Influence of Diffusivity and Sorption on Helium and Hydrogen Separations in Hydrocarbon, Silicon, and Fluorocarbon-Based Polymers

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• 作者：Zachary P. Smith ; Rajkiran R. Tiwari ; Michelle E. Dose ; Kristofer L. Gleason ; Thomas M. Murphy ; David F. Sanders ; Gabriella Gunawan ; Lloyd M. Robeson ; Donald R. Paul ; Benny D. Freeman
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：May 13, 2014
• 年：2014
• 卷：47
• 期：9
• 页码：3170-3184
• 全文大小：753K
• 年卷期：v.47,no.9(May 13, 2014)
• ISSN：1520-5835

文摘

The permeability鈥搒electivity upper bounds show that perfluoropolymers have uniquely different separation characteristics than hydrocarbon-based polymers. For separating helium from hydrogen, these differences are particularly dramatic. At a given helium permeability, the upper bound defined by perfluoropolymers has helium/hydrogen selectivities that are 2.5 times higher than that of the upper bound defined by hydrocarbon-based polymers. Robeson hypothesized that these differences in transport properties resulted from the unusual sorption relationships of gases in perfluoropolymers compared to hydrocarbon-based polymers, and this paper seeks to test this hypothesis experimentally. To do so, the gas permeability, sorption, and diffusion coefficients were determined at 35 掳C for hydrogen and helium in a series of hydrocarbon-, silicon-, and fluorocarbon-based polymers. Highly or completely fluorinated polymers have separation characteristics above the upper-bound for helium/hydrogen separation because they maintain good diffusivity selectivities for helium over hydrogen and they have helium/hydrogen sorption selectivities much closer to unity than those of hydrocarbon-based samples. The silicon-based polymer had intermediate sorption selectivities between those of hydrocarbon-based polymers and perfluoropolymers. Comparisons of hydrogen and helium sorption data in the literature more broadly extend the conclusion that helium/hydrogen sorption selectivity is rather different in hydrocarbon and fluorocarbon-based media.