Preparation method of recyclable N-butyldiethanolamine

Abstract

The application discloses a preparation method of recyclable N-butyl diethanolamine, and belongs to the technical field of medical intermediates. The preparation method of the N-butyl diethanolamine comprises the following steps: adding n-butylamine and a magnetic mesoporous solid catalyst into a reaction kettle, replacing the system with nitrogen, heating, slowly introducing ethylene oxide gas, and reacting; cooling, applying an external magnetic field outside the reaction kettle to make the catalyst adsorbed on the inner wall of the kettle, extracting the clear liquid, and directly reserving the catalyst adsorbed on the wall in the kettle for the next batch of recycling; vacuum flash separation is performed on the extracted clear liquid, the unreacted n-butylamine collected is directly supplemented as raw material in the preparation of the next batch, and the intercepted liquid is N-butyl diethanolamine. The N-butyl diethanolamine prepared in the application has high n-butylamine conversion rate, product selectivity and purity, and the separation time is significantly shortened.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical intermediates technology, and specifically to a method for preparing recyclable N-butyldiethanolamine. Background Technology

[0002] N-Butyldiethanolamine is an important fine chemical intermediate, widely used in natural gas desulfurization and decarbonization purification, special polyurethane coatings, textile printing and dyeing auxiliaries and pharmaceutical synthesis. Industrially, N-Butyldiethanolamine is usually prepared by ethoxylation of n-butylamine with ethylene oxide. However, the existing preparation process usually has the following defects: (1) Difficult catalyst separation and high energy consumption. Existing technologies mostly use water, alcohols or conventional acids and bases as homogeneous catalysts. After the reaction, since the catalyst is miscible with the high-boiling-point product, a high-energy-consuming vacuum distillation process must be used for separation, which not only increases the production cost, but also easily leads to discoloration and deterioration of the product at high temperature for a long time. (2) Many side reactions and low selectivity. Ethylene oxide is extremely reactive. After the target product N-Butyldiethanolamine is generated, the two hydroxyl groups on its molecule are very easy to continue to undergo chain growth reaction with ethylene oxide to generate polyetheramine by-products. This not only reduces the yield of the target product, but also increases the difficulty of subsequent purification. (3) The process is not closed-loop. In existing separation processes, unreacted n-butylamine and lost catalyst are often treated as waste liquid, which cannot achieve true green and non-destructive recycling. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing recyclable N-butyldiethanolamine.

[0004] A method for preparing recyclable N-butyldiethanolamine includes the following steps: n-Butylamine and a magnetic mesoporous solid catalyst were added to a reactor. After purging with nitrogen, the system was sealed, heated, and ethylene oxide gas was slowly introduced to initiate the reaction. The reactor was then cooled, and an external magnetic field was applied to the outside of the reactor to adsorb the catalyst onto the inner wall. The clear liquid was extracted, and the adsorbed catalyst was retained in the reactor for reuse in the next batch. The extracted clear liquid was then separated by vacuum flash evaporation. The unreacted n-butylamine collected was directly used as a raw material to supplement the preparation of the next batch, and the retained liquid was N-butyldiethanolamine.

[0005] The magnetic mesoporous solid catalyst is prepared by the following method: S1: Deionized water, FeCl3·6H2O and FeCl2·4H2O were stirred and mixed, heated, and the pH was adjusted to 10 with alkali solution under stirring. After reaction, superparamagnetic nanoparticles were obtained after post-treatment. S2: Deionized water, anhydrous ethanol, and superparamagnetic nanoparticles were ultrasonically dispersed evenly, hexadecyltrimethylammonium bromide was added, and the mixture was stirred at room temperature. Ammonia water was added, and tetraethyl orthosilicate was added under stirring conditions. The mixture was heated and reacted. After post-treatment, a magnetic mesoporous carrier was obtained. S3: Anhydrous toluene and magnetic mesoporous support are ultrasonically dispersed evenly, 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride is added, the mixture is heated and reacted, and after post-treatment, a magnetic mesoporous solid catalyst is obtained.

[0006] In step S1, the molar ratio of FeCl3·6H2O to FeCl2·4H2O is 2:1; in step S2, the mass ratio of the superparamagnetic nanoparticles to hexadecyltrimethylammonium bromide is 1:1.5; in step S3, the mass ratio of the magnetic mesoporous support to 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride is 1:2.

[0007] In step S1, the post-processing operations are as follows: cooling to room temperature, using an external magnet for magnetic separation, discarding the supernatant, washing, and vacuum drying.

[0008] In step S2, the post-processing operation is as follows: cooling to room temperature, using an external magnet for magnetic separation, washing; redispersing the collected solids, reflux extraction; using an external magnet for magnetic separation again, washing, and vacuum drying.

[0009] In step S3, the post-processing operation is as follows: cooling to room temperature, using an external magnet for magnetic separation, discarding the supernatant, and performing Soxhlet extraction on the solid; adding the extracted solid to anhydrous potassium hydroxide ethanol solution and stirring; using an external magnet for magnetic separation, washing, and vacuum drying.

[0010] The amount of the magnetic mesoporous solid catalyst fed is 1%-2% of the mass of n-butylamine; the molar ratio of n-butylamine to ethylene oxide is 1:(1.8-2).

[0011] The reaction is carried out at a temperature of 80-100℃ for 1.5-2 hours.

[0012] The magnetic induction intensity of the applied external magnetic field is 0.3-0.5T, and the application duration is 30-60s.

[0013] The pressure during the vacuum flash separation process is 0.03-0.05 MPa, and the temperature is 60-80℃.

[0014] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: (1) Significantly improve the selectivity of the target product by utilizing the spatial confinement effect: In this invention, the catalytic active center of the ionic liquid is covalently grafted into the mesoporous channel. Based on the spatial confinement effect of the mesoporous system, when the target product N-butyldiethanolamine molecule is generated in the channel, it is restricted by the steric hindrance in the channel, which effectively prevents the subsequent ethylene oxide molecule from approaching and forming a large-volume polymerization transition state. This effectively suppresses the occurrence of polyetherification side reactions and effectively improves the selectivity of the target product.

[0015] (2) Achieving low-energy in-situ separation and long-term stable reuse of catalyst: The solid catalyst prepared by this invention has a superparamagnetic Fe3O4 core, which can be uniformly dispersed in the reaction system without an external magnetic field, ensuring the mass transfer efficiency of the catalytic reaction; after the reaction, by applying an external magnetic field, the catalyst can quickly and directionally adsorb to achieve in-situ solid-liquid separation in a short time. This separation method replaces the traditional high-energy-consuming vacuum distillation or cumbersome centrifugal filtration steps, greatly reducing the separation energy consumption and the mechanical loss of the catalyst during the transfer process, so that the catalyst can be stably recycled in multiple batches in the original reactor.

[0016] (3) Constructing a solvent-free closed-loop process to improve the environmental friendliness and economy of the process: The reaction system provided by this invention is carried out without the addition of water or organic solvents. Through process design, the in-situ magnetic catalyst separation technology is coupled with the micro-negative pressure vacuum flash evaporation technology, which not only realizes the closed-loop retention of the solid catalyst, but also realizes the condensation recovery and direct reuse of the slightly excess unreacted n-butylamine. The entire process avoids the generation of a large amount of waste liquid in the traditional separation and purification process, and has significant environmental benefits and industrial application prospects. Attached Figure Description

[0017] Figure 1 Transmission electron microscopy image of the magnetic mesoporous solid catalyst prepared in Example 1; Figure 2 The image shows the X-ray diffraction pattern of the magnetic mesoporous solid catalyst prepared in Example 1. Detailed Implementation

[0018] Example 1: Preparation of magnetic mesoporous solid catalysts S1: Under nitrogen protection, 100 ml of deionized water, 0.02 mol FeCl3·6H2O, and 0.01 mol FeCl2·4H2O were stirred and mixed. The mixture was heated to 80 °C, and 25 wt% ammonia was slowly added dropwise to adjust the pH of the solution to 10 while stirring at 500 rpm. The reaction was allowed to proceed for 1 h. After the reaction was completed, the mixture was cooled to room temperature and magnetically separated using an external magnet. The supernatant was discarded, and the mixture was washed alternately with deionized water and anhydrous ethanol until neutral. The mixture was then vacuum dried at 60 °C for 12 h to obtain superparamagnetic Fe3O4 nanoparticles. S2: Mix 80 ml deionized water, 40 ml anhydrous ethanol, and 1 g superparamagnetic Fe3O4 nanoparticles, and disperse by sonication (40 kHz) for 30 min. Add 1.5 g cetyltrimethylammonium bromide, stir at 200 rpm for 30 min at room temperature, add 2 ml 25 wt% ammonia water, and add 4 ml tetraethyl orthosilicate dropwise under stirring at 400 rpm. React at 40 °C for 12 h. After the reaction is complete, cool to room temperature and perform magnetic separation using an external magnet. Wash with deionized water and anhydrous ethanol alternately until neutral. Disperse the collected solid in a solution containing 100 ml anhydrous ethanol and 2 ml 36 wt% concentrated hydrochloric acid, and reflux for 24 h. After reflux, perform magnetic separation using an external magnet, wash with anhydrous ethanol until neutral, and vacuum dry at 60 °C for 12 h to obtain a magnetic mesoporous carrier. S3: Under nitrogen protection, 50 ml of anhydrous toluene and 1 g of magnetic mesoporous support were mixed and ultrasonically dispersed (40 kHz) for 10 min. 2 g of 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride was added, and the mixture was heated to reflux for 24 h. After the reaction was completed, the mixture was cooled to room temperature and magnetically separated using an external magnet. The supernatant was discarded, and the crude product solid was transferred into a cellulose filter paper sleeve and placed in a Soxhlet extractor. 150 ml of dichloromethane was used as the solvent, and the mixture was refluxed for 8 h. 150 ml of anhydrous ethanol was then replaced, and reflux extraction was continued for another 8 h. The extracted solid was added to 100 ml of 0.5 mol / L potassium hydroxide anhydrous ethanol solution and stirred at 100 rpm for 12 h at room temperature. Magnetic separation was performed using an external magnet. The solid was repeatedly washed with anhydrous ethanol until the washing solution was neutral and no silver chloride white precipitate was produced when tested with 0.1 mol / L silver nitrate solution. The solid was vacuum dried at 60 °C for 12 h to obtain the magnetic mesoporous solid catalyst.

[0019] Figure 1 The image shows a transmission electron microscope (TEM) image of the prepared magnetic mesoporous solid catalyst. As can be seen from the image, the catalyst exhibits a relatively uniform spherical core-shell structure with good overall particle dispersion and only a small amount of contact agglomeration. The central region is darker in color and has a higher electron density, which can be attributed to the Fe3O4 magnetic core. The outer layer is lighter in color and exhibits a worm-like mesoporous texture, indicating that the silica mesoporous layer has been uniformly coated on the surface of the magnetic particles.

[0020] Figure 2The XRD pattern of the prepared magnetic mesoporous solid catalyst is shown in the figure. It can be seen from the figure that obvious diffraction peaks appear at 2θ of approximately 30.1°, 35.5°, 43.1°, 53.5°, 57.0° and 62.6°, which correspond to the (220), (311), (400), (422), (511) and (440) crystal planes of Fe3O4, respectively, indicating that the magnetic crystal phase of Fe3O4 was successfully formed during the preparation process. At the same time, a relatively wide diffuse peak appears in the range of approximately 20-25° of 2θ, which can be attributed to the characteristic signal of the amorphous silica mesoporous shell layer, indicating that a mesoporous silica coating layer was formed on the surface of Fe3O4.

[0021] Example 2: Preparation of recyclable N-butyldiethanolamine 2 mol of n-butylamine and 1.46 g of magnetic mesoporous solid catalyst were added to a high-pressure reactor. After purging with nitrogen three times, the system was sealed and heated to 80°C. 3.6 mol of ethylene oxide gas was slowly introduced (the pressure inside the reactor was controlled at 0.3 MPa during this period, and the feeding time was 2 hours). The reaction was carried out for 2 hours. The temperature was then lowered to 30°C. An external magnetic field with a magnetic induction intensity of 0.3 T was applied to the outside of the reactor and maintained for 30 seconds to allow the catalyst to adsorb onto the inner wall of the reactor. The clear liquid was extracted, and the catalyst adsorbed onto the wall was directly retained in the reactor for reuse in the next batch. The extracted clear liquid was placed in a vacuum flash evaporator equipped with a condensation recovery device. The system pressure was controlled at 0.03 MPa and the flash temperature was controlled at 60°C. The unreacted n-butylamine that was flash vaporized and collected by condensation was directly used as raw material to supplement the preparation of the next batch. The liquid retained at the bottom of the flash evaporator was N-butyldiethanolamine.

[0022] Example 3: Preparation of recyclable N-butyldiethanolamine 3 mol of n-butylamine and 4.39 g of magnetic mesoporous solid catalyst were added to a high-pressure reactor. After purging with nitrogen three times, the system was sealed and heated to 100°C. 6 mol of ethylene oxide gas was slowly introduced (the pressure inside the reactor was controlled at 0.5 MPa, and the feeding time was 3 hours). The reaction was carried out for 1.5 hours. The temperature was then lowered to 40°C. An external magnetic field with a magnetic induction intensity of 0.5 T was applied to the outside of the reactor and maintained for 60 seconds to allow the catalyst to adsorb onto the inner wall of the reactor. The clear liquid was extracted, and the catalyst adsorbed onto the wall was directly retained in the reactor for reuse in the next batch. The extracted clear liquid was placed in a vacuum flash evaporator equipped with a condensation recovery device. The system pressure was controlled at 0.05 MPa, and the flash temperature was controlled at 80°C. The unreacted n-butylamine that was flash vaporized and collected by condensation was directly used as raw material to supplement the preparation of the next batch. The liquid retained at the bottom of the flash evaporator was N-butyldiethanolamine.

[0023] Example 4: Preparation of N-butyldiethanolamine by in-situ reuse of catalyst for the 20th time. Keeping the reactor with the adsorbed catalyst unchanged after the first reaction in Example 2, without performing any washing operations, directly add the n-butylamine recovered from the previous batch of flash evaporation into the reactor (the insufficient part is supplemented with fresh n-butylamine to 2 mol), and then follow the same operation as in Example 2 to continuously cycle the catalyst until the 20th time, and collect the N-butyldiethanolamine at the bottom of the 20th flash evaporation tank.

[0024] Comparative Example 1 N-Butyldiethanolamine is prepared by the following method: 2 mol of n-butylamine and 10 g of deionized water were added to a high-pressure reactor. After purging with nitrogen three times, the system was sealed, heated to 80°C, and 3.6 mol of ethylene oxide gas was slowly introduced (the pressure inside the reactor was controlled at 0.3 MPa during this period, and the feeding time was 2 hours). The reaction was allowed to proceed for 2 hours. The temperature was then lowered to 30°C, and the entire reaction mixture was transferred to a distillation column for separation. The operating parameters of the distillation column were controlled as follows: pressure 0.01 MPa, reboiler temperature 100°C, and the fraction with a top temperature between 25-50°C was collected. The distillation time was 4 hours, and water and unreacted n-butylamine were removed by vaporization and condensation from the top of the column. After distillation, the liquid retained at the bottom of the distillation column was N-butyldiethanolamine.

[0025] Comparative Example 2 The preparation method of recyclable N-butyldiethanolamine is basically the same as that in Example 2, except that the magnetic mesoporous solid catalyst is replaced with an equal weight of magnetic solid catalyst. Magnetic solid catalysts are prepared by the following method: S1: Under nitrogen protection, 100 ml of deionized water, 0.02 mol FeCl3·6H2O, and 0.01 mol FeCl2·4H2O were stirred and mixed. The mixture was heated to 80 °C, and 25 wt% ammonia was slowly added dropwise to adjust the pH of the solution to 10 while stirring at 500 rpm. The reaction was allowed to proceed for 1 h. After the reaction was completed, the mixture was cooled to room temperature and magnetically separated using an external magnet. The supernatant was discarded, and the mixture was washed alternately with deionized water and anhydrous ethanol until neutral. The mixture was then vacuum dried at 60 °C for 12 h to obtain superparamagnetic Fe3O4 nanoparticles. S2: Mix 80 ml of deionized water, 40 ml of anhydrous ethanol, and 1 g of superparamagnetic Fe3O4 nanoparticles, disperse by sonication (40 kHz) for 30 min, stir at 200 rpm for 30 min at room temperature, add 2 ml of 25 wt% ammonia water, and add 4 ml of tetraethyl orthosilicate dropwise under stirring at 400 rpm. React at 40 °C for 12 h. After the reaction is completed, cool to room temperature, perform magnetic separation using an external magnet, wash alternately with deionized water and anhydrous ethanol until neutral, and vacuum dry at 60 °C for 12 h to obtain the magnetic carrier. S3: Under nitrogen protection, 50 ml of anhydrous toluene and 1 g of magnetic support were mixed and ultrasonically dispersed (40 kHz) for 10 min. 2 g of 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride was added, and the mixture was heated to reflux for 24 h. After the reaction was completed, the mixture was cooled to room temperature and magnetically separated using an external magnet. The supernatant was discarded, and the crude product solid was transferred into a cellulose filter paper sleeve and placed in a Soxhlet extractor. 150 ml of dichloromethane was used as the solvent, and the mixture was refluxed for 8 h. 150 ml of anhydrous ethanol was then replaced, and reflux extraction was continued for another 8 h. The extracted solid was added to 100 ml of 0.5 mol / L potassium hydroxide anhydrous ethanol solution and stirred at 100 rpm for 12 h at room temperature. Magnetic separation was performed using an external magnet. The solid was repeatedly washed with anhydrous ethanol until the washing solution was neutral and no white silver chloride precipitate was formed when tested with 0.1 mol / L silver nitrate solution. The solid was vacuum dried at 60 °C for 12 h to obtain a magnetic solid catalyst.

[0026] Comparative Example 3 The preparation method of recyclable N-butyldiethanolamine is basically the same as that in Example 2, except that the magnetic mesoporous solid catalyst is replaced with an equal weight of physically supported magnetic mesoporous solid catalyst. Physically supported magnetic mesoporous solid catalysts were prepared by the following method: S1: Under nitrogen protection, 100 ml of deionized water, 0.02 mol FeCl3·6H2O, and 0.01 mol FeCl2·4H2O were stirred and mixed. The mixture was heated to 80 °C, and 25 wt% ammonia was slowly added dropwise to adjust the pH of the solution to 10 while stirring at 500 rpm. The reaction was allowed to proceed for 1 h. After the reaction was completed, the mixture was cooled to room temperature and magnetically separated using an external magnet. The supernatant was discarded, and the mixture was washed alternately with deionized water and anhydrous ethanol until neutral. The mixture was then vacuum dried at 60 °C for 12 h to obtain superparamagnetic Fe3O4 nanoparticles. S2: Mix 80 ml deionized water, 40 ml anhydrous ethanol, and 1 g superparamagnetic Fe3O4 nanoparticles, and disperse by sonication (40 kHz) for 30 min. Add 1.5 g cetyltrimethylammonium bromide, stir at 200 rpm for 30 min at room temperature, add 2 ml 25 wt% ammonia water, and add 4 ml tetraethyl orthosilicate dropwise under stirring at 400 rpm. React at 40 °C for 12 h. After the reaction is complete, cool to room temperature and perform magnetic separation using an external magnet. Wash with deionized water and anhydrous ethanol alternately until neutral. Disperse the collected solid in a solution containing 100 ml anhydrous ethanol and 2 ml 36 wt% concentrated hydrochloric acid, and reflux for 24 h. After reflux, perform magnetic separation using an external magnet, wash with anhydrous ethanol until neutral, and vacuum dry at 60 °C for 12 h to obtain a magnetic mesoporous carrier. S3: Mix 50 ml of anhydrous ethanol and 1 g of magnetic mesoporous support, disperse by ultrasonication (40 kHz) for 10 min, add 2 g of 1-butyl-3-methylimidazolium hydroxide, stir at 100 rpm for 12 h at room temperature, rotary evaporate at 60 °C to constant weight, and vacuum dry at 60 °C for 12 h to obtain a physically supported magnetic mesoporous solid catalyst.

[0027] The N-butyldiethanolamine prepared in the examples and comparative examples was quantitatively analyzed using gas chromatography. The test results are shown in Table 1.

[0028] The conversion rate of n-butylamine is calculated using the following formula:

[0029] In the formula, The initial number of moles of n-butylamine added to the reaction (mol). This represents the total number of moles (mol) of n-butylamine in the liquid phase at the end of the reaction.

[0030] The selectivity of the target product is calculated using the following formula:

[0031] In the formula, The actual number of moles (mol) of n-butylamine consumed to generate N-butyldiethanolamine. The total number of moles (mol) of n-butylamine consumed in the reaction.

[0032] Separation time test: Use a stopwatch to time the moment the external magnetic field is turned on outside the reactor. The endpoint is the moment when the mixture is observed to change from turbid to clear and transparent, and no black catalyst suspended particles are observed in the clear liquid with the naked eye. The recorded time is the separation time of a single test.

[0033] Table 1 Performance Test Data

[0034] As can be seen from the data in Table 1, the N-butyldiethanolamine prepared in this application has a high n-butylamine conversion rate, product selectivity and purity, and the separation time is significantly shortened.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing recyclable N-butyldiethanolamine, characterized in that, Includes the following steps: n-Butylamine and a magnetic mesoporous solid catalyst were added to a reactor. After purging with nitrogen, the system was sealed, heated, and ethylene oxide gas was slowly introduced to initiate the reaction. The reactor was then cooled, and an external magnetic field was applied to the outside of the reactor to adsorb the catalyst onto the inner wall. The clear liquid was extracted, and the adsorbed catalyst was retained in the reactor for reuse in the next batch. The extracted clear liquid was then separated by vacuum flash evaporation. The unreacted n-butylamine collected was directly used as a raw material to supplement the preparation of the next batch, and the retained liquid was N-butyldiethanolamine.

2. The method for preparing recyclable N-butyldiethanolamine according to claim 1, characterized in that, The magnetic mesoporous solid catalyst is prepared by the following method: S1: Deionized water, FeCl3·6H2O and FeCl2·4H2O were stirred and mixed, heated, and the pH was adjusted to 10 with alkali solution under stirring. After reaction, superparamagnetic Fe3O4 nanoparticles were obtained after post-treatment. S2: Deionized water, anhydrous ethanol, and superparamagnetic Fe3O4 nanoparticles were ultrasonically dispersed evenly, hexadecyltrimethylammonium bromide was added, and the mixture was stirred at room temperature. Ammonia water was added, and tetraethyl orthosilicate was added under stirring conditions. The mixture was heated and reacted. After post-treatment, a magnetic mesoporous carrier was obtained. S3: Anhydrous toluene and magnetic mesoporous support are ultrasonically dispersed evenly, 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride is added, the mixture is heated and reacted, and after post-treatment, a magnetic mesoporous solid catalyst is obtained.

3. The method for preparing recyclable N-butyldiethanolamine according to claim 2, characterized in that, In step S1, the molar ratio of FeCl3·6H2O to FeCl2·4H2O is 2:1; in step S2, the mass ratio of the superparamagnetic nanoparticles to hexadecyltrimethylammonium bromide is 1:1.5; in step S3, the mass ratio of the magnetic mesoporous support to 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride is 1:

2.

4. The method for preparing recyclable N-butyldiethanolamine according to claim 2, characterized in that, In step S1, the post-processing operations are as follows: cooling to room temperature, using an external magnet for magnetic separation, discarding the supernatant, washing, and vacuum drying.

5. The method for preparing recyclable N-butyldiethanolamine according to claim 2, characterized in that, In step S2, the post-processing operation is as follows: cooling to room temperature, using an external magnet for magnetic separation, washing; redispersing the collected solids, reflux extraction; using an external magnet for magnetic separation again, washing, and vacuum drying.

6. The method for preparing recyclable N-butyldiethanolamine according to claim 2, characterized in that, In step S3, the post-processing operation is as follows: cooling to room temperature, using an external magnet for magnetic separation, discarding the supernatant, and performing Soxhlet extraction on the solid; adding the extracted solid to anhydrous potassium hydroxide ethanol solution and stirring; using an external magnet for magnetic separation, washing, and vacuum drying.

7. The method for preparing recyclable N-butyldiethanolamine according to claim 1, characterized in that, The amount of the magnetic mesoporous solid catalyst fed is 1%-2% of the mass of n-butylamine; the molar ratio of n-butylamine to ethylene oxide is 1:(1.8-2).

8. The method for preparing recyclable N-butyldiethanolamine according to claim 1, characterized in that, The reaction is carried out at a temperature of 80-100℃ for 1.5-2 hours.

9. The method for preparing recyclable N-butyldiethanolamine according to claim 1, characterized in that, The magnetic induction intensity of the applied external magnetic field is 0.3-0.5T, and the application duration is 30-60s.

10. The method for preparing recyclable N-butyldiethanolamine according to claim 1, characterized in that, The pressure during the vacuum flash separation process is 0.03-0.05 MPa, and the temperature is 60-80℃.

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