Preparation method of microporous water-permeable membrane with high hydrothermal stability

Abstract

The invention discloses a preparation method of a microporous water-permeable membrane with high hydrothermal stability, which specifically comprises the following steps: preparing Al-doped BTESE sol by taking 1, 2-bis (triethoxysilyl) ethane (BTESE for short) as a precursor, and effectively removing components without hydrothermal stability in a hybrid SiO2 microporous membrane network structure by adopting a water vapor atmosphere sintering method. The stability of the hybrid microporous membrane under the condition of high-temperature water vapor is obviously superior to that of a pure SiO2 microporous membrane, and the water vapor permeability is also higher than that of the pure SiO2 microporous membrane. Within 240 hours and under the hydrothermal condition of 300 DEG C, the average flux of water vapor of the membrane is 14.3 kg.m <-2 >. H <-1 >, and the membrane has a good application prospect in the water vapor recovery process in a high-temperature environment.

Description

Technical Field

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

[0002] Microporous SiO2 membranes have the advantages of good acid and alkali resistance, thermal stability, and adjustable pore size. In recent years, they have been widely studied in the fields of gas separation, pervaporation, and membrane catalytic reactors, and have potential application prospects. However, the surface of the first generation of pure SiO2 membranes prepared with tetraethyl orthosilicate (TEOS) as a precursor is rich in hydroxyl groups, which can easily cause the collapse of the Si-O-Si skeleton of the membrane when used in a high-temperature water vapor environment, and the hydrothermal stability is poor, thus limiting its application.

[0003] Researchers have done a lot of research on the hydrothermal stability of microporous SiO2 membranes. European patent EP-A1089806 discloses a hydrophobic microporous SiO2 membrane, hoping to improve the hydrothermal stability of the membrane by improving the hydrophobicity of the membrane. However, the -Si-O-Si- of the SiO2 membrane prepared with methyltriethoxysilane (MTES) and TEOS is still easily hydrolyzed, and the hydrothermal stability after modification has not been greatly improved.

[0004] Patent CN 101664647A discloses a method for preparing an organic-inorganic composite SiO2 gas separation membrane. The invention content is as follows: an organic-inorganic composite SiO2 gas separation membrane is prepared by an acid-catalyzed two-step sol-gel method. The membrane maintains stable gas permeability in a 200°C water vapor environment. The pore size of the membrane is 0.2-0.55nm, which overcomes the problem of large pore size of SiO2 membranes prepared by a one-step sol-gel method using BTESE as a precursor. It also has 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 requirements on hydrothermal stability and water permeability of SiO2 membranes. 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 to 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 to 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 then the solution is 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; and a transparent Al-BTESE sol is obtained.

[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-making solution, and a film is applied 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 in a protective gas atmosphere containing water vapor, with a water vapor content of 1%-20%, heated to 400-700°C under gas protection, kept warm for 2-5 hours, and then cooled; a hybrid SiO2 microporous membrane is obtained.

[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 ions of the Al source are consistent with the acid 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, which provides good conditions for water vapor recovery of the SiO2 microporous membrane in a high temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The 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 the test, b: surface after the test, c: cross section before the test, d: cross section after the test);

[0020] Figure 2 The surface and cross section of the undoped SiO2 film (pure SiO2 film) prepared under the same conditions 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);

[0021] Figure 3 This is a flux performance diagram obtained by conducting a water vapor flux test on the hybrid SiO2 membrane and the pure SiO2 membrane prepared in the present invention under a 300°C hydrothermal environment. 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 Film Using BTESE as Precursor

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

[0026] Comparative Example

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

[0028] Take 5 mL of BTESE and anhydrous ethanol, pour them into a conical flask and place it in an ice bath. Mix the two 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, and then the mixed solution was added drop by drop into the mixed solution of BTESE and anhydrous ethanol using a constant pressure funnel. The solution was stirred continuously during the addition process to avoid excessive local concentration. The above solution was then placed in a 60°C water bath for reflux reaction for 1.5 hours; 0.3 mL of nitric acid (1 mol·L -1 ) and 5mL of anhydrous ethanol were mixed evenly in a beaker, and after reflux reaction for 1.5 hours, the mixture was added and refluxed in a water bath at 60°C for 1.5 hours to obtain BTESE sol. It was stored at -16°C for use. The sol was diluted with anhydrous ethanol in a volume ratio of 1:4 to obtain a film-making solution, and the tubular γ-Al2O3 film was pulled and dipped in the film-making solution. After drying at 40°C for 3 hours, it 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 keeping it for 3 hours, it was cooled at the same rate to obtain an undoped pure SiO2 film with BTESE as a precursor.

[0029] See also Figure 1 The surface and cross section of the prepared hybrid SiO2 membrane before and after the water vapor flux test in a 300℃ hydrothermal environment (a: surface before test, b: surface after test, c: cross section before test, d: cross section after test); As can be seen from Figure (a), the hybrid SiO2 membrane has an obvious three-layer asymmetric structure, in which the bottom layer is an α-Al2O3 substrate, the transition layer is a γ-Al2O3 modified layer with a thickness of about 2μm, and the separation layer is a hybrid SiO2 membrane with a thickness of about 100nm. The membrane surface is smooth, dense and defect-free. As can be seen from Figures (a) and (b), after the hybrid SiO2 membrane is tested, the surface morphology of the membrane does not change significantly, there are no cracks, and no defects. As can be seen from Figures (c) and (d), after the test, the cross-sectional morphology of the membrane does not change significantly.

[0030] See also Figure 2The surface and cross section of the prepared pure SiO2 membrane before and after the water vapor flux test in a 300℃ hydrothermal environment (a: surface before test, b: surface after test, c: cross section before test, d: cross section after test); As can be seen from Figure (a), the pure SiO2 membrane has an obvious three-layer asymmetric structure, in which the bottom layer is an α-Al2O3 substrate, the transition layer is a γ-Al2O3 modified layer with a thickness of about 2μm, and the separation layer is a pure SiO2 membrane with a thickness of about 100nm. The membrane surface is smooth, dense and defect-free. As can be seen from Figures (a) and (b), the surface morphology of the pure SiO2 membrane did not change significantly after the test, and there were no cracks or defects. As can be seen from Figures (c) and (d), after the test, the separation layer of the pure SiO2 membrane showed obvious structural collapse and infiltration.

[0031] See also Figure 3 The flux performance diagram of the hybrid SiO2 membrane and the pure SiO2 membrane obtained by water vapor flux test 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 is maintained at 12-20kg·m -2 ·h -1 The water vapor flux of pure SiO2 membrane showed a trend of first being stable and then rising. 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 300°C hydrothermal environment 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 the 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 then the solution is 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; b. Coating process The Al-BTESE sol and the solvent are diluted in a volume ratio of 1:2 to 1:20 to prepare a film-making solution, and a film is applied on the surface of the carrier 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 in a protective gas atmosphere containing water vapor, the water vapor content of which is 1%-20%, and heated to 400-700°C, kept warm for 2-5 hours and then cooled; a hybrid SiO2 microporous membrane is obtained.

2. The method for preparing a highly hydrothermally stable water-permeable membrane according to claim 1, characterized in that: In the step a, 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.

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

10.

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

10.

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

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

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