Modified adsorbent and method for preparing the same, and purification process for nitrogen trifluoride

Abstract

The method for purifying nitrogen trifluoride and synthesizing the modified adsorbent used therefor employs the following steps: Step S1, which involves removing impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O from nitrogen trifluoride using a cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm; Step S2, which involves reducing the concentration of CF4 in Step S1 to 3-8 ppm or less using a high-pressure boiling method; and Step S3, which involves selectively adsorbing and desorbing NF3 using a modified adsorbent to obtain a high-purity NF3 gas with a CF4 content of less than 2 ppm. In the nitrogen trifluoride purification process according to the present invention, by performing a two-step CF4 removal process in which impurity gases F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O are removed by a cold trap method, and then CF4 impurity gas is removed by a high-pressure boiling method and a modified adsorbent, it becomes possible to reduce the CF4 content in the obtained high-purity NF3 gas to less than 2 ppm.

Description

Cross-reference

[0001] This application claims priority based on a Chinese patent application with application number 202310688334.1, titled "Nitrogen Trifluoride Purification Process and Synthesis Method of Modified Adsorbent Used Therein", filed with the China National Intellectual Property Administration on June 12, 2023, and the entire content thereof is incorporated herein by reference.

Technical Field

[0002] The present invention relates to the field of chemical industry technology, specifically to a modified adsorbent and its preparation method, as well as a nitrogen trifluoride purification process.

Background Art

[0003] Nitrogen trifluoride is an excellent plasma etching agent and cleaning agent, mainly applied in the microelectronics industry. In particular, it is quite excellent in terms of etching speed and selectivity for semiconductor materials such as silicon and silicon nitride. On the other hand, when used as a gas cleaning agent, the cleaning efficiency of nitrogen trifluoride is high and no traces remain. In recent years, with the rapid development of the global semiconductor industry, liquid crystal display industry, and solar power generation industry, the demand for high-purity nitrogen trifluoride has increased rapidly, and its purification process has attracted attention.

[0004] Currently, nitrogen trifluoride gas is mainly prepared by chemical synthesis or electrolysis. However, these two methods only yield crude NF3 gas containing high levels of impurity gases such as F2, HF, CF4, N2, O2, CO, CO2, N2F2, N2F4, and N2O. These impurity gases, F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O, can be removed by methods such as cold trapping, low-temperature rectification, absorption, and adsorption, based on their properties. However, since NF3 and CF4 have very similar physical properties, such as molecular size (NF3: 4.5 Å, CF4: 4.8 Å), boiling point (NF3: -129°C, CF4: -128°C), and heat of adsorption (dipole moment, NF3: 0.235D, CF4: 0D), the aforementioned methods cannot effectively separate them, and special processing is required to obtain high-purity NF3 gas. While the high-pressure boiling method can reduce the CF4 gas content to around 10 ppm, it remains difficult to meet the purity requirements for nitrogen trifluoride needed in specialized industries. To effectively separate NF3 gas and CF4 gas, adsorbents (activated alumina, activated carbon, synthetic zeolite, etc.) may be used. However, using activated alumina or activated carbon as adsorbents is ineffective and costly, and while using synthetic zeolite, i.e., molecular sieves, as a selective adsorbent can yield NF3 gas with a purity of 99.99% or higher, the preparation of synthetic zeolite using conventional techniques is time-consuming and generates large amounts of wastewater that is difficult to treat, making it difficult to meet economic and environmental protection requirements.

[0005] CN101014400A discloses a method for purifying nitrogen trifluoride gas using zeolite exchanged with alkaline earth metals. In this method, first, an appropriate amount of alkaline earth metal (beryllium, magnesium, calcium, strontium, barium) is used to perform ion exchange on zeolite 3A, 4A, or 5A to change the pore size of the zeolite. Then, a mixed gas of NF3 and CF4 is mixed with an inert gas and introduced onto a bed of alkaline earth metal-exchanged zeolite 3A, 4A, or 5A. After selective adsorption of NF3 gas by the bed, high-purity NF3 gas is obtained by desorption, and the desorption rate of CF4 gas reaches 99.6%. However, the synthetic zeolite obtained by this method needs to be heat-treated at 150-600°C for 0.5-100 hours, the efficiency is low, and it is difficult to control the content of the metals to be exchanged (which varies in the range of 20-95 wt%), making it unsuitable for large-scale dissemination and application.

[0006] CN106276828B discloses a method for adsorbing and purifying nitrogen trifluoride, in which a carrier material is a mixture of 5A molecular sieve and cerium tetradecyl phosphate, zinc dialkyldithiophosphate and 3-fluoro-nitrogen-methylaniline are supported on the carrier by liquid-phase sedimentation, the reaction is carried out at 40-80°C for 10-20 hours, the product is separated and dried to obtain an adsorbent, and the crude product of nitrogen trifluoride is applied to an adsorption column charged with the adsorbent to perform adsorption, resulting in nitrogen trifluoride with a purity of up to 99.99%. However, the synthesis of this adsorbent takes a long time, and the large amount of wastewater that is difficult to treat is difficult, making it difficult to meet the requirements of economic efficiency and environmental protection.

[0007] The nitrogen trifluoride purification methods and adsorbents disclosed to date have shortcomings, including poor purification efficiency, long preparation times for adsorbents, and the generation of large amounts of difficult-to-treat wastewater during the synthesis process. Therefore, it is important to develop a nitrogen trifluoride purification process and adsorbents that have a short preparation time, good purification effect, and are environmentally friendly. [Overview of the project] [Problems that the invention aims to solve]

[0008] The technical problem that this invention aims to solve is to provide a modified adsorbent, a method for preparing the same, and a process for purifying nitrogen trifluoride, in response to the shortcomings of the conventional technology. [Means for solving the problem]

[0009] This invention adopts the following technical approach. This application provides a modified adsorbent having an average pore size of 1 Å to 10 Å, comprising a zeolite and a nickel layer compounded on the surface of the zeolite.

[0010] In some specific embodiments, the modified adsorbent has an average pore size of 4.5 Å to 4.8 Å.

[0011] In some specific embodiments, the zeolite has a particle size of 10 to 50 mesh.

[0012] Furthermore, this application also provides a method for preparing the modified adsorbent, which includes obtaining a modified zeolite by performing a nickel plating treatment on the zeolite.

[0013] In some specific embodiments, the nickel plating solution in the nickel plating process is It contains 20-60 g / L of nickel sulfate hexahydrate, 20-60 g / L of ammonium chloride, 20-60 g / L of sodium citrate, and 10-45 g / L of sodium hypophosphite.

[0014] In some specific embodiments, the nickel plating process is performed at a temperature of 20 to 90°C for a duration of 5 to 60 seconds.

[0015] In some embodiments of CO, the nickel plating process is as follows: Step 301 involves preparing a mixture at room temperature, in which 20-60 g / L by mass concentration nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate, and 10-45 g / L sodium hypophosphite are dissolved in distilled water, and then ammonia water is added to adjust the pH value to obtain a nickel plating solution. Step 302 involves flowing the nickel plating solution while adjusting and maintaining the temperature of the plating solution between 20 and 90°C using a constant-temperature magnetic stirrer. The process includes step 303, in which 25 to 100 g / L of zeolite is added to the nickel plating solution prepared in step 302, the rotation speed of a constant-temperature magnetic stirrer is adjusted to 100 to 1000 r / min to suspend the zeolite in the nickel plating solution, deposition is carried out for 5 to 60 s, followed by suction filtration, washing, and drying to obtain a modified adsorbent.

[0016] In some specific embodiments, the nickel plating solution has a pH of 7 to 9.

[0017] In some specific embodiments, the zeolite is commercially available zeolite 5A, which is spherical in shape and has a particle size of 10 to 50 mesh.

[0018] In some specific embodiments, the suction filtration and washing process in step 303 is performed two to three times, and the water used for washing is distilled water.

[0019] Furthermore, this application also provides a method for purifying nitrogen trifluoride, which includes removing CF4 from a mixed gas of NF3 and CF4 by high-pressure boiling to obtain an impurity-removed gas, and selectively adsorbing and desorbing NF3 in the impurity-removed gas using a modified adsorbent described in the above-mentioned technical proposal or a modified adsorbent prepared by the preparation method described in the above-mentioned technical proposal to obtain an NF3 gas.

[0020] In some specific embodiments, the process involves treating nitrogen trifluoride by a cold trap method before employing the high-pressure boiling method to remove impurities such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4, N2O, etc.

[0021] In addition, the present invention includes the following steps: A step S1 of removing impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O from nitrogen trifluoride by the cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm; A step S2 of reducing the concentration of CF4 in step S1 to 3 to 8 ppm or less by the high-pressure boiling method; A purification process of nitrogen trifluoride that employs a step S3 of selectively adsorbing NF3 using a modified adsorbent, desorbing it, and then obtaining high-purity NF3 gas with a CF4 content of less than 2 ppm.

[0022] The temperature of the cold trap in step S1 of the process according to the present invention is -150°C ± 3°C.

[0023] In step S2 according to the present invention, the high-pressure boiling method has a pressure of 30 to 50 atmospheres and a temperature of -30 to -55°C.

[0024] The adsorption temperature in step S3 of the process according to the present invention is -40 to 10°C.

[0025] The modified adsorbent of the process according to the present invention is obtained by plating zeolite with nickel.

[0026] In addition, the present invention includes the following steps: Step 301 of adding aqueous ammonia to a mixture of nickel sulfate hexahydrate at a mass concentration of 20 to 60 g / L, ammonium chloride at a mass concentration of 20 to 60 g / L, sodium citrate at a mass concentration of 20 to 60 g / L, and sodium hypophosphite at a mass concentration of 10 to 45 g / L dissolved in distilled water to adjust the pH value and obtain a nickel plating solution; Step 302 of flowing the nickel plating solution while adjusting and maintaining the temperature of the plating solution at 20 to 90°C using a constant temperature magnetic stirrer; The present invention provides a method for synthesizing a modified adsorbent used in the purification of nitrogen trifluoride, which involves adding 25-100 g / L of zeolite to a nickel plating solution prepared in step 302, adjusting the rotation speed of a constant-temperature magnetic stirrer to 100-1000 r / min to suspend the zeolite in the nickel plating solution, depositing it for 5-60 s, and then obtaining the modified adsorbent through suction filtration, washing, and drying in step 303.

[0027] In the method according to the present invention, the pH value of the nickel plating solution is 7 to 9.

[0028] In the method according to the present invention, the zeolite is commercially available zeolite 5A, which is spherical in shape and has a particle size of 10 to 50 mesh.

[0029] In the method according to the present invention, the suction filtration and washing process in step 303 is performed two to three times, and the water used for washing is distilled water. [Effects of the Invention]

[0030] The present invention offers the following positive effects. (1) In the nitrogen trifluoride purification process according to the present invention, impurity gases such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O are removed by a general cold trap method, and then CF4 impurity gas is further removed by a high-pressure boiling method and a modified adsorbent. This two CF4 removal process makes it possible to reduce the CF4 content in the prepared high-purity NF3 gas to less than 2 ppm. Compared to conventional technology (CF4 content higher than 10 ppm), the present invention results in an even lower CF4 content. (2) In the present invention, amorphous nickel is deposited on the zeolite by a chemical nickel plating method, and amorphous nickel is preferentially deposited at the opening of the hollow zeolite to reduce the pore size of the zeolite, thereby adjusting the pore size of zeolite 5A. This allows the modified adsorbent to selectively adsorb NF3 gas, while CF4 cannot pass through the zeolite pores and is discharged from the end of the adsorption tower. The synthesis method of the modified adsorbent according to the present invention is simple, controllable, has a short synthesis time, and the deposition process only needs to be 5 to 60 seconds. [Modes for carrying out the invention]

[0031] The modified adsorbent provided by the present invention, its preparation method, and the nitrogen trifluoride purification process will be described in more detail below with reference to examples.

[0032] [Example 1] At room temperature, a mixture of 30 g / L nickel sulfate hexahydrate, 40 g / L ammonium chloride, 30 g / L sodium citrate, and 15 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 60°C using a constant-temperature magnetic stirrer. 35 g of commercially available 20-mesh zeolite 5A was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 500 r / min to suspend the zeolite in the nickel plating solution. After deposition for 10 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed twice, and distilled water was used as the washing water.

[0033] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.7 Å.

[0034] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 35 atmospheric pressure and -35°C, reducing the concentration of CF4 in step S1 to 6 ppm. In step S3, NF3 was selectively adsorbed at -40°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 1 ppm.

[0035] [Example 2] At room temperature, a mixture of 35 g / L nickel sulfate hexahydrate, 45 g / L ammonium chloride, 30 g / L sodium citrate, and 25 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 65°C using a constant-temperature magnetic stirrer. 50 g of commercially available zeolite 5A with a particle size of 30 mesh was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 800 r / min to suspend the zeolite in the nickel plating solution. After deposition for 15 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed three times, and distilled water was used as the washing water.

[0036] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.6 Å.

[0037] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 40 atmospheric pressure and -45°C, reducing the concentration of CF4 in step S1 to 4 ppm. In step S3, NF3 was selectively adsorbed at -30°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 0.5 ppm.

[0038] [Example 3] At room temperature, a mixture of 45 g / L nickel sulfate hexahydrate, 45 g / L ammonium chloride, 30 g / L sodium citrate, and 20 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 9, and 1 L of nickel plating solution was obtained. In step 302, the nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 55°C using a constant-temperature magnetic stirrer. In step 303, 75 g of commercially available zeolite 5A with a particle size of 40 mesh was added to the nickel plating solution, and the rotation speed of the constant-temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After deposition for 45 sq. a.m., the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed twice, and distilled water was used as the washing water.

[0039] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.8 Å.

[0040] Nitrogen trifluoride was purified using the aforementioned modified adsorbent in a process that included the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 45 atmospheric pressure and -50°C, reducing the concentration of CF4 in step S1 to 4 ppm. In step S3, NF3 was selectively adsorbed at -40°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 1.4 ppm.

[0041] [Example 4] At room temperature, a mixture of 50 g / L nickel sulfate hexahydrate, 35 g / L ammonium chloride, 40 g / L sodium citrate, and 35 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 65°C using a constant-temperature magnetic stirrer. 45 g of commercially available 20-mesh zeolite 5A was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 800 r / min to suspend the zeolite in the nickel plating solution. After deposition for 15 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed three times, and distilled water was used as the washing water.

[0042] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.6 Å.

[0043] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was performed at 50 atmospheric pressure and -50°C, reducing the concentration of CF4 in step S1 to 6 ppm. In step S3, NF3 was selectively adsorbed at -20°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 0.8 ppm.

[0044] [Example 5] At room temperature, a mixture of 30 g / L nickel sulfate hexahydrate, 30 g / L ammonium chloride, 25 g / L sodium citrate, and 20 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 60°C using a constant-temperature magnetic stirrer.

[0045] 50 g of commercially available zeolite 5A with a particle size of 10 mesh was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After deposition for 20 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed three times, and distilled water was used as the washing water.

[0046] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.5 Å.

[0047] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 45 atmospheric pressure and -55°C, reducing the concentration of CF4 in step S1 to 2 ppm. In step S3, NF3 was selectively adsorbed at -40°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 0.2 ppm.

[0048] [Example 6] At room temperature, a mixture of 30 g / L nickel sulfate hexahydrate, 30 g / L ammonium chloride, 25 g / L sodium citrate, and 25 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 65°C using a constant-temperature magnetic stirrer.

[0049] 40 g of commercially available zeolite 5A with a particle size of 40 mesh was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After deposition for 15 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed three times, and distilled water was used as the washing water.

[0050] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.5 Å.

[0051] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 45 atmospheric pressure and -35°C, reducing the concentration of CF4 in step S1 to 4 ppm. In step S3, NF3 was selectively adsorbed at -35°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 0.3 ppm.

[0052] [Example 7] At room temperature, a mixture of 50 g / L nickel sulfate hexahydrate, 35 g / L ammonium chloride, 45 g / L sodium citrate, and 40 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8.5, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 90°C using a constant-temperature magnetic stirrer.

[0053] 100 g of commercially available zeolite 5A with a particle size of 60 mesh was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 300 r / min to suspend the zeolite in the nickel plating solution. After deposition for 55 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed twice, and distilled water was used as the washing water.

[0054] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.8 Å.

[0055] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 30 atmospheric pressure and -40°C, reducing the concentration of CF4 in step S1 to 4 ppm. In step S3, NF3 was selectively adsorbed at -10°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 1.9 ppm.

[0056] [Example 8] At room temperature, a mixture of 25 g / L nickel sulfate hexahydrate, 25 g / L ammonium chloride, 20 g / L sodium citrate, and 25 g / L sodium hypophosphite was dissolved in distilled water. Ammonia water was added to this mixture to adjust the pH to 8, and 1 L of nickel plating solution was obtained. The nickel plating solution was flowed while adjusting and maintaining the temperature of the plating solution at 90°C using a constant-temperature magnetic stirrer.

[0057] 35 g of commercially available zeolite 5A with a particle size of 30 mesh was added to the nickel plating solution, and the rotation speed of a constant-temperature magnetic stirrer was adjusted to 1000 r / min to suspend the zeolite in the nickel plating solution. After deposition for 15 seconds, the modified adsorbent was obtained by suction filtration, washing, and drying. Here, the suction filtration and washing processes were performed three times, and distilled water was used as the washing water.

[0058] When the modified adsorbent was characterized, it was found that the average pore size of the modified adsorbent was 4.6 Å.

[0059] Using the aforementioned modified adsorbent, nitrogen trifluoride was purified in a process comprising the following steps. In step S1, impurities F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O were removed from nitrogen trifluoride using a general cold trap method to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm. The cold trap temperature was -150°C. In step S2, a high-pressure boiling process was carried out at 35 atmospheric pressure and -55°C, reducing the concentration of CF4 in step S1 to 5 ppm. In step S3, NF3 was selectively adsorbed at -35°C using a modified adsorbent, and the purified gas was collected after desorption. The CF4 content in the purified gas was 0.6 ppm.

[0060] Table 1 shows the measurement results of the CF4 content in high-purity nitrogen trifluoride purified by Examples 1-8 and general cold trap and high-pressure boiling methods.

[0061] [Table 1]

[0062] As can be seen from the above examples and Table 1, in the nitrogen trifluoride purification process according to the present invention, after removing impurity gases such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O by a general cold trap method, a two-step CF4 removal process is performed in which the CF4 impurity gas is further removed by a high-pressure boiling method and a modified adsorbent. As a result, the CF4 content in the obtained high-purity NF3 gas was made lower than 2 ppm. Compared to conventional technology (CF4 content higher than 10 ppm), the present invention resulted in an even lower CF4 content.

[0063] By using the nickel plating solution of the present invention, amorphous nickel is deposited on a zeolite, and amorphous nickel is deposited in the pores of the hollow zeolite to reduce the pore size of the zeolite. With amorphous nickel obtained by controlling the nickel plating solution in this way, the pore size of zeolite 5A can be adjusted, allowing the modified adsorbent to selectively adsorb NF3 gas, while CF4 cannot pass through the zeolite pores and is discharged from the adsorption tower. The synthesis method of the modified adsorbent described in the present invention is simple, controllable, has a short synthesis time, and the deposition process only needs to be 5 to 60 seconds.

[0064] The above descriptions are merely specific embodiments of the present invention and do not limit the invention in any way. Based on the technical essence of the present invention, simple modifications, changes, and equivalent modifications to the above embodiments are all covered within the scope of the technical proposal of the present invention.

Claims

1. A modified adsorbent characterized by comprising zeolite and a nickel layer compounded on the surface of the zeolite, and having an average pore size of 1 Å to 10 Å.

2. The modified adsorbent according to claim 1, characterized by having an average pore size of 4.5 Å to 4.8 Å.

3. The modified adsorbent according to claim 1 or 2, characterized in that the zeolite has a particle size of 10 to 50 mesh.

4. A method for preparing a modified adsorbent, characterized by comprising obtaining a modified zeolite by performing a nickel plating treatment on a zeolite.

5. The nickel plating solution used in the aforementioned nickel plating process is The preparation method according to claim 4, characterized by comprising 20 to 60 g / L of nickel sulfate hexahydrate, 20 to 60 g / L of ammonium chloride, 20 to 60 g / L of sodium citrate, and 10 to 45 g / L of sodium hypophosphite.

6. The preparation method according to claim 5, characterized in that the nickel plating treatment is performed at a temperature of 20 to 90°C and for a duration of 5 to 60 s.

7. Step 301 involves preparing a mixture at room temperature, in which 20-60 g / L by mass concentration nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate, and 10-45 g / L sodium hypophosphite are dissolved in distilled water, and then ammonia water is added to adjust the pH value to obtain a nickel plating solution. Step 302 involves flowing the nickel plating solution while adjusting and maintaining the temperature of the plating solution between 20 and 90°C using a constant-temperature magnetic stirrer. The preparation method according to claim 4, characterized by comprising step 303, which includes adding 25 to 100 g / L of zeolite to the nickel plating solution prepared in step 302, adjusting the rotation speed of a constant-temperature magnetic stirrer to 100 to 1000 r / min to suspend the zeolite in the nickel plating solution, depositing it for 5 to 60 s, and then obtaining a modified adsorbent by suction filtration, washing and drying.

8. The preparation method according to any one of claims 5 to 7, characterized in that the nickel plating solution has a pH value of 7 to 9.

9. The preparation method according to any one of claims 5 to 7, characterized in that the zeolite is commercially available zeolite 5A, which is spherical in shape and has a particle size of 10 to 50 mesh.

10. The preparation method according to claim 7, characterized in that the suction filtration and washing process in step 303 is performed two to three times, and the water used for washing is distilled water.

11. NF by high-pressure boiling method ３ and CF ４ From the mixed gas CF ４ To remove impurities and obtain an impurity-removed gas, Using the modified adsorbent described in claim 1 or 2, or the modified adsorbent prepared by the preparation method described in any one of claims 3 to 10, NF in the impurity removal gas ３ It selectively adsorbs, detaches, and then NF ３ A method for purifying nitrogen trifluoride, including obtaining a gas.

12. Removing impurities F ２ , HF, N ２ , O ２ , CO, CO ２ , N ２ F ２ , N ２ F ４ and N ２ O from nitrogen trifluoride by the cold trap method to obtain a mixed gas of NF ３ and CF ４ with a content of 260 ppm in step S1; CF in process S1 by high-pressure boiling method ４ Step S2 reduces the concentration to 8 ppm or less, Using modified adsorbents NF ３ It selectively adsorbs and detaches before CF ４ High-purity NF with a content lower than 2 ppm ３ The purification method according to claim 11, further comprising step S3 of obtaining a gas.

13. The purification method according to claim 12, characterized in that the temperature of the cold trap in step S1 is -150°C ± 3°C.

14. The purification method according to claim 12, characterized in that the high-pressure boiling method in step S2 is performed at a pressure of 30 to 50 atmospheric pressure and a temperature of -30 to -55°C.

15. The purification method according to claim 1, characterized in that the adsorption temperature in step S3 is -40 to 10°C.

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