A MOF composite membrane for amine / water separation and a preparation method thereof

Abstract

The present application relates to the technical field of amine / water separation, and particularly relates to a MOF composite membrane for amine / water separation and a preparation method thereof, which comprises the following steps: weighing 2-methylimidazole and dissolving it in deionized water to obtain solution A, taking a solution containing Cu element as a metal source solution B, then mixing solution A with solution B, forming a casting solution after stirring, pouring the casting solution on a porous support layer, and standing until a crystal film layer is formed on the surface of the casting solution, the film layer is a MOF membrane, extracting the solution below the membrane to make the MOF membrane layer below free of visible impurities, and obtaining a pure MOF composite membrane after drying. The MOF composite membrane can be directly used for separating and recycling the water part in the rich amine solution of the absorption method carbon capture, and the rich amine solution is concentrated, so that the heat load of the regeneration process is reduced. The MOF membrane is simple, green, clean, and has good pressure resistance.

Description

Technical Field

[0001] This invention relates to the field of amine / water separation technology, and more specifically to a MOF composite membrane for amine / water separation and its preparation method. Background Technology

[0002] With the continued intensification of global warming and climate change, carbon dioxide (CO2) emission control has become a focus of international attention. Fossil fuel combustion remains the mainstay of the current energy system, widely used in industries such as power, chemicals, steel, and cement, leading to a continuous rise in CO2 emissions. To achieve carbon peaking and carbon neutrality goals, countries have deployed carbon capture, storage, and utilization (CCUS) technologies as a key supporting link in emission reduction systems. Among these, CO2 capture technology, as the primary link in the CCUS chain, directly determines the energy efficiency and economic viability of subsequent storage and utilization processes. Currently, the most mature CO2 capture technology for industrial application is the chemical absorption method. Its core is the reversible chemical reaction between organic amine solutions (such as monoethanolamine MEA, diethanolamine DEA, and N-methyldiethanolamine MDEA) and CO2 in flue gas, forming bicarbonates or carbamates, which are then regenerated through heated desorption. This method has been widely used in coal-fired power plants, natural gas purification, and chemical waste gas treatment. However, the biggest bottleneck of this process is the high energy consumption for regeneration: about 60% or even more of the system's energy consumption is used for heating and moisture vaporization during the absorbent regeneration process, resulting in huge losses of sensible and latent heat.

[0003] To address these issues, researchers have begun to explore coupling membrane separation technology with amine absorption. This leverages the selective permeability of the membrane process to achieve efficient separation and recycling of absorbent solution components, thereby reducing the thermal regeneration load. Membrane separation technology offers advantages such as low energy consumption, compact structure, continuous operation, and no phase change. Without altering the original absorption process, it can further increase the concentration and reduce the flow rate of the rich amine solution entering the regeneration tower by separating some of the water in the amine solution, thus effectively reducing steam consumption and overall energy consumption during the regeneration process.

[0004] Existing studies have shown that MEA exhibits the greatest water permeation resistance and is difficult to dehydrate under the same operating conditions due to strong hydrogen bonds, high polarity, and strong water adsorption within the membrane. MDEA has a water flux that is approximately 30%-50% higher than MEA, and its separation coefficient is also more favorable. Carbamates (such as MEACOO) -Aminocarbamate ions are charged ions and completely non-volatile. In any membrane process driven by vapor pressure difference (such as vacuum membrane distillation and air-gap membrane distillation), only neutral molecules (water, free amine, and potentially soluble CO2) can volatilize and permeate through the membrane. Aminocarbamate ions are 100% retained on the feed side. Therefore, from the perspective of preventing their permeation through the membrane, it is the easiest component to handle. Thus, in designing membrane systems for the separation of amine-rich solutions, the MEA / H2O separation performance should be the primary focus. Existing amine / water separation membrane designs, centered on pervaporation, partially separate CO2 from the amine-rich solution, but fail to effectively reduce the heat load of the regeneration tower. Summary of the Invention

[0005] The purpose of this invention is to provide a MOF composite membrane for amine / water separation and its preparation method, thereby solving the technical problem that the prior art has failed to effectively reduce the heat load of the regeneration tower.

[0006] This invention discloses a method for preparing a MOF composite membrane for amine / water separation, comprising the following steps: 2-Methylimidazole was weighed and dissolved in deionized water to obtain solution A. A solution containing Cu was used as the metal source solution B. Solution A and solution B were then mixed and stirred to form a casting solution. The casting solution was poured onto a porous support layer and allowed to stand until a crystalline film layer formed on the surface of the casting solution. This film layer is a MOF membrane. The solution below the membrane was extracted to ensure that there were no visible impurities below the MOF membrane layer. After drying, a pure MOF composite membrane was obtained.

[0007] Furthermore, the porous support layer is a polyethersulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), or polyvinyl chloride (PVC) water treatment membrane with a molecular weight cutoff of 1000~100000 Da.

[0008] Furthermore, in solution A, 2-methylimidazole is dissolved in deionized water to obtain a ligand concentration of 0.32 mol / L.

[0009] Furthermore, the Cu element concentration in solution B is 0.04 mol / L.

[0010] Furthermore, solution A and solution B are mixed in a volume ratio of 10:1 to 1:1.

[0011] Furthermore, solution B is a Cu(NO3)2·3H2O solution.

[0012] Furthermore, the molar ratio of 2-methylimidazole to Cu(NO3)2·3H2O in solution A and solution B is 80:1 to 8:1.

[0013] Furthermore, the settling time after the casting solution is poured onto the porous support layer is at least 5 minutes and less than 20 minutes, preferably 10 minutes. A short settling time is not conducive to film formation, while a long settling time results in a thicker film with poor surface continuity, potential leaks, and hinders the separation process.

[0014] A MOF composite membrane for amine / water separation is prepared using the method described above.

[0015] An application of a MOF composite membrane for amine / water separation.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This application develops a method for preparing Cu-based MOF composite films. This method uses polymer films such as PES or PAN as a support layer and utilizes Cu... 2+ A surface crystalline layer is formed by coordination with 2-methylimidazole, followed by washing to prepare a defect-free MOF composite membrane. This MOF composite membrane has microporous / mesoporous channels, which can facilitate water molecule transport while hindering the transport of larger ethanolamine molecules. Furthermore, the metal center can form hydrogen bonds and coordination interactions with ethanolamine, further increasing transport resistance and thus improving the membrane's water / ethanolamine separation performance. It also exhibits good mechanical properties. The MOF composite membrane of this application can be directly used to separate and reuse the water portion of the amine-rich solution from the carbon capture process, and to concentrate the amine-rich solution, thereby reducing the heat load of the regeneration process. This MOF membrane is simple to prepare, environmentally friendly, clean, and has good pressure resistance.

[0017] 2. This application selects Cu, which can interact with ethanolamine through coordination and hydrogen bonding. 2+ Using 2-methylimidazole as the metal source and ligand, a MOF composite membrane with a microporous / mesoporous structure was prepared. In addition to the above-mentioned interactions, the inherent pore structure of the MOF composite membrane can also hinder the mass transfer of ethanolamine to a certain extent, thereby significantly improving the water / ethanolamine separation performance to a certain extent.

[0018] 3. This application controls the type of support layer and the volume ratio of metal solution to ligand solution. After MOF growth, the water flux of the MOF membrane can reach 200 L·m. -2 ·h -1 ·bar -1 The ethanolamine retention rate is above 30%.

[0019] 4. The composite membrane prepared in this application is prepared by dip coating, which reduces equipment investment by more than 10 times compared with other composite membrane preparation methods such as spin coating and spray coating, and reduces energy consumption by 20% or more. In addition, the material utilization rate is high during the dip coating process of the composite membrane prepared in this application, which can significantly reduce membrane preparation costs and significantly improve economic benefits.

[0020] 5. The MOF composite membrane of this application uses polymer membranes such as PES or PAN as the support layer, which has good mechanical properties and can be directly used to separate water from the amine-rich solution of carbon capture by absorption method. It can concentrate the concentration of amine-rich solution from 30% to more than 40% and reduce the heat load of the regeneration process by more than 10%. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the MOF membrane preparation process of the present invention.

[0023] Figure 2 Cu in the MOF film of this invention 2+ A schematic diagram of the coordination mechanism with 2-methylimidazole.

[0024] Figure 3 The results of thermogravimetric analysis (TGA) of the MOF film in Example 1 of this invention are shown.

[0025] Figure 4 The results are infrared test results of the MOF film in Example 1 of this invention.

[0026] Figure 5 The XRD test results are for the MOF film in Example 1 of this invention.

[0027] Figure 6 The N2 adsorption-desorption curves are shown for the MOF film in Example 1 of this invention.

[0028] Figure 7 This is a pore size distribution diagram of the MOF membrane in Embodiment 1 of the present invention.

[0029] Figure 8 This is a solid image of the MOF film in Embodiment 1 of the present invention.

[0030] Figure 9 This is a SEM image (10 min) of the MOF film surface in Example 1 of the present invention.

[0031] Figure 10 This is a schematic SEM image of the cross-section of the MOF membrane in Example 1 of the present invention (10 min).

[0032] Figure 11 This is a schematic SEM image of the cross-section of the MOF membrane in Example 5 of the present invention (20 min).

[0033] Figure 12 The results of water / ethanolamine separation in MOF composite membranes with PES as the support layer in Examples 1 and 3 of the present invention are shown, wherein the temperature is 25 °C, 2 bar, and the ratio of ligand to metal source is 1:1.

[0034] Figure 13 To assess the long-term stability of water / ethanolamine separation in the MOF composite membrane with PES as the support layer in Example 1 of this invention, the conditions were: 25 °C, 2 bar, ligand:metal source = 1:1.

[0035] Figure 14 The results of water / ethanolamine separation in MOF composite membranes with different ligand:metal source volume ratios using PAN as the support layer in Comparative Example 4 and Examples 3-4 are shown, at 25 °C and 2 bar.

[0036] Figure 15 The image shown is a SEM image of Comparative Example 1, where the ratio of ligand to metal source is 1:1.

[0037] Figure 16 The image shown is a SEM image of Comparative Example 2, where the ligand:metal source ratio is 1:1, and 1 ml of glacial acetic acid is used.

[0038] Figure 17 This is the SEM image of Comparative Example 5.

[0039] Figure 18 This is the SEM image of Comparative Example 6. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] Example 1 This embodiment discloses a MOF composite membrane for amine / water separation and its preparation method, including the following steps: PES with a molecular weight cutoff of 100,000 Da is selected as the support layer, and it is washed with water for 4 hours to remove impurities from the surface of the support layer. After drying, it is cut into 10 cm × 10 cm rectangles and pasted onto a glass plate.

[0042] 1.314 g of 2-methylimidazole was dissolved in 50 ml of deionized water to form a 0.32 mol / L ligand solution A. 0.4832 g of Cu(NO3)2·3H2O was dissolved in 50 ml of deionized water to form a 0.04 mol / L metal source solution B. Solutions A and B were mixed in a 1:1 volume ratio (the molar ratio of 2-methylimidazole to Cu(NO3)2·3H2O was 8:1), stirred, and then transferred to a PES support to grow a MOF membrane. The mixture was allowed to stand for 10 min. The casting solution below the membrane (above the support layer) was extracted using a syringe. The membrane was then repeatedly washed three times with deionized water and dried to obtain a pure MOF composite membrane.

[0043] MOF membranes can be used at room temperature -200°C. o Maintains thermal stability within the range of C, meeting the operating environment requirements such as temperature for the coupled technology of membrane separation and amine absorption (thermogravimetric curve as shown in the figure). Figure 3 In addition, the infrared test results of the MOF film ( Figure 4 ) 1305 cm -1 1360 cm -1 and 1419 cm -1 The peak value corresponds to the stretching vibration and ring vibration of the C=N bond, 740 cm⁻¹. -1 The significant peak value corresponds to the bending vibration of CH, 991 cm. -1 The prominent absorption peak corresponds to the stretching vibration of Cu-N, indicating that Cu 2+ There is a coordination binding with 2-methylimidazole. The XRD results of the MOF membrane show ( Figure 5 The significant characteristic peaks indicate that it has a crystal structure. Its N2 adsorption-desorption curves and pore size distribution are shown below. Figure 6 and 7 As shown, the MOF membrane possesses a good pore structure, and the pore size distribution is well-defined within the microporous / mesoporous regions. In actual MOF composite membranes, the MOF layer can uniformly cover the surface of the PES support layer. Figure 8 SEM images of the MOF film surface and cross-section are shown below. Figure 9 and 10 Its water / ethanolamine separation performance is as follows Figure 12 As shown, the water flux of the MOF composite membrane is 205 L / (m²). 2 The MEA retention rate was 32% (bar·h). Furthermore, its stability was tested, and no decrease was observed during 72 hours of continuous operation. Figure 13 ).

[0044] Example 2 A 100,000 Da PAN was selected as the support layer, and other conditions were the same as in Example 1. Its water / ethanolamine separation performance was as follows: Figure 14 As shown, the water flux of the MOF composite membrane is 8.6 L·m. -2 ·h-1 ·bar -1 The ethanolamine rejection rate can reach over 25%.

[0045] Example 3 Under the same conditions as in Example 2, solutions A and B were mixed at a volume ratio of 10:1 (the molar ratio of 2-methylimidazole and Cu(NO3)2·3H2O was 80:1), and their water / ethanolamine separation performance was as follows. Figure 14 As shown, the water flux of the MOF composite membrane is 205 L·m. -2 ·h -1 ·bar -1 The ethanolamine rejection rate can reach over 27%.

[0046] Example 4 Under the same conditions as in Example 2, solutions A and B were mixed in a 2:1 volume ratio (the molar ratio of 2-methylimidazole and Cu(NO3)2·3H2O was 16:1), and their water / ethanolamine separation performance was as follows. Figure 14 As shown, the water flux of the MOF composite membrane is 18.2 L·m. -2 ·h -1 ·bar -1 The ethanolamine rejection rate can reach over 25%.

[0047] Comparative Example 1 1.314 g of 2-methylimidazole was dissolved in 50 ml of deionized water to form a 0.32 mol / L ligand solution A. 0.4832 g of Cu(NO3)2·3H2O was dissolved in 50 ml of deionized water to obtain a 0.04 mol / L metal source solution B. Solutions A and B were mixed in a 1:1 ratio (the molar ratio of 2-methylimidazole to Cu(NO3)2·3H2O was 8:1). After stirring for 10 min, the casting solution below the membrane (above the support layer) was extracted using a syringe, dried, and its SEM image is shown below. Figure 15 As shown in the figure, MOFs are dispersed as fine particles, making it difficult to form a continuous membrane surface. This indicates that the preparation of MOF composite membranes requires static conditions, and stirring conditions are insufficient to achieve the formation of MOF membranes.

[0048] Comparative Example 2 1.314 g of 2-methylimidazole was dissolved in 50 ml of deionized water to obtain ligand solution A. 0.4832 g of Cu(NO3)2·3H2O was dissolved in 50 ml of deionized water to form a 0.04 mol / L metal source solution B. Solutions A and B were mixed in a 1:1 ratio (the molar ratio of 2-methylimidazole to Cu(NO3)2·3H2O was 8:1). 1 ml of glacial acetic acid, a commonly used modifier in MOF preparation, was added. The mixture was then transferred to a PAN support to grow a MOF film, which exhibited a 2D morphology. However, this method is difficult to completely form a MOF film. Its SEM image is shown below. Figure 16 As shown, this is mainly because an acidic environment alters the solution environment, thereby affecting the self-alignment of the 2-methylimidazole linker, making it difficult for it to form a surface array and subsequently a MOF film.

[0049] Comparative Example 3 Using a PES support layer as the separation layer, amine / water separation was achieved with the following results: Figure 12 As shown, although the water flux of PES is higher than that of PES+MOF composite membrane, its selectivity is poor, making it difficult to achieve efficient amine / water separation.

[0050] Comparative Example 4 Using a PAN support layer as the separation layer, amine / water separation was achieved with the following results: Figure 14 As shown, although the water flux of PAN is higher than that of PAN+MOF composite membrane, its selectivity is poor, making it difficult to achieve efficient amine / water separation.

[0051] Comparative Example 5 Based on Example 1, only the resting time was changed to 3 minutes. In this short time, the MOF membrane is difficult to grow into a continuous and complete film layer, resulting in numerous defects. The SEM image of the film layer is as follows: Figure 17 .

[0052] Comparative Example 6 Based on Example 1, solutions A and B were mixed in a volume ratio of 20:1 (the molar ratio of 2-methylimidazole and Cu(NO3)2·3H2O was 160:1). Due to the extremely high ligand-metal molar ratio, no visible MOF film was formed. After evaporating the solution, it appeared as spherical particles. Figure 18 It is difficult to prepare MOF composite membranes.

[0053] Comparative Example 7 Under the same conditions as in Example 1, the standing time was 20 minutes. After drying, SEM images of the surface and cross-section of the pure MOF membrane were obtained as follows. Figure 11 Due to the long settling time, the number of non-layered MOFs in the lower part of the membrane increases, resulting in poor overall membrane continuity and defects.

[0054] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A method for preparing a MOF composite membrane for amine / water separation, characterized in that: Includes the following steps: 2-Methylimidazole was weighed and dissolved in deionized water to obtain solution A. A solution containing Cu was used as the metal source solution B. Solution A and solution B were then mixed and stirred to form a casting solution. The casting solution was poured onto a porous support layer and allowed to stand until a crystalline film layer formed on the surface of the casting solution. This film layer is a MOF membrane. The solution below the membrane was extracted to ensure that there were no visible impurities below the MOF membrane layer. After drying, a pure MOF composite membrane was obtained.

2. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: The porous support layer is a polyethersulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), or polyvinyl chloride (PVC) water treatment membrane with a molecular weight cutoff of 1000~100000 Da.

3. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: In solution A, 2-methylimidazole was dissolved in deionized water to obtain a ligand concentration of 0.32 mol / L.

4. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: The concentration of Cu in solution B is 0.04 mol / L.

5. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: Solution A and solution B are mixed in a volume ratio of 10:1 to 1:

1.

6. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: Solution B is a Cu(NO3)2·3H2O solution.

7. The method for preparing a MOF composite membrane for amine / water separation according to claim 6, characterized in that: The molar ratio of 2-methylimidazole to Cu(NO3)2·3H2O in solutions A and B is 80:1 to 8:

1.

8. The method for preparing a MOF composite membrane for amine / water separation according to claim 1, characterized in that: The casting solution is poured onto the porous support layer and allowed to stand for at least 5 minutes and less than 20 minutes, preferably 10 minutes.

9. A MOF composite membrane for amine / water separation, characterized in that: The MOF composite membrane for amine / water separation is prepared according to any one of claims 1-8.

10. The MOF composite membrane prepared by the method for preparing an amine / water separation according to any one of claims 1-8, or the application of the MOF composite membrane according to claim 9, characterized in that: Used for amine / water separation.

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