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

Process for fractionation of a largely anhydrous gas resulting from the pyrolysis of hydrocarbons (1), containing hydrogen and hydrocarbons, particularly hydrocarbons from C1 to C3, including ethylene, propylene, and acetylene, in at least one hydrogen and/or methane-enriched current, at least one ethylene-enriched and acetylene-poor current, and at least one propylene-enriched current, characterized in that:

• a) said gas resulting from pyrolysis of hydrocarbons (1) is cooled and liquefied progressively under pressure by passage into a series of increasingly cold heat-exchange zones (2, 6, 9, 20);
• from said pyrolysis gas (1) there is separated at least one condensate after passage into each heat-exchange zone, at least one of the condensates (15) being propylene-enriched, and at least one other condensate (23) being ethylene- and ethane-enriched, and containing in solution a smaller proportion of hydrogen, methane, and acetylene;
• the residual hydrogen-rich gas (27) is collected;
• b) by reduction in pressure, the ethylene- and ethane-enriched condensate (23) and the propylene-enriched condensate (15) are at least partly evaporated, and they are heated, independently or otherwise, in at least one of said heat-exchange zones (2, 6, 9, 20) by thermal exchange with fluids to be cooled, including at least the gas resulting from pyrolysis (1), to provide, respectively, a fraction (25) at least partly evaporated due to the pressure reduction and the heating of the ethylene- and ethane-enriched fraction (23), and a fraction (17) at least partly evaporated due to the pressure reduction and the heating of the propylene-enriched fraction (15), to provide at least part of the cold necessary for the progressive cooling and liquefaction of at least said gas resulting from hydrocarbon pyrolysis (1) upon passage into said successive heat-exchange zones (2, 6, 9, 20);
• c) at least partly evaporated fractions (17, 25) resulting from stage (b) are introduced into part of a distillation column (C1) called the de-ethanizer, the ethylene- and ethane-rich condensate (25) which is at least partly evaporated being admitted in one point of said distillation column (C1) which is higher than the partly evaporated propylene-rich condensate (17), said part of the distillation column (C1) operating under conditions of temperature and pressure allowing for the separation, in an upper part, of a first head gas current (31) 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 (18) enriched with propylene, which is collected;
• d) the first ethylene- and ethane-rich head gas current (31) from stage (c) is sent into an acetylene elimination zone (R1) by extraction with a solvent and/or by selective hydrogenation of acetylene by means of the hydrogen contained in said first head gas current (31) to provide a current (36) essentially free of acetylene, and
• e) in a part of a distillation column called the de-methanizer (C2), the largely acetylene-free gas current (36) from stage (d) is cooled and fractionated into a second head gas fraction (44) enriched with hydrogen and/or methane, which is collected, and a second bottom liquid fraction (43), enriched with ethylene and ethane, and essentially free of acetylene, which is also collected.