A method for preparing a high hydrothermally stable microporous water permeable membrane

Abstract

The application discloses a preparation method of a microporous water-permeable membrane with high hydrothermal stability, specifically using 1,2-di(triethoxysilyl)ethane (BTESE for short) as a precursor to prepare an Al-doped BTESE sol, and using a water vapor atmosphere sintering method to effectively remove components without hydrothermal stability in a hybrid SiO2 microporous membrane network structure. The stability of the hybrid microporous membrane under high-temperature water vapor conditions is obviously better than that of a pure SiO2 microporous membrane, and the water vapor permeation rate is also higher than that of the pure SiO2 microporous membrane. Under the hydrothermal condition of 300 DEG C for 240 hours, the average water vapor flux of the membrane is 14.3 kg·m ‑2 ·h ‑1 , and the water vapor recovery process under a high-temperature environment has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation materials, and particularly relates to a method for preparing a microporous water-permeable membrane with high hydrothermal stability. Background Art

[0002] Microporous SiO2 membranes have advantages such as excellent acid and alkali resistance, thermal stability, and designable pore size. In recent years, they have been widely studied in fields such as gas separation, pervaporation, and membrane catalytic reactors, and have potential application prospects. However, the first generation of pure SiO2 membranes prepared using tetraethyl orthosilicate (TEOS) as a precursor are rich in hydroxyl groups on the surface. This easily causes the membrane's Si-O-Si skeleton to collapse when used in high-temperature, water-containing environments, resulting in poor hydrothermal stability, which limits their application.

[0003] Researchers have conducted extensive research on the hydrothermal stability of microporous SiO2 membranes. European Patent EP-A1089806 discloses hydrophobic microporous SiO2 membranes, hoping to improve their hydrothermal stability by increasing their hydrophobicity. However, the -Si-O-Si- structure of SiO2 membranes prepared with methyltriethoxysilane (MTES) and TEOS remains susceptible to hydrolysis, and the hydrothermal stability of these membranes has not been significantly improved after modification.

[0004] Patent CN 101664647A discloses a method for preparing an organic-inorganic composite SiO2 gas separation membrane. The invention details the following: The organic-inorganic composite SiO2 gas separation membrane is prepared via an acid-catalyzed two-step sol-gel process. The membrane maintains stable gas permeability in a 200°C water vapor environment, with a pore size of 0.2-0.55 nm. This overcomes the larger pore size problem of SiO2 membranes prepared using a one-step sol-gel process using BTESE as a precursor. The membrane also exhibits excellent CO2 / He separation performance and hydrothermal stability in a 200°C water vapor environment.

[0005] However, for waste incineration plants, there is a large amount of 200-300°C water vapor that needs to be recovered, and at the same time, excellent water permeability is required, which puts higher hydrothermal stability and water permeability requirements on the SiO2 membrane. Summary of the Invention

[0006] The purpose of the present invention is to improve the stability of the existing SiO2 microporous membrane in a water vapor environment and propose a method for preparing a highly hydrothermally stable water-permeable membrane, so as to solve the problem in the prior art that the hydrothermal stability of the SiO2 microporous membrane is difficult to use in waste incineration plants to recover high-temperature water vapor of 200-300°C, while improving the water permeability to enhance the steam recovery efficiency.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a microporous water-permeable membrane with high hydrothermal stability, comprising the following steps:

[0008] a. Preparation of Al-BTESE sol

[0009] BTESE and a solvent are mixed in a volume ratio of 1:1 to 1:5 and placed in an ice bath. A catalyst is added thereto, and the solution is then placed in a constant temperature water bath at 50 to 70° C. to react for 1 to 2 hours. After the reaction, a solution containing an Al source is added and the mixture is reacted in a constant temperature water bath for 1 to 2 hours to obtain a transparent Al-BTESE sol.

[0010] b. Coating process

[0011] The above sol and solvent are diluted in a volume ratio of 1:2 to 1:20 to prepare a film-forming liquid, and a film is coated on the surface of the carrier by dipping and pulling.

[0012] c. Drying and sintering process

[0013] The coated carrier is placed in an oven at 25-80°C and dried for 2-24 hours; sintered in a tubular furnace using a protective gas atmosphere containing water vapor, with a water vapor content of 1%-20%, and heated to 400-700°C under gas protection, kept warm for 2-5 hours, and then cooled to obtain a hybrid SiO2 microporous membrane.

[0014] Furthermore, the total volume ratio of the precursor to the solvent in the above step a is between 1:1 and 1:10.

[0015] Furthermore, in the above step a, the molar ratio of Al element to Si element is between 1:1 and 1:10.

[0016] Furthermore, in the above step a, the acid radical ions of the Al source are consistent with the acid radical ions of the catalyst.

[0017] Furthermore, in the above step c, the protective gas is nitrogen, helium or argon; the water vapor content introduced along with the protective gas is 1% to 20%; and the heating and cooling rates are 0.5 to 5°C / min.

[0018] The beneficial effect of the present invention is that the hydrothermal stability of the hybrid SiO2 microporous membrane prepared with BTESE as a precursor is further enhanced by doping with metal Al. Compared with the pure SiO2 microporous membrane prepared under the same conditions, the water permeability of the SiO2 microporous membrane is simultaneously enhanced, providing good conditions for water vapor recovery of the SiO2 microporous membrane in a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Surface and cross-section of the hybrid SiO2 membrane prepared in the present invention before and after the water vapor flux test in a 300°C hydrothermal environment (a: surface before test, b: surface after test, c: cross-section before test, d: cross-section after test);

[0020] Figure 2 Surface and cross-section of an undoped SiO2 film (pure SiO2 film) prepared under the same conditions before and after water vapor flux testing in a 300°C hydrothermal environment (a: surface before test, b: surface after test, c: cross-section before test, d: cross-section after test);

[0021] Figure 3 This is a flux performance diagram obtained by testing the water vapor flux of the hybrid SiO2 membrane and the pure SiO2 membrane prepared in the present invention under a hydrothermal environment at 300°C. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0023] Example

[0024] Preparation of Al-doped Hybrid SiO2 Films Using BTESE as Precursor

[0025] Take 5 mL each of BTESE and anhydrous ethanol, pour them into a conical flask and place it in an ice bath, and mix them evenly by magnetic stirring; take 0.54 mL of nitric acid (1 mol·L -1 ) and 5 mL of anhydrous ethanol were mixed in a beaker, and then the mixed solution was added dropwise to the mixed solution of BTESE and anhydrous ethanol using a constant pressure funnel. The solution was stirred continuously during the addition to avoid excessive local concentration. The above solution was then placed in a 60°C water bath for reflux reaction for 1.5 hours; 2.25 g of Al(NO3)3·9H2O powder and 0.54 ml of nitric acid (1 mol·L -1 ) and 5 mL of anhydrous ethanol were mixed in a beaker and refluxed for 1.5 hours. The mixture was then refluxed in a 60°C water bath for another 1.5 hours to produce an Al-BTESE sol. This sol was then stored at -16°C until use. The sol was diluted with anhydrous ethanol in a volume ratio of 1:4 to produce a film-forming solution. A tubular γ-Al2O3 membrane was then dip-coated in the solution. After drying at 40°C for 3 hours, the solution was sintered at a heating rate of 0.5°C / min in a nitrogen atmosphere with a water vapor content of 1% to 20%. After reaching 400°C and maintaining for 3 hours, the temperature was lowered at the same rate to produce an Al-doped hybrid SiO2 film with BTESE as the precursor.

[0026] Comparative Example

[0027] Preparation of undoped pure SiO2 film using BTESE as precursor

[0028] Take 5 mL each of BTESE and anhydrous ethanol, pour them into a conical flask and place it in an ice bath, and mix them evenly by magnetic stirring; take 0.24 mL of nitric acid (1 mol·L -1 ) and 5 mL of anhydrous ethanol were mixed in a beaker. Then, the mixed solution was added dropwise to the mixed solution of BTESE and anhydrous ethanol using a constant pressure funnel. The solution was stirred continuously during the addition to avoid excessive local concentration. The above solution was then placed in a 60°C water bath and refluxed for 1.5 hours. Then, 0.3 mL of nitric acid (1 mol·L -1 ) and 5 mL of anhydrous ethanol were mixed in a beaker and refluxed for 1.5 hours. The mixture was then refluxed in a 60°C water bath for another 1.5 hours to obtain a BTESE sol. This sol was then stored at -16°C until use. The sol was diluted with anhydrous ethanol in a volume ratio of 1:4 to obtain a film-forming solution. A tubular γ-Al2O3 membrane was then dip-coated in the solution. After drying at 40°C for 3 hours, the solution was sintered at a heating rate of 0.5°C / min in a nitrogen atmosphere with a water vapor content of 1% to 20%. After reaching 400°C and maintaining for 3 hours, the temperature was lowered at the same rate to obtain an undoped pure SiO2 film with BTESE as the precursor.

[0029] See also Figure 1 Surface and cross-section images of the prepared hybrid SiO2 membrane before and after water vapor flux testing in a 300°C hydrothermal environment (a: surface before test, b: surface after test, c: cross-section before test, d: cross-section after test). Figure (a) shows that the hybrid SiO2 membrane has a distinct three-layer asymmetric structure: the bottom layer is an α-Al2O3 substrate, the transition layer is a γ-Al2O3 modified layer with a thickness of approximately 2μm, and the separation layer is the hybrid SiO2 membrane with a thickness of approximately 100nm. The membrane surface is smooth, dense, and free of defects. Figures (a) and (b) show that the surface morphology of the hybrid SiO2 membrane remained unchanged after testing, with no cracks or defects. Figures (c) and (d) show that the cross-sectional morphology of the membrane remained unchanged after testing.

[0030] See also Figure 2Surface and cross-section images of a prepared pure SiO2 membrane before and after a water vapor flux test in a 300°C hydrothermal environment (a: surface before test, b: surface after test, c: cross-section before test, d: cross-section after test). Figure (a) shows that the pure SiO2 membrane has a distinct three-layer asymmetric structure: the bottom layer is an α-Al2O3 substrate, the transition layer is a γ-Al2O3 modified layer with a thickness of approximately 2μm, and the separation layer is a pure SiO2 membrane with a thickness of approximately 100nm. The membrane surface is smooth, dense, and free of defects. Figures (a) and (b) show that the surface morphology of the pure SiO2 membrane remained unchanged after testing, with no cracks or defects. Figures (c) and (d) show that the separation layer of the pure SiO2 membrane exhibited significant structural collapse and seepage after testing.

[0031] See also Figure 3 The flux performance diagram of the hybrid SiO2 membrane and the pure SiO2 membrane obtained by water vapor flux testing in a 300℃ hydrothermal environment. It can be seen from the figure that the overall trend of the water vapor flux of the hybrid SiO2 membrane in a 300℃ hydrothermal environment is relatively stable, and the water vapor flux remains in the range of 12-20 kg·m -2 ·h -1 The water vapor flux of pure SiO2 membrane showed a trend of first being stable and then increasing. Figure 2 It can be speculated that the collapse and infiltration of the separation layer structure of the pure SiO2 membrane caused defects in the membrane, resulting in an increase in water vapor flux; it can be seen that the hydrothermal stability of the hybrid SiO2 membrane in a hydrothermal environment of 300°C is significantly better than that of the pure SiO2 membrane; when the membrane performance is stable, the water vapor flux of the hybrid SiO2 membrane is slightly higher than that of the pure SiO2 membrane.

Claims

1. A method for preparing a water-permeable microporous membrane with high hydrothermal stability, the specific steps of which are: a. Preparation of Al-BTESE sol The precursor BTESE and solvent are mixed in a volume ratio of 1:1 to 1:5 and placed in an ice bath. A catalyst is added to the mixture, and the solution is then placed in a constant temperature water bath at 50 to 70°C for 1 to 2 hours. After the reaction, a solution containing an Al source is added and the mixture is allowed to react in a constant temperature water bath for 1 to 2 hours to obtain a transparent Al-BTESE sol. The Al source is Al(NO3)3·9H2O, Al2(SO4)3 and AlCl3; the solution containing the Al source is composed of a solvent, an Al source and a catalyst; b. Coating process The Al-BTESE sol and solvent are diluted in a volume ratio of 1:2 to 1:20 to prepare a film-forming solution, and a film is applied on the surface of the support by dipping and pulling; c. Drying and sintering process The coated carrier is placed in an oven at 25-80°C and dried for 2-24 hours; sintered in a tubular furnace under a protective gas atmosphere containing water vapor with a water vapor content of 1%-20%, heated to 400-700°C, kept warm for 2-5 hours, and then cooled to obtain a hybrid SiO2 microporous membrane.

2. The method for preparing a highly hydrothermally stable water-permeable membrane according to claim 1, wherein: The total volume ratio of the precursor to the solvent in the above step a is between 1:1 and 1:

10.

3. The method for preparing a highly hydrothermally stable water-permeable membrane according to claim 1, wherein: In the above step a, the molar ratio of Al element to Si element is between 1:1 and 1:

10.

4. The method for preparing a highly hydrothermally stable water-permeable membrane according to claim 1, wherein: In the above step a, the acid radical ions of the Al source are consistent with the acid radical ions of the catalyst.

5. The method for preparing a highly hydrothermally stable water-permeable membrane according to claim 1, wherein: In step c, the protective gas is nitrogen, helium or argon; the water vapor content introduced along with the protective gas is 1% to 20%; and the heating and cooling rates are 0.5 to 5°C / min.

Images