A diaphragm for preparing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride, its preparation method and application

Abstract

The present invention provides a diaphragm for electrolyzing molten ammonium hydrogen fluoride to produce nitrogen trifluoride, which comprises a tetrafluoro orifice plate layer and an outer spray coating sprayed on the outer surface of the tetrafluoro orifice plate layer; the tetrafluoro orifice plate layer comprises carbon fiber and PFA resin, and the outer spray coating comprises Nafion resin. The present invention also provides a preparation method and application of the above diaphragm. Due to the characteristics of high strength, good ion permeability and difficult bubble penetration of the diaphragm of the present invention, after being applied to the electrolysis process of electrolyzing molten ammonium hydrogen fluoride to produce nitrogen trifluoride, the production capacity of electrolyzing molten ammonium hydrogen fluoride to produce nitrogen trifluoride can be greatly improved, the energy consumption can be reduced, and good economic and social benefits can be brought.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic preparation of nitrogen trifluoride gas, and specifically relates to a diaphragm for electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, a preparation method thereof, and an application thereof. Background Art

[0002] Industrially, it is often prepared by electrolyzing a molten salt of ammonium bifluoride and hydrogen fluoride. Electrolyzing the molten (NH4HF2 + xHF) mixed electrolyte can obtain crude NF3 gas. The anode of the electrolytic cell is made of nickel plate, and the cathode is made of carbon steel plate, nickel plate or Monel plate, and the inter-pole voltage is 7-9V. During the electrolysis process, NF3 gas is generated at the anode, and H2 gas is generated at the cathode. During the electrolysis process, the electrolyte is a molten system, and the electrolysis temperature is controlled at 90-135°C. Therefore, HF is inevitably carried out at the cathode and anode. The electrolysis reaction equation is as follows:

[0003] Electrolysis reaction: NH4HF2 + HF → NF3 (anode) + 3H2 (cathode).

[0004] Currently, the electrolytic cell for preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride salt used industrially includes a cell cover, an insulating gasket, a cell body and its accessory systems. The cathode assembly, anode assembly and isolation skirt for separating the cathode and anode gases are suspended on the cell cover. The cell body and the cell cover are connected by a flange structure, and the insulating gasket uses a polytetrafluoroethylene-based gasket. This type of electrolytic cell only sets an isolation skirt for separating the gases produced by the cathode and anode at the upper part of the cathode and anode assemblies, and there is no isolation between the cathode and anode in the area participating in the electrolysis. To prevent the nitrogen trifluoride produced by the anode from mixing and exploding with the hydrogen produced by the cathode, the distance between the cathode and anode is usually 50-80mm. To meet the industrial production capacity requirements, the electrolysis voltage is usually 7-9V, resulting in a great waste of electric energy. At the same time, in order to prevent explosion, nitrogen is swept in the upper part of the cathode and anode areas to ensure safety, resulting in a waste of nitrogen and the cost of subsequent purification and refining to remove nitrogen. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a diaphragm for electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, a preparation method thereof, and an application thereof. The diaphragm of the present invention has the characteristics of high strength, good ion permeability and difficult bubble penetration. After being applied to the electrolysis process of electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, it can greatly improve the production capacity of electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, reduce energy consumption, and bring good economic and social benefits.

[0006] The technical solution adopted by the present invention is:

[0007] The present invention provides a diaphragm for producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride, which comprises a tetrafluoro orifice plate layer and an outer spray coating sprayed on the outer surface of the tetrafluoro orifice plate layer; the tetrafluoro orifice plate layer comprises carbon fiber and PFA resin, the outer spray coating comprises Nafion resin, and the mass ratio of each component of the diaphragm is as follows:

[0008] Carbon fiber: 2-5%;

[0009] PFA resin: 85-90%;

[0010] Nafion resin: 8-13%.

[0011] Further, the pore density of the tetrafluoro orifice plate layer is 200-900 pores per square centimeter.

[0012] Further, the pore diameter range of the tetrafluoro orifice plate layer is 5-12 μm.

[0013] Further, the carbon fiber is a corrosion-resistant high-strength carbon fiber.

[0014] Further, the carbon fiber is a polyacrylonitrile carbon fiber.

[0015] Further, the airtightness of the diaphragm is 5-12 Kpa.

[0016] The present invention also provides a preparation method of the above-mentioned diaphragm, which comprises the following steps:

[0017] Step 1: Material mixing, mixing carbon fiber and PFA resin;

[0018] Step 2: Injection molding and pressing, molding the mixture obtained in Step 1 into a porous plate with a thickness of 1-3 mm;

[0019] Step 3: Surface spraying, spraying Nafion resin on the surface of the porous plate obtained in Step 2;

[0020] Step 4: Molding and sintering, performing molding and sintering on the product obtained in Step 3, and repeating Step 2 and Step 3 for 3-7 times until a diaphragm with a thickness of 1.5 mm is finally obtained.

[0021] The present invention also provides an application of the above-mentioned diaphragm in producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride.

[0022] Further, the diaphragm is used in an electrolytic cell for producing nitrogen trifluoride from molten ammonium hydrogen fluoride, and the diaphragm is arranged between the negative electrode plate and the positive electrode plate, and between the negative electrode plate and the positive electrode plate in the electrolytic cell.

[0023] The beneficial effects of the present invention are as follows:

[0024] The diaphragm for preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride of the present invention has the characteristics of corrosion resistance, high strength, high temperature resistance, and good wettability. It has high strength, good ion permeability, and is difficult for bubbles to pass through. It can be applied to the electrolysis process of preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride. It can greatly improve the production capacity of preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride, reduce energy consumption, and bring good economic and social benefits. Description of the Drawings

[0025] Figure 1 It is a front view structural schematic diagram of an electrolytic cell for preparing nitrogen trifluoride from molten ammonium bifluoride to which the diaphragm in the present invention is applied;

[0026] Figure 2 It is a structural schematic diagram of the diaphragm in the present invention arranged between the positive and negative plates of the electrolytic cell;

[0027] Figure 3 It is a left view structural schematic diagram of an electrolytic cell for preparing nitrogen trifluoride from molten ammonium bifluoride to which the diaphragm in the present invention is applied;

[0028] Figure 4 It is a right view structural schematic diagram of an electrolytic cell for preparing nitrogen trifluoride from molten ammonium bifluoride to which the diaphragm in the present invention is applied;

[0029] Figure 5 It is a process flow schematic diagram of the diaphragm prepared in the present invention.

[0030] In the figure, 1 is the negative terminal plate, 2 is the diaphragm, 3 is the positive plate, 4 is the negative plate, and 5 is the positive terminal plate. Detailed Embodiments

[0031] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. The described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0032] It should be noted that the terms used here are only for describing the specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used here, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Example 1

[0034] The present invention provides a diaphragm for electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, which comprises a tetrafluoro orifice plate layer and an outer spray coating sprayed on the outer surface of the tetrafluoro orifice plate layer; the tetrafluoro orifice plate layer comprises carbon fiber and PFA resin, the outer spray coating comprises Nafion resin, and the mass ratio of each component of the diaphragm is as follows:

[0035] Carbon fiber 3%;

[0036] PFA resin 89%;

[0037] And Nafion resin 8%.

[0038] In this embodiment, the carbon fiber is a corrosion-resistant and high-strength carbon fiber, specifically polyacrylonitrile carbon fiber. The polyacrylonitrile fiber is a synthetic fiber made of polyacrylonitrile or an acrylonitrile copolymer with an acrylonitrile content greater than 85% (mass percentage).

[0039] Perfluorosulfonic acid resin (Nafion-H) is the known strongest solid superacid, with characteristics such as good heat resistance, high chemical stability and mechanical strength. As a green solid acid catalyst, perfluorosulfonic acid resin has good catalytic activity and selectivity for many reactions.

[0040] Soluble polytetrafluoroethylene, English name: Polyfluoroalkoxy, Teflon PFA, generally abbreviated as: PFA. PFA plastic is a copolymer of a small amount of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. The melt adhesion is enhanced and the melt viscosity decreases, while the performance remains unchanged compared with polytetrafluoroethylene.

[0041] In this embodiment, the pore density of the tetrafluoro orifice plate layer is 500 pores per square centimeter, and the tetrafluoro orifice plate layer is a tetrafluoro orifice plate with a pore diameter of 9 μm and a thickness of 2 mm.

[0042] The pore diameter range of the tetrafluoro orifice plate layer is 9 μm.

[0043] The air tightness of the diaphragm is 10 Kpa.

[0044] The preparation method of the diaphragm of the present invention comprises the following steps:

[0045] Step 1: Material mixing, mechanically mixing carbon fiber and PFA resin in a horizontal spiral ribbon dry powder mixer to make the materials mix evenly;

[0046] Step 2: Injection molding and pressing, injection molding and pressing the mixture obtained in Step 1 into a tetrafluoro orifice plate with 500 pores per square centimeter, a pore diameter of 9 μm and a thickness of 2 mm;

[0047] Step 3: Surface spraying, spraying Nafion resin on the surface of the porous plate obtained in Step 2;

[0048] Step 4: Compression molding and sintering. The product obtained in Step 3 is subjected to compression molding and sintering. After 5 times of spraying, compression molding and sintering, a separator with a thickness of 1.5 mm and a pore diameter of 9 μm, which is corrosion-resistant, high-strength, high-temperature-resistant and has good wettability, is formed. The surface of the separator is uniform and flat. After the water pressure airtightness test, no bubbles are generated under a pressure of 10 KPa.

[0049] Example 2

[0050] The present invention provides a separator for electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride, which comprises a tetrafluoro orifice plate layer and an outer spray coating layer sprayed on the outer surface of the tetrafluoro orifice plate layer; the tetrafluoro orifice plate layer comprises carbon fiber and PFA resin, and the tetrafluoro orifice plate layer is a porous plate made of a corrosion-resistant and high-strength carbon fiber and PFA resin mixture. The outer spray coating layer comprises Nafion resin, and the mass ratio of each component of the separator is as follows:

[0051] Carbon fiber: 5%;

[0052] PFA resin: 85%;

[0053] And Nafion resin: 10%.

[0054] In this embodiment, the carbon fiber is a corrosion-resistant and high-strength carbon fiber, specifically polyacrylonitrile carbon fiber.

[0055] Perfluorosulfonic acid resin (Nafion-H) is the known strongest solid superacid, which has characteristics such as good heat resistance, high chemical stability and high mechanical strength. As a green solid acid catalyst, perfluorosulfonic acid resin has good catalytic activity and selectivity for many reactions.

[0056] Soluble polytetrafluoroethylene, English name: Polyfluoroalkoxy, Teflon PFA, generally abbreviated as: PFA. PFA plastic is a copolymer of a small amount of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. The melt bonding property is enhanced, the melt viscosity decreases, and the performance remains unchanged compared with polytetrafluoroethylene.

[0057] In this embodiment, the pore density of the tetrafluoro orifice plate layer is 900 pores per square centimeter, and the tetrafluoro orifice plate layer is a tetrafluoro orifice plate with a pore diameter of 5 μm and a thickness of 2 mm.

[0058] The pore diameter range of the tetrafluoro orifice plate layer is 5 μm.

[0059] The airtightness of the separator is 12 Kpa.

[0060] Referring to Figure 5 , the preparation method of the separator of the present invention comprises the following steps.

[0061] Step 1: Material mixing. Mechanically mix carbon fiber and PFA resin in a dry powder single-cone double-helix mixer to make the materials evenly mixed;

[0062] Step 2: Injection molding and pressing. Inject and mold the mixture obtained in Step 1 into a tetrafluoroethylene pore plate with 900 pores per square centimeter, a pore diameter of 5 μm, and a thickness of 1 mm;

[0063] Step 3: Surface spraying. Spray Nafion resin on the surface of the porous plate obtained in Step 2;

[0064] Step 4: Molding and sintering. Conduct molding and sintering treatments on the product obtained in Step 3. After 3 times of spraying, molding, and sintering, a diaphragm with a thickness of 1.5 mm, a pore diameter of 5 μm, corrosion resistance, high strength, high temperature resistance, and good wettability is obtained, and the surface of the diaphragm is uniform and flat; After the water pressure airtightness test, no bubbles are generated under a pressure of 12 KPa.

[0065] Example 3

[0066] The difference between this example and Example 1 is that the mass ratio of each component in this example is:

[0067] Carbon fiber 2%;

[0068] PFA resin 90%;

[0069] And Nafion resin 8%.

[0070] In this example, the carbon fiber is a corrosion-resistant and high-strength carbon fiber, specifically polyacrylonitrile carbon fiber.

[0071] In this example, the pore density of the tetrafluoroethylene pore plate layer is 200 pores per square centimeter, and the tetrafluoroethylene pore plate layer is a tetrafluoroethylene pore plate with a pore diameter of 12 μm and a thickness of 3 mm.

[0072] The pore diameter range of the tetrafluoroethylene pore plate layer is 12 μm.

[0073] The airtightness of the diaphragm is 5 Kpa.

[0074] Refer to Figure 5 , the preparation method of the diaphragm of the present invention includes the following steps,

[0075] Step 1: Material mixing. Mechanically mix carbon fiber and PFA resin in a dry powder single-cone double-helix mixer to make the materials evenly mixed;

[0076] Step 2: Injection molding and pressing. Inject and mold the mixture obtained in Step 1 into a tetrafluoroethylene pore plate with 200 pores per square centimeter, a pore diameter of 12 μm, and a thickness of 3 mm;

[0077] Step 3: Surface spraying. Spray Nafion resin on the surface of the porous plate obtained in Step 2.

[0078] Step 4: Compression molding and sintering. Perform compression molding and sintering on the product obtained in Step 3. After 7 times of spraying, compression molding and sintering, a diaphragm with a thickness of 1.5 mm and a pore diameter of 5 μm, which is corrosion-resistant, high-strength, high-temperature resistant and has good wettability, is formed. The surface of the diaphragm is uniform and flat. After the water pressure airtightness test, no bubbles are generated under a pressure of 5 KPa.

[0079] Example 4

[0080] The difference between this example and Example 1 is that the mass ratio of each component in this example is as follows:

[0081] Carbon fiber: 2%;

[0082] PFA resin: 85%;

[0083] And Nafion resin: 13%.

[0084] In this example, the pore density of the tetrafluoro pore plate layer is 300 pores per square centimeter, and the tetrafluoro pore plate layer is a tetrafluoro pore plate with a pore diameter of 12 μm and a thickness of 3 mm.

[0085] The pore diameter range of the tetrafluoro pore plate layer is 8 μm.

[0086] The airtightness of the diaphragm is 10 Kpa.

[0087] Refer to Figure 5 , the preparation method of the diaphragm of the present invention includes the following steps.

[0088] Step 1: Material mixing. Mechanically mix carbon fiber and PFA resin in a dry powder double-cone mixer to make the materials evenly mixed.

[0089] Step 2: Injection molding and compression molding. Inject and compress the mixture obtained in Step 1 into a tetrafluoro pore plate with 300 pores per square centimeter, a pore diameter of 8 μm and a thickness of 3 mm.

[0090] Step 3: Surface spraying. Spray Nafion resin on the surface of the porous plate obtained in Step 2.

[0091] Step 4: Compression molding and sintering. Perform compression molding and sintering on the product obtained in Step 3. After 6 times of spraying, compression molding and sintering, a diaphragm with a thickness of 1.5 mm and a pore diameter of 8 μm, which is corrosion-resistant, high-strength, high-temperature resistant and has good wettability, is formed. The surface of the diaphragm is uniform and flat. After the water pressure airtightness test, no bubbles are generated under a pressure of 10 KPa.

[0092] The diaphragm of the present invention is used in the electrolysis of molten ammonium bifluoride to produce nitrogen trifluoride, and plays the role of a diaphragm in the process of electrolysis of molten hydrogen fluoride. Specifically, the diaphragm is used in an electrolytic cell for producing nitrogen trifluoride from molten ammonium bifluoride, and the diaphragm is arranged between the negative terminal plate and the positive plate of the electrolytic cell and between two adjacent negative plates and the positive plate.

[0093] Reference Figures 1-4 As shown, when the diaphragm of the present invention is used in an electrolytic cell for preparing nitrogen trifluoride from molten ammonium bifluoride, the electrolytic cell is specifically: an external circulation parallel electrolytic cell consisting of end plates (negative end plate 1) at both ends of the electrolytic cell, diaphragm 2, positive plate 3, diaphragm 2, negative plate 4, diaphragm 2, positive plate 3, diaphragm 2, negative plate 4, diaphragm 2, (in the middle is a repeating unit of positive plate 3, diaphragm 2, negative plate 4, diaphragm 2), and the other end plate (positive end plate 5) at both ends of the electrolytic cell. In this way, the nitrogen trifluoride produced at the anode is well isolated from the hydrogen produced at the cathode, and the fluoride ions and hydrogen ions in the molten ammonium bifluoride electrolyte can pass through the diaphragm to complete the electrolysis. The performance of the diaphragm determines which ions can pass through. The nitrogen trifluoride produced at the anode enters the purification and refining unit through a pipeline, and the hydrogen produced at the cathode enters the environmentally friendly treatment tower through a pipeline and is then discharged.

[0094] The diaphragm of the present invention is used in the electrolytic cell process of electrolyzing molten ammonium bifluoride to produce nitrogen trifluoride. When the distance between the cathode and the anode is 6 mm and the current density is 120-150 mA / mm2, the voltage is 5.6-6.5 V. Compared with the existing industrial electrolytic cell with a voltage of 7-8.5 V at the same current density, it can save 20-30% of electric energy and has very good economic benefits.

[0095] Compared with the traditional technical means (in order to ensure safety, the cathode and anode areas of the electrolytic cell are continuously scavenged with nitrogen during normal production), the waste of nitrogen is effectively eliminated, and the economic benefits of the process of preparing nitrogen trifluoride by electrolysis of molten ammonium bifluoride are greatly improved.

[0096] Molten ammonium bifluoride can be used to prepare nitrogen trifluoride. After the cathode chamber and the anode chamber are separated by the diaphragm of the present invention, the following can be ensured:

[0097] 1. The air is full and cannot pass through;

[0098] 2. Can be wetted by electrolyte;

[0099] 3. Have sufficient mechanical strength;

[0100] 4. The resistance when conductive ions pass through is small;

[0101] 5. It is not corroded by the electrolyte and has strong chemical stability;

[0102] 6. The diaphragm proposed by the present invention is cheap and suitable for industrial use.

[0103] The diaphragm for preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride of the present invention has the characteristics of corrosion resistance, high strength, high temperature resistance and good wettability, with high strength, good ion permeability and difficult bubble penetration, and can be applied to the electrolysis process of preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride. It can greatly improve the production capacity of preparing nitrogen trifluoride by electrolyzing molten ammonium bifluoride, reduce energy consumption, and bring good economic and social benefits.

[0104] At present, the technical solution of the present invention has been pilot-tested, that is, small-scale experiments before large-scale production; after the pilot test, user usage research has been carried out on a small scale, and the research results show that user satisfaction is relatively high; now preparations are underway for the formal industrial production of the product (including research on intellectual property risk early warning).

[0105] The above-described embodiments are the preferred embodiments of the present invention, rather than an exhaustive list of feasible embodiments of the present invention. For those skilled in the art, various improvements made without departing from the spirit and essence of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A diaphragm for producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride, characterized in that, It includes a tetrafluoro orifice plate layer and an outer spray coating sprayed on the outer surface of the tetrafluoro orifice plate layer; the tetrafluoro orifice plate layer includes carbon fiber and PFA resin, the outer spray coating includes Nafion resin, and the mass ratio of each component of the diaphragm is as follows: Carbon fiber: 2-5%; PFA resin: 85-90%; Nafion resin: 8-13%.

2. A diaphragm for preparing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride according to claim 1, characterized in that, The pore density of the tetrafluoro orifice plate layer is 200-900 pores per square centimeter.

3. A diaphragm for preparing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride according to claim 2, characterized in that, The pore diameter range of the tetrafluoro orifice plate layer is 5-12 μm.

4. A diaphragm for producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride according to claim 1, characterized in that, The carbon fiber is corrosion-resistant high-strength carbon fiber.

5. A diaphragm for producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride according to claim 4, characterized in that, The carbon fiber is polyacrylonitrile carbon fiber.

6. A diaphragm for producing nitrogen trifluoride by electrolyzing molten ammonium hydrogen fluoride according to claim 1, characterized in that, The airtightness of the diaphragm is 5-12 Kpa.

7. A method for preparing a diaphragm according to any one of claims 1-6, characterized in that, It includes the following steps. Step 1: Material mixing, mixing carbon fiber and PFA resin; Step 2: Injection molding and pressing, molding the mixture obtained in Step 1 into a porous plate with a thickness of 1-3 mm; Step 3: Surface spraying, spraying Nafion resin on the surface of the porous plate obtained in Step 2; Step 4: Molding and sintering, performing molding and sintering on the product obtained in Step 3, and repeating Step 2 and Step 3 for 3-7 times until a diaphragm with a thickness of 1.5 mm is finally obtained.

8. Application of a diaphragm according to any one of claims 1-6 in the electrolysis of molten ammonium bifluoride to produce nitrogen trifluoride.

9. The application according to claim 8, characterized in that, The diaphragm is used in an electrolytic cell for the electrolysis of molten ammonium bifluoride to produce nitrogen trifluoride, and the diaphragm is arranged between the negative electrode plate and the positive electrode plate, and between the negative electrode plate and the positive electrode plate in the electrolytic cell.

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