Catalyst for preparing 2-amino-N, 3-dimethylbenzamide through continuous hydrogenation as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing 2-amino-N, 3-dimethyl benzamide through continuous hydrogenation as well as a preparation method and application of the catalyst, Pd and Co are adopted to modify a Ni-series catalyst, 2-nitro-N, 3-dimethyl benzamide reacts with hydrogen through a continuous hydrogenation process, and hydrogenation reaction liquid is treated by a closed spray drying process. According to the method, the 2-amino-N, 3-dimethyl benzamide can be continuously prepared, and the product purity is gt; the percentage is 99.2%. Compared with an existing kettle type hydrogenation process and a separation mode, the method has the advantages that the production efficiency and the product stability are improved, the product yield is increased, the economic benefit is increased, meanwhile, the method is more advantageous in safety and environmental protection, basically no waste gas is continuously discharged, no high-ammonia-nitrogen wastewater is generated, the process flow is simplified, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of pharmaceutical and pesticide intermediates, and relates to a preparation method of 2-amino-N,3-dimethylbenzamide, and particularly relates to a catalyst for continuously hydrogenating to prepare 2-amino-N,3-dimethylbenzamide, a preparation method thereof and an application thereof. Background Art

[0002] 2-Amino-N,3-dimethylbenzamide has important applications in the field of pesticide synthesis and is an important intermediate for preparing the insecticide chlorantraniliprole. At present, the production of 2-amino-N,3-dimethylbenzamide in China mostly adopts the batch kettle process, and is prepared by catalytic hydrogenation or chemical reduction methods. However, the batch kettle process has many problems such as safety and environmental protection, unstable product quality, difficult separation of the hydrogenation reaction liquid from the catalyst, high energy consumption and material consumption, and limited production capacity.

[0003] In addition, for the conventional crystallization separation method, the separation process is complex, the solid-liquid separation process is prone to blockage, and the biggest problem is that a large amount of wastewater is generated. For every 1 ton of product produced, the amount of wastewater generated is about 2 tons, and the wastewater has a high ammonia nitrogen content, making the wastewater treatment difficult, bringing great safety and environmental protection problems to the production. At the same time, when using crystallization separation, the product yield will be reduced, about 80-82%, and some products are lost with the wastewater.

[0004] CN 117222617 A discloses a method for preparing 2-amino-N,3-dimethylbenzamide by hydrogenating 2-nitro-N,3-dimethylbenzamide. Using a kettle reaction process, through a supported nickel or Raney nickel catalyst, under the reaction pressure of 1-3 MPa and the temperature of 100 °C, the reaction selectivity of 2-amino-N,3-dimethylbenzamide is at most about 95.4%. Summary of the Invention

[0005] The main object of the present invention is to provide a method for continuously hydrogenating to prepare 2-amino-N,3-dimethylbenzamide. By using a fixed-bed process to replace the traditional batch hydrogenation process, the continuous operation of the hydrogenation section is realized. At the same time, by using the developed catalyst, on the one hand, the selectivity of the hydrogenation reaction is improved, the product purity is enhanced, and the hydrogenation reaction efficiency is also increased, which can greatly increase the production capacity; on the other hand, the continuous hydrogenation process avoids the disadvantages of the separation of the catalyst and the hydrogenation product brought by the batch process, which not only avoids the ineffective loss of the catalyst, but also avoids the problem that the catalyst powder is entrained into the product and affects the product quality. In addition, when separating the product, through the supporting closed spray drying process, not only the situation of easy blockage in the solid-liquid separation brought by the traditional crystallization separation process is completely solved, the wastewater can be greatly reduced by 80%-90%, and at the same time, the generation of high-ammonia-nitrogen and high-COD wastewater is avoided. In addition, by using the spray drying separation process, the product yield can be close to the theoretical value of 84.5%, and the yield can be increased by 2-3% compared with the traditional crystallization separation process. The technical solution of the present invention can stably prepare 2-amino-N,3-dimethylbenzamide products with a product purity > 99.2%.

[0006] To achieve the above object, in the first aspect of the present invention, a catalyst for continuously hydrogenating to prepare 2-amino-N,3-dimethylbenzamide is provided. The catalyst includes a carrier and an active component supported on the carrier. The active component is Ni and Co, and the promoter is Pd; the Ni content is 20-70% of the total weight of the catalyst, preferably 30-60%; the Co content is 0.5-5% of the total weight of the catalyst, preferably 1.0-3.0%, and the Pd content is 0.01-0.1% of the total weight of the catalyst, preferably 0.02-0.05%, and the balance is alumina.

[0007] Among them, in the catalyst, the molar ratio of Ni and Co can be (10-30):1.

[0008] In the second aspect of the present invention, a method for preparing a catalyst is provided. The method includes: Loading the active component on the carrier, and the active component is Ni and Co; wherein, the molar ratio of Ni and Co is 10-30:1.

[0009] A method for preparing a catalyst for continuously hydrogenating to prepare 2-amino-N,3-dimethylbenzamide, the method includes the following steps: Step 1: Dissolve the soluble precursors of Ni, Co and Pd together in deionized water to prepare an aqueous solution with a certain concentration; Step 2: Prepare an aqueous solution of the precipitant with the required concentration; Step 3: The solutions obtained in Step 1 and Step 2 are titrated into the precipitation tank at a uniform speed under stirring at 40 - 80 °C by the co-current method for reaction, and the pH value is maintained at 9 - 11; Step 4: The precipitate obtained in Step 3 is aged at a constant temperature for 4 - 8 h; Step 5: The aged precipitate in Step 5 is filtered and washed several times with deionized water until the pH is neutral, and the precipitated substance is obtained by filtration; Step 6: The precipitate obtained in Step 5 is slurried and mixed evenly with pseudo-boehmite. The obtained solid substance is placed in a blast drying oven at 100 - 120 °C for 6 - 12 h of drying, and then calcined in a muffle furnace at 300 - 500 °C for 2 - 8 h. Preferably, the calcination temperature is 350 - 480 °C. After calcination, the catalyst is ground into powder for tableting, or directly ground and sieved to obtain the catalyst; Step 7: The catalyst obtained in Step 6 is activated with nitrogen + hydrogen, and the activation temperature is 300 - 500 °C, preferably 350 - 450 °C. The catalyst is reserved after activation.

[0010] The metal compound of the active component element is formulated into an aqueous solution with a certain concentration. The precursor of Ni is one or a mixture of nickel nitrate and nickel chloride, and the formulated concentration is 0.51 - 1.02 moL / L. The precursor of Co is one or a mixture of cobalt nitrate or cobalt chloride, and the formulated concentration is 0.017 - 0.051 moL / L. The precursor of Pd is palladium acetate and chloropalladic acid, and the formulated concentration is 1.88×10 -4 -4.7×10 -4 mol / L.

[0011] The types of the precipitant are one or several of sodium carbonate, sodium bicarbonate, and sodium hydroxide, and the concentration is 1.50 - 2.50 moL / L.

[0012] The third aspect of the present invention provides a method for continuously hydrogenating to prepare 2-nitro-N,3-dimethylbenzamide, which includes contacting 2-nitro-N,3-dimethylbenzamide and hydrogen with a hydrogenation catalyst under hydrogenation reaction conditions. Among them, the hydrogenation catalyst is the catalyst of the present invention.

[0013] The fourth aspect of the present invention also provides a closed spray drying method for a 2-amino-N,3-dimethylbenzamide product solution. The method includes that under certain process conditions, the hydrogenated liquid enters the cavity through a top spray head by a peristaltic pump; nitrogen is heated to the required temperature by a heater and enters the cavity. After gas-liquid contact, the liquid raw material is rapidly dried, and methanol and water therein are rapidly vaporized and separated through a first-stage and a second-stage cyclone in the back path (equipped with a dust removal bag to prevent dust from entering the back path cooling system). The solid product enters the collection tank at the bottom of the separator, the gas phase is cooled by a cooler and collected in a liquid collection tank, and the gas phase after separating methanol and water continues to circulate in the system through a circulation fan.

[0014] In the 2-nitro-N,3-dimethylbenzamide methanol solution, the mass ratio of 2-nitro-N,3-dimethylbenzamide to methanol is 1:(3 - 20), preferably 1:(4 - 9).

[0015] The contact includes a first contact and a second contact. In the first contact, under first hydrogenation reaction conditions, a 2-nitro-N,3-dimethylbenzamide methanol solution, hydrogen, and a hydrogenation catalyst are contacted to obtain a first contact product mixture; in the second contact, under second hydrogenation reaction conditions, the first contact product mixture, supplementary hydrogen, and a hydrogenation catalyst are contacted to obtain a second contact product mixture.

[0016] The temperature of the first contact is 40 - 100°C, and the temperature of the second contact is 50 - 100°C; preferably, the temperature of the first contact is 50 - 80°C; preferably, the temperature of the second contact is 60 - 85°C. In the first contact and the second contact, the pressure is the same, being 1 - 5 MPa, preferably 1 - 3 MPa, and the pressure is gauge pressure; preferably, the effective weight hourly space velocity of the first contact is 0.2 - 0.5 -1 , and the effective weight hourly space velocity of the second contact is 0.1 - 0.3 h -1 , and the weight hourly space velocity is calculated based on the treatment amount of 2-nitro-N,3-dimethylbenzamide.

[0017] The first contact is carried out in a fixed-bed reactor, and the fixed-bed reactor can be a conventional reactor or a shell-and-tube reactor; the 2-nitro-N,3-dimethylbenzamide methanol solution can enter the reactor in an upflow-downflow manner or a downflow-upflow manner, and preferably, it is selected to enter the shell-and-tube reactor in a downflow-upflow manner; preferably, the second contact is carried out in a common fixed-bed reactor, and the first contact product mixture preferably passes through the fixed-bed reactor in an upflow-downflow manner.

[0018] The molar ratio of the 2-nitro-N,3-dimethylbenzamide methanol solution, recycled hydrogen, and supplementary hydrogen is 1:10 - 30:2 - 3.

[0019] The spray drying system is a closed system in a full-nitrogen environment. In the embodiment of the 5L model closed spray drying system, the drying process conditions are as follows: the inlet air temperature is 120 - 190 °C, and the corresponding outlet air temperature is 70 - 110 °C, and the circulating air volume is 150 - 250 m 3 / h.

[0020] The effect achieved by the present invention is that the catalyst according to the present invention is suitable for continuous production processes, so that the continuous preparation of 2-amino-N,3-dimethylbenzamide products can be realized, and the product quality is high and stable. The yield of the product can be increased by 2 - 3% compared with the traditional separation process.

[0021] The technical solution of the present invention uses a Pd and Co modified catalyst to improve the selectivity of the product, and the selectivity of the product 2-amino-N,3-dimethylbenzamide reaches more than 99.20%.

[0022] The present invention adopts the technology of spray drying to separate products. Compared with the existing crystallization separation process, it not only completely solves the problem of easy blockage in solid-liquid separation caused by the traditional crystallization separation process, can greatly reduce wastewater by 80% - 90%, at the same time avoids the generation of high-ammonia-nitrogen and high-COD wastewater. In addition, adopting the spray drying separation process, the yield can be increased by 2 - 3% compared with the traditional crystallization separation process. Description of the Drawings

[0023] Figure 1 Used to illustrate a preferred embodiment of the hydrogenation reaction method according to the present invention.

[0024] Description of the Reference Numerals 1 - Hydrogen heater, 2 / 3 - Hydrogen flowmeter, 4 - Raw material preparation tank, 5 - Metering pump, 6 - Raw material buffer tank, 7 - Feed pump, 8 - Heater, 9 - Main hydrogenation tube reactor, 10 - Cooler, 11 - Post-hydrogenation fixed bed reactor, 12 - Cooler, 13 - High-pressure separator Figure 2 Used to illustrate the spray drying method according to the present invention.

[0025] Description of the Reference Numerals 21 - Raw material tank, 22 - Peristaltic pump, 23 - Nitrogen induced draft fan, 24 - Heater, 25 - Main cavity of spray drying, 26 - Primary cyclone separator, 27 - Secondary cyclone separator, 28 - Condenser, 29 - Refrigeration unit, 30 - Circulating machine, 31 - Recovered methanol tank. Detailed Embodiments

[0026] Embodiment of Catalyst Preparation Preparation Example 1 In this example, the hydrogenation catalyst A is as follows: based on the total amount of the catalyst, the nickel element content is 40% by weight, the Co content is 1.0% by weight, the Pd content is 0.02%, and the balance is alumina content. It is prepared by the following method: (1) At 60 °C and with stirring, an aqueous solution containing nickel nitrate, cobalt nitrate, and chloropalladic acid is co-precipitated with an aqueous solution containing sodium hydroxide and sodium carbonate (the molar ratio of sodium hydroxide to sodium carbonate is (1:2)) in a parallel flow, controlling the final pH value to be 10 - 11. The resulting reaction mixture is filtered, and the collected precipitate is washed with deionized water until the pH is neutral to obtain a co-precipitate.

[0027] (2) The precipitate is mixed with boehmite, slurried, then dried at 120 °C for 6 h and calcined at 400 °C for 3 h. The calcined powder is tableted to obtain a catalyst precursor.

[0028] (3) The catalyst precursor is activated in a mixed atmosphere of hydrogen and nitrogen (the hydrogen content is gradually increased from 10% to over 90%), and the maximum activation temperature is 400 °C to obtain the hydrogenation catalyst A according to the present invention.

[0029] Preparation of Comparative Example 1 In this preparation example, the hydrogenation catalyst A2 is as follows: based on the total amount of the catalyst, the nickel element content is 40% by weight, the Co content is 1.0%, and the balance is alumina content. It is prepared by the following method: The hydrogenation catalyst is prepared by the same method as in Preparation Example 1, except that chloropalladic acid is not added in step (1), thereby obtaining the hydrogenation catalyst A2.

[0030] Preparation Example 2 In this example, the hydrogenation catalyst B is as follows: based on the total amount of the catalyst, the nickel element content is 30% by weight, the Co content is 3.0%, the Pd content is 0.03%, and the balance is alumina content. It is prepared by the following method: (1) At 60 °C and with stirring, an aqueous solution containing nickel chloride, cobalt chloride, and palladium acetate is co-precipitated with an aqueous solution containing sodium hydroxide and sodium bicarbonate (the molar ratio of sodium hydroxide to sodium carbonate is (1:2)) in a parallel flow, controlling the final pH value to be 9 - 10. The resulting reaction mixture is filtered, and the collected precipitate is washed with deionized water until the pH is neutral to obtain a co-precipitate.

[0031] (2) The precipitate is mixed with pseudo-boehmite, slurried, then dried at 120 °C for 6 h and calcined at 350 °C for 3 h. The calcined powder is tableted to obtain a catalyst precursor.

[0032] (3) The catalyst precursor is activated in a mixed atmosphere of hydrogen and nitrogen (the hydrogen content is gradually increased from 10% to over 90%), and the highest activation temperature is 350 °C to obtain the hydrogenation catalyst B according to the present invention.

[0033] Preparation Example 3 In this preparation example, the hydrogenation catalyst C is: based on the total amount of the catalyst, the nickel element content is 60% by weight, the Co content is 1.0% by weight, the Pd content is 0.04%, and the balance is alumina. The preparation method is the same as that in Example 1.

[0034] Preparation Example 4 In this preparation example, the hydrogenation catalyst D is: based on the total amount of the catalyst, the nickel element content is 30% by weight, the Co content is 1.0% by weight, the Pd content is 0.03%, and the balance is alumina. The preparation method is the same as that in Example 2.

[0035] Preparation Example 5 In this preparation example, the hydrogenation catalyst E is: based on the total amount of the catalyst, the nickel element content is 60% by weight, the Co content is 3.0% by weight, the Pd content is 0.05%, and the balance is alumina. The preparation method is as follows: (1) At 40 °C with stirring, an aqueous solution containing nickel nitrate, cobalt nitrate and chloropalladic acid is co-precipitated with an aqueous solution containing sodium bicarbonate and sodium carbonate (the molar ratio of sodium bicarbonate to sodium carbonate is (1:1)), and the end point pH value is controlled to be 10 - 11. The obtained reaction mixture is filtered, and the collected precipitate is washed with deionized water until the pH is neutral to obtain a co-precipitate.

[0036] (2) The precipitate is mixed with boehmite, slurried, then dried at 120 °C for 6 h and calcined at 480 °C for 3 h. The calcined powder is tableted to obtain a catalyst precursor.

[0037] (3) The catalyst precursor is activated in a mixed atmosphere of hydrogen and nitrogen (the hydrogen content is gradually increased from 10% to over 90%), and the highest activation temperature is 450 °C to obtain the hydrogenation catalyst E according to the present invention.

[0038] Preparation Example 6 In this preparation example, the hydrogenation catalyst F is: based on the total amount of the catalyst, the nickel element content is 50% by weight, the Co content is 1.5% by weight, the Pd content is 0.02%, and the balance is alumina. It is prepared by the following method: (1) At 50 °C with stirring, an aqueous solution containing nickel nitrate, cobalt nitrate, and chloropalladic acid is co-precipitated with an aqueous solution containing sodium hydroxide and sodium bicarbonate (the molar ratio of sodium hydroxide to sodium bicarbonate is 1:2) in a parallel flow manner, controlling the final pH value to be 10 - 11. The resulting reaction mixture is filtered, and the collected precipitate is washed with deionized water until the pH is neutral to obtain a co-precipitate.

[0039] (2) The nickel precipitate is mixed with boehmite, slurried, then dried at 120 °C for 6 h and calcined at 480 °C for 3 h. The calcined powder is tableted to obtain a catalyst precursor.

[0040] (3) The catalyst precursor is subjected to an activation treatment in a mixed atmosphere of hydrogen and nitrogen (the hydrogen content is gradually increased from 10% to over 90%), and the maximum activation temperature is 420 °C to obtain the hydrogenation catalyst F according to the present invention.

[0041] Preparation of Comparative Example 2 In this preparation example, the hydrogenation catalyst F2 is as follows: based on the total amount of the catalyst, the nickel element content is 50% by weight, the Co content is 1.5% by weight, the Pd content is 0.02%, and the alumina content is the balance. It is prepared by the following method: The hydrogenation catalyst is prepared by the same method as in Preparation Example 6, except that in step (2), the calcination temperature is 300 °C, thereby obtaining the catalyst F2.

[0042] Preparation of Comparative Example 3 In this preparation example, the hydrogenation catalyst F3 is as follows: based on the total amount of the catalyst, the nickel element content is 50% by weight, the Co content is 1.5% by weight, the Pd content is 0.02%, and the alumina content is the balance. It is prepared by the following method: The hydrogenation catalyst is prepared by the same method as in Preparation Example 6, except that in step (3), the activation temperature is 300 °C, thereby obtaining the catalyst F3.

[0043] Examples 1 - 9 are used to illustrate the hydrogenation reaction method and separation method according to the present invention.

[0044] Examples 1 - 9 refer to Figure 1 and Figure 2 In the manner shown, using the conditions listed in Table 1 and Table 2, 2-nitro-N,3-dimethylbenzamide is subjected to a hydrogenation reaction to prepare 2-amino-N,3-dimethylbenzamide. The specific process flow is described as follows: Hydrogenation process section (such as Figure 1 ) : The raw material of 2-nitro-N,3-dimethylbenzamide and the methanol solvent are in Figure 1In the raw material preparation tank, stirring and dissolution are carried out to form a raw material liquid containing 5-20% by weight of 2-nitro-N,3-dimethylbenzamide. The raw material liquid is sent into the hydrogenation raw material buffer tank. After being metered and pressurized by a metering pump, the raw material liquid is mixed with high-pressure hydrogen metered by a flow controller in a pipeline, and then the mixture enters the main hydrogenation tubular reactor from bottom to top together, contacts with the hydrogenation catalyst filled in the tubes of the main hydrogenation tubular reactor, and undergoes the main hydrogenation reaction. The outlet mixture of the main hydrogenation tubular reactor is cooled by a cooler and then mixed with high-pressure supplementary hydrogen metered by a flow controller in a pipeline, and then the mixture enters the post-hydrogenation fixed-bed reactor from top to bottom together, contacts with the hydrogenation catalyst filled in the post-hydrogenation fixed-bed reactor, and undergoes the hydrogenation reaction. The outlet mixture of the post-hydrogenation fixed-bed reactor is cooled by a condenser and then enters a high-pressure separator for gas-liquid separation. The separated hydrogen enters the hydrogen recycling system after removing a small amount of vaporized solvent carried along, and the hydrogenated product solution separated enters the drying system.

[0045] Drying process section (such as Figure 2 ): The solution in the hydrogenated product tank enters the cavity through a top spray head by a peristaltic pump; nitrogen is heated to the required temperature by a heater and enters the cavity. After gas-liquid contact, the liquid raw material is quickly dried, and the methanol and water in it are quickly vaporized and carried into the first-stage and second-stage of the back path by the circulating nitrogen for two-stage cyclone separation (a dust removal bag is provided to prevent dust from entering the back path cooling system). The solid product enters the collection tank at the bottom of the separator, and the gas phase is cooled by a cooler and then collected into the solvent tank for use in the raw material preparation of the hydrogenation unit. The gas phase after separating methanol and water continues to circulate in the system by a circulating fan.

[0046] The specific hydrogenation reaction conditions and reaction results are listed in Table 1.

[0047] Table 1 Reaction results under different hydrogenation conditions Table 2 (The following data is based on 5L closed spray drying as an example) It can be seen from the data in Table 1 that the hydrogenation catalyst according to the present invention shows high catalytic activity in the hydrogenation reaction of 2-nitro-N,3-dimethylbenzamide. Even when the hydrogenation reaction is carried out at a lower temperature, good catalytic reaction effects can be obtained. The results in Table 1 and Table 2 also confirm that the hydrogenation catalyst according to the present invention is suitable for continuous production and can prepare 2-amino-N,3-dimethylbenzamide products with stable quality. The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including the combination of each technical feature in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A catalyst for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation, comprising active component elements of Ni and Co, wherein the molar ratio of Ni to Co is (10-30):1; the Ni content is 20-70% of the total weight of the catalyst, preferably 30-60%; the Co content is 0.5-5% of the total weight of the catalyst, preferably 1.0-3.0%; the additive is Pd, the Pd content is 0.01-0.1% of the total weight of the catalyst, preferably 0.02-0.05%; the balance is alumina.

2. A method for preparing a catalyst for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation, the method comprising the following steps: Step 1: Dissolve soluble precursors of Ni, Co and additive Pd in ​​deionized water to prepare an aqueous solution of a certain concentration; Step 2: preparing the precipitant into an aqueous solution of desired concentration; Step 3: The solutions obtained in step 1 and step 2 are titrated into a precipitation tank at a constant speed at 40-80° C. under stirring by a parallel flow method to react, and the pH value is maintained at 9-11; Step 4: ageing the precipitate obtained in step 3 at a constant temperature for 4-8 hours; Step 5: Filter the precipitate after aging in step 5, wash it with deionized water several times until the pH is neutral, and filter the precipitate; Step 6: The precipitate obtained in the mixing step 5 is mixed evenly with the pseudo-boehmite by slurrying, and the obtained solid material is placed in a 100-120° C. forced air drying oven for 6-12 hours, and then roasted in a muffle furnace at 300-500° C. for 2-8 hours, preferably at a roasting temperature of 350-480° C. After roasting, the catalyst is ground into powder for tableting, or directly ground and sieved to obtain the catalyst; Step 7: Activate the catalyst obtained in step 6 with nitrogen + hydrogen at an activation temperature of 300-500° C., preferably 350-450° C. The activated catalyst is ready for use.

3. The method for preparing a catalyst for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 2, characterized in that In step 1, the metal compound of the active component element is prepared into an aqueous solution of a certain concentration, wherein the precursor of Ni is one of nickel nitrate and nickel chloride or a mixture thereof, and the prepared concentration is 0.51-1.02 mol / L, and the precursor of Co is one of cobalt nitrate and cobalt chloride or a mixture thereof, and the prepared concentration is 0.017-0.051 mol / L; The Pd precursor is palladium acetate and / or chloropalladic acid, and the concentration is 1.88×10 -4 -4.7×10 -4 mol / L.

4. The method for preparing a catalyst for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 2, characterized in that The type of precipitant described in step 3 is one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide, and the concentration is 1.50-2.50 mol / L.

5. A method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation, the method comprising: (1) contacting a 2-nitro-N,3-dimethylbenzamide methanol solution with the catalyst according to claim 1 in a hydrogen atmosphere; (2) The hydrogenated liquid obtained after the contact in step (1) is transported to a closed spray drying system, and the solid obtained by drying under certain process conditions is 2-amino-N,3-dimethylbenzamide; the spray drying system is a closed system in a full nitrogen environment, and the drying process conditions are preferably an inlet air temperature of 120-190°C, a corresponding outlet air temperature of 70-110°C, and a circulating air volume of 150-250m3 for a 5L spray drying system. 3 / h.

6. The method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 5, characterized in that In the 2-nitro-N,3-dimethylbenzamide methanol solution, the mass ratio of 2-nitro-N,3-dimethylbenzamide to methanol is 1:(3-20), preferably 1:(4-9).

7. The method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 5, characterized in that The contact comprises a first contact and a second contact. In the first contact, under a first hydrogenation reaction condition, a 2-nitro-N,3-dimethylbenzamide methanol solution and hydrogen are contacted with a hydrogenation catalyst to obtain a first contact product mixture. In the second contact, under a second hydrogenation reaction condition, the first contact product mixture and supplementary hydrogen are contacted with a hydrogenation catalyst to obtain a second contact product mixture. The molar ratio of the 2-nitro-N,3-dimethylbenzamide methanol solution, the circulating hydrogen and the supplementary hydrogen is 1:10-30:2-3.

8. The method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 7, characterized in that The temperature of the first contact is 40-100°C, and the temperature of the second contact is 50-100°C; preferably, the temperature of the first contact is 50-80°C; preferably, the temperature of the second contact is 60-85°C.

9. The method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to claim 7, characterized in that In the first contact and the second contact, the pressure is the same, 1-5MPa, preferably 1-3MPa, and the pressure is gauge pressure; preferably, the effective weight hourly space velocity of the first contact is 0.2-0.5h -1 The effective weight hourly space velocity of the second contact is 0.1-0.3h -1 , the weight hourly space velocity is based on the treatment amount of 2-nitro-N,3-dimethylbenzamide.

10. The method for preparing 2-amino-N,3-dimethylbenzamide by continuous hydrogenation according to any one of claims 7 to 9, characterized in that The first contact is carried out in a fixed bed reactor, which is a conventional reactor or a shell-and-tube reactor; the 2-nitro-N,3-dimethylbenzamide methanol solution enters the reactor in an upper-in-lower-out manner or a lower-in-upper-out manner, preferably, the lower-in-upper-out manner is selected to enter the shell-and-tube reactor; preferably, the second contact is carried out in a common fixed bed reactor, and the first contact product mixture preferably passes through the fixed bed reactor in an upper-in-lower-out manner.

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