Fabrication of fluoropolymer hollow fibers for asymmetric membranes
AssigneeHoechst Celanese Corporation
InventorsTai-Shung Chung, Edward R. Kafchinski, Paul Foley
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Abstract
Asymmetric hollow fibers comprising a fluoropolymer, and a process for making such fibers. The hollow fibers are useful for making fluid separation membranes, especially gas separation membranes. In one embodiment of the process of this invention, a polymer dope having a viscosity of about 3000 poise or greater is prepared by solvating the polymer in a solvent system containing about 40%-90% N-methyl-2-pyrrolidone and about 60%-10% propionic acid by weight. The dope is dry-jet wet-spun into hollow fibers using a water-NMP core solvent. The fibers are coagulated in methanol. The fibers are then coated with a highly permeable material.
Claims13
A process for making asymmetric hollow fiber comprising the steps of:
- preparing a dope having a viscosity of at least about 3000 poise at 25.degree. C. by dissolving a fluoropolymer in a solvent consisting essentially of NMP and a second liquid in a ratio in the approximate range of from 90/10 to 40/60;
- spinning said dope through a hollow fiber die while simultaneously passing a core solvent through the center of said die to form a hollow fiber having an outer layer that is denser and less porous than the interior, wherein said outer layer is no more than about one micron thick;
- passing said fiber through an air gap and into a methanol bath;
- removing said fiber from said bath and collecting said fiber;
- and,
- subsequently coating said fiber with a composition that is highly permeable to gases.
A process according to claim wherein said fluoropolymer is a polyimide.
A process according to claim wherein said second liquid is propionic acid.
A process according to claim wherein said coating composition comprises silicone.
A process for making asymmetric hollow fiber for gas separations, said fiber having an oxygen/nitrogen separation factor of at least about five, comprising the steps of:
- preparing a dope having a viscosity of at least about 3000 poise at 25.degree. C. by dissolving a fluoropolymer in a solvent consisting essentially of NMP and propionic acid in a ratio in the approximate range of from 90/10 to 40/60;
- preparing a core solvent consisting essentially of water and NMP wherein said core solvent is from about 20% to about 100% water by weight;
- spinning said dope through a hollow fiber die at a temperature of approximately 25.degree.-100.degree. C. while simultaneously passing said core solvent through the center of said die to form a hollow fiber having an outer layer that is denser and less porous than the interior, wherein said outer layer is no more than about one micron thick;
- passing said fiber through an air gap no greater than ten inches and into a methanol bath, said bath being at a temperature of about 25.degree. C.;
- removing said fiber from said bath and collecting said fiber;
- and,
- subsequently coating said fiber with a silicone-containing composition that is highly permeable to gases to a coating thickness of about 3-8 microns.
Dependencies are inferred from the claim text.