Improvement of CO2/CH4 separation characteristics of polyimides by chemical crosslinking |
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| Institution: | 1. Angewandte Thermodynamik, Physikalisch-Chemisches Institut, Universität Heidelberg Im Neuenheimer Feld 253D-69120 HeidelbergGermany;2. Department of Chemical Engineering, The University of TexasAustin, TX 78758USA;1. Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 133-791, Republic of Korea;2. College of Chemistry and Chemical Engineering, Hunan University of Arts and Science, Changde, Hunan 415000, PR China;3. State Key Laboratory of Engines, School of Mechanical Engineering, Tianjin University, Tianjin 300072, PR China;1. King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering Division (BESE), Advanced Membranes and Porous Materials Center, Thuwal, 23955-6900, Saudi Arabia;2. King Abdullah University of Science and Technology (KAUST), Physical Science and. Engineering Division (PSE), Advanced Membranes and Porous Materials Center, Thuwal, 23955-6900, Saudi Arabia;3. King Abdullah University of Science and Technology (KAUST), Core Labs, Thuwal, 23955-6900, Saudi Arabia;1. Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA;2. Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA;3. The Commonwealth Scientific and Industrial Research Organization (CSIRO) Manufacturing, Private Bag 10, Clayton, South Victoria 3169, Australia |
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| Abstract: | Uncrosslinked and crosslinked polyimides and copolyimides have been synthesized in order to increase selectivity without an unacceptable loss in permeability. The goal was to reduce undesirable effects caused by CO2 induced swelling in CO2/CH4 separation processes by stabilizing the polyimide structure with crosslinks. In the polymerization reaction 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride) was used as dianhydride monomer and mPD (m-phenylene diamine) and DABA (diamino benzoic acid) were used as diamine monomers. With copolyimides containing strong polar carboxylic acid groups (i.e. 6 FDA–mPD/DABA 9:1) reduced plasticization was seen up to a pure CO2 feed pressure of 14 atm, presumably due to hydrogen bonding between the carboxylic acid groups. By chemical crosslinking of the free carboxylic acid groups of the 6FDA–mPD/DABA 9:1 with ethylene glycol, the swelling effects due to CO2 can be reduced at least up to a pure CO2 feed pressure of 35 atm. With increasing degree of crosslinking, increasing CO2/CH4 selectivity was found because of reduced swelling and polymer chain mobility. By using ethylene glycol as a crosslinking agent, CO2 permeability was not significantly lowered because the reduced chain mobility was compensated by the additional free volume caused by the crosslinks. |
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