A process for the preparation of dimethyl azelate

Abstract

This invention discloses a method for preparing dimethyl azelaate, comprising the steps of: preparing a catalyst; reacting azelaic acid and methanol in the presence of the catalyst to generate dimethyl azelaate; separating and recovering the catalyst and the product; wherein the catalyst is a supported solid acid catalyst HPW / HMSMs; wherein HPW is phosphotungstic acid and HMSMs is hollow mesoporous silica. The method for preparing dimethyl azelaate provided by this invention achieves high catalytic efficiency, good stability, and environmental friendliness by using the supported solid acid catalyst HPW / HMSMs, while also balancing conversion rate, selectivity, and product purity.

Description

Technical Field

[0001] This invention relates to the field of chemical intermediate synthesis technology, and in particular to a method for preparing dimethyl azelaate. Background Technology

[0002] Dimethyl azelate, with the chemical formula C11H20O4, is a colorless to pale yellow liquid with excellent heat resistance, chemical stability, and plasticizing properties. It is widely used in high-end lubrication fields such as aerospace turbine engine lubricants, precision instrument oils, and automotive engine oils. It can also be used as a plasticizer and solvent in the plastics and rubber industries, as well as an intermediate in pharmaceuticals and cosmetics. With the rapid development of high-end manufacturing and the fine chemical industry, the market demand for high-purity dimethyl azelate continues to grow.

[0003] Currently, the preparation of dimethyl azelaate mainly uses azelaic acid and methanol as raw materials, synthesized through an esterification reaction. Traditional processes often use concentrated sulfuric acid as a catalyst. However, this process has many drawbacks: concentrated sulfuric acid is highly corrosive, which can severely corrode production equipment, increasing equipment maintenance costs and safety risks; side reactions (such as carbonization and etherification) are prone to occur during the reaction, leading to a decrease in product purity and increasing the difficulty of subsequent separation and purification; after the reaction, the waste acid needs to be neutralized, generating a large amount of saline wastewater, which puts significant pressure on environmental treatment.

[0004] To address the aforementioned problems, existing technologies attempt to replace concentrated sulfuric acid with solid acid catalysts, such as Fe2O3 and SO42-. 2- -SO4 2- Solid superacids such as -SnO2, -TiO2, and -Al2O3 are available as catalysts, but these catalysts suffer from problems such as insufficient catalytic activity stability, limited recycling cycles, and complex preparation processes, making large-scale industrial application difficult. Furthermore, existing processes have poor control over reaction conditions, resulting in a difficulty in simultaneously achieving high conversion rates of azelaic acid and high selectivity for dimethyl azelaate, with yields generally remaining around 92%-93%, thus hindering improvements in production efficiency.

[0005] Therefore, there is an urgent need for a method to prepare dimethyl azelaate that has high catalytic efficiency, good stability, is environmentally friendly and pollution-free, and can balance conversion rate, selectivity and product purity. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the current processes and methods for preparing dimethyl azelaate, the present invention provides a method for preparing dimethyl azelaate that can achieve high catalytic efficiency, good stability, environmental protection and no pollution, and can take into account the effects of conversion rate, selectivity and product purity.

[0007] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0008] A method for preparing dimethyl azelaate includes the following steps: preparing a catalyst; reacting azelaic acid and methanol in the presence of the catalyst to produce dimethyl azelaate; separating and recovering the catalyst and the product; wherein the catalyst is a supported solid acid catalyst, and the supported solid acid catalyst is an HPW / HMSMs catalyst.

[0009] According to one aspect of the present invention, the refined azelaic acid includes the following steps: dissolving azelaic acid raw material in hot water at 80-90°C, stirring until completely dissolved, adding 0.1-0.2% (by weight of azelaic acid) of activated carbon, keeping warm for adsorption for 30-40 minutes, filtering to remove activated carbon and mechanical impurities, cooling to crystallize, and then filtering and drying to obtain refined azelaic acid.

[0010] According to one aspect of the present invention, the preparation of the catalyst includes the steps of: preparing a mesoporous hollow silica support by a hard template method; dissolving phosphotungstic acid in deionized water to prepare a phosphotungstic acid solution; adding the HMSMs support to the phosphotungstic acid solution, stirring and impregnating, and then evaporating the solution to obtain a precursor; drying the precursor overnight, calcining and cooling to obtain an HPW / HMSMs catalyst.

[0011] According to one aspect of the invention, the phosphotungstic acid loading of the HPW / HMSMs catalyst is 30-35 wt%.

[0012] According to one aspect of the present invention, the concentration of the phosphotungstic acid solution is 0.1-0.15 g / mL.

[0013] According to one aspect of the present invention, the azelaic acid and methanol are subjected to an esterification reaction to obtain an esterification reaction solution, wherein the molar ratio of the azelaic acid and methanol is 1:4 to 1:6.

[0014] According to one aspect of the present invention, the amount of HPW / HMSMs catalyst added during the esterification reaction of azelaic acid and methanol is 1.5-2.5% of the mass of azelaic acid.

[0015] According to one aspect of the present invention, the separation and recovery of the catalyst includes the steps of: cooling the esterification reaction solution; filtering to separate the HPW / HMSMs catalyst; washing and drying.

[0016] According to one aspect of the present invention, the separation and recovery of the product includes the steps of: distilling to recover excess methanol; continuing vacuum distillation, collecting the fraction to obtain crude dimethyl azelate; purifying the crude product with an eluent, collecting the target eluent, and concentrating under vacuum to remove the eluent.

[0017] According to one aspect of the invention, the eluent comprises cyclohexane and ethyl acetate, wherein the volume ratio of cyclohexane to ethyl acetate is 5:2.

[0018] The advantages of this invention are: (1) The reactants and catalysts are stable and safe, not highly corrosive, and will not corrode production equipment, thus reducing equipment maintenance costs and safety risks; (2) There are no side reactions during the reaction process, which improves the purity of the product; (3) The reaction process is simple and the separation and purification are easy; (4) The reaction process is environmentally friendly and pollution-free; (5) The catalytic efficiency is high, taking into account the conversion rate and selectivity and improving the purity of the product. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] A method for preparing dimethyl azelaate includes the following steps: preparing a catalyst; reacting azelaic acid and methanol in the presence of the catalyst to produce dimethyl azelaate; separating and recovering the catalyst and the product; wherein the catalyst is a supported solid acid catalyst HPW / HMSMs.

[0021] In practical applications, the azelaic acid undergoes pretreatment, which includes the following steps: dissolving azelaic acid in hot water at 80-90℃, stirring until completely dissolved, adding 0.1-0.2% (by weight of azelaic acid) of activated carbon, maintaining the temperature for adsorption for 30-40 minutes, filtering to remove activated carbon and mechanical impurities, cooling to crystallize, and then filtering and drying to obtain refined azelaic acid.

[0022] In practical applications, impurities that need to be removed from azelaic acid include nonanoic acid, fatty acids, and mechanical impurities.

[0023] In practical applications, the purity of refined azelaic acid is ≥99.5%.

[0024] In practical applications, methanol is dehydrated to control the moisture content of methanol to ≤0.05wt%.

[0025] In practical applications, the preparation of the catalyst includes the following steps: preparing a mesoporous hollow silica support using a hard template method; dissolving phosphotungstic acid in deionized water to prepare a phosphotungstic acid solution; adding the HMSMs support to the phosphotungstic acid solution, stirring and impregnating, and then evaporating the solution to obtain the precursor; drying the precursor overnight, then calcining and cooling.

[0026] In practical applications, the steps for preparing mesoporous hollow silica carriers using the hard template method include: using polystyrene microspheres as a hard template, using tetraethyl orthosilicate to hydrolyze and coat the template, and high-temperature calcination to remove the polymer template to obtain hollow mesoporous HMSMs carriers.

[0027] In practical applications, the concentration of phosphotungstic acid solution is 0.1-0.15 g / mL. The calcination process adopts programmed temperature rise at a rate of 5℃ / min, and is heated from room temperature to 350-400℃ before constant temperature calcination.

[0028] In practical applications, HMSMs support is added to phosphotungstic acid solution, stirred and impregnated at 25-30℃ for 4-6 hours, and then rotary evaporated at 60-80℃ until all water is evaporated to obtain the precursor.

[0029] In practical applications, the stirring rate is 200-300 r / min, and the reaction progress is checked every 1 hour during the reaction. The reaction is stopped when the conversion rate of azelaic acid is ≥99%.

[0030] In practical applications, the precursor is dried overnight at 100-120℃ and then calcined at 350-400℃ for 3-4 hours.

[0031] In practical applications, the precursor is cooled to obtain an HPW / HMSMs catalyst with a phosphotungstic acid loading of 30-35 wt%.

[0032] In practical applications, azelaic acid and methyl ester undergo esterification under the action of HPW / HMSMs catalyst to produce dimethyl azelaic acid.

[0033] In practical applications, refined azelaic acid, dehydrated methanol, and HPW / HMSMs catalyst are sequentially added to a reactor equipped with a stirring device, a reflux condenser, and a water separator to prepare for an esterification reaction.

[0034] In practical applications, the molar ratio of azelaic acid to methanol is 1:4 to 1:8.

[0035] In practical applications, the amount of HPW / HMSMs catalyst added is 1.5-2.5% of the mass of azelaic acid.

[0036] In practical applications, nitrogen is introduced to replace the air in the reactor before the esterification reaction. The nitrogen flow rate is 0.5-1 L / min, and the replacement time is 10-15 min.

[0037] In practical applications, after the esterification reaction, the temperature inside the reactor is raised to 85-95℃, and the reaction is stirred for 3-5 hours under normal pressure. During the reaction, the generated water is separated by a water separator to promote the forward reaction.

[0038] In practical applications, the separation and recovery of catalysts specifically includes: cooling the reaction solution to 40-50℃, separating the HPW / HMSMs catalyst by filtration, and recycling the catalyst after washing and drying.

[0039] In practical applications, the catalyst is washed 2-3 times with dehydrated methanol and then dried at 100-120℃ for 2-3 hours.

[0040] In practical applications, the steps for separating and purifying the product include: filtering and distilling to recover excess methanol; vacuum distilling and collecting the fraction to obtain crude dimethyl azelaate; and silica gel chromatography to purify dimethyl azelaate.

[0041] In practical applications, the recovery of excess methanol by distillation after filtration includes: sending the filtered reaction solution into a vacuum distillation apparatus and distilling to recover excess methanol under a vacuum of 0.08-0.09 MPa and a temperature of 60-70°C.

[0042] In practical applications, methanol recovered by distillation can be recycled for esterification reactions after dehydration.

[0043] In practical applications, the product is further distilled under reduced pressure at a vacuum of 0.095-0.098 MPa and a temperature of 160-180℃, and the fraction is collected to obtain crude dimethyl azelaate.

[0044] In practical applications, crude dimethyl azelaate is purified by silica gel chromatography, the target eluent is collected, and the eluent is removed by vacuum concentration to obtain high-purity dimethyl azelaate product.

[0045] In practical applications, the eluent is a mixture of cyclohexane and ethyl acetate, with a volume ratio of cyclohexane to ethyl acetate of 5:2.

[0046] In practical applications, the amount of silica gel used is 5-8 times the mass of crude dimethyl azelaate, and the eluent flow rate is 1-2 mL / min.

[0047] Example 1

[0048] 100g of azelaic acid raw material with a purity of 98.2% was dissolved in hot water at 85℃ and stirred until completely dissolved. 0.15g of activated carbon was added, and the mixture was kept at 85℃ for adsorption for 35 minutes. The activated carbon and mechanical impurities were removed by filtration. The mixture was cooled to room temperature for crystallization, filtered, and dried to obtain 92.3g of refined azelaic acid with a purity of 99.6%. Industrial methanol was dehydrated using molecular sieves to control the moisture content to 0.03wt% and set aside for later use.

[0049] Mesoporous hollow silica support (HMSMs) was prepared by hard template method. 30 g of phosphotungstic acid was dissolved in 200 mL of deionized water to prepare a phosphotungstic acid solution with a concentration of 0.15 g / mL. 100 g of HMSMs support was added to the above phosphotungstic acid solution and stirred and impregnated at 28 °C for 5 h. Then, the precursor was obtained by rotary evaporation at 70 °C until the water was completely evaporated. The precursor was dried at 110 °C overnight and then heated to 380 °C by programmed temperature increase (5 °C / min). It was calcined at a constant temperature for 3.5 h and cooled to obtain an HPW / HMSMs catalyst with a phosphotungstic acid loading of 30 wt%.

[0050] Add 50g of purified azelaic acid (0.258mol), 65.2g of dehydrated methanol (2.038mol, azelaic acid to methanol molar ratio 1:7.9), and 1.0g of 30wt% HPW / HMSMs catalyst (2% of the mass of azelaic acid) to a 250mL three-necked flask in sequence. Purge with nitrogen gas (flow rate 0.8L / min) for 12min. Heat to 90℃, stir at 250r / min, and react at atmospheric pressure for 4h. Take samples every 1h during the reaction. When the conversion rate of azelaic acid is 99.2% after 4h, stop the reaction.

[0051] The reaction solution was cooled to 45°C, and the HPW / HMSMs catalyst was separated by filtration. It was washed three times with dehydrated methanol and dried at 110°C for 2.5 hours for later use.

[0052] The filtered reaction solution was fed into a vacuum distillation apparatus to recover excess methanol under a vacuum of 0.085 MPa and 65 °C, yielding 52.8 g of recovered methanol, which was then dehydrated and recycled. The remaining material was distilled under vacuum at 0.096 MPa and 170 °C, and the fraction was collected to obtain 56.3 g of crude dimethyl azelaate. The crude dimethyl azelaate was purified by silica gel chromatography using 338 g of silica gel and a mixture of cyclohexane and ethyl acetate (volume ratio 5:2) as the eluent at a flow rate of 1.5 mL / min. The target eluent was collected and concentrated under reduced pressure to remove the eluent, yielding 54.9 g of dimethyl azelaate product.

[0053] The obtained dimethyl azelaate product had a purity of 99.9% and a yield of 97.5%.

[0054] Example 2

[0055] 200g of azelaic acid (98.5% purity) was dissolved in hot water at 90℃ and stirred until completely dissolved. 0.3g of activated carbon was added, and the mixture was kept at 90℃ for 30 minutes for adsorption. Impurities were removed by filtration, followed by cooling and crystallization. After filtration and drying, 186.5g of refined azelaic acid (99.7% purity) was obtained. Methanol was dehydrated to a moisture content of 0.04wt% and set aside for later use.

[0056] The recovered HPW / HMSMs catalyst, which had been used four times, was dried at 110°C for 2 hours before use.

[0057] To a 500 mL three-necked flask, add 100 g of purified azelaic acid (0.516 mol), 120.5 g of dehydrated methanol (3.766 mol, molar ratio 1:7.3), and 2.2 g of recovered HPW / HMSMs catalyst (2.2% of the mass of azelaic acid). Purge with nitrogen (flow rate 1.0 L / min) for 15 min. Heat to 95 °C, stir at 300 r / min, and carry out the esterification reaction at atmospheric pressure for 3.5 h. When the conversion rate of azelaic acid is 99.1%, stop the reaction.

[0058] The reaction solution was cooled to 50°C, the catalyst was separated by filtration, washed, and dried for later use.

[0059] The filtered reaction solution was fed into a vacuum distillation apparatus to recover excess methanol under a vacuum of 0.085 MPa and 65 °C, yielding 52.8 g of recovered methanol, which was then dehydrated and recycled. The remaining material was distilled under vacuum at 0.096 MPa and 170 °C, and the fraction was collected to obtain 111.4 g of crude dimethyl azelaate. The crude dimethyl azelaate was purified by silica gel chromatography using 338 g of silica gel and a mixture of cyclohexane and ethyl acetate (volume ratio 5:2) as the eluent at a flow rate of 1.5 mL / min. The target eluent was collected and concentrated under reduced pressure to remove the eluent, yielding 108.2 g of dimethyl azelaate product.

[0060] The obtained dimethyl azelaate product had a purity of 99.8% and a yield of 97.1%.

[0061] Example 3

[0062] Hollow mesoporous silica HMSMs supports were prepared using a polystyrene microsphere hard template method. The supports had a specific surface area of ​​265 m² / g and a pore size of 4–10 nm. 35 g of phosphotungstic acid solid was dissolved in 200 mL of deionized water to prepare a 0.175 g / mL phosphotungstic acid aqueous solution, which was stirred at room temperature until completely dissolved. 100 g of HMSMs supports were weighed and added to the above phosphotungstic acid solution, and stirred at 28 °C and 250 r / min for 5 h. After impregnation, all free water was removed by rotary evaporation at 70 °C to obtain a solid precursor. The precursor was dried overnight in an oven at 110 °C. The temperature was increased by 5 °C / min to 380 °C, and calcined at this temperature for 3.5 h. After natural cooling to room temperature, a phosphotungstic acid theoretical loading of 35 wt% HPW / HMSMs catalyst was obtained.

[0063] Take 100g of industrial azelaic acid with a purity of 98.2%, add it to 85℃ hot water and stir until completely dissolved. Add 0.15g of activated carbon, keep it at 85℃ for 35 min for adsorption, filter to remove impurities, cool to crystallize, filter and dry to obtain refined azelaic acid with a purity of 99.6%. Dehydrate with molecular sieve and control the methanol moisture content to ≤0.03 wt% for later use.

[0064] Add 50 g of purified azelaic acid (0.258 mol), 65.2 g of dehydrated methanol (2.038 mol, azelaic acid:methanol molar ratio 1:7.9), and 1.0 g of 35wt% HPW / HMSMs catalyst (added at 2% of the azelaic acid mass) to a 250 mL three-necked reaction flask; purge the air in the reactor with nitrogen at a flow rate of 0.8 L / min for 12 min; heat to 90 °C, stir at 250 r / min, and react at atmospheric pressure and constant temperature for 4 h; continuously separate the water generated by the reaction using a water separator, and take samples every 1 h to detect the conversion rate of azelaic acid.

[0065] The reaction solution was cooled to 45℃, filtered to separate the HPW / HMSMs catalyst, washed three times with dehydrated methanol, and dried at 110℃ for 2.5 h, which could be directly recycled. The filtrate was distilled under vacuum at 0.085 MPa and 65℃ to recover excess methanol. The recovered methanol was dehydrated and recycled. The remaining material was distilled under vacuum at 0.096 MPa and 170℃, and the fraction was collected to obtain crude dimethyl azelate. The crude product was purified by silica gel column chromatography with silica gel used at a volume ratio of 6 times the crude product mass. The volume ratio of cyclohexane to ethyl acetate in the eluent was 5:2, and the elution flow rate was 1.5 mL / min. The target component was collected, and the eluent was removed under reduced pressure to obtain 54.6 g of the final product.

[0066] The purity of the obtained dimethyl azelaate product was 99.8%, the conversion rate of azelaic acid was 99.0%, and the product yield was 97.0%.

[0067] Catalyst phenomena: In the 35 wt% loaded HPW / HMSMs catalyst, there was no obvious agglomeration of phosphotungstic acid, the mesoporous channels of the support were not completely blocked, and the catalytic activity was only slightly lower than that of the 30 wt% loaded HPW / HMSMs catalyst sample, still meeting the requirements of industrial esterification; after 4 cycles, the conversion rate can still be maintained above 96.5%, and the stability is excellent.

[0068] In this embodiment, an HPW / HMSMs catalyst with a phosphotungstic acid loading of 35 wt% was prepared to verify the effect of the upper limit of the loading range on the esterification effect of azelaic acid. The pretreatment, esterification, separation and purification processes of the remaining raw materials were completely consistent with those in Example 1.

[0069] The results of Examples 1 (30 wt%) and 3 (35 wt%) show that when the phosphotungstic acid loading mass fraction is in the range of 30-35 wt%, the conversion rate of azelaic acid is ≥99.0%, the product purity is ≥99.8%, and the yield is consistently maintained at 97.0% or higher. This proves that 30-35 wt% is the optimal loading range for this esterification system. When the loading is below 30 wt%, there are insufficient active sites and the conversion rate decreases. When the loading is above 35 wt%, phosphotungstic acid will agglomerate and block the pores of the support, resulting in reduced mass transfer efficiency and a significant decrease in catalytic performance.

[0070] Comparative Example 1

[0071] Add 50g of purified azelaic acid and 65.2g of dehydrated methanol to a 250mL three-necked flask, then add 1mL of concentrated sulfuric acid, and stir in an oil bath at 110℃ for 3h.

[0072] After the reaction was completed, the mixture was neutralized to neutral with sodium carbonate solution, filtered, and methanol was recovered by distillation. The remaining material was then distilled under reduced pressure to obtain the crude product.

[0073] Dimethyl azelaate was obtained after purification with silica gel.

[0074] The conversion rate of azelaic acid was 94.3%, and the yield of dimethyl azelaate was 89.5%, with a purity of 98.2%.

[0075] Comparative Example 2

[0076] This comparative example uses Fe2O, a common technology in the current field. 3─ SO4 2- Solid superacid was used as the catalyst, and the pretreatment, esterification, separation and purification processes of the other raw materials were kept the same as in Example 2. The differences in catalytic performance were compared.

[0077] 200g of azelaic acid (98.5% purity) was dissolved in hot water at 90℃ and stirred until completely dissolved. 0.3g of activated carbon was added, and the mixture was kept at 90℃ for 30 minutes for adsorption. Impurities were removed by filtration, followed by cooling and crystallization. After filtration and drying, 186.5g of refined azelaic acid (99.7% purity) was obtained. Methanol was dehydrated to control its moisture content at 0.04wt% and set aside for later use.

[0078] The recovered HPW / HMSMs catalyst, which had been used four times, was dried at 110°C for 2 hours before use.

[0079] Add 100g purified azelaic acid (0.516mol), 120.5g dehydrated methanol (3.766mol, molar ratio 1:7.3), and 2.2g Fe2O3 to a 500mL three-necked flask in sequence. 3─ SO4 2-Solid acid catalyst; nitrogen gas (flow rate 1.0 L / min) was introduced for 15 min to purge; the temperature was raised to 95 °C, the stirring rate was 300 r / min, and the reaction was carried out at atmospheric pressure for 3.5 h.

[0080] After the reaction was completed, the reaction solution was cooled to 50°C, the solid catalyst was separated by filtration, washed twice with dehydrated methanol, and dried at 110°C for 2 hours before being put into use for cycle stability testing.

[0081] The filtered reaction solution was fed into a vacuum distillation apparatus and distilled at a vacuum of 0.085 MPa and 65°C to recover excess methanol. The recovered methanol was dehydrated and recycled. The remaining material was distilled under vacuum at 0.096 MPa and 170°C, and the fraction collected yielded crude dimethyl azelaate. The crude product was purified by silica gel chromatography, using six times the volume of silica gel as the eluent. The eluent was a 5:2 volume ratio of cyclohexane to ethyl acetate, and the elution flow rate was 1.5 mL / min. The target eluent was collected, concentrated under reduced pressure to remove the eluent, and the final dimethyl azelaate product was obtained.

[0082] The conversion rate of azelaic acid was 96.8%, and the yield of dimethyl azelaate was 102.7g, with a product yield of 92.3% and a purity of 99.0%. After the catalyst was recycled three times, the conversion rate of azelaic acid dropped to 87.2%, and the product yield was only 82.1%, indicating a significant decrease in catalytic activity.

[0083] Compared to the HPW / HMSMs catalyst of this invention, conventional Fe2O 3─ SO4 2- Solid acids have lower single-cycle conversion and yield, shorter cycle life, and severe activity decay, making them unsuitable for long-term stable use in the continuous preparation of dimethyl azelaate.

[0084] The advantages of this invention are: (1) The reactants and catalysts are stable and safe, not highly corrosive, and will not corrode production equipment, thus reducing equipment maintenance costs and safety risks; (2) There are no side reactions during the reaction process, which improves the purity of the product; (3) The reaction process is simple and the separation and purification are easy; (4) The reaction process is environmentally friendly and pollution-free; (5) The catalytic efficiency is high, taking into account the conversion rate and selectivity and improving the purity of the product.

[0085] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing dimethyl azelaate, characterized in that, The preparation method of the dimethyl azelaate includes the following steps: preparing a catalyst; reacting azelaic acid and methanol in the presence of the catalyst to produce dimethyl azelaate; separating and recovering the catalyst and the product; wherein the catalyst is a supported solid acid catalyst, and the supported solid acid catalyst is an HPW / HMSMs catalyst.

2. The method for preparing dimethyl azelaate according to claim 1, characterized in that, The azelaic acid is pretreated, and the pretreatment includes the following steps: dissolving azelaic acid in hot water at 80-90℃, stirring until completely dissolved, adding 0.1-0.2% activated carbon by weight of azelaic acid, keeping warm for adsorption for 30-40 minutes, filtering to remove activated carbon and mechanical impurities, cooling to crystallize, filtering and drying to obtain refined azelaic acid.

3. The method for preparing dimethyl azelaate according to claim 1, characterized in that, The catalyst preparation includes the following steps: preparing a mesoporous hollow silica support using a hard template method; dissolving phosphotungstic acid in deionized water to prepare a phosphotungstic acid solution; adding the HMSMs support to the phosphotungstic acid solution, stirring and impregnating, and then evaporating the solution to obtain a precursor; drying, calcining, and cooling the precursor to obtain the HPW / HMSMs catalyst.

4. The method for preparing dimethyl azelaate according to claim 3, characterized in that, The phosphotungstic acid loading of the HPW / HMSMs catalyst is 30-35 wt%.

5. The method for preparing dimethyl azelaate according to claim 3, characterized in that, The concentration of the phosphotungstic acid solution is 0.1-0.15 g / mL.

6. The method for preparing dimethyl azelaate according to claim 1, characterized in that, The azelaic acid and methanol undergo an esterification reaction to obtain an esterification reaction solution, wherein the molar ratio of azelaic acid to methanol is 1:4-1:

8.

7. The method for preparing dimethyl azelaate according to claim 6, characterized in that, The amount of HPW / HMSMs catalyst added during the esterification reaction of azelaic acid and methanol is 1.5-2.5% of the mass of azelaic acid.

8. The method for preparing dimethyl azelaate according to claim 6, characterized in that, The catalyst separation and recovery process includes the following steps: cooling the esterification reaction solution; filtering to separate the HPW / HMSMs catalyst; washing and drying.

9. The method for preparing dimethyl azelaate according to claim 1, characterized in that, The separation and recovery of the product includes the following steps: distillation to recover excess methanol; vacuum distillation to collect the fraction and obtain crude dimethyl azelate; purification of the crude product using an eluent, collection of the target eluent, and vacuum concentration to remove the eluent.

10. The method for preparing dimethyl azelaate according to claim 9, characterized in that, The eluent comprises cyclohexane and ethyl acetate, wherein the volume ratio of cyclohexane to ethyl acetate is 5:2.