A process for the reductive amination of acetophenone to prepare phenethylamine and catalysts used

Abstract

The application discloses a method for preparing phenylethylamine by reducing and aminating acetophenone and a catalyst used in the method. The catalyst is prepared by a preparation method comprising the following steps: 1) loading active metal oxide on a support to obtain an active metal oxide / support; 2) synthesizing a molecular sieve carrier in the presence of the active metal oxide / support to obtain a catalyst precursor; 3) treating the catalyst precursor with an acid solution to obtain an acid-modified catalyst precursor; and 4) calcining and reducing the acid-modified catalyst precursor to obtain the catalyst. The acid is selected from citric acid and / or naphthalene carboxylic acid; and the molar concentration of the acid solution is 0.05-0.2 mol / L. The catalyst is used to accurately control the adsorption mode of acetophenone, the reaction selectivity is improved, the target product is easy to separate, and the purity of the target product is very high after purification.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to a method for preparing phenethylamine by the reductive amination of acetophenone and the catalyst used therein. Background Technology

[0002] Phenethylamine, an important class of aromatic amine compounds, possesses unique chemical activity due to the synergistic effect of the amino group and benzene ring in its molecular structure, making it widely used in pharmaceuticals, pesticides, and fine chemicals. Currently, the industrial preparation of phenethylamine mainly relies on the reductive amination reaction of acetophenone. This reaction uses acetophenone, ammonia, and hydrogen as raw materials, and achieves the conversion of the carbonyl group to the amino group under the action of a catalyst.

[0003] However, acetophenone molecules contain both a carbonyl group and a benzene ring, both of which are capable of hydrogenation. This makes them prone to side reactions during the reaction process: on the one hand, the benzene ring may be hydrogenated and reduced to produce byproducts such as cyclohexylethylamine; on the other hand, the generated phenethylamine may further undergo a secondary reductive amination reaction with acetophenone to produce polyalkylated products such as diphenylethylamine. These side reactions reduce the selectivity and yield of the target product, phenethylamine, and increase the difficulty of subsequent separation and purification. In particular, the cyclohexylethylamine byproduct has a very close boiling point to the target product, phenethylamine, making them difficult to separate using traditional distillation purification. This results in the target product, phenethylamine, having a purity that is difficult to achieve, especially above 99%, even after purification. Furthermore, the difficulty of separation and purification also increases production costs.

[0004] Currently, the research and industrial application of acetophenone reductive amination to synthesize phenethylamine revolve around two main directions: "catalyst system innovation" and "reaction process control".

[0005] Regarding catalyst systems, a major category employs traditional noble metal catalyst systems. These systems typically use noble metals such as Pt, Pd, Rh, and Ru as active components, supported on carriers such as Al₂O₃, SiO₂, activated carbon, or covalent triazine frameworks. Liquid ammonia or ammonia water is used as the amine source, and hydrogen is used as the reducing agent. The reaction is carried out under specific temperature and pressure conditions to obtain phenethylamine. For example, Japanese Patent JP1979132534A discloses a Pd / C catalyst system with a reaction pressure of 3 MPa and a temperature of 120 °C. The result is an acetophenone conversion rate ≥90%, but the phenethylamine yield is only 78%, with benzene ring hydrogenation as a byproduct accounting for approximately 15%. This demonstrates that the target product of this catalyst system has low selectivity, and the noble metals are costly.

[0006] Another major category employs non-precious metal catalyst systems. These systems typically use non-precious metals such as Ni, Co, Fe, and Bi as the core, optimizing performance through in-situ generation, additive addition, or support loading. The amine source is usually 28-30% ammonia water, and the reaction conditions are relatively mild. Although non-precious metals are less expensive, their catalytic activity is generally lower than that of precious metals. For example, their conversion rate and reaction selectivity are both lower, and Fe and Ni-based catalysts require reaction temperatures above 100°C; Bi-based catalysts have poor substrate adaptability, and the suppression of side reactions depends on an excess amine source, leading to increased costs for subsequent separation.

[0007] The challenge in synthesizing phenethylamine by the reductive amination of acetophenone is to achieve a high conversion rate of acetophenone, a high reaction selectivity of the target product phenethylamine, and easy separation of the target product with a high purity (e.g., over 99%), all while keeping costs under control. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide an improved method for preparing phenethylamine by reductive amination of acetophenone, which can achieve high conversion rate of acetophenone and high reaction selectivity of the target product phenethylamine under the premise of controllable cost. Furthermore, the target product is easy to separate and has a high purity after purification, for example, above 99%.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing phenethylamine, using acetophenone, hydrogen, and ammonia as raw materials, involves a reductive amination reaction in the presence of a catalyst to generate the phenethylamine. The catalyst is prepared by a method comprising the following steps: 1) loading an active metal oxide onto a support to obtain an active metal oxide / support; 2) synthesizing a molecular sieve support in the presence of the active metal oxide / support to obtain a catalyst precursor; 3) treating the catalyst precursor with an acid solution to obtain an acid-modified catalyst precursor; 4) calcining and reducing the acid-modified catalyst precursor to obtain the catalyst; wherein the acid is selected from citric acid and / or naphthoic acid; and the molar concentration of the acid solution is 0.05-0.2 mol / L.

[0010] In the aforementioned catalyst preparation method, the loading in step 1) is a conventional loading method, such as impregnation or hydrolysis. The active metal oxide component in the resulting active metal oxide / support is typically located on the surface of the support. In step 2), in the presence of the active metal oxide / support, a molecular sieve support is synthesized in situ using raw materials for the molecular sieve support. The synthesized molecular sieve support will fix and encapsulate most of the active metal oxide within its crystal structure, thus obtaining a catalyst precursor. Then, this invention uses specific organic acids with larger molecular structures, namely citric acid and / or naphthoic acid, to treat the catalyst precursor. These acids can react and remove a small amount of active metal oxide from the surface of the catalyst precursor. However, due to their large molecular structure, the acid has difficulty penetrating the pores and crystal structure inside the molecular sieve support, resulting in the active metal oxide remaining inside the molecular sieve support. After calcination and reduction, the corresponding active metal oxide is transformed into an active metal component, which is also located inside the crystal structure of the molecular sieve support. By almost completely removing the active components on the surface, the formation of byproducts from the hydrogenation of the benzene ring can be reduced, thereby improving the purity of the product phenethylamine.

[0011] In the reductive amination reaction of acetophenone, the acetophenone molecule contains two hydrogenation sites: a carbonyl group and a benzene ring. The carbonyl group is vertically adsorbed onto the active component of the catalyst, while the benzene ring is horizontally adsorbed onto the active component. Since the benzene ring structure is significantly larger than the carbonyl group structure, the hydrogenation side reaction of the benzene ring structure can only occur on the active component on the outer surface of the catalyst, and is difficult to occur on the active component inside the catalyst channels and crystal structure. This invention, through the specific acid treatment process in step 4) mentioned above, can essentially remove a small amount of the active component from the outer surface of the catalyst, leaving almost only the active component inside the molecular sieve support crystal structure. Therefore, it can effectively reduce the hydrogenation side reaction of the benzene ring portion, improve the selectivity of the reaction, and increase the purity of the purified target product.

[0012] In some embodiments, the mass ratio of the acid solution to the catalyst precursor is 30-60:1.

[0013] In some embodiments, the acid solution is used to treat the catalyst precursor for 1-3 hours.

[0014] In some embodiments, the catalyst includes a molecular sieve support and an active metal component immobilized within the crystal structure of the molecular sieve support.

[0015] In some embodiments, the molecular sieve support is selected from one or a combination of two of ZSM-5 molecular sieves and Beta molecular sieves. Specifically, the ZSM-5 molecular sieve has a ten-membered ring pore structure with a window size of approximately 0.55 nm; the Beta molecular sieve has a twelve-membered ring pore structure with a window size of approximately 0.66 nm. Both can effectively confine the active components of the catalyst, which is beneficial for further improving the selectivity of the reaction.

[0016] In some embodiments, the active metal component is selected from one or more combinations of Ni, Co, Cu, Pt, and Pd.

[0017] In some embodiments, the catalyst comprises, by weight percentage, 5%-25% of an active metal component and 75%-95% of a molecular sieve support.

[0018] In some embodiments, the active metal component is selected from one or more combinations of Ni, Co, and Cu, and the catalyst comprises 15%-25% of the active metal component by mass percentage.

[0019] In some embodiments, the active metal component is selected from one or more combinations of Pt and Pd, and the catalyst comprises 5%-10% of the active metal component by mass percentage.

[0020] In some embodiments, the support is selected from one or a combination of two of ZSM-5 molecular sieves and Beta molecular sieves.

[0021] In some embodiments, the type of the support is the same as the type of the molecular sieve carrier.

[0022] In some embodiments, in step 1), an active metal oxide is loaded onto the support by an impregnation method. In this invention, during the impregnation method, a water-soluble salt solution of the active metal component is impregnated onto the support. After impregnation, the resulting solid is calcined to obtain the active metal oxide / support. The impregnation method can employ methods such as equal-volume impregnation, which means that during impregnation, the amount of the active component precursor solution is controlled to be exactly equal to the total pore volume of the support, i.e., the liquid just fills the internal pores of the support without any excess droplets flowing out.

[0023] In some embodiments, step 2) specifically involves: subjecting a silicon source, an aluminum source, an organic amine template agent, the active metal oxide / support, and water to a hydrothermal reaction, followed by filtration and calcination to obtain the catalyst precursor.

[0024] In some embodiments, the silicon source is selected from one or more combinations of silica sol, silica gel, and sodium silicate.

[0025] In some embodiments, the aluminum source is selected from one or more combinations of sodium aluminate, aluminum hydroxide, boehmite, alumina, and aluminum isopropoxide.

[0026] In some embodiments, the organic amine template agent is selected from tetrapropylammonium hydroxide or tetraethylammonium hydroxide.

[0027] In some embodiments, the molar ratio of silicon in the silicon source, aluminum in the aluminum source, organic amine template agent, and water is 1: 0.02-0.03: 0.2-0.4: 15-20.

[0028] In some embodiments, the mass ratio of the silicon source to the active metal oxide / support is 1:0.3-1.1.

[0029] In some embodiments, the temperature of the hydrothermal reaction is 100-200°C.

[0030] In some embodiments, the calcination temperature is 400-600°C when preparing the catalyst precursor.

[0031] In some embodiments, the catalyst preparation method further includes, prior to step 4), subjecting the acid-modified catalyst precursor to ion exchange and calcination with an aqueous solution of an ammonium salt to obtain a hydrogen-form catalyst precursor; and modifying the hydrogen-form catalyst precursor with a modifier selected from one or more combinations of phosphorus compounds, magnesium compounds, and calcium compounds. The modifier can regulate the acid strength of the catalyst precursor.

[0032] In some embodiments, the modifier is selected from one or more combinations of phosphoric acid, ammonium phosphate, magnesium nitrate, magnesium chloride, calcium nitrate, and calcium chloride.

[0033] In some embodiments, the catalyst comprises, by weight percentage, 5%-25% of an active metal component, 0.5%-1% of a modifier, and 74%-94.5% of a molecular sieve support.

[0034] In some embodiments, the modification is performed by impregnating the hydrogen-form catalyst precursor in an aqueous solution of a modifier.

[0035] In some embodiments, the molar concentration of the aqueous solution of the modifier is 0.03-0.1 mol / L; the mass ratio of the aqueous solution of the modifier to the hydrogen-form catalyst precursor is 30-60:1.

[0036] In some embodiments, the ammonium salt is selected from one or a combination of two of ammonium chloride and ammonium nitrate.

[0037] In some embodiments, the molar concentration of the aqueous solution of the ammonium salt is 0.1-0.2 mol / L.

[0038] In some embodiments, the mass ratio of the aqueous solution of the ammonium salt to the acid-modified catalyst precursor is 30-60:1.

[0039] In some embodiments, in step 4), the calcination temperature is 400-600°C.

[0040] In some implementations, in step 4), the reduction is carried out in a hydrogen atmosphere.

[0041] In some implementations, in step 4), the reduction temperature is 400-600°C.

[0042] In some embodiments, the reductive amination reaction is carried out in a fixed-bed reactor.

[0043] In some embodiments, the mass hourly space velocity (MSV) of the acetophenone is 0.1-5 h⁻¹. -1 .

[0044] In some embodiments, the molar ratio of acetophenone to hydrogen is 1:1-10.

[0045] In some embodiments, the molar ratio of acetophenone to ammonia is 1:10-30.

[0046] In some embodiments, the reductive amination reaction is carried out in an organic solvent, the organic solvent being selected from methanol.

[0047] In some embodiments, the organic solvent is fed together with acetophenone, wherein the molar ratio of acetophenone to organic solvent is 1:8-15.

[0048] In some embodiments, the temperature of the reductive amination reaction is 110-150°C.

[0049] In some embodiments, the pressure of the reductive amination reaction is 0.1-3 MPa.

[0050] The present invention also provides the aforementioned catalyst.

[0051] The present invention also provides a method for preparing the aforementioned catalyst, the method comprising the following steps: 1) loading an active metal oxide onto a support to obtain an active metal oxide / support; 2) synthesizing a molecular sieve support in the presence of the active metal oxide / support to obtain a catalyst precursor; 3) treating the catalyst precursor with an acid solution to obtain an acid-modified catalyst precursor; 4) calcining and reducing the acid-modified catalyst precursor to obtain the catalyst; wherein the acid is selected from citric acid and / or naphthoic acid; and the molar concentration of the acid solution is 0.05-0.2 mol / L.

[0052] In some embodiments, the method for preparing the catalyst further includes, prior to step 4), subjecting the acid-modified catalyst precursor to ion exchange and calcination with an aqueous solution of ammonium salt to obtain a hydrogen-form catalyst precursor; and modifying the hydrogen-form catalyst precursor with a modifier; wherein the modifier is selected from one or more combinations of phosphorus compounds, magnesium compounds, and calcium compounds.

[0053] Compared with the prior art, the present invention has the following advantages: The method for preparing phenethylamine by the reductive amination of acetophenone of the present invention can achieve high conversion rate of acetophenone and high reaction selectivity of the target product phenethylamine under controllable cost conditions. Furthermore, the target product is easy to separate and has a high purity after purification, for example, above 99%. The reaction selectivity can reach above 96%. Attached Figure Description

[0054] Figure 1 This is a chromatogram of the reaction system before distillation after the synthesis reaction in Example 1 is completed; Figure 2 for Figure 1 Corresponding peak area data; Figure 3 The chromatogram of the reaction system before distillation after the synthesis reaction of Comparative Example 1 is completed; Figure 4 for Figure 1 The corresponding peak area data. Detailed Implementation

[0055] The industrial production of phenethylamine mainly relies on the reductive amination reaction of acetophenone. This reaction uses acetophenone, ammonia, and hydrogen as raw materials, and achieves the conversion of the carbonyl group to an amino group under the action of a catalyst. However, the acetophenone molecule contains two hydrogenation sites, a carbonyl group and a benzene ring, which easily lead to side reactions during the reaction: on the one hand, the benzene ring may be hydrogenated and reduced to generate byproducts such as cyclohexylethylamine; on the other hand, the generated phenethylamine may further undergo a secondary reductive amination reaction with acetophenone to generate polyalkylated products such as diphenylethylamine. These side reactions reduce the selectivity and yield of the target product phenethylamine, and increase the difficulty of subsequent separation and purification. In particular, the cyclohexylethylamine byproduct has a very close boiling point to the target product phenethylamine, making them difficult to separate in traditional distillation purification. As a result, even after purification, the purity of the target product phenethylamine is difficult to achieve, especially above 99%, and the difficulty of separation and purification also increases production costs.

[0056] To address this issue, this invention employs a novel catalyst to catalyze the reaction. In preparing the catalyst, an active metal oxide is first supported on a support, resulting in an active metal oxide / support, with the active metal oxide component typically located on the support surface. Then, in its presence, a molecular sieve support is synthesized in situ using raw materials for molecular sieve support synthesis. The synthesized molecular sieve support immobilizes and encapsulates the majority of the active metal oxide within its crystal structure, thus yielding a catalyst precursor. Next, this invention uses specific organic acids with larger molecular structures, namely citric acid and / or naphtholic acid, to treat the catalyst precursor. These acids can react and remove a small amount of active metal oxide from the surface of the catalyst precursor. Due to their large molecular structure, the acids have difficulty penetrating the pores and crystal structure within the molecular sieve support, ensuring that the active metal oxide remains within the molecular sieve support. After calcination and reduction, the corresponding active metal oxide is transformed into an active metal component, which is also almost entirely located within the crystal structure of the molecular sieve support. By almost completely removing the surface active component, the formation of byproducts from benzene ring hydrogenation can be reduced, thereby improving the purity of the product phenethylamine.

[0057] In the reductive amination reaction of acetophenone, the acetophenone molecule contains two hydrogenation sites: a carbonyl group and a benzene ring. The carbonyl group is vertically adsorbed onto the active component of the catalyst, while the benzene ring is horizontally adsorbed onto the active component. Since the benzene ring structure is significantly larger than the carbonyl group structure, the hydrogenation side reaction of the benzene ring structure can only occur on the active component on the outer surface of the catalyst, and is difficult to occur on the active component inside the catalyst channels and crystal structure. This invention, through the specific acid treatment process in step 4) mentioned above, can essentially remove the active component from the outer surface of the catalyst, while retaining almost only the active component inside the molecular sieve support crystal structure. Therefore, it can effectively reduce the hydrogenation side reaction of the benzene ring portion, improve the selectivity of the reaction, and increase the purity of the purified target product.

[0058] This invention precisely controls the adsorption mode of acetophenone by coating an active metal into the pore structure of an in-situ synthesized zeolite molecular sieve and removing a small amount of active components from the outer surface of the molecular sieve support. This is achieved through the pore confinement effect of the zeolite molecular sieve and the catalytic effect of the active metal, thereby improving the selectivity of the target product phenethylamine and significantly reducing the formation of cyclohexylethylamine byproduct, which is beneficial for the separation and purification of phenethylamine.

[0059] In addition, when preparing catalysts, modifying the catalyst precursor with modifiers such as phosphorus compounds, magnesium compounds, or calcium compounds can regulate the strong acid sites of the molecular sieve and reduce the adsorption capacity of the support for ammonia and amines.

[0060] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0061] In this invention, the expression "metal component / carrier" refers to the carrier directly loading the metal component through methods such as impregnation. In this case, the metal component is usually located on the surface of the carrier. For example, Co3O4-NiO / ZSM-5 means that Co3O4-NiO is located on the surface of ZSM-5. On the other hand, "metal component@carrier" means that the carrier fixes and coats the metal component. In this case, the metal component is usually located inside the crystal structure of the carrier. For example, CoNi@ZSM-5 means that CoNi is located inside the crystal structure of ZSM-5.

[0062] Example 1 This embodiment provides a catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: 1) Preparation of NiO / ZSM-5: ZSM-5 zeolite molecular sieve was impregnated in an aqueous solution of nickel nitrate (molar concentration 3.2 mol / L) using an equal-volume impregnation method. After impregnation, the powder was dried and then calcined at 450 °C for 4 h. This process was repeated three times to prepare the NiO / ZSM-5 catalyst precursor. The mass content of Ni was determined to be 36% by ICP.

[0063] 2) Preparation of Ni@ZSM-5 catalyst: Fine silica gel, sodium aluminate (NaAlO2), tetrapropylammonium hydroxide (TPAOH) (35% aqueous solution by mass), and water were added and mixed in a molar ratio of SiO2:NaAlO2:TPAOH:H2O = 1:0.02:0.2:15. Then, 90% by mass of the fine silica gel obtained in step 1) was added. After stirring for half an hour, the mixture was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner, sealed, and heated to 160°C. Crystallization was carried out under its own pressure for 72 h. After the reaction was completed, the solid was washed with deionized water until the pH of the filtered water reached 7, yielding TPAOH-NiO@ZSM-5. The filtered solid was calcined at 550°C for 4 h to obtain NiO@ZSM-5.

[0064] The above-mentioned NiO@ZSM-5 was treated in a 0.2M citric acid aqueous solution (solid-liquid ratio of 1:50), and after treatment for 1 hour, it was washed with water and dried to obtain the surface-treated NiO@ZSM-5.

[0065] The surface-treated NiO@ZSM-5 was exchanged three times in a 0.1M ammonium chloride aqueous solution (solid-liquid ratio of 1:50) and then calcined at 550 °C for 2 h to obtain NiO@H-ZSM-5.

[0066] NiO@H-ZSM-5 was modified in a 0.05M ammonium phosphate aqueous solution (solid-liquid ratio 1:50), and after 1 h of modification, it was calcined at 550 °C for 2 h to obtain NiO@H-ZSM-5-P.

[0067] NiO@H-ZSM-5-P was reduced at 500°C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Ni@H-ZSM-5-P. The mass content of Ni was 21% and the mass content of P was 0.8% as determined by ICP.

[0068] 3) Catalyst evaluation and synthesis reaction: The prepared Ni@H-ZSM-5-P catalyst was granulated to 20-40 mesh (the catalyst passed through a 20-mesh sieve, but not a 40-mesh sieve), and 4g of catalyst was placed in a fixed-bed reactor evaluation device. Acetophenone was used as the feedstock. The reactor was then tested at a feedstock mass hourly space velocity of 0.2 / h, a molar ratio of hydrogen to acetophenone of 5, and ammonia to acetophenone of 20, at a reaction temperature of 115℃ and a reaction pressure of 0.2MPa. The test results showed that the acetophenone conversion rate was 99.5%, the α-phenylethylamine selectivity was approximately 96.3%, and the purity of the phenylethylamine product after distillation was 99.2%.

[0069] The chromatogram of the reaction system after the reaction and before distillation is as follows: Figure 1 As shown, the corresponding peak area data is as follows: Figure 2 As shown, besides the target product α-phenylethylamine, only about 0.58% of the byproduct cyclohexylethylamine (a peak with a retention time of 3.561 min) exists in the reaction system, indicating that the catalyst has strong selectivity for the target product.

[0070] Example 2 This embodiment provides a catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: 1) Preparation of PdO / Beta: Beta zeolite molecular sieves were impregnated in an aqueous solution of palladium chloride at a molar concentration of 1.63 mol / L using an equal-volume impregnation method. After impregnation, the powder was dried and then calcined at 450 °C for 4 h to prepare the PdO / Beta catalyst precursor. The mass content of Pd was determined to be 10% by ICP.

[0071] 2) Preparation of Pd@Beta catalyst: Silica, aluminum hydroxide, tetrapropylammonium hydroxide (TPAOH) (35% aqueous solution by mass percentage), and water were added and mixed in a molar ratio of SiO2 (SiO2 in silica):Al(OH)3:TPAOH:H2O = 1:0.03:0.4:20. Then, 110% by mass of PdO / Beta obtained in step 1) of the silica mixture was added. After stirring for half an hour, the mixture was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner, sealed, and heated to 140°C. Crystallization was carried out under its own pressure for 72 h. After the reaction was completed, the solid was washed with deionized water until the pH of the filtered water reached 7, yielding TPAOH-PdO@Beta. The filtered solid was calcined at 550°C for 4 h to obtain PdO@Beta.

[0072] The above PdO@Beta was treated in a 0.05M aqueous solution of naphthoic acid (solid-liquid ratio of 1:50). After treatment for 2 hours, it was washed with a mixture of water and ethanol (volume ratio of 1:1) and dried to obtain the surface-treated PdO@Beta.

[0073] The surface-treated PdO@Beta was exchanged three times in a 0.1M ammonium nitrate aqueous solution (solid-liquid ratio of 1:50) and then calcined at 550 °C for 2 h to obtain PdO@H-Beta.

[0074] PdO@H-Beta was modified in a 0.05M aqueous solution of magnesium phosphate (solid-liquid ratio of 1:50), and after 2 hours of modification, it was calcined at 550 °C for 2 hours to obtain PdO@H-Beta-Mg.

[0075] PdO@H-Beta-Mg was reduced at 500°C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Pd@H-Beta-Mg. The mass content of Pd was 6% and the mass content of Mg was 0.5% as determined by ICP.

[0076] 3) Catalyst evaluation and synthesis reaction: The prepared Pd@H-Beta-Mg catalyst was granulated to 20-40 mesh, and 4g of the catalyst was placed in a fixed-bed reactor evaluation device. The feedstock was a mixture of acetophenone and methanol, with a molar ratio of acetophenone to methanol of 1:10, where methanol was used as the reaction solvent. The acetophenone was fed at a mass hourly space velocity (MHSV) of 0.3 / h, with a molar ratio of hydrogen to acetophenone of 4 and ammonia to acetophenone of 15. The reaction temperature was 120℃, and the reaction pressure was 0.3 MPa. The test results showed that the acetophenone conversion rate was 99.8%, the α-phenylethylamine selectivity was 95.7%, and the purity of the phenylethylamine product after distillation was 99.1%.

[0077] Example 3 This embodiment provides a catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: 1) Preparation of Co3O4 / ZSM-5: ZSM-5 zeolite molecular sieve was impregnated in an aqueous solution of cobalt nitrate at a molar concentration of 3.3 mol / L using an equal-volume impregnation method. After impregnation, the powder was dried and then calcined at 450 °C for 4 h. This process was repeated three times to prepare the Co3O4 / ZSM-5 catalyst precursor. The mass content of Co was determined to be 35% by ICP.

[0078] 2) Preparation of Co@ZSM-5 catalyst: Silica sol (30% by mass of silica gel), aluminum isopropoxide, tetrapropylammonium hydroxide (TPAOH) (35% by mass aqueous solution), and water were added and mixed in a molar ratio of SiO2:aluminum isopropoxide:TPAOH:H2O = 1:0.03:0.4:20. Then, 30% by mass of the Co3O4 / ZSM-5 prepared in step 1) was added. After stirring for half an hour, the mixture was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner, sealed, and heated to 160°C. Crystallization was carried out under its own pressure for 72 h. After the reaction was completed, the solid was washed with deionized water until the pH of the filtered water reached 7, yielding TPAOH-NiO@ZSM-5. The filtered solid was calcined at 550°C for 4 h to obtain Co3O4@ZSM-5.

[0079] The above Co3O4@ZSM-5 was treated in a 0.05M citric acid aqueous solution (solid-liquid ratio of 1:50) for 3 hours, then washed with water and dried to obtain surface-treated Co3O4@ZSM-5.

[0080] The surface-treated Co3O4@ZSM-5 was exchanged three times in a 0.1M ammonium nitrate aqueous solution (solid-liquid ratio of 1:50) and then calcined at 550 °C for 2 h to obtain Co3O4@H-ZSM-5.

[0081] Co3O4@H-ZSM-5 was modified in a 0.05M calcium nitrate aqueous solution (solid-liquid ratio 1:50), and after 1 h of modification, it was calcined at 550 °C for 2 h to obtain Co3O4@H-ZSM-5-Ca.

[0082] Co3O4@H-ZSM-5-Ca was reduced at 500 °C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Co@H-ZSM-5-Ca. The mass content of Co was 17% and the mass content of Ca was 0.8% as determined by ICP.

[0083] 3) Catalyst evaluation and synthesis reaction: The prepared Co@H-ZSM-5-Ca catalyst was granulated to 20-40 mesh, and 4g of the catalyst was placed in a fixed-bed reactor evaluation device. The feed was a mixture of acetophenone and methanol, with a molar ratio of acetophenone to methanol of 1:10. The reactor was then fed at an acetophenone mass hourly space velocity of 0.3 / h, a molar ratio of hydrogen to acetophenone of 4, and ammonia to acetophenone of 15, at a reaction temperature of 120℃ and a reaction pressure of 0.3MPa. The test results showed that the acetophenone conversion rate was 99.3%, the α-phenylethylamine selectivity was 95.3%, and the purity of the phenylethylamine product after distillation was 99.3%.

[0084] Example 4 This embodiment provides a catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: 1) Preparation of CuO / ZSM-5: ZSM-5 zeolite molecular sieve was impregnated in an aqueous solution of copper nitrate at a molar concentration of 5.2 mol / L using an equal-volume impregnation method. Equal-volume impregnation means that the aqueous solution just covers the ZSM-5 zeolite molecular sieve after it is added. After impregnation, the powder was dried and then calcined at 450℃ for 4 hours. This process was repeated once more to prepare the CuO / ZSM-5 catalyst precursor. The Cu content was determined to be 31% by ICP.

[0085] 2) Preparation of Cu@ZSM-5 catalyst: Fine silica gel, sodium aluminate (NaAlO2), tetrapropylammonium hydroxide (TPAOH) (35% aqueous solution by mass), and water were added and mixed in a molar ratio of SiO2:NaAlO2:TPAOH:H2O = 1:0.02:0.2:15. Then, 90% by mass of the CuO / ZSM-5 obtained in step 1) was added. After stirring for half an hour, the mixture was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner, sealed, and heated to 160°C. Crystallization was carried out under its own pressure for 72 h. After the reaction was completed, the solid was washed with deionized water until the pH of the filtered water reached 7, yielding TPAOH-CuO@ZSM-5. The filtered solid was calcined at 550°C for 4 h to obtain CuO@ZSM-5.

[0086] The CuO@ZSM-5 was treated in a 0.2M citric acid aqueous solution (solid-liquid ratio of 1:50) for 3 hours, then washed with water and dried to obtain the surface-treated CuO@ZSM-5.

[0087] The surface-treated CuO@ZSM-5 was exchanged three times in a 0.1M ammonium chloride aqueous solution (solid-liquid ratio of 1:50) and then calcined at 550 °C for 2 h to obtain CuO@H-ZSM-5.

[0088] CuO@H-ZSM-5 was modified in a 0.05M ammonium phosphate aqueous solution (solid-liquid ratio 1:50), and after 1 h of modification, it was calcined at 550 °C for 2 h to obtain CuO@H-ZSM-5-P.

[0089] CuO@H-ZSM-5-P was reduced at 500°C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Cu@H-ZSM-5-P. The mass content of Cu was 15% and the mass content of P was 0.8% as determined by ICP.

[0090] 3) Catalyst evaluation and synthesis reaction: The prepared Cu@H-ZSM-5-P catalyst was granulated to 20-40 mesh, and 4g of the catalyst was placed in a fixed-bed reactor evaluation device. Acetophenone was used as the feedstock. The reactor was then fed at a mass hourly space velocity (MHSV) of 0.2 / h, a molar ratio of hydrogen to acetophenone of 5, and ammonia to acetophenone of 20, at a reaction temperature of 115℃ and a reaction pressure of 0.2 MPa. The test results showed that the acetophenone conversion rate was 99.5%, the α-phenylethylamine selectivity was approximately 95.1%, and the purity of the phenylethylamine product after distillation was 99.0%.

[0091] Example 5 This embodiment provides a catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: 1) Preparation of PtO2 / ZSM-5: ZSM-5 zeolite molecular sieve was impregnated in an aqueous solution of chloroplatinic acid at a molar concentration of 1.36 mol / L using an equal-volume impregnation method. Equal-volume impregnation means that the ZSM-5 zeolite molecular sieve was added to the aqueous solution until the solution just covered the ZSM-5. After impregnation, the powder was dried and then calcined at 450℃ for 4 hours. The Pt content was determined to be 14% by ICP.

[0092] 2) Preparation of Pt@ZSM-5 catalyst: Fine silica gel, sodium aluminate (NaAlO2), tetrapropylammonium hydroxide (TPAOH) (35% aqueous solution by mass), and water were added and mixed in a molar ratio of SiO2:NaAlO2:TPAOH:H2O = 1:0.02:0.2:15. Then, 90% by mass of the fine silica gel obtained in step 1) of the PtO2 / ZSM-5 mixture was added. After stirring for half an hour, the mixture was transferred to a stainless steel synthesis reactor with a polytetrafluoroethylene liner, sealed, and heated to 160°C. Crystallization was carried out under its own pressure for 72 h. After the reaction was completed, the solid was washed with deionized water until the pH of the filtered water reached 7, yielding TPAOH-PtO@ZSM-5. The filtered solid was calcined at 550°C for 4 h to obtain PtO2@ZSM-5.

[0093] The above PtO2@ZSM-5 was treated in a 0.2M citric acid aqueous solution (solid-liquid ratio of 1:50) for 3 hours, then washed with water and dried to obtain surface-treated PtO2@ZSM-5.

[0094] The surface-treated PtO2@ZSM-5 was exchanged three times in a 0.1M ammonium chloride aqueous solution (solid-liquid ratio of 1:50) and then calcined at 550 °C for 2 h to obtain PtO2@H-ZSM-5.

[0095] PtO2@H-ZSM-5 was modified in a 0.05M ammonium phosphate aqueous solution (solid-liquid ratio 1:50), and after 1 h of modification, it was calcined at 550 °C for 2 h to obtain PtO2@H-ZSM-5-P.

[0096] PtO2@H-ZSM-5-P was reduced at 500°C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Pt@H-ZSM-5-P. The mass content of Pt was 7% and the mass content of P was 0.7% as determined by ICP.

[0097] 3) Catalyst evaluation and synthesis reaction: The prepared Pt@H-ZSM-5-P catalyst was granulated to 20-40 mesh, and 4g of catalyst was placed in a fixed-bed reactor evaluation device. Acetophenone was used as the feedstock. The reactor was then fed at a mass hourly space velocity (MHSV) of 0.2 / h, a molar ratio of hydrogen to acetophenone of 5, and ammonia to acetophenone of 20, at a reaction temperature of 115℃ and a reaction pressure of 0.2 MPa. The test results showed that the acetophenone conversion rate was 99.5%, the α-phenylethylamine selectivity was approximately 96.0%, and the purity of the phenylethylamine product after distillation was 99.4%.

[0098] Comparative Example 1 This comparative example provides a comparative catalyst, which is used to catalyze the reductive amination of acetophenone to prepare phenethylamine. The catalyst preparation method is basically the same as in Example 1, except that NiO@ZSM-5 is not treated with citric acid aqueous solution, but directly exchanged in ammonium chloride aqueous solution. The resulting catalyst is thus obtained.

[0099] Catalyst evaluation: Same as in Example 1. The test results showed that the conversion rate of acetophenone was 99.4%, the selectivity of α-phenylethylamine was approximately 88.9%, and the purity of the phenylethylamine product after distillation was 95.0%.

[0100] The chromatogram of the reaction system after the reaction and before distillation is as follows: Figure 3 As shown, the corresponding peak area data is as follows: Figure 4 As shown, in addition to the target product α-phenylethylamine, the reaction system also contains approximately 4.18% of the byproduct cyclohexylethylamine (a peak with a retention time of 3.487 min), which is present in a relatively high amount.

[0101] Because the catalyst precursor is not treated with citric acid, a small amount of active components on the outer surface of the catalyst cannot be removed. These active components will catalyze the hydrogenation side reaction of the benzene ring, resulting in the presence of cyclohexylethylamine byproduct in the reaction system after the reaction is completed. Its boiling point is very close to that of phenylethylamine, making it difficult to separate and purify by distillation. As a result, even after purification, the purity of the styrene product is difficult to reach a very high level.

[0102] Comparative Example 2 This comparative example provides a comparative catalyst, which is used to catalyze the reductive amination of acetophenone to prepare phenethylamine. The catalyst preparation method is basically the same as in Example 1, except that the citric acid aqueous solution used to treat NiO@ZSM-5 is replaced with an acetic acid aqueous solution, while maintaining the concentration of the acetic acid aqueous solution at 0.2M. The resulting catalyst is thus obtained.

[0103] Catalyst evaluation: Same as in Example 1. The test results showed that the conversion rate of acetophenone was 90.1%, the selectivity of α-phenylethylamine was 93.2%, and the purity of the phenylethylamine product after distillation was 96.2%.

[0104] It is evident that when formic acid, with its smaller molecular structure, is used to replace citric acid in the present invention, the conversion rate of acetophenone is significantly reduced during the reaction catalyzed by the corresponding catalyst. The selectivity and purity of the target product, α-phenylethylamine, are also slightly decreased. This is because when formic acid, with its smaller molecular structure, is used to treat the catalyst precursor, it not only reacts with a small amount of active components on the outer surface of the catalyst precursor but also enters the pores of the catalyst precursor, reacting with some of the active components within the pores. This results in a reduction in the effective content of active components in the final catalyst, leading to a significant decrease in conversion rate and a slight impact on selectivity and purity.

[0105] Comparative Example 3 This comparative example provides a comparative catalyst and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine. The preparation method of the catalyst is basically the same as in Example 1, except that the concentration of the citric acid aqueous solution treated with NiO@ZSM-5 is replaced with 0.02M.

[0106] Catalyst evaluation: Same as in Example 1. The test results showed that the conversion rate of acetophenone was 99.3%, the selectivity of α-phenylethylamine was 95.8%, and the purity of the phenylethylamine product after distillation was 97.8%.

[0107] It is evident that when the concentration of the citric acid aqueous solution used to treat the catalyst precursor is too low, the selectivity and purity of the α-phenylethylamine target product decrease, making it difficult to achieve a purity above 99%. This is because when the concentration of the acid used is too low, there is insufficient acid to react with the small amount of active component on the outer surface of the catalyst precursor, resulting in the presence of active component on the outer surface of the catalyst precursor. This active component causes partial hydrogenation of the benzene ring in the acetophenone reaction feedstock, producing the byproduct cyclohexylethylamine, which is difficult to separate from the target product through distillation.

[0108] Comparative Example 4 This comparative example provides a catalyst Ni / ZSM-5 (without pre-fixation or modification of the active component), and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: ZSM-5 zeolite molecular sieve was impregnated in an aqueous solution of nickel nitrate (molar concentration 3.2 mol / L) by an equal-volume impregnation method. After impregnation, the powder was dried and then calcined at 450 °C for 4 h. The same operation was then repeated once more to prepare the NiO / ZSM-5 catalyst precursor.

[0109] The NiO / ZSM-5 catalyst precursor was reduced at 500 °C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Ni / ZSM-5, and the mass content of Ni was determined to be 19% by ICP.

[0110] Catalyst evaluation: Same as in Example 1. The test results showed that the conversion rate of acetophenone was 99.5%, the selectivity of α-phenylethylamine was 80.1%, and the purity of the phenylethylamine product after distillation was 90.1%.

[0111] It is evident that when the active component is not fixed or modified before catalyst preparation, the selectivity and purity of the target product are significantly reduced.

[0112] Comparative Example 5 This comparative example provides a catalyst Ni / Al2O3 (without pre-fixation or modification of the active component), and uses it to catalyze the reductive amination of acetophenone to prepare phenethylamine, as detailed below: Al2O3 was impregnated in an aqueous solution of nickel nitrate (molar concentration 3.2 mol / L) by an equal-volume impregnation method. After impregnation, the powder was dried and then calcined at 450 °C for 4 h. The process was then repeated once more to prepare the NiO / Al2O3 catalyst precursor.

[0113] The NiO / Al2O3 catalyst precursor was reduced at 500 °C for 6 h in a hydrogen atmosphere to obtain the reduced catalyst Ni / Al2O3. The mass content of Ni was determined to be 19% by ICP.

[0114] Catalyst evaluation: Same as in Example 1. The test results showed that the conversion rate of acetophenone was 99.2%, the selectivity of α-phenylethylamine was 78.1%, and the purity of the phenylethylamine product after distillation was 89.1%.

[0115] It is evident that when the active component is not fixed or modified before catalyst preparation, the selectivity and purity of the target product are significantly reduced.

[0116] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing phenethylamine, comprising using acetophenone, hydrogen, and ammonia as raw materials, and conducting a reductive amination reaction in the presence of a catalyst to generate the phenethylamine, characterized in that: The catalyst is composed of The catalyst precursor is prepared by a method including the following steps: 1) loading an active metal oxide onto a support to obtain an active metal oxide / support; 2) synthesizing a molecular sieve support in the presence of the active metal oxide / support to obtain a catalyst precursor. 3) The catalyst precursor is treated with an acid solution to obtain an acid-modified catalyst precursor; 4) The acid-modified catalyst precursor is calcined and reduced to obtain the catalyst; the acid is selected from citric acid and / or naphthoic acid; the molar concentration of the acid solution is 0.05-0.2 mol / L.

2. The method for preparing phenylethylamine according to claim 1, characterized in that: The mass ratio of the acid solution to the catalyst precursor is 30-60:1; and / or the acid solution treats the catalyst precursor for 1-3 hours.

3. The method for preparing phenylethylamine according to claim 1, characterized in that: The catalyst comprises a molecular sieve support and an active metal component fixed within the crystal structure of the molecular sieve support.

4. The method for preparing phenylethylamine according to claim 3, characterized in that: The molecular sieve support is selected from one or a combination of two of ZSM-5 molecular sieve and Beta molecular sieve; and / or, the active metal component is selected from one or a combination of Ni, Co, Cu, Pt, Pd; and / or, by mass percentage, the catalyst comprises 5%-25% of the active metal component and 75%-95% of the molecular sieve support.

5. The method for preparing phenylethylamine according to claim 3, characterized in that: The active metal component is selected from one or more combinations of Ni, Co, and Cu, and the catalyst comprises 15%-25% of the active metal component by mass percentage; or, the active metal component is selected from one or more combinations of Pt and Pd, and the catalyst comprises 5%-10% of the active metal component by mass percentage.

6. The method for preparing phenylethylamine according to claim 1, characterized in that: The support is selected from one or a combination of two of ZSM-5 molecular sieves and Beta molecular sieves; and / or, in step 1), an active metal oxide is loaded onto the support by an impregnation method.

7. The method for preparing phenylethylamine according to claim 1, characterized in that: Step 2) Specifically involves: subjecting the silicon source, aluminum source, organic amine template agent, the active metal oxide / support, and water to a hydrothermal reaction, followed by filtration and calcination to obtain the catalyst precursor.

8. The method for preparing phenylethylamine according to claim 7, characterized in that: The silicon source is selected from one or more combinations of silica sol, silica gel, and sodium silicate; and / or, the aluminum source is selected from one or more combinations of sodium aluminate, aluminum hydroxide, boehmite, alumina, and aluminum isopropoxide; and / or, the organic amine template agent is selected from tetrapropylammonium hydroxide or tetraethylammonium hydroxide.

9. The method for preparing phenylethylamine according to claim 7, characterized in that: The molar ratio of silicon in the silicon source, aluminum in the aluminum source, organic amine template agent, and water is 1: 0.02-0.03: 0.2-0.4: 15-20; and / or, the mass ratio of the silicon source to the active metal oxide / support is 1: 0.3-1.

1.

10. The method for preparing phenylethylamine according to claim 1, characterized in that: The catalyst preparation method further includes, before step 4), ion-exchange and calcining the acid-modified catalyst precursor with an aqueous solution of ammonium salt to obtain a hydrogen-form catalyst precursor; and modifying the hydrogen-form catalyst precursor with a modifier. The modifier is selected from one or more combinations of phosphorus compounds, magnesium compounds, and calcium compounds.

11. The method for preparing phenylethylamine according to claim 10, characterized in that: The modifier is selected from one or more combinations of phosphoric acid, ammonium phosphate, magnesium nitrate, magnesium chloride, calcium nitrate, and calcium chloride; and / or, the hydrogen-form catalyst precursor is impregnated in an aqueous solution of the modifier to carry out the modification.

12. The method for preparing phenylethylamine according to claim 11, characterized in that: The molar concentration of the aqueous solution of the modifier is 0.03-0.1 mol / L; the mass ratio of the aqueous solution of the modifier to the hydrogen-form catalyst precursor is 30-60:

1.

13. The method for preparing phenylethylamine according to claim 10, characterized in that: The ammonium salt is selected from one or a combination of ammonium chloride and ammonium nitrate; and / or, the molar concentration of the aqueous solution of the ammonium salt is 0.1-0.2 mol / L; and / or, the mass ratio of the aqueous solution of the ammonium salt to the acid-modified catalyst precursor is 30-60:

1.

14. The method for preparing phenylethylamine according to claim 1, characterized in that: In step 4), the calcination temperature is 400-600℃; and / or, in step 4), the reduction is carried out in a hydrogen atmosphere; and / or, the reduction temperature is 400-600℃.

15. The method for preparing phenylethylamine according to claim 1, characterized in that: The mass hourly space velocity (MSV) of the acetophenone is 0.1-5 h⁻¹. -1 ; and / or, the molar ratio of acetophenone to hydrogen is 1:1-10; and / or, the molar ratio of acetophenone to ammonia is 1:10-30; and / or, the reductive amination reaction is carried out in an organic solvent, wherein the organic solvent is methanol; and / or, the temperature of the reductive amination reaction is 110-150°C; and / or, the pressure of the reductive amination reaction is 0.1-3 MPa.

16. The catalyst used in the method for preparing phenethylamine according to any one of claims 1-15.

Images