Method for preparing azelaic acid by oxidative cracking of epoxy fatty acid

Abstract

The invention discloses a method for preparing azelaic acid by oxidative cracking of epoxy fatty acid, which comprises the following steps: by taking chitin quaternary ammonium salt loaded with phosphotungstic acid as a catalyst and taking epoxy fatty acid methyl ester and hydrogen peroxide as raw materials, preparing the azelaic acid through oxidative cracking and hydrolysis reaction. Compared with the existing other catalysts, the chitin quaternary ammonium salt catalyst loaded with phosphotungstic acid prepared by the invention has higher catalytic activity and high yield in azelaic acid synthesis by oxidative cracking of epoxy fatty acid methyl ester. And the azelaic acid synthesis process is simple and can be repeatedly used, the defects that the catalyst is difficult to separate, the cracking reaction temperature is high, the use amount of hydrogen peroxide is large and the like in the same product synthesis method are overcome, and industrial application is more facilitated.

Description

Technical Field

[0001] The invention belongs to the field of oil and fat chemical industry, and specifically relates to a method for preparing azelaic acid by oxidative cracking of epoxy fatty acid. Background Art

[0002] Azelaic acid replaces petroleum-based dibasic acids and is used to produce high-performance nylon, polyurethane and other new materials that are supported by the state. At present, the preparation of such compounds is mainly obtained by oxidative cracking of unsaturated fatty acids such as oleic acid. The main oxidants currently used for oxidative cracking of unsaturated fatty acids are ozone and hydrogen peroxide. Ozone oxidation consumes high energy and requires special equipment, while hydrogen peroxide is widely available and inexpensive, making it an ideal oxidant.

[0003] However, in the process of oxidative cracking of unsaturated fatty acids, it is necessary to go through the steps of double bond epoxidation, ring opening, cracking, etc., the amount of hydrogen peroxide used is large (usually 6-8 times the amount of unsaturated fatty acid substances), and the reaction temperature is usually over 100°C, which is explosive. If epoxy fatty acids can be directly used as raw materials for the reaction, the amount of hydrogen peroxide used in the reaction process can be reduced, the cracking reaction temperature can be reduced, and the safety of the reaction can be improved, which is of great significance.

[0004] The prior art CN115945215A reports a sodium lignin sulfonate quaternary ammonium salt-loaded phosphotungstic acid catalyst for catalytic oxidation of oleic acid to prepare azelaic acid. Although the catalyst loss is reduced, the applicant found that the catalytic performance of the catalyst when used for epoxy fatty acids still has much room for improvement.

[0005] At the same time, epoxy fatty acids are currently mainly used to produce surfactants and plasticizers, with low added value and problems such as overcapacity. Summary of the invention

[0006]

Technical issues

[0007] Based on the above-mentioned deficiencies of the unsaturated fatty acid oxidative cleavage reaction and the problem of low added value of epoxy fatty acids, the present invention proposes a novel phosphotungstate chitosan quaternary ammonium salt solid base catalyst, which can realize the efficient preparation of the intermediate monomethyl azelaic acid using epoxy fatty acids as raw materials, and then produce azelaic acid, thereby solving the problems existing in the current preparation process of azelaic acid to meet the needs of industrial production.

[0008] In addition, by oxidatively cleaving the epoxy bonds in epoxy fatty acids to obtain azelaic acid, the added value of epoxy fatty acids can be greatly increased, while reducing the amount of hydrogen peroxide and the reaction temperature, thereby improving the safety and economy of the reaction.

[0009]

Technical solution

[0010] In order to prepare azelaic acid by reacting epoxy fatty acid methyl ester and hydrogen peroxide, the present invention synthesizes a chitin quaternary ammonium salt catalyst loaded with phosphotungstic acid, prepares azelaic acid monomethyl ester by a solvent-free one-step reaction, and then obtains azelaic acid by high-pressure hydrolysis.

[0011] The present invention provides a more green and efficient method for preparing azelaic acid by reacting epoxy fatty acid methyl ester with hydrogen peroxide. The catalyst of the method is simple to prepare, easy to separate and reusable, and the oxidation cracking reaction temperature is low and the amount of hydrogen peroxide used is small.

[0012] Specific location:

[0013] On the one hand, the present invention provides a phosphotungstate chitosan quaternary ammonium salt solid base catalyst, and the preparation method of the catalyst comprises the following steps:

[0014] S1: chitosan, NaOH aqueous solution and epichlorohydrin are mixed and stirred at a constant temperature, and then the pH is adjusted to 7-9, washed with deionized water, and dried to obtain etherified chitosan;

[0015] S2: mixing the etherified chitosan and the NaOH solution, then dropping an alkyl tertiary amine, stirring at a constant temperature, adjusting the pH to acidic after the reaction, washing with deionized water, and drying to obtain a chitosan quaternary ammonium salt;

[0016] S3: dissolving chitosan quaternary ammonium salt in water, adding phosphotungstic acid aqueous solution, reacting at a constant temperature, and after the reaction is completed, filtering, collecting solids, drying, and grinding to obtain phosphotungstic acid chitosan quaternary ammonium salt solid base catalyst.

[0017] As a specific implementation of the present invention, the concentration of the NaOH aqueous solution is 3-8 mol / L; specifically, 6 mol / L may be selected.

[0018] As a specific implementation of the present invention, in step S1, the mass ratio of chitosan to sodium hydroxide is 1:(2-5); specifically, 1:3 may be selected.

[0019] As a specific implementation of the present invention, in step S1, the mass ratio of chitosan to epichlorohydrin is 1:(2-8); specifically, 1:4 may be selected.

[0020] As a specific embodiment of the present invention, in step S1, 2 mol / L disodium hydrogen phosphate is used to adjust the pH to 7-9.

[0021] As a specific implementation of the present invention, the temperature in step S1 is kept constant at 50-80°C; specifically, 65°C may be selected.

[0022] As a specific implementation of the present invention, the stirring time in step S1 is 1-8 hours, and specifically 5 hours can be selected.

[0023] As a specific embodiment of the present invention, the alkyl tertiary amine in step S2 is selected from: dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, hexadecyl dimethyl tertiary amine, and octadecyl dimethyl tertiary amine.

[0024] As a specific implementation of the present invention, in step S2, the mass ratio of etherified chitosan to NaOH is 1:(0.05-0.1). Specifically, it can be 1:0.072.

[0025] As a specific embodiment of the present invention, in step S2, the mass ratio of etherified chitosan to alkyl tertiary amine is 1:(2-4), and specifically 1:2.4.

[0026] As a specific embodiment of the present invention, the concentration of the NaOH solution in step S2 is 0.1-0.5 mol / L, and can be 0.3 mol / L.

[0027] As a specific embodiment of the present invention, in step S2, 1 mol / L hydrochloric acid is used to adjust the pH to acidic.

[0028] As a specific embodiment of the present invention, the pH in step S2 is 3-5.

[0029] As a specific implementation of the present invention, the temperature in step S2 is kept constant at 50-80°C; specifically, 65°C may be selected.

[0030] As a specific implementation of the present invention, the stirring time in step S2 is 1-8 hours; specifically, 4 hours can be selected.

[0031] As a specific embodiment of the present invention, in step S3, the mass ratio of chitosan quaternary ammonium salt to phosphotungstic acid is 1:(2-4).

[0032] As a specific embodiment of the present invention, in step S3, the concentration of the chitosan quaternary ammonium salt dissolved in water is 0.05-0.5 g / mL; specifically, 0.1 g / mL may be selected.

[0033] As a specific embodiment of the present invention, the concentration of the phosphotungstic acid aqueous solution in step S3 is 0.1-0.5 g / mL; further, it can be 0.2-0.3 g / mL.

[0034] As a specific implementation of the present invention, the temperature in step S3 is kept constant at 50-80°C; specifically, 60°C may be selected.

[0035] As a specific implementation of the present invention, the reaction time in step S3 is 0.5-2h; specifically, 1h can be selected.

[0036] In another aspect, the present invention provides a method for preparing azelaic acid monoester by a solvent-free one-pot process, comprising the following steps:

[0037] The chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid, epoxy fatty acid ester and hydrogen peroxide are mixed and heated for reaction to obtain azelaic acid monoester.

[0038] As a specific embodiment of the present invention, the epoxy fatty acid ester can specifically be epoxy fatty acid methyl ester.

[0039] As a specific embodiment of the present invention, the azelaic acid monoester can be specifically azelaic acid monomethyl ester.

[0040] The structure of the monomethyl azelate is

[0041] As a specific embodiment of the present invention, after the reaction is completed, the solid-liquid separation and the solid collection can be carried out to recover the chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid and continue to use it.

[0042] In another aspect, the present invention provides a method for preparing azelaic acid, comprising the following steps:

[0043] (1) Preparation of azelaic acid monoester by a solvent-free one-pot method: The chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid, epoxy fatty acid ester and hydrogen peroxide are mixed and heated for reaction to obtain azelaic acid monoester in one step; and the chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid is recovered;

[0044] (2) Azelaic acid monoester is hydrolyzed to obtain azelaic acid.

[0045] The structure of azelaic acid is

[0046] As a specific embodiment of the present invention, the process of preparing azelaic acid monolipid by a one-pot method without solvent also includes separation of the product after the reaction is completed: the oil phase is separated by extraction operation.

[0047] As a specific embodiment of the present invention, the solvent used for extraction is isooctane.

[0048] As a specific embodiment of the present invention, in the process of preparing azelaic acid monoester by a solvent-free one-pot method, the hydrogen peroxide can be selected from 30 wt % hydrogen peroxide aqueous solution.

[0049] As a specific embodiment of the present invention, in the process of preparing azelaic acid monolipid by a solvent-free one-pot method, the molar ratio of epoxy fatty acid methyl ester: hydrogen peroxide is 1:(3.5-5.0); more preferably 1:(4-5).

[0050] As a specific embodiment of the present invention, in the process of preparing azelaic acid monoester by a solvent-free one-pot method, the amount of catalyst used is 4wt%-10wt% of the epoxy fatty acid ester; more preferably 5wt%-10wt%;.

[0051] As a specific embodiment of the present invention, in the process of preparing azelaic acid monoester by a solvent-free one-pot method, the reaction time is 2-5 hours, and more preferably 3-4 hours.

[0052] As a specific embodiment of the present invention, during the solvent-free one-pot process for preparing azelaic acid monoester, the reaction temperature is 60-90°C, more preferably 70-90°C, and most preferably 80°C.

[0053] As a specific embodiment of the present invention, the reaction temperature in step (2) is 200-250°C; more preferably 220°C.

[0054] As a specific embodiment of the present invention, the hydrolysis process in step (2) is also carried out under a certain pressure, and the reaction pressure is 4-6Mpa, preferably 5Mpa.

[0055] Beneficial effects of the present invention:

[0056] (1) The present invention uses epoxy fatty acid ester and hydrogen peroxide as raw materials, and the chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid is prepared, and azelaic acid is obtained by oxidative cracking and high-pressure hydrolysis. The chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid prepared by the present invention has higher catalytic activity and high yield in the synthesis of azelaic acid compared with other catalysts.

[0057] (2) The chitosan quaternary ammonium salt catalyst loaded with phosphotungstic acid of the present invention is simple to prepare, plays an important role in the cracking of epoxy fatty acid esters, and has high stability. After being recycled for 5 times, the recovery rate can still reach more than 92%.

[0058] (3) The present invention successfully provides a direct, efficient and green method for preparing nonanoic acid and nonanedioic acid monoesters by oxidative cleavage of epoxy oleate. Compared with the prior art, the present invention prepares chitosan quaternary ammonium salt HPW-CT-QAS loaded with phosphotungstic acid. 16 The catalyst and the reaction product, azelaic acid monoester, can be separated by simple solid-liquid separation methods, which not only overcomes the defects of using precious metal catalysts, high oxidant toxicity, poor selectivity, and environmental pollution in the synthesis of azelaic acid monoester, but also realizes the chitin quaternary ammonium salt HPW-CT-QAS loaded with phosphotungstic acid. 16 Rapid and efficient recovery of the catalyst, thereby realizing the chitosan quaternary ammonium salt HPW-CT-QAS loaded with phosphotungstic acid 16 The catalyst can be reused multiple times.

[0059] (4) The process of the present invention is simple, the product selectivity is high, and the product is easy to separate from the catalyst and can be reused, which solves the shortcomings of the catalyst being difficult to separate and the product having low purity and poor selectivity in the synthesis method of the same product. The intermediate azelaic acid monoester has high selectivity, mild reaction conditions, and a small amount of hydrogen peroxide, which is more conducive to industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 CT, CY-QAS, HPW-CT-QAS 16 , infrared spectrum of HPW. DETAILED DESCRIPTION

[0061] In order to facilitate further understanding of the present invention, the following examples are provided to illustrate it in more detail. However, these examples are only to help better understand the invention and are not intended to limit the scope or implementation principles of the present invention. The implementation methods of the present invention are not limited to the following contents.

[0062] Example 1 Preparation of phosphotungstate chitosan quaternary ammonium salt solid base catalyst

[0063] (1) Preparation of etherified alkaline chitosan (ECT)

[0064] S1: Pour 5 g of chitosan (CT), 60 mL of 6 mol / L NaOH aqueous solution, and 17 mL (20 g) of epichlorohydrin into a 250 mL three-necked flask to obtain solution Ⅰ-1, and stir at a constant temperature of 65°C for 5 h.

[0065] S2: Adjust the pH of solution Ⅰ-1 to about 7 with an appropriate amount of 2 mol / L disodium hydrogen phosphate to obtain solid Ⅱ-1;

[0066] S3: Rinse solid II-1 with a large amount of deionized water and dry at 60°C for 12 h to obtain relatively pure etherified chitosan ECT.

[0067] (2) Preparation of quaternary ammonium salt of alkaline chitosan (CT-QAS 16 )

[0068] S1: Add 5 g of the obtained etherified alkaline chitosan solid into a 250 mL three-necked flask containing 30 mL of 0.3 mol / L NaOH, and dropwise add 15 mL (12 g) of hexadecyl dimethyl tertiary amine; stir at 65° C. for 4 h to obtain solution I-2;

[0069] S2: Adjust the pH of solution Ⅰ-2 to acidic (pH=5) with 1 mol / L hydrochloric acid to obtain solid Ⅱ-2;

[0070] S3: Rinse the solid II-2 with a large amount of deionized water and dry it at 60°C for 12 h to obtain chitosan quaternary ammonium salt CT-QAS 16 .

[0071] (3) Preparation of phosphotungstate chitosan quaternary ammonium salt solid base catalyst HPW-CT-QAS 16

[0072] S1: Dissolve 1 g of alkaline chitosan quaternary ammonium salt in 10 mL of deionized water, and 2.88 g of phosphotungstic acid in 10 mL of deionized water, then mix and add the mixture into a 100 mL round-bottom flask to obtain solution I-3;

[0073] S2: Heat solution I-3 at 60°C for 1 h, cool to room temperature, and filter to obtain solid II-3;

[0074] S3: Dry the solid II-3 in an oven at 60°C for 12 h to obtain phosphotungstate chitosan quaternary ammonium salt HPW-CT-QAS 16 .

[0075] Example 2 Preparation of azelaic acid monomethyl ester and azelaic acid by catalytic cracking of epoxy fatty acid methyl ester using phosphotungstate chitosan quaternary ammonium salt solid base catalyst

[0076] (1) Preparation of monomethyl azelaic acid by one-pot solvent-free method:

[0077] 0.3g of phosphotungstate chitosan quaternary ammonium salt solid base catalyst, 6g of epoxy fatty acid methyl ester and 9g of 30% hydrogen peroxide (the molar ratio of epoxy fatty acid methyl ester to hydrogen peroxide is 1:4) were mixed and put into a 100mL three-necked flask, and condensed and refluxed at 80°C for 3h; after the reaction was completed, the reaction liquid was slightly cooled and filtered to separate the catalyst; the filtrate was separated into oil and water phases, and the oil phase was monomethyl azelaic acid ester, and the selectivity of monomethyl azelaic acid ester was 96.2%.

[0078] NMR characterization of monomethyl azelaic acid ester product: 1 H NMR (400 MHz, DMSO-d 6 )δ11.87(s,1H),3.62(s,3H),2.17-2.20(m,4H),1.49-1.52(m,4H),1.29(m,6H). 13 C NMR (101 MHz, DMSO-d 6 )δ176.3,172.8,51.6,34.0,33.6,28.8,24.5,24.1.

[0079] (2) Preparation of azelaic acid:

[0080] Add 50 wt % of water to 5 g of the separated monomethyl azelaic acid, and react at 220° C. and 5 MPa for 3 hours. The reaction solution is extracted with hot water, frozen and crystallized, filtered and dried to obtain the azelaic acid product. The selectivity of azelaic acid is 96.6%.

[0081] NMR characterization of azelaic acid product: 1 H NMR (400 MHz, DMSO-d 6 )δ11.95(s,2H),2.18-2.22(m,4H),1.46-1.48(m,4H),1.27(m,6H). 13 C NMR (101 MHz, DMSO-d 6 )δ176.5,33.6,28.4,24.5.

[0082] Selectivity of monomethyl azelaic acid (%) = proportion of monomethyl azelaic acid / proportion of theoretical products based on epoxy fatty acid methyl ester.

[0083] Azelaic acid selectivity (%) = azelaic acid percentage / theoretical product percentage based on monomethyl azelate.

[0084] Example 3 Effect of different temperatures on the selectivity of monomethyl azelaic acid

[0085] Referring to Example 2, the only difference is that the reaction temperature in the solvent-free one-pot process for preparing monomethyl azelaic acid is adjusted to 60-80°C.

[0086] The test results are as follows: at 80°C, the selectivity of monomethyl azelaic acid reaches 96.2%, and when the temperature rises to 90°C, the selectivity decreases first; this is because when the temperature is greater than 80°C, hydrogen peroxide will decompose, resulting in the remaining hydrogen peroxide being insufficient to convert epoxy fatty acid methyl ester into monomethyl azelaic acid, proving that 80°C is the optimal reaction temperature.

[0087] Table 1 Effect of changing the reaction temperature in the solvent-free one-pot preparation of monomethyl azelaic acid on the selectivity of monomethyl azelaic acid

[0088]

[0089] Example 4 Effect of different reaction times on the selectivity of monomethyl azelaic acid

[0090] Referring to Example 2, the only difference is that the reaction time in the solvent-free one-pot process for preparing monomethyl azelaic acid is adjusted to 10-60 min.

[0091] The test results are as follows: Epoxy fatty acid methyl ester was completely converted in 3 hours, and the selectivity of the product increased rapidly with time. At 3 hours, the selectivity of monomethyl azelaic acid reached 96.2%. The selectivity hardly changed when the reaction time was further extended. Therefore, 3 hours was the best reaction time.

[0092] Table 2 Effect of changing the reaction time in the solvent-free one-pot preparation of monomethyl diacid ester on the selectivity of monomethyl azelaic acid ester

[0093]

[0094] Example 5 Effect of Catalyst Amount on the Selectivity of Monomethyl Azelaic Acid

[0095] Refer to Example 2, the only difference is that the amount of catalyst in the solvent-free one-pot process for preparing monomethyl azelaic acid is adjusted to 3-10 wt%.

[0096] The test results are as follows: When the amount of catalyst increases from 3wt% to 5wt%, the selectivity of monomethyl azelaic acid increases from 64.8% to 96.2%. When the amount is further increased, it is found that the conversion rate of the substrate and the selectivity of the product hardly increase. It is proved that the optimal amount of catalyst is 5wt%.

[0097] Table 3 Effect of changing the amount of catalyst in the solvent-free one-pot preparation of monomethyl azelaic acid on the selectivity of monomethyl azelaic acid

[0098]

[0099] Example 6 Effect of the amount of oxidant on the selectivity of monomethyl azelaic acid

[0100] Refer to Example 2, the only difference is that the ratio of the amounts of epoxy fatty acid methyl ester and hydrogen peroxide in the first step of preparing monomethyl azelaic acid ester by a one-pot solvent-free process is adjusted.

[0101] The test results are as follows: When the molar ratio of epoxy fatty acid methyl ester to hydrogen peroxide increases from 1:3 to 1:4, the selectivity of azelaic acid monomethyl ester also increases from 67.8% to 96.2%. When the amount of hydrogen peroxide is further increased, the selectivity remains basically unchanged.

[0102] Table 4 Effect of changing the amount of oxidant in the solvent-free one-pot preparation of monomethyl azelaic acid on the selectivity of monomethyl azelaic acid

[0103]

[0104] Example 7 HPW-CT-QAS 16 Stability test of catalytic synthesis of monomethyl azelaic acid and azelaic acid

[0105] (1) Prepare monomethyl azelaic acid and azelaic acid according to the method of Example 2.

[0106] (2) recovering the catalyst by simple filtration, drying and using it as a catalyst for preparing nonanoic acid, nonanedioic acid monomethyl ester and nonanedioic acid in Example 5;

[0107] Repeat step (2) 5 times. After each reaction, analyze and calculate the selectivity of the product, monomethyl azelaic acid.

[0108] Table 5 HPW-CT-QAS 16 Stability test of catalytic synthesis of monomethyl azelaic acid

[0109] Use times Catalyst recovery rate % Selectivity of monomethyl azelaic acid ester % Selectivity of Azelaic Acid % 1 95.2 96.2 96.6 2 93.2 95.4 96.0 3 91.1 93.2 92.1 4 90.6 92.5 91.8 5 90.2 91.3 90.6

[0110] Catalyst recovery rate (%) = mass of catalyst recovered after reaction / mass of catalyst added before reaction * 100%.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that chitosan is omitted and the monobasic quaternary ammonium salt catalyst loaded with phosphotungstic acid is prepared.

[0113] The specific process is as follows:

[0114] Weigh 5.760g of phosphotungstic acid into a three-necked flask, add 15mL of deionized water to dissolve it, and after magnetic stirring at room temperature for 1h, add an aqueous solution containing 1.92g of hexadecyldimethylammonium chloride into the three-necked flask, and stir while dropping to make it fully react. A white precipitate is slowly generated. After the addition is completed, continue to stir at room temperature for 4h. After the precipitation is complete, filter, wash, and dry at 65℃. The obtained catalyst is referred to as phosphotungstic acid-hexadecyldimethylammonium chloride.

[0115] Referring to Example 2, the obtained phosphotungstic acid-hexadecyldimethylammonium chloride catalyst was used to prepare monomethyl azelaic acid and azelaic acid. The results are shown in Table 6.

[0116] Comparative Example 2

[0117] The difference between this comparative example and Example 1 is that a sodium lignin sulfonate quaternary ammonium salt catalyst with a hexadecyl chain length loaded with phosphotungstic acid is prepared. The specific process is as follows:

[0118] S1: 0.93 g of epichlorohydrin, 10 mL of concentrated hydrochloric acid (36% to 38%), and 2.69 g of hexadecyl dimethyl tertiary amine were placed in a flask, stirred evenly, and kept warm at 50°C to allow the solution to fully dissolve. The pH was adjusted to 8 to 9 using an aqueous NaOH solution, and the reaction was continued for 3 h to obtain an intermediate of glycidyl hexadecyl dimethyl ammonium chloride;

[0119] S2: Add 2.67 g of sodium lignin sulfonate and 15 mL of deionized water into a flask, adjust the pH to 10-12 with NaOH solution, keep warm in a 50°C water bath for 30 min, add the intermediate obtained in step S1 and stir at 50°C for 3 h, filter, wash with deionized water, and dry in a 60°C oven for 12 h to obtain sodium lignin sulfonate quaternary ammonium salt;

[0120] S3: 0.90 g of sodium lignin sulfonate quaternary ammonium salt was placed in 10 mL of deionized water, followed by adding 10 mL of an aqueous solution containing 2.9 g of phosphotungstic acid, and the mixed solution was heated at 60° C. for 1 h, and filtered after cooling. The obtained solid was washed with water and dried in an oven at 60° C. for 12 h to obtain a catalyst, referred to as phosphotungstic acid-sodium lignin sulfonate hexaquaternary ammonium salt.

[0121] Referring to Example 2, the obtained phosphotungstic acid-sodium lignin sulfonate hexadecane quaternary ammonium salt was used to prepare azelaic acid, and the results are shown in Table 6.

[0122] Table 6

[0123]

[0124] Example 8

[0125] Referring to the catalyst preparation method in Example 1, dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, and octadecyl dimethyl tertiary amine were used to replace hexadecyl dimethyl tertiary amine to prepare phosphotungstate chitosan quaternary ammonium salt catalysts with tertiary amine carbon chain lengths of 12, 14, and 18, respectively named HPW-CT-QAS 12 、HPW-CT-QAS 14 and HPW-CT-QAS 18 .

[0126] Refer to Example 2, the only difference is that the catalyst type is adjusted to HPW-CT-QAS 12 、HPW-CT-QAS 14 and HPW-CT-QAS 18 .

[0127] The test results are as follows:

[0128] Table 7 Effect of changing the amount of oxidant in the step of preparing azelaic acid by acidified oil oxidation cracking on the yield of azelaic acid

[0129] catalyst Catalyst recovery rate % Selectivity of monomethyl azelaic acid ester % <![CDATA[HPW-CT-QAS 12 ]]> 67.8 76.5 <![CDATA[HPW-CT-QAS 14 ]]> 76.4 82.7 <![CDATA[HPW-CT-QAS 18 ]]> 95.6 92.6

[0130] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A phosphotungstate chitosan quaternary ammonium salt solid base catalyst, characterized in that: The preparation method of the catalyst comprises the following steps: S1: chitosan, NaOH aqueous solution and epichlorohydrin are mixed and stirred at a constant temperature, and then the pH is adjusted to 7-9, washed with deionized water, and dried to obtain etherified chitosan; S2: mixing the etherified chitosan and the NaOH solution, then dropping an alkyl tertiary amine, stirring at a constant temperature, adjusting the pH to acidic after the reaction, washing with deionized water, and drying to obtain a chitosan quaternary ammonium salt; S3: dissolving chitosan quaternary ammonium salt in water, adding phosphotungstic acid aqueous solution, reacting at a constant temperature, and after the reaction is completed, filtering, collecting solids, drying, and grinding to obtain phosphotungstic acid chitosan quaternary ammonium salt solid base catalyst.

2. The phosphotungstate chitosan quaternary ammonium salt solid base catalyst according to claim 1, characterized in that In step S1, the mass ratio of chitosan to sodium hydroxide is 1:(2-5); the mass ratio of chitosan to epichlorohydrin is 1:(2-8).

3. The phosphotungstate chitosan quaternary ammonium salt solid base catalyst according to claim 1, characterized in that In step S2, the alkyl tertiary amine is selected from: dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, hexadecyl dimethyl tertiary amine, and octadecyl dimethyl tertiary amine.

4. The phosphotungstate chitosan quaternary ammonium salt solid base catalyst according to claim 1, characterized in that In step S2, the mass ratio of etherified chitosan to NaOH is 1:(0.05-0.1); the mass ratio of etherified chitosan to alkyl tertiary amine is 1:(2-4).

5. The phosphotungstate chitosan quaternary ammonium salt solid base catalyst according to any one of claims 1 to 4, characterized in that: In step S3, the mass ratio of chitosan quaternary ammonium salt to phosphotungstic acid is 1:(2-4); the concentration of chitosan quaternary ammonium salt dissolved in water is 0.05-0.5 g / mL; and the concentration of phosphotungstic acid aqueous solution is 0.1-0.5 g / mL.

6. A method for preparing azelaic acid monoester by a solvent-free one-pot process, characterized in that: The steps include: The phosphotungstate chitosan quaternary ammonium salt solid base catalyst described in any one of claims 1 to 5, epoxy fatty acid ester and hydrogen peroxide are mixed and heated for reaction to obtain azelaic acid monoester.

7. The method according to claim 6, characterized in that The molar ratio of epoxy fatty acid ester: hydrogen peroxide is 1:(3.5-5.0).

8. The method according to claim 6, characterized in that The amount of the catalyst used is 4wt%-10wt% of the epoxy fatty acid ester.

9. The method according to claim 6, characterized in that The reaction time is 20-50 minutes, and the reaction temperature is 60-90°C.

10. A method for preparing azelaic acid, characterized in that: The steps include: (1) preparing azelaic acid monoester according to the method of any one of claims 6 to 9; (2) The azelaic acid monoester is then hydrolyzed to obtain azelaic acid.

Images