CN113956126A - Butadiene separation method by recycling acetonitrile - Google Patents
Butadiene separation method by recycling acetonitrile Download PDFInfo
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- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 title claims abstract description 477
- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 title claims abstract description 78
- 238000000926 separation method Methods 0.000 title claims abstract description 20
- 238000004064 recycling Methods 0.000 title claims abstract description 8
- 238000000605 extraction Methods 0.000 claims abstract description 84
- 239000002904 solvent Substances 0.000 claims abstract description 62
- 239000012452 mother liquor Substances 0.000 claims abstract description 52
- 239000000463 material Substances 0.000 claims abstract description 39
- 230000018044 dehydration Effects 0.000 claims abstract description 36
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 36
- 239000012528 membrane Substances 0.000 claims abstract description 32
- 238000005373 pervaporation Methods 0.000 claims abstract description 29
- 238000000746 purification Methods 0.000 claims abstract description 29
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000002994 raw material Substances 0.000 claims abstract description 6
- 238000010992 reflux Methods 0.000 claims description 18
- 239000007788 liquid Substances 0.000 claims description 16
- 239000012535 impurity Substances 0.000 claims description 14
- 238000009835 boiling Methods 0.000 claims description 12
- 239000000126 substance Substances 0.000 claims description 6
- 238000000034 method Methods 0.000 abstract description 10
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 12
- BZLVMXJERCGZMT-UHFFFAOYSA-N Methyl tert-butyl ether Chemical compound COC(C)(C)C BZLVMXJERCGZMT-UHFFFAOYSA-N 0.000 description 10
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 8
- 238000010926 purge Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000012141 concentrate Substances 0.000 description 3
- 238000005265 energy consumption Methods 0.000 description 3
- VXNZUUAINFGPBY-UHFFFAOYSA-N 1-Butene Chemical compound CCC=C VXNZUUAINFGPBY-UHFFFAOYSA-N 0.000 description 2
- 150000001335 aliphatic alkanes Chemical class 0.000 description 2
- IAQRGUVFOMOMEM-UHFFFAOYSA-N butene Natural products CC=CC IAQRGUVFOMOMEM-UHFFFAOYSA-N 0.000 description 2
- 238000000895 extractive distillation Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229920000459 Nitrile rubber Polymers 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- 150000001345 alkine derivatives Chemical class 0.000 description 1
- 239000001273 butane Substances 0.000 description 1
- 239000013064 chemical raw material Substances 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000012510 hollow fiber Substances 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229920003048 styrene butadiene rubber Polymers 0.000 description 1
- 125000000383 tetramethylene group Chemical group [H]C([H])([*:1])C([H])([H])C([H])([H])C([H])([H])[*:2] 0.000 description 1
- 238000004065 wastewater treatment Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/005—Processes comprising at least two steps in series
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C253/00—Preparation of carboxylic acid nitriles
- C07C253/32—Separation; Purification; Stabilisation; Use of additives
- C07C253/34—Separation; Purification
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/04—Purification; Separation; Use of additives by distillation
- C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
- C07C7/08—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by extractive distillation
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Water Supply & Treatment (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a butadiene separation method for recycling acetonitrile, which comprises the following steps: (1) c4 raw materials sequentially pass through a first extraction tower and a second extraction tower, and butadiene is separated from the top of the second extraction tower; (2) feeding a second tower bottom material of the second extraction tower into the solvent tank as a recycled solvent; (3) part of acetonitrile mother liquor in the solvent tank enters an acetonitrile purification tower to be purified and then returns to the solvent tank; (4) and the acetonitrile mother liquor in the solvent tank is used as an acetonitrile solvent and enters the first extraction tower and the second extraction tower. The pervaporation membrane dehydration device is used for separating water in the acetonitrile mother liquor, improving the acetonitrile content in the acetonitrile mother liquor and keeping the acetonitrile content in the acetonitrile mother liquor discharged from the pervaporation membrane dehydration device between 80 and 99 weight percent; by using the method, the consumption of acetonitrile can be greatly reduced, and the consumption of acetonitrile per ton of butadiene is only 0.1-0.3 ton; meanwhile, due to intensification of each device, the occupied area of the device is reduced, and the resource utilization rate is improved.
Description
Technical Field
The invention relates to a butadiene separation method for recycling acetonitrile.
Background
The C4 fraction is a mixture of butane, butylene, butadiene, alkyne and the like, wherein butadiene is an important chemical raw material for producing styrene butadiene rubber, nitrile rubber, nylon and the like. Therefore, the separation and extraction of butadiene from the C4 mixture is an important part of the comprehensive utilization of the C4 fraction. The acetonitrile extractive distillation method is a common method for industrially separating butadiene at present, and the method changes the relative volatility of each component in a C4 system by adding an acetonitrile solvent, and obtains a high-purity butadiene product after multistage acetonitrile extractive distillation. However, as the number of extraction cycles increases, the acetonitrile solvent contains methanol, acetone, methyl tert-butyl ether (MTBE), water and the like which are continuously enriched, so that the acetonitrile concentration is gradually reduced, and the product yield of butadiene is further influenced.
At present, separation technologies such as rectification, adsorption and the like are generally adopted for treating the recycled solvent, acetonitrile and water are easy to form an azeotrope, the problems of high energy consumption, complex process and the like exist in the conventional separation method, and meanwhile, the recycled solvent is generally treated in other places, so that environmental pollution is easily caused in the transportation and treatment processes, and the operation cost of enterprises is increased.
Disclosure of Invention
In order to solve the problems, the invention provides a butadiene separation method for recycling acetonitrile, which comprises the following steps:
(1) c4 raw material enters a first extraction tower, and the first tower bottom material of the first extraction tower enters a second extraction tower; separating low-boiling-point substances from a first reflux tank at the top of the first extraction tower, and separating butadiene from a second reflux tank at the top of the second extraction tower; the acetonitrile solvent enters the first extraction tower from the top of the first extraction tower, and enters the second extraction tower from the top of the second extraction tower;
(2) feeding a second tower bottom material of the second extraction tower into the solvent tank as a recycled solvent;
(3) part of acetonitrile mother liquor in the solvent tank enters an acetonitrile purification tower, the acetonitrile purification tower is a rectifying tower, low-boiling-point impurities are separated from the top of the acetonitrile purification tower, and a third tower bottom material of the acetonitrile purification tower returns to the solvent tank; the tower bottom of the acetonitrile purification tower is connected with a pervaporation membrane dehydration device, the residual liquid outlet of the pervaporation membrane dehydration device is communicated with a solvent tank, and the pervaporation membrane dehydration device is used for concentrating the bottom material of the third tower;
(4) and the acetonitrile mother liquor in the solvent tank is used as an acetonitrile solvent and enters the first extraction tower and the second extraction tower.
In this application, set up acetonitrile purifying column and pervaporation membrane dewatering device, acetonitrile purifying column wherein is used for purifying the acetonitrile mother liquor in the solvent jar to the low boiling impurity such as methyl alcohol, acetone, MTBE that the desorption contains reduces the impurity content in the acetonitrile mother liquor, reduces the influence of these impurities to first extraction column and second extraction column, guarantees the normal operating of first extraction column and second extraction column. The pervaporation membrane dehydration device is used for separating water in the acetonitrile mother liquor, and improving the acetonitrile content in the acetonitrile mother liquor, so that the acetonitrile content in the acetonitrile mother liquor discharged from the pervaporation membrane dehydration device is kept between 80 and 99 weight percent.
Utilize acetonitrile purge column and pervaporation membrane dewatering device to carry out real-time processing to the acetonitrile mother liquor, make the acetonitrile concentration in the acetonitrile mother liquor keep in setting for the within range, not only avoided the drawback of handling unqualified acetonitrile mother liquor outward, still reduced the replenishment volume of acetonitrile, because most acetonitrile can the retrieval and utilization in this application, consequently except that need once only supply a large amount of acetonitrile when driving, in normal operating, only need supply a small amount of acetonitrile, in order to compensate inevitable acetonitrile consumption in each step, these acetonitrile consumption include along with the low boiling thing of first extraction column separation, butadiene that the second extraction column separated, and acetonitrile purge column low boiling point material exhaust acetonitrile such as impurity. By using the method, the consumption of acetonitrile can be greatly reduced, and the consumption of acetonitrile per ton of butadiene is only 0.1-0.3 ton.
Because this application adopts the unqualified acetonitrile mother liquor of on-the-spot processing to realize the cyclic utilization of acetonitrile, showing the manufacturing cost who has reduced the product, promote the competitiveness of product. Meanwhile, due to intensification of each device, the occupied area of the device is reduced, the resource utilization rate is improved, and the energy consumption can be saved by more than 20% compared with the traditional process.
Specifically, the first top temperature of the first extraction tower is 35-40 ℃, and the first bottom temperature of the first extraction tower is 60-65 ℃. The main function of the first extraction tower is to separate low-boiling-point substances such as alkane and butene in the C4 raw material, under the temperature control, the low-boiling-point substances can be guaranteed to be removed to the maximum extent, and the loss of effective component butadiene is avoided, so that the content of the low-boiling-point substances in the first tower bottom material of the first extraction tower can be reduced to be below 0.5 wt%.
Specifically, in order to ensure the yield of butadiene, the second top temperature of the second extraction tower is 45-55 ℃, and the second bottom temperature of the second extraction tower is 80-120 ℃. Under the temperature control, the yield of the butadiene can reach more than 95 percent.
Furthermore, in order to reduce the subsequent treatment cost, in the step (1), the purity of the butadiene separated by the second reflux tank is more than or equal to 98 wt%.
Further, in order to avoid that the acetonitrile content in the acetonitrile mother liquor is too low and affects the yield of butadiene, in the step (3), when the acetonitrile content in the acetonitrile mother liquor in the solvent tank is lower than a first set proportion, part of the acetonitrile mother liquor enters an acetonitrile purification tower to be purified, and the first set proportion is 80-95 wt%. This design can make the acetonitrile content in the acetonitrile mother liquor in the solvent jar in time reply on first settlement proportion, avoids acetonitrile concentration to hang down excessively, influences the normal operating of first extraction column and second extraction column. Make partial acetonitrile mother liquor enter into the acetonitrile purge column and purify, when guaranteeing acetonitrile content in the acetonitrile mother liquor, can also reduce the load of acetonitrile purge column to reduce the working costs, if make the acetonitrile mother liquor that acetonitrile content surpassed the settlement proportion enter into the acetonitrile purge column and purify, though can improve the content of acetonitrile in the acetonitrile mother liquor, but do not have big influence to the yield of butadiene, make the acetonitrile purge column be in high load running state on the contrary, improved the working costs.
In the operation process, once the acetonitrile content in the acetonitrile mother liquor in the solvent tank is lower than a first set proportion, part of the acetonitrile mother liquor enters the acetonitrile purification tower to be purified so as to improve the acetonitrile content in the acetonitrile mother liquor, the content in the acetonitrile mother liquor is quickly raised above the first set proportion, the acetonitrile content in the acetonitrile mother liquor is fluctuated within a small range of the first set proportion, the fluctuation range of the acetonitrile content in the acetonitrile mother liquor can be controlled within +/-1 wt%, and the stability of the acetonitrile content is maintained.
In the operation process, the acetonitrile solvent enters into in first extraction tower and the second extraction tower in succession, concentration fluctuation in the acetonitrile mother liquor short time in the solvent jar can not influence first extraction tower and the normal work of second extraction tower, consequently in time because the concentration of the acetonitrile mother liquor in the solvent jar is lower, nevertheless the third tower bottom material after the acetonitrile purifying column is concentrated can in time supply the solvent jar in, with the concentration of the acetonitrile mother liquor in the improvement solvent jar, thereby can in time improve the concentration of acetonitrile solvent, guarantee the normal work of first extraction tower and second extraction tower, this makes the concentration of acetonitrile in the acetonitrile solvent that enters into in first extraction tower and the second extraction tower be in the state of a wave band.
Furthermore, in order to avoid that the operation of the first extraction tower and the second extraction tower is influenced by excessive low-boiling-point impurities carried in the acetonitrile mother liquor, the content of the low-boiling-point impurities in the bottom material of the third tower is less than 1 wt%.
Specifically, the temperature of the third tower bottom of the acetonitrile purifying tower is 80-85 ℃, and the temperature of the third tower top is 65-70 ℃. At the temperature, low boiling point impurities such as methanol, acetone, MTBE and the like in the acetonitrile mother liquor can be separated to the maximum extent, the content of the impurities is lower than 0.5 wt%, and the excessive consumption of acetonitrile is avoided.
Further, when the water content in the third tower bottom material is more than or equal to 20 wt%, dehydrating and concentrating the third tower bottom material by a pervaporation membrane dehydration device to form concentrated solution, and feeding the concentrated solution into a solvent tank; when the water content in the third column bottoms is less than 20 wt%, the third column bottoms is fed directly into the solvent tank. The configuration of the membrane material of the pervaporation membrane dehydration device can adopt any one of a plate type, a tubular type, a roll type or a hollow fiber type, wherein the membrane material can adopt an organic or inorganic membrane, such as a PVA membrane, a molecular sieve membrane and the like. The efficient dehydration performance of the pervaporation membrane dehydration device can be fully utilized due to the design, and the pervaporation membrane dehydration device has the efficient dehydration performance, so that only the third tower bottom material with the water content of more than or equal to 20 wt% enters the pervaporation membrane dehydration device, the efficient dehydration performance of the pervaporation membrane dehydration device can be effectively utilized, the dehydration is ensured, the operation efficiency is improved, the configuration capacity of equipment is reduced, and the manufacturing and safety cost of the equipment is reduced. The design can keep the acetonitrile content in the acetonitrile mother liquor in the solvent tank between 80 and 99 weight percent, and ensure the smooth production.
Further, in order to improve the operation efficiency of the equipment, the third tower bottom material is dehydrated and concentrated by a pervaporation membrane dehydration device, wherein the concentration of acetonitrile in the concentrated solution is 80-99 wt%. Preferably, the concentration of acetonitrile in the concentrate is 10 to 30 wt% higher than that in the mother liquid of acetonitrile.
Specifically, in order to ensure the efficient operation of the pervaporation membrane dehydration device, the working temperature of the pervaporation dehydration device is 30-150 ℃, and the working pressure is 0-0.4 Mpa.
Drawings
FIG. 1 is a schematic flow chart diagram of an embodiment of the present invention.
Detailed Description
Referring to fig. 1, a butadiene separation method recycling acetonitrile includes the following steps:
(1) the raw material C4 enters into the first extraction tower 10 through the middle part of the first extraction tower 10, the first bottom material of the first extraction tower is discharged from the bottom of the first extraction tower 10 and divided into two parts, wherein one part of the first bottom material is heated by the first reboiler 13 and then returns into the first extraction tower 10, and the other part of the first bottom material enters into the second extraction tower through the middle part of the second extraction tower 20 through the first pipeline 14.
The vapor at the top of the first extraction tower 10 enters a first reflux tank 12 after passing through a first condenser 11, a part of the liquid in the first reflux tank 12 is returned to the first extraction tower 10 as reflux liquid, and the other part of the liquid in the first reflux tank 12 is discharged as low boiling point components 91, wherein the main components of the low boiling point components are low boiling point components such as alkane and butene in the C4 raw material.
The vapor at the top of the second extraction tower 20 passes through the second condenser 21 and enters the second reflux drum 22, a part of the liquid in the second reflux drum 22 is returned to the second extraction tower 20 as reflux liquid, and the other part of the liquid in the second reflux drum 22 is discharged as butadiene 92.
The acetonitrile mother liquor 31 in the solvent tank 30 is fed into the first extraction column from the top of the first extraction column as an acetonitrile solvent, and the acetonitrile solvent is fed into the second extraction column from the top of the second extraction column.
In this example, the first top temperature of the first extraction column was 38 ℃ and the first bottom temperature of the first extraction column was 63 ℃. The second top temperature of the second extraction column is 50 ℃ and the second bottom temperature of the second extraction column is 110 ℃. It was found that the content of low boiling substances in the bottom material of the first column was 0.48% by weight.
(2) The second bottom material of the second extraction column 20 is discharged from the bottom of the second extraction column 20 and divided into two streams, wherein one stream of the second bottom material is heated by the second reboiler 23 and then returned to the second extraction column 20, and the other stream of the second bottom material is used as the recycling solvent 81 and enters the solvent tank 30 through the second pipeline 24. A solvent feed 32 for adding fresh acetonitrile 100 is installed on the solvent tank 30.
(3) A part of the acetonitrile mother liquor 31 in the solvent tank 30 enters an acetonitrile purification tower 40, which is a rectification tower. In the production process, the amount of the acetonitrile mother liquor entering the acetonitrile purification tower is adjusted according to the acetonitrile content in the acetonitrile mother liquor, when the acetonitrile content in the acetonitrile mother liquor is more than or equal to 80 wt%, the acetonitrile mother liquor is suspended from entering the acetonitrile purification tower, when the acetonitrile content in the acetonitrile mother liquor is less than 80 wt%, part of the acetonitrile mother liquor enters the acetonitrile purification tower to be purified and returns to the solvent tank, so that the acetonitrile content in the acetonitrile mother liquor in the solvent tank is quickly increased to more than 80 wt%, namely the first set proportion of the acetonitrile content in the acetonitrile mother liquor in the solvent tank is 80 wt%. In this example, the acetonitrile content in the acetonitrile mother liquor in the solvent tank can be stabilized within 80 ± 1 wt%.
It will be appreciated that in other embodiments the first set ratio may also be set to 85 wt%, 90 wt% or 95 wt%, although other ratios between 80 and 95 wt% are possible.
The temperature of the third tower bottom of the acetonitrile purification tower is 82 ℃, and the temperature of the third tower top of the acetonitrile purification tower is 68 ℃.
The vapor at the top of the acetonitrile purification tower 40 passes through the third condenser 41 and enters the third reflux tank 42, a part of the liquid in the third reflux tank 42 is returned to the acetonitrile purification tower 40 as a reflux liquid, and the other part of the liquid in the third reflux tank 42 is discharged as low-boiling impurities 93, wherein the low-boiling impurities 93 comprise components such as methanol, acetone, MTBE and the like. After purification, the content of low-boiling impurities in the bottom material of the third column was 0.45% by weight.
Three pipelines, namely a purification tower reboiling pipe 431, a straight return pipe 44 and a dehydration pipe 45, are led out from the tower bottom of the acetonitrile purification tower 40, a third reboiler 43 is connected in series to the purification tower reboiling pipe 431, the dehydration pipe 45 is connected to a liquid inlet 51 of a pervaporation membrane dehydration device 50, a residual liquid outlet 52 of the pervaporation membrane dehydration device 50 is connected to the solvent tank 30 through a liquid outlet pipe 54, and a fourth cooler 55 is connected in series to the liquid outlet pipe 54.
The third tower bottom material discharged from the tower bottom of the acetonitrile purification tower is divided into two streams, wherein one stream is the tower bottom reboiling material, the other stream is the tower outlet material, the tower bottom reboiling material is heated by a third reboiler 43 and then returns to the acetonitrile purification tower, and the tower outlet material returns to the solvent tank 30 through a straight return pipe 44 or a dehydration pipe 45 according to different conditions.
When the water content in the third tower bottom material is more than or equal to 20 wt%, the tower bottom material enters the pervaporation membrane dehydration device through the dehydration pipe 45 for dehydration and concentration to form a concentrated solution, the concentrated solution is cooled by the fourth cooler 55 and then returns to the solvent tank 30, and the water separated from the pervaporation membrane dehydration device is discharged through the water outlet 53 and enters the wastewater treatment system.
In the embodiment, when the pervaporation membrane dehydration device works, the working temperature is 90-110 ℃, and the working pressure is 0.2-0.3 Mpa. The concentration of acetonitrile in the concentrate is 95-99 wt%, it being understood that in other embodiments, the concentration of acetonitrile in the concentrate can be controlled to be within 80-85 wt%, 85-90 wt%, or 90-95 wt%.
When the water content in the third column bottoms is less than 20 wt%, the third column bottoms is fed directly into the solvent tank through the return line 44.
A first valve 46 is provided in the return pipe 44, a second valve 47 is provided in the dewatering pipe 45, and the first valve 46 and the second valve 47 are switched in accordance with the water content in the third column bottom material, so that the discharged material is returned to the solvent tank through different pipes.
(4) And the acetonitrile mother liquor in the solvent tank is used as an acetonitrile solvent and enters the first extraction tower and the second extraction tower.
In this example, the yield of butadiene was 96.8%, the purity of butadiene was 98.6 wt%, and the amount of acetonitrile consumed per ton of butadiene was only 250 kg. Wherein the comprehensive energy consumption is saved by 15-17%.
Claims (10)
1. A butadiene separation method capable of recycling acetonitrile is characterized by comprising the following steps:
(1) c4 raw material enters a first extraction tower, and the first tower bottom material of the first extraction tower enters a second extraction tower; separating low-boiling-point substances from a first reflux tank at the top of the first extraction tower, and separating butadiene from a second reflux tank at the top of the second extraction tower; the acetonitrile solvent enters the first extraction tower from the top of the first extraction tower, and enters the second extraction tower from the top of the second extraction tower;
(2) feeding a second tower bottom material of the second extraction tower into the solvent tank as a recycled solvent;
(3) part of acetonitrile mother liquor in the solvent tank enters an acetonitrile purification tower, the acetonitrile purification tower is a rectifying tower, low-boiling-point impurities are separated from the top of the acetonitrile purification tower, and a third tower bottom material of the acetonitrile purification tower returns to the solvent tank;
the tower bottom of the acetonitrile purification tower is connected with a pervaporation membrane dehydration device, the residual liquid outlet of the pervaporation membrane dehydration device is communicated with a solvent tank, and the pervaporation membrane dehydration device is used for concentrating the bottom material of the third tower;
(4) and the acetonitrile mother liquor in the solvent tank is used as an acetonitrile solvent and enters the first extraction tower and the second extraction tower.
2. The butadiene separation process according to claim 1,
the first tower top temperature of the first extraction tower is 35-40 ℃, and the first tower bottom temperature of the first extraction tower is 60-65 ℃.
3. The butadiene separation process according to claim 1,
the second tower top temperature of the second extraction tower is 45-55 ℃, and the second tower bottom temperature of the second extraction tower is 80-120 ℃.
4. The butadiene separation process according to claim 1,
in the step (1), the purity of the butadiene separated by the second reflux tank is more than or equal to 98 wt%.
5. The butadiene separation process according to claim 1,
in the step (3), when the acetonitrile content in the acetonitrile mother liquor in the solvent tank is lower than a first set proportion, part of the acetonitrile mother liquor enters an acetonitrile purification tower for purification, and the first set proportion is 80-95 wt%.
6. The butadiene separation process according to claim 1,
the content of low-boiling impurities in the third column bottoms was < 1% by weight.
7. The butadiene separation process according to claim 1,
the temperature of the third tower bottom of the acetonitrile purifying tower is 80-85 ℃, and the temperature of the third tower top is 65-70 ℃.
8. The butadiene separation process according to claim 1,
when the water content in the third tower bottom material is more than or equal to 20 wt%, dehydrating and concentrating the third tower bottom material by a pervaporation membrane dehydration device to form concentrated solution, and feeding the concentrated solution into a solvent tank; when the water content in the third column bottoms is less than 20 wt%, the third column bottoms is fed directly into the solvent tank.
9. The butadiene separation process of claim 8,
and dehydrating and concentrating the bottom material of the third tower by using a pervaporation membrane dehydration device, wherein the concentration of acetonitrile in the concentrated solution is 80-99 wt%.
10. The butadiene separation process of claim 8,
the pervaporation dehydration device has the working temperature of 30-150 ℃ and the working pressure of 0-0.4 Mpa.
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