixture gases 50% CO 2 /50% CH 4 and 50% C 3 H 6 /50% C 3 H 8. This study investigated the effects of pyrolysis temperature, O 2 doping, and precrosslinking on the separation performance of 6FDA/DETDA:DABA(3:2) CMS membranes. Comparing to the precursor membranes, separation performance of all 6FDA/DETDA:DABA(3:2) CMS membranes improves significantly with both higher permeability and selectivity. The CMS film pyrolyzed with a novel method, i.e., 800 o C with precrosslinking, shows very attractive separation performance with CO 2 and O 2 permeability of 4678 Barrer and 683 Barrer, CO 2 /CH 4 , O 2 /N 2 selectivity of 71.5 and 8.0. Sorption measurements provide insight into the pore size distributions among these CMS membranes. The effects of these three parameters during pyrolysis on the CMS membranes gas separation performance are
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