NOVELTY - A diolefin hydrocarbon stream is purified by contacting at least a partially spent selective hydrogenation zone with a polymer solvent consisting of 4-8C alkane compound, and hydrogen to reduce the polymer content of the catalyst and increase hydrogenation activity.    USE - For purification of diolefin compounds used to produce products and precursor products utilizing diolefin production processes including naphtha cracking processes.    ADVANTAGE - The method produces a high quality diolefin hydrocarbon having extremely low levels of acetylene over an extended period because of the ability to readily generate catalyst contained in an off-line reaction zone while continuing to operate an on-line selective hydrogenation reaction zone.    DETAILED DESCRIPTION - Purification of diolefin hydrocarbon stream involves introducing a stream containing trace quantities of acetylene compounds and elemental hydrogen into a selective hydrogenation zone to selectively hydrogenate at least a portion of the acetylene compounds and to produce an at least partially spent selective hydrogenation catalyst. The resulting effluent from the selective hydrogenation zone is passed to a fractionation zone to produce a diolefin hydrocarbon stream having a reduced concentration of acetylene compounds. The at least partially spent selective hydrogenation catalyst in the selective hydrogenation zone is contacted with a polymer solvent consisting of 4-8C alkane compound and hydrogen to reduce the polymer content of the selective hydrogenation catalyst to increase hydrogenation activity. The resulting effluent from the selective hydrogenation zone is passed to the fractionation zone to produce a stream comprising polymer solvents and polymer compounds. At least a portion of the stream comprising polymer solvent and polymer compounds is recycled to provide at least a portion of the polymer solvent, and at least another portion of it is recovered. The diolefinic hydrocarbon stream having a reduced concentration of acetylene compounds is recovered. The diolefinic hydrocarbon stream containing trace quantities of acetylene compounds and elemental hydrogen is introduced into the hydrogenation zone after contact with the polymer solvent and hydrogen.