阅读说明：本技术 衍生自6fda-dam型均聚聚酰亚胺的芳族共聚聚酰亚胺气体分离膜 (Aromatic copolyimide gas separation membranes derived from 6FDA-DAM type homopolypolyimides ) 是由 加尔巴·奥洛列格贝·叶海亚 阿里·哈耶克 阿卜杜勒卡里姆·阿尔萨马 艾哈迈德·巴哈姆丹 于 2020-02-26 设计创作，主要内容包括：用于分离含硫天然气的组分的共聚聚酰亚胺膜包含至少三种聚合在一起的不同部分,这些部分包括基于2,2'-双(3,4-二羧基苯基)六氟丙烷二酐(6FDA)的部分；基于2,4,6-三甲基-间苯二胺(DAM)的部分；和选自由以下部分组成的组中的至少一种组分：基于的4,4'-(六氟异亚丙基)二苯胺(6FpDA)的部分；基于9,9-双(4-氨基苯基)芴(CARDO)的部分；基于2,3,5,6-四甲基-1,4-苯二胺(四甲基对苯二胺)的部分；基于2,2'-双(三氟甲基)联苯胺(ABL-21)的部分；基于3,3'-二羟基联苯胺的部分；和基于3,3'-(六氟异亚丙基)二苯胺的部分。(A copolyimide membrane for separating components of sulfur-containing natural gas comprises at least three different moieties polymerized together, including moieties based on 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6 FDA); moieties based on 2,4, 6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: a moiety based on 4,4' - (hexafluoroisopropylidene) diphenylamine (6 FpDA); moieties based on 9, 9-bis (4-aminophenyl) fluorene (CARDO); moieties based on 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethyl-p-phenylenediamine); moieties based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21); 3,3' -dihydroxybenzidine-based moieties; and moieties based on 3,3' - (hexafluoroisopropylidene) diphenylamine.)

1. A membrane for separating components of a sour natural gas feed, the membrane comprising:

at least three different moieties polymerized together, said moieties comprising 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) -based moieties; moieties based on 2,4, 6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: a moiety based on 4,4'- (hexafluoroisopropylidene) diphenylamine (6FpDA), a moiety based on 9, 9-bis (4-aminophenyl) fluorene (CARDO), a moiety based on 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21), a moiety based on 3,3 '-dihydroxybenzidine, and a moiety based on 3,3' - (hexafluoroisopropylidene) diphenylamine.

2. The film of claim 1, wherein the film comprises a random copolymer.

3. The film of claim 2, wherein the film comprises 6 FpDA-based moieties.

4. The membrane of claim 3, wherein the molar ratio of the 6 FpDA-based fraction to the DAM-based fraction is between 1:3 and 3: 1.

5. The film of claim 2, wherein the film comprises the CARDO-based portion.

6. The membrane of claim 5, wherein the molar ratio of CARDO-based moiety to DAM-based moiety is between 1:3 and 3: 1.

7. The film of claim 2, wherein the film comprises ABL-21 based moieties.

8. The membrane of claim 7, wherein the molar ratio of the ABL-21 based moiety to the DAM based moiety is between 1:3 and 3: 1.

9. The film of claim 1, wherein the film comprises a block copolymer.

10. The film of claim 9, wherein the film comprises the 6 FpDA-based portion.

11. The film of claim 9, wherein the film comprises the CARDO-based portion.

12. The film of claim 9, wherein the film comprises the ABL-21 based portion.

13. The membrane of claim 9, wherein the block copolymer comprises the 6FDA based portion and the DAM based portion having a polymer block length L, and comprises the 6FDA based portion and the 6FpDA based portion having a polymer block length M, and the ratio of the block lengths of L to M is between (1,000-20,000) to (1,000-20,000).

14. The membrane of claim 9, wherein the block copolymer comprises the 6FDA based portion and the DAM based portion having a polymer block length L and comprises the 6FDA based portion and the CARDO based portion having a polymer block length M, and the ratio of the block lengths of L to M is between (1,000-20,000) to (1,000-20,000).

15. The membrane of claim 9, wherein the block copolymer comprises the 6FDA based moiety and the DAM based moiety having a polymer block length L, and comprises the 6FDA based moiety and the ABL-21 based moiety having a polymer block length M, and the ratio of the block lengths of L to M is between (1,000-20,000) and (1,000-20,000).

16. A gas separation process, the process comprising the steps of:

use of a membrane according to claim 1 for separating at least 2 components of a mixed gas stream.

17. The process of claim 16, wherein the mixed gas stream has a feed pressure of up to 800psig on the feed side of the membrane, and the mixed gas stream has a H₂The S content is up to 20 vol%.

18. The method of claim 16, wherein the mixed gas stream comprises CO₂、CH₄、N₂、C₂H₆And H₂S。

19. A process for making a membrane for separating components of a sour natural gas feed, the process comprising the steps of:

a combining step of combining at least three different monomers to form a copolyimide, the monomers including 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6 FDA); 2,4, 6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: 4,4'- (hexafluoroisopropylidene) diphenylamine (6FpDA), 9-bis (4-aminophenyl) fluorene (CARDO), 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), 2' -bis (trifluoromethyl) benzidine (ABL-21), 3 '-dihydroxybenzidine, and 3,3' - (hexafluoroisopropylidene) diphenylamine; and

a preparation step of preparing a dense film from the copolymerized polyimide using a solution casting method.

20. The method of claim 19, further comprising the step of using the dense membrane to separate components of a gas stream.

21. The method of claim 19, wherein the combining step is performed to produce a random copolymer.

22. The method of claim 21, wherein the combining step comprises combining the 6FDA, the DAM, and the 6 FpDA.

23. The method of claim 22, wherein the molar ratio of the DAM to the 6FpDA is between 1:3 and 3: 1.

24. The method of claim 21, wherein the combining step comprises combining the 6FDA, the DAM, and the CARDO.

25. The method of claim 24, wherein the molar ratio of DAM to CARDO is between 1:3 to 3: 1.

26. The method of claim 21, wherein the combining step comprises combining the 6FDA, the DAM, and the ABL-21.

27. The method of claim 26, wherein the molar ratio of DAM to ABL-21 is between 1:3 and 3: 1.

28. The method of claim 19, wherein the combining step is performed to produce a block copolymer.

29. The method of claim 28, wherein the combining step comprises combining the 6FDA, the DAM, and the 6 FpDA.

30. The method of claim 28, wherein the combining step comprises combining the 6FDA, the DAM, and the CARDO.

31. The method of claim 28 wherein the combining step comprises combining the 6FDA, the DAM, and the ABL-21.

32. A membrane for separating components of a sour natural gas feed, the membrane comprising:

a moiety based on 2,2 '-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21).

33. A membrane for separating components of a sour natural gas feed, the membrane comprising:

at least three different moieties polymerized together, the moieties comprising 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;

moieties based on 2,4, 6-trimethyl-m-phenylenediamine (DAM); and

at least one component selected from the group consisting of: a moiety based on 4,4'- (hexafluoroisopropylidene) diphenylamine (6FpDA), a moiety based on 9, 9-bis (4-aminophenyl) fluorene (CARDO), a moiety based on 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21), a moiety based on 3,3 '-dihydroxybenzidine, and a moiety based on 3,3' - (hexafluoroisopropylidene) diphenylamine.

Technical Field

Embodiments of the present disclosure relate to membranes for hydrocarbons and hydrocarbon separation. In particular, embodiments of the present disclosure show a copolyimide membrane for natural gas related sour gas separation.

Background

In recent years, there has been an increase in the interest of clean energy and the worldwide demand for clean burning natural gas has also increased. From about 2,600BCM (billionths of a cubic meter) in 2005 to about 3,900BCM in 2020, natural gas consumption may increase at a compound annual growth rate of about 2.7%. Based on the estimates in 2006, the reserve to production ratio for natural gas was 61 years and the resource to production ratio was 133 years.

The composition of the feed natural gas varies greatly depending on its source of extraction. Although methane is a key component constituting the raw natural gas, the raw natural gas may also contain a considerable amount of impurities, including water, hydrogen sulfide (H)₂S), carbon dioxide, nitrogen, and other hydrocarbons. Natural gas (methane) is the main feedstock for the chemical industry and with the potential increase in natural gas demand, there is a need for separation technologies with high efficiency to be able to develop gas fields that have not been commercialized due to high pollutant content.

The majority of qi in the worldBulk storage resources are of low quality with high levels of impurities, including acid gases (carbon dioxide (CO)₂) And hydrogen sulfide (H)₂S)), water, heavy hydrocarbons (C)₃₊) And other contaminants such as helium, nitrogen, mercaptans, and the like. In order for natural gas to meet sales gas specifications, it is desirable to remove these contaminants, particularly the acid gases that constitute the largest amount of impurities in many existing natural gas storage resources. One requirement of natural gas desulfurization processes relates to the separation of acid gases from natural gas, and such treatment is critical to prevent corrosion of transport pipelines, reduce atmospheric pollution, and avoid other harmful effects.

In some systems, acid gas removal occurs prior to delivering the gas to a pipeline or stored as compressed natural gas in portable cylinders. At high concentrations, acid gases can corrode the delivery pipe and have a number of other detrimental effects. Furthermore, H₂S is toxic, and H₂S combustion produces harmful SO₂A gas. Therefore, it is desirable to desulfurize natural gas (to remove, for example, H)₂S, etc.) to reduce pipeline corrosion, prevent atmospheric pollution, increase the fuel heating value of natural gas, and reduce the volume of gas to be transported in pipelines and cylinders.

Currently, natural gas treatment and upgrading integrates industrial gas separation processes. Examples of natural gas processing technologies that have been widely used include, for example, absorption and adsorption of acid gases by amine absorption and Pressure Swing Adsorption (PSA) processes, respectively. However, conventional techniques are associated with several issues including high energy requirements and high capital costs.

Examples of commercially available natural gas purification alternatives are absorption of acid gases in basic solvents such as liquid amines and hot aqueous potassium carbonate solutions, and Pressure Swing Adsorption (PSA). However, these processes suffer from a number of disadvantages because they rely on energy intensive thermal regeneration steps, large footprints, heavy maintenance requirements and high capital costs.

Very little research has been conducted to develop membrane materials for separation of sulfur-containing gases. The reported studies include the use of rubbery polymer membranes for H₂S/CH₄Study of separation Performance. However, fromThe separation from the rubbery polymer material is based on solubility selectivity, so the rubbery polymer membrane CO₂/CH₄The separation capacity drops dramatically and is much lower than other glassy polymers such as Cellulose Acetate (CA). Furthermore, the mechanical stability of rubbery polymers tends to be significantly lower than that of glassy polymer materials. Some existing membranes require severe pretreatment of water and heavy hydrocarbon content, since in heavy hydrocarbons; benzene, toluene and xylene (BTX); water; and other condensable gases, the film swells and plasticizes very easily.

Glassy polyimide is a polymer membrane that has been investigated for the separation of acid gases from natural gas. These high glass transition temperature (Tg) (Tg > about 300 ℃) materials have the ability to separate certain acid gases based on size selectivity. Natural gas is normally processed at high pressures (up to and greater than about 900psi) and is typically treated with heavy hydrocarbons (C)₃₊) And water vapor saturates the natural gas. The insufficient performance of currently existing polymer membranes prevents the full utilization of separation membranes on an industrial scale. Some challenges include the inability to achieve both high permeability and selectivity, selectivity-permeability trade-off, membrane plasticization, and physical aging. These problems inhibit long-term gas separation performance and membrane stability. Therefore, a polymeric membrane material with high permeability properties (i.e., both high permeability and selectivity) is essential for the feasibility of membrane-based mixed natural gas separation and membrane absorption processes.

Various methods and techniques have been developed to separate and recover helium from a multi-component gas stream. Such methods include stand-alone membrane units, stand-alone cryogenic units, and combinations of membrane units, cryogenic units, and Pressure Swing Adsorption (PSA) units. A separate cryogenic process has been used to produce crude helium at high recovery from natural gas or other streams containing low purity helium. When the helium concentration in the feed is reduced to low levels (e.g., below about 1 mole percent), processes using separate cryogenic units are inefficient and impractical. Helium is typically present in natural gas at levels below about 0.5 mole percent and is extracted primarily as crude helium through the Liquefied Natural Gas (LNG) train. The demand for helium worldwide is increasing and as the demand for high purity helium product begins to exceed supply, this is expected to put pressure on the production facilities. In view of these trends, there is a need for treatment methods that overcome inefficient low temperature processes, particularly less than 0.5 mole% He in natural gas.

In order to reinforce and optimize polyimide materials for gas separation membranes, further improvements in their performance are needed, and this can be achieved by chemical modification of the polymers.

Disclosure of Invention

Applicants have recognized a need for an efficient membrane separation apparatus, method, and system for selectively separating sour gas and undesirable components from a sour natural gas feed. The present disclosure provides apparatus, methods, and systems employing membranes that exhibit efficient, surprising, and unexpected separation of undesirable components from a sour natural gas feed. Unlike conventional techniques, the membrane-based separations of the present disclosure do not exhibit the drawbacks of conventional techniques because they are much more energy efficient, have less footprint, and are flexible to operate. The use of a high performance membrane or a combination of membranes and any of the other methods described previously to achieve a satisfactorily high helium recovery to separate helium from natural gas can improve the efficiency of the separation process.

Limited data has been reported for developing membrane materials for aggressive sulfur-containing gas separations. The disclosed embodiments of natural gas membrane separation exhibit surprising and unexpected advantages over commercially available membranes because of the advantages over current membranes used for CO₂The isolated industry standard membrane material Cellulose Acetate (CA) provides superior efficiency, productivity, and resistance to penetrant-induced plasticization compared to the aromatic block copolyimides disclosed herein. Embodiments disclosed herein demonstrate that polyimide membrane gas separation applications are suitable for separating acid or sulfur-containing gas feeds and recovering helium from, in particular, low quality natural gas using aromatic copolyimide membranes derived from 6FDA-DAM type homopolyimides. In addition, embodiments represent newly developed membranes in extreme and more aggressive environments (i.e., for CO-containing applications)₂、CH₄、N₂、C₂H₆And H₂Gas mixture of S, H₂S content of up to about 5 vol%, about 10 vol%, about 15 vol%, and about 20 vol%, and feed pressure of up to about 400psig, about 500psig, about 600psig, about 700psig, and about 800 psig). The prior art membranes are generally suitable for use at low H₂S concentration and separation at low feed pressure.

Embodiments of the present disclosure show membrane gas separation applications for separating acid gas feeds from natural gas and recovering helium using newly developed aromatic copolyimide membranes derived from 6FDA-DAM (4,4' - (hexafluoroisopropylidene) diphthalic anhydride-2, 4, 6-trimethyl-m-phenylenediamine) homopolypolyimide. The membrane exhibits advantageous, surprising and unexpected permeation properties for pure gases and gas mixtures. Pure gaseous CO obtained at 35 ℃ and feed pressures up to about 300psig₂Has a permeability in the range of about 105Barrer to 118Barrer, and CO₂/CH₄The selectivity is up to about 40. Similarly, the permeability range for pure gas He obtained under the same experimental conditions is about 132Barrer to 170Barrer, and He/CH₄The selectivity is up to about 52.

In addition, CO was investigated from 10 vol%, 57 vol% to 59 vol%, 10 vol%, 1 vol% to 3 vol%, and 20 vol%, respectively₂、CH₄、N₂、C₂H₆And H₂S composition simulates the permeation performance of a sulfur-containing gas mixture through a membrane and subjects the membrane to H₂S up to about 20 vol% of the feed gas mixture. Random copolymerized polyimide 6FDA-DAM/6FpDA (millimole DAM: millimole 6FpDA is 1:3) CO₂/CH₄And H₂S/CH₄The ideal selectivities are 29 and 19, respectively; with CO₂And H₂The S permeability was 80Barrer and 50Barrer, respectively. Similarly, the random copolyimide 6FDA-DAM/CARDO (millimole DAM: millimole CARDO is 1:3) CO₂/CH₄And H₂S/CH₄The desired selectivities are 19 and 21, respectively, with CO₂And H₂The S permeabilities were 48Barrer and 51Barrer, respectively.

Compared with some existing high-performance polymer filmsThe values and separation performance exhibited by the copolymerized polyimide are favorable compared to the values obtained in (1). One important point to note is that in the medium feed pressure and feed gas mixture, H₂Up to 20 volume percent S, the desired selectivity and permeability remain suitable for the copolyimides of the present disclosure. Further, CO of the copolymerized polyimide₂/CH₄The selectivity is not reduced to nearly the same extent as reported for Cellulose Acetate (CA), even in the more aggressive environments shown herein. At medium pressure and high H₂This stability at S concentration is attractive and unique and is surprising and unexpected.

Aromatic random and block copolymerized polyimide films of the present disclosure can be developed from a wide range of monomers including: 4,4' - (hexafluoroisopropylidene) diphthalic anhydride, also known as 2, 2-bis (3, 4-dicarboxyphenyl) -1,1,1,3,3, 3-hexafluoropropane dianhydride (6 FDA); benzophenone-3, 3',4,4' -tetracarboxylic dianhydride (BTDA); pyromellitic dianhydride (PMDA); 9, 9-bis (4-aminophenyl) fluorene (CARDO); 4,4' - (hexafluoroisopropylidene) diphenylamine (6 FpDA); 2,2' -bis (trifluoromethyl) benzidine (ABL-21); and 2,4, 6-trimethyl-m-phenylenediamine (DAM) to form block polymers that are random and of varying block lengths, e.g., 6 FDA-DAM/CARDO; 6FDA-DAM/6 FpDA; and 6FDA-DAM/ABL-21 copolyimide.

In addition, the development of these aromatic copolyimides may also consider other monomers, including 3,3' -dihydroxybenzidine, 3- (hexafluoroisopropylidene) diphenylamine and other bulky diamines, to form such exemplary copolymers: 6FDA-DAM/CARDO (3: 1); 6FDA-DAM/CARDO (1: 1); 6FDA-DAM/CARDO (1: 3); (6FDA-DAM)/(6FDA-CARDO) (1,000-20,000)/(1,000-20,000); 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) (1,000-20,000)/(1,000-20,000); (6FDA-DAM)/(6FDA-CARDO)/(6FDA-6 FpDA); (6FDA-DAM)/(6FDA-ABL-21)/(6 FDA-CARDO); (6FDA-ABL-21)/(6FDA-CARDO)/(6FDA-6 FpDA); and combinations thereof.

Crosslinking of the polymer can be achieved using different types and sizes of functional groups. Except for the affinity for CO₂Outside the radicals or as CO-philic₂Examples of substitutions of groups include, but are not limited to, polar or H-philic₂S groups functionalized or grafted, these groups including bromine (Br); sulfonic acid (SO)₃H) (ii) a Diallylamine; acrylonitrile; jeffamines; and combinations thereof. Crosslinking can also be achieved using such crosslinking agents as N, N-dimethylpiperazine, p-xylylenediamine, m-xylylenediamine, aliphatic diamines, polyethyleneimine and 1, 3-cyclohexane-bis (methylamine). In some embodiments of the present disclosure, including exemplary embodiments, crosslinking is not required, and film formation is performed without crosslinking or without a crosslinking agent.

In embodiments of the present disclosure, for random copolymerized polyimides, the ratio (l: m) refers to the millimolar ratio of first non-FDA monomer to second non-FDA monomer, e.g., in 6FDA-DAM/CARDO (1:3), the ratio is 1 millimolar DAM to 3 millimolar CARDO. For block copolyimides, the ratio of (l: m) or (l)/(m) is one of the block length l to the block length m, or the ratio of the block lengths l to m, for example as shown in the block copolymer of FIG. 1.

The 6FDA based polyimide provides high rigidity and tunable transmission properties due to the general comonomer selection and resulting chemical structure. Furthermore, some 6FDA based polyimides have been found to have significantly higher gas selectivity compared to other glassy polymers of comparable permeability; and by systematically exhibiting higher selectivity at permeability values comparable to other polymers, it consistently deviates from the general relationship between permeability and permselectivity.

In addition, the presence of fluorine in 6FDA based polyimides generally reduces the coefficient of thermal expansion and provides increased solubility. One approach herein is to introduce a flexible linkage between the aromatic rings of the diamine and dianhydride. Modified polyimides with flexible bonds providing improved solubility have been successfully utilized. Due to the inhibited polymer chain packing and rigid backbone, 6FDA-DAM is a permeable polyimide with moderate selectivity in some gas separation applications. 6FDA-DAM is particularly useful for butane isomer separations and other situations where high throughput is required.

Blending, surface modification and copolymerization are methods used to adjust polymer properties. However, some of these methods have several limitations. For membrane applications, blend modification would involve complex phase behavior in membrane fabrication, as most polymers are immiscible. Although membranes formed from crosslinked polyimides have improved environmental stability and excellent gas selectivity compared to corresponding uncrosslinked polyimides, the crosslinking reaction typically results in reduced solubility in organic solvents and very high glass transition temperatures. These properties make it difficult to make the material by conventional techniques.

To overcome these limitations, several structural modifications have been employed. One direction is structural modification of the polymer backbone, which involves the addition of bulky side substituents, flexible alkyl side chains, non-coplanar biphenylene moieties, and kinking comonomers. These methods have been used to alter polymer properties by reducing interchain interactions and/or by reducing the stiffness of the polymer backbone. In addition, the copolyimide offers the possibility of producing a membrane having gas permeability and selectivity that cannot be obtained with the homopolyimide, and the gas separation performance can be adjusted by changing the monomer ratio.

In view of the above-described technical problems, embodiments of the present disclosure address these problems, as compared to current uses for CO₂The aromatic copolyimides disclosed herein generally give superior efficiency, productivity and resistance to penetrant-induced plasticization compared to the isolated industry standard film material CA. Among the polymers for gas separation membranes, these aromatic polyimides are one of the most attractive and promising materials due to their excellent properties such as high thermal stability, chemical resistance and mechanical strength. These polymer properties help membrane structures made from copolyimide to withstand degradation due to the humid conditions often found in natural gas streams.

The copolyimides exemplified herein exhibit CO₂/CH₄And H₂S/CH₄The ideal selectivity is as high as 29 and 19 respectively; and the random copolymerized polyimide 6FDA-DAM/6FpDA (1:3) CO₂And H₂S permeability is as high as 80Barrer and 50Barrer respectively. Similarly, H in the intermediate feed pressure and feed gas mixture₂Random copolyimide 6FDA-DAM/CARDO (1:3) CO up to 20 vol.% S₂/CH₄And H₂S/CH₄The ideal selectivity is up to 19 and 21 respectively, and CO is simultaneously generated₂And H₂S permeability was up to 48Barrer and 51Barrer, respectively. This property is much higher than that obtained in many current commercial membranes. Further, CO of the copolymerized polyimide₂/CH₄And H₂S/CH₄The selectivity does not decrease to nearly the same extent as reported for CA and other commercial membranes, even in the more aggressive environments employed herein. At medium pressure and high H₂This stability at S concentration is attractive, unique, surprising and unexpected.

The novel 6FDA-DAM type aromatic copolyimide membranes exhibit advantageous pure gas and gas mixture permeation properties for gas separations, particularly for the separation of sulfur-containing gas feeds from natural gas. These properties are unique and superior to the properties of many glassy polymers used in industry. Many prior art membranes are only concerned with low H₂S concentration and low pressure, and in many cases not reported in H₂Performance data in the presence of S.

Currently, only limited data have been reported in the development of aggressive sulfur-containing gas separation membrane materials. Embodiments of these membranes disclosed herein exhibit advantages over commercially available membranes because of the advantages currently used for CO₂The aromatic copolyimides of the present invention provide superior selectivity, permeability and resistance to permeant-induced plasticization compared to the isolated industry standard membrane material CA.

As previously mentioned, the polyimides of the present disclosure are promising materials for natural gas separation (particularly natural gas with sulfur-containing gases) due to their chemical, thermal and mechanical stability. Polyimide base filmHave been shown to be characteristic for gas separation applications, in particular for the removal of CO from gas streams₂。CO₂The removal techniques can be applied to natural gas desulfurization and carbon capture techniques. Membrane-based natural gas separation according to the present disclosure is advantageous because membrane-based natural gas separation is lower in capital cost, higher in energy savings, smaller in size, environmentally friendly, and more economically viable compared to conventional technologies such as independent Pressure Swing Adsorption (PSA) and independent absorption processes.

In hexafluorodianhydride ("6 FDA") based polyimides (e.g., prepared using 4,4' - (hexafluoroisopropylidene) diphthalic anhydride), CF is present in the polymer₃The presence of groups results in chain stiffness, which makes certain membranes containing 6FDA more effective in separating molecules based on steric bulk. Due to inhibition of chain stacking, CF₃The groups also provide for increased permeability. As a result, the 6 FDA-based polyimide may exhibit greater selectivity and greater permeability on the same order of magnitude when compared to other high performance polymers. As used throughout, the acronym for the starting monomeric units/moieties will be used to refer to the final polymerization product, e.g., 6FDA-DAM/CARDO, even though some of the oxygen atoms of the anhydride groups of, e.g., 6FDA have been substituted with nitrogen atoms (see, e.g., fig. 1).

Further, the gas separation performance of the polyimide can be improved by copolymerization with other homopolypolyimide. The advantage of the copolyimides is the production of membranes with gas permeability and selectivity not obtainable with homopolyimides. The present disclosure provides a unique material for gas separation membrane applications, particularly for separating sour and sour gas feeds from natural gas.

To minimize methane reduction, in some applications, at 900psig and H₂S concentration up to 20 mol% in wet sulfur-containing gas, and in C₃₊Membrane to CO in the presence of heavy hydrocarbons (about 3 mol%) and in the presence of about 1,000ppm of benzene, toluene and xylenes (BTX)₂/CH₄And H₂S/CH₄The uniform selectivity exhibited needs to be greater than 30. Under the aforementioned conditions, the membrane should also be resistant to CO₂And H₂S represents 100 GPUs (Gas permeability units).

To this end, disclosed herein is a membrane for separating components of a sour natural gas feed, the membrane comprising: at least three different moieties polymerized together, the moieties including a 2,2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) -based moiety; moieties based on 2,4, 6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: a moiety based on 4,4'- (hexafluoroisopropylidene) diphenylamine (6FpDA), a moiety based on 9, 9-bis (4-aminophenyl) fluorene (CARDO), a moiety based on 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21), a moiety based on 3,3 '-dihydroxybenzidine, and a moiety based on 3,3' - (hexafluoroisopropylidene) diphenylamine. In some embodiments, the film comprises a random copolymer. In certain embodiments, the film comprises 6 FpDA-based moieties. In other embodiments, the molar ratio of the 6 FpDA-based fraction to the DAM-based fraction is between about 1:3 to about 3: 1. In still other embodiments, the membrane comprises a CARDO based moiety.

In certain embodiments, the molar ratio of the CARDO-based moiety to the DAM-based moiety is between about 1:3 to about 3: 1. In still other embodiments, the film comprises an ABL-21 based moiety. In some embodiments, the molar ratio of the ABL-21-based moiety to the DAM-based moiety is between about 1:3 to about 3: 1. In still other embodiments, the film comprises a block copolymer. In certain embodiments of the block copolymer, the membrane comprises a 6 FpDA-based moiety in addition to or as an alternative to the CARDO-based moiety, in addition to or as an alternative to the ABL-21-based moiety. In some embodiments, the block copolymer comprises polymer blocks of a 6FDA based moiety and a DAM based moiety of length L and polymer blocks of a 6FDA based moiety and a 6FpDA based moiety of length M, and the ratio of the block lengths of L to M is between about (1,000-20,000) to (1,000-20,000). Also in other embodiments, the block copolymer comprises polymer blocks of a 6FDA based moiety and a DAM based moiety of length L and polymer blocks of a 6FDA based moiety and a CARDO based moiety of length M, and the ratio of the block lengths of L to M is between about (1,000-20,000) to (1,000-20,000).

In certain embodiments, the block copolymer comprises a polymer block of a 6 FDA-based moiety and a DAM-based moiety of length L, and a polymer block of a 6 FDA-based moiety and an ABL-21-based moiety of length M, and the ratio of the block lengths of L to M is between about (1,000-20,000) to (1,000-20,000).

Further, a method of gas separation is disclosed herein, the method comprising the steps of: either a block or random copolymer membrane is used to separate at least 2 components of a mixed gas stream. In some embodiments, the mixed gas stream has a feed pressure to the feed side of the membrane of up to about 500psig, about 800psig, or about 900psig, and H in the mixed gas stream₂The S content is up to about 20 vol%. In other embodiments, the mixed gas stream comprises CO₂、CH₄、N₂、C₂H₆And H₂S。

Further, disclosed herein is a process for making a membrane for separating components of a sour natural gas feed, the process comprising the steps of: combining at least three different monomers to form a copolyimide, 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) diphenylamine (6FpDA), 9-bis (4-aminophenyl) fluorene (CARDO), 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), 2' -bis (trifluoromethyl) benzidine (ABL-21), 3 '-dihydroxybenzidine, and 3,3' - (hexafluoroisopropylidene) diphenylamine; and preparing a dense film from the copolymerized polyimide using a solution casting method.

In some embodiments, the method includes the step of using a dense membrane to separate the components of the gas stream. In some embodiments, the combining step is performed to produce a random copolymer. In still other embodiments, the combining step comprises combining 6FDA, DAM, and 6 FpDA. In certain embodiments, the molar ratio of DAM to 6FpDA is between about 1:3 to about 3: 1. In still other embodiments, the combining step comprises combining 6FDA, DAM, and CARDO. In still other embodiments, the molar ratio of DAM to CARDO is between about 1:3 to about 3: 1. In some embodiments, the combining step comprises combining 6FDA, DAM and ABL-21. In still other embodiments, the molar ratio of DAM to ABL-21 is between about 1:3 and about 3: 1.

In some embodiments of this method, the combining step is performed to produce a block copolymer. In still other embodiments, the step of combining to produce a block polymer comprises combining 6FDA, DAM, and 6 FpDA. In some embodiments, the step of combining to produce a block polymer comprises combining 6FDA, DAM, and CARDO. In still other embodiments, the step of combining to produce a block polymer comprises combining 6FDA, DAM and ABL-21.

Further, the present application discloses a membrane for separating components of a sour natural gas feed, the membrane comprising: a moiety based on 2,2 '-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21).

Further, the present application discloses a membrane for separating components of a sour natural gas feed, the membrane comprising: at least three different moieties polymerized together, the moieties comprising 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; moieties based on 2,4, 6-trimethyl-m-phenylenediamine (DAM); and at least one component selected from the group consisting of: a moiety based on 4,4'- (hexafluoroisopropylidene) diphenylamine (6FpDA), a moiety based on 9, 9-bis (4-aminophenyl) fluorene (CARDO), a moiety based on 2,3,5, 6-tetramethyl-1, 4-phenylenediamine (tetramethylp-phenylenediamine), a moiety based on 2,2' -bis (trifluoromethyl) benzidine (ABL-21), a moiety based on 3,3 '-dihydroxybenzidine, and a moiety based on 3,3' - (hexafluoroisopropylidene) diphenylamine.

Drawings

The above and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings. It is to be noted, however, that the appended drawings illustrate only several embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

FIG. 1 is a reaction scheme for making the following random copolymers: 6FDA-DAM/6FpDA (1:3), 6FDA-DAM/CARDO (1: 3); and 6FDA-DAM/ABL-21(1: 3).

FIG. 2 is a reaction scheme of homopolymer (homopolypolyimide) 6FDA-ABL-21 that has been characterized and studied.

FIG. 3 shows CDCl₃Of medium random copolymerized polyimide 6FDA-DAM/6FpDA (1:3)¹H NMR spectrum.

Fig. 4A shows a Fourier Transform Infrared (FTIR) spectrum of the prepared copolyimide: (I)6FDA-DAM/6FpDA (1: 3); (II)6FDA-DAM/CARDO (1: 3); and (III)6FDA-DAM/ABL-21(1: 3).

Fig. 4B shows a thermogram of the prepared copolymerized polyimide, represented by a thermogravimetric analysis (TGA) curve.

FIG. 4C shows a derivative thermogravimetric analysis plot based on the data of FIG. 4B.

Detailed Description

So that the manner in which embodiments of the apparatus, system, and method for separating a sulfur-containing gas feed 6FDA-DAM homopolymeric polyimide-based copolyimide membrane from natural gas, as well as other features and advantages, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure, briefly summarized above, may be had by reference to the various embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the appended drawings illustrate only various embodiments of this disclosure and are therefore not to be considered limiting of its scope, for it may admit to other effective embodiments.

The present disclosure illustrates a copolyimide membrane for acid gas separation and helium recovery. To enhance separation performance and optimize the copolyimides for gas separation, chemical modifications can be made that include substitution of other moieties and bulky functional groups of the copolyimide backbone. These modification steps can significantly improve the performance of the copolyimide film. Thus, it is contemplated that aromatic copolyimides can be developed from other monomers with and without crosslinking or without crosslinking.

The transport properties of pure gases and gas mixtures through dense polymer membranes are governed by solution diffusion mechanisms. According to this model, gas permeation follows a three-step process, i.e., gas dissolution on the upstream side of the membrane, diffusion down through the membrane with a concentration gradient, and desorption from the downstream side of the membrane. Thus, the volumetric (molar) flux J of component i across the membrane is given by equation (1)_i：

Wherein l is the film thickness [ cm ]]，p_i(o)Partial pressure of component i on the feed side of the membrane, p_i(l)As partial pressure of component i on the permeate side, D_iIs a diffusion coefficient [ cm ]²/s]And S is_iIs the dissolution coefficient [ cm of permeated gas³(STP)/cm of Polymer³Per pressure]. Product of diffusion coefficient and dissolution coefficient (D)_iS_i) Membrane permeability P referred to as component i_iWhich represents the ability of the membrane to permeate gas based on differences in membrane solubility and diffusivity. Barrer is the conventional unit of permeability, where 1Barrer is 10^-10(cm³(STP)x cm)/(cm²x s x cmHg)。

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

The permeability coefficient of each gas component in the gas mixture (particularly at low pressure) can be determined from equation 3.

Wherein x_i(0)And x_i(1)The mole fractions of the gas components in the feed stream and the permeate stream, J, respectively_iVolume (molar) flux (cm) of component i³/(cm²x s)), and p_fAnd p_pThe pressures (cmHg absolute) were respectively on the feed side and the permeate side of the membrane.

The ability of a membrane to separate two components is referred to as the desired selectivity or permselectivity alpha_ijExpressed as the ratio of the permeability of the component i having a higher permeability through the membrane to the permeability of the component j having a lower permeability through the membrane, as shown in equation (4).

WhereinAndrespectively the dissolution selectivity and the diffusion selectivity of the two gases. These terms denote the relative solubility and mobility of the two gases in the membrane.

However, in gas mixtures, the separation factor α is frequently used^m _i/j，α^m _i/jAre commonly used to determine separation efficiency and are routinely shown below:

wherein x_i(0)And x_i(1)The mole fractions of gas component i in the feed stream and the permeate stream, respectively; and x_j(0)And x_j(1)The mole fractions of gas component j in the feed stream and the permeate stream, respectively. However, for non-ideal gas mixtures, it is instead more appropriate to determine the permselectivityFor reflecting the characteristics of the film material. The osmotic selectivity is the ratio of the mixed gas permeabilities of components i and j defined using the fugacity driving force for permeability. Thus, it is possible to provide

WhereinAndis the permeability of components i and j based on mixed gas fugacity. Equation (6) was used in this study to calculate the permselectivity of each component in the gas mixture. The permeability of gas through dense polymer membranes is also affected by changes in operating temperature, which can be described by the van-hoff arrhenius equation, as shown in equation (7) below.

P₀Is the pre-finger factor [ Barrer]R is a general gas constant [ 8.314X 10 ]^-3kJ/(mol x K)]T is absolute temperature [ K ]]，E_pActivation energy for osmosis [ kJ/mol ]]。

Aromatic copolyimide membranes derived from 6FDA-DAM homopolypolyimide exhibit advantageous gas permeability and gas mixture permeability properties. Aromatic random and block copolyimide films can be developed from a wide range of commercially available monomers including the following: 4,4'- (hexafluoroisopropylidene) diphthalic anhydride, also known as 2,2' -bis (3, 4-dicarboxyphenyl) -hexafluoropropane dianhydride (6 FDA); benzophenone-3, 3',4,4' -tetracarboxylic dianhydride (BTDA); pyromellitic dianhydride (PMDA); 9, 9-bis (4-aminophenyl) fluorene (CARDO); 4,4' - (hexafluoroisopropylidene) diphenylamine (6 FpDA); 2,2' -bis (trifluoromethyl) benzidine (ABL-21); and 2,4, 6-trimethyl-m-phenylenediamine (DAM) to form the following different random polymers and polymers of varying block lengths: 6 FDA-DAM/CARDO; 6FDA-DAM/6 FpDA; and 6FDA-DAM/ABL-21 copolyimide.

In addition, the development of these aromatic copolyimides may also consider other monomers including, but not limited to, 3 '-dihydroxybenzidine, 3' - (hexafluoroisopropylidene) diphenylamine and others. Certain exemplary copolymers may include copolymers 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)/(1,000-20,000); 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) (1,000-20,000)/(1,000-20,000); (6FDA-DAM)/(6FDA-CARDO)/(6FDA-6 FpDA); (6FDA-DAM)/(6FDA-ABL-21)/(6 FDA-CARDO); (6FDA-ABL-21)/(6FDA-CARDO)/(6FDA-6 FpDA); and combinations thereof.

Crosslinking of the polymer can be achieved using different types and sizes of functional groups. Except for the affinity for CO₂Outside the radicals or as CO-philic₂Examples of substitution of groups include, but are not limited to, substitution with polar or H-philic groups₂S groups functionalized or grafted, these groups including bromine (Br); sulfonic acid (SO)₃H) (ii) a Diallylamine; acrylonitrile; jeffamines; and combinations thereof. Crosslinking can also be achieved using such crosslinking agents as N, N-dimethylpiperazine, p-xylylenediamine, m-xylylenediamine, aliphatic diamines, polyethyleneimine and 1, 3-cyclohexane-bis (methylamine).

The present disclosure provides certain relationships between permeability and component ratios of 6FDA-DAM homopolypolyimide and other monomer moieties. One reason for choosing homopolypolyimide 6FDA-DAM is that it has a high permeability, but a relatively low selectivity for a particular gas pair, while other monomer moieties have a high selectivity and a relatively low permeability. Copolyimides have been developed with improved permeability and selectivity. Embodiments provide enhanced gas separation performance. By investigating pure gases and by investigating CO₂、CH₄、N₂、C₂H₆、HeAnd H₂The mixed gas composed of S passes through the copolymerized polyimide 6 FDA-DAM/CARDO; 6FDA-DAM/6 FpDA; and 6 dense membranes of FDA-DAM/ABL-21 to simultaneously separate CO from a natural gas stream₂、N₂He and H₂S to examine the physical and gas transport properties of a particular membrane.

Examples

To illustrate embodiments of the present invention, the following examples are given; it should be understood, however, that these examples are merely illustrative in nature and that the method embodiments of the present invention are not necessarily limited thereto.

As shown in fig. 1, an exemplary copolyimide was synthesized in m-cresol by a one-step process by keeping the comonomers 6FDA and DAM constant while changing the second diamine comonomer from 6FpDA to CARDO and then to ABL-21. Under nitrogen atmosphere, in a device equipped with a Dean-Stark apparatus,The reaction was carried out in a 100mL three-necked round bottom flask with a EUROSTAR 20 digital mechanical stirrer at elevated temperature (180 ℃). The Dean-Stark apparatus is used to remove water formed during the reaction to drive the reaction to form the copolyimide. Separately and specifically, 6FDA-ABL-21 homopolypolyimide has been prepared, characterized, and gas transport properties have been investigated. FIG. 2 is a reaction scheme of homopolymer 6FDA-ABL-21 that has been characterized and studied.

Three random copolymers were prepared by adding dianhydride monomer 6FDA to a mixture of m-cresol solutions containing two diamine comonomers (DAM in addition to 6FpDA, CARDO or ABL-21) and then raising the temperature to 180 ℃ for 8 hours. In all cases, the molar ratios DAM:6FpDA, DAM: CARDO and DAM: ABL-21 were fixed at 1:3 in order to conduct comparative studies between the three comonomers 6FpDA, CARDO and ABL-21.

Example 1: preparation of aromatic random copolyimide 6FDA-DAM/6FpDA (1: 3).

A random aromatic 6FDA-DAM/6FpDA (1:3) copolyimide (FIG. 3) was synthesized from 2,2 '-bis- (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) (from Alfa Aesar), 2,4, 6-trimethyl-m-phenylenediamine (DAM) (from TCI America), and 4,4' - (hexafluoroisopropylidene) diphenylamine (6FpDA) (from TCI America) according to the following procedure. Solvents used included methanol (available from ThermoFisher Scientific) and m-cresol (available from Alfa Aesar). All chemicals and solvents used in this study were used directly without further purification.

Synthesis of random copolyimide 6FDA-DAM/6FpDA (1:3) (I): DAM (0.300g, 1.994mmol), 6FpDA (2.00g, 5.98mmol) and 6FDA (3.54g, 7.98mmol) were combined in m-cresol (16.00mL) in a 100mL three-necked round bottom flask equipped with a nitrogen inlet and a mechanical stirrer. The mixture was heated at 180 ℃ for 8 hours. The solution was diluted with another 10mL of m-cresol while hot and the resulting high viscosity solution was poured into methanol. The resulting fibrous polymer was stirred in methanol overnight, then filtered and partially dried. The solid polymer was washed twice with methanol (2X 300mL) over two days. The final product, 6FDA-DAM/6FpDA (1:3) (5.15g, 3.87mmol, 97% yield), was filtered off and dried at 150 ℃ under reduced pressure for two days. The characterization results are shown below:¹H NMR(500MHz,CDCl₃)δ_H 8.14–7.78(m,24H,ArH_6FDA),7.64–7.44(AB system,J_AB＝8.4Hz,24H,ArH_6FpDA),7.24(br s,1H,ArH_DAM),2.21(s,6H,–CH_3DAM),1.97(s,3H,–CH_3DAM)。

one of ordinary skill in the art will appreciate that for the synthesis of block copolyimides, rather than synthesizing random copolyimides, the 6FDA and DAM can be first combined to produce a block of (6FDA-DAM), and then the 6FDA and 6FpDA can be combined with each other and the block of (6FDA-DAM) to produce blocks of different chain lengths (6FDA-DAM)/(6FDA-6FpDA), for example, (1,000-.

Example 2: preparation of aromatic random copolymerized polyimide 6FDA-DAM/CARDO (1: 3).

Random aromatic 6FDA-DAM/CARDO (1:3) copolyimides were synthesized from 6FDA (available from Alfa Aesar), DAM (available from TCI America) and CARDO (available from TCI America) according to the following procedure. Solvents used included methanol (obtained from ThermoFisher Scientific) and m-cresol (obtained from Alfa Aesar). All chemicals and solvents used in this study were used directly without further purification.

Synthesis of random copolyimide 6FDA-DAM/CARDO (1:3) (II): the following amounts of starting materials were used, using a procedure analogous to that for the preparation of the copolyimide (I): DAM (0.287g, 1.913mmol), CARDO (2.00g, 5.74mmol) and 6FDA (3.40g,7.65mmol) in m-cresol (15.00 ml). The final product 6FDA-DAM/CARDO (1:3) (II) (4.65g, 3.46mmol, 90% yield) was obtained as an off-white solid. The characterization results were as follows:¹H NMR(500MHz,CDCl₃)δ_H 8.05–7.81(m,24H,ArH_6FDA),7.79(d,J＝7.4Hz,6H,ArH_CARDO),7.45(d,J＝7.4Hz,6H,ArH_CARDO),7.41–7.28(m,24H,ArH_CARDO),7.23(br s,1H,ArH_DAM),2.21(s,6H,–CH_3DAM),1.97(s,3H,–CH_3DAM)。

example 3: preparation of aromatic random copolyimide 6FDA-DAM/ABL-21(1: 3).

Random aromatic 6FDA-DAM/ABL-21 copolyimides were synthesized from 6FDA (available from Alfa Aesar), DAM (available from TCI America) and ABL-21 (available from TCI America) according to the following procedure. Solvents used included methanol (available from ThermoFisher Scientific) and m-cresol (available from Alfa Aesar). The chemicals and solvents used in this study were used directly without further purification.

Synthesis of random copolyimide 6FDA-DAM/ABL-21(1:3) (III): the following amounts of starting materials were used, using a procedure analogous to that for the preparation of the copolyimide (I): DAM (0.383g, 2.55mmol), ABL-21(2.45g, 7.65mmol) and 6FDA (4.53g,10.20mmol) in m-cresol (20.00 ml). The final product 6FDA-DAM/ABL-21(1:3) (III) was obtained as an off-white solid product (6.38g, 4.84mmol, 95% yield). The characterization of the obtained product was as follows:¹H NMR(500MHz,CDCl₃)δ_H 8.14–7.87(m,30H,ArH_6FDA,ArH_ABL-21),7.74(d,J＝7.2Hz,6H,ArH_ABL-21),7.51(d,J＝7.5Hz,6H,ArH_ABL-21),7.25(br s,1H,ArH_DAM),2.22(s,6H,–CH_3DAM),1.98(s,3H,–CH_3DAM)。

example 4: synthesis of homopolypolyimide 6 FDA-ABL-21.

ABL-21(2.44g, 7.62mmol) and 6FDA (3.55g, 8.00mmol) were dissolved in m-cresol (15mL) in a 100mL three-necked round bottom flask equipped with a nitrogen inlet and a mechanical stirrer and the mixture was heated at 180 ℃ for 8 h. The solution was diluted with another 10mL of m-cresol while hot and the resulting high viscosity solution was poured into methanol. The resulting fibrous polymer was stirred in methanol overnight, then filtered and partially dried. The solid polymer was washed twice with methanol (2X 400mL) over two days. The final product, 6FDA-ABL-21(5.5g, 7.25mmol, 95% yield), was filtered off and then dried under reduced pressure at 150 ℃ for two days. The characterization results were as follows (see fig. 2):¹H NMR(500MHz,CDCl₃)δ_H 8.12(d,J＝8.0Hz,2H,ArH_6FDA),8.01(s,2H,ArH_6FDA),7.94(m,4H,ArH_6FDA,ArH_ABL-21),7.74(d,J＝8.6Hz,2H,ArH_ABL-21),7.51(d,J＝8.3Hz,2H,ArH_ABL-21)。

¹H-NMR analysis

By reaction in deuterated chloroform (CDCl)₃) In (1)¹H Nuclear Magnetic Resonance (NMR) analysis confirmed the chemical structure of the prepared copolyimide. FIG. 3 shows the preparation of a random copolyimide 6FDA-DAM/6FpDA (1:3) as a model spectrum of the prepared copolyimide¹H NMR spectrum. The spectra show the presence of corresponding peaks for 6FpDA (a and b), 6FDA (c, d and e) and DAM (f, g and h). The corresponding peaks of the aromatic protons of 6FpDA (7.59ppm and 7.54ppm, a and b) and the methylene (-CH) of DAM₃) The signal integrals of the corresponding peaks of (1.97ppm, h) were used to verify the expected molar ratio between the two comonomers in the copolyimide backbone. For a 1:3 DAM:6FpDA molar ratio, the integral of the corresponding DAM and 6FpDA peaks should be 3 protons and 24 protons (3X 8 protons), respectively, which is clearly shown in the spectrum of FIG. 3. Thus, the DAM:6FpDA molar ratio was confirmed to be the desired 1: 3.

In the same manner, the same signal integration method was used to determine the molar ratio of DAM: CARDO and DAM: ABL-21 in the other copolyimides prepared (see alsoIn the experimental part¹H NMR signal integral assignment).

Fourier Transform Infrared (FTIR) spectroscopy

As shown in FIG. 4A, the structure of the copolymerized polyimide completely imidized in one step and prepared was confirmed from their FTIR spectra. Fig. 4A shows a Fourier Transform Infrared (FTIR) spectrum of the prepared copolyimide: (I)6FDA-DAM/6FpDA (1: 3); (II)6FDA-DAM/CARDO (1: 3); and (III)6FDA-DAM/ABL-21(1: 3).

By the absence of any peak corresponding to the intermediate comprising amide functions (3500-^–1And 1700-1650 cm^–1) Complete imidization was confirmed. In addition, as an indication of the relatively high molecular weight of the copolyimide produced, at 3490cm^-1There is a very weak absorption band, which may be caused by the peripheral amine groups (N-H bonds) of the polymer chain.

Asymmetric and symmetric stretching of the carbonyl groups (C ═ O, imide I and II bands) are respectively exhibited at 1787cm^-1And 1727cm^-1In the two absorption bands. In 1360cm^-1The C-N bond stretch (imide III band) absorption band is shown. 1257-1190 cm^–1The multiple strong vibration peaks at (A) may be-CF of the 6FDA, 6FpDA and ABL-21 moieties₃Caused by a group.

For the case of 6FDA-DAM/CARDO, the peak is less intense because of-CF₃The only source of groups was 6FDA, in contrast to the other copolymers 6FDA-DAM/6FpDA and 6FDA-DAM/ABL-21, which, in addition to 6FDA, have a-CF present in 6FpDA and ABL-21, respectively₃A group. At 3074cm^-1The absorption bands at (A) are due to stretching of the aromatic C-H, however, at 2950-2835 cm respectively^–1And 1517cm^–1The presence of the absorption band confirms stretching and bending of the aliphatic C-H. The aliphatic C-H bond corresponds to the methyl group of DAM.

Fig. 4B shows thermal analysis of the prepared copolymerized polyimide as represented by a thermogravimetric analysis (TGA) curve. FIG. 4C shows a derivative thermogravimetric analysis plot based on the data of FIG. 4B.

Table 1 lists the temperatures corresponding to 5% weight loss and 10% weight loss. These values are reported as an index of thermal stability of the copolymerized polyimide. TGA traces were recorded at a rate of 10 ℃/min over a temperature range between 100 ℃ and 650 ℃. The temperatures corresponding to the fastest decomposition rates obtained from the DTG curves of the prepared copolymerized polyimide films are also shown in table 1.

Table 1: characteristic temperatures of TGA and DTG.

T described in Table 1_d5％And T_d10％The values of (A) indicate that the films prepared are all within a similar thermal stability range, with a slight advantage recorded by 6FDA-DAM/CARDO (1: 3).

The smooth region between 100 ℃ and 200 ℃ in all TGA curves indicates the absence of residual solvents (m-cresol and DMF) used to prepare the copolyimides and their corresponding films, respectively. The first derivative of TGA, referred to as DTG in figure 4C, provides valuable information about the kinetics of degradation of the material under investigation. The DTG curve depicted in fig. 4C shows that the fastest thermal decomposition of the prepared film occurs in the temperature range between 550 ℃ and 585 ℃ (see also table 1). Furthermore, the glass transition temperature (T) of the copolymers prepared_g) Are shown in Table 1. Differential Scanning Calorimetry (DSC) traces were recorded at a rate of 10 ℃/min over a temperature range between 30 ℃ and 450 ℃. The temperature values shown in table 1 were obtained after the second run. A first run was performed to remove the thermal history of the corresponding polymer, followed by rapid cooling using a liquid nitrogen cooling system before performing a second run.

The density value of the prepared copolymerized polyimide was measured using a Mettler Toledo XPE205 balance equipped with a density kit. The flotation liquid used comprised cyclohexane at 20 ℃ and its density was determined to be d 0.777g/cm³. The density values reported in table 2 are the average of at least five different measurements with an error value (standard deviation) below 2%. These density measurements were used to calculate the free volume fraction (FFV) of the prepared copolyimide film using the group contribution method.

TABLE 2 Density and free volume fraction (FFV) values of the prepared copolyimides.

The reported FFV values for the corresponding homopolymers are consistent with their gas transport properties. To some extent, with 6FDA-DAM (0.2023) as the permeability enhancing moiety used herein, high FFV values generally result in relatively high permeability values. To some extent, due to the higher ratio of 6FpDA, CARDO and ABL-21 relative to DAM (3:1), the corresponding random copolymers had similar FFV values to their corresponding homopolymers. Such FFV values help to maintain a relatively high CO₂/CH₄And (4) selectivity. The copolyimides disclosed herein advantageously maintain relatively high permeability values and selectivities.

A copolymerized polyimide dense film was prepared as follows: a dense film was prepared by solution casting. A 2 to 3 wt% polymer solution was prepared in chloroform or Dimethylformamide (DMF), and the solution was filtered through a 0.45 μm filter. In the case of membranes made from chloroform, the solution was then cast onto dry, clean petri dishes and evaporated overnight at room temperature in a clean nitrogen-rich environment. The film was then slowly heated to about 60 ℃ in a slow nitrogen flow in an oven for about 24 hours. However, in the case of film formation with DMF, the solution covered with perforated aluminum foil was placed in an oven at 70 ℃ for about 24 hours in a clean nitrogen-rich environment. After complete drying, the resulting membrane was finally dried in a vacuum oven at 150 ℃ overnight to remove any residual solvent, then the membrane was cooled to room temperature and peeled from the petri dish after soaking in deionized water for about 15 minutes. The membrane was then dried at ambient temperature in a clean nitrogen environment for about 8 hours to remove any residual water.

Embodiments of the dense membrane herein are dense flat plates and do not include asymmetric hollow fiber membranes or are operable in the absence of asymmetric hollow fiber membranes.

Example 5: 6FDA-DAM/CARDO (1:3) prepared in examples 1 to 3; 6FDA-DAM/6FpDA (1:3) and 6CO of FDA-DAM/ABL-21(1:3) copolymerized polyimide film₂/CH₄；He/CH₄(ii) a And N₂/CH₄Evaluation of pure gas separation performance.

By passing gas through a series of copolyimide membranes 6FDA-DAM/CARDO (1: 3); 6FDA-DAM/6FpDA (1: 3); and 6FDA-DAM/ABL-21(1:3) identification including He, CO₂、CH₄And N₂And the permeability coefficient of pure gas (A) and the composition comprises He/CH₄、N₂/CH₄And CO₂/CH₄The desired selectivity of the gas pair (c). The upstream pressures studied were up to 300psig and temperatures up to 35 ℃, with results as shown in tables 3-6. The permeability characteristics of all of the permeate gases depicted are an average of at least two or more measurements and the error in permeability coefficient is less than ± 5% of the value shown.

CO of random copolymer 6FDA-DAM/6FpDA (1:3)₂And He have pure gas permeability values of about 94Barrer and 132Barrer, respectively, and CO₂/CH₄And He/CH₄The selectivities are about 37 and 52, respectively, which are the same target properties sought for separating industrial acid gases from natural gas applications and recovering helium. A similar separation performance was obtained for the random copolymer 6FDA-DAM/CARDO (1:3), where CO was₂And He have permeability values of 119Barrer and 120Barrer, respectively, and CO₂/CH₄And He/CH₄The selectivities were about 30 and 31, respectively. Furthermore, random copolymer 6FDA-DAM/ABL-21(1:3) exhibits a CO₂And He have permeability values of about 90Barrer and 129Barrer, respectively, and CO₂/CH₄And He/CH₄The selectivities were about 36 and 52, respectively. These values and separation performance exhibited by the copolyimides are advantageous compared to those obtained in some high performance polymer membranes.

As shown in tables 4 to 6, for all copolymerized polyimide films, He, CO were included₂、CH₄And N₂The pure gas permeability coefficient of most permeants remains relatively constant or increases slightly (particularly He and CO) as the feed pressure increases up to about 300psig₂). However, as shown, the membrane exhibited CO₂/CH₄A slight decrease in selectivity; at the same time, it finds He/CH₄The selectivity is slightly increased. In addition, except for CO₂In addition to selectivity to He, these copolyimides are also N-selective for methane₂Is selective and thus permeable to both acid gases and N₂Both, while maintaining the methane in the high pressure feed stream.

Example 6: 6FDA-DAM/CARDO (1:3) prepared in examples 1 to 3; 6FDA-DAM/6FpDA (1:3) and 6FDA-DAM/ABL-21(1:3) copolyimide membrane vs CO₂/CH₄；N_2/CH₄(ii) a And C₂H₆/CH₄Evaluation of mixed gas separation performance.

For random copolymerized polyimide film 6FDA-DAM/CARDO (1: 3); 6FDA-DAM/6FpDA (1:3) and 6FDA-DAM/ABL-21(1:3), studied at different upstream pressures, consisting of 10, 59, 30 and 1% by volume CO, respectively₂、CH₄、N₂And C₂H₆The permeation performance of the gas mixture of four part composition through the copolyimide membrane is summarized in tables 7 to 9.

Random copolyimide 6FDA-DAM/6FpDA (1:3) CO at high pressure of 800psig₂Permeability and CO₂/CH₄Selectivity was reduced to about 68Barrer and 30, respectively, CO of random copolyimide 6FDA-DAM/CARDO (1:3)₂Permeability and CO₂/CH₄Selectivities were about 57Barrer and 29, respectively; and random copolymerization of polyimide 6FDA-DAM/ABL-21(1:3) with CO₂Permeability and CO₂/CH₄The selectivities were about 48Barrer and 33, respectively. These values are still quite favorable for natural gas separations, particularly at high pressures such as 800 psig.

Example 7: 6FDA-DAM/CARDO (1:3) prepared in examples 1 to 3; 6FDA-DAM/6FpDA (1: 3); and 6FDA-DAM/ABL-21(1:3) vs. CO₂/CH₄And H₂S/CH₄Evaluation of separation Performance of the sulfur-containing mixed gas.

As shown in tables 10 to 12, at different gas feed pressures, the pressure ranges from 10 vol%, 57 vol% to 59 vol% were investigated10 vol%, 1 to 3 vol% and 20 vol% of CO₂、CH₄、N₂、C₂H₆And H₂S composition simulates the permeation performance of a sulfur-containing gas mixture through a membrane. Up to 20% by volume of H in the feed gas₂S is applied to the membrane. CO obtained from random copolymerization of polyimide 6FDA-DAM/6FpDA (1:3)₂/CH₄And H₂S/CH₄Desirably selectivity is up to about 29 and 19, respectively; and CO₂And H₂S permeability was as high as about 80Barrer and 50Barrer, respectively (table 10). Similarly, the random copolyimide 6FDA-DAM/CARDO (1:3) CO₂/CH₄And H₂S/CH₄d desirably has selectivity up to about 19 and 21, respectively, and CO₂And H₂S permeability was as high as about 48Barrer and 51Barrer, respectively (table 11).

Further, the random copolymerized polyimide film 6FDA-DAM/ABL-21(1:3) exhibited CO₂/CH₄And H₂S/CH₄The desired selectivity is up to about 26 and 13, respectively, and CO₂And H₂S permeability was as high as about 51Barrer and 26Barrer, respectively (table 12). These values and separation performance exhibited by the copolyimides are advantageous compared to those obtained in some high performance polymer membranes. One important point to note is that at moderate feed pressures and feed gas mixtures H₂The desired selectivity and permeability of the copolyimide is still moderate up to 20% by volume S. Further, CO of the copolymerized polyimide₂/CH₄The selectivity is not reduced to nearly the same extent as reported for Cellulose Acetate (CA), even in a more aggressive environment. At medium pressure and high H₂The stability at S concentration is attractive and unique and is surprising and unexpected.

Table 3: pure gas permeability (Barrer) and selectivity coefficient in random 6FDA-DAM type copolyimide membranes measured at 100psig feed pressure and 35 ℃.

Table 4: pure gas permeability of a random copolymerized polyimide 6FDA-DAM/6FpDA (1:3) membrane at 35 ℃.

Table 5: pure gas permeability of random copolymerized polyimide 6FDA-DAM/CARDO (1:3) membrane at 35 ℃.

Table 6: pure gas permeability of random copolymerized polyimide 6FDA-DAM/ABL-21(1:3) membrane at 35 ℃.

Table 7: at 22 ℃ with a composition comprising 10, 60 and 30% by volume of CO respectively₂、CH₄And N₂As a function of feed pressure, the mixed gas permeability and selectivity coefficient of the random copolyimide 6FDA-DAM/6FpDA (1:3) membrane.

Table 8: at 22 ℃ with a composition comprising 10, 60 and 30% by volume of CO respectively₂、CH₄And N₂As a function of feed pressure, the mixed gas permeability and selectivity coefficient of the random copolyimide 6FDA-DAM/6FpDA (1:3) membrane.

Table 9: at 22 ℃ containing 10 volumes each% 60% by volume and 30% by volume of CO₂、CH₄And N₂As a function of feed pressure, the mixed gas permeability and selectivity coefficient of the random copolyimide 6FDA-DAM/ABL-21(1:3) membrane.

Table 10: at 22 ℃ and using a solution containing 10% by volume of each; 57 to 59 volume%; 10% by volume; 1 to 3 and 20% by volume of CO₂、CH₄、N₂、C₂H₆And H₂S sulfur containing feed gas mixture the sulfur containing mixed gas permeability and selectivity coefficient of the random copolyimide 6FDA-DAM/6FpDA (1:3) membranes were determined.

Table 11: at 22 ℃ and using a solution containing 10% by volume of each; 59% by volume; 10% by volume; sulfur containing mixed gas permeability and selectivity coefficients for random copolyimide 6FDA-DAM/CARDO (1:3) membranes were determined at 1 and 20% by volume sulfur containing feed gas mixtures of CO2, CH4, N2, C2H6 and H2S.

Table 12: at 22 ℃ and using a solution containing 10% by volume of each; 59% by volume; 10% by volume; 1% and 20% by volume of CO₂、CH₄、N₂、C₂H₆And H₂S sulfur containing feed gas mixture the sulfur containing mixed gas permeability and selectivity coefficient of the random copolyimide 6FDA-DAM/ABL-21(1:3) membrane were determined.

Embodiments of the present disclosure show membrane-based gas separation applications, particularly the separation of acid gases from natural gas and the recovery of helium using a unique 6FDA-DAM type aromatic copolyimide membrane. The membranes exhibit advantageous permeation properties for pure gases and gas mixtures, with pure gas CO at 35 ℃ and feed pressures up to 300psig₂Permeability is in the range of about 105Barrer to 118Barrer, and CO₂/CH₄The selectivity is up to about 40.

Similarly, the permeability of pure gas He obtained under the same experimental conditions is in the range of about 132Barrer to 170Barrer, and He/CH₄The selectivity is up to about 52. In addition, a composition of 10% by volume; 57 to 59 volume%; 10% by volume; 1 to 3 and 20% by volume of CO₂、CH₄、N₂、C₂H₆And H₂S composition to simulate the permeation of a sulfur-containing gas mixture through an exemplary membrane, and H₂Up to 20% by volume of S feed gas is applied to the membrane.

CO obtained from random copolymerization of polyimide 6FDA-DAM/6FpDA (1:3)₂/CH₄And H₂S/CH₄Desirably selectivity of up to about 29 and about 19, respectively; and CO₂And H₂The permeability of S is up to about 80Barrer and 50Barrer, respectively. Similarly, for the random copolyimide 6FDA-DAM/CARDO (1:3), CO₂/CH₄And H₂S/CH₄The desired selectivity is up to about 19 and 21, respectively, and CO₂And H₂S permeability is up to about 48Barrer and 51Barrer, respectively. These values and separation performance exhibited by the copolyimides are advantageous compared to those obtained in some high performance polymer membranes. At moderate feed pressure and in the feed gas mixture H₂The desired selectivity and permeability of the copolyimide is still moderate up to 20% by volume S. Further, CO of the copolymerized polyimide₂/CH₄The selectivity is not reduced to nearly the same extent as reported for Cellulose Acetate (CA), even in the more aggressive environment herein. In thatMedium pressure and high H₂This stability at S concentration is attractive, unique, surprising and unexpected.

Another unique result obtained is that the copolyimide membranes not only have acid gas selectivity, but also are comparable to CH₄To N₂Having selectivity (i.e., N)₂Permeability in aromatic polyimides higher than CH₄). This provides separation advantages and saves energy because the membrane is permeable to both acid gases and N₂Both of them, to make CH₄Remaining on the high pressure side of the membrane.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

In the drawings and specification, there have been disclosed embodiments, and other embodiments, of an apparatus, system, and method for aromatic copolyimide membranes for sulfur-containing natural gas separation, and although specific terms are employed, they 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 particular reference to these illustrated embodiments. It will, however, be evident that various modifications and changes may be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are considered equivalent to and part of the disclosure.