A method for preparing azelaic acid by selective oxidation of oleic acid

Abstract

This invention discloses a method for the selective oxidation of oleic acid to prepare azelaic acid, belonging to the field of fine chemical preparation technology. The invention dissolves oleic acid in a mixed solvent composed of nonanoic acid, hexanoic acid, and low-polarity small-molecule ester solvents with strong solubility and low viscosity, and carries out an ozonooxidation reaction at 20-35℃. Ozone has good compatibility in this mixed solvent and can completely convert oleic acid into ozonates in a short time (≤180 min). A synthetic organic acid manganese(II)-copper(II) bimetallic complex is used as a catalyst for the oleic acid ozonate oxidation reaction. By adjusting the type of organic ligand and the ratio of manganese(II) source to copper(II) source in the catalyst, the efficiency and selectivity of the catalyst are improved. Azelaic acid can be obtained at a reaction temperature of 85-130℃ and a reaction time of 6-12 h, with a yield as high as 85.41% and a purity ≥99.8%.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical preparation technology, specifically relating to a method for efficiently preparing high-purity azelaic acid through a two-step ozono-catalytic oxidation of oleic acid in a mixed solvent. Background Technology

[0002] Azelaic acid, also known as azelaic acid, is an important chemical raw material with a wide range of applications. It is used in lubricant additives, plasticizers, and the textile industry (nylon). At higher purity levels, it can be used in food, pharmaceuticals, cosmetics, capacitors, and electrolytes. In 2020, demand reached one million tons, but domestic annual production was less than 20,000 tons, relying mainly on imports. Therefore, developing low-cost, high-efficiency technologies for preparing azelaic acid is crucial.

[0003] Oxidation of oleic acid and oleate esters is currently the main method for preparing azelaic acid. Oxidation strategies can be categorized into three phases based on the state of the oxidant: gas-phase, liquid-phase, and solid-phase. Gas-phase oxidation includes ozone oxidation, oxygen oxidation, and air oxidation; liquid-phase oxidation includes oxidation with nitric acid, hydrogen peroxide, and organic peroxyacids; and solid-phase oxidation generally uses sodium hypochlorite, potassium permanganate, or potassium dichromate. In comparison, gas-phase oxidation is a highly efficient, low-cost, and environmentally friendly method. In 1957, Emery Company in the United States developed an ozono-oxidation method for preparing azelaic acid, which is now used industrially. However, the ozono-oxidation method still faces challenges in production and low reaction efficiency. The main difficulties of this reaction are twofold: ① The ozono-oxidation reaction of oleic acid has low efficiency, is violently exothermic, and the temperature of the reaction system is difficult to control, increasing the risk of ozonooxide explosion due to thermal runaway; ② The oxidation reaction has poor selectivity, the product composition is complex, separation is difficult, and the product purity is low. Most of the reported methods use acetic acid as the reaction solvent. Ozone has very limited solubility in acetic acid (saturation concentration <20 mmol / L at room temperature). As ozonides are generated, the viscosity of the system increases, further hindering the dissolution of ozone in the solvent, making it difficult for the ozonation reaction to proceed completely. At the same time, the increased viscosity of the system reduces the heat transfer efficiency, and the accumulation of heat may lead to local overheating and safety accidents. In addition, acetic acid is acidic (pKa = 4.75, 25℃) and highly hygroscopic, causing serious corrosion to equipment during application, and its strong odor is not conducive to operation. This is also one of the reasons why azelaic acid production is difficult. As early as 2006, Sun Zicai et al. reported the preparation of azelaic acid by using water, nonanoic acid and acetic acid as a mixed solvent for the ozonation-oxidation reaction of oleic acid (Sun Zicai, Zhang Yagang, Wu Manjiang Aili, Hu Shuming, Gao Junjun. Study on the process of catalytic oxidation cracking of oleic acid to synthesize azelaic acid under mixed solvent [J]. China Oils and Fats, 2006, 31(3):40-42). However, the rapid decomposition of ozone in water and the presence of large amounts of water can cause phase separation in the system, both of which severely affect ozonation efficiency, increasing ozonation time and leading to incomplete ozonation reactions. Currently reported catalysts are mostly water-soluble inorganic salts (such as CoCl2, MnCl2, CuCl2, etc.) and acetates (such as cobalt acetate, manganese acetate, etc.), as well as solid oxides (such as MoO3, PbO2, MnO2, V2O5, etc.) and heteropoly acids (such as tungstic acid, phosphotungstic acid, etc.). However, these catalysts have poor compatibility with the feedstock oleic acid, preventing sufficient contact during the reaction and affecting the selectivity and efficiency of the oxidation reaction. Therefore, exploring suitable mixed solvent systems to increase ozone compatibility and reduce the viscosity of the reaction system, thereby increasing ozonation efficiency while reducing safety risks; and synthesizing homogeneous catalysts with good compatibility with oleic acid to improve the efficiency and selectivity of the catalytic oxidation of oleic acid ozonides to azelaic acid, are of great significance for achieving large-scale production of azelaic acid. Summary of the Invention

[0004] To address the shortcomings and deficiencies of the existing technologies, the present invention aims to provide a highly efficient, safe, and easy-to-operate method for the ozonation-catalytic oxidation of oleic acid to prepare azelaic acid. The present invention first provides a mixed solvent system free of water and acetic acid for the ozonation-catalytic oxidation of oleic acid. This solvent system is composed of nonanoic acid: hexanoic acid: propyl acetate / butyl acetate / dimethyl carbonate / diethyl carbonate. This mixed solvent system avoids the use of acetic acid and water, preventing solvent corrosion of equipment and avoiding phase separation in the reaction system. Nonanoic acid is miscible with C5-C8 monocarboxylic acids and small molecule ester solvents, increasing the solubility of oleic acid in the solvent while reducing the viscosity of the solvent system, which is beneficial for mass and heat transfer during the reaction. Moreover, ozone has high solubility, good stability, and is not easily decomposed in the mixed solvent, which is conducive to the ozonation of double bonds in oleic acid. Therefore, oleic acid can be rapidly and completely converted into oleic acid ozonates in this solvent system. Oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complexes serve as catalysts for the oxidation of oleic acid ozonides. The carboxylate or sulfonate groups on the long-chain acid coordinate with the metal center, forming coordinate and feedback bonds that regulate the electron density and orientation of the metal center. Mn(II) and Cu(II) have similar atomic radii, allowing for the formation of bimetallic center structures with different electronic configurations with the ligands. During the reaction, electrons freely migrate between the ligands and the metal center, increasing the electron transfer space, which is beneficial for charge transfer and dispersion, preventing side reactions, and increasing the selectivity of oleic acid ozonide oxidation. The long-chain organic acid ligands also increase the compatibility of the catalyst with the system, ensuring sufficient contact between the catalytic center and the reaction site, thus increasing reaction efficiency. Using oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complexes as catalysts, and introducing air, the catalytic oxidation of oleic acid ozonides to azelaic acid yields ≥85.41% with a purity ≥99.8%.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for the selective oxidation of oleic acid to prepare azelaic acid, comprising the following steps:

[0007] Step (1): Mix nonanoic acid, C5-C8 monocarboxylic acid and low-polarity solvent of small molecule ester evenly as a mixed solvent, add oleic acid, the volume ratio of oleic acid to mixed solvent is 10:100-100:10, control the temperature at 20-40℃, and pass ozone-containing oxygen or ozone-containing air through the mixture while stirring to carry out the ozonation reaction. Stop the reaction when the reaction solution can no longer decolorize Br2 / CCl4.

[0008] Step (2): Dissolve long-chain organic carboxylic acids or long-chain organic sulfonic acids in alcoholic organic solvents, add manganese (II) source and copper (II) source, ultrasonically disperse evenly, solvothermal treatment at 120-200℃ for 4-24h, and after cooling, wash and dry the resulting oily substance to obtain oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complex catalyst;

[0009] Step (3): Add the oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complex catalyst obtained in step (2) to the solution after the reaction in step (1), introduce air, and carry out the oxidation reaction at a temperature of 80-150℃ until the peroxide value in the reaction system remains unchanged and is below 10. -5 The reaction stops when the concentration reaches mol / g.

[0010] Step (4): Add boiling water to the reaction solution obtained in step (3) for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude azelaic acid product again with boiling water, filter the solution through a solid adsorbent while hot, and cool and recrystallize the filtrate again to obtain refined azelaic acid product.

[0011] Preferably, the volume ratio of nonanoic acid, C5-C8 monocarboxylic acid and low-polarity ester solvent in the mixed solvent in step (1) is 30-90:5-50:5-50.

[0012] Preferably, the low-polarity solvent of small molecule esters mentioned in step (1) is one or a combination of two or more of propyl acetate, butyl acetate, dimethyl carbonate, and diethyl carbonate.

[0013] Preferably, the C5-C8 monocarboxylic acid mentioned in step (1) is one or a combination of two or more of valeric acid, hexanoic acid, heptanoic acid, and octanoic acid.

[0014] Preferably, the stirring speed in step (1) is 200-1000 rpm.

[0015] Preferably, in step (1), the ozone concentration in the ozone-containing oxygen or ozone-containing air is 50-150 mg / L, the flow rate is 100-1000 mL / min, and the ozonation reaction time is 100-200 min.

[0016] Preferably, the long-chain organic carboxylic acid or long-chain organic sulfonic acid mentioned in step (2) is a long-chain organic carboxylic acid or long-chain organic sulfonic acid with 8-18 carbon atoms.

[0017] Preferably, the manganese(II) source in step (2) is one of manganese carbonate, basic manganese carbonate, or manganese hydroxide, and the copper(II) source is one of copper carbonate, basic copper carbonate, or copper hydroxide. The molar ratio of Mn(II) to Cu(II) is 9:1 to 1:9. The total molar amount of Mn(II) and Cu(II) is 0.1 to 0.9 times the molar amount of long-chain organic carboxylic acids or long-chain organic sulfonic acids.

[0018] Preferably, the alcohol solvent mentioned in step (2) is one of ethanol, ethylene glycol, propanol, propylene glycol, butanol, butanediol, and isopropanol.

[0019] Preferably, the reaction time for the heat of solution in step (2) is 10-24 h.

[0020] Preferably, the amount of catalyst used in step (3) is 1wt%-5wt% of the amount of oleic acid, and the reaction temperature is 85-130℃.

[0021] Preferably, the solid adsorbent in step (4) is natural bentonite or kaolin.

[0022] Compared with the prior art, the preparation method of the present invention has the following advantages and beneficial effects:

[0023] (1) The present invention uses a mixed solvent with strong solubility and low viscosity, which can increase the solubility of ozone and oleic acid, reduce the viscosity of the system, help disperse heat, improve the efficiency of ozonation reaction, and ensure the safety of reaction.

[0024] (2) The present invention synthesizes long-chain acid Mn(II)-Cu(II) bimetallic complex as a catalyst. On the one hand, the bimetallic center can give full play to the synergistic effect of the two and improve the reaction activity and selectivity. On the other hand, the long-chain organic acid ligand can increase the compatibility between the catalyst and the system, so that the catalytic center and the reaction site can be fully contacted and the reaction efficiency can be increased.

[0025] (3) In the process of refining azelaic acid, the present invention uses natural bentonite or kaolin to adsorb and remove trace organic impurities, which can remove impurities and reduce product loss.

[0026] (4) The method for producing azelaic acid by ozonation-oxidation of oleic acid proposed in this invention is simple to operate, and has high safety and efficiency. It is suitable for practical application of ozonation-oxidation of oleic acid and facilitates industrial-scale production. Attached Figure Description

[0027] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0028] Figure 1 This is the HPLC chromatogram of the azelaic acid product prepared in Example 1 of the present invention.

[0029] Figure 2 The infrared spectrum of the azelaic acid product prepared in Example 1 of this invention is shown.

[0030] Figure 3 The azelaic acid product prepared in Example 1 of this invention 1 H NMR spectrum.

[0031] Figure 4 The azelaic acid product prepared in Example 1 of this invention 13 C10 NMR spectrum. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0033] Example 1

[0034] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0035] Step (1): Mix nonanoic acid, hexanoic acid and propyl acetate in a volume ratio of 60:20:20 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce a 60 mg / L ozone / oxygen mixture at a flow rate of 300 mL / min to carry out the ozonation reaction. After 170 min, if the reaction solution sample cannot decolorize Br2 / CCl4, it is confirmed that the double bonds in oleic acid have completely reacted.

[0036] Step (2): 10g of dodecanoic acid was placed in 120mL of ethanol, and manganese carbonate and copper hydroxide (with a molar ratio of 3:1 to 0.5 times that of dodecanoic acid) were added. The mixture was ultrasonically dispersed and solvothermal treated at 150℃ for 12h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble dodecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0037] Step (3): Add 3 wt% dodecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 110℃, and after 6 h of reaction, the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0038] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through kaolin while hot, cool and recrystallize the filtrate again, filter and dry to obtain 10.13g of refined azelaic acid product with a yield of 85.41%. The purity of the product was determined to be >99.8% by high performance liquid chromatography with external standard method.

[0039] The structure of the obtained azelaic acid product was analyzed by infrared chromatography, proton nuclear magnetic resonance spectroscopy, and carbon spectroscopy. Figure 2-4 This is consistent with the results reported in the literature.

[0040] Example 2

[0041] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0042] Step (1): Mix nonanoic acid, hexanoic acid and butyl acetate in a volume ratio of 65:25:10 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce an ozonolysis reaction with a mixed gas of 80 mg / L ozone / oxygen at a flow rate of 250 mL / min. After 150 min, if the reaction solution sample cannot decolorize Br2 / CCl4, it is confirmed that the double bonds in oleic acid have completely reacted.

[0043] Step (2): 10g of octadecanoic acid was placed in 120mL of ethanol, and basic manganese carbonate and basic copper hydroxide (with a molar ratio of manganese (II) to copper (II) of 0.5 times that of octadecanoic acid) were added. The mixture was ultrasonically dispersed and solvothermal treated at 150℃ for 12h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble octadecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0044] Step (3): Add 3 wt% octadecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 110℃, and after 6 h of reaction, the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0045] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through kaolin while hot, cool and recrystallize the filtrate again, filter and dry to obtain 9.87g of refined azelaic acid product with a yield of 83.22%. The purity of the product was determined to be >99.5% by high performance liquid chromatography with external standard method.

[0046] Example 3

[0047] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0048] Step (1): Mix nonanoic acid, hexanoic acid and propyl acetate in a volume ratio of 40:50:10 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce an ozonolysis reaction with a concentration of 80 mg / L ozone / oxygen mixed gas at a flow rate of 350 mL / min. After 110 min, the solution becomes colorless and transparent. The reaction solution sample cannot cause Br2 / CCl4 to decolorize, confirming that the double bonds in oleic acid have completely reacted.

[0049] Step (2): 10g of tetradecanoic acid was placed in 120mL of ethanol, and manganese carbonate and copper hydroxide (with a molar ratio of 1:1 to 0.5 times that of tetradecanoic acid) were added. The mixture was ultrasonically dispersed and solvothermal treated at 150℃ for 12h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble tetradecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0050] Step (3): Add 3 wt% tetradecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 115℃, and carry out the oxidation reaction for 8 hours. After this process, the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0051] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through bentonite while hot, cool and recrystallize the filtrate again, filter and dry to obtain 9.66g of refined azelaic acid product with a yield of 81.45%. The purity of the product was determined to be >99.8% by high performance liquid chromatography with external standard method.

[0052] Example 4

[0053] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0054] Step (1): Mix nonanoic acid, hexanoic acid and diethyl carbonate in a volume ratio of 55:40:5 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce a 95 mg / L ozone / oxygen mixture at a flow rate of 300 mL / min to carry out the ozonation reaction. After 120 min, if the reaction solution sample cannot decolorize Br2 / CCl4, it is confirmed that the double bonds in oleic acid have completely reacted.

[0055] Step (2): 10g of hexadecanoic acid was placed in 120mL of ethanol, and manganese carbonate and copper hydroxide (with a molar ratio of 4:1 to 0.5 times that of hexadecanoic acid) were added. The mixture was ultrasonically dispersed and solvothermal treated at 150℃ for 12h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble hexadecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0056] Step (3): Add 5 wt% hexadecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 120℃, and carry out the oxidation reaction for 10 h. After this reaction, the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0057] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through kaolin while hot, cool and recrystallize the filtrate again, filter and dry to obtain 9.36g of refined azelaic acid product with a yield of 78.91%. The purity of the product was determined to be >99.6% by high performance liquid chromatography with external standard method.

[0058] Example 5

[0059] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0060] Step (1): Mix nonanoic acid, hexanoic acid and dimethyl carbonate in a volume ratio of 50:40:10 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce a 120 mg / L ozone / oxygen mixture at a flow rate of 150 mL / min to carry out the ozonation reaction. After 180 min, if the reaction solution sample cannot decolorize Br2 / CCl4, it is confirmed that the double bonds in oleic acid have completely reacted.

[0061] Step (2): 10g of dodecanoic acid was placed in 120mL of ethanol, and basic manganese carbonate and basic copper carbonate (with a molar ratio of manganese (II) to copper (II) of 0.5 times that of dodecanoic acid) were added. The mixture was ultrasonically dispersed and solvothermal treated at 180℃ for 24h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble dodecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0062] Step (3): Add 3 wt% dodecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 110℃, and carry out the oxidation reaction for 10 h until the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0063] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through kaolin while hot, cool and recrystallize the filtrate again, filter and dry to obtain 9.29 g of purified azelaic acid product with a yield of 78.32%. The purity of the product was determined to be >99.4% by high performance liquid chromatography with external standard method.

[0064] Example 6

[0065] This embodiment provides a method for efficiently preparing high-purity azelaic acid via a two-step ozono-catalytic oxidation process using oleic acid in a mixed solvent, comprising the following steps:

[0066] Step (1): Mix nonanoic acid, hexanoic acid and butyl acetate in a volume ratio of 30:30:40 to form a mixed solvent. Dissolve 20 mL of oleic acid in 80 mL of the mixed solvent. Control the temperature at 20-35℃ and the rotation speed at 500 rpm. Introduce a 100 mg / L ozone / oxygen mixture at a flow rate of 300 mL / min to carry out the ozonation reaction. After 115 min, if the reaction solution sample cannot decolorize Br2 / CCl4, it is confirmed that the double bonds in oleic acid have completely reacted.

[0067] Step (2): 10g of dodecanoic acid was placed in 120mL of ethanol, and manganese carbonate and copper hydroxide (with a molar ratio of 1:2 of manganese(II) and copper(II)) were added in 0.5 times the molar amount of dodecanoic acid. The mixture was ultrasonically dispersed and solvothermal treated at 150℃ for 12h. After cooling, the resulting oily substance was washed and dried to obtain an oil-soluble dodecanoic acid Mn(II)-Cu(II) bimetallic complex catalyst.

[0068] Step (3): Add 3 wt% dodecanoic acid Mn(II)-Cu(II) bimetallic complex as a catalyst to the solution after the reaction in step (1), introduce air, raise the reaction temperature to 100℃, and after 8 hours of reaction, the peroxide value in the reaction system remains unchanged and is below 10. -5 At a concentration of mol / g, the ozonides are considered to have reacted completely.

[0069] Step (4): Add boiling water to the reaction solution for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude product again with boiling water, filter the solution through kaolin while hot, cool and recrystallize the filtrate again, filter and dry to obtain 9.19g of refined azelaic acid product with a yield of 77.48%. The purity of the product was determined to be >98.3% by high performance liquid chromatography with external standard method.

[0070] Comparative Example 1

[0071] In step (1), the solvent was acetic acid, and the other conditions were the same as in Example 1. After 310 min, the ozonolysis was complete, and 6.51 g of purified azelaic acid product was finally obtained, with a yield of 54.88% and a product purity of >92.5%.

[0072] Comparative Example 2

[0073] In step (1), the solvent was nonanoic acid: acetic acid: water in a volume ratio of 40:30:30. Other conditions were the same as in Example 1. After 360 min, ozonolysis was complete, and 5.94 g of purified azelaic acid product was finally obtained, with a yield of 50.08% and a product purity of >94.1%.

[0074] Comparative Example 3

[0075] No catalyst was added in step (3), and other conditions were the same as in Example 1. After 170 min, ozonation was complete, and 3.96 g of purified azelaic acid product was finally obtained, with a yield of 33.38% and a product purity of >91.5%.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for the selective oxidation of oleic acid to prepare azelaic acid, characterized in that, Includes the following steps: Step (1): Mix nonanoic acid, hexanoic acid and low polarity solvent of small molecule ester evenly as a mixed solvent, add oleic acid, the volume ratio of oleic acid to mixed solvent is 10:100-100:10, control the temperature at 20-40°C, and pass ozone-containing oxygen or ozone-containing air through the mixture while stirring to carry out the ozonation reaction. Stop the reaction when the reaction solution can no longer decolorize Br2 / CCl4. Step (2): Dissolve long-chain organic carboxylic acids in alcohol organic solvents, add manganese (II) source and copper (II) source, disperse evenly by ultrasonication, and solvothermal treatment at 120-200℃ for 4-24 h. After cooling, wash and dry the resulting oily substance to obtain oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complex catalyst. Step (3): The oil-soluble long-chain acid Mn(II)-Cu(II) bimetallic complex catalyst obtained in step (2) is added to the solution after the reaction in step (1), air is introduced, and the oxidation reaction is carried out at a temperature of 80-150°C until the peroxide value in the reaction system is constant and less than 10 -5 mol / g, and the reaction is stopped. Step (4): Add boiling water to the reaction solution obtained in step (3) for extraction, separate the aqueous phase, cool and recrystallize to obtain crude azelaic acid product. Dissolve the crude azelaic acid product again with boiling water, filter the solution through a solid adsorbent while hot, and cool and recrystallize the filtrate again to obtain refined azelaic acid product. The volume ratio of nonanoic acid, hexanoic acid and low-polarity small molecule ester solvent in the mixed solvent in step (1) is 30-90:5-50:5-50; the low-polarity small molecule ester solvent in step (1) is one or a combination of two or more of propyl acetate, butyl acetate, dimethyl carbonate and diethyl carbonate. In step (2), the molar ratio of Mn(II) to Cu(II) is 9:1-1:9; the total molar amount of Mn(II) and Cu(II) is 0.1-0.9 times the molar amount of the long-chain organic carboxylic acid; the long-chain organic carboxylic acid is a long-chain organic carboxylic acid with 8-18 carbon atoms.

2. The method according to claim 1, characterized in that, The stirring speed in step (1) is 200-1000 rpm.

3. The method according to claim 1, characterized in that, In step (1), the ozone concentration in the ozone-containing oxygen or air is 50-150 mg / L, the flow rate is 100-1000 mL / min, and the ozonation reaction time is 100-200 min.

4. The method according to claim 1, characterized in that, The manganese(II) source mentioned in step (2) is one of manganese carbonate, basic manganese carbonate, or manganese hydroxide, and the copper(II) source is one of copper carbonate, basic copper carbonate, or copper hydroxide.

5. The method according to claim 1, characterized in that, The alcohol solvent mentioned in step (2) is one of ethanol, ethylene glycol, propanol, propylene glycol, butanol, butanediol, and isopropanol; the reaction time for the heat of solution is 10-24 h.

6. The method according to claim 1, characterized in that, The amount of catalyst used in step (3) is 1wt%-5wt% of the amount of oleic acid, and the reaction temperature is 85-130°C.

7. The method according to claim 1, characterized in that, The solid adsorbent mentioned in step (4) is natural bentonite or kaolin.

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