Crude Lf -> - 2^- 4

US 20110286911A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2011/0286911 A1 Hagiwara et al. (43) Pub. Date: Nov. 24, 2011

(54) HYDROGEN FLUORIDE PURIFICATION Publication Classification METHOD (51) Int. Cl. COIB 7/19 (2006.01) (75) Inventors: Rika Hagiwara, Kyoto (JP); Kazuhiko Matsumoto, Kyoto (JP) (52) U.S. Cl...... 423/484; 423/483 (57) ABSTRACT (73) Assignee: KYOTO UNIVERSITY, Kyoto-shi, Kyoto (JP) To provide a novel method for purifying hydrogen fluoride, capable of efficiently reducing the content of arsenic in (21) Appl. No.: 13/131,703 hydrogen fluoride. The step (a) of bringing a crude hydrogen fluoride containing (22) PCT Fled: Nov. 25, 2009 arsenic trifluoride into contact with an oxidizing agent of a metal fluoride in a liquid State is carried out, for example, in (86) PCT NO.: PCT/UP2009/069836 a reactor (11) to obtain a reaction mixture wherein arsenic pentafluoride is formed by oxidizing arsenic trifluoride with S371 (c)(1), the oxidizing agent of the metal fluoride through a liquid (2), (4) Date: Aug. 15, 2011 liquid reaction; and the step (b) of separating purified hydro gen fluoride from the reaction mixture is carried out, for (30) Foreign Application Priority Data example, by a separator (13), the thus obtained purified hydrogen fluoride having a lower content of arsenic than that Nov. 28, 2008 (JP) ...... 2008-304711 of the crude hydrogen fluoride. Crude lf -> - 2^- 4.

Pur ified HF 11 Patent Application Publication Nov. 24, 2011 Sheet 1 of 2 US 2011/0286911 A1

Fig. 2 Crude HF

--- Pur fied HF

Purified HF Patent Application Publication Nov. 24, 2011 Sheet 2 of 2 US 2011/0286911 A1

Fig. 4 Crude HF->

w Pir fed HF US 2011/02869 11 A1 Nov. 24, 2011

HYDROGEN FLUORIDE PURIFICATION of arsenic is used as a reaction raw material, while a low METHOD quality fluorite having a high content of arsenic is not used at present. TECHNICAL FIELD Citation List 0001. The present invention relates to a method for puri Patent Literature fying hydrogen fluoride, and more particularly to a method 0005 Patent Literature 1: JP 47-16407B for reducing the content of arsenic in hydrogen fluoride. The 0006 Patent Literature 2: JP 61-151002 A present invention also relates to a method for purifying hydro 0007 Patent Literature 3: JP 2-502277 A gen fluoride using Such a purification method. 0008 Patent Literature 4: JP 3-146401 A 0009 Patent Literature 5: JP 3-205304A BACKGROUND ART 0010 Patent Literature 6: JP 6-263406 A O011 Patent Literature 7: JP 7-504149A 0002 Hydrogen fluoride is industrially produced by react ing fluorite (containing CaF2 as a main component) with SUMMARY OF INVENTION sulfuric acid (HSO) under heating (CaF+HSO->2HF + Technical Problem CaSO4), and collecting the reaction mixture, which contains thus generated hydrogen fluoride (HF), in the form of a gas, 0012 However, a high-quality fluorite is unevenly distrib followed by distillation. uted, and almost all of the high-quality fluorites is produced in 0003. A rude ore of fluorite may contain, in addition to China, presently. Therefore, exhaustion of resource is con cerned. Further, due to export restraint of the Chinese Gov calcium fluoride (CaF2) as a main component, impurities ernment, the permitted export quantity of the high-quality Such as silicon dioxide (SiO2), calcium carbonate (CaCO) fluorite has decreased, which has caused an increase in its and arsenic (AS). Usually, a commercially available fluorite price. has already been purified, and those which are now used in the 0013 Under these circumstances, there has been an industrial production of hydrogen fluoride contain usually increase in demand for utilization of a low-quality fluorite in about 1% by mass of impurities such as silicon dioxide an industrial scale in place of the high-quality fluorite. In (SiO2), calcium carbonate (CaCO) and arsenic (As). When order to obtain a high-purity hydrogen fluoride having a low hydrogen fluoride is produced by using such fluorite, silicon content of arsenic by using the low-quality fluorite, it is pos dioxide reacts with hydrogen fluoride to form silicon fluoride sible to take either a measure in which the low-quality fluorite (SiF). Silicon fluoride can be removed comparatively easily is purified in advance thereby reducing the content of arsenic by distillation (silicon fluoride and hydrogen fluoride can be thereof and then hydrogen fluoride is obtained using the puri separated from each other by distillation, the former as a fied fluorite, or a measure in which a crude hydrogen fluoride gaseous Substance and the latter as a condensate). Calcium is obtained using the low-quality fluorite and then the crude carbonate reacts with sulfuric acid to form calcium sulfate hydrogen fluoride is purified thereby reducing the content of (CaSO), carbon dioxide (CO) and water (H2O). Calcium arsenic thereof. However, since a conventional purification Sulfate remains in a reacting furnace and is not mixed in method of fluorite has not sufficient arsenic removing ability, hydrogen fluoride collected in the form of a gaseous Sub it is difficult to take the former measure. Therefore, in order to stance, and water can be easily removed by simple distillation take the latter measure, it has been desired to develop a and also carbon dioxide can be removed comparatively easily method for purifying hydrogen fluoride capable of efficiently by distillation. Therefore, both of them are not mixed in reducing the content of arsenic in hydrogen fluoride. hydrogen fluoride. In contrast, arsenic, what kind of form 0014. There have been proposed, as the method for puri which takes in fluorite is not clearly understood, reacts with fying hydrogen fluoride capable of reducing the content of hydrogen fluoride to form arsenic trifluoride (ASF). Since a arsenic in hydrogen fluoride, a method in which hydrofluoric difference in a boiling point between arsenic trifluoride and acid is treated with potassium permanganate (KMnO) and/or potassium dichromate (KCr2O7) and then distillation is car hydrogen fluoride is small (a boiling point of HF is 19.5°C., ried out in the presence of an inorganic salt of a divalent iron a boiling point of ASF is 63°C.), it is difficult to completely (Patent Literature 1), a method in which a fluorine gas is remove arsenic trifluoride by distillation, and therefore added to hydrofluoric acid and then distillation is carried out arsenic trifluoride is mixed in hydrogen fluoride as a product. (Patent Literature 2), a method in which an anhydrous hydro 0004 Hydrogen fluoride is utilized as a starting substance gen fluoride is brought into contact with hydrogen peroxide in for chlorofluorocarbon gases and fluororesins, which are the presence of a catalyst and then distillation is carried out fluorine chemical products, and is also utilized as an etching (Patent Literature 3), methods in which an anhydrous hydro agent in the production of a semiconductor. When arsenic is gen fluoride is reacted with a Sulfur compound (for example, mixed in hydrogen fluoride, there are problems that in the HS) or an iodine compound (for example, HI) to form a production of a chlorofluorocarbon gas, a catalyst can be precipitate of arsenic sulfide or arsenic iodide (Patent Litera poisoned, and that in the production of a semiconductor, tures 4 and 5), methods in which hydrofluoric acid is sub arsenic can diffuse into a semiconductor device thereby exert jected to an electrolytic operation (Patent Literatures 6 and 7) ing an adverse influence on operation of the device. There and the like. However, these methods have problems that a fore, there is a demand for a high-purity hydrogen fluoride reaction requires a long time (Patent Literatures 1, 2 and 3), a which contains as little arsenic as possible. In the process of large amount of waste is generated (Patent Literature 1), it is producing a high-purity hydrogen fluoride in an industrial difficult to remove a fluorine gas (Patent Literature 2), it is scale, a high-quality fluorite having an originally low content impossible to sufficiently decrease the content of arsenic US 2011/02869 11 A1 Nov. 24, 2011

(Patent Literatures 2, 4 and 5), and an electrolytic membrane 0023. According to one aspect of the present invention, has insufficient durability (Patent Literatures 6 and 7). there is provided a method for purifying hydrogen fluoride, 0015. An object of the present invention is to provide a which comprises the steps of: novel method for purifying hydrogen fluoride, capable of at 0024 (a) bringing a crude hydrogen fluoride containing least partially alleviating the aforementioned problems in the arsenic trifluoride into contact with an oxidizing agent of a prior art, and efficiently reducing the content of arsenic in metal fluoride in a liquid State to obtain a reaction mixture hydrogen fluoride. wherein arsenic pentafluoride is formed by oxidizing arsenic trifluoride with the oxidizing agent of the metal fluoride Solution to Problem through a liquid-liquid reaction, and 0016 Since arsenic existing in hydrogen fluoride takes a 0025 (b) separating purified hydrogen fluoride from the form of arsenic trifluoride (ASE), the present inventors have reaction mixture, the thus obtained purified hydrogen fluoride organized and studied methods of separating arsenic trifluo having a lower content of arsenic than that of the crude hydro ride from hydrogen fluoride. gen fluoride. 0017. As described above, since a difference in a boiling 0026. According to the method for purifying hydrogen point between arsenic trifluoride and hydrogen fluoride is fluoride of the present invention, at least the aforementioned small (a boiling point of HF is 19.5°C., a boiling point of problems in the prior art can be partially alleviated and the AsF is 63°C.) and also it is difficult to form a complex salt content of arsenic in hydrogen fluoride can be efficiently together with HF (thus, it is difficult to undergo ionization in decreased. HF), it is difficult to remove arsenic trifluoride from hydrogen fluoride only by simple distillation. 0027 More particularly, there is a remarkable advantage 0018. The basic principle of the widely used methods that the use of an oxidizing agent of a metal fluoride in the step among conventional methods for purifying hydrogen fluo (a) of the present invention can realize an oxidation reaction rides is that arsenic trifluoride (ASF) is converted into arsenic converting arsenic trifluoride into arsenic pentafluoride in a pentafluoride (ASFs) and then arsenic pentafluoride is sepa liquid-liquid reaction, and the reaction rate thereof is higher rated from hydrogen fluoride by distillation (see, for example, than those of a Solid-liquid reaction and a gas-liquid reaction. Patent Literatures 1-3). This utilizes the fact that, whereas Therefore, while not intending to limit the present invention, arsenic trifluoride (ASF) is volatile, arsenic pentafluoride for example, the step (a), preferably the entirety of the steps (ASFs) forms complex salt together with HF and undergoes (a) and (b) can also be continuously carried out. The reaction ionization in HF (likely to remain in a liquid phase). mixture obtained by the step (a) of the present invention may 0019. In order to convert arsenic trifluoride into arsenic contain, in addition to hydrogen fluoride, a metal fluoride (an pentafluoride, oxidation of arsenic trifluoride with solid oxi oxidizing agent of a metal fluoride and a reduced metal fluo dizing agents such as potassium permanganate (KMnO) ride derived therefrom) and arsenic pentafluoride. In the step and/or potassium dichromate (KCr2O7) is utilized (see (b), the metal fluoride and arsenic pentafluoride can be easily Patent Literature 1). However, there is a problem that the separated and removed, for example, by a distillation or rec reaction rate is low because of a solid-liquid reaction, and also tification operation, and thus a purified hydrogen fluoride can there is a disadvantage that it requires dispose of MnO, and be obtained. Cr-O as wastes, which are by-produced in the oxidation 0028. The oxidizing agent of the metal fluoride may be reaction. those comprising a metal fluoride which is able to oxidize 0020. In order to convert arsenic trifluoride into arsenic arsenic trifluoride into arsenic pentafluoride in hydrogen pentafluoride, it is the most excellent way to react arsenic fluoride. Although such metal fluoride can be selected by a trifluoride with a fluorine (F) gas (see, for example, Patent trial-and-error procedure, it can be taken into account as one Literature 2) in respect of elimination of by-products. How selection indicator that an oxidation-reduction potential of ever, there is a problem that the reaction rate is comparatively the following reaction for the metal fluoride: low because of a gas-liquid reaction, and also there is a fundamental problem that it is difficult to remove an excess F. gas from hydrogen fluoride in respect of purification of wherein M represents a metal atom, n represents an integer of hydrogen fluoride. 2 or more, m represents an integer of 1 or more, and n and n-m 0021. Then, the present inventors focused on fluorine. represent an oxidation number which can be possessed by a Fluorine is an element which has the smallest ionic radius metal atom M among halogens and the largest electronegativity among all is higher than an oxidation-reduction potential of the follow elements, and is able to form compounds with many other ing reaction: elements at different oxidation states, and especially able to form a compound in a particularly high oxidation state (a compound containing more fluorine elements). Particularly, Herein, the oxidation-reduction potential is an oxidation-re since a metal fluoride easily varies the oxidation state and also duction potential in HF. is able to take various forms (so that it can be dissolved in 0029 Specifically, it is possible to use, as the oxidizing hydrogen fluoride), it is considered that the metal fluoride is agent of the metal fluoride, fluorides of metals such as tita Suited for use as an oxidizing agent capable of converting nium, Vanadium, chromium, manganese, iron, cobalt, nickel, arsenic trifluoride into arsenic pentafluoride so as to purify copper, Zinc, Zirconium, niobium, molybdenum, ruthenium, hydrogen fluoride. rhodium, palladium, silver, cadmium, hafnium, tantalum, 0022. The present inventors have intensively studied tungsten, rhenium, osmium, iridium, platinum, gold, mercury based on the above viewpoint, and thus the present invention and bismuth, wherein the fluorides of metals comprises a has been completed. metal fluoride in a higher oxidation state than a stable state. US 2011/02869 11 A1 Nov. 24, 2011

0030. More specifically, the metal fluoride which can be AMF utilized as the oxidizing agent comprises, for example, at least one kind of metal fluoride selected from the group consisting and of the following formulas: AMF, MF, wherein MIFF, A-Li, Na, Ag, K, Rb, or Cs, MF, A'=Ca, Sr, Ba, Cd, or Hg, and M'=Ag, MFs M'=Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Rh, wherein Pod, Ag, Ir, or Au, M-Ti,V, Cr, Mn, Co, Ni, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, W, Re, Os, Ir, Pt, or Hg, M'=Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Rh, Pod, Ag, Ir, or Au, and M-Ti,V, Cr, Mn, Co, Ni, Zr, Nb, Mo, Ru, Rh, Pd, M=Nb, Mo, Ru, Rh, Ta, W, Re, Os, Ir, Pt, Au, or Bi Ag, Cd, Hf, W, Re, Os, Ir, Pt, or Hg, (it should be noted that these groups comprise AgFASF and and KNiFe which are respectively used in below-mentioned Embodiments 1 and 2, and KMnF, etc.). M=Nb, Mo, Ru, Rh, Ta, W, Re, Os, Ir, Pt, Au, or Bi. 0037. As the oxidizing agent of the metal fluoride, these 0031. Among these, those having high solubility in hydro double salts or complexes of metal fluorides may be used gen fluoride are preferable. alone, or any two or more kinds of them may be used in 0032. The oxidizing agent of the metal fluoride may con combination. tain such a metal fluoride alone, or may contain any two or 0038. The reaction mixture obtained in the step (a) may more kinds of them in combination. comprise a reduced metal fluoride derived from the oxidizing 0033. The aforementioned metal fluoride per se is often agent. It is preferred to utilize this reduced metal fluoride so as insoluble in hydrogen fluoride, but can be dissolved in hydro to obtain the oxidizing agent of the metal fluoride. Thereby, gen fluoride by being used in the form of a double salt or a the metal fluoride can be recycled without forming wastes. complex salt. 0039. In one embodiment of the present invention, the step 0034. In the present invention, “double salt or complex (b) can be carried out by the steps of: salt' means a salt obtained from two or more kinds of salts, 0040 (i) bringing the reaction mixture into contact with a and may be either of those which generate the same ions as Lewis basic fluoride to form a double salt or a complex salt of those in the original salts (double salt) and those which gen arsenic pentafluoride and the Lewis basic fluoride, thereby erate ions different from those in the original salts (complex obtaining a contact mixture in which arsenic pentafluoride is salt). immobilized, and 0035. It is possible to use, as the compound which can 0041 (ii) separating a purified hydrogen fluoride from the form a double salt or complex salt together with the metal contact mixture. fluoride, either or both of a Lewis acidic compound (a com 0042. Although arsenic pentafluoride may be separated by pound which accepts an electron pair from the metal fluoride) the distillation or rectification operation as described above, and a Lewis basic compound (a compound which donates an arsenic pentafluoride, according to this embodiment, forms a electron pair to the metal fluoride) according to the metal double salt or complex salt together with a Lewis basic fluo fluoride. As the Lewis acidic and/or Lewis basic compound, it ride to be immobilized, so that a higher-purity purified hydro is preferred to use a Lewis acidic and/or Lewis basic fluoride gen fluoride can be obtained simply and easily. So as to obtain a higher-purity hydrogen fluoride. However, it 0043. This embodiment can be applied to the cases using is not limited thereto. For example, a Lewis acidic and/or Some among the aforementioned double salt or complex of Lewis basic chloride or oxide can be used. the metal fluoride, for example, AgFASF, AgFSbF, AgF 0036 Specifically, the double salt or complex of the metal BiF and the like are used as the oxidizing agent. fluoride comprises, for example, at least one kind selected 0044. In this embodiment, the step (i) may comprise sepa from the group consisting of AgFASF, AgFSbFe, AgFBiF. rating a hydrogen fluoride fraction containing arsenic pen AgFBF, AgFAuFe, AgFIrF. AgFRuF. AgFAuF. tafluoride from the reaction mixture and bringing this hydro CSKAgF and the following formulas: gen fluoride fraction into contact with a Lewis basic fluoride. As mentioned above, the reaction mixture obtained by the A/M/F step (a) of the present invention may contain, in addition to hydrogen fluoride, a metal fluoride (an oxidizing agent of a AMIF, metal fluoride and a reduced metal fluoride derived there from) and arsenic pentafluoride. Thus, when the hydrogen AMIFs, fluoride fraction containing arsenic pentafluoride is separated AM'Fs, from the reaction mixture, resulting in a state where the metal fluoride is not contained, and then the hydrogen fluoride AMF fraction is brought into contact with the Lewis basic fluoride, US 2011/02869 11 A1 Nov. 24, 2011

the metal fluoride is not mixed in the obtained contact mix 0053 Any of a crude hydrogen fluoride can be used in the ture, and therefore it is advantageous to recycle the metal purification method of the present invention, as long as it fluoride. contains arsenic in the form of arsenic trifluoride. It is pos 0045 Examples of the Lewis basic fluoride include LiF, sible to use the crude hydrogen fluoride of which content of NaF. KF, Rbf, CsP, AgF. BeF. MgF, SrF, CaF2, BaF2 and arsenic is, for example, about 10,000 ppm by mass or less, the like. Among these Lewis basic fluorides, NaF and KF, particularly about 3,000 ppm by mass or less and, for which have strong Lewis basicity and are inexpensive, are example, about 0.1 ppm by mass or more, particularly 3 ppm preferable. by mass or more. 0046 Lewis basic fluorides may be used alone, or any two 0054 The purified hydrogen fluoride obtained by the puri or more kinds of them may be used in combination. fication method of the present invention may have any content 0047. In another embodiment of the present invention, of arsenic, as long as it is decreased from the original crude 0048 a double salt or a complex salt of arsenic pentafluo hydrogen fluoride. For example, it is possible to decrease to ride and the metal fluoride derived from the oxidizing agent is about 10 ppm by mass or less, and preferably about 3 ppm by formed in the reaction mixture obtained in the step (a), mass or less, although depending on the content of arsenic of thereby immobilizing arsenic pentafluoride, and the original crude hydrogen fluoride. In case the content of arsenic of the crude hydrogen fluoride is not so high, the 0049 step (b) can be carried out by directly separating a content of arsenic of the obtained purified hydrogen fluoride purified hydrogen fluoride from the reaction mixture. becomes much lower. 0050. According to the metal fluoride used as the oxidiz 0055 According to another aspect of the present inven ing agent, arsenic pentafluoride can be immobilized early by tion, there is also provided a method for producing hydrogen forming a double salt or a complex salt together with the fluoride, which comprises: metal fluoride in the reaction mixture as in the above, also in 0056 reacting fluorite with sulfuric acid to obtain a crude this embodiment, a high-purity purified hydrogen fluoride hydrogen fluoride, and can be obtained simply and easily. 0057 subjecting the crude hydrogen fluoride to the afore 0051. This embodiment can be applied in the cases using mentioned method for purifying hydrogen fluoride of the Some among the aforementioned double salt or complex of present invention to obtain a purified hydrogen fluoride. the metal fluoride, for example, at least one kind selected 0.058 According to the method for producing hydrogen from the group consisting of AgFBF, AgFAuF. AgFIrF. fluoride of the present invention, it becomes possible to obtain AgFRuF. AgFAuF, CSKAgF and the following formu a high-purity hydrogen fluoride even in a case of using a las: low-quality fluorite of which content of arsenic is compara A.MF4. tively high. 0059. It is possible to use, as fluorite used in the production A.MIIIF4. method of the present invention, fluorite of which content of arsenic is, for example, about 10,000 ppm by mass or less and, AllMF 5 for example, about 0.1 ppm by mass or more, particularly 3 AMF, ppm by mass or more.

AIMF s ADVANTAGEOUSEFFECTS OF INVENTION 0060 According to the present invention, the novel AMF method for purifying hydrogen fluoride is provided. In the and method for purifying hydrogen fluoride of the present inven tion, arsenic trifluoride is oxidized into arsenic pentafluoride AMF 7 by a liquid-liquid reaction using an oxidizing agent of a metal fluoride and then a purified hydrogen fluoride is separated, wherein and thereby allowing an oxidation reaction to proceed A-Li, Na, Ag, K, Rb, or Cs, quickly, the content of arsenic in hydrogen fluoride can be efficiently decreased. A'=Ca, Sr, Ba, Cd, or Hg, 0061 Also, according to the present invention, the method M'=Ag, for producing hydrogen fluoride utilizing the purification method is also provided. According to the method for pro M'=Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Rh, ducing hydrogen fluoride of the present invention, a high Pod, Ag, Ir, or Au, purity hydrogen fluoride can be obtained even in a case of using a low-quality fluorite in which the content of arsenic is M-Ti,V, Cr, Mn, Co, Ni, Zr, Nb, Mo, Ru, Rh, Pd, comparatively high. Ag, Cd, Hf, W, Re, Os, Ir, Pt, or Hg, BRIEF DESCRIPTION OF DRAWINGS and 0062 FIG. 1 is a diagram schematically explaining a M=Nb, Mo, Ru, Rh, Ta, W, Re, Os, Ir, Pt, Au, or Bi. method for purifying hydrogen fluoride in one embodiment 0052. In the present invention, “immobilization' com of the present invention. prises the fact that a portion of the product due to complex 0063 FIG. 2 is a diagram schematically explaining modi ation may be dissolved, but also comprises that preferably fication of the embodiment of FIG. 1. most of the product, more preferably substantially the entire 0064 FIG. 3 is a diagram schematically explaining product is in a solid state. another modification of the embodiment of FIG. 1. US 2011/02869 11 A1 Nov. 24, 2011

0065 FIG. 4 is a diagram schematically explaining a 0075. The objective HF is separated as a hydrogen fluoride method for purifying hydrogen fluoride in another embodi fraction in a vapor phase state, for example, by distillation ment of the present invention. through heating of the reactor 11, and then taken out of the reactor 11 through a line 4. DESCRIPTION OF EMBODIMENTS 0076 AsFs is contained in the hydrogen fluoride fraction. 0077 On the other hand, since the metal fluoride generally 0066. Some representative embodiments of the present has little vapor pressure, AgASF and AgFASF remain in the invention will be described below with reference to the reactor 11 without being taken out as a vapor. accompanying drawings. 0078. The hydrogen fluoride fraction (HF and ASEs) taken out of the reactor 11 in a vapor phase state is transferred to a Embodiment 1 separator 13, in which a Lewis basic fluoride has been charged in advance, in a liquid state through a line 6 via a 0067. The present embodiment relates to an embodiment condenser, thereby bringing the hydrogen fluoride fraction of a method for purifying hydrogen fluoride in which arsenic into contact with the Lewis basic fluoride. pentafluoride generated by an oxidation reaction of arsenic 0079. In the present embodiment, NaF is used as the Lewis trifluoride is free in the reaction mixture (arsenic pentafluo basic fluoride. NaF is excessively charged (or filled) in the ride is not immobilized as a result of the formation of a double separator 13 in a solid State, for example, as particles in salt or a complex Salt with a metal fluoride used as an oxidiz advance. While not intending to limit the present embodi ing agent). ment, since HF exists in a comparatively large amount, NaF 0068 Referring to FIG. 1, a crude hydrogen fluoride (an can be dissolved in HF. hydrous) is Supplied in a liquid State to a reactor 11, in which 0080. In the separator 13, AsFs contained in the hydrogen an oxidizing agent of a metal fluoride has been charged in fluoride fraction is complexed with NaF to form NaAsF in a advance, through a line 2, thereby bringing the crude hydro Solid state. gen fluoride into contact with the oxidizing agent of the metal fluoride in the liquid state. 0069. The crude hydrogen fluoride contains, in addition to I0081. This complexation is, for example, carried out under HF, arsenic in the form of AsF. The content of arsenic of the about 0.01 to 1 MPa at about 0 to 30° C. crude hydrogen fluoride may be, for example, about 10,000 I0082. The contact mixture obtained in the separator 13 ppm by mass or less, particularly about 3,000 ppm by mass or includes HF, NaAsF and the unreacted NaF, and AsFs is less and, for example, about 0.1 ppm by mass or more, par immobilized as NaAsP in this contact mixture. ticularly 3 ppm by mass or more. Although the crude hydro I0083. The objective HF is separated as a purified hydrogen gen fluoride may contain other impurities, purity of hydrogen fluoride in a vapor form, for example, by distillation through fluoride is, for example, about 99% by mass or more, and heating of the separator 13, and then taken out of the separator preferably 99.9% by mass or more. 13 through a line 8. 0070. In the present embodiment, AgFASF is used as the I0084. On the other hand, NaAsF and the unreacted NaF oxidizing agent of the metal fluoride. AgFASF is excessively remain in the separator 13 in a solid State. charged in the reactor 11 in advance in the form of a HF I0085. In this way, the purified hydrogen fluoride is solution. However, AgFASF per se may be charged in the obtained, if necessary in a liquid state via the condenser. The reactor 11. As below mentioned, AgFAsF may be those obtained purified hydrogen fluoride has a decreased content obtained by regeneration or those prepared from Ag ASF. of arsenic and, for example, it is possible to decrease to about AgFASF is a complex salt of a metal fluoride AgF2 and a 3 ppm by mass or less, and preferably about 1 ppm by mass or Lewis acidic fluoride AsFs, and is dissolved in HF in a liquid less. state as a result of the generation of a cation AgF and an I0086. In the method for purifying hydrogen fluoride of the anion ASF. present embodiment, the reaction rate is high since the oxi (0071. In the reactor 11, AsF contained in the crudehydro dation reaction in the reactor 11 can be carried out by a gen fluoride is oxidized by a liquid-liquid reaction with the liquid-liquid reaction. Therefore, supply of the crude hydro oxidizing agent AgFASF to form ASFs. Simultaneously, the gen fluoride to the reactor 11 and taking of the hydrogen oxidizing agent AgFASF is reduced into AgASF. fluoride fraction from the reactor 11 can be continuously carried out. Furthermore, when supply to the immobilizing separator 13 and taking of the purified hydrogen fluoride from 0072. This oxidation reaction can be carried out, for the immobilizing separator 13 are also continuously carried example, under about 0.01 to 1 MPa at about 0 to 30° C. out, the entire process for purification of hydrogen fluoride 0073 While not intending to limit the present invention, it can be continuously carried out. is practical to apply a minutely reduced pressure (for I0087 AgAsF formed as the by-product by the oxidation example, about 0.09 MPa) so as to reduce costs required for reaction in the reactor 11 can be reacted with a F2 gas to power such as a pump while preventing the risk of HF leak. regenerate AgFASF. Since the oxidation reaction can proceed at room tempera ture, it is practical to apply a temperate which is minutely 2AgASF-F-2AgFASF lower than a boiling point of HF under the pressure, so as to I0088 Such regeneration can be carried out, for example, reduce costs required for the Subsequent distillation step and charging a solid AgASF in HF, supplying an F. gas thereto cooling. (the F gas may be diluted, if appropriate, and the F gas can 0.074 The reaction mixture obtained in the reactor 11 be supplied by bubbling or the like, the same shall apply in the includes HF, ASFs by-produced AgASF and the unreacted present description unless otherwise specified), and causing AgFASF. the aforementioned reaction. US 2011/02869 11 A1 Nov. 24, 2011

0089. The aforementioned regeneration in the present 0100. According to the present embodiment and the modi embodiment has an advantage that it is easy to carry out the fications thereof, the regeneration or preparation of the oxi regeneration continuously since the regeneration proceeds dizing agent can be easily carried out. This is an advantage only by reacting it with the F gas. that can be obtained in case of using an Ag-based fluoride as 0090 The regenerated AgFASF can be used again as the the oxidizing agent. oxidizing agent. Therefore, according to the present embodi 0101. In another modification, referring to FIG. 3, a puri ment, wastes are not generated. fied hydrogen fluoride can also be obtained by Supplying the 0091. When NaAsF formed by complexation in the sepa hydrogen fluoride fraction obtained by the reactor 11 to a rator 13 is placed in water, it is decomposed into NaF. distillation column 15, and Subjecting to a rectification opera HASO and HF. NaF can be recycled as the Lewis basic tion. As mentioned above, the hydrogen fluoride fraction fluoride so as to immobilize AsFs. includes HF and ASEs in a vapor phase. However, in a liquid 0092. Many modifications are possible in the present phase, ASFs can form complex salts such as HFASF and/or embodiment. For example, referring to FIG. 2, a method for HFASF with HF. Since these complex salts have a higher purifying hydrogen fluoride can be carried out using reactors boiling point than that of arsenic trifluoride, they can be 11 and 11", and separators 13 and 13", each being arranged in separated by the rectification operation. The purified hydro parallel. More specifically, this modification can be carried gen fluoride is taken out as a low-boiling point component out by the following procedure. from the column top side of the distillation column 15 through 0093. Using the reactor 11 and the separator 13 for puri a line 9. fying hydrogen fluoride as mentioned above, while the reac 0102. As to these complex salts, dissociation equilibrium tor 11' and the separator 13' are disconnected from the line of exists and those in an ionic state are dissolved in HF (and purification of hydrogen fluoride (using a valve (not shown), therefore entrained in the purified hydrogen fluoride). the same shall apply hereinafter). 0094. As the oxidizing agent AgFASF is consumed by the oxidation reaction in the reactor 11, the reactor 11 is switched to another reactor 11' and a crude hydrogen fluoride is Sup 0103) Therefore, in order to obtain a higher-purity purified plied to the reactor 11 through a line 2', and then a hydrogen hydrogen fluoride, ASFs is preferably separated and removed fluoride fraction is extracted from the reactor 11 through a by immobilization, as shown in FIG. 1 or 2. line 4". While the oxidation reaction is carried out in the reactor 11', an F, gas is supplied to the reactor 11 through a Embodiment 2 line5 and regeneration of the oxidizing agent is carried out. In this way, the oxidation reaction and the regeneration of the 0104. The present embodiment relates to an embodiment oxidizing agent are carried out by alternately switching in the of a method for purifying hydrogen fluoride in which arsenic reactors 11 and 11'. pentafluoride generated by an oxidation reaction of arsenic 0095. As NaF is consumed by the complexation in the trifluoride is immobilized in the reaction mixture (arsenic separator 13, the separator 13 is switched to another separator pentafluoride is immobilized as a result of the formation of a 13' and a hydrogen fluoride fraction is supplied to the sepa double salt or a complex salt with a metal fluoride used as an rator 13' through a line 6', and then a purified hydrogen oxidizing agent). Unless otherwise explained, the aforemen fluoride is taken out of the separator 13' through a line 8'. tioned description in Embodiment 1 is also applied to the While the complexation is carried out in the separator 13', present embodiment. NaF is exchanged by taking out a Solid phase of NaASF (and 0105 Referring to FIG. 4, a crude hydrogen fluoride (an the unreacted NaF) from the separator 13 and filling fresh hydrous) is Supplied to a reactor 21, in which an oxidizing NaF. In this way, the complexation (immobilization) and the agent of a metal fluoride has been charged in advance, in a exchange of NaF are carried out by alternately switching in liquid state through a line 2, thereby bringing the crude hydro the separators 13 and 13'. gen fluoride into contact with the oxidizing agent of the metal 0096 Switching of the reactors 11 and 11" and switching fluoride in the liquid state. of the separators 13 and 13" may be carried out at the same or 0106. In the present embodiment, KNiFe is used as the different timing. oxidizing agent of the metal fluoride. KNiFe is excessively 0097. According to such modification, purification of charged in the reactor 21 in advance in the form of a HF hydrogen fluoride can be continuously carried out without solution. KNiFe is a complex salt of a metal fluoride NiF being stopped. and a Lewis basic fluoride KF, and dissolved in HF in a liquid state as a result of the generation of a cation K" and an anion 0098. Alternately, the oxidizing agent may be prepared in NiF3. place of the regeneration of the oxidizing agent. 0107. In the reactor 21, AsF contained in the crudehydro 0099. The oxidizing agent can be prepared by, for gen fluoride is oxidized by a liquid-liquid reaction with the example, firstly charging AgF in HF. Supplying an F2 gas oxidizing agent KNiFe to form ASFs. Simultaneously, the thereto to cause the following reactions: oxidizing agent KNiFe is reduced into NiF and also KF is formed.

0108. Furthermore, in the reactor 21, KF freed by the AgF+ASFs AgASF6 oxidation reaction is complexed with ASFs to form KASF in (ASF exists as impurities) and thus obtain AgASF, Supply a Solid State. At this time, KASF is deposited (or precipi ing an F2 gas thereto to cause the aforementioned reaction tated). with respect to the regeneration of the oxidizing agent. US 2011/02869 11 A1 Nov. 24, 2011

0109 KF is consumed by the aforementioned reaction, or kiln, the fluorite is reacted with sulfuric acid under heating to deposited (or precipitated) as KNiF and/or KNiF. form hydrogen fluoride (CaF+HSO->2HF +CaSO4). 0110. This oxidation reaction and complexation can be, 0.124. A portion of sulfuric acid to be supplied may be for example, carried out under about 0.01 to 1 MPa at about 0 fuming Sulfuric acid, thereby enabling fuming Sulfuric acid to to 30° C. absorb water, which may be minutely formed, resulting in 0111. The reaction mixture obtained in the reactor 21 Suppression of corrosion of the prereactor, the rotary kiln and includes HF, the unreacted KNiFi by-produced NiF. SO. O. KNiF and/or KNiF, and KASF, and Aslfs is immobilized 0.125. The reaction conditions (temperature, pressure and as KASF in this reaction mixture. the like) can be appropriately selected, but may be in, for 0112 The objective HF is separated as a purified hydrogen example, about 100 to 300° C. and about 0.05 to 0.2 MPa. fluoride in a vapor phase, for example, by distillation through 0.126 The hydrogen fluoride (HF) thus formed is taken out heating of the reactor 21, and then taken out of the reactor 21 from the vicinity of an upper inlet of the rotary kiln in the form through a line 4. ofagaseous Substance containing HF. This gaseous Substance 0113. On the other hand, since the metal fluoride generally can contain, in addition to HF. SiFi, CO, ASF and so on has little vapor pressure, KNiF and NiF KNiF and/or which are formed and derived from impurities of the fluorite. KNiF and deposited KASF remain in the reactor 21 with Gypsum (CaSO) as the by-product and so on are taken out out being taken out as a vapor. Therefore, the reactor 21 in the from a lower outlet of the rotary kiln. present embodiment is also a separator. I0127. The obtained gaseous substance is converted into a 0114. In this way, the purified hydrogen fluoride is liquid Substance by cooling and transferred to a distillation obtained, if necessary in a liquid state via a condenser. column, where the liquid Substance is subjected to a distilla 0115. In the method for purifying hydrogen fluoride of the tion operation. There is no particular limitation on the number present embodiment, the reaction rate is high since the oxi of distillation columns, operation method and the like, and dation reaction in the reactor 21 can be carried out by a any proper operation can be carried out. liquid-liquid reaction, and the separation can be quickly car I0128 By this distillation operation, SiF and CO are ried out in the reactor 21. Therefore, supply of the crude separated to obtain a crude hydrogen fluoride including HF hydrogen fluoride to the reactor 21 and taking of the purified and ASF. hydrogen fluoride from the reactor 21, namely, the entire I0129. The obtained crude hydrogen fluoride is subjected process for purification of hydrogen fluoride can be continu to the aforementioned purification method in Embodiment 1 ously carried out. (including modifications) and Embodiment 2 to obtainapuri 0116 NiF formed as the by-product by the oxidation fied hydrogen fluoride. reaction in the reactor 21 can be converted into NiCl, and then reacted with an F. gas together with KCl to regenerate Examples KNiF. (Method for Quantitative Determination of Arsenic) 0.130. In the following Examples, a sample was prepared 0117 The regenerated KNiFe can be used again as the in accordance with JIS K8819 and the content of arsenic was oxidizing agent. Therefore, according to the present embodi measured by Subjecting the obtained sample to ICP analysis. ment, wastes are not generated. Specific procedure is as follows. 0118. The deposited KASF is also contained in the resi I0131. After taking 50 g of a sample (specimen) in a plati due in the reactor 21. The deposited KASF can be easily num dish, 4 ml of nitric acid (1+1), 5 ml of saturated bromine separated from NiF and the unreacted KNiF by a solid water and 5 ml of sulfuric acid (1+9) are added thereto, and liquid separation. then the resultant in the dish is subjected to evaporation on a water bath until the residual volume becomes about 0.5 ml. 0119 When KASF formed by complexation in the sepa An inner wall of the dish for evaporation is washed with a rator 21 is placed in water, it is decomposed into KF. HASO Small amount of water, and the resultant in the dish is Sub and HF. KF can be recycled as the Lewis basic fluoride so as jected to evaporation again on the water bath until the residual to obtain an oxidizing agent KNiF (and to immobilize Volume becomes about 0.5 ml, and then water is added thereto ASFs). to make it into 20 ml. 0120 According to the present embodiment, the oxidation 0.132. The obtained sample is analyzed by using an ICP reaction and immobilization due to complexation can be inte optical emission spectrometer SPS3000 (m Seiko Instru grally carried out, without a separate step of bringing into ments Inc.) to determine its content (concentration) of contact with the Lewis basic fluoride as in Embodiment 1. arsenic. Embodiment 3 Example 1 0121 The present embodiment relates to a method for I0133. The present Example is an example of Embodiment producing hydrogen fluoride. 1. In the following description, “distillation” refers to an 0122. In the present embodiment, used as fluorite is a operation of transferring a substance from one system (pre so-called low-quality fluorite, which is fluorite containing distillation) at room temperature to other system (post-depo impurities such as silicon dioxide (SiO2), calcium carbonate sition) cooled at -30 to -196°C. (CaCO) and arsenic (AS) and having a content of arsenic of 0.134 Preparation of Crude Hydrogen Fluoride about 1,000 to 3 ppm by mass. 0.135 Synthesized AsF (trace amount) was introduced by 0123 First, this fluorite and sulfuric acid are separately distillation into a T-shaped reaction vessel (having a Volume Supplied to a prereactor and the obtained mixture is then of about 20 ml) made of PFA (polytetrafluoroethylene per transferred to a rotary kiln. In the prereactor and the rotary fluorovinyl ether copolymer) and connected to a vacuum line US 2011/02869 11 A1 Nov. 24, 2011

made of stainless steel, and a commercially available anhy and transfer the fraction to another vessel made of PFA. The drous hydrogen fluoride (4 ml) was introduced thereon by obtained fraction of anhydrous hydrogen fluoride was dis distillation. After mixing the both by thoroughly stirring at tilled again to obtain a first fraction (70%) thereof as a crude room temperature, a half of the anhydrous hydrogen fluoride hydrogen fluoride. In this way, the crude hydrogen fluoride containing ASF was poured into branch pipe and this was (about 4 ml) was obtained, and a half thereof was separated as separated as a sample before treatment (crude hydrogen fluo a sample before treatment (crude hydrogen fluoride contain ride containing AsF). ing ASFs). 0.136 Purification of Hydrogen Fluoride (O150 Purification of Hydrogen Fluoride 0.137 The remaining half (crude hydrogen fluoride con 0151. Using the remaining half (crude hydrogen fluoride taining ASF) was introduced by distillation into a vessel containing ASF), the same operation as in the purification of made of PFA which contains AgFASF (100mg), followed by hydrogen fluoride in Example 1 was carried out, except for stirring it at room temperature for 5 minutes. The obtained using AgFASF (100 mg) and NaF (100 mg). mixture was distilled to separate a portion thereofas a sample 0152 Results after pretreatment and to introduce the remaining mixture 0153. The content of arsenic of each sample thus obtained into another vessel made of PFA which contains NaF (109 was determined in the same manner as in Example 1. Results mg), followed by stirring it at room temperature for 10 min showed that the content of arsenic was 515 ppm in the sample utes. The obtained mixture was distilled to transfer a portion before treatment, and that the content of arsenic was 3 ppm or thereof into another vessel made of PFA, as a sample after less in the sample after treatment. treatment. 0138 Results INDUSTRIAL APPLICABILITY 0.139. Each sample (2 ml) thus obtained was weighed and diluted with distilled water to obtain 50 ml of an aqueous 0154) Even when a fluorite ore containing a large amount Solution, and then the content of arsenic was determined. of arsenic is used as a raw material, it is possible to obtain a Results showed that the content of arsenic was 464 ppm in the high-purity hydrogen fluoride of which amount of arsenic is sample before treatment, and that the content of arsenic was 2 as less as that in the case of using a conventional high-purity ppm or less in the sample after treatment. In the sample after fluorite as a raw material, at low cost. pretreatment, the content of arsenic was about 5 ppm. 0.155) Even when a low-quality fluorite containing arsenic is used, it is possible to industrially purify or obtain a high Example 2 purity hydrogen fluoride, and thus utilization of a fluorine resource can be enlarged. 0140 The present Example is an example of Embodiment 2. 0141 Preparation of Crude Hydrogen Fluoride REFERENCE SIGNS LIST 0142. The same operation as in the preparation of the 0156 2, 2', 4,4', 5, 5, 6, 6", 8, 8, 9 Line crude hydrogen fluoride in Example 1 was carried out. O157 11, 11' Reactor 0143 Purification of Hydrogen Fluoride 0158 13, 13 Separator 0144. The remaining half (crude hydrogen fluoride con taining ASE) was introduced by distillation into a vessel 0159. 15 Distillation column made of PFA which contains KNiF (128 mg), followed by 0160 21 Reactor (which concurrently serves as Separator) stirring it at room temperature for 5 minutes. The obtained mixture was distilled to transfera portion thereof into another 1. A method for purifying hydrogen fluoride, which com vessel made of PFA, as a sample after treatment. prises the steps of (0145 Results (a) bringing a crude hydrogen fluoride containing arsenic 0146 The content of arsenic of each sample thus obtained trifluoride into contact with an oxidizing agent of a metal was determined in the same manner as in Example 1. Results fluoride in a liquid state to obtain a reaction mixture showed that the content of arsenic was 489 ppm in the sample wherein arsenic pentafluoride is formed by oxidizing before treatment, and that the content of arsenic was 2 ppm or arsenic trifluoride with the oxidizing agent of the metal less in the sample after treatment. fluoride through a liquid-liquid reaction, and (b) separating purified hydrogen fluoride from the reaction Example 3 mixture, the thus obtained purified hydrogen fluoride having a lower content of arsenic than that of the crude 0147 The present Example is an example of Embodiment hydrogen fluoride. 3 2. The method according to claim 1, wherein the oxidizing 0148 Preparation of Crude Hydrogen Fluoride agent of the metal fluoride comprises at least one kind of a 0149 Fluorite produced in Mexico (30 g) and concen metal fluoride selected from the group consisting of the fol trated sulfuric acid (98%, 40 g) were mixed in a vessel (hav lowing formulas: ing a volume of about 100 ml) made of PFA, and the mixture was heated to 110° C., and the generated vapor thereby was MF, collected under vacuum at a liquid nitrogen temperature. The obtained mixture was distilled to transfer a first fraction MIF, (70%) thereof to another vessel made of PFA which contains concentrated sulfuric acid (50 g), followed by dehydration MF, while stirring it at room temperature for 30 minutes. The and obtained mixture was distilled to separate a fraction of an anhydrous hydrogen fluoride from concentrated Sulfuric acid US 2011/02869 11 A1 Nov. 24, 2011

wherein and M=Nb, Mo, Ru, Rh, Ta, W, Re, Os, Ir, Pt, Au, or Bi. 5. The method according to claim 1, wherein the reaction M'=Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Rh, mixture obtained in the step (a) comprises a reduced metal Pod, Ag, Ir, or Au, fluoride derived from the oxidizing agent, and the reduced metal fluoride is utilized so as to obtain the oxidizing agent of M-Ti,V, Cr, Mn, Co, Ni, Zr, Nb, Mo, Ru, Rh, Pd, the metal fluoride. Ag, Cd, Hf, W, Re, Os, Ir, Pt, or Hg, 6. The method according to claim 1, wherein the step (b) is and carried out by the steps of: (i) bringing the reaction mixture into contact with a Lewis M=Nb, Mo, Ru, Rh, Ta, W, Re, Os, Ir, Pt, Au, or Bi. basic fluoride to form a double salt or a complex salt of arsenic pentafluoride and the Lewis basic fluoride, 3. The method according to claim 1, wherein the oxidizing thereby obtaining a contact mixture in which arsenic agent of the metal fluoride is used in the form of a double salt pentafluoride is immobilized, and or a complex salt of the metal fluoride. (ii) separating a purified hydrogen fluoride from the con tact mixture. 4. The method according to claim 3, wherein the double 7. The method according to claim 6, wherein the step (i) salt or complex Salt of the metal fluoride comprises at least comprises separating a hydrogen fluoride fraction containing one kind selected from the group consisting of AgFASF arsenic pentafluoride from the reaction mixture, and bringing AgFSbF AgFBiFAgFBFAgFAuFAgFIrFAgFRuF. the hydrogen fluoride fraction into contact with the Lewis AgFAuF, CSKAgF, and the following formulas: basic fluoride. 8. The method according to claim 6, wherein the Lewis AM/F basic fluoride contains at least one kind selected from the group consisting of LiF, NaF. KF, RbF, CSF, AgF. BeF. AMIF, MgF, SrF, CaF2, and BaF. 9. The method according to claim 1, wherein a double salt A/MIF, or a complex Salt of arsenic pentafluoride and the metal fluo ride derived from the oxidizing agent is formed in the reaction AMF, mixture obtained in the step (a), thereby immobilizing arsenic pentafluoride, and AMF step (b) is carried out by directly separating a purified hydrogen fluoride from the reaction mixture. AMF 10. The method according to claim 1, wherein the content of arsenic of the crude hydrogen fluoride is from 3,000 to 3 and ppm by mass. AMF, 11. The method according to claim 1, wherein the content of arsenic of the purified hydrogen fluoride is 3 ppm by mass wherein or less. 12. A method for producing hydrogen fluoride, which com A-Li, Na, Ag, K, Rb, or Cs prises: reacting fluorite with sulfuric acid to obtain a crude hydro A'-Ca, Sr, Ba, Cd, or Hg gen fluoride, and Subjecting the crude hydrogen fluoride to the purification M'=Ag, method according to claim 1 to obtain a purified hydro M'=Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Rh, gen fluoride. Pod, Ag, Ir, or Au, 13. The method according to claim 12, wherein the content of arsenic of fluorite is from 10,000 to 3 ppm by mass. M-Ti,V, Cr, Mn, Co, Ni, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, W, Re, Os, Ir, Pt, or Hg, c c c c c