Process for preparing membranes

Abstract

A process for preparing a composite membrane comprising the steps: a) applying a radiation-curable composition to a porous support; b) irradiating the composition and thereby forming a gutter layer of cured polymer; and c) forming a discriminating layer on the gutter layer; wherein the radiation-curable composition comprises a partially crosslinked, radiation-curable polymer comprising epoxy groups and siloxane groups, a photoinitiator and is substantially free from mono-epoxy compounds. Composite membranes and gas separation cartridges are also claimed.

Claims

1. A process for preparing a composite membrane comprising the steps: a) applying a radiation-curable composition to a porous support; b) irradiating the composition and thereby forming a gutter layer of cured polymer; and c) forming a discriminating layer on the gutter layer; wherein the radiation-curable composition comprises a partially crosslinked, radiation-curable polymer comprising epoxy groups and siloxane groups, a photoinitiator and is substantially free from mono-epoxy compounds.

2. The process according to claim 1, wherein the radiation-curable composition contains less than 0.1 wt % of mono-epoxy compounds and the discriminating layer is formed from a composition containing less than 0.1 wt % of mono-epoxy compounds.

3. The process according to claim 1, wherein the radiation-curable composition contains less than 0.01 wt % of mono-epoxy compounds and the discriminating layer is formed from a composition containing less than 0.01 wt % of mono-epoxy compounds.

4. The process according to claim 1, wherein the radiation-curable composition is free from mono-epoxy compounds and the discriminating layer is formed from a composition which is free from mono-epoxy compounds.

5. The process according to claim 1, wherein the discriminating layer comprises a polyimide, cellulose acetate, polybenzoxazole, polyethyleneoxide or polyetherimide.

6. The process according to claim 1, wherein the discriminating layer comprises a polyimide comprising trifluoromethyl groups.

7. The process according to claim 1, wherein the discriminating layer comprises poly([({2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{5-carboxylic-1,3-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}]).

8. The process according to claim 1, wherein: the radiation-curable composition is applied continuously to the porous support in step a) by means of a manufacturing unit comprising a radiation-curable composition application station, step b) is performed using an irradiation source located downstream from the radiation-curable composition application station, the discriminating layer is formed on the layer of cured polymer in step c) by a discriminating layer application station, and the resultant composite membrane is collected at a collecting station, wherein the manufacturing unit comprises a means for moving the porous support from the radiation-curable composition application station to the irradiation source and to the discriminating layer application station and to the composite membrane collecting station.

9. The process according to any of the previous claim 1, wherein step a) and/or step b) is or are performed by curtain coating, meniscus type dip coating, kiss coating, pre-metered slot die coating, reverse or forward kiss gravure coating, multi roll gravure coating, spin coating and/or slide bead coating.

10. A composite membrane prepared by the method according claim 1.

11. A gas separation cartridge comprising the composite membrane according to claim 1 wherein the cartridge is of plate-and-frame, spiral-wound, hollow-fibre, tubular or envelope type.

12. The process according to claim 1 wherein: (a) the radiation-curable composition contains less than 0.1 wt % of mono-epoxy compounds; (b) the discriminating layer is formed from a composition containing less than 0.1 wt % of mono-epoxy compounds; and (c) the discriminating layer comprises poly([({2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{5-carboxylic-1,3-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}]).

13. The process according to claim 12 wherein the radiation-curable composition contains less than 0.01 wt % of mono-epoxy compounds and the discriminating layer is formed from a composition containing less than 0.01 wt % of mono-epoxy compounds.

14. The process according to claim 1 wherein: the radiation-curable composition is applied continuously to the porous support in step a) by means of a manufacturing unit comprising a radiation-curable composition application station, step b) is performed using an irradiation source located downstream from the radiation-curable composition application station, the discriminating layer is formed on the layer of cured polymer in step c) by a discriminating layer application station, and the resultant composite membrane is collected at a collecting station, wherein the manufacturing unit comprises a means for moving the porous support from the radiation-curable composition application station to the irradiation source and to the discriminating layer application station and to the composite membrane collecting station and wherein the discriminating layer comprises poly([({2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{5-carboxylic-1,3-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}]).

15. The process according to claim 14 wherein step a) and/or step b) is or are performed by curtain coating, meniscus type dip coating, kiss coating, pre-metered slot die coating, reverse or forward kiss gravure coating, multi roll gravure coating, spin coating and/or slide bead coating.

16. A composite membrane comprising: i) a porous support; ii) a gutter layer obtained from curing a radiation-curable composition comprising a photoinitiator and a partially crosslinked, radiation-curable polymer comprising epoxy groups and siloxane groups, said composition being substantially free from mono-epoxy compounds; and iii) a discriminating layer on the gutter layer.

17. The composite membrane according to claim 16 wherein the discriminating layer has been obtained from a composition which is substantially free from mono-epoxy compounds.

18. The composite membrane according to claim 16 wherein the discriminating layer comprises poly([({2,3,5,6-tetramethyl-1,4-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)})-co-[{5-carboxylic-1,3-phenylenediamine}-alt-{5,5-[2,2,2-trifluoro-1-(trifluoromethyl)ethane-1,1-diyl]bis(isobenzofuran-1,3-dione)}]).

19. A gas separation cartridge comprising the composite membrane according to claim 16 wherein the cartridge is of plate-and-frame, spiral-wound, hollow-fibre, tubular or envelope type.

20. A gas separation cartridge comprising the composite membrane according to claim 17 wherein the cartridge is of plate-and-frame, spiral-wound, hollow-fibre, tubular or envelope type.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

Stage a) Preparation of the PCP Polymer

(1) A solution of a PCP Polymer (PCP Polymer 1) was prepared by heating the components described in Table 1 together for 105 hours at 95 C. The resultant solution of PCP Polymer 1 had a viscosity of about 64,300 mPas when measured at 25 C.

(2) TABLE-US-00001 TABLE 1 Ingredients used to prepare PCP Polymer 1 Ingredient Amount (w/w %) UV9300 75 Ti(OiPr).sub.4 1.5 n-Heptane 23.5

Stage b) Preparation of Radiation Curable Compositions (RCCs) 1 to 5

(3) Portions of the solution of PCP Polymer 1 obtained in stage a) above were cooled to 20 C., diluted with n-heptane and then filtered through a filter paper having an average pore size of 2.7 m. The remaining ingredients indicated in Table 2 below were added to make RCC1 to 5 as indicated in Table 2 below.

(4) TABLE-US-00002 TABLE 2 RCC1 RCC4 RCC5 (comp.) RCC2 RCC3 (comp.) (comp.) Inert n-Heptane 84.9 84.9 84.9 84.8 84.1 solvent (w/w %) MEK 1.6 1.6 1.6 1.6 1.6 (w/w %) PCP PCP Polymer 1 13.3 13.3 13.3 13.3 13.3 Polymer (w/w %) Photo- UV-9390c.sup.1 0.2 0 0 0 1.0 initiator (w/w %) I0591.sup.2 0 0.2 0 0.2 0 (w/w %) AB153366.sup.2 0 0 0.2 0 0 (w/w %) Epoxy GE 0 0 0 0.1 0 com- pound Notes: .sup.1The commercial form of UV-9390c contained about 28 wt % of mono-epoxy compounds. Therefore CEX1 and CEX3 contain epoxy compounds derived from the UV-9390c. .sup.2I0591 and AB153366 contained no detectable mono-epoxy compounds. 3. Comp. means Comparative.

Stage c) Preparation of Compositions Used to Form a Discriminating Layer

(5) Compositions DSL1 to DSL9 were prepared by mixing the components shown in Table 3 and filtering the mixtures through a filter paper having an average pore size of 2.7 m.

(6) TABLE-US-00003 TABLE 3 DSL1 DSL2 DSL3 DSL4 DSL5 DSL6 DSL7 DSL8 DSL9 PI 2.00 2.00 2.00 0 0 0 0 0 0 (w/w %) CA 0 0 0 1.3 1.3 1.3 0 0 0 (w/w %) PBA 0 0 0 0 0 0 1.3 1.3 1.3 (w/w %) CH 6.00 6.00 6.00 94.9 94.77 94.77 0 0 0 (w/w %) MEK 92.00 91.8 91.6 3.8 3.8 3.8 0 0 0 (w/w %) THF 0 0 0 0 0 0 98.7 98.57 98.57 GE 0 0.2 0.4 0 0 0 0 0 0 UV- 0 0 0 0 0.13 0 0 0.13 0 9390c (w/w %) I0591 0 0 0 0 0 0.13 0 0 0.13 (w/w %)

Stage d) Preparation of Composite Membranes

(7) Composite membranes were prepared using the combinations of radiation-curable composition and discriminating layers described in Table 4.

(8) The radiation-curable compositions RCC1 to 5 were applied to a porous PAN substrate (step a)) at a speed of 10 m/min by a meniscus dip coating and irradiated. Irradiation (step b)) was performed using a Light Hammer LH10 from Fusion UV Systems fitted with a D-bulb and irradiating with an intensity of 16.8 kW/m (70%). The resultant gutter layers had a dry thickness of 300 nm. Discriminating layers were formed on the gutter layers (step c)) using the compositions DSL1 to DSL9 as indicated in Table 4, using a meniscus type coating T 10 m/min coating speed. In Examples 1 to 4 and CEx1 to CEx4, the discriminating layers comprised PI. In Examples 5, 6 and 7, the discriminating layers comprised cellulose acetate. In Examples 8, 9 and 10, the discriminating layers comprised a polybenzoxazole.

(9) After steps a) to c) had been completed, the resultant composite membranes were dried and tested. The test results are shown in Table 4 below.

(10) TABLE-US-00004 TABLE 4 Example CEx1 Ex1 Ex2 CEx2 CEx3 Ex3 Ex4 CEx4 Ex5 Ex6 Ex7 Ex8 Ex9 Ex10 Radiation- RCC1 RCC2 RCC3 RCC4 RCC5 RCC2 RCC2 RCC1 RCC2 RCC2 RCC2 RCC2 RCC2 RCC2 curable Composition Coating speed 10 10 10 10 10 10 10 10 10 10 10 10 10 10 (m/min) Coating 3 3 3 3 3 3 3 3 3 3 3 3 3 3 amount (ml/m.sup.2) Dry layer 300 300 300 300 300 300 300 300 300 300 300 300 300 300 thickness of gutter layer (nm) Discriminating DSL1 DSL1 DSL1 DSL1 DSL1 DSL2 DSL3 DSL2 DSL4 DSL5 DSL6 DSL7 DSL8 DSL9 layer composition Coating 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 8.4 amount (ml/m.sup.2) Dry layer 120 120 120 120 120 120 120 120 120 120 120 120 120 120 thickness of discrimi- nating layer (nm) Q.sub.CO2 of 63 60 61 63 65 65 70 72 60 40 46 190 190 185 composite 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 10.sup.6 membrane (cm.sup.3(STP)/ cm.sup.2 .Math. cm Hg .Math. s) .sub.CO2/CH4 of 20 35 33 20 15 15 10 5 17 14 17 13 10 13 composite membrane

(11) Examples 1 to 4 and Comparative Examples 1 to 4 illustrate composite membranes comprising a discriminating layer containing a polyimide. As can be seen from Table 4, for this discriminating later, the best selectivity (.sub.CO2/CH4) was obtained from Examples 1 and 2 where both the gutter layer and the discriminating layer were obtained from compositions free from mono epoxy compounds. In Examples 3 and 4, the gutter layer was obtained from compositions free from mono epoxy compounds but the discriminating layer contained such compounds. The selectivity in Examples 3 and 4 was not as good as for Examples 1 and 2, but it was better than Comparative Example 4 where both the gutter layer and the discriminating layer were obtained from compositions containing mono epoxy compounds. Comparative Example 1 shows that the presence of mono epoxy compounds in the gutter layer reduces selectivity relative to Examples 1 and 2.

(12) Example 5, 6 and 7 show results for composite membranes comprising a cellulose acetate discriminating layer. Examples 5 and 6, both of which comprised discriminating layers obtained from compositions free from epoxy compounds, had superior selectivity to Ex 7 (where the cellulose acetate discriminating layer was obtained from a composition containing mono-epoxy compounds).

(13) Examples 8, 9 and 10 show results for composite membranes comprising a polybenzoxazole discriminating layer. Examples 8 and 10, both of which comprised discriminating layers obtained from compositions free from epoxy compounds, had superior selectivity to Example 9 (where the PBA discriminating layer was obtained from a composition containing mono-epoxy compounds).