Method for carrying out photocatalytic chlorination reaction by using carbon nitride microspheres in micro-channel reactor

Abstract

The invention discloses a method for synthesizing 2-chloro-1, 3, 5-trimethoxybenzene by photocatalytic chlorination of carbon nitride microspheres in a microchannel reactor, and belongs to the technical field of chemical synthesis. The method comprises the following steps: adhering high-crystallinity carbon nitride to the surfaces of glass beads by using a binder to prepare carbon nitride microspheres, filling the carbon nitride microspheres into a micro-channel reactor as a photocatalyst, taking 1, 3, 5-trimethoxybenzene as a raw material, taking a hydrochloric acid solution as a chlorine source, and carrying out photocatalytic chlorination reaction in the micro-channel reactor to synthesize 2-chloro-1, 3, 5-trimethoxybenzene. According to the present invention, the method has characteristics of simple operation, low cost and low environmental pollution, can achieve the conversion rate of 95% and the selectivity of 97%, can achieve the gram-level preparation of the product, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for synthesizing 2-chloro-1,3,5-trimethoxybenzene by using carbon nitride microspheres for photocatalytic chlorination in a microchannel reactor. Background Art

[0002] Aromatic chlorides have important application value in the fields of organic synthesis, natural products and materials, because the introduction of chlorine atoms can regulate the physicochemical properties of substances, improve pharmacokinetics and pharmacological properties, etc. 2-Chloro-1,3,5-trimethoxybenzene is a key organic synthesis intermediate. It is the raw material for the synthesis of Bulllomedil, a new drug for the treatment of peripheral vascular dysfunction and dilation. 2-Chloro-1,3,5-trimethoxybenzene can be synthesized by a variety of methods, including direct chlorination, electrophilic substitution and free radical substitution. Among them, under the action of light and catalyst, highly active chlorine radicals and aromatic radical cations can be formed to generate chloroaromatic hydrocarbons. This method does not require the use of free radical initiators, which can not only reduce economic costs, but also simplify the separation and purification process of the product.

[0003] Polymer carbon nitride includes bulk carbon nitride and highly crystalline carbon nitride. As a heterogeneous photocatalyst, it has attracted extensive attention in the field of photocatalytic drug synthesis due to its advantages such as low cost, non-toxicity, stability, adjustable structure, convenient recycling and simplified product post-processing process. Although there are some reports on the photocatalytic synthesis of 2-chloro-1,3,5-trimethoxybenzene using polymer carbon nitride, most of them use powder catalysts and are only at the milligram level, making it difficult to scale up the reaction.

[0004] In the field of photocatalysis, microchannel reactors have advantages such as high light energy utilization and good mass transfer efficiency, but they are mainly suitable for liquid-gas reactions. Therefore, the traditional polymer carbon nitride photocatalytic reaction using solid powder is difficult to be amplified using a microchannel reactor. In the gas-liquid solid phase microchannel photoreactor, the fixed microchannel photoreactor can effectively avoid problems such as solid blockage, but maintaining the activity and stability of the immobilized catalyst is the key to its smooth operation. In order to solve this problem, patent CN 110124720A provides a method for connecting carbon nitride to glass beads using silane under high temperature conditions, but since it is a monomer that is polymerized at high temperature and connected to glass beads, it is only suitable for the loading of bulk carbon nitride, and high-crystalline carbon nitride is made again by high-temperature salt dissolution method on the basis of bulk carbon nitride, so that it has a more regular crystal structure, which makes the method of linking carbon nitride to glass beads through silane unsuitable for the loading of high-crystalline carbon nitride. Summary of the invention

[0005] The present invention aims at the problems faced by the existing photocatalytic chlorination reaction in the process of scale-up, and proposes a method for synthesizing 2-chloro-1,3,5-trimethoxybenzene by photocatalytic chlorination of carbon nitride microspheres in a microchannel reactor. On the basis of using a microchannel reactor, carbon nitride microspheres with high activity and stability are constructed, and the microspheres are applied to the photocatalytic chlorination reaction of 1,3,5-trimethoxybenzene, thereby realizing the gram-level preparation of 2-chloro-1,3,5-trimethoxybenzene. The present invention is simple to operate, low in cost, and has little environmental pollution, and has broad application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solution: A method for synthesizing 2-chloro-1,3,5-trimethoxybenzene by photocatalytic chlorination using carbon nitride microspheres in a microchannel reactor, wherein 1,3,5-trimethoxybenzene is dissolved in an organic solvent, and a hydrochloric acid solution is used as a chlorine source, and the mixture is continuously introduced into a microchannel reactor, and the carbon nitride microspheres are used for photocatalytic chlorination, thereby obtaining 2-chloro-1,3,5-trimethoxybenzene; the reaction formula is as follows: .

[0007] The method specifically comprises the following steps: 1) Preparation of carbon nitride microspheres: The binder and N,N-dimethylacetamide are stirred and mixed to obtain a binder slurry, and then high-crystallinity carbon nitride is added and stirred and mixed, and then glass beads are added and stirred and mixed, and then dried to obtain carbon nitride microspheres; 2) Loading of carbon nitride microspheres: loading the prepared carbon nitride microspheres into a gas-liquid-solid phase microchannel photoreactor; 3) Photooxidative chlorination reaction: 1,3,5-trimethoxybenzene is mixed with hydrochloric acid solution and organic solvent, and then the resulting mixed solution is sent into a gas-liquid-solid phase microchannel photoreactor, where carbon nitride microspheres loaded therein are used as photocatalysts to carry out photocatalytic chlorination reaction to generate 2-chloro-1,3,5-trimethoxybenzene.

[0008] Furthermore, the binder in step 1) is one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, acidic silica sol, etc.

[0009] Furthermore, the mass ratio of the binder used in step 1) to N,N-dimethylacetamide is 1:(8-10).

[0010] Furthermore, the mass ratio of the high-crystallinity carbon nitride to the binder slurry used in step 1) is 1:(1-3).

[0011] Furthermore, the particle size of the glass beads used in step 1) is 1.0 mm-2.5 mm.

[0012] Furthermore, in step 1), the amount of glass beads added is 8-20 times the mass of the high-crystallinity carbon nitride.

[0013] The present invention uses glass beads as carriers, which can increase the solid loading of the catalyst by utilizing their large surface area, and can reduce economic costs by being cheap and readily available. By bonding the catalyst to the surface of the glass beads, the clogging problem caused by particle size differences during long-term reactions can be effectively solved, and the catalyst recovery process can be simplified.

[0014] Furthermore, the drying temperature in step 1) is 55°C-60°C, and the drying time is 5h-8h.

[0015] Furthermore, the mass concentration of the hydrochloric acid solution in step 3) is 36%.

[0016] Furthermore, the organic solvent in step 3) is one or more of ethanol, acetonitrile, dichloromethane and ethyl acetate.

[0017] Furthermore, in step 3), the molar ratio of 1,3,5-trimethoxybenzene in the mixed solution to the hydrochloric acid and organic solvent in the hydrochloric acid solution is 1:(5-8):(6-18).

[0018] Furthermore, in step 3), the flow rate of the mixed solution is 5 mL / min-20 mL / min.

[0019] Furthermore, the photocatalytic chlorination reaction in step 3) is carried out for 24-48 hours under the conditions of a light source wavelength of 365 nm-465 nm and an ambient temperature of 0°C.

[0020] The present invention has the following beneficial effects: (1) The present invention provides a method for photocatalytically synthesizing 2-chloro-1,3,5-trimethoxybenzene using carbon nitride microspheres in a microchannel reactor. The method uses a new type of supported carbon nitride microspheres as a catalyst to carry out a photocatalytic chlorination reaction in a microchannel reactor, and successfully synthesizes 2-chloro-1,3,5-trimethoxybenzene.

[0021] (2) Compared with the traditional method, the present invention fixes the catalyst on the glass bead carrier by a binder. The catalyst does not need to be recovered. After the reaction is completed, only new reaction liquid needs to be replaced to continue the reaction. This can not only extend the service life of the catalyst, but also realize the effective recycling of the catalyst, thereby reducing the process cost.

[0022] (3) The present invention can effectively promote the photocatalytic oxidation and chlorination reaction of 1,3,5-trimethoxybenzene by combining with a microchannel reactor, and realize gram-scale preparation. Experimental results show that the raw material conversion rate of this method can reach more than 95%, the selectivity can reach 97%, and the catalyst can be used continuously for up to 9 days in a strong acidic environment without falling off.

[0023] (4) The method of the present invention is easy to operate, low in cost, and has little environmental pollution, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD patterns of the MCN prepared in Example 1 and the carbon nitride microspheres prepared in Example 2.

[0025] Figure 2 This is a scanning electron microscope image of the carbon nitride microspheres prepared in Example 2.

[0026] Figure 3 This is a sample picture of the carbon nitride microsphere catalytic module prepared in Application Example 1.

[0027] Figure 4 This is a schematic diagram of the device connection for photocatalytic synthesis of 2-chloro-1,3,5-trimethoxybenzene using carbon nitride microspheres based on a microchannel reactor in Example 1.

[0028] Figure 5 This is the gas chromatography analysis spectrum of the effluent collected after the reaction in Application Example 1. DETAILED DESCRIPTION

[0029] A method for synthesizing 2-chloro-1,3,5-trimethoxybenzene by photocatalytic chlorination using carbon nitride microspheres in a microchannel reactor, comprising the following steps: 1) Preparation of carbon nitride microspheres: The binder and N,N-dimethylacetamide are stirred and mixed at a mass ratio of 1:(8-10), and then high-crystalline carbon nitride is added at a mass ratio of high-crystalline carbon nitride to binder slurry of 1:(1-3), stirred and mixed, and then glass beads (particle size 1.0mm-2.5mm) 8-20 times the mass of high-crystalline carbon nitride are added, stirred evenly, and then dried at 55℃-60℃ for 5h-8h to obtain carbon nitride microspheres; 2) Loading of carbon nitride microspheres: The prepared carbon nitride microspheres are loaded into a fluorinated ethylene propylene copolymer tube (FEP tube) to obtain a carbon nitride microsphere catalytic module, which is then loaded into a gas-liquid-solid phase microchannel photoreactor; 3) Photooxidative chlorination reaction: Mix 1,3,5-trimethoxybenzene with 36wt% hydrochloric acid solution and organic solvent in a molar ratio of 1:(5-8):(6-18), and then send the resulting mixture into a gas-liquid-solid phase microchannel photoreactor at a flow rate of 5 mL / min-20 mL / min. Perform photocatalytic chlorination reaction at 365 nm-465 nm and 0°C for 24-48 hours to obtain 2-chloro-1,3,5-trimethoxybenzene.

[0030] Wherein, the binder in step 1) is one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, acidic silica sol, etc.

[0031] The organic solvent in step 3) is one or more of ethanol, acetonitrile, dichloromethane and ethyl acetate.

[0032] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0033] The gas-liquid-solid three-phase microreactor used in the embodiment is composed of a carbon nitride microsphere catalytic module, a cold bath, a light source, a light source condensing device, a bubbler, an oxygen cylinder, and a peristaltic pump.

[0034] Example 1 The preparation of high crystallinity carbon nitride (MCN) is carried out in the following specific steps: 1) 10 g of melamine was placed in a crucible and placed in a muffle furnace. The temperature was raised to 550°C over 4 hours with an initial temperature of 30°C. The crucible was kept at 550°C for 4 hours and then cooled naturally to obtain bulk carbon nitride (BCN).

[0035] 2) 600.0 mg of the prepared BCN, 3.3 g of potassium chloride and 2.7 g of lithium chloride were added to a mortar, ground for 15 minutes, added to a corundum boat, and placed in a tubular furnace in a nitrogen atmosphere. The initial temperature was 30°C, and the temperature was raised for 4 hours to 550°C. After keeping the temperature at 550°C for 4 hours, it was allowed to cool naturally to obtain high crystalline carbon nitride (MCN).

[0036] Example 2 The specific steps for preparing carbon nitride microspheres are as follows: 1) Add 5 g of polyvinylidene fluoride (PVDF) and 45 g of N,N-dimethylacetamide into a 100 mL beaker, stir for 12 hours at room temperature and then stand for 12 hours to prepare a 10 wt% PVDF binder; 2) 600 mg of the PVDF binder prepared in step 1) and 300 mg of the MCN prepared in Example 1 were added to a 50 mL centrifuge tube and stirred to prepare an MCN-PVDF slurry; 3) The MCN-PVDF slurry obtained in step 2) was mixed evenly with 5.0 g of glass beads with a particle size of 2.5 mm, and then spread on a surface dish with a diameter of 10.0 cm, and dried in a 60.0° C. forced air drying oven for 6.0 hours to obtain carbon nitride microspheres.

[0037] Example 3 The specific steps for preparing carbon nitride microspheres are as follows: 1) Add 5 g of polyvinylidene fluoride (PVDF) and 45 g of N,N-dimethylacetamide into a 100 mL beaker, stir for 12 hours at room temperature and then stand for 12 hours to prepare a 10 wt% PVDF binder; 2) 600 mg of the PVDF binder prepared in step 1) and 300 mg of the MCN prepared in Example 1 were added to a 50 mL centrifuge tube and stirred to prepare an MCN-PVDF slurry; 3) The MCN-PVDF slurry obtained in step 2) was mixed evenly with 5.0 g of glass beads with a particle size of 2.0 mm, and then spread on a surface dish with a diameter of 10.0 cm, and dried in a 60.0° C. forced air drying oven for 6.0 hours to obtain carbon nitride microspheres.

[0038] Example 4 The specific steps for preparing carbon nitride microspheres are as follows: 1) Add 5 g of polyvinylidene fluoride (PVDF) and 45 g of N,N-dimethylacetamide into a 100 mL beaker, stir for 12 hours at room temperature and then stand for 12 hours to prepare a 10 wt% PVDF binder; 2) 600 mg of the PVDF binder prepared in step 1) and 300 mg of the MCN prepared in Example 1 were added to a 50 mL centrifuge tube and stirred to prepare an MCN-PVDF slurry; 3) The MCN-PVDF slurry obtained in step 2) was mixed evenly with 5.0 g of glass beads with a particle size of 1.0 mm, and then spread on a surface dish with a diameter of 10.0 cm, and dried in a 60.0° C. forced air drying oven for 6.0 hours to obtain carbon nitride microspheres.

[0039] Application Example 1 The specific steps of the catalytic synthesis of 2-chloro-1,3,5-trimethoxybenzene and the cycle experiment using carbon nitride microspheres in a microchannel photoreactor are as follows: 1) Filling the carbon nitride microspheres prepared in Example 2 into a 60 cm long FEP tube to prepare a carbon nitride microsphere catalytic module; 2) connecting the carbon nitride microsphere catalytic module prepared in step 1) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microchannel photoreactor; 3) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 4) Turn on the light source and peristaltic pump, keep the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the carbon nitride microsphere catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis; 5) A new batch of reaction solution was replaced every 36 hours of reaction, and the total reaction time was 216 hours.

[0040] The results showed that the raw material conversion rate was 95.0%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 97.9%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 2.7%. The conversion rate and selectivity of each batch of reaction liquid remained basically stable.

[0041] Application Example 2 Carbon nitride microspheres catalyze the synthesis of 2-chloro-1,3,5-trimethoxybenzene in a microchannel photoreactor, and the specific steps are as follows: 1) Filling the carbon nitride microspheres prepared in Example 3 into a 60 cm long FEP tube to prepare a carbon nitride microsphere catalytic module; 2) connecting the carbon nitride microsphere catalytic module prepared in step 1) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microchannel photoreactor; 3) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 4) Turn on the light source and peristaltic pump, keep the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the carbon nitride microsphere catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis.

[0042] The results showed that the raw material conversion rate was 76.6%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 98.3%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 1.7%.

[0043] Application Example 3 Carbon nitride microspheres catalyze the synthesis of 2-chloro-1,3,5-trimethoxybenzene in a microchannel photoreactor, and the specific steps are as follows: 1) Filling the carbon nitride microspheres prepared in Example 4 into a 60 cm long FEP tube to prepare a carbon nitride microsphere catalytic module; 2) connecting the carbon nitride microsphere catalytic module prepared in step 1) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microchannel photoreactor; 3) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 4) Turn on the light source and peristaltic pump, keep the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the carbon nitride microsphere catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis.

[0044] The results showed that the raw material conversion rate was 20.6%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 98.1%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 1.9%.

[0045] Comparative Example 1 The specific steps of synthesizing 2-chloro-1,3,5-trimethoxybenzene by the kettle method are as follows: 1) Take 2.0 mg of MCN prepared in Example 1, 20.0 mg of 1,3,5-trimethoxybenzene, 0.1 mL of 36 wt% hydrochloric acid solution, and 2.5 mL of acetonitrile solvent, and add them into a 10 mL Shrek tube.

[0046] 2) Place the Shrek tube in step 1) in liquid nitrogen, freeze it, evacuate the air in the tube, fill the tube with high-purity oxygen, and then illuminate it at a light source with a wavelength of 420 nm at room temperature for 12 hours before performing gas chromatography (GC) analysis.

[0047] The results showed that the raw material conversion rate was 93%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 86.6%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 6.8%.

[0048] Comparative Example 2 Bulk carbon nitride microspheres catalyze the synthesis of 2-chloro-1,3,5-trimethoxybenzene in a microchannel photoreactor, and the specific steps are as follows: 1) The BCN prepared in Example 1 is prepared into bulk carbon nitride microspheres in the same manner as in Example 3; 2) Filling the prepared carbon nitride microspheres into a 60 cm long FEP tube to prepare a bulk carbon nitride microsphere catalytic module; 3) connecting the bulk carbon nitride microsphere catalytic module prepared in step 2) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microreactor; 4) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 5) Turn on the light source and peristaltic pump, keep the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the bulk carbon nitride microsphere catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis.

[0049] The results showed that the raw material conversion rate was 24.6%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 99.3%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 0.3%.

[0050] Comparative Example 3 Photocatalyst potassium polyheptazine imide (K-PHI) was used to catalyze the synthesis of 2-chloro-1,3,5-trimethoxybenzene in a microchannel photoreactor. The specific steps are as follows: 1) 1.2 g of 5-amino-1-methyltetrazole, 2.7 g of lithium chloride and 3.3 g of potassium chloride were taken, ground in a mortar for 15 minutes and then added to a corundum boat; the boat was placed in a tubular furnace in a nitrogen atmosphere, and the temperature was raised to 550°C for 4 hours at an initial temperature of 30°C, and then kept at 550°C for 4 hours and allowed to cool naturally to obtain a photocatalyst K-PHI; 2) The prepared K-PHI was prepared into microspheres in the same manner as in Example 3, and then filled into a 60 cm long FEP tube to prepare a catalytic module; 3) connecting the catalytic module prepared in step 2) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microchannel photoreactor; 4) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 5) Turn on the light source and peristaltic pump, maintain the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis.

[0051] The results showed that the raw material conversion rate was 55.6%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 98.5%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 1.5%.

[0052] Comparative Example 4 Photocatalyst oxygen-doped polymer carbon nitride (CN-OA) was used to catalyze the synthesis of 2-chloro-1,3,5-trimethoxybenzene in a microchannel photoreactor. The specific steps are as follows: 1) Take 1.0g urea and 1.0g oxalic acid, grind them in a mortar for 15 minutes, and then add them into a corundum boat; place it in a muffle furnace with air atmosphere, take 30℃ as the initial temperature, heat it to 550℃ at a rate of 120℃ / h, and keep it at 550℃ for 3 hours and let it cool down naturally to prepare the photocatalyst CN-OA; 2) The prepared CN-OA was prepared into microspheres in the same manner as in Example 3, and then filled into a 60 cm long FEP tube to prepare a catalytic module; 3) connecting the catalytic module prepared in step 2) with a premixer, a cold bath, a light source, a bubbler, an oxygen cylinder, a gas-liquid mixer, and a peristaltic pump to form a gas-liquid-solid phase microchannel photoreactor; 4) Add 1.345 g of 1,3,5-trimethoxybenzene, 4.0 mL of 36.0 wt% hydrochloric acid solution, and 50 mL of acetonitrile to the premixer and stir to mix; 5) Turn on the light source and peristaltic pump, maintain the cold bath at 0°C, and allow the mixed reaction solution in step 3) to flow through the catalytic module at a flow rate of 10 mL / min. After 36 hours of reaction, collect the effluent for GC analysis.

[0053] The results showed that the raw material conversion rate was 24.4%, the selectivity of 2-chloro-1,3,5-trimethoxybenzene was 98.4%, and the selectivity of 2,4-dichloro-1,3,5-trimethoxybenzene was 1.6%.

[0054] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for synthesizing 2-chloro-1,3,5-trimethoxybenzene by photocatalytic chlorination of carbon nitride microspheres in a microchannel reactor, characterized in that: The following steps are involved: 1) Preparation of carbon nitride microspheres: The binder and N,N-dimethylacetamide are stirred and mixed to obtain a binder slurry, and then high-crystallinity carbon nitride is added and stirred and mixed, and then glass beads are added and stirred and mixed, and then dried to obtain carbon nitride microspheres; 2) Loading of carbon nitride microspheres: loading the prepared carbon nitride microspheres into a gas-liquid-solid phase microchannel photoreactor; 3) Photooxidative chlorination reaction: 1,3,5-trimethoxybenzene is mixed with hydrochloric acid solution and organic solvent, and then the resulting mixed solution is sent into a gas-liquid-solid phase microchannel photoreactor, and the carbon nitride microspheres loaded therein are used as photocatalysts to carry out photocatalytic chlorination reaction to generate 2-chloro-1,3,5-trimethoxybenzene.

2. The method according to claim 1, characterized in that: The binder in step 1) is one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, and acidic silica sol.

3. The method according to claim 1, characterized in that The mass ratio of the binder used in step 1) to N,N-dimethylacetamide is 1:(8-10).

4. The method according to claim 1, characterized in that: The mass ratio of the high crystallinity carbon nitride to the binder slurry used in step 1) is 1:(1-3).

5. The method according to claim 1, characterized in that In step 1), the amount of glass beads added is 8-20 times the mass of high-crystallinity carbon nitride.

6. The method according to claim 1, characterized in that The mass concentration of the hydrochloric acid solution in step 3) is 36%.

7. The method according to claim 1, characterized in that The organic solvent in step 3) is one or more of ethanol, acetonitrile, dichloromethane and ethyl acetate.

8. The method according to claim 1, characterized in that Step 3) The molar ratio of 1,3,5-trimethoxybenzene to hydrochloric acid and organic solvent in the mixed solution is 1:(5-8):(6-18).

9. The method according to claim 1, characterized in that: The flow rate of the mixed solution in step 3) is 5 mL / min-20 mL / min.

10. The method according to claim 1, characterized in that The photocatalytic chlorination reaction in step 3) is carried out for 24-48 hours under the conditions of a light source wavelength of 365 nm-465 nm and an ambient temperature of 0°C.

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