Method for preparing nitrogen trifluoride gas through electrolysis

Abstract

The invention relates to a method for preparing nitrogen trifluoride gas by electrolysis, which comprises the following steps of: assembling carbon fluoride / graphite serving as an electrolytic anode and nickel serving as an electrolytic cathode into an electrolytic tank; uniformly mixing ammonium bifluoride and hydrogen fluoride, heating to form molten NH4HF2-HF, and then adding AFx to prepare an electrolyte; and the electrolyte is introduced into an electrolytic cell for an electrolytic reaction, and nitrogen trifluoride gas is prepared. A carbon fluoride / graphite electrode (CFx) n (0 < x < = 0.8) is adopted as an electrolytic anode to replace traditional metal nickel for electrolysis to prepare NF3, and as the CFx electrode has the characteristics of high conductivity and excellent binding energy, the negative influence possibly brought by a nickel anode is effectively eliminated while high-current-density stable operation is ensured, and the NF3 can be effectively prepared. Therefore, the content of the nitrogen trifluoride gas is maintained at a relatively high level, the preparation efficiency is improved, and the product quality is also remarkably improved; meanwhile, the (CFx) n anode is adopted, so that the electrolysis period is effectively prolonged, and the electrolyte loss caused by anode loss is reduced.

Description

Technical Field

[0001] The invention belongs to the field of electronic chemical industry, and in particular relates to a method for preparing nitrogen trifluoride gas by electrolysis. Background Art

[0002] In the field of microelectronics industry and semiconductor manufacturing, nitrogen trifluoride (NF3) is a key specialty gas with a wide range of applications. It is mainly used for cleaning chemical vapor deposition (CVD) equipment and etching in plasma processes, especially in the etching of silicon compounds and silicon nitride, where it exhibits excellent etching rate and selectivity.

[0003] Traditional methods for preparing nitrogen trifluoride mainly include chemical synthesis and electrolysis. Although the chemical synthesis method is relatively safe, it has disadvantages such as complex equipment and high impurity content, which makes it difficult to meet the needs of the microelectronics industry for high-purity gases. In contrast, the electrolysis method has the advantage of being easier to obtain high-purity products, and has gradually become the mainstream method for preparing nitrogen trifluoride.

[0004] In the process of preparing nitrogen trifluoride by electrolysis, the design of the electrolytic cell and the selection of electrolytic conditions are key. Most traditional electrolytic cells use nickel as the anode material, but the nickel anode is prone to corrosion during the electrolysis process, contaminating the electrolyte and causing a decrease in electrolysis efficiency. In addition, the price of nickel electrodes is relatively high, which increases production costs. Therefore, the development of new electrode materials to improve electrolysis efficiency and reduce costs has become a research hotspot.

[0005] In recent years, with the development of carbon material science, carbon electrodes have gradually attracted attention due to their good conductivity and low price. Studies have shown that using carbon electrodes as anodes in electrolytic cells can significantly improve electrolysis efficiency and reduce production costs. However, carbon electrodes also face some problems during the electrolysis process, such as anode effect and gas adhesion, which need to be solved by optimizing electrolysis conditions and electrode surface treatment.

[0006] CN101624708A provides a method for electrolytic synthesis of nitrogen trifluoride, including electrolytic synthesis of nitrogen trifluoride gas from ammonium fluoride in a molten salt mixture containing ammonium fluoride under the condition of using a carbonaceous electrode as a positive electrode, wherein the method includes the following steps: dissolving such metal ions in the molten salt mixture, the metal ions can electrolytically produce highly oxidized metal fluorides by reacting with fluorine free radicals (F·), the fluorine free radicals (F·) are produced when fluoride ions that are components of the ammonium fluoride are discharged, so that the metal ions and the fluorine free radicals (F·) react to produce the highly oxidized metal fluorides, and the highly oxidized metal fluorides react with ammonium ions on the surface of the electrode and in the solution to synthesize nitrogen trifluoride gas. However, due to the existence of problems such as anode polarization, swelling and decomposition, the content of impurity CF4 generated by electrolysis is continuously high, making it impossible for graphite anodes to be applied to NF3 electrolytic production on a large scale.

[0007] Therefore, how to overcome the above-mentioned problems of the prior art and provide a method for continuously and stably preparing nitrogen trifluoride gas is the key to the research. Summary of the invention

[0008] In order to overcome the technical problems in the prior art of high corrosion rate of nickel as electrolytic anode and continuous high content of impurity CF4 generated by electrolysis when graphite is used as electrolytic anode, the present invention provides a method for preparing nitrogen trifluoride gas by electrolysis.

[0009] To achieve the purpose of the present invention, the specific technical solutions provided by the present invention are as follows:

[0010] A method for preparing nitrogen trifluoride gas by electrolysis, the method comprising: using carbon fluoride as an electrolysis anode and nickel as an electrolysis cathode, assembling them into an electrolytic cell;

[0011] Mix ammonium bifluoride and hydrogen fluoride, heat to form molten NH4HF2-HF, and then add AF x , preparing an electrolyte;

[0012] The electrolyte is passed into the electrolytic cell to carry out electrolytic reaction to prepare nitrogen trifluoride gas.

[0013] Preferably, the carbon fluoride electrolysis anode is a carbon fluoride / graphite electrode (CF x ) n .

[0014] Preferably, the carbon fluoride / graphite electrode (CF x ) n It is a surface defluorinated modified carbon / graphite electrode, 0<x≤0.8.

[0015] Preferably, the electrolytic cathode nickel undergoes surface treatment before assembly, including decontamination, water washing, polishing and activation.

[0016] Preferably, the electrolytic cell is a PVDF skirt-type electrolytic cell.

[0017] Preferably, the mass ratio of ammonium bifluoride to hydrogen fluoride is 6 to 14:1.

[0018] Preferably, the AF x It is a mixture of NiF2 and LiF, the molar ratio of NiF2 to LiF is 25:1 to 1:25, and AF is added x The ratio is 0.01 to 0.05 wt % of the electrolyte.

[0019] Preferably, after the electrolyte is passed into the electrolytic cell, a pre-electrolysis treatment is performed, the pre-electrolysis voltage is 2.5 to 4.5 V, and the pre-electrolysis time is 26 to 30 hours.

[0020] Preferably, the electrolysis voltage of the electrolysis reaction to prepare nitrogen trifluoride gas is 4.5-6.5V, and the electrolysis temperature is 90-150°C.

[0021] Preferably, during the process of preparing nitrogen trifluoride gas by electrolysis reaction, the electrolyte is continuously replenished, and the electrolysis process can continue to work for more than 180 days.

[0022] The present invention provides a method for preparing nitrogen trifluoride gas by electrolysis, which has the following beneficial effects:

[0023] 1. The present invention adopts carbon fluoride / graphite electrode (CF x ) n (where 0<x≤0.8) as electrolytic anode, replacing the traditional metal nickel electrolysis to prepare NF3, due to CF x The electrode has high conductivity and excellent binding energy characteristics. While ensuring stable operation at high current density, it effectively eliminates the negative effects that may be caused by the nickel anode, thereby ensuring that the content of nitrogen trifluoride gas is maintained at a high level and reducing the generation of impurity CF4, which not only improves the preparation efficiency, but also significantly improves the product quality; at the same time, by adopting (CF x ) n Anode, this technical solution effectively extends the electrolysis cycle and reduces the electrolyte loss caused by anode loss. It not only improves production continuity, but also reduces raw material consumption and production costs, bringing significant economic benefits to the enterprise.

[0024] 2. The present invention adds a mixture of NiF2 and LiF to the molten NH4HF2-HF electrolyte. These metal fluorides can form a stable solid electrolyte interface (SEI) film on the surface of the anode and cathode, effectively preventing the fluoride ions in the electrolyte from being embedded in the anode, thereby extending the service life of the anode; secondly, they can also improve the overall conductivity of the electrolyte, further optimize the electrolysis process, and improve the overall performance.

[0025] 3. The present invention achieves the optimization of process conditions by finely regulating the electrolysis voltage (4.5-6.5V) and the electrolysis temperature (90-150°C) and combining the use of PVDF skirt electrolytic cells. In addition, the electrolytic cathode nickel is pretreated, including decontamination, washing, polishing and activation, which further improves the electrolysis efficiency and stability. DETAILED DESCRIPTION

[0026] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the preferred embodiments.

[0027] Example 1

[0028] A method for preparing nitrogen trifluoride comprises: mixing ammonium bifluoride and hydrogen fluoride at a mass ratio of 6:1 at room temperature, then heating under sealed conditions to form molten NH4HF2-HF, then adding 0.01wt% of a mixture of NiF2 and LiF, wherein the molar ratio of NiF2 to LiF is 1:1, to prepare an electrolyte, and passing the electrolyte into an electrolytic cell for electrolytic reaction.

[0029] Fluorinated carbon is used as an electrolytic anode and nickel is used as an electrolytic cathode in the electrolytic cell. The anode and cathode are assembled into a PVDF skirt electrolytic cell to form an electrolytic device. The electrolytic cell is made of PVDF material to enhance the corrosion resistance and extend the service life of the electrolytic cell.

[0030] Among them, the electrolytic anode carbon fluoride is a surface defluorinated modified carbon / graphite electrode (CF x ) n (x=0.1), (CF x ) n It has much higher thermal stability (greater than 400°C) than other graphene derivatives, high dielectric strength (about 10MV / cm), high degree of functionalization, wide energy gap and good dispersibility, which is beneficial to improve the conductivity and the transfer rate of ions and electrons between particles;

[0031] The nickel cathode needs to be surface treated before use, including the use of organic solvents, alkaline or acidic cleaning agents to remove oil and impurities on the surface of the nickel cathode; thoroughly rinse the nickel cathode with deionized water or purified water to remove the residual cleaning agent to avoid adverse effects on the subsequent electrolysis process; use metallographic sandpaper or mechanical grinding equipment to polish the surface of the nickel cathode to remove the oxide layer, scratches and other defects on the surface. When polishing, sandpaper of different mesh sizes can be selected as needed, and the process can be carried out from coarse to fine to obtain a smooth surface. Polishing can be performed if necessary. Polishing can improve the brightness and flatness of the surface, which is beneficial to the uniformity and stability of the electrolysis process; finally, the nickel cathode is activated by electrochemical pretreatment directly in the electrolytic cell. By applying a certain voltage and current, a layer of active substances is formed on the surface of the nickel cathode, which is beneficial to the subsequent electrolysis process.

[0032] Using the above electrolyte, electrode and electrolytic cell, NF3 was prepared by electrolysis. First, pre-electrolysis was carried out for 30 hours at a voltage of 2.5V.

[0033] After the pre-electrolysis is completed, the electrolysis voltage is increased, and the formal operation of electrolytic preparation of nitrogen trifluoride is carried out. The electrolysis voltage is increased to 4.5V, and the electrolysis temperature is maintained at 120°C. The process of electrolytic preparation of nitrogen trifluoride runs stably for 180 days. During the electrolysis process, the electrolyte prepared according to the above ratio is replenished in real time to keep the electrolyte level in the electrolytic cell to meet the electrolysis requirements and maintain the stability of the electrolysis process.

[0034] The prepared electrolytic gas was collected and tested, and the average contents of the main components of the electrolytic gas during the operation cycle were: NF3: 68.8%, H2: 0.021%, N2: 29.4%, CF4: 5.4ppm.

[0035] After the electrolysis was completed after 180 days of operation, the electrolytic cell was treated and the loss of electrolyte entrained in the electrolytic solid waste was determined by acid-base titration and fluoride ion electrode titration.

[0036] Example 2

[0037] A method for preparing nitrogen trifluoride comprises: mixing ammonium bifluoride and hydrogen fluoride at a molar ratio of 10:1 at room temperature, then heating under sealed conditions to form molten NH4HF2-HF, then adding 0.03wt% of a mixture of NiF2 and LiF, wherein the molar ratio of NiF2 to LiF is 25:1, to prepare an electrolyte, and passing the electrolyte into an electrolytic cell for electrolytic reaction.

[0038] The electrolytic cell uses carbon fluoride as the electrolytic anode and nickel as the electrolytic cathode. The anode and cathode are assembled into a PVDF skirt electrolytic cell, wherein the electrolytic anode carbon fluoride is a surface defluorinated modified carbon / graphite electrode (CF x) n (x=0.8), the nickel cathode needs to be surface treated before use.

[0039] Using the above electrolyte, electrode and electrolytic cell, NF3 was prepared by electrolysis. First, pre-electrolysis was carried out for 27 hours at a voltage of 2.9V. After the pre-electrolysis was completed, the electrolysis voltage was increased to 5.5V, and the electrolysis temperature was maintained at 90°C. The process of preparing nitrogen trifluoride by electrolysis was stably operated for 200 days. During the electrolysis process, the electrolyte prepared in the above ratio was replenished in real time to keep the electrolyte level in the electrolytic cell to meet the electrolysis requirements and maintain the stability of the electrolysis process.

[0040] The prepared electrolytic gas was collected and tested, and the average contents of the main components of the electrolytic gas during the operation cycle were: NF3: 67.5%, H2: 0.031%, N2: 30.1%, CF4: 4.9ppm.

[0041] After the electrolysis was completed after 200 days of operation, the electrolytic cell was treated and the loss of electrolyte entrained in the electrolytic solid waste was determined by acid-base titration and fluoride ion electrode titration.

[0042] Example 3

[0043] A method for preparing nitrogen trifluoride comprises: mixing ammonium bifluoride and hydrogen fluoride at a molar ratio of 14:1 at room temperature, then heating under sealed conditions to form molten NH4HF2-HF, then adding 0.05wt% of a mixture of NiF2 and LiF, wherein the molar ratio of NiF2 to LiF is 1:25, to prepare an electrolyte, and passing the electrolyte into an electrolytic cell for electrolytic reaction.

[0044] The electrolytic cell uses carbon fluoride as the electrolytic anode and nickel as the electrolytic cathode. The anode and cathode are assembled into a PVDF skirt electrolytic cell, wherein the electrolytic anode carbon fluoride is a surface defluorinated modified carbon / graphite electrode (CF x ) n (x=0.6), the nickel cathode needs to be surface treated before use.

[0045] Using the above electrolyte, electrode and electrolytic cell, NF3 was prepared by electrolysis. First, pre-electrolysis was carried out for 26 hours at a voltage of 4.5V. After the pre-electrolysis was completed, the electrolysis voltage was increased to 6.5V, and the electrolysis temperature was maintained at 150°C. The process of preparing nitrogen trifluoride by electrolysis was stably operated for 178 days. During the electrolysis process, the electrolyte prepared in the above ratio was replenished in real time to keep the electrolyte level in the electrolytic cell to meet the electrolysis requirements and maintain the stability of the electrolysis process.

[0046] The prepared electrolytic gas was collected and tested, and the average contents of the main components of the electrolytic gas during the operation cycle were: NF3: 67.7%, H2: 0.024%, N2: 31.1%, CF4: 5.1ppm.

[0047] After the electrolysis was completed after 178 days of operation, the electrolytic cell was treated and the loss of electrolyte entrained in the electrolytic solid waste was determined by acid-base titration and fluoride ion electrode titration.

[0048] Comparative Example 1

[0049] Compared with Examples 1-3, nickel used for conventional production of nitrogen trifluoride was used as the electrolytic anode, and other parameters were consistent with those of Example 1. The electrode was used for 180 days, the electrolytic cell was treated, and the loss of electrolyte entrained in the electrolytic solid waste was determined by acid-base titration and fluoride ion electrode titration.

[0050] It is calculated that the loss of electrolyte entrained in the electrolytic solid waste in Examples 1-3 of the present invention is reduced by 79% to 85% compared with the loss in Comparative Example 1. Therefore, the process of the present invention has lower operating costs than conventional production processes.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing nitrogen trifluoride gas by electrolysis, characterized in that: The method comprises: using carbon fluoride as an electrolytic anode and nickel as an electrolytic cathode, and assembling them into an electrolytic cell; Mix ammonium bifluoride and hydrogen fluoride, heat to form molten NH4HF2-HF, and then add AF x , preparing an electrolyte; The electrolyte is introduced into the electrolytic cell to carry out electrolytic reaction to prepare nitrogen trifluoride gas.

2. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: The anode of carbon fluoride electrolysis is carbon fluoride / graphite electrode (CF x ) n .

3. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 2, characterized in that: Carbon fluoride / graphite electrode (CF x ) n It is a surface defluorinated modified carbon / graphite electrode, 0<x≤0.

8.

4. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: The electrolytic cathode nickel undergoes surface treatment before assembly, including decontamination, washing, polishing and activation.

5. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: The electrolytic cell adopts PVDF skirt type electrolytic cell.

6. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: The mass ratio of ammonium bifluoride to hydrogen fluoride is 6 to 14:

1.

7. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: AF x It is a mixture of NiF2 and LiF, the molar ratio of NiF2 to LiF is 25:1 to 1:25, and AF is added x The ratio is 0.01 to 0.05 wt % of the electrolyte.

8. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: After the electrolyte is passed into the electrolytic cell, a pre-electrolysis treatment is carried out, the pre-electrolysis voltage is 2.5 to 4.5 V, and the pre-electrolysis time is 26 to 30 hours.

9. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: The electrolysis voltage for preparing nitrogen trifluoride gas by electrolysis reaction is 4.5-6.5V, and the electrolysis temperature is 90-150°C.

10. The method for preparing nitrogen trifluoride gas by electrolysis according to claim 1, characterized in that: During the electrolytic reaction to prepare nitrogen trifluoride gas, the electrolyte is continuously replenished and the electrolytic process can continue to work for more than 180 days.