Method and system for continuous separation of a mixture of chlorobenzene, methanol and water

Abstract

The present invention belongs to the field of chemical separation technology, and specifically relates to a method and system for continuously separating a mixture of chlorobenzene, methanol, and water. The method of the present invention comprises the following steps: S1. adding n-alkanes as entrainers to perform azeotropic distillation on the raw materials; obtaining a mixture of alkanes and methanol at the top of the tower, and obtaining a mixture of chlorobenzene, water, and methanol at the bottom of the tower; S2. phase-splitting the mixture of alkanes, methanol, and water obtained in step S1 to obtain an alkane phase and a methanol / alkane / water phase; distilling the methanol / alkane / water phase to obtain alkanes at the top of the tower, and obtaining a methanol and water mixture at the bottom of the tower; S3. distilling the methanol and water mixture obtained in step S2 to obtain a methanol product at the top of the tower; S4. phase-splitting the mixture of chlorobenzene, water, and alkanes obtained in step S1 to obtain a water phase and a chlorobenzene / alkane phase; distilling the chlorobenzene / alkane phase to obtain a chlorobenzene product at the bottom of the tower. The present invention achieves complete separation of the raw materials.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation, and in particular relates to a method and system for continuously separating a mixture of chlorobenzene, methanol and water. Background Art

[0002] In the preparation of organic compounds such as pesticides and medicines, a variety of solvents are often used. Among them, chlorobenzene and methanol are commonly used solvents. The simultaneous use of chlorobenzene and methanol as solvents in the preparation of compounds results in the production of a mixture of chlorobenzene, methanol and water; chlorobenzene, methanol and water need to be separated, and the purity of chlorobenzene and methanol must reach more than 99.9% before returning to the reaction section. When trying to separate the above mixture, it was found that methanol and chlorobenzene form a similar azeotrope at normal pressure, and the two-phase phase diagram of the two is shown in Figure 1 The boiling point of a similar azeotrope is 70°C, while the boiling point of methanol is 64°C. The difference in boiling points is so small that conventional distillation methods cannot completely separate the two. This is especially true when the feedstock contains a high content of methanol and low contents of chlorobenzene and water. Simple phase separation processes will not produce phase separation. Extractive distillation using water as the extractant also fails to effectively separate methanol and chlorobenzene.

[0003] Therefore, a method for completely separating a mixture of chlorobenzene, methanol and water is needed to obtain high-purity chlorobenzene and methanol. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for continuously separating a mixture of chlorobenzene, methanol and water. The method adopts continuous azeotropic distillation combined with overhead phase separation and atmospheric pressure continuous distillation to separate methanol and chlorobenzene, thereby obtaining high-purity methanol and chlorobenzene.

[0005] The specific technical solutions are as follows:

[0006] One of the objects of the present invention is to provide a method for continuously separating a mixture of chlorobenzene, methanol and water, which comprises the steps of:

[0007] S1. Adding an alkane as an azeotropic agent, azeotropic distillation of a mixture of chlorobenzene, methanol and water as a raw material; the alkane is a normal alkane; the top of the tower is a mixture of alkanes, methanol and water, and the bottom of the tower is a mixture of chlorobenzene, water and alkanes;

[0008] S2. The mixture of alkanes, methanol and water obtained in step S1 is phase-separated to obtain an alkane phase and a methanol / alkane / water phase; the methanol / alkane / water phase is distilled to obtain alkanes at the top and a mixture of methanol and water at the bottom;

[0009] S3. The mixture of methanol and water obtained in step S2 is distilled to obtain a methanol product at the top of the tower;

[0010] S4. The mixture of chlorobenzene, water and alkanes obtained in step S1 is phase-separated to obtain an aqueous phase and a chlorobenzene / alkane phase; the chlorobenzene / alkane phase is distilled to obtain alkanes at the top of the tower and a chlorobenzene product in the bottom of the tower.

[0011] The mechanism of the present method is as follows: methanol and chlorobenzene form a similar azeotrope at normal pressure, with a boiling point very close to that of methanol, making them difficult to separate. To address this issue, the present invention uses n-alkanes as entrainers, first passing through an azeotropic distillation tower to produce an azeotrope of methanol, alkanes, and a small amount of water. The alkanes are then separated from the methanol and water by phase separation, and the methanol-water mixture is distilled to produce the methanol product. The chlorobenzene-water mixture in the bottom of the tower contains a small amount of alkanes, and after phase separation, chlorobenzene mixed with a small amount of alkanes is obtained, which is then distilled to produce the chlorobenzene product.

[0012] Furthermore, the n-alkanes are preferably at least one of n-pentane, n-hexane and n-heptane.

[0013] Furthermore, in step S1, the mass ratio of the raw material to the alkane is preferably 1:(0.3-4).

[0014] Furthermore, the alkane obtained in step S2 can be returned to the azeotropic distillation for recycling as an entrainer. The alkane obtained from the top of the methanol / alkane / water phase distillation column, which also contains a small amount of methanol, is preferably subjected to phase separation before being returned to the azeotropic distillation for recycling.

[0015] Furthermore, the alkane obtained in step S4 can be returned to the azeotropic distillation for recycling as an entrainer.

[0016] Furthermore, in step S2, the mixture of alkane, methanol and water is condensed, cooled and then phase-separated, and the phase separation temperature is preferably 3-45°C.

[0017] Furthermore, in step S4, the mixture of chlorobenzene, water and alkane is cooled and then phase-separated, and the phase separation temperature is preferably 3 to 45°C.

[0018] Furthermore, in step S1, the process conditions of azeotropic distillation are preferably: carried out under normal pressure, with a top temperature of 50-60°C, a bottom temperature of 60-80°C, an azeotropic ratio of (0.5-5):1, and a reflux ratio of 4-10.

[0019] Furthermore, in step S2, the distillation process conditions are preferably: carried out under normal pressure, with a tower top temperature of 50-66°C, a tower bottom temperature of 60-90°C, and a reflux ratio of 3-15.

[0020] Furthermore, in step S3, the distillation process conditions are preferably: carried out under normal pressure, with a tower top temperature of 64-68° C., a tower bottom temperature of 98-103° C., and a reflux ratio of 1-12.

[0021] Furthermore, in step S4, the distillation process conditions are preferably: carried out under normal pressure, with a tower top temperature of 50-70° C., a tower bottom temperature of 130-140° C., and a reflux ratio of 0.5-5.

[0022] Furthermore, in the mixture of chlorobenzene, methanol and water used as raw materials, the methanol content is 45wt% to 90wt%, the chlorobenzene content is 3wt% to 20wt%, and the water content is 7wt% to 35wt%.

[0023] A second object of the present invention is to provide a system for continuously separating a mixture of chlorobenzene, methanol, and water, which can be used to implement the above-mentioned method for continuously separating a mixture of chlorobenzene, methanol, and water. The system comprises an azeotropic distillation column TI, a methanol / alkane distillation column TII, a methanol distillation column TIII, and a chlorobenzene / alkane distillation column TIV.

[0024] The top of the azeotropic distillation tower TI leads to the TI top phase separator, and the TI top phase separator leads to the methanol / alkane distillation tower TII; the bottom of the methanol / alkane distillation tower TII leads to the methanol distillation tower TIII;

[0025] The bottom of the azeotropic distillation tower TI leads to the phase separator of the bottom of the tower TI; and the phase separator of the bottom of the tower TI leads to the chlorobenzene / alkane distillation tower TIV.

[0026] Furthermore, a TI condenser and a TI top cooler are sequentially arranged on the pipeline from the azeotropic distillation tower TI to the TI tower top phase separator; a TI tower bottom cooler is arranged on the pipeline from the azeotropic distillation tower TI to the TI tower bottom phase separator; and the condensed and cooled fractions are further phase-separated.

[0027] Specifically, it is preferred to set up two stages of TI condensers, namely a TI primary condenser and a TI secondary condenser.

[0028] Furthermore, the top phase separator of the TI tower leads to the azeotropic distillation tower TI; the top of the methanol / alkane distillation tower TII leads to the top phase separator of the TI tower; and the top of the chlorobenzene / alkane distillation tower TIV leads to the azeotropic distillation tower TI.

[0029] Specifically, a TII top cooler is preferably provided on the pipeline from the top of the methanol / alkane distillation tower TII to the TII top phase separator.

[0030] Furthermore, a TI methanol / alkane receiving tank is provided on the pipeline from the TI tower top phase separator to the methanol / alkane distillation tower TII for receiving the methanol / alkane / water phase obtained after phase separation.

[0031] Furthermore, the TI tower bottom phase separator is connected to a TI chlorobenzene / alkane receiving tank and a TI process water receiving tank, respectively, for receiving the chlorobenzene / alkane phase and the water phase obtained after phase separation.

[0032] Furthermore, the bottoms of the azeotropic distillation tower TI, the methanol / alkane distillation tower TII, the methanol distillation tower TIII and the chlorobenzene / alkane distillation tower TIV are all connected to heaters;

[0033] Furthermore, the tops of the methanol / alkane distillation tower TII, the methanol distillation tower TIII and the chlorobenzene / alkane distillation tower TIV are all connected to condensers.

[0034] Specifically, a two-stage condenser is preferably provided at the top of each distillation tower, and the condensers are connected to a reflux tank, and the reflux tank leads to the top of the corresponding distillation tower.

[0035] The beneficial effects of the present invention are as follows:

[0036] The present invention utilizes continuous azeotropic distillation combined with overhead phase separation and atmospheric continuous distillation, using n-alkanes as entrainers to nearly completely separate a mixture of methanol, chlorobenzene, and water. The resulting products are methanol with a purity of ≥99.9% and chlorobenzene with a purity of ≥99.95%, respectively, which can be returned to the reaction section. Furthermore, wastewater with an organic solvent content of ≤500 ppm is produced, which can be reused as process water. The process of the present invention is suitable for large-scale solvent recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The two-phase phase diagram of methanol and chlorobenzene (x is the molar fraction of methanol in the liquid phase, and y is the molar fraction of methanol in the vapor phase; the T-xy diagram can be used to determine whether the two substances are easy to separate. The wider the two lines are, the easier they are to separate. Overlapping parts indicate azeotropic properties).

[0038] Figure 2 Schematic diagram of a system for continuous separation of a mixture of chlorobenzene, methanol and water in accordance with a specific embodiment of the present invention;

[0039] Figure 2: 1. Azeotropic distillation tower TI; 2. TI raw material feed pump; 3. TI heater; 4. TI primary condenser; 5. TI secondary condenser; 6. TI top cooler; 7. TI top phase separator; 8. TI methanol / alkane receiving tank; 9. TI bottom extraction pump; 10. TI bottom cooler; 11. TI bottom phase separator; 12. TI chlorobenzene / alkane receiving tank; 13. TI process water receiving tank; 14. TI process water extraction pump; 15. TI chlorobenzene / alkane extraction pump; 16. TI methanol / alkane extraction pump; 17. Methanol / alkane distillation tower TII; 18. TI heater; 19. TI primary condenser; 20. TI secondary condenser; 21. TI reflux tank; 22. TI reflux pump; 23. TⅡ tower top cooler; 24. TⅡ tower bottom extraction pump; 25. TⅡ tower bottom cooler; 26. Methanol distillation tower TⅢ; 27. TⅢ heater; 28. TⅢ primary condenser; 29. TⅢ secondary condenser; 30. TⅢ reflux tank; 31. TⅢ reflux pump; 32. TⅢ tower top cooler; 33. TⅢ tower bottom extraction pump; 34. Chlorobenzene / alkane distillation tower TⅣ; 35. TⅣ heater; 36. TⅣ primary condenser; 37. TⅣ secondary condenser; 38. TⅣ reflux tank; 39. TⅣ reflux pump; 40. TⅣ tower top cooler; 41. TⅣ tower bottom extraction pump; 42. TⅣ tower bottom cooler; 43. Raw materials; 44. Entrainer; 45. Tail gas; 46. Methanol product; 47. Chlorobenzene product; 48. Process water; DETAILED DESCRIPTION

[0040] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0041] Example 1

[0042] A system for continuously separating a mixture of chlorobenzene, methanol and water, comprising an azeotropic distillation tower TⅠ1, a methanol / alkane distillation tower TⅡ17, a methanol distillation tower TⅢ26 and a chlorobenzene / alkane distillation tower TⅣ34;

[0043] The bottom of the azeotropic distillation tower TⅠ1 is connected to a TⅠ heater 3; the top of the azeotropic distillation tower TⅠ1 leads to a TⅠ tower top phase separator 7, and the TⅠ tower top phase separator 7 leads to a methanol / alkane distillation tower TⅡ17; a TⅠ condenser and a TⅠ tower top cooler 6 are sequentially arranged on the pipeline from the azeotropic distillation tower TⅠ1 to the TⅠ tower top phase separator 7; the TⅠ condenser includes a TⅠ primary condenser 4 and a TⅠ secondary condenser 5, both of which are A TI methanol / alkane receiving tank 8 is provided on the pipeline leading to the TI tower top cooler 6; the TI tower top phase separator 7 leads to the methanol / alkane distillation tower TⅡ17; a TI methanol / alkane extraction pump 16 is provided on the pipeline leading to the TI methanol / alkane distillation tower TⅡ17; the TI tower top phase separator 7 leads to the azeotropic distillation tower TⅠ1; a TI raw material feed pump 2 is provided on the raw material feed pipeline of the azeotropic distillation tower TⅠ1;

[0044] The bottom of the methanol / alkane distillation tower TⅡ17 leads to the methanol distillation tower TⅢ26; a TⅡ bottom cooler 25 is provided on the pipeline leading to the methanol / alkane distillation tower TⅡ17 and the TⅡ bottom cooler 25; a TⅡ bottom extraction pump 24 is provided on the pipeline leading to the TⅡ bottom cooler 25 of the methanol / alkane distillation tower TⅡ17; the bottom of the methanol / alkane distillation tower TⅡ17 is connected to the TⅡ heater 18; the top of the methanol / alkane distillation tower TⅡ17 leads to the TⅡ condenser and the TⅡ reflux tank 21 in sequence; The TII condenser includes a TII primary condenser 19 and a TII secondary condenser 20, both of which lead to a TII reflux tank 21; the TII reflux tank 21 leads to the top of the methanol / alkane distillation tower TII17, and a TII reflux pump 22 is provided on the pipeline leading from the TII reflux tank 21 to the top of the methanol / alkane distillation tower TII17; the top of the methanol / alkane distillation tower TII17 leads to the TⅠ tower top phase separator 7; the pipeline leading from the top of the methanol / alkane distillation tower TII17 to the TⅠ tower top phase separator 7 is provided with a TⅡ tower top cooler 23;

[0045] The bottom of the methanol distillation tower TⅢ26 is connected to a TⅢ heater 27; the top of the methanol distillation tower TⅢ26 leads to a TⅢ condenser and a TⅢ reflux tank 30 in sequence; the TⅢ condenser includes a TⅢ primary condenser 28 and a TⅢ secondary condenser 29, both of which lead to a TⅢ reflux tank 30; the TⅢ reflux tank 30 leads to the top of the methanol distillation tower TⅢ26, and a TⅢ reflux pump 31 is provided on the pipeline leading from the TⅢ reflux tank 30 to the top of the methanol distillation tower TⅢ26; a TⅢ top cooler 32 is provided on the top extraction pipeline of the methanol distillation tower TⅢ26; a TⅢ bottom extraction pump 33 is provided on the bottom extraction pipeline of the methanol distillation tower TⅢ26;

[0046] The azeotropic distillation tower TⅠ1 is connected to the TⅠ tower kettle phase separator 11; the TⅠ tower kettle phase separator 11 is connected to the chlorobenzene / alkane distillation tower TⅣ34; the pipeline from the azeotropic distillation tower TⅠ1 to the TⅠ tower kettle phase separator 11 is provided with a TⅠ tower kettle cooler 10, and the pipeline from the azeotropic distillation tower TⅠ1 to the TⅠ tower kettle cooler 10 is provided with a TⅠ tower kettle extraction pump 9; the TⅠ tower kettle separator A TI chlorobenzene / alkane receiving tank 12 is provided on the pipeline from the phase separator 11 to the chlorobenzene / alkane distillation tower TIV34, and a TI chlorobenzene / alkane extraction pump 15 is provided on the pipeline from the TI chlorobenzene / alkane receiving tank 12 to the chlorobenzene / alkane distillation tower TIV34; the TI tower bottom phase separator 11 leads to the TI process water receiving tank 13; a TI process water extraction pump 14 is provided on the extraction pipeline of the TI process water receiving tank 13;

[0047] The bottom of the chlorobenzene / alkane distillation tower TIV34 is connected to a TIV heater 35; the top of the chlorobenzene / alkane distillation tower TIV34 leads to a TIV condenser and a TIV reflux tank 38 in sequence; the TIV condenser includes a TIV primary condenser 36 and a TIV secondary condenser 37, both of which lead to a TIV reflux tank 38; the TIV reflux tank 38 leads to the top of the chlorobenzene / alkane distillation tower TIV34, and a TIV reflux pump 39 is provided on the pipeline from the TIV reflux tank 38 to the top of the chlorobenzene / alkane distillation tower TIV34; a TIV top cooler 40 is provided on the top extraction pipeline of the chlorobenzene / alkane distillation tower TIV34; a TIV bottom extraction pump 41 and a TIV bottom cooler 42 are provided on the bottom extraction pipeline of the chlorobenzene / alkane distillation tower TIV34.

[0048] The above system is used to continuously separate a mixture of chlorobenzene, methanol and water. The composition of the raw material is as follows: methanol content is 70.2wt%, chlorobenzene content is 8.3wt%, and water content is 21.5wt%.

[0049] The steps of the continuous separation method are as follows:

[0050] S1. Azeotropic distillation using n-hexane as an entrainer: Raw material 43 enters the lower portion of azeotropic distillation column T11 from outside the boundary zone via raw material feed pump 2. The material falling into the bottom of the column is heated and vaporized by heater 3 in T1. The gas rises and contacts the entrainer 44 (n-hexane) entering from the top of the column in a countercurrent manner. Methanol, n-hexane, and a small amount of water rise to the top of the column, while chlorobenzene, water, and a small amount of n-hexane fall into the bottom of the column.

[0051] The process conditions of the azeotropic distillation tower TⅠ1 are as follows: under normal pressure conditions, the tower top temperature is 54±2℃, the tower bottom temperature is 66±2℃, the azeotropic ratio is 2±0.5:1, the reflux ratio is 5.5±0.5; the mass ratio of raw material to n-hexane is 1:0.5.

[0052] S2. Phase separation at the top of the tower and distillation of the methanol / n-hexane / water phase: the gas (methanol, n-hexane and a small amount of water) rising to the top of the azeotropic distillation tower TI1 is condensed by the TI primary condenser 4 and the TI secondary condenser 5, and the condensate enters the TI top cooler 6 for cooling. The cooled liquid is phase-separated by the TI top phase separator 7 to obtain a n-hexane phase and a methanol / n-hexane / water phase; the separated n-hexane phase is refluxed to the top of the azeotropic distillation tower TI1 for recycling, and the separated methanol / n-hexane / water phase enters the TI methanol / alkane receiving tank 8; the methanol and n-hexane in the TI methanol / alkane receiving tank 8 are The mixture of alkanes and water is transported by the TII methanol / alkane extraction pump 16 and enters the lower middle portion of the methanol / alkane distillation tower TII 17. The material falling into the tower bottom is heated and vaporized by the TII heater 18. The gas rises to the top of the tower and is condensed by the TII primary condenser 19 and the TII secondary condenser 20. The condensate enters the TII reflux tank 21. A portion of it is refluxed to the methanol / alkane distillation tower TII 17 by the TII reflux pump 22, and a portion (n-hexane) is cooled by the TII tower top cooler 23 and then returned to the TII tower top phase separator 7. The methanol and water mixture is obtained in the tower bottom. The tail gas 45 generated by the tower top condensation is sent to the tail gas absorption system.

[0053] The phase separation temperature is 15±5℃; the process conditions of the methanol / alkane distillation tower TⅡ17 are as follows: it is carried out under normal pressure conditions, the top temperature is 57±2℃, the bottom temperature is 70±2℃, and the reflux ratio is 5±1.

[0054] S3. Distilling the methanol-water mixture: The methanol-water mixture in the bottom of the methanol / alkane distillation tower TII 17 is transported to the TII bottom cooler 25 via the TII bottom extraction pump 24 for cooling. The mixture is then sent to the bottom of the methanol distillation tower TIII 26. The mixture is heated and vaporized by the TIII heater 27. The gas rises to the top of the tower and is condensed by the TIII primary condenser 28 and the TIII secondary condenser 29. The condensate enters the TIII reflux tank 30. A portion of the mixture is refluxed to the top of the methanol distillation tower TIII 26 via the TIII reflux pump 31, and a portion of the mixture is cooled by the TIII top cooler 32 and removed to the outside of the delimited area to obtain methanol product 46. Process water 48 is obtained from the bottom of the tower and transported to the outside of the delimited area via the TIII bottom extraction pump 33. The tail gas 45 generated by the top condensation is sent to the tail gas absorption system.

[0055] The process conditions of the methanol distillation tower TⅢ26 are as follows: it is carried out under normal pressure conditions, the tower top temperature is 66±2℃, the tower bottom temperature is 101±2℃, and the reflux ratio is 2±0.5.

[0056] S4. Phase separation in the bottom of the tower and distillation of the mixture of chlorobenzene and normal hexane: The mixture of chlorobenzene, water and normal hexane obtained in the bottom of the azeotropic distillation tower TI1 in step S1 is transported to the TI bottom cooler 10 for cooling via the bottom extraction pump 9, and after cooling, enters the TI bottom phase separator 11 for phase separation, and the heavy phase water phase after phase separation enters the TI process water receiving tank 13, and then is transported to the outside of the boundary area via the TI process water extraction pump 14; the light phase chlorobenzene / normal hexane phase after phase separation enters the TI chlorobenzene / alkane receiving tank 12; the material in the TI chlorobenzene / alkane receiving tank 12 is transported to the chlorobenzene / alkane refiner via the TI chlorobenzene / alkane extraction pump 15 The distillation tower TIV 34 is fed from the lower part of the tower. The material falling into the tower bottom is heated and vaporized by the TIV heater 35. The n-hexane gas rises to the top of the tower and is condensed by the TIV primary condenser 36 and the TIV secondary condenser 37. The condensate enters the TIV reflux tank 38. A portion of it is refluxed by the TIV reflux pump 39, and a portion (n-hexane) is cooled by the TIV tower top cooler 40 and returned to the top of the azeotropic distillation tower TⅠ1 for recycling as an entrainer. The tower bottom contains chlorobenzene, which is transported to the TIV tower bottom cooler 42 by the TIV tower bottom extraction pump 41 and then removed from the boundary area to obtain the chlorobenzene product 47. The tail gas 45 generated by the tower top condensation is sent to the tail gas absorption system.

[0057] The phase separation temperature is 15±5℃; the process conditions of the chlorobenzene / alkane distillation tower TⅣ34 are as follows: it is carried out under normal pressure conditions, the top temperature is 63±2℃, the bottom temperature is 134±2℃, and the reflux ratio is 1.5±0.5.

[0058] The product indicators obtained by the above method are shown in Table 1.

[0059] Table 1 Product indicators obtained in Example 1

[0060] Methanol chlorobenzene water purity 99.99wt% 99.97wt% Organic matter content 495ppm Recovery rate 99％ 98.5％ /

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for continuously separating a mixture of chlorobenzene, methanol and water, characterized in that: The steps include: S1. Adding an alkane as an azeotropic agent, azeotropic distillation of a mixture of chlorobenzene, methanol and water as a raw material; the alkane is a normal alkane; the top of the tower is a mixture of alkanes, methanol and water, the bottom of the tower is a mixture of chlorobenzene, water and alkanes; S2. The mixture of alkanes, methanol and water obtained in step S1 is phase-separated to obtain an alkane phase and a methanol / alkane / water phase; the methanol / alkane / water phase is distilled to obtain alkanes at the top and a mixture of methanol and water at the bottom; S3 the methanol and water mixture obtained in step S2 is distilled to obtain a methanol product at the top of the tower; S4. The mixture of chlorobenzene, water and alkanes obtained in step S1 is phase-separated to obtain an aqueous phase and a chlorobenzene / alkane phase; the chlorobenzene / alkane phase is distilled to obtain alkanes at the top and chlorobenzene product at the bottom.

2. The method according to claim 1, characterized in that The n-alkanes are at least one of n-pentane, n-hexane and n-heptane.

3. The method according to claim 1, characterized in that In step S1, the mass ratio of the raw material to the alkane is 1:(0.3~4).

4. The method according to claim 1, wherein The alkane obtained in step S2 is returned to the azeotropic distillation for recycling as an entrainer; The alkane obtained in step S4 is returned to the azeotropic distillation for recycling as an entrainer.

5. The method according to claim 1, wherein In step S2, the mixture of alkane, methanol and water is condensed, cooled and then phase-separated; In step S4, the mixture of chlorobenzene, water and alkane is cooled and then phase-separated.

6. The method according to claim 5, characterized in that In step S2, the phase separation temperature of the mixture of alkane, methanol and water is 3-45°C; In step S4, the phase separation temperature of the mixture of chlorobenzene, water and alkane is 3-45°C.

7. The method according to any one of claims 1 to 6, characterized in that The mixture of chlorobenzene, methanol and water comprises: a methanol content of 45 wt% to 90 wt%, a chlorobenzene content of 3 wt% to 20 wt%, and a water content of 7 wt% to 35 wt%.

8. A system for continuously separating a mixture of chlorobenzene, methanol and water, characterized in that: It includes an azeotropic distillation tower TⅠ (1), a methanol / alkane distillation tower TⅡ (17), a methanol distillation tower TⅢ (26) and a chlorobenzene / alkane distillation tower TⅣ (34); The top of the azeotropic distillation tower TI (1) leads to the TI top phase separator (7), and the TI top phase separator (7) leads to the methanol / alkane distillation tower TII (17); the bottom of the methanol / alkane distillation tower TII (17) leads to the methanol distillation tower TIII (26); The bottom of the azeotropic distillation tower TI (1) leads to the TI bottom phase separator (11); the TI bottom phase separator (11) leads to the chlorobenzene / alkane distillation tower TIV (34); The top phase separator (7) of the TⅠ tower leads to the azeotropic distillation tower TⅠ (1); the top of the methanol / alkane distillation tower TⅡ (17) leads to the top phase separator (7) of the TⅠ tower; and the top of the chlorobenzene / alkane distillation tower TⅣ (34) leads to the azeotropic distillation tower TⅠ (1).

9. The system according to claim 8, characterized in that A TI condenser and a TI top cooler (6) are sequentially arranged on the pipeline from the azeotropic distillation tower TI (1) to the TI tower top phase separator (7); a TI tower bottom cooler (10) is arranged on the pipeline from the azeotropic distillation tower TI (1) to the TI tower bottom phase separator (11).

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