NOVELTY - A stream containing hydrogen, methane, 2-6C olefin and paraffin, 2-6C acetylene, diene, benzene, toluene, xylene and 6C or more components is passed over hydrogenation catalyst contained in downflow boiling point reactor (10). The heat of reaction is absorbed by the boiling liquid to produce liquid/vapor effluent (I) and portion of acetylene and diene are converted to corresponding olefin and paraffin. Effluent (I) is separated to liquid and vapor, and portion of separated liquid is supplied to reactor. Effluent (II) produced by condensing the vapor is separated.    USE - For hydrogenating acetylene and diene.    ADVANTAGE - The method enables selective hydrogenation of acetylene and diene.    DETAILED DESCRIPTION - A stream containing hydrogen, methane, 2-6C olefins and paraffin, 2-6C acetylenes, diene, benzene, toluene, xylene, and 6C or more components is passed over a hydrogenation catalyst contained in downflow boiling point reactor operated at the boiling point of the mixture in the reactor. The heat of reaction is absorbed by the boiling liquid to produce liquid/vapor effluent (I) and a portion of the acetylenes and diene are converted to their corresponding olefins and paraffin. The liquid/vapor effluent (I) are separated to liquid and vapor, and a portion of the separated liquid is supplied to downflow boiling point reactor in an amount to ensure that the catalyst is fully wetted at all positions within the reactor. A portion of the vapor corresponding to the mass evaporated in the reactor is condensed to produce liquid/vapor effluent (II). The liquid/vapor effluent (II) is separated and the separated liquid is returned to the reactor, controlling the steady state composition of the material flowing through the reactor.    DESCRIPTION OF DRAWING(S) - The figure shows the hydrogenation process.    Downflow boiling point reactor (10)    Vapor/liquid separator vessel (20)    Liquid/vapor separator (30)    5C/6C splitter (50)    Receiver separator (60)