Synthesis process of N-methylaniline

Abstract

The invention belongs to the technical field of organic synthetic chemistry, and particularly relates to a synthesis process of N-methylaniline. By adopting the special biomass porous carbon loaded nickel-copper bimetallic catalyst, the selectivity and the conversion rate of the reaction are improved, and the generation of byproducts is reduced, so that the burden of subsequent separation is reduced, the utilization rate of the raw materials is improved, and the yield is increased by introducing the micro-channel reactor and combining a microwave heating technology. Compared with the prior art, the method has the advantages that the mixing efficiency and the heat mass transfer rate of materials are improved, the reaction time is shortened, in the separation and purification process, a membrane separation and rectification combined technology and an efficient phase splitter are adopted, salt water is not needed, salt-containing wastewater is avoided, meanwhile, the recovery efficiency of methanol and aniline is improved, and cyclic utilization of a solvent is achieved. The whole process reduces the energy consumption, improves the production efficiency, reduces the emission of pollutants and meets the requirements of green chemistry through waste heat recovery, heating mode optimization and separation process.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthetic chemistry, and particularly relates to a synthesis process of N-methylaniline. Background Art

[0002] N-methylaniline (NMA) is an oily flammable liquid, which gradually changes from colorless to brown in the air. Its boiling point is 196.25 °C, relative density is 0.9793, melting point is -56 °C, slightly soluble in water, and has good solubility in reagents such as ethanol, ether, and chloroform. It easily reacts with alkylating reagents to form N-alkyl derivatives. It is widely used in the preparation of key organic intermediates in the fields of pesticides, dye industry, pharmaceutical industry, rubber industry, explosives and other chemical industries. In addition, it can also be used as a solvent in the production of pharmaceutical intermediates and organic synthesis reactions. In recent years, due to various applications in the chemical industry, the demand for N-methylaniline has been increasing continuously.

[0003] At present, the synthesis of N-methylaniline in industry mainly adopts the alkylation reaction of aniline and methanol under the action of a catalyst. In the traditional process, aniline and methanol are usually mixed in a certain proportion, vaporized and then enter a fixed-bed reactor, using a copper-zinc-chromium catalyst or a molecular sieve catalyst, and reacting under the conditions of 200 - 300 °C and 1.0 - 2.0 MPa. This method has many deficiencies: firstly, the activity and selectivity of the catalyst are limited, there are many side reactions, and it is easy to generate by-products such as N,N-dimethylaniline and benzylamine, resulting in difficult separation and purification of the product, low yield, and the raw material utilization rate is less than 85%; secondly, the reaction conditions are harsh, high temperature and high pressure lead to high energy consumption, increased equipment investment and operating costs; thirdly, the traditional catalyst has poor stability and short service life, generally needs to be replaced every 3 - 6 months. Frequent replacement of the catalyst not only increases the production cost, but also generates a large amount of solid waste.

[0004] In terms of separation and purification, the existing technology mostly uses a multi-stage distillation column for separation. First, methanol is recovered by atmospheric distillation in a methanol column, then aniline and water are separated by an aniline azeotropic column, and finally the product is obtained through an N-methylaniline distillation column. The energy consumption of this process accounts for more than 60% of the total process. And when treating the aqueous phase, the salting-out method is often used to assist in stratification, which will generate a large amount of salty wastewater, with high subsequent treatment costs and causing great pressure on the environment. In addition, the recovery efficiency of the by-product N,N-dimethylaniline is low, and it is usually treated as waste, resulting in resource waste and economic losses.

[0005] In recent years, although there have been research attempts to improve the synthesis process, such as using new catalysts and optimizing reaction conditions, etc., the problems of high energy consumption and low efficiency have not been fundamentally solved. Therefore, developing a green, environmentally friendly, highly efficient and energy-saving N-methylaniline synthesis process is of great significance for promoting the sustainable development of related industries. Summary of the Invention

[0006] The object of the present invention is to provide a synthesis process of N-methylaniline in view of the existing problems.

[0007] The present invention is achieved by the following technical solutions:

[0008] A synthesis process of N-methylaniline includes the following steps:

[0009] S1. After mixing aniline and methanol in a molar ratio of 1:1.2 to 1.6 through a mixer, the mixture is circulated and mixed in a preparation metering tank for 1 to 3 hours to obtain a mixed material.

[0010] S2. Using a microchannel reactor, with microwave heating combined with heat transfer oil auxiliary heating, the mixed material is vaporized at 180 to 220 °C and reacts at 190 to 240 °C under the action of a nickel-copper bimetallic catalyst supported on biomass porous carbon to obtain a gas-phase product.

[0011] S3. After condensing and liquefying the gas-phase product, crude N-methylaniline is obtained. The crude product is separated by membrane to remove most of the methanol, and phase separation is adjusted by temperature without using brine. The bottom material of the aniline tower is cooled and recycled. High-quality N-methylaniline is obtained in the N-methylaniline rectification tower, and the aqueous phase of the wastewater tower enters the sewage treatment station after being treated by resin to meet the standards.

[0012] Further, the stirring speed during the circulating and mixing in step S1 is 200 to 300 r / min.

[0013] Further, the preparation of the nickel-copper bimetallic catalyst supported on biomass porous carbon in step S2 includes the following steps:

[0014] (1) Crush and dry crop straw, then immerse it in a citric acid solution with a mass fraction of 5%, stir and impregnate at 30 to 40 °C for 18 to 24 hours. After impregnation, wash it with deionized water until neutral, then place it in a drying oven, dry for 12 to 16 hours, and transfer it to a tubular furnace for carbonization treatment under a nitrogen atmosphere to obtain primary porous carbon for standby.

[0015] (2) Add the obtained primary porous carbon and urea to a mortar in a mass ratio of 1:2 to 3, grind and mix evenly, then place it in a microwave reaction kettle for microwave irradiation treatment. After completion, cool it to room temperature, take it out, wash it 3 to 5 times with deionized water, and then dry it in a vacuum drying oven at 60 to 70 °C for 6 to 10 hours to obtain a nitrogen-doped biomass porous carbon carrier for standby.

[0016] (3) Add ZIF-8 particles (particle size 50 - 100 nm, pore size about 1.2 nm) to the mixed metal salt solution. After ultrasonic dispersion until uniform, add the above nitrogen-doped biomass porous carbon support. After stirring and mixing evenly, add the chitosan solution. After ultrasonic dispersion until uniform, perform freeze-drying to obtain the carbon support loaded with the bimetallic precursor;

[0017] (4) Immerse the carbon support loaded with the bimetallic precursor in a 5% mass fraction of tea polyphenol solution. After microwave treatment under microwave conditions and cooling to room temperature, then wash 3 - 5 times with deionized water and immerse in a 0.1 M acetic acid solution. After stirring at room temperature for 12 - 16 h, perform suction filtration, wash with deionized water until neutral, then place in a vacuum drying oven and dry at 60 - 70 °C for 10 - 12 h. After annealing in a hydrogen atmosphere at 200 °C for 1 - 2 h, expose to air for 10 - 12 h.

[0018] Further, the crop straw in step (1) is one or more of rice straw, corn straw, or wheat straw;

[0019] Before the carbonization treatment, nitrogen (purity ≥ 99.99%) is introduced into the tubular furnace at a gas flow rate of 500 mL / min to displace the air in the furnace for 30 min. Then, heat up to 550 - 650 °C at a rate of 4 - 6 °C / min and perform carbonization treatment at this temperature for 2 - 3 h.

[0020] Further, during the microwave irradiation in step (2), control the power to be 300 - 400 W and the irradiation time to be 10 - 14 min.

[0021] Further, the preparation method of the mixed metal salt solution in step (3) is: Dissolve nickel nitrate (Ni(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) in the ethanol-water mixed solution according to the molar ratio of Ni:Cu of 1 - 3:1, and prepare a mixed solution with a total metal salt concentration of 0.2 mol / L;

[0022] The addition amount of the ZIF-8 particles is 1 - 2 times the total mass of the metal salts;

[0023] The mass-volume ratio of the nitrogen-doped biomass porous carbon support to the mixed metal salt solution is 1 g:5 - 10 mL.

[0024] Further, the preparation method of the chitosan solution in step (3) is: Add chitosan to a 2% mass fraction of acetic acid aqueous solution to prepare a chitosan solution with a mass fraction of 1 - 2%;

[0025] The volume of the chitosan solution is 1 / 6 - 1 / 5 of the volume of the mixed metal salt solution.

[0026] Further, during the microwave treatment in step (4), the power is controlled at 500 - 600 W and the irradiation time is 10 - 20 min;

[0027] During the exposure to air, the environmental humidity is controlled at 40 - 60% and the temperature is 20 - 25°C.

[0028] Further, the temperature during the condensation and liquefaction in step S3 is 10 - 16°C.

[0029] Further, step S3 is specifically as follows: The gas-phase product is condensed and liquefied to obtain crude N-methylaniline. The crude product is subjected to membrane separation to remove most of the methanol, and the remaining material enters the aniline azeotropic tower for treatment. At -0.095 to -0.085 MPa and 155 - 165°C, the gas-phase medium is condensed by a condenser and then separated into layers at 5 - 10°C. The organic phase enters the aniline tower, where it azeotropes at 100 - 105°C at the top, is condensed and then phase-separated. The aqueous phase enters the wastewater tower, and the organic phase returns to the tower. When the water content at the bottom of the aniline tower is less than 1%, it is cooled to below 40°C and returned to the batching process. The material at the bottom of the azeotropic tower enters the N-methylaniline rectification tower, and is rectified to obtain the refined product at -0.098 to -0.092 MPa and 155 - 165°C. The material at the bottom of the tower enters the N,N-dimethylaniline distillation tower, and the by-product is recovered at -0.098 to -0.092 MPa and 170 - 175°C. The kettle residue is discharged once every 20 - 30 days. The aqueous phase of the wastewater tower is treated by resin and then enters the sewage treatment station after passing the qualification.

[0030] The present invention has the following advantages compared with the prior art:

[0031] 1. The present invention uses a special biomass porous carbon-supported nickel-copper bimetallic catalyst, which improves the selectivity and conversion rate of the reaction, reduces the generation of by-products, thereby reducing the burden of subsequent separation, improving the utilization rate of raw materials. The introduction of a microchannel reactor and the combination of microwave heating technology improve the mixing efficiency of materials and the heat and mass transfer rate, shortening the reaction time. During the separation and purification process, the present invention adopts a technology combining membrane separation and rectification, as well as an efficient phase separator, without using brine, avoiding the generation of saline wastewater, and at the same time improving the recovery efficiency of methanol and aniline, realizing the recycling of solvents. The entire process reduces energy consumption, improves production efficiency, reduces pollutant emissions through waste heat recovery, optimizing the heating method and separation process. The wastewater treatment adopts environmental protection methods such as resin adsorption, meeting the requirements of green chemistry.

[0032] 2. The catalyst of the present invention uses crop straw as a carbon source and green reagents such as citric acid, urea, and tea polyphenols, avoiding the use of harmful chemical reagents in the preparation process of traditional catalysts, reducing environmental pollution. Through impregnation with a citric acid solution and carbonization treatment, primary porous carbon is formed at 600 °C, constructing a rich pore structure. Then, nitrogen doping is carried out with urea and microwave irradiation to introduce N-C active sites, improving the specific surface area and surface activity of the carrier, enhancing the loading capacity for metal particles and the interaction with metals, providing a good support environment for catalytic reactions. Subsequently, ZIF-8 template-assisted impregnation is adopted, and the synergistic effect of the nanoscale pores of ZIF-8 and chitosan realizes the uniform adsorption and loading of nickel nitrate and copper nitrate metal ions. After subsequent reduction, nickel-copper bimetallic nanoparticles with a particle size in a certain range (5 - 15 nm) and good dispersion can be obtained, which helps to improve the activity, selectivity, and stability of the catalyst, reduce the generation of by-product N,N-dimethylaniline, and improve the raw material utilization rate and product yield. Description of the Drawings

[0033] Figure 1 It is a graph showing the stability test results of the catalyst in Example 2. Detailed Embodiments

[0034] In order to further explain the present invention, the following specific embodiments are described below.

[0035] Example 1

[0036] A synthesis process of N-methylaniline includes the following steps:

[0037] S1. After aniline and methanol are mixed in a mixer according to a molar ratio of 1:1.2, the mixture is circulated and mixed in a preparation metering tank at a rotation speed of 200 r / min for 1 h to obtain a mixed material;

[0038] S2. Using a microchannel reactor, microwave heating combined with heat transfer oil-assisted heating, the mixed material is vaporized at 180 °C and reacts at 190 °C under the action of a biomass porous carbon-supported nickel-copper bimetallic catalyst to obtain a gas-phase product;

[0039] The preparation of the biomass porous carbon-supported nickel-copper bimetallic catalyst includes the following steps:

[0040] (1) The rice straw was crushed and dried, and then immersed in a 5% citric acid solution, stirred and immersed at 30°C for 18 hours. After the impregnation, it was washed with deionized water until neutral, and then placed in a drying oven. After drying for 12 hours, it was transferred to a tube furnace, and nitrogen (purity ≥99.99%) was introduced into the tube furnace at a gas flow rate of 500 mL / min to replace the air in the furnace for 30 minutes. Then, the temperature was raised to 550°C at a rate of 4°C / min, and carbonized at this temperature for 2 hours to obtain primary porous carbon for use;

[0041] (2) The obtained primary porous carbon and urea were added into a mortar in a mass ratio of 1:2, ground and mixed evenly, and then placed in a microwave reactor for microwave irradiation treatment at a controlled power of 300 W for 10 min. After cooling to room temperature, the product was taken out and washed with deionized water three times, and then dried in a vacuum drying oven at 60 ° C for 6 h to obtain a nitrogen-doped biomass porous carbon support for use;

[0042] (3) Nickel nitrate (Ni(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) were dissolved in an ethanol-water mixed solution at a Ni:Cu molar ratio of 1:1 to prepare a mixed solution with a total metal salt concentration of 0.2 mol / L. ZIF-8 particles (particle size 50 nm, pore size about 1.2 nm) were added to the metal salt mixed solution. The amount of ZIF-8 particles added was 1 times the total mass of the metal salt. After ultrasonic dispersion, the nitrogen-doped biomass porous carbon support was added. The mass volume ratio of the nitrogen-doped biomass porous carbon support to the metal salt mixed solution was 1 g:5 mL. After stirring and mixing, chitosan solution was added. After ultrasonic dispersion, the mixture was freeze-dried to obtain a carbon support loaded with a bimetallic precursor.

[0043] The chitosan solution is prepared by adding chitosan to an acetic acid aqueous solution with a mass fraction of 2% to prepare a chitosan solution with a mass fraction of 1%;

[0044] The volume of the chitosan solution is 1 / 6 of the volume of the metal salt mixed solution;

[0045] (4) The carbon support loaded with the bimetallic precursor was immersed in a 5% tea polyphenol solution, treated under microwave conditions, and then cooled to room temperature. The power was controlled to be 500 W and the irradiation time was 10 min. The carbon support was then washed with deionized water three times and immersed in a 0.1 M acetic acid solution. After stirring at room temperature for 12 h, it was filtered and washed with deionized water until neutral. The carbon support was then placed in a vacuum drying oven and dried at 60 ° C for 10 h. After annealing in a hydrogen atmosphere at 200 ° C for 1 h, the carbon support was exposed to air, and the ambient humidity was controlled at 40%, the temperature was 20 ° C, and it was left to stand for 10 h.

[0046] S3. Condense and liquefy the gaseous product at 10°C to obtain the crude N-methylaniline. The crude product is subjected to membrane separation to remove most of the methanol, and the remaining material enters the aniline azeotropic tower for treatment. At -0.095 MPa and 155°C, the gaseous medium is condensed by a condenser and then separated into layers at 5°C. The organic phase enters the aniline tower, where it azeotropes at 100°C at the top. After condensation, it is phase-separated. The aqueous phase enters the wastewater tower, and the organic phase returns to the tower. When the water content at the bottom of the aniline tower is less than 1%, it is cooled to below 40°C and returned to the batching process. The material at the bottom of the azeotropic tower enters the N-methylaniline rectification tower, and is rectified at -0.098 MPa and 155°C to obtain the refined product. The material at the bottom of the tower enters the N,N-dimethylaniline distillation tower, and the by-product is recovered at -0.098 MPa and 170°C. The kettle residue is discharged once every 20 days. The aqueous phase of the wastewater tower is treated by resin and then enters the sewage treatment station after passing the quality inspection.

[0047] Example 2

[0048] A synthesis process of N-methylaniline includes the following steps:

[0049] S1. Mix aniline and methanol in a molar ratio of 1:1.4 through a mixer, and then circulate and mix in a preparation metering tank at a speed of 250 r / min for 2 h to obtain a mixed material;

[0050] S2. Use a microchannel reactor, adopt microwave heating combined with heat transfer oil auxiliary heating, vaporize the mixed material at 200°C, and react at 210°C under the action of a nickel-copper bimetallic catalyst supported on biomass porous carbon to obtain a gaseous product;

[0051] The preparation of the nickel-copper bimetallic catalyst supported on biomass porous carbon includes the following steps:

[0052] (1) Crush and dry rice straw, then immerse it in a 5% citric acid solution, stir and impregnate at 35°C for 21 h. After impregnation, wash it with deionized water until neutral, then place it in a drying oven, dry for 14 h, and transfer it to a tubular furnace. Pass nitrogen (purity ≥ 99.99%) into the tubular furnace at a gas flow rate of 500 mL / min to displace the air in the furnace for 30 min, then heat it up to 600°C at a rate of 5°C / min, and perform carbonization treatment at this temperature for 2.5 h to obtain primary porous carbon for standby;

[0053] (2) Add the obtained primary porous carbon and urea to a mortar in a mass ratio of 1:2.5, grind and mix evenly, then place it in a microwave reaction kettle for microwave irradiation treatment. Control the power at 350 W, irradiate for 12 min, then cool to room temperature, take it out, wash it 4 times with deionized water, and then dry it in a vacuum drying oven at 65°C for 8 h to obtain a nitrogen-doped biomass porous carbon carrier for standby;

[0054] (3) Dissolve nickel nitrate (Ni(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) in an ethanol-water mixed solution according to a Ni:Cu molar ratio of 2:1 to prepare a mixed solution with a total metal salt concentration of 0.2 mol / L. Add ZIF-8 particles (particle size 80 nm, pore size about 1.2 nm) to the metal salt mixed solution. The addition amount of ZIF-8 particles is 1.5 times the total mass of the metal salts. After ultrasonic dispersion, add the above nitrogen-doped biomass porous carbon carrier. The mass-volume ratio of the nitrogen-doped biomass porous carbon carrier to the metal salt mixed solution is 1 g:7.5 mL. After stirring and mixing evenly, add the chitosan solution. After ultrasonic dispersion, perform freeze-drying to obtain a carbon carrier loaded with a bimetallic precursor;

[0055] The preparation method of the chitosan solution is as follows: Add chitosan to an aqueous acetic acid solution with a mass fraction of 2% to prepare a chitosan solution with a mass fraction of 1.5%;

[0056] The volume of the chitosan solution is 1 / 6 of the volume of the metal salt mixed solution;

[0057] (4) Immerse the carbon carrier loaded with the bimetallic precursor in a tea polyphenol solution with a mass fraction of 5%, perform microwave treatment under microwave conditions and then cool to room temperature. When performing microwave treatment, control the power at 550 W and the irradiation time at 15 min. Then wash 4 times with deionized water and immerse in a 0.1 M acetic acid solution. Stir at room temperature for 14 h, then filter by suction, wash with deionized water until neutral, then place in a vacuum drying oven and dry at 65 °C for 11 h. After annealing in a hydrogen atmosphere at 200 °C for 1.5 h, expose to air, control the environmental humidity at 50%, and the temperature at 23 °C, and let it stand for 11 h;

[0058] Cool and liquefy the gas-phase product at 13 °C to obtain a crude product of N-methylaniline. The crude product is subjected to membrane separation to remove most of the methanol, and the remaining material enters the aniline azeotropic tower for treatment. At -0.09 MPa and 160 °C, the gas-phase medium is condensed by a condenser and then separated into layers at 8 °C. The organic phase enters the aniline tower, and the top of the tower is azeotropic at 102 °C. After condensation, it is separated into phases. The aqueous phase enters the wastewater tower, and the organic phase returns to the tower. When the water content at the bottom of the aniline tower is less than 1%, it is cooled to below 40 °C and returned to the batching process. The material at the bottom of the azeotropic tower enters the N-methylaniline rectification tower, and is rectified at -0.095 MPa and 160 °C to obtain a refined product. The material at the bottom of the tower enters the N,N-dimethylaniline distillation tower, and the by-product is recovered at -0.095 MPa and 172 °C. The kettle residue is discharged once every 25 days. The aqueous phase of the wastewater tower is treated by resin and then enters the sewage treatment station.

[0059] Example 3

[0060] A synthesis process of N-methylaniline, comprising the following steps:

[0061] S1. After mixing aniline and methanol in a molar ratio of 1:1.6 through a mixer, the mixture is circulated and mixed in a preparation metering tank at a rotation speed of 300 r / min for 3 h to obtain a mixed material;

[0062] S2. Using a microchannel reactor, with microwave heating combined with heat transfer oil assisted heating, the mixed material is vaporized at 220 °C and reacts at 240 °C under the action of a nickel-copper bimetallic catalyst supported on biomass porous carbon to obtain a gas-phase product;

[0063] The preparation of the nickel-copper bimetallic catalyst supported on biomass porous carbon includes the following steps:

[0064] (1) After crushing and drying rice straw, it is immersed in a 5% citric acid solution, stirred and impregnated at 40 °C for 24 h. After impregnation, it is washed with deionized water until neutral, then placed in a drying oven, dried for 16 h and transferred to a tubular furnace. Nitrogen (purity ≥ 99.99%) is introduced into the tubular furnace at a gas flow rate of 500 mL / min to displace the air in the furnace for 30 min, and then it is heated to 650 °C at a rate of 6 °C / min and carbonized at this temperature for 3 h to obtain primary porous carbon for standby;

[0065] (2) The obtained primary porous carbon and urea are added to a mortar according to a mass ratio of 1:3, ground and mixed evenly, then placed in a microwave reaction kettle for microwave irradiation treatment. The power is controlled at 400 W, and after irradiation for 14 min, it is cooled to room temperature, taken out, washed 5 times with deionized water, and then dried in a vacuum drying oven at 70 °C for 10 h to obtain a nitrogen-doped biomass porous carbon carrier for standby;

[0066] (3) Nickel nitrate (Ni(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) are respectively dissolved in an ethanol-water mixed solution according to a Ni:Cu molar ratio of 3:1 to prepare a mixed solution with a total metal salt concentration of 0.2 mol / L. ZIF-8 particles (particle size 100 nm, pore diameter about 1.2 nm) are added to the metal salt mixed solution, and the addition amount of ZIF-8 particles is 2 times the total mass of the metal salts. After ultrasonic dispersion, the above-mentioned nitrogen-doped biomass porous carbon carrier is added. The mass-volume ratio of the nitrogen-doped biomass porous carbon carrier to the metal salt mixed solution is 1 g:10 mL. After stirring and mixing evenly, a chitosan solution is added. After ultrasonic dispersion, it is freeze-dried to obtain a carbon carrier loaded with a bimetallic precursor;

[0067] The preparation method of the chitosan solution is: adding chitosan to an acetic acid aqueous solution with a mass fraction of 2% to prepare a chitosan solution with a mass fraction of 2%;

[0068] The volume of the chitosan solution is 1 / 5 of the volume of the metal salt mixed solution;

[0069] (4) Immerse the carbon support loaded with the bimetallic precursor in a 5% mass fraction of tea polyphenol solution, perform microwave treatment under microwave conditions and then cool to room temperature. During microwave treatment, control the power at 600 W and the irradiation time at 20 min. Then wash with deionized water 5 times and immerse in 0.1 M acetic acid solution. Stir at room temperature for 16 h, then filter by suction, wash with deionized water until neutral, and then place in a vacuum drying oven and dry at 70 °C for 12 h. After annealing in a hydrogen atmosphere at 200 °C for 2 h, expose to air, control the environmental humidity at 60%, the temperature at 25 °C, and let stand for 12 h;

[0070] S3. Condense and liquefy the gas-phase product at 16 °C to obtain the crude product of N-methylaniline. The crude product is subjected to membrane separation to remove most of the methanol, and the remaining material enters the aniline azeotropic tower for treatment. At -0.085 MPa and 165 °C, the gas-phase medium is condensed by a condenser and then separated into layers at 10 °C. The organic phase enters the aniline tower, where it azeotropes at 105 °C, is condensed and then phase-separated. The aqueous phase enters the wastewater tower, and the organic phase returns to the tower. When the water content at the bottom of the aniline tower is less than 1%, it is cooled to below 40 °C and returned to the batching process. The material at the bottom of the azeotropic tower enters the N-methylaniline rectification tower, and is rectified at -0.092 MPa and 165 °C to obtain the refined product. The material at the bottom of the tower enters the N,N-dimethylaniline distillation tower, and the by-product is recovered at -0.092 MPa and 175 °C. The residue in the kettle is discharged once every 30 days. The aqueous phase of the wastewater tower enters the sewage treatment station after being treated by resin to meet the standards.

[0071] Comparative Example 1

[0072] On the basis of the example, replace the biomass porous carbon-supported nickel-copper bimetallic catalyst with Cu7Zn2Cr1O x catalyst disclosed in the reference document "Application of Copper-Zinc System Catalysts in the N-Methylation Reaction of Aniline", and the rest of the technical solutions are the same as those in Example 2.

[0073] Comparative Example 2

[0074] Replace step S2 with the following steps:

[0075] S2. Pump the obtained mixed material into the gasification kettle through a feed diaphragm metering pump for gasification. The gasification kettle uses heat transfer oil as a heat source for heating, and the material is gasified at a temperature of 200 °C. The gas phase enters the fixed-bed reactor through a pipeline. The fixed-bed reactor (the biomass porous carbon-supported nickel-copper bimetallic catalyst prepared by the method of Example 2) uses heat transfer oil as a heat source for heating to keep the temperature at 210 °C for reaction to generate N-methylaniline.

[0076] The rest of the technical solutions are the same as those in Example 2.

[0077] Performance Test

[0078] 1. Product Qualitative and Quantitative Method

[0079] The product was qualitatively analyzed by gas chromatography - mass spectrometry (GC - MS) produced by Agilent Technologies, Inc. The chromatographic column was HP - 5 chromatographic column. The split ratio was 10:1, and the carrier gas was helium. Quantitative analysis was carried out using a gas chromatograph model 8890 produced by Agilent Technologies, Inc. The chromatographic column was AT.OV - 1701 (30m * 0.32mm * 1.00μm), and the detector was a flame ionization detector. Chromatographic conditions: Carrier gas: High - purity argon; Column inlet pressure: 0.08MPa; Vaporization chamber temperature: 250°C; Detection chamber temperature: 300°C; Column temperature: Programmed temperature rise, the initial temperature was 60°C, then it was heated to 140°C at a rate of 20°C / min, and then heated to 260°C at a rate of 6°C / min and held for 6min. Splitless injection. Methanol or ethyl acetate was used as the dilution solvent. The needle - washing solvent was ethyl acetate and absolute ethanol. The retention times of the raw materials and the main product in the liquid chromatography were calibrated with the standard samples of aniline and the product N - methylaniline respectively.

[0080] The conversion rate of aniline and the selectivity of N - methylaniline were calculated according to the following method.

[0081] (1) Conversion rate of aniline

[0082]

[0083] In the formula: C aniline is the conversion rate of aniline, M r0 is the initial molar amount of aniline in the reaction raw materials, M r is the molar amount of remaining aniline in the reaction solution during sampling.

[0084] (2) Selectivity of N - methylaniline (NMA)

[0085]

[0086] In the formula: S NMA is the selectivity of N - methylaniline (NMA), S p is the amount of substance of N - methylaniline (NMA), and ∑Si is the sum of the amounts of substance of all reaction products.

[0087] The results are shown in Table 1 below.

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from Table 1 above, the conversion rates of aniline in Examples 1 to 3 are 97.1 to 97.8%, and the selectivity of N-methylaniline is 99%. Compared with the comparative examples, the improvement of the catalyst and synthesis process of the present invention is helpful for the activity of the aniline N-methylation reaction.

[0092] Figure 1 The stability result of the catalyst in the aniline N-methylation reaction of Example 2 is shown. It can be observed that the catalyst has good stability in the N-methylation reaction of aniline and methanol, and there is no obvious deactivation after 51 hours of reaction.

[0093] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A synthesis process of N-methylaniline, characterized in that, It includes the following steps: S1. After mixing aniline and methanol in a molar ratio of 1:1.2 - 1.6 through a mixer, circulate and mix them in a preparation metering tank for 1 - 3 h to obtain a mixed material; S2. Use a microchannel reactor, adopt microwave heating combined with heat transfer oil assisted heating, vaporize the mixed material at 180 - 220 °C, and react at 190 - 240 °C under the action of a biomass porous carbon supported nickel - copper bimetallic catalyst to obtain a gas - phase product; S3. Condense and liquefy the gas - phase product to obtain crude N - methylaniline. The crude product is separated by a membrane to remove most of the methanol, and phase separation is carried out by temperature adjustment without using brine. The bottom material of the aniline tower is cooled and recycled. High - quality products are obtained in the N - methylaniline rectification tower, and the aqueous phase of the wastewater tower enters the sewage treatment station after being treated by resin to meet the standards.

2. The synthesis process of N-methylaniline according to claim 1, characterized in that, The stirring speed during the circulation mixing in step S1 is 200 - 300 r / min.

3. The synthetic process of N-methylaniline according to claim 1, characterized in that, The preparation of the biomass porous carbon supported nickel - copper bimetallic catalyst described in step S2 includes the following steps: (1) Crush and dry crop straw, then immerse it in a 5% citric acid solution, stir and impregnate it at 30 - 40 °C for 18 - 24 h. After impregnation, wash it with deionized water until neutral, then place it in a drying oven, dry it for 12 - 16 h, and transfer it to a tubular furnace. Carry out carbonization treatment under a nitrogen atmosphere to obtain primary porous carbon for standby; (2) Add the obtained primary porous carbon and urea to a mortar in a mass ratio of 1:2 - 3, grind and mix them evenly, then place them in a microwave reaction kettle for microwave irradiation treatment. After completion, cool to room temperature, take it out, wash it 3 - 5 times with deionized water, and then dry it in a vacuum drying oven at 60 - 70 °C for 6 - 10 h to obtain a nitrogen - doped biomass porous carbon carrier for standby; (3) Add ZIF - 8 particles to a metal salt mixed solution, ultrasonically disperse them evenly, then add the above - mentioned nitrogen - doped biomass porous carbon carrier, stir and mix evenly, add a chitosan solution, ultrasonically disperse it evenly, and then carry out freeze - drying to obtain a carbon carrier loaded with a bimetallic precursor; (4) Immerse the carbon carrier loaded with the bimetallic precursor in a 5% tea polyphenol solution, carry out microwave treatment under microwave conditions and then cool to room temperature, then wash it 3 - 5 times with deionized water and immerse it in a 0.1 M acetic acid solution, stir and process it at room temperature for 12 - 16 h, then filter, wash it with deionized water until neutral, and then place it in a vacuum drying oven and dry it at 60 - 70 °C for 10 - 12 h. Then anneal it in a hydrogen atmosphere at 200 °C for 1 - 2 h and expose it to air for 10 - 12 h.

4. The synthesis process of N-methylaniline according to claim 3, wherein The crop straw described in step (1) is one or more of rice straw, corn straw or wheat straw; Before the carbonization treatment, nitrogen is introduced into the tubular furnace at a gas flow rate of 500 mL / min to displace the air in the furnace for 30 min, then the temperature is raised to 550 - 650 °C at a rate of 4 - 6 °C / min, and carbonization treatment is carried out at this temperature for 2 - 3 h.

5. The synthesis process of N-methylaniline according to claim 3, characterized in that, During the microwave irradiation in step (2), the power is controlled at 300 - 400 W and the irradiation time is 10 - 14 min.

6. The synthetic process of N-methylaniline according to claim 3, wherein, The preparation method of the metal salt mixed solution described in step (3) is as follows: nickel nitrate (Ni(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) are respectively dissolved in the ethanol-water mixed solution according to the Ni:Cu molar ratio of 1-3:1 to prepare a mixed solution with a total metal salt concentration of 0.2 mol / L; The addition amount of the ZIF-8 particles is 1-2 times the total mass of the metal salts; The mass-volume ratio of the nitrogen-doped biomass porous carbon carrier to the metal salt mixed solution is 1 g:5-10 mL.

7. The synthesis process of N-methylaniline according to claim 3, characterized in that, The preparation method of the chitosan solution described in step (3) is as follows: chitosan is added to an acetic acid aqueous solution with a mass fraction of 2% to prepare a chitosan solution with a mass fraction of 1-2%; The volume of the chitosan solution is 1 / 6-1 / 5 of the volume of the metal salt mixed solution.

8. The synthesis process of N-methylaniline according to claim 3, characterized in that, During the microwave treatment in step (4), the power is controlled at 500-600 W and the irradiation time is 10-20 min; When exposed to air, the environmental humidity is controlled at 40-60% and the temperature is 20-25 °C.

9. The synthesis process of N-methylaniline according to claim 1, wherein, The temperature during the condensation and liquefaction in step S3 is 10-16 °C.

10. The synthesis process of N-methylaniline according to claim 1, characterized in that, Step S3 is specifically as follows: the gaseous product is condensed and liquefied to obtain crude N-methylaniline. The crude product is subjected to membrane separation to remove most of the methanol, and the remaining material enters the aniline azeotropic tower for treatment. At -0.095 to -0.085 MPa and 155 to 165 °C, the gaseous medium is condensed by a condenser and then separated into layers at 5 to 10 °C. The organic phase enters the aniline tower, and azeotropy occurs at the top of the tower at 100 to 105 °C. After condensation, phase separation is carried out. The aqueous phase enters the wastewater tower, and the organic phase returns to the tower. When the water content at the bottom of the aniline tower is less than 1%, it is cooled to below 40 °C and returned to the batching process. The material at the bottom of the azeotropic tower enters the N-methylaniline rectification tower, and refined product is obtained by rectification at -0.098 to -0.092 MPa and 155 to 165 °C. The material at the bottom of the tower enters the N,N-dimethylaniline distillation tower, and the by-product is recovered at -0.098 to -0.092 MPa and 170 to 175 °C. The kettle residue is discharged once every 20 to 30 days. The aqueous phase of the wastewater tower enters the sewage station after being treated by resin to meet the standards.

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