Curable compositions and membranes
A curable composition comprising the components (i) 0 to 60 wt % non-ionic crosslinker(s); (ii) 20 to 85 wt % curable ionic compound(s) comprising an anionic group and at least one ethylenically unsaturated group; (iii) 15 to 45 wt % solvent(s); (iv) 0 to 10 wt % of photoinitiator(s); and (v) 2 to 45 wt % of structure modifier(s); wherein the molar ratio of component (v): (ii) is 0.25 to 0.65. The compositions are useful for preparing membranes for (reverse) electrodialysis.
1. A process for preparing a membrane comprising the following steps:
(i) applying a curable composition to a support; and
(ii) curing the composition to form a membrane;
wherein the curable composition comprises the components:
(i) 0 to 60 wt % non-ionic crosslinker(s);
(ii) 20 to 85 wt % curable ionic compound(s) comprising an anionic group and at least one ethylenically unsaturated group;
(iii) 15 to 45 wt % solvent(s);
(iv) 0 to 10 wt % of photoinitiator(s); and
(v) 2 to 45 wt % of structure modifier(s) selected from the group consisting of polyvalent metal salts and organic compounds comprising at least two groups selected from amino and quaternary ammonium groups;
wherein the molar ratio of component (v):(ii) is 0.25 to 0.65.
2. The process according to claim 1 wherein the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane.
3. The process according to claim 1 wherein the composition comprises the components:
(i) 2 to 40 wt % non-ionic crosslinker(s);
(ii) (a) 20 to 60 wt % curable ionic compound(s) comprising an anionic group and one ethylenically unsaturated group; and
(b) 0 to 60 wt % curable ionic compound(s) comprising an anionic group and at least two ethylenically unsaturated groups;
(iii) 15 to 45 wt % solvent(s);
(iv) 0 to 5 wt % of photoinitiator(s); and
(v) 4 to 35 wt % of structure modifier(s) capable of forming ionic bonds with at least two of said anionic group(s);
wherein the molar ratio of component (v):(ii) is 0.25 to 0.65.
4. The process according to claim 1 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499.
5. The process according to claim 1 wherein the curing is performed using electron beam or UV radiation.
6. The process according to claim 1 wherein the composition is cured by irradiation with an electron beam or UV light for a period of less than 30 seconds.
7. The process according to claim 1 which further comprises the step of removing at least some of the structure modifier from the membrane.
8. The process according to claim 1 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.
9. The process according to claim 1 wherein the structure modifier is or comprises a polyvalent metal salt and some or all of the structure modifier is removed from the membrane by ion exchange and/or washing.
10. The process according to claim 1 wherein the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.
11. The process according to claim 1 wherein the curable composition is applied continuously to a moving support by means of a manufacturing unit comprising a curable composition application station, an irradiation source for curing the composition, a membrane collecting station and a means for moving the support from the curable composition application station to the irradiation source and to the membrane collecting station.
12. The process according to claim 1 wherein the ethylenically unsaturated group(s) is or are acrylic groups.
13. The process according to claim 1 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499 and wherein the composition is cured by irradiation with an electron beam or UV light.
14. The process according to claim 1 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light and the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane.
15. The process according to claim 1 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light and the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.
16. The process according to claim 1 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light, the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane and the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.
17. The process according to claim 15 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.
18. The process according to claim 16 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.
19. The process according to claim 1 wherein the support is a porous support.
20. A membrane obtained by performing the process of claim 1 .
21. The membrane according to claim 20 which has a ratio of the electrical resistance of the membrane for magnesium ions to that of sodium ions of less than 3, when measured at an ion concentration of 0.5M.
22. The membrane according to claim 20 which has an electrical resistance for sodium ions of less than 3 ohm·cm 2 and for magnesium ions of less than 7 ohm·cm 2 , when measured at an ion concentration of 0.5M.