Composite Membranes

Abstract

A composite membrane comprising: (a) a porous support; (b) optionally a gutter layer; (c) a polyimide discriminating layer; and (d) a protective layer comprising dialkylsiloxane groups and having an average thickness of 825 to 2,000 nm; wherein the polyimide discriminating layer comprises 2,4,6-trimethyl-1,3-phenylene groups, each such group independently having an atom or substituent other than H at the 5-position.

Claims

1. A composite membrane comprising: (a) a porous support; (b) optionally a gutter layer; (c) a polyimide discriminating layer; and (d) a protective layer comprising dialkylsiloxane groups and having an average thickness of 825 to 2,000 nm; wherein the polyimide discriminating layer comprises 2,4,6-trimethyl-1,3 phenylene groups, each such group independently having an atom or substituent other than H at the 5-position.

2. The composite membrane according to claim 1 wherein the polyimide discriminating layer comprises 2,4,6-trimethyl-1,3-phenylene groups, each such group independently having an atom or substituent other than H at the 5-position.

3. The composite membrane according to claim 1 wherein the atom or substituent other than H at the 5-position of each 2,4,6-trimethyl-1,3-phenylene group is selected from the group consisting of sulfamoyl, alkoxysulfonyl, carboxy, hydroxy, amide, thiol, acyloxy and halogen.

4. The composite membrane according to claim 1 wherein the polyimide discriminating layer comprises a repeat unit of ##STR00011## the formula (I): wherein: each X.sup.a independently is sulfamoyl, alkoxysulfonyl, carboxy, hydroxy, amide, sulphinic, sulphonic, thiol, acyloxy or halogen; and each R independently is a tetravalent linking group.

5. The composite membrane according claim 4, wherein the tetravalent linking group is selected from one of the following Formulae (I-1) to (I-28): ##STR00012## ##STR00013## ##STR00014## wherein: each X.sup.1, X.sup.2 and X.sup.3 independently is a single bond or a divalent linking group; and each L independently is CHCH, CH.sub.2CH.sub.2 or CH.sub.2; each R.sup.1 and R.sup.2 independently is H, alkyl or halogen; and the symbols * represent a binding site with respect to a carbonyl group shown in Formula (I) above.

6. The composite membrane according claim 4, wherein the tetravalent linking group is according following Formulae (II-1): ##STR00015## wherein X.sup.1 is a single bond or a divalent linking group; and the symbols * represent a binding site with respect to a carbonyl group shown in Formula (I).

7. The composite membrane according claim 4, wherein the tetravalent linking group is of the Formula (II-2): ##STR00016## wherein the symbols * represent a binding site with respect to a carbonyl group shown in Formula (I).

8. The composite membrane according to claim 1 wherein gutter layer and the protective layer are obtained from curable compositions which comprise the same components.

9. The composite membrane according to claim 1 wherein the amount of each component used to make the protective layer is within at most 10% of the amount of the same component used to make the gutter layer.

10. The composite membrane according to claim 1 wherein the discriminating layer has an average thickness of 5 to 120 nm.

11. The composite membrane according to claim 1 wherein the total thickness of the gutter layer, discriminating layer and protective layer is 1500 nm or less.

12. The composite membrane according to claim 1 wherein the discriminating layer is free from 2,3,5,6-tetramethyl-1,3-phenylene groups

13. The composite membrane according to claim 1 wherein (i) the gutter layer and the protective layer comprise alkoxysilane group; (ii) the gutter layer and the protective layer are obtained from curable compositions which comprise the same components; (iii) the amount of each component used to make the protective layer is within at most 10% of the amount of the same component used to make the gutter layer; and (iv) the discriminating layer is free from 2,3,5,6-tetramethyl-1,3-phenylene groups.

14. A process for preparing a composite membrane according to claim 1 comprising the steps of: a. optionally applying a composition to the porous support and curing the composition to form a gutter layer; b. applying a polyimide composition to the gutter layer when present, or to the porous support when the gutter layer is not present, to form the discriminating layer; and c. applying a composition to the discriminating layer and curing the composition to form the protective layer having an average thickness of 800 to 2,000 nm comprising dialkylsiloxane groups; wherein the composition used in step b. comprises a component having 2,4,6-trimethyl-1,3-phenylene groups, each such group independently having an atom or substituent other than H at the 5-position.

15. The process according to claim 14 wherein the compositions applied in steps a. and c. comprise the same components.

16. The process according to claim 15 wherein the amount of each component present in the composition used in step c. is within at most 10% of the amount of the same component present in the composition used in step a.

17. The process according to claim 14 wherein the compositions used in steps a. and c. are identical.

18. The process according to claim 14 wherein the composition referred to in step a. is cured to form the gutter layer before the composition referred to in step b. is applied, the composition referred to in step b. is cured and/or dried to form the discriminating layer before the composition referred to in step c. is applied, and the composition referred to in step c. is cured to form the protective layer.

19. A gas separation cartridge comprising a composite membrane according to claim 1.

20. (canceled)

Description

EXAMPLES

[0135] The following materials were used in the Examples (all without further purification): [0136] PAN is a support (polyacrylonitrile L14 ultrafiltration membrane from GMT Membrantechnik GmbH, Germany). [0137] X-22-162C is a dual end reactive silicone having carboxylic acid reactive groups, a viscosity of 220 mm.sup.2/s and a reactive group equivalent weight of 2,300 g/mol] from Shin-Etsu Chemical Co., Ltd. (MWT 4,600).

##STR00006## [0138] DBU is 1,8-diazabicyclo[5.4.0]undec-7-ene from Sigma Aldrich. [0139] UV9300 is SilForce UV9300 from Momentive Performance Materials Holdings having an epoxy equivalent weight of 950 g/mole oxirane (MWT 9,000, determined by viscometry).

##STR00007## [0140] I0591 is 4-isopropyl-4-methyldiphenyliodoniumtetrakis(pentafluorophenyl) borate (C.sub.40H.sub.18BF.sub.20I) from Tokyo Chemical Industries N.V. (Belgium)

##STR00008## [0141] Ti(OiPr).sub.4 is titanium (IV) isopropoxide from Dorf Ketal Chemicals (MWT 284). [0142] n-heptane is n-heptane from Brenntag Nederland BV. [0143] MEK is 2-butanone from Brenntag Nederland BV. [0144] MIBK is methylisobutyl ketone from Brenntag Nederland BV. [0145] DIOX is 1,3-dioxolane from Brenntagg Nederland BV. [0146] APTMS is 3-trimethoxysilyl propan-1-amine from Sigma Aldrich. [0147] PI1 is 6FDA-TeMPD.sub.x/DABA.sub.y, x/y=20/80; obtained from FUJIFILM Corporation, having the following structure:

##STR00009## [0148] PI2 is 6FDA-DATMBX m/DABA n, m/n=90/10 wherein X is SO.sub.2NH.sub.2; obtained from FUJIFILM Corporation, having the following structure:

##STR00010## [0149] PI3 has the same structure as PI2 above except that the ratio of m/n is 20/80. This material was obtained FUJIFILM Corporation. [0150] PI4 has the same structure as PI2 above except that the ratio of m/n is 20/80 and X is SO.sub.2NHCF.sub.3. This material was obtained FUJIFILM Corporation. [0151] PI5 has the same structure as PI2 above except that the ratio of m/n is 90/10 and X is CONH.sub.2. This material was obtained FUJIFILM Corporation.

Evaluation of Gas Flux and Selectivity

(A) Gas Flux

[0152] The flux of CH.sub.4 and CO.sub.2 through the membranes was measured at 40 C. and gas feed pressure of 6000 kPa using a gas permeation cell with a measurement diameter of 2.0 cm and a feed gas composition of 13 v/v % CO.sub.2 and 87 v/v % CH.sub.4. Gas fluxes are desirably at least 3.0.Math.10.sup.7 m.sup.3(STP)/m.sup.2.Math.kPa.Math.s.

[0153] The flux of each gas was calculated based on the following equation:

Q.sub.i=(.sub.Perm.Math.X.sub.Perm,i)/(A.Math.(P.sub.Feed.Math.X.sub.Feed,l.Math.P.sub.Perm.Math.X.sub.Perm,i))

Where:

[0154] Q.sub.i=Flux of each gas (m.sup.3(STP)/m.sup.2.Math.kPa.Math.s) [0155] .sub.Perm=Permeate flow (m.sup.3(STP)/s) [0156] X.sub.Perm,l=Volume fraction of each gas in the permeate [0157] A=Membrane area (m.sup.2) [0158] P.sub.Feed=Feed gas pressure (kPa) [0159] X.sub.Feed,l=Volume fraction of each gas in the feed [0160] P.sub.Perm=Permeate gas pressure (kPa) STP is standard temperature and pressure, which is defined here as 25.0 C.
and 1 atmosphere (101.325 kPa).

(B) Selectivity

[0161] The selectivity (.sub.CO2/CH4) for the membranes was calculated from Q.sub.CO2 and Q.sub.CH4 calculated above, based on following equation:

.sub.CO2/CH4=Q.sub.CO2/Q.sub.CH4

[0162] Desirably selectivity is above 15.

(C) Crack Resistance

[0163] The composite membranes were wound onto a spool at a winding tension force of 100 N/m.sup.2. The composite membranes were then examined for crack defects by dyeing the top-surface of the membrane, washing the membrane with water (5 litres) at room temperature and then visually examining the membrane. The presence of blue dye lines indicated the presence of cracks. The dye was a 5 wt % solution of tetrapotassium 2-(4-{5-[1-(2,5-disulfonatophenyl)-4,5dihydro-3-ethylmethanoate-5-oxopyrazol-4-ylidene]-1,3-pentadienyl}-3-ethylmethanoate-5-hydroxypyrazol-1-yl)benzene-1,4-disulfonate in water.

[0164] The extent of cracking of the composite membranes under evaluation was scored as follows on samples of size 12.6 cm.sup.2:

[0165] +=no cracks were visible;

[0166] +/=1 to 5 cracks were visible; and

[0167] =more than 5 cracks were visible.

Preparation of Radiation-Curable Polymer PCP1 Comprising Dialkylsiloxane Groups

[0168] The components UV9300, X-22-162C and DBU are dissolved in n-heptane in the amounts indicated in Table 1 and maintained at a temperature of 91 C. for 168 hours. The resultant polymer, PCP1, had an Si content (meq/g polymer) of 12.2 and the resultant solution of PCP1 had a viscosity of 125 mPas at 25.0 C.

TABLE-US-00001 TABLE 1 Ingredients used to Prepare PCP1 Ingredient Amount (w/w %) UV9300 (w/w %) 46.395 X-22-162C (w/w %) 13.596 DBU (w/w %) 0.009 n-Heptane (w/w %) 40.000

Preparation of the Curable Compositions C1, C2 and C3 Used to Provide the Gutter and Protective Layers

[0169] The solution of PCP1 arising from the previous step above was cooled to 20 C. and diluted using n-heptane to give the PCP1 concentration indicated in Table 2 below. The solution was then filtered through a filter paper having a pore size of 2.7 m. The photoinitiator 10591 and a metal complex (Ti(OiPr).sub.4) were then added in the amounts (wt/wt %) indicated in Table 2 to give curable composition C1, C2 or C3. The amount of Ti(OiPr).sub.4 present in C1, C2 and C3 corresponded to 55.4 mol of Ti(OiPr).sub.4 per gram of PCP1. Also the molar ratio of metal:silicon in C1, C2 and C3 was 0.0065.

TABLE-US-00002 TABLE 2 Preparation of Curable Compositions C1, C2 and C3 Ingredient (in wt/wt %) C1 C2 C3 PCP1 10.000 7.000 9.488 I0591 0.105 0.074 0.251 Ti(OiPr).sub.4 0.226 0.158 0.214 DBU 0.001 0.001 0.001 MEK 2.009 1.406 4.764 n-Heptane 87.660 91.361 85.282 Viscosity (mPas at 25 C.) 1.72 1.02 1.65

[0170] C1 was used to prepare the gutter layer. C2 and C3 were used to prepare the protective layer, as described in more detail below.

Step a. Formation of the Gutter Layer

[0171] C1 was applied to a support (PAN) by spin coating and subsequently cured using a Light Hammer LH10 from Fusion UV Systems fitted with a D-bulb with an intensity of 24 kW/m and dried. This resulted in a support having a gutter layer of thickness 600 nm, comprising a metal complex and dialkylsiloxane groups. The gutter layer thickness was verified by cutting through the PAN+gutter layer composite and measuring the thickness from the surface of the PAN support outwards by SEM.

Step b. Formation of the Discriminating Layers

[0172] The compositions DL1, DL2, DL3, DL4 and DL5 were used to prepare the discriminating layer by mixing the ingredients indicated in Table 3 in the amounts shown (wt/wt %):

TABLE-US-00003 TABLE 3 Ingredient DL1 DL2 DL3 DL4 DL5 PI1 1.00 0 0 0 0 PI2 0 1.00 0 0 0 PI3 0 0 1.00 0 0 PI4 0 0 0 1.00 0 PI5 0 0 0 0 1.00 APTMS 0.010 0.005 0.005 0.005 0.005 MIBK 3.00 3.00 3.00 3.00 3.00 DIOX 4.99 4.995 4.995 4.995 4.995 MEK 91.00 91.00 91.00 91.00 91.00

[0173] Discriminating layers were formed on the gutter layer by applying compositions DL1, DL2, DL3, DL4 and DL5 respectively to the gutter layers by spin coating. In this way, a series of PAN+gutter layer+discriminating layer composites were prepared. The thicknesses of the layers in these composites were determined by cutting through the composites and measuring the thickness of the various layers by Scanning Electron Microscopy (SEM) or by ellipsometry. All discriminating layers in the Examples and Comparative Examples had a thickness of 90 nm.

Step c. Formation of the Protective Layer

[0174] A series of membranes according to the invention was prepared having different thicknesses of protective layer (e.g. 600 nm, 900 nm, 1200 nm or 1800 nm thickness) were prepared as follows:

[0175] The radiation-curable composition C2 or C3 described in Table 2 were applied by spin coating to the PAN+gutter layer+discriminating layer composites arising from step b. The composition was cured thereon using a Light Hammer LH10 from Fusion UV Systems fitted with a D-bulb with an intensity of 24 kW/m and dried. This resulted in composite membranes according to the present invention.

[0176] The average thicknesses of the protective layers was measured by cutting through the composite membranes in several places (e.g. 4 or 5 places) and measuring the thickness of the outermost layer from the surface of the discriminating layer in each place by SEM or by ellipsometry, then calculating the average of those measured thicknesses.

[0177] The resultant composite membranes had the gutter layer thickness, Q.sub.CO2 and selectivity and crack evaluation indicated in Table 4 below:

TABLE-US-00004 TABLE 4 CEx 1 CEx2 CEx3 CEx4 Protective Layer C2 C2 C2 C2 composition Protective Layer 600 600 600 600 Thickness (nm) Discriminating Layer Composition DL1 DL2 DL4 DL5 Does the discriminating layer comprise No Yes Yes Yes optionally substituted 2,4,6-trimethyl- 1,3-phenylene groups having an atom or substituent other than H at the 5- position? Gutter Layer Composition/ C1/600 C1/600 C1/600 C1/600 Thickness (nm) Results Selectivity (.sub.CO2/CH4) 30 4 6 4 Flux - Q (10.sup.7 m.sup.3(STP)/m.sup.2 .Math. kPa .Math. s) 2.40 5.25 1.88 5.10 Extent of Cracking + Ex1 Ex2 Ex3 Ex4 Ex5 Protective Layer C3 C3 C3 C3 C3 composition Protective Layer 900 1,200 1,600 2,000 1,200 Thickness (nm) Discriminating Layer DL2 DL2 DL2 DL2 DL3 Composition Does the discriminating layer Yes Yes Yes Yes Yes comprise optionally substituted 2,4,6-trimethyl-1,3-phenylene groups having an atom or substituent other than H at the 5-position? Gutter Layer Composition/ C1/600 C1/600 C1/600 C1/600 C1/600 Thickness (nm) Results Selectivity (.sub.CO2/CH4) 28 30 30 31 33 Flux - Q (10.sup.7 5.03 4.88 4.13 3.00 3.00 m.sup.3(STP)/m.sup.2 .Math. kPa .Math. s) Extent of Cracking +/ + + + + CEx5 CEx6 CEx7 CEx8 CEx9 Protective Layer C3 C3 C3 C3 C3 composition Protective Layer 2,200 600 2,200 2,200 2,200 Thickness (nm) Discriminating Layer DL2 DL3 DL3 DL4 DL5 Composition Does the discriminating layer Yes Yes Yes Yes Yes comprise optionally substituted 2,4,6-trimethyl-1,3-phenylene groups having an atom or substituent other than H at the 5-position? Gutter Layer Composition/ C1/600 C1/600 C1/600 C1/600 C1/600 Thickness (nm) Results Selectivity (.sub.CO2/CH4) 31 10 34 33 30 Flux - Q (10.sup.7 1.88 3.6 1.73 0.94 1.65 m.sup.3(STP)/m.sup.2 .Math. kPa .Math. s) Extent of Cracking + + + + CEx10 CEx11 Protective Layer C2 C2 composition Protective Layer 1,200 2,200 Thickness (nm) Discriminating Layer Composition DL1 DL1 Does the discriminating layer comprise No No optionally substituted 2,4,6-trimethyl-1,3- phenylene groups having an atom or substituent other than H at the 5-position? Gutter Layer Composition/ C1/600 nm C1 /600 nm Thickness (nm) Results Selectivity (.sub.CO2/CH4) 31 31 Flux - Q (10.sup.7 m.sup.3(STP)/m.sup.2 .Math. kPa .Math. s) 2.25 1.50 Extent of Cracking + + (Notes: CEx means Comparative Example and Ex means Example)

[0178] From Table 4 it can be seen that Examples 1 to 5 of the present invention demonstrate a valuable combination of good selectivity (.sub.CO2/CH4 of at least 28), flux (at least 3.0.Math.10.sup.7 m.sup.3(STP)/m.sup.2.Math.kPa.Math.s) and in most cases no cracking. In contrast, the Comparative Examples are all deficient in at least one respect compared to the actual Examples.