Composite gas separation membranes with dialkysiloxane intermediate layer

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.