Hybrid hydrophobic modification method of silica gel and application thereof

Abstract

The application discloses a hybrid hydrophobic modification method of silica gel and application thereof, and belongs to the technical field of adsorbing materials. The application adopts alkylsilane as a modifier to modify silica gel multiple times, and comprises the following steps: after vacuumizing pretreated silica gel, alkylsilane is added to generate a primary condensation reaction; and the silica gel obtained in the last step is pretreated again and subjected to a secondary reaction with alkylsilane. The application adopts single or multiple alkylsilanes to modify silica gel, maximally utilizes the condensation reaction of the hydroxyl groups on the surface of the silica gel, thereby grafting the same or different coupling agents, increasing the water contact angle of the silica gel, improving the hydrophobic and oleophilic properties of the silica gel, and enabling the silica gel to be better applied in the recovery and treatment of VOCs.

Description

Technical Field

[0001] This application belongs to the field of adsorption materials technology, specifically relating to a method and application of silica gel hybrid hydrophobic modification. Background Technology

[0002] Silica gel is a polymer composed of silicon oxides. Its surface silanol groups readily bind to water molecules, making it commonly used as a desiccant, but it struggles to adsorb non-polar substances. Its hydrophilicity, a significant characteristic, easily leads to the replacement of adsorbed organic vapors by water molecules, resulting in adsorption competition. Furthermore, excessive water adsorption can disrupt the rigid structure of silica gel, causing it to break down. However, silica gel's non-flammability has made it a valuable adsorbent for VOCs, leading to the development of modified silica gels with hydrophobic properties and high adsorption capacity—a current research hotspot in the chemical and environmental fields.

[0003] Methods for hydrophobic modification of silicone mainly include heat treatment, adding modifiers followed by heat treatment, and impregnation with organosilicon compounds to remove or replace silanol groups, thereby improving the hydrophobicity of silicone. For example, He Junqian et al. used tetraethyl orthosilicate (TEOS) as a hydrophobic modifier to obtain modified silicone with certain hydrophobicity through hydroxyl grafting reaction on the surface of silicone. Chinese patent CN111804007B provides a method for hydrophobicating hydrophilic materials by introducing hydrophobic groups into the hydroxyl groups (-OH) on the surface of hydrophilic materials in the presence of amino acids. Chinese patent CN105771905A provides a method for hydrophobic modification of silicone under ultrasonic action using n-heptane and ethanol as solvents and trimethylchlorosilane as a modifier.

[0004] However, there are no reports of using one or more alkylsilanes to repeatedly modify silica gel to prepare hydrophobic and oleophilic silica gel for adsorption and recovery of VOCs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application aims to provide a method for hybrid hydrophobic modification of silica gel, employing one or more silanes with carbon chains or similar structures to modify silica gel and prepare a hydrophobic adsorbent. Another technical problem this application aims to solve is to provide an application of the hydrophobic adsorbent obtained by the above preparation method in the adsorption and recovery of VOCs.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is as follows:

[0007] A method for modifying silica gel by hybrid hydrophobicity: silicone gel is modified multiple times using alkylsilanes.

[0008] The aforementioned method for modifying silica gel with hybrid hydrophobicity includes the following steps:

[0009] 1) Silica gel and alkylsilane modifier are stirred and mixed under vacuum to undergo a condensation reaction. After preliminary silanization treatment, the mixture is filtered, washed and vacuum dried to obtain primary modified silica gel.

[0010] 2) The silica gel obtained in step 1) is mixed with the alkylsilane modifier under vacuum. After the reaction is completed, the mixture is filtered, washed and vacuum dried.

[0011] 3) Repeat step 2) more than once to obtain multiple modified silicone.

[0012] The hybrid hydrophobic modification method further includes a pretreatment before modification, wherein the pretreatment includes activation of silica gel with an alkali.

[0013] In the hybrid hydrophobic modification method, the alkali activation involves stirring the silica gel at low speed in an alkaline solution, followed by ultrasonication, washing, and drying.

[0014] The alkaline solution in the pretreatment is a 0.5%–2% NaOH solution, and the low-speed stirring speed is 20–100 r / min; in the ultrasonic process, the ultrasonic time is 5–10 min; in the washing process, the silica gel is washed with deionized water in small amounts and multiple times until the silica gel pH value is neutral; in the drying process, the drying temperature is 120–180℃, and the drying time is 1–2 h.

[0015] In the hybrid hydrophobic modification method, when silica gel reacts with alkylsilane, the silica gel is completely immersed in the alkylsilane solution; in the filtration process, filtration is completed when no liquid drips and the surface of the silica gel particles is dry; in the vacuum drying process, the vacuum drying temperature is 120-180℃ and the time is 1-2 hours.

[0016] The alkylsilane is a carbon chain silane coupling agent with the following general structural formula:

[0017] CH3(CH2) n Si(OR)3

[0018] In the formula, n is an integer from 0 to 17; R is selected from methyl or ethyl.

[0019] The silane coupling agents with the structures shown include, but are not limited to, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, n-hexyltriethoxysilane, octyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane.

[0020] The alkylsilane used in the repetition can be the same as or different from the alkylsilane used in the previous modification.

[0021] The concentration of the alkylsilane is 0.5–0.2 g / mL, and the solvent is ethanol.

[0022] The silica gel obtained by the hybrid hydrophobic modification method described above.

[0023] The application of silica gel in the adsorption of VOCs.

[0024] The average pore size of the silicone is 3–12 nm.

[0025] Existing high-temperature heat treatment-modified silica gel structures are prone to cracking and the effects are generally limited. This application addresses this issue by using a mixed grafting alkyl chain method to induce a condensation reaction between the hydrophilic silanol groups and ethoxy groups, reducing the number of silanol groups on the silica gel surface, thereby decreasing hydrophilicity and improving VOCs adsorption efficiency.

[0026] Beneficial effects: Compared with the prior art, the technical advantages of this application include: This application uses single or multiple alkylsilanes to hybridize and modify silica gel, maximizing the use of hydroxyl groups on the surface of silica gel to undergo condensation reactions, thereby grafting the same or different coupling agents, improving the hydrophobicity and oleophilicity of silica gel, making it better applicable in the recycling and treatment of VOCs, and quickly reaching adsorption equilibrium. Attached Figure Description

[0027] Figure 1 This is a diagram of the adsorption testing apparatus. Detailed Implementation

[0028] This application does not impose any specific limitations on the mixing method; any mixing method well-known to those skilled in the art can be used. Unless otherwise specified, the equipment and raw materials used are all commercially available products well-known to those skilled in the art or commonly used in this industry. The chemical instruments used are ordinary commercially available chemical instruments.

[0029] In the following examples: room temperature refers to a temperature of 20–30°C. The silicone used is commercially available silicone with an average pore size of 10 nm.

[0030] Example 1

[0031] The hybrid hydrophobic modification process of silicone in this embodiment is as follows:

[0032] 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel.

[0033] 2) Weigh 3g of the silica gel pretreated in step 1), place it in a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1g / mL hexyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Dry at 150℃ for 2 hours, and then cool to room temperature.

[0034] 2) Place the silica gel obtained in step 2) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL methyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Dry at 150°C for 2 hours, cool to room temperature, and then seal for storage.

[0035] Example 2

[0036] The hybrid hydrophobic modification process of silicone in this embodiment is as follows:

[0037] 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel.

[0038] 2) Weigh 3g of the silica gel pretreated in step 1), place it in a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1g / mL octadecyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Dry at 150℃ for 2 hours, and then cool to room temperature.

[0039] 3) Place the silica gel obtained in step 2) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL hexyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Finally, dry at 150°C for 2 hours and cool to room temperature.

[0040] 4) Place the silica gel obtained in step 3) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL methyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Dry at 150°C for 2 hours, cool to room temperature, and then seal for storage.

[0041] Comparative Example 1

[0042] The method for modifying the silica gel using hybrid hydrophobicity in this comparative example is the same as in Example 1, except that the alkylsilane used in step 2) is methyltriethoxysilane, and the alkylsilane used in step 3) is n-hexyltriethoxysilane. The specific operation is as follows:

[0043] 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel.

[0044] 2) Weigh 3g of pretreated silica gel and place it in a two-necked flask. Add a rotor and evacuate the flask for 1 hour to create a vacuum. Then, inject a prepared 0.1g / mL methyltriethoxysilane solution into the flask until the silica gel sample is submerged. Stir at low speed for 2 hours and then filter the solution until the silica gel surface is dry. Dry the silica gel at 150℃ for 2 hours and then cool it to room temperature.

[0045] 3) Place the silica gel obtained in step 2 into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state. Then, inject the prepared 0.1 g / mL hexyltriethoxysilane solution using a syringe until the silica gel sample is submerged. Stir at low speed for 2 hours, then filter to remove excess solution until the silica gel surface is dry. Dry at 150°C for 2 hours, cool to room temperature, and then seal for storage.

[0046] Comparative Example 2

[0047] The method for modifying the silica gel with hybrid hydrophobicity in this comparative example is the same as in Example 1, except that only n-hexyltriethoxysilane is used to modify the silica gel once, without step 3). The specific operation is as follows:

[0048] 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel.

[0049] 2) Weigh 3g of pretreated silica gel and place it in a two-necked flask. Add a rotor and evacuate the flask for 1 hour to create a vacuum. Then, inject a prepared 0.1g / mL hexyltriethoxysilane solution into the flask until the silica gel sample is submerged. Stir at low speed for 2 hours and then filter the solution until the silica gel surface is dry. Dry the sample at 150℃ for 2 hours and then cool it to room temperature before storing.

[0050] Application examples

[0051] Weigh out 1g each of Examples 1 and 2, Comparative Examples 1 and 2, and 1g of unmodified silica gel, and activate them by vacuum drying at 150℃ for 2 hours. Place the activated samples in... Figure 1 In the apparatus shown, water or n-hexane is added to the solvent tube in the sample tube for adsorption testing. The main process of the adsorption test is as follows: the silica gel to be tested is activated and placed in the sample tube, and the adsorbate to be tested is placed in the solvent tube. The pressure gauge is zeroed, and residual air in the apparatus is removed by a vacuum pump. The weight of the activated silica gel and the test temperature are recorded. Based on the saturated vapor pressure Pn of the adsorbate at the experimental pressure and temperature, the pressure gauge reading is calculated for each rotation of the solvent tube valve and recorded as P1, P2...Pn (generally 20 times). When the pressure gauge reading stabilizes, the solvent tube valve is closed and the sample tube valve is opened to allow adsorption. When the pressure gauge reading stabilizes, the corresponding readings are recorded as P1', P2'...Pn'. The amount of solvent adsorbed at different pressure values ​​can be calculated using the ideal gas law PV=nRT. An adsorption curve can be obtained by plotting the amount or mass of substance against P / P0. The test results are shown in Table 1.

[0052] Table 1 Adsorption test results

[0053]

[0054]

[0055] Table 1 shows that, with varying alkyl silane carbon chain lengths and whether or not the silica gel was mixed, the adsorption capacity of water decreased significantly after modification, while the adsorption capacity of n-hexane increased significantly. This is sufficient to prove that the grafting of alkyl silanes onto the silica gel surface enhances its hydrophobic and oleophilic properties. In Example 1, the water contact angle reached 158°. The difference in n-hexane adsorption capacity caused by the different alkyl chain lengths and the different alkyl silanes before and after mixing is due to two factors: changes in the pore structure of the silica gel and the different alkyl silanes grafted onto the silica gel surface.

[0056] In summary, the silica gel hybrid hydrophobic modification method of this application uses single or multiple alkylsilanes to hybridize and modify silica gel, maximizing the utilization of the hydroxyl groups on the silica gel surface to undergo condensation reactions, thereby grafting the same or different coupling agents, increasing the water contact angle of silica gel, improving the hydrophobicity and oleophilicity of silica gel, making it better suited for the recycling and treatment of VOCs, and quickly reaching adsorption equilibrium.

Claims

1. Application of silica gel obtained by hybrid hydrophobic modification method in the adsorption of n-hexane; the steps of the hybrid hydrophobic modification method are as follows: 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel. 2) Weigh 3g of the silica gel pretreated in step 1), place it in a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1g / mL n-hexyltriethoxysilane solution into the flask until the silica gel sample is submerged. Stir at low speed for 2 hours and then filter to remove excess solution until the silica gel surface is dry. Then, dry at 150℃ for 2 hours and then cool to room temperature. 3) Place the silica gel obtained in step 2) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL methyltriethoxysilane into the flask until the silica gel sample is submerged in the solution. Stir at low speed for 2 hours and then filter to remove excess solution until the silica gel surface is dry. Then, dry at 150°C for 2 hours, cool to room temperature, and seal for storage.

2. Application of silica gel obtained by the hybrid hydrophobic modification method in the adsorption of n-hexane; the steps of the hybrid hydrophobic modification method are as follows: 1) Weigh 10g of silica gel, prepare 1% NaOH solution, stir at low speed for 2h under magnetic stirring at 100r / min, sonicate for 10min, wash the soaked silica gel with anhydrous ethanol to remove residual NaOH and impurities until neutral, filter, vacuum dry at 150℃ for 1h, and then cool to room temperature to obtain pretreated silica gel. 2) Weigh 3g of the silica gel pretreated in step 1), place it in a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1g / mL octadecyltriethoxysilane solution into the flask until the silica gel sample is submerged. Stir at low speed for 2 hours and then filter to remove excess solution until the silica gel surface is dry. Then, dry at 150℃ for 2 hours and then cool to room temperature. 3) Place the silica gel obtained in step 2) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL n-hexyltriethoxysilane into the flask until the silica gel sample is submerged in the solution. Stir at low speed for 2 hours and then filter to remove excess solution until the silica gel surface is dry. Then, dry at 150°C for 2 hours and cool to room temperature. 4) Place the silica gel obtained in step 3) into a two-necked flask, add a rotor, and evacuate for 1 hour to create a vacuum state in the flask. Then, inject the prepared 0.1 g / mL methyltriethoxysilane into the flask until the silica gel sample is submerged in the solution. Stir at low speed for 2 hours and then filter to remove excess solution until the silica gel surface is dry. Then, dry at 150°C for 2 hours, cool to room temperature, and seal for storage.

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