Abstract
In this study, based on the preparation of hexaazatriphenylene-ternary-anhydride (HAT-T), polyimide membranes were prepared by reaction of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′-diaminodiphenyl sulfide (SDA), 2,2′-bis (trifluoromethyl)diaminobiphenyl (TFDB) and 5-amino-2-(4-aminophenyl) benzimidazole (PABZ). Polyimide films with a hexazobenzo structure have good film-forming properties, high molecular weight (Mn = 0.79–11.79 × 106, Mw = 1.03–16.60 × 106) and narrow molecular weight distribution (polymer dispersity index = 1.17–1.54). With the introduction of rigid HAT-T, the tensile strength and elongation at break of polyimide films are 195.63–510.37 MPa and 4.00–9.70%, respectively, with excellent mechanical properties. The gas separation performance test shows that hexaazatriphenylene-containing polyimide films have good gas selectivity for CO2/CH4. In particular, the separation performance of PIc-t (6FDA/PABZ/HAT-T) surpasses the “2008 Robeson Upper Bound”. The selectivity of 188.43 for CO2/CH4 gas reveals its potential value in the separation and purification of methane gas.
Highlights
Compared with other separation processes, membrane separation has the advantages of energy saving, less investment, easy installation, light weight, no pollution and easy-toadjust operation [1,2,3,4]
For PI membranes, we found that the high rigidity and large free volume structure in the membrane are conducive to good gas separation performance
The results show that the rigid PI with hexaazatriphenylene structure introduced by ternary anhydride is easy to prepare but is a potential gas separation membrane material
Summary
Compared with other separation processes, membrane separation has the advantages of energy saving, less investment, easy installation, light weight, no pollution and easy-toadjust operation [1,2,3,4]. Rigid structures in PIs can be obtained by monomer design or by crosslinking PIs to form networks The two methods both lead to a decrease in gas penetration flux. Some researchers have used the combination of rigid and twisted structures to increase the free volume while reducing the activity of the segment These molecular structures can achieve the goal of increasing both the permeable flux and the gas selectivity [20,21,22,23]. The results show that the rigid PI with hexaazatriphenylene structure introduced by ternary anhydride is easy to prepare but is a potential gas separation membrane material. HCBHAT (0.625 g, 23.8 mmol) was added to 30 mL acetic anhydride, protected by N2, stirred at 115 ◦C for 1 h, cooled to room temperature, vacuum rotary evaporated to remove the solvent and recrystallized with acetonitrile/benzene
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