A method of preparing aerogels from azeotropes

Abstract

The application belongs to the technical field of silica aerogel material preparation, and particularly relates to a method for preparing aerogel from azeotrope, wherein skeleton type halogen-containing silane provides a skeleton, low-functionality organosilane provides a hydrophobic group, the microstructure and hydrophilic and hydrophobic properties of the aerogel material are regulated, and thus aerogel materials meeting different performance requirements are obtained. The preparation method comprises the following steps: 1) mixing azeotrope by-produced from organosilicon and an alcohol solvent, and performing pre-alcoholysis to obtain a reaction solution in which Si-Cl groups and Si-OR groups coexist; 2) adding water to the reaction solution, and performing hydrolysis and polycondensation under the condition of not adding an alkali solution to form a wet gel; 3) aging the wet gel, washing with water, and detecting Cl ‑ in the last washing solution and the gel extraction solution; 4) when the chlorine removal index is reached, sequentially performing alcohol solvent replacement, low-surface-tension solvent replacement and normal-pressure drying to obtain hydrophobic silica aerogel. The application solves the problems of too fast direct hydrolysis of skeleton type halogen-containing silane, excessive low-functionality organosilane affecting continuous gelation, and difficulty in controlling residual chlorine in the wet gel, and the prepared aerogel has a water contact angle of 136-155°, a BET specific surface area of 555-860 m² / g, and a thermal conductivity of 0.018-0.026 W / (m·K).

Description

Technical Field

[0001] This invention belongs to the field of silica aerogel material preparation technology, specifically relating to a method for preparing aerogels from azeotropes. Background Technology

[0002] Silica aerogels are characterized by low density, high porosity, and low thermal conductivity, making them suitable for applications such as building insulation, industrial insulation, and composite fillers. Common silicon sources include tetraethyl orthosilicate, water glass, and silicon tetrachloride. Tetraethyl orthosilicate has a milder reaction but is more expensive; water glass is cheaper but usually requires desalination; silicon tetrachloride is highly reactive and inexpensive, but it hydrolyzes rapidly upon contact with water, releasing HCl and causing problems such as white fumes, localized exothermic reactions, rapid precipitation, equipment corrosion, and residual chlorine.

[0003] The production of organosilicon generates a byproduct azeotrope containing silicon tetrachloride and trimethylchlorosilane. Silicon tetrachloride can form a continuous Si-O-Si framework; trimethylchlorosilane can participate in partial end-capping and introduce hydrophobic groups. However, their effects differ: if silicon tetrachloride hydrolyzes too quickly, it can easily form uneven precipitation; if the proportion of trimethylchlorosilane is too high, it will reduce the sites for further polymerization, prolonging the gelation time and even causing phase separation. Therefore, this byproduct azeotrope cannot be simply used directly as a single silicon source.

[0004] In the prior art, CN116692879A uses an industrial azeotrope containing silicon tetrachloride and trimethylchlorosilane to be directly hydrolyzed in water and non-alcoholic organic solvents; CN115010140B uses chlorosilane to react with alcohol, then adds water and removes HCl by reflux, and then adds water and alkali to catalyze polycondensation; CN117303380B uses two alcohol-water reactions, distillation and reflux to remove HCl, and adds an alcohol-alkali solution to adjust the pH to form a gel. However, the aforementioned existing technical routes are all limited to a single mode of direct hydrolysis or alcoholysis-hydrolysis of chlorosilanes, failing to solve the problem of activity competition between end-capping components and backbone components in the by-product azeotrope, and lacking means to directionally control the end-capping components; moreover, none of them set up an independent limited pre-alcoholization step before adding water to form a gel, resulting in uncontrollable hydrolysis rate of silicon tetrachloride, which is prone to local boiling, non-uniform precipitation and gel structure collapse; at the same time, relying on external alkaline catalysts to force polycondensation, rather than controlling the gelation process through the reaction activity of the precursor itself, increases the risk of impurity introduction and process complexity; in addition, existing methods generally neglect the deep removal and online monitoring of residual chlorine in the product, and lack a graded detection and release mechanism for free chlorine and bound chlorine, which cannot meet the stringent requirements for chlorine content in high-end thermal insulation materials.

[0005] Therefore, there is an urgent need to develop a continuous process method that includes end-capping component control, limited pre-alcoholization, alkali-free autocatalytic gelation, and dual residual chlorine detection for release. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing aerogels from azeotropes. This method solves the problems of rapid reaction of skeletal halogenated silanes with water, which easily leads to white smoke, exothermic reactions and local precipitation; excessive low-functionality organosilanes affecting the formation of continuous gel networks; and residual chlorine causing material shrinkage, performance fluctuations and equipment corrosion.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing aerogels from azeotropes includes the following steps: 1) Pre-alcoholization The organosilicon byproduct azeotrope was mixed with an alcohol solvent and pre-alcoholized to obtain a reaction solution in which Si-Cl groups and Si-OR groups coexist. 2) Hydrolysis and condensation Water is added to the reaction solution using a metering pump, and hydrolysis and condensation occur without the addition of an alkaline solution to form a wet gel. 3) Residual chlorine control The wet gel was aged, washed with water, and the Cl- content of the final wash solution was measured. - Concentration and soluble Cl in gel extract - If the chlorine content does not reach the dechlorination target, continue washing. 4) Aerogel preparation Once the dechlorination target is met, alcohol solvent replacement, low surface tension solvent replacement, and atmospheric pressure drying are performed sequentially to obtain hydrophobic silica aerogel. The main components of the organosilicon by-product azeotrope are low-functionality organosilicon alkane and framework-type halosilane, and the molar ratio of low-functionality organosilicon alkane to framework-type halosilane is 0.05-0.50:1. The specific dechlorination index is: Cl in the final washing solution. - The concentration is not higher than 10 mg / kg, and the soluble Cl in the gel extract is... - The content is not higher than 50 mg / kg.

[0008] This invention uses halogenated silanes as a framework and low-functionality organosilanes as in-situ modifiers to regulate the microstructure and hydrophilicity / hydrophobicity of the prepared aerogels, thereby obtaining aerogel materials with different properties. If the molar ratio of low-functionality organosilanes to framework-type halogenated silanes is too high, the difficulty of gelation control increases, and the shrinkage rate is too high.

[0009] Preferably, the raw material ratio adjustment of the organosilicon by-product azeotrope is achieved by mixing different batches of by-product azeotrope, adding skeletal halogenated silanes and / or low-functionality organosilicon silanes.

[0010] Preferably, the molar ratio of the low-functionality organosilane to the framework-type halosilane is 0.10-0.15:1.

[0011] Preferably, the skeletal halosilane is selected from one or more of silicon tetrachloride, methyltrichlorosilane, trichlorosilane, vinyltrichlorosilane, phenyltrichlorosilane, and hexachlorosilane; The low-functionality organosilane is selected from one or more of trimethylchlorosilane, dimethyldichlorosilane, methyldichlorosilane, vinylmethyldichlorosilane, and methylphenyldichlorosilane.

[0012] Through the above technical solution, water is not actively added during the pre-alcoholization stage. Instead, alcohol solvents are added to the azeotrope with the raw material ratio adjusted, causing some Si–Cl to convert to Si–OR. This step is not to convert all chlorosilanes into alkoxysilanes, but to reduce the instantaneous reaction rate when water is added later. After pre-alcoholization, water is added, and both the remaining Si–Cl and Si–OR can form Si–OH. Subsequently, Si–OH continues to condense to form a Si–O–Si network. Framework-type halogenated silanes are mainly responsible for forming the framework, while low-functionality organosilanes mainly participate in some end-capping. This invention does not require an external alkaline catalyst as a necessary condition for gelation. After the wet gel is formed, it is aged and then washed with water. During the washing process, the Cl in the final washing solution is detected. - Furthermore, water extraction was performed on the gel to detect the soluble Cl inside. - If the dechlorination target is not met, washing continues, with dual residual chlorine testing used as the basis for determining the washing endpoint. Once the dechlorination target is met, the water in the channels is first replaced with ethanol, and then the ethanol is replaced with a low surface tension solvent.

[0013] Preferably, in step 1), the alcohol solvent is selected from one or more of methanol, ethanol, isopropanol, n-propanol or n-butanol; the molar ratio of the alcohol solvent to the skeletal halogenated silane is 7-25:1; the pre-alcoholization temperature is 0-10℃ and the time is 0.5-2 h.

[0014] Preferably, in step 2), the molar ratio of water to framework-type halosilane is 10-20:1; and the water addition rate is 5-10 mL / min.

[0015] Preferably, the HCl-containing tail gas generated during the pre-alcoholization and hydrolysis polycondensation processes is condensed and then introduced into an alkaline absorption device or other acid-resistant tail gas treatment device.

[0016] Preferably, in step 3), the aging time is 48-96 h; after water washing, a final washing solution Cl is simultaneously applied. - Detection and gel water extraction of Cl - The test serves as the basis for determining the washing endpoint.

[0017] Preferably, the Cl -The detection method employs one or more of the following: chloride ion selective electrode, potentiometric titration, or ion chromatography. The AgNO3 method is used for qualitative determination.

[0018] Preferably, in step 4), the specific process of alcohol solvent replacement and low surface tension solvent replacement is as follows: first, ethanol is used to replace the water in the gel channels, and then one or more of n-heptane, n-hexane or hexamethyldisiloxane are used for low surface tension solvent replacement.

[0019] Preferably, the atmospheric pressure drying is carried out using a programmed temperature rise method, with a drying temperature of 60–150°C; Preferably, the drying process is carried out in stages at 80℃, 100℃ and 120℃.

[0020] The present invention also provides a hydrophobic silica aerogel prepared by the above method, which has a water contact angle of 136–155°, a BET specific surface area of ​​555–860 m² / g, an average pore size of 8–18 nm, a porosity of 85–93%, and a thermal conductivity of 0.018–0.026 W / (m·K).

[0021] The beneficial effects of this invention are: (1) In this invention, the low-functionality organosilane in the azeotrope is controlled within a range suitable for gelation. A low proportion of low-functionality organosilane is beneficial for both gelation and hydrophobicity. When the molar ratio of low-functionality organosilane to framework-type halosilane is 0.10-0.15:1, aerogels with high BET specific surface area and water contact angle can be obtained simultaneously.

[0022] (2) Pre-alcoholization reduces the intensity of direct water addition and is beneficial to stable gel formation; the present invention does not require the addition of an alkaline catalyst as a necessary condition for gelation.

[0023] (3) This invention effectively controls residual chlorine, using Cl - Quantitative detection stops water washing to ensure that Cl can be dissolved before drying. - The corrosion of metal parts during the drying process was controlled, and the catalytic shrinkage of the Si-O-Si framework by acid residues was avoided. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the preparation process of the aerogel of the present invention.

[0025] Figure 2 This is a nitrogen adsorption-desorption curve of the aerogel obtained in Example 1 of the present invention.

[0026] Figure 3 This is a pore size distribution diagram of the aerogel obtained in Example 1 of the present invention.

[0027] Figure 4This is a SEM image of the aerogel obtained in Example 1 of the present invention.

[0028] Figure 5 This refers to the water contact angle of the aerogel obtained in Example 1 of the present invention.

[0029] Figure 6 The image shows the FTIR spectrum of the aerogel obtained in Example 1 of this invention.

[0030] Figure 7 The image shows the XRD pattern of the aerogel obtained in Example 1 of this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of trimethylchlorosilane to silicon tetrachloride was adjusted to 0.10:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Ethanol was added dropwise at a molar ratio of ethanol to silicon tetrachloride of 10:1. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 5 mL / min. The molar ratio of water to silicon tetrachloride is 12:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h, washed 7 times with deionized water, and the pH of the final wash solution was 6.5, Cl... - At a concentration of 7 mg / kg, the gel was ultrasonically extracted with 1 g sample / 100 mL of water for 20 min, which yielded Cl. - The content is 20 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, and the product was dried in stages at 80℃, 100℃ and 120℃ under normal pressure to obtain hydrophobic silica aerogel.

[0033] The BET specific surface area of ​​the aerogel obtained in this embodiment is shown in [reference]. Figure 2 For average aperture, please refer to Figure 3 See SEM structure Figure 4 For water contact angle, see [reference]. Figure 5 Fourier transform infrared image as follows Figure 6 XRD patterns as follows Figure 7 .

[0034] Example 2 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of dimethyldichlorosilane to silicon tetrachloride was adjusted to 0.10:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Ethanol was added dropwise at a molar ratio of ethanol to silicon tetrachloride of 12:1. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 7 mL / min. The molar ratio of water to silicon tetrachloride is 15:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h, then washed 5 times with deionized water. The pH of the final wash solution was 6.8, and the Cl content was... - At a concentration of 8 mg / kg, the gel was ultrasonically extracted at a ratio of 1 g sample / 100 mL water for 20 min, which yielded Cl. - The content is 30 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0035] Example 3 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of trimethylchlorosilane to trichlorosilane was adjusted to 0.08:1. The azeotrope was added to a corrosion-resistant reactor equipped with stirring, condensation and alkaline tail gas absorption devices. n-Butanol was added dropwise. The molar ratio of n-butanol to trichlorosilane was 7:1. The pre-alcoholization temperature was 10℃ and the time was 0.5 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 10 mL / min. The molar ratio of water to silicon tetrachloride is 10:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h, washed 5 times with deionized water, and the final washing solution contained Cl. - At a concentration of 9 mg / kg, the gel extract can dissolve Cl. - The content is 38 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0036] Example 4 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of trimethylchlorosilane to methyltrichlorosilane was adjusted to 0.20:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 5°C. Isopropanol was added dropwise at a molar ratio of 16:1 to methyltrichlorosilane. After the addition was complete, the mixture was stirred for 2 hours to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 5 mL / min. The molar ratio of water to methyltrichlorosilane is 18:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 72 h, washed 6 times with deionized water, and the final wash solution contained Cl. - At a concentration of 9 mg / kg, the gel extract can dissolve Cl. - The content is 48 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0037] Example 5 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of methylphenyldichlorosilane to vinyltrichlorosilane was adjusted to 0.05:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Methanol was added dropwise at a molar ratio of 12:1 to vinyltrichlorosilane. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 5 mL / min. The molar ratio of water to vinyltrichlorosilane is 12:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h, washed 7 times with deionized water, and the final wash solution contained Cl. - At a concentration of 9 mg / kg, the gel extract can dissolve Cl. - The content is 27 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0038] Example 6 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of vinylmethyldichlorosilane to hexachlorodichlorosilane was adjusted to 0.50:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Ethanol was added dropwise at a molar ratio of ethanol to hexachlorodichlorosilane of 12:1. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 10 mL / min. The molar ratio of water to hexachlorosilane is 20:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 96 h, washed 8 times with deionized water, and the final wash solution contained Cl. - At a concentration of 9 mg / kg, the gel extract can dissolve Cl. - The content is 38 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0039] Example 7 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of methyldichlorosilane to vinyltrichlorosilane was adjusted to 0.15:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Ethanol was added dropwise at a molar ratio of ethanol to vinyltrichlorosilane of 10:1. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 5 mL / min. The molar ratio of water to vinyltrichlorosilane is 15:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h, followed by staged water washing. The first to sixth washing solutions contained Cl. - The concentrations were successively 3200, 950, 260, 85, 34 and 7 mg / kg, followed by water extraction, and the gel could dissolve Cl. - The content is 27 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0040] Example 8 A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of dimethyldichlorosilane to phenyltrichlorosilane was adjusted to 0.12:1. The azeotrope was added to a 5L corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 5℃. Ethanol was added dropwise at a molar ratio of ethanol to phenyltrichlorosilane of 11:1. After the addition was complete, the mixture was stirred for 1.5 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 5 mL / min. The molar ratio of water to phenyltrichlorosilane is 15:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 72 h, washed 6 times with deionized water, and the final wash solution contained Cl. -At a concentration of 6 mg / kg, the gel extract can dissolve Cl. - The content is 30 mg / kg; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure to obtain hydrophobic silica aerogel.

[0041] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not undergo pre-alcoholization.

[0042] A method for preparing aerogels from azeotropes includes the following steps: The organosilicon byproduct azeotrope was detected by gas chromatography. The molar ratio of trimethylchlorosilane to silicon tetrachloride was adjusted to 0.10:1. The azeotrope was added to a corrosion-resistant reactor equipped with stirring, condensation and alkaline tail gas absorption devices at 0°C. Water was added to the reactor using a metering pump at a rate of 250 mL / min. The molar ratio of water to silicon tetrachloride was 12:1. During the water addition process, obvious white smoke and localized heat release were observed, along with the appearance of white precipitate and uneven gel blocks. The wet gel was aged in the mother liquor for 48 hours and washed 7 times with deionized water. The gel extract from the last wash could dissolve Cl. - The content is 2100 mg / kg; Subsequently, ethanol and n-heptane replacement were performed, followed by drying at normal pressure to obtain a hydrophobic silica aerogel. The resulting aerogel shrank significantly and partially powdered.

[0043] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not involve residual chlorine control.

[0044] A method for preparing aerogels from azeotropes includes the following steps: 1) Gas chromatography was used to detect the organosilicon by-product azeotrope. The molar ratio of trimethylchlorosilane to silicon tetrachloride was adjusted to 0.10:1. The azeotrope was added to a corrosion-resistant reactor equipped with a stirrer, condenser, and alkaline tail gas absorption device at 0°C. Ethanol was added dropwise at a molar ratio of ethanol to silicon tetrachloride of 10:1. After the addition was complete, the mixture was stirred for 1 h to obtain the reaction solution. 2) Add water to the reaction solution using a metering pump at a rate of 250 mL / min. The molar ratio of water to silicon tetrachloride is 12:1. A wet gel is formed at room temperature. 3) The wet gel was aged in the mother liquor for 48 h and washed twice with deionized water; 4) Subsequently, ethanol replacement and n-heptane replacement were performed, followed by drying at normal pressure. During the drying process, there was a distinct acidic odor and corrosion marks appeared on the metal parts, resulting in hydrophobic silica aerogel.

[0045] Effect Example The performance of the aerogels prepared in Examples 1-8 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0046] Table 1

[0047] As shown in Table 1, the aerogels prepared in Examples 1-8 can be extracted to dissolve Cl. - The content is 20-48 mg / kg, the water contact angle is 136-155°, the BET specific surface area is 555-860 m² / g, the porosity is 85-93%, and the thermal conductivity is 0.018-0.026 W / (m·K). This indicates that the present invention utilizes partial pre-alcoholization of alcohols, controlled hydrolysis and polycondensation, washing to remove chlorine, and Cl... - Low-chlorinated hydrophobic silica aerogels were obtained through detection, solvent replacement, and atmospheric pressure drying processes.

[0048] Figure 2 This is the nitrogen adsorption-desorption curve of the aerogel obtained in Example 1, which exhibits the typical Type IV isotherm of silica aerogels. Figure 2 It can be determined that the specific surface area of ​​BET is 820 m² / g.

[0049] Depend on Figure 3 It can be seen that the aerogel is a mesoporous material with an average pore size of 8 nm.

[0050] Figure 4 In the study, the microstructure of the aerogel exhibits a typical nanoporous three-dimensional network structure.

[0051] Depend on Figure 5 It can be seen that the aerogel is a hydrophobic material with a water contact angle of 149°.

[0052] Figure 6 This is the FTIR spectrum of SiO2 aerogel, where 1088 cm⁻¹... - ¹ represents the antisymmetric stretching vibration peak of the Si-O-Si group, a characteristic peak of SiO2, indicating that the main component of the sample is SiO2; 1260, 850, 762 cm⁻¹ - ¹ represents the stretching vibration peak of Si-CH3. This group is the main reason for the hydrophobicity of SiO2 aerogel, indicating that the material is a hydrophobic silica aerogel.

[0053] Figure 7 The image shows the XRD pattern of silica aerogel, with a typical broad peak of amorphous SiO2 at position 23.

[0054] In Examples 1, 2, 7, and 8, the molar ratio of low-functionality organosilanes to framework-type halosilanes was 0.10-0.15, and the final washing solution contained Cl. -When the concentration is below 10 mg / kg, aerogel extraction can dissolve Cl. - The content is 20-30 mg / kg, the water contact angle is ≥149°, and the BET specific surface area is ≥744 m² / g. When soluble Cl... - When the content is higher than 30 mg / kg, the BET specific surface area decreases significantly to 555-685 m² / g, and the contact angle drops to 136-142°. This indicates that higher residual chlorine is usually accompanied by higher residual acidic substances, which leads to pore structure shrinkage, reduced specific surface area and decreased hydrophobicity.

[0055] The results of the graded washing in Example 7 show that as the number of washing cycles increases, the Cl in the washing solution... - The concentration was gradually decreased from 3200 mg / kg to 7 mg / kg; the final washing solution Cl in Examples 1, 2, 7, and 8 - Concentrations of 7, 8, 7, and 6 mg / kg correspond to the amount of Cl that can be dissolved inside the gel. - The content is 20, 30, 27, 30 mg / kg, indicating that Cl was used. - The detection and determination of the washing endpoint are more accurate and direct.

[0056] Comparative Example 1, without pre-alcoholization, showed that Cl could be dissolved through aerogel extraction. - Up to 2100 mg / kg, with a specific surface area of ​​only 285 m² / g; Comparative Example 2 without Cl - The detection is used as a process criterion; soluble Cl - The concentration was 1650 mg / kg, indicating corrosion in the equipment.

[0057] This invention utilizes alcoholic solvent pre-alcoholization and controlled hydrolysis-condensation, while simultaneously controlling the ratio of framework-type halosilanes to low-functionality organosilanes, to achieve both continuous gel formation and the introduction of hydrophobic end groups. After wet gel formation, the system is washed to remove chlorine and Cl. - After testing and meeting the standards, alcohol replacement, low surface tension solvent replacement, and drying were performed to obtain low-chlorine hydrophobic silica aerogel.

[0058] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing aerogels from azeotropic compounds, characterized in that, Includes the following steps: 1) Pre-alcoholization The organosilicon byproduct azeotrope was mixed with an alcohol solvent and pre-alcoholized to obtain a reaction solution in which Si-Cl groups and Si-OR groups coexist. 2) Controllable hydrolysis and condensation Water is added to the reaction solution using a metering pump, and hydrolysis and condensation occur without the addition of an alkaline solution to form a wet gel. 3) Residual chlorine control The wet gel was aged, washed with water, and the Cl- content of the final wash solution was measured. - Concentration and soluble Cl in gel extract - If the chlorine content does not reach the dechlorination standard, continue washing. 4) Aerogel preparation Once the dechlorination target is met, alcohol solvent replacement, low surface tension solvent replacement, and atmospheric pressure drying are performed sequentially to obtain hydrophobic silica aerogel. The main components of the organosilicon by-product azeotrope are low-functionality organosilicon alkane and framework-type halosilane, and the molar ratio of low-functionality organosilicon alkane to framework-type halosilane is 0.05-0.50:

1. The dechlorination index is: Cl in the final washing solution. - The concentration is not higher than 10 mg / kg, and the soluble Cl in the gel extract is... - The content is not higher than 50 mg / kg.

2. The method according to claim 1, characterized in that, The skeletal type halosilane is selected from one or more of silicon tetrachloride, methyltrichlorosilane, trichlorosilane, vinyltrichlorosilane, phenyltrichlorosilane, and hexachlorosilane; The low-functionality organosilane is selected from one or more of trimethylchlorosilane, dimethyldichlorosilane, methyldichlorosilane, vinylmethyldichlorosilane, and methylphenyldichlorosilane.

3. The method according to claim 1, characterized in that, In step 1), the alcohol solvent is selected from one or more of methanol, ethanol, isopropanol, n-propanol or n-butanol; the molar ratio of the alcohol solvent to the skeletal halogenated silane is 7-25:1; the pre-alcoholization temperature is 0–10℃ and the time is 0.5–2 h.

4. The method according to claim 1, characterized in that, In step 2), the molar ratio of water to framework-type halosilane is 10-20:1; the water addition rate is 5-10 mL / min.

5. The method according to claim 1, characterized in that, The HCl-containing tail gas generated during the pre-alcoholization and hydrolysis polycondensation processes is condensed and then introduced into an alkaline absorption device or other acid-resistant tail gas treatment device.

6. The method according to claim 1, characterized in that, In step 3), the aging time is 48-96 hours; after water washing, a final washing solution Cl is simultaneously applied. - Detection and gel water extraction of Cl - The test serves as the basis for determining the washing endpoint.

7. The method according to claim 6, characterized in that, The Cl - The detection method employs one or more of the following: chloride ion selective electrode, potentiometric titration, or ion chromatography. The AgNO3 method is used for qualitative determination.

8. The method according to claim 1, characterized in that, In step 4), the specific process of alcohol solvent replacement and low surface tension solvent replacement is as follows: first, ethanol is used to replace the water in the gel channels, and then one or more of n-heptane, n-hexane or hexamethyldisiloxane are used for low surface tension solvent replacement.

9. The method according to claim 1, characterized in that, The atmospheric pressure drying is carried out using a programmed temperature rise method, with a drying temperature of 60–150℃.

10. A hydrophobic silica aerogel prepared by the method according to any one of claims 1–10, having a water contact angle of 136–155°, a BET specific surface area of ​​555–860 m² / g, an average pore size of 8–18 nm, a porosity of 85–93%, and a thermal conductivity of 0.018–0.026 W / (m·K).

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