Process and installation for recovery and purification of ethylene produced by pyrolysis of hydrocarbons, and gases obtained by this process

A process for fractionation of a substantially anhydrous gas resulting from pyrolysis of hydrocarbons, containing hydrogen and hydrocarbons, particularly hydrocarbons from C1 to C3, including ethylene, propylene, and acetylene, in at least one of a hydrogen and a methane-enriched current, at least one of an ethylene-enriched and an acetylene-poor current, and at least one propylene-enriched current, the process comprising, in stages:

• a) cooling and liquefying a gas resulting from pyrolysis of hydrocarbons, progressively, under pressure by passage through a series of increasingly cold successive heat-exchange zones, separating at least one condensate after passage into each heat-exchange zone, at least a first of the condensates being propylene-enriched, and at least a second of the condensates being ethylene- and ethane-enriched, and containing, in solution, a smaller proportion of hydrogen, methane, and acetylene;
• and collecting a residual hydrogen-rich gas;
• b) at least partially evaporating, by a reduction in pressure, the second, ethylene- and ethane-enriched condensate and the first, propylene-enriched, condensate, and heating, in at least one of said successive heat-exchange zones, by thermal exchange with fluids to be cooled, including at least the gas resulting from pyrolysis, to provide, respectively, a first fraction at least partly evaporated due to the reduction in pressure and the heating of the ethylene- and ethane-enriched condensate, and a second fraction at least partly evaporated due to the reduction of pressure and the heating of the propylene-enriched condensate, to provide at least part of the cooling necessary for the cooling and liquefying of the gas resulting from hydrocarbon pyrolysis upon passage into the successive heat-exchange zones successively;
• c) introducing the at least partly evaporated first and second fractions resulting from stage (b) into a part of a distillation column called a de-ethanizer, the ethylene- and ethane-rich first fraction which is at least partly evaporated, at a point of said distillation column higher than a point of introduction of the partly evaporated propylene-rich fraction after the partial evaporation, the part of the distillation column operating under conditions of temperature and pressure for separation, in an upper part, of a first head gas current rich in ethylene and ethane and containing, in a smaller proportion, acetylene, hydrogen, and methane, and in a lower part, a first bottom liquid current enriched with propylene, and collecting the first bottom liquid current;
• d) sending the first head gas current from stage (c) into an acetylene elimination zone eliminating acetylene by one of extraction with a solvent and selective hydrogenation of acetylene with the hydrogen contained in the first head gas current to provide a current essentially free of acetylene, and
• e) cooling and fractionating, in a part of a distillation column called the de-methanizer, the current essentially free of acetylene to produce a second head gas fraction enriched with one of hydrogen and methane, collecting the second head gas fraction, and a second bottom liquid fraction, enriched with ethylene and ethane, and essentially free of acetylene, and collecting the second bottom liquid fraction.