Fluorinated copolyimide membranes for sour mixed‐gas upgrading

Abstract

Three random and two block 4,4 0 -(hexafluoroisopropylidene)diphthalic anhydride (6FDA)-based copolyimides with different 6FpDA:Durene molar ratio varying from 25 to 80% were prepared and characterized. The pure-gas permeation data of their membranes were investigated at 100 psi and 22 C. The CO 2 /CH 4 ideal selectivity coefficient increased to around 47 with the increase of the 6FpDA content to 80% in the copolymer backbone while the CO 2 permeability coefficient found to be the highest (378 barrer) with highest Durene content copolymer. Based on its attractive pure-gas permeation properties(CO 2 /CH 4 = 47), 6FDA-6FpDA/6FDA-Durene (4:1) block copolyimide was selected for further analyses, where the effect of pressure and temperature on its gas transport properties was evaluated. Furthermore, the mixed-gas permeation properties were investigated using multicomponent sweet and sour gas mixtures prepared from N 2 (30% or 10%), CH 4 (59%), C 2 H 6 (1%), CO 2 (10%), and H 2 S (0% or 20%)accordingly. The sweet mixed-gas CO 2 /CH 4 selectivity and CO 2 permeability coefficients of 6FDA-6FpDA/6FDA-Durene (4:1) are around 39 and 45 barrer, respectively, at elevated pressure (800 psi). The polymer, however, showed nonideal behavior when subjected to high H 2 S-content gas mixture (20 vol. % H 2 S), where the CO 2 /CH 4 selectivity value dropped to around 21 and the H 2 S/CH 4 selectivity coefficient is 13. The CO 2 and H 2 S permeability coefficients are 42 and 26 barrer, respectively, at an upstream pressure up to 500 psi. When plotted on the combined acid gas permeability-selectivity curve, the polymer separation efficiency was nearby the high-performing polymers reported in the literature, and way superior to the industrial standard glassy polymer, cellulose acetate, used currently in gas separation.

Molecular Design of Poly(imide–oxadiazole) Membranes for High-Pressure Mixed-Gas Separation

“…Chain rigidity could affect the chain packing density within the membrane matrix, which in turn might affect the membrane performance during gas separation . All measured T g values were greater than 360 °C, similar to the T g values of several polyimides studied previously in our group. ,,, …”

“…CO 2 permeability–CO 2 /CH 4 selectivity relationship chart depicting the pure-gas permeation performance of poly­(imide–oxadiazole) membranes compared to those of previously reported materials. Literature data refs − .…”

Unprecedented Sour Mixed-Gas Permeation Properties of Fluorinated Polyazole-Based Membranes

“…(a) Column chart comparison of sour mixed-gas permeation performance of POz-CF 3 and FPT-Ph­(OH) membranes at 700 psi and 22 ° C. (b) Column chart comparison of sweet and sour mixed-gas permeation performance of POz-CF 3 and FPT-Ph­(OH) membranes at 500 psi and 22 ° C. (c) Sour mixed-gas plot to compare the H 2 S separation ability of prepared polymeric membranes to some reported membranes performances in the literature: CA, 6FDA-DAM, PIM-6FDA–OH, 6FDA-TPA­( t -Bu), TEG-6FDA-DAM:DABA (3:2), 6FDA-Durene/CARDO (1:3), 6FDA-Durene/MDEA (1:3), and 6FDA-6FpDA/6FDA-Durene (4:1) …”

“…are limited by their modest performance. Compared to the massive works on CO 2 /CH 4 application, only few studies have aimed at the development of membrane materials for removal of natural sour gas components due to safety concerns and regulations when dealing with the highly toxic H 2 S. − The aforementioned barriers made the literature for H 2 S removal studies extremely stingy and not reflecting the real aggressivity in terms of H 2 S percentage and feed pressure. − …”

Molecularly Engineered 6FDA‐Based Polyimide Membranes for Sour Natural Gas Separation

“…A recent study demonstrated that the glassy 6FDA‐DAM polyimide membrane exhibited an even better H 2 S and CO 2 co‐removal efficiency than most reported rubbery polymer membranes under high pressure sour natural gas feeds (>46 bar). Recently, Hayek et al . have developed 6FDA‐based copolyimide membranes with different 6FpDA:Durene molar ratios and investigated their separation performance under sour natural gas feeds with different H 2 S concentrations.…”