Method for preparing cyclohexylamine based on reductive amination of cyclohexanone

Abstract

The invention discloses a method for preparing cyclohexylamine based on reductive amination of cyclohexanone, and belongs to the technical field of fine chemical engineering. The preparation method comprises the following steps: adding a reactant cyclohexanone into a reaction kettle containing a certain amount of solvent, ammonia water and hydrogen atmosphere, and carrying out reductive amination reaction in the presence of a catalyst to obtain cyclohexylamine. The catalyst is CoyAl-LDHs loaded with metal active components, the CoyAl-LDHs are layered cobalt-aluminum bimetal hydroxides, and cobalt ions and precious metal ions in laminates are subjected to spontaneous oxidation-reduction reaction, so that the precious metal ions can be efficiently reduced into active metal nanoparticles. The layered cobalt-aluminum double-metal hydroxide not only has abundant surface acid-base sites, but also has high dispersity of loaded metal nanoparticles. The catalyst preparation and reductive amination reaction conditions are mild, the yield is high, the reaction system is simple and easy to separate, and the method is suitable for industrial production of cyclohexylamine.

Description

Technical Field

[0001] The present invention belongs to the technical field of fine chemical engineering, and particularly relates to a method for preparing cyclohexylamine by reductive amination of cyclohexanone. Background Art

[0002] Primary amines are important compounds and are widely used in the production of fine chemicals, agrochemicals, pharmaceuticals, functional materials and other fields. The synthesis of primary amines is crucial, and various synthesis methods have been developed, including reductive amination of carbonyl compounds, N-alkylation of ammonia with haloalkanes or alcohols, etc. Among these methods, the reductive amination of carbonyl compounds using ammonia (NH3) and hydrogen as the ammonia source and reducing agent is the most attractive route because carbonyl compounds, NH3 and hydrogen are all cheap and widely available raw materials. In addition, the reductive amination of carbonyl compounds can be carried out under relatively mild conditions, and water is the main by-product, which makes the reductive amination of carbonyl compounds an atom-efficient and environmentally friendly method for producing primary amines.

[0003] As a typical carbonyl compound, cyclohexanone can be synthesized from the petrochemical route on the one hand, and can be synthesized in large quantities by hydrogenation of lignin phenolic model compounds on the other hand. A large number of phenolic compounds can be obtained by pyrolysis of lignin, and cyclohexanone can be synthesized by hydrogenation of phenol. This reaction route is more environmentally friendly and conforms to the concept of green carbon science. At present, scientists have developed a variety of catalysts, especially supported metal catalysts, for the reductive amination conversion of cyclohexanone. For example, E. Kolobova et al. prepared 5 different gold catalysts by the deposition-precipitation method in Kolobova E, Mäki-Arvela P, Pestryakov A, et al. Reductive amination of ketones with benzylamine over gold supported on different oxides[J]. Catalysis Letters, 2019, 149: 3432-3446, which were respectively supported on TiO2, La2O3 / TiO2, CeO2 / TiO2, La2O3 and CeO2, and the size of gold nanoparticles was between 2.6 and 3.6 nm. Among them, the 4 wt%Au / CeO2 / TiO2 catalyst had the best catalytic effect on the reductive amination of cyclohexanone under the conditions of 100 °C, 3 MPa hydrogen pressure and toluene as the solvent, and the amine yield was 79%.

[0004] However, the above-mentioned reductive amination reaction of cyclohexanone still faces some problems, such as harsh reaction conditions, low catalyst activity, poor stability, and the selectivity of the target product primary amine needs to be improved, etc., which limit its large-scale industrial application. Summary of the Invention

[0005] The object of the present invention is to overcome the above-mentioned drawbacks of the prior art and provide a method for preparing cyclohexylamine by catalytic reductive amination of cyclohexanone, so as to solve the problems of harsh reaction conditions, low catalyst activity, poor stability and the need to improve the selectivity of cyclohexylamine in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing cyclohexylamine by catalytic reductive amination of cyclohexanone, comprising the following steps: adding cyclohexanone, a catalyst and ammonia water into a solvent in a reaction vessel, carrying out a pressurized reaction in a hydrogen atmosphere, cooling the whole system to room temperature after the reaction is completed, and obtaining cyclohexylamine after solid-liquid separation; The catalyst is M x @Co y Al-LDHs, where M is any one of palladium, ruthenium, platinum, rhodium or gold, x represents the loading amount of metal M, and Co y Al-LDHs represents a layered double metal hydroxide composed of Co and Al, wherein the molar ratio of y to 1 is (1 to 4):1, and the mass fraction of M in the catalyst is 0.5 to 5 wt%.

[0007] A further improvement of the present invention lies in: Preferably, the solvent is any one or more of methanol, ethanol, n-propanol, dioxane, water, tetrahydrofuran, cyclohexane, isopropanol, ethyl acetate and γ-valerolactone.

[0008] Preferably, the mass ratio of cyclohexanone to the catalyst is (3 to 50):1.

[0009] Preferably, the reaction temperature is 60 to 150 °C, the reaction time is 0.1 to 8 h, and the reaction pressure is 0.1 to 3 MPa.

[0010] Preferably, the preparation process of the M x @Co y Al-LDHs is as follows: (1) Mix urea, cobalt nitrate hexahydrate and aluminum nitrate nonahydrate, and prepare a Co y Al-LDHs precursor by hydrothermal treatment; (2) Load metal M nanoparticles on the Co y Al-LDHs precursor by a spontaneous redox method.

[0011] Preferably, the specific reaction process of step (1) is as follows: Cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and urea are ultrasonically dispersed and stirred, dissolved in water. The whole system is sealed and subjected to crystallization reaction for growth. After the crystallization is completed, the whole system is filtered and washed until neutral, and then dried and ground to obtain Co y Al-LDH precursor.

[0012] Preferably, the mixing ratio of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and urea is (1.310~2.095) g : (0.675~1.688) g : (0.901~3.604) g.

[0013] Preferably, the crystallization reaction temperature is 80~120 °C, and the reaction time is 12~36 h.

[0014] Preferably, the specific reaction process of step (2) is as follows: The Co y Al-LDHs precursor is ultrasonically dispersed in water to obtain a precursor aqueous dispersion. An aqueous solution of M metal source is added dropwise to the precursor aqueous dispersion. After stirring and reacting, the reaction product obtained is M x @Co y Al-LDHs.

[0015] Preferably, in step (2), the stirring temperature is room temperature, and the stirring time is 8 - 24 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing cyclohexylamine by selective reductive amination of cyclohexanone. In this preparation method, the reactant cyclohexanone is added into a reaction kettle containing a certain amount of solvent, ammonia water, and hydrogen atmosphere, and reductive amination reaction is carried out in the presence of a catalyst to obtain cyclohexylamine. The catalyst is Co y Al-LDHs loaded with metal active components, where Co yAl-LDHs are layered cobalt-aluminum double metal hydroxides. Through the spontaneous redox reaction between cobalt ions and noble metal ions in the layer board, noble metal ions can be efficiently reduced to active metal nanoparticles. In the present invention, the layered cobalt-aluminum double metal hydroxide not only has abundant surface acid-base sites, but also the loaded metal nanoparticles have high dispersion and uniform size, with characteristics such as high monodispersity, regular structure, and controllable particle size distribution. The preparation of this catalyst and the reductive amination reaction conditions are mild, with high yield, simple reaction system, high activity, good selectivity, high stability of the used catalyst, no pollution to the environment, being green and efficient, and easy to separate, which is suitable for the industrial production of cyclohexylamine. Compared with the traditional method, this catalytic system has high yield, does not require external acid or alkaline additives, and has high industrial application value. The process of preparing cyclohexylamine by reductive amination of cyclohexanone includes the amination of cyclohexanone to form imine and the hydrogenation reduction to form the target product cyclohexylamine, along with the generation of some by-products. The specific reaction path is as Figure 1 shown. To promote the development of the cyclohexanone reductive amination reaction system and achieve the efficient conversion of cyclohexanone to cyclohexylamine, it is crucial to develop highly efficient and stable metal catalysts.

[0017] Furthermore, due to the unique metal-support interaction and metal cation confinement effect, that is, Co y Al-LDHs acts as both a support and a reducing agent at the same time. The highly dispersed divalent cobalt ions therein can spontaneously in-situ reduce the noble metal M to metal nanoparticles, which not only provides excellent protection for the noble metal M component, but also effectively improves the dispersion and utilization rate of the noble metal active component. The layered double metal hydroxide supported metal nanoparticle catalyst prepared in the present invention can significantly improve the stability of the metal nanocatalyst and alleviate the situation where the catalytic activity is not high or even deactivated due to agglomeration or oxidation of the metal nanoparticles during the reaction. For the catalyst prepared in the present invention, its metal nanoparticles are fine and evenly distributed. The Lewis acid sites on the surface of the layered cobalt-aluminum double metal hydroxide support and the highly dispersed active metal centers with a particle size of about 2 nm form a bifunctional catalyst, which effectively promotes the local tandem reaction and the adsorption, stabilization, and selective activation of the transition states of reactants, intermediates, or products, making its catalytic activity for the reductive amination of cyclohexanone and the selectivity for cyclohexylamine high and the stability good. The present invention uses a heterogeneous catalyst, with a simple reaction system, being green and efficient and having no pollution to the environment, meeting the requirements of sustainable development, and having good industrial application prospects. Description of the Drawings

[0018] Figure 1 It is the reaction path diagram of the preparation of cyclohexylamine by reductive amination of cyclohexanone and the involved side reactions in the present invention; Figure 2 It is the X-ray diffraction pattern of the Co3Al-LDHs precursor prepared in Example 3 and the catalyst prepared in Example 6; Figure 3 SEM photograph of the catalyst prepared in Example 6; Figure 4 TEM photograph of the catalyst prepared in Example 6. Detailed implementation manners

[0019] The present invention will be further described in detail below with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art with respect to the present invention. In case of conflict, the definition in this specification shall prevail.

[0020] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0021] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0022] Conventional instrument and equipment in the art are used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0023] The present invention discloses a method for preparing cyclohexylamine by reductive amination of cyclohexanone. Using a reaction kettle as the reaction vessel, cyclohexanone, a catalyst, and ammonia water are respectively added to a solvent. Using toluene as an internal standard, the gas in the reaction kettle is replaced with hydrogen four to five times. After replacing the gas in the reaction kettle, hydrogen is filled into the kettle to increase the pressure to the reaction pressure. After reacting at a certain temperature, it is cooled to room temperature and solid-liquid separation is carried out using a needle-type organic filter to obtain the target product cyclohexylamine.

[0024] The catalyst is a layered cobalt-aluminum double metal hydroxide loaded with a metal active component M, i.e., M x @Co yAl-LDHs, where M is any one of palladium, ruthenium, platinum, rhodium, and gold, x represents the loading amount of metal M, and Co y Al-LDHs represents a layered double metal hydroxide composed of Co and Al with a molar ratio of y:1, and y:1 is (1~4):1.

[0025] The mass percentage of the metal active component in the catalyst, that is, the loading amount x of metal M, is 0.5~5 wt%.

[0026] In some embodiments of the present invention, the reaction temperature is 60~150 °C, the reaction time is 0.1~8 h; the reaction pressure is 0.1~3 MPa.

[0027] In some embodiments of the present invention, the mass ratio of cyclohexanone to the catalyst is (4~20):1; In some embodiments of the present invention, the mass ratio of ammonia water to the catalyst is (23~114):1.

[0028] The solvent is any one of methanol, ethanol, n-propanol, dioxane, water, tetrahydrofuran, cyclohexane, isopropanol, ethyl acetate, and γ-valerolactone.

[0029] In some embodiments of the present invention, the catalyst is prepared by a method combining urea hydrolysis, hydrothermal treatment, and spontaneous oxidation-reduction method.

[0030] The preparation of the catalyst includes the following steps: (1) Preparation of Co y Al-LDHs precursor by urea hydrolysis combined with hydrothermal treatment; According to the molar ratio of urea to metal ions (Co 2+ and Al 3+ ) of (5~20):3, cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and urea are ultrasonically dispersed and strongly stirred, fully dissolved in water, and the above solution is sealed in a hydrothermal autoclave and crystallized at 80~120 °C for 12~36 h. After crystallization, it is filtered and washed with a large amount of deionized water until neutral, and then dried and ground to obtain the Co y Al-LDHs precursor.

[0031] (2) Loading metal M nanoparticles on the precursor by spontaneous oxidation-reduction method.

[0032] Disperse the Co y Al-LDHs precursor ultrasonically in water, dropwise add the aqueous solution of M metal source, stir the above mixed system, then wash it by centrifugation with deionized water and dry it in a vacuum drying oven to obtain the M x @Co y Al-LDHs catalyst.

[0033] It should be noted that in this process, there is no special concentration requirement for the metal source aqueous solution, and the dosage of the metal source is determined according to the required loading amount. The metal source aqueous solution is a corresponding aqueous solution prepared from any one of palladium chloride, palladium nitrate, potassium tetrachloropalladate, chloroplatinic acid, ruthenium trichloride, rhodium trichloride, chloroauric acid, and hydrated iridium trichloride.

[0034] As a preferred solution, during the preparation of the catalyst, the mixing ratio of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and urea is: (1.310 - 2.095) g : (0.675 - 1.688) g : (0.901 - 3.604) g.

[0035] The catalyst exhibits excellent structural stability in the cyclohexanone reductive amination reaction, and its catalytic activity and selectivity do not significantly decrease during five catalytic cycles.

[0036] In a specific embodiment of the present invention, the preparation process of the Co y Al-LDHs precursor is disclosed: Weigh 4.5 - 7.2 mmol of Co(NO3)2·6H2O and 1.8 - 4.5 mmol of Al(NO3)3·9H2O in proportion and dissolve them in 60 mL of deionized water to prepare a salt solution with a Co / Al molar ratio of 1 - 4 and a metal ion concentration C(Co 2+ +Al 3+ ) = 0.15 mol / L. Then weigh 15 - 60 mmol of urea, where the molar ratio of urea to metal ions is (5 - 20) : 3. Completely dissolve the urea in the above solution and mix them well. Subsequently, transfer the polytetrafluoroethylene inner liner containing the above mixed solution to a hydrothermal reactor, seal it, and place it in an oven at 80 - 120 °C for 12 - 36 h for crystallization. After crystallization, filter it with a large amount of deionized water until it is neutral and then dry and grind it to obtain the Co y Al-LDHs precursor with a cobalt-aluminum ratio of y : 1, and y : 1 is (1 - 4) : 1.

[0037] In a specific embodiment of the present invention, the preparation process of the M x @Co y Al-LDHs catalyst is disclosed: To prepare M x @Co y Al-LDHs (x = 0.5 - 5 wt%) catalysts with different M loadings, first weigh 200 mg of Co yThe Al-LDHs precursor was added to a round-bottom flask containing 190 ml of deionized water and sonicated for 30 min. Then it was stirred for 30 min, and 10 ml of an aqueous solution of the M metal source (this volume could ensure complete dissolution of the metal source) was added dropwise, and stirring was continued for 8 - 24 h. After the stirring was completed, the solution was centrifuged and washed to remove excess impurities and reactants. Finally, the obtained sample was dried in vacuo at 60 °C to obtain the dried M x @Co y Al-LDHs catalyst. Specifically, the M metal source is any one of palladium chloride, palladium nitrate, potassium tetrachloropalladate, chloroplatinic acid, ruthenium trichloride, rhodium trichloride, chloroauric acid, and hydrated iridium trichloride.

[0038] The technical solutions of the present invention will be described in detail below in conjunction with several embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0039] The experimental materials used in the following examples can be obtained from conventional biochemical reagent stores without special instructions.

[0040] Example 1 (Co1Al-LDHs) According to the molar ratio of urea to metal ions of 5:3, 1.310 g of Co(NO3)2·6H2O, 1.688 g of Al(NO3)3·9H2O, and 0.901 g of urea were weighed, ultrasonically dispersed, and strongly stirred, and dissolved in 60 mL of deionized water and mixed well. Subsequently, the polytetrafluoroethylene liner containing the above mixed solution was transferred to a hydrothermal autoclave, sealed, and placed in an oven at 110 °C for 24 h for crystallization. After the crystallization was completed, it was filtered with a large amount of deionized water until neutral and dried and ground.

[0041] Example 2 (Co2Al-LDHs) According to the molar ratio of urea to metal ions of 10:3, 1.749 g of Co(NO3)2·6H2O, 1.125 g of Al(NO3)3·9H2O, and 1.802 g of urea were weighed, ultrasonically dispersed, and strongly stirred, and dissolved in 60 mL of deionized water and mixed well. Subsequently, the polytetrafluoroethylene liner containing the above mixed solution was transferred to a hydrothermal autoclave, sealed, and placed in an oven at 110 °C for 24 h for crystallization. After the crystallization was completed, it was filtered with a large amount of deionized water until neutral and dried and ground.

[0042] Example 3 (Co3Al-LDHs) Weigh 1.964 g of Co(NO3)2·6H2O, 0.844 g of Al(NO3)3·9H2O and 1.802 g of urea according to the molar ratio of urea to metal ions of 10:3. After ultrasonic dispersion and strong stirring, dissolve them in 60 mL of deionized water and mix well. Then transfer the polytetrafluoroethylene inner liner containing the above mixed solution to a hydrothermal autoclave, seal it, and place it in an oven at 110 °C for 24 h for crystallization. After crystallization is completed, filter it with a large amount of deionized water until neutral and dry and grind it.

[0043] Example 4 (Co4Al-LDHs) Weigh 2.095 g of Co(NO3)2·6H2O, 0.675 g of Al(NO3)3·9H2O and 3.604 g of urea according to the molar ratio of urea to metal ions of 20:3. After ultrasonic dispersion and strong stirring, dissolve them in 60 mL of deionized water and mix well. Then transfer the polytetrafluoroethylene inner liner containing the above mixed solution to a hydrothermal autoclave, seal it, and place it in an oven at 110 °C for 24 h for crystallization. After crystallization is completed, filter it with a large amount of deionized water until neutral and dry and grind it.

[0044] Example 5 (Pd2@Co2Al-LDHs) Weigh 200 mg of the Co2Al-LDHs precursor prepared with a molar ratio of urea to metal ions of 10:3 and add it to a round-bottom flask containing 190 ml of deionized water, and ultrasonically treat it for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water dissolved with 12.5 mg of K2PdCl4 powder, and continue stirring for 14 h. Finally, centrifuge and wash the solution and dry it under vacuum at 60 °C.

[0045] Example 6 (Pd2@Co3Al-LDHs) Weigh 200 mg of the Co3Al-LDHs precursor prepared with a molar ratio of urea to metal ions of 10:3 and add it to a round-bottom flask containing 190 ml of deionized water, and ultrasonically treat it for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water dissolved with 12.5 mg of K2PdCl4 powder, and continue stirring for 14 h. Finally, centrifuge and wash the solution and dry it under vacuum at 60 °C.

[0046] Example 7 (Pd2@Co4Al-LDHs) Weigh 200 mg of the Co4Al-LDHs precursor prepared with a molar ratio of urea to metal ions of 10:3 and add it to a round-bottom flask containing 190 ml of deionized water, then perform ultrasonic treatment for 30 min. Next, stir for 30 min, and gradually dropwise add 10 ml of deionized water in which 12.5 mg of K2PdCl4 powder is dissolved, and continue stirring for 14 h. Finally, centrifuge and wash the solution and dry it under vacuum at 60 °C.

[0047] Examples 8 - 10 Determine Pd x @Co y In the catalytic reductive amination reaction of cyclohexanone by the Pd2@Co y Al-LDHs catalyst, the influence of the molar ratio of cobalt to aluminum in LDHs on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. Add 10 mg of Pd2@Co

[0048] Al-LDHs catalysts with different cobalt-aluminum molar ratios (Examples 5 - 7), 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into a 15 mL stainless steel high-temperature reaction kettle liner. After replacing the gas 5 times with high-purity hydrogen, fill with hydrogen to 0.4 MPa, heat to 100 °C, maintain for 4 h, with a rotation speed of 500 rpm. After the reaction ends, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and use a needle-type organic filter to filter out the clear liquid for gas chromatography detection.

[0049] After the reaction ends, calculate the conversion rate of cyclohexanone and the selectivity of cyclohexylamine according to the following formula.

[0050]

[0051]

[0052] The specific results are shown in Table 1: Table 1 Influence of catalysts with different cobalt-aluminum molar ratios on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine

[0053] Result analysis: As can be seen from Table 1, on the premise that other reaction conditions remain the same, when the cobalt-aluminum molar ratio is 3:1, the catalytic performance is the best.

[0054] Example 11 (Pd 0.5 @Co3Al-LDHs) Weigh 200 mg of Co3Al-LDHs precursor and add it to a round-bottom flask containing 190 ml of deionized water, then ultrasonically treat for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water in which 3.1 mg of K2PdCl4 powder is dissolved, and continue stirring for 14 h. Finally, centrifuge and wash the solution and vacuum dry it at 60 °C.

[0055] Example 12 (Pd 2.5 @Co3Al-LDHs) Weigh 200 mg of Co3Al-LDHs precursor and add it to a round-bottom flask containing 190 ml of deionized water, then ultrasonically treat for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water in which 15.6 mg of K2PdCl4 powder is dissolved, and continue stirring for 14 h. Finally, centrifuge and wash the solution and vacuum dry it at 60 °C.

[0056] Example 13 (Pd5@Co3Al-LDHs) Weigh 200 mg of Co3Al-LDHs precursor and add it to a round-bottom flask containing 190 ml of deionized water, then ultrasonically treat for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water in which 31.2 mg of K2PdCl4 powder is dissolved, and continue stirring for 14 h. Finally, centrifuge and wash the solution and vacuum dry it at 60 °C.

[0057] Examples 14 - 15 Determine the influence of different Pd loadings on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine in the catalytic reduction amination reaction of cyclohexanone by Pd x @Co y Al-LDHs catalyst. Add 10 mg of Pd x @Co3Al-LDHs catalyst with different loadings, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After replacing the gas 5 times with high-purity hydrogen, fill the hydrogen to 0.4 MPa, heat to 100 °C, maintain for 4 h, and the rotation speed is 500 rpm. After the reaction is completed, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection. The specific results are shown in Table 2: Table 2 Influence of catalysts with different Pd loadings on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine

[0058] Result analysis: As can be seen from Table 2, when other reaction conditions remain the same, the catalytic performance is the best when the Pd loading is 2 wt%. Under the condition of ensuring the highest conversion rate of cyclohexanone and selectivity of cyclohexylamine, the use cost of Pd noble metal is saved as much as possible.

[0059] Examples 16 - 17 Determine Pd x @Co y In the reductive amination reaction of cyclohexanone catalyzed by the Al-LDHs catalyst, the effects of different hydrogen pressures on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, fill the hydrogen to the target pressure, heat to 100 °C, maintain for 4 h, and the rotation speed is 500 rpm. After the reaction, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection. The specific results are shown in Table 3 as follows: Table 3 Effects of different pressures on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine

[0060] Result analysis: As can be seen from Table 3, when other reaction conditions remain the same, compared with other hydrogen pressure conditions, the catalyst used in the present invention has the best reaction effect under a hydrogen pressure of 0.4 MPa. Under the condition of ensuring the highest conversion rate of cyclohexanone and the selectivity of cyclohexylamine, the use cost of hydrogen is saved as much as possible.

[0061] Examples 18 - 19 Determine Pd x @Co y In the reductive amination reaction of cyclohexanone catalyzed by the Al-LDHs catalyst, the effects of different ammonia water dosages on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and a certain amount of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, fill the hydrogen to 0.4 MPa, heat to 100 °C, maintain for 4 h, and the rotation speed is 500 rpm. After the reaction, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection. The specific results are shown in Table 4 as follows: Table 4 Effects of Different Ammonia Water Dosages on the Conversion Rate of Cyclohexanone and the Selectivity of Cyclohexylamine

[0062] Result Analysis: As can be seen from Table 4, when other reaction conditions remain the same, compared with other ammonia water dosage conditions, the catalyst used in the present invention shows the best reaction effect under the condition of 1 mL ammonia water dosage. While ensuring the highest conversion rate of cyclohexanone and the selectivity of cyclohexylamine, the use cost of ammonia water is saved as much as possible.

[0063] Examples 20 - 21 Determine Pd x @Co y In the reduction amination reaction of cyclohexanone catalyzed by Pd2@Co3Al-LDHs catalyst, the effects of catalyst dosage on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. A certain amount of Pd2@Co3Al-LDHs catalyst, 0.5 mmol cyclohexanone, 5 mL methanol solvent, and 1 mL ammonia water were added into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, hydrogen was filled to 0.4 MPa, heated to 100 °C, maintained for 4 h, and the rotation speed was 500 rpm. After the reaction ended, the reaction kettle was cooled to room temperature in water and then the gas was released. Additionally, 0.5 mmol of toluene was added as an internal standard, and the clear liquid was filtered out using a needle-type organic filter for gas chromatography detection. The specific results are shown in Table 5: Table 5 Effects of Different Catalyst Dosages on the Conversion Rate of Cyclohexanone and the Selectivity of Cyclohexylamine

[0064] Result Analysis: As can be seen from Table 5, when other reaction conditions remain the same, compared with other catalyst dosage conditions, the catalyst used in the present invention shows the best reaction effect under the condition of 10 mg catalyst dosage. While ensuring the highest conversion rate of cyclohexanone and the selectivity of cyclohexylamine, the use cost of the catalyst is saved as much as possible.

[0065] Examples 22 - 26 On the basis of the above examples, further determine the effects of different solvents on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol cyclohexanone, 5 mL solvent, and 1 mL ammonia water were added into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, hydrogen was filled to 0.4 MPa, heated to 100 °C, maintained for 4 h, and the rotation speed was 500 rpm. After the reaction ended, the reaction kettle was cooled to room temperature in water and then the gas was released. Additionally, 0.5 mmol of toluene was added as an internal standard, and the clear liquid was filtered out using a needle-type organic filter for gas chromatography detection. The specific results are shown in Table 6: Table 6 Effects of Different Solvents on the Conversion Rate of Cyclohexanone and the Selectivity of Cyclohexylamine

[0066] Result analysis: As can be seen from Table 6, during the reductive amination of cyclohexanone, the solvent has a great influence on the selectivity of cyclohexylamine, and methanol is the optimal reaction solvent among them.

[0067] Examples 27 - 30 Determine Pd x @Co y In the reductive amination reaction of cyclohexanone catalyzed by Pd2@Co3Al-LDHs catalyst, the effects of reaction time on the conversion rate of cyclohexanone and the selectivity of cyclohexylamine. Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner liner of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, fill hydrogen to 0.4 MPa, heat to 100 °C, maintain for a certain time, the rotation speed is 500 rpm. After the reaction is completed, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection. The results are shown in Table 7: Table 7 Effects of Different Reaction Times on the Conversion Rate of Cyclohexanone and the Selectivity of Cyclohexylamine

[0068] Result analysis: As can be seen from Table 7, during the reductive amination of cyclohexanone, with the extension of the reaction time, the selectivity of the target product cyclohexylamine gradually increases. Cyclohexanone reaches complete conversion at 4 hours, and the selectivity of cyclohexylamine is the largest. Therefore, the reaction time of 4 hours is the best.

[0069] Example 31 Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner liner of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, fill hydrogen to 0.4 MPa, heat to 80 °C, maintain for 4 h, the rotation speed is 500 rpm. After the reaction is completed, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection.

[0070] The results show that the conversion rate of cyclohexanone is 85% and the selectivity of cyclohexylamine is 73%.

[0071] Example 32 Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reactor. After purging the gas 5 times with high-purity hydrogen, fill the reactor with hydrogen to 0.4 MPa, heat it to 100 °C, maintain the temperature for 4 h, with a rotation speed of 500 rpm. After the reaction is completed, cool the reactor in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and use a needle-type organic filter to filter out the clear liquid for gas chromatography detection.

[0072] The results show that the conversion rate of cyclohexanone is 100% and the selectivity of cyclohexylamine is 98%.

[0073] Example 33 Add 10 mg of Pd2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reactor. After purging the gas 5 times with high-purity hydrogen, fill the reactor with hydrogen to 0.4 MPa, heat it to 110 °C, maintain the temperature for 4 h, with a rotation speed of 500 rpm. After the reaction is completed, cool the reactor in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and use a needle-type organic filter to filter out the clear liquid for gas chromatography detection.

[0074] The results show that the conversion rate of cyclohexanone is 100% and the selectivity of cyclohexylamine is 89%.

[0075] Example 34 The difference from Example 32 is that the catalyst recovered in Example 32 is recycled. The treatment of the catalyst is as follows: Wash the catalyst recovered in Example 32 three times repeatedly with methanol, dry it in a vacuum drying oven at 60 °C, and then put it into use.

[0076] Example 35 The difference from Example 34 is that the catalyst recovered in Example 34 is recycled. The treatment of the catalyst is as follows: Wash the catalyst recovered in Example 34 three times repeatedly with methanol, dry it in a vacuum drying oven at 60 °C, and then put it into use.

[0077] Example 36 The difference from Example 35 is that the catalyst recovered in Example 35 is recycled. The treatment of the catalyst is as follows: Wash the catalyst recovered in Example 35 three times repeatedly with methanol, dry it in a vacuum drying oven at 60 °C, and then put it into use.

[0078] Example 37 It is different from Example 36 in that the catalyst recovered in Example 36 is recycled. The treatment of the catalyst is as follows: The catalyst recovered in Example 36 is washed repeatedly with methanol three times, dried in a vacuum drying oven at 60 °C, and then put into use.

[0079] Example 38 It is different from Example 37 in that the catalyst recovered in Example 37 is recycled. The treatment of the catalyst is as follows: The catalyst recovered in Example 37 is washed repeatedly with methanol three times, dried in a vacuum drying oven at 60 °C, and then put into use.

[0080] Test results: The test results of Examples 34 - 38 are shown in Table 8: Table 8 Conversion rate of cyclohexanone and selectivity of cyclohexylamine in Examples 34 - 38

[0081] Result analysis: As can be seen from Table 8, the catalyst used in the present invention can maintain its high catalytic activity well in the recycling experiment.

[0082] Example 39 (Ru2@Co3Al-LDHs) Weigh 200 mg of Co3Al-LDHs precursor and add it to a round-bottom flask containing 190 ml of deionized water, and ultrasonically treat it for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water dissolved with 8.3 mg of ruthenium trichloride, and continue stirring for 14 h. Finally, centrifuge and wash the solution and dry it in a vacuum at 60 °C.

[0083] Example 40 Add 10 mg of Ru2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water into the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After replacing the gas 5 times with high-purity hydrogen, fill hydrogen to 0.4 MPa, heat to 80 °C, keep for 4 h, the rotation speed is 500 rpm. After the reaction is completed, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid with a needle-type organic filter for gas chromatography detection.

[0084] The results show that the conversion rate of cyclohexanone is 100% and the selectivity of cyclohexylamine is 92%.

[0085] Example 41 (Pt2@Co3Al-LDHs) Weigh 200 mg of the Co3Al-LDHs precursor and add it to a round-bottom flask containing 190 ml of deionized water, then ultrasonically treat it for 30 min. Then stir for 30 min, dropwise add 10 ml of deionized water containing 11.1 mg of potassium chloroplatinate, and continue stirring for 14 h. Finally, centrifuge and wash the solution and vacuum dry it at 60 °C.

[0086] Example 42 Add 10 mg of the Pt2@Co3Al-LDHs catalyst, 0.5 mmol of cyclohexanone, 5 mL of methanol solvent, and 1 mL of ammonia water to the inner lining of a 15 mL stainless steel high-temperature reaction kettle. After purging the gas 5 times with high-purity hydrogen, fill the hydrogen to 0.4 MPa, heat to 80 °C, keep for 4 h, with a rotation speed of 500 rpm. After the reaction is completed, cool the reaction kettle in water to room temperature and then release the gas. Additionally, add 0.5 mmol of toluene as an internal standard, and filter out the clear liquid using a needle-type organic filter for gas chromatography detection.

[0087] The results show that the conversion rate of cyclohexanone is 100% and the selectivity of cyclohexylamine is 83%.

[0088] Figure 2 Figure 1 is the X-ray diffraction pattern of the Co3Al-LDHs precursor prepared in Example 3 and the catalyst prepared in Example 6. It shows typical layered LDHs structural characteristic peaks near 2θ = 11.5°, 22.8°, 33.4°, 60.4°, and 61.6°, corresponding to the (003), (006), (009), (110), and (113) crystal planes of the LDHs crystal (JCPDS15-0087). There are no other impurity peaks, indicating that the Co3Al-LDHs precursor was successfully prepared using the urea hydrolysis method combined with the hydrothermal treatment method. In addition, there are no obvious Pd metal characteristic peaks in the XRD pattern, indicating that the Pd nanoparticles are highly dispersed on the Co3Al-LDHs support and have a small metal particle size, thus obtaining high metal atom utilization and high catalytic activity.

[0089] Figure 3 Figure 2 is the scanning electron microscope photograph of the Pd2@Co3Al-LDHs catalyst in Example 6. In the SEM image, a typical two-dimensional layered structure can be clearly observed. Since the urea decomposition method was used in the process of synthesizing the LDHs precursor, the pH value inside the solution remained stable during the hydrothermal reaction, and the supersaturation of the solution was low. The synthesized LDHs had high crystallinity and micron-sized large crystals could be prepared.

[0090] Figure 4It is the transmission electron microscope photograph of the Pd2@Co3Al-LDHs catalyst in Example 6. It can be seen from the figure that in the prepared catalyst, the metal Pd nanoparticles are uniformly dispersed on the support without agglomeration.

[0091] In summary, the noble metal M nanoparticles supported on the layered cobalt-aluminum double metal hydroxide catalyst of the present invention can well reduce aminate cyclohexanone to produce cyclohexylamine, and the methods for preparing the catalyst and cyclohexylamine both have good industrial prospects.

[0092] The present invention provides a method for preparing cyclohexylamine from cyclohexanone. In this method, cyclohexanone, ammonia water, a catalyst and a solvent are added into a reaction kettle, and after a reductive amination reaction is carried out under a hydrogen atmosphere, the target product cyclohexylamine is obtained. The catalyst is a layered cobalt-aluminum double metal hydroxide loaded with a metal active component M, that is, M x @Co y Al-LDHs, M is any one of palladium, ruthenium, platinum, rhodium, and gold, x represents the loading amount of the metal M, and Co y Al-LDHs represents a layered double metal hydroxide composed of a molar ratio of Co to Al of y:1, and y:1 is (1~4):1. The main structure of this catalyst is a layered double metal hydroxide. Taking this layered structure as a support, through a spontaneous redox process, highly dispersed noble metal nanoparticles are loaded on its surface. The unique metal cation confinement effect and metal-support interaction of this catalyst provide excellent protection for the noble metal M component, effectively disperse and stabilize the active metal component, and regulate the electronic properties of the active metal surface. At the same time, the synergistic effect of the Lewis acid sites on the surface of the catalyst support and the highly dispersed active metal centers with a particle size of about 2 nm can enhance the adsorption and selective activation of cyclohexanone and Schiff base intermediates on the catalyst surface, and improve the activity and selectivity of the reductive amination of cyclohexanone to produce cyclohexylamine. The catalyst preparation process of the present invention is simple, the reductive amination reaction conditions are mild, the conversion rate of cyclohexanone and the selectivity of cyclohexylamine are high, the reaction system is simple, green and efficient, and it is pollution-free to the environment, meeting the requirements of sustainable development and having broad industrial application prospects.

[0093] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing cyclohexylamine by reductive amination of cyclohexanone, characterized in that, It includes the following steps: adding cyclohexanone, a catalyst and ammonia water into the solvent in the reaction vessel, carrying out a pressurized reaction under a hydrogen environment, cooling the whole system to room temperature after the reaction ends, and obtaining cyclohexylamine after solid-liquid separation; The catalyst is M x @Co y Al-LDHs, where M is any one of palladium, ruthenium, platinum, rhodium or gold, x represents the loading amount of metal M, Co y Al-LDHs represents a layered double metal hydroxide composed of Co and Al, where the molar ratio of y to 1 is (1 to 4):1, and the mass percentage of M in the catalyst is 0.5 to 5 wt%.

2. The method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 1, characterized in that, The solvent is any one or several of methanol, ethanol, n-propanol, dioxane, water, tetrahydrofuran, cyclohexane, isopropanol, ethyl acetate and γ-valerolactone.

3. A method for preparing cyclohexylamine by the reductive amination of cyclohexanone according to claim 1, characterized in that, The mass ratio of the cyclohexanone to the catalyst is (3 - 50):

1.

4. A method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 1, characterized in that, The reaction temperature is 60 - 150 °C, the reaction time is 0.1 - 8 h, and the reaction pressure is 0.1 - 3 MPa.

5. A method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 1, characterized in that, The said M x @Co y The preparation process of Al-LDHs is as follows: (1) After mixing urea, cobalt nitrate hexahydrate, and aluminum nitrate nonahydrate, prepare the Co y Al-LDHs precursor by hydrothermal treatment; (2) Loading metal M nanoparticles on the Co y Al-LDHs precursor by a spontaneous redox method.

6. A method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 5, characterized in that, The specific reaction process of step (1) is as follows: Cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and urea are ultrasonically dispersed and stirred, dissolved in water, the whole system is sealed and subjected to crystallization reaction for growth. After the crystallization is completed, the whole system is filtered by suction, washed until neutral, dried and ground to obtain Co y Al-LDH precursor.

7. A method for preparing cyclohexylamine by the reductive amination of cyclohexanone according to claim 6, characterized in that, The mixing ratio of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate and urea is (1.310 - 2.095) g:(0.675 - 1.688) g:(0.901 - 3.604) g.

8. A method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 6, characterized in that, The crystallization reaction temperature is 80 - 120 °C, and the reaction time is 12 - 36 h.

9. A method for preparing cyclohexylamine based on the reductive amination of cyclohexanone according to claim 5, characterized in that, The specific reaction process of step (2) is as follows: Co y Al-LDHs precursor is ultrasonically dispersed in water to obtain a precursor aqueous dispersion. An aqueous solution of M metal source is added dropwise to the precursor aqueous dispersion. After stirring and reacting, the reaction product obtained is M x @Co y Al-LDHs.

10. The method for preparing cyclohexylamine by reductive amination of cyclohexanone according to claim 9, characterized in that, In step (2), the stirring temperature is room temperature, and the stirring time is 8 - 24 h.

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