Preparation method and application of hydrophobic silicon dioxide

Abstract

The invention belongs to the technical field of silicon dioxide, and discloses a preparation method and application of hydrophobic silicon dioxide, and the method comprises the following steps: pretreating raw materials, selecting silica gel, and carrying out vacuum activation on the silica gel at 150 DEG C for 3 hours; preparing a mixed solvent; preparing a composite silane modifier; in the first stage, the pretreated silica gel is dispersed in a mixed solvent system, a composite silane modifier is slowly dropwise added, and a reaction is performed for 8 hours at the temperature of 50 DEG C; in the second stage, adding triethylamine as a catalyst, heating to 65 DEG C, and continuously reacting for 10 hours; gradient drying; treating with a composite cleaning agent; carrying out post-treatment and modification, and carrying out surface hole sealing treatment; and sealing and packaging in a nitrogen environment. Through a controllable slow-release adsorption technology and multistage surface modification, slow adsorption of water is realized, adsorption heat is effectively reduced, and the service life of silica gel is prolonged; while the high adsorption capacity is maintained, the adsorption rate and adsorption heat are remarkably reduced, and the problem of structural damage caused by adsorption heat of traditional silica gel is effectively solved.

Description

Technical Field

[0001] This application relates to the field of silica technology, and more specifically, to a method for preparing hydrophobic silica and its application. Background Technology

[0002] Throughout the entire lifecycle of petroleum products, a large amount of VOCs are released, which, after reacting with ultraviolet light and ozone, produce significant amounts of acid rain, causing environmental pollution. Besides environmental hazards, this also results in substantial economic losses. For example, the average loss rate for crude oil from refineries to refined product storage tanks is around 2%, while the loss rate for refined products from production to the customer can reach around 3%. Numerous pharmaceutical companies, CRO pharmaceutical enterprises, and organic chemistry laboratories in universities worldwide generate large quantities of organic waste gas. This organic waste gas also poses significant environmental hazards and requires adsorption materials to absorb organic pollutants and reduce their environmental impact.

[0003] The prior art publication CN102198942A discloses a method for preparing precipitated silica, comprising the following steps: preparing sodium silicate solution A; adding sodium silicate solution B, with a SiO2 / Na2O molar ratio of M = 3.40–3.60 and a sodium silicate mass concentration of 22–26%, in stages to a reaction vessel containing sodium silicate solution A at varying rates, while simultaneously controlling the addition rate of concentrated sulfuric acid in each stage to maintain a constant pH of the reaction medium; stopping the addition of sodium silicate solution B, and continuing to add concentrated sulfuric acid to adjust the pH of the material obtained in the previous step to 3.0–4.0, thereby obtaining a precipitated silica suspension. An organic surfactant is added to the suspension obtained in the above steps and the mixture is aged; the suspension is then filtered, washed, dried, and post-treated by pulverization to obtain the precipitated silica product. This method not only overcomes the disadvantage of poor dispersibility of silica in high-temperature vulcanized silicone rubber, but also improves the yellowing properties of the product, increases filtration and washing efficiency, shortens washing time, and saves washing water.

[0004] While the existing technical solutions described above can achieve the relevant beneficial effects through their structures, they still have the following drawbacks: Oil and gas recovery is a direct means of reducing harm and losses. Currently, activated carbon is the most widely used method for oil and gas recovery and collection of organic experimental waste gases. However, activated carbon can overheat after adsorbing large amounts of aldehydes and ketones, posing a fire hazard. Silica, as a commonly used adsorbent material, has advantages over activated carbon, including comparable specific surface area, controllable pore size, excellent thermal conductivity, and non-combustibility. However, silica has a large number of hydroxyl groups on its surface. Therefore, when adsorbing organic waste gases, moisture in the environment will preferentially compete for these hydroxyl groups, thus reducing the adsorption rate. Ordinary silica generates a large amount of heat during rapid water adsorption. Simultaneously, due to the large number of dead pores (non-penetrating pores) in silica, a significant amount of adsorption heat cannot be fully dissipated, causing the silica to break and crumble, forming fine silica powder particles that can clog industrial equipment and affect its operation.

[0005] In view of this, we propose a method for preparing hydrophobic silica and its application. Summary of the Invention

[0006] 1. Technical problems to be solved

[0007] The purpose of this application is to provide a method for preparing hydrophobic silica and its application, which solves the technical problem mentioned in the background art of silica gel cracking and damage caused by excessively rapid adsorption of water. It achieves slow adsorption of water through controllable slow-release adsorption technology and multi-level surface modification, effectively reducing the heat of adsorption and extending the service life of silica gel. While maintaining high adsorption capacity, it significantly reduces the adsorption rate and heat of adsorption, effectively solving the structural damage problem of traditional silica gel caused by the heat of adsorption. This enables hydrophobic silica to exhibit the advantages of high adsorption capacity, resistance to water vapor interference, and long-term stable operation in the recovery of organic waste gas and oil and gas.

[0008] 2. Technical Solution

[0009] This application provides a method for preparing hydrophobic silica, comprising the following steps:

[0010] S1. Raw material pretreatment: Select silica gel with the following parameters: particle size 230-400 mesh, pore size 9nm, and specific surface area 400-600m². 2 / g; Vacuum activation of silica gel at 150℃ for 3 hours removes physically adsorbed moisture from the surface.

[0011] S2, Preparation of mixed solvents:

[0012] S21. Solvent Metering and Premixing: Transfer an ethanol:water ratio of 70:30 (volume ratio) to a stainless steel premixing vessel equipped with a stirrer and a jacketed temperature control. Turn on the anchor stirrer (100-150 rpm), and circulate cooling water through the jacket to maintain the temperature at 20-25°C to prevent solvent evaporation due to exothermic mixing. Premix for 15 minutes to form the base solvent.

[0013] S22. Additive Dissolution: Transfer 20%-30% of the volume of the base solvent from the premixing vessel to the main reactor and start stirring (increasing the speed to 180-220 rpm). Slowly add polyethylene glycol (PEG-400) at a rate of 5-10 g / min, while simultaneously monitoring the particle size distribution of the solution in real time using a laser particle size analyzer. After the PEG-400 is completely dissolved and the average particle size stabilizes below 1 μm, pump the remaining base solvent from the premixing vessel into the main reactor at a uniform rate through a pipeline, and continue stirring for 15 minutes to form a homogeneous and stable mixed solvent system.

[0014] S3. Preparation of composite silane modifier: The silane combination is a mixture of sodium trimethylsilanolate (60%) and trimethylmethoxysilane (40%); optionally, the silanes may also be trimethylsilanol, sodium dimethyldisilicate, and dimethyldisilicate, etc.

[0015] S31. Silane ratio: After weighing, transfer the two silane reagents to a glass container with a sealed lid, and use a vortex shaker to mix for 5 minutes to make the two initially evenly mixed.

[0016] S32. Enhanced Dissolution Process: The mixed silane reagent is slowly added to the mixed solvent system using a peristaltic pump at a rate of 2-5 mL / min. During dissolution at 40℃, a magnetic stirrer is used at a speed of 200-250 rpm, while nitrogen gas is introduced for protection at a flow rate of 50-100 mL / min. Samples are taken every 15 minutes, and the dissolution status of the silane reagent is detected using Fourier Transform Infrared Spectroscopy (FT-IR). Dissolution is considered complete when the intensity of the characteristic absorption peak of silane no longer changes. The dissolution time is 60-90 minutes, yielding the composite silane modifier.

[0017] S4, multi-level surface modification reaction:

[0018] First stage: Disperse the pretreated silica gel in a mixed solvent system, slowly add the composite silane modifier, and react at 50°C for 8 hours; preferably, control the addition amount according to the ratio of 100g silica gel: 800-1000ML mixed solvent system: 5-10g composite silane modifier;

[0019] Second stage: Add 0.1% (mass fraction) of triethylamine as a catalyst, heat to 65℃ and continue the reaction for 10 hours; obtain hydrophobic silica;

[0020] Reaction control: The stability of the reaction system is maintained by nitrogen protection and mechanical stirring.

[0021] S5, Gradient Drying:

[0022] Preliminary drying: After the reaction is complete, the hydrophobic silica is dried under vacuum at 120°C for 24 hours;

[0023] Gradient heating: Increase the temperature to 135℃ at a rate of 5℃ / hour, and continue drying for 12 hours;

[0024] Cooling treatment: Allow to cool naturally to room temperature to avoid structural stress caused by a sudden drop in temperature.

[0025] S6. Treatment with composite cleaning agents:

[0026] First cleaning: Clean with methanol:water = 80:20 (volume ratio) until pH value reaches 7.0-7.5;

[0027] Second cleaning: Clean with pure methanol to remove residual impurities;

[0028] Cleaning control: Centrifugation is performed after each cleaning to ensure cleaning effectiveness;

[0029] S7. Post-processing and modification:

[0030] Secondary drying: Vacuum drying at 100℃ for 8 hours;

[0031] Surface sealing: A small amount of hexamethyldisilazane (HMDS) vapor is introduced to perform surface sealing treatment;

[0032] Finished product packaging: Sealed packaging in a nitrogen atmosphere to prevent moisture absorption.

[0033] The hydrophobic silica prepared by the above technical solution and method can be used for organic waste gas recovery, water pollution treatment, and oil and gas recovery. It efficiently adsorbs non-polar organic compounds such as benzene, toluene, and gasoline vapor, achieving a recovery rate of over 98% in gas station oil and gas recovery devices. It can adsorb 20-30 times its own weight in diesel and engine oil, and its hydrophobic surface does not absorb water, facilitating subsequent recovery.

[0034] As an optional embodiment of the present invention, in step S1, a vacuum drying oven with programmed temperature control is used for silica gel activation. The equipment has a real-time vacuum monitoring and adjustment function to ensure that the vacuum level is maintained at 0.1-1 Pa during the activation process. During the activation process at 150°C, the temperature and vacuum level data inside the drying oven are recorded every 30 minutes. If the temperature fluctuation exceeds ±2°C or the vacuum level deviates from the set value by more than 10%, the compensation adjustment mechanism is automatically activated. After activation, a dew point meter is used to detect the residual moisture content on the silica gel surface. The residual moisture content must be below 0.1% before proceeding to the next process.

[0035] Furthermore, in step S4, the reaction is carried out in a glass reactor equipped with a reflux condenser, pressure sensor, online oxygen analyzer, temperature sensor, pH meter, and nitrogen inlet. The reactor is equipped with a mechanical stirrer using a paddle-type stirrer, with the stirring speed adjustable within the range of 150-250 rpm via a variable frequency motor. The temperature sensor has an accuracy of ±0.5℃, monitoring the reaction temperature in real time and feeding back to the temperature control system to ensure that the reaction temperature is controlled within ±1℃ of the set value. The pressure inside the reactor is maintained at 0.105-0.11 MPa (gauge pressure approximately 5-10 kPa). Real-time monitoring via a pressure sensor at the top of the reactor ensures a balance between the nitrogen inlet and outlet flow rates.

[0036] In the first stage of the reaction, a peristaltic pump is used to slowly add the silane solution dropwise into the reactor containing pretreated silica gel. The dropping rate is adjusted according to the adsorption rate of the silica gel, generally controlled at 3-5 mL / min. The nitrogen flow rate is controlled at 80-100 mL / min (higher flow rate). In the initial stage of silane addition, the silanol groups (Si-OH) in the system are highly reactive and readily react with moisture. The high flow rate of nitrogen can quickly remove residual moisture from the system, preventing silane hydrolysis and condensation that could lead to aggregation. During the reaction, samples are taken every hour, and thermogravimetric analysis (TGA) is used to detect the amount of silane modification on the silica gel surface. When the modification amount reaches 60-70% of the target value, the second stage of the reaction begins.

[0037] In the second stage, after adding the triethylamine catalyst, the heating rate was controlled at 1-2℃ / min. During the heating process, the pH of the reaction system was continuously monitored to ensure it remained within the range of 8-9. After the reaction, the surface morphology of the silica gel was observed using a scanning electron microscope (SEM) to ensure uniform coverage of the silane-modified layer without localized agglomeration. The nitrogen flow rate was controlled at 50-70 mL / min (lower flow rate). After heating to 65℃, the moisture in the system was largely eliminated, and the reaction rate between the silane and the silica gel surface accelerated.

[0038] A comprehensive parameter correlation model is constructed to dynamically adjust the parameters during the reaction process: The comprehensive parameter correlation model is as follows:

[0039] M = k1e-[Ea / RT] [1-e-(QN2×t / V)]×f(pH)×g(P);

[0040] f(pH) = 1 + k2(pH-8); g(P) = P / P0; where M is the amount of silane modification, the mass of silane grafted onto the silica gel surface / the total mass of silica gel, which can be measured by TGA thermogravimetric analysis; T is the reaction temperature, which needs to be converted to absolute temperature for calculation. QN2 is the nitrogen flow rate, t is the reaction time; V is the volume of the reactor, determined according to the actual equipment specifications; P is the pressure inside the reactor; pH is the pH value of the reaction system; k1 is the comprehensive reaction rate constant, an empirical coefficient calibrated through experiments, which is related to the characteristics of silica gel, silane concentration, etc.; Ea is the activation energy of the reaction, the activation energy of the silane modification reaction, which needs to be fitted by the reaction rate at different temperatures (Arrhenius equation); R is the gas constant, a fixed value of 8.314 J / (mol·K). f(pH) is the pH catalytic function, k2 is the pH influence coefficient; g(P) is the pressure correction function, P0 = 0.1 MPa (standard atmospheric pressure), correcting the effect of pressure on gas solubility.

[0041] The impact of each parameter on the silane modification effect was quantitatively evaluated using a comprehensive parameter correlation model.

[0042] As an optional embodiment of the present invention, in step S5, a vacuum drying oven with programmable temperature control is used for gradient drying. The drying oven needs to have segmented heating, holding, and cooling functions. In the initial drying stage, the vacuum degree is set to 0.1-1 Pa, the temperature is 120°C, and the holding time is 24 hours. During this process, the temperature, vacuum degree, and sample mass change data in the drying oven are recorded every hour.

[0043] During the gradient heating phase, the temperature was increased to 135℃ at a rate of 5℃ / hour, while maintaining a stable vacuum level throughout the heating process. After heating, the sample was dried at 135℃ for another 12 hours. Samples were taken every 2 hours during the drying process, and the specific surface area and pore size changes were detected using a surface area and porosity analyzer (BET) to ensure that the drying process did not damage the pore structure of the silica gel.

[0044] During the cooling process, the heating power should be turned off, and the sample should be allowed to cool naturally to room temperature. A vacuum should be maintained during cooling to prevent external moisture from entering. After cooling, the moisture content of the sample should be measured using a moisture analyzer, and the moisture content should be below 0.5% by mass.

[0045] As an optional embodiment of the present invention, in step S6, the cleaning process is carried out in a stainless steel cleaning tank equipped with a stirring device. A paddle-type stirring blade is used, and the rotation speed is controlled at 80-120 rpm. For the first cleaning, a cleaning solution is prepared by mixing methanol and water at a ratio of 80:20 (volume ratio), with the volume of the cleaning solution being 3-5 times the volume of the silica gel. The dried silica gel is added to the cleaning solution, and the mixture is stirred and cleaned for 30-60 minutes. The pH value of the cleaning solution is monitored in real time using pH test paper or a pH meter. When the pH value reaches 7.0-7.5, stirring is stopped, and centrifugation is performed at a speed of 3000-4000 rpm for 5-10 minutes.

[0046] The second cleaning uses pure methanol, and the cleaning steps are the same as the first, but the cleaning time can be shortened to 15-30 minutes. After cleaning, the silica gel is centrifuged again, and then transferred to a vacuum drying oven for preliminary drying at 50-60℃ to remove most of the residual methanol. The drying time is 2-3 hours.

[0047] Gas chromatography-mass spectrometry (GC-S) was used to detect residual impurities on the silica gel surface after cleaning, with a focus on detecting the residual amounts of silane reagents, additives, and solvents, requiring the total residual amount to be below 100 ppm. Simultaneously, infrared spectroscopy was used to detect changes in functional groups on the silica gel surface to ensure that the cleaning process did not damage the hydrophobic modification layer on the silica gel surface.

[0048] As an optional solution of the present invention, in step S7, a vacuum drying oven is used for secondary drying, with the temperature set at 100°C, the vacuum degree at 0.1-1 Pa, and the drying time at 8 hours. The sample mass change is recorded once every hour during the drying process, and the drying is considered complete when the sample mass no longer changes.

[0049] Surface sealing treatment was carried out in a vacuum reactor equipped with a gas inlet device. The dried silica gel was placed in the reactor, and a vacuum of 0.1-1 Pa was applied. Then, hexamethyldisilazane (HMDS) vapor was introduced at a flow rate of 10-20 mL / min. The reaction temperature was controlled at 80-90℃, and the reaction time was 60-90 minutes. After the reaction was completed, the HMDS vapor inlet was stopped, and the vacuum was maintained for another 30 minutes to remove any residual HMDS vapor.

[0050] 3. Beneficial effects

[0051] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0052] 1. This invention achieves slow adsorption of moisture through controlled slow-release adsorption technology and multi-level surface modification, effectively reducing adsorption heat and extending the service life of silica gel.

[0053] 2. The hydrophobic silica of the present invention maintains high adsorption capacity while significantly reducing adsorption rate and adsorption heat, effectively solving the structural damage problem caused by adsorption heat in traditional silica gel, and has broad application prospects.

[0054] 3. Hydrophobic silica exhibits advantages such as high adsorption capacity, resistance to water vapor interference, and long-term stable operation in the recovery of organic waste gas and oil and gas, making it particularly suitable for industrial scenarios with high humidity and complex composition, thereby reducing operating costs. Attached Figure Description

[0055] Figure 1 The curve showing the change in average pore size before and after silica modification in the method for preparing hydrophobic silica disclosed in a preferred embodiment of this application.

[0056] Figure 2 The curve showing the change in water adsorption capacity of modified silica gel as a function of bonding amount in the preparation method of hydrophobic silica disclosed in a preferred embodiment of this application.

[0057] Figure 3 This is a schematic diagram of the weighing mechanism of the hydrophobic silica preparation system disclosed in a preferred embodiment of this application;

[0058] Figure 4 This is a schematic diagram of the rotation drive structure of the hydrophobic silica preparation system disclosed in a preferred embodiment of this application;

[0059] Figure 5 This is a schematic diagram of the adjustment mechanism of the hydrophobic silica preparation system disclosed in a preferred embodiment of this application;

[0060] Figure 6 This table shows the cracking of silica spheres after silicone modification in a preferred embodiment of the method for preparing hydrophobic silica disclosed in this application. Detailed Implementation

[0061] The present application will be further described in detail below with reference to the accompanying drawings.

[0062] Reference Figure 1 This application provides a method for preparing hydrophobic silica, comprising the following steps:

[0063] S1. Raw material pretreatment: Select silica gel with the following parameters: particle size 230-400 mesh (approximately 40-63μm), pore size 9nm, and specific surface area 400-600m². 2 / g; preferably, use Bonkai's self-made silica gel. The silica gel is vacuum activated at 150℃ for 3 hours to remove physically adsorbed moisture from the surface.

[0064] S2, Preparation of mixed solvents:

[0065] S21. Solvent Metering and Premixing: Ethanol and water are metered using a high-precision mass flow meter (accuracy ±0.1%). The ethanol:water ratio of 70:30 (volume ratio) is separately delivered to a stainless steel premixing vessel equipped with a stirrer and jacketed temperature control. The anchor-type stirrer is turned on (speed 100-150 rpm), and circulating cooling water is introduced into the jacket to control the temperature at 20-25℃ to prevent solvent evaporation due to exothermic mixing. Premix for 15 minutes to form the base solvent.

[0066] S22. Additive Dissolution: Transfer 20%-30% of the volume of the base solvent from the premixing vessel to the main reactor and start stirring (increasing the speed to 180-220 rpm). Slowly add polyethylene glycol (PEG-400) at a rate of 5-10 g / min, while simultaneously monitoring the particle size distribution of the solution in real time using a laser particle size analyzer. After the PEG-400 is completely dissolved and the average particle size stabilizes below 1 μm, pump the remaining base solvent from the premixing vessel into the main reactor at a uniform rate through a pipeline, and continue stirring for 15 minutes to form a homogeneous and stable mixed solvent system.

[0067] S3. Preparation of composite silane modifier: The silane combination is a mixture of sodium trimethylsilanolate (60%) and trimethylmethoxysilane (40%); optionally, the silanes may also be trimethylsilanol, sodium dimethyldisilicate, and dimethyldisilicate, etc.

[0068] S31. Silane ratio: The weighing of sodium trimethylsilanolate and trimethylmethoxysilane is performed using an electronic balance with an accuracy of 0.01% in a fume hood to prevent the silane reagents from becoming damp and deteriorating. After weighing, the two silane reagents are transferred to a glass container with a sealed lid and mixed using a vortex mixer for 5 minutes to ensure initial homogeneity.

[0069] S32. Enhanced Dissolution Process: The mixed silane reagent is slowly added to the mixed solvent system using a peristaltic pump at a rate of 2-5 mL / min. During dissolution at 40℃, a magnetic stirrer is used at a speed of 200-250 rpm, while nitrogen gas is introduced for protection at a flow rate of 50-100 mL / min. Samples are taken every 15 minutes, and the dissolution status of the silane reagent is detected using Fourier Transform Infrared Spectroscopy (FT-IR). Dissolution is considered complete when the intensity of the characteristic absorption peak of silane no longer changes. The dissolution time is 60-90 minutes, yielding the composite silane modifier.

[0070] S4, multi-level surface modification reaction:

[0071] First stage: Disperse the pretreated silica gel in a mixed solvent system, slowly add the composite silane modifier, and react at 50°C for 8 hours; preferably, control the addition amount according to the ratio of 100g silica gel: 800-1000ML mixed solvent system: 5-10g composite silane modifier;

[0072] Second stage: Add 0.1% (mass fraction) of triethylamine as a catalyst, heat to 65℃ and continue the reaction for 10 hours; obtain hydrophobic silica;

[0073] Reaction control: The stability of the reaction system is maintained by nitrogen protection and mechanical stirring.

[0074] S5, Gradient Drying:

[0075] Preliminary drying: After the reaction is complete, the hydrophobic silica is dried under vacuum at 120°C for 24 hours;

[0076] Gradient heating: Increase the temperature to 135℃ at a rate of 5℃ / hour, and continue drying for 12 hours;

[0077] Cooling treatment: Allow to cool naturally to room temperature to avoid structural stress caused by a sudden drop in temperature.

[0078] S6. Treatment with composite cleaning agents:

[0079] First cleaning: Clean with methanol:water = 80:20 (volume ratio) until pH value reaches 7.0-7.5;

[0080] Second cleaning: Clean with pure methanol to remove residual impurities;

[0081] Cleaning control: Centrifugation is performed after each cleaning to ensure cleaning effectiveness;

[0082] S7. Post-processing and modification:

[0083] Secondary drying: Vacuum drying at 100℃ for 8 hours;

[0084] Surface sealing: A small amount of hexamethyldisilazane (HMDS) vapor is introduced to perform surface sealing treatment;

[0085] Finished product packaging: Sealed packaging in a nitrogen atmosphere to prevent moisture absorption.

[0086] Reference Figure 1 The average pore size change curves largely overlap before and after modification, with no significant change. Therefore, there is no significant change in pore size data before and after modification.

[0087] In this technical solution, the hydrophobic silica prepared by the above method is used for organic waste gas recovery, water pollution treatment, and oil and gas recovery. It efficiently adsorbs non-polar organic compounds such as benzene, toluene, and gasoline vapor, achieving a recovery rate of over 98% in gas station oil and gas recovery devices. It can adsorb 20-30 times its own weight in diesel and engine oil, and its hydrophobic surface does not absorb water, facilitating subsequent recovery.

[0088] Furthermore, in step S1, a vacuum drying oven with programmed temperature control is used to activate the silica gel. The equipment has real-time vacuum monitoring and adjustment capabilities to ensure that the vacuum level is maintained between 0.1 and 1 Pa during the activation process. During activation at 150°C, the temperature and vacuum level data inside the drying oven are recorded every 30 minutes. If the temperature fluctuation exceeds ±2°C or the vacuum level deviates from the set value by more than 10%, the compensation and adjustment mechanism is automatically activated. After activation, a dew point meter is used to detect the residual moisture content on the silica gel surface. The residual moisture content must be below 0.1% before proceeding to the next process.

[0089] Furthermore, in step S4, the reaction is carried out in a glass reactor equipped with a reflux condenser, pressure sensor, online oxygen analyzer, temperature sensor, pH meter, and nitrogen inlet. The reactor is equipped with a mechanical stirrer using a paddle-type stirrer, with the stirring speed adjustable within the range of 150-250 rpm via a variable frequency motor. The temperature sensor has an accuracy of ±0.5℃, monitoring the reaction temperature in real time and feeding back to the temperature control system to ensure that the reaction temperature is controlled within ±1℃ of the set value. The pressure inside the reactor is maintained at 0.105-0.11 MPa (gauge pressure approximately 5-10 kPa). Real-time monitoring via a pressure sensor at the top of the reactor ensures a balance between the nitrogen inlet and outlet flow rates.

[0090] In the first stage of the reaction, a peristaltic pump is used to slowly add the silane solution dropwise into the reactor containing pretreated silica gel. The dropping rate is adjusted according to the adsorption rate of the silica gel, generally controlled at 3-5 mL / min. The nitrogen flow rate is controlled at 80-100 mL / min (higher flow rate). In the initial stage of silane addition, the silanol groups (Si-OH) in the system are highly reactive and readily react with moisture. The high flow rate of nitrogen can quickly remove residual moisture from the system, preventing silane hydrolysis and condensation that could lead to aggregation. During the reaction, samples are taken every hour, and thermogravimetric analysis (TGA) is used to detect the amount of silane modification on the silica gel surface. When the modification amount reaches 60-70% of the target value, the second stage of the reaction begins.

[0091] In the second stage, after adding the triethylamine catalyst, the heating rate was controlled at 1-2 °C / min. During the heating process, the pH of the reaction system was continuously monitored to ensure it remained within the range of 8-9. After the reaction, the surface morphology of the silica gel was observed using a scanning electron microscope (SEM) to ensure uniform coverage of the silane modification layer without localized agglomeration. The nitrogen flow rate was controlled at 50-70 mL / min (lower flow rate). After heating to 65 °C, the moisture in the system was largely eliminated, and the reaction rate between the silane and the silica gel surface accelerated. At this point, reducing the flow rate could decrease the heat carried away by the gas and solvent evaporation, maintaining the stability of the reaction temperature.

[0092] A comprehensive parameter correlation model is constructed to dynamically adjust the parameters during the reaction process: The comprehensive parameter correlation model is as follows:

[0093] M = k1e -[Ea / RT] [1-e-(QN2×t / V)]×f(pH)×g(P);

[0094] f(pH) = 1 + k2(pH-8); g(P) = P / P0; where M is the amount of silane modification, the mass of silane grafted onto the silica gel surface / the total mass of silica gel, which can be measured by TGA thermogravimetric analysis; T is the reaction temperature, which needs to be converted to absolute temperature for calculation. QN2 is the nitrogen flow rate, t is the reaction time; V is the volume of the reactor, determined according to the actual equipment specifications; P is the pressure inside the reactor; pH is the pH value of the reaction system; k1 is the comprehensive reaction rate constant, an empirical coefficient calibrated through experiments, which is related to the characteristics of silica gel, silane concentration, etc.; Ea is the activation energy of the reaction, the activation energy of the silane modification reaction, which needs to be fitted by the reaction rate at different temperatures (Arrhenius equation); R is the gas constant, a fixed value of 8.314 J / (mol·K). f(pH) is the pH catalytic function, k2 is the pH influence coefficient; g(P) is the pressure correction function, P0 = 0.1 MPa (standard atmospheric pressure), correcting the effect of pressure on gas solubility.

[0095] The impact of each parameter on the silane modification effect was quantitatively evaluated using a comprehensive parameter correlation model.

[0096] Furthermore, in step S5, a vacuum drying oven with programmable temperature control is used for gradient drying. The drying oven must have segmented heating, holding, and cooling functions. In the initial drying stage, the vacuum degree is set to 0.1-1 Pa, the temperature is 120℃, and the holding time is 24 hours. During this process, the temperature, vacuum degree, and sample mass change data inside the drying oven are recorded every hour.

[0097] During the gradient heating phase, the temperature was increased to 135℃ at a rate of 5℃ / hour, while maintaining a stable vacuum level throughout the heating process. After heating, the sample was dried at 135℃ for another 12 hours. Samples were taken every 2 hours during the drying process, and the specific surface area and pore size changes were detected using a surface area and porosity analyzer (BET) to ensure that the drying process did not damage the pore structure of the silica gel.

[0098] During the cooling process, the heating power should be turned off, and the sample should be allowed to cool naturally to room temperature. A vacuum should be maintained during cooling to prevent external moisture from entering. After cooling, the moisture content of the sample should be measured using a moisture analyzer, and the moisture content should be below 0.5% by mass.

[0099] Furthermore, in step S6, the cleaning process is carried out in a stainless steel cleaning tank equipped with a stirring device. A paddle-type stirring blade is used, and the rotation speed is controlled at 80-120 rpm. For the first cleaning, a cleaning solution is prepared by mixing methanol and water at a ratio of 80:20 (volume ratio), with the volume of the cleaning solution being 3-5 times the volume of the silica gel. The dried silica gel is added to the cleaning solution, and the mixture is stirred and cleaned for 30-60 minutes. The pH value of the cleaning solution is monitored in real time using pH test paper or a pH meter. When the pH value reaches 7.0-7.5, stirring is stopped, and centrifugation is performed at a speed of 3000-4000 rpm for 5-10 minutes.

[0100] The second cleaning uses pure methanol, and the cleaning steps are the same as the first, but the cleaning time can be shortened to 15-30 minutes. After cleaning, the silica gel is centrifuged again, and then transferred to a vacuum drying oven for preliminary drying at 50-60℃ to remove most of the residual methanol. The drying time is 2-3 hours.

[0101] Gas chromatography-mass spectrometry (GC-S) was used to detect residual impurities on the silica gel surface after cleaning, with a focus on detecting the residual amounts of silane reagents, additives, and solvents, requiring the total residual amount to be below 100 ppm. Simultaneously, infrared spectroscopy was used to detect changes in functional groups on the silica gel surface to ensure that the cleaning process did not damage the hydrophobic modification layer on the silica gel surface.

[0102] Furthermore, in step S7, a vacuum drying oven is used for the secondary drying, with the temperature set at 100℃, the vacuum degree at 0.1-1Pa, and the drying time at 8 hours. The sample mass change is recorded once every hour during the drying process, and the drying is considered complete when the sample mass no longer changes.

[0103] Surface sealing treatment was carried out in a vacuum reactor equipped with a gas inlet device. The dried silica gel was placed in the reactor, and a vacuum of 0.1-1 Pa was applied. Then, hexamethyldisilazane (HMDS) vapor was introduced at a flow rate of 10-20 mL / min. The reaction temperature was controlled at 80-90℃, and the reaction time was 60-90 minutes. After the reaction was completed, the HMDS vapor inlet was stopped, and the vacuum was maintained for another 30 minutes to remove any residual HMDS vapor.

[0104] The hydrophobic properties of hydrophobic silica were tested using a contact angle meter, requiring a static contact angle greater than 120°. Simultaneously, adsorption performance was tested at 25°C and 60% relative humidity, measuring its adsorption capacity for water vapor, with a requirement that the adsorption capacity over 24 hours not exceed 5% (mass fraction).

[0105] The packaging process takes place in a nitrogen-protected glove box, using aluminum foil bags as the packaging material. Before packaging, nitrogen is injected into the aluminum foil bags to replace the air inside, and then the hydrophobic silica is quickly filled into the bags and sealed for storage. Each batch of products comes with a detailed test report, including raw material information, manufacturing process parameters, and various performance test data.

[0106] Reference Figure 2 , Figure 3 , Figure 4 and Figure 5 The hydrophobic silica obtained by the technical solution of this application was analyzed through specific experiments:

[0107] Example 1: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.1 g of sodium trimethylsilanolate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, stir for 14-16 h, after the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, after the packing material has cooled, take it out, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0108] Example 2: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.2 g of sodium trimethylsilanolate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, stir for 14-16 h, after the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, after the packing material has cooled, take it out, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0109] Example 3: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.3 g of sodium trimethylsilanolate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, stir for 14-16 h, after the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, after the packing material is cooled, take it out, wash it with methanol 3 times each time (30 mL), and dry the packing material under vacuum at 100 °C.

[0110] Example 4: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.4 g of sodium trimethylsilanolate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, stir for 14-16 h, after the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, after the packing material has cooled, take it out, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0111] Example 5: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.5 g of sodium trimethylsilanolate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, stir for 14-16 h, after the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, after the packing material has cooled, take it out, wash it with methanol 3 times each time (30 mL), and vacuum dry the packing material at 100 °C.

[0112] Example 6: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.1 g of trimethylsilanol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7-7.5, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 115 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0113] Example 7: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.2 g of trimethylsilanol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7-7.5, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 115 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0114] Example 8: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.3 g of trimethylsilanol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7-7.5, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 115 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0115] Example 9: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.4 g of trimethylsilanol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7-7.5, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 115 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0116] Example 10: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.5 g of trimethylsilanol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7-7.5, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 115 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0117] Example 11: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.5 g of trimethylmethoxysilane to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7.5-8, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0118] Example 12: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.5 g of sodium dimethyldisiloxate to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7.5-8, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0119] Example 13: Add 40 mL of anhydrous ethanol to a 100 mL three-necked flask, add 10 g of silica gel to the three-necked flask, add 0.5 g of dimethyldisilol to the three-necked flask, adjust the stirring speed to between 100-250 r / min, adjust and maintain the pH value at 7.5-8, stir for 14-16 h. After the reaction time is completed, filter the packing material through a G2 sintered glass funnel, dry the packing material in an oven at 110 °C under vacuum for 36 h, remove the packing material after cooling, wash it three times with 30 mL of methanol each time, and then vacuum dry the packing material at 100 °C.

[0120] The experimental results are shown in Appendix 1, Appendix 2 and Appendix 3.

[0121] In the above embodiments, the silica gel used was self-made by Bangkai, with silica gel parameters of particle size 230-400 and pore size of 9nm. All reagents used in the reaction were industrial grade reagents.

[0122] Results analysis:

[0123] 1. The effect of silane dosage on performance:

[0124] Hydrophobic properties: With the increase of sodium trimethylsilanolate and trimethylsilane, the static contact angle was significantly improved. The contact angle of Example 5 (0.5g sodium trimethylsilanolate) reached 138°, which was 35.3% higher than that of Example 1 (0.1g). This shows that increasing the amount of silane can effectively improve the surface hydrophobic layer coverage and reduce the water adsorption rate.

[0125] Adsorption performance: The amount of water vapor adsorbed over 24 hours decreased with the increase of silane dosage. The adsorption amount in Example 5 was only 0.8%, demonstrating the significant effect of hydrophobic modification on slowing down water adsorption.

[0126] 2. Effect of silane type on performance: The sample modified with trimethylmethoxysilane (Example 11) had a contact angle of 130° and an adsorption capacity of 4.8%, which was better than that of sodium dimethyldisilol (Example 12) and dimethyldisilol (Example 13). This indicates that the methoxy group in the silane molecule structure is more conducive to the formation of a dense hydrophobic layer.

[0127] 3. Changes in structural parameters: Specific surface area and pore size decrease with increasing degree of silane modification; for example, the specific surface area in Example 5 decreased to 315 m². 2 / g, the pore size shrinks to 8.4nm. This is due to the deposition of silane molecules on the surface of the silica gel pores, resulting in a reduction in effective pore volume, but it is still maintained within a reasonable range to ensure adsorption performance.

[0128] 4. Positive correlation between bond density and fracture resistance: Refer to Figure 2 and Figure 6 ,

[0129] Low bonded phase content (1% to 2%): The surface modification of silica gel is insufficient, leaving a large number of hydrophilic hydroxyl groups. After absorbing water, the internal stress is generated due to volume expansion, which leads to particle breakage.

[0130] High bonded phase content (≥3%): Organic modifiers fully cover the surface of silica gel, hydrophilic groups are replaced by hydrophobic groups, water absorption capacity is significantly reduced, and the modified layer enhances structural strength to prevent cracking.

[0131] Conclusion: When the amount of sodium trimethylsilanolate is 0.5 g, the prepared hydrophobic silica achieves a static contact angle of 138° and a water vapor adsorption capacity of only 2.8% after 24 hours, exhibiting the best overall performance. Among different silane types, trimethylmethoxysilane shows the best modification effect and can be used as the preferred silane reagent.

[0132] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing hydrophobic silica, characterized in that, Includes the following steps: S1. Raw material pretreatment: Select silica gel with the following parameters: particle size 230-400 mesh, pore size 9nm, and specific surface area 400-600m². 2 / g; Vacuum activation of silica gel at 150℃ for 3 hours; S2, preparation of mixed solvents; S3, Preparation of composite silane modifier; S4. Multi-stage surface modification reaction: In the first stage, the pretreated silica gel is dispersed in a mixed solvent system, and a composite silane modifier is slowly added dropwise. The reaction is carried out at 50°C for 8 hours. In the second stage, 0.1% triethylamine is added as a catalyst, and the temperature is raised to 65°C to continue the reaction for 10 hours to obtain hydrophobic silica. S5. Gradient drying: Dry the hydrophobic silica under vacuum at 120°C for 24 hours; then raise the temperature to 135°C at a rate of 5°C / hour and continue drying for 12 hours; then cool naturally to room temperature. S6. Compound cleaning agent treatment: The first cleaning uses a volume ratio of methanol:water = 80:20 to clean until the pH value is 7.0-7.5; the second cleaning uses pure methanol to remove residual impurities; centrifugation is performed after each cleaning to ensure the cleaning effect; S7. Post-treatment and modification: Secondary drying at 100℃ under vacuum for 8 hours; a small amount of hexamethyldisilazane vapor is introduced for surface sealing treatment; sealed and packaged under nitrogen atmosphere.

2. The method for preparing hydrophobic silica according to claim 1, characterized in that: Step S2 includes the following steps: S21. Solvent metering and premixing: Ethanol:water = 70:30 by volume is delivered to a stainless steel premixing vessel equipped with a stirrer and jacket temperature control; the anchor stirrer is turned on at a speed of 100-150 rpm, and the jacket is circulated with cooling water to control the temperature at 20-25℃. The premixing is carried out for 15 minutes to form the base solvent. S22. Additive Dissolution: Transfer 20%-30% of the volume of the base solvent in the premixing vessel to the main reactor, start stirring, and increase the speed to 180-220 rpm; slowly add polyethylene glycol at a rate of 5-10 g / min. After the polyethylene glycol is completely dissolved and the average particle size is stable below 1 μm, pump the remaining base solvent in the premixing vessel into the main reactor at a uniform rate, and continue stirring for 15 minutes to form a mixed solvent system.

3. The method for preparing hydrophobic silica according to claim 1, characterized in that: Step S3 includes the following steps: S31. Silane ratio: The silane combination is a mixture of 60% sodium trimethylsilanolate and 40% trimethylmethoxysilane. After weighing, the two silane reagents are transferred to a glass container with a sealed lid and mixed by vortexing for 5 minutes to make the two initially uniformly mixed. S32. Enhanced dissolution process: The mixed silane reagent is slowly added to the mixed solvent system, and the addition rate is controlled at 2-5 mL / min using a peristaltic pump. During the dissolution process at 40℃, a magnetic stirrer is used to stir at a speed of 200-250 rpm, while nitrogen is introduced for protection at a flow rate of 50-100 mL / min. The dissolution time is 60-90 minutes to obtain the composite silane modifier.

4. The method for preparing hydrophobic silica according to claim 3, characterized in that: In step S4, the amount of silica gel added is controlled according to the ratio of 100g: 800-1000ML of mixed solvent system: 5-10g of composite silane modifier.

5. The method for preparing hydrophobic silica according to claim 1, characterized in that: In step S1, a vacuum drying oven with programmed temperature control is used to activate the silica gel, and the vacuum level is maintained at 0.1-1 Pa during the activation process.

6. The method for preparing hydrophobic silica according to claim 1, characterized in that: In step S4, the reaction is carried out in a glass reactor equipped with a reflux condenser, pressure sensor, online oxygen analyzer, temperature sensor, pH meter, and nitrogen inlet. The reactor is equipped with a mechanical stirrer, and the stirring speed is adjustable within the range of 150-250 rpm by a variable frequency motor. The pressure inside the reactor is maintained at 0.105-0.11 MPa. A comprehensive parameter correlation model is constructed to dynamically adjust the parameters during the reaction process. The influence of each parameter on the silane modification effect is quantitatively evaluated through the comprehensive parameter correlation model.

7. The method for preparing hydrophobic silica according to claim 6, characterized in that: In the first stage of the reaction, a peristaltic pump was used to slowly add the silane solution dropwise into the reactor containing the pretreated silica gel, at a rate of 3-5 mL / min; the nitrogen flow rate was controlled at 80-100 mL / min; during the reaction, samples were taken every hour, and the amount of silane modification on the silica gel surface was detected by thermogravimetric analysis (TGA). When the amount of modification reached 60-70% of the target value, the second stage of the reaction was initiated. After adding triethylamine catalyst in the second stage, the heating rate is controlled at 1-2℃ / min. During the heating process, the pH value is maintained in the range of 8-9. The nitrogen flow rate is controlled at 50-70mL / min. After heating to 65℃, the water in the system is removed.

8. The method for preparing hydrophobic silica according to claim 1, characterized in that: In step S5, a vacuum drying oven with programmable temperature control is used for gradient drying. In the initial drying stage, the vacuum degree is set to 0.1-1 Pa, the temperature is 120℃, and the temperature is maintained for 24 hours. In the gradient heating stage, the temperature is increased to 135℃ at a rate of 5℃ / hour. After the heating is completed, drying continues at 135℃ for 12 hours. During the cooling process, the temperature is naturally cooled to room temperature, and the vacuum state is maintained during the cooling process.

9. The method for preparing hydrophobic silica according to claim 1, characterized in that: In step S6, the cleaning process is carried out in a stainless steel cleaning tank equipped with a stirring device, with the rotation speed controlled at 80-120 rpm; stirring and cleaning for 30-60 minutes; when the pH value reaches 7.0-7.5, stirring is stopped, and centrifugation is performed using a centrifuge at a speed of 3000-4000 rpm for 5-10 minutes; the second cleaning uses pure methanol for 15-30 minutes; after cleaning, centrifugation is performed again, and then the silica gel is transferred to a vacuum drying oven for preliminary drying at 50-60℃ for 2-3 hours.

10. The hydrophobic silica prepared by the method for preparing hydrophobic silica according to any one of claims 1 to 9, characterized in that: It is used for organic waste gas recovery, water oil pollution treatment, and oil and gas recovery.

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