Preparation method and application of MOFs ceramic membrane with membrane dispersion-catalysis function

Abstract

The application discloses a preparation method and application of a MOFs ceramic membrane with membrane dispersion-catalysis function. The method comprises the following steps: vertically placing the ceramic membrane after pretreatment in step (1) in a reaction kettle containing a mixed solution in step (2), sealing, reacting at 70-180 DEG C for 6-30 h, and obtaining the ceramic membrane with MOFs crystals loaded on the surface; taking out the composite membrane from the reaction kettle, cleaning with a second cleaning agent, then immersing in anhydrous methanol for 12-72 h for solvent exchange, and then vacuum drying to obtain the MOFs ceramic membrane with membrane dispersion-catalysis function. The preparation process is simple and has good repeatability, and in the process of sulfite oxidation, the gas is synergistically strengthened in efficient dispersion and catalytic oxidation.

Description

Technical Field

[0001] This invention belongs to the fields of flue gas desulfurization, wastewater treatment and ceramic membrane preparation, specifically relating to the preparation method and application of MOF ceramic membranes for membrane dispersion-catalysis function. Background Technology

[0002] Wet flue gas desulfurization (FGD) is an important method for flue gas desulfurization and air pollution control. It involves absorbing sulfur dioxide with an absorbent to produce sulfites, which are then oxidized to sulfates. The efficient oxidation of sulfites plays a crucial role in improving sulfur dioxide absorption efficiency, achieving sulfur dioxide fixation, and preventing secondary spillage. However, the desulfurization wastewater generated during the process also contains a large amount of sulfites due to incomplete oxidation, becoming a significant pollutant. Traditional air oxidation methods suffer from slow oxidation rates and low efficiency; therefore, the oxidation of sulfites and its process intensification have become common problems in both flue gas desulfurization and wastewater treatment.

[0003] Transition metals exhibit excellent catalytic effects on sulfite oxidation. CN102030436A discloses a method for catalytic oxidation of sulfite by adding MnO2 or manganese sand to sulfite-containing wastewater and adjusting the solution pH with HCl and NaOH. CN116139929A ​​discloses a method for preparing a Co-BTC catalyst, which is used to catalyze the desulfurization of magnesium sulfite, a byproduct of magnesium oxide desulfurization. The catalyst modulates the structure of metal nanoclusters at the atomic level to maximize atom utilization and catalytic performance.

[0004] Metal-organic frameworks (MOFs) are three-dimensional structures formed by the coordination of metal ions and organic ligands. Due to their rich topological structures and designable functional ligands, they have wide applications in catalysis, gas purification, and energy storage. MOFs have a large number of metal ions exposed on their surface, which has a very good effect on the catalytic oxidation of sulfite. For example, the Wang Lidong research group at North China Electric Power University prepared Co-MOF-74 catalyst by solvothermal method. The catalyst was added to 200 mL of magnesium sulfite solution and a mixture of oxygen and nitrogen gas with an air flow rate of 1 L / min was introduced. At pH 8, its oxidation rate reached a peak of about 0.08 mmol / L·s [Li M, Guo Q, Xing L, Yang L, Qi T. Xu P, Zhang S. Wang, L. Cobalt-Based Metal-Organic Frameworks Promoting Magnesium Sulfite Oxidation with Ultrahigh Catalytic Activity and Stability[J]. Journal of colloid and interface science, 2020, 559, 88–95.]. However, powdered MOFs are difficult to recover in practical applications, and the catalysts suffer from problems such as catalyst ion loss and secondary pollution of the solution. Therefore, in order to maximize the catalytic function of MOFs, MOF catalysts are loaded, which can be directly recovered and reused after the reaction. Summary of the Invention

[0005] The purpose of this invention is to address the problems of catalyst recovery and loss in the aforementioned background technology by providing a method for preparing and applying MOF ceramic membranes with membrane dispersion-catalysis functions. This method utilizes a solvothermal approach, vertically placing the ceramic membrane into a MOF-74 precursor solution. Under specific temperature and time conditions, metal ions coordinate with organic ligands, growing and crystallizing on the ceramic membrane surface. The membrane is then placed in a membrane dispersion reactor for the catalytic oxidation of sulfite. Simultaneously, the membrane reactor is constructed to achieve synergistic enhancement of efficient gas dispersion and catalytic oxidation during the sulfite oxidation process. This invention features a simple preparation process, good reproducibility, and ease of promotion, representing a highly efficient method for preparing catalytic composite membranes.

[0006] This invention provides the following technical solution:

[0007] A method for preparing a MOF ceramic membrane with membrane dispersion-catalysis function, the method comprising the following steps:

[0008] (1) Ceramic membrane pretreatment:

[0009] Place the ceramic membrane in the first cleaning agent and ultrasonically clean it at room temperature for 20-40 minutes, then dry it for later use.

[0010] (2) Preparation of MOF precursor solution:

[0011] Metal salts, organic ligands, and solvents are added to the polytetrafluoroethylene liner of the reactor and magnetically stirred for 10–40 min to form a MOF precursor solution.

[0012] The molar ratio of metal salt to organic ligand is 1:0.05–2.00; 0.5–5 mmol of metal salt is added per 30 mL of solvent.

[0013] The metal salt is Co(NO3)2·6H2O, FeCl2·4H2O, FeCl3·6H2O, Mg(NO3)2·6H2O, Ni(NO3)2·6H2O or Mn(NO3)2·6H2O;

[0014] The organic ligand is 2,5-dihydroxyterephthalic acid (H4DOBDC);

[0015] (3) Preparation of MOF composite membranes:

[0016] The ceramic membrane pretreated in step (1) was placed vertically in a reaction vessel containing the mixed solution from step (2), sealed, and reacted at 70–180°C for 6–30 h to obtain a ceramic membrane with MOF crystals loaded on its surface.

[0017] (4) After the composite membrane is removed from the reactor, it is cleaned with the second cleaning agent, then immersed in anhydrous methanol for 12h to 72h for solvent exchange, and then dried under vacuum to obtain MOF ceramic membrane with membrane dispersion-catalysis function.

[0018] During solvent exchange, anhydrous methanol should be replaced every 6–18 hours.

[0019] In step (1), the ceramic membrane is a sheet or tubular Al2O3, TiO2 or ZrO2 ceramic material with a pore size of 0.1 to 5 μm.

[0020] The first cleaning agent in step (1) is one or more of ultrapure water, anhydrous ethanol and acetone, and the ultrasonic cleaning time is 20 to 40 minutes.

[0021] The solvent in step (2) is one or more of N,N-dimethylformamide (DMF), ultrapure water and anhydrous ethanol / anhydrous methanol, and must contain N,N-dimethylformamide; the volume ratio is (5-20):(0-10):(0-10).

[0022] The second cleaning agent in step (4) is one or more of DMF, anhydrous ethanol and ultrapure water.

[0023] In step (4), the vacuum drying temperature is 60-150℃ and the drying time is 12-36h.

[0024] The metal-organic framework loaded on a ceramic membrane described in this invention is a hydrothermal method, which is an in-situ growth method. A certain ratio of metal salt and organic ligand is added to a specific solvent. By controlling the reaction time and reaction temperature, the loading amount and crystal morphology can be controlled.

[0025] The MOF ceramic membrane with membrane dispersion-catalysis function prepared by the method is used for membrane dispersion-catalytic oxidation of sulfite.

[0026] Specifically, the steps include: immersing the MOF ceramic membrane with membrane dispersion-catalysis function in a solution containing sulfite and reacting at room temperature for 0.1 to 1 hour to oxidize the sulfite into sulfate;

[0027] The concentration range of the sulfite-containing solution is 0.03 mol / L to 0.5 mol / L.

[0028] The sulfite mentioned is specifically sodium sulfite, magnesium sulfite, or manganese sulfite.

[0029] The essential features of this invention are:

[0030] This invention utilizes a solvothermal method to vertically immerse a ceramic membrane in a precursor solution of MOF-74. Under specific temperature and time conditions, metal ions coordinate with organic ligands and crystallize on the surface of the ceramic membrane, thereby preparing a ceramic membrane with catalytic properties. This ceramic membrane is then used to construct a membrane dispersion-membrane catalysis device to achieve efficient oxidation of sulfite. In other words, the membrane is used to form tiny air bubbles, and the catalyst on the membrane surface catalyzes the oxidation of sulfite by air.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. The ceramic membrane of this invention has a porous structure with controllable pore size, and possesses Lewis acid sites, mechanical properties, and thermal stability. It is resistant to acids and alkalis and is widely used as a catalyst support or adsorbent. Its abundant hydroxyl functional groups on the surface coordinate with metal ions, effectively reducing the nucleation energy barrier of MOFs on the substrate surface. Loading MOFs into the ceramic membrane allows for control of the pore size within the range of 0.3–0.7 μm, achieving uniform dispersion of bubbles in water.

[0033] 2. The hydrothermal method involved in this invention has the advantages of simple operation and strong controllability, and the method has the advantages of universality, scalability and simple operation.

[0034] 3. The composite membrane prepared in this embodiment is used in a membrane reactor (see attached diagram). Figure 1 The catalytic oxidation of sulfite was carried out in the experiment. Air was pumped into the device by an air compressor. The air was dispersed into microbubbles through the porous structure of the ceramic membrane, thereby enhancing gas-liquid mass transfer. The supported catalyst can accelerate the oxidation process of sulfite. The coupling of membrane dispersion and membrane catalysis allows the composite membrane of the present invention to achieve a high catalytic rate (0.93 mmol / L·min) even at low air flow rates and room temperature. Attached Figure Description

[0035] Figure 1 Diagram of the membrane reactor experimental setup;

[0036] Figure 2 These are field emission scanning electron microscope (FESEM) characterization images of the composite membranes under different hydrothermal times in Examples 2-4;

[0037] Figure 3 Field emission scanning electron microscopy (FESEM) characterization images of composite films with different precursor concentrations in Examples 5-8;

[0038] Figure 4 The catalytic performance of the composite membranes under different hydrothermal times in Examples 9-11;

[0039] Figure 5 XRD patterns at different hydrothermal temperatures in Examples 9-11

[0040] Among them, 1-air compressor; 2-buffer tank; 3-fine-tuning valve; 4-rotameter; 5-covered glass reactor; 6-water bath device; 7-membrane tank; 8-sealing clamp; 9-composite membrane; Specific implementation methods

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be understood that the following embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the above invention.

[0042] The experimental apparatus for the membrane reactor of this invention is as follows: Figure 1 As shown, an air compressor (1) stores air in a buffer tank (2). The air flow rate is controlled by a micro valve (3) and enters the reactor (5) at a certain flow rate. The flow rate can be measured by a flow meter (4). The temperature of the reaction process is controlled by a water bath device (6). The gas is dispersed into tiny bubbles by a composite membrane (7). The oxygen in the bubbles can be oxidized by the catalytic action of the catalytic layer on the membrane surface.

[0043] Example 1

[0044] (1) Ceramic membrane pretreatment

[0045] A circular alumina ceramic membrane with a diameter of 20 mm, a thickness of 2 mm, and a pore size of 2 μm was sequentially placed in ultrapure water, anhydrous ethanol, and acetone solutions and ultrasonically treated for 30 min each. After cleaning, it was removed and placed in a forced-air drying oven for drying.

[0046] (2) Preparation of MOF-74 precursor solution

[0047] Dissolve 1 mmol of Co(NO3)2·6H2O and 0.25 mmol of 2,5-dihydroxyterephthalic acid in a 30 mL mixed solution of DMF, anhydrous ethanol and ultrapure water in a volume ratio of 13:1:1, and stir magnetically for 30 min to form a homogeneous solution.

[0048] (3) Preparation of composite membrane

[0049] The cleaned and dried composite membrane was vertically placed into the precursor solution from step (2), and then sealed in a reaction vessel. The composite membrane was prepared at a hydrothermal temperature of 120°C for 8 hours. After the reaction, the composite membrane was removed after the reaction vessel had naturally cooled to room temperature.

[0050] (4) Cleaning of composite membrane

[0051] After the reaction, the composite membrane was washed sequentially with DMF, anhydrous ethanol and ultrapure water. In order to remove the high-boiling-point DMF, the composite membrane was placed in 50 mL of anhydrous methanol for solvent exchange for 3 days, with fresh solvent replaced every 12 hours. Then it was placed in a vacuum drying oven and dried overnight at 60 °C.

[0052] Examples 2-4

[0053] The other steps are the same as in Example 1, except that the hydrothermal time in step (3) is changed from 8 hours to 12, 16 and 20 hours respectively.

[0054] From the appendix Figure 2 It can be seen that as the preparation time increases, the size of the crystals increases, and the crystals transform from fine needle-like shapes to hexagonal prisms. Under the condition of 20h, uniform hexagonal prisms are formed, which conforms to the shape of MOF-74, indicating that 20h is the optimal time.

[0055] The composite membranes prepared in Examples 1-4 were subjected to sulfite catalytic oxidation experiments. The composite membranes were then passed through a sealed clamp ( Figure 1The membrane tank device shown at point 7 on the right (the same applies to the following examples) was fixed and placed in a glass reactor. 500 mL of a 0.05 mol / L sodium sulfite solution was poured into the glass reactor, and the aeration air flow rate was controlled at 100 mL / min. The catalytic performance of the composite membrane was tested at room temperature. 1 mL of solution was taken every 5 minutes from time 0 using a pipette, and the sulfite content in the solution was determined by iodometric titration. The catalytic oxidation rate was obtained by fitting the sulfite content to time. The catalytic rates of the composite membranes prepared in Examples 1-4 were 0.61811, 0.67123, 0.69863, and 0.72585 mmol / L·min, respectively.

[0056] Example 5

[0057] (1) Ceramic membrane pretreatment

[0058] A circular alumina ceramic membrane with a diameter of 20 mm, a thickness of 2 mm, and a pore size of 2 μm was sequentially placed in ultrapure water, anhydrous ethanol, and acetone solutions and ultrasonically treated for 30 min each. After cleaning, it was removed and placed in a forced-air drying oven for drying.

[0059] (2) Preparation of MOF-74 precursor solution

[0060] Dissolve 1 mmol of Co(NO3)2·6H2O and 1 mmol of 2,5-dihydroxyterephthalic acid in a 30 mL mixture of DMF, anhydrous ethanol and ultrapure water in a volume ratio of 13:1:1, and stir magnetically for 30 min to form a homogeneous solution.

[0061] (3) Preparation of composite membrane

[0062] The cleaned and dried composite membrane was vertically placed into the precursor solution from step (2), and then sealed in a reaction vessel. The composite membrane was prepared at a hydrothermal temperature of 120°C for 20 hours. After the reaction, the composite membrane was removed after the reaction vessel had naturally cooled to room temperature.

[0063] (4) Cleaning of composite membrane

[0064] After the reaction, the composite membrane was washed sequentially with DMF, anhydrous ethanol and ultrapure water. In order to remove the high-boiling-point DMF, the composite membrane was placed in 50 mL of anhydrous methanol for solvent exchange for 3 days, with fresh solvent replaced every 12 hours. Then it was placed in a vacuum drying oven and dried overnight at 60 °C.

[0065] Examples 6-8

[0066] The other steps are the same as in Example 5, except that the amount of metal salt in step (3) is changed to 1.5, 2, and 4 mmol, respectively.

[0067] From the appendix Figure 2 It can be seen that as the preparation time increases, the size of the crystals increases, and the crystals transform from fine needle-like shapes to hexagonal prisms. Under the condition of 20h, uniform hexagonal prisms are formed, which conforms to the shape of MOF-74, indicating that 20h is the optimal time.

[0068] The composite membranes prepared in Examples 5-8 were used to conduct sulfite catalytic oxidation experiments. The composite membranes were fixed in a sealed clamp and placed in a glass reactor. 500 mL of a 0.05 mol / L sodium sulfite solution was added to the glass reactor. The aeration air flow rate was controlled at 100 mL / min, and the catalytic performance of the composite membranes was tested at room temperature. 1 mL of solution was taken every 5 minutes from time 0 using a pipette, and the sulfite content in the solution was determined by iodometric titration. The catalytic oxidation rate was obtained by fitting the sulfite content against time. The catalytic rates of the composite membranes prepared in Examples 5-8 were 0.3895, 0.51445, 0.78817, and 0.84947 mmol / L·min, respectively.

[0069] Example 9

[0070] (1) Ceramic membrane pretreatment

[0071] A circular alumina ceramic membrane with a diameter of 20 mm, a thickness of 2 mm, and a pore size of 2 μm was sequentially placed in ultrapure water, anhydrous ethanol, and acetone solutions for ultrasonic treatment for 30 min. After cleaning, it was removed and placed in a forced-air drying oven for drying.

[0072] (2) Preparation of MOF-74 precursor solution

[0073] Dissolve 1 mmol of Co(NO3)2·6H2O and 0.25 mmol of 2,5-dihydroxyterephthalic acid in a 30 mL mixed solution of DMF, anhydrous ethanol and ultrapure water in a volume ratio of 13:1:1, and stir magnetically for 30 min to form a homogeneous solution.

[0074] (3) Preparation of composite membrane

[0075] The cleaned and dried composite membrane was vertically placed into the precursor solution from step (2), and then sealed in a reaction vessel. The composite membrane was prepared at a hydrothermal temperature of 80°C for 20 hours. After the reaction, the composite membrane was removed after the reaction vessel had naturally cooled to room temperature.

[0076] (4) Cleaning of composite membrane

[0077] After the reaction, the composite membrane was washed sequentially with DMF, anhydrous ethanol and ultrapure water. In order to remove the high-boiling-point DMF, the composite membrane was placed in 50 mL of anhydrous methanol for solvent exchange for 3 days, with fresh solvent replaced every 12 hours. Then it was placed in a vacuum drying oven and dried overnight at 60 °C.

[0078] Examples 10-11

[0079] The other steps are the same as in Example 9, except that the hydrothermal temperature in step (3) is changed from 80°C to 100°C and 120°C respectively.

[0080] From the appendix Figure 5 It can be seen that as the hydrothermal temperature increases, the peak intensity of Al2O3 decreases, while the characteristic peak of MOF-74 gradually becomes more prominent. At a hydrothermal temperature of 100℃, the characteristic peak intensity of MOF-74 is the strongest, indicating that 100℃ is the optimal preparation temperature.

[0081] The composite membranes prepared in Examples 9-11 were subjected to sulfite catalytic oxidation experiments. The composite membranes were fixed in a sealed clamp and placed in a glass reactor. 500 mL of a 0.05 mol / L sodium sulfite solution was added to the glass reactor. The aeration air flow rate was controlled at 100 mL / min. The catalytic performance of the composite membranes was tested at room temperature. 1 mL of solution was taken every 5 minutes from time 0 using a pipette, and the sulfite content in the solution was determined by iodometric titration. The catalytic oxidation rate was obtained by fitting the sulfite content to time. The catalytic rates of the composite membranes prepared in Examples 9-11 were 0.71, 0.93, and 0.76 mmol / L·min, respectively (see attached figure). Figure 4 (As shown).

[0082] In summary, by loading a metal-organic framework onto the surface of a porous ceramic membrane, this invention not only effectively solves the problem of catalyst loss, but also utilizes the dispersion effect of micropores in the membrane to disperse gas and form microbubbles, thereby achieving coupling between the membrane dispersion process and the solid-phase catalytic process, and ultimately leading to the oxidation of sulfite in the membrane reactor.

[0083] Matters not covered in this invention are common knowledge.

Claims

1. An application of a MOF ceramic membrane with membrane dispersion-catalysis function, characterized in that it is used for... Membrane-dispersed catalytic oxidation of sulfite; comprising the following steps: immersing a MOF ceramic membrane with membrane dispersion-catalysis function into a solution containing sulfite, reacting at room temperature for 0.1~1h, so that the sulfite is oxidized to sulfate; The concentration range of the sulfite-containing solution is 0.03 mol / L to 0.5 mol / L; The sulfite mentioned is specifically sodium sulfite, magnesium sulfite, or manganese sulfite; The method for preparing MOF ceramic membranes with membrane dispersion-catalysis function includes the following steps: (1) Ceramic membrane pretreatment: The ceramic membrane is ultrasonically cleaned and dried for later use. (2) Preparation of MOF precursor solution: Metal salts, organic ligands, and solvents are added to the polytetrafluoroethylene liner of the reactor and magnetically stirred for 10-40 min to form a MOF precursor solution. The molar ratio of metal salt to organic ligand is 1:0.05~2.00; 0.5~5 mmol of metal salt is added per 30 mL of solvent; The metal salt is Co(NO3)2·6H2O, FeCl2·4H2O, FeCl3·6H2O or Mn(NO3)2·6H2O; The organic ligand is 2,5-dihydroxyterephthalic acid (H4DOBDC). (3) Preparation of MOF composite membranes: The ceramic membrane pretreated in step (1) was placed vertically in a reaction vessel containing the mixed solution from step (2), sealed, and reacted at 70~180℃ for 6~30 h to obtain a ceramic membrane with MOF crystals loaded on its surface. (4) After the composite membrane is taken out of the reactor and cleaned, it is then immersed in anhydrous methanol for 12h~72h for solvent exchange, and then dried under vacuum to obtain MOF ceramic membrane with membrane dispersion-catalysis function. In step (1), the ceramic membrane is a sheet or tubular Al2O3, TiO2 or ZrO2 ceramic material with a pore size of 0.1~5μm; The solvent in step (2) is N,N-dimethylformamide (DMF), ultrapure water and anhydrous ethanol, or N,N-dimethylformamide (DMF), ultrapure water and anhydrous methanol, and must contain N,N-dimethylformamide; the volume ratio is (5~20):(0~10):(0~10).

2. The application of the MOF ceramic membrane with membrane dispersion-catalysis function as described in claim 1, characterized in that: The cleaning in step (1) involves ultrasonic treatment in ultrapure water, anhydrous ethanol, and acetone solution for 20-40 min respectively; the cleaning in step (4) involves rinsing in DMF, anhydrous ethanol, and ultrapure water in sequence.

3. The application of the MOF ceramic membrane with membrane dispersion-catalysis function as described in claim 1, characterized in that: In step (4), the vacuum drying temperature is 60~150℃ and the drying time is 12~36h.

4. The application of the MOF ceramic membrane with membrane dispersion-catalysis function as described in claim 1, characterized in that: During solvent exchange, replace with anhydrous methanol every 6 to 18 hours.

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