Process for producing acrylonitrile separation membranes in fibrous form

Claim 1

A process for producing acrylonitrilic hollow fiber, which comprises dissolving an acrylonitrile polymer in formamide-containing dimethylformamide to prepare an acrylonitrile polymer solution containing more than 80 wt.% of acrylonitrile units, the molecular weight of said acrylonitrile polymer expressed by [η] as measured in DMF at 30° C., being 0.4-4 and the concentration of said acrylonitrile polymer in said solution being from 10 to 35 wt.% based on the weight of said solution; shaping said polymer solution into a hollow fibrous product while maintaining the temperature of the solution at a temperature above the gellation temperature, determining the gellation temperature by the following procedure: pouring about 150 to 180 g of a sample solution into a beaker which is about 5.5 cm in diameter and about 11 cm in height; dipping said beaker into a temperature-controlled water bath maintained at the same temperature level as the dissolution temperature, then lowering the temperature of the solution at the rate of about 10° C./hour, accompanied by lowering the temperature of the water bath, and at a given point in time during this temperature lowering, placing a glass rod which is 3 mm in outer diameter and 2.5 g in weight, vertically on the surface of the solution while being supported lightly at its upper portion by a ring-shaped holder, then permitting the glass rod to penetrate into the solution under the action of its own weight and sinking, measuring the time elapsed until a sinking depth of 5 cm is attained, and employing the solution temperature at which the time elapsed first exceeds 5 seconds as the gellation temperature of the solution; bringing the surface layer of the hollow fibrous product into contact with an aqueous solution, at a temperature below 10° C., containing more than 30 wt.% of a water-soluble solvent compatible with the mixed solvent, said aqueous solution being referred to as solvent removal treatment medium A, immediately or after bringing it into contact with an inert atmosphere; bringing the core of the hollow fibrous product immediately into contact with an aqueous solution, at a temperature above 10° C., containing less than 30 wt.% of a water-soluble solvent compatible with said mixed solvent or an inert medium, said aqueous solution or said inert medium being referred to as solvent removal treatment medium B, or bringing it into contact with said solution after bringing it into contact with an inert atmosphere, thereby removing the solvent; and then stretching the solidified fiber thus obtained.