WO2024255163A1 - Modified adsorbent, preparation method therefor, and nitrogen trifluoride purification process - Google Patents

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

This application claims priority to a 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

The 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

Nitrogen trifluoride is an excellent plasma etchant and cleaning agent, mainly used in the microelectronics industry, especially for semiconductor materials such as silicon and silicon nitride, it has excellent etching speed and selectivity; and as a gas cleaning agent, nitrogen trifluoride has high cleaning efficiency and leaves no traces. In recent years, with the rapid development of the global semiconductor industry, liquid crystal display industry and photovoltaic industry, the demand for high-purity nitrogen trifluoride has risen sharply, and its purification process has attracted much attention.

At present, nitrogen trifluoride gas is mainly prepared by chemical synthesis or electrolysis, but these two methods can only obtain crude NF ₃ gas, which contains high content of impurity gases, such as F ₂ , HF, CF ₄ , N ₂ , O ₂ , CO, CO ₂ , N ₂ F ₂ , N ₂ F ₄ and N ₂ O. Based on the properties of the above impurity gases, F ₂ , HF, N ₂ , O ₂ , CO, CO ₂ , N ₂ F ₂ , N ₂ F ₄ and N ₂ O can be removed by cold trap method, low temperature distillation method, absorption, adsorption and other methods. However, since the physical properties of NF ₃ and CF ₄ are quite similar, such as molecular size (NF ₃ : _CF4 : ), boiling point (NF ₃ : -129°C, CF ₄ : -128°C) and adsorption heat (dipole moment, NF ₃ : 0.235D, CF ₄ : 0D), etc. Therefore, the above method cannot effectively separate the two, and special means must be used to obtain high-purity NF ₃ gas. The high-pressure boiling method can reduce the CF ₄ gas content to about 10ppm, but it is still difficult to meet the purity requirements of special industries for nitrogen trifluoride. Adsorbents (activated alumina, activated carbon, synthetic zeolite, etc.) can also be used to effectively separate NF ₃ and CF ₄ gases. Among them, activated alumina and activated carbon as adsorbents have poor effects and high costs, while synthetic zeolite, that is, molecular sieves as selective adsorbents can obtain NF ₃ gas with a purity of more than 99.99%. However, the existing technology for preparing synthetic zeolites takes a long time and produces a large amount of wastewater that is difficult to treat, which is difficult to meet the requirements of economy and environmental protection.

CN101014400A discloses a method for refining nitrogen trifluoride gas by using zeolite exchanged with alkaline earth metals. First, an appropriate amount of alkaline earth metals (beryllium, magnesium, calcium, strontium, barium) are used to perform ion exchange on zeolite 3A, 4A or 5A to change the pore size of the zeolite. Then, a gas mixture of _NF3 and _CF4 is mixed with an inert gas and introduced into a bed of zeolite 3A, 4A or 5A exchanged with alkaline earth metals. The bed selectively adsorbs _NF3 gas and then desorbs to obtain high-purity _NF3 gas. The removal rate of _CF4 gas can reach 99.6%. However, the synthetic zeolite obtained by this method needs to be heat-treated at 150-600°C for 0.5-100h, which has low efficiency and difficult to control the exchange metal content (fluctuation range is 20-95wt%), which is not conducive to large-scale promotion and use.

CN106276828B discloses a method for purifying nitrogen trifluoride by adsorption, which uses 5A molecular sieve and tetradecyl cerium phosphate as carrier raw materials, then loads dialkyl dithiophosphate zinc and 3-fluoro-nitrogen-methylaniline on the carrier by liquid phase sedimentation method, reacts at 40-80°C for 10-20h, separates and dries the product to obtain an adsorbent, and the crude nitrogen trifluoride is adsorbed in an adsorption column equipped with the adsorbent, and the purity of the obtained nitrogen trifluoride can reach up to 99.99%. However, the adsorbent takes a long time to synthesize and will produce a large amount of wastewater that is difficult to treat, which is difficult to meet the requirements of economy and environmental protection.

The currently disclosed nitrogen trifluoride purification methods and adsorbents have certain defects, such as poor purification effect, long adsorbent preparation cycle, and a large amount of difficult-to-treat wastewater generated during the synthesis process. Therefore, it is very important to develop a nitrogen trifluoride purification process with a short cycle, good purification effect and environmental protection and the adsorbent used therein.

Summary of the invention

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.

The present invention adopts the following technical solution:

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

The average pore size of the modified adsorbent is

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

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

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

The zeolite is subjected to nickel plating treatment to obtain modified zeolite.

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

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

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

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

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.

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

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

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

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

High pressure boiling method is used to remove CF ₄ from the mixed gas of NF ₃ and CF ₄ to obtain impurity-free gas;

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 NF ₃ in the impurity removal gas, and NF ₃ gas is obtained after desorption.

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 .

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

Step S1, using a cold trap method to remove F ₂ , HF, N ₂ , O ₂ , CO, CO ₂ , N ₂ F ₂ , N ₂ F ₄ and N ₂ O impurities in nitrogen trifluoride to obtain a mixed gas of NF ₃ and CF ₄ with a content of 260 ppm;

Step S2, reducing the _CF4 concentration in step S1 to below 3-8 ppm by high pressure boiling method;

Step S3: selectively adsorb NF ₃ using a modified adsorbent, and obtain high-purity NF ₃ gas with a CF ₄ content of less than 2 ppm after desorption.

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

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.

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

The modified adsorbent of the process of the present invention is obtained by nickel plating zeolite.

The present invention discloses a method for synthesizing a modified adsorbent for purifying nitrogen trifluoride, which comprises the following steps:

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 the modified adsorbent.

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

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.

The filtration and washing process 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.

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 by a conventional cold trap method, and then uses a high-pressure boiling method and a modified adsorbent to remove _CF4 impurity gas. After two steps of _CF4 removal, 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 reduces the _CF4 content.

(2) The present invention utilizes a chemical nickel plating method to deposit amorphous nickel on zeolite. Amorphous nickel is preferentially deposited at the hollow zeolite mouth, reducing the pore size of the zeolite. In this way, the pore size of zeolite 5A can be adjusted, so that the modified adsorbent can selectively adsorb _NF3 gas, while _CF4 cannot pass through the pore of the zeolite 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

The modified adsorbent, preparation method and nitrogen trifluoride purification method provided by the present invention are described below in conjunction with the embodiments. The process is described in further detail.

Example 1

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 60°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

35 g of zeolite 5A with a particle size of 20 mesh purchased on the market was added to the above nickel plating solution, and 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 modified adsorbent was obtained by filtration, washing and drying. The filtration and washing processes were both repeated twice, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -40°C. The CF ₄ content in the purified gas collected after desorption is 1 ppm.

Example 2

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 65°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

50 g of zeolite 5A with a particle size of 30 mesh purchased on the market was added to the nickel plating solution, and the speed of the constant temperature magnetic stirrer was adjusted to 800 r/min to suspend the zeolite in the nickel plating solution. After sedimentation for 15 seconds, the zeolite was filtered, washed and dried to obtain the modified adsorbent. The filtration and washing processes were performed 3 times, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -30°C. The CF ₄ content in the purified gas collected after desorption is 0.5 ppm.

Example 3

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 ammonia water was added to the mixture to adjust the pH value to 9 to obtain 1 L nickel plating solution;

Step 302, using a constant temperature magnetic stirrer to adjust the plating solution temperature to 55°C and allow the nickel plating solution to flow;

Step 303, adding 75g of zeolite 5A with a particle size of 40 mesh purchased on the market to the above nickel plating solution, adjusting the speed of the constant temperature magnetic stirrer to 600r/min, so that the zeolite is suspended in the nickel plating solution, and after sedimentation for 45s, filtering, washing and drying are performed to obtain the modified adsorbent, and the filtering and washing processes are both performed twice, and the water used for washing is all distilled water;

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

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

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -40°C. The CF ₄ content in the purified gas collected after desorption is 1.4 ppm.

Example 4

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 65°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

45 g of zeolite 5A with a particle size of 20 mesh purchased on the market was added to the nickel plating solution, and the speed of the constant temperature magnetic stirrer was adjusted to 800 r/min to suspend the zeolite in the nickel plating solution. After sedimentation for 15 seconds, the zeolite was filtered, washed and dried to obtain the modified adsorbent. The filtration and washing processes were performed 3 times, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -20°C. The CF ₄ content in the purified gas collected after desorption is 0.8 ppm.

Example 5

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 60°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

50 g of zeolite 5A with a particle size of 10 mesh purchased on the market was added to the nickel plating solution, and the speed of the constant temperature magnetic stirrer was adjusted to 600 r/min to suspend the zeolite in the nickel plating solution. After sedimentation for 20 seconds, the zeolite was filtered, washed and dried to obtain the modified adsorbent. The filtration and washing processes were performed 3 times, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: Use modified adsorbent to selectively adsorb NF ₃ . The adsorption process is carried out at -40°C. The CF ₄ content in the purified gas collected after absorption was 0.2 ppm.

Example 6

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 65°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

40 g of zeolite 5A with a particle size of 40 mesh purchased on the market was added to the nickel plating solution, and the speed of the constant temperature magnetic stirrer was adjusted to 600 r/min to suspend the zeolite in the nickel plating solution. After sedimentation for 15 seconds, the zeolite was filtered, washed and dried to obtain the modified adsorbent. The filtration and washing processes were performed 3 times, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -35°C. The CF ₄ content in the purified gas collected after desorption is 0.3 ppm.

Example 7

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 ammonia water was added to the mixture to adjust the pH value to 8.5 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 90°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

100 g of zeolite 5A with a particle size of 60 mesh purchased on the market was added to the nickel plating solution, and 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.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -10°C. The CF ₄ content in the purified gas collected after desorption is 1.9 ppm.

Example 8

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 ammonia water was added to the mixture to adjust the pH value to 8 to obtain 1 L nickel plating solution;

The temperature of the plating solution was regulated to 90°C by a constant temperature magnetic stirrer, and the nickel plating solution was allowed to flow;

35 g of zeolite 5A with a particle size of 30 mesh purchased on the market was added to the nickel plating solution, and the speed of the constant temperature magnetic stirrer was adjusted to 1000 r/min to suspend the zeolite in the nickel plating solution. After sedimentation for 15 seconds, the zeolite was filtered, washed and dried to obtain the modified adsorbent. The filtration and washing processes were performed 3 times, and the water used for washing was distilled water.

The modified adsorbent is characterized, and the average pore size of the modified adsorbent is

The modified adsorbent is used to purify nitrogen trifluoride, comprising the following steps:

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 260ppm, the cold trap temperature is -150℃ _;

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;

Step S3: selectively adsorb NF ₃ using a modified adsorbent. The adsorption process is carried out at -35°C. The CF ₄ content in the purified gas collected after desorption is 0.6 ppm.

The results of testing the _CF4 content in high-purity nitrogen trifluoride purified by Examples 1 to 8, conventional cold trap method and high-pressure boiling method are shown in Table 1.

Table 1

Through the above examples 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 conventional cold trap method , and} then uses high pressure boiling method and modified adsorbent to remove _CF4 impurity gas. After two steps of _CF4 removal process, the _CF4 content in the prepared high-purity _NF3 gas can be made lower than 2ppm; compared with the prior art ( _CF4 content is higher than 10ppm), the present invention makes the _CF4 content lower.

The nickel plating solution of the present invention deposits amorphous nickel on the zeolite, and the amorphous nickel is deposited at the hollow zeolite mouth to reduce the pore size of the zeolite. In this way, the amorphous nickel of 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 pore of the zeolite and is discharged from 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.

The above description is only a specific implementation 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 embodiments according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims (15)

A modified adsorbent, characterized in that it comprises zeolite and a nickel layer composited on the surface of the zeolite; the average pore size of the modified adsorbent is The modified adsorbent according to claim 1, characterized in that the average pore size of the modified adsorbent is The modified adsorbent according to claim 1 or 2, characterized in that the particle size of the zeolite is 10 to 50 meshes. A method for preparing a modified adsorbent, characterized by comprising: The zeolite is subjected to nickel plating treatment to obtain modified zeolite. 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. The preparation method according to claim 5 is characterized in that the temperature of the nickel plating treatment is 20 to 90° C. and the time is 5 to 60 seconds. The preparation method according to claim 4, characterized in that it comprises the following steps: 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. 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 to 9. The preparation method according to any one of claims 5 to 7, characterized in that the zeolite is commercially available zeolite 5A, spherical, and has a particle size of 10 to 50 meshes. The preparation method according to claim 7, characterized in that the filtration and The cleaning process is performed 2 to 3 times, and the water used for cleaning is distilled water. A method for purifying nitrogen trifluoride, comprising: High pressure boiling method is used to remove CF ₄ from the mixed gas of NF ₃ and CF ₄ 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 NF ₃ in the impurity removal gas, and NF ₃ gas is obtained after desorption. The purification method according to claim 11, characterized in that the following steps are adopted: Step S1, using a cold trap method to remove F ₂ , HF, N ₂ , O ₂ , CO, CO ₂ , N ₂ F ₂ , N ₂ F ₄ and N ₂ O impurities in nitrogen trifluoride to obtain a mixed gas of NF ₃ and CF ₄ 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 NF ₃ using a modified adsorbent, and obtain high-purity NF ₃ gas with a CF ₄ content of less than 2 ppm after desorption. The purification method according to claim 12, characterized in that the cold trap temperature in step S1 is -150°C ± 3°C. The purification method according to claim 12 is 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. The purification method according to claim 1, characterized in that the adsorption temperature in step S3 is -40 to 10°C.