JP6836334B2 - Method for producing inorganic iodine compound powder - Google Patents

Description

The present invention relates to a method for producing an inorganic iodine compound powder.

Traditionally, inorganic iodine compounds have been used in various fields as chemical raw materials, raw materials for manufacturing pharmaceutical products, and the like. For example, sodium iodide is a commonly used inorganic iodine compound used in the manufacturing process of medical pesticides. Further, lithium iodide is an inorganic iodine compound (hereinafter, also referred to as an inorganic iodide) that has been used in all-solid-state lithium batteries, dye-sensitized solar cells and the like and has been attracting attention in recent years.

Here, the inorganic iodine compound has high hygroscopicity and deliquescent property. In addition, there are many that have water of crystallization in the crystal. However, for non-aqueous applications, an inorganic iodine compound from which water has been sufficiently removed is desired.

Many conventionally known methods for drying an inorganic iodine compound to remove water have been performed, and a method of heating a solid inorganic iodine compound has been performed (Non-Patent Documents 1 to 3). In addition to this, for example, a method of removing water by extracting or azeotropically boiling water of crystallization contained in an inorganic iodine compound using an organic solvent has been proposed (Patent Documents 1 and 2). Further, a method of removing water by firing or drying a lithium iodide powder has also been proposed (Patent Documents 3 and 4).

Japanese Unexamined Patent Publication No. 2004-196560 Japanese Unexamined Patent Publication No. 2013-256416 Japanese Unexamined Patent Publication No. 2013-103851 JP-A-2015-214472

Iodine theory, Kasumigaseki Publishing, Keiichiro Matsuoka, published in February 1974 New Experimental Chemistry Course, Volume 8, Chemical Society of Japan, 1997, p462-463 Experimental Chemistry Course, 5th Edition, Volume 23, Inorganic Compounds, p322, edited by The Chemical Society of Japan, published on March 10, 2005 Application of thermogravimetric analysis to dry weight loss test and water content measurement of pharmaceutical products, Shiki Sasaki, Fumi Kitajima et al., Bull. Natl. Inst. Health Sci. , 115, 144-146 (1997) Development of powder processing equipment using vibration principle, Nagoya Institute of Technology Academic Institution Repository, Eiichi Mizutani, 2004

However, the conventional method cannot sufficiently reduce the amount of water contained in the inorganic iodine compound.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing an inorganic iodine compound powder, which can obtain an inorganic iodine compound powder having a sufficiently reduced water content.

In the method for producing an inorganic iodine compound powder of the present invention, an aqueous solution of the inorganic iodine compound and a crushed ball are oscillated in a container under reduced pressure conditions to concentrate the aqueous solution, and the precipitated inorganic iodine compound is pulverized and dried. Have a process.

It is preferable that the inorganic iodine compound has a polymorph containing water of crystallization.

^{L *} values in ^{the L} * ^a * ^{b *} system chromaticity coordinates according to a color difference meter of the inorganic iodine compound powder is 95 or more, ^{a *} value of 1.5 or less, and ^{b *} values is preferably a 1.5 or less ..

The inorganic iodine compound is preferably sodium iodide or lithium iodide.

It is preferable that the inorganic iodine compound is lithium iodide and the elliptical vibration is performed in a range where the product temperature is 200 to 240 ° C.

According to the above production method, an inorganic iodine compound powder having a particle size of 500 μm or less can be obtained with a recovery rate of 70% by mass or more.

It is preferable that the inorganic iodine compound powder contains 99.0% by mass or more of the inorganic iodine compound, and the water content of the inorganic iodine compound powder is 0.1% by mass or less.

According to the present invention, it is possible to provide a method for producing an inorganic iodine compound powder, which can obtain an inorganic iodine compound powder having a sufficiently reduced water content.

In this embodiment, it is a schematic diagram for demonstrating how the contents of a container vibrate elliptical.

In the method for producing the inorganic iodine compound powder of the present embodiment, the aqueous solution of the inorganic iodine compound and the crushed ball are oscillated in a container under reduced pressure conditions to concentrate the aqueous solution, and the precipitated inorganic iodine compound is crushed and dried. Have a process. In the production method of the present embodiment, since the aqueous solution of the inorganic iodine compound and the crushed ball are oscillated, the precipitated inorganic iodine compound can be efficiently crushed by the crushed ball, so that the amount of water is reduced. The compound powder can be easily obtained. Here, the water content is the ratio (mass%) of the mass of water contained in the powder to the total mass of the obtained inorganic iodine compound powder.

The inorganic iodine compound in the present embodiment is not particularly limited, but is preferably a metal iodide salt. Examples of the metal contained in the metal iodide salt include alkali metals, alkaline earth metals, transition metals and the like.
Some of the above-mentioned inorganic iodine compounds have polymorphs having water of crystallization. Examples of inorganic iodine compounds having polyforms including crystalline water include aluminum iodide, calcium iodide, cobalt iodide, strontium iodide, cerium iodide, iron iodide, sodium iodide, barium iodide, and magnesium iodide. , Manganese iodide, and lithium iodide. As the inorganic iodine compound of the present embodiment, an alkali metal iodide salt which is particularly frequently used in industry is preferable, and lithium iodide or sodium iodide is particularly preferable.

In the case of an inorganic iodine compound having water of crystallization, when an attempt is made to obtain an anhydride by drying, a phenomenon occurs in which the compound itself is redissolved by the water of crystallization in the molecule, and it is not easy to produce an anhydride or even a powder product. Absent. In addition, as the water content decreases, the highly viscous resinous inorganic iodine compound adheres to the drying container and the stirring blade, so that heat transfer deteriorates and drying does not proceed easily.
Further, when an anhydrous powder is to be obtained from an aqueous solution, not only the boiling point elevation due to concentration makes it difficult for water to volatilize, but also the water of crystallization contained in the generated inorganic iodine compound solid becomes free water by heating, so that the solid Occurs a phenomenon in which the water dissolves again. As a result, it becomes a highly viscous aqueous solution, and when the water content is further reduced, the whole tends to become a large resinous mass. Therefore, it is not easy to bring a compound having water of crystallization in the molecule to the anhydride.
In the production method of the present embodiment, since the precipitated inorganic iodine compound is dried while being crushed with a crushing ball, it is possible to prevent sticking to a container or the like and formation of a resinous lump as described above. Therefore, the production method of the present embodiment can be particularly preferably applied when an inorganic iodine compound having water of crystallization is used.

As the inorganic iodine compound, a commercially available compound may be used, or a compound synthesized by a known method may be used. As a method for synthesizing an inorganic iodine compound, a method for obtaining an inorganic iodine compound by a neutralization reaction between a corresponding hydroxide or carbonate and hydroiodic acid is well known. It is preferable that these reactions are carried out in an aqueous solution.

When an alkali metal iodide salt is used as the inorganic iodine compound, as a method for producing the alkali metal iodide salt, for example, an aqueous solution of iodine and an alkali metal hydroxide salt is reacted with a formic acid which is an organic reducing agent. Two methods can be adopted: the method (method 1) and the method (method 2) obtained by the neutralization reaction of alkali metal carbonate and hydroiodic acid.

Taking lithium iodide as an example, in the case of the formic acid method of Method 1, iodine and formic acid are added and reacted while stirring an aqueous solution of lithium hydroxide. The reaction formula is expressed by the following formula.
I ₂ + 2LiOH + HCOOH → 2LiI + CO ₂ + 2H ₂ O
The temperature inside the reactor is preferably in the range of 60 to 110 ° C., and particularly preferably in the range of 80 to 100 ° C. from the viewpoint of ease of production. When the temperature is 60 ° C. or higher, the reaction rate of iodine and formic acid is sufficiently high, and when the temperature is 110 ° C. or lower, the loss due to sublimation of iodine is reduced.

Further, in the above reaction, it is preferable to adjust the pH of the obtained aqueous solution of lithium iodide. The adjusted pH is preferably adjusted within the range of 5-9, more preferably 6-8. As the pH adjuster, lithium hydroxide or hydroiodic acid in the reaction step can be used.

Since the aqueous solution of lithium iodide after the reaction is slightly colored by the liberated iodine, it is preferable to adopt a method of adsorbing the free iodine with a porous adsorbent. A known material such as zeolite can be used as the porous adsorbent, but it is preferable to use activated carbon that has been pretreated with acid cleaning or the like in advance and then washed with water. As a result, free iodine is adsorbed, and free iodine in the obtained solution can be obtained as an almost colorless solution having an amount of 0.2% by mass or less. It is also possible to add, for example, a phosphorus compound such as hypophosphorous acid, a sulfur compound such as sulfurous acid, or a reducing agent of a hydrazine compound to the reaction solution as a stabilizer, but it is not added because impurities increase. Is preferable.

Further, in the reaction of Method 2, lithium carbonate described in Non-Patent Document 1 is used as a lithium source, and a neutralization reaction with hydrogen iodide acid is carried out. As the raw material hydrogen iodide acid, a 57% by mass solution can be used as a commercially available product. The hydroiodic acid can be used even at a low concentration, but it is preferably in the range of 20 to 58% by mass so that the concentration of the obtained lithium iodide does not become too low. The concentration of the lithium carbonate aqueous solution is preferably in the range of 20 to 60 w / v%, more preferably 55 to 60 w / v%. Further, in order to suppress the generation of free iodine, it is preferable to carry out under the condition of an inert gas such as nitrogen gas or argon gas. The reaction formula of this reaction is as follows.
Li ₂ CO ₃ + 2HI → 2LiI + CO ₂ + H ₂ O
Since the acid and alkali are neutralized, heat is generated and carbon dioxide gas is also generated. Therefore, the hydrogen iodide acid is added dropwise and reacted while keeping the temperature range of 30 to 50 ° C. while stirring.

Next, the pH in the reaction vessel is checked while keeping the temperature at 30 ° C., and the pH is adjusted with an acid or alkaline solution. The concentration of the aqueous solution to be used may be appropriately selected. If it is alkaline, for example, 57% by mass iodide. It is preferable to add a hydrogen acid, and if it is acidic, add a powder or an aqueous solution of lithium hydroxide to adjust the pH to 6.0 to 9.0. As a result, a colorless lithium iodide solution can be obtained.

The aqueous solution of the inorganic iodine compound can be prepared by dissolving the inorganic iodine compound in water. Further, the aqueous solution of the inorganic iodine compound obtained by the above methods 1, 2 and the like may be used as it is. Here, the aqueous solution may contain formic acid used as a reaction raw material, an organic solvent used as a reaction solvent, and an organic substance as an antioxidant. However, it is preferable that the content of the organic substance is 10% by mass or less, and it is more preferable that the content of the organic substance or the organic solvent is substantially not contained.

As the crushing balls in the present embodiment, ordinary crushing or dispersing alumina balls and alumina lining balls can also be used, but they are determined in consideration of the production size, chemical composition, Biccus hardness, wear rate and the like. Is desirable. In order to prevent contamination, it is preferable to use alumina-based balls or zirconia-based balls for high-impact pulverization having a Vickers hardness (HV10) of JIS R1610 of 1,000 or more. By using such a crushing ball, contamination can be suppressed as compared with the case where a stirring blade is used. The particle size of the crushed ball affects the particle size of lithium iodide after drying and crushing, the amount of residual powder, and the drying time, and it may be selected according to the purpose. A crushed ball having a particle size of 5 to 25 mmφ can be used. It is more preferably 5 to 20 mmφ, and further preferably 5 to 15 mmφ.

In the production method of the present embodiment, as described in Non-Patent Document 5, the elliptical vibration contains an aqueous solution of an inorganic iodine compound and a crushed ball, and is arranged so that the central axis is substantially horizontal. It can be generated by applying vibration to the container including the direction perpendicular to the central axis. Examples of the means for applying the vibration include a vibration motor. The vibration motor may be installed at the bottom of the container. Examples of the vibration include linear vibration, circular vibration, elliptical vibration and the like. Examples of the vibration motor capable of causing such vibration include those having an eccentric weight formed on the rotation shaft of the vibration motor so as to shift the center of gravity with respect to the rotation shaft. In such a vibration motor, the vibration can be generated by rotating the rotating shaft together with the eccentric weight. FIG. 1 is a schematic diagram for explaining how the contents of a container containing an aqueous solution of an inorganic iodine compound, a precipitated solid iodine compound, and crushed balls vibrate elliptically due to the concentration of the aqueous solution in the present embodiment. .. FIG. 1 shows a cylindrical container 1 and a content 2 contained in the container 1 and containing an aqueous solution of an inorganic iodine compound, a precipitated iodine compound solid, and a crushed ball. When the container 1 is moved upward in the circumferential direction of the container 1, the content 2 rises upward along the inner wall of the container 1. Then, due to the gravity acting on the content 2 and the drag force from the wall of the container, the raised portion of the content 2 flows downward. As a result, the content 2 generates an elliptical vibration shown by an arrow in FIG. The frequency applied to the container is preferably 8 to 30 Hz, more preferably 20 to 30 Hz. The amplitude applied to the container (in the case of elliptical vibration, the magnitude of displacement in the major axis direction) is preferably 0.5 to 10 mm.

Examples of the device capable of generating the elliptical vibration include a horizontal vibration dryer and a vertical vibration dryer. As the material of the container in the horizontal vibration dryer and the vertical vibration dryer, the standard specification SUS material is preferable. Here, in the vertical vibration dryer, since the discharge port is located below, the heat transfer near the outlet is deteriorated, and the powder that has not been sufficiently dried tends to stick to the discharge port. Further, as the aqueous solution of the inorganic iodine compound is concentrated in the container, the water level of the aqueous solution of the inorganic iodine compound drops, and the iodine compound adheres to the wall surface at a position higher than the water surface of the aqueous solution of the inorganic iodine compound. The iodine compound attached in this way is difficult to recover, and since it is an agglomerate, it tends to be insufficiently dried. Therefore, the amount of the recovered inorganic iodine compound is reduced, and the water content tends to be difficult to be sufficiently reduced. On the other hand, in the horizontal vibration dryer, even when the inorganic iodine compound is fixed on the wall surface, the fixed iodine compound can be scraped off and crushed by the crushing ball, so that the amount of the inorganic iodine compound recovered is large. , It is preferable because the water content is also lower. Therefore, it is preferable to use a horizontal vibration dryer.

The material of the vertical or horizontal vibration dryer is a standard specification, and is preferably a SUS material.
There are two types of horizontal vibration dryers, downward discharge and horizontal discharge, depending on the position of the discharge port. In this embodiment, both can be used, but in the case of downward discharge, even if it is a horizontal vibration dryer, it may adhere to the vicinity of the discharge port like the vertical vibration dryer, and it may be difficult to discharge the dried powder. is there. Moreover, even if it can be discharged, the residual ratio tends to be relatively large. Therefore, the horizontal discharge type is more preferable than the downward discharge type.

(Manufacturing method of inorganic iodine compound powder)
An aqueous solution of an inorganic iodine compound is prepared and put into a device capable of causing the above-mentioned elliptical vibration together with a crushed ball. The concentration of the inorganic iodine compound in the aqueous solution is not particularly limited, but 30 w / v% or more is desirable because the fluidity of the aqueous solution of the inorganic iodine compound to be added can be maintained and a high concentration is desirable from the viewpoint of production efficiency. Preferably, 50 w / v% or more is more preferable. The upper limit of the concentration is not particularly limited and may be a saturated aqueous solution, but it is preferably 70 w / v% or less. The amount of powder balls charged varies depending on the amount of powder, but is preferably 25 to 40% of the amount of powder.

The aqueous solution of the inorganic iodine compound and the crushed ball are elliptically vibrated under reduced pressure conditions to concentrate the aqueous solution, and the precipitated inorganic iodine compound is crushed and dried. At this time, when the inorganic iodine compound contains water, the risk of releasing iodine by heat or oxygen increases. Since the production method of the present embodiment is carried out under reduced pressure conditions, it can be concentrated and dried at a low temperature, and the release of iodine can be suppressed. As the depressurizing condition, it is preferable that the pressure in the container in which the aqueous solution of the inorganic iodine compound and the crushed balls are housed is 0.5 to 14 kPa. Although it differs depending on the substance, it is generally preferable to set the heating temperature of the container to a condition in which the maximum temperature of the product temperature is 110 to 260 ° C.

Further, in order to prevent the inorganic iodine compound from being hydrolyzed or thermally decomposed by heating to liberate iodine, it is preferable to temporarily replace the inside of the apparatus with an inert gas of nitrogen or argon and then perform vacuum heating. ..
Further, by using a pulverized ball having good heat transfer in combination in the concentration and drying steps of the vibration dryer, the thermal efficiency is improved, and the precipitated inorganic iodine compound is pulverized at the same time.

As a result of diligent studies by the present inventor, when the inorganic iodine compound is lithium iodide, in order to obtain an anhydride at normal pressure from the thermogravimetric analysis of lithium iodide, 240 ° C. to 250 ° C. to 250 ° C. with respect to solid lithium iodide It was found that heating at ° C was required.
The concentration of the lithium iodide aqueous solution to be added is preferably 30 w / v% or more, and the concentration of lithium iodide corresponding to the trihydrate of lithium iodide is about 71.3% by mass, so that it does not exceed 70 w / v. A concentration of% or less is desirable.
From the screening results, it is important to keep the product temperature low. The product temperature is preferably 240 ° C. or lower, more preferably 200 to 240 ° C., and even more preferably 200 to 235 ° C. Here, the product temperature refers to the temperature of the contents of the container when the ellipse is vibrated. When the product temperature is 200 ° C. or higher, the water content can be sufficiently reduced even under a reduced pressure condition of about 1.3 kPa (≈10 torr), and the desired low-moisture anhydrous powder can be easily obtained. On the contrary, when the product temperature is 240 ° C. or lower, the risk of iodine being released from the iodine compound tends to be suppressed. Since the aqueous solution is added and the solution is concentrated, the degree of vacuum does not increase initially due to the generated water vapor, but the final degree of vacuum reaches 1.3 kPa (≈10 torr).
When an aqueous solution of lithium iodide is used, the adhesive force between the low hydrate produced during concentration and drying and the drying container is extremely high. In the manufacturing method of the present embodiment, since elliptical vibration is performed using a crushed ball having high heat transferability, there is no sliding part such as a rotary blade, so that it is directly linked to the finally obtained anhydrous lithium iodide. Friction is reduced. Therefore, the contamination of the product due to friction can be reduced as compared with the case where the stirring blade is used. In addition, since the thermal efficiency is improved, exposure to high temperature for a long time is reduced, and the risk of thermal decomposition is reduced. The obtained anhydrous powder preferably has a whiteness of L ^* value of 95 or more, a redness a ^* value of 1.5 or less, and a yellowness b ^* value of 1.5 or less. Such a powder is a white powder with little visual coloring.
The powder of the inorganic iodine compound obtained by the method of the present embodiment is anhydrous with a content of the inorganic iodine compound of 99.0% by mass or more and a water content of 0.1% by mass or less (substantially 0.06% by mass or less). It is preferably a powder. Further, it is preferable that the particle size of the powder of the inorganic iodine compound is 500 μm or less. The lower limit of the water content is not particularly limited, but can be 10 ppm. In most cases, the recovery rate of particles having a particle size of 500 μm or less can be industrially produced at a ratio of 70% by mass or more with respect to the input amount.
The method for producing anhydrous powder of inorganic iodide according to the present embodiment is an industrially feasible and efficient production method, and provides powdered sodium iodide anhydrous or lithium anhydrous iodide which is excellent in handling. Can be done.

When the inorganic iodine compound is sodium iodide, the production method of the present embodiment can be carried out under a final reduced pressure condition of 1.3 kPa (≈10 torr), and the product temperature can be in the range of 110 to 160 ° C., 110 to 140. It is preferably in the range of ° C. The drying time is preferably 7 to 18 hours, and by concentrating and drying these, a powder of sodium iodide having a content of 99.0% by weight or more and a water content of 0.1% by weight or less can be obtained as particles of 500 μm or less. it can.

Among the inorganic iodine compounds, for example, green iron iodide, rose red magnesium iodide, or black nickel iodide crystals are known as transition metal iodides, and most of them are colored.
On the other hand, alkali metal iodides such as lithium iodide, sodium iodide and potassium iodide, and alkaline earth metal iodides such as calcium iodide, magnesium iodide and strontium iodide are all examples, but they are all white. It is an inorganic iodide of.

Hereinafter, the appearance color quality control method for the white powder of the alkali metal iodide salt and the alkaline earth metal iodide salt will be described. If any coloration is observed in these white iodides, quality deterioration is suspected only in appearance before other analysis. Therefore, color control of the appearance of white crystals is one of the important items.
However, the quality control of the appearance color is insufficient in the sensory expression that the white crystal is sufficiently white or slightly colored, and it is important to control the chromaticity by the numerical value measured by the color difference meter. For example, in the pulp or paper-related industry, ISO whiteness of 90% or more is called high whiteness, and at the same time, color control minimizes quality variation.
^{In the method of the present embodiment, several points of L *} a ^* b ^* of the anhydrous powder of lithium iodide were measured using a color difference meter CR-5 manufactured by Konica Minolta, and color evaluation was performed. In addition to the pulp or paper industry ISO whiteness, there is a standard for whiteness called hunter whiteness. For white inorganic iodine compounds such as lithium iodide, the whiteness can be determined using the Hunter whiteness (WH) of the following formula.
WH = 100-[(100-L) ^ 2 + (a ^ 2 + b ^ 2)] ^ 0.5
The values used here are L ^* a ^* b ^* system chromaticity coordinates, where L ^* represents lightness, where L ^* value 100 is perfect white and L ^* value 0 is perfect black. The a ^* value is redness and a negative value represents greenness, and the b ^* value is yellowness and a negative value represents bluishness.

High-quality alkali metal iodide salts are white in color, but when overheated in the drying process, they not only reduce the water content of the sample, but also generate free iodine by thermal decomposition, which is the color of the inorganic iodine compound. May be colored yellow or red. When iodine is liberated, the a ^* value indicating redness increases and the L ^* value and hunter whiteness WH decrease.
Yellowness b ^* may increase. The higher the product temperature during drying, the greater the risk of thermal decomposition of lithium iodide, and even under reduced pressure conditions, samples exceeding 240 ° C. lose their whiteness to the naked eye, and coloring may be observed.

Since the obtained anhydrous powder of inorganic iodide is almost white, the L ^* value is 95 or more, and the a ^* value and b ^* value, which are indicators of coloring, are low. Therefore, the relationship between the hunter whiteness WH and the L ^* value is approximately WH = L, and the L ^* value can be adopted instead of the hunter whiteness WH obtained by calculation.
For example, ^{a sample showing an L *} value of 95.54, an a ^* value of 1.17, and a b ^* value of 0.61 has a hunter whiteness of WH = 95.3, which approximately matches the ^{L * value.} This sample has a ^{slightly higher redness a *} value, but the target value a ^* value is 1.5 or less, the yellowness b ^* value is 1.5 or less, the appearance is white, and the coloring is acceptable. ..
^{Further, the L *} value (brightness) and a ^* (redness) actually measured at n = 7 show a high correlation with a correlation coefficient R ^ 2 = 0.98 by quadratic approximation. That is, the ^{larger the L *} value, the higher the hunter whiteness, which is an evaluation index of whiteness, and the ^{lower the a *} value. On the other hand, ^{the correlation between the redness a *} value and the yellowness b ^* value and the correlation between the lightness L ^* value and the yellowness b ^* value are low, and no direct correlation is observed. The white anhydrous powder of high quality iodide ^{preferably has an L *} value of 95 or higher. Further, the a ^* value of redness is preferably 1.5 or less, more preferably 1.0 or less, and the b ^* value of yellowness is preferably 1.5 or less, more preferably 1.0 or less. preferable.

The content of the inorganic iodine compound, metal impurities, the water content in the crystal, and the chromaticity of the product can be measured by the following methods.
[Content analysis]
The iodine content in the inorganic iodine compound can be determined by capturing the change in potential with a potassium iodic acid standard solution, quantifying the iodine ion concentration with an automatic titrator, and converting it to the concentration of the inorganic iodine compound.
Although this analysis method is not the same method, it is a method according to JIS K8913 of potassium iodide (reagent).
Metal impurities can be determined by analysis using high frequency inductively coupled plasma emission spectroscopy (ICP emission spectroscopy).
[Moisture measurement method]
In the case of lithium iodide, it can be determined by the vaporization method (280 ° C) in which the Karl Fischer moisture measuring device of Hiranuma Sangyo Co., Ltd. is combined with the vaporizer, and in the case of sodium iodide, it can be measured by the coulometric titration method by the direct method. ..
As can be seen from the pharmaceutical moisture analysis method of Non-Patent Document 5, sodium iodide cannot be accurately obtained by the vaporization method (130 ° C.) that has been carried out in the past.
The water content is preferably 0.1% by mass or less with respect to the total mass of the obtained inorganic iodine compound powder.

[Measurement of chromaticity of anhydrous powder]
It can be obtained by measuring several points ^{of L *} a ^* b ^* of the anhydrous powder of lithium iodide of the present invention using a color difference meter CR-5 manufactured by Konica Minolta and calculating the average value thereof.

Examples are shown below, and embodiments of the present invention will be described in more detail. However, it goes without saying that the changes in the details of the present invention are not limited to the contents shown in the examples. The technical scope also includes embodiments obtained by appropriately combining the disclosed technical means which can be changed within the scope of the claims.

[Reaction method of lithium iodide]
[Production Example 1] Formic acid method Lithium iodide was produced by the formic acid method. First, 140 ml of a 56 w / v% lithium iodide aqueous solution was put into the reaction vessel having a capacity of 2 L equipped with a stirrer and a thermometer. While stirring with a stirring blade, 600 g (2.36 mol) of iodine was charged from the solid input port of the reaction vessel. After adding iodine, the aqueous solution in the reaction vessel was heated to 60 ° C., and then 1130 g (4.72 mol) of a 10 w / v% lithium hydroxide aqueous solution was slowly poured into the aqueous solution. Subsequently, half of 143.8 g (2.38 mol) of a 76 mass% formic acid aqueous solution was added from the dropping funnel. When the temperature inside the reaction vessel was maintained and the generation of carbon dioxide gas subsided, the remaining formic acid was added dropwise while gradually increasing the temperature. When the internal temperature of the reaction vessel reached 85 ° C., the reaction vessel was heated to 105 ° C. after waiting for the generation of carbon dioxide to subside.

Next, check the pH of the solution in the reaction vessel while keeping the internal temperature of the reaction vessel at about 105 ° C. If it is alkaline, add hydroiodic acid, and if it is acidic, add lithium hydroxide powder or aqueous solution. The pH of the solution was adjusted to 6.8 to 7.2. After adjusting the pH, the mixture was stirred for 60 minutes and aged while maintaining the temperature. Next, granular activated carbon was added for the purpose of adsorbing unreacted iodine. After stirring the above solution for 30 minutes, the solution was filtered through a 1 micron filter to obtain a colorless and transparent lithium iodide aqueous solution. The concentration of the obtained lithium iodide solution was 37.9% by mass, and the density of the solution was 1.375 g / ml.

[Production Example 2] A 57% by mass solution of hydrogen iodide was used for the reaction reaction of Li and HI carbonate, and an aqueous solution of about 60% by mass was used as the lithium carbonate aqueous solution. The reaction was carried out in a nitrogen gas atmosphere in order to suppress the generation of free iodine.
In this reaction, since the acid and the alkali are neutralized, heat is generated and carbon dioxide gas is also generated. Therefore, the hydrogen iodide acid was added dropwise and reacted while keeping the temperature range of 30 to 50 ° C. while stirring.

Next, check the pH in the reaction vessel while keeping the temperature at 30 ° C., add 57% by mass of hydrogen iodide acid if alkaline, and add powdered lithium hydroxide if acidic, and adjust the pH from 6.0 to 6.0. Adjusted to 9.0. While maintaining the temperature, the mixture was stirred for 60 minutes for aging.
The obtained lithium iodide aqueous solution was almost a colorless solution and was finished at a concentration of about 60 w / v%. At this time, the density of the aqueous solution was about 1.70 g / ml. This solution was used in the next vibration dryer test.

[Example 1]
The lithium iodide aqueous solution obtained in [Production Example 2] and the Vickers hardness HV10 of 1,100 kgf / mm in consideration of the reduction of metal contamination risk in a VH-25 type horizontal vibration dryer manufactured by Chuo Kakoki Co., Ltd. ^A zirconia-based crushed ball having 2 = 10.8 GPa or more, a rubbing wear rate of 0.5 ppm / h or less, and a density of 6.1 g / cm ^{3 was charged.} As a result, the concentration of the aqueous solution proceeded, and the precipitated lithium iodide hydrate solid was dried to anhydrous and pulverized at the same time. The VH-25 type horizontal vibration dryer used has a body diameter of 250 mm, a body length of 500 mm, a heat transfer area of 0.39 m ² , and a total capacity of 23 L, while the actual capacity is 13.8 L, which is 60 vol% of the volume. is there.

The vibration dryer is provided with a jacket so as to cover the tubular container body, and has a structure in which the heated heat medium passes through the jacket to indirectly heat the container body. Since there is no unevenness inside the vibration dryer, there are no sliding parts such as stirring blades. In the container body, a vibration motor for generating vibrations attached to the lower part of the body causes the iodine-precipitated solid powder to be dried generated by concentration to move in the vertical direction up and down the circumference. The vibration motor has an eccentric weight formed so as to shift the center of gravity, and the rotating shaft rotates together with the eccentric weight to generate vibration to generate vibration in the circumferential direction.
As a result, the object to be dried is vibrated, and the lump of lithium iodide generated during heating is crushed by the action of the vibration dryer and the action of the powder balls. The structure is such that the water vapor generated by concentrating the solution is exhausted from the exhaust port, cooled by a condenser, and recovered as a drain.

As the zirconia-based crushed ball, one having a diameter of 5 mm was selected, and 5.31 kg was weighed and charged before the start of liquid charging. Next, 18.06 kg of the above lithium iodide solution (liquid concentration 56.9 w / v%) in terms of pure content was added as a raw material. However, the total amount of the planned solution was not added at once, and after about 2/3 of the solution was added, the remaining solution was additionally added using the negative pressure in the container when the concentration proceeded.
The amplitude number of the horizontal vibration dryer is fixed at 3 mm, and the frequency is set to the maximum of 25 Hz (= 1,500 rpm).
Since no significant difference was observed in the timing of operating the vibration of the vibration dryer even after the solution was concentrated, the operation of the vibration was started immediately after the solution was added.
The heat medium temperature of the vibration dryer was set to 220 ° C. The initial value of the degree of vacuum was 12.3 kPa (≈99.8 torr), and when the concentration proceeded, the degree of vacuum reached 1.31 kPa (≈9.8 torr). According to the internal observation of the dryer, the slurry changed to a sherbet-like shape as the liquid was concentrated, then solidified by crystallization (heat generation), and further changed to a fluid powder by lowering the water content.
The endothermic peak due to melting was observed in the process of changing from the solidified form by crystallization to powder, and the shape changed significantly in the concentration and drying steps. The maximum value of the product temperature in the dryer during the concentration and drying operations was about 207 ° C., and the time required for this operation time was about 7.0 hours. After the drying was completed, the dryer was cooled, and since the horizontal vibration dryer was tilted, the anhydrous powder of lithium iodide was discharged by opening the discharge valve and applying vibration. The anhydrous powder that could be discharged was sieved to eliminate large particles to obtain a powder having a particle size of 500 μm or less. Table 1 shows the recovery amount of the anhydrous powder having a particle size of 500 μm or less and the ratio (recovery rate) of the recovery amount to the amount of lithium iodide contained in the raw material lithium iodide aqueous solution.

The total amount of anhydrous lithium iodide discharged was 14.59 kg, the discharge rate was 80.8% by weight, and the percentage remaining in the dryer and not being discharged was 19.2% by weight. The amount of anhydrous lithium iodide powder of 500 μm or less obtained by sieving was 14.41 kg and the recovery rate was 79.8% by weight, and the obtained particles were composed of particles of approximately 300 μm or less and had a particle size. The top peak of the distribution was 125 μm. If necessary, the obtained powder can be further commercialized as a fine powder. The purity of this anhydrous powder calculated from the measured values of iodide ions by an automatic titrator was 99.8% by weight, and the water content determined by the Karl Fischer method vaporization method (280 ° C.) was 0.052% by weight. It was. Impurities Zr, Fe, Ni, and Al derived from the crushed balls and the drying container SUS material were not detected, and the others were only derived from the raw materials and had Na of 161 ppm and Ca of 17 ppm. The lithium content was also measured by ICP emission spectroscopy and confirmed to be equivalent to the value obtained based on the iodine standard.
When the obtained powder was evaluated for chromaticity with a color difference meter CR-5, it was L ^* 97.07, a ^* 0.51, and b ^* 0.41. The hunter whiteness WH, which is an evaluation index of whiteness, is 97.6, and the standard of powder color is L ^* value of 95 or more, a ^* value of 1.5 or less, and b ^* value of 1.5. From the following, a white powder sufficiently satisfying the target was obtained.

[Examples 2 and 3]
Using the lithium iodide aqueous solution obtained in [Production Example 2] in a VH-25 type inclined horizontal vibration dryer manufactured by Chuo Kakoki Co., Ltd., 10 mmφ was used instead of the zirconia-based crushed ball 5 mmφ of Example 3. Alternatively, 25 mmφ was used. The test results are shown in Table 1.

In [Example 3] using a crushed ball having a diameter of 25 mm, the purity of the obtained anhydrous lithium iodide was 99.8% by weight, and the water content determined by the Karl Fischer method vaporization method (280 ° C.) was 0. It was 052% by weight. Impurities from the device and powder balls were not included.
The chromaticity evaluation with the color difference meter CR-5 was L ^* 96.95, a ^* 0.54, and b ^* 0.41. The L ^* value is 95 or more, the a ^* value and b ^* value are both 1.5 or less, and the hunter whiteness, which is an evaluation index of whiteness, is 96.9. No coloring is visually observed, and the chromaticity target. A white powder satisfying the value was obtained. The discharge rate of the obtained anhydrous powder was 75.4% by weight, and the recovery rate of particles of 500 μm or less was 69.2% by weight.
From these results, it is possible that the discharge rate and the recovery rate of particles of 500 μm or less tend to increase when the crushed balls to be put into the vibration dryer have a smaller particle size than those with a larger particle size. Do you get it.

[Example 4]
19.79 kg of lithium iodide solution as a pure content was put into a VH-25 type inclined horizontal vibration dryer. As the crushing ball, a ball having a diameter of 5 mm was used. The product temperature was 243.5 ° C. The discharge amount was 17.48 kg and the discharge rate was 88.33% by weight.
The anhydrous powder of 500 μm or less weighed 15.32 kg and had a recovery rate of 77.4% by weight. Moisture could be reduced to 0.05% by weight.
The chromaticity evaluation with the color difference meter CR-5 was L ^* 90.89, a ^* 5.15, b ^* 1.44, and the hunter whiteness HW, which is an evaluation index of whiteness, was 89.4. ..
^{Since the product temperature exceeded 240 ° C. due to the high drying temperature, the redness a *} value and yellowness were compared with Examples 1 to 3 due to the free iodine generated from the thermal decomposition of lithium iodide. It is presumed that b ^{* was raised.} However, although the result of the chromaticity evaluation was inferior to that of Examples 1 to 3, the water content could be sufficiently reduced.

[Example 5]
In the same manner as in [Example 1], 13.62 kg of the lithium iodide aqueous solution was charged into the VH-25 type inclined horizontal vibration dryer in terms of pure content. The crushed ball used was 5 mmφ. When the product temperature was limited to 181 ° C., the degree of vacuum also increased only to 3.31 kPa. The drying time was about 11 hours. The water content of the obtained lithium iodide powder was 0.12% by mass.

[Comparative Example 1]
The 55% by mass lithium iodide aqueous solution obtained in [Production Example 2] was put into a vibration dryer. However, the same procedure as in Example 1 was carried out except that the crushed balls were not used. It was difficult to dry and took 9.28 hours. The outlet was opened and the powder was obtained, but there was a lot of adhesion to the heat transfer surface, the powder was reddish, and the whiteness was low at ^{L * = 91.5, a *} = 3.10, b ^* = 2. .61 and L ^* values are well below the target value of 95, redness a ^* value and ^{whiteness b *} value are also above 1.5, and ^{none of the L *} a ^* b ^* measured values meet the target value. The water content was 0.33%, which did not meet the standard.

In the case of anhydrous sodium iodide, as in the method for producing anhydrous powder of lithium iodide, a horizontal vibration dryer was used in combination with crushed balls, and an aqueous sodium iodide solution prepared by the formic acid method was 1.3 kPa (≈). It can be manufactured by concentrating and drying under the condition of a product temperature of 110 to 160 ° C. with a vacuum degree of 10 torr). As an example, the test was carried out using a 54% by mass sodium iodide aqueous solution prepared by the formic acid method. As a result of drying the product at 140 ° C. for 12 hours under the condition of reaching a reduced pressure of 1.3 kPa, an analysis example of the obtained sodium iodide powder shows that the content is 99.6% by mass, and Karl Fischer. The water content measured by the direct method of the method was 0.07% by mass.
Further, since it is a white inorganic powder like lithium iodide, a method of controlling by the values ^{of L *} , a ^*, and b ^{* of the L *} a ^* b ^* system chromaticity coordinates is adopted as the appearance color management method. To. Taking an example of the obtained chromaticity measurement value of sodium iodide, L ^* = 98.9, a ^* = −0.08, b ^* = 0.85, and the hunter whiteness WH is 98.6. It was. Good quality products with a sufficiently white appearance were obtained, satisfying the target ^{values of L *} = 95 or more and a ^* and b ^* = 1.5 or less of the appearance quality control values.

1 ... container, 2 ... contents.

Claims (6)

A step is provided in which an aqueous solution of an inorganic iodine compound and a crushed ball are elliptically vibrated in a container under reduced pressure conditions to concentrate the aqueous solution, and the precipitated inorganic iodine compound is crushed and dried.
The inorganic iodine compound includes aluminum iodide, calcium iodide, cobalt iodide, strontium iodide, cerium iodide, iron iodide, sodium iodide, barium iodide, magnesium iodide, manganese iodide, or lithium iodide. A method for producing an inorganic iodine compound powder. The ^{L *} value in ^{the L} * ^a * ^{b *} system chromaticity coordinates of inorganic iodine compound powder is 95 or more, ^{a *} value of 1.5 or less, and ^{b *} value is 1.5 or less, according to claim 1 Manufacturing method. The production method according to claim 1 or 2, wherein the inorganic iodine compound is sodium iodide or lithium iodide. The production method according to any one of claims 1 to 3, wherein the inorganic iodine compound is lithium iodide and the elliptical vibration is performed in a range where the product temperature is 200 to 240 ° C. The production method according to any one of claims 1 to 4, wherein the inorganic iodine compound powder having a particle size of 500 μm or less can be obtained with a recovery rate of 70% by mass or more. The invention according to any one of claims 1 to 5, wherein the inorganic iodine compound powder contains 99.0% by mass or more of the inorganic iodine compound, and the water content of the inorganic iodine compound powder is 0.1% by mass or less. Production method.

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