Aromatic co-polyimide gas separation membranes derived from 6FDA-6FpDA-type homo-polyimides

Abstract

Co-polyimide membranes for separating components of sour natural gas including at least three distinct moieties polymerized together, the moieties including a 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) based moiety; a 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) based moiety; and at least one component selected from the group consisting of: a 9,9-bis(4-aminophenyl) fluorene (CARDO) based moiety; a 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene diamine) based moiety; a 2,2′-bis(trifluoromethyl)benzidine (ABL-21) based moiety; a 3,3′-dihydroxybenzidine based moiety; and a 3,3′-(hexafluoroisopropylidene)dianiline based moiety.

Claims

1. A membrane for separating the components of a sour natural gas feed, the membrane comprising: at least three distinct moieties polymerized together, the moieties including a 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) based moiety; a 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) based moiety; and at least one component selected from the group consisting of: a 9,9-bis(4-aminophenyl) fluorene (CARDO) based moiety; a 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene diamine) based moiety; a 2,2′-bis(trifluoromethyl)benzidine (ABL-21) based moiety; a 3,3′-dihydroxybenzidine based moiety; and a 3,3′-(hexafluoroisopropylidene)dianiline based moiety, wherein the molar ratio of the 6FpDA based moiety to the at least one component selected from the group is between about 3:1 and about 1:3 to control segmental moiety variation in transport properties of the membrane including permeability and selectivity to target performance suitable for acid gas separations and helium recovery in industrial natural gas applications.

2. The membrane according to claim 1, where the membrane comprises random co-polymers.

3. The membrane according to claim 2, where the membrane comprises the CARDO based moiety.

4. The membrane according to claim 3, where the molar ratio of the CARDO based moiety to the 6FpDA based moiety is between about 1:3 to about 3:1.

5. The membrane according to claim 2, where the membrane comprises the durene diamine based moiety.

6. The membrane according to claim 5, where the molar ratio of the durene diamine based moiety to the 6FpDA based moiety is between about 1:3 to about 3:1.

7. The membrane according to claim 1, where the membrane comprises block co-polymers.

8. The membrane according to claim 7, where the membrane comprises the CARDO based moiety.

9. The membrane according to claim 7, where the membrane comprises the durene diamine based moiety.

10. The membrane according to claim 9, where the block co-polymers include a polymer block length L of the 6FDA and the durene diamine based moiety, and include a polymer block length M of the 6FDA and the 6FpDA based moiety, and L is about between 1,000-20,000 units and M is about between 1,000-20,000 units.

11. The membrane according to claim 10, where the block ratio of L:M is between about 1:1 and about 1:4.

12. The membrane according to claim 10, where L is about 2,500 units and M is about 2,500 units.

13. The membrane according to claim 10, where L is about 5,000 units and M is about 5,000 units.

14. The membrane according to claim 10, where L is about 15,000 units and M is about 15,000 units.

15. A method of gas separation, the method comprising the step of: applying the membrane of claim 1 to separate at least 2 components of a mixed gas stream.

16. The method according to claim 15, where feed pressure of the mixed gas stream to a feed side of the membrane is up to about 800 psig and H.sub.2S content of the mixed gas stream is up to about 20 volume percent.

17. The method according to claim 15, where the mixed gas stream comprises CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6, and H.sub.2S.

18. A method for making a membrane for separating components of a sour natural gas feed, the method comprising the steps of: combining at least three different monomers to form a co-polyimide, the monomers including 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA); 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA); and at least one component selected from the group consisting of: 9,9-bis(4-aminophenyl) fluorene (CARDO); a 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene diamine); 2,2′-bis(trifluoromethyl)benzidine (ABL-21); 3,3′-dihydroxybenzidine; and 3,3′-(hexafluoroisopropylidene)dianiline, wherein the molar ratio of the 6FpDA based moiety to the at least one component selected from the group is between about 3:1 and about 1:3 to control segmental moiety variation in transport properties of the membrane including permeability and selectivity to target performance suitable for acid gas separations and helium recovery in industrial natural gas applications; and preparing a dense film from the co-polyimide using a solution casting process.

19. The method of gas separation, the method comprising the step of: using the dense film of claim 18 to separate at least 2 components of a mixed gas stream.

20. The method according to claim 18, where the step of combining is carried out to create random co-polymers.

21. The method according to claim 20, where the step of combining includes combining the 6FDA, the 6FpDA, and the CARDO.

22. The method according to claim 21, where the molar ratio of the CARDO to the 6FpDA is between about 1:3 to about 3:1.

23. The method according to claim 20, where the step of combining includes combining the 6FDA, the 6FpDA, and the durene diamine.

24. The method according to claim 23, where the molar ratio of the durene diamine to the 6FpDA is between about 1:3 to about 3:1.

25. The method according to claim 18, where the step of combining is carried out to create block co-polymers.

26. The method according to claim 25, where the step of combining includes combining the 6FDA, the 6FpDA, and the CARDO.

27. The method according to claim 25, where the step of combining includes combining the 6FDA, the 6FpDA, and the durene diamine.

28. The method according to claim 25, where the block co-polymers include a polymer block length L of the 6FDA and the durene diamine and include a polymer block length M of the 6FDA and the 6FpDA, and L is between about 1,000-20,000 units and M is between about 1,000-20,000 units.

29. The method according to claim 28, where the block ratio of L:M is between about 1:1 and about 1:4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 is a reaction scheme for the production of a random or block copolymer from 6FDA, 6FpDA, and durene diamine.

(3) FIG. 2 is a reaction scheme for the production of a random copolymer from 6FDA, 6FpDA, and CARDO.

(4) FIG. 3A shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA) as a model spectrum for the exemplified co-polyimides.

(5) FIG. 3B shows an enlarged portion from FIG. 3A for the .sup.1H NMR spectrum of random co-polyimide 6FDA-durene/6FpDA (1:1) as a model spectrum for the exemplified co-polyimides.

(6) FIG. 3C shows the molecule characterized by the analysis of FIGS. 3A and 3B. The reference letters in FIG. 3C correspond to the identification peaks shown in FIGS. 3A and 3B.

(7) FIG. 4A shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) as a model spectrum for the exemplified co-polyimides.

(8) FIG. 4B shows an enlarged portion from FIG. 4A for the .sup.1H NMR spectrum of random co-polyimide 6FDA-CARDO/6FpDA (1:3) as a model spectrum for the exemplified co-polyimides.

(9) FIG. 4C shows the molecule characterized by the analysis of FIGS. 4A and 4B. The moiety references in FIG. 4C correspond to the identification peaks shown in FIG. 4B.

(10) FIG. 5 shows Fourier-transform infrared spectroscopy (FTIR) spectra of prepared co-polyimides: (I) 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA); (II) 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA); (III) 6FDA-durene/6FpDA (3:1) (millimoles durene diamine:millimoles 6FpDA); (IV) block (6FDA-durene)/(6FDA-6FpDA) (1:1); and (V) block (6FDA-durene)/(6FDA-6FpDA) (1:4).

(11) FIG. 6 shows FTIR spectra of prepared co-polyimides: (VI) 6FDA-CARDO/6FpDA (1:1) (millimoles CARDO:millimoles 6FpDA); (VII) 6FDA-CARDO/6FpDA (3:1) (millimoles CARDO:millimoles 6FpDA; and (VIII) 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA).

(12) FIG. 7A shows overlapping thermogravimetric analysis (TGA) curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides.

(13) FIG. 7B shows overlapping derivative TGA curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides.

(14) FIG. 8A shows overlapping TGA curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides.

(15) FIG. 8B shows overlapping derivative TGA curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides.

(16) FIG. 9 shows a differential scanning calorimetry (DSC) trace graph for the prepared co-polyimides of 6FDA-durene/6FpDA.

(17) FIG. 10 shows a DSC trace graph for the prepared co-polyimides of 6FDA-CARDO/6FpDA.

(18) FIG. 11 shows the .sup.1H NMR spectrum of block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:1).

(19) FIG. 12 shows the .sup.1H NMR spectrum of block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4).

DETAILED DESCRIPTION

(20) So that the manner in which the features and advantages of the embodiments of apparatus, systems, and methods for 6FDA-6FpDA homo-polyimide-based co-polyimide membranes for sour gas feed separations from natural gas, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the various embodiments, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

(21) The present disclosure exemplifies co-polyimide membranes useful for acid gas separations and helium recovery. In order to enhance separation performance and optimize co-polyimides for gas separations, chemical modifications can be made, which include substitution of other pertinent moieties and bulky functional groups in the co-polyimide backbone. These modification steps can significantly improve the performance of co-polyimide membranes. Thus, the development of aromatic co-polyimides can be considered from other monomers with and without, or in the absence of, crosslinking.

(22) Transport properties of pure gases and gas mixtures through dense polymeric membranes are governed by the solution-diffusion mechanism. According to this model, gas permeation follows a three-step process, which is gas dissolution in the upstream side of the membrane, diffusion down a concentration gradient through the membrane, and desorption from the downstream side of the membrane. From this, the volumetric (molar) flux of a component i, J.sub.i, through the membrane is given by equation (1)

(23) $\begin{array}{cc}{J}_i=\frac{D_i{S}_i\left(p_i\left(o\right)-p_{i\left(l\right)}\right)}{l}=\frac{P_i\left(p_i\left(o\right)-p_{i\left(l\right)}\right)}{l}& \mathrm{Eq}.\left(1\right)\end{array}$

(24) where l is membrane thickness [cm], p.sub.i(o) is the partial pressure of component i at the feed side of the membrane, p.sub.i(l) is the partial pressure of component i at permeate side, D.sub.i is the diffusion coefficient [cm.sup.2/s], S.sub.i is the solubility coefficient [cm.sup.3 (STP) of penetrant gas/cm.sup.3 of polymer per pressure]. The product of diffusion and solubility coefficients (D.sub.i S.sub.i) is called the membrane permeability of component i, P.sub.i, which indicates the ability of a membrane to permeate gases based on their membrane solubility and diffusivity differences. Barrer is the conventional unit of permeability, where 1 Barrer=10.sup.−10 (cm.sup.3(STP)×cm)/(cm.sup.2×s×cmHg).

(25) The pure gas permeability coefficient, especially at low pressures, can be calculated using equation 2.

(26) $\begin{array}{cc}{P}_i=D_i{S}_i=\frac{j_i.Math.l}{p_i\left(o\right)-p_{i\left(l\right)}}& \mathrm{Eq}.\left(2\right)\end{array}$

(27) The permeability coefficient of each gas component in the gas mixture, especially at low pressures, can be determined from the equation 3.

(28) $\begin{array}{cc}{P}_i=\frac{x_{i\left(l\right)}{J}_i.Math.l}{\left(P_f{x}_{i\left(o\right)}-P_p{x}_{i\left(l\right)}\right)}& \mathrm{Eq}.\left(3\right)\end{array}$

(29) where x.sub.i(0) and x.sub.i(1) are the mole fractions of the gas components in the feed and permeate streams respectively, J.sub.i is the volumetric (molar) flux of a component i (cm.sup.3/(cm.sup.2×s)), and p.sub.f and p.sub.p are the pressures (cmHg absolute) on the feed and permeate side of the membrane respectively.

(30) The ability of the membrane to separate two components is called the ideal selectivity or permselectivity, α.sub.ij, which is represented by the ratio of permeability of the more permeable component i to that of the less permeable component j through the membrane as shown in equation (4).

(31) $\begin{array}{cc}{\alpha }_{ij}=\frac{P_i}{P_j}=\frac{S_i}{S_j}\times \frac{D_i}{D_j}& \mathrm{Eq}.\left(4\right)\end{array}$

(32) where

(33) $\frac{s_i}{s_j}\mathrm{and}\frac{D_i}{D_j}$
and are the solubility selectivity and diffusivity selectivity of two gases, respectively. These terms represent the relative solubility and mobility of two gases in the membrane.

(34) In a gas mixture, however, the separation factor, α.sup.m.sub.i/j, is often used, which is typically used to measure separation efficiency and this is conventionally given as equation (5):

(35) $\begin{array}{cc}{\alpha }_{i/j}^m=\frac{x_{i\left(l\right)}/x_{j\left(l\right)}}{x_{i\left(o\right)}/x_{j\left(o\right)}}& \mathrm{Eq}.\left(5\right)\end{array}$

(36) where x.sub.i(0) and x.sub.i(1) are the mole fractions of the gas component i in the feed and permeate streams respectively; and x.sub.j(0) and x.sub.j(1) are the mole fractions of the gas component j in the feed and permeate streams respectively. For non-ideal gas mixtures, however, a more appropriate alternative measure of permselectivity is used to reflect the properties of the membrane material, ∝.sub.i/j.sup.m,*. This permselectivity is the ratio of the mixed gas permeabilities of components i and j, as determined using the fugacity driving force definition of permeability. Thus

(37) $\begin{array}{cc}{\propto }_{i/j}^{m,*}=\frac{P_i^{*}}{P_j^{*}}& \mathrm{Eq}.\left(6\right)\end{array}$

(38) where P.sub.i* and P.sub.j* are the mixed gas fugacity-based permeabilities of component i and j. Equation (6) is used in this study to calculate the permselectivity of each component in the gas mixtures. The permeation properties of gases through dense polymeric membranes are also affected by variation in operating temperatures and its influence can be described by Van't Hoff-Arrhenius equation as given below in equation (7).

(39) $\begin{array}{cc}P=P_0\exp \left(\frac{-E_p}{RT}\right)& \mathrm{Eq}.\left(7\right)\end{array}$

(40) P.sub.0 is the pre-exponential factor [Barrer], R is the universal gas constant [8.314×10.sup.−3 kJ/(mol×K)], T is the absolute temperature [K], and E.sub.p is the activation energy of permeation [kJ/mol].

(41) Embodiments of the disclosure show the preparation of aromatic co-polyimide membranes derived from 6FDA-6FpDA homo-polyimide and other monomers, such as durene and CARDO moieties. In addition, physical and gas transport properties of the membranes are examined by investigating separations of pure and mixed gas streams consisting of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6, He and H.sub.2S through the dense films of the co-polyimides 6FDA-durene/6FpDA and 6FDA-CARDO/6FpDA for simultaneous separation of CO.sub.2, N.sub.2, He and H.sub.2S from natural gas streams.

(42) Example 1 shows synthesis of certain random and block co-polyimides from 6FDA, 6FpDA, and durene diamine. Example 2 shows synthesis of certain random co-polyimides from 6FDA, 6FpDA, and CARDO. Examples 3-5 test the properties of these random and block co-polyimides acting as membranes for aggressive natural gas separation. Table 3 for example shows high permeability and selectivity of the membranes for non-methane components of a natural gas stream.

(43) The following examples are given for the purpose of illustrating embodiments of the invention, however, it is to be understood that these examples are merely illustrative in nature, and that the embodiments of the present invention are not necessarily limited thereto.

Example 1: Preparation of Aromatic Co-Polyimide Random 6FDA-Durene/6FpDA and Block (6FDA-Durene)/(6FDA-6FpDA)

(44) Series of random and block aromatic co-polyimides comprising 6FDA, durene diamine, and 6FpDA based-moieties (see for example FIG. 1) were synthesized according to the following procedures from 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) (also known as 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride) (obtained from Alfa Aesar); 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene diamine) (obtained from TCI America); and 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA) (obtained from TCI America). Solvents used included methanol (obtained from ThermoFisher Scientific) and m-cresol (obtained from Alfa Aesar). All the chemicals and the solvents used in the experiments discussed here were used as received without any further purification. In block co-polyimides of the present disclosure block length (l)/(m) in FIG. 1 can be about between (1,000-20,000)/(1,000-20,000), and a block ratio of l:m can be between about 4:1 to about 1:4, for example about 1:1.

(45) A random co-polyimide 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA) (I) was synthesized as follows: In a 100-mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer, durene diamine (1.849 g, 11.26 mmol); 6FpDA (3.76 g, 11.26 mmol); and 6FDA (10.0 g, 22.51 mmol) were dissolved in m-cresol (19.00 ml). The mixture was heated at 180° C. for 8 hours (see FIG. 1). The volume was kept constant at 19.00 ml with m-cresol during the course of the reaction. The resulting viscous solution was poured into methanol (400 mL). The solid polymer obtained was stirred in methanol overnight, then filtered and dried partially. The washing process was repeated twice (2×400 mL of methanol). A final white off-solid product 6FDA-durene/6FpDA (14.38 g, 10.69 mmol, 95% yield) was filtered off then dried under reduced pressure at 150° C. for two days. Characterization resulted in the following: δ.sub.H (500 MHz, CDCl.sub.3) 8.10-8.06 (4H, m, ArH.sub.6FDA), 7.98 (6H, br s, ArH.sub.6FDA), 7.89 (2H, br d, J=7.45 Hz, ArH.sub.6FDA), 7.60 (4H, d, J=6.87 Hz, ArH.sub.6FpDA), 7.54 (4H, d, J=8.02 Hz, ArH.sub.6FpDA), 2.13 (12H, s, —CH.sub.3durene).

(46) A random co-polyimide 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA) (II) was synthesized as follows: A similar procedure for preparing co-polyimide (I) was employed using the following starting materials and amounts: durene diamine (0.819 g, 4.99 mmol), 6FpDA (5.00 g, 14.96 mmol), and 6FDA (8.86 g, 19.94 mmol) in m-cresol (19.00 ml). The final product 6FDA-durene/6FpDA (1:3) (II) (12.61 g, 9.37 mmol, 94% yield) was obtained as a white off-solid product. Characterization of the product resulted in the following: δ.sub.H (500 MHz, CDCl.sub.3) 8.10-8.06 (3H, m, ArH.sub.6FDA), 7.98 (3H, br s, ArH.sub.6FDA), 7.89 (2H, br d, J=7.45 Hz, ArH.sub.6FDA), 7.60 (4H, d, J=8.02 Hz, ArH.sub.6FpDA), 7.54 (4H, d, J=8.59 Hz, ArH.sub.6FpDA), 2.12 (4H, s, —CH.sub.3durene).

(47) A random co-polyimide 6FDA-durene/6FpDA (3:1) (millimoles durene diamine:millimoles 6FpDA) (III) was synthesized as follows: A similar procedure for preparing co-polyimide (I) was employed using the following starting materials and amounts: durene diamine (2.77 g, 16.88 mmol), 6FpDA (1.881 g, 5.63 mmol) and 6FDA (10.0 g, 22.51 mmol) m-cresol (19.00 ml). The final product 6FDA-durene/6FpDA (3:1) (III) (14.38 g, 10.69 mmol, 95% yield) was obtained as a white off-solid product. Characterization of the product resulted in the following: δ.sub.H (500 MHz, CDCl.sub.3) 8.09-8.05 (8H, m, ArH.sub.6FDA), 7.98-7.96 (14H, m, ArH.sub.6FDA), 7.89 (2H, br d, J=7.45 Hz, ArH.sub.6FDA), 7.60 (4H, d, J=7.45 Hz, ArH.sub.6FpDA), 7.55 (4H, d, J=8.02 Hz, ArH.sub.6FpDA), 2.13 (36H, s, —CH.sub.3durene).

(48) A block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:1) (IV) was synthesized as follows: In a 100 mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer, 6FpDA (5.01 g, 15.00 mmol) was dissolved in m-cresol (13.00 ml), then 6FDA (5.66 g, 12.74 mmol) was added with m-cresol (12.00 ml). The mixture was heated at 180° C. for 8 hours. The amount of m-cresol was kept constant during the course of the reaction. Later, the mixture was cooled to room temperature and durene diamine (2.76 g, 16.83 mmol), 6FDA (8.48 g, 19.09 mmol), and m-cresol (25.00 ml) were added. The mixture was heated again at 180° C. during 8 hours. The amount of m-cresol was kept constant during the course of the reaction. While still hot, the resulting viscous solution was poured into 400 mL of methanol in thin fibers/powder. The solid was stirred in methanol overnight. This procedure was repeated twice (2×400 mL methanol) over two days. Finally, the white off-solid product was filtered and dried at 150° C. under vacuum for two days to afford the final product block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (21.50 g, 15.99 mmol, 95% yield). Characterization of the product resulted in the following: δ.sub.H (500 MHz, CDCl.sub.3) 8.09-8.06 (4H, m, ArH.sub.6FDA), 7.97 (6H, br s, ArH.sub.6FDA), 7.89 (2H, br d, J=7.45 Hz, ArH.sub.6FDA), 7.60 (4H, d, J=8.02 Hz, ArH.sub.6FpDA), 7.54 (4H, d, J=8.54 Hz, ArH.sub.6FpDA), 2.13 (12H, s, —CH.sub.3durene).

(49) A block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) (V) was synthesized as follows: A similar procedure for preparing co-polyimide (IV) was employed using the following starting materials and amounts: 6FpDA (4.3 g, 12.86 mmol) and 6FDA (5.44 g, 12.24 mmol) were mixed in m-cresol (11.00 mL and 10.00 mL, respectively). Then, durene diamine (0.703 g, 4.28 mmol) and 6FDA (2.150 g, 4.84 mmol) were mixed in m-cresol (25.00 ml). The final product (6FDA-durene)/(6FDA-6FpDA) (1:4) (V) (11.67 g, 0.583 mmol, 95% yield) was obtained as a white off-solid product. The product was characterized as follows: δ.sub.H (500 MHz, CDCl.sub.3) 8.07 (3H, d, J=8.02 Hz, ArH.sub.6FDA), 7.97 (3H, s, ArH.sub.6FDA), 7.89 (2H, d, J=7.45 Hz, ArH.sub.6FDA), 7.60 (4H, d, J=8.02 Hz, ArH.sub.6FpDA), 7.53 (4H, d, J=8.59 Hz, ArH.sub.6FpDA), 2.13 (3H, s, —CH.sub.3durene).

Example 2: Preparation of Aromatic Random Co-Polyimide 6FDA-CARDO/6FpDA

(50) Series of random aromatic 6FDA-CARDO/6FpDA co-polyimides (see for example FIG. 2) were synthesized according to the following procedures from 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) (also known as 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride) (obtained from Alfa Aesar); 9,9-bis(4-aminophenyl) fluorene (CARDO) (obtained from TCI America); and 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA) (obtained from TCI America). The solvents used included methanol (ThermoFisher Scientific) and m-cresol (Alfa Aesar). All the chemicals and the solvents used in this work were used as received without any further purification.

(51) A random co-polyimide 6FDA-CARDO/6FpDA (1:1) (millimoles CARDO:millimoles 6FpDA) (VI) was synthesized according to the following: In a 100-mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer, 6FpDA (1.500 g, 4.49 mmol), CARDO (1.564 g, 4.49 mmol), and 6FDA (3.99 g, 8.98 mmol) were suspended in m-cresol (21 ml). The reaction mixture was heated at 180° C. for 8 hours. The amount of m-cresol was kept constant during the course of the reaction. The resulting viscous solution was poured into methanol (400 mL). The solid polymer obtained was stirred in methanol overnight, then filtered and dried partially. This washing process was repeated twice (2×400 mL of methanol). The final white off-solid product 6FDA-6FpDA/CARDO (1:1) (6.52 g, 4.26 mmol, 95% yield) was filtered off then dried under reduced pressure at 150° C. for two days. The product was characterized as follows: δ.sub.H (500 MHz, CDCl.sub.3) 8.07-7.82 (12H, m, ArH.sub.6FDA), 7.79 (2H, d, J=7.79 Hz, ArH.sub.CARDO), 7.60-7.53 (8H, AB system, J=7.59 Hz, ArH.sub.6FDA), 7.45 (2H, d, J=7.45 Hz, ArH.sub.CARDO), 7.39-7.30 (12H, m, ArH.sub.CARDO).

(52) A random co-polyimide 6FDA-CARDO/6FpDA (3:1) (millimoles CARDO:millimoles 6FpDA) (VII) was synthesized as follows: A similar procedure for preparing co-polyimide (VI) was employed using the following starting materials and amounts: 6FpDA (1.000 g, 2.99 mmol), CARDO (3.13 g, 8.98 mmol), and 6FDA (5.32 g, 11.97 mmol) in m-cresol (28.00 ml). The final product 6FDA-CARDO/6FpDA (3:1) (VII) (8.69 g, 5.68 mmol, 95% yield) was obtained as a white off-solid product. The product was characterized as follows: δ.sub.H (500 MHz, CDCl.sub.3) 8.05-7.82 (8H, m, ArH.sub.6FDA), 7.78 (2H, d, J=7.79 Hz, ArH.sub.CARDO), 7.60-7.52 (2.69H, AB system, J=7.59 Hz, ArH.sub.6FDA), 7.45 (2H, d, J=7.45 Hz, ArH.sub.CARDO), 7.38-7.29 (12H, m, ArH.sub.CARDO).

(53) A random co-polyimide 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) (VIII) was synthesized as follows: A similar procedure for preparing co-polyimide (VI) was employed using the following starting materials and amounts: 6FpDA (4.32 g, 12.91 mmol), CARDO (1.500 g, 4.30 mmol), and 6FDA (7.65 g, 17.22 mmol) in m-cresol (40.00 ml). The final product 6FDA-CARDO/6FpDA (1:3) (VIII) (12.76 g, 8.34 mmol, 97% yield) was obtained as a white off-solid product. The product was characterized as follows: δ.sub.H (500 MHz, CDCl.sub.3) 8.07-7.84 (8H, m, ArH.sub.6FDA), 7.78 (0.67H, d, J=7.79 Hz, ArH.sub.CARDO), 7.60-7.53 (8H, AB system, J=7.59 Hz, ArH.sub.6FDA), 7.45 (0.67H, d, J=7.45 Hz, ArH.sub.CARDO), 7.39-7.30 (4H, m, ArH.sub.CARDO).

(54) The chemical structures of the prepared co-polyimides were confirmed by .sup.1H nuclear magnetic resonance (NMR) analysis in deuterated chloroform (CDCl.sub.3). FIG. 3A shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA) as a model spectrum for the exemplified co-polyimides. FIG. 3B shows an enlarged portion from FIG. 3A for the .sup.1H NMR spectrum of random co-polyimide 6FDA-durene/6FpDA (1:1) as a model spectrum for the exemplified co-polyimides. FIG. 3C shows the co-polyimide molecule characterized by the analysis of FIGS. 3A and 3B. The reference letters in FIG. 3C correspond to the identification peaks shown in FIGS. 3A and 3B. The spectrum shows the presence of the corresponding peaks of 6FpDA (a and b), 6FDA (c, d, and e) and durene (f).

(55) FIG. 4A shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) as a model spectrum for the exemplified co-polyimides. FIG. 4B shows an enlarged portion from FIG. 4A for the .sup.1H NMR spectrum of random co-polyimide 6FDA-CARDO/6FpDA (1:3) as a model spectrum for the exemplified co-polyimides. FIG. 4C shows the molecule characterized by the analysis of FIGS. 4A and 4B. The moiety references in FIG. 4C correspond to the identification peaks shown in FIG. 4B. The .sup.1H NMR spectrum of this co-polymer confirms the 1:3 molar ratio of CARDO:6FpDA through the signal integration of their corresponding signals. For a sum of 8 protons corresponding to the 6FpDA hydrogen atoms it was found a sum of around 5.3 protons corresponding to the CARDO hydrogen atoms which represents one third of the 16 protons found in a CARDO moiety.

(56) FIG. 11 shows the .sup.1H NMR spectrum of block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:1). FIG. 12 shows the .sup.1H NMR spectrum of block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4). The block ratios were confirmed by the corresponding .sup.1H NMR in deuterated chloroform. For the (6FDA-durene)/(6FDA-6FpDA) ratio of (1:1), the signal integration of aromatic protons of 6FpDA shown at 7.61 to 7.53 ppm and the aliphatic protons of duene shown at 2.13 ppm correspond to 8 and 12 protons, respectively. However, for the (6FDA-durene)/(6FDA-6FpDA) ratio of (1:4), the signal integration corresponding to 6FpDA and durene are 8 and 3 protons, respectively.

(57) The complete one-step imidization and the structure of the prepared co-polyimides could be confirmed from their Fourier-transform infrared spectroscopy (FTIR) spectra depicted in FIGS. 5 and 6. FIG. 5 shows Fourier-transform infrared spectroscopy (FTIR) spectra of prepared co-polyimides: (I) 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA); (II) 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA); (III) 6FDA-durene/6FpDA (3:1) (millimoles durene diamine:millimoles 6FpDA); (IV) block (6FDA-durene)/(6FDA-6FpDA) (1:1); and (V) block (6FDA-durene)/(6FDA-6FpDA) (1:4). FIG. 6 shows FTIR spectra of prepared co-polyimides: (VI) 6FDA-CARDO/6FpDA (1:1) (millimoles CARDO:millimoles 6FpDA); (VII) 6FDA-CARDO/6FpDA (3:1) (millimoles CARDO:millimoles 6FpDA; and (VIII) 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA). The complete imidization is confirmed from the absence of any peaks that correspond to the intermediate species which contains amide functional groups (3500-3100 cm.sup.−1 and 1700-1650 cm.sup.−1).

(58) Thermogravimetric analysis was used to study the thermal stability of the prepared co-polyimides. FIG. 7A shows overlapping thermogravimetric analysis (TGA) curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides. FIG. 7B shows overlapping derivative TGA curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides. The reference numerals of FIGS. 7A and 7B correspond as follows: (I) random 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA); (II) random 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA); (III) random 6FDA-durene/6FpDA (3:1) (millimoles durene diamine:millimoles 6FpDA); (IV) block (6FDA-durene)/(6FDA-6FpDA) (1:1); and (V) block (6FDA-durene)/(6FDA-6FpDA) (1:4).

(59) FIG. 8A shows overlapping thermogravimetric analysis (TGA) curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides. FIG. 8B shows overlapping derivative TGA curves obtained for certain synthesized polymers of the present disclosure, used to study the thermal stability of the prepared co-polyimides. The reference numerals of FIGS. 8A and 8B correspond as follows: (VI) 6FDA-CARDO/6FpDA (1:1) (millimoles CARDO:millimoles 6FpDA); (VII) 6FDA-CARDO/6FpDA (3:1) (millimoles CARDO:millimoles 6FpDA); and (VIII) 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA).

(60) FIGS. 7A-B and 8A-B show typical TGA curves obtained for the synthesized polymers. The temperatures (Td) at 5% weight loss in nitrogen are shown in Tables 1 and 6 for the 6FDA-durene/6FpDA and 6FDA-CARDO/6FpDA co-polyimides, respectively. The results show that all synthesized co-polyimides have a highly-performing, surprising, and unexpected thermal stability of about at least 500° C.

(61) The differential scanning calorimetry (DSC) traces for the prepared co-polyimides were recorded. FIG. 9 shows a differential scanning calorimetry (DSC) trace graph for the prepared co-polyimides of 6FDA-durene/6FpDA. FIG. 10 shows a DSC trace graph for the prepared co-polyimides of 6FDA-CARDO/6FpDA. FIG. 9 reference numerals correspond as follows: (I) random 6FDA-durene/6FpDA (1:1) (millimoles durene diamine:millimoles 6FpDA); (II) random 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA); (III) random 6FDA-durene/6FpDA (3:1) (millimoles durene diamine:millimoles 6FpDA); (IV) block (6FDA-durene)/(6FDA-6FpDA) (1:1); and (V) (6FDA-durene)/(6FDA-6FpDA) (1:4). FIG. 10 reference numerals correspond as follows: (VI) random 6FDA-CARDO/6FpDA (1:1) (millimoles CARDO:millimoles 6FpDA); (VII) random 6FDA-CARDO/6FpDA (3:1) (millimoles CARDO:millimoles 6FpDA); and (VIII) 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA).

(62) The DSC traces were recorded within a temperature range between 30° C. and 450° C. at a rate of 10° C./min. The glass transition temperature (T.sub.g) of the synthesized polymers are also shown in Tables 1 and 6 for the copolymers respectively. T.sub.g is an indicator of the cooperative motion of polymeric chains and the presence of a single glass transition temperature indicates that there is no phase separation in both random and block co-polyimide types.

(63) The density values of the prepared co-polyimides were measured using a Mettler Toledo XPE205 balance equipped with a density kit using cyclohexane as the buoyant solvent. The density values reported in Table 6 for the two copolymers are the average values of at least five different measurements, with error values (standard deviation) below 2%. These density values were used to calculate the fractional free volume (FFV) (depicted in Tables 1 and 6) of the co-polyimide membranes using a group contribution method.

(64) The molar mass distribution profiles of the 6FDA-durene/6FpDA co-polyimides were determined by gel permeation chromatography (GPC). Using a cirrus GPC data analysis tool, a calibration plot was obtained from the polystyrene standards. The peak average molecular weight (Mp), the number average molecular weight (Mn), the weight average molecular weight (Mw) and polydispersity index (PDI) values of the polymers were interpolated from the calibration plot and are presented in Table 2.

(65) The co-polyimide dense film membranes were prepared as follows: Dense films were prepared by a solution casting method. A 2-3 wt. % polymer solution was prepared in chloroform or dimethyl formamide (DMF) and the solution filtered through a 0.45 μm filter. The solution was then cast onto a dry clean Petri dish and left to evaporate at room temperature under a clean nitrogen enriched environment overnight in the case of a membrane made using chloroform. Embodiments of the dense film membranes here are dense flat sheets, and do not include or are operable in the absence of asymmetric hollow fiber membranes.

(66) The film was then slowly heated in an oven under a slow nitrogen flow to about 60° C. for about 24 hours. However in the case of membranes made using DMF, the solution, covered with perforated aluminum foil, was left in the oven at 70° C. under a clean nitrogen enriched environment for about 24 hours. After being dried completely, the resulting film was finally dried in a vacuum oven at 150° C. overnight to remove any residual solvent, and then, the membranes were cooled to room temperature and peeled off from Petri dish after soaking in deionized water for about 15 mins. The membrane was then dried at ambient temperature under a clean nitrogen environment for about 8 hours to remove any residual water.

Example 3: Evaluation of the CO.SUB.2./CH.SUB.4., He/CH.SUB.4., and N.SUB.2./CH.SUB.4 .Pure Gas Separation Performance of 6FDA-Durene/6FpDA and 6FDA-CARDO/6FpDA Membranes Prepared in Examples 1 and 2

(67) The permeability coefficients of pure gases including He, CO.sub.2, CH.sub.4, and N.sub.2 and ideal selectivities of gas pairs including He/CH.sub.4, N.sub.2/CH.sub.4, and CO.sub.2/CH.sub.4 through the series of co-polyimide 6FDA-durene/6FpDA and 6FDA-CARDO/6FpDA membranes were measured and calculated at an upstream pressure of up to 300 psig and at 35° C. Results are shown in Tables 3-4 and Tables 7-8 for the two copolymers, respectively. The permeation properties of all penetrant gases depicted are an average of at least two or more measurements, and error in permeability coefficients is less than +5% of the values shown.

(68) For the random co-polyimides, the content of 6FpDA in the copolymers was varied from 25% to 75% (3:1 to 1:3) in order to investigate the effect of segmental moiety variation in transport properties of the copolymers. As can be observed in Tables 3 and 7, all the penetrants permeabilities decrease, while the selectivities, especially CO.sub.2/CH.sub.4 and He/CH.sub.4 increase, as the 6FpDA moiety content increases in the copolymers (i.e., 3:1 to 1:3) (millimoles durene diamine:millimoles 6FpDA). The pure gas permeability values of about 100 and 165 Barrers for CO.sub.2 and He, respectively and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of about 36 and 59, respectively obtained for the random copolymer 6FDA-durene/6FpDA (1:3) (millimoles durene diamine:millimoles 6FpDA) with the highest content of 6FpDA moiety (75%) are substantially similar to target performance being sought for acid gas separations and helium recovery in industrial natural gas applications. Similar separation performance was obtained for the random copolymer 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) with the highest content of 6FpDA moiety (75%), as the permeability values of about 80 and about 110 Barrers for CO.sub.2 and He, respectively, and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of about 42 and 58, respectively, were obtained (see Table 7).

(69) For the multi block co-polyimides, the block ratio was varied from 1:1 to 1:4 in order to see effect of this variation in permeation properties of the copolymers. As can be observed, all the penetrants permeabilities decrease, while the selectivities, especially CO.sub.2/CH.sub.4 and He/CH.sub.4 increase as the block ratio increases. Surprising, unexpected, and advantageous values of CO.sub.2 and He permeabilities of about 65 and 125 Barrers, respectively, and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of about 47 and about 91, respectively, were obtained for a block copolymer (6FDA-durene)/(6FDA-6FpDA) (1:4) (Table 3). These values and separation performance exhibited by the co-polyimides are advantageous as compared to the values obtained in some of the high performance polymeric membranes that have been reported in the literature.

(70) As shown in Tables 4 and 8 for the block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) and random co-polyimide 6FDA-CARDO/6FpDA (1:3) membranes, pure gas permeability coefficients of most of the penetrants that include He, CO.sub.2, CH.sub.4 and N.sub.2 stay relatively constant or slightly increases (especially CO.sub.2) with increase in feed pressure of up to 300 psig. The membranes also showed almost constant or slight increase (especially CO.sub.2/CH.sub.4) in most of the penetrants selectivities with respect to CH.sub.4 as depicted in the tables.

(71) Furthermore, in addition to being selective to both CO.sub.2 and He, these co-polyimides are also selective to N.sub.2 as compared to methane and thus could simultaneously permeate both acid gas and N.sub.2, while keeping methane in the high-pressure feed stream.

Example 4: Evaluation of the CO.SUB.2./CH.SUB.4.; N.SUB.2./CH.SUB.4.; and C.SUB.2.H.SUB.6./CH.SUB.4 .Mixed Gas Separation Performance of 6FDA-Durene/6FpDA and 6FDA-CARDO/6FpDA Membranes Prepared in Examples 1 and 2

(72) The permeability properties of quaternary gas mixtures consisting of 10, 59, 30, and 1 volume % CO.sub.2, CH.sub.4, N.sub.2 and C.sub.2H.sub.6, respectively, through the co-polyimide membranes were studied at different upstream pressures and are summarized in Tables 5 and 9 for block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) and random co-polyimide 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) membranes, respectively. CO.sub.2 permeability and CO.sub.2/CH.sub.4 selectivity reduced to about 45 Barrers and about 39, respectively for block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) and about 35 Barrers and about 35, respectively for random co-polyimide 6FDA-CARDO/6FpDA (1:3) (millimoles CARDO:millimoles 6FpDA) membranes at an elevated pressure of 800 psig. These values are quite advantageous at the elevated pressure of 800 psig.

Example 5: Evaluation of the CO.SUB.2./CH.SUB.4 .and H.SUB.2.S/CH.SUB.4 .Sour Mixed Gas Separation Performance of the Block (6FDA-Durene)/(6FDA-6FpDA) (1:4) and Random 6FDA-CARDO/6FpDA (1:3) Membranes Prepared in Examples 1 and 2

(73) The permeation properties of simulated sour gas mixtures consisting of 10, 57-59, 10, 1-3, and 20 volume % of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6 and H.sub.2S, respectively, through the membranes were studied at different gas feed pressures as shown in Tables 10-11. The CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities obtained for the block (6FDA-durene)/(6FDA-6FpDA) (1:4) are about 24 and about 14 respectively; while CO.sub.2 and H.sub.2S permeabilities are about 42 and about 24 Barrers, respectively (see Table 10).

(74) Similarly for the random co-polyimide 6FDA-CARDO/6FpDA (1:3), CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities are about 17.8 and about 17.9, respectively, while CO.sub.2 and H.sub.2S permeabilities are 37.9 and 38 Barrers, respectively (see Table 11). The values and separation performances exhibited by the co-polyimides are advantageous, surprising, and unexpected. One important point to note is that at moderate feed pressure and up to 20 vol. % H.sub.2S in the feed gas mixture, ideal selectivities and permeabilities are still moderate in the co-polyimides. Moreover, the CO.sub.2/CH.sub.4 selectivity of the co-polyimides does not degrade to anywhere near the same extent as was reported for cellulose acetate (CA), even under these much more aggressive environments. This stability at moderate pressures and high H.sub.2S concentration is surprising and unexpected. While not being bound to any theory or mechanism, the monomer moieties of the present disclosure when combined in random and block co-polyimides exhibit a synergistic effect allowing for increased permeabilities and selectivities for components such as CO.sub.2 and H.sub.2S not found in other materials.

(75) TABLE-US-00001 TABLE 1 Thermal and physical properties of the synthesized 6FDA-durene/6FpDA co-polyimides. T.sub.d at 5% weight loss (N.sub.2) T.sub.g density Co-polyimide Type (° C.) (° C.) (g/cm.sup.3) FFV 6FDA-durene/6FpDA (3:1) Random 505 398 1.3782 0.1743 (millimoles durene diamine:,illimoles 6FpDA) 6FDA-durene/6FpDA (1:1) Random 500 374 1.4063 0.1723 (millimoles durene diamine:millimoles 6FpDA) 6FDA-durene/6FpDA (1:3) Random 505 327 1.4317 0.1724 (millimoles durene diamine:millimoles 6FpDA) (6FDA-durene)/ Block 497 366 1.3777 0.1891 (6FDA-6FpDA) (1:1) (6FDA-durene)/ Block 507 339 1.4210 0.1838 (6FDA-6FpDA) (1:4)

(76) TABLE-US-00002 TABLE 2 The weight-average and number-average molecular weights, and PDI of the prepared 6FDA-durene/6FpDA co-polyimides. Co-polyimide Type Mw (g/mol) Mn (g/mol) PDI 6FDA-durene/6FpDA (3:1) Random 27736 10687 2.62 6FDA-durene/6FpDA (1:1) Random 31898 13675 2.34 6FDA-durene/6FpDA (1:3) Random 31556 12821 2.46 (6FDA-durene)/ Block 36212 14043 2.59 (6FDA-6FpDA) (1:1) (6FDA-durene)/ Block 44693 12712 3.53 (6FDA-6FpDA) (1:4)

(77) TABLE-US-00003 TABLE 3 Pure gas permeability and selectivity coefficients in the random and block co-polyimide 6FDA-durene/ 6FpDA membranes measured at 100 psi feed pressure and at 35° C. Permeability, Barrer Selectivity Co-polyimide Type N.sub.2 CH.sub.4 He CO.sub.2 N.sub.2/CH.sub.4 He/CH.sub.4 CO.sub.2/CH.sub.4 6FDA-durene/6FpDA Random 25.3 19.1 312 378 1.32 16.34 19.79 (3:1) 6FDA-durene/6FpDA Random 8.40 5.00 180 148 1.68 36.00 29.62 (1:1 ) 6FDA-durene/6FpDA Random 5.60 2.80 165 99.6 2.00 59.00 35.57 (1:3) (6FDA-durene)/ Block 11.7 7.25 211 206 1.61 29.10 28.41 (6FDA-6FpDA) (1:1) (6FDA-durene)/ Block 3.00 1.38 125 64.9 2.17 90.58 47.03 (6FDA-6FpDA) (1:4)

(78) TABLE-US-00004 TABLE 4 Pure gas permeation properties of block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) membranes at 35° C. Pressure Permeability (Barrer) Selectivity (psi) CO.sub.2 CH.sub.4 He N.sub.2 CO.sub.2/CH.sub.4 He/CH.sub.4 N.sub.2/CH.sub.4 100 64.90 1.38 125 3.00 47.03 90.6 2.17 200 67.46 1.35 123 3.24 49.88 90.8 2.40 300 73.21 1.32 123 3.29 55.26 93.0 2.49

(79) TABLE-US-00005 TABLE 5 Mixed gases permeability and selectivity coefficients in the block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) membrane as function of feed pressure at 22° C. using gas mixture containing 10; 59; 30 and 1 vol. % of CO.sub.2, CH.sub.4, N.sub.2 and C.sub.2H.sub.6 respectively. Pressure Permeability (Barrer) Ideal selectivity (psi) CO.sub.2 CH.sub.4 N.sub.2 C.sub.2H.sub.6 CO.sub.2/CH.sub.4 N.sub.2/CH.sub.4 C.sub.2H.sub.6/CH.sub.4 500 61.04 1.37 1.93 0.79 44.50 1.40 0.57 600 54.78 1.27 1.78 0.72 43.23 1.41 0.56 700 58.90 1.40 1.97 0.07 42.11 1.41 0.05 800 44.74 1.15 1.63 0.61 38.94 1.41 0.53

(80) TABLE-US-00006 TABLE 6 Thermal and physical properties of the synthesized 6FDA-CARDO/6FpDA co-polyimides. T.sub.d at 5% weight loss T.sub.g density Co-polyimide Type (N.sub.2) (° C.) (° C.) (g/cm.sup.3) FFV 6FDA-CARDO/6FpDA (3:1) Random 537 372 1.3669 0.1720 6FDA-CARDO/6FpDA (1:1) Random 528 349 1.4005 0.1707 6FDA-CARDO/6FpDA (1:3) Random 531 341 1.4189 0.1792

(81) TABLE-US-00007 TABLE 7 Pure gas permeability and selectivity coefficients in the random co-polyimide 6FDA-CARDO/6FpDA membranes measured at 100 psig feed pressure and at 35° C. Selectivity Permeability, Barrer N.sub.2/ He/ CO.sub.2/ Co-polyimide Type N.sub.2 CH.sub.4 He CO.sub.2 CH.sub.4 CH.sub.4 CH.sub.4 6FDA-CARDO/ Ran- 3.2 2.3 86.0 77.7 1.39 37.39 33.78 6FpDA (3:1) dom 6FDA-CARDO/ Ran- 1.8 1.1 74.4 38.5 1.66 69.53 35.93 6FpDA (1:1) dom 6FDA-CARDO/ Ran- 3.3 1.9 110 78.9 1.74 58.00 41.53 6FpDA (1:3) dom

(82) TABLE-US-00008 TABLE 8 Pure gas permeation properties of random co-polyimide 6FDA-CARDO/6FpDA (1:3) membranes at 35° C. Pressure Permeability (Barrer) Selectivity (psi) CO.sub.2 CH.sub.4 He N.sub.2 CO.sub.2/CH.sub.4 He/CH.sub.4 N.sub.2/CH.sub.4 100 78.90 1.90 110 3.30 41.53 57.89 1.74 200 81.95 1.96 101 3.41 41.80 51.29 1.74 300 84.32 1.87 101 3.27 45.09 54.05 1.75

(83) TABLE-US-00009 TABLE 9 Mixed gases permeability and selectivity coefficients in the random co-polyimide 6FDA-CARDO/6FpDA (1:3) membrane as a function of feed pressure at 22° C. using a gas mixture containing 10; 59; 30 and 1 vol. % of CO.sub.2, CH.sub.4, N.sub.2 and C.sub.2H.sub.6, respectively. Pressure Permeability (Barrer) Ideal selectivity (psi) CO.sub.2 CH.sub.4 N.sub.2 C.sub.2H.sub.6 CO.sub.2/CH.sub.4 N.sub.2/CH.sub.4 C.sub.2H.sub.6/CH.sub.4 300 47.73 1.06 1.65 0.68 44.89 1.55 0.64 400 43.41 0.92 1.41 0.57 47.11 1.53 0.62 500 39.82 0.92 1.37 0.57 43.45 1.50 0.62 600 40.07 0.98 1.45 0.60 41.07 1.48 0.61 800 35.23 1.00 1.48 0.58 35.12 1.47 0.58

(84) TABLE-US-00010 TABLE 10 Sour mixed gas permeability and selectivity coefficients in the block co-polyimide (6FDA-durene)/(6FDA-6FpDA) (1:4) membrane measured at 22° C. and using sour feed gas mixture containing 10; 59; 10; 1 and 20 vol. % of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6 and H.sub.2S respectively. H.sub.2S C.sub.2H.sub.6 Total feed comp. comp pressure Permeability (Barrer) Ideal selectivity vol. % vol. % (psig) N.sub.2 CH.sub.4 C.sub.2H.sub.6 CO.sub.2 H.sub.2S CO.sub.2/CH.sub.4 H.sub.2S/CH.sub.4 20.0 1.0 350 2.2 1.8 1.4 42.0 24.4 23.57 13.68 500 2.2 2.0 1.6 41.7 26.4 20.75 13.12

(85) TABLE-US-00011 TABLE 11 Sour mixed gas permeability and selectivity coefficients in the random co-polyimide 6FDA-CARDO/6FpDA (1:3) membrane measured at 22° C. and using sour feed gas mixture containing 10; 57; 10; 3 and 20 vol. % of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6 and H.sub.2S respectively. H.sub.2S Total Ideal comp. C.sub.2H.sub.6 feed selectivity vol. comp pressure Permeability (Barrer) CO.sub.2/ H.sub.2S/ % vol. % (psi) N.sub.2 CH.sub.4 C.sub.2H.sub.6 CO.sub.2 H.sub.2S CH.sub.4 CH.sub.4 20.0 3.0 400 3.1 2.1 2.0 37.9 38.0 17.83 17.88

(86) The present disclosure shows co-polyimide membranes suitable and advantageous for acid gas separation and helium recovery from natural gas using the newly-developed 6FDA-6FpDA-type aromatic co-polyimide membranes. The membranes exhibit surprising and unexpected pure and gas mixture permeation properties, as the pure gas CO.sub.2 and He permeabilities are about 65 and 125 Barrers, respectively and CO.sub.2/CH.sub.4 and He/CH4 selectivities are about 47 and 91, respectively obtained at 35° C. and feed pressure of 100 psi for the (6FDA-durene)/(6FDA-6FpDA) (1:4) block co-polyimide membrane.

(87) In addition, the random copolymer 6FDA-CARDO/6FpDA (1:3) exhibited advantageous, surprising, and unexpected separation performance as the pure gas permeability values of 79 and 110 Barrers for CO.sub.2 and He, respectively, and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of 42 and 58 were respectively obtained for the copolymer. Furthermore, the permeation properties of simulated sour gas mixtures consisting of 10; 57-59; 10; 1-3; and 20 vol. % of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6 and H.sub.2S respectively, through the membrane were studied at different gas feed pressures. The CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities obtained for the block (6FDA-durene)/(6FDA-6FpDA) (1:4) are 24 and 14 respectively; while CO.sub.2 and H.sub.2S permeabilities are 42 and 24 Barrers, respectively. Similarly for the random co-polyimide 6FDA-CARDO/6FpDA (1:3), CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities are 17.8 and 17.9 respectively, while CO.sub.2 and H.sub.2S permeabilities are 37.9 and 38 Barrers respectively.

(88) The values and separation performance exhibited by the co-polyimides are advantageous as compared to the values obtained in some existing high performance polymeric membranes. One important advantage here is that at moderate feed pressure and up to 20 vol. % H.sub.2S in a feed gas mixture, ideal selectivities and permeabilities are still suitable in the co-polyimide membranes. Moreover, the CO.sub.2/CH.sub.4 selectivity of the co-polyimides does not degrade to anywhere near the same extent as was reported for cellulose acetate (CA), even under the much presently disclosed aggressive environments. This stability at moderate pressures and high H.sub.2S concentration is impressive and unique.

(89) Another unique result obtained is the co-polyimide membranes are not only acid gas, most especially CO.sub.2 selective, but also slightly selective to N.sub.2 as compare to CH.sub.4 (i.e., the permeation of N.sub.2 in aromatic polyimides is higher than CH.sub.4). This is an advantage and energy can be saved as the membrane simultaneously permeates both acid gas and N.sub.2, while keeping CH.sub.4 in the high pressure zone of a separation device or process.

(90) The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

(91) In the drawings and specification, there have been disclosed embodiments of apparatus, systems, and methods for aromatic co-polyimide membranes for sour natural gas separation, as well as others, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.