Solvent resistant polyamide nanofiltration membranes
The present invention relates to a composite membrane for nanofiltration of a feed stream solution comprising a solvent and dissolved solutes and showing preferential rejection of the solutes. The composite membrane comprises a thin polymeric film formed by interfacial polymerization on a support membrane. The support membrane is further impregnated with a conditioning agent and is stable in polar aprotic solvents. The composite membrane is optionally treated in a quenching medium, where the interfacial polymerization reaction can be quenched and, in certain embodiments, membrane chemistry can be modified. Finally the composite membrane is treated with an activating solvent prior to nanofiltration.
1. An interfacial polymerization process for forming a composite membrane suitable for nanofiltration operations in polar aprotic solvents, said process comprising the sequential steps of:
(a) impregnating a porous support membrane comprising a first conditioning agent, with a first reactive monomer solution comprising:
(i) a first solvent for the said first reactive monomer and
(ii) a first reactive monomer;
wherein the first conditioning agent is polyethylene glycol, and
wherein said support membrane is stable in polar aprotic solvents and is formed from crosslinked polyimide, crosslinked polybenzimidazole, crosslinked polyacrylonitrile, Teflon, polypropylene, or polyether ether ketone (PEEK), or sulfonated polyether ether ketone (S-PEEK);
(b) contacting the impregnated support membrane with a second reactive monomer solution comprising:
(i) a second solvent for the second reactive monomer and
(ii) a second reactive monomer;
wherein the first solvent and the second solvent form a two-phase system;
(c) after a reaction period, immersing the resulting composite membrane into a quench medium;
(d) treating the resulting composite membrane with an activating solvent,
wherein the activating solvent is selected from the group consisting of dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, or a mixture thereof, and:
(e) optionally, impregnating the resulting composite membrane with a second conditioning agent,
wherein the second conditioning agent is a non-volatile liquid, and
wherein the use of both the first conditioning agent and the activating solvent increases the organic solvent flux of the composite membrane.
2. A process according to claim 1 , wherein the support membrane is formed from crosslinked polyimide.
3. A process according to claim 1 , wherein the first reactive monomer solution comprises an aqueous solution of a polyamine.
4. A process according to claim 1 , wherein the first reactive monomer solution comprises an aqueous solution of a 1,6 hexenediamine, m-phenylenediamine, or poly(ethyleneimine).
5. A process according to claim 1 , wherein the second reactive monomer solution contains a polyacyl chloride.
6. A process according to claim 1 , wherein the composite membrane is treated in step (d) with the activating solvent by immersion or by washing in the activating solvent.
7. A process according to claim 1 , wherein the composite membrane is treated in step (d) with the activating solvent by filtration through the membrane using the activating solvent.
8. A process according claim 1 , wherein the activating solvent is dimethylformamide or dimethyl sulfoxide.
9. A process according to claim 1 in which the contacting in step (b) is performed in a time between about 5 seconds and about 5 hours.
10. A process according to claim 1 in which the temperature of the solution in step (b) is held between about 10° C. and about 100° C.
11. The process according to claim 1 , wherein the second reactive monomer solution contains trimesoyl chloride, iso-phthaloyl dichloride, sebacoyl chloride, or a mixture thereof.
12. The process according to claim 1 , wherein the activating solvent is dimethylformamide.
13. The process according to claim 1 , wherein the concentration of the first reactive monomer in the first reactive monomer solution, and the second reactive monomer in the second reactive monomer solution, is 0.01 to 5 wt. %.
14. The process according to claim 1 , wherein the first reactive monomer is m-phenylenediamine, the second reactive monomer is trimesoyl chloride, and the activating solvent is dimethylformamide.
15. The process according to claim 1 , wherein the second conditioning agent is selected from one or more of synthetic oils, mineral oils, vegetable fats and oils, higher alcohols, glycerols, and glycols.
16. A method comprising the step of:
performing nanofiltration of a feed stream solution using the membrane produced by the process of claim 1 , wherein the feed stream solution comprises a solvent and dissolved solutes.