Method to make carbon molecular sieve hollow fiber membranes

Abstract

An asymmetric hollow fiber (CMS) carbon molecular sieve is made by providing a dope solution comprised of a polvimide and a solvent, at a temperature greater than 250° C. that is less than the storage modulus at a temperature of 250° C., but no more than ten times less as measured using dynamic mechanical thermal analysis from 250° C. to a temperature where the polyimide carbonizes. The polvimide is shaped into a hollow polvimide fiber, the solvent removed and the polyimide hollow fiber is heated to pyroiyze the polvimide and form the asymmetric hollow carbon molecular sieve. The asymmetric hollow fiber carbon molecular sieve has a wall that is defined by an inner surface and outer surface of said fiber and the wall has an inner porous support region extending from the inner surface to an outer raicroporous separation region that extends from the inner porous support region to the outer surface. Surprisingly, when the polyimide has the particular storage modulus characteristics, the method allows for the hollow fiber CMS to be made without any pre-treatmenis or additives to inhibit stractural collapse of the inner microporous region.