Continuous production method of isobutyric anhydride

Abstract

The invention relates to the technical field of separation and purification, and discloses a continuous production method of isobutyric anhydride, which is used for continuously producing isobutyric anhydride by combining a rectifying tower I, a rectifying tower II, a rectifying tower III and a rectifying tower IV. According to the method, the problems that the conversion rate of acetic acid-isobutyric anhydride is low and the purity of an isobutyric anhydride product accumulated at the bottom of a single rectifying tower is obviously reduced under the condition that an isobutyric acid raw material and an acetic anhydride raw material are fed at a large flow rate in the single rectifying tower are solved; and the accumulated acetic acid-isobutyric anhydride is further converted into the isobutyric anhydride and the acetic acid by supplementing the isobutyric anhydride into the rectifying tower II, so that the conversion rate of the acetic acid-isobutyric acid is remarkably improved, and the purity of an isobutyric anhydride product is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, in particular to a method for continuously producing isobutyric anhydride. Background Art

[0002] Isobutyric anhydride is an important derivative of isobutyric acid, mainly used for the synthesis of isobutyric ester plasticizers, flavors, fragrances and pharmaceutical intermediates. Limited by the small market demand in its application field, the domestic isobutyric anhydride production capacity has been maintained at a low level for a long time, and the industry is mainly intermittent production. However, with the development of the high performance trend of polyester, the demand for high-end monomers continues to increase. As the main raw material for the synthesis of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, the market demand for isobutyric anhydride will increase rapidly with the expansion of production scale; however, the existing intermittent production process has the problems of difficult operation, low product purity, unstable quality, high energy consumption and material consumption, which cannot meet the production demand of isobutyric anhydride; therefore, it is urgent to develop a continuous production process of isobutyric anhydride to improve the production efficiency and capacity of isobutyric anhydride and meet the industrial amplification needs of downstream products.

[0003] The reaction of isobutyric acid and acetic anhydride to synthesize isobutyric anhydride is carried out in two steps, namely, isobutyric acid and acetic anhydride react to generate acetic acid-isobutyric anhydride and acetic acid, and then acetic acid-isobutyric anhydride reacts with isobutyric acid to generate isobutyric anhydride and acetic acid. Both steps are endothermic reactions and are limited by chemical equilibrium. The generated acetic acid and isobutyric anhydride need to be separated in time to improve the yield of isobutyric anhydride. In the prior art, a single reactor is used for isobutyric anhydride production, such as the technical solutions disclosed in CN112047834A, US2026985, US7049467B2 and US2005001497A1. The present application finds that as the feed amount of isobutyric acid and acetic anhydride increases, insufficient liquid holdup will occur, resulting in a decrease in the conversion rate of the raw material isobutyric acid and acetic anhydride, and the purity of the bottom / top product of the tower is reduced and does not meet the standard. This makes the single reactor unable to be applied to the expanded production. Summary of the invention

[0004] In order to overcome the problem that the conversion rate of isobutyric acid and acetic acid decreases and the purity of the product does not meet the standard when isobutyric anhydride is produced in a single reactor in the prior art as the amount of raw materials increases, the present invention provides a method for continuously producing isobutyric anhydride, wherein isobutyric anhydride is continuously produced by combining a first distillation tower, a second distillation tower, a third distillation tower and a fourth distillation tower. The method solves the problem that the conversion rate of acetic acid-isobutyric anhydride is low when the isobutyric acid raw material and the acetic anhydride raw material are fed at a large flow rate in a single distillation tower, and the isobutyric anhydride product purity is significantly reduced due to accumulation at the bottom of the tower. The acetic acid-isobutyric anhydride accumulated in the first distillation tower is transferred to the second distillation tower, and isobutyric anhydride is added to the second distillation tower to further convert the accumulated acetic acid-isobutyric anhydride into isobutyric anhydride and acetic acid, thereby significantly improving the conversion rate of acetic acid-isobutyric acid and significantly improving the purity of the isobutyric anhydride product.

[0005] The specific technical scheme of the present invention is: A method for continuously producing isobutyric anhydride comprises the following steps: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material respectively and feeding them into a distillation tower to react and obtain a light component in a tower and a heavy component in a tower; Step 2: The heavy components in tower 1 enter into distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components in tower 2, wherein the conversion-promoting reaction includes adding isobutyric acid and increasing the temperature; Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3; Step 4: The heavy components from tower three enter into distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four.

[0006] The invention provides a method for continuously producing isobutyric anhydride. The method adopts a multi-tower combination to continuously produce isobutyric anhydride from isobutyric acid raw materials and acetic anhydride raw materials. Compared with a single reactor, the method can significantly improve the yield and purity of isobutyric anhydride when isobutyric anhydride is produced from a large flow of isobutyric anhydride raw materials and acetic anhydride raw materials. Since the relative volatility of the isobutyric acid raw materials and the acetic anhydride raw materials is different and the feeding position of isobutyric acid is located above the acetic anhydride, after the isobutyric anhydride raw materials and the acetic anhydride raw materials enter the distillation tower, the isobutyric anhydride raw materials flow downwards and countercurrently contact with the acetic anhydride raw materials to generate isobutyric anhydride. In the first step, butyric anhydride and acetic anhydride react to generate acetic acid and acetic acid-isobutyric anhydride. In the second step, the isobutyric acid raw material reacts with acetic acid-isobutyric anhydride to generate isobutyric anhydride and acetic acid. Acetic acid is evaporated from the top of the tower. Since the first reaction is faster than the second reaction, the conversion rate of the first reaction decreases less with the increase of feed flow rate, while the conversion rate of the second reaction decreases significantly. The decrease in the conversion rate of the second reaction makes it impossible for the reactants to complete the reaction and distillation separation in the packing section. The site of the reaction distillation is transferred from the packing section to the bottom of the tower, resulting in a decrease in the purity of isobutyric anhydride in the bottom of the tower.

[0007] The present invention continuously produces isobutyric anhydride by combining a distillation tower 1, a distillation tower 2, a distillation tower 3 and a distillation tower 4. The present invention adds isobutyric acid raw material and acetic anhydride raw material into the distillation tower 1, and controls the feeding positions of the isobutyric acid raw material and the acetic anhydride raw material to suppress the problem that the conversion rate of the second reaction decreases too quickly. Then, the heavy components of the first tower (isobutyric anhydride, acetic acid-isobutyric anhydride and part of the unreacted isobutyric acid) prepared in the distillation tower 1 are transferred to the distillation tower 2 and the isobutyric anhydride is added. The acid significantly improves the purity of the final isobutyric acid product (heavy components in tower two). The light components in tower one and tower two are merged and enter into distillation tower three to purify acetic acid. Then the heavy components in tower three (isobutyric acid, acetic anhydride and acetic acid-isobutyric anhydride) enter into distillation tower four to separate isobutyric acid by distillation. The separated and recovered isobutyric acid can be reused as raw material in distillation tower one and distillation tower two, which significantly improves the utilization rate of raw materials in each stage and improves the purity and conversion rate of isobutyric anhydride product.

[0008] Preferably, the molar ratio of the additional isobutyric acid to the heavy components in the tower is 0 to 0.5.

[0009] Preferably, the difference between the feed position of isobutyric acid and the feed position of acetic anhydride is ≥ 3 theoretical plates, and the feed position of isobutyric acid is located above the feed position of acetic anhydride.

[0010] Preferably, the molar ratio of isobutyric acid to acetic acid is 1.0 to 2.2.

[0011] Preferably, the temperature of the feed is 25-155°C.

[0012] Preferably, the reaction pressure of the distillation tower 1 is 0.2-1.2 atm.

[0013] Preferably, the reaction pressure of the second distillation tower is 0.2-1.2 atm.

[0014] Preferably, the reaction pressure of the distillation tower three is 0.2-1.0 atm.

[0015] Preferably, the reaction pressure of the distillation tower 4 is 0.2-1.4 atm.

[0016] Preferably, the refined isobutyric acid and the isobutyric acid raw material are fed into a distillation tower.

[0017] Preferably, the crude acetic acid product enters an acetic acid refining unit to be refined to obtain an acetic acid product.

[0018] Preferably, the quartet of components in the tower enters an isobutyric anhydride distillation device to produce isobutyric anhydride.

[0019] Compared with the prior art, this application has the following technical effects: The invention continuously produces isobutyric anhydride by combining a first distillation tower, a second distillation tower, a third distillation tower and a fourth distillation tower. The method solves the problem that when a single distillation tower is fed with isobutyric acid raw materials and acetic anhydride raw materials at a large flow rate, the conversion rate of acetic acid-isobutyric anhydride is low and the purity of the isobutyric anhydride product is significantly reduced. The acetic acid-isobutyric anhydride accumulated in the first distillation tower is transferred to the second distillation tower, and isobutyric anhydride is added to the second distillation tower to further convert the accumulated acetic acid-isobutyric anhydride into isobutyric anhydride and acetic acid, thereby significantly improving the conversion rate of acetic acid-isobutyric acid and significantly improving the purity of the isobutyric anhydride product. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the embodiments.

[0021] Embodiment 1: A method for continuously producing isobutyric anhydride comprises the following steps: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material with a molar ratio of 2:1 respectively, feeding the isobutyric acid raw material into the distillation tower 1 at a feed rate of 18.6 g / min, a feed temperature of 71°C and a feed position of the 16th theoretical stage, feeding the acetic anhydride raw material into the distillation tower 1 at a feed rate of 10.8 g / min, a feed temperature of 71°C and a feed position of the 18th theoretical stage, the total theoretical stage of the distillation tower 1 is 38 stages, the distillation tower 1 includes a tower body 1, a tower body 2 and a tower body 3, the wall insulation temperature of the tower body 1 is 180°C, the wall insulation temperature of the tower body 2 is 145°C, the wall insulation temperature of the tower body 3 is 120°C, and the reaction pressure of the distillation tower 1 is 1.0 atm; Step 2: The heavy component of tower 1 is transported to reactive distillation tower 2 through a feed pump. The feed position of the heavy component of tower 1 is the 16th theoretical stage of distillation tower 2. The heavy component of tower 1 enters distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components of tower 2. The conversion-promoting reaction adopts supplementary isobutyric acid. The flow rate of supplementary isobutyric acid is 7.0 g / min. The position of supplementary isobutyric acid is the 18th theoretical stage of distillation tower 2. The reaction pressure of distillation tower 2 is 1.0 atm. Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3. The crude acetic acid is refined by acetic acid refining unit to obtain acetic acid product. The reaction pressure of distillation tower 3 is 1.0 atm. Step 4: The heavy components from tower three enter distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four. The heavy components from tower four enter the isobutyric anhydride distillation device to obtain isobutyric anhydride. The refined isobutyric acid is mixed with the isobutyric acid raw material and recycled to distillation tower one. The reaction pressure of distillation tower four is 1.0 atm.

[0022] The distillation towers of the distillation tower 1 and the distillation tower 2 used above are composed of a glass tower body, a condenser, a reflux ratio control system, a tower kettle heating system, a control system and a feeding and discharging system. The glass tower body is composed of three glass tower sections with an inner diameter of 50 mm and a height of 800 mm, including tower body 1, tower body 2 and tower body 3 from top to bottom. Tower body 2 is provided with four feed ports, tower body 3 is provided with six feed ports, and glass spring packing is provided in the glass tower body. Tower body 1, tower body 2 and tower body 3 are separated by a polytetrafluoroethylene gasket with a circular hole. A condenser is provided on the top of the tower. The condenser uses The tower steam is cooled by tap water. The reflux ratio control system consists of a fractionating head and a reflux ratio controller. The reflux liquid condensed from the condenser passes through the fractionating head and is refluxed and distributed at the top of the tower at the set reflux ratio under the control of the reflux ratio controller. The tower kettle heating system consists of an electric heating jacket with a heating power of 2.6KW and a maximum heating temperature of 300℃. Electric heating belts and thermal insulation cotton are wrapped around the outside of the tower body for heating and insulation. All heating and insulation temperatures are set by instruments, and the heating voltage or heating temperature can be adjusted manually.

[0023] Embodiment 2: A method for continuously producing isobutyric anhydride comprises the following steps: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material with a molar ratio of 2:1 respectively, feeding the isobutyric acid raw material into the distillation tower 1 at a feed rate of 37.2 g / min, a feed temperature of 71°C and a feed position of the 16th theoretical stage, feeding the acetic anhydride raw material into the distillation tower 1 at a feed rate of 21.6 g / min, a feed temperature of 71°C and a feed position of the 18th theoretical stage, the total theoretical stage of the distillation tower 1 is 38 stages, the distillation tower 1 includes a tower body 1, a tower body 2 and a tower body 3, the wall insulation temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C with wall heating, the wall insulation temperature of the tower body 3 is 120°C, and the reaction pressure of the distillation tower 1 is 1.05 atm; Step 2: The heavy component of tower 1 is transported to reactive distillation tower 2 through a feed pump. The feed position of the heavy component of tower 1 is the 16th theoretical stage of distillation tower 2. The heavy component of tower 1 enters distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components of tower 2. The conversion-promoting reaction is carried out by adding isobutyric acid. The flow rate of adding isobutyric acid is 15.2 g / min. The position of adding isobutyric acid is the 18th theoretical stage of distillation tower 2. The reaction pressure of distillation tower 2 is 1.0 atm. Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3. The crude acetic acid is refined by acetic acid refining unit to obtain acetic acid product. The reaction pressure of distillation tower 3 is 0.90 atm. Step 4: The heavy components from tower three enter distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four. The heavy components from tower four enter the isobutyric anhydride distillation device to obtain isobutyric anhydride. The refined isobutyric acid is mixed with the isobutyric acid raw material and recycled to distillation tower one. The reaction pressure of distillation tower four is 1.1 atm.

[0024] The distillation towers of the distillation tower 1 and the distillation tower 2 used above are composed of a glass tower body, a condenser, a reflux ratio control system, a tower kettle heating system, a control system and a feeding and discharging system. The glass tower body is composed of three glass tower sections with an inner diameter of 50 mm and a height of 800 mm, including tower body 1, tower body 2 and tower body 3 from top to bottom. Tower body 2 is provided with four feed ports, tower body 3 is provided with six feed ports, and glass spring packing is provided in the glass tower body. Tower body 1, tower body 2 and tower body 3 are separated by a polytetrafluoroethylene gasket with a circular hole. A condenser is provided on the top of the tower. The condenser uses The tower steam is cooled by tap water. The reflux ratio control system consists of a fractionating head and a reflux ratio controller. The reflux liquid condensed from the condenser passes through the fractionating head and is refluxed and distributed at the top of the tower at the set reflux ratio under the control of the reflux ratio controller. The tower kettle heating system consists of an electric heating jacket with a heating power of 2.6KW and a maximum heating temperature of 300℃. Electric heating belts and thermal insulation cotton are wrapped around the outside of the tower body for heating and insulation. All heating and insulation temperatures are set by instruments, and the heating voltage or heating temperature can be adjusted manually.

[0025] Embodiment 3: A method for continuously producing isobutyric anhydride comprises the following steps: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material with a molar ratio of 1:1 respectively, feeding the isobutyric acid raw material into the distillation tower 1 at a feed rate of 9.3 g / min, a feed temperature of 71°C and a feed position of the 16th theoretical stage, feeding the acetic anhydride raw material into the distillation tower 1 at a feed rate of 10.8 g / min, a feed temperature of 71°C and a feed position of the 18th theoretical stage, the total theoretical stage of the distillation tower 1 is 38 stages, the distillation tower 1 includes a tower body 1, a tower body 2 and a tower body 3, the wall insulation temperature of the tower body 1 is 180°C, the wall insulation temperature of the tower body 2 is 145°C, the wall insulation temperature of the tower body 3 is 120°C, and the reaction pressure of the distillation tower 1 is 0.1 atm; Step 2: The heavy component of tower 1 is transported to reactive distillation tower 2 through a feed pump. The feeding position of the heavy component of tower 1 is the 16th theoretical stage of distillation tower 2. The heavy component of tower 1 is fed into distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components of tower 2. The conversion-promoting reaction is promoted by adding isobutyric acid. The flow rate of adding isobutyric acid is 16.3 g / min. The position of adding isobutyric acid is the 18th theoretical stage of distillation tower 2. The reaction pressure of distillation tower 2 is 0.1 atm. Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3. The crude acetic acid is refined by acetic acid refining unit to obtain acetic acid product. The reaction pressure of distillation tower 3 is 0.5 atm. Step 4: The heavy components from tower three enter distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four. The heavy components from tower four enter the isobutyric anhydride distillation device to obtain isobutyric anhydride. The refined isobutyric acid is mixed with the isobutyric acid raw material and recycled to distillation tower one. The reaction pressure of distillation tower four is 0.5 atm.

[0026] The distillation towers of the distillation tower 1 and the distillation tower 2 used above are composed of a glass tower body, a condenser, a reflux ratio control system, a tower kettle heating system, a control system and a feeding and discharging system. The glass tower body is composed of three glass tower sections with an inner diameter of 50 mm and a height of 800 mm, including tower body 1, tower body 2 and tower body 3 from top to bottom. Tower body 2 is provided with four feed ports, tower body 3 is provided with six feed ports, and glass spring packing is provided in the glass tower body. Tower body 1, tower body 2 and tower body 3 are separated by a polytetrafluoroethylene gasket with a circular hole. A condenser is provided on the top of the tower. The condenser uses The tower steam is cooled by tap water. The reflux ratio control system consists of a fractionating head and a reflux ratio controller. The reflux liquid condensed from the condenser passes through the fractionating head and is refluxed and distributed at the top of the tower at the set reflux ratio under the control of the reflux ratio controller. The tower kettle heating system consists of an electric heating jacket with a heating power of 2.6KW and a maximum heating temperature of 300℃. Electric heating belts and thermal insulation cotton are wrapped around the outside of the tower body for heating and insulation. All heating and insulation temperatures are set by instruments, and the heating voltage or heating temperature can be adjusted manually.

[0027] Embodiment 4: A method for continuously producing isobutyric anhydride comprises the following steps: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material with a molar ratio of 2.2:1 respectively, feeding the isobutyric acid raw material into the distillation tower 1 at a feed rate of 40.9 g / min, a feed temperature of 71°C and a feed position of the 16th theoretical stage, feeding the acetic anhydride raw material into the distillation tower 1 at a feed rate of 21.6 g / min, a feed temperature of 71°C and a feed position of the 18th theoretical stage, the total theoretical stage of the distillation tower 1 is 38 stages, the distillation tower 1 includes a tower body 1, a tower body 2 and a tower body 3, the wall insulation temperature of the tower body 1 is 180°C, the wall insulation temperature of the tower body 2 is 145°C, the wall insulation temperature of the tower body 3 is 120°C, and the reaction pressure of the distillation tower 1 is 1.2 atm; Step 2: The heavy component of tower 1 is transported to reactive distillation tower 2 through a feed pump. The feeding position of the heavy component of tower 1 is the 16th theoretical stage of distillation tower 2. The heavy component of tower 1 is fed into distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components of tower 2. The conversion-promoting reaction is promoted by adding isobutyric acid. The flow rate of adding isobutyric acid is 15.2 g / min. The position of adding isobutyric acid is the 18th theoretical stage of distillation tower 2. The reaction pressure of distillation tower 2 is 1.2 atm. Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3. The crude acetic acid is refined by acetic acid refining unit to obtain acetic acid product. The reaction pressure of distillation tower 3 is 1.0 atm. Step 4: The heavy components from tower three enter distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four. The heavy components from tower four enter the isobutyric anhydride distillation device to obtain isobutyric anhydride. The refined isobutyric acid is mixed with the isobutyric acid raw material and recycled to distillation tower one. The reaction pressure of distillation tower four is 1.4 atm.

[0028] The distillation towers of the distillation tower 1 and the distillation tower 2 used above are composed of a glass tower body, a condenser, a reflux ratio control system, a tower kettle heating system, a control system and a feeding and discharging system. The glass tower body is composed of three glass tower sections with an inner diameter of 50 mm and a height of 800 mm, including tower body 1, tower body 2 and tower body 3 from top to bottom. Tower body 2 is provided with four feed ports, tower body 3 is provided with six feed ports, and glass spring packing is provided in the glass tower body. Tower body 1, tower body 2 and tower body 3 are separated by a polytetrafluoroethylene gasket with a circular hole. A condenser is provided on the top of the tower. The condenser uses The tower steam is cooled by tap water. The reflux ratio control system consists of a fractionating head and a reflux ratio controller. The reflux liquid condensed from the condenser passes through the fractionating head and is refluxed and distributed at the top of the tower at the set reflux ratio under the control of the reflux ratio controller. The tower kettle heating system consists of an electric heating jacket with a heating power of 2.6KW and a maximum heating temperature of 300℃. Electric heating belts and thermal insulation cotton are wrapped around the outside of the tower body for heating and insulation. All heating and insulation temperatures are set by instruments, and the heating voltage or heating temperature can be adjusted manually.

[0029] Comparative Example 1: Compared with the embodiment, comparative example 1 adopts a conventional single reactor, the feed flow rate of the isobutyric acid raw material changes at 6.2 g / min, the feed flow rate of the acetic anhydride raw material changes at 3.6 g / min, the feed position of the isobutyric acid raw material is at the 16th theoretical stage of the distillation tower, the feed position of the acetic anhydride raw material is at the 18th theoretical stage, the total theoretical stage of the distillation tower is 38 stages, the reflux ratio is 3, the molar ratio of the isobutyric acid raw material to the acetic anhydride raw material is 2:1, and the feed temperature is 71°C. In order to establish a steady state of the system, the extraction flow rates of the tower top and the tower bottom are controlled, and in order to prevent the distillation tower from avoiding heat dissipation and affecting the gas-liquid balance in the tower, the distillation tower is heat-insulated in sections, wherein: the temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C, and the temperature of the tower body 3 is 120°C. The height of the packing of the distillation tower is 2.4m, and the packing type is glass spring.

[0030] Comparative Example 2: Compared with the embodiment, comparative example 2 adopts a conventional single reactor, the feed flow rate of the isobutyric acid raw material changes at 12.4 g / min, the feed flow rate of the acetic anhydride raw material changes at 7.2 g / min, the feed position of the isobutyric acid raw material is at the 16th theoretical stage of the distillation tower, the feed position of the acetic anhydride raw material is at the 18th theoretical stage, the total theoretical stage of the distillation tower is 38 stages, the reflux ratio is 3, the molar ratio of the isobutyric acid raw material to the acetic anhydride raw material is 2:1, and the feed temperature is 71°C. In order to establish a steady state of the system, the extraction flow rates of the tower top and the tower bottom are controlled, and in order to prevent the distillation tower from avoiding heat dissipation and affecting the gas-liquid balance in the tower, the distillation tower is sectioned and insulated, wherein: the temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C, and the temperature of the tower body 3 is 120°C. The height of the packing of the distillation tower is 2.4m, and the packing type is glass spring.

[0031] Comparative Example 3: Compared with the embodiment, comparative example 2 adopts a conventional single reactor, the feed flow rate of the isobutyric acid raw material changes at 18.6 g / min, the feed flow rate of the acetic anhydride raw material changes at 10.8 g / min, the feed position of the isobutyric acid raw material is at the 16th theoretical stage of the distillation tower, the feed position of the acetic anhydride raw material is at the 18th theoretical stage, the total theoretical stage of the distillation tower is 38 stages, the reflux ratio is 3, the molar ratio of the isobutyric acid raw material to the acetic anhydride raw material is 2:1, and the feed temperature is 71°C. In order to establish a steady state of the system, the extraction flow rates of the tower top and the tower bottom are controlled, and in order to prevent the distillation tower from avoiding heat dissipation and affecting the gas-liquid balance in the tower, the distillation tower is heat-insulated in sections, wherein: the temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C, and the temperature of the tower body 3 is 120°C. The height of the packing of the distillation tower is 2.4m, and the packing type is glass spring.

[0032] Comparative Example 4: Compared with the embodiment, comparative example 2 adopts a conventional single reactor, the feed flow rate of the isobutyric acid raw material changes at 31 g / min, the feed flow rate of the acetic anhydride raw material changes at 18 g / min, the feed position of the isobutyric acid raw material is at the 16th theoretical stage of the distillation tower, the feed position of the acetic anhydride raw material is at the 18th theoretical stage, the total theoretical stage of the distillation tower is 38 stages, the reflux ratio is 3, the molar ratio of the isobutyric acid raw material to the acetic anhydride raw material is 2:1, and the feed temperature is 71°C. In order to establish a steady state of the system, the extraction flow rates of the tower top and the tower bottom are controlled, and in order to prevent the distillation tower from avoiding heat dissipation and affecting the gas-liquid balance in the tower, the distillation tower is heat-insulated in sections, wherein: the temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C, and the temperature of the tower body 3 is 120°C. The height of the packing of the distillation tower is 2.4m, and the packing type is glass spring.

[0033] Comparative Example 5: Compared with the embodiment, comparative example 2 adopts a conventional single reactor, the feed flow rate of the isobutyric acid raw material changes at 37.2 g / min, the feed flow rate of the acetic anhydride raw material changes at 21.6 g / min, the feed position of the isobutyric acid raw material is at the 16th theoretical stage of the distillation tower, the feed position of the acetic anhydride raw material is at the 18th theoretical stage, the total theoretical stage of the distillation tower is 38 stages, the reflux ratio is 3, the molar ratio of the isobutyric acid raw material to the acetic anhydride raw material is 2:1, and the feed temperature is 71°C. In order to establish a steady state of the system, the extraction flow rates of the tower top and the tower bottom are controlled, and in order to prevent the distillation tower from avoiding heat dissipation and affecting the gas-liquid balance in the tower, the distillation tower is heat-insulated in sections, wherein: the temperature of the tower body 1 is 180°C, the temperature of the tower body 2 is 145°C, and the temperature of the tower body 3 is 120°C. The height of the packing of the distillation tower is 2.4m, and the packing type is glass spring.

[0034] Test example: The samples of Examples 1 to 4 and Comparative Examples 1 to 5 were analyzed by gas chromatography. The gas chromatography used a Shimadzu GC-2030 gas chromatograph, and the chromatographic column models were SH-Wax and HP-50+, respectively. The peak area normalization method was used for quantification. Isobutyric anhydride was used as the reference substance s, and the relative correction factor of component i and isobutyric anhydride was used for quantitative analysis. The relative correction factor of component i was: The test results are shown in Table 2. In Table 1, B0 is the steady-state composition of the tower bottom full reflux stage, that is, the composition at time 0 of the feeding stage; B is the final tower bottom average composition; D is the final tower top average composition; B1 refers to the tower bottom product composition at steady state, and D1 refers to the steady-state tower top product composition. Accurately weigh the components and the reference material, and perform chromatographic analysis on the prepared mixed solution. Substitute the obtained peak area and the mass of each component into the formula to obtain the relative correction factor of each component. The gas chromatography operation steps include: (1) Establishing stable inlet and outlet: Simultaneously turn on the tower bottom discharge pump, isobutyric acid feed pump, acetic anhydride feed pump and tower top reflux ratio controller (set the reflux ratio, for example, R=3 means reflux for 18s and extraction for 6s; calibrate the tower bottom discharge flow rate and the isobutyric acid and acetic anhydride feed flow rates to the set values ​​using an electronic scale; (2) Recording of inlet and outlet balance data: After starting feeding, After that, the weight of the tower bottom extraction, the weight of the isobutyric acid feed, and the weight of the acetic anhydride feed were recorded every 5 minutes to correct the flow rate. The valve of the tower top extraction and collection device was switched every 30 minutes, and the mass of the light components extracted from the tower top within 30 minutes was weighed to calculate the average tower top extraction flow rate (g / min); (3) Temperature data recording and control: After the start of feeding, the tower bottom liquid temperature, tower bottom wall temperature, tower body first wall temperature, tower body second wall temperature, tower body third wall temperature and tower top air temperature were recorded every 5 minutes using an external thermometer; (4) Sampling and analysis of concentration: After the start of feeding, samples were taken from the tower top and the tower bottom every 30 minutes, and their composition was analyzed by gas chromatography; (5) Steady state of feeding stage: When the tower bottom liquid temperature rises to a stable level after 60 minutes, it can be considered that the system has reached the feeding steady state stage, and then the experiment can be stopped. The test results are shown in Table 1; Table 1 Test results As shown in Table 1, Comparative Examples 1 to 5 are technical solutions using a single distillation tower. From the results of Comparative Examples 1 to 5, it can be seen that as the feed amounts of isobutyric acid and acetic anhydride increase, the conversion rates of isobutyric acid and acetic anhydride gradually decrease, and the content of acetic acid-isobutyric anhydride in the tower kettle gradually increases. Although the conversion rate of acetic anhydride can still be maintained at more than 90%, the reaction efficiency of acetic acid-isobutyric anhydride and isobutyric acid decreases rapidly, resulting in the gradual accumulation of acetic acid-isobutyric anhydride in the tower kettle, resulting in a significant decrease in the purity of isobutyric anhydride; Examples 1 to 4 are technical solutions using a single distillation tower. By using the continuous production method of isobutyric anhydride provided by the present application, the conversion rate of acetic acid-isobutyric anhydride in Examples 1 to 4 can reach 93.76%, and the purity of the isobutyric anhydride product finally obtained can reach 97.7%. The results show that the acetic isobutyric anhydride accumulated in the bottom of the distillation tower 1 is transferred to the distillation tower 2, and the accumulated acetic acid-isobutyric anhydride is further converted into isobutyric anhydride and acetic acid by adding isobutyric acid, thereby improving the conversion rate of acetic acid-isobutyric anhydride, significantly improving the conversion rate of isobutyric anhydride, and significantly improving the purity of isobutyric anhydride.

[0035] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for continuous production of isobutyric anhydride, Its characteristics are: The following steps are involved: Step 1: preheating the isobutyric acid raw material and the acetic anhydride raw material respectively and feeding them into a distillation tower to react and obtain a light component in a tower and a heavy component in a tower; Step 2: The heavy components in tower 1 enter into distillation tower 2 for a conversion-promoting reaction to obtain isobutyric anhydride and light components in tower 2, wherein the conversion-promoting reaction includes adding isobutyric acid and increasing the temperature; Step 3: The light components of tower 1 and tower 2 enter into distillation tower 3 for distillation to obtain crude acetic acid and heavy components of tower 3; Step 4: The heavy components from tower three enter into distillation tower four for distillation to obtain refined isobutyric acid and heavy components from tower four.

2. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The molar ratio of isobutyric acid to acetic anhydride is 1.0 to 2.

2.

3. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The feed temperature of the distillation tower 1 is 25-155°C.

4. The method for continuous production of isobutyric anhydride according to claim 1 or 3, Its characteristics are: The reaction pressure of the distillation tower 1 is 0.2-1.2 atm.

5. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The reaction pressure of the distillation tower 2 is 0.2-1.2 atm.

6. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The reaction pressure of the distillation tower three is 0.2~1.0 atm.

7. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The reaction pressure of the distillation tower 4 is 0.2~1.4 atm.

8. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The refined isobutyric acid and the isobutyric acid raw material are fed into the first distillation tower.

9. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The crude acetic acid product enters the acetic acid refining unit to be refined to obtain the acetic acid product.

10. The method for continuous production of isobutyric anhydride according to claim 1, Its characteristics are: The four components of the tower enter the isobutyric anhydride distillation device to produce the isobutyric anhydride product.

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