Aromatic co-polyimide gas separation membranes derived from 6FDA-DAM-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 2,4,6-trimethyl-m-phenylenediamine (DAM) based moiety; and at least one component selected from the group consisting of: a 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) based moiety; 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 2,4,6-trimethyl-m-phenylenediamine (DAM) based moiety; and at least one component selected from the group consisting of: a 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) based moiety; 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 DAM based moiety to the at least one component selected from the group is about 1:3 to control fractional free volume of the membrane and to maintain the fractional free volume of the membrane similar to a fractional free volume of a homo-polyimide comprising 6FDA and the at least one component selected from the group to maintain suitable values of permeability and selectivity for sour natural gas separations.

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 6FpDA based moiety.

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

5. The membrane according to claim 2, where the membrane comprises the ABL-21 based moiety.

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

7. The membrane according to claim 6, where the membrane comprises the 6FpDA based moiety.

8. The membrane according to claim 6, where the membrane comprises the CARDO based moiety.

9. The membrane according to claim 6, where the membrane comprises the ABL-21 based moiety.

10. The membrane according to claim 6, where the block co-polymers include a polymer block of length L of the 6FDA and the DAM based moieties, and include a polymer block of length M of the 6FDA and the 6FpDA based moieties, and a block length ratio of L to M is about between (1,000-20,000) to (1,000-20,000).

11. The membrane according to claim 6, where the block co-polymers include a polymer block of length L of the 6FDA and the DAM based moieties, and include a polymer block of length M of the 6FDA and the CARDO based moieties, and a block length ratio of L to M is about between (1,000-20,000) to (1,000-20,000).

12. The membrane according to claim 6, where the block co-polymers include a polymer block of length L of the 6FDA and the DAM based moieties, and include a polymer block of length M of the 6FDA and the ABL-21 based moieties, and a block length ratio of L to M is about between (1,000-20,000) to (1,000-20,000).

13. 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.

14. The method according to claim 13, 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.

15. The method according to claim 13, where the mixed gas stream comprises CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6, and H.sub.2S.

16. 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); 2,4,6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA); 9,9-bis(4-aminophenyl) fluorene (CARDO); 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; and preparing a dense film from the co-polyimide using a solution casting process, wherein the molar ratio of the DAM based moiety to the at least one component selected from the group is about 1:3 to control fractional free volume of the membrane and to maintain the fractional free volume of the membrane similar to a fractional free volume of a homo-polyimide comprising 6FDA and the at least one component selected from the group to maintain suitable values of permeability and selectivity for sour natural gas separations.

17. A method of gas separation, the method comprising the step of: using the dense film of claim 16 to separate at least 2 components of a mixed gas stream.

18. The method according to claim 16, where the step of combining is carried out to create random co-polymers.

19. The method according to claim 18, where the step of combining includes combining the 6FDA, the DAM, and the 6FpDA.

20. The method according to claim 18, where the step of combining includes combining the 6FDA, the DAM, and the CARDO.

21. The method according to claim 18, where the step of combining includes combining the 6FDA, the DAM, and the ABL-21.

22. The method according to claim 16, where the step of combining is carried out to create block co-polymers.

23. The method according to claim 22, where the step of combining includes combining the 6FDA, the DAM, and the 6FpDA.

24. The method according to claim 22, where the step of combining includes combining the 6FDA, the DAM, and the CARDO.

25. The method according to claim 22, where the step of combining includes combining the 6FDA, the DAM, and the ABL-21.

26. 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 dianhydride selected from the group consisting of: a 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) based moiety; a benzophenone-3,3′, 4,4′-tetracarboxylic dianhydride (BTDA) based moiety; and a pyromellitic dianhydride (PMDA) based moiety; a 2,4,6-trimethyl-m-phenylenediamine (DAM) based moiety; and at least one component selected from the group consisting of: a 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) based moiety; 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 DAM based moiety to the at least one component selected from the group consisting of the 6FpDA based moiety, the CARDO based moiety, the durene diamine based moiety, the ABL-21 based moiety, the 3,3′-dihydroxybenzidine based moiety, and the 3,3′-(hexafluoroisopropylidene)dianiline based moiety is about 1:3 to control fractional free volume of the membrane and to maintain the fractional free volume of the membrane similar to a fractional free volume of a homo-polyimide comprising 6FDA and the at least one component selected from the group consisting of the 6FpDA based moiety, the CARDO based moiety, the durene diamine based moiety, the ABL-21 based moiety, the 3,3′-dihydroxybenzidine based moiety, and the 3,3′-(hexafluoroisopropylidene)dianiline based moiety to maintain suitable values of permeability and selectivity for sour natural gas separations.

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 random co-polymers: 6FDA-DAM/6FpDA (1:3), 6FDA-DAM/CARDO (1:3); and 6FDA-DAM/ABL-21 (1:3).

(3) FIG. 2 is a reaction scheme for the homo-polymer (homo-polyimide) 6FDA-ABL-21, which has been characterized and studied,

(4) FIG. 3 shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-DAM/6FpDA (1:3) in CDCl.sub.3.

(5) FIG. 4A shows Fourier Transform Infrared (FTIR) spectra of prepared co-polyimides: (I) 6FDA-DAM/6FpDA (1:3); (II) 6FDA-DAM/CARDO (1:3); and (III) 6FDA-DAM/ABL-21 (1:3).

(6) FIG. 4B shows thermal analysis of the prepared co-polyamides represented by a thermogravimetric analysis (TGA) plot.

(7) FIG. 4C shows a derivative thermogravimetric chart based on the data from FIG. 4B.

DETAILED DESCRIPTION

(8) So that the manner in which the features and advantages of the embodiments of apparatus, systems, and methods for 6FDA-DAM 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.

(9) 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.

(10) 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):

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

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

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

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

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

(16) where x.sub.i(0) and x.sub.i(l) 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.

(17) 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).

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

(19) where

(20) $\begin{array}{cc}\frac{s_i}{s_j}\mathrm{and}\frac{D_i}{D_j}& \end{array}$
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.

(21) 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:

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

(23) where x.sub.i(0) and x.sub.i(l) 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(l) 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

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

(25) 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 the Van't Hoff-Arrhenius equation as given below in equation (7).

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

(27) 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].

(28) Aromatic co-polyimide membranes derived from a 6FDA-DAM homo-polyimide exhibit advantageous gas and gas mixture permeation properties. Aromatic random and block co-polyimide membranes can be developed from wide range of commercially available monomers including 4,4′-(hexafluoroisopropylidene) diphthalic dianhydride, also known as 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, (6FDA); benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA); pyromellitic dianhydride (PMDA); 9,9-bis(4-aminophenyl)fluorene (CARDO); 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA); 2,2′-Bis(trifluoromethyl)benzidine (ABL-21); and 2,4,6-trimethyl-m-phenylenediamine (DAM) to form different random and a variety of block length polymers of 6FDA-DAM/CARDO; 6FDA-DAM/6FpDA; and 6FDA-DAM/ABL-21 co-polyimides.

(29) In addition, the development of these aromatic co-polyimides can also be considered from other monomers including, but not limited to, 3,3′-dihydroxybenzidine, 3,3′-(hexafluoroisopropylidene) dianiline, and others. Certain example polymers can include co-polymers such as 6FDA-DAM/CARDO (3:1); 6FDA-DAM/CARDO (1:1); 6FDA-DAM/CARDO (1:3); (6FDA-DAM)/(6FDA-CARDO) (1,000-20,000)/(1000-20,000); 6FDA-DAM/6FpDA (3:1); 6FDA-DAM/6FpDA (1:1); 6FDA-DAM/6FpDA (1:3); (6FDA-DAM)/(6FDA-6FpDA) (1,000-20,000)/(1,000-20,000); 6FDA-DAM/ABL-21 (3:1); 6FDA-DAM/ABL-21 (1:1); 6FDA-DAM/ABL-21 (1:3); (6FDA-DAM)/(6FDA-ABL-21) (1000-20,000)/(1000-20,000); (6FDA-DAM)/(6FDA-CARDO)/(6FDA-6FpDA); (6FDA-DAM)/(6FDA-ABL-21)/(6FDA-CARDO); (6FDA-ABL-21)/(6FDA-CARDO)/(6FDA-6FpDA) and combination thereof.

(30) Crosslinking of the polymers can be achieved using different types and sizing of functional groups. Examples include and are not limited to functionalization or grafting with polar or H.sub.2S-philic, in addition to or alternative to CO.sub.2-philic, groups that include Bromine (Br); sulfonate (SO.sub.3H); diallyl amine; acrylonitrile; jeffamines; and combinations thereof. Crosslinking can also be achieved using such cross-linkers as N,N-dimethylpiperizine, p-xylenediamine, m-xylenediamine, aliphatic diamine, polyethyleneimine, 1,3-cyclohexane-bis(methylamine) for example.

(31) The disclosure provides certain relationships between the permeabilities and component ratios of the 6FDA-DAM homo-polyimide and other monomer moieties. One reason for choosing the homo-polyimide 6FDA-DAM is that it has a greater permeability, but a relatively low selectivity for a specific gas pair, while other monomer moieties have higher selectivity with a relatively low permeability. Co-polyimides with improved permeability and selectivity have been developed. Embodiments allow for enhancement in gas separation properties. Physical and gas transport properties of certain membranes are examined by investigating properties of pure and mixed gases, consisting of CO.sub.2, CH.sub.4, N.sub.2, C.sub.2H.sub.6, He and H.sub.2S, passing through the dense films of the co-polyimides 6FDA-DAM/CARDO; 6FDA-DAM/6FpDA; and 6FDA-DAM/ABL-21 allowing for simultaneous separation of CO.sub.2, N.sub.2, He, and H.sub.2S from natural gas streams.

EXAMPLES

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

(33) Exemplified co-polyimides were synthesized by a one-step method in m-cresol by keeping the co-monomers 6FDA and DAM constant, while varying a second diamine co-monomer from 6FpDA to CARDO then ABL-21 as depicted in FIG. 1. Reactions were carried out at high temperature (180° C.) in a 100-mL three neck round bottomed flask equipped with a Dean-Stark apparatus, an IKA® EUROSTAR 20 digital mechanical stirrer under a nitrogen atmosphere. The Dean-Stark apparatus was used to remove water formed during the reaction in order to drive the reaction toward the formation of the co-polyimide. Separately and specifically, a 6FDA-ABL-21 homo-polyimide has been prepared, characterized, and the gas transport properties studied. FIG. 2 is a reaction scheme for the home-polymer 6FDA-ABL-21, which has been characterized and studied.

(34) Three random co-polymers were prepared by adding the dianhydride monomer 6FDA to a mixture that contained both diamine co-monomers (DAM, in addition to 6FpDA, CARDO, or ABL-21) in m-cresol and the temperature was then increased to 180° C. for 8 hours. In all cases the molar ratios DAM:6FpDA, DAM:CARDO and DAM:ABL-21 was fixed to 1:3 to allow a comparative study between the three co-monomers 6FpDA, CARDO, and ABL-21.

Example 1: Preparation of Aromatic Random Co Polyimide 6FDA-DAM/6FpDA (1:3)

(35) Random aromatic 6FDA-DAM/6FpDA (1:3) co-polyimide (FIG. 3) was synthesized according to the following procedure from 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) (obtained from Alfa Aesar), 2,4,6-trimethyl-m-phenylenediamine (DAM) (obtained from TCI America), and 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) (obtained from TCI America). The solvents used include Methanol (obtained from ThermoFisher Scientific) and m-cresol (obtained from Alfa Aesar). All the chemicals and solvents used in this work were used as received without any further purification.

(36) Synthesis of random co-polyimide 6FDA-DAM/6FpDA (1:3) (I): In a 100-mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer DAM (0.300 g, 1.994 mmol), 6FpDA (2.00 g, 5.98 mmol), and 6FDA (3.54 g, 7.98 mmol) were mixed in m-cresol (16.00 ml). The mixture was heated at 180° C. for 8 hours. The solution was diluted with additional 10 mL of m-cresol while still hot and the resulting highly viscous solution was poured into methanol. The fibrous polymer obtained was stirred in methanol overnight, then filtered and dried partially. The solid polymer was washed twice (2×300 mL) with methanol over two days. The final product 6FDA-DAM/6FpDA (1:3) (5.15 g, 3.87 mmol, 97% yield) was filtered off then dried under reduced pressure at 150° C. for two days. Characterization results showed the following: .sup.1H NMR (500 MHz, CDCl.sub.3) δ.sub.H 8.14-7.78 (m, 24H, ArH.sub.6FDA), 7.64-7.44 (AB system, J.sub.AB=8.4 Hz, 24H, ArH.sub.6FpDA), 7.24 (br s, 1H, ArH.sub.DAM), 2.21 (s, 6H, —CH.sub.3DAM), 1.97 (s, 3H, —CH.sub.3DAM).

(37) One of ordinary skill in the art will understand that in order to synthesize a block, rather than random, co-polyimide, 6FDA and DAM could be first combined to create a block of (6FDA-DAM) and then 6FDA and 6FpDA could be combined with each other and together with the block of (6FDA-DAM) to create block (6FDA-DAM)/(6FDA-6FpDA) of varying chain length for example (1,000-20,000)/(1,000-20,000).

Example 2: Preparation of Aromatic Random Co Polyimide 6FDA-DAM/CARDO (1:3)

(38) Random aromatic 6FDA-DAM/CARDO (1:3) co-polyimide was synthesized according to the following procedure from 6FDA (obtained from Alfa Aesar), DAM (obtained from TCI America) and CARDO (obtained from TCI America). The solvents used included methanol (obtained from ThermoFisher Scientific) and m-cresol (obtained from Alfa Aesar). All the chemicals and the solvents used in this work were used as received without any further purification.

(39) Synthesis of random co-polyimide 6FDA-DAM/CARDO (1:3) (II): A similar procedure for preparing co-polyimide (I) was employed using the following amounts of starting materials: DAM (0.287 g, 1.913 mmol), CARDO (2.00 g, 5.74 mmol), and 6FDA (3.40 g, 7.65 mmol) in m-cresol (15.00 ml). The final product 6FDA-DAM/CARDO (1:3) (II) (4.65 g, 3.46 mmol, 90% yield) was obtained as a white off solid material. Characterization resulted in the following: .sup.1H NMR (500 MHz, CDCl.sub.3) δ.sub.H 8.05-7.81 (m, 24H, ArH.sub.6FDA), 7.79 (d, J=7.4 Hz, 6H, ArH.sub.CARDO), 7.45 (d, J=7.4 Hz, 6H, ArH.sub.CARDO), 7.41-7.28 (m, 24H, ArH.sub.CARDO), 7.23 (br s, 1H, ArH.sub.DAM), 2.21 (s, 6H, —CH.sub.3DAM), 1.97 (s, 3H, —CH.sub.3DAM).

Example 3: Preparation of Aromatic Random Co Polyimide 6FDA-DAM/ABL-21 (1:3)

(40) Random aromatic 6FDA-DAM/ABL-21 co-polyimide was synthesized according to the following procedure from 6FDA (obtained from Alfa Aesar), DAM (obtained from TCI America) and ABL-21 (obtained from TCI America). The solvents used included methanol (obtained from ThermoFisher Scientific) and m-cresol (obtained from Alfa Aesar). The chemicals and the solvents used in this work were used as received without any further purification.

(41) Synthesis of random co-polyimide 6FDA-DAM/ABL-21 (1:3) (III): A similar procedure for preparing co-polyimide (I) was employed using the following amounts of starting materials: DAM (0.383 g, 2.55 mmol), ABL-21 (2.45 g, 7.65 mmol), and 6FDA (4.53 g, 10.20 mmol) in m-cresol (20.00 ml). The final product 6FDA-DAM/ABL-21 (1:3) (III) (6.38 g, 4.84 mmol, 95% yield) was obtained as a white solid product. Characterization of the product resulted in the following: .sup.1H NMR (500 MHz, CDCl.sub.3) δ.sub.H 8.14-7.87 (m, 30H, ArH.sub.6FDA, ArH.sub.ABL-21), 7.74 (d, J=7.2 Hz, 6H, ArH.sub.ABL-21), 7.51 (d, J=7.5 Hz, 6H, ArH.sub.ABL-21), 7.25 (br s, 1H, ArH.sub.DAM), 2.22 (s, 6H, —CH.sub.3DAM), 1.98 (s, 3H, —CH.sub.3DAM).

Example 4: Synthesis of Homo-Polyimide 6FDA-ABL-21

(42) In a 100-mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer, ABL-21 (2.44 g, 7.62 mmol) and 6FDA (3.55 g, 8.00 mmol) were dissolved in m-cresol (15 ml), and the mixture was heated at 180° C. for 8 hours. The solution was diluted with an additional 10 mL of m-cresol while still hot and the resulting highly viscous solution was poured into methanol. The fibrous polymer obtained was stirred in methanol overnight, then filtered and dried partially. The solid polymer was washed twice (2×400 mL) with methanol over two days. The final product 6FDA-ABL-21 (5.5 g, 7.25 mmol, 95% yield) was filtered off then dried under reduced pressure at 150° C. for two days. Characterization resulted in the following (see FIG. 2): .sup.1H NMR (500 MHz, CDCl.sub.3) δ.sub.H 8.12 (d, J=8.0 Hz, 2H, ArH.sub.6FDA), 8.01 (s, 2H, ArH.sub.6FDA), 7.94 (m, 4H, ArH.sub.6FDA, ArH.sub.ABL-21), 7.74 (d, J=8.6 Hz, 2H, ArH.sub.ABL-21), 7.51 (d, J=8.3 Hz, 2H, ArH.sub.ABL-21).

(43) .sup.1H-NMR Analysis

(44) 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. 3 shows the .sup.1H NMR spectrum of random co-polyimide 6FDA-DAM/6FpDA (1:3) as a model spectrum for the prepared co-polyimides. The spectrum shows the presence of the corresponding peaks of 6FpDA (a and b), 6FDA (c, d and e) and DAM (f, g and h). The signal integration of the corresponding peaks of the aromatic protons of 6FpDA (7.59 ppm and 7.54 ppm, a and b) and that of the methylene groups (—CH.sub.3) of DAM (1.97 ppm, h) were used to validate the expected molar ratio between the two co-monomers in the co-polyimide backbone. For a 1:3 DAM:6FpDA molar ratio, the integration of the corresponding DAM and 6FpDA peaks should account for 3 and 24 protons (3×8 protons) respectively, which is clearly shown in the spectrum in FIG. 3. Thus, the DAM:6FpDA molar ratio is confirmed to be 1:3 as desired.

(45) In a similar way, the DAM:CARDO and DAM:ABL-21 molar ratios in the other prepared co-polyimides were determined using the same methodology of signal integrations (refer to the .sup.1H NMR signal integration assignments in the experimental section).

(46) Fourier-Transform Infrared (FTIR) Spectroscopy Analysis

(47) A complete one-step imidization and the structure of the prepared co-polyimides was confirmed from their FTIR spectra depicted in FIG. 4A. FIG. 4A shows Fourier Transform Infrared (FTIR) spectra of prepared co-polyimides: (I) 6FDA-DAM/6FpDA (1:3); (II) 6FDA-DAM/CARDO (1:3); and (III) 6FDA-DAM/ABL-21 (1:3).

(48) 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). Moreover, as an indication to a relatively high molecular weight of the prepared co-polyimides is a very weak absorption band at 3490 cm.sup.−1, which can be attributed to the peripheral amine groups (N—H bond) of the polymeric chains.

(49) Asymmetric and symmetric stretching of the carbonyl groups (C═O, imide I and II bands) are illustrated in the two absorption bands at 1787 cm.sup.−1 and 1727 cm.sup.−1, respectively. The C—N bond stretching (imide III band) absorption band is illustrated at 1360 cm.sup.−1. Strong multiple vibration peaks at 1257-1190 cm.sup.−1 can be attributed to the —CF.sub.3 groups of the 6FDA, 6FpDA and ABL-21 moieties.

(50) Peaks are less intense in the case of 6FDA-DAM/CARDO, since the only source of —CF.sub.3 groups is the 6FDA in contrast to the other copolymers 6FDA-DAM/6FpDA and 6FDA-DAM/ABL-21, where the —CF.sub.3 groups exist in addition to 6FDA in 6FpDA and ABL-21 respectively. The absorption band at 3074 cm.sup.−1 is attributed to the aromatic C—H stretching, however, the aliphatic C—H stretching and bending are confirmed by the presence of the absorption bands at 2950-2835 cm.sup.−1 and 1517 cm.sup.−1 respectively. The aliphatic C—H bonds correspond to the methyl groups of DAM.

(51) FIG. 4B shows thermal analysis of the prepared co-polyimides represented by a thermogravimetric analysis (TGA) plot. FIG. 4C shows a derivative thermogravimetric (DTG) chart based on the data from FIG. 4B.

(52) The temperatures corresponding to 5% and 10% weight losses are listed in Table 1. These values are reported as an indication to the co-polyimides' thermal stability. The TGA traces were recorded within a temperature range between 100° C. and 650° C. at a rate of 10° C./min. The temperatures corresponding to the fastest rate of decomposition taken from the DTG curves of the prepared co-polyimide membranes are also listed in Table 1.

(53) TABLE-US-00001 TABLE 1 Characteristic temperatures for TGA and DTG. TGA (° C.) Co-polyimide membrane T.sub.d5% T.sub.d10% DTG (° C.) Tg (° C.) 6FDA-DAM 516 530 545 395 6FDA-6FpDA 524 538 558 323 6FDA-CARDO 543 555 553 393 6FDA-ABL-21 512 536 597 348 6FDA-DAM/6FpDA (1:3) 517 532 550 336 6FDA-DAM/CARDO (1:3) 527 545 550 395 6FDA-DAM/ABL-21 (1:3) 502 528 558, 585 352

(54) The values of T.sub.d5% and T.sub.d10% depicted in Table 1 show that prepared membranes are all within a similar range of thermal stability, with a slight advantage recorded to 6FDA-DAM/CARDO (1:3).

(55) The smooth region between 100 to 200° C. in all the TGA curves indicates the absence of residual solvents (m-cresol and DMF) used to prepare the co-polyimides and their corresponding membranes, respectively. The TGA first derivative known as DTG of FIG. 4C provides valuable information about the kinetics of degradation of the materials studied. The DTG curves depicted in FIG. 4C show that the fastest thermal decomposition of the prepared membranes occurs in a temperature range between 550 and 585° C. (see also Table 1). Moreover, the glass temperatures (T.sub.g) of the prepared co-polymers are listed in Table 1. The differential scanning calorimetry (DSC) traces were recorded within a temperature range between 30° C. and 450° C. at a rate of 10° C./min. The temperature values shown in Table 1 were obtained after a second run. A first run was performed to remove the thermal history of the corresponding polymer, which was followed by a fast cooling using a liquid nitrogen cooling system before performing the second run.

(56) Density values of prepared co-polyimides were measured using a Mettler Toledo XPE205 balance equipped with a density kit. Buoyant liquid used included cyclohexane at 20° C., where its density was measured to be d=0.777 g/cm.sup.3. The density values reported in Table 2 are the average values of at least five different measurements, with error values (standard deviation) below 2%. These density measurements were used to calculate the fractional free volume (FFV) of the prepared co-polyimide membranes using a group contribution method.

(57) TABLE-US-00002 TABLE 2 Density and fractional free volume (FFV) values of the prepared co-polyimides. V.sub.0 V d Polyimide (cm.sup.3/g) (cm.sup.3/g) (g/cm.sup.3) FFV 6FDA-DAM 0.6038 0.7570 1.3211 0.2023 6FDA-6FpDA 0.5648 0.6765 1.4781 0.1651 6FDA-CARDO 0.6193 0.7587 1.3180 0.1840 6FDA-ABL-21 0.5537 0.6799 1.4927 0.1735 6FDA-DAM/6FpDA (1:3) 0.5746 0.6866 1.4564 0.1632 6FDA-DAM/CARDO (1:3) 0.6154 0.7532 1.3277 0.1829 6FDA-DAM/ABL-21 (1:3) 0.5662 0.6807 1.4691 0.1681

(58) The reported FFV values of the corresponding homo-polymers are in line with their gas transport properties. The high FFV value in general leads to a relatively high permeability value, which is the case of 6FDA-DAM (0.2023) which is being used here, in part, as a permeability enhancing moiety. Due in part to the higher ratio of 6FpDA, CARDO, and ABL-21 relative to DAM (3:1), the corresponding random co-polymers have their FFV values similar to their corresponding homo-polymers. Such FFV values help maintain a relatively high CO.sub.2/CH.sub.4 selectivity. Co-polyimides disclosed here advantageously maintain relatively high values of permeability and selectivity.

(59) Co-polyimide dense film membranes were prepared as follow: 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 was 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 membrane made from chloroform. 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 membrane made with DMF, the solution was covered with perforated aluminum foil and was left in the oven at 70° C. under a clean nitrogen enriched environment for about 24 hours. After being dried completely, the resulting films were 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 dishes 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.

(60) 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.

Example 5: 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-DAM/CARDO (1:3); 6FDA-DAM/6FpDA (1:3) and 6FDA-DAM/ABL-21 (1:3) Co Polyimide Membranes Prepared in Examples 1-3

(61) The permeability coefficients of pure gases, including He, CO.sub.2, CH.sub.4 and N.sub.2, along with ideal selectivities of gas pairs, including He/CH.sub.4, N.sub.2/CH.sub.4, and CO.sub.2/CH.sub.4, were identified by passing the gases through the series of co-polyimide membranes 6FDA-DAM/CARDO (1:3); 6FDA-DAM/6FpDA (1:3); and 6FDA-DAM/ABL-21 (1:3). Upstream pressures of up to 300 psig and temperatures up to 35° C. were studied and the results are shown in Tables 3-6. 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.

(62) Pure gas permeability values of about 94 and 132 Barrers for CO.sub.2 and He, respectively, and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of about 37 and 52, respectively, were obtained for the random copolymer 6FDA-DAM/6FpDA (1:3), which are similar to target performances being sought for industrial acid gas separations and helium recovery from natural gas applications. Similar separation performance was obtained for the random copolymer 6FDA-DAM/CARDO (1:3), with permeability values of 119 and 120 Barrers for CO.sub.2 and He, respectively, and CO.sub.2/CH.sub.4 and He/CH.sub.4 selectivities of about 30 and 31, respectively. Moreover, random copolymer 6FDA-DAM/ABL-21 (1:3) exhibits the permeability values of about 90 and 129 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 52, respectively. These values and separation performances exhibited by the co-polyimides are advantageous as compared to the values obtained in some high performance polymeric membranes.

(63) As shown in Tables 4-6 for all the co-polyimide membranes, pure gas permeability coefficients of most of the penetrants, including He, CO.sub.2, CH.sub.4 and N.sub.2, stay relatively constant or slightly increase (especially He and CO.sub.2) with increase in feed pressure up to a feed pressure of about 300 psig. However, the membranes showed slight decrease in CO.sub.2/CH.sub.4 selectivities; while He/CH.sub.4 selectivities were found to slightly increase as depicted in the tables. 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 6: 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 the 6FDA-DAM/CARDO (1:3); 6FDA-DAM/6FpDA (1:3); and 6FDA-DAM/ABL-21 (1:3) Co Polyimide Membranes Prepared in Examples 1-3

(64) Permeability properties of quaternary gas mixtures consisting of 10, 59, 30, and 1 vol. % 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 7-9 for the random co-polyimide membranes 6FDA-DAM/CARDO (1:3); 6FDA-DAM/6FpDA (1:3) and 6FDA-DAM/ABL-21 (1:3).

(65) CO.sub.2 permeability and CO.sub.2/CH.sub.4 selectivity reduced to about 68 Barrer and 30, respectively, for random co-polyimide 6FDA-DAM/6FpDA (1:3); about 57 Barrer and 29, respectively, for the random co-polyimide 6FDA-DAM/CARDO (1:3); and about 48 Barrer and 33, respectively, for the random co-polyimide 6FDA-DAM/ABL-21 (1:3) at an elevated pressure of 800 psig. These values are still quite advantageous for natural gas separations, especially at this elevated pressure of 800 psig.

Example 7: Evaluation of the CO.SUB.2./CH.SUB.4 .and H.SUB.2.S/CH.SUB.4 .Sour Mixed Gas Separation Performance of the 6FDA-DAM/CARDO (1:3); 6FDA-DAM/6FpDA (1:3); and 6FDA-DAM/ABL-21 (1:3) Co Polyimide Membranes Prepared in Examples 1-3

(66) 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 membranes were studied at different gas feed pressures as shown in Table 10-12. Up to a maximum of 20 vol. % H.sub.2S in the feed gas was applied to the membranes. The CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities obtained for the random co-polyimide 6FDA-DAM/6FpDA (1:3) are up to about 29 and 19, respectively; while CO.sub.2 and H.sub.2S permeabilities are up to about 80 and 50 Barrers, respectively (Table 10). Similarly for the random co-polyimide 6FDA-DAM/CARDO (1:3), CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities are up to about 19 and 21, respectively, while CO.sub.2 and H.sub.2S permeabilities are up to about 48 and 51 Barrers, respectively (Table 11).

(67) In addition, random co-polyimide membrane 6FDA-DAM/ABL-21 (1:3) exhibits CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities of up to about 26 and 13, respectively, while CO.sub.2 and H.sub.2S permeabilities are up to about 51 and 26 Barrers, respectively (Table 12). These values and separation performances exhibited by the co-polyimides are advantageous as compared to the values obtained in some high performance polymeric membranes. One important point to note 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 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 much more aggressive environments. Stability at moderate pressures and high H.sub.2S concentration is impressive and unique as well as surprising and unexpected.

(68) TABLE-US-00003 TABLE 3 Pure gas permeability (Barrer) and selectivity coefficients in the random 6FDA-DAM-type co-polyimide membranes measured at 100 psig feed pressure and at 35° C. Polymer Name He N.sub.2 CH.sub.4 CO.sub.2 He/CH.sub.4 N.sub.2/CH.sub.4 CO.sub.2/CH.sub.4 6FDA-DAM 332 35 24 522 13.78 1.44 21.64 6FDA-6FpDA 133 3.4 1.5 66.5 88.33 2.27 44.33 6FDA-CARDO 100 3.2 2.2 80.0 45.45 1.45 36.36 6FDA-ABL-21 108 2.5 1.2 46.4 93.57 2.17 40.35 6FDA-DAM/ 132 4.8 2.6 93.5 51.57 1.88 36.67 6FpDA (1:3) 6FDA-DAM/ 120 5.6 3.9 119 30.74 1.42 30.49 CARDO (1:3) 6FDA-DAM/ 129 5.1 2.5 89.6 51.60 2.04 35.84 ABL-21 (1:3)

(69) TABLE-US-00004 TABLE 4 Pure gas permeation properties of random co-polyimide 6FDA-DAM/6FpDA (1:3) membranes at 35° C. Pressure Permeability (Barrer) Selectivity (psig) 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.4 100 105 2.60 132 4.8 40.35 50.53 1.84 200 105 3.31 155 5.6 31.70 46.81 1.69 300 118 4.02 170 6.4 29.32 42.15 1.59

(70) TABLE-US-00005 TABLE 5 Pure gas permeation properties of random co-polyimide 6FDA-DAM/CARDO (1:3) membranes at 35° C. Pressure Permeability (Barrer) Selectivity (psig) 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.4 100 113 3.90 120 5.61 28.82 30.72 1.44 200 113 3.55 152 6.51 31.84 42.93 1.83 300 117 4.02 169 7.07 28.97 42.14 1.76

(71) TABLE-US-00006 TABLE 6 Pure gas permeation properties of random co-polyimide 6FDA-DAM/ABL-21 (1:3) membranes at 35° C. Pressure Permeability (Barrer) Selectivity (psig) 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.4 100 100 2.51 129 5.11 39.91 51.48 2.04 200 95.5 2.74 155 5.82 34.80 56.55 2.12 300 100 2.86 167 6.33 34.92 58.54 2.21

(72) TABLE-US-00007 TABLE 7 Mixed gases permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/6FpDA (1:3) membrane as a function of feed pressure at 22° C. using a gas mixture containing 10, 60, and 30 vol. % of CO.sub.2, CH.sub.4 and N.sub.2, respectively. Pressure Permeability (Barrer) Ideal selectivity (psig) CO.sub.2 CH.sub.4 N.sub.2 CO.sub.2/CH.sub.4 N.sub.2/CH.sub.4 100 86.23 3.90 5.92 22.09 1.52 200 105.0 2.79 4.33 37.61 1.55 300 102.7 2.64 4.03 38.86 1.53 400 93.48 2.60 3.92 35.89 1.51 500 87.32 2.56 3.82 34.11 1.49 600 68.49 2.02 3.00 33.88 1.49 800 68.15 2.29 3.34 29.82 1.46

(73) TABLE-US-00008 TABLE 8 Mixed gases permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/CARDO (1:3) membrane as function of feed pressure at 22° C. using a gas mixture containing 10, 60, and 30 vol. % of CO.sub.2, CH.sub.4 and N.sub.2, respectively. Pressure Permeability (Barrer) Ideal selectivity (psig) CO.sub.2 CH.sub.4 N.sub.2 CO.sub.2/CH.sub.4 N.sub.2/CH.sub.4 200 65.95 1.31 1.32 50.29 1.01 400 66.47 1.79 1.75 37.20 0.98 600 60.30 1.90 1.82 31.73 0.96 800 57.09 1.99 1.90 28.68 0.95

(74) TABLE-US-00009 TABLE 9 Mixed gases permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/ABL-21 (1:3) membrane as function of feed pressure at 22° C. using gas mixture containing 10, 60, and 30 vol. % of CO.sub.2, CH.sub.4 and N.sub.2, respectively. Pressure Permeability (Barrer) Ideal selectivity (psig) CO.sub.2 CH.sub.4 N.sub.2 CO.sub.2/CH.sub.4 N.sub.2/CH.sub.4 200 84.54 1.91 3.09 44.20 1.62 400 58.39 1.40 2.25 41.85 1.62 600 50.75 1.38 2.21 36.76 1.60 800 48.18 1.44 2.31 33.47 1.60

(75) TABLE-US-00010 TABLE 10 Sour mixed gas permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/6FpDA (1:3) membrane measured at 22° C. and using sour feed gas mixture containing 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. 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 1.0 200 3.9 2.7 3.4 80.2 50.4 29.49 18.54 350 3.0 2.4 3.0 61.0 43.7 25.14 18.00 500 3.5 3.3 4.1 69.7 51.9 21.30 15.88 20.0 3.0 350 2.8 2.9 2.3 77.7 38.2 27.14 13.34

(76) TABLE-US-00011 TABLE 11 Sour mixed gas permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/CARDO (1:3) 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 2.0 2.5 2.7 47.5 51.2 19.21 20.71 500 2.2 2.9 3.0 46.3 54.1 16.23 18.95

(77) TABLE-US-00012 TABLE 12 Sour mixed gas permeability and selectivity coefficients in the random co-polyimide 6FDA-DAM/ABL-21 (1:3) 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 2.4 2.0 2.7 50.5 26.1 25.74 13.32 500 2.3 2.0 3.0 47.2 27.3 23.57 13.65

(78) Embodiments of the disclosure show membrane-based gas separation applications particularly for acid gas separation and helium recovery from natural gas using unique 6FDA-DAM-type aromatic co-polyimide membranes. The membranes exhibit advantageous pure and gas mixture permeation properties, with pure gas CO.sub.2 permeability in the range of about 105-118 Barrer and CO.sub.2/CH.sub.4 selectivity of up to about 40 at 35° C. and a feed pressure of up to 300 psig.

(79) Similarly, pure gas He permeability in the range of about 132-170 Barrer and He/CH.sub.4 selectivity of up to about 52 were obtained with the same experimental conditions. 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 exemplified membranes were studied, and up to 20 vol. % H.sub.2S in the feed gas was applied to the membranes.

(80) The CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities obtained for the random co-polyimide 6FDA-DAM/6FpDA (1:3) are up to about 29 and 19, respectively, while CO.sub.2 and H.sub.2S permeabilities are up to about 80 and 50 Barrers, respectively. Similarly for the random co-polyimide 6FDA-DAM/CARDO (1:3), CO.sub.2/CH.sub.4 and H.sub.2S/CH.sub.4 ideal selectivities are up to about 19 and 21, respectively, while CO.sub.2 and H.sub.2S permeabilities are up to about 48 and 51 Barrers, respectively. These values and separation performances exhibited by the co-polyimides are advantageous as compared to the values obtained in some high performance polymeric membranes. At moderate feed pressures and up to 20 vol. % H.sub.2S in a feed gas mixture, ideal selectivities and permeabilities are still moderate in the co-polyimides. Moreover, 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 more aggressive environments here. This stability at moderate pressures and high H.sub.2S concentration is impressive, unique, surprising, and unexpected.

(81) Another unique results obtained is the co-polyimide membranes are not only acid gas selective, but also selective to N.sub.2 as compared to CH.sub.4 (i.e., the permeation of N.sub.2 in aromatic polyimides is higher than CH.sub.4). This provides a separation advantage and energy is being saved as the membrane simultaneously permeates both acid gas and N.sub.2, while keeping CH.sub.4 on the high pressure side of the membrane.

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

(83) 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.