Fluorinated copolyimide membranes for sour mixed‐gas upgrading

ABSTRACT Three random and two block 4,4′‐(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 CO2/CH4 ideal selectivity coefficient increased to around 47 with the increase of the 6FpDA content to 80% in the copolymer backbone while the CO2 permeability coefficient found to be the highest (378 barrer) with highest Durene content copolymer. Based on its attractive pure‐gas permeation properties(CO2/CH4 = 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 N2 (30% or 10%), CH4 (59%), C2H6 (1%), CO2 (10%), and H2S (0% or 20%)accordingly. The sweet mixed‐gas CO2/CH4 selectivity and CO2 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 H2S‐content gas mixture (20 vol. % H2S), where the CO2/CH4 selectivity value dropped to around 21 and the H2S/CH4 selectivity coefficient is 13. The CO2 and H2S 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. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48336.