Preparation process of methylparaben

Abstract

The invention relates to the technical field of organic matter preparation, in particular to a methylparaben preparation process which comprises the following steps: S1, performing esterification reaction on p-hydroxybenzoic acid and methanol under the catalysis of modified zeolite, distilling and dealcoholizing a product, and performing neutralization elutriation and primary centrifugal filtration crystallization; and S2, transferring the primary crystallization product into a desolventizing kettle for dissolution and desorption, carrying out secondary crystallization and centrifugal separation after desolventizing, and drying a wet material to obtain the methylparaben. According to the method, the dependence on strong acid, especially liquid strong acid, in the production of methylparaben can be effectively reduced, so that the generation of colored condensation impurities is reduced, the generation amount of acid-containing wastewater is correspondingly reduced, traditional decolorization treatment is not needed, and the difficulty and the cost of wastewater treatment are reduced. Meanwhile, the purity and the yield of the prepared methylparaben are relatively high, and certain economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of organic matter preparation, in particular to a preparation process of methylparaben. Background Art

[0002] Methylparaben, also known as methyl parahydroxybenzoate, is widely used in food, cosmetics, medicine and other fields. Methylparaben appears as white crystalline powder or colorless crystals, is easily soluble in alcohol, ether and acetone, but very slightly soluble in water, and has a boiling point of 270-280°C. As an excellent preservative, methylparaben has a broad-spectrum antibacterial property, has good efficacy against molds and yeasts, but is relatively weak against bacteria. Under the condition of pH 3-6, its preservative effect is strong and its properties are stable, but it gradually hydrolyzes above pH 8, and its antibacterial effect weakens. Methylparaben can be used alone or in combination with other methylparabens and other antibacterial preservatives to enhance the preservative effect. For example, methylparaben is used in combination with propylparaben and is often used as an antibacterial agent in various injection preparations. In addition, the antibacterial activity of methylparaben increases with the increase of the length of the hydrocarbon chain, but the water solubility decreases, so a mixture of methylparabens is usually used to achieve an effective antibacterial and preservative effect.

[0003] In the prior art, methylparaben is usually prepared by esterification reaction with p-hydroxybenzoic acid and methanol as raw materials. During the preparation process, it is usually necessary to add an excessive amount of strong acid, and colored condensation impurities will be generated during the reaction. After the reaction is completed, the excessive acid and the generated colored impurities need to be treated with a large amount of water and washing liquid, thereby generating a large amount of acid-containing wastewater, which has relatively high processing difficulty and cost. The treated salt solution needs to be extracted and precipitated multiple times, and the process is relatively complicated, which increases the production cost, and some reagents are difficult to recover and reuse. Summary of the invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention provides a preparation process of methylparaben.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A preparation process of methylparaben comprises the following steps: S1, solid p-hydroxybenzoic acid is sucked into the esterification kettle by vacuum, the esterification kettle is equipped with modified zeolite, methanol in the tank area is pumped into the high-level tank through a pipeline, and then put into the esterification kettle through a pipeline, and stirring is turned on at the same time. After the jacket steam is turned on, the temperature is increased once, and sulfuric acid is slowly added dropwise to the esterification kettle. After the addition is completed, the temperature is increased twice, and the reaction is refluxed and kept warm at normal pressure for 6-7 hours. After the reaction is completed, the temperature of the esterification kettle is controlled, and the atmospheric distillation is performed for 2-3 hours. The generated methanol vapor is condensed and recovered into the methanol receiving tank through a condenser for subsequent process application, and the soda ash solution is passed into the esterification kettle for neutralization reaction. The temperature of the esterification kettle is controlled, and the reaction time is 2-3 hours. Soft water is then pumped into the esterification kettle through a pipeline, and the temperature is controlled for crystallization for 2-3 hours. When obvious crystals are precipitated, the valve at the bottom of the kettle is opened, and the crystals are transferred to a vortex screw centrifuge. The centrifuge rotor is turned on to separate and obtain wet cake one and filtrate one; S2, the wet filter cake 1 is transferred into a desolventizing kettle, methanol is introduced for dissolution, the steam jacket is opened, the temperature is increased, and the desolventizing is performed by atmospheric distillation for 5-6 hours to obtain a desolventizing material, and the generated methanol vapor is condensed and recovered to a methanol receiving tank through a condenser for subsequent refining process application, the desolventizing material is pumped into a crystallization kettle, the temperature of the crystallization kettle is controlled to, secondary crystallization is performed at normal pressure for 3-4 hours to obtain a secondary crystallized material, the secondary crystallized material is passed into a closed centrifuge, the centrifuge rotor is opened, and the wet material and filtrate 2 are separated, and the wet material is transferred to a double cone dryer for drying to obtain methylparaben.

[0006] Furthermore, in step S1, the temperature is raised to 60-65°C once and to 70-75°C twice, the temperature of atmospheric distillation is 85-90°C, the temperature of neutralization reaction is 65-75°C, and the crystallization is specifically to first control the temperature of the esterification kettle to 55-65°C, and then reduce the temperature in the kettle to 20-25°C after 5-6 hours.

[0007] Furthermore, in step S2, the temperature of desolventizing is 70-80°C, and the temperature of secondary crystallization is 20-25°C.

[0008] Furthermore, the drying conditions in step S2 are a temperature of 85-95° C. and a pressure of -0.08-(-0.07) MPa.

[0009] Furthermore, in step S1, the mass ratio of p-hydroxybenzoic acid, methanol, sulfuric acid and modified zeolite is (100-110): (60-65): (4-5): (1-2).

[0010] Furthermore, the modified zeolite in step S1 is prepared by the following steps: A1. Silica sol (SiO 2content is 25-30wt%) and aluminum hydroxide are pre-dried at 120-130°C for 4-6h and then put into a reactor, tetrapropylammonium hydroxide and water are added, heated to 70-80°C, stirred at a speed of 100-150rpm for 1-2h, the reactor is sealed and placed in a constant temperature box, the crystallization temperature is set to 150-160°C, the crystallization time is 48-72h, and stirred once every 12h during the crystallization process, each time at a speed of 50-100rpm for 5-10min. After the reaction is completed, it is cooled to room temperature, the reactor cover is opened, the solid product is taken out, washed, placed in a drying oven, and dried to constant weight at 100°C to obtain a zeolite molecular sieve; A2. Tetrabutyl zirconate and niobium oxalate are put into a reaction kettle, soft water is introduced, and after stirring at 50-100 rpm for 30-60 min, 1 mol / L concentrated ammonia water is added dropwise to a pH value of 10-11 under vigorous stirring at 300-400 rpm. After the addition is completed, the stirring speed is maintained, the temperature is raised to 70-80°C, zeolite molecular sieve is added, and the reaction is carried out for 2-3 hours. After the reaction is completed, it is allowed to stand at room temperature for aging for 8-10 hours, filtered, added to a calcining furnace, calcined at 400-600°C for 2-4 hours, and ground into particles to obtain a modified zeolite.

[0011] Furthermore, the method further comprises a filtrate distillation step, specifically comprising: The filtrate 1 and filtrate 2 are pumped into a distillation tower for distillation. The temperature of the distillation tower is 63-64°C at the top of the tower and 100-101°C in the bottom of the tower. The distillation is carried out at normal pressure for 5-6 hours. The methanol vapor generated at the top of the tower is condensed and recovered into the methanol receiving tank through a condenser. The distillation mother liquor generated in the bottom of the tower is passed into the acid precipitation kettle, and sulfuric acid is slowly added dropwise. After the addition is completed, the temperature of the acid precipitation kettle is lowered to 30-35°C, and the reaction is kept at normal pressure for 1-2 hours. The bottom valve of the acid precipitation kettle is opened, and the acid precipitation material is pumped into a filter press for pressure filtration for 1-2 hours to separate and obtain wet cake 2 and filtrate 3. The wet cake 2 is reused for p-hydroxybenzoic acid. The filtrate 3 is pumped into a neutralization kettle, and a sodium hydroxide solution is passed into the neutralization kettle. The temperature of the neutralization kettle is controlled to be 30-35°C, and the reaction is carried out at normal pressure for 0.5-1 hour. The bottom valve of the neutralization kettle is opened, and the material is pumped into a multi-effect desalination evaporator to obtain centralized treatment of waste salt.

[0012] Furthermore, in step A1, the mass ratio of silica sol, aluminum hydroxide, tetrapropylammonium hydroxide and water is (20-50):1:(2-10):(20-150).

[0013] Furthermore, in step A2, the feed mass ratio of tetrabutyl zirconate, niobium oxalate and zeolite molecular sieve is (1.8-2.4):(0.9-1.2):(5-8).

[0014] Beneficial effects of the present invention: 1. In the technical solution of the present invention, the modified tetrabutyl zirconate prepared by the coprecipitation method is tightly combined with the pores and surface structure of the zeolite. The composite of niobium oxalate and zirconate enhances the acidity of the system, introduces new acid sites, and maintains the original regular porous characteristics of the zeolite. The new acid sites can more effectively catalyze the esterification reaction of p-hydroxybenzoic acid and methanol, and improve the reaction rate and yield. Secondly, the pore structure of the modified zeolite promotes the diffusion and transmission of reactants and products, reduces mass transfer resistance, and further improves the reaction efficiency. In addition, the high stability and easy regeneration of the modified zeolite also ensure that it can maintain high activity and selectivity during long-term catalysis, while facilitating recycling.

[0015] 2. In the technical solution of the present invention, modified zeolite is used as a catalyst, which effectively reduces the dependence on strong acid, especially liquid strong acid, in the production of methylparaben, thereby reducing the generation of colored condensation impurities, and correspondingly reducing the amount of acid-containing wastewater, so there is no need to carry out traditional decolorization treatment, reducing the difficulty and cost of wastewater treatment. At the same time, the purity and yield of the obtained methylparaben are also high, and the reaction temperature is also low, which has certain economic benefits. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Unless otherwise specified, the raw materials used in the present invention are all from conventional products purchased from the market, wherein the SiO2 content in the silica sol is 28.6 wt%.

[0018] Preparation Example 1 The modified zeolite in step S1 comprises the following steps: A1. Pre-dry 20 kg of silica sol and 1 kg of aluminum hydroxide at 120 ° C for 4 hours and then put them into a reactor, add 2 kg of tetrapropylammonium hydroxide and 20 kg of water, heat to 70 ° C, stir at a speed of 100 rpm for 1 hour, seal the reactor, put it in a constant temperature box, set the crystallization temperature to 150-160 ° C, the crystallization time to 48-72 hours, stir once every 12 hours during the crystallization process, and stir at a speed of 50-100 rpm for 5-10 minutes each time. After the reaction is completed, cool to room temperature, open the reactor cover, take out the solid product, wash it, put it in a drying oven, and dry it at 100 ° C to constant weight to obtain a zeolite molecular sieve; A2. Add 1.8 kg of tetrabutyl zirconate and 0.9 kg of niobium oxalate to the reactor, pass 10 kg of soft water, stir at 50 rpm for 30 min, and under vigorous stirring at 300 rpm, add 1 mol / L concentrated ammonia water dropwise until the pH value is 10. After the addition is completed, maintain the stirring speed, heat up to 70°C, add 5 kg of zeolite molecular sieve, react for 2 h, and after the reaction is completed, stand and age at room temperature for 8 h, filter, add to a calcining furnace, calcine at 400°C for 2 h, and grind into granules to obtain modified zeolite.

[0019] Preparation Example 2 The modified zeolite in step S1 comprises the following steps: A1. Pre-dry 34 kg of silica sol and 1 kg of aluminum hydroxide at 125 ° C for 5 hours and then put them into a reactor, add 6 kg of tetrapropylammonium hydroxide and 60 kg of water, heat to 75 ° C, stir at a speed of 130 rpm for 1.5 hours, seal the reactor, put it in a constant temperature box, set the crystallization temperature to 155 ° C, the crystallization time to 60 hours, stir once every 12 hours during the crystallization process, and stir at a speed of 60 rpm for 6 minutes each time. After the reaction is completed, cool to room temperature, open the reactor cover, take out the solid product, wash it, put it in a drying oven, and dry it at 100 ° C to constant weight to obtain a zeolite molecular sieve; A2. Add 2.1 kg of zirconium sulfate and 1.05 kg of niobium oxalate into the reactor, pass into 10 kg of soft water, stir at 60 rpm for 40 min, and under vigorous stirring at 350 rpm, add 1 mol / L concentrated ammonia water dropwise until the pH value is 10. After the addition is completed, maintain the stirring speed, heat up to 75°C, add 6.5 kg of zeolite particles, react for 2.5 hours, and after the reaction is completed, stand and age at room temperature for 9 hours, filter, add to a calcining furnace, calcine at 500°C for 3 hours, and grind into particles to obtain modified zeolite.

[0020] Preparation Example 3 The modified zeolite in step S1 comprises the following steps: A1. Pre-dry 50 kg of silica sol and 1 kg of aluminum hydroxide at 130 ° C for 6 hours and then put them into a reactor, add 10 kg of tetrapropylammonium hydroxide and 150 kg of water, heat to 80 ° C, stir at a speed of 150 rpm for 2 hours, seal the reactor, put it in a constant temperature box, set the crystallization temperature to 160 ° C, the crystallization time to 72 hours, stir once every 12 hours during the crystallization process, and stir at a speed of 100 rpm for 10 minutes each time. After the reaction is completed, cool to room temperature, open the reactor cover, take out the solid product, wash it, put it in a drying oven, and dry it at 100 ° C to constant weight to obtain a zeolite molecular sieve; A2. Add 2.4 kg of zirconium phosphate and 1.2 kg of niobium oxalate into the reactor, pass into 10 kg of soft water, stir at 100 rpm for 60 min, and under vigorous stirring at 400 rpm, add 1 mol / L concentrated ammonia water dropwise until the pH value is 11. After the addition is completed, maintain the stirring speed, heat up to 80°C, add 8 kg of zeolite particles, react for 3 h, and after the reaction is completed, stand and age at room temperature for 10 h, filter, add to a calcining furnace, calcine at 600°C for 4 h, grind into particles to obtain modified zeolite. Example 1

[0021] A preparation process of methylparaben comprises the following steps: S1. 10 kg of solid p-hydroxybenzoic acid is sucked into the esterification kettle by vacuum. The esterification kettle is filled with 0.1 kg of modified zeolite prepared in Preparation Example 1. 6 kg of methanol in the tank area is pumped into the high-level tank through a closed pipeline, and then put into the esterification kettle through a pipeline. At the same time, stirring is turned on. After the jacket steam is opened and heated to 60 ° C, 0.4 kg of sulfuric acid is slowly added dropwise to the esterification kettle. After the addition is completed, the temperature is raised to 70 ° C, and refluxed and kept warm for 6 hours at normal pressure. After the reaction is completed, the temperature in the kettle is controlled to 85 ° C and the pressure is kept at normal pressure. Distill for 2 hours, and the generated methanol vapor is condensed and recovered into the methanol receiving tank through the condenser for subsequent process application. 10 kg of soda ash solution is introduced into the esterification kettle for neutralization reaction. The temperature of the esterification kettle is controlled at 65 ° C. The reaction time is 2 hours. Then 10 kg of soft water is pumped into the esterification kettle through a closed pipeline to control the temperature of the esterification kettle to 55 ° C. After 5 hours, the temperature in the kettle drops to 20 ° C. After crystallization for 2 hours, the valve at the bottom of the kettle is opened, and the crystals are transferred to the vortex screw centrifuge. The centrifuge rotor is opened to separate the wet cake 1 and the filtrate 1; S2, the wet filter cake 1 is transferred into a desolventizing kettle, 5 kg of methanol is introduced for dissolution, the steam jacket is opened, the kettle temperature is raised to 70 ° C, and the desolventizing is carried out by atmospheric distillation for 5 hours to obtain the desolventizing material, and the generated methanol vapor is condensed and recovered to the methanol receiving tank through a condenser for subsequent refining process application, the desolventizing material is pumped into a crystallization kettle, the temperature of the crystallization kettle is controlled to 20 ° C, and crystallized at atmospheric pressure for 3 hours to obtain a secondary crystallization material, the secondary crystallization material is passed into a closed centrifuge, the centrifuge rotor is opened, and the wet material and the filtrate 2 are separated, and the wet material is transferred to a double cone dryer, and dried at 85 ° C and -0.08 MPa to obtain methylparaben. Example 2

[0022] A preparation process of methylparaben comprises the following steps: S1. 10.5 kg of solid p-hydroxybenzoic acid is sucked into the esterification kettle by vacuum. The esterification kettle is filled with 0.15 kg of modified zeolite prepared in Preparation Example 2. 6.3 kg of methanol in the tank area is pumped into the high-level tank through a closed pipeline, and then put into the esterification kettle through a pipeline. At the same time, stirring is turned on. After the jacket steam is opened and heated to 62 ° C, 0.45 kg of sulfuric acid is slowly added dropwise to the esterification kettle. After the addition is completed, the temperature is raised to 72 ° C, and refluxed and kept warm for 6.5 hours at normal pressure. After the reaction is completed, the temperature in the kettle is controlled to 87 ° C and the pressure is kept at normal pressure. Distill for 2.5 hours, and the generated methanol vapor is condensed and recovered into the methanol receiving tank through the condenser for subsequent process application. 10 kg of soda ash solution is introduced into the esterification kettle for neutralization reaction, and the temperature of the esterification kettle is controlled at 70°C. The reaction time is 2.5 hours, and then 10 kg of soft water is pumped into the esterification kettle through a closed pipeline to control the temperature of the esterification kettle at 60°C. After 5.5 hours, the temperature in the kettle drops to 22°C. After crystallization for 2.5 hours, the valve at the bottom of the kettle is opened, and the crystals are transferred to the vortex centrifuge. The centrifuge rotor is opened to separate the wet cake 1 and the filtrate 1. S2, the wet cake one is transferred into a desolventizing kettle, 5 kg of methanol is introduced for dissolution, the steam jacket is opened, the kettle temperature is raised to 75 ° C, and the desolventizing is carried out by atmospheric distillation for 5.5 hours to obtain the desolventizing material, and the generated methanol vapor is condensed and recovered to the methanol receiving tank through a condenser for subsequent refining process application, the desolventizing material is pumped into a crystallization kettle, the temperature of the crystallization kettle is controlled to 22 ° C, and the crystallization is carried out at atmospheric pressure for 3.5 hours to obtain a secondary crystallization material, the secondary crystallization material is passed into a closed centrifuge, the centrifuge rotor is opened, and the wet material and the filtrate two are separated, and the wet material is transferred to a double cone dryer, and dried at 90 ° C and -0.08 MPa to obtain methylparaben. Example 3

[0023] A preparation process of methylparaben comprises the following steps: S1. 11 kg of solid p-hydroxybenzoic acid is sucked into the esterification kettle by vacuum. The esterification kettle is filled with 0.2 kg of modified zeolite prepared in Preparation Example 3. 6.5 kg of methanol in the tank area is pumped into the high-level tank through a closed pipeline, and then put into the esterification kettle through a pipeline. At the same time, stirring is turned on. After the jacket steam is opened and heated to 65°C, 0.5 kg of sulfuric acid is slowly added dropwise to the esterification kettle. After the addition is completed, the temperature is raised to 75°C, and refluxed and kept warm for 7 hours under normal pressure. After the reaction is completed, the temperature in the kettle is controlled to 90°C. The distillation was carried out at normal pressure for 3 hours, and the methanol vapor produced was condensed and recovered into the methanol receiving tank through the condenser for subsequent process application. 10 kg of soda ash solution was introduced into the esterification kettle for neutralization reaction, and the temperature of the esterification kettle was controlled at 75°C. The reaction time was 3 hours, and then 10 kg of soft water was pumped into the esterification kettle through a closed pipeline, and the temperature of the esterification kettle was controlled at 65°C. After 6 hours, the temperature in the kettle dropped to 25°C, and crystallization was carried out for 3 hours. The valve at the bottom of the kettle was opened, and the crystals were transferred to the vortex centrifuge. The centrifuge rotor was opened to separate the wet cake 1 and the filtrate 1; S2, the wet filter cake 1 is transferred into a desolventizing kettle, 5 kg of methanol is introduced for dissolution, the steam jacket is opened, the kettle temperature is raised to 80 ° C, and the desolventizing is carried out by atmospheric distillation for 6 hours to obtain the desolventizing material, and the generated methanol vapor is condensed and recovered to the methanol receiving tank through a condenser for subsequent refining process application, the desolventizing material is pumped into a crystallization kettle, the temperature of the crystallization kettle is controlled to 25 ° C, and crystallized at atmospheric pressure for 4 hours to obtain a secondary crystallization material, the secondary crystallization material is passed into a closed centrifuge, the centrifuge rotor is opened, and the wet material and the filtrate 2 are separated, and the wet material is transferred to a double cone dryer, and dried at 95 ° C and -0.08 MPa to obtain methylparaben.

[0024] Comparative Example 1 The difference between this comparative example and Example 1 is that tetrabutyl zirconate is used instead of modified zeolite, and the remaining steps are the same as those of Example 1.

[0025] Comparative Example 2 The difference between this comparative example and Example 1 is that niobium oxalate is used instead of modified zeolite, and the remaining steps are the same as those of Example 1.

[0026] Comparative Example 3 The difference between this comparative example and Example 2 is that tetrabutyl zirconate is used instead of modified zeolite, and the remaining steps are the same as those in Example 2.

[0027] Comparative Example 4 The difference between this comparative example and Example 2 is that niobium oxalate is used instead of modified zeolite, and the remaining steps are the same as those in Example 2.

[0028] Comparative Example 5 The difference between this comparative example and Example 3 is that tetrabutyl zirconate is used instead of modified zeolite, and the remaining steps are the same as those in Example 3.

[0029] Comparative Example 6 The difference between this comparative example and Example 3 is that ordinary zeolite particles are used instead of modified zeolite, and the remaining steps are the same as those of Example 3.

[0030] The purity of Examples 1-3 and Comparative Examples 1-6 was determined by high performance liquid chromatography, and the chromatographic conditions were: octadecylsilane bonded silica gel as filler, methanol-1% glacial acetic acid (60:40) as mobile phase, and detection wavelength of 254 nm. The yield was calculated, and the results are shown in Table 1: Table 1. Purity and yield results of Examples 1-3 and Comparative Examples 1-6

[0031] serial number purity(%) Yield (%) Example 1 99.5 94.2 Example 2 99.6 94.6 Example 3 99.5 94.7 Comparative Example 1 96.2 90.1 Comparative Example 2 95.8 89.5 Comparative Example 3 97.0 90.3 Comparative Example 4 95.2 89.7 Comparative Example 5 95.9 89.9 Comparative Example 6 90.4 87.2 As shown in Table 1, the purity of methylparaben obtained by embodiment 1-3 has reached 99.5% and above, with higher purity, and the purity of methylparaben obtained by comparative example 1-6 is lower than that of embodiment, wherein the purity of comparative example 6 is the lowest. Modified zeolite may improve the adsorption capacity and catalytic efficiency of reactant by optimizing its pore structure, surface characteristics and catalytic active sites, thereby promoting the carrying out of esterification, reducing the generation of by-products, and improving the purity of product. Single component catalyst may be due to its catalytic activity is relatively low, poor selectivity or pore structure is not suitable for the reaction, resulting in incomplete reaction or the generation of more by-products, thereby reducing the purity of product.

[0032] The yield of methylparaben that embodiment 1-3 obtains all reaches 94.2% and above, has higher yield, and the yield of methylparaben that comparative example 1-6 obtains is also all lower than embodiment.Modified zeolite may promote the conversion of reactant by improving catalytic efficiency, improves the yield of product.In addition, modified zeolite may have higher selectivity, makes reaction more partial to generate methylparaben, thereby improves the yield of product.

[0033] In summary, the modified zeolite prepared in Preparation Examples 1-3 exhibits a significant catalytic effect in the production of methylparaben, so that the methylparaben prepared in Examples 1-6 has a higher purity and yield, further reducing the production cost. At the same time, the by-products are recovered, reducing environmental pollution, and having economic and environmental benefits.

[0034] In the description of the specification, the description with reference to the terms "preparation example", "embodiment", "various embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or preparation example are included in at least one embodiment or preparation example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or preparation example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or preparation examples in a suitable manner.

[0035] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process for preparing methylparaben, characterized in that: The following steps are involved: S1. Add p-hydroxybenzoic acid to an esterification kettle containing modified zeolite, pump in methanol, start a stirring device, heat up once, slowly drop sulfuric acid, heat up twice after the dropwise addition, reflux and keep warm for 6-7 hours at normal pressure, after the reaction is completed, control the temperature and distill at normal pressure for 2-3 hours, introduce soda ash solution, control the temperature for neutralization reaction, neutralize for 2-3 hours, then pump in soft water, control the temperature for crystallization for 2-3 hours, centrifuge after obvious crystals are precipitated, and separate to obtain wet cake 1 and filtrate 1; S2. The wet filter cake 1 is transferred into a desolventizing kettle, methanol is introduced, and the temperature is controlled for desolventizing for 5-6 hours to obtain a desolventized material. The desolventized material is pumped into a crystallization kettle, and the temperature is controlled for secondary crystallization for 3-4 hours to obtain a secondary crystallized material. After centrifugation, the wet material and the filtrate 2 are separated and dried to obtain methylparaben.

2. A process for preparing methylparaben according to claim 1, characterized in that, In step S1, the temperature is raised to 60-65°C once, and then to 70-75°C for the second time. The temperature of atmospheric distillation is 85-90°C, and the temperature of neutralization reaction is 65-75°C. Specifically, the temperature of the esterification kettle is first controlled to be 55-65°C, and then the temperature in the kettle is reduced to 20-25°C after 5-6 hours.

3. A process for preparing methylparaben according to claim 1, characterized in that, The temperature of desolventizing in step S2 is 70-80°C, and the temperature of secondary crystallization is 20-25°C.

4. A process for preparing methylparaben according to claim 1, characterized in that, The drying conditions in step S2 are a temperature of 85-95° C. and a pressure of -0.08-(-0.07) MPa.

5. A process for preparing methylparaben according to claim 1, characterized in that, In step S1, the mass ratio of p-hydroxybenzoic acid, methanol, sulfuric acid and modified zeolite is (100-110): (60-65): (4-5): (1-2).

6. A process for preparing methylparaben according to claim 1, characterized in that, The modified zeolite in step S1 comprises the following steps: A1. Pre-dry the silica sol and aluminum hydroxide at 120-130°C for 4-6h and then put them into a reactor, add tetrapropylammonium hydroxide and water, heat to 70-80°C, stir at a speed of 100-150rpm for 1-2h, seal the reactor, put it in a constant temperature box, set the crystallization temperature to 150-160°C, the crystallization time to 48-72h, stir once every 12h during the crystallization process, and stir at a speed of 50-100rpm for 5-10min each time. After the reaction is completed, cool to room temperature, open the reactor cover, take out the solid product, wash it, put it in a drying oven, and dry it at 100°C to constant weight to obtain a zeolite molecular sieve; A2. Tetrabutyl zirconate and niobium oxalate are put into a reaction kettle, soft water is introduced, and after stirring at 50-100 rpm for 30-60 min, 1 mol / L concentrated ammonia water is added dropwise to a pH value of 10-11 under vigorous stirring at 300-400 rpm. After the addition is completed, the stirring speed is maintained, the temperature is raised to 70-80°C, zeolite molecular sieve is added, and the reaction is carried out for 2-3 hours. After the reaction is completed, it is allowed to stand at room temperature for aging for 8-10 hours, filtered, added to a calcining furnace, calcined at 400-600°C for 2-4 hours, and ground into particles to obtain a modified zeolite.

7. A process for preparing methylparaben according to claim 1, characterized in that: The filtrate distillation step is also included, specifically: The filtrate 1 and filtrate 2 are pumped into a distillation tower for distillation. The temperature of the distillation tower is 63-64°C at the top of the tower and 100-101°C in the bottom of the tower. The distillation is carried out at normal pressure for 5-6 hours. The methanol vapor generated at the top of the tower is condensed and recovered into the methanol receiving tank through a condenser. The distillation mother liquor generated in the bottom of the tower is passed into the acid precipitation kettle, and sulfuric acid is slowly added dropwise. After the addition is completed, the temperature of the acid precipitation kettle is lowered to 30-35°C, and the reaction is kept at normal pressure for 1-2 hours. The bottom valve of the acid precipitation kettle is opened, and the acid precipitation material is pumped into a filter press for pressure filtration for 1-2 hours to separate and obtain wet cake 2 and filtrate 3. The wet cake 2 is reused for p-hydroxybenzoic acid. The filtrate 3 is pumped into a neutralization kettle, and a sodium hydroxide solution is passed into the neutralization kettle. The temperature of the neutralization kettle is controlled to be 30-35°C, and the reaction is carried out at normal pressure for 0.5-1 hour. The bottom valve of the neutralization kettle is opened, and the material is pumped into a multi-effect desalination evaporator to obtain centralized treatment of waste salt.

8. A process for preparing methylparaben according to claim 6, characterized in that: In step A1, the mass ratio of silica sol, aluminum hydroxide, tetrapropylammonium hydroxide and water is (20-50):1:(2-10):(20-150).

9. A process for preparing methylparaben according to claim 6, characterized in that: In step A2, the feed mass ratio of tetrabutyl zirconate, niobium oxalate and zeolite molecular sieve is (1.8-2.4):(0.9-1.2):(5-8).