Method for preparing cyclohexyl formic acid through benzoic acid fixed bed catalytic hydrogenation

Abstract

The invention provides a method for preparing cyclohexyl formic acid through benzoic acid fixed bed catalytic hydrogenation. The method comprises the steps of raw material liquid preparation, catalytic hydrogenation, gas-liquid separation, solvent removal and purification rectification. Wherein a catalyst used for catalytic hydrogenation comprises a carrier and active metal loaded on the carrier, and the hydroxyl density of the surface of the carrier is less than or equal to 5 mu mol / g. The hydrogenation catalyst has ultrahigh hydrogenation activity and cyclohexyl formic acid selectivity, and can inhibit esterification reaction between an alcohol solvent and benzoic acid and cyclohexyl formic acid. The method provided by the invention not only realizes efficient preparation of cyclohexyl formic acid hydrogenation, greatly reduces the device construction cost and the operation cost, but also remarkably improves the intrinsic safety attribute of the process, obtains extremely high cyclohexyl formic acid yield, and has excellent economic benefits and industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis, and more specifically, to a method for preparing cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid. Background Technology

[0002] Cyclohexylcarboxylic acid is an important intermediate in organic synthesis. It serves not only as a raw material for the synthesis of photoinitiator 184, caprolactam, the anti-pregnancy drug 392, and the novel schistosomiasis treatment drug praziquantel, but also directly as a compatibilizer for vulcanized rubber and a petroleum clarifying agent. Derivatives of cyclohexylcarboxylic acid, such as methyl cyclohexylcarboxylate and trans-4-isopropylcyclohexylcarboxylic acid, are also important intermediates in the synthesis of many chemical products and pharmaceuticals.

[0003] Currently, there are more than twenty methods for preparing cyclohexylcarboxylic acid, mainly including: cyclohexylcarboxaldehyde oxidation, DA reaction, Grignard reagent method, benzoic acid catalytic hydrogenation, cyclohexene addition method, and method using cyclohexanone as a raw material. The one-step hydrogenation method of benzoic acid to prepare cyclohexylcarboxylic acid has advantages in many aspects such as atom economy and environmental protection. However, existing one-step hydrogenation methods of benzoic acid mainly adopt batch reactor processes, resulting in low conversion rate, low selectivity, easy loss of precious metal catalysts, and complex operation. These methods also have drawbacks in terms of safety, operating cost, processing cost, and processing capacity.

[0004] For example, Chinese patent CN107365251A discloses a method for preparing cyclohexanecarboxylic acid, using a nickel-aluminum-iron-copper alloy treated with alkali as the catalyst and a batch reactor. Chinese patent CN1749234A discloses a new method for the hydrogenation of benzoic acid to synthesize cyclohexylcarboxylic acid. Benzoic acid, in the presence of a supported transition metal rhodium catalyst, is synthesized using a batch reactor with supercritical carbon dioxide and cyclohexylcarboxylic acid solvent under mild reaction conditions through a cyclocatalytic reaction with hydrogen. Chinese patent CN 209005708U discloses a tower reactor for the synthesis of cyclohexylcarboxylic acid. Compared to existing batch preparation processes, represented by batch reactions, continuous flow hydrogenation processes have significant advantages in terms of safety, operating costs, processing costs, and processing capacity.

[0005] Currently, the continuous flow hydrogenation process of benzoic acid based on a fixed-bed system has two key aspects: continuous feed and a highly active catalyst. Continuous feed of benzoic acid can be achieved through melt feed or dissolution feed. Benzoic acid has a melting point of 122℃. To ensure stable operation, the feed temperature is appropriately higher than this melting point. Furthermore, the hydrogenation reaction is highly exothermic, ultimately leading to a dramatic increase in reaction temperature. This results in a severe aggravation of side reactions, primarily decarboxylation, significantly reducing the selectivity and yield of the product cyclohexanecarboxylic acid, and consequently decreasing technical and economic efficiency.

[0006] Compared to melt feed, dissolve feed allows for continuous feeding at relatively lower temperatures, making the search for a suitable solvent to improve solubility crucial. Chinese patent CN111217695A discloses a method for the continuous synthesis of cyclohexylcarboxylic acid, using cyclohexylcarboxylic acid as the solvent and a benzoic acid and cyclohexylcarboxylic acid emulsion as the reaction feed. Chinese patent CN 114433164A discloses a fixed-bed catalytic hydrogenation method for benzoic acid to cyclohexylcarboxylic acid, using any one of 1,4-dioxane, o-dichlorobenzene, N-methylpyrrolidone, cyclohexylcarboxylic acid, and acetone as the solvent.

[0007] In the aforementioned existing technologies, cyclohexane carboxylic acid has low solubility for benzoic acid, resulting in excessively high energy consumption in the subsequent separation system when used as a solvent, leading to poor technical and economic efficiency. When ethyl acetate, 1,4-dioxane, N-methylpyrrolidone, or acetone are used as solvents, the hydrogenation and deoxygenation side reactions of the solvents occur violently, also resulting in poor technical and economic efficiency.

[0008] Therefore, how to select a more suitable solvent and catalyst system, and based on a dissolution-feed method, to provide a fixed-bed catalytic hydrogenation method for the preparation of cyclohexylformic acid from benzoic acid, so that benzoic acid can be catalytically hydrogenated to cyclohexylformic acid with high conversion and high selectivity, is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0009] The main objective of this invention is to provide a method for preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, in order to solve the problems of low benzoic acid conversion, low selectivity and poor techno-economic efficiency caused by unsatisfactory solvent, catalyst system and reaction conditions in the existing fixed-bed catalytic hydrogenation method for benzoic acid.

[0010] To achieve the above objectives, the present invention provides a method for preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, comprising: step S1, preparation of feed solution: dissolving benzoic acid in an alcohol solvent to obtain a feed solution; step S2, catalytic hydrogenation: the feed solution enters a fixed-bed reactor packed with a catalyst for catalytic hydrogenation to obtain a reactant; step S3, gas-liquid separation: the reactant enters a gas-liquid separator for gas-liquid separation to obtain a separated material and unreacted hydrogen; step S4, solvent removal: the separated material enters a solvent removal tower for solvent removal to obtain a solvent-removed material and a solvent removed; step S5, purification distillation: the solvent-removed material enters a distillation tower to obtain cyclohexylcarboxylic acid; the alcohol solvent is selected from one or more C1-C8 alcohols; the catalyst comprises a support and an active metal supported thereon, and the hydroxyl density on the surface of the support is ≤5 μmol / g.

[0011] Further, the alcohol solvent is a monohydric alcohol and / or a polyhydric alcohol; preferably, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-butanol, isobutanol, n-hexanol and isooctanol; more preferably, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-hexanol and isooctanol; even more preferably, the alcohol solvent is methanol and n-propanol, and the volume ratio of methanol to n-propanol is 1:(1.8-2.0).

[0012] Furthermore, the carrier is selected from one or more of activated carbon, alumina, silicon dioxide, titanium dioxide, and zirconium oxide.

[0013] Further, the active metal is selected from one or more of nickel, cobalt, ruthenium, palladium, platinum and rhodium; preferably, the active metal is rhodium and platinum, and the weight ratio of rhodium to platinum is 1:(3-5).

[0014] Furthermore, the loading of the active metal in the catalyst is 0.5–20 wt%.

[0015] Further, the alcohol solvent is methanol, the catalyst is Pd / Al2O3, and the Pd loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the Al2O3 support surface is 0.50–0.55 μmol / g; and / or, the alcohol solvent is n-hexanol, the catalyst is Pt / SiO2, and the Pt loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the SiO2 support surface is 4.3–4.5 μmol / g; and / or, the alcohol solvent is isooctanol, the catalyst is Rh-Pt / Al2O3-SiO2, and the Rh loading in the catalyst is 0.10–0.12 wt%, the Pt loading is 0.40–0.45 wt%, and the hydroxyl density on the Al2O3-SiO2 support surface is 2.6–3.0 μmol / g.

[0016] Furthermore, in step S1, the mass concentration of benzoic acid in the raw material solution is 5-60%.

[0017] Furthermore, in step S1, the preparation of the raw material liquid is carried out under heating conditions, and the heating temperature is 30-60℃.

[0018] Further, in step S2, the reaction conditions for catalytic hydrogenation are: a reaction temperature of 60–180 °C; and / or a reaction pressure of 1.0–10.0 MPa; and / or a molar ratio of benzoic acid to hydrogen of 1:(6–18); and / or a weight hourly space velocity of 0.1–1.0 h⁻¹. -1 .

[0019] Furthermore, step S3 also includes returning unreacted hydrogen to step S2 for catalytic hydrogenation, and step S4 also includes returning the desolventized hydrogen to step S1 for feedstock preparation.

[0020] By applying the technical solution of this invention, and addressing the poor solubility of benzoic acid, an alcohol solvent system is employed, along with a corresponding catalyst system comprising a support with a specific surface hydroxyl density. Utilizing the provided alcohol solvent and catalyst system, a continuous-flow hydrogenation process based on fixed-bed benzoic acid is achieved for the efficient preparation of cyclohexylformic acid via a dissolution-feed method. The method provided by this invention not only achieves efficient continuous-flow hydrogenation of cyclohexylformic acid with high conversion and high selectivity, significantly reducing the construction and operating costs of related equipment, but also significantly improves the intrinsic safety properties of the preparation process, demonstrating superior economic benefits and promising industrial application prospects. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 The process flow diagram for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid provided by the present invention is shown. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0024] As described in the background section, existing technologies suffer from low benzoic acid conversion, low selectivity, and poor techno-economic efficiency due to unsatisfactory solvent, catalyst system, and reaction conditions in the fixed-bed catalytic hydrogenation of benzoic acid. To address these technical problems, this invention provides a method for preparing cyclohexylcarboxylic acid via fixed-bed catalytic hydrogenation of benzoic acid, comprising: Step S1, preparation of the feed solution: dissolving benzoic acid in an alcohol solvent to obtain a feed solution; Step S2, catalytic hydrogenation: the feed solution enters a fixed-bed reactor packed with a catalyst for catalytic hydrogenation to obtain a reactant; Step S3, gas-liquid separation: the reactant enters a gas-liquid separator for gas-liquid separation to obtain a separated material and unreacted hydrogen; Step S4, solvent removal: the separated material enters a solvent removal tower for solvent removal to obtain a solvent-removed material and the removed solvent; Step S5, purification distillation: the solvent-removed material enters a distillation tower to obtain cyclohexylcarboxylic acid; the alcohol solvent is selected from one or more C1-C8 alcohols; the catalyst comprises an active metal and a support, and the hydroxyl density on the support surface is ≤5 μmol / g.

[0025] The present invention provides a fixed-bed catalytic hydrogenation method for the preparation of cyclohexylformic acid from benzoic acid. This method addresses the problem of poor solubility of benzoic acid in conventional organic solvents by employing an alcohol solvent system and introducing a catalyst supported on a carrier with a specific surface hydroxyl density. Through a dissolution-feed method, continuous flow hydrogenation of benzoic acid based on a fixed bed is achieved, thereby realizing the efficient production of cyclohexylformic acid.

[0026] This method utilizes C1-C8 alcohols as solvents to achieve continuous dissolution and feeding of benzoic acid in a fixed bed. Alcohols are excellent solvents for benzoic acid, being inexpensive and readily available. Furthermore, compared to existing technologies that rely on fixed-bed catalytic hydrogenation of benzoic acid and commonly use solvents such as esters, ketones, or 1,4-dioxanes, alcohols are better suited to the solubility of benzoic acid, thus more effectively meeting the reaction requirements for dissolution and feeding. However, in contrast to their excellent solubility, alcohols inevitably undergo esterification reactions with benzoic acid and cyclohexanecarboxylic acid under reaction conditions, leading to a decrease in product yield. This is a technical problem that is difficult to solve in existing technologies. Based on the technical solution containing alcohol solvents provided by this invention, the inventors have creatively provided a catalyst system comprising both an active metal and a support, wherein the hydroxyl density on the surface of the support in this catalyst system is ≤5 μmol / g. It has been found that a catalyst support with this hydroxyl density can significantly inhibit the esterification reaction of alcohol solvents during the catalytic hydrogenation of benzoic acid. This may be attributed to the fact that the hydroxyl groups on the support surface are acidic and act as catalysts for the esterification reaction between alcohol solvents and benzoic acid and cyclohexanecarboxylic acid. Based on the above-mentioned alcohol solvent system and the catalyst system containing a support with a specific surface hydroxyl density, the efficient fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylcarboxylic acid has been successfully achieved via a dissolution-feed method.

[0027] In several typical embodiments, the hydroxyl density on the catalyst support surface is 0.5–1.5 μmol / g. Through extensive experimentation, the inventors discovered that when the hydroxyl density on the catalyst support surface is within this range, even when benzoic acid is dissolved in an alcohol solvent at a high concentration and fed into the catalyst, the esterification reaction can be more effectively suppressed, resulting in higher selectivity for cyclohexylcarboxylic acid. Simultaneously, the amount of active metal supported on the catalyst does not exceed 0.5 wt%, enabling highly selective catalytic hydrogenation of benzoic acid to cyclohexylcarboxylic acid at a lower cost.

[0028] Further, the preparation method of the catalyst support includes: (1) dissolving the support source in a first solvent at a molar concentration of 0.01-0.1 mol / L under a humidity range of 0-12% RH to obtain a first mixed solution; (2) adding an alkali source to the first mixed solution to obtain a second mixed solution; (3) placing the second mixed solution in a crystallization kettle and crystallizing to obtain a first solid; (4) drying the first solid to obtain the support; in the second mixed solution, the molar concentration ratio of the support source to the alkali source is 1:(0.3-2); the crystallization conditions are 120-200℃. The inventors designed the preparation method of the support through a large number of experiments and optimized the various conditions involved, and finally obtained the above preparation method. The catalyst support prepared by this method can better meet the requirement of hydroxyl density on the support surface ≤5μmol / g, thereby effectively inhibiting the esterification reaction of alcohol solvents in the catalytic hydrogenation of benzoic acid and improving the conversion rate of cyclohexylcarboxylic acid.

[0029] In several preferred embodiments, the catalyst support is prepared under a humidity range of 5–10% RH. The inventors optimized the humidity conditions through extensive experiments and found that preparing the catalyst support under these conditions significantly reduced the introduction of water, resulting in a surface hydroxyl density of 0.5–1.5 μmol / g for the final catalyst support, thereby further enhancing the selectivity of cyclohexylcarboxylic acid.

[0030] Furthermore, the carrier source is selected from one or more of tetraethyl silicate, aluminum isopropoxide, tetraethyl titanate, and tetraethyl zirconate; the alkali source is selected from one or more of urea, ammonia, and ammonia gas; and the first solvent is selected from anhydrous ethanol and / or isopropanol.

[0031] The alcohol solvent used in the solution provided by this invention is further selected from monohydric alcohols and / or polyhydric alcohols. In several preferred embodiments, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-butanol, isobutanol, n-hexanol, and isooctanol. The inventors have optimized the above-mentioned alcohol solvents through extensive experiments. Compared with other types of C1-C8 monohydric alcohols and / or polyhydric alcohols in the art, these alcohols can better dissolve benzoic acid and are better compatible with the catalyst system provided by this invention, thus the esterification reaction is more effectively suppressed, and ultimately the selectivity of cyclohexylcarboxylic acid is improved. In several more preferred embodiments, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-hexanol, and isooctanol. Through extensive experiments and comparisons, the inventors have further optimized these alcohol solvents based on the above-mentioned alcohol solvents and found that when these alcohols are used as solvents for benzoic acid, catalytic results with higher selectivity for cyclohexylcarboxylic acid can be obtained. More preferably, the alcohol solvent is methanol and n-propanol, and the volume ratio of methanol to n-propanol is 1:(1.8 to 2.0). Based on the above, the inventors compounded the two alcohol solvents and further optimized their type, combination and ratio, and found that under this condition, the selectivity of cyclohexylcarboxylic acid is higher.

[0032] In several preferred embodiments, the support is selected from one or more of activated carbon, alumina, silicon dioxide, titanium dioxide, and zirconium oxide. Theoretically, the type of support is not limited to these; conventional active metal supports in the art can be selected as needed. However, for the catalytic system provided by this invention, the inventors, through extensive experiments and comparisons, have found that the aforementioned supports are more effective in reacting with benzoic acid using alcohols as solvents, dissolving the feed and catalytically hydrogenating it via a fixed bed. They also facilitate control of the hydroxyl density on the surface, thereby more effectively inhibiting esterification reactions and comprehensively improving the conversion rate of benzoic acid and the selectivity of cyclohexylcarboxylic acid.

[0033] In the catalyst system included in the method provided by the present invention, preferably, the active metal is selected from one or more of nickel, cobalt, ruthenium, palladium, platinum and rhodium. Based on the above-mentioned active metals, the inventors conducted a large number of experiments and in a preferred embodiment preferred rhodium and platinum as the active metals, and the weight ratio of rhodium to platinum is 1:(3-5). That is, by combining the two active metals, higher catalytic efficiency is achieved in a bimetallic synergistic manner, and the selectivity of cyclohexylcarboxylic acid is also improved simultaneously.

[0034] Furthermore, the loading of the active metal in the catalyst is 0.5–20 wt%. Theoretically, there is a positive correlation between the amount of active metal in the catalyst and the catalytic efficiency. However, if the amount of active metal is too large, the production cost will increase accordingly, which is not conducive to improving the added value of cyclohexylcarboxylic acid. Therefore, the inventors screened the loading of the active metal through a large number of experiments and optimized the range of 0.5–20 wt%, finding that within this range, efficient hydrogenation of benzoic acid can be achieved at a lower cost. The minimum loading of the active metal can be as low as 0.5 wt%, effectively reducing the cost.

[0035] In several typical embodiments, the alcohol solvent is methanol, the catalyst is Pd / Al2O3, and the Pd loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the Al2O3 support surface is 0.50–0.55 μmol / g; and / or, the alcohol solvent is n-hexanol, the catalyst is Pt / SiO2, and the Pt loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the SiO2 support surface is 4.3–4.5 μmol / g; and / or, the alcohol solvent is isooctanol, the catalyst is Rh-Pt / Al2O3-SiO2, and the Rh loading in the catalyst is 0.10–0.12 wt%, the Pt loading is 0.40–0.45 wt%, and the hydroxyl density on the Al2O3-SiO2 support surface is 2.6–3.0 μmol / g. The inventors further screened and combined the solvent and catalyst systems in the method of fixed-bed catalytic hydrogenation of benzoic acid to prepare cyclohexylcarboxylic acid, and optimized the above-mentioned schemes through a large number of experiments. The alcohol solvent type, active metal type and hydroxyl density on the support surface can be better matched. Using these schemes to catalytically hydrogenate benzoic acid, experimental results were obtained with higher benzoic acid conversion rate and cyclohexylcarboxylic acid selectivity.

[0036] The feed concentration of benzoic acid is one of the important parameters in its fixed-bed catalytic hydrogenation technology, affecting not only product distribution and the temperature operation of the apparatus, but also the energy consumption and economy of the reaction itself. In the method provided by this invention, the inventors optimized the feed concentration of benzoic acid, i.e., the mass concentration of benzoic acid in the feed solution, through extensive experiments. In several typical experimental methods, it was found that in step S1, when the mass concentration of benzoic acid in the feed solution is 5-60%, the yield of cyclohexylcarboxylic acid is higher, and the cost of the catalytic hydrogenation reaction is also lower.

[0037] Based on the above technical solution, in order to improve the solubility of benzoic acid in alcohol solvents and achieve a higher benzoic acid mass concentration in the raw material solution, the preparation of the raw material solution in step S1 is further carried out under heating conditions, and the heating temperature is 30-60℃. Through extensive experiments, the inventors optimized the heating temperature during the preparation of the raw material solution, i.e., the dissolution process of benzoic acid in alcohol solvents, and found that a temperature of 30-60℃ achieves better dissolution results and effectively avoids potential esterification reactions during this process, thereby further improving the yield and selectivity of cyclohexylcarboxylic acid.

[0038] In several typical embodiments, the reaction conditions for catalytic hydrogenation in step S2 are: a reaction temperature of 60–180 °C; and / or a reaction pressure of 1.0–10.0 MPa; and / or a molar ratio of benzoic acid to hydrogen of 1:(6–18); and / or a weight hourly space velocity of 0.1–1.0 h⁻¹. -1 In the process of preparing cyclohexylcarboxylic acid by hydrogenation of benzoic acid, in addition to the main reaction of benzene ring hydrogenation, there may be further hydrogenation of cyclohexylcarboxylic acid to cyclohexylmethanol, further hydrogenation of cyclohexylmethanol to methylcyclohexane, hydrogenation and cracking of methylcyclohexane to methane and cyclohexane, hydrogenation of benzoic acid to benzyl alcohol, further hydrogenation of benzyl alcohol to toluene, and hydrogenation and cracking of toluene to methane and benzene. Furthermore, there is also an esterification reaction between benzoic acid and cyclohexylcarboxylic acid with the solvent ethanol. The occurrence of these side reactions will affect the final selectivity and yield of the products. Therefore, for the reaction system provided in this invention, the inventors systematically investigated and optimized the reaction temperature, reaction pressure, molar ratio of benzoic acid to hydrogen (i.e., DA / H2 molar ratio), and weight hourly space velocity during the catalytic hydrogenation process through numerous experiments, and found that under the above conditions, a higher yield of cyclohexylcarboxylic acid can be obtained at a lower cost.

[0039] Furthermore, step S3 also includes returning unreacted hydrogen to step S2 for catalytic hydrogenation, thereby further reducing costs and improving hydrogen utilization. More preferably, step S4 also includes returning the removed solvent to step S1 for feedstock preparation, so as to facilitate solvent recovery and improve economic value.

[0040] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0042] Hydroxyl density test on catalyst support surface

[0043] The determination was performed using a Micrometrics AutoChem 2910 chemisorption analyzer (USA). 1.0 g of sample was accurately weighed and placed in a sample tube. After treatment at 600 °C under a helium atmosphere for 1.0 h, the temperature was lowered to 100 °C, and ammonia gas was introduced. Once adsorption saturation was achieved, the temperature was increased to 600 °C at a rate of 20 °C / min. The corresponding NH3 desorption signal was detected by a TCD to obtain the ammonia desorption amount. The ammonia desorption amount, converted to μmol, was then used as the surface hydroxyl density of the sample.

[0044] Example 1

[0045] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0046] 1. Preparation of catalyst support:

[0047] (1) Under 5% RH humidity conditions, weigh aluminum isopropoxide and dissolve it in isopropanol to make the concentration of aluminum isopropoxide in the resulting solution reach 0.1 mol / L, heat to 45℃, and stir until completely dissolved;

[0048] (2) Slowly add pre-ground urea to the isopropanol solution of aluminum isopropoxide until the urea concentration reaches 0.05 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a stainless steel crystallization kettle lined with polytetrafluoroethylene.

[0049] (3) The stainless steel crystallization kettle was placed in an oven at 150°C and crystallized for 36 hours. After being taken out and allowed to cool naturally to room temperature, the material was taken out and the solid sample obtained by filtration was placed in an oven at 120°C and dried for 2 days to obtain the Al2O3 support required for the preparation of the catalyst.

[0050] (4) The hydroxyl density on the surface of the Al2O3 support was determined by ammonia desorption (NH3-TPD) to be 0.5 μmol / g.

[0051] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0052] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent methanol are mixed at a ratio of 6:4 (mass ratio), heated to 60°C to dissolve completely, and the raw material solution is prepared.

[0053] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Pd / Al2O3 catalyst with a Pd loading of 0.5 wt% (Al2O3 was prepared in step 1, and its surface hydroxyl density was 0.5 μmol / g). Hydrogenation was carried out at a temperature of 60 °C, a hydrogen pressure of 3 MPa, and a weight hourly space velocity of 0.5 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 6 to complete the catalytic hydrogenation reaction;

[0054] (3) Hydrogen circulation: The reacted material enters the gas-liquid separator to separate hydrogen from the liquid phase, and the hydrogen enters step (2) for circulation;

[0055] (4) Solvent circulation: The liquid material flowing out of the gas-liquid separator enters the solvent removal tower to remove the solvent, and the solvent enters step (1) for circulation;

[0056] (5) Purification and separation of cyclohexylcarboxylic acid: The material after solvent removal enters the distillation column to achieve purification and separation of cyclohexylcarboxylic acid, and obtain the finished product cyclohexylcarboxylic acid.

[0057] The relevant process flow is shown below. Figure 1 .

[0058] Example 2

[0059] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0060] 1. Preparation of catalyst support:

[0061] (1) Under 10% RH humidity conditions, weigh out tetraethyl silicate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl silicate in the resulting solution reach 0.05 mol / L. Control the temperature at 35℃ and stir until completely dissolved.

[0062] (2) Slowly add pre-ground urea to the above solution until the urea concentration reaches 0.1 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a stainless steel crystallization kettle lined with polytetrafluoroethylene.

[0063] (3) Place the stainless steel crystallization kettle in a 120℃ oven and crystallize for 24 hours. After crystallization, take it out and let it cool naturally to room temperature. Then take out the material and filter it. Place the solid sample obtained in a 120℃ oven and dry it for 1 day to obtain the SiO2 support required for the preparation of the catalyst.

[0064] (4) The hydroxyl density on the surface of the SiO2 support was determined by ammonia desorption (NH3-TPD) to be 1.5 μmol / g.

[0065] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0066] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent ethanol are mixed in a ratio of 5:5 (mass ratio), heated to 55°C to dissolve completely, and the raw material solution is prepared.

[0067] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Ni / SiO2 catalyst with a Ni loading of 20 wt% (SiO2 was prepared in step 1, and its surface hydroxyl density was 1.5 μmol / g). Hydrogenation was carried out at a temperature of 180 °C, a hydrogen pressure of 10 MPa, and a weight hourly space velocity of 0.1 h⁻¹. -1The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 18, completing the catalytic hydrogenation reaction;

[0068] Steps (3) to (5) are the same as in Example 1.

[0069] Example 3

[0070] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0071] 1. Preparation of catalyst support:

[0072] (1) Under 11% RH humidity conditions, weigh out tetraethyl titanate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl titanate in the resulting solution reach 0.03 mol / L. Control the temperature at 30℃ and stir until completely dissolved.

[0073] (2) Slowly add pre-ground urea to the above solution until the urea concentration reaches 0.05 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a polytetrafluoroethylene-lined stainless steel crystallization kettle.

[0074] (3) The stainless steel crystallization kettle was placed in an oven at 140℃ and crystallized for 36 hours. After being taken out and allowed to cool naturally to room temperature, the material was taken out and the solid sample obtained by filtration was placed in an oven at 140℃ and dried for 1 day to obtain the TiO2 support required for the preparation of the catalyst.

[0075] (4) The hydroxyl density on the surface of the TiO2 support was determined to be 2.2 μmol / g by ammonia-induced desorption (NH3-TPD).

[0076] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0077] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent n-propanol are mixed at a ratio of 1:2 (mass ratio), heated to 50°C to dissolve completely, and the raw material solution is prepared.

[0078] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Co / TiO2 catalyst with a Co loading of 10 wt% (TiO2 was prepared in step 1, and its surface hydroxyl density was 2.2 μmol / g). Hydrogenation was carried out at a temperature of 160 °C, a hydrogen pressure of 9 MPa, and a weight hourly space velocity of 0.2 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 10 to complete the catalytic hydrogenation reaction;

[0079] Steps (3) to (5) are the same as in Example 1.

[0080] Example 4

[0081] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0082] 1. Preparation of catalyst support:

[0083] (1) Under 12% RH humidity conditions, weigh out tetraethyl zirconate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl silicate in the resulting solution reach 0.03 mol / L. Control the temperature at 40℃ and stir until completely dissolved.

[0084] (2) Slowly add pre-ground urea to the above solution until the urea concentration reaches 0.02 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a polytetrafluoroethylene-lined stainless steel crystallization kettle.

[0085] (3) Place the stainless steel crystallization kettle in a 160℃ oven and crystallize for 36 hours. After crystallization, take it out and let it cool naturally to room temperature. Then take out the material and filter it. Place the solid sample obtained in a 120℃ oven and dry it for 1 day to obtain the ZrO2 support required for the preparation of the catalyst.

[0086] (4) The hydroxyl density on the surface of the ZrO2 support was determined by ammonia desorption (NH3-TPD) at elevated temperature.

[0087] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0088] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent n-butanol are mixed in a ratio of 3:7 (mass ratio), heated to 55°C to dissolve completely, and the raw material solution is prepared.

[0089] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Ru / ZrO2 catalyst with a Ru loading of 1.0 wt% (ZrO2 was prepared in step 1, and its surface hydroxyl density = 3.6 μmol / g), and hydrogen was added at a temperature of 100 °C, a hydrogen pressure of 8 MPa, and a weight hourly space velocity of 1.0 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 9 to complete the catalytic hydrogenation reaction;

[0090] Steps (3) to (5) are the same as in Example 1.

[0091] Example 5

[0092] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0093] 1. Preparation of catalyst support:

[0094] (1) Under 12% RH humidity conditions, weigh out tetraethyl silicate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl silicate in the resulting solution reach 0.05 mol / L. Control the temperature at 30℃ and stir until completely dissolved.

[0095] (2) Slowly add 25% ammonia water to the above solution until the ammonia concentration reaches 0.05 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a polytetrafluoroethylene-lined stainless steel crystallization kettle.

[0096] (3) Place the stainless steel crystallization kettle in a 120℃ oven and crystallize for 24 hours. After crystallization, take it out and let it cool naturally to room temperature. Then take out the material and filter it. Place the solid sample obtained in a 120℃ oven and dry it for 1 day to obtain the SiO2 support required for the preparation of the catalyst.

[0097] (4) The hydroxyl density on the surface of the SiO2 support was determined by ammonia desorption (NH3-TPD) to be 4.4 μmol / g.

[0098] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0099] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent n-hexanol are mixed at a ratio of 1:9 (mass ratio), heated to 40°C to dissolve completely, and the raw material solution is prepared.

[0100] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Pt / SiO2 catalyst with a Pt loading of 0.5 wt% (SiO2 was prepared in step 1, and its surface hydroxyl density = 4.4 μmol / g), and hydrogen was added at a temperature of 90 °C, a hydrogen pressure of 3 MPa, and a weight hourly space velocity of 0.8 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 9 to complete the catalytic hydrogenation reaction;

[0101] Steps (3) to (5) are the same as in Example 1.

[0102] Example 6

[0103] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0104] 1. Preparation of catalyst support:

[0105] (1) Under 8% RH humidity conditions, weigh out tetraethyl silicate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl silicate in the resulting solution reach 0.01 mol / L. Control the temperature at 30℃ and stir until completely dissolved.

[0106] (2) Slowly introduce dry ammonia gas into the above solution until the concentration of ammonia gas reaches 0.02 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a stainless steel crystallization kettle lined with polytetrafluoroethylene.

[0107] (3) Place the stainless steel crystallization kettle in a 120℃ oven and crystallize for 24 hours. After crystallization, take it out and let it cool naturally to room temperature. Then take out the material and filter it. Place the solid sample obtained in a 120℃ oven and dry it for 1 day to obtain the SiO2 support required for the preparation of the catalyst.

[0108] (4) The hydroxyl density on the surface of the SiO2 support was determined by ammonia desorption (NH3-TPD) to be 0.7 μmol / g.

[0109] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0110] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent isooctyl alcohol are mixed at a ratio of 1:19 (mass ratio), heated to 30°C to dissolve completely, and the raw material solution is prepared.

[0111] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Rh / SiO2 catalyst with a Rh loading of 0.5 wt% (SiO2 was prepared in step 1, and its surface hydroxyl density was 0.7 μmol / g). Hydrogenation was carried out at a temperature of 95 °C, a hydrogen pressure of 1 MPa, and a weight hourly space velocity of 0.6 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 12, thus completing the catalytic hydrogenation reaction.

[0112] Steps (3) to (5) are the same as in Example 1.

[0113] Example 7

[0114] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0115] 1. Preparation of catalyst support:

[0116] (1) Under 11% RH humidity conditions, weigh out tetraethyl silicate and dissolve it in anhydrous ethanol to make the concentration of tetraethyl silicate in the resulting solution reach 0.09 mol / L. Control the temperature at 35℃ and stir until completely dissolved.

[0117] (2) Continue to slowly add aluminum isopropoxide to the above solution until the concentration of aluminum isopropoxide in the resulting solution reaches 0.01 mol / L, control the temperature at 35℃, and stir until completely dissolved;

[0118] (2) Slowly add pre-ground urea to the above solution until the urea concentration reaches 0.02 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a polytetrafluoroethylene-lined stainless steel crystallization kettle.

[0119] (3) The stainless steel crystallization kettle was placed in an oven at 180℃ and crystallized for 24 hours. After being taken out and cooled to room temperature, the material was taken out and the solid sample obtained by filtration was placed in an oven at 120℃ and dried for 1 day to obtain the Al2O3-SiO2 support required for the preparation of the catalyst.

[0120] (4) The hydroxyl density on the surface of the SiO2 support was determined by ammonia desorption (NH3-TPD) to be 2.8 μmol / g.

[0121] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0122] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent isooctyl alcohol are mixed at a ratio of 1:9 (mass ratio), heated to 60°C to dissolve completely, and the raw material solution is prepared.

[0123] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Rh-Pt / Al2O3-SiO2 catalyst with a Rh loading of 0.1 wt% and a Pt loading of 0.4 wt% (Al2O3-SiO2 was prepared in step 1, with a surface hydroxyl density of 2.8 μmol / g). Hydrogenation was carried out at a temperature of 105 °C, a hydrogen pressure of 6 MPa, and a weight hourly space velocity of 0.8 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 10 to complete the catalytic hydrogenation reaction;

[0124] Steps (3) to (5) are the same as in Example 1.

[0125] Example 8

[0126] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0127] The only difference between this embodiment and Example 1 is that in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the solvent used in the preparation and preheating of the feed solution is a mixed alcohol solvent obtained by mixing methanol and n-propanol in a volume ratio of 1:2, instead of methanol solvent.

[0128] Example 9

[0129] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0130] The only difference between this embodiment and Example 1 is that the loading of active metal Pd in ​​the catalyst used in the process of benzoic acid fixed-bed catalytic hydrogenation to prepare cyclohexylcarboxylic acid is 0.3 wt%, instead of 0.5 wt%.

[0131] Example 10

[0132] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0133] The only difference between this embodiment and Embodiment 2 is that, in the process of catalytic hydrogenation of benzoic acid to prepare cyclohexylcarboxylic acid, the loading of active metal Ni in the catalyst is 22 wt%, instead of 20 wt%.

[0134] Example 11

[0135] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0136] The only difference between this embodiment and Example 2 is that in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the mass ratio of benzoic acid to solvent n-butanol in the preparation and preheating step is 7:3 instead of 5:5, that is, the mass concentration of benzoic acid in the alcoholic solution of benzoic acid is 70%, and the temperature is raised to 80°C to ensure complete dissolution.

[0137] Example 12

[0138] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0139] The only difference between this embodiment and Example 1 is that in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the mass ratio of benzoic acid to solvent methanol in the preparation and preheating step is 1:24 instead of 6:4, that is, the mass concentration of benzoic acid in the alcohol solution is 4%, and no heating process is carried out, but it is dissolved only at room temperature (i.e., 25°C).

[0140] Example 13

[0141] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0142] The only difference between this embodiment and Example 1 is that the reaction conditions for the fixed-bed hydrogenation of benzoic acid to cyclohexylformic acid are different, specifically: temperature 190°C, hydrogen pressure 0.8 MPa, and weight hourly space velocity 1.2 h⁻¹. -1 Hydrogen / benzoic acid (molar ratio) = 20.

[0143] Example 14

[0144] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0145] The only difference between this embodiment and Example 1 is that the reaction conditions for the fixed-bed hydrogenation of benzoic acid to cyclohexylformic acid are different, specifically: temperature 50°C, hydrogen pressure 12 MPa, and weight hourly space velocity 0.08 h⁻¹. -1 Hydrogen / benzoic acid (molar ratio) = 5.

[0146] Comparative Example 1

[0147] 1. Preparation of catalyst support:

[0148] (1) Under 50% RH humidity conditions, weigh aluminum isopropoxide and dissolve it in anhydrous ethanol to make the concentration of aluminum isopropoxide in the resulting solution reach 0.02 mol / L. Control the temperature at 30℃ and stir until completely dissolved.

[0149] (2) Continue to slowly add tetraethyl silicate to the above solution until the concentration of tetraethyl silicate in the resulting solution reaches 0.08 mol / L, and stir until completely dissolved;

[0150] (2) Slowly add pre-ground urea to the above solution until the urea concentration reaches 0.03 mol / L. After stirring and mixing thoroughly, transfer the resulting mixed solution into a polytetrafluoroethylene-lined stainless steel crystallization kettle.

[0151] (3) The stainless steel crystallization kettle was placed in an oven at 170℃ and crystallized for 20 hours. After being taken out and cooled to room temperature, the material was taken out and the solid sample obtained by filtration was placed in an oven at 120℃ and dried for 1 day to obtain the Al2O3-SiO2 support required for the preparation of the catalyst.

[0152] (4) The hydroxyl density on the surface of the SiO2 support was determined by ammonia desorption (NH3-TPD) to be 12 μmol / g.

[0153] 2. Fixed-bed catalytic hydrogenation of benzoic acid to cyclohexylformic acid:

[0154] (1) Preparation and preheating of raw material solution: Benzoic acid and solvent isooctyl alcohol are mixed at a ratio of 1:9 (mass ratio), heated to 60°C to dissolve completely, and the raw material solution is prepared.

[0155] (2) Fixed-bed hydrogenation: The fixed bed was filled with a Rh-Pt / Al2O3-SiO2 catalyst with a Rh loading of 0.1 wt% and a Pt loading of 0.4 wt% (Al2O3-SiO2 was prepared in step 1, with a surface hydroxyl density of 12 μmol / g). Hydrogenation was carried out at a temperature of 105 °C, a hydrogen pressure of 6 MPa, and a weight hourly space velocity of 0.8 h⁻¹. -1 The hydrogen / benzoic acid (molar ratio) flows continuously through a fixed-bed reactor under the condition of 10 to complete the catalytic hydrogenation reaction;

[0156] Steps (3) to (5) are the same as in Example 1.

[0157] Comparative Example 2

[0158] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0159] The only difference between this comparative example and Example 1 is that, in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the solvent used in the preparation and preheating of the feed solution is ethyl acetate, rather than an alcohol solvent.

[0160] Comparative Example 3

[0161] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0162] The only difference between this comparative example and Example 1 is that, in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the solvent used in the preparation and preheating of the feed solution is 1,4-dioxane, rather than an alcohol solvent.

[0163] Comparative Example 4

[0164] A method for the preparation of cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid:

[0165] The only difference between this comparative example and Example 1 is that, in the process of preparing cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid, the solvent used in the preparation and preheating of the feed solution is cyclohexylcarboxylic acid, rather than an alcohol solvent.

[0166] In the above embodiments and comparative examples, the benzoic acid conversion rate and cyclohexylcarboxylic acid selectivity for the preparation of cyclohexylcarboxylic acid by fixed-bed catalytic hydrogenation of benzoic acid are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: the reaction solution containing a high concentration of benzoic acid was prepared using an alcohol solvent, and the highly active catalyst with a surface hydroxyl density ≤5μmol / g not only significantly suppressed the esterification side reaction between benzoic acid and the alcohol solvent, but also ultimately obtained a high conversion rate and high selectivity of cyclohexylcarboxylic acid by using a fixed-bed hydrogenation process.

[0171] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate, so that the embodiments of this application described herein can be implemented, for example, in orders other than those described herein. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing cyclohexylformic acid by fixed-bed catalytic hydrogenation of benzoic acid, characterized in that, The method includes the following steps: Step S1, Preparation of raw material solution: Dissolve benzoic acid in an alcohol solvent to obtain the raw material solution; Step S2, catalytic hydrogenation: The feed liquid enters a fixed-bed reactor packed with catalyst to carry out the catalytic hydrogenation and obtain the reactants; Step S3, gas-liquid separation: The reactants enter a gas-liquid separator for gas-liquid separation to obtain separated materials and unreacted hydrogen. Step S4, solvent removal: The separated material enters the solvent removal tower for solvent removal, resulting in solvent-removed material and solvent removed; Step S5, purification and distillation: The desolventized material enters a distillation column to obtain cyclohexylformic acid; The alcohol solvent is selected from one or more C1 to C8 alcohols; The catalyst comprises a support and an active metal supported thereon, and the hydroxyl density on the surface of the support is ≤5 μmol / g.

2. The method according to claim 1, characterized in that, The alcohol solvent is a monohydric alcohol and / or a polyhydric alcohol; Preferably, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-butanol, isobutanol, n-hexanol, and isooctanol; More preferably, the alcohol solvent is selected from one or more of methanol, ethanol, n-propanol, n-hexanol, and isooctanol; More preferably, the alcohol solvent is methanol and n-propanol, and the volume ratio of methanol to n-propanol is 1:

1. (1.8～2.0)。 3. The method according to claim 1 or 2, characterized in that, The carrier is selected from one or more of activated carbon, alumina, silicon dioxide, titanium dioxide, and zirconium oxide.

4. The method according to claim 3, characterized in that, The active metal is selected from one or more of nickel, cobalt, ruthenium, palladium, platinum and rhodium; preferably, the active metal is rhodium and platinum, and the weight ratio of rhodium to platinum is 1:(3-5).

5. The method according to claim 3 or 4, characterized in that, In the catalyst, the loading of the active metal is 0.5 to 20 wt%.

6. The method according to any one of claims 1 to 5, characterized in that, The alcohol solvent is methanol, the catalyst is Pd / Al₂O₃, and the Pd loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the Al₂O₃ support surface is 0.50–0.55 μmol / g; and / or, The alcohol solvent is n-hexanol, the catalyst is Pt / SiO2, and the Pt loading in the catalyst is 0.50–0.55 wt%, and the hydroxyl density on the SiO2 support surface is 4.3–4.5 μmol / g; and / or, The alcohol solvent is isooctanol, the catalyst is Rh-Pt / Al2O3-SiO2, and the loading of Rh in the catalyst is 0.10-0.12 wt%, the loading of Pt is 0.40-0.45 wt%, and the hydroxyl density on the surface of the Al2O3-SiO2 support is 2.6-3.0 μmol / g.

7. The method according to any one of claims 1 to 6, characterized in that, In step S1, the mass concentration of benzoic acid in the raw material solution is 5-60%.

8. The method according to any one of claims 1 to 7, characterized in that, In step S1, the preparation of the raw material liquid is carried out under heating conditions, and the heating temperature is 30-60°C.

9. The method according to any one of claims 1 to 8, characterized in that, In step S2, the reaction conditions for catalytic hydrogenation are as follows: The reaction temperature is 60–180 °C; and / or, The reaction pressure is 1.0–10.0 MPa; and / or, The molar ratio of benzoic acid to hydrogen is 1:(6–18); and / or, The weight hourly space velocity is 0.1–1.0 h⁻¹. -1 .

10. The method according to any one of claims 1 to 9, characterized in that, Step S3 further includes returning the unreacted hydrogen to step S2 for catalytic hydrogenation, and step S4 further includes returning the removed solvent to step S1 for the preparation of the feed solution.

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