A device and process for the continuous synthesis of nitrobenzene

Abstract

This invention discloses a continuous synthesis apparatus and process for nitrobenzene. The synthesis apparatus includes a mixed acid preparation system, a continuous benzene nitration system, an organic phase continuous stratification system, and a continuous water washing-alkali washing-water washing system. The process includes: concentrated sulfuric acid and concentrated nitric acid are pumped into the mixing module of the mixed acid preparation system to obtain a mixed acid solution; benzene and the mixed acid solution are pumped into the microchannel reactor of the continuous benzene nitration system; the nitrated material is cooled and then pumped into the continuous organic phase stratification system; the resulting intermediate organic phase nitrate enters the next processing unit; the organic phase nitrate and water enter the continuous water washing-alkali washing-water washing system for washing to obtain the final product, nitrobenzene. The synthesis apparatus and process of this invention achieve continuous production of nitrobenzene throughout the entire process, realizing continuous and automated operation from raw material benzene to the final product, nitrobenzene.

Description

Technical Field

[0001] This invention belongs to the field of nitrobenzene synthesis technology, specifically relating to a continuous synthesis apparatus and process for nitrobenzene. Background Technology

[0002] Nitrobenzene is an important intermediate in organic chemical raw materials and is widely used in pharmaceuticals, dyes, and other fields. Existing synthesis methods focus on the continuous nitration reaction of benzene and mixed acids, mainly including microchannel continuous synthesis, tubular continuous synthesis, and batch reactor synthesis. Compared with the traditional batch reactor process, the continuous nitration reaction process greatly improves production efficiency, reduces liquid holdup in the reaction zone, and enhances reaction safety.

[0003] Patent CN202210741547.1 discloses a method for producing nitrobenzene, which mainly involves mixing benzene with a mixed acid and then feeding it into a microreactor for nitration, followed by continuous washing and separation in a centrifuge. This production method cannot achieve continuous reaction. Currently, there are few reports on the overall continuity of the nitrobenzene reaction, including the continuity of mixed acid preparation and post-treatment operations. Summary of the Invention

[0004] In view of the problems existing in the background technology, the present invention provides a continuous synthesis apparatus and process for nitrobenzene, which can realize the continuous synthesis of nitrobenzene throughout the entire process.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A continuous synthesis apparatus for nitrobenzene includes a mixed acid preparation system, a continuous benzene nitration system, a continuous organic phase layering system, and a continuous water washing-alkali washing-water washing system.

[0007] The mixed acid preparation system includes a concentrated sulfuric acid feed pipe, a concentrated nitric acid feed pipe, and a mixing module. The concentrated sulfuric acid feed pipe and the concentrated nitric acid feed pipe are respectively connected to the mixing module via a delivery pump and a metering pump.

[0008] The benzene continuous nitration reaction system includes a microchannel reactor, a heat exchanger, and a cooling module, with the cooling module located at the outlet of the microchannel reactor and the heat exchanger located outside the microchannel reactor.

[0009] The organic phase continuous stratification system includes a nitrated material feed pipe, a separation tank and an organic phase nitrate discharge pipe. The top of the separation tank is provided with a waste gas outlet connected to a waste gas treatment system, and the bottom of the tank is provided with an acid layer outlet connected to a waste acid treatment system. The middle two sides of the separation tank are provided with inlet and outlet ports, which are respectively connected to the nitrate solution feed pipe and the organic phase nitrate discharge pipe.

[0010] The continuous water washing-alkali washing-water washing system consists of three centrifugal extractors;

[0011] The mixing module is equipped with an outlet connected to the mixed acid feed pipe, which is connected to the benzene feed pipe and the microchannel reactor feed port in the benzene continuous nitration reaction system via a transfer pump. The microchannel reactor outlet is connected to the nitrated material feed pipe via a transfer pump, and the organic phase nitrate outlet pipe is connected to the first centrifugal extractor in the continuous water washing-alkali washing-water washing process.

[0012] Furthermore, the mixing module of the present invention is a strong mass transfer mixing structure, which realizes rapid mixing of concentrated sulfuric acid and concentrated nitric acid. The mixing module is composed of modules with special microchannel structures, which are either direct-flow channels or flat pipe microchannel structures with rectangular cross-sections.

[0013] Furthermore, the microchannel reactor of the present invention is composed of reaction modules with special microstructures arranged together. The special microstructures are selected from any one of pulse-variable diameter rectangular flat pipes, chain-type structures, and fish-shaped structures. The pulse-variable diameter rectangular flat pipes include disc-type pulse-variable diameter rectangular flat pipes, rhomboid disc-type pulse-variable diameter rectangular flat pipes, enhanced mixing disc-type rectangular flat pipes, and enhanced mixing rhomboid disc-type rectangular flat pipes.

[0014] Furthermore, in the continuous water washing-alkali washing-water washing of the present invention, the first centrifugal extractor consists of a water inlet pipe, a nitrated washing liquid, and an outlet pipe; the second centrifugal extractor consists of a liquid alkali inlet pipe, a nitrated washing liquid, and an outlet pipe; and the third centrifugal extractor consists of a water inlet pipe, a nitrated washing liquid, and an outlet pipe.

[0015] Furthermore, the organic phase continuous stratification system of the present invention also includes a nitrate-sulfur mixed acid solution feed pipe I, which is connected to the mixed acid preparation system and the separation tank respectively.

[0016] The present invention also provides a continuous process for the synthesis of nitrobenzene based on the above-mentioned apparatus, comprising the following steps:

[0017] (1) Continuous preparation of mixed acid: Concentrated sulfuric acid and concentrated nitric acid are respectively transported to the mixing module of the mixed acid preparation system by a transfer pump. The concentrated sulfuric acid and concentrated nitric acid are mixed in the mixing module to obtain a nitric acid-sulfuric acid mixed acid solution.

[0018] The concentrated nitric acid has a mass concentration of 60%, the concentrated sulfuric acid has a mass concentration of 98%, and the mass ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is (2-3):1;

[0019] (2) Continuous nitration: Benzene and the nitric acid-sulfuric acid mixed acid solution obtained in step (1) are respectively pumped into the microchannel reactor of the benzene continuous nitration system. Relying on the strong mass transfer and strong heat transfer of the microchannel reactor, the benzene is completely nitrated. The temperature is controlled by an external heat exchanger. The reaction residence time is controlled by adjusting the pump flow rate and the channel length of the microchannel. The nitrated material is cooled by the cooling module and then flows out from the outlet of the microchannel reactor.

[0020] The molar ratio of benzene to nitric acid is (1–1.07):1;

[0021] The reaction temperature of benzene and mixed acid solution in the microchannel reactor is 25-40℃, and the residence time in the microchannel reactor is 2.6-4.3 min.

[0022] The cooled material is at room temperature, preferably 20°C;

[0023] (3) Organic phase continuous stratification: The nitrated material cooled in step (2) enters the organic phase continuous stratification system through the conveying pump and the nitrated material feed pipe. In the separation tank of the organic phase continuous stratification system, the waste gas generated by nitration is connected to the waste gas treatment system through the top of the tank, the acid layer at the bottom of the tank enters the waste acid treatment system, and the organic phase nitrate I in the middle layer enters the next treatment unit.

[0024] (4) Continuous water washing-alkali washing-water washing: The organic phase nitrate I and water obtained in step (3) are washed in the first centrifugal extractor to obtain wastewater and nitrate II. The wastewater enters the wastewater treatment system. Nitrate II and alkali solution are washed in the second centrifugal extractor to obtain wastewater and nitrate III. The wastewater enters the wastewater treatment system. Nitrate III and water are washed in the third centrifugal extractor to obtain wastewater and nitrate IV. The wastewater enters the wastewater treatment system. Nitrate IV is the nitrobenzene required by this invention and enters the nitrobenzene collection system.

[0025] Further, in step (4) of the present invention, the mass ratio of nitrate I to water is 1:(1-3), and it is washed in the first centrifugal extractor; the mass ratio of nitrate II to alkali solution is 1:(2-3), and it is washed in the second centrifugal extractor; the mass ratio of nitrate III to water is 1:(1-3), and it is washed in the third centrifugal extractor. The washing time in the first, second, and third centrifugal extractors, which are continuously water-wash-alkali-wash, is controlled at 3-10 min, the rotation speed is 800-1000 r / min, and the alkali solution is selected from any one or more of sodium hydroxide, calcium hydroxide, sodium carbonate, and sodium bicarbonate, with a mass concentration of 30-50%.

[0026] Furthermore, in step (3) of this invention, the separation tank is connected to the mixed acid preparation system, so that the concentration of waste acid after nitration reaction is controlled at 3-10%. The organic phase continuous stratification system realizes the stratification of benzene and mixed acid. The upper layer is the organic phase, which overflows into the subsequent water washing system after reaching a certain liquid level. The lower acid phase enters the waste acid treatment system, and is purified and recycled to the mixed acid preparation system.

[0027] The benzene continuous nitration reaction system of the present invention comprises two parts. The first part is the continuous nitration of benzene to synthesize nitrobenzene in a microchannel reactor, and the second part is the cooling of the reaction materials to reduce the temperature of the materials from the reaction temperature to room temperature.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Compared with existing nitrobenzene synthesis technology, the synthesis device and process described in this invention complete the continuous production of nitrobenzene throughout the entire process, realizing continuous and automated operation from raw material benzene to final product nitrobenzene;

[0030] (2) The continuous mixed acid preparation system replaces the traditional batch mixing method, realizing on-demand preparation, reducing the storage of mixed acid, and improving safety;

[0031] (3) The benzene continuous nitration reaction system adopts a microchannel reactor, which reduces the reaction time from several hours to several minutes, improves the reaction efficiency, and at the same time reduces the liquid holdup in the reaction zone;

[0032] (4) The organic phase continuous stratification system has changed the original batch production method that required several hours of settling, and has realized the instant separation of organic matter and acid layer, thus improving efficiency;

[0033] (5) The continuous water washing, alkaline washing and water washing system has changed the traditional kettle-type stirring washing method, greatly shortened the washing time, reduced the amount of detergent used, and reduced the generation of waste. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the nitrobenzene full-process synthesis apparatus described in this invention.

[0035] Figure 2 This is a flowchart illustrating the complete synthesis process of nitrobenzene according to the present invention.

[0036] Figure 3 This is a schematic diagram of the organic phase continuous layered system structure described in this invention.

[0037] Figure 4 This is a schematic diagram of the structure and flow of the continuous water washing, alkaline washing, and water washing system described in this invention.

[0038] Figure 5This is a diagram of the channel structure of the microchannel used in this invention, where a-DC type channel, b-rectangular flat tube microchannel, c-disc-type pulse variable diameter rectangular flat tube, d-rhomboid-disc-type pulse variable diameter rectangular flat tube, e-enhanced hybrid disc-type rectangular flat tube, f-enhanced hybrid rhomboid-disc-type rectangular flat tube, g-chain type, h-fish-shaped.

[0039] Figure 1 The components are labeled as follows: 1, 2, 3, 4, 5 transfer pumps; 6, 7 metering pumps; 8 concentrated nitric acid feed pipe; 9 concentrated sulfuric acid feed pipe; 10 mixing module; 11 microchannel reactor; 12 heat exchanger; 13 cooling module; 14 mixed acid feed pipe; 15 benzene feed pipe; 16 nitrated material feed pipe; 17 organic phase continuous stratification system; 18 waste gas outlet; 19 acid layer outlet; 20 organic phase nitrate discharge pipe; 21 continuous water washing, alkali washing, and water washing system. Detailed Implementation

[0040] The following is a further explanation with reference to the accompanying drawings.

[0041] A continuous synthesis apparatus for nitrobenzene includes a mixed acid preparation system, a continuous benzene nitration system, an organic phase continuous layering system 17, and a continuous water washing-alkali washing-water washing system 21.

[0042] The mixed acid preparation system includes a concentrated sulfuric acid feed pipe 9, a concentrated nitric acid feed pipe 8, and a mixing module 10. The concentrated sulfuric acid feed pipe and the concentrated nitric acid feed pipe are connected to the mixing module 10 through a delivery pump 1, 2 and a metering pump 7, 6, respectively.

[0043] The benzene continuous nitration reaction system includes a microchannel reactor 11, a heat exchanger 12 and a cooling module 13, with the cooling module located at the outlet of the microchannel reactor and the heat exchanger located outside the microchannel reactor.

[0044] The organic phase continuous stratification system includes a nitrated material feed pipe 16, a separation tank and an organic phase nitrate discharge pipe. The top of the separation tank is provided with a waste gas outlet 18 connected to a waste gas treatment system, and the bottom of the tank is provided with an acid layer outlet 19 connected to a waste acid treatment system. The upper part of the separation tank is provided with inlet and outlet ports on both sides, which are respectively connected to the nitrate solution feed pipe and the organic phase nitrate discharge pipe 20.

[0045] The continuous water washing-alkali washing-water washing system 21 consists of three centrifugal extractors;

[0046] The mixing module is provided with an outlet connected to the mixed acid feed pipe 14, which is connected to the benzene feed pipe 15 and the microchannel reactor 11 in the benzene continuous nitration reaction system via a feed pump. The outlet of the microchannel reactor is connected to the nitrated material feed pipe via a delivery pump, and the organic phase nitrate outlet pipe is connected to the first centrifugal extractor in the continuous water washing-alkali washing-water washing process.

[0047] Furthermore, the mixing module of the present invention is a strong mass transfer mixing structure, which realizes rapid mixing of concentrated sulfuric acid and concentrated nitric acid. The mixing module is composed of modules with special microchannel structures, which are either direct-flow channels or flat pipe microchannel structures with rectangular cross-sections.

[0048] Furthermore, the microchannel reactor of the present invention is composed of reaction modules with special microstructures arranged together. The special microstructures are selected from any one of pulse-variable diameter rectangular flat pipes, chain-type structures, and fish-shaped structures. The pulse-variable diameter rectangular flat pipes include disc-type pulse-variable diameter rectangular flat pipes, rhomboid disc-type pulse-variable diameter rectangular flat pipes, enhanced mixing disc-type rectangular flat pipes, and enhanced mixing rhomboid disc-type rectangular flat pipes.

[0049] Furthermore, in the continuous water washing-alkali washing-water washing of the present invention, the first centrifugal extractor consists of a water inlet pipe, a nitrated washing liquid, and an outlet pipe; the second centrifugal extractor consists of a liquid alkali inlet pipe, a nitrated washing liquid, and an outlet pipe; and the third centrifugal extractor consists of a water inlet pipe, a nitrated washing liquid, and an outlet pipe.

[0050] Furthermore, the organic phase continuous stratification system of the present invention also includes a nitrate-sulfur mixed acid solution feed pipe I, which is connected to the mixed acid preparation system and the separation tank respectively.

[0051] A continuous process for the synthesis of nitrobenzene includes the following steps:

[0052] (1) Continuous preparation of mixed acid: Concentrated sulfuric acid and concentrated nitric acid are respectively transported to the mixing module of the mixed acid preparation system by a transfer pump. The concentrated sulfuric acid and concentrated nitric acid are mixed in the mixing module to obtain a nitric acid-sulfuric acid mixed acid solution.

[0053] The concentrated nitric acid has a mass concentration of 60%, the concentrated sulfuric acid has a mass concentration of 98%, and the mass ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is (2-3):1;

[0054] (2) Continuous nitration: Benzene and the nitric acid-sulfuric acid mixed acid solution obtained in step (1) are respectively pumped into the microchannel reactor of the benzene continuous nitration system. Relying on the strong mass transfer and strong heat transfer of the microchannel reactor, the benzene is completely nitrated. The temperature is controlled by an external heat exchanger. The reaction residence time is controlled by adjusting the pump flow rate and the channel length of the microchannel. The nitrated material is cooled by the cooling module and then flows out from the outlet of the microchannel reactor.

[0055] The molar ratio of benzene to nitric acid is (1–1.07):1;

[0056] The reaction temperature of benzene and mixed acid solution in the microchannel reactor is 25-40℃, and the residence time in the microchannel reactor is 2.6-4.3 min.

[0057] The cooled material is at room temperature, preferably 20°C;

[0058] (3) Continuous stratification of organic phase: The nitrated material cooled in step (2) enters the continuous separation system of organic phase through the conveying pump and the nitrated material feed pipe. In the separation tank of the continuous stratification system of organic phase, the waste gas generated by nitration is connected to the waste gas treatment system through the top of the tank, the acid layer at the bottom of the tank enters the waste acid treatment system, and the organic phase nitrate I in the middle layer enters the next treatment unit.

[0059] (4) Continuous water washing-alkali washing-water washing: The organic phase nitrate I and water obtained in step (3) are washed in the first centrifugal extractor to obtain wastewater and nitrate II. The wastewater enters the wastewater treatment system. Nitrate II and alkali solution are washed in the second centrifugal extractor to obtain wastewater and nitrate III. The wastewater enters the wastewater treatment system. Nitrate III and water are washed in the third centrifugal extractor to obtain wastewater and nitrate IV. The wastewater enters the wastewater treatment system. Nitrate IV is the nitrobenzene required by this invention and enters the nitrobenzene collection system.

[0060] Further, in step (4) of the present invention, the mass ratio of nitrate I to water is 1:(1-3), and it is washed in the first centrifugal extractor; the mass ratio of nitrate II to alkali solution is 1:(2-3), and it is washed in the second centrifugal extractor; the mass ratio of nitrate III to water is 1:(1-3), and it is washed in the third centrifugal extractor. The washing time in the first, second, and third centrifugal extractors, which are continuously water-wash-alkali-wash, is controlled at 3-10 min, the rotation speed is 800-1000 r / min, and the alkali solution is selected from any one or more of sodium hydroxide, calcium hydroxide, sodium carbonate, and sodium bicarbonate, with a mass concentration of 30-50%.

[0061] Furthermore, the organic phase continuous stratification system described in step (3) of the present invention realizes the stratification of benzene and mixed acid. The upper layer is the organic phase, which overflows into the subsequent water washing system after reaching a certain liquid level. The lower acid phase enters the waste acid treatment system, and is purified and recycled for use in the mixed acid preparation system.

[0062] The benzene continuous nitration reaction system of the present invention comprises two parts. The first part is the continuous nitration of benzene to synthesize nitrobenzene in a microchannel reactor, and the second part is the cooling of the reaction materials to reduce the temperature of the materials from the reaction temperature to room temperature.

[0063] Example

[0064] In this embodiment, the mixed acid preparation system consists of a concentrated sulfuric acid feed pipe for introducing concentrated sulfuric acid solution and a concentrated nitric acid feed pipe for introducing concentrated nitric acid solution, connected by a metering pump and components. In the mixed acid-nitrogenate mixture, m(60% nitric acid) / m(98% sulfuric acid) = 2.3:1. The continuous benzene nitration system consists of a benzene feed pipe for introducing benzene solution and a mixed acid feed pipe connected by a raw material benzene feed pump and a mixed acid feed pump, respectively. The molar ratio of benzene to nitric acid is n(benzene) / n(nitric acid) = 1.07:1, the temperature is 35°C, and the residence time is 3.5 min. The continuous organic phase stratification system consists of a nitrate feed pipe synthesized from the continuous benzene nitration reaction and a mixed acid-nitrogenate solution feed pipe entering the organic phase stratification device. The concentration of the waste acid after the nitration reaction is controlled at 3-10%, achieving stratification of benzene and mixed acid. The continuous organic phase stratification system is connected to an organic... The phase and mixed acid separation tank is connected to a tail gas absorption system at the top, a continuous water washing, alkali washing, and water washing system at the upper part of the tank, and a waste acid treatment system at the bottom. The continuous water washing, alkali washing, and water washing system consists of three centrifugal extraction machines. Nitrobenzene and water enter the first centrifugal extraction machine from the inlet, with the mass ratio of nitrate I to water being 1:1. After washing, nitrobenzene enters the second centrifugal extraction machine for washing with liquid alkali, with the mass ratio of nitrate II to alkali being 1:2 and the sodium hydroxide mass concentration being 30%. Then it enters the third centrifugal extraction machine for washing with water, with the mass ratio of nitrate III to water being 1:1. The continuous water washing-alkali washing-water washing process takes 3 minutes in the centrifugal extraction machine at a speed of 800 r / min. Nitrobenzene compound is obtained at the outlet. The conversion rate of the raw material benzene is 99.9%, and the selectivity of nitrobenzene is 99.5%.

[0065] In this embodiment, the benzene continuous nitration system relies on the strong mass and heat transfer of the microchannel reactor to achieve complete benzene nitration. The organic phase continuous stratification system is formed by the nitrate solution from the benzene continuous nitration system entering the stratification system. The upper layer is the organic phase, which overflows into the subsequent water washing system after reaching a certain liquid level. The lower acid phase enters the waste acid treatment system through the discharge pipe, and is purified and recycled into the mixed acid preparation system. The continuous water washing, alkali washing, and water washing system consists of three centrifugal extraction machines. The first centrifugal extraction machine consists of a water inlet pipe, nitrate washing liquid, and water outlet pipe. The second centrifugal extraction machine consists of a liquid alkali inlet pipe, nitrate washing liquid, and water outlet pipe. The third centrifugal extraction machine consists of a water inlet pipe, nitrate washing liquid, and water outlet pipe.

[0066] In this embodiment, a nitrobenzene production system based on a microchannel reactor is used. Benzene, as the main raw material, undergoes a nitration reaction with a mixed acid of nitrate and sulfur to obtain nitrobenzene. This method employs a continuous flow microchannel reactor with different microstructures to enhance mass and heat transfer performance, maintain a constant reaction temperature, avoid runaway reactions, reduce the generation of dinitro byproducts, and significantly reduce the amount of concentrated sulfuric acid and nitric acid used, thus reducing waste acid generation. The reaction time is shortened from several hours in traditional batch reactor processes to tens of seconds to several minutes, significantly improving reaction efficiency and product selectivity. Furthermore, the reaction temperature is above 25°C, reducing the viscosity of the reactants and the pressure drop of the reaction system, greatly reducing reaction energy consumption and improving the economics of the reaction. The process of this invention is a continuous flow reaction throughout the entire process from feeding, preheating, mixing, and reaction separation, avoiding the need for additional equipment and leakage during transfer that occurs in conventional batch reactions. During industrial implementation, it effectively reduces the liquid holdup in the reactor, lowers reaction safety risks, and improves the inherent safety of benzene nitration to nitrobenzene.

[0067] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for the continuous synthesis of nitrobenzene in a full flow process, characterized by, It includes a mixed acid preparation system, a benzene continuous nitration system, an organic phase continuous stratification system (17) and a continuous water washing-alkali washing-water washing system (21); The mixed acid preparation system includes a concentrated sulfuric acid feed pipe (9), a concentrated nitric acid feed pipe (8), and a mixing module (10). The concentrated sulfuric acid feed pipe (9) and the concentrated nitric acid feed pipe (8) are respectively connected to the mixing module (10). The benzene continuous nitration reaction system includes a microchannel reactor (11), a heat exchanger (12) and a cooling module (13), with the cooling module (13) located at the outlet of the microchannel reactor (11) and the heat exchanger (12) located outside the microchannel reactor (11). The organic phase continuous stratification system includes a nitrated material feed pipe, a separation tank and an organic phase nitrate discharge pipe. The top of the separation tank is provided with a waste gas outlet (18) connected to the waste gas treatment system, and the bottom of the tank is provided with an acid layer outlet (19) connected to the waste acid treatment system. The middle two sides of the separation tank are provided with inlet and outlet ports connected to the nitrate solution feed pipe (16) and the organic phase nitrate discharge pipe (20) respectively. The continuous water washing-alkali washing-water washing system (21) consists of three centrifugal extractors; the first and third centrifugal extractors each consist of a water inlet pipe, a nitrate washing liquid and an outlet pipe, and the second centrifugal extractor consists of a liquid alkali inlet pipe, a nitrate washing liquid and an outlet pipe. The mixing module is provided with an outlet connected to the mixed acid feed pipe (14), and the benzene feed pipe (15) is connected to the microchannel reactor feed port in the benzene continuous nitration reaction system via transfer pumps (3, 4); the outlet of the microchannel reactor (11) is connected to the nitrated material feed pipe (16) via a transfer pump, and the organic phase nitrate discharge pipe (20) is connected to the first centrifugal extractor in the continuous water washing-alkali washing-water washing process.

2. The synthesis device of claim 1, wherein, The concentrated sulfuric acid feed pipe and the concentrated nitric acid feed pipe are connected to the mixing module (10) via the transfer pump (1, 2) and the metering pump (7, 6), respectively.

3. The synthesis device of claim 1, wherein, The mixing module is a strong mass transfer mixing structure, which is composed of modules with special microchannel structures. These special microchannel structures are either direct current channels or flat pipe microchannel structures with rectangular cross-sections.

4. The synthesis device of claim 1, wherein, Furthermore, the microchannel reactor of the present invention is composed of reaction modules with special microstructures arranged together. The special microstructures used are selected from any one of pulse-diameter-variable rectangular flat pipes, chain-type structures, and fish-shaped structures. The pulse-diameter-changing rectangular flat pipe includes a disc-type pulse-diameter-changing rectangular flat pipe, a rhomboid disc-type pulse-diameter-changing rectangular flat pipe, a reinforced hybrid disc-type rectangular flat pipe, and a reinforced hybrid rhomboid disc-type rectangular flat pipe.

5. A continuous process for the synthesis of nitrobenzene based on the synthetic apparatus according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Continuous preparation of mixed acid: Concentrated sulfuric acid and concentrated nitric acid are respectively transported to the mixing module of the mixed acid preparation system by a transfer pump. The concentrated sulfuric acid and concentrated nitric acid are mixed in the mixing module to obtain a nitric acid-sulfuric acid mixed acid solution. (2) Continuous nitration: Benzene and the nitric acid-sulfuric acid mixed acid solution obtained in step (1) are respectively fed into the microchannel reactor of the benzene continuous nitration system through a delivery pump. The temperature is controlled by an external heat exchanger. The reaction residence time is controlled by adjusting the pump flow rate and the channel length of the microchannel. The nitrated material is cooled to room temperature by the cooling module and then flows out from the outlet of the microchannel reactor. (3) Organic phase continuous stratification: The nitrated material cooled in step (2) enters the organic phase continuous stratification system through the conveying pump and the nitrated material feed pipe. In the separation tank of the organic phase continuous stratification system, the waste gas generated by nitration is connected to the waste gas treatment system through the top of the tank, the acid layer at the bottom of the tank enters the waste acid treatment system, and the organic phase nitrate I in the middle layer enters the next treatment unit. (4) Continuous water washing-alkali washing-water washing: The organic phase nitrate I and water obtained in step (3) are washed in the first centrifugal extractor to obtain wastewater and nitrate II. The wastewater enters the wastewater treatment system. Nitrate II and alkali solution are washed in the second centrifugal extractor to obtain wastewater and nitrate III. The wastewater enters the wastewater treatment system. Nitrate III and water are washed in the third centrifugal extractor to obtain wastewater and nitrate IV. The wastewater enters the wastewater treatment system. Nitrate IV is the desired nitrobenzene and enters the nitrobenzene collection system.

6. The synthesis process of claim 5, wherein, In step (1), the concentrated nitric acid has a mass concentration of 60%, the concentrated sulfuric acid has a mass concentration of 98%, and the mass ratio of the concentrated nitric acid solution to the concentrated sulfuric acid solution is (2-3):

1. The molar ratio of benzene to nitric acid in step (2) is (1-1.07):

1.

7. The synthesis process of claim 5, wherein, The reaction temperature of benzene and mixed acid solution in step (2) in the microchannel reactor is 25-40℃, and the residence time in the microchannel reactor is 2.6-4.3 min.

8. The synthesis process of claim 5, wherein, In step (4), the mass ratio of nitrate I to water is 1:(1-3), the mass ratio of nitrate II to alkali solution is 1:(2-3), and the mass ratio of nitrate III to water is 1:(1-3). The washing time in each centrifugal extractor was controlled at 3 to 10 minutes, and the rotation speed was 800 to 1000 r / min.

9. The synthesis process of claim 5, wherein, The type of alkaline solution mentioned in step (4) is selected from any one or a mixture of sodium hydroxide, calcium hydroxide, sodium carbonate and sodium bicarbonate, and the mass concentration of the alkaline solution is 30-50%.

10. The synthetic process of claim 5, wherein, The separation tank in the organic phase continuous stratification system is also connected to the mixed acid preparation system, so that the waste acid concentration of the material in the separation tank after nitration reaction is controlled at 3-10%.

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