A method for preparing piperidine

Abstract

This invention discloses a method for preparing piperidine. The method uses δ-valerol derived from biomass as the initial raw material, first sequentially generating 5-hydroxyvalerate and 4-cyanobutyraldehyde, then using a core-shell structured material with an Al₂O₃ shell as a catalyst to synthesize piperidine under mild reaction conditions. The catalytic reaction involved in this invention is a low-pressure reaction, requiring less sophisticated reaction equipment and improving the economic feasibility of the reaction; the byproducts of the catalytic process are pollution-free, resulting in minimal waste and achieving green and sustainable production of piperidine.

Description

Technical Field

[0001] This invention relates to a technique for preparing piperidine, a nitrogen-containing heterocyclic compound, and particularly to a method for preparing piperidine from δ-valerolactone as a starting material and its catalyst. Background Technology

[0002] Piperidine is an important nitrogen-containing heterocyclic compound widely used in the preparation of local anesthetics, analgesics, bactericides, wetting agents, curing agents for epoxy resins, and vulcanization accelerators for rubber. Its derivatives are widely found in natural products and are used as pharmaceutical intermediates. Currently, piperidine is mainly prepared via the catalytic hydrogenation of pyridine. However, pyridine hydrogenation requires not only high reaction temperatures and pressures but also the use of precious metal catalysts, resulting in high costs and significant process risks.

[0003] Besides the pyridine hydrogenation method for preparing piperidine, there are other process routes for synthesizing piperidine, such as the 1,5-pentanediol amination method and the valeronamide hydrogenation method. The former faces problems such as the difficulty in obtaining raw materials and high operational risks; the latter uses noble metal complex catalysts (mainly Rh6(CO)). 16 -Re2(CO) l0 (etc.) have problems such as complex preparation process, inability to be recycled, and high catalyst cost.

[0004] In summary, the synthesis of piperidine from biomass-derived δ-valerolactone using heterogeneous, non-precious metal catalysts represents a green and sustainable technological route. Therefore, researching safe and industrially viable piperidine production methods and corresponding catalyst systems is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing piperidine. This method uses δ-valerol derived from biomass as the initial raw material, first sequentially generating 5-hydroxyvaleronitrile and 4-cyanobutyraldehyde, and then using a core-shell structured material with an Al₂O₃ shell as a catalyst to synthesize piperidine under mild reaction conditions. This invention avoids the inherent safety hazards of existing processes and achieves green and sustainable production of piperidine.

[0006] The technical solution of this invention is as follows:

[0007] A method for preparing piperidine, the method comprising the following steps:

[0008] (1) After being heated and vaporized, δ-valerol and ammonia are mixed and then introduced into a fixed-bed reactor loaded with catalyst I. Under normal pressure, at 250℃~300℃, they undergo an ammonia addition nitrification reaction to generate 5-hydroxyvaleronitrile.

[0009] The molar ratio of δ-valerolactone to ammonia was 1:3-10; the volume hourly space velocity (VHSV) of the δ-valerolactone and ammonia mixture passing through catalyst bed I was 200 h⁻¹. -1 ~1000h -1 ;

[0010] The catalyst I is an oxide of metal M, and the catalyst particle size is 4 mesh to 20 mesh;

[0011] The metal M is one of Al, Zr, Ti, and Si;

[0012] The catalyst is prepared by kneading and extrusion; the calcination temperature of the catalyst is 400℃.

[0013] (2) 5-hydroxypentanilide, NaClO solution and catalyst II were mixed in a microchannel reactor and subjected to catalytic oxidation reaction under reaction conditions of 10℃~-10℃ and residence time of 0.5s~2.5s to obtain 4-cyanobutyraldehyde;

[0014] The concentration of the NaClO solution was 1.1 mol / L to 2.0 mol / L; the pH value was 8.5 to 13.5; the mass ratio of 5-hydroxypentanilide to NaClO solution was 1:0.9 to 1.3; and the mass ratio of 5-hydroxypentanilide to catalyst II was 10 to 50:1.

[0015] Catalyst II is a 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxo radical (4-OH-TEMPO);

[0016] The pore size of the microchannel reactor is 1 mm to 2 mm.

[0017] (3) 4-Cyanobenal and ammonia are loaded into a reactor containing catalyst III, and hydrogen is introduced into the reactor. The reaction is carried out at 60℃~120℃ for 3-9h to produce piperidine by reduction ammoniation.

[0018] The mass ratio of 4-cyanobutyraldehyde to catalyst is 5-10:1; the molar ratio of 4-cyanobutyraldehyde to ammonia is 1:8-13; and the hydrogen pressure is 1-3 MPa.

[0019] The concentration of ammonia water is 15wt% to 28wt%.

[0020] The catalyst III has a core-shell structure, which consists of an Al2O3 shell and a metal core; wherein the metal core is metal M1 and metal M2, which are Ni and Co respectively; the total molar amount of Ni and Co accounts for 75%-91% of the total catalyst, and the molar ratio of metal Ni to Co is 9-5:1-5.

[0021] The preparation method of catalyst III includes the following steps:

[0022] (1) Preparation of metal cores:

[0023] Metal nitrate and precipitant Na2CO3 were added to distilled water, and solutions A and B were obtained after stirring. Solutions A and B were then passed into a membrane dispersion microreactor at the same flow rate, and precipitates were generated immediately at 60-70°C. The precipitates were collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 300-450°C for 2-4 hours to obtain metal oxide nanoparticles.

[0024] In solution A, the concentration of metallic nitrate is 0.1–0.3 mol / L; the metals are Ni and Co, and the molar ratio of Ni to Co is 9–5:1–5.

[0025] The concentration of Na₂CO₃ in solution B is 0.3–0.6 mol / L; the flow rate is 5 mL / min–20 mL / min; the pore size of the membrane disperser is 0.5–5 μm.

[0026] (2) A shell is formed around the metal core:

[0027] Add 0.2–1 wt% of the metal oxide nanoparticles obtained in the previous step to anhydrous ethanol and sonicate for 30–60 min. Then, add the shell-forming reagent and NH3·H2O under sonication. After the addition is complete, continue the reaction under sonication for 30–60 min. Centrifuge, wash with ethanol and distilled water, dry, and reduce with H2 at 450℃–600℃ for 2–3 h to obtain the catalyst.

[0028] The molar ratio of the shell-forming agent to the metal nanoparticles is 0.1–0.3; the shell-forming agent of the catalyst is Al(NO3)2·9H2O (at this time, the shell of the catalyst is Al2O3); the mass ratio of ammonia to metal nanoparticles is 2.0–15.0.

[0029] The molar amount of the metal nanoparticles is calculated as the sum of the molar amounts of Ni and Co.

[0030] The thickness and pore size of the catalyst shell are determined by the ratio of oxide shell (shell-forming agent) to metal. The molar ratio of shell-forming agent to metal is 0.1 to 0.3. As the ratio increases from 0.1 to 0.3 (molar ratio), the shell thickness tends to increase.

[0031] The catalyst is represented by xM1-yM2@SiO2-z, where M1 and M2 represent metals, x and y represent the molar ratio of M1 to M2 in the catalyst, and z represents the molar ratio of Al(NO3)2·9H2O to (M1+M2) in the catalyst.

[0032] The essential features of this invention are:

[0033] The raw material δ-valerol in this invention is derived from biomass, which aligns with the concept of sustainable development. Furthermore, the synthesis of 5-hydroxyvaleronitrile from δ-valerol and the oxidation of 5-hydroxyvaleronitrile to 4-cyanobutyraldehyde are both novel reaction routes. The continuous reaction of 5-hydroxyvaleronitrile to 4-cyanobutyraldehyde is achieved through a microchannel reactor (current technologies mostly involve batch reactions (NaClO oxidizes alcohols to aldehydes)). In the third step, the synthesis of piperidine from 4-cyanobutyraldehyde utilizes a core-shell structured Al2O3-coated Ni-Co bimetallic heterogeneous catalyst. Due to the amphoteric nature of the Al2O3 shell, it promotes the dehydration and cyclization of the reaction intermediate 5-aminovalerol, thus avoiding the formation of pentanediamine to some extent and improving the selectivity of the product piperidine.

[0034] The core-shell structured Al2O3-coated Ni-Co bimetallic heterogeneous catalyst of this invention changes the preparation of the metal core from batch to continuous, greatly shortening the catalyst preparation time. Furthermore, among core-shell structured catalysts, reports on the shell layer are mostly SiO2, with relatively few reports on Al2O3 shell layers; this invention found that an Al2O3 shell layer is beneficial for the cyclization of carbonyl compounds during reduction. In contrast, literature reports that a SiO2 shell layer is beneficial for the amine formation of carbonyl compounds.

[0035] The beneficial effects of this invention are as follows:

[0036] This invention provides a novel method for synthesizing piperidine from δ-valerolactone, overcoming the drawbacks of existing production processes, such as high difficulty and high risk. Furthermore, the catalyst used in this invention is simple to prepare using conventional methods; the catalyst shell support and the metal core active component are inexpensive and readily available.

[0037] The catalytic reaction of this invention is a normal or low-pressure reaction, which does not require sophisticated reaction equipment and improves the economic feasibility of the reaction. The byproducts of the catalytic process are pollution-free, resulting in minimal waste. In the first step, the conversion rate of δ-valerolactone can reach 94.0%, and the selectivity of 5-hydroxyvaleronitrile is 75.54%; in the second step, the conversion rate of 5-hydroxyvaleronitrile is 99.0%, and the selectivity of 4-cyanobutyraldehyde is 94.7%; in the third step, the conversion rate of 4-cyanobutyraldehyde is 99.0%, and the selectivity of piperidine is 63.8%. Detailed Implementation

[0038] The synthetic route of this invention is shown below:

[0039]

[0040] The technical features of the present invention are further illustrated below through examples:

[0041] Example 1: Preparation of Catalyst I by Kneading and Extrusion Method

[0042] Weigh 25.0g of commercial Al2O3 powder, add 0.7g of guar gum powder (binder) and an appropriate amount of water to form a gel, and grind thoroughly until the mixture is homogeneous and forms a paste. Use an extruder to form strips of catalyst precursor with a diameter of approximately 2mm. Allow the precursor to air dry naturally at room temperature for 12 hours, then dry it in a forced-air dryer at 80℃ for 4-5 hours. Calcine the dried catalyst precursor in a muffle furnace at a heating rate of 2℃ / min to 400℃ for 3 hours, and pulverize it to a particle size of 4-20 mesh to obtain catalyst I, Al2O3.

[0043] Separately, TiO2, SiO2, and ZrO2 powders were taken and catalyst I (TiO2, SiO2, ZrO2) was obtained using the same method; Example 2: Preparation of 9Ni-1Co nanoparticles

[0044] 26.1 g Ni(NO3)2·6H2O (0.09 mol) and 2.9 g Co(NO3)2·6H2O (0.01 mol) were added to 500 mL of distilled water; 21.2 g Na2CO3 (0.20 mol) was added to 500 mL of distilled water. After thorough stirring, two mixed solutions were obtained. The two solutions were then passed into a membrane dispersion microreactor with a pore size of 1 μm at a flow rate of 15 mL / min. Under the mixing action of the membrane dispersion microreactor, the two solutions were mixed and reacted instantaneously, and a precipitate was rapidly obtained at 70 °C. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 300 °C for 3 h to obtain 9Ni-1Co nanoparticles.

[0045] Example 3: Preparation of 8Ni-2Co nanoparticles

[0046] 23.2 g Ni(NO3)2·6H2O (0.08 mol) and 5.8 g Co(NO3)2·6H2O (0.02 mol) were added to 500 mL of distilled water; 31.8 g Na2CO3 (0.30 mol) was added to 500 mL of distilled water. After thorough stirring, two mixed solutions were obtained. The two solutions were then passed into a membrane dispersion microreactor with a pore size of 2 μm at a flow rate of 10 mL / min. A precipitate was rapidly obtained at 70 °C. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 450 °C for 2 h to obtain 8Ni-2Co nanoparticles.

[0047] Example 4: Preparation of 7Ni-3Co nanoparticles

[0048] 20.3 g Ni(NO3)2·6H2O (0.07 mol) and 8.7 g Co(NO3)2·6H2O (0.03 mol) were added to 500 mL of distilled water; 15.9 g Na2CO3 (0.15 mol) was added to 500 mL of distilled water. After thorough stirring, two mixed solutions were obtained. The two solutions were then passed into a membrane dispersion microreactor with a pore size of 0.5 μm at a flow rate of 5 mL / min. Three precipitates were rapidly obtained at 60 °C. The precipitates were collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 400 °C for 3 h to obtain 7Ni-3Co nanoparticles.

[0049] Example 5: Preparation of 6Ni-4Co nanoparticles

[0050] 17.1 g Ni(NO3)2·6H2O (0.06 mol) and 11.6 g Co(NO3)2·6H2O (0.04 mol) were added to 500 mL of distilled water; 21.2 g Na2CO3 (0.20 mol) was added to 500 mL of distilled water. After thorough stirring, two mixed solutions were obtained. The two solutions were then passed into a membrane dispersion microreactor with a pore size of 5 μm at a flow rate of 20 mL / min. A precipitate was rapidly obtained at 70 °C. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 400 °C for 4 h to obtain 6Ni-4Co nanoparticles.

[0051] Example 6: Preparation of 5Ni-5Co nanoparticles

[0052] 14.5 g Ni(NO3)2·6H2O (0.05 mol) and 14.6 g Co(NO3)2·6H2O (0.05 mol) were added to 500 mL of distilled water; 21.2 g Na2CO3 (0.20 mol) was added to 500 mL of distilled water. After thorough stirring, two mixed solutions were obtained. The two solutions were then passed into a membrane dispersion microreactor with a pore size of 1 μm at a flow rate of 15 mL / min. A precipitate was rapidly obtained at 70 °C. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 400 °C for 4 h to obtain 5Ni-5Co nanoparticles.

[0053] Example 7: Preparation of Ni-Co@Al2O3-0.1 catalyst

[0054] Add 0.3 g (i.e. 4.0160 mmol) of NiO-CoO nanoparticles (obtained from Examples 2-6) to 50 mL of anhydrous ethanol and sonicate for 30 min. Then, in an ultrasonic bath, under ultrasonic treatment (40 min), 0.1506 g (i.e., 0.4014 mmol) of Al(NO3)2·9H2O (corresponding to a molar ratio of 0.1 between the shell-forming reagent and the metal core) and 10 mL of NH3·H2O (25 wt%, containing 0.13 mol of ammonia) were added sequentially. The mixture was dried at 80 °C for 10 h and then reduced to its original state with H2 at 550 °C for 2 h, yielding five core-shell catalysts with different Ni / Co molar ratios: 9Ni-1Co@Al2O3-0.1, 8Ni-2Co@Al2O3-0.1, 7Ni-3Co@Al2O3-0.1, 6Ni-4Co@Al2O3-0.1, and 5Ni-5Co@Al2O3-0.1.

[0055] Example 8: Preparation of Ni-Co@Al2O3-0.2 catalyst

[0056] 0.30 g (4.0160 mmol) of NiO-CoO nanoparticles (obtained from Examples 2-6) were added to 50 mL of anhydrous ethanol and subjected to ultrasonic treatment for 60 min. Then, in an ultrasonic bath, 0.3013 g (0.8032 mmol) of Al(NO3)2·9H2O (corresponding to a molar ratio of 0.2 between the shell-forming reagent and the metal core) and 10 mL of NH3·H2O (25 wt%, containing 0.13 mol of ammonia) were added sequentially under ultrasonic treatment (60 min). Five core-shell catalysts with different Ni / Co molar ratios were obtained by drying at 80℃ for 10 h and reducing with H2 at 450℃ for 3 h: 9Ni-1Co@Al2O3-0.2, 8Ni-2Co@Al2O3-0.2, 7Ni-3Co@Al2O3-0.2, 6Ni-5Co@Al2O3-0.2, and 5Ni-5Co@Al2O3-0.2.

[0057] Example 9: Preparation of Ni-Co@Al2O3-0.3 catalyst

[0058] 0.30 g (4.0160 mmol) of NiO-CoO nanoparticles (obtained from Examples 2-6) were added to 50 mL of anhydrous ethanol and subjected to ultrasonic treatment for 45 min. Then, in an ultrasonic bath, 0.4519 g (1.2048 mmol) of Al(NO3)2·9H2O (corresponding to a molar ratio of 0.3 between the shell-forming reagent and the metal core) and 10 mL of NH3·H2O (25 wt%, containing 0.13 mol of ammonia) were added sequentially under ultrasonic treatment (30 min). Five core-shell catalysts with different Ni / Co molar ratios were obtained by drying at 80℃ for 10 h and reducing with H2 at 600℃ for 2 h: 9Ni-1Co@Al2O3-0.3, 8Ni-2Co@Al2O3-0.3, 7Ni-3Co@Al2O3-0.3, 6Ni-4Co@Al2O3-0.3, and 5Ni-5Co@Al2O3-0.3.

[0059] Example 10: Catalytic amination of δ-valerolactone

[0060] 25 mL of the catalyst prepared in Example 1 was added to a fixed-bed reactor (12 mm in diameter and 600 mm in length). The reactor was heated to 250 °C under nitrogen protection. Then, ammonia and δ-valerol (which were vaporized by heating at 250 °C to form a mixed gas) were introduced into the fixed-bed reactor. The volume hourly space velocity of the mixed gas through the catalyst bed was 200 h⁻¹. -1 The reaction mixture, in which the molar ratio of ammonia to δ-valerolactone was 10:1 and the reaction system was at atmospheric pressure, was catalytically ammonia-based nitrification to obtain a reaction solution containing 5-hydroxyvaleronitrile, an intermediate in the production of piperidine. Gas chromatography with internal standard analysis showed that the conversion rate of δ-valerolactone was 7.92%–94.22%, and the selectivity of 5-hydroxyvaleronitrile was 14.66%–62.78%. The obtained reaction solution was first recrystallized to separate solid impurities, and then distilled under reduced pressure; the distillate was 5-hydroxyvaleronitrile, which was used directly in the next step.

[0061] Example 11: Catalytic amination of δ-valerolactone

[0062] 25 mL of the TiO2 catalyst prepared in Example 1 was added to a fixed-bed reactor (12 mm in diameter and 600 mm in length). The reactor was heated to 300 °C under nitrogen protection. Then, ammonia and δ-valerol (which were vaporized by heating to form a mixed gas, with a volume hourly space velocity of 1000 h⁻¹ through the catalyst bed) were introduced into the fixed-bed reactor. -1The reaction mixture, in which the molar ratio of ammonia to δ-valerolactone was 8:1, was prepared under atmospheric pressure. Catalytic ammonia nitrification yielded a reaction solution containing 5-hydroxyvaleronitrile, an intermediate in the production of piperidine. Gas chromatography with internal standard analysis showed a δ-valerolactone conversion rate of 94.0% and a 5-hydroxyvaleronitrile selectivity of 75.54%. The resulting reaction solution was first recrystallized to separate solid impurities, then distilled under reduced pressure; the distillate was 5-hydroxyvaleronitrile, which was used directly in the next step.

[0063] Example 12: Catalytic amination of δ-valerolactone

[0064] 25 mL of the TiO2 catalyst prepared in Example 1 was added to a fixed-bed reactor (12 mm in diameter and 600 mm in length). The reactor was heated to 280 °C under nitrogen protection. Then, ammonia and δ-valerol (which were vaporized by heating to form a mixed gas, with a volume hourly space velocity of 600 h⁻¹ through the catalyst bed) were introduced into the fixed-bed reactor. -1 The reaction mixture, in which the molar ratio of ammonia to δ-valerolactone was 3:1, was prepared under atmospheric pressure. Catalytic ammonia nitrification yielded a reaction solution containing 5-hydroxyvaleronitrile, an intermediate in the production of piperidine. Gas chromatography with internal standard analysis showed a δ-valerolactone conversion rate of 92.3% and a 5-hydroxyvaleronitrile selectivity of 70.4%. The resulting reaction solution was first recrystallized to separate solid impurities, then distilled under reduced pressure; the distillate was 5-hydroxyvaleronitrile, which was used directly in the next step.

[0065] Example 13: Catalytic oxidation of 5-hydroxypentanilide

[0066] 5-Hydroxypentanilide (9.91 g, 0.1 mol) and Cat II (0.3964 g, 4-OH-TEMPO) were dissolved in 100 mL of dichloromethane and denoted as solution A; the NaClO solution was denoted as solution B. The NaClO solution concentration was 1.8 M and pH was 8.5. Under 0 °C, solutions A and B were mixed in a 27 mL microchannel reactor with a pore size of 2 mm at flow rates of 3.6 mL / min and 4.32 mL / min, respectively. After catalytic oxidation, a reaction solution containing 4-cyanobutyraldehyde, an intermediate for the production of piperidine, was obtained. Gas chromatography with internal standard analysis showed that the conversion rate of 5-hydroxypentanilide was 99.00% and the selectivity was 85.0%. The obtained reaction solution was subjected to liquid-liquid extraction, and the organic phase was washed three times with saturated Na2S2O3 solution and then three times with distilled water. The solvent was separated under vacuum using a rotary evaporator to obtain the product 4-cyanobutyraldehyde, which was used directly in the next step.

[0067] Example 14: Catalytic oxidation of 5-hydroxypentanilide

[0068] 5-Hydroxypentanilide (9.91 g, 0.1 mol) and Cat II (4-OH-TEMPO, 0.4955 g) were dissolved in 100 mL of dichloromethane and denoted as solution A; the NaClO solution was denoted as solution B. The NaClO solution concentration was 1.8 M and pH was 13.5. Under conditions of -10 °C, solutions A and B were mixed in a 27 mL microchannel reactor with a pore size of 2 mm at flow rates of 3.6 mL / min and 3.2 mL / min, respectively. After catalytic oxidation, a reaction solution containing 4-cyanobutyraldehyde, an intermediate for the production of piperidine, was obtained. Gas chromatography with internal standard analysis showed that the conversion rate of 5-hydroxypentanilide was 99.00% and the selectivity was 94.7%. The obtained reaction solution was subjected to liquid-liquid extraction, and the organic phase was washed three times with saturated Na2S2O3 solution and then three times with distilled water. The solvent was separated under vacuum using a rotary evaporator to obtain the product 4-cyanobutyraldehyde, which was used directly in the next step.

[0069] Example 15: Catalytic oxidation of 5-hydroxypentanilide

[0070] 5-Hydroxypentanilide (9.91 g, 0.1 mol) and Cat II (4-OH-TEMPO, 0.1982 g) were dissolved in 100 mL of dichloromethane and denoted as solution A; the NaClO solution was denoted as solution B. The NaClO solution concentration was 1.8 M and pH was 9.5. Under 10 °C, solutions A and B were mixed in a 27 mL microchannel reactor with a pore size of 2 mm at flow rates of 3.6 mL / min and 3.6 mL / min, respectively. After catalytic oxidation, a reaction solution containing 4-cyanobutyraldehyde, an intermediate for the production of piperidine, was obtained. Gas chromatography with internal standard analysis showed that the conversion rate of 5-hydroxypentanilide was 96.00% and the selectivity was 93.5%. The obtained reaction solution was subjected to liquid-liquid extraction, and the organic phase was washed three times with saturated Na2S2O3 solution and then three times with distilled water. The solvent was separated under vacuum using a rotary evaporator to obtain the product 4-cyanobutyraldehyde, which was used directly in the next step.

[0071] Example 14: Reductive amination of 4-cyanobutyraldehyde

[0072] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 50 mg of the 9Ni-1Co@Al2O3-0.2 catalyst obtained in Example 8, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3 g (25 wt%, containing 0.044 mol of ammonia). Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (3 MPa) and temperature (80 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 25.6%.

[0073] Example 15: Reductive amination of 4-cyanobutyraldehyde

[0074] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 75 mg of the 8Ni-2Co@Al2O3-0.2 catalyst obtained in Example 8, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 4.06 g (containing 0.060 mol of ammonia). Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (1 MPa) and temperature (70 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 33.1%.

[0075] Example 16: Reductive amination of 4-cyanobutyraldehyde

[0076] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 50 mg of the 7Ni-3Co@Al2O3-0.2 catalyst obtained in Example 8, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3.5 g (0.051 mol) of ammonia. Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (2 MPa) and temperature (100 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 43.2%.

[0077] Example 17: Reductive amination of 4-cyanobutyraldehyde

[0078] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 50 mg of the 6Ni-4Co@Al2O3-0.2 catalyst obtained in Example 8, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3.5 g (0.051 mol) of ammonia. Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (2 MPa) and temperature (120 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 25.5%.

[0079] Example 18: Reductive amination of 4-cyanobutyraldehyde

[0080] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 5Ni-5Co@Al2O3-0.2 catalyst (50 mg) obtained in Example 8, 4-cyanobutyraldehyde (0.5 g, 5.14 mmol), and ammonia (3.5 g, 0.051 mol). Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (3 MPa) and temperature (60 °C) with a stirring rate of 1500 rpm. After 9 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 20.2%.

[0081] Example 19: Reductive amination of 4-cyanobutyraldehyde

[0082] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 50 mg of the 7Ni-3Co@Al2O3-0.1 catalyst obtained in Example 7, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3.5 g (0.051 mol) of ammonia. Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (2 MPa) and temperature (80 °C) with a stirring rate of 1500 rpm. After 3 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 38.2%.

[0083] Example 20: Reductive amination of 4-cyanobutyraldehyde

[0084] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 50 mg of the 7Ni-3Co@Al2O3-0.3 catalyst obtained in Example 9, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3.5 g (0.051 mol) of ammonia. Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (2 MPa) and temperature (80 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 40.2%.

[0085] Example 21: Reductive amination of 4-cyanobutyraldehyde

[0086] The reaction was carried out in a 25 mL stainless steel reactor, with the addition of 100 mg of the 7Ni-3Co@Al2O3-0.2 catalyst obtained in Example 8, 0.5 g (5.14 mmol) of 4-cyanobutyraldehyde, and 3.5 g (0.051 mol) of ammonia. Before the reaction, the reactor was purged five times with H2 to replace residual air. Hydrogenation was then carried out at a constant H2 pressure (2 MPa) and temperature (80 °C) with a stirring rate of 1500 rpm. After 5 h of reaction, the liquid product was separated from the catalyst and further analyzed by gas chromatography with internal standard. The conversion rate of 4-cyanobutyraldehyde was 99%, and the selectivity for piperidine was 63.8%.

[0087] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing piperidine, characterized in that the method comprises the following steps: (1) After the mixture of δ-valerolactone and ammonia gas is heated and vaporized, it is introduced into a fixed bed reactor loaded with catalyst I, and subjected to an ammoniation reaction at normal pressure and 250-300°C to produce 5-hydroxyvaleronitrile; wherein The molar ratio of δ-valerolactone:ammonia = 1 :3-10; the volume space velocity of the mixed gas of δ-valerolactone and ammonia through the catalyst I bed is 200 h -1 -1000 h -1 ; Said catalyst I is an oxide of metal M; said metal M is one of Al, Zr, Ti and Si; (2) 5-hydroxyvaleronitrile, NaClO solution and catalyst II are mixed in a microchannel reactor, and subjected to a catalytic oxidation reaction under the reaction conditions of 10- -10°C and a residence time of 0.5-2.5 s to produce 4-cyanobutyraldehyde; The concentration of the NaClO solution is 1.1-2.0 mol / L; the pH value is 8.5-13.5; the mass ratio of 5-hydroxyvaleronitrile to NaClO solution is 1:0.9-1.3; and the mass ratio of 5-hydroxyvaleronitrile to catalyst II is 10-50:1; Said catalyst II is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl radical (4-OH-TEMPO); (3) 4-cyanobutyraldehyde and ammonia water are introduced into a reactor loaded with catalyst III, and hydrogen gas is introduced into the reactor, and subjected to a reductive amination reaction at 60-120°C for 3-9 h to produce piperidine; The mass ratio of 4-cyanobutyraldehyde to catalyst is 5-10:1; the molar ratio of 4-cyanobutyraldehyde to ammonia is 1:8-13; and the hydrogen pressure is 1-3 MPa; Said catalyst III has a core-shell structure, and comprises an Al2O3 shell and a metal core; the metal core is composed of metal M1 and metal M2, which are Ni and Co respectively; the total molar amount of Ni and Co accounts for 75%-91% of the whole catalyst, and the molar ratio of Ni to Co is 9-5:1-5.

2. The process for the preparation of piperidine according to claim 1, characterized in that In step (1), the particle size of the catalyst is 4-20 mesh; the catalyst is prepared by kneading and extruding; and the calcination temperature of the catalyst is 400°C.

3. The process for the preparation of piperidine according to claim 1, characterized in that In step (2), the pore size of the microchannel reactor is 1-2 mm.

4. The process for the preparation of piperidine according to claim 1, characterized in that In step (3), the concentration of the ammonia water is 15-28 wt%.

5. The method for preparing piperidine according to claim 1, characterized in that the preparation method of the catalyst III comprises the following steps: (1) Preparation of the metal core: Metal nitrate and precipitant Na2CO3 are added into distilled water respectively, and after stirring, solution A and solution B are obtained, and then solution A and solution B are introduced into a membrane dispersion microreactor at the same flow rate, and a precipitate is immediately produced at 60-70°C; the precipitate is collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 300-450°C for 2-4 h to obtain metal oxide nanoparticles; wherein The concentration of the metal nitrate in solution A is 0.1-0.3 mol / L; the metal is Ni and Co, and the molar ratio of Ni to Co is 9-5:1-5; The concentration of Na2CO3 in solution B is 0.3-0.6 mol / L; (2) Coating of the shell on the metal core: The metal oxide nanoparticles obtained in the above step are added to anhydrous ethanol in an amount of 0.2-1 wt%, and ultrasonic treatment is performed for 30-60 min, then a shell forming reagent and NH3·H2O are added under ultrasonic condition, and after the addition is completed, the reaction is continued under ultrasonic condition for 30-60 min; centrifugation is performed, and the product is washed with ethanol and distilled water, dried, and reduced by H2 at 450-600°C for 2-3 h to obtain a catalyst; The molar ratio of the shell forming reagent to the metal nanoparticles is 0.1-0.3; the shell forming reagent of the catalyst is Al(NO3)2·9H2O; and the mass ratio of ammonia to the metal nanoparticles is 2.0-15.

0. The molar amount of the metal nanoparticles is calculated based on the sum of the molar amounts of Ni and Co.

6. The process for the preparation of piperidine according to claim 5, characterized in that In step (1), the flow rate is 5-20 mL / min; and the membrane disperser has a pore size of 0.5-5 μm.

7. The method for preparing piperidine according to claim 5, wherein the thickness and pore size of the shell layer of the catalyst are determined by the ratio of the oxide shell layer (shell forming reagent) to the metal, the molar ratio of the shell forming reagent to the metal is 0.1-0.3, and the thickness of the shell layer tends to increase as the ratio increases from 0.1 to 0.3 (molar ratio).

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