Process for the production of solvent stable polymeric membranes
The present invention relates to a process for preparing an asymmetric integrally skinned membrane for the separation of at least one solute from a solution, comprising the steps of: (a) preparing a polybenzimidazole dope solution comprising: (i) a polybenzimidazole polymer, and (ii) a solvent system for said polybenzimidazole which is water miscible; (b) casting a film of said dope solution onto a support; (c) immersing the film cast on the support into a coagulating medium to form an asymmetric integrally skinned membrane; (d) treating the membrane from step (c) with a cross-linking agent; (e) treating the membrane from step (d) with a cross-link modification agent. Further aspects relate to an asymmetric integrally skinned membrane and uses thereof.
1. A process for preparing an asymmetric integrally skinned membrane for the separation of at least one solute from a solution, comprising the steps of:
(a) preparing a polybenzimidazole dope solution comprising:
(i) a polybenzimidazole polymer, and
(ii) a solvent system for said polybenzimidazole which is water miscible;
(b) casting a film of said dope solution onto a support;
(c) immersing the film cast on the support into a coagulating medium to form an asymmetric integrally skinned membrane;
(d) treating the membrane from step (c) with a cross-linking agent, wherein the cross-linking agent is at least difunctionalised and comprises an electrophilic functional group; and
(e) treating the membrane from step (d) with a cross-link modification agent, wherein the cross-link modification agent comprises a functional group capable of reacting with an electrophilic functional group on the cross-linking agent, the functional group being selected from an amine, a thiol, a thiolate, a phenoxide, a sulfonate, a phosphate, a phosphonate, a hydroxylamine, an oximate, a hydrazine, a hydrazone, an imide, and a hydrazide.
2. A process according to claim 1 wherein the polybenzimidazole polymer has the following general repeat structure I shown below:
where R is a tetravalent aromatic nucleus, typically symmetrically substituted, with the nitrogen atoms forming the benzimidazole rings being paired upon adjacent carbon atoms of the aromatic nucleus, and R 1 is a divalent substituent selected from aliphatic, alicyclic and aromatic radicals.
3. A process according to claim 1 wherein the polybenzimidazole polymer has the following formula:
wherein n is an integer in the range of 10 to 5000.
4. A process according to claim 1 , wherein the cross-linking agent is a multifunctional halide, multifunctional sulfonate ester or a divinyl sulfone.
5. A process according to claim 1 , wherein the cross-linking agent is selected from dibromoxylene, dibromobutane, tribromopropane, trichloropropane, pentaerythrityl tetrabromide, pentaerythrityl tetrachloride, 1,3,5-tri(bromomethyl)benzene, 1,2,4,5-tetra(bromomethyl)benzene and divinyl sulfone.
6. A process according to claim 1 , wherein the cross-link modification agent is an amine.
7. A process according to claim 1 , wherein the cross-link modification agent is a polyetheramine.
8. An asymmetric integrally skinned membrane obtainable by the process according to claim 1 .
9. A process according to claim 2 wherein the polybenzimidazole polymer has the following formula:
wherein n is an integer in the range of 10 to 5000.
10. A process according to claim 9 , wherein the cross-linking agent is a multifunctional halide, multifunctional sulfonate ester or a divinyl sulfone.
11. A process according to claim 10 , wherein the cross-link modification agent is an amine.
12. A process according to claim 10 , wherein the cross-link modification agent is a polyetheramine.
13. An asymmetric integrally skinned membrane for the separation of at least one solute from a solution wherein the membrane comprises a cross-linked polybenzimidazole polymer cross-linked by a cross-linking agent, wherein the polymer comprises a cross-link modifier,
wherein the cross-linking agent is at least difunctionalised and comprises an electrophilic functional group;
wherein the cross-link modifier is a residue of a cross-link modification agent after it has reacted with an unreacted functional group of the cross-linking agent, wherein the cross-link modification agent comprises a functional group capable of reacting with an electrophilic functional group on the cross-linking agent, the functional group being selected from an amine, a thiol, a thiolate, a phenoxide, a sulfonate, a phosphate, a phosphonate, a hydroxylamine, an oximate, a hydrazine, a hydrazone, an imide, and a hydrazide.
14. A membrane according to claim 13 wherein the polybenzimidazole polymer has the following general repeat structure shown below:
where R is a tetravalent aromatic nucleus, typically symmetrically substituted, with the nitrogen atoms forming the benzimidazole rings being paired upon adjacent carbon atoms of the aromatic nucleus, and R 1 is a divalent substituent selected from aliphatic, alicyclic and aromatic radicals.
15. A membrane according to claim 13 , wherein the cross-link modifier is the residue of a cross-link modification agent comprising an amine functional group.