A method for preparing alanine

Abstract

The application discloses a method for preparing alanine. The method comprises the following steps: loading pyruvic acid and ammonia water into a reaction kettle loaded with a catalyst, introducing hydrogen into the reaction kettle, and reacting at 90 DEG C to 120 DEG C for 1 to 3 hours to generate alanine through a reductive amination reaction; the catalyst is a core-shell structure, and is composed of a silica shell and a metal core; the metal core is metal M1 and metal M2, and is Ni and Co respectively; the total molar amount of Ni and Co accounts for 75% to 91% of the whole catalyst, and the molar ratio of metal Ni to Co is 1 to 9: 9 to 1. The application avoids the essential safety hazard existing in the original process, and realizes green and sustainable production of alanine.

Description

Technical Field

[0001] This invention relates to a technique for preparing alanine, an amino acid product, and particularly to a method for preparing alanine from pyruvate as an initial raw material and its catalyst. Background Technology

[0002] Currently, alanine is produced through both bio-fermentation and chemical synthesis, but both methods have inherent drawbacks. Bio-fermentation suffers from difficulties in strain cultivation and domestication, complex product separation processes, low efficiency, and high energy consumption. While chemical synthesis of alanine offers high production efficiency, the widely adopted industrial routes, whether the Strecker or Bucherer-Bergs route, require highly toxic cyanide as a raw material, posing significant harm to human health and the environment.

[0003] Currently, several new methods for alanine synthesis have been documented, including the catalytic amination of lactic acid and the catalytic oxidation of aminopropanol. From the perspective of raw material sources, these methods avoid the use of highly toxic cyanides; however, the noble metal complex catalysts used (mainly Ru(CO)ClH(PPh3)3 and Ru3(CO)) are problematic. 12 The preparation processes for these routes (such as lactic acid, aminopropanol, etc.) are complex, they cannot be recycled, and the catalysts are expensive. Furthermore, the lactic acid route suffers from low yields (only 53%), and the aminopropanol route faces the problem of unavailable raw materials.

[0004] In summary, the synthesis of alanine via amination using relatively inexpensive and readily available pyruvate as a raw material under the action of heterogeneous, non-precious metal catalysts is a green and sustainable process route. Therefore, it is of great significance to study a safe and high-yield alanine production method suitable for industrial production and its corresponding catalyst system. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing alanine. This method employs a core-shell catalyst to synthesize alanine in high yield via the catalytic amination of pyruvate. The core-shell structure of the catalyst prevents the direct reduction of the carbonyl group of pyruvate during the reaction, improving reaction selectivity. Changing the thickness of the catalyst shell can regulate the catalyst's dehydration performance, preventing the carboxyl group of pyruvate from undergoing a dehydration reaction with ammonia to form amides, further improving reaction selectivity. The bimetallic ratio of the metal core can regulate the electronic effect of the catalyst, thereby improving its imine hydrogenation activity. This invention avoids the inherent safety hazards of existing processes, achieving green and sustainable production of alanine.

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

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

[0008] Pyruvic acid and ammonia are loaded into a reaction vessel containing a catalyst. Hydrogen gas is introduced into the reaction vessel and the reaction is carried out at 90℃~120℃ for 1-3 hours to produce alanine through a reduction ammoniation reaction.

[0009] The mass ratio of pyruvate to catalyst is 10-50:1; the molar ratio of pyruvate to ammonia is 1:20-50; and the hydrogen pressure is 1-3 MPa.

[0010] The catalyst has a core-shell structure, consisting of a silica shell and a metal core; 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 1-9:9-1.

[0011] The diameter of the metal core is 10-30 nm, and the shell thickness is 5-25 nm.

[0012] The method for preparing the catalyst includes the following steps:

[0013] (1) Preparation of metal cores:

[0014] The nitrate of the nuclear metal and polyethylene glycol were added sequentially to distilled water. After stirring the solution for 30-60 minutes, urea was added to obtain a mixed solution. The mixture was heated to 80-95°C and reacted for 10-24 hours. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 400-600°C for 2-4 hours to obtain metal oxide nanoparticles.

[0015] In the mixed solution, the concentration of nitrate of the nuclear metal is 1-5 wt%, the concentration of polyethylene glycol (PEG-20000) is 2-6 wt%, and the concentration of urea is 2-6 wt%.

[0016] (2) A shell is formed around the metal core:

[0017] Add 0.2–1 wt% metal oxide nanoparticles to anhydrous ethanol and sonicate for 30–60 min. Then, add a shell-forming reagent and NH3·H2O under sonication. After the addition is complete, continue the reaction under sonication for another 30–60 min. Centrifuge, wash with ethanol and distilled water, dry, calcine at 400–600℃ for 2–4 h, and reduce with H2 at 400–600℃ for 2–3 h to obtain the catalyst.

[0018] The molar ratio of the shell-forming agent to the metal nanoparticles is 0.1 to 0.3, and the shell-forming agent of the catalyst is tetraethyl orthosilicate (in this case, the shell of the catalyst is SiO2); the mass ratio of ammonia to metal nanoparticles is 2.0 to 25.0.

[0019] The molar amount of the metal nanoparticles is the sum of the molar amounts of the two metals.

[0020] The concentration of NH3·H2O is 25 wt%.

[0021] The metal core contains Ni as metal M1 and Co as metal M2; the molar ratio of metal M1 to M2 is 1-9:9-1.

[0022] 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 0.1–0.3. As the ratio increases from 0.1 to 0.3 (molar ratio), the shell thickness tends to increase, from 5 nm to 25 nm; the specific surface area increases from 44.44 m². 2 / g decreased to 21.69m 2 / g, the average pore size decreased from 6.58nm to 3.41nm, and the specific surface area and pore size in the shell showed a decreasing trend.

[0023] 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 tetraethyl orthosilicate to (M1+M2) in the catalyst.

[0024] The essential features of this invention are:

[0025] In the core-shell structured Ni-Co bimetallic heterogeneous catalyst with silica coating used in this invention, the presence of the silica shell enhances the selectivity of the reductive amination process of pyruvate. Firstly, by precisely designing the core-shell structure of the catalyst, the direct reduction of the carbonyl group of pyruvate during the reaction is prevented, thus improving the reaction selectivity. Secondly, by controlling the dehydration properties of the catalyst, the dehydration reaction of the carboxyl group of pyruvate with ammonia to form amides is prevented, further improving the reaction selectivity.

[0026] The mutual doping of Ni and Co within the shell enhances the activity of imine hydrogenation and promotes the conversion of intermediates.

[0027] Ultimately, by leveraging the advantages of its core-shell structure and controllable shell pore size, it is possible to achieve efficient and highly selective reduction and amination of pyruvate to generate alanine.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention provides a method for synthesizing alanine from pyruvate, which overcomes the drawbacks of existing production processes, such as high difficulty, severe environmental pollution, and low yield. Furthermore, the catalyst used in this invention is simple to prepare using conventional methods, and the catalyst shell support and the metal core active component are inexpensive and readily available.

[0030] The catalytic amination reaction of this invention is a low-temperature, low-pressure reaction, which does not require sophisticated reaction equipment and improves the economic feasibility of the reaction. During the catalytic process, there are no byproducts, no pollution, and minimal waste. The conversion rate of pyruvate can reach 99%, and the selectivity for alanine is 99%. Attached Figure Description

[0031] Figure 1 The image shows a TEM image of the 3Ni-7Co@SiO2-0.2 catalyst obtained in Example 11 (corresponding to the metal core prepared in Example 3, and then the catalyst prepared according to Example 11).

[0032] Figure 2 TEM images of the catalysts obtained in Examples 10, 11 and 12;

[0033] Figure 3 The pore size distribution diagrams are for the catalysts obtained in Examples 10, 11 and 12. Detailed Implementation

[0034] The synthetic route of this invention is shown in the reaction formula below:

[0035]

[0036] The technical features of the present invention are further illustrated below through examples:

[0037] Example 1: Preparation of 1Ni-9Co nanoparticles

[0038] 0.29 g Ni(NO3)2·6H2O (0.001 mol) and 2.62 g Co(NO3)2·6H2O (0.009 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 90 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 1Ni-9Co nanoparticles.

[0039] Example 2: Preparation of 2Ni-8Co nanoparticles

[0040] 0.58 g Ni(NO3)2·6H2O (0.002 mol) and 2.33 g Co(NO3)2·6H2O (0.008 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 90 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 2Ni-8Co nanoparticles.

[0041] Example 3: Preparation of 3Ni-7Co nanoparticles

[0042] 0.87 g Ni(NO3)2·6H2O (0.003 mol) and 2.04 g Co(NO3)2·6H2O (0.007 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 90 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 3Ni-7Co nanoparticles.

[0043] Example 4: Preparation of 4Ni-6Co nanoparticles

[0044] 1.16 g Ni(NO3)2·6H2O (0.004 mol) and 1.75 g Co(NO3)2·6H2O (0.006 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 90 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 4Ni-6Co nanoparticles.

[0045] Example 5: Preparation of 5Ni-5Co nanoparticles

[0046] 1.45 g Ni(NO3)2·6H2O (0.005 mol) and 1.46 g Co(NO3)2·6H2O (0.005 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 90 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 5Ni-5Co nanoparticles.

[0047] Example 6: Preparation of 6Ni-4Co nanoparticles

[0048] 1.71 g Ni(NO3)2·6H2O (0.006 mol) and 1.16 g Co(NO3)2·6H2O (0.004 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 85 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 6Ni-4Co nanoparticles.

[0049] Example 7: Preparation of 7Ni-3Co nanoparticles

[0050] 2.03 g Ni(NO3)2·6H2O (0.007 mol) and 0.87 g Co(NO3)2·6H2O (0.003 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 85 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 7Ni-3Co nanoparticles.

[0051] Example 8: Preparation of 8Ni-2Co nanoparticles

[0052] 2.32 g Ni(NO3)2·6H2O (0.008 mol) and 0.58 g Co(NO3)2·6H2O (0.002 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 85 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 8Ni-2Co nanoparticles.

[0053] Example 9: Preparation of 9Ni-1Co nanoparticles

[0054] 2.61 g Ni(NO3)2·6H2O (0.009 mol) and 0.29 g Co(NO3)2·6H2O (0.001 mol) were added to 100 mL of distilled water containing 3.00 g polyethylene glycol (PEG-20000). After stirring the solution for 30 min, 4.5 g urea was added, and the mixture was heated to 85 °C and reacted for 24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried at 100 °C for 10 h, and calcined in air at 500 °C for 4 h to obtain 9Ni-1Co nanoparticles.

[0055] Example 10: Preparation of Ni-Co@SiO2-0.1 catalyst

[0056] 0.25 g (3.3471 mmol) of NiO-CoO nanoparticles (obtained from Examples 1-9) were added to 50 mL of anhydrous ethanol and subjected to ultrasonic treatment for 30 min. Then, in an ultrasonic bath, 0.0697 g (0.3346 mmol) of tetraethyl orthosilicate (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 under ultrasonic treatment (60 min). Nine core-shell catalysts with different Ni / Co molar ratios were obtained by drying at 80℃ for 10 h, calcining at 550℃ for 2 h, and reducing with H2 at 550℃ for 2 h. These catalysts were 1Ni-9Co@SiO2-0.1, 2Ni-8Co@SiO2-0.1, 3Ni-7Co@SiO2-0.1, 4Ni-6Co@SiO2-0.1, 5Ni-5Co@SiO2-0.1, 6Ni-4Co@SiO2-0.1, 7Ni-3Co@SiO2-0.1, 8Ni-2Co@SiO2-0.1, and 9Ni-1Co@SiO2-0.1.

[0057] Example 11: Preparation of Ni-Co@SiO2-0.2 catalyst

[0058] 0.25 g (3.3471 mmol) of NiO-CoO nanoparticles (obtained from Examples 1-9) were added to 50 mL of anhydrous ethanol and subjected to ultrasonic treatment for 30 min. Then, in an ultrasonic bath, 0.1394 g (0.6692 mmol) of tetraethyl orthosilicate (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). Nine core-shell catalysts with different Ni / Co molar ratios were obtained by drying at 80℃ for 10 h, calcining at 550℃ for 2 h, and reducing with H2 at 550℃ for 2 h. These catalysts were 1Ni-9Co@SiO2-0.2, 2Ni-8Co@SiO2-0.2, 3Ni-7Co@SiO2-0.2, 4Ni-6Co@SiO2-0.2, 5Ni-5Co@SiO2-0.2, 6Ni-4Co@SiO2-0.2, 7Ni-3Co@SiO2-0.2, 8Ni-2Co@SiO2-0.2, and 9Ni-1Co@SiO2-0.2.

[0059] Example 12: Preparation of Ni-Co@SiO2-0.3 catalyst

[0060] 0.25 g (3.3471 mmol) of NiO-CoO nanoparticles (obtained from Examples 1-9) were added to 50 mL of anhydrous ethanol and subjected to ultrasonic treatment for 30 min. Then, in an ultrasonic bath, 0.2091 g (1.0038 mmol) of tetraethyl orthosilicate (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 (60 min). Nine core-shell catalysts with different Ni / Co molar ratios were obtained by drying at 80℃ for 10 h, calcining at 550℃ for 2 h, and reducing with H2 at 550℃ for 2 h. These catalysts were 1Ni-9Co@SiO2-0.3, 2Ni-8Co@SiO2-0.3, 3Ni-7Co@SiO2-0.3, 4Ni-6Co@SiO2-0.3, 5Ni-5Co@SiO2-0.3, 6Ni-4Co@SiO2-0.3, 7Ni-3Co@SiO2-0.3, 8Ni-2Co@SiO2-0.3, and 9Ni-1Co@SiO2-0.3.

[0061] Figure 1The image shows a TEM image of the Ni-Co@SiO2-0.2 catalyst obtained in Example 11 (corresponding to the metal core prepared in Example 3, and subsequently the catalyst prepared according to Example 11). The TEM image shows that the diameter of the metal core is 15-25 nm. The molar ratio of the two metals was determined by ICP characterization and is consistent with the theoretical value.

[0062] Figure 2 In Figure 'a', the image is a TEM image of the Ni-Co@SiO2-0.1 catalyst obtained in Example 10. The molar ratio of the shell-forming agent to the metal core is 0.1 (this molar ratio was determined by ICP characterization; tetraethyl orthosilicate was completely hydrolyzed and coated on the surface of the metal). Figure 2 In the image, b is a TEM image of the Ni-Co@SiO2-0.2 catalyst obtained in Example 11, where the molar ratio of the shell-forming agent to the metal core is 0.2. Figure 2 In the image, 'c' represents the TEM image of the Ni-Co@SiO2-0.3 catalyst obtained in Example 12, with a molar ratio of 0.3 between the shell-forming agent and the metal core. From... Figure 2 It can be seen that as the molar ratio of the shell-forming reagent to the metal oxide increases from 0.1 to 0.3 (molar ratio), the shell thickness tends to increase, from 5 nm to 25 nm.

[0063] Figure 3 The figures show the pore size distribution of the catalysts in Examples 10, 11, and 12. In the figures, catalyst 3Ni-7Co@SiO2-0.1 corresponds to Example 10, 3Ni-7Co@SiO2-0.2 corresponds to Example 11, and 3Ni-7Co@SiO2-0.3 corresponds to Example 12. The average pore size values ​​of the corresponding catalysts are listed in Table 1.

[0064] As can be seen from the above examples and spectra, firstly, the core-shell structure of the catalyst can prevent the carbonyl group of pyruvate from being directly reduced during the reaction, thus improving the selectivity of the reaction; secondly, by changing the thickness of the catalyst shell, the dehydration performance of the catalyst can be controlled, preventing the carboxyl group of pyruvate from undergoing a dehydration reaction with ammonia to form amides, further improving the selectivity of the reaction. Thirdly, by changing the bimetallic ratio of the metal core, the electronic effect of the catalyst can be controlled, thereby improving the imine hydrogenation activity of the catalyst.

[0065] Table 1. Average pore size and specific surface area of ​​the 3Ni-7Co@SiO2-z catalyst.

[0066]

[0067] Depend on Figure 3 As shown in Table 1, the specific surface area and pore size in the shell decrease as the molar ratio increases from 0.1 to 0.3. The specific surface area decreases from 44.44 m² / g. 2 / g decreased to 21.69m 2 / g, the average pore size decreased from 6.58nm to 3.41nm.

[0068] Example 13: Reductive amination of pyruvate

[0069] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 1Ni-9Co@SiO2-0.1 catalyst obtained in Example 10, 0.0881 g (1 mmol) of pyruvate, and 3 mL (25 wt%, containing 0.04 mol of ammonia) (according to Example 10). Before the reaction, the reactor was purged five times with H2 to replace the residual air. Hydrogenation was then carried out at a constant H2 pressure (1 MPa) and temperature (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 30%.

[0070] Example 14: Reductive amination of pyruvate

[0071] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 2Ni-8Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 33%.

[0072] Example 15: Reductive amination of pyruvate

[0073] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 3Ni-7Co@SiO2-0.1 catalyst obtained in Example 10, 0.0881 g (1 mmol), and 3 mL 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 67%.

[0074] Example 16: Reductive amination of pyruvate

[0075] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 4Ni-6Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 34%.

[0076] Example 17: Reductive amination of pyruvate

[0077] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 5Ni-5Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 33%.

[0078] Example 18: Reductive amination of pyruvate

[0079] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 6Ni-4Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 25%.

[0080] Example 19: Reductive amination of pyruvate

[0081] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 7Ni-3Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 41%.

[0082] Example 20: Reductive amination of pyruvate

[0083] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 8Ni-2Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 19%.

[0084] Example 21: Reductive amination of pyruvate

[0085] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 9Ni-1Co@SiO2-0.1 catalyst obtained in Example 10, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 21%.

[0086] Example 22: Reductive amination of pyruvate

[0087] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 3Ni-7Co@SiO2-0.2 catalyst obtained in Example 11, 0.0881 g (1 mmol), and 3 mL 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 86%.

[0088] Example 23: Reductive amination of pyruvate

[0089] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 2.20 mg of the 3Ni-7Co@SiO2-0.3 catalyst obtained in Example 12, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 45%.

[0090] Example 24: Reductive amination of pyruvate

[0091] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 3Ni-7Co@SiO2-0.2 catalyst (3.30 mg) obtained in Example 11, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 91%.

[0092] Example 25: Reductive amination of pyruvate

[0093] The reaction was carried out in a 15 mL stainless steel reactor, with the addition of 4.40 mg of the 3Ni-7Co@SiO2-0.2 catalyst obtained in Example 11, pyruvate (0.0881 g, 1 mmol), and ammonia (3 mL). 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 (110 °C) with a stirring rate of 1500 rpm. After 2 h of reaction, the liquid product was separated from the catalyst and further analyzed by high-performance liquid chromatography (HPLC) with external standard method. The conversion rate of pyruvate was 99%, and the selectivity for alanine was 99%.

[0094] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing alanine, characterized in that the method comprises the following steps: Pyruvic acid and ammonia were loaded into a reactor containing a catalyst, and hydrogen gas was introduced into the reactor. The reaction was carried out at 90 ℃~120 ℃ for 1-3 h, and a reductive ammoniation reaction was carried out to produce alanine. in, The mass ratio of pyruvate to catalyst is 10~50:1; the molar ratio of pyruvate to ammonia is 1:20~50; the hydrogen pressure is 1~3 MPa. The catalyst has a core-shell structure, and its composition includes a silica shell and a metal core; The metal core consists 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 total catalyst, and the molar ratio of metal Ni to Co is 1~9:9~1. The method for preparing the catalyst includes the following steps: (1) Preparation of metal cores: The nitrate of the nuclear metal and polyethylene glycol were added sequentially to distilled water. After stirring the solution for 30-60 min, urea was added to obtain a mixed solution. The mixture was then heated to 80-95 °C and reacted for 10-24 h. The precipitate was collected by centrifugation, washed with ethanol and distilled water, dried, and calcined in air at 400 ℃~600 ℃ for 2~4 h to obtain metal oxide nanoparticles. In the mixed solution, the concentration of nitrate of the nuclear metal is 1-5 wt%, the concentration of polyethylene glycol is 2-6 wt%, and the concentration of urea is 2-6 wt%. (2) A shell surrounds the metal core: Add 0.2–1 wt% metal oxide nanoparticles to anhydrous ethanol and sonicate for 30–60 min. Then, add a 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 anhydrous ethanol and distilled water, dry, calcine at 400 ℃–600 ℃ for 2–4 h, and reduce H2 to NH3 at 400 ℃–600 ℃ for 2–3 h to obtain the catalyst. The molar ratio of the shell-forming agent to the metal oxide nanoparticles is 0.1~0.3, and the shell-forming agent of the catalyst is tetraethyl orthosilicate; the mass ratio of ammonia to metal oxide nanoparticles is 2.0-25.

0. The concentration of NH3·H2O in step (2) is 25wt%.

2. The method for preparing alanine as described in claim 1, characterized in that the diameter of the metal core is 10-30 nm and the shell thickness is 5-25 nm.

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