Fluid separation membranes and use thereof
A process is disclosed for the production of highly asymmetric hollow fibers suitable for use as permselective gas separation membranes and for the fabrication of composite membranes derived from polyetherimide. The resulting polyetherimide membranes exhibit superior selectivity and permeability characteristics and are particularly advantageous for the separation of carbon dioxide from natural gas, biogas, and other gas streams containing acid gases.
1 . A hollow fiber comprising a polymer composition comprising a blend of polyetherimide (PEI) and a compatible polyimide, said hollow fiber produced by a method comprising the steps of:
(i) forming a spinning solution comprised of polyetherimide (PEI) or a blend of polyetherimide with a compatible polyimide in a mixture of an aprotic solvent and glycol ether non-solvent;
(ii) extruding said spinning solution through a spinneret to form a nascent hollow fiber while injecting a bore fluid;
(iii) passing the nascent hollow fiber through an air gap;
(iv) passing the nascent hollow fiber through a coagulation bath to solidify the hollow fiber;
(v) washing the hollow fiber to remove solvent and non-solvent, and
(vi) collecting the solidified hollow fiber,
wherein the polyimide is a condensation polymer of dianhydride and diamine of the following formulae:
or a polyimide derived from aromatic dianhydrides and aromatic diisocyanates based on a 3,3′4,4′-benzophenone tetracarboxylic dianhydride and 80% methylphenylene-diamine+20% methylene diamine co-polyimide precursor (BTDA-TDI/MDI).
2 . The hollow fiber of claim 1 , wherein the aprotic solvent is N-methyl pyrrolidone, dimethylacetamide, dimethylformamide, or a mixture thereof.
3 . The hollow fiber of claim 1 , wherein the glycol ether is of the following general structure:
R—O—CH 2 —CH 2 —OH,
wherein R is an alkyl or aryl group.
4 . The hollow fiber of claim 1 , wherein the glycol ether comprises at least one of the following: glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, 2-butoxyethanol, 2-(hexyloxy) ethanol, and mixtures thereof.
5 . The hollow fiber of claim 1 , wherein the polyetherimide is benzene-1,3-diamine; 5-[4-[2-[4-[(1,3-dioxo-2-benzofuran-5-yl)oxy]phenyl]propan-2-yl]phenoxy]-2-benzofuran-1,3-dione of the following formulae:
or sulfone group containing polyetherimide of the following formulae:
6 . The hollow fiber of claim 1 , wherein a polymer concentration in the solution ranges from 25 to 45 weight percent.
7 . The hollow fiber of claim 6 , wherein a weight ratio of polyetherimide to the compatible polyimide is 5:1 or higher.
8 . The hollow fiber of claim 7 , wherein the weight ratio of polyetherimide to the compatible polyimide is 10:1 or higher.
9 . The hollow fiber of claim 1 , wherein the air gap is maintained at a sub-atmospheric pressure between 15.0 to 54.0 cm Hg.
10 . The hollow fiber of claim 9 , wherein the air gap is maintained at a sub-atmospheric pressure between 20.0 and 47.0 cm Hg.
11 . The hollow fiber of claim 1 , wherein the hollow fiber is a subject to an additional drying step (vii).
12 . The hollow fiber of claim 11 , wherein the drying step is carried out from an alcohol or hydrocarbon solvent.
13 . The hollow fiber of claim 1 , wherein a coating of a polymer is applied to a surface of the hollow fiber.
14 . The hollow fiber of claim 13 , wherein the polymer is applied from a solution.
15 . The hollow fiber of claim 14 , wherein the polymer is a rubbery or glassy polymer that enhances a surface integrity and gas separation performance of the hollow fiber.
16 . The hollow fiber of claim 15 , wherein the rubbery polymer is a silicone-based polymer, poly(dimethylsiloxane), a polyurethane, or an elastomeric crosslinkable polymer.
17 . The hollow fiber of claim 15 , wherein the glassy polymer is a cellulose acetate, ethyl cellulose, or sulfonated polyphenylene oxide.
18 . The hollow fiber of claim 13 , wherein the coated hollow fiber is annealed at a temperature below a glass transition temperature of the polyetherimide.
19 . The hollow fiber of claim 1 , wherein the spinning solution contains an additive.
20 . The hollow fiber of claim 19 , wherein the additive is a surfactant, a salt, or a mixture thereof.
21 . The hollow fiber of claim 1 , wherein said hollow fiber has an asymmetric pore structure.
22 . A gas separation membrane comprising the hollow fiber of claim 1 .