Preparation method, production system and production method of hydrophobic nano silicon dioxide

Abstract

The invention provides a preparation method of hydrophobic nano silicon dioxide, which comprises the following steps: introducing dimethyl dichlorosilane gas and methyl trichlorosilane gas into hydrophilic nano silicon dioxide, and reacting at 250-400 DEG C to generate the hydrophobic nano silicon dioxide. The preparation method comprises the following steps: directly introducing dimethyl dichlorosilane and methyl trichlorosilane into hydrophilic nano silicon dioxide at the temperature of 250-400 DEG C in the form of gas, and directly reacting the dimethyl dichlorosilane and the methyl trichlorosilane at high temperature to obtain the hydrophobic nano silicon dioxide. Monomethyl trichlorosilane is taken as a main hydrophobic raw material, so that the production cost can be remarkably reduced, and in order to improve the yield of hydrophobic nano silicon dioxide obtained by monomethyl trichlorosilane and hydrophilic nano silicon dioxide, dimethyldichlorosilane gas is also used, so that the yield of the hydrophobic nano silicon dioxide is improved. The two gases jointly promote the mutual reaction with the hydrophilic nano silicon dioxide, so that low-cost and high-efficiency preparation of the hydrophobic nano silicon dioxide is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nano-silica production, in particular to a preparation method, production system and production method of hydrophobic nano-silica. BACKGROUND

[0002] The hydrophobic nano-silica refers to the nano-silica surface which is treated specially to have the hydrophobic property.

[0003] The patent application disclosure document CN116462203A discloses a preparation method of hydrophobic silica aerogel, which mixes hydrophilic silica aerogel with trimethylchlorosilane or dichloromethane for modification to obtain a modified product, but the method has the disadvantages of high cost of trimethylchlorosilane and dichloromethane, and low reaction yield in liquid state, which is not suitable for industrial production.

[0004] The patent application disclosure document CN118908231A discloses a preparation method of hydrophobic deodorant silica, which adds an alkylating agent to fumed silica to obtain hydrophobic silica after reaction. The alkylating agent used in the method is any one of hexamethyldisilazane, trimethoxyoctadecylsilane, dimethyldichlorosilane or trimethylchlorosilane, which also has the problem of high cost. On the other hand, the method directly adds the alkylating agent to the fumed silica and then heats for reaction, which has low yield in the reaction process and is not suitable for industrial production.

[0005] The patent application disclosure document CN106629742A discloses a preparation method of hydrophobic fumed silica, which sends the fumed silica into a hydrophobic treatment device, controls the oxygen concentration to be below 1% by passing in nitrogen, pumps in water and dimethyldichlorosilane or monomethyltrichlorosilane, and obtains hydrophobic modified fumed silica after hydrophobic modification. The method needs to control the oxygen concentration additionally, and the reaction process is complex. SUMMARY

[0006] The technical problem to be solved by the present application is the high cost, low yield and complex process of the prior art for preparing hydrophobic nano-silica.

[0007] To solve the above problems, the present application provides a preparation method of hydrophobic nano-silica, which comprises: passing dimethyldichlorosilane gas and monomethyltrichlorosilane gas into hydrophilic nano-silica, and generating hydrophobic nano-silica at 250-400 DEG C; the ratio of dimethyldichlorosilane to the sum of the mass of dimethyldichlorosilane gas and monomethyltrichlorosilane gas is not more than 10%; and the ratio of hydrophilic nano-silica to the sum of the mass of dimethyldichlorosilane and monomethyltrichlorosilane is 1: (0.01-0.25).

[0008] By the above scheme, the dimethyldichlorosilane and monomethyltrichlorosilane are directly introduced into the hydrophilic nanosilica in the form of gas at a temperature of 250-400 DEG C, and the dimethyldichlorosilane and monomethyltrichlorosilane directly react at high temperature to obtain the hydrophobic nanosilica.

[0009] The hydrophobic raw material used in the application is mainly monomethyltrichlorosilane, which can significantly reduce the production cost. In order to improve the amount of monomethyltrichlorosilane and hydrophilic nanosilica to obtain hydrophobic nanosilica, the application also uses dimethyldichlorosilane gas, wherein the content of dimethyldichlorosilane is not more than 10%. The two gases promote the reaction of each other with the hydrophilic nanosilica, and the hydrophobic nanosilica is prepared at low cost and high efficiency.

[0010] In order to further reduce the production cost of the hydrophobic nanosilica and reduce the waste of reaction raw materials, according to the above preparation method of the application, the preparation method of the hydrophobic nanosilica of the application further comprises: the dimethyldichlorosilane gas and monomethyltrichlorosilane gas which do not participate in or do not completely participate in the above reaction are continuously introduced into another reactor containing the hydrophilic nanosilica to continue the hydrophobic treatment, and the semi-finished product of the hydrophobic nanosilica which is pre-hydrophobic treated is obtained.

[0011] Further, the dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the semi-finished product of the hydrophobic nanosilica, and the reaction is carried out at 250-400 DEG C to generate the hydrophobic nanosilica.

[0012] By the above scheme, the production cost of the hydrophobic nanosilica can be significantly reduced, and the waste of reaction raw materials can be reduced.

[0013] In order to perform the deacidification treatment on the hydrophobic nanosilica directly obtained by the hydrophobic reaction, according to the above preparation method of the application, the preparation method of the hydrophobic nanosilica of the application further comprises: the deacidification of the hydrophobic nanosilica, and preferably, the pH value of the hydrophobic nanosilica after the deacidification is greater than or equal to 4.0.

[0014] Based on the inventive concept of the above preparation method, the application further provides a production system of the hydrophobic nanosilica, which comprises: a first reactor and a deacidifier.

[0015] The first reactor comprises a dimethyldichlorosilane gas inlet device and a monomethyltrichlorosilane gas inlet device connected to the bottom of the first reactor. The deacidifier is connected with the first reactor, and the deacidifier comprises a nitrogen gas inlet device and a water vapor inlet device connected to the bottom of the deacidifier, and an acid gas washing device connected to the top of the deacidifier.

[0016] The hydrophobic nanometer silicon dioxide preparation method can be efficiently applied to industrial production by using the reactor.

[0017] In order to make full use of the raw materials used in the hydrophobic nanometer silicon dioxide preparation method and reduce the waste of raw materials, the production system further comprises a second reactor, the discharge port of the second reactor is connected to the feed port of the first reactor, and the exhaust port at the top of the first reactor is connected to the gas inlet at the bottom of the second reactor.

[0018] In order to remove the acidic gas in the unreacted gas, in one improvement of the production system, a gas washing device is arranged between the exhaust port at the top of the first reactor and the gas inlet at the bottom of the second reactor.

[0019] Based on the hydrophobic nanometer silicon dioxide preparation method and the production system, the application further provides a hydrophobic nanometer silicon dioxide production method, which comprises the following steps: The hydrophilic nanometer silicon dioxide is loaded into the reaction cavity of the first reactor, and the hydrophilic nanometer silicon dioxide is heated to 250-400°C; The dimethyldichlorosilane gas and the monomethyltrichlorosilane gas are introduced into the first reactor; After the dimethyldichlorosilane gas and the monomethyltrichlorosilane gas react with the hydrophobic nanometer silicon dioxide, the hydrophobic nanometer silicon dioxide and the unreacted dimethyldichlorosilane gas and monomethyltrichlorosilane gas are obtained.

[0020] By using the above method, the low-cost monomethyltrichlorosilane can be used to prepare the hydrophobic nanometer silicon dioxide at low cost and high efficiency.

[0021] Further, in order to reduce the acidic gas in the hydrophobic nanometer silicon dioxide, the hydrophobic nanometer silicon dioxide is introduced into a deacidification device, the hydrophobic nanometer silicon dioxide in the deacidification device is heated to 400-600°C, then nitrogen and water vapor are introduced into the deacidification device, and the pH of the deacidified hydrophobic nanometer silicon dioxide is greater than or equal to 4.0.

[0022] Further, in order to make full use of the unreacted gas raw material or the unreacted gas raw material, the hydrophilic nanometer silicon dioxide is loaded into the reaction cavity of the second reactor, and the hydrophilic nanometer silicon dioxide is heated to 250-400°C; The unreacted dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the second reactor for pre-hydrophobic treatment, and the semi-finished hydrophobic nanometer silicon dioxide is obtained, and the semi-finished hydrophobic nanometer silicon dioxide is introduced into the reaction cavity of the first reactor for hydrophobic treatment.

[0023] The technical effect of the application is that: The hydrophobic raw material used in the application is mainly monomethyltrichlorosilane, which can significantly reduce the production cost. In order to improve the amount of hydrophobic nanosilica obtained from monomethyltrichlorosilane and hydrophilic nanosilica, the application also uses dimethyldichlorosilane gas. The two gases promote the reaction of each other with hydrophilic nanosilica, achieving low-cost and high-efficiency preparation of hydrophobic nanosilica.

[0024] In order to further reduce the production cost of hydrophobic nanosilica and reduce the waste of reaction raw materials, the application continues to pass the dimethyldichlorosilane gas and monomethyltrichlorosilane gas, which are not involved in the reaction or not completely involved in the reaction, into another reactor containing hydrophilic nanosilica for hydrophobic treatment, obtaining a pre-hydrophobic treatment of semi-finished hydrophobic nanosilica.

[0025] In order to better industrialize the method of the application, the production system of the application not only can efficiently prepare hydrophobic nanosilica, but also can fully utilize the raw materials not involved in the reaction or not completely involved in the reaction, and perform efficient deacidification treatment. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a hydrophobic nanosilica production system according to an embodiment of the application.

[0027] Figure 2 is another hydrophobic nanosilica production system according to an embodiment of the application.

[0028] BRIEF DESCRIPTION OF DRAWINGS: 1, first reactor; 2, dimethyldichlorosilane gas inlet device; 3, monomethyltrichlorosilane gas inlet device; 4, deacidifier; 5, nitrogen gas inlet device; 6, water vapor inlet device; 7, acid gas washing device; 8, second reactor; 9, gas washing device; 10, tail gas washing device. DETAILED DESCRIPTION

[0029] The embodiments of the technical solutions of the application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, and therefore only serve as examples, and cannot limit the protection scope of the application.

[0030] In the method for preparing the hydrophobic nanosilica, dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the hydrophilic nanosilica, and the reaction is carried out at 250-400°C to generate the hydrophobic nanosilica; wherein the ratio of dimethyldichlorosilane to the sum of the mass of dimethyldichlorosilane gas and monomethyltrichlorosilane gas is not more than 10%; and the ratio of the hydrophilic nanosilica to the sum of the mass of dimethyldichlorosilane and monomethyltrichlorosilane is 1:(0.01-0.25).

[0031] It should be noted that the dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the hydrophilic nanosilica in a continuous manner in the present application. In the present application, the hydrophilic nanosilica used conforms to the relevant technical indexes of fumed silica in the national standard "Fumed Silica" (GB / T20020-2003), and the specific surface area of the hydrophilic nanosilica used in the present application is 100-400 m 3 / g. It should be noted that although the typical value of NSA of fumed silica in the "Fumed Silica" (GB / T20020-2003) is 90 m 3 / g-380 m 3 / g, which is not in conflict with the range value of 100-400 m 3 / g of the specific surface area in the present application.

[0032] Through the above method of the present application, the hydrophobic nanosilica with the hydrophobic group accounting for 0.1%-5.0% of the total mass of the hydrophobic nanosilica can be obtained, and the percentage of the above hydrophobic group in the total mass of the hydrophobic nanosilica is essentially the percentage of carbon element in the total mass of the hydrophobic group in the hydrophobic nanosilica.

[0033] In the above description, the ratio of the hydrophilic nanosilica to the sum of the mass of dimethyldichlorosilane and monomethyltrichlorosilane is 1:(0.01-0.25), which means that the range value contains 0.01 and 0.25.

[0034] Since part of the dimethyldichlorosilane gas and monomethyltrichlorosilane gas does not participate in the reaction or does not completely participate in the reaction in the preparation of the hydrophobic nanosilica by introducing the dimethyldichlorosilane gas and monomethyltrichlorosilane gas into the hydrophilic nanosilica, in order to reduce the waste of raw materials, the dimethyldichlorosilane gas and monomethyltrichlorosilane gas which do not participate in the reaction or do not completely participate in the reaction are continuously introduced into another reactor containing the hydrophilic nanosilica to continue the hydrophobic treatment, and a semi-finished product of the hydrophobic nanosilica is obtained. Based on the semi-finished product of the hydrophobic nanosilica, the dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the semi-finished product of the hydrophobic nanosilica, and the reaction is carried out at 250-400°C to obtain the hydrophobic nanosilica. In this way, the production cost can be reduced, and the waste of raw materials can be reduced. In order to perform the deacidification treatment on the hydrophobic nanosilica directly obtained by the hydrophobic reaction, the hydrophobic nanosilica is deacidified, and preferably, when the pH value of the hydrophobic nanosilica after the deacidification is greater than or equal to 4.0, the deacidification treatment is completed.

[0035] As Figure 1 A production system of the hydrophobic nanosilica of the present application is illustrated, which comprises: a first reactor 1, a dimethyldichlorosilane gas inlet device 2 and a monomethyltrichlorosilane gas inlet device 3 connected to the bottom of the first reactor 1; a deacidifier 4 connected to the first reactor 1, a nitrogen gas inlet device 5 and a water vapor inlet device 6 connected to the bottom of the deacidifier 4, and an acid gas washing device 7 connected to the top of the deacidifier 4. The above system satisfies the production of the hydrophobic nanosilica.

[0036] In order to reduce the production cost and reduce the waste of raw materials, as Figure 2 The production system of the present application further comprises: a second reactor 8, and the discharge port of the second reactor 8 is connected to the feed port of the first reactor 1; and the exhaust port of the top of the first reactor 1 is connected to the gas inlet port of the bottom of the second reactor 8.

[0037] In order to remove the acidic gas in the dimethyldichlorosilane gas and monomethyltrichlorosilane gas discharged from the top of the first reactor 1, a gas washing device 9 is arranged between the exhaust port of the top of the first reactor 1 and the gas inlet port of the bottom of the second reactor 8. The top of the second reactor is connected to a tail gas washing device 10.

[0038] The method for producing the hydrophobic nanosilica by using the above production system comprises: The hydrophilic nanosilica is loaded into the reaction cavity of the first reactor, and the hydrophilic nanosilica is heated to 250-400°C; generally, the heating can be performed by using electric heating.

[0039] The dimethyldichlorosilane gas and the monomethyltrichlorosilane gas are introduced into the first reactor; After the reaction of the dimethyldichlorosilane gas and the monomethyltrichlorosilane gas with the hydrophobic nanosilica is completed, the hydrophobic nanosilica and the dimethyldichlorosilane gas and the monomethyltrichlorosilane gas remaining in the reaction are obtained.

[0040] The hydrophobic nanosilica is introduced into the deacidifier, and the hydrophobic nanosilica in the deacidifier is heated (electric heating can be used) to 400-600℃, and then nitrogen and water vapor are introduced into the deacidifier to deacidify the hydrophobic nanosilica, and the pH of the deacidified hydrophobic nanosilica is greater than or equal to 4.0.

[0041] Further comprising: loading the hydrophilic nanosilica into the reaction cavity of the second reactor, and heating the hydrophilic nanosilica to 250-400℃; The dimethyldichlorosilane gas and the monomethyltrichlorosilane gas remaining in the first reactor are introduced into the second reactor for pre-hydrophobic treatment, and the semi-finished hydrophobic nanosilica is obtained, and the semi-finished hydrophobic nanosilica is introduced into the reaction cavity of the first reactor for hydrophobic treatment.

[0042] The application will be described below in combination with specific examples: Example 1 S1, first reactor reaction: 1000g of hydrophilic nanosilica is loaded into the first reactor and heated to 350±5℃; 12.5g of dimethyldichlorosilane gas and 237.5g of monomethyltrichlorosilane gas are continuously introduced into the first reactor for reaction; After the reaction, the obtained solid product is introduced into the deacidification tower for deacidification, so that the pH of the solid product is 4.2±0.1; After deacidification, 1001.03g of hydrophobic nanosilica with a carbon content of 0.1% is obtained; S2, second reactor reaction: 1000g of hydrophilic nanosilica is loaded into the second reactor and heated to 350±5℃; The gas discharged from the top of the first reactor is introduced into the second reactor after being washed by the washing tower for reaction, and 1000.54g of semi-finished hydrophobic nanosilica with a carbon content of 0.054% is obtained after the reaction; S3, first reactor reaction again: The semi-finished hydrophobic nanosilica with a carbon content of 0.054% is loaded into the first reactor and heated to 350±5℃; The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5°C; After the reaction, the solid product was passed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1001.57 g of hydrophobic nanosilica with a carbon content of 0.1% was obtained; Example 1 used 25 g of dimethyldichlorosilane gas and 475 g of monomethyltrichlorosilane gas, and 2000 g of hydrophilic nanosilica to obtain 2002.60 g of hydrophobic nanosilica with a carbon content of 0.1%. See Table 1 for details.

[0043] Example 2 S1, first reactor reaction: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5°C; The first reactor was continuously charged with 25 g of dimethyldichlorosilane gas and 225 g of monomethyltrichlorosilane gas for reaction; After the reaction, the solid product was passed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1052.87 g of hydrophobic nanosilica with a carbon content of 5.0% was obtained; S2, second reactor reaction: The second reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5°C; The gas discharged from the top of the first reactor was passed into the second reactor after passing through a shower tower for reaction, and 1025.72 g of semi-finished hydrophobic nanosilica with a carbon content of 2.5% was obtained after the reaction; S3, first reactor reaction again: The first reactor was charged with 1025.72 g of semi-finished hydrophobic nanosilica with a carbon content of 2.5% and heated to 350±5°C; The first reactor was continuously charged with 25 g of dimethyldichlorosilane gas and 250 g of monomethyltrichlorosilane gas for reaction; After the reaction, the solid product was passed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1080.10 g of hydrophobic nanosilica with a carbon content of 5.0% was obtained; Example 2 used 50 g of dimethyldichlorosilane gas and 450 g of monomethyltrichlorosilane gas, and 2000 g of hydrophilic nanosilica to obtain 2132.97 g of hydrophobic nanosilica with a carbon content of 5.0%. See Table 1 for details.

[0044] Example 3 S1, first reactor reaction: 1000g of hydrophilic nanosilica was loaded into the first reactor and heated to 395±5°C; 25g of dimethyldichlorosilane gas and 225g of monomethyltrichlorosilane gas were continuously introduced into the first reactor for reaction; After the reaction, the obtained solid product was introduced into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1039.68g of hydrophobic nanosilica with a carbon content of 3.8% was obtained; S2, second reactor reaction: 1000g of hydrophilic nanosilica was loaded into the second reactor and heated to 395±5°C; The gas discharged from the top of the first reactor was introduced into the second reactor after passing through a shower tower for reaction, and 1019.51g of semi-finished hydrophobic nanosilica with a carbon content of 1.9% was obtained after reaction; S3, first reactor reaction again: 1019.51g of semi-finished hydrophobic nanosilica with a carbon content of 1.9% was loaded into the first reactor and heated to 395±5°C; 25g of dimethyldichlorosilane gas and 250g of monomethyltrichlorosilane gas were continuously introduced into the first reactor for reaction; After the reaction, the obtained solid product was introduced into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1059.97g of hydrophobic nanosilica with a carbon content of 3.8% was obtained; Example 3 used 50g of dimethyldichlorosilane gas and 450g of monomethyltrichlorosilane gas, and 2000g of hydrophilic nanosilica to obtain 2099.65g of hydrophobic nanosilica with a carbon content of 3.8%. See Table 1 for details.

[0045] Example 4 S1, first reactor reaction: 1000g of hydrophilic nanosilica was loaded into the first reactor and heated to 255±5°C; 0.5g of dimethyldichlorosilane gas and 9.5g of monomethyltrichlorosilane gas were continuously introduced into the first reactor for reaction; After the reaction, the obtained solid product was introduced into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1001.01g of hydrophobic nanosilica with a carbon content of 0.1% was obtained; S2, second reactor reaction: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 255±5°C; The gas discharged from the top of the first reactor was introduced into the second reactor after passing through the washing tower for reaction, and 1000.50 g of semi-finished hydrophobic nanosilica with a carbon content of 0.5% was obtained after reaction; S3, the first reactor was reacted again: The first reactor was charged with 1000.50 g of semi-finished hydrophobic nanosilica with a carbon content of 0.5% and heated to 255±5°C; 5 g of dimethyldichlorosilane gas and 95 g of monomethyltrichlorosilane gas were continuously introduced into the first reactor for reaction; After reaction, the obtained solid product was introduced into the deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1001.51 g of hydrophobic nanosilica with a carbon content of 0.1% was obtained; In example 4, 10 g of dimethyldichlorosilane gas and 190 g of monomethyltrichlorosilane gas were used, and 2000 g of hydrophilic nanosilica obtained 2002.52 g of hydrophobic nanosilica with a carbon content of 0.1%. See Table 1 for details.

[0046] Comparative example 1 Comparative example 1 is different from example 2 in that no dimethyldichlorosilane is introduced, and steps S2 and S3 are not included, as follows: S1, the first reactor was reacted: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5°C; 250 g of monomethyldichlorosilane gas was continuously introduced into the first reactor for reaction; After reaction, the obtained solid product was introduced into the deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1037.51 g of hydrophobic nanosilica with a carbon content of 3.6% was obtained; Comparative example 1 used 250 g of monomethyldichlorosilane gas, and 1000 g of hydrophilic nanosilica obtained 1037.51 g of hydrophobic nanosilica with a carbon content of 3.6%. See Table 1 for details.

[0047] Comparative example 2 Comparative example 2 is different from example 2 in that no monomethyltrichlorosilane is introduced, and steps S2 and S3 are not included, as follows: S1, the first reactor was reacted: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5°C; The first reactor was continuously fed with 250 g of dimethyltrichlorosilane gas for reaction; After reaction, the obtained solid product was fed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1043.14 g of hydrophobic nanosilica with a carbon content of 4.1% was obtained. Comparative Example 2 used 250 g of dimethyldichlorosilane gas, and 1000 g of hydrophilic nanosilica to obtain 1043.14 g of hydrophobic nanosilica with a carbon content of 4.1%. See Table 1 for details.

[0048] Comparative Example 3 Comparative Example 3 differed from Example 2 in that the remaining gas after the first reactor reaction in step S1 was not used, and the details are as follows: S1, first reactor reaction: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5℃; The first reactor was continuously fed with 25 g of dimethyldichlorosilane gas and 225 g of monomethyltrichlorosilane gas for reaction; After reaction, the obtained solid product was fed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1052.87 g of hydrophobic nanosilica with a carbon content of 5.0% was obtained. S2, first reactor reaction: The first reactor was charged with 1000 g of hydrophilic nanosilica and heated to 350±5℃; The first reactor was continuously fed with 25 g of dimethyldichlorosilane gas and 225 g of monomethyltrichlorosilane gas for reaction; After reaction, the obtained solid product was fed into a deacidification tower for deacidification, so that the pH of the solid product was 4.2±0.1; After deacidification, 1052.87 g of hydrophobic nanosilica with a carbon content of 5.0% was obtained.

[0049] Comparative Example 3 used 50 g of dimethyldichlorosilane gas and 450 g of monomethyltrichlorosilane gas, and 2000 g of hydrophilic nanosilica to obtain 2105.74 g of hydrophobic nanosilica with a carbon content of 5.0%.

[0050] Table 1 Data table of Examples 1-4 and Comparative Examples 1-2 From Examples 1-4, it can be seen that the reaction efficiency at 255±5℃ and 395±5℃ is lower than that at 355±5℃.

[0051] It can be seen from Example 2 and Comparative Example 3 that the hydrophobic nano-silica semi-finished product prepared by passing the remaining gas in step S1 into the second reactor is passed into the first reactor again for reaction, which can reduce the use amount of dimethyldichlorosilane gas and monomethyltrichlorosilane gas.

[0052] It can be seen from the examples and Comparative Examples 1 and 2 that the use of dimethyldichlorosilane gas and monomethyltrichlorosilane gas in combination can obtain hydrophobic nano-silica with higher carbon content than the use of any one of the gases alone for hydrophobic modification.

[0053] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions described in the foregoing examples can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing hydrophobic nano-silica, characterized in that, include: Dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into hydrophilic nano-silica, and the reaction is carried out at 250℃~400℃ to generate hydrophobic nano-silica. The proportion of dimethyldichlorosilane to the total mass of dimethyldichlorosilane gas and monomethyltrichlorosilane gas does not exceed 10%; The ratio of the hydrophilic nano-silica to the sum of the masses of dimethyldichlorosilane and monomethyltrichlorosilane is 1:(0.01~0.25).

2. The preparation method according to claim 1, characterized in that, It also includes passing the dimethyldichlorosilane gas and monomethyltrichlorosilane gas discharged after participating in the reaction into another reactor containing hydrophilic nano-silica for further hydrophobic treatment, to obtain a pre-hydrophobic semi-finished product of hydrophobic nano-silica.

3. The preparation method according to claim 2, characterized in that, Also includes: Dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the semi-finished hydrophobic nano-silica, and the reaction is carried out at 250℃~400℃ to generate hydrophobic nano-silica.

4. The preparation method according to any one of claims 1 or 3, characterized in that, Also includes: The hydrophobic nano-silica is deacidified, preferably with a pH value ≥ 4.0 after deacidification.

5. A production system for hydrophobic nano-silica, characterized in that, include: First reactor (1), and a dimethyl dichlorosilane inlet device (2) and a monomethyl trichlorosilane inlet device (3) connected to the bottom of the first reactor (1); A deacidifier (4) connected to the first reactor (1), a nitrogen inlet device (5) and a water vapor inlet device (6) connected to the bottom of the deacidifier (4), and an acid rinsing device (7) connected to the top of the deacidifier (4).

6. The production system according to claim 5, characterized in that, It also includes a second reactor (8), the outlet of which is connected to the inlet of the first reactor (1); the exhaust port at the top of the first reactor (1) is connected to the air inlet at the bottom of the second reactor (8).

7. The production system according to claim 6, characterized in that, A gas scrubbing device (9) is provided between the exhaust port at the top of the first reactor (1) and the air inlet at the bottom of the second reactor (8).

8. A method for producing hydrophobic nano-silica, characterized in that, Using the production system according to any one of claims 5 to 7, comprising: Hydrophilic nano-silica is loaded into the reaction chamber of the first reactor, and the hydrophilic nano-silica is heated to 250~400℃; Dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the first reactor; After the dimethyldichlorosilane gas and monomethyltrichlorosilane gas react with the hydrophobic nano-silica, hydrophobic nano-silica and dimethyldichlorosilane gas and monomethyltrichlorosilane gas that did not fully participate in the reaction are obtained.

9. The production method according to claim 8, characterized in that, Also includes: The hydrophobic nano-silica is introduced into a deacidifier, and the hydrophobic nano-silica in the deacidifier is heated to 400~600℃. Nitrogen and water vapor are then introduced into the deacidifier to deacidify the hydrophobic nano-silica to a pH ≥ 4.

0.

10. The production method according to claim 8, characterized in that, Also includes: Hydrophilic nano-silica is loaded into the reaction chamber of the second reactor, and the hydrophilic nano-silica is heated to 250~400℃. The partially reacted dimethyldichlorosilane gas and monomethyltrichlorosilane gas are introduced into the second reactor for pre-hydrophobic treatment to obtain semi-finished hydrophobic nano-silica. The semi-finished hydrophobic nano-silica is then introduced into the reaction chamber of the first reactor for hydrophobic treatment.

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