A azeotropic distillation process for separating pyridine and water

Abstract

The invention relates to an azeotropic distillation process for separating pyridine and water. The crude pyridine raw material from the tank area is mixed with the benzene of the reflux pump of the azeotropic distillation tower in a stirring tank; the fully mixed crude pyridine and benzene enter the azeotropic distillation tower for distillation; by controlling the process parameters of the azeotropic distillation tower, the separation of water and crude pyridine from the top of the tower is realized; the water phase and the entrainer benzene obtained from the top of the azeotropic distillation tower enter the reflux tank of the azeotropic distillation tower, and the water phase at the bottom of the reflux tank is extracted to the waste benzene tank through static stratification, and the upper benzene phase is refluxed or recycled; the crude pyridine after dehydration at the bottom of the azeotropic distillation tower enters the crude pyridine evaporation kettle heat exchanger, and is vaporized and separated by steam heating. The gas phase at the top of the kettle enters the subsequent aniline separation section, and the residue at the bottom of the evaporation kettle is condensed and extracted into the phenol oil tank. The process flow of the invention is simple and reasonable, there is no catalyst in the reaction process, benzene is used as the entrainer, the equipment investment is small, the working temperature and pressure are low, the energy consumption is small, and the economy is excellent.

Description

Technical Field

[0001] The invention relates to an azeotropic distillation process for separating pyridine and water, and specifically uses crude pyridine as a raw material, benzene as an azeotropic agent, and separates water and crude pyridine through azeotropic distillation in the absence of a catalyst. Background Art

[0002] Pyridine, also known as nitrogen benzene, has a molecular formula of C5H5N and a relative molecular mass of 79.10. It is a six-membered heterocyclic compound containing a nitrogen atom. Pyridine is an important fine chemical raw material, solvent and organic synthesis catalyst. It is one of the most widely used heterocyclic compounds at present. It is mainly used in the chemical and pharmaceutical fields, such as raw materials for synthesizing medicines, dyes, and resins, as well as in the preparation of fertilizer synergists, herbicides, livestock anthelmintics, rubber accelerators, dye intermediates, and other fields.

[0003] Pyridine and its homologue methylpyridine are mainly present in certain enzymes and alkaloids; natural substances such as coal and oil shale produce pyridine products during degradation, and coal gas and coal tar obtained during coal coking contain pyridine compounds. Although there are many studies on the extraction of pyridine compounds from coal tar, there are almost no methods on how to purify high-purity pyridine series products from pyridine compounds. Therefore, it is of great significance to separate and purify crude pyridine from medium and low temperature coal tar to obtain high-purity pyridine series products.

[0004] The existing coal tar pyridine production process has the disadvantage of not being able to completely remove trace moisture, but the presence of trace moisture will greatly affect the product quality. At room temperature and pressure, pyridine is a flammable colorless or slightly yellow liquid with a foul odor and strong hygroscopicity. Pyridine and water form an azeotrope with a boiling point of 92-94°C. The azeotrope composition is equivalent to C6H5N·3H2O. The weight percentage of water in the azeotrope is 42%, which cannot be separated using ordinary distillation methods. Therefore, the development of an industrialized process route that can produce high-quality pyridine products and operate continuously and stably will not only help to make up for the rare resource gap of some pyridine compounds, but also improve my country's utilization of coal tar.

[0005] The commonly used industrial dehydration and purification process for pyridine is mainly the alkali-adding and stratification method. Since pyridine is liquid at room temperature and miscible with water, and its aqueous solution is alkaline, the stratification of pyridine and water is achieved by changing the alkalinity of the solution, thereby preparing high-purity pyridine. However, this method requires a long period of static stratification after adding alkali solution, and the product purity is not high. The generated alkaline water cannot be directly discharged, and the alkali solution cannot be recycled, which has poor economic efficiency.

[0006] At present, the reported methods for separating pyridine from water include extractive distillation, salt-adding distillation, azeotropic distillation, azeotropic distillation, vacuum distillation, etc. There are few reports on extractive distillation for separating pyridine from water in practical applications; salts are rarely used in actual industry due to problems such as easy clogging and corrosion of equipment; azeotropic distillation has complicated steps and is not easy to industrialize; while azeotropic distillation is widely used due to its advantages of simple equipment, low investment and maintenance costs, and recyclable entrainer.

[0007] Azeotropic distillation is a special distillation separation technology suitable for the separation of azeotropic systems. Specifically, a new entrainer is added to the distillation tower containing the azeotrope to form a new azeotrope with one or more substances in the system to be separated, so as to change the relative volatility between the original components to achieve the purpose of separation. The newly added entrainer should not only reduce the difficulty of separation of the original system, but also be removed from the system by a simple method and take into account the requirements of convenient recycling. Therefore, the selection of an entrainer suitable for the separation system is a key difficulty that needs to be solved in the large-scale industrialization process of this technology.

[0008] At present, there are few literature reports on the separation of pyridine and water systems by azeotropic distillation. CN108191743A, CN109516646A, CN109593059A, CN108586322A and CN106866504A disclose azeotropic distillation technology for aqueous pyridine and its homologues, but the process flow used is complicated and the equipment investment cost is large, which restricts its application and promotion. Therefore, it is very promising to develop an azeotropic distillation process with simple process, small industrial investment and stable operation, which has great industrial prospects and economic value.

[0009] Figure 1 The schematic diagram of the unit process of traditional azeotropic distillation separation of pyridine and water system, wherein the water-containing pyridine is introduced into the azeotropic distillation tower T1, and the rising vapor from the top of the tower is condensed by the condenser E2 and enters the separator D1, in which the liquid is separated into two phases, the organic phase is refluxed from the top of the tower, and the water phase enters the water recovery tower T2 for subsequent treatment; the tower bottom extracts pyridine with a water content of 0.5wt%. The process flow of traditional azeotropic distillation separation of pyridine and water system has problems such as low separation efficiency, complex process, and high cost, which restricts its industrial development.

[0010] Therefore, how to save the cost of the existing technical solution, reduce project investment, save energy consumption, take environmental protection into consideration, and efficiently separate crude pyridine and water to improve the economic efficiency of the solution has become an issue that the industry urgently needs to solve and break through. Summary of the invention

[0011] The present invention aims at the problems of high investment, large energy consumption, serious pollution and low pyridine-water separation efficiency of the existing technology project, and provides an azeotropic distillation process method for separating pyridine and water. Benzene as an azeotropic agent is introduced, and benzene can form a stable heterogeneous binary minimum azeotrope with water, destroying the azeotropic composition of pyridine and water, realizing azeotropic distillation dehydration, and the azeotropic agent benzene can be recycled. The method has the advantages of energy saving, environmental protection, high efficiency, etc.

[0012] The present invention provides an azeotropic distillation process for separating pyridine and water, comprising the following steps:

[0013] (1) The crude pyridine raw material is fully mixed and heated in a stirring tank (D1), and then sent to an azeotropic distillation tower (T1) for azeotropic distillation;

[0014] (2) The water phase and entrainer benzene obtained from the top of the azeotropic distillation tower (T1) enter the reflux tank (D2), and the water phase in the liquid collecting bag at the bottom of the reflux tank is extracted to the outside through static stratification. Part of the upper benzene phase is refluxed to the azeotropic distillation tower (T1), part of it is mixed with the crude pyridine raw material from the tank area for recycling, and the other part is transported to the waste benzene tank. The flow of the three streams is accurately controlled by a flow regulating control valve;

[0015] (3) After dehydration in the bottom of the azeotropic distillation tower (T1), part of the crude pyridine is vaporized by the action of the bottom reboiler (E3) and returned to the azeotropic distillation tower (T1) through the bottom for distillation and purification. The other part enters the crude pyridine evaporator heat exchanger (E4) and is vaporized and separated by steam heating. The gas phase at the top of the tank (mainly pyridine and aniline) enters the subsequent aniline separation section. The residue at the bottom of the evaporator (mainly composed of high-boiling point components (boiling point ≥ 225°C) and inorganic salts such as Na2SO4 and Na2CO3) is condensed by the condenser (E5) and taken out of the boundary area and enters the phenol oil tank.

[0016] The azeotropic distillation tower T1 does not use a catalyst during the distillation process and uses benzene as an azeotropic agent. In the azeotropic distillation tower T1, since the azeotropic point of benzene and water is lower, the azeotropic composition of pyridine and water is destroyed, thereby separating water and crude pyridine from the top of the tower, and obtaining a crude pyridine material with a water content of ≤0.05wt% in the bottom of the tower.

[0017] The feed molar ratio of benzene to crude pyridine is 1:1 to 4:1; the feed is heated to a temperature of 40-120°C before feeding.

[0018] The azeotropic distillation tower (T1) is an inclined hole plate distillation tower. The inclined hole plate has a relatively high plate efficiency, a simple structure and low equipment cost, and can achieve the separation effect required by the material system in this article. The number of plates is 40 to 80, and the position range of benzene and crude pyridine is the 20th to 40th plates. Preferably, the middle plate number is selected for feeding, the mass reflux ratio is 1 to 5, and the molar extraction ratio of the top fraction is 0.4 to 0.7.

[0019] The operating temperature of the azeotropic distillation tower (T1) is 40-120°C, and the operating pressure is 10-20 kPaG. The temperatures of the tower top and the tower bottom are both controlled by the heat exchange load of the tower bottom reboiler.

[0020] In the azeotropic distillation tower T1, the feed molar ratio of entrainer benzene to crude pyridine raw material is 2:1, the tower top temperature is 68.36°C, the tower bottom temperature is 97.29°C, the whole tower is operated at normal pressure, and the pressure is maintained at 15kPaG. The number of plates is 60, the entrainer benzene and the crude pyridine raw material are fed on the 30th tower plate, the mass reflux ratio is 0.76, and the molar recovery ratio of the tower top fraction is 0.25. Among them, the molar recovery ratio of the tower top fraction has the same meaning as the distillate recovery rate (i.e., D / F) in the textbook "Principles of Chemical Engineering".

[0021] The crude pyridine raw material is obtained by conventional extraction from medium- and low-temperature coal tar.

[0022] The reflux and circulation molar ratio of benzene in the overhead fraction of the azeotropic distillation tower (T1) is 1 to 5. The water content in the crude pyridine material is controlled by changing the reflux ratio of the entrainer benzene. Preferably, the flow ratio of the stream 7 to the waste benzene tank: the stream 9 refluxed to the azeotropic distillation tower: the stream 8 mixed with the crude pyridine raw material from the tank area is 2:2:1.

[0023] The present invention further proposes an azeotropic distillation process device for separating pyridine and water, comprising an azeotropic distillation tower (T1), a stirring tank (D1), a tower top condenser (E2), a distillation tower reflux tank (D2), a tower bottom reboiler (E3), and an evaporating kettle heat exchanger (E4), wherein:

[0024] The azeotropic distillation tower (T1) is provided with a feed port for a crude pyridine and azeotropic benzene mixture, and the top of the azeotropic distillation tower (T1) is provided with a top condenser (E2) and a distillation tower reflux tank (D2) which are connected to each other, a part of the benzene at the outlet of the distillation tower reflux tank (D2) is connected to the top of the azeotropic distillation tower (T1), a part is connected to the feed port of the azeotropic distillation tower (T1), and the other part is transported to a waste benzene tank; the water phase at the outlet of the liquid collecting bag of the distillation tower reflux tank (D2) is transported to a sewage treatment section; the azeotropic distillation tower (T1) is provided with a discharge port which is respectively connected to a tower kettle reboiler (E3) and an evaporating kettle heat exchanger (E4).

[0025] Wherein, T1 is an inclined hole plate distillation tower, and according to actual needs, a condenser (E2) and a reflux tank (D2) are arranged on the top of the tower.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0027] (1) The present invention is based on distillation separation technology and is a modification of the pyridine dehydration process. In order to overcome the drawbacks of traditional water removal methods, the present invention proposes an azeotropic distillation operation characterized by benzene as an entrainer. The entrainer benzene enters the distillation tower together with the crude pyridine raw material. Benzene can form a stable heterogeneous binary minimum azeotrope with water, destroying the azeotropic composition of pyridine and water, and solving the problem of the difficulty of azeotropic separation of pyridine and water. The entrainer and the water in the pyridine / water solution form a low azeotrope and the mixed steam is extracted from the top of the tower, and then the entrainer and water are separated by condensation and phase separation. Pyridine is extracted from the bottom of the tower and then heated to a gas phase by a heat exchanger. The present invention realizes the efficient separation of pyridine and water, and the bottom of the azeotropic distillation tower T1 obtains a pyridine material with a water content of ≤0.05wt%, and the entrainer reaches a purity that can be reused.

[0028] (2) The pyridine of the azeotropic distillation technology described in the present application has a high economic value, is not easily biodegradable in the environment, and has a high toxicity. In the traditional separation process of pyridine and water, pyridine and water cannot be completely separated, resulting in part of the pyridine being directly discharged with the water, which not only harms the environment, but also causes serious economic losses. In the present invention, the process of heterogeneous azeotropic distillation is adopted to obtain a crude pyridine material with a water content of ≤0.05wt%, thereby achieving complete separation of pyridine and water, avoiding the discharge of industrial waste liquid into the environment, reducing the cost of wastewater treatment, and reducing pollution to protect the environment. The process is simple to operate, has low equipment cost investment, high product recovery rate, and has the advantages of good separation effect, low production cost, and low energy consumption. It is easy to industrialize production and can be quickly converted into productivity, promoting the development of the crude pyridine refining high-purity pyridine series product industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the conventional pyridine and water distillation unit process;

[0030] Figure 2 This is a schematic flow diagram of the present invention, wherein T1 is an azeotropic distillation tower, and the fully mixed crude pyridine and azeotropic benzene enter the azeotropic distillation tower for distillation; by controlling the process parameters of the azeotropic distillation tower, the separation of water and crude pyridine from the top of the tower is achieved; the water phase and entrainer obtained from the top of the azeotropic distillation tower enter the reflux tank of the azeotropic distillation tower, and the water phase at the bottom of the reflux tank is extracted to the waste benzene tank through static stratification, and the top benzene is refluxed or recycled; the crude pyridine dehydrated at the bottom of the azeotropic distillation tower enters the crude pyridine evaporator heat exchanger, and is vaporized and separated by steam heating. The gas phase at the top of the tank enters the subsequent aniline separation section distillation section, and the residue at the bottom of the evaporator is condensed and extracted into the phenol oil tank. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the technical solution of the present invention, specific embodiments of the relevant technical solution are given below in combination with the contents of the specification. It should be understood that the following embodiments do not constitute a limitation on the protection scope of the present invention, and any technical solution formed by the evolution and improvement of the present invention without creative labor by any technician in the relevant technical field belongs to the protection scope of the present invention.

[0032] The present invention uses a device such as Figure 2 As shown, it includes an azeotropic distillation tower (T1), a stirring tank (D1), a tower top condenser (E2), a distillation tower reflux tank (D2), a tower bottom reboiler (E3), and an evaporator heat exchanger (E4), wherein the azeotropic distillation tower (T1) is provided with a feed port for a crude pyridine and azeotropic benzene mixture, and the top of the azeotropic distillation tower (T1) is provided with an interconnected tower top condenser (E2) and a distillation tower reflux tank (D2), a part of the benzene at the outlet of the distillation tower reflux tank (D2) is connected to the top of the azeotropic distillation tower (T1), a part is connected to the feed port of the azeotropic distillation tower (T1), and the other part is transported to the waste benzene tank; the water phase at the outlet of the distillation tower reflux tank (D2) is transported to the sewage treatment section. The azeotropic distillation tower (T1) is provided with a discharge port, which is respectively connected to the tower bottom reboiler (E3) and the evaporator heat exchanger (E4).

[0033] Wherein, the azeotropic distillation tower (T1) is a diagonal hole plate distillation tower.

[0034] The azeotropic distillation process of pyridine and water is described in detail below through specific examples.

[0035] Example 1

[0036] according to Figure 2In the process shown, the crude pyridine raw material (logistics 1) from the tank area and the azeotropic benzene with the azeotropic distillation tower reflux pump enter the stirring tank D1 respectively, the crude pyridine and azeotropic benzene (logistics 2) stirred evenly are heated by the heater E1 and sent to the azeotropic distillation tower T1, by controlling the temperature and pressure parameters of the azeotropic distillation tower T1, the fraction containing water and entrainer benzene (logistics 3) is evaporated from the top of the tower, and the mixed solution (logistics 4) condensed by the condenser E2 is sent to the reflux tank D2, and the water phase (logistics 6) in the liquid collecting bag at the bottom of the reflux tank D2 is extracted to the boundary area by static stratification, a part of the benzene on the top (logistics 5) is pumped back (logistics 9) to the azeotropic distillation tower T1, a part (logistics 8) is mixed with the crude pyridine raw material from the tank area for recycling, and the other part (logistics 7) is transported to the waste benzene tank. After dehydration in the bottom of the azeotropic distillation tower T1, a part of the crude pyridine (logistics 17) is vaporized (logistics 18) under the action of the tower bottom reboiler E3 and returned to the azeotropic distillation tower T1 for distillation and purification, and another part of the logistics 10 enters the crude pyridine evaporator heat exchanger E4, is vaporized and separated by steam heating, and the gas phase at the top of the kettle (logistics 21) enters the subsequent aniline separation section, and a part of the residue at the bottom of the evaporator (logistics 12) is transported by the delivery pump P2 (logistics 13) and condensed by the condenser E5 (logistics 14) and taken out of the boundary area into the phenol oil tank. Among them, logistics 15, logistics 16, logistics 19 and logistics 20 are used for heat exchange in the evaporator heat exchanger and the tower bottom reboiler.

[0037] In this embodiment, the crude pyridine raw material flow rate is 8t / h, the pressure is 400kPaG, the temperature is 40°C, and its mass composition is 31.93% pyridine, 51.94% benzene, 10.11% aniline, and 6.02% water. The molar feed ratio of the entrainer benzene to the crude pyridine raw material of the azeotropic distillation tower T1 is 2:1, the tower top temperature is 68.36°C, the tower bottom temperature is 97.29°C, the whole tower is operated at normal pressure, and the pressure is maintained at 15kPaG. The number of tower plates is 60, and the entrainer benzene and the crude pyridine raw material are fed on the 30th tower plate, the mass reflux ratio is 0.76, and the tower top fraction extraction ratio is 0.25.

[0038] The composition of the top and bottom streams of the azeotropic distillation tower T1 is shown in Table 1.

[0039] Table 1

[0040] Logistics Number 2 3 9 10 Pyridine, mass% 28.12 0.03 0.03 44.29 Benzene, mass% 56.52 89.87 99.97 41.83 Water, mass% 5.27 10.10 0.00 0.03 Aniline, mass% 8.79 0.00 0.00 13.85 Waste residue, mass% 1.30 0.00 0.00 0.00

[0041] As can be seen from Table 1, the water content of the crude pyridine product meets the requirements by adopting the inventive method, and this method is compared with the traditional method. In order to overcome the drawbacks of the traditional water removal method, the present invention proposes an azeotropic distillation operation using benzene as an entrainer. Entrainer benzene enters the distillation tower together with the crude pyridine raw material, and it forms a stable heterogeneous binary minimum azeotrope with water, destroying the azeotropic composition of pyridine and water, and solving the problem of azeotropic separation difficulty of pyridine and water. Through the above-mentioned improvement, compared with the traditional method, the process is simple to operate, the equipment cost investment is small, the product recovery rate is high, and there are advantages such as good separation effect, low production cost, and low energy consumption.

[0042] Example 2

[0043] The reaction was carried out according to the conditions and steps described in Example 1. The feed ratio of entrainer benzene to crude pyridine raw material in the azeotropic distillation tower T1 was 2:1, the tower top temperature was 68.35°C, the tower bottom temperature was 97.29°C, the whole tower was operated at normal pressure, and the pressure was maintained at 15 kPaG. The number of plates was 60, the entrainer benzene and the crude pyridine raw material were fed on the 40th tower plate, the mass reflux ratio was 0.76, and the molar recovery ratio of the tower top fraction was 0.25.

[0044] The results of Example 2 show the universality of the scheme of the present invention, that is, the change of the feed position will not have a significant impact on the purity of the final product, and it has excellent ability to resist fluctuations and human errors, and has great potential for industrialization.

[0045] The composition of the top and bottom streams of the azeotropic distillation tower T1 is shown in Table 2.

[0046] Table 2

[0047] Logistics Number 2 3 9 10 Pyridine, mass% 28.12 7.88e-5 8.76e-5 44.28 Benzene, mass% 56.52 89.89 99.99 41.85 Water, mass% 5.27 10.10 0.00 0.03 Aniline, mass% 8.79 1.75e-19 8.56e-20 13.84 Waste residue, mass% 1.30 0.00 0.00 0.00

[0048] Example 3

[0049] The reaction was carried out according to the conditions and steps described in Example 1. The feed ratio of entrainer benzene to crude pyridine raw material in the azeotropic distillation tower T1 was 3:2, the tower top temperature was 68.36°C, the tower bottom temperature was 99.48°C, the whole tower was operated at normal pressure, and the pressure was maintained at 15 kPaG. The number of plates was 60, the entrainer benzene and crude pyridine raw material were fed on the 30th tower plate, the mass reflux ratio was 0.56, and the molar recovery ratio of the tower top fraction was 0.38.

[0050] The results of Example 3 show the universality of the scheme of the present invention, that is, the change in the content of the entrainer benzene will not have a significant impact on the purity of the final product, which further illustrates that the scheme has a wide operating range and broad industrial prospects.

[0051] The composition of the top and bottom streams of the azeotropic distillation tower T1 is shown in Table 3.

[0052] Table 3

[0053] Logistics Number 2 3 9 10 Pyridine, mass% 30.94 0.03 0.03 51.61 Benzene, mass% 50.40 89.87 99.97 32.23 Water, mass% 5.63 10.10 0.00 0.05 Aniline, mass% 8.44 5.74e-16 6.48e-18 16.11 Waste residue, mass% 1.39 0.00 0.00 0.00

Claims

1. An azeotropic distillation process for separating pyridine and water, comprising the following steps: (1) The crude pyridine raw material is fully mixed and heated in a stirring tank (D1), and then fed into an azeotropic distillation tower (T1) for azeotropic distillation. The crude pyridine raw material is obtained from medium-low temperature coal tar, and the feed molar ratio of benzene to crude pyridine is 1:1-4:1; the feed is heated to a temperature of 40-120°C before feeding; (2) The water phase and entrainer benzene obtained from the top of the azeotropic distillation tower (T1) enter the reflux tank (D2), and the water phase in the liquid collecting bag at the bottom of the reflux tank is extracted to the outside through static stratification. Part of the upper benzene phase is refluxed to the azeotropic distillation tower (T1), part of it is mixed with the crude pyridine raw material from the tank area for recycling, and the other part is transported to the waste benzene tank; (3) After dehydration in the bottom of the azeotropic distillation tower (T1), part of the crude pyridine is vaporized by the action of the bottom reboiler (E3) and returned to the azeotropic distillation tower (T1) for distillation and purification, and the other part enters the crude pyridine evaporator heat exchanger (E4) for vaporization and separation by steam heating. The gas phase at the top of the evaporator enters the subsequent aniline separation section, and the residue at the bottom of the evaporator is condensed by the condenser (E5) and taken out of the boundary area and enters the phenol oil tank. in, The azeotropic distillation tower (T1) is an inclined hole plate distillation tower with 40 to 80 plates, the position range of benzene and crude pyridine is the 20th to 40th plates, the mass reflux ratio is 1 to 5, and the molar extraction ratio of the top fraction is 0.4 to 0.7; the reflux and circulation molar ratio of benzene in the top fraction of the azeotropic distillation tower (T1) is 1 to 5.

2. The method according to claim 1, characterized in that The operating temperature of the azeotropic distillation tower (T1) is 40-120°C, and the operating pressure is 10-20 kPaG.

3. An azeotropic distillation device for separating pyridine and water, characterized in that: It includes an azeotropic distillation tower (T1), a stirring tank (D1), a tower top condenser (E2), a distillation tower reflux tank (D2), a tower bottom reboiler (E3), and an evaporating kettle heat exchanger (E4), wherein: The azeotropic distillation tower (T1) is provided with a feed port for a crude pyridine and azeotropic benzene mixture, and the top of the azeotropic distillation tower (T1) is provided with a top condenser (E2) and a distillation tower reflux tank (D2) which are connected to each other, a part of the benzene at the outlet of the distillation tower reflux tank (D2) is connected to the top of the azeotropic distillation tower (T1), a part is connected to the feed port of the azeotropic distillation tower (T1), and the other part is transported to a waste benzene tank; the water phase at the outlet of the liquid collecting bag of the distillation tower reflux tank (D2) is transported to a sewage treatment section; the azeotropic distillation tower (T1) is provided with a discharge port which is respectively connected to a tower kettle reboiler (E3) and an evaporating kettle heat exchanger (E4).

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