# US 5,702,503 A · Composite gas separation membranes and making thereof

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- Number: US 5,702,503 A
- Document ID: US5702503A
- Status: Granted
- Kind: A
- Application number: 08/557,119
- Filed: 1995-12-25
- Granted: 1997-12-30
- Earliest claimed: 1995-12-25
- Assignees: Uop LLC
- Inventors: Man-Wing Tse Tang
- Web page: https://patentgrep.com/patent/US5702503A

## CPC

- B01D 53/228: {characterised by specific membranes}
- B01D 69/122: {Separate manufacturing of ultra-thin membranes}
- B01D 71/643: {Polyether-imides}
- B01D 71/68: Polysulfones; Polyethersulfones
- Y10T 428/249989: Integrally formed skin
- Y10T 428/31721: Of polyimide
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A composite membrane made of an asymmetric porous support and an ultrathin layer having a thickness of less than 100 nm is provided. A method of making the membrane and method for carrying out gas separations using the membrane are also provided.

## Claims

### Claim 1

A composite membrane comprising a porous asymmetric support having a first and a second surface area, said first surface area contacting an ultrathin polymer layer with a thickness less than 100 nm, said first surface area having an average pore diameter of about 5 nm to about 20 nm, and said second surface area having a pore diameter greater than that of the first surface area.

### Claim 2 (depends on 1)

A composite membrane according to claim 1, wherein the first surface area has about 10.sup.10 to about 10.sup.11 pores/cm.sup.2 and the second surface area has fewer pores/cm than the first surface area.

### Claim 3 (depends on 1)

A composite membrane according to claim 1, wherein the thickness of the ultrathin polymer layer is <40 nm.

### Claim 4 (depends on 3)

A composite membrane according to claim 3 wherein the thickness is 20-30 nm.

### Claim 5 (depends on 1)

A composite membrane according to claim 1, wherein the polymer of the ultrathin layer is a membrane forming polymer being selected from the group consisting of cellulose triacetate (CTA), hexafluoropolysulfone (6F-PS), polytrimethylsilylpropyne (PTMSP), polysulfone (PS), polyetherimide (PEI), polypropylene oxide (PPO) and mixtures thereof.

### Claim 6 (depends on 1)

A composite membrane according to claim 1 wherein the asymmetric porous support is a polyetherimide.

### Claim 7 (depends on 6)

A composite membrane according to claim 6 wherein the polyetherimide is a reaction product of at least one phenoxy-phenyldicarboxylic acid anhydride and at least one phenylenediamine.

### Claim 8 (depends on 1)

A composite membrane according to claim 1 further comprising a porous structural support which is in contact with the asymmetric porous support.

### Claim 9 (depends on 8)

A composite membrane according to claim 8 in which the porous structural support is a woven fabric.

### Claim 10

A process for making a composite gas separation membrane comprising the following steps:
(A) Providing a base support having a first planar surface;
(B) Forming on said first planar surface an asymmetric porous support, such asymmetric porous support comprising mutually coplanar first and second regions, the thickness of said first region being substantially greater than the thickness of said second region, said first region having a microporous structure and being placed adjacent to said first planar surface, said second region having a high density of pores having an average diameter of less than about 1,000 .ANG.ngstroms, said second region comprising a first surface integrally connected to said first region and a second surface;
(C) Preparing a dissolved polymer solution comprising (1) at least one 6FDA-type polyimide polymer having been formed by the dehydration of the condensation reaction product of at least one aromatic dianhydride and at least one aromatic diamine; and (2) a solvent for the polyimide polymer which is immiscible with a selected liquid, said selected liquid being a nonsolvent for the polyimide polymer and having a higher surface tension than said dissolved polymer solution;
(D) Providing a bath containing a pool of said selected liquid, said pool having a smooth surface with high surface tension; means for depositing the dissolved polymer solution onto said smooth surface at a deposition point; and means for conveying the smooth surface away from the deposition point;
(E) Depositing said dissolved polymer solution onto said smooth surface, and removing the solvent from the dissolved polymer solution to yield an ultrathin 6-FDA type polyimide polymer selective membrane film having a leading edge, being the farthest-most edge of said polymer film floating away from said deposition point on said smooth surface, which leading edge is conveyed by the smooth surface away from the deposition point;
(F) Conveying said asymmetric porous support into a position so that said second surface is adjacent to said leading edge; and (G) Picking up said leading edge onto said second surface and conveying said second surface tangentially away from said smooth surface;
yielding a composite membrane comprising an ultrathin 6FDA-type polyimide polymer selective membrane film.

### Claim 11 (depends on 10)

The process of claim 10 comprising the following additional steps:
(H) Preparing a solution comprising a sealing polymer and a sealing polymer solvent;
(I) Depositing a layer of such solution onto said ultrathin 6FDA-type polyimide polymer selective membrane film; and
(J) Removing said sealing polymer solvent and curing said polymer, yielding a composite membrane comprising a nonporous protective sealing polymer layer.

### Claim 12 (depends on 11)

The process of claim 11 in which the sealing polymer is a polydimethylsiloxane.

### Claim 13 (depends on 11)

A composite gas separation membrane made by the process of claim 11.

### Claim 14 (depends on 10)

The process of claim 10 in which said base support is a woven fabric and the first planar surface is highly uniform and smooth.

### Claim 15 (depends on 10)

The process of claim 10 in which the asymmetric porous support is stripped away from the base support subsequent to step (B).

### Claim 16 (depends on 15)

The process of claim 15 in which the base support is a web comprising laminated layers of metal and plastic.

### Claim 17 (depends on 15)

The process of claim 15 in which the base support is a glass plate.

### Claim 18 (depends on 15)

A composite gas separation membrane made by the process of claim 15.

### Claim 19 (depends on 10)

The process of claim 10 in which the asymmetric porous support is formed on said first planar surface by solvent cast phase inversion.

### Claim 20 (depends on 19)

A composite gas separation membrane made by the process of claim 19.

### Claim 21 (depends on 10)

The process of claim 10 in which the asymmetric porous support is made of a polyetherimide polymer.

### Claim 22 (depends on 21)

A composite gas separation membrane made by the process of claim 21.

### Claim 23 (depends on 10)

The process of claim 10 in which each aromatic dianhydride is selected from the group consisting of: 5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethyl-idene-bis-1,3-isobenzofurane dione; 3,4,3',4'-diphenyltetracarboxylic dianhydride; 1,2,4,5-benzene-tetracarboxylic dianhydride; 3,3',4,4'-benzophenonetetracarboxylic-dianhydride; pyromellitic dianhydride; and mixtures.

### Claim 24 (depends on 23)

The process of claim 23 in which each 6FDA-type polyimide polymer is derived from the condensation of a mixture of reagents comprising 5,5'-2,2,2-trifluoro-1-(trifluoromethyl)ethylidene-bis-1,3-isobenzofuraned ione with at least one aromatic diamine.

### Claim 25 (depends on 24)

A composite gas separation membrane made by the process of claim 24.

### Claim 26 (depends on 10)

The process of claim 10 in which each aromatic diamine is selected from the group consisting of:2,4,6-trimethyl-1,3-phenylene-diamine;4,4'-›1,4-phenylenebis(1-methyl-e thylidene)!bisaniline; 2,2-bis›4-(4-aminophenoxy)-phenyl!propane; 2,7-bis(4-aminophenoxy)-naphthalene; 4,4'-methyl-ene-bis(2,6-diisopropylaniline); 1,4-bis(4-aminophenoxy)benzene;4,4'-bis(4-aminophenoxy)-biphenyl; 1,3-bis(4-aminophenoxy)benzene; and 4,4'-(methylethylidene)bisaniline; 4-isopropyl-1,3-diaminobenzene; 4,4'-diaminodiphenylether; metaphenylenediamine; paraphenylenediamine; N,N'-metaphenylenebis(m-aminobenzanilide); and 3,3'-diaminobenz-anilide; 2-carboxy-3,5-diaminotoluene; 3,3'-diphenylhexafluoroisopropylidene diamine; 4,4'-diphenylhexafluoroisopropylidene diamine; 1,3-diaminobenzene; 2,3,5,6-tetramethyl-1,4-phenylenediamine; 1,5-diaminonaphthalene; 3,5-diaminobenzonitrile; 3,5-diaminomethylbenzoate; 3,3'-diaminophenylsulfone; 4,4'-diaminophenylsulfone; 3,7-diamino-2,8-dimethyldiphenylenesulfone; and mixtures.

### Claim 27 (depends on 26)

The process of claim 26 in which each aromatic diamine is selected from the group consisting of: 3,3'-diphenylhexafluoroisopropylidene diamine;4,4'-diphenylhexafluoroisopropylidene diamine; 1,3-diaminobenzene; 2,3,5,6-tetramethyl-1,4-phenylenediamine; 1,5-diaminonaphthalene; 3,5-diaminobenzonitrile; 3,5-diaminomethylbenzoate; 3,3'diaminophenylsulfone; 44'-diaminophenylsulfone; 3,7-diamino-2,8-dimethyldiphenylenesulfone; and mixtures.

### Claim 28 (depends on 27)

A composite gas separation membrane made by the process of claim 27.

### Claim 29 (depends on 10)

The process of claim 10 in which the ultrathin 6FDA-type polyimide polymer selective membrane film has a thickness of less than about 1,000 .ANG.ngstroms.

### Claim 30 (depends on 29)

The process of claim 29 in which the ultrathin 6FDA-type polyimide polymer selective membrane film has a thickness of less than about 400 .ANG.ngstroms.

### Claim 31 (depends on 30)

The process of claim 30 in which the ultrathin 6FDA-type polyimide polymer selective membrane film has a thickness of between about 200 and about 300 .ANG.ngstroms.

### Claim 32 (depends on 29)

A composite gas separation membrane made by the process of claim 29.

### Claim 33 (depends on 10)

The process of claim 10 in which each 6FDA-type polyimide polymer is derived from the condensation of a mixture of reagents comprising 3,3',4,4'-benzophenone-tetracarboxylic dianhydride and 5(6)-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane.

### Claim 34 (depends on 10)

A composite gas separation membrane made by the process of claim 10.

### Claim 35 (depends on 34)

A gas separation process comprising:
A. providing a gas separation membrane according to claim 34, having feed and permeate sides;
B. contacting the membrane with a mixed feed gas composition under pressure;
C. collecting separated permeate gas from the permeate side of the membrane; and
D. collecting retentate gas from the feed side of the membrane.

### Claim 36 (depends on 35)

The process of claim 35, in which the mixed feed gas composition comprises two or more members of the group consisting of methane, nitrogen, carbon dioxide, hydrogen, oxygen, carbon monoxide, hydrogen sulfide, water, helium, propane, and ethane.

### Claim 37 (depends on 36)

The process of claim 36, in which the mixed feed gas composition comprises a mixture of gases selected from the group of mixtures consisting of: air; nitrogen and oxygen; nitrogen and carbon dioxide; hydrogen and at least one hydrocarbon; carbon monoxide and hydrogen; carbon dioxide and at least one hydrocarbon; hydrogen sulfide and at least one hydrocarbon; hydrogen and nitrogen; helium and nitrogen; and helium and at least one hydrocarbon.