Catalyst for adipic acid synthesis, preparation method therefor, and use thereof

Abstract

The present invention provides a catalyst for adipic acid synthesis, a preparation method therefor, and a use thereof. The preparation method comprises: 1) dissolving tetrapropylammonium hydroxide and organic amine in water to obtain a first mixed solution; 2) preparing a metal salt solution, and adding ammonia water into the metal salt solution to obtain a second mixed solution; 3) adding the second mixed solution, a silicon source, and a titanium source into the first mixed solution to obtain a glue solution; and carrying out hydrothermal crystallization, washing, drying and calcination on the glue solution to obtain catalyst raw powder; 4) using an organic acid solution to carry out acid treatment on the catalyst raw powder to obtain acid-treated catalyst raw powder; and 5) using a tetrapropylammonium hydroxide solution to carry out alkali treatment on the acid-treated catalyst raw powder, and carrying out washing, drying and calcining to obtain the catalyst for adipic acid synthesis. The prepared catalyst is used for the reaction of 1,2-cyclohexanediol with an oxidizing agent to form adipic acid, has high conversion rate and selectivity, is convenient to recycle, has a long service life, and is suitable for large-scale industrial production.

Description

A catalyst for adipic acid synthesis and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a catalyst for adipic acid synthesis, a preparation method and an application thereof. Background Art

[0002] Adipic acid, also known as fatty acid, is an important chemical raw material for the production of synthetic fibers. It is primarily used in condensation reactions with other compounds to produce nylon polymers. In the nylon industry, adipic acid is primarily condensed with hexamethylenediamine to produce nylon 66. With the rapid development of my country's adiponitrile industry in recent years, market demand for adipic acid has also continued to expand. Currently, the main production processes for adipic acid include the cyclohexane process, the cyclohexene process, air oxidation, and peroxide oxidation processes.

[0003] The cyclohexane process is currently the world's most predominant method for producing adipic acid. This process uses benzene as a raw material, which is hydrogenated to produce cyclohexane. Cyclohexane is then reacted with air to produce a mixture of cyclohexanol and cyclohexanone (KA oil). This alcohol-ketone mixture can then be used to produce adipic acid. This process utilizes a relatively simple feedstock, is well-established in production technology, consumes minimal raw materials, and is energy-efficient, making it the primary method used by most adipic acid manufacturers worldwide. However, its drawbacks include a complex process, numerous byproducts, and the generation of significant industrial waste ("three wastes"). Furthermore, the high consumption of nitric acid, which can corrode equipment, produces highly polluting nitrogen oxides.

[0004] The cyclohexene process uses benzene and hydrogen as raw materials. First, benzene is hydrogenated to produce cyclohexene, which is then hydrated with water to produce cyclohexanol. Finally, the cyclohexanol is oxidized with nitric acid to produce adipic acid. Compared to the cyclohexane process, this process reduces energy and raw material consumption, is safer, and offers high product quality and yield. However, this process still requires large amounts of nitric acid, and nitrogen oxide pollution remains a concern.

[0005] The air oxidation method uses air as an oxidant to react with cyclohexane to synthesize adipic acid. It usually uses cobalt salts as catalysts and acetic acid as solvent. Compared with other methods, this method requires a longer residence time of 2 to 6 hours, and the reaction selectivity is low, only 70 to 80%. Therefore, this process is still in the development stage and has not yet been industrialized.

[0006] The hydrogen peroxide method uses hydrogen peroxide as an oxidant and cyclohexene, cyclohexanol, and cyclohexanone as raw materials to produce adipic acid through a single or multi-step reaction. Given that oxidation with nitric acid produces large amounts of nitrogen oxides, developing environmentally friendly adipic acid production processes is a key topic in chemical research. Hydrogen peroxide, as a green oxidant, produces water as the only byproduct of the oxidation reaction, making it an ideal oxidant with no environmental impact. It offers advantages such as high adipic acid yield, few byproducts, and minimal pollution.

[0007] The peroxide oxidation method, similar to the hydrogen peroxide method, uses cyclohexene, cyclohexanol, and other raw materials, and peroxides such as cumene peroxide, ethylbenzene peroxide, and peracetic acid as oxidants. Adipic acid is produced through one or more steps in the presence of a catalyst. Compared to industrial methods, this method offers the advantages of lower raw material costs, higher molecular weight utilization, lower waste emissions, and no production of pollutants such as nitrogen oxides.

[0008] Existing technologies for producing adipic acid using hydrogen peroxide and peroxide oxidation methods mostly use heteropolyacid phase transfer catalysts, such as tungstic acid and salt-free catalysts. While these catalysts offer excellent performance, achieving adipic acid yields exceeding 90%, they suffer from poor durability and suffer from significant loss of ions after a period of use. Consequently, these catalyst performance limitations hinder the industrialization of these methods. Summary of the Invention

[0009] In response to the deficiencies in the prior art, the present invention discloses a catalyst for adipic acid synthesis, a preparation method, and applications thereof. The titanium silicon molecular sieve catalyst prepared by the preparation method is used to catalyze the reaction of 1,2-cyclohexanediol and an oxidant to produce adipic acid. The catalyst has high conversion rate and selectivity, is easy to recycle, and has a long service life, making it suitable for large-scale industrial production.

[0010] In order to achieve the above technical objectives, on the one hand, the present invention provides a method for preparing a catalyst for adipic acid synthesis, comprising the following steps:

[0011] (1) dissolving tetrapropylammonium hydroxide and an organic amine in water to obtain a first mixed solution;

[0012] (2) preparing a metal salt solution, and adding ammonia water to the metal salt solution to obtain a second mixed solution;

[0013] (3) adding the second mixed solution, silicon source and titanium source to the first mixed solution to obtain a glue solution; hydrothermally crystallizing the glue solution, washing, drying and calcining the solution to obtain a catalyst raw powder;

[0014] (4) treating the catalyst raw powder with an organic acid solution to obtain an acid-treated catalyst raw powder;

[0015] (5) The catalyst powder after the acid treatment is subjected to alkali treatment using a tetrapropylammonium hydroxide solution, and the catalyst for adipic acid synthesis is obtained through washing, drying and calcining.

[0016] In the above technical solution, a metal salt is introduced into the molecular sieve as a catalyst active component in step (2). Ammonia water is further added to the metal salt solution to form a uniform complex solution between the metal salt and ammonia. Subsequently, hydrothermal crystallization with a template agent, tetrapropylammonium hydroxide, is performed. Ultimately, the uniform formation and deposition of metal oxide active sites is promoted, significantly improving the selectivity of the reaction. The present invention and comparative examples explore the effects of introducing a metal salt and adding ammonia water to the metal salt solution on the catalytic activity and selectivity of the catalyst.

[0017] In addition, in step (4) of the above technical solution, the prepared catalyst powder is acid-treated with an organic acid to remove the metal oxide particles deposited on the surface of the catalyst powder, so that the active sites of the prepared catalyst can be evenly distributed in the molecular sieve pores, thereby improving the selectivity of the catalyst. At the same time, it can also reduce the deactivation and deactivation of the sites and extend the service life of the catalyst.

[0018] Furthermore, in step (5) of the above technical solution, tetrapropylammonium hydroxide solution is used to perform pore expansion treatment on the catalyst raw powder after acid treatment, effectively eliminating the diffusion limitation of the molecular sieve catalyst, strengthening the stability of the crystal structure, enhancing mass transfer, reducing the diffusion resistance of reactants and products within the catalyst, and improving the catalytic performance and service life. The examples of the present invention and the comparative examples explore the effects of acid treatment and base treatment on the catalytic activity, selectivity, and service life of the catalyst.

[0019] In a further example of the present invention, the type and amount of the organic amine added in step (1) are optimized. Optionally, the organic amine includes one or more of n-butylamine, triethylamine, tri-n-propylamine, n-propylamine, diethylamine, and ethylenediamine; and optionally, the mass ratio of tetrapropylammonium hydroxide to the organic amine is 1:(0.02-0.8), preferably 1:(0.3-0.5).

[0020] In a further example of the present invention, the metal salt solution is prepared by dissolving a metal salt in water, and the cations of the metal salt may be transition metal cations, and may further include one or more of iron ions, cobalt ions, nickel ions, copper ions, manganese ions, vanadium ions, chromium ions, and zinc ions. The catalyst prepared by doping with the above cations exhibits excellent conversion rate, selectivity, and catalyst service life in the reaction of catalyzing the reaction of 1,2-cyclohexanediol with an oxidant to produce adipic acid.

[0021] In a further embodiment of the present invention, the mass ratio of the metal salt to the ammonia water in step (2) is optimized to promote sufficient complexation between the metal salt and the ammonia gas. Optionally, the molar ratio of the metal salt to the ammonia water used to prepare the metal salt solution is 1:(1-10), preferably 1:(4-8). It should be noted that the ammonia gas will be evaporated during the hydrothermal crystallization process in the subsequent step.

[0022] In a further example of the present invention, the anion of the metal salt used to prepare the metal salt solution in step (2) is optimized. Optionally, the anion of the metal salt is one or more of acetate, citrate, sulfate, nitrate, and chloride, thereby improving the efficiency of catalyst preparation by using a soluble salt of the metal salt cation to prepare the metal salt solution.

[0023] It should be noted that the execution order of steps (1) and (2) in the above technical solution is not limited.

[0024] In a further example of the present invention, the type of the silicon source is optimized. Optionally, the silicon source includes one or more of fumed silicon oxide, tetraethyl orthosilicate, and silica sol.

[0025] In a further example of the present invention, the type of the titanium source is optimized. Optionally, the titanium source includes one or more of isobutyl titanate, titanium oxide powder, and titanium tetrachloride.

[0026] In a further example of the present invention, the amounts of the silicon source and titanium source were optimized. Optionally, the molar ratio of the silicon source to the titanium source was 1:(0.01-0.2), more preferably 1:(0.02-0.05). The present invention demonstrates that catalysts prepared within this mass ratio range exhibit excellent conversion, selectivity, and catalyst life.

[0027] In a further example of the present invention, control conditions for hydrothermal crystallization were explored. Optionally, the hydrothermal crystallization temperature is 80-220°C, preferably 150-190°C, and the hydrothermal crystallization time is 10-120 hours, preferably 48-84 hours, to gradually evaporate ammonia. The morphology of the prepared catalyst can be controlled by adjusting the hydrothermal crystallization temperature and time.

[0028] It should be noted that the present invention does not limit the equipment for hydrothermal crystallization, and a hydrothermal kettle may be selected. Those skilled in the art may select other equipment according to actual use requirements, but the technical solutions formed thereby do not deviate from the basic principles of the present invention and are all within the scope of protection of the present invention.

[0029] In a further example of the present invention, the type of organic acid used in the acid treatment is optimized. The present invention can optionally use a weak acid for acid treatment to dissolve and remove the metal oxide particles deposited on the surface of the catalyst raw powder, but will not excessively dissolve the metal oxide in the molecular sieve pores. Further optionally, the organic acid solution includes an aqueous solution of one or more of acetic acid, propionic acid, acrylic acid, citric acid, oxalic acid, and benzoic acid; in a further example of the present invention, the concentration of the organic acid used in the acid treatment is optimized. Optionally, the concentration of the organic acid solution is 1% to 10%, preferably 3% to 5%; in addition, in a further example of the present invention, the control conditions of the acid treatment are optimized. Optionally, the temperature of the acid treatment is 20 to 100°C, preferably 50 to 80°C; the time of the acid treatment is 10 to 200 minutes. It should be noted that the concentration of the organic acid solution is the mass concentration.

[0030] It should be noted that the technical solution of the present invention also includes separating the acid-treated catalyst powder from the organic acid solution and washing it to neutrality after the acid treatment.

[0031] The technical solution of the present invention is to perform pore expansion treatment on the catalyst powder after acid treatment by alkali treatment. In a further example of the present invention, the addition amount of tetrapropylammonium hydroxide and the catalyst powder after acid treatment during the alkali treatment is optimized. Optionally, the mass ratio of tetrapropylammonium hydroxide to the catalyst powder after acid treatment in step (5) is 1: (1 to 20), preferably 1: (3 to 7). In addition, in a further example of the present invention, the control conditions of the alkali treatment are optimized. Optionally, the temperature of the alkali treatment is 80 to 220°C, preferably 150 to 190°C; the time of the alkali treatment is 20 to 80 hours, thereby obtaining a porous catalyst for adipic acid synthesis with a stable crystal structure.

[0032] It should be noted that the present invention does not limit the equipment used for alkali treatment, and a hydrothermal kettle may be selected. Those skilled in the art may select other equipment according to actual use requirements, and the technical solutions thus formed are all within the scope of protection of the present invention.

[0033] It should be noted that the technical solution of the present invention also includes separating the solid phase catalyst from the tetrapropylammonium hydroxide solution and washing the solid catalyst to neutrality after the alkali treatment.

[0034] It should be noted that the technical solution of the present invention does not limit the control conditions of the calcination operations in steps (3) and (5), and the calcination temperature can be selected from 300 to 800° C., and the calcination time can be selected from 6 hours.

[0035] On the other hand, the present invention provides a catalyst for adipic acid synthesis prepared by the above preparation method.

[0036] On the other hand, the present invention provides a method for synthesizing adipic acid, which comprises: dissolving 1,2-cyclohexanediol in a solvent, and reacting the solvent with an oxidant in the presence of the above-mentioned catalyst for synthesizing adipic acid to produce adipic acid.

[0037] Furthermore, the present invention optimizes the control conditions, solvents, oxidants, and the amounts of the raw material 1,2-cyclohexanediol, solvent, catalyst, and oxidant in the above-mentioned adipic acid synthesis method. Specifically:

[0038] The reaction temperature of the adipic acid synthesis method can be selected to be 60-100° C., and further can be selected to be 70-90° C.; within this temperature range, the product selectivity and the service life of the catalyst can be improved.

[0039] The reaction time of the adipic acid synthesis method can be selected to be 30 to 240 minutes. In actual operation, the reaction is terminated when the concentration of the reactants no longer changes significantly.

[0040] The solvent may optionally include one or more of methanol, ethanol, isopropanol, tert-butanol, formic acid, acetic acid, acetonitrile, and 1,2-dichloroethane.

[0041] The oxidant may optionally include one or more of cumene hydroperoxide, tert-butyl hydroperoxide, ethylbenzene peroxide, and hydrogen peroxide.

[0042] The mass ratio of the 1,2-cyclohexanediol, the solvent and the catalyst for adipic acid synthesis may be 1:(1-10):(0.1-6), and may further be 1:(4-6):(0.3-1).

[0043] The molar ratio of 1,2-cyclohexanediol to the oxidant may be 1:(0.2-1), and may further be 1:(0.5-0.8).

[0044] On the other hand, the present invention provides a method for synthesizing adipic acid, which comprises: S1, cyclohexene is oxidized to obtain 1,2-cyclohexanediol; S2, the 1,2-cyclohexanediol is dissolved in a solvent, and reacted with an oxidant in the presence of the above-mentioned catalyst for adipic acid synthesis to produce adipic acid.

[0045] It should be noted that the present invention does not limit the specific operation of the oxidation reaction of cyclohexene to obtain 1,2-cyclohexanediol and the catalyst used. Existing phase transfer catalysts, such as tungsten-containing phase transfer catalysts, can be used to catalyze the oxidation of cyclohexene to obtain 1,2-cyclohexanediol.

[0046] In a further example of the present invention, the control conditions, solvents, oxidants used, and the amounts of the raw material 1,2-cyclohexanediol, solvent, catalyst, and oxidant of the above-mentioned adipic acid synthesis method are optimized.

[0047] The beneficial effects of the present invention are:

[0048] Compared with the prior art, the preparation method of the catalyst for adipic acid synthesis of the present invention is simple in process and highly operable. The prepared titanium silicon molecular sieve catalyst can be used for producing adipic acid by peroxide oxidation method, has the advantages of high catalytic activity, high conversion rate and selectivity, long service life, etc., and is suitable for large-scale industrial production of adipic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0050] FIG1 is an electron microscope morphology of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0051] To facilitate understanding of the present invention, the present invention will be described in more detail below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are merely for the purpose of further explanation and should not be understood as limiting the present invention in any form, i.e., they are not intended to limit the scope of protection of the present invention. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0052] The evaluation method for the relevant parameters of the catalyst prepared in the embodiment of the present invention in the reaction of 1,2-cyclohexanediol and an oxidant to produce adipic acid is as follows:

[0053] The raw material conversion rate is used to characterize the actual conversion percentage of the 1,2-cyclohexanediol raw material after the reaction; in the embodiment of the present invention, the raw material conversion rate = 1-(mass of unreacted 1,2-cyclohexanediol / mass of 1,2-cyclohexanediol raw material)*100%.

[0054] The theoretical conversion rate is used to indicate the percentage of 1,2-cyclohexanediol converted after the 1,2-cyclohexanediol raw material reacts completely with the oxidant added in the test example to produce all adipic acid. In the embodiments of the present invention, the theoretical conversion rate = the mass of cyclohexanediol theoretically involved in the reaction / the mass of the 1,2-cyclohexanediol raw material * 100%.

[0055] Product yield: the ratio of the mass of adipic acid actually produced to the mass of the 1,2-cyclohexanediol raw material, multiplied by the molecular weight coefficient; in the embodiment of the present invention, product yield = 0.795 * mass of adipic acid produced / mass of 1,2-cyclohexanediol raw material.

[0056] Catalyst life is the reaction time during which the catalyst retains 90% of its initial performance during use.

[0057] Example 1

[0058] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Dissolve 5g of cobalt acetate in water, add 15g of concentrated ammonia water, and stir until the solution is clear. Add this clear solution, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine, and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. Filter and separate the resulting solid, wash it until it is neutral, dry it with hot air, and then calcine it at 800°C for 6 hours to obtain the catalyst powder.

[0059] Prepare a 1% acetic acid solution, heat the acetic acid solution to 100°C, add the catalyst powder into the acetic acid solution and treat for 200 minutes, then separate the acid-treated catalyst and wash it to neutrality.

[0060] 100 g of tetrapropylammonium hydroxide was dissolved in water to obtain a tetrapropylammonium hydroxide solution. 100 g of the acid-treated catalyst powder was placed in the tetrapropylammonium hydroxide solution and stirred until a stable slurry was formed. The slurry was then transferred to a hydrothermal kettle and treated at 220°C for 80 hours. The treated catalyst was then separated and washed to neutrality, dried with hot air, and calcined at 800°C for 6 hours to obtain the catalyst for adipic acid synthesis, i.e., the 1,2-cyclohexanediol oxidation reaction catalyst.

[0061] Example 2

[0062] Dissolve 200g of tetrapropylammonium hydroxide and 160g of diethylamine in water and stir until dissolved. Dissolve 2g of copper sulfate in water, add 2.3g of concentrated ammonia, and stir until the solution becomes clear. Add this clear solution, 150g of ethyl orthosilicate, and 24.5g of isobutyl titanate to the mixed solution of tetrapropylammonium hydroxide and diethylamine, and stir until a uniform gel is formed. Continue stirring the gel for 2 hours, transfer it to a hydrothermal autoclave, and crystallize it at 80°C for 48 hours. The resulting solid is filtered, separated, washed until neutral, dried with hot air, and calcined at 300°C for 6 hours to obtain the raw powder of the 1,2-cyclohexanediol oxidation catalyst.

[0063] Prepare a 5% citric acid solution, heat the citric acid solution to 80°C, immerse the catalyst powder in the citric acid solution for 100 minutes, and then separate and clean the treated catalyst to neutrality.

[0064] 200 g of tetrapropylammonium hydroxide was dissolved in water, and 10 g of the acid-treated catalyst powder was placed in the tetrapropylammonium hydroxide solution and stirred until a stable slurry was formed. The slurry was then transferred to a hydrothermal kettle and treated at 80°C for 80 hours. The treated catalyst was then separated and washed to neutrality, dried with hot air, and calcined at 300°C for 6 hours to obtain the catalyst for adipic acid synthesis, i.e., the 1,2-cyclohexanediol oxidation reaction catalyst.

[0065] Example 3

[0066] Dissolve 200g of tetrapropylammonium hydroxide and 100g of tri-n-propylamine in water and stir until dissolved. Dissolve 4g of ferric acetate in water, add 14g of concentrated ammonia, and stir until the solution is clear. Add this clear solution, 150g of 30% silica sol, and 7.1g of titanium tetrachloride to the mixed solution of tetrapropylammonium hydroxide and tri-n-propylamine and stir until a uniform gel is formed. Continue stirring the gel for 2 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 190°C for 10 hours. Filter and separate the resulting solid, wash it until neutral, dry it with hot air, and calcine it at 700°C for 6 hours to obtain the catalyst powder.

[0067] Prepare a 10% oxalic acid solution, heat the oxalic acid solution to 20°C, immerse the original powder of the 1,2-cyclohexanediol oxidation reaction catalyst in the oxalic acid solution for 10 minutes, and then separate the treated catalyst and wash it to neutrality.

[0068] 210 g of tetrapropylammonium hydroxide was dissolved in water, and 30 g of the acid-treated catalyst powder was placed in the tetrapropylammonium hydroxide solution and stirred until a stable slurry was formed. The slurry was then transferred to a hydrothermal kettle and treated at 190°C for 20 hours. The treated catalyst was then separated and washed to neutrality, dried with hot air, and calcined at 800°C for 6 hours to obtain the catalyst for adipic acid synthesis, i.e., the 1,2-cyclohexanediol oxidation reaction catalyst.

[0069] Comparative Example 1

[0070] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Dissolve 5g of cobalt acetate in water, add 15g of concentrated ammonia water, and stir until the solution is clear. Add this clear solution, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine, and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. The resulting solid is filtered, separated, washed until neutral, dried with hot air, and then calcined at 800°C for 6 hours to obtain the catalyst.

[0071] Comparative Example 2

[0072] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Dissolve 5g of cobalt acetate in water, add 15g of concentrated ammonia water, and stir until the solution is clear. Add this clear solution, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine, and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. Filter and separate the resulting solid, wash it until it is neutral, dry it with hot air, and then calcine it at 800°C for 6 hours to obtain the catalyst powder.

[0073] Dissolve 100g of tetrapropylammonium hydroxide in water, place 100g of catalyst powder in the tetrapropylammonium hydroxide solution, and stir until a stable slurry is formed. The slurry is then transferred to a hydrothermal autoclave and treated at 220°C for 80 hours. The treated catalyst is then separated and cleaned to neutrality, dried with hot air, and calcined at 800°C for 6 hours to obtain the catalyst.

[0074] Comparative Example 3

[0075] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Dissolve 5g of cobalt acetate in water, add 15g of concentrated ammonia water, and stir until the solution is clear. Add this clear solution, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine, and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. Filter and separate the resulting solid, wash it until it is neutral, dry it with hot air, and then calcine it at 800°C for 6 hours to obtain the catalyst powder.

[0076] Prepare 1% acetic acid solution, heat the acetic acid solution to 100℃, add the catalyst powder into the acetic acid solution and treat for 200min, then separate and wash the treated catalyst to neutrality, and then calcine at 800℃ for 6h to obtain the catalyst.

[0077] Comparative Example 4

[0078] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Add 40g of fumed silica and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine and stir until a uniform gel solution is formed. Continue stirring the gel solution for 12 hours, transfer it to a hydrothermal autoclave, and crystallize it at 220°C for 120 hours. The resulting solid is filtered, separated, washed to neutrality, dried with hot air, and then calcined at 800°C for 6 hours to obtain a 1,2-cyclohexanediol oxidation catalyst.

[0079] Comparative Example 5

[0080] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Add this solution, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. Filter and separate the resulting solid, wash it to neutrality, dry it with hot air, and calcine it at 800°C for 6 hours to obtain the catalyst powder.

[0081] Prepare a 1% acetic acid solution, heat the acetic acid solution to 100°C, add the catalyst powder into the acetic acid solution and treat for 200 minutes, then separate the treated catalyst and wash it to neutrality.

[0082] Dissolve 100g of tetrapropylammonium hydroxide in water, then place 100g of the acid-treated catalyst powder in the tetrapropylammonium hydroxide solution and stir until a stable slurry forms. The slurry is then transferred to a hydrothermal autoclave and treated at 220°C for 80 hours. The treated catalyst is then separated and cleaned to neutrality, dried with hot air, and calcined at 800°C for 6 hours to obtain the catalyst.

[0083] Comparative Example 6

[0084] Dissolve 200g of tetrapropylammonium hydroxide and 4g of ethylenediamine in water and stir until dissolved. Dissolve 5g of cobalt acetate in water and stir until uniform. Add this liquid, 40g of fumed silica, and 0.5g of titanium oxide powder to the mixed solution of tetrapropylammonium hydroxide and ethylenediamine and stir until a uniform gel is formed. Continue stirring the gel for 12 hours, transfer the gel to a hydrothermal autoclave, and crystallize at 220°C for 120 hours. Filter and separate the resulting solid, wash it until neutral, dry it with hot air, and calcine it at 800°C for 6 hours to obtain the catalyst powder.

[0085] Prepare a 1% acetic acid solution, heat the acetic acid solution to 100°C, add the catalyst powder into the acetic acid solution and treat for 200 minutes, then separate the treated catalyst and wash it to neutrality.

[0086] Dissolve 100g of tetrapropylammonium hydroxide in water, then place 100g of the acid-treated catalyst powder in the tetrapropylammonium hydroxide solution and stir until a stable slurry forms. The slurry is then transferred to a hydrothermal autoclave and treated at 220°C for 80 hours. The treated catalyst is then separated and cleaned to neutrality, dried with hot air, and calcined at 800°C for 6 hours to obtain the catalyst.

[0087] In Test Examples 1-3 and Comparative Test Examples 1-9, the catalysts prepared in Examples 1-3 and Comparative Example 1-7 were used to catalyze the reaction of 1,2-cyclohexanediol with an oxidant to produce adipic acid. During the test, the reaction conditions were controlled, and the raw material conversion rate, theoretical conversion rate, product yield and catalyst service life in the product liquids prepared in different test examples were detected.

[0088] Test Example 1

[0089] Dissolve 100g of 1,2-cyclohexanediol in 100g of 1,2-dichloroethane. Add 10g of the 1,2-cyclohexanediol oxidation catalyst obtained in Example 1. Stir until the mixture forms a uniform slurry. Heat the slurry to 60°C, then gradually add 300g of 20% ethylbenzene peroxide to initiate the reaction. Maintain the temperature for 30 minutes. The theoretical conversion rate for this test example is 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion of 48.12% and adipic acid selectivity of 94.25%.

[0090] The service life of the 1,2-cyclohexanediol oxidation catalyst prepared in Example 1 was also tested. Specifically, 100 g of adipic acid alcohol was dissolved in 100 g of 1,2-dichloroethane, and 10 g of the 1,2-cyclohexanediol oxidation catalyst obtained in Example 1 was added. Stirring was initiated until the liquid formed a uniform slurry. The slurry was heated to 60°C, and 1.32 g of 1,2-cyclohexanediol, 1.66 g of 1,2-dichloroethane, and 5 g of 20% ethylbenzene peroxide were added to the slurry every minute. Simultaneously, 7.99 g of the liquid phase was withdrawn from the slurry every minute. Long-term evaluation revealed a catalyst service life of 2100 hours.

[0091] Test Example 2

[0092] Dissolve 100g of 1,2-cyclohexanediol in 1000g of acetic acid, add 600g of the 1,2-cyclohexanediol oxidation catalyst obtained in Example 2, and stir until the mixture forms a uniform slurry. Heat the slurry to 100°C, then gradually add 98g of 30% hydrogen peroxide to initiate the reaction. Maintain the temperature for 80 minutes. The theoretical conversion rate for this test example is 100%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion of 98.65% and adipic acid selectivity of 95.44%.

[0093] In addition, the service life of the 1,2-cyclohexanediol oxidation reaction catalyst prepared in Example 2 was also tested. The specific catalyst life test method was the same as that of Test Example 1, and the catalyst life was measured to be 2338 hours after long-term evaluation.

[0094] Test Example 3

[0095] Dissolve 100g of 1,2-cyclohexanediol in 400g of ethanol, add 100g of the 1,2-cyclohexanediol oxidation catalyst obtained in Example 3, and stir until the liquid forms a uniform slurry. Heat the slurry to 90°C, then gradually add 87g of 30% cumene peroxide to initiate the reaction. Maintain the temperature for 240 minutes. The theoretical conversion rate for this test example is 20%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion of 19.03% and adipic acid selectivity of 97.15%.

[0096] In addition, the service life of the 1,2-cyclohexanediol oxidation reaction catalyst prepared in Example 3 was also tested. The specific catalyst life test method was the same as that in Test Example 1, and after long-term evaluation, the catalyst life was measured to be 2984 hours.

[0097] Comparative test example 1

[0098] Dissolve 100g of 1,2-cyclohexanediol in 100g of 1,2-dichloroethane. Add 10g of the 1,2-cyclohexanediol oxidation catalyst obtained in Comparative Example 1, and stir until the liquid forms a uniform slurry. Heat the slurry to 60°C, then gradually add 300g of 20% ethylbenzene peroxide to initiate the reaction. Maintain the temperature for 30 minutes. The theoretical conversion rate for this comparative test example is 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion of 41.11% and adipic acid selectivity of 36.73%.

[0099] Comparative test example 2

[0100] The raw materials, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Comparative Test Example 1, except that the 1,2-cyclohexanediol oxidation catalyst prepared in Comparative Example 2 was used. The theoretical conversion rate in this comparative test example was 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion rate of 48.17% and adipic acid selectivity of 83.74%.

[0101] Comparative test example 3

[0102] The raw materials, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Comparative Test Example 1, except that the 1,2-cyclohexanediol oxidation catalyst prepared in Comparative Example 3 was used. The theoretical conversion rate in this comparative test example was 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion rate of 36.05% and adipic acid selectivity of 83.97%.

[0103] Comparative test example 4

[0104] The raw materials, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Comparative Test Example 1, except that the 1,2-cyclohexanediol oxidation catalyst prepared in Comparative Example 4 was used. The theoretical conversion rate in this comparative test example was 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion rate of 37.73% and adipic acid selectivity of 46.74%.

[0105] Comparative test example 5

[0106] The raw materials, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Comparative Test Example 1, except that the 1,2-cyclohexanediol oxidation catalyst prepared in Comparative Example 5 was used. The theoretical conversion rate in this comparative test example was 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion rate of 33.73% and adipic acid selectivity of 57.74%.

[0107] Comparative Test Example 6

[0108] The raw materials, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Comparative Test Example 1, except that the 1,2-cyclohexanediol oxidation catalyst prepared in Comparative Example 6 was used. The theoretical conversion rate in this comparative test example was 50%. Analysis of the product liquid revealed a 1,2-cyclohexanediol conversion rate of 41.84% and adipic acid selectivity of 62.95%.

[0109] Based on the above tests, it can be verified that compared with the comparative test examples 1-6, the actual raw material conversion rate of the test examples using the catalyst prepared by Examples 1-3 is closer to the theoretical raw material conversion rate, reflecting that the catalytic reaction using the catalyst prepared by the embodiment of the present invention runs well and is more efficient.

[0110] Comparative test example 7

[0111] The raw materials, catalyst, oxidant, solvent, and control conditions used in this comparative test example were the same as those in Test Example 1. The difference was that after 1,2-cyclohexanediol, 1,2-dichloroethane, and the catalyst were stirred into a uniform slurry, the slurry was heated to 140°C, and 147 g of 30% hydrogen peroxide was gradually added to initiate the reaction. The reaction was then maintained at this temperature for 80 minutes. The theoretical conversion rate in this comparative test example was 100%. Analysis of the product liquid revealed a 100% conversion rate for 1,2-cyclohexanediol and a selectivity for adipic acid of 35.96%.

[0112] Combining Test Example 1 and Comparative Test Example 7, it can be confirmed that the temperature in the adipic acid synthesis process is one of the important control parameters. The reaction temperature can be selected from 60 to 100°C, and further selected from 70 to 90°C. Within this temperature range, the product selectivity and catalyst service life can be improved.

[0113] Comparative test example 8

[0114] In this comparative test, 146g of adipic acid was dissolved in 300g of tert-butyl alcohol. 25g of phosphotungstic acid and 100g of oxalic acid were added as catalysts. Stirring was initiated until the liquid became uniform. Heating was initiated, maintaining the slurry temperature at a constant 60°C. 1.88g of 30% hydrogen peroxide and 0.50g of cyclohexanediol were added to the slurry every minute, while 1.36g of the liquid phase was withdrawn from the slurry every minute. Long-term evaluation was performed, and the catalyst life was measured to be 8 hours.

[0115] Combined with Test Examples 1-3 and Comparative Test 8, it can be confirmed that compared with the existing adipic acid preparation system using phosphotungstic acid as a catalyst, the catalyst for the 1,2-cyclohexanediol oxidation reaction of the present invention has a longer service life, can reduce production costs and process difficulty in large-scale industrial production, and has good economic benefits and market promotion value.

[0116] It should be noted that the above content is a further detailed description of the present invention in conjunction with specific implementation methods, and the specific implementation of the present invention cannot be considered to be limited to these descriptions; the dimensional data of this embodiment does not necessarily limit the technical solution, but only illustrates one specific working condition. For those skilled in the art of the present invention, simple improvements and modifications can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for adipic acid synthesis, characterized in that: The following steps are involved: (1) dissolving tetrapropylammonium hydroxide and an organic amine in water to obtain a first mixed solution; (2) preparing a metal salt solution, and adding ammonia water to the metal salt solution to obtain a second mixed solution; (3) adding the second mixed solution, the silicon source and the titanium source to the first mixed solution to obtain a glue solution; The glue solution is subjected to hydrothermal crystallization, washing, drying and calcination to obtain catalyst raw powder; (4) treating the catalyst raw powder with an organic acid solution to obtain an acid-treated catalyst raw powder; (5) The catalyst powder after the acid treatment is subjected to alkali treatment using a tetrapropylammonium hydroxide solution, and the catalyst for adipic acid synthesis is obtained through washing, drying and calcining.

2. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein The metal salt solution is prepared by dissolving a metal salt in water, wherein the cations of the metal salt include transition metal cations, preferably including one or more of iron ions, cobalt ions, nickel ions, copper ions, manganese ions, vanadium ions, chromium ions, and zinc ions; Preferably, the molar ratio of the metal salt to aqueous ammonia is 1:(1-10), preferably 1:(4-8); Preferably, the anion of the metal salt is one or more of acetate, citrate, sulfate, nitrate and chloride.

3. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein The organic acid solution includes an aqueous solution of one or more of acetic acid, propionic acid, acrylic acid, citric acid, oxalic acid, and benzoic acid; Preferably, the mass concentration of the organic acid solution is 1% to 10%, preferably 3% to 5%; Preferably, the temperature of the acid treatment in step (4) is 20 to 100° C., preferably 50 to 80° C.; and the time of the acid treatment is 10 to 200 minutes.

4. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein The mass ratio of the acid-treated catalyst powder to tetrapropylammonium hydroxide in step (5) is 1:(1-20), preferably 1:(3-7); Preferably, the temperature of the alkali treatment in step (5) is 80 to 220° C., preferably 150 to 190° C.; and the time of the alkali treatment is 20 to 80 hours.

5. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein The organic amine includes one or more of n-butylamine, triethylamine, tri-n-propylamine, n-propylamine, diethylamine, and ethylenediamine; Preferably, in step (1), the mass ratio of the tetrapropylammonium hydroxide to the organic amine is 1:(0.02-0.8), preferably 1:(0.3-0.5).

6. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein: The silicon source includes one or more of fumed silicon oxide, ethyl orthosilicate, and silica sol; Preferably, the titanium source includes one or more of isobutyl titanate, titanium oxide powder, and titanium tetrachloride; Preferably, the molar ratio of the silicon source to the titanium source is 1:(0.01-0.1), more preferably 1:(0.02-0.05).

7. The method for preparing a catalyst for adipic acid synthesis according to claim 1, wherein: The temperature of the hydrothermal crystallization is 80 to 220° C., preferably 150 to 190° C.; the time of the hydrothermal crystallization is 10 to 120 hours, preferably 48 to 84 hours.

8. A catalyst for adipic acid synthesis prepared by the preparation method according to any one of claims 1 to 7.

9. A method for synthesizing adipic acid, characterized in that: 1,2-cyclohexanediol is dissolved in a solvent and reacted with an oxidant in the presence of the catalyst for adipic acid synthesis according to claim 8 to produce adipic acid.

10. The method for synthesizing adipic acid according to claim 9, wherein The reaction temperature is 60-100°C, preferably 70-90°C; Preferably, the solvent comprises one or more of methanol, ethanol, isopropanol, tert-butanol, formic acid, acetic acid, acetonitrile, and 1,2-dichloroethane; Preferably, the oxidant comprises one or more of cumene hydroperoxide, tert-butyl hydroperoxide, ethylbenzene peroxide, and hydrogen peroxide; Preferably, the mass ratio of the 1,2-cyclohexanediol, the solvent and the catalyst for adipic acid synthesis is 1:(1-10):(0.1-6), preferably 1:(4-6):(0.3-1); Preferably, the molar ratio of the 1,2-cyclohexanediol to the oxidant is 1:(0.2-1), preferably 1:(0.5-0.8).

11. A method for synthesizing adipic acid, characterized in that: The following steps are involved: S1, cyclohexene is oxidized to obtain 1,2-cyclohexanediol; S2, dissolving the 1,2-cyclohexanediol in a solvent and reacting it with an oxidant in the presence of the catalyst according to claim 8 to produce adipic acid.

12. The method for synthesizing adipic acid according to claim 11, wherein The reaction temperature of step S2 is 60-100°C, preferably 70-90°C, and the reaction time is 30-240 min; Preferably, the solvent comprises one or more of methanol, ethanol, isopropanol, tert-butanol, formic acid, acetic acid, acetonitrile, and 1,2-dichloroethane; Preferably, the oxidant comprises one or more of cumene hydroperoxide, tert-butyl hydroperoxide, ethylbenzene peroxide, and hydrogen peroxide; Preferably, the mass ratio of the 1,2-cyclohexanediol, the solvent and the catalyst for adipic acid synthesis is 1:(1-10):(0.1-6), preferably 1:(4-6):(0.3-1); Preferably, the molar ratio of the 1,2-cyclohexanediol to the oxidant is 1:(0.2-1), preferably 1:(0.5-0.8).

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