Composite gas separation membranes with dialkysiloxane intermediate layer

Abstract

A composite membrane comprising: (a) a porous support; (b) a gutter layer; (c) a discriminating layer having an average thickness of at most 90 nm; and (d) a protective layer having an average thickness 150 nm to 600 nm comprising dialkylsiloxane groups.

Claims

1. A composite gas separation membrane comprising: (a) a porous support; (b) a gutter layer; (c) a discriminating layer having an average thickness of at most 90 nm; and (d) a protective layer having an average thickness 150 nm to 600 nm comprising dialkylsiloxane groups; wherein: (i) the discriminating layer is formed from a composition comprising a component having groups which are reactive with a surface component of the gutter layer; (ii) the gutter layer comprises dialkylsiloxane groups; (iii) the discriminating layer comprises a polyimide, cellulose acetate, polyethyleneoxide, or polyetherimide; and (iv) one of the gutter layer and the discriminating layer comprises epoxy groups, trialkoxysilyl groups, oxetane groups, or a combination thereof, and the other comprises groups which are reactive therewith selected from the group consisting of carboxylic acid groups, sulphonic acid groups, hydroxyl groups, thiol groups, and a combination thereof.

2. The composite gas separation membrane according to claim 1, wherein the discriminating layer comprises a polymer having groups selected from the group consisting of carboxylic acid, hydroxyl, sulphonic acid, and a combination thereof, and the gutter layer comprises epoxy groups, trialkoxysilyl groups, oxetane groups, or a combination thereof.

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

4. A composite gas separation membrane comprising: (a) a porous support; (b) a gutter layer; (c) a discriminating layer having an average thickness of at most 90 nm; and (d) a protective layer having an average thickness 150 nm to 600 nm comprising dialkylsiloxane groups; wherein: (i) the discriminating layer is formed from a composition comprising a component having groups which are reactive with a surface component of the gutter layer; (ii) the gutter layer and the protective layer each comprise an alkoxysilane group; (iii) one of the gutter layer and the discriminating layer comprises epoxy groups, trialkoxysilyl groups, oxetane groups, or a combination thereof, and the other comprises groups which are reactive therewith selected from the group consisting of carboxylic acid groups, sulphonic acid groups, hydroxyl groups, thiol groups, and a combination thereof; and (iv) the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

5. A process for preparing a composite gas separation membrane according to claim 1, comprising the steps of: a. applying a composition to the porous support and curing the composition to form the gutter layer; b. applying a composition to the gutter layer to form the discriminating layer having an average thickness of up to 90 nm; and c. applying a composition to the discriminating layer and curing the composition to form the protective layer having an average thickness 150 nm to 600 nm comprising dialkylsiloxane groups; wherein the composition used to form the gutter layer comprises: (1) 0.5 to 25 wt % of radiation-curable component(s), at least one of which comprises dialkylsiloxane groups; (2) 0 to 5 wt % of a photo-initiator; (3) 70 to 99.5 wt % of inert solvent; and (4) 0.01 to 5 wt % of metal complex; wherein the composition has a molar ratio of metal:silicon of at least 0.0005.

6. The process according to claim 5 wherein the composition applied in step c. comprises the same components as the composition used in step a.

7. The process according to claim 6 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.

8. The process according to claim 5 wherein the composition used in step c. is identical to the composition used in step a.

9. The process according to claim 5 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, dried, or both, 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.

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

11. The composite membrane according to claim 4 wherein the discriminating layer has an average thickness of up to 60 nm and the total thickness of the gutter layer, discriminating layer and protective layer is 1500 nm or less.

12. The process according to claim 6 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, dried, or both 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.

13. The process according to claim 7 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, dried, or both, 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.

14. The process according to claim 8 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, dried, or both, 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.

15. A gas separation cartridge comprising a composite gas separation membrane according to claim 4.

16. A gas separation cartridge comprising a composite gas separation membrane according to claim 11.

17. The composite gas separation membrane according to claim 1 wherein the compositions used to form the gutter layer and the protective layer each independently comprise: (1) 0.5 to 25 wt % of radiation-curable component(s), at least one of which comprises dialkylsiloxane groups; (2) 0 to 5 wt % of a photo-initiator; (3) 70 to 99.5 wt % of inert solvent; and (4) 0.01 to 5 wt % of metal complex; wherein the composition has a molar ratio of metal:silicon of at least 0.0005.

18. The composite gas separation membrane according to claim 1, wherein the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

Description

EXAMPLES

(1) The following materials were used in the Examples (all without further purification): PAN is a support (polyacrylonitrile L10 ultrafiltration membrane from GMT Membrantechnik GmbH, Germany). 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).

(2) ##STR00002## DBU is 1,8-diazabicyclo[5.4.0]undec-7-ene from Sigma Aldrich. 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).

(3) ##STR00003## I0591 4-isopropyl-4-methyldiphenyliodoniumtetrakis(pentafluorophenyl) borate (C.sub.40H.sub.18BF.sub.20I) from Tokyo Chemical Industries N.V. (Belgium)

(4) ##STR00004## Ti(OiPr).sub.4 is titanium (IV) isopropoxide from Dorf Ketal Chemicals (MWT 284). n-heptane is n-heptane from Brenntag Nederland BV. MEK is 2-butanone from Brenntag Nederland BV. MIBK is methylisobutyl ketone from Brenntag Nederland BV. APTMS is 3-trimethoxysilylpropan-1-amine from Sigma Aldrich. THF is tetrahydrofuran from Brenntag Nederland BV. PI1 is 6FDA-TeMPD.sub.x/DABA.sub.y, x/y=20/80; obtained from Fujifilm Corporation, having the following structure:

(5) ##STR00005##
Evaluation of Gas Flux and Selectivity
(A) Gas Flux

(6) 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 3.0 cm and a feed gas composition of 13 v/v % CO.sub.2 and 87 v/v % CH.sub.4.

(7) 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,IP.sub.Perm.Math.X.sub.Perm,i))
Where:
Q.sub.i=Flux of each gas (m.sup.3(STP)/m.sup.2.Math.kPa.Math.s)
.sub.Perm=Permeate flow (m.sup.3(STP)/s)
X.sub.Perm,I=Volume fraction of each gas in the permeate
A=Membrane area (m.sup.2)
P.sub.Feed=Feed gas pressure (kPa)
X.sub.Feed,I=Volume fraction of each gas in the feed
P.sub.perm=Permeate gas pressure (kPa)

(8) STP is standard temperature and pressure, which is defined here as 25.0 C. and 1 atmosphere (101.325 kPa).

(9) (B) Selectivity

(10) 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
Preparation of Radiation-Curable Polymers PCP1 Comprising Dialkylsiloxane Groups

(11) The components UV9300, X-22-162C and DBU dissolved in n-heptane in the amounts indicated in Table 1 and maintained at a temperature of 95 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 22.8 mPas at 25.0 C.

(12) TABLE-US-00001 TABLE 1 Ingredients used to Prepare PCP1 Ingredient Amount (w/w %) UV9300 (w/w %) 39.078 X-22-162C (w/w %) 10.789 DBU (w/w %) 0.007 n-Heptane (w/w %) 50.126
Preparation of the Curable Composition Used to Provide the Gutter and Protective Layers

(13) 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 indicated in Table 2 to give curable composition C1. The amount of Ti(OiPr).sub.4 present in C1 corresponded to 105.6 mol of Ti(OiPr).sub.4 per gram of PCP1. Also the molar ratio of metal:silicon in C1 was 0.0087.

(14) TABLE-US-00002 TABLE 2 Preparation of Curable Composition C1 Amount Ingredient (w/w %) PCP1 5.0 I0591 0.1 Ti(OiPr).sub.4 0.15

(15) C1 was used to prepare both the gutter layer and the protective layer, as described in more detail below.

(16) Step a. Formation of the Gutter Layer

(17) 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.

(18) Step b. Formation of the Discriminating Layer

(19) The composition C2 used to prepare the discriminating layer was prepared by mixing the ingredients indicated in Table 3:

(20) TABLE-US-00003 TABLE 3 Ingredient Parts (w/w %) PI1 1.50 APTMS 0.015 MIBK 4.50 THF 7.485 MEK 86.50

(21) A discriminating layer was formed on the gutter layer by the composition C2 described in Table 3 thereto by spin coating. A series of PAN+gutter layer+discriminating layer composites was prepared having different discriminating layer thicknesses of 50 nm, 65 nm or 90 nm. The thicknesses were verified by cutting through the membrane and measuring the thickness from the surface of the gutter layer outwards by SEM or by ellipsometry.

(22) Step c. Formation of the Protective Layer

(23) The radiation-curable composition C1 described in Table 1 was 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.

(24) A series of membranes according to the invention was prepared having different thicknesses of protective layer (i.e. 200 nm, 300 nm or 600 nm thickness). The protective layer thickness was measured by cutting through the composite membrane and measuring the thickness of the outermost layer from the surface of the discriminating layer by SEM or by ellipsometry.

(25) The resultant composite membranes had the gutter layer thickness, Q.sub.CO2 and selectivity indicated in Tables 4 and 5 below:

(26) TABLE-US-00004 TABLE 4 CEX 1 CEX 2 EX 1 EX 2 EX 3 Protective Layer Thickness No Protective Layer 200 nm Discriminating Layer Thickness 65 nm 50 nm 90 nm 65 nm 50 nm Gutter Layer Thickness 600 nm 600 nm 600 nm 600 nm 600 nm Selectivity (CO.sub.2/CH.sub.4) 25.6 25.0 27.7 26.5 25.8 CO.sub.2 flux (M3/ms .Math. kPa .Math. s) 6.5E07 6.65E07 5.42E07 5.66E07 5.88E07

(27) TABLE-US-00005 TABLE 5 EX 4 EX 5 EX 6 EX 7 EX 8 EX 9 Protective Layer Thickness 300 nm 600 nm Discriminating Layer Thickness 90 nm 65 nm 50 nm 90 nm 65 nm 50 nm Gutter Layer Thickness 600 nm 600 nm 600 nm 600 nm 600 nm 600 nm Selectivity (CO.sub.2/CH.sub.4) 29.8 29.6 28.0 29.6 29.1 28.1 CO.sub.2 flux (M3/ms .Math. kPa .Math. s) 5.21E07 5.41E07 5.82E07 5.02E07 5.36E07 5.37E07 (Note: CEX means Comparative Example and EX means Example)