Preparation of Al-MOF-NF with high-density metal sites and application of Al-MOF-NF in carbon capture

Abstract

The invention belongs to the technical field of membrane material preparation, and provides preparation of Al-MOF-NF with high-density metal sites and application of the Al-MOF-NF in carbon capture, and a mixed matrix membrane capable of efficiently separating CO2 is formed by physically blending the prepared Al-MOF-NF and a polyether-polyamide block copolymer Pebax. According to the special structure of Al-MOF-NF, efficient capture and rapid transmission of CO2 can be synchronously realized in an interlayer channel formed by exposing a Lewis acid site Al < 3 + > on the surface of a sheet layer, efficiently selecting CO2 molecules, and stacking metal-ligand bonds and hydrogen bonds through interaction force. The preparation process of the mixed matrix membrane is simple, reaction is controllable, raw materials are cheap and easy to obtain, and conditions are mild. The method provided by the invention has good application in separation of CO2 / CH4 mixed gas, and provides a new effective strategy for efficient separation of CO2.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of mixed matrix membrane materials, and particularly relates to the preparation of Al-MOF-NF with high-density metal sites and its application in carbon capture. Background Art

[0002] CO2 gas is a greenhouse gas that causes climate warming. The CO2 emitted into the atmosphere is mainly caused by the combustion of fossil fuels, and the flue gas emitted by fossil fuel power plants is the main source of CO2 emissions. At the same time, CO2 widely exists in fuel gases such as natural gas and biogas. The presence of CO2 not only reduces the purity of the fuel gas, but also, during the transportation of natural gas, the acidic gas formed by combining with moisture in the pipeline under low-temperature conditions seriously corrodes the transportation pipeline. Therefore, it is urgent to develop efficient CO2 separation technologies, which is of great significance for effectively reducing greenhouse gas emissions and purifying energy gases.

[0003] Among the common CO2 separation methods, the membrane separation method is considered to be one of the most promising CO2 separation technologies because of its advantages of high efficiency, low energy consumption and low cost. The core of the membrane separation method is the membrane material. Common CO2 separation membranes include organic membranes, inorganic membranes and mixed matrix membranes. Mixed matrix membranes (MMMs) are composed of dispersed fillers and continuous polymer matrices. Compared with traditional organic membranes and inorganic membranes, MMMs combine the advantages of organic and inorganic membrane materials and are a new type of membrane material with the potential to overcome the trade-off effect and exceed the Robeson upper limit.

[0004] At present, common modification processes usually rely on complex chemical modifications or interfacial regulations, which increase the preparation cost and experimental complexity. On the other hand, modified materials often have problems such as inactivation of functional sites or decline in structural stability, which limits the sustainability of their practical applications. Therefore, it is of great significance to break through the limitations of existing modification methods and further improve the performance of MMMs. At present, there is no relevant report on the application of Al-MOF-NF with high-density metal sites and high-efficiency gas separation performance in CO2 separation technology. Summary of the Invention

[0005] To solve this problem, the present invention designs an Al-MOF-NF filler by changing the structural characteristics of the 2D material itself. Al-MOF-NF significantly improves the CO2 separation performance in MMMs through enhanced adsorption sites. The special structure of Al-MOF-NF exposes denser Lewis acid sites Al on the surface of the sheet 3+, it can efficiently select CO2 molecules. The three-dimensional structure formed by the nanosheets has a larger CO2 accommodation space, which is conducive to its efficient diffusion. By exposing acid sites to enhance the adsorption effect, efficient CO2 capture and rapid transmission can be simultaneously achieved within the interlayer channels formed by the stacking of metal-ligand bonds and hydrogen bond interactions, improving the gas separation performance and being used in CO2 capture applications. To achieve the above invention objectives, the present invention adopts the following technical solutions:

[0006] In a specific embodiment, the present invention provides a preparation method of Al-MOF-NF with high-density metal sites, and the method includes the steps:

[0007] The method includes the following steps:

[0008] (1) Dissolve aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and sodium sulfate (Na2SO4) in deionized water to form solution A; dissolve terephthalic acid (PTA) in DMAC to form solution B; mix solution A and solution B to obtain a clear solution C.

[0009] (2) Transfer the clear solution in step (1) to a stainless steel autoclave, heat and react at a constant temperature for several hours, and then cool to room temperature to obtain a suspension D.

[0010] (3) Filter and separate the reaction product in step (2), wash it three times with deionized water and ethanol respectively, and finally dry it to a constant weight at a constant temperature to obtain the Al-MOF-NF product.

[0011] Furthermore, in the A solution system in step (1), the dosage relationship of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), sodium sulfate (Na2SO4) and deionized water is: 225 mg: 17.2 mL: 18 mL; the dosage relationship of terephthalic acid (PTA) and DMAC in the A solution system is 166.2 mg: 18 mL. Stir solution A and B evenly at room temperature and mix them to obtain a clear solution C, and the stirring speed is 500 - 800 rpm, and the stirring temperature is 15 - 35 °C.

[0012] (2) The reaction conditions in step (2) are that the suspension C is transferred to a stainless steel autoclave and hydrothermally reacted at a constant temperature. The temperature of the hydrothermal reaction is 145 °C - 175 °C, and the hydrothermal reaction time is 2 - 4 h.

[0013] (3) Centrifuge and wash the reaction solution C described in step (2). The amount of deionized water used is 200 - 500 mL, and the amount of ethanol used is 200 - 500 mL. The centrifuge speed is 8500 - 10000 rpm. Collect the solid product D and dry it to a constant weight at a constant temperature. The temperature is 50 - 80 °C, and dry for 48 h - 72 h to obtain the Al-MOF-NF product.

[0014] In a specific embodiment, the present invention also provides Al-MOF-NF with high-density metal sites obtained by the above preparation method.

[0015] In a specific embodiment, the present invention also provides the application of Al-MOF-NF with high-density metal sites in the field of CO2 / CH4 mixed gas separation.

[0016] In a specific embodiment, the present invention also provides a mixed matrix membrane. The mixed matrix membrane uses Al-MOF-NF with high-density metal sites as a filler and polyether polyimide block Pebax as a polymer matrix, and is formed after physical blending of the filler and the polymer matrix at room temperature. The thickness of the mixed matrix membrane is 109 - 132 μm; the mass percentage of the filler in the mixed matrix membrane is 1% - 7%.

[0017] Furthermore, the present invention also provides the application of the above mixed matrix membrane in carbon capture. Compared with the prior art, the beneficial effects of the present invention are:

[0018] Compared with the prior art, the Al-MOF-NF material of the present invention shows significant advantages in gas separation. The Al-MOF-NF material of the present invention has obvious advantages in gas separation. It significantly improves the CO2 separation performance in MMMs by enhancing the adsorption sites. The unique layered structure of this material exposes more Al 3+ Lewis acid sites, which can efficiently and selectively adsorb CO2. This innovative design not only improves the gas separation efficiency but also enhances the stability of the membrane, providing a more competitive solution for efficient CO2 separation.

[0019] In addition, compared with monolayer nanosheets, the three-dimensional structure of the Al-MOF-NF material of the present invention has a larger CO2 accommodation space, which is conducive to its efficient diffusion. By exposing acid sites to enhance the adsorption effect, efficient CO2 capture and rapid transmission can be simultaneously achieved in the interlayer channels formed by the stacking of metal-ligand bonds and hydrogen bond interactions. Compared with existing materials, the composite membrane of the present invention has higher CO2 selectivity and permeability, and particularly exhibits excellent performance in CO2 / CH4 gas separation, demonstrating great application potential in the field of energy gas purification. The preparation process of the mixed matrix membrane is simple, the reaction is controllable, the raw materials are cheap and easy to obtain, and the conditions are mild, which can promote the complementary advantages of the filler and the polymer matrix. The research results show that the highest CO2 flux of the permeation selectivity of the CO2 / CH4 mixed gas of the present invention is 381±6.5 Barrer, and the CO2 / CH4 selectivity is 38±1.0, which can reach the Robeson upper limit in 2008, providing a new effective strategy for the efficient separation of CO2. Description of the Drawings

[0020] Figure 1 is the scanning electron microscope image of Al-MOF-NF.

[0021] Figure 2 is the transmission electron microscope image of Al-MOF-NF.

[0022] Figure 3 is the atomic force microscope image of Al-MOF-NF.

[0023] Figure 4 is the cross-sectional scanning electron microscope image of the prepared Pebax / Al-MOF-NF-1 mixed matrix membrane;

[0024] Figure 5 is the cross-sectional scanning electron microscope image of the prepared Pebax / Al-MOF-NF-3 mixed matrix membrane;

[0025] Figure 6 is the cross-sectional scanning electron microscope image of the prepared Pebax / Al-MOF-NF-5 mixed matrix membrane;

[0026] Figure 7 is the cross-sectional scanning electron microscope image of the prepared Pebax / Al-MOF-NF-7 mixed matrix membrane;

[0027] Figure 8 is the cross-sectional scanning electron microscope image of the prepared pure Pebax membrane. Detailed Embodiments

[0028] The present invention will be further elaborated below. These examples are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions noted in the examples, they are all carried out according to conventional conditions. The reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0029] Example 1

[0030] (1) In the A solution system described in step (1), the dosage relationship of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), sodium sulfate (Na2SO4) and deionized water is: 225 mg: 17.2 mL: 18 mL; the dosage relationship of terephthalic acid (PTA) and DMAC in the A solution system is 166.2 mg: 18 mL. Solution A and B are respectively stirred evenly at room temperature and then mixed to obtain a clear solution C. The stirring speed is 500 - 800 rpm, and the stirring temperature is 15 - 35 °C.

[0031] (2) In step (2), the reaction conditions are as follows: the suspension C is transferred to a stainless steel autoclave and subjected to a hydrothermal reaction at a constant temperature. The temperature of the hydrothermal reaction is 145 °C - 175 °C, and the hydrothermal reaction time is 2 - 4 h.

[0032] (3) The reaction solution C after step (2) is centrifuged and washed. The dosage of deionized water is 200 - 500 mL, and the dosage of ethanol is 200 - 500 mL. The centrifugation speed is 8500 - 10000 rpm. The solid product D is collected and dried to a constant weight at a constant temperature. The temperature is 50 - 80 °C, and it is dried for 48 h - 72 h to obtain the Al-MOF-NF product.

[0033] 3. Application of the Al-MOF-NF with high-density metal sites as claimed in claim 1 in the field of CO2 / CH4 mixed gas separation.

[0034] Figure 1 is the scanning electron microscope image of Al-MOF-NF, Figure 2 is the transmission electron microscope image of Al-MOF-NF, Figure 3 is the atomic force microscope image of Al-MOF-NF. It can be seen from Figure 1 that Al-MOF-NF presents a uniform three-dimensional morphology, Figure 2 it can be seen that Al-MOF-NF is formed by the ordered assembly of clearly visible nano-sheet secondary structures. It can be seen from Figure 3 that the thickness of the edge lamellae is about 1 nm. All of the above show that this morphology constructs a three-dimensional transmission space, while retaining the inter-sheet transfer path, effectively changing the coordination structure, providing a basis for the highly exposed Lewis acid sites. Further preparation of MMMs can significantly improve the capture and transfer efficiency of CO2, effectively enhancing the gas separation performance and being used for efficient CO2 capture.

[0035] Example 2

[0036] Weigh 0.537 g 1657 was dissolved in 10 mL of a mixed solution of ethanol and water with a mass fraction ratio of 7:3, and heated and stirred in a water bath at 80 °C for 2 h to completely dissolve the Pebax particles, obtaining a 6 wt% Pebax matrix solution. Take 0.0056 g of the Al-MOF-NF prepared in Example 1 and physically blend it with the 6 wt% Pebax matrix solution, and stir at room temperature for 4 h to obtain a casting solution. Pour the casting solution onto a clean petri dish for casting; dry it at room temperature (25 °C) for 48 h, and then vacuum dry it at 40 °C in a vacuum drying oven to remove the residual solvent on the surface of the mixed matrix membrane, obtaining a Pebax / Al-MOF-NF-1 mixed matrix membrane with a thickness of 116 μm. The weight percentage of Al-MOF-NF in the Pebax / Al-MOF-NF-1 mixed matrix membrane is 1%, so it is named Pebax / Al-MOF-NF-1 mixed matrix membrane.

[0037] Figure 4 is the cross-sectional scanning electron micrograph of the prepared Pebax / Al-MOF-NF-1 mixed matrix membrane. From Figure 4 It can be seen that after introducing Pebax / Al-MOF-NF-1 into the Pebax matrix, the cross-sectional view of the mixed matrix membrane becomes rough, which can prove that the introduction of the filler under the conditions of 25 °C and 2 bar, the Pebax / Pebax / Al-MOF-NF-1 mixed matrix membrane was used for CO2 / CH4 mixed gas separation testing. A mixed gas of 80 vol% CH4 and 20 vol% CO2 was used as the feed gas. The dried MMMs membrane was wetted with deionized water, and the wetted volume was about twice the original volume, and then placed in a membrane cell for permeability testing. A circular stainless steel tank was placed in the oven to study the separation performance of the membrane (12.56 cm 2 , central part). In order to test the gas permeability of MMMs under different loadings, the feed gas was introduced to the upstream of the membrane, and the flow rate was controlled at 50 mL / min, and the pressure range was 0.2 - 0.8 MPa. In addition, the permeabilities of CO2 and CH4 were calculated based on the sweep gas flow rate and its composition. The influence of H2 back-diffusion and concentration polarization on data analysis can be ignored because the volume of the feed gas is much larger than the sweep gas (H2), and the back-diffusion of H2 cannot change the composition of the feed gas. Therefore, H2 is suitable as the sweep gas on the downstream side of the membrane, and the flow rate is controlled at 30 ml / min. A gas chromatograph (GC 2014C) was used to measure the content of each component in the permeate gas. The test results showed that its CO2 flux was 350 barrer (1 barrer = 10 -10 cm 3 cm / cm2 (scmHg), and the CO2 / CH4 selectivity is 31.

[0038] Example 3

[0039] In this example, 0.0168 g of the Al-MOF-NF prepared in Example 1 was physically blended with a 6 wt% Pebax matrix solution, and stirred at room temperature for 4 h to obtain a casting solution. The casting solution was poured onto a clean petri dish for casting; dried at room temperature (25 °C) for 48 h, and then vacuum dried at 40 °C in a vacuum drying oven to remove the residual solvent on the surface of the mixed matrix membrane, obtaining a Pebax / Al-MOF-NF-3 mixed matrix membrane with a thickness of 125 μm. The weight percentage of Al-MOF-NF in the Pebax Al-MOF-NF-3 mixed matrix membrane is 3%, named Pebax / Al-MOF-NF-3 mixed matrix membrane.

[0040] Figure 5 is the cross-sectional scanning electron microscopy image of the prepared Pebax / Al-MOF-NF-3 mixed matrix membrane. From Figure 5 it can be seen that after introducing Al-MOF-NF into the Pebax matrix, the cross-sectional image of the mixed matrix membrane becomes rough, thus proving the introduction of the filler. Moreover, Al-MOF-NF is evenly distributed in the mixed matrix membrane without large-area agglomeration. Under the conditions of 25 °C and 2 bar, the prepared Pebax / Al-MOF-NF mixed matrix membrane was used for the separation test of a CO2 / CH4 mixed gas with a CO2 volume fraction of 20%. The test process was the same as that in Example 2. After testing, its CO2 flux was 381 barrer, and the CO2 / CH4 selectivity was 38.

[0041] Example 4

[0042] In this example, 0.0280 g of the Al-MOF-NF prepared in Example 1 was physically blended with a 6 wt% Pebax matrix solution, and stirred at room temperature for 4 h to obtain a casting solution. The casting solution was poured onto a clean petri dish for casting; dried at room temperature (25 °C) for 48 h, and then vacuum dried at 40 °C in a vacuum drying oven to remove the residual solvent on the surface of the mixed matrix membrane, obtaining a Pebax / Al-MOF-NF-5 mixed matrix membrane with a thickness of 132 μm. The weight percentage of Al-MOF-NF in the Pebax / Al-MOF-NF-5 mixed matrix membrane is 5%, named Pebax / Al-MOF-NF-5 mixed matrix membrane.

[0043] Figure 6 is the cross-sectional scanning electron microscopy image of the prepared Pebax / Al-MOF-NF-5 mixed matrix membrane. From Figure 6It can be seen that after the introduction of Al-MOF-NF into the Pebax matrix, the cross-sectional view of the mixed matrix membrane becomes rough, thus proving the introduction of the filler. Moreover, Al-MOF-NF is evenly distributed in the mixed matrix membrane without agglomeration. Under the conditions of 25 °C and 2 bar, the prepared Pebax / Al-MOF-NF-5 mixed matrix membrane was used for the separation test of CO2 / CH4 mixed gas with a CO2 volume fraction of 20%. Its CO2 flux was 369 barrer, and the CO2 / CH4 selectivity was 33, showing a significant improvement in gas separation performance.

[0044] Example 5

[0045] In this example, 0.0392 g of Al-MOF-NF prepared in Example 1 was physically blended with a 6 wt% Pebax matrix solution, and stirred at room temperature for 4 h to obtain a casting solution. The casting solution was poured onto a clean petri dish for casting; dried at room temperature (25 °C) for 48 h, and then dried in a vacuum drying oven at 40 °C under vacuum to remove the residual solvent on the surface of the mixed matrix membrane, obtaining a Pebax / Al-MOF-NF-7 mixed matrix membrane with a thickness of 129 μm. The weight percentage of Al-MOF-NF in the Pebax / Al-MOF-NF mixed matrix membrane was 2.0%, named Pebax / Al-MOF-NF-7 mixed matrix membrane.

[0046] Figure 7 is the scanning electron microscope cross-sectional view of the prepared Pebax / Al-MOF-NF-7 mixed matrix membrane. From Figure 7 It can be seen that after the introduction of Al-MOF-NF into the Pebax matrix, the cross-sectional view of the mixed matrix membrane becomes rough, thus proving the introduction of the filler. Moreover, the filling amount of Al-MOF-NF is too high, resulting in uneven distribution of Al-MOF-NF in the mixed matrix membrane and agglomeration.

[0047] Under the conditions of 25 °C and 2 bar, the prepared Pebax / Al-MOF-NF-7 mixed matrix membrane was used for the separation test of CO2 / CH4 mixed gas with a CO2 volume fraction of 20%. Its CO2 flux was 332 barrer, and the CO2 / CH4 selectivity was 32.

[0048] Comparative Example 1

[0049] For comparison, 0.537 g of Pebax particles were dissolved in a mixed solution of 70% ethanol / 30% water by mass. After stirring at 80 °C for 2 h, the obtained casting solution was poured onto a clean ultra-flat surface dish for casting, dried at room temperature (25 °C) for 48 h, and then placed in a 40 °C vacuum oven for 24 h to remove the residual solvent, obtaining a Pebax membrane with a thickness of 109 μm.

[0050] Figure 8 is the SEM cross-sectional view of the prepared pure Pebax membrane. From Figure 8 it can be seen that the cross-section of the pure Pebax membrane exhibits the typical morphology of a smooth, dense and defect-free polymer membrane. Under the conditions of 25 °C and 2 bar, the Pebax membrane was used for the separation test of a CO2 / CH4 mixed gas with a CO2 volume fraction of 20% (the volume ratio of CO2 to CH4 is 2:8). After testing, its CO2 flux is 280 barrer and the CO2 / CH4 selectivity is 24.

[0051] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of Al-MOF-NF with high-density metal sites, characterized in that, The preparation method includes the following steps: (1) Dissolve aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and sodium sulfate (Na2SO4) in deionized water to form solution A; dissolve terephthalic acid (PTA) in DMAC to form solution B; mix solution A and solution B to obtain a clear solution C. (2) Transfer the clear solution in step (1) to a stainless-steel autoclave, heat and react at a constant temperature for several hours, and then cool to room temperature to obtain a suspension D. (3) Filter and separate the reaction product in step (2), wash it three times with deionized water and ethanol respectively, and finally dry it to a constant weight at a constant temperature to obtain the Al-MOF-NF product.

2. The preparation method according to claim 1, wherein: (1) In the A solution system in step (1), the dosage relationship of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), sodium sulfate (Na2SO4) and deionized water is: 225 mg: 17.2 mL: 18 mL; the dosage relationship of terephthalic acid (PTA) and DMAC in the A solution system is 166.2 mg: 18 mL. Stir solution A and B evenly at room temperature and then mix them to obtain a clear solution C. The stirring speed is 500 - 800 rpm, and the stirring temperature is 15 - 35 °C. (2) The reaction conditions in step (2) are as follows: transfer suspension C to a stainless-steel autoclave and carry out hydrothermal reaction at a constant temperature. The temperature of the hydrothermal reaction is 145 °C - 175 °C, and the hydrothermal reaction time is 2 - 4 h. (3) Carry out centrifugation and washing operations on the reaction solution C in step (2). The dosage of deionized water is 200 - 500 mL, and the dosage of ethanol is 200 - 500 mL. The centrifugation speed is 8500 - 10000 rpm. Collect the solid product D and dry it to a constant weight at a constant temperature. The temperature is 50 - 80 °C, and dry it for 48 h - 72 h to obtain the Al-MOF-NF product.

3. Application of the Al-MOF-NF with high-density metal sites according to claim 1 in the field of CO2 / CH4 mixed gas separation.

4. A mixed matrix membrane, which is formed by physically blending Al-MOF-NF as a filler and polyether block amide Pebax as a base material at room temperature; the thickness of the mixed matrix membrane is 109 - 132 μm; the mass percentage of the filler in the mixed matrix membrane is 1% - 7%.

5. Application of the mixed matrix membrane according to claim 4 in CO2 capture.

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