Preparation method of multichannel NaA molecular sieve membrane

Abstract

The invention belongs to the technical field of preparation of molecular sieve membrane materials, and discloses a preparation method of a multichannel NaA molecular sieve membrane, which comprises the following steps: (1) sealing a carrier; (2) a PEI modification method; (3) synthesizing a molecular sieve membrane; and (4) quenching the reaction kettle with tap water after the reaction is finished, taking out the membrane tube, and soaking in deionized water until the membrane tube is neutral. According to the preparation method, the use of seed crystals is reduced by controlling the concentration of amino modifiers such as PEI, the synthesis process of the molecular sieve membrane is simplified, meanwhile, the problem that the coating binding force of the seed crystals is not strong is solved, and the method is high in universality and more beneficial to large-scale preparation of the molecular sieve membrane.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve membrane material preparation technology, and relates to a method for preparing a multi-channel LTA molecular sieve membrane. Background Technology

[0002] In the search for lower-energy-consumption seawater desalination technologies, membrane separation technology has attracted much attention due to its potential energy efficiency advantages. Zeolite molecular sieve membranes, especially LTA-type molecular sieve membranes with regular sub-nanometer pore sizes and excellent chemical stability, have demonstrated superior separation performance in solvent dehydration. Their multi-channel tubular configuration has been proven to be an effective engineering solution for achieving high-throughput, large-scale membrane separation processes. Naturally, applying this mature multi-channel molecular sieve membrane structure to seawater desalination to replace or supplement existing reverse osmosis membranes has become an attractive research direction. However, this technological approach faces fundamental challenges. The core of seawater desalination is the removal of salt ions (such as Na+) from the water. + and Cl - Its hydration diameter is typically less than 0.8 nanometers, which requires the separation membrane to have a finer pore size (typically less than 0.7 nanometers) and a very strong electrostatic repulsion for ions.

[0003] Therefore, existing technologies indicate that directly applying existing multichannel LTA molecular sieve membranes to seawater desalination is not yet mature. There is an urgent need in this field for a novel membrane material or membrane structure design that can inherit the high flux and high stability engineering advantages of multichannel membranes while achieving efficient and stable separation against high salt ion concentrations in seawater. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a method for preparing a multi-channel LTA molecular sieve membrane, which has a continuous and dense membrane layer and excellent performance in pervaporation and desalination.

[0005] The technical solution of the present invention: A method for preparing a multi-channel NaA molecular sieve membrane, comprising the following steps: (1) Sealing of the carrier; (2) PEI modification method: PEI solution is prepared by using organic solvent. Polytetrafluoroethylene tape is wrapped around the outer surface of the carrier obtained in step (2). After preheating in an oven at 140℃~175℃ for 3 hours, it is taken out and immersed in PEI solution. After immersion, it is placed in an oven for curing. (3) Synthesis of molecular sieve membrane: The silicon source, aluminum source, alkali source and water are mixed and stirred to form a synthesis solution. The molar ratio of the synthesis solution is Al2O3 / SiO2 = 4~5, Na2O / Al2O3 = 40~50, H2O / Al2O3 = 800~1000. After the prepared synthesis solution is aged, the PEI-modified carrier in step (4) is loaded into the reactor, the synthesis solution is poured in, and hydrothermal synthesis is performed. The oven speed is controlled during the synthesis of molecular sieve membrane. (4) After the reaction is complete, use tap water to cool the reactor quickly, remove the membrane tube, and soak it in deionized water until it is neutral.

[0006] Sealing of the carrier in step (1): First, soak the carrier in deionized water, then dry it, preheat it to 80°C, vertically immerse one end of the carrier in the glaze for 30 seconds, naturally drain the excess glaze from the carrier, then dry it. After it is dry, immerse the other end. The glaze immersion steps for both ends are the same, and the length of the glaze immersion at both ends is 1.5 to 2 cm. Repeat the glaze immersion step for each end of the carrier twice. Place the dried carrier on a support, heat it to 1250°C at a heating rate of 3°C / min, keep it for 6 hours, and cool it down at a rate of 3°C / min. Then take it out.

[0007] The carrier is a multi-channel alumina or zirconium oxide, and the pore size on the carrier surface is 100nm~2000nm.

[0008] The concentration of the PEI solution is 5wt%~15wt%, the organic solvent is anhydrous ethanol or isopropanol, and the immersion time of the PEI solution is 30s~120s.

[0009] The PEI was replaced with 3-aminopropyl-3-ethoxysilane.

[0010] The oven rotates at a speed of 5 rpm to 15 rpm.

[0011] The hydrothermal synthesis temperature is 60℃~100℃, and the synthesis time is 3h~24h.

[0012] The aging time is 3 to 9 hours.

[0013] The beneficial effects of this invention are that by controlling the concentration of amino modifiers such as PEI, the use of seed crystals is reduced, simplifying the synthesis process of molecular sieve membranes. At the same time, it reduces the problem of weak adhesion of seed crystal coating. This method has strong universality and is more conducive to the large-scale preparation of molecular sieve membranes.

[0014] The desalination performance of a membrane can be represented by two parameters: the liquid permeate flux J and the separation coefficient α. The liquid permeate flux J represents the mass of liquid passing through a unit area of ​​the membrane per unit time, J = M / (A×t), with units of kg / (m²). 2 h), the rejection rate is R=(1-Cp / Cf)×100%, where Cp is the solute concentration in the feed liquid and Cf is the solute concentration in the permeate (product water). Attached Figure Description

[0015] Figure 1 This is a SEM image of the film layer in Example 1; Figure 2 SEM cross-sectional view of the film layer in Example 1; Figure 3 This is the experimental flowchart for LTA molecular sieve membranes; Figure 4 This is a SEM image of the film layer in Example 2; Figure 5 This is a SEM cross-sectional image of the film layer in Example 2; Detailed Implementation

[0016] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0017] Example 1 (1) Sealing of the carrier: The number of channels of the multi-channel carrier is 7 and 19. First, the carrier is soaked in deionized water, then dried in an oven, preheated to 80°C, and one end of the carrier is vertically immersed in the glaze liquid for 30 seconds. The excess glaze liquid in the carrier is naturally drained, and then placed in an oven to dry for 20 minutes. After it is dry, the other end is immersed. The steps are the same. The glaze liquid immersion length at both ends is 1.5 to 2 cm. The glaze liquid immersion step at each end of the carrier is repeated twice. The dried carrier is placed on a support and the glaze is fired in a high-temperature box furnace. The heating rate is 3°C / min. The temperature is raised to 1250°C and held for 6 hours. The cooling rate is also 3°C / min. After sintering is completed, the carrier is taken out. (2) Introduction of PEI: Wrap the outside of the sealed multichannel carrier in step (1) with polytetrafluoroethylene tape, place it in an oven at 140℃ for preheating for more than 3 hours, weigh 24g of PEI, dissolve it in 216g of anhydrous ethanol to prepare a 10wt% PEI solution, immerse the preheated carrier in the PEI solution for 60s, and after immersion, take out the carrier and place it in an oven at 80℃ for curing for more than 3 hours.

[0018] (3) Synthesis of molecular sieve membrane: Weigh 6.2171g NaAlO2 and 101.0064g NaOH into a beaker, add 438.7556g H2O to prepare an aluminum source solution, stir evenly, weigh 18.7406g silica sol AS-40, add silica sol dropwise to the aluminum source solution, age at 30℃ for 6h, wrap the outside of the PEI-introduced carrier with polytetrafluoroethylene tape, put it into the reactor, pour the aged synthesis solution along the inner wall of the reactor, seal it and put it into a rotary oven, set the reaction temperature to 70℃, the reaction time to 16h, and the oven speed to 10 rpm.

[0019] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 8.78 kg / (m²). 2 h), with a retention rate of 99.96%.

[0020] Example 2 (1) Sealing of the carrier: Same as in Example 1.

[0021] (2) Same as in Example 1, except that the PEI concentration is 15% and the PEI immersion time is 30s.

[0022] (3) Same as in Example 1, except that the aging time is 5h, the crystallization time is 24h, and the crystallization temperature is 60℃.

[0023] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 6.45 kg / (m²). 2 h), with a retention rate of 99.96%.

[0024] Example 3 (1) Sealing of the carrier: Same as in Example 1.

[0025] (2) Same as in Example 1, except that the PEI concentration is 5% and the PEI immersion time is 120s.

[0026] (3) Same as in Example 1, except that the aging time is 9h, the crystallization time is 24h, and the crystallization temperature is 60℃.

[0027] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 10.53 kg / (m²). 2 h), with a retention rate of 98.53%.

[0028] Example 4 (1) Sealing of the carrier: Same as in Example 1.

[0029] (2) Same as in Example 1.

[0030] (3) Same as in Example 1, except that the aging time is 9h, the crystallization time is 3h, and the crystallization temperature is 100℃.

[0031] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 8.96 kg / (m²). 2 h), with a retention rate of 99.94%.

[0032] Example 5 (1) Sealing of the carrier: Same as in Example 1.

[0033] (2) Same as in Example 1.

[0034] (3) Same as in Example 1, except that the rotational speed of the oven is 15 rpm.

[0035] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 7.63 kg / (m²). 2 h), with a retention rate of 99.92%.

[0036] Example 6 (1) Sealing of the carrier: Same as in Example 1.

[0037] (2) Same as in Example 1.

[0038] (3) Same as in Example 1, except that the rotational oven speed is 5 rpm.

[0039] The molecular sieve membrane synthesized in this embodiment exhibits the following pervaporation desalination performance (3.5% wt NaCl solution) at 75°C: permeation flux 6.48 kg / (m²). 2 h), with a retention rate of 99.91%.

Claims

1. A method for preparing a multi-channel NaA molecular sieve membrane, characterized in that, The steps are as follows: (1) Sealing of the carrier; (2) PEI modification method: PEI solution is prepared by using organic solvent. Polytetrafluoroethylene tape is wrapped around the outer surface of the carrier obtained in step (2). After preheating in an oven at 140℃~175℃ for 3 hours, it is taken out and immersed in PEI solution. After immersion, it is placed in an oven for curing. (3) Synthesis of molecular sieve membrane: Silicon source, aluminum source, alkali source and water are mixed and stirred to form a synthesis solution. The molar ratio of the synthesis solution is Al2O3 / SiO2 = 4~5, Na2O / Al2O3 = 40~50, H2O / Al2O3 = 800~1000. After the prepared synthesis solution is aged, the PEI modified carrier in step (4) is loaded into the reaction vessel, the synthesis solution is poured in, and hydrothermal synthesis is performed. Controlling the oven speed during the synthesis of molecular sieve membranes; (4) After the reaction is complete, use tap water to cool the reactor quickly, remove the membrane tube, and soak it in deionized water until it is neutral.

2. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, Sealing of the carrier in step (1): First, soak the carrier in deionized water, then dry it, preheat it to 80°C, vertically immerse one end of the carrier in the glaze for 30 seconds, naturally drain the excess glaze from the carrier, then dry it. After it is dry, immerse the other end. The glaze immersion steps for both ends are the same, and the length of the glaze immersion at both ends is 1.5 to 2 cm. Repeat the glaze immersion step for each end of the carrier twice. Place the dried carrier on a support, heat it to 1250°C at a heating rate of 3°C / min, keep it for 6 hours, and cool it down at a rate of 3°C / min. Then take it out.

3. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The carrier is a multi-channel alumina or zirconium oxide, and the pore size on the carrier surface is 100nm~2000nm.

4. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The concentration of the PEI solution is 5wt%~15wt%, the organic solvent is anhydrous ethanol or isopropanol, and the immersion time of the PEI solution is 30s~120s.

5. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The PEI was replaced with 3-aminopropyl-3-ethoxysilane.

6. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The oven rotates at a speed of 5 rpm to 15 rpm.

7. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The hydrothermal synthesis temperature is 60℃~100℃, and the synthesis time is 3h~24h.

8. The method for preparing a multi-channel NaA molecular sieve membrane according to claim 1, characterized in that, The aging time is 3 to 9 hours.

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