NOVELTY - An ethane/ethylene separation membrane prepared by a process comprising dissolving an amount of 3,3',4,4'-benzo-phenonetetracarboxylic acid dianhydride 5(6)-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane 4,4-bismaleimidodiphenyl-methane in a solvent such that a solution is formed; forming a film or hollow fibers from the solution; drying the film or the hollow fibers; and at least partially pyrolyzing the film or the hollow fibers under vacuum or in an inert atmosphere to form a carbon molecular sieve membrane.    USE - The membrane is useful for separating ethane and ethylene from one another (claimed).    ADVANTAGE - Pyrolysis condition variables, including ramp rate, thermal soak time and temperature, are used to optimize the membrane's separation performance. The carbon molecular sieve membranes show high selectivity in ethylene/ethane separations.    DETAILED DESCRIPTION - An ethane/ethylene separation membrane prepared by a process comprising dissolving an amount of 3,3',4,4'-benzo-phenonetetracarboxylic acid dianhydride 5(6)-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane 4,4-bismaleimidodiphenyl-methane in a solvent such that a solution is formed; forming a film or hollow fibers from the solution; drying the film or the hollow fibers; and at least partially pyrolyzing the film or the hollow fibers under vacuum or in an inert atmosphere to form a carbon molecular sieve membrane, the carbon molecular sieve membrane having as a property differential diffusion of ethane and ethylene when ethylene and ethane are flowed, this property enabling utility of the carbon molecular sieve membrane as an ethane/ethylene separation membrane. An INDEPENDENT CLAIM is a process for separating ethane and ethylene from one another comprising flowing a mixture of gases including ethane and ethylene through an ethane/ethylene separation membrane prepared by a process including dissolving an amount of 3, 3', 4,4'-benzo-phenonetetracarboxylic acid dianhydride 5(6)-amino-1-(4'-aminophenyl)-1,3,3- trimethylindane 4,4-bismaleimido-diphenyl-methane in a solvent such that a solution is formed; forming a film or hollow fibers from the solution; drying the film or the hollow fibers; and at least partially pyrolyzing the film or the hollow fibers under vacuum or in an inert atmosphere to form a carbon molecular sieve membrane, the carbon molecular sieve membrane having as a property differential diffusion of ethane and ethylene when ethylene and ethane are flowed, this property enabling utility of the carbon molecular sieve membrane as an ethane/ethylene separation membrane; such that the ethylene and the ethane are separated from one another.