Patent Application
20240150519
This document relates to copolyimides containing hydroxyl-functionalized CARDO and to membranes containing the copolyimides. This document also relates to methods of using the membranes for sour natural gas purification applications.
It is often unpredictable to incorporate hydroxyl groups into a polymer backbone of a polymeric membrane. It has been shown that hydroxyl groups can form interchain hydrogen-bond interactions which brings the polymeric chains closer, and therefore reduces excess free volume, leading to a decrease in gas permeability of membranes used in gas purification applications. Thus, it is not easy to predict the outcome of incorporating hydroxyl groups into the polymer backbone. Moreover, it becomes even more challenging when dealing with gas mixtures containing hydrogen sulfide, because membranes are prone to plasticization due to the high affinity of H2S molecules to polymeric materials due to the polar nature of H2S molecules.
Membranes containing polymeric backbones functionalized with groups such as alkyl or acyl groups have been prepared; however, there is a typically a permeability-selectivity trade-off, and such membranes typically do not exhibit both favorable diffusivity and solubility properties. The current development of membranes suffers from poor permeation properties and/or plasticization resistance at elevated gas feed pressures, which limits their used in natural gas upgrading.
Accordingly, there is a need for a membrane that can be used for sour natural gas purification applications that simultaneously exhibits improved solubility and diffusivity of gas molecules through the membrane.
Provided in the present disclosure are polymers that contain a structural repeat unit of Formula (I):
and
a structural repeat unit of Formula (II):
wherein:
In some embodiments, A is phenylene optionally substituted with one, two, three, or four R5.
In some embodiments, each R5 is independently C1-4 alkyl. In some embodiments, each R5 is methyl.
In some embodiments, X and Y are each C1 alkylene, each optionally substituted with one or two R6. In some embodiments, each R6 is independently C1 alkyl optionally substituted with one, two, or three R6, and each R6 is independently halo.
In some embodiments, X and Y are each C1 alkylene, wherein each C1 alkylene is substituted with two —CF3.
In some embodiments, R3 and R4 are each independently selected from H, —OH, halo, C1-4 alkyl, phenyl, —C1-2 alkyl-phenyl, —NH2, and —N(CH3)2, wherein at least one of R3 and R4 is —OH. In some embodiments, R3 is —OH and R4 is selected from H, —OH, halo, C1-4 alkyl, phenyl, —C1-2 alkyl-phenyl, —NH2, and —N(CH3)2. In some embodiments, R3 and R4 are each —OH.
In some embodiments, a and b are each independently 0 or 1.
In some embodiments, the polymer contains the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) in a molar ratio of about 3:1 to about 1:3. In some embodiments, the polymer contains the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) in a molar ratio of about 2:1 to about 1:2. In some embodiments, the polymer contains the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) in a molar ratio of about 1:1.
In some embodiments, the polymer has a number-average molecular weight of about 1,000 g/mol to about 1,000,000 g/mol. In some embodiments, the polymer has a number-average molecular weight of about 100,000 g/mol to about 500,000 g/mol.
In some embodiments of the polymer, the structural repeat unit of Formula (I) is a structural repeat unit of Formula (I-B):
and
the structural repeat unit of Formula (II) is a structural repeat unit of Formula (II-B):
wherein:
In some embodiments of Formula (II-B), R3 and R4 are each —OH.
In some embodiments of Formula (I-B), each R5 is methyl.
In some embodiments, n is 3 or 4.
In some embodiments, the polymer contains the structural repeat unit of Formula (I-B) and the structural repeat unit of Formula (II-B) in a molar ratio of about 2:1 to about 1:2. In some embodiments, the polymer contains the structural repeat unit of Formula (I-B) and the structural repeat unit of Formula (II-B) in a molar ratio of about 1:1.
Also provided in the present disclosure is a membrane that contains the polymer of Formula (I). In some embodiments, the membrane contains at least about 80 wt % of the polymer.
Also provided in the present disclosure is a method for separating CO2 and H2S from natural gas. In some embodiments, the method includes introducing a natural gas stream to the membrane of the present disclosure; and separating the CO2 and the H2S from the natural gas stream.
In some embodiments of the method, the natural gas stream contains about 1 vol % to about 30 vol % of CO2 and about 1 vol % to about 40 wt % of H2S, prior to separating the CO2 and the H2S from the natural gas stream.
Provided in the present disclosure are polymeric membranes prepared from polyimides containing hydroxyl-functionalized 9,9-bis(4-aminophenyl)fluorene (CARDO) moieties for sour natural gas purification applications. Also provided in this disclosure are methods for preparing polyimide structures containing symmetric or asymmetric hydroxyl-functionalized CARDO moieties. One or two hydroxyl groups can be positioned in the 2 and/or 7 positions of the fluorenyl group of the CARDO moiety to serve as polar groups which can simultaneously improve the solubility and diffusivity of gas molecules through the polymeric matrix of membranes containing such moieties.
It has surprisingly been found that polymers such as CARDO that have been functionalized with hydroxyl groups tend to behave differently than what someone skilled in the art would predict. In some embodiments, the permeability coefficients of membranes containing such polymers increased. Without wishing to be bound by any particular theory, it is believed that the excess free volume within the membrane matrix is increased due to a particular special arrangement of hydroxyl groups, such as similar to what happens in ice. The dynamic free volume within the membrane matrix can separate the gas molecules based on the difference of their sizes (kinetic diameters, Dk) according to a kinetic phenomenon (rate of diffusion), since methane (Dk=3.80 Å, the main component of natural gas) is larger in size than the undesired existent impurities in natural gas (Dk=3.30 Å for CO2 and Dk=3.60 Å for H2S). Additionally, improving the gas-polymer affinity allows better solubility of polar gas molecules, such as H2S, or molecules containing polar bonds, such as CO2, to favor their permeation through the membrane matrix, while not influencing the transport of methane.
Thus, the presence of a hydroxyl group in the polymer backbone is beneficial since it enhances the polymer/polymer interactions and the gas/polymer affinity. In particular, it increases the gas/polymer affinity of polar gases such as hydrogen sulfide, or gases containing polar bonds such as carbon dioxide. Alkyl and alkoxy groups affect the interchain interactions through adding weaker interactions than hydrogen bond (which is the case for a hydroxyl group) and increasing the excess free volume through adding bulkiness to the polymeric chain.
The CARDO-based compounds of the present disclosure that are functionalized with one or more hydroxyl groups have increased van der Waals volume as compared to the same CARDO moiety without the hydroxyl groups. For example, adding a hydroxyl group to the CARDO structure increases its van der Waals volume [338.51 Å3 for 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol and 321.61 Å3 for 9,9-bis(4-aminophenyl)fluorene]. Therefore, adding one or more hydroxyl groups to the polymer backbone allows for fine-tuning the diffusivity and solubility of gas molecules by increasing the dynamic free volume within the membrane matrix and the gas-polymer affinity, respectively.
Additionally, the hydroxyl groups also can enhance the possibility of thermal self-crosslinking (by allowing two adjacent phenol groups to react to form a covalent bond which serves as a crosslinker) at high temperatures, such as at temperatures greater than about 180° C.
Thus, provided in the present disclosure are polymeric membranes with improved performance for use in natural gas separation applications. Use of the membranes of the present disclosure allow for enhanced productivity, efficiency, and resistance to plasticization at elevated operational conditions of pressure and temperature during sweet and/or sour mixed-gas separation, which can reduce the capital expenditure (CAPEX) and operational expenditure (OPEX) of the membrane-based natural gas purification process.
Reference will now be made in detail to certain embodiments of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.
Unless otherwise defined, all technical and scientific terms used in this document have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. Methods and materials are described in this document for use in the present application; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, sequences, database entries, and other references mentioned in this document are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.
Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges (for example, 0.1% to 0.5%, 1.1% to 2.2%, and 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.
The term “about,” as used in this disclosure, can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.
As used in this disclosure, the terms “a,” “an,” and “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed in this disclosure, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.
In the methods described in this disclosure, the acts can be carried out in any order, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.
The terms “sour” or “sour gas” mean that the gas stream contains hydrogen sulfide (H2S).
As used in the present disclosure, the term “monomer unit,” used in reference to a polymer, refers to a monomer, or residue of a monomer, that has been incorporated into at least a portion of the polymer.
As used in the present disclosure, the term “polymerization product,” used in reference to one or more monomers, refers to a polymer that can be formed by a chemical reaction of the one or more monomers. For example, a “polymerization product” of acrylic acid is a polymer containing acrylic acid monomer units.
As used in the present disclosure, the term “Cn-m alkyl” refers to any linear or branched saturated hydrocarbon group having n to m carbons. Alkyl groups include, but are not limited to, methyl, ethyl, propyl such as propan-1-yl, propan-2-yl (iso-propyl), butyl such as butan-1-yl, butan-2-yl (sec-butyl), 2-methyl-propan-1-yl (iso-butyl), 2-methyl-propan-2-yl (t-butyl), pentyl, hexyl, octyl, dectyl, and the like. As used in the present disclosure, the term “alkylene” refers to a bivalent alkyl.
As used in the present disclosure, the term “polycyclic aromatic hydrocarbon” refers to any multiple-condensed ring system of two or more fused, all-carbon aromatic rings. Polycyclic aromatic hydrocarbons include, but are not limited to, naphthalene, anthracene, triphenylene, pyrene, perylene, and the like.
As used in the present disclosure, the term “halo” refers to —F, —Cl, —Br, or —I.
As used in the present disclosure, the term “hydroxyl” refers to —OH.
As used in the present disclosure, the term “amino” refers to —NH2.
As used in the present disclosure, the term “thiol” refers to —SH.
As used in the present disclosure, the term “carboxyl” refers to —C(O)OH.
As used in the present disclosure, the term “azido” refers to —N3.
Where a variable of the present disclosure defines a group having more than one substituent (for example, group A of Formula (I)) and the Markush group definition for that variable lists, for example, a polycyclic aromatic hydrocarbon, then it is understood that the polycyclic aromatic hydrocarbon represents a substituent having the necessary valency.
The polymers of the present disclosure contain hydroxyl-functionalized CARDO moieties. In some embodiments, the CARDO moiety is functionalized with a hydroxyl moiety at the 2 position, the 7 position, or both. Scheme 1 depicts an exemplary synthetic scheme of a hydroxyl-functionalized CARDO moiety of the present disclosure As shown in Scheme 1, the hydroxyl-functionalized CARDO moiety could be symmetric or asymmetric in a way such that the substituents X1 and X2 are the same or different. In some embodiments, X1=X2=—OH. In some embodiments, X1≠X2, where one of X1 or X2 is a hydroxyl group (—OH), and the second is a different atom (for example, hydrogen or halogen) or group (for example, alkyl, aryl, amine derivative).
Exemplary symmetric and asymmetric hydroxyl-functionalized CARDO diamine monomers that can be prepared and used in the polymers and membranes of the present disclosure include, but are not limited to:
The prepared hydroxyl-functionalized CARDO diamine monomers can be reacted with a variety of dianhydride monomers to afford homopolyimides (Scheme 2) and a variety of dianhydride and other aromatic diamine monomers to afford copolyimides (Scheme 3), where Ar1 and Ar2 represent the various aromatic moieties that can be used in the preparation of the hydroxyl-functionalized CARDO-based homopolyimides and copolyimides of the present disclosure. The homopolyimides are prepared using a hydroxyl-functionalized CARDO moiety and a dianhydride monomer while the copolyimides are prepared using a hydroxyl-functionalized CARDO moiety and a dianhydride monomer in addition to another diamine monomer. The copolymerization aims to combine the gas permeation properties of two separate homopolymers into one copolymer structure. The homopolyimides and copolyimides can be used to prepare polymeric membranes with improved sweet and/or sour mixed-gas separation properties for natural gas purification applications. In some embodiments, the second diamine monomer is chosen to complement the properties provided by the hydroxyl-functionalized CARDO-based homopolyimide to either improve the permeability or selectivity of the copolyimide membrane.
Exemplary dianhydride monomers that can be used in the polymers and membranes of the present application include, but are not limited to:
The aromatic diamine monomer used in the preparation of the copolyimides of the present disclosure can be used to provide polymer segments that can tailor the properties of the targeted polymeric materials. Exemplary diamine monomers that can be used in the polymers and membranes of the present application include, but are not limited to:
Thus, provided in the present disclosure are polymers that contain a structural repeat unit of Formula (I):
and
wherein:
X and Y are each independently selected from a bond, —O—, —C(O)—, —O-phenyl-Z-phenyl-O—, and C1-4 alkylene optionally substituted with one or more R6;
each R5 and R6 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, —N3, and C1-4 alkyl optionally substituted with one or more R7, wherein each R7 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, and —N3; and
In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) make up at least about 80 wt % of the polymer. In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) make up at least about 85 wt %, at least about 90 wt %, at least about 95 wt %, at least about 97.5 wt %, at least about 98 wt %, at least about 98.5 wt %, or at least about 99 wt % of the polymer.
In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) are present in the polymer in a molar ratio of about 5:1 to about 1:5. In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) are present in the polymer in a molar ratio of about 5:1 to about 1:4, about 5:1 to about 1:3, about 5:1 to about 1:2, about 4:1 to about 1:5, about 4:1 to about 1:4, about 4:1 to about 1:3, about 4:1 to about 1:2, about 3:1 to about 1:5, about 3:1 to about 1:4, about 3:1 to about 1:3, about 3:1 to about 1:2, about 2:1 to about 1:5, about 2:1 to about 1:4, about 2:1 to about 1:3, or about 2:1 to about 1:2. In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) are present in the polymer in a molar ratio of about 3:1. In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) are present in the polymer in a molar ratio of about 2:1. In some embodiments, the structural repeat unit of Formula (I) and the structural repeat unit of Formula (II) are present in the polymer in a molar ratio of about 1:1.
In some embodiments, the polymer has a number-average molecular weight of about 1,000 g/mol to about 1,000,000 g/mol, such as about 1,000 g/mol to about 900,000 g/mol, about 10,000 g/mol to about 800,000 g/mol, about 50,000 g/mol to about 700,000 g/mol, about 100,000 g/mol to about 600,000 g/mol, about 200,000 g/mol to about 500,000 g/mol, about 300,000 g/mol, or about 1,000 g/mol, about 5,000 g/mol, about 10,000 g/mol, about 25,000 g/mol, about 50,000 g/mol, about 100,000 g/mol, about 150,000 g/mol, about 200,000 g/mol, about 250,000 g/mol, about 300,000 g/mol, about 350,000 g/mol, about 400,000 g/mol, about 450,000 g/mol, about 500,000 g/mol, about 550,000 g/mol, about 600,000 g/mol, about 650,000 g/mol, about 700,000 g/mol, about 750,000 g/mol, about 800,000 g/mol, about 850,000 g/mol, about 900,000 g/mol, about 950,000 g/mol, or about 1,000,000 g/mol.
The polymers of the present disclosure can be prepared according to any suitable method. For example, polymers including a structural repeat unit of Formula (I) and a structural repeat unit of Formula (II) can be prepared by polycondensation of a dianhydride monomer, a hydroxyl-functionalized CARDO monomer, and an aromatic diamino monomer. In some embodiments, the polymer includes the polymerization product of a diphthalic anhydride monomer (for example, 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione), a hydroxyl-functionalized CARDO monomer (for example, CARDO(OH)), and an aromatic diamino monomer (for example, 2,3,5,6-tetramethylbenzene-1,4-diamine (durene) or 2,4,6-trimethylbenzene-1,3-diamine (DAM)).
The synthetic methodology described in the present disclosure allows for the preparation of a large variety of hydroxyl-functionalized CARDO-based polymers, including, but not limited to, homopolymers, random copolymers, block copolymers, terpolymers, alternating copolymers, and so on.
In some embodiments, A is phenylene, biphenylene, terphenylene, naphthalenylene, or anthracenylene. In some embodiments, A is phenylene. In some embodiments, A is optionally substituted with one, two, three, or four R5. In some embodiments, A is substituted with two or three R5. In some embodiments, A is phenylene substituted with three R5. In some embodiments, at least one R5 is independently C1-4 alkyl. In some embodiments, each R5 independently C1-4 alkyl. In some embodiments, each R5 is unsubstituted C1-4 alkyl. For example, in some embodiments, each R5 is unsubstituted C1 alkyl. In some embodiments, A has the structure:
In some embodiments, A has the structure:
In some embodiments, X is selected from a bond, —O—, —C(O)—, —O-phenyl-Z-phenyl-O—, and C1-4 alkylene optionally substituted with one or more R6.
In some embodiments, X is a bond.
In some embodiments, X is —O—.
In some embodiments, X is —C(O)—.
In some embodiments, X is —O-phenyl-Z-phenyl-O—. In some embodiments, Z is C1-4 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1-3 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1-2 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1 alkylene optionally substituted with one or more R6.
In some embodiments, X is C1-4 alkylene optionally substituted with one or more R6. In some embodiments, X is C1-3 alkylene optionally substituted with one or more R6. In some embodiments, X is C1-2 alkylene optionally substituted with one or more R6. In some embodiments, X is C1 alkylene optionally substituted with one or more R6.
In some embodiments, each R6 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, —N3, and C1-4 alkyl optionally substituted with one or more R7, wherein each R7 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, and —N3. In some embodiments, each R6 is independently selected from C1-4 alkyl optionally substituted with one or more R7. In some embodiments, R7 is halo. In some embodiments, X is C1 alkylene substituted with two —CF3. In some embodiments, X is —O-phenyl-Z-phenyl-O—, where Z is Z is C1 alkylene substituted with two —CH3.
In some embodiments, X is C1 alkylene. In some embodiments, X is optionally substituted with one or two R6. For example, in some embodiments, X is substituted with one or two R6. In some embodiments of Formula (I), one or more R6 are each independently C1 alkyl optionally substituted with one, two, or three halo. In some embodiments of Formula (I), each R6 is independently C1 alkyl optionally substituted with one, two, or three halo. In some embodiments of Formula (I), each R6 is independently C1 alkyl substituted with three halo. In some embodiments, one or more halo are —F. In some embodiments each halo is —F.
In some embodiments, each a is independently 0 or 1. In some embodiments, each a is 0.
In some embodiments, the structural repeat unit of Formula (I) is a structural repeat unit of Formula (I-A):
In some embodiments, n is 0, 1, 2, 3, or 4. On some embodiments, n is 0. In some embodiments, n is 1. In some embodiments, n is 2. In some embodiments, n is 3. In some embodiments, n is 4.
In certain embodiments of Formula (I-A), X is the same as Y of Formula (II) or Formula (II-A) of the present disclosure. In some embodiments of Formula (I-A), X is C1 alkylene substituted with one or two R6. In some embodiments, Formula (I-A) includes three or four R5 groups. In certain embodiments of Formula (I-A), each R5 is independently unsubstituted C1-4 alkyl, and each R6 is independently C1-4 alkyl substituted with three halo.
In some embodiments, the structural repeat unit of Formula (I) is a structural repeat unit of Formula (I-B):
In some embodiments, n is 0, 1, 2, 3, or 4. On some embodiments, n is 0. In some embodiments, n is 1. In some embodiments, n is 2. In some embodiments, n is 3. In some embodiments, n is 4.
In some embodiments of Formula (I-B), each R5 is independently unsubstituted C1-4 alkyl. In certain such embodiments, each R5 is unsubstituted C1 alkyl. In some embodiments, Formula (I-B) includes three or four R5 groups.
In some embodiments, Y is selected from a bond, —O—, —C(O)—, —O-phenyl-Z-phenyl-O—, and C1-4 alkylene optionally substituted with one or more R6.
In some embodiments, Y is a bond.
In some embodiments, Y is —O—.
In some embodiments, Y is —C(O)—.
In some embodiments, Y is —O-phenyl-Z-phenyl-O—. In some embodiments, Z is C1-4 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1-3 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1-2 alkylene optionally substituted with one or more R6. In some embodiments, Z is C1 alkylene optionally substituted with one or more R6.
In some embodiments, Y is C1-4 alkylene optionally substituted with one or more R6. In some embodiments, Y is C1-3 alkylene optionally substituted with one or more R6. In some embodiments, Y is C1-2 alkylene optionally substituted with one or more R6. In some embodiments, Y is C1 alkylene optionally substituted with one or more R6.
In some embodiments, each R6 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, —N3, and C1-4 alkyl optionally substituted with one or more R7, wherein each R7 is independently selected from halo, —OH, —NH2, —SH, —C(O)OH, and —N3. In some embodiments, each R6 is independently selected from C1-4 alkyl optionally substituted with one or more R7. In some embodiments, R7 is halo. In some embodiments, Y is C1 alkylene substituted with two —CF3. In some embodiments, Y is —O-phenyl-Z-phenyl-O—, where Z is C1 alkylene substituted with two —CH3.
In some embodiments, Y is C1 alkylene. In some embodiments, Y is optionally substituted with one or two R6. For example, in some embodiments, Y is substituted with one or two R6. In some embodiments of Formula (I), one or more R6 are each independently C1 alkyl optionally substituted with one, two, or three halo. In some embodiments of Formula (I), each R6 is independently C1 alkyl optionally substituted with one, two, or three halo. In some embodiments of Formula (I), each R6 is independently C1 alkyl substituted with three halo. In some embodiments, one or more halo are —F. In some embodiments each halo is —F.
In some embodiments, at least one of R3 and R4 is —OH. In some embodiments, R3 and R4 are each independently selected from H, —OH, halo, C1-6 alkyl, C1-6 haloalkyl, phenyl, —C1-4 alkyl-phenyl, and —NRaRb, wherein Ra and Rb are each independently selected from H and C1-6 alkyl. In some embodiments, one of R3 and R4 is —OH, and the other is selected from —H, —OH, —F, —Cl, —Br, —I, C1-4 alkyl, —NH2, —N(CH3)2, phenyl, and —CH2-phenyl. In some embodiments, R3 and R4 are each —OH.
In some embodiments, each b is independently 0 or 1. In some embodiments, each b is 0.
In some embodiments, the structural repeat unit of Formula (II) is a structural repeat unit of Formula (II-A):
In certain embodiments of Formula (II-A), Y is the same as X of Formula (I) or Formula (I-A) of the present disclosure. In some embodiments of Formula (II-A), Y is C1 alkylene substituted with one or two R6. In some embodiments, Formula (II-A) includes three or four R5 groups. In certain embodiments of Formula (II-A), each R5 is independently unsubstituted C1-4 alkyl, and each R6 is independently C1-4 alkyl substituted with three halo.
In some embodiments, the structural repeat unit of Formula (II) is a structural repeat unit of Formula (II-B):
Also provided in the present disclosure are membranes including a polymer including a structural repeat unit of Formula (I) and a structural repeat unit of Formula (II). In some embodiments, the membrane includes any polymer of the present disclosure.
In some embodiments, the membrane includes at least about 80 wt % of the polymer. For example, in some embodiments, the membrane includes at least about 85 wt %, at least about 90 wt %, at least about 95 wt %, at least about 97.5 wt %, at least about 98 wt %, at least about 98.5 wt %, or at least about 99 wt % of the polymer.
Also provided in the present disclosure are methods for preparing a membrane of the present disclosure. Polymeric membranes are thin semipermeable barriers that selectively separate some gas compounds from others. The membranes are dense films that do not operate as a filter, but rather separate gas compounds based on how well the different compounds dissolve into the membrane and diffuse through it (the solution-diffusion model). The membranes of the present disclosure are useful for any gas separation application, including, but not limited to, natural gas sweetening, oxygen enrichment, hydrogen purification, and nitrogen and organic compounds removal from natural gas. In some embodiments, the membranes of the present disclosure are used for the separation of CO2 and H2S from sour gas.
In some embodiments, the method includes preparing a solution of any polymer of the present disclosure. In some embodiments, the polymer is added to a solvent and dissolved. In some embodiments, the solvent is an organic solvent. In some embodiments, the solvent is dimethylformamide (DMF). In some embodiments, the polymer is dissolved at room temperature. In some embodiments, the polymer is dissolved completely in the solvent before proceeding to the next step. In some embodiments, the polymer is filtered. In some embodiments, the polymer is filtered with a PTFE filter.
In some embodiments, the solution contains about 1 wt % to about 10 wt % polymer, such as about 2 wt % to about 5 wt %, or about 3 wt % polymer. In some embodiments, the solution containing the polymer is poured into a flat-bottomed container in order to prepare a film. In some embodiments, the film is dried to allow for evaporation of solvent. In some embodiments, the film is dried at an elevated temperature under a flow of nitrogen gas. In some embodiments, the film is further dried in a vacuum oven, for example, at about 100° C. to about 275° C., or about 150° C. to about 200° C. for at least about 4 hours, about 6 hours, about 12 hours, about 18 hours, about 24 hours, about 30 hours, about 36 hours, about 42 hours, about 48 hours, or more.
In some embodiments, after drying, the film is soaked in a second solvent. In certain such embodiments, the second solvent is deionized water. In some embodiments, the film is soaked in the second solvent for at least a few minutes or more. In some embodiments, the second solvent is removed from the film, and then the film is dried to provide the membrane. In some embodiments, the second solvent is removed from the film, and then the film is dried in a vacuum oven, for example, at about 60° C. for about 6 hours.
Also provided in the present disclosure are membranes prepared by the methods of the present disclosure. In general, for natural gas purification, it is desired to improve the permeability of impurities (such as carbon dioxide (CO2) and hydrogen sulfide (H2S)) and the membrane selectivities (CO2/CH4 and H2S/CH4) toward the main hydrocarbons constituting the natural gas (methane (CH4)). In another aspect, it is desired to increase the plasticization resistance of polymeric membranes during high pressure mixed-gas separation. In some embodiments, the polar hydroxyl groups of the hydroxyl-functionalized CARDO groups form a hydrogen bond or dipole-dipole type interaction between the polymeric chains which limits their mobility under harsh separation conditions of temperature and pressure. Moreover, in some embodiments, the hydroxyl groups allow two adjacent phenol groups to react to form a covalent bond under high temperature (>180° C.) which will serve as a crosslinker, referred to in the present disclosure as thermal self-crosslinking. This strategy has proven to improve the permeation properties and plasticization resistance of the polymeric membranes during mixed-gas separation at high feed pressures.
In some embodiments, the membranes of the present disclosure demonstrate improved gas transport properties in natural gas separation, for example, sour gas separation, as compared to conventional polymer-based membranes that do not contain a hydroxyl-modified CARDO moiety. In some embodiments, the membranes of the present disclosure demonstrate high CO2/CH4 selectivity, high H2S/CH4 selectivity, and resistance to plasticization, for example, at a feed pressure up to about 900 psi, as compared to conventional polyimide-based membranes that do not contain a hydroxyl-modified CARDO moiety. The membranes of the present disclosure possess increased CO2 permeation coefficients and comparable CO2/CH4 selectivity as compared to convention polyimide-based membranes that do not contain a hydroxyl-modified CARDO moiety.
Current natural gas purification technology involves the use of liquid amines to remove acid gases from natural gas reserves. The use of liquid amines includes a liquid amine regeneration step which requires the consumption of a substantial amount of energy; a step that renders the process costly. The gas separation membranes of the present disclosure provide an alternative energy efficient method. The membranes of the present disclosure possess a set of specifications related to their gas permeability (or permeance) (H2S and CO2) and selectivity (CO2/CH4 and H2S/CH4) that allow this technology to compete or be conjugated with current technology. In some embodiments, the membranes exhibit mixed sour gas selectivity for CO2/CH4 and H2S/CH4 from 15 up to 25 and permeance up to 80 GPU for CO2 and H2S. Thus, the membranes of the present disclosure can be used in a bulk acid gas removal process. In some embodiments, the hydroxyl-functionalized CARDO-based polyimides provide for an improved membrane system for sweet and sour mixed-gas separation.
Thus, also provided in the present disclosure are methods for using a membrane of the present disclosure. In some embodiments, the methods include separating CO2, H2S, or both from natural gas by introducing a natural gas stream to any membrane of the present disclosure, and separating the CO2, H2S, or both from the natural gas stream. In some embodiments, the natural gas stream includes about 1 vol % to about 30 vol % of CO2 before separating. For example, in some embodiments, the natural gas stream includes about 1 vol % to about 20 vol %, about 1 vol % to about 15 vol %, about 3 vol % to about 30 vol %, about 3 vol % to about 20 vol %, or about 3 vol % to about 15 vol % of CO2 before separating. In some embodiments, the natural gas stream includes about 1 vol % to about 40 vol % of H2S before separating. For example, in some embodiments, the natural gas stream includes about 1 vol % to about 30 vol %, about 1 vol % to about 25 vol %, about 5 vol % to about 40 vol %, about 5 vol % to about 30 vol %, or about 5 vol % to about 25 vol % of H2S before separating.
In some embodiments, the natural gas stream includes at least about 30 vol %, for example, at least about 40 vol %, or at least about 50 vol % of CH4 before separating. In some embodiments, the natural gas stream further includes N2, C2H6, or both.
To a 500 mL three-neck round bottom flask equipped with a nitrogen inlet, condenser, and a magnetic bar, 2,7-dihydroxy-9H-fluoren-9-one (10.6 g, 50.0 mmol), aniline (36.4 mL, 400 mmol), and methanesulfonic acid (1.621 mL, 24.98 mmol) were added and the mixture was heated to 150° C. for 14 hours. The reaction mixture was then cooled down to room temperature and poured into a solution of 2.0 M sodium hydroxide in 200 mL of ethanol and stirred at the same temperature overnight. The precipitated solid was collected by filtration and washed thoroughly by ethanol and distilled water several times, then dried under vacuum overnight to provide 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (14.00 g, 36.8 mmol, 73.7% yield) as a pale-yellow solid. 1H NMR (500 MHz, DMSO-d6) δ 9.28 (s, 2H), 7.45 (d, J=7.7 Hz, 2H), 6.80-6.51 (m, 8H), 6.42 (d, J=7.5 Hz, 4H), 4.90 (s, 4H).
In a 100 mL three-neck round bottom flask equipped with a nitrogen inlet and a mechanical stirrer, 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (0.798 g, 2.098 mmol) [CARDO(OH)] and 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.932 g, 2.098 mmol) (6FDA) were dissolved in m-cresol (8.00 mL). A catalytic amount (4 drops) of isoquinoline was added to the reaction mixture, and the mixture was then heated gradually to 180° C. and kept for 8 hours. The heat was removed, and the reaction mixture was allowed to cool down to room temperature. The resulting viscous solution was poured into methanol (30 mL), then washed three times (3×30 mL) to remove the residual m-cresol solvent. The final product 6FDA-CARDO(OH) (1.631 g, 1.993 mmol, 95% yield) was dried in an oven pre-set to 75° C. for 24 hours. 1H NMR (500 MHz, DMSO-d6) δ 9.26 (s, 2H), 8.12 (d, J=7.5 Hz, 2H), 7.93 (s, 2H), 7.78 (s, 2H), 7.57 (d, J=7.8 Hz, 2H), 7.40 (d, J=7.6 Hz, 4H), 7.29 (d, J=7.6 Hz, 4H), 6.84 (s, 2H), 6.79 (d, J=7.6 Hz, 2H).
In a 100 mL three-neck round bottom flask equipped with a nitrogen inlet and a magnetic stir bar, 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.574 g, 1.293 mmol) (6FDA) and 2,3,5,6-tetramethylbenzene-1,4-diamine (0.250 g, 1.522 mmol) (durene) were introduced and dissolved in m-cresol (12.0 mL) and the reaction mixture was heated to 180° C. and stirred for 8 hours. The heat was stopped overnight and the reaction was allowed to cool down to room temperature. The reaction mixture was preheated to 160° C., then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.778 g, 1.751 mmol) (6FDA) and 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (0.579 g, 1.522 mmol) [CARDO(OH)] were added, followed by m-cresol (12.00 mL) and the mixture was heated to 180° C. and stirred for 8 hours. The heat was removed and the reaction mixture was allowed to cool down below 100° C., then the resulting highly viscous solution was poured into methanol in thin fibers. The fibrous polymer obtained was ground, rinsed with methanol, filtered, and dried under reduced pressure for 24 h at 60° C. to afford 6FDA-durene/6FDA-CARDO(OH) (1:1) (2.075 g, 1.492 mmol, 98% yield) as an off-white powder. 1H NMR (500 MHz, DMSO-d6) δ 9.24 (s, 2H), 8.27-8.08 (m, 4H), 8.12-7.83 (m, 8H), 7.78 (s, 2H), 7.57 (d, J=7.2 Hz, 2H), 7.47-7.18 (m, 8H), 6.92-6.75 (m, 4H), 2.09 (s, 12H).
The same procedure as described in Example 3 was followed, using 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.574 g, 1.293 mmol) (6FDA), 2,3,5,6-tetramethylbenzene-1,4-diamine (0.250 g, 1.522 mmol) (durene), and m-cresol (12.0 mL), then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.439 g, 0.989 mmol) (6FDA), and 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (0.290 g, 0.761 mmol) [CARDO(OH)], followed by m-cresol (12.00 mL) to afford 6FDA-durene/6FDA-CARDO(OH) (2:1) (2.011 g, 1.446 mmol, 95% yield) as an off-white powder. 1H NMR (500 MHz, DMSO-d6) δ 9.24 (s, 2H), 8.23-7.75 (m, 18H), 7.57 (d, J=7.9 Hz, 2H), 7.35 (dd, J=55.9, 7.9 Hz, 8H), 6.89-6.72 (m, 4H), 2.09 (s, 24H).
The same procedure as described in Example 3 was followed, using 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.574 g, 1.293 mmol) (6FDA), 2,3,5,6-tetramethylbenzene-1,4-diamine (0.250 g, 1.522 mmol) (durene), and m-cresol (12.0 mL), then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.327 g, 0.737 mmol) (6FDA), and 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (0.193 g, 0.507 mmol) [CARDO(OH)], followed by m-cresol (12.00 mL) to afford 6FDA-durene/6FDA-CARDO(OH) (3:1) (1.990 g, 1.431 mmol, 94% yield) as an off-white powder. 1H NMR (500 MHz, DMSO-d6) δ 9.22 (s, 2H), 8.18-7.72 (m, 24H), 7.53 (d, J=8.3 Hz, 2H), 7.30 (dd, J=56.0, 8.4 Hz, 8H), 6.83-6.69 (m, 4H), 2.04 (s, 36H).
In a 100 mL three-neck round bottom flask equipped with a nitrogen inlet and a magnetic stir bar, 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.628 g, 1.414 mmol) (6FDA) and 2,4,6-trimethylbenzene-1,3-diamine (0.250 g, 1.664 mmol) (DAM) were introduced and dissolved in m-cresol (8.00 mL) and the reaction mixture was heated to 180° C. and stirred for 8 hours. The heat was stopped overnight and the reaction was allowed to cool down to room temperature. The reaction mixture was preheated to 160° C., then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.357 g, 0.804 mmol) (6FDA) and 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (0.211 g, 0.554 mmol) [CARDO(OH)] were added, followed by m-cresol (8.00 mL) and the mixture was heated to 180° C. and stirred for 8 hours. The heat was removed and the reaction mixture was allowed to cool down below 100° C., then the resulting highly viscous solution was poured into methanol in thin fibers. The fibrous polymer obtained was ground, rinsed with methanol, filtered and dried under reduced pressure for 24 h at 60° C. to afford 6FDA-DAM/6FDA-CARDO(OH) (3:1) (1.465 g, 1.064 mmol, 96% yield) as an off-white powder. 1H NMR (500 MHz, DMSO-d6) δ 9.24 (s, 2H), 8.20-7.76 (m, 24H), 7.57 (d, J=7.6 Hz, 2H), 7.46-7.25 (m, 11H), 6.90-6.72 (m, 4H), 2.15 (s, 18H), 1.92 (s, 9H).
The chemical structures and purity of the compounds described in Examples 1-6 were confirmed using proton nuclear magnetic spectroscopy (1H NMR) in corresponding deuterated solvents (i.e., DMSO-d6).
The chemical structure of the CARDO(OH) monomer was confirmed by its 1H NMR spectrum in deuterated DMSO-d6 as illustrated in
The presence of functional groups within the structure of CARDO(OH) monomer, such as the primary amine groups, were confirmed using Fourier Transform Infrared (FTIR) spectroscopy, and the spectrum is illustrated in
In a similar fashion, the chemical structures and purity of the final product of the polymers described in Examples 1-6 were confirmed using 1H-NMR in DMSO-d6. For example, the 1H-NMR of the homopolymer 6FDA-CARDO(OH) was measured in DMSO-d6 and it is depicted in
For the copolyimides of Examples 3-6, in addition to determining their chemical structures and purities, the 1H NMR spectra were further used to determine the molecular ratio of the co-monomers within the copolymer backbone. For example, the desired molar ratio between the co-monomers durene and CARDO(OH) in the 6FDA-durene/6FDA-CARDO(OH) (2:1) block copolymer described in Example 4 is calculated from the area integration of the aromatic peaks of CARDO(OH) and aliphatic peak of durene, from the spectrum illustrated in
For instance, the durene monomer does not have aromatic protons; however, it possesses 12 aliphatic protons, which appear as a singlet at 2.09 ppm, that correspond to its four methyl groups. If the total integration of the aromatic peaks that correspond to CARDO(OH) are set for a total of 14 protons that correspond to one CARDO(OH) molecule, the singlet peak at 2.09 ppm for durene integrates for 24 protons, which indicates a molar ratio of 2:1 between durene and CARDO(OH) co-monomers.
In a similar way, the molar ratios between durene and CARDO(OH) comonomers in 6FDA-durene/6FDA-CARDO(OH) (1:1) and 6FDA-durene/6FDA-CARDO(OH) (3:1) block copolymers (Examples 3 and 5, respectively), and DAM and CARDO(OH) in 6FDA-DAM/6FDA-CARDO(OH) (3:1) block copolymer (Example 6) were determined using their corresponding 1H NMR spectra.
The FTIR spectra of all the described polymers were recorded to ensure that the polycondensation reaction was complete (
The thermal properties of the prepared polymers were measured using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) and the results are illustrated in
The decomposition temperatures at 5% and 10% were determined (Table) to evaluate the thermal stability of the prepared polymers during the harsh industrial conditions of gas separation application. All Td5% of the prepared copolymers were recorded to be higher than 485° C. which was similar to high thermally stable membranes used in gas separation technology. The first derivatives of the TGA curves (
The glass transition temperatures (Tg) of the polymers described in Examples 1-6 were calculated from their corresponding DSC traces and the values are listed in Table 1. To obtain the Tg values, polymer samples were heated for two cycles. The first heating cycle was used to clear the thermal history of the polymer, where the Tg was recorded after the second heating cycle. All the recorded Tg values were greater than 390° C. These high temperatures indicated the rigidity of the polymeric chains, which could be correlated to their performance during gas separation testing. The values obtained were similar to other glassy polymers used in gas separation technology.
Dense polymeric films of ˜80-100 um thickness were prepared by casting 3 wt % solutions of the prepared polymers in DMF onto flat glass Petri dishes. Beforehand, the solutions were filtered using 0.45 μm PTFE filters to remove undissolved polymer material or impurities. The casted solutions were placed on a leveled surface in an oven preheated to 85° C. under a gentle nitrogen flow for slow solvent evaporation. The membranes obtained were then placed in an oven heated at 200° C. under vacuum. When needed, when the membranes were peeled from the Petri dishes, the membrane samples were soaked in deionized water for a few minutes and then dried at 60° C. in a vacuum oven for 6 hours to remove water.
The pure-gas permeation properties of membranes prepared from the polymers described in Examples 1-6 were determined using a constant-volume permeation system. For this study, four different single gases were used: He, N2, CH4 and CO2. The permeability coefficients of the polymeric membranes were calculated from the steady state of the pressure versus time curve, using a constant feed pressure of 100 psi and an operating temperature of 22° C. The permeability coefficients are expressed in Barrer [1 Barrer=10−10 cm3(STP)·cm/cm2·s·cmHg]. The ideal selectivity coefficients were calculated by dividing the permeability coefficient of a corresponding gas (He, N2 or CO2) by that of methane. The obtained results are listed in Table 2. The pure-gas permeation properties of 6FDA-CARDO(OH) homopolyimide could not be measured, since mechanically stable membranes could not be obtained.
Copolymerization methodology is one of the methods employed to improve membranes mechanical properties and their gas permeation through the selection of comonomers that possess desired properties. Durene (2,3,5,6-tetramethylbenzene-1,4-diamine) and DAM (2,4,6-trimethylbenzene-1,3-diamine) are two potential comonomers known for forming membranes with good mechanical and gas permeation properties. Thus, a series of copolyimides containing durene:CARDO(OH) with various molar ratios 1:1, 2:1, and 3:1, and a DAM:CARDO(OH) molar ratio of 3:1 were prepared. These copolyimides formed mechanically stable membranes, with the exception of 6FDA-durene/6FDA-CARDO(OH) (1:1). The pure-gas permeation properties of formed membranes were measured and the results are listed in Table 2.
As part of the molecular design of new polymeric materials, the durene moiety was replaced by a DAM moiety, with a DAM:CARDO(OH) molar ratio equal to 3:1 to form the 6FDA-DAM/6FDA-CARDO(OH) (3:1) block copolyimide. This polymer afforded a membrane with 39% higher CO2/CH4 selectivity coefficient than its equivalent 6FDA-durene/6FDA-CARDO(OH) (3:1) with ˜27% lower permeability coefficient.
In general, membranes prepared from glassy polymers suffer from a permeability-selectivity trade-off relationship (
To better understand the separation process through the prepared membranes, the CO2 and CH4 diffusivity coefficients (in cm2/s) were measured using the “time-lag” method. The obtained results are listed in Table 3.
The diffusivity coefficients for both CO2 and CH4 for the series of durene:CARDO(OH) copolyimides increased with higher durene molar ratio within the copolymer backbones.
Since the permeability coefficient (P) is calculated from the product of diffusivity (D) and solubility (S) coefficients, the solubility coefficients of the prepared polymers were calculated using the following equation:
The obtained solubility coefficients [in cm3(STP)/cm3·cmHg] are listed in Table 4.
The CO2/CH4 diffusivity and solubility selectivity coefficients were calculated and the results are listed in Table 3 and Table 4, respectively. The CO2/CH4 diffusivity selectivity coefficients of the durene:CARDO(OH) copolyimides were in the range of 4.18-6.79, while the CO2/CH4 solubility selectivity coefficients were between 3.52-4.67, indicating that the separation through these polymeric membranes was equally solubility and diffusivity driven.
Similarly, the CO2/CH4 diffusivity selectivity coefficient of 6FDA-DAM/6FDA-CARDO(OH) (3:1) equaled 2.02, while the CO2/CH4 solubility selectivity coefficient was found to be 13.6, indicating that the separation through this polymeric membrane was solubility driven.
Since natural gas is a mixture of different gases, the mixed-gas separation performance of the polymeric membranes was evaluated. For that, the mixed-gas separation performance of the described polymers in Examples 1-6 were measured using a sweet gas mixture containing 10, 59, 30 and 1 vol % of CO2, CH4, N2 and C2H6, respectively. The permeation measurements were recorded at different feed pressures (500-900 psi) with an increment of 200 psi at a fixed temperature of 22° C. The obtained results are listed in Table 5.
For the durene:CARDO(OH) copolyimide series, the mixed-gas CO2-permeability coefficients along with their corresponding mixed-gas CO2/CH4 selectivity coefficients at the various feed pressures studied are illustrated in
As a result of the decrease on the mixed-gas CO2 permeability coefficients with slight changes on mixed-gas CH4 permeability coefficients, the CO2/CH4 selectivity coefficients decreased when the pressure increased from 500 to 900 psi for all copolyimides (
These results of permeability and selectivity at such elevated feed pressures and for such a multicomponent gas mixture, make the durene:CARDO(OH) series of copolyimides very attractive potential materials for industrial natural gas sweetening applications.
Moreover, membranes prepared from 6FDA-DAM/6FDA-CARDO(OH) (3:1) were studied in a similar fashion to that of durene/CARDO(OH) series using the same gas mixture composition and same testing conditions of pressure and temperature. The obtained data are listed in Table 5 and
As can be seen from
The corresponding CO2/CH4 selectivity coefficients of 6FDA-DAM/6FDA-CARDO(OH) (3:1) illustrated in
Finally, the sweet mixed-gas separation performances at 900 psi of 6FDA-durene/6FDA-CARDO(OH) (3:1) and 6FDA-DAM/6FDA-CARDO(OH) (3:1) copolyimides membranes were used to study the effect of comonomer type on the CARDO(OH)-containing copolyimide. As can be seen from
An important aspect of the hydroxyl-functionalized CARDO-based polymers is that they are capable of self-crosslinking at high temperatures (greater than about 180° C.) during the drying process of the membranes. This crosslinking was observed through a change in coloration of the membrane (from light yellow to dark red-brown) and the fact that the solubility of the membranes became very low in the same solvent used to prepare them in the first place. The proposed self-crosslinking mechanism is illustrated in
This self-crosslinking is considered very advantageous since it improves the mechanical properties of the membrane and more importantly it improves the plasticization resistance at elevated feed pressures, which is very important during sour mixed-gas separation.
It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.
