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

Abstract

The effect of hydroxyl functionalization on the m-phenylene diamine moiety of 6FDA dianhydride-based polyimides was investigated for gas separation applications. Pure-gas permeability coefficients of He, H 2 , N 2 , O 2 , CH 4 , and CO 2 were measured at 35 °C and 2 atm.The introduction of hydroxyl groups in the diamine moiety of 6FDA-diaminophenol (DAP) and 6FDA-diamino resorcinol (DAR) polyimides tightened the overall polymer structure due to increased charge transfer complex formation compared to unfunctionalized 6FDA-m-phenylene diamine (mPDA). The BET surface areas based on nitrogen adsorption of 6FDA-DAP (54 m 2 g -1 )and of 6FDA-DAR (45 m 2 g -1 ) were ~18% and 32% lower than that of 6FDA-mPDA (66 m 2 g -1 ).6FDA-mPDA had a pure-gas CO 2 permeability of 14 Barrer and CO 2 /CH 4 selectivity of 70. The hydroxyl-functionalized polyimides 6FDA-DAP and 6FDA-DAR exhibited very high pure-gas CO 2 /CH 4 selectivities of 92 and 94 with moderate CO 2 permeability of 11 and 8 Barrer, respectively. It was demonstrated that hydroxyl-containing polyimide membranes maintained very high CO 2 /CH 4 selectivity (~ 75 at CO 2 partial pressure of 10 atm) due to CO 2 plasticization resistance when tested under high-pressure mixed-gas conditions. Functionalization with hydroxyl groups may thus be a promising strategy towards attaining highly selective polyimides for economical membrane-based natural gas sweetening.

High-performance intrinsically microporous dihydroxyl-functionalized triptycene-based polyimide for natural gas separation

“…The solubility coefficient of carbon dioxide in dihydroxylfunctionalized TPDA-DAR was 12% higher than that of TPDA-mPDA. This finding is in agreement with previous work, which showed that the introduction of hydroxyl groups into 6FDA-based polyimide membranes increased the solubility of CO 2 [42,53]. More importantly, however, is the decrease in diffusion coefficients and increase in diffusion selectivity in the TPDA-DAR polyimide due to hydroxyl functionalization; for example, the CO 2 diffusion coefficient decreased by 45% from 6.95 to 3.84 x 10 -8 cm 2 s -1 .…”

“…ACCEPTED MANUSCRIPT [42,58]. As expected, the increase in selectivity was coupled with a 38% decrease in CO 2 permeability from 349 barrers to 215 barrers.…”

“…2 shows the emission spectra (400 nm excitation) for TPDA-mPDA and TPDA-DAR films. For dihydroxylfunctionalized TPDA-DAR a strong intensity peak was observed at 607 nm, clearly indicating CTC formation, which is typically formed between the nucleophilic five-member rings and electrophilic six-member rings in polyimides [42,[53][54][55][56]. The fluorescence intensity of the TPDA-mPDA polyimide showed essentially no indication of CTC formation, as shown in Fig.…”

Nanocellulose-based membranes for CO2 capture

“…Unfortunately, differently from what observed for the latter materials, MFC-Lup membranes show a selectivity that decreases when the RH exceeds 50 %, leading to a worsening of the general separation performance. This fact seems once again related to the effect of water on the materials transport properties: plasticization and swelling, are indeed known to decrease membrane selectivity as they increases to a bigger extent the diffusion coefficient of the gases with larger kinetic diameters[58][59][60][61]. The CO 2 /N 2 or CO 2 /CH 4 separation factor of many glassy polymers, for example, is reported to be negatively affected by the presence of CO 2 concentrations able to swell the membrane matrix[23,60,61], so that ideal selectivity results are much higher than the one measured under real conditions, when both the gaseous penetrants are present within the membrane matrix.…”

“…This fact seems once again related to the effect of water on the materials transport properties: plasticization and swelling, are indeed known to decrease membrane selectivity as they increases to a bigger extent the diffusion coefficient of the gases with larger kinetic diameters[58][59][60][61]. The CO 2 /N 2 or CO 2 /CH 4 separation factor of many glassy polymers, for example, is reported to be negatively affected by the presence of CO 2 concentrations able to swell the membrane matrix[23,60,61], so that ideal selectivity results are much higher than the one measured under real conditions, when both the gaseous penetrants are present within the membrane matrix. It should be noticed however that, in the present case, water plasticization effects, are far more important than that induced by the incondensable penetrants, so that present ideal selectivity values should remain almost unchanged also in case of mixed gas experiments performed at similar RH.Figure 10.…”