A process and apparatus for separating monoolefins from diolefins comprising contacting a mixture of monoolefins and diolefins with a complexing agent selected from the group consisting of copper(I) salts of sulfonic acids and copper(I) salts of dialkylphosphates and a suitable hydrocarbon solvent for the complexing agent under such conditions that the monoolefins and diolefins form complexes with the complexing agent. The monoolefin complex can be separated from the diolefin complex based either on the relative solubilities of the two complexes in the hydrocarbon solvent for the complexing agent or based on the relative strengths of the two complexes.