Method for processing ammonium polyfluoride

Abstract

The invention relates to methods for processing ammonium polyfluoride and producing nitrogen trifluoride (NF3). The technical result is the creation of a comprehensive, low-waste, explosion-proof technology for producing nitrogen trifluoride and, additionally, a group of inorganic fluorides: nitrogen trifluoride, carbon tetrafluoride, carbonyl fluoride, hydrogen fluoride and hydrofluoric acid. The proposed method envisages removing excess liquid ammonium polyfluoride from a reactor and sending it to be flaked or reacting it with oxygen, or with oxygen and carbon, or with oxygen and hydrogen-containing substances, or with oxygen and carbon and hydrogen-containing substances, or with fluorine, or with fluorine and hydrogen-containing substances, and recovering low-boiling substances by distillation and isolating hydrogen fluoride or hydrofluoric acid.

Description

METHOD FOR PROCESSING AMMONIUM POLYFLUORIDE

[0001] The invention relates to inorganic chemistry, to methods for processing ammonium polyfluoride and obtaining nitrogen trifluoride NF3 (hereinafter referred to as TFA), namely, to the technology for obtaining it by fluorinating ammonium polyfluoride with elemental fluorine.

[0002] Under normal conditions, TFA is a gaseous substance and can be used as a fluorine carrier for dry etching of silicon and its compounds in the semiconductor industry, cleaning of chemical vapor deposition chambers, as an oxidizer for high-energy fuels in rocket technology, etc.

[0003] When using TFA in the semiconductor industry, high purity of the commercial product is required - usually the content of the main substance exceeds 99.99%.

[0004] TFA is obtained by fluorinating a melt of ammonium polyfluoride with fluorine, and, depending on the reaction conditions, the reaction mixture contains, in addition to the target product, by-products, in particular, nitrogen, difluoroamine NF2H, tetrafluorohydrazine N2F4, dinitrogen difluoride N2F2, etc.

[0005] The consumption of ammonium polyfluoride in the fluorination reactor is compensated by feeding ammonia into the same reactor.

[0006] In the presence of moisture in ammonium polyfluoride (when the reactor is started, when water with ammonia and oxygen with fluorine are supplied), ammonium hydroxide is formed, which is fluorinated with the formation of nitrous oxide and fluoride-nitrogen oxides.

[0007] A method for producing TFA is known [US 4091081, published 05 / 23 / 1978] by fluorinating ammonium bifluoride with fluorine.

[0008] According to the method, liquid ammonium bifluoride is fluorinated with fluorine at a temperature preferably between 127 and 160°C, ensuring that contact between the fluorine and ammonia, which is present in the gas phase above the ammonium bifluoride melt, is avoided. Ammonia introduced into the ammonium bifluoride bath through a bubbler not only replenishes the reagent but also binds HF, a byproduct of the reaction. The formation of ammonium bifluoride reduces the volume of HF, which is sent to the product recovery system.

[0009] The ammonium bifluoride impurity is removed from the product mixture exiting the ammonium bifluoride bath and returned to the bath. It is then passed through a scrubber containing potassium hydroxide, which reacts with the byproduct hydrogen fluoride (HF) to form a salt and is thus recovered. The gas stream is then purified, and virtually all of the TFA is condensed, yielding a crude product that is collected at the bottom of the condenser and held under vacuum to remove residual nitrogen. The resulting product is heated and stored.

[0010] In this method, using undiluted fluorine, at an ammonium bifluoride temperature of 127-160°C, the yield of TFA was low, ranging from 29 to 40% in terms of fluorine. Using fluorine with an active substance content of 99% and containing nitrogen, carbon tetrafluoride, and hydrogen fluoride as impurities, TFA with an active substance content of 95% by weight was obtained.

[0011] A method is known [RU 2178384, published 20.01.2002], which is used to fluorinate a melt of ammonium acid fluorides of the general formula NH4H (x-1) F x , where x = 2.5-3, with gaseous fluorine at atmospheric pressure, at a temperature of 80-153 C. The method is carried out with stirring, ensuring the circulation of the reagents, at a specific fluorine consumption of 0.1-0.5 cm 3 / min per unit melt volume. Depending on the reactor temperature, a nitrogen fluoride mixture with an increased content of one of the above-mentioned compounds is obtained. If necessary, additional gas-phase fluorination is performed in a separate reactor to increase the TFA yield. For this purpose, the reaction products from the first reactor, or a portion thereof, and additional fluorine are fed to the gas-phase fluorination reactor, and the reaction is carried out at 200–400°C. This method allows for varying the composition of the resulting nitrogen fluorides, with a preferential yield of one of the compounds.

[0012] This method uses fluorine obtained by electrolysis of KF 2HF in a carbon-anode electrolyzer. Therefore, the fluorine always contains carbon tetrafluoride CF4 in quantities of hundreds and thousands of parts per million (ppm). Given the fluorine consumption coefficient for TFA production, the CF4 concentration in TFA can reach 1%. TFA is used in microelectronics, and the CF4 concentration in TFA should not exceed 0.005%. The boiling points of TFA and CF4 are virtually identical, and it is not possible to separate them by distillation. Furthermore, TFA and CF4 have similar chemical reactivity. Therefore, the TFA obtained by this method is not suitable for use in microelectronics.

[0013] A known method [RU 2317251, published 20.02.2008] for producing TFA includes a stage of TFA synthesis by fluorinating a melt of ammonium bifluoride with fluorine and a stage of purification of the synthesized TFA, absorption extraction of impurities with an alkaline solution and removal of moisture from the gas stream. The method includes preliminary purification of fluorine by thermal decomposition of the oxygen fluoride contained therein. This stage is carried out at a temperature of 300-350°C in a reactor with nickel packing. After this, low-volatile impurities are removed first by cryogenic condensation at a temperature of minus 170 to minus 180°C, then by cryogenic distillation at a pressure of 0.15-0.17 MPa.

[0014] However, some impurities migrate from the starting reagents into the target product. Other impurities are obtained as byproducts during the fluorination of ammonium bifluoride with fluorine.

[0015] The stage of purification of the obtained TFA includes thermal decomposition of by-product nitrogen fluorides and removal of volatile impurities by cryogenic distillation at a pressure of 0.3-0.5 MPa.

[0016] During the research, it was established that the TFA obtained by this synthesis method contains tetrafluoromethane CF4 impurity in quantities commensurate with the contribution of this impurity along with fluorine. Removing CF4 from the fluorine used for TFA synthesis by cryogenic distillation reduces the CF4 content in the resulting TFA.

[0017] Based on analytical testing, the total impurity content in the target product does not exceed 90 ppm, including 28 ppm of tetrafluoromethane CF4. The TFA fluorine yield is at least 80%.

[0018] The disadvantages of the known method include the risks associated with liquid fluorine, which is formed during cryogenic distillation. Industrial-scale work with liquid fluorine has been associated with devastating explosions at many facilities using liquid fluorine in various processes.

[0019] The explosions were likely related to the presence and accumulation (for example, on the surfaces of cryogenic equipment) of substances capable of reacting with fluorine, releasing heat. These substances include perfluoroalkanes, which, along with CF4, can form during the fluorination of the carbon anode in the electrolyzer, as well as sulfur compounds and water, which are present in trace amounts in the hydrogen fluoride fed to the electrolysis. Therefore, cryogenic distillation of fluorine is advisable only after the causes of the explosions have been determined and a set of methods for combating them has been developed.

[0020] Furthermore, the known method does not address the use or disposal of the main byproduct of TFA production—ammonium polyfluoride, the amount of which can reach 1.5 kg per 1 kg of TFA. The method also contains no information on the use of mixtures consisting of nitrogen fluorides, nitrogen fluoride oxides, and nitrogen oxides, which are formed during reactor startup when using wet ammonium polyfluoride. Technical challenge

[0021] The challenge facing the developers of the proposed method is to obtain TFA with a content of CF4 and other impurities regulated in microelectronics, using fluorine without its cryogenic (explosive) purification, and involving by-products of the developed technology in the production process in order to obtain commercially significant substances suitable for use in microelectronics.

[0022] The purpose of the invention is to create a method for processing ammonium polyfluoride, which is a by-product of the production of extractive phosphoric acid from fluorapatite and some other industries, allowing for the production of high-purity fluorides (with a main substance content of up to 99.999%) - nitrogen trifluoride, carbon tetrafluoride, hydrogen fluoride, hydrofluoric acid - for their use, including in microelectronics.

[0023] The technical result is the creation of a complex, low-waste, explosion-proof technology for producing TFA and, in addition, a group of inorganic fluorides that are used in microelectronics - nitrogen trifluoride, carbon tetrafluoride, carbon difluoride-oxide, hydrogen fluoride, hydrofluoric acid. Solution to the problem

[0024] The specified technical result in terms of the method for processing ammonium polyfluoride is achieved by the fact that the claimed method includes the following stages.

[0025] Fluorination of the ammonium polyfluoride melt with fluorine is carried out, the gas flow is neutralized and dried, volatile impurities are removed, fluorine is fed to the fluorination stage, maintaining the acidity of the ammonium polyfluoride in the range from NH4F 1.2HF to NH4F 2HF by adding ammonia.

[0026] In this case, the purification of nitrogen trifluoride from difluoramine, tetrafluorohydrazine and dinitrogen difluoride is carried out in a thermocatalytic reactor, the purification of nitrogen trifluoride from fluorine, hydrogen fluoride, silicon tetrafluoride, sulfur-containing acid gases and carbon dioxide is carried out with an alkaline solution.

[0027] The gas flow is dried using zeolite, and impurities with a boiling point lower than that of nitrogen trifluoride are removed by low-temperature distillation.

[0028] Carbon tetrafluoride is separated from nitrogen trifluoride by absorption, whereby gaseous by-products containing nitrogen trifluoride enriched in carbon tetrafluoride or nitrous oxide and fluorides-nitrogen oxides, obtained at the absorption separation stage and during reactor start-up, are brought into interaction with carbon or with hydrogen-containing substances, or with carbon and hydrogen-containing substances, or with hydrogen-containing substances and oxygen, or with carbon, hydrogen-containing substances and oxygen substances with separation by rectification of low-boiling substances and isolation of carbon tetrafluoride or hydrogen fluoride.

[0029] In this case, after separating the excess liquid ammonium polyfluoride from the reactor, it is sent for flaking or it is reacted with oxygen, or with oxygen and carbon, or with oxygen and hydrogen-containing substances, or with oxygen, carbon, and hydrogen-containing substances, or with fluorine, or with fluorine and hydrogen-containing substances with separation by rectification of low-boiling substances and the isolation of hydrogen fluoride or hydrofluoric acid.

[0030] The specified technical result in terms of the method for producing nitrogen trifluoride used in the method for processing ammonium polyfluoride is achieved by the fact that the claimed method includes the following stages.

[0031] Fluorination of ammonium polyfluoride melt with fluorine, neutralization and drying of the gas flow, and removal of volatile impurities are carried out.

[0032] Fluorine is fed to the fluorination stage, maintaining the acidity of ammonium polyfluoride in the range from NH4F·1.2HF to NH4F·2HF by adding ammonia.

[0033] In this case, the purification of nitrogen trifluoride from difluoramine, tetrafluorohydrazine and dinitrogen difluoride is carried out in a thermocatalytic reactor, and the purification of nitrogen trifluoride from fluorine, hydrogen fluoride, silicon tetrafluoride, sulfur-containing acid gases and carbon dioxide is carried out with an alkaline solution.

[0034] The gas flow is dried using zeolite, and impurities with a boiling point lower than that of nitrogen trifluoride are removed by low-temperature distillation; carbon tetrafluoride is separated from nitrogen trifluoride by absorption.

[0035] There are possible options for developing the main technical solutions, in which:

[0036] - purification of nitrogen trifluoride from acidic impurities is carried out with an alkaline solution at an alkali concentration in the aqueous solution above 10 mass %;

[0037] - substances with a boiling point lower than that of nitrogen trifluoride are separated by rectification at a temperature from -110ºС in the column bottom to -170ºС in the dephlegmator;

[0038] - separation of nitrogen trifluoride and carbon tetrafluoride is carried out by absorption using halogenated liquids. Figure 1

[0039] A schematic diagram of a plant for producing nitrogen trifluoride from ammonium polyfluoride is presented.

[0040] pos.1 – reactor unit with ammonium polyfluoride fluorination reactor;

[0041] pos.2 – fluorine supply unit with a given flow rate without preliminary purification from CF4;

[0042] pos.3 – ammonia supply unit with its drying;

[0043] pos. 4 – by-product collection unit - ammonium polyfluoride;

[0044] pos.5 – unit for conversion of by-products of the process during interaction with carbon; or with oxygen; or with both carbon and oxygen; or with hydrogen-containing substances; or with both hydrogen-containing substances and oxygen; or with both hydrogen-containing substances and carbon; or with both hydrogen-containing substances and oxygen and carbon; or with fluorine; or with fluorine and hydrogen-containing substances;

[0045] pos. 6 – unit for collecting a mixture of by-products of the process - nitrogen oxide fluorides, nitrogen oxides, nitrogen fluorides, formed during operation in unit 1 with wet ammonium polyfluoride;

[0046] pos. 7 – unit for fluorination of fluoride oxides and nitrogen oxides, unsaturated nitrogen fluorides with the production of TFA in a thermocatalytic reactor;

[0047] pos. 8 – unit for alkaline neutralization of the gas flow under conditions when the formation of oxygen difluoride is excluded;

[0048] pos.9 – gas flow drying unit with zeolite;

[0049] pos.10 – cryogenic rectification unit;

[0050] pos. 11 – unit for separating TPA and CF4 absorption;

[0051] pos.12 – unit for cleaning TFA from absorbent vapors by rectification;

[0052] pos.13 – unit for compression of commercial TFA;

[0053] pos.14 – unit for purification of carbon tetrafluoride, hydrogen fluoride and hydrofluoric acid by rectification;

[0054] pos.15 – ammonium polyfluoride flaking unit;

[0055] pos.16 – stripping (rectification) column for separating FNO from TFA, N2, F2.

[0056] The process flow diagram consists of the following main units: a reactor unit with an ammonium polyfluoride fluorination reactor equipped with a thermal stabilization system, a phase separator and systems for removing liquid (ammonium polyfluoride) and gaseous reaction products; a fluorine supply unit at a given flow rate without preliminary purification from CF4; an ammonia supply unit with its drying; a by-product collection unit - ammonium polyfluoride; a unit for converting by-products of the process during interaction with carbon; or with oxygen; or with both carbon and oxygen; or with hydrogen-containing substances; or with both hydrogen-containing substances and oxygen; or with both hydrogen-containing substances and carbon; or with both hydrogen-containing substances, oxygen, and carbon; or with fluorine; or with fluorine and with hydrogen-containing substances in combustion mode to produce carbon tetrafluoride, hydrogen fluoride or hydrofluoric acid;a collection unit for a mixture of by-products of the process - nitrogen fluoride oxides, nitrogen oxides, nitrogen fluorides formed during operation in unit 1 with wet ammonium polyfluoride; a unit for fluorination of nitrogen fluoride oxides and oxides, unsaturated nitrogen fluorides to obtain TFA in a thermocatalytic reactor; a unit for alkaline neutralization of a gas stream under conditions when the formation of oxygen difluoride is excluded; a unit for drying a gas stream with zeolite; a cryogenic rectification unit; a unit for separating TFA and CF4 by absorption; a unit for purifying TFA from absorbent vapors by rectification; a unit for compressing commercial TFA; a unit for purifying carbon tetrafluoride, carbon difluoride oxide, hydrogen fluoride and hydrofluoric acid by rectification; an ammonium polyfluoride flaking unit.

[0057] The fluorine feed unit is designed to feed fluorine (electrolysis gas with a fluorine content greater than 90%, or after separation of hydrogen fluoride from fluorine by condensation or adsorption) into the ammonium polyfluoride fluorination reactor. Unlike the prototype, this unit does not purify the fluorine from CF4.

[0058] The ammonia supply unit is designed for dosing pre-dried ammonia with a moisture content of less than 1 vol.% into the ammonium polyfluoride fluorination reactor unit.

[0059] The reactor unit is designed for the fluorination of liquid ammonium polyfluoride at temperatures of 100-160°C. Two streams emerge from the reactor unit: a gas-phase stream containing TFA and a liquid-phase stream consisting of ammonium polyfluoride. Ammonium polyfluoride is the main byproduct of the TFA synthesis process, producing approximately 1.5 kg of ammonium polyfluoride per 1 kg of TFA.

[0060] Ammonium polyfluoride is collected in unit 4. To reduce production waste and improve efficiency, ammonium polyfluoride is processed using one of the following methods in units 5 and 15.

[0061] In one embodiment of the developed method, ammonium polyfluoride is flaked in unit 15 and stored for shipment to potential customers. It is used in the recovery of ore concentrates, such as titanium-containing ones, in cementing oil and gas wells, and elsewhere.

[0062] The second option for using ammonium polyfluoride is to obtain hydrofluoric acid after treatment in a methane and oxygen flame in unit 5. The third option is for ammonium polyfluoride to be treated in the combustion front of carbon in oxygen in unit pos. 5 to obtain hydrogen fluoride, which can be used for fluorine production.

[0063] The fourth option is that ammonium polyfluoride is treated by combustion in fluorine in unit pos. 5 to produce hydrogen fluoride.

[0064] For each specific production implementation, the most commercially viable option is selected.

[0065] The advantage of processing by-product ammonium polyfluoride using the carbon method is the production of hydrogen fluoride in quantities sufficient to produce half of the fluorine required for the production of TFA.

[0066] If the reactor contains ammonium hydroxide in addition to ammonium polyfluoride (for example, during the startup period), the process products, along with nitrogen, TFA, and other nitrogen fluorides, also contain nitrous oxide and nitrogen fluoride-oxides. As ammonium polyfluoride is treated with fluorine, the concentration of ammonium hydroxide decreases, and the yield of oxygen-containing compounds decreases. If the concentration of nitrous oxide and nitrogen fluoride-oxides is high (on the order of tens of percent), the mixture is collected in unit 6 and sent to the production of commercial products—hydrogen fluoride using a hydrogen-containing substance, or carbon tetrafluoride and carbon difluoride-oxide using carbon, pos. 5:

[0067] N2O + FNO + NF3+ H2(CH4…) → HF + N2+ O2(CO2), (1)

[0068] N2O + FNO + NF3+ C → CF4+ COF2+ N2+ CO x . (2)

[0069] Hydrogen fluoride is used to produce fluorine, which is needed for the fluorination of ammonium polyfluoride to produce TFA.

[0070] Carbon tetrafluoride, like TFA, is used as a gaseous carrier of fluorine in the etching of silicon in the semiconductor industry.

[0071] Carbon difluoride COF2 is considered a gaseous fluorine carrier for etching silicon and its compounds, leaving no carbon particles on the etched part. Furthermore, COF2 is used in the production of perfluorinated alkyl vinyl ethers.

[0072] The method can be carried out in such a way that the mixture of fluorination products of wet ammonium polyfluoride is sent to a thermocatalytic reactor for fluorination of unsaturated nitrogen fluorides, nitrous oxide and fluoride-nitrogen oxides at a temperature of 200-500 C (pos. 7), into which a fluorine stream is fed, and then to a stripping (rectification) column for separating FNO from TFA, N2, F2 (pos. 16). The stream of oxygen-containing compounds from the bottom of the stripping (rectification) column is sent to unit (pos.) for processing according to schemes (1) and (2). And the stream containing TFA is sent to the alkaline neutralization unit (pos. 8).

[0073] If the concentration of oxygen-containing compounds at the outlet of reactor 1 is low (less than 10%), then the product flow after the thermal catalytic reactor pos. 7 is directed to the neutralization unit pos. 8, where the concentration of alkali in its aqueous solution is selected so as to exclude the formation of oxygen difluoride (the concentration of alkali in its aqueous solution is higher than 10 wt.%).

[0074] The flow then passes from the alkaline neutralization unit pos. 8 to the adsorber pos. 9, filled with zeolite (for example, NaA) to remove nitrous oxide, carbon dioxide and water vapor from the flow.

[0075] The stream from the adsorber (pos. 9) then passes through the compressor to the cryogenic rectification unit (pos. 10) with a temperature in the condenser-dephlegmator of minus 160 to minus 170ºC and in the column still of approximately minus 110ºC. The high-boiling component is TFA, and the low-boiling components are nitrogen, carbon monoxide, and oxygen.

[0076] From the bottom of the distillation column (pos. 10), the TFA stream, containing CF4, enters unit (pos. 11) for separation of TFA and CF4 by absorption. Halogenated liquids, in which the solubility of CF4 is significantly lower than that of TFA, are used as the absorbent. From unit (pos. 11), the TFA stream, with a reduced CF4 content (down to several tens of ppm), is withdrawn dissolved in the absorbent, while the TFA stream, enriched in CF4 to several tens of percent, is withdrawn in the gas phase. The liquid and gas flows in unit (pos. 11) move in countercurrent mode.

[0077] Unit 11 not only separates TFA from CF4, but also separates TFA from SF6. The majority of the SF6, which enters the process with fluorine in quantities of tens of parts per million, is removed from unit 11 as part of the TFA stream enriched with CF4.

[0078] The TFA is extracted from the absorbent by reducing the pressure. The degassed absorbent is sent to unit 11, and the gas flow is sent to the absorbent vapor separation unit by rectification (unit 12), and then to compression and loading into transport tanks in unit 13.

[0079] The TFA stream enriched with CF4 (about 10%) and SF6 (less than 1%) is directed either to the production of hydrogen fluoride or to the production of CF 4, or CF 4, or COF2 (in case of using oxygen) into the apparatus pos. 5 according to the interaction schemes:

[0080] CF4+SF6+NF3+H2(CH4)+O2→ HF+CO2+N2+SO2, (3)

[0081] CF4+SF6+NF3+C → CF4+N2+CS2+S, (4)

[0082] CF4+SF6+NF3+C+O2→ CF4+COF2+CO x +SF y O z . (5)

[0083] The production capacity of CF4 according to scheme (4) depends on its content in fluorine, which is fed into the ammonium polyfluoride fluorination reactor pos. 1 and the operating mode of unit pos. 11, in which commercial TFA with a CF content is obtained 4,According to customer requirements. With CF4 content in fluorine typical for modern electrolysis plants (on the order of hundreds of parts per million), the CF4 production capacity according to scheme (4) can be approximately 10% of the TFA production capacity.

[0084] Thus, the proposed method enables the development of a comprehensive technology capable of synthesizing TFA that meets market requirements (with a main substance content greater than 99.99%) and other commercial products for which demand is stable. Furthermore, the closed-loop process reduces production costs and minimizes environmental emissions.

[0085] Example No. 1

[0086] The ammonium polyfluoride fluorination reactor (synthesis reactor) pos.1 with a volume of 2 liters, equipped with an internal coaxial pipe acting as a circulation circuit, a mixing device and a thermostatting system, is filled with a melt of acidic ammonium polyfluoride NH4F∙1.2HF in an amount of 2.1 kg, the temperature of the melt is increased to 125˚C, the mixing device is turned on and dried fluorine is fed into the internal pipe at a flow rate of 6.4 cm 3 / s (36.5 g / hour), and into the annular space between the reactor body and the inner tube - ammonia at a flow rate of 5.0 cm 3 / s (12.85 g / hour). Gaseous products are removed from the reactor through the top of the phase separator located on the reactor lid, the liquid phase is removed through a pipe in the middle of the phase separator.

[0087] The reaction products enter the thermocatalytic reactor pos. 7, where the reaction of unsaturated nitrogen fluorides and nitrogen fluoride oxides with fluorine that has not reacted in the synthesis reactor takes place, and then to the unit pos. 8 for alkaline neutralization of fluorine and hydrogen fluoride with a KOH solution, the unit for drying with zeolite pos. 9, the unit for cryogenic rectification for purification from low-boiling gases (nitrogen and oxygen) pos. 10 and the unit for absorption separation of TFA and CF4 (carbon tetrachloride is used as the absorbent) pos. 11. TFA purified from CF4, after desorption, enters the rectification unit for purification from absorbent vapors pos. 12. TFA enriched in CF4 enters the unit pos. 5 for the conversion of TFA into CF4 on carbon.

[0088] The residual hydrogen fluoride content in the gas stream leaving the alkaline neutralization unit (item 8) is less than 1 ppm. The drying unit (item 9) removes water vapor, carbon dioxide, and nitrous oxide from the gas mixture, which entered the flow in the alkaline neutralization unit. The residual content of water vapor, nitrous oxide, and carbon dioxide is less than 50 ppm each. Absorbent vapors are present in the product entering purification at a level of 5%. TFA losses during rectification do not exceed 0.5%. The consumption of finished TFA is 18.6 g / hour. The residual absorbent content in the TFA does not exceed 10 ppm.

[0089] The main byproduct of the TFA synthesis process, PFA, is fed in liquid form into a 3-liter reactor with a fixed bed of granular carbon (Item 5) at a flow rate of 27.58 g / hour using a metering pump through a thermostatically controlled nozzle. Oxygen is also fed coaxially with the ammonium polyfluoride flow into the same reactor at a flow rate of 18.24 g / hour. Hydrofluoric acid with a hydrogen fluoride content of 92% is collected at the reactor outlet and sent for distillation to produce azeotropic hydrofluoric acid and anhydrous hydrogen fluoride (Item 14).

[0090] The second byproduct of the process—a mixture of TFA and CF4 with a 20.1% CF4 content—is sent to the CF4 production unit, which is a 3-liter reactor with a fixed bed of granular carbon (item 5). The mixture of TFA and CF4 is fed through a cooled nozzle at a flow rate of 1.19 g / hour into the carbon filtration combustion zone in the TFA. The resulting mixture of CF4 and nitrogen is separated by cryogenic distillation (item 14). The resulting CF4 product has a CF4 content of over 99.9%.

[0091] Thus, in the given example, in addition to TFA, the main product of the process, two other commercial products are obtained – anhydrous hydrogen fluoride and CF4, ensuring the practical waste-free nature of the technological process.

[0092] The output is TFA with a content of the main substance of more than 99.995%.

[0093] Example No. 2

[0094] A reactor similar to that described in example 1 is filled with 2.1 kg of ammonium acid polyfluoride NH4F∙2HF (PFA) melt, the melt temperature is increased to 135˚C, the mixing device is turned on, and fluorine is fed into the inner tube at a flow rate of 10.2 cm 3 / s (58.4 g / hour), and into the annular space between the reactor body and the inner tube - ammonia at a flow rate of 8.0 cm 3 / s (20.6 g / hour).

[0095] The gaseous products enter a thermal catalytic reactor, where unsaturated nitrogen fluorides and nitrogen fluoride oxides are fluorinated with additional fluorine. They are then transferred to an alkaline neutralization unit for hydrogen fluoride with a KOH solution, a zeolite drying unit, a cryogenic distillation unit for nitrogen removal, and an absorption unit for the separation of TFA and CF4 (carbon tetrachloride is used as the absorbent). After stripping, the TFA, purified from CF4, is fed to a distillation unit for removal of absorbent vapors.

[0096] TFA enriched in CF4 is fed into a tunnel-burner reactor along with methane and oxygen through a coaxial nozzle. The tunnel-burner reactor is a 50 mm diameter, 400 mm long tube equipped with a three-component nozzle. In the reactor, TFA and CFM react with methane and oxygen in combustion mode to form hydrogen fluoride, carbon dioxide, water, and nitrogen. The hydrogen fluoride concentration in the collected hydrofluoric acid is 90%. Anhydrous hydrogen fluoride and azeotropic hydrofluoric acid are obtained from the hydrofluoric acid by distillation.

[0097] The cryogenic distillation unit purifies the reaction mixture of nitrogen, leaving a residual nitrogen content of less than 100 ppm. TFA losses in the cryogenic distillation unit do not exceed 0.5%. Absorbent vapors are present in the product entering purification at a level of no more than 5%, so TFA losses during distillation do not exceed 0.5%. The flow rate of finished TFA is 30.75 g / hour. The concentration of sorbent vapor is no more than 10 ppm.

[0098] The main byproduct of the TFA synthesis process, ammonium polyfluoride, is fed in liquid form into a tunnel burner reactor using a three-component atomizing nozzle at a flow rate of 45.71 g / hour. Fluorine is also fed through the same nozzle at a flow rate of 49.26 g / hour and methane at a flow rate of 0.171 g / hour. The components react in combustion mode to form hydrogen fluoride, CF4, and nitrogen, which are separated by condensation to produce anhydrous hydrogen fluoride.

[0099] A mixture of CF4, nitrogen, and hydrogen fluoride vapor is fed to an alkaline column, then to a zeolite drying unit. The nitrogen and CF4 are separated by cryogenic distillation, producing CF4 with a purity of over 99.9%. These operations are similar to those used for TFA purification.

[0100] Thus, in the given example, in addition to TFA, the main product of the process, two other commercial products are obtained: anhydrous hydrogen fluoride and CF4, ensuring a virtually waste-free process. Processing is carried out by feeding ammonium polyfluoride (a byproduct of the TFA synthesis process) along with fluorine and methane into the reactor. Hydrofluoric acid is isolated by condensation. From hydrofluoric acid, anhydrous hydrogen fluoride and azeotropic hydrofluoric acid are obtained by distillation. Purification of CF4 from hydrogen fluoride and water vapor and separation of CF4 and nitrogen are carried out similarly to the corresponding TFA purification operations.

[0101] The output is TFA with a content of the main substance of more than 99.99%.

[0102] Losses of CF4 during cryogenic distillation are less than 1%.

[0103] Example No. 3

[0104] All operations are carried out similarly to example No. 2, but ammonium polyfluoride, a by-product of the TFA synthesis process, is processed in a tunnel burner reactor by reacting it with oxygen in the presence of methane in combustion mode to produce hydrofluoric acid.

[0105] Thus, in addition to nitrogen trifluoride, two other commercial products are obtained: anhydrous hydrogen fluoride and hydrofluoric acid. The main byproduct of the TFA synthesis process, ammonium polyfluoride, is fed in liquid form into a tunnel-burner reactor with an internal diameter of 50 mm and a length of 400 mm using a metering pump through a thermostatted spray nozzle. Oxygen and methane are fed into the same reactor coaxially with the ammonium polyfluoride flow. Hydrofluoric acid, containing approximately 40% hydrogen fluoride, is collected at the reactor outlet and can be used as a finished product.

[0106] Example No. 4

[0107] A reactor similar to that described in example 1 is filled with 2.1 kg of ammonium acid polyfluoride NH4F∙1.5HF melt, the melt temperature is increased to 130˚C, the mixing device is turned on, and fluorine is fed into the inner tube at a flow rate of 8.0 cm 3 / s (45.8 g / hour), and into the annular space between the reactor body and the inner tube - ammonia at a flow rate of 6.8 cm 3 / s (17.45 g / hour). See Table 4.1.

[0108] Since the initial ammonium polyfluoride has a moisture content of up to 1.5%, nitrogen oxides and oxyfluorides are present in the reaction products at the beginning of the synthesis process. Therefore, until the concentration of nitrogen oxides and fluorides-oxides in the gas stream at the reactor outlet falls below 5 vol.%, the gaseous products are sent from the synthesis reactor to the CF4 production unit, which is a 3-liter reactor with a fixed bed of granular carbon. The gaseous products are fed through a cooled nozzle at a flow rate of 25.95 g / hour into the carbon filtration combustion zone in the TFA. The resulting gas mixture, consisting of CF4, COF2, N2, CO2, and HF, is neutralized and dried in a manner similar to the TFA purification process. The CF4 and N2 mixture is separated by cryogenic distillation, similar to the TFA distillation, yielding CF4 with a main substance content of over 99.9%. See Table 4.2.

[0109] The ammonium polyfluoride byproduct formed during the synthesis process is fed in liquid form to a tunnel burner reactor, as described in Example 3, into which oxygen is added along with the ammonium polyfluoride. Hydrofluoric acid with a hydrogen fluoride content of 50-60% is collected at the reactor outlet and sent for distillation to produce azeotropic hydrofluoric acid and anhydrous hydrogen fluoride.

[0110] As a result, along with TFA, two more commercial products are obtained: anhydrous hydrogen fluoride and hydrofluoric acid.

[0111] Example #5

[0112] The process is carried out similarly to example 1, but the resulting ammonium polyfluoride, together with oxygen and methane, as described in example 3, is fed into a reactor with granulated carbon, as described in example 1. Hydrofluoric acid with a concentration of 90-95% is obtained, which is sent for rectification to obtain anhydrous hydrogen fluoride and azeotropic hydrofluoric acid.

[0113] Thus, in addition to TFA, two commercial products are obtained: anhydrous hydrogen fluoride and hydrofluoric acid.

[0114] Example 6.

[0115] The process is carried out similarly to example 2, but when processing ammonium polyfluoride, only fluorine is fed into a tunnel burner reactor, producing anhydrous hydrogen fluoride.

[0116] Thus, anhydrous hydrogen fluoride is obtained from the by-product of the TFA synthesis process – ammonium polyfluoride.

[0117] Example 7.

[0118] The process is similar to Example 2, but only methane is fed into the tunnel burner reactor along with the mixture of TFA and CF4. The resulting products are anhydrous hydrogen fluoride and CF4, which, after purification, become marketable products.

[0119] Example 8.

[0120] The process is similar to Example 4, but the mixture of TFA, nitrous oxide, and fluoride-nitrogen oxides is fed along with methane into a tunnel burner reactor. Hydrofluoric acid is produced, the concentration of which depends on the ratio of components in the mixture of TFA, nitrous oxide, and fluoride-nitrogen oxides. This acid is then sent for distillation to produce anhydrous hydrogen fluoride and azeotropic hydrofluoric acid.

[0121] Example 9.

[0122] The process is similar to Example 4, but a mixture of TFA, nitrous oxide, and nitrogen oxide fluorides, along with methane, is fed into a reactor with a granular carbon bed. Depending on the amount of methane fed, either HF or a mixture of CF4 and HF is produced, which are then sent for separation and purification to obtain marketable products.

[0123] Example 10.

[0124] The process is similar to Example 1, but methane is fed into a reactor with a granular carbon bed along with a mixture of TFA and CF4. Depending on the amount of methane fed, either HF or a mixture of CF4 and HF is produced, which are then sent for separation and purification to obtain marketable products.

[0125] Example 11.

[0126] The process is similar to Example 8, but oxygen is fed into the tunnel burner reactor along with a mixture of TFA, nitrous oxide, nitrogen fluoride oxides, and methane. Depending on the amount of methane fed, either HF or a mixture of CF4 and HF is produced, which are then sent for separation and purification to obtain marketable products. Result

[0127] Thus, the problem facing the developers of the proposed method has been solved: obtaining TFA with a content of CF4 and other impurities regulated in microelectronics, using fluorine without its cryogenic (explosive) purification and involving by-products of the developed technology in the production process in order to obtain commercially significant substances suitable for use in microelectronics.

[0128] As a result, a comprehensive, low-waste, explosion-proof technology for producing TFA was created, as well as a group of inorganic fluorides that are used in microelectronics – nitrogen trifluoride, carbon tetrafluoride, carbon difluoride-oxide, and fluoride.

[0129] The claimed invention meets the criterion of industrial applicability, since it can be manufactured using known technical means. Patent literature

[0130] Patent 1978 - US 4091081

[0131] Patent 2002 - RU 2178384

[0132] Patent 2008 - RU 2317251

Claims

A method for processing ammonium polyfluoride comprising fluorinating an ammonium polyfluoride melt with fluorine, neutralizing and drying a gas stream, removing volatile impurities, fluorine is fed to the fluorination stage, maintaining the acidity of ammonium polyfluoride in the range from NH4F 1.2HF to NH4F 2HF by adding ammonia, characterized in that the purification of nitrogen trifluoride from difluoramine, tetrafluorohydrazine and dinitrogen difluoride is carried out in a thermocatalytic reactor, the purification of nitrogen trifluoride from fluorine, hydrogen fluoride, silicon tetrafluoride, sulfur-containing acid gases and carbon dioxide is carried out with an alkaline solution, the drying of the gas stream is carried out with zeolite, and impurities with a boiling point lower than that of nitrogen trifluoride are removed by low-temperature rectification, carbon tetrafluoride is separated from nitrogen trifluoride by absorption, at these are gaseous by-products containing nitrogen trifluoride enriched with carbon tetrafluoride or nitrous oxide and fluoride-nitrogen oxides,obtained at the absorption separation stage and during reactor start-up, are brought into interaction with carbon or with hydrogen-containing substances, or with carbon and hydrogen-containing substances, or with hydrogen-containing substances and oxygen, or with carbon, hydrogen-containing substances and oxygen with separation by rectification of low-boiling substances and the isolation of carbon tetrafluoride or hydrogen fluoride, while after separation of the excess liquid ammonium polyfluoride from the reactor, it is sent for flaking or is reacted with oxygen, or with oxygen and carbon, or with oxygen and hydrogen-containing substances, or with both oxygen and carbon and hydrogen-containing substances, or with fluorine, or with fluorine and hydrogen-containing substances with separation by rectification of low-boiling substances and the isolation of hydrogen fluoride or hydrofluoric acid. The method according to paragraph 1, wherein the purification of nitrogen trifluoride from acidic impurities is carried out with an alkaline solution at an alkali concentration in the aqueous solution above 10% by weight. The method according to paragraph 1, wherein substances with a boiling point lower than that of nitrogen trifluoride are separated by rectification at a temperature from -110ºC in the bottom of the column to -170ºC in a dephlegmator. The method according to claim 1, wherein the separation of nitrogen trifluoride and carbon tetrafluoride is carried out by absorption using halogenated liquids. A method for producing nitrogen trifluoride used in a method for processing ammonium polyfluoride, comprising fluorinating an ammonium polyfluoride melt with fluorine, neutralizing and drying a gas stream, removing volatile impurities, wherein fluorine is fed to the fluorination stage, maintaining the acidity of ammonium polyfluoride in the range from NH4F 1.2HF to NH4F 2HF by adding ammonia, characterized in that the purification of nitrogen trifluoride from difluoroamine, tetrafluorohydrazine and dinitrogen difluoride is carried out in a thermocatalytic reactor, the purification of nitrogen trifluoride from fluorine, hydrogen fluoride, silicon tetrafluoride, sulfur-containing acid gases and carbon dioxide is carried out with an alkaline solution, the drying of the gas stream is carried out with zeolite, and impurities with a boiling point lower than that of nitrogen trifluoride are removed by low-temperature rectification, Carbon tetrafluoride is separated from nitrogen trifluoride by absorption. The method according to paragraph 5, wherein the purification of nitrogen trifluoride from acidic impurities is carried out with an alkaline solution at an alkali concentration in the aqueous solution above 10% by weight. The method according to paragraph 5, wherein substances with a boiling point lower than that of nitrogen trifluoride are separated by rectification at a temperature from -110ºC in the bottom of the column to -170ºC in a dephlegmator. The method according to claim 5, wherein the separation of nitrogen trifluoride and carbon tetrafluoride is carried out by absorption using halogenated liquids.

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