Catalytic ammonia permeation membrane and application of catalytic ammonia permeation membrane in ammonia preparation by coupling with electro-catalysis

Abstract

The invention relates to a catalytic ammonia permeable membrane and application thereof in ammonia preparation by coupling with electro-catalysis, and belongs to the field of membrane material preparation and membrane reactor application. According to the invention, by utilizing the advantages of pore channels in the sub-angstrom-scale range of the ammonia-permeable membrane, the ammonia synthesis process has higher production efficiency and has more sufficient adjustment space in the aspects of balanced reaction rate and separation rate. The ammonia-permeable membrane and electro-catalysis coupling mode is adopted, reaction-separation integration is achieved, ammonia molecules are separated in situ through the membrane separation process, and the energy consumption in the ammonia preparation process can be greatly reduced while the reaction conversion rate is increased.

Description

Technical Field

[0001] The invention relates to a catalytic ammonia permeable membrane and its application in producing ammonia by coupling with electrocatalysis, and belongs to the field of membrane material preparation and membrane reactor application. Background Art

[0002] Ammonia, a core raw material for the fertilizer industry and basic organic chemicals, is one of the most widely used basic chemicals worldwide. By 2023, global synthetic ammonia production had reached approximately 220 million tons. Currently, ammonia production is primarily based on the Haber-Bosch process, a method with a history spanning over a century. This process consumes a lot of energy and accounts for 10%-20% of the chemical industry's carbon emissions. Electrocatalytic ammonia synthesis has attracted considerable attention due to its ability to efficiently synthesize ammonia at room temperature and pressure, significantly reducing energy consumption and environmental pollution. Yin Anxiang et al. (Nat. Catal., 2019, 2:448–456) achieved highly selective ammonia synthesis using water and nitrogen as feedstocks via electrocatalysis at room temperature and pressure (25°C, 1 atm), providing a new approach and pathway for efficient ammonia synthesis under mild conditions using sustainable energy. Xue Jianfu et al. (Joule, 2023, 7(6):1333-1346) developed a highly efficient electrochemical proton-conducting membrane reactor that achieved electrochemical ammonia synthesis at atmospheric pressure and medium temperature, providing new research ideas for the development of ammonia synthesis. The above reports all focused on the ammonia synthesis process, and subsequent ammonia separation work has not been effectively developed.

[0003] Currently, conventional ammonia separation and purification processes in the chemical industry often rely on traditional, energy-intensive methods such as cryogenic separation, which suffer from low separation efficiency and environmental pollution. Membrane separation technology offers significant energy savings compared to separation technologies such as distillation, making the selection of suitable ammonia-permeable membrane materials crucial. For membrane materials to be applicable in ammonia separation, they must exhibit high selectivity and stability. Miyamoto et al. (Int. J. Hydrogen Energy, 2014, 39:10154-10160) reported a Pd membrane for hydrogen / ammonia selective separation that preferentially permeates hydrogen. However, due to limited membrane separation performance, membrane materials that only permeate the feedstock cannot improve single-pass conversion and reaction rate, making both of these membrane materials unsuitable for ammonia synthesis. To further improve the efficiency of ammonia synthesis, researchers have begun exploring the integration of ammonia production with various membrane materials and membrane separation technologies. Zeolite molecular sieve membranes, with their regular pore structure and tunable nanoscale pore size, offer high selectivity and stability, making them a promising new separation membrane material.

[0004] Due to the demanding reaction conditions and complex separation processes in the ammonia synthesis process, the development of high-performance membrane materials that integrate reaction and separation is urgently needed. Coupling electrocatalytic ammonia synthesis with membrane separation technology significantly reduces the energy and water consumption required for the cycle, meeting future market requirements for green and environmentally friendly ammonia synthesis. This provides a highly efficient and environmentally friendly method for ammonia synthesis and is expected to drive significant advancements in low-temperature, low-pressure ammonia synthesis technology. Summary of the Invention

[0005] The present invention provides a catalytic ammonia permeable membrane and its application in ammonia production coupled with electrocatalysis. By leveraging the sub-angstrom pores of the ammonia permeable membrane, the ammonia synthesis process achieves higher production efficiency and greater flexibility in balancing reaction and separation rates. By coupling the catalytic ammonia permeable membrane with electrocatalysis, a reaction-separation integration is achieved. Ammonia molecules are separated in situ through the membrane separation process, significantly reducing energy consumption in the ammonia production process while improving reaction conversion.

[0006] First, the present invention provides a catalytic ammonia permeable membrane coupled with electrocatalysis, the catalytic ammonia permeable membrane comprising a porous tubular support, an ammonia permeable layer, and a catalyst layer that catalyzes ammonia. The ammonia permeable layer comprises a molecular sieve, and the catalyst layer is supported on the outer surface of the ammonia permeable layer. The catalytic ammonia permeable membrane has an ammonia / hydrogen selectivity of 100 to 1000, and the ammonia permeable layer has a pore size of 0.26 to 0.28 nm.

[0007] Preferably, the ammonia permeable layer is a molecular sieve membrane or a molecular sieve / polymer mixed matrix membrane, the molecular sieve membrane is one or more of a CHA molecular sieve membrane, an AEI molecular sieve membrane, and an Sr-LTA molecular sieve membrane, the molecular sieve in the molecular sieve / polymer mixed matrix membrane is selected from one or more of a CHA type, an AEI type or an A type zeolite molecular sieve, and the polymer is one or more of a polyimide membrane, a polyamide membrane, a polyurethane membrane, a polyethylene membrane, a polytetrafluoroethylene membrane, a polymethacrylic acid membrane, a polybenzodioxane membrane, a polybenzoxazole membrane, a polysulfone membrane, a polyethylene terephthalate membrane, a polyetherimide membrane or a polyethersulfone membrane.

[0008] Preferably, the catalyst in the catalyst layer is an iron-based catalyst, a ruthenium-based catalyst, a molybdenum-based catalyst, a nickel-based catalyst, a cobalt-based catalyst, a platinum-based catalyst or a palladium-based catalyst; and the loading amount of the catalyst on the surface of the ammonia permeable membrane is 0.02-0.1 g / cm 2 .

[0009] Preferably, the porous tubular carrier is selected from alumina, mullite, silicon carbide or silicon oxide, the average pore size of the porous tubular carrier is 50~2000 nm, the porosity is 30%~60%, the inner diameter of each channel of the porous tubular carrier is 1~20 mm, and the tube length is 50~1000 mm.

[0010] Secondly, the present invention also provides a method for preparing a catalytic ammonia permeable membrane coupled with electrocatalysis, wherein the ammonia permeable layer of the catalytic ammonia permeable membrane is a molecular sieve membrane, and the preparation method comprises the following steps: (1) Preparation of ammonia permeable molecular sieve membrane: a template agent, sodium hydroxide, silicon source, and aluminum source water are mixed in a certain proportion, stirred, and aged to prepare a membrane-forming sol; a porous tubular carrier is loaded with molecular sieve seeds to form a seeded carrier, which is placed in the membrane-forming sol and hydrothermally synthesized at 100-220 °C for 1-72 h. After the reaction is completed, the ammonia permeable molecular sieve membrane is obtained by washing, drying, and calcining; (2) An ammonia synthesis catalyst is loaded on the surface of the ammonia permeable molecular sieve membrane to form a catalyst layer, thereby obtaining the catalytic ammonia permeable membrane.

[0011] Preferably, when the ammonia permeable layer is a CHA molecular sieve membrane, the film-forming sol further contains a crystallization promoter, wherein the aluminum source is one of aluminum hydroxide, sodium metaaluminate, aluminum thin stone, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder or aluminum oxide, the silicon source is one of silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder, the alkali source is sodium hydroxide or potassium hydroxide, the template agent is N,N,N-trimethyl-1-adamantanammonium hydroxide, the crystallization promoter is polydiallyldimethylammonium salt, and the amount of crystallization promoter added is 0.01~6 wt% of the total mass of the sol.

[0012] When the ammonia permeable layer is an AEI molecular sieve membrane, the aluminum source is one or more of aluminum hydroxide, aluminum isopropoxide, metallic aluminum, sodium metaaluminate or aluminum sec-butoxide, the silicon source is one or more of silica sol, silicate, silicon powder or sodium silicate, and the template agent is one or more of N,N-diethyl-2,6-dimethylpiperidinium hydroxide, tetrabutylphosphine hydroxide, tetraethylphosphine hydroxide, tetrapropylphosphine hydroxide or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide.

[0013] When the ammonia permeable layer is an Sr-LTA molecular sieve membrane, the film-forming sol further contains a crystallization promoter and a modifier. The film-forming sol further contains a modifier, wherein the aluminum source is one of aluminum hydroxide, sodium aluminate, aluminum thin stone, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder or aluminum oxide, the silicon source is one of silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder, the modifier is strontium hydroxide, the crystallization promoter is a polycationic salt selected from polydiallylethylbenzyl ammonium chloride, polydiallyldimethylammonium chloride, polydimethyldiallyl ammonium chloride, polydiallylmethylbenzyl ammonium chloride or a mixture of several thereof, and the amount of crystallization promoter added is 0.05~5 wt% of the total mass of the sol.

[0014] In addition, the present invention also provides a method for preparing a catalytic ammonia permeable membrane, wherein the ammonia permeable layer of the catalytic ammonia permeable membrane is a molecular sieve membrane or a molecular sieve / polymer mixed matrix membrane, and the preparation method comprises the following steps: (1) Preparation of molecular sieves: The raw materials for synthesizing molecular sieves are mixed in a certain proportion, stirred, and aged to prepare a sol; the aged sol is hydrothermally synthesized at 100-200 °C for 4-60 h; after the reaction, the product is centrifuged, washed with water to neutrality, dried, calcined, and ball-milled to obtain a nano-sized molecular sieve; (2) Preparation of an ammonia permeable membrane: adding the nano-sized molecular sieve to an organic solvent containing an organic polymer, stirring uniformly to form a polymer solution, and uniformly loading the polymer solution on a porous tubular support, and drying at 25 to 200 °C for 1 to 48 h to obtain an ammonia permeable molecular sieve / polymer mixed matrix membrane; (3) An ammonia synthesis catalyst is loaded on the surface of a molecular sieve / polymer mixed matrix membrane to obtain a catalytic ammonia permeable membrane.

[0015] Preferably, the organic polymer is one or more of polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), polyester (PE), polyesteramide (PEA), polytetrafluoroethylene (PTFE) or polyamidoamine (PAMAM); and the molar ratio of molecular sieve / organic polymer in the polymerization solution is 0.1 to 0.6.

[0016] Furthermore, the present invention also provides an integrated membrane electrode based on a catalytic ammonia permeable membrane, wherein the integrated membrane electrode comprises the catalytic ammonia permeable membrane and a metal wire serving as a cathode electrode, wherein the metal wire is supported on the outside of the catalyst layer of the catalytic ammonia permeable membrane, and a negative pressure or vacuum state is formed in the inner cavity of the porous tubular carrier of the catalytic ammonia permeable membrane so that ammonia generated by catalysis on the outside of the catalytic ammonia permeable membrane passes through the ammonia permeable layer for enrichment and removal.

[0017] Finally, the present invention also provides a method for producing ammonia based on the electrocatalytic coupling of the above-mentioned integrated membrane electrode, wherein the integrated membrane electrode is immersed in an electrolyte, and the porous tubular carrier of the integrated membrane electrode is connected to a vacuum. Under the drive of negative pressure, ammonia formed by the catalyst layer selectively passes through the ammonia permeable membrane and enters the interior of the porous tubular carrier and is removed.

[0018] Compared with the prior art, the present invention has the following beneficial effects: First, in terms of membrane materials, the ammonia permeable membrane provided by the present invention exhibits significant advantages. Its unique sub-angstrom pore structure, high selectivity, and high stability enable efficient separation of ammonia in complex mixed gas environments. The selectivity of ammonia / hydrogen and ammonia / nitrogen far exceeds that of membrane materials in the prior art. The molecular sieve membrane or molecular sieve / polymer mixed matrix membrane provided by the present invention separates small molecule inorganic gases such as ammonia, hydrogen, or nitrogen from ammonia / hydrogen / nitrogen mixed gases and is suitable for industrial processes of ammonia separation and purification. Among them, the ammonia permeation rate is greater than 1×10 -7 mol / (m 2 s Pa), ammonia / hydrogen selectivity greater than 100, and ammonia / nitrogen selectivity greater than 200. This precise pore size control and material diversity not only provide a highly efficient solution for ammonia separation and purification, but also broaden the possibilities of membrane materials in industrial applications, meet the needs of different scenarios, and promote the further development of membrane separation technology.

[0019] At the process level, this invention achieves an integrated reaction-separation system, tightly integrating an ammonia-permeable membrane with the electrocatalytic ammonia production process. This innovative process, which can be performed at room temperature and isothermal conditions, not only improves ammonia synthesis efficiency but also significantly reduces energy consumption and environmental pollution. Compared to traditional ammonia synthesis and separation processes, this method does not require high temperature and high pressure, significantly reducing equipment investment and operating costs, while improving the economic and environmental performance of the entire process, bringing revolutionary changes to the synthetic ammonia industry.

[0020] Furthermore, this invention demonstrates exceptional process flexibility and scalability. By adjusting the membrane material, catalyst loading, and optimizing process parameters, it can easily adapt to production needs of varying scales, demonstrating exceptional process adaptability. This flexibility not only enables the method to be widely applied in various ammonia synthesis scenarios but also enables its integration with other advanced technologies. This is expected to further improve and develop the ammonia synthesis process system, providing the future market with more efficient and environmentally friendly ammonia synthesis solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 SEM images of the ammonia-permeable Sr-LTA molecular sieve membrane synthesized in Example 1 of the present invention (a-surface, b-cross-section); Figure 2 This is the XRD pattern of the ammonia permeable Sr-LTA molecular sieve membrane synthesized in Example 1 of the present invention; Figure 3 SEM images of the ammonia-permeable CHA molecular sieve membrane synthesized in Example 2 of the present invention (a-surface, b-cross-section); Figure 4 This is the XRD pattern of the ammonia permeable CHA molecular sieve membrane synthesized in Example 2 of the present invention; Figure 5 SEM images of the ammonia-permeable AEI molecular sieve membrane synthesized in Example 3 of the present invention (a-surface, b-cross-section); Figure 6 This is the XRD pattern of the ammonia permeable AEI molecular sieve membrane synthesized in Example 3 of the present invention; Figure 7 This is a SEM image of the AEI molecular sieve synthesized in Example 4 of the present invention; Figure 8 This is the XRD pattern of the AEI molecular sieve synthesized in Example 4 of the present invention; Figure 9 This is a flow chart of the ammonia production test of the ammonia permeable membrane and electrocatalytic external coupling in the present invention; wherein, 1, anode electrode; 2, catalyst support layer; 3, cathode electrode; 4, ammonia permeable separation membrane assembly; 5, vacuum pump; Figure 10 A flow chart of ammonia production by coupling catalytic ammonia permeable membrane and electrocatalysis in the present invention; wherein: 1, anode electrode; 5, vacuum pump; a, catalyst layer; b, ammonia permeable layer; c, metal wire; d, integrated membrane electrode; e, vacuum chamber. DETAILED DESCRIPTION

[0022] In order to further describe the present invention, specific examples of implementing the present invention are given below, but the scope of protection requested by the present invention is not limited to the examples.

[0023] Example 1 Preparation of Sr-LTA Molecular Sieve Membrane with Catalytic Ammonia Permeability and Performance Testing (1) Preparation of ammonia-permeable Sr-LTA molecular sieve membrane Sodium hydroxide, strontium hydroxide solution, poly(diallyldimethylammonium chloride), and deionized water were mixed in a specific ratio and stirred at room temperature for 15 minutes to form a homogeneous solution. Sodium metaaluminate and silica sol were then added to the solution, heated and stirred until clear, cooled to room temperature, and aged for 6 hours to obtain a synthetic solution with the following molar ratios: SiO₂ / Al₂O₃=3, Na₂O / SiO₂=10, H₂O / SiO₂=200, Sr / SiO₂=0.15. The amount of poly(diallyldimethylammonium chloride) added was 0.1 wt% of the total mass of the sol. A seeded single-channel tubular support (asymmetric alumina single-channel support with an outer diameter of 10 mm, an inner diameter of 7 mm, a length of 6 mm, and an average pore size of 200 nm) was placed in a stainless steel reactor containing the sol and reacted at 90°C for 6 hours. After the reaction, the membrane was washed and dried, and then calcined at 480 °C for 6 h in air to remove the template, with the heating and cooling rates both being 1 °C / min, to obtain an activated ammonia-permeable Sr-LTA molecular sieve membrane.

[0024] The SEM image of the synthesized Sr-LTA molecular sieve membrane is shown in Figure 1 As shown in Figure 2, the film layer is continuous and dense with a thickness of 1 μm. The XRD pattern of the Sr-LTA molecular sieve membrane is shown in Figure 2. Figure 2 As shown, the molecular sieve membrane crystal layer is pure LTA molecular sieve crystals.

[0025] like Figure 9 As shown, the non-catalytic ammonia permeable membrane described above was tested using an external coupling device. The external coupling device is an electrolytic cell, comprising an anode chamber and a cathode chamber. The anode chamber is equipped with an anode electrode 1, and the cathode chamber is loaded with a cathode electrode 2 loaded with a catalyst-supported layer 2. 10 mL of a mixed electrolyte solution of 0.5 mol / L Na₂SO₄ and 0.05 mmol / L NaNO₃ at a pH of 9 is placed on each side of the electrolytic cell, separated by a proton exchange membrane. Nitrogen gas is introduced into the cathode chamber, where it is catalyzed by the catalyst-supported layer 2 on the cathode electrode 3 to produce ammonia gas. The crude ammonia gas, containing unreacted nitrogen, enters an ammonia permeable membrane assembly 4 loaded with a non-catalytic ammonia permeable membrane. A vacuum pump 5 is connected to the permeate side of the ammonia permeable membrane assembly 4, and the retentate side of the ammonia permeable membrane assembly 4 is connected to the nitrogen feed side.

[0026] In this step, the ammonia permeable Sr-LTA molecular sieve membrane is placed in the ammonia permeable separation membrane assembly 4, and hydrogen, nitrogen and ammonia are fed in a molar ratio of 14:5:1. The test temperature is 25-200°C, the test pressure is 0.1-2 MPa, and the space velocity in the ammonia permeable Sr-LTA molecular sieve membrane channel is 8000 ml·g -1 •h -1Ammonia molecules were selectively separated from the membrane assembly, with ammonia / hydrogen selectivity ranging from 200 to 10,000 and ammonia / nitrogen selectivity ranging from 100 to 10,000. Separation performance is shown in Table 1. As shown in Table 1, the NH3 / H2 separation selectivity reached a high of 350, indicating that the ammonia permeation rate was much higher than the hydrogen permeation rate (the hydrogen permeation rate was almost the test limit). This indicates that the pore size of the Sr-LTA molecular sieve membrane lies between the kinetic diameters of ammonia (0.26 nm) and hydrogen (0.28 nm), with a pore size range of 0.26 to 0.28 nm.

[0027] (2) Preparation of Sr-LTA molecular sieve membrane for catalytic ammonia permeation Preparation of catalyst coating: 80 g of iron-based catalyst was crushed several times, and 200 g of deionized water was added to prepare the coating. The coating was stirred at room temperature to prevent sedimentation at a stirring rate of 800 r / min.

[0028] Preparation process of aluminum sol: Take 6 g of pseudo-boehmite, slowly add 1 mL of concentrated nitric acid until it is completely dissolved, then add 30 g of deionized water, and stir at room temperature to prevent precipitation. The stirring rate is 800 r / min.

[0029] Preparation of coating raw material: slowly add aluminum sol to the prepared catalyst solution and stir at room temperature for 2 hours to ensure that the aluminum sol and the catalyst solution are fully mixed to obtain a uniform coating raw material.

[0030] Coating of molecular sieve membrane: Pass the ceramic tube through the inner side of the ammonia permeable membrane tube prepared above and seal the membrane tube on both sides with polytetrafluoroethylene tape. Place the sealed membrane tube into a stainless steel tray with coating material and perform dip coating for about 1 minute. After the dip coating is completed, remove the excess coating material and dry it in an 80℃ oven for 8 hours. The dried membrane tube is heated at 200℃ with a speed of 50 Nm 3 The catalytic ammonia permeable Sr-LTA molecular sieve membrane with a catalytic layer thickness of about 20-50 μm was obtained by calcining for 48 h at a nitrogen flow rate of 1 °C / min and a heating / cooling rate of 1 °C / min.

[0031] (3) Coupling of catalytic ammonia permeation Sr-LTA molecular sieve membrane with electrocatalytic ammonia production and its performance testing The above-mentioned catalytic ammonia permeation Sr-LTA molecular sieve membrane is used as an ammonia permeation membrane to prepare an integrated membrane electrode, such as Figure 10 As shown, the integrated membrane electrode d comprises an ammonia permeable layer b grown on a porous tubular support, a catalyst layer a supported on the outside of the ammonia permeable layer b, and a titanium wire c welded to the outside of the catalyst layer. The titanium wire is connected to the negative electrode of the power supply. The porous tubular support is connected to a vacuum chamber e, which is further connected to a vacuum pump 5. Polytetrafluoroethylene (PTFE) flanges are used to clamp the ends of the porous tubular support.O The ring prevents leakage.

[0032] like Figure 10 As shown, the electrolytic cell consists of a cathode chamber and an anode chamber. In the cathode chamber, an integrated membrane electrode serves as the working electrode, directly immersed in the electrolyte. In the anode chamber, a counter electrode serves as the anode. The working electrode is placed in an H-type three-electrode electrolytic cell. 10 mL of a mixed electrolyte solution of 0.5 mol / L Na₂SO₄ and 0.05 mmol / L NaNO₃ at pH 9 is placed on each side of the cell, separated by a proton exchange membrane. An Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet serve as the reference electrode and counter electrode (anode electrode 1), respectively. Under conditions of 30°C, atmospheric pressure, and a vacuum pressure of 100 Pa, a 20 mL / min argon flow was introduced for 10 minutes to remove some dissolved gases, such as O₂ and CO₂, from the solution. Cyclic voltammetry scans were then performed for 200 cycles to activate the catalyst and expel absorbed gases. Nitrogen was directly introduced into the cathode chamber of the reactor through a mass flow controller (MFC). The side with ammonia catalytic activity and ammonia selective permeability was in contact with the electrolyte. The sealing element prevented fluid short circuit. The porous tubular support of the ammonia permeable membrane was connected to the vacuum. The cathode potential (vs. RHE) was -0.4 V and the current density was 3.5 mA / cm 2 Ammonia is synthesized by electrolysis at room temperature and atmospheric pressure. Driven by a negative pressure of 200 Pa, the generated ammonia gas selectively permeates the ammonia permeable layer and is absorbed by vacuum pumping, shifting the reaction in the forward direction. This improves electrocatalytic efficiency and separates the ammonia product. Ammonia's solubility in water decreases with increasing temperature. By controlling the electrolyte temperature, the solubility of ammonia can be reduced, thereby promoting its release.

[0033] Comparative Example 1 Preparation and performance testing of Sr-free ammonia permeable membrane As a control, an ammonia permeable membrane without Sr addition was also prepared. The preparation process of the LTA molecular sieve membrane without Sr modification is as follows: Sol preparation: Sodium hydroxide (NaOH, 98 wt%), polydiallyldimethylammonium chloride (98 wt%), and deionized water were mixed in appropriate proportions and stirred at room temperature for 15 minutes to form a homogeneous solution. Sodium metaaluminate (NaAlO2, 99 wt%) and silica sol (40 wt% aqueous solution) were added, and the mixture was heated and stirred until clear. After cooling, the mixture was aged for 6 hours.

[0034] Sol molar ratio: SiO2 / Al2O3=3, Na2O / SiO2=10, H2O / SiO2=200, Sr / SiO2=0 (strontium hydroxide solution omitted), and the addition amount of polydiallyldimethylammonium chloride was 0.1 wt% of the total mass of the sol.

[0035] Hydrothermal synthesis: The seeded support was placed in a stainless steel reactor and reacted at 90°C for 6 h. After the reaction, it was cleaned and dried, and then calcined at 480°C in air for 6 h (heating / cooling rate of 1°C / min) to obtain an unmodified LTA molecular sieve membrane.

[0036] Gas permeation testing revealed that the pore size of the unmodified LTA membrane was approximately 0.4 nm, larger than the 0.26–0.28 nm of the Sr-LTA membrane. Hydrogen, nitrogen, and ammonia were fed in a 14:5:1 molar ratio at a temperature of 25–200°C, a pressure of 0.1–2 MPa, and a space velocity of 8000 ml·g⁻¹·h⁻¹. The NH₃ / H₂ selectivity ranged from 80–120, significantly lower than the 200–10,000 ratio of the Sr-LTA membrane. The NH₃ / N₂ selectivity ranged from 50–100, indicating that the unmodified membrane had poor ammonia screening capabilities. Example 2

[0037] Preparation and performance testing of CHA molecular sieve membrane for catalytic ammonia permeation (1) Preparation of ammonia permeable CHA molecular sieve membrane Sodium hydroxide, aluminum hydroxide, silica sol, crystallization promoter polydiallyldimethylammonium bromide and water were mixed and stirred for 12 hours to obtain a membrane synthesis solution with a molar ratio of SiO2 / Al2O3 = 20, NaOH / SiO2 = 0.5, crystallization promoter / SiO2 = 0.1, H2O / SiO2 = 40. The seeded carrier was placed in the sol and hydrothermally synthesized at 100-220 °C for 1-72 hours. After the reaction was completed, it was washed and dried and calcined at 100-300 °C in a low-temperature ozone atmosphere for 1-50 hours with a heating / cooling rate of 0.1-5 °C / min. After removing the template, the CHA molecular sieve membrane was obtained. The SEM and XRD patterns of the CHA molecular sieve membrane synthesized under these conditions are shown as follows. Figure 3 and Figure 4 As shown, the membrane layer is pure CHA molecular sieve crystals, with dense growth and a thickness of approximately 14 µm. The ammonia permeable CHA molecular sieve membrane was tested at 100°C and 1 MPa. The separation and reaction performance are shown in Table 1.

[0038] (2) A catalytic ammonia permeable CHA molecular sieve membrane was prepared as in step (2) of Example 1, except that the molecular sieve membrane was the above-mentioned ammonia permeable CHA molecular sieve membrane.

[0039] (3) The catalytic ammonia permeation CHA molecular sieve membrane was tested as in step (3) of Example 1. The separation and reaction performances are shown in Table 2. Example 3

[0040] Preparation and performance testing of AEI molecular sieve membrane for catalytic ammonia permeation (1) Preparation of ammonia permeable AEI molecular sieve membrane Sodium hydroxide, deionized water, aluminum hydroxide, N,N-dimethyl-3,5-dimethylpiperidine, and silica sol (AS-40) were mixed in a specific ratio and stirred for 5 hours before aging to obtain a membrane synthesis solution with a molar ratio of SiO₂ / Al₂O₃=20, TMPOH / SiO₂=0.3, NaOH / SiO₂=0.25, and H₂O / SiO₂=35. The seeded support was placed in the membrane synthesis solution and hydrothermally reacted at 170°C for 36 hours. After the reaction was complete, the solution was washed and dried, and then calcined at 480°C in air for 6 hours to remove the template. The heating and cooling rates were both 1°C / min, resulting in an activated AEI silica-alumina molecular sieve membrane. Figure 5 This is the SEM image of the synthesized AEI molecular sieve membrane. The membrane layer is continuous and dense, with a thickness of about 2.9 µm. Figure 6 This is the XRD pattern of the synthesized AEI molecular sieve membrane, which is a pure AEI molecular sieve crystal layer. The ammonia permeable AEI molecular sieve membrane was tested at 100°C and 1 MPa. The separation and reaction performance are shown in Table 1.

[0041] (2) A catalytic ammonia permeable AEI molecular sieve membrane was prepared as in step (2) of Example 1, except that the molecular sieve membrane was the above-mentioned ammonia permeable AEI molecular sieve membrane.

[0042] (3) The catalytic ammonia permeation AEI molecular sieve membrane was tested as in step (3) of Example 1. The separation and reaction performances are shown in Table 2. Example 4

[0043] Preparation and performance testing of AEI molecular sieve / polymer mixed matrix membranes for catalytic ammonia permeation (1) Preparation of AEI molecular sieve Mix 1,1,3,5-tetramethylpiperidinium hydroxide (TMPOH), NaOH, silicon source and deionized water in a certain proportion, heat and stir at 150 ℃ for 5 h; then add USY molecular sieve, stir and mix evenly to obtain a synthetic liquid with a molar ratio of: Al2O3 / SiO2=0.017, TMPOH / SiO2=0.17, NaOH / SiO2=0.4, H2O / SiO2=12; finally, pour the synthetic liquid into a Teflon high-pressure reactor and react at 180 ℃ for 72 h. After the reaction is complete, take out, clean and dry. Calcinate at 480 ℃ in an air atmosphere for 48 h to remove the template, with a heating / cooling rate of 0.5 ℃ / min. Take out after cooling to obtain AEI molecular sieve. Figure 7 As shown in Figure 2, the size of the synthesized AEI molecular sieve is approximately 1.5 µm. Figure 8 As shown, the synthesized molecular sieve is a pure phase AEI molecular sieve crystal.

[0044] (2) Preparation and performance testing of ammonia permeable AEI molecular sieve / polymer mixed matrix membranes The prepared AEI molecular sieve was ball-milled at 450 r / min for 24 hours. The milled zeolite was then added to a polyvinylidene fluoride-N-methylpyrrolidone solution (4 wt% methylpyrrolidone) at a zeolite concentration of 16 wt%. The mixture was stirred at room temperature for 36 hours to ensure uniform mixing. The mixture was then coated onto a porous tubular support using a spatula at a speed of 4 cm / s and dried at 60°C for 6 hours to produce an ammonia-permeable AEI molecular sieve / polymer mixed matrix membrane. The ammonia-permeable AEI molecular sieve membrane was tested at 100°C and 1 MPa. The separation and reaction performance are shown in Table 1.

[0045] (3) A catalytic ammonia permeable AEI molecular sieve / polymer mixed matrix membrane was prepared as in step (2) of Example 1, except that the molecular sieve membrane was the above-mentioned ammonia permeable AEI molecular sieve / polymer mixed matrix membrane.

[0046] (3) The catalytic ammonia permeation AEI molecular sieve / polymer mixed matrix membrane was tested as in step (3) of Example 1. The separation and reaction performances are shown in Table 2. Example 5

[0047] (1) The operation steps are the same as step (1) of Example 1; (2) The operation steps are the same as step (2) in Example 1; (3) The operation steps are the same as step (3) of Example 1, except that the electrolysis reaction temperature is 50°C. The separation and reaction performance are shown in Table 2. Example 6

[0048] (1) The operation steps are the same as step (1) of Example 1, except that the reaction time is 12 h; (2) The operation steps are the same as step (2) in Example 1; (3) The operation steps are the same as step (3) of Example 1, except that the electrolysis reaction temperature is 50°C; the separation and reaction performance are shown in Table 2. Example 7

[0049] (1) The operation steps are the same as step (1) of Example 1; (2) The operation steps are the same as step (2) of Example 1, except that the ruthenium-based catalyst is granulated; (3) The operation steps are the same as step (3) of Example 1, and the electrolysis reaction temperature is 50°C; the separation and reaction performance are shown in Table 2.

[0050] Comparative Example 2 Traditional electrocatalytic method: The working electrode containing the iron-based catalyst was placed in an H-type three-electrode electrolytic cell. A mixed electrolyte solution of 0.5 mol / L Na₂SO₄ and 0.05 mmol / L NaNO₃ at pH 9 was placed on each side of the cell, separated by a proton exchange membrane. An Ag / AgCl electrode (3 mol / L KCl) and a platinum sheet served as the reference and counter electrodes, respectively. Under conditions of 30°C and atmospheric pressure, a 20 mL / min argon flow was introduced for 10 minutes to remove dissolved O₂ and CO₂ from the solution. Cyclic voltammetry was then performed for 200 cycles to activate the catalyst and expel absorbed gases. Catalysis was then carried out at various potentials for 30 minutes, and the electrolyte was collected for ammonia detection. The reaction performance is shown in Table 2.

[0051] Table 1 Ammonia permeability membrane separation performance of the embodiment

[0052] As can be seen from the data in Table 1, under a test pressure of 1 MPa, the ammonia-permeable membranes of all Examples exhibited high ammonia selectivity, with Example 1 achieving an ammonia / nitrogen selectivity of 876 and an ammonia / hydrogen selectivity of 350, demonstrating particularly outstanding performance. While the ammonia selectivity of Examples 5-7 fluctuated slightly with increasing test temperature, it remained at a high level, demonstrating the stability of the ammonia-permeable membranes under high-temperature conditions. Overall, the ammonia-permeable membranes of the present invention possess significant advantages in ammonia separation, effectively improving ammonia purity and providing high-quality feed gas for the subsequent ammonia synthesis process.

[0053] Table 2 Electrolyte ammonia production efficiency of the examples and comparative examples

[0054] The data in Table 2 shows the ammonia synthesis rates of different examples and comparative examples during the electrocatalytic ammonia production process. As can be seen from the data, the ammonia synthesis rates of Examples 1-7 are all higher than those of the conventional electrocatalytic method of Comparative Example 2. Furthermore, as the test temperature increases, the ammonia synthesis rates of Examples 5-7 also increase, indicating that the catalytic ammonia permeable membrane and electrocatalytic coupled ammonia production method provided by the present invention can still maintain a high ammonia production efficiency at higher temperatures. Overall, the catalytic ammonia permeable membrane and ammonia production method of the present invention have significant advantages in increasing the ammonia synthesis rate and are expected to promote the further development of low-temperature, low-pressure ammonia synthesis technology.

Claims

1. A catalytic ammonia permeable membrane coupled with electrocatalysis, characterized in that: The catalytic ammonia permeable membrane comprises a porous tubular support, an ammonia permeable layer, and a catalyst layer that catalyzes ammonia. The ammonia permeable layer comprises a molecular sieve, and the catalyst layer is supported on the outer surface of the ammonia permeable layer. The catalytic ammonia permeable membrane has an ammonia / hydrogen selectivity of 100-1000, and the ammonia permeable layer has a pore size of 0.26-0.28 nm.

2. The catalytic ammonia permeable membrane according to claim 1, characterized in that: The ammonia permeable layer is a molecular sieve membrane or a molecular sieve / polymer mixed matrix membrane, the molecular sieve membrane is one or more of a CHA molecular sieve membrane, an AEI molecular sieve membrane, and an Sr-LTA molecular sieve membrane, the molecular sieve in the molecular sieve / polymer mixed matrix membrane is selected from one or more of a CHA type, an AEI type or an A type zeolite molecular sieve, and the polymer is one or more of a polyimide membrane, a polyamide membrane, a polyurethane membrane, a polyethylene membrane, a polytetrafluoroethylene membrane, a polymethacrylic acid membrane, a polybenzodioxane membrane, a polybenzoxazole membrane, a polysulfone membrane, a polyethylene terephthalate membrane, a polyetherimide membrane or a polyethersulfone membrane.

3. The catalytic ammonia permeable membrane according to claim 1, characterized in that: The catalyst in the catalyst layer is an iron-based catalyst, a ruthenium-based catalyst, a molybdenum-based catalyst, a nickel-based catalyst, a cobalt-based catalyst, a platinum-based catalyst or a palladium-based catalyst; the loading amount of the catalyst on the surface of the ammonia permeable membrane is 0.02-0.1 g / cm 2 .

4. The catalytic ammonia permeable membrane according to claim 1, characterized in that The porous tubular carrier is made of alumina, mullite, silicon carbide or silicon oxide. The average pore size of the porous tubular carrier is 50-2000 nm, the porosity is 30%-60%, the inner diameter of each channel of the porous tubular carrier is 1-20 mm, and the tube length is 50-1000 mm.

5. A method for preparing a catalytic ammonia permeable membrane coupled with electrocatalysis according to claim 1, wherein the ammonia permeable layer of the catalytic ammonia permeable membrane is a molecular sieve membrane, the preparation method comprising the following steps: (1) Preparation of ammonia permeable molecular sieve membrane: a template agent, sodium hydroxide, silicon source, and aluminum source water are mixed in a certain proportion, stirred, and aged to prepare a membrane-forming sol; a porous tubular carrier is loaded with molecular sieve seeds to form a seeded carrier, which is placed in the membrane-forming sol and hydrothermally synthesized at 100-220 °C for 1-72 h. After the reaction is completed, the ammonia permeable molecular sieve membrane is obtained by washing, drying, and calcining; (2) An ammonia synthesis catalyst is loaded on the surface of the ammonia permeable molecular sieve membrane to form a catalyst layer, thereby obtaining the catalytic ammonia permeable membrane.

6. The preparation method according to claim 5, wherein When the ammonia permeable layer is a CHA molecular sieve membrane, the film-forming sol further contains a crystallization accelerator, wherein the aluminum source is one of aluminum hydroxide, sodium metaaluminate, aluminum thin stone, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder or aluminum oxide; the silicon source is one of silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder; the alkali source is sodium hydroxide or potassium hydroxide; the template agent is N,N,N-trimethyl-1-adamantanammonium hydroxide; the crystallization accelerator is polydiallyldimethylammonium salt, and the amount of the crystallization accelerator added is 0.01-6 wt% of the total mass of the sol; When the ammonia permeable layer is an AEI molecular sieve membrane, the aluminum source is one or more of aluminum hydroxide, aluminum isopropoxide, metallic aluminum, sodium metaaluminate or aluminum sec-butoxide, the silicon source is one or more of silica sol, silicate, silicon powder or sodium silicate, and the template is one or more of N,N-diethyl-2,6-dimethylpiperidinium hydroxide, tetrabutylphosphine hydroxide, tetraethylphosphine hydroxide, tetrapropylphosphine hydroxide or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide; When the ammonia permeable layer is an Sr-LTA molecular sieve membrane, the film-forming sol further contains a crystallization promoter and a modifier. The film-forming sol further contains a modifier, wherein the aluminum source is one of aluminum hydroxide, sodium aluminate, aluminum thin stone, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder or aluminum oxide, the silicon source is one of silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder, the modifier is strontium hydroxide, the crystallization promoter is a polycationic salt selected from polydiallylethylbenzyl ammonium chloride, polydiallyldimethylammonium chloride, polydimethyldiallyl ammonium chloride, polydiallylmethylbenzyl ammonium chloride or a mixture of several thereof, and the amount of crystallization promoter added is 0.05~5 wt% of the total mass of the sol.

7. A method for preparing a catalytic ammonia permeable membrane according to claim 1, wherein the ammonia permeable layer of the catalytic ammonia permeable membrane is a molecular sieve membrane or a molecular sieve / polymer mixed matrix membrane, and the preparation method comprises the following steps: (1) Preparation of molecular sieves: The raw materials for synthesizing molecular sieves are mixed in a certain proportion, stirred, and aged to prepare a sol; the aged sol is hydrothermally synthesized at 100-200 °C for 4-60 h; after the reaction, the product is centrifuged, washed with water to neutrality, dried, calcined, and ball-milled to obtain a nano-sized molecular sieve; (2) Preparation of an ammonia permeable membrane: adding the nano-molecular sieve to an organic solvent containing an organic polymer, stirring uniformly to form a polymer solution, and uniformly loading the polymer solution on a porous tubular support, and drying at 25 to 200 ° C for 1 to 48 hours to obtain an ammonia permeable molecular sieve / polymer mixed matrix membrane; (3) An ammonia synthesis catalyst is loaded on the surface of a molecular sieve / polymer mixed matrix membrane to obtain a catalytic ammonia permeable membrane.

8. The preparation method according to claim 7, characterized in that The organic polymer is one or more of polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), polyester (PE), polyesteramide (PEA), polytetrafluoroethylene (PTFE) or polyamidoamine (PAMAM); the molar ratio of molecular sieve / organic polymer in the polymerization solution is 0.1 to 0.

6.

9. An integrated membrane electrode based on the catalytic ammonia permeable membrane according to claim 1, characterized in that: The integrated membrane electrode comprises the catalytic ammonia permeable membrane and a metal wire serving as a cathode electrode. The metal wire is supported on the outside of the catalyst layer of the catalytic ammonia permeable membrane, and a negative pressure or vacuum state is formed in the inner cavity of the porous tubular carrier of the catalytic ammonia permeable membrane to allow ammonia generated by catalysis on the outside of the catalytic ammonia permeable membrane to pass through the ammonia permeable layer for enrichment and removal.

10. A method for producing ammonia based on the electrocatalytic coupling of the integrated membrane electrode according to claim 9, characterized in that: The integrated membrane electrode is immersed in an electrolyte, and the porous tubular carrier of the integrated membrane electrode is connected to a vacuum. Under negative pressure driving, ammonia formed by the catalyst layer selectively passes through the ammonia permeable membrane and enters the porous tubular carrier and is removed.

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