A process for the preparation of 2,5-dimethylfuran

Abstract

The application belongs to the technical field of chemical synthesis, and particularly relates to a method for preparing 2,5-dimethylfuran. 2,5-dimethylfuran is synthesized from 2,5-hexanedione under the catalysis of tungsten diselenide. The preparation method provided by the application has the advantages of simple process, mild reaction condition, shortened reaction time, improved reaction conversion rate and yield, and high reaction continuity which is conducive to continuous and uninterrupted scale-up production. The raw material conversion rate of the application can reach 100%, and the product yield can be up to 99%. The catalyst tungsten diselenide used in the application still has good catalytic effect after multiple cycles, has high reaction selectivity and is easy to control, is convenient for synthesis, and is suitable for mass production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical synthesis, and particularly relates to a method for preparing 2,5-dimethylfuran. BACKGROUND

[0002] With the rapid development of agricultural economy, the yield of agricultural products is rapidly increasing, and solid waste represented by straw is also increasing. A new technology and industry that is clean and environmentally friendly and can increase farmers' income is urgently needed to make good use of these solid waste such as straw and to create good economic, social and ecological benefits. At present, China has the resource conditions, technical conditions and institutional conditions to develop the biomass energy industry. China has great potential to develop the biomass energy industry, especially the straw raw material biomass energy industry. The cellulose from straw and other crops is low in cost and large in quantity. 2,5-dimethylfuran (DMF) is a new type of liquid biomass fuel that can replace fossil energy and is an intermediate obtained from cellulose. It is of great significance to alleviate the current energy crisis. In view of its excellent properties and broad application prospects, the preparation of DMF from biomass resources through green and economical methods has gradually become a hot spot of scientific research.

[0003] In recent years, some progress has been made in the preparation of DMF using solid catalysts. Some documents report that an ultrathin MoS2 layer doped with a single atom of Ir is used to catalyze 5-hydroxymethylfurfural (HMF) to generate DMF through hydrogenolysis and then remove two oxygen atoms. However, the preparation process of the catalyst is complex and expensive, which is not conducive to large-scale production. The Paal-Knorr synthesis method refers to a classical method for synthesizing five-membered heterocyclic compounds such as furan, pyrrole or thiophene using 1,4-dicarbonyl compounds as raw materials. First, the raw material reacts with a nucleophile to form an imine intermediate, and then the intermediate undergoes intramolecular cyclization under the action of a catalyst to form a five-membered heterocycle. The reaction yield is moderate, but the cyclization usually requires refluxing in an acid solution for a long time, which is a relatively harsh condition and is not suitable for substrates containing acid-sensitive functional groups. In addition, there are problems in controlling the side reactions during the cyclization reaction, and the inevitable by-products generated bring about complicated post-treatment operations. Ashraful Azam et al. studied the catalytic properties and applications of tungsten diselenide (WSe2), in which it is mentioned that the thermal conductivity of the metal material tungsten diselenide is low, that is, the heat in the system is not easy to dissipate. Single-layer WSe2 has attracted widespread attention due to its potential applications as an electrocatalyst and photocatalyst, especially in the catalytic hydrogen evolution reaction (HER). This is due to its low cost, unique electronic band structure, large number of active catalytic sites, and electronic and surface adsorption properties, which can be further manipulated by introducing vacancies and dopants on the basal plane. The present application provides a method for preparing 2,5-dimethylfuran. SUMMARY

[0004] The technical problem solved by the present application is to provide a method for preparing 2,5-dimethylfuran.

[0005] To solve the above technical problem, the technical scheme adopted by the present application is as follows:

[0006] The present application discloses a method for preparing 2,5-dimethylfuran, in which 2,5-hexanedione is catalytically synthesized into 2,5-dimethylfuran under the catalysis of tungsten diselenide.

[0007] In some embodiments, the molar ratio of 2,5-hexanedione to tungsten diselenide is 6-10:1; and the catalysis is carried out at 95-150℃.

[0008] In some embodiments, preferably, the molar ratio of 2,5-hexanedione to tungsten diselenide is 7-8:1, and more preferably 8:1; and the catalysis is carried out at 120-150℃, and more preferably at 150℃.

[0009] In some embodiments, the morphology of the tungsten diselenide is any one of nanosheet, nanoparticle, or nanowire, and is preferably nanosheet or nanoparticle; when the morphology of the tungsten diselenide is nanosheet, the thickness of the nanosheet is 3-20 nm; and when the morphology of the tungsten diselenide is nanoparticle, the particle size of the nanoparticle is 30-70 nm.

[0010] In some embodiments, the 2,5-dimethylfuran is synthesized by using a conventional reactor or a micro-channel reaction device.

[0011] In some embodiments, preferably, the 2,5-dimethylfuran is synthesized by using a micro-channel reaction device, comprising the following steps:

[0012] 2,5-hexanedione is dissolved in a first solvent to obtain a reaction liquid; the reaction liquid is pumped into a micro-channel reactor of a micro-channel reaction device to carry out catalytic reaction, thereby obtaining 2,5-dimethylfuran;

[0013] In some embodiments, the micro-channel reactor is loaded with tungsten diselenide.

[0014] In some embodiments, the first solvent is any one or a combination of toluene, ethyl acetate, dichloromethane, and dimethyl sulfoxide; and the concentration of 2,5-hexanedione in the reaction liquid is 0.01-0.06 g / mL.

[0015] In some embodiments, preferably, the first solvent is toluene; and the concentration of 2,5-hexanedione in the reaction liquid is 0.03-0.05 g / mL, and more preferably 0.03 g / mL.

[0016] In some embodiments, the flow rate of the reaction solution pumped into the microchannel reactor of the microchannel reaction device is 0.036-0.16 mL / min; the catalytic reaction is carried out at a temperature of 95-150°C, and the residence time of the reaction is 10 min-45 min.

[0017] In some embodiments, preferably, the flow rate of the reaction solution pumped into the microchannel reactor of the microchannel reaction device is 0.036-0.16 mL / min; the catalytic reaction is carried out at a temperature of 120-150°C, and the residence time of the reaction is 10 min-45 min, and further preferably, the reaction temperature is 150°C.

[0018] In some embodiments, the molar ratio of 2,5-hexanedione in the reaction solution to the tungsten diselenide loaded in the microchannel reactor is 6-10:1.

[0019] In some embodiments, the molar ratio of 2,5-hexanedione in the reaction solution to the tungsten diselenide loaded in the microchannel reactor is 7-8:1, and further preferably 8:1.

[0020] In some embodiments, the reaction solution is all pumped into the microchannel reactor of the microchannel reaction device, and after the catalytic reaction is completed, the tungsten diselenide in the microchannel reactor is taken out and recovered, washed with ethanol for several times, and then placed in a vacuum drying box for drying for 12 h before being used for the next cycle of reaction, and the microchannel reactor is reloaded with a catalytic amount of tungsten diselenide.

[0021] In some embodiments, the microchannel reaction device comprises a syringe pump, a microchannel reactor, and a receiver; wherein the injection head of the syringe pump is connected to the inlet end of the microchannel reactor through a Luer adapter; and the outlet end of the microchannel reactor is provided with a receiver.

[0022] In some embodiments, the microchannel reactor is a tubular microchannel reactor, and the inner diameter of the pipe is 0.5-1.0 mm.

[0023] In some embodiments, preferably, the microchannel reactor is a tubular microchannel reactor, and the inner diameter of the pipe is 0.8 mm.

[0024] In some embodiments, the pipe material of the microchannel reactor is perfluoroalkoxy alkane (PFA) or polytetrafluoroethylene, and preferably polytetrafluoroethylene.

[0025] In some embodiments, the length of the pipe of the microchannel reactor is 3.00-5.00 m, and preferably 3.18 m.

[0026] In some embodiments, the heating of the microchannel reactor is oil bath heating, and a Heidolph stirrer is used for stirring and heating.

[0027] Beneficial effects:

[0028] (1) The preparation method provided by the application has simple process, mild reaction condition, shortened reaction time, improved reaction conversion rate and yield, and high reaction continuity, which is conducive to continuous and uninterrupted large-scale production.

[0029] (2) The raw material conversion rate of the application can reach 100%, and the product yield can reach up to 99%.

[0030] (3) The catalyst used in the application, tungsten diselenide, still has good catalytic effect after multiple cycles, has high reaction selectivity and is easy to control, is convenient for synthesis, and is suitable for mass production. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and / or other aspects of the application will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings.

[0032] Figure 1 It is a physical diagram of the microchannel reaction device used in the embodiments of the application.

[0033] Figure 2 It is a reaction formula for preparing 2,5-dimethylfuran by using tungsten diselenide as a catalyst and 2,5-hexanedione as a raw material in the embodiments of the application.

[0034] Figure 3 It is a nuclear magnetic resonance spectrum of 2,5-dimethylfuran prepared in embodiment 1 of the application.

[0035] Figure 4 It is a graph showing the repeated use capability of the catalyst tungsten diselenide in the dehydration reaction of 2,5-hexanedione. DETAILED DESCRIPTION

[0036] In the following examples, the experimental methods described are conventional methods unless otherwise specified; and the reagents and materials described are commercially available unless otherwise specified.

[0037] In the embodiments of the application, the 2,5-hexanedione used has a Mw of 114; and the tungsten diselenide has a Mw of 341.77.

[0038] The physical diagram of the microchannel reaction device used in the embodiments of the application is shown in Figure 1 The microchannel reaction device includes a syringe pump, a microchannel reactor, and a receiver; wherein the injection head of the syringe pump is connected to the inlet end of the microchannel reactor through a Luer joint; and the outlet end of the microchannel reactor is provided with a receiver.

[0039] The microchannel reactor is a tubular microreactor, and the inner diameter of the pipeline is 0.8 mm; and the volume of the microchannel reactor is 1.6 mL.

[0040] The pipe material of the micro-channel reactor is polytetrafluoroethylene.

[0041] The pipe length of the micro-channel reactor is 3.18 m.

[0042] The heating of the micro-channel reactor is oil bath heating, and a Hatachi stirrer is used for stirring and heating.

[0043] In the embodiment of the present application, the reaction formula for preparing 2,5-dimethylfuran by using tungsten diselenide as a catalyst and 2,5-hexanedione as a raw material is shown in the following formula (I). Figure 2

[0044] Example 1

[0045] 2,5-hexanedione (1 g, 0.00880 mol) is weighed and dissolved in 20 mL of toluene to obtain a reaction solution; tungsten diselenide (0.30252 g, 0.00088 mol) is weighed, the morphology of the tungsten diselenide is nanoparticle (the particle size is 30-70 nm), and the tungsten diselenide is filled in the pipe of the micro-channel reactor.

[0046] The reaction solution is pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.036 mL / min and reacted at 95℃ for 45 min; the micro-channel reactor is a tubular micro-reactor, the inner diameter of the pipe is 0.8 mm, and the volume of the micro-channel reactor is 1.6 mL. After the reaction is completed, the catalyst tungsten diselenide is washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran is subjected to gas phase detection, and the yield of 2,5-dimethylfuran is 65.4%, the conversion rate is 82%, and the selectivity is 83%.

[0047] The nuclear magnetic resonance spectrum of 2,5-dimethylfuran prepared in Example 1 is shown in the following formula (II). Figure 3

[0048] Example 2

[0049] 2,5-hexanedione (1 g, 0.00880 mol) is weighed and dissolved in 20 mL of toluene to obtain a reaction solution; tungsten diselenide (0.50260 g, 0.00146 mol) is weighed, the morphology of the tungsten diselenide is nanoparticle (the particle size is 30-70 nm), and the tungsten diselenide is filled in the pipe of the micro-channel reactor.

[0050] ​​The reaction liquid is pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.036 mL / min and reacted at 95°C for 45 min; wherein the micro-channel reactor is a tubular micro-reactor, the inner diameter of the pipeline is 0.8 mm, and the volume of the micro-channel reactor is 1.6 mL. After the reaction is completed, the catalyst tungsten diselenide is washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran is subjected to gas phase detection, and the yield of 2,5-dimethylfuran is 65%, the conversion rate is 70%, and the selectivity is 80%.

[0051] Example 3:

[0052] 2,5-hexanedione (1 g, 0.00880 mol) is weighed and dissolved in 20 mL of toluene to obtain a reaction liquid; tungsten diselenide (0.41253 g, 0.00120 mol) is weighed, the morphology of the tungsten diselenide is nanoparticle (particle size is 30-70 nm), and the tungsten diselenide is filled in the pipeline of the micro-channel reactor.

[0053] The reaction liquid is pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.036 mL / min and reacted at 95°C for 45 min; wherein the micro-channel reactor is a tubular micro-reactor, the inner diameter of the pipeline is 0.8 mm, and the volume of the micro-channel reactor is 1.6 mL. After the reaction is completed, the catalyst tungsten diselenide is washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran is subjected to gas phase detection, and the yield of 2,5-dimethylfuran is 65%, the conversion rate is 70%, and the selectivity is 80%.

[0054] Example 4:

[0055] 2,5-hexanedione (1 g, 0.00880 mol) is weighed and dissolved in 20 mL of toluene to obtain a reaction liquid; tungsten diselenide (0.41253 g, 0.00120 mol) is weighed, the morphology of the tungsten diselenide is nanoparticle (particle size is 30-70 nm), and the tungsten diselenide is filled in the pipeline of the micro-channel reactor.

[0056] The reaction liquid is pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.036 mL / min and reacted at 95°C for 45 min; wherein the micro-channel reactor is a tubular micro-reactor, the inner diameter of the pipeline is 0.8 mm, and the volume of the micro-channel reactor is 1.6 mL. After the reaction is completed, the catalyst tungsten diselenide is washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran is subjected to gas phase detection, and the yield of 2,5-dimethylfuran is 65%, the conversion rate is 70%, and the selectivity is 80%.

[0057] Example 5:

[0058] The 2,5-hexanedione (1 g, 0.00880 mol) was weighed and dissolved in 30 mL of toluene to obtain a reaction solution; tungsten diselenide (0.41597 g, 0.00121 mol) was weighed, the morphology of the tungsten diselenide was nanosheet (thickness of 3-20 nm), and the tungsten diselenide was filled in the pipeline of the micro-channel reactor.

[0059] The reaction solution was pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.036 mL / min and reacted at 95°C for 45 min; wherein the micro-channel reactor was a tubular micro-reactor, the pipeline inner diameter was 0.8 mm, and the micro-channel reactor volume was 1.6 mL. After the reaction, the catalyst tungsten diselenide was washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 91%, the conversion rate was 94%, and the selectivity was 97%.

[0060] Example 6:

[0061] The 2,5-hexanedione (1 g, 0.00880 mol) was weighed and dissolved in 30 mL of toluene to obtain a reaction solution; tungsten diselenide (0.40566 g, 0.00118 mol) was weighed, the morphology of the tungsten diselenide was nanosheet (thickness of 3-20 nm), and the tungsten diselenide was filled in the pipeline of the micro-channel reactor.

[0062] The reaction solution was pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.053 mL / min and reacted at 95°C for 30 min; wherein the micro-channel reactor was a tubular micro-reactor, the pipeline inner diameter was 0.8 mm, and the micro-channel reactor volume was 1.6 mL. After the reaction, the catalyst tungsten diselenide was washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 80%, the conversion rate was 84%, and the selectivity was 99%.

[0063] Example 7:

[0064] The 2,5-hexanedione (1 g, 0.00880 mol) was weighed and dissolved in 30 mL of toluene to obtain a reaction solution; tungsten diselenide (0.37815 g, 0.00110 mol) was weighed, the morphology of the tungsten diselenide was nanosheet (thickness of 3-20 nm), and the tungsten diselenide was filled in the pipeline of the micro-channel reactor.

[0065] The reaction liquid was pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.053 mL / min and reacted at 120°C for 30 min; wherein the micro-channel reactor was a tubular micro-reactor with an inner diameter of 0.8 mm and a volume of 1.6 mL. After the reaction, the catalyst tungsten diselenide was washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 93%, the conversion rate was 98%, and the selectivity was 95%.

[0066] Example 8:

[0067] 2,5-hexanedione (1 g, 0.00880 mol) was weighed and dissolved in 30 mL of toluene to obtain a reaction liquid; tungsten diselenide (0.40909 g, 0.00119 mol) was weighed, the morphology of the tungsten diselenide was nanosheet (thickness of 3-20 nm), and the tungsten diselenide was filled in the pipeline of the micro-channel reactor.

[0068] The reaction liquid was pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.16 mL / min and reacted at 120°C for 10 min; wherein the micro-channel reactor was a tubular micro-reactor with an inner diameter of 0.8 mm and a volume of 1.6 mL. After the reaction, the catalyst tungsten diselenide was washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 83%, the conversion rate was 91%, and the selectivity was 95%.

[0069] Example 9:

[0070] 2,5-hexanedione (1 g, 0.00880 mol) was weighed and dissolved in 30 mL of toluene to obtain a reaction liquid; tungsten diselenide (0.40909 g, 0.00119 mol) was weighed, the morphology of the tungsten diselenide was nanosheet (thickness of 3-20 nm), and the tungsten diselenide was filled in the pipeline of the micro-channel reactor.

[0071] The reaction liquid was pumped into the micro-channel reactor of the micro-channel reaction device at a flow rate of 0.16 mL / min and reacted at 150°C for 10 min; wherein the micro-channel reactor was a tubular micro-reactor with an inner diameter of 0.8 mm and a volume of 1.6 mL. After the reaction, the catalyst tungsten diselenide was washed with ethanol for multiple times and then placed in a vacuum drying box for drying for 12 h, ready for the next cycle reaction. The reaction effluent containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 98%, the conversion rate was 100%, and the selectivity was 98%.

[0072] The recycled tungsten diselenide catalyst was used in the reaction conditions of this example, and the experiment was repeated 5 times to investigate the ability of the tungsten diselenide catalyst to be reused in the dehydration reaction of 2,5-hexanedione. The specific experimental data are shown in Table 1. Figure 4 As can be seen from the figure, the tungsten diselenide catalyst has good recycling performance. Note: DMF in the figure represents 2,5-dimethylfuran.

[0073] Comparative Example 1:

[0074] 2,5-hexanedione (1 g, 0.008800 mol) was weighed and dissolved in 30 mL of toluene, and then tungsten diselenide (0.37815 g, 0.00110 mol) was weighed and added to the three-necked flask. The three-necked flask was equipped with a water separator and a condenser. Then the reaction was carried out at 95°C for 6h. After the reaction was completed, the reaction liquid containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 70%, the conversion rate was 80%, and the selectivity was 85%.

[0075] Comparative Example 2:

[0076] 2,5-hexanedione (1 g, 0.008800 mol) was weighed and dissolved in 30 mL of toluene, and then tungsten diselenide (0.37815 g, 0.00110 mol) was weighed and added to the three-necked flask. The three-necked flask was equipped with a water separator and a condenser. Then the reaction was carried out at 150°C for 3h. After the reaction was completed, the reaction liquid containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 65%, the conversion rate was 80%, and the selectivity was 81%.

[0077] Comparative Example 3:

[0078] 2,5-hexanedione (1 g, 0.008800 mol) was weighed and dissolved in 30 mL of toluene, and then butyltin trichloride (0.31040 g, 0.00110 mol) was weighed and added to the three-necked flask. The three-necked flask was equipped with a water separator and a condenser. Then the reaction was carried out at 150°C for 3h. After the reaction was completed, the reaction liquid containing 2,5-dimethylfuran was subjected to gas phase detection, and the yield of 2,5-dimethylfuran was 50%, the conversion rate was 65%, and the selectivity was 88%.

[0079] Comparative Example 4:

[0080] Take 2,5-hexanedione (1g, 0.008800mol), dissolve in 30mL of toluene, and then take p-toluenesulfonic acid (0.18942g, 0.00110mol), add into a three-necked flask, and then add a water separator and a condenser device on the three-necked flask. Then react at 150℃ for 3h. After the reaction is completed, the reaction solution containing 2,5-dimethylfuran is subjected to gas phase detection, and the yield of 2,5-dimethylfuran is 50%, the conversion rate is 66%, and the selectivity is 80%.

[0081] The experimental results show that the present application uses tungsten diselenide as a catalyst for preparing 2,5-dimethylfuran from 2,5-hexanedione, has moderate reaction temperature, high yield, and good selectivity of the target product. At the same time, the method is simple in operation, low in cost, and can be continuously produced without interruption, and has good industrial application prospect.

[0082] The present application provides a method for preparing 2,5-dimethylfuran. There are many methods and ways to realize this technical solution. The above description is only the preferred embodiment of the present application. It should be pointed out that for ordinary technical personnel in this technical field, some improvements and refinements can be made without departing from the principle of the present application. These improvements and refinements should also be considered as the protection scope of the present application. The components not explicitly described in the embodiment can be realized by using existing technology.

Claims

1. A method for preparing 2,5-dimethylfuran, characterized in that: 2,5-hexanedione was used to synthesize 2,5-dimethylfuran in the presence of tungsten diselenide as a catalyst; The molar ratio of the 2,5-hexanedione to the tungsten diselenide is 6-10:1; the catalysis is carried out at 95-150°C; 2,5-dimethylfuran was synthesized using a microchannel reaction device; The morphology of the tungsten diselenide is nanosheets or nanoparticles.

2. The method according to claim 1, characterized in that The synthesis of 2,5-dimethylfuran using a microchannel reaction device comprises the following steps: dissolving 2,5-hexanedione in a first solvent to obtain a reaction liquid; pumping the reaction liquid into a microchannel reactor of a microchannel reaction device to perform a catalytic reaction, thereby obtaining 2,5-dimethylfuran; Wherein, tungsten diselenide is loaded in the microchannel reactor.

3. The method according to claim 1, characterized in that The first solvent is any one of toluene, ethyl acetate, dichloromethane and dimethyl sulfoxide, or a combination thereof; and the concentration of 2,5-hexanedione in the reaction solution is 0.01-0.06 g / mL.

4. The method according to claim 1, wherein The reaction liquid is pumped into the microchannel reactor of the microchannel reaction device at a flow rate of 0.036-0.16 mL / min; the catalytic reaction has a reaction temperature of 95-150° C. and a reaction residence time of 10 min-45 min.

5. The method according to claim 1, wherein The molar ratio of 2,5-hexanedione in the reaction solution to tungsten diselenide loaded in the microchannel reactor is 6-10:

1.

6. The method according to claim 1, characterized in that The microchannel reaction device includes a syringe pump, a microchannel reactor and a receiver; wherein the injection head of the syringe pump is connected to the inlet end of the microchannel reactor through a Luer docking connector; and the outlet end of the microchannel reactor is provided with a receiver.

7. The method according to claim 6, characterized in that The microchannel reactor is a tubular microchannel reactor, and the inner diameter of the tube is 0.5-1.0 mm.

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