Hydroxypropyl acrylate supported catalyst as well as preparation method and application thereof

Abstract

The invention discloses a hydroxypropyl acrylate supported catalyst and a preparation method and application thereof.The catalyst is prepared by loading active metal ions and polymerization inhibition groups on an amino-functionalized modified molecular sieve NH2-MCM-41, the catalyst is used for a hydroxypropyl acrylate reaction system, the synergistic catalysis effect of the metal ions and tertiary amine groups is achieved, and the reaction efficiency is improved. And the catalyst has the advantages of good catalytic activity, strong stability, easiness in separation and recyclability, overcomes the problems that the traditional homogeneous catalyst is difficult to separate and the product is easy to color, and is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis and relates to a supported catalyst and a preparation method thereof and application thereof in the preparation process of hydroxypropyl acrylate. Background Art

[0002] Hydroxypropyl acrylate, referred to as HPA, is a colorless, transparent liquid with two functional groups: carbon-carbon double bonds and hydroxyl groups. It has a wide range of applications and can be used as an active diluent and adhesive in the fields of fiber processing, coatings, photocurable resins, rubber, etc.

[0003] At present, the main synthesis process of HPA is the intermittent ring-opening reaction method, which is prepared by the reaction of acrylic acid and propylene oxide in the presence of a catalyst and an inhibitor. The inhibitors include hydroquinone, p-hydroxyanisole, phenothiazine, copper dibutyl dithiocarbamate, etc., while the catalysts commonly used include pyridine, chromium trichloride, chromium acetate, chromium acetylacetonate, ferric chloride or organic iron compounds.

[0004] Patent CN102584581A discloses a method for preparing hydroxypropyl acrylate, which is prepared by reaction under vacuum and nitrogen protection, with a preferred chromium acetate catalyst and hydroquinone or p-hydroxyanisole as inhibition.

[0005] Patent US6465681B2 uses chromium acetate as a catalyst, p-hydroxyanisole as an inhibitor, a reaction temperature of 55-70°C, a reaction time of 6.5h, and a yield of 94.3% for preparing HPA; wherein the chromium catalyst exhibits good catalytic activity and selectivity, but the catalyst is difficult to recycle.

[0006] Patent CN103524343A discloses a supported KF-Fe2O3 / ZrO2 solid base catalyst, with p-hydroxyanisole as an inhibitor, acrylic acid and propylene oxide react at a reaction temperature of 70-110°C to prepare HPA, with a propylene oxide conversion rate of 97.7%. The catalyst in this patent can be recycled, but the reaction process requires additional addition of an inhibitor.

[0007] Patent CN103288641A discloses a method for synthesizing hydroxypropyl methacrylate, using a magnetic zeolite molecular sieve as a catalyst, methacrylic acid and propylene oxide react at a reaction temperature of 80-85°C to prepare hydroxypropyl methacrylate (HPMA), and the HPMA yield can reach more than 96%. The catalyst in the present invention can be recycled without the need to add an additional inhibitor; after 8 cycles, the HPMA yield is 93%. In fact, when iron salt is used as an inhibitor, it is generally believed that its mechanism of action is a single electron transfer reaction. With the decrease of the metal valence state, the catalytic activity of the molecular sieve gradually decreases. After repeated cycles, the HPMA yield decreases.

[0008] In the prior art, in the process of preparing hydroxypropyl acrylate using acrylic acid and propylene oxide as starting materials, the reaction needs to be carried out under the conditions of a catalyst and a polymerization inhibitor. In addition, the catalyst is generally difficult to recover or the activity of the catalyst decreases significantly after recycling. The polymerization inhibitor is generally a phenolic structure such as hydroquinone or p-hydroxyanisole, which is an aerobic polymerization inhibitor and has a poor polymerization inhibition effect under high temperature and nitrogen atmosphere. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a hydroxypropyl acrylate supported catalyst and a preparation method and application thereof.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] In a first aspect, the present invention provides a method for preparing a supported catalyst of hydroxypropyl acrylate, the steps comprising:

[0012] (1) Preparation of amino-functionalized modified molecular sieve NH2-MCM-41: A silane coupling agent containing an amino group and a MCM-41 molecular sieve are subjected to a reflux reaction in an organic solvent, and then filtered, washed, and vacuum dried to obtain an amino-functionalized NH2-MCM-41 molecular sieve;

[0013] (2) using the amino-functionalized NH2-MCM-41 molecular sieve obtained in the above step (1) as a carrier, heating and refluxing with tetramethylpiperidinol nitroxide free radical in a solvent, and then filtering, washing, and vacuum drying to obtain the NH2-MCM-41 molecular sieve loaded with inhibitory groups;

[0014] (3) The NH2-MCM-41 molecular sieve loaded with polymerization inhibitor groups is impregnated in a chromium or iron metal salt solution for modification, and then filtered, washed, and vacuum dried to obtain a loaded catalyst of hydroxypropyl acrylate.

[0015] Preferably, in step (1), the amino-containing silane coupling agent is selected from 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane;

[0016] Preferably, in step (1), the organic solvent is selected from one or more of methanol, ethanol, n-propanol, and isobutanol;

[0017] Preferably, in step (1), the reflux reaction temperature is 60-110° C. and the time is 10-24 h;

[0018] Preferably, the MCM-41 molecular sieve can be synthesized by conventional hydrothermal crystallization method, or a conventional commercial product can be purchased. Further, the silicon source of the conventional hydrothermal crystallization method can be selected from at least one of silica sol, tetraethyl orthosilicate, sodium silicate, water glass, silica gel powder, white carbon silicon and silicon dioxide powder; the crystallization temperature is 50°C-200°C, and the crystallization time is 0-72 hours; the template agent used can be selected from at least one of ethylamine, propylamine, ethylenediamine, triethylamine, n-butylamine, tetrapropylammonium hydroxide, hexadecyltrimethylammonium bromide and tetrapropylammonium bromide.

[0019] Preferably, in step (1), the mass ratio of MCM-41 molecular sieve, amino-containing silane coupling agent and organic solvent is 1:0.5-10:50-100.

[0020] In the present invention, the amino-functionalized NH2-MCM-41 molecular sieve obtained in step (1) has primary amine groups; preferably, in step (2), the molar ratio of primary amine groups to tetramethylpiperidinol nitrogen oxide free radicals in the amino-functionalized NH2-MCM-41 molecular sieve is 1:2-5; wherein the molar amount of the primary amine groups is calculated by the nitrogen content in the amino-functionalized NH2-MCM-41 molecular sieve.

[0021] Preferably, in step (2), the solvent is selected from one or more of cumene, toluene and ethylbenzene;

[0022] Preferably, in step (2), the reflux reaction temperature is 110-160° C. and the time is 12-24 h;

[0023] In step (2) of the present invention, the primary amine group in the amino-functionalized NH2-MCM-41 molecular sieve is bonded to the inhibition group to form a tertiary amine structure, thereby obtaining the NH2-MCM-41 molecular sieve loaded with the inhibition group. The inhibition structure (i.e., the tertiary amine structure) is as follows:

[0024]

[0025] Preferably, in step (3), the chromium metal salt is one or more of chromium acrylate, chromium acetate, chromium chloride, and chromium acetylacetonate; the iron metal salt is one or more of ferric phosphate, ferric acetate, ferric chloride, and ferric acetylacetonate;

[0026] Preferably, in step (3), the solvent of the metal salt solution is one or more of water, ethanol, n-propanol, and n-butanol, and the concentration of the metal salt solution is preferably 0.02-0.8wt%; the concentration of the NH2-MCM-41 molecular sieve loaded with inhibitory groups in the metal salt solution is 80-120g / L.

[0027] Preferably, in step (3), the immersion temperature is room temperature, preferably 20-25° C., and the immersion time is 8-24 h.

[0028] The preparation method of the present invention also includes operations such as filtration, washing, and vacuum drying, which are all conventional technical means in the field and are not particularly limited by the present invention; preferably, the vacuum drying temperature is 60-100° C. and the time is 6-12 h.

[0029] In a second aspect, the present invention provides a supported catalyst of hydroxypropyl acrylate prepared by the above method, wherein the chromium or iron metal loading is 0.1-1 wt % based on the total mass of the catalyst.

[0030] In a third aspect, the present invention also provides an application of the above catalyst in the preparation process of hydroxypropyl acrylate.

[0031] Exemplarily, the present invention provides a method for preparing hydroxypropyl acrylate using acrylic acid and propylene oxide as raw materials, comprising the following steps: uniformly loading a catalyst in a fixed bed or tubular reactor, controlling the nitrogen pressure to 0.3-0.6 MPaA, heating to 60-90° C., then pumping acrylic acid and propylene oxide into the reactor in a fixed ratio, adjusting the residence time according to the reaction temperature and the amount of catalyst, sampling and analyzing the reactor outlet, cooling and discharging the material after the acrylic acid conversion rate reaches 99.9%, and transferring to a subsequent separation process.

[0032] Preferably, in the above method for preparing hydroxypropyl acrylate, the molar ratio of acrylic acid to propylene oxide is 1:1.025-1.05.

[0034] Preferably, in the above method for preparing hydroxypropyl acrylate, the mass ratio of acrylic acid to catalyst is 100:10-40; and the reaction time is 1-4h.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The catalyst carrier of the present invention adopts amino-functionalized mesoporous molecular sieve, and the larger specific surface area in the pores is conducive to the catalytic reaction of the active components and avoids the active metals being covered by macromolecular polymers; the tertiary amine structure can synergistically load the metal for catalytic reaction and achieve high catalytic activity.

[0037] 2. The supported catalyst of the present invention immobilizes highly efficient nitroxide free radical inhibition groups, has a wide operating temperature range, and can also be used in a nitrogen atmosphere. Since the inhibition structure is in a solid-supported form, there is no problem of separation color number.

[0038] 3. The supported catalyst of the present invention is used in the synthesis of hydroxypropyl acrylate under mild reaction conditions, with an acrylic acid conversion rate of ≥99.9% and a hydroxypropyl acrylate yield of ≥96%. Subsequently, a qualified product can be obtained by simple short-path evaporation, and the catalyst is easy to separate and can be used for a long period of time, thereby reducing production costs and being suitable for industrial production. DETAILED DESCRIPTION

[0039] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0040] Unless otherwise specified, the main raw materials and reagents involved in the present invention were purchased from commercially available products.

[0041] Reagents Specification Manufacturer MCM-41 molecular sieve 3-5nm Xianfeng Nanomaterials Tetramethylpiperidinol nitroxide free radical 99％ Nanjing Huikang Biological 3-Aminopropyltriethoxysilane 97％ Aladdin Reagent Anhydrous ethanol ≥99.5％ Aladdin Reagent Chromium acetate 99.9％ Aladdin Reagent Chromium acetylacetonate 99.9％ Aladdin Reagent Ferric chloride 99.9％ Aladdin Reagent Propylene oxide 55％ Aladdin Reagent

[0042] Gas chromatography (GC): analysis of the composition of the epoxidation reaction liquid, model Shimadzu GC-2010-plus; parameters: chromatographic column DB-5, column temperature: starting temperature 50°C, heating to 300°C, maintaining for 10 min, inlet temperature: 280°C, detector temperature: 300°C, air flow rate: 400 ml / min, hydrogen flow rate: 40 ml / min, tail gas flow rate: 30 ml / min, pressure: 77.7 kPa.

[0043] Analysis of nitrogen, chromium and iron elements: Agilengt-720 inductively coupled plasma emission spectrometer was used; parameters: power 1.2KW, plasma gas flow 15.0L / min, nebulizer flow 0.8L / min, auxiliary gas flow 1.5L / min, instrument stabilization time 15s, injection delay 50s, cleaning time 50s.

[0044] [Example 1]

[0045] The supported catalyst was prepared as follows:

[0046] (1) 3-aminopropyltriethoxysilane and commercially available MCM-41 molecular sieve were refluxed in anhydrous ethanol at 78°C for 10 hours; wherein the mass ratio of MCM-41 molecular sieve, 3-aminopropyltriethoxysilane and anhydrous ethanol was 1:1:50, filtered, washed with anhydrous ethanol, and vacuum dried at 60°C for 6 hours to obtain amino-functionalized NH2-MCM-41 molecular sieve;

[0047] (2) After mixing 200 g of the above-mentioned amino-functionalized NH2-MCM-41 molecular sieve (N 2.66 wt%, 0.38 mol primary amine group), 130.9 g (0.76 mol) of tetramethylpiperidinol nitroxide free radical and 600 g of isopropylbenzene solution, stirring and reflux reaction was carried out at 154°C for 24 h, and the obtained solid was filtered and washed with anhydrous ethanol, and vacuum dried at 60°C for 12 h to obtain the NH2-MCM-41 molecular sieve catalyst loaded with inhibitory groups.

[0048] (3) 100 g of the above-mentioned NH2-MCM-41 molecular sieve catalyst loaded with polymerization inhibitor groups was added to 1 L of a 0.1% chromium acetate aqueous solution, stirred and immersed at room temperature for 24 h, then filtered, washed with anhydrous ethanol, and vacuum dried at 100° C. for 8 h to obtain a loaded catalyst.

[0049] Based on the total mass of the catalyst, the loading amount of the active component chromium is 0.23 wt%.

[0050] Hydroxypropyl acrylate synthesis:

[0051] 4.21 g of the above-mentioned supported catalyst was uniformly loaded into a 316 L fixed bed reactor; the fixed bed reactor had a diameter of 7 mm and a height of 1 m; the jacket was heated to 90° C. under a nitrogen pressure of 0.6 MPaA; acrylic acid and propylene oxide were then added at a mass space velocity of 9.13 h / min. -1 (molar ratio PO / AA=1.025) was pumped into the fixed bed with a residence time of 1 hour. Samples were taken at the outlet for analysis and the acrylic acid conversion rate was 99.95% and the product HPA selectivity was 96.5%.

[0052] Under the above conditions, the process was run continuously for about 2200 hours. Sampling analysis showed that the acrylic acid conversion rate was 99.9% and the product HPA selectivity was 92.5%.

[0053] [Example 2]

[0054] The supported catalyst was prepared as follows:

[0055] (1) 200 g of silica was dispersed in 1 L of deionized water, and the pH was adjusted to 12 with 30% sodium hydroxide solution. The formed gel was stirred at room temperature for 1 h, and then 280 g of a 20% aqueous solution of hexadecyltrimethylammonium bromide was added, and stirred at 60° C. for 1 h. The mixed gel was placed in a stainless steel autoclave lined with tetrafluoroethylene, and a hydrothermal synthesis reaction was carried out at 180° C. After 12 h, the solid product was taken out, filtered, washed, dried in an oven at 100° C. for 6 h, and then calcined in a muffle furnace at 550° C. in an air atmosphere for 8 h to obtain MCM-41 molecular sieve;

[0056] 3-aminopropyltrimethoxysilane and the MCM-41 molecular sieve prepared above were refluxed in n-propanol at 97°C for 24h; wherein the mass ratio of MCM-41 molecular sieve, 3-aminopropyltrimethoxysilane and n-propanol was 1:10:100, filtered, washed with anhydrous ethanol, and vacuum dried at 100°C for 12h to obtain amino-functionalized NH2-MCM-41 molecular sieve;

[0057] (2) After mixing 200 g (N 4.2 wt%, 0.6 mol primary amine) of the amino-functionalized NH2-MCM-41 molecular sieve and 258.3 g (1.5 mol) of tetramethylpiperidinol nitroxide free radical with 1000 g of ethylbenzene solution, the mixture was stirred and refluxed at 136° C. for 24 h. The solid was filtered and washed with anhydrous ethanol, and then dried under vacuum at 80° C. for 6 h to obtain the NH2-MCM-41 molecular sieve catalyst loaded with inhibitory groups.

[0058] (3) 100 g of the above-mentioned NH2-MCM-41 molecular sieve catalyst loaded with the polymerization inhibitor group was added to 1 L of an ethanol solution of chromium acetylacetonate with a mass concentration of 0.68%, stirred and immersed at room temperature for 8 h, then filtered, washed with anhydrous ethanol, and vacuum dried at 60°C for 10 h to obtain a loaded catalyst.

[0059] Based on the total mass of the catalyst, the loading amount of the active component chromium is 1 wt%.

[0060] Hydroxypropyl acrylate synthesis:

[0061] 0.52 g of the above-mentioned supported catalyst was uniformly loaded into a 316 L tubular reactor; the tubular reactor had an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 3000 mm; an oil bath was heated to 80° C. under a nitrogen pressure of 0.4 MPaA; acrylic acid and propylene oxide were then added at a mass space velocity of 18.12 h -1 (molar ratio PO / AA=1.03) was pumped into a tubular reactor with a residence time of 4 hours. Samples taken at the outlet were analyzed for acrylic acid conversion rate of 99.97% and product HPA selectivity of 96.9%.

[0062] Under the above conditions, the process was run continuously for about 2800 h. Sampling analysis showed that the acrylic acid conversion rate was 99.89% and the product HPA selectivity was 93.2%.

[0063] [Example 3]

[0064] The supported catalyst was prepared as follows:

[0065] (1) 3-aminopropyltriethoxysilane and commercially available MCM-41 molecular sieve were refluxed in isobutanol at 105°C for 12 hours; wherein the mass ratio of MCM-41 molecular sieve, 3-aminopropyltriethoxysilane and isobutanol was 1:4:70, filtered, washed with anhydrous ethanol, and vacuum dried at 80°C for 10 hours to obtain amino-functionalized NH2-MCM-41 molecular sieve;

[0066] (2) After mixing 200 g of the above-mentioned amino-functionalized NH2-MCM-41 molecular sieve (N 3.15 wt%, 0.45 mol primary amine group), 172.2 g (1.0 mol) of tetramethylpiperidinol nitroxide free radical and 700 g of toluene solution, stirring and reflux at 110° C. for 20 h, filtering the obtained solid, washing it with anhydrous ethanol, and vacuum drying it at 80° C. for 6 h to obtain the NH2-MCM-41 molecular sieve catalyst loaded with inhibitory groups.

[0067] (3) 100 g of the above-mentioned NH2-MCM-41 molecular sieve catalyst loaded with polymerization inhibition groups was stirred with 1 L of 0.03% ferric chloride aqueous solution at room temperature for 12 h, filtered, washed with anhydrous ethanol, and dried under vacuum at 90° C. for 6 h to obtain a loaded catalyst.

[0068] Based on the total mass of the catalyst, the loading amount of active component iron is 0.1 wt%.

[0069] Hydroxypropyl acrylate synthesis:

[0070] 1.36 g of the above-mentioned supported catalyst was uniformly loaded into a 316 L tubular reactor; the tubular reactor had an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 1000 mm; an oil bath was heated to 60° C. under a nitrogen pressure of 0.3 MPaA; acrylic acid and propylene oxide were then added at a mass space velocity of 4.62 h / min. -1 (molar ratio PO / AA=1.05) was pumped into a tubular reactor with a residence time of 2 hours. Samples were taken from the outlet for analysis and the acrylic acid conversion rate was 99.98%, and the product HPA selectivity was 96.9%.

[0071] Under the above conditions, the system was operated continuously for about 4200 hours. Sampling analysis showed that the acrylic acid conversion rate was 99.94% and the product HPA selectivity was 94.0%.

[0072] [Comparative Example 1]

[0073] Refer to the synthesis method of hydroxypropyl acrylate in Example 3, except that the commercially available catalyst chromium acetate (0.2% by mass of acrylic acid) is used as the catalyst, and the inhibitor is tetramethylpiperidinol nitroxide free radical (0.1% by mass of acrylic acid). Other operations and conditions remain unchanged. The intermittent reaction is carried out for 4 hours. The gas phase analysis shows that the acrylic acid conversion rate is 81.0%, and the product HPA selectivity is 87.2%. Since the catalyst is dissolved in the reaction solution, it is subsequently separated from the heavy components by short-path evaporation and cannot be recovered by a simple engineering method.

[0074] [Comparative Example 2]

[0075] The catalyst was prepared by referring to the method of Example 3, except that step (1) amino functionalization was omitted, and the MCM-41 molecular sieve was directly treated with steps (2) and (3), and other operations and conditions remained unchanged to obtain a supported catalyst.

[0076] Based on the total mass of the catalyst, the loading amount of active component iron is 0.1 wt%.

[0077] The above catalyst was used in the hydroxypropyl acrylate synthesis method of Example 3. The gas phase analysis showed an acrylic acid conversion rate of 67.0% and a product HPA selectivity of 76.4%. Since the catalyst could not load the polymerization inhibitor, acrylic acid polymerization caused the reaction tube to be blocked after about 8 hours of continuous operation.

[0078] [Comparative Example 3]

[0079] The catalyst was prepared by referring to the method of Example 3, except that step (3) of loading iron was omitted, and the MCM-41 molecular sieve was directly treated with steps (1) and (2), and other operations and conditions remained unchanged to obtain a loaded catalyst.

[0080] The above catalyst was used in the hydroxypropyl acrylate synthesis method of Example 3. The outlet sampling analysis showed that the acrylic acid conversion rate was 89.7% and the product HPA selectivity was 92.9%.

[0081] Under the above conditions, the process was run continuously for about 4200 h. Sampling analysis showed that the acrylic acid conversion rate was 88.6% and the product HPA selectivity was 87.4%.

[0082] [Comparative Example 4]

[0083] The catalyst was prepared by referring to the method of Example 3, except that step (2) of loading the polymerization inhibitor was omitted, and the MCM-41 molecular sieve was directly treated with steps (1) and (3), and other operations and conditions remained unchanged to obtain a loaded catalyst.

[0084] The above catalyst was used in the hydroxypropyl acrylate synthesis method of Example 3, except that 0.1 wt % of tetramethylpiperidinol nitroxide free radical was dissolved in acrylic acid. Other operations and conditions remained unchanged. Sample analysis of the outlet showed an acrylic acid conversion rate of 69.7% and a product HPA selectivity of 85.8%.

[0085] Under the above conditions, the system was operated continuously for about 4200 hours. Sampling analysis showed that the acrylic acid conversion rate was 63.6% and the product HPA selectivity was 82.9%.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a hydroxypropyl acrylate supported catalyst, characterized in that: The following steps are involved: (1) Preparation of amino-functionalized modified molecular sieve NH2-MCM-41: A silane coupling agent containing an amino group and a MCM-41 molecular sieve are subjected to a reflux reaction in an organic solvent, and then filtered, washed, and dried to obtain an amino-functionalized NH2-MCM-41 molecular sieve; (2) using the amino-functionalized NH2-MCM-41 molecular sieve obtained in the above step (1) as a carrier, heating and refluxing with tetramethylpiperidinol nitroxide free radical in a solvent, and then filtering, washing, and drying to obtain the NH2-MCM-41 molecular sieve loaded with inhibitory groups; (3) The NH2-MCM-41 molecular sieve loaded with the polymerization inhibitor group is impregnated and modified in a chromium or iron metal salt solution, and then filtered, washed, and dried to obtain a hydroxypropyl acrylate loaded catalyst.

2. The method according to claim 1, characterized in that In the step (1), the amino-containing silane coupling agent is selected from 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane; the organic solvent is preferably one or more of methanol, ethanol, n-propanol, and isobutanol; the reflux reaction temperature is preferably 60-110° C., and the time is 10-24 h; and the drying temperature after the reflux is preferably 60-100° C., and the time is 6-12 h.

3. The method according to any one of claims 1 to 2, characterized in that: In the step (1), the mass ratio of the MCM-41 molecular sieve, the amino-containing silane coupling agent and the organic solvent is 1:0.5-10:50-100.

4. The method according to claim 1, characterized in that In the step (2), the solvent is selected from one or more of cumene, toluene and ethylbenzene; the reflux reaction temperature is preferably 110-160° C., and the reaction time is 12-24 h.

5. The method according to claim 1, characterized in that In the step (2), the NH2-MCM-41 molecular sieve contains primary amine groups, wherein the molar ratio of the primary amine groups to the tetramethylpiperidinol nitroxide free radicals is 1:2-5.

6. The method according to claim 1, characterized in that In the step (3), the chromium metal salt is one or more of chromium acrylate, chromium acetate, chromium chloride, and chromium acetylacetonate; the iron metal salt is one or more of ferric phosphate, ferric acetate, ferric chloride, and ferric acetylacetonate; and the chromium or iron metal loading is preferably 0.1-1 wt % based on the total mass of the catalyst.

7. The method according to claim 1, characterized in that In the step (3), the immersion temperature is room temperature and the time is 8-24 hours; the drying temperature is preferably 60-100° C. and the time is 6-12 hours.

8. A method for preparing hydroxypropyl acrylate, characterized in that: The method comprises the following steps: uniformly loading the catalyst in a fixed bed or tubular reactor, controlling the nitrogen pressure to 0.3-0.6MpaA, heating to 60-90°C, then pumping acrylic acid and propylene oxide into the reactor in a fixed ratio, adjusting the residence time according to the reaction temperature and the amount of catalyst, sampling and analyzing at the reactor outlet, cooling and discharging the material after the acrylic acid conversion rate reaches 99.9%.

9. The method according to claim 8, characterized in that The molar ratio of acrylic acid to propylene oxide is 1:1.025-1.

05.

10. The method according to any one of claims 8 to 9, characterized in that: The mass ratio of acrylic acid to catalyst is 100:10-40; the reaction time is 1-4h.

Images