Method for recovering high-purity nitrogen trifluoride from purified waste gas

Abstract

The invention provides a method for recovering high-purity nitrogen trifluoride from purified waste gas, which comprises the following steps: carrying out gas-liquid separation on crude nitrogen trifluoride gas by cooling, pumping out waste gas, gasifying liquid and carrying out low-pressure rectification, pumping out waste gas subjected to low-pressure rectification, recovering high-purity nitrogen trifluoride liquid from the bottom of the low-pressure rectification tower, and recovering high-purity nitrogen trifluoride liquid from the bottom of the low-pressure rectification tower. The pumped waste gas is pressurized and then introduced into a high-pressure rectifying tower for light component removal treatment, non-toxic and harmless gas impurities are directly emptied at the tower top, and high-purity nitrogen trifluoride liquid is recycled at the tower bottom. According to the method, the NF3 in the evacuated waste gas is recycled through a high-pressure rectification technology, and a high-purity NF3 gas product with the purity being 99.99% or above, the O2 content being smaller than 3 ppm, the N2 content being smaller than 3 ppm and the HF content being smaller than 1 ppm is obtained. According to the method, the technical defects of the original process are overcome, the NF3 gas yield is increased, and the economic benefit is high.

Description

Technical Field

[0001] The present invention relates to the technical field of gas purification, and particularly relates to a method for recovering high-purity nitrogen trifluoride from purified waste gas. Background Art

[0002] Nitrogen trifluoride (NF 3 ) is a colorless and odorless gas at room temperature with strong oxidizing properties. The fluoride ions in it have characteristics such as high etching selectivity and excellent cleaning efficiency. It is one of the most widely used electronic gases globally and is widely used in high-end fields such as integrated circuit manufacturing, high-energy lasers, chemical vapor deposition, and the synthesis of fluorine-containing compounds. However, the above technologies have extremely strict requirements for the purity, dryness, and cleanliness of nitrogen trifluoride. Therefore, a series of complex deep purification processes need to be carried out after synthesis to obtain high-purity nitrogen trifluoride gas with a purity higher than 99.99% and qualified key impurity contents. Therefore, the domestic independent production of high-purity NF 3 electronic gas is of great strategic significance for ensuring national security and enhancing comprehensive national strength.

[0003] Currently, a separation tower is mainly used to liquefy nitrogen trifluoride, and a vacuum system is used to remove some light-component gases. The above light-component gases include N 2 , O 2 and a small amount of NF 3 , and the content of NF 3 is about 2% - 3%; a low-pressure rectification tower is used to remove the remaining light-component gases, including N 2 , O 2 and a small amount of NF 3 , and the content of NF 3 is about 4% - 5%; NF 3 is a greenhouse gas, and direct evacuation will seriously affect the ecology and environment. Currently, the above light-component gases are first pyrolyzed at high temperature, nitrogen trifluoride decomposes into nitrogen and fluorine gas, and then the fluorine gas is removed through a reduction tower and an alkali scrubbing tower, and finally the remaining nitrogen and oxygen are evacuated for treatment; the above process results in the inability to recover nitrogen trifluoride in the purified waste gas, resulting in a decrease in product yield and poor economic benefits. Summary of the Invention

[0004] The present invention overcomes the disadvantages of the existing technology and provides a method for recovering high-purity nitrogen trifluoride from purified waste gas, which can improve the yield of the target product and has good economic benefits.

[0005] The technical solution of the present invention is as follows:

[0006] A method for recovering high-purity nitrogen trifluoride from purified waste gas, comprising the following steps:

[0007] The crude nitrogen trifluoride gas is subjected to gas-liquid separation by cooling, the waste gas is evacuated, the liquid is vaporized for low-pressure rectification, the waste gas from the low-pressure rectification is evacuated, high-purity nitrogen trifluoride liquid is recovered at the bottom of the low-pressure rectification column, and the evacuated waste gas is pressurized and boosted and then introduced into a high-pressure rectification column for light component removal. The non-toxic and harmless gas impurities are directly vented at the top of the column, and high-purity nitrogen trifluoride liquid is recovered at the bottom of the column.

[0008] Preferably, the temperature range for the gas-liquid separation is -190°C to -140°C, and the pressure range is -0.03 to 0 MPa.

[0009] Preferably, the temperature for liquid vaporization is -80°C to -40°C, and the pressure is -0.03 to 0 MPa.

[0010] Preferably, the temperature range of the low-pressure rectification column is -190°C to -80°C, and the pressure range is -0.03 to 0 MPa.

[0011] Preferably, the pressurization and boosting process is achieved by using a booster fan, and the booster fan is a centrifugal fan, a static blade adjustable axial flow fan or a moving blade adjustable axial flow fan.

[0012] Preferably, the booster fan is a static blade adjustable axial flow fan.

[0013] Preferably, the booster fan boosts the pressure to 1 to 4 MPa.

[0014] Preferably, the operating temperature at the top of the high-pressure rectification column is -80°C to -40°C, the operating pressure is 1 to 4 MPa, the number of theoretical plates is 5 to 20, and the reflux ratio is 1 to 20.

[0015] Preferably, the purity of the high-purity nitrogen trifluoride is not less than 99.999%.

[0016] A method for recovering high-purity nitrogen trifluoride from purified waste gas, and the system used includes a separation column. The top outlet of the separation column is connected to the top inlet of a low-pressure rectification column, the top outlet of the low-pressure rectification column is connected to a vacuum pump, the vacuum pump is connected to a booster fan, the booster fan is connected to the inlet of a high-pressure rectification column, an exhaust port is provided at the upper part of the high-pressure rectification column, a discharge port is provided at the lower part of the high-pressure rectification column, the discharge port at the lower part of the high-pressure rectification column is connected to a high-purity nitrogen trifluoride storage tank, the bottom outlet of the low-pressure rectification column is connected to the high-purity nitrogen trifluoride storage tank, and a charging pump is provided on the pipeline connecting the bottom outlet of the low-pressure rectification column and the high-purity nitrogen trifluoride storage tank.

[0017] The separation process of the present invention:

[0018] NF of the present invention 3 After the crude gas enters the separation column, 97% to 98% of the nitrogen trifluoride is liquefied, and some light component impurities (N 2 、O2 , a small amount of NF 3 ) is pumped out through a vacuum pump; the crude gas containing residual light component impurities enters the low-pressure distillation column, and high-purity nitrogen trifluoride product is produced at the bottom of the column, and the remaining light component impurities (N 2 , O 2 , a small amount of NF 3 ) is pumped out through a vacuum pump; the above-mentioned vacuum-pumped gas is boosted by a booster fan and then introduced into a high-pressure distillation column for the recovery of NF 3 . At the top of the distillation column, non-toxic and harmless N 2 , O 2 are directly discharged, and NF 3 liquid is obtained at the bottom of the column. This method can obtain high-purity NF 3 with a purity of more than 99.999%, improving the product yield and economic benefits.

[0019] The method for recovering nitrogen trifluoride from the waste gas of the separation column of the present invention includes the following steps:

[0020] (1) Adjust the separation column to -190°C to -140°C under the conditions to liquefy the NF 3 gas. At this time, the low-boiling substances are still in the gas state and are discharged from the separation column by vacuum pumping to -0.03 to 0 MPa. Then, by slowly heating up to -80°C to -40°C, the NF 3 liquid in the separation column is vaporized and sent to the low-pressure distillation process.

[0021] (2) Adjust the low-pressure distillation column to -190°C to -80°C under the conditions. The low-boiling substances at the top of the column are still in the gas state and are discharged from the low-pressure distillation column by vacuum pumping to -0.03 to 0 MPa; the high-purity nitrogen trifluoride liquid at the bottom of the column enters the high-purity nitrogen trifluoride storage tank for storage;

[0022] (3) Boost the waste gas by a booster fan and enter the high-pressure distillation column to remove N 2 and O 2 and other light component impurities. The operating temperature is -80°C to -40°C, the operating pressure is 1 to 4 MPa, the number of theoretical plates is 5 - 20, and the operating reflux ratio is 1 - 20. The bottom material of the high-pressure distillation column is high-purity NF 3 liquid, which enters the high-purity nitrogen trifluoride storage tank, and the light component impurities at the top of the column are discharged.

[0023] Compared with the prior art, the preparation and purification method provided by the present invention has the following advantages:

[0024] Recover NF 3 in the evacuated waste gas through high-pressure distillation technology to obtain high-purity NF with a purity of more than 99.99% and an O 2 content of less than 3 ppm, an N 2 content of less than 3 ppm, and an HF content of less than 1 ppm 3Gas products.

[0025] The advantage of the present invention is that by performing rectification operations on the purified extraction air, the yield of nitrogen trifluoride is increased, improving economic efficiency. Brief Description of the Drawings

[0026] Figure 1 It is the process flow diagram of the present invention;

[0027] In the drawings, C101 - separation tower, P101 - vacuum pump, P102 - feeding pump, F101 - booster fan, T101 - low-pressure rectification tower, T102 - high-pressure rectification tower, V101 - high-purity nitrogen trifluoride storage tank. Detailed Embodiments

[0028] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments.

[0029] As Figure 1 shown, a system for recovering high-purity nitrogen trifluoride from purified waste gas includes a separation tower C101. The top outlet of the separation tower C101 is connected to the top inlet of a low-pressure rectification tower T101. The top outlet of the low-pressure rectification tower T101 is connected to a vacuum pump P101. The vacuum pump P101 is connected to a booster fan F101. The booster fan F101 is connected to the inlet of a high-pressure rectification tower T102. An exhaust port is provided at the upper part of the high-pressure rectification tower T102, and a discharge port is provided at the lower part of the high-pressure rectification tower T102. The discharge port at the lower part of the high-pressure rectification tower T102 is connected to a high-purity nitrogen trifluoride storage tank V101. The bottom outlet of the low-pressure rectification tower T101 is connected to the high-purity nitrogen trifluoride storage tank V101, and a feeding pump P102 is provided on the pipeline connecting the bottom outlet of the low-pressure rectification tower T101 and the high-purity nitrogen trifluoride storage tank V101. Examples 1 - 4 all adopt this system.

[0030] Example 1

[0031] Adjust the temperature of the separation tower C101 to -160 °C. After the NF 3 gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge some light component impurities. Among them, the N 2 content is 60.2%, the O 2 content is 37.5%, and the NF 3 content is 2.3%. Adjust the temperature of the separation tower C101 to -80 °C. After the NF 3 liquid is vaporized, it enters the low-pressure rectification tower T101.

[0032] Adjust the temperature of the low-pressure rectification tower T101 to -120 °C. Wait for the NF 3After the gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge the remaining light component impurities, among which the content of N 2 is 58.2%, and the content of O 2 is 37%, and the content of NF 3 is 4.8%.

[0033] Boost the light component gas to 1 MPa through the booster fan F101 and introduce it into the high-pressure rectification tower T102 for rectification treatment. The bottom temperature of the tower is -153 °C, the top temperature of the tower is -78 °C, the operating pressure is 1 MPa, the number of theoretical plates is 10, the operating reflux ratio is 2, and the light component impurities such as N 2 and O 2 are removed from the top of the tower. NF 3 with a purity of 99.9994% is obtained at the bottom of the tower, the nitrogen content is 3 ppm, and the oxygen content is 2 ppm.

[0034] Example 2

[0035] Adjust the temperature of the separation tower C101 to -165 °C. After the NF 3 gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge the high-boiling-point gas, among which the content of N 2 is 55.7%, and the content of O 2 is 42.1%, and the content of NF 3 is 2.2%. Adjust the temperature of the separation tower C101 to -40 °C. After the NF 3 liquid vaporizes, it enters the low-pressure rectification tower T101.

[0036] Adjust the temperature of the low-pressure rectification tower T101 to -124 °C. After the NF 3 gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge the remaining light component impurities, among which the content of N 2 is 58.2%, and the content of O 2 is 37.3%, and the content of NF 3 is 4.5%.

[0037] Boost the light component gas to 4 MPa through the booster fan F101 and introduce it into the high-pressure rectification tower T102 for rectification treatment. The bottom temperature of the tower is -132 °C, the top temperature of the tower is -43 °C, the operating pressure is 4 MPa, the number of theoretical plates is 10, the operating reflux ratio is 15, and the light component impurities such as N 2 and O 2 are removed from the top of the tower. NF 3 with a purity of 99.9998% is obtained at the bottom of the tower, the nitrogen content is 1 ppm, and the oxygen content is 1 ppm.

[0038] Example 3

[0039] Adjust the temperature of the separation column C101 to -140 °C and wait for NF 3 After the gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge part of the light component impurities. Among them, the content of N 2 is 65.4%, and the content of O 2 is 33.5%, and the content of NF 3 is 1.1%. Adjust the temperature of the separation column C101 to -60 °C and wait for NF 3 After the liquid is vaporized, it enters the low-pressure rectification column T101.

[0040] Adjust the temperature of the low-pressure rectification column T101 to -190 °C and wait for NF 3 After the gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.02 MPa, and discharge the remaining light component impurities. Among them, the content of N 2 is 58.3%, and the content of O 2 is 37.6%, and the content of NF 3 is 4.1%.

[0041] Boost the pressure of the light component gas to 2 MPa through the booster fan F101 and introduce it into the high-pressure rectification column T102 for rectification treatment. The bottom temperature is -147 °C, the top temperature is -66 °C, the operating pressure is 2 MPa, the number of theoretical plates is 5, the operating reflux ratio is 1, and N 2 and O 2 and other light component impurities are removed from the top, and NF 3 with a purity of 99.999%, a nitrogen content of 3 ppm, and an oxygen content of 3 ppm is obtained at the bottom.

[0042] Example 4

[0043] Adjust the temperature of the separation column C101 to -190 °C and wait for NF 3 After the gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.03 MPa, and discharge part of the light component impurities. Among them, the content of N 2 is 58.2%, and the content of O 2 is 38.8%, and the content of NF 3 is 3.0%. Adjust the temperature of the separation column C101 to -50 °C and wait for NF 3 After the liquid is vaporized, it enters the low-pressure rectification column T101.

[0044] Adjust the temperature of the low-pressure rectification column T101 to -81 °C and wait for NF 3 After the gas is liquefied, start the vacuum pump P101 to reduce the system pressure to -0.03 MPa, and discharge the remaining light component impurities. Among them, the content of N 2 is 57.2%, and the content of O 2 is 35.5%, and the content of NF 3 is 7.0%.

[0045] The light-component gas is pressurized to 1 MPa by the booster fan F101 and fed into the high-pressure rectification column T102 for rectification. The bottom temperature of the column is -164 °C, the top temperature is -60 °C, the operating pressure is 1 MPa, the number of theoretical plates is 20, the operating reflux ratio is 20, and N 2 , O 2 and other light-component impurities are removed from the top of the column, and NF 3 with a purity of 99.999%, a nitrogen content of 3 ppm, and an oxygen content of 2 ppm is obtained at the bottom of the column.

[0046] The above is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as the content of the technical solution of the present invention is not departed from, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for recovering high-purity nitrogen trifluoride from purified waste gas, characterized in that: The following steps are involved: The crude nitrogen trifluoride gas is separated into gas and liquid by cooling, the waste gas is pumped away, the liquid is gasified for low-pressure distillation, the waste gas of the low-pressure distillation is pumped away, and high-purity nitrogen trifluoride liquid is recovered at the bottom of the low-pressure distillation tower. The pumped away waste gas is pressurized and then passed into a high-pressure distillation tower for light removal treatment, non-toxic and harmless gas impurities are directly discharged at the top of the tower, and high-purity nitrogen trifluoride liquid is recovered at the bottom of the tower.

2. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The gas-liquid separation temperature range is -190°C to -140°C, and the pressure range is -0.03 to 0 MPa.

3. A method for recovering high-purity nitrogen trifluoride gas from purified waste gas according to claim 1, characterized in that: The liquid vaporization temperature is -80℃~-40℃, and the pressure is -0.03~0MPa.

4. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The temperature range of the low-pressure distillation tower is -190°C to -80°C, and the pressure range is -0.03 to 0 MPa.

5. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The boosting and pressure increasing process is realized by using a boosting fan, and the boosting fan is a centrifugal fan, an axial flow fan with adjustable stationary blades, or an axial flow fan with adjustable moving blades.

6. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 5, characterized in that: The booster fan is an axial flow fan with adjustable stator blades.

7. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 6, characterized in that: The booster fan increases the pressure to 1-4 MPa.

8. The method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The operating temperature of the top of the high-pressure distillation tower is -80°C to -40°C, the operating pressure is 1 to 4MPa, the number of theoretical plates is 5 to 20, and the reflux ratio is 1 to 20.

9. A method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The purity of the high-purity nitrogen trifluoride is not less than 99.999%.

10. The method for recovering high-purity nitrogen trifluoride from purified waste gas according to claim 1, characterized in that: The adopted system includes a separation tower, the top outlet of the separation tower is connected with the top inlet of a low-pressure distillation tower, the top outlet of the low-pressure distillation tower is connected with a vacuum pump, the vacuum pump is connected with a booster fan, the booster fan is connected with an inlet of a high-pressure distillation tower, an exhaust port is arranged at the top of the high-pressure distillation tower, a discharge port is arranged at the bottom of the high-pressure distillation tower, the discharge port at the bottom of the high-pressure distillation tower is connected with a high-purity nitrogen trifluoride storage tank, the bottom outlet of the low-pressure distillation tower is connected with the high-purity nitrogen trifluoride storage tank, and a feed pump is arranged on the pipeline connecting the bottom outlet of the low-pressure distillation tower and the high-purity nitrogen trifluoride storage tank.

Images