Gas Separation Membranes

1 - 9 . (canceled)

10 . A gas separation membrane comprising:

(i) a porous substrate;

(ii) a gutter layer comprising a cross-linked polysiloxane polymer;

(iii) a discriminating layer comprising at least 60 w/w % of ethylene oxide (EO) groups and at least 0.15 mmol/g of thioether groups of the formula —CH 2 —S—CH 2 —; and

(iv) a protective layer comprising a cross-linked polysiloxane polymer;

wherein:

(a) the gutter layer has an average thickness of less than 2.5 μm; and

(b) the discriminating layer has an average thickness of greater than 0.2 μm and less than 5 μm;

(c) the protective layer has an average thickness of 800 nm to 2000 nm.

11 . The gas separation membrane according to claim 10 wherein the discriminating layer is comprising between 0.15 and 0.60 mmol/g thioether groups of the formula —CH2-S—CH2-.

12 . The gas separation membrane according to claim 10 wherein the H2S permeance is at least 400 GPU.

13 . The gas separation membrane according to claim 10 wherein the porous substrate comprises polyacrylonitrile, polysulphone, polyvinylidenefluoride, polyether ether ketone or polytetrafluoroethylene.

14 . A process for preparing a gas separation membrane according claim 10 having a comprising the steps of:

(i) forming a gutter layer of average thickness of less than 2.5 μm on a porous substrate;

(ii) forming on the gutter layer a discriminating layer comprising at least 60 w/w % of EO groups and at least 0.15 mmol/g of thioether groups of the formula —CH 2 —S—CH 2 —, and having an average thickness greater than 0.2 μm and less than 5; and

(iii) forming on the discriminating layer a protective layer comprising a cross-linked polysiloxane polymer and having an average thickness of 800 nm to 2000 nm.

15 . A gas separation module comprising a gas separation membrane according to claim 10 .

16 . The gas separation module according to claim 15 wherein the gas separation membrane is in the form of a flat sheet, a spiral-wound sheet or a hollow-fibre.