A method for preparing N-methylaniline by low alcohol amine ratio reaction

Abstract

The present invention relates to the technical field of N-methylaniline, and discloses a method for preparing N-methylaniline by low alcohol amine ratio reaction. The present invention selects the reaction process of low alcohol amine ratio, and reduces the content of impurity N, N-dimethylaniline in product N-methylaniline by multi-stage reaction. At the same time, a mode of adding a small amount of methanol at each stage is selected, so that each stage of reaction exothermicity is limited, even if all methanol reacts, it will not overheat, and the problem of possible overheating in current industrial devices is solved. The reactor adopts a multi-stage radial reactor, and a quench distributor is set in the treatment of each stage of methanol, and the overall material can pass through the catalyst bed evenly, changing the temperature unevenness phenomenon caused by the small heat exchange tube and uneven catalyst loading in the existing industrial device shell and tube reactor. At the same time, the bed pressure drop is reduced, and the pressure of the reaction system is low, which can reduce the impurity N, N-dimethylaniline generation.

Description

Technical Field

[0001] The invention relates to the technical field of N-methylaniline, in particular to a method for preparing N-methylaniline by reaction with a low alcohol amine ratio. Background Art

[0002] N-methylaniline is an important chemical raw material. Its main uses include: the main intermediate of the new generation of low-toxic herbicides mefenacet, the raw material for the synthesis of low-toxic insecticide buprofezin, the production of pharmaceutical intermediates and cationic dye intermediates, and the high-clean non-metallic gasoline antiknock agent to increase the octane number. The production of N-methylaniline mainly adopts the production method of the gas phase reaction process of aniline and methanol. Aniline and methanol are synthesized by reaction in a tubular reactor loaded with an acidic catalyst.

[0003] Although the current industrialized shell-and-tube gas phase reaction process can produce N-methylaniline products, there are also a lot of problems. (1) The reaction process conditions are not set reasonably. From the process principle, in order to avoid excessive production of the main side reaction N,N-dimethylaniline, a low alcohol amine ratio process condition should be adopted. However, in order to reduce the use of more expensive aniline, the existing industrial equipment adopts a high alcohol amine ratio of 1.5-2.5. The process condition leads to a large increase in the secondary substitution side reaction of N-methylaniline and methanol. N,N-dimethylaniline accounts for about 1.5%-4.5% of the reaction product, while the impurity N,N-dimethylaniline content in the qualified HG / T3409-2010 product N-methylaniline is up to 0.9%. Therefore, a distillation tower has to be set in the distillation unit to separate N-methylaniline and N,N-dimethylaniline with a boiling point difference of 3°C, which greatly increases energy consumption. Moreover, due to the small difference in boiling points, it is difficult to completely separate N,N-dimethylaniline from N-methylaniline. The separated by-product N,N-dimethylaniline contains about 50% N-methylaniline, which increases the material consumption of the device. (2) The heat transfer oil of the reactor is uneven, resulting in the hot spot temperature of the reactor exceeding 250°C and uneven distribution, and the temperature difference between different reaction tubes is more than 15°C. Since the reaction is a highly exothermic reaction, the heat removal of the shell-and-tube reactor is not timely, which may bring safety hazards of overheating and overpressure of the reaction system. In addition, the high temperature further increases the secondary substitution side reaction of N-methylaniline and methanol, which will increase the difficulty of distillation separation and the content of impurity components in the product. When operated according to the designed process, the product cannot meet the product indicators of high-quality products. (3) The shell-and-tube reactor type also has certain defects. In industrial equipment, in order to better remove heat, it is necessary to select a reaction tube with a small diameter of φ32mm, while the equivalent diameter of the catalyst is 5mm. There are a large number of reaction tubes, and it is easy to produce uneven catalyst loading and different flow resistance during loading, which leads to uneven distribution of reaction materials, reduces reaction efficiency, and affects the service life of the catalyst. It needs to be replaced within 1 year, which increases operating costs.

[0004] With the increase in the market consumption and product indicators of N-methylaniline, how to produce high-purity premium N-methylaniline more safely has become a research hotspot. At present, the research is mainly focused on the research reports of catalysts, hoping to change the current problems of industrial equipment by increasing the temperature fluctuation resistance of the catalyst and the reaction selectivity at higher temperatures. However, the performance of the catalyst has not made any progress, and the catalyst used in industrial equipment is still the conventional CNW-1 model catalyst. Therefore, if the reaction process and reactor can be improved, the reaction temperature can be controlled to not soar and have uniformity, the selectivity of N-methylaniline can be improved, and the amount of by-product N,N-dimethylaniline generated can be reduced, the problems of the existing equipment can be solved in time.

[0005] Patent CN116159602A reports a reduction process of a copper catalyst for N-methylaniline synthesis, wherein a mixture of methanol and water is used to reduce the copper catalyst, and the copper catalyst is successively reduced by the mixed gas gradient and deeply dehydrated, so that the obtained copper catalyst for N-methylaniline has better activity, longer catalyst life, higher selectivity for the product N-methylaniline, and less by-products. The essence of this reduction is to control the concentration of hydrogen participating in the reduction reaction and the activation temperature conditions of the active center. This method has a certain impact on the catalyst strength due to the introduction of a large amount of water vapor.

[0006] Patent CN103028411A reports a new type of chromium-free gas phase catalyst for synthesizing N-methylaniline. The catalyst does not contain chromium, but contains 30%-70% copper, 10%-50% zinc, 5%-20% alkaline earth metals, and 0.2%-2% rare earth elements cerium or lanthanum by weight (in terms of oxide). The catalyst does not contain chromium, which reduces chromium pollution in catalyst production, as well as in the catalyst use process and downstream products. When this catalyst is used to produce N-methylaniline, the content of N,N-dimethylaniline formed by overreaction is extremely low. The performance of the catalyst reaches and exceeds the performance of products currently used in industrial devices, with high strength, high conversion rate and high selectivity. Catalyst use conditions: pressure is normal pressure, the molar ratio of methanol to aniline is 1.5:1, and the liquid space velocity is 0.6h -1 .

[0007] The above patents are all reports related to catalyst preparation and reduction, and fail to truly and fundamentally solve the problems that may occur in the reaction, such as high hot spot temperatures causing over-temperature safety hazards, uneven temperature distribution, and excessive production of N,N-dimethylaniline as a reaction by-product. Summary of the invention

[0008] (I) Technical problems to be solved: In view of the deficiencies in the prior art, the present invention provides a method for preparing N-methylaniline by low alcohol amine ratio reaction.

[0009] (II) Technical solution: A method for preparing N-methylaniline by low alcohol amine ratio reaction: S1. Aniline is added to a raw material vaporizer. The vaporized aniline enters a reaction preheater for heat exchange of the reaction material. Then, the aniline is added to a raw material heater 5 and heated to 203-207° C. The aniline is mixed with the first stream of low-temperature methanol at 58-62° C. produced by vaporization of a methanol vaporizer. The mixed material is heated to 198-202° C. and then enters the first stage catalyst reaction bed of a multi-stage gas phase quenching reactor for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0010] S2. The reaction material generated by the catalyst reaction bed in S1 is heated to 203-207°C, and mixed with the second stream of low-temperature methanol at 58-62°C produced by the methanol vaporizer, and the mixed material is heated to 198-202°C and enters the second stage catalyst reaction bed for reaction.

[0011] S3, heating the reaction material generated in S2 to 203-207°C, and mixing it with the nth stream of low-temperature methanol at 58-62°C, heating the mixture to 198-202°C, and entering the nth stage catalyst reaction bed for reaction; n is any integer between 2 and 20.

[0012] S4. After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it exchanges heat with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0013] The reaction discharge in S5 and S4 enters the stabilization tower of the distillation system for gas-liquid separation, and the gas phase at the top of the tower enters the absorption tower to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The kettle liquid phase of the stabilization tower enters the product coarse fractionation tower for treatment; aniline is distilled from the top of the product coarse fractionation tower, and aniline is returned to the raw material vaporizer in the form of liquid phase as the raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower and enters the N-methylaniline product tower. The top distillate of the product tower is the refined N-methylaniline product.

[0014] Preferably, the total molar ratio of methanol to aniline is 0.61-0.92:1, and the molar ratio of aniline to each stream of methanol is 14-15:1.

[0015] Preferably, the preparation method of the copper-zinc composite catalyst is: A1. Add porous nano-silica and toluene diisocyanate in a mass ratio of 1:(3-5) to toluene, heat to 80-90°C in a nitrogen atmosphere, stir and react for 5-10 hours, filter and wash with toluene, dry and add the product into water, heat to 90-95°C, stir and react for 36-48 hours, filter, wash with water and dry to obtain amino porous nano-silica.

[0016] A2. Add amino porous nano-silica, copper nitrate and zinc nitrate in a mass ratio of 1: (6-15): (1.8-5.2) to water, stir for 2-4 hours, then heat to 65-80°C, then add sodium carbonate solution, react for 3-4 hours, let stand for aging for 2-3 hours, filter, wash with water, and dry the product. Then calcine it in a muffle furnace at 450-500°C for 2-3 hours to obtain a copper-zinc composite catalyst.

[0017] Preferably, the gas phase at the top of the stabilization tower enters the absorption tower to recover unreacted aniline and methanol in the material using the circulating absorbent aniline, the bottom product of the absorption tower is sent to the oil-water separation tank for oil-water separation, the oil phase of the oil-water separation tank enters the analysis tower to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank enters the methanol recovery tower to recover methanol, the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material, and the process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0018] Preferably, the multi-stage gas phase quenching reactor is a multi-stage radial reactor, and the catalyst reaction bed of each stage adopts the type of fixed packing bed with material outer cylinder inlet and inner cylinder outlet. A methanol quenching distributor is set at each stage, and the overall material can pass through the catalyst bed evenly, changing the temperature unevenness caused by the small heat exchange tube and uneven catalyst loading in the existing industrial device shell and tube reactor. A quencher is set in the middle of each two stages, and the quencher is an annular distributor. The distributor is located in the interval between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst loading area. The catalyst outer cylinder is 60-180mm higher than the top of the annular distributor to prevent methanol from diffusing out of the material mixing area. The bottom of the annular distributor is 600-800mm higher than the top of the catalyst, so that the quenched methanol and the raw material aniline are fully mixed and uniform, ensuring that the material entering the radial catalyst bed is uniform. The annular distributor is provided with 3-5 rows of distribution holes to accelerate the material mixing and quenching speed. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction, and the reaction discharge flows downward along the inner cylinder after mixing in the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a thin bed with low pressure drop, and the total reactor pressure drop is 8-10 KPa. The pressure of the reaction system is correspondingly reduced from more than 30 KPa in the current industrial device to about 10 KPa. Since the low reaction pressure is conducive to the balanced reaction to produce more target product N-methylaniline, the amount of impurity N,N-dimethylaniline generated is further reduced.

[0019] (III) Beneficial technical effects: The present invention uses toluene diisocyanate to modify the surface of nano-silica, and then the isocyanate is hydrolyzed to generate amino groups to obtain amino-modified porous nano-silica. The surface-modified carbamate groups and amino groups are used to complex copper and zinc ions, so that a large amount of copper and zinc ions are uniformly adsorbed on the surface and pores of porous nano-silica. After coprecipitation reaction and high-temperature calcination, a copper-zinc composite catalyst with porous nano-silica as a carrier is obtained. The copper-zinc catalyst is uniformly loaded into the porous nano-silica matrix, showing higher selective catalytic performance, and can be used to catalyze the reaction of methanol and aniline to prepare N-methylaniline. The obtained N-methylaniline has high purity, less side reactions and impurities.

[0020] The present invention utilizes a new reaction process and radial reactor type, and through multi-stage reaction, controls the addition of a small amount of methanol at each stage, so that the heat release of each stage reaction is limited, and solves the problem of possible overheating in the current industrial device. In addition, this process selects a low alcohol amine ratio of about 0.7 (methanol molar amount is less than aniline), and designs that the raw material aniline is added at one time, and methanol is added in multiple stages. The molar amount of methanol in each stage of the reaction bed is only about one-tenth of the molar amount of aniline. In each stage of the reaction, even if the methanol is completely converted, the heat released by the reaction can only make the catalyst bed temperature rise less than 8°C. The conventional design catalyst bed temperature rise is about 5°C, and the catalyst bed is fundamentally controlled not to overheat. After the reaction material is heated from 200°C to 205°C, the low-temperature methanol raw material is added to the next stage, and the temperature is cooled to 200°C to enter the catalyst bed for reaction. After undergoing multiple stages of rapid cooling reaction, the total heat released by the reaction of the device of the same scale is released in stages, and there is no safety hazard due to untimely heat transfer in the existing device.

[0021] The reactor of the present invention adopts a multi-stage gas phase quenching reactor, and each stage of the reaction bed adopts the type of a fixed packing bed with materials entering from an outer tube and exiting from an inner tube. A quenching distributor is provided for each stage of methanol, so that the overall material can pass through the catalyst bed evenly, thereby changing the temperature unevenness caused by the small heat exchange tubes and uneven catalyst loading in the existing industrial device shell-and-tube reactor. Moreover, after adopting a fixed bed reactor, the bed pressure drop is reduced from 30KPa of the existing device to about 10KPa, and the pressure of the reaction system is reduced accordingly. Since the low reaction pressure is conducive to the balanced reaction to proceed in the direction of generating more target product N-methylaniline, the amount of impurity N,N-dimethylaniline generated is further reduced.

[0022] According to the reaction equation of N-methylaniline and N,N-dimethylaniline, the molar amount of methanol in each stage of reaction is designed to be much smaller than the molar amount of aniline, so that the equilibrium reaction proceeds in the direction of generating more target product N-methylaniline. Due to the small amount of methanol, there will not be too much methanol to further react with N-methylaniline to generate N,N-dimethylaniline, and the content of N,N-dimethylaniline in the generated reaction product is reduced from about 3% of the existing process to less than 0.6%. Since the qualified product index of product HG / T3409-2010 requires that the content of N,N-dimethylaniline is less than 0.9%, after adopting the new process, there is no need to set up a separate distillation tower in the distillation section to separate N,N-dimethylaniline and N-methylaniline, thereby reducing the energy consumption of the device.

[0023] This patent adopts a low alcohol-amine ratio, multi-stage gas phase quenching reaction process system. Methanol and aniline are vaporized and overheated separately. Gas phase aniline is added to the reactor at one time. Methanol is added to the reactor in multiple stages corresponding to the number of reactor stages. The amount of quenching methanol matches the number of reaction stages. Adding a small amount of methanol to each stage has the following effects. (1) Low temperature can be used as a quenching material to reduce the temperature of the material entering the next stage of reaction and reduce the amount of secondary substitution side reaction of N-methylaniline and methanol caused by temperature increase; (2) Since the amount of methanol added in each stage is small, even if the methanol is completely converted, the heat released by the reaction makes the temperature rise of the material less than 8°C. It is preferred to design the temperature rise of the material in each bed layer to be 2-5°C. (3) Since the amount of methanol added in each stage is small, relatively speaking, the molar ratio of aniline to methanol in each stage is about 15, and aniline is greatly in excess, so that the equilibrium reaction proceeds in the direction of generating more target product N-methylaniline. Since there is less methanol, there will not be too much methanol to further react with N-methylaniline to generate N,N-dimethylaniline. The content of N,N-dimethylaniline in the reaction product is reduced from about 3% in the existing process to less than 0.6%, thereby increasing the selectivity of N-methylaniline and reducing the material consumption of the device.

[0024] This process sets up a corresponding distillation separation system according to the reaction conditions. Since the amount of N,N-dimethylaniline generated by the reaction is less than 0.6% (compared with the mass of N-methylaniline generated), even if all N,N-dimethylaniline enters the product N-methylaniline, it will not affect the product quality of N-methylaniline. Therefore, the distillation system cancels the existing industrial device to set up a separate tower for separating N-methylaniline and N,N-dimethylaniline, and the process flow is more simplified. The distillation separation process is: the reaction materials first enter the stabilization tower for light component removal, and the materials at the top of the stabilization tower are set according to the process flow of absorption tower-oil-water separation tank-desorption tower-methanol recovery tower to recover methanol and part of aniline in the tail gas for reuse; the materials at the bottom of the stabilization tower enter the product coarse separation tower for separation, and the aniline at the top of the coarse separation tower is used in the recycling reaction unit, and the coarse product is obtained at the bottom of the coarse separation tower. The crude N-methylaniline then enters the product tower to recover the N-methylaniline product, and a small amount of heavy components in the bottom of the tower are sent to the tank area for storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a production process flow chart for preparing N-methylaniline.

[0026] Figure 2 It is a schematic diagram of the structure of a multi-stage gas phase rapid cooling reactor.

[0027] In the figure: 1 raw material vaporizer, 2 methanol vaporizer, 3 preheater, 4 multi-stage gas phase quenching reactor, 5 raw material heater, 6 stabilization tower, 7 coarse separation tower, 8 product tower, 9 absorption tower, 10 oil-water separation tank, 11 desorption tower, 12 methanol recovery tower. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0029] Porous nano-silica, model SS-S200J, Hangzhou Jikang New Materials Co., Ltd. Nano-silica, Hangzhou Jikang New Materials Co., Ltd.

[0030] Example 1

[0031] (1) Add 30 g of porous nano-silica and 90 g of toluene diisocyanate to 1.2 L of toluene, heat to 90 ° C in a nitrogen atmosphere, stir and react for 5 h, filter and wash with toluene, dry and add the product to water, heat to 90 ° C, stir and react for 48 h, filter, wash with water, and dry to obtain amino-porous nano-silica.

[0032] (2) Add 10 g of amino-modified porous nano-silica, 150 g of copper nitrate and 52 g of zinc nitrate to 1.2 L of water, stir for 4 h, then heat to 65 °C, then add sodium carbonate solution, adjust the pH of the reaction solution to 9, stir for 3 h, let stand for 2 h, filter, wash with water, dry the product, and calcine it in a muffle furnace at 450 °C for 3 h to obtain a copper-zinc composite catalyst.

[0033] (3) Aniline is added to the raw material vaporizer 1. The vaporized aniline enters the reaction preheater 3 for heat exchange with the reaction material, and then is added to the raw material heater 5 and heated to 205°C. It is mixed with the first stream of low-temperature methanol at 60°C produced by the methanol vaporizer 2, and the mixed material is heated to 200°C. Then, it enters the first stage catalyst reaction bed of the multi-stage gas phase quenching reactor 4 for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0034] (4) The reaction material generated by the catalyst reaction bed is heated to 205°C and mixed with the second stream of low-temperature methanol at 60°C produced by methanol vaporizer 2. The mixed material is heated to 200°C and enters the second stage catalyst reaction bed for reaction.

[0035] (5) The reaction material generated by the reaction is heated to 205°C and mixed with the third stream of low-temperature methanol at 60°C. The mixed material is heated to 200°C and enters the third stage catalyst reaction bed for reaction. The above operation is repeated. There are 7 stages of catalyst reaction beds in total. The total molar ratio of methanol to aniline is controlled to be 0.7:1.

[0036] (6) After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it is heat exchanged with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0037] (7) The reaction discharge enters the stabilization tower 6 of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower 9 to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The liquid phase in the kettle of the stabilization tower 6 enters the product coarse fractionation tower 7 for treatment. Aniline is distilled from the top of the product coarse fractionation tower 7 and returned to the raw material vaporizer 1 in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower 7 and enters the N-methylaniline product tower 8. The top distillate of the product tower 8 is the refined N-methylaniline product.

[0038] (8) The gas phase at the top of the stabilization tower 6 enters the absorption tower 9 to recover the unreacted aniline and methanol in the material using the circulating absorbent aniline. The bottom product of the absorption tower 9 is sent to the oil-water separation tank 10 for oil-water separation. The oil phase of the oil-water separation tank 10 enters the desorption tower 11 to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank 10 enters the methanol recovery tower 12 to recover methanol, and the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material. The process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0039] (9) The multi-stage gas phase quenching reactor 4 is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts the type of fixed packing bed with materials entering from the outer cylinder and exiting from the inner cylinder. A methanol quenching distributor is set at each stage, and the overall material passes through the catalyst bed evenly. A quencher is set between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 120mm higher than the top of the annular distributor, and the bottom of the annular distributor is 800mm higher than the top of the catalyst. The annular distributor is provided with 5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8 KPa.

[0040] Example 2

[0041] (1) Add 30 g of porous nano-silica and 150 g of toluene diisocyanate to 1.5 L of toluene, heat to 80 ° C in a nitrogen atmosphere, stir and react for 10 h, filter and wash with toluene, dry and add the product to water, heat to 95 ° C, stir and react for 36 h, filter, wash with water, and dry to obtain amino-porous nano-silica.

[0042] (2) Add 10 g of amino-modified porous nano-silica, 60 g of copper nitrate and 18 g of zinc nitrate to 1.2 L of water, stir for 2 h, then heat to 80 °C, then add sodium carbonate solution, adjust the pH of the reaction solution to 9, stir the reaction for 4 h, let it stand for 2 h, filter, wash with water, dry the product, and calcine it in a muffle furnace at 500 °C for 2 h to obtain a copper-zinc composite catalyst.

[0043] (3) Aniline is added to the raw material vaporizer 1. The vaporized aniline enters the reaction preheater 3 for heat exchange with the reaction material, and then is added to the raw material heater 5 and heated to 205°C. It is mixed with the first stream of low-temperature methanol at 60°C produced by the methanol vaporizer 2, and the mixed material is heated to 200°C. Then, it enters the first stage catalyst reaction bed of the multi-stage gas phase quenching reactor 4 for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0044] (4) The reaction material generated by the catalyst reaction bed is heated to 205°C and mixed with the second stream of low-temperature methanol at 60°C produced by methanol vaporizer 2. The mixed material is heated to 200°C and enters the second stage catalyst reaction bed for reaction.

[0045] (5) The reaction material generated by the reaction is heated to 205°C and mixed with the third stream of low-temperature methanol at 60°C. The mixed material is heated to 200°C and enters the third stage catalyst reaction bed for reaction. The above operation is repeated. There are 7 stages of catalyst reaction beds in total. The total molar ratio of methanol to aniline is controlled to be 0.7:1.

[0046] (6) After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it is heat exchanged with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0047] (7) The reaction discharge enters the stabilization tower 6 of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower 9 to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The liquid phase in the kettle of the stabilization tower 6 enters the product coarse fractionation tower 7 for treatment. Aniline is distilled from the top of the product coarse fractionation tower 7 and returned to the raw material vaporizer 1 in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower 7 and enters the N-methylaniline product tower 8. The top distillate of the product tower 8 is the refined N-methylaniline product.

[0048] (8) The gas phase at the top of the stabilization tower 6 enters the absorption tower 9 to recover the unreacted aniline and methanol in the material using the circulating absorbent aniline. The bottom product of the absorption tower 9 is sent to the oil-water separation tank 10 for oil-water separation. The oil phase of the oil-water separation tank 10 enters the desorption tower 11 to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank 10 enters the methanol recovery tower 12 to recover methanol, and the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material. The process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0049] (9) The multi-stage gas phase quenching reactor 4 is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts the type of fixed packing bed with materials entering from the outer cylinder and exiting from the inner cylinder. A methanol quenching distributor is set at each stage, and the overall material passes through the catalyst bed evenly. A quencher is set between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 120mm higher than the top of the annular distributor, and the bottom of the annular distributor is 800mm higher than the top of the catalyst. The annular distributor is provided with 5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8 KPa.

[0050] Comparative Example 1: (1) Add 150 g of copper nitrate and 52 g of zinc nitrate to 1.2 L of water, stir for 4 h, then heat to 65 °C, then add sodium carbonate solution, adjust the pH of the reaction solution to 9, stir for 3 h, let stand for 2 h, filter, wash with water, dry the product, and calcine it in a muffle furnace at 450 °C for 3 h to obtain a copper-zinc composite catalyst.

[0051] (2) Aniline is added to the raw material vaporizer 1. The vaporized aniline enters the reaction preheater 3 for heat exchange with the reaction material, and then is added to the raw material heater 5 and heated to 205°C. It is mixed with the first stream of low-temperature methanol at 60°C produced by the methanol vaporizer 2, and the mixed material is heated to 200°C. Then, it enters the first stage catalyst reaction bed of the multi-stage gas phase quenching reactor 4 for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0052] (3) The reaction material generated by the catalyst reaction bed is heated to 205°C and mixed with the second stream of low-temperature methanol at 60°C produced by methanol vaporizer 2. The mixed material is heated to 200°C and enters the second stage catalyst reaction bed for reaction.

[0053] (4) The reaction material generated by the reaction is heated to 205°C and mixed with the third stream of low-temperature methanol at 60°C. The mixed material is heated to 200°C and enters the third stage catalyst reaction bed for reaction. The above operation is repeated. There are 7 stages of catalyst reaction beds in total. The total molar ratio of methanol to aniline is controlled to be 0.7:1.

[0054] (5) After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it is heat exchanged with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0055] (6) The reaction discharge enters the stabilization tower 6 of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower 9 to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The liquid phase in the kettle of the stabilization tower 6 enters the product coarse fractionation tower 7 for treatment. Aniline is distilled from the top of the product coarse fractionation tower 7 and returned to the raw material vaporizer 1 in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower 7 and enters the N-methylaniline product tower 8. The top distillate of the product tower 8 is the refined N-methylaniline product.

[0056] (7) The gas phase at the top of the stabilization tower 6 enters the absorption tower 9 to recover the unreacted aniline and methanol in the material using the circulating absorbent aniline. The bottom product of the absorption tower 9 is sent to the oil-water separation tank 10 for oil-water separation. The oil phase of the oil-water separation tank 10 enters the desorption tower 11 to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank 10 enters the methanol recovery tower 12 to recover methanol, and the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material. The process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0057] (8) The multi-stage gas phase quenching reactor 4 is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts the type of fixed packing bed with materials entering from the outer cylinder and exiting from the inner cylinder. A methanol quenching distributor is set at each stage, and the overall material passes through the catalyst bed evenly. A quencher is set between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 120mm higher than the top of the annular distributor, and the bottom of the annular distributor is 800mm higher than the top of the catalyst. The annular distributor is provided with 5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8 KPa.

[0058] Comparative Example 2: (1) Add 30 g of nano-silica and 90 g of toluene diisocyanate to 1.2 L of toluene, heat to 90 ° C in a nitrogen atmosphere, stir and react for 5 h, filter and wash with toluene, dry and add the product to water, heat to 90 ° C, stir and react for 48 h, filter, wash with water, and dry to obtain amino-modified nano-silica.

[0059] (2) Add 10 g of amino-modified nano-silica, 150 g of copper nitrate and 52 g of zinc nitrate to 1.2 L of water, stir for 4 h, then heat to 65 °C, then add sodium carbonate solution, adjust the pH of the reaction solution to 9, stir for 3 h, let stand for 2 h, filter, wash with water, dry the product, and calcine it in a muffle furnace at 450 °C for 3 h to obtain a copper-zinc composite catalyst.

[0060] (3) Aniline is added to the raw material vaporizer 1. The vaporized aniline enters the reaction preheater 3 for heat exchange with the reaction material, and then is added to the raw material heater 5 and heated to 205°C. It is mixed with the first stream of low-temperature methanol at 60°C produced by the methanol vaporizer 2, and the mixed material is heated to 200°C. Then, it enters the first stage catalyst reaction bed of the multi-stage gas phase quenching reactor 4 for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0061] (4) The reaction material generated by the catalyst reaction bed is heated to 205°C and mixed with the second stream of low-temperature methanol at 60°C produced by methanol vaporizer 2. The mixed material is heated to 200°C and enters the second stage catalyst reaction bed for reaction.

[0062] (5) The reaction material generated by the reaction is heated to 205°C and mixed with the third stream of low-temperature methanol at 60°C. The mixed material is heated to 200°C and enters the third stage catalyst reaction bed for reaction. The above operation is repeated. There are 7 stages of catalyst reaction beds in total. The total molar ratio of methanol to aniline is controlled to be 0.7:1.

[0063] (6) After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it is heat exchanged with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0064] (7) The reaction discharge enters the stabilization tower 6 of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower 9 to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The liquid phase in the kettle of the stabilization tower 6 enters the product coarse fractionation tower 7 for treatment. Aniline is distilled from the top of the product coarse fractionation tower 7 and returned to the raw material vaporizer 1 in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower 7 and enters the N-methylaniline product tower 8. The top distillate of the product tower 8 is the refined N-methylaniline product.

[0065] (8) The gas phase at the top of the stabilization tower 6 enters the absorption tower 9 to recover the unreacted aniline and methanol in the material using the circulating absorbent aniline. The bottom product of the absorption tower 9 is sent to the oil-water separation tank 10 for oil-water separation. The oil phase of the oil-water separation tank 10 enters the desorption tower 11 to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank 10 enters the methanol recovery tower 12 to recover methanol, and the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material. The process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0066] (9) The multi-stage gas phase quenching reactor 4 is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts the type of fixed packing bed with materials entering from the outer cylinder and exiting from the inner cylinder. A methanol quenching distributor is set at each stage, and the overall material passes through the catalyst bed evenly. A quencher is set between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 120mm higher than the top of the annular distributor, and the bottom of the annular distributor is 800mm higher than the top of the catalyst. The annular distributor is provided with 5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8 KPa.

[0067] Comparative Example 3: (1) Add 10 g of porous nano-silica, 150 g of copper nitrate and 52 g of zinc nitrate to water, stir for 4 h, then heat to 65 °C, then add sodium carbonate solution, adjust the pH of the reaction solution to 9, stir for 3 h, let stand for 2 h, filter, wash with water, dry the product, and calcine it in a muffle furnace at 450 °C for 3 h to obtain a copper-zinc composite catalyst.

[0068] (2) Aniline is added to the raw material vaporizer 1. The vaporized aniline enters the reaction preheater 3 for heat exchange with the reaction material, and then is added to the raw material heater 5 and heated to 205°C. It is mixed with the first stream of low-temperature methanol at 60°C produced by the methanol vaporizer 2, and the mixed material is heated to 200°C. Then, it enters the first stage catalyst reaction bed of the multi-stage gas phase quenching reactor 4 for reaction. The catalyst reaction bed contains a copper-zinc composite catalyst.

[0069] (3) The reaction material generated by the catalyst reaction bed is heated to 205°C and mixed with the second stream of low-temperature methanol at 60°C produced by methanol vaporizer 2. The mixed material is heated to 200°C and enters the second stage catalyst reaction bed for reaction.

[0070] (4) The reaction material generated by the reaction is heated to 205°C and mixed with the third stream of low-temperature methanol at 60°C. The mixed material is heated to 200°C and enters the third stage catalyst reaction bed for reaction. The above operation is repeated. There are 7 stages of catalyst reaction beds in total. The total molar ratio of methanol to aniline is controlled to be 0.7:1.

[0071] (5) After the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it is heat exchanged with the raw material aniline, and then the reaction effluent enters the product distillation system.

[0072] (6) The reaction discharge enters the stabilization tower 6 of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower 9 to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the thermal oil furnace. The liquid phase in the kettle of the stabilization tower 6 enters the product coarse fractionation tower 7 for treatment. Aniline is distilled from the top of the product coarse fractionation tower 7 and returned to the raw material vaporizer 1 in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower 7 and enters the N-methylaniline product tower 8. The top distillate of the product tower 8 is the refined N-methylaniline product.

[0073] (7) The gas phase at the top of the stabilization tower 6 enters the absorption tower 9 to recover the unreacted aniline and methanol in the material using the circulating absorbent aniline. The bottom product of the absorption tower 9 is sent to the oil-water separation tank 10 for oil-water separation. The oil phase of the oil-water separation tank 10 enters the desorption tower 11 to recover methanol and aniline, and returns to the raw material tank as a reaction raw material; the aniline desorbed at the bottom of the tower is recycled as an absorbent; the water phase of the oil-water separation tank 10 enters the methanol recovery tower 12 to recover methanol, and the methanol recovered at the top of the tower is returned to the raw material tank as a reaction raw material. The process water at the bottom of the tower enters the sewage treatment facility for treatment.

[0074] (8) The multi-stage gas phase quenching reactor 4 is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts the type of fixed packing bed with materials entering from the outer cylinder and exiting from the inner cylinder. A methanol quenching distributor is set at each stage, and the overall material passes through the catalyst bed evenly. A quencher is set between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 120mm higher than the top of the annular distributor, and the bottom of the annular distributor is 800mm higher than the top of the catalyst. The annular distributor is provided with 5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder for reaction. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the next radial reactor. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8 KPa.

[0075] The overhead product of the product tower 8, which is the main material component of the refined N-methylaniline product (the remainder is high boiling point substances), was analyzed by liquid chromatography. The test results are shown in Table 1.

[0076] Table 1: Test results Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Appearance Light yellow transparent liquid Colorless transparent liquid Brown liquid Reddish brown liquid Reddish brown liquid <![CDATA[Density (20 °C, g / cm 3 )]]> 0.9894 0.9897 0.9909 0.9904 0.9902 N-methylaniline content (%) 99.502 99.537 88.273 93.024 94.688 Aniline content (%) 0.173 0.128 5.569 1.526 0.862 N,N-dimethylaniline content (%) 0.241 0.250 6.213 4.869 3.925 Moisture (%) 0.021 0.027 0.025 0.029 0.024 Low boiling matter (%) 0.012 0.014 0.074 0.061 0.056 After testing, the N-methylaniline content of Example 1 and Example 2 reached 99.502-99.537%, which was significantly higher than that of Comparative Examples 1-3, and the by-products aniline and N,N-dimethylaniline were very small.

Claims

1. A method for preparing N-methylaniline by low alcohol amine ratio reaction, characterized in that: The method comprises: S1, adding aniline to a raw material vaporizer (1), the vaporized aniline enters a reaction preheater (3), performs heat exchange with the reaction material, then enters a raw material heater (5) to be heated to a pretreatment temperature, mixes with the first stream of low-temperature methanol vaporized by a methanol vaporizer (2), heats the mixture to a reaction temperature, and then enters a first-stage catalyst reaction bed layer of a multi-stage gas phase rapid cooling reactor (4) to react, wherein the catalyst reaction bed layer contains a copper-zinc composite catalyst; S2, heating the reaction material generated in the catalyst reaction bed in S1 to the pretreatment temperature, and mixing it with the second stream of low-temperature methanol vaporized by the methanol vaporizer (2), heating the mixed material to the reaction temperature, and entering the second stage catalyst reaction bed to react; S3, heating the reaction material generated in S2 to the pretreatment temperature, mixing it with the nth stream of low-temperature methanol, heating the mixture to the reaction temperature, and entering the nth stage catalyst reaction bed layer for reaction; S4, after the reaction effluent obtained from the last stage catalyst reaction bed flows out of the reaction catalyst bed, it exchanges heat with the raw material aniline, and then the reaction effluent enters the product distillation system; The reaction output in S5 and S4 enters the stabilization tower (6) of the distillation system for gas-liquid separation. The gas phase at the top of the tower enters the absorption tower (9) to recover the unreacted aniline and methanol in the material. The tail gas is discharged from the top of the absorption tower as fuel for the heat transfer oil furnace. The liquid phase in the kettle of the stabilization tower (6) enters the product coarse fractionation tower (7) for treatment. Aniline is distilled from the top of the product coarse fractionation tower (7) and returned to the raw material vaporizer (1) in the form of liquid phase as a raw material for the reaction. The material rich in N-methylaniline is extracted from the bottom of the coarse fractionation tower (7) and enters the N-methylaniline product tower (8). The top distillate of the product tower (8) is the refined N-methylaniline product.

2. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The temperature of the low-temperature methanol from S1 to S3 is 58-62°C.

3. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The pretreatment temperature of S1 to S3 is 203-207°C, and the reaction temperature is 198-202°C.

4. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The n is any integer between 2 and 20.

5. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The total molar ratio of the methanol to the aniline is 0.61-0.92:1, and the molar ratio of the aniline to each methanol is 14-15:

1.

6. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The distillation separation process in the distillation system is as follows: the reaction materials first enter the stabilization tower for light component removal treatment, the materials at the top of the stabilization tower are arranged according to the process flow of absorption tower-oil-water separator-desorption tower-methanol recovery tower, and methanol and part of aniline in the tail gas are recovered for reuse; the materials at the bottom of the stabilization tower enter the product coarse fractionation tower for separation, the aniline at the top of the coarse fractionation tower is used in the recycling reaction unit, the coarse product is obtained at the bottom of the coarse fractionation tower, and the crude N-methylaniline then enters the product tower to recover the N-methylaniline product, and a small amount of heavy components in the bottom of the tower are sent to the tank area for storage.

7. The method for preparing N-methylaniline by low alcohol amine ratio reaction according to claim 1, characterized in that: The multi-stage gas phase quenching reactor (4) is a multi-stage radial reactor. The catalyst reaction bed of each stage adopts a fixed packing bed type in which the material enters from the outer cylinder and exits from the inner cylinder. A methanol quenching distributor is arranged at each stage, and the overall material passes through the catalyst bed evenly. A quencher is arranged between every two stages. The quencher is an annular distributor. The distributor is located in the area between the reactor cylinder and the catalyst outer cylinder extending outside the catalyst filling area. The catalyst outer cylinder is 60-180 mm higher than the top of the annular distributor, and the bottom of the annular distributor is 600-800 mm higher than the top of the catalyst. The annular distributor is provided with 3-5 rows of distribution holes. The material enters the catalyst reaction bed from the catalyst outer cylinder to react. After the reaction discharge is mixed in the inner cylinder, it flows downward along the inner cylinder and enters the radial reactor of the next stage. The catalyst reaction bed is a low pressure drop thin bed, and the total reactor pressure drop is 8-10 KPa.

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