Process for preparing hollow fiber having selective gas permeability

Claim 1

A process for preparing a hollow, asymmetric, gas-separating fiber which comprises extruding through the annular space between the inner and outer tubes of a double tube spinneret, a solution containing from about 22 to about 33 percent by weight of a fiber-forming cellulose ester or a fiber-forming cellulose ether dissolved in an organic solvent and having a viscosity of from about 300 to about 1500 poise at a temperature of 20° C. and simultaneously extruding through the inner tube of said spinneret water containing dissolved therein from one to 20 weight percent of a water-soluble salt, said spinneret being submerged in an aqueous coagulating liquid bath having a temperature of from 0° to 30° C. whereby to coagulate said solution directly in said bath to produce a hollow fiber; maintaining the fiber in said coagulating bath for at least about 20 minutes; then removing the fiber from said coagulating bath and then, without permitting said fiber to dry, immersing it in water having a temperature of 50° to 100° C. for at least 3 minutes; then removing free water present on the exterior and interior surfaces of said fiber; then applying to the fiber a liquid coolant having a temperature of below minus 40° C. to freeze the fiber, said coolant being a non-solvent for said cellulose ether or said cellulose ester and being immiscible with water; and then vacuum drying the fiber under a pressure of less than 0.5 mmHg absolute, for more than 12 hours at a temperature of below minus 30° C.