WO2005068356A1 - Method for producing hydrogen fluoride - Google Patents

Abstract

A method for producing hydrogen fluoride which comprises using the calcium sulfate by-produced in the production of hydrogen fluoride for fixing hydrogen fluoride in a fluorine-containing solution, reacting the calcium fluoride formed by the fixation with sulfuric acid, to produce hydrogen fluoride, and supplying the calcium sulfate by-produced in the above step to a step for fixing the fluorine in the above fluorine-containing solution. The above method provides a fluorine recycle system, which can eliminate the generation of the industrial waste associated with the treatment of fixing the fluorine present in a solution such as a waste water as calcium fluoride, and simultaneously produces hydrogen fluoride, which is a key material in a fluorine chemical industry, with no use of natural potassium fluoride (fluorite) being a scanty resource, and utilizes calcium sulfate by-produced in the production of hydrogen fluoride for the fixation of fluorine in a waste water.

Description

Method for producing hydrogen fluoride

Technical field

 The present invention relates to a method for producing hydrogen fluoride, and more particularly, to a method capable of effectively utilizing fluorine in a fluorine-containing solution to reduce the amount of solid waste.

The present invention relates to a method for producing hydrogen nitride.

 Rice field

Background art

 Usually, the treatment of a fluorine-containing solution such as a fluorine-containing wastewater is performed by reacting with a calcium compound such as quick lime, slaked lime or calcium chloride to fix most of the fluorine as hardly soluble calcium fluoride. If necessary, further treatments such as the aluminium / minium salt method, the fluoroapatite method, the activated alumina method, the basic anion exchange resin method, and the A1 chelate resin method are carried out.

 The calcium fluoride obtained by the immobilization treatment in this way has a very fine particle size and cannot be filtered as it is, so it is flocculated using a flocculant, and then subjected to sedimentation separation and filter press filtration. I have. As a result, the water content is as high as 50 to 80%, making it difficult to reuse it for industrial purposes. Therefore, a part of the generated calcium fluoride sludge is returned to its original state, and the amount of sludge to be discarded is reduced by increasing the particle size at least a little by giving a role of seed crystal (for example, Drainage, Vol. 42, No. 10, page 27-32 (2000)).

In addition, for dilute fluorine-containing solutions of several hundred PPm, calcium fluoride crystals are grown to a large particle size (for example, “Clean Technology”, May issue, pp. 40-42 (2001), Nippon Kogyo Publishing Co., Ltd.). The technology for reusing collected materials has not been established yet, and is currently treated as industrial waste.

 Attempts have been made to use calcium fluoride (recovered fluoridation power) obtained by the process of immobilizing fluorine mixed with fluorite, a raw material for hydrogen fluoride production. Due to problems such as small average particle diameter of secondary particles, low bulk density (about 1/2 to 1/4 of fluorite), and high impurities (especially chlorine), there are problems such as It is poorly used with stones and is rarely used because of an increase in impurities in the product hydrogen fluoride.

Among them, by passing the fluorine-containing solution naturally carbonate Cal Shiumu having uniform particle size in order to increase the particle size _{(C a C 0 3 + 2} HF → C a F 2 + H 2 O + CO 2: formula ( 1)), an attempt has been made to produce calcium fluoride while almost maintaining the skeleton of natural calcium carbonate (for example, Japanese Patent Application Laid-Open No. 6-63561). At this time, there are problems such as the escape of generated carbon dioxide gas, the generated calcium fluoride flocks, and the center of calcium carbonate remaining unreacted.However, this method mixes recovered calcium fluoride with fluorite. (For example, the New Energy and Industrial Technology Development Organization 2001 fiscal year report (FY2001 global warming prevention related technology development "Development of HFC23 destruction technology")).

In addition, the recovered calcium fluoride is mixed with gypsum. A method has also been proposed in which the particles are dried to increase the particle size, and mixed with fluorite for use (Japanese Patent Application Laid-Open No. 2002-53434). Disclosure of the invention An object of the present invention is to fix fluorine present in a solution such as wastewater as calcium fluoride, use it as a raw material for hydrogen fluoride production, and use calcium fluoride produced as a by-product of hydrogen fluoride production as a solution. It is used to fix fluorine in water. By combining these, it is possible to reduce the amount of industrial waste associated with the process of solidifying fluorine to zero, and at the same time, use natural calcium fluoride (fluorite), which is scarce in terms of resources. The company will produce hydrogen fluoride, a key material in the fluorine chemical industry, without using, and provide a fluorine recycling system that uses sulfuric acid as a by-product to fix fluorine in wastewater. The gist of the present invention is that calcium sulfate produced as a by-product in the production of hydrogen fluoride is used for immobilizing fluorine in a fluorine-containing solution, and calcium fluoride obtained by the immobilization is reacted with sulfuric acid. A method for producing hydrogen fluoride, comprising producing hydrogen fluoride, and subjecting the by-produced calcium sulfate to the step of immobilizing fluorine in the fluorine-containing solution. Brief Description of Drawings

 Figure 1 is a conceptual diagram of the fluorine recycling system of the present invention.

 FIG. 2 shows a hydrogen fluoride generator used in an example (beaker test) of the present invention.

 FIG. 3 shows a hydrogen fluoride generator used in an embodiment (pilot test) of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

In the method for producing hydrogen fluoride of the present invention, calcium sulfate by-produced in producing hydrogen fluoride is used for immobilizing fluorine in a fluorine-containing solution, and the fluoride obtained by the immobilization is used. Hydrogen fluoride is produced by reacting calcium with sulfuric acid. To a step of immobilizing fluorine in a fluorine-containing solution. The fluorine-containing solution is not particularly limited, and fluorine-containing wastewater discharged from various production processes can be suitably used.

The calcium sulfate used for immobilizing fluorine may be anhydrous, hemihydrate or gypsum. . Fluorine immobilization reaction _{(C a SO 4 + 2 F-} → C a F 2 + SO 4 2 one: Equation (2)) is solid one-pack reaction salt exchange, yet retaining the shape of the calcium sulfate Since the reaction proceeds as it is, the average particle size of calcium sulfate is preferably 200 μm or less. In consideration of increasing the purity of the calcium fluoride after the reaction and filterability, 10 to 200 / zm is preferable, and 30 to 150 μπι is more preferable. However, exceeding 200 μπι only decreases the content of fluorinated calcium, and does not hinder use in the next hydrogen fluoride production process.

 The following results were obtained by comparing the conversion to calcium fluoride using anhydrous gypsum of various particle sizes. That is, a solution containing 1.3 equivalents of fluorine (fluorine concentration: 100,000 ppm) with anhydrous gypsum classified into each particle size using a sieve was stirred at room temperature for 1 hour. After the reaction, the conversion rate was 37% when the particle diameter was 2,000 μm or more; the conversion rate was 43% when the particle diameter was 2,000 to 1, Ο Ομππ; The conversion was 49% at 0 to 500 μm; the conversion was 87% at 250 to 160 / xm; and the conversion was 92% at 160 μm or less.

The calcium fluoride obtained in the present invention has excellent sedimentation properties, and can be easily dehydrated by ordinary filtration means. For example, when dehydration is performed using a normal suction filtration device in a laboratory, calcium fluoride having a water content of about 25 to 35% can be obtained. Furthermore, the use of a centrifugal dehydrator or a filter press can easily reduce the water content to about 15 to 20%. Compared to 50-60%, it can be less than half. In producing hydrogen fluoride by reacting the resulting fluoridated solution with sulfuric acid, it is preferable to use calcium fluoride having a water content of 40% or less, and more preferably to a water content of 25%. It is as follows.

 Further, the calcium fluoride obtained in the present invention has a loss on ignition (500 ° C, 1 hour) after drying (120 ° C, 2 hours) of 5% or less, preferably 3% or less, usually It is around 2%, which is different from that obtained by ordinary fluorine immobilization treatment at 7 to 10%.

 Thus, the calcium fluoride obtained in the present invention can be dried with a small amount of energy due to a small amount of water and a small loss on ignition, and is suitable as a raw material for producing hydrogen fluoride.

First, the bulk specific gravity is about 1/2 to 1/3 smaller than that of fluorite. This is because fluorite is almost crystalline but porous. Hydrogen fluoride generating reaction with Conoco _{(C a F 2 + H 2} SO 4 → C a SO 4 + 2 HF: Equation (3)) positive effect on the reactivity of the.

 Fluorite used as a raw material for the production of hydrogen fluoride is generally a powder having an average particle size of about 50 to 100 μm and containing about 10% water to prevent scattering. The whole amount is imported from overseas. The reaction between fluorite and sulfuric acid with good crystallinity gradually progresses from the surface of the fluorite, and is covered with the generated sulfuric acid. Therefore, the mixture is sufficiently mixed and then mixed with a rotary kiln. It is usually carried out at a temperature of up to 500 ° C. for 6 to 8 hours. However, the large particles do not react completely, leaving calcium fluoride in the core.

On the other hand, the calcium fluoride obtained in the present invention is a porous and polycrystalline substance, and the reaction of the above formula (3) occurs smoothly. Therefore, the reaction is usually completed in about 200 ° C. for about 1 hour. It is possible even below 150 ° C. As described above, the relatively mild reaction conditions cause the equipment materials and reactor The range of choices will be expanded, and it will be possible to design inexpensive and compact equipment. Thus, in the present invention, when the calcium fluoride obtained by the immobilization is reacted with sulfuric acid to produce hydrogen fluoride, the reaction is usually carried out at a temperature of 250 ° C. or lower, preferably 100 ° C. or less. It can be performed at 200 ° C. It is preferable that the content of calcium fluoride used is higher, but there is no problem even if the content is about 60%, as described later, since most of the impurities are calcium sulfate.

 Furthermore, the calcium fluoride obtained by the reaction of the formula (2) hardly contains silica, which is a major impurity of fluorite, and therefore has the advantage of not producing the problematic by-product ky hydrofluoric acid. Have.

 The sulfuric acid to be used is fuming sulfuric acid or a mixture of fuming sulfuric acid and sulfuric acid.The amount of sulfuric acid is proportional to the content of calcium fluoride, but it is preferable to use sulfuric acid having an equivalent amount or less with respect to the amount of calcium fluoride. is there. An excessive amount of sulfuric acid remains in the generated calcium sulfate and is not preferable because it is wasted. On the other hand, if the amount is less than the equivalent, unreacted calcium fluoride remains, but it is used for the next immobilization of fluorine. In order to increase the recovery rate of hydrogen fluoride and the corrosion resistance of the apparatus, it is preferable to minimize the amount of water present in the reaction system. Therefore, use fuming sulfuric acid that matches the amount of water in the sulfuric acid and the water loss corresponding to the ignition loss of calcium fluoride, or prepare a fuming sulfuric acid of about 10% by mixing fuming sulfuric acid and sulfuric acid in advance. It is preferable to keep it. As described above, in the present invention, it is most preferable to use sulfuric acid in an amount equivalent to 0.8 times the amount of calcium fluoride.

The solid content mainly composed of calcium sulfate by-produced in this reaction is preferably pulverized to an average particle diameter of 200 μm or less in order to use the solid content of fluorine in a fluorine-containing solution. . The pulverization may be either dry or wet. Also, to increase reactivity, slaked lime, hydroxylated It is preferable to adjust the pH of the fluorine-containing solution to 5 to 9 by adding an alkaline substance such as sodium.

 As described above, according to the present invention, calcium sulfate by-produced during the production of hydrogen fluoride is used for immobilizing fluorine in a fluorine-containing solution, and the calcium fluoride obtained here is reacted with sulfuric acid. Provided is a fluorine recycling system for producing hydrogen fluoride and using the by-produced calcium sulfate for immobilizing fluorine in the above-mentioned fluorine-containing solution. Figure 1 shows the outline.

Further, in the present invention, in the method of mixing calcium sulfate with a fluorine-containing solution and fixing and recovering fluorine in the solution as calcium fluoride, the calcium sulfate has a particle diameter of 10 to 200. μ is Paiiota, and the molar ratio of calcium in the calcium sulfate to fluorine _{(M ca / 2 M F)} ( wherein, M _ca / the number of moles of calcium; M _F is the number of moles of fluorine). force SO 8 or more, Less than 1.2. The molar ratio is preferably at least 0.8 and less than 1.1.

 By rubbing such a configuration, fluorine can be recovered from various fluorine-containing solutions by immobilizing it as calcium fluoride having a relatively large particle size and good filterability. This method is particularly useful when the obtained calcium fluoride is not used for the production of hydrogen fluoride but is recovered using a membrane such as a hollow fiber membrane or a filter press.

 Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1

Anhydrous gypsum produced as a by-product in a hydrofluoric acid production brand was pulverized (average particle size: 65 μπι) (100 g) and inorganic fluoride synthetic wastewater (fluorine concentration: 8,800 ppm) (40 kg). , Placed in a 50 L polyethylene reaction vessel equipped with a stirrer, stirred for 1 hour, and settled solids for a while Then, the supernatant was removed, and the mixture was dehydrated using a suction filter to collect 820 g of a solid. After drying in a warm air dryer set at 120 ° C for 2 hours (loss on drying 26.5%), solid matter (loss on ignition 1.7%, calcium fluoride content 87.8) %, Calcium sulfate content: 10.5%). At this time, the fluorine concentration of the treated water had dropped to 1,700 ppm.

Example 2

 20.5 g of the solid obtained in Example 1 (ignition loss 1.7%, calcium fluoride content 87.8%, calcium sulfate content 10.5%) was made from the fluororesin PFA shown in Fig. 2. Weighs 98.85 g of 98% sulfuric acid, equivalent to the theoretical amount of calcium fluoride placed in the reactor, into a sulfuric acid dropping funnel (2) made of fluororesin PFA. They were set as shown in Figure 2 (A for calcium fluoride, B for sulfuric acid, C for silicon oil, and D for ice / saline). Sulfuric acid is slowly dropped, and after confirming that the sulfuric acid has become fully compatible with calcium fluoride, gradually raise the temperature of the oil path (3) and raise the temperature to 180 ° C over 3 hours. ((4) is a fluorine resin PFA cooler). At this point the reaction is complete,

92.5 g of hydrogen fluoride was collected in a hydrogen fluoride recovery trap (5) made of fluororesin PFA (recovery yield: 82.2%) ((6) is a Duty bottle). After cooling the reaction vessel, 43.3.9 g of solid matter was recovered from inside.

 The collected solids are ground to 200 μm or less, of which 353.2 g and inorganic fluoride synthetic wastewater (fluorine concentration of 12,200 ppm)

10 kg was placed in a polyethylene reaction vessel equipped with a 10 L stirrer and stirred. To make the pH of the slurry solution neutral, 81.5 g of a 25.1% aqueous sodium hydroxide solution was added. After 1 hour, stop stirring and allow the solid to settle for a while, then remove the supernatant and use a suction filter. After dehydration, 37.8 g of a solid was recovered. Dry in a warm air dryer set at 120 ° C for 2 hours (loss on drying 32.1%) and solid (loss on ignition 2.1%, calcium fluoride content 90.8%, sulfuric acid) (Calcium content 7.1%) 29.3 g was obtained.

Example 3

 The solid matter recovered in the same manner as in Example 2 was similarly immobilized with fluorine without being ground. The calcium fluoride content in the obtained solid was 56%.

Example 4

 Solids with low calcium fluoride content (2.3% loss on ignition, 58.0% calcium fluoride content, 39.7% calcium sulfate content) 30.1 g of 30.1 in a fluoroplastic PFA container Then, 233.3 g of 98% sulfuric acid corresponding to the theoretical amount of calcium fluoride placed in the reactor was weighed into a sulfuric acid dropping funnel made of fluororesin PFA and set as shown in FIG. Sulfuric acid is slowly added dropwise, and after confirming that the sulfuric acid has become sufficiently compatible with the calcium fluoride, gradually raise the temperature of the oil path and raise the temperature to 180 ° C over 3 hours. Was. At this point, the reaction was completed, and 58.9 g of hydrogen fluoride had accumulated in the hydrogen fluoride recovery trap made of fluororesin PFA (recovery yield: 66.1%). After cooling the reaction vessel, 460.5 g of a solid substance was recovered from the inside.

Grind the collected solids to less than 200 μππι, and add 350.1 g of the solid waste and 10 kg of inorganic fluoride synthetic wastewater (fluorine concentration of 12,200 ppm) to a 10 L stirrer. The mixture was stirred in a polyethylene reaction vessel provided. To make the pH of the slurry solution neutral, 92.0 g of a 25.1% aqueous sodium hydroxide solution was added. After 1 hour, the stirring was stopped to allow a solid to settle for a while, then the supernatant was removed, and the solid was dehydrated using a suction filter to collect 377.5 lg of the solid. Warm air set at 120 ° C Dry in a dryer for 2 hours (loss on drying 28.2%) and solid matter (loss on ignition 2.3%, content of calcium fluoride 91.6%, content of calcium sulfate 7.1%) 26 9.2 g were obtained.

Example 5

 252.3 g of the solid obtained in Example 1 (lost loss of 1.7%, calcium fluoride content of 87.8%, calcium sulfate content of 10.5%) was prepared from a fluororesin PFA. 5% fuming sulfuric acid (prepared by mixing sulfuric acid and 25% fuming sulfuric acid) equivalent to the theoretical amount of calcium fluoride put in a vessel and placed in a reactor 27.8.3 g of sulfuric acid made of fluoroplastic PFA It was weighed on a dropping funnel and set as shown in Fig.2. Slowly add 5% fuming sulfuric acid, and after confirming that sulfuric acid has become sufficiently compatible with calcium fluoride, gradually raise the temperature of the oil path and raise the temperature to 180 ° C over 3 hours. I let it. At this point, the reaction was completed, and 105.2 g of hydrogen fluoride had accumulated in the hydrogen fluoride recovery trap made of fluororesin PFA (recovery yield 92.6%). After cooling the reaction vessel, 418 g of a solid was recovered from the inside.

 Grind the collected solid to 200 μηη or less, and equip it with 350.6 g and 10 kg of inorganic fluoride synthetic wastewater (fluorine concentration 12, 00 Oppm) with 10 L of stirrer. And stirred in a polyethylene reaction vessel. To make the pH of the slurry liquid neutral, 20.4 g of a 25.1% aqueous sodium hydroxide solution was added. One hour later, stirring was stopped to allow a solid to settle for a while, then the supernatant was removed, and the solid was dehydrated using a suction filter to collect 287.2 g of a solid. Dry in a warm air dryer set at 120 ° C for 2 hours (loss on drying 26.8%) and solid matter (loss on burning 2.1%, calcium fluoride content 91.6%, sulfuric acid) (Calcium content 6.3%) 20.2 g was obtained.

Example 6 7,003 g of solid matter obtained by treating calcium sulfate and inorganic fluorine compound synthetic wastewater (loss on ignition 1.8%, calcium fluoride content 91.2%, calcium sulfate content 7.0%) Put into a Hastelloy C22 10 L reaction vessel (11) equipped with a stirrer, steam jacket, thermometer, etc., and add 5% fuming sulfuric acid equivalent to the theoretical amount of calcium fluoride put in the reaction vessel (11%). (Prepared by mixing sulfuric acid and 25% fuming sulfuric acid) 8,034 g was weighed into a sulfuric acid dropping funnel (12) made of fluororesin PFA, and set as shown in Fig. 3 (A is Calcium fluoride, B is sulfuric acid). After slowly dropping 5% fuming sulfuric acid with stirring, steam was flowed through the jacket (13) to gradually raise the temperature. The internal temperature was raised to 150 ° C over about 3 hours ((14) is a SUS316 cooler). At this point, the reaction was completed and 2,997 g of hydrogen fluoride had accumulated in the SUS316 hydrogen fluoride recovery trap (15) (recovery yield: 91.5%). ). After cooling the reaction vessel, 11, 922 g of solid matter was recovered from the inside.

 The collected solid is ground to 200 μππ or less, and the entire amount is made up of inorganic fluoride synthetic wastewater (fluorine concentration: 12,100 ppm). And stirred. To make the pH of the slurry solution neutral, 670 g of a 20% aqueous calcium hydroxide solution was added. One hour later, the stirring was stopped to allow a solid to settle for a while, and then the supernatant was removed, followed by dehydration using a suction filter to recover 8,498 g of the solid. Dry in a warm air dryer set at 120 ° C for 2 hours (loss on drying 17.5%) and solid matter (loss on burning 2.3%, calcium fluoride content 91.5%, (Calcium sulfate content 7.2%) 7,011 g was obtained.

Example 7 '

The solid obtained in Example 6 (ignition loss 2.3 ° /., Calcium fluoride) (91.5%, calcium sulfate content 7.2%) 6, 998 g was placed in a 10 L reaction vessel made of Hastelloy C22 equipped with a stirrer, steam jacket, thermometer, etc., and reacted. 5% fuming sulfuric acid (prepared by mixing sulfuric acid and 25% fuming sulfuric acid) corresponding to the theoretical amount of calcium fluoride in a container 8,045 g was weighed into a sulfuric acid dropping funnel made of fluoroplastic PFA. And set as shown in Figure 3. After slowly dropping 5% fuming sulfuric acid with stirring, steam was flowed through the jacket to gradually raise the temperature. The internal temperature was raised to 150 ° C. over about 3 hours. At this point, the reaction was completed, and 2,969 g of hydrogen fluoride had accumulated in the SUS316 hydrogen fluoride recovery trap (recovery yield: 90.3%). After cooling the reaction vessel, 11,908 g of solid matter was recovered from inside.

 The collected solid is ground to 200 μππ or less, and the entire amount is made up of inorganic fluoride synthetic wastewater (fluorine concentration: 12,100 ppm). And stirred. To make the pH of the slurry liquid neutral, 712 g of a 20% aqueous calcium hydroxide solution was added. After 1 hour, stirring was stopped to allow a solid to settle for a while, then the supernatant was removed, and dehydration was performed using a suction filter to recover 8,416 g of the solid. Dry in a warm air dryer set at 120 ° C for 2 hours (loss on drying 16.8%), and solid matter (loss on burning 2.0%, calcium fluoride content 92.2%, (Calcium sulfate content: 5.8%) 7,002 g was obtained. Industrial potential

According to the present invention, hydrogen fluoride, which is a key material of the fluorine chemical industry, is capable of efficiently immobilizing fluorine in a solution and not using natural calcium fluoride (fluorite) which is scarce in resources. Manufacture Here, a fluorine recycling system that uses the calcium sulfate by-produced here to fix fluorine in wastewater will be provided.

Claims

1. Calcium sulfate, which is a by-product of hydrogen fluoride production, is used for immobilizing fluorine in a fluorine-containing solution, and the calcium fluoride obtained by the immobilization is reacted with sulfuric acid to produce hydrogen fluoride. The calcium sulfate by-produced there is fixed to fluorine in the above-mentioned fluorine-containing solution.  One bite A method for producing hydrogen fluoride.  2. The average particle size of calcium sulfate used for immobilizing fluorine is 20%. 2. The method for producing hydrogen fluoride according to claim 1, which is 0 μπι or less.  3. The method for producing hydrogen fluoride according to claim 1, wherein the amount of the fluorine-containing solution is adjusted to 5 to 9 when immobilizing fluorine in the fluorine-containing wastewater.  4. Claims 1 to 3 in which the calcium fluoride obtained by the immobilization loses 5% or less after burning (500 ° C, 1 hour) after drying (120 ° C, 2 hours). The method for producing hydrogen fluoride according to any one of the above.  5. The method for producing hydrogen fluoride according to any one of claims 1 to 4, wherein the reaction is carried out at a temperature of 250 ° C or less when producing calcium fluoride by reacting calcium fluoride obtained by the immobilization with sulfuric acid. Method.  6. The method for producing hydrogen fluoride according to claim 5, wherein the reaction is carried out at 100 to 200 ° C.  7. The method according to any one of claims 1 to 6, wherein, in producing calcium fluoride by reacting calcium fluoride obtained by the immobilization with sulfuric acid, an amount of sulfuric acid equal to or less than the amount of calcium fluoride is used. A method for producing hydrogen.  8. The method for producing hydrogen fluoride according to claim 7, wherein sulfuric acid is used in an amount equivalent to 0.8 times the amount of calcium fluoride. 9. The sulfuric acid is fuming sulfuric acid or a mixture of fuming sulfuric acid and sulfuric acid Item 10. The method for producing hydrogen fluoride according to any one of Items 1 to 8. 100. In a method of mixing calcium sulfate having a particle size of 10 to 200 μm with a fluorine-containing solution and fixing and recovering fluorine in the solution as calcium fluoride, the calcium sulfate particle size is recovered. a There 1 0~ 2 0 0 μ m, and the molar ratio of calcium in the calcium sulfate to fluorine _{(M ca / 2 M F)} ( wherein, M _ca / the number of moles of calcium; M _F is the number of moles of fluorine ) Is 0.8 or more and less than 1.2.  11. The method according to claim 10, wherein the molar ratio is 1.1 or more and less than 1.1.