1. A method for synthesizing benzoic acid based on photocatalysis of a microchannel reactor is characterized by comprising the following steps: the method comprises the following steps: the method comprises the steps of mixing toluene, photocatalyst and a solvent to form a mixed solution, pumping the mixed solution into a microchannel reactor through an advection pump, pumping an oxidant into the microchannel reactor through a pump to be mixed with the mixed solution, and reacting for 5-12 hours under the illumination of a high-pressure mercury lamp.

2. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the photocatalyst is one of sodium trifluoromethanesulfonate, carbon tetrabromide, carbon tetrachloride, ammonium bromide or triethylamine.

3. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the molar ratio of the toluene to the photocatalyst is 1: 0.05-0.3.

4. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the solvent is one of acetonitrile, tetrahydrofuran, benzene, acetone or dichloromethane.

5. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the addition amount of the solvent is 2-8 times of the volume of the toluene.

6. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the oxidant is oxygen or air.

7. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the reaction temperature under the illumination of a high-pressure mercury lamp is 20-80 ℃.

8. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the wavelength of the light of the high-pressure mercury lamp is 350-450 nm.

9. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the flow rate of the oxidant is 5-18 ml/min, and the flow rate of the mixed liquid is 6-16 ml/min.

10. The photocatalytic synthesis method of benzoic acid based on microchannel reactor as claimed in claim 1, wherein: the microchannel reactor consists of a glass microchannel plate.

Background

Benzoic acid is an organic compound of the aromatic acid type widely found in nature in the form of the free acid, ester or derivative thereof. The method is mainly used for preparing the sodium benzoate preservative and synthesizing medicaments and dyes; it is also used for preparing plasticizer, mordant, bactericide, perfume, etc. Carboxylic acids are important organic compounds that are used as synthetic precursors for a variety of high value-added chemicals. In conventional oxidation processes, the synthesis of such compounds is carried out in the presence of a stoichiometric load of harmful oxidizing agents, such as dichromate/permanganate, ketonic and periodate reagents, with the presence of large amounts of heavy metal-containing waste products, which are environmentally undesirable. Therefore, it is important to develop a simple, efficient and environmentally friendly process to synthesize high value products from simple and readily available starting materials.

Photochemistry is a chemical branch subject for researching permanent chemical effects caused by interaction of light and substances, the development of photochemistry has important contribution to improvement of a synthesis process of organic compounds, organic reactions induced by visible light are important chemical conversions in organic chemistry, and free radical reactions induced by illumination are often not very high in reaction temperature and very mild in reaction conditions. The photochemical method is used for organic synthesis, so that harsh reaction conditions, toxic, harmful and explosive reagents can be avoided, and the process safety can be improved; in addition, the light energy is different from the heat energy used in the traditional organic synthesis, and the cost of the light energy is lower than that of the heat energy.

The microreactor is a microchannel reactor established on a continuous flow basis and is used for replacing traditional batch reactors such as glass flasks, funnels, and reaction kettles commonly used in industrial organic synthesis. The micro-reactor has a large number of micro-reaction channels which are manufactured by precise processing technology, and can provide extremely large specific surface area and extremely high mass and heat transfer efficiency. In addition, the microreactor operates continuously instead of intermittently, making it possible to control the residence time of the reactants accurately. These characteristics allow the organic synthesis reaction to be precisely controlled on a microscopic scale, and provide possibility for improving reaction selectivity and operation safety.

Disclosure of Invention

Aiming at the defects of the technology, the invention provides a method for synthesizing benzoic acid by photocatalysis based on a microchannel reactor, which does not need to adopt reagents with high corrosivity and toxicity, improves the cleanness of the synthesis process, and has the advantages of low cost, simple operation, mild reaction conditions and high reaction efficiency.

In order to achieve the purpose, the invention designs a method for synthesizing benzoic acid by photocatalysis based on a microchannel reactor, which comprises the following steps: the method comprises the steps of mixing toluene, photocatalyst and a solvent to form a mixed solution, pumping the mixed solution into a microchannel reactor through an advection pump, pumping an oxidant into the microchannel reactor through a pump to be mixed with the mixed solution, and reacting for 5-12 hours under the illumination of a high-pressure mercury lamp.

Preferably, the photocatalyst is one of sodium trifluoromethanesulfonate, carbon tetrabromide, carbon tetrachloride, ammonium bromide or triethylamine

Preferably, the molar ratio of the toluene to the photocatalyst is 1: 0.05-0.3.

Preferably, the solvent is one of acetonitrile, tetrahydrofuran, benzene, acetone or dichloromethane.

Preferably, the addition amount of the solvent is 2-8 times of the volume of the toluene.

Preferably, the oxidant is oxygen or air.

Preferably, the reaction temperature under the illumination of a high-pressure mercury lamp is 20-80 ℃.

Preferably, the wavelength of the lamp light of the high-pressure mercury lamp is 350-450 nm.

Preferably, the flow rate of the oxidant is 5-18 ml/min, and the flow rate of the mixed liquid is 6-16 ml/min.

Preferably, the microchannel reactor consists of a glass microchannel plate.

Compared with the prior art, the invention has the following advantages:

1. high-toxicity and high-corrosivity reagents in the traditional synthetic method are avoided, and the cleanness and the safety of the reaction process are improved;

2. oxygen is used as an oxidant, the reagent is cheap and environment-friendly, and the atom economy is high;

3. the microchannel reactor is used as a reaction device, so that the mixing and illumination efficiency of raw materials can be enhanced, and the reaction efficiency is improved;

4. the reaction condition is mild, the light source is used for replacing a heat source, the energy is saved, and the cost is reduced.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

Example 1

Toluene and sodium trifluoromethanesulfonate are mixed according to a molar ratio of 1:0.1, then acetonitrile with the volume being 3 times that of toluene is added and fully mixed to form a mixed solution, an advection pump is used for pumping the mixed solution into a microchannel reactor at the flow rate of 12ml/min, an oxygen pump is used for pumping oxygen into the microchannel reactor at the flow rate of 5ml/min to be mixed with the mixed solution, the oxygen and the mixed solution react for 10 hours in the microchannel reactor under the irradiation of a high-pressure mercury lamp with the temperature of 250W and 365nm at the temperature of 40 ℃, after the reaction is finished, a sample is taken, the product composition is analyzed by gas chromatography, and the calculated yield is 95.8%.

Example 2

Mixing toluene and sodium trifluoromethanesulfonate according to a molar ratio of 1:0.12, adding tetrahydrofuran with the volume 4 times that of the toluene, fully mixing to form a mixed solution, pumping the mixed solution into a microchannel reactor at a flow rate of 6ml/min by using an advection pump, pumping oxygen into the microchannel reactor at a flow rate of 7ml/min by using an oxygen pump to mix with the mixed solution, reacting the oxygen and the mixed solution in the microchannel reactor at the irradiation of a high-pressure mercury lamp with the wavelength of 250W and 400nm at the temperature of 20 ℃ for 5 hours, sampling after the reaction is finished, analyzing the composition of a product by using gas chromatography, and obtaining the yield of 89.9% by calculation.

Example 3

Mixing toluene and carbon tetrabromide according to a molar ratio of 1:0.05, then adding acetone with 2 times of toluene volume to fully mix to form a mixed solution, pumping the mixed solution into a microchannel reactor at a flow rate of 8ml/min by using an advection pump, pumping oxygen into the microchannel reactor at a flow rate of 14ml/min by using an oxygen pump to mix with the mixed solution, reacting the oxygen and the mixed solution in the microchannel reactor under the irradiation of a high-pressure mercury lamp with the temperature of 250W and 350nm at 40 ℃ for 8 hours, sampling after the reaction is finished, analyzing the composition of a product by using gas chromatography, and obtaining the calculated yield of 87.2%.

Example 4

Toluene and triethylamine are mixed according to a molar ratio of 1:0.3, dichloromethane with 5 times of toluene volume is added to be fully mixed to form mixed liquid, an advection pump is used for pumping the mixed liquid into a microchannel reactor at a flow rate of 9ml/min, an oxygen pump is used for pumping oxygen into the microchannel reactor at a flow rate of 18ml/min to be mixed with the mixed liquid, the oxygen and the mixed liquid react for 9 hours in the microchannel reactor under the irradiation of a high-pressure mercury lamp with the wavelength of 250W and 365nm at 70 ℃, after the reaction is finished, sampling is carried out, the composition of a product is analyzed by gas chromatography, and the calculated yield is 97.5%.

Example 5

Toluene and carbon tetrachloride are mixed according to a molar ratio of 1:0.09, then tetrahydrofuran with 6 times of the volume of toluene is added and fully mixed to form a mixed solution, an advection pump is used for pumping the mixed solution into a microchannel reactor at a flow rate of 16ml/min, an oxygen pump is used for pumping oxygen into the microchannel reactor at a flow rate of 12ml/min to be mixed with the mixed solution, the oxygen and the mixed solution react for 12 hours in the microchannel reactor under the irradiation of a high-pressure mercury lamp with the temperature of 45 ℃ and the wavelength of 250W and 450nm, after the reaction is finished, sampling is carried out, the composition of a product is analyzed by gas chromatography, and the calculated yield is 89.7%.

Example 6

Toluene and ammonium bromide are mixed according to a molar ratio of 1:0.13, then benzene with 8 times of toluene volume is added and fully mixed to form a mixed solution, an advection pump is used for pumping the mixed solution into a microchannel reactor at a flow rate of 14ml/min, an oxygen pump is used for pumping air into the microchannel reactor at a flow rate of 9ml/min to be mixed with the mixed solution, oxygen and the mixed solution react for 7 hours in the microchannel reactor under the irradiation of a high-pressure mercury lamp with the temperature of 80 ℃ of 250W and 420nm, after the reaction is finished, sampling is carried out, the composition of a product is analyzed by gas chromatography, and the calculated yield is 84.6%.

In the above embodiments, the microchannel reactor is composed of a glass microchannel plate.

The method for synthesizing the benzoic acid based on the photocatalysis of the microchannel reactor avoids high-toxicity and high-corrosivity reagents in the traditional synthesis method, and improves the cleanness and the safety of the reaction process; oxygen is used as an oxidant, the reagent is cheap and environment-friendly, and the atom economy is high; the microchannel reactor is used as a reaction device, so that the mixing and illumination efficiency of raw materials can be enhanced, and the reaction efficiency is improved; the reaction condition is mild, the light source is used for replacing a heat source, the energy is saved, and the cost is reduced.