Hydrophobic mesoporous confinement type Sn2-SO3H double-acid-site magnetic polymer solid acid catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of preparation of hydroxybutyl acrylate by a continuous rectification device, and particularly relates to a hydrophobic mesoporous confinement type Sn < 2 + >-SO3H double-acid-site magnetic polymer solid acid catalyst as well as a preparation method and application of the hydrophobic mesoporous confinement type Sn < 2 + >-SO3H double-acid-site magnetic polymer solid acid catalyst. The invention synthesizes a hydrophobic mesoporous confinement type Sn < 2 + >-SO3H double-acid-site magnetic polymer solid acid catalyst Fe3O4 (at) mP (St-FD-Sn)-SO3H, the catalyst integrates two different catalytic active centers (Sn with Lewis acidity and-SO3H with Bronsted acidity), the catalyst has a better catalytic effect, and the ester exchange reaction can reach a higher yield. Compared with the traditional purification method that rectification purification is carried out after continuous extraction, the method adopting continuous rectification for product purification has the advantages that the introduction of an extracting agent is reduced, the product is purer in quality and higher in yield, and the production cost is obviously reduced.

Description

Technical Field

[0001] This invention belongs to the field of continuous distillation apparatus for the preparation of hydroxybutyl acrylate, specifically relating to a hydrophobic mesoporous confined Sn... 2+ -SO3H dual-acid-site magnetic polymer solid acid catalyst, its preparation method and application. Background Technology

[0002] 4-Hydroxybutyl acrylate (4-HBA), a highly reactive (iso)bifunctional monomer, possesses an acryloyloxy group with high reactivity, suitable for UV curing or thermosetting processes. The hydroxyl group, a polar group, provides excellent adhesion and can react with other functional groups (such as isocyanates) to form cross-linked networks. This bifunctional characteristic makes 4-HBA an ideal monomer for preparing high-performance polymers. The chemical resistance, weather resistance, scratch resistance, and excellent adhesion of 4-HBA demonstrate significant application potential in high-end automotive topcoats, UV-cured coatings, and adhesives. Compared to common hydroxyethyl acrylate (HEA) and hydroxypropyl acrylate (HPA), 4-HBA exhibits significant performance advantages, especially its long carbon chain structure, which imparts better flexibility and low-temperature compliance to the polymer. In recent years, with the rapid development of the automotive and high-end coating industries, the demand for 4-HBA has been increasing, making it a research hotspot in the field of acrylate monomers. Germany and Japan have a clear advantage in the research and application of 4-HBA, while my country's research in this area is still in its early stages. Therefore, in-depth research on the synthetic routes of 4-HBA is of great significance for promoting my country's independent innovation capabilities in the field of high-end acrylate monomers and improving product quality.

[0003] Transesterification is one of the important process routes for synthesizing hydroxybutyl 4-acrylate. Its core principle is to allow 1,4-butanediol to undergo transesterification with alkyl acrylate in the presence of a catalyst to produce hydroxybutyl 4-acrylate and the corresponding alcohol.

[0004] Osaka Organic Chemicals Co., Ltd. has developed a patented technology that uses dialkyltin oxides with 4-18 alkyl carbon atoms as transesterification catalysts, particularly dioctyltin oxide and dilauryltin oxide. These catalysts exhibit high catalytic activity and selectivity at specific dosages (0.00001-0.01 mol of catalyst per 1 mol of alkyl acrylate). The process uses cyclohexane as the organic solvent, and the product is purified through a multi-step extraction process: first, an extraction solvent containing water and cyclohexane is mixed to allow 4-HBA to enter the aqueous phase; then, the aqueous phase is mixed with an extraction solvent containing aromatic hydrocarbons, allowing 4-HBA to be re-extracted into the organic phase, thus achieving product purification and catalyst recovery and reuse.

[0005] The transesterification method for synthesizing hydroxybutyl 4-acrylate offers mild reaction conditions, effectively controlling the self-polymerization of alkyl acrylates. Using alkyl acrylates as raw materials simplifies storage and handling. The catalysts exhibit high activity and selectivity, particularly the application of novel dialkyltin oxide catalysts, enabling the reaction to proceed at lower temperatures. However, the transesterification method also has significant limitations: firstly, catalyst separation is difficult, and residual catalyst can lead to poor product storage stability and even disproportionation side reactions; secondly, product purification is cumbersome, requiring multiple extraction steps, which may affect the yield.

[0006] To achieve widespread application of 4-HBA, a series of technical challenges still need to be addressed. The first is cost; currently, the production cost of 4-HBA is relatively high, limiting its large-scale application. However, production costs can be effectively reduced through catalyst optimization, process simplification, and process intensification. Summary of the Invention

[0007] The purpose of this invention is to provide a hydrophobic mesoporous confined Sn 2+ -SO3H dual-acid-site magnetic polymer solid acid catalyst, its preparation method and application: using the catalyst for the catalytic synthesis of 4-hydroxybutyl acrylate, and then using continuous distillation to purify 4-hydroxybutyl acrylate, reducing its loss and increasing the yield.

[0008] To achieve the purpose of the invention, this invention provides a hydrophobic mesoporous confined Sn 2+ The preparation method of the SO3H dual-acid-site magnetic polymer solid acid catalyst includes the following steps: (1) Synthesis of magnetic Fe3O4@SiO2 cores (coprecipitation method and Stöber method); (2) Synthesis of the hydrophobic monomer 9-fluorenylmethanol acrylate (FMAA); (3) Construction of a hydrophobic mesoporous polymer coating layer (Fe3O4@mP(St-FD-Sn)): S1. Preparation of pre-emulsion: Fe3O4@SiO2 magnetic cores and surfactant sodium dodecyl sulfate (SDS) were ultrasonically dispersed in an ethanol / water mixed solvent; styrene (St), crosslinking agent divinylbenzene, FMAA (functional monomer), divinylferrocene (porogen), and di(acrylate)dibutyltin (tin source) were added sequentially; the mixture was ultrasonically treated for 30-60 minutes to form a uniform pre-emulsion. S2. Polymerization reaction: Initiator AIBN was dissolved in ethanol to obtain solution A; the pre-emulsion was placed under N2 protection, mechanically stirred at 500-700 rpm, and heated in an oil bath; solution A was added; the reaction was continued; S3. Etching to create holes: After the reaction was completed, the product was thoroughly washed with THF to remove unreacted monomers and linear polymers; the product was dispersed in 1M HCl / ethanol solution and stirred continuously to selectively etch away divinylferrocene and create mesopores in the polymer shell; after filtration, it was washed with ethanol and water until neutral and vacuum dried to obtain the target product precursor Fe3O4@mP(St-FD-Sn). (4) Selective sulfonation (Fe3O4@mP(St-FD-Sn)-SO3H): S1. Preparation of acetylsulphate: Concentrated sulfuric acid was slowly added dropwise to acetic anhydride with stirring at 0°C (ice-water bath) to obtain an acetylsulphate solution. S2. Sulfonation reaction: The precursor Fe3O4@mP(St-FD-Sn) obtained in step (3) was dispersed in anhydrous dichloroethane and cooled to obtain a dispersion. An acetylsulphate solution was added to a dry constant-pressure dropping funnel and slowly added dropwise to the Fe3O4@mP(St-FD-Sn) dichloroethane dispersion under N2 protection and ice bath stirring, controlling the dropping rate to maintain the reaction temperature at 0-5°C. After the addition was complete, the ice bath was removed, and the temperature was raised to 30-50°C to continue the reaction. S3. Post-processing: After the reaction was completed, the reaction solution was poured into ice water to terminate the reaction; the solution was washed repeatedly with deionized water until it was neutral; then it was washed once with anhydrous ethanol and dried under vacuum to finally obtain the black solid product Fe3O4@mP(St-FD-Sn)-SO3H catalyst.

[0009] Preferably, the mass ratio of the Fe3O4@SiO2 magnetic core to the surfactant sodium dodecyl sulfate (SDS) in step (3) S1 is 5-10:1.

[0010] Preferably, the volume ratio of ethanol to water in step (3) S1 is 4:1; the solid content of the magnetic core is 6-7 g / L.

[0011] Preferably, in step (3) S1, the volume fraction of styrene (St) is 5-7%; the molar ratio of divinylbenzene (DVB) to styrene is 5-6:25; the molar ratio of FMAA to styrene is 3.2-6.4:100; the volume ratio of divinyl ferrocene to styrene is 2-5:100; and the mass ratio of dibutyltin diacrylate to styrene is 1-5:50; thus forming a uniform pre-emulsion.

[0012] Preferably, in step (3), S2, the pre-emulsion is heated in an oil bath to 70-90°C; the mass of the AIBN is 1.0-1.5% of the mass of the solute in the pre-emulsion; and the reaction is carried out at 70-80°C for 24-48 hours.

[0013] Preferably, in step (3) S3, the solid-liquid ratio of the product to the HCl / ethanol solution is 1:100-200, g / mL; the stirring time is 12-24 hours; and the vacuum drying conditions are vacuum drying at 60-80℃ for 12-24 hours.

[0014] Preferably, the volume ratio of concentrated sulfuric acid to acetic anhydride in step (4) S1 is 1:20.

[0015] Preferably, the mass ratio of concentrated sulfuric acid in step (4) S1 to the precursor in step (3) is 1:2.

[0016] Preferably, in step (4) S2, the solid-liquid ratio of the precursor Fe3O4@mP(St-FD-Sn) to anhydrous dichloroethane is 1:30, g / mL; the reaction is carried out at a high temperature for 5-8 hours.

[0017] Preferably, the vacuum drying conditions in step (4) S3 are vacuum drying at 60-80°C for 12-24 hours.

[0018] The present invention also provides the application of the above catalyst in the catalytic synthesis of hydroxybutyl 4-acrylate.

[0019] A method for preparing hydroxybutyl 4-acrylate includes the following steps: a. Preparation of the reaction solution: The catalyst in the fixed bed is Fe3O4@mP(St-FD-Sn)-SO3H solid acid catalyst, wherein the molar ratio of 1,4-butanediol to methyl acrylate is 1-3:1, and the polymerization inhibitor is hydroquinone, added at 0.1-0.3 wt% of methyl acrylate; the reaction solution is prepared at a space velocity of 20-30 h⁻¹. -1 The mixture enters the fixed-bed microreactor R101 at a reaction temperature of 90-110℃, and then the reaction solution is discharged at a flow rate of 1.5 kg / h. b. After discharge, the product enters continuous distillation, with the following separation targets: 4-HBA product purity ≥ 99%, and BDO recycling purity > 95%; The reaction solution first enters the T-101 distillation column (de-alcoholization and de-esterification column) at a rate of 1.5 kg / h, mainly separating the light component (MA / MeOH) from the heavy component (BDO / 4-HBA / BDA / HQ). The internal components are glass sieve plates or packing. The column diameter is 30 mm, the column height is 2 m, the operating pressure is 40 kPa, the reflux ratio is 1-3, the feed temperature is 60°C, the column top temperature is 40-42°C (boiling point of MA / MeOH azeotrope), the column bottom temperature is 72-76°C (ensuring that MA / MeOH has been completely distilled), and the column top discharge flow rate is 0.193 kg / h. c. After preheating (to 85℃), the liquid in the bottom of column T101 enters distillation column T-102 (product purification column) to accurately separate 4-HBA and BDO. It uses structured glass packing, has a column diameter of 25mm, a column height of 2.5m, an operating pressure of 3 kPa, a reflux ratio of 5-20, a top temperature of 95-100℃ (light components and a small amount of BDO), and uses total reflux at the top. The side stream temperature is 115-120℃ (high-purity 4-HBA vapor phase), the bottom temperature is 140-146℃, the side stream product flow rate is 0.648 kg / h, and the bottom distillate flow rate is 0.659 kg / h. d. The liquid from the bottom of tower T102 enters tower T-103 (BDO recovery tower) for BDO recovery. Corrugated mesh packing is used, with a tower diameter of 20 mm, a tower height of 1.5 m, an operating pressure of 1.5 kPa, a reflux ratio of 1-5, a tower top temperature of 125-130℃ (recovered BDO), a tower bottom temperature of 160-168℃ (concentrated BDO), a tower top discharge flow rate of 0.535 kg / h, and a tower bottom discharge flow rate of 0.124 kg / h.

[0020] The beneficial effects of this invention are as follows: (1) A hydrophobic mesoporous confined Sn was synthesized. 2+ The Fe3O4@mP(St-FD-Sn)-SO3H dual-acid magnetic polymer solid acid catalyst integrates two different catalytic active centers (Lewis acidic Sn and Brønsted acidic -SO3H), exhibiting good catalytic performance and enabling high yields in transesterification reactions.

[0021] (2) After the reaction is completed, the catalyst can be selectively and quickly separated from the reaction solution using only an external magnet, without the need for cumbersome centrifugation, filtration and other operations. This greatly simplifies the operation process, reduces the loss of catalyst during the separation process, and lays the foundation for the recycling and economic feasibility of the catalyst.

[0022] (3) The catalyst integrates a polymer skeleton (crosslinked polystyrene) and a SiO2 interlayer, providing robust mechanical and chemical protection for the catalyst. It has high chemical stability, which can protect the internal magnetic core from acid and oxygen erosion, prevent the leaching and loss of active components, and has strong structural stability. The robust support can prevent the catalyst from structurally collapsing during the reaction and recovery process, thereby extending the service life of the catalyst.

[0023] (4) The mesoporous polymer shell (mp) of the catalyst has a high specific surface area and tunable nanoscale pores. The high loading capacity can carry a large number of catalytic active sites. The open pores promote mass transfer, allowing reactant molecules to diffuse rapidly to the active sites and product molecules to leave smoothly, thereby increasing the reaction rate.

[0024] (5) Using continuous distillation for product purification reduces the introduction of extractant compared to traditional purification which uses continuous extraction followed by distillation. This results in purer product quality, higher yield, significantly reduced production costs, and a reduction in the number of equipment required, thus lowering equipment procurement costs. Attached Figure Description

[0025] Figure 1 Flowchart of the continuous distillation process for preparing HBA. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1 A hydrophobic mesoporous confined Sn 2+ The preparation method of the SO3H dual-acid-site magnetic polymer solid acid catalyst includes the following steps: (1) Synthesis of magnetic Fe3O4@SiO2 cores (coprecipitation method and Stöber method): In a 500 mL three-necked flask, add 200 mL of deoxygenated deionized water (purged with N2 for 30 minutes) and heat to 80 °C. Quickly add 2.70 g (10.0 mmol) FeCl3·6H2O and 1.00 g (5.0 mmol) FeCl2·4H2O, and stir (800 rpm) under N2 protection to dissolve. Slowly add 15 mL of ammonia water dropwise using a constant pressure dropping funnel; the solution gradually turns black. Continue the reaction at 80 °C for 1 hour. Wash with 60 °C deionized water until neutral, then wash twice with anhydrous ethanol. Dry under vacuum at 60 °C for 6 hours to obtain black Fe3O4 powder.

[0028] The 1.00 g of dried Fe3O4 powder was dispersed in a mixture of 160 mL anhydrous ethanol, 40 mL deionized water, and 2.0 mL concentrated ammonia, and sonicated for 30 minutes. Under mechanical stirring, 1.0 mL of LTEOS (tetraethyl orthosilicate) was slowly added dropwise. The reaction was carried out at room temperature for 6 hours. The mixture was washed three times with anhydrous ethanol and dried under vacuum at 60 °C for 6 hours to obtain Fe3O4@SiO2. 1.00 g of this was used for the next step.

[0029] (2) Synthesis of the hydrophobic monomer 9-fluorenylmethyl acrylate (FMAA): In a 250 mL three-necked flask, 1.80 g (10.0 mmol) of 9-fluorenylmethanol and 1.21 g (12.0 mmol) of triethylamine were dissolved in 50 mL of anhydrous tetrahydrofuran (THF), and the mixture was cooled to 0 °C in an ice-water bath. While stirring, a mixture of 1.10 mL (13.5 mmol) of acryloyl chloride and 10 mL of anhydrous THF was slowly added dropwise over approximately 30 minutes. The ice bath was removed, and the reaction was allowed to proceed at room temperature for 12 hours. After the reaction was complete, the triethylamine hydrochloride precipitate was removed by filtration, and THF was removed by rotary evaporation to obtain the crude product. Recrystallization from ethanol / water yielded white crystalline FMAA.

[0030] (3) Construction of a hydrophobic mesoporous polymer coating layer (Fe3O4@mP(St-FD-Sn)): S1. Preparation of pre-emulsion: Fe3O4@SiO2 magnetic cores and surfactant sodium dodecyl sulfate (SDS) were ultrasonically dispersed in an ethanol / water mixed solvent; styrene (St), crosslinking agent divinylbenzene, FMAA (functional monomer), divinyl ferrocene (porogen), and dibutyltin diacrylate (tin source) were added sequentially; the mixture was ultrasonically treated for 30 minutes to form a uniform pre-emulsion; the mass ratio of Fe3O4@SiO2 magnetic cores to surfactant sodium dodecyl sulfate (SDS) was 5:1; the volume ratio of ethanol to water was 4:1; the solid content of the magnetic cores was 6 g / L; the volume fraction of styrene (St) was 5%; the molar ratio of divinylbenzene (DVB) to styrene was 5:25; the molar ratio of FMAA to styrene was 3.2:100; the volume ratio of divinyl ferrocene to styrene was 3:100; and the mass ratio of dibutyltin diacrylate to styrene was 2:50.

[0031] S2. Polymerization reaction: Initiator AIBN was dissolved in ethanol to obtain solution A; the preemulsion was placed under N2 protection, mechanically stirred at 500 rpm, and heated in an oil bath; solution A was added; the reaction was continued; the preemulsion was heated in an oil bath to 80°C; the mass of AIBN was 1.0% of the mass of the solute in the preemulsion; the reaction was continued at 70°C for 36 hours.

[0032] S3. Etching to create holes: After the reaction was completed, the product was thoroughly washed with THF to remove unreacted monomers and linear polymers. The product was dispersed in a 1M HCl / ethanol solution and stirred continuously to selectively etch away divinylferrocene, creating mesopores in the polymer shell. After filtration, the product was washed with ethanol and water until neutral, and then vacuum dried to obtain the target product precursor Fe3O4@mP(St-FD-Sn). The solid-liquid ratio of the product to the HCl / ethanol solution was 1:100, g / mL. The stirring time was 18 hours. The vacuum drying conditions were 70°C for 16 hours.

[0033] (4) Selective sulfonation (Fe3O4@mP(St-FD-Sn)-SO3H): S1. Preparation of acetylsulphate: Under stirring at 0°C (ice-water bath), concentrated sulfuric acid is slowly added dropwise to acetic anhydride to obtain an acetyl sulfate solution; the volume ratio of the concentrated sulfuric acid to acetic anhydride is 1:20; the mass ratio of the concentrated sulfuric acid to the precursor in step (3) is 1:2.

[0034] S2. Sulfonation reaction: The precursor Fe3O4@mP(St-FD-Sn) obtained in step (3) was dispersed in anhydrous dichloroethane and cooled to obtain a dispersion. Acetyl sulfate solution was added to a dry constant pressure dropping funnel and slowly added dropwise to the dichloroethane dispersion of Fe3O4@mP(St-FD-Sn) under N2 protection and ice bath stirring, controlling the dropping rate to maintain the reaction temperature at 0-5°C. After the addition was completed, the ice bath was removed and the temperature was raised to 45°C to continue the reaction. The solid-liquid ratio of the precursor Fe3O4@mP(St-FD-Sn) to the anhydrous dichloroethane was 1:30, g / mL. The reaction was carried out at a high temperature for 6 hours.

[0035] S3. Post-processing: After the reaction was completed, the reaction solution was poured into ice water to terminate the reaction; the solution was washed repeatedly with deionized water until it was neutral; then washed once with anhydrous ethanol and dried under vacuum to finally obtain the black solid product Fe3O4@mP(St-FD-Sn)-SO3H catalyst; the vacuum drying conditions were 80°C for 12 hours.

[0036] Example 2 A method for preparing hydroxybutyl 4-acrylate includes the following steps: a. Preparation of the reaction solution: The catalyst in the fixed bed is the Fe3O4@mP(St-FD-Sn)-SO3H solid catalyst obtained in Example 1, wherein the molar ratio of 1,4-butanediol to methyl acrylate is 2:1, and the polymerization inhibitor is hydroquinone (HQ), added at 0.1 wt% of methyl acrylate; Figure 1 As shown, at an airspeed of 20h-1 The mixture enters a fixed-bed microreactor R101 at a reaction temperature of 100℃. The reaction solution is then discharged at a flow rate of 1.5 kg / h. The composition of the discharged product (wt%) is: methyl acrylate (MA): 1.293% (0.019 kg / h), methanol (MeOH): 11.545% (0.173 kg / h), 1,4-butanediol (BDO): 36.195% (0.543 kg / h), 4-hydroxybutyl acrylate (4-HBA): 48.703% (0.731 kg / h), 1,4-butanediol diacrylate (BDA) and others: 1.5% (0.034 kg / h). The HBA yield reaches 90%.

[0037] Then it enters continuous distillation, with the following separation targets: 4-HBA product purity ≥99%, and BDO recycling purity >95%.

[0038] The reaction solution first enters the T-101 distillation column (de-alcoholization and de-esterification column) at a rate of 1.5 kg / h, mainly separating the light components (MA / MeOH) from the heavy components (BDO / 4-HBA / BDA / HQ). The internal components are glass sieve plates or packing. The column diameter is 30 mm, the column height is 2 m, the operating pressure is 40 kPa, the reflux ratio is 2, the feed temperature is 60°C, the top temperature is 40°C (boiling point of MA / MeOH azeotrope), the bottom temperature is 72°C (ensuring that MA / MeOH has been completely distilled), the top discharge flow rate is 0.193 kg / h (MA accounts for 10.1 wt%, MeOH accounts for 89.9 wt%), and the bottom discharge flow rate is 1.307 kg / h (BDO accounts for 41.5 wt%, 4-HBA accounts for 55.9 wt%, BDA and others account for 2.6 wt%).

[0039] The liquid in the T101 column bottom is preheated (to 85℃) and then enters the T-102 distillation column (product purification column) for precise separation of 4-HBA and BDO. It uses structured glass packing, has a column diameter of 25mm, a column height of 2.5m, an operating pressure of 3 kPa, a reflux ratio of 15, a top temperature of 100℃ (light components and a small amount of BDO), and uses total reflux at the top. The side stream outlet temperature is 120℃ (high-purity 4-HBA vapor phase outlet), the bottom temperature is 140℃, the side stream product flow rate is 0.648 kg / h (BDO 0.8wt%, 4-HBA 99.2wt%, yield: 88%), and the bottom distillate flow rate is 0.659 kg / h (BDO 81.6wt%, 4-HBA 13.3wt%, BDA and others 5.2wt%).

[0040] The liquid from the bottom of tower T102 enters tower T-103 (BDO recovery tower) for BDO recovery. Corrugated mesh packing is used, with a tower diameter of 20mm, a tower height of 1.5m, an operating pressure of 1.5kPa, a reflux ratio of 3, a top temperature of 125-130℃ (recovered BDO), a bottom temperature of 160-168℃ (concentrated BDA residue), a top discharge flow rate of 0.535 kg / h (BDO 96.0wt%, 4-HBA 4.0wt%), and a bottom discharge flow rate of 0.124 kg / h (BDO 19.1wt%, 4-HBA 53.5wt%, BDA and others 27.4wt%).

Claims

1. A hydrophobic mesoporous confined Sn 2+ The method for preparing a -SO3H dual-acid-site magnetic polymer solid acid catalyst is characterized by, The preparation method includes the following steps: (1) Synthesis of magnetic Fe3O4@SiO2 cores (coprecipitation method and Stöber method); (2) Synthesis of the hydrophobic monomer 9-fluorenylmethanol acrylate (FMAA); (3) Construction of a hydrophobic mesoporous polymer coating layer (Fe3O4@mP(St-FD-Sn)): S1. Preparation of pre-emulsion: Fe3O4@SiO2 magnetic cores and surfactant sodium dodecyl sulfate (SDS) were ultrasonically dispersed in an ethanol / water mixed solvent; styrene (St), crosslinking agent divinylbenzene, FMAA (functional monomer), divinylferrocene (porogen), and di(acrylate)dibutyltin (tin source) were added sequentially; the mixture was ultrasonically treated for 30-60 minutes to form a uniform pre-emulsion. S2. Polymerization reaction: Initiator AIBN was dissolved in ethanol to obtain solution A; the pre-emulsion was placed under N2 protection, mechanically stirred at 500-700 rpm, and heated in an oil bath; solution A was added; the reaction was continued; S3. Etching to create holes: After the reaction was completed, the product was washed thoroughly with THF; the product was dispersed in 1M HCl / ethanol solution and stirred continuously; after filtration, it was washed with ethanol and water until neutral, and dried under vacuum to obtain the target product precursor Fe3O4@mP(St-FD-Sn); (4) Selective sulfonation (Fe3O4@mP(St-FD-Sn)-SO3H): S1. Preparation of acetylsulphate: Concentrated sulfuric acid was slowly added dropwise to acetic anhydride with stirring in an ice-water bath at 0°C to obtain an acetylsulphate solution. S2. Sulfonation reaction: The precursor Fe3O4@mP(St-FD-Sn) obtained in step (3) was dispersed in anhydrous dichloroethane and cooled to obtain a dispersion. Acetyl sulfate solution was added to a dry constant pressure dropping funnel and slowly added dropwise to the dichloroethane dispersion of Fe3O4@mP(St-FD-Sn) under N2 protection and ice bath stirring conditions. The dropping rate was controlled to maintain the reaction temperature at 0-5°C. After the addition was completed, the ice bath was removed and the temperature was raised to 30-50°C to continue the reaction. S3. Post-processing: After the reaction was completed, the reaction solution was poured into ice water to terminate the reaction; the solution was washed repeatedly with deionized water until it was neutral; then it was washed once with anhydrous ethanol and dried under vacuum to finally obtain Fe3O4@mP(St-FD-Sn)-SO3H solid acid catalyst.

2. The preparation method according to claim 1, characterized in that, In step (3) S1, the mass ratio of the Fe3O4@SiO2 magnetic core to the surfactant sodium dodecyl sulfate (SDS) is 5-10:1; the volume ratio of ethanol to water is 4:1; the solid content of the magnetic core is 6-7 g / L; the volume fraction of styrene (St) is 5-7%; the molar ratio of divinylbenzene (DVB) to styrene is 5-6:25; the molar ratio of FMAA to styrene is 3.2-6.4:100; the volume ratio of divinylferrocene to styrene is 2-5:100; and the mass ratio of dibutyltin diacrylate to styrene is 1-5:

50.

3. The preparation method according to claim 1, characterized in that, In step (3), S2, the pre-emulsion is heated in an oil bath to 70-90°C; the mass of AIBN is 1.0-1.5% of the mass of the solute in the pre-emulsion; the continuous reaction conditions are 24-48 hours at 70-80°C.

4. The preparation method according to claim 1, characterized in that, In step (3), S3, the solid-liquid ratio of the product to the HCl / ethanol solution is 1:100-200, g / mL; the stirring time is 12-24 hours; and the vacuum drying conditions are 60-80℃ for 12-24 hours.

5. The preparation method according to claim 1, characterized in that, The volume ratio of concentrated sulfuric acid to acetic anhydride in step (4) S1 is 1:20; the mass ratio of concentrated sulfuric acid to the precursor in step (3) is 1:

2.

6. The preparation method according to claim 1, characterized in that, In step (4) S2, the solid-liquid ratio of the precursor Fe3O4@mP(St-FD-Sn) to anhydrous dichloroethane is 1:30, g / mL; the reaction is carried out at a high temperature for 5-8 hours.

7. The preparation method according to claim 1, characterized in that, In step (4) S3, the vacuum drying conditions are vacuum drying at 60-80°C for 12-24 hours.

8. The Fe3O4@mP(St-FD-Sn)-SO3H solid acid catalyst obtained by the preparation method according to any one of claims 1-7.

9. The application of the Fe3O4@mP(St-FD-Sn)-SO3H solid acid catalyst as described in claim 8 in the catalytic synthesis of hydroxybutyl 4-acrylate.

10. A method for preparing hydroxybutyl 4-acrylate, characterized in that, The preparation method includes the following steps: a. Preparation of the reaction solution: The catalyst in the fixed bed is the Fe3O4@mP(St-FD-Sn)-SO3H solid acid catalyst as described in claim 8, with the addition of 1,4-butanediol and methyl acrylate, the molar ratio of 1,4-butanediol to methyl acrylate being 1-3:1, and the polymerization inhibitor being hydroquinone, added at an amount of 0.1-0.3 wt% of methyl acrylate; the reaction is carried out at a space velocity of 20-30 h⁻¹. -1 The mixture enters the fixed-bed microreactor R101 at a reaction temperature of 90-110℃, and then the reaction solution is discharged at a flow rate of 1.5 kg / h. b. After discharge, the product enters continuous distillation, with the following separation targets: 4-HBA product purity ≥99%, and BDO recycling purity >95%; The reaction solution first enters the distillation column T-101 (de-alcoholization and de-esterification column) at a rate of 1.5 kg / h. The internal components are glass sieve plates or packing. The column diameter is 30 mm, the column height is 2 m, the operating pressure is 40 kPa, the reflux ratio is 1-3, the feed temperature is 60°C, the column top temperature is 40-42°C, the column bottom temperature is 72-76°C, and the column top discharge flow rate is 0.193 kg / h. c. After being preheated to 85℃, the liquid in the bottom of column T101 enters the distillation column T-102 (product purification column) to accurately separate 4-HBA and BDO. It uses structured glass packing, has a column diameter of 25mm, a column height of 2.5m, an operating pressure of 3 kPa, a reflux ratio of 5-20, a top temperature of 95-100℃, uses total reflux at the top, a side stream temperature of 115-120℃ (high-purity 4-HBA vapor phase), a bottom temperature of 140-146℃, a side stream product flow rate of 0.648 kg / h, and a bottom distillate flow rate of 0.659 kg / h. d. The liquid from the bottom of tower T102 enters tower T-103 (BDO recovery tower) for BDO recovery. Corrugated mesh packing is used, with a tower diameter of 20mm, a tower height of 1.5m, an operating pressure of 1.5 kPa, a reflux ratio of 1-5, a tower top temperature of 125-130℃ (recovered BDO), a tower bottom temperature of 160-168℃, a tower top discharge flow rate of 0.535kg / h, and a tower bottom discharge flow rate of 0.124kg / h.

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