284193 TR Polymers for Olefin/Paraffin Separation

Tuesday, October 30, 2012: 5:15 PM
403 (Convention Center )
Zachary P. Smith1, David F. Sanders1, Ruilan Guo2, Benny Freeman1, Donald R. Paul1 and James E. McGrath3, (1)Department of Chemical Engineering, The University of Texas at Austin, Austin, TX, (2)The University of Notre Dame, Notre Dame, IN, (3)Chemistry, Virginia Tech, Blacksburg, VA

Ethylene and propylene are currently the two largest, by volume, organic chemical feedstocks produced in the U.S [1].  These olefins must be purified for polyolefin synthesis by separating ethylene from ethane and propylene from propane, a thermally intensive process that requires approximately 0.12 Quads of energy per year and distillation columns containing nearly 200 trays [2].  This study focuses on determining the performance and plasticization resistance for a thermally rearranged (TR) polymer for olefin/paraffin separation. 

Polyimides containing reactive functional groups ortho-position to the diamine can be chemically transformed into TR polymers at elevated temperatures [3].  For this study, a polyimide was prepared from 3,3'-dihydroxy-4,4'-diamino-biphenyl (HAB) and 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) via chemical, thermal, and solid-state imidization [4, 5].  Chemical imidization produces polyimides with ortho-functional acetate groups, while thermal and solid-state imidization produce polyimides with ortho-functional hydroxyl groups.  Furthermore, each imidization technique alters the non-equilibrium nature of the polymer film, thus producing polyimides with unique transport properties.  All films were characterized by 1HNMR, DSC, FT-IR, TGA-MS, and pure gas permeation.

For ethylene, ethane, propylene, and propane, increasing polyimide conversion dramatically increased gas permeation.  For example, partial conversion of the chemically imidized HAB-6FDA polyimide to its corresponding TR polymer increased ethylene permeability by over two orders of magnitude.  Furthermore, ethylene/ethane selectivity decreased by less than 10%.  For ethylene/ethane and propylene/propane separation, HAB-6FDA TR polymers showed combinations of permeability and selectivity near the polymer upper bound [6, 7].  Propylene plasticization pressure curves were determined for TR polymers derived from all three synthesis routes, and the thermally imidized TR polymer had the highest plasticization pressure point of approximately 4 bar at 35°C.

1.         Facts & Figures: Output Declines in U.S., Europe, in Chemical & Engineering News. 2010. 54-62.

2.         Eldrige, R.B., Olefin/paraffin separation technology: A review. Industrial & Engineering Chemistry Research, 1993. 32(10), 2208-2212.

3.         Park, H.B., C.H. Jung, Y.M. Lee, A.J. Hill, S.J. Pas, S.T. Mudie, E. Van Wagner, B.D. Freeman, and D.J. Cookson, Polymers with cavities tuned for fast selective transport of small molecules and ions. Science, 2007. 318(5848), 254-258.

4.         Ghosh, M.K. and K.L. Mital, Polyimides: Fundamentals and applications. 1996, New York: Marcel.

5.         Ohya, H., V.V. Kudryavtsev, and S.I. Semenova, Polyimide membranes: Applications, fabrications, and properties. 1996, Amsterdam: Gordon and Breach Publishers.

6.         Burns, R.L. and W.J. Koros, Defining the challenges for C3H6/C3H8 separation using polymeric membranes. Journal of Membrane Science, 2003. 211(2), 299-309.

7.         Staudt-Bickel, C. and W.J. Koros, Olefin/paraffin gas separations with 6FDA-based polyimide membranes. Journal of Membrane Science, 2000. 170(2), 205-214.

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