JPH0347501A - Drying method for high-concentration aqueous dispersed material of fine particle - Google Patents

Abstract

PURPOSE:To lower dry cohesive force between the suspended particles at a time of drying by dissolving specified substance in the high-concn. aqueous dispersed material system of fine particles and thereafter evaporating water while fine foams are generated in the system at pressurization or reduced pressure. CONSTITUTION:At least one kind or more kinds of substance described hereunder are dissolved in the high-concn. aqueous dispersion system of fine particles at 0.0001-0.1mol per 1mol suspended particle as total mount at the arbitrary temp. and normal pressure or pressurization. This substance is water-soluble at normal temp. and normal pressure and capable of generating gas by decomposition or reaction at 100 deg.C or below in the respective peroxide, carbonate, inorganic acid or organic acid and various gasses. Then while fine foams are generated in the dispersion system by heating or reduced pressure or both the two, water is evaporated to dry this dispersion system. The particles having >=5m<2>/g BET specific surface area are preferably utilized as the suspended particles in the disersion system.

Description

[Detailed description of the invention] [Industrial application field]

The present invention aims to reduce the drying cohesive force between suspended particles by interposing air bubbles when drying a highly concentrated aqueous dispersion system of fine particles (hereinafter referred to as slurry, including cake-like and paste-like forms). This method enables easy and low-cost pulverization and pulverization of dried materials up to the particle size distribution of the particles suspended in the slurry before drying.

[Conventional technology]

Conventionally, when drying a slurry with a high concentration of fine particles, the finer the particles, for example, the BET specific surface area of the dried product is 5 ffl/g.
As mentioned above, especially at 10rrf/g or more, the higher the solid content concentration is, for example 30% by weight or more, especially 60% by weight or more, the dry cohesive force increases and the dried material becomes strong and difficult to break. , various surface treatment agents have been used to prevent suspended particles from drying and agglomerating.

[Problem to be solved by the invention]

However, surface treatment agents for the purpose of preventing dry agglomeration are limited to carbon a type anionic surfactants, fatty acids and sulfate ester type anionic surfactants, and these are not always sufficient. Furthermore, when using dry powder as a pigment or filler, surface treatment agents for the purpose of imparting functionality may actually increase dry agglomeration, and depending on the application, untreated powder may be required. Sometimes it is done. Taking these conditions into account, some drying equipment includes, for example, a fluidized bed type drying equipment that uses media to crush the dried material by collision of the media, or a flash dryer that is equipped with a crusher. The reason for the crushing of drying equipment that involves crushing is to improve drying efficiency. Basically, it is not intended for crushing. Therefore, in order to obtain a dry powder with the particle size distribution of the particles suspended in the slurry before drying, steps such as pulverization and precision classification are required after the drying process, which significantly increases manufacturing costs. This was the actual situation, and it was an issue that needed to be solved.

[Means to solve the problem]

In view of these circumstances, the present inventors have proposed that if a highly concentrated slurry of fine particles is dried with air bubbles interposed therein, the drying cohesive force between suspended particles will be reduced no matter what type of drying device is used. In the crushing process, we discovered that simply by crushing with a relatively low-energy crusher, a powder with the particle size distribution of the particles suspended in the slurry could be obtained. In the dispersion system, peroxides, carbonates, inorganic acids or organic acids, and various gases, each of which is water-soluble at room temperature and normal pressure, and one type of substance that can generate gas by decomposition or reaction at 100°C or less, or The total of two or more types is 0.0001 to 0 per 1 volume of suspended particles.
．． A fine particle high concentration aqueous dispersion characterized by dissolving 1 mol at a desired temperature under normal pressure or pressure, and drying by evaporating water while generating fine bubbles in the system by heating or reduced pressure or both. The drying method of
It was issued by J. Furthermore, water is evaporated and dried while air bubbles are mixed in the highly concentrated aqueous dispersion system of the fine particles using an incubation nozzle or the like at an arbitrary temperature and under normal pressure or pressurization at 10 to 70% by volume (calculated at normal temperature and normal pressure). At the same time, they solved the problem by developing a method for drying a highly concentrated aqueous dispersion of fine particles, which is characterized by the following characteristics: Here, suspended particles in a highly concentrated aqueous dispersion system of fine particles are:
The base particles are made by grinding and pulverizing naturally occurring or synthetic inorganic substances using water as a medium, and the particle size of the dry product is 5Tr in BET specific surface area! /g or more and water, and the solid content concentration is 30% by weight or more. In the present invention, the BET specific surface area refers to one or more means measured by a single point or multi-point method using an adsorption measuring device such as a volumetric method using a nitrogen adsorption method, a single weight method, or a flow method. , becomes as follows. The particles suspended in the slurry used in the present invention are inorganic substances, naturally occurring or synthetic, such as silicic acid, kaolin clay, waxite clay, talc, asbestos, mica,
bentonite, zeolite. Silica sand powder, pumice grains, feldspar powder, white carbon, wollastonite, calcium silicate, magnesium silicate, aluminum silicate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, calcium carbonate, basic calcium carbonate, calcium hydroxide, sulfuric acid Calcium, aluminum oxide, aluminum hydroxide, titanium oxide, silicon carbide, silicon nitride, basic zinc carbonate, barium titanate,
Precipitated barium sulfate, barium carbonate, zircon silicate, zircon oxide, potassium titanate, molybdenum disulfide. These are particles made by grinding and pulverizing iron oxide, zinc oxide, antimony dioxide, litharge, etc. using water as a medium. BET of these dried products, including those treated with organic or inorganic surface treatment agents using these particles as a matrix.
Specific surface area is 5rt? /g or more of particles. These particles I! ! The viscosity of the slurry and suspended particles can be used to mix air bubbles into the turbid slurry. Although it is necessary to consider the method of generating air bubbles depending on the conditions and type of drying method, peroxides, carbonates,
For each of inorganic acids, organic acids, and various gases, one or more types of substances that are soluble in water at room temperature and normal pressure and can generate gas by decomposition or reaction at 100°C or less are combined to make 1 mol of suspended particles. 0.0001~0.1 per
mol, preferably 0.001 to 0.05 mol, is dissolved at any temperature under normal pressure or pressure, and bubbles are generated by heating or reduced pressure or both, or by using a bubble generating nozzle in the system, at any temperature. 10 to 70% by volume (calculated at room temperature and pressure) under normal pressure or pressure, preferably 3
It has been found that these air bubbles, such as air bubbles mixed at 0 to 50% by volume, reduce dry agglomeration of suspended particles during drying. If the amount of air bubbles is below the range of air bubble ratio in the slurry,
Air bubbles are not uniformly interposed between individual suspended particles, and dry agglomeration cannot be reduced. Furthermore, if the amount of bubbles exceeds the above range, the effect of reducing dry agglomeration is diminished because air bubbles that exceed the size of the suspended particles are formed due to collision and aggregation of the bubbles and can be interposed between individual particles and disappear. Examples of water-soluble peroxides used here include hydrogen peroxide, sodium peroxide, potassium permanganate, calcium permanganate, and sodium permanganate. Among these, hydrogen peroxide is preferred, and as water-soluble carbonates, ammonium carbonate, ammonium hydrogen carbonate carbamate, ammonium hydrogen carbonate, etc. are preferred. Next, regarding water-soluble inorganic or organic acids. Suspended particles in the slurry are limited to substances that can react with acids to generate gases, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and formic acid, acetic acid, propionic acid, butyric acid. Examples include maleic acid, acrylic acid, methacrylic acid, and citric acid. Furthermore, as a water-soluble gas. Examples include carbon dioxide, sulfur dioxide, and chlorine. Among these, carbon dioxide is the best. When mixing air bubbles, use the aeration method.
By feeding air under pressure through a porous plate or a fine dispersion nozzle, fine air bubbles can be mixed into the slurry, which is effective for reducing dry agglomeration of suspended particles. As a drying device for slurry mixed with the above air bubbles,
Drying methods include flash drying, fluidized bed drying, air drying, spray drying, vacuum drying, conductive heat drying, and radiant heat drying to dry solids and liquids. A drying device using a gaseous fuel and electric heating, resistance heating, induction heating, electric field heating, high frequency heating, far infrared heating, etc. as a heat source can be used.

[Action and effect]

By adding the above-mentioned substances within a specific range to an aqueous dispersion with a high concentration of fine particles, fine air bubbles are uniformly contained in the aqueous dispersion with a high concentration of fine particles, and when drying, the particles are separated from each other. Dry cohesive force can be reduced. Here, dry cohesive force is defined as the interaction (cohesive force) that acts between particles; (i) universally acts between particles (intermolecular forces and electrostatic forces); and (i) through liquids or solids existing between particles. It is broadly classified into two types: force due to liquid and solid crosslinking, and refers to the latter. In addition, this dry cohesive force, the latter force due to liquid bridges, is the result of attraction between particles due to capillary negative pressure and interfacial tension inside the liquid bridge, and this attraction shows a negative correlation with interparticle distance and particle size. . Next, to explain the slurry drying process from the structural forms of solid, liquid, and gas systems, as the water evaporates, the slurry forms I) slurry region, tr) capillary region, m) elementary region, ■) suspended region, ■)
Drying is performed through a structural form such as an adsorption zone. (2) Sludge zone: This is a slurry state before drying, and the interaction between particles here is due to the intermolecular force mentioned in (2) above. ■) Capillary region: Although water fills the entire void group of the particle layer in the state of a saturated capillary liquid, the particles begin to undergo large interactions due to capillary force. ■) Cord-like region: Water becomes a crosslinking liquid and interacts with the particle layer due to capillary negative pressure and interfacial tension, and the particles come into close contact with each other, reaching the limit state of contraction. IV) Suspension zone: Water acts as a bridging liquid and interacts mainly with interfacial tension in the details between particles, resulting in stronger dry aggregation. It is considered that dry aggregation is almost completed by this point. This dry cohesive force, that is, the force due to liquid crosslinking, shows a negative correlation with the distance between particles and the particle diameter, so the air bubbles interposed between particles widen the distance between particles in the slurry, and It seems that it acts to maintain the distance between particles even in the suspended region and the suspended region, reducing the dry cohesive force. The electrical repulsion generated from the charged potential on the particle surface caused by conventionally known surface treatment agents such as carboxylic acid type anionic surfactants cannot prevent dry agglomeration of suspended particles at high concentrations. It is not possible to obtain the strong effect of air bubbles. The above effect is particularly important when the particle size of the dry material is 5r in terms of BET specific surface area.
When drying a slurry with a solid content concentration of 30% by weight or more consisting of particles of rl'/g or more, the presence of air bubbles in the slurry reduces the cohesive force between suspended particles, and as mentioned above, the drying equipment Regardless of the type, this method is extremely effective as a method for obtaining dried products with little dry agglomeration. The method of the present invention has the effect of obtaining a dry powder having the particle size distribution of the particles suspended in the slurry before drying. No process was required, and manufacturing costs were significantly reduced.

【Example】

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these in any way. Example 1 Kaolin (Al, 03-25iO, -2H,0) 10
Add 0.3 parts of sodium polyphosphate as a dispersant to 0 parts, suspend it in water using a disper so that the solid content concentration is 60% by weight, and add this slurry to Universal Mill H8.
BET specific surface area (
micromeritics FlowSorb II
2300) Wet milling was carried out so that S = LL, 5 i/g and the average particle size by Sedigraph (micromeritics 500011!T) was 0.9 pm. The particle size distribution of this slurry is shown in FIG. Particle size distribution was measured using an X-ray transmission method Sedigraph (MICR
Using a 0.2% aqueous solution of sodium hexametaphosphate as a solvent, a suspension of 3 to 7% by weight of the sample was stirred with a magnetic stirrer for 3 minutes, and then subjected to ultrasonic dispersion for 5 minutes. Measurements were made on the following items. To the thus obtained slurry was added 0.015 mol of hydrogen peroxide per 1 mol of suspended kaolin at room temperature and normal pressure, and after stirring with a disper, the mixture was heated to 130°C using a one-box type aerated dryer.
The dried material was pulverized in one pass using only a micron mill (detailed micron) without using a classifier. The particle size distribution of the nine kaolin powders thus obtained was measured using a Sedigraph, and the results are shown in FIG. Comparative Example 1 The particle size distribution measurement results of kaolin powder obtained by drying without using hydrogen peroxide and pulverizing in the same manner as in Example 1 are also shown in FIG. 2 by dotted lines. Example 2 0.7 parts of sodium polyacrylate was added to 100 parts of heavy calcium carbonate, suspended in water using a disper so that the solid content concentration was 75% by weight, and this slurry was milled in a pearl mill (PM25TEX-H Wet milling was carried out using a dry material (type Ashizawa) so that the BET specific surface area S of the dried material was 12.5rrr/g and Sedigraph D = 0.9-. The particle size distribution of this slurry is shown in FIG. Carbon dioxide (purity 99%) is blown into the thus obtained slurry at room temperature and gauge pressure 4/d to dissolve 35% by volume in terms of gas under pressure at room temperature. Mitsubishi Kakoki) was used for drying by spraying all at once into hot air at a pressure of -300 mH and an temperature of 300° C. from a spray nozzle. The particle size distribution of the thus obtained heavy calcium carbonate powder was measured using a Sedigraph, and the results are shown in FIG. Comparative Example 2 The particle size distribution measurement results of the heavy calcium carbonate powder obtained by drying without using carbon dioxide in Example 2 are also shown in FIG. 4 by dotted lines. Example 3 0.4 parts of sodium polyphosphate was added as a dispersant to 100 parts of titanium oxide (rutile type), and the slurry was suspended in water using a disper so that the solid content concentration was 70% by weight. BET specific surface area of dried material 5 = 14.5-7g by mill () (S type Mitsui Miike Kakoki)
Wet milling was performed so that Sedigraph D, , = 0.7 μs. The particle size distribution is shown in FIG. 0.001 ammonium hydrogen carbonate per 1a+ol of titanium oxide suspended in the slurry thus obtained at room temperature and normal pressure.
5 mol was added, and after stirring with a disper, it was dried at 80° C. using a vacuum dryer, and the dried product was pulverized for one bath using only a micron mill (detailed micron) without using a classifier. The particle size distribution of the obtained titanium oxide powder was measured using a Sedigraph, and the results are shown in FIG. Comparative Example 3 The particle size distribution measurement results of titanium oxide powder obtained by drying and pulverizing in the same manner as in Example 3 without using ammonia hydrogen carbonate are also shown in FIG. 6 by dotted lines. Example 4 0.5 parts of sodium polyacrylate was added as a dispersant to 100 parts of heavy calcium carbonate to give a solid concentration of 75 parts.
Suspend the slurry in water using a disper so that it becomes % by weight, and use a universal mill (H8 model Mitsui Miike Kakoki) to reduce the BET specific surface area of the dry product to S = 12.5rrF/
Wet milling was carried out so that g and Sedigraph D, g = 0.9-. Its particle size distribution is shown in FIG. Acrylic acid monomer 0.0 per 1 mol of calcium carbonate suspended in the slurry thus obtained at room temperature and normal pressure.
03 mol was added and stirred in a kneader, followed by drying at 300° C. using a micro dryer (MDV-1 type Hosho Micron). The particle size distribution of the thus obtained heavy calcium carbonate powder was measured using a Sedigraph, and the results are shown in FIG. Comparative Example 4 The particle size distribution measurement results of the heavy calcium carbonate powder obtained by drying without using the acrylic acid monomer in Example 4 are also shown in FIG. 8 by dotted lines. Example 5 0.7 parts of sodium polyacrylate was added to 100 parts of heavy calcium carbonate, and the slurry was soaked in water using a disper so that the solid content concentration was 75%. BET specific surface area of the dry material 5 = 12.5 rf/g according to Type Ashizawa) and Sedigraph D1. Wet milling was performed so that g = 0.0-. The particle size distribution is shown in FIG. The slurry thus obtained was heated at room temperature and at a gauge pressure of 4k.
g/aJ of air is blown through a porous plate at a rate of 35% by volume in terms of gas under pressure at room temperature.
Drying was carried out by spraying all at once from a spray nozzle into hot air at 300° C. under a water column of 00 mH and O. The particle size distribution of the thus obtained heavy calcium carbonate powder was measured using a Sedigraph, and the results are shown in FIG. Comparative Example 5 The particle size distribution measurement results of the heavy calcium carbonate powder obtained by drying without using air in Example 5 were also
It is shown by the dotted line in Figure 0. As mentioned above, as is clear from the comparison of the graphs in Figures 1 to 10, the particle size of the dried material dried by the drying method according to the present invention is the same regardless of the drying method and the type of suspended particles. It can be seen that the particle size distribution is almost the same as the particle size distribution when the particles were cloudy.

[Brief explanation of drawings]

Figures 1 to 10 are graphs of particle size distribution obtained by X-ray transmission type Sedigraph, and
．． Figure 9 shows the particle size distribution of the slurry before drying.
Figures 6, 8, and 10 show the particle size distribution of the slurry after drying, in which the solid line is for the method of the present invention, and the dotted line is for the conventional method. that's all

Claims (1)

[Claims] 1. Peroxide, carbonate,
For each of inorganic acids, organic acids, and various gases, one or more types of substances that are soluble in water at room temperature and normal pressure and can generate gas by decomposition or reaction at 100°C or less are combined to produce 1 mol of suspended particles. 0.0001~0.1m per
ol at any temperature under normal pressure or pressure,
A method for drying a high-concentration aqueous dispersion of fine particles, which is characterized by evaporating water and drying the dispersion while generating fine bubbles in the system by heating, reducing pressure, or both. 2 Drying by evaporating moisture while mixing air bubbles of 10 to 70% by volume (calculated at room temperature and normal pressure) at a desired temperature and under normal pressure or pressure using a bubble generating nozzle or the like in a highly concentrated aqueous dispersion system of fine particles. A method for drying a highly concentrated aqueous dispersion of fine particles, characterized by: 3. The suspended particles in the highly concentrated aqueous dispersion system of fine particles are particles whose base material is obtained by grinding or pulverizing naturally occurring or synthetic inorganic substances using water as a medium, and the particle size of the dry product is BET. The method for drying a high-concentration aqueous dispersion of fine particles according to claim 1 or 2, which comprises particles having a specific surface area of 5 m^2/g or more and water, and has a solid content concentration of 30% by weight or more.