Non-metallic element doped silicon dioxide hybrid membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of pervaporation membranes, and particularly relates to a non-metallic element doped silicon dioxide hybrid membrane as well as a preparation method and application thereof. The structure of an organosilane precursor is regulated and controlled by doping non-metallic elements in synthetic sol, so that the high-performance non-metallic element doped silicon dioxide hybrid membrane is prepared. The membrane has high-flux and high-selectivity pervaporation dehydration performance at room temperature. The preparation process is simple and easy to operate, and the prepared hybrid membrane also has excellent long-time hydrothermal stability. When the prepared B-SiO2 / gamma-Al2O3 / alpha-Al2O3 membrane is applied to a reaction-separation coupling system to synthesize ester organic matters, the conversion rate of the reaction and the product yield can be remarkably improved. Compared with a pure esterification reaction, the reaction efficiency is remarkably improved, and the energy consumption and the process complexity are reduced. Meanwhile, the membrane separation process has the advantages of low energy consumption and no pollution, and shows a good industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of pervaporation membranes, and particularly relates to a non-metal element doped silica hybrid membrane, a preparation method thereof, and applications thereof, and applications thereof in an esterification reaction separation coupling system. Background Art

[0002] Organic solvents play a crucial role in global chemical and materials manufacturing and are widely used in pharmaceutical, coating, petrochemical and other industrial fields. With the acceleration of industrial applications, the demand for organic solvents has increased sharply, driving the rapid growth of the global economy. However, environmental pollution and emission problems brought about by the life cycle of industrial solvents (including their production, transportation, use and final disposal) have become an important threat to human health and the ecological environment. Therefore, recycling and reusing solvents has become a key strategy to reduce solvent use and environmental impact. The recycling and reuse of solvents mainly rely on efficient separation technologies to extract solvents from mixtures and purify them to meet quality standards.

[0003] Although traditional solvent recovery technologies such as distillation and reverse osmosis can achieve solvent recovery to a certain extent, they often face challenges such as high energy consumption and limited separation efficiency. In contrast, pervaporation technology has shown great application potential in the field of organic solvent recovery and purification due to its low energy consumption and high separation performance. Pervaporation technology utilizes the selective permeability of membranes to efficiently separate solvents without relying on complex thermodynamic processes, which makes it show significant advantages when dealing with low-concentration solvents or complex solutions. Therefore, pervaporation technology provides a more economical and environmentally friendly solution for the recycling and reuse of organic solvents, promoting the process of green chemistry and sustainable development.

[0004] As a membrane material with excellent separation performance, silica membranes have been widely studied in the fields of gas separation, membrane catalytic reactors, pervaporation, etc. in recent years and have potential application prospects. For example, Patent CN103102082A discloses a superhydrophobic nano-silica membrane prepared using tetraethyl orthosilicate as a silicon source and amino silicone oil as a modifier. Patent CN103170253A discloses a modified silica membrane for separating CH4 / CO2 prepared by doping a silane coupling agent. Patent CN102218270A discloses a phenyl-modified organic-inorganic hybrid hydrophobic silica membrane with a contact angle of 125.0±0.4°, and the permeability of H2 reaches 8.71x10 -7 mol·m -2 Pa -1 ·s -1. Patent CN111097297A discloses a boron-doped silica hybrid membrane for seawater desalination treatment, with a permeate water flux of 12.0 - 31.0 kg·m - ²·h - ¹ and a desalination rate higher than 99.99%.

[0005] However, in practical applications, the silica membrane has poor hydrothermal stability in organic solvents or high-temperature and high-humidity environments. For example, at room temperature, the membrane has a low permeation flux and poor stability. Especially under extreme conditions, the Si–O–Si bonds in the membrane are prone to hydrolysis, resulting in a significant reduction in membrane performance.

[0006] The present invention provides a non-metal element-doped silica hybrid membrane. Using organosilane as a precursor, a non-metal element-doped silica hybrid membrane is prepared by the sol-gel method by incorporating non-metal elements into the synthetic sol. Compared with the prior art, for example, patent CN111097297A mainly uses an intermediate layer with a single structure, which is prone to structural collapse in a high-humidity environment, leading to a decline in membrane performance. The present invention optimizes the intermediate layer, which plays a key role in ensuring that the membrane has no cracks and is also the basis for improving the long-term stability and separation performance of the membrane. Summary of the Invention

[0007] Aiming at the defects of the above-mentioned SiO2 membrane, the present invention aims to provide a non-metal element-doped silica hybrid membrane, its preparation method and application. By doping non-metal elements in the synthetic sol, designing the structure of the organosilane precursor, and controlling the preparation conditions, a high-performance non-metal-doped silica hybrid membrane is prepared. This membrane has high separation performance (permeation flux and water content) and long-term hydrothermal stability, and is particularly suitable for the separation of high-concentration organic mixed solutions that are difficult to handle by pervaporation membrane technology.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A non-metal element-doped silica hybrid membrane, which is prepared by sequentially coating an intermediate layer and a separation layer on a porous support; the intermediate layer is obtained by coating an AlOOH sol added with PVA on the surface of the porous support by the sol-gel method and then calcining; the separation layer is prepared by using organosilane as a precursor, and by incorporating non-metal elements into the synthetic sol by the sol-gel method to obtain a non-metal element-doped silica sol, and coating the non-metal element-doped silica sol on the intermediate layer of the porous support and then calcining.

[0009] Further, the organosilane precursor is one or more mixtures of tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)methane, and 1,2-bis(triethoxysilyl)ethylene; the doped non-metallic element is boron, and the boron source is one or more mixtures of boric acid and triethyl borate.

[0010] The present invention also provides a method for preparing the non-metallic element-doped silica hybrid film, comprising the following steps: (1) Add aluminum isopropoxide to deionized water, stir vigorously at a certain temperature and then carry out condensation reflux; after the hydrolysis of aluminum isopropoxide, add an acid solution and continue to stir vigorously. After the solution becomes clear, remove the alcohol by opening to the air and carry out condensation reflux. After the reaction is completed, an AlOOH sol is obtained; (2) Add a certain amount of PVA to the AlOOH sol obtained in step (1) to prepare a coating solution, and then immerse the α-Al2O3 porous support in the coating solution for dip coating. First, dry at room temperature and then calcine at a high temperature; (3) Repeat the dip coating, drying, and calcination steps in step (2) 2 to 4 times to obtain a γ-Al2O3 intermediate layer; (4) Add boric acid and BTESE to 42 g of EtOH in a certain proportion, stir vigorously to form a uniform and stable precursor solution to ensure that the reactants are fully dispersed and have good reaction activity; subsequently, add an acid solution and water to adjust the pH value of the sol, stir vigorously to promote the full hydrolysis-condensation reaction of boric acid and BTESE, and obtain a boron-doped silica sol; (5) Immerse the γ-Al2O3 intermediate layer prepared in step (3) in the silica sol obtained in step (4) for dip coating, first dry at room temperature and then calcine at a high temperature; (6) Repeat the dip coating, drying, and calcination steps in step (5) 2 to 4 times to obtain a non-metallic element-doped silica hybrid film B-SiO2 / γ-Al2O3 / α-Al2O3.

[0011] Further, the synthesis ratio molar ratio of the AlOOH sol in step (1) is aluminum isopropoxide: water: acid (AIP:H2O:H + ) = 1:100~250:0.1~1.0; the stirring temperature is 50-100 °C, the stirring time is 6-24 h, the time for removing alcohol by opening to the air is 5-60 min, and the condensation reflux time is 0.5-6 h.

[0012] Further, the acid solution in step (1) or step (4) is one or more mixtures of hydrochloric acid and nitric acid.

[0013] Further, the shape of the α-Al2O3 porous support described in step (2) can be sheet-like, tubular, or hollow fiber-like, and its average pore diameter is 20-200 nm.

[0014] Further, in (2), the dip coating time is 30-90 s, the drying time is 6-24 h, the high-temperature calcination temperature is 200-600 °C, and the high-temperature calcination time is 1-6 h.

[0015] Further, the synthesis ratio molar ratio of the silica sol described in step (4) is 1,2-bis(triethoxysilyl)ethane:boric acid:nitric acid:water (BTESE / H3BO3 / H + / H2O) = 1:0~1:0.1~0.5:15~75.

[0016] The stirring temperature is 65-80 °C, the stirring time is 6-24 h, and the pH value is 3-4.

[0017] Further, in step (5), the dip coating time is 30-90 s, the drying time is 6-24 h, the high-temperature calcination temperature is 200-600 °C, and the high-temperature calcination time is 1-6 h.

[0018] The present invention also provides an application of the non-metal element-doped silica hybrid membrane prepared above in pervaporation dehydration.

[0019] Further, one application method is to use the prepared non-metal element-doped silica hybrid membrane to perform pervaporation dehydration treatment on the organic / water mixed solution: place the membrane in the membrane module for pervaporation testing, with one side of the membrane being the feed liquid side and the other side being the permeation side. The operating pressure is atmospheric pressure (0.1 MPa), and the permeation side is evacuated by a vacuum pump to a pressure less than 100 Pa to form a transmembrane pressure difference to drive the volatile components in the feed liquid to permeate through the membrane. The steam on the permeation side is condensed and collected by a cold trap to ensure the effective recovery of the permeated components. The separation performance of the membrane is evaluated by two parameters: the permeation flux J (kg·m - ²·h - ¹ ) and the water content in the permeate (%): The permeation flux J is the mass t of the permeate measured per unit membrane area A per unit time m: J = m / At ; The water content in the permeate is measured by a KF moisture meter.

[0020] Furthermore, another application method is a reactive separation coupling system with a non-metal element-doped silica hybrid membrane module as the separation core, that is, placing the prepared non-metal element-doped silica hybrid membrane in a membrane module for a pervaporation-reaction coupling system to perform pervaporation dehydration treatment on the esterification reaction.

[0021] In the coupling system, the progress of the esterification reaction is evaluated by the reaction conversion rate: In the experiment, a Shimadzu GC-2014 gas chromatograph was used for quantitative analysis by the internal standard method, and the reaction conversion rate was obtained according to the internal standard curve and peak area ratio of ethyl propionate and ethanol.

[0022] A 1 f 1 / A 2 f 2= w 1 / w 2(1) w 1 / w 2= M 1(1- X ) / M 2 X (2) Where: f is the correction factor of substance i , and the ratio of its correction factors can be obtained according to the fitted internal standard curve. M is the relative molecular mass of the substance. w 1 and w 2 conversion rates are the contents of ethanol and ethyl propionate, X which can be obtained according to the peak area ratio of ethanol and ethyl propionate.

[0023] Compared with the prior art, the beneficial effects of the present invention are: (1) The non-metal doped silica hybrid membrane prepared by the present invention has high-flux, high-selectivity, and high-stability pervaporation dehydration performance at room temperature; the water removal rate for the ester / water mixed solution is more than 97.89%, and the membrane has long-term hydrothermal stability, which is particularly suitable for the separation of high-concentration organic mixed solutions that are difficult to be treated by pervaporation membrane technology.

[0024] (2) The preparation process of the non-metal doped silica hybrid membrane of the present invention is simple and easy to operate.

[0025] (3) Using the non-metal doped silica hybrid membrane of the present invention as a membrane separation reactor in an esterification reaction coupling system, the esterification reaction breaks the conventional reaction equilibrium, and the reaction conversion rate is increased to more than 96.41%. Compared with the traditional process, this system significantly improves the reaction efficiency, reduces the energy consumption and process complexity. At the same time, the membrane separation process has the advantages of low energy consumption and no pollution, showing good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Effects of different calcination times on the performance of the intermediate layer of the silica membrane. a: Surface morphology of γ-Al2O3 / α-Al2O3 calcined once; b: Surface morphology of γ-Al2O3 / α-Al2O3 calcined twice; c: Surface morphology of γ-Al2O3 / α-Al2O3 calcined three times; d: Cross-sectional morphology of γ-Al2O3 / α-Al2O3 calcined once; e: Cross-sectional morphology of γ-Al2O3 / α-Al2O3 calcined twice; f: Cross-sectional morphology of γ-Al2O3 / α-Al2O3 calcined three times.

[0027] Figure 2 Effects of the non-metal doped silica hybrid membrane of Example 2 on the pervaporation performance of ethyl propionate / aqueous solution with different water contents.

[0028] Figure 3 Effects of different B / Si contents on the pervaporation performance of the non-metal doped silica hybrid membrane.

[0029] Figure 4 Effects of different coating times on the pervaporation performance of the non-metal doped silica hybrid membrane.

[0030] Figure 5 Long-term stability performance diagram of the non-metal doped silica hybrid membrane in an organic / water mixed solution.

[0031] Figure 6 Effects of the feed liquid flow rate on the conversion rate of the esterification reaction in the coupling process.

[0032] Figure 7 Comparison diagram between the conversion rate of continuously synthesizing ethyl propionate in the reaction-separation coupling system and the simple esterification reaction. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels.

[0034] In the following examples, BTESE was purchased from Aladdin Reagent Co., Ltd. with a concentration of 96%; tetraethyl orthosilicate was purchased from Shanghai Macklin Biochemical Co., Ltd. with a concentration of 98%; absolute ethanol was purchased from Beijing Innochem Science & Technology Co., Ltd.; concentrated nitric acid was purchased from Sinopharm Chemical Reagent Co., Ltd.; boric acid was purchased from Shanghai Macklin Biochemical Co., Ltd. with a concentration greater than 99.5%; triethyl borate was purchased from Shanghai Macklin Biochemical Co., Ltd. with a concentration of 97%.

[0035] A method for preparing a non-metal element-doped silica hybrid membrane includes the following steps: (1) Add aluminum isopropoxide to deionized water at a molar ratio of aluminum isopropoxide: water: hydrogen ion (AIP:H2O:H + ) = 1:100~250:0.1~1.0, and stir vigorously at 50 - 100 °C for 6 - 24 h, then condense and reflux; after the hydrolysis of aluminum isopropoxide, add an acid solution and continue to stir vigorously for 6 - 24 h. After the solution becomes clear, remove the alcohol by opening to the air for 5 - 60 min, and condense and reflux for 0.5 - 6 h. After the reaction is completed, obtain an AlOOH sol; (2) Add PVA with a final concentration of 0.5 wt% to the AlOOH sol obtained in step (1) to prepare a coating solution, and then immerse the α-Al2O3 porous support into the coating solution for dip coating. First, dry at room temperature, and then calcine at a high temperature; the shape of the α-Al2O3 porous support can be sheet-like, tubular, or hollow fiber-like, and its average pore diameter is 20~200 nm; the dip coating time is 30 - 90 s, the drying time is 6 - 24 h, the high-temperature calcination temperature is 200 - 600 °C, and the high-temperature calcination time is 1 - 6 h; (3) Repeat the dip coating, drying, and calcination steps in step (2) 2 - 4 times to obtain a γ-Al2O3 intermediate layer; (4) Add boric acid and BTESE to EtOH at a molar ratio of 1,2-bis(triethoxysilyl)ethane: boric acid: hydrogen ion: water (BTESE / H3BO3 / H + / H2O) = 1:0~1:0.1~0.5:15~75, stir vigorously to form a uniform and stable precursor solution to ensure that the reactants are fully dispersed and have good reaction activity; then, dropwise add an acid solution and water to adjust the pH value of the sol, and stir vigorously to promote the full hydrolysis-condensation reaction of boric acid and BTESE to obtain a boron-doped silica sol; the stirring temperature is 65 - 80 °C, the stirring time is 6 - 24 h, and the pH value is 3 - 4.

[0036] (5) Immerse the γ-Al2O3 intermediate layer prepared in step (3) into the silica sol obtained in step (4) for dip coating, first dry at room temperature, and then calcine at high temperature; the dip coating time is 30 - 90 s, the drying time is 6 - 24 h, the high-temperature calcination temperature is 200 - 600 °C, and the high-temperature calcination time is 1 - 6 h.

[0037] (6) After repeating the dip coating, drying, and calcination steps in step (5) above 2 - 4 times, a non-metal-doped silica hybrid membrane B-SiO2 / γ-Al2O3 / α-Al2O3 is obtained.

[0038] The hydrogen ions in the above step (1) or (4) are derived from an acid solution; the acid solution is one or a mixture of hydrochloric acid and nitric acid.

[0039] Example 1 A method for preparing a non-metal element-doped silica hybrid membrane, comprising the following steps: (1) According to the molar ratio AIP:H2O:HNO3 = 1:214:0.5, add aluminum isopropoxide (AIP) in small batches to deionized water. After mixing evenly, add 3 g of absolute ethanol dropwise to a three-necked flask and stir vigorously at 85 °C for 1.5 h under reflux condensation. After the hydrolysis of aluminum isopropoxide, gradually add concentrated nitric acid dropwise to adjust the pH value of the sol, and continue to stir vigorously for 1.5 h. After the solution becomes clear, remove the alcohol by opening the flask for 20 min, and then carry out reflux condensation for 2.5 h to obtain an AlOOH sol; (2) Add polyvinyl alcohol (PVA) with a final concentration of 0.5 wt% to the AlOOH sol obtained in step (1) to obtain a coating solution. Immerse a tubular α-Al2O3 porous support with an average pore size of 100 nm into the coating solution for coating. After dip coating for 60 s, dry at room temperature for 18 h, and calcine in a muffle furnace at 600 °C in an air atmosphere for 2 h; (3) After repeating the coating, drying, and calcination steps in step (2) above 1 - 3 times, a γ-Al2O3 intermediate layer with a uniform surface is obtained.

[0040] The influence of different calcination times on the performance of the intermediate layer can be seen Figure 1The results show that the surface of the membrane calcined once is relatively rough, the particle distribution is uneven, and there may be undissolved precursors locally. The membrane layer is thin and the structure is loose, with more pores inside. This may be because the temperature and time of calcination once are insufficient, and the decomposition of the precursor and the sintering of particles are incomplete, resulting in a lack of densification and uniformity on the surface. The surface of the membrane calcined three times is the smoothest and the particle distribution is uniform, without obvious cracks or accumulation. The membrane layer has a moderate thickness, a dense structure, and significantly reduced pores. This may be due to the multi-step heat treatment of calcination three times, which fully decomposes the precursor and enhances the sintering of particles, making the particles inside the membrane layer tightly combined, with the lowest porosity, forming a uniform and smooth surface, indicating that calcination three times can optimize the surface quality of the membrane layer.

[0041] Example 2 A method for preparing a non-metal element doped silica hybrid membrane, comprising the following steps: (1) According to the molar ratio AIP:H2O:HNO3 = 1:214:0.5, add aluminum isopropoxide in small batches to deionized water. After mixing evenly, add 3 g of absolute ethanol dropwise to a three-necked flask and stir vigorously at 85 °C, with reflux condensation for 1.5 h; after the hydrolysis of aluminum isopropoxide, dropwise add concentrated nitric acid to adjust the pH value of the sol, and continue to stir vigorously for 1.5 h; after the solution becomes clear, remove the alcohol by opening to the air for 20 min, and obtain an AlOOH sol after reflux condensation for 2.5 h; (2) Add 0.5 wt% PVA to the AlOOH sol obtained in step (1) to obtain a coating solution. Immerse a tubular α-Al2O3 porous support with an average pore size of 100 nm into the coating solution for coating. After dipping for 60 s, dry at room temperature for 18 h, and calcine in a muffle furnace at 600 °C in an air atmosphere for 2 h; (3) After repeating the coating, drying, and calcination steps in step (2) three times, a γ-Al2O3 carrier intermediate layer with a uniform surface can be obtained. After testing, the average pore size of the membrane is about 5 nm; (4) According to the molar ratio BTESE:H3BO3:HNO3:H2O = 1:0.25:45:0.21, add boric acid and BTESE (5 wt%) in small batches to 42 g of absolute ethanol and stir vigorously for 12 h; then, dropwise add concentrated nitric acid and water to adjust the pH value of the sol and stir vigorously for 12 h to promote the full hydrolysis-condensation reaction of boric acid and BTESE to obtain a boron-doped silica sol; (5) Immerse the γ-Al2O3 carrier intermediate layer obtained in step (3) into the boron-doped silica sol in step (4) for coating, dip for 20 s, dry at room temperature for 2 h, and calcine in a muffle furnace at 300 °C for 3 h; (6) After repeating step (5) three times, a non-metal doped silica hybrid membrane is obtained.

[0042] (7) The prepared non-metal doped silica hybrid membrane was used to investigate the pervaporation dehydration performance of the membrane by pervaporation experiment. Ethyl propionate / water solutions with water contents of 5 wt%, 10 wt%, 20 wt%, 40 wt%, and 50 wt% were used as the feed solutions, and the dehydration performance of the membrane was tested at 60 °C.

[0043] The membrane was placed in a membrane module for pervaporation testing. One side of the membrane was the feed solution side, and the other side was the permeate side. The operating pressure was atmospheric pressure (0.1 MPa), and the permeate side was evacuated to a pressure less than 100 Pa by a vacuum pump to form a transmembrane pressure difference to drive the volatile components in the feed solution to permeate through the membrane. The vapor on the permeate side was condensed and collected by a cold trap to ensure the effective recovery of the permeated components. The separation performance of the membrane was evaluated by two parameters: the permeation flux J (kg·m - ²·h - ¹) and the water content in the permeate (%) The permeation flux J was the mass m of the permeate measured per unit membrane area t per unit time A : J = m / At ; The water content in the permeate was determined by a KF moisture meter. The research results showed ( Figure 2 ), that as the water content increased from 5% to 50%, the permeation flux (Flux) of the membrane increased from 1.02 kg·m - ²·h - ¹ to 2.09 kg·m - ²·h - ¹, and then decreased to 1.66 kg·m - ²·h - ¹, showing a trend of first increasing rapidly and then stabilizing, while the separation performance (water content in the permeate) remained at a relatively high level (>95.10%), showing excellent selectivity.

[0044] Example 3 The organosilane precursor was changed to tetraethyl orthosilicate, and the boron source was triethyl borate. Other preparation conditions were the same as in Example 2. The obtained silica hybrid membrane was placed in an ethyl propionate / water solution with an initial concentration of 10 wt%, and the pervaporation performance of the silica hybrid membrane was tested at 60 °C.

[0045] Example 4 Change the H3BO3:BTESE ratio (0, 0.125, 0.25, 0.5, 0.75, 1), keep other contents in the silica sol unchanged, and keep other preparation conditions the same as in Example 2, a series of silica hybrid membranes with different B / Si doping ratios can be obtained. Using an ethyl propionate / aqueous solution with an initial concentration of 10 wt% as the feed liquid, test the pervaporation performance of these silica hybrid membranes at 60 °C, and the results are shown in Figure 3 .

[0046] The results show that the boric acid content has an important influence on both the permeation flux and selectivity of the composite membrane. When the boric acid content is 0.25 eq, the permeation flux and water content reach 2.362 kg·m - ²·h - ¹ and about 96.75% respectively, indicating that the membrane has excellent water molecule selective permeation ability at this time. At lower boric acid contents (0 eq and 0.125 eq), the permeation flux of the membrane is lower, probably due to the underdeveloped pore structure. When the boric acid content exceeds 0.5 eq, although the permeation flux increases slightly, the selectivity of water decreases significantly, indicating that the separation performance of the membrane is damaged at high boric acid contents.

[0047] Example 5 Change the coating times of the silica sol, keep other preparation conditions the same as in Example 2, a series of silica hybrid membranes with different coating times can be obtained. Using an ethyl propionate / aqueous solution with an initial concentration of 10 wt% as the feed liquid, test the pervaporation performance of these silica hybrid membranes at 60 °C, and the results are shown in Figure 4 .

[0048] The results show that the coating times have a significant influence on both the permeation flux and selectivity of the membrane. For the membrane with a single coating, the permeation flux is relatively high (about 2.88 kg·m - ²·h - ¹), but the water content selectivity is relatively low, about 87.5%, which may be due to the relatively low surface flatness of the membrane layer at this time. As the coating times increase to 3 times, the permeation flux drops to about 2.47 kg·m - ²·h - ¹, but the selectivity of water increases significantly to 96.7%, indicating that the water / organic separation performance of the membrane is the best at this time.

[0049] Example 6 For the silica hybrid membrane prepared in Example 2, using an ethyl propionate / aqueous solution with a water content of 10 wt% as the feed liquid, test the long-term pervaporation stability performance of the membrane at 60 °C, and the results are shown in Figure 5 .

[0050] The results show that after 150 minutes of continuous dehydration, both the permeation flux and separation performance of the membrane remain highly stable. The flux is stable at about 1.82 kg·m - ²·h - ⁻¹, and the water content measured by permeation remains at 96.4%, indicating the high separation performance and good hydrothermal stability of the membrane.

[0051] Example 7 Ethanol reacts with propionic acid to form ethyl propionate and water. This reaction is reversible. Water will react with ethyl propionate to form ethanol and propionic acid, consuming ethyl propionate and thus reducing the yield. Therefore, removing water from the reaction system is an effective method to promote the reaction to continue in the direction of forming ethyl propionate. The present invention realizes an esterification reaction with high conversion rate through a reaction-separation coupling system introduced by a membrane module. In this example, the silica hybrid membrane separator prepared in Example 2 was used for pervaporation dehydration.

[0052] Under the conditions of ethanol / ethyl propionate = 1:1.6 and a temperature of 80 °C, an experimental study on the efficient production of ethyl propionate by removing water through a silica membrane module using this reaction-separation coupling device was carried out. Sampling was taken from the permeate every 30 minutes to detect the contents of ethanol and ethyl propionate.

[0053] The progress of the esterification reaction in the coupling system is evaluated by the reaction conversion rate: In the experiment, a Shimadzu GC-2014 gas chromatograph was used for quantitative analysis by the internal standard method, and the reaction conversion rate was obtained based on the internal standard curves and peak area ratios of ethyl propionate and ethanol.

[0054] A 1 f 1 / A 2 f 2= w 1 / w 2(1) w 1 / w 2= M 1(1 - X ) / M 2 X (2) Where: f is the correction factor of substance i , and the ratio of its correction factors can be obtained according to the fitted internal standard curve. M is the relative molecular mass of the substance. w 1 and w 2 conversion rates are the contents of ethanol and ethyl propionate, X and can be obtained according to the peak area ratio of ethanol and ethyl propionate.

[0055] Figure 6 The results show that at different recycle flow rates, the conversion rate of the reaction system gradually increases with time. However, at high recycle flow rates (such as 3.3 mL / min and 4.4 mL / min), the conversion rate increases more rapidly and reaches stability earlier. This phenomenon indicates that the recycle flow rate has an important regulatory effect on the kinetic characteristics of the esterification reaction by affecting the separation efficiency of the membrane and the mass transfer rate of the reaction system. A moderate recycle flow rate (such as 2.2 mL / min) can ensure the stable operation of the equipment while improving the reaction conversion rate and separation efficiency. These flow conditions can effectively weaken the concentration polarization effect, increase the separation rate of water molecules, and maintain sufficient contact between the reactants and the catalyst, thereby increasing the reaction kinetic rate.

[0056] Example 8 Under the conditions of a feed liquid flow rate of 2.2 mL / min, ethanol / ethyl propionate = 1:1.6, and a temperature of 80 °C, other operations were the same as in Example 6. The results are shown in Figure 7 .

[0057] The results show that after 500 min, the calculated conversion rate of this reaction-separation reaction can reach 96.41%, approaching complete conversion, which is a significant improvement compared to the conversion rate of less than 75% in the simple esterification reaction, proving the industrial application prospects of the present invention.

[0058] As mentioned above, the above are only specific embodiments with relatively good creativity of the present invention. However, the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A non-metal element doped silica hybrid film, characterized in that, The non-metal element doped silica hybrid membrane is prepared by sequentially coating an intermediate layer and a separation layer on a porous support; the intermediate layer is prepared by coating an AlOOH sol added with PVA on the surface of the porous support by the sol-gel method and then calcining; the separation layer is prepared by using an organosilane as a precursor, and by the sol-gel method, a non-metal element doped silica sol is prepared by doping a non-metal element in a synthetic sol, and the non-metal element doped silica sol is coated on the intermediate layer of the porous support and then calcined.

2. The non-metal element-doped silica hybrid film according to claim 1, wherein The organosilane precursor is one or a mixture of more of tetraethyl orthosilicate, 1,2-bis(triethoxysilyl)ethane, 1,2-bis(triethoxysilyl)methane, 1,2-bis(triethoxysilyl)ethylene; the doped non-metal element is boron, and the boron source is one or a mixture of more of boric acid and triethyl borate.

3. The preparation method of a non-metal element-doped silica hybrid film according to claim 1, characterized in that, It includes the following steps: (1) Add aluminum isopropoxide to deionized water, stir vigorously at a certain temperature and then carry out reflux condensation; after the hydrolysis of aluminum isopropoxide, add an acid solution and continue to stir vigorously. After the solution becomes clear, remove the alcohol by opening to the air and carry out reflux condensation. After the reaction is completed, an AlOOH sol is obtained; (2) Add a certain amount of PVA to the AlOOH sol obtained in step (1) to prepare a coating solution, then immerse the α-Al2O3 porous support in the coating solution for dip coating, first dry at room temperature, and then calcine at a high temperature; (3) After repeating the dip coating, drying, and calcining steps in step (2) 2 to 4 times, a γ-Al2O3 intermediate layer is obtained; (4) Add boric acid and BTESE to absolute ethanol in a certain proportion, stir vigorously to form a uniform and stable precursor solution to ensure that the reactants are fully dispersed and have good reaction activity; subsequently, add an acid solution and water to adjust the pH value of the sol, stir vigorously to promote the full hydrolysis-condensation reaction of boric acid and BTESE, and obtain a boron-doped silica sol; (5) Immerse the γ-Al2O3 intermediate layer prepared in step (3) in the silica sol in step (4) for dip coating, first dry at room temperature, and then calcine at a high temperature; (6) After repeating the dip coating, drying, and calcining steps in step (5) 2 to 4 times, a non-metal doped silica hybrid membrane B-SiO2 / γ-Al2O3 / α-Al2O3 is obtained.

4. The preparation method according to claim 3, characterized in that: The acid solution described in step (1) or step (4) is one or a mixture of more of hydrochloric acid and nitric acid.

5. The preparation method according to claim 3, characterized in that: The synthesis ratio molar ratio of the AlOOH sol described in step (1) is aluminum isopropoxide: water: H + = 1: 100 - 250: 0.1 - 1.0; the stirring temperature in step (1) is 50 - 100 °C, the stirring time is 6 - 24 h, the reflux time is 0.5 - 6 h, and the open - mouth alcohol - removing time is 5 - 60 min.

6. The preparation method according to claim 3, characterized in that, In step (2), the dip coating time is 30 - 90 s, the drying time is 6 - 24 h, the high-temperature calcination temperature is 200 - 600 °C, and the high-temperature calcination time is 1 - 6 h.

7. The preparation method according to claim 3, wherein The synthesis ratio molar ratio of the silica sol described in step (4) is 1,2-bis(triethoxysilyl)ethane: boric acid: H + : water = 1: 0 to 1: 0.1 to 0.5: 15 to 75.

8. The preparation method according to claim 3, characterized in that, In step (4), the stirring temperature is 65 - 80 °C, the stirring time is 6 - 24 h, and the pH value is 3 - 4.

9. The preparation method according to claim 3, wherein, In step (5), the dip coating time is 30 - 90 s, the drying time is 6 - 24 h, the high-temperature calcination temperature is 200 - 600 °C, and the high-temperature calcination time is 1 - 6 h.

10. The application of the non-metal element doped silica hybrid membrane as described in claim 1 in a reaction separation coupling system.

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