TW202106612A - Method for producing hydrogen fluoride - Google Patents

Abstract

The present invention addresses the problem of providing a method for producing hydrogen fluoride, whereby it becomes possible to provide hydrogen fluoride with high efficiency using synthetic fluorite or the like. The present invention is a method for producing hydrogen fluoride, comprising: a first step of reacting a mixture comprising at least one compound selected from an alkali metal fluoride and an alkaline earth metal fluoride, an inorganic acid and an Si element-containing compound to produce an aqueous solution A containing hydrogen fluoride and hexafluorosilicic acid and at least one compound selected from an alkali metal salt and an alkaline earth metal salt; a second step of condensing the aqueous solution A to produce an aqueous solution B which is a condensed solution containing hydrogen fluoride and hexafluorosilicic acid; and a third step of adding sulfuric acid to the aqueous solution B to generate a gas containing silicon tetrafluoride and hydrogen fluoride, and then separating and collecting hydrogen fluoride from the gas.

Description

Manufacturing method of hydrogen fluoride

This disclosure relates to a method for producing hydrogen fluoride.

Hydrogen fluoride is used as an etching material for semiconductor devices or as a raw material for manufacturing various fluorides in the state of an aqueous solution or gas.

As an industrial production method of hydrogen fluoride (HF), a method of _{mixing natural fluorite containing calcium fluoride (CaF 2} ) as a main component with sulfuric acid and heating is known. Generally speaking, a combination of a pre-reactor with a sleeve called a ko-kneader and an externally heated rotary kiln is used to produce hydrogen fluoride (HF) through a two-stage reaction step. The rotary kiln is heated by circulating hot air of about 500°C in the sleeve. The temperature of the reaction mixture is about 100°C near the entrance of the rotary kiln connected to the pre-reactor, toward the outlet of the rotary kiln on the opposite side. The rise is about 300°C near the exit. Anhydrous gypsum in a solid shape is produced as a by-product.

In this method, research is also underway to use artificial fluorite obtained by immobilization of fluorine instead of natural fluorite. However, the particle size or impurity content of artificial fluorite is very different from that of natural fluorite, so its reactivity is also very different. Therefore, the utilization of artificial fluorite remains to the extent that about 20% of artificial fluorite is mixed with natural fluorite. In order to increase the proportion of artificial fluorite, designs for improving the particle size and impurity content of artificial fluorite are also being studied (for example, Patent Document 1 and Patent Document 2). However, these designs have a problem that the price of artificial fluorite, which is a raw material of hydrogen fluoride, is too high.

As a method of producing hydrofluoric acid using artificial fluorite without using a rotary kiln, for example, a method described in Patent Document 3 is a method of reacting calcium fluoride with sulfuric acid to produce hydrogen fluoride, which includes: (a ) The molar ratio of sulfuric acid/calcium fluoride is 0.9-1.1, and calcium fluoride particles with an average particle diameter of 1 μm-40 μm and sulfuric acid are mixed and reacted at a temperature of 0°C to 70°C to obtain a solid And (b) the step of heating the solid reaction mixture to a temperature of 100°C to 200°C and reacting to generate hydrogen fluoride in the gas phase. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2015-74575 [Patent Document 2] Japanese Patent Laid-Open No. 2015-54809 [Patent Document 3] Japanese Patent Laid-Open No. 2011-011964

[The problem to be solved by the invention] The inventors conducted studies, and as a result, it was found that in the invention described in Patent Document 3, the content of hydrogen fluoride in the solid reaction mixture is low, and it is difficult to efficiently convert the fluorine in the artificial fluorite into hydrogen fluoride. Therefore, the subject of the present disclosure is to provide a method for producing hydrogen fluoride that can efficiently supply hydrogen fluoride using artificial fluorite or the like.

[Means to solve the problem] This disclosure relates to, for example, the following [1] to [11]. [1] A manufacturing method of hydrogen fluoride, which includes: The first step is to react a mixture containing at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides, inorganic acids, and Si element-containing compounds to obtain an aqueous solution A containing hydrogen fluoride and hexafluorosilicic acid, and At least one compound selected from alkali metal salts and alkaline earth metal salts; In the second step, the aqueous solution A is concentrated to obtain an aqueous solution B as a concentrated solution containing hydrogen fluoride and hexafluorosilicic acid; and In the third step, sulfuric acid is applied to the aqueous solution B to generate a gas containing silicon tetrafluoride and hydrogen fluoride, and the hydrogen fluoride is separated from the gas and recovered. [2] The method for producing hydrogen fluoride as described in [1], wherein the Si element-containing compound is at least one selected from the group consisting of silicon tetrafluoride and silicon dioxide. [3] The method for producing hydrogen fluoride according to [1] or [2], wherein at least one compound selected from the alkali metal salt and alkaline earth metal salt is dihydrate gypsum having a water ratio of 19% by mass or more . [4] The method for producing hydrogen fluoride according to any one of [1] to [3], wherein the first step is performed under the conditions that the concentration of the inorganic acid is 40% by mass or less and the temperature is 90° C. or less. [5] The method for producing hydrogen fluoride according to any one of [1] to [4], wherein as a raw material containing at least one compound selected from the alkali metal fluoride and alkaline earth metal fluoride, it is used to dry Artificial fluorite containing 60% by weight or more of calcium fluoride. [6] The method for producing hydrogen fluoride according to any one of [1] to [5], wherein an inorganic acid of 1.0 is used relative to 1 mol of at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides Mol ~ 1.5 mol, Si element-containing compound 0.2 mol ~ 1.0 mol. [7] The method for producing hydrogen fluoride according to any one of [1] to [6], wherein the content of hexafluorosilicic acid in the aqueous solution B is 35% by mass or more relative to the total mass of the aqueous solution B , And the molar ratio (F/Si) of the F element to the Si element in the aqueous solution B is 6.0 or more. [8] The method for producing hydrogen fluoride according to any one of [1] to [7], wherein the third step is to add 75% by mass or more of concentrated sulfuric acid or fuming sulfuric acid to the aqueous solution B to perform Dehydrate and decompose to produce gas containing silicon tetrafluoride and hydrogen fluoride, The hydrogen fluoride is absorbed by 80% by mass or more of sulfuric acid to obtain an absorption liquid, The absorption liquid is heated to above 100°C to volatilize the hydrogen fluoride and recover the hydrogen fluoride. [9] The method for producing hydrogen fluoride according to any one of [1] to [8], wherein the inorganic acid aqueous solution obtained after separating and recovering the hydrogen fluoride generated in the third step is used as the At least a part of the inorganic acid aqueous solution. [10] The method for producing hydrogen fluoride according to any one of [1] to [9], wherein the inorganic acid aqueous solution obtained after separating and recovering the hydrogen fluoride generated in the third step increases the concentration, and the third step Steps to reuse. [11] The method for producing hydrogen fluoride according to any one of [1] to [10], wherein silicon tetrafluoride that is by-produced when hydrogen fluoride is generated in the third step is recovered, and the silicon tetrafluoride and At least one of the reaction products of silicon tetrafluoride and water is used as at least a part of the Si element-containing compound in the first step, or is added to the aqueous solution B in the third step use.

[Effects of the invention] According to the method for producing hydrogen fluoride of the present disclosure, it is possible to provide a method for producing hydrogen fluoride that can efficiently supply hydrogen fluoride using artificial fluorite. In addition, in the hydrogen fluoride production method of the present disclosure, the gypsum obtained as a by-product is not anhydrous gypsum or hemihydrate gypsum, but is commercially useful dihydrate gypsum. Therefore, the hydrogen fluoride production method of the present disclosure is excellent in economy . In addition, in the method for producing hydrogen fluoride of the present disclosure, the purity of silicon dioxide obtained as a by-product is high, and therefore, the method for producing hydrogen fluoride of the present disclosure is excellent in economy. In addition, in the production method of hydrogen fluoride of the present disclosure, other by-products such as sulfuric acid or silicon tetrafluoride can be used in the production method of hydrogen fluoride of the present disclosure. Therefore, the production method of hydrogen fluoride of the present disclosure is excellent in economy.

The manufacturing method of hydrogen fluoride of the present disclosure includes the following first step, second step, and third step. <First step> The first step is to react a mixture containing at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides, inorganic acids, and Si element-containing compounds to obtain hydrogen fluoride (HF) and hexafluoride A step of an aqueous solution A of silicic acid (H ₂ SiF ₆ ) and at least one compound selected from alkali metal salts and alkaline earth metal salts.

In the first step, a compound containing Si is used to fix hydrogen fluoride (HF) generated by the reaction of at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides with an aqueous inorganic acid solution as hexafluorosilicon Acid (H ₂ SiF ₆ ). In the first step, in the absence of a Si element-containing compound, the reaction of calcium fluoride (CaF ₂ ) as a representative example of alkaline earth metals and sulfuric acid (aqueous solution) as a representative example of inorganic acids is in accordance with the following formula ( 1) Proceed. In this reaction, since the generated hydrogen fluoride stays in the solution, the equilibrium relationship of the formula (1) is established, and the reaction stops in the middle. For example, in a 30% by mass sulfuric acid aqueous solution, the reaction stops when the reaction rate is about 30%.

[Equation 1] CaF ₂ (s)+H ₂ SO ₄ (sol)⇄CaSO ₄ ·2H ₂ O+2HF (sol) (1)

In the first step of the present disclosure, with the Si element-containing compound, the balance of formula (1) is tilted to the right, so that the decomposition of _{calcium fluoride (CaF 2) can be promoted.} Therefore, it is considered that the decomposition rate of calcium fluoride is excellent.

In order to increase _{the decomposition rate of CaF 2} , that is, to advance the formula (1) to the right, for example, consider (i) volatilize the HF generated in the formula (1) and exclude it from the system, or (ii) use the formula (1) The generated HF reacts with silicic acid and boric acid and is converted into H ₂ SiF ₆ , HBF ₄ and other compounds. In the present disclosure, in (ii), a Si element-containing compound that reacts with HF is added to the reaction system, thereby converting HF into H ₂ SiF ₆ , and formula (1) is advanced to the right.

Depending on the type of the Si element-containing compound, the ratio of the reacted HF varies as shown in the following formulas (2) and (3), but the same effect can be obtained. For example, when SiO _{2 is} used as the Si element-containing compound, it becomes formula (2), and when SiF ₄ is used, it becomes formula (3). [Equation 2] SiO ₂ (s) + 6HF (sol) → H ₂ SiF ₆ (sol) + 2H ₂ O (2) SiF ₄ (g) + 2HF (sol) → H ₂ SiF ₆ (sol) (3 )

As described above, in the production method of hydrogen fluoride of the present disclosure, not only the alkali metal or alkali metal fluoride is reacted with the inorganic acid, but also the reaction product is reacted with the Si element-containing compound, thereby promoting the alkali metal Or the decomposition of alkali metal fluoride is excellent in efficiency. In addition, an alkali metal salt or alkaline earth metal salt can be obtained as a by-product, so it has the advantage of less waste.

As said alkali metal fluoride, lithium fluoride, sodium fluoride, potassium fluoride, etc. are mentioned. As said alkaline earth metal fluoride, calcium fluoride, strontium fluoride, barium fluoride, etc. are mentioned. The at least one compound selected from alkali metal fluorides and alkaline earth metal fluorides is not particularly limited, and calcium fluoride (CaF ₂ ) can be preferably used.

Examples of the raw material containing CaF ₂ include fluorite or artificial fluorite, and these raw materials can be directly used in the method for producing hydrogen fluoride of the present disclosure. From the viewpoint of utilizing the characteristics of the present disclosure, artificial fluorite can be preferably used.

The higher the content of calcium fluoride (CaF ₂ ) in the artificial fluorite, the better, and it is preferably 60% by mass or more in terms of dry content, and more preferably 80% by mass or more. Different from the previous method of producing hydrogen fluoride, the method of producing hydrogen fluoride of the present disclosure does not directly produce HF _{from CaF 2 but obtains HF from H 2} SiF _6. Therefore, it may be used in the previous production method of hydrogen fluoride using artificial fluorite. The problematic _{impurities such as SiO 2} , CaCO ₃ , and Ca(OH) ₂ are unlikely to be a problem. Therefore, as at least one compound selected from alkali metal fluorides and alkaline earth metal fluorides, artificial fluorite is preferably used.

As the inorganic acid used in the first step, for example, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid and the like can be cited. Among these, from the viewpoint of further improving the reactivity with artificial fluorite, sulfuric acid is preferred. From the viewpoint of ease of handling, sulfuric acid is preferably used in the form of an aqueous sulfuric acid solution. As the inorganic acid used in the first step, an inorganic acid such as 65% by mass to 80% by mass of sulfuric acid that is by-produced in the third step described later may be added so as to be 40% by mass or less.

The concentration of the inorganic acid in the reaction liquid is not particularly limited as long as the reaction proceeds. From the viewpoint of obtaining dihydrate gypsum, it is preferably 40% by mass or less, and more preferably 20% by mass to 30% by mass. The concentration of the inorganic acid in the reaction solution refers to the concentration of the inorganic acid when the total amount of the inorganic acid is added at the time when the reaction starts. Therefore, when the inorganic acid is added dropwise, the actual concentration of the inorganic acid in the reaction solution may be different from the concentration of the inorganic acid in the reaction solution described here. In addition, the concentration of the inorganic acid in the reaction solution means the total concentration when a plurality of types of inorganic acids are included.

The Si element-containing compound used in the first step is not particularly limited, and examples thereof include _{silicon dioxide (SiO 2} ), silicon tetrafluoride (SiF ₄ ), and the like. From the viewpoint of improving reaction efficiency, it is preferably at least one selected from the group consisting of silicon tetrafluoride and silicon dioxide. In the case of using artificial fluorite, SiO ₂ contained as an impurity in the artificial fluorite can also be used as a Si element-containing compound. Further, in a third step generates SiF _4, or the second step in the volatile SiF _4, resulting in a second step, SiO _2, etc. can also be used as the compound containing Si element.

As a material containing SiO _{2 , diatomaceous earth with SiO 2} as the main component, silicic acid powder, by-product colloidal silica, silica-containing dust, silica gel, water glass, and pearlite can be used. And other silicate compounds. In addition, from the viewpoint of further improving the filterability described later, a seed crystal of an alkali metal salt or an alkaline earth metal salt may be included. The seed crystal is not particularly limited, but it is preferable to use a part of the slurry liquid produced in the first step.

In the first step, with respect to 1 mol of at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides, it is preferable to use an inorganic acid of 1.0 mol to 1.5 mol, and a Si element-containing compound of 0.2 mol. ~1.0 mol, more preferably inorganic acid 1.0 mol ~ 1.4 mol, Si element-containing compound 0.30 mol ~ 0.50 mol, more preferably inorganic acid 1.0 mol ~ 1.4 mol, Si element-containing Compound 0.30 mol ~ 0.40 mol.

Regarding the amount of the inorganic acid, from the viewpoint of further increasing the yield of dihydrate gypsum and further reducing the concentration of the remaining inorganic acid to make the third step described later more efficient, it is preferably set to the upper limit or less. In order to promote the decomposition reaction of calcium fluoride and the like, it is preferably set to be more than the above-mentioned lower limit. Regarding the amount of the Si element-containing compound, in order to further improve the filterability, it is preferably set below the upper limit, in order to further promote the decomposition reaction of calcium fluoride and the like, that is, in order to make the formula (1) more to the right The movement is preferably set to be equal to or higher than the above-mentioned lower limit.

The reaction in the first step can be carried out, for example, by mixing at least one compound selected from alkali metal fluorides and alkaline earth metal fluorides with water, adding an inorganic acid such as sulfuric acid to the mixed solution dropwise, and adding a Si element-containing compound.

From the viewpoint of increasing the decomposition rate of calcium fluoride and the like, the reaction temperature in the first step is preferably high. On the other hand, from the viewpoint of increasing the water content of gypsum to obtain dihydrate gypsum, the reaction temperature is preferably 95°C or lower, more preferably 90°C or lower, still more preferably 80°C or lower, particularly preferably 70°C the following. In addition, from the viewpoint of further improving the filterability described later, the reaction temperature is preferably 80°C or lower. The reaction temperature can be set to, for example, 10°C to 95°C, preferably normal temperature to 90°C, more preferably 30°C to 80°C, and still more preferably 50°C to 70°C. In the reaction of the first step, the calorific value varies according to the type and amount of the Si element-containing compound used, and it is preferable to heat or cool as necessary to maintain the reaction temperature within the above range.

From the viewpoint of further increasing the decomposition rate of calcium fluoride and the like, the reaction time in the first step, that is, the total amount of inorganic acid addition or the time from the start of dropwise addition to the end of the reaction is preferably long. On the other hand, if the reaction time is long, the efficiency is poor. From the viewpoint of both the decomposition rate and efficiency, the reaction time can be set to, for example, 0.5 hours to 8 hours, preferably 1 hour to 7 hours, more preferably 2 hours to 6 hours, and still more preferably 2.5 hours to 5 hours.

The concentration and temperature conditions of the inorganic acid in the first step are preferably conditions where the inorganic acid is 40% by mass or less and the temperature is 90°C or less. If it is this range, dihydrate gypsum can be obtained efficiently, and there exists a tendency for the filtration efficiency to be excellent.

In the first step, a mixture of an aqueous solution A containing hydrogen fluoride and hexafluorosilicic acid and at least one compound selected from alkali metal salts and alkaline earth metal salts as a solid is obtained. Since the aqueous solution A is used in the second step, it is preferable to divide the mixture obtained in the first step into the aqueous solution A and solids such as alkali metal salts or alkaline earth metals. The classification method is not particularly limited as long as the second step can be performed. As a method of classification, for example, filtering can be cited. The specific method of filtration is not particularly limited as long as the second step can be carried out, and for example, it can be carried out using a cartridge filter or the like.

The molar ratio (F/Si) of the fluorine component to the silicon component in the aqueous solution A is preferably 3.0 or more, more preferably 3.5 or more. The upper limit of the molar ratio of F/Si is not particularly limited, but it is actually 6.0 or less. If F/Si is more than the lower limit, the second step can be shortened, and the energy efficiency is excellent, so it is preferable.

From the viewpoint of shortening the second step and the viewpoint of improving energy efficiency, the concentration of hexafluorosilicic acid in the aqueous solution A is preferably 20% by mass to 35% by mass. The concentration of the inorganic acid in the aqueous solution A, that is, the concentration of the inorganic acid after the completion of the reaction, is preferably 1% by mass to 5% by mass. If the concentration of the remaining inorganic acid is 5 mass% or less, the recovery efficiency of hydrogen fluoride in the third step described later tends to be further improved. The reason is that hydrogen fluoride is easily dissolved in an aqueous inorganic acid solution such as sulfuric acid, and is likely to remain when separated from the aqueous inorganic acid solution.

As at least one compound selected from alkali metal salts and alkaline earth metal salts obtained in the first step, examples thereof include sodium chloride, sodium sulfate, sodium nitrate, sodium phosphate, potassium chloride, potassium sulfate, potassium nitrate, and potassium phosphate , Magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium phosphate, calcium chloride, calcium sulfate, calcium nitrate, calcium phosphate, etc. Among them, calcium sulfate is preferred. Furthermore, examples of calcium sulfate include anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum. Among these, from the viewpoint of further suppressing moisture absorption over time, dihydrate gypsum is preferred. Dihydrate gypsum has little moisture absorption over time, so it is a dihydrate gypsum with high utility value as an industrial raw material. From the viewpoint of further suppressing moisture absorption over time, the amount of the water of synthesis contained in the dihydrate gypsum is preferably 19% by mass or more. As described above, according to the method for producing hydrogen fluoride of the present disclosure, at least one compound selected from alkali metal salts and alkaline earth metal salts can be obtained, and this compound is a compound with high utility value as an industrial raw material.

<Second Step> The second step is a step of concentrating the aqueous solution A to obtain an aqueous solution B as a concentrated solution containing hydrogen fluoride (HF) and hexafluorosilicic acid (H ₂ SiF ₆ ). If the aqueous solution A is supplied to the third step described later without going through the second step, the amount of inorganic acid per unit of hydrogen fluoride produced in the third step increases, and the amount of residual hydrogen fluoride in the by-produced aqueous inorganic acid solution also increases. The amount of hydrogen fluoride recovered is correspondingly reduced. That is, by performing concentration in the second step, hydrogen fluoride can be efficiently recovered.

The main purpose of the second step is to concentrate _{H 2} O and SiF _{4 while leaving HF in the aqueous solution.} In this way, the final HF recovery efficiency can be improved.

H ₂ SiF ₆ is a strong acid, which is only stable in aqueous solutions and has no anhydride. It is reported that _{even if H 2} SiF ₆ is concentrated under reduced pressure at room temperature, it can be concentrated to only 60.92% by mass. H ₂ SiF ₆ H ₂ SiF ₆ as a non-volatile, decomposed as SiF ₄ and HF was evaporated, but the high priority evaporated volatile SiF _4. In the concentration of the aqueous solution A, when the H ₂ SiF ₆ concentration is low, almost only water evaporates, and when the H ₂ SiF ₆ concentration is close to 35% by mass, SiF ₄ evaporates together with water. This situation indicates that as _{the concentration of H 2} SiF ₆ becomes higher, [Equation 3] H ₂ SiF ₆ ⇄SiF ₄ +2HF in the solution is _{promoted to dissociate, and SiF 4} becomes easy to volatilize. Most of the HF generated by the decomposition of H ₂ SiF ₆ remains in the solution, and the HF is concentrated. If it is further concentrated, the HF also starts to evaporate and finally becomes an azeotropic mixture. Meanwhile, with regard to _{the concentration of H 2} SiF ₆ in the aqueous solution A, it initially increased together with the concentration, and changed to a decrease as HF increased.

In the present disclosure, by stopping the concentration before the evaporation of HF becomes significant, for example, by stopping the concentration at normal pressure at 116°C to 118°C, the concentration can be concentrated to _{a content rate of H 2} SiF ₆ or more of 35% by mass. And the molar ratio (F/Si) is 6.0 or more. Therefore, it is preferable that the concentrated liquid is that the hexafluorosilicic acid content of the concentrated liquid is 35% by mass or more relative to the total mass of the concentrated liquid, and the molar ratio of the F element to the Si element in the concentrated liquid (F/Si) Above 6.0.

By increasing the concentration of H ₂ SiF ₆ and HF in the aqueous solution B obtained by concentration, particularly the concentration of HF, the recovery amount of anhydrous hydrogen fluoride in the third step can be increased and the amount of concentrated sulfuric acid used can be reduced.

_{If SiF 4} and H ₂ O evaporated by the second step of concentration are cooled and condensed, a slurry of hexafluorosilicic acid aqueous solution and SiO _{2 is obtained. The SiO 2} obtained here is obtained _{by condensing SiF 4} evaporated by concentration and H ₂ O. The hexafluorosilicic acid present in the attached mother liquor can be easily volatilized by drying, so it can be used as extremely high purity Of amorphous silicon dioxide to be recycled.

The concentration method in the second step is not particularly limited as long as the aqueous solution A can be concentrated. For example, it may be performed by a known method such as distillation at normal temperature and distillation under reduced pressure. Among them, distillation at normal temperature and distillation under reduced pressure are preferred. In particular, distillation under reduced pressure is easy to concentrate, so it is preferred.

In the case of distillation under normal pressure, it is preferable to raise the temperature of the aqueous solution A to 100°C to 120°C, preferably 110°C to 120°C, more preferably 116°C to 118°C. Regarding the temperature of the aqueous solution A, in order to increase the concentration rate, it is preferably equal to or higher than the above-mentioned lower limit, and from the viewpoint of reducing the loss of hydrogen fluoride, it is preferably equal to or lower than the above-mentioned upper limit. In the case of performing distillation under reduced pressure, it is preferable to heat the aqueous solution to 68°C to 85°C under the condition of 20 kPa (absolute pressure).

In the aqueous solution B obtained in the second step, the molar ratio (F/Si) is preferably 6.0 or more, more preferably 6.5 to 8.0, and still more preferably 6.8 to 7.2. From the viewpoint of making the third step more efficient, the molar ratio (F/Si) is preferably equal to or higher than the lower limit value, and can be set to be equal to or lower than the upper limit value as a practically possible value. The molar ratio (F/Si) can be changed by adjusting the temperature at the end point.

In the aqueous solution B obtained in the second step, _{the content of H 2} SiF ₆ is preferably 35% by mass or more, more preferably 37.0% to 44.0% by mass. From the viewpoint of improving the efficiency of the third step, the content of H ₂ SiF ₆ is preferably equal to or higher than the lower limit, and can be set to be equal to or lower than the upper limit as a practically possible value.

<Third step> The third step is a step of applying sulfuric acid to the aqueous solution B to generate _{a gas containing silicon tetrafluoride (SiF 4} ) and hydrogen fluoride (HF), and separating and recovering hydrogen fluoride from the gas. In addition, the hydrogen fluoride recovered from the gas can be evaporated and cooled again to be liquefied to increase the concentration.

The purpose of the third step is to separate hydrogen fluoride from the concentrated solution produced in the second step, that is, the aqueous solution B, so as to reduce the concentration of _{H 2} SiF ₆ and SiF _4. As long as the purpose of the third step can be achieved, the specific means is not limited, but in the third step, it is preferable to perform the following (i) and (ii), and optionally perform (iii).

(I) Add 75% by mass or more of concentrated sulfuric acid or fuming sulfuric acid to the aqueous solution B, and perform dehydration and decomposition to generate a gas _{containing HF and SiF 4.} In this step, by dehydration and decomposition, hydrogen fluoride and silicon tetrafluoride, hydrogen fluoride and silicon tetrafluoride are volatilized simultaneously. (Ii) The hydrogen fluoride is absorbed by 80% by mass or more of sulfuric acid to obtain an absorption liquid. In this step, _{80% by mass or more of sulfuric acid is added to the mixed gas of HF and SiF 4} to make the sulfuric acid absorb HF to prepare an absorption liquid, and HF is selectively recovered from the mixed gas. (Iii) Heating the absorption liquid to above 100°C to volatilize hydrogen fluoride and recover hydrogen fluoride. In this step, it is preferable to cool and liquefy the volatilized hydrogen fluoride for recovery.

Regarding the temperature of the aqueous solution B when concentrated sulfuric acid or fuming sulfuric acid is added in (i), as long as _{HF and SiF 4} generated by the decomposition _{of H 2} SiF ₆ with sulfuric acid can be vaporized, there is no It is particularly limited, and for example, it can be set to 80°C to 130°C, more preferably 100°C to 130°C.

The decomposition reaction using sulfuric acid in (i) can be carried out under normal pressure or under reduced pressure. From the viewpoint of reducing the amount of HF remaining in the aqueous solution and further increasing the yield, it is preferably performed under reduced pressure.

In the above (i), from the viewpoint of reducing the amount of HF remaining in the aqueous solution and further increasing the yield, it is preferable to ventilate with an inert gas. Examples of the inert gas include nitrogen, argon, and SiF ₄ gas. The aeration of the inert gas may be performed from the time of adding sulfuric acid, or may be performed after the decomposition of sulfuric acid is performed or after the end. According to this method, even when 2% by mass of HF remains, the residual amount can be reduced to about 0.5% by mass.

In the above (i), from the viewpoint of reducing the amount of HF remaining in the aqueous solution and further increasing the yield, it is preferable to add a hydrocarbon such as alkane having a relatively low boiling point.

The aqueous solution after (i) is dilute sulfuric acid containing a small amount of HF. By changing the concentration of the concentrated solution or the addition amount of concentrated sulfuric acid, the sulfuric acid concentration in the dilute sulfuric acid can be set to 60% by mass to 85% by mass, for example. From the viewpoint of further reducing the content of HF, the sulfuric acid concentration in the dilute sulfuric acid is preferably 80% by mass to 85% by mass. In addition, from the viewpoint of facilitating reuse, the sulfuric acid concentration in the dilute sulfuric acid is preferably 70% by mass to 80% by mass. Dilute sulfuric acid can be used as a part of raw materials such as phosphoric acid factories, or used in each step of the present disclosure, for example.

From the viewpoint of efficient recovery of HF, the content of HF in the dilute sulfuric acid is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, particularly preferably 1% by mass or less .

In the above (ii), concentrated sulfuric acid is added to the mixed gas, and HF is dissolved in the concentrated sulfuric acid to prepare an absorption liquid _{containing HF and H 2} SO _4. The mixed gas also contains H ₂ O. The H ₂ O is absorbed by concentrated sulfuric acid and therefore contained in the absorption liquid. The concentration of HF in the absorption liquid is, for example, 30% by mass or more, preferably 35% by mass or more.

In the above (ii), the SiF ₄ gas is not absorbed but remains. Therefore, it is preferable to recover the silicon tetrafluoride that is by-produced when hydrogen fluoride is generated, and use at least one of the silicon tetrafluoride and the reaction product of the silicon tetrafluoride and water as the content in the first step. At least a part of the compound of Si element is used, or it is added to the aqueous solution B in the third step and used. Since the number of compounds discharged to the outside of the system is reduced, the economy tends to be excellent.

In the above (iii), the absorbing liquid is heated to 100°C or higher, preferably 120°C, and maintained, for example, for 30 minutes, and the volatilized gas is cooled, thereby obtaining an aqueous solution with a HF concentration of 99% by mass .

The residual liquid after separating and recovering the generated hydrogen fluoride becomes an aqueous sulfuric acid solution. It is preferable to use the sulfuric acid aqueous solution as at least a part of the inorganic acid in the first step. Since the number of compounds discharged to the outside of the system is reduced, the economy tends to be excellent. In addition, it is preferable to increase the concentration of the sulfuric acid aqueous solution and reuse it in the third step. Since the number of compounds discharged to the outside of the system is reduced, the economy tends to be excellent. As a method of increasing the concentration, for example, dehydration distillation can be cited.

As a method similar to the previously known third step of the present disclosure, there is the following method: using a two-stage reactor, in the first stage almost only SiF _{4 is} evaporated, and in the second stage under stricter conditions, HF is mainly volatilized . However, it is difficult to _{evaporate SiF 4} and HF separately, and sometimes the yield of HF may decrease. In contrast, according to the third step of the present disclosure, operations such as volatilization are easy, and HF can be recovered in a high yield.

As described above, according to the method for producing hydrogen fluoride of the present disclosure, the dihydrate gypsum and SiO ₂ are discharged out of the system in addition to HF. _{The dihydrate gypsum and SiO 2} obtained by the manufacturing method of the present disclosure have low impurity content, and can be directly sold as products on the market. [Example]

The various measurement methods performed in the examples are shown below. (1) Measuring method of content rate (1-1) Analysis of F content rate F content rate is the fluoride ion electrode 9409BN manufactured by Thermo (Thermo) is installed on the ion meter F-72 of Horiba Manufacturing Co., Ltd., and fluorine is used. The ion meter method is used for the measurement. (1-2) Analysis of Si content The Si content is measured by the atomic absorption method using the polarized Zeeman atomic absorption photometer ZA3300 manufactured by Hitachi High-technologies. (1-3) Analysis of _{H 2} SO _{4 Regarding SO 4} ^2- , column AS18 was installed on the ion chromatography ICS-1600 manufactured by Dionex Co., Ltd., the eluent was KOH, and ion chromatography was used. Method to perform the measurement. Calculate the H ₂ SO ₄ content based on the measured SO ₄ ^2- content.

(2) Method for measuring the water of dihydrate gypsum The combined water of dihydrate gypsum is measured in accordance with JIS R 9101 (1995). The heating temperature was set to 250°C.

[Example 1]-The first step-In a 12 L fluororesin lined reactor equipped with a stirrer and a sleeve, artificial fluorite B obtained in the general chemical industry (dried product: CaF ₂ content: 85.0% by mass, SiO ₂ content: 2.4% by mass) 1,848 g and 6,180 g of water were made into a slurry form, stirred and heated to 60°C. It took 30 minutes to drop 2,896 g of 75% by mass sulfuric acid, and 1,654 g of _{SiF 4 gas was blown into the reaction tank.} During this period, heat removal was performed so that the reaction temperature did not exceed 70°C. After the dropwise addition of sulfuric acid was completed, stirring was continued for 2 hours for maturation. The slurry was filtered with a cartridge filter, and 4,118 g of solid content and 8,440 g of filtrate (aqueous solution A) were recovered. The solid content is dihydrate gypsum, washed with methanol, and the weight after drying at 50°C is 3,500 g. The filtrate (aqueous solution A) contains hydrogen fluoride (HF) and hexafluorosilicic acid (H ₂ SiF ₆ ). The concentration of hexafluorosilicic acid was 27.6% by mass, and _{the concentration of H 2} SO ₄ was 3.2% by mass. In addition, the molar ratio (F/Si) was 5.71. The combined water of dihydrate gypsum is 19.5% by mass.

-Second step- To a 1,000 ml fluororesin bottle (made by welding a commercially available bottle) that includes two thermometer protection tubes (for measuring the temperature of liquid and gas phase) and a gas outlet, 1,055 g of the filtrate obtained in the first step was charged, and concentrated and distilled under normal pressure until the liquid temperature reached 118°C, thereby obtaining 773 g of concentrated liquid. The first step and the second step were repeated twice to obtain 1,546 g of concentrated solution. The concentrated solution (aqueous solution B) contained 37.6% by mass of hexafluorosilicic acid, _{7.4% by mass of H 2} SO ₄ , and a molar ratio (F/Si) of 7.01.

-The third step (i) (ii)-A 2,000 ml Teflon (registered trademark) reactor including a stirrer and a thermometer was immersed in an oil bath, stirred and kept at 120°C. Using a tube pump, 928 g of the concentrated solution (hexafluorosilicic acid: 37.6 mass%, molar ratio (F/Si): 7.01, H ₂ SO ₄ : 7.4 mass%) and 98 mass% sulfuric acid 1,840 were simultaneously added dropwise thereto. g, start the dehydration decomposition of hexafluorosilicic acid. The concentrated solution and concentrated sulfuric acid were adjusted so that the dripping was ended simultaneously in about 60 minutes. Simultaneously with the end of the dripping, the SiF ₄ gas discharged from the absorption bottle described later was returned by an air pump, bubbling for 30 minutes, and HF in the reaction solution was removed. Put 90 g of 98% by mass sulfuric acid into two fluororesin absorption bottles connected in series with the volatilized gas between them to make the sulfuric acid absorb HF by foaming. The absorption bottle was immersed in a cold water bath set at 10°C for cooling.

2,412 g of residual liquid was recovered from the Teflon (registered trademark) reactor. Its composition is about 75% by mass H ₂ SO ₄ containing 0.5% by mass of HF. 309 g of sulfuric acid absorption liquid was recovered from the two absorption bottles. The composition is H ₂ SO ₄ : 55.3% by mass, HF: 36.4% by mass, and H ₂ O: 8.3% by mass. _{The SiF 4} produced here is used for HF elimination purposes, and is additionally absorbed by a water scrubber to recover _{the aqueous solution containing SiO 2} and hexafluorosilicic acid. The molar ratio (F/Si) of this aqueous solution was 5. Repeat steps 1 to 3 (i) and (ii) twice to obtain 618 g of sulfuric acid absorption solution. The composition of the sulfuric acid absorption solution is as described above.

-The third step (iii)- A single distillation apparatus made of fluororesin including a 500 ml evaporator, a cold water condenser (5°C), and a 100 ml receiver immersed in a cold water bath (5°C) was used to perform the extraction from the sulfuric acid absorption liquid HF recovery. Put 450 g of sulfuric acid absorption liquid into an evaporation tank, heat it to evaporate HF, use a cold water condenser to condense the evaporated HF, and store the condensed liquid in a receiver. The heating was performed slowly, and the temperature of the sulfuric acid absorption liquid was increased to 120° C. in about 1 hour, and the temperature was maintained for 30 minutes. After being left to cool, 293 g of residual liquid and 157 g of condensed liquid in the evaporation tank were recovered. The residual liquid in the evaporation tank contains 2.3% by mass of HF. The composition of the condensed liquid is 99% by mass of HF.

[Comparative Example 1] The first step was performed in the same manner as in Example 1, and 8,440 g of the filtrate (aqueous solution A) was recovered. The filtrate (aqueous solution A) contains hydrogen fluoride (HF) and hexafluorosilicic acid (H ₂ SiF ₆ ). The concentration of hexafluorosilicic acid was 27.6% by mass, and _{the concentration of H 2} SO ₄ was 3.2% by mass. In addition, the molar ratio (F/Si) was 5.71.

The filtrate (aqueous solution A) was used in the third steps (i) and (ii) without performing the second step. Specifically, a 2,000 ml Teflon (registered trademark) reactor including a stirrer and a thermometer was immersed in an oil bath, stirred and maintained at 120°C. Using a tube pump, the filtrate (aqueous solution A) (hexafluorosilicic acid: 27.6 mass%, molar ratio (F/Si): 5.71, H ₂ SO ₄ : 3.2 mass%) 718.6 g and 98 mass% sulfuric acid was added dropwise to it at the same time 1840 g, the dehydration decomposition of hexafluorosilicic acid began. The concentrated solution and concentrated sulfuric acid were adjusted so that the dripping was ended at the same time in about 60 minutes. Simultaneously with the end of the dripping, the SiF ₄ gas discharged from the absorption bottle described later was returned by an air pump, bubbling for 30 minutes, and HF in the reaction solution was removed. Put 90 g of 98% by mass sulfuric acid into two fluororesin absorption bottles connected in series with the volatilized gas between them to make the sulfuric acid absorb HF by foaming. The absorption bottle was immersed in a cold water bath set at 10°C for cooling.

236 g of sulfuric acid absorption liquid was recovered from the two absorption bottles. The composition is H ₂ SO ₄ : 62.3% by mass, HF: 15.7% by mass, and H ₂ O: 8.1% by mass. In this comparative example 1, the same amount of sulfuric acid for absorption as in Example 1 was used. However, the concentration of HF that can be recovered from the absorption bottle as boiling sulfuric acid is 15.7% by mass in Comparative Example 1 with respect to 36.4% by mass in Example 1. Therefore, it can be seen that the efficiency of this comparative example 1 which does not go through the second step is significantly lower than that of the example 1.

[Test Example 1] As a raw material, artificial fluorite A (dried product: CaF ₂ content: 78.4 mass%, SiO ₂ : 0.88 mass%, CaSO ₄ ·2H ₂ O: 9.3 mass%) discharged from the semiconductor industry was used as a raw material. Concentrated sulfuric acid was diluted to 75% by mass of sulfuric acid, _{diatomaceous earth commercially available as a source of SiO 2} , and the first step was implemented. Weigh 99.6 g of artificial fluorite A ( _{1.0 mol based on CaF 2} ) and diatomaceous earth containing 0.33 mol in total based on SiO ₂ and put them into a 500 ml fluororesin container. Add 150 g of water to make a slurry Materialize, stir and raise the temperature to 65°C. Then, 75% by mass H ₂ SO _{4 containing 1.3 mol in H 2} SO _{4 was} dropped over 30 minutes using a separatory funnel. The reaction was carried out in accordance with the aforementioned formula (1), the reaction was stopped 4 hours after the end of the sulfuric acid dropwise addition, and filtration was immediately performed to obtain a filtrate (aqueous solution A). After the filtration residue was washed with water and methanol, it was dried at 105°C for 1 hour to obtain a dry solid content.

(1) Evaluation of filterability Based on the residence time of the slurry during filtration, the filterability was evaluated in accordance with the following evaluation criteria. In addition, the filtration is performed using a filter device in which a membrane filter with a mesh of 1 μm is installed on a filter holder with an inner diameter of 4.5 cm at a portion through which the solution passes, and is carried out while being sucked by a vacuum pump. ～Evaluation Criteria～ A: The residence time of the slurry is 60 seconds or less. B: The residence time of the slurry exceeds 60 seconds and is 90 seconds or less. C: The residence time of the slurry exceeds 90 seconds.

(2) Evaluation of combined water Based on the obtained dry solid content, the amount of combined water is determined in accordance with the method described. (3) Determination of decomposition rate Weigh the mass of the dry solid content, and calculate the decomposition rate based on the mass of the dry solid content and the mass of the artificial fluorite used as a raw material. The decomposition rate is expressed by the following formula. Decomposition rate (%)=[mass of dry solid content (g)/mass of artificial fluorite (g)]×100

[Test Example 2-Test Example 15] The first step was carried out in the same manner as in Test Example 1, except that the molar ratio, reaction temperature, and reaction time of the raw materials used were changed as described in Table 1. Table 1 shows the evaluation results of filterability, combined water, and decomposition rate.

[Table 1] Raw material (mole ratio) Reaction conditions Filterability Combined water (mass%) Decomposition rate (%) CaF ₂ H ₂ SO ₄ SiO ₂ Reaction temperature (℃) Time (h) Test example 1 1 1.3 0.33 65 4 A 20.4 95.9 Test example 2 1 1.3 0.33 75 4 A 17.7 95 Test example 3 1 1.3 0.33 85 4 C 11.4 95.8 Test Example 4 1 1.3 0.33 Room temperature 4 A 19.6 91 Test Example 5 1 1 0.33 65 4 B 18.1 85.2 Test Example 6 1 1.05 0.33 65 4 A 20.1 92.1 Test Example 7 1 1.05 0.33 65 2 A 20.2 94 Test Example 8 1 1.05 0.3 65 2 A Not determined 90.2 Test Example 9 1 1.1 0.33 65 4 A 19.6 91.3 Test Example 10 1 1.1 0.33 Room temperature 4 A 19.2 83.6 Test Example 11 1 1.1 0.47 65 4 B 19.1 90.5 Test Example 12 1 1.1 0.7 65 4 C 17.3 87.8 Test Example 13 1 1.1 0.33 65 1 C Not determined 78.8 Test Example 14 1 2 0.33 65 2 A Not determined 96.2 Test Example 15 1 1.3 0.0 65 4 C 9.9 26.3

Examination of the evaluation results relative to the test example (regarding the reaction temperature) In "Test Example 1 to Test Example 4", "Test Example 9, Test Example 10", the conditions other than the reaction temperature were the same, and only the reaction temperature was changed. From the results shown in Table 1, it can be seen that the higher the reaction temperature, the higher the CaF ₂ decomposition rate. On the other hand, it can be seen that if the reaction temperature becomes higher, the amount of combined water decreases, if it exceeds 80°C, hemihydrate gypsum is formed, and if it exceeds 90°C, anhydrous gypsum is formed, and filterability is reduced. From the above, the reaction temperature in the first step is preferably 80°C or lower, more preferably 50°C to 70°C.

(Regarding the _{amount of SiO 2} ) In Test Example 15 where _{SiO 2} was not added and only 0.014 mol of SiO ₂ derived from artificial fluorite was used as SiO _{2 , the decomposition rate of CaF 2} was 30% or less. In other test examples of _{SiO 2 , the decomposition rate of CaF 2} is all 70% or more. According to the comparison of "Test Example 7, Test Example 8" and "Test Example 9, Test Example 11, Test Example 12" that differ _{only in the amount of SiO 2} added, it can be seen that the addition _{of SiO 2 in Test Example 7 and Test Example 9} When the amount is 0.33 mol, the decomposition rate is the highest. When _{the addition amount of SiO 2} is less than 0.33 mol and more than 0.33 mol, the decomposition rate decreases. In addition, from the comparison of "Test Example 9, Test Example 11, and Test Example 12", it can be seen that if _{there is too much SiO 2} , the filterability decreases. It is considered that this is because the unreacted fine SiO ₂ remains in the slurry.

(Regarding the amount of sulfuric acid) If the amount of sulfuric acid (molar ratio) _{relative to CaF 2 is increased, the decomposition rate of CaF 2} becomes higher, but the amount of sulfuric acid remaining in the filtrate increases. In the next second step, SiF ₄ and HF are easy to volatilize. In _{the presence of SiO 2} , even the equivalent of sulfuric acid, the decomposition rate is more than 85%, 90% to 94% when 1.05 times the equivalent amount, and 96.2% when 2 times the equivalent amount.

(Regarding residence time) According to the results of Test Example 9 and Test Example 13, if the residence time during the reaction ( _{reaction time after dropping H 2} SO ₄ ) is prolonged, the decomposition rate will increase and the gypsum crystals will tend to increase, but Like Test Example 6 and Test Example 7, if the residence time during the reaction exceeds 2 hours, no difference is seen. Therefore, it can be seen that it is sufficient when the residence time is 2 hours to 4 hours.

[Test Example 16] (Vacuum Distillation) Using a 1 L fluororesin vacuum distillation apparatus, the filtrate obtained in the first step of Example 1 (hexafluorosilicic acid: 27.6 mass%, molar ratio (F /Si): 5.71, H ₂ SO ₄ : 3.2% by mass) 910 g, concentrated and distilled under an absolute pressure of 15 kPa. Distillation was performed until the temperature of the tank residue reached 75°C. As a result, 402 g of concentrated liquid was obtained as tank residue. Its composition was hexafluorosilicic acid: 38.5 mass%, molar ratio (F/Si): 7.03, H ₂ SO ₄ : 7.2% by mass.

[Test Example 17] (No foaming operation) In Example 1, the foaming operation of the third step (i) was not performed, and the third steps (i) and (ii) were performed in the same manner as in Example 1, except that the foaming operation of the third step (i) was not performed. . The composition of the recovered sulfuric acid absorption liquid was an approximately 75% by mass H ₂ SO ₄ solution containing 2.2% by mass of HF.

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Claims (11)

A method for manufacturing hydrogen fluoride, which includes: The first step is to react a mixture containing at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides, inorganic acids, and Si element-containing compounds to obtain an aqueous solution A containing hydrogen fluoride and hexafluorosilicic acid, and At least one compound selected from alkali metal salts and alkaline earth metal salts; In the second step, the aqueous solution A is concentrated to obtain an aqueous solution B as a concentrated solution containing hydrogen fluoride and hexafluorosilicic acid; and In the third step, sulfuric acid is applied to the aqueous solution B to generate a gas containing silicon tetrafluoride and hydrogen fluoride, and the hydrogen fluoride is separated from the gas and recovered. The method for producing hydrogen fluoride according to claim 1, wherein the Si element-containing compound is at least one selected from the group consisting of silicon tetrafluoride and silicon dioxide. The method for producing hydrogen fluoride according to claim 1 or 2, wherein at least one compound selected from the alkali metal salt and alkaline earth metal salt is dihydrate gypsum having a water ratio of 19% by mass or more. The method for producing hydrogen fluoride according to any one of claims 1 to 3, wherein the first step is performed under the conditions that the concentration of the inorganic acid is 40% by mass or less and the temperature is 90°C or less. The method for producing hydrogen fluoride according to any one of Claims 1 to 4, wherein as a raw material containing at least one compound selected from the alkali metal fluorides and alkaline earth metal fluorides, a dry weight containing Artificial fluorite containing 60% by mass or more of calcium fluoride. The method for producing hydrogen fluoride according to any one of claims 1 to 5, wherein the inorganic acid is used from 1.0 mol to 1 mol of at least one compound selected from the group consisting of alkali metal fluorides and alkaline earth metal fluorides. 1.5 mol, Si element-containing compound 0.2 mol ~ 1.0 mol. The method for producing hydrogen fluoride according to any one of claims 1 to 6, wherein the content of hexafluorosilicic acid in the aqueous solution B is 35% by mass or more relative to the total mass of the aqueous solution B, and The molar ratio (F/Si) of the F element to the Si element in the aqueous solution B is 6.0 or more. The method for producing hydrogen fluoride according to any one of claims 1 to 7, wherein the third step is to add 75% by mass or more of concentrated sulfuric acid or fuming sulfuric acid to the aqueous solution B for dehydration and decomposition, And produce gas containing silicon tetrafluoride and hydrogen fluoride, The hydrogen fluoride is absorbed by 80% by mass or more of sulfuric acid to obtain an absorption liquid, The absorption liquid is heated to above 100°C to volatilize the hydrogen fluoride and recover the hydrogen fluoride. The method for producing hydrogen fluoride according to any one of claims 1 to 8, wherein the inorganic acid aqueous solution obtained after the hydrogen fluoride generated in the third step is separated and recovered is used as the inorganic acid aqueous solution in the first step At least part of. The method for producing hydrogen fluoride according to any one of claims 1 to 9, wherein the inorganic acid aqueous solution obtained after separating and recovering the hydrogen fluoride generated in the third step increases the concentration, and is reused in the third step . The method for producing hydrogen fluoride according to any one of claims 1 to 10, wherein silicon tetrafluoride that is by-produced when hydrogen fluoride is generated in the third step is recovered, and the silicon tetrafluoride and the At least one of the reaction products of silicon tetrafluoride and water is used as at least a part of the Si element-containing compound in the first step, or is added to the aqueous solution B in the third step and used .