Reverse osmosis membranes made with PFSA ionomer and ePTFE
View Patent ↗A method for forming a membrane includes a step of dissolving a lithium salt in a solution including an ionomer that includes protogenic groups to form a modified solution. A membrane is formed from the solution containing the lithium salt and the ionomer that includes protogenic groups. The membrane is dried and then contacted with water to form a plurality of pores therein.
1. A method for forming a membrane, the method comprising:
a) dissolving lithium salt in a solution including an ionomer with protogenic groups to form a modified solution;
b) forming a membrane from the modified solution;
c) drying the membrane; and
d) contacting the membrane with water to form a plurality of pores therein.
2. The method of claim 1 wherein the lithium salt is lithium chloride.
3. The method of claim 1 wherein the pore size varies along the thickness of the membrane.
4. The method of claim 3 wherein the pore size decreases along the thickness of the membrane.
5. The method of claim 4 wherein the membrane has a region substantially free of pores.
6. The method of claim 1 wherein the membrane in step b) is formed by contacting a polymeric support with the modified solution.
7. The method of claim 6 wherein the polymeric support is expanded polytetrafluoroethylene.
8. The method of claim 1 wherein the protogenic groups are selected from the group consisting of —SO 2 X, —PO 3 H 2 , and COX where X is an —OH, a halogen, or a C 1-6 ester.
9. The method of claim 1 wherein the ionomer having protogenic groups is a perfluorosulfonic acid polymer.
10. The method of claim 9 wherein the perfluorosulfonic acid polymer is a copolymer containing a polymerization unit based on tetrafluoroethylene and a polymerization unit based on a perfluorovinyl compound represented by:
CF 2 ═CF—(OCF 2 CFX 1 ) m —O r —(CF 2 ) q —SO 3 H
where m represents an integer of from 0 to 3, q represents an integer of from 1 to 12, r represents 0 or 1, and X 1 represents a fluorine atom or a trifluoromethyl group.
11. The method of claim 1 wherein the ionomer having protogenic groups is a perfluorocyclobutyl-containing polymer.
12. The method of claim 1 further comprising incorporating the membrane into a battery as a battery separator.
13. The method of claim 1 further comprising incorporating the membrane into a humidifier.
14. The method of claim 13 wherein the membrane is contacted with acid to form the free acid form of the ionomer.
15. The method of claim 1 further comprising incorporating the membrane into a reverse osmosis system.
16. The method of claim 1 wherein the membrane is contacted in step d) with a component consisting of water to form the pores.