Gas separation properties of 6FDA-based polyimide membranes with a polar group

Abstract

6FDA-based polyimides were prepared from the thermal imidization reaction of 6FDA with diamines of BAPAF, DAP, and DABA having a polar group of hydroxyl or carboxyl. Properties of the dense polyimide membranes were characterized and their gas permeation properties for H 2 , CO 2 , O 2 , N 2 , and CH 4 were investigated. Permeabilities, diffusion coefficients and diffusivity selectivities of polar group-containing polyimide membranes including 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA polymer for the gases did not change largely. The separation properties of 6FDA-TrMPD polyimide membrane used as a reference polymer were compared with those of the polyimide membranes mentioned above. It was found that the polyimides of 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA, which were soluble in alcohol or/and 2-methoxyethanol, could be applicable to the preparation of a dense composite membrane by dip-coating method.

Effects of hydroxyl-functionalization and sub-T thermal annealing on high pressure pure- and mixed-gas CO2/CH4 separation by polyimide membranes based on 6FDA and triptycene-containing dianhydrides

“…However, a glass transition was observed for the 6FDA-APAF (Fig. S7) around 315 1C as previously reported [25]. Because of differences in polarity, the polymers were cast from the solvents indicated in Table 2 into self-standing and transparent isotropic films 40-60 μm in thickness.…”

“…For example, substituting acetyl with hydroxyl moieties in cellulose acetate suppressed any pressure-dependent increase in pure-gas CO 2 permeability, which was attributed to the replacement of weak acetyl-acetyl interactions with stronger hydroxyl-hydroxyl inter-chain hydrogen bonding that better resists matrix dilations [23]. Hydroxyl-and carboxyl-functionalization of low-free-volume polyimides [24][25][26][27] and high-free-volume poly(diphenylacetylenes) [28] as well as tetrazole- [29] and amidoxime- [30] functionalization of microporous PIM-1 resulted in outstanding combinations of CO 2 permeabilities and CO 2 /CH 4 selectivities, significantly surpassing the performance of commercial Matrimid and CA membranes. The studies on PIM-1 specifically highlight the potential for the "open" structures of PIM-PIs to retain higher CO 2 permeability than lowfree-volume polyimides along with high CO 2 /CH 4 selectivity even upon strengthening of inter-chain interactions (e.g., CTCs, hydrogen bonding).…”

Pure- and mixed-gas permeation properties of highly selective and plasticization resistant hydroxyl-diamine-based 6FDA polyimides for CO2/CH4 separation

“…For example, 4,4-(hexafluoroisopropylidene) diphthalic anhydride-2,4-diaminophenol (6FDA-DAP) and 4,4-(hexafluoroisopropylidene) diphthalic anhydride-4,6-diamino resorcinol (6FDA-DAR) showed pure-gas CO 2 /CH 4 selectivities of 94 and 75, respectively, combined with moderate CO 2 permeability of about 8 Barrer. Other groups later reported similar promising results with a variety of hydroxyl-diamine-based 6FDA polyimides [33][34][35][36]. A recent paper by Comesaña-Gándara et al re-investigated the pure-gas permeation properties of 6FDA-DAP and 6FDA-DAR and their polybenzoxazole derivatives formed by thermal rearrangement as well as their nonfunctionalized counterpart polyimide (6FDA-mPDA) [37].…”

“…In this application, glassy polymeric membranes are used exclusively due to their good gas separation and mechanical properties as well as their solution processability for the production of either asymmetric or thin-film composite membranes [5][6][7][8]. The most commonly used commercial membrane materials for CO 2 removal from natural gas are based on cellulose diacetate, triacetate or blends thereof, which have pure-gas selectivity values of about [32][33][34][35] coupled with CO 2 permeability of 1.84 to 6.56 Barrer at 1 atm and 35 °C (1 Barrer = 10 -10 cm3(STP)·cm/cm 2 ·s·cmHg) depending on the degree of acetylation [9]. However, under highpressure, mixed-gas conditions, the CO 2 /CH 4 selectivity often drops to less than 15 making the process economics only marginally acceptable due to excessive methane loss [10,11].…”

Synthesis, Characterization and Gas Separation Properties of Polyimides Containing Fluorene Units

“…Since the first report of the membrane-based separation concept by Graham in 1866 [1] , membranes have been developed and utilized on an industrial scale for air separation, hydrogen recovery, and hydrocarbon/light gas separation. An advantage of polymeric composite membranes is that their gas permeability and selectivity can be controlled by the combination of various polymer components [2,3] . Among the various membrane materials used for gas separation application, aromatic polyimides are a class of high-performance materials.…”