CN110698333A - Method for continuously synthesizing o-phthalaldehyde by using microchannel reaction device - Google Patents

Abstract

The invention discloses a method for continuously synthesizing o-phthalaldehyde in a micro-channel reactor. Using 1,3-dihydroisobenzofuran and nitric acid as raw materials, a micro-channel reaction device is used to continuously synthesize o-phthalaldehyde. Process steps such as extraction, distillation and drying to obtain ortho-phthalaldehyde product. Compared with the prior art, the process reaction of the present invention makes full use of the characteristics of the micro-channel reactor to strengthen heat transfer and mass transfer and can realize precise control, and overcomes the existing reaction of the existing batch reactor to produce o-phthalaldehyde. It takes a long time, cannot be continuously produced, has low safety performance, and needs to add a large amount of acid inhibitors in the reaction, causing large pollution and other problems. It can realize continuous production and automatic control of the process, and the production is efficient and safe. The product has high purity, high yield, low energy consumption and green economy, which is conducive to the promotion and use of ortho-phthalaldehyde in chemical and medical industries.

Description

A kind of method for continuously synthesizing ortho-phthalaldehyde by microchannel reaction device

technical field

The content of the invention belongs to the technical field of chemical synthesis technology, and relates to a method for continuously synthesizing o-phthalaldehyde in a microchannel reaction device.

Background technique

O-phthalaldehyde (OPA), as an important pharmaceutical and chemical intermediate, has been widely used in amine alkaloids, fluorometer histamine determination and medical inspection in the past. , which has now been developed into a new generation of efficient medical disinfectants. Compared with traditional glutaraldehyde disinfectants, phthalaldehyde has the characteristics of shorter duration and excellent bactericidal performance, and can be widely used in the disinfection of medicine and medical equipment.

There are many reports about the synthetic route of o-phthalaldehyde in this area at present, mainly including: o-xylene bromination hydrolysis method, o-xylene chlorinated hydrolysis method, nitric acid direct oxidation method, naphthalene ozonation hydrogenation method and high temperature oxidation method Wait. Wherein: the ortho-xylene brominated hydrolysis method needs to use bromine as the raw material, and the cost is higher; the ortho-xylene chlorinated hydrolysis method is easily sterically hindered due to the chlorination reaction in structure, the single-pass yield is low, and the loss is relatively large; The direct oxidation method of nitric acid is due to the severe exothermic reaction, and the depth of oxidation is difficult to control, resulting in a low conversion rate (less than 70%) of the reaction. In addition, a large amount of acetic acid needs to be added in the reaction as an inhibitor for organic acid generation, which not only causes waste, but also causes acid. The gas pollution is more serious; the ozonation and hydrogenation of naphthalene has problems such as the use of precious metals as catalysts in the reaction, the products after the reaction are not easy to separate and the process conditions are difficult to control, the product purity is low, the catalyst is inconvenient to recycle, and the investment in the reaction equipment is too high. It is difficult to realize industrialized production; while the reaction conditions of the high-temperature oxidation method are relatively harsh, and the operation is inconvenient, difficult to control, and the product selectivity is poor.

In addition, the existing above-mentioned synthetic methods all adopt traditional reaction kettles (bottles) to prepare, correspondingly all have low selectivity and yield, relatively high cost, relatively violent reaction exotherm in the production process, difficult control of technological operation, and inconvenience. The disadvantages of safety, low level of equipment and self-control, inability to continuous production, and cumbersome production operations also greatly limit the promotion and use of ortho-phthalaldehyde as a new generation of high-efficiency disinfectants in many industries.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the deficiencies existing in the prior art, and to provide a method for the continuous synthesis of o-phthalaldehyde in a microchannel reaction device that adopts relatively easy-to-obtain 1,3-dihydroisobenzofuran as starting material. The synthesis method of the invention has the characteristics of mild reaction conditions, short reaction period, no need to add organic acid inhibitors in the reaction, simple post-treatment process, low energy consumption, reduced environmental pollution, high conversion rate and product purity, etc. It is beneficial to the promotion and use of phthalaldehyde in chemical and medical industries.

The technical solutions adopted to achieve the above purpose of the invention are as follows.

A method for the continuous synthesis of o-phthalaldehyde by a microchannel reaction device, comprising the following synthesis steps:

a. Build and configure a microchannel reaction device, which consists of a heat-conducting oil heating furnace, two oil bath raw material storage tanks, two filters, two plunger metering pumps, a micromixer, and a microchannel reaction device. It consists of a thermostatic oil bath, a constant temperature oil bath, a cooling tank, a product storage tank, a tail gas absorption device, and a nitrogen bottle. The micro mixer and the micro channel reactor are set in a constant temperature oil bath with a temperature control of 30 to 80 ° C. The heat source of the heat transfer oil heating furnace The output ends are respectively connected with the first oil bath raw material storage tank and the second oil bath raw material storage tank through connecting pipelines with ball valves on them, and the outlet end of the first oil bath raw material storage tank is connected to the first column through the first filter The inlet end of the plunger metering pump, the outlet end of the second oil bath raw material storage tank is connected to the inlet end of the second plunger metering pump through the second filter, the first plunger metering pump and the second plunger metering The outlet end of the pump is connected in parallel and then enters the constant temperature oil bath and then connects to the inlet end of the micro mixer. The outlet end of the micro mixer is connected to the inlet end of the cooling tank filled with tap water or salt water through the micro channel reactor, and the outlet end of the cooling tank Both the end and the outlet end of the nitrogen cylinder enter the product storage tank through a pipeline equipped with a ball valve, and the by-product tail gas outlet end of the product storage tank is connected to the exhaust gas absorption device through a pipeline equipped with a ball valve;

b. The raw materials 1,3-dihydroisobenzofuran and nitric acid are placed in two oil bath raw material storage tanks respectively, and the raw materials are preheated to 30-80 ℃ through a heat-conducting oil heating furnace;

c. Enter the preheated 1,3-dihydroisobenzofuran and nitric acid into the micro-mixer through the first plunger metering pump and the second plunger metering pump respectively according to the flow volume ratio of 1:0.5 to 4. Carry out mixing, further pass into the microchannel reactor and stay for 5-30min to carry out oxidation reaction to synthesize the o-phthalaldehyde product mixed solution, and then make it enter the product storage tank;

d. Bubble nitrogen into the product storage tank at 1-10mL/min through a nitrogen bottle through a nitrogen pipeline, and purge the generated nitrogen oxide by-product into the tail gas absorption device. The nitrogen oxide by-product is at a pH value of 1- Under the catalysis of 3% nitric acid, a redox reaction occurs with urea with a concentration of 5% to 10% to reduce it to nitrogen; to the reaction product purged with nitrogen, add twice the volume of deionized water, stir for 30min, and cool to room temperature Then, stand to separate out the water phase, extract 3 times with equal volume of ethyl acetate, combine the extracts, and recover ethyl acetate by distillation to obtain o-phthalaldehyde;

e. Place the distilled ortho-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50°C for 4 hours to obtain the ortho-phthalaldehyde product.

A further technical solution of the present invention further includes: the pipe diameter of the microchannel reactor in step a is 0.1-5 mm.

Further technical solutions of the present invention further include: the concentration of nitric acid in step b is 30%-98%, preferably 50%-69%; the raw material preheating temperature is preferably 60-80°C.

Further technical solutions of the present invention also include: the flow volume ratio of 1,3-dihydroisobenzofuran and nitric acid described in step c is preferably 1:1 to 2, and the preferred residence time of the mixed solution in the microchannel reactor is The time is 10 to 20 minutes.

To sum up, the present invention designs a method for continuously synthesizing o-phthalaldehyde by using 1,3-dihydroisobenzofuran (C ₈ H ₈ O) and nitric acid as raw materials and using a microchannel reaction device. Compared with the prior art, the process reaction of the present invention makes full use of the characteristics of the micro-channel reactor to strengthen heat transfer and mass transfer and can realize precise control, and overcomes the existing reaction of the existing batch reactor to produce o-phthalaldehyde. It takes a long time, cannot be continuously produced, has low safety performance, and needs to add a large amount of acid inhibitors in the reaction, causing large pollution and other problems. It can realize continuous production and automatic control of the process, and the production is efficient and safe. The product has high purity, high yield, low energy consumption and green economy, which is conducive to the promotion and use of ortho-phthalaldehyde in chemical and medical industries.

Description of drawings

FIG. 1 is a schematic structural diagram of a microchannel reaction device used in the present invention, and is also a schematic diagram of a reaction route of the present invention.

Figure 2 is an IR diagram of the preparation of ortho-phthalaldehyde in one embodiment of the present invention (Example 1).

Fig. 3 is a ¹ HNMR chart of the preparation of ortho-phthalaldehyde shown in Fig. 2 (Example 1).

Fig. 4 is the GC chart of the ortho-phthalaldehyde prepared as shown in Fig. 2 (Example 1).

The names of the numbers in the drawings are: 1- the first oil bath raw material storage tank, 2- ball valve, 3- the first filter, 4- the first plunger metering pump, 5- the second oil bath raw material storage tank Tank, 6-ball valve, 7-second filter, 8-first plunger metering pump, 9-heating oil heating furnace, 10-ball valve, 11-first high-temperature oil pump, 12-ball valve, 13-thermostatic oil bath , 14-micro mixer, 15-microchannel reactor, 16-cooling tank, 17-ball valve, 18-product storage tank, 19-ball valve, 20-exhaust gas absorption device, 21-ball valve, 22-nitrogen cylinder, 23- (For constant temperature oil bath) heat transfer oil heating furnace, 24-ball valve, 25-ball valve, 26-second high temperature oil pump.

Detailed ways

The content of the present invention will be further described below with reference to the accompanying drawings.

Referring to the accompanying drawings, the synthesis process steps of the present invention are as follows.

1. Construction and configuration of a microchannel reaction device. As shown in Figure 1, the microchannel reaction device consists of a heat transfer oil heating furnace 9, a first oil bath raw material storage tank 1, and a second oil bath raw material storage tank 5 connected by corresponding pipelines. , the first filter 3, the second filter 7, the first plunger metering pump 4, the second plunger metering pump 8, the micro mixer 14, the microchannel reactor 15, the constant temperature oil bath 13, the cooling tank 16 , product storage tank 18, tail gas absorption device 20, nitrogen cylinder 22, first high temperature oil pump 11, second high temperature oil pump 26 and a plurality of ball valves (2, 6, 10, 12, 17, 19) mounted on each connecting pipeline , 21, 24, 25) etc. In the specific implementation structure, the heat transfer oil heating furnace 9 has two heat source output ends, and one heat source output end is connected to the first oil bath raw material storage tank 1 through a connecting pipeline equipped with a ball valve 12, which is the first oil bath raw material storage tank. The raw material in 1 is preheated, and the output end of the other heat source is connected to the second oil bath raw material storage tank 5 through the connecting pipeline equipped with the ball valve 10 and the first high temperature oil pump, which is the raw material in the second oil bath raw material storage tank 5. Preheating; the outlet end of the first oil bath raw material storage tank 1 is connected to the inlet end of the first plunger metering pump 4 through the pipeline equipped with the ball valve 2 through the first filter 3, and the second oil bath raw material storage tank 5 The outlet end is connected to the inlet end of the second plunger metering pump 8 through the pipeline equipped with the ball valve 6 through the second filter 7, and the outlet of the first plunger metering pump 4 and the second plunger metering pump 8 After the ends are connected in parallel, they enter the constant temperature oil bath tank 13, and then connect to the inlet end of the micro-mixer 14. The outlet end of the micro-mixer 14 is connected to the inlet end of the cooling tank 16 filled with tap water or salt water through the micro-channel reactor 15. , the outlet end of the cooling tank 16 enters the product storage tank 18 through a pipeline equipped with a ball valve 17, and the by-product tail gas outlet end of the product storage tank 18 is connected to the exhaust gas absorption device 20 through a pipeline equipped with a ball valve 19. Inside. In addition, the outlet end of the nitrogen cylinder 22 also enters the product storage tank 18 through a pipeline with a ball valve 21 on it. During operation, nitrogen gas can be blown into the product storage tank 18 through the nitrogen cylinder 22 at 1-10 mL/min. Oxide by-products undergo a redox reaction with urea with a concentration of 5% to 10% under the catalysis of nitric acid with a pH value of 1 to 3 to reduce it to nitrogen. In the present invention, the diameter of the micro-channel reactor 15 is 0.1-5 mm, the micro-mixer 14 and the micro-channel reactor 15 are arranged in the constant temperature oil bath 13, immersed in heat-conducting oil, and the oil temperature is controlled at 30-80° C. The heat transfer oil heating furnace 23 used in the constant temperature oil bath 13 in 1 is communicated with the constant temperature oil bath 13 through the ball valve 24, the second high temperature oil pump 26 and the ball valve 25, and is used to control the reaction temperature of the raw materials.

2. Put the raw material 1,3-dihydroisobenzofuran and the nitric acid with a concentration of 30% to 98% (preferably a concentration of 50% to 69%) into two raw material storage tanks, respectively, and pass the heat transfer oil heating furnace The raw material is preheated to 30-80°C, preferably 60-80°C.

3. Pass the preheated 1,3-dihydroisobenzofuran and nitric acid respectively through the first plunger metering pump 4 and the second according to the flow volume ratio of 1:0.5-4 (preferably 1:1-2) The plunger-type metering pump 8 enters the micro-mixer 14 for mixing, and further passes into the micro-channel reactor 15 to stay for 5 to 30 minutes (preferably the residence time is 10 to 20 minutes) for oxidation reaction to synthesize the o-phthalaldehyde product mixture, and then It goes to the product storage tank.

4. Bubble nitrogen into the product storage tank 18 through the nitrogen gas pipeline at a rate of 1-10 mL/min, and purge the generated nitrogen oxide by-product into the tail gas absorption device 20. Under catalysis, a redox reaction occurs with urea with a concentration of 5% to 10% to reduce it to nitrogen; add twice the volume of deionized water to the reaction product after nitrogen purging, stir for 30min, cool to room temperature, The aqueous phase was separated, extracted three times with an equal volume of ethyl acetate, the extracts were combined, and the ethyl acetate was recovered by distillation to obtain o-phthalaldehyde.

5. Place the distilled ortho-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 °C for 4 hours to obtain the ortho-phthalaldehyde product.

Example 1

The raw materials 1,3-dihydroisobenzofuran and 98% nitric acid are preheated to 30°C, and the preheated 1,3-dihydroisobenzofuran and 98% nitric acid are pumped respectively according to the flow volume ratio of 1:0.5 Put into a micro-mixer for mixing, and then pass through a micro-channel reactor with a diameter of 0.3 mm, and stay at 30°C for a reaction time of 10 minutes to obtain the target product mixture of o-phthalaldehyde, and make it into the product Tank 18. Nitrogen gas is blown into the product storage tank 18 at a rate of 5 ml/min through the nitrogen cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 2 and a concentration of 5% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with an equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 ° C and dry for 4 hours to obtain o-phthalaldehyde product with a content of 95.5% and a yield of 69.7 %. The IR chart, ¹ HNMR chart and GC chart of the preparation of o-phthalaldehyde in this example are shown in Figure 2, Figure 3, and Figure 4, respectively.

Example 2

The raw material 1,3-dihydroisobenzofuran and nitric acid were preheated to 50°C. The preheated 1,3-dihydroisobenzofuran and 50% nitric acid were respectively pumped into the micro-mixer according to the flow volume ratio of 1:2 for mixing, and further passed through the micro-channel reactor, the micro-channel and the tube of the reactor. The diameter is 0.3 mm, and the reaction time is 10 min at a temperature of 50° C. to obtain a mixed solution of the o-phthalaldehyde target product, which is fed into the product storage tank 18 . Nitrogen gas is blown into the product storage tank 18 at 5 ml/min through the nitrogen gas cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 2.5 and a concentration of 10% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with an equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 ° C and dry for 4 hours to obtain o-phthalaldehyde product with a content of 96.1% and a yield of 81.6 %.

Example 3

The raw material 1,3-dihydroisobenzofuran and nitric acid were preheated to 40°C. The preheated 1,3-dihydroisobenzofuran and 60% nitric acid were respectively pumped into the micro-mixer according to the flow volume ratio of 1:1.3 for mixing, and further passed through the micro-channel reactor, the micro-channel and the tube of the reactor. The diameter is 0.5 mm, and the reaction time is kept at 40° C. for 20 minutes to obtain the o-phthalaldehyde target product mixed solution, which is fed into the product storage tank 18 . Nitrogen gas is blown into the product storage tank 18 at 3 ml/min through the nitrogen gas cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 3 and a concentration of 10% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with an equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 °C for 4 hours to obtain o-phthalaldehyde product, with a content of 96.4% and a yield of 70.4 %.

Example 4

The raw material 1,3-dihydroisobenzofuran and nitric acid were preheated to 60°C. The preheated 1,3-dihydroisobenzofuran and 68% nitric acid were respectively pumped into the micro-mixer according to the flow volume ratio of 1:1.5 for mixing, and further passed through the micro-channel reactor, the micro-channel and the tube of the reactor. The diameter is 0.5 mm, and the reaction time is kept at 60° C. for 15 minutes to obtain the o-phthalaldehyde target product mixed solution, which is fed into the product storage tank 18 . Nitrogen gas is blown into the product storage tank 18 at 10 ml/min through the nitrogen gas cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 2.5 and a concentration of 8% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 °C for 4 hours to obtain o-phthalaldehyde product, with a content of 99.2% and a yield of 88.4 %.

Example 5

The raw material 1,3-dihydroisobenzofuran and nitric acid were preheated to 80°C. The preheated 1,3-dihydroisobenzofuran and 30% nitric acid were respectively pumped into the micro-mixer according to the flow volume ratio of 1:4 for mixing, and further passed through the micro-channel reactor, the micro-channel and the tube of the reactor. The diameter is 2 mm, and the reaction time is held at 80° C. for 25 min to obtain the o-phthalaldehyde target product mixed solution, which is fed into the product storage tank 18 . Nitrogen gas is blown into the product storage tank 18 at 5 ml/min through the nitrogen gas cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 1.5 and a concentration of 10% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with an equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 ° C and dry for 4 hours to obtain o-phthalaldehyde product with a content of 99.5% and a yield of 84.7 %.

Example 6

The raw material 1,3-dihydroisobenzofuran and nitric acid were preheated to 70°C. The preheated 1,3-dihydroisobenzofuran and 40% nitric acid were respectively pumped into the micro-mixer according to the flow volume ratio of 1:3.5 for mixing, and further passed through the micro-channel reactor, the micro-channel and the reactor tube. The diameter is 2 mm, and the reaction time is 30 min at a temperature of 70° C. to obtain a mixed solution of the o-phthalaldehyde target product, which is made to enter the product storage tank 18 . Nitrogen gas is blown into the product storage tank 18 at 10 ml/min through the nitrogen gas cylinder 22 through the nitrogen pipeline, and the generated nitrogen oxide by-product is swept into the tail gas absorption device 20. Under the catalysis of nitric acid with a pH value of 3 and a concentration of 5% of urea undergoes a redox reaction, reducing it to nitrogen. After nitrogen purging, add twice the volume of deionized water to the reaction product mixture, stir for 30 min, cool to room temperature, stand to separate out the water phase, extract three times with an equal volume of ethyl acetate, combine the extracts, and recover by distillation Ethyl acetate to obtain o-phthalaldehyde; place o-phthalaldehyde in a vacuum drying oven with a vacuum degree of 50-60 Pa and a temperature of 50 ° C and dry for 4 hours to obtain o-phthalaldehyde product with a content of 97.8% and a yield of 79.3 %.

Claims (4)

1. A method for continuously synthesizing o-phthalaldehyde by a microchannel reaction device is characterized by comprising the following synthesis steps:

a. the method comprises the steps of constructing and configuring a microchannel reaction device, wherein the microchannel reaction device comprises a heat-conducting oil heating furnace (9), two oil bath raw material storage tanks (1, 5), two filters (3, 7), two plunger type metering pumps (4, 8), a micro mixer (14), a microchannel reactor (15), a constant-temperature oil bath (13), a cooling tank (16), a product storage tank (18), a tail gas absorption device (20) and a nitrogen bottle (22), wherein the micro mixer (14) and the microchannel reactor (15) are arranged in the constant-temperature oil bath (13) with the temperature controlled at 30-80 ℃, a heat source output end of the heat-conducting oil heating furnace (9) is respectively connected with a first oil bath raw material storage tank (1) and a second oil bath raw material storage tank (5) through a connecting pipeline with ball valves arranged on the heat source output end, an outlet end of the first oil bath raw material storage tank (1) is connected to an inlet end of the first plunger type metering pump (4) through the first filter, the outlet end of a second oil bath raw material storage tank (5) is connected to the inlet end of a second plunger type metering pump (8) through a second filter (7), the outlet ends of the first plunger type metering pump (4) and the second plunger type metering pump (8) are connected in parallel and then enter a constant temperature oil bath groove (13) and then are connected to the inlet end of a micro mixer (14), the outlet end of the micro mixer (14) is connected to the inlet end of a cooling groove (16) filled with tap water or saline water through a micro channel reactor (15), the outlet end of the cooling groove (16) and the outlet end of a nitrogen bottle (22) both enter a product storage tank (18) through a pipeline provided with a ball valve, and the byproduct tail gas outlet end of the product storage tank (18) is connected to a tail gas absorption device (20) through a pipeline provided with a;

b. respectively putting raw materials 1, 3-dihydroisobenzofuran and nitric acid into two oil bath raw material storage tanks (1, 5), and preheating the raw materials to 30-80 ℃ by using a heat conduction oil heating furnace (9);

c. the preheated 1, 3-dihydroisobenzofuran and nitric acid respectively enter a micro mixer (14) through a first plunger type metering pump (4) and a second plunger type metering pump (8) according to the flow volume ratio of 1: 0.5-4 for mixing, and further enter a microchannel reactor (15) for staying for 5-30 min for oxidation reaction to synthesize a phthalic dicarboxaldehyde product mixed solution, and then the phthalic dicarboxaldehyde product mixed solution enters a product storage tank (18);

d. blowing nitrogen into the product storage tank (18) through a nitrogen bottle (22) through a nitrogen pipeline at a rate of 1-10 mL/min, blowing the generated nitrogen oxide byproduct into a tail gas absorption device (20), and carrying out an oxidation-reduction reaction on the nitrogen oxide byproduct and urea with the concentration of 5-10% under the catalysis of nitric acid with the pH value of 1-3 to reduce the nitrogen oxide byproduct into nitrogen; adding deionized water with the volume twice that of the reaction product subjected to nitrogen purging, stirring for 30min, cooling to room temperature, standing to separate out a water phase, extracting for 3 times by using ethyl acetate with the same volume, combining extract liquor, and distilling to recover ethyl acetate to obtain o-phthalaldehyde;

e. and (3) drying the distilled o-phthalaldehyde in a vacuum drying oven with the vacuum degree of 50-60 Pa and the temperature of 50 ℃ for 4 hours to obtain an o-phthalaldehyde product.

2. The method for continuously synthesizing o-phthalaldehyde by using the microchannel reaction device according to claim 1, wherein the method comprises the following steps: in the step a, the pipe diameter of the microchannel reactor (15) is 0.1-5 mm.

3. The method for continuously synthesizing o-phthalaldehyde by using the microchannel reaction device according to claim 1, wherein the method comprises the following steps: in the step b, the concentration of the nitric acid is 30-98%, and the preferable concentration is 50-69%; the preheating temperature of the raw materials is preferably 60-80 ℃.

4. The method for continuously synthesizing o-phthalaldehyde by using the microchannel reaction device according to claim 1, wherein the method comprises the following steps: the flow volume ratio of the 1, 3-dihydroisobenzofuran to the nitric acid in the step c is preferably 1: 1-2, and the preferable retention time of the mixed solution in the microchannel reactor (15) is 10-20 min.

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