System and method for preparing m-trifluoromethylnitrobenzene using a microchannel reactor

Abstract

The present application relates to a kind of system and method for preparing m-trifluoromethyl nitrobenzene using microchannel reactor, including nitric acid feed tank, sulfuric acid feed tank, trifluoromethyl benzene feed tank, mixed acid mixer, nitration reactor and product receiving tank, wherein the mixing flow channel is arranged inside the nitration reactor, and the mixing flow channel includes input cavity, shunt section and vertical mixing flow channel section connected in sequence, the mixed acid feed port is communicated with the upper end of the input cavity by mixed acid feed flow channel, the trifluoromethyl benzene feed port is communicated with the lower end of the input cavity by trifluoromethyl benzene feed flow channel, the lower end of the vertical mixing flow channel section is communicated with the reaction discharge port by discharge flow channel, and the position corresponding to the mixing flow channel in the nitration reactor is provided with heat exchange module.The present application can make material mix quickly and sufficiently, improve product composition, reduce separation cost, and the present application controls reaction temperature in stages, improves the safety of reaction, reduces equipment cost and reaction time.

Description

Technical Field

[0001] This invention relates to the field of mixed acid nitration technology, specifically a system and method for preparing m-trifluoromethylnitrobenzene using a microchannel reactor. Background Technology

[0002] m-Trifluoromethylnitrobenzene is an important pharmaceutical and pesticide intermediate. For example, herbicides with a wide range of applications can be synthesized using m-trifluoromethylnitrobenzene as the main raw material and other raw materials. Alternatively, excellent and widely used anti-caking agents can be synthesized using m-trifluoromethylnitrobenzene as a raw material.

[0003] In the existing technology, the synthesis of m-trifluoromethylnitrobenzene is mainly carried out by batch method. Since the nitration reaction is characterized by a large amount of heat release, if the heat removal cannot be controlled, the nitration reaction is very likely to cause danger. Moreover, as the reaction temperature increases, the content of nitration byproducts will also increase significantly, which will lead to an increase in subsequent separation costs and thus reduce economic benefits. Furthermore, existing micro-mixers only consider liquid collision mixing along the flow direction, without considering collision mixing perpendicular to the flow direction. This can affect the mixing effect for fluids with relatively high viscosity. For example, the invention patent CN115041038A discloses a continuous flow-diverting and merging mixer. When this device is working, the mixture is mixed in the flow direction by arc-shaped, gear-shaped, and triangular turbulence modules set in the chamber. Multiple of these modules are repeatedly set to enhance mass transfer. However, this mixer does not have a heat exchange module, which poses a safety hazard for mixing fluids with high exothermic reactions such as nitration, thus limiting its application. In addition, this device does not have collision mixing in the vertical flow direction. In actual production, it has been found that for fluids with viscosity, the higher the viscosity of the mixture, the worse the mixing effect. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for preparing m-trifluoromethylnitrobenzene using a microchannel reactor, which enables rapid and thorough mixing of materials, improves product composition, reduces separation costs, and improves reaction safety by controlling the reaction temperature in stages, while reducing equipment costs and reaction time.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor includes a nitric acid feed tank, a sulfuric acid feed tank, a trifluoromethylbenzene feed tank, a mixed acid mixer, a nitration reactor, and a product receiving tank. The mixed acid mixer has a first inlet, a second inlet, and a mixing outlet. The nitration reactor has a mixed acid inlet, a trifluoromethylbenzene inlet, and a reaction outlet. The nitric acid feed tank is connected to the first inlet via a first pipeline equipped with a nitric acid delivery pump. The sulfuric acid feed tank is connected to the second inlet via a second pipeline equipped with a sulfuric acid delivery pump. The mixing outlet is connected to the mixed acid inlet via a third pipeline equipped with a mixed acid delay pipe. The trifluoromethylbenzene... The feed tank is connected to the trifluoromethylbenzene inlet via a fourth pipeline, and a trifluoromethylbenzene delivery pump is installed on the fourth pipeline. The reaction outlet is connected to the product receiving tank via a fifth pipeline, and a nitration delay pipe is installed on the fifth pipeline. The nitration reactor has a mixing channel inside, and the mixing channel includes an input chamber, a diversion mixing section, and a vertical mixing channel section connected in sequence. The mixed acid inlet is connected to the upper end of the input chamber via the mixed acid inlet channel, the trifluoromethylbenzene inlet is connected to the lower end of the input chamber via the trifluoromethylbenzene inlet channel, and the lower end of the vertical mixing channel section is connected to the reaction outlet via the discharge channel. A heat exchange module is installed inside the nitration reactor corresponding to the position of the mixing channel.

[0007] The lower end of the input cavity of the mixing channel is provided with a diversion protrusion, and a diversion channel is formed between the two sides of the diversion protrusion and the corresponding cavity wall at the lower end of the input cavity. The output end of the trifluoromethylbenzene inlet is provided with a liquid-distributing pad, and the liquid-distributing pad is provided with two through holes. After the trifluoromethylbenzene liquid passes through the two through holes of the liquid-distributing pad, it is sprayed to form two liquid columns, and each liquid column is injected into the diversion channel on the corresponding side.

[0008] The flow mixing section includes a first flow mixing section in the shape of a ring and a second flow mixing section in the shape of a rhombus. The inner diameter of the flow channel in the first flow mixing section first decreases, the inner diameter of the flow channel in the upper half of the second flow mixing section then increases, and the inner diameter of the flow channel in the lower half of the second flow mixing section then decreases.

[0009] The vertical mixing channel section of the mixing channel is provided with a plurality of mixing protrusions in sequence, and the mixing protrusions include an inclined surface on the input side and a vertical surface on the output side. The vertical mixing channel section is provided with a plurality of second diverter columns, and the mixing protrusions and the second diverter columns are arranged alternately.

[0010] The input end of the vertical mixing channel section is provided with a first diverter column.

[0011] The heat exchange module includes a heat exchange cavity, and the heat exchange cavity has a cooling medium inlet on one side and a cooling medium outlet on the other side. The interior of the heat exchange cavity has multiple strip-shaped protrusions parallel to the flow direction of the cooling medium.

[0012] The nitration reactor includes a first mounting block and a second mounting block connected by bolts. The trifluoromethylbenzene inlet and the trifluoromethylbenzene feed channel are located in the first mounting block, while the mixed acid inlet, the mixed acid feed channel, the heat exchange module, the reaction outlet and the discharge channel are located in the second mounting block.

[0013] The third pipe is equipped with a first temperature sensor, the fourth pipe is equipped with a second temperature sensor, and the fifth pipe is equipped with a third temperature sensor and a fourth temperature sensor, with the third temperature sensor and the fourth temperature sensor located at opposite ends of the nitration delay pipe.

[0014] The mixed acid delay tube is located in the first heat exchange shell, and the nitration delay tube is located in the second heat exchange shell.

[0015] A method for using the system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor, as described above, involves first weighing fuming nitric acid, concentrated sulfuric acid, and trifluoromethylbenzene, and placing them into nitric acid feed tank, sulfuric acid feed tank, and trifluoromethylbenzene feed tank, respectively. Then, the internal temperatures of the first heat exchange shell, heat exchange module, and second heat exchange shell are controlled to reach set temperatures. Simultaneously, the nitric acid delivery pump and sulfuric acid delivery pump are turned on. After the mixed acid passes through the mixed acid mixer and mixed acid delay tube, the temperature detected by the first temperature sensor is checked. Once the temperature detected by the first temperature sensor reaches the set value, the trifluoromethylbenzene delivery pump is turned on to allow the mixed acid and trifluoromethylbenzene to react in the nitration reactor. When the feed rate and the temperatures detected by each temperature sensor are stable, the product receiving tank is opened to receive the nitrated product.

[0016] The advantages and positive effects of this invention are as follows:

[0017] 1. This invention utilizes a mixing channel inside a nitration reactor to achieve material mixing. The mixing channel includes an input chamber, a diversion mixing section, and a vertical mixing channel section connected in sequence. The mixed acid is input from the upper end of the input chamber, and a diversion protrusion is provided at the lower end of the input chamber. Diversion channels are formed on both sides of the diversion protrusion. A liquid-separating pad is provided at the output end of the trifluoromethylbenzene inlet. The trifluoromethylbenzene liquid passes through two through-holes in the liquid-separating pad and is sprayed to form two liquid columns, which are respectively injected into the corresponding diversion channels to mix with the mixed acid solution. This structure can, on the one hand, increase the velocity of the dispersed phase trifluoromethylbenzene when injected into the continuous phase mixed acid; on the other hand, the trifluoromethylbenzene liquid column is injected and mixed with the mixed acid solution along a direction perpendicular to the flow direction of the mixed acid solution, which can increase radial mass transfer, reduce the mixing time, and reduce the formation of nitration reaction byproducts.

[0018] 2. The mixing section of the mixing channel of the nitration reactor of the present invention includes multiple mixing parts with different mixing shapes. The inner diameter of each part of the mixing section first decreases, then increases, and then decreases again. The present invention continuously changes the flow rate of the mixed liquid by changing the inner diameter of the channel, thereby achieving the effect of rapid mixing and mass transfer. In addition, the increase in the inner diameter of the channel can also reduce the reactor pressure.

[0019] 3. In the vertical mixing channel section of the nitration reactor of the present invention, multiple mixing protrusions are sequentially arranged. Each mixing protrusion includes an inclined surface on the input side and a vertical surface on the output side. The mixed liquid first tends to flow upward and collide with the inclined surface, and then suddenly tends to flow downward and collide with the vertical surface. In this way, the mixing channel of the present invention first continuously changes the axial (i.e., the direction of flow of the mixed liquid) and radial (i.e., the direction perpendicular to the flow of the mixed liquid) velocity in the channel through the design of the diversion mixing section and the vertical mixing channel section to achieve the purpose of rapidly mixing the continuous phase and the dispersed phase. The mixing protrusions and the second diversion column arranged in the vertical mixing channel section further realize the axial and radial mixing of the mixed liquid. The radial flow tendency of the mixed liquid passing through the inclined surface of the mixing protrusion is relatively large, but at the same time, a part of the mixed liquid will still flow along the axial trend. The mixed liquid with the axial trend flow is diverted and remixed through the second diversion column. Therefore, the present invention reduces the mixing time of the mixed liquid and the generation of by-products through the above two-stage axial and radial mixing structure.

[0020] 4. The heat exchange module of the present invention has a cooling medium inlet on one side and a cooling medium outlet on the other side. The heat exchange chamber is provided with multiple strip-shaped protrusions parallel to the flow direction of the cooling medium inside. The cooling medium is input into the heat exchange chamber through the cooling medium inlet and flows along the gap between two adjacent protrusions. This can increase the flow rate of the heat exchange medium. At the same time, the shape of the heat exchange chamber reduces the existence of dead corners in the chamber, which can better remove the large amount of heat released by the nitration reaction. This is especially important for reducing the formation of nitration side reactions in the early stage.

[0021] 5. Compared with batch processes, the present invention can increase the safety of the reaction, and the nitration reactor of the present invention can quickly and fully mix the oil and water two-phase flow to achieve better mass transfer effect, thereby improving the product composition and reducing separation cost.

[0022] 6. Compared with continuous processes, this invention reduces equipment costs and reaction time by adjusting the process and controlling the reaction temperature in stages. This invention connects the mixed acid preparation section and the nitration reaction section in series to prepare m-nitrotrifluorotoluene in situ, which is simple and safe to operate. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 for Figure 1 Schematic diagram of the intermediate nitration reactor.

[0025] Figure 3 for Figure 2 A schematic diagram of the decomposition process in a medium nitration reactor.

[0026] Figure 4 for Figure 3 Schematic diagram of the structure of the mixing channel.

[0027] Figure 5 for Figure 2 A schematic diagram of the structure of the heat exchange module.

[0028] Figure 6 for Figure 2 Software simulation diagram of the mixing state of the intermediate nitration reactor Figure 1 ,

[0029] Figure 7 for Figure 6 Enlarged view of point A in the image.

[0030] Figure 8 for Figure 2 Software simulation diagram of the mixing state of the intermediate nitration reactor Figure 2 ,

[0031] Figure 9 for Figure 1 A schematic diagram of the structure of the heat exchange shell outside the intermediate mixed acid delay tube and the nitration delay tube.

[0032] Among them, 1 is the nitric acid feed tank; 2 is the sulfuric acid feed tank; 3 is the trifluoromethylbenzene feed tank; 4 is the nitric acid transfer pump; 5 is the sulfuric acid transfer pump; 6 is the trifluoromethylbenzene transfer pump; 7 is the mixed acid mixer; 8 is the mixed acid delay pipe; 9 is the nitration reactor; 901 is the mixed acid inlet; 9011 is the mixed acid feed channel; 902 is the trifluoromethylbenzene inlet; 9021 is the trifluoromethylbenzene feed channel; 903 is the reaction outlet; 9031 is the outlet channel; 904 is the heat exchange module; 9041 is the protrusion; 9042 is the cooling medium inlet; 9043 is the cooling medium outlet; 905 is the connecting screw hole; 906 is the mixing channel; and 9061 is the mixed acid inlet. 9062 is the diversion protrusion, 9063 is the output port, 9064 is the input chamber, 9065 is the first diversion mixing section, 9066 is the second diversion mixing section, 9067 is the vertical mixing channel section, 90671 is the inclined surface, 90672 is the vertical surface, 90673 is the second diversion column, 90674 is the first diversion column, 907 is the liquid separating pad, 9071 is the through hole, 10 is the nitration delay tube; 11 is the product receiving tank; 12 is the first temperature sensor, 13 is the second temperature sensor, 14 is the third temperature sensor, 15 is the fourth temperature sensor, 16 is the heat exchange medium outlet, 17 is the heat exchange medium inlet, and 18 is the delay tube port. Detailed Implementation

[0033] The invention will now be described in further detail with reference to the accompanying drawings.

[0034] like Figures 1-8 As shown, the present invention includes a nitric acid feed tank 1, a sulfuric acid feed tank 2, a trifluoromethylbenzene feed tank 3, a mixed acid mixer 7, a nitration reactor 9, and a product receiving tank 11. The mixed acid mixer 7 has a first inlet, a second inlet, and a mixing outlet. The nitration reactor 9 has a mixed acid inlet 901, a trifluoromethylbenzene inlet 902, and a reaction outlet 903. The nitric acid feed tank 1 is connected to the first inlet via a first pipeline, and a nitric acid transfer pump 4 is installed on the first pipeline. The sulfuric acid feed tank 2 is connected to the second inlet via a second pipeline, and a sulfuric acid transfer pump 5 is installed on the second pipeline. The mixing outlet is connected to the mixed acid inlet 901 via a third pipeline, and a mixed acid delay pipe 8 is installed on the third pipeline. The trifluoromethylbenzene feed tank 3 is connected to the trifluoromethylbenzene inlet 902 via a fourth pipeline, and a trifluoromethylbenzene transfer pump 6 is installed on the fourth pipeline. The reaction outlet 903 is connected to the product receiving tank 11 via a fifth pipeline, and a nitration delay pipe 10 is installed on the fifth pipeline. Figures 2-8As shown, the nitration reactor 9 is provided with a mixing channel 906 inside, and the mixing channel 906 includes an input chamber 9064, a diversion mixing section and a vertical mixing channel section 9067 connected in sequence. The mixed acid inlet 901 is connected to the upper end of the input chamber 9064 through the mixed acid inlet channel 9011, the trifluoromethylbenzene inlet 902 is connected to the lower end of the input chamber 9064 through the trifluoromethylbenzene inlet channel 9021, and the lower end of the vertical mixing channel section 9067 is connected to the reaction outlet 903 through the outlet channel 9031. A heat exchange module 904 is provided inside the nitration reactor 9 at a position corresponding to the mixing channel 906.

[0035] like Figure 4 As shown, the lower end of the input cavity 9064 of the mixing channel 906 is provided with a diversion protrusion 9062, and diversion channels are formed between the two sides of the diversion protrusion 9062 and the corresponding cavity walls at the lower end of the input cavity 9064. After passing through the diversion protrusion 9062, the mixed acid solution is divided into two streams and flows along the corresponding diversion channels. Figures 2-3 As shown, the output end of the trifluoromethylbenzene inlet 902 is provided with a liquid separating pad 907, and the liquid separating pad 907 is provided with two through holes 9071, as shown. Figure 6 As shown, trifluoromethylbenzene liquid is sprayed through the two through holes 9071 of the separating pad 907 to form two liquid columns, and each liquid column is injected into the corresponding flow channel to mix with the mixed acid solution. This invention uses the separating pad 907 to form two liquid columns of trifluoromethylbenzene liquid, which on the one hand increases the injection velocity of the dispersed phase trifluoromethylbenzene into the continuous phase mixed acid; on the other hand, the trifluoromethylbenzene liquid column is injected and mixed with the mixed acid solution along a direction perpendicular to the flow direction, which increases the radial mass transfer effect, reduces the mixing time, and reduces the formation of nitration byproducts. In this embodiment, the diameter of the through holes 9071 on the separating pad 907 is 0.3 mm.

[0036] like Figure 4As shown, the diversion mixing section includes multiple diversion mixing parts with different diversion mixing shapes. In this embodiment, the diversion mixing part includes a first diversion mixing part 9065 in an annular shape and a second diversion mixing part 9066 in a rhomboid shape. The inner diameter of the flow channel of the first diversion mixing part 9065 first decreases relative to the diversion flow channels on both sides of the diversion protrusion 9062. The inner diameter of the flow channel of the upper part of the second diversion mixing part 9066 then increases relative to the inner diameter of the flow channel of the first diversion mixing part 9065. The inner diameter of the flow channel of the lower part of the second diversion mixing part 9066 then decreases again relative to the inner diameter of the flow channel of the upper part of the second diversion mixing part 9066. The present invention continuously changes the flow rate of the mixed liquid by the continuous change of the inner diameter of the flow channel, thereby achieving the effect of rapid mixing and mass transfer. In addition, the increase in the inner diameter of the flow channel of the upper part of the second diversion mixing part 9066 can also reduce the reactor pressure.

[0037] like Figure 4 As shown, the vertical mixing channel section 9067 of the mixing channel 906 is provided with a plurality of mixing protrusions in sequence, and as shown in the figure... Figures 6-7 As shown, the mixing protrusion includes an inclined surface 90671 on the input side and a vertical surface 90672 on the output side. The mixed liquid first flows upward and collides with the inclined surface 90671, and then suddenly flows downward and collides with the vertical surface 90672. This achieves the purpose of continuously changing the flow rate and colliding and mixing the mixed liquid along the direction perpendicular to the flow direction.

[0038] like Figure 4 and Figure 7 As shown, the vertical mixing channel section 9067 has a first diversion column 90674 at its input end and multiple second diversion columns 90673 inside. The mixing protrusions and the second diversion columns 90673 are staggered. After the liquid passes through the first diversion column 90674, it first achieves initial diversion and mixing. When the liquid passes through the inclined surface 90671 of the mixing protrusion, the mixture tends to flow upward and collide along the inclined surface 90671, and then suddenly tends to flow downward and collide along the vertical surface. However, due to factors such as flow inertia, the mixture will actually be divided into two directions of movement: axial (mixture flow direction) and radial (perpendicular to the mixture flow direction). The radial trend is larger, but at the same time, a part of the mixture will still flow along the axial trend. Therefore, in order to further improve the mixing effect, the present invention sets a second diversion column 90673 between adjacent mixing protrusions to achieve the purpose of diverting and remixing the axially flowing mixture.

[0039] Therefore, the mixing channel 906 of the present invention first changes the axial (i.e., the flow direction of the mixture) and radial (i.e., the direction perpendicular to the flow direction of the mixture) speed of the mixture in the mixing channel 906 by the design of the diversion mixing section and the vertical mixing channel section 9067, so as to achieve the purpose of rapidly mixing the continuous phase and the dispersed phase. The mixing protrusion and the second diversion column 90673 in the vertical mixing channel section 9067 further realize the axial and radial mixing of the mixture. Through the above two-stage axial and radial mixing structure, the present invention can reduce the mixing time of the mixture and also reduce the generation of by-products.

[0040] In this embodiment, the first diversion column 90674 is crescent-shaped, and the second diversion column 90673 is cylindrical.

[0041] like Figure 2 and Figure 5 As shown, the heat exchange module 904 includes a heat exchange cavity, with a cooling medium inlet 9042 on one side and a cooling medium outlet 9043 on the other side. The heat exchange cavity is elliptical, and multiple strip-shaped protrusions 9041 are arranged parallel to the flow direction of the cooling medium inside the heat exchange cavity. The cooling medium is input into the heat exchange cavity through the cooling medium inlet 9042, and the flow of the cooling medium along the gap between two adjacent protrusions 9041 can increase the flow rate of the heat exchange medium. At the same time, the shape of the heat exchange cavity reduces the existence of dead corners in the cavity, which can better remove the large amount of heat released by the nitration reaction. This is especially important for reducing the formation of nitration side reactions in the early stage. Then, the cooling medium is output from the cooling medium outlet 9043 to carry away the heat of the reaction.

[0042] like Figures 2-8 As shown, the nitration reactor 9 includes a first mounting block and a second mounting block connected by bolts. The trifluoromethylbenzene inlet 902 and trifluoromethylbenzene feed channel 9021 are located in the first mounting block, while the mixed acid inlet 901, mixed acid feed channel 9011, heat exchange module 904, reaction outlet 903, and outlet channel 9031 are located in the second mounting block. Figure 3 The second mounting block has a slot forming the mixing channel 906 on the side near the first mounting block, and as described above... Figure 2 As shown, each corner of the first mounting block and each corner of the second mounting block are provided with connecting screw holes 905 for connecting the two mounting blocks into a whole module, and at this time, the complete mixing channel 906 is formed between the first mounting block and the second mounting block.

[0043] like Figure 1As shown, in addition to the mixed acid delay tube 8, the third pipeline is equipped with a first temperature sensor 12; in addition to the trifluoromethylbenzene delivery pump 6, the fourth pipeline is equipped with a second temperature sensor 13; and the fifth pipeline is equipped with a third temperature sensor 14 and a fourth temperature sensor 15, which are respectively located at both ends of the nitration delay tube 10. The mixed acid mixer 7, the mixed acid delay tube 8, the nitration delay tube 10, and each temperature sensor are all technologies known in the art and are commercially available products.

[0044] The mixed acid delay tube 8 is disposed in the first heat exchange shell to maintain the temperature, and the nitration delay tube 10 is disposed in the second heat exchange shell to maintain the temperature. Figure 9 As shown, the first heat exchange shell and the second heat exchange shell have the same structure. One end of the shell has a heat exchange medium outlet 16 on the upper side and a heat exchange medium inlet 17 on the lower side of the other end. The shell end has a delay tube port 18.

[0045] The working principle of this invention is as follows:

[0046] When this invention is in operation, fuming nitric acid, concentrated sulfuric acid and trifluoromethylbenzene are first loaded into the corresponding feed tanks. Then, the temperatures of the first heat exchange shell (corresponding to the mixed acid delay tube 8), the heat exchange module 904 and the second heat exchange shell (corresponding to the nitration delay tube 10) are controlled to reach the set temperatures, and then the feeding begins.

[0047] During feeding, nitric acid pump 4 and sulfuric acid pump 5 are simultaneously turned on. The mixed acid is mixed through the mixed acid mixer 7 and then enters the nitration reactor 9 through the mixed acid delay pipe 8. The first temperature sensor 12 is then checked. Once the set temperature is reached, the trifluoromethylbenzene pump 6 is turned on to allow trifluoromethylbenzene to be introduced into the nitration reactor 9 to react with the mixed acid. The trifluoromethylbenzene passes through the two through-holes 9071 of the separating pad 907 in the nitration reactor 9 and is sprayed to form two liquid columns. Each liquid column is injected into the separating channels on both sides of the separating protrusion 9062 to mix with the mixed acid solution. This increases the speed at which the dispersed phase trifluoromethylbenzene is injected into the continuous phase mixed acid. Furthermore, the trifluoromethylbenzene liquid column is injected and mixed with the mixed acid solution along a direction perpendicular to the flow direction of the mixed acid solution, which can increase... The radial mass transfer effect reduces the mixing time and the formation of nitration byproducts. When the mixture passes through the diversion mixing section of the mixing channel 906, the axial (i.e., the direction of flow) velocity of the mixture within the mixing channel 906 continuously changes. When the mixture passes through the vertical mixing channel section 9067 of the mixing channel 906, the radial (i.e., the direction perpendicular to the flow) velocity of the mixture within the mixing channel 906 continuously changes. Thus, the design of the mixing channel 906, through the diversion mixing section and the vertical mixing channel section 9067, continuously alters the axial (i.e., the direction of flow) and radial (i.e., the direction perpendicular to the flow) velocities of the mixture within the mixing channel 906 to achieve rapid mixing of the continuous and dispersed phases. Figure 4 and Figure 7 As shown, the mixing protrusion and the second diverter column 90673 in the vertical mixing channel section 9067 further realize the axial and radial mixing of the mixture. Therefore, the present invention reduces the mixing time of the mixture and the generation of by-products through the above two-stage axial and radial mixing structure.

[0048] Furthermore, when the mixture reacts in the mixing channel 906 of the nitration reactor 9, the heat generated by the reaction is promptly carried away by the cooling medium in the heat exchange module 904. The heat exchange chamber of the heat exchange module 904 has multiple strip-shaped protrusions 9041 arranged parallel to the flow direction of the cooling medium. The cooling medium flows along the gap between two adjacent protrusions 9041 that suddenly decrease in size, which increases the flow rate of the heat exchange medium. At the same time, the shape of the heat exchange chamber reduces the existence of dead corners in the chamber. All of these factors can better remove the large amount of heat released by the nitration reaction, which is particularly important for reducing the formation of nitration side reactions in the early stage.

[0049] Figure 8 The image shows the fluid fraction at 0 seconds in an application example of this invention, where different colors on the cross-section represent the mixed acid volume fraction (%) in different parts of the flow channel. Figure 6The figure shown is the modulus fraction graph at 0.1 seconds in this application example. Figure 6 and Figure 8 As can be seen, this application example can achieve uniform mixing in 0.1 seconds, and there are no dead zones inside the reactor after mixing.

[0050] The reaction product output from the nitration reactor 9 enters the product receiving tank 11 after passing through the nitration delay tube 10. Finally, the nitrated product is treated by acid separation, alkali washing and water washing to obtain the final product.

[0051] In this invention, 98% fuming nitric acid, 98% concentrated sulfuric acid, and trifluoromethylbenzene are used for preparation, with a molar ratio of (1-1.1):(1.86-3.31):1. The temperature of the first heat exchange shell (corresponding to the mixed acid delay tube 8) is set to 0-5℃, the temperature of the heat exchange module 904 is set to 5-20℃, and the temperature of the second heat exchange shell (corresponding to the nitration delay tube 10) is set to 30-50℃. The flow rate of the mixed liquid in the mixing channel 906 in the nitration reactor 9 is 10-30 ml / min, and the residence time is 10-15 min. The specific temperature and time are set according to actual needs.

[0052] The following example illustrates this further.

[0053] Application Example 1

[0054] First, accurately weigh 472.5g of fuming nitric acid, 1032.5g of concentrated sulfuric acid, and 1032.50g of trifluoromethylbenzene, with a molar ratio of 1.05:1.86:1. Place these into their respective feed tanks on a balance for later use. Then, control the internal temperature of the first heat exchange shell to 1℃, the internal temperature of heat exchange module 904 to 10℃, and the internal temperature of the second heat exchange shell to 50℃. Simultaneously turn on the nitric acid and sulfuric acid feed pumps, setting their flow rates to 1.32ml / min and 4.63ml / min respectively. The mixed acid then passes through the mixed acid mixer 7 and... After the temperature in the mixed acid delay tube 8 stabilizes at around 5°C, the trifluoromethylbenzene feed pump 6 is turned on, with a flow rate set to 4.08 ml / min. The temperature of the mixed acid and trifluoromethylbenzene after reacting in the nitration reactor 9 is maintained at 8-15°C. After the reaction product passes through the nitration delay tube 10, its temperature is maintained at around 45°C. The total residence time is 12 min. Finally, the nitrated product is treated with acid, alkali washing, and water washing to obtain the sample. The sample is analyzed by gas chromatography, and the conversion rate of the raw material trifluoromethylbenzene is 100%, with a selectivity of 89.2%.

Claims

1. A system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor, characterized in that: The system includes a nitric acid feed tank (1), a sulfuric acid feed tank (2), a trifluoromethylbenzene feed tank (3), a mixed acid mixer (7), a nitration reactor (9), and a product receiving tank (11). The mixed acid mixer (7) has a first inlet, a second inlet, and a mixing outlet. The nitration reactor (9) has a mixed acid inlet (901), a trifluoromethylbenzene inlet (902), and a reaction outlet (903). The nitric acid feed tank (1) is connected to the first inlet via a first pipeline, and a nitric acid transfer pump (4) is installed on the first pipeline. The sulfuric acid feed tank (2) is connected to the second inlet via a second pipeline, and a sulfuric acid transfer pump (5) is installed on the second pipeline. The mixing outlet is connected to the mixed acid inlet (901) via a third pipeline, and a mixed acid delay pipe (8) is installed on the third pipeline. The trifluoromethylbenzene feed tank (3) is connected to the trifluoromethylbenzene inlet (902) via a fourth pipeline, and a product receiving tank (11) is installed on the fourth pipeline. The trifluoromethylbenzene transfer pump (6) is connected to the product receiving tank (11) via a fifth pipeline, and a nitration delay pipe (10) is provided on the fifth pipeline; the nitration reactor (9) is provided with a mixing channel (906) inside, and the mixing channel (906) includes an input chamber (9064), a diversion mixing section and a vertical mixing channel section (9067) connected in sequence, wherein the mixed acid inlet (901) is connected to the mixed acid feed stream. The channel (9011) is connected to the upper end of the input cavity (9064), the trifluoromethylbenzene inlet (902) is connected to the lower end of the input cavity (9064) through the trifluoromethylbenzene inlet channel (9021), the lower end of the vertical mixing channel section (9067) is connected to the reaction outlet (903) through the outlet channel (9031), and a heat exchange module (904) is provided inside the nitration reactor (9) at the position corresponding to the mixing channel (906). The lower end of the input cavity (9064) of the mixing channel (906) is provided with a diversion protrusion (9062), and a diversion channel is formed between the two sides of the diversion protrusion (9062) and the corresponding cavity wall at the lower end of the input cavity (9064). The output end of the trifluoromethylbenzene inlet (902) is provided with a liquid-distributing pad (907), and the liquid-distributing pad (907) is provided with two through holes (9071). After the trifluoromethylbenzene liquid passes through the two through holes (9071) of the liquid-distributing pad (907), it is sprayed to form two liquid columns, and each liquid column is injected into the diversion channel on the corresponding side. The vertical mixing channel section (9067) of the mixing channel (906) is provided with a plurality of mixing protrusions in sequence, and the mixing protrusions include an inclined surface (90671) on the input side and a vertical surface (90672) on the output side. The vertical mixing channel section (9067) is provided with a plurality of second diverter columns (90673), and the mixing protrusions and the second diverter columns (90673) are staggered. The input end of the vertical mixing channel section (9067) is provided with a first diverter column (90674).

2. The system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 1, characterized in that: The flow mixing section includes a first flow mixing section (9065) in the shape of a ring and a second flow mixing section (9066) in the shape of a rhombus. The inner diameter of the flow channel of the first flow mixing section (9065) first decreases, the inner diameter of the flow channel of the upper part of the second flow mixing section (9066) then increases, and the inner diameter of the flow channel of the lower part of the second flow mixing section (9066) then decreases.

3. The system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 1, characterized in that: The heat exchange module (904) includes a heat exchange cavity, and the heat exchange cavity has a cooling medium inlet (9042) on one side and a cooling medium outlet (9043) on the other side. The heat exchange cavity has multiple strip-shaped protrusions (9041) arranged parallel to the flow direction of the cooling medium inside.

4. The system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 1, characterized in that: The nitration reactor (9) includes a first mounting block and a second mounting block connected by bolts, wherein the trifluoromethylbenzene inlet (902) and the trifluoromethylbenzene feed channel (9021) are located in the first mounting block, and the mixed acid inlet (901), the mixed acid feed channel (9011), the heat exchange module (904), the reaction outlet (903), and the discharge channel (9031) are located in the second mounting block.

5. The system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 1, characterized in that: The third pipeline is provided with a first temperature sensor (12), the fourth pipeline is provided with a second temperature sensor (13), and the fifth pipeline is provided with a third temperature sensor (14) and a fourth temperature sensor (15). The third temperature sensor (14) and the fourth temperature sensor (15) are respectively located at both ends of the nitration delay tube (10).

6. The system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 5, characterized in that: The mixed acid delay tube (8) is located in the first heat exchange shell, and the nitration delay tube (10) is located in the second heat exchange shell.

7. A method of using the system for preparing m-trifluoromethylnitrobenzene using a microchannel reactor according to claim 6, characterized in that: During preparation, fuming nitric acid, concentrated sulfuric acid and trifluoromethylbenzene are weighed and placed into nitric acid feed tank (1), sulfuric acid feed tank (2) and trifluoromethylbenzene feed tank (3) respectively. Then, the internal temperatures of the first heat exchange shell, heat exchange module (904) and the second heat exchange shell are controlled to reach the set temperature. Then, the nitric acid delivery pump (4) and sulfuric acid delivery pump (5) are turned on at the same time. After the mixed acid passes through the mixed acid mixer (7) and the mixed acid delay tube (8), the temperature detected by the first temperature sensor (12) is checked. When the temperature detected by the first temperature sensor (12) reaches the set value, the trifluoromethylbenzene delivery pump (6) is turned on to make the mixed acid and trifluoromethylbenzene react in the nitration reactor (9). When the feed rate and the temperature detected by each temperature sensor are stable, the product receiving tank (11) is opened to receive the nitrated product.

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