A feed device in a process for the production of nitrogen trifluoride by electrolysis and a method of using the same

Abstract

The application discloses a feeding device in a process for preparing nitrogen trifluoride by electrolysis and a use method thereof, and the feeding device comprises a raw material tank and a batching unit; the batching unit (A) comprises four micro-channel reactors, a liquid ammonia storage tank (5) is sequentially connected with a first micro-channel (1), a first terminal purifier (6) and a first pressure stabilizing device (7), then is divided into two paths, one path is connected with a third micro-channel (3) through a first adjusting valve (8), and the other path is connected with a fourth micro-channel (4) through a second adjusting valve (9); a hydrogen fluoride storage tank (10) is sequentially connected with a second micro-channel (2), a second terminal purifier (11), a second pressure stabilizing device (12), a third adjusting valve (13), the third micro-channel (3), the fourth micro-channel (4) and a densimeter (14), and then goes to the inside of an electrolytic cell. The feeding device can stabilize the physical properties of hydrogen fluoride fluid, strengthens the mass transfer and heat transfer in the inside of the electrolytic cell, and does not bring adverse impact on the electrolysis process.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of nitrogen trifluoride preparation, and particularly relates to a feeding device in a process for preparing nitrogen trifluoride by electrolysis and a use method thereof. BACKGROUND

[0002] The electrolytic preparation of nitrogen trifluoride takes hydrogen fluoride and ammonia as raw materials, and the raw materials, anhydrous hydrogen fluoride and high-purity ammonia, required in the electrolysis process come from the tank area arranged in the factory. The raw materials are fed into the electrolytic cell in two ways: one is that gaseous ammonia and liquid or gaseous hydrogen fluoride are respectively fed into a single electrolytic cell, as in document CN112626548; the other is that a molten salt electrolyte is first prepared in proportion, and then fed into the electrolytic cell through a molten salt conveying system or a molten salt transfer device, as in patent document CN104947135.

[0003] Due to the physical properties of liquid anhydrous hydrogen fluoride, such as small viscosity, about one tenth of that of water, easy gasification, unique corrosion characteristics, and very small flow rate of hydrogen fluoride required for metering in the existing process, for example, the electrolysis current of a single nitrogen trifluoride electrolytic cell is 6000A-20000A, and the flow rate of hydrogen fluoride fed into the electrolytic cell is only 2-8kg / h, the above-mentioned first feeding method has the disadvantage that it is difficult to select a small flow meter and self-control valve suitable for liquid anhydrous hydrogen fluoride. There are patents that use program control to concentrate the feeding of liquid hydrogen fluoride into the electrolytic cell at a certain moment, then use inert gas to purge the pipeline, and then wait for the next cycle. This process is equivalent to increasing the instantaneous flow rate and increasing the selection range of the flow meter. The disadvantage is that the intermittent feeding disrupts the smooth electrolysis process, the reaction heat caused by the instantaneous high concentration of raw materials exacerbates the corrosion of the equipment, and the pipeline is prone to blockage during the waiting process; there are patents that select the weight metering method of hydrogen fluoride, which increases the investment cost and maintenance difficulty; there are patents that use a centralized gasification device, which requires a large buffer tank to be designed to stabilize the gas pressure, and then distributed to each electrolytic cell. Due to the effect of hydrogen bonding, hydrogen fluoride molecules have associated properties at normal temperature and pressure, exhibiting some abnormal physical properties. When the temperature is greater than 82℃, gaseous HF is basically in a monomolecular state, at which time the hydrogen fluoride flow measurement can be more accurate, but the energy consumption problem is obvious. In summary, the existing nitrogen trifluoride electrolysis process does not have a good solution for hydrogen fluoride metering.

[0004] For the raw material ammonia, due to its large solubility, the process of feeding into the molten salt is easy to cause pipeline blockage, and gas phase feeding needs to be used. According to the above-mentioned electrolysis current, the ammonia gas flow rate is in the range of 1000-4000NL / h. The method of directly feeding hydrogen fluoride or ammonia into the electrolytic cell interferes with the electrolysis process, and in order to ensure the smoothness of the pipeline, a large amount of nitrogen gas is used for purging, which also has an adverse effect on the electrolysis process. In the existing technology, the blockage problem is difficult to avoid, which increases the labor intensity of the operators and the danger in the processing process.

[0005] Theoretically, the feeding of ammonium bifluoride molten salt improves the electrolysis process, makes the concentration distribution in the electrolytic cell more reasonable, reduces the corrosion of the electrolytic cell and its internal structure, and has a beneficial effect on the purity of the product. This batching process is equivalent to preparing ammonium bifluoride, which has the problems of corrosion of reaction equipment and difficulty in reaction process control. Ammonium bifluoride is a solid particle at room temperature, easy to absorb moisture, with a melting range of 90-110℃. The way of adding it to the electrolytic cell in solid form has been eliminated. The way of adding it in molten liquid form has the problems of molten salt pipeline heating and transportation or molten salt storage tank transfer. The disadvantages are that the feeding process is complex, inefficient and unsafe. SUMMARY

[0006] To solve the above technical problems, the first object of the present application is to provide a feeding device in the process of preparing nitrogen trifluoride by electrolysis, which uses the molten salt ammonium bifluoride in the electrolytic cell to provide the heat required for the gasification of liquid hydrogen fluoride and liquid ammonia, and makes the temperature of gaseous hydrogen fluoride greater than 80℃, ensuring that the hydrogen fluoride molecules are not in an associated state, at which time the physical properties of hydrogen fluoride fluid are stable; the convection heat transfer of molten salt ammonium bifluoride in the electrolytic cell takes away the reaction heat of gaseous hydrogen fluoride and ammonia gas, indirectly using the cooling system of the electrolytic cell, which strengthens the mass transfer and heat transfer in the electrolytic cell without adversely affecting the electrolysis process.

[0007] The second object of the present application is to provide a method for using the feeding device.

[0008] To achieve the first object of the invention, the technical solution of the present application is: a feeding device in the process of preparing nitrogen trifluoride by electrolysis, comprising a raw material tank and a batching unit; the batching unit A comprises four microchannel reactors, a liquid ammonia storage tank 5 is connected in turn to a first microchannel 1-a first terminal purifier 6-a first pressure stabilizing device 7, then divided into two paths, one path is connected through a first regulating valve 8 to a third microchannel 3, the other path is connected through a second regulating valve 9 to a fourth microchannel 4; a hydrogen fluoride storage tank 10 is connected in turn to a second microchannel 2-a second terminal purifier 11-a second pressure stabilizing device 12-a third regulating valve 13-a third microchannel 3-a fourth microchannel 4-a density meter 14, and then goes to the inside of the electrolytic cell. The feeding device is assembled with the electrolytic cell for use, the batching unit A is placed in the electrolytic cell, and the other components are located outside the electrolytic cell.

[0009] The feeding device and the cell body can be welded together, preferably assembled with the cell cover, which is convenient for maintenance when the electrolytic cell is disassembled and inspected.

[0010] The first microchannel 1 is the gasification site of liquid ammonia, the second microchannel 2 is the gasification site of liquid hydrogen fluoride, the third microchannel 3 is the site where part of the gaseous ammonia and gaseous hydrogen fluoride are mixed and reacted, and the fourth microchannel 4 is the site where part of the gaseous ammonia is mixed and reacted with the electrolyte coming out of the third microchannel 3.

[0011] The first terminal purifier 6 and the second terminal purifier 11 are filled with filtering material and adsorbing material, the filtering material is preferably hydrophobic and oleophilic fluororesin, and the adsorbing material is preferably spherical aluminum trifluoride. After the liquid ammonia is gasified in the first microchannel 1 by using the electrolytic cell heat, the liquid ammonia is filtered and adsorbed by the first terminal purifier 6. Meanwhile, after the anhydrous hydrogen fluoride is gasified in the second microchannel 2 by using the electrolytic cell heat, the anhydrous hydrogen fluoride is filtered and adsorbed by the second terminal purifier 11.

[0012] Preferably, each microchannel is preferably made of Monel material or silicon carbide material.

[0013] Preferably, the liquid ammonia storage tank 5 can supply multiple electrolytic cells at the same time, and the liquid ammonia is introduced into the branch pipeline of each electrolytic cell through the main pipeline.

[0014] Preferably, the hydrogen fluoride storage tank 10 can supply multiple electrolytic cells at the same time, and the hydrogen fluoride is introduced into the branch pipeline of each electrolytic cell through the main pipeline.

[0015] The technical scheme of the present application does not use the mode of centralized preparation of ammonium bifluoride, the amount of hydrogen fluoride and ammonia required by a single electrolytic cell is moderate, after the material is gasified, purification and pressure reduction are performed, and the reaction is mixed in the microchannel, and overall, the reaction heat is controllable, and the problems of equipment corrosion, molten salt distribution, automatic control complexity and even product purity caused by large reaction scale and concentrated heat release are solved. The beneficial aspect of using the cooling system of the electrolytic cell itself is that the gasification heat absorption and the reaction heat release strengthen the flow of ammonium bifluoride in the electrolytic cell. The combination mode of the feeding device and the electrolytic cell solves the problems of blockage and energy consumption caused by the long-distance molten salt conveying system.

[0016] The two streams of ammonia gas have the beneficial effect of further slowing down the concentrated heat release degree of the reaction. The reaction process uses the cooling system of the electrolytic cell for heat dissipation, and the ammonium bifluoride enters the electrolytic cell in a molten state. The microchannel of the feeding device is located inside the electrolytic cell, providing a gasification, mixing and reaction site; the microchannel has a small diameter, which strengthens heat dissipation, and the throughflow meets the material requirements of a single electrolytic cell; the electrolyte ammonium bifluoride after the mixing reaction in the microchannel is in a molten state, and is pushed into the electrolytic cell by the pressure generated by the system front end pressure and the material gasification.

[0017] The feeding device controls the pressure of the gas hydrogen fluoride and ammonia gas in the range of 0.1-0.2 MPa through a pressure stabilizing device, which is a throttle orifice plate structure, simple and durable. The automatic regulating valve adjusts the valve opening degree according to the feedback signals such as the electrolytic cell liquid level and the ammonium bifluoride concentration, so as to adjust the raw material ratio and the material flow, and to keep the ammonium bifluoride concentration in the electrolytic cell at a normal state. The feeding device of the present application has the benefits of low equipment cost, stable electrolysis process, easy operation, reduction of manual operation, and further improvement of product quality.

[0018] To achieve the second invention purpose, the technical scheme of the application is: a method for using a feeding device in a process for preparing nitrogen trifluoride by electrolysis, comprising the following steps:

[0019] 1. Liquid ammonia and liquid anhydrous hydrogen fluoride are respectively passed through the first microchannel 1 and the second microchannel 2 placed inside the electrolytic cell, and are gasified by using the heat of the electrolytic cell; the temperature at the outlet of the first microchannel 1 is 70-120℃, and the temperature at the outlet of the second microchannel 2 is 80-110℃;

[0020] 2. The two materials are converted into gaseous state, the gaseous ammonia is filtered and adsorbed by the first terminal purifier 6, and is depressurized to 0.1-0.2MPa by the first pressure stabilizing device 7; the gaseous hydrogen fluoride is filtered and adsorbed by the second terminal purifier 11, and is depressurized and flow-limited by the second pressure stabilizing device 12, and is depressurized to 0.1-0.2MPa;

[0021] 3. The gasification process of the raw materials provides the driving force for the advancement of the materials, the gasified hydrogen fluoride is returned to the third microchannel 3 inside the electrolytic cell, and the gasified ammonia is divided into two streams and is respectively introduced into the third microchannel 3 and the fourth microchannel 4 to mix and react, and the reaction heat is taken away by the ammonium hydrogen fluoride electrolyte inside the electrolytic cell; the temperature of the material at the outlet of the third microchannel 3 is controlled to be 130-150℃; the temperature of the material at the outlet of the fourth microchannel 4 is controlled to be 110-130℃, so as to ensure that the molten ammonium hydrogen fluoride salt flows into the electrolytic cell.

[0022] Preferably, the ammonia gas introduced into the third microchannel 3 accounts for 1 / 3-1 / 2 of the total amount of ammonia gas, so as to avoid the blockage of the pipeline by the locally generated high-melting-point NH4F·mHF.

[0023] The feeding device of the application improves the mode of using a large amount of nitrogen gas for purging when the feeding device is stopped for a short time, adopts a nitrogen pressure stabilizing device, avoids the blockage of the pipeline, and solves the problem of disturbance of the nitrogen purging pipeline to the electrolysis process.

[0024] In order to make the feeding device stably run in the use process and play a greater role, a plurality of measuring tools and methods are adopted, including:

[0025] The on-line densimeter is used to indirectly represent the concentration of the fresh ammonium hydrogen fluoride after batching, so as to solve the lag in the chemical measurement of the concentration of ammonium hydrogen fluoride and the safety problem in the sampling process;

[0026] The liquid level measurement methods of the nitrogen trifluoride electrolytic tank with two different principles: radar liquid level meter and infrared thermal imaging liquid level meter, have the advantages of improving the measurement accuracy and production safety. The infrared thermal imaging liquid level meter directly shoots the liquid level line on the side surface of the electrolytic tank, and the thermal infrared imaging liquid level meter customized and fixed on a single electrolytic tank is preferably selected, and the commercial thermal imaging equipment with higher accuracy is used as the inspection equipment, which is also an economical and feasible method; the beneficial effect of the non-contact measurement of the ammonium bifluoride liquid level is that the dangerous factors in the manual measurement of the liquid level and the sampling process are eliminated;

[0027] The viscosity of the ammonium bifluoride in the electrolytic tank is measured on-line to indirectly represent the ammonium bifluoride concentration, and the measurement method has a confidence degree of 90% in the first two-thirds of the running period of the whole electrolysis process. In the later electrolysis, the deviation of the viscosity for indirectly representing the ammonium bifluoride concentration becomes large, but it can still meet the purpose of the present application, and can be used as a criterion for the running life of the electrolytic tank. The viscosity meter is preferably an oscillation type viscosity meter;

[0028] The hydrogen flow and concentration are analyzed by using a gas chromatograph, the electrolysis efficiency is calculated, then the consumption of raw materials is calculated through the change of the product composition of the cathode and the anode, and the change trend of the ammonium bifluoride concentration is estimated. The specific method is to introduce nitrogen gas with a certain rate as a reference at the cathode and the anode. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the feeding device described in the present application.

[0030] 1. First microchannel 2. Second microchannel, 3. Third microchannel 4. Fourth microchannel 5. Liquid ammonia storage tank 6. First terminal purifier 7. First pressure stabilizing device 8. First regulating valve 9. Second regulating valve 10. Hydrogen fluoride storage tank 11. Second terminal purifier 12. Second pressure stabilizing device 13. Third regulating valve 14. Density meter A. Dosing unit.

[0031] Figure 2 It is a schematic diagram of the control points related to the feeding device and the dosing process described in the present application.

[0032] 15. Radar liquid level meter 16. Infrared thermal imaging liquid level meter 17. Viscosity meter 18. First gas chromatograph 19. Second gas chromatograph DETAILED DESCRIPTION

[0033] The present application will be further described below in combination with the drawings and examples.

[0034] Example 1

[0035] As Figure 1As shown, a feed device in a process for preparing nitrogen trifluoride by electrolysis, comprising a raw material tank and a batching unit; the batching unit A comprises four micro-channel reactors, the liquid ammonia storage tank 5 is connected with the first micro-channel 1-the first terminal purifier 6-the first pressure stabilizing device 7 in turn, and then is divided into two paths, one path is connected with the third micro-channel 3 through the first regulating valve 8, and the other path is connected with the fourth micro-channel 4 through the second regulating valve 9; the hydrogen fluoride storage tank 10 is connected with the second micro-channel 2-the second terminal purifier 11-the second pressure stabilizing device 12-the third regulating valve 13-the third micro-channel 3-the fourth micro-channel 4-the densimeter 14 in turn, and then goes to the inside of the electrolytic cell. The first terminal purifier 6 and the second terminal purifier 11 are filled with filtering material and adsorbing material, the filtering material is hydrophobic and oleophilic fluororesin, and the adsorbing material is spherical aluminum trifluoride. Each micro-channel is preferably made of Monel material or silicon carbide material. The feed device is assembled with the electrolytic cell for use, the batching unit A is arranged in the inside of the electrolytic cell, and other components are arranged outside the electrolytic cell. The feed device is assembled with the cell cover, so that maintenance is facilitated when the electrolytic cell is disassembled and inspected.

[0036] The anhydrous hydrogen fluoride in the hydrogen fluoride storage tank 10 is pressed out by nitrogen gas, the nitrogen gas pressure is 0.6 MPa, and the pipeline is distributed to the batching unit A. The anhydrous hydrogen fluoride is gasified in the second micro-channel 2 in the batching unit A by using the heat of the electrolytic cell, the outlet temperature of the second micro-channel 2 is 80-110 ℃, and the second terminal purifier 11 is used for filtering and adsorbing. After removing trace hydrocarbon substances and impurities such as fluorosilicic acid, the second pressure stabilizing device 12 is used for throttling and pressure reduction to 0.2 MPa. At the same time, the high-purity liquid ammonia in the liquid ammonia storage tank 5 is distributed to the first micro-channel 1 in the batching unit A, the outlet temperature of the first micro-channel 1 is 70-120 ℃, and after gasification, the first terminal purifier 6 is used for removing trace hydrocarbon impurities and the like, and then the first pressure stabilizing device 7 is used for throttling and pressure reduction to 0.2 MPa. The hydrogen fluoride gas is a stream, the flow rate is about 2.2-8.8 Nm 3 / h by adjusting the first regulating valve 8. The ammonia gas is divided into two streams, the second regulating valve 9 and the third regulating valve 13 are used for adjusting and distributing, so that the flow rate of each stream is in the range of 0.5-2 Nm 3 / h, and the ammonia gas entering the third micro-channel accounts for 1 / 3-1 / 2 of the total ammonia gas, and the ammonia gas is mixed and reacted with the hydrogen fluoride gas in the third micro-channel 3, and is reacted with the molten ammonium bifluoride in the fourth micro-channel 4; the outlet material temperature of the third micro-channel 3 is 130-150 ℃, the outlet material temperature of the fourth micro-channel 4 is controlled to be 110-130 ℃, and the molten ammonium bifluoride after reaction passes through the online densimeter 14 based on the principle of the Coriolis force to indirectly represent the concentration Ct (μ) of the outlet ammonium bifluoride, as shown in Table 1.

[0037] Table 1 Relationship between electrolyte composition and density and viscosity

[0038]

[0039] The tank uses two different principles of liquid level measuring device, one is radar liquid level meter 15 on-line measurement, the other is red-hot imaging liquid level meter 16 inspection measurement, see Figure 2 The liquid level fluctuation range δL is controlled at ±50mm, preferably ±20mm.

[0040] The steps of analyzing the cathode gas composition are as follows: opening the valve to introduce the reference gas nitrogen into the hydrogen pipeline at a known flow rate, or introducing the reference gas nitrogen into the cathode chamber of the electrolytic tank at a known flow rate, absorbing hydrogen fluoride with 50℃ hot alumina, extracting a quantitative sample gas into the second gas chromatograph 19 for analysis, obtaining the hydrogen concentration C H2 and flow rate V 阴 .

[0041] The steps of analyzing the anode gas composition are as follows: introducing the reference gas nitrogen into the anode chamber of the electrolytic tank at a known flow rate, absorbing hydrogen fluoride in the anode outlet gas through 50℃ hot alumina, and then entering the first gas chromatograph 18 for analysis, obtaining the nitrogen trifluoride gas concentration C Nf3 and flow rate V 阳 .

[0042] The calculation process is as follows:

[0043] The electrolysis efficiency η = F(C H2 , V 阴 , A)

[0044] The electrolyte concentration C t ' in the tank at time t = F(C0, η, C NF3 , V 阳 , A, δt, δL)

[0045] A-electrolysis current, t-time, C0-electrolyte concentration indirectly represented by the viscometer 17 or analyzed by chemical method, Ct' electrolyte concentration at a certain time.

[0046] The liquid level L measured by the radar liquid level meter 15, the fresh electrolyte concentration C ρ indirectly represented by the densimeter 14, and the change of electrolyte concentration δCt' in the tank, establish a mathematical model, then the opening of the hydrogen fluoride gas flow regulating valve:

[0047] V CL，HF = F(L, C ρ , C t ')

[0048] The opening of the ammonia gas flow regulating valve:

[0049] V CL，NH3 = F(V CL，HF , K), K is a preset proportional coefficient.

Claims

1. A feeding device for preparing nitrogen trifluoride by electrolysis, characterized in that The invention comprises a raw material tank and a batching unit; the batching unit (A) comprises four microchannel reactors, the liquid ammonia storage tank (5) is sequentially connected to the first microchannel (1) - the first terminal purifier (6) - the first pressure stabilizing device (7), and then divided into two paths, one path is connected to the third microchannel (3) through the first regulating valve (8), and the other path is connected to the fourth microchannel (4) through the second regulating valve (9); the hydrogen fluoride storage tank (10) is sequentially connected to the second microchannel (2) - the second terminal purifier (11) - the second pressure stabilizing device (12) - the third regulating valve 13 - the third microchannel (3) - the fourth microchannel (4) - the density meter (14), and then goes to the inside of the electrolytic cell; the liquid ammonia storage tank (5) supplies multiple electrolytic cells at the same time, and enters the branch pipeline of each electrolytic cell through the main pipeline; the hydrogen fluoride storage tank (10) supplies multiple electrolytic cells at the same time, and enters the branch pipeline of each electrolytic cell through the main pipeline.

2. A method for using the feeding device according to claim 1, comprising the following steps: (1) liquid ammonia and liquid anhydrous hydrogen fluoride are passed through a first microchannel (1) and a second microchannel (2) disposed inside an electrolytic cell, respectively, and gasified using the heat of the electrolytic cell; (2) The two materials are converted into gaseous state. The gaseous ammonia is filtered and adsorbed by the first terminal purifier (6), and the pressure is reduced to 0.1-0.2 MPa by the first pressure stabilizing device (7); the gaseous hydrogen fluoride is filtered and adsorbed by the second terminal purifier (11), and the pressure is reduced to 0.1-0.2 MPa by the second pressure stabilizing device (12); (3) The gasification process of the raw materials provides the driving force for the materials to move forward. The gasified hydrogen fluoride is all returned to the third microchannel (3) inside the electrolytic cell. The gasified ammonia is divided into two streams, which enter the third microchannel (3) and the fourth microchannel (4) respectively to mix and react. The ammonium bifluoride electrolyte in the electrolytic cell is used to remove the reaction heat; the molten ammonium bifluoride molten salt flows into the interior of the electrolytic cell.

3. The method for using the feeding device according to claim 2, characterized in that The outlet temperature of the first microchannel (1) is 70-120°C; the outlet temperature of the second microchannel (2) is 80-110°C; the flow rate of the first regulating valve (8) is 2.2-8.8 Nm 3 / h; the flow rate of the second regulating valve (9) and the third regulating valve (13) is 0.5~2Nm 3 / h; the gaseous ammonia entering the third microchannel (3) accounts for 1 / 3 to 1 / 2 of the total ammonia volume; the temperature of the material at the outlet of the third microchannel (3) is 130 to 150°C; the temperature of the material at the outlet of the fourth microchannel 4 is 110 to 130°C.

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