Method for directionally preparing high-purity azelaic acid from oleic acid based on microchannel reactor

Abstract

The invention discloses a method for directionally preparing high-purity azelaic acid from oleic acid based on a micro-channel reactor, which comprises the following steps: mixing oleic acid and hydrogen peroxide dissolved with a catalyst, and feeding the mixture into the micro-channel reactor for oxidative cracking reaction to obtain oxidation liquid mainly containing the azelaic acid and the oleic acid; standing and layering the oxidation liquid to obtain a water phase A and an oil phase A; hot water is introduced into the oil phase A containing the nonanoic acid and the azelaic acid for extraction and liquid separation, and a water phase B and an oil phase B are obtained; fractionating the oil phase B to obtain high-purity nonanoic acid; cooling and crystallizing the water phase B to obtain a crude azelaic acid product, and melting and evaporating the crude product to remove moisture to obtain high-purity azelaic acid. Based on the microchannel reactor, hydrogen peroxide is used as an oxidizing agent, oleic acid double bonds can be directionally oxidized through a catalyst system, oleic acid is directly oxidized and cracked into nonanoic acid and azelaic acid in a short time, the reaction efficiency can be greatly improved, the reaction time can be shortened, and the use of a solvent and a phase transfer catalyst is avoided; the method has the advantages of high selectivity, high safety and remarkable environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic acid preparation, in particular, it relates to a method for preparing high-purity azelaic acid based on a micro-channel reactor. BACKGROUND

[0002] As a straight-chain saturated fatty acid containing 9 carbon atoms, nonanoic acid has a rapid expansion trend in application fields such as chemical industry, high-end manufacturing, food and medicine, due to its unique molecular structure. In the field of biological medicine, nonanoic acid can be used as a transdermal absorption enhancer, and when the purity is >98%, it can significantly improve the skin penetration rate of antibiotic ointment. In addition, nonanoic acid ester plasticizers generated by the reaction of nonanoic acid and ether substances can gradually replace ortho-phthalic plasticizers for the preparation of medical PVC infusion tubes. In the field of high-end manufacturing, nonanoic acid can be converted into electronic-grade nonylamine after ammoniation and hydrogenation, which is often used as a cleaning agent for semiconductor chips, and the purity of nonanoic acid raw material is required to be ≥99.5%. In addition, ester substances synthesized from nonanoic acid and pentaerythritol are widely used in lubricants in the field of aerospace, and the purity of nonanoic acid is required to be ≥98% to ensure the low-temperature flow performance of the lubricant. In the field of new energy, nonanoic acid with a purity of >98.5% can be used as an electrolyte additive to inhibit the excessive growth of SEI film and improve the cycle life of the battery. In the field of food, nonanoic acid with a purity of ≥98% and a total content of heavy metals (Pb / Hg / As) of <0.1 ppm is widely used as a food flavoring agent in baked foods.

[0003] At present, the mainstream process for industrial production of nonanoic acid is to use ozone oxidation cracking method to prepare nonanoic acid in a traditional static mixing reactor with oleic acid as raw material. This process has mild reaction conditions and high selectivity for the generation of nonanoic acid, but it also has the following obvious technical shortcomings: the diameter of ozone in the traditional static mixing reactor is large, the gas-liquid contact area is small, which leads to very low gas-liquid mass transfer efficiency, and the utilization rate of ozone is usually less than 30%, a large amount of ozone is wasted; in addition, this process needs to add mixed fatty acids as reaction solvents, which affects the separation and purification effect of nonanoic acid, and the purity of the final nonanoic acid product can only reach about 95%, which cannot meet the use requirements of high-purity nonanoic acid in downstream fields.

[0004] Azelaic acid, as a high-value-added dicarboxylic acid, is experiencing a surge in market demand for products with "high purity and low impurities" due to continuous technological advancements in its application fields. In the pharmaceutical sector, according to USP-NF standards, pharmaceutical-grade azelaic acid must meet stringent requirements: purity ≥99.5% and total heavy metal (Pb / Hg / As) content ≤10ppm. Especially in the treatment of moderate to severe rosacea, impurities can easily induce skin irritation; therefore, clinical applications heavily rely on products meeting purity standards. In the cosmetics field, INCI standards explicitly stipulate that cosmetic-grade azelaic acid must have a purity ≥99%, and the free fatty acid content must not exceed 0.5%. This is because its oil-controlling and whitening effects are highly dependent on the activity stability provided by high purity. In the polymer materials field, when synthesizing high-performance PA69, a 0.1% decrease in azelaic acid purity reduces the tensile strength of PA69 by 1.2-1.5MPa; therefore, this industry requires polymer-grade azelaic acid to have a purity of ≥99.8%. According to the 2024 Global Fine Chemicals Report, the market supply and demand gap for pharmaceutical and cosmetic grade azelaic acid is 35%-40%, and the current key constraint is that existing preparation processes cannot effectively balance high yield and high purity.

[0005] Currently, the preparation of azelaic acid mainly relies on two major technical routes: chemical oxidation and bio-fermentation. Chemical oxidation can be further divided into two categories: one is the oxidative cracking process based on unsaturated fatty acids, and the other is the direct oxidation process using nonanediol (aldehyde) as a raw material. Bio-fermentation, on the other hand, utilizes microbial transformation technology to gradually convert n-alkanes into dicarboxylic acids, thereby producing azelaic acid. However, this process has significant drawbacks—the microbial fermentation cycle is long, lasting 24-72 hours, resulting in low production efficiency; precise control of strain selection and cultivation conditions is difficult, posing a high technical barrier; and fluctuations in strain activity can easily lead to unstable product quality and poor consistency. On the other hand, while the direct oxidation method using nonanediol (aldehyde) is feasible, it requires a large amount of expensive raw material nonanediol (aldehyde), resulting in a significant cost disadvantage and making it difficult to meet the needs of large-scale production.

[0006] After decades of development, the mainstream azelaic acid production process in current industrial production has shifted to a synthetic route using oleic acid and ozone as core raw materials. Specifically, this process involves ozonation in a stirred tank reactor to generate ozonooxide intermediates, which are then subjected to deep oxidative pyrolysis to obtain crude azelaic acid. Finally, the refined product is obtained through separation and purification. The advantage of this process is that oleic acid is widely available and inexpensive, significantly reducing production costs. However, its application also faces many challenges: ozone is prone to thermal decomposition, releasing a large amount of heat, which can lead to thermal runaway and safety accidents, requiring efficient cooling systems and temperature interlock control, increasing system complexity; ozone leakage can cause environmental pollution and personal injury, requiring dedicated ozone generators and exhaust gas treatment systems; ozone has low solubility in oleic acid and low gas-liquid mass transfer efficiency, requiring efficient gas dispersion systems to increase the gas-liquid contact area; in addition, traditional stirred tank reactors have a large equivalent, uneven heat and mass transfer, low reaction efficiency, long reaction cycle, poor selectivity of azelaic acid during the reaction, high proportion of by-products, and high cost of subsequent separation and purification. These problems seriously restrict the sustainable development potential of this process.

[0007] Therefore, developing novel continuous reaction synthesis methods for nonanoic acid and azelaic acid to reduce the instability of the reaction process, shorten the reaction time, improve the purity and yield of nonanoic acid and azelaic acid, and reduce production costs are urgent problems to be solved.

[0008] In view of the above, this application is hereby submitted. Summary of the Invention

[0009] The existing technologies have problems such as the inability to achieve continuous production, poor process stability, long reaction time, low yield, and insufficient purity in the existing methods for preparing nonanoic acid and azelaic acid. In order to solve the above technical problems, the present invention provides a method for the directional preparation of high-purity azelaic acid based on oleic acid using a microchannel reactor. This method can directionally oxidize oleic acid to prepare high-purity nonanoic acid and azelaic acid, thereby meeting the production needs of high-purity nonanoic acid and azelaic acid.

[0010] This invention is achieved through the following technical solution: This invention provides a method for the directional preparation of high-purity azelaic acid from oleic acid using a microchannel reactor, comprising the following steps: S1, the filtered and preheated raw material oleic acid and hydrogen peroxide containing catalyst are respectively transported to the T-type mixer by a high-pressure constant flow pump and mixed. Then, they enter the microchannel reactor for oxidative cracking reaction to obtain an oxidized liquid mainly composed of nonanoic acid and azelaic acid. S2, the oxidizing liquid is transported to a separation tank for static separation, and the oil and water phases are separated by an intelligent liquid separator to obtain water phase A and oil phase A; S3, after concentrating the aqueous phase A containing catalyst, a small amount of hydrogen peroxide and azelaic acid, it is transferred to the aqueous phase intermediate tank. After detecting the catalyst ion concentration by ICP-MS, fresh catalyst and hydrogen peroxide are added according to the results, and the new feed liquid is circulated into the microchannel reactor to participate in the reaction. S4, the oil phase A containing nonanoic acid and azelaic acid is transferred to the extraction tower, and hot water is simultaneously introduced for extraction and separation to obtain aqueous phase B and oil phase B; S5, the oil phase B, which is mainly composed of nonanoic acid, is transferred to the fractionation tower for fractionation. A small amount of water and low fractions are removed from the top, and high-purity nonanoic acid product is obtained from the side stream. The bottom feed is transferred to the oil phase A for recycling extraction. S6, the aqueous phase B, mainly containing azelaic acid, is transferred to the crystallizer for cooling and crystallization. After filtration, crude azelaic acid and an aqueous solution containing a small amount of azelaic acid are obtained. After melting and evaporating to remove water, high-purity azelaic acid product is obtained. The azelaic acid aqueous solution is concentrated and then transferred to the extraction tower for recycling.

[0011] In a specific implementation, in step S1, the preheating operation is as follows: the raw material oleic acid is preheated at 40-60°C for 30-60 minutes.

[0012] In a specific embodiment, in step S1, the microchannel reactor is a series-tube type microchannel reactor, comprising a preheating section, a reaction section, and a cooling section; the preheating section and the reaction section use oil bath circulation for temperature control, with a temperature range of 0-300℃; the cooling section uses ice-water bath circulation, with a temperature range of 0-5℃; the oxidation reaction temperature of the microchannel reactor is controlled at 60-100℃, the back pressure of the microchannel reactor is controlled at 0.1-1.0 MPa, and the residence time of the mixed reactants in the microchannel reaction section is controlled at 30-300 s.

[0013] In a specific embodiment, in step S1, the raw material oleic acid includes 75-80% oleic acid and 10-15% linoleic acid, and the mass percentage of hydrogen peroxide in the raw material hydrogen peroxide is 20%-50%; the molar ratio of oleic acid to hydrogen peroxide is 1:4-6.

[0014] In a specific embodiment, in step S1, the catalyst is one or more of sodium tungstate, sodium molybdate, sodium phosphotungstate, phosphotungstic acid, and phosphomolybdic acid, and the amount of catalyst used is 0.2-1% of the amount of oleic acid.

[0015] In one specific embodiment, a co-catalyst is added in step S1. The co-catalyst is phosphoric acid, which is used to adjust the pH of the hydrogen peroxide solution to 2-4.

[0016] In a specific implementation, in step S2, the oil-water two-phase separation is performed after the oxidizing liquid has been allowed to stand for 30-120 minutes.

[0017] In a specific embodiment, in step S3, after the aqueous phase A is concentrated, fresh hydrogen peroxide and catalyst are added in proportion according to the amount of hydrogen peroxide, catalyst and oleic acid used. After stirring and mixing evenly, it is recycled as a raw material liquid.

[0018] In one specific embodiment, in step S4, hot water is added to extract azelaic acid. The temperature of the hot water is controlled at 70-100°C, and the volume ratio of the hot water to the oil phase A entering the extraction tower is 5-15:1.

[0019] In a specific implementation, in step S5, the pressure of the fractionation tower is controlled at 50-300 kPa and the temperature is controlled at 100-200 °C during the fractionation process.

[0020] In a specific embodiment, in step S6, the crystallizer temperature is controlled at 20-50°C during the crystallization process, the azelaic acid melting temperature is controlled at 80-130°C, and the evaporator pressure is controlled at 1-10 kPa and the temperature is controlled at 180-280°C during the evaporation process.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The method for directional preparation of high-purity azelaic acid based on microchannel reactor provided in this embodiment of the invention uses hydrogen peroxide as an oxidant and a catalyst system to directionally oxidize the double bond of oleic acid, directly oxidizing and cracking oleic acid into nonanoic acid and azelaic acid in a short time. This method can greatly improve reaction efficiency, shorten reaction time, avoid the use of solvents and phase transfer catalysts, reduce the emission of waste, and has strong selectivity, safety and significant environmental advantages. 2. The method for directional preparation of high-purity azelaic acid based on microchannel reactor provided in this embodiment of the invention has a simple raw material system and oxidation liquid system, which significantly reduces the difficulty of subsequent separation and purification of nonanoic acid and azelaic acid, reduces losses in the separation and purification process, and improves the purity of nonanoic acid and azelaic acid products, thus having significant economic benefits. 3. The method for directional preparation of high-purity azelaic acid based on microchannel reactor provided in this embodiment of the invention separates and purifies azelaic acid through processes such as extraction, crystallization, filtration, and evaporation. The heavy components and azelaic acid aqueous solution in the process are recycled, achieving an effective balance between high yield and high purity of azelaic acid. 4. The method for directional preparation of high-purity azelaic acid based on microchannel reactor provided in this embodiment of the invention utilizes the structural characteristics and hydrodynamic advantages of microchannel reactor. By using the strong shear force generated by the high specific surface area, the oil phase is broken into micron-sized droplets and dispersed in the aqueous phase, forming a large number of O / W type emulsion systems. This greatly enhances the mass transfer efficiency of the heterogeneous system and eliminates the dependence on the use of phase transfer catalysts. 5. The method for directional preparation of high-purity azelaic acid based on oleic acid using a microchannel reactor provided in this embodiment of the invention has excellent process stability and reproducibility. At the same time, the defects of the scale-up effect of the batch reactor can be eliminated by parallel scale-up, realizing continuous industrial production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the process for the directional preparation of high-purity azelaic acid from oleic acid using a microchannel reactor, as provided in Embodiment 1 of the present invention. Figure 2 The GC detection spectrum of high-purity oleic acid provided in Example 1 of this invention; Figure 3 This is the GC detection spectrum of nonanoic acid provided in Example 1 of the present invention; Figure 4 The GC detection spectrum of azelaic acid provided in Example 1 of this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0025] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0026] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “an embodiment,” “an example,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0027] Developing novel continuous reaction synthesis methods for nonanoic acid and azelaic acid to reduce reaction instability, shorten reaction time, improve the purity and yield of nonanoic acid and azelaic acid, and lower production costs are urgent problems to be solved. To address these technical issues: This invention provides a method for the directional preparation of high-purity azelaic acid from oleic acid using a microchannel reactor, comprising the following steps: S1, the filtered and preheated raw material oleic acid and hydrogen peroxide containing catalyst are respectively transported to the T-type mixer by a high-pressure constant flow pump and mixed. Then, they enter the microchannel reactor for oxidative cracking reaction to obtain an oxidized liquid mainly composed of nonanoic acid and azelaic acid. S2, the oxidizing liquid is transported to a separation tank for static separation, and the oil and water phases are separated by an intelligent liquid separator to obtain water phase A and oil phase A; S3, after concentrating the aqueous phase A containing catalyst, a small amount of hydrogen peroxide and azelaic acid, it is transferred to the aqueous phase intermediate tank. After detecting the catalyst ion concentration by ICP-MS, fresh catalyst and hydrogen peroxide are added according to the results, and the new feed liquid is circulated into the microchannel reactor to participate in the reaction. S4, the oil phase A containing nonanoic acid and azelaic acid is transferred to the extraction tower, and hot water is simultaneously introduced for extraction and separation to obtain aqueous phase B and oil phase B; S5, the oil phase B, which is mainly composed of nonanoic acid, is transferred to the fractionation tower for fractionation. A small amount of water and low fractions are removed from the top, and high-purity nonanoic acid product is obtained from the side stream. The bottom feed is transferred to the oil phase A for recycling extraction. S6, the aqueous phase B, mainly containing azelaic acid, is transferred to the crystallizer for cooling and crystallization. After filtration, crude azelaic acid and an aqueous solution containing a small amount of azelaic acid are obtained. After melting and evaporating to remove water, high-purity azelaic acid product is obtained. The azelaic acid aqueous solution is concentrated and then transferred to the extraction tower for recycling.

[0028] In a specific implementation, in step S1, the preheating operation is as follows: the raw material oleic acid is preheated at 40-60°C for 30-60 minutes.

[0029] In a specific embodiment, in step S1, the microchannel reactor is a series-tube type microchannel reactor, comprising a preheating section, a reaction section, and a cooling section; the preheating section and the reaction section use oil bath circulation for temperature control, with a temperature range of 0-300℃; the cooling section uses ice-water bath circulation, with a temperature range of 0-5℃; the oxidation reaction temperature of the microchannel reactor is controlled at 60-100℃, the back pressure of the microchannel reactor is controlled at 0.1-1.0 MPa, and the residence time of the mixed reactants in the microchannel reaction section is controlled at 30-300 s.

[0030] In a specific embodiment, in step S1, the raw material oleic acid includes 75-80% oleic acid and 10-15% linoleic acid, and the mass percentage of hydrogen peroxide in the raw material hydrogen peroxide is 20%-50%; the molar ratio of oleic acid to hydrogen peroxide is 1:4-6.

[0031] In a specific embodiment, in step S1, the catalyst is one or more of sodium tungstate, sodium molybdate, sodium phosphotungstate, phosphotungstic acid, and phosphomolybdic acid, and the amount of catalyst used is 0.2-1% of the amount of oleic acid.

[0032] In one specific embodiment, a co-catalyst is added in step S1. The co-catalyst is phosphoric acid, which is used to adjust the pH of the hydrogen peroxide solution to 2-4.

[0033] In a specific implementation, in step S2, the oil-water two-phase separation is performed after the oxidizing liquid has been allowed to stand for 30-120 minutes.

[0034] In a specific embodiment, in step S3, after the aqueous phase A is concentrated, fresh hydrogen peroxide and catalyst are added in proportion according to the amount of hydrogen peroxide, catalyst and oleic acid used. After stirring and mixing evenly, it is recycled as a raw material liquid.

[0035] In one specific embodiment, in step S4, hot water is added to extract azelaic acid. The temperature of the hot water is controlled at 70-100°C, and the volume ratio of the hot water to the oil phase A entering the extraction tower is 5-15:1.

[0036] In a specific implementation, in step S5, the pressure of the fractionation tower is controlled at 50-300 kPa and the temperature is controlled at 100-200 °C during the fractionation process.

[0037] In a specific embodiment, in step S6, the crystallizer temperature is controlled at 20-50°C during the crystallization process, the azelaic acid melting temperature is controlled at 80-130°C, and the evaporator pressure is controlled at 1-10 kPa and the temperature is controlled at 180-280°C during the evaporation process.

[0038] Example 1 like Figure 1As shown, this embodiment of the invention provides a method for the directional preparation of high-purity azelaic acid from oleic acid using a microchannel reactor, comprising the following steps: (1) The raw material selected is high-purity oleic acid commonly used in the production of azelaic acid. The results of the raw material testing are shown in Table 1, where the GC spectrum is as follows: Figure 2 As shown.

[0039] Table 1 Key Indicators of Raw Material Oleic Acid Material Acid value mg KOH / g C16-0 acid % C18-0 acid % C18-1 acid % C18-2 acid % Total acid % High purity oleic acid 198.8 5.402 1.604 78.67 12.34 100 The test and analysis results of high-purity oleic acid meet the usage standards.

[0040] 141g (approximately 0.5mol) of high-purity oleic acid after filtration was preheated at 40℃ for 30min. 4.42g (approximately 0.0015mol) of sodium phosphotungstenate was completely dissolved in 340g (approximately 2.5mol) of 25% hydrogen peroxide, and the pH of the hydrogen peroxide was adjusted to approximately 4 using phosphoric acid. The mixture was then allowed to stand to eliminate air bubbles. The oleic acid and hydrogen peroxide were then pumped through two pipelines to a T-type mixer via a high-pressure constant flow pump for mixing, and subsequently introduced into a microchannel reactor for oxidative cracking. The oxidation reaction temperature in the microchannel reactor was controlled at 80℃, the back pressure was set at 0.3MPa, and the residence time of the mixed reactants in the microchannel reaction section was controlled at 120s, yielding an oxidation solution mainly composed of nonanoic acid and azelaic acid. Samples of the oxidation solution were taken and analyzed; the results are shown in Table 2.

[0041] Table 2 Key Indicators of Oxidation Solution Material Octanoic acid % Nonanoic acid % Azelaic acid % C18 acid % Oxidation liquor 0.928 47.625 50.646 0.375 (2) The oxidizing liquid was allowed to stand and separate into aqueous phase A and oil phase A. Aqueous phase A was concentrated and reused as raw material for subsequent experiments. 1800g of water (oil-to-water volume ratio of about 1:10) at 90℃ was added to oil phase A, and extraction and separation were performed while hot to obtain aqueous phase B and oil phase B. Oil phase B, which mainly contains nonanoic acid, was distilled through a distillation column. The pressure of the distillation column was controlled at about 100kPa and the temperature of the distillation column bottom was 130-160℃. The initial fraction containing more water and low carbonic acid was discarded to obtain 49.5g of nonanoic acid with higher purity.

[0042] (3) The aqueous phase B, mainly containing azelaic acid, was transferred to a crystallizer for cooling crystallization. The crystallizer temperature was controlled at 35-40℃. After filtration, crude azelaic acid and an aqueous solution of azelaic acid were obtained. The aqueous solution of azelaic acid was concentrated and reused. The crude azelaic acid was melted at 110℃ to remove water, and then placed in an evaporator for evaporation. The evaporator pressure was controlled at about 2-5 kPa, and the evaporator temperature was controlled at 200-230℃, to obtain 56.7g of azelaic acid with high purity.

[0043] The oxidation solution analysis results show that the conversion rate of oleic acid in the microchannel reactor is 99.6%. The purified nonanoic acid and azelaic acid were then analyzed using GC spectroscopy. Figure 3 , Figure 4 As shown. The purity of nonanoic acid is 98.18%, and the yield of nonanoic acid is 79.6%. The purity of azelaic acid is 99.14%, and the yield of azelaic acid is 66.3%.

[0044] Example 2 Compared to Example 1, this embodiment only changed the residence time of the mixed reactants in the microchannel reaction section to 90 s, while keeping other process parameters and procedures unchanged. The final yield was 49.4 g of nonanoic acid and 56.2 g of azelaic acid. The purity of the nonanoic acid was 98.25%, and the yield was 79.5%. The purity of the azelaic acid was 99.18%, and the yield was 65.7%.

[0045] Example 3 Compared to Example 1, this embodiment only changed the reaction temperature of the microchannel reactor to 90°C, while keeping other process parameters and procedures unchanged. The final yield was 49.8 g of nonanoic acid and 57.5 g of azelaic acid. The purity of the nonanoic acid was 98.09%, and the yield was 80.1%. The purity of the azelaic acid was 99.25%, and the yield was 67.3%.

[0046] Example 4 Compared to Example 3, this embodiment only changed the back pressure of the microchannel reactor to 0.4 MPa, while keeping other process parameters and procedures unchanged. The final yield was 48.8 g of nonanoic acid and 57.2 g of azelaic acid. The purity of the nonanoic acid was 98.03%, and the yield was 78.5%. The purity of the azelaic acid was 99.21%, and the yield was 66.9%.

[0047] Example 5 Compared to Example 3, this embodiment only changed the molar ratio of oleic acid to hydrogen peroxide to 1:6, i.e., adding 408g (approximately 3.0mol) of 25% hydrogen peroxide. All other process parameters and procedures remained unchanged, ultimately yielding 49.8g of nonanoic acid and 57.3g of azelaic acid. The purity of the nonanoic acid was 98.26%, and the yield was 80.1%. The purity of the azelaic acid was 99.19%, and the yield was 67.0%.

[0048] Example 6 Compared to Example 3, this embodiment only changed the mass fraction of hydrogen peroxide to 30%, i.e., adding 283.3g (approximately 2.5mol) of hydrogen peroxide. Other process parameters and procedures remained unchanged, ultimately yielding 50.2g of nonanoic acid and 57.8g of azelaic acid. The purity of the nonanoic acid was 98.15%, and the yield was 80.8%. The purity of the azelaic acid was 99.23%, and the yield was 67.6%.

[0049] Example 7 Compared to Example 6, this example only changed the mass of the catalyst, sodium phosphotungstenate, to 5.89 g (approximately 0.002 mol), while keeping other process parameters and procedures unchanged. The final yield was 49.6 g of nonanoic acid and 57.0 g of azelaic acid. The purity of the nonanoic acid was 98.25%, and the yield was 79.8%. The purity of the azelaic acid was 99.28%, and the yield was 66.7%.

[0050] Example 8 Compared to Example 6, this example only changed the catalyst to phosphotungstic acid, specifically by adding 4.32 g (approximately 0.0015 mol) of phosphotungstic acid. All other process parameters and procedures remained unchanged, ultimately yielding 50.3 g of nonanoic acid and 58.1 g of azelaic acid. The purity of the nonanoic acid was 98.17%, and the yield was 80.9%. The purity of the azelaic acid was 99.20%, and the yield was 68.0%.

[0051] Example 9 Compared to Example 8, this embodiment only changed the hydrogen peroxide mass fraction to 35%, i.e., adding 242.8g of hydrogen peroxide (approximately 2.5mol). Other process parameters and procedures remained unchanged, ultimately yielding 49.8g of nonanoic acid and 58.3g of azelaic acid. The purity of the nonanoic acid was 98.28%, and the yield was 80.1%. The purity of the azelaic acid was 99.23%, and the yield was 68.2%.

[0052] Example 10 Compared to Example 8, this embodiment only changed the hydrogen peroxide mass fraction to 50%, i.e., adding 170g of hydrogen peroxide (approximately 2.5mol). Other process parameters and procedures remained unchanged, ultimately yielding 47.7g of nonanoic acid and 54.9g of azelaic acid. The purity of the nonanoic acid was 98.05%, and the yield was 76.8%. The purity of the azelaic acid was 99.12%, and the yield was 64.2%.

[0053] Comparative Example 1 Compared to Example 8, this comparative example only omits the filtration and preheating process of high-purity oleic acid. Instead, 141g (approximately 0.5mol) of high-purity oleic acid was directly fed into a microchannel for mixing and reaction. All other process parameters and procedures remained unchanged, ultimately yielding 45.2g of nonanoic acid and 52.8g of azelaic acid. The purity of nonanoic acid was 98.12%, and the yield was 72.7%. The purity of azelaic acid was 99.08%, and the yield was 61.7%.

[0054] Comparative Example 2 Compared to Example 9, this comparative example only omits the filtration and preheating processes for high-purity oleic acid. Instead, 141g (approximately 0.5mol) of high-purity oleic acid is directly fed into a microchannel for mixing and reaction. All other process parameters and procedures remain unchanged, ultimately yielding 45.7g of nonanoic acid and 53.7g of azelaic acid. The purity of nonanoic acid is 98.09%, and the yield is 73.5%. The purity of azelaic acid is 99.06%, and the yield is 62.8%.

[0055] Comparative Example 3 Compared to Example 8, this comparative example only omits the use of phosphoric acid as a co-catalyst for pH adjustment; instead, the hydrogen peroxide solution containing the catalyst is directly introduced into the microchannel for mixing and reaction. All other process parameters and procedures remain unchanged. The final yields were 43.8 g of nonanoic acid and 52.1 g of azelaic acid. The purity of the nonanoic acid was 98.05%, and the yield was 70.4%. The purity of the azelaic acid was 99.15%, and the yield was 60.9%.

[0056] Comparative Example 4 Compared to Example 9, this comparative example only omits the use of phosphoric acid as a co-catalyst for pH adjustment; instead, the hydrogen peroxide solution containing the catalyst is directly introduced into the microchannel for mixing and reaction. All other process parameters and procedures remain unchanged. The final yield is 44.5 g of nonanoic acid and 52.8 g of azelaic acid. The purity of nonanoic acid is 98.11%, and the yield is 71.6%. The purity of azelaic acid is 99.15%, and the yield is 61.7%.

[0057] Comparative Example 5 Compared to Example 8, this comparative example only changed the oxidation liquid treatment process. Instead of directly allowing the reacted oxidation liquid to stand and separate into phases, it was mixed with hot water at 60°C at a 1:1 volume ratio, followed by extraction and phase separation. Other process parameters and procedures remained unchanged, ultimately yielding 42.8 g of nonanoic acid and 49.3 g of azelaic acid. The purity of nonanoic acid was 98.15%, and the yield was 68.8%. The purity of azelaic acid was 99.18%, and the yield was 57.6%.

[0058] Comparative Example 6 Compared to Example 9, this comparative example only changed the oxidation liquid treatment process. Instead of directly allowing the reacted oxidation liquid to stand and separate into phases, it was mixed with hot water at 60°C at a 1:1 volume ratio, followed by extraction and phase separation. Other process parameters and procedures remained unchanged, ultimately yielding 44.1 g of nonanoic acid and 50.4 g of azelaic acid. The purity of nonanoic acid was 98.19%, and the yield was 70.9%. The purity of azelaic acid was 99.20%, and the yield was 58.9%.

[0059] Comparative Example 7 Compared to Example 8, this comparative example only changed the purification process of nonanoic acid and azelaic acid, while keeping other process parameters and procedures unchanged. Specifically, oil phase B was directly distilled, with a slight discarding of the foremilk, yielding 48.6g of nonanoic acid with high purity; aqueous phase B was directly subjected to cooling crystallization at 5°C, and the crystals were dried at 60°C for 4 hours to obtain 55.3g of azelaic acid with high purity. The purity of nonanoic acid was 96.35%, and the yield was 78.2%. The purity of azelaic acid was 96.62%, and the yield was 64.7%.

[0060] Comparative Example 8 Compared to Example 9, this comparative example only changed the purification process of nonanoic acid and azelaic acid, while keeping other process parameters and procedures unchanged. Specifically, oil phase B was directly distilled, with a slight discarding of the foremilk, yielding 48.9g of nonanoic acid with high purity; aqueous phase B was directly subjected to cooling crystallization at 5°C, and the crystals were dried at 60°C for 4 hours to obtain 54.6g of azelaic acid with high purity. The purity of nonanoic acid was 96.26%, and the yield was 78.6%. The purity of azelaic acid was 96.81%, and the yield was 63.8%.

[0061] Based on the results of Comparative Examples 1 and 8, and Comparative Examples 2 and 9, it can be seen that compared to filtration and preheating of the raw material oleic acid, directly mixing and reacting oleic acid with hydrogen peroxide resulted in no significant change in the purity of the obtained nonanoic acid and azelaic acid products, but a 5-8 percentage point decrease in yield. Comparative Examples 3 and 8, and Comparative Examples 4 and 9, compared to using a co-catalyst to adjust pH, showed no significant change in the purity of the nonanoic acid and azelaic acid products obtained without using a co-catalyst, but a 7-10 percentage point decrease in yield. Comparative Examples 5 and 8, and Comparative Examples 9... Compared with Example 6 and Example 9, the purity of nonanoic acid and azelaic acid products obtained by direct 1:1 hot water extraction and phase separation was not significantly different from that obtained by allowing the oxidation liquid to stand and separate into layers, but the yield decreased by 10-12 percentage points. Compared with Example 8 and Example 9, the yield of nonanoic acid product obtained by direct distillation of crude nonanoic acid was not significantly different, but the purity decreased by about 2 percentage points. The purity of azelaic acid product obtained by direct cooling crystallization and drying of crude azelaic acid decreased by about 1.5 percentage points, and the yield decreased by about 4 percentage points.

[0062] In summary, pretreatment of raw materials and the addition of co-catalysts can promote the directional oxidative cracking of oleic acid into nonanoic acid and azelaic acid, reducing the occurrence of side reactions. Refining the separation and purification process of nonanoic acid and azelaic acid can reduce process losses and effectively improve the purity and yield of the products.

[0063] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for the directed preparation of high purity azelaic acid from oleic acid based on a microchannel reactor, characterized in that, The method comprises the following steps: S1, respectively, the filtered and preheated raw material oleic acid and the catalyst dissolved in hydrogen peroxide are transported into a mixer for mixing, and then are introduced into a micro-channel reactor for oxidative cracking reaction to obtain an oxidation liquid containing nonanoic acid and azelaic acid; S2, the oxidation liquid is transported into a layered tank for static layering, and oil-water two phases are separated by an intelligent liquid layering instrument to obtain water phase A and oil phase A; S3, the water phase A containing the catalyst, a small amount of hydrogen peroxide and azelaic acid is concentrated and then transferred into a water phase intermediate tank, the ion concentration of the catalyst is detected by ICP-MS, fresh catalyst and hydrogen peroxide are added as new raw material liquid to participate in the reaction in the micro-channel reactor; S4, the oil phase A containing nonanoic acid and azelaic acid is transferred into an extraction tower, and hot water is introduced for extraction and separation to obtain water phase B and oil phase B; S5, the oil phase B containing nonanoic acid as the main component is transferred into a fractional distillation column for fractional distillation, a small amount of water and low-boiling fraction are removed from the top to obtain high-purity nonanoic acid product, and the column stillage is transferred into the oil phase A for cyclic extraction; S6, the water phase B containing azelaic acid as the main component is transferred into a crystallizer for cooling crystallization, and azelaic acid crude product and an aqueous solution containing a small amount of azelaic acid are obtained by filtration, the azelaic acid crude product is melted and evaporated to remove water to obtain high-purity azelaic acid product, and the azelaic acid aqueous solution is concentrated and then transferred into the extraction tower for cyclic utilization.

2. The method of claim 1, wherein the high purity azelaic acid is produced by the microchannel reactor based oleic acid directed preparation, characterized in that, In step S1, the specific operation of preheating is that the raw material oleic acid is preheated at 40-60℃ for 30-60min.

3. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S1, the micro-channel reactor adopts a series pipe type micro-channel reactor, which comprises a preheating section, a reaction section and a cooling section; the preheating section and the reaction section adopt oil bath circulation temperature control, and the temperature range is 0-300℃; the cooling section adopts ice water bath circulation, and the temperature range is 0-5℃; the oxidation reaction temperature of the micro-channel reactor is controlled at 60-100℃, the back pressure of the micro-channel reactor is controlled at 0.1-1.0Mpa, and the residence time of the mixed reactants in the micro-channel reaction section is controlled at 30-300s.

4. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S1, the raw material oleic acid comprises 75-80% of oleic acid and 10-15% of linoleic acid, and the mass fraction of hydrogen peroxide in the raw material hydrogen peroxide is 20-50%; the molar ratio of oleic acid to hydrogen peroxide is 1:4-6.

5. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S1, the catalyst adopts one or more of sodium tungstate, sodium molybdate, sodium phosphotungstate, phosphotungstic acid and phosphomolybdic acid, and the catalyst dosage is 0.2-1% of the molar amount of oleic acid; an auxiliary catalyst is also added in step S1, and the auxiliary catalyst is phosphoric acid, which is used to adjust the pH of the hydrogen peroxide solution to 2-4.

6. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S2, the oxidation liquid is static for 30-120min, and then oil-water two-phase layering is performed.

7. The method of claim 1, wherein the microchannel reactor is oriented to direct the flow of oil to the first microchannel and the flow of water to the second microchannel. In step S3, after the water phase A is concentrated, fresh hydrogen peroxide and catalyst are added according to the dosage of hydrogen peroxide and catalyst and oleic acid, and are stirred and mixed uniformly to be used as raw material liquid for recycling.

8. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S4, hot water is added for extraction of azelaic acid, the hot water temperature is controlled at 70-100℃, and the volume ratio of hot water to oil phase A entering the extraction tower is 5-15:

1.

9. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S5, the fractional distillation process is carried out at a pressure of 50-300kpa and a temperature of 100-200℃.

10. The method of claim 1, wherein the microchannel reactor is oriented to produce high purity azelaic acid from oleic acid. In step S6, the temperature of the crystallizer is controlled at 20-50°C during crystallization, the temperature of the nonanedioic acid is controlled at 80-130°C, the pressure of the evaporator is controlled at 1-10 kPa during evaporation, and the temperature is controlled at 180-280°C.

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