Device and method for continuously producing itaconic anhydride by taking itaconic acid as raw material

Abstract

The invention discloses a device and a method for continuously producing itaconic anhydride by taking itaconic acid as a raw material. The device comprises a mixing kettle, a rectifying tower and a crystallization kettle which are connected in sequence, a suspension flow cylinder and a plurality of tower plates are arranged in the rectifying tower; the suspended flow cylinder is positioned below the tower plate, two ends of the suspended flow cylinder are respectively provided with horn mouths with opposite openings, and the horn mouths are communicated through a zigzag flow channel. Itaconic acid and a solvent are mixed in a mixing kettle; entering a tower kettle of a rectifying tower for dehydration reaction, continuously separating water from the tower top, and extracting a mixed solution containing itaconic anhydride from the tower kettle; the mixed solution enters a crystallization kettle, itaconic anhydride crystals containing a solvent are separated out, then the itaconic anhydride crystals sequentially enter a cyclone, a continuous centrifugal machine and a dryer to be concentrated, separated and dried, and a finished product of itaconic anhydride is obtained. The invention provides a device and a method for continuously producing itaconic anhydride, which have the advantages of continuous production, stable product quality and performance, no waste catalyst and high safety level.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical processes, and specifically relates to an apparatus and method for continuously producing itaconic anhydride using itaconic acid as a raw material. Background Art

[0002] Itaconic anhydride is an important derivative of itaconic acid and a fine chemical raw material. Due to the presence of active functional groups such as carbon-carbon unsaturated double bonds and ligands in its molecule, it has become an important polymerization monomer in the production of polymer materials and is widely used as a raw material or auxiliary agent for metal bonding promoters, esterifying agents, anti-discoloration agents, herbicides, insecticides, synthetic resins, synthetic fibers, ion exchange resins, surfactants, lubrication additives, non-toxic packaging materials, etc.

[0003] In recent years, as the country's requirements for the safety and reliability of chemical projects have become increasingly strict, continuous reactions have received more and more attention. There has even been a document requiring that continuous processes be compulsorily adopted for some chemical projects with a relatively high reaction safety risk assessment level. Therefore, continuous production has become one of the important development directions in the field of chemical process intensification. The existing processes for preparing itaconic anhydride are mainly divided into two categories. One category uses dehydration catalysts such as concentrated sulfuric acid, organic sulfonic acid, or phosphorus pentoxide in batch kettle reactions. Although the reaction temperature is relatively low, there are problems such as high product hydrolysis rate, waste catalyst pollution, and equipment corrosion. The other category uses azeotropic dehydration in batch kettle reactions with organic solvents. Although problems such as waste catalyst pollution and equipment corrosion have been solved, there are still problems such as high hydrolysis rate and high reaction safety risk level assessment, and it faces elimination in industrialization. If itaconic anhydride is continuously produced using itaconic acid as a raw material by rectification dehydration, the water generated after itaconic acid dehydration becomes water vapor and is discharged from the top of the rectification tower. However, there will be a problem of entrainment of liquid droplets by the water vapor, that is, the water vapor will entrain itaconic anhydride liquid and be discharged from the top of the tower. And itaconic acid dehydration is a dynamic equilibrium reaction, and the water vapor will cause itaconic anhydride to hydrolyze into itaconic acid at the tower plate. The above problems will all affect the yield of itaconic anhydride. Therefore, continuously producing itaconic anhydride using itaconic acid as a raw material requires both realizing continuous production and solving problems such as high hydrolysis rate and low yield of itaconic anhydride. Summary of the Invention Aiming at the above-mentioned prior art, the purpose of the present invention is to provide an apparatus and method for continuously producing itaconic anhydride using itaconic acid as a raw material. The present invention aims at the problems of existing batch kettle reactions, a large amount of waste catalysts, and high product hydrolysis rate, and provides an apparatus and method for continuously producing itaconic anhydride that can achieve continuous production, stable product quality and performance, no waste catalyst, and high safety level.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect of the present invention, there is provided an apparatus for continuously producing itaconic anhydride from itaconic acid, comprising a mixing kettle, a rectification column and a crystallization kettle connected in sequence; a suspension cylinder and a plurality of trays are provided in the rectification column; the suspension cylinder is located below the trays, and flared mouths with opposite openings are respectively provided at both ends of the suspension cylinder, and the flared mouths are connected through a zigzag flow channel.

[0005] Preferably, the mixing kettle is connected to the middle part of the rectification column through a pipeline; the bottom of the rectification column is connected to the top of the crystallization kettle through a pipeline.

[0006] Preferably, the top of the rectification column is connected to the upper part of the rectification column through a rectification condenser and a separation tank in sequence; a return port is provided at the lower part of the rectification column; the return port is connected to the bottom of the rectification column through a reboiler; the bottom of the crystallization kettle is connected to a hydrocyclone, a continuous centrifuge and a dryer through pipelines in sequence.

[0007] Preferably, the hydrocyclone is also connected to the top of the crystallization kettle; the continuous centrifuge is also connected to a mother liquor storage tank and a static mixer in sequence; the static mixer is also connected to an itaconic acid storage tank; the top of the mixing kettle is also connected to the static mixer; the suspension cylinder is located between the first tray and the return port Preferably, the length of the flow channel is 0.5 - 1 m, the zigzag angle of the flow channel is 30 - 60°, and the number of zigzags of the flow channel is 2; the opening angle of the flared mouth is 120 - 150°.

[0008] In the second aspect of the present invention, there is provided a method for continuously producing itaconic anhydride from itaconic acid by using the above apparatus, comprising the following steps: (1) Adding itaconic acid and a solvent into the mixing kettle and mixing evenly to obtain a mixed solution; (2) The mixed solution enters the bottom of the rectification column from the mixing kettle for dehydration reaction, and the removed water becomes water vapor and rises to the top of the column through the suspension cylinder and then enters the rectification condenser and the separation tank in sequence from the top of the column to continuously separate water, and a mixed solution containing itaconic anhydride obtained by the reaction is taken out from the bottom of the column; (3) The mixed solution containing itaconic anhydride enters the crystallization kettle, and itaconic anhydride crystals containing the solvent are precipitated. The itaconic anhydride crystals containing the solvent enter a hydrocyclone, a continuous centrifuge and a dryer in sequence for concentration, separation and drying to obtain itaconic anhydride products; the separated mother liquor enters the mother liquor storage tank, and the mother liquor and the itaconic acid in the itaconic acid storage tank are sent into the mixing kettle together for continued use.

[0009] Preferably, in step (1), the mass ratio of itaconic acid to the solvent is 1:3 - 5, and the solvent is toluene, xylene or mesitylene.

[0010] Preferably, in step (2), the temperature of the bottom of the tower is 130 - 190 °C, the temperature of the top of the tower is 100 - 110 °C; the temperature of the suspension cylinder is 130 - 190 °C.

[0011] Preferably, in step (3), the temperature of the crystallization kettle is 60 - 90 °C; the temperature of the dryer is 50 - 55 °C, and the pressure is -0.1 - -0.09 Mpa.

[0012] In the third aspect of the present invention, there is provided an application of the above method in reducing the hydrolysis rate of itaconic anhydride and increasing the yield of itaconic anhydride.

[0013] Advantages of the present invention: (1) The continuous production device and method of itaconic anhydride of the present invention fundamentally solve the problems of high cost of dehydration catalyst, high product hydrolysis rate, and a large amount of waste catalyst salts in the traditional process. The cost is reduced by 30 - 50%, and it has a beneficial effect on environmental protection. The amount of waste salt is reduced by 60 - 70%.

[0014] (2) By setting a suspension cylinder in the rectifying column, through gas-liquid suspension, the centripetal force of the liquid material is increased, promoting gas-liquid separation. The gas phase without product entrainment enters the tray, and the liquid droplets entraining the product return to the bottom of the tower. This device effectively solves the problem of hydrolysis of the product itaconic anhydride on the rectifying column tray caused by gas phase entraining liquid droplets during the rectifying process. It reduces the hydrolysis of the product itaconic anhydride and promotes the forward movement of the reaction.

[0015] (3) The continuous production device and method of itaconic anhydride of the present invention adopt a "crystallization kettle + hydrocyclone + continuous centrifuge" model. Thanks to the way that the discharge pipeline at the top of the hydrocyclone in the separation process contains the itaconic anhydride crystal solution returning to the crystallization kettle, it plays the role of crystal seeds and effectively solves the problems of uneven product particle size distribution and small product particle size causing leakage filtration. (4) The continuous production device and method of itaconic anhydride of the present invention shorten the production cycle, save the time for intermittent reaction charging and discharging, greatly improve the utilization rate of equipment. Most importantly, it reduces the reaction safety risk level from the process essence and meets the safety technical requirements of the national emergency department.

[0016] (5) The continuous production device and method of itaconic anhydride of the present invention have a high degree of automation, reduce manual operation, reduce the contact frequency between personnel and materials, not only reduce the labor cost, but also improve the safety factor. At the same time, it greatly reduces the generation amount of wastewater and waste salts from the process essence and reduces the production cost. Description of the drawings

[0017] Figure 1 : Schematic diagram of the device for continuous production of itaconic anhydride; Figure 2 : Schematic diagram of the suspension cylinder structure; Figure 3 :Schematic diagram of the tortuous angle of the flow channel; Among them, 1 - mixing kettle, 2 - rectification tower, 3 - rectification condenser, 4 - stratification tank, 5 - crystallization kettle, 6 - cyclone, 7 - continuous centrifuge, 8 - dryer, 9 - mother liquor temporary storage tank, 10 - itaconic acid storage tank, 11 - static mixer, 12 - reboiler, 13 - suspension cylinder, 14 - bell mouth, 15 - flow channel, 16 - tray, 17 - first tray, 18 - return port. Specific implementation manner

[0018] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0019] As introduced in the background art section, if the azeotropic dehydration method is used to continuously produce itaconic anhydride with itaconic acid as the raw material, the water generated after the dehydration of itaconic acid becomes water vapor and is discharged from the top of the rectification tower. However, there will be a problem of entrainment of material foam in the water vapor, that is, the water vapor entrains the itaconic anhydride liquid and is discharged from the top of the tower; and the dehydration of itaconic acid is a dynamic equilibrium reaction, and the water vapor will hydrolyze itaconic anhydride into itaconic acid at the tray. The above problems will all affect the yield of itaconic anhydride.

[0020] Based on this, the object of the present invention is to provide a device and method for continuously producing itaconic anhydride using itaconic acid as a raw material. The present invention adopts a continuous suspension reactive distillation column, which not only effectively reduces the water content in the reaction system, but also solves the pollution problem of waste dehydrating agent. The traditional process uses azeotropic water removal, and the azeotropic dehydration potential must accumulate to a certain oil-water azeotropic composition. At this time, the reaction temperature is high, resulting in hydrolysis of the product itaconic anhydride, thereby reducing the product yield. Another type of process uses concentrated sulfuric acid, organic sulfonic acid or phosphorus pentoxide as a dehydrating agent, which is difficult to recover, increases the post-treatment cost, and causes environmental pollution. In the present invention, the setting of the suspension cylinder can ensure that water vapor does not entrain the product and rise to the tray, thereby preventing the hydrolysis of itaconic anhydride; the inside of the distillation column is under positive pressure. Under the temperature and pressure conditions in the column, itaconic anhydride is in a solution state. In order to ensure that water vapor does not cause entrainment of liquid droplets to ensure that the dynamic reaction continuously proceeds in one direction, and thus maintain an extremely low water content in the reaction system, improve the purity and yield of itaconic anhydride, the present invention provides a suspension cylinder. In this way, the water generated by the reaction will be taken away in time through the suspension cylinder, acting as a dehydrating agent. Therefore, the present invention does not require additional addition of a dehydrating agent and will not cause environmental pollution. The setting of the suspension cylinder does not achieve the reduction of liquid droplet entrainment through the temperature setting of the suspension cylinder. The opening angle, flow path length and tortuous angle of the flow path of the suspension cylinder are calculated according to the density difference between the gas phase and the liquid phase using the centrifugal force formula in a non-inertial system, and are continuously adjusted in combination with the actual production process. The suspension cylinder uses the density difference through the structural design to prevent the itaconic anhydride entrained by water vapor from passing through, and only water vapor can pass through, avoiding the hydrolysis of itaconic anhydride at the tray. The suspension cylinder is located between the first tray and the return port because this is where the gas-liquid entrainment is relatively serious and the water content here is relatively high. The present invention also adopts a "crystallization kettle + hydrocyclone + continuous centrifuge" model. The mixed liquid coming out of the bottom of the column contains not only itaconic anhydride but also itaconic acid, etc. The solubility difference between itaconic anhydride and itaconic acid can be utilized to precipitate itaconic anhydride crystals, and then the hydrocyclone is used to concentrate the precipitated itaconic anhydride, and finally solid-liquid separation is achieved through a continuous centrifuge, thereby obtaining a high-purity itaconic anhydride product. The seed crystal is a key factor in inducing the crystallization and growth of the product during the crystallization process. The activity of the seed crystal (the activity of the seed crystal is an index to measure the ability of the seed crystal to promote crystal growth or chemical reaction efficiency under specific conditions. It reflects the number, distribution of the surface active sites of the seed crystal and its interaction ability with the reactants or the solution) and size directly determine the number and size of the crystal nuclei during the crystallization process of itaconic anhydride, which further affects the final particle size of the product and further affects the centrifugation efficiency of the product. In the present invention, the liquid remaining after concentration by the hydrocyclone contains some small-sized crystal grains. After they are returned to the crystallization kettle, they can act as seed crystals and increase the size of the crystallization particles, effectively solving the problems of uneven particle size distribution of the product and small product particles leaking through the filter.

[0021] In the present invention, the reaction process and apparatus adopt rectification dehydration to replace the azeotropic dehydration in the traditional process, thereby reducing the reaction safety risk assessment level in terms of the reaction essence. The traditional process uses azeotropic dehydration, resulting in Tp = MTT during the reaction process (Tp is the target process operating temperature, and MTT is the highest technical temperature, taking the design temperature and the system bubble point temperature). In terms of safety, it is easy to cause the reaction materials to boil and lead to the occurrence of the risk of material flushing. The reaction risk assessment level is level 3, which does not meet the national safety specifications. The present invention adopts the method of changing the operating pressure to increase the MTT of the reaction system. Therefore, Tp < MTT, thereby reducing the reaction risk assessment level and improving the safety of the reaction system, meeting the national standard specifications.

[0022] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0023] The test materials used in the embodiments of the present invention are all conventional test materials in the art and can be obtained through commercial channels.

[0024] Embodiment 1. Apparatus: As Figures 1 - 2 shown, the apparatus for continuously producing itaconic anhydride using itaconic acid as a raw material includes a mixing kettle 1, a rectification tower 2, and a crystallization kettle 5 connected in sequence; a suspension cylinder and a plurality of trays are provided in the rectification tower 2; the suspension cylinder 13 is located below the tray 16, and opposite-opening trumpet-shaped openings 14 are respectively provided at both ends of the suspension cylinder 13, and the trumpet-shaped openings 14 are connected through a zigzag flow channel 15.

[0025] The mixing kettle 1 is connected to the middle part of the rectification tower through a pipeline; the bottom of the rectification tower 2 is connected to the top of the crystallization kettle 5 through a pipeline. The top of the rectification tower 2 is sequentially connected to the upper part of the rectification tower 2 through a rectification condenser 3 and a separation tank 4; a return port 18 is provided at the lower part of the rectification tower 2; the return port 18 is connected to the bottom of the rectification tower 2 through a reboiler 12; the bottom of the crystallization kettle 5 is sequentially connected to a hydrocyclone 6, a continuous centrifuge 7, and a dryer 8 through pipelines. The hydrocyclone 6 is also connected to the top of the crystallization kettle 5; the continuous centrifuge 7 is also sequentially connected to a mother liquor storage tank 9 and a static mixer 11; the static mixer 11 is also connected to an itaconic acid storage tank 10; the top of the mixing kettle 1 is also connected to the static mixer 11.

[0026] The suspension cylinder 13 is located between the first tray 17 and the return port 18. The length of the flow channel 15 is 1 m, the zigzag angle of the flow channel 15 is 45°, and the number of zigzags of the flow channel is 2; the opening angle of the trumpet-shaped opening 14 is 120°.

[0027] The zigzag angle of the flow channel is the included angle formed by the center lines of the flow channel. Specifically, asFigure 3 as shown

[0028] 2. Specific process: (1) Add 2000 kg of itaconic acid and 6000 kg of toluene into the mixing kettle, start stirring, and turn on the regulating motor speed to make the materials reach the turbulent state.

[0029] (2) Open the discharge valve at the bottom of the mixing kettle, control through the flowmeter and regulating valve, and enter the kettle of distillation column 2 at a flow rate of 100 kg / h for reaction. Open the steam valve at the kettle bottom. After the kettle of the distillation column reaches a certain liquid level, continuously separate water at the top of the column, continuously extract the reaction liquid at the kettle bottom. The reaction temperature at the kettle bottom is about 145 °C, the temperature at the top of the column is about 105 °C, and the pressure inside the column is slightly positive.

[0030] (3) The liquid extracted from the kettle of the distillation column enters the crystallization kettle and is mixed with the liquid in the kettle, and then rapidly cools down. The precipitated product, the toluene solution of itaconic anhydride, enters the hydrocyclone for thickening and concentration. The temperature of the crystallization kettle is controlled at about 70 °C.

[0031] (4) The separated solid enters the dryer for drying under reduced pressure to obtain the product itaconic anhydride.

[0032] (5) After the separated mother liquor enters the mother liquor temporary storage tank, open the discharge valve at the bottom of the mother liquor temporary storage tank and the discharge valve at the bottom of the itaconic acid storage tank. Through the interlock control of the flowmeter and the valve, they enter the static mixer respectively, and the mixed solution returns to the mixing kettle for reuse.

[0033] When continuously producing for 48 hours, the purity of itaconic anhydride is detected to be > 99%, the yield is detected to be 95.2%, and the size of the crystal particles is 5.5 - 10 mm; the cost per ton of the finished product itaconic anhydride is about 32000 yuan / ton.

[0034] Comparative Example 1 The difference from the example is that phosphorus pentoxide is added again, and the molar amount of phosphorus pentoxide ≥ the molar amount of itaconic acid; no suspension cylinder and no hydrocyclone are set in the distillation column.

[0035] The process of using concentrated sulfuric acid, organic sulfonic acid or phosphorus pentoxide as a dehydrating agent to produce itaconic anhydride from itaconic acid can also adopt a continuous production method. The difference between the device adopted in the prior art and the example is that there is no suspension cylinder and no hydrocyclone is set. However, the hydrolysis rate is high, resulting in a low yield, the solvent and so on cannot be recycled, and phosphorus pentoxide combines with water to generate phosphorus-containing wastewater, and the phosphorus-containing wastewater needs to be treated before discharge, increasing the production cost.

[0036] When continuously producing for 48 hours, the purity of itaconic anhydride is detected to be 96.1%, the yield is 79.4%, and the crystal particle size of the finished product itaconic anhydride is 3.0 - 6.0 mm; the cost per ton of the finished product itaconic anhydride is about 90000 yuan / ton.

[0037] Comparative Example 2 The difference from Example 1 is that the suspension cylinder is not provided in the rectifying column. The final product is itaconic anhydride. When continuously producing for 48 h, the purity of itaconic anhydride is detected to be 96.8%, the yield is 82.8%, and the size of the crystal particles is 5.0 - 9.0 mm.

[0038] Comparative Example 3 The difference from Example 1 is that the flow channel angle of the suspension cylinder is 90°. The final product is itaconic anhydride. When continuously producing for 48 h, the purity of itaconic anhydride is detected to be 97.1%, the yield is 84.1%, and the size of the crystal particles is 5.0 - 9.5 mm.

[0039] Comparative Example 4 The difference from Example 1 is that the length of the flow channel of the suspension cylinder is 1.5 m and the number of twists is 3. The final product is itaconic anhydride. When continuously producing for 48 h, the purity of itaconic anhydride is detected to be 97.9%, and the yield is 92.1%.

[0040] Comparative Example 5 The difference from Example 1 is that the cyclone is not provided. The final product is itaconic anhydride. When continuously producing for 48 h, the purity of itaconic anhydride is detected to be 96.8%, the yield is 95.3%, and the size of the crystal particles of the finished itaconic anhydride is 3.0 - 6.0 mm.

[0041] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An apparatus for continuously producing itaconic anhydride using itaconic acid as a raw material, characterized in that, It includes a mixing kettle, a rectifying column, and a crystallization kettle connected in sequence; a suspension cylinder and several trays are provided in the rectifying column; the suspension cylinder is located below the trays, and flared mouths with opposite openings are respectively provided at both ends of the suspension cylinder, and the flared mouths are connected through a zigzag flow channel.

2. The device according to claim 1, characterized in that, The mixing kettle is connected to the middle of the rectifying column through a pipeline; the bottom of the rectifying column is connected to the top of the crystallization kettle through a pipeline.

3. The device according to claim 1, characterized in that, The top of the rectifying column is connected to the upper part of the rectifying column through a rectifying condenser and a separation tank in sequence; a return port is provided at the lower part of the rectifying column; the return port is connected to the bottom of the rectifying column through a reboiler; the bottom of the crystallization kettle is connected to a hydrocyclone, a continuous centrifuge, and a dryer through a pipeline in sequence.

4. The device according to claim 3, characterized in that, The hydrocyclone is also connected to the top of the crystallization kettle; the continuous centrifuge is also connected to a mother liquor storage tank and a static mixer in sequence; the static mixer is also connected to an itaconic acid storage tank; the top of the mixing kettle is also connected to the static mixer; the suspension cylinder is located between the first tray and the return port.

5. The device according to claim 1, characterized in that, The length of the flow channel is 0.5 - 1 m, the zigzag angle of the flow channel is 30 - 60°, and the number of zigzags of the flow channel is 2; the opening angle of the flared mouth is 120 - 150°.

6. A method for continuously producing itaconic anhydride using the device according to any one of claims 1 to 5, characterized in that It includes the following steps: (1) Add itaconic acid and a solvent into the mixing kettle and mix evenly to obtain a mixed solution. (2) The mixed solution enters the bottom of the rectifying column from the mixing kettle for dehydration reaction. The removed water becomes water vapor, rises to the top of the tower through the suspension cylinder, and enters the rectifying condenser and the separation tank in sequence from the top of the tower to continuously separate water, and a mixed solution containing itaconic anhydride obtained from the reaction is drawn from the bottom of the tower. (3) The mixed solution containing itaconic anhydride enters the crystallization kettle, and itaconic anhydride crystals containing the solvent are precipitated. The itaconic anhydride crystals containing the solvent enter a hydrocyclone, a continuous centrifuge, and a dryer in sequence for concentration, separation, and drying to obtain itaconic anhydride products; the separated mother liquor enters the mother liquor storage tank, and the mother liquor and the itaconic acid in the itaconic acid storage tank are sent to the mixing kettle for continued use.

7. The method according to claim 6, characterized in that, In step (1), the mass ratio of itaconic acid to the solvent is 1:3 - 5, and the solvent is toluene, xylene, or mesitylene.

8. The method according to claim 6, characterized in that, In step (2), the temperature of the bottom of the tower is 130 - 190 °C, and the temperature of the top of the tower is 100 - 110 °C; the temperature of the suspension cylinder is 130 - 190 °C.

9. The method according to claim 6, wherein In step (3), the temperature of the crystallization kettle is 60 - 90 °C; the temperature of the dryer is 50 - 55 °C, and the pressure is -0.1 - -0.09 Mpa.

10. Application of the method according to claims 6 - 9 in reducing the hydrolysis rate of itaconic anhydride and increasing the yield of itaconic anhydride.

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