Preparation process of sulfur-containing silane coupling agent

Abstract

The invention provides a preparation process of a sulfur-containing silane coupling agent, the preparation process comprises the following steps: dropwise adding chloropropyltriethoxysilane and simultaneously adding amino-containing or sulfydryl-containing siloxane through an aqueous solution system, the amino in amino silane provides an alkaline microenvironment and activates polysulfide anions, and meanwhile, Na < + > can be complexed to promote phase transfer and improve the reaction process; reaction time is shortened, and the final chromaticity of the product can be effectively reduced; sulfydryl in sulfydryl silane can be directly exchanged with polysulfide to generate mixed sulfide, the sulfydryl silane can be used as a chain transfer agent to control the sulfur chain length, so that the sulfur chain length and the average sulfur content of the product Si69 are more stable, the sulfur-containing silane coupling agent with stable sulfur content can be obtained only through simple liquid separation and sedimentation decoloration, the process conditions are mild, the raw materials are easy to obtain, and the production cost is low. The method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of silane coupling agent technology, specifically to a preparation process for a sulfur-containing silane coupling agent. Background Technology

[0002] Sulfur-containing silanes are a common type of silane coupling agent, primarily used as additives in tire rubber to improve tire tear resistance, abrasion resistance, and wet grip. The most widely used sulfur-containing silanes are bis-(triethoxysilylpropyl) polysulfides, mainly bis-(triethoxysilylpropyl) disulfide and bis-(triethoxysilylpropyl) tetrasulfide, accounting for over 90% of the total sulfur-containing silane usage. Bis-(triethoxysilylpropyl) tetrasulfide (trade name Si69), as a highly efficient and multifunctional silane coupling agent, plays an irreplaceable role in the rubber industry, especially in the manufacture of green tires. The triethoxysilyl group in its molecular structure can react with the silanol groups on the surface of silica, while the tetrasulfide bond participates in the rubber vulcanization process, forming a molecular bridge between the inorganic filler, coupling agent, and rubber. This unique structure solves the core problem of poor dispersion of silica in rubber, reducing tire rolling resistance by 30%, increasing wear resistance by 50%, and significantly improving wet skid resistance. The global green tire market is expanding at an annual growth rate of 20%, driving a continued increase in demand for Si69.

[0003] Currently, all major technological approaches in industry face significant bottlenecks:

[0004] 1. Sodium hydrosulfide route

[0005] The reaction is carried out using sodium hydrosulfide (NaHS), sulfur, and γ-chloropropyltriethoxysilane (γ2) in ethanol.

[0006] 2(C2H5O)3Si(CH2)3Cl + Na2S4 → [(C2H5O)3Si(CH2)3]2S4 + 2NaCl

[0007] The fatal flaw of this process lies in the continuous release of highly toxic hydrogen sulfide (H2S) gas during the reaction, requiring an alkali absorption tower to treat the exhaust gas. Each ton of product generates 0.8-1.2 tons of sulfur-containing wastewater with a COD exceeding 5000 mg / L, and treatment costs account for 15% of production costs. Furthermore, residual mercaptan impurities in the product cause a darkening of color during storage (APHA>200), limiting its application in light-colored rubber products.

[0008] 2. Anhydrous sodium sulfide route

[0009] Sodium polysulfide was prepared by reacting anhydrous Na₂S and sulfur in anhydrous ethanol, and then reacted with γ₂:

[0010] Na₂S + 3S → Na₂S₄

[0011] Na2S4 + 2Cl(CH2)3Si(OC2H5)3 → Si69 + 2NaCl

[0012] While this method avoids H2S generation, the sensitivity of the raw materials presents a new problem. Anhydrous sodium sulfide is highly hygroscopic and oxidizes easily (weight gain rate in air >5% / h), which may cause spontaneous combustion and explosion risks during operation. Furthermore, it requires nitrogen protection throughout the process, the reaction time is as long as 8-12 hours, and energy consumption is 40% higher than other processes.

[0013] 3. Sodium ethoxide-sodium hydrosulfide route

[0014] Using sodium metal, ethanol, sodium hydrosulfide, sulfur, and γ2 as raw materials, it is synthesized in two steps:

[0015] 2C2H5OH + 2Na → 2C2H5ONa + H2

[0016] C2H5ONa + NaHS →C2H5OH + Na2S

[0017] Na₂S + 3S → Na₂S₄

[0018] While this route achieves ethanol recycling, the use of metallic sodium poses a high risk of operational hazards. The reaction between metallic sodium and ethanol is violently exothermic (ΔH=-184 kJ / mol), requiring specialized temperature control equipment; residual sodium particles may cause fires, with an actual production accident rate of 0.3 incidents per thousand tons.

[0019] Based on existing processes, the industry faces four major technological bottlenecks:

[0020] Solvent dependence and safety risks: The use of organic solvents such as ethanol and diethyl ether reaches 300-500 kg / ton of product, which not only increases costs (solvents account for 35% of raw material costs), but also leads to excessive VOC emissions (>120 ppm) and the risk of fire and explosion.

[0021] Byproduct pollution: H2S waste gas, saline wastewater (8-12t / ton of product), and heavy metal waste residue form a triple pollution problem, with end-of-pipe treatment costs accounting for more than 25% of the total cost.

[0022] Product quality defects: Products made using traditional processes contain impurities such as trithiocarbonate (>4.0%), have a heating loss of >2.5%, and have a color that rises to APHA>150 after more than 3 months of storage, which cannot meet the requirements of high-end rubber products.

[0023] Low reaction efficiency: The batch reaction has a long time (5-9 hours), γ2 conversion rate <90%, uneven sulfur distribution (S4 content <80%), and significant scale-up effect, resulting in limited production capacity.

[0024] The existing technology is as follows:

[0025] Patent document CN102875587A describes a method for synthesizing sulfur-containing silanes from sodium polysulfide. The method involves reacting sodium hydroxide with sulfur followed by vacuum dehydration to first prepare solid sodium polysulfide. Then, the solid sodium polysulfide is dissolved in anhydrous ethanol and reacted with γ-2 to synthesize a sulfur-containing silane coupling agent. This method first synthesizes solid sodium polysulfide, which requires high-temperature vacuum dehydration, resulting in a long process, high energy consumption, and the solid sodium polysulfide readily absorbs water, affecting its quality and leading to low product purity.

[0026] Patent document CN108250233 A describes a method for preparing the silane coupling agent Si-69 in an aqueous phase. The reaction rate is increased and the reaction time shortened by adding a phase transfer catalyst and KI; a buffer solution is used to control the pH of the solution phase, preventing the hydrolysis and gelation of the raw material γ-chloropropyltriethoxysilane and the formation of the byproduct hydrogen sulfide. However, the buffer has low solubility, requiring a large amount to prepare the solution. In industrial production, controlling the pH requires a large amount of buffer, resulting in low yield per batch and high cost.

[0027] In his article "Synthesis and Application of Bis-(3-Triethoxysilylpropyl)tetrasulfide" published in *Fine Chemicals*, Tian Ruiting employed an alkali metal synthesis method. Under nitrogen protection, sodium alkali metal reacts with anhydrous ethanol to produce sodium ethoxide. Then, under specific temperature and pressure, sodium sulfide (or sodium hydrosulfide) and sulfur are added to generate sodium polysulfide. Finally, γ-chloropropyltriethoxysilane is added to obtain the final product. This method offers advantages such as relatively mild synthesis conditions, relatively low equipment requirements, high yield, stable product properties, and no pollution. However, the raw material, sodium metal, is expensive, and the reaction conditions require strict control, demanding high operational standards.

[0028] Shin-Etsu Chemical Co., Ltd. of Japan produces sodium sulfide by removing moisture using the three-phase azeotropic principle to generate anhydrous sodium sulfide. Anhydrous ethanol and sulfur are then added to produce sodium polysulfide. Chloropropyltriethoxysilane is then added dropwise under specific temperature and conditions to finally produce Si-69. While the three-phase azeotropic principle results in a relatively low azeotropic point, benzene also has a low boiling point, but it is highly toxic, volatile, and has a very low flash point, making its use quite dangerous.

[0029] US Patent document US5489701 describes a method for preparing Si69 by first contacting hydrogen sulfide gas with an active metal alkoxide solution, and then reacting the product with a haloalkylalkoxysilane such as chloropropyltriethoxysilane. This method uses hydrogen sulfide gas, while existing green processes strictly prohibit the use of hazardous and toxic gaseous raw materials.

[0030] Therefore, it is necessary to design a process suitable for the efficient industrial production of sulfur-containing silane coupling agents. Summary of the Invention

[0031] This invention proposes a preparation process for sulfur-containing silane coupling agents that improves production efficiency and product quality while ensuring cost and safety, making it suitable for industrial-scale production.

[0032] The technical solution of this invention is implemented as follows:

[0033] A process for preparing a sulfur-containing silane coupling agent, comprising the following steps:

[0034] S1. Obtain or prepare an aqueous solution of sodium tetrasulfide;

[0035] S2. Under stirring, add an alkaline buffer and a phase transfer catalyst to the sodium tetrasulfide aqueous solution, and then heat to near the synthesis reaction temperature;

[0036] S3. Chloropropyltriethoxysilane and siloxanes containing amino and / or mercapto groups are added dropwise to the solution obtained in step S2 under stirring. After the addition is complete, the reaction is kept at a constant temperature, allowed to stand, and the aqueous layer is separated. The organic layer is then settled and decolorized to obtain a sulfur-containing silane coupling agent.

[0037] Further, in step S3, the amount of the amino- and / or mercapto-containing siloxane added is 1-5% of the mass of chloropropyltriethoxysilane;

[0038] And / or, the amino-containing siloxane is selected from at least one of aminopropyltriethoxysilane and aminopropylmethyldiethoxysilane;

[0039] And / or, the mercapto-containing siloxane is selected from at least one of mercaptopropyltriethoxysilane and mercaptopropylmethyltriethoxysilane.

[0040] Furthermore, the amount of aminopropyltriethoxysilane and / or mercaptopropyltriethoxysilane added is 1-5% of the mass of chloropropyltriethoxysilane.

[0041] Further, in step S2, the phase transfer catalyst is tetrabutylammonium bromide; and / or, the alkaline buffer is sodium bicarbonate.

[0042] Furthermore, in step S2, the temperature during the heating process is controlled at 70-80℃; and / or the stirring time is 10-20 min.

[0043] Furthermore, in step S3, the heat preservation reaction temperature is 75-80℃, and the reaction time is 1.5-2h.

[0044] Furthermore, in step S3, the drop acceleration rate is 4-25 g / min.

[0045] Further, in step S1, the sodium tetrasulfide is obtained by heating sodium sulfide and sulfur powder in water.

[0046] Preferably, the mass ratio of sulfur, sodium sulfide, sodium bicarbonate, phase transfer catalyst, chloropropyltriethoxysilane and water used in step S1 is 1: (1.35-1.5): (0.3-0.6): (0.05-0.075): (5-5.5): (4-8).

[0047] Preferably, in step S1, the reaction temperature is 50-60℃ and the reaction time is 40-60 min.

[0048] Furthermore, in step S3, the decolorization process uses a cation exchange resin.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] In this invention, during the dropwise addition of chloropropyltriethoxysilane, amino-containing silanes and / or mercapto-containing siloxanes are added simultaneously. The amino groups in the aminosilanes provide an alkaline microenvironment, activating polysulfide anions and simultaneously complexing Na+. + Promoting phase transfer, accelerating the reaction process, and shortening the reaction time can effectively reduce the final color of the product. The mercapto group in mercaptosilane can directly exchange with polysulfides to generate mixed sulfides. At the same time, it acts as a chain transfer agent to control the sulfur chain length, making the sulfur chain length and average sulfur content of the product Si69 more stable.

[0051] The preparation process described in this invention uses an aqueous solution system. While adding sodium bicarbonate as a buffer to reduce the hydrolysis rate of the product, a phase transfer catalyst is used to promote the reaction, which effectively improves the conversion rate of the reaction product. The product can be obtained as a stable and high-purity bis-(triethoxysilylpropyl)tetrasulfide by simple separation, sedimentation and decolorization. The conditions are mild, the raw materials are readily available, and it is suitable for industrial production.

[0052] The preparation process described in this invention uses water as the reaction solvent, and sodium bicarbonate can be directly fed as a solid, increasing the utilization rate of raw materials and reaction equipment, saving energy, improving the utilization rate of industrial production equipment, and increasing output. Attached Figure Description

[0053] Figure 1 This is a liquid chromatogram of the sulfur-containing silane coupling agent prepared in Example 1 of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0055] This invention provides a process for preparing a sulfur-containing silane coupling agent, comprising the following steps:

[0056] S1. Nitrogen gas is introduced into the reactor to replace the oxygen in the reactor;

[0057] S2. While stirring, add deionized water, sodium sulfide, and sulfur powder to the reactor in sequence, and heat to react.

[0058] S3. Add sodium bicarbonate and phase transfer catalyst to the product of S2 in sequence, continue stirring the reaction and raise the temperature;

[0059] S4. Add chloropropyltriethoxysilane and amino- and / or mercapto-containing siloxanes to the product of S3. After the addition is complete, maintain a constant temperature and continue stirring.

[0060] S5. After stopping stirring, let stand, separate the lower colorless and transparent aqueous phase, leaving the upper transparent oily liquid to obtain bis-(triethoxysilylpropyl)tetrasulfide;

[0061] The mass ratio of each raw material is as follows:

[0062] Sulfur: Sodium sulfide: Sodium bicarbonate solid: Phase transfer catalyst: Chloropropyltriethoxysilane: Water = 1:1.35~1.5:0.3~0.6:0.05~0.075:5~5.5:4~8.

[0063] In the above process, the amino group in the aminosilane provides an alkaline microenvironment, activates polysulfide anions, and can also complex Na+. + Promoting phase transfer, accelerating the reaction process, and shortening the reaction time can effectively reduce the final color of the product. The mercapto group in mercaptosilane can directly exchange with polysulfides to generate mixed sulfides. At the same time, it acts as a chain transfer agent to control the sulfur chain length, making the sulfur chain length and average sulfur content of the product more stable, with the average sulfur chain length reaching 3.8~3.9.

[0064] Preferably, in step S3, the amount of the amino- and / or mercapto-containing siloxane added is 1-5% of the mass of chloropropyltriethoxysilane; the amino-containing siloxane is selected from at least one of aminopropyltriethoxysilane and aminopropylmethyldiethoxysilane; the mercapto-containing siloxane is selected from at least one of mercaptopropyltriethoxysilane and mercaptopropylmethyldiethoxysilane.

[0065] Preferably, the phase transfer catalyst is tetrabutylammonium bromide.

[0066] Sodium sulfide has a purity of not less than 60%; sulfur powder, sodium bicarbonate, tetrabutylammonium bromide, and chloropropyltriethoxysilane are all industrial standard products, with a preferred purity of 99%.

[0067] Preferably, nitrogen gas is introduced into S1 for 5-10 minutes.

[0068] Preferably, the reaction temperature in S2 is 50-60℃ and the reaction time is 40-60 min.

[0069] Preferably, the stirring time in S3 is 10-20 minutes, and the temperature is raised to 75-80℃.

[0070] Preferably, the feedstock addition time for S4 is 1.5-2 hours, the reaction temperature is 75-80°C, and the reaction time is 1.5-2 hours.

[0071] Preferably, the settling time in S5 is 20-30 minutes.

[0072] The preparation process described above in this invention utilizes an aqueous solution system. Sodium bicarbonate is added as a buffer to adjust the pH and reduce the product hydrolysis rate. Simultaneously, a phase transfer catalyst is used to promote the reaction, effectively improving the conversion rate of the reaction product. The product only requires simple separation, sedimentation, and decolorization to obtain a sulfur-containing silane coupling agent with stable sulfur content. Existing processes all use buffer solutions, which have low concentrations and require large quantities, resulting in low yield per batch. While solid feeding is difficult, this invention uses an automatic unpacking machine to transport the solid material to the metering tank via a hinge, reducing manual operation. Furthermore, the subsequent addition is done while the material is warm, improving the solubility of sodium bicarbonate and further increasing the equipment utilization rate by over 100% compared to traditional methods.

[0073] Example 1

[0074] The preparation process of sulfur-containing silane coupling agents is as follows:

[0075] 1) Purge nitrogen gas into the reaction flask for 5 minutes to replace the oxygen in it; while stirring, add 450g of deionized water, 135g of sodium sulfide, and 100g of sulfur powder in sequence, heat to 50℃, and react for 60 minutes.

[0076] 2) Add 40g of sodium bicarbonate and 6g of tetrabutylammonium bromide sequentially, stir for 20min, heat to 77℃, and add 510g of chloropropyltriethoxysilane and 25.5g of mercaptopropyltriethoxysilane in a continuous flow for 2h; after the addition is complete, heat to 80℃ and react for 2h. Take a sample to test the residual γ2 content, which should be less than 2%. Stop the reaction after it is qualified.

[0077] 3) After cooling the crude product, separate the brine layer and the organic layer, and then separate the organic layer by sedimentation to obtain the crude product of sulfur-containing silane coupling agent.

[0078] 4) Put the crude product into a decolorization bottle, add the pre-treated cation exchange resin, decolorize for 2 hours, and filter to obtain 517g of a pale yellow to yellow transparent liquid product.

[0079] The results of the liquid chromatography analysis of the finished product are as follows: Figure 1 As shown in the figure, the sulfur chain segments are more uniform and stable, with an average chain length of 3.82.

[0080] Example 2

[0081] The preparation process of sulfur-containing silane coupling agents is as follows:

[0082] 1) Purge nitrogen gas into the reaction flask for 5 minutes to replace the oxygen in it; while stirring, add 2500g of deionized water, 690g of sodium sulfide, and 500g of sulfur powder in sequence, heat to 60℃, and react for 60 minutes.

[0083] 2) Add 200g of sodium bicarbonate and 30g of tetrabutylammonium bromide sequentially, stir for 20 minutes, heat to 77℃, and add 2500g of chloropropyltriethoxysilane and 120g of aminopropyltriethoxysilane over 2 hours; after the addition is complete, react at 80℃ for 2 hours. Take a sample to test the residual γ2 content, which should be less than 2%. Stop the reaction after it passes the test.

[0084] 3) After the crude product is cooled, the brine layer and the organic layer are separated. Then the organic layer is separated by sedimentation to obtain the crude Si69 product.

[0085] 4) The crude product was placed in a decolorization bottle, and pre-treated cation exchange resin was added. After decolorization for 2 hours, the product was filtered to obtain 2543g of a pale yellow to yellow transparent liquid sulfur-containing silane coupling agent. The average chain length was measured to be 3.83.

[0086] Example 3

[0087] The preparation process of sulfur-containing silane coupling agents is as follows:

[0088] 1) Purge nitrogen gas into the reaction flask for 5 minutes to replace the oxygen in it; while stirring, add 1600g of deionized water, 440g of sodium sulfide, and 320g of sulfur powder in sequence, heat to 60℃, and react for 60 minutes.

[0089] 2) Add 160g of sodium bicarbonate and 16g of tetrabutylammonium bromide sequentially, stir for 20 minutes, heat to 80℃, and add 1600g of chloropropyltriethoxysilane and 70g of mercaptopropylmethyldiethoxysilane over 2 hours; after the addition is complete, react at 80℃ for 2 hours. Take a sample to test the residual γ2 content, which should be less than 2%. Stop the reaction after it passes the test.

[0090] 3) After cooling the crude product, separate the brine layer and the organic layer, and then separate the organic layer by sedimentation to obtain the crude product of sulfur-containing silane coupling agent.

[0091] 4) The crude product was placed in a decolorization bottle, and pre-treated cation exchange resin was added. After decolorization for 2 hours, the product was filtered to obtain 1625g of a pale yellow to yellow transparent liquid sulfur-containing silane coupling agent. The average chain length was measured to be 3.80.

[0092] Industrial Examples

[0093] The preparation process of sulfur-containing silane coupling agents is as follows:

[0094] 1) Towards 10m 3 Nitrogen gas was introduced into the reactor for 5 minutes to replace the oxygen. Under stirring, 4500 kg of deionized water, 1350 kg of sodium sulfide, and 1000 kg of sulfur powder were added in sequence. The temperature was raised to 60°C and the reaction was carried out for 60 minutes.

[0095] 2) Add 450 kg of solid sodium bicarbonate and 50 kg of tetrabutylammonium bromide sequentially, stirring for 20 min. Heat to 80°C, then add 5000 kg of chloropropyltriethoxysilane and 200 kg of mercaptopropyltriethoxysilane in a continuous flow for 2 h. After the addition is complete, react at 80°C for 2 h. Sampling and testing show that the residual γ2 content is less than 2%. Stop the reaction after confirming the above levels are met.

[0096] 3) After cooling the crude product, separate the brine layer and the organic layer, and then separate the organic layer by sedimentation to obtain the crude product of sulfur-containing silane coupling agent.

[0097] 4) The crude product was put into a decolorization kettle, and pre-treated cation exchange resin was added. After decolorization for 2 hours, the product was filtered to obtain a pale yellow to yellow transparent liquid sulfur-containing silane coupling agent. The final product yield was 5210 kg. The average chain length was measured to be 3.87.

[0098] This industrial implementation achieves an overall plant utilization rate of 50%.

[0099] Comparative Example 1

[0100] The preparation process of sulfur-containing silane coupling agents is as follows:

[0101] 1) Towards 10m 3 Nitrogen gas was introduced into the reactor for 5 minutes to replace the oxygen. Under stirring, 2500 kg of deionized water, 500 kg of sodium sulfide, and 675 kg of sulfur powder were added in sequence. The temperature was raised to 60°C and the reaction was carried out for 60 minutes.

[0102] 2) Add 4200 kg of 9.6% saturated sodium bicarbonate buffer and 25 kg of tetrabutylammonium bromide, stir for 20 min, heat to 80℃, and add 2500 kg of chloropropyltriethoxysilane over 2 h; after the addition is complete, react at 80℃ for 2 h. Take a sample to test the residual γ2 content, which should be less than 2%. Stop the reaction after it passes the test.

[0103] 3) After cooling the crude product, separate the brine layer and the organic layer, and then separate the organic layer by sedimentation to obtain the crude product of sulfur-containing silane coupling agent.

[0104] 4) The crude product was put into the decolorization kettle, and the pre-treated cation exchange resin was added. After decolorization for 2 hours, the product was filtered to obtain the sulfur-containing silane coupling agent. The final product yield was 2460 kg.

[0105] The overall utilization rate of Si69 products in the equipment is only 24%.

[0106] Comparative Example 2

[0107] The preparation process of the sulfur-containing silane coupling agent differs from that of Example 1 in that mercaptopropyltriethoxysilane is not added, while the amounts of other components and the preparation steps are the same. A final product of 485g of a pale yellow to yellow transparent liquid was obtained. The average chain length was 3.36.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation process for a sulfur-containing silane coupling agent, characterized in that the steps include... include: S1. Obtain or prepare an aqueous solution of sodium tetrasulfide; S2. Under stirring, add an alkaline buffer and a phase transfer catalyst to the sodium tetrasulfide aqueous solution, and then heat to near the synthesis reaction temperature; S3. Chloropropyltriethoxysilane and siloxanes containing amino and / or mercapto groups are added dropwise to the solution obtained in step S2 under stirring. After the addition is complete, the reaction is kept at a constant temperature, allowed to stand, and the aqueous layer is separated. The organic layer is then settled and decolorized to obtain a sulfur-containing silane coupling agent.

2. The preparation process according to claim 1, characterized in that, In step S3, the amount of the amino- and / or mercapto-containing siloxane added is 1-5% of the mass of chloropropyltriethoxysilane; And / or, the amino-containing siloxane is selected from at least one of aminopropyltriethoxysilane and aminopropylmethyldiethoxysilane; And / or, the mercapto-containing siloxane is selected from at least one of mercaptopropyltriethoxysilane and mercaptopropylmethyltriethoxysilane.

3. The preparation process according to claim 1, characterized in that, In step S2, the phase transfer catalyst is tetrabutylammonium bromide.

4. The preparation process according to claim 1, characterized in that, In step S2, the temperature during the heating process is controlled at 70-80℃; and / or the stirring time is 10-20 min.

5. The preparation process according to claim 1, characterized in that, In step S3, the heat preservation reaction temperature is 75-80℃, and the reaction time is 1.5-2h.

6. The preparation process according to claim 1, characterized in that, In step S3, the drop acceleration rate is 4-25 g / min.

7. The preparation process according to claim 1, characterized in that, In step S1, the sodium tetrasulfide is obtained by heating sodium sulfide and sulfur powder in water.

8. The preparation process according to claim 7, characterized in that, The mass ratio of sulfur, sodium sulfide, alkaline buffer reagent, phase transfer catalyst, chloropropyltriethoxysilane and water used in step S1 is 1: (1.35-1.5): (0.3-0.6): (0.05-0.075): (5-5.5): (4-8).

9. The preparation process according to claim 7, characterized in that, In step S1, the reaction temperature is 50-60℃ and the reaction time is 40-60 min.

10. The preparation process according to claim 1, characterized in that, In step S3, the decolorization process uses a cation exchange resin.

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