High-Performance Polyimide Gas Separation Membranes Based on Triptycene Dianhydrides and Di-Hydroxy-Diamino-Triptycene Monomers.
AuthorsAlqahtani, Abdulaziz Q.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Permanent link to this recordhttp://hdl.handle.net/10754/652826
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AbstractDistillation technology involves capital- and energy-intensive processes for light olefin/paraffin separation. Global demand for propylene has already exceeded 110 million tons per year. Therefore, distillation processes used for the separation of C3H6/C3H8 should be replaced or debottlenecked with more efficient and cost-effective technology. In the last three decades, membrane-based gas separation processes have successfully emerged, thus competing with conventional separation processes. Membranes potentially offer lower capital investment and operation cost than distillation columns. In this study, the use of advanced membrane materials for C3H6/C3H8 separation was investigated. Three novel triptycene-based polyimides were synthesized by Dr. Bader Ghanem from one diamine monomer, namely 2,6-dihydroxy-3,7-diaminotriptycene (DTA1-OH), and three dianhydride monomers, (i) non-substituted triptycene tetracarboxylic dianhydride (TDA), (ii) 9,10-dimethyltriptycene tetracarboxylic dianhydride (TDA1) and (iii) 9,10-iso-propyltriptycene tetracarboxylic dianhydride (TDAi3). It is important to note that polyimide membranes based on triptycene dianhydrides and triptycene diamines have never been reported in the literature before. Pure-gas permeability coefficients of He, H2, N2, O2, CO2, CH4, C3H6, and C3H8 were determined at 2 bar and 35 °C. Furthermore, C3H6 and C3H8 gas sorption isotherms were measured by gravimetric techniques, and experimental data were collected up to 7 bar at 35 °C. TDA-DAT1-OH, TDA1-DAT1-OH, TDAi3-DAT1-OH exhibited C3H6 permeability of 12.1, 16.6, and 5.64 Barrer with pure-gas C3H6/C3H8 selectivity of 35.7, 29.6, and 32.8 respectively. These properties exceeded the 2003 pure-gas upper bound for C3H6/C3H8. The BET surface area increased in the order of TDA-DAT1-OH (437 m2/g) < TDAi3-DAT1-OH (467 m2/g) < TDA1-DAT1-OH (557 m2/g). The frecational free volume (FFV) increased in the order of TDAi3-DAT1-OH (0.25) < TDA-DAT1-OH (0.28) < TDA1-DAT1-OH (0.30). TDA1-DAT1-OH (109 μm) showed less and slower physical aging than TDA-DAT1-OH (94 μm) after 60 days, where the O2 and CO2 permeability of both polyimides decreased by about 40% and 69%, respectively. After 30 days, TDAi3-DAT1-OH displayed the highest selectivity gain relative to its counterparts and exceeded the 2008 upper bound for CO2/CH4. TDA1-DAT1-OH exhibited 7-fold higher C3H6 permeability coupled with almost 3-fold higher C3H6/C3H8 selectivity relative to a previously reported commercial polyphenylene oxide (PPO) membrane.