On-line treatment process for fumed silica with controllable modification rate and low dispersion

Abstract

According to the online treatment process for the fumed silica with the controllable modification rate and the low dispersion degree, provided by the invention, the modified fumed silica with the controllable modification rate and the extremely low dispersion degree can be obtained by adding a modifier in a fumed silica production and aggregation process section through the online treatment process. Spraying a certain proportion of modifier into a fumed silica aggregation section in a certain physical form, further carrying out high-temperature and high-speed mixing modification in the aggregation section, and then carrying out conventional cyclone separation and degassing treatment processes to obtain a surface-modified fumed silica product. In the continuous production process of the fumed silica obtained by the invention, the standard deviation of each performance index of the product obtained by multi-period sampling is lower than 0.02, and the carbon content is regulated and controlled in the range of 0-10%.

Description

Technical Field

[0001] The present invention relates to the field of nanomaterials, and specifically relates to an online processing process for fumed silicon dioxide with a controllable modification rate and low dispersion. Background Art

[0002] At present, the production process of fumed silica is high-temperature hydrolysis of silane, and its surface contains a large number of active silanol groups. Existing theories determine that the formation of silica particles goes through primary particle size to aggregates to agglomerates, in which the silanol groups on the surface of the primary particle size form aggregates through high-temperature dehydration condensation, and the aggregates are further combined into agglomerates through hydrogen bonds or other physical forms. Since the aggregates still contain a large number of silanol groups, firstly, the fumed silica is easy to absorb water when exposed to the air, and its further application is limited; secondly, a large number of hydrogen bonds and other physical entanglement methods lead to the interaction force between aggregates that cannot be ignored, making the agglomerates difficult to open, and further surface treatment of fumed silica is usually uneven and inefficient. For example, in the production of liquid silicone rubber, even if hydrophobically modified fumed silica (especially online treatment products) is used, a certain amount of silazane still needs to be added.

[0003] As for the surface treatment of fumed silica, the existing technical means are all focused on the post-treatment of the hydrophilic fumed silica products. For example, CN111286215B first pre-treats the finished fumed silica by refining and fluffing, and then further modifies the surface. CN115975399A further modifies the surface of the finished fumed silica after mixing it with sulfuric acid and hydrogen peroxide. This technology requires further ultrasonic dispersion, grinding, etc., has complex process and technical means, and produces unfavorable factors such as organic waste liquid, which is not suitable for industrial promotion. CN106629742B also needs to prepare the finished hydrophilic fumed silica first. Summary of the invention

[0004] To solve the above problems, the present invention discloses an online treatment process for fumed silica with controllable modification rate and low dispersion. By introducing a modifier during the production process of fumed silica, the modification rate of fumed silica can be effectively controlled, the online product is stable, and the dispersion of various performance indicators is low.

[0005] The technical solution of the present invention is an online treatment process for fumed silica with controllable modification rate and low dispersion, which includes a fumed silica reactor, a modifier adding furnace, a concentrator and a product post-treatment device.

[0006] An online treatment process for fumed silica with a controllable modification rate and low dispersion comprises the following processes: a mixed gas containing silica obtained by high-temperature hydrolysis in a fumed silica reactor enters a multi-coil long pipe concentrator, a modifier is pumped into the tail of the coil of the concentrator, and the gasified modifier is brought into the concentrator in the form of nitrogen bubbling; after the mixture undergoes an aggregation reaction, it enters a cyclone separator for gas-solid separation, and the obtained solid is subjected to deacidification treatment to obtain a modified fumed silica product.

[0007] At present, the existing fumed silica production process is to hydrolyze chlorosilane at high temperature in a hydrogen-oxygen flame. Its chemical equation is as follows (taking silicon tetrachloride as an example): .

[0008] By controlling the raw material ratio, the reaction temperature and flow rate can be further controlled to obtain fumed silica products with different properties. In the white carbon black process in this field, hydrogen and oxygen are firstly burned violently to obtain gaseous water, which will hydrolyze with Si-Cl bonds to obtain Si-OH, and Si-OH will condense under high temperature conditions, which is also an important process for the aggregation of white carbon black particles. Adding a modifier at this time can promote the modification effect.

[0009] The speed of the fumed silica entering the multi-coil long pipe concentrator is 15-30 m / s; the inlet temperature is 700-800°C.

[0010] Since the gas-solid mixture after hydrolysis will be cooled in the reactor and still be at a high temperature when entering the aggregator, if it can be cooled quickly, the silanol condensation ratio will decrease, but the equipment requirements are very high. The speed of the present invention is also a means to prevent the silanol condensation of white carbon black. The aggregator is a long pipeline with slow speed and high temperature. The white carbon black particles formed by excessive condensation of silanol are larger and more difficult to disperse. In addition, different flow rates can correspond to products with different specific surface areas.

[0011] The multi-coil long pipe concentrator is formed by welding multi-section coils; the concentrator has a length of 100m-200m.

[0012] The modifier is loaded into the adding furnace, and the outlet of the modifier adding furnace is connected to the concentrator pipe at an angle less than 15°. In some embodiments, the joint part may be 5-10 cm away from the coil elbow welding.

[0013] The modifier enters the first 1 / 2 coil of the self-aggregator. In some preferred cases, the modifier is pumped into the modifier from the tail of the first coil of the self-aggregator, or the modifier is pumped into the modifier from the tail of the second coil of the self-aggregator, or the modifier is pumped into the modifier from the tail of the third coil of the self-aggregator.

[0014] The temperature of the modifier in the adding furnace is 100-250° C.; the temperature of the modifier when entering the concentrator is 400-500° C. The modifier outlet on the modifier adding furnace can be designed with an atomizing device to achieve atomization loading at the outlet.

[0015] The temperature of the modifier in the furnace refers to the gasification temperature of the modifier. Generally, the boiling point of small silane molecules will not exceed 200°C, so they can be brought into the aggregator through nitrogen; entering the aggregator at around 450°C is to avoid thermal decomposition of the modifier under too high a temperature.

[0016] The modifier is selected from silane, siloxane, cyclosiloxane, polysiloxane and silazane; wherein the silane includes chlorosilane and fluorine-containing silane; the polysiloxane has a relative molecular weight of 200-5000 and includes inert end-capping groups of methyl and phenyl, and functional groups of carboxyl, amino and thiol.

[0017] The silane is selected from monomethyltrichlorosilane, dimethylchlorosilane, vinylmethyldichlorosilane, methyldichlorosilane, trimethylchlorosilane, phenylchlorosilane, trifluoropropylchlorosilane and the like.

[0018] The siloxane is selected from hexamethyldisiloxane, divinyltetramethyldisiloxane, diphenyltetramethyldisiloxane and the like.

[0019] The cyclosiloxane is selected from hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, decamethylcyclopentasiloxane, tetramethyltetraphenylcyclotetrasiloxane, trifluoropropylcyclotrisiloxane and the like.

[0020] The polysiloxane is selected from methyl silicone oil, vinyl silicone oil, phenyl silicone oil, fluorine-containing silicone oil, amino silicone oil, carboxyl-modified methyl silicone oil, mercapto-modified methyl silicone oil and the like.

[0021] The silazane is selected from hexamethyldisilazane, tetramethyldivinyldisilazane, hexamethylcyclotrisilazane, trivinyltrimethylcyclotrisilazane and the like.

[0022] The nitrogen flow rate is 0.1-2.5 L / h, so as to carry the modifier into the aggregator.

[0023] The reaction principles involved in the present invention are mainly (taking polysiloxane as an example):

[0024]

[0025] The present invention has the following beneficial effects: 1. The surface of fumed silica aggregates and agglomerates is treated at the formation stage. After a long reaction and mixing process, the modification is more thorough and uniform, the dispersion of product performance indicators at each production time point is low, and the production cost is reduced; 2. The hydrogen chloride and water produced during the production of fumed silica will accelerate the hydrolysis, ring opening and cracking of the modifier, and further react with the hydroxyl groups on the surface of silica, resulting in a better modification effect; 3. By adjusting the dosage of the modifier, a hydrophobic fumed silica product with controllable carbon content can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the online treatment process of fumed silicon dioxide provided by the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below through specific implementation modes, but the protection scope of the present invention is not limited thereto.

[0028] Example 1 An online treatment process for fumed silica with a controllable modification rate and low dispersion is prepared by the following steps: The silica-containing mixed gas obtained by high-temperature hydrolysis in the fumed silica reactor enters a 100m long concentrator at 15m / s, with an inlet temperature of 750℃. The modifier octamethylcyclotetrasiloxane is added 10cm away from the elbow at the tail of the first coil, with an inlet temperature of 450℃; the temperature of the modifier addition furnace is 250℃, the internal pressure is 0.04Mpa, and the gasified modifier is brought into the concentrator in the form of nitrogen bubbling; after the mixture passes through the concentrator, it enters the cyclone separator at a material temperature of 220℃ for gas-solid separation, and the obtained solid is deacidified to obtain the modified fumed silica product. By controlling the nitrogen flow rate to 0.2L / h, 0.4L / h, and 1.2L / h, the carbon content of the hydrophobic fumed silica is 1.2%, 2.3%, and 6.9%, respectively. The production processes of the three hydrophobic fumed silicas were monitored for 24 hours, and samples were taken every 2 hours to detect the carbon content. The discrete degrees were 0.015, 0.017, and 0.020, respectively.

[0029] Example 2 An online treatment process for fumed silica with a controllable modification rate and low dispersion is prepared by the following steps: The silica-containing mixed gas obtained by high-temperature hydrolysis in the fumed silica reactor enters a 150m long concentrator at 20m / s, with an inlet temperature of 780°C. The modifier dimethyldichlorosiloxane is added 5cm away from the tail elbow of the second coil, with an inlet temperature of 400°C; the temperature of the modifier addition furnace is 100°C, the internal pressure is 0.01MPa, and the gasified modifier is brought into the concentrator in the form of nitrogen bubbling; after the mixture passes through the concentrator, it enters the cyclone separator at a material temperature of 150°C for gas-solid separation, and the obtained solid is deacidified to obtain the modified fumed silica product. By controlling the nitrogen flow rate to 0.2L / h, 0.4L / h, and 1.2L / h, the carbon content of the hydrophobic fumed silica is 0.3%, 0.6%, and 1.9%, respectively. The production processes of the three hydrophobic fumed silicas were monitored for 24 hours, and samples were taken every 2 hours to detect the carbon content. The discrete degrees were 0.019, 0.011, and 0.016, respectively.

[0030] Example 3 An online treatment process for fumed silica with a controllable modification rate and low dispersion is prepared by the following steps: The silica-containing mixed gas obtained by high-temperature hydrolysis in the fumed silica reactor enters a 100m long concentrator at 17m / s, with an inlet temperature of 800℃. The modifier hexamethyldisiloxane is added 10cm away from the tail elbow of the second coil, with an inlet temperature of 400℃; the temperature of the modifier addition furnace is 150℃, the internal pressure is 0.02MPa, and the gasified modifier is brought into the concentrator in the form of nitrogen bubbling; after the mixture passes through the concentrator, it enters the cyclone separator at a material temperature of 200℃ for gas-solid separation, and the obtained solid is deacidified to obtain the modified fumed silica product. By controlling the nitrogen flow rate to 0.1L / h, 0.4L / h, and 0.8L / h, the carbon content of the hydrophobic fumed silica is 0.5%, 1.7%, and 3.7%, respectively. The production processes of the three hydrophobic fumed silicas were monitored for 24 hours, and samples were taken every 2 hours to detect the carbon content. The discrete degrees were 0.012, 0.012, and 0.015, respectively.

[0031] Example 4 An online treatment process for fumed silica with a controllable modification rate and low dispersion is prepared by the following steps: The silica-containing mixed gas obtained by high-temperature hydrolysis in the fumed silica reactor enters a 170m long concentrator at 25m / s, with an inlet temperature of 700℃. The modifier hydroxy silicone oil is added 5cm away from the tail elbow of the first coil, and the inlet temperature is 500℃; the temperature of the modifier addition furnace is 100℃, the internal pressure is 0.02MPa, and the atomized modifier is brought into the concentrator in the form of spray; after the mixture passes through the concentrator, it enters the cyclone separator at a material temperature of 240℃ for gas-solid separation, and the obtained solid is deacidified to obtain the modified fumed silica product. By controlling the molecular weight of the modifier to 237, 1750, and 4760, the carbon content of the hydrophobic fumed silica is 9.7%, 7.5%, and 3.3%, respectively. The production process of the above three hydrophobic fumed silica is monitored for 24 hours, and the carbon content is tested every 2 hours, and the discreteness is 0.013, 0.017, and 0.019, respectively.

[0032] Example 5 An online treatment process for fumed silica with a controllable modification rate and low dispersion is prepared by the following steps: The silica-containing mixed gas obtained by high-temperature hydrolysis in the fumed silica reactor enters a 100m long concentrator at 18m / s, with an inlet temperature of 690°C. The modifier hexamethyldisilazane is added 10cm away from the elbow at the tail of the first coil, with an inlet temperature of 400°C; the temperature of the modifier addition furnace is 150°C, the internal pressure is 0.01MPa, and the modifier is brought into the concentrator in a gasified form; after the mixture passes through the concentrator, it enters the cyclone separator at a material temperature of 180°C for gas-solid separation, and the obtained solid is deacidified and deaminated to obtain the modified fumed silica product. By controlling the nitrogen flow rate to 0.3L / h, 1.0 L / h, and 2.2 L / h, the carbon content of the hydrophobic fumed silica is 0.7%, 1.9%, and 5.5%, respectively. The production processes of the three hydrophobic fumed silicas were monitored for 24 hours, and samples were taken every 2 hours to detect the carbon content. The discrete degrees were 0.013, 0.011, and 0.013, respectively.

[0033] Comparative Example 1 The specific surface area is selected as 150 m 2 / g of hydrophilic fumed silica, enters a 100m length concentrator at 15m / s, and other production conditions are the same as in Example 1. By controlling the nitrogen flow rate to 0.2L / h, 0.4L / h, and 1.2L / h, the carbon contents of the hydrophobic fumed silica are 1.2%, 2.3%, and 6.9%, respectively. The above three hydrophobic fumed silica production processes are monitored for 24h, and the carbon content is sampled and tested every 2h, and the discreteness is 1.2, 2.7, and 5.5, respectively.

[0034] Comparative Example 2 The specific surface area is selected as 300 m 2 / g of hydrophilic fumed silica, enters a 150m length concentrator at 20m / s, and other production conditions are the same as in Example 2. By controlling the nitrogen flow rate to 0.2L / h, 0.4L / h, and 1.2L / h, the carbon content of the hydrophobic fumed silica is 0.3%, 0.6%, and 1.9%, respectively. The above three hydrophobic fumed silica production processes are monitored for 24h, and the carbon content is sampled and tested every 2h, and the discreteness is 0.8, 0.5, and 3.3, respectively.

[0035] Comparative Example 3 The specific surface area is selected as 300 m 2 / g of hydrophilic fumed silica, enters a 100m length concentrator at 17m / s, and other production conditions are the same as in Example 3. By controlling the nitrogen flow rate to 0.1L / h, 0.4L / h, and 0.8L / h, the carbon contents of the hydrophobic fumed silica are 0.5%, 1.7%, and 3.7%, respectively. The above three hydrophobic fumed silica production processes are monitored for 24h, and the carbon content is sampled and tested every 2h, and the discreteness is 1.5, 2.7, and 7.9, respectively.

[0036] Comparative Example 4 The specific surface area is selected as 200 m 2 / g of hydrophilic fumed silica, enters a 170m length concentrator at 25m / s, and other production conditions are the same as in Example 4. By controlling the molecular weight of the modifier to 237, 1750, and 4760, the carbon contents of the hydrophobic fumed silica are 9.7%, 7.5%, and 3.3%, respectively. The production processes of the above three hydrophobic fumed silica are monitored for 24 hours, and the carbon content is detected by sampling every 2 hours, and the discreteness is 7.7, 9.2, and 9.1, respectively.

[0037] Comparative Example 5 The specific surface area is selected as 380 m 2 / g of hydrophilic fumed silica, enters a 100m length concentrator at 18m / s, and other production conditions are the same as in Example 5. By controlling the nitrogen flow rate to 0.3L / h, 1.0L / h, and 2.2L / h, the carbon content of the hydrophobic fumed silica is 0.7%, 1.9%, and 5.5%, respectively. The above three hydrophobic fumed silica production processes are monitored for 24 hours, and the carbon content is sampled every 2 hours, and the discreteness is 0.9, 0.7, and 0.9, respectively. .

[0038] Application Testing The hydrophobic fumed silica prepared in the above example was added to 100 parts of 5000cp vinyl silicone oil, and the added amount was 10 parts. A comparative example with the same modifier treatment and similar specific surface area and carbon content was selected to test the viscosity after mixing. A certain amount of silazane was added to the experimental sample with high viscosity and post-treated to obtain a silicone base glue with similar viscosity, and the proportion of silazane usage (silazane / vinyl silicone oil) was obtained and compared.

[0039] The application test results are detailed in the table below.

[0040] As can be seen from the above table, in the vinyl silicone oil mixed system, the silazane-treated product still has obvious advantages, the mixed system has the lowest viscosity, and the thickening effect is not obvious. However, under the same modifier comparison conditions, the hydrophobic fumed silica prepared by the present invention has a lower thickening effect in the vinyl silicone oil mixed system than the comparative example, and the additional silazane ratio is as low as 3%, and the highest reaches 10.8%, which undoubtedly increases the additional cost. This is because the fumed silica silanol of the present invention is more active under high temperature, high humidity and acidic conditions, and after aggregators and post-processing processes, particle collisions are more violent, the reaction is more thorough, and the mixture is evenly mixed.

[0041] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention, such as changes in the modified ion groups or other extended applications.

Claims

1. An online processing process for fumed silica with controllable modification rate and low dispersion, characterized in that: The process includes the following: a silica-containing mixed gas obtained by high-temperature hydrolysis in a fumed silica reactor enters a multi-coil long pipe concentrator, a modifier is added to the tail of the coil of the concentrator, and the modifier is brought into the concentrator in the form of nitrogen bubbling or atomization; after the mixture undergoes an aggregation reaction, it enters a cyclone separator for gas-solid separation, and the obtained solid is degassed to obtain a modified fumed silica product.

2. The online processing process of controlled modification rate and low discreteness fumed silica according to claim 1, characterized in that: The speed of the fumed silica entering the multi-coil long pipe concentrator is 15-30 m / s; the inlet temperature is 700-800°C.

3. The online processing process of controllable modification rate and low discreteness fumed silica according to claim 1, characterized in that: The multi-coil long pipe concentrator is welded from multi-section coils; the concentrator has a length of 100m-200m.

4. The online processing process of controlled modification rate and low discreteness fumed silica according to claim 1, characterized in that: The modifier is loaded into the adding furnace, the outlet of the modifier adding furnace is connected to the concentrator pipe at an angle less than 15°, and the joint part is 5-10 cm away from the coil elbow welding.

5. The online processing process of controllable modification rate and low discreteness fumed silica according to claim 4, characterized in that: The temperature of the modifier in the adding furnace is 100-250°C; the temperature of the modifier when entering the aggregator is 400-500°C.

6. The online processing process of controlled modification rate and low discreteness fumed silica according to claim 5, characterized in that: The modifier is selected from silane, siloxane, cyclosiloxane, polysiloxane and silazane; wherein the silane includes chlorosilane and fluorine-containing silane; the polysiloxane has a relative molecular weight of 200-5000 and includes inert end-capping groups of methyl and phenyl, and functional groups of carboxyl, amino and mercapto.

7. The online processing process of controlled modification rate and low discreteness fumed silica according to claim 6, characterized in that: The nitrogen flow rate is 0.1-2.5 L / h.

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