Efficient purification system and method for chlorophthalic anhydride

Abstract

The invention relates to the technical field of chemical separation and purification, and particularly discloses an efficient chlorophthalic anhydride purification system and method.The efficient chlorophthalic anhydride purification system comprises a rectifying tower and a plurality of receiving tanks connected with the rectifying tower, and the receiving tanks comprise the first receiving tank, the second receiving tank, the third receiving tank and the fourth receiving tank; the first receiving tank is used for collecting a mixture of light components and 4-chlorophthalic anhydride, the second receiving tank is used for collecting a pure product of 4-chlorophthalic anhydride, the third receiving tank is used for collecting a mixture of 4-chlorophthalic anhydride and 3-chlorophthalic anhydride, and the fourth receiving tank is used for collecting a crude product of 3-chlorophthalic anhydride; a 3-chlorophthalic anhydride crude product extracted from the top of the rectifying tower is not cooled and enters the melt crystallizer in a direct molten state, and the 3-chlorophthalic anhydride crude product is treated by the melt crystallizer to obtain a 3-chlorophthalic anhydride pure product. According to the method, high-purity 3-chlorophthalic anhydride and 4-chlorophthalic anhydride can be obtained, and meanwhile, the energy consumption of the system is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical separation and purification, and in particular to a high-efficiency chloro-phthalic anhydride purification system and method. BACKGROUND

[0002] 3-chloro-phthalic anhydride and 4-chloro-phthalic anhydride are important monomers for preparing electronic-grade polyimide, and the purity thereof directly affects the performance of the polyimide product. In the prior art, simple rectification or solvent crystallization is usually used for purification. However, since the boiling point difference between 3-chloro-phthalic anhydride and 4-chloro-phthalic anhydride is small (only about 2℃), more than 70 theoretical trays, a reflux ratio of 5:1 to 10:1, and operation under extreme vacuum are required for simple rectification, resulting in large equipment investment and high energy consumption. Although the solvent crystallization method can improve the purity to a certain extent, it has problems such as difficulty in solvent recovery, complex operation, and environmental pollution. Therefore, there is an urgent need for a purification method with low energy consumption, high efficiency, and high purity. SUMMARY

[0003] In order to solve the problem of low purification efficiency of chloro-phthalic anhydride in the prior art, the present application provides a high-efficiency chloro-phthalic anhydride purification system and method.

[0004] In one aspect, the present application provides a high-efficiency chloro-phthalic anhydride purification system, which adopts the following technical solution:

[0005] A high-efficiency chloro-phthalic anhydride purification system comprises:

[0006] A rectification tower for supplying chlorination reactants, the chlorination reactants being discharged after being separated by the rectification tower;

[0007] A plurality of receiving tanks, each of which is connected to the rectification tower, the receiving tanks comprising a first receiving tank, a second receiving tank, a third receiving tank, and a fourth receiving tank, the first receiving tank being used for collecting a mixture of light components and 4-chloro-phthalic anhydride, the second receiving tank being used for collecting 4-chloro-phthalic anhydride pure product, the third receiving tank being used for collecting a mixture of 4-chloro-phthalic anhydride and 3-chloro-phthalic anhydride, and the fourth receiving tank being used for collecting 3-chloro-phthalic anhydride crude product;

[0008] A melt crystallizer connected to the fourth receiving tank at the top, the 3-chloro-phthalic anhydride crude product collected at the top of the rectification tower being directly fed into the melt crystallizer in a molten state without cooling, and the 3-chloro-phthalic anhydride crude product being treated by the melt crystallizer to obtain 3-chloro-phthalic anhydride pure product.

[0009] By adopting the technical scheme, the chlorinated reactants are pre-separated by the rectifying tower, the components are separated in stages by the fourth receiving tank, high-purity raw materials are provided for subsequent melt crystallization, the coupling process of melt crystallization secondary purification is further adopted, the materials taken out from the top of the rectifying tower are directly fed into the melt crystallizer in a molten state without cooling, and high-purity 3-chlorophthalic anhydride can be obtained, the co-melt oil and sweating liquid of the melt crystallizer are returned to the rectifying tower in a molten state, and the intermediate process does not pass through the slicing and cooling process, so that the energy consumption is greatly reduced.

[0010] In some embodiments, the melt crystallizer comprises a melt shell, a melt jacket and a receiving tank, the melt jacket is arranged outside the melt shell, a circulating heat conducting oil is arranged in the melt jacket, a feed inlet connected with the rectifying tower is arranged at the top of the melt shell, a discharge outlet is arranged at the bottom of the melt shell, the discharge outlet is connected with the receiving tank through a discharge pipe, and the receiving tank is used for collecting 3-chlorophthalic anhydride pure product.

[0011] In some embodiments, the melt crystallizer is provided with a main pipe and a branch pipe, the main pipe is connected with the third receiving tank and used for returning the sweating liquid and the co-melt oil to the third receiving tank, a circulating pump is arranged on the branch pipe, one end of the branch pipe is connected with the discharge outlet of the melt crystallizer through the main pipe, and the other end is connected with the feed inlet.

[0012] In some embodiments, the melt jacket of the melt crystallizer is divided into three independent temperature control zones, and an independent heat conducting oil circulating system and a temperature sensor are arranged in each zone.

[0013] In some embodiments, the rectifying tower comprises a tower kettle, a tower section and an internal reflux distributor, the tower kettle is connected with the tower section, a raw material inlet is arranged on the tower kettle, a raw material outlet is arranged at the top of the tower section, the internal reflux distributor is connected to the top of the tower section, the internal reflux distributor is connected with the receiving tank, and the internal reflux distributor is used for uniformly spraying the reflux liquid back to the rectifying tower.

[0014] In some embodiments, the internal reflux distributor comprises a collecting tray and a distribution pipe, the collecting tray is installed on the inner wall of the tower section, a gas riser is coaxially connected to the collecting tray, the distribution pipe is arranged at the bottom of the collecting tray, and the distribution pipe is arranged in a spaced manner along the circumference of the collecting tray.

[0015] In some embodiments, the internal reflux distributor further comprises a guide vane, the guide vane is sleeved outside the distribution pipe, and the diameter of the guide vane near one end of the distribution pipe is greater than the diameter of the guide vane away from the other end of the distribution pipe.

[0016] In some embodiments, a heating ring is arranged at the outlet of the distribution pipe, the heating ring is spirally wound on the outlet section of the distribution pipe, and a circulating heat conducting oil is arranged in the heating ring.

[0017] In some embodiments, a heat preservation sleeve is arranged between the fourth receiving tank and the melt crystallizer, a heat conducting oil is used as the heating medium in the heat preservation sleeve, so as to maintain the temperature in the heat preservation sleeve greater than 150 DEG C, and a polytetrafluoroethylene coating is sprayed on the inner wall of the heat preservation sleeve.

[0018] In another aspect, the application further provides a method for purifying chloro-phthalic anhydride, which is purified by using the chloro-phthalic anhydride purification system according to any one of the above, and comprises the following steps:

[0019] S1: continuously or intermittently feeding the crude product containing 3-chloro-phthalic anhydride and 4-chloro-phthalic anhydride into the tower kettle of the rectifying tower;

[0020] S2: starting the reboiler to heat the tower kettle, and simultaneously starting the vacuum pumping system and controlling the reflux ratio;

[0021] S3: sequentially collecting the mixture of phthalic anhydride and 4-chloro-phthalic anhydride, the pure 4-chloro-phthalic anhydride, the mixture of 4-chloro-phthalic anhydride and 3-chloro-phthalic anhydride, and the crude 3-chloro-phthalic anhydride from the top and the side line of the tower;

[0022] S4: directly feeding the crude 3-chloro-phthalic anhydride obtained in step S3 into the melt crystallizer in a molten state;

[0023] S5: performing programmed cooling, temperature rising sweating and temperature rising discharge in the melt crystallizer to obtain the pure 3-chloro-phthalic anhydride, the sweating liquid and the eutectic oil;

[0024] S6: returning the sweating liquid and the eutectic oil obtained in step S5 to the feeding port of the rectifying tower in a molten state, and re-performing the rectification after mixing with the fresh crude product.

[0025] Compared with the prior art, the application has at least one of the following beneficial technical effects:

[0026] 1. The chlorination reactants are pre-separated by the rectifying tower, the components are separated in stages by the four-stage receiving tank, and the coupling process of the secondary purification by the melt crystallization is used, so that the high-purity 4-chloro-phthalic anhydride and 3-chloro-phthalic anhydride can be finally obtained, and the eutectic oil and the sweating liquid of the melt crystallizer are returned to the feeding port of the rectifying tower in a molten state to reduce the energy consumption of the equipment;

[0027] 2. The melt crystallizer directly processes the crude 3-chloro-phthalic anhydride in a molten state, the high selectivity of the melt crystallization to the isomers is utilized to improve the product purity, and the purity of the pure 3-chloro-phthalic anhydride can be higher than 99.5%;

[0028] 3. The internal reflux distributor uniformly sprays the reflux liquid to the cross section of the tower section, so as to solve the problem of the separation efficiency reduction caused by the wall flow effect of the traditional tower. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is the flow chart of the rectification in the embodiment of the application.

[0030] Figure 2 is a flow chart of the melt crystallization in the embodiment of the present application.

[0031] Figure 3 is a structural schematic diagram of the melt crystallizer in the embodiment of the present application.

[0032] Figure 4 is a structural schematic diagram of the internal reflux distributor in the embodiment of the present application.

[0033] Figure 5 is a top view of the internal reflux distributor in the embodiment of the present application.

[0034] in the figure:

[0035] 1, rectifying column; 11, column kettle; 110, raw material inlet; 111, raw material outlet; 12, column section; 13, internal reflux distributor; 131, liquid collecting pan; 132, distribution pipe; 133, riser pipe; 134, guide vane; 135, heating ring; 2, receiving tank; 21, first receiving tank; 22, second receiving tank; 23, third receiving tank; 24, fourth receiving tank; 3, melt crystallizer; 31, melt outer shell; 32, melt jacket; 33, receiving tank; 34, feed inlet; 35, discharge outlet; 36, main pipe; 37, branch pipe; 38, circulating pump. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the term “and / or” in the present application is only to describe the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can mean that there are three cases of A alone, A and B together, and B alone. In addition, the character “ / ” in the present application generally represents an “or” relationship between the associated objects, unless otherwise specified.

[0038] Referring to Figure 1 and Figure 2The application provides a chlorinated phthalic anhydride high-efficiency purification system, which comprises a rectifying tower 1, a plurality of receiving tanks 2 and a melt crystallizer 3. The rectifying tower 1 is used for feeding chlorinated reactants, and the chlorinated reactants are discharged after being separated by the rectifying tower 1. Each receiving tank 2 is connected with the rectifying tower 1. The receiving tank 2 comprises a first receiving tank 21, a second receiving tank 22, a third receiving tank 23 and a fourth receiving tank 24. The rectifying tower 1 forms a temperature gradient decreasing from top to bottom by heating through a tower bottom reboiler and cooling through a tower top condenser. Each component is separated in turn according to the boiling point from low to high. The first receiving tank 21 is used for collecting a mixture of phthalic anhydride and 4-chlorinated phthalic anhydride. The second receiving tank 22 is used for collecting 4-chlorinated phthalic anhydride pure product. The third receiving tank 23 is used for collecting a mixture of 4-chlorinated phthalic anhydride and 3-chlorinated phthalic anhydride. The fourth receiving tank 24 is used for collecting 3-chlorinated phthalic anhydride crude product. The top end of the melt crystallizer 3 is connected with the fourth receiving tank 24. The 3-chlorinated phthalic anhydride crude product collected at the top of the rectifying tower 1 is directly in a molten state and enters the melt crystallizer 3 without cooling. The 3-chlorinated phthalic anhydride crude product is treated by the melt crystallizer 3 to obtain 3-chlorinated phthalic anhydride pure product.

[0039] The top end of the melt crystallizer 3 is connected with the fourth receiving tank 24. The 3-chlorinated phthalic anhydride crude product collected at the top of the rectifying tower 1 is directly in a molten state and enters the melt crystallizer 3 without cooling. The 3-chlorinated phthalic anhydride crude product is treated by the melt crystallizer 3 to obtain 3-chlorinated phthalic anhydride pure product. The 3-chlorinated phthalic anhydride crude product is directly in a molten state and enters the melt crystallizer 3. The high selectivity of melt crystallization to isomers improves the purity of 3-chlorinated phthalic anhydride, saves the energy consumption of cooling, solidification and remelting, and reduces the energy consumption required by the traditional crystallization method. The purity of 3-chlorinated phthalic anhydride and 4-chlorinated phthalic anhydride obtained by the chlorinated phthalic anhydride purification system provided by the application is more than 99.5% by high-performance liquid chromatography.

[0040] Reference Figures 1 to 3 Further, in the embodiment, the melt crystallizer 3 comprises a melt shell 31, a melt jacket 32 and a receiving tank 33. The melt jacket 32 is arranged outside the melt shell 31, and the melt jacket 32 is provided with circulating heat conduction oil. The top of the melt shell 31 is provided with a feeding port 34 connected with the fourth receiving tank 24. The bottom of the melt shell 31 is provided with a discharging port 35 connected with the receiving tank 33 through a discharging pipe. The receiving tank 33 is used for collecting 3-chlorinated phthalic anhydride pure product. The circulating heat conduction oil jacket design ensures that the temperature in the crystallization process is uniform and stable, and prevents local supercooling from causing impurities to be wrapped. The receiving tank 33 directly collects high-purity molten products, saves the centrifugation / filtration step of the traditional crystallization, and reduces product loss.

[0041] The bottom of the melt crystallizer 3 is provided with a main pipe 36 connected with the third receiving tank 23 for returning the sweating liquid and the concomitant oil to the third receiving tank 23, and a branch pipe 37 provided with a circulating pump 38, one end of the branch pipe 37 being connected with the discharge port 35 of the melt crystallizer 3 through the main pipe 36, and the other end being connected with the feed port 34. The melt crystallizer 3 separates and purifies the mixture by using the difference in melting points of the components, heats the material to complete melting, slowly cools according to the program, and makes the target component first reach supersaturation and precipitate crystals, and then keeps the temperature slightly higher than the melting point of the crystals, so that the mother liquor and impurities wrapped on the surface of the crystals are sweated out, and the purity of the crystals is further improved. Finally, the purified 3-chlorophthalic anhydride crystals are all melted to obtain high-purity liquid 3-chlorophthalic anhydride product. The sweating liquid and the concomitant oil are returned to the rectifying tower 1 through the main pipe 36 to be separated again, so as to reduce the generation of waste materials and improve the output of 3-chlorophthalic anhydride pure product.

[0042] Further, the melt jacket 32 of the melt crystallizer 3 is divided into three independent temperature control zones, each of which is provided with an independent heat conduction oil circulation system and a temperature sensor, and the temperature of each temperature control zone can be set according to the temperature required for melt crystallization, which is not limited herein. By segmenting the temperature control, the programmed cooling, the sweating by heating, and the discharging by heating are realized, and each segment supplies heat as needed, which is helpful to reduce energy consumption compared with the overall temperature control.

[0043] In some embodiments, the rectifying tower 1 includes a tower kettle 11, a tower section 12, and an internal reflux distributor 13, the tower kettle 11 being in communication with the tower section 12, the tower kettle 11 being provided with a raw material inlet 110, the tower section 12 being provided with a raw material outlet 111 at the top, and the internal reflux distributor 13 being connected to the top of the tower section 12 and connected with the receiving tank 2, the internal reflux distributor 13 being used for uniformly spraying the reflux liquid back to the rectifying tower 1. By providing the internal reflux distributor 13, the reflux liquid can be uniformly sprayed to the cross section of the tower section 12, so as to solve the problem of reduced separation efficiency caused by wall flow effect in the traditional tower.

[0044] In other embodiments, the melt crystallizer can be a vertical falling film crystallizer, a tower type continuous crystallizer, etc., which are not limited herein; and the rectifying tower can be a plate tower, a packed tower, etc., which are not limited herein.

[0045] Reference Figure 4 and Figure 5Specifically, the inner reflux distributor 13 comprises a collecting tray 131 and a distribution pipe 132. The collecting tray 131 is installed on the inner wall of the tower section 12, and a gas lifting pipe 133 is coaxially connected to the collecting tray 131. The distribution pipe 132 is arranged at the bottom of the collecting tray 131 and is arranged at intervals along the circumference of the collecting tray 131. The inner reflux distributor 13 further comprises a flow guide vane 134, which is sleeved outside the distribution pipe 132. The caliber of the flow guide vane 134 near one end of the distribution pipe 132 is larger than that of the flow guide vane 134 away from the other end of the distribution pipe 132. A heating ring 135 is arranged at the outlet of the distribution pipe 132. The heating ring 135 is spirally wound on the outlet section of the distribution pipe 132, and a circulating heat conducting oil is arranged in the heating ring 135.

[0046] The collecting tray 131 can collect the condensate at the top of the tower, the gas lifting pipe 133 can prevent the short circuit of the gas phase, the structure of the collecting tray 131 and the distribution pipe 132 can uniformly distribute the reflux liquid, and the wall flow of the rectifying tower 1 can be avoided. The flow guide vane 134 enlarges the liquid dispersion area, and the heating ring 135 can maintain the outlet temperature of the distribution pipe 132 greater than 150 DEG C, so as to avoid the condensation plugging problem of 3-chlorophthalic anhydride at the top of the tower as much as possible.

[0047] In some embodiments, the inner wall of the tower section 12 is provided with a guide groove, the guide groove comprises a first guide part and a second guide part, the first guide part and the second guide part are communicated, the first guide part is arranged along the axial direction of the tower section 12, the second guide part is arranged along the circumferential direction of the tower section 12, the outer wall of the collecting tray 131 is provided with a guide block, and the guide block is slidably arranged in the guide groove. By sliding the guide block along the first guide part and sliding into the second guide part, the collecting tray 131 is rotated to make the guide block clamped in the second guide part, so that the guiding and positioning of the collecting tray 131 are realized during the installation of the collecting tray 131.

[0048] A heat preservation sleeve (not shown in the figure) is arranged between the fourth receiving tank 24 and the melt crystallizer 3. The heat conducting oil is used as the heating medium in the heat preservation sleeve, so as to maintain the temperature in the heat preservation pipe greater than 150 DEG C. The inner wall of the heat preservation sleeve is sprayed with a polytetrafluoroethylene coating. The temperature of the heat preservation pipe is greater than 150 DEG C, so as to ensure that the 3-chlorophthalic anhydride always enters the melt crystallizer 3 in a molten state, avoid the solid phase precipitation, and cause the pipeline to be blocked.

[0049] In another aspect, the application further provides a high-efficiency purification method of chlorophthalic anhydride, which is purified by using the above-mentioned high-efficiency purification system of chlorophthalic anhydride, and comprises the following steps:

[0050] S1: continuously or intermittently sending the crude product containing 3-chlorophthalic anhydride and 4-chlorophthalic anhydride into the tower kettle 11 of the rectifying tower 1;

[0051] S2: starting the reboiler to heat the tower kettle 11, and simultaneously starting the vacuum pumping system to control the reflux ratio;

[0052] S3: sequentially collecting the mixture of phthalic anhydride and 4-chlorophthalic anhydride, pure 4-chlorophthalic anhydride, the mixture of 4-chlorophthalic anhydride and 3-chlorophthalic anhydride, and crude 3-chlorophthalic anhydride from the top and side lines of the column;

[0053] S4: directly feeding the crude 3-chlorophthalic anhydride obtained in step S3 into the melt crystallizer 3 in a molten state;

[0054] S5: performing programmed cooling, temperature rising sweating, and temperature rising discharge in the melt crystallizer 3 to obtain pure 3-chlorophthalic anhydride, sweating liquid, and eutectic oil;

[0055] S6: returning the sweating liquid and eutectic oil obtained in step S5 to the feed inlet 34 of the rectification column 1 in a molten state, and performing rectification again after mixing with fresh crude product.

[0056] The 3-chlorophthalic anhydride and 4-chlorophthalic anhydride are separated by the rectification column 1 in stages to reduce the amount of melt crystallization processing, and the crude 3-chlorophthalic anhydride is directly fed in a molten state, thereby omitting the melting process before crystallization, shortening the production cycle, and improving the purity of the pure 3-chlorophthalic anhydride. The sweating liquid and eutectic oil are reused to form a closed loop, thereby reducing energy consumption, improving the total yield, and meeting the green chemical standard without waste liquid discharge.

[0057] The above are preferred embodiments of the present application, and do not limit the protection scope of the present application, so: any equivalent changes made on the basis of the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A high-efficiency purification system for chlorophthalic anhydride, characterized in that, include: A distillation column (1) is used to supply chlorinated reactants, which are then discharged after being separated by the distillation column (1). Multiple receiving tanks, each of the receiving tanks (2) being connected to the distillation column (1), the receiving tanks (2) including a first receiving tank (21), a second receiving tank (22), a third receiving tank (23) and a fourth receiving tank (24), the first receiving tank (21) being used to collect a mixture of light components and 4-chlorophthalic anhydride, the second receiving tank (22) being used to collect pure 4-chlorophthalic anhydride, the third receiving tank (23) being used to collect a mixture of 4-chlorophthalic anhydride and 3-chlorophthalic anhydride, and the fourth receiving tank (24) being used to collect crude 3-chlorophthalic anhydride; The top of the melt crystallizer (3) is connected to the fourth receiving tank (24). The crude 3-chlorophthalic anhydride extracted from the top of the distillation column (1) is directly molten and enters the melt crystallizer (3) without cooling. After being processed by the melt crystallizer (3), the crude 3-chlorophthalic anhydride is purified to obtain pure 3-chlorophthalic anhydride.

2. The high-efficiency purification system for chlorophthalic anhydride according to claim 1, characterized in that: The melt crystallizer (3) includes a melt shell (31), a melt jacket (32), and a receiving tank (33). The melt jacket (32) is located outside the melt shell (31). The melt jacket (32) is filled with circulating heat transfer oil. The top of the melt shell (31) is provided with an inlet (34) connected to the fourth receiving tank (24). The bottom of the melt shell (31) is provided with an outlet (35). The outlet (35) is connected to the receiving tank (33) through an outlet pipe. The receiving tank (33) is used to collect the pure 3-chlorophthalic anhydride.

3. The high-efficiency purification system for chlorophthalic anhydride according to claim 2, characterized in that: The bottom of the melt crystallizer (3) is provided with a main pipe (36) and a branch pipe (37). The main pipe (36) is connected to the third receiving tank (23) and is used to return sweat and eutectic oil to the third receiving tank (23). A circulation pump (38) is provided on the branch pipe (37). One end of the branch pipe (37) is connected to the outlet (35) of the melt crystallizer (3) through the main pipe (36), and the other end is connected to the inlet (34).

4. The high-efficiency purification system for chlorophthalic anhydride according to claim 2, characterized in that: The melting jacket (32) of the melting crystallizer (3) is divided into three independent temperature control zones, each of which is equipped with an independent heat transfer oil circulation system and a temperature sensor.

5. The high-efficiency purification system for chlorophthalic anhydride according to claim 1, characterized in that: The distillation column (1) includes a reboiler (11), a column section (12), and an internal reflux distributor (13). The reboiler (11) is connected to the column section (12). The reboiler (11) is provided with a raw material inlet (110). The column section (12) is provided with a raw material outlet (111) at the top. The internal reflux distributor (13) is connected to the top of the column section (12) and is connected to the receiving tank. The internal reflux distributor (13) is used to evenly distribute the reflux liquid back to the distillation column (1).

6. The high-efficiency purification system for chlorophthalic anhydride according to claim 5, characterized in that: The internal reflux distributor (13) includes a liquid collection tray (131) and a distribution pipe (132). The liquid collection tray (131) is installed on the inner wall of the tower section (12). A riser pipe (133) is coaxially connected to the liquid collection tray (131). The distribution pipe (132) is located at the bottom of the liquid collection tray (131) and is arranged at intervals along the circumference of the liquid collection tray (131).

7. The high-efficiency purification system for chlorophthalic anhydride according to claim 6, characterized in that: The internal return distributor (13) also includes a guide vane (134), which is sleeved on the outside of the distribution pipe (132). The diameter of the guide vane (134) at the end near the distribution pipe (132) is larger than the diameter at the end away from the distribution pipe (132).

8. The high-efficiency purification system for chlorophthalic anhydride according to claim 7, characterized in that: A heating ring (135) is provided at the outlet of the distribution pipe (132). The heating ring (135) is spirally wound around the outlet section of the distribution pipe (132). Circulating heat transfer oil is provided inside the heating ring (135).

9. The high-efficiency purification system for chlorophthalic anhydride according to claim 6, characterized in that: A heat-insulating sleeve is provided between the fourth receiving tank (24) and the melting crystallizer (3). The heating medium in the heat-insulating sleeve is heat-conducting oil to maintain the temperature inside the heat-insulating sleeve above 150°C. The inner wall of the heat-insulating sleeve is coated with polytetrafluoroethylene.

10. A method for efficient purification of chlorophthalic anhydride, characterized in that, Purification is performed using any one of the high-efficiency purification systems for chlorophthalic anhydride according to claims 1-9, characterized by comprising the following steps: S1: The crude product containing 3-chlorophthalic anhydride and 4-chlorophthalic anhydride is continuously or intermittently fed into the bottom (11) of the distillation column (1); S2: Turn on the reboiler to heat up the column (11), and at the same time start the vacuum system to control the reflux ratio; S3: The mixture of phthalic anhydride and 4-chlorophthalic anhydride, pure 4-chlorophthalic anhydride, the mixture of 4-chlorophthalic anhydride and 3-chlorophthalic anhydride, and crude 3-chlorophthalic anhydride are successively collected from the top and side stream of the tower. S4: The crude 3-chlorophthalic anhydride obtained in step S3 is directly fed into the melt crystallizer (3) in a molten state; S5: The crude molten 3-chlorophthalic anhydride is subjected to programmed cooling, heating and sweating, and heating and discharge in a melt crystallizer (3) to obtain pure 3-chlorophthalic anhydride, as well as sweating liquid and eutectic oil; S6: The sweating liquid and eutectic oil obtained in step S5 are returned to the feed inlet (34) of the distillation column (1) in a molten state, mixed with the fresh crude product, and then distilled again.

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