Patent EA-003348-B1 (EA)
Title: Process and installation for recovery and purification of ethylene produced by pyrolysis of hydrocarbons, and gases obtained by this process
Inventor: KAISER VICTOR
IPC: F25J3/02
Filed: 2001-12-07
Abstract: 1. 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. 2. Process according to claim 1, characterized in that the current of gas from hydrocarbon pyrolysis (1) is at a pressure of 15-50 bar, preferably 28-38 bar, and in that the distillation zone (C1) is at a pressure of 10-30 bar, preferably 14-24 bar, lower than the pressure of the pyrolysis gas. 3. Process according to claim 1 or claim 2, characterized in that the evaporated condensates introduced into the part of the distillation column (C1) called the de-ethanizer contain dissolved hydrogen in a proportion such that said first head gas current (31) contains 2-10%, preferably 4-5%, in moles, of hydrogen, and in that stage (d) is implemented by selective hydrogenation essentially in ethylene of the acetylene contained in the first head gas current (31) by means of the hydrogen contained in said first head gas current of stage (c), the temperature of the hydrogenation zone between 0 degree C and 160 degree C., inclusive. 4. Process according to any of claims 1-3, characterized in that the hydrogen dissolved in the evaporated condensates introduced into the part of the distillation column (C1) called the de-ethanizer is the only hydrogen used for the hydrogenation carried out in stage (d). 5. Process according to any of claims 1-4, characterized in that two or three condensates obtained after successive passage of the pyrolysis gas, respectively, into two or three heat-exchange zones of stage (a) are sent into the upper part of the de-ethanizer C1 of stage (c), considering that the first heat-exchange zone is the one which is the first to be in contact with the pyrolysis gas (1). 6. Process according to any of claims 1-5, characterized in that the second head gas fraction (44) exiting the de-methanizer is purified by distillation to recover the ethylene and the ethane. 7. Process according to any of claims 1-5, characterized in that the pyrolysis gas (1) is a gas for pyrolysis of ethane or an ethane/propane mixture, and in that the second head gas fraction (44) exiting the de-methanizer is mixed with the pyrolysis gas (1) without ethylene recovery, for a new treatment in mixture with the pyrolysis gas (1) in stage (a). 8. Process according to any of claims 1-7, characterized in that the hydrogen content of the first head gas current (31) exiting the de-ethanizer is increased by the addition of hydrogen (27) from the head of a separator (22 or 22A) of a partly condensed fluid (24C), said fluid (24C) coming from the refrigeration in a heat-exchange zone (26) of the residual gaseous fluid (24) from the refrigeration in the successive heat-exchange zones (2, 6, 9, 20) of the pyrolysis gas (1). 9. Process according to any of claims 1-8, characterized in that part of the second liquid bottom fraction (43) from the de-methanizer is recycled into the de-ethanizer, to reduce the acetylene concentration of the first head gas current (31) from the de-ethanizer. 10. Process according to any of claims 1-9, characterized in that stage (d) is implemented by extraction of acetylene by means of a solvent. 11. Process according to any of the preceding claims, characterized in that the carbon monoxide concentration contained in the first head gas current (31) has a moderating effect on the rate of the reaction catalyzed in the acetylene elimination zone (R1). 12. Gases enriched with hydrogen and/or methane and/or higher hydrocarbons obtained by the process according to any of the preceding claims. 13. Ethylene-enriched product obtained by the process according to any of the preceding claims. 14. Installation for fractionation of a gas resulting from 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-rich current, at least one ethylene-rich and acetylene poor current, and at least one propylene-rich current, characterized in that it contains: a) means for progressively cooling and liquefying said gas from the pyrolysis of hydrocarbons (1) under pressure by passage into a series of increasingly colder heat-exchange zones (2, 6, 9, 20), means to separate from said pyrolysis gas (1) 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, and the means to collect the residual hydrogen-rich gas (27); b) means to evaporate at least in part, by reduction of pressure, the ethylene- and ethane-enriched condensate (23) and the propylene-enriched condensate (15) and means to heat them independently in at least one of said heat-exchange zones (2, 6, 9, 20) by thermal exchange with fluids to be cooled, to provide, respectively, a fraction (25) at least partly evaporated, resulting from the pressure reduction and heating of the ethylene- and ethane-enriched fraction (23), and a fraction (17) at least partly evaporated, resulting from 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 from the pyrolysis of hydrocarbons (1) upon successive passage into said heat-exchange zones (2, 6, 9, 20); c) means to introduce the partially evaporated fractions (17, 25) from stage (b) into a part of a distillation column (C1) called the de-ethanizer, the ethylene- and ethane-enriched partly evaporated condensate (25) being admitted in a point of said part of the distillation column (C1) which is higher than the propylene-rich partly evaporated condensate (17), said part of the distillation column (C1) operating under conditions of temperature and pressure which make it possible to separate, in an upper part, a first ethylene- and ethane-rich head gas current (31) containing, in a smaller proportion, acetylene, hydrogen, and methane, and in a lower part, a propylene-rich first bottom liquid current (18), which is collected; d) means for sending the first ethylene- and ethane-rich head gas current (31) from stage (c) into an acetylene elimination zone (R1) by extraction of the 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) means for cooling and fractionating, in part of a distillation column called the de-methanizer (C2), the largely acetylene-free gas current (36) resulting from stage (d) in a second hydrogen- and/or m