Carbon molecular sieve dense film membranes derived from Matrimid® for ethylene/ethane separation
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AbstractDevelopment of dense film carbon molecular sieve (CMS) membranes for ethylene/ethane (C 2H 4/C 2H 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 2H 4 and C 2H 6 permeation at 35 °C, 50 psia feed pressure. The effects on C 2H 4/C 2H 6 separation caused by different final vacuum pyrolysis temperatures from 500 to 800 °C are reported. For all pyrolysis temperatures separation surpassed the estimated 'upper bound' solution processable polymer line for C 2H 4 permeability vs. C 2H 4/C 2H 6 selectivity. C 2H 4 permeability decreased and selectivity increased with increasing pyrolysis temperature until 650-675 °C where an optimum combination of C 2H 4 permeability ∼14-15 Barrer with C 2H 4/C 2H 6 selectivity ∼12 was observed. A modified heating rate protocol for 675 °C showed further increase in permeability with no selectivity loss. CMS films produced from argon pyrolysis showed results comparable to vacuum pyrolysis. Further, mixed gas (63.2 mol% C 2H 4 + 36.8 mol% C 2H 6) permeation showed a slightly lower C 2H 4 permeability with C 2H 4/C 2H 6 selectivity increase rather than a decrease that is often seen with polymers. The high selectivity of these membranes was shown to arise from a high 'entropic selection' indicating that the 'slimmer' ethylene molecule has significant advantage over ethane in passing through the rigid 'slit-shaped' CMS pore structure. © 2011 Elsevier Ltd. All rights reserved.
CitationRungta M, Xu L, Koros WJ (2012) Carbon molecular sieve dense film membranes derived from Matrimid® for ethylene/ethane separation. Carbon 50: 1488–1502. Available: http://dx.doi.org/10.1016/j.carbon.2011.11.019.
SponsorsThe authors thank The Dow Chemical Company for funding this work. The authors especially thank Mark Brayden, Marcos Martinez and Duncan Coffey for helpful discussions and comments regarding this work. The authors also acknowledge additional support provided by King Abdullah University of Science and Technology (KAUST).