A dual-site pore filling ammonia separation membrane and method of making same

Abstract

The application discloses a kind of dual-function site pore filling ammonia separation membrane and preparation method thereof, carry out quaternary ammonium reaction to N-heterocyclic small molecule containing vinyl and functionalized alkane containing Lewis acid group, PTFE or PVDF porous base membrane is soaked in the mixed solution of quaternary ammonium product, crosslinking agent and initiator, then heat polymerization is carried out, after the membrane obtained is soaked in metal chloride solution and is carried out chelation reaction, obtain the final pore filling ammonia separation membrane with dual-function site.The pore filling ammonia separation membrane prepared in the application has Lewis acid group and transition metal ion, and can promote the preferential and rapid transport of ammonia by their high affinity for ammonia, thereby imparting the prepared pore filling membrane with high ammonia selective permeation separation performance, at the same time, PTFE and PVDF porous membrane can impart the membrane with excellent mechanical properties, thereby meeting the actual application requirements.

Description

Technical Field

[0001] This invention relates to the field of new chemical materials technology, specifically to an ammonia separation membrane with dual-functional site pore filling and its preparation method. Background Technology

[0002] Ammonia plays a vital role in industry. It is not only a key raw material for agricultural fertilizer production but also widely used in pharmaceuticals, the synthesis of organic compounds, and polymer materials. As a hydrogen source, ammonia also has important applications in the hydrogen energy sector. Furthermore, ammonia is one of the most produced and widely used chemicals in the global chemical industry. Its core role in agriculture, energy, and chemical industries has established its irreplaceable position in global economic and technological development. The Haber-Bosch process is currently the most mature and widely used method for ammonia production. Its basic principle is the chemical reaction of nitrogen (N2) and hydrogen (H2) under high temperature and high pressure conditions to produce ammonia (NH3). However, it also has some significant drawbacks. In particular, because ammonia synthesis is an exothermic reaction, the equilibrium constant is low at high temperatures, which limits the conversion rate of ammonia. Typically, the ammonia conversion rate of the Haber-Bosch process is only 10-20%, and about 3% of the ammonia remains in the recycle gas, greatly increasing the energy consumption of ammonia synthesis. Therefore, developing efficient technologies to recover residual ammonia is extremely important.

[0003] Ammonia separation technology is crucial in industrial production, with common methods including liquid absorption and solid adsorption. Liquid absorption separates ammonia by utilizing the difference in solubility of ammonia in liquid solvents. This method typically leverages the high solubility of ammonia in water, acidic solutions, or other specific solvents to separate ammonia from a gas mixture. Solid adsorption separates ammonia from a gas mixture by physically or chemically adsorbing it using porous solid materials (such as activated carbon, zeolites, or metal-organic frameworks). It is worth noting that both liquid absorption and solid adsorption require adsorbent regeneration, a process involving ammonia phase change, resulting in high energy consumption and difficulty in achieving continuous operation. Membrane separation technology is gaining increasing attention in ammonia separation. Compared to traditional liquid absorption and solid adsorption methods, membrane separation relies on the difference in transport rates between ammonia and other gaseous components within the membrane material, avoiding gas-liquid or gas-solid phase change processes. Therefore, it consumes less energy. Furthermore, membrane separation does not require chemical solvents, eliminating the problems of solvent regeneration, treatment, and emissions. More importantly, membrane separation is suitable for continuous production, enabling uninterrupted ammonia separation operations and significantly improving production efficiency. Compared to adsorption separation, which requires periodic regeneration, the continuity of membrane separation significantly reduces operational complexity and downtime. However, existing ammonia separation membranes suffer from poor separation performance and inadequate mechanical strength, severely hindering industrial applications. Summary of the Invention

[0004] To address the problems of poor ammonia selective separation performance and inadequate mechanical strength in existing ammonia separation membranes, this invention provides an ammonia separation membrane with dual functional sites and its preparation method. The prepared ammonia separation membrane has Lewis acid groups and transition metal ions, which can promote the preferential and rapid transport of ammonia through their high affinity for ammonia, thereby endowing the prepared pore-filled membrane with high ammonia selective permeation separation performance, achieving high selectivity and high throughput separation of ammonia.

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

[0006] A method for preparing an ammonia separation membrane with dual-functional site-filled pores includes the following steps:

[0007] S1. A small N-heterocyclic molecule with a vinyl group is subjected to a quaternization reaction with a functionalized alkane to obtain a quaternized product;

[0008] S2. Dissolve the quaternization product, crosslinking agent, and initiator together in a polar solvent to form functional solution A;

[0009] S3. Immerse the PTFE or PVDF porous base membrane in functional solution A. After the membrane pores of the porous base membrane are fully wetted by functional solution A, take it out, remove the residual liquid on the surface, and then thermally polymerize it at 80-120℃ for 1-12 hours to obtain a thermally polymerized membrane.

[0010] S4. The polymer membrane is immersed in a functional solution B containing metal chloride for chelation reaction, then removed, washed, and dried to obtain the final pore-filled ammonia separation membrane with dual functional sites.

[0011] In step S1, the N-heterocyclic small molecule containing vinyl groups is one of vinylimidazole, 4-methyl-5-vinylthiazole, 4-vinylpyridine, and N-vinylcarbazole.

[0012] The functionalized alkane in step S1 has the general chemical formula X(CH2). n R, where X represents Cl or Br, and R represents a Lewis acid group, which is -OH or -NH3. + Cl - One of -COOH, n = 3-6.

[0013] In step S2, the mass ratio of the quaternization product, crosslinking agent, and initiator is 1:(0.04-0.2):(0.01-0.08).

[0014] In step S2, the crosslinking agent is a small molecule containing at least two double bonds, and can be selected from one of divinylbenzene, butadiene, N,N′-methylenebisacrylamide, and tripropylene glycol diacrylate.

[0015] In step S2, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, potassium persulfate, and ammonium persulfate.

[0016] In step S2, the polar solvent is one of ethanol, diethyl ether, chloroform, benzene, and acetone.

[0017] In step S2, the mass concentration of functional solution A is 20%-60%.

[0018] In step S4, the mass concentration of functional solution B is 1%-20%, wherein the solute is one of CoCl2, NiCl2, SnCl2, CuCl2, MnCl2 and FeCl2, and the solvent is one of ethanol, acetone and diethyl ether.

[0019] The chelation reaction in step S4 is carried out at a temperature of 30-80℃ for 4-48 hours.

[0020] A dual-functional site-filled ammonia separation membrane prepared according to the above preparation method.

[0021] The technical solution of this invention has the following advantages:

[0022] A. The pore-filled ammonia separation membrane with dual functional sites prepared in this invention has two types of active sites, one of which is -OH and -NH3. + Cl - The active sites are Lewis acid sites such as -COOH, and chelating transition metal ion sites. Both of these active sites have good ammonia affinity and can synergistically promote the high selectivity and high throughput separation of ammonia.

[0023] B. The pore-filled ammonia separation membrane with dual functional sites obtained in this invention uses membranes with excellent mechanical properties such as PVDF or PTFE as substrates, which effectively improves the film strength and meets the needs of practical applications.

[0024] C. The pore-filled ammonia separation membrane with dual functional sites obtained by the present invention has a high efficiency in ammonia separation. When separating residual gas from synthetic ammonia, its ammonia permeability is as high as 2401.5 Barrer, and its ammonia / nitrogen and ammonia / hydrogen selectivity are as high as 515.2 and 138.7, respectively. Its tensile strength is >60MPa, and it has good potential for industrial application. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1:

[0027] Vinylimidazole (0.05 mol, 4.81 g) and 3-chloropropionic acid (0.075 mol, 8.22 g) were added to a flask, followed by 100 mL of acetonitrile. Under Ar atmosphere protection, the mixture was heated to 80 °C and stirred for 30 h. After the reaction was complete, the resulting mixture was washed five times with ethyl acetate to remove unreacted reactants. Finally, the washed product was dried in a vacuum oven at 40 °C for 24 h to obtain a quaternized product containing a -COOH group.

[0028] Quaternization products, divinylbenzene, and azobisisobutyronitrile were dissolved in ethanol at a mass ratio of 1:0.04:0.01 to form a 20% functional solution A. The PVDF porous membrane was immersed in functional solution A for 12 hours, then removed, and the surface solution was removed. The membrane was then subjected to a polymerization reaction at 80°C for 24 hours. Finally, the polymerized membrane was immersed in a 1% CoCl2 / ethanol solution for a chelation reaction at 80°C for 4 hours to obtain the final pore-filled ammonia separation membrane with dual functional sites.

[0029] The tensile strength of the membrane was measured to be 63 MPa. Further, a gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen, and the permeability of the three gases was tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the membrane was 2895.2 Barrer, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 138.4 and 48.9, respectively.

[0030] Example 2:

[0031] The film was prepared using a method similar to that in Example 1, except that the mass ratio of the quaternized product, divinylbenzene, and azobisisobutyronitrile was changed to 1:0.06:0.03.

[0032] The tensile strength of the membrane was measured to be 66 MPa. Furthermore, a gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen, and the permeability of the three gases was tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the membrane's pure ammonia permeability was as high as 2401.5 Barrer, and the ammonia / nitrogen and ammonia / hydrogen selectivities were as high as 515.2 and 138.7, respectively.

[0033] Example 3:

[0034] The film was prepared using a method similar to that in Example 1, except that the mass ratio of the quaternized product, divinylbenzene, and azobisisobutyronitrile was changed to 1:0.2:0.08.

[0035] The tensile strength of the membrane was measured to be 72 MPa. Further, a gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen, and the permeability of the three gases was tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the membrane's pure ammonia permeability was as high as 1407.4 Barrer, and the ammonia / nitrogen and ammonia / hydrogen selectivities were as high as 624.2 and 179.6, respectively.

[0036] As can be seen from Examples 1-3, increasing the crosslinking agent content leads to a decrease in the ammonia permeability of the membrane and an increase in selectivity, and vice versa. The experimental results show that the effect is best when the crosslinking agent mass is 6% of the quaternization product mass.

[0037] Example 4:

[0038] Vinylimidazole (0.05 mol, 4.81 g) and 3-chloropropylamine hydrochloride (0.06 mol, 7.96 g) were added to a flask, followed by 50 mL of N,N-dimethylformamide. Under Ar atmosphere, the mixture was heated to 70 °C and stirred for 48 h. After the reaction was complete, the resulting mixture was washed five times with ethyl acetate to remove unreacted reactants. Finally, the washed product was dried in a vacuum oven at 40 °C for 24 h to obtain a product containing -NH3. + Cl- Quaternized products of the group.

[0039] Quaternization products, butadiene, and azobisisobutyronitrile were dissolved in diethyl ether at a mass ratio of 1:0.06:0.03 to form a 40% functional solution A. The PTFE porous membrane was immersed in functional solution A for 12 hours, then removed and the surface solution was removed. The membrane was then subjected to a polymerization reaction at 120°C for 1 hour. Finally, the polymerized membrane was immersed in a 20% NiCl2 / acetone solution for a chelation reaction at 30°C for 48 hours to obtain the final pore-filled ammonia separation membrane with dual functional sites.

[0040] The tensile strength of the membrane was measured to be 63 MPa. Further, a gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen, and the permeability of the three gases was tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the membrane was 2048.3 Barrer, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 404.3 and 88.2, respectively.

[0041] Example 5:

[0042] Vinylimidazole (0.05 mol, 4.81 g) and 6-bromo-1-hexanol (0.06 mol, 10.86 g) were added to a flask, followed by 50 mL of N,N-dimethylformamide. Under Ar atmosphere, the mixture was heated to 70 °C and stirred for 48 h. After the reaction, the resulting mixture was washed five times with ethyl acetate to remove unreacted reactants. Finally, the washed product was dried in a vacuum oven at 40 °C for 24 h to obtain a product containing -NH3. + Cl - Quaternized products of the group.

[0043] The quaternized product, N,N′-methylenebisacrylamide, and benzoyl peroxide were dissolved in chloroform at a mass ratio of 1:0.06:0.03 to form a 60% functional solution A. The PTFE porous membrane was immersed in functional solution A for 12 hours, then removed, the surface solution was removed, and then a polymerization reaction was carried out at 120°C for 1 hour. Finally, the polymerized membrane was immersed in a 20% SnCl2 / ether solution for chelation reaction at 30°C for 48 hours to obtain the final pore-filled ammonia separation membrane with dual functional sites.

[0044] The tensile strength of the membrane was measured to be 63 MPa. Further, a gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen, and the permeability of the three gases was tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the membrane was 2002.5 Barrer, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 385.3 and 87.9, respectively.

[0045] Example 6:

[0046] The membrane was prepared using a method similar to that in Example 2, except that the N-heterocyclic molecule containing vinyl groups was replaced with 4-methyl-5-vinylthiazole, the crosslinking agent was replaced with tripropylene glycol diacrylate, the initiator was replaced with potassium persulfate, the solvent of functional solution A was replaced with benzene, and the solute of functional solution B was replaced with CuCl2. The resulting membrane had similar performance to that in Example 2.

[0047] Example 7:

[0048] A membrane was prepared using a method similar to that in Example 2, except that the solute in functional solution B was changed to FeCl2, resulting in a membrane with performance similar to that in Example 2.

[0049] In summary, the pore-filled ammonia separation membrane with dual functional sites prepared in this invention has two types of active sites, one of which is -OH and -NH3. + Cl - The active sites are Lewis acid sites such as -COOH, and chelating transition metal ion sites. Both of these active sites have good ammonia affinity and can synergistically promote the high selectivity and high throughput separation of ammonia.

[0050] The pore-filled ammonia separation membrane with dual functional sites obtained in this invention uses membranes with excellent mechanical properties such as PVDF or PTFE as substrates, which effectively improves the film strength and meets the needs of practical applications.

[0051] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing an ammonia separation membrane with dual-functional site-filled pores, characterized in that, Includes the following steps: S1. A small N-heterocyclic molecule with a vinyl group is subjected to a quaternization reaction with a functionalized alkane to obtain a quaternized product; S2. Dissolve the quaternization product, crosslinking agent, and initiator together in a solvent to form functional solution A; S3. Immerse the PTFE or PVDF porous base membrane in functional solution A. After the membrane pores of the porous base membrane are fully wetted by functional solution A, take it out, remove the residual liquid on the surface, and then thermally polymerize it at 80-120℃ for 1-12 hours to obtain a thermally polymerized membrane. S4. The thermally polymerized membrane is immersed in a functional solution B containing metal chloride for chelation reaction, then removed, washed, and dried to obtain the final pore-filled ammonia separation membrane with dual functional sites. In step S1, the N-heterocyclic small molecule containing vinyl groups is one of vinylimidazole, 4-methyl-5-vinylthiazole, 4-vinylpyridine, and N-vinylcarbazole. The functionalized alkane in step S1 has the general chemical formula X(CH2). n R, where X represents Cl or Br, and R represents -OH or -NH3. + Cl − One of -COOH, n=3-6; In step S2, the mass ratio of the quaternization product, crosslinking agent, and initiator is 1:(0.04~0.2):(0.01~0.08). In step S2, the crosslinking agent is a small molecule containing at least two double bonds, selected from one of divinylbenzene, butadiene, N,N′-methylenebisacrylamide and tripropylene glycol diacrylate. The metal chloride is one of CoCl2, NiCl2, SnCl2, CuCl2, MnCl2, and FeCl2.

2. The preparation method according to claim 1, characterized in that: In step S2, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, potassium persulfate, and ammonium persulfate.

3. The preparation method according to claim 1, characterized in that: The solvent in step S2 is one of ethanol, diethyl ether, chloroform, benzene, and acetone.

4. The preparation method according to claim 1, characterized in that: In step S2, the mass concentration of functional solution A is 20%-60%.

5. The preparation method according to claim 1, characterized in that: In step S4, the mass concentration of functional solution B is 1%-20%, and the solvent is one of ethanol, acetone, and diethyl ether.

6. The preparation method according to claim 1, characterized in that: The chelation reaction in step S4 is carried out at a temperature of 30-80℃ for 4-48 hours.

7. An ammonia separation membrane with dual-functional site pores, prepared by the method according to any one of claims 1 to 6.