Mofs composite membrane for ammonia separation and preparation method thereof

Abstract

The application discloses a kind of MOFs composite membrane for ammonia separation and preparation method thereof, comprising the following steps: S1, metal compound, organic ligand and solvent are mixed according to specific molar ratio, react at specific temperature, form MOF material and activate, as seed crystal;S2, MOF material is prepared into solution of specific concentration, and it is mixed uniformly by stirring, ultrasonic, impregnation or the method of combination of three, then the solution is introduced to one main surface of porous support layer, and the support layer film piece is obtained;S3, the same molar ratio of metal organic framework material synthesis solution in step S1 is prepared, then the support layer film piece with seed crystal introduced on the surface is placed in the metal organic framework material synthesis solution, and is activated under the same reaction condition with step S1, vacuum heating drying is formed MOFs composite membrane.The composite membrane obtained by the application has high-efficiency ammonia separation effect, when separating ammonia-containing gas, ammonia permeability is as high as 2956.9 GPU, ammonia / nitrogen and ammonia / hydrogen selectivity are as high as 620.1 and 180.8 respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation membranes, and in particular to a MOFs composite membrane for ammonia separation and a preparation method thereof. Background Art

[0002] Ammonia (NH3) plays a vital role in the chemical industry, with important applications in agricultural fertilizers, pharmaceuticals, organic compounds, and polymer material synthesis. To date, the vast majority of NH3 is still produced through the traditional Haber-Bosch process, which produces NH3 through a catalytic reaction between nitrogen (N2) and hydrogen (H2) under high temperature and high pressure conditions. It is important to note that the NH3 synthesis conversion rate of the Haber-Bosch process is relatively low, at only 10-20%, and is generally collected by physical cooling and liquefaction. However, approximately 3% of NH3 still remains in the circulating gas, reducing synthesis efficiency and affecting production capacity. Therefore, recovering low-concentration NH3 is crucial.

[0003] Membrane separation technology has the advantages of energy sustainability, simple operation and easy control, environmental protection, and high efficiency, and has great application potential in the field of gas separation. At present, the biggest limitation of membrane separation technology is the lack of membrane materials with excellent NH3 / H2 and NH3 / N2 separation selectivity and good NH3 permeability. The organic polymer membranes currently developed have a trade-off between selectivity and permeability. Metal-Organic Frameworks (MOFs) are a new type of crystalline porous material with regular pores or pore structures. The size, shape and surface chemical properties of their pores or cavities are highly adjustable. The diversity and modifiability of MOFs have become promising building blocks for constructing membranes with high separation performance, allowing researchers to select appropriate MOFs structures according to the target separation system to achieve efficient separation of the target system. Summary of the Invention

[0004] To address the low ammonia selectivity and permeation flux of ammonia separation membranes in the prior art, the present invention provides an aluminum-based metal-organic framework membrane for ammonia separation and a method for preparing the membrane. A seed layer is directly generated using a metal source and organic ligands from a support layer. During this process, the metal substrate, as one of the synthetic raw materials, enhances its interaction with the MOF layer. A simple and easily scalable reactive seeding method is used to in situ grow MIL-116 or MIL-118, producing ultrathin, defect-free, pure-phase MIL-116 or MIL-118 membranes on an anodic aluminum oxide (AAO) substrate.

[0005] The present invention adopts the following technical solutions:

[0006] A MOFs composite membrane for ammonia separation comprises a porous support layer and an aluminum-based metal organic framework crystal layer formed on the porous support layer by a secondary growth method, wherein the crystal layer is uniformly distributed on the porous support and tightly combined with the porous support.

[0007] Preferably, the porous support layer is anodized aluminum oxide (AAO) or an organic porous support, wherein the organic porous support is one of polyethersulfone (PES), nylon (PA), and polyvinylidene fluoride (PVDF); and the crystal layer is one of MIL-116 membrane and MIL-118 membrane.

[0008] More preferably, the pore size of the porous support layer is 20 nm-50 nm; and the thickness of the crystal layer is 3 μm-20 μm.

[0009] A method for preparing a MOFs composite membrane for ammonia separation comprises the following steps:

[0010] S1. Preparation of MOF materials: Mixing a metal compound, an organic ligand, and a solvent in a specific molar ratio to form a metal organic framework material synthesis solution, reacting at a specific temperature for a period of time to form a MOF material, and vacuum drying and activating the solution to serve as a seed crystal;

[0011] S2. Introducing seed crystals: The MOF material is prepared into a solution of a specific concentration and mixed uniformly by stirring, ultrasound, immersion, or a combination of the three. The solution is then introduced onto one main surface of the porous support layer and heated and dried to obtain a support layer membrane with seed crystals introduced onto the surface.

[0012] S3, MOF membrane secondary growth: prepare a metal organic framework material synthesis solution with the same molar ratio as in step S1, then place the support layer membrane with seed crystals introduced on the surface into the metal organic framework material synthesis solution, and under the same reaction conditions as step S1, vacuum heat drying and activation are performed to form the MOFs composite membrane.

[0013] In step S1, the metal compound is aluminum nitrate nonahydrate (Al(NO3)3·9H2O), the organic ligand is one of benzene hexacarboxylic acid (H6mel) and 1,2,4,5-benzenetetracarboxylic acid (H4btec), and the solvent is deionized water. The molar ratio of the three is (2-3):(1-4):(10-30).

[0014] In step S1, the reaction temperature is 150-210° C., and the reaction time is 12-24 hours.

[0015] In the step S1, the MOF material is one of MIL-116 and MIL-118.

[0016] In the step S2, the MOF material is prepared into a 0.5 wt% deionized water solution.

[0017] In step S2, the heating temperature is 30-60° C. and the drying time is 3-5 hours.

[0018] The vacuum activation condition in step S3 is heating and drying in a vacuum oven at 100° C. for 4 hours.

[0019] An application of the MOFs composite membrane prepared according to the above preparation method in the separation of ammonia nitrogen and ammonia hydrogen.

[0020] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0021] A. The present invention uses MIL-116 and MIL-118 as the composite membrane selection layer. The functional groups of the organic ligands benzene hexacarboxylic acid (H6mel) and 1,2,4,5-benzene tetracarboxylic acid (H4btec) are weakly acidic and have good affinity for NH3. The hydrogen bonding and Lewis acid-base synergy between the MIL-116 and MIL-118 membranes and NH3 significantly enhance the NH3 separation performance. In addition, the pore size of the MOFs is between the gas pairs to be separated, which is beneficial for the transmission and separation of gases within the membrane. According to the present invention, the aluminum-based metal organic framework membrane is prepared and ammonia separation is performed by membrane separation, which can achieve continuous, rapid, and low-energy separation of ammonia.

[0022] B. The uniform and continuous MIL-116 and MIL-118 films prepared by the reactive seed method of the present invention have good self-support and certain mechanical strength.

[0023] C. The aluminum-based metal-organic framework membrane obtained in the present invention has a highly efficient ammonia separation effect. When separating the residual gas of synthetic ammonia, the ammonia permeability can be as high as 2956.9 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities are as high as 620.1 and 180.8, respectively.

[0024] D. The present method uses MIL-116 and MIL-118 as the composite membrane selection layer. Its ultra-thin, porous structure can significantly shorten the gas transmission path, reduce gas permeation resistance, and increase the gas flux of the membrane. This method has low raw material costs and simple operation. DETAILED DESCRIPTION

[0025] The present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the present invention to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0026] Example 1:

[0027] This embodiment provides a method for preparing a uniform and continuous MIL-116 / AAO film using a secondary growth method, comprising the following steps:

[0028] S1. Preparation of MOF material (MIL-116):

[0029] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), deionized water were mixed in a molar ratio of Al 3+ : H6mel: H2O = 2:1:10 are mixed, and a uniform solution is prepared by stirring, ultrasound, impregnation or a combination of the three, and synthesized at 210°C for 24 hours, and then filtered, centrifuged and dried to form MIL-116 material powder as a seed crystal.

[0030] S2. Introducing MIL-116 seed crystals:

[0031] First, a 0.5 wt% aqueous solution of the above-mentioned seed crystals is prepared, and a uniform solution is prepared as a seed solution through stirring, ultrasound, immersion, or a combination of the three. The solution is reacted on an anodic aluminum oxide (AAO) support layer under hydrothermal conditions to obtain a substrate membrane with a seed crystal layer.

[0032] S3, MIL-116 / AAO film secondary growth:

[0033] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), deionized water were mixed in a molar ratio of Al 3+ : H6mel: H2O = 2:1:10 are mixed evenly, and the above-mentioned AAO membrane with MIL-116 seeds is gently placed in a polytetrafluoroethylene-lined reactor, and then reacted at 210°C for 24 hours. After cooling, the membrane is taken out, and then rinsed and soaked with deionized water for 3 times, and heated and dried in a vacuum oven at 100°C for 4 hours to obtain a MIL-116 / AAO membrane.

[0034] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were measured, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the mixed matrix membrane had a pure ammonia permeability of 2956.9 GPU, and ammonia / nitrogen and ammonia / hydrogen selectivities as high as 620.1 and 180.8, respectively.

[0035] Example 2:

[0036] This embodiment provides a method for preparing a uniform and continuous MIL-118 / AAO film using a secondary growth method, comprising the following steps:

[0037] S1. Preparation of MOF material (MIL-118):

[0038] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), 1,2,4,5-benzene tetracarboxylic acid (H4btec), deionized water were mixed in a molar ratio of Al 3+ : H4btec: H2O = 2:1:10 are mixed and a uniform solution is prepared by stirring, ultrasound, impregnation or a combination of the three. The solution is synthesized at 210°C for 24 hours, and then filtered, centrifuged and dried to form MIL-118 material powder as a seed crystal.

[0039] S2. Introducing MIL-118 seed crystals:

[0040] First, a 0.5 wt% aqueous solution of the above-mentioned seed crystals is prepared, and a uniform solution is prepared as a seed solution through stirring, ultrasound, immersion, or a combination of the three. The solution is reacted on an anodic aluminum oxide (AAO) support layer under hydrothermal conditions to obtain a substrate membrane with a seed crystal layer.

[0041] S3, MIL-118 / AAO film secondary growth:

[0042] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), 1,2,4,5-benzene tetracarboxylic acid (H4btec), deionized water were mixed in a molar ratio of Al 3+ : H4btec: H2O = 2:1:10, the above AAO membrane with MIL-118 seeds was gently placed in a polytetrafluoroethylene-lined reactor, and then reacted at 210°C for 24 hours. After cooling, the membrane was taken out, and then rinsed and soaked with deionized water for 3 times, and heated and dried in a vacuum oven at 100°C for 4 hours to obtain a MIL-118 / AAO membrane.

[0043] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were measured, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the mixed matrix membrane had a pure ammonia permeability of 820.7 GPU, and ammonia / nitrogen and ammonia / hydrogen selectivities of 506.5 and 110.3, respectively.

[0044] Example 3:

[0045] This embodiment provides a method for preparing a uniform and continuous MIL-116 / PES membrane using a secondary growth method, comprising the following steps:

[0046] S1. Preparation of MOF material (MIL-116):

[0047] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), deionized water were mixed in a molar ratio of Al3+ : H6mel: H2O = 2:1:10 are mixed and a uniform solution is prepared by stirring, ultrasound, impregnation or a combination of the three, and synthesized at 150°C for 12 hours, then filtered, centrifuged and dried to form MIL-116 material powder as a seed crystal.

[0048] S2. Introducing MIL-116 seed crystals:

[0049] First, a 0.5 wt% aqueous solution of the above-mentioned seed crystals is prepared, and a uniform solution is prepared as a seed solution through stirring, ultrasound, immersion or a combination of the three methods. The solution is reacted on a polyethersulfone (PES) support layer under hydrothermal conditions to obtain a substrate membrane with a seed crystal layer.

[0050] S3, MIL-116 / PES membrane secondary growth:

[0051] Aluminum nitrate nine hydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), deionized water were mixed in a molar ratio of Al 3+ : H6mel: H2O = 2:1:10 are mixed evenly, and the above-mentioned polyethersulfone (PES) membrane with MIL-116 seeds is gently placed in a polytetrafluoroethylene-lined reactor, and then reacted at 150°C for 12 hours. After cooling, the membrane is taken out, and then rinsed and soaked with deionized water for 3 times, and heated and dried in a vacuum oven at 100°C for 4 hours to obtain a MIL-116 / PES membrane.

[0052] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were measured, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the MIL-116 / PES membrane had an ammonia permeability of 1420.2 GPU, and ammonia / nitrogen and ammonia / hydrogen selectivities of 580.3 and 143.5, respectively.

[0053] Combined with Examples 1-3, it can be seen that compared with the MIL-118 metal-organic framework material, the MIL-116 cavity has more free carboxylic acid groups (-COOH). The hydrogen bonding and Lewis acid-base synergistic effect between the MIL-116 membrane and NH3 significantly enhance the separation performance of NH3, which is more conducive to the transmission and separation of ammonia in the membrane.

[0054] Example 4:

[0055] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. When other parameters remained unchanged, aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H4mel), and deionized water were added at a molar ratio of Al 3+ :H4mel:H2O=2:1:20 mixture, similar results were obtained.

[0056] Example 5:

[0057] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. When other parameters remained unchanged, aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H4mel), and deionized water were added at a molar ratio of Al 3+ :H4mel:H2O=3:1:30 mixed, obtained similar results.

[0058] Example 6:

[0059] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. When other parameters remained unchanged, aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H4mel), and deionized water were added at a molar ratio of Al 3+ :H4mel:H2O=3:4:30 mixed, obtained similar results.

[0060] Example 7:

[0061] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. When other parameters remained unchanged, aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H4mel), and deionized water were added at a molar ratio of Al 3+ :H4mel:H2O=3:4:30 mixed, obtained similar results.

[0062] Example 8:

[0063] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. With other parameters unchanged, the hydrothermal reaction conditions were changed to 210° C. for 12 h, and similar results were obtained.

[0064] Example 9:

[0065] The MIL-116 / AAO membrane was prepared by the same method as in Example 1. With other parameters unchanged, the hydrothermal reaction conditions were changed to 170° C. for 24 h, and similar results were obtained.

[0066] Example 10:

[0067] The MIL-116 membrane was prepared by the same method as in Example 1. With other parameters unchanged, the hydrothermal reaction conditions were changed to 150° C. for 24 h, and similar results were obtained.

[0068] In summary, the present invention uses aluminum-based metal-organic framework materials as the selective layer and prepares MIL-116 membrane and MIL-118 membrane by a secondary growth method. The functional groups of the organic ligands benzene hexacarboxylic acid (H6mel) and 1,2,4,5-benzene tetracarboxylic acid (H4btec) are weakly acidic and have good affinity for NH3. The hydrogen bonds and Lewis acid-base synergy between the MIL-116 and MIL-118 membranes and NH3 significantly enhance the separation performance of NH3. In addition, the pore size of MOFs is between the gas pairs to be separated, which is beneficial to the transmission and separation of gases within the membrane. According to the preparation method of the present invention, the aluminum-based metal-organic framework membrane is prepared and ammonia separation is performed by membrane separation, which can achieve continuous, rapid and low-energy separation of ammonia.

[0069] The mixed matrix membrane obtained by the present invention has a high-efficiency ammonia separation effect. When separating the residual gas of synthetic ammonia, the ammonia permeability can reach up to 2956.9 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities are as high as 620.1 and 180.8, respectively.

[0070] The raw materials for preparing the aluminum-based metal organic framework membrane of the present invention are either commercially available or can be synthesized at low cost, thereby significantly reducing the cost of membrane production and facilitating its large-scale application.

[0071] Any matters not described in the present invention are applicable to the prior art.

[0072] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a MOFs composite membrane for ammonia separation, characterized in that: The steps include: S1. Preparation of MOF materials: Mixing a metal compound, an organic ligand, and a solvent in a specific molar ratio to form a metal organic framework material synthesis solution, reacting at a specific temperature for a period of time to form a MOF material, and vacuum drying and activating the solution to serve as a seed crystal; The metal compound is aluminum nitrate nonahydrate, the organic ligand is one of benzene hexacarboxylic acid and 1,2,4,5-benzenetetracarboxylic acid, and the solvent is deionized water. The molar ratio of the three is 2-3:1-4:10-30. The MOF material is one of MIL-116 and MIL-118; S2. Introducing seed crystals: The MOF material is prepared into a solution of a specific concentration and mixed uniformly by stirring, ultrasound, immersion, or a combination of the three. The solution is then introduced onto one main surface of the porous support layer and heated and dried to obtain a support layer membrane with seed crystals introduced onto the surface. S3, MOF membrane secondary growth: prepare a metal organic framework material synthesis solution with the same molar ratio as in step S1, then place the support layer membrane with seed crystals introduced on the surface into the metal organic framework material synthesis solution, and under the same reaction conditions as step S1, vacuum heat drying and activation are performed to form the MOFs composite membrane.

2. The preparation method according to claim 1, wherein: In step S1, the reaction temperature is 150-210° C., and the reaction time is 12-24 hours.

3. The preparation method according to claim 1, wherein: In the step S2, the MOF material is prepared into a 0.5 wt% deionized water solution.

4. The preparation method according to claim 1, wherein: In step S2, the heating temperature is 30-60° C. and the drying time is 3-5 hours.

5. The preparation method according to claim 1, wherein: The vacuum activation condition in step S3 is heating and drying in a vacuum oven at 100° C. for 4 h.

6. A MOFs composite membrane for ammonia separation prepared by the preparation method according to any one of claims 1 to 5, characterized in that: It comprises a porous support layer and an aluminum-based metal organic framework crystal layer formed on the porous support layer by a secondary growth method, wherein the crystal layer is evenly distributed on the porous support and is tightly combined with the porous support; The porous support layer is anodized aluminum or an organic porous support, wherein the organic porous support is one of polyethersulfone, nylon, and polyvinylidene fluoride; the crystal layer is one of MIL-116 membrane and MIL-118 membrane.

7. The MOFs composite membrane for ammonia separation according to claim 6, characterized in that: The pore size of the porous support layer is 20 nm to 50 nm; the thickness of the crystal layer is 3 μm to 20 μm.

8. Use of a MOFs composite membrane prepared by the preparation method according to any one of claims 1 to 5 in the separation of ammonia nitrogen and ammonia hydrogen.