Method for continuous nitration reaction of m-dichlorobenzene in microreactor

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a method for continuous nitration reaction of m-dichlorobenzene in a microreactor. The method comprises the following steps: by taking m-dichlorobenzene and fuming nitric acid as raw materials, carrying out continuous nitration reaction in a microreactor to obtain 2, 4-dichloronitrobenzene and 2, 6-dichloronitrobenzene. The problems of tedious operation and waste acid recovery are effectively solved. The microreactor has high mass transfer and heat transfer efficiency, and can quickly remove heat released by nitration reaction of m-dichlorobenzene; according to the invention, the liquid-liquid two-phase complete mixing time of m-dichlorobenzene and the nitrating agent in the channel can be prolonged, so that the nitration reaction process becomes mild and controllable, the occurrence of temperature runaway and explosion accidents is avoided, the intrinsic safety of the process is improved, and industrial production is easy to carry out.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical industry, and particularly relates to a method for continuous nitration reaction of m-dichlorobenzene in a micro-reactor. BACKGROUND

[0002] 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are important organic compounds, which can be used for producing pesticides, medicines, dyes and other organic chemical products. 2,4-dichloronitrobenzene is usually used as a raw material for 5-chloro-2-nitroaniline and 2,4-difluoronitrobenzene, wherein 5-chloro-2-nitroaniline is an important precursor for producing prothioconazole, flurbiprofen and other similar compounds. Starting from m-dichlorobenzene, through nitration reaction and further conversion, nearly 20 kinds of halogenated benzene nitro compounds can be derived, which can be used for synthesizing nearly 100 kinds of fine chemical products, and have a broad market prospect. At present, the nitration reaction process of m-dichlorobenzene still uses a traditional batch stirred tank reactor, and the nitration agent is usually a mixed acid composed of nitric acid and sulfuric acid. This method has the disadvantages of dangerous operation, complicated steps, many side reactions (oxidation, over-nitration or sulfonation), strong corrosion, etc., and is prone to cause safety accidents such as explosion and fire, and belongs to a high-risk process which is supervised by the state. Due to the slow heat transfer rate of the reactor, the reaction temperature needs to be strictly controlled, the production efficiency is low, and the uneven mixing of materials caused by ordinary stirring inevitably leads to low raw material conversion rate and high content of by-products.

[0003] The micro-reactor is a new type of pipeline reactor based on micro-processing technology, which integrates mixing, heat transfer, reaction and separation operation units. Due to the small internal size of the channel and the small unit liquid holding capacity, it has excellent mass transfer and heat transfer performance, and improves the intrinsic safety of the process. The micro-reactor can realize the scale-up of the process by size amplification and equipment parallel connection, and almost has no scale-up effect, which improves the efficiency, safety and flexibility of the production of high-risk chemical reaction processes. Therefore, the nitration reaction process of m-dichlorobenzene using the micro-reactor can improve the intrinsic safety of the reaction, improve the production efficiency, and has potential industrial production prospect.

[0004] At present, patents CN115093328A and CN104478730A have reported the nitration reaction of m-dichlorobenzene in a micro-reactor to synthesize 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene. However, the nitration methods reported in the two patents are both using a mixed acid composed of nitric acid and sulfuric acid as the nitration agent, and the patent CN115093328A further adds an organic solvent dichloroethane, which leads to the need for desolventization operation after the reaction; the patent CN104478730A designs two temperature zones and divides the mixed acid into two feeds, which is complicated to operate. At the same time, both methods have the problem of waste acid treatment and recovery. SUMMARY

[0005] In order to solve the problems existing in the current m-dichlorobenzene nitration reaction process in the micro-reactor, the purpose of the present application is to provide a method for continuous nitration reaction of m-dichlorobenzene in the micro-reactor. The method is simple to operate, high in process safety, high in production efficiency and can realize the recycling of waste acid.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is: A method for continuous nitration reaction of m-dichlorobenzene in a micro-reactor, using m-dichlorobenzene and fuming nitric acid as raw materials, carrying out continuous nitration reaction in a micro-reactor to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene, and the reaction equation is: .

[0007] Further, the m-dichlorobenzene solution and the fuming nitric acid solution are respectively introduced into the micro-reactor for continuous nitration reaction, a water solution is introduced at the outlet of the reactor to quench the reaction liquid, and then after separation and drying, 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are obtained.

[0008] Further, the m-dichlorobenzene solution and the fuming nitric acid solution are respectively introduced into the micro-reactor for continuous nitration reaction, a water solution is introduced at the outlet of the reactor to quench the reaction liquid, and then after separation and drying, 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are obtained.

[0009] Further, the quenched reaction liquid is washed with water, washed with alkali, washed with water again, separated, and the organic phase is dried to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene products.

[0010] The temperature of the nitration reaction in the micro-reactor is 20-80℃, preferably the temperature of the nitration reaction is 30-60℃.

[0011] The residence time of the nitration reaction in the micro-reactor is 10-100s, preferably the residence time of the nitration reaction is 30-100s.

[0012] The preparation method of fuming nitric acid is: under the condition of 5-15℃, slowly drop the concentrated nitric acid into the deionized water solution with stirring to prepare the fuming nitric acid solution, and the concentration of the fuming nitric acid solution is 95-98%. Or by mixing the concentrated nitric acid solution and the water solution in the channel through the micro-reactor, temperature control is carried out through the micro-reactor heat exchange, and the temperature is maintained within the range of 5-15℃.

[0013] The molar ratio of m-dichlorobenzene to fuming nitric acid is 1:1-8. Preferably, the molar ratio of m-dichlorobenzene to fuming nitric acid is 1:3.

[0014] A device used in the method comprises a feed pump 1, a feed pump 2, a feed pump 3, a microreactor 4, a capillary 5, a cold water pool 6, wherein the outlets of the feed pump 1 and the feed pump 2 are connected with the inlet of the microreactor 4 respectively, the outlet of the microreactor 4 is connected with the inlet of the capillary 5, the outlet of the capillary 5 is connected with the cold water pool 6, the cold water pool 6 is connected with a product tank, and the outlet of the feed pump 3 is connected with the inlet of the capillary 5.

[0015] The internal structure type of the microreactor is one of a heart type, an S type, a diamond type and a fishbone type.

[0016] The upper side of the microreactor is provided with a heat exchange plate for heat exchange, and the heat exchange plate is separated from the microreactor by a mirror plate.

[0017] The present application is to realize the continuous nitration reaction of m-dichlorobenzene and fuming nitric acid to synthesize 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene by using a microreactor, and compared with traditional batch stirring reactors and other continuous flow processes, the present application has the following advantages: (1) The present application effectively solves the problems of complicated operation and waste acid recovery. The microreactor has high mass transfer and heat transfer efficiency, can quickly remove the heat released by the nitration reaction of m-dichlorobenzene, can improve the time for complete mixing between the liquid-liquid two phases of m-dichlorobenzene and the nitrating agent in the channel, makes the nitration reaction process become mild and controllable, avoids the occurrence of over-temperature and explosion accidents, improves the process safety, and is easy to industrialize.

[0018] (2) The nitration reaction time of m-dichlorobenzene in the microreactor is only tens of seconds, which avoids the occurrence of side reactions and greatly improves the production efficiency. At the same time, the waste acid after reaction can be recycled and used, which further saves the production cost and improves the atomic economic utilization rate.

[0019] (3) The present application uses fuming nitric acid for nitration reaction, which is mild and has high selectivity, and almost no by-product of dinitro is generated; the reaction rate is easy to control, which improves the safety of the reaction process; after the reaction is completed, it can be recycled through simple separation and concentration, and the three wastes are less. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a nitration reaction process diagram of m-dichlorobenzene in the microreactor in the present application.

[0021] Figure 2 It is a microreactor internal structure diagram in the present application.

[0022] Figure 3 It is a nuclear magnetic spectrum of 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene products prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate and show the advantages of the present application, the following will be in-depth analysis with specific examples and drawings. However, these examples are only preferred embodiments, and do not represent all possible application forms. Professionals in this field make basic substitutions or improvements, etc. Adjustments such as adjustments are within the scope of the technical solutions protected by the present application.

[0024] As shown in Figure 1 The microreaction system: the nitration reaction process of m-dichlorobenzene in the microreactor is as shown in Figure 1 As shown in Figure 1 The microreaction system: the nitration reaction process of m-dichlorobenzene in the microreactor is as shown in Figure 1 As shown in

[0025] The feed pumps 1 and 2 introduce m-dichlorobenzene and fuming nitric acid solution respectively, and mix and react through the microreactor. The residence time is adjusted by increasing or decreasing the number of reaction plates. After the reaction is completed, water solution is introduced into the reactor outlet through the feed pump 3 to quench the reaction system. The quenched mixture enters the capillary tube placed in the cold water pool to avoid secondary reaction. The capillary output material flows into the product tank, and after static stratification, the lower aqueous phase waste nitric acid is concentrated and mixed with 98% nitric acid to prepare a ready-to-use solution.

[0026] The temperature of the entire microreaction system is controlled by a high and low temperature circulation machine, and the entire reaction process is maintained at a stable reaction temperature setting value.

[0027] The internal structure type of the microreactor is heart-shaped, and the reaction plate is composed of a series of heart-shaped cell structures in series. The microstructure reactor is as shown in Figure 2 The upper side of the microreactor is provided with a heat exchange plate, and the heat exchange plate and the microreactor are separated by a mirror plate.

[0028] Example 1 The fuming nitric acid solution with a concentration of 98% and the m-dichlorobenzene solution were preheated and then pumped into the microreactor by the metering pump, wherein the flow rate of the fuming nitric acid solution was 32.5 mL / min and the flow rate of the m-dichlorobenzene solution was 27.5 mL / min, at this time the molar ratio of fuming nitric acid to m-dichlorobenzene was 2:1, the reaction temperature was controlled at 40°C, and the residence time was 30 s. After the reaction was completed, the product was quenched by water introduced by the metering pump, and the quenched mixture was introduced into the capillary placed in the cold water pool to avoid secondary reaction. The capillary output material flowed into the product tank, and the product was separated by static layering. The upper organic phase was washed with 10% sodium hydroxide solution and deionized water, respectively, and finally dried with anhydrous sodium sulfite to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene crude products. Gas chromatography detection showed that the conversion rate of m-dichlorobenzene was 100%, the selectivity of 2,4-dichloronitrobenzene was 2.1%, the selectivity of 2,6-dichloronitrobenzene was 96.1%, and the dinitro by-product was 1.8%. The nuclear magnetic resonance spectrum of the 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene products is shown in Figure 3 ,1H NMR (500 MHz, DMSO-d6) δ 8.11 (d, J = 8.7 Hz, 1H),7.98 (d, J = 2.2 Hz, 1H), 7.79 (d, J = 8.1 Hz, 0H), 7.69 (dd, J = 8.8, 2.2Hz, 1H).

[0029] Example 2 The fuming nitric acid solution with a concentration of 97.5% and the m-dichlorobenzene solution were preheated and then pumped into the microreactor by the metering pump, wherein the flow rate of the fuming nitric acid solution was 34 mL / min and the flow rate of the m-dichlorobenzene solution was 26 mL / min, at this time the molar ratio of fuming nitric acid to m-dichlorobenzene was 3:1, the reaction temperature was controlled at 60°C, and the residence time was 30 s. After the reaction was completed, the product was quenched by water introduced by the metering pump, and the quenched mixture was introduced into the capillary placed in the cold water pool to avoid secondary reaction. The capillary output material flowed into the product tank, and the product was separated by static layering. The upper organic phase was washed with 10% sodium hydroxide solution and deionized water, respectively, and finally dried with anhydrous sodium sulfite to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene crude products. Gas chromatography detection showed that the conversion rate of m-dichlorobenzene was 100%, the selectivity of 2,4-dichloronitrobenzene was 1.8%, the selectivity of 2,6-dichloronitrobenzene was 96.7%, and the dinitro by-product was 1.5%.

[0030] Example 3 The nitric acid solution with a concentration of 96% and the m-dichlorobenzene solution were preheated and pumped into the micro-reactor by the metering pump, wherein the flow rate of the nitric acid solution was 36 mL / min and the flow rate of the m-dichlorobenzene solution was 24 mL / min, the molar ratio of the nitric acid to the m-dichlorobenzene was 3:1, the reaction temperature was controlled at 40°C, and the residence time was 60 s. After the reaction, the product was quenched by water introduced by the metering pump, and the quenched mixture was introduced into the capillary tube placed in the cold water pool to avoid secondary reaction. The capillary output flowed into the product tank, and the product was separated by static layering. The upper organic phase was washed by 10% sodium hydroxide solution and deionized water, and finally dried by anhydrous sodium sulfite to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene crude products. The conversion rate of m-dichlorobenzene was 100%, the selectivity of 2,4-dichloronitrobenzene was 1.5%, and the selectivity of 2,6-dichloronitrobenzene was 98.5% by gas chromatography detection.

[0031] Waste nitric acid recycling experiment The separated lower layer waste nitric acid solution had a concentration of 60-70% and no by-products were detected. After concentration, the concentration of the nitric acid reached 80-84%. The experimental operation conditions were the same as those of Example 3, and the experimental data after recycling were as shown in Table 1.

[0032] Table 1. Results of waste nitric acid recycling experiment

[0033] Comparative Example 1 Nitric acid-sulfuric acid mixed acid continuous process The nitric acid solution with a concentration of 90% and the sulfuric acid solution with a concentration of 90% were mixed to prepare a mixed acid solution with a molar ratio of 1:3. The m-dichlorobenzene solution and the mixed acid were preheated and pumped into the micro-reactor by the metering pump, wherein the flow rate of the mixed acid solution was 35 mL / min and the flow rate of the m-dichlorobenzene solution was 25 mL / min, the molar ratio of the nitric acid, the sulfuric acid to the m-dichlorobenzene was 1.1:3.15:1, the reaction temperature was controlled at 30°C, and the residence time was 30 s. After the reaction, the product was quenched by water introduced by the metering pump. The product was separated by static layering, and the upper organic phase was washed by 10% sodium hydroxide solution and deionized water, and finally dried by anhydrous sodium sulfite to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene crude products. The conversion rate of m-dichlorobenzene was 100%, the selectivity of 2,4-dichloronitrobenzene was 8.3%, the selectivity of 2,6-dichloronitrobenzene was 87%, and the multi-nitro by-products were 4.7% by gas chromatography detection.

[0034] Comparative Example 2 Concentrated nitric acid continuous process The concentrated nitric acid solution with a concentration of 90% and the m-dichlorobenzene solution are respectively preheated and then pumped into the microreactor by the metering pump, wherein the flow rate of the nitric acid solution is 38 mL / min, the flow rate of the m-dichlorobenzene solution is 22 mL / min, the molar ratio of nitric acid to m-dichlorobenzene is 3:1, the reaction temperature is controlled at 40℃, the residence time is 60s, and the product is quenched by water introduced by the metering pump after the reaction is completed. The product is separated by static layering, the upper organic phase is washed by 10% sodium hydroxide solution and deionized water respectively, and finally dried by anhydrous sodium sulfite to obtain 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene crude products. The conversion rate of m-dichlorobenzene is 80%, the selectivity of 2,4-dichloronitrobenzene is 1.4%, and the selectivity of 2,6-dichloronitrobenzene is 78.6% by gas chromatography detection.

[0035] As can be seen from the above examples, the present application provides a continuous nitration production process of m-dichlorobenzene and fuming nitric acid. The present application uses m-dichlorobenzene and fuming nitric acid as raw materials, realizes the continuous nitration production of m-dichlorobenzene through the microchannel reactor, the conversion rate of raw materials reaches 100%, and the selectivity of mononitro product is greater than 98%. The continuous production process of the present application is simple, the product selectivity is good, waste acid is recycled and applied, and meets the requirements of industrial production. At the same time, since the microchannel reactor used in the present application has the ability to quickly remove the heat generated in the nitration reaction process, continuous production is realized, the production process is safe, stable and controllable, the intrinsic safety of the nitration process is improved. Further, the recycling and application of waste nitric acid also greatly reduces the cost and three wastes, and is more environmentally friendly than the prior art.

Claims

1. A process for the continuous nitration of m-dichlorobenzene in a microreactor, characterized in that, 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are obtained by continuous nitration reaction of m-dichlorobenzene and fuming nitric acid in a microreactor.

2. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 1, characterized in that, The m-dichlorobenzene solution and the fuming nitric acid solution are respectively introduced into the microreactor for continuous nitration reaction, water solution is introduced into the outlet of the microreactor for quenching of the reaction liquid, and then 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are obtained by separation and drying.

3. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 1, characterized in that, The m-dichlorobenzene solution and the fuming nitric acid solution are respectively introduced into the microreactor for continuous nitration reaction, water solution is introduced into the outlet of the microreactor for quenching of the reaction liquid, and then 2,4-dichloronitrobenzene and 2,6-dichloronitrobenzene are obtained by separation and drying.

4. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 3, characterized in that, The concentration of the fuming nitric acid solution is 95-98%.

5. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 3, characterized in that, The molar ratio of m-dichlorobenzene to fuming nitric acid is 1:1-1:

8.

6. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 1, characterized in that, The temperature of the nitration reaction in the microreactor is 20-80℃.

7. The process for continuous nitration of m-dichlorobenzene within a microreactor according to claim 1, characterized in that, The residence time of the nitration reaction in the microreactor is 10-100s.

8. An apparatus for use in the method of claim 1, wherein The apparatus comprises a feed pump (1), a feed pump (2), a feed pump (3), a microreactor (4), a capillary tube (5) and a cold water pool (6), wherein the outlets of the feed pumps (1) and (2) are respectively connected to the inlet of the microreactor (4), the outlet of the microreactor (4) is connected to the inlet of the capillary tube (5), the outlet of the capillary tube (5) is connected to the cold water pool (6), and the outlet of the feed pump (3) is connected to the inlet of the capillary tube (5).

9. The apparatus for use in the method of claim 8, characterized in that The internal structure of the microreactor (4) is one of heart-shaped, S-shaped, rhombic and fishbone-shaped.

10. The apparatus for use in the method of claim 8, wherein, The upper side of the microreactor (4) is provided with a heat exchange plate for heat exchange, and the heat exchange plate is separated from the microreactor by a mirror plate.

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