Method for inhibiting aromatic hydrocarbon over-nitrification side reaction

Abstract

The invention relates to a method for inhibiting an aromatic hydrocarbon over-nitrification side reaction. The method for inhibiting the aromatic hydrocarbon over-nitrification side reaction comprises the following steps: 1) adding sulfuric acid into nitric acid to obtain a mixed acid solution A; 2) simultaneously conveying the mixed acid solution A and the aromatic hydrocarbon B into a continuous flow reactor for nitration reaction to obtain mononitro aromatic hydrocarbon; wherein the mass ratio of the nitric acid to the sulfuric acid is greater than 1: 6 and less than 50: 1, and the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B in the step 2) is 1: 10-5: 1. According to the method disclosed by the invention, by regulating and controlling the concentration and dosage of sulfuric acid, the solubility of nitro-aromatic hydrocarbon in an acid phase main body is remarkably reduced, and the dilution effect of water generated by main reaction on sulfuric acid is enhanced, so that the side reaction of over-nitrification in the acid phase main body is inhibited, and the selectivity of mononitration of aromatic hydrocarbon can be remarkably improved; the huge energy consumption of product separation after the reaction is finished is saved, and the treatment capacity and the cost of waste acid after the reaction is finished are obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemistry and chemical engineering, and relates to a method for inhibiting the side reaction of overnitration of aromatic hydrocarbons. Background Art

[0002] Aromatic nitration is one of the basic reaction types in chemistry. It is widely used in the production of medicines, dyes, pesticides and energetic materials, and is an important part of the nitrogen cycle in nature. Most aromatic nitrations have the characteristics of fast reaction rate and strong exothermic reaction. 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 overnitration reaction is the most difficult side reaction process to inhibit in aromatic nitration, and it forms a typical tandem reaction process with the aromatic mononitration reaction. Under the stirring process, a longer reaction time will be more conducive to the occurrence of overnitration side reactions, resulting in reduced reaction selectivity.

[0003] In the emerging continuous flow aromatic nitration technology in the past 20 years, due to its inherent safety and excellent mass transfer performance, the restriction on the reaction rate of aromatic nitration has been reduced, making aromatic nitration show a faster reaction rate, but it is also accompanied by stronger reaction exotherm and sulfuric acid dilution heat, causing the system temperature to increase. Since the activation energy of the pernitration reaction is higher than that of the mononitration reaction, the increase in system temperature will also aggravate the occurrence of pernitration side reactions. Therefore, the current continuous flow aromatic nitration technology usually shows higher side reaction selectivity, causing safety hazards and huge costs for product separation. It is urgent to develop effective methods to inhibit the occurrence of pernitration side reactions in aromatic nitration.

[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 nitrating benzene with nitric and sulfuric acid mixed acid, which uses a two-stage nitration process in which a microreactor and a stirred nitration reactor are connected in series to improve the selectivity of nitrobenzene. Although this method can improve the total conversion rate of benzene and the selectivity of mononitrobenzene, it is difficult to achieve the amplification of the continuous process by coupling the microreactor and the stirred tank, and the reaction adopts a relatively low temperature, a low sulfuric acid concentration and a high sulfuric acid dosage, and the reaction efficiency is low.

[0005] Citations

[0006] Patent document 1: CN101613285A Summary of the invention

[0007] Problem that the invention aims to solve

[0008] The nitration reaction of aromatics 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, resulting in low reaction efficiency. At the same time, since the overnitration side reaction and the main reaction are typical tandem reactions, a long residence time will be more conducive to the occurrence of overnitration side reactions, which will reduce the reaction selectivity. In the continuous process, the restriction of mass transfer on the reaction rate is reduced, so that the nitration of aromatics shows a faster reaction rate, but at the same time it is accompanied by faster sulfuric acid dilution heat and reaction exothermic rate, resulting in an increase in system temperature, further exacerbating the occurrence of overnitration side reactions. Therefore, it is urgent to develop methods to inhibit overnitration side reactions, so as to improve the selectivity of aromatic mononitration reactions, improve safety and reduce separation energy consumption and waste acid treatment costs.

[0009] Solutions for solving problems

[0010] The present invention provides a method for inhibiting the side reaction of aromatic hydrocarbon pernitration, which comprises the following steps:

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

[0012] 2) The mixed acid solution A and the aromatic hydrocarbon B are simultaneously transported to a continuous flow reactor for nitration reaction to obtain mononitroaromatic hydrocarbons;

[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 to 5:1.

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

[0016] According to the above method, the mass ratio of the nitric acid to the sulfuric acid is greater than 1:1 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 to 1:1.2.

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

[0019] According to the method described above, 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, in step 2), the continuous flow reactor is a tubular reactor or a microreactor.

[0021] According to the method described above, 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, it also includes the following steps:

[0023] 3) Oil-water separation is performed at the outlet of the continuous flow reactor, and the obtained organic phase is mononitroaromatic hydrocarbons.

[0024] Effects of the Invention

[0025] The present invention uses nitric acid and sulfuric acid of a specific concentration in combination, suppresses the occurrence of overnitration side reactions, and thus improves the selectivity of aromatic mononitration. The solubility of nitroaromatics is reduced by using low sulfuric acid concentration, and the low sulfuric acid dosage further reduces the amount of nitroaromatics dissolved, and strengthens the dilution effect of water generated in the nitration main reaction on the sulfuric acid concentration, significantly reducing the total amount of nitroaromatics dissolved in the acid phase, thereby suppressing the overnitration side reaction in the acid phase, and significantly improving the selectivity of aromatic mononitration, thereby saving the huge energy consumption of product separation after the reaction is completed, and at the same time significantly reducing the amount and cost of waste acid treatment after the reaction is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the process flow diagram of the continuous parallel flow system.

[0027] Figure 2 This is the process flow chart of a continuous multi-stage countercurrent system.

[0028] Figure 3 This is the process flow diagram of the continuous countercurrent system. DETAILED DESCRIPTION

[0029] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0030] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0031] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0032] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0033] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0034] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0035] The "aromatic hydrocarbons" in this specification include but are not limited to benzene, toluene, chlorobenzene, biphenyl and the like.

[0036] The "normal temperature" in this manual is 15-25°C.

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

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

[0039] 2) The mixed acid solution A and the aromatic hydrocarbon B are simultaneously transported to a continuous flow reactor for nitration reaction to obtain mononitroaromatic hydrocarbons;

[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 to 5:1.

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

[0043] 3) Oil-water separation is performed at the outlet of the continuous flow reactor, and the obtained organic phase is mononitroaromatic hydrocarbons.

[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, take the mass of nitric acid determined above, and then take the mass of sulfuric acid determined by the above calculation, add sulfuric acid to the nitric acid, and obtain a mixed acid solution A.

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

[0049] In some specific embodiments of the present invention, the mass fraction of nitric acid may be 60-98%, for example, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. In the present invention, the molar ratio of aromatic hydrocarbon B to nitric acid in the mixed acid solution A may be 1:0.9 to 1:1.2, for example, 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 invention, the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B can be 1:10 to 5:1, for example, 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 invention, the mass ratio of nitric acid to sulfuric acid in the mixed acid solution A is greater than 1:6 and less than 50:1. For example, it 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 invention, the use of fuming nitric acid can improve the nitration efficiency, and by using a specific amount of sulfuric acid, the over-nitration side reaction can be effectively suppressed, thereby significantly improving the selectivity of aromatic mononitration.

[0053] Step 2)

[0054] The mixed acid solution A and the aromatic hydrocarbon B are simultaneously conveyed to a continuous flow reactor at the predetermined volume flow ratio to carry out nitration reaction, thereby obtaining mononitroaromatic hydrocarbons.

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

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

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

[0058] A certain amount of mixed acid solution A and aromatic hydrocarbon B are transported to a continuous flow reactor and then stay for a period of time (also referred to as residence time) to allow nitric acid and aromatic hydrocarbon to undergo nitration reaction. In the present invention, the residence time is not particularly limited until the reaction is completed. In some specific embodiments, it can be 4 to 20 minutes, for example, 5 minutes, 7 minutes, 9 minutes, 10 minutes, 12 minutes, 15 minutes, 18 minutes, etc.

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

[0060] In the present invention, the flow mode of the continuous flow reactor includes continuous cocurrent, continuous countercurrent, multi-stage countercurrent, etc. For example, the following can be used: Figure 1 , Figure 2 , Figure 3 The continuous flow system shown implements, but is not limited to Figure 1 , Figure 2 , Figure 3 The system shown.

[0061] Step 3)

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

[0063] The following combination Figure 1 , Figure 2 and Figure 3The synthesis process of the present invention will be described.

[0064] Figure 1 The process flow diagram of the continuous parallel flow system of the present invention is shown. Figure 1 As shown, the mixed acid solution A and the aromatic hydrocarbon raw material B are simultaneously transported from the same side to a continuous flow reactor at a certain volume flow rate for nitration reaction, and a phase separator (not shown in the figure) is set at the outlet of the reactor to effectively separate the organic phase from the acid solution, and the organic phase is the product mononitroaromatic hydrocarbon.

[0065] Figure 2 The process flow diagram of the continuous multi-stage countercurrent system of the present invention is shown. Figure 2 As shown, phase separators are connected to the outlets of the first-stage reactor and the second-stage reactor, respectively. The aromatic raw material B and the aqueous phase solution D (mixed acid solution) passing through the phase separator of the second-stage reactor are introduced into the first-stage reactor together for nitration reaction. The organic phase E (containing aromatics) passing through the phase separator of the first-stage reactor is introduced 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 mononitroaromatic hydrocarbon. .

[0066] Figure 3 The process flow diagram of the continuous countercurrent system of the present invention is shown. Figure 3 As shown, the mixed acid solution A and the aromatic hydrocarbon raw material B are simultaneously transported to the continuous flow reactor from opposite sides at a certain volume flow rate for nitration reaction, and a phase separator (not shown in the figure) is set at the outlet of the reactor to effectively separate the organic phase from the acid solution, and the organic phase is the product mononitroaromatic hydrocarbon.

[0067] Example

[0068] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0069] Example 1

[0070] The molar ratio of nitric acid to toluene is 1.01. Take 436g of toluene and 301g of fuming nitric acid, add 75% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 2mL / min, a volume flow rate of toluene of 4mL / min, and a volume flow ratio of the two phases of 1:2. The mixed acid solution is transported to a tubular reactor as follows. Figure 1The reaction was carried out in the continuous parallel flow mode shown, the reaction system was placed at 70°C for constant temperature reaction, the residence time was 5 minutes, oil-water separation was carried out at the reactor outlet, and the organic phase was the product mononitrotoluene.

[0071] The liquid chromatography test results of the mononitrotoluene prepared in Example 1 were: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0072] Example 2

[0073] The molar ratio of nitric acid to toluene is 1.01. Take 436g of toluene and 301g of fuming nitric acid, add 70% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 0.2mL / min, a volume flow rate of toluene of 0.4mL / min, and a volume flow rate ratio of the two phases of 1:2. The mixed acid solution is transported to the microreactor as follows. Figure 1 The reaction takes place in the continuous parallel flow mode shown, the reaction system is placed at a constant temperature of 80°C for reaction, the residence time is 5 minutes, oil-water separation is performed at the reactor outlet, and the organic phase is the product mononitrotoluene.

[0074] The liquid chromatography detection results of the mononitrotoluene prepared in Example 2 were: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0075] Example 3

[0076] The molar ratio of nitric acid to toluene is 1.01. Take 436g of toluene and 301g of fuming nitric acid, add 70% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 2mL / min, a volume flow rate of toluene of 4mL / min, and a volume flow rate ratio of the two phases of 1:2. The mixed acid solution is transported to the microreactor as follows. Figure 3 The reaction is carried out in a continuous countercurrent mode as shown, the reaction system is placed at a constant temperature of 90°C for reaction, the residence time is 5 minutes, oil-water separation is carried out at the reactor outlet, and the organic phase is the product mononitrotoluene.

[0077] The liquid chromatography detection results of the mononitrotoluene prepared in Example 3 were: toluene conversion rate 99.9%, mononitrotoluene selectivity 99.8%.

[0078] Example 4

[0079] The molar ratio of nitric acid to benzene is 1.01. Take 440g of benzene and 358g of fuming nitric acid, add 75% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 4mL / min, a volume flow rate of 4mL / min of benzene, and a volume flow ratio of 1:1. The mixed acid solution is transported to a tubular reactor as follows. Figure 1The reaction takes place in the continuous parallel flow mode shown, the reaction system is placed at a constant temperature of 90°C for reaction, the residence time is 5 minutes, oil-water separation is performed at the reactor outlet, and the organic phase is the product nitrobenzene.

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

[0081] Example 5

[0082] The molar ratio of nitric acid to chlorobenzene is 1.01. Take 554g of chlorobenzene and 313g of fuming nitric acid, add 80% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 8mL / min, a volume flow rate of chlorobenzene of 8mL / min, and a volume flow ratio of the two phases of 1:1. The mixed acid solution is transported to a tubular reactor as follows. Figure 1 The reaction takes place in the continuous parallel flow mode shown, the reaction system is placed at a constant temperature of 100°C for reaction, the residence time is 5 minutes, oil-water separation is performed at the reactor outlet, and the organic phase is the product mononitrochlorobenzene.

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

[0084] Example 6

[0085] The molar ratio of nitric acid to toluene is 1.01. Take 436g of toluene and 301g of fuming nitric acid, add 70% concentrated sulfuric acid to the fuming nitric acid to obtain a mixed acid solution. The mixed acid solution has a volume flow rate of 0.25mL / min, a volume flow rate of toluene of 0.5mL / min, and a volume flow rate ratio of the two phases of 1:2. The mixed acid solution is transported to the microreactor as follows. Figure 1 The reaction takes place in the continuous parallel flow mode shown, the reaction system is placed at a constant temperature of 90°C for reaction, the residence time is 8 minutes, oil-water separation is performed at the reactor outlet, and the organic phase is the product mononitrotoluene.

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

[0087] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for inhibiting the side reaction of aromatic hydrocarbon pernitration, characterized in that: The following steps are involved: 1) adding sulfuric acid to nitric acid to obtain a mixed acid solution A; 2) The mixed acid solution A and the aromatic hydrocarbon B are simultaneously transported to a continuous flow reactor for 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, In step 2), the volume flow ratio of the mixed acid solution A to the aromatic hydrocarbon B is 1:10 to 5:

1.

2. The method according to claim 1, wherein in step 1), The mass fraction of the sulfuric acid is 40-90%.

3. The method according to claim 1 or 2, wherein: The mass ratio of the nitric acid to the sulfuric acid is greater than 1:1 and less than 50:

1.

4. The method according to any one of claims 1 to 3, wherein 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 to 1:1.

2.

5. The method according to any one of claims 1 to 4, wherein in step 2), the solubility of the aromatic hydrocarbon B and the mononitroaromatic hydrocarbon in the sulfuric acid solution is 10 -2 mol / L or less.

6. The method according to any one of claims 1 to 5, wherein in step 2), the temperature of the nitration reaction is less than or equal to the boiling point of the aromatic hydrocarbon B.

7. The method according to any one of claims 1 to 6, wherein in step 2), the continuous flow reactor is a tubular reactor or a microreactor.

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

9. The method according to any one of claims 1 to 8, further comprising the following steps: 3) Oil-water separation is performed at the outlet of the continuous flow reactor, and the obtained organic phase is mononitroaromatic hydrocarbons.

Images