Method and system for comprehensively utilizing aqueous phase in aniline methylation reaction product

Abstract

The invention discloses a method and system for comprehensively utilizing a water phase in an aniline methylation reaction product, and the method comprises the following steps: firstly, taking the water phase in the aniline methylation reaction product as a raw material, and rectifying the raw material to obtain a methanol distillate and a mixed solution containing aniline, N-methylaniline, trace N, N-dimethylaniline organic matters and water; a low-boiling-point aromatic hydrocarbon solvent is used as an extraction agent, the obtained mixed solution is used as a raw material, and the raw material and the extraction agent are subjected to multiple times of reverse contact for extraction; standing and layering to obtain an extraction phase and a raffinate phase; wherein the extraction phase is a mixture of an amine organic matter and an extraction agent, and the raffinate phase contains wastewater with the content of the amine organic matter reduced. According to the method, the methanol, the amine mixed organic matters and the extraction agent can be recycled, the content of the organic matters in the water can be remarkably reduced, the water can be discharged after reaching the standard after being subjected to further biochemical treatment, and the resource comprehensive utilization of the water phase solution is realized.

Description

Technical Field

[0001] The invention relates to a method and system for chemical separation, and in particular to a method and system for comprehensive utilization of a water phase in a product of aniline methylation reaction. Background Art

[0002] Aniline is an important chemical raw material. A series of derivative products synthesized from aniline and methanol have a wide range of uses. Among the derivative products, N-methylaniline and N,N-dimethylaniline are used in the production of many important industrial products such as papermaking, textile dyes, medicines, spices and explosives. The product of aniline methylation to N,N-dimethylaniline is divided into two layers, in which the aqueous phase contains a considerable amount of methanol, N-methylaniline, trace amounts of N,N-dimethylaniline and a small amount of aniline components. Since there are three groups of binary azeotropes in the aqueous phase, namely water-aniline, water-N,N-dimethylaniline and aniline-N,N-dimethylaniline, it is difficult to achieve separation effect by conventional distillation. At present, the main methods for separating aniline, N-methylaniline and N,N-dimethylaniline from the aqueous phase include extraction distillation, adsorption and membrane separation.

[0003] Reference 1 (Li Mingyu, Yan Qishe, Tang Qihong, et al. Extraction and separation of aniline from water by emulsion liquid membrane method [J]. Journal of Chemical Industry and Engineering, 2003, 54(6):836-840) The extraction of aniline from water was studied by using a non-flowing carrier emulsion liquid membrane method. Hydrochloric acid solution was used as the inner aqueous phase, aniline aqueous solution was used as the outer aqueous phase, and kerosene was used as the oil phase. Aniline reacted with hydrochloric acid at the interface of the inner aqueous phase of the membrane to form aniline hydrochloride, so that the concentration of aniline in the aqueous phase was close to 0. The aniline in the outer aqueous phase was gradually enriched in the aqueous phase in the form of amine salt, thereby achieving the purpose of efficient extraction and separation of aniline. Reference 2 (Shi Zhongliang, Wang Chuansheng, Shen Hua. Research on the treatment of aniline wastewater by emulsion membrane separation technology [J]. Journal of Shenyang Chemical University, 2006, 20(1): 1-3.) uses an emulsion membrane to treat aniline aqueous solution (mass concentration of 480 mg / L), and the aniline removal rate can reach more than 96%. Due to the complexity of the above method and process, and the relatively low aniline removal rate, it has not yet been applied on a large scale. Reference 3 (Wang Zhishun, Gu Zhenggui, Huang Xin. Synthesis of N,N-dimethylaniline by continuous tubular reaction and its purification simulation [J]. Chemical Engineering and Technology, 2018, 8(2): 9.) Using N,N-dimethylformamide as the extractant, the N-methylation product of aniline was separated and purified by the method of coupling extractive distillation and continuous side-line distillation. Under the optimal conditions, the content and yield of N,N-dimethylaniline reached 98.63% and 97.14% respectively. Since the extractive distillation process of this method requires multiple heating and condensation steps, the process energy consumption is relatively high. Reference 4 (Feng Xiaogen. Research on the treatment of aniline and nitrobenzene wastewater by solvent extraction [D]. Zhejiang University of Technology, 2006.) Using liquid-liquid extraction method and biodiesel as the extraction solvent, the aniline removal rate of 99.98% was achieved after the aniline wastewater was subjected to three-stage cross-flow extraction of biodiesel. Reference 5 (Li Fengjiao. Treatment of industrial aniline wastewater [J]. Fine Chemical Intermediates, 2002, 32: 42-43) used N, N-bis (1-methylheptyl) acetamide as the extractant and adopted multi-stage cross-flow liquid-liquid extraction to treat industrial aniline wastewater. After three-stage extraction, the aniline removal rate reached 99.91%. In the above method, the amount of cross-flow extractant is large, and the boiling points of biodiesel (boiling point higher than 300°C) and N, N-bis (1-methylheptyl) acetamide (boiling point of 324°C) are high, and the energy consumption in the process of extractant recovery is high.

[0004] As global awareness of energy conservation, emission reduction and effective comprehensive utilization of resources increases, the treatment of wastewater containing organic matter has received more and more attention. Therefore, it is necessary to provide a method with simple process, low energy consumption and high separation efficiency for the resource recovery of organic matter in wastewater. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for comprehensive utilization of the aqueous phase in the aniline methylation reaction product with simple process, low energy consumption and high separation efficiency; A second object of the present invention is to provide a system used in the above method.

[0006] Technical solution: The method for comprehensive utilization of the aqueous phase in the aniline methylation reaction product of the present invention comprises the following steps: (1) Using the aqueous phase of the aniline methylation reaction product as a raw material, the raw material is distilled to obtain a methanol distillate and a mixed solution containing aniline, N-methylaniline, trace amounts of N,N-dimethylaniline organic matter and water; (2) Using a low-boiling point aromatic hydrocarbon solvent as an extractant and the mixed solution obtained after distillation in step (1) as a raw material, the raw material and the extractant are subjected to multiple reverse contacts for extraction; after standing and stratification, an extraction phase and a raffinate phase are obtained; wherein the extraction phase is a mixture of amine organic matter and the extractant, and the raffinate phase contains wastewater with a reduced content of amine organic matter.

[0007] Wherein, in step (1), the methanol distillate obtained after distillation is circulated to the reaction raw material.

[0008] Wherein, in step (2), the extract phase obtained after extraction is refined in a solvent regeneration tower, and the extractant is distilled out and recycled; the obtained mixture of aniline, N-methylaniline and trace amounts of N,N-dimethylaniline is recycled to the reaction raw material.

[0009] Wherein, in step (2), the low boiling point aromatic hydrocarbon solvent is cumene.

[0010] Wherein, in step (2), the mass ratio of the extractant to the raw material is 0.2:1 to 1.8:1.

[0011] Wherein, in step (2), the extractant and the raw material are stirred by a multi-stage impeller to perform countercurrent contact extraction; the number of stages of the impeller is 4-14.

[0012] Wherein, in step (2), the extractant and the raw material are subjected to countercurrent contact extraction by multi-stage impeller stirring; the impeller stirring speed is 350-950 rpm.

[0013] The system used in the above method includes a distillation tower, a liquid-liquid extraction tower and a solvent recovery tower; the distillation tower is provided with a methanol outlet and a material outlet; the material outlet is connected to the raw material feed port of the liquid-liquid extraction tower, the extraction phase outlet of the liquid-liquid extraction tower is connected to the liquid inlet of the solvent recovery tower; the condensate outlet of the solvent recovery tower is connected to the extractant inlet of the liquid-liquid extraction tower.

[0014] The upper and lower ends of the liquid-liquid extraction tower are respectively provided with a raw material feed port and an extractant feed port, a multi-stage stirring impeller is arranged inside the liquid-liquid extraction tower, an extraction phase static section is arranged at the top of the tower, a raffinate phase static section is arranged at the bottom, the extraction phase static section is provided with an extraction phase overflow port, and the raffinate phase static section is provided with a raffinate phase discharge port; the extraction phase overflow port is connected to the liquid inlet of the solvent recovery tower.

[0015] The bottoms of the distillation tower and the solvent recovery tower are respectively connected with reboilers, and the tops are respectively connected with a condenser and a reflux tank to form a circulation loop.

[0016] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: (1) The present invention uses a mixed solution containing aniline, N-methylaniline and trace amounts of N,N-dimethylaniline organic matter and water obtained by distilling the aqueous phase of the aniline methylation reaction product as a raw material, and uses a low-boiling point aromatic hydrocarbon solvent as an extractant. The raw material and the extractant are subjected to multiple reverse contacts for extraction, thereby effectively extracting methanol and amine organic matter in the aqueous phase of the aniline methylation reaction product, and using them as reaction raw materials, which is beneficial to reducing production costs; at the same time, the organic matter content in the wastewater is significantly reduced, and after further biochemical treatment, it can meet the discharge standards, thereby realizing the resource utilization of the aqueous phase solution. (2) The present invention uses a low-boiling point aromatic hydrocarbon solvent, cumene, as an extractant, which can effectively reduce the content of organic matter in the wastewater. At the same time, compared with other extractants, cumene has the advantage of lower miscibility between cumene and water. (3) The liquid-liquid extraction process in the method of the present invention is carried out at room temperature, with low energy consumption, and the extractant can be recycled, which is in line with the concept of green development in the chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a process flow chart of the distillation and liquid-liquid extraction integrated technology of the present invention; Figure 2 This is a diagram of the multi-stage stirred countercurrent liquid-liquid extraction device of the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in further detail below.

[0019] Example 1

[0020] like Figure 1 As shown, the system used in the method for comprehensive utilization of the water phase in the aniline methylation reaction product of the present invention includes a distillation tower 1, a liquid-liquid extraction tower 2 and a solvent recovery tower 3.

[0021] A methanol liquid outlet is provided at the top of the distillation tower 1, and the methanol liquid outlet is connected to a condenser 5, which is connected to a reflux tank 4, and the reflux tank 4 is respectively connected to the distillation tower 1 and the top fraction methanol storage tank V102; a discharge port is provided at the bottom of the distillation tower 1, and the discharge port is connected to the bottom discharge storage tank V101, and the bottom discharge port of the distillation tower 1 also forms a circulation loop with the reboiler 6.

[0022] like Figure 2 As shown, the upper and lower ends of the liquid-liquid extraction tower 2 of the present invention are respectively provided with a raw material F feed port 2-1 and an extractant S feed port 2-2, a multi-stage stirring impeller 2-5 is provided in the tower, an extraction phase static section 2-6 is provided above the multi-stage stirring impeller 2-5 in the tower, and a raffinate phase static section 2-7 is provided below, and the multi-stage stirring impeller body is connected to a speed regulating motor 2-8; the extraction phase static section 2-6 is provided with an extraction phase overflow port 2-3, and the extraction phase overflow port 2-3 is connected to the extraction phase storage tank V105; the raffinate phase static section 2-7 is provided with a raffinate phase discharge port 2-4, and the raffinate phase discharge port 2-4 is connected to the raffinate phase storage tank V103; the liquid outlet of the extraction phase storage tank V105 is connected to the inlet of the solvent recovery tower 3.

[0023] The top of the solvent recovery tower 3 is connected to a condenser 5, which is connected to a reflux tank 4, which is respectively connected to the solvent recovery tower 3 and an extractant storage tank V104; the bottom discharge port of the solvent recovery tower 3 is connected to an amine organic matter storage tank V106, and the bottom discharge port of the solvent recovery tower 3 also forms a circulation loop with a reboiler 6; the outlet of the extractant storage tank V104 is connected to the extractant S feed port 2-2 of the liquid-liquid extraction tower 2.

[0024] Utilizing the above system, the method for comprehensive utilization of the aqueous phase in the aniline methylation reaction product of the present invention comprises the following steps: The raw material comes from the aqueous phase of the aniline methylation synthesis product, and its composition and physical property data are shown in Table 1.

[0025] First, the aqueous phase of the aniline methylation synthesis product is pretreated by a distillation process in a distillation tower 1, and methanol is distilled from the top of the tower and enters a condenser 5 and a reflux tank 4 connected to the distillation tower 1 in sequence, a part of which is circulated to the reaction raw material, and the excess is stored in a top fraction methanol storage tank V102; the bottom discharge of the distillation tower 1 is stored in a bottom discharge storage tank V101; the bottom discharge of the distillation tower 1 is used as the raw material F of the liquid-liquid extraction process, and at room temperature, the raw material F enters from the upper feed port 2-1 of the liquid-liquid extraction tower 2 at a flow rate of 1.0 kg / h for the raw material F and 1.0 kg / h for the extractant S, the extractant S is stored in the extractant storage tank V104, and the extractant S enters from the lower feed port 2-2 of the liquid-liquid extraction tower 2, and the liquid-liquid extraction tower 2 adopts an 8-stage stirring impeller at a speed of 650 The raw material F and the extractant S are stirred and mixed at a rate of rpm, and the raw material F and the extractant S are contacted in reverse in the liquid-liquid extraction tower 2. After standing and stratification, the raffinate is left standing for more than 15 minutes in the raffinate phase standing section 2-6, and the organic matter content in the raffinate phase is reduced to less than 300 ppm; the extract phase flowing out of the overflow port 2-3 at the top of the liquid-liquid extraction tower 2 is stored in the extract phase storage tank V105, and transported to the solvent recovery tower 3 for treatment. The extractant is taken from the top of the tower and stored in the extractant storage tank V104 through the condenser 5 and reflux tank 4 connected to the solvent recovery tower 3, and circulated into the liquid-liquid extraction tower 2 for repeated use. The amine organic matter in the bottom discharge is stored in the amine organic matter storage tank V106 and circulated to the reaction raw material for use. The composition of the extract phase and the raffinate phase after separation is shown in Table 2.

[0026]

[0027]

[0028] Example 2

[0029] The basic steps are similar to those of Example 1, except that the solvent ratio is different. The liquid-liquid extraction separation results are shown in Table 3.

[0030]

[0031] It can be seen from Table 3 that as the solvent ratio increases, the organic matter content in the raffinate phase gradually decreases, and the water content in the extraction phase also gradually decreases. When the solvent ratio continues to increase to 1.0:1, the water content in the extraction phase is less than 0.1%. At this time, the organic matter content in the raffinate phase is less than 300 ppm, and it can meet the emission standards after further biochemical treatment. Therefore, considering the production cost and other issues, the solvent ratio of 1.0:1 is selected as the optimal solvent ratio.

[0032] Example 3

[0033] The basic steps are similar to those of Example 1, except that the number of extraction stages is different. The liquid-liquid extraction separation results are shown in Table 4.

[0034]

[0035] It can be seen from Table 4 that with the increase of the number of extraction stages, the organic matter content in the raffinate phase water first gradually decreases and then remains unchanged, and the water content in the extraction phase has basically no change. When the number of extraction stages increases to 8, the organic matter content in the raffinate phase water is less than 300 ppm, and it can reach the discharge standard after further biochemical treatment. Since the increase in the number of extraction stages will increase the equipment investment cost, after comprehensive consideration, the extraction stage 8 is selected as the optimal extraction stage.

[0036] Example 4

[0037] The basic steps are similar to those of Example 1, except that the stirring rate is different. The liquid-liquid extraction separation results are shown in Table 5.

[0038]

[0039] It can be seen from Table 5 that with the increase of stirring rate, the content of organic matter in the raffinate phase gradually decreases. When the stirring rate reaches a certain level, the reduction of organic matter in the raffinate phase is significantly reduced, and the water content in the extraction phase remains basically unchanged. Since the higher the rotation rate, the greater the energy consumption, when the stirring rate reaches 650rpm, the content of organic matter in the raffinate phase is less than 300ppm, and it can meet the emission standards after further biochemical treatment. Therefore, the optimal stirring rate is 650rpm.

[0040] Comparative Example 1 The basic steps are similar to those of Example 1, except that a different extractant is used. The liquid-liquid extraction separation effect is shown in Table 6.

[0041]

[0042] Based on the principle of liquid-liquid extraction, through the calculation and comparison of the selectivity coefficients in Table 6, it can be found that among the ethers, esters, alkanes, and aromatic hydrocarbon extractants, the selectivity coefficients of aromatic hydrocarbon extractants are higher than those of ethers, esters, and alkanes. Therefore, a low-boiling point solvent among aromatic hydrocarbons, that is, a boiling point lower than the boiling point of aniline in the separation system by more than 30°C, is selected for further experimental discussion; through the comparison of the selectivity coefficients among low-boiling point aromatic hydrocarbon solvents, it can be found that when isopropylbenzene is used as the extraction solvent, the selectivity coefficient has the largest value, and when the content of organic matter in the raffinate phase is higher than 1000ppm, it will increase the difficulty of subsequent biochemical treatment of the wastewater. Therefore, isopropylbenzene is preferred among the low-boiling point aromatic hydrocarbon solvents.

[0043] Comparative Example 2 The basic steps are as in Example 1, except that the extractant used is different. The extractant of this comparative example is a mixed solvent of cumene and benzene in a mass ratio of 1:1. The compositions of the extract phase and the raffinate phase after separation are shown in Table 7.

[0044]

[0045] It can be seen from Comparative Example 2 that when a mixed extractant of cumene and benzene is used, the separation effect is better than that of the single benzene extractant in Comparative Example 1.

[0046] Comparative Example 3 The basic steps are as in Example 1, except that the extractant used is different. The extractant of this comparative example is a mixed solvent of cumene and toluene in a mass ratio of 1:1. The compositions of the extract phase and the raffinate phase after separation are shown in Table 8.

[0047]

[0048] It can be seen from Comparative Example 3 that when a mixed extractant of cumene and toluene is used, the separation effect is better than that of the single toluene extractant in Comparative Example 1.

[0049] Comparative Example 4 The basic steps are as in Example 1, except that the extractant used is different, and the extractant of this comparative example is a mixed solvent of cumene and ethylbenzene in a mass ratio of 1:1. The compositions of the extract phase and the raffinate phase after separation are shown in Table 9.

[0050]

[0051] It can be seen from Comparative Example 4 that when a mixed extractant of cumene and ethylbenzene is used, the separation effect is better than that of the single ethylbenzene extractant in Comparative Example 1.

Claims

1. A method for comprehensive utilization of water phase in aniline methylation reaction products, characterized in that: The following steps are involved: (1) Using the aqueous phase of the aniline methylation reaction product as a raw material, the raw material is distilled to obtain a methanol distillate and a mixed solution containing aniline, N-methylaniline, trace amounts of N,N-dimethylaniline organic matter and water; (2) Using a low-boiling point aromatic hydrocarbon solvent as an extractant and the mixed solution obtained after distillation in step (1) as a raw material, the raw material and the extractant are subjected to multiple reverse contacts for extraction; after standing and stratification, an extraction phase and a raffinate phase are obtained; wherein the extraction phase is a mixture of amine organic matter and the extractant, and the raffinate phase contains wastewater with a reduced content of amine organic matter.

2. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (2), the extract phase obtained after extraction is refined in a solvent regeneration tower, and the extractant is distilled out and recycled; the obtained mixture of aniline, N-methylaniline and trace amounts of N,N-dimethylaniline is recycled to the reaction raw material.

3. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (2), the low boiling point aromatic hydrocarbon solvent is cumene.

4. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (2), the mass ratio of the extractant to the raw material is 0.2:1 to 1.8:

1.

5. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (2), the extractant and the raw material are stirred by a multi-stage impeller to perform countercurrent contact extraction; the number of stages of the impeller is 4-14.

6. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (2), the extractant and the raw material are subjected to countercurrent contact extraction by multi-stage impeller stirring; the impeller stirring speed is 350-950 rpm.

7. The method for comprehensive utilization of water phase in the aniline methylation reaction product according to claim 1, characterized in that: In step (1), the methanol distillate obtained after distillation is circulated to the reaction raw material.

8. A system used in the method according to claim 1, characterized in that: The invention comprises a distillation tower (1), a liquid-liquid extraction tower (2) and a solvent recovery tower (3); the distillation tower (1) is provided with a methanol outlet and a material outlet; the material outlet is connected to a raw material feed port of the liquid-liquid extraction tower (2); the extraction phase outlet of the liquid-liquid extraction tower (2) is connected to a liquid inlet of the solvent recovery tower (3); the condensate outlet of the solvent recovery tower (3) is connected to an extractant inlet of the liquid-liquid extraction tower (2).

9. The system according to claim 8, characterized in that The upper and lower ends of the liquid-liquid extraction tower (2) are respectively provided with a raw material feed port (2-1) and an extractant feed port (2-2); a multi-stage stirring impeller (2-5) is provided inside the liquid-liquid extraction tower (2); an extraction phase static section (2-6) is provided at the top of the tower; a raffinate phase static section (2-7) is provided at the bottom; the extraction phase static section (2-6) is provided with an extraction phase overflow port (2-3); and the raffinate phase static section (2-7) is provided with a raffinate phase discharge port (2-4); the extraction phase overflow port (2-3) is connected to the liquid inlet of the solvent recovery tower (3).

10. The system according to claim 8, characterized in that The bottoms of the distillation tower (1) and the solvent recovery tower (3) are respectively connected to a reboiler (7), and the tops are respectively connected to a condenser (5) and a reflux tank (4) to form a circulation loop.

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