A method for preparing nitrogen trifluoride gas by electrolysis

Abstract

This invention relates to a method for electrolytically preparing nitrogen trifluoride gas, comprising: assembling fluorinated carbon / graphite as the electrolytic anode and nickel as the electrolytic cathode in an electrolytic cell; mixing ammonium bifluoride and hydrogen fluoride, heating to form molten NH4HF2-HF, and then adding AF. x An electrolyte is prepared; the electrolyte is then passed into an electrolytic cell to carry out an electrolytic reaction, producing nitrogen trifluoride gas. This invention employs a carbon fluoride / graphite electrode (CF2). x ) n (0<x≤0.8) is used as the electrolytic anode to replace the traditional electrolytic preparation of NF3 with metallic nickel, because CF x The electrode possesses high conductivity and superior binding energy characteristics. While ensuring stable operation at high current densities, it effectively eliminates the potential negative impacts of nickel anodes, thereby maintaining a high level of nitrogen trifluoride gas content. This not only improves preparation efficiency but also significantly enhances product quality. Furthermore, by employing (CF... x ) n In terms of the anode, this technical solution effectively extends the electrolysis cycle and reduces electrolyte loss caused by anode loss.

Description

Technical Field

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

[0002] In the 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 processes in plasma processes, exhibiting excellent etching rates and selectivity, particularly in the etching of silicon compounds and silicon nitrides.

[0003] Traditional methods for preparing nitrogen trifluoride mainly include chemical synthesis and electrolysis. While chemical synthesis offers higher safety, it suffers from drawbacks such as complex equipment and high impurity content, making it difficult to meet the high-purity gas requirements of the microelectronics industry. In contrast, electrolysis offers the advantage of more readily obtaining high-purity products, and has therefore gradually become the mainstream method for preparing nitrogen trifluoride.

[0004] In the electrolytic preparation of nitrogen trifluoride, the design of the electrolytic cell and the selection of electrolysis conditions are crucial. Traditional electrolytic cells mostly use nickel as the anode material; however, nickel anodes are prone to corrosion during electrolysis, contaminating the electrolyte and leading to decreased electrolysis efficiency. Furthermore, nickel electrodes are expensive, increasing production costs. Therefore, developing novel electrode materials to improve electrolysis efficiency and reduce costs has become a research hotspot.

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

[0006] CN101624708A provides a method for electrolytically synthesizing nitrogen trifluoride, comprising electrolytically synthesizing nitrogen trifluoride gas from ammonium fluoride in a molten salt mixture containing ammonium fluoride under conditions using a carbon electrode as the positive electrode. The method includes the following steps: dissolving metal ions in the molten salt mixture that are capable of electrolytically producing highly oxidized metal fluorides by reacting with fluoride radicals (F·), wherein the fluoride radicals (F·) are generated during the discharge of fluoride ions that are components of the ammonium fluoride, thereby causing the metal ions and the fluoride radicals (F·) to react to produce the highly oxidized metal fluorides; and reacting the highly oxidized metal fluorides with ammonium ions on the surface of the electrode and in solution to synthesize nitrogen trifluoride gas. However, due to problems such as anodic polarization, swelling, and decomposition, the content of the impurity CF4 generated during electrolysis remains consistently high, preventing the large-scale application of graphite anodes in the electrolytic production of NF3.

[0007] Therefore, the key research area is how to overcome the problems of the existing technology and provide a method for the continuous and stable preparation of nitrogen trifluoride gas. Summary of the Invention

[0008] To overcome the technical problems of high corrosion rate when nickel is used as the electrolytic anode and persistently high CF4 content when graphite is used as the electrolytic anode in existing technologies, this invention provides a method for electrolytically preparing nitrogen trifluoride gas.

[0009] To achieve the objectives of this invention, the specific technical solution provided by this invention is as follows:

[0010] A method for electrolytically preparing nitrogen trifluoride gas, the method comprising: using fluorinated carbon as an electrolytic anode and nickel as an electrolytic cathode, assembling them in an electrolytic cell;

[0011] Ammonium bifluoride and hydrogen fluoride are mixed and heated to form molten NH4HF2-HF, then AF is added. x Prepared into an electrolyte;

[0012] The electrolyte is passed into an electrolytic cell to carry out an electrolytic reaction, thereby producing nitrogen trifluoride gas.

[0013] Preferably, the fluorinated carbon electrolytic anode is a fluorinated carbon / graphite electrode (CF3). x ) n .

[0014] Preferably, the fluorinated carbon / graphite electrode (CF) x ) n For surface-defluorinated modified carbon / graphite electrodes, 0 < x ≤ 0.8.

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

[0016] Preferably, the electrolytic cell is a PVDF skirted 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, with a molar ratio of NiF2 to LiF of 25:1 to 1:25, with the addition of AF. x The proportion is 0.01 to 0.05 wt% of the electrolyte.

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

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

[0021] Preferably, during the electrolytic reaction to prepare nitrogen trifluoride gas, the electrolyte is continuously replenished, and the electrolytic process can operate continuously for more than 180 days.

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

[0023] 1. This invention employs a fluorinated carbon / graphite electrode (CF). x ) n (where 0 < x ≤ 0.8) is used as the electrolytic anode to replace the traditional electrolytic preparation of NF3 with metallic nickel, because CF x The electrode possesses high conductivity and superior binding energy characteristics. While ensuring stable operation at high current densities, it effectively eliminates the negative impacts that nickel anodes might bring, thereby ensuring that the nitrogen trifluoride gas content remains at a high level and reducing the formation of impurity CF4. This not only improves preparation efficiency but also significantly enhances product quality. Furthermore, by employing (CF4)... x ) n In terms of the anode, this technical solution effectively extends the electrolysis cycle and reduces 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 enterprises.

[0024] 2. In this invention, a mixture of NiF2 and LiF is added to the molten NH4HF2-HF electrolyte. These metal fluorides can form a stable solid electrolyte interphase (SEI) film on the anode and cathode surfaces, effectively preventing fluoride ions in the electrolyte from embedding into 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. This invention optimizes process conditions by precisely controlling the electrolysis voltage (4.5–6.5V) and electrolysis temperature (90–150℃), combined with the use of a PVDF skirt-type electrolytic cell. Furthermore, pretreatment of the electrolytic cathode nickel, including decontamination, washing, polishing, and activation, further enhances electrolysis efficiency and stability. Detailed Implementation

[0026] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0027] Example 1

[0028] A method for preparing nitrogen trifluoride includes: mixing ammonium bifluoride and hydrogen fluoride at room temperature in a mass ratio of 6:1, 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 then passing the electrolyte into an electrolytic cell for electrolysis.

[0029] Fluorocarbon is used as the electrolytic anode and nickel as the electrolytic cathode in the electrolytic cell. The anode and cathode are assembled into a PVDF skirt-type electrolytic cell to form an electrolytic device. The electrolytic cell is made of PVDF material, which can enhance the corrosion resistance of the electrolytic cell and extend its service life.

[0030] Among them, the electrolytic anode fluorinated carbon is a surface-defluorinated modified carbon / graphite electrode (CF). x ) n (x=0.1), (CF) x ) n It possesses properties such as thermal stability (greater than 400℃), high dielectric strength (about 10MV / cm), high degree of functionalization, wide bandgap and good dispersibility, which are beneficial to improving electrical conductivity and the transfer rate of ions and electrons between particles.

[0031] Before use, nickel cathodes require surface treatment, including removing oil and impurities from the surface using organic solvents, alkaline or acidic cleaning agents; thoroughly rinsing the nickel cathode with deionized or purified water to remove cleaning agent residue and avoid adverse effects on subsequent electrolysis; and polishing the surface of the nickel cathode using metallographic sandpaper or mechanical polishing equipment to remove the oxide layer, scratches, and other defects. During polishing, different grit sandpaper can be selected as needed, progressing from coarse to fine to obtain a smooth surface. Polishing can be performed if necessary, as it improves surface gloss and smoothness, which is beneficial for the uniformity and stability of the electrolysis process. Finally, the nickel cathode undergoes electrochemical pretreatment to activate it directly in the electrolytic cell. By applying a certain voltage and current, an active material is formed on the surface of the nickel cathode, which is beneficial for subsequent electrolysis.

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

[0033] After pre-electrolysis, the electrolysis voltage is increased to carry out the formal operation of electrolytically preparing nitrogen trifluoride. The electrolysis voltage is increased to 4.5V, and the electrolysis temperature is maintained at 120℃. The process of electrolytically preparing nitrogen trifluoride is carried out 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 meeting the electrolysis requirements and to maintain the stability of the electrolysis process.

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

[0035] After 180 days of operation and electrolysis, the electrolytic cells were decommissioned and the amount of electrolyte lost due to entrainment 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 includes: mixing ammonium bifluoride and hydrogen fluoride at room temperature in a molar ratio of 10:1, 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 then passing the electrolyte into an electrolytic cell for electrolysis.

[0038] Fluorinated carbon is used as the electrolytic anode and nickel as the electrolytic cathode in the electrolytic cell. The anode and cathode are assembled in a PVDF skirt-type electrolytic cell. The fluorinated carbon anode is a surface-defluorinated modified carbon / graphite electrode (CF3). x) n (x=0.8), the nickel cathode needs to be surface treated before use.

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

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

[0041] After 200 days of operation and electrolysis, the electrolytic cells were decommissioned and the amount of electrolyte lost due to entrainment 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 includes: mixing ammonium bifluoride and hydrogen fluoride at room temperature in a molar ratio of 14:1, 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 then passing the electrolyte into an electrolytic cell for electrolysis.

[0044] Fluorinated carbon is used as the electrolytic anode and nickel as the electrolytic cathode in the electrolytic cell. The anode and cathode are assembled in a PVDF skirt-type electrolytic cell. The fluorinated carbon anode is a surface-defluorinated modified carbon / graphite electrode (CF3). x ) n (x=0.6), the nickel cathode needs to be surface treated before use.

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

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

[0047] After 178 days of operation and electrolysis, the electrolytic cells were decommissioned and the amount of electrolyte lost due to entrainment 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, which is conventionally used to produce nitrogen trifluoride, was used as the electrolytic anode. Other parameters were the same as in Example 1. The electrode was used for 180 days. The electrolytic cell was subjected to a tank treatment. The amount of electrolyte loss carried by the electrolytic solid waste was determined by acid-base titration and fluoride ion electrode titration.

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

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for electrolytically preparing nitrogen trifluoride gas, characterized in that, The method includes: using fluorinated carbon as the electrolytic anode, wherein the fluorinated carbon electrolytic anode is a fluorinated carbon / graphite electrode (CF). x ) n Fluorinated carbon / graphite electrode (CF) x ) n In the case where 0 < x ≤ 0.8, nickel is used as the electrolytic cathode and assembled into the electrolytic cell; Ammonium bifluoride and hydrogen fluoride are mixed and heated to form molten NH4HF2-HF. Then, a mixture of NiF2 and LiF is added to prepare an electrolyte. The electrolyte is passed into an electrolytic cell to carry out an electrolytic reaction, thereby producing nitrogen trifluoride gas.

2. The method for electrolytically preparing nitrogen trifluoride gas according to claim 1, characterized in that, Before assembly, the electrolytic cathode nickel undergoes surface treatment, including decontamination, washing, and polishing.

3. The method for electrolytically preparing nitrogen trifluoride gas according to claim 1, characterized in that, The electrolytic cell is a PVDF skirted electrolytic cell.

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

1.

5. The method for electrolytically preparing nitrogen trifluoride gas according to claim 1, characterized in that, The molar ratio of NiF2 to LiF is 25:1 to 1:25, and the proportion of NiF2 and LiF added is 0.01 to 0.05 wt% of the electrolyte.

6. The method for electrolytically preparing nitrogen trifluoride gas according to claim 1, characterized in that, After the electrolyte is introduced into the electrolytic cell, it undergoes pre-electrolysis treatment. The pre-electrolysis voltage is 2.5–4.5V, and the pre-electrolysis time is 26–30h.

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

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