Industrial acetonitrile online purification method and device

Abstract

The invention discloses an online purification method of industrial acetonitrile, which comprises the following steps: by taking organic sewage as a raw material, carrying out double-tower rectification, removing organic materials containing ethanol, acetonitrile and the like in the sewage through an atmospheric tower, feeding the removed organic materials into a pressurizing tower, and realizing effective separation of light components such as ethanol and the like in the organic materials from acetonitrile in the pressurizing tower; acetonitrile in organic materials is recycled, the loss of acetonitrile is reduced to 0.4 or below, the loss of acetonitrile is reduced to the maximum extent, light component impurities such as acetone and ethanol in circulating solvent acetonitrile in the extraction section of a butadiene extraction device are indirectly reduced to 1wt% or below, and accumulation of the light component impurities such as acetone and ethanol in the circulating solvent acetonitrile is inhibited.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering production, and specifically relates to an industrial acetonitrile online purification method and device. Background Art

[0002] As an important chemical raw material, acetonitrile is widely used as a solvent in the chemical industry because of its good solubility. At present, some domestic companies use the acetonitrile extraction process to separate and purify the C4 fraction of ethylene cracking to produce 1,3-butadiene products, and acetonitrile is used as an extractant for recycling. During the continuous operation of the device, a large amount of alcohol, ketone oxygen-containing organic matter and 1,3-butadiene dimers, polymers and other impurities began to accumulate in the circulating solvent acetonitrile. The change in the composition of the circulating acetonitrile reduces the solvent extraction performance. What's worse, the solvent foaming causes the extraction distillation system to flood. Continued development will accelerate the formation of rubber in the extraction system, block the tower plate, and cause the device to fail to operate normally. Therefore, the quality of the circulating acetonitrile solvent is related to whether the butadiene extraction process device can operate stably and economically for a long period of time, and the purification of the circulating acetonitrile solvent needs to be solved urgently.

[0003] Existing process (see attached Figure 1 ) is to extract 1-1.5% of the solvent from the circulating solvent and enter the alkyne water washing tower to remove dimers, and the acetonitrile water in the tower bottom and the first extraction tower and the second extraction tower enter the solvent regeneration tower together to remove other impurities, and the regenerated acetonitrile with a mass fraction of 78% is obtained at the top of the tower. The regenerated acetonitrile enters the upper section of the first extraction tower. Since the water content of the regenerated solvent is relatively large and the dehydration capacity of the entire device is limited, the regeneration amount is small. In addition, the circulating solvent contains a part of accumulated light component impurities such as alcohol ketones that cannot be removed. The gradual accumulation of alcohol ketones makes the quality of the solvent worse and worse, affecting the extraction effect. Therefore, it is necessary to replace all or part of the fresh solvent during maintenance, which is costly. At the same time, the replaced alcohol ketone-containing acetonitrile must be treated as hazardous waste liquid, which further increases the maintenance and operation costs of the device.

[0004] Patent CN116217434A provides a solvent regeneration method and device for 1,3-butadiene extraction process by acetonitrile method, the method is to extract a circulating acetonitrile solvent into the middle of the light removal tower, obtain an azeotrope containing organic matter at the top of the tower, and obtain the acetonitrile solvent after light removal in the bottom of the tower; the acetonitrile solvent after light removal is sent to the heavy removal tower to obtain the regenerated acetonitrile solvent at the top of the heavy removal tower and the heavy component product in the bottom of the heavy removal tower, and the regenerated acetonitrile solvent at the top of the heavy removal tower is returned to the extraction system. This method can reduce the light component impurity content in the regenerated solvent to ≤0.1wt%, but the acetonitrile loss (the amount of acetonitrile lost per unit mass of ethanol removed) is nearly 1.19, the number of plates and reflux ratio of the light removal tower are relatively large, which greatly increases the cost of light component removal. Summary of the invention

[0005] The purpose of the present invention is to solve a series of problems in the existing process, such as impurities such as alcohols and ketones are difficult to remove in the circulating solvent acetonitrile, and the separation of acetonitrile and ethanol is difficult due to the presence of four groups of azeotropes among ethanol, water and acetonitrile, and the loss of acetonitrile is high. The present invention provides an online purification method and device for industrial acetonitrile, which uses the circulating organic sewage in a butadiene extraction device as a raw material, realizes the effective removal of light components such as ethanol by removing light components in a normal pressure tower and separating light components in a pressure tower, reduces the loss of acetonitrile to the maximum extent, and indirectly removes light components such as alcohols and ketones in the circulating solvent acetonitrile in the butadiene extraction process.

[0006] The present invention is achieved through the following technical solutions:

[0007] An industrial acetonitrile online purification method comprises the following steps:

[0008] Step 1: atmospheric distillation;

[0009] The organic wastewater from the butadiene extraction unit enters the lower part of the atmospheric pressure tower.

[0010] The atmospheric pressure tower has a theoretical plate number of 20 to 40, a bottom temperature of 85 to 130° C., and a reflux ratio of 2 to 20;

[0011] Atmospheric pressure distillate is taken from the top of the tower, and atmospheric pressure residue is taken from the bottom of the tower;

[0012] The organic wastewater from the butadiene extraction device contains 0.7-9wt% acetonitrile, 0.10-3wt% light components, and the rest is water.

[0013] The light component includes at least one of acetone, methanol and ethanol;

[0014] Under normal pressure: 52.46wt% ethanol-43.70wt% acetonitrile-3.84wt% water has a ternary azeotrope with a boiling point of 72.89°C; 58.01wt% ethanol-41.99wt% acetonitrile has a binary azeotrope with a boiling point of 73.05°C, 82.38wt% acetonitrile-17.62wt% water has a binary azeotrope with a boiling point of 76.65°C, and 95.62wt% ethanol-4.38wt% water has a binary azeotrope with a boiling point of 78.15°C. These four groups of azeotropes make it difficult to separate light components such as light component ethanol in the prior art;

[0015] The organic wastewater from the butadiene extraction device is the sedimentation water in the water bag of the first extraction tower reflux tank, the sedimentation water in the water bag of the second extraction tower reflux tank, the raffinate water washing tower kettle water, the butadiene water washing tower kettle water, and the alkyne water washing tower kettle water;

[0016] The atmospheric distillate includes: acetone, methanol, ethanol, acetonitrile and other oxygen-containing organic substances and a small amount of water;

[0017] The water content of the atmospheric pressure residue is ≥99.9wt%, and the organic matter content is ≤0.1wt%; wherein the organic matter includes: ethanol, acetonitrile and other organic matter;

[0018] Step 2: Pressure distillation

[0019] The atmospheric distillate from step 1 enters the middle part of the pressure tower for pressure distillation;

[0020] The theoretical plate number of the pressure tower is 30 to 50, the bottom temperature is 90 to 150°C, the top pressure is 0.2 to 0.5 MPaG (gauge pressure), and the reflux ratio is 10 to 30;

[0021] The pressurized distillate is taken out from the top of the tower, and the pressurized residue is taken out from the bottom of the tower;

[0022] The ethanol content in the pressurized distillate is 60-69 wt %; the acetonitrile content is less than 28 wt %;

[0023] The pressurized residue is purified industrial acetonitrile, wherein the acetonitrile content is ≥80wt%.

[0024] In the above technical solution, step 1: atmospheric distillation: the atmospheric pressure tower is fed at the position of 15 to 30 theoretical plates;

[0025] In the above technical solution, step 1: atmospheric distillation: the light components include at least acetone, methanol and ethanol;

[0026] In the above technical solution, step 2: pressure distillation: the pressure tower is fed at a position where the theoretical plate number is 15 to 25;

[0027] In the above technical solution, the pressurized residue is purified industrial acetonitrile, wherein the ethanol content is ≤0.2wt%, and the water content is ≤17.8wt%.

[0028] In the above technical scheme, the online purification method of acetonitrile is a continuous operation or an intermittent operation mode.

[0029] In the above technical solution, the normal pressure residue is discharged into the sewage pool of the device; the pressurized residue is industrial acetonitrile which is recycled to the production process after purification.

[0030] As a further preferred technical solution, step 1: atmospheric distillation: the atmospheric tower has a theoretical plate number of 25 to 35, a bottom temperature of 95 to 110° C., a reflux ratio of 3 to 15, and feed at a theoretical plate number of 18 to 26;

[0031] As a further preferred technical solution, step 2: atmospheric distillation: the atmospheric tower has a theoretical plate number of 35 to 45, a bottom temperature of 100 to 135° C., a reflux ratio of 10 to 23, and feed at the theoretical plate number of 17 to 23;

[0032] Another object of the present invention is to provide an industrial acetonitrile online purification device.

[0033] An industrial acetonitrile online purification device comprises: an atmospheric pressure tower and a pressure tower;

[0034] The middle and lower part of the atmospheric tower body is provided with an atmospheric tower feed port, the top of the tower is provided with an atmospheric tower top discharge port, and the tower bottom is provided with an atmospheric tower bottom discharge port;

[0035] The pressurized tower body is provided with a pressurized tower feed port in the middle, a pressurized tower top discharge port is provided at the tower top, and a pressurized tower bottom discharge port is provided at the tower bottom;

[0036] The top discharge port of the atmospheric tower is connected with the feed port of the pressure tower through a pipeline.

[0037] In the above technical solution, the industrial acetonitrile online purification device also includes: a light component tank; the top discharge port of the pressure tower is connected to the light component tank through a pipeline.

[0038] In the above technical solution, an atmospheric tower reflux pump is arranged on the pipeline connecting the atmospheric tower top discharge port and the pressure tower feed port, and the atmospheric tower reflux pump outlet is respectively connected to the pressure tower feed port and the atmospheric tower top reflux port.

[0039] In the above technical solution, a pressurizing tower reflux pump is arranged on the pipeline connected to the discharge port at the top of the pressurizing tower, and the outlet of the pressurizing tower reflux pump is respectively connected to the light component tank and the reflux port at the top of the pressurizing tower.

[0040] The beneficial effects of the present invention are as follows:

[0041] The organic sewage is used as raw material, and the organic materials including ethanol, acetonitrile, etc. are removed from the sewage by double-tower distillation. The removed organic materials enter the pressure tower, and the light components such as ethanol in the organic materials are effectively separated from acetonitrile in the pressure tower, and the acetonitrile in the organic materials is recovered, and the acetonitrile loss is reduced to less than 0.4 (the acetonitrile loss is the mass ratio of acetonitrile corresponding to the loss of one unit mass of ethanol removed, that is, the mass ratio of acetonitrile to ethanol in the pressurized distillate), the acetonitrile loss is reduced to the maximum extent, and the light component impurities such as acetone and ethanol in the circulating solvent acetonitrile of the extraction section of the butadiene extraction device are indirectly reduced to less than 1wt%, and the accumulation of light component impurities such as acetone and ethanol in the circulating solvent acetonitrile is suppressed. Thus, a new technology for online separation and purification of acetonitrile for butadiene extraction is developed, which is organically combined with the existing device circulating solvent acetonitrile treatment system, realizes the steady-state control and ultra-long cycle operation of impurities in acetonitrile, and solves the high cost and environmental protection problem of overall replacement and external disposal of circulating solvent acetonitrile in the overhaul of the existing device. The double-tower distillation device can select a continuous light removal mode or an intermittent light removal mode for distillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a simplified process flow diagram of the acetonitrile extraction process for separating and purifying the C4 fraction of ethylene cracking to produce 1,3-butadiene products;

[0043] Figure 2 The process flow diagram of the online purification of industrial acetonitrile of the present invention is

[0044] 1—organic wastewater feed from butadiene extraction unit, 2—atmospheric pressure tower, 3—atmospheric pressure tower condenser, 4—atmospheric pressure tower reflux tank, 5—atmospheric pressure tower reflux pump, 6—atmospheric pressure tower reboiler, 7—atmospheric pressure residue (wastewater) discharge, 8—atmospheric pressure tower distillate / pressurized tower feed, 9—pressurized tower, 10—pressurized tower condenser, 11—pressurized tower reflux tank, 12—pressurized tower reflux pump, 13—pressurized tower kettle pressurized residue discharge, 14—pressurized tower reboiler, 15—pressurized tower top pressurized distillate (light component waste such as ethanol).

[0045] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments.

[0047] Example 1

[0048] An industrial acetonitrile online purification device comprises an atmospheric tower 2, an atmospheric tower condenser 3, an atmospheric tower reflux tank 4, an atmospheric tower reflux pump 5, an atmospheric tower reboiler 6, a pressure tower 9, a pressure tower condenser 10, a pressure tower reflux tank 11, a pressure tower reflux pump 12, and a pressure tower reboiler 14. The lower part of the atmospheric tower body is provided with an organic sewage feed port, which is connected to the butadiene extraction device of the production system via a feed pipeline 1; the top of the atmospheric tower is provided with a condenser, which is connected to the atmospheric tower reflux tank via a pipeline; the atmospheric tower kettle is provided with a reboiler, and the atmospheric tower kettle is provided with a discharge port, which is connected to a sewage pool via a discharge pipeline 7. The atmospheric tower reflux tank is connected to the atmospheric tower reflux pump via a pipeline. The atmospheric tower reflux pump outlet pipeline is divided into two routes, one route is connected to the atmospheric tower top reflux port via a pipeline, and the other route is connected to the feed port in the middle of the pressure tower body via pipeline 8. The pressure tower body is provided with a feed port in the middle, which is connected to the atmospheric tower reflux pump via a feed pipeline 8; the pressure tower top is provided with a condenser, which is connected to the pressure tower reflux tank via a pipeline; the pressure tower kettle is provided with a reboiler, and the pressure tower kettle is provided with a discharge port, which is connected to the butadiene extraction device of the production system via a discharge pipeline 13. The recovered pressurized residue is rich in acetonitrile and returned to the system (i.e., the attached Figure 1The pressure tower reflux tank is connected to the pressure tower reflux pump via a pipeline, and the outlet pipeline of the pressure tower reflux pump is divided into two paths, one of which is connected to the reflux port at the top of the pressure tower via a pipeline, and the other is connected to the light component tank via a discharge pipeline 15.

[0049] The following Example 2 uses the device in Example 1 to purify industrial acetonitrile

[0050] Example 2

[0051] A 200,000 tons / year acetonitrile-based 1,3-butadiene extraction unit, with an initial acetonitrile solvent load of 800 tons, had a circulating solvent composition of 2.11wt% of light impurities such as ethanol and acetone, 90.77wt% of acetonitrile, 6.80wt% of water, and 0.32wt% of heavy impurities such as dimers and acetic acid. The organic wastewater in the water bag (i.e., organic wastewater from the butadiene extraction unit) was composed of 0.05wt% acetone, 0.01wt% methanol, 1.8wt% ethanol, 2.76% acetonitrile, and 95.38wt% water.

[0052] A 1t / h stream of organic wastewater is drawn out for light separation.

[0053] The number of plates of the atmospheric tower is 31, the feed is on the 21st plate, the feed temperature is 45°C, the tower top temperature is 73.2°C, the tower bottom temperature is 101.3°C, and the reflux ratio is 5;

[0054] The number of plates of the pressurized tower is 40, the feed is fed to the 20th plate, the feed temperature is 45°C, the tower top temperature is 115.6°C, the tower bottom temperature is 122.8°C, the reflux ratio is 20; the tower top pressure is 0.3MPaG;

[0055] The composition of the top distillate of the atmospheric tower is as follows: acetone: 0.96wt%, methanol: 0.19wt%, ethanol: 34.62wt%, acetonitrile: 53.08%, and water: 11.15wt%.

[0056] The ethanol-rich pressurized distillate at the top of the pressurized tower is composed of acetone: 1.82wt%, methanol: 0.36wt%, ethanol: 65.32wt%, acetonitrile: 25.42%, water: 7.08wt%, and the acetonitrile loss is 0.3891. The pressurized residue in the kettle of the pressurized tower is composed of 0.17wt% ethanol and 84.10wt% acetonitrile. The other components are only water, which is returned to the butadiene extraction unit for reuse.

[0057] The removal of organic light components such as ethanol is done once a year, with a removal cycle of 14 to 21 days.

[0058] After the light components such as ethanol and acetone in the water-containing organic wastewater are removed, the light component impurities such as alcohols and ketones in the circulating solvent acetonitrile are indirectly reduced from 2.11wt% to 0.98wt%, meeting the technical index requirements of the butadiene extraction process for extracting the circulating solvent acetonitrile.

[0059] Example 3

[0060] The second phase of a 200,000 tons / year acetonitrile-based 1,3-butadiene extraction unit, with an initial acetonitrile solvent load of 800 tons, had a circulating solvent composition of 2.34wt% light component impurities such as ethanol and acetone, 91.11wt% acetonitrile, 6.27wt% water, and 0.28wt% heavy component impurities such as dimers and acetic acid. The organic wastewater in the water bag was composed of 0.04wt% acetone, 0.01wt% methanol, 1.85wt% ethanol, 2.74% acetonitrile, and 95.39wt% water.

[0061] A 1t / h stream of organic wastewater is drawn out for light separation.

[0062] The number of plates of the atmospheric tower is 25, the feed is on the 19th plate, the feed temperature is 45°C, the tower top temperature is 73.0°C, the tower bottom temperature is 100.2°C, and the reflux ratio is 14;

[0063] The number of plates of the pressurized tower is 40, the feed is fed to the 20th plate, the feed temperature is 45°C, the tower top temperature is 120.6°C, the tower bottom temperature is 130.7°C, the reflux ratio is 15, and the tower top pressure is 0.35MPaG;

[0064] The composition of the atmospheric tower overhead distillate: acetone: 0.79wt%, methanol: 0.20wt%, ethanol: 36.30wt%, acetonitrile: 54.04%, water: 8.67wt%.

[0065] The ethanol-rich pressurized distillate at the top of the pressurized tower is composed of acetone: 1.44wt%, methanol: 0.36wt%, ethanol: 66.39wt%, acetonitrile: 23.24%, water: 8.57wt%, and the acetonitrile loss is 0.3501. The pressurized residue in the kettle of the pressurized tower is composed of 0.10wt% ethanol, 91.11wt% acetonitrile, and the other components are only water, which is returned to the butadiene extraction unit for reuse.

[0066] The removal of organic light components such as ethanol is done once a year, with a removal cycle of 21 to 26 days.

[0067] After the light components such as ethanol and acetone in the water-included organic wastewater are removed, the light component impurities such as alcohols and ketones in the circulating solvent acetonitrile are indirectly reduced from 2.34wt% to 0.95wt%, meeting the technical index requirements of the butadiene extraction process for extracting the circulating solvent acetonitrile.

[0068] For ease of explanation, relational terms such as “first” and “second” and the like are merely used to distinguish one component from another having the same name, but do not necessarily require or imply any such actual relationship or order between these components.

[0069] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. An online purification method for industrial acetonitrile, characterized in that: The following steps are involved: Step 1: atmospheric distillation; The organic wastewater from the butadiene extraction unit enters the lower part of the atmospheric pressure tower. The atmospheric pressure tower has a theoretical plate number of 20 to 40, a bottom temperature of 85 to 130° C., and a reflux ratio of 2 to 20; Atmospheric pressure distillate is taken from the top of the tower, and atmospheric pressure residue is taken from the bottom of the tower; The organic wastewater from the butadiene extraction device contains 0.7-9wt% acetonitrile, 0.10-3wt% light components, and the rest is water. The light component includes at least one of acetone, methanol and ethanol; Step 2: Pressure distillation The atmospheric distillate from step 1 enters the middle part of the pressure tower for pressure distillation; The theoretical plate number of the pressure tower is 30 to 50, the bottom temperature is 90 to 150°C, the top pressure is 0.2 to 0.5 MPaG (gauge pressure), and the reflux ratio is 10 to 30; The pressurized distillate is taken out from the top of the tower, and the pressurized residue is taken out from the bottom of the tower; The ethanol content in the pressurized distillate is 60-69 wt %; the acetonitrile content is less than 28 wt %; The pressurized residue is purified industrial acetonitrile, wherein the acetonitrile content is ≥80wt%.

2. The method for online purification of industrial acetonitrile according to claim 1, characterized in that: The organic wastewater from the butadiene extraction device includes the sedimentation water in the water bag of the first extraction tower reflux tank, the sedimentation water in the water bag of the second extraction tower reflux tank, the raffinate water washing tower kettle water, the butadiene water washing tower kettle water, and the alkyne water washing tower kettle water; The atmospheric distillate includes: acetone, methanol, ethanol, acetonitrile and other oxygen-containing organic matter and water; The water content of the atmospheric pressure residue is ≥99.9wt%, and the organic matter content is ≤0.1wt%; wherein the organic matter comprises at least one of ethanol and acetonitrile.

3. The online purification method for industrial acetonitrile according to claim 1, characterized in that: Step 1: atmospheric distillation: the atmospheric tower is fed at the position of 15 to 30 theoretical plates; Step 1: atmospheric distillation: the light components include at least acetone, methanol and ethanol.

4. The online purification method for industrial acetonitrile according to claim 1, characterized in that: Step 2: pressure distillation: the pressure tower is fed at a position where the theoretical plate number is 15 to 25; The pressurized residue is purified industrial acetonitrile; The ethanol content is ≤0.2wt%, and the water content is ≤17.8wt%.

5. The method for online purification of industrial acetonitrile according to claim 1, characterized in that: The normal pressure residue is discharged into the sewage pool of the device; the pressurized residue is industrial acetonitrile which is recycled to the production process after purification.

6. The method for online purification of industrial acetonitrile according to claim 1, characterized in that: Step 1: atmospheric distillation: the atmospheric tower has a theoretical plate number of 25 to 35, a bottom temperature of 95 to 110° C., a reflux ratio of 3 to 15, and feed at a theoretical plate number of 18 to 26; Step 2: pressure distillation: the atmospheric pressure tower has a theoretical plate number of 35 to 45, a bottom temperature of 100 to 135° C., a reflux ratio of 10 to 23, and feed at the position of 17 to 23 theoretical plates.

7. An industrial acetonitrile online purification device, characterized in that: include: Atmospheric tower and pressure tower; The middle and lower part of the atmospheric tower body is provided with an atmospheric tower feed port, the top of the tower is provided with an atmospheric tower top discharge port, and the tower bottom is provided with an atmospheric tower bottom discharge port; The pressurized tower body is provided with a pressurized tower feed port in the middle, a pressurized tower top discharge port is provided at the tower top, and a pressurized tower bottom discharge port is provided at the tower bottom; The top discharge port of the atmospheric tower is connected with the feed port of the pressure tower through a pipeline.

8. The industrial acetonitrile online purification device according to claim 7, characterized in that: The industrial acetonitrile online purification device also includes: a light component tank; a top discharge port of the pressure tower is connected with the light component tank through a pipeline.

9. The industrial acetonitrile online purification device according to claim 7, characterized in that: A reflux pump for the atmospheric tower is arranged on the pipeline connecting the atmospheric tower top outlet and the pressure tower feed port, and the atmospheric tower reflux pump outlet is respectively connected to the pressure tower feed port and the atmospheric tower top reflux port.

10. The industrial acetonitrile online purification device according to claim 7, characterized in that: A pressurizing tower reflux pump is arranged on the pipeline connected to the discharge port at the top of the pressurizing tower, and the outlet of the pressurizing tower reflux pump is respectively connected to the light component tank and the reflux port at the top of the pressurizing tower.

Images