Thin film gas separation membranes

1. A gas separation membrane comprising a blend of polyethersulfone (PES) and aromatic polyimide polymers that comprise a plurality of first repeating units of formula (I)

wherein

X 1 is selected from the group consisting of

and mixtures thereof;

X 2 is selected from the group consisting of

and mixtures thereof; and

X 3 is selected from the group consisting of

and mixtures thereof,

wherein the phenyl groups of X 1 , X 2 and X 3 are optionally substituted with one or more substituents independently selected from the group consisting of C 1 -C 3 alkyl, C 1 -C 3 alkoxy, halogen, nitro and —NR 1 R 2 ,

wherein R a , R b , R c and R d are each independently C 1 -C 3 alkyl,

R 1 and R 2 are H or C 1 -C 3 alkyl, provided that both R 1 and R 2 are not H, and

the gas separation membrane has a layer of said blend of PES and aromatic polyimide polymers with a thickness from about 0.1 micron to about 3.0 microns.

2. The gas separation membrane of claim 1 , wherein each of R a , R b , R c and R d are CH 3 and the phenyl groups of X 1 , X 2 and X 3 are unsubstituted.

3. The gas separation membrane of claim 2 wherein at least one of the polyimides comprises sulfone groups.

4. The gas separation membrane of claim 3 wherein the at least one polyimide comprises poly(3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride-3,3′,5,5′-tetramethyl-4,4′-methylene dianiline) (PDT).

5. The gas separation membrane of claim 4 wherein the membrane has a shape of a cylinder formed concentrically formed around a hollow core.

6. The gas separation membrane of claim 5 wherein a ratio of PES to PDT is about 7 to 1.

7. A gas separation unit comprising:

a thin-film gas separation membrane;

a support structure for the membrane, the support structure comprising a polyethersulfone polymer; and

wherein the gas separation membrane comprises a blend of polyethersulfone and aromatic polyimide polymers that comprise a plurality of first repeating units of formula (I)

wherein

X 1 is selected from the group consisting of

and mixtures thereof;

X 2 is selected from the group consisting of

and mixtures thereof; and

X 3 is selected from the group consisting of

and mixtures thereof,

wherein the phenyl groups of X 1 , X 2 and X 3 are optionally substituted with one or more substituents independently selected from the group consisting of C 1 -C 3 alkyl, C 1 -C 3 alkoxy, halogen, nitro and —NR 1 R 2 ,

wherein R a , R b , R c and R d are each independently C 1 -C 3 alkyl, and

R 1 and R 2 are H or C 1 -C 3 alkyl, provided that both R 1 and R 2 are not H.

8. The gas separation membrane of claim 7 , wherein each of R a , R b , R c and R d are CH 3 and the phenyl groups of X 1 , X 2 and X 3 are unsubstituted.

9. The gas separation unit of claim 8 wherein the support structure comprises PES.

10. The gas separation unit of claim 9 wherein the support structure is a hollow cylinder.

11. The gas separation unit of claim 10 wherein the gas separation membrane is a thin film formed concentrically on the hollow cylinder support structure.

12. The gas separation unit of claim 11 wherein the blend comprises at least one polyimide that includes a sulfone dianhydride.

13. The gas separation unit of claim 12 wherein the blend includes poly(DSDA-TMMDA) (PDT).

14. The gas separation unit of claim 13 wherein the gas separation membrane is dense enough to separate oxygen (O 2 ) from air.

15. The gas separation membrane of claim 14 wherein selectivity α O2/N2 is at least as high as 3 and permeability for O 2 is at least as high as 9 Barrer.

16. A gas separation membrane comprising an isolated blend of polyethersulfone (PES) and aromatic polyimide polymers that comprise a plurality of first repeating units of formula (I)

wherein

X 1 is selected from the group consisting of

and mixtures thereof;

X 2 is selected from the group consisting of

and mixtures thereof; and

X 3 is selected from the group consisting of

and mixtures thereof,

wherein the phenyl groups of X 1 , X 2 and X 3 are optionally substituted with one or more substituents independently selected from the group consisting of C 1 -C 3 alkyl, C 1 -C 3 alkoxy, halogen, nitro and —NR 1 R 2 ,

wherein R a , R b , R c and R d are each independently C 1 -C 3 alkyl,

R 1 and R 2 are H or C 1 - 3 alkyl, provided that both R 1 and R 2 are not H, and

a ratio of PES to polyimide is about 7 to 1.

17. The gas separation membrane of claim 16 wherein at least one of the polyimides comprises sulfone groups.

18. The gas separation membrane of claim 16 wherein the at least one polyimide comprises poly(3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride-3,3′,5,5′-tetramethyl-4,4′-methylene dianiline) (PDT).

19. The gas separation membrane of claim 16 further comprising a support structure for the membrane, the support structure comprising a polyethersulfone polymer.