JP2944928B2 - Method for producing magnesium hydroxide and its aqueous suspension - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a neutralizing agent, a desulfurizing agent,
Method for producing particulate magnesium hydroxide useful as fertilizer, additive for burning heavy oil, pulp digester, etc., method for producing particulate magnesium hydroxide obtained by this method and aqueous suspension containing the same About.

[0002]

2. Description of the Related Art Magnesium hydroxide is used for neutralizing flue gas desulfurization and wastewater. This magnesium hydroxide has been conventionally produced by a method of reacting magnesium chloride in seawater with slaked lime. However, this method has a very small magnesium content in seawater, and the production process is complicated. In addition, since the aqueous slurry containing magnesium hydroxide has a high viscosity despite its concentration of about 30% by weight, it is difficult to increase the concentration, and the production and transportation costs increase.

On the other hand, it is possible to obtain magnesium hydroxide by hydrating (sludging) magnesium oxide. However, since the reaction rate is slow, a high temperature of 100 ° C. or more and a high pressure exceeding normal pressure are obtained using an autoclave. It is necessary to react with. In order to solve such a problem, Japanese Patent Application Laid-Open No. Hei 3-252511 proposes a method for hydrating lightly burned magnesia obtained by firing natural magnesite. Also, JP-A-6-206722 discloses that
A method is disclosed for hydrating lightly burned magnesia in the presence of an alkaline aqueous medium while wet milling. In such a method, when a magnesium hydroxide aqueous suspension is used for neutralization of flue gas desulfurization and wastewater, the particle size of magnesium hydroxide is required in order to allow the reaction to proceed smoothly and neutralize efficiently. Needs to be smaller. However, as the particle size decreases, the slurry viscosity increases. On the other hand, when the particle size of magnesium hydroxide is increased to reduce the viscosity, the neutralization efficiency is reduced and a precipitate is easily formed.
Further, in the case of a suspension having a high magnesium hydroxide concentration, the viscosity is remarkably increased, and transport and transportation are difficult. In addition, in order to reduce the transportation and transportation costs of the aqueous slurry obtained by the above-mentioned method, it is also possible to remove a large amount of water from the aqueous slurry to obtain powdered magnesium hydroxide. However, in order to obtain powdered magnesium hydroxide, a step of hydrating lightly burned magnesia in the aqueous medium and a step of removing a large amount of water from the generated aqueous slurry are required. Therefore, a large amount of energy is required, and it is difficult to obtain powdery magnesium hydroxide simply and efficiently. Further, since magnesium hydroxide has a large specific gravity, it is difficult to maintain the dispersion stability of the aqueous suspension for a long period of time. That is,
When the aqueous magnesium hydroxide suspension is stored for a long period of time, the fluidity is reduced or the precipitate is solidified densely, thereby producing a hard cake which is difficult to redisperse.

[0004] In order to enhance the viscosity stability and fluidity of an aqueous slurry, JP-A-6-115930 discloses that water is mixed by stirring magnesium hydroxide, an anionic polymer dispersant and a water-soluble alkali metal salt. A method for producing an aqueous slurry of magnesium oxide is disclosed. JP-A-6-191832 discloses activated hydroxylation by adding light-burned magnesia to a warm aqueous solution containing an anionic surfactant mainly composed of an alkali metal salt of a fatty acid, followed by slaking while heating. A method for preparing magnesium is disclosed. Also, Czechoslovak Patent No. 236626 discloses that in order to increase the reaction rate,
A method for producing magnesium hydroxide that hydrates magnesia in the presence of a surfactant is disclosed. However, even with such a method, it is necessary to remove a large amount of water from the aqueous slurry in order to obtain powdery magnesium hydroxide. In addition, since the aqueous slurry becomes highly viscous or caked with the removal of water and cannot be stirred, the operation of separating and drying the powdery (solid) magnesium hydroxide becomes complicated. Therefore, it is difficult to efficiently produce powdery magnesium hydroxide industrially.

[0005] Japanese Patent Publication No. 47-22942 discloses that when lime, magnesium oxide or a mixture thereof is digested by reacting with water using a digester, the reaction is started to promote the penetration of water into the crushed mass. A digestion method is disclosed in which the pressure inside the fire extinguisher is reduced beforehand, and the pressure reduction operation is stopped after the reaction starts. According to this document, as a specific method, a method is used in which the inside of a fire extinguisher is depressurized, 75 g of water equivalent to 1.2 times the theoretical amount is poured into 200 g of crushed lump of quicklime, and the decompression operation is stopped to digest. Is described. However, this method not only requires a decompression operation, but when applied to magnesia digestion, agitation becomes impossible, and it is difficult to industrially efficiently produce powdered magnesium hydroxide.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for easily and efficiently producing powdered magnesium hydroxide. Another object of the present invention is to provide a powdery magnesium hydroxide useful for reducing storage, transfer and transportation costs and a method for producing the same. Still another object of the present invention is to provide a method for producing powdery magnesium hydroxide from solid magnesia with high hydration efficiency. Another object of the present invention is to provide a powdery and granular magnesium hydroxide useful for obtaining an aqueous slurry having high water dispersibility and storage stability even in the form of a powder, and a method for producing the same.
Still another object of the present invention is to provide a method capable of obtaining an aqueous suspension of magnesium hydroxide by a simple operation.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and found that, in the presence of a small amount of water, dry mixing or dry kneading of powdered magnesia while maintaining fluidity, The hydration reaction occurs with high efficiency, and powdered magnesium hydroxide is efficiently produced, and when a catalyst and / or a dispersant is added to a dry mixing system or a dry kneading system,
The present inventors have found that the hydration efficiency is further improved and the water dispersibility is improved, and the present invention has been completed.

That is, in the method of the present invention, magnesia is hydrated while dry-mixing or dry-kneading magnesia in the presence of moisture to produce powdered magnesium hydroxide. In this method, the amount of water used may be within a range where the fluidity of magnesia can be ensured in a dry mixing or dry kneading system and the hydration reaction is not impaired. In the method of the present invention, for example, (1) magnesia powder may be dry-mixed or dry-kneaded while being wetted with 25 parts by weight or less of water per 100 parts by weight of magnesia to obtain powdered magnesium hydroxide. (2) Magnesium hydroxide may be obtained by reacting magnesia and water while forming a continuous gas phase in the gap between solids. As the magnesia, light burnt magnesia or the like can be used, and the form may be a lamp, a coarsely crushed material, a finely crushed material, or the like. Water can be added to magnesia in gaseous or liquid form, or as a water-containing slurry or cake. The hydration reaction may be performed in the presence of a catalyst and / or a dispersant.

[0009] The present invention also provides a powdered magnesium hydroxide obtained by the above method. Furthermore, the method of the present invention includes a method of producing a magnesium hydroxide aqueous suspension by dispersing the powdered and granular magnesium hydroxide obtained by the above method in water. In this method, the particulate magnesium hydroxide may be dispersed in an aqueous medium in the presence of a dispersant.

[0010] In the present specification, "dry mixing or dry kneading" refers to mixing or kneading powders and granules in a fluid-granular form containing water. Further, in the method for producing a powdery magnesium hydroxide,
The amount of `` water '' or `` water '' in a dry-mixing system or a dry-kneading system means the amount of free water present in the reaction system, excluding water consumed by the reaction and water evaporated or volatilized, and It is the amount for magnesia.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The magnesia used in the present invention is not particularly limited, and may be hard-burned magnesia obtained by firing natural magnesite (periclase) at a high temperature. Light-burned magnesia fired at about 1500 ° C., preferably about 650 to 1300 ° C., and more preferably about 800 to 1200 ° C. is often used. The use of light-burned magnesia obtained at such a firing temperature makes it possible to obtain magnesium hydroxide having an extremely high activity (activated magnesium hydroxide).

[0012] The size of the magnesia is not particularly limited as long as it can be granulated. For example, magnesia
Lamps that can be crushed or crushed by mixing or kneading (lumps of uncrushed light-burned magnesia), coarsely crushed materials, or finely crushed materials may be used. As the lamp, for example, a maximum particle size of 1
Light burned magnesia having a particle size of about 0 to 200 mm (for example, 10 to 100 mm) and an average particle diameter of about 3 to 60 mm (for example, 3 to 40 mm) can be used. (For example, about 0.5 to 10 mm), and an average particle diameter of 0.1 to 3 mm (for example, 0.5 to 3 m).
m). Further, as a finely pulverized product, a maximum particle size of 1 to 3000 μm (preferably 1 to 100 μm)
0 μm, for example, about 40 to 100 μm), average particle size 1
Lightly burned magnesia having a thickness of about 300 to 300 μm (for example, about 10 to 70 μm) can be used.

[0013] Preferable light-burned magnesia includes granules, agglomerates, and granules obtained by crushing (for example, a maximum particle size of 3000 μm).
m or less, average particle size of 0.1 to 300 μm, preferably 1 to
200 μm, more preferably about 2 to 100 μm).

By hydrating such magnesia while dry mixing or dry kneading in the presence of water, powdered magnesium hydroxide can be produced. That is, the feature of the present invention is that water is supplied to a dry mixing system or a dry kneading system within a range that does not impair the fluidity, and the water content of the reaction system is maintained in a specific range, and magnesia is hydrated. is there. Therefore, in the present invention, the water content has a great influence on the mixing or kneading operability, and the uniform fluidity and hydration reaction of magnesia.

The amount of water maintained in the reaction system during the reaction is
The dry mixing or kneading property of magnesia, the kneading property, the fluidity and the hydration reaction may be within a range that does not impair the magnesia, and for example, 25 parts by weight or less (but does not substantially contain 0), preferably 100 parts by weight of magnesia Is 0.1 to 20 parts by weight (for example, 0.2 to 15 parts by weight), more preferably 0.2 to 20 parts by weight.
About 10 to 10 parts by weight, and often about 0.3 to 15 parts by weight (for example, 0.4 to 7.5 parts by weight). When the water content exceeds 25 parts by weight with respect to 100 parts by weight of magnesia, mixing and kneading become difficult, and it is difficult to efficiently produce magnesium hydroxide in a uniform mixing or kneading system. Note that the above water content is an amount based on the raw material magnesia because magnesium hydroxide is generated with the progress of the reaction and the magnesia content decreases as described above. When the water content of the reaction system is less than about 10 parts by weight with respect to 100 parts by weight of magnesia, a uniform mixing or kneading system can be maintained, and as the water content further increases, the mixture becomes a wet mixing or kneading system, and 25 parts by weight becomes If it exceeds, the stirring power of the mixing or kneading system sharply increases, and a squeaky sound and the like are easily generated, and it becomes easy to adhere to the stirring blades and the wall surface, and it is difficult to uniformly perform the hydration reaction. . Furthermore, when excess water is added, the mixing system or the kneading system becomes muddy, deviates from the dry mixing or the dry kneading system, and the conventional hydration reaction occurs.

By allowing such a small amount of water to exist in the reaction system, magnesia and water can react with each other and hydrate while forming a continuous gas phase in the gap between solid magnesia. That is, in the method of the present invention, the packing state of the granular material, the liquid and the gas is (a) a dry (Dry) state in which a solid phase and a gas phase are continuous and almost no liquid phase is present; Pendula with continuous phase and discontinuous liquid phase
The reaction is carried out while mixing or kneading in the r) state, (c) solid phase, gas phase and liquid phase in a continuous Funicular I state. Such a filling form may be apparently a rough or dry mixing or kneading (mull).
ing) system ("Mixing and kneading technology", 2nd edition, edited by Japan Powder Industry Association, published by Nikkan Kogyo Shimbun, April 30, 1986). Therefore, when such a mixing or kneading system is used, the mixing or kneading can be uniformly performed with a small stirring power, and the apparatus can be simplified. Can be made uniform in particle size distribution.

As long as the water content in the reaction system is kept within the above range,
Water can be supplied or added to magnesia in gaseous (steam) or liquid (droplet) form. The water may be continuously or sequentially supplied to the mixing or kneading system by a method such as dropping or spraying, or may be supplied intermittently. In many cases, water is supplied while replenishing the amount of water consumed by the hydration reaction. The supply amount of water varies depending on the reaction temperature and the like, and is usually 1 to 100 parts by weight of magnesia.
It is about 0 to 100 parts by weight / hr, preferably about 20 to 80 parts by weight / hr, and more preferably about 25 to 75 parts by weight / hr. The adjustment of the water content can be performed not only based on the value measured by the moisture meter, but also based on the value of stirring power accompanying mixing or kneading.

Further, the water may be caused by the water of coexistent substances (slurries, cakes, etc.) coexisting in the reaction system. For example, in the reaction system, an aqueous slurry or cake (eg, magnesium hydroxide (seawater mug) obtained by reacting magnesium chloride and slaked lime in seawater) with the magnesia and water non-reactive. When coexisting with the cake, the water consumed by the reaction with the magnesia may be derived from the water in the aqueous slurry or the cake.
By supplying or adding water using such a slurry or cake, a uniform reaction system can be easily formed. In addition,
The slurry or cake may be added all at once, or may be added continuously or intermittently. The water content of the slurry or cake is not particularly limited, and is, for example, about 10 to 90% by weight, and preferably about 20 to 80% by weight. In such a method, the water in the slurry or cake can be removed by reaction with magnesia, and the slurry and cake can be dried at the same time.

The total amount of water used varies depending on the magnesia component and its ratio, the content of magnesium oxide, the purity, etc., but is usually 40 to 100 parts by weight of magnesia.
It is about 55 parts by weight, preferably about 41 to 55 parts by weight, and more preferably about 43 to 52 parts by weight.

The hydration reaction can be carried out under suitable conditions which do not impair the reaction between magnesia and water.
The temperature is 30 to 150 ° C, preferably 50 to 130 ° C (for example, 60 to 120 ° C), and more preferably 70 to 110 ° C.
C. (80 to 110.degree. C.). If the reaction temperature is lower than 30 ° C, the hydration reaction rate is low,
If it exceeds, partial thermal decomposition is likely to occur, and the hydration rate may decrease. The reaction pressure is, for example, 1 to 10
Atm, preferably about 1 to 5 atm, more preferably 1 atm.
The reaction proceeds smoothly even at about normal pressure. The reaction temperature can be controlled by a conventional method, for example, external heating or cooling.

Although the hydration reaction proceeds smoothly even in the absence of a catalyst, it is preferable to dry-mix or dry-knead in the presence of a catalyst in order to promote the slaking reaction. The catalyst may be added directly to magnesia or may be added as a mixture with water. In addition, water-soluble catalysts (acetic acid, magnesium acetate, etc.) and catalysts that gasify at the reaction temperature (acetic acid, etc.)
Is usually used as a mixture with water in many cases.

The catalyst includes a conventional acid or a salt thereof, for example, (A) an organic acid or a salt thereof, (B) an acid phosphate or an acid sulfate or a salt thereof, and (C) an inorganic acid or a salt thereof. And (D) an alkali metal hydroxide.

The (A) organic acid includes (A1) a monofunctional organic acid and (A2) an organic acid having two or more functional groups. (A1) Examples of monofunctional organic acids include, for example, aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, acrylic acid, crotonic acid (for example,
C1-4 aliphatic monocarboxylic acids); halogenated aliphatic monocarboxylic acids such as monochloroacetic acid, dichloroacetic acid and trichloroacetic acid (e.g. halogenated aliphatic monocarboxylic acids having 1 to 4 carbon atoms); cyclopentane Alicyclic monocarboxylic acids such as carboxylic acid and cyclohexanecarboxylic acid (for example, alicyclic monocarboxylic acids having 4 to 10 carbon atoms); aromatic monocarboxylic acids such as benzoic acid and toluic acid (for example, having 7 to 7 carbon atoms) Alkyl sulfonic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, and ethanesulfonic acid (e.g., alkylsulfonic acids having 1 to 10 carbon atoms); benzenesulfonic acid, p-toluenesulfonic acid, Aryl sulfonic acids such as naphthalene sulfonic acid (for example, having 6 to 6 carbon atoms)
20 arylsulfonic acids). Preferred (A1) monofunctional carboxylic acids include saturated aliphatic monocarboxylic acids, halogenated aliphatic monocarboxylic acids, alkylsulfonic acids, arylsulfonic acids and the like. More preferably, a water-soluble monocarboxylic acid (for example, an aliphatic monocarboxylic acid having about 1 to 4 carbon atoms which may have a halogen atom such as formic acid, acetic acid, monochloroacetic acid, dichloroacetic acid, propionic acid, and butyric acid) In particular, an aliphatic monocarboxylic acid having about 1 to 3 carbon atoms which may have a halogen atom (particularly, acetic acid) is frequently used.

(A2) The organic acid having two or more functional groups has at least one carboxyl group,
Further, an organic acid having one or more functional groups (for example, a carboxyl group, a hydroxyl group, a mercapto group, an alkoxy group, an alkylthio group, a carbonyl group, a thiocarbonyl group, an amino group, an amide group, and a cyano group) is included. Such organic acids often have chelating ability. Representative examples of the (A2) organic acid having two or more functional groups include, for example, polycarboxylic acids, hydroxycarboxylic acids, alkoxycarboxylic acids, oxocarboxylic acids,
Aminocarboxylic acid and the like. Examples of the polycarboxylic acid include aliphatic polycarboxylic acids such as malonic acid, succinic acid, adipic acid, and maleic acid (for example, aliphatic polycarboxylic acids having 2 to 12 carbon atoms); phthalic acid, isophthalic acid Such as aromatic polycarboxylic acids (for example, 8-15
Aromatic polycarboxylic acid). Preferred polycarboxylic acids include aliphatic polycarboxylic acids having 2 to 8 carbon atoms (particularly dicarboxylic acids) such as malonic acid and adipic acid; and aromatic polycarboxylic acids having 8 to 12 carbon atoms such as phthalic acid ( Dicarboxylic acid). Examples of hydroxycarboxylic acids include, for example, glycolic acid, lactic acid,
Aliphatic hydroxycarboxylic acids such as glyceric acid, malic acid, tartaric acid, citric acid, and gluconic acid (for example, aliphatic hydroxycarboxylic acids having 2 to 12 carbon atoms); aromatic hydroxycarboxylic acids such as salicylic acid and gallic acid (for example, An aromatic hydroxycarboxylic acid having 7 to 15 carbon atoms). Preferred hydroxycarboxylic acids include
Hydroxycarboxylic acids having two or more hydroxyl groups such as tartaric acid and gluconic acid (for example, hydroxyl groups having two or more hydroxyl groups).
(About 6 to about 2 to 12 carbon atoms). The alkoxycarboxylic acids include, for example, aliphatic or aromatic alkoxycarboxylic acids such as methoxyacetic acid, ethoxyacetic acid, and anisic acid (for example, alkoxycarboxylic acids having about 2 to 15 carbon atoms). Oxocarboxylic acids include, for example,
Glyoxylic acid, pyruvic acid, acetoacetic acid, oxaloacetic acid and the like have about 2 to 12 carbon atoms, preferably 2 to 1 carbon atoms.
About 0 oxocarboxylic acid and the like are included. Aminocarboxylic acids include, for example, glycine, alanine, leucine,
2 carbon atoms such as glutamic acid and ethylenediaminetetraacetic acid
About 15 to about 15, preferably about 2 to 10 carbon atoms.

(B) The acidic phosphate ester includes, for example,
Monoethyl phosphate, diethyl phosphate, monobutyl phosphate, monododecyl phosphate, monophenyl phosphate, phytic acid, etc. having about 1 to 15 carbon atoms, preferably 1 to 15 carbon atoms
About 10 monovalent or polyvalent acidic phosphates are included. Preferred phosphate esters include polyvalent acidic phosphate esters such as phytic acid. Also,
(B) The acidic sulfates include mono- or polyvalent acidic sulfates having 1 to 15 carbon atoms, preferably about 1 to 10 carbon atoms, such as monomethyl sulfate, monoethyl sulfate, monobutyl sulfate, and monododecyl sulfate. It is. Polyvalent acidic phosphates or acidic sulfates often have chelating ability.

The inorganic acids (C) include, for example, hydrochloric acid, hypochlorous acid, hydrobromic acid, sulfuric acid, sulfurous acid, sulfamic acid, nitric acid, nitrous acid, phosphoric acid, phosphorous acid, polyphosphoric acid (for example, Pyrophosphoric acid, triphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, etc.), and carbonic acid. Of these inorganic acids, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid and the like are often used, and inorganic acids having chelate forming ability such as polyphosphoric acid (tripolyphosphoric acid and the like) are often used.

Examples of the acid salts include alkali metal salts such as lithium salt, sodium salt and potassium salt; alkaline earth metal salts such as magnesium salt and calcium salt; salts of metals belonging to groups 3 to 15 of the periodic table (for example, Salts of metals belonging to Group 7 or 12 of the periodic table such as manganese, zinc, etc., especially zinc salts); ammonia, amines (eg, trimethylamine, triethylamine, diethanolamine, triethanolamine, dimethylaminoethanol, morpholine, etc.) or basic Salts with a nitrogen-containing heterocyclic compound (such as pyridine) are exemplified.

Preferred (A) organic acid salts include alkali metal salts such as sodium salts (eg, monocarboxylic acid alkali metal salts such as sodium acetate; hydroxycarboxylic acid alkali metal salts such as sodium gluconate; ethylenediaminetetraacetic acid diacetate). Alkaline earth metal salts such as aminocarboxylates such as sodium) and magnesium salts (eg, alkaline earth metal salts of monocarboxylic acids such as magnesium acetate; alkaline earth metal salts of hydroxycarboxylic acids such as magnesium tartrate) ) Is included. Preferred (C) salts of inorganic acids include alkali metal halides such as sodium chloride, potassium chloride, sodium bromide and potassium bromide; and alkaline earth metal halides such as calcium chloride, magnesium chloride and magnesium bromide. Ammonium halides such as ammonium chloride and ammonium bromide; alkali metal sulfates such as sodium sulfate and potassium sulfate; alkaline earth metal sulfates such as magnesium sulfate; iron sulfate such as ferric sulfate; aluminum sulfate; Ammonium sulfate; alkali metal sulfite (hydrogen) such as sodium bisulfite, sodium sulfite, potassium bisulfite
Salts; alkaline earth metal sulfites (hydrogen), such as calcium bisulfite and magnesium bisulfite; alkali metal nitrates, such as sodium nitrate and potassium nitrate; alkaline earth metal nitrates, such as calcium nitrate and magnesium nitrate; ferric nitrate, etc. Iron nitrate; aluminum nitrate; zinc nitrate; ammonium nitrate; alkali metal phosphates such as sodium phosphate and potassium phosphate; alkaline earth metal phosphates such as magnesium phosphate; ammonium phosphate; sodium pyrophosphate, sodium tripolyphosphate Alkali metal polyphosphates such as magnesium and potassium tripolyphosphate; alkaline earth metal polyphosphates such as magnesium pyrophosphate and magnesium tripolyphosphate; alkali metal carbonates such as sodium carbonate, sodium hydrogencarbonate and potassium carbonate (water And the like alkaline earth metal carbonates such as magnesium carbonate;) salt.

The alkali metal hydroxide (D) includes lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Preferred alkali metal hydroxides are sodium hydroxide and the like.

As the catalyst, for example, an organic acid or a salt thereof (especially acetic acid or a salt thereof) or an alkali metal hydroxide is often used from the viewpoints of industry and economy. When using an organic acid and an alkali metal hydroxide in combination,
Instead of these two components, an alkali metal salt of an organic acid (for example, sodium acetate or the like) may be used.

These catalysts may be used alone,
The same or different acids or salts described above may be used in combination. The hydration rate may be significantly improved by combining the two or more acids or salts thereof. For example, as the catalyst component, (1) (A1) a monofunctional organic acid or a salt thereof, (2) (A2) an organic acid having two or more functional groups or a salt thereof, (B) an acid phosphate or When used in combination with a component selected from the group consisting of an acidic sulfate or a salt thereof and (C) an inorganic acid or a salt thereof, not only can the hydration reaction be promoted, but also when magnesium hydroxide is formed into an aqueous slurry, The viscosity of the slurry suspension can be suppressed, and the redispersibility is improved even if a cake is formed. When at least one of the acid components (A) to (C) is used in combination with the alkali metal hydroxide (D), or when the alkali metal salts of the acid components (A) to (C) are used, The dispersibility of the particulate magnesium hydroxide in water is improved, and the slurry can be prevented from being caked.

The amount of the catalyst to be used can be selected from a wide range in which the dry mixing or the dry kneading system can be maintained depending on the type of the catalyst. For example, 0.01 to 100 parts by weight of magnesia can be used.
About 20 parts by weight, preferably about 0.1 to 15 parts by weight, more preferably about 0.5 to 10 parts by weight, and often about 1 to 15 parts by weight (particularly about 2 to 15 parts by weight). As the amount of the catalyst used increases, the hydration ratio can be greatly improved even in a dry mixing or dry kneading system. Further, as the hydration rate increases, the dispersion stability is high even if the produced powdery magnesium hydroxide is dispersed in water, and even if a cake is formed, the cake is soft and easily redispersed.

When a plurality of catalyst components are used in combination, the ratio of each catalyst component can be appropriately selected. For example, (1) (A1) a monofunctional organic acid component and (2) (A1)
2) an organic acid component having two or more functional groups, (B) an acid phosphate or acid sulfate component, and (C)
When combining with a component selected from the inorganic acid component,
The amount of the (A1) organic acid component used is, for example, 0.01 to 15 parts by weight (preferably 0.02 to 10 parts by weight, more preferably 0.05 to 100 parts by weight based on 100 parts by weight of magnesia).
5 parts by weight), (A2), (B) and (C)
The amount of the component selected from, for example, Magnesia 1
0.01 to 15 parts by weight (preferably 0.02 to 10 parts by weight, more preferably 0.05 to 5 parts by weight)
Parts by weight).

Further, in the method of the present invention, magnesium hydroxide may be produced from magnesia by dry mixing or dry kneading in the presence of a dispersant. The dispersant may be either a low molecular weight surfactant or a high molecular surfactant. Examples of low molecular weight surfactants include fatty acid alkali metal salts (such as alkyl metal salts, ammonium salts, and amine salts of higher fatty acids having about 10 to 30 carbon atoms), alkylbenzene sulfonates, α-olefin sulfonates, and sucrose fatty acids. Esters and the like. A preferred dispersant is a polymer surfactant, and when a polymer surfactant is used as an aqueous slurry, high-concentration water is maintained while maintaining high dispersion stability and storage stability. Even a magnesium oxide aqueous suspension can be reduced in viscosity.

The molecular weight of the high molecular surfactant is, for example, 1
× 10 ³ or more (for example, 1 × 10 ³ to 1 × 10 ⁶ ), preferably 1 × 10 ³ to 1 × 10 ⁵ , more preferably 2 × 10 ³
It is about × 10 ³ to 1 × 10 ⁵ . The degree of polymerization of the polymer surfactant can be appropriately selected within a range that does not impair the fluidity and dispersibility of the aqueous magnesium hydroxide suspension. For example, the viscosity of a 1% by weight aqueous solution of the polymer surfactant at 25 ° C. ,
1.2 to 1000 cps (centipoise), preferably 1.5 to 500 cps, more preferably 1.8 to 20
It is about 0 cps.

The polymeric surfactant includes an anionic surfactant and a nonionic surfactant. Examples of the anionic surfactant include a carboxylic acid type anionic surfactant which is a polymer carboxylic acid having a carboxyl group in the molecule or a salt thereof; a polymer sulfonic acid having a sulfonic acid group in the molecule or a salt thereof A sulfuric acid type anionic surfactant which is an acidic polymeric sulfate having an acidic sulfate group in the molecule or a sulfate type anionic surfactant which is a salt thereof; an acidic phosphate group or an acidic phosphorous acid in the molecule Examples thereof include a phosphoric acid type anionic surfactant which is a polymeric phosphoric acid having an acid ester group, a polymeric phosphorous acid, or a salt thereof. The carboxyl group,
An acidic group such as a sulfonic acid group, an acidic sulfate group, an acidic phosphate group, an acidic phosphite group, or a salt thereof may be simply referred to as an “anionic group”.

The carboxylic acid type anionic surfactants include:
Synthetic polymeric carboxylic acids and natural or semi-synthetic polymeric carboxylic acids are included. As the synthetic polymer carboxylic acid, for example, acrylic acid, methacrylic acid, maleic acid,
Homopolymers and copolymers using an unsaturated carboxylic acid such as fumaric acid, itaconic acid, crotonic acid, or a salt or acid anhydride thereof as a monomer component are exemplified. Examples of the polymerizable monomer copolymerizable with the unsaturated carboxylic acid include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and (meth) Octyl acrylate,
(Meth) such as 2-ethylhexyl (meth) acrylate
Acrylic ester; styrene, vinyl toluene, α-
Styrene monomers such as methylstyrene; vinyl acetate,
Vinyl ester monomers such as vinyl propionate; and vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, isopropyl vinyl ether, butyl vinyl ether, and isobutyl vinyl ether. Specific examples of the synthetic high molecular carboxylic acid include, for example, polyacrylic acid, polymethacrylic acid, (meth) acrylate- (meth) acrylic acid copolymer, vinyl ether-unsaturated carboxylic acid copolymer (for example, butyl vinyl ether-
Maleic anhydride copolymer), polycrotonic acid, styrene- (meth) acrylic acid copolymer, styrene-maleic anhydride copolymer, and the like. The acid value of the synthetic high molecular carboxylic acid is in a range that can impart water solubility, for example, 30 to 800 KOH mg / g, preferably 50 to 5 KOH mg / g.
It is about 00KOHmg / g. Examples of the natural or semi-synthetic high molecular carboxylic acid include polysaccharides having a carboxyl group such as alginic acid, carboxymethylcellulose, hydroxycarboxymethylcellulose, carboxymethylated starch, gum arabic, tragacanth, pectin, and hyaluronic acid.

Examples of the sulfonic acid type anionic surfactant include β-naphthalene sulfonic acid formalin condensate, melamine sulfonic acid formalin condensate, triazine sulfonic acid formalin condensate, polyethylene sulfonic acid, polystyrene sulfonic acid, and lignin sulfonic acid. And the like. Examples of the sulfate type anionic surfactant include sulfated polyvinyl alcohol, cellulose sulfate, carrageenan, agar, chondroitin sulfate, and the like. Examples of the phosphate type anionic surfactant include phosphorylated polyvinyl alcohol, cellulose phosphate, cellulose phosphite and the like.

The anionic surfactant can be used as a salt. Examples of the salt include alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as magnesium salt, calcium salt and barium salt; salts of metals belonging to Group 12 of the periodic table such as zinc salt; ammonia and amines (Trimethylamine, triethylamine, diethanolamine, triethanolamine, dimethylaminoethanol, morpholine and the like) or a salt with a basic nitrogen-containing heterocyclic compound (pyridine and the like); and quaternary ammonium salts such as tetraethylammonium and trimethylbenzylammonium. Can be Preferred salts include alkali metal salts, salts with ammonia or amines, the quaternary ammonium salts and the like. When a molecule has a plurality of acidic groups, the counter ion of each acidic group may be the same or different.

Among the above-mentioned anionic surfactants, carboxylic acid type, sulfonic acid type and sulfuric acid type anionic surfactants are preferable. In particular, carboxylic acid-type anionic surfactants (particularly, natural or semi-synthetic high molecular carboxylic acids such as polysaccharides having a carboxyl group such as carboxymethylcellulose and alginic acid or salts thereof) are extremely high in aqueous slurry. Has a thickening effect. Further, the sulfonic acid type anionic surfactant and the sulfate type anionic surfactant have an effect of suppressing the hardening of the cake to be formed even when the aqueous magnesium hydroxide slurry is stored for a long period of time, together with the above-mentioned viscosity lowering effect. Having. The anionic surfactant only needs to have at least one anionic group in the molecule, and the anionic surfactant has two or more anionic groups (for example,
A polyanionic polymer surfactant having about 2 to 10,000 (preferably 4 to 1000) is preferred. When the molecule has a plurality of anionic groups, the anionic groups may be the same or different.

Examples of the nonionic surfactant include alkyl polyoxyethylene ether, alkylphenyl polyoxyethylene ether, alkylcarbonyloxy polyoxyethylene, adducts of fatty acid polyhydric alcohol esters with ethylene oxide, and fatty acid sucrose. Adducts of esters and ethylene oxide, polyoxyalkylene block copolymers and the like can be mentioned. Among the nonionic surfactants, polyoxyalkylene block copolymers (such as ethylene oxide-propylene oxide block copolymer) have a large effect of lowering the viscosity of the aqueous slurry.

These dispersants can be used alone or in combination of two or more, and a high molecular surfactant and a low molecular weight surfactant may be used in combination. In particular, when the carboxylic acid type anionic surfactant and the sulfonic acid type or sulfate type anionic surfactant are used in combination, not only can the aqueous slurry be imparted with high dispersion stability and storage stability, but also long-term storage Even if a precipitate cake is formed, the resulting cake is soft and easily redispersed by shaking, stirring, or the like, so that the redispersibility is significantly improved.

The amount of the dispersant used is, for example, magnesia 1
0.001 to 15 parts by weight, preferably 0.005 to 10 parts by weight, more preferably 0.0
It is about 1 to 5 parts by weight, and often about 0.03 to 2.5 parts by weight (for example, 0.05 to 2 parts by weight).

When a carboxylic acid type anionic surfactant and a sulfonic acid type or sulfate type anionic surfactant are used in combination, the ratio of both is, for example, the former / the latter =
It is about 0.1 to 20 (weight ratio), preferably about 0.5 to 15 (weight ratio), and more preferably about 1 to 10 (weight ratio).

The aqueous slurry has a high magnesium hydroxide content, for example, 65% by weight or more (65-7%).
(About 5% by weight), the viscosity of the aqueous slurry may not decrease so much even when a small amount of a dispersant is added. In such a case, the content of the dispersant, particularly the polymer surfactant, is set to 1 to 100 parts by weight of magnesium hydroxide.
It is preferably about 10 parts by weight, preferably about 3 to 10 parts by weight, more preferably about 5 to 10 parts by weight.

For dry mixing or dry kneading, kneaders such as kneaders, pressure kneaders, and internal mixers (Banbury mixers), as well as conventional digesters, for example, screw type,
Kritzer style, Schaffer
Type, overflow type, start band type, warm stell (Warm
estelle, Schilde, Eiri
Atmospheric pressure digesters such as ch) and Kennedy types, and pressurized digesters such as Woodville type, Corson type and Yoshizawa lime type can be used.

The powdery magnesium hydroxide thus obtained may have an appropriate particle size and particle size distribution according to the application.
It is about 1000 μm (for example, 1 to 1000 μm), preferably about 2 to 100 μm (for example, 3 to 75 μm), and more preferably about 3 to 30 μm (for example, 5 to 20 μm). In the particle size distribution, magnesium hydroxide may have not only a single peak but also two or more peaks.

The hydration rate of the resulting powdered magnesium hydroxide depends on the reaction conditions and the like, but is usually from 70 to 1
00% (for example, 78-100%), preferably 80-
It is about 100% (for example, 85 to 100%), and more preferably about 90 to 100% (for example, 93 to 100%). The powdered magnesium hydroxide produced not only has high water dispersibility, but also has better storage stability than conventional aqueous slurries,
High transportability and transportability. Therefore, the powdered magnesium hydroxide can be easily converted into an aqueous slurry on site by a simple operation of mixing / stirring, which is useful for preparing the aqueous slurry and can realize a significant cost reduction.
Particularly high granular hydrated magnesium hydroxide, for example,
Hydration rate is 90-100% (preferably 92-100%)
Even if the aqueous slurry containing no dispersing agent is prepared, a high degree of powdery magnesium hydroxide exhibits high dispersion stability, and even if a cake is formed, it is redispersed by a simple operation such as shaking and stirring.

When dry mixing or dry kneading is performed in a system containing the dispersant or a system not containing the dispersant, the resulting powdery magnesium hydroxide is treated with a dispersant, or in the presence of a dispersant. The generated powdery magnesium hydroxide may be dispersed in water. In such treatment or dispersion, the amount of the dispersant used can be appropriately selected from a range corresponding to the total amount of the dispersant used.

The obtained powdery magnesium hydroxide is
If necessary, pulverization, granulation, by subjecting to operations such as classification by a sieve, for a wide range of applications, for example, for neutralization, for flue gas desulfurization, for fertilizer, heavy oil combustion additives, pulp digesters,
It can be suitably used as a plastic additive, a colorant, a formulation additive, and the like. Powdered magnesium hydroxide is
It can be used as it is for fertilizers and the like, and is useful for preparing an aqueous slurry (aqueous suspension) in applications such as a neutralizing agent by utilizing its high water dispersibility.

The aqueous magnesium hydroxide suspension can be prepared by dispersing powdered magnesium hydroxide in an aqueous medium. As described above, the particulate magnesium hydroxide may be dispersed in an aqueous medium in the absence of a dispersant, but when the particulate magnesium hydroxide is dispersed in water in the presence of the dispersant, dispersion stability is improved. It is possible to reliably obtain an aqueous slurry (water suspension) having a high property.

The order of adding water and the dispersant to the powdered magnesium hydroxide is not particularly limited. For example, a dispersant (preferably a polymer surfactant) is added to an aqueous suspension of magnesium hydroxide. Alternatively, a mixed solution of water and a dispersant may be added to the powdered magnesium hydroxide, or water may be added after treating the powdered magnesium hydroxide with the dispersant. Further, the magnesium hydroxide may be dispersed in water by mixing the above components at the same time. The dispersion and mixing can be performed by a conventional method such as stirring, shaking, and ultrasonic irradiation. The dispersion / mixing may be performed under forced stirring in which a shearing force acts on the powdered magnesium hydroxide. When dispersed and mixed under forced stirring, the cake is easily re-dispersed by re-stirring even if the solid content and water are separated by long-term storage of the obtained aqueous magnesium hydroxide suspension. In addition, the resulting aqueous suspension dispersed and mixed under forced stirring has a characteristic of having a low viscosity even at a high concentration. In particular, when a polymer surfactant is used as a dispersant, an increase in viscosity and formation of a hard cake can be suppressed, and an aqueous magnesium hydroxide suspension that can be easily redispersed even after long-term storage can be obtained.

The forced stirring may be performed by increasing the rotation speed of various mixing stirrers, for example, a stirrer having a stirring blade,
It can be performed by a method such as applying a strong shearing force with a stirrer such as a homogenizer or a super mixer. The peripheral speed accompanying the forced stirring is, for example, 300 m / min or more, and preferably about 350 to 5000 m / min. The stirring time can be selected according to the peripheral speed and the form of the mixing and stirring system. For example, at a peripheral speed of 400 m / min, it is 30 minutes or more, preferably 1 hour or more, more preferably about 2 to 20 hours, and a peripheral speed of 1000 m / min. In this case, 3 minutes or more (preferably about 5 minutes to 1 hour) is sufficient.

Because of the high dispersibility of the powdered magnesium hydroxide, the content of magnesium hydroxide in the aqueous suspension can be selected in a wide range, for example, 10 to 85% by weight.
(For example, 15 to 80% by weight), preferably 30 to 75%.
% By weight (for example, 35 to 70% by weight), and more preferably about 35 to 70% by weight.

The aqueous magnesium hydroxide suspension thus obtained has characteristics of high dispersion stability and low viscosity even at a high concentration. Therefore, by increasing the concentration, transportation and storage costs can be significantly reduced. Further, since the fluidity of the aqueous slurry is high, workability such as storage of the slurry and transport of pipes can be improved. Further, since the dispersion stability and the dilution stability are high, an aqueous magnesium hydroxide suspension having a desired concentration can be easily prepared.
The viscosity of the aqueous magnesium hydroxide suspension at 25 ° C. is, for example, 10 to 2500 cps, preferably 40 cps.
~ 2000 cps, more preferably 40 ~ 1500 c
It is about ps.

[0056]

According to the present invention, powdery magnesium hydroxide can be produced simply and efficiently by a simple operation of dry mixing or dry kneading while maintaining a predetermined water content. Further, since magnesium hydroxide can be obtained in the form of powder, it is useful in reducing storage, transfer and transportation costs. Moreover, with the simple operation as described above, powdery magnesium hydroxide can be produced from solid magnesia with high hydration efficiency. Furthermore, since the water-dispersibility is high even in the form of powder, an aqueous slurry (water suspension) can be obtained by a simple operation of dispersing the powdered magnesium hydroxide in water.

[0057]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. In addition, the viscosity in an Example shows the value at 25 degreeC, and "%" shows "weight%" unless there is particular indication. In addition, the degree of hydrolysis was measured as follows. That is, the sample (magnesium hydroxide) was dried at 150 ° C. to a constant weight, then finely pulverized in a mortar, and baked in an electric furnace at 600 ° C. to a constant weight. Then, the degree of hydrolysis was calculated. The neutralization time is the time required to add 12.70 g of a 200-mesh pass sample obtained by crushing and sieving to 200 g of 2N-sulfuric acid and reach pH 6. Further, the water separation rate means a ratio (%) of the height of the separated water layer to the entire height after the suspension is put into a cylindrical container to a predetermined height and left for 6 days. The amount of water in the reaction system was determined based on the stirring power (the degree of deflection of the needle of the ammeter). That is, the relationship between the water content and the stirring power is determined by a preliminary test. The water content is 15% by weight or less when the needle of the ammeter does not oscillate, and the water content is less than 15% by weight when the needle of the ammeter slightly oscillates. Was 18% by weight or less, and the amount of water in the reaction system was estimated by using the fact that the amount of water was 25% by weight when the needle of the ammeter fluctuated. The water content of the reaction system was determined by quenching a sample sampled from the reaction system, stopping the reaction, measuring the weight, washing with methanol, drying at 150 ° C., and measuring the weight. It was calculated from the weight loss.

Example 1 A jacketed stainless steel kneader (3 L in inner volume) having two Z-shaped stirring blades inside, and equipped with two dropping funnels, one reflux condenser, and a thermometer on the top. , 1000g light magnesia (330 mesh pass),
Heated to 60 ° C. While stirring the lightly-baked magnesia at 75 rpm, 500 g of water was added to the mixture using the two dropping funnels.
The solution was added dropwise over 6 hours. The water content of the reaction system during this dropping process was 18% by weight or less,
After 5 minutes, the internal temperature rises to 75 ° C and the maximum temperature is 87 ° C.
° C was reached. After completion of the dropwise addition, the mixture was heated for 1 hour and then cooled to obtain magnesium hydroxide having a water content of 4.4% based on the product and a hydrolyzing rate of 79.7%.

Example 2 A reaction was conducted in the same manner as in Example 1 except that 1000 g of lightly-baked magnesia (120-mesh pass) was used instead of lightly-baked magnesia (330-mesh pass). Reached. The water content (product basis) of the obtained magnesium hydroxide is 4.8%, and the degree of hydrolysis is 8
3.1%.

Example 3 1000 g of lightly burned magnesia (120 mesh pass) was added to 8
While stirring at 5 ° C., a mixed solution of 20 g of acetic acid and 480 g of water was added dropwise over 1 hour, and the reaction was carried out in the same manner as in Example 1 except for stirring for 2 hours. 5% of magnesium hydroxide having a hydrolyzing rate of 99.5% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less. The obtained powdery magnesium hydroxide was dispersed in water to prepare a 50% by weight aqueous suspension, and the viscosity was 65 cps (130 cp after 6 days).
s), pH 9.9, syneresis rate 3%, and almost no cake was formed. The neutralization time using the aqueous suspension is 11
It was 0 seconds.

Example 4 1000 g of lightly burned magnesia (330 mesh pass) was added to 7
While stirring at 5 ° C., a mixed solution of 30 g of acetic acid and 470 g of water was added dropwise over 2 hours, and the reaction was carried out in the same manner as in Example 1 except that the mixture was further stirred for 1 hour. 7% of magnesium hydroxide having a hydrolyzing rate of 89.7% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less.

Example 5 1000 g of lightly burned magnesia (120 mesh pass) was added to 8
While stirring at 8 ° C., a mixed solution of 50 g of acetic acid and 450 g of water was added dropwise over 1 hour, and the reaction was carried out in the same manner as in Example 1 except for stirring for 1 hour. 2% of magnesium hydroxide having a hydrolyzing rate of 99.4% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less. The obtained powdered magnesium hydroxide was dispersed in water to prepare a 50% by weight aqueous suspension, and the viscosity was 13,000 cps (375% after 6 days).
00 cps), pH 9.9, syneresis rate 0%, and no cake was formed. Further, the obtained powdered magnesium hydroxide was dispersed in water to prepare a 37% by weight aqueous suspension, and the viscosity was 240 cps (1600 cp after 6 days).
s), pH 9.8, syneresis rate 6.8%, and no cake was formed.

Example 6 1000 g of lightly burned magnesia (330 mesh pass) was added to 8
While stirring at 6 ° C., a mixed solution of 50 g of acetic acid and 450 g of water was added dropwise over 1 hour, and the mixture was reacted in the same manner as in Example 1 except for stirring for 1 hour. 5% of a magnesium hydroxide having a hydrolyzing rate of 96.1% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less. The obtained powdered magnesium hydroxide was dispersed in water to prepare a 50% by weight aqueous suspension, and the viscosity was 11,000 cps (290 days after 290 cps).
00 cps), pH 9.9, syneresis rate 0%, and no cake was formed. Further, the obtained particulate magnesium hydroxide was dispersed in water to prepare a 37% by weight aqueous suspension, and the viscosity was 220 cps (840 cps after 6 days).
The pH was 9.9, the water separation rate was 5.5%, and no cake was formed.

Example 7 1000 g of lightly burned magnesia (330 mesh pass) was added to 8
While stirring at 8 ° C., a mixed solution of 120 g of acetic acid and 400 g of water was added dropwise over 1 hour and 30 minutes, and further 1 hour and 30 minutes.
When the reaction was carried out in the same manner as in Example 1 except for stirring for a minute, a magnesium hydroxide having a water content of 5.3% and a hydrolyzing rate of 96.8% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less.

Example 8 1000 g of lightly burned magnesia (330 mesh pass) was added to 9
While stirring at 6 ° C., 50 g of sodium hydroxide and 50 g of water
The reaction was carried out in the same manner as in Example 1 except that a mixed solution with 0 g was added dropwise over 1 hour and 30 minutes, and the mixture was further stirred for 3 hours and 30 minutes. 0.0% of magnesium hydroxide was obtained. In addition,
The water content of the reaction system during the dropping process was 18% by weight or less.

EXAMPLE 9 1000 g of lightly burned magnesia (330 mesh pass) was added to 9
While stirring at 0 ° C., a mixed solution of 10 g of sulfuric acid and 500 g of water was dropped over 1 hour and 30 minutes, and the reaction was carried out in the same manner as in Example 1 except for stirring for 2 hours and 30 minutes. Moisture content 5.9%, hydrolysis rate 84.5
% Of magnesium hydroxide was obtained. The water content of the reaction system during the dropping process was 18% by weight or less. The obtained powdered magnesium hydroxide was dispersed in water, and the dispersion was 50% by weight.
When a water suspension was prepared, the viscosity was 35 cps (35 cps after 6 days) and the pH was 11.2.

Example 10 1000 g of lightly burned magnesia (330 mesh pass) was added to 8
While stirring at 5 ° C, magnesium acetate tetrahydrate 75.
A mixed solution of 3 g and 475 g of water was added dropwise over 2 hours.
The reaction was carried out in the same manner as in Example 1 except for further stirring for 1 hour. As a result, magnesium hydroxide having a water content of 5.6% based on the product and a hydrolyzing ratio of 94.2% was obtained. In addition,
The water content of the reaction system during the dropping process was 15% by weight or less. The obtained powdered magnesium hydroxide was dispersed in water to prepare a 50% by weight aqueous suspension.
000 cps (88000 cps after 6 days), pH 10.
0, the water separation rate was 0%, and no cake was formed. The obtained powdery magnesium hydroxide was dispersed in water to prepare a 37% by weight aqueous suspension.
0 cps (1140 cps after 6 days), pH 9.9, water separation 4.2%, and no cake was formed.

Example 11 1000 g of lightly burned magnesia (330 mesh pass) was added to 8
While stirring at 4 ° C., 10 g of acetic acid and sodium polyacrylate (Polymaster D-45, manufactured by Hakuto Chemical Co., Ltd., 1
% Viscosity: 3 cps) A mixed solution of 1 g and 500 g of water was added dropwise over 3 hours, and the reaction was carried out in the same manner as in Example 1 except that the mixture was further stirred for 1 hour. Thus, magnesium hydroxide having a conversion of 96.2% was obtained. The water content of the reaction system during the dropping process was 1
It was less than 5% by weight.

Example 12 1000 g of lightly burned magnesia (120 mesh pass) was added to 8
While stirring at 0 ° C., 10 g of sodium hydroxide and sodium carboxymethylcellulose (CMC112
0, manufactured by Daicel Chemical Industries, Ltd., 1% viscosity: 11 cp
s) A mixed solution of 1 g and 500 g of water was divided into 5 portions to give 2
Dropping over time and stirring for an additional 3 hours and 30 minutes
When the reaction was carried out in the same manner as in Example 1, magnesium hydroxide having a water content of 5.0% based on the product and a hydrolyzing rate of 89.0% was obtained. The water content of the reaction system during the dropping process was 15% by weight or less.

Example 13 An apparatus in which a dryer (internal volume 200 L) equipped with two charging ports, a jacket and four stirring blades, and a vacuum pump were sequentially connected via a cyclone, a bag filter, and a condenser. Using. 50 kg of lightly-baked magnesia (120 mesh pass) is charged into the dryer, and
After heating to ℃, 25 kg of an aqueous solution containing 1 kg of acetic acid was added over 30 minutes while stirring the lightly-baked magnesia. The amount of water in the reaction system during this addition process was measured to be 5.0% by weight or less. Although the maximum temperature reached 101 ° C., no acetic acid odor was generated. After completion of the addition of the acetic acid aqueous solution, excess water was removed by a vacuum pump to obtain 3.2 kg of drain water. The water content (product basis) of 68.5 kg of the obtained magnesium hydroxide is 3.4.
%, And the degree of hydrolysis was 95.9%. The obtained granular magnesium hydroxide was dispersed in water to prepare a 50% by weight aqueous suspension, and the viscosity was 7,800 cps (67 days after 67 days).
00 cps), pH 9.9, syneresis rate 0%, and no cake was formed. Further, the obtained powdered magnesium hydroxide was dispersed in water to prepare a 37% by weight aqueous suspension, and the viscosity was 520 cps (1960 cp after 6 days).
s), pH 9.9, water separation 1.5%, and no cake was formed.

Example 14 A magnesium hydroxide / water slurry (slurry concentration: 3) obtained by the reaction of magnesium chloride and slaked lime in seawater
(5% by weight) was filtered under reduced pressure using a Nutsche equipped with a filter paper (5A) to obtain a magnesium hydroxide cake (A). The cake (A) had a water content of 39.2% by weight and a degree of hydrolysis of 93.3%. Using the kneader of Example 1, the water in the cake (A) was reacted with lightly-baked magnesia to obtain powdered magnesium hydroxide. Light kneaded magnesia (120 mesh pass)
While kneading with 887 g, the cake (A) to which 25.6 g of acetic acid had been added in advance was added in small portions over 45 minutes. About 30 minutes after the addition of the cake (A), the internal temperature exceeded 100 ° C., and generation of steam was observed. After the addition was completed, kneading was continued for 1 hour, and then cooled to room temperature.
A smooth powdered magnesium hydroxide (product-based water content 0.9% by weight, hydrolyzing rate 93.3%) was obtained.

Example 15 The cake (A) of Example 14 was loosened and exposed to air at room temperature, and the water was evaporated to obtain a cake (B) having a water content of 29.5% by weight. This cake (B) 1000
g, acetic acid 23.3 g and lightly-baked magnesia (120 mesh pass) except that 636 g was used, the reaction was carried out in the same manner as in Example 14. The maximum temperature of the reaction reached 80 ° C. The obtained smooth powdered magnesium hydroxide has a water content of 7.6% by weight based on the product and a hydrolyzing rate of 8%.
It was 9.0%. Magnesium hydroxide 200 obtained
292.8 g of water was added to the resulting mixture, and the pH was adjusted to 13.1 with a small amount of caustic soda while stirring to obtain a 37.5% by weight aqueous suspension. The viscosity of this water suspension after one day is 670.
cps (after 6 days, 680 cps), water separation rate after 6 days is 1
4.7%, and almost no cake was formed. The neutralization time using this suspension was 60 seconds.

Comparative Example 1 The reaction was carried out in the same manner as in Example 1 except that 500 g of water was added all at once. As a result, the internal temperature rose to 63 ° C. 10 minutes after the start of the addition, and a squeaking noise was generated. In addition, the mixture adhered to the wall surface and the stirring blade, and a lump formed, and the stirring became impossible. In addition, the water content of the surface layer part of the lump was 0.6%, and the degree of hydrolysis was 63.9%.

Continuation of the front page (56) References JP-A-64-282214 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01F 5/16

Claims (15)

(57) [Claims] 1. A method for producing powdered and granular magnesium hydroxide, wherein hydrated magnesia is dry-mixed or dry-kneaded in the presence of moisture. 2. The method for producing magnesium hydroxide according to claim 1, wherein the magnesia powder is dry-mixed or dry-kneaded while being wetted with 25 parts by weight or less of water per 100 parts by weight of magnesia. 3. The method for producing magnesium hydroxide according to claim 1, wherein magnesia and water are reacted while forming a continuous gas phase in a solid gap. 4. The method for producing magnesium hydroxide according to claim 1, wherein the magnesia is light-burned magnesia. 5. The method for producing magnesium hydroxide according to claim 1, wherein the magnesia is a lamp, a crushed material or a finely crushed material. 6. The method for producing magnesium hydroxide according to claim 1, wherein gaseous or liquid water or a water-containing slurry or cake is added to magnesia for hydration. 7. The method for producing magnesium hydroxide according to claim 1, wherein water is added to the dry mixing system or the dry kneading system while keeping the water content to 0.1 to 20 parts by weight based on 100 parts by weight of magnesia. 8. A temperature of 30 to 150 ° C. and a pressure of 1 to 10.
The method for producing magnesium hydroxide according to claim 1, wherein the reaction is performed at atmospheric pressure. 9. The method for producing magnesium hydroxide according to claim 1, wherein dry mixing or dry kneading is performed in the presence of a catalyst. 10. The method for producing magnesium hydroxide according to claim 9, wherein the amount of the catalyst used is 0.01 to 20 parts by weight based on 100 parts by weight of magnesia. 11. The method for producing magnesium hydroxide according to claim 1, wherein dry mixing or dry kneading is performed in the presence of a dispersant. 12. A method for producing powdered and granular magnesium hydroxide in which light-baked magnesia is dry-mixed or dry-kneaded and hydrated while maintaining a water content of 0.2 to 15 parts by weight based on 100 parts by weight of light-baked magnesia. 13. A powdery magnesium hydroxide obtained by the method according to claim 1. 14. A method for producing an aqueous magnesium hydroxide suspension, wherein the granular magnesium hydroxide obtained by the method of claim 1 is dispersed in water. 15. The method for producing a magnesium hydroxide aqueous suspension according to claim 14, wherein the powdery magnesium hydroxide is dispersed in water in the presence of a dispersant.