Plate-type micro-channel reactor and method for nitrifying trifluoromethoxybenzene by using plate-type micro-channel reactor

Abstract

The invention provides a plate-type micro-channel reactor and a method for nitrifying trifluoromethoxybenzene by using the plate-type micro-channel reactor, and belongs to the technical field of organic synthesis. The plate type microchannel reactor comprises a first heat exchange plate, a reaction plate and a second heat exchange plate, the reaction plate is positioned between the first heat exchange plate and the second heat exchange plate; a feeding channel, a first shunting section, a first mixing section, a second shunting mixing section, a third shunting mixing section, a fourth shunting mixing section and a discharging channel which are connected in sequence are arranged on the reaction plate; and the feeding channel comprises a first feeding channel and a second feeding channel. According to the method, trifluoromethoxybenzene is taken as a raw material and is subjected to nitration reaction by using plate type micro-channel reactors connected in series, so that high-selectivity continuous nitration of trifluoromethoxybenzene is realized, the nitration reaction can be completed within 5 minutes, and the contents of byproduct meta-position and dinitrate can be controlled to be lower than 0.05% and 0.5% respectively.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, in particular to a plate-type microchannel reactor and a method for nitrating trifluoromethoxybenzene by using the plate-type microchannel reactor. Background Art

[0002] 1-Nitro-4-trifluoromethoxybenzene (p-trifluoromethoxyaniline) is an important fluorine-containing organic intermediate, which is widely used in the synthesis of high-efficiency and low-residue insecticides such as indoxacarb, allergic drugs such as nicotinamide and tolamide, and polymer materials such as epoxy resins, and the demand is increasing year by year. The main synthesis method of p-trifluoromethoxyaniline is to nitrate trifluoromethoxybenzene and then hydrogenate and reduce it. The meta-position and dinitro by-products produced during the nitration reaction are difficult to separate from the product, which affects the purity and subsequent use of the product. At present, the industrial production method still uses a large amount of concentrated sulfuric acid and a low temperature (cooling medium below -20°C) batch process, and controls the by-product content by slowly dropping the reaction. There are problems such as high energy consumption, high risk, and limited capacity improvement. Patent CN107266321B discloses a continuous microchannel synthesis method, but it fails to achieve full conversion of raw materials, and the content of key difficult-to-separate by-products fails to reach the level of batch production technology (meta-position ≤0.06%, dinitro ≤0.7%), which affects the subsequent use of products.

[0003] Among the trifluoromethoxybenzene nitration products, only the para-nitration product has high application value, and the other by-products generally need to be separated from the product after the hydrogenation reaction. Among them, para-trifluoromethoxyaniline and meta-trifluoromethoxyaniline are very similar in boiling point and solubility. It is difficult to separate a trace amount of meta-trifluoromethoxyaniline by-product from the para-trifluoromethoxyaniline product by traditional distillation and extraction methods. Therefore, the best way is to start from the source of the reaction and control the amount of meta-by-products generated during the reaction. Shi Zuopan from Nanjing University of Science and Technology added a small amount of polyphosphoric acid to the traditional nitric-sulfuric acid mixed acid nitration system, which improved the selectivity of the para-product and the ortho-to-product ratio reached 91:9, but did not solve the problems of by-product content and intermittent process; Chen Guangwen's team from Dalian Institute of Chemical Physics, Chinese Academy of Sciences, realized the above-mentioned continuous nitration process using a microreactor / tubular reactor. The substrate and nitrating agent were added at one time, and the reaction was highly exothermic at the beginning, but no targeted design was made on the reactor structure, which may lead to hot spots inside the reactor. Therefore, the by-product content was slightly higher than that of the intermittent process, but the time-space efficiency and safety were greatly optimized compared to the intermittent process. Therefore, it is of great significance to study a plate microchannel reactor and use it to produce trifluoromethoxyaniline to improve its selectivity. Summary of the invention

[0004] The object of the present invention is to provide a plate-type microchannel reactor and a method for nitrating trifluoromethoxybenzene using the plate-type microchannel reactor, so as to solve the problem of high content of meta- and dinitro by-products in the nitration reaction of trifluoromethoxybenzene in the prior art.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a plate-type microchannel reactor, which comprises a first heat exchange plate, a reaction plate and a second heat exchange plate; the reaction plate is located between the first heat exchange plate and the second heat exchange plate; a feed channel, a first diversion section, a first mixing section, a second diversion mixing section, a third diversion mixing section, a fourth diversion mixing section and a discharge channel which are connected in sequence are arranged on the reaction plate; the feed channel comprises a first feed channel and a second feed channel.

[0007] Preferably, the first diversion section comprises an upper diversion section and a lower diversion section; the upper diversion section and the lower diversion section are symmetrical, and the upper diversion section and the lower diversion section are connected by a slit; the first feed channel is connected to the upper diversion section; the second feed channel is connected to the lower diversion section; and diversion fluids are respectively arranged in the upper diversion section and the lower diversion section.

[0008] Preferably, the first mixing section is a slit between an upper flow-dividing section and a lower flow-dividing section; the bottom of the slit narrows from wide to narrow and is connected to the inlet end of the second flow-dividing mixing section.

[0009] Preferably, the second diversion mixing section has a main channel and a rectangular diversion channel, and the main channel and the rectangular diversion channel are arranged alternately; triangular convex edges are arranged at the feed end and the discharge end of the rectangular diversion channel; the outlet end of the second diversion mixing section is connected to the inlet end of the third diversion mixing section.

[0010] Preferably, the third diversion mixing section comprises an inlet channel, a mixing channel, and a merging channel connected in sequence; the mixing channel has a main channel and a rectangular diversion channel, and the main channel and the rectangular diversion channel are alternately arranged; the mixing channel and the merging channel are alternately arranged; the outlet end of the third diversion mixing section is connected to the inlet end of the fourth diversion mixing section.

[0011] Preferably, the fourth flow splitting and mixing section has a main flow channel and a hexagonal flow splitting channel; the outlet end of the fourth flow splitting and mixing section is connected to the discharge flow channel.

[0012] The present invention also provides a method for nitrating trifluoromethoxybenzene using a plate-type microchannel reactor, comprising the following steps: trifluoromethoxybenzene and a nitrating agent enter the series-connected plate-type microchannel reactors in sequence through a first feed channel and a second feed channel respectively to perform a nitrification reaction;

[0013] The nitrating agent is a mixed acid of fuming nitric acid and concentrated sulfuric acid.

[0014] Preferably, the molar ratio of nitric acid to trifluoromethoxybenzene in the mixed acid is 1.0-2.0:1.

[0015] Preferably, the nitrating agent is added in batches through a series of plate-type microchannel reactors.

[0016] Preferably, the temperature of the nitration reaction is -10 to 5°C, and the time of the nitration reaction is 1 to 5 minutes.

[0017] Beneficial effects of the present invention:

[0018] (1) The plate-type microchannel reactor provided by the present invention is combined with the nitration process to achieve the continuous nitration of trifluoromethoxybenzene and the control of the difficult-to-separate byproducts. The internal structure of the plate-type microreactor is designed to reduce the mixing time of the heterogeneous reactants and improve the heat exchange efficiency of the reactor.

[0019] (2) The present invention realizes the split addition of the nitrating agent by connecting the plate-type microchannel reactors in series, and distributes the heat originally released in the initial stage of the reaction to a gradual release during the reaction, thereby avoiding the generation of local hot spots; the influence of water generated during the reaction is reduced by reducing the water content of the nitrating agent, and the reaction rate at low temperature is accelerated to a certain extent, thereby realizing high-selective continuous nitration of trifluoromethoxybenzene. The nitration reaction can be completed within 5 minutes, the para / ortho ratio in the product is greater than 92:8, and the by-product meta and dinitrate contents can be controlled to be less than 0.05% and 0.5%, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the overall structure of the plate-type microchannel reactor of the present invention, wherein 9 is a first heat exchange plate, 10 is a second heat exchange plate, 11 is a metal plate, and 12 is a reaction plate;

[0021] Figure 2 Schematic diagram of the structure of the reaction plate 12 in the plate-type microchannel reactor of the present invention, wherein 1 is a first feed channel, 2 is a second feed channel, 3 is a first split flow section, 4 is a first mixing section, 5 is a second split flow mixing section, 6 is a third split flow mixing section, 7 is a fourth split flow mixing section, 8 is a discharge channel, 13 is a screw hole, and 14 is a sealing ring;

[0022] Figure 3 3 is a partial enlarged view of the first flow dividing section and the first mixing section in the reaction plate, wherein 3 is the first flow dividing section and 4 is the first mixing section;

[0023] Figure 4 A detailed diagram of the connection between the first mixing section and the second flow-dividing mixing section in the reaction plate;

[0024] Figure 5 is a flow chart of the nitration reaction of trifluoromethoxybenzene in Example 1;

[0025] Figure 6 Flow chart of the nitration reaction of trifluoromethoxybenzene in Example 2. DETAILED DESCRIPTION

[0026] The present invention provides a plate-type microchannel reactor, which comprises a first heat exchange plate 9, a reaction plate 12 and a second heat exchange plate 10; the reaction plate 12 is located between the first heat exchange plate 9 and the second heat exchange plate 10; the reaction plate 12 is provided with a feed channel, a first diversion section 3, a first mixing section 4, a second diversion mixing section 5, a third diversion mixing section 6, a fourth diversion mixing section 7 and a discharge channel 8 which are connected in sequence; the feed channel comprises a first feed channel 1 and a second feed channel 2.

[0027] In the present invention, a metal plate 11 is disposed between the reaction plate 12 and the second heat exchange plate 10, and the front side of the reaction plate 12 corresponds to the metal plate 11. The metal plate 11 is used to separate the reaction plate 12 and the second heat exchange plate 10 to prevent the two from directly contacting each other.

[0028] In the present invention, there is no special limitation on the fixing method of the first heat exchange plate 9, the reaction plate 12, the metal plate 11 and the second heat exchange plate 10. In the present invention, preferably, screw holes 13 are provided at the edges and middle parts of the first heat exchange plate 9, the reaction plate 12, the metal plate 11 and the second heat exchange plate 10, and the first heat exchange plate 9, the reaction plate 12, the metal plate 11 and the second heat exchange plate 10 are fixed together by bolts.

[0029] In the present invention, sealing rings 14 are arranged at the edges and middle parts of the first heat exchange plate 9, the reaction plate 12, the metal plate 11 and the second heat exchange plate 10. The sealing rings are made of perfluoroether material to increase the sealing between the plates.

[0030] In the present invention, the reaction plate 12 is made of Hastelloy (HC276), and the feed channel, the first diversion section, the first mixing section, the second diversion mixing section, the third diversion mixing section, the fourth diversion mixing section and the discharge channel on the reaction plate are all made by computer digital controlled precision machining (CNC).

[0031] In the present invention, the surface finish of the first heat exchange plate 9, the reaction plate 12, the metal plate 11 and the second heat exchange plate 10 is Ra≤0.4, and the flatness is 0.04. The edges and middle parts of each plate have grooves, and the sealing ring 14 is embedded in the groove. The plates are fastened by bolts passing through each plate to achieve mirror sealing between the plates.

[0032] In the present invention, the first heat exchange plate 9 and the second heat exchange plate 10 have heat exchange medium flow channels to ensure that the heat exchange medium can flow quickly.

[0033] In the present invention, the first diversion section 3 includes an upper diversion section and a lower diversion section; the upper diversion section and the lower diversion section are symmetrical, and the upper diversion section and the lower diversion section are connected by a slit; the first feed channel 1 is connected to the upper diversion section; the second feed channel 2 is connected to the lower diversion section; and a plurality of diversion bodies are arranged in the upper diversion section and the lower diversion section.

[0034] In the present invention, the split flow is a rectangular or rounded rectangular split flow, the purpose of which is to cut the reaction raw materials entering the feed channel into multiple streams and then mix them.

[0035] In the present invention, the first mixing section 4 is a slit between an upper flow-dividing section and a lower flow-dividing section; the bottom of the slit narrows from wide to narrow and is connected to the inlet end of the second flow-dividing mixing section 5 .

[0036] In the present invention, a cylindrical fluid distributor is arranged on the slit, wherein the diameter of the cylindrical fluid distributor is 0.7 mm and the height is consistent with the depth of the flow channel. The function of the cylindrical fluid distributor is to enhance the mixing of the reaction liquid and prevent stratification.

[0037] In the present invention, the second diversion mixing section 5 has a main channel and a rectangular diversion channel, and the main channel and the rectangular diversion channel are arranged alternately; triangular convex edges are arranged at the feed end and the discharge end of the rectangular diversion channel; the outlet end of the second diversion mixing section 5 is connected to the inlet end of the third diversion mixing section 6.

[0038] In the present invention, the third diversion mixing section 6 includes an inlet flow channel, a mixing flow channel, and a merging flow channel connected in sequence; the mixing flow channel has a main flow channel and a rectangular diversion flow channel, and the main flow channel and the rectangular diversion flow channel are alternately arranged; the mixing flow channel and the merging flow channel are alternately arranged; the outlet end of the third diversion mixing section 6 is connected to the inlet end of the fourth diversion mixing section 7.

[0039] In the present invention, the outlet end of the inlet flow channel is divided into two and connected to the mixing flow channel. The outlet end of the mixing flow channel is connected to the merging flow channel. The outlet end of the merging flow channel is divided into two and then enters the mixing flow channel, and finally enters the fourth diversion mixing section 7 through the merging flow channel.

[0040] In the present invention, a cylindrical flow divider is arranged in the flow channel between the second flow divider mixing section 5 and the third flow divider mixing section 6, wherein the diameter of the cylindrical flow divider is 0.7 mm and the height is consistent with the depth of the flow channel. The function of the cylindrical flow divider is to enhance the mixing of the reaction liquid and prevent stratification.

[0041] In the present invention, the fourth flow splitting and mixing section 7 has a main flow channel and a hexagonal flow splitting channel; the outlet end of the fourth flow splitting and mixing section 7 is connected to the discharge flow channel 8 .

[0042] In the present invention, the width of the main channel of the second diverter mixing section 5, the main channel of the mixing channel in the third diverter mixing section 6, and the main channel of the fourth diverter mixing section is twice the width of the diverter channel, and the depth is the same, wherein the channel depth is 0.4 mm.

[0043] In the present invention, the first diversion section 3 cuts the raw material into multiple streams, which are then quickly collided and evenly mixed in the first mixing section 4, and then continuously mixed in the second diversion mixing section 5, the third diversion mixing section 6, and the fourth diversion mixing section 7 before flowing out of the reactor.

[0044] The present invention also provides a method for nitrating trifluoromethoxybenzene using a plate-type microchannel reactor, comprising the following steps: trifluoromethoxybenzene and a nitrating agent enter the series-connected plate-type microchannel reactors in sequence through a first feed channel 1 and a second feed channel 2 respectively to perform a nitrification reaction;

[0045] The nitrating agent is a mixed acid of fuming nitric acid and concentrated sulfuric acid.

[0046] In the present invention, the trifluoromethoxybenzene and the nitrating agent are initially heat exchanged in a heat exchanger before entering the plate-type microchannel reactor, and the temperature after the heat exchange is controlled between -5 and 5°C.

[0047] In the present invention, the molar ratio of nitric acid to trifluoromethoxybenzene in the mixed acid is 1.0-2.0:1, preferably 1.02:1.

[0048] In the present invention, the number of the plate-type microchannel reactors connected in series is preferably 5; the nitrating agent is added in batches through the plate-type microchannel reactors connected in series.

[0049] In the present invention, it is characterized in that the temperature of the nitration reaction is -10 to 5°C, and the time of the nitration reaction is 1 to 5 minutes.

[0050] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0051] Example 1

[0052] Pure trifluoromethoxybenzene is used as a raw material, a mixed acid of fuming nitric acid and concentrated sulfuric acid is used as a nitrating agent, the molar ratio of nitric acid to trifluoromethoxybenzene in the nitrating agent is 1.02, and the mass concentration of sulfuric acid in the nitrating agent is 13.8%. Through two horizontal flow pumps, trifluoromethoxybenzene is fed at a feed rate of 14.8 mL / min, and the nitrating agent is fed at a feed rate of 16.7 mL / min, and they enter the heat exchanger for preliminary heat exchange respectively. The temperature of the heat exchanger is set to 0°C, and then trifluoromethoxybenzene is transported to the inside of the microchannel reactor through the first feed channel 1 and the nitrating agent is transported to the inside of the microchannel reactor through the second feed channel 2, and sequentially passes through the first diversion section 3, the first mixing section 4, the second diversion mixing section 5, the third diversion mixing section 6, and the fourth diversion mixing section 7. After completing multiple diversion and mixing operations of the solution, it enters the first feed channel 1 of another plate-type microreactor in series through the discharge channel 8 (the second feed channel 2 is blocked with a dead plug), and so on, a total of five microchannel reactors are connected in series, and the temperatures of each reactor are 1°C, 1°C, 2°C, 2°C and 4°C, respectively, to complete the final nitration reaction, and the reaction residence time is 200s.

[0053] According to gas chromatography analysis, the reaction was basically completed at a reaction time of 160s, with a raw material conversion rate of 99.7%, para-91.65%, ortho-7.42%, meta-0.069%, and dinitrate 0.48%. Further extension of the reaction time will lead to an increase in dinitrate by-products. The composition of the products at different residence times is shown in Table 1:

[0054] Table 1 Composition of products at different residence times

[0055]

[0056]

[0057] Example 2

[0058] Pure trifluoromethoxybenzene is used as a raw material, and a mixed acid of fuming nitric acid and concentrated sulfuric acid is used as a nitrating agent. The molar ratio of nitric acid to trifluoromethoxybenzene in the nitrating agent is 1.02, and the mass concentration of sulfuric acid in the nitrating agent is 85%. Trifluoromethoxybenzene is transported by a feed pump with a feed amount of 13.5 mL / min, and the digester (mixed acid) is transported by 5 feed pumps with a total feed amount of 13.6 mL / min. The raw material and the nitrating agent are preliminarily heat exchanged through their respective heat exchangers, wherein trifluoromethoxybenzene is precooled to -3°C, and the mixed acid is precooled to -4°C. Then, trifluoromethoxybenzene is transported to the inside of the microchannel reactor through the first feed channel 1, and the first mixed acid is transported to the inside of the microchannel reactor through the second feed channel 2, and sequentially passes through the first diversion section 3, the first mixing section 4, The second split mixing section 5, the third split mixing section 6, and the fourth split mixing section 7 complete the multiple split and mixing operations of the solution, and then enter the first feed channel 1 of another plate microreactor in series through the discharge channel 8, and react with the second mixed acid entering through the second feed channel 8 of the second plate microreactor. By analogy, a total of five microchannel reactors are connected in series, and the temperatures of each reactor are -7°C, -7°C, -5°C, -3°C and 1°C, respectively, to complete the final nitration reaction, and the reaction residence time is 300s. After gas chromatography analysis, the raw material conversion rate is 99.9%, the para position is 93.32%, the ortho position is 5.92%, the meta position is 0.047%, and the dinitrogen is 0.46%. The composition of the products at different residence times is shown in Table 2:

[0059] Table 2 Composition of products at different residence times

[0060]

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A plate-type microchannel reactor, characterized in that: The plate-type microchannel reactor comprises a first heat exchange plate, a reaction plate and a second heat exchange plate; the reaction plate is located between the first heat exchange plate and the second heat exchange plate; a feed channel, a first diversion section, a first mixing section, a second diversion mixing section, a third diversion mixing section, a fourth diversion mixing section and a discharge channel connected in sequence are arranged on the reaction plate; the feed channel comprises a first feed channel and a second feed channel.

2. The plate type microchannel reactor according to claim 1, characterized in that: The first diversion section includes an upper diversion section and a lower diversion section; the upper diversion section and the lower diversion section are symmetrical, and the upper diversion section and the lower diversion section are connected by a slit; the first feed channel is connected to the upper diversion section; the second feed channel is connected to the lower diversion section; and diversion fluids are respectively arranged in the upper diversion section and the lower diversion section.

3. The plate type microchannel reactor according to claim 2, characterized in that: The first mixing section is a slit between the upper flow-dividing section and the lower flow-dividing section; the bottom of the slit becomes narrower from wide to connected to the inlet end of the second flow-dividing mixing section.

4. The plate-type microchannel reactor according to any one of claims 1 to 3, characterized in that: The second flow-dividing and mixing section has a main flow channel and a rectangular flow-dividing channel, which are alternately arranged; the feed end and the discharge end of the rectangular flow-dividing channel are provided with triangular convex edges; the outlet end of the second flow-dividing and mixing section is connected to the inlet end of the third flow-dividing and mixing section.

5. The plate type microchannel reactor according to claim 4, characterized in that: The third diversion and mixing section includes an inlet flow channel, a mixing flow channel, and a merging flow channel connected in sequence; the mixing flow channel has a main flow channel and a rectangular diversion flow channel, and the main flow channel and the rectangular diversion flow channel are alternately arranged; the mixing flow channel and the merging flow channel are alternately arranged; the outlet end of the third diversion and mixing section is connected to the inlet end of the fourth diversion and mixing section.

6. The plate type microchannel reactor according to claim 5, characterized in that: The fourth flow splitting and mixing section has a main flow channel and a hexagonal flow splitting flow channel; the outlet end of the fourth flow splitting and mixing section is connected to the discharge flow channel.

7. A method for nitrating trifluoromethoxybenzene using the plate-type microchannel reactor according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: trifluoromethoxybenzene and a nitrating agent enter a series-connected plate-type microchannel reactor through a first feed channel and a second feed channel in sequence to perform a nitration reaction; The nitrating agent is a mixed acid of fuming nitric acid and concentrated sulfuric acid.

8. The method for nitrating trifluoromethoxybenzene using a plate-type microchannel reactor according to claim 7, characterized in that: The molar ratio of nitric acid to trifluoromethoxybenzene in the mixed acid is 1.0-2.0:

1.

9. The method for nitrating trifluoromethoxybenzene using a plate-type microchannel reactor according to claim 7 or 8, characterized in that: The nitrating agent is added in batches through the plate-type microchannel reactors connected in series.

10. The method for nitrating trifluoromethoxybenzene using a plate-type microchannel reactor according to claim 9, characterized in that: The temperature of the nitration reaction is -10 to 5°C, and the time of the nitration reaction is 1 to 5 minutes.

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