A highly stable MOF membrane, preparation and gas-liquid separation applications thereof

Abstract

The application discloses a kind of high-stability MOF membranes and its preparation and gas-liquid separation application.First, dense MIL-140s seed layer is deposited on porous support;Then it is placed in precursor liquid containing metal source and organic ligand, and gradually fills the gap between seed layer by coordination reaction of metal source and organic ligand through certain period of thermally induced growth, finally forming continuous well anastomosed MIL-140s membrane layer;Gas (liquid) body separation test shows that MIL-140s membrane has excellent gas-liquid separation performance.It is particularly pointed out that changing thermally induced growth temperature can significantly control and optimize MIL-140s membrane microstructure (such as crystal orientation, membrane thickness, intercrystalline defect, etc.), thereby changing MIL-140s membrane separation channel size and corresponding separation system.The above research results are expected to realize the directional design and controllable optimization of MOF membrane microtopography and separation performance, and have good industrial application prospect.

Description

A highly stable MOF membrane, its preparation and gas-liquid separation application Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a highly stable MOF membrane, its preparation, and its gas-liquid separation application. Background Technology

[0002] Separation and purification play a crucial role in the chemical industry, but existing separation technologies are energy-intensive, necessitating the development of new, highly efficient separation technologies. Membrane separation, as a novel separation process driven by pressure difference, offers significant advantages such as high separation efficiency, low energy consumption, and simple operation. Crystalline molecular sieve membranes, especially metal-organic framework (MOF) membranes, as a new type of microporous membrane material, have demonstrated excellent performance in various gas-liquid separation fields in recent years due to their uniform and controllable pore size and excellent directional design characteristics. Considering the demands of actual separation conditions, such as high-temperature and high-pressure (~50℃ / 20bar) propylene / propane separation and high-humidity CO2 capture, the stability of the membrane material is also crucial. Therefore, an ideal MOF membrane should possess both excellent separation performance and operational stability, and the core of this is the MOF material itself; the pore environment, surface chemistry, and structural stability of the MOF material significantly affect the overall separation performance of the membrane.

[0003] High-valence metal ions and carboxylate ligands, considered hard bases, can be used to construct MOF materials with ultra-stable topologies based on the hard-soft acid-base theory, such as UiO-66 and MIL-125. Using these as building blocks, highly stable MOF membranes can be created to meet the demands of stringent separation conditions. However, existing highly stable MOF materials have relatively large pore sizes (e.g., UiO-66 pore size ~). The precise sieving of numerous gas (liquid) molecules with significant industrial value using appropriate membrane materials remains extremely challenging. The fabrication of ultramicroporous high-valence metal MOF crystalline molecular sieve membranes, possessing both excellent separation performance and operational stability, and enabling efficient gas-liquid separation under various complex operating conditions, holds significant scientific importance and immense application value for the field of membrane separation.

[0004] MIL-140s are a type of protein derived from Zr. 4+ Given the emerging series of highly stable MOF frameworks formed by metal ions and 1,4-phthalic acid and its derivatives, we infer that constructing highly stable crystalline MIL-140s films would be extremely attractive. Specific analysis is as follows: 1) Suitable pore size. The altered coordination mode allows MIL-140s to have pore sizes in the ultramicroporous range, such as MIL-140A with a pore size of ~ 1) Precise sieving of various small molecule mixtures such as H2 / CO2, CO2 / CH4, C2-C3 olefins / alkanes with the same number of carbon atoms, and water / alcohols; 2) One-dimensional straight channels along the c-axis. The triangular channel arrangement of MIL-140s is parallel to the c-axis, precisely controlling the grain stacking orientation and fully exposing its one-dimensional straight channels along the c-axis to construct rapid mass transfer channels for target molecules; 3) Abundant designability. Diverse carboxylate ligands and metal nodes provide multiple possibilities for fine-tuning of the pore size and directional regulation of the pore microenvironment of MIL-140s membranes; 4) Excellent stability. MIL-140s is a rare intrinsically hydrophobic MOF material. The reduction of coordination nodes and hydrophilic groups further improves its heat resistance, pressure resistance, and acid resistance. However, to date, there are few research reports on the preparation and application of crystalline MIL-140s membranes internationally. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a highly stable MIL-140s membrane, its structure control, and its gas-liquid separation application. First, a dense MIL-140s seed layer is deposited on a porous support; then, it is placed in a precursor liquid containing a metal source and organic ligands. Through a certain period of thermodynamic growth, the gaps between the seed layers are gradually closed by the coordination reaction of the metal source and organic ligands, ultimately forming a continuous and well-intercalated MIL-140s membrane. It is particularly noteworthy that changing the thermodynamic growth temperature can significantly control and optimize the microstructure and mesostructure of the MIL-140s membrane (such as crystal orientation, membrane thickness, intergranular defects, etc.), thereby altering the sieving channel size and the corresponding separation system of the MIL-140s membrane, showing promising prospects for industrial applications.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a highly stable MOF membrane includes the following steps: firstly, a dense MIL-140s seed layer is deposited on a porous support; then, it is placed in a precursor liquid containing a metal source and an organic ligand, and after a certain period of thermodynamic growth, the gaps between the seed layers are gradually closed through the coordination reaction of the metal source and the organic ligand, and finally a continuous and well-grown MIL-140s membrane is formed.

[0008] Preferably, the porous carrier has a flat, tubular, or hollow fiber structure; the porous carrier is a porous metal oxide, porous metal, porous non-metal oxide, porous carbide, or porous polymer carrier. Further, the porous metal oxide is porous alumina, porous titanium oxide, porous zirconium oxide, or porous YSZ; the porous metal is porous stainless steel or porous nickel; the porous non-metal oxide is porous silica or porous glass; the porous carbide is porous silicon carbide; and the porous polymer carrier is polyvinylidene fluoride, polyethersulfone, polyacrylonitrile, or polyamide. Even further, the porous carrier is a flat porous alumina carrier.

[0009] Preferably, the pore size of the porous carrier is 1 nm to 5 μm. More specifically, the pore size of the porous carrier is 5 nm to 1 μm.

[0010] Preferably, the deposition technique is a physical deposition technique such as dip coating, wiping coating, spin coating, doctor blade coating, drop coating, vacuum filtration, etc., or a chemical deposition technique such as layer-by-layer self-assembly chemical deposition, chemical reaction deposition, etc. Further, the deposition technique is a dip coating, spin coating, or doctor blade coating.

[0011] Preferably, the seed layer has a thickness of 10 nm to 5 μm and a particle size of 10 nm to 5 μm. Further, the seed layer has a thickness of 20 nm to 2 μm and a particle size of 20 nm to 2 μm.

[0012] Preferably, the metal source is a metal containing zirconium (Zr), hafnium (Hf), cerium (Ce), or a metal compound containing zirconium (Zr), hafnium (Hf), and cerium (Ce). The metal compound may be a metal salt, metal oxide, metal sulfide, metal hydroxide, or a mixture of the aforementioned zirconium (Zr), hafnium (Hf), and cerium (Ce) metal compounds. Further, the metal source may be a metal salt, metal oxide, or metal sulfide containing zirconium (Zr), hafnium (Hf), and cerium (Ce).

[0013] Preferably, the concentration of the metal source in the precursor fluid is 0.001–10 mol / L. Further, the concentration of the metal source in the precursor fluid is 0.05–1 mol / L.

[0014] Preferably, the organic ligand is 1,4-benzenedicarboxylate (BDC), or BDC modified with side chain groups (side chain groups such as amino, methyl, nitro, fluoro, fluoromethyl, diamino, dimethyl, difluoromethyl, etc.), or BDC with extended ligands (extended ligands such as naphthyl, biphenyl phthalic acid, etc.), or a mixture of the above-mentioned BDC ligands. Further, the organic ligand is BDC, or BDC modified with side chain groups, or BDC with extended ligands.

[0015] Preferably, the concentration of the organic ligand in the precursor fluid is 0.001–10 mol / L. Further, the concentration of the organic ligand in the precursor fluid is 0.05–1 mol / L.

[0016] Preferably, the solvent in the precursor fluid is water or an organic solvent such as methanol, ethanol, acetone, dichloromethane, tetrahydrofuran, acetonitrile, benzene, toluene, N,N-dimethylformamide (DMF), or any mixture of the above solvents. Further, the solvent is N,N-dimethylformamide.

[0017] Preferably, the precursor fluid may contain a regulator, which is a carboxylic acid compound containing a -COOH functional group, such as formic acid, acetic acid, trifluoroacetic acid, or benzoic acid. Further, the regulator is formic acid, acetic acid, trifluoroacetic acid, or benzoic acid.

[0018] Preferably, the concentration of the regulator in the precursor fluid is 0–20 mol / L. Further, the concentration of the regulator in the precursor fluid is 0–5 mol / L.

[0019] Preferably, the thermodynamic growth temperature is from room temperature to 300°C, and the time is from 10 min to 72 h. Further, the thermodynamic growth temperature is from 60 to 200°C, and the time is from 3 h to 36 h.

[0020] Preferably, the thickness of the MIL-140s film is 10 nm to 20 μm, and the grain size is 10 nm to 10 μm. Further, the thickness of the MIL-140s film is 50 nm to 5 μm, and the particle size is 50 nm to 3 μm.

[0021] The present invention also provides a MIL-140s membrane synthesized by the above method for gas or liquid separation. Further, the MIL-140s membrane is applied to the separation of light component mixtures or olefin / alkane systems with small molecular dynamic diameters; or the MIL-140s membrane is applied to the separation of systems such as alcohol-water mixtures, seawater desalination, ion sieving, and organic mixtures.

[0022] Furthermore, the light component mixing system is H2 / CH4, H2 / N2, H2 / CO2, CO2 / N2, or CO2 / CH4; the olefin / alkane system with a smaller molecular dynamic diameter is C2H4 / C2H6, C3H6 / C3H8, or n / isobutane.

[0023] Furthermore, the alcohol-water mixture is methanol / water, ethanol / water, isopropanol / water, or n-butanol / water; the seawater desalination is metal chloride, sulfate, carbonate, etc.; the ion sieving is lithium, sodium, potassium, magnesium, aluminum, and other metal ions; and the organic mixture is an alcohol / ester mixture, an aromatic / aliphatic hydrocarbon mixture, isomers, gasoline sulfides, etc.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1) The method provided by this invention is a novel method for preparing ultramicroporous, highly stable crystalline MIL-140s membranes. It should be noted that ultramicroporous, highly stable crystalline MOF membranes are a popular and excellent membrane material with urgent demand in various gas-liquid separation fields; however, their preparation is difficult, and there are very few existing corresponding membrane materials. This invention focuses on MIL-140s and, through exploration and optimization of the seed-layer-assisted secondary growth process, successfully developed a high-performance MIL-140s membrane preparation method. The successful development of the above preparation method is expected to promote the entry of a series of MIL-140s membrane materials into the field of crystalline molecular sieve membranes, for efficient separation of gas-liquid systems under various complex working conditions, and has significant research value and application prospects.

[0026] 2) One of the significant features of the method provided by this invention is that the microstructure (such as crystal orientation, film thickness, intergranular defects, etc.) of the MIL-140s membrane can be significantly controlled and optimized by changing the thermodynamic growth temperature, thereby changing the sieving channel size of the MIL-140s membrane and the corresponding separation system. For example, in a high-temperature growth environment, the orientation reversal of the (200) seed layer can be achieved to obtain a continuous MIL-140A membrane with (h0h) orientation, achieving efficient separation of systems such as CO2 / N2 and CO2 / CH4. Conversely, in a low-temperature growth environment, the orientation epitaxial growth of the (200) seed layer can be achieved to obtain an ultrathin MIL-140A membrane with (200) orientation, achieving efficient separation of systems such as H2 / CO2 and CH4 / CO2. Based on the above results, we believe that in the future, by designing different MIL-140s seed layers and optimizing and controlling the growth process, it is expected to achieve customized preparation of MOF membranes for different gas (liquid) separation systems. Attached Figure Description

[0027] Figure 1 shows the X-ray diffraction (XRD) pattern of the MIL-140A seed crystals prepared in Example 1;

[0028] Figure 2 is a scanning electron microscope (SEM) image of the MIL-140A seed crystals prepared in Example 1;

[0029] Figure 3 shows the XRD pattern of the MIL-140A seed layer prepared in Example 2;

[0030] Figure 4 is a SEM image of the MIL-140A seed layer prepared in Example 2;

[0031] Figure 5 shows the XRD pattern of the MIL-140A membrane prepared in Example 3;

[0032] Figure 6 is a SEM image of the MIL-140A membrane prepared in Example 3;

[0033] Figure 7 is a cross-sectional SEM image of the MIL-140A membrane prepared in Example 3;

[0034] Figure 8 shows the XRD pattern of the MIL-140A membrane prepared in Example 5;

[0035] Figure 9 is a SEM image of the MIL-140A membrane prepared in Example 5;

[0036] Figure 10 is a cross-sectional SEM image of the MIL-140A membrane prepared in Example 5. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0038] Example 1: Synthesis of MIL-140A Seed Crystals by Solvothermal Method

[0039] Using zirconium tetrachloride as the metal source, terephthalic acid as the organic ligand, acetic acid as the modifier, and DMF as the solvent, with a molar ratio of metal source, organic ligand, modifier, and solvent of 1:1:3:20, MIL-140A crystals were synthesized via a solvothermal method (150℃, 24h). XRD (Figure 1) and SEM (Figure 2) confirmed the successful synthesis of plate-like pure-phase MIL-140A crystals.

[0040] Example 2: Deposition of MIL-140A seed layer by spin coating

[0041] The MIL-140A crystals prepared in Example 1 were dispersed in methanol, and then stirred and sonicated to form a homogeneous MIL-140A crystal suspension (0.5 wt%). The prepared MIL-140A crystal suspension (~0.3 ml) was coated onto a porous alumina support (pore size: ~70 nm; diameter: 18 mm) using a spin-coating method. XRD (Figure 3) and SEM (Figure 4) showed that a dense (200) oriented MIL-140A seed layer was successfully deposited on the porous support.

[0042] Example 3: Preparation of oriented MIL-140A film by solvothermal method (h0h)

[0043] 1) Using zirconium tetrachloride as the metal source, terephthalic acid as the organic ligand, acetic acid as the modifier, and DMF as the solvent, the molar ratio of the metal source, organic ligand, modifier, and solvent is 1:1:3:20, to form a homogeneous precursor solution.

[0044] 2) The (200) oriented deposited MIL-140A seed layer prepared in Example 2 and the precursor solution described in step 1) are placed together in a reaction vessel.

[0045] 3) After sealing the reaction vessel, place it in a forced-air drying oven for high-temperature growth (200℃, 24h) to obtain a continuous (h0h) oriented MIL-140A film.

[0046] XRD (Figure 5) and SEM (Figure 6) show that a continuous, defect-free (h0h) oriented MIL-140A film with a thickness of ~3.8 μm was successfully prepared on a porous support layer modified with a MIL-140A seed layer (Figure 7).

[0047] Example 4 (h0h) Gas separation performance of oriented MIL-140A membrane

[0048] The gas separation performance of the (h0h) oriented MIL-140A membrane prepared in Example 3 under long-term conditions of ambient temperature and pressure for a CO2 / CH4 mixture (molar ratio: 1:1) was systematically evaluated. Within 50 hours, the CO2 permeability (~108.4 GPU) and CO2 / CH4 mixture selectivity (~26.7) of the MIL-140A membrane remained stable, demonstrating excellent performance stability.

[0049] Example 5: Preparation of (200) oriented MIL-140A film by solvothermal method

[0050] The difference from Example 3 is that in step 3, the food is grown at a low temperature (75°C, 24h) in a forced-air oven.

[0051] XRD (Figure 8) and SEM (Figure 9) show that a continuous, defect-free (200) oriented MIL-140A film with a thickness of ~700 nm was successfully prepared on a porous support layer modified with a MIL-140A seed layer (Figure 10).

[0052] Example 6 (200) Mixed gas separation performance of oriented MIL-140A membrane

[0053] The gas separation performance of the (200) oriented MIL-140A membrane prepared in Example 3 under long-term H2 / CO2 mixed components (molar ratio: 1:1) at room temperature and pressure was systematically evaluated. Within 50 h, the H2 permeability (~632.6 GPU) and H2 / CO2 mixed gas selectivity (~405.3) of the MIL-140A membrane remained stable, demonstrating excellent performance stability.

Claims

1. A method for preparing a highly stable MOF membrane, characterized in that, The process includes the following steps: First, a MIL-140s seed layer is deposited on a porous support; then, it is placed in a precursor solution containing a metal source and an organic ligand, and a MIL-140s film is prepared through thermodynamic growth over a certain period of time; the metal source is a zirconium, hafnium or cerium-containing metal or a zirconium, hafnium or cerium-containing metal salt, metal oxide, metal sulfide or metal hydroxide, or a mixture of the above zirconium, hafnium or cerium-containing metal salt, metal oxide, metal sulfide or metal hydroxide.

2. The preparation method according to claim 1, characterized in that: The porous carrier has a flat, tubular, or hollow fiber structure; the porous carrier is a porous metal oxide, porous metal, porous non-metal oxide, porous carbide, or porous polymer carrier; the pore size of the porous carrier is 1 nm to 5 μm.

3. The preparation method according to claim 1, characterized in that: The deposition technique is a physical deposition technique such as dip coating, wiping coating, spin coating, scraping coating, drop coating, or vacuum filtration, or a chemical deposition technique such as layer-by-layer self-assembly chemical deposition or chemical reaction deposition.

4. The preparation method according to claim 1, characterized in that: The seed layer has a thickness of 10 nm to 5 μm and a particle size of 10 nm to 5 μm.

5. The preparation method according to claim 1, characterized in that: The concentration of the metal source in the precursor fluid is 0.001~10 mol / L.

6. The preparation method according to claim 1, characterized in that: The organic ligand is terephthalic acid, or terephthalic acid modified with side chain groups, or terephthalic acid with extended ligands, or a mixture of the above terephthalic acid ligands; the concentration of the organic ligand in the precursor fluid is 0.001~10 mol / L.

7. The preparation method according to claim 1, characterized in that: The solvent in the precursor fluid is water or an organic solvent such as methanol, ethanol, acetone, dichloromethane, tetrahydrofuran, acetonitrile, benzene, toluene, N,N-dimethylformamide, or a mixture of any of the above solvents; the precursor fluid contains a regulator, which is formic acid, acetic acid, trifluoroacetic acid, or benzoic acid; the concentration of the regulator in the precursor fluid is 0~20 mol / L.

8. The preparation method according to claim 1, characterized in that: The thermodynamic growth temperature ranges from room temperature to 300℃, and the time ranges from 10 min to 72 h.

9. The preparation method according to claim 1, characterized in that: The thickness of the MIL-140s film is 10 nm to 20 μm, and the grain size is 10 nm to 10 μm.

10. The application of the highly stable MOF membrane as described in claim 1 in gas or liquid separation, characterized in that: The MIL-140s membrane is used in the separation of light component mixtures or olefin / alkane systems with small molecular dynamic diameters; or the MIL-140s membrane is used in the separation of alcohol-water mixtures, seawater desalination, dye retention, water purification, ion sieving, or organic mixture systems.

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