Energy-saving and consumption-reducing butadiene extraction method

Abstract

The invention discloses an energy-saving and consumption-reducing butadiene extraction method which comprises the following steps: a mixed C4 raw material is sequentially subjected to extractive distillation in a first extractive distillation tower and a second extractive distillation tower, and a liquid phase of a tower kettle of the second extractive distillation tower circularly enters the first extractive distillation tower from a side extraction part of the first extractive distillation tower; a tower kettle of the first extractive distillation tower is heated by two reboilers, and a liquid phase extracted from the tower kettle directly enters a desorption tower for desorption without being heated. The first extractive distillation tower adopts two reboilers for heating, so that the extractive distillation temperature in the first extractive distillation tower is increased, and the content of butadiene in the liquid phase discharged material of the tower kettle of the lower tower is reduced; the circulating quantity of butadiene in the tower kettle of the lower tower of the first extractive distillation tower, the desorption tower, the circulating gas cooling tower, the compressor and the tower kettle of the lower tower of the first extractive distillation tower can be obviously reduced, and the energy consumption of the system is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical process, and in particular relates to a butadiene extraction method with energy saving and consumption reduction. Background Art

[0002] Butadiene is an important basic chemical raw material, used to produce styrene-butadiene rubber (SBR), polybutadiene rubber (PBR), styrene thermoplastic elastomer (SBS), acrylonitrile-butadiene-styrene copolymer (ABS), nitrile rubber and styrene-butadiene latex, etc. In addition, it can also be used to produce organic chemical products such as adiponitrile, hexamethylenediamine, nylon 66 and 1,4-butanediol. Butadiene can also be used to produce fine chemical products such as cyclopentane sulfone, n-octanol, hexanediol, cyclooctadiene, 1,5,9-cyclododecatriene, etc.

[0003] There are two main sources of butadiene. One is the butadiene produced as a byproduct of ethylene cracking, which accounts for more than 90% of the butadiene output. The other source is the crude butadiene obtained by oxidative dehydrogenation of refinery C4, UPC mixed C4, MTO C4 or residual C4 after pretreatment. The butadiene content in the C4 components of these two butadiene sources is 10-85wt%. In addition to butadiene, the C4 of these two butadiene sources also contains butene, butane, alkyne and a small amount of C3 and C5. The boiling points of each component are very close, and some components also form azeotropes with butadiene. The relative volatility between key components during ordinary distillation is close to 1. It is difficult to separate polymerization-grade butadiene from it using ordinary distillation methods. Special methods are required for separation. In industry, a method combining an extractive distillation tower and ordinary distillation is commonly used for separation. At present, the commonly used solvents in the extractive distillation process are acetonitrile (ACN), N-methylpyrrolidone (NMP) and dimethylformamide (DMF). Due to the toxicity and environmental issues of DMP, it has rarely been used in new equipment in recent years. Compared with the use of CAN solvent for extraction, the NMP solvent extraction method has the advantages of low energy consumption, low material consumption, low toxicity, less wastewater generation, low investment, and low operating costs.

[0004] Patent CN110198923 discloses a method for separating pure 1,3-butadiene from a crude C4 fraction by extractive distillation using a selective solvent, wherein the crude C4 fraction is introduced into a pre-distillation tower, a first low-boiling fraction containing C3 hydrocarbons is taken out as an overhead stream, a gaseous C4 fraction is taken out as a side stream, and a first high-boiling fraction is taken out as a bottom stream, the gaseous C4 fraction is contacted with a selective solvent in at least one extraction tower to obtain an overhead fraction containing butanes and butenes and a bottom fraction containing 1,3-butadiene and a selective solvent, crude 1,3-butadiene is parsed from the bottom fraction in at least one stripping tower to obtain a stripped selective solvent, the stripped selective solvent is recycled to the extraction tower, and at least a portion of the crude 1,3-butadiene is supplied to a pure distillation tower to separate a second high-boiling fraction. However, the pre-distillation function and structure of this method are relatively complex, the heat carried by the lean solvent is not fully utilized, and the temperature of the solvent entering the extraction tower cannot be flexibly adjusted. There is still room for research in energy saving and consumption reduction as well as stable and long-term operation of the system. Summary of the invention

[0005] The present invention aims to provide a butadiene extraction method which is energy-saving and consumption-reducing, in view of the technical problem of high energy consumption of existing butadiene extraction devices.

[0006] The energy-saving and consumption-reducing butadiene extraction method of the present invention comprises the following steps:

[0007] Step S1, the mixed C4 raw material enters the first extraction distillation tower and is countercurrently contacted with the extraction solvent from the analytical tower, and after extraction distillation, the gas phase including crude butadiene is extracted from the side extraction part of the first extraction distillation tower;

[0008] Step S2, the extracted gas phase enters the kettle of the second extractive distillation tower, and is countercurrently contacted with the extraction solvent from the analytical tower in the second extractive distillation tower. After extractive distillation, the gaseous crude butadiene is extracted from the top of the second extractive distillation tower, and the liquid phase in the kettle of the second extractive distillation tower is circulated into the first extractive distillation tower from the side extraction part of the first extractive distillation tower;

[0009] Step S3, the liquid-phase rich solvent in the kettle of the first extractive distillation tower enters the decomposition tower for decomposition, the gas phase formed after decomposition is extracted from the top of the decomposition tower and circulated into the first extractive distillation tower after cooling in the circulating gas cooling tower, and the lean solvent after decomposition is extracted from the kettle of the decomposition tower as the extraction solvent and enters the first extractive distillation tower and the second extractive distillation tower respectively;

[0010] in,

[0011] In step S3, the bottom of the first extractive distillation tower is heated by two reboilers, namely the first reboiler of the first extractive distillation tower and the second reboiler of the first extractive distillation tower, and the liquid phase extracted from the bottom of the first extractive distillation tower directly enters the decomposition tower for decomposition without being heated.

[0012] Preferably,

[0013] The top temperature of the first extractive distillation tower is in the range of 44-50°C, the bottom temperature of the first extractive distillation tower is in the range of 105°C-135°C, and the feed temperature of the extraction solvent of the first extractive distillation tower is in the range of 35°C to the tray temperature of the solvent feed port;

[0014] The top temperature of the second extractive distillation tower ranges from 40 to 45°C, the bottom temperature of the second extractive distillation tower ranges from 65 to 85°C, and the feed temperature of the extraction solvent to the second extractive distillation tower ranges from 35°C to the plate temperature of the solvent feed port, wherein the feed temperature of the extraction solvent to the second extractive distillation tower is 5 to 15°C lower than the feed temperature of the extraction solvent to the first extractive distillation tower.

[0015] Preferably,

[0016] The mass ratio of the extraction solvent feed to the mixed C4 feed of the first extraction distillation column is 4 to 16;

[0017] The range of the amount of extraction solvent fed into the second extraction distillation tower is as follows: the mass ratio of the extraction solvent feed into the second extraction distillation tower to the bottom feed of the second extraction distillation tower is 2-5.

[0018] Preferably,

[0019] In step S3, the parsed lean solvent is taken out from the bottom of the parsing tower as the extraction solvent and enters the first extractive distillation tower and the second extractive distillation tower respectively, which specifically includes the following sub-steps:

[0020] In step T1, the decomposed lean solvent is extracted from the kettle of the decomposition tower as the extraction solvent, and firstly heat-exchanged with the second reboiler of the first extraction distillation tower, the middle boiler of the first extraction distillation tower, the first reboiler of the deweighting tower and the first reboiler of the feed evaporation tower in sequence through the solvent circulation loop;

[0021] In step T2a, the first part of the solvent after heat exchange in step T1 enters the first downstream circulation branch and enters the first extraction distillation tower as the extraction solvent after temperature adjustment by the first solvent cooler;

[0022] In step T2b, the second part of the solvent after heat exchange in step T1 enters the second downstream circulation branch and enters the second extraction distillation tower as the extraction solvent after temperature adjustment by the second solvent cooler.

[0023] Preferably,

[0024] In step S3, the gas phase formed after the analysis is extracted from the top of the analysis tower and circulated into the first extraction distillation tower after being cooled by the circulating gas cooling tower, which specifically includes the following sub-steps:

[0025] In step E1, the top gas phase after being cooled in the circulating gas cooling tower is extracted from the top of the tower, and after being pressurized by the compressor, enters the lower part of the first extractive distillation tower;

[0026] In step E2, the bottom liquid phase after being cooled by the circulating gas cooling tower is extracted from the bottom of the tower and is divided into a first liquid phase and a second liquid phase. The first liquid phase exchanges heat with the second reboiler of the feed evaporation tower and is cooled, and then flows back to the top of the circulating gas cooling tower to countercurrently contact with the gas phase formed after desorption for heat exchange, and the second liquid phase is pumped into the lower part of the first extractive distillation tower by a pump;

[0027] Preferably, the first liquid phase exchanges heat with the second reboiler of the feed evaporation tower and is cooled by a circulating wash water cooler and then refluxes to the top of the circulating gas cooling tower to countercurrently contact with the gas phase formed after desorption for heat exchange.

[0028] Preferably,

[0029] The energy-saving and consumption-reducing butadiene extraction method further comprises:

[0030] Step S4, the crude butadiene produced from the top of the second extractive distillation tower enters the butadiene light-removing tower to remove light components and the butadiene heavy-removing tower to remove heavy components in sequence, and finally polymerization-grade butadiene is produced from the top of the butadiene heavy-removing tower.

[0031] Preferably,

[0032] The first extractive distillation tower also has an upper tower and a lower tower, and step S1 specifically includes:

[0033] The mixed C4 raw material enters the upper tower and contacts with the extraction solvent from the analytical tower in countercurrent, undergoes extraction and rectification, forms a gas phase which is extracted from the top of the upper tower, and a liquid phase enters the lower tower;

[0034] The extraction and distillation are continued in the lower tower, and the gas phase including crude butadiene is extracted from the side extraction part of the lower tower, and then enters the second extraction and distillation tower through the kettle of the second extraction and distillation tower to continue extraction and distillation; the liquid phase in the kettle of the second extraction and distillation tower is circulated into the lower tower through the side extraction part of the lower tower; the gas phase at the top of the lower tower enters the kettle of the upper tower, and the kettle of the lower tower forms a liquid-phase rich solvent.

[0035] Preferably,

[0036] The energy-saving and consumption-reducing butadiene extraction method further comprises:

[0037] Step S0, the mixed C4 raw material first enters the feed evaporation tower for vaporization to remove heavy components in the raw material, and forms a gas phase mixed C4 raw material at the top of the tower, and then the gas phase mixed C4 raw material enters the upper tower of the first extraction distillation tower.

[0038] Preferably,

[0039] The tower kettle of the feed evaporation tower is heated by the first reboiler of the feed evaporation tower and the second reboiler of the feed evaporation tower respectively;

[0040] The lower tower of the first extractive distillation tower is further heated by the boiler in the first extractive distillation tower;

[0041] The kettle of the analytical tower is heated by a analytical tower reboiler;

[0042] The kettle of the butadiene light-removal tower is heated by a light-removal tower reboiler;

[0043] The kettle of the butadiene deweighting tower is heated by the first reboiler of the deweighting tower and the second reboiler of the deweighting tower.

[0044] Preferably,

[0045] The mixed C4 raw material is selected from one or more of the following raw materials: C4 from ethylene cracking, C4 from oxidative dehydrogenation of butene, C4 from oxidative dehydrogenation of butane, and C4 from direct production of olefins from crude oil; preferably, the content of 1,3-butadiene in the mixed C4 raw material is in the range of 10 to 85 wt%;

[0046] The extraction solvent is selected from acetonitrile (ACN), N-methylpyrrolidone (NMP) and dimethylformamide (DMF), preferably the extraction solvent is selected from N-methylpyrrolidone (NMP).

[0047] Another object of the present invention is to provide an energy-saving and consumption-reducing butadiene extraction device, the energy-saving and consumption-reducing butadiene extraction device comprising:

[0048] A first extractive distillation tower having a feed inlet;

[0049] A second extractive distillation tower, wherein the bottom of the second extractive distillation tower is connected to the side line outlet of the first extractive distillation tower, and the top of the second extractive distillation tower is provided with a crude butadiene outlet;

[0050] A decomposition tower, wherein the bottom of the first extractive distillation tower is connected to the upper part of the decomposition tower, and the top of the decomposition tower is connected to the bottom of the first extractive distillation tower through a circulating gas cooling tower;

[0051] The bottom of the first extractive distillation tower is directly isothermally connected to the upper part of the analytical tower, and the bottom of the first extractive distillation tower comprises a first reboiler of the first extractive distillation tower and a second reboiler of the first extractive distillation tower.

[0052] Preferably,

[0053] The bottom of the analytical tower is connected to the inlet end of the solvent circulation loop, wherein the first outlet end of the solvent circulation loop is connected to the upper part of the first extractive distillation tower after being temperature-adjusted by the first solvent cooler, and the second outlet end of the solvent circulation loop is connected to the upper part of the second extractive distillation tower after being temperature-adjusted by the second solvent cooler.

[0054] Preferably,

[0055] The gas phase at the top of the circulating gas cooling tower is pressurized by a compressor and then connected to the gas phase space of the bottom of the first extractive distillation tower;

[0056] The liquid phase in the first branch of the tower kettle of the circulating gas cooling tower is refluxed to the upper part of the circulating gas cooling tower after heat exchange and cooling in the second reboiler of the feed evaporation tower;

[0057] The second branch of the bottom of the circulating gas cooling tower is connected to the liquid phase space of the bottom of the first extractive distillation tower through a pump.

[0058] Preferably,

[0059] The energy-saving and consumption-reducing butadiene extraction device also includes:

[0060] A butadiene light component removal tower, wherein the crude butadiene extraction port at the top of the second extractive distillation tower is connected to the feed port of the butadiene light component removal tower, and the top of the butadiene light component removal tower has a light component extraction port;

[0061] A butadiene de-heavy tower, wherein the bottom of the butadiene de-heavy tower is connected to the feed port of the butadiene de-heavy tower, the top of the butadiene de-heavy tower is provided with a polymerization-grade butadiene outlet, and the bottom of the butadiene de-heavy tower is provided with a heavy component outlet.

[0062] Preferably,

[0063] The first extractive distillation tower also has:

[0064] An upper tower, wherein the feed inlet is at the bottom of the upper tower;

[0065] The lower tower, the bottom of the upper tower is connected to the top of the lower tower, and the side line extraction port is on the side of the lower tower.

[0066] Preferably,

[0067] The energy-saving and consumption-reducing butadiene extraction device also has:

[0068] A feed evaporation tower, having a feed inlet at the top, the top of the feed evaporation tower being connected to a feed inlet at the gas phase space at the bottom of the upper tower of the first extractive distillation tower;

[0069] Preferably, the tower bottom of the feed evaporation tower comprises a first reboiler of the feed evaporation tower and a second reboiler of the feed evaporation tower.

[0070] Preferably,

[0071] The lower tower of the first extractive distillation tower comprises a first extractive distillation tower middle boiler, a first extractive distillation tower first reboiler and a first extractive distillation tower second reboiler;

[0072] The first outlet end of the solvent circulation loop has a first downstream circulation branch, and the second outlet end of the solvent circulation loop has a second downstream circulation branch, the first downstream circulation branch is connected to the upper part of the upper tower of the first extractive distillation tower, and the second downstream circulation branch is connected to the upper part of the second extractive distillation tower;

[0073] The solvent circulation loop is sequentially connected to the second reboiler of the first extraction distillation tower, the middle boiler of the first extraction distillation tower, the first reboiler of the weight removal tower, and the first reboiler of the feed evaporation tower for heat exchange;

[0074] The first downstream circulation branch is connected to the upper part of the upper tower of the first extractive distillation tower after being connected by temperature adjustment and heat exchange of the first solvent cooler;

[0075] The second downstream circulation branch is connected to the upper part of the second extraction distillation tower after being connected through the temperature adjustment and heat exchange of the second solvent cooler.

[0076] Preferably,

[0077] The liquid phase in the first branch of the tower kettle of the circulating gas cooling tower is heat exchanged in the second reboiler of the feed evaporation tower, cooled in the circulating wash water cooler, and then refluxed to the upper part of the circulating gas cooling tower.

[0078] Preferably,

[0079] The butadiene light-removal tower kettle has a light-removal tower reboiler;

[0080] The butadiene deweighting tower kettle comprises a first deweighting tower reboiler and a second deweighting tower reboiler;

[0081] The tower kettle of the analytical tower has an analytical tower reboiler.

[0082] The positive and progressive effects of the present invention are:

[0083] 1) The energy-saving and consumption-reducing butadiene extraction method of the present invention increases the temperature of the extractive distillation in the first extractive distillation tower by heating the tower kettle of the lower tower of the first extractive distillation tower with two reboilers, namely, the first reboiler of the first extractive distillation tower and the second reboiler of the first extractive distillation tower, thereby reducing the content of butadiene in the liquid phase discharge of the lower tower kettle, and further significantly reducing the circulation amount of butadiene between the tower kettle of the lower tower of the first extractive distillation tower, the analytical tower, the circulating gas cooling tower, the compressor, and then to the lower tower kettle of the first extractive distillation tower, thereby increasing the extraction rate of butadiene. At the same time, the diameters of the analytical tower and the circulating gas cooling tower are also reduced, and the energy consumption of the system is reduced.

[0084] 2) The present invention also provides a first solvent cooler and a second solvent cooler in front of the solvent inlet of the first extractive distillation tower and the solvent inlet of the second extractive distillation tower respectively, so as to specifically adjust the respective temperatures and dosage ratios of the extractive solvents entering the first extractive distillation tower and the second extractive distillation tower, so as to improve the quality of butadiene extracted and distilled at a higher temperature;

[0085] 3) The lean solvent in the bottom of the analytical tower of the present invention is further heat exchanged in the boiler in the first extractive distillation tower. Compared with the heat exchange process of the bottom reboiler, the heat exchange temperature difference is large, the waste heat is more fully utilized, and the steam consumption is greatly reduced;

[0086] 4) The energy-saving and consumption-reducing butadiene extraction method and device of the present invention can be applied to ethylene cracking C4, butylene (butane) oxidative dehydrogenation C4, crude oil direct olefin C4, etc. or a mixture of these C4s, and has a wide range of applicability;

[0087] 5) The present invention introduces the second reboiler of the first extractive distillation tower and the second reboiler of the butadiene de-weighting tower, which are heated by steam and condensate respectively, to solve the problem that the feed evaporation tower and the lower tower of the first extractive distillation tower have excessive heat consumption due to low butadiene content in the feed, and the lean solvent after analysis in the kettle of the analysis tower is insufficient to provide heat for the feed evaporation tower, the lower tower of the first extractive distillation tower and the butadiene de-weighting tower, thereby improving the applicability and stability of the butadiene extraction device. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a structural schematic diagram of the energy-saving and consumption-reducing butadiene extraction device of the present invention;

[0089] Figure 2 Schematic diagram of the structure of a butadiene extraction unit for comparison. DETAILED DESCRIPTION

[0090] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0091] like Figure 1 The figure shows a schematic structural diagram of the energy-saving and consumption-reducing butadiene extraction device of the present invention, which specifically includes a feed evaporation tower T1, a first extractive distillation tower, a second extractive distillation tower T4, a decomposition tower T5, a circulating gas cooling tower T6, a butadiene weight removal tower T7, a butadiene light removal tower T8, a compressor K1, a first reboiler E1 of the feed evaporation tower, a second reboiler E2 of the feed evaporation tower, a first solvent cooler E3, a second solvent cooler E4, a middle reboiler E6 of the first extractive distillation tower, a first reboiler E7 of the first extractive distillation tower, a second reboiler E5 of the first extractive distillation tower, a circulating wash water cooler E8, a decomposition tower reboiler E9, a first reboiler E10 of the weight removal tower, a second reboiler E11 of the weight removal tower and a reboiler E13 of the light removal tower, wherein the first extractive distillation tower also includes an upper tower T2 and a lower tower T3.

[0092] Continue as Figure 1 As shown, the upper part of the feed evaporation tower T1 has a feed inlet, and the top of the tower is connected to the feed inlet at the gas phase space at the bottom of the upper tower T2 of the first extractive distillation tower. The tower kettle of the feed evaporation tower T1 is provided with a first reboiler E1 of the feed evaporation tower and a second reboiler E2 of the feed evaporation tower, which are used to heat the C4 raw material in the feed evaporation tower T1 to remove part of the heavy components. The tower kettle of the upper tower T2 is connected to the top of the lower tower T3, and the side of the lower tower T3 is provided with a side line extraction port, which is also the side extraction part, and is located at a higher butadiene concentration and is connected to the tower kettle of the second extractive distillation tower T4. The top of the second extractive distillation tower T4 is provided with a crude butadiene extraction port, and the second extractive distillation tower T4 is connected to the feed inlet at the top of the butadiene light removal tower T8 through the crude butadiene extraction port. The top of the butadiene light-removal tower T8 is provided with a light component extraction outlet, and the bottom of the tower is provided with a light-removal tower reboiler E13 for heat supply, which is heated by steam condensate. Meanwhile, the bottom of the butadiene light-removal tower T8 is also connected to the upper part of the butadiene heavy-removal tower T7. The top of the butadiene heavy-removal tower T7 has a polymerization-grade butadiene extraction outlet, and the bottom of the tower has a heavy component extraction outlet. The bottom of the tower is also provided with a first reboiler E10 for the heavy-removal tower and a second reboiler E11 for the heavy-removal tower, wherein the second reboiler E11 for the heavy-removal tower is heated by condensate steam. Figure 1As shown, the lower tower T3 is also provided with a first extractive distillation tower middle boiler E6, a first extractive distillation tower first reboiler E7 and a first extractive distillation tower second reboiler E5, wherein the first extractive distillation tower first reboiler E7 and the first extractive distillation tower second reboiler E5, a total of two reboilers, are arranged in the tower kettle of the lower tower T3 to supply heat to the lower tower T3, and the first extractive distillation tower first reboiler E7 is heated by steam. The tower kettle of the lower tower T3 can be directly isothermally connected to the upper part of the analytical tower T5, that is, the kettle liquid of the tower kettle of the lower tower T3 is directly entered into the analytical tower T5 without being heated after being extracted.

[0093] The top of the analytical tower T5 is connected to the bottom of the lower tower T3 through the circulating gas cooling tower T6. Figure 1 As shown, the top of the analytical tower T5 is first connected to the lower part of the circulating gas cooling tower T6, and then the top of the circulating gas cooling tower T6 is connected to the gas phase space of the tower kettle of the lower tower T3 through the compressor K1. The tower kettle of the circulating gas cooling tower T6 is provided with a first tower kettle branch and a second tower kettle branch. The first tower kettle branch is connected to the upper part of the circulating gas cooling tower T6 after heat exchange with the second reboiler E2 of the feed evaporation tower and the circulating wash water cooler E8 in turn, and the second tower kettle branch is directly connected to the liquid phase space of the tower kettle of the lower tower T3 through a pump. As shown in the figure, a solvent circulation loop is provided at the tower kettle of the analytical tower T5, and the tower kettle of the analytical tower T5 is connected to the inlet end of the solvent circulation loop, and the outlet end of the solvent circulation loop is divided into a first outlet end and a second outlet end, wherein the first outlet end is provided with a first downstream circulation branch, and the second outlet end is provided with a second downstream circulation branch. The first downstream circulation branch is connected to the upper part of the upper tower T2 of the first extractive distillation tower after temperature adjustment and heat exchange by the first solvent cooler E3, and the second downstream circulation branch is connected to the upper part of the second extractive distillation tower T4 after temperature adjustment and heat exchange by the second solvent cooler E4. That is, the tower kettle of the analytical tower T5 is connected to the upper tower T2 of the first extractive distillation tower through the solvent circulation loop and the first outlet end of the solvent circulation loop and the first downstream circulation branch in sequence, and the tower kettle of the analytical tower T5 is also connected to the upper tower T4 of the second extractive distillation tower through the solvent circulation loop and the second outlet end of the solvent circulation loop and the second downstream circulation branch. In addition, the above-mentioned solvent circulation loop is connected to the second reboiler E5 of the first extractive distillation tower, the middle boiler E6 of the first extractive distillation tower, the first reboiler E10 of the deweighting tower, and the first reboiler E1 of the feed evaporation tower in sequence, so that the lean solvent extracted from the analytical tower T5 can be heat-exchanged with the above-mentioned reboilers in sequence, further improving the utilization rate of thermal energy. Of course, the bottom of the analysis tower T5 is also provided with an analysis tower reboiler E9 for analysis heating, and a side line discharge port and a solvent aqueous solution feed port are also provided on the side of the analysis tower T5.

[0094] The energy-saving and consumption-reducing butadiene extraction method of the present invention adopts the energy-saving and consumption-reducing butadiene extraction device mentioned above, and the specific steps are as follows:

[0095] Step S0, the mixed C4 raw material first enters the feed evaporation tower T1 from the feed inlet of the feed evaporation tower T1 to be vaporized to remove some heavy components in the raw material, and forms a gas phase mixed C4 raw material at the top of the tower, and then the gas phase mixed C4 raw material enters the upper tower T2 of the first extractive distillation tower, and the tower bottom of the feed evaporation tower T1 is heated by the first reboiler E1 of the feed evaporation tower and the second reboiler E2 of the feed evaporation tower. The mixed C4 raw material is selected from one or more of the following raw materials: ethylene cracking C4, butene oxidative dehydrogenation C4, butane oxidative dehydrogenation C4 and crude oil direct olefin C4, and the content of 1,3-butadiene in the mixed C4 raw material ranges from 10 to 85wt%.

[0096] Step S1, the gas phase mixed C4 raw material enters the upper tower T2 of the first extractive distillation tower and contacts with the extraction solvent from the analytical tower T5 in countercurrent. The extraction solvent is selected from acetonitrile, N-methylpyrrolidone and dimethylformamide, and preferably the extraction solvent is selected from N-methylpyrrolidone (NMP). After extraction and distillation by the upper tower T2, the gas phase containing propylene, butane and butene is extracted from the top of the upper tower T2, and the liquid phase containing butadiene, vinyl acetylene, butyne, propyne, C5 and a small amount of 2-butene and NMP solvent enters the lower tower T3 from the bottom of the tower, and the extraction and distillation is continued in the lower tower T3, and the gas phase containing crude butadiene is extracted from the side extraction part of the lower tower T3.

[0097] In step S2, the gas phase including crude butadiene produced enters the kettle of the second extractive distillation tower T4, and is countercurrently contacted with the extraction solvent such as NMP from the analytical tower T5 in the second extractive distillation tower T4. After extraction and distillation in the second extractive distillation tower T4, the gaseous crude butadiene is produced from the top of the second extractive distillation tower T4, and the liquid phase including vinyl acetylene, butyne and butadiene is circulated from the kettle of the second extractive distillation tower T4 through the side extraction part of the lower tower T3 into the lower tower T3 along with the solvent.

[0098] Step S3, after extractive distillation in the lower tower T3, the formed gas phase enters the tower kettle of the upper tower T2 from the top of the lower tower T3, and the formed liquid phase rich solvent accumulates in the tower kettle of the lower tower T3. The lower tower T3 is heated by the first extractive distillation tower middle boiler E6, the first extractive distillation tower first reboiler E7 and the first extractive distillation tower second reboiler E5. The tower kettle of the lower tower T3 is heated by two reboilers, namely, the first reboiler E7 of the first extractive distillation tower and the second reboiler E5 of the first extractive distillation tower. Compared with the existing butadiene extraction device, the extractive distillation temperature of the lower tower T3 of the first extractive distillation tower is increased, the content of butadiene in the liquid phase discharge of the tower kettle is reduced, and the liquid phase rich solvent extracted from the tower kettle does not need to be heated again and directly enters the analytical tower T5 for analytical analysis. Thereby, the circulation amount of butadiene between the tower kettle of the lower tower T3 of the first extractive distillation tower, the analytical tower T5, the circulating gas cooling tower T6, the compressor K1, and then to the tower kettle of the lower tower T3 of the first extractive distillation tower can be significantly reduced, thereby improving the extraction rate of butadiene. In addition, the diameters of the analytical tower T5 and the circulating gas cooling tower T6 are also reduced, and the energy consumption of system extraction is reduced. Specifically, the tower kettle of the analytical tower T5 is heated by the analytical tower reboiler E9, and the gas phase containing butadiene formed after the analytical tower T5 is analyzed is also extracted from the top of the analytical tower T5 and enters the circulating gas cooling tower T6 for cooling. The gas phase cooled by the circulating gas cooling tower T6 is extracted from the top of the tower and enters the lower part of the lower tower T3 after being pressurized by the compressor K1. The cooled liquid phase is extracted from the bottom of the circulating gas cooling tower T6 and is divided into the first liquid phase and the second liquid phase. The first liquid phase exchanges heat with the second reboiler E2 of the feed evaporation tower and is cooled by the circulating wash water cooler E8 and then flows back to the top of the circulating gas cooling tower T6 to countercurrently contact with the gas phase formed after the analysis to exchange heat, making full use of the heat energy. The second liquid phase is pumped into the lower tower T3 by a pump. In addition, in the analysis tower T5, part of the gas phase containing vinyl acetylene is extracted from the side line discharge port on the side of the tower. At the same time, in order to maintain the balance of the solvent in the tower, the solvent-containing aqueous solution is supplemented from the solvent aqueous solution feeding port on the side of the tower. Furthermore, the lean solvent forming the liquid phase after the analysis is extracted from the bottom of the analysis tower T5, and after the solvent circulation loop is connected with the second reboiler E5 of the first extraction distillation tower, the middle boiler E6 of the first extraction distillation tower, the first reboiler E10 of the deweighting tower, and the first reboiler E1 of the feed evaporation tower for heat exchange, it is divided into the first part of the solvent and the second part of the solvent, wherein the first part of the solvent enters the first downstream circulation branch and enters the first extraction distillation tower upper tower T2 as the extraction solvent after temperature adjustment by the first solvent cooler E3. At this time, the top temperature range of the first extraction distillation tower upper tower T2 is 44-50°C, the bottom discharge temperature range of the first extraction distillation tower lower tower T3 is 105°C-135°C, the extraction solvent feed temperature range of the upper tower T2 is 35°C-solvent feed port plate temperature, and the mass ratio of the extraction solvent feed of the first extraction distillation tower upper tower T2 to the mixed carbon four feed is 4-16.The second part of the solvent enters the second downstream circulation branch and enters the second extractive distillation tower T4 as the extractive solvent after being temperature-adjusted by the second solvent cooler E4. At this time, the top temperature of the second extractive distillation tower T4 is in the range of 40-45°C, the bottom temperature is in the range of 65-85°C, and the extractive solvent feed temperature of the second extractive distillation tower T4 is in the range of 35°C to the plate temperature of the solvent feed port. The mass ratio of the extractive solvent feed to the second extractive distillation tower to the bottom feed of the second extractive distillation tower is 2-5.

[0099] Since the lower tower T3 is heated by two reboilers and one intermediate boiler, the temperature in the entire first extractive distillation tower is increased. The two independent first solvent coolers E3 and second solvent coolers E4 are used to specifically adjust the optimal feed temperature and mass ratio of the extractive solvents entering the first and second extractive distillations, respectively. Compared with using one solvent cooler, the consumption of circulating water and heating steam can be further reduced.

[0100] Step S4, the crude butadiene extracted from the top of the second extractive distillation tower T4 enters the butadiene light-removing tower T8 and the butadiene heavy-removing tower T7 in sequence. Among them, the tower kettle of the butadiene light-removing tower T8 is heated by the light-removing tower reboiler E13, and light components such as propyne and water are removed in the butadiene light-removing tower T8. The tower kettle of the butadiene heavy-removing tower T7 is heated by the first reboiler E10 of the heavy-removing tower and the second reboiler E11 of the heavy-removing tower, and heavy components such as cis-2-butene carried over are removed in the butadiene heavy-removing tower T7, and finally polymerization-grade butadiene is extracted from the top of the butadiene heavy-removing tower T7.

[0101] Example 1

[0102] according to Figure 1As shown, 40.6 t / h of mixed C4 raw material 1 with a butadiene content of 54.7 wt% enters the top of the feed evaporation tower T1. After some heavy components are removed from the feed evaporation tower T1, the top gasification discharge enters the bottom of the upper tower T2 of the first extractive distillation tower, and is countercurrently contacted with 444 t / h, 53°C extraction solvent (N-methylpyrrolidone content of 91.7 wt%) feed 21 entering the upper tower T2 of the first extractive distillation tower in the tower for extractive distillation. The top temperature of the upper tower T2 is 45°C, and butane and butene 5 are distilled from the top of the upper tower T2 of the first extractive distillation tower. 49.6 t / h of gaseous material 6 is taken out from the side line of the lower tower T3 of the first extractive distillation tower and enters the bottom of the second extractive distillation tower T4, and is countercurrently contacted with the 99.7 t / h, 38°C extraction solvent feed 22 entering the second extractive distillation tower T4. The top temperature of the second extractive distillation tower T4 is 43°C, and the bottom temperature is 76°C. Crude butadiene 8 is obtained at the top of the tower, and the bottom forms a mixed stream 7 and returns to the lower tower T3 of the first extractive distillation tower. A liquid stream is drawn out from the middle of the lower tower T3 of the first extractive distillation tower, and is returned to the tower after heat exchange with the lean solvent stream 17. The second reboiler E5 of the first extractive distillation tower T3 of the first extractive distillation tower provides heat through the lean solvent 16 of the kettle of the analytical tower T5, and the second reboiler E7 of the first extractive distillation tower T3 of the first extractive distillation tower provides heat through steam. The bottom pressure of the first extractive distillation tower T3 of the first extractive distillation tower is 0.41MPag, the temperature is 120℃, the flow rate of the kettle liquid 9 of the first extractive distillation tower T3 of the first extractive distillation tower is 522t / h, and then enters the top of the analytical tower T5 after decompression. The pressure of the analytical tower T5 is 0.075MPag, and the temperature of the vapor phase discharge 10 at the top of the tower is 104℃, which enters the bottom of the circulating cooling tower T6, contacts with the circulating coolant in countercurrent and cools to 43℃, and then is sent to the compressor K1 to increase the pressure to 0.45MPag, and the pressurized circulating crude butadiene 12 enters the kettle of the lower tower T3. The side line of the analytical tower T5 extracts the logistics 23 of vinyl acetylene and other materials and enters the subsequent water washing system, and the solvent-containing aqueous solution 24 after water washing returns to the analytical tower T5. The reboiler E9 at the bottom of the analysis tower T5 uses steam to provide heat. The temperature of the lean solvent 16 after analysis in the bottom of the analysis tower T5 is 150°C. The heat is recovered in sequence through the second reboiler E5 of the first extraction distillation tower, the middle boiler E6 of the first extraction distillation tower, the first reboiler E10 of the butadiene deweighting tower and the first reboiler E1 of the feed evaporation tower. The circulating water is further cooled to 53°C and 38°C respectively through the first solvent cooler E3 and the second solvent cooler E4, and then returned to the upper tower T2 of the first extraction distillation tower and the second extraction distillation tower T4 for recycling.

[0103] Example 2

[0104] according to Figure 1As shown, 49.9 t / h of mixed C4 raw material 1 with a butadiene content of 28.1 wt% enters the top of the feed evaporation tower T1. After some heavy components are removed from the feed evaporation tower T1, the top gasification discharge enters the bottom of the upper tower T2 of the first extractive distillation tower, and is countercurrently contacted with 296 t / h, 53°C extraction solvent (N-methylpyrrolidone content of 91.7 wt%) feed 21 entering the upper tower T2 of the first extractive distillation tower in the tower for extractive distillation. The top temperature of the upper tower T2 is 45°C, and butane and butene 5 are distilled from the top of the upper tower T2 of the first extractive distillation tower. 32.7 t / h of gaseous material 6 is taken out from the side line of the lower tower T3 of the first extractive distillation tower and enters the bottom of the second extractive distillation tower T4, and is countercurrently contacted with the 66.1 t / h, 38°C extraction solvent feed 22 entering the second extractive distillation tower T4. The top temperature of the second extractive distillation tower T4 is 43°C, and the bottom temperature is 76°C. Crude butadiene 8 is obtained at the top of the tower, and the bottom forms a mixed stream 7 and returns to the lower tower T3 of the first extractive distillation tower. A liquid stream is drawn out from the middle of the lower tower T3 of the first extractive distillation tower, and is returned to the tower after heat exchange with the lean solvent stream 17. The second reboiler E5 of the first extractive distillation tower T3 of the first extractive distillation tower provides heat through the lean solvent 16 of the bottom of the analytical tower T5, and the first reboiler E7 of the first extractive distillation tower T3 of the first extractive distillation tower provides heat through steam. The bottom pressure of the first extractive distillation tower T3 of the first extractive distillation tower is 0.41MPag, the temperature is 120℃, the flow rate of the bottom liquid 9 of the first extractive distillation tower T3 of the first extractive distillation tower is 397t / h, and then enters the top of the analytical tower T5 after decompression. The pressure of the analytical tower T5 is 0.075MPag, and the temperature of the vapor phase discharge 10 at the top of the tower is 104℃, and enters the bottom of the circulating cooling tower T6, and is contacted with the circulating coolant in countercurrent and cooled to 43℃, and then sent to the compressor K1 to increase the pressure to 0.45MPag, and the pressurized circulating crude butadiene 12 enters the bottom of the lower tower T3. The side line of the analytical tower T5 produces vinyl acetylene and other logistics 23 and enters the subsequent water washing system, and the solvent-containing aqueous solution 24 after water washing returns to the analytical tower T5. The decomposition tower reboiler E9 at the bottom of the decomposition tower T5 uses steam to provide heat, and the temperature of the lean solvent 16 after decomposition in the decomposition tower kettle is 150°C. The heat is recovered in sequence through the second reboiler E5 of the first extractive distillation tower, the middle boiler E6 of the first extractive distillation tower, the first reboiler E10 of the butadiene deweighting tower and the first reboiler E1 of the feed evaporation tower. The circulating water is further cooled to 53°C and 38°C respectively through the first solvent cooler E3 and the second solvent cooler E4, and then returned to the upper tower T2 of the first extractive distillation tower and the second extractive distillation tower T4 for recycling.

[0105] Comparative Example 1

[0106] The process corresponding to this comparative example 1 is as follows Figure 2As shown, 40.6t / h of mixed C4 raw material 1 with a butadiene content of 54.7wt% enters the feed evaporation tower T1. The difference from Example 1 is that the extraction solvent is only heat-exchanged to 38°C by a common solvent cooler E14, and then enters the first extraction distillation tower T2 in an amount of 487t / h, and enters the second extraction distillation tower T4 in an amount of 99.7t / h. The top temperature of the first extraction distillation tower T2 is 43°C, and the top temperature of the second extraction distillation tower T4 is 45°C, and the bottom temperature is 76°C. The lower tower T3 of the first extractive distillation tower has only one lower tower kettle liquid heater E5A to provide heat except for the intermediate boiler E6. The tower bottom pressure is 0.41 MPag and the temperature is 103°C. 49.6 t / h of gaseous material 6 is produced from the side line of the lower tower T3 of the first extractive distillation tower and enters the bottom of the second extractive distillation tower T4, and is countercurrently contacted with 99.7 t / h of extraction solvent feed 22 entering the second extractive distillation tower T4 in the tower. The kettle liquid 9 of the lower tower T3 of the first extractive distillation tower is pressurized and enters the feed heater E12 of the analytical tower to be preheated to 120°C, and then decompressed and enters the top of the analytical tower T5. The temperature of the lean solvent 16 after analysis in the analysis tower bottom is 150°C. As in Example 1, heat is recovered in sequence through the lower bottom liquid heater E5A of the first extraction distillation tower, the butadiene deweighting tower reboiler E10 and the first reboiler E1 of the feed evaporation tower, but the difference is that the circulating water is finally used to further cool to 38°C through a common solvent cooler E14 and return to the two extraction systems for recycling.

[0107] Comparative Example 2

[0108] The process corresponding to this comparative example 2 is as follows Figure 2As shown, 49.9t / h of mixed C4 raw material 1 with a butadiene content of 28.1wt% enters the feed evaporation tower T1. The difference from Example 2 is that the extraction solvent is only heat-exchanged to 38°C by a common solvent cooler E14, and then enters the first extraction distillation tower T2 in an amount of 324t / h, and enters the second extraction distillation tower T4 in an amount of 66.1t / h. The top temperature of the first extraction distillation tower T2 is 43°C, and the top temperature of the second extraction distillation tower T4 is 45°C, and the bottom temperature is 76°C. The lower tower T3 of the first extractive distillation tower has only one lower tower kettle liquid heater E5A to provide heat except for the intermediate boiler E6. The tower bottom pressure is 0.41MPag and the temperature is 103°C. 32.7t / h of gaseous material 6 is produced from the side line of the lower tower T3 of the first extractive distillation tower and enters the bottom of the second extractive distillation tower T4, and is countercurrently contacted with 66.1t / h of extraction solvent feed 22 entering the second extractive distillation tower T4 in the tower. The kettle liquid 9 of the lower tower T3 of the first extractive distillation tower is pressurized and enters the feed heater E12 of the analysis tower to be preheated to 120°C, and then decompressed and enters the top of the analysis tower T5. The temperature of the lean solvent 16 after analysis in the analysis tower bottom is 150°C. As in Example 1, heat is recovered in sequence through the lower bottom liquid heater E5A of the first extraction distillation tower, the butadiene deweighting tower reboiler E10 and the first reboiler E1 of the feed evaporation tower, but the difference is that the circulating water is finally used to further cool to 38°C through a common solvent cooler E14 and return to the extraction system for recycling.

[0109] Table 1 Energy consumption data of Example 1 of the present invention and Comparative Example 1

[0110]

[0111]

[0112] Comparative Example 1

[0113]

[0114] As shown in Table 1, the energy consumption of the mixed C4 raw material with a butadiene content of 54.7wt% in Example 1 is 181.23kg standard oil / t butadiene, and the energy consumption of the mixed C4 raw material with a butadiene content of 54.7wt% in Comparative Example 1 is 195.86kg standard oil / t butadiene, and the energy consumption per ton of butadiene product is reduced by 14.63kg standard oil. The consumption of steam, electric energy and circulating water has decreased to varying degrees.

[0115] Table 2 Energy consumption data of Example 2 of the present invention and Comparative Example 2

[0116]

[0117]

[0118] As shown in Table 2, the energy consumption of the mixed C4 raw material with a butadiene content of 28.1wt% in Example 2 is 261.63kg standard oil / t butadiene, and the energy consumption of the mixed C4 raw material with a butadiene content of 28.1wt% in Comparative Example 2 is 275.89kg standard oil / t butadiene, and the energy consumption per ton of butadiene product is reduced by 14.26kg standard oil. The consumption of steam, electric energy and circulating water has decreased to varying degrees.

[0119] Table 3 Comparison of the composition of No. 5 and No. 8 logistics in Example 1 of the present invention and Comparative Example 1

[0120]

[0121] As can be seen from Table 3, the content of 1,3-butadiene in the residual carbon four extracted from the top of the first extractive distillation tower in Example 1 of the present invention and Comparative Example 1 is 0.0000wt%, without obvious change; the content of 1,3-butadiene in the crude butadiene stream from the top of the second extractive distillation tower in Example 1 of the present invention and Comparative Example 1 is 98.8683wt% and 98.8702wt%, respectively, and the product quality has no significant change.

[0122] Table 4 Comparison of the composition of No. 5 and No. 8 logistics in Example 2 of the present invention and Comparative Example 2

[0123]

[0124] As can be seen from Table 4, the content of 1,3-butadiene in the residual carbon four extracted from the top of the first extractive distillation tower in Example 2 of the present invention and Comparative Example 2 is 0.0000wt%, without obvious change; the content of 1,3-butadiene in the crude butadiene stream from the top of the second extractive distillation tower in Example 1 of the present invention and Comparative Example 1 is 98.8523wt% and 98.8546wt%, respectively, and the product quality has no significant change.

[0125] Table 5 Effect of different process flows on equipment size and butadiene loss

[0126]

[0127] As can be seen from Table 5, compared with Comparative Example 1, Example 1 reduces the butadiene loss by 51 kg / h, and the equipment size is also reduced to a certain extent; compared with Comparative Example 2, Example 2 reduces the butadiene loss by 37 kg / h, and the equipment size is also reduced to a certain extent.

[0128] The present invention uses two reboilers and one intermediate boiler in the lower tower of the first extractive distillation tower, and sets the optimal temperature and solvent ratio for the solvent to enter the first extractive distillation tower and the second extractive distillation tower, so that the consumption of steam, electric energy and circulating water can be reduced, and the circulation amount of butadiene-rich materials in the lower tower kettle of the first extractive distillation tower, the analytical tower, the circulating gas cooling tower, the compressor and the lower tower kettle of the first extractive distillation tower can be significantly reduced in sequence, and the energy consumption of the device and the size of the main equipment can be further reduced, thereby improving the device efficiency and the butadiene extraction rate.

[0129] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, some details in the embodiments should not be construed as limiting the present invention, and the present invention shall be protected by the scope defined by the attached claims.

Claims

1. A method for extracting butadiene with energy saving and consumption reduction, the method comprising: Step S1, the mixed C4 raw material enters the first extraction distillation tower and is countercurrently contacted with the extraction solvent from the analytical tower, and after extraction distillation, the gas phase including crude butadiene is extracted from the side extraction part of the first extraction distillation tower; Step S2, the extracted gas phase enters the kettle of the second extractive distillation tower, and is countercurrently contacted with the extraction solvent from the analytical tower in the second extractive distillation tower. After extractive distillation, the gaseous crude butadiene is extracted from the top of the second extractive distillation tower, and the liquid phase in the kettle of the second extractive distillation tower is circulated into the first extractive distillation tower from the side extraction part of the first extractive distillation tower; Step S3, the liquid-phase rich solvent in the kettle of the first extractive distillation tower enters the decomposition tower for decomposition, the gas phase formed after decomposition is extracted from the top of the decomposition tower and circulated into the first extractive distillation tower after cooling in the circulating gas cooling tower, and the lean solvent after decomposition is extracted from the kettle of the decomposition tower as the extraction solvent and enters the first extractive distillation tower and the second extractive distillation tower respectively; Features In step S3, the bottom of the first extractive distillation tower is heated by two reboilers, namely the first reboiler of the first extractive distillation tower and the second reboiler of the first extractive distillation tower, and the liquid phase extracted from the bottom of the first extractive distillation tower directly enters the decomposition tower for decomposition without being heated.

2. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that The top temperature of the first extractive distillation tower is in the range of 44-50°C, the bottom temperature of the first extractive distillation tower is in the range of 105°C-135°C, and the feed temperature of the extraction solvent of the first extractive distillation tower is in the range of 35°C to the tray temperature of the solvent feed port; The top temperature of the second extractive distillation tower ranges from 40 to 45°C, the bottom temperature of the second extractive distillation tower ranges from 65 to 85°C, and the feed temperature of the extraction solvent to the second extractive distillation tower ranges from 35°C to the plate temperature of the solvent feed port, wherein the feed temperature of the extraction solvent to the second extractive distillation tower is 5 to 15°C lower than the feed temperature of the extraction solvent to the first extractive distillation tower.

3. The energy-saving and consumption-reducing butadiene extraction method according to claim 2, characterized in that: The mass ratio of the extraction solvent feed to the mixed C4 feed of the first extraction distillation column is 4 to 16; The mass ratio of the extraction solvent feed to the second extraction distillation tower to the bottom feed of the second extraction distillation tower is 2-5.

4. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that In step S3, the parsed lean solvent is taken out from the bottom of the parsing tower as the extraction solvent and enters the first extractive distillation tower and the second extractive distillation tower respectively, which specifically includes the following sub-steps: In step T1, the decomposed lean solvent is extracted from the kettle of the decomposition tower as the extraction solvent, and firstly heat-exchanged with the second reboiler of the first extraction distillation tower, the middle boiler of the first extraction distillation tower, the first reboiler of the deweighting tower and the first reboiler of the feed evaporation tower in sequence through the solvent circulation loop; In step T2a, the first part of the solvent after heat exchange in step T1 enters the first downstream circulation branch and enters the first extraction distillation tower as the extraction solvent after temperature adjustment by the first solvent cooler; In step T2b, the second part of the solvent after heat exchange in step T1 enters the second downstream circulation branch and enters the second extraction distillation tower as the extraction solvent after temperature adjustment by the second solvent cooler.

5. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that In step S3, the gas phase formed after the analysis is extracted from the top of the analysis tower and circulated into the first extraction distillation tower after being cooled by the circulating gas cooling tower, which specifically includes the following sub-steps: In step E1, the top gas phase after being cooled in the circulating gas cooling tower is extracted from the top of the tower, and after being pressurized by the compressor, enters the lower part of the first extractive distillation tower; In step E2, the bottom liquid phase after being cooled by the circulating gas cooling tower is extracted from the bottom of the tower and is divided into a first liquid phase and a second liquid phase. The first liquid phase exchanges heat with the second reboiler of the feed evaporation tower and is cooled, and then flows back to the top of the circulating gas cooling tower to countercurrently contact with the gas phase formed after desorption for heat exchange, and the second liquid phase is pumped into the lower part of the first extractive distillation tower by a pump; Preferably, the first liquid phase exchanges heat with the second reboiler of the feed evaporation tower and is cooled by a circulating wash water cooler and then refluxes to the top of the circulating gas cooling tower to countercurrently contact with the gas phase formed after desorption for heat exchange.

6. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that The energy-saving and consumption-reducing butadiene extraction method further comprises: Step S4, the crude butadiene produced from the top of the second extractive distillation tower enters the butadiene light-removing tower to remove light components and the butadiene heavy-removing tower to remove heavy components in sequence, and finally polymerization-grade butadiene is produced from the top of the butadiene heavy-removing tower.

7. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that The first extractive distillation tower also has an upper tower and a lower tower, and step S1 specifically includes: The mixed C4 raw material enters the upper tower and contacts with the extraction solvent from the analytical tower in countercurrent, undergoes extraction and rectification, forms a gas phase which is extracted from the top of the upper tower, and a liquid phase enters the lower tower; The extraction and distillation are continued in the lower tower, and the gas phase including crude butadiene is extracted from the side extraction part of the lower tower, and then enters the second extraction and distillation tower through the kettle of the second extraction and distillation tower to continue extraction and distillation; the liquid phase in the kettle of the second extraction and distillation tower is circulated into the lower tower through the side extraction part of the lower tower; the gas phase at the top of the lower tower enters the kettle of the upper tower, and the kettle of the lower tower forms a liquid-phase rich solvent.

8. The energy-saving and consumption-reducing butadiene extraction method according to claim 6, characterized in that The energy-saving and consumption-reducing butadiene extraction method further comprises: Step S0, the mixed C4 raw material first enters the feed evaporation tower for vaporization to remove heavy components in the raw material, and forms a gas phase mixed C4 raw material at the top of the tower, and then the gas phase mixed C4 raw material enters the upper tower of the first extraction distillation tower.

9. The energy-saving and consumption-reducing butadiene extraction method according to claim 8, characterized in that The tower kettle of the feed evaporation tower is heated by the first reboiler of the feed evaporation tower and the second reboiler of the feed evaporation tower respectively; The lower tower of the first extractive distillation tower is further heated by the boiler in the first extractive distillation tower; The kettle of the analytical tower is heated by a analytical tower reboiler; The kettle of the butadiene light-removal tower is heated by a light-removal tower reboiler; The kettle of the butadiene deweighting tower is heated by the first reboiler of the deweighting tower and the second reboiler of the deweighting tower.

10. The energy-saving and consumption-reducing butadiene extraction method according to claim 1, characterized in that The mixed C4 raw material is selected from one or more of the following raw materials: C4 from ethylene cracking, C4 from oxidative dehydrogenation of butene, C4 from oxidative dehydrogenation of butane, and C4 from direct production of olefins from crude oil; preferably, the content of 1,3-butadiene in the mixed C4 raw material is in the range of 10 to 85 wt%; The extraction solvent is selected from acetonitrile, N-methylpyrrolidone and dimethylformamide, preferably the extraction solvent is selected from N-methylpyrrolidone.

Images