A method for suppressing the overnitration side reaction of aromatics

Abstract

This invention relates to a method for suppressing the overnitration side reaction of aromatic hydrocarbons. The method comprises the following steps: 1) adding sulfuric acid to nitric acid to obtain a mixed acid solution A; 2) simultaneously feeding the mixed acid solution A and aromatic hydrocarbon B into a continuous flow reactor for a nitration reaction to obtain mononitroaromatic hydrocarbons; wherein the mass ratio of the nitric acid to the sulfuric acid is greater than 1:6 and less than 50:1, and the volumetric flow rate ratio of the mixed acid solution A to the aromatic hydrocarbon B in step 2) is 1:10 to 5:1. This method significantly reduces the solubility of nitroaromatic hydrocarbons in the acid phase by controlling the concentration and amount of sulfuric acid, and enhances the dilution effect of the water produced in the main reaction on the sulfuric acid, thereby suppressing the overnitration side reaction in the acid phase. This significantly improves the selectivity of mononitration of aromatic hydrocarbons, saving the huge energy consumption of product separation after the reaction and significantly reducing the amount and cost of waste acid treatment after the reaction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical engineering, and relates to a method for inhibiting a side reaction of aromatic hydrocarbon per-nitration. BACKGROUND

[0002] Aromatic hydrocarbon nitration is one of basic reaction types in chemistry, is widely applied in the production of medicines, dyes, pesticides and energetic materials, and is an important link in the nitrogen cycle in nature. Aromatic hydrocarbon nitration mostly has the characteristics of fast reaction rate and strong reaction exothermicity. In the traditional stirring process, in order to ensure the safety of the reaction process, the reaction is usually controlled at low temperature and low concentration, and the reaction efficiency is low. However, the per-nitration reaction is the most difficult to be inhibited in the aromatic hydrocarbon nitration process, and forms a typical series reaction process with the mononitration reaction of aromatic hydrocarbons. The longer reaction time in the stirring process will be more conducive to the occurrence of the per-nitration side reaction, resulting in the reduction of the reaction selectivity.

[0003] In the continuous flow aromatic hydrocarbon nitration technology emerging in the past 20 years, due to the intrinsic safety and excellent mass transfer performance, the limitation on the reaction rate of aromatic hydrocarbon nitration is reduced, so that the aromatic hydrocarbon nitration shows a faster reaction rate. However, at the same time, it is accompanied by stronger reaction exothermicity and dilution heat of sulfuric acid, resulting in an increase in the system temperature. Since the activation energy of the per-nitration reaction is higher than that of the mononitration reaction, the increase in the system temperature will also intensify the occurrence of the per-nitration side reaction. Therefore, the current continuous flow aromatic hydrocarbon nitration technology usually shows higher side reaction selectivity, which causes safety hazards and huge costs of product separation, and an effective method for inhibiting the occurrence of the per-nitration side reaction in the aromatic hydrocarbon nitration process needs to be developed.

[0004] There are also methods for improving the benzene conversion rate and obtaining high-purity nitrobenzene in the prior art. For example, patent document 1 discloses a method for synthesizing high-purity nitrobenzene by nitration of benzene with nitro-sulfur mixed acid, which uses a two-stage nitration process in which a microreactor and a stirring type nitration reactor are connected in series to improve the selectivity of nitrobenzene. Although this method can improve the total conversion rate of benzene and improve the selectivity of mononitrobenzene, it is difficult to realize the scale-up of the continuous process by coupling the microreactor and the stirred tank, and the reaction uses a lower temperature, a lower sulfuric acid concentration and a higher sulfuric acid dosage, and the reaction efficiency is low.

[0005] CITATION LIST

[0006] Patent document 1: CN101613285A SUMMARY

[0007] The problem to be solved by the invention

[0008] The aromatic nitration reaction has the characteristics of fast reaction rate and strong exothermicity. In order to ensure the safety of the reaction process, the stirring process is usually carried out at low temperature, and a large amount of sulfuric acid solvent and cooling medium need to be added, which leads to low reaction efficiency. At the same time, since the over-nitration side reaction and the main reaction are typical series reactions, long residence time will be more conducive to the occurrence of over-nitration side reaction, which reduces the reaction selectivity. In the continuous process, the mass transfer limits the reaction rate, which makes the aromatic nitration show a faster reaction rate, but at the same time, it is accompanied by faster dilution heat of sulfuric acid and reaction exothermic rate, which leads to the increase of system temperature, further aggravating the occurrence of over-nitration side reaction. Therefore, it is urgent to develop a method for inhibiting the over-nitration side reaction, so as to improve the selectivity of aromatic mononitration reaction, improve the safety and reduce the separation energy consumption and waste acid treatment cost.

[0009] The solution to the problem

[0010] The present application provides a method for inhibiting the over-nitration side reaction of aromatic hydrocarbon, which comprises the following steps:

[0011] 1) adding sulfuric acid to nitric acid to obtain mixed acid solution A;

[0012] 2) simultaneously conveying the mixed acid solution A and aromatic hydrocarbon B into a continuous flow reactor for nitration reaction to obtain mononitro aromatic hydrocarbon;

[0013] wherein the mass ratio of the nitric acid to the sulfuric acid is greater than 1:6 and less than 50:1,

[0014] In step 2), the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B is 1:10-5:1.

[0015] According to the above method, in step 1), the mass fraction of the sulfuric acid is 40-90%.

[0016] According to the above method, the mass ratio of the nitric acid to the sulfuric acid is 1:1 or more and less than 50:1.

[0017] According to the above method, in step 1), the molar ratio of the aromatic hydrocarbon B to the nitric acid in the mixed acid solution A is 1:0.9-1:1.2.

[0018] According to the above method, in step 2), the solubility of the aromatic hydrocarbon B and the mononitro aromatic hydrocarbon in the sulfuric acid solution is 10 -2 mol / L or less.

[0019] According to the above method, in step 2), the temperature of the nitration reaction is less than or equal to the boiling point of the aromatic hydrocarbon B.

[0020] According to the method described above, wherein in step 2), the continuous flow reactor is a tubular reactor or a microreactor.

[0021] According to the method described above, wherein in step 2), the flow mode of the continuous flow reactor is continuous co-current, continuous counter-current or multi-stage counter-current.

[0022] According to the method described above, further comprising the following steps:

[0023] 3) performing oil-water separation at the outlet of the continuous flow reactor, and the obtained organic phase is the mononitro aromatic hydrocarbon.

[0024] Effects of the invention

[0025] The present application uses nitric acid and a specific concentration of sulfuric acid in combination, which suppresses the occurrence of the pernitration side reaction, thereby improving the selectivity of the mononitration of aromatic hydrocarbons. The low sulfuric acid concentration reduces the solubility of nitro aromatic hydrocarbons, the low sulfuric acid dosage further reduces the amount of nitro aromatic hydrocarbons dissolved, and the dilution effect of the water produced in the main nitration reaction on the concentration of sulfuric acid is strengthened, which significantly reduces the total amount of nitro aromatic hydrocarbons dissolved in the main acid phase, thereby suppressing the pernitration side reaction in the main acid phase, and significantly improving the selectivity of the mononitration of aromatic hydrocarbons, thereby saving the huge energy consumption of product separation after the reaction is completed, and significantly reducing the treatment amount and cost of waste acid after the reaction is completed. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Process flow diagram for continuous co-current system.

[0027] Figure 2 Process flow diagram for continuous multi-stage counter-current system.

[0028] Figure 3 Process flow diagram for continuous counter-current system. DETAILED DESCRIPTION

[0029] Various illustrative embodiments, features and aspects of the present application are described below in detail. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0030] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art will understand that the present application can be practiced without certain specific details. In some instances, well-known methods, means, instruments and steps have not been described in detail in order to highlight the principles of the present application.

[0031] Unless otherwise stated, the units used in the present specification are international standard units, and the numerical values, numerical value ranges appearing in the present application should be understood as including systematic errors that are inevitable in industrial production.

[0032] In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0033] In the present specification, "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", and the like refer to specific elements (for example, features, structures, properties, and / or characteristics) described in relation to the embodiments, which are included in at least one embodiment described herein, and can or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0034] In the present specification, the numerical value range indicated by "numerical value A to numerical value B" refers to a range including the end point numerical values A and B.

[0035] In the present specification, "aromatic hydrocarbon" includes, but is not limited to, benzene, toluene, chlorobenzene, biphenyl, and the like.

[0036] In the present specification, "room temperature" is 15-25℃.

[0037] The present application provides a method for inhibiting the side reaction of aromatic hydrocarbon nitration, characterized in that it comprises the following steps:

[0038] 1) adding sulfuric acid to nitric acid to obtain mixed acid solution A;

[0039] 2) simultaneously feeding mixed acid solution A and aromatic hydrocarbon B into a continuous flow reactor to perform nitration reaction, to obtain mononitro aromatic hydrocarbon;

[0040] wherein the mass ratio of the nitric acid to the sulfuric acid is greater than 1:6 and less than 50:1,

[0041] In step 2), the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B is 1:10-5:1.

[0042] In some preferred embodiments, the synthesis method of the present application further comprises

[0043] 3) performing oil-water separation at the outlet of the continuous flow reactor, and the obtained organic phase is the mononitro aromatic hydrocarbon.

[0044] Each step is described in detail below.

[0045] Step 1)

[0046] First, the mass of the aromatic hydrocarbon B is determined, the mass of the nitric acid is determined according to the molar ratio of the aromatic hydrocarbon B to the nitric acid, and the mass of the sulfuric acid is calculated according to the predetermined volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B.

[0047] Then, the nitric acid with the determined mass is taken, the sulfuric acid with the mass determined by the calculation is taken, the sulfuric acid is added to the nitric acid, and the mixed acid solution A is obtained.

[0048] In some specific embodiments of the present application, the mass fraction of the sulfuric acid can be 40-90%, for example, can be 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc.

[0049] In some specific embodiments of the present application, the mass fraction of the nitric acid can be 60-98%, for example, can be 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. In the present application, the molar ratio of the aromatic hydrocarbon B to the nitric acid in the mixed acid solution A can be 1:0.9-1:1.2, for example, can be 1:0.95, 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.1, 1:1.15, etc.

[0050] In the present application, the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B can be 1:10-5:1, for example, can be 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 2:3, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, etc.

[0051] In the present application, the mass ratio of the nitric acid to the sulfuric acid in the mixed acid solution A is greater than 1:6 and less than 50:1. For example, can be 1:5, 1:4, 1:3, 1:2, 2:3, 1:1, 1.2:1, 1.5:1, 2:1, 2.5:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, etc.

[0052] In some specific embodiments of the present application, the use of fuming nitric acid can improve the nitration efficiency, and by using a specific amount of sulfuric acid, the nitration side reaction can be effectively suppressed, and the selectivity of the aromatic hydrocarbon mononitration can be significantly improved.

[0053] Step 2)

[0054] The mixed acid solution A and the aromatic hydrocarbon B are simultaneously transported into the continuous flow reactor at the predetermined volume flow ratio to perform the nitration reaction, and the mononitroaromatic hydrocarbon is obtained.

[0055] In some embodiments of the present application, the volume flow rate of the mixed acid solution A can be 0.2-8 mL / min, and the volume flow rate of the aromatic hydrocarbon B can be 0.2-8 mL / min.

[0056] In the present application, as the nitration reaction proceeds, the nitric acid is continuously consumed, and the water produced in the nitration reaction continuously dilutes the concentration of sulfuric acid. By regulating the initial concentration and the amount of sulfuric acid, the dilution effect of the water produced in the main reaction on the concentration of sulfuric acid is strengthened, so that the solubility of the aromatic hydrocarbon B and the mononitroaromatic hydrocarbon in the sulfuric acid solution is less than 10 mol / L, and the solubility further decreases as the reaction proceeds, which can effectively inhibit the pernitration side reaction in the acid phase main body and significantly improve the selectivity of the aromatic hydrocarbon mononitration. -2

[0057] In the present application, the temperature of the nitration reaction is less than or equal to the boiling point of the aromatic hydrocarbon B. In some embodiments, the temperature of the nitration reaction can be normal temperature to the boiling point of the aromatic hydrocarbon B, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, etc.

[0058] After a certain amount of the mixed acid solution A and the aromatic hydrocarbon B are delivered into the continuous flow reactor and stay for a period of time (also referred to as residence time), the nitration reaction of the nitric acid with the aromatic hydrocarbon is carried out. In the present application, the residence time is not particularly limited until the reaction is completed. In some embodiments, it can be 4-20 min, for example, it can be 5 min, 7 min, 9 min, 10 min, 12 min, 15 min, 18 min, etc.

[0059] In the present application, the continuous flow reactor includes but is not limited to a tubular reactor, a microreactor, etc.

[0060] In the present application, the flow mode of the continuous flow reactor includes continuous parallel flow, continuous countercurrent flow, multi-stage countercurrent flow, etc. For example, the continuous flow system shown in Figure 1 、 Figure 2 、 Figure 3 can be used, but is not limited to the system shown in Figure 1 、 Figure 2 、 Figure 3 .

[0061] Figure 1

[0062] A phase separator is provided at the outlet of the continuous flow reactor to separate oil and water, and the obtained organic phase is the mononitroaromatic hydrocarbon.

[0063] The following will be described in combination with Figure 2 、 Figure 3 and Step 3) ​to illustrate the synthetic process of the present application.

[0064] Figure 1 A process flow diagram of the continuous parallel flow system of the present application is shown. As shown in the figure, the mixed acid solution A and the aromatic hydrocarbon feedstock B are simultaneously fed into the continuous flow reactor from the same side at a certain volumetric flow rate for nitration reaction. A phase separator (not shown in the figure) is arranged at the outlet of the reactor to effectively separate the organic phase from the acid solution, and the organic phase is the product mononitro aromatic hydrocarbon. Figure 2

[0065] A process flow diagram of the continuous multi-stage countercurrent system of the present application is shown. As shown in the figure, phase separators are respectively arranged at the outlets of the first-stage reactor and the second-stage reactor. The aromatic hydrocarbon feedstock B and the aqueous phase solution D (which is a mixed acid solution) passing through the phase separator of the second-stage reactor are fed into the first-stage reactor for nitration reaction. The organic phase E (containing aromatic hydrocarbon) passing through the phase separator of the first-stage reactor is fed into the second-stage reactor together with the mixed acid solution A for nitration reaction. The organic phase F obtained at the phase separator of the second-stage reactor is the product mononitro aromatic hydrocarbon. Figure 3 Figure 1 A process flow diagram of the continuous countercurrent system of the present application is shown. As shown in the figure, the mixed acid solution A and the aromatic hydrocarbon feedstock B are simultaneously fed into the continuous flow reactor from opposite sides at a certain volumetric flow rate for nitration reaction. A phase separator (not shown in the figure) is arranged at the outlet of the reactor to effectively separate the organic phase from the acid solution, and the organic phase is the product mononitro aromatic hydrocarbon.

[0066] Figure 1 Example Figure 2 The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. The specific conditions not indicated in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not indicated by the manufacturer are all conventional products that can be obtained by purchase.

[0067] Example 1

[0068] The molar ratio of nitric acid to toluene is 1.01. 436 g of toluene and 301 g of fuming nitric acid are taken. Concentrated sulfuric acid with a mass fraction of 75% is added to the fuming nitric acid to obtain a mixed acid solution. The volumetric flow rate of the mixed acid solution is 2 mL / min, the volumetric flow rate of toluene is 4 mL / min, and the volumetric flow rate ratio of the two phases is 1:2. The two phases are fed into a tubular reactor for nitration reaction. The reaction temperature is 60°C, the reaction pressure is 0.5 MPa, and the reaction time is 30 min.

[0069]

[0070] The molar ratio of nitric acid to toluene is 1.01. 436 g of toluene and 301 g of fuming nitric acid are taken. Concentrated sulfuric acid with a mass fraction of 75% is added to the fuming nitric acid to obtain a mixed acid solution. The volumetric flow rate of the mixed acid solution is 2 mL / min, the volumetric flow rate of toluene is 4 mL / min, and the volumetric flow rate ratio of the two phases is 1:2. The two phases are fed into a tubular reactor for nitration reaction. The reaction temperature is 60°C, the reaction pressure is 0.5 MPa, and the reaction time is 30 min. Figure 2 ​​The reaction occurs in the continuous parallel flow mode shown, the reaction system is placed in a constant temperature reaction at 70°C, the residence time is 5 min, oil-water separation is performed at the outlet of the reactor, and the organic phase is the product mononitrotoluene.

[0071] The liquid chromatography detection result of the mononitrotoluene prepared in this embodiment 1 is: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0072] Embodiment 2

[0073] The molar ratio of nitric acid to toluene is 1.01, 436 g of toluene and 301 g of fuming nitric acid are taken, 70% concentrated sulfuric acid is added to the fuming nitric acid to obtain a mixed acid solution. The volume flow rate of the mixed acid solution is 0.2 mL / min, the volume flow rate of toluene is 0.4 mL / min, the volume flow rate ratio of the two phases is 1:2, and they are transported into the microreactor to react in the continuous parallel flow mode shown. Figure 3 The reaction occurs in the continuous parallel flow mode shown, the reaction system is placed in a constant temperature reaction at 70°C, the residence time is 5 min, oil-water separation is performed at the outlet of the reactor, and the organic phase is the product mononitrotoluene.

[0074] The liquid chromatography detection result of the mononitrotoluene prepared in this embodiment 2 is: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0075] Embodiment 3

[0076] The molar ratio of nitric acid to toluene is 1.01, 436 g of toluene and 301 g of fuming nitric acid are taken, 70% concentrated sulfuric acid is added to the fuming nitric acid to obtain a mixed acid solution. The volume flow rate of the mixed acid solution is 0.2 mL / min, the volume flow rate of toluene is 0.4 mL / min, the volume flow rate ratio of the two phases is 1:2, and they are transported into the microreactor to react in the continuous parallel flow mode shown. Figure 3 The reaction occurs in the continuous parallel flow mode shown, the reaction system is placed in a constant temperature reaction at 70°C, the residence time is 5 min, oil-water separation is performed at the outlet of the reactor, and the organic phase is the product mononitrotoluene.

[0077] The liquid chromatography detection result of the mononitrotoluene prepared in this embodiment 3 is: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0078] Embodiment 4

[0079] The molar ratio of nitric acid to toluene is 1.01, 436 g of toluene and 301 g of fuming nitric acid are taken, 70% concentrated sulfuric acid is added to the fuming nitric acid to obtain a mixed acid solution. The volume flow rate of the mixed acid solution is 0.2 mL / min, the volume flow rate of toluene is 0.4 mL / min, the volume flow rate ratio of the two phases is 1:2, and they are transported into the microreactor to react in the continuous parallel flow mode shown. Figure 1The reaction occurs in a continuous co-current mode as shown. The reaction system is placed at a constant temperature of 90°C for a residence time of 5 minutes. Oil-water separation is performed at the reactor outlet, and the organic phase is the product nitrobenzene.

[0080] The liquid chromatography results of the nitrobenzene prepared in Example 4 were as follows: benzene conversion rate 99.9% and nitrobenzene selectivity 99.9%.

[0081] Example 5

[0082] The molar ratio of nitric acid to chlorobenzene is 1.01. 554 g of chlorobenzene and 313 g of fuming nitric acid are taken, and concentrated sulfuric acid (80% by mass) is added to the fuming nitric acid to obtain a mixed acid solution. The volumetric flow rate of the mixed acid solution is 8 mL / min, the volumetric flow rate of chlorobenzene is 8 mL / min, and the volumetric flow rate ratio of the two phases is 1:1. This solution is then fed into a tubular reactor to proceed as follows: Figure 1 The reaction occurs in a continuous co-current mode as shown. The reaction system is placed at a constant temperature of 100°C for 5 minutes. Oil-water separation is performed at the reactor outlet, and the organic phase is the product mononitrochlorobenzene.

[0083] The liquid chromatography results of the nitrobenzene prepared in Example 5 were as follows: chlorobenzene conversion rate 99.9%, mononitrochlorobenzene selectivity 99.99%.

[0084] Example 6

[0085] The molar ratio of nitric acid to toluene is 1.01. 436 g of toluene and 301 g of fuming nitric acid are added. Concentrated sulfuric acid (70% by mass) is added to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a flow rate of 0.25 mL / min, and the toluene has a flow rate of 0.5 mL / min, with a flow rate ratio of 1:2. This solution is then transferred to a microreactor to... Figure 3 Figure 1 Figure 1 Figure 1 The reaction occurs in a continuous co-current mode as shown. The reaction system is kept at a constant temperature of 90°C for 8 minutes. Oil-water separation is performed at the reactor outlet, and the organic phase is the product mononitrotoluene.

[0086] The liquid chromatography results of the mononitrotoluene prepared in Example 6 were as follows: toluene conversion rate 99.9% and mononitrotoluene selectivity 99.9%.

[0087] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method of suppressing side reactions of aromatic hydrocarbon pernitration, characterized by, The method comprises the following steps: 1) adding sulfuric acid into nitric acid to obtain a mixed acid solution A; 2) simultaneously feeding the mixed acid solution A and an aromatic hydrocarbon B into a continuous flow reactor to perform a nitration reaction to obtain a mononitro aromatic hydrocarbon; wherein, in step 1), the mass fraction of the sulfuric acid is 40-90%; the mass ratio of the nitric acid to the sulfuric acid is greater than or equal to 2:3 and less than 50:1; the molar ratio of the aromatic hydrocarbon B to the nitric acid in the mixed acid solution A is 1:0.9-1:1.2; in step 2), the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B is 1:10-5:

1.

2. The method according to claim 1, wherein in step 2), the volume flow of the mixed acid solution A is 0.2-8 mL / min, and the volume flow of the aromatic hydrocarbon B can be 0.2-8 mL / min.

3. The method according to claim 1 or 2, wherein in step 2), the residence time of the mixed acid solution A and the aromatic hydrocarbon B in the continuous flow reactor is 4-20 min.

4. The process according to claim 1 or 2, wherein in step 2) the solubility of both the aromatic hydrocarbon B and the mononitroaromatic hydrocarbon in the sulfuric acid solution is 10 -2 mol / L or less.​ 5. The method according to claim 1 or 2, wherein in step 2), the temperature of the nitration reaction is less than or equal to the boiling point of the aromatic hydrocarbon B.

6. The method according to claim 1 or 2, wherein in step 2), the continuous flow reactor is a tubular reactor or a microreactor.

7. The method according to claim 1 or 2, wherein in step 2), the flow mode of the continuous flow reactor is continuous co-current, continuous counter-current or multi-stage counter-current.

8. The method according to claim 1 or 2, further comprising the following step: 3) performing oil-water separation at the outlet of the continuous flow reactor, and the obtained organic phase is the mononitro aromatic hydrocarbon.

Images