A continuous process for the preparation of cyclohexylamine

Abstract

The application provides a continuous preparation method of cyclohexylamine and belongs to the technical field of chemical reaction engineering. The method is that aniline is dissolved in a solvent a to obtain a substrate solution, the substrate solution is fully mixed with hydrogen in a fixed bed reactor provided with a catalyst through a flow meter, and reaction is carried out under temperature and pressure control; after the reaction is completed, the cyclohexylamine solution is obtained after temperature control and cooling, and then the solvent is removed under reduced pressure to obtain the cyclohexylamine. The method has the advantages of accurate feeding and controllable temperature, and has the advantages of mild reaction condition, low energy consumption, good strengthening mixing effect, few side reactions, high production efficiency, stable product quality, less tail gas pollution and green environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis, specifically relating to a continuous preparation method of cyclohexylamine. Background Technology

[0002] Cyclohexylamine, as a key alicyclic amine fine chemical intermediate, is widely used in rubber vulcanization accelerator CBS, food cyclamate, metal corrosion inhibitors, water treatment agents, epoxy resin curing agents, pesticide and dye intermediates, and other fields. Downstream demand continues to grow, and there is an urgent need for large-scale, green, continuous, and highly selective industrial preparation technologies.

[0003] The current mainstream industrial route for cyclohexylamine synthesis is the catalytic hydrogenation reduction of aniline, which is divided into two types of processes: atmospheric pressure gas-phase fixed-bed hydrogenation and high-pressure liquid-phase batch hydrogenation. The catalysts and processes for the catalytic amination of cyclohexanol are not yet mature and are difficult to implement on a large scale. Summary of the Invention

[0004] To address the problems of existing technologies and safety, this invention provides a continuous preparation method for cyclohexylamine.

[0005] A continuous preparation method for cyclohexylamine, characterized by the following reaction formula:

[0006]

[0007] Includes the following steps:

[0008] (1) Aniline is dissolved in solvent a to obtain a substrate solution, which is then replaced with nitrogen and thoroughly mixed with hydrogen in a fixed-bed reactor containing a catalyst via a flow meter, and the reaction is carried out under controlled temperature and pressure.

[0009] (2) After the hydrogen is no longer absorbed, the reaction is completed. After cooling under controlled temperature, a cyclohexylamine solution is obtained. Then, the solvent is removed under reduced pressure to obtain cyclohexylamine.

[0010] Further, the solvent a mentioned in step (1) is one or more of ethanol, acetone, methanol, tetrahydrofuran, water, and isopropanol; preferably water and ethanol.

[0011] Further, the solvents water and ethanol mentioned in step (1) have a volume ratio of water to ethanol of 2 to 5:1; preferably, the volume ratio of water to ethanol is 3:1.

[0012] Further, the catalyst mentioned in step (1) is a modified Ru / Al2O3 catalyst containing an additive, wherein Ru is the active component; Al2O3 is the support; and the additive is any one of LiOH, NaOH, KOH, LiNO3, NaNO3, and KNO3; preferably LiOH.

[0013] Further, in step (1), the mass content of the auxiliary in the catalyst is 0.2% to 0.5% of the catalyst mass; preferably 0.4%; the mass of the catalyst is 0.5% to 1% of the raw material aniline mass, preferably 0.8% of the raw material aniline mass.

[0014] Furthermore, the temperature control temperature mentioned in step (1) is 80-100℃; preferably 90℃.

[0015] Furthermore, the pressure in step (1) is controlled at 2-7 MPa; preferably 6 MPa.

[0016] Further, the mass concentration of aniline in solution a in step (1) is 5wt%-15wt%, preferably 10wt%.

[0017] Further, the feed flow rate of the aniline solution in step (1) is 2-7 L / h, preferably 6 L / h, and the feed flow rate of hydrogen is 20-30 L / h, preferably 25 L / h.

[0018] Furthermore, the temperature control and cooling temperature mentioned in step (2) is 20-50℃; preferably 30℃.

[0019] The beneficial effects of this invention are:

[0020] (1) Using a fixed-bed reactor for the reaction results in milder reaction conditions and enhanced reaction process, thus increasing reaction efficiency;

[0021] (2) It achieves precise feeding of materials, especially the Ru / Al2O3 catalyst containing the auxiliary agent LiOH, which can improve reaction selectivity and reduce the occurrence of side reactions. Detailed Implementation

[0022] Example 1: Preparation of lithium hydroxide-modified ruthenium hydrotalcite catalyst by impregnation method.

[0023] (1) At room temperature, 0.27 g of RuCl 3。 Dissolve 3H2O in 10mL of deionized water, add 20g of aluminum oxide while stirring, and continue stirring for 10min to obtain a metal aqueous solution, which is then soaked for 4h.

[0024] (2) Filter the mixed solution obtained in step (1), wash and filter the precipitate with deionized water and ethanol, and dry it at 100°C for 8 hours to obtain a solid complex.

[0025] (3) The solid composite obtained in step (2) is calcined at 200°C for 5 hours in an air atmosphere, and then reduced and activated at 250°C for 6 hours in a mixed gas of H2 and N2 (H2 volume fraction is 10%) to obtain the reduced solid catalyst.

[0026] (4) Dissolve the catalyst obtained in step (3) in 50 mL of deionized water, add 0.4% lithium hydroxide (based on the total mass of the catalyst) while stirring, and continue stirring for 24 h.

[0027] (5) Filter the mixed solution obtained in step (4), wash and filter the precipitate with deionized water and ethanol, and dry it at 100°C for 12 h to obtain the modified Ru / Al2O3 catalyst modified with lithium hydroxide.

[0028] Example 2:

[0029] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0030] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 3:1; wherein the mass concentration of aniline was 10 wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing lithium hydroxide-modified Ru / Al2O3 catalyst. The feed flow rate of aniline solution was 6L / h, the feed flow rate of hydrogen was 25L / h, the pressure was controlled at 6MPa, the temperature was controlled at 90℃, the mass of catalyst was 0.8% of the mass of aniline, and the mass of lithium hydroxide auxiliary was 0.4% of the mass of catalyst.

[0031] (2) After the hydrogen absorption is complete, the reaction is cooled at 30°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 100% and the product selectivity is 99.2%.

[0032] Example 3:

[0033] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0034] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 5:1; wherein the mass concentration of aniline was 15 wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing lithium hydroxide-modified Ru / Al2O3 catalyst via a flow meter. The feed flow rate of aniline solution was 7L / h, the feed flow rate of hydrogen was 30L / h, the pressure was controlled at 7MPa, the temperature was controlled at 100℃, the mass of catalyst was 1% of the mass of raw material aniline, and the mass of lithium hydroxide auxiliary was 0.5% of the mass of catalyst.

[0035] (2) After the hydrogen absorption is completed, the reaction is cooled at 50°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 100% and the product selectivity is 98.7%.

[0036] Example 4:

[0037] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0038] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 2:1; wherein the mass concentration of aniline was 5wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing lithium hydroxide-modified Ru / Al2O3 catalyst via a flow meter. The feed flow rate of aniline solution was 2L / h, the feed flow rate of hydrogen was 20L / h, the pressure was controlled at 2MPa, the temperature was controlled at 80℃, the mass of catalyst was 0.5% of the mass of raw material aniline, and the mass of lithium hydroxide auxiliary was 0.2% of the mass of catalyst.

[0039] (2) After the hydrogen absorption is complete, the reaction is cooled at 20°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 100% and the product selectivity is 98.5%.

[0040] Example 5:

[0041] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0042] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 1:1; wherein the mass concentration of aniline was 3wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing lithium hydroxide-modified Ru / Al2O3 catalyst via a flow meter. The feed flow rate of aniline solution was 1L / h, the feed flow rate of hydrogen was 15L / h, the pressure was controlled at 1MPa, the temperature was controlled at 70℃, the mass of catalyst was 0.2% of the mass of raw material aniline, and the mass of lithium hydroxide auxiliary was 0.1% of the mass of catalyst.

[0043] (2) After the hydrogen absorption is complete, the reaction is cooled at 15°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 92% and the product selectivity is 95.3%.

[0044] Example 6:

[0045] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0046] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 7:1; wherein the mass concentration of aniline was 25 wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing lithium hydroxide-modified Ru / Al2O3 catalyst. The feed flow rate of the aniline solution was 8L / h, the feed flow rate of hydrogen was 35L / h, the pressure was controlled at 8MPa, the temperature was controlled at 110℃, the mass of the catalyst was 2% of the mass of the raw material aniline, and the mass of the lithium hydroxide auxiliary was 0.8% of the mass of the catalyst.

[0047] (2) After the hydrogen absorption is complete, the reaction is cooled at 60°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 93% and the product selectivity is 94.7%.

[0048] Example 7:

[0049] A continuous preparation method for cyclohexylamine, comprising the following steps:

[0050] (1) 20g of aniline was dissolved in water and ethanol to obtain a substrate solution, wherein the volume ratio of water to ethanol was 3:1; wherein the mass concentration of aniline was 10 wt%, nitrogen was used for purging, and the solution was thoroughly mixed with hydrogen in a fixed-bed reactor containing Ru / Al2O3 catalyst via a flow meter. The feed flow rate of aniline solution was 6L / h, the feed flow rate of hydrogen was 25L / h, the pressure was controlled at 6MPa, the temperature was controlled at 90℃, and the mass of catalyst was 0.8% of the mass of aniline.

[0051] (2) After the hydrogen absorption is complete, the reaction is cooled at 30°C to obtain a cyclohexylamine solution. Then, the solvent is removed under reduced pressure to obtain a cyclohexylamine solution for analysis. The conversion rate is 91% and the product selectivity is 93.2%.

[0052] Comparative Example 1: Batch Reaction Hydrogenation Experiment

[0053] 1) Feeding: Add 20g aniline, 167.4g methanol, 0.93g 5wt% Ru / C catalyst, and 0.19g sodium hydroxide sequentially to the intermittent high-pressure reactor;

[0054] 2) Gas replacement: In a sealed reactor, the air inside the reactor is first replaced three times with high-purity nitrogen. Each time, the pressure is increased to 1.0 MPa and then slowly released to completely remove the air from the reactor. Then, high-purity hydrogen is used to replace the air three times.

[0055] 3) Heating and pressurizing: Charge hydrogen into the reactor to an initial pressure of 3.0 MPa, turn on the mechanical stirrer, control the stirring speed to 800 r / min, and raise the temperature to the reaction temperature of 120℃ through the program, with a heating rate of 5℃ / min;

[0056] 4) Intermittent hydrogenation reaction: Under constant temperature of 120℃, high-purity hydrogen is continuously added to maintain a constant reaction pressure of 5.0MPa in the reactor and an intermittent constant temperature hydrogenation reaction is carried out for 5 hours; during this period, the hydrogen absorption rate is monitored in real time. When the hydrogen absorption rate drops below 0.01L / h, the reaction is determined to have reached the endpoint and heating is stopped.

[0057] 5) Post-processing: Keep stirring and allow to cool naturally to room temperature (25±2℃). Slowly depressurize to atmospheric pressure and replace the residual hydrogen in the reactor twice with high-purity nitrogen. Open the reactor and separate and recover the solid catalyst by passing the reaction liquid through a precision filter (0.22μm filter membrane pore size). (After activation, it can be reused more than 5 times without significant decrease in catalytic activity). Distill the filtrate at atmospheric pressure to recover the methanol solvent (recovery rate ≥96.0%). The remaining crude product is subjected to vacuum distillation, controlling the column top temperature at 85℃ and the vacuum degree at 2.0kPa. Collect the target fraction to obtain a cyclohexylamine solution. Then, remove the solvent under vacuum to obtain a cyclohexylamine solution for analysis. The conversion rate is 98% and the product selectivity is 95.4%.

[0058] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A continuous preparation method for cyclohexylamine, characterized in that, The reaction formula is shown below: Includes the following steps: (1) Aniline is dissolved in solvent a to obtain a substrate solution, which is then replaced with nitrogen and thoroughly mixed with hydrogen in a fixed-bed reactor containing a catalyst via a flow meter, and the reaction is carried out under controlled temperature and pressure. (2) After the hydrogen is no longer absorbed, the reaction is completed. After cooling under controlled temperature, a cyclohexylamine solution is obtained. Then, the solvent is removed under reduced pressure to obtain cyclohexylamine.

2. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The solvent a mentioned in step (1) is one or more of ethanol, acetone, methanol, tetrahydrofuran, water, and isopropanol; preferably water and ethanol.

3. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The solvents water and ethanol mentioned in step (1) have a volume ratio of water to ethanol of 2 to 5:1; preferably, the volume ratio of water to ethanol is 3:

1.

4. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The catalyst mentioned in step (1) is a modified Ru / Al2O3 catalyst containing an additive, wherein Ru is the active component; Al2O3 is the support; and the additive is any one of LiOH, NaOH, KOH, LiNO3, NaNO3, and KNO3; preferably LiOH.

5. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The mass content of the additive in the catalyst described in step (1) is 0.2% to 0.5% of the catalyst mass; preferably 0.4%; the catalyst mass is 0.5% to 1% of the raw material aniline mass, preferably 0.8% of the raw material aniline mass.

6. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The temperature control temperature mentioned in step (1) is 80-100℃; preferably 90℃.

7. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The pressure control in step (1) is 2-7 MPa; preferably 6 MPa.

8. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, In step (1), the mass concentration of aniline in solution a is 5wt%-15wt%, preferably 10wt%.

9. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The feed flow rate of the aniline solution in step (1) is 2-7 L / h, preferably 6 L / h, and the feed flow rate of hydrogen is 20-30 L / h, preferably 25 L / h.

10. The continuous preparation method of cyclohexylamine according to claim 1, characterized in that, The temperature control and cooling temperature mentioned in step (2) is 20-50℃; preferably 30℃.

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