A method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid ester.

Abstract

This invention discloses a microwave-assisted autocatalytic hydrolysis method for preparing azelaic acid from monomethyl azelaic acid. Using monomethyl azelaic acid, a downstream product of oils and fats, as raw material, it is mixed with a certain proportion of water and subjected to an autocatalytic hydrolysis reaction in a microwave reactor. After heat preservation and layering, cooling crystallization, vacuum filtration, and vacuum drying, azelaic acid product is obtained with a purity of over 99%. This invention cleverly utilizes microwaves to enhance the ionization of the carboxyl hydrogen groups of the reactant monomethyl azelaic acid and the product azelaic acid, increasing the hydrogen ion concentration in the system and accelerating the ester hydrolysis reaction of monomethyl azelaic acid. Simultaneously, microwaves enhance the mixing and mass transfer of the oil and water phases, accelerating the vaporization of the byproduct methanol, promoting the forward hydrolysis reaction, and accelerating the hydrolysis rate. The conversion rate of monomethyl azelaic acid reaches over 99%. This invention has the advantages of simple process, green and renewable raw materials, no need for catalysts, and high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of biodiesel downstream product development technology, specifically relating to a method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid ester. Background Technology

[0002] Azelaic acid, also known as azelaic acid, is a medium- to long-chain dicarboxylic acid with a wide range of industrial applications. In industry, it is primarily used to synthesize dioctyl azelate and isobutyl azelate plasticizers. In the pharmaceutical field, azelaic acid is added to ointments for its antibacterial activity to treat skin diseases, and it is also used in the production of cosmetics to inhibit pigmentation abnormalities. In addition, azelaic acid can be used to produce lubricants, fragrances, emulsifiers, high-molecular-weight nylon 69, capacitors, flame retardants, flocculants, and more, demonstrating its high practical value.

[0003] Currently, oleic acid is mainly used industrially as a raw material for the ozone oxidative cracking method to prepare azelaic acid, which is then purified by vacuum distillation, solvent extraction, and crystallization. However, the cracking products from oleic acid to azelaic acid contain a large amount of alcohols, aldehydes, acidic reaction byproducts, and unreacted saturated fatty acids. The hydrogen bonding between the carboxyl and hydroxyl groups makes the separation and purification process complex and the production cost high. CN 108164416 B attempts to prepare monomethyl azelaic acid from purified methyl oleate via ozone oxidative cracking. The crude monomethyl azelaic acid can be purified to obtain high-purity monomethyl azelaic acid through distillation. Azelaic acid monomethyl ester can be hydrolyzed in an acidic environment to obtain azelaic acid product with high purity. The conversion rate of the hydrolysis reaction can reach 99% under the catalyst of strong acids such as sulfuric acid, indicating that the preparation of azelaic acid by hydrolysis of azelaic acid monomethyl ester is technically feasible. However, it generates a large amount of acidic wastewater, and the product has a high sulfur content, making the subsequent separation process more complicated. In the hydrolysis system without a catalyst, the hydrogen ion content of azelaic acid monomethyl ester is low, and the conversion efficiency of the hydrolysis reaction is low under the catalysis of hydrated hydrogen ions. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of this invention is to provide a method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid ester, which is particularly suitable for the preparation of azelaic acid from downstream oil products.

[0005] The technical solution adopted in this invention is as follows: The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid includes the following steps: using monomethyl azelaic acid, a downstream product of oils, as raw material, it is mixed with deionized water, and the reaction solution is transferred to a microwave reactor for reaction under microwave radiation. Under microwave action, both the monomethyl azelaic acid raw material and the subsequently produced azelaic acid product undergo dipole polarization and ion mass transfer, thereby dissociating hydrogen ions and realizing the rapid autocatalytic hydrolysis reaction of monomethyl azelaic acid. During the reaction, methanol vapor is continuously distilled out and collected by condensation. After the reaction is completed, the reaction solution is successively subjected to heat preservation and layering, cooling and crystallization, vacuum filtration, and vacuum drying to obtain the product azelaic acid.

[0006] Furthermore, the mass ratio of the raw material monomethyl azelaic acid to deionized water is 1:8~16, preferably 1:10~12.

[0007] Furthermore, the hydrolysis reaction temperature is 90~99℃, preferably 95~99℃.

[0008] Furthermore, the hydrolysis reaction takes 1 to 6 hours, preferably 2.5 to 4 hours.

[0009] Furthermore, the cooling crystallization temperature is 10-30℃, preferably 10-20℃.

[0010] Furthermore, the microwave heating power is 200W-600W, preferably 300W-500W.

[0011] The preparation method of the present invention has the following advantages and beneficial effects: (1) In this invention, the carboxyl group of the raw material azelaic acid monomethyl ester has strong polarity and is prone to dipole polarization and ion mass transfer in a microwave field, thereby increasing the hydrogen ion concentration of the system, increasing the hydrated hydrogen ion concentration, and enhancing the autocatalytic effect on the hydrolysis reaction; at the same time, as the reaction proceeds, the two carboxyl groups of the product azelaic acid further undergo dipole polarization and ion mass transfer under microwave action, dissociating more hydrogen ions and increasing the hydrated hydrogen ion concentration, thereby realizing the rapid autocatalytic hydrolysis reaction of azelaic acid monomethyl ester.

[0012] (2) In this invention, the raw material monomethyl azelaic acid molecules and water molecules move and collide at high speed under the action of microwave field, which enhances the mass transfer between the oil and water phases and greatly accelerates the hydrolysis reaction rate. On the other hand, microwave heating helps the by-product methanol vaporization, changes the phase equilibrium, promotes the hydrolysis reaction to proceed in the forward direction, and improves the conversion rate of monomethyl azelaic acid (the methanol vapor evaporated in the reaction will carry a large amount of water, which can be condensed and returned to the microwave reactor first, and then the uncondensed methanol can be condensed and collected).

[0013] (3) This invention does not require the addition of acidic catalysts such as sulfuric acid, thus avoiding problems such as equipment corrosion and acidic wastewater pollution. It has the advantages of simple process flow, green, high efficiency and low energy consumption. Attached Figure Description

[0014] Figure 1 This is a schematic flowchart of the microwave-assisted autocatalytic hydrolysis method for preparing azelaic acid from monomethyl azelaic acid ester according to the present invention. Detailed Implementation

[0015] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0016] A schematic flowchart of the method for preparing azelaic acid in this embodiment of the invention is shown below. Figure 1 As shown, methanol vapor is continuously distilled out during the reaction, and the moisture carried by the vapor condenses and returns to the reactor.

[0017] Example 1 12.20 g of 99.5% monomethyl azelaic acid raw material was mixed with water and placed in a microwave reactor. Under microwave power of 300 W and hydrolysis temperature of 95 °C, the mass ratio of monomethyl azelaic acid to deionized water was 1:12.3. The reaction was carried out in the microwave reactor for 4.0 h, and the conversion rate of monomethyl azelaic acid reached over 99%. The conversion rate comparison is shown in Table 1. After the reaction was completed, the mixture was placed in a heat-insulated separatory funnel and allowed to stand for 1 h. The lower aqueous phase was cooled and crystallized at 15 °C, and then filtered under reduced pressure and dried under vacuum to obtain 10.71 g of azelaic acid.

[0018] The yield and purity of azelaic acid were determined according to the standard HG / T 4481-2012 for industrial azelaic acid. In this example, the final purity of azelaic acid was 99.57%, and the yield was 94.80%. The comparison results between the obtained azelaic acid product and commercially available azelaic acid product are shown in Table 2.

[0019] Example 2 12.22 g of 99.5% (w / w) monomethyl azelaic acid was mixed with water and placed in a microwave reactor. Under microwave power of 400 W and hydrolysis temperature of 99 °C, the mass ratio of monomethyl azelaic acid to deionized water was 1:13.6. The reaction was carried out in the microwave reactor for 3.0 h, achieving a conversion rate of over 99% for monomethyl azelaic acid. The conversion rate comparison is shown in Table 1. After the reaction, the mixture was placed in a heat-insulated separatory funnel and allowed to stand for 1 h. The lower aqueous phase was cooled and crystallized at 20 °C, then filtered under reduced pressure and dried under vacuum to obtain 10.88 g of azelaic acid.

[0020] The yield and purity of azelaic acid were determined according to the standard HG / T 4481-2012 for industrial azelaic acid. In this example, the final purity of azelaic acid was 99.52%, and the yield was 96.15%. The comparison results between the obtained azelaic acid product and commercially available azelaic acid product are shown in Table 2.

[0021] Example 3 12.18 g of 99.5% monomethyl azelaic acid raw material was mixed with water and placed in a microwave reactor. Under microwave power of 500 W and hydrolysis temperature of 99 °C, the mass ratio of monomethyl azelaic acid to deionized water was 1:13.7. The reaction was carried out in the microwave reactor for 2.5 h, and the conversion rate of monomethyl azelaic acid reached over 99%. The conversion rate comparison is shown in Table 1. After the reaction was completed, the mixture was placed in a heat-insulated separatory funnel and allowed to stand for 1 h. The lower aqueous phase was cooled and crystallized at 15 °C, and then filtered under reduced pressure and dried under vacuum to obtain 10.78 g of azelaic acid.

[0022] The yield and purity of azelaic acid were determined according to the standard HG / T 4481-2012 for industrial azelaic acid. In this example, the final purity of azelaic acid was 99.53%, and the yield was 95.58%. The comparison results between the obtained azelaic acid product and commercially available azelaic acid product are shown in Table 2.

[0023] Example 4 12.33 g of 99.5% monomethyl azelaic acid raw material was mixed with water and placed in a microwave reactor. Under microwave power of 500 W and hydrolysis temperature of 95 °C, the mass ratio of monomethyl azelaic acid to deionized water was 1:11.2. The reaction was carried out in the microwave reactor for 3.0 h, and the conversion rate of monomethyl azelaic acid reached over 99%. The conversion rate comparison is shown in Table 1. After the reaction was completed, the mixture was placed in a heat-insulated separatory funnel and allowed to stand for 1 h. The lower aqueous phase was cooled and crystallized at 13 °C, and then filtered under reduced pressure and dried under vacuum to obtain 10.74 g of azelaic acid.

[0024] The yield and purity of azelaic acid were determined according to the standard HG / T 4481-2012 for industrial azelaic acid. In this example, the final purity of azelaic acid was 99.48%, and the yield was 94.07%. The comparison results between the obtained azelaic acid product and commercially available azelaic acid product are shown in Table 2.

[0025] Comparative Example 1 12.21 g of 99.5% (w / w) monomethyl azelaic acid was mixed with water and placed in a reactor. The reactor was heated in a conventional oil bath at a hydrolysis temperature of 98℃ and a mass ratio of monomethyl azelaic acid to deionized water of 1:12.2 for 6.0 h. The conversion rate of monomethyl azelaic acid was approximately 5%, as shown in Table 1. After the reaction, the mixture was placed in a separatory funnel and allowed to stand for 1 h. The lower aqueous phase was cooled and crystallized at 15℃, and then filtered under reduced pressure and dried under vacuum to obtain 0.56 g of azelaic acid.

[0026] The yield and purity of azelaic acid were determined according to the standard HG / T 4481-2012 for industrial azelaic acid. In this example, the final purity of azelaic acid was 92.1%, and the yield was 4.56%. The comparison results between the obtained azelaic acid product and commercially available azelaic acid product are shown in Table 2.

[0027] As can be seen from Table 1, in Comparative Example 1, using conventional oil bath heating, the azelaic acid monomethyl ester raw material rarely undergoes hydrolysis in water under an acid-free environment. In contrast, the conversion rate of the hydrolysis reaction using acid as a catalyst in the existing technology can reach 99%, indicating that the preparation of azelaic acid by hydrolysis of azelaic acid monomethyl ester under acidic conditions is technically feasible.

[0028] However, in Examples 1-4 of this invention, a microwave reaction is used, which eliminates the need for additional acid catalysts. The conversion rate of the hydrolysis reaction of azelaic acid monomethyl ester can reach over 99%. The microwave reaction of this invention promotes the dissociation of more hydrogen ions and increases the concentration of hydrated hydrogen ions, thereby achieving a rapid autocatalytic hydrolysis reaction of azelaic acid monomethyl ester and achieving unexpected technical effects.

[0029] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid ester, characterized in that... Includes the following steps: Using monomethyl azelaic acid, a downstream product of oils and fats, as a raw material, the mixture is combined with deionized water, and the reaction solution is transferred to a microwave reactor for reaction under microwave radiation. Under microwave action, both the monomethyl azelaic acid raw material and the subsequently produced azelaic acid product undergo dipole polarization and ion mass transfer, thereby dissociating hydrogen ions and realizing the rapid autocatalytic hydrolysis reaction of monomethyl azelaic acid. During the reaction, methanol vapor is continuously distilled off and collected by condensation. After the reaction is completed, the reaction solution is successively subjected to heat preservation and layering, cooling and crystallization, vacuum filtration, and vacuum drying to obtain the product azelaic acid. The mass ratio of the raw material monomethyl azelaate to deionized water is 1:8~16; The hydrolysis reaction temperature is 90~99℃; the hydrolysis reaction time is 1~6h; and the microwave heating power is 200W-600W.

2. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 1, characterized in that... The mass ratio of the raw material, monomethyl azelaic acid, to deionized water is 1:10~12.

3. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 1, characterized in that... The hydrolysis reaction temperature is 95~99℃.

4. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 1, characterized in that... The hydrolysis reaction takes 2.5 to 4 hours.

5. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 1, characterized in that... The cooling crystallization temperature is 10-30℃.

6. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 5, characterized in that... The cooling crystallization temperature is 10-20℃.

7. The method for preparing azelaic acid by microwave-assisted autocatalytic hydrolysis of monomethyl azelaic acid as described in claim 1, characterized in that... The heating power of microwaves is 300-500W.

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