Method for improving crystallization efficiency of trimellitic anhydride

Abstract

The invention relates to a method for improving crystallization efficiency of trimellitic anhydride, which comprises the following steps: a material enters a feeding section through a material inlet, and is uniformly sprayed downwards on a conical heating plate of an uppermost heating assembly through a feeding pipeline, and light components in the material are quickly gasified under the action of negative pressure and heating, so that the crystallization efficiency of trimellitic anhydride is improved. The remaining materials slide downwards along the outer wall of the conical heating plate under the action of gravity and fall onto the inverted-conical heating plate through the first opening, the inverted-conical heating plate continues to heat to gasify light components in the materials, and the remaining materials continue to slide downwards along the inner wall of the inverted-conical heating plate and fall onto the conical heating plate of the heating assembly below through the second opening; the materials sequentially slide downwards to pass through a flash evaporation crystallization area and a heat conduction oil crystallization area, are gradually crystallized to form high-purity crystals and finally fall into a blanking kettle for heating and heat preservation; according to the method disclosed by the invention, multi-stage crystallization is realized in a vacuum flash evaporation and distributed heating manner, the long-time high-temperature crystallization time is shortened, the product quality is improved, and the product yield is increased.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and in particular to a method for improving the crystallization efficiency of trimellitic anhydride. Background Technology

[0002] Trimeric trioxide (TMA), or simply trioxide, has a wide range of applications in the production of PVC resin plasticizers, polyimide resin paints, water-soluble alkyd resins, epoxy resin curing agents, impregnating agents for low-voltage and pulsed power capacitors, film, water treatment agents, and surfactants.

[0003] Currently, the main production method for trimellitic anhydride involves dissolving trimellitene in acetic acid and reacting it with air or oxygen under the action of a catalyst to produce trimellitic acid. The trimellitic acid material contains a large amount of light components, mainly consisting of acetic acid (the solvent from the trimellitene oxidation reaction), water, and unoxidized trimellitene, along with small amounts of organic impurities. After removing acetic acid and light components, the trimellitic acid material crystallizes and finally undergoes anhydride formation to obtain the final product.

[0004] The removal of light components from trimellitic acid is mainly achieved through intermittent heating and evaporation in a crystallizer or stirring evaporation in a crystallizer. The advantage of intermittent heating and evaporation in a crystallizer is its simple operation and lowest cost. However, its disadvantages include long heating time, high heating temperature, resulting in numerous side reactions, low efficiency, and reduced yield. The advantage of stirring evaporation in a crystallizer is its significantly improved efficiency. However, its disadvantages include complex equipment structure, high requirements for mechanical seals, and susceptibility to corrosion and leakage in high-temperature environments, leading to a higher maintenance rate.

[0005] Therefore, this invention proposes a method to improve the crystallization efficiency of trimellitic anhydride in order to solve the above problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for improving the crystallization efficiency of trimellitic anhydride by achieving multi-stage crystallization through vacuum flash evaporation and distributed heating, thereby reducing the long-term high-temperature crystallization time of trimellitic anhydride, reducing side reactions, improving product quality, and increasing product yield.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for improving the crystallization efficiency of trimellitic anhydride, the innovation of which is: the method is completed by a crystallization system, the crystallization system including a crystallization tower and a feeding vessel set at the bottom of the crystallization tower; The crystallization tower includes a tower body, inside which there is a feeding section and four crystallization sections arranged below the feeding section. The four crystallization sections are arranged sequentially from top to bottom. The feeding section is equipped with a feeding pipeline with a feeding nozzle. The tower body is equipped with a material inlet for conveying material to the feeding pipeline. The top of the tower body has a top gas phase outlet, and each crystallization section on the side wall of the tower body has a lateral gas phase outlet. The tower body is equipped with five heating plate assemblies arranged from top to bottom between the feed section and the uppermost crystallization section, between adjacent crystallization sections, and at the bottom of the lowermost crystallization section. Each heating plate assembly includes a conical heating plate and an inverted conical heating plate. The conical heating plate is positioned above the inverted conical heating plate. The bottom edge of the conical heating plate has a first opening for material to fall onto the inverted conical heating plate, and the bottom of the inverted conical heating plate has a second opening for material to fall onto. The three upper heating plate assemblies cooperate to form a flash crystallization zone, and the two lower heating plate assemblies cooperate to form a heat transfer oil crystallization zone. The method includes the following process: the material enters the feeding section through the material inlet and is evenly sprayed downwards onto the conical heating plate of the uppermost heating component through the feeding pipeline. Under negative pressure and heating, the light components in the material are rapidly vaporized. The remaining material slides downwards along the outer wall of the conical heating plate under gravity and falls onto the inverted conical heating plate through the first opening. The inverted conical heating plate continues to heat and vaporize the light components in the material. The remaining material continues to slide downwards along the inner wall of the inverted conical heating plate and falls onto the conical heating plate of the lower heating component through the second opening. The vaporized light components leave the tower body through the top gas phase outlet and the side gas phase outlet for removal. The material slides downwards sequentially through the flash crystallization zone and the heat transfer oil crystallization zone, gradually crystallizing to form high-purity crystals and finally falling into the feeding kettle for heating and heat preservation.

[0008] Furthermore, the crystallization system also includes a first vacuum pump, a second vacuum pump, a first receiving tank, and a second receiving tank; The inlet of the first vacuum pump is connected to the top gas phase outlet through the first condenser, and the first receiving tank is connected to the first condenser. The inlet of the second vacuum pump is connected to the side gas phase outlet through the second condenser, and the second receiving tank is connected to the second condenser. The top feed port of the feeding vessel is connected to the second opening of the inverted conical heating plate of the heating component at the bottom of the tower. The bottom discharge port of the feeding vessel is connected to the second vacuum pump through the transfer tank. The outer side of the feeding vessel is equipped with a heat transfer oil jacket for heating the feeding vessel, and the heat transfer oil jacket is equipped with an oil inlet and an oil outlet; the side wall of the tower body is equipped with three hot water inlets and three hot water outlets, the three hot water inlets are used to introduce hot water into the three heating plate assemblies of the flash crystallization zone respectively, and the three hot water outlets are respectively connected to the three heating plate assemblies of the flash crystallization zone; the side wall of the tower body is equipped with two heat transfer oil inlets and two heat transfer oil outlets, the two heat transfer oil inlets are respectively introduced into the two heating plate assemblies of the heat transfer oil crystallization zone, and the two heat transfer oil outlets are respectively connected to the two heating plate assemblies of the heat transfer oil crystallization zone.

[0009] Furthermore, the detailed operation steps of the method are as follows: S1. Open the valve of the hot water inlet on the crystallization tower body and the valve of the hot water outlet on the crystallization tower body to introduce hot water into the conical heating plates and inverted conical heating plates of each heating plate assembly in the flash crystallization zone to preheat the flash crystallization zone of the crystallization tower. S2. Open the valve at the inlet of the heat transfer oil on the crystallization tower body and the valve at the outlet of the heat transfer oil on the crystallization tower body to introduce heat transfer oil into the conical heating plates and inverted conical heating plates of each heating plate assembly in the heat transfer oil crystallization area to preheat and raise the temperature of the heat transfer oil crystallization area of ​​the crystallization tower. S3. Open the inlet and outlet valves of the heat transfer oil jacket of the feeding vessel, and introduce heat transfer oil into the heat transfer oil jacket of the feeding vessel to preheat the feeding vessel. S4. Open the inlet valves of the first and second vacuum pumps, and start the first and second vacuum pumps to evacuate the crystallization tower. S5. When the temperature inside the crystallizer is preheated to above 80°C and the vacuum degree is reduced to below 3000Pa, prepare to feed the material. S6. Slowly open the material inlet valve, control the material feed flow rate, pay attention to maintaining stable pressure inside the crystallizer, and observe the temperature inside the crystallizer. At this time, the temperature of the crystallizer begins to rise rapidly. S7. Continue to increase the material feed, keep the temperature and pressure inside the crystallizer stable, and the liquid levels in the first and second receiving tanks rise. S8. Half an hour after the material is fed, open the valve at the bottom outlet of the feeding vessel. The high-purity crystals in the feeding vessel are transferred to the transfer tank, where samples are taken and analyzed.

[0010] Furthermore, in step S1, the preheating temperature of the flash crystallization zone in the crystallization tower is controlled at 80-85℃.

[0011] Furthermore, in step S2, the preheating temperature of the heat transfer oil crystallization zone in the crystallization tower is controlled at 150-170℃.

[0012] Furthermore, in step S3, the preheating temperature of the feeding vessel is controlled at 150-170℃.

[0013] Furthermore, in step S4, the vacuum level inside the crystallization tower is controlled at 2000-3000 Pa during the evacuation process.

[0014] Furthermore, in step S6, the material feed flow rate is controlled at 2.5-3 m³ / h. 3 / min.

[0015] Furthermore, in step S7, the temperature of the flash crystallization zone inside the crystallization tower is controlled between 90-95°C, the temperature of the heat transfer oil crystallization zone is controlled between 220-250°C, and the liquid level in the first and second receiving tanks is controlled between 30-60%.

[0016] Furthermore, in step S8, before opening the valve at the bottom outlet of the feeding vessel, the transfer tank is first evacuated to balance the pressure inside the transfer tank with the pressure inside the crystallizing tower.

[0017] The advantages of this invention are: In the method of this invention, the material is removed by vacuum flash evaporation and multi-stage evaporation during the light-light crystallization process. The material is continuously fed and heated, which results in lower energy consumption and higher system light-light removal efficiency compared to traditional intermittent heating for light-light removal.

[0018] In the method of the present invention, different heating media are used in the continuous evaporation and heating process of the material, the contact area between the material and the heating plate is large, the evaporation efficiency is high, the material heating time is short, the product side reaction is small, and the product quality is improved.

[0019] In the method of the present invention, the material is subjected to staged evaporation. The first receiving tank is used to receive and recover acetic acid, and the second receiving tank is used to receive and recover light components. Acetic acid and light components in the material have been initially separated, which improves the separation efficiency and reduces the subsequent separation cost.

[0020] The method of this invention provides a practical crystallization system with a clear and concise structure, convenient equipment operation and maintenance, good corrosion resistance, and is conducive to long-term continuous operation. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 This is a schematic diagram of the connection of the crystallization system of the present invention. Detailed Implementation

[0023] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0024] Example This embodiment provides a method for improving the crystallization efficiency of trimellitic anhydride, which is accomplished using a crystallization system.

[0025] like Figure 1 As shown, the crystallization system includes a crystallization tower 1, a feeding vessel 2 located at the bottom of the crystallization tower 1, a first vacuum pump 4, a second vacuum pump 7, a first receiving tank 6, and a second receiving tank 9.

[0026] The crystallization tower 1 includes a tower body, inside which there is a feed section D1 and four crystallization sections located below the feed section. The four crystallization sections are designated as first crystallization section D2, second crystallization section D3, third crystallization section D4, and fourth crystallization section D5, arranged sequentially from top to bottom. The feed section D1 is equipped with two feed pipelines 101 with feed nozzles. The tower body is provided with a material inlet for conveying material to the feed pipelines 101. The top of the tower body has a top gas phase outlet 104, and each crystallization section on the side wall of the tower body has a lateral gas phase outlet 105.

[0027] The tower body is equipped with five heating plate assemblies, which are arranged from top to bottom between the feed section D1 and the first crystallization section D2, between the first crystallization section D2 and the second crystallization section D3, between the second crystallization section D3 and the third crystallization section D4, between the third crystallization section D4 and the fourth crystallization section D5, and at the bottom of the fourth crystallization section D5. Each heating plate assembly includes a conical heating plate 102 and an inverted conical heating plate 103. The conical heating plate 102 is positioned above the inverted conical heating plate 103. The bottom edge of the conical heating plate 102 has a first opening for material to fall downwards onto the inverted conical heating plate 103, and the bottom of the inverted conical heating plate 103 has a second opening for material to fall downwards. The three upper heating plate assemblies cooperate to form a flash crystallization zone, and the two lower heating plate assemblies cooperate to form a heat transfer oil crystallization zone.

[0028] The tower body has three hot water inlets and three hot water outlets on its side wall. The three hot water inlets are used to supply hot water to the three heating plate assemblies in the flash crystallization zone, and valves b, d, and f are installed on the three hot water inlets respectively. The three hot water outlets are connected to the three heating plate assemblies in the flash crystallization zone, and valves a, c, and e are installed on the three hot water outlets respectively. The tower body also has two heat transfer oil inlets and two heat transfer oil outlets on its side wall. The two heat transfer oil inlets supply heat transfer oil to the two heating plate assemblies in the heat transfer oil crystallization zone, and valves h and j are installed on the two heat transfer oil inlets respectively. The two heat transfer oil outlets are connected to the two heating plate assemblies in the heat transfer oil crystallization zone, and valves g and i are installed on the two heat transfer oil outlets respectively.

[0029] The inlet of the first vacuum pump 4 is connected to the top gas phase outlet 104 through the first condenser 5. The heat source inlet of the first condenser 5 is connected to the top gas phase outlet 104. The heat source gas phase outlet of the first condenser 5 is connected to the inlet of the first vacuum pump 4. The first receiving tank 6 is connected to the heat source liquid phase outlet of the first condenser 5. The heat source inlet, heat source gas phase outlet, and heat source liquid phase outlet of the first condenser 5 are interconnected. The first condenser 5 also has an interconnected cold source inlet and cold source outlet.

[0030] The inlet of the second vacuum pump 7 is connected to the side gas phase outlet 105 through the second condenser 8. The heat source inlet of the second condenser 8 is connected to the side gas phase outlet 105. The heat source gas phase outlet of the second condenser 8 is connected to the inlet of the second vacuum pump 7. The second receiving tank 9 is connected to the heat source liquid phase outlet of the second condenser 8. The heat source inlet, heat source gas phase outlet, and heat source liquid phase outlet of the second condenser 8 are interconnected. The second condenser 8 also has an interconnected cold source inlet and cold source outlet.

[0031] The top inlet of the feeding vessel 2 is connected to the second opening of the inverted conical heating plate of the heating component at the bottom of the tower body. The bottom outlet of the feeding vessel is connected to the inlet of the second vacuum pump 7 through the transfer tank 3. A valve n is installed at the bottom outlet of the feeding vessel. A heat transfer oil jacket 201 for heating the feeding vessel 2 is provided on the outside of the feeding vessel 2. The heat transfer oil jacket 201 is provided with an oil inlet and an oil outlet. A valve k and a valve m are installed on the oil inlet and the oil outlet, respectively.

[0032] The crystallization system also includes a hot water source that supplies hot water to each hot water inlet and a heat transfer oil source that supplies heat transfer oil to each heat transfer oil inlet. The hot water source also supplies hot water to the cold source inlets of the first condenser and the second condenser, and the heat transfer oil source also supplies heat transfer oil to the oil inlet on the heat transfer oil jacket 201.

[0033] The crystallization system has a clear and concise structure, is easy to operate and maintain, has good corrosion resistance, and is conducive to long-term continuous operation.

[0034] The method for improving the crystallization efficiency of trimellitic anhydride includes the following process: The material enters the feed section D1 through the material inlet and is evenly sprayed downwards through the feed pipeline 101 onto the conical heating plate 102 of the uppermost heating component. Under negative pressure and heating, the light components in the material are rapidly vaporized. The remaining material slides downwards along the outer wall of the conical heating plate 102 under gravity and falls onto the inverted conical heating plate 103 through the first opening. The inverted conical heating plate 103 continues to heat and vaporize the light components in the material. The remaining material continues to slide downwards along the inner wall of the inverted conical heating plate 103 and falls onto the conical heating plate of the lower heating component through the second opening. The vaporized light components leave the tower body through the top gas phase outlet and the side gas phase outlet for removal. The material slides downwards sequentially through the flash crystallization zone and the heat transfer oil crystallization zone and gradually crystallizes to form high-purity crystals and finally falls into the feed kettle 2 for heating and heat preservation.

[0035] The detailed operating steps are as follows: S1. Open valves b, d, and f at the hot water inlet of crystallization tower 1, and valves a, c, and e at the hot water outlet of crystallization tower 1. Introduce hot water into the conical heating plates and inverted conical heating plates of each heating plate assembly in the flash crystallization zone to preheat the flash crystallization zone of the crystallization tower. The preheating temperature of the flash crystallization zone of the crystallization tower is controlled at 80-85℃.

[0036] S2. Open valves h and j at the inlet of the heat transfer oil on the crystallization tower 1, and valves g and i at the outlet of the heat transfer oil on the crystallization tower body. Introduce heat transfer oil into the conical heating plates and inverted conical heating plates of each heating plate assembly in the heat transfer oil crystallization area to preheat the heat transfer oil crystallization area of ​​the crystallization tower. The preheating temperature of the heat transfer oil crystallization area of ​​the crystallization tower is controlled at 150-170℃.

[0037] S3. Open the inlet valve k and outlet valve m of the heat transfer oil jacket 201 of the feeding vessel, and introduce heat transfer oil into the heat transfer oil jacket 201 of the feeding vessel to preheat the feeding vessel 2. The preheating temperature of the feeding vessel 2 is controlled at 150-170℃.

[0038] S4. Open the inlet valves of the first vacuum pump 4 and the second vacuum pump 7, and start the first vacuum pump 4 and the second vacuum pump 7 to evacuate the crystallization tower 1. The vacuum degree inside the tower is controlled at 2000-3000Pa.

[0039] S5. When the temperature inside crystallizer 1 is preheated to above 80°C and the vacuum degree is reduced to below 3000Pa, prepare to feed the material.

[0040] S6. Slowly open the material inlet valve to control the material feed flow rate at 2.5-3 m³ / h. 3 / min, pay attention to keeping the pressure inside crystallization tower 1 stable, control the pressure between 2000Pa and 3000Pa, and at the same time observe the temperature inside crystallization tower 1. At this time, the temperature of crystallization tower begins to rise rapidly.

[0041] S7. Continue to increase the material feed, keep the temperature inside the crystallization tower 1 stable, control the temperature of the flash crystallization zone inside the crystallization tower between 90-95℃, control the temperature of the heat transfer oil crystallization zone between 220-250℃, keep the pressure stable, the liquid level in the first receiving tank and the second receiving tank rises, and control the liquid level in the first receiving tank 6 and the second receiving tank 7 between 30-60%. Open the vacuum valve of the transfer tank 3 and use the second vacuum pump 7 to evacuate the transfer tank 3.

[0042] S8. When the liquid level in the first and second receiving tanks reaches more than 30% after half an hour of material feeding, and the pressure in the transfer tank 3 reaches equilibrium with the pressure in the crystallization tower 1, open valve n at the bottom outlet of the feeding vessel 2. The high-purity crystals in the feeding vessel 2 are transferred to the transfer tank 3, where samples are taken and analyzed.

[0043] This embodiment analyzes samples of trimellitic anhydride crystals obtained by a method to improve the crystallization efficiency of trimellitic anhydride, and compares them with trimellitic anhydride crystals obtained by the existing intermittent heating evaporation crystallization method in a crystallizer. The comparison data is shown in Table 1.

[0044] Table 1 Comparison results of trimellitic anhydride crystals project Intermittent heating evaporation crystallization method Methods to improve the crystallization efficiency of trimellitic anhydride Appearance White or slightly colored flaky solid White or slightly colored flaky solid Trimeric triglyceride, w / % 95.0-96.5 ≥98.5 Phthalic anhydride, w / % 0.08-0.10 ≤0.03 Acid value (as KOH) / (mg / g) 865-880 ≥900 Melt color / Hazen units (platinum-cobalt color code) 120-150 ≤100 Yield, % 83-86 ≥95 As can be seen from the data comparison in Table 1, compared with the existing intermittent heating evaporation crystallization method in the crystallization vessel, the method of the present invention for improving the crystallization efficiency of trimellitic anhydride has a significantly increased trimellitic anhydride content in the obtained trimellitic anhydride crystals, a significantly improved product color, and a product yield of over 95%, which is much higher than the yield of the intermittent heating evaporation crystallization method, and has lower energy consumption.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for improving the crystallization efficiency of trimellitic anhydride, characterized in that: The method is accomplished using a crystallization system, which includes a crystallization tower and a feeding vessel located at the bottom of the crystallization tower. The crystallization tower includes a tower body, inside which there is a feeding section and four crystallization sections arranged below the feeding section. The four crystallization sections are arranged sequentially from top to bottom. The feeding section is equipped with a feeding pipeline with a feeding nozzle. The tower body is equipped with a material inlet for conveying material to the feeding pipeline. The top of the tower body has a top gas phase outlet, and each crystallization section on the side wall of the tower body has a lateral gas phase outlet. The tower body is equipped with five heating plate assemblies arranged from top to bottom between the feed section and the uppermost crystallization section, between adjacent crystallization sections, and at the bottom of the lowermost crystallization section. Each heating plate assembly includes a conical heating plate and an inverted conical heating plate. The conical heating plate is positioned above the inverted conical heating plate. The bottom edge of the conical heating plate has a first opening for material to fall onto the inverted conical heating plate, and the bottom of the inverted conical heating plate has a second opening for material to fall onto. The three upper heating plate assemblies cooperate to form a flash crystallization zone, and the two lower heating plate assemblies cooperate to form a heat transfer oil crystallization zone. The method includes the following process: the material enters the feeding section through the material inlet and is evenly sprayed downwards onto the conical heating plate of the uppermost heating component through the feeding pipeline. Under negative pressure and heating, the light components in the material are rapidly vaporized. The remaining material slides downwards along the outer wall of the conical heating plate under gravity and falls onto the inverted conical heating plate through the first opening. The inverted conical heating plate continues to heat and vaporize the light components in the material. The remaining material continues to slide downwards along the inner wall of the inverted conical heating plate and falls onto the conical heating plate of the lower heating component through the second opening. The vaporized light components leave the tower body through the top gas phase outlet and the side gas phase outlet for removal. The material slides downwards sequentially through the flash crystallization zone and the heat transfer oil crystallization zone, gradually crystallizing to form high-purity crystals and finally falling into the feeding kettle for heating and heat preservation.

2. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 1, characterized in that: The crystallization system also includes a first vacuum pump, a second vacuum pump, a first receiving tank, and a second receiving tank; The inlet of the first vacuum pump is connected to the top gas phase outlet through the first condenser, and the first receiving tank is connected to the first condenser. The inlet of the second vacuum pump is connected to the side gas phase outlet through the second condenser, and the second receiving tank is connected to the second condenser. The top feed port of the feeding vessel is connected to the second opening of the inverted conical heating plate of the heating component at the bottom of the tower. The bottom discharge port of the feeding vessel is connected to the second vacuum pump through the transfer tank. The outer side of the feeding vessel is equipped with a heat transfer oil jacket for heating the feeding vessel, and the heat transfer oil jacket is equipped with an oil inlet and an oil outlet; the side wall of the tower body is equipped with three hot water inlets and three hot water outlets, the three hot water inlets are used to introduce hot water into the three heating plate assemblies of the flash crystallization zone respectively, and the three hot water outlets are respectively connected to the three heating plate assemblies of the flash crystallization zone; the side wall of the tower body is equipped with two heat transfer oil inlets and two heat transfer oil outlets, the two heat transfer oil inlets are respectively introduced into the two heating plate assemblies of the heat transfer oil crystallization zone, and the two heat transfer oil outlets are respectively connected to the two heating plate assemblies of the heat transfer oil crystallization zone.

3. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 2, characterized in that: The detailed operation steps of the method are as follows: S1. Open the valve of the hot water inlet on the crystallization tower body and the valve of the hot water outlet on the crystallization tower body to introduce hot water into the conical heating plates and inverted conical heating plates of each heating plate assembly in the flash crystallization zone to preheat the flash crystallization zone of the crystallization tower. S2. Open the valve at the inlet of the heat transfer oil on the crystallization tower body and the valve at the outlet of the heat transfer oil on the crystallization tower body to introduce heat transfer oil into the conical heating plates and inverted conical heating plates of each heating plate assembly in the heat transfer oil crystallization area to preheat and raise the temperature of the heat transfer oil crystallization area of ​​the crystallization tower. S3. Open the inlet and outlet valves of the heat transfer oil jacket of the feeding vessel, and introduce heat transfer oil into the heat transfer oil jacket of the feeding vessel to preheat the feeding vessel. S4. Open the inlet valves of the first and second vacuum pumps, and start the first and second vacuum pumps to evacuate the crystallization tower. S5. When the temperature inside the crystallizer is preheated to above 80°C and the vacuum degree is reduced to below 3000Pa, prepare to feed the material. S6. Slowly open the material inlet valve, control the material feed flow rate, pay attention to maintaining stable pressure inside the crystallizer, and observe the temperature inside the crystallizer. At this time, the temperature of the crystallizer begins to rise rapidly. S7. Continue to increase the material feed, keep the temperature and pressure inside the crystallizer stable, and the liquid levels in the first and second receiving tanks rise. S8. Half an hour after the material is fed, open the valve at the bottom outlet of the feeding vessel. The high-purity crystals in the feeding vessel are transferred to the transfer tank, where samples are taken and analyzed.

4. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S1, the preheating temperature of the flash crystallization zone in the crystallization tower is controlled at 80-85℃.

5. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S2, the preheating temperature of the heat transfer oil crystallization zone in the crystallization tower is controlled at 150-170℃.

6. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S3, the preheating temperature of the feeding vessel is controlled at 150-170℃.

7. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S4, the vacuum level inside the crystallization tower is controlled at 2000-3000 Pa during the evacuation process.

8. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S6, the material feed flow rate is controlled at 2.5-3 m³ / h. 3 / min.

9. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S7, the temperature of the flash crystallization zone inside the crystallization tower is controlled between 90-95°C, the temperature of the heat transfer oil crystallization zone is controlled between 220-250°C, and the liquid level in the first and second receiving tanks is controlled between 30-60%.

10. The method for improving the crystallization efficiency of trimellitic anhydride according to claim 3, characterized in that: In step S8, before opening the valve at the bottom outlet of the feeding vessel, the transfer tank is first evacuated to balance the pressure inside the transfer tank with the pressure inside the crystallizing tower.

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