A membrane for N2 / CH4 separation utilizing a dual selection mechanism and its preparation method

Abstract

This invention relates to a gas separation membrane for N2 / CH4 using a dual-selectivity mechanism and its preparation method. Chromium nitrate nonahydrate, an organic acid, acetylacetone, ethyl acetate, and acetone are mixed and dissolved to obtain a dark green solution. The dark green solution is poured into sufficient diethyl ether to precipitate the precipitate, which is then dried in a vacuum oven to obtain chromium cluster powder. An MXene colloidal solution is lyophilized to obtain MXene sheet material. Deionized water and chromium cluster powder are mixed to form solution A. The MXene sheet material is added to solution A to obtain mixture B. Mixture B is deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane, which is then placed in a vacuum oven to activate the chromium clusters. A Cr-MXene gas separation membrane rich in Cr clusters between MXene sheets is prepared. The prepared membrane possesses both diffusion-selectivity and reaction-selectivity mechanisms, enabling efficient separation of the N2 / CH4 system.

Description

Technical Field

[0001] This invention relates to a Cr-MXene membrane that utilizes a dual selection mechanism to achieve N2 / CH4 separation and its preparation method. Background Technology

[0002] With the continuous decline in proven conventional natural gas reserves, the development of economical and efficient denitrification and CH4 purification technologies to achieve the efficient utilization of unconventional natural gas will play an important role in alleviating my country's energy crisis. Among these technologies, the use of N2 preferential permeation separation membranes for denitrification and CH4 purification of unconventional natural gas has advantages such as energy saving, high efficiency, and environmental protection, and has broad development prospects.

[0003] Gas separation membranes separate gaseous systems based on the differences in the physical and chemical properties of gas molecules. The main separation selection mechanisms fall into three categories: diffusion selection, dissolution selection, and reaction selection. Diffusion selection utilizes differences in the size of gas molecules; dissolution selection utilizes differences in the solubility of gas molecules in the membrane material; and reaction selection utilizes differences in the chemical reactivity of gas molecules with the membrane material.

[0004] From the perspective of facilitating natural gas transportation, CH4, as the product gas, should be maintained at a relatively high pressure. Using an N2-preferential permeation membrane allows CH4 gas to be retained on the retrieval side of the membrane, maintaining a higher pressure and facilitating gas transportation. However, because the physicochemical properties of N2 and CH4 are very similar, and CH4 preferentially permeates through the membrane compared to N2, achieving efficient separation between the two is very difficult. Currently reported N2-preferential permeation membrane processes rely solely on enhanced diffusion selection mechanisms, fully utilizing the fact that the diameter of N2 molecules is slightly smaller than that of CH4 molecules to achieve separation. For example, a few polymer membranes, such as polyimide membranes... [1,2] And most molecular sieve membranes, such as carbon molecular sieve membranes. [3] SSZ-13 [4] Membranes, among others, demonstrate potential for separating N2 and CH4 mixtures through enhanced diffusion selectivity mechanisms. Among them, commercially available polyimide... The membrane N2 permeability was only 0.0032 GPU, and the corresponding N2 / CH4 separation factor was 1.06. [2] The carbon molecular sieve membrane achieved an N2 permeability of 0.07 GPU, with a corresponding N2 / CH4 separation factor of 5.94. [3] The SSZ-13 membrane achieved an N2 permeability of 265.67 GPU, with a corresponding N2 / CH4 separation factor of 10. [4]Furthermore, as a novel layered material, MXene can be deposited on a substrate using a vacuum filtration method to form films for N2 / CH4 separation. Testing and calculations show that the average interlayer spacing of the fabricated film lies between the molecular dynamic diameters of N2 and CH4; therefore, MXene membranes can also separate N2 and CH4 based on diffusion selectivity. Currently, there are no reports of commercially available MXene membranes for N2 / CH4 separation. Under laboratory conditions, MXene membranes prepared solely based on enhanced diffusion selectivity exhibit a permeability of approximately 48 GPU, with a maximum N2 / CH4 separation performance of 3.2. [5] .

[0005] References

[0006] [1]Wang LN, Cao YM, Zhou MQ, Ding XL, Liu QH, Yuan Q. The gaspermeation properties of 6FDA-2,4,6-trimethyl-1,3-phenylenediamine(TMPDA) / 1,3-phenylenediamine(mPDA)copolyimides[J]. Polymer Bulletin, 2008, 60: 137-147.

[0007] [2]Zhao HY,Cao YM,Ding XL,Zhou MQ,Liu JH,Yuan Q.Poly(ethyleneoxide)induced cross-linking modification of Matrimid membranes for selectiveseparation of CO2[J].Journal of Membrane Science,2008,320:179-184.

[0008] [3]Ning X,Koros WJ,Carbon molecular sieve membranes derived fromMatrimid polyimide for nitrogen / methane separation[J].Carbon.2014,66,511-522.

[0009] [4]Song SC,Gao F,Zhang Y,Li XP,Zhou M,Wang B,Zhou RF,Preparation of SSZ-13membranes with enhanced fluxes using asymmetric alumina supports forN2 / CH4 and CO2 / CH4 separations[J].Separation and Purification Technology,2019,209:946-954.

[0010] [5]Ding L, Wei YY, Li LB, Zhang T, Wang HH, Xue J, Ding LX, Wang SQ, Caro J, Gogotsi Y, MXene molecular sieving membranes for highly efficient gasseparation[J]. Nature Communications, 2018, 9, 155. Summary of the Invention

[0011] This invention relates to a Cr-MXene membrane for efficient N2 / CH4 separation utilizing a dual-selectivity mechanism and its preparation method. The method has a relatively simple preparation process, and the resulting gas separation membrane exhibits stable performance, effectively improving N2 / CH4 separation performance.

[0012] This invention introduces chromium cluster materials prepared using the transition metal chromium (Cr) into the spaces between MXene sheet materials to create a gas separation membrane rich in Cr clusters between MXene sheets, termed a Cr-MXene membrane. In the Cr-MXene membrane, fluorine present in the MXene material can form hydrogen bonds with hydrogen on the chromium clusters, ensuring the chromium clusters are firmly fixed between the MXene sheets. This method increases the spacing between MXene sheets, providing a wide transport channel for gas molecules. Furthermore, after activation treatment, the chromium cluster material exposes unsaturated coordination metal sites that specifically interact with N2 molecules, thereby preferentially adsorbing N2 molecules and hindering CH4 molecules from entering the membrane channels, achieving efficient separation of N2 and CH4. It is worth noting that while there have been reports on using reaction selectivity to achieve gas separation through membranes, these mainly rely on basic groups for systems containing acidic gases, such as mixtures of CO2, SO2, and H2S. This invention introduces unsaturated coordination metal sites into the membrane to specifically interact with N2 molecules, thus preparing a Cr-MXene membrane that achieves N2 / CH4 separation through reaction selectivity—a process not previously reported. Compared to polymer membranes, molecular sieve membranes, and pure MXene membranes, the Cr-MXene membrane in this invention achieves an N2 permeability of 365.8 GPU and an N2 / CH4 separation factor of 12.3, respectively, demonstrating a significant improvement in permeation selectivity.

[0013] This invention is achieved through the following technical solution:

[0014] A membrane for N2 / CH4 separation using a dual selection mechanism is prepared by introducing chromium cluster material prepared with transition metal element Cr into the interlayer material MXene to prepare a gas separation membrane Cr-MXene with Cr clusters rich in the interlayer of MXene sheets.

[0015] The present invention provides a method for preparing a membrane for N2 / CH4 separation utilizing a dual-selectivity mechanism, comprising the following steps:

[0016] 1) Chromium nitrate nonahydrate, organic acid, acetylacetone, ethyl acetate and acetone are mixed and dissolved to react and obtain a dark green solution. The dark green solution is then poured into sufficient diethyl ether to precipitate. After filtration, a dark green flocculent precipitate is obtained. The precipitate is dried in a vacuum oven to obtain chromium cluster powder.

[0017] 2) The commercial MXene colloidal solution was freeze-dried to obtain MXene sheet material;

[0018] 3) Mix deionized water with the chromium cluster powder obtained in step 1) to form solution A; add the MXene sheet material obtained in step 2) to solution A to obtain mixture B;

[0019] 4) The mixture B is deposited on nylon filter paper to form a gas separation membrane by vacuum filtration, and then placed in a vacuum oven to activate the chromium clusters.

[0020] In step 1), the mass ratio of chromium nitrate nonahydrate, organic acid, acetylacetone, ethyl acetate, and acetone is 1:(0.6-1):(0.1-0.3):(1-5):(10-12.5).

[0021] In step 1), the reaction temperature is 60-80℃ and the reaction time is 2-8h.

[0022] The dark green flocculent precipitate obtained in step 1) is dried in a vacuum oven at 60-80℃.

[0023] In step 3), the mass ratio of deionized water to chromium cluster in solution A is 200:(0.005-0.015); after adding MXene sheet material to solution A, the mass ratio of deionized water, chromium cluster, and MXene in mixture B is 200:(0.005-0.015):(0.0025-0.01).

[0024] The activation temperature of the film prepared in step 4) in the vacuum oven is 130-170℃, and the activation time is 6-10h.

[0025] The gas separation membrane prepared using the above steps was used to test the permeability selectivity of a mixed gas (composition: N2 / CH4 = 10:90 vol%). The results showed that the N2 permeation rate of the gas separation membrane was 112.9-365.8 GPU, and the N2 / CH4 separation factor was 5.8-12.3.

[0026] This invention offers the following advantages: a separation membrane is prepared by introducing chromium clusters into the MXene sheet material using a simple filtration method. After activation, the pore size of this membrane not only expands but also gains the ability to preferentially bind N2 molecules. Compared to traditional MXene membranes that rely solely on diffusion-selective mechanisms for separation, the membrane prepared in this invention possesses both diffusion-selective and reaction-selective mechanisms. This dual-selectivity membrane enables highly efficient separation of the N2 / CH4 system. Attached Figure Description

[0027] Figure 1 Electron micrograph of the cross-sectional morphology of the MXene gas separation membrane after chromium clusters were introduced between the layers and activated. Detailed Implementation

[0028] Example 1:

[0029] 8g of chromium nitrate nonahydrate, 6.4g of organic acid, 1.6g of acetylacetone, 40g of ethyl acetate, and 100g of acetone were mixed to form a solution. The solution was reacted at 80℃ for 4 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 60℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0030] Take 200g of deionized water and mix it with 0.005g of chromium cluster powder to form a homogeneous solution A; then take 0.005g of MXene sheet material and add it to solution A to obtain a mixed solution B.

[0031] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 150°C for 8 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0032] Example 2:

[0033] 8g of chromium nitrate nonahydrate, 7.2g of organic acid, 1.2g of acetylacetone, 24g of ethyl acetate, and 95g of acetone were mixed to form a solution. The solution was reacted at 70℃ for 6 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 70℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0034] Take 200g of deionized water and mix it with 0.012g of chromium cluster powder to form a homogeneous solution A; then take 0.0045g of MXene sheet material and add it to solution A to obtain a mixed solution B.

[0035] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 140°C for 9 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0036] Example 3:

[0037] 8g of chromium nitrate nonahydrate, 4.8g of organic acid, 2.4g of acetylacetone, 32g of ethyl acetate, and 90g of acetone were mixed to form a solution. The solution was reacted at 60℃ for 5 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 65℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0038] Take 200g of deionized water and mix it with 0.01g of chromium cluster powder to form a homogeneous solution A; then take 0.01g of MXene sheet material and add it to solution A to obtain a mixed solution B.

[0039] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 135°C for 7 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0040] Example 4:

[0041] 8g of chromium nitrate nonahydrate, 8g of organic acid, 0.8g of acetylacetone, 12g of ethyl acetate, and 85g of acetone were mixed to form a solution, which was reacted at 65℃ for 7 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 75℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0042] Take 200g of deionized water and mix it with 0.008g of chromium cluster powder to form a homogeneous solution A; then take 0.0025g of MXene sheet material and add it to solution A to obtain a mixture B.

[0043] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 170°C for 10 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0044] Example 5:

[0045] 8g of chromium nitrate nonahydrate, 5.6g of organic acid, 2g of acetylacetone, 18g of ethyl acetate, and 88g of acetone were mixed to form a solution, which was reacted at 68℃ for 8 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 72℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0046] Take 200g of deionized water and mix it with 0.015g of chromium cluster powder to form a homogeneous solution A; then take 0.0085g of MXene sheet material and add it to solution A to obtain a mixed solution B.

[0047] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 165°C for 6 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0048] like Figure 1 As shown in the figure, the cross-sectional morphology of the MXene gas separation membrane after chromium clusters were introduced between the layers and activated is shown in the figure.

[0049] Example 6:

[0050] 8g of chromium nitrate nonahydrate, 6g of organic acid, 2.2g of acetylacetone, 8g of ethyl acetate, and 80g of acetone were mixed to form a solution. The solution was reacted at 75℃ for 2 hours to obtain a dark green solution. The dark green solution was then poured into sufficient diethyl ether to precipitate a dark green flocculent precipitate. After filtration, the dark green precipitate was obtained and dried in a vacuum oven at 80℃ to obtain chromium cluster powder. A commercial MXene colloidal solution was lyophilized to obtain MXene sheet material.

[0051] Take 200g of deionized water and mix it with 0.006g of chromium cluster powder to form a homogeneous solution A; then take 0.0075g of MXene sheet material and add it to solution A to obtain a mixed solution B.

[0052] MXene and chromium clusters in mixture B were deposited onto nylon filter paper using vacuum filtration to form a gas separation membrane. The membrane was then placed in a vacuum oven at 130°C for 8 hours to activate the chromium clusters. The membrane was then tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0053] Comparative example:

[0054] For commercial use Prepare an N2 / CH4 separation membrane using AD 60 perfluoropolymer. Take 1g AD 60 was dissolved in 20g of perfluoropolyether solvent to prepare a casting solution with a mass fraction of 5%. The solution was then evaporated at room temperature to form a homogeneous membrane. The prepared membrane was tested in a mixed gas system (N2 / CH4 = 10:90 vol%). The test results are shown in Table 2.

[0055] Test Results and Conclusions

[0056] Using first-principles calculations and density functional theory (DFT), the interaction energy between the activated chromium cluster and N2 and CH4 molecules was simulated and calculated. The results are shown in Table 1.

[0057] Table 1. Interaction energies of chromium clusters with N2 and CH4 molecules after activation treatment.

[0058]

[0059] As shown in Table 1, the interaction energies of the chromium cluster with N2 and CH4 molecules are negative, proving that the adsorption process is exothermic. Furthermore, the absolute value of the interaction energy of the chromium cluster with N2 is greater than that with CH4, indicating that the binding of the chromium cluster with N2 is more stable. This confirms that the activated chromium cluster material can preferentially adsorb N2 molecules.

[0060] The permeability and selectivity of the fabricated membrane were tested using a laboratory-assembled gas separation membrane performance testing platform. Test conditions: feed gas composition N2 / CH4 = 10:90 vol%; feed gas pressure 0.05 MPa; purge gas (helium) flow rate 2 mL / min. Test results are shown in Table 2.

[0061] Table 2 shows the N2 / CH4 permeation selectivity of the MXene gas separation membranes prepared.

[0062]

[0063] Note: 1 Permeability is used to characterize the rate at which N2 and CH4 permeate through a membrane. It is defined as the volume of gas that permeates through a unit membrane area per unit time and unit transmembrane pressure difference, and the unit is GPU (1 GPU = 10^6 kilometres per second). -6 cm 3 (STP)·cm 2 ·s -1 ·cmHg -1 ).

[0064] 2 The separation factor is the ratio of N2 permeability to CH4 permeability, reflecting the membrane's ability to separate the two gases.

[0065] As shown in Table 2, the data above indicates that compared with the comparative example, the N2 permeability and N2 / CH4 separation factor of the three embodiments were improved, proving that the separation membrane using two separation mechanisms has better performance than the separation membrane using only one separation mechanism prepared with commercial materials. This shows that the invention can effectively improve the N2 / CH4 separation performance of MXene membranes.

[0066] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A membrane for N2 / CH4 separation using a dual selection mechanism; characterized in that, A gas separation membrane Cr-Mxene with Cr clusters between MXene layers is prepared by introducing chromium cluster materials prepared from transition metal element Cr into MXene layer materials; The preparation method comprises the following steps: 1) mixing and dissolving chromium nitrate nonahydrate, organic acid, acetylacetone, ethyl acetate and acetone to obtain a dark green solution, then pouring the dark green solution into sufficient diethyl ether to precipitate, and obtaining dark green flocculent precipitate by filtration, and drying the precipitate in a vacuum oven to obtain chromium cluster powder; 2) freeze-drying a commercial MXene colloidal solution to obtain MXene layer material; 3) mixing deionized water and the chromium cluster powder obtained in step 1) to form solution A, and adding the MXene layer material obtained in step 2) to solution A to obtain mixture B; 4) depositing mixture B on a nylon filter paper by vacuum filtration to form a gas separation membrane, and activating the chromium clusters in a vacuum oven.

2. The membrane for N2 / CH4 separation using a dual selection mechanism according to claim 1, wherein the membrane is characterized by, In step 1), the mass ratio of chromium nitrate nonahydrate, organic acid, acetylacetone, ethyl acetate and acetone is 1: (0.6-1): (0.1-0.3): (1-5): (10-12.5).

3. The membrane for N2 / CH4 separation using a dual selection mechanism according to claim 1, wherein the membrane is characterized by, In step 1), the reaction temperature is 60-80 ℃, and the reaction time is 2-8 h.

4. The membrane for N2 / CH4 separation using a dual selection mechanism according to claim 1, wherein the membrane is characterized by, In step 1), the dark green flocculent precipitate is dried in a vacuum oven at 60-80 ℃.

5. The membrane for N2 / CH4 separation using a dual selection mechanism according to claim 1, wherein the membrane is characterized by, In step 3), the mass ratio of deionized water and chromium cluster powder in solution A is 200: (0.005-0.015), and the mass ratio of deionized water, chromium cluster powder and MXene in mixture B after adding the MXene layer material to solution A is 200: (0.005-0.015): (0.0025-0.01).

6. The membrane for N2 / CH4 separation using dual selection mechanism according to claim 1, wherein, In step 4), the activation temperature of the prepared membrane in the vacuum oven is 130-170 ℃, and the activation time is 6-10 h.

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