Systems and methods for purifying meta-dichlorobenzene from a mixture of dichlorobenzenes

Abstract

The application discloses a system and method for purifying meta-dichlorobenzene from mixed dichlorobenzene. The system for purifying meta-dichlorobenzene from mixed dichlorobenzene comprises a meta-position tower A and a meta-position tower B, a tower kettle of the meta-position tower A is connected with a feeding port of the meta-position tower B, a tower top of the meta-position tower B is connected with the feeding port of the meta-position tower A, and a meta-position outlet is arranged on the tower top of the meta-position tower A; the meta-position tower A and the meta-position tower B are both packed rectification towers, wherein the packing is high-efficiency silk screen packing, and the theoretical plate number of the meta-position tower A and the meta-position tower B is not less than 100. The purification system of the application uses simple rectification equipment, the purity of the purified meta-dichlorobenzene is high, the product yield is high, and the equipment and operation cost are low.

Description

TECHNICAL FIELD

[0001] The present application relates to a system and method for purifying meta-dichlorobenzene from a mixture of dichlorobenzene. BACKGROUND

[0002] Meta-dichlorobenzene, also known as 1,3-dichlorobenzene, has a molecular formula of C6H4Cl2, is a colorless liquid with a pungent odor, is insoluble in water, soluble in alcohol and ether, can undergo chlorination, nitration, sulfonation, hydrolysis reaction, and reacts violently with aluminum, and is an organic compound with the same molecular formula as para-dichlorobenzene and ortho-dichlorobenzene. Meta-dichlorobenzene is a very important fine chemical organic chemical raw material, mainly used in the production of pharmaceuticals, pigments, dyes and pesticides, and also used in organic synthesis and organic solvents, and is an indispensable chemical product. In recent years, the medical field has developed rapidly, and the market demand for high-purity meta-dichlorobenzene has increased sharply, and the domestic and foreign markets are in short supply. Direct chlorination of benzene and transposition reaction of para-dichlorobenzene are the main synthesis methods for preparing meta-dichlorobenzene, and both methods produce a mixture of three isomers. Therefore, how to obtain high-purity meta-dichlorobenzene from a mixture of three isomers has always been a hot topic in the field.

[0003] The traditional method for separating meta-dichlorobenzene is a combination of crystallization and rectification. Soviet Union patents 1460061 and 1766898 report similar methods. This method is to separate para-dichlorobenzene from a mixture of dichlorobenzene isomers by crystallization, and the mother liquor is distilled, ortho-dichlorobenzene is enriched in the distillation residue, and the distillate is recrystallized to precipitate para-dichlorobenzene and obtain a mother liquor enriched in meta-dichlorobenzene. This method does not produce high-purity meta-dichlorobenzene, has low separation efficiency, and has high cost; in addition, the purification method combining crystallization and rectification requires a large number of equipment, which has high equipment cost. European patent EP451720 proposes adding extractants hexamethylphosphoramide and sulfolane to a mixture of meta-dichlorobenzene and para-dichlorobenzene to separate the two isomers by extractive distillation. The disadvantages of this method are that the purity and yield of the obtained meta-dichlorobenzene are not ideal. SUMMARY

[0004] The technical problem solved by the present application is to overcome the defects of low separation purity, low product yield and high equipment cost in the prior art method for purifying meta-dichlorobenzene from a mixture of dichlorobenzene, and to provide a system and method for purifying meta-dichlorobenzene from a mixture of dichlorobenzene. The purification system of the present application uses only rectification equipment, has high-purity meta-dichlorobenzene, high product yield, and low equipment and operating cost.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The present application provides a system for purifying meta-dichlorobenzene from mixed dichlorobenzene, which comprises: a meta-tower A and a meta-tower B, the tower bottom of the meta-tower A is connected with the feed inlet of the meta-tower B, the tower top of the meta-tower B is connected with the feed inlet of the meta-tower A, and the tower top of the meta-tower A is provided with a meta-extraction outlet; the meta-tower A and the meta-tower B are both packed distillation towers, wherein the packing is high-efficiency silk screen packing, the theoretical plate number of the meta-tower A is not less than 100, and the theoretical plate number of the meta-tower B is not less than 100.

[0007] In the present application, the theoretical plate number of the meta-tower A is preferably 100-120.

[0008] In the present application, the theoretical plate number of the meta-tower B is preferably 100-120.

[0009] In the present application, preferably, the position of the feed inlet of the meta-tower A is in the tower.

[0010] In the present application, preferably, the tower bottom of the meta-tower A is further connected with a reboiler A, and the outlet of the reboiler A is connected with the tower bottom of the meta-tower A.

[0011] In the present application, preferably, the reboiler A is a falling film reboiler.

[0012] Due to the gas phase and gravity, the descending of the liquid phase in the falling film reboiler is accelerated, thereby shortening the residence time, reducing the pressure drop, reducing the temperature difference between the inlet and outlet, and being more suitable for heat-sensitive substances.

[0013] In the present application, it is generally understood by those skilled in the art that the meta-extraction outlet is a meta-dichlorobenzene extraction outlet.

[0014] In the present application, the tower bottom of the meta-tower B is further connected with a reboiler B, and the outlet of the reboiler B is connected with the tower bottom of the meta-tower B.

[0015] In the present application, preferably, the reboiler B is a falling film reboiler.

[0016] In the present application, preferably, the tower bottom of the meta-tower B is further provided with an ortho-extraction outlet.

[0017] In the present application, the ortho-extraction outlet generally extracts ortho-toluene, para-xylene and some by-product trichloromethylbenzene.

[0018] In the present application, the system preferably further comprises a heavy component removal tower, the tower top of the heavy component removal tower is connected with the feed inlet of the meta-tower A, and the heavy component removal tower is used for removing tar, salt and heavy components in the mixed dichlorobenzene.

[0019] In the present application, the heavy components are generally materials that are not easy to evaporate.

[0020] The heavy component removal column is preferably a packed distillation column. The packing can be conventional in the art, and is preferably a plate wave structured packing.

[0021] The number of theoretical plates of the heavy component removal column can be calculated conventionally in the art, and is preferably 18-25, more preferably 20.

[0022] The position of the feed inlet of the heavy component removal column is preferably in the middle of the column.

[0023] Preferably, the column sump of the heavy component removal column is further connected to a wiped film evaporator or a stirred tank, and is preferably further connected to a stirred tank, the overhead outlet of which is connected to the column sump of the heavy component removal column for refluxing the vaporized gas components in the stirred tank to the column sump of the heavy component removal column.

[0024] Further preferably, the sump of the stirred tank is further connected to a reboiler C, the outlet of which is connected to the column sump of the heavy component removal column.

[0025] The reboiler C is preferably a falling film reboiler.

[0026] Further preferably, the sump of the stirred tank is connected to a heavy component outlet for withdrawing part of the liquid in the sump of the stirred tank.

[0027] In the present application, the system preferably further comprises a light component removal column, the column sump of which is connected to the feed inlet of the meta-position column A for removing light components in the mixed dichlorobenzene.

[0028] The light components can be components conventionally present in the mixed dichlorobenzene having a boiling point lower than that of the meta-dichlorobenzene, and generally include chlorobenzene.

[0029] The light component removal column is preferably a packed distillation column. The packing can be conventional in the art, and is preferably a plate wave structured packing.

[0030] The number of theoretical plates of the light component removal column can be calculated conventionally in the art, and is preferably 15-25.

[0031] The position of the feed inlet of the light component removal column can be conventional in the art, and is preferably in the upper half of the light component removal column.

[0032] Preferably, the column sump of the light component removal column is further connected to a reboiler D, the outlet of which is connected to the column sump of the light component removal column.

[0033] Preferably, the column top of the light component removal column is provided with a light component outlet.

[0034] In some preferred embodiments of the present application, the system comprises, in sequence, the heavy-removing column, the light-removing column, the meta-column A and the meta-column B, the top of the heavy-removing column is connected to the feed inlet of the light-removing column, and the bottom of the light-removing column is connected to the feed inlet of the meta-column A.

[0035] In the present application, the system preferably further comprises an ortho-column, which is a rectifying column, the feed inlet of the ortho-column is connected to the bottom of the meta-column B, for separating the ortho-dichlorobenzene and the para-dichlorobenzene in the bottom liquid of the meta-column B.

[0036] In the present application, the ortho-column is preferably a packed rectifying column.

[0037] The packing in the packed rectifying column is preferably plate-corrugated regular packing.

[0038] In the present application, the number of theoretical plates of the ortho-column is preferably 15-25, more preferably 20

[0039] In the present application, the feed inlet of the ortho-column is preferably located in the lower half of the ortho-column.

[0040] In the present application, the bottom of the ortho-column is preferably further connected to a reboiler E, the outlet of the reboiler E is connected to the bottom of the ortho-column.

[0041] In the present application, the bottom of the ortho-column is preferably further provided with a trichlorobenzene outlet.

[0042] In the present application, the top of the ortho-column is preferably further provided with an ortho-column outlet.

[0043] The present application further provides a method for purifying meta-dichlorobenzene from mixed dichlorobenzene, which comprises the following steps: using the system for purifying meta-dichlorobenzene from mixed dichlorobenzene as described above, feeding the mixed dichlorobenzene into the feed inlet of the meta-column A, and the meta-dichlorobenzene purified is taken out from the meta-column outlet; the mixed dichlorobenzene comprises meta-dichlorobenzene, para-dichlorobenzene and ortho-dichlorobenzene, the pressure drop of the meta-column A is not more than 30 mbar, and the pressure drop of the meta-column B is not more than 30 mbar.

[0044] In the present application, the mass percentage of the meta-dichlorobenzene in the mixed dichlorobenzene is preferably not less than 45%, more preferably 48%.

[0045] In the present application, the mass percentage of the para-dichlorobenzene in the mixed dichlorobenzene is preferably not more than 25%, for example 24%.

[0046] In the present application, the mass percentage of the ortho-dichlorobenzene in the mixed dichlorobenzene can be conventional in the art, and is preferably not more than 25%, for example 20%.

[0047] In the present application, the feed temperature of the meta-tower A is preferably 139.9-145°C, more preferably 139.9°C.

[0048] In the present application, the reflux temperature of the meta-tower A can be conventional in the art, preferably 50°C.

[0049] In the present application, the reflux of the meta-tower A is preferably 10-20, more preferably 13-17, and further more preferably 15.

[0050] In the present application, the feed temperature of the meta-tower B is preferably 136-145°C, more preferably 142.3°C.

[0051] In the present application, the reflux temperature of the meta-tower B can be conventional in the art, preferably 50°C.

[0052] In the present application, the reflux of the meta-tower B is preferably 15-25, more preferably 20.

[0053] In the present application, preferably, when the mixed dichlorobenzene further comprises organic salts and heavy components, the system further comprises the heavy component removal tower, and the mixed dichlorobenzene is fed into the feed inlet of the heavy component removal tower.

[0054] The heavy components refer to tar or other components difficult to evaporate generated in the synthesis of meta-dichlorobenzene.

[0055] The mass percentage of the organic salts and the heavy components in the mixed dichlorobenzene is conventional in the art, and has little effect on the separation and purification effect of the present application.

[0056] The pressure drop of the heavy component removal tower is preferably not more than 10 mbar, more preferably 10 mbar.

[0057] The feed temperature of the heavy component removal tower can be conventional in the art, preferably 110-130°C, more preferably 115-125°C, and further more preferably 120°C.

[0058] The reflux temperature of the heavy component removal tower is preferably 55-65°C, more preferably 60°C.

[0059] The reflux of the heavy component removal tower is preferably 0.8-1.5, more preferably 1.

[0060] In the present application, preferably, when the mixed dichlorobenzene further comprises light components, the system further comprises the light component removal tower, and the mixed dichlorobenzene is fed into the feed inlet of the light component removal tower.

[0061] The light component can be a component with a boiling point lower than the m-dichlorobenzene, generally including chlorobenzene.

[0062] The mass percentage of the light component in the mixed dichlorobenzene can be conventional in the art, and has little effect on the separation and purification of the m-dichlorobenzene.

[0063] The pressure drop of the light-removing column is preferably not more than 10 mbar, and more preferably 10 mbar.

[0064] The feed temperature of the light-removing column can be conventional in the art, and is preferably 139-145°C, and more preferably 144.5°C.

[0065] The reflux temperature at the top of the light-removing column is preferably 45-55°C, and more preferably 50°C.

[0066] The reflux ratio of the light-removing column is preferably 8-15, and more preferably 10.

[0067] In the present application, preferably, when the mixed dichlorobenzene further includes trichlorobenzene, the system further includes the ortho column, and the ortho outlet of the m-position column B is connected to the feed inlet of the ortho column.

[0068] The trichlorobenzene is a by-product produced in the synthesis process of the m-dichlorobenzene, and is generally 1,2,4-trichlorobenzene.

[0069] The mass percentage of the trichlorobenzene in the mixed dichlorobenzene can be conventional in the art, and has little effect on the separation and purification of the m-dichlorobenzene.

[0070] The pressure drop of the ortho column is preferably not more than 10 mbar, and more preferably 10 mbar.

[0071] The feed temperature of the ortho column can be conventional in the art, and is preferably 138-145°C, and more preferably 143.3°C.

[0072] The reflux temperature at the top of the ortho column is preferably 65-75°C, and more preferably 70°C.

[0073] The reflux ratio of the ortho column is preferably 1.5-3, and more preferably 2.

[0074] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0075] The reagents and raw materials used in the present application are commercially available.

[0076] The positive progress effect of the present application is that:

[0077] (1) The system flow of the rectification system is simple, and a composite process of rectification and crystallization is not needed. Only by using high-efficiency packing, the purpose of purifying meta-dichlorobenzene is achieved by rectification, and the purity of meta-dichlorobenzene is more than 80%.

[0078] (2) The first yield is high. In the rectification process, the yield of meta-dichlorobenzene is more than 98wt%. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 The system flow chart of purifying meta-dichlorobenzene from mixed dichlorobenzene in Example 1.

[0080] Reference Signs:

[0081] T101 - heavy-removing column, T102 - light-removing column, T103 - meta-position column A, T104 - meta-position column B, T105 - ortho-position column. DETAILED DESCRIPTION

[0082] The present application will be further described by way of examples, but the present application is not limited in the scope of the examples. The experimental methods in the following examples, if not specified, are selected according to the conventional methods and conditions, or according to the commercial instruction.

[0083] Example 1

[0084] Reference Figure 1As shown, the system for purifying meta-dichlorobenzene from mixed dichlorobenzene of the embodiment includes a heavy-removing column T101, a light-removing column T102, a meta-position column A T103, a meta-position column B T104, and an ortho-position column T105. The top of the heavy-removing column T101 is connected to the feed inlet of the light-removing column T102. The top of the light-removing column T102 is provided with a light component outlet. The column bottom of the light-removing column T102 is connected to the feed inlet of the meta-position column A T103. The column bottom of the meta-position column A T103 is connected to the feed inlet of the meta-position column B T104. The top of the meta-position column B T104 is connected to the feed inlet of the meta-position column A T103. The column bottom of the meta-position column B T104 is connected to the feed inlet of the ortho-position column T105. The column bottom of the heavy-removing column T101 is connected to a stirred tank. The top of the stirred tank is connected to the column bottom of the heavy-removing column T101. The bottom of the stirred tank is connected to a heavy component outlet for taking out part of the liquid at the bottom of the stirred tank. The bottom of the stirred tank is also connected to a falling film reboiler C. The outlet of the falling film reboiler C is connected to the column bottom of the heavy-removing column T101. The column bottom of the light-removing column T102 is connected to the inlet of a falling film reboiler D. The outlet of the falling film reboiler D is connected to the column bottom of the light-removing column T102. The column bottom of the meta-position column A T103 is connected to the inlet of a falling film reboiler A. The outlet of the falling film reboiler A is connected to the column bottom of the meta-position column A T103. The column bottom of the meta-position column B T104 is connected to the inlet of a falling film reboiler B. The outlet of the falling film reboiler B is connected to the column bottom of the meta-position column B T104. The column bottom of the ortho-position column T105 is connected to the inlet of a falling film reboiler E. The outlet of the falling film reboiler E is connected to the column bottom of the ortho-position column T105. The top of the light-removing column T102 is provided with a light component outlet. The top of the meta-position column A T103 is provided with a meta-position outlet. The top of the ortho-position column T105 is provided with an ortho-position outlet. The column bottom of the ortho-position column T105 is provided with a trichlorobenzene outlet. The heavy-removing column T101, the light-removing column T102, the meta-position column A T103, the meta-position column B T104, and the ortho-position column T105 are all packed distillation columns. The packing of the meta-position column A T103 and the meta-position column B T104 is high-efficiency silk screen packing. The packing of the heavy-removing column T101, the light-removing column T102, and the ortho-position column T105 is plate corrugated structured packing. The theoretical plate number and the feed location of each column are shown in Table 1.

[0085] The mixed dichlorobenzene contains 48% meta-dichlorobenzene, 24% para-dichlorobenzene, 20% ortho-dichlorobenzene, 4% chlorobenzene, 2.9% 1,2,4-trichlorobenzene, 1% heavy components and 0.1% H2O. The mixed dichlorobenzene is introduced into the system as above through the feed inlet of the heavy component removal column T101, and the pressure drop of each column, the reflux ratio of the column top and the reflux temperature of the column top are shown in Table 1 respectively. The salt and heavy components are taken out from the stirred tank bottom of the heavy component removal column T101, the light components are taken out from the column top of the light component removal column T102, the meta-dichlorobenzene is taken out from the meta-position outlet of the column top of the meta-position column A T103, the ortho-dichlorobenzene and para-dichlorobenzene are taken out from the ortho-position outlet of the column top of the ortho-position column T105, and the 1,2,4-trichlorobenzene is taken out from the trichlorobenzene outlet of the column bottom of the ortho-position column T105. Figure 1 The compositions and qualities of the streams in the system are shown in Table 2, Figure 1 The temperature, pressure and phase state of each stream are shown in Table 3.

[0086] Table 1 System parameters and process parameters of each column in Example 1

[0087]

[0088] Table 2 Quality and composition table of each stream

[0089]

[0090]

[0091] Table 3 Phase state, temperature and pressure table of each stream

[0092] Logistics number Phase Temperature / °C Pressure / mbar 101 Liquid phase 120.0 3000 102 Gas phase 144.5 455 103 Liquid phase 80.0 3000 104 Liquid phase 139.9 3000 105 Liquid phase 93.5 3000 106 Liquid phase 142.3 3000 107 Liquid phase 131.7 3000 108 Liquid phase 143.3 3000 109 Liquid phase 131.6 3000 110 Liquid phase 139.5 3000 111 ​ 102.2 3000

[0093] As can be seen from Table 2, the purity of the meta-dichlorobenzene separated and purified in the present example is as high as 82%, the total quality taken out from the meta-position outlet is 747 kg, and the calculated recovery rate of the meta-dichlorobenzene is 98.16%. The content of chlorobenzene in the light components separated by the light component removal column is 97.5924%, realizing high concentration purification of chlorobenzene; the purity of the trichlorobenzene taken out from the column bottom of the light component removal column is as high as 99.9474%, the components taken out from the column top of the light component removal column are mainly ortho-dichlorobenzene and para-dichlorobenzene, and the concentrations of the two are 40.3660% and 58.7847% respectively, and the sum of the concentrations of the two is 99.1507%. It can be seen that the separation system and the separation process of the present example realize high purity and high yield purification of the meta-dichlorobenzene in the mixed dichlorobenzene, and at the same time, the main impurity components chlorobenzene and trichlorobenzene are all realized high purity recovery, and at the same time, the mixture of ortho-dichlorobenzene and para-dichlorobenzene is realized high purity recovery.

[0094] From Table 3, it can be seen that the overhead vapor temperature of T103 and T104 is higher than 130℃, which can be used to regenerate steam, recover heat and reduce energy consumption; the use of falling film reboiler can reduce the residence time of materials in the rectification process, reduce the heat exchange temperature difference, reduce the coking phenomenon at high temperature and reduce the amount of tar in the rectification process.

Claims

1. A system for purifying meta-dichlorobenzene from a mixture of dichlorobenzenes, characterized in that, The system comprises a meta-position tower A and a meta-position tower B, the tower kettle of the meta-position tower A is connected with the feed inlet of the meta-position tower B, the tower top of the meta-position tower B is connected with the feed inlet of the meta-position tower A, and the tower top of the meta-position tower A is provided with a meta-position outlet; the meta-position tower A and the meta-position tower B are both packed rectification towers, wherein the packing is high-efficiency silk screen packing, and the theoretical plate number of the meta-position tower A and the meta-position tower B is not less than 100; The system further comprises a heavy component removal tower, and the tower top of the heavy component removal tower is connected with the feed inlet of the meta-position tower A; The system further comprises a light component removal tower, the tower kettle of the light component removal tower is connected with the feed inlet of the meta-position tower A, and the light component removal tower is used for removing light components in the mixed dichlorobenzene; The system further comprises an ortho-position tower, the ortho-position tower is a rectification tower, the feed inlet of the ortho-position tower is connected with the tower kettle of the meta-position tower B, and the ortho-position tower is used for separating ortho-dichlorobenzene and para-dichlorobenzene in the tower kettle liquid of the meta-position tower B.

2. The system for purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 1, wherein, The theoretical plate number of the meta-position tower A is 100-120; And / or, the theoretical plate number of the meta-position tower B is 100-120; And / or, the position of the feed inlet of the meta-position tower A is the middle part of the tower; And / or, the tower kettle of the meta-position tower A is further connected with a reboiler A, and the outlet of the reboiler A is connected with the tower kettle of the meta-position tower A; And / or, the tower kettle of the meta-position tower B is further connected with a reboiler B, and the outlet of the reboiler B is connected with the tower kettle of the meta-position tower B; And / or, the tower kettle of the meta-position tower B is further provided with an ortho-position outlet.

3. The system for purifying m-dichlorobenzene from mixed dichlorobenzenes according to claim 1, wherein The heavy component removal tower is a packed rectification tower with plate corrugated regular packing.

4. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The theoretical plate number of the heavy component removal tower is 18-25.

5. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 4, wherein, The theoretical plate number of the heavy component removal tower is 20.

6. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The feeding position of the heavy component removal tower is the middle part of the tower.

7. The system for purifying m-dichlorobenzene from mixed dichlorobenzenes of claim 1, wherein, The tower kettle of the heavy component removal tower is further connected with a wiped film evaporator or a stirred tank, the kettle top outlet of the stirred tank is connected with the tower kettle of the heavy component removal tower, and the evaporated gas components in the stirred tank are returned to the tower kettle of the heavy component removal tower.

8. The system for purifying m-dichlorobenzene from mixed dichlorobenzenes according to claim 7, wherein The kettle bottom of the stirred tank is further connected with a reboiler C, and the outlet of the reboiler C is connected with the tower kettle of the heavy component removal tower.

9. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The light component removal tower is a packed rectification tower with plate corrugated regular packing.

10. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes according to claim 1, wherein The theoretical plate number of the light component removal tower is 15-25.

11. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The position of the feed inlet of the light component removal tower is the upper half of the light component removal tower.

12. The system for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 1 wherein, The tower kettle of the light component removal tower is further connected with a reboiler D, and the outlet of the reboiler D is connected with the tower kettle of the light component removal tower.

13. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The tower top of the light component removal tower is provided with a light component outlet.

14. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The ortho-position tower is a packed rectification tower with plate corrugated regular packing.

15. The system for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 1 wherein, The theoretical plate number of the ortho-position tower is 15-25.

16. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes according to claim 15, wherein The theoretical plate number of the ortho-position tower is 20.

17. The system for purifying m-dichlorobenzene from a mixture of dichlorobenzenes of claim 1, wherein, The position of the feed inlet of the ortho-position tower is the lower half of the ortho-position tower.

18. The system for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 1 wherein, The tower kettle of the ortho-position tower is further connected with a reboiler E, and the outlet of the reboiler E is connected with the tower kettle of the ortho-position tower.

19. The system for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 1 wherein, The tower kettle of the ortho-position tower is further provided with a trichlorobenzene outlet.

20. The system for purification of m-dichlorobenzene from mixed dichlorobenzenes of claim 1, wherein, The tower top of the ortho-position tower is further provided with an ortho-position outlet.

21. A process for purifying meta-dichlorobenzene from a mixture of dichlorobenzenes, characterized by, It comprises the following steps: it is carried out by using the system for purifying meta-dichlorobenzene in mixed dichlorobenzene as claimed in any one of claims 1-20, the mixed dichlorobenzene is fed from the feed port of the heavy-removing tower, and the meta-dichlorobenzene collected from the meta-tower outlet is the purified meta-dichlorobenzene; the mixed dichlorobenzene comprises meta-dichlorobenzene, para-dichlorobenzene and ortho-dichlorobenzene, the pressure drop of the meta-tower A is not more than 30 mbar, and the pressure drop of the meta-tower B is not more than 30 mbar.

22. The process for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 21, wherein, The mass percentage of the meta-dichlorobenzene in the mixed dichlorobenzene is not less than 45%; And / or, the mass percentage of the para-dichlorobenzene in the mixed dichlorobenzene is not more than 25%; And / or, the mass percentage of the ortho-dichlorobenzene in the mixed dichlorobenzene is not more than 25%.

23. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 22, wherein, The mass percentage of the meta-dichlorobenzene in the mixed dichlorobenzene is 48%; And / or, the mass percentage of the para-dichlorobenzene in the mixed dichlorobenzene is 24%; And / or, the mass percentage of the ortho-dichlorobenzene in the mixed dichlorobenzene is 20%.

24. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The feed temperature of the meta-tower A is 139.9-145℃; And / or, the reflux temperature at the top of the meta-tower A is 50℃; And / or, the reflux ratio at the top of the meta-tower A is 10-20; And / or, the feed temperature of the meta-tower B is 136-145℃; And / or, the reflux temperature at the top of the meta-tower B is 50℃; And / or, the reflux ratio at the top of the meta-tower B is 15-25.

25. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 24, wherein, The feed temperature of the meta-tower A is 139.9℃; And / or, the reflux ratio at the top of the meta-tower A is 13-17; And / or, the feed temperature of the meta-tower B is 142.3℃; And / or, the reflux ratio at the top of the meta-tower B is 20.

26. The process for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 25, wherein, The reflux ratio at the top of the meta-tower A is 15.

27. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The pressure drop of the heavy-removing tower is not more than 10 mbar.

28. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 27, wherein, The pressure drop of the heavy-removing tower is 10 mbar.

29. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The feed temperature of the heavy-removing tower is 110-130℃.

30. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 29, wherein, The feed temperature of the heavy-removing tower is 115-125℃.

31. The process for purification of m-dichlorobenzene from mixed dichlorobenzenes as claimed in claim 30 wherein, The feed temperature of the heavy-removing tower is 120℃.

32. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The reflux temperature at the top of the heavy-removing tower is 55-65℃.

33. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 32, wherein, The reflux temperature at the top of the heavy-removing tower is 60℃.

34. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The reflux ratio at the top of the heavy-removing tower is 0.8-1.

5.

35. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 34, wherein, The reflux ratio at the top of the heavy-removing tower is 1.

36. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The pressure drop of the light-removing tower is not more than 10 mbar.

37. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 36, wherein, The pressure drop of the light-removing tower is 10 mbar.

38. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The feed temperature of the light-removing tower is 139-145℃.

39. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 38, wherein, The feed temperature of the light-removing tower is 144.5℃.

40. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The reflux temperature at the top of the light-removing tower is 45-55℃.

41. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 40, wherein, The reflux temperature at the top of the light-removing tower is 50℃.

42. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The reflux ratio at the top of the light-removing tower is 8-15.

43. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 42, wherein, The reflux ratio at the top of the light-removing tower is 10.

44. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The pressure drop of the ortho-tower is not more than 10 mbar.

45. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 44, wherein, The pressure drop of the ortho-tower is 10 mbar.

46. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The feed temperature of the ortho-tower is 138-145℃.

47. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes according to claim 46, wherein, The feed temperature of the ortho-tower is 143.3℃.

48. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The reflux temperature at the top of the ortho-tower is 65-75℃.

49. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 48, wherein, The reflux temperature at the top of the ortho-tower is 70℃.

50. The process of purifying m-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 21, wherein, The overhead reflux ratio of the adjacent tower is 1.5-3.

51. The process of purifying meta-dichlorobenzene from a mixture of dichlorobenzenes as claimed in claim 50, wherein, The overhead reflux ratio of the adjacent tower is 2.

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