Abstract: In a process for the separation of a gas mixture comprising a major amount of hydrocarbons, e.g., C.sub.1 -C.sub.3, wherein the gas mixture is liquefied by single or multi-stage partial condensation, where the liquid fractions thus formed are further separated in a first rectifying column, and where following the last stage of partial condensation the resultant gaseous fraction is subjected to rectification in a second rectifying column,the improvement which comprises the intermediate step of stripping substantially all the most volatile components e.g., C.sub.1, from the liquid fractions before the latter are fed into said first rectifying column.

Abstract: Vacuum residue is used for production of olefins by first separating, preferably by solvent extraction, the asphalt therein, blending resultant asphalt depleted fraction with a lighter fraction, e.g., a vacuum gas oil, and then subjecting the blend to a conventional catalytic hydrogenation step prior to thermal cracking. The hydrogenate may be separated into fractions with the heavy fraction only being thermally cracked.