PURPOSE: To remove acetylenes efficiently from a 4C hydrocarbon mixture without loss of butadiene, by hydrogenating acetylenes existing in the mixture which contains a substantial amount of butadiene, in a relatively high concentration. selectively under specific conditions.

CONSTITUTION: A 4C hydrocarbon liquid mixture containing butadiene and acetylenes in continuously supplied from the upper part of a reactor containing a catalyst, together with a hydrogen-containing gas. As the catalyst, a precious motal of Group VIII supported on the surface of solid particles is used. The hydrogen- containing gas is supplied so that the partial pressure of hydrogen is below 1.5kg/ cm2 a and the hydrogen-containing gas becomes a continuous phase substantially in the reactor. Acetylenes are hydrogenated at 5W80°C by flowing down the 4C hydrocarbon mixture on the surface of the catalyst. The reaction mixture is taken out of the lower part of the reactor, and sent to the recovery step of butadiene. Acetylenes contained in the raw material in an amount of above 3000 ppm, can be removed to below 50 ppm.