Method and device for purifying crude nitrogen trifluoride gas

Abstract

The invention relates to a method and a device for purifying crude nitrogen trifluoride gas, and belongs to the technical field of nitrogen trifluoride gas purification, and the method comprises the following steps: sequentially carrying out preheating, cracking, hydrogen fluoride washing, reduction, alkali washing, water ring pressurization, water removal and secondary rectification on nitrogen trifluoride electrolytic gas prepared by adopting an electrolytic method. According to the method, the high-purity nitrogen trifluoride gas with the purity of 99.995 vol% or above can be obtained, and the method is safe to operate, low in cooling medium consumption and low in energy consumption; the device comprises a preheater, a cracking tower, a buffer tank, a hydrogen fluoride washing tower, a reduction tower, an alkaline washing tower, a water ring compressor, water removal equipment, a rectification system and a filling system, and the method and the device are simple in structure, high in operation safety, strong in operability, low in operation cost, suitable for large-scale production and wide in application prospect.

Description

Technical Field

[0001] This invention relates to a method and apparatus for purifying crude nitrogen trifluoride gas, belonging to the field of nitrogen trifluoride gas purification technology. Background Technology

[0002] Nitrogen trifluoride (NiF) gas is widely used in the electronics industry as an etching agent and cleaning agent. In recent years, domestic semiconductor companies have accelerated their research and development and production, leading to a year-on-year increase in the demand for NiF. NiF gas can be prepared by two methods: direct chemical reaction and electrolysis. The electrolysis method uses the electrolysis of a molten NH4F-x hydrogen fluoride mixture, which can produce crude NiF gas in just one step. Furthermore, the equipment used has low production costs and high product yield, making it widely used in the industry.

[0003] Chinese Patent ZL202110364068.8 discloses a method and apparatus for preparing high-purity nitrogen trifluoride gas. The method is safe to operate, has low preparation cost, and can effectively remove impurity gases from nitrogen trifluoride electrolysis gas. By optimizing the process conditions, high-purity nitrogen trifluoride gas with a purity of over 99.995 vol% can be obtained. In addition, the apparatus has a simple structure, high operational safety, strong operability, and low operating cost, making it suitable for large-scale production and with broad application prospects. However, this method has obvious disadvantages: (1) The electrolytic gas has to go through two stages of cracking, and the working temperature of the cracking tower is relatively high. The electrolytic gas needs to be heated when it enters each stage of equipment. On the other hand, the temperature of the crude gas after exiting the main cracking tower is very high, and it needs to be cooled once or twice. Heating and cooling involve a large energy consumption; (2) After the room temperature crude gas enters the dehydration tower, it is refrigerated and dehydrated. The outlet is low temperature crude gas. After being pressurized by the diaphragm compressor, it is sent to the distillation tower. During this process, the crude gas changes from room temperature to low temperature and then to gas above room temperature before entering the distillation tower. The repeated cooling of the crude gas causes a waste of energy; (3) Refrigeration and dehydration will cause frequent switching of the first-stage dehydration tower. Summary of the Invention

[0004] This invention provides a method and apparatus for purifying crude nitrogen trifluoride gas. The method is safe to operate, has low operating costs, and can effectively remove impurities from nitrogen trifluoride electrolytic gas to obtain high-purity nitrogen trifluoride gas with a purity of over 99.995 vol%. The apparatus has a simple structure, high operational safety, strong operability, low operating costs, is suitable for large-scale production, and has broad application prospects.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for purifying crude nitrogen trifluoride gas includes the following steps:

[0007] S1. Nitrogen trifluoride electrolytic gas is prepared by electrolysis;

[0008] S2 and nitrogen trifluoride electrolytic gas sequentially pass through a preheater and a cracking tower to remove polyfluorides (N). x F y ), thus obtaining intermediate A;

[0009] S3. Intermediate A enters the buffer tank and, after temperature and pressure buffering, yields intermediate B.

[0010] S4. Intermediate B enters the 2nd to 5th stage hydrogen fluoride scrubbing tower to remove most of the hydrogen fluoride and some fluorine gas, yielding intermediate C.

[0011] S5. Intermediate C enters the reduction tower to remove oxygen difluoride and fluorine gas, and then enters the alkaline washing tower to remove carbon dioxide and hydrogen fluoride, yielding intermediate D.

[0012] S6 and intermediate D are subjected to 2 to 4 stages of dehydration equipment to remove water vapor, and then undergo two stages of distillation to obtain high-purity nitrogen trifluoride gas.

[0013] Preferably, the volume content of nitrogen trifluoride in the nitrogen trifluoride electrolytic gas in step S1 is 40% to 70%;

[0014] In step S2, the gas at the outlet of the cracking tower is preheated with electrolytic gas, and the temperature of the gas at the outlet of the cracking tower after heat exchange is reduced to 90-190℃.

[0015] The tube-side medium of the preheater is trifluoride electrolytic gas, the inlet temperature of the preheater is 0-40℃, and the outlet temperature is 60-180℃; the shell-side medium of the preheater is electrolytic gas treated by the cracking tower, the inlet temperature is 150-350℃, and the outlet temperature is 90-190℃; the tube-side and shell-side pressures of the preheater are both -0.01-0MPa.

[0016] Preferably, in step S3, the pressure of the buffer tank is -0.01 to 0 MPa; the temperature of the buffer tank is 20 to 60°C.

[0017] Preferably, in step S4, the intake air volumetric flow rate is the spray volumetric flow rate (m³ / s). 3 20 to 50 times that of / h);

[0018] The hydrogen fluoride scrubbing tower uses a spray method for washing, with an operating temperature of 10~60℃ and an operating pressure of -0.03~-0.01MPa;

[0019] Hydrofluoric acid byproducts with a mass concentration of 35% to 55% were obtained from the first-stage hydrogen fluoride scrubbing tower;

[0020] After the first-stage hydrogen fluoride scrubbing tower removes the hydrofluoric acid byproduct, low-concentration hydrofluoric acid is transferred from the subsequent stages of the hydrogen fluoride scrubbing tower to the previous stage, and finally water is added to the final stage of the hydrogen fluoride scrubbing tower.

[0021] Because the first-stage hydrogen fluoride scrubber absorbs the most hydrogen fluoride, and the concentration decreases sequentially in subsequent stages, after the first stage removes the hydrofluoric acid, a portion of the hydrofluoric acid from the second-stage scrubber (with the next lowest concentration) is transferred back to the first stage, and so on. The final-stage scrubber transfers the lowest concentration hydrofluoric acid to the stage preceding it. After this transfer, the amount of low-concentration hydrofluoric acid in the final-stage scrubber decreases, lowering the liquid level in the equipment. To ensure stable operation of the production line and to allow for the subsequent transfer of low-concentration hydrofluoric acid to the preceding stage, water must be added. Adding water to the normal operating level corresponds to the volume of water added for the volume of hydrofluoric acid transferred out.

[0022] Preferably, in step S5, a reducing aqueous solution is used for reduction in the reduction tower, the reduction temperature is 10–50℃, and the reduction pressure is -0.05–-0.03 MPa; the reducing aqueous solution is a sodium thiosulfate aqueous solution or a sodium sulfite aqueous solution, and the concentration of the reducing aqueous solution is 1–4 mol / L; the air inlet flow rate in the reduction tower is the reducing aqueous solution spray rate (m³ / s). 3 80 to 120 times that of / h);

[0023] Alkaline washing is performed in the alkaline washing tower using an alkaline aqueous solution. The washing temperature is 10–50℃, and the washing pressure is -0.07–-0.05 MPa. The alkaline aqueous solution is either potassium hydroxide or sodium hydroxide, with a concentration of 2–5 mol / L. The air inlet flow rate in the alkaline washing tower is equal to the alkaline aqueous solution spray rate (m³ / s). 3 80 to 120 times that of / h).

[0024] Preferably, in step S6, before the intermediate D enters the dehydration equipment, the crude gas is first pressurized from -0.07 to -0.05 MPa to 0 to 0.05 MPa by a first-stage water ring compressor; and the crude gas is pressurized from 0 to 0.05 MPa to 0.1 to 1.0 MPa by a second-stage water ring compressor.

[0025] The first-stage dehydration equipment uses ethylene glycol solution at -40 to -10℃, calcium chloride aqueous solution at -40 to -10℃, or nitrogen refrigerant at -170 to -110℃ for cooling, with an outlet temperature of 0 to 20℃; most of the water vapor is condensed into liquid water and continuously discharged from the equipment; the second to fourth-stage dehydration equipment uses nitrogen at -170 to -110℃ for cooling, and the residual moisture in the crude nitrogen trifluoride gas is removed by freezing, with an outlet temperature of -110 to -60℃;

[0026] The two-stage cryogenic distillation process removes light component impurities and heavy component impurities respectively. The distillation column temperature for both stages is -140 to -80℃, and the pressure is 0.1 to 1.0 MPa.

[0027] Preferably, the purity of high-purity nitrogen trifluoride gas is 99.995 vol% or higher.

[0028] An apparatus for purifying crude nitrogen trifluoride gas includes a preheater, a cracking tower, a buffer tank, a hydrogen fluoride scrubbing tower, a reduction tower, an alkaline scrubbing tower, a water ring compressor, a dehydration device, a distillation system, and a filling system, which are connected in sequence via pipelines; the water ring compressor includes a primary water ring compressor and a secondary water ring compressor connected in sequence.

[0029] A first regulating valve is installed on the pipeline between the buffer tank and the hydrogen fluoride scrubbing tower, and a second regulating valve is installed on the pipeline between the alkaline scrubbing tower and the first-stage water ring compressor; these are used to stably control the pressure of the buffer tank and the pressure at the inlet of the first-stage water ring compressor.

[0030] The hydrogen fluoride scrubbing tower is equipped with a hydrogen fluoride circulation pump, the reduction tower is equipped with a reduction tower circulation pump, and the alkaline scrubbing tower is equipped with an alkaline scrubbing tower circulation pump.

[0031] Furthermore, the hydrogen fluoride scrubbing tower has 2 to 5 stages, the alkali scrubbing tower has 2 stages, the water removal equipment has 2 to 4 stages, and the distillation system includes a two-stage distillation tower.

[0032] Furthermore, a first flow meter is installed on the pipeline between the primary water ring compressor and the secondary water ring compressor, and a second flow meter is installed on the pipeline between the distillation system and the filling system.

[0033] This invention includes at least one of the following beneficial effects:

[0034] (1) Using the high-temperature crude gas from the cracking tower outlet to preheat the electrolytic gas, the height of the low-temperature section of the total cracking tower can be reduced by increasing the temperature of the electrolytic gas at the inlet of the total cracking tower, thereby increasing the nitrogen content. x F y The thermal decomposition effect is improved, while the heating power of the cracking tower is reduced, thus achieving energy saving. In addition, the heat exchange of the preheater reduces the temperature of the gas produced by the total cracking tower entering the subsequent equipment, making the production process more gentle.

[0035] (2) The method of using a 2- to 5-stage hydrogen fluoride scrubbing tower can maximize the absorption of hydrogen fluoride and fluorine in the electrolytic gas (crude gas) after the cracking tower treatment, and obtain hydrofluoric acid by-product.

[0036] (3) A two-stage water ring compressor is used in series as the power source for gas flow in the entire process system. With the cooperation of the regulating valve, large pressure fluctuations in the entire process system are avoided, and the gas flows smoothly.

[0037] (4) By pressurizing and then removing water, the pressure of the crude gas is increased, thereby improving the heat exchange efficiency. On the other hand, by first cooling the crude gas to condense the water vapor into liquid water and continuously discharge it, and then using the method of freezing to remove water, the frequent switching of the dewatering equipment to defrost the ice when only using freezing to remove water can be avoided, thus improving production efficiency.

[0038] (5) The crude gas after being dehydrated by freezing directly enters the distillation system instead of being pressurized by a compressor (which raises the gas temperature to room temperature or even higher) before entering the distillation system. This can reduce the amount of liquid nitrogen used in the distillation column and reduce operating costs.

[0039] In summary, the method described in this invention, through the rational design of removal methods and steps for different impurities and the optimization of process conditions for removing different impurities, can effectively remove impurity gases from nitrogen trifluoride electrolytic gas, obtaining high-purity nitrogen trifluoride gas with a purity of over 99.995 vol%. Moreover, this method is safe to operate and has low energy consumption and cooling medium consumption. Furthermore, the device described in this invention has a simple structure, high operational safety, strong operability, and low operating costs, making it suitable for large-scale production and possessing broad application prospects. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the device used in the embodiment.

[0041] Figure 2 This is a schematic diagram of the device used in Comparative Example 1.

[0042] In the diagram, 1-preheater, 2-cracking tower, 3-buffer tank, 4-hydrogen fluoride scrubbing tower, 5-hydrofluoric acid circulating pump, 6-reduction tower, 7-reduction tower circulating pump, 8-alkali scrubbing tower, 9-alkali scrubbing tower circulating pump, 10-first-stage water ring compressor, 11-second-stage water ring compressor, 12-water removal equipment, 13-distillation system, 14-filling system, 15-first regulating valve, 16-second regulating valve, 17-first flow meter, 18-second flow meter, 19-first regulating valve. 20-Second regulating valve, 21-Third regulating valve, 22-Fourth regulating valve, 23-Electrolytic cell, 24-First-stage cracking tower, 25-Second-stage cracking tower, 26-First buffer tank, 27-Cooler, 28-Second buffer tank, 29-Water washing tower, 30-Reduction tower II, 31-Alkali washing tower II, 32-Water ring compressor II, 33-Water removal tower, 34-Diaphragm compressor, 35-Flow meter, 36-First-stage distillation tower, 37-Second-stage distillation tower, 38-Second filling system. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments. Unless otherwise specified, the methods described are conventional methods, and the raw materials described are obtainable from publicly available commercial sources.

[0044] Device Examples

[0045] like Figure 1 As shown, an apparatus for purifying crude nitrogen trifluoride gas includes a preheater 1, a cracking tower 2, a buffer tank 3, a hydrogen fluoride scrubbing tower 4, a reduction tower 6, an alkaline scrubbing tower 8, a water ring compressor, a dehydration device 12, a distillation system 13, and a filling system 14, which are connected in sequence by pipelines; the water ring compressor includes a primary water ring compressor 10 and a secondary water ring compressor 11 connected in sequence.

[0046] A first regulating valve 15 is installed on the pipeline between the buffer tank 3 and the hydrogen fluoride washing tower 4, and a second regulating valve 16 is installed on the pipeline between the alkaline washing tower 8 and the first-stage water ring compressor 10; a first flow meter 17 is installed on the pipeline between the first-stage water ring compressor 10 and the second-stage water ring compressor 11, and a second flow meter 18 is also installed on the pipeline between the distillation system 13 and the filling system 14.

[0047] The hydrogen fluoride washing tower 4 is equipped with a hydrogen fluoride circulation pump 5, the reduction tower 6 is equipped with a reduction tower circulation pump 7, and the alkaline washing tower 8 is equipped with an alkaline washing tower circulation pump 9.

[0048] The hydrogen fluoride scrubbing tower 4 has 2 to 5 stages, the alkali scrubbing tower 8 has 2 stages, the water removal equipment 12 has 2 to 4 stages, and the distillation system 13 includes a two-stage distillation tower. This apparatus is used in the method embodiment.

[0049] Method Example 1

[0050] A method for purifying crude nitrogen trifluoride gas includes the following steps:

[0051] (1) Nitrogen trifluoride electrolytic gas was prepared by electrolysis of molten NH4F-x hydrogen fluoride system; the components of nitrogen trifluoride electrolytic gas were analyzed by gas chromatography, and the results are detailed in Table 1.

[0052] Table 1

[0053]

[0054] (2) The electrolytic gas passes sequentially through preheater 1 and cracking tower 2 to remove N. x F y The gas at the outlet of the cracking tower was cooled to obtain intermediate A. The compositional analysis results of intermediate A are detailed in Table 2.

[0055] The tube inlet temperature of preheater 1 is 25℃, the pyrolysis temperature and pyrolysis pressure of pyrolysis tower 2 are 250℃ and -0.005MPa, respectively, and the outlet gas temperature of pyrolysis tower 2 is reduced to 140℃ after heat exchange in the preheater.

[0056] Table 2

[0057]

[0058] (3) Intermediate A enters the buffer tank and is buffered by temperature and pressure to obtain intermediate B;

[0059] The temperature of the crude gas after passing through the buffer tank is reduced to 40℃; the pressure of the buffer tank is controlled by an automatic valve installed on the outlet pipe of the buffer tank, which is -0.005MPa.

[0060] (4) After the intermediate B passes through the buffer tank 3 to buffer the temperature and pressure, it enters the 3-stage hydrogen fluoride scrubbing tower 4, where most of the hydrogen fluoride and some fluorine gas are removed by spray washing, and intermediate C is obtained.

[0061] The hydrogen fluoride scrubbing tower operates at a temperature of 40℃, an operating pressure of -0.02MPa, an inlet air flow rate of 510kg / h, and a spray liquid flow rate of 20m³. 3 / h, the spray liquid is hydrofluoric acid from the bottom of the hydrogen fluoride scrubbing tower after being pressurized by the circulating pump, and the hydrofluoric acid byproduct with a purity of 50% is obtained from the bottom of the first-stage hydrogen fluoride scrubbing tower;

[0062] (5) Intermediate C enters reduction tower 6 and is reduced in 2 mol / L Na2S2O3 aqueous solution to remove oxygen difluoride and fluorine gas. Then it enters alkaline washing tower 8 and is alkaline washed in 3 mol / L KOH aqueous solution to remove CO2 and hydrogen fluoride, to obtain intermediate D.

[0063] The reduction temperature and pressure in reduction tower 6 are 30℃ and -0.04MPa, respectively; the alkali washing temperature and pressure in alkali washing tower 8 are 35℃ and -0.06MPa, respectively.

[0064] (6) The intermediate D, which is operating under negative pressure, is first converted to positive pressure by the first-stage water ring compressor 10, and then enters the second-stage water ring compressor for further pressurization. Then it enters the dewatering equipment 12 to remove water vapor from the intermediate D, and then passes through the distillation system 13 to finally purify and obtain nitrogen trifluoride product. Finally, the product is filled through the filling system 14.

[0065] The inlet pressure of the first-stage water ring compressor 10 is -0.06MPa, the outlet pressure is 0.03MPa, and the outlet pressure of the second-stage water ring compressor 11 is 0.4MPa.

[0066] The dewatering equipment 12 consists of three stages connected in series. The first-stage dewatering tower is cooled by a -20°C ethylene glycol solution, and the outlet crude nitrogen trifluoride gas temperature is 5°C. The second and third-stage dewatering towers are both cooled by -170°C cold nitrogen gas from the distillation system, and the outlet crude nitrogen trifluoride gas temperature is -80°C.

[0067] The product after passing through distillation system 13 was subjected to component analysis, and the results are detailed in Table 3. The yield, liquid nitrogen consumption, and electrical energy consumption of high-purity nitrogen trifluoride gas with a purity greater than 99.995 vol% obtained using the purification method described in this embodiment are detailed in Table 4.

[0068] Table 3

[0069]

[0070] Table 4

[0071]

[0072] Method Example 2

[0073] A method for purifying crude nitrogen trifluoride gas includes the following steps:

[0074] (1) Use the electrolytic gas from step (1) of Example 1 as the raw material for the purification system;

[0075] (2) The electrolytic gas passes sequentially through preheater 1 and cracking tower 2 to remove N. x F y The gas exiting the cracking tower was precooled to obtain intermediate A. The compositional analysis results of intermediate product A are detailed in Table 2.

[0076] The tube inlet temperature of preheater 1 is 25℃, the pyrolysis temperature and pyrolysis pressure of pyrolysis tower 2 are 150℃ and -0.01MPa, respectively, and the outlet gas temperature of pyrolysis tower 2 is reduced to 60℃ after heat exchange in the preheater.

[0077] Table 5

[0078]

[0079] (3) Intermediate A enters the buffer tank and is buffered by temperature and pressure to obtain intermediate B;

[0080] The temperature of the crude gas after passing through the buffer tank is reduced to 30℃; the pressure of the buffer tank is controlled by an automatic valve installed on the outlet pipe of the buffer tank, which is -0.01MPa.

[0081] (4) After the intermediate B passes through the buffer tank 3 to buffer the temperature and pressure, it enters the 3-stage hydrogen fluoride scrubbing tower 4, where most of the hydrogen fluoride and some fluorine gas are removed by spray washing, and intermediate C is obtained.

[0082] The hydrogen fluoride scrubbing tower operates at a temperature of 10℃, an operating pressure of -0.03MPa, an inlet air flow rate of 510kg / h, and a spray liquid flow rate of 20m³. 3 / h, the spray liquid is hydrofluoric acid from the bottom of the hydrogen fluoride scrubbing tower after being pressurized by the circulating pump, and the hydrofluoric acid byproduct with a purity of 55% is obtained from the bottom of the first-stage hydrogen fluoride scrubbing tower;

[0083] (6) Intermediate C enters reduction tower 6 and is reduced in 2 mol / L Na2S2O3 aqueous solution to remove oxygen difluoride and fluorine gas. Then it enters alkaline washing tower 8 and is alkaline washed in 3 mol / L KOH aqueous solution to remove CO2 and hydrogen fluoride, to obtain intermediate D.

[0084] The reduction temperature and pressure in reduction tower 6 are 10℃ and -0.05MPa, respectively; the alkali washing temperature and pressure in alkali washing tower 8 are 10℃ and -0.07MPa, respectively.

[0085] (5) The intermediate D, which is operating under negative pressure, is first converted to positive pressure by the first-stage water ring compressor 10, and then enters the second-stage water ring compressor for further pressurization. Then it enters the dewatering equipment 15 to remove water vapor from the intermediate D, and then passes through the distillation system 13 to finally purify and obtain nitrogen trifluoride product. Finally, the product is filled through the filling system 14.

[0086] The inlet pressure of the first-stage water ring compressor 10 is -0.07 MPa, the outlet pressure is 0 MPa, and the outlet pressure of the second-stage water ring compressor 11 is 0.1 MPa.

[0087] The dewatering equipment 12 consists of three stages connected in series. The first-stage dewatering tower is cooled by a calcium chloride solution at -40°C, and the outlet crude nitrogen trifluoride gas has a temperature of 1°C. The second and third-stage dewatering towers are both cooled by cold nitrogen gas at -170°C from the distillation system, and the outlet crude nitrogen trifluoride gas has a temperature of -110°C.

[0088] The product after passing through distillation system 13 was subjected to component analysis, and the results are detailed in Table 3. The yield, storage volume, liquid nitrogen consumption, and electrical energy consumption of high-purity nitrogen trifluoride gas with a purity greater than 99.995 vol% obtained using the purification method described in this embodiment are detailed in Table 4.

[0089] Table 6

[0090]

[0091] Table 7

[0092] Production kg / h Hydrofluoric acid production kg / h <![CDATA[Nitrogen liquid consumption m 3 / h]]> Electricity consumption (kW) 422 25 2.57 95

[0093] Method Example 3

[0094] A method for purifying crude nitrogen trifluoride gas includes the following steps:

[0095] (1) Use the electrolytic gas from step (1) of Example 1 as the raw material for the purification system;

[0096] (2) The electrolytic gas passes sequentially through preheater 1 and cracking tower 2 to remove N. x F y The gas exiting the cracking tower was precooled to obtain intermediate A. The compositional analysis results of intermediate A are detailed in Table 8.

[0097] The tube inlet temperature of preheater 1 is 25℃, the pyrolysis temperature and pyrolysis pressure of pyrolysis tower 2 are 350℃ and -0.002MPa, respectively, and the outlet gas temperature of pyrolysis tower 2 is reduced to 190℃ after heat exchange in the preheater.

[0098] Table 8

[0099]

[0100]

[0101] (3) Intermediate A enters the buffer tank and is buffered by temperature and pressure to obtain intermediate B;

[0102] The temperature of the crude gas after passing through the buffer tank is reduced to 60℃; the pressure of the buffer tank is controlled by an automatic valve installed on the outlet pipe of the buffer tank, and the pressure is 0MPa.

[0103] (4) After the intermediate B passes through the buffer tank 3 to buffer the temperature and pressure, it enters the 3-stage hydrogen fluoride scrubbing tower 4, where most of the hydrogen fluoride and some fluorine gas are removed by spray washing, and intermediate C is obtained.

[0104] The hydrogen fluoride scrubbing tower operates at a temperature of 60℃, an operating pressure of -0.01MPa, an inlet air flow rate of 510kg / h, and a spray liquid flow rate of 20m³. 3 / h, the spray liquid is hydrofluoric acid from the bottom of the hydrogen fluoride scrubbing tower after being pressurized by the circulating pump, and the hydrofluoric acid by-product with a purity of 45% is obtained from the bottom of the first-stage hydrogen fluoride scrubbing tower.

[0105] (6) Intermediate C enters reduction tower 6 and is reduced in 2 mol / L Na2S2O3 aqueous solution to remove oxygen difluoride and fluorine gas. Then it enters alkaline washing tower 8 and is alkaline washed in 3 mol / L KOH aqueous solution to remove CO2 and hydrogen fluoride, to obtain intermediate D.

[0106] The reduction temperature and pressure in reduction tower 6 are 50℃ and -0.03MPa, respectively; the alkali washing temperature and pressure in alkali washing tower 8 are 50℃ and -0.05MPa, respectively.

[0107] (5) The intermediate D, which is operating under negative pressure, is first converted to positive pressure by the first-stage water ring compressor 10, and then enters the second-stage water ring compressor for further pressurization. Then it enters the dewatering equipment 15 to remove water vapor from the intermediate D, and then passes through the distillation system 13 to finally purify and obtain nitrogen trifluoride product. Finally, the product is filled through the filling system 14.

[0108] The inlet pressure of the first-stage water ring compressor 10 is -0.05MPa, the outlet pressure is 0.05MPa, and the outlet pressure of the second-stage water ring compressor 11 is 1.0MPa.

[0109] The dewatering equipment 12 consists of three stages connected in series. The first-stage dewatering tower is cooled by a calcium chloride solution at -10℃, and the outlet crude nitrogen trifluoride gas temperature is 20℃. The second and third-stage dewatering towers are both cooled by cold nitrogen gas at -110℃ from the distillation system, and the outlet crude nitrogen trifluoride gas temperature is -60℃.

[0110] The product after passing through distillation system 13 was subjected to component analysis, and the results are detailed in Table 3. The yield, storage volume, liquid nitrogen consumption, and electrical energy consumption of high-purity nitrogen trifluoride gas with a purity greater than 99.995 vol% obtained using the purification method described in this embodiment are detailed in Table 10.

[0111] Table 9

[0112]

[0113] Table 10

[0114] Production kg / h Hydrofluoric acid production kg / h <![CDATA[Liquid nitrogen consumption m 3 / h]]> Electricity consumption (kW) 419 25 2.66 102

[0115] Comparative Example 1

[0116] like Figure 2 As shown in Comparative Example 1, an apparatus for purifying crude nitrogen trifluoride gas includes an electrolytic cell 23, a primary cracking tower 24, a secondary cracking tower 25, a first buffer tank 26, a cooler 27, a second buffer tank 28, a water washing tower 29, a second reduction tower 30, a second alkaline washing tower 31, a second water ring compressor 32, a dehydration tower 33, a diaphragm compressor 34, a primary distillation tower 36, a secondary distillation tower 37, and a second filling system 38, connected in sequence. A first regulating valve 19 is installed between the secondary cracking tower 25 and the first buffer tank 26; a second regulating valve 20 is installed between the second alkaline washing tower 31 and the second water ring compressor 32; a third regulating valve is installed between the dehydration tower 33 and the diaphragm compressor 34; and a fourth regulating valve 22 is installed between the secondary distillation tower 37 and the second filling system 38. A flow meter 35 is installed between the diaphragm compressor 34 and the primary distillation tower 36.

[0117] The composition of the gas produced by the electrolyzer is shown in Table 11.

[0118] Table 11

[0119]

[0120] The nitrogen trifluoride electrolytic gas produced from every 5 electrolyzers is fed into a primary cracking tower for primary cracking, and the gas output from every 10 primary cracking towers is fed into a secondary cracking tower 2 for secondary cracking to remove nitrogen. x F y Intermediate E was obtained, and the compositional analysis results of intermediate product E are detailed in Table 12.

[0121] The pyrolysis temperature and pyrolysis pressure of the first-stage pyrolysis tower are 260℃ and -0.005MPa, respectively; the pyrolysis temperature and pyrolysis pressure of the second-stage pyrolysis tower are 240℃ and -0.006MPa, respectively.

[0122] Table 12

[0123]

[0124] (3) After passing through the first buffer tank, intermediate E enters the cooler for cooling to remove most of the hydrogen fluoride, thus obtaining intermediate F.

[0125] The cooling temperature and cooling pressure in the cooler are -65℃ and -0.01MPa, respectively.

[0126] (4) After passing through the second buffer tank, intermediate F first enters the water washing tower and is washed by spraying to remove some fluorine and hydrogen fluoride. Then it enters the reduction tower 30 and is reduced in 2.5 mol / L Na2S2O3 aqueous solution to remove oxygen difluoride and fluorine. Then it enters the alkaline washing tower 31 and is alkaline washed in 3.5 mol / L KOH aqueous solution to remove CO2 and hydrogen fluoride, to obtain intermediate G.

[0127] The water washing temperature and pressure in the water washing tower are 40℃ and -0.025MPa, respectively. The air inlet flow rate in the water washing tower is 510kg / h, and the spray volume is 5m³ / h. 3 / h; The reduction temperature and reduction pressure in reduction tower 2 30 are 35℃ and -0.035MPa, respectively; The alkali washing temperature and alkali washing pressure in alkali washing tower 2 31 are 30℃ and -0.05MPa, respectively;

[0128] (5) The intermediate G, which is operating under negative pressure, is first converted to positive pressure by the water ring compressor 32, and then enters the dewatering tower 33 to remove water vapor from the intermediate G. Then it is pressurized by the diaphragm compressor, and finally undergoes primary distillation and secondary distillation in sequence through the primary distillation tower 36 and the secondary distillation tower 37. Finally, the product after secondary distillation is filled through the filling system 38.

[0129] The water ring compressor 32 has an inlet pressure of -0.055 MPa and an outlet pressure of 0.08 MPa. The water vapor removal tower 33 removes water vapor at temperatures of -85℃ and pressures of 0.08 MPa. The diaphragm compressor 34 has an inlet pressure of 0.07 MPa and an outlet pressure of 0.31 MPa. The first-stage distillation column is used to remove light component impurities, and the second-stage distillation column is used to remove heavy component impurities. The distillation temperature and pressure of the first-stage distillation column 36 are -105℃ and 0.30 MPa, respectively, and the distillation temperature and pressure of the second-stage distillation column 37 are -108℃ and 0.25 MPa, respectively. Both the first-stage and second-stage distillation columns use liquid nitrogen as the cooling medium for the exhaust gas, and the low-temperature nitrogen gas generated after using liquid nitrogen in the first-stage and second-stage distillation columns is used as the cooling medium for the cooler 27 and the water removal tower 33.

[0130] The product after two-stage distillation was subjected to component analysis, and the results are detailed in Table 13. The yield, liquid nitrogen consumption, and electrical energy consumption for preparing high-purity nitrogen trifluoride gas with a purity greater than 99.995 vol% using the method described in this comparative example are detailed in Table 14.

[0131] Table 13

[0132]

[0133] Table 14

[0134] Production kg / h <![CDATA[Liquid nitrogen consumption m 3 / h]]> Electricity consumption (kW) 418 2.96 126

[0135] Although the nitrogen trifluoride gas purity obtained in the embodiments of the present invention and Comparative Example 1 both met the qualified standards, however:

[0136] (1) The embodiments of the present invention employ first-stage pyrolysis, ensuring N x F y Under the premise of complete decomposition, the comparison ratio saves on the use of pyrolysis towers and their associated pipes, valves, and instruments, thus saving investment costs;

[0137] (2) In this embodiment of the invention, the gas outlet of the cracking tower is used to heat the electrolytic gas from the electrolysis process, which not only saves heating power consumption, but also reduces the temperature of the next stage equipment, making the operation more gentle;

[0138] (3) The embodiments of the present invention obtained hydrofluoric acid by-products, which saved the use of water washing towers and investment costs compared with Comparative Example 1;

[0139] (4) The first-stage dewatering process used in the embodiment of the present invention can greatly reduce the load on the subsequent dewatering equipment and extend the switching cycle. In the comparative example, only freezing dewatering is used. The cooled water turns into ice, which is easy to cause ice blockage in the first-stage dewatering tower. At this time, it will be necessary to switch to de-ice.

[0140] (5) In the embodiment of the present invention, a two-stage water ring compressor is used to pressurize the gas to the pressure required by the distillation system. Water is removed before entering the distillation system. On the one hand, the water removal pressure is high and the efficiency is high. On the other hand, the low-temperature crude gas after water removal directly enters the distillation system, which reduces the amount of liquid nitrogen used during low-temperature distillation. In contrast, in the comparative example, the gas after water removal is pressurized by a room temperature diaphragm compressor and the temperature rises. This part of the gas will consume more liquid nitrogen to cool down after entering the low-temperature distillation system.

[0141] Therefore, the process flow of the embodiments of the present invention is more reasonable, requires less investment, has lower energy consumption, and consumes less liquid nitrogen, making it more advantageous overall compared to the comparative model.

[0142] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of purifying a crude nitrogen trifluoride gas, characterized by: The steps are as follows: S1, using electrolysis method to prepare nitrogen trifluoride electrolysis gas; S2, the nitrogen trifluoride electrolysis gas sequentially passes through a preheater and a cracking tower to obtain intermediate A; S3, the intermediate A enters a buffer tank, and after temperature buffering and pressure buffering, intermediate B is obtained; S4, the intermediate B enters 2-5 stages of hydrogen fluoride washing towers to remove hydrogen fluoride and fluorine gas to obtain intermediate C; S5, the intermediate C enters a reduction tower to remove oxygen difluoride and fluorine gas, and then enters an alkali washing tower to remove carbon dioxide and hydrogen fluoride to obtain intermediate D; S6, the intermediate D is removed of water vapor by 2-4 stages of water removal equipment, and then is subjected to two-stage rectification to obtain high-purity nitrogen trifluoride gas.

2. The method according to claim 1, characterized in that: In step S1, the volume content of nitrogen trifluoride in the nitrogen trifluoride electrolysis gas is 40-70%; In step S2, the cracking tower outlet gas preheats the electrolysis gas, and the temperature of the cracking tower outlet gas after heat exchange is reduced to 90-190℃.

3. The method of purifying a crude nitrogen trifluoride gas of claim 1, wherein: In step S3, the pressure of the buffer tank is -0.01-0 MPa, and the temperature of the buffer tank is 20-60℃.

4. The method of purifying a crude nitrogen trifluoride gas of claim 1, wherein: In step S4, the gas volume flow rate is 20-50 times the spraying volume flow rate; The hydrogen fluoride washing tower is washed by spraying, the operation temperature is 10-60℃, and the operation pressure is -0.03--0.01 MPa; From the first stage of hydrogen fluoride washing tower, a hydrogen fluoride acid byproduct with a mass concentration of 35-55% is obtained; After the first stage of hydrogen fluoride washing tower transfers away the hydrogen fluoride acid byproduct, low-concentration hydrogen fluoride acid is sequentially transferred from the subsequent stages of hydrogen fluoride washing tower to the previous stage, and finally water is supplemented to the last stage of hydrogen fluoride washing tower.

5. The method of purifying a crude nitrogen trifluoride gas of claim 1, wherein: In step S5, a reducing aqueous solution is used for reduction in the reduction tower, the reduction temperature is 10-50℃, the reduction pressure is -0.05--0.03 MPa, the reducing aqueous solution is sodium thiosulfate aqueous solution or sodium sulfite aqueous solution, the concentration of the reducing aqueous solution is (1-4) mol / L, and the gas flow rate in the reduction tower is 80-120 times the spraying amount of the reducing aqueous solution; In the alkali washing tower, an alkaline aqueous solution is used for alkali washing, the alkali washing temperature is 10-50℃, the alkali washing pressure is -0.07--0.05 MPa, the alkaline aqueous solution is potassium hydroxide aqueous solution or sodium hydroxide aqueous solution, the concentration of the alkaline aqueous solution is 2-5 mol / L, and the gas flow rate in the alkali washing tower is 80-120 times the spraying amount of the alkaline aqueous solution.

6. The method of purifying a crude nitrogen trifluoride gas of claim 1, wherein: In step S6, before the intermediate D enters the water removal equipment, the crude gas is first pressurized from -0.07--0.05 MPa to 0-0.05 MPa by a first-stage water ring compressor, and then is pressurized from 0-0.05 MPa to 0.1-1.0 MPa by a second-stage water ring compressor; The first-stage water removal equipment is cooled by -40--10℃ ethylene glycol solution, -40--10℃ calcium chloride aqueous solution or -170--110℃ nitrogen refrigerant, and the outlet temperature is 0-20℃; the second-stage to fourth-stage water removal equipment is cooled by -170--110℃ nitrogen, and the outlet temperature is -110--60℃. The two-stage low-temperature rectification process has two-stage rectification towers with a temperature of-140 to-80 DEG C and a pressure of 0.1 to 1.0 MPa.

7. The method of purifying a crude nitrogen trifluoride gas of claim 1, wherein: The high-purity nitrogen trifluoride gas has a purity of 99.995 vol% or above.

8. An apparatus for purifying a crude nitrogen trifluoride gas based on the method for purifying a crude nitrogen trifluoride gas according to any one of claims 1 to 7, characterized by: The system comprises, in sequence through pipelines, a preheater, a cracking tower, a buffer tank, a hydrogen fluoride washing tower, a reduction tower, an alkali washing tower, a water ring compressor, a water removal device, a rectification system and a filling system; the water ring compressor comprises, in sequence through pipelines, a first-stage water ring compressor and a second-stage water ring compressor; A first regulating valve is arranged on the pipeline between the buffer tank and the hydrogen fluoride washing tower, and a second regulating valve is arranged on the pipeline between the alkali washing tower and the first-stage water ring compressor; A hydrogen fluoride circulating pump is arranged on the hydrogen fluoride washing tower, a reduction tower circulating pump is arranged on the reduction tower, and an alkali washing tower circulating pump is arranged on the alkali washing tower.

9. A device for purifying a crude nitrogen trifluoride gas according to claim 8, characterized in that: The hydrogen fluoride washing tower has 2 to 5 stages, the alkali washing tower has 2 stages, the water removal device has 2 to 4 stages, and the rectification system comprises two-stage rectification towers.

10. A device for purifying a crude nitrogen trifluoride gas according to claim 8, characterized by: A first flow meter is arranged on the pipeline between the first-stage water ring compressor and the second-stage water ring compressor, and a second flow meter is arranged on the pipeline between the rectification system and the filling system.

Images