A method for continuously preparing benzylamine compounds by hydrogenation

Abstract

The application provides a method for continuously preparing benzyl amine compounds by hydrogenation, and belongs to the technical field of organic synthesis, and comprises the following steps: a catalyst is prepared by contacting a molecular sieve carrier with a nickel salt-citric acid complex impregnation solution, drying, calcination, 1-[3-(triethoxysilyl)propyl]-1H-imidazole graft modification and in-situ reduction of hydrogen; then, benzyl cyanide, toluene and liquid ammonia are prepared into liquid phase raw materials, hydrogen is continuously introduced into a reactor filled with the catalyst to perform hydrogenation reaction, and benzyl amine or dibenzyl amine is prepared through first or second reaction conditions respectively. The application can improve the selectivity of target products and reduce the generation of by-products such as tri-benzyl amine.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for the continuous hydrogenation preparation of benzylamine compounds. Background Technology

[0002] Benzylamine and dibenzylamine are important nitrogen-containing organic intermediates widely used in pharmaceuticals, pesticides, surfactants, resin curing agents, rubber additives, and other fine chemicals. With the increasing demand for related downstream products, developing efficient, stable, and continuous production processes for benzylamine compounds is of great significance.

[0003] In existing technologies, the preparation methods for benzylamine compounds mainly include benzyl chloride ammonolysis, benzaldehyde reductive amination, and benzonitrile catalytic hydrogenation. The benzyl chloride ammonolysis process is relatively mature, but it easily generates chlorine-containing byproducts during the reaction, leading to problems such as equipment corrosion, large waste salt volumes, and heavy post-processing burdens. The benzaldehyde reductive amination process typically requires the presence of a hydrogenation catalyst or reducing agent, resulting in a complex reaction system and demanding high standards for side reaction control and product separation.

[0004] The catalytic hydrogenation of benzonitrile uses benzonitrile and hydrogen as the main raw materials, avoiding the corrosion and waste salt problems associated with chlorine-containing raw materials, making it a preparation route with considerable industrial application value. However, during the hydrogenation process of benzonitrile, competing reactions may occur simultaneously, such as the formation of benzylamine, dibenzylamine, and further alkylation or hydrogenolysis. The selectivity of the target product is easily affected by factors such as catalyst type, reaction temperature, pressure, residence time, and system composition.

[0005] Currently, catalysts used for this type of reaction mainly include skeletal nickel, supported nickel, and noble metal catalysts such as palladium and platinum. Noble metal catalysts are relatively expensive; although ordinary nickel catalysts are less expensive, they may still suffer from problems such as insufficient dispersion of active components, difficulty in controlling surface properties, unstable selectivity of target products, and high amounts of by-products in continuous hydrogenation processes.

[0006] Therefore, it is still necessary to develop a low-cost and selectively tunable method for the hydrogenation of benzonitrile to prepare benzylamine or dibenzylamine, which is suitable for continuous hydrogenation systems, in order to improve the yield of the target product, reduce the formation of by-products, and improve the stability of continuous process operation. Summary of the Invention

[0007] In view of the above situation and to overcome the defects of the prior art, the purpose of the present invention is to provide a method for the continuous hydrogenation preparation of benzylamine compounds, so as to at least partially solve the problems mentioned in the background art.

[0008] The technical solution adopted in this invention is as follows: This invention proposes a method for the continuous hydrogenation preparation of benzylamine compounds, comprising the following steps: The molecular sieve support was contacted with a nickel salt-citric acid complex impregnation solution, and then dried and calcined to obtain a NiO-containing molecular sieve precursor. The NiO-containing molecular sieve precursor was grafted with 1-[3-(triethoxysilyl)propyl]-1H-imidazolium to obtain a modified nickel-based catalyst precursor. The modified nickel-based catalyst precursor was reduced in situ with hydrogen to obtain a modified supported nickel catalyst. Benzonitrile, toluene, and liquid ammonia were formulated into a liquid-phase feedstock. The liquid feedstock and hydrogen are continuously fed into a reactor packed with the modified supported nickel catalyst for a hydrogenation reaction. Specifically, when the target product is benzylamine, the hydrogenation reaction is controlled to proceed under the first reaction conditions; when the target product is dibenzylamine, the hydrogenation reaction is controlled to proceed under the second reaction conditions.

[0009] In some embodiments of the present invention, the molecular sieve support is selected from one of β molecular sieve, ZSM-5 molecular sieve, Y-type molecular sieve, MCM-41 molecular sieve, and SBA-15 molecular sieve.

[0010] In some embodiments of the present invention, the nickel salt is one of nickel nitrate, nickel acetate, and nickel chloride; the nickel loading in the catalyst is 5-30 wt% based on metallic nickel; and the molar ratio of citric acid to nickel is (0.3-1.5):1.

[0011] In some embodiments of the present invention, the molecular sieve carrier is contacted with the nickel salt-citric acid complex impregnation solution by equal volume impregnation, ultrasonic impregnation, or excessive impregnation; the drying temperature is 80-120℃, and the drying time is 6-12h; the calcination temperature is 450-500℃, and the calcination time is 2-6h.

[0012] In some embodiments of the present invention, the grafting modification is carried out in anhydrous toluene, the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium is 2-20 wt% of the mass of the NiO-containing molecular sieve precursor, the grafting modification temperature is 90-115°C, and the grafting modification time is 4-12 h.

[0013] In some embodiments of the present invention, the temperature for in-situ hydrogen reduction is 250-320°C, and the reduction time is 2-8 hours.

[0014] In some embodiments of the present invention, the mass ratio of benzonitrile, toluene and liquid ammonia is (2-4):(5-8):(0.05-1.5).

[0015] In some embodiments of the present invention, the reactor is a fixed-bed tubular reactor; before the liquid raw material and hydrogen are introduced into the reactor, the feeding system and the reaction system are purged with nitrogen and hydrogen respectively; after the reaction effluent of the hydrogenation reaction is separated into gas and liquid phases, the hydrogen in the gas phase is returned to the reactor for recycling, and the liquid phase is separated by ammonia stripping, solvent recovery and distillation to obtain benzylamine or dibenzylamine products.

[0016] In some embodiments of the present invention, the first reaction conditions include: a hydrogenation reaction temperature of 65-80°C, a hydrogenation reaction pressure of 5.5-7.0 MPa, and a liquid hourly space velocity of 0.2-2.0 h⁻¹. -1 The molar ratio of hydrogen to benzonitrile is (3-20):1.

[0017] In some embodiments of the present invention, the second reaction conditions include: a hydrogenation reaction temperature of 75-95°C, a hydrogenation reaction pressure of 6.5-8.5 MPa, and a liquid hourly space velocity of 0.1-1.5 h⁻¹. - ¹, The molar ratio of hydrogen to benzonitrile is (3-15):1.

[0018] The beneficial effects achieved by this invention are as follows: This invention employs a catalyst prepared by nickel salt-citric acid complex impregnation, drying and calcination, 1-[3-(triethoxysilyl)propyl]-1H-imidazolium graft modification, and in-situ hydrogen reduction on a molecular sieve support for the continuous hydrogenation reaction of benzonitrile. The above catalyst preparation method is beneficial for improving the dispersion of the nickel active component on the molecular sieve support, and the graft modification adjusts the surface and pore environment of the catalyst, thereby improving the competition between primary amine formation, secondary amine formation, and further side reactions during benzonitrile hydrogenation, increasing the selectivity of the target product, and reducing the formation of byproducts such as tribenzylamine and hydrogenolysis products.

[0019] Simultaneously, this invention prepares benzonitrile, toluene, and liquid ammonia into a liquid-phase feedstock, which is then continuously fed with hydrogen into a reactor packed with the catalyst for hydrogenation. Under the same catalyst and continuous reaction system, by controlling the first or second reaction conditions, the selective formation of benzylamine or dibenzylamine can be promoted respectively, allowing the process to be switched according to the target product requirement. This improves the problems of unstable target product selectivity and insufficient process adaptability in the existing benzonitrile hydrogenation process. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this invention.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] To address the problems mentioned in the background art, embodiments of the present invention provide a method for the continuous hydrogenation preparation of benzylamine compounds. This method uses benzonitrile as a reactant and hydrogen as a hydrogenating agent, and carries out a continuous hydrogenation reaction under the action of a catalyst. By controlling different reaction conditions, the reaction system can be biased towards either the benzylamine or dibenzylamine formation pathway, thereby achieving the selective preparation of benzylamine or dibenzylamine.

[0024] Specifically, the method comprises three main parts: catalyst preparation, liquid-phase feedstock preparation, and continuous hydrogenation reaction.

[0025] First, the molecular sieve support is contacted with a nickel salt-citric acid complex impregnation solution, and then dried and calcined to obtain a NiO-containing molecular sieve precursor.

[0026] In this step, the molecular sieve support serves as the main carrier of the nickel active component, and its surface and pore structure provide dispersion sites for nickel species. Nickel salts provide the nickel source, while citric acid forms a complex with nickel ions, allowing the nickel species to be more uniformly distributed on the surface and pore areas of the molecular sieve support during impregnation. Compared to direct impregnation with nickel salt solution, the nickel salt-citric acid complex impregnation solution helps to slow down the migration and aggregation of nickel species during drying and calcination, thereby improving the dispersion of the nickel active component in the subsequent catalyst. The contact can be equal-volume impregnation, excess impregnation, ultrasonic-assisted impregnation, or stirring impregnation. After impregnation, the system is dried to remove moisture, leaving the nickel species on the molecular sieve support. Subsequently, calcination decomposes the nickel salt into NiO and removes organic components such as citric acid, yielding a NiO-containing molecular sieve precursor. Calcination also improves the bonding state between the nickel species and the support and facilitates the formation of a suitable pore environment for the diffusion of reactants and products.

[0027] Then, the NiO-containing molecular sieve precursor was grafted with 1-[3-(triethoxysilyl)propyl]-1H-imidazolium to obtain a modified nickel-based catalyst precursor.

[0028] In this step, 1-[3-(triethoxysilyl)propyl]-1H-imidazolium, as an imidazolium-containing silane modifier, has its triethoxysilyl group capable of condensing with hydroxyl groups on the surface or within the pores of the molecular sieve support, allowing the imidazolium group to be linked to the molecular sieve support via siloxane bonds. This grafting modification introduces nitrogen-containing organic basic sites into the surface and pore regions of the NiO-containing molecular sieve precursor, thereby regulating the acid-base environment on the catalyst surface and within the pores. During the hydrogenation of benzonitrile, the adsorption and desorption behavior of substances such as benzonitrile, imine intermediates, benzylamine, and dibenzylamine on the catalyst surface directly affects the selectivity of the target product. By grafting imidazolium groups, it is beneficial to weaken the promoting effect of excessively acidic sites in the molecular sieve support on side reactions and regulate the residence state of intermediates and products on the catalyst surface, thereby reducing the possibility of the formation of byproducts such as tribenzylamine and hydrogenolysis products.

[0029] Next, the modified nickel-based catalyst precursor is reduced in situ with hydrogen to obtain a modified supported nickel catalyst. In this step, in-situ hydrogen reduction refers to placing the modified nickel-based catalyst precursor in the reactor or reduction apparatus used for subsequent hydrogenation reactions and performing reduction treatment under a hydrogen atmosphere, so that at least part of the NiO in the precursor is converted into zero-valent nickel species with hydrogenation activity. Using in-situ reduction reduces the risk of re-oxidation when the catalyst is exposed to air after reduction, helps maintain the effective state of the nickel active sites, and improves the stability of subsequent continuous hydrogenation reactions.

[0030] The catalyst prepared through the above steps simultaneously possesses nickel hydrogenation active centers, a porous structure provided by a molecular sieve support, and a surface-controlled environment formed by imidazolyl silane grafting. The nickel active centers promote the hydrogenation conversion of benzonitrile; the molecular sieve support supports and disperses nickel species; and the imidazolyl silane grafting structure regulates the adsorption and desorption behavior of reactants, intermediates, and products on the catalyst surface and within the pores. These three elements work synergistically, making the catalyst suitable for the continuous hydrogenation of benzonitrile to prepare benzylamine or dibenzylamine.

[0031] Subsequently, benzonitrile, toluene, and liquid ammonia were prepared as a liquid-phase feedstock. Benzonitrile is the main reactant for the preparation of benzylamine or dibenzylamine; toluene, as an organic solvent, is used to dilute benzonitrile, improve material flowability, and facilitate the stable operation of the continuous feeding process; liquid ammonia is used to regulate the ammonia-containing environment of the reaction system, affecting the conversion equilibrium between the imine intermediate, benzylamine, and dibenzylamine during the hydrogenation of benzonitrile. By pre-preparing benzonitrile, toluene, and liquid ammonia as a liquid-phase feedstock, the composition of the materials entering the reactor can be kept relatively stable, thereby reducing fluctuations in the continuous hydrogenation process.

[0032] In practice, when preparing liquid feedstocks, benzonitrile and toluene can be mixed first, followed by the addition of liquid ammonia; alternatively, benzonitrile, toluene, and liquid ammonia can be added and mixed in a closed batching system according to a set ratio. During the batching process, the system temperature should be controlled to prevent excessive volatilization of the liquid ammonia and to ensure thorough mixing of the feedstocks. The batching system can be purged with an inert gas before feeding to reduce the risk of oxygen entering the subsequent hydrogenation system.

[0033] Subsequently, the liquid feedstock and hydrogen are continuously fed into a reactor packed with the modified supported nickel catalyst for a hydrogenation reaction. In this step, after the liquid feedstock and hydrogen are continuously introduced into the reactor, they contact the catalyst and undergo a hydrogenation reaction. Benzonitrile first undergoes hydrogenation conversion under the action of the nickel active center to form an imine intermediate, which can then be further hydrogenated to generate benzylamine; under certain reaction conditions, the imine intermediate can also condense with benzylamine and undergo further hydrogenation to generate dibenzylamine. Since the formation pathways of benzylamine and dibenzylamine are in competition, the reaction pathway needs to be controlled by adjusting the reaction conditions.

[0034] When the target product is benzylamine, the hydrogenation reaction is controlled to proceed under the first reaction conditions. The first reaction conditions are those that favor the hydrogenation of benzonitrile to benzylamine and inhibit the further condensation or conversion of benzylamine. Under these conditions, the reaction system is more inclined to allow benzonitrile to undergo further hydrogenation via an imine intermediate to generate benzylamine, and to promote the timely desorption of benzylamine from the catalyst surface, thereby improving the selectivity of benzylamine and reducing the formation of byproducts such as dibenzylamine and tribenzylamine.

[0035] When the target product is dibenzylamine, the hydrogenation reaction is controlled to proceed under the second reaction conditions. The second reaction conditions refer to reaction conditions that favor the formation of dibenzylamine from benzylamine via a condensation-hydrogenation pathway. Under these second reaction conditions, the reaction system can moderately enhance the dibenzylamine formation pathway, shifting the target product from benzylamine to dibenzylamine. Simultaneously, due to the modification of the catalyst surface and pore environment with imidazolylsilane, the tendency for dibenzylamine to further react and form tribenzylamine can be reduced, thereby improving the selectivity for dibenzylamine.

[0036] Therefore, this method does not achieve target product switching solely through changes in temperature or pressure. Instead, it leverages the structural characteristics of the modified supported nickel catalyst and the synergy between the first and second reaction conditions to selectively control the continuous hydrogenation reaction of benzonitrile between the benzylamine and dibenzylamine formation pathways. This approach improves upon the problems of unstable target product selectivity and excessive byproduct formation during the hydrogenation of benzonitrile using conventional nickel catalysts and is suitable for continuous production.

[0037] In some embodiments, the molecular sieve support is selected from one of β-zeolite, ZSM-5 molecular sieve, Y-type molecular sieve, MCM-41 molecular sieve, and SBA-15 molecular sieve; the molecular sieve support is a granular, strip-shaped, or columnar shaped support. All of the above-mentioned molecular sieve supports have high specific surface area and a certain pore structure, which can provide dispersion and loading sites for nickel species. Among them, β-zeolite, ZSM-5 molecular sieve, and Y-type molecular sieve have relatively stable silica-alumina framework structures, suitable for used as supported catalysts in fixed-bed reactions; MCM-41 molecular sieve and SBA-15 molecular sieve have relatively regular mesoporous channels, which is conducive to the diffusion of molecules such as benzonitrile, benzylamine, and dibenzylamine within the catalyst. The use of granular, strip-shaped, or columnar shaped molecular sieve supports is beneficial for catalyst loading in fixed-bed reactors, reducing bed pressure drop, and improving mechanical stability during continuous reaction processes. If the support particle size is too small, it can easily cause increased bed resistance; if the support particle size is too large, it may lead to a decrease in mass transfer efficiency. Therefore, the forming method and particle size of the carrier can be selected according to the reactor size, feed flow rate and pressure drop requirements.

[0038] In some embodiments, the nickel salt is one of nickel nitrate, nickel acetate, and nickel chloride; the nickel loading in the catalyst is 5-30 wt% based on metallic nickel; the molar ratio of citric acid to nickel is (0.3-1.5):1. The nickel salt is used to provide a nickel source, which can be converted into NiO after drying and calcination, and forms zero-valent nickel active centers after in-situ reduction with hydrogen. Nickel nitrate, nickel acetate, and nickel chloride can all be used as soluble nickel salts, among which nickel nitrate has better solubility and fewer residual impurities after calcination, making it more suitable for impregnation methods to prepare supported nickel catalysts. Controlling the nickel loading within the range of 5-30 wt% is beneficial for balancing catalyst activity and dispersibility. If the nickel loading is too low, the catalyst's hydrogenation activity is insufficient, which may lead to a decrease in benzonitrile conversion; if the nickel loading is too high, nickel species are prone to agglomeration during drying, calcination, and reduction, resulting in a decrease in the utilization rate of effective active sites and potentially increasing side reactions. Maintaining a molar ratio of citric acid to nickel within the range of 0.3:1 to 1.5:1 allows citric acid to exert its complexing and dispersing effects. If the amount of citric acid is too low, its complexing and dispersing effect on nickel species is insufficient; if the amount is too high, the organic components decompose violently during calcination, potentially affecting the stability of the support structure or causing localized pore blockage. Therefore, the above-mentioned ratio range is beneficial for obtaining NiO-containing molecular sieve precursors with good dispersibility.

[0039] In some embodiments, the contact method between the molecular sieve support and the nickel salt-citric acid complex impregnation solution is equal-volume impregnation, ultrasonic impregnation, or excessive impregnation; the drying temperature is 80-120℃, and the drying time is 6-12h; the calcination temperature is 450-500℃, and the calcination time is 2-6h. Equal-volume impregnation allows the impregnation solution to be largely absorbed by the support pores, which is beneficial for controlling the distribution of nickel salts in the support; ultrasonic impregnation facilitates the entry of the impregnation solution into the support pores, improving the dispersion of nickel species in the inner pores; excessive impregnation ensures sufficient contact between the support surface and the pore area. All of the above methods can be used to load the nickel salt-citric acid complex onto the molecular sieve support. The drying step is used to remove moisture from the system after impregnation, allowing the nickel species to remain on the support surface and within the pores. If the drying temperature is too low, moisture removal will be insufficient; if the temperature is too high or the drying is too fast, nickel species may migrate with the solvent and accumulate on the outer surface of the support. Therefore, controlling the drying temperature at 80-120℃ and the drying time at 6-12h is beneficial for improving the uniformity of the precursor composition. The calcination step is used to decompose the nickel salt into NiO, while simultaneously removing organic components such as citric acid. Controlling the calcination temperature at 450-500℃ ensures sufficient decomposition of the nickel salt and organic components while avoiding excessive sintering of nickel species due to excessively high temperatures. This calcination treatment yields a NiO-containing molecular sieve precursor, providing a stable foundation for subsequent grafting modification and in-situ reduction.

[0040] In some embodiments, the grafting modification is carried out in anhydrous toluene, the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazole is 2-20 wt% of the mass of the NiO-containing molecular sieve precursor, the grafting modification temperature is 90-115°C, and the grafting modification time is 4-12 h. Anhydrous toluene, as the reaction medium for grafting modification, can disperse the NiO-containing molecular sieve precursor and provide a suitable environment for the condensation reaction between the silane modifier and the hydroxyl groups on the molecular sieve surface. Using an anhydrous system helps reduce the self-polymerization of the silane modifier in solution, allowing it to react more readily with the hydroxyl groups on the surface or within the pores of the molecular sieve support. Controlling the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazole within the range of 2-20 wt% is beneficial for introducing appropriate amounts of imidazole groups onto the catalyst surface and within the pores. When the dosage is too low, the surface regulation effect is not obvious; when the dosage is too high, excessive organosilane may cover some nickel species or narrow the pores, thus affecting the diffusion of benzonitrile and product molecules and the hydrogenation contact efficiency. Controlling the grafting temperature at 90-115℃ and the grafting time at 4-12h allows for sufficient reaction between the silane modifier and the hydroxyl groups on the support surface. Through this grafting modification, the catalyst surface and pore environment are regulated, which is beneficial for improving the adsorption and desorption behavior of intermediates and products during benzonitrile hydrogenation, thereby increasing the selectivity of the target product.

[0041] In some embodiments, the in-situ hydrogen reduction temperature is 250-320°C, and the reduction time is 2-8 hours. The in-situ reduction step is used to convert the NiO-containing modified nickel-based catalyst precursor into a catalyst with hydrogenation activity. If the reduction temperature is too low, NiO reduction is insufficient, resulting in inadequate catalyst hydrogenation activity; if the reduction temperature is too high, nickel particles may sinter, leading to a reduction in active sites. Therefore, controlling the reduction temperature within the range of 250-320°C is beneficial for reducing nickel particle agglomeration while ensuring the reduction effect. It is not required that all NiO in the catalyst be completely converted to zero-valent nickel; it is sufficient to form effective nickel active sites that can promote the hydrogenation reaction of benzonitrile. Using in-situ reduction allows the catalyst to directly enter the continuous hydrogenation reaction state after reduction, reducing the possibility of re-oxidation during transfer and exposure, thereby improving the stability during the reaction start-up stage and continuous operation.

[0042] In some embodiments, the mass ratio of benzonitrile, toluene, and liquid ammonia is (2-4):(5-8):(0.05-1.5). Benzonitrile is the reaction substrate, toluene is the solvent, and liquid ammonia is used to regulate the ammonia environment in the reaction system. Controlling the amount of toluene within the above range helps reduce the viscosity of the liquid-phase feedstock, improves flowability, and maintains good dispersion of benzonitrile during continuous feeding. If the amount of toluene is too low, the material viscosity and local concentration may increase, affecting mass transfer and reaction stability; if the amount of toluene is too high, it will reduce the amount of benzonitrile processed per unit time. Controlling the amount of liquid ammonia within the range of 0.05-1.5 allows for adjustment of the reaction system according to the target product. A higher proportion of liquid ammonia generally helps inhibit the continued condensation of benzylamine, thereby improving benzylamine selectivity; a lower proportion of liquid ammonia helps promote the dibenzylamine formation pathway under appropriate conditions. By adjusting the proportion of liquid ammonia within the above range, selective preparation of different target products can be achieved by combining the first reaction condition or the second reaction condition.

[0043] In some embodiments, the reactor is a fixed-bed tubular reactor. Before introducing the liquid feedstock and hydrogen into the reactor, the batching system and reaction system are purged with nitrogen and hydrogen, respectively. The batching system includes a batching vessel and a feed line connected to it; the reaction system includes a fixed-bed tubular reactor, a gas-liquid separator, and related hydrogen lines. The fixed-bed tubular reactor is suitable for loading shaped catalysts and is applicable to continuous hydrogenation reactions of liquid feedstock and hydrogen. Compared to batch reactions, continuous fixed-bed reactions allow for stable contact between reactants and catalysts, facilitating control of residence time, temperature, and pressure, thereby improving the stability of the reaction process and product selectivity. Purging the batching system and reaction system with nitrogen before introducing the liquid feedstock and hydrogen reduces the oxygen content in the system, decreasing the risk of forming an explosive mixture upon hydrogen introduction. Purging with hydrogen after nitrogen purging helps establish a suitable hydrogen environment for the hydrogenation reaction. This purging process improves the safety and operational stability of the continuous hydrogenation process.

[0044] In some embodiments, the first reaction conditions include: a hydrogenation reaction temperature of 65-80°C, a hydrogenation reaction pressure of 5.5-7.0 MPa, and a liquid hourly space velocity of 0.2-2.0 h⁻¹. -1 The molar ratio of hydrogen to benzonitrile is (3-20):1. The first reaction condition is mainly used to prepare benzylamine. Under these conditions, benzonitrile can be hydrogenated to benzylamine under the action of the nickel active center. Simultaneously, by controlling the appropriate temperature, pressure, liquid hourly space velocity (LHSV), and hydrogen ratio, the further condensation of benzylamine with the intermediate to form dibenzylamine or tribenzylamine can be inhibited. Controlling the hydrogenation temperature within the range of 65-80℃ is beneficial for the smooth progress of the benzonitrile hydrogenation reaction, while avoiding excessively high temperatures that promote the formation of dibenzylamine or other byproducts. Controlling the hydrogenation pressure within the range of 5.5-7.0 MPa provides sufficient hydrogen partial pressure for the hydrogenation of benzonitrile. The LHSV is controlled within 0.2-2.0 h⁻¹. -1 Within a certain range, it is beneficial to ensure that the reactants and catalyst have an appropriate contact time; if the space velocity is too low, the product will remain in the catalyst bed for too long, which may increase the depth of reaction; if the space velocity is too high, it may lead to incomplete conversion of benzonitrile. Therefore, by combining the first reaction conditions with the modified supported nickel catalyst, the reaction system can be made more favorable for the formation and desorption of benzylamine, thereby improving the selectivity of benzylamine.

[0045] In some embodiments, the second reaction conditions include: a hydrogenation reaction temperature of 75-95°C, a hydrogenation reaction pressure of 6.5-8.5 MPa, and a liquid hourly space velocity of 0.1-1.5 h⁻¹. -¹, The molar ratio of hydrogen to benzonitrile is (3-15):1. The second reaction condition is mainly used to prepare dibenzylamine. Compared with the first reaction condition, the second reaction condition typically uses a higher reaction temperature and pressure, and can employ a relatively lower liquid hourly space velocity (LHSV), thereby enhancing the condensation-hydrogenation pathway between benzylamine and the imine intermediate, thus improving the selectivity of dibenzylamine. Controlling the hydrogenation temperature within the range of 75-95℃ is beneficial for promoting the dibenzylamine formation pathway; controlling the hydrogenation pressure within the range of 6.5-8.5 MPa is beneficial for ensuring further hydrogenation of the condensation intermediate to form dibenzylamine; and controlling the LHSV within 0.1-1.5 h⁻¹ is beneficial for the formation of dibenzylamine. - Within the specified range, the reactants and intermediates can have appropriate contact time, thereby increasing the proportion of dibenzylamine formed. Simultaneously, because the catalyst is modified by imidazolylsilane grafting, the surface and pore environment of the catalyst can be adjusted, which is beneficial for inhibiting the further formation of tribenzylamine from dibenzylamine.

[0046] Furthermore, after gas-liquid separation, the hydrogen in the gas phase is returned to the reactor for recycling, while the liquid phase is separated by ammonia stripping, solvent recovery, and distillation to obtain benzylamine or dibenzylamine products. Gas-liquid separation allows unreacted hydrogen to be separated from the liquid-phase reactants and products, which can then be compressed or purified and returned to the reactor for recycling, thereby improving hydrogen utilization. Ammonia stripping of the liquid phase allows for the recovery of ammonia from the system; solvent recovery allows for the recovery of toluene; and finally, distillation yields benzylamine or dibenzylamine products. This post-processing method facilitates the recycling of raw materials and the purification of products in continuous production.

[0047] The present invention will be described below through specific embodiments. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0048] Example 1: Take 100g of β-molecular sieve granules, sieve to 20-40 mesh, and dry at 110℃ for 8 hours for later use.

[0049] Nickel nitrate hexahydrate and citric acid were added to deionized water and stirred to dissolve, yielding a nickel salt-citric acid complex impregnation solution. The nickel loading was calculated as 15 wt% of the final catalyst mass, and the molar ratio of citric acid to nickel was 0.8:1.

[0050] The dried β-zeolite support was contacted with the nickel salt-citric acid complex impregnation solution and impregnated using an equal-volume impregnation method. During the impregnation process, ultrasonic treatment was performed for 30 minutes to ensure that the impregnation solution fully penetrated the surface and pore areas of the zeolite support. After impregnation, the resulting solid was aged at room temperature for 6 hours and then dried at 110°C for 10 hours. Subsequently, the temperature was increased to 480°C at a rate of 2°C / min and calcined in air for 4 hours to obtain a NiO-containing zeolite precursor.

[0051] The obtained NiO-containing molecular sieve precursor was added to anhydrous toluene, followed by the addition of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium. The amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium was 8 wt% of the mass of the NiO-containing molecular sieve precursor. Under nitrogen protection, the system was heated to 110 °C and refluxed for 8 h. After the reaction, the mixture was filtered, and the resulting solid was washed successively with toluene and ethanol, then dried under vacuum at 100 °C for 8 h to obtain the modified nickel-based catalyst precursor.

[0052] The modified nickel-based catalyst precursor was packed into a fixed-bed tubular reactor. After the reactor was packed, nitrogen gas was first introduced for purging, then switched to hydrogen gas, and the reactor was reduced in situ at 280°C for 4 hours to at least partially convert the NiO in the precursor into zero-valent nickel active centers, thus obtaining the catalyst.

[0053] 210g of benzonitrile and 420g of toluene were added to a sealed mixing vessel and stirred until mixed. Then, 70g of liquid ammonia was added, and the temperature of the mixing system was controlled below 50℃. The mixture was stirred until the materials were homogeneous to obtain a liquid-phase raw material. The mass ratio of benzonitrile, toluene, and liquid ammonia was 3:6:1.

[0054] Before the reaction, the batching system, feed pipeline and fixed bed tubular reactor were purged with nitrogen 5 times, each purging pressure was 0.3 MPa; then hydrogen was purged 3 times, each purging pressure was 0.3 MPa.

[0055] After the displacement is completed, the liquid feedstock and hydrogen are continuously fed into a fixed-bed tubular reactor packed with the catalyst for hydrogenation. The hydrogenation reaction temperature is controlled at 72°C, the hydrogenation reaction pressure at 6.5 MPa, and the liquid hourly space velocity at 0.5 h⁻¹. - ¹, The molar ratio of hydrogen to benzonitrile is 8:1.

[0056] After gas-liquid separation, the hydrogen in the gas phase is compressed and returned to the fixed-bed tubular reactor for recycling; the liquid phase is successively subjected to ammonia stripping, toluene recovery and distillation to obtain benzylamine product.

[0057] Example 2: This embodiment is basically the same as Example 1, except that the target product of the continuous hydrogenation reaction is dibenzylamine.

[0058] In this embodiment, the catalyst preparation method, liquid phase raw material composition, raw material formulation method, system replacement method, and post-treatment method are all the same as in Example 1.

[0059] After the displacement is completed, the liquid feedstock and hydrogen are continuously fed into a fixed-bed tubular reactor packed with the catalyst for hydrogenation. The hydrogenation reaction temperature is controlled at 82°C, the hydrogenation reaction pressure at 7.2 MPa, and the liquid hourly space velocity at 0.3 h⁻¹. - ¹, The molar ratio of hydrogen to benzonitrile is 6:1.

[0060] The reaction effluent was subjected to gas-liquid separation, ammonia stripping, toluene recovery, and distillation to obtain dibenzylamine product.

[0061] Example 3: This embodiment is basically the same as Embodiment 2, except that the mass ratio of benzonitrile, toluene and liquid ammonia in the liquid phase raw materials is adjusted to 3:6:0.3.

[0062] Specifically, 210g of benzonitrile and 420g of toluene are added to a closed mixing vessel, stirred and mixed, and then 21g of liquid ammonia is added. The temperature of the mixing system is controlled to be below 50℃, and the mixture is stirred until the materials are evenly mixed to obtain liquid raw materials.

[0063] The catalyst preparation method, fixed-bed tubular reactor, system replacement method, and post-treatment method were all the same as in Example 2. The hydrogenation reaction temperature was controlled at 82°C, the hydrogenation reaction pressure at 7.2 MPa, and the liquid hourly space velocity at 0.3 h⁻¹. - ¹, Dibenzylamine was prepared by continuous hydrogenation with a molar ratio of hydrogen to benzonitrile of 6:1.

[0064] Example 4: This embodiment is basically the same as Embodiment 1, except that: ZSM-5 molecular sieve shaped particles are used instead of β molecular sieve shaped particles as the carrier; the nickel loading is calculated as 10 wt% of the final catalyst mass; the molar ratio of citric acid to nickel is 0.5:1; and the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium is 5 wt% of the mass of the NiO-containing molecular sieve precursor.

[0065] In this embodiment, the drying temperature after impregnation is 100℃ and the drying time is 12h; the calcination temperature is 450℃ and the calcination time is 4h; the in-situ hydrogen reduction temperature is 260℃ and the reduction time is 4h.

[0066] The composition of the liquid-phase feedstock, the feeding method, the system replacement method, and the post-treatment method were all the same as in Example 1. In the continuous hydrogenation reaction, the hydrogenation reaction temperature was controlled at 70°C, the hydrogenation reaction pressure at 6.0 MPa, and the liquid hourly space velocity at 0.6 h⁻¹. - ¹, with a molar ratio of hydrogen to benzonitrile of 8:1, benzylamine product was prepared.

[0067] Example 5: This embodiment is basically the same as Embodiment 2, except that: the nickel loading is calculated as 20 wt% of the final catalyst mass; the molar ratio of citric acid to nickel is 1.0:1; and the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium is 12 wt% of the mass of the NiO-containing molecular sieve precursor.

[0068] In this embodiment, the calcination temperature is 500℃ and the calcination time is 3h; the in-situ hydrogen reduction temperature is 300℃ and the reduction time is 3h.

[0069] The composition of the liquid-phase feedstock, the batching method, the system replacement method, and the post-treatment method were all the same as in Example 2. In the continuous hydrogenation reaction, the hydrogenation reaction temperature was controlled at 85°C, the hydrogenation reaction pressure at 7.5 MPa, and the liquid hourly space velocity at 0.3 h⁻¹. - ¹, Dibenzylamine was prepared by using a hydrogen to benzonitrile molar ratio of 6:1.

[0070] Comparative Example 1 The difference between this comparative example and Example 1 is that citric acid is not added during the catalyst preparation process. Instead, nickel nitrate hexahydrate is dissolved in deionized water to form a nickel salt impregnation solution, which is then used to impregnate the β-molecular sieve particles. The remaining catalyst preparation steps, liquid phase raw material composition, continuous hydrogenation reaction conditions, and post-treatment methods are the same as in Example 1.

[0071] Comparative Example 2 The difference between this comparative example and Example 1 is that, in the catalyst preparation process, the NiO-containing molecular sieve precursor is not grafted with 1-[3-(triethoxysilyl)propyl]-1H-imidazolium for modification, but is directly reduced in situ with hydrogen after calcination to obtain a supported nickel catalyst. The remaining catalyst preparation steps, liquid-phase raw material composition, continuous hydrogenation reaction conditions, and post-treatment methods are the same as in Example 1.

[0072] Comparative Example 3 The difference between this comparative example and Example 2 is that the catalyst prepared in Example 2 by nickel salt-citric acid complex impregnation, grafting modification, and in-situ hydrogen reduction from a molecular sieve support is not used. Instead, a commercially available fixed-bed molded framework nickel catalyst is used as the hydrogenation catalyst. The commercially available fixed-bed molded framework nickel catalyst is a 20-40 mesh granular catalyst with metallic nickel as the main active component and a nickel content of approximately 85 wt%. Before use, the catalyst storage solution is replaced with toluene, and the catalyst is activated at 120°C for 2 hours under a hydrogen atmosphere.

[0073] Except for the catalyst, the liquid phase feedstock composition, system replacement method, continuous hydrogenation reaction conditions, and post-treatment method are the same as in Example 2.

[0074] To verify the beneficial effects of the present invention, performance tests were conducted on the products obtained in the above embodiments and comparative examples.

[0075] Test method: 1. Product composition detection The contents of benzonitrile, benzylamine, dibenzylamine, tribenzylamine and other organic byproducts in the gas-liquid phase samples obtained during the stable operation phase of each embodiment and comparative example were detected by gas chromatography. The liquid phase samples were deaminated and diluted before detection.

[0076] During testing, a sample of the reaction solution after stable operation is taken, appropriately diluted, and then injected for analysis. The product content is calculated using the area normalization method; when precise yield calculation is required, the internal standard method can be used for correction.

[0077] 2. Calculation of benzonitrile conversion rate The conversion rate of benzonitrile is calculated according to the following formula: Benzonitrile conversion rate = (molar amount of benzonitrile consumed in the reaction / molar amount of benzonitrile fed) × 100%.

[0078] 3. Calculation of target product yield When the target product is benzylamine, the yield of benzylamine is calculated as the ratio of the actual molar amount of benzylamine produced to the theoretical molar amount of benzylamine produced by benzonitrile.

[0079] When the target product is dibenzylamine, the yield of dibenzylamine is calculated as the ratio of the actual molar amount of dibenzylamine produced to the theoretical molar amount of dibenzylamine produced by benzonitrile; theoretically, 2 mol of benzonitrile corresponds to 1 mol of dibenzylamine.

[0080] 4. Stable sampling operation All examples and comparative examples were run continuously for at least 8 hours after the reaction conditions stabilized, and samples were taken for analysis during the stable operation phase. Each group of samples was tested in parallel at least 3 times, and the average value was taken as the test result.

[0081] Test results: Table 1 Test Results

[0082] As shown in Table 1, and as illustrated in Examples 1 and 2, the modified supported nickel catalyst prepared by the method of this invention can selectively prepare benzylamine and dibenzylamine under the same benzonitrile, toluene, and liquid ammonia liquid-phase feedstock system and the same fixed-bed continuous hydrogenation reaction mode, simply by adjusting the hydrogenation reaction temperature, pressure, liquid hourly space velocity, and the molar ratio of hydrogen to benzonitrile. Specifically, in Example 1, the benzylamine content reached 99.6%, the dibenzylamine content was only 0.25%, and the tribenzylamine content was no higher than 0.03%; in Example 2, the dibenzylamine content reached 99.5%, the benzylamine content was only 0.30%, and the tribenzylamine content was no higher than 0.05%. These results demonstrate that the method of this invention not only improves the hydrogenation conversion rate of benzonitrile but also effectively controls the competitive relationship between the formation of primary amines, secondary amines, and further over-alkylation side reactions during the hydrogenation process of benzonitrile.

[0083] Furthermore, a comparison between Example 2 and Comparative Example 3 shows that, under the conditions for dibenzylamine preparation, when using a commercially available fixed-bed molded framework nickel catalyst, the dibenzylamine content was 94.8% and the tribenzylamine content was 1.10%; while when using the modified supported nickel catalyst of this invention, the dibenzylamine content increased to 99.5%, and the tribenzylamine content decreased to no more than 0.05%. In other words, this invention not only increases the content of the target product, dibenzylamine, but also significantly reduces the generation of excessive alkylation byproducts such as tribenzylamine. Since both dibenzylamine and tribenzylamine are high-boiling-point amine compounds, their separation during subsequent distillation is difficult. Reducing the tribenzylamine content can significantly alleviate the burden of post-processing, improve product purification efficiency, and reduce product quality fluctuations caused by byproduct accumulation.

[0084] A comparison of Example 1 and Comparative Example 1 shows that without citric acid complex impregnation, the benzonitrile conversion rate decreased from 99.8% to 97.8%, the benzylamine content decreased from 99.6% to 96.7%, while the dibenzylamine content increased to 2.10% and the tribenzylamine content increased to 0.35%. This result indicates that citric acid complex impregnation is not merely an auxiliary step in catalyst preparation, but rather improves the dispersion of nickel species on the molecular sieve support, enabling the nickel active centers to maintain good hydrogenation activity and selectivity during continuous hydrogenation, thereby reducing the formation of byproducts caused by uneven local activity or stalled reactions.

[0085] A comparison of Example 1 and Comparative Example 2 shows that without 1-[3-(triethoxysilyl)propyl]-1H-imidazolium graft modification, the benzylamine content decreased from 99.6% to 97.2%, the dibenzylamine content increased to 1.85%, and the tribenzylamine content increased to 0.42%. This result indicates that imidazolium silane graft modification can regulate the acid-base environment on the catalyst surface and within the pores, improving the adsorption and desorption behavior of the imine intermediate, benzylamine, and dibenzylamine on the catalyst surface during benzonitrile hydrogenation, thereby inhibiting further condensation or excessive alkylation of benzylamine to form tribenzylamine.

[0086] The results of Examples 1 and 2, and Comparative Examples 1 and 2, show that the "nickel salt-citric acid complex impregnation" and "imidazolium silane grafting modification" in this invention have a synergistic effect. The former is beneficial for improving the dispersion of the nickel active component, while the latter is beneficial for adjusting the catalyst surface and pore environment. The combination of the two results in a catalyst that not only exhibits high benzonitrile hydrogenation activity but also allows for more precise control of the reaction pathway. Therefore, under the first reaction conditions, the reaction can mainly stop at the benzylamine formation stage; under the second reaction conditions, the reaction can promote the formation of dibenzylamine while inhibiting the further conversion of dibenzylamine into byproducts such as tribenzylamine.

[0087] As shown in Example 3, in the dibenzylamine preparation mode, adjusting the mass ratio of benzonitrile, toluene, and liquid ammonia from 3:6:1 to 3:6:0.3 further increases the dibenzylamine content to 99.6%, reduces the benzylamine content to 0.20%, and maintains the tribenzylamine content at a level not exceeding 0.05%. This result indicates that the amount of liquid ammonia used can be coordinated with the second reaction conditions to regulate the competitive formation relationship between benzylamine and dibenzylamine; simultaneously, the catalyst of this invention can effectively suppress the formation of deep byproducts such as tribenzylamine even under conditions that promote dibenzylamine formation.

[0088] As can be seen from Examples 4 and 5, high benzonitrile conversion and target product selectivity can still be obtained by changing the molecular sieve support, nickel loading, citric acid dosage, grafting agent dosage, calcination temperature, and reduction temperature. Specifically, the benzylamine content in Example 4 was 99.0%, the dibenzylamine content in Example 5 was 99.3%, and the tribenzylamine content remained at a low level. These results demonstrate that the technical solution of this invention has good applicability within the range of catalyst composition and process parameters defined in the claims, and does not rely solely on a single specific implementation parameter to achieve the target effect.

[0089] In summary, the key advantages of this invention are: under continuous hydrogenation conditions, by combining a specific modified supported nickel catalyst with the reaction conditions, it not only achieves highly selective preparation of benzylamine or dibenzylamine, but also significantly reduces the formation of difficult-to-separate byproducts such as tribenzylamine. Compared with conventional fixed-bed molded framework nickel catalysts, the catalyst of this invention exhibits better reaction pathway control and byproduct suppression capabilities, which is beneficial for improving product purity, reducing post-processing difficulty, and improving the stability of continuous production processes.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for the continuous hydrogenation preparation of benzylamine compounds, characterized in that, Includes the following steps: The molecular sieve support was contacted with a nickel salt-citric acid complex impregnation solution, and then dried and calcined to obtain a NiO-containing molecular sieve precursor. The NiO-containing molecular sieve precursor was grafted with 1-[3-(triethoxysilyl)propyl]-1H-imidazolium to obtain a modified nickel-based catalyst precursor. The modified nickel-based catalyst precursor was reduced in situ with hydrogen to obtain a modified supported nickel catalyst. Benzonitrile, toluene, and liquid ammonia were formulated into a liquid-phase feedstock. The liquid feedstock and hydrogen are continuously fed into a reactor packed with the modified supported nickel catalyst for a hydrogenation reaction. Specifically, when the target product is benzylamine, the hydrogenation reaction is controlled to proceed under the first reaction conditions; when the target product is dibenzylamine, the hydrogenation reaction is controlled to proceed under the second reaction conditions.

2. The method according to claim 1, characterized in that, The molecular sieve support is selected from one of the following: β molecular sieve, ZSM-5 molecular sieve, Y-type molecular sieve, MCM-41 molecular sieve, and SBA-15 molecular sieve.

3. The method according to claim 1, characterized in that, The nickel salt is one of nickel nitrate, nickel acetate, and nickel chloride; the nickel loading in the catalyst is 5-30 wt% based on metallic nickel; the molar ratio of citric acid to nickel is (0.3-1.5):

1.

4. The method according to claim 1, characterized in that, The molecular sieve carrier is contacted with the nickel salt-citric acid complex impregnation solution by equal volume impregnation, ultrasonic impregnation, or excessive impregnation; the drying temperature is 80-120℃, and the drying time is 6-12h; the calcination temperature is 450-500℃, and the calcination time is 2-6h.

5. The method according to claim 1, characterized in that, The grafting modification is carried out in anhydrous toluene, the amount of 1-[3-(triethoxysilyl)propyl]-1H-imidazolium is 2-20 wt% of the mass of the NiO-containing molecular sieve precursor, the grafting modification temperature is 90-115℃, and the grafting modification time is 4-12 h.

6. The method according to claim 1, characterized in that, The in-situ reduction of hydrogen is carried out at a temperature of 250-320℃ for 2-8 hours.

7. The method according to claim 1, characterized in that, The mass ratio of benzonitrile, toluene and liquid ammonia is (2-4):(5-8):(0.05-1.5).

8. The method according to claim 1, characterized in that, The reactor is a fixed-bed tubular reactor. Before the liquid raw material and hydrogen are introduced into the reactor, the feeding system and the reaction system are purged with nitrogen and hydrogen, respectively. After gas-liquid separation, the hydrogen in the gas phase is returned to the reactor for recycling, and the liquid phase is separated by ammonia stripping, solvent recovery and distillation to obtain benzylamine or dibenzylamine products.

9. The method according to claim 1, characterized in that, The first reaction conditions include: a hydrogenation reaction temperature of 65-80℃, a hydrogenation reaction pressure of 5.5-7.0 MPa, and a liquid hourly space velocity of 0.2-2.0 h⁻¹. -1 The molar ratio of hydrogen to benzonitrile is (3-20):

1.

10. The method according to claim 1, characterized in that, The second reaction conditions include: a hydrogenation reaction temperature of 75-95℃, a hydrogenation reaction pressure of 6.5-8.5 MPa, and a liquid hourly space velocity of 0.1-1.5 h⁻¹. - ¹, The molar ratio of hydrogen to benzonitrile is (3-15):1.

Images