MOFs composite membrane for ammonia separation and preparation method thereof

Abstract

The invention discloses an MOFs composite membrane for ammonia separation and a preparation method thereof, and the preparation method comprises the following steps: S1, mixing a metal compound, an organic ligand and a solvent according to a specific molar ratio, reacting at a specific temperature to form an MOF material, and activating the MOF material as a seed crystal; s2, preparing the MOF material into a solution with a specific concentration, uniformly mixing the MOF material with the solution through a stirring, ultrasonic treatment and impregnation method or a method combining stirring, ultrasonic treatment and impregnation, and then introducing the solution to one main surface of a porous support layer to obtain a support layer membrane; and S3, preparing a metal organic framework material synthetic solution with the same molar ratio as that in the step S1, then putting the support layer membrane with seed crystal introduced on the surface into the metal organic framework material synthetic solution, and performing vacuum heating, drying and activating under the same reaction condition as that in the step S1 to form the MOFs composite membrane. The obtained composite membrane has an efficient ammonia separation effect, and when the composite membrane is used for separating ammonia-containing gas, the ammonia permeability reaches up to 2956.9 GPU, and the ammonia / nitrogen selectivity and the ammonia / hydrogen selectivity respectively reach up to 620.1 and 180.8.

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 an important role in the chemical industry and has important applications in the fields of agricultural fertilizers, pharmaceuticals, organic compounds and polymer material synthesis. So far, most NH3 is still produced through the traditional Haber-Bosch process, which produces NH3 through the catalytic reaction of nitrogen (N2) and hydrogen (H2) under high temperature and high pressure conditions. It must be noted that the NH3 synthesis conversion rate of the Haber-Bosch process is low, only 10-20%, and is generally collected by physical cooling and liquefaction. However, about 3% of NH3 will still remain in the circulating gas, reducing the synthesis efficiency and affecting production capacity. Therefore, it is very important to recover low-concentration NH3.

[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, 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, and the size, shape and surface chemical properties of its pores or cavities are highly adjustable. The diversity and modifiability of MOFs have become promising building blocks for constructing membranes with high separation performance, enabling 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] In view of the problems of low ammonia selectivity and low ammonia 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 preparation method thereof. A seed layer is directly generated by using a metal source and an organic ligand of a support layer. In this process, the metal substrate, as one of the synthetic raw materials, can enhance the interaction between the metal substrate and the MOF layer. A simple and easily scalable reaction seed method is used to in-situ grow MIL-116 or MIL-118 to produce an ultra-thin, defect-free, pure-phase MIL-116 membrane or MIL-118 membrane on an anodic aluminum oxide (AAO) substrate.

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

[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 is 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; 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: Mix metal compounds, organic ligands and solvents in a specific molar ratio to form a metal organic framework material synthesis solution, react at a specific temperature for a period of time to form a MOF material, and vacuum dry and activate it to serve as a seed crystal;

[0011] S2, introducing seed crystals: preparing the MOF material into a solution of a specific concentration, and mixing it evenly by stirring, ultrasound, immersion or a combination of the three methods, and then introducing the solution to a main surface of the porous support layer, heating and drying, to obtain a support layer membrane with seed crystals introduced on the surface;

[0012] S3, secondary growth of MOF membrane: 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 and dry to activate, so as 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 the 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 selects 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 bond 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 in the membrane. According to the preparation method of the present invention, the aluminum-based metal organic framework membrane is used for ammonia separation 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 reaction seed method of the present invention have good self-support and certain mechanical strength.

[0023] C. The aluminum-based metal organic framework 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 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 method of the present invention uses MIL-116 and MIL-118 as the composite membrane selection layer, and its ultra-thin and porous structure can greatly shorten the gas transmission path, reduce the gas permeation resistance, and increase the gas flux of the membrane. The method has low raw material cost and simple operation. DETAILED DESCRIPTION

[0025] The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that the present disclosure will be thorough and complete and will fully convey the concept of the present invention to those skilled in the art. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0026] Embodiment 1:

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

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

[0029] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), and deionized water were mixed at a molar ratio of Al 3+ : H6mel: H2O = 2: 1: 10 is 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 crystal solution through stirring, ultrasound, immersion or a combination of the three methods, and reacted on an anodized 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 nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), and deionized water were mixed at 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 in deionized water for 3 times, 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 mixed gas containing ammonia, nitrogen and hydrogen, and the permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the mixed matrix membrane was 2956.9 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were as high as 620.1 and 180.8, respectively.

[0035] Embodiment 2:

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

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

[0038] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O), 1,2,4,5-benzenetetracarboxylic acid (H4btec), and deionized water were mixed in a molar ratio of Al 3+ : H4btec: H2O = 2:1:10 is mixed, and a uniform solution is prepared by stirring, ultrasound, impregnation or a combination of the three. It 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 crystal solution through stirring, ultrasound, immersion or a combination of the three methods, and reacted on an anodized 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 nonahydrate (Al(NO3)3·9H2O), 1,2,4,5-benzenetetracarboxylic acid (H4btec), and deionized water were mixed in a molar ratio of Al 3+ : H4btec: H2O = 2: 1: 10, the AAO membrane with MIL-118 seeds was gently placed into a polytetrafluoroethylene-lined reactor, and then reacted at 210°C for 24 hours. After cooling, the membrane was taken out, rinsed and soaked in 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 mixed gas containing ammonia, nitrogen and hydrogen, and the permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the mixed matrix membrane was 820.7 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 506.5 and 110.3, respectively.

[0044] Embodiment 3:

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

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

[0047] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), and deionized water were mixed at a molar ratio of Al3+ : H6mel: H2O = 2: 1: 10 is 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, and 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 seed crystals is prepared, and a uniform solution is prepared as a seed crystal solution by stirring, ultrasound, immersion or a combination of the three methods, and 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 nonahydrate (Al(NO3)3·9H2O), benzene hexacarboxylic acid (H6mel), and deionized water were mixed at 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 into 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 mixed gas containing ammonia, nitrogen and hydrogen, and the permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the ammonia permeability of the MIL-116 / PES membrane was 1420.2GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 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), and the hydrogen bonding and Lewis acid-base synergy 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] Embodiment 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 mixed, obtained similar results.

[0056] Embodiment 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] Embodiment 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] Embodiment 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] Embodiment 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] Embodiment 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] Embodiment 10:

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

[0068] In summary, the present invention uses aluminum-based metal organic framework materials as the selection layer, and prepares MIL-116 membrane and MIL-118 membrane by a secondary growth method. The functional groups of 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 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 in the membrane. According to the preparation method of the present invention, aluminum-based metal organic framework membranes are 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 highly efficient 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 greatly reducing the cost of membrane preparation and facilitating its large-scale application.

[0071] Anything not described in the present invention is applicable to the prior art.

[0072] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. However, the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A MOFs composite membrane for ammonia separation, characterized in that: The invention 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. The crystal layer is evenly distributed on the porous support and is tightly combined with the porous support.

2. The MOFs composite membrane for ammonia separation according to claim 1, characterized in that: The porous support layer is anodized aluminum (AAO) or an organic porous support, wherein the organic porous support is one of polyethersulfone (PES), nylon (PA), and polyvinylidene fluoride (PVDF); the crystal layer is one of a MIL-116 membrane and a MIL-118 membrane.

3. The MOFs composite membrane for ammonia separation according to claim 2, characterized in that: The pore size of the porous support layer is 20nm-50nm; the thickness of the crystal layer is 3μm-20μm.

4. A method for preparing a MOFs composite membrane for ammonia separation, characterized in that: The steps include: S1. Preparation of MOF materials: Mix metal compounds, organic ligands and solvents in a specific molar ratio to form a metal organic framework material synthesis solution, react at a specific temperature for a period of time to form a MOF material, and vacuum dry and activate it to serve as a seed crystal; S2, introducing seed crystals: preparing the MOF material into a solution of a specific concentration, and mixing it evenly by stirring, ultrasound, immersion or a combination of the three methods, and then introducing the solution to a main surface of the porous support layer, heating and drying, to obtain a support layer membrane with seed crystals introduced on the surface; S3, secondary growth of MOF membrane: 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 and dry to activate, so as to form the MOFs composite membrane.

5. The preparation method according to claim 4, characterized in that: 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).

6. The preparation method according to claim 4, characterized in that: In the step S1, the reaction temperature is 150-210° C. and the reaction time is 12-24 hours.

7. The preparation method according to claim 4, characterized in that: In the step S1, the MOF material is one of MIL-116 and MIL-118.

8. The preparation method according to claim 4, characterized in that: In the step S2, the MOF material is prepared into a 0.5 wt% deionized water solution.

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

10. The preparation method according to claim 4, characterized in that: The vacuum activation condition in step S3 is heating and drying in a vacuum oven at 100° C. for 4 hours.

11. Use of the MOFs composite membrane prepared by the preparation method according to any one of claims 4 to 10 in the separation of ammonia nitrogen and ammonia hydrogen.