A process for the preparation of N,N-dimethylcyclohexylamine having improved storage stability

Abstract

The application discloses a preparation method of N,N-dimethylcyclohexylamine with improved storage stability, which comprises the following steps: reacting cyclohexylamine, N,N-dimethylcyclohexylamine, formaldehyde and hydrogen under the action of a supported palladium-based catalyst; in the raw materials, the addition amount of N,N-dimethylcyclohexylamine is 1-5% of the mass of the cyclohexylamine, preferably 2-3%. The N,N-dimethylcyclohexylamine can be prepared at a high yield by the method, and the content of N-cyclohexylformamide impurities can be controlled to be below 10 ppm, and it is found that the low-temperature storage stability is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a synthetic method of organic matter, in particular to a preparation method of N,N-dimethylcyclohexylamine with improved storage stability. BACKGROUND

[0002] N,N-dimethylcyclohexylamine (abbreviated as DMCHA) is mainly used in the polyurethane catalyst industry, which is a low-viscosity medium-active amine catalyst that can provide balanced catalytic performance for the foaming reaction and gelation reaction of hard foam, and has a wide application in the preparation of refrigerator materials and board materials.

[0003] There are many preparation routes of N,N-dimethylcyclohexylamine, mainly including: N,N-dimethyl aniline catalytic hydrogenation method, phenol and dimethylamine hydrogenation method, cyclohexylamine and dimethylamine hydrogenation method, cyclohexanone (alcohol) and dimethylamine hydrogenation method, etc. Among them, N,N-dimethyl aniline catalytic hydrogenation method, phenol and dimethylamine hydrogenation method, cyclohexylamine and dimethylamine hydrogenation method are only limited to laboratory research and have not been industrialized. At present, the mainstream suppliers at home and abroad all use cyclohexanone and dimethylamine hydrogenation method to produce N,N-dimethylcyclohexylamine intermittently, such as the technical solutions disclosed in patents CN1092061A, CN1990456A and CN109608340A. However, the overall yield of these known technologies is low, the environmental pollution problem is serious, and the product purity is low.

[0004] The improved patent CN111333520A proposed by the present inventors uses cheap and readily available bulk chemicals such as cyclohexylamine, formaldehyde and hydrogen as raw materials for reaction, which can obtain N,N-dimethylcyclohexylamine with a high yield of ≥99.3%, and a product purity of ≥99.5%, compared with the existing cyclohexanone route, which has the advantages of simple process, high product yield and high purity.

[0005] However, the present inventors found in subsequent continuous research that a small amount of crystals of N,N-dimethylcyclohexylamine prepared by this method would be precipitated under low-temperature storage conditions, which not only affects the appearance of the product in the eyes of the customers, but also causes uneven foam when used as a foam catalyst, affecting the performance of the foam. Therefore, it is necessary to propose an improved production process to solve the above problems. SUMMARY

[0006] In order to solve the above technical problems, the present application proposes a preparation method of N,N-dimethylcyclohexylamine with improved storage stability.

[0007] In the continuous research on the production of N,N-dimethylcyclohexylamine from cyclohexylamine and formaldehyde, the inventors found that the inevitable presence of formic acid in formaldehyde leads to the production of a certain amount of formic acid and cyclohexylamine reaction product N-cyclohexyl formamide during the reaction. In further in-depth research, it was found that N-cyclohexyl formamide is the main factor causing the product to flocculate and precipitate at low temperature. Based on this, the present application proposes a method for preparing N,N-dimethylcyclohexylamine with improved storage stability. This method not only has a high product yield, but also can control the content of N-cyclohexyl formamide to below 10 ppm, with obvious low-temperature storage advantages.

[0008] A method for preparing N,N-dimethylcyclohexylamine with improved storage stability, characterized by reacting cyclohexylamine, N,N-dimethylcyclohexylamine, formaldehyde, and hydrogen under the action of a supported palladium-based catalyst. In the raw materials, the addition amount of N,N-dimethylcyclohexylamine is 1-5% of the mass of cyclohexylamine, preferably 2-3%.

[0009] N,N-dimethylcyclohexylamine reacts faster with formic acid as a tertiary amine. After formaldehyde aqueous solution is added to the reaction system, it can quickly form a quaternary ammonium salt with the formic acid introduced in the raw materials, thereby avoiding the reaction of cyclohexylamine with formic acid to generate N-cyclohexyl formamide, thereby completing the present application.

[0010] As a preferred embodiment of the present application, the supported palladium-based catalyst comprises palladium, an auxiliary agent, and a modified carrier.

[0011] The auxiliary agent comprises a first auxiliary agent and a second auxiliary agent. The first auxiliary agent is selected from one or more of copper, nickel, cobalt, platinum, and ruthenium, preferably cobalt and / or ruthenium. The second auxiliary agent is selected from one or more of lanthanum, bismuth, zinc, iron, rhenium, and cerium, preferably at least one of iron, cerium, and zinc.

[0012] The modified carrier comprises a carrier matrix and a modified auxiliary agent. The carrier matrix is selected from one or more of alumina, silica, diatomite, and hydrogen-type ZSM-5. The modified auxiliary agent is magnesium oxide and / or barium oxide.

[0013] As a preferred embodiment of the present application, the content of palladium is 0.5-15 wt%, preferably 4-8 wt%, based on the total mass of the supported palladium-based catalyst. The content of the first auxiliary agent is 0.1-1 wt%, preferably 0.2-0.5 wt%. The content of the second auxiliary agent is 0.01-0.5 wt%, preferably 0.05-0.2 wt%.

[0014] Preferably, the mass ratio of the first auxiliary agent to the second auxiliary agent is (0.5-30):1, further preferably (1-10):1.

[0015] Preferably, the content of the modifying agent in the modified carrier is 1-10wt%, preferably 2-5wt%.

[0016] As a preferred scheme of the present application, the amount of the supported palladium-based catalyst is 0.5-3% of the mass of cyclohexylamine, preferably 1-2%.

[0017] Preferably, the molar ratio of formaldehyde to cyclohexylamine is (2.01-2.02):1; the amount of formaldehyde is slightly higher than the theoretical amount, which is beneficial to the complete reaction of cyclohexylamine to form N,N-dimethylcyclohexylamine.

[0018] As a preferred scheme of the present application, the reaction temperature is 100-140℃, preferably 110-130℃; the reaction pressure is 2-8MPa, preferably 3-5MPa.

[0019] As a preferred scheme of the present application, the formaldehyde aqueous solution is slowly added at the reaction temperature, and the addition is completed in 3-12h, preferably 6-8h, and the reaction is continued for 10-60min, preferably 20-40min.

[0020] As a preferred scheme of the present application, the mass concentration of the formaldehyde aqueous solution is 37-55wt%.

[0021] As a preferred scheme of the present application, a solvent is further added in the reaction, and the solvent includes one or more of methanol, water, and tetrahydrofuran;

[0022] Preferably, the mass ratio of the solvent to cyclohexylamine is (0.5-3):1, preferably (1-2):1.

[0023] As a preferred scheme of the present application, after the reaction is completed, a lye is added to adjust the pH to 11-14, preferably 12-13, and then high-temperature phase separation is performed to purify the oil phase to obtain N,N-dimethylcyclohexylamine;

[0024] Preferably, the phase separation conditions are controlled as follows: the temperature is 60-100℃, preferably 80-90℃; and the residence time for phase separation is 0.5-5h, preferably 2-3h.

[0025] Preferably, the purification by rectification adopts atmospheric or reduced pressure rectification, preferably reduced pressure rectification; the pressure is 0.1-50KPa, preferably 2-5KPa; the theoretical plate number of the rectification column is 10-30, preferably 15-20; and the reflux ratio is 0.1-5:1, preferably 0.5-2:1.

[0026] As a preferred scheme of the present application, the lye is an aqueous solution of sodium hydroxide or potassium hydroxide. The addition of the lye can promote the re-decomposition of the quaternary ammonium salt formed by cyclohexylamine and formic acid to form N,N-dimethylcyclohexylamine and formic acid, and the rapid reaction with formic acid to form a salt, which is beneficial to improve the product yield.

[0027] The beneficial effects of the present application over the prior art are:

[0028] The method of the present application can produce N,N-dimethylcyclohexylamine with high yield, and the content of N-cyclohexylformamide impurities can be controlled below 10 ppm, and it is found that the low-temperature storage stability is significantly improved. DETAILED DESCRIPTION

[0029] The present application will be further described below by specific examples, and the examples described in the present application are only used to illustrate the present application, and do not limit the scope of the present application.

[0030] In the present application, the raw materials and reagents can be purchased through commercial channels unless otherwise specified.

[0031] The conditions for gas chromatography analysis of the reaction liquid composition are as follows: Agilent DB-5 chromatographic column, injection port temperature 280℃, FID detector temperature 300℃, column flow rate 1.5ml / min, hydrogen flow rate 35ml / min, air flow rate 350ml / min, and the program temperature rising mode is 60℃ for 1min, then rising to 280℃ at 20℃ / min, and keeping for 10min.

[0032] Turbidity test: HACH 2100N series turbidimeter is used for testing, and the unit is NTU.

[0033] The 1# to 4# supported palladium-based catalyst precursors used in the following examples were prepared according to the methods in patent CN111333520A examples 1-4, respectively.

[0034]

Example 1

[0035] (1) 4g of 1# supported palladium-based catalyst precursor was added to a 1.5L high-pressure reaction kettle, 400ml of deionized water was added, and the 1# supported palladium-based catalyst was obtained by activating at a temperature of 150℃ and a hydrogen pressure of 4MPa for 6h.

[0036] (2) The deionized water was filtered through the built-in filter of the high-pressure reactor, 198 g of cyclohexylamine, 9.9 g of N,N-dimethylcyclohexylamine and 99 g of methanol were added, and the reactor was replaced with 1 MPa of nitrogen and hydrogen for three times. The reactor was filled with hydrogen to 3 MPa, and the stirring was started at 700 rpm. The material in the reactor was heated and maintained at 110°C, and the hydrogen pressure was maintained at 5 MPa. Then 55% formaldehyde aqueous solution was added by a laminar pump, and the molar ratio of formaldehyde to cyclohexylamine was 2.02:1. The dropwise addition time was controlled for 8 h. After the dropwise addition was completed, the reaction was continued for 10 min, and then the reaction was stopped. The temperature was lowered to below 50°C, the pressure was released, and the reactor was replaced with 1 MPa of nitrogen for three times. The reaction liquid in the reactor was filtered, and the catalyst was retained in the reactor for continuous use. The sample was analyzed by gas chromatography, and the conversion rate of cyclohexylamine was 100%, and the selectivity of N,N-dimethylcyclohexylamine was 99.93%.

[0037] (3) The reaction liquid was transferred to a phase separator and heated to 100°C. A 10wt% KOH solution was added to control the pH of the system to 11, and high-temperature phase separation was carried out. The phase separation residence time was 0.5 h, and oil and water two phases were obtained. The oil phase was subjected to vacuum rectification at a pressure of 1 KPa (absolute pressure) using a packed column with 20 theoretical plates. The reflux ratio was 1:1, and the dehydration was carried out. The N,N-dimethylcyclohexylamine product was collected at the top of the tower at a temperature of about 50°C. The purity of N,N-dimethylcyclohexylamine was 99.96% by gas chromatography analysis, and the content of N-cyclohexylformamide was 8 ppm.

[0038]

Example 2

[0039] (1) 6 g of 2# supported palladium-based catalyst precursor was added to a 1.5 L high-pressure reactor, and 400 ml of deionized water was added. The 2# supported palladium-based catalyst was activated at a temperature of 180°C and a hydrogen pressure of 6 MPa for 8 h.

[0040] (2) The deionized water was filtered through the built-in filter of the high-pressure reactor, 198 g of cyclohexylamine, 1.98 g of N,N-dimethylcyclohexylamine and 396 g of tetrahydrofuran were added, 1 MPa of nitrogen and hydrogen were replaced three times, the reaction kettle was filled with hydrogen to 4 MPa, the stirring was started at 700 rpm, the material in the reaction kettle was heated and maintained at 100°C, the hydrogen pressure was maintained at 8 MPa, then 40% formaldehyde aqueous solution was added by a laminar pump, the molar ratio of formaldehyde to cyclohexylamine was 2.01:1, the dropwise addition time was controlled at 12 h, after the dropwise addition was completed, the reaction was continued for 40 min and then stopped, the temperature was lowered to below 50°C, the pressure was released and replaced with 1 MPa of nitrogen three times, the reaction liquid in the kettle was filtered, the catalyst was left in the reaction kettle for continuous use and evaluation. The sample was analyzed by gas chromatography, the conversion rate of cyclohexylamine was 100%, and the selectivity of N,N-dimethylcyclohexylamine was 99.94%.

[0041] (3) The reaction liquid was transferred to a phase separator and heated to 60°C, a 30wt% NaOH solution was added, the pH of the system was controlled at 14, high-temperature phase separation was carried out, the phase separation residence time was 5 h, and oil and water two phases were obtained. The oil phase was subjected to vacuum rectification under a pressure of 50 KPa (absolute pressure) using a packed column with 10 theoretical plates, and the reflux ratio was 2:1 to remove water, and N,N-dimethylcyclohexylamine product was collected at the top of the tower at a temperature of about 132°C. The purity of N,N-dimethylcyclohexylamine was 99.95% by gas chromatography analysis, and the content of N-cyclohexylformamide was 3 ppm.

[0042]

Example 3

[0043] (1) 1 g of 3# supported palladium-based catalyst precursor was added to a 1.5 L high-pressure reactor, 400 ml of deionized water was added, and the temperature was 130°C, the hydrogen pressure was 5 MPa, and the activation time was 12 h to obtain a 3# supported palladium-based catalyst.

[0044] (2) The deionized water was filtered through the built-in filter of the high-pressure reactor, 198 g of cyclohexylamine, 3.96 g of N,N-dimethylcyclohexylamine and 198 g of water were added, 1 MPa of nitrogen and hydrogen were replaced three times, the reaction kettle was filled with hydrogen to 2 MPa, the stirring was started at 700 rpm, the material in the reaction kettle was heated and maintained at 120°C, the hydrogen pressure was maintained at 3 MPa, then 37% formaldehyde aqueous solution was added by a laminar pump, the molar ratio of formaldehyde to cyclohexylamine was 2.01:1, the dropwise addition time was controlled at 6 h, after the dropwise addition was completed, the reaction was continued for 20 min and then stopped, the temperature was lowered to below 50°C, the pressure was released and replaced with 1 MPa of nitrogen for three times, the reaction liquid in the kettle was filtered, the catalyst was left in the reaction kettle for continuous use and evaluation. The sample was analyzed by gas chromatography, the conversion rate of cyclohexylamine was 100%, and the selectivity of N,N-dimethylcyclohexylamine was 99.91%.

[0045] (3) The reaction liquid was transferred to a phase separator and heated to 80°C, a 20wt% NaOH solution was added, the pH of the system was controlled at 12, high-temperature phase separation was carried out, the phase separation residence time was 2 h, and oil and water two phases were obtained. The oil phase was subjected to vacuum rectification under a pressure of 40 KPa (absolute pressure) using a packed column with 15 theoretical plates, and the reflux ratio was 0.5:1 to remove water, and N,N-dimethylcyclohexylamine product was collected at the top of the tower at a temperature of about 126°C. The purity of N,N-dimethylcyclohexylamine was 99.93% by gas chromatography analysis, and the content of N-cyclohexylformamide was 4 ppm.

[0046]

Example 4

[0047] (1) 2 g of 4# supported palladium-based catalyst precursor was added to a 1.5 L high-pressure reactor, 400 ml of deionized water was added, and the 4# supported palladium-based catalyst was activated at a temperature of 200°C and a hydrogen pressure of 4 MPa for 8 h.

[0048] (2) The deionized water was filtered through the built-in filter of the high-pressure reactor, 198 g of cyclohexylamine, 5.94 g of N,N-dimethylcyclohexylamine and 396 g of water were added, and each was replaced with 1 MPa of nitrogen and hydrogen for three times. The reactor was filled with hydrogen to 1 MPa, and the stirring was started at 700 rpm. The material in the reactor was heated and maintained at 130℃, and the hydrogen pressure was maintained at 2 MPa. Then 37% formaldehyde aqueous solution was added dropwise by a laminar pump, and the molar ratio of the formaldehyde dosage to the cyclohexylamine dosage was 2.02:1. The dropwise time was controlled for 3 h. After the dropwise addition was completed, the reaction was continued for 60 min and then stopped. The temperature was lowered to below 50℃, the pressure was released, and the reactor was replaced with 1 MPa of nitrogen for three times. The reaction liquid in the reactor was filtered, and the catalyst remained in the reactor for continuous use. The sample was analyzed by gas chromatography, and the conversion rate of cyclohexylamine was 100%, and the selectivity of N,N-dimethylcyclohexylamine was 99.92%.

[0049] (3) The reaction liquid was transferred to a phase separator and heated to 90℃, and a 20wt% KOH solution was added to control the pH of the system to 13 for high-temperature phase separation. The phase separation residence time was 3h, and oil and water two phases were obtained. The oil phase was subjected to vacuum rectification under a pressure of 5KPa (absolute pressure) using a packed column with 30 theoretical plates, and the reflux ratio was 1.5:1 for dehydration. N,N-dimethylcyclohexylamine product was collected at the top of the tower at a temperature of about 88℃. The purity of N,N-dimethylcyclohexylamine was 99.97% by gas chromatography analysis, and the content of N-cyclohexylformamide was 5ppm.

[0050]

Example 5

[0051] N,N-dimethylcyclohexylamine was prepared by the same method as in Example 3, except that no NaOH solution was added to adjust the pH before high-temperature phase separation in step (3). In this example, the reaction yield was 99.81%, and the purity of the prepared N,N-dimethylcyclohexylamine was 99.92%, and the content of N-cyclohexylformamide was 3ppm.

[0052]

Comparative Example 1

[0053] N,N-dimethylcyclohexylamine was prepared by the same method as in Example 3, except that no N,N-dimethylcyclohexylamine was added in the initial reaction stage in step (2). In this comparative example, the reaction yield was 99.84%, and the purity of the prepared N,N-dimethylcyclohexylamine was 99.88%, and the content of N-cyclohexylformamide was 1100ppm.

[0054] The product N,N-dimethylcyclohexylamine prepared in Examples 1-5 and Comparative Example 1 was subjected to low-temperature (-10℃) storage stability test, and the results are shown in Table 1:

[0055] Table 1, Low-temperature storage stability test results

[0056]

[0057]

[0058] The above description is only the preferred embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the method of the present application, several improvements and supplements can also be made, which should be considered as the protection scope of the present application.

Claims

1. A process for the preparation of N,N-dimethylcyclohexylamine having improved storage stability, characterized in that, Prepared from cyclohexylamine, N,N-dimethylcyclohexylamine, formaldehyde, hydrogen under the action of a supported palladium-based catalyst; in the raw material, the added amount of N,N-dimethylcyclohexylamine is 1-5% of the mass of cyclohexylamine.

2. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 1, wherein, The added amount of N,N-dimethylcyclohexylamine is 2-3% of the mass of cyclohexylamine.

3. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 1, wherein, The supported palladium-based catalyst comprises palladium, an auxiliary agent and a modified carrier; The auxiliary agent comprises a first auxiliary agent and a second auxiliary agent, the first auxiliary agent is selected from one or more of copper, nickel, cobalt, platinum and ruthenium; and the second auxiliary agent is selected from one or more of lanthanum, bismuth, zinc, iron, rhenium and cerium; The modified carrier comprises a carrier matrix and a modified auxiliary agent, the carrier matrix is selected from one or more of alumina, silica, diatomite and hydrogen-type ZSM-5, and the modified auxiliary agent is magnesium oxide and / or barium oxide.

4. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability according to claim 3, characterized in that, The first auxiliary agent is selected from cobalt and / or ruthenium; and the second auxiliary agent is selected from at least one of iron, cerium and zinc.

5. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 3, wherein, The content of palladium is 0.5-15wt% based on the total mass of the supported palladium-based catalyst, the content of the first auxiliary agent is 0.1-1wt%, and the content of the second auxiliary agent is 0.01-0.5wt%.

6. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 5, wherein, The content of palladium is 4-8wt% based on the total mass of the supported palladium-based catalyst, the content of the first auxiliary agent is 0.2-0.5wt%, and the content of the second auxiliary agent is 0.05-0.2wt%.

7. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 5, wherein, The mass ratio of the first auxiliary agent to the second auxiliary agent is (0.5-30):

1.

8. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 7, wherein, The mass ratio of the first auxiliary agent to the second auxiliary agent is (1-10):

1.

9. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 5, wherein, The content of the modified auxiliary agent in the modified carrier is 1-10wt%.

10. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 9, wherein, The content of the modified auxiliary agent in the modified carrier is 2-5wt%.

11. Process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability according to any one of claims 1 to 10, characterized in that The amount of the supported palladium-based catalyst is 0.5-3% of the mass of cyclohexylamine.

12. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 11, wherein, The amount of the supported palladium-based catalyst is 1-2% of the mass of cyclohexylamine.

13. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 11, wherein, The molar ratio of formaldehyde to cyclohexylamine is (2.01-2.02):

1.

14. Process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability according to any one of claims 1 to 10, characterized in that The reaction temperature is 100-140℃, and the reaction pressure is 2-8MPa in terms of gauge pressure.

15. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 14, wherein, The reaction temperature is 110-130℃, and the reaction pressure is 3-5MPa in terms of gauge pressure.

16. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 14, wherein, The formaldehyde aqueous solution is slowly added at the reaction temperature, and the addition is completed in 3-12h, and the reaction is continued for 10-60min.

17. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 14, wherein, The formaldehyde aqueous solution is slowly added at the reaction temperature, and the addition is completed in 6-8h, and the reaction is continued for 20-40min.

18. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 16, wherein, The mass concentration of the formaldehyde aqueous solution is 37-55wt%.

19. Process for the preparation of N,N-dimethylcyclohexylamine having improved storage stability according to any one of claims 1 to 10, characterized in that, A solvent is further added in the reaction, and the solvent comprises one or more of methanol, water and tetrahydrofuran.

20. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 19, wherein, The mass ratio of the solvent to cyclohexylamine is (0.5-3):

1.

21. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 20, wherein, The mass ratio of the solvent to cyclohexylamine is (1-2):

1.

22. Process for the preparation of N,N-dimethylcyclohexylamine having improved storage stability according to any one of claims 1 to 10, characterized in that, After the reaction is completed, lye is added to adjust the pH to 11-14, then high-temperature phase separation is performed, and the oil phase is purified by rectification to obtain N,N-dimethylcyclohexylamine.

23. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 22, wherein, After the reaction is completed, lye is added to adjust the pH to 12-13.

24. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 22, wherein, The phase separation condition is controlled as follows: the temperature is 60-100℃, and the residence time for phase separation is 0.5-5h.

25. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 24, wherein, The phase separation condition is controlled as follows: the temperature is 80-90℃, and the residence time for phase separation is 2-3h.

26. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 22, wherein, The rectification purification is carried out by vacuum rectification; the pressure is 0.1-50KPa; the number of theoretical plates of rectification column is 10-30; and the reflux ratio is 0.1-5:

1.

27. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 26, wherein, The pressure of rectification purification is 2-5KPa; the number of theoretical plates of rectification column is 15-20; and the reflux ratio is 0.5-2:

1.

28. The process for the preparation of N,N-dimethylcyclohexylamine with improved storage stability as claimed in claim 22, wherein, The alkali liquor is an aqueous solution of sodium hydroxide or potassium hydroxide.

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