Gas Separation Membranes

1 . A gas separation membrane comprising the following layers:

(i) a support layer;

(ii) a discriminating layer;

(iii) a non gas separation selective further layer, wherein the further layer comprises groups of Formula (1):

M-(O—) x   Formula (1)

wherein:

each M independently is a metal or metalloid atom;

O is an oxygen atom; and

each x independently has a value of at least 4; and

(iv) optionally a protective layer;

wherein:

(a) the support layer (i) and the further layer (iii) are on opposite sides of discriminating layer (ii); and

(b) the further layer (iii) comprises 1.5 to 10 atomic % of M of Formula (1) groups, wherein M is as hereinbefore defined.

2 . The gas separation membrane according to claim 1 wherein the further layer (iii) is formed by a plasma deposition process using precursors in the absence of oxygen.

3 . The gas separation membrane according to claim 1 wherein the discriminating layer (ii) comprises more than 10 atomic % and less than 50 atomic % of M of Formula (1) groups.

4 . The gas separation membrane according to claim 1 wherein the further layer (iii) has an average thickness in the range 1 nm to 1,500 nm.

5 . The gas separation membrane according to claim 2 wherein the further layer (iii) has an average thickness in the range 5 nm to 1,000 nm.

6 . The gas separation membrane according to claim 1 wherein the further layer (iii) comprises an average value for the atomic % of M of Formula (1) groups which is substantially constant throughout its depth.

7 . The gas separation membrane according to claim 1 which comprises a protective polysiloxane layer (iv).

8 . The gas separation membrane according to claim 7 wherein the protective layer (iv) has an average thickness in the range 10 to 10,000 nm.

9 . A process for forming a gas separation membrane according to claim 1 which comprises the steps of:

(a) applying the discriminating layer (ii) to the support layer (i) by a wet coating process, physical vapor deposition process, chemical vapor deposition process, initiated deposition process or atomic layer deposition process or a plasma enhanced chemical deposition process; and

(b) applying the further layer (iii) to the discriminating layer (ii) by a plasma treatment process; and optionally

(c) applying a protective layer (iv) to the further layer (iii).

10 . The process according to claim 9 wherein step (b) is performed by a plasma treatment process in the presence of one or more of the following precursor compounds: teraethyl orthosilicate, hexamethyldisiloxane, tetramethyl orthosilicate, 1,3,5,7-tetramethylcyclotetrasiloxane, octamethyl cyclotetrasiloxane, decarnethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, bis(triethoxysilyl)ethane, tetrapropylorthotitanate, titanium ethoxide, titanium tetraisopropoxide or zirconium tetra-tert-butoxide.

11 . The process according to claim 9 wherein step (b) is performed in an atmosphere free from oxygen.

12 . The process according to claim 9 wherein step (a) comprises applying the discriminating layer (ii) to the support layer (i) by a plasma treatment process and step (b) comprises applying the further layer (iii) to the discriminating layer (ii) by a plasma treatment process in an atmosphere free from oxygen and in the presence of one or more of the following precursor compounds: tetraethyl orthosilicate hexamethyldisiloxane tetramethyl orthosilicate 1,3,5,7-tetramethylcyclotetrasiloxane, octamethyl, cyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, bis(triethoxysilyl)ethane, tetrapropylorthotitanate, titanium ethoxide, titanium tetraisopropoxide or zirconium tetra-tert-butoxide.

13 . The process according to claim 12 wherein step (a) provides discriminating layer (ii) having more than 10 atomic % and less than 50 atomic % of M of Formula (1) groups and step (b) provides the further layer (iii) having 1.5 to 10 atomic % of M of Formula (1) groups.

14 . A gas separation module comprising a gas separation membrane according to claim 1 .

15 . (canceled)