Method for purifying nitrogen trifluoride gas

Abstract

The invention relates to a method for purifying nitrogen trifluoride gas, which comprises the following steps: carrying out cooling treatment on nitrogen trifluoride crude gas to obtain cooled gas and a cooled enriched product; carrying out first cracking treatment on the obtained cooling gas to obtain first cracked gas; the obtained first pyrolysis gas is pressurized and then subjected to defluorination treatment; then carrying out rectification treatment to obtain nitrogen trifluoride gas with the purity of 99.99 vol% or above; hF and N2O in the cooled enriched product are separated; and carrying out second cracking treatment on the obtained N2O, carrying out alkali washing treatment on the obtained second cracking gas, and emptying. According to the method, the NF3 crude gas with the purity of about 50 vol% can be purified to 99.99 vol% or above, meanwhile, substances such as NxFy and OxFy in the NF3 crude gas can be subjected to harmless treatment, HF entrained in the NF3 crude gas is recycled, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of special gases and relates to a method for purifying gas, in particular to a method for purifying nitrogen trifluoride gas. Background Art

[0002] Nitrogen trifluoride (NF3) is a colorless and odorless gas, mainly used in the field of microelectronics industry, and is an excellent plasma etchant and cleaning agent. As an etchant, nitrogen trifluoride has excellent etching speed and selectivity for silicon semiconductor materials; as a cleaning agent, nitrogen trifluoride has the advantages of high cleaning efficiency and no traces. However, as an electronic gas, the microelectronics industry has high requirements for the purity of NF3 (≥99.99%), which makes it difficult to prepare high-purity NF3 gas.

[0003] At present, the industry often adopts the electrolysis method with NH4F-HF as the electrolyte system to prepare NF3 gas. The crude gas contains a lot of impurities, and a series of purification and refining processes are required to obtain high-purity NF3 gas. The crude NF3 gas contains a lot of light and heavy impurities, among which the light impurities include N2, O2, F2 and OF2, and the heavy impurities include HF, N2O, N2F2 and N4F4, and also contains CF4 with a relatively close boiling point.

[0004] CN1450202A provides a process for preparing nitrogen trifluoride gas, which removes NH4F and HF carried by the crude gas from the NF3 electrolytic gas through a low-temperature cooling tower, and then enters an ultra-low temperature cold trap for liquefaction and collection. The cold trap is evacuated to remove low-boiling impurities such as N2 and O2. After a certain amount of impurities are collected, the temperature is increased and the gas is pressed into a crude NH3 gas storage tank for storage. This process does not involve the subsequent purification process of the crude NF3 gas, nor does it involve the collection and treatment of high-boiling HF, N2O, N2F2, N4F4 and other components. Moreover, the enriched N2F2 and N4F4 are energetic materials, and long-term storage has the risk of explosion; the light components discharged contain a small amount of fluorine gas, and no specific subsequent treatment measures are involved.

[0005] CN1450203A discloses a method for refining nitrogen trifluoride gas, which comprises removing impurities such as H2O and HF carried by NF3 crude gas through a HF removal tower; x F y , O x F yThe substances are decomposed into impurities such as F2, N2, and O2; impurities such as N2O are removed in the oxidation tower; oxidative impurities such as F2 are removed in the reduction tower; acidic gases such as HF and NO2 are removed in the alkali washing tower; a large amount of water introduced by the reduction and alkali washing processes is removed in the dehydration tower, and finally enters the distillation tower for purification. However, this refining method does not involve the production and collection of NF3 crude gas, the purification process route is relatively long, and impurities such as water are introduced into the original process gas.

[0006] Therefore, in the prior art, when purifying nitrogen trifluoride gas, there is a problem that the NF3 raw gas is first enriched in the cold trap tank and then heated, which wastes the liquid nitrogen cooling source; the frozen enrichment and storage of energetic by-products such as N2F2 and N4F4 poses a safety hazard of explosion; the acidic gas generated in the high-temperature cracking, oxidation, reduction and other processes needs to be eliminated by alkali washing, and water is introduced into the NF3 raw gas, which requires the addition of a low-temperature dehydration tower, resulting in the complexity of the overall process route. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a method for purifying nitrogen trifluoride gas, which can purify NF3 crude gas with a purity of about 50 vol% to above 99.99 vol%, and can also purify N in the NF3 crude gas. x F y , O x F y The substances are harmlessly treated, and the HF entrained in the NF3 raw gas is recycled and utilized, thus reducing the production cost.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for purifying nitrogen trifluoride gas, the method comprising the following steps:

[0010] (1) The nitrogen trifluoride crude gas is subjected to cooling treatment to obtain a cooling gas and a cooling enrichment;

[0011] (2) The cooling gas obtained in step (1) is subjected to a first cracking treatment to obtain a first cracking gas; the first cracking gas is pressurized and then subjected to a defluorination treatment; and then subjected to a rectification treatment to obtain nitrogen trifluoride gas with a purity of 99.99 vol% or more;

[0012] (3) separating HF and N2O in the cooling concentrate of step (1); subjecting the obtained N2O to a second cracking treatment, and subjecting the obtained second cracking gas to an alkali washing treatment and then to emptying;

[0013] Step (2) and step (3) are performed in no particular order.

[0014] The method provided by the present invention can purify NF3 crude gas with a purity of about 50 vol% to above 99.99 vol%, and at the same time can purify N in the NF3 crude gas. x F y , O x F y The substances are harmlessly treated, and the HF entrained in the NF3 raw gas is recycled and utilized, thus reducing the production cost.

[0015] Specifically, the crude nitrogen trifluoride gas contains N2, HF, O2, N2O, OF2, CF4, N x F y and O x F y After cooling, HF and N2O are separated from the cooling gas in liquid or solid form (cooling enrichment); the cooling gas contains a small amount of N x F y and O x F y , after the first cracking treatment, it is decomposed into gases such as N2, F2 and O2, and after pressurization, it is defluorinated to remove F2; then it is distilled to remove the entrained N2 and O2, so as to obtain nitrogen trifluoride gas with a purity of more than 99.99vol%; the cooling enrichment obtained by the cooling treatment mainly contains HF and N2O, and HF and N2O are separated by controlling the ambient temperature and pressure. HF is recycled for the electrolytic preparation of nitrogen trifluoride, and N2O is decomposed into N2 and O2 by the second cracking treatment, and then the entrained HF is removed by alkaline washing to meet the emptying requirements.

[0016] Among them, the principle of the first cracking treatment includes:

[0017] N x F y →N2+F2;

[0018] O x F y →O2+F2.

[0019] The principles of the second pyrolysis treatment include:

[0020] N2O→N2+O2.

[0021] Preferably, the temperature of the cooling treatment in step (1) is -120°C to -70°C, for example, it can be -120°C, -110°C, -100°C, -90°C, -80°C or -70°C, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably -110°C to -90°C.

[0022] Preferably, the surface pressure of the cooling treatment in step (1) is -1000Pa to 1000Pa, for example, it can be -1000Pa, -800Pa, -500Pa, -300Pa, 0Pa, 200Pa, 300Pa, 500Pa, 800Pa or 1000Pa, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable, preferably -500Pa to 500Pa.

[0023] Preferably, the temperature of the first cracking treatment in step (2) is 120°C to 250°C, for example, it can be 120°C, 150°C, 160°C, 180°C, 200°C, 220°C or 250°C, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable, preferably 160°C to 220°C.

[0024] If the temperature of the first cracking treatment is too high, it will cause the decomposition of NF3 gas; if the temperature of the first cracking treatment is too low, it will cause N x F y The decomposition is insufficient, therefore, as a preferred technical solution, the temperature of the first cracking needs to be 120°C to 250°C.

[0025] Preferably, the surface pressure of the first cracking treatment in step (2) is -1000Pa to 1000Pa, for example, it can be -1000Pa, -800Pa, -500Pa, -300Pa, 0Pa, 200Pa, 300Pa, 500Pa, 800Pa or 1000Pa, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably -500Pa to 500Pa.

[0026] Preferably, the time for the first cracking treatment in step (2) is 2 min to 10 min, for example, 2 min, 3 min, 5 min, 6 min, 8 min or 10 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 3 min to 6 min.

[0027] Preferably, the temperature of the second cracking treatment in step (3) is 350°C to 600°C, for example, it can be 350°C, 380°C, 400°C, 450°C, 480°C, 500°C, 550°C, 580°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 400°C to 500°C.

[0028] Preferably, the surface pressure of the second cracking treatment in step (3) is 0.1 MPa to 0.4 MPa, for example, it can be 0.1 MPa, 0.2 MPa, 0.3 MPa or 0.4 MPa, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 0.1 MPa to 0.2 MPa.

[0029] Preferably, the time for the second cracking treatment in step (3) is 2 min to 10 min, for example, 2 min, 3 min, 4 min, 5 min, 6 min, 8 min or 10 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 3 min to 6 min.

[0030] Preferably, the surface pressure of the defluorination treatment in step (2) is 0.2 MPa to 0.8 MPa, for example, it can be 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa or 0.8 MPa, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 0.4 MPa to 0.6 MPa.

[0031] Preferably, the defluorination agent used in the defluorination treatment in step (2) includes any one of magnesium oxide, calcium oxide, aluminum oxide, tungsten, aluminum or magnesium, or a combination of at least two thereof.

[0032] The defluorination treatment of the present invention uses a defluorination agent to treat F2 under relatively high pressure conditions. Taking the defluorination agent as calcium oxide as an example, the mechanism of the defluorination treatment is:

[0033] F2+CaO→CaF2+O2.

[0034] Taking tungsten as the defluorination agent as an example, the mechanism of defluorination treatment is:

[0035] F2+W→WF6.

[0036] Preferably, the distillation temperature of the distillation treatment in step (2) is -180°C to -80°C, for example, it can be -180°C, -160°C, -150°C, -120°C, -100°C, -90°C or -80°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the surface pressure of the distillation treatment in step (2) is 0.2 MPa to 0.8 MPa, for example, it can be 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa or 0.8 MPa, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 0.4 MPa to 0.6 MPa.

[0038] Preferably, the washing liquid used in the alkaline washing treatment in step (3) is a sodium hydroxide solution and / or a potassium hydroxide solution with a concentration of 5wt% to 25wt%.

[0039] In the present invention, the concentration of the washing liquid used in the alkaline washing treatment is 5wt% to 25wt%, for example, it can be 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt% or 25wt%, but is not limited to the listed values, and the remaining unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the method is carried out in a purification device system; the purification device system comprises a cold trap, a first cracking device, a gas pressurizing device, a defluorination device and a distillation device connected in sequence; the purification device system also comprises an HF collecting device, a second cracking device and an alkali washing device; the cooling enrichment outlet of the cold trap is connected to the HF collecting device; the gas outlet of the HF collecting device is connected to the second cracking device; and the gas outlet of the second cracking device is connected to the alkali washing device.

[0041] Preferably, the alkali washing device is a spray tower structure.

[0042] Preferably, the gas pressurizing device comprises a membrane compressor.

[0043] As a preferred technical solution of the method of the present invention, the method comprises the following steps:

[0044] (1) The crude nitrogen trifluoride gas is passed into a cold trap having an operating temperature of -120°C to -70°C and a gauge pressure of -1000 Pa to 1000 Pa, and cooled to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0045] (2) The cooling gas obtained in step (1) enters a first cracking device and undergoes a first cracking treatment at a temperature of 120° C. to 250° C. and a gauge pressure of −1000 Pa to 1000 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking device is 2 min to 10 min.

[0046] The first cracked gas is pressurized to a gauge pressure of 0.2 MPa to 0.8 MPa by a gas booster, and defluorinated in a defluorination device; the defluorination agent in the defluorination device includes any one of magnesium oxide, calcium oxide, aluminum oxide, tungsten, aluminum or magnesium, or a combination of at least two thereof; and then distilled in a distillation device at a distillation temperature of -180°C to -80°C and a gauge pressure of 0.2 MPa to 0.8 MPa to obtain nitrogen trifluoride gas with a purity of more than 99.99 vol%;

[0047] (3) The cooled enriched product obtained in step (1) enters an HF collecting device. The temperature of the HF collecting device when collecting the material is -120°C to -70°C and the gauge pressure is -1000Pa to 1000Pa. When the HF collecting device is discharged, the temperature is controlled to be -80°C to -40°C and the gauge pressure is 0.1MPa to 0.4MPa. Nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking device for a second cracking treatment. The liquid HF is reused in the nitrogen trifluoride electrolytic cell.

[0048] The N2O gas is subjected to a second cracking treatment in a second cracking device at a temperature of 350°C to 600°C, a gauge pressure of 0.1MPa to 0.4MPa, and a residence time of 2min to 10min to obtain a second cracking gas; the second cracking gas is subjected to an alkali washing treatment in an alkali washing device and then discharged;

[0049] Step (2) and step (3) are performed in no particular order.

[0050] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The method provided by the present invention can purify NF3 crude gas with a purity of about 50 vol% to more than 99.99 vol%, meeting the quality requirements of nitrogen trifluoride products in the national standard GB / T 21287-2021, and can be directly used as an etchant and cleaning agent for high-density integrated circuits in the microelectronics industry; at the same time, N in the NF3 crude gas can be purified to obtain a 99.99 vol% NF3 crude gas. x F y , O x F y The substances are harmlessly treated, and the HF entrained in the NF3 raw gas is recycled and utilized, thus reducing the production cost. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. In order to clearly illustrate the technical solution of the present invention, the components of the crude gas and the purified product gas in the specific embodiments are calculated by volume percentage.

[0054] Example 1

[0055] The main composition of the crude nitrogen trifluoride gas in the specific implementation manner is shown in Table 1. The composition of the crude nitrogen trifluoride gas is only for the purpose of clearly illustrating the technical solution of the present invention and is not regarded as a further limitation of the technical solution.

[0056] Table 1

[0057]

[0058] This embodiment provides a method for purifying nitrogen trifluoride gas, the method comprising the following steps:

[0059] (1) The crude nitrogen trifluoride gas is passed into a cold trap with an operating temperature of -100°C and a gauge pressure of 300 Pa, and subjected to a cooling treatment with a residence time of 3 minutes to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0060] (2) The cooling gas obtained in step (1) enters a first cracking tower and undergoes a first cracking treatment at a temperature of 200° C. and a gauge pressure of 300 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking tower is 3 min. Impurities such as N2F2 and OF2 in the cooling gas are decomposed into N2, F2 and O2.

[0061] The first cracked gas is pressurized to a gauge pressure of 0.4 MPa by a membrane compressor, and defluorinated at a temperature of 25°C and a residence time of 5 minutes in a defluorination tower; the defluorination agent in the defluorination tower is a spherical calcium oxide filler; and then distilled at a distillation temperature of -165°C and a gauge pressure of 0.4 MPa in a distillation tower to obtain nitrogen trifluoride gas;

[0062] Calculated by volume percentage, the main composition of the obtained nitrogen trifluoride gas is shown in Table 2. The product quality meets the quality requirements for nitrogen trifluoride products in the national standard GB / T 21287-2021.

[0063] Table 2

[0064]

[0065] (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -100°C and the gauge pressure is 300 Pa; when the HF collecting device is discharged, the temperature is controlled to be -50°C and the gauge pressure is 0.2 MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking tower for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer;

[0066] The N2O gas is subjected to a second cracking treatment in a second cracking tower at a temperature of 450°C, a gauge pressure of 0.2 MPa and a residence time of 3 min to obtain a second cracking gas; the second cracking gas is subjected to an alkali washing treatment in an alkali washing tower using a KOH solution with a concentration of 20wt%, and then is exhausted; the volume percentage of N2 in the exhausted gas is 82%, the volume percentage of O2 is 18%, and N2O is not detected.

[0067] Example 2

[0068] This embodiment provides a method for purifying nitrogen trifluoride gas. The components of the product crude gas are shown in Table 3 below:

[0069] Table 3

[0070]

[0071] The method comprises the following steps:

[0072] (1) The crude nitrogen trifluoride gas is passed into a cold trap with an operating temperature of -110°C and a gauge pressure of -500 Pa, and subjected to a cooling treatment with a residence time of 3 minutes to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0073] (2) The cooling gas obtained in step (1) enters a first cracking tower and undergoes a first cracking treatment at a temperature of 160° C. and a gauge pressure of −500 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking tower is 3 min. Impurities such as N2F2 and OF2 in the cooling gas are decomposed into N2, F2 and O2.

[0074] The first cracked gas is pressurized to a gauge pressure of 0.2 MPa by a membrane compressor, and defluorinated in a defluorination tower at a temperature of 25°C and a residence time of 5 min; the defluorination agent in the defluorination tower is spherical calcium oxide filler; then, distillation is carried out in a distillation tower at a distillation temperature of -180°C and a gauge pressure of 0.2 MPa to obtain nitrogen trifluoride product gas. The analysis data are shown in Table 4 below. The product quality meets the quality requirements for nitrogen trifluoride products in the national standard GB / T 21287-2021.

[0075] Table 4

[0076]

[0077] (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -110°C and the gauge pressure is -500Pa; when the HF collecting device is discharged, the temperature is controlled to be -50°C and the gauge pressure is 0.1MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking tower for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer;

[0078] The N2O gas was subjected to a second cracking treatment at a temperature of 400°C, a gauge pressure of 0.2 MPa, and a residence time of 3 minutes in the second cracking tower to obtain a second cracking gas; the second cracking gas was subjected to an alkali washing treatment using a 10wt% NaOH solution in an alkali washing tower, and then evacuated. The volume percentage of N2 in the evacuated gas was 85%, the volume percentage of O2 was 15%, and N2O was not detected.

[0079] Example 3

[0080] This embodiment provides a method for purifying nitrogen trifluoride gas. The components of the product crude gas are shown in Table 5 below:

[0081] Table 5

[0082]

[0083] The method comprises the following steps:

[0084] (1) The crude nitrogen trifluoride gas is passed into a cold trap with an operating temperature of -90°C and a gauge pressure of 500 Pa, and subjected to a cooling treatment with a residence time of 6 minutes to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0085] (2) The cooling gas obtained in step (1) enters the first cracking tower and undergoes a first cracking treatment at a temperature of 220° C. and a gauge pressure of 500 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking tower is 6 min. Impurities such as N2F2 and OF2 in the cooling gas are decomposed into N2, F2 and O2.

[0086] The first cracked gas is pressurized to a gauge pressure of 0.6 MPa by a membrane compressor, and defluorinated in a defluorination tower at a temperature of 25°C and a residence time of 5 min; the defluorination agent in the defluorination tower is spherical calcium oxide filler; then, distillation is carried out in a distillation tower at a distillation temperature of -100°C and a gauge pressure of 0.6 MPa to obtain nitrogen trifluoride gas. The analysis data are shown in Table 6 below. The product quality meets the quality requirements for nitrogen trifluoride products in the national standard GB / T 21287-2021.

[0087] Table 6

[0088]

[0089] (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -90°C and the gauge pressure is 500 Pa; when the HF collecting device is discharged, the temperature is controlled to be -60°C and the gauge pressure is 0.2 MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking tower for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer;

[0090] The N2O gas was subjected to a second cracking treatment at a temperature of 500°C, a gauge pressure of 0.2 MPa, and a residence time of 6 minutes in the second cracking tower to obtain a second cracking gas; the second cracking gas was subjected to an alkali washing treatment using a 20wt% NaOH solution in an alkali washing tower, and then evacuated. The volume percentage of N2 in the evacuated gas was 80%, the volume percentage of O2 was 20%, and N2O was not detected.

[0091] Example 4

[0092] This embodiment provides a method for purifying nitrogen trifluoride gas. The components of the product crude gas are shown in Table 7 below:

[0093] Table 7

[0094]

[0095] The method comprises the following steps:

[0096] (1) The crude nitrogen trifluoride gas is passed into a cold trap with an operating temperature of -120°C and a gauge pressure of -1000 Pa, and subjected to a cooling treatment with a residence time of 3 minutes to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0097] (2) The cooling gas obtained in step (1) enters the first cracking tower and undergoes a first cracking treatment at a temperature of 120° C. and a gauge pressure of −1000 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking tower is 2 min. Impurities such as N2F2 and OF2 in the cooling gas are decomposed into N2, F2 and O2.

[0098] The first cracking gas is pressurized to a gauge pressure of 0.2 MPa by a membrane compressor, and defluorination treatment is carried out in a defluorination tower at a temperature of 25°C and a residence time of 5 min; the defluorination agent in the defluorination tower is spherical calcium oxide filler; then, distillation treatment is carried out in a distillation tower at a distillation temperature of -180°C and a gauge pressure of 0.2 MPa to obtain nitrogen trifluoride gas. The analysis data are shown in Table 8 below. Although the purity of NF3 in the table meets the requirements of the national standard GB / T 21287-2021, the contents of components such as O2, CO, and CO2 are high, and the N2F2 content exceeds the standard.

[0099] Table 8

[0100]

[0101] (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -120°C and the gauge pressure is -1000Pa; when the HF collecting device is discharged, the temperature is controlled to be -60°C and the gauge pressure is 0.2MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking tower for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer;

[0102] The N2O gas is subjected to a second cracking treatment at a temperature of 350°C, a gauge pressure of 0.2MPa, and a residence time of 2min in the second cracking tower to obtain a second cracking gas; the second cracking gas is subjected to an alkali washing treatment using a NaOH solution with a concentration of 5wt% in the alkali washing tower, and then evacuated. The volume percentage of N2 in the evacuated gas is 81.5%, the volume percentage of O2 is 15%, and the volume percentage of N2O is 3.5%.

[0103] The data show that the N2O gas is not completely decomposed in the second cracking tower, and there is a small amount of residue.

[0104] Example 5

[0105] This embodiment provides a method for purifying nitrogen trifluoride gas. The components of the product crude gas are shown in Table 9 below:

[0106] Table 9

[0107]

[0108] The method comprises the following steps:

[0109] (1) The crude nitrogen trifluoride gas is passed into a cold trap with an operating temperature of -70°C and a gauge pressure of 1000 Pa, and subjected to a cooling treatment with a residence time of 3 minutes to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap;

[0110] (2) The cooling gas obtained in step (1) enters a first cracking tower and undergoes a first cracking treatment at a temperature of 250° C. and a gauge pressure of 1000 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking tower is 10 min. Impurities such as N2F2 and OF2 in the cooling gas are decomposed into N2, F2 and O2.

[0111] The first cracked gas is pressurized to a gauge pressure of 0.8 MPa by a membrane compressor, and defluorinated in a defluorination tower at a temperature of 25°C and a residence time of 5 min; the defluorination agent in the defluorination tower is spherical calcium oxide filler; then, the gas is distilled in a distillation tower at a distillation temperature of -80°C and a gauge pressure of 0.8 MPa to obtain nitrogen trifluoride gas. The analysis data are shown in Table 10 below. Although the NF3 purity in the table meets the requirements of the national standard GB / T 21287-2021, the N2O content exceeds the standard.

[0112] Table 10

[0113]

[0114] (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -70°C and the gauge pressure is 1000 Pa; when the HF collecting device is discharged, the temperature is controlled to be -60°C and the gauge pressure is 0.2 MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking tower for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer;

[0115] The N2O gas is subjected to a second cracking treatment at a temperature of 600°C, a gauge pressure of 0.2MPa, and a residence time of 10min in the second cracking tower to obtain a second cracking gas; the second cracking gas is subjected to an alkali washing treatment using a 25wt% NaOH solution in the alkali washing tower, and then emptied. The volume percentage of N2 in the evacuated gas is 99.2%, the volume percentage of O2 is 0.8%, and N2O is not detected. The low content of O2 indicates that the amount of N2O gas collected in the HF collection device is small.

[0116] Example 6

[0117] This embodiment provides a method for purifying nitrogen trifluoride gas, which is the same as that of embodiment 1 except that the temperature of the first cracking treatment is 120° C. The concentrations of the components of the crude gas are shown in Table 11, and the concentrations of the components of the product after distillation are shown in Table 12.

[0118] Table 11

[0119]

[0120] Table 12

[0121]

[0122] The volume percentage of N2 in the exhaust gas after the second pyrolysis treatment is 83%, the volume percentage of O2 is 17%, and N2O is not detected.

[0123] It can be seen from Table 12 that although the purity of NF3 in the table meets the requirements of the national standard GB / T 21287-2021, because the temperature of the first pyrolysis treatment is too low, N2F2 is not completely decomposed, the content exceeds the standard, and the product quality is unqualified.

[0124] Example 7

[0125] This embodiment provides a method for purifying nitrogen trifluoride gas, which is the same as that of embodiment 1 except that the temperature of the first cracking treatment is 250° C. The concentrations of the components of the crude gas are shown in Table 13, and the concentrations of the components of the product after distillation are shown in Table 14.

[0126] Table 13

[0127]

[0128] Table 14

[0129]

[0130] The volume percentage of N2 in the exhaust gas after the second pyrolysis treatment is 79%, the volume percentage of O2 is 21%, and N2O is not detected.

[0131] The purity of the product meets the control requirements of the national standard GB / T 21287-2021, but the high temperature of the first-stage pyrolysis may cause NF3 decomposition and a decrease in product yield.

[0132] In the above embodiments, the purity of the obtained nitrogen trifluoride gas is shown in Table 15 based on volume percentage; the volume percentages of N2, O2 and N2O in the exhaust gas are shown in Table 15.

[0133] Table 15

[0134]

[0135] In summary, the method provided by the present invention can purify NF3 crude gas with a purity of about 50 vol% to more than 99.99 vol% within the control range of the optimized parameters, meet the quality requirements of nitrogen trifluoride products in the national standard GB / T21287-2021, and can be directly used as an etchant and cleaning agent for high-density integrated circuits in the microelectronics industry; at the same time, it can purify N in the NF3 crude gas. x F y , O x F y The substances are harmlessly treated, and the HF entrained in the NF3 raw gas is recycled and utilized, thus reducing the production cost.

[0136] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for purifying nitrogen trifluoride gas, characterized in that: The method comprises the following steps: (1) The nitrogen trifluoride crude gas is subjected to cooling treatment to obtain a cooling gas and a cooling enrichment; (2) The cooling gas obtained in step (1) is subjected to a first cracking treatment to obtain a first cracking gas; the first cracking gas is pressurized and then subjected to a defluorination treatment; and then subjected to a rectification treatment to obtain nitrogen trifluoride gas with a purity of 99.99 vol% or more; (3) separating HF and N2O in the cooling concentrate of step (1); subjecting the obtained N2O to a second cracking treatment, and subjecting the obtained second cracking gas to an alkali washing treatment and then to emptying; Step (2) and step (3) are performed in no particular order.

2. The method according to claim 1, characterized in that The temperature of the cooling treatment in step (1) is -120°C to -70°C, preferably -110°C to -90°C; Preferably, the surface pressure of the cooling treatment in step (1) is -1000Pa to 1000Pa, preferably -500Pa to 500Pa.

3. The method according to claim 1 or 2, characterized in that: Step (2) The temperature of the first cracking treatment is 120°C to 250°C, preferably 160°C to 220°C; Preferably, the surface pressure of the first cracking treatment in step (2) is -1000Pa to 1000Pa, preferably -500Pa to 500Pa; Preferably, the time for the first cracking treatment in step (2) is 2 min to 10 min, preferably 3 min to 6 min.

4. The method according to any one of claims 1 to 3, characterized in that: Step (3) The temperature of the second cracking treatment is 350°C to 600°C, preferably 400°C to 500°C; Preferably, the surface pressure of the second cracking treatment in step (3) is 0.1 MPa to 0.4 MPa, preferably 0.1 MPa to 0.2 MPa; Preferably, the time for the second cracking treatment in step (3) is 2 min to 10 min, preferably 3 min to 6 min.

5. The method according to any one of claims 1 to 4, characterized in that: The surface pressure of the defluorination treatment in step (2) is 0.2 MPa to 0.8 MPa; Preferably, the defluorination agent used in the defluorination treatment in step (2) includes any one of magnesium oxide, calcium oxide, aluminum oxide, tungsten, aluminum or magnesium, or a combination of at least two thereof.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The distillation temperature of the distillation treatment in step (2) is -180°C to -80°C; Preferably, the surface pressure of the distillation treatment in step (2) is 0.2 MPa to 0.8 MPa.

7. The method according to any one of claims 1 to 6, characterized in that: The washing liquid used in the alkaline washing treatment in step (3) is a sodium hydroxide solution and / or a potassium hydroxide solution with a concentration of 5wt% to 25wt%.

8. The method according to any one of claims 1 to 7, characterized in that: The method is carried out in a purification device system; The purification device system comprises a cold trap, a first cracking device, a gas pressurizing device, a defluorination device and a distillation device connected in sequence; The purification device system also includes an HF collection device, a second cracking device and an alkali washing device; the cooling enrichment outlet of the cold trap is connected to the HF collection device; the gas outlet of the HF collection device is connected to the second cracking device; The gas outlet of the second cracking device is connected to the alkali washing device.

9. The method according to claim 8, characterized in that The gas pressurizing device comprises a diaphragm compressor.

10. The method according to claim 8 or 9, characterized in that: The method comprises the following steps: (1) The crude nitrogen trifluoride gas is passed into a cold trap having an operating temperature of -120°C to -70°C and a gauge pressure of -1000 Pa to 1000 Pa, and cooled to obtain a cooling enrichment and cooling gas enriched at the bottom of the cold trap; (2) The cooling gas obtained in step (1) enters a first cracking device and undergoes a first cracking treatment at a temperature of 120° C. to 250° C. and a gauge pressure of −1000 Pa to 1000 Pa to obtain a first cracked gas. The residence time of the cooling gas in the first cracking device is 2 min to 10 min. The first cracked gas is pressurized to a gauge pressure of 0.2 MPa to 0.8 MPa by a gas booster, and defluorinated in a defluorination device; the defluorination agent in the defluorination device includes any one of magnesium oxide, calcium oxide, aluminum oxide, tungsten, aluminum or magnesium, or a combination of at least two thereof; and then distilled in a distillation device at a distillation temperature of -180°C to -80°C and a gauge pressure of 0.2 MPa to 0.8 MPa to obtain nitrogen trifluoride gas with a purity of more than 99.99 vol%; (3) The cooled enriched product obtained in step (1) enters an HF collecting device, and the temperature of the HF collecting device when collecting the material is -120°C to -70°C, and the gauge pressure is -1000Pa to 1000Pa; when the HF collecting device is discharged, the temperature is controlled to be -80°C to -40°C, and the gauge pressure is 0.1MPa to 0.4MPa, and nitrogen is used for purging, and the N2O gas in the HF collecting device is blown into a second cracking device for a second cracking treatment, and the liquid HF is reused in the nitrogen trifluoride electrolyzer; The N2O gas is subjected to a second cracking treatment in a second cracking device at a temperature of 350°C to 600°C, a gauge pressure of 0.1MPa to 0.4MPa, and a residence time of 2min to 10min to obtain a second cracking gas; the second cracking gas is subjected to an alkali washing treatment in an alkali washing device and then discharged; Step (2) and step (3) are performed in no particular order.

Images