Experimental Mixed-Gas Permeability, Sorption and Diffusion of CO2-CH4 Mixtures in 6FDA-mPDA Polyimide Membrane: Unveiling the Effect of Competitive Sorption on Permeability Selectivity

Abstract

The nonideal behavior of polymeric membranes during separation of gas mixtures can be quantified via the solution-diffusion theory from experimental mixed-gas solubility and permeability coefficients. In this study, CO2-CH4 mixtures were sorbed at 35 °C in 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA)-m-phenylenediamine (mPDA)—a polyimide of remarkable performance. The existence of a linear trend for all data of mixed-gas CO2 versus CH4 solubility coefficients—regardless of mixture concentration—was observed for 6FDA-mPDA and other polymeric films; the slope of this trend was identified as the ratio of gas solubilities at infinite dilution. The CO2/CH4 mixed-gas solubility selectivity of 6FDA-mPDA and previously reported polymers was higher than the equimolar pure-gas value and increased with pressure from the infinite dilution value. The analysis of CO2-CH4 mixed-gas concentration-averaged effective diffusion coefficients of equimolar feeds showed that CO2 diffusivity was not affected by CH4. Our data indicate that the decrease of CO2/CH4 mixed-gas diffusion, and permeability selectivity from the pure-gas values, resulted from an increase in the methane diffusion coefficient in mixtures. This effect was the result of an alteration of the size sieving properties of 6FDA-mPDA as a consequence of CO2 presence in the 6FDA-mPDA film matrix.

Sorption-enhanced mixed-gas transport in amine functionalized polymers of intrinsic microporosity (PIMs)

“…3a and S6. This modeling approach has demonstrated good agreement with experimental mixed-gas sorption for PIM-1, TZ-PIM, PTMSP, 6FDA-HAB and its TR450 analog, 6FDA-mPDA, CTA, and PMMA 20,22,24,25,30,52,76 . Thermodynamically rigorous models such as the nonequilibrium lattice fluid (NELF) 77 model would provide more robust mixed-gas predictions 24,78 , but lattice fluid parameters (i.e., , ) cannot be directly determined for * * , * the PIMs studied in this work because the polymers degrade below their glass transition temperature 79,80 .…”

Plasticization-Resistant Carboxyl-Functionalized 6FDA-Polyimide of Intrinsic Microporosity (PIM–PI) for Membrane-Based Gas Separation

“…38 When we tested these PIM-PI polymers using a 50:50 molar CO 2 -CH 4 mixture, the permeability vs. partial pressure behavior was preserved; in addition, we found that for both polymers over the entire pressure range, CO 2 and CH 4 mixed-gas permeabilities were lower than the corresponding pure-gas values ( Figure selectivity is predominant and lowers the CO 2 /CH 4 mixed-gas permeability selectivity of a polymer membrane material relative to its respective pure-gas value. [41][42][43] However, some polymers that can better resist CO 2 -induced plasticization demonstrated CO 2 /CH 4 mixture permselectivity matching or even slightly outperforming their respective pure-gas values. 16,25 This is also the case for 6FDA-TrMCA and 6FDA-TrMPD, (Figure 10), some hydroxyl-functionalized polyimides and their thermally rearranged derivatives such as 6FDA-HAB 44 and TDA1-APAF 45 .…”

“…Furthermore, it is important to consider the polymer matrix plasticization capability of CO 2 in mixed-gas environment. In fact, the presence of CO 2 locally dilates the glassy polymer matrix, thereby enhances the methane diffusion coefficient leading to faster CH 4 diffusion in mixed-gas conditions than obtained in pure-gas tests [41][42][43]. Thus, CO 2 -induced plasticization depresses the diffusion selectivity of glassy polymers; this counteracts with the fact that solubility selectivities of CO 2 -CH 4 mixtures are higher than those obtained under ideal pure-gas conditions -as demonstrated and quantified in several examples [41][42][43].…”

Synthesis and Gas-Permeation Characterization of a Novel High-Surface Area Polyamide Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene: Towards Polyamides of Intrinsic Microporosity (PIM-PAs)

“…Contrarily to the just described permeation behavior of CO 2 in the mixture, CH 4 mixed-gas permeability of both 6FBBA-TMDAT and CA increased with partial pressure. Experimental studies on CO 2 –CH 4 pure- and mixed-gas permeability, sorption and diffusion in glassy polyimide and rubbery polydimethylsiloxane membranes [ 66 , 67 ] showed that this CH 4 permeability enhancement is directly correlated to CO 2 sorption; i.e., increasing CO 2 content in the polymer matrix activates chain mobility thus boosting CH 4 diffusion coefficient. Hence, the occurrence of this phenomenon explains the decrease in CO 2 /CH 4 permselectivity under mixed-gas conditions in both 6FBBA-TMDAT and CA ( Figure 11 c).…”