Steam modified zif-8 membranes, methods of making and using the same

Abstract

The application provides a steam modified ZIF-8 membrane and a preparation method and application thereof, and belongs to the technical field of membrane materials. The preparation method of the steam modified ZIF-8 membrane provided by the application comprises the following steps: S1, placing a ZIF-8 membrane and an acetylacetone salt in a closed environment and vacuumizing, the active surface of the ZIF-8 membrane faces the acetylacetone salt and is fixed; S2, heating the acetylacetone salt in step S1 to generate acetylacetone salt steam, and making the acetylacetone salt steam contact and react with the active surface of the ZIF-8 membrane; and S3, activating the ZIF-8 membrane after the reaction in step S2 in a vacuum oven to obtain the steam modified ZIF-8 membrane. The steam modified ZIF-8 membrane prepared by the preparation method has the advantages of low preparation cost and good separation performance.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically, to a vapor-modified ZIF-8 membrane, its preparation method, and its application. Background Technology

[0002] In the field of industrial carbon capture, efficient separation of CO2 / N2 is one of the core challenges in achieving low carbon emissions. Traditional amine absorption methods suffer from high energy consumption, strong corrosiveness, and secondary pollution. While inorganic membrane separation technologies based on molecular sieving principles (such as zeolite membranes and MOF membranes) have the advantage of low energy consumption, they still face key bottlenecks in practical applications. Taking ZIF-8 membranes as an example, their crystallographic pore size (approximately 3.4 Å) lies between the kinetic diameters of CO2 (3.3 Å) and N2 (3.64 Å), theoretically allowing for selective separation through molecular sieving. However, existing unmodified ZIF-8 membranes have the following inherent defects: First, the flexibility of the ZIF-8 framework leads to dynamic fluctuations in the actual pore size, weakening sieving accuracy; second, the membrane surface lacks specific adsorption sites, making it difficult to utilize the quadrupole moment characteristic of CO2 to enhance selectivity; third, the unmodified pores do not exhibit sufficient adsorption difference for CO2 / N2, resulting in significant competitive adsorption effects in low-concentration CO2 environments, leading to a separation factor far lower than the theoretical value.

[0003] To improve the performance of ZIF-8 membranes, modification is necessary. Vapor phase modification is a common method for ZIF-8 modification, which involves reacting the vapor generated by heating with the solid phase to avoid the influence of solvents on the membrane. However, the metal precursors used (such as chlorides and nitrates) have high thermal decomposition temperatures (usually above 200°C), far exceeding the thermal stability limit of ZIF-8 (250°C). This makes the membrane skeleton structure of ZIF-8 easily damaged during the modification process, leading to a deterioration in the separation performance of the final product.

[0004] In summary, existing ZIF-8 modification technologies struggle to balance the contradiction between "selectivity enhancement" and "permeability maintenance," and the modification processes carry a high risk of structural damage, severely hindering the large-scale application of ZIF-8 membranes in industrial carbon capture. There is an urgent need to develop a mild, targeted, and highly compatible modification method that can precisely control the ZIF-8 pore structure while introducing high-density CO2 adsorption sites, thereby achieving a breakthrough improvement in CO2 / N2 separation performance. Summary of the Invention

[0005] The purpose of this invention is to provide a ZIF-8 membrane modification method with mild reaction conditions that does not easily damage the ZIF-8 membrane structure.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a vapor-modified ZIF-8 membrane, comprising the following steps: S1: Place the ZIF-8 membrane and acetylacetone salt in a sealed environment and evacuate the vacuum. The active side of the ZIF-8 membrane faces the acetylacetone salt and is fixed. S2: The acetylacetone salt in step S1 is heated to generate acetylacetone salt vapor, which then comes into contact with and reacts with the active surface of the ZIF-8 membrane. S3: Activate the ZIF-8 membrane that has completed the reaction in step S2 in a vacuum oven to obtain a vapor-modified ZIF-8 membrane.

[0007] This invention achieves precise modification of acetylacetone salts on the active surface of ZIF-8 membranes through directional vapor deposition in a vacuum-sealed environment. This method avoids membrane swelling defects caused by liquid-phase immersion, while utilizing the low invasiveness of the vapor-phase reaction to form a uniform metal modification layer within the pores. This introduces CO2-specific adsorption sites and moderately shrinks the pore size (approaching the CO2 kinetic diameter), significantly improving CO2 / N2 separation selectivity and maintaining the high gas permeation flux of the ZIF-8 membrane.

[0008] Preferably, in step S1, the acetylacetone salt is selected from one or more of acetylacetone iron, acetylacetone copper, acetylacetone aluminum, acetylacetone nickel, acetylacetone titanium, acetylacetone magnesium, or acetylacetone ferrous.

[0009] In the preparation method provided by the present invention, the role of acetylacetone salt is to provide metal active sites for ZIF-8 membrane to specifically bind with CO2 molecules, thereby enhancing the CO2 selectivity of ZIF-8 membrane. In addition, acetylacetone salt can also modify the pore inlet of ZIF-8 membrane to achieve rapid transport of CO2 in ZIF-8.

[0010] Preferably, in step S2, the heating temperature is 120~180℃.

[0011] This invention ensures that the acetylacetone salt is fully vaporized while avoiding structural distortion of the ZIF-8 framework due to high temperatures (above 200°C). This temperature range allows the acetylacetone salt to diffuse into the membrane pores in a molecular state, achieving mild and controllable modification.

[0012] Preferably, the reaction time between acetylacetone salt vapor and the active surface of the ZIF-8 membrane is 0.5 to 5 hours.

[0013] Preferably, the ZIF-8 membrane has a support, which is aluminum oxide.

[0014] Using an alumina-based ZIF-8 membrane can support the ZIF-8 membrane layer and maintain its fixed shape during subsequent activation, preventing membrane peeling during steam treatment. At the same time, alumina can react with the ZIF-8 crystal layer, improving the interfacial stability of ZIF-8.

[0015] Preferably, in step S3, the activation temperature is 80~120℃ and the activation time is 2~8h.

[0016] This invention utilizes an activation temperature of 80-120°C combined with a vacuum environment to effectively remove unreacted acetylacetonate and byproducts, while simultaneously modifying the activity of the modification sites.

[0017] Preferably, in step S3, the vacuum degree during activation is not greater than -100 kPa.

[0018] A second aspect of the present invention provides a vapor-modified ZIF-8 membrane, wherein the vapor-modified ZIF-8 membrane is prepared by the preparation method described in the first aspect.

[0019] A third aspect of the present invention provides an application of the vapor-modified ZIF-8 membrane described in the second aspect, wherein the application is to use the vapor-modified ZIF-8 membrane for the separation of CO2 / N2 mixed gases.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The method for preparing vapor-modified ZIF-8 membrane provided by this invention involves vapor deposition to construct a functional modification layer on the ZIF-8 surface, thereby optimizing the adsorption and diffusion synergistic mechanism of the ZIF-8 membrane: due to the presence of acetylacetonate, the CO2 adsorption capacity of the ZIF-8 membrane is significantly improved, while N2 is difficult to adsorb due to its weak polarity, thus improving the selectivity of the ZIF-8 membrane; the modification layer and the intrinsic pores of ZIF-8 form a hierarchical structure, and CO2 can be rapidly transported through the synergistic path of surface adsorption-pore diffusion, while N2 is selectively retained due to the pore confinement effect caused by its molecular size, thereby achieving a simultaneous improvement in permeation flux and selectivity; 2. The method for preparing vapor-modified ZIF-8 membrane provided by the present invention adopts a vacuum directional deposition process. It only requires controlling the reaction temperature and reaction time to achieve the modification of ZIF-8 membrane. No complicated equipment or solvents are required for post-treatment, which can effectively shorten the time required for ZIF-8 membrane modification. 3. The operation method of the present invention is simple, the modification cost is low, and it is suitable for the large-scale preparation of steam-modified ZIF-8 membranes; 4. The vapor-modified ZIF-8 membrane provided by this invention is suitable for separating low, medium and high concentrations of CO2 / N2 mixed gas, and can be used directly without pretreatment of the mixed gas, making it convenient to use. Attached Figure Description

[0021] Figure 1 The results are the single-component gas permeability test results of product M1 in Example 1 of this invention; Figure 2The XRD analysis results are for products M1, M2, M3, M4, and ZIF-8 membranes in Example 2 of this invention. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0023] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] As described in the background section, existing ZIF-8 modification methods suffer from drawbacks such as high thermal decomposition temperatures and easy destruction of the ZIF-8 structure. Therefore, this invention provides a specific embodiment... A specific embodiment of the present invention provides a method for preparing a vapor-modified ZIF-8 membrane, comprising the following steps: S1: Place the ZIF-8 membrane and acetylacetone salt in a sealed environment and evacuate the vacuum. The active side of the ZIF-8 membrane faces the acetylacetone salt and is fixed. S2: The acetylacetone salt in step S1 is heated to generate acetylacetone salt vapor, which then comes into contact with and reacts with the active surface of the ZIF-8 membrane. S3: Activate the ZIF-8 membrane that has completed the reaction in step S2 in a vacuum oven to obtain a vapor-modified ZIF-8 membrane.

[0025] In step S1 of the above embodiment, the acetylacetone salt is selected from one or more of acetylacetone iron, acetylacetone copper, acetylacetone aluminum, acetylacetone nickel, acetylacetone titanium, acetylacetone magnesium, or acetylacetone ferrous.

[0026] In step S2 of the above embodiment, the heating temperature is 120~180℃.

[0027] In step S2 of the above embodiment, the reaction time between acetylacetone salt vapor and the active surface of the ZIF-8 membrane is 0.5~5h.

[0028] In the above embodiments, the ZIF-8 membrane has a support, which is aluminum oxide.

[0029] In step S3 of the above embodiment, the vacuum degree during activation is no greater than -100 kPa.

[0030] The vapor-modified ZIF-8 membrane prepared by the method described in the above embodiments is suitable for the separation of CO2 / N2 mixed gases.

[0031] The technical solutions of the present invention are further described below through specific embodiments. Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art. In some cases, terms with conventional meanings are limited herein for clarification or ease of reference, and such limitations should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and have been employed by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments shall be performed according to the manufacturer's instructions and parameters.

[0032] Example 1 Acetylacetone iron vapor-modified ZIF-8 membrane S1: Place the alumina-supported ZIF-8 membrane and 0.5g of acetylacetone iron in a glass sample bottle and evacuate the glass sample bottle. The active side of the ZIF-8 membrane should face the acetylacetone iron and be fixed. S2: Heat the iron acetylacetone in step S1 to 160°C to generate iron acetylacetone vapor, so that the iron acetylacetone vapor comes into contact with the active surface of the ZIF-8 membrane and reacts at 160°C for 3 hours. S3: Activate the ZIF-8 membrane that has completed the reaction in step S2 in a vacuum oven at 100℃ for 3 hours to obtain the vapor-modified ZIF-8 membrane Fe-ZIF-8-160-1h, which is marked as M1.

[0033] The single-component gas permeability of product M1 was measured, and the results are as follows: Figure 1 As shown, by Figure 1 It is evident that the steam-modified ZIF-8 membrane prepared by the method provided in this invention has an effective size sieving effect for CO2 / N2.

[0034] The CO2 / N2 separation selectivity and permeability of product M1 were tested, and the test results are shown in Table 1.

[0035] Table 1 As shown in Table 1, the CO2 / N2 mixed gas separation selectivity of product M1 is 50.0, and the propylene permeability is 80.8 × 10⁻⁶. -9mol m -2 s -1 Pa -1 Product M1 has effective separation performance for CO2 / N2.

[0036] Example 2 Acetylacetone iron vapor-modified ZIF-8 membrane at different reaction times S1: Place the alumina-supported ZIF-8 membrane and 0.5g of acetylacetone iron in a glass sample bottle and evacuate the glass sample bottle. The active side of the ZIF-8 membrane should face the acetylacetone iron and be fixed. S2: Heat the iron acetylacetone in step S1 to 160°C to generate iron acetylacetone vapor, and bring the iron acetylacetone vapor into contact with the active surface of the ZIF-8 membrane and react at 160°C for 0.5h, 3h and 5h respectively. S3: Activate the ZIF-8 membrane that has completed the reaction in step S2 in a vacuum oven at 100℃ for 3 hours to obtain the vapor-modified ZIF-8 membrane Fe-ZIF-8-160-0.5h membrane, product marked as M2; Fe-ZIF-8-160-3h membrane, product marked as M3; Fe-ZIF-8-160-5h membrane, product marked as M4.

[0037] XRD analysis was performed on products M1, M2, M3, M4, and ZIF-8 films. The XRD diffraction patterns are shown below. Figure 2 As shown, by Figure 2 The results show that the modified ZIF-8 films prepared by reacting iron acetylacetonate at 160℃ for 0.5h, 1h, 3h and 5h do not damage the original ZIF-8 crystal form.

[0038] The CO2 / N2 separation selectivity and permeability of products M2, M3, and M4 were tested, and the test results are shown in Table 2.

[0039] Table 2 As can be seen from the test results in Table 2, the steam-modified ZIF-8 membranes M2, M3, and M4 prepared with different reaction times all have high separation performance for CO2 / N2.

[0040] Example 3 ZIF-8 membrane modified with acetylacetone iron vapor at different reaction temperatures S1: Place the alumina-supported ZIF-8 membrane and 0.5g of acetylacetone iron in a glass sample bottle and evacuate the glass sample bottle. The active side of the ZIF-8 membrane should face the acetylacetone iron and be fixed. S2: Heat the iron acetylacetone in step S1 to 120℃, 140℃ and 180℃ respectively to generate iron acetylacetone vapor, so that the iron acetylacetone vapor comes into contact with the active surface of the ZIF-8 membrane and reacts at the corresponding temperature for 3 hours. S3: Activate the ZIF-8 membrane that has completed the reaction in step S2 in a vacuum oven at 100℃ for 3 hours to obtain the vapor-modified ZIF-8 membrane Fe-ZIF-8-120-1h membrane, which is marked as M5; Fe-ZIF-8-140-1h membrane is marked as M6; Fe-ZIF-8-180-1h membrane is marked as M7.

[0041] The CO2 / N2 separation selectivity and permeability of products M5, M6, and M7 were tested, and the test results are shown in Table 3.

[0042] Table 3 As can be seen from the test results in Table 3, the steam-modified ZIF-8 membranes M5, M6, and M7 prepared at different reaction temperatures all exhibit high separation performance for CO2 / N2.

[0043] Example 4 ZIF-8 membranes modified by vapor of different acetylacetone salts S1: Take 0.5g of copper acetylacetone, aluminum acetylacetone, nickel acetylacetone, titanium acetylacetone, magnesium acetylacetone, and ferrous acetylacetone into different glass sample bottles. Place the alumina-supported ZIF-8 membrane into the glass sample bottle and evacuate the glass sample bottle. The active side of the ZIF-8 membrane faces the corresponding acetylacetone salt and is fixed. S2: Heat the acetylacetone salt in step S1 to 160°C to generate acetylacetone iron vapor, so that the acetylacetone iron vapor comes into contact with the active surface of the ZIF-8 membrane and reacts at 160°C for 1 hour. S3: Activate the ZIF-8 membrane from step S2 at 100℃ in a vacuum oven for 3 hours to obtain vapor-modified ZIF-8 membranes, Cu-ZIF-8-160-1h membranes, labeled M8; Al-ZIF-8-160-1h membranes, labeled M9; Ni-ZIF-8-160-1h membranes, labeled M10; Ti-ZIF-8-160-1h membranes, labeled M11; Mg-ZIF-8-160-1h membranes, labeled M12; Fe... 2+ -ZIF-8-160-1h membrane, product marking is M13.

[0044] The CO2 / N2 separation selectivity and permeability of products M8, M9, M10, M11, M12, and M13 were tested, and the test results are shown in Table 4.

[0045] Table 4 As can be seen from the test results in Table 4, the steam-modified ZIF-8 membranes M8, M9, M10, M11, M12, and M13 prepared with different acetylacetonates all have high separation performance for CO2 / N2.

[0046] As can be seen from the above embodiments, the steam-modified ZIF-8 membrane prepared by the method of the present invention has high separation performance for CO2 / N2 mixed gas.

[0047] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing a vapor-modified ZIF-8 membrane, characterized in that, Includes the following steps: S1: Place the alumina-supported ZIF-8 membrane and 0.5g of acetylacetone iron in a glass sample bottle and evacuate the glass sample bottle. The active side of the ZIF-8 membrane faces the acetylacetone iron and is fixed. S2: Heat the iron acetylacetone in step S1 to 160°C to generate iron acetylacetone vapor, and bring the iron acetylacetone vapor into contact with the active surface of the ZIF-8 membrane and react at 160°C for 0.5 h. S3: Activate the ZIF-8 membrane obtained from the reaction in step S2 in a vacuum oven at 100℃ for 3 hours to obtain a vapor-modified ZIF-8 membrane.

2. A vapor-modified ZIF-8 membrane, characterized in that, The vapor-modified ZIF-8 membrane was prepared by the preparation method described in claim 1.

3. An application of the vapor-modified ZIF-8 membrane according to claim 2, characterized in that, The vapor-modified ZIF-8 membrane was used for the separation of CO2 / N2 mixed gases.

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