Abstract: A method of separating a gaseous hydrocarbon mixture residing in cooling same by stages, with the resulting liquid condensate composed of the olefins and methane with an admixture of hydrogen being withdrawn at each cooling stage, recovering a gaseous methane-hydrogen mixture with some admixed ethylene produced by demethanization in a demethanizer, and further cooling same, withdrawing the resulting liquid condensate adapted for use as a spraying means in the process of demethanization. Expanding the remaining gaseous methane-hydrogen mixture with the application of the vortex effect providing thereby a hot gasiform stream and a cold gasiform stream. Mixing said hot and cold gasiform streams and again expanding the resulting mixture with the application of vortex effect.