JP2007290918A - Method for producing ammonium cryolite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing ammonium cryolite being a raw material for producing nitrogen trifluoride useful as a cleaning gas. <P>SOLUTION: The method comprises reacting solid ammonium aluminum tetrafluoride with gaseous ammonia and gaseous hydrogen fluoride, reacting solid aluminum fluoride with gaseous ammonia and gaseous hydrogen fluoride, or reacting solid ammonium aluminum tetrafluoride and aluminum fluoride with gaseous ammonia and gaseous hydrogen fluoride. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing ammonium cryolite which is a raw material for producing nitrogen trifluoride useful as a cleaning gas.

Conventionally, as a method for producing ammonium cryolite ((NH ₄ ) ₃ AlF ₆ ), a method in which aluminum hydroxide, hydrofluoric acid (hydrogen fluoride aqueous solution), an aqueous ammonia solution are used as raw materials, or a tetrafluoroaluminum is used. A method of producing ammonium (NH ₄ AlF ₄ ) from a hydrofluoric acid slurry and ammonia (Patent Documents 1 to 5) or a method of producing a solution from hexafluoroaluminic acid (H ₃ AlF ₆ ) and an aqueous ammonia solution (Patent Document 6) Etc. are known. However, each of these methods is a reaction in an aqueous solution system, and there are problems that facilities are complicated and it is difficult to ensure safety because hydrofluoric acid is used. In particular, there is a problem that incidental equipment such as a dryer is necessary and the equipment cost is higher than that of the dry method.

As for the synthesis method of ammonium cryolite by dry method, ammonium cryolite is formed at 180 ° C from the results of differential thermogravimetric analysis on solid-solid reaction between alumina powder and ammonium fluoride (NH ₄ F). Has been reported by A.M.ABDEL REHIM (Non-Patent Document 1). Further, it is described that more stable tetrafluoroaluminum ammonium is produced from ammonium cryolite by thermal decomposition at 300 ° C. AKTYYAGI is a white ammonium cryolite film obtained by reacting metal Al shavings or plate with ammonium hydrogen difluoride (NH ₄ HF ₂ ) at 140 ° C. for 8 hours or at room temperature for 4 days. Has been reported (Non-patent Document 2).

  In these studies, the formation of ammonium cryolite was reported by the reaction between solids, but the yield and other matters are unknown, and ammonium cryolite is selectively used in industrially applicable purity and yield. It was unclear whether it could be obtained.

Further, it is disclosed that ammonium cryolite can be used for the synthesis of nitrogen trifluoride (NF ₃ ) (Patent Document 7). However, when ammonium cryolite is used to produce nitrogen trifluoride, tetrafluoroaluminum ammonium is produced as a reaction residue. Further, when the reaction temperature is 170 ° C. or higher, aluminum fluoride (AlF ₃ ) is also generated as a residue. At present, these residues are only treated as waste and are not effectively used. In order to reduce the environmental burden, it is desired to reduce the amount of waste, that is, to effectively use the residue.
Japanese Patent No. 2856636 Japanese Patent No. 3187544 JP 2002-121020 A JP 2001-048531 A JP 2000-169141 A US Pat. No. 3,773,905 Japanese Patent Application Laid-Open No. 60-071503 THERMAl ANALYSIS., 6th, 1, 357-362 (1980) Synth. React. Inorg. Met.org. Chem., 26 (1), 139-146 (1996)

  An object of the present invention is to easily and easily regenerate ammonium cryolite from tetrafluoroaluminum ammonium and aluminum fluoride, which are residues of ammonium cryolite used in the production of nitrogen trifluoride.

  As a result of intensive studies in view of the above-mentioned problems, the inventors of the present invention have made it possible to easily produce ammonium in a high yield simply by reacting solid tetrafluoroaluminum ammonium or aluminum fluoride with gaseous ammonia and gaseous hydrogen fluoride. The inventors have found that cryolite can be produced and have reached the present invention.

  That is, the present invention reacts solid tetrafluoroaluminum ammonium with gaseous ammonia and gaseous hydrogen fluoride, or reacts solid aluminum fluoride with gaseous ammonia and gaseous hydrogen fluoride. Or a method for producing ammonium cryolite characterized by reacting solid tetrafluoroaluminum ammonium and aluminum fluoride, gaseous ammonia and gaseous hydrogen fluoride.

  By the method of the present invention, ammonium cryolite that is a raw material for producing nitrogen trifluoride can be easily synthesized. In addition, by regenerating tetrafluoroaluminum ammonium or aluminum fluoride, which has been discarded as unnecessary materials, into ammonium cryolite, it is possible to reduce waste and help protect the environment.

  In the present invention, the ratio of adding tetrafluoroaluminum ammonium or aluminum fluoride and ammonia and hydrogen fluoride is only one equivalent because the reaction proceeds almost stoichiometrically in the gas sealing method. Although there is no restriction | limiting in particular in the temperature at the time of making it react, 15 to 250 degreeC is preferable, More preferably, 50 to less than 200 degreeC is good. If it is less than 15 ° C., it takes time for the reaction to proceed, and if it exceeds 250 ° C., the decomposition of ammonium cryolite becomes remarkable and the corrosion of the metal reactor becomes remarkable, which is not preferable.

  In the present invention, when the amount of ammonia and hydrogen fluoride added to tetrafluoroaluminum ammonium or aluminum fluoride exceeds 1 equivalent, ammonium fluoride or ammonium difluoride is generated as a by-product. Producing nitrogen trifluoride using ammonium cryolite containing ammonium fluoride or ammonium difluoride as a raw material is not preferable because the amount of nitrogen in nitrogen trifluoride increases. Therefore, it is necessary to remove by-products in these raw materials. As a result of intensive studies, the inventors have found that ammonium fluoride or ammonium hydrogen difluoride can be removed by evacuation in the temperature range of 50 ° C to 190 ° C. The pressure condition for evacuation is not particularly limited as long as it is below atmospheric pressure.

  Furthermore, regarding the details of the input amounts of ammonia and hydrogen fluoride in the present invention, in the case of tetrafluoroaluminum ammonium, the input amount of ammonia and hydrogen fluoride to be added is 1.8 to 3.0 in terms of a molar ratio with respect to tetrafluoroaluminum ammonium. The following is preferable, and more preferably 2.0 or more and 2.2 or less. If the input ratio of ammonia and hydrogen fluoride is less than 1.8 in terms of a molar ratio with respect to tetrafluoroaluminum ammonium, the purity of ammonium cryolite produced in the present invention will be low. This interferes with the production of nitrogen fluoride. Further, when the amount of ammonia and hydrogen fluoride input exceeds 3.0 in terms of molar ratio to tetrafluoroaluminum ammonium, the amount of ammonium fluoride or ammonium difluoride generated as a by-product increases, so this by-product It takes time to remove and is not efficient.

  In the case of aluminum fluoride, the amount of ammonia and hydrogen fluoride added is preferably 2.7 or more and 4.5 or less, more preferably 3.0 or more and 3.2 or less in terms of molar ratio to aluminum fluoride. . If the input amount of ammonia and hydrogen fluoride is less than 2.7 in terms of molar ratio to tetrafluoroaluminum ammonium, the purity of the ammonium cryolite produced in the present invention will be low. This interferes with the production of nitrogen fluoride. Furthermore, if the amount of ammonia and hydrogen fluoride input exceeds 4.5 by molar ratio with respect to tetrafluoroaluminum ammonium, the amount of ammonium fluoride or ammonium difluoride produced as a by-product increases, so this by-product It takes time to remove and is not efficient.

When a mixture of tetrafluoroaluminum ammonium and aluminum fluoride is used, the upper and lower limits of the preferable amounts of ammonia and hydrogen fluoride vary depending on the ratio of tetrafluoroaluminum ammonium and aluminum fluoride in the mixture.
Hereinafter, the present invention will be described in detail by way of examples.

Examples 1-4
In a 1000 cc PTFE container, 0.04 mol of tetrafluoroaluminum ammonium powder, 0.08 mol of hydrogen fluoride gas, and 0.08 mol of ammonia gas are placed and left for 14 hours, and then X-ray diffraction analysis of the powder is performed. The reaction yield of ammonium cryolite was calculated. Table 1 shows the reaction conditions and the calculation results of the yield. From the results in Table 1, it can be seen that ammonium cryolite has been generated.

Examples 5 and 6
A solid residue after producing nitrogen trifluoride by the reaction of ammonium cryolite and fluorine (F ₂ ) was collected and subjected to X-ray diffraction analysis. As a result, a powder of 100 wt% tetrafluoroaluminum ammonium was obtained. there were. 500 g of this powder was placed in a pan-type granulator with a lid having a diameter of 30 cm and fixed at a temperature of 130 ° C. (Example 5) or 150 ° C. (Example 6). Furthermore, in any case, the rotation speed of the bread granulator is fixed at 45 rpm, and the powder in the bread granulator is hydrogen fluoride gas at 850 SCCM, nitrogen gas at 100 SCCM, and ammonia gas at 850 SCCM at a flow rate of 220. As a result of spraying for a minute, it was confirmed by X-ray diffraction analysis that the powder in the bread granulator was 100 wt% ammonium cryolite.

Example 7
Put 0.04 mol of aluminum fluoride powder in a 1000 cc PTFE container, mix 0.12 mol of hydrogen fluoride gas and 0.12 mol of ammonia gas, and leave it at 100 ° C. for 14 hours. As a result of X-ray diffraction analysis, 75 wt% ammonium cryolite was produced. The remainder was 24 wt% aluminum fluoride and 1 wt% tetrafluoroaluminum ammonium.

Example 8
The solid residue after producing nitrogen trifluoride by the reaction of ammonium cryolite and fluorine was collected and subjected to X-ray diffraction analysis. As a result, tetrafluoroaluminum ammonium was 97.6 wt%, aluminum fluoride. Was 2.4 wt%. 500 g of this residue was put into a stainless steel reactor equipped with a powder stirrer heated to 100 ° C. Furthermore, the rotation speed of the stirrer is fixed at 10 rpm, and the flow rate of hydrogen fluoride gas is 850 SCCM, nitrogen gas is 100 SCCM, and ammonia gas is 850 SCCM while adjusting the pressure inside the reactor to atmospheric pressure by the pressure control valve. For 300 minutes. Thereafter, the powder inside the reactor was taken out and analyzed by X-ray diffraction. As a result, it was found to be a mixture of 57 wt% ammonium cryolite, 40 wt% ammonium fluoride, and 3 wt% ammonium difluoride. Next, the mixture powder is heated to 150 ° C. while being stirred in the reactor, evacuated at a pressure between 0.1 kPa and 1.4 kPa for 2 hours, and then the powder inside the reactor is taken out. An analysis by X-ray diffraction confirmed that it was almost 100% ammonium cryolite.

  Furthermore, when this powder was put into a reactor equipped with a stirrer and fluorine was circulated at a flow rate of 100 SCCM at 150 ° C. for 2 hours, the gas was analyzed by infrared absorption analysis and gas chromatography analysis, and nitrogen trifluoride, hydrogen fluoride and Generation of nitrogen was confirmed, and the residue was confirmed to be a mixture of tetrafluoroaluminum ammonium and ammonium cryolite by X-ray diffraction analysis.

Example 9, Comparative Example 1
The solid residue after producing nitrogen trifluoride was recovered by the reaction of ammonium cryolite synthesized from aluminum hydroxide, aqueous ammonia and aqueous hydrogen fluoride with fluorine. As a result of X-ray diffraction analysis of this residue, 99 wt% of tetrafluoroaluminum ammonium and 1 wt% of aluminum fluoride were found. 121 g of this residue was placed in a PFA container heated to 150 ° C., and hydrogen fluoride gas was circulated at a flow rate of 100 SCCM, nitrogen gas at 25 SCCM, and ammonia gas at a flow rate of 100 SCCM for 5 hours. Then, after heating to 70 ° C. and evacuating at a pressure of 0.13 kPa for 10 minutes, the internal powder was analyzed by X-ray diffraction, and it was confirmed that it was almost 100% ammonium cryolite. (Example 9) However, when the drying temperature is raised to 260 ° C. and evacuation is carried out at a pressure of 0.13 kPa for 10 minutes, the decomposition of ammonia cryolite proceeds and it can be obtained only in a state where 16 wt% of tetrafluoroaluminum ammonium is mixed. There wasn't. (Comparative Example 1)

Claims (3)

Tetrafluoroaluminum ammonium (NH ₄ AlF ₄ ), ammonium cryolite ((NH ₄ ) ₃ AlF ₆ ) characterized by reacting gaseous hydrogen fluoride (HF) and gaseous ammonia (NH ₃ ) Production method. A method for producing ammonium cryolite ((NH ₄ ) ₃ AlF ₆ ), comprising reacting aluminum fluoride (AlF ₃ ), gaseous hydrogen fluoride (HF), and gaseous ammonia (NH ₃ ). Ammonium cryolite characterized by reacting tetrafluoroaluminum ammonium (NH ₄ AlF ₄ ), aluminum fluoride (AlF ₃ ), gaseous hydrogen fluoride (HF) and gaseous ammonia (NH ₃ ) (( NH ₄ ) ₃ AlF ₆ ) production method.