Continuous preparation method of mononitro aromatic hydrocarbon

Abstract

The invention discloses a method for continuously preparing mononitro-aromatic hydrocarbon, which comprises the following steps: respectively pumping an aromatic hydrocarbon compound and a polyfluoro-substituted alcohol solution of nitric acid from two inlets of a microreactor, mixing, reacting, quenching with ice water, extracting with an organic solvent, washing with water, and drying to obtain mononitro-aromatic hydrocarbon, the aromatic hydrocarbon compound is selected from at least one of benzene, monosubstituted aromatic hydrocarbon toluene, tert-butylbenzene, fluorobenzene, chlorobenzene, and disubstituted aromatic hydrocarbon o-xylene, m-xylene and p-xylene; the polyfluoro substituted alcohol is selected from at least one of trifluoroethanol, hexafluoroisopropanol and nonafluoro tert-butyl alcohol. The polyfluoro-substituted alcohol which is easy to recover is used as the cosolvent, so that the aromatic hydrocarbon raw material and the nitration reagent in the microreactor form a homogeneous nitration system, the mononitro aromatic hydrocarbon selectivity is controllable, and the problem of excessive nitration of the heterogeneous nitration system of nitric acid and sulfuric acid is effectively avoided. The method is safer, more efficient and easy to amplify, and a new way is provided for large-scale preparation of mononitro-aromatic hydrocarbon by a micro-reaction technology.

Description

Technical Field

[0001] The present application relates to a method for the continuous preparation of mononitroaromatic hydrocarbons, belonging to the field of organic synthesis. Background Art

[0002] As important organic intermediates, mononitroaromatic compounds play a significant role in the fields of medicine, pesticides, explosives, fragrances, etc. Highly selective, safe and efficient mononitroaromatic compound synthesis technology has always been an important research direction and goal pursued by the chemical industry.

[0003] At present, the industry generally uses a nitric acid-sulfuric acid mixed acid composed of concentrated nitric acid and concentrated sulfuric acid to nitrate aromatic compounds to synthesize mononitroaromatic compounds. The mixed acid reaction system has the following characteristics: (1) Since the solubility of aromatics in concentrated sulfuric acid is low, the reaction system is heterogeneous, the intrinsic reaction rate of the nitration reaction is fast, and the mixed acid nitration is mostly controlled by mass transfer; (2) The viscosity of the nitric acid-sulfuric acid mixed acid is large, the two phases are difficult to disperse, and the energy consumption is high; (3) The reaction releases a large amount of heat. Since the reaction system is heterogeneous, the local reaction is violent and it is easy to produce local hot spots, which may cause multiple nitration reactions at the least, resulting in high energy consumption for subsequent separation and purification of the product, and may cause safety accidents such as explosions at the worst. In addition, the mixed acid nitration process produces a large amount of waste acid, the waste acid treatment cost is high, and the environmental pressure is great. With the continuous improvement of the country's legal requirements for environmental protection and the high attention to chemical production safety in recent years, the development space of mixed acid nitration has been gradually compressed, and it is urgent to develop a highly selective, safe and efficient technology for synthesizing mononitroaromatic compounds.

[0004] Microchemical technology is a process intensification technology with microreactors with characteristic sizes ranging from hundreds of micrometers to several millimeters as core equipment. It has received continuous attention from academia and industry in the past two decades due to its excellent mixing, mass transfer and heat transfer performance. In recent years, many works on the preparation of mononitroaromatics in microreactors have emerged. Yang et al. prepared mononitrotoluene by nitrating toluene with mixed nitric and sulfuric acid in a microreactor, with a toluene conversion rate of 81.3%, a mononitrotoluene selectivity of 91.3%, and a dinitrotoluene selectivity of 8.7% (Research on Chemical Intermediates (2022) 48: 4373-4390). Fu et al. prepared mononitrotoluene by nitrating toluene with mixed nitric and sulfuric acid in a microreactor, with a toluene conversion rate of 86.0%, a mononitrotoluene selectivity of 95.0%, and a dinitrotoluene selectivity of 5.0% (Process Safety and Environmental Protection (2022) 160: 385-396). Han et al. prepared mononitrotoluene and mononitrochlorobenzene respectively by nitrating toluene and chlorobenzene with nitric acid and sulfuric acid in a microreactor, wherein the toluene conversion rate was 100%, the mononitrotoluene selectivity was 91.5%, the dinitrotoluene selectivity was 8.5%, the chlorobenzene conversion rate was 96.4%, the mononitrochlorobenzene selectivity was 97.5%, and the dinitrochlorobenzene selectivity was 2.5% (Chemical Engineering Research and Design (2024) 205: 343-353). It can be found that the preparation of mononitroaromatics by nitrating aromatics with nitric acid and sulfuric acid in a microreactor can effectively solve the safety problem of the reaction process, but it still cannot solve the selectivity problem of mononitroaromatics in the reaction process. This is due to the essential characteristics of the heterogeneous system of mixed acid nitration. In order to achieve the highly selective, safe and efficient preparation of mononitroaromatics, it is urgent to develop a new homogeneous nitration system.

[0005] Polyfluorinated alcohols, such as trifluoroethanol, hexafluoroisopropanol, nonafluorotert-butanol, etc., have high polarity relative to conventional organic solvents, and combine both hydrophilic and lipophilic properties, so they can be used as co-solvents for aromatic hydrocarbons and nitric acid, thus making the nitration reaction a homogeneous system. In addition, polyfluorinated alcohols have more fluorine atoms with high electronegativity on their carbon chains. Due to the strong electronic effect, the polarization degree of the -OH of the hydroxyl group is greater than that of general alkyl alcohols, the bond energy is weakened, and the proton acidity is greatly increased. For example, the acidity of hexafluoroisopropanol in aqueous solution (pKa = 9.3) is about 7 orders of magnitude higher than that of isopropanol, making it a stronger hydrogen bond donor. Due to the electron-withdrawing effect of fluorine atoms, the charge density of oxygen atoms decreases, making polyfluorinated alcohols weaker in nucleophilicity. In the nitration reaction, these two characteristics are very conducive to promoting the self-dissociation and dehydration of nitric acid molecules to generate the real nitrification species NO2 +, and avoid using a large amount of sulfuric acid as a dehydrating agent and catalyst to promote the nitration reaction. In addition, polyfluoro substituted alcohols have good redox stability and can stably exist without reacting with high concentration nitric acid for a long time. It can be seen that polyfluoro substituted alcohols can be used as excellent co-solvents for nitration reactions and promote the nitration reaction. Therefore, the development of nitric acid-polyfluoro substituted alcohol homogeneous nitration system and the implementation of process intensification through microreactors are expected to solve the problems of excessive nitration and the treatment of a large amount of waste acid caused by mixed acid nitration without sacrificing the nitration reaction rate. However, there is no report on the preparation of mononitroaromatics using nitric acid-polyfluoro substituted alcohol homogeneous nitration system in a microreactor. Summary of the invention

[0006] The purpose of the present invention is to provide a method for continuously preparing mononitroaromatic hydrocarbons in a microreactor, so as to realize the continuous synthesis of mononitroaromatic hydrocarbons with high selectivity, safety and high efficiency.

[0007] According to one aspect of the present application, a method for continuously preparing mononitroaromatic hydrocarbons is provided, comprising the following steps:

[0008] The aromatic compound and the polyfluorinated alcohol solution of nitric acid are pumped into the two inlets of the microreactor respectively, mixed, reacted, quenched with ice water, extracted with an organic solvent, washed with water, and dried to obtain mononitroaromatic hydrocarbons;

[0009] The aromatic compound is selected from at least one of benzene, monosubstituted aromatic toluene, tert-butylbenzene, fluorobenzene, chlorobenzene, disubstituted aromatic o-xylene, m-xylene and p-xylene;

[0010] The polyfluorinated substituted alcohol is selected from at least one of trifluoroethanol, hexafluoroisopropanol, and nonafluorotert-butyl alcohol.

[0011] In the polyfluorinated alcohol solution of nitric acid, the concentration of nitric acid is 4 to 20 mol / L;

[0012] The mass fraction of the nitric acid is 80-95wt%.

[0013] The molar ratio of the nitric acid to the aromatic hydrocarbon compound is 1.0 to 3.0.

[0014] The reaction temperature is 30-70°C;

[0015] The reaction time is 30 to 300 seconds.

[0016] The microreactor is selected from a plate microreactor, a coil microreactor and a tubular reactor filled with a microstructure static mixer.

[0017] The channel size of the microreactor is 0.5-8 mm.

[0018] The beneficial effects of this application include:

[0019] (1) When polyfluorinated alcohols are used as co-solvents, the reaction system is homogeneous and there is no interphase mass transfer.

[0020] (2) No sulfuric acid is used and the viscosity of the reaction system is low.

[0021] (3) The reaction conditions are mild, the post-treatment is simple, and the amount of waste acid is small.

[0022] (4) The selectivity for mononitroaromatic hydrocarbons is high, and almost no dinitroaromatic hydrocarbons are produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a simplified process flow diagram of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described and illustrated below in conjunction with the embodiments of the present invention, but the present invention is not limited to the following specific implementation examples.

[0025] Figure 1 The process flow diagram of the continuous synthesis of mononitroaromatics in the microreactor of the present invention is composed of three parts: raw material transportation, reaction, and post-treatment. Aromatic compounds and nitric acid-polyfluoro substituted alcohol solution are transported to the two inlets of the microreactor by a metering pump at a given flow rate for mixing and reaction. The reaction temperature in the microreactor is controlled by a high and low temperature integrated circulation machine. The reaction liquid is collected at the outlet of the microreactor, ice water is added to quench the reaction, and the reaction liquid is extracted with an organic solvent, washed with water, and dried to obtain the product mononitroaromatics.

[0026] Example 1

[0027] 51.6g of nitric acid with a mass fraction of 95wt.% was dissolved in 100g of hexafluoroisopropanol to prepare an 8mol / L nitric acid-hexafluoroisopropanol solution as a nitrating agent, and the aromatic compound to be nitrated was toluene. The flow rates of the nitrating agent and toluene were set to 0.28ml / min and 0.22ml / min, respectively, and transported to the microreactor by a syringe pump for mixing and reaction. The molar ratio of nitric acid to toluene was 1.1. The inner diameter of the microreactor was 0.8mm. The reaction temperature in the microreactor was controlled at 55°C by a high and low temperature cycle integrated machine, and the residence time of the material in the microreactor was 300s. The reaction liquid was collected at the outlet of the microreactor for a certain period of time, quenched with an ice-water mixture, extracted with dichloromethane, washed with water, and dried. The sample composition was analyzed by gas chromatography, with a toluene conversion rate of 51.9%, a mononitrotoluene selectivity of 100%, of which o-nitrotoluene: m-nitrotoluene: p-nitrotoluene was 54.9:2.7:42.4, and no dinitrotoluene was detected.

[0028] Comparative Example 1

[0029] In this comparative example, nitric acid and sulfuric acid were used to nitrate toluene. 61.8g of 98wt.% sulfuric acid was added to 17.7g of water, and then 20.5g of 95wt.% nitric acid was added to form a nitric acid and sulfur molar ratio of 0.5, and a nitric acid and sulfur mixed acid with a water mass fraction of 20wt.% was used as a nitrating agent. The flow rates of nitric acid and sulfur mixed acid and toluene were set to 0.33ml / min and 0.17ml / min, respectively, and transported to the microreactor via a syringe pump for mixing and reaction. The molar ratio of nitric acid to toluene was 1.1. The inner diameter of the microreactor was 0.8mm. The reaction temperature in the microreactor was controlled at 55°C by a high and low temperature circulation integrated machine, and the residence time of the material in the microreactor was 300s. The reaction solution was collected at the outlet of the microreactor for a certain period of time, quenched with an ice-water mixture, extracted with dichloromethane, washed with water, and dried. The composition of the sample was analyzed by gas chromatography, and the toluene conversion rate was 50.1%, the mononitrotoluene selectivity was 96.4%, wherein the ratio of o-nitrotoluene:m-nitrotoluene:p-nitrotoluene was 57.7:4.4:37.7, and the dinitrotoluene selectivity was 3.6%.

[0030] Comparative Example 2

[0031] In this comparative example, 95wt.% nitric acid was used to nitrate toluene. The flow rates of nitric acid and toluene were set to 0.34ml / min and 0.16ml / min, respectively, and transported to the microreactor via a syringe pump for mixing and reaction. The molar ratio of nitric acid to toluene was 1.1. The reaction temperature in the microreactor was controlled at 55°C by a high and low temperature circulation integrated machine, and the residence time of the material in the microreactor was 300s. The reaction solution was collected at the outlet of the microreactor for a certain period of time, quenched with an ice-water mixture, extracted with dichloromethane, washed with water, and dried. The sample composition was analyzed by gas chromatography, with a toluene conversion rate of 46.0%, a mononitrotoluene selectivity of 93.1%, wherein o-nitrotoluene: m-nitrotoluene: p-nitrotoluene was 54.4:4.0:41.6, and a dinitrotoluene selectivity of 6.9%.

[0032] Example 2

[0033] In this embodiment, the difference from Example 1 is that the flow rates of the nitrating agent and toluene are set to 0.35 ml / min and 0.15 ml / min respectively, and are transported to the microreactor via a syringe pump for mixing and reaction. The molar ratio of nitric acid to toluene is 2.0. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the toluene conversion rate is 99%, the mononitrotoluene selectivity is 100%, wherein o-nitrotoluene: m-nitrotoluene: p-nitrotoluene is 54.9:2.7:42.4, and no dinitrotoluene is detected.

[0034] Example 3

[0035] In this embodiment, the difference from Example 1 is that the flow rates of the nitrating agent and toluene are set to 0.36 ml / min and 0.14 ml / min, respectively, and the molar ratio of nitric acid to toluene is 2.2. The residence time of the material in the microreactor is 180 s. The sample composition is analyzed by gas chromatography, and the toluene conversion rate is 100%, the mononitrotoluene selectivity is 100%, wherein o-nitrotoluene:m-nitrotoluene:p-nitrotoluene is 54.7:2.7:42.6, and no dinitrotoluene is detected.

[0036] Example 4

[0037] In this embodiment, the difference from Example 1 is that the flow rates of the nitrating agent and toluene are set to 2.20 ml / min and 0.94 ml / min, respectively. The molar ratio of nitric acid to toluene is 2.0. The inner diameter of the microreactor is 2 mm. The sample composition is analyzed by gas chromatography, and the toluene conversion rate is 99.4%, the mononitrotoluene selectivity is 100%, wherein the ratio of o-nitrotoluene:m-nitrotoluene:p-nitrotoluene is 54.6:2.7:42.7, and no dinitrotoluene is detected.

[0038] Example 5

[0039] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is tert-butylbenzene. The flow rates of the nitrating agent and tert-butylbenzene are set to 0.32 ml / min and 0.18 ml / min, respectively, and the molar ratio of nitric acid to tert-butylbenzene is 2.2. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the conversion rate of tert-butylbenzene is 100%, the selectivity of mononitrotoluene is 99.8%, wherein the ratio of o-nitrobenzene to m-nitrobenzene to p-nitrobenzene is 15.3:6.4:78.3, and the selectivity of dinitrotert-butylbenzene is 0.2%.

[0040] Example 6

[0041] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is benzene. The flow rates of the nitrating agent and benzene are set to 0.38 ml / min and 0.12 ml / min, respectively, and the molar ratio of nitric acid to benzene is 2.2. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the benzene conversion rate is 99.4%, the nitrobenzene selectivity is 100%, and no dinitrobenzene is detected.

[0042] Example 7

[0043] In this embodiment, the difference from Example 1 is that 364g of 95wt.% nitric acid is dissolved in 100g of hexafluoroisopropanol to form an 18mol / L nitric acid-hexafluoroisopropanol solution as a nitrating agent, and the nitrated aromatic compound is benzene. The flow rates of the nitrating agent and benzene are set to 0.3ml / min and 0.2ml / min, respectively, and the molar ratio of nitric acid to benzene is 2.4. The residence time of the material in the microreactor is 240s. The sample composition is analyzed by gas chromatography, and the benzene conversion rate is 100%, the nitrobenzene selectivity is 100%, and no dinitrobenzene is detected.

[0044] Example 8

[0045] In this embodiment, the difference from Example 1 is that the nitrated aromatic compound is fluorobenzene. The flow rates of the nitrating agent and fluorobenzene are set to 0.39 ml / min and 0.11 ml / min, respectively, and the molar ratio of nitric acid to fluorobenzene is 2.6. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the fluorobenzene conversion rate is 99.5%, the mononitrofluorobenzene selectivity is 100%, wherein o-nitrofluorobenzene: m-nitrofluorobenzene: p-nitrofluorobenzene is 17.9:0.1:83.0, and no dinitrofluorobenzene is detected.

[0046] Example 9

[0047] In the present embodiment, the difference from Example 1 is that 750.7g of nitric acid with a mass fraction of 95wt.% is dissolved in 100g of hexafluoroisopropanol, and a 20mol / L nitric acid-hexafluoroisopropanol solution is configured as a nitrating agent, and the nitrated aromatic compound is fluorobenzene. The flow rates of the nitrating agent and fluorobenzene are set to 0.29ml / min and 0.21ml / min, respectively, and the molar ratio of nitric acid to fluorobenzene is 2.6. The residence time of the material in the microreactor is 240s. The sample composition is analyzed by gas chromatography, and the fluorobenzene conversion rate is 99.9%, the mononitrofluorobenzene selectivity is 100%, wherein o-nitrofluorobenzene: m-nitrofluorobenzene: p-nitrofluorobenzene is 17.4:0.2:82.4, and no dinitrofluorobenzene is detected.

[0048] Example 10

[0049] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is chlorobenzene. The flow rates of the nitrating agent and chlorobenzene are set to 0.39 ml / min and 0.11 ml / min, respectively, and the molar ratio of nitric acid to chlorobenzene is 2.8. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the chlorobenzene conversion rate is 99.9%, the mononitrochlorobenzene selectivity is 100%, wherein o-nitrochlorobenzene: m-nitrochlorobenzene: p-nitrochlorobenzene is 40.6:0.3:59.1, and no dinitrochlorobenzene is detected.

[0050] Embodiment 11

[0051] In this embodiment, the difference from Example 1 is that 364g of 95wt.% nitric acid is dissolved in 100g of hexafluoroisopropanol to form an 18mol / L nitric acid-hexafluoroisopropanol solution as a nitrating agent, and the nitrated aromatic compound is chlorobenzene. The flow rates of the nitrating agent and chlorobenzene are set to 0.3ml / min and 0.2ml / min, respectively, and the molar ratio of nitric acid to chlorobenzene is 2.8. The residence time of the material in the microreactor is 240s. The sample composition is analyzed by gas chromatography, and the chlorobenzene conversion rate is 100%, the mononitrochlorobenzene selectivity is 100%, wherein o-nitrochlorobenzene: m-nitrochlorobenzene: p-nitrochlorobenzene is 37.3:0.5:62.2, and no dinitrochlorobenzene is detected.

[0052] Example 12

[0053] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is o-xylene. The flow rates of the nitrating agent and o-xylene are set to 0.36 ml / min and 0.14 ml / min, respectively, and the molar ratio of nitric acid to o-xylene is 2.4. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the o-xylene conversion rate is 99.6%, the mononitro o-xylene selectivity is 97.3%, wherein the ratio of 3-nitro o-xylene to 4-nitro o-xylene is 50.3:49.7, and the selectivity of dinitro o-xylene is 2.7%.

[0054] Example 13

[0055] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is m-xylene. The flow rates of the nitrating agent and m-xylene are set to 0.36 ml / min and 0.14 ml / min, respectively, and the molar ratio of nitric acid to m-xylene is 2.4. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the m-xylene conversion rate is 98.8%, the mononitro m-xylene selectivity is 94.8%, wherein the ratio of 2-nitro m-xylene to 4-nitro m-xylene is 12.4:87.6, and the selectivity of dinitro m-xylene is 5.2%.

[0056] Embodiment 14

[0057] In this embodiment, the difference from Example 1 is that the aromatic compound to be nitrated is p-xylene. The flow rates of the nitrating agent and p-xylene are set to 0.35 ml / min and 0.15 ml / min, respectively, and the molar ratio of nitric acid to p-xylene is 2.4. The residence time of the material in the microreactor is 240 s. The sample composition is analyzed by gas chromatography, and the p-xylene conversion rate is 95.9%, the mononitro p-xylene selectivity is 94.7%, and the dinitro p-xylene selectivity is 5.3%.

[0058] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for the continuous preparation of mononitroaromatic hydrocarbons, characterized in that: The following steps are involved: The aromatic compound and the polyfluorinated alcohol solution of nitric acid are pumped into the two inlets of the microreactor respectively, mixed, reacted, quenched with ice water, extracted with an organic solvent, washed with water, and dried to obtain mononitroaromatic hydrocarbons; The aromatic compound is selected from at least one of benzene, monosubstituted aromatic toluene, tert-butylbenzene, fluorobenzene, chlorobenzene, disubstituted aromatic o-xylene, m-xylene and p-xylene; The polyfluorinated substituted alcohol is selected from at least one of trifluoroethanol, hexafluoroisopropanol, and nonafluorotert-butyl alcohol.

2. The method according to claim 1, characterized in that In the polyfluorinated alcohol solution of nitric acid, the concentration of nitric acid is 4 to 20 mol / L; The mass fraction of the nitric acid is 80-95wt%.

3. The method according to claim 1, characterized in that: The molar ratio of the nitric acid to the aromatic hydrocarbon compound is 1.0 to 3.

0.

4. The method according to claim 1, characterized in that: The reaction temperature is 30-70°C; The reaction time is 30 to 300 seconds.

5. The method according to claim 1, characterized in that The microreactor is selected from a plate microreactor, a coil microreactor and a tubular reactor filled with a microstructure static mixer.

6. The method according to claim 1, characterized in that The channel size of the microreactor is 0.5-8 mm.

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