Modified adsorbent, preparation method therefor, and nitrogen trifluoride purification process

Abstract

A nitrogen trifluoride purification process and a method for synthesizing an employed modified adsorbent. The nitrogen trifluoride purification process comprises the following steps: step S1, using a cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 having a content of 260 ppm; step S2, using a high-pressure boiling method to reduce the concentration of CF4 in step S1 to below 3-8 ppm; and step S3, using a modified adsorbent to selectively adsorb NF3, and after desorption, obtaining a high-purity NF3 gas having a CF4 content of less than 2 ppm. According to the nitrogen trifluoride purification process, the impurity gases such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O are removed by using the cold trap method, and then the CF4 impurity gas is removed by using the high-pressure boiling method and the modified adsorbent; upon the two steps of CF4 removal, the content of CF4 in the produced high-purity NF3 gas can be made less than 2 ppm.

Description

Modified adsorbent, preparation method thereof and nitrogen trifluoride purification process

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on June 12, 2023, with application number 202310688334.1 and invention name “A nitrogen trifluoride purification process and a method for synthesizing the modified adsorbent used therein”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of chemical industry, in particular to a modified adsorbent, a preparation method thereof and a nitrogen trifluoride purification process. Background Art

[0003] Nitrogen trifluoride (NF) is an excellent plasma etchant and cleaning agent primarily used in the microelectronics industry, particularly for semiconductor materials such as silicon and silicon nitride, where it exhibits exceptional etching speed and selectivity. As a gaseous cleaning agent, NF is highly efficient and leaves no residue. In recent years, with the rapid development of the global semiconductor, liquid crystal display, and photovoltaic industries, the demand for high-purity NF has skyrocketed, and its purification process has garnered significant attention.

[0004] Currently, nitrogen trifluoride gas is mainly produced by chemical synthesis or electrolysis, but these two methods can only produce crude NF3 gas, which contains high levels of impurity gases such as F2, HF, CF4, N2, O2, CO, CO2, N2F2, N2F4, and N2O. Based on the properties of the above impurity gases, F2, HF, N2, O2, CO, CO2, N2F2, N2F4, and N2O can be removed by cold trapping, cryogenic distillation, absorption, adsorption, and other methods. However, due to the very similar physical properties of NF3 and CF4, such as molecular size (NF3: CF4: ), boiling point (NF3: -129°C, CF4: -128°C), and heat of adsorption (dipole moment, NF3: 0.235D, CF4: 0D), so the above methods cannot effectively separate the two, requiring special processing to obtain high-purity NF3 gas. High-pressure boiling can reduce the CF4 gas content to approximately 10 ppm, but this still fails to meet the purity requirements of nitrogen trifluoride in certain industries. Adsorbents (such as activated alumina, activated carbon, and synthetic zeolites) can also effectively separate NF3 and CF4 gases. However, activated alumina and activated carbon are ineffective and costly as adsorbents. Using synthetic zeolites, or molecular sieves, as selective adsorbents can produce NF3 gas with purities exceeding 99.99%. However, existing methods for preparing synthetic zeolites require a long production cycle and generate large amounts of difficult-to-treat wastewater, making them difficult to meet economic and environmental requirements.

[0005] CN101014400A discloses a method for refining nitrogen trifluoride gas using alkaline earth metal-exchanged zeolites. The method comprises first performing ion exchange on zeolite 3A, 4A, or 5A with an appropriate amount of alkaline earth metals (beryllium, magnesium, calcium, strontium, or barium) to change the pore size of the zeolite. A gas mixture of NF and CF is then introduced into a bed of alkaline earth metal-exchanged zeolite 3A, 4A, or 5A mixed with an inert gas. The bed selectively adsorbs the NF gas and, after desorption, produces high-purity NF gas. The CF gas removal rate can reach 99.6%. However, the synthetic zeolite obtained by this method requires heat treatment at 150 to 600°C for 0.5 to 100 hours, resulting in low efficiency and difficulty in controlling the exchange metal content (fluctuation range is 20 to 95 wt%), making it unsuitable for large-scale promotion and use.

[0006] CN106276828B discloses a method for purifying nitrogen trifluoride by adsorption. The method uses a 5A molecular sieve compounded with tetradecylcerium phosphate as a carrier raw material. Then, zinc dialkyldithiophosphate and 3-fluoro-nitrogen-methylaniline are loaded onto 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. The crude nitrogen trifluoride is then adsorbed in an adsorption column containing the adsorbent. The resulting nitrogen trifluoride can have a purity of up to 99.99%. However, the adsorbent synthesis time is long and it produces a large amount of wastewater that is difficult to treat, making it difficult to meet economic and environmental requirements.

[0007] Currently available nitrogen trifluoride purification methods and adsorbents have certain drawbacks, such as poor purification results, long adsorbent preparation cycles, and the generation of large amounts of difficult-to-treat wastewater during the synthesis process. Therefore, the development of a nitrogen trifluoride purification process and adsorbent with a short cycle time, excellent purification results, and environmental friendliness is crucial.

[0008] Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a modified adsorbent, a preparation method thereof and a nitrogen trifluoride purification process in view of the above-mentioned deficiencies in the prior art.

[0010] The present invention adopts the following technical solutions:

[0011] The present application provides a modified adsorbent comprising zeolite and a nickel layer composited on the surface of the zeolite;

[0012] The average pore size of the modified adsorbent is

[0013] In some specific implementations, the average pore size of the modified adsorbent is

[0014] In some specific implementations, the particle size of the zeolite is 10-50 mesh.

[0015] The present application also provides a method for preparing the modified adsorbent, comprising:

[0016] The zeolite is subjected to nickel plating treatment to obtain modified zeolite.

[0017] In some specific implementations, the nickel plating solution in the nickel plating process includes:

[0018] 20-60 g / L nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate and 10-45 g / L sodium hypophosphite.

[0019] In some specific implementations, the nickel plating treatment is performed at a temperature of 20 to 90° C. and for a time of 5 to 60 seconds.

[0020] In some specific implementations, the nickel plating process includes the following steps:

[0021] Step 301: dissolving 20-60 g / L nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate, and 10-45 g / L sodium hypophosphite in distilled water at room temperature, and adding aqueous ammonia to the mixture to adjust the pH value to obtain a nickel plating solution;

[0022] Step 302: Using a constant temperature magnetic stirrer to control the plating solution temperature to 20-90° C. and to achieve the flow of the nickel plating solution;

[0023] Step 303: add 25-100 g / L zeolite to the nickel plating solution prepared in step 302, adjust the speed of the constant temperature magnetic stirrer to 100-1000 r / min, suspend the zeolite in the nickel plating solution, and after sedimentation for 5-60 seconds, filter, wash and dry to obtain a modified adsorbent.

[0024] In some specific implementations, the pH value of the nickel plating solution is 7-9.

[0025] In some specific implementations, the zeolite is commercially available zeolite 5A, which is spherical and has a particle size of 10 to 50 mesh.

[0026] In some specific implementations, the filtration and washing processes in step 303 are both performed 2 to 3 times, and the water used for washing is distilled water.

[0027] The present application also provides a method for purifying nitrogen trifluoride, comprising:

[0028] High-pressure boiling method is used to remove CF4 from the mixed gas of NF3 and CF4 to obtain impurity-free gas;

[0029] The modified adsorbent described in the above technical solution or the modified adsorbent prepared by the preparation method described in the above technical solution is used to selectively adsorb NF3 in the impurity removal gas, and NF3 gas is obtained after desorption.

[0030] In some specific implementations, before the high-pressure boiling method is used, the nitrogen trifluoride is treated by a cold trap method to remove impurities such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O.

[0031] The present invention provides a nitrogen trifluoride purification process, which comprises the following steps:

[0032] Step S1, using a cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm;

[0033] Step S2: using a high-pressure boiling method to reduce the CF4 concentration in step S1 to below 3-8 ppm;

[0034] Step S3: selectively adsorb NF3 using a modified adsorbent, and obtain high-purity NF3 gas with a CF4 content of less than 2 ppm after desorption.

[0035] The temperature of the cold trap in step S1 of the process of the present invention is -150°C ± 3°C.

[0036] In step S2 of the present invention, the gas pressure of the high-pressure boiling method is 30 to 50 atmospheres, and the temperature is -30 to -55°C.

[0037] The adsorption temperature in step S3 of the process of the present invention is -40 to 10°C.

[0038] The modified adsorbent in the process of the present invention is obtained by nickel plating zeolite.

[0039] The present invention provides a method for synthesizing a modified adsorbent for purifying nitrogen trifluoride, comprising the following steps:

[0040] Step 301: dissolving 20-60 g / L nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate, and 10-45 g / L sodium hypophosphite in distilled water at room temperature, and adding aqueous ammonia to the mixture to adjust the pH value to obtain a nickel plating solution;

[0041] Step 302: Using a constant temperature magnetic stirrer to control the plating solution temperature to 20-90° C. and to achieve the flow of the nickel plating solution;

[0042] Step 303: add 25-100 g / L zeolite to the nickel plating solution prepared in step 302, adjust the speed of the constant temperature magnetic stirrer to 100-1000 r / min, suspend the zeolite in the nickel plating solution, and after sedimentation for 5-60 seconds, filter, wash and dry to obtain the modified adsorbent.

[0043] The pH value of the nickel plating solution in the method of the present invention is 7-9.

[0044] The zeolite used in the method of the present invention is commercially available zeolite 5A, which is spherical and has a particle size of 10 to 50 meshes.

[0045] The filtration and washing processes in step 303 of the method of the present invention are both performed 2 to 3 times, and the water used for washing is distilled water.

[0046] The positive effects of the present invention are as follows: (1) The nitrogen trifluoride purification process of the present invention removes impurity gases such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O through a conventional cold trap method, and then uses a high-pressure boiling method and a modified adsorbent to remove the CF4 impurity gas. After a two-step CF4 removal process, the CF4 content in the prepared high-purity NF3 gas can be reduced to less than 2ppm; compared with the prior art (CF4 content is higher than 10ppm), the present invention can reduce the CF4 content even further.

[0047] (2) The present invention utilizes a chemical nickel plating method to deposit amorphous nickel on the zeolite. The amorphous nickel is preferentially deposited at the hollow zeolite mouth, reducing the pore size of the zeolite. This allows the pore size of zeolite 5A to be adjusted, so that the modified adsorbent can selectively adsorb NF3 gas, while CF4 cannot pass through the zeolite pore and is discharged from the end of the adsorption tower. The modified adsorbent synthesis method of the present invention is simple, controllable and has a short cycle, and the deposition process only takes 5 to 60 seconds. DETAILED DESCRIPTION

[0048] The modified adsorbent, its preparation method and nitrogen trifluoride purification process provided by the present invention are further described in detail below with reference to the examples.

[0049] Example 1

[0050] At room temperature, 30 g / L nickel sulfate hexahydrate, 40 g / L ammonium chloride, 30 g / L sodium citrate, and 15 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0051] The plating solution temperature was controlled at 60°C using a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

[0052] 35 g of zeolite 5A with a particle size of 20 mesh purchased on the market was added to the above-mentioned nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 500 r / min to suspend the zeolite in the nickel plating solution. After sedimentation for 10 seconds, the zeolite was filtered, washed and dried to obtain a modified adsorbent. The filtration and washing processes were both performed twice, and the water used for washing was distilled water.

[0053] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0054] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0055] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0056] Step S2, performing a high-pressure boiling process at 35 atmospheres and -35°C to reduce the CF4 concentration in step S1 to 6 ppm;

[0057] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -40°C. The CF4 content in the purified gas collected after desorption is 1 ppm.

[0058] Example 2

[0059] At room temperature, 35 g / L nickel sulfate hexahydrate, 45 g / L ammonium chloride, 30 g / L sodium citrate, and 25 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0060] The plating solution temperature was controlled at 65°C using a constant temperature magnetic stirrer and the nickel plating solution was allowed to flow;

[0061] 50 g of commercially available zeolite 5A with a particle size of 30 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 800 r / min to suspend the zeolite in the nickel plating solution. After settling for 15 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were repeated three times, and the water used for washing was distilled water.

[0062] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0063] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0064] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0065] Step S2, performing a high-pressure boiling process at 40 atmospheres and -45°C to reduce the CF4 concentration in step S1 to 4 ppm;

[0066] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -30°C. The CF4 content in the purified gas collected after desorption is 0.5 ppm.

[0067] Example 3

[0068] At room temperature, 45 g / L nickel sulfate hexahydrate, 45 g / L ammonium chloride, 30 g / L sodium citrate, and 20 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 9 to obtain 1 L of nickel plating solution.

[0069] Step 302: Using a constant temperature magnetic stirrer, the plating solution temperature is controlled to be 55° C., and the nickel plating solution is allowed to flow;

[0070] Step 303: 75 g of commercially available zeolite 5A with a particle size of 40 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After settling for 45 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed twice, and the water used for washing was distilled water.

[0071] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0072] The modified adsorbent is used to purify nitrogen trifluoride, and the process comprises the following steps:

[0073] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0074] Step S2, performing a high-pressure boiling process at 45 atmospheres and -50°C to reduce the CF4 concentration in step S1 to 4 ppm;

[0075] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -40°C. The CF4 content in the purified gas collected after desorption is 1.4 ppm.

[0076] Example 4

[0077] At room temperature, 50 g / L nickel sulfate hexahydrate, 35 g / L ammonium chloride, 40 g / L sodium citrate, and 35 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0078] The plating solution temperature was controlled at 65°C using a constant temperature magnetic stirrer and the nickel plating solution was allowed to flow;

[0079] 45 g of commercially available zeolite 5A with a particle size of 20 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 800 r / min to suspend the zeolite in the nickel plating solution. After settling for 15 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed three times, and the water used for washing was distilled water.

[0080] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0081] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0082] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0083] Step S2, performing a high-pressure boiling process at 50 atmospheres and -50°C to reduce the CF4 concentration in step S1 to 6 ppm;

[0084] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -20°C. The CF4 content in the purified gas collected after desorption is 0.8 ppm.

[0085] Example 5

[0086] At room temperature, 30 g / L nickel sulfate hexahydrate, 30 g / L ammonium chloride, 25 g / L sodium citrate, and 20 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0087] The plating solution temperature was controlled at 60°C using a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

[0088] 50 g of commercially available zeolite 5A with a particle size of 10 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After settling for 20 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed three times, and the water used for washing was distilled water.

[0089] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0090] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0091] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0092] Step S2, performing a high-pressure boiling process at 45 atmospheres and -55°C to reduce the CF4 concentration in step S1 to 2 ppm;

[0093] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -40°C. The CF4 content in the purified gas collected after desorption is 0.2 ppm.

[0094] Example 6

[0095] At room temperature, 30 g / L nickel sulfate hexahydrate, 30 g / L ammonium chloride, 25 g / L sodium citrate, and 25 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0096] The plating solution temperature was controlled at 65°C using a constant temperature magnetic stirrer and the nickel plating solution was allowed to flow;

[0097] 40 g of commercially available zeolite 5A with a particle size of 40 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 600 r / min to suspend the zeolite in the nickel plating solution. After settling for 15 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed three times, and the water used for washing was distilled water.

[0098] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0099] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0100] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0101] Step S2, performing a high-pressure boiling process at 45 atmospheres and -35°C to reduce the CF4 concentration in step S1 to 4 ppm;

[0102] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -35°C. The CF4 content in the purified gas collected after desorption is 0.3 ppm.

[0103] Example 7

[0104] At room temperature, 50 g / L nickel sulfate hexahydrate, 35 g / L ammonium chloride, 45 g / L sodium citrate, and 40 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8.5 to obtain 1 L of nickel plating solution.

[0105] The plating solution temperature was controlled at 90°C using a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

[0106] 100 g of commercially available zeolite 5A with a particle size of 60 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 300 r / min to suspend the zeolite in the nickel plating solution. After sedimentation for 55 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed twice, and the water used for washing was distilled water.

[0107] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0108] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0109] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0110] Step S2, performing a high-pressure boiling process at 30 atmospheres and -40°C to reduce the CF4 concentration in step S1 to 4 ppm;

[0111] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -10°C. The CF4 content in the purified gas collected after desorption is 1.9 ppm.

[0112] Example 8

[0113] At room temperature, 25 g / L nickel sulfate hexahydrate, 25 g / L ammonium chloride, 20 g / L sodium citrate, and 25 g / L sodium hypophosphite were dissolved in distilled water, and aqueous ammonia was added to the mixture to adjust the pH to 8 to obtain 1 L of nickel plating solution.

[0114] The plating solution temperature was controlled at 90°C using a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

[0115] 35 g of commercially available zeolite 5A with a particle size of 30 mesh was added to the nickel plating solution. The speed of the constant temperature magnetic stirrer was adjusted to 1000 r / min to suspend the zeolite in the nickel plating solution. After settling for 15 seconds, the zeolite was filtered, washed, and dried to obtain the modified adsorbent. The filtration and washing processes were performed three times, and the water used for washing was distilled water.

[0116] The modified adsorbent was characterized and the average pore size of the modified adsorbent was

[0117] Purification of nitrogen trifluoride using the modified adsorbent comprises the following steps:

[0118] Step S1, using a conventional cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm, and the cold trap temperature is -150°C;

[0119] Step S2, performing a high-pressure boiling process at 35 atmospheres and -55°C to reduce the CF4 concentration in step S1 to 5 ppm;

[0120] Step S3: Selectively adsorb NF3 using a modified adsorbent. The adsorption process is carried out at -35°C. The CF4 content in the purified gas collected after desorption is 0.6 ppm.

[0121] The results of testing the CF4 content in high-purity nitrogen trifluoride obtained by Examples 1 to 8 and the conventional cold trap method and high-pressure boiling method are shown in Table 1.

[0122] Table 1

[0123] According to the above embodiments and Table 1, the nitrogen trifluoride purification process of the present invention removes impurity gases such as F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O by a conventional cold trap method, and then uses a high-pressure boiling method and a modified adsorbent to remove the CF4 impurity gas. After the two-step CF4 removal process, the CF4 content in the prepared high-purity NF3 gas can be reduced to less than 2ppm; compared with the prior art (CF4 content is greater than 10ppm), the present invention can reduce the CF4 content even further.

[0124] The nickel plating solution of the present invention deposits amorphous nickel on the zeolite. The amorphous nickel is deposited at the hollow zeolite mouth, reducing the pore size of the zeolite. In this way, the amorphous nickel in the nickel plating solution can be controlled to adjust the pore size of the zeolite 5A, so that the modified adsorbent can selectively adsorb NF3 gas, while CF4 cannot pass through the zeolite pore and is discharged from the adsorption tower. The modified adsorbent synthesis method of the present invention is simple, controllable and has a short cycle. The deposition process only takes 5 to 60 seconds.

[0125] The above description is only a specific embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A modified adsorbent, characterized in that: The invention comprises zeolite and a nickel layer composited on the surface of the zeolite; the average pore size of the modified adsorbent is 2. The modified adsorbent according to claim 1, characterized in that The average pore size of the modified adsorbent is 3. The modified adsorbent according to claim 1 or 2, characterized in that: The particle size of the zeolite is 10-50 meshes.

4. A method for preparing a modified adsorbent, characterized in that: include: The zeolite is subjected to nickel plating treatment to obtain modified zeolite.

5. The preparation method according to claim 4, characterized in that: The nickel plating solution in the nickel plating process comprises: 20-60 g / L nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate and 10-45 g / L 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 time of 5 to 60 seconds.

7. The preparation method according to claim 4, characterized in that: The steps include: Step 301, at room temperature, dissolving 20-60 g / L nickel sulfate hexahydrate, 20-60 g / L ammonium chloride, 20-60 g / L sodium citrate and 10-45 g / L sodium hypophosphite in distilled water, adding ammonia water to the mixture to adjust the pH value, and obtaining a nickel plating solution; Step 302, using a constant temperature magnetic stirrer to control the plating solution temperature to 20-90° C. and achieve the flow of the nickel plating solution; Step 303, adding 25-100 g / L zeolite to the nickel plating solution prepared in step 302, adjusting the speed of the constant temperature magnetic stirrer to 100-1000 r / min, suspending the zeolite in the nickel plating solution, and after sedimentation for 5-60 seconds, filtering, washing and drying to obtain a modified adsorbent.

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

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 and has a particle size of 10 to 50 meshes.

10. The preparation method according to claim 7, characterized in that: The filtration and washing process in step 303 are both performed 2 to 3 times, and the water used for washing is distilled water.

11. A method for purifying nitrogen trifluoride, comprising: High pressure boiling method is used to remove CF4 from the mixed gas of NF3 and CF4 to obtain impurity-free gas; The modified adsorbent according to any one of claims 1 to 2 or the modified adsorbent prepared by the preparation method according to any one of claims 3 to 10 is used to selectively adsorb NF3 in the impurity removal gas, and NF3 gas is obtained after desorption.

12. The purification method according to claim 11, characterized in that Use the following steps: Step S1, using a cold trap method to remove F2, HF, N2, O2, CO, CO2, N2F2, N2F4 and N2O impurities in nitrogen trifluoride to obtain a mixed gas of NF3 and CF4 with a content of 260 ppm; Step S2, reducing the CF4 concentration in step S1 to below 8 ppm by high pressure boiling method; Step S3: selectively adsorb NF3 using a modified adsorbent, and obtain high-purity NF3 gas with a CF4 content of less than 2 ppm after desorption.

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: In step S2, the gas pressure of the high pressure boiling method is 30 to 50 atmospheres, and the temperature is -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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