Process for separating monoolefins from a monoolefin mixture

A process and apparatus for separating monoolefins from other monoolefins comprising contacting a mixture of different monoolefins with a complexing agent selected from the group consisting of copper (I) salts of sulfonic acids and copper (I) salts of dialkyl phosphates and a suitable hydrocarbon solvent for the complexing agent under such conditions that the monoolefins form different strength complexes with the complexing agent. The different strength of the complexes provides a mechanism by which even closely boiling monoolefin isomers may be separated.