Solvent regeneration method for extracting 1, 3-butadiene by acetonitrile method

Abstract

The invention discloses a solvent regeneration method for extracting 1, 3-butadiene by an acetonitrile method, which comprises the following steps: leading out acetonitrile extracted in a 1, 3-butadiene extraction process from a circulating system, feeding into a solvent adsorption unit for adsorption, preheating, feeding into a solvent rectifying tower to remove residual impurities, and obtaining regenerated acetonitrile from a tower kettle. According to the method disclosed by the invention, different types of impurities in the circulating acetonitrile solvent can be effectively removed in a mode of combining adsorption and azeotropic distillation, so that the total amount of the impurities in the refined acetonitrile solvent is as low as 10ppm or below, the metal ions are controlled to be 1ppm or below, and the loss amount of acetonitrile is controlled to be 1wt.% or below. According to the method, intermittent or continuous flexible operation can be realized, and the operation period of a butadiene device is greatly prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of ethylene cracking C4 fraction separation, and specifically relates to a solvent regeneration method for extracting 1,3-butadiene by an acetonitrile method. Background Art

[0002] Butadiene extraction uses mixed C4 as raw material. Because the mixed C4 component contains many components with similar relative volatility to 1,3-butadiene, and may form azeotropes at the same time, it is impossible to separate them using ordinary distillation methods. At present, the combination of extractive distillation and ordinary distillation is widely used in industry to obtain high-purity 1,3-butadiene. The acetonitrile method 1,3-butadiene extraction process uses acetonitrile as an extractant to separate butadiene from the C4 component, and then obtains high-purity 1,3-butadiene through a series of processes such as water washing and distillation. In this process, the acetonitrile solvent is in a continuous circulation process. Due to various reasons such as self-hydrolysis, azeotropy and external additives, heavy components such as oxygen-containing compounds such as alcohols, aldehydes, acids, ethers, dimers, and polymers continue to accumulate, which will affect the extraction and separation effect of the acetonitrile solvent and accelerate the polymerization rate of butadiene. In addition, in order to prevent the polymerization of butadiene, most production units add inhibitors in the extraction process, which further increases the types and contents of impurities in the acetonitrile solvent, resulting in a significant reduction in the service life of the acetonitrile solvent. Therefore, regenerating and refining the circulating acetonitrile solvent can greatly extend the operating cycle of the device without affecting the operation of the extraction device.

[0003] In the existing process, the circulating acetonitrile solvent can remove heavy components such as some dimers in the alkyne water scrubber, but its removal effect is very limited, and there is no way to effectively remove oxygen-containing compound impurities such as alcohol, aldehyde, acid and ether in the solvent, and these trace impurities will promote the polymerization of butadiene during the extraction and distillation process, thereby causing the tower plate or heat exchanger to be blocked, and the separation efficiency is reduced. In order to avoid the continuous accumulation of these impurities in the solvent, the waste acetonitrile solvent must be continuously extracted from the system, and fresh acetonitrile is added to the system to maintain the extraction and separation effect. But the supplementary acetonitrile is not only expensive, but also a difficult problem to handle the waste acetonitrile solvent. Therefore, how to refine the waste acetonitrile solvent and reuse it is a difficult point in current research.

[0004] Patent CN 116217434A provides a regeneration method for 1,3-butadiene extraction process using acetonitrile, which uses a light removal tower and a heavy removal tower to regenerate and purify the circulating acetonitrile, that is, a stream of the extracted circulating solvent is sent to the middle of the light removal tower, an azeotrope containing organic matter is obtained at the top of the tower, and light-removed acetonitrile is obtained in the bottom of the tower; the acetonitrile solvent after light removal is then sent to the middle of the heavy removal tower, and heavy components such as dimers are removed in the heavy removal tower, and regenerated acetonitrile is obtained from the top of the heavy removal tower. However, its operating cost and construction cost are high, and due to the azeotropic reaction of acetonitrile with some impurities in the solvent, the impurities cannot be removed to a low level.

[0005] Patent CN 113528197A discloses a method for recovering hydrocarbons and acetonitrile using an acetonitrile-based butadiene extraction device, in which dimers in the acetonitrile solvent are removed by washing with tower water. However, due to the large difference in polarity between the dimer and water, the removal effect is limited, and water and acetonitrile easily form azeotropes, which is not conducive to controlling the water content in the waste acetonitrile solvent, thereby increasing the loss of acetonitrile. The removal effect of other oxygen-containing organic impurities is also unknown. Summary of the invention

[0006] In order to deal with the harm of various trace impurities in the waste acetonitrile solvent to the butadiene extraction device, it is necessary to use a combination of multiple processes to remove the impurity content in the waste acetonitrile solvent to a lower level as much as possible, so as to extend the operation cycle of the device to the greatest extent and improve production efficiency. To this end, the present invention provides a solvent regeneration method for extracting 1,3-butadiene by acetonitrile method, which uses a combined adsorption and distillation process to remove light components such as alcohols, acids, organic matter and heavy components such as dimers and polymers in the circulating acetonitrile, and the regeneration effect is obvious.

[0007] To achieve the above object, the present invention adopts the following technical solution: A solvent regeneration method for extracting 1,3-butadiene by acetonitrile method, comprising the following steps: 1) The recycled acetonitrile extracted in the 1,3-butadiene extraction process is sent to the solvent adsorption unit for adsorption; 2) The adsorbed acetonitrile is preheated in a raw material heat exchanger and then transported to the middle section of a solvent distillation tower; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The acetonitrile solvent obtained from the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material preheating heat exchanger and the temperature is reduced.

[0008] Furthermore, in step 1), at least one of ion exchange resin, non-ionic resin, molecular sieve and activated carbon is used as an adsorbent in the solvent adsorption unit.

[0009] Furthermore, the ion exchange resin includes at least one of a weakly acidic anion exchange resin, a weakly acidic cation exchange resin and a weakly basic cation exchange resin, preferably a weakly acidic cation exchange resin and a weakly basic cation exchange resin.

[0010] Furthermore, the non-ionic resin includes at least one of polystyrene resin, polyacrylic acid resin and polyacrylamide resin, preferably polystyrene resin and polyacrylic acid resin.

[0011] Furthermore, the molecular sieve includes one or more of microporous molecular sieve, mesoporous molecular sieve and macroporous molecular sieve, preferably mesoporous molecular sieve and macroporous molecular sieve.

[0012] Furthermore, the activated carbon comprises at least one of various types of coal-based, bamboo-based and coconut shell-based activated carbons, with a particle size of 0.2-2 mm and a specific surface area greater than 500 m 2 / g.

[0013] Furthermore, the bed height of activated carbon in the solvent adsorption unit is 0.5 m, and the bed height of the remaining adsorbents is 1 m.

[0014] Furthermore, in step 1), the temperature of the solvent adsorption unit is -20-100°C, the pressure is 0.01-0.5 MPaG, and the mass space velocity of the circulating acetonitrile is 0.00001-1000h -1 .

[0015] Furthermore, in step 2), the outlet temperature after preheating in the raw material heat exchanger is 50-100°C, and the outlet pressure is 0.01-1 MPaG.

[0016] Furthermore, in step 2), the number of plates of the solvent distillation tower is 10-80, preferably 20-75, the bottom temperature is 50-200° C., the top pressure is 0.01-0.8 MPaG, and the reflux ratio is 2-40.

[0017] Furthermore, in step 4), the impurity content of the acetonitrile obtained from the bottom of the tower is as low as below 10 ppm, the metal ion content is below 1 ppm, and the total acetonitrile loss is below 1 wt.%.

[0018] The beneficial effects of the present invention are as follows: The present invention firstly uses an adsorption unit to pretreat the circulating acetonitrile in the 1,3-butadiene extraction process, so that impurities, metal ions and heavy component impurities that are easy to form azeotropy with acetonitrile are adsorbed, and then the remaining impurities in the circulating acetonitrile are removed by distillation, so that the impurity content in the regenerated acetonitrile is lower than 10 ppm (except water), the metal ions are controlled below 1 ppm, the acetonitrile loss is below 1 wt.%, and the regeneration effect is obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic flow diagram of the solvent regeneration method adopted in the present invention. DETAILED DESCRIPTION

[0020] A solvent regeneration method for extracting 1,3-butadiene by acetonitrile method, comprising the following steps: 1) The recycled acetonitrile extracted from the 1,3-butadiene extraction process is sent to the solvent adsorption unit for adsorption at -20-100°C and pressure 0.01-0.5 MPaG. The mass space velocity of the recycled acetonitrile is 0.00001-1000h -1 ; 2) The adsorbed acetonitrile is sent to the raw material heat exchanger for preheating and then sent to the middle section of the solvent distillation tower; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The acetonitrile obtained in the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material preheating heat exchanger and the temperature is reduced.

[0021] Wherein, the acetonitrile content in the circulating acetonitrile in step 1) is 75-95 wt.%, the light component impurity content is 1-5 wt.%, and the heavy component impurity content is 0.1-2 wt.%. The rest is water. The light component impurities include some C4 components and oxygen-containing compounds such as alcohols, aldehydes, ketones, acids, and ethers, and the heavy component impurities include butadiene dimers and polymers such as toluene and 4-vinylcyclohexene.

[0022] Step 1) The solvent adsorption unit uses at least one of ion exchange resin, non-ionic resin, molecular sieve, and activated carbon as an adsorbent. The ion exchange resin includes at least one of weakly acidic anion exchange resin, weakly acidic cation exchange resin, and weakly basic cation exchange resin. The non-ionic resin includes at least one of polystyrene resin, polyacrylic acid resin, and polyacrylamide resin. The molecular sieve includes one or more of microporous molecular sieve, mesoporous molecular sieve, and macroporous molecular sieve. The activated carbon includes at least one of various types of coal-based, bamboo-based, and coconut shell-based activated carbons, with a particle size of 0.2-2 mm and a specific surface area greater than 500 m 2 / g.

[0023] Step 2) The outlet temperature after preheating in the raw material heat exchanger is 50-100°C, and the outlet pressure is 0.01-1 MPaG. The number of plates of the solvent distillation tower is 10-80, the bottom temperature is 50-200°C, the top pressure is 0.01-0.8 MPaG, and the reflux ratio is 2-40.

[0024] Step 4) The impurity content of acetonitrile obtained from the bottom of the tower is as low as below 10 ppm, the metal ion content is below 1 ppm, and the total acetonitrile loss is below 1 wt.%.

[0025] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0026] The composition of the circulating solvent used in the embodiment is: acetonitrile 91 wt.%, impurity content 9 wt.%, including methanol 0.01 wt.%, ethanol 1.5 wt.%, acetone 0.02 wt.%, water 6.82 wt.%, vinyl acetylene 0.01 wt.%, toluene 0.25 wt.%, 4-vinylcyclohexene 0.2 wt.%, ethyl acetate 0.01 wt.%, 1,4,7,10-cyclododecaene 0.08 wt.%, 4-phenyl-1-cyclohexene 0.1 wt.%, and about 180 ppm of metal impurities, which comes from a 130,000 tons / year acetonitrile method 1,3-butadiene extraction plant that has been in continuous operation for four years.

[0027] Embodiment 1: The circulating solvent is regenerated in an intermittent manner, and the operation is as follows: 1) The circulating solvent is sent to the solvent adsorption unit for adsorption; the solvent adsorption unit is composed of ion exchange resin (weakly basic styrene series, mass exchange capacity of 4.0mmol / g, water content of 40%, specific surface area of ​​800m 2 / g), non-ionic resin (acrylic acid, specific surface area 600m 2 / g), molecular sieve (specific surface area 780m 2 / g) and coconut shell activated carbon (specific surface area 900m 2 / g) as adsorbents in series, where the activated carbon bed height is 0.5m, the other adsorbents bed height is 1m, the adsorption temperature is 15℃, the adsorption pressure is 0.3MPaG, and the mass space velocity is 1h -1 ; The eluate after adsorption contained 91.79 wt.% of acetonitrile and 8.21 wt.% of impurities and 0.8 ppm of metal ions; 2) The eluate after adsorption is sent to the raw material heat exchanger for preheating to 70°C and then sent to the middle section of the solvent distillation tower; the solvent distillation tower has 60 plates, 25 feed plates, a bottom temperature of 105°C, a top pressure of 0.3MPaG, and a reflux ratio of 30; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The solvent obtained from the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material heat exchanger and the temperature is reduced.

[0028] The composition of the regenerated solvent obtained from the bottom of the tower is 93.58 wt.% of acetonitrile, 6.41 wt.% of water, and the content of other impurities is 7.8 ppm, of which the content of metal ions is 0.9 ppm; the loss of acetonitrile is 41.25 kg / h, and the loss rate is 0.91%.

[0029] Embodiment 2: The circulating solvent is regenerated in an intermittent manner, and the operation is as follows: 1) The circulating solvent is sent to the solvent adsorption unit for adsorption; the solvent adsorption unit is composed of molecular sieves (specific surface area 780m 2 / g), non-ionic resin (acrylic acid, specific surface area 600m 2 / g), ion exchange resin (weakly alkaline styrene series, mass exchange capacity of 4.0mmol / g, water content of 40%, specific surface area of ​​800m 2 / g) and coconut shell activated carbon (specific surface area 900m 2 / g) as adsorbents in series, where the activated carbon bed has a layer height of 0.5m, the other adsorbents have a bed height of 1m, the adsorption temperature is 15°C, the adsorption pressure is 0.3MPaG, and the mass space velocity is 1h -1 ; The eluate after adsorption contained 91.32 wt.% of acetonitrile and 8.68 wt.% of impurities and 5.4 ppm of metal ions; 2) The eluate after adsorption is sent to the raw material heat exchanger for preheating to 70°C and then sent to the middle section of the solvent distillation tower; the solvent distillation tower has 50 plates, 20 feed plates, a bottom temperature of 120°C, a top pressure of 0.2MPaG, and a reflux ratio of 22; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The solvent obtained from the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material heat exchanger and the temperature is reduced.

[0030] The composition of the regenerated solvent obtained from the bottom of the tower is 92.88 wt.% of acetonitrile, 7.08 wt.% of water, and the content of other impurities is 425 ppm, of which the content of metal ions is 22 ppm; the loss of acetonitrile is 92.82 kg / h, and the loss rate is 2.04%.

[0031] Embodiment 3: The circulating solvent is regenerated in an intermittent manner, and the operation is as follows: 1) The circulating solvent is sent to the solvent adsorption unit for adsorption; the solvent adsorption unit is composed of ion exchange resin (weakly basic styrene series, mass exchange capacity of 4.0mmol / g, water content of 40%, specific surface area of ​​800m 2 / g), molecular sieve (specific surface area 780m 2 / g) and coconut shell activated carbon (specific surface area 900m 2 / g) as adsorbents in series, where the activated carbon bed has a layer height of 0.5m, the other adsorbents have a bed height of 1m, the adsorption temperature is 15°C, the adsorption pressure is 0.3MPaG, and the mass space velocity is 1h -1 ; The eluate after adsorption contained 91.55 wt.% of acetonitrile, 8.45 wt.% of impurities, and 15.2 ppm of metal ions; 2) The eluate after adsorption is sent to the raw material heat exchanger for preheating to 70°C and then sent to the middle section of the solvent distillation tower; the solvent distillation tower has 50 plates, 20 feed plates, a bottom temperature of 120°C, a top pressure of 0.2MPaG, and a reflux ratio of 22; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The solvent obtained from the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material heat exchanger and the temperature is reduced.

[0032] The composition of the regenerated solvent obtained from the bottom of the tower is 91.86 wt.% of acetonitrile, 8.07 wt.% of water, and 642 ppm of other impurities, including 108 ppm of metal ions; the acetonitrile loss is 150.24 kg / h, and the loss rate is 3.30%.

[0033] Embodiment 4: The circulating solvent is regenerated in an intermittent manner, and the operation is as follows: 1) The circulating solvent is sent to the solvent adsorption unit for adsorption; the solvent adsorption unit is composed of ion exchange resin (weakly basic styrene series, mass exchange capacity of 4.0mmol / g, water content of 40%, specific surface area of ​​800m 2 / g), non-ionic resin (acrylic acid, specific surface area 600m 2 / g), coconut shell activated carbon (specific surface area 900m 2 / g) and molecular sieve (specific surface area 780m 2 / g) as adsorbents in series, where the activated carbon bed has a layer height of 0.5m, the other adsorbents have a bed height of 1m, the adsorption temperature is 15°C, the adsorption pressure is 0.3MPaG, and the mass space velocity is 1h -1; The eluate after adsorption contained 91.22 wt.% of acetonitrile, 8.73 wt.% of impurities, and 1 ppm of metal ions; 2) The eluate after adsorption is sent to the raw material heat exchanger for preheating to 70°C and then sent to the middle section of the solvent distillation tower; the solvent distillation tower has 50 plates, 20 feed plates, a bottom temperature of 120°C, a top pressure of 0.2MPaG, and a reflux ratio of 22; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, and then a part of it is returned to the solvent distillation tower as liquid phase reflux, and the other part is used for backwashing of the adsorption unit; 4) The solvent obtained from the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material heat exchanger and the temperature is reduced.

[0034] The composition of the regenerated solvent obtained from the bottom of the tower is 91.76 wt.% of acetonitrile, 8.16 wt.% of water, and the remaining impurities are 752 ppm, of which the metal ion content is 8 ppm; the acetonitrile loss is 237.06 kg / h, and the loss rate is 5.21%.

[0035] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A solvent regeneration method for extracting 1,3-butadiene by acetonitrile method, characterized in that: The following steps are involved: 1) The recycled acetonitrile extracted in the 1,3-butadiene extraction process is sent to the solvent adsorption unit for adsorption; 2) The adsorbed acetonitrile is preheated in a raw material heat exchanger and then transported to the middle section of a solvent distillation tower; 3) The liquid obtained by condensation at the top of the tower is collected in the top reflux tank, part of which is returned to the solvent distillation tower as liquid reflux, and the other part is used for backwashing of the adsorption unit; 4) The acetonitrile obtained in the bottom of the tower is sent into the circulation system for recycling after the heat is recovered through the raw material heat exchanger and the temperature is reduced.

2. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 1, characterized in that: Step 1) The solvent adsorption unit uses at least one of ion exchange resin, non-ionic resin, molecular sieve and activated carbon as an adsorbent.

3. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 2, characterized in that: The ion exchange resin includes at least one of a weakly acidic anion exchange resin, a weakly acidic cation exchange resin and a weakly basic cation exchange resin.

4. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 2, characterized in that: The nonionic resin includes at least one of polystyrene resin, polyacrylic acid resin and polyacrylamide resin.

5. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 2, characterized in that: The molecular sieve includes one or more of microporous molecular sieve, mesoporous molecular sieve and macroporous molecular sieve.

6. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 2, characterized in that: The activated carbon comprises at least one of various types of coal-based, bamboo-based and coconut shell-based activated carbons, and has a particle size of 0.2-2 mm and a specific surface area of ​​more than 500 m 2 / g.

7. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 1, characterized in that: Step 1) The temperature of the solvent adsorption unit is -20-100°C, the pressure is 0.01-0.5 MPaG, and the mass space velocity of the circulating acetonitrile is 0.00001-1000h -1 .

8. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 1, characterized in that: Step 2) The outlet temperature after preheating in the raw material heat exchanger is 50-100°C, and the outlet pressure is 0.01-1MPaG.

9. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 1, characterized in that: The number of plates of the solvent distillation tower in step 2) is 10-80, the bottom temperature is 50-200° C., the top pressure is 0.01-0.8 MPaG, and the reflux ratio is 2-40.

10. The solvent regeneration method for extracting 1,3-butadiene by acetonitrile method according to claim 1, characterized in that: Step 4) The impurity content of the acetonitrile solvent obtained from the bottom of the tower is as low as below 10 ppm, the metal ion content is below 1 ppm, and the total acetonitrile loss is below 1 wt.%.

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