Hydrophobic nanosilica for mineral oil antifoam and method of making same

Abstract

This invention relates to the field of nano-silica modification technology, and particularly to a hydrophobic nano-silica for mineral oil defoamers and its preparation method. The preparation method includes the following steps: activating hydrophilic nano-silica by heating under nitrogen; then adding an atomized surface modifier solution, sealing and mixing to allow the reaction to proceed; and then sequentially undergoing a first depressurization, a vacuuming process, and a second depressurization to obtain hydrophobic nano-silica for mineral oil defoamers; the surface modifier solution includes a highly active surface modifier and a low-activity surface modifier. This preparation method uses a compound of a highly active surface modifier and a low-activity surface modifier, reacting them with the heated and activated hydrophilic nano-silica, simultaneously achieving the condensation and encapsulation reaction of silanol groups on the surface of the hydrophilic nano-silica, resulting in highly dispersed, anti-settling hydrophobic nano-silica for mineral oil defoamers.

Description

Technical Field

[0001] This invention relates to the field of nano-silica modification technology, and in particular to a hydrophobic nano-silica for mineral oil defoamers and its preparation method. Background Technology

[0002] In industrial production processes, a large amount of foam is generated due to the mixing of gas and liquid phases caused by agitation and other factors. Foam typically has a honeycomb structure, in which gas-containing units are surrounded by a liquid film. Most foam is harmful, reducing the effective load of equipment and increasing energy consumption. Therefore, defoamers are needed to treat the foam. The defoaming mechanism involves the defoamer entering the foam interface, forming a bridge between two adjacent foam films, causing the foam film surface to expand. As the defoamer expands further, the foam film thins and eventually ruptures, resulting in foam collapse and achieving the defoaming effect.

[0003] Mineral oil defoamers are widely used in inks, adhesives, coatings, and other fields. For example, a mineral oil defoamer disclosed in Chinese invention patent application number 201410739657.X is mainly composed of mineral oil, fatty acid metal soaps, alkyl silicone oil, hydrophobic nano-silica, defoaming aids, and emulsifiers. Among these, the hydrophobic nano-silica greatly increases the depth and rate at which defoamer droplets penetrate the foam layer, directly affecting defoaming and foam-suppressing performance. The basic preparation process of mineral oil defoamers involves mixing mineral oil and hydrophobic nano-silica under certain conditions to facilitate the dispersion of the hydrophobic nano-silica particles in the mineral oil, followed by the addition of an emulsifier to achieve self-emulsification and dispersion of the defoamer in water. Mineral oil is the main component of the defoamer, but its solubility and dispersibility are low, requiring the assistance of hydrophobic nano-silica and other dispersing aids to improve its dispersion effect. Hydrophobic nano-silica particles have small particle size, large specific surface area, and high surface energy, enabling them to form a powerful adsorption force on air bubbles. Together with mineral oil, they attack and break these bubbles, thus achieving a defoaming effect. Therefore, hydrophobic nano-silica acts like a "needle tip" in defoamers—small in quantity but with a significant impact, exhibiting a complex, efficient, and synergistic defoaming effect. Hydrophobic nano-silica plays a crucial role in the dispersion and adsorption of mineral oil defoamers, influencing their defoaming and foam-suppressing properties. However, ordinary hydrophobic nano-silica particles are difficult to disperse in mineral oil and have poor anti-settling properties, easily forming hard sedimentation during storage, severely affecting the defoaming and foam-suppressing performance of mineral oil defoamers.

[0004] Therefore, how to select modifiers and modification processes to perform surface hydrophobic treatment on nano-silica, improve the dispersibility of hydrophobic nano-silica in mineral oil, solve the problem of hard sedimentation during storage, and develop highly efficient hydrophobic nano-silica with high dispersion and anti-settling properties in mineral oil defoamers has become an urgent technical problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a highly dispersible, anti-settling hydrophobic nano-silica for mineral oil defoamers and its preparation method.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing hydrophobic nano-silica for mineral oil defoamer, comprising the following steps: activating hydrophilic nano-silica by heating under nitrogen; then adding atomized surface modifier, sealing and mixing to carry out the reaction; and then sequentially undergoing a first depressurization, a vacuuming process, and a second depressurization to obtain hydrophobic nano-silica for mineral oil defoamer; wherein the surface modifier includes a highly active surface modifier and a low-activity surface modifier.

[0007] Another technical solution adopted in this invention is: hydrophobic nano-silica prepared by the above-mentioned method for preparing hydrophobic nano-silica for mineral oil defoamers.

[0008] The beneficial effects of the present invention are as follows: The preparation method of the present invention uses a surface modifier with high surface activity and a surface modifier with low surface activity to react with hydrophilic nano-silica after heating and activation, thereby realizing the condensation and encapsulation reaction of silanol groups on the surface of hydrophilic nano-silica, and obtaining hydrophobic nano-silica for mineral oil defoamer with high dispersion and anti-settling properties. Detailed Implementation

[0009] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0010] A method for preparing hydrophobic nano-silica for mineral oil defoamers includes the following steps: activating hydrophilic nano-silica by heating under nitrogen; then adding atomized surface modifiers, sealing and mixing to carry out the reaction; and then sequentially undergoing a first depressurization, a vacuuming process, and a second depressurization to obtain hydrophobic nano-silica for mineral oil defoamers; wherein the surface modifiers include highly active surface modifiers and low-activity surface modifiers.

[0011] As described above, the beneficial effects of this invention are as follows: This invention combines a highly active surface modifier and a low-activity surface modifier and sprays them in an atomized form into an activated hydrophilic nano-silica fluid for a thorough gas-solid mixing reaction. The highly active surface modifier reacts with the silanol groups on the surface of the hydrophilic nano-silica, reducing the silanol content on the nano-silica surface and preventing the formation of hydrogen bonds and sedimentation of silanol groups during the storage of the mineral oil defoamer. Under high temperature and high pressure conditions, the low-activity surface modifier fully encapsulates the reacted nano-silica, forming a surface layer with better miscibility with mineral oil, ensuring that the hydrophobic nano-silica disperses rapidly in the mineral oil without forming agglomerates. After the reaction, excess alcohol byproducts and moisture adsorbed on the surface and pores of the nano-silica are largely removed by nitrogen gas through a pressure relief valve during the pressure relief process. However, a small amount of byproducts and moisture remain in the pores, which are completely removed by vacuuming.

[0012] The preparation method of the present invention improves the dispersibility, defoaming and foam suppression performance, and anti-settling ability of hydrophobic nano-silica in mineral oil defoamers by selecting modifiers and hydrophobic modification process of hydrophilic nano-silica, while minimizing the generation of by-products.

[0013] Furthermore, the specific surface area of ​​hydrophilic nano-silica is 130–150 m². 2 / g.

[0014] Furthermore, the oil absorption value of hydrophilic nano-silica is 2.40–2.60 cm⁻¹. 3 / g.

[0015] As described above, excessively high specific surface area and oil absorption value are detrimental to the dispersion of modified silica in mineral oil and easily lead to hard sedimentation. Therefore, the specific surface area of ​​hydrophilic nano-silica is limited to 130–150 m². 2 / g, oil absorption value 2.40~2.60cm 3 / g.

[0016] Furthermore, the reaction process is carried out in a reactor equipped with a stirrer, with a stirring rate of 30–35 r / min.

[0017] Furthermore, the agitator is either a frame agitator or a spiral agitator.

[0018] Furthermore, the heating activation temperature is 100–130°C, and the time is 30–70 min.

[0019] Preferably, the temperature for heating activation is 100–110°C and the time is 60–70 min.

[0020] As can be seen from the above description, the hydrophilic nano-silica is fully activated into a fluid at a certain temperature to ensure that the surface modifier and the hydrophilic nano-silica are fully mixed after atomization.

[0021] Furthermore, highly reactive surface modifiers include siloxanes and / or silane coupling agents, while low-reactive surface modifiers include hydroxyl-terminated polydimethyl silicone oil and / or polydimethyl silicone oil.

[0022] Furthermore, the mass ratio of the highly active surface modifier to the low-activity surface modifier is 0.1 to 1:1.

[0023] Preferably, the mass ratio of the highly active surface modifier to the low-activity surface modifier is 0.25 to 0.5:1.

[0024] As can be seen from the above description, highly active surface modifiers help improve the stratification, anti-settling properties and foam suppression of hydrophobic silica in mineral oil defoamers, while low-active surface modifiers help improve the dispersion and defoaming properties of hydrophobic silica in mineral oil defoamers. When the two are in a suitable ratio, excellent dispersion, stratification, anti-settling defoaming and foam suppression properties can be obtained simultaneously.

[0025] Furthermore, the mass ratio of the surface modifier to the hydrophilic nano-silica is 0.05 to 0.2:1.

[0026] As can be seen from the above description, if the content of surface modifier is too low, the hydrophobic nano silica is difficult to disperse and easily settles in the mineral oil defoamer; if the content is too high, there will be too much organic matter on the surface, and the defoaming and foam-suppressing performance of the hydrophobic nano silica in the mineral oil defoamer will be poor.

[0027] Furthermore, the sealed mixing reaction is specifically carried out as follows: the mixture is sealed at 100-130°C for 30-40 minutes, and then the temperature is raised to 200-400°C for 2-5 hours. During the reaction, the pressure is controlled at 0.1-0.6 MPa.

[0028] Preferably, the sealed mixing reaction is carried out by: sealing and mixing at 100-130°C for 30-40 minutes, and then raising the temperature to 300-400°C for 3-4 hours, with the pressure controlled at 0.3-0.4 MPa during the reaction.

[0029] As described above, a higher temperature during the reaction process is beneficial for the surface modifier to react with the nano-silica. The reaction temperature affects the hydrophobic modification of the hydrophilic nano-silica by the surface modifier; if the temperature is too low, the reaction rate of highly active surface modifiers is slow, while the coating effect of low-activity surface modifiers is poor, thus affecting the various properties of the hydrophobic nano-silica in mineral oil defoamers.

[0030] Furthermore, the vacuuming process specifically involves evacuating at a negative pressure of -0.03 to -0.08 MPa for 30 to 60 minutes.

[0031] As can be seen from the above description, the purpose of vacuuming is to fully remove the byproducts and moisture adsorbed on and inside the hydrophobic nano-silica surface.

[0032] Another technical solution adopted in this invention is: hydrophobic nano-silica prepared by the above-mentioned method for preparing hydrophobic nano-silica for mineral oil defoamers.

[0033] Example 1 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0034] Step 1: Dissolve 20g of dimethyldiethoxysilane and 80g of polydimethylsiloxane in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0035] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0036] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0037] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 300℃ and the pressure is controlled at 0.3MPa during the reaction. The timing starts when the reaction temperature reaches 300℃ and is maintained for 4 hours before slowly releasing the pressure.

[0038] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0039] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0040] Example 2 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0041] Step 1: Dissolve 40g of dimethyldiethoxysilane and 60g of polydimethylsiloxane in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0042] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0043] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0044] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 300℃ and the pressure is controlled at 0.3MPa during the reaction. The timing starts when the reaction temperature reaches 300℃ and is maintained for 4 hours before slowly releasing the pressure.

[0045] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0046] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0047] Example 3 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0048] Step 1: Dissolve 50g of dimethyldiethoxysilane and 50g of polydimethylsiloxane in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0049] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0050] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0051] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 300℃ and the reaction is carried out. The pressure is controlled at 0.35MPa during the reaction. The timing is started when the reaction temperature reaches 300℃ and maintained for 4 hours before slowly releasing the pressure.

[0052] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0053] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0054] Example 4 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0055] Step 1: Dissolve 20g of dimethyldiethoxysilane and 80g of polydimethylsiloxane in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0056] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0057] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0058] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 200℃ and the pressure is controlled at 0.35MPa during the reaction. When the reaction temperature reaches 300℃, the timing is started and maintained for 4 hours before slowly releasing the pressure.

[0059] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0060] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0061] Comparative Example 1 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0062] Step 1: Dissolve 100g of dimethyldiethoxysilane in 20g of ethanol to prepare a surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0063] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0064] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0065] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 300℃ and the pressure is controlled at 0.3MPa during the reaction. The timing starts when the reaction temperature reaches 300℃ and is maintained for 4 hours before slowly releasing the pressure.

[0066] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0067] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0068] Comparative Example 2 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0069] Step 1: Dissolve 100g of polydimethyl silicone oil in 20g of ethanol to prepare a surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0070] Step 2: 1 kg of material with a specific surface area of ​​150 m² 2 / g, DBP oil absorption value is 2.50cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 32r / min, nitrogen gas was introduced, stirring was started and heating was set to 120℃.

[0071] Step 3: When the material temperature rises to 120℃, start the activation timer for 60 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 40 minutes.

[0072] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 300℃ and the reaction is carried out. The pressure is controlled at 0.3MPa during the reaction. The timing is started when the reaction temperature reaches 150℃ and maintained for 4 hours before slowly releasing the pressure.

[0073] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 50 minutes, with a negative pressure of -0.08 MPa.

[0074] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, ultimately yielding a hydrophobic nano-silica product for mineral oil defoaming. A sample is mixed with mineral oil at a mass ratio of 92:8. A two-blade stirrer is used at a speed of 400 r / min, ensuring complete dispersion of the hydrophobic nano-silica in the mineral oil. The methanol value of the hydrophobic nano-silica, its dispersion in mineral oil, the time to stratification and hard settling, and its defoaming and foam-suppressing properties are tested.

[0075] Table 1 shows the dispersion time, stratification time, hard sedimentation time, defoaming time, and foam suppression properties of the hydrophobic nano-silica used in mineral oil defoamers prepared in Examples 1-4 and Comparative Examples 1-2. The specific methods for defoaming and foam suppression tests are as follows: (1) Dissolve 8g LAS and 2g NP-10 in 1L deionized water to prepare a foaming solution; mix mineral oil and hydrophobic nano-silica at a mass ratio of 92:8, stir with a two-blade stirrer at a speed of 400r / min, and completely disperse the hydrophobic nano-silica in the mineral oil to prepare a mineral oil defoamer; (2) Add 40mL of deionized water to a 200ml stoppered graduated cylinder; (3) Add 2g of foaming solution to the deionized water; (4) After shaking up and down 20 times, add 3 drops of mineral oil defoamer; (5) Record the time when the foam completely disappears, i.e., the defoaming time; (6) After shaking up and down 20 times, record the height of the foam produced, i.e., the foam suppression property.

[0076] Table 1

[0077]

[0078] As shown in Table 1, Examples 1-3 and Comparative Examples 1 and 2 illustrate how the ratio of highly active to low-active surface modifiers affects stratification, dispersion, anti-settling, defoaming, and foam suppression properties. These properties significantly impact the shelf life and performance of mineral oil defoamers, making them crucial parameters. The optimal weight ratio of highly active to low-active surface modifiers is 0.25-1. The comparative examples exhibited poor dispersion, stratification, anti-settling, defoaming, and foam suppression properties, indicating that single modifiers have poor hydrophobic reaction effects and exhibit poor performance in various aspects of mineral oil defoamers.

[0079] Examples 1 and 4 illustrate the effect of reaction temperature on the hydrophobic modification of hydrophilic nano-silica by surface modifiers. When the temperature is too low, the reaction rate of highly active surface modifiers is slow, and the surface modifiers with low activity cannot be fully atomized, resulting in poor coating effect, which affects the various properties of hydrophobic nano-silica in mineral oil defoamers.

[0080] Example 5 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0081] Step 1: Dissolve 9.1g of silane coupling agent and 90.9g of hydroxyl-terminated polydimethyl silicone oil in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0082] Step 2: Take 500g of material with a specific surface area of ​​130m² 2 / g, DBP oil absorption value is 2.60cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a frame-type stirring paddle, the stirring speed was set to 30r / min, nitrogen gas was introduced, stirring was turned on and heating was started, and the temperature was set to 100℃.

[0083] Step 3: When the material temperature rises to 100℃, start the activation timer for 70 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 350 minutes.

[0084] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 400℃ and the pressure is controlled at 0.1MPa during the reaction. The timing starts when the reaction temperature reaches 400℃ and is maintained for 2 hours before slowly releasing the pressure.

[0085] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 30 minutes, with a negative pressure of -0.03 MPa;

[0086] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, and a hydrophobic nano silica product for mineral oil defoamer is finally obtained.

[0087] Example 6 of the present invention is: a method for preparing hydrophobic nano-silica for mineral oil defoamers, the steps of which are as follows:

[0088] Step 1: Dissolve 20g of dimethyldiethoxysilane and 80g of hydroxyl-terminated polydimethylsiloxane in 20g of ethanol to prepare a composite surface modifier solution. Prepare and use immediately, based on the amount needed for the day.

[0089] Step 2: Take 2 kg of material with a specific surface area of ​​140 m² 2 / g, DBP oil absorption value is 2.40cm 3 / g of hydrophilic nano-silica was added to a sealed reactor with a spiral propeller, the stirring speed was set to 35r / min, nitrogen gas was introduced, stirring was started and heating was set to 130℃.

[0090] Step 3: When the material temperature rises to 130℃, start the activation timer for 30 minutes, then spray the prepared surface modifier solution into the reactor through a high-pressure pump and mix in a sealed environment for 30 minutes.

[0091] Step 4: After the vaporized surface modifier and hydrophilic nano silica are fully mixed, the reaction temperature is raised to 200℃ and the pressure is controlled at 0.6MPa during the reaction. When the reaction temperature reaches 300℃, the timing is started and the pressure is slowly released after 5 hours.

[0092] Step 5: After the pressure in the reactor reaches atmospheric pressure, close the pressure relief valve and open the vacuum valve to evacuate the reactor for 60 minutes, with a negative pressure of -0.05 MPa.

[0093] Step 6: After vacuuming, the pressure in the reactor is released to atmospheric pressure, and a hydrophobic nano silica product for mineral oil defoamer is finally obtained.

[0094] Example 7 of the present invention is: hydrophobic nano-silica for mineral oil defoamer prepared by the preparation method of Example 1.

[0095] In summary, the hydrophobic nano-silica for mineral oil defoamers and its preparation method provided by this invention have the following advantages:

[0096] 1. A surface modifier composed of a high-activity surface modifier and a low-activity surface modifier is used to modify hydrophilic nano-silica. This can simultaneously achieve the condensation and encapsulation reaction of silanol groups on the surface of hydrophilic nano-silica, thereby improving the dispersibility, defoaming and foam-suppressing performance of hydrophobic nano-silica in mineral oil defoamers and its anti-settling ability during storage.

[0097] 2. The surface modifier is atomized, and the hydrophilic nano-silica is pre-activated into a fluid to allow for a thorough gas-solid mixing reaction.

[0098] 3. Excess alcohol byproducts and moisture adsorbed on the surface and pores of nano-silica are completely removed by depressurization and vacuuming.

[0099] 4. By controlling the specific surface area and oil absorption value of hydrophilic nano-silica, dispersibility and anti-settling ability can be further improved.

[0100] 5. Using a higher temperature during the modification process is beneficial to the modification reaction.

[0101] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing hydrophobic nano-silica for mineral oil defoamers, characterized in that, Includes the following steps: Hydrophilic nano-silica is activated by heating under nitrogen; then an atomized surface modifier is added, and the mixture is sealed and mixed to carry out the reaction; then, the mixture undergoes a first depressurization, a vacuuming process, and a second depressurization in sequence to obtain hydrophobic nano-silica for mineral oil defoamer; the surface modifier includes a high-activity surface modifier and a low-activity surface modifier; The highly active surface modifier includes a silane coupling agent, and the low-activity surface modifier includes hydroxyl-terminated polydimethyl silicone oil and / or polydimethyl silicone oil. The mass ratio of the highly active surface modifier to the low-activity surface modifier is 0.1 to 1:1; The mass ratio of the surface modifier to hydrophilic nano-silica is 0.05~0.2:1; The sealed mixing reaction is specifically carried out by: sealing and mixing at 100~130℃ for 30~40 minutes, and then raising the temperature to 200~400℃ for 2~5 hours, with the pressure controlled at 0.1~0.6MPa during the reaction.

2. The method for preparing hydrophobic nano-silica for mineral oil defoamer according to claim 1, characterized in that, The specific surface area of ​​the hydrophilic nano-silica is 130~150m². 2 / g.

3. The method for preparing hydrophobic nano-silica for mineral oil defoamer according to claim 1, characterized in that, The hydrophilic nano-silica has an oil absorption value of 2.40~2.60 cm. 3 / g.

4. The method for preparing hydrophobic nano-silica for mineral oil defoamer according to claim 1, characterized in that, The heating activation temperature is 100~130℃, and the time is 30~70min.

5. The method for preparing hydrophobic nano-silica for mineral oil defoamer according to claim 1, characterized in that, The vacuuming process specifically involves evacuating for 30 to 60 minutes at a negative pressure of -0.03 to -0.08 MPa.

6. Hydrophobic nano-silica prepared by the method for preparing mineral oil defoamer according to any one of claims 1-5.

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