Gas separation membranes
A gas separation membrane comprising the following layers: (i) a support layer; (ii) a buffer layer; (iii) a discriminating layer; (iv) optionally a fluorinated polymer layer; and (v) optionally a protective layer; wherein: (a) the buffer layer (ii) and the discriminating layer (iii) each independently comprise 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; (b) the buffer layer (ii) comprises a surface comprising 4 to 10 atomic % of M of Formula (1) groups, wherein M is as hereinbefore defined; (c) the discriminating layer (iii) comprises a surface comprising more than 10 atomic % of M of Formula (1) groups, wherein M is as hereinbefore defined; and (d) layer (ii) is located between layers (i) and (iii).
1 . A gas separation membrane comprising the following layers:
(i) a support layer;
(ii) a non-selective buffer layer formed by plasma treatment using a precursor;
(iii) a discriminating layer;
(iv) optionally a fluorinated polymer layer; and
(v) optionally a protective layer;
wherein:
(a) the buffer layer (ii) and the discriminating layer (iii) each independently comprise 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;
(b) the buffer layer (ii) comprises a surface comprising 4 to 10 atomic % of M of Formula (1) groups, wherein M is as hereinbefore defined;
(c) the discriminating layer (iii) comprises a surface comprising more than 10 atomic % of M of Formula (1) groups, wherein M is as hereinbefore defined; and
(d) layer (ii) is located between layers (i) and (iii).
2 . The gas separation membrane according to claim 1 wherein said discriminating layer is formed by plasma treatment using the following precursor compounds: TEOS (tetraethyl orthosilicate), HMDSO (hexamethyldisiloxane), TMOS (tetramethyl orthosilicate), TMCTS (1,3,5,7-tetramethylcyclotetrasiloxane), D4 OMCTS (octamethyl cyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), D6 (dodecamethylcyclohexasiloxane), silane (SiH 4 ), bis(triethoxysilyl)ethane (BTESE), TPOT (tetrapropylorthotitanate), TEOT (titanium ethoxide), TTIP (titanium tetraisopropoxide), ZTB (zirconium tetra-tert-butoxide), Zr(N(C 2 H 5 ) 2 ) 4 , (Cp)Zr(N(CH 3 ) 2 ) 3 or TMA (trimethylaluminium).
3 . The gas separation membrane according to claim 1 wherein said discriminating layer is formed by plasma treatment.
4 . The gas separation membrane according to claim 3 wherein the buffer layer (ii) comprises a surface comprising 4.5 to 9 atomic % of M of Formula (1) groups.
5 . The gas separation membrane according to claim 1 wherein each M independently is silicon, titanium, zirconium or aluminium.
6 . The gas separation membrane according to claim 3 wherein the buffer layer (ii) comprises a oxygen-carbon (O/C) ratio above 0.7 to 1.7.
7 . The gas separation membrane according to claim 1 wherein the discriminating layer (iii) comprises a oxygen-silicon (O/total Si) ratio between 1.8 and 100.
8 . The gas separation membrane according to claim 1 wherein the atomic % of M in the buffer layer (ii) is substantially constant throughout the depth of the buffer layer (ii) and the atomic % of M in the discriminating layer (iii) decreases as the distance from the buffer layer (ii) decreases.
9 . A process for forming a gas separation membrane according to claim 1 which comprises the steps of:
(a) applying layer (ii) to layer (i) by a plasma treatment in an atmosphere free of oxygen; and
(b) applying layer (iii) to layer (ii) by a plasma treatment in an atmosphere comprising oxygen.
10 . A gas separation module comprising a gas separation membrane according to claim 1 .