Carbon molecular sieve (cms) hollow fiber membranes and preparation thereof from pre-oxidized polyimides

A process for preparing a carbon molecular sieve membrane from a polyimide for separation of hydrogen and ethylene from one another comprising sequential steps as follows:

• a) placing a membrane fabricated from fibers of a polyimide selected from a group consisting of ((5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis -1,3-isobenofurandione (6FDA), 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), 2,4,6-trimethyl-1,3-phenylene diamine (DAM)) (614DA/BPDA-DAM) polyimides and polyimides that i) have a glass transition temperature (Tg) of at least 400° C. and ii) include a bridged phenyl compound in contact with an oxygen-containing atmosphere or gas at a temperature within a range of from greater than 300° C. to less than 400° C. and for a time within that temperature range of from greater than or equal to five minutes up to 200 hours to produce a pre-oxidized and pre-carbonized polymeric membrane that is insoluble in hot (110° C.) n-methylpyrolidone and substantially free of substructure collapse;
• and b) pyrolyzing the pre-oxidized and pre-carbonized polymeric membrane in the presence of a purge gas at a temperature within a range of from 450° C. to 1000° C. and for a time within a range of from 1 minute to 100 hours, to yield a carbon molecular sieve membrane that has at least one of a hydrogen permeance and a hydrogen/ethylene selectivity greater than that of a carbon molecular sieve membrane prepared from the same membrane using only pyrolysis as in step b).