A catalyst for synthesizing nipagin methyl ester, its preparation method and application

Abstract

This invention discloses a catalyst for the synthesis of methylparaben, its preparation method, and its application, belonging to the field of fine chemical catalyst technology. The catalyst includes a main catalyst and an auxiliary agent; the main catalyst is one or more of SiO2, TiO2, ZrO2, MnO2, and SnO2; the auxiliary agent is one or more of CaO, MgO, Al2O3, Fe2O3, Cr2O3, V2O5, and MoO3; the above catalyst serves as a catalytic material for the esterification reaction of p-hydroxybenzoic acid and methanol to synthesize methylparaben. This invention uses a low-corrosion solid acid as a catalyst, ensuring process safety, high reaction efficiency, and environmental friendliness. Furthermore, it significantly shortens the post-treatment process, and the catalyst can be recycled, effectively solving the corrosion and high pollution problems of the concentrated sulfuric acid catalytic process for methylparaben synthesis.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical catalyst technology, specifically relating to a catalyst for the synthesis of methylparaben, its preparation method, and its application. Background Technology

[0002] Methylparaben, also known as hydroxybenzoate, is widely used as a preservative in pharmaceuticals, cosmetics, and food, and is also used as a feed preservative. It is also an intermediate in pharmaceutical and organic synthesis. The traditional production process of methylparaben involves using p-hydroxybenzoic acid and methanol as raw materials under concentrated sulfuric acid catalysis. After heating and reflux, an alkaline solution is added for neutralization, washing, and decolorization, followed by crystallization to obtain the target product. However, the concentrated sulfuric acid used in this process is highly corrosive to equipment, posing significant safety risks and generating large amounts of waste liquid and high-salt wastewater, causing environmental pollution. Furthermore, the strong oxidizing properties of concentrated sulfuric acid lead to numerous side reactions, resulting in a darker reaction solution and requiring more separation and decolorization steps, making the process lengthy.

[0003] In response to the corrosion and environmental problems associated with concentrated sulfuric acid processes, the development of safe, green, and environmentally friendly new processes for the synthesis of methylparaben has become a major trend in production route innovation. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a catalyst for the synthesis of methylparaben, its preparation method, and its application. The catalyst uses a low-corrosive solid acid as a catalyst, ensuring a safe process, high reaction efficiency, and a green and environmentally friendly process. Furthermore, the post-processing is significantly shortened, and the catalyst can be recycled, effectively solving the corrosion and high pollution problems of the concentrated sulfuric acid catalytic process for methylparaben synthesis.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides a catalyst for the synthesis of methylparaben, comprising a main catalyst and an auxiliary agent;

[0007] The main catalyst is one or more of SiO2, TiO2, ZrO2, MnO2 and SnO2;

[0008] The auxiliary agent is one or more of CaO, MgO, Al2O3, Fe2O3, Cr2O3, V2O5 and MoO3;

[0009] The molar ratio of the main catalyst to the auxiliary agent is 1:(0.01~0.5).

[0010] This invention also provides a method for preparing the catalyst for the synthesis of methylparaben, comprising the following steps:

[0011] S1: Using a co-precipitation method, ammonia water is used to hydrolyze the metal salt or soluble compound solution corresponding to the main catalyst and the metal salt or soluble compound solution corresponding to the auxiliary agent to obtain a mixed hydroxide precipitate.

[0012] S2: The mixed hydroxide precipitate is filtered, dried, and then calcined to obtain a catalyst for the synthesis of methylparaben.

[0013] In the specific implementation process, the metal salt corresponding to the main catalyst or the soluble compound solution corresponding to the main catalyst is one or more of the nitrate, organometallic ester compound and ammonium salt of the main catalyst; the metal salt corresponding to the auxiliary agent or the soluble compound solution corresponding to the auxiliary agent is one or more of the nitrate, organometallic ester compound and ammonium salt of the auxiliary agent.

[0014] In the specific implementation process, the pH value of the co-precipitation method is 8-10; the molar concentration of the ammonia water is 3-8 mol / L.

[0015] In the specific implementation process, the roasting is carried out in an air atmosphere, the roasting temperature is 500-800℃, and the roasting time is 2-5 hours.

[0016] The present invention also provides an application of the catalyst for the synthesis of methylparaben, wherein the catalyst serves as a catalytic material for the synthesis of methylparaben via an esterification reaction using p-hydroxybenzoic acid and methanol as raw materials.

[0017] In the specific implementation process, the synthesis of methylparaben via esterification reaction using p-hydroxybenzoic acid and methanol as raw materials is as follows:

[0018] p-hydroxybenzoic acid, methanol and catalyst were added to a reaction vessel and stirred to carry out an esterification reaction to obtain a reaction solution.

[0019] Methanol and the generated water are recovered by flash evaporation, the catalyst is removed by filtration, the remaining p-hydroxybenzoic acid is neutralized with sodium bicarbonate, and then methylparaben is obtained by water washing and recrystallization.

[0020] In the specific implementation process, the mass ratio of p-hydroxybenzoic acid to methanol is 1:(1.0~4.0); the amount of catalyst used is 1%~5% of the mass of p-hydroxybenzoic acid.

[0021] In the specific implementation process, the reaction temperature of the esterification reaction is 80℃~220℃.

[0022] In the specific implementation process, the reaction time of the esterification reaction is 1.5 to 8 hours.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention provides a catalyst for the synthesis of methylparaben. The catalyst is a low-corrosion solid acid. Using a solid acid catalyst avoids the use of concentrated sulfuric acid, thus solving the problems of large amounts of waste and corrosion associated with using concentrated sulfuric acid as a catalyst. Furthermore, using the solid acid catalyst provided by this invention, the conversion rate of p-hydroxybenzoic acid can reach over 95%, and the selectivity of methylparaben can reach over 99%. The reaction efficiency using a solid acid catalyst is high, and the catalyst can be filtered and recycled. Product post-processing is simple and low-cost; the reaction process is short and environmentally friendly, which is beneficial for industrial production. Detailed Implementation

[0025] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0026] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0027] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0028] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0029] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0030] This invention provides a catalyst for the synthesis of methylparaben, its preparation method, and its application.

[0031] The first aspect of this invention provides a catalyst for synthesizing methylparaben. The catalyst is a solid acid catalyst used to synthesize methylparaben from p-hydroxybenzoic acid and methanol, comprising a main catalyst and an auxiliary agent. The main catalyst is one or more of SiO2, TiO2, ZrO2, MnO2, and SnO2, and the auxiliary agent is one or more of CaO, MgO, Al2O3, Fe2O3, Cr2O3, V2O5, and MoO3. Further, the molar ratio of the main catalyst to the auxiliary agent is 1:(0.01–0.5).

[0032] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst for the synthesis of methylparaben, comprising the following steps:

[0033] S1: Using a co-precipitation method, ammonia water is used to hydrolyze the metal salt or soluble compound solution corresponding to the main catalyst and the metal salt or soluble compound solution corresponding to the auxiliary agent to obtain a mixed hydroxide precipitate.

[0034] S2: The mixed hydroxide precipitate is filtered, dried, and then calcined to obtain a catalyst for the synthesis of methylparaben.

[0035] Preferably, the metal salt corresponding to the main catalyst or the soluble compound solution corresponding to the main catalyst is one or more of nitrates, organometallic esters, and ammonium salts.

[0036] Among them, the metal salts or soluble compound solutions corresponding to SiO2 include tetramethoxysilane (TMOS), Si(OC2H5)4 tetraethoxysilane (TEOS) and ammonium silicate (NH4)2SiO3;

[0037] The metal salts or soluble compound solutions corresponding to TiO2 include Ti(NO3)4, Ti(NO3)2, Ti(OC2H5)4, and (NH4)2TiF6;

[0038] The metal salts or soluble compound solutions corresponding to ZrO2 include Zr(NO3)4, ZrO(NO3)2, and (NH4)2ZrF6;

[0039] The metal salts or soluble compound solutions corresponding to MnO2 include Mn(NO3)2 or Mn(NO3)3, and NH4MnO4;

[0040] The metal salts or soluble compound solutions corresponding to SnO2 include Sn(NO3)4 and (NH4)2SnO3;

[0041] The metal salts or soluble compound solutions corresponding to CaO, MgO, Al2O3, Fe2O3, Cr2O3, V2O5, and MoO3 include Ca(NO3)2, Mg(NO3)2, Al(NO3)3, Fe(NO3)3, Cr(NO3)3, V(NO3)3, NH4VO3, Mo(NO3)3, and (NH4)6Mo7O. 24 .

[0042] Preferably, the co-precipitation method is carried out under a constant pH of 8 to 10, and the molar concentration of the ammonia water used is 3 to 8 mol / L.

[0043] Preferably, the calcination is carried out in an air atmosphere at 500–800°C for 2–5 hours.

[0044] A third aspect of this invention provides the application of the aforementioned catalyst, which serves as a catalytic material for the synthesis of methylparaben via an esterification reaction using p-hydroxybenzoic acid and methanol as raw materials. Specifically, methylparaben is obtained by esterification of p-hydroxybenzoic acid and methanol under the catalysis of the catalyst.

[0045] Specifically, the process of synthesizing methylparaben through esterification using p-hydroxybenzoic acid and methanol as raw materials is as follows:

[0046] p-hydroxybenzoic acid, methanol and catalyst were added to a reaction vessel and stirred to carry out an esterification reaction to obtain a reaction solution.

[0047] Methanol and the generated water are recovered by flash evaporation, the catalyst is removed by filtration, the remaining p-hydroxybenzoic acid (a small amount of acid) is neutralized with sodium bicarbonate, and then methylparaben is obtained by water washing and recrystallization.

[0048] Preferably, the mass ratio of p-hydroxybenzoic acid to methanol is 1:(1.0 to 4.0); the amount of catalyst used is 1 wt% to 5 wt% of p-hydroxybenzoic acid, that is, the amount of catalyst used is 1% to 5% of the mass of p-hydroxybenzoic acid.

[0049] Preferably, the reaction temperature of the esterification reaction is 80℃~220℃, and the reaction time is 1.5~8h.

[0050] The stirring rate of the above stirring is 50 to 400 r / min.

[0051] Specifically, the reaction apparatus used in the above-mentioned synthesis of methylparaben includes a reaction vessel, a condenser, and a recovery tank. The processing procedure using the above-mentioned reaction apparatus is as follows:

[0052] The esterification reaction is carried out in a reactor, which is equipped with a condenser and a recovery tank.

[0053] The gas escaping from the reactor is condensed by a condenser and then enters a recovery tank for recycling.

[0054] After the reaction was completed, the catalyst was flash-evaporated, filtered out, and the unreacted small amount of acid was neutralized with sodium bicarbonate. After washing with water and recrystallization, methylparaben was obtained.

[0055] This invention uses a solid acid catalyst, avoiding the use of concentrated sulfuric acid and solving the problems of large amounts of waste generated in the reaction and corrosion in the process. Furthermore, the conversion rate of p-hydroxybenzoic acid can reach over 95%, and the selectivity of methylparaben can reach over 99%, demonstrating high reaction efficiency. Simultaneously, the catalyst can be filtered and recycled, resulting in simple and low-cost post-processing of the product. The reaction process is short, environmentally friendly, and conducive to industrial production.

[0056] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0057] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0058] Example 1

[0059] Si(OC2H5)4 and Fe(NO3)3 were dissolved in ethanol at a molar ratio of 1:0.1 to achieve a silicon ester concentration of 0.25 mol / L. The mixture was thoroughly stirred and then simultaneously added dropwise with 6 mol / L ammonia solution to an ammonia solution with pH = 9. The pH was monitored using a pH meter to maintain a constant pH of 9 throughout the addition process. After the addition was complete, stirring was continued for 20 minutes, followed by aging at room temperature for 24 hours. The resulting hydroxide precipitate was filtered, washed, dried, and calcined at 600℃ for 3 hours to obtain the Fe2O3-SiO2 catalyst.

[0060] The Fe2O3-SiO2 catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.01:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 80 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were removed by neutralization with sodium bicarbonate. The product was then recrystallized to obtain methylparaben. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 80%, the selectivity of methylparaben was 99%, and the product yield was 69%.

[0061] Example 2

[0062] The difference between this embodiment and Embodiment 1 is that the reaction temperature in this embodiment is different from that in Embodiment 1.

[0063] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.01:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 100 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 86%, the selectivity of methylparaben was 99%, and the product yield was 80%.

[0064] Example 3

[0065] The difference between this embodiment and Embodiment 1 is that the reaction temperature in this embodiment is different from that in Embodiment 1.

[0066] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.01:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 120 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 92%, a methylparaben selectivity of 99%, and a product yield of 85%.

[0067] Example 4

[0068] The difference between this embodiment and Example 1 is that the mass ratio of Fe2O3-SiO2 catalyst, p-hydroxybenzoic acid and methanol, and the reaction temperature are different in this embodiment than in Example 1.

[0069] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.01:1:1.5. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 140 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 93%, a methylparaben selectivity of 99%, and a product yield of 88%.

[0070] Example 5

[0071] The difference between this embodiment and Example 1 is that the mass ratio of Fe2O3-SiO2 catalyst, p-hydroxybenzoic acid and methanol, and the reaction temperature are different in this embodiment than in Example 1.

[0072] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.02:1:1.7. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 160 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion of 95%, a methylparaben selectivity of 95%, and a product yield of 83%.

[0073] Example 6

[0074] The difference between this embodiment and Example 1 is that the mass ratio of Fe2O3-SiO2 catalyst, p-hydroxybenzoic acid and methanol, and the reaction temperature are different in this embodiment than in Example 1.

[0075] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.05:1:4. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 120 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 95%, a methylparaben selectivity of 99.9%, and a product yield of 91%.

[0076] Example 7

[0077] The difference between this embodiment and Example 1 is that the mass ratio of Fe2O3-SiO2 catalyst, p-hydroxybenzoic acid and methanol, and the reaction temperature are different in this embodiment than in Example 1.

[0078] The Fe2O3-SiO2 catalyst from Example 1, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.05:1:1. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 120 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 71%, a methylparaben selectivity of 99%, and a product yield of 65%.

[0079] Example 8

[0080] ZrO(NO3)2 and Cr(NO3)3 were dissolved in water at a molar ratio of 1:0.2 to achieve a zirconium salt concentration of 0.25 mol / L. The mixture was thoroughly stirred and then added dropwise, along with 6 mol / L ammonia solution, to an ammonia solution with a pH of 9. The pH was monitored using a pH meter to maintain a constant level of 9 throughout the addition process. After the addition was complete, stirring was continued for 20 minutes, followed by aging at room temperature for 24 hours. The resulting hydroxide precipitate was filtered, washed, dried, and calcined at 600℃ for 3 hours to obtain the Cr2O3-ZrO2 catalyst.

[0081] The Cr2O3-ZrO2 catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.02:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 140 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation, the catalyst was removed by filtration, unreacted organic acids were removed by neutralization with sodium bicarbonate, and methylparaben was obtained by recrystallization. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 94%, the selectivity of methylparaben was 99%, and the product yield was 89%.

[0082] Example 9

[0083] (NH4)2SnO3 and Ca(NO3)2 were dissolved in water at a molar ratio of 1:0.5 to achieve an ammonium salt concentration of 0.25 mol / L. The mixture was thoroughly stirred and then, along with 6 mol / L ammonia solution, added dropwise to an ammonia solution with a pH of 9. The pH was monitored using a pH meter to maintain a constant level of 9 throughout the addition process. After the addition was complete, stirring was continued for 20 minutes, followed by aging at room temperature for 24 hours. The resulting hydroxide precipitate was filtered, washed, dried, and calcined at 600℃ for 3 hours to obtain the CaO-SnO2 catalyst.

[0084] The CaO-SnO2 catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.02:1:1.5. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 140 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation, the catalyst was removed by filtration, unreacted organic acids were removed by neutralization with sodium bicarbonate, and methylparaben was obtained by recrystallization. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 86%, the selectivity of methylparaben was 95%, and the product yield was 79%.

[0085] Example 10

[0086] ZrO(NO3)2 and Mg(NO3)2 were dissolved in water at a molar ratio of 1:0.2 to achieve a zirconium salt concentration of 0.25 mol / L. The mixture was thoroughly stirred and then added dropwise simultaneously with 6 mol / L ammonia solution to an ammonia solution with a pH of 9. The pH was monitored using a pH meter to maintain a constant pH of 9 throughout the addition process. After the addition was complete, stirring was continued for 20 minutes, followed by aging at room temperature for 24 hours. The resulting hydroxide precipitate was filtered, washed, dried, and calcined at 600℃ for 3 hours to obtain the MgO-ZrO2 catalyst.

[0087] The MgO-ZrO2 catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:1.5. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 140 °C, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation, the catalyst was removed by filtration, unreacted organic acids were removed by neutralization with sodium bicarbonate, and methylparaben was obtained by recrystallization. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 96%, the selectivity of methylparaben was 99%, and the product yield was 92%.

[0088] Example 11

[0089] Mn(NO3)2, Ca(NO3)2, NH4VO3, and (NH4)6Mo7O are mixed in a molar ratio of 1:0.1:0.1:0.014. 24 Dissolve the manganese salt in water to achieve a concentration of 0.25 mol / L, mix thoroughly, and then add it dropwise simultaneously with 3 mol / L ammonia solution to an ammonia solution with pH = 9 while stirring. The pH is monitored using a pH meter to maintain a constant pH of 8 throughout the addition process. After the addition is complete, continue stirring for 20 minutes and allow to stand at room temperature for 24 hours. The resulting hydroxide precipitate is filtered, washed, dried, and calcined at 500℃ for 5 hours to obtain the CaO-V₂O₅-MoO₃-MnO₂ catalyst.

[0090] The CaO-V₂O₅-MoO₃-MnO₂ catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.02:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 140 °C, and a reaction time of 8 h. After the reaction was completed, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were removed by neutralization with sodium bicarbonate. The product was then recrystallized to obtain methylparaben. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 93%, the selectivity of methylparaben was 99.5%, and the product yield was 89%.

[0091] Example 12

[0092] Mn(NO3)2, Ti(OC2H5)4, Si(OC2H5)4, and Al(NO3)3 were dissolved in ethanol in a molar ratio of 0.2:0.3:0.5:0.014 to achieve a (manganese salt + titanium ester + silicon ester) concentration of 0.25 mol / L. The mixture was thoroughly stirred and then added dropwise simultaneously with 8 mol / L ammonia solution to an ammonia solution with pH = 9. The pH was monitored using a pH meter and maintained constant at 10 throughout the addition process. After the addition was complete, stirring was continued for 20 minutes, followed by aging at room temperature for 24 hours. The resulting hydroxide precipitate was filtered, washed, dried, and calcined at 800℃ for 2 hours to obtain the Al2O3-MnO2-TiO2-SiO2 catalyst.

[0093] The Al2O3-MnO2-TiO2-SiO2 catalyst prepared in this embodiment, p-hydroxybenzoic acid, and methanol were added to the reactor in a mass ratio of 0.02:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a reaction temperature of 220℃, and a reaction time of 1.5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation, the catalyst was removed by filtration, unreacted organic acids were removed by neutralization with sodium bicarbonate, and methylparaben was obtained by recrystallization. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 92%, the selectivity of methylparaben was 99%, and the product yield was 88%.

[0094] Comparative Example 1

[0095] Compared with Example 1, this comparative example does not use a catalyst and directly carries out the esterification reaction.

[0096] p-Hydroxybenzoic acid and methanol were added to a reaction vessel at a mass ratio of 1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 80℃, and a reaction time of 5 h. After the reaction was completed, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were removed by neutralization with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed that the conversion rate of p-hydroxybenzoic acid was 31%, the selectivity of methylparaben was 99%, and the product yield was 26%.

[0097] Comparative Example 2

[0098] Compared with Example 1, this comparative example only adds SiO2 as a catalyst to directly carry out the esterification reaction.

[0099] SiO2, p-hydroxybenzoic acid, and methanol were added to a reactor at a mass ratio of 0.01:1:2.0. The reaction was carried out at a stirring rate of 250 r / min, a temperature of 80℃, and a reaction time of 5 h. After the reaction, excess methanol and a small amount of water were recovered by flash evaporation. The catalyst was removed by filtration, and unreacted organic acids were neutralized with sodium bicarbonate. Recrystallization yielded methylparaben. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 50%, a methylparaben selectivity of 99%, and a product yield of 43%.

[0100] Comparative Example 3

[0101] p-hydroxybenzoic acid and methanol were added to a reaction flask equipped with a water separator at a mass ratio of 1:2.0. Concentrated sulfuric acid (10% by mass of p-hydroxybenzoic acid) was added dropwise with stirring, and the reaction was carried out at reflux for 6 hours. After the reaction was complete, a brownish-red reaction solution was obtained. Excess methanol was evaporated off, and the concentrated sulfuric acid and unreacted organic acids were neutralized with sodium bicarbonate. Activated carbon and ethanol were added for decolorization. After decolorization, the activated carbon was removed by filtration, and the ethanol was evaporated off. Recrystallization was then carried out using a methanol-water system (mass ratio 3:7). After centrifugation and drying, methylparaben was obtained. Liquid chromatography analysis showed a p-hydroxybenzoic acid conversion rate of 94%, a methylparaben selectivity of 98%, and a product yield of 87%.

[0102] Comparing Example 1 with Comparative Example 1, it can be seen that the reaction conversion rate and product yield were significantly improved after using the solid acid catalyst proposed in this invention to synthesize methylparaben from p-hydroxybenzoic acid and methanol. Comparing Example 1 with Comparative Example 2, the reaction conversion rate and product yield were significantly improved after adding an auxiliary agent to the main catalyst. Furthermore, comparing Examples 1-12 with Comparative Example 3, it can be seen that, compared with the concentrated sulfuric acid process, the solid acid catalyst proposed in this invention, when applied to the reaction of synthesizing methylparaben from p-hydroxybenzoic acid and methanol, not only avoids the corrosion of equipment by concentrated sulfuric acid, but also improves the selectivity of the reaction, shortens the process flow, and significantly reduces wastewater, thereby improving reaction efficiency, reducing production costs, and meeting the requirements of green processes.

[0103] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. Use of a catalyst for the synthesis of propyl gallate, characterized in that, The catalyst is used as a catalyst for the synthesis of methylparaben through esterification reaction using p-hydroxybenzoic acid and methanol as raw materials. The catalyst for synthesizing methylparaben includes a main catalyst and an auxiliary agent; The main catalyst is one or more of SiO2, TiO2, ZrO2, and MnO2; The auxiliary agent is one or more of CaO, MgO, Fe2O3, Cr2O3, V2O5 and MoO3; The molar ratio of the main catalyst to the auxiliary agent is 1:(0.01~0.5). The catalyst for the synthesis of methylparaben was prepared by the following method: S1: Using a co-precipitation method, ammonia water is used to hydrolyze the metal salt or soluble compound solution corresponding to the main catalyst and the metal salt or soluble compound solution corresponding to the auxiliary agent to obtain a mixed hydroxide precipitate. S2: The mixed hydroxide precipitate was filtered, dried, and then calcined to obtain a catalyst for the synthesis of methylparaben; The catalyst for synthesizing methylparaben exhibits a p-hydroxybenzoic acid conversion rate ≥95% and a methylparaben selectivity ≥99% in the esterification reaction using p-hydroxybenzoic acid and methanol as raw materials.

2. Use of a catalyst for the synthesis of nepetalic acid methyl ester according to claim 1, characterized in that, The metal salt corresponding to the main catalyst or the soluble compound solution corresponding to the main catalyst is one or more of the nitrate, organometallic ester compound and ammonium salt of the main catalyst; the metal salt corresponding to the auxiliary agent or the soluble compound solution corresponding to the auxiliary agent is one or more of the nitrate, organometallic ester compound and ammonium salt of the auxiliary agent.

3. Use of a catalyst for the synthesis of nepetalic acid methyl ester according to claim 1, characterized in that, The pH value for the co-precipitation method is 8-10; the molar concentration of the ammonia solution is 3-8 mol / L.

4. Use of a catalyst for the synthesis of nepetalic acid methyl ester according to claim 1, characterized in that, The calcination is carried out in an air atmosphere, the calcination temperature is 500~800℃, and the calcination time is 2~5 h.

5. Use of the catalyst for synthesizing nepetalic acid methyl ester according to claim 1, characterized in that, The process for synthesizing methylparaben via esterification reaction using p-hydroxybenzoic acid and methanol as raw materials is as follows: p-hydroxybenzoic acid, methanol and catalyst were added to a reaction vessel and stirred to carry out an esterification reaction to obtain a reaction solution. Methanol and the generated water are recovered by flash evaporation, the catalyst is removed by filtration, the remaining p-hydroxybenzoic acid is neutralized with sodium bicarbonate, and then methylparaben is obtained by water washing and recrystallization.

6. Use of a catalyst for the synthesis of nepetalic acid methyl ester according to claim 5, characterized in that, The mass ratio of p-hydroxybenzoic acid to methanol is 1:(1.0~4.0); the amount of catalyst used is 1%~5% of the mass of p-hydroxybenzoic acid.

7. Use of the catalyst for synthesizing nepetalic acid methyl ester according to claim 5, characterized in that, The reaction temperature for the esterification reaction is 80℃~220℃.

8. Use of a catalyst for the synthesis of nepetalic acid methyl ester according to claim 5, characterized in that, The esterification reaction takes 1.5 to 8 hours.