JP2516473B2 - Method for modifying acidic sodium metaphosphate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to powdery sodium acid metaphosphate having a very high hygroscopicity and a high P ₂ O ₅ content, which is modified and granulated with water, whereby High to improve hygroscopicity and powder flowability
The present invention relates to a method for modifying powdered sodium acid metaphosphate having a P ₂ O ₅ content.

[Prior Art] Sodium metaphosphate is a generic term for condensed phosphates obtained by melting equimolar reaction products of caustic soda of phosphoric acid or sodium carbonate at high temperature and dehydrating and condensing, and in terms of molecular structure, It is not a single substance, but a mixture of neutral condensed phosphates having a cyclic structure or a long chain structure.

On the other hand, sodium acid metaphosphate is a polymer acidic condensed phosphate mixture obtained by melting phosphoric acid and an alkali less than the equimolar amount and a reaction product, and dehydration-condensed, and a molar ratio of raw materials, Depending on the production conditions such as reaction temperature, different compositions can be obtained, but in terms of molecular structure, cyclic compounds,
In addition to the chain-like structure, it has a remarkable feature in that it contains a network-like structure not found in neutral metaphosphate.

It is well known that sodium metaphosphate has an excellent metal ion sequestering ability, and is widely used in cleaning agents, water treatment agents, food industry, dyeing industry and the like.

On the other hand, acidic metaphosphate has a usefulness not found in metaphosphate because it exhibits a stable pH buffering action and unique properties as an acidic powder in addition to the same sequestering action. are doing.

In addition, since sodium acid metaphosphate has a large number of highly reactive hydroxyl groups and active sites in the molecule, the metal ion concealing action and pH buffering action are exhibited not only in the aqueous solution but also in the powder mixture. To do. And, the powdery sodium acid metaphosphate mixed in the powder product is caused by the decomposition and alteration of the powder product itself and the change of pH induced by the trace amount of metal components contained as impurities in the powder product. The deterioration of the quality can be effectively prevented, and therefore, the powdered sodium acid metaphosphate is a very useful substance for stabilizing the powder mixture.

[Problems to be Solved by the Invention] However, on the other hand, sodium acid metaphosphate, as described above, has a large number of highly reactive hydroxyl groups and active sites in its molecule, and therefore is handled due to its reactivity. The above problems are inevitable.

That is, sodium acid metaphosphate has strong hygroscopicity,
Due to moisture absorption, the powder becomes viscous and loses fluidity, making it difficult to maintain good use characteristics as a powder, which is a major drawback.

By the way, Na ₂ O / P among acidic sodium metaphosphate
_The smaller the ₂ O ₅ molar ratio, and thus the higher the P ₂ O ₅ content, the higher the hygroscopicity, and the above-mentioned drawbacks are more prominent.
That is, powdery sodium acid metaphosphate having a high P ₂ O ₅ content (72 to 77% P ₂ O ₅ content) has an extremely high hygroscopic property, and as a result, as described above, good use as a powder. It has a drawback that the characteristics cannot be maintained.

Further, even when this powdery sodium acid metaphosphate having a high P ₂ O ₅ content is produced and immediately sealed and stored in a moisture resistant packaging material, it is inevitable that it rapidly absorbs moisture and becomes sticky when it is opened. This is considered to be due to the highly hydrophilic hydroxyl group and the network structure unique to this sodium acid metaphosphate, and especially the phosphorus atom located at the branch point of the network structure is structurally unstable, and it is easy to It is conceivable that the reaction causes a cleavage due to hydrolysis, the content rate of the hydrophilic component increases, and thereby the moistening occurs.

Generally, powdery sodium acid metaphosphate is produced as a glassy substance by a melting reaction, and then powdered through a crushing step.The water taken from the working environment in the crushing step causes a chain hygroscopic reaction. Tends to accelerate.
Then, the powdery sodium acid metaphosphate forms a viscous candy-like surface with an increase in the amount of moisture absorption, and binds to each other to form a sticky lump. As a result, the fluidity of the powder is rapidly lost and a large amount adheres to the container wall, etc.
This will cause a significant hindrance to handling, such as difficulty in uniform powder mixing. Furthermore, the formation of sticky agglomerates hinders the dispersion of the particles in the solution, resulting in a reduction of the dissolution surface area, which significantly reduces the dissolution rate, which is a major obstacle during dissolution use. In particular, it is remarkable in the case of powdered sodium acid metaphosphate having a high P ₂ O ₅ content (72 to 77% P ₂ O ₅ content).

The disadvantage of this powdery sodium acid metaphosphate having a high P ₂ O ₅ content is that it is the opposite of its characteristics, so that the hygroscopicity is suppressed, and the acidic metallophosphate that maintains good powder fluidity is maintained. The emergence of sodium acidate is strongly desired today.

Therefore, the present invention has a problem that the high P ₂ O ₅ content suppresses the hygroscopic reactivity on the particle surface of the powdery sodium acid metaphosphate to improve the fluidity characteristics, and solves the dissolution disorder. An object of the present invention is to provide a method for modifying powdery sodium acid metaphosphate having a high P ₂ O ₅ content, which meets the demand.

[Means for Solving the Problems] By the way, prior to the present invention, the present inventors have performed interparticle bonding of powdered ortho, meta, and pyrophosphate alkaline salts without using a binder other than water. A method for preventing the ramping phenomenon peculiar to the alkali phosphates by using granules has been proposed (see JP-A-60-36314).

Specifically, the above-mentioned alkali phosphates are bonded to each other by a dry granulation method, a stirring granulation method or a fluidized granulation method without using a binder other than water, and an average particle diameter of about 150 μm. This is a ramping phenomenon peculiar to alkaline salts of phosphoric acid. When using powdered alkaline salts of phosphoric acid dissolved in water, the powders form a unity substance in water and prevent dissolution. The effect of preventing the phenomenon) occurs.

Further, prior to the present invention, the present inventors have also proposed that the phosphoric acid alkali salt to be blended with the amorphous refractory is made into a granular form (see JP-A-62-119171).

This is because alkaline phosphates are usually used in powder form, but due to moisture absorption, the particle surface becomes sticky or forms aggregates, making it difficult to uniformly disperse in the refractory and hindering the kneading work. In order to prevent this, the alkaline salt of phosphoric acid is made into a granular form. And, as this granule means, after spraying water while stirring the fine powder particles to granulate, a method of heating and stirring to remove added water to obtain a granule and stirring the raw material fine powder particles in an air stream While
A fluidized granulation method in which water is sprayed for granulation is proposed.

The present inventors have found that among these alkaline phosphates, sodium acid metaphosphate, in particular, as described above, has a very high hygroscopicity and a high P ₂ O ₅ content (72-
Focusing on powdered sodium acid metaphosphate (77% P ₂ O ₅ content), further research was conducted on means for suppressing the moisture absorption reactivity on the particle surface to improve the flow characteristics and to eliminate dissolution obstacles. As a result, the present invention has been completed.

If specifically this, the present inventors have powdered acidic sodium metaphosphate of the high P ₂ O ₅ content, granulated under certain conditions,蒿密of 0.5 to 1.0 g / cc granular and By doing
Powdered sodium acid metaphosphate having a high P ₂ O ₅ content, which is obtained by modifying these sodium acid metaphosphate particles, has low hygroscopicity, and has excellent characteristics not found in conventional products in terms of both fluidity and solubility. The present invention has been completed by finding that the above can be obtained.

That is, the present invention, powdered sodium acid metaphosphate having a P ₂ O ₅ content of 72 to 77%, using a fluidizing gas having a water content of 20 g / m ³ or less, is 2 to 15% by weight with respect to the raw material powder as a binder. % Water is used to granulate by the fluidized granulation method, and the density of the persimmon is 0.5 to
This is a method for modifying powdery sodium acid metaphosphate having a high P ₂ O ₅ content, which is characterized in that it has a granular form of 1.0 g / cc.

 The present invention will be described in detail below.

In the present invention, the powdered acidic sodium metaphosphate of high P ₂ O ₅ content, and phosphoric acid, the temperature of the reaction product 400 to 750 ° C. of less sodium hydroxide or sodium carbonate than equimolar with respect to phosphoric acid in melted, the glass-like substance obtained by dehydration condensation is obtained by powdering, product Na ₂ O
/ P ₂ O ₅ in molar ratio of less than 1 P ₂ O ₅ content of 72 to 77% (w /
w), powder with a density of about 1.20 g / cc.

Such powdery sodium acid metaphosphate having a high P ₂ O ₅ content, as described above, exhibits extremely strong hygroscopic reactivity, becomes rapidly sticky due to moisture in the air, and has a physical property that the fluidity as a powder is lowered. It has a physical property.

However, according to the present invention, it is possible to modify the particle surface of the powdery sodium acid metaphosphate having a high P ₂ O ₅ content and to obtain a more stable powder product.

Various methods have been conventionally known as a method for granulating powder, but according to the study of the present inventors, modification by granulation of powdery sodium acid metaphosphate is described in detail below. Thus, it is possible only by the fluidized granulation method under specific conditions.

In the present invention, as the granulation means, a known fluidized granulator is used, and while fluidizing the powdery sodium acid metaphosphate by fluidizing gas, granules are formed using a binder and dried. Granulation is carried out by a general process of taking out the powder.

However, the present invention is particularly suitable as a fluidizing gas for high P ₂ O ₅
A gas inert to the content of powdered sodium acid metaphosphate, such as air, nitrogen, carbon dioxide, etc.,
In addition, it is an essential requirement that the water content in the fluidizing gas be 20 g / m ³ or less (preferably 10 g / m ³ or less). The water content is
When it is higher than 20 g / m ^3, the fluidization of the raw material powder in the apparatus becomes incomplete, and a sufficient reforming effect cannot be obtained.

Further, the present invention makes it essential to use water as a binder for forming granules and to add this water. This water reacts not only as a binder but with the raw material powder of sodium metametaphosphate particles having a high P ₂ O ₅ content,
It acts as a modifier that modifies the surface structure. The amount of water used varies slightly depending on the particle size distribution of the raw material powder and the particle size of the target granules, but in the present invention, it is 2 to 15% (w / w), preferably 3 to 10% (w
/ w). The reason for this is that if it is less than 2% (w / w), the stabilization of the surface will be incomplete, the particles will not bond sufficiently, and stable granule formation will not be achieved.
On the other hand, if it exceeds 15% (w / w), coarse lumps are formed, which causes flow problems.

Further, in the present invention, the operating temperature of the granulating device is 40 to 80.
C. is preferred. At 40 ° C or lower, granule formation and surface modification become insufficient, while at 80 ° C or higher, sodium acid metaphosphate decomposes and deteriorates to make the particle surface sticky, and also coarse aggregates are formed. Neither of them can form granules due to flow obstruction.

Part of the water evaporates in the drying process, and the rest contributes to the modified binding on the surface of the particles and remains as a constituent of the granules.

The bulk density of the granules thus obtained varies depending on the particle size distribution of the raw material powder and the granules, and also changes depending on the granulation conditions, but the hygroscopicity is extremely high and the high P ₂ O ₅ content is powdery acidic metaphosphoric acid. With sodium, it is essentially difficult to finely pulverize, and therefore, the particle size of the raw material powder is limited by itself, so in the present invention, the bulk density is 0.5 g / cc.
It is difficult to produce the following granules. However, granules having a bulk density of 1.0 g / cc or more do not sufficiently improve the flow characteristics. Therefore, in the present invention, the bulk density of the granules exhibiting a good modifying effect is in the range of 0.5 to 1.0 g / cc, and this range of bulk density is also an essential requirement of the present invention.

The present invention can also use a dilute aqueous solution containing some solute as the modified binder. Granulation with such a dilute aqueous solution is also within the scope of the present invention as long as the solute does not impair the properties of powdered sodium acid metaphosphate having a high P ₂ O ₅ content, and it is appropriately used as necessary. be able to. Various types of solutes are conceivable depending on the use of powdered sodium acid metaphosphate having a high P ₂ O ₅ content, and for example, for food additives, salt and sodium glutamate can be mentioned. .

The granules obtained by the present invention have lower hygroscopicity than the raw material powder, and in particular, the effect of improving the powder fluidity is remarkable, so that the handling troubles of conventional products can be greatly reduced. . When powders are mixed, uniform and quick work is possible, and good dispersibility in water even when dissolved,
No sticky lumps formed. It is considered that this is because the particle surface of the raw material powder is partly modified by the water used as the binder to change to a surface structure stable to water.

Further, the hygroscopicity of the granules obtained by the present invention is obviously lower than that of the raw material powder, and the improving effect is recognized, but the fluidity improving effect is more remarkable. This indicates that the improvement in fluidity according to the present invention is due to not only the decrease in hygroscopicity associated with the formation of granules but also the decrease in the amount of sticky substances produced by the reaction between water and the active sites on the surface of the particles. ing.

The molecular structure of powdered sodium acid metaphosphate with a high P ₂ O ₅ content is characterized by a complex network structure including unstable active sites and the presence of hydrophilic hydroxyl groups bonded to phosphorus atoms. As described above, in the present invention,
Spraying water acts on the active sites on the surface of the powdery sodium acid metaphosphate particles with high P ₂ O ₅ content flowing in the fluidized granulator to stabilize unstable phosphorus atoms and at the same time to improve the molecular structure. It is reorganized, and the surface layer changes to phosphate having a structure that is relatively stable to water, and the reactivity to water decreases.
As a result, on the surface of the granule, no rapid formation of an adhesive substance as seen in powder particles is observed, and the fluidity is improved in combination with the void effect of the granule.

Therefore, the granules obtained according to the present invention are not a mere water-mediated interparticle bond, but are produced by a bond involving a surface modification reaction.

In the present invention, such a modification reaction occurs only in the surface layer of the powdery sodium acid metaphosphate particles having a high P ₂ O ₅ content, and inside the granules, the original properties are maintained and the usefulness is improved. The effect is that the powder fluidity and solubility can be improved without damage.

[Examples] Examples of the present invention will be described below to describe the present invention in more detail.

Example 1. Na ₂ O / P ₂ O ₅ molar ratio 0.52, P ₂ O ₅ content 75.3%, bulk density 1.2
10 g of acidic sodium metaphosphate of 3 g / cc was granulated by a fluidized bed granulation coating device (manufactured by Freund Sangyo Co., Ltd.). A water content of 10 g / m ³ air was used as the fluidizing gas, 850 ml of bound water was used, and the gas temperature at the outlet was adjusted to 50 ° C. The hygroscopicity, fluidity, solubility and bulk density of the obtained granules were measured and are shown in Table 1.

Example 2. Na ₂ O / P ₂ O ₅ molar ratio 0.71, P ₂ O ₅ content 72.3%, bulk density 1.2
Using 10 kg of 1 g / cc of sodium acid metaphosphate, the mixture was granulated in the same manner as in Example 1 under the conditions of 500 ml of bound water and 55 ° C. of outlet gas temperature while fluidizing with air having a water content of 8 g / m ³ . The results of measuring hygroscopicity, fluidity, solubility and bulk density of the obtained granules are also shown in Table 1.

Example 3.Na ₂ O / P ₂ O ₅ molar ratio 0.41, P ₂ O ₅ content 76.8%, bulk density 1.23 g
Granules were granulated in the same manner as in Example 1 under the conditions of 800 ml of bound water and an outlet temperature of 50 ° C. while fluidizing with air having a water content of 10 g / m ³ , using 10 kg of sodium acid metaphosphate of / cc. The hygroscopicity, fluidity, solubility and bulk density of the obtained granules were measured and are also shown in Table 1.

Examples 4 to 6 Granules were granulated in the same manner as in Example 1 except that 10 kg of sodium acid metaphosphate of Example 1 was used, the water content of the fluidizing gas and the amount of bound water used were changed. The fluidity, solubility and bulk density of the obtained granules were measured and are also shown in Table 1.

Comparative Examples 1 to 3 Hygroscopicity, fluidity and solubility of sodium acid metaphosphate, which is a raw material powder used in Examples 1, 2 and 3, were measured, and Comparative Examples 1, 2 and 3 are also shown in Table 1. Show.

Comparative Example 4 Granulation was carried out in the same manner as in Example 1 except that 10 kg of sodium acid metaphosphate of Example 1 was used, a water content of 22 g / m ³ was used, and 1000 ml of bound water was used. The hygroscopicity, fluidity, solubility and bulk density of the obtained granules were measured and are also shown in Table 1.

Comparative Example 5 Granulation was carried out in the same manner as in Example 1 except that 10 kg of sodium acid metaphosphate of Example 1 was used, a water content of 25 g / m ³ air was used, and 500 ml of bound water was used. The hygroscopicity, fluidity, solubility and bulk density of the obtained granules were measured and are also shown in Table 1.

Comparative Example 6 Using 10 kg of the powdered sodium acid metaphosphate of Example 3, 100 m of bound water while fluidizing with air having a water content of 10 g / m ^3.
Granulation was carried out in the same manner as in Example 1 under conditions of an outlet temperature of 50 ° C.
The fluidity, solubility and bulk density of the obtained granules were measured and are also shown in Table 1.

Comparative Example 7 Using 10 kg of the powdered sodium acid metaphosphate of Example 3, 180 g of bound water was obtained while fluidizing with air having a water content of 10 kg / m ³ .
Granulation was performed under the conditions of 0 ml and an outlet temperature of 55 ° C. However, it was difficult to maintain the fluid state because the powder particles were excessively bound and coarsened in the apparatus, and the desired granules could not be formed.

The "hygroscopicity", "fluidity", "solubility" and "bulk density" in Table 1 are as follows.

[Hygroscopicity] 5 g of the sample immediately after preparation is placed in an open container having an inner diameter of 55 mm and a height of 30 mm, and left standing at 20 ° C. and 100% RH for 3 hours. It is difficult to obtain an accurate measurement value in powdery acidic sodium metaphosphate having a high P ₂ O ₅ content because the surface layer portion becomes sticky due to moisture absorption to prevent the diffusion of water into the inside. (The indicated numerical value is a reference value.) [Fluidity] The fluidity of a sample that had been left for 30 minutes at 20 ° C and 100% RH after preparation was measured. Several kinds of hourglass-shaped glass funnels with an outflow hole diameter of 10 to 18 m / m were prepared and the outflow state of the sample was observed. Pore diameter 10
Those that passed m / m were rated as good, those that did not pass 18 m / m were rated as bad, and those in the middle were rated as good.

[Solubility] 20 g of the sample was put into 200 ml of water at 25 ° C., allowed to stand for 1 minute, stirred with a magnetic stirrer, and the time until complete dissolution was measured.

[Bulk Density] Sample 10 using a specific volume sampler manufactured by Ishiyama Scientific Instruments
It was measured under the conditions of g, drop 4.5 cm, and number of drops 200.

As is clear from Table 1, (1) The water content of the gas (water content in the fluidized gas) is 20 g /
and m ³ or less, (2) bound water (amount of water added as a binding agent) 2-15
It can be understood that the hygroscopicity, the fluidity and the solubility are improved for the first time by setting the weight percentage to (3) and the bulk density to 0.5 to 1.0 g / cc.

That is, in Examples 1 to 6 which are within the above-mentioned condition ranges (1) to (3) specified in the present invention, the hygroscopicity, the fluidity and the solubility are all improved as compared with those outside the condition range. It is clear that

If this is described in detail, it can be understood that the improvement with respect to the raw material powder is remarkable by comparing Examples 1 to 3 with Comparative Examples 1 to 3. Further, in Comparative Examples 4 and 5 (gas moisture 22 g / m ³ and 25 g / m ³ ) where only the condition (1) is not satisfied, the fluidity is “poor”, the solubility is not improved, and the condition ( Comparative Examples 6 and 7 (100 ml and 1800 ml of combined water, which satisfy the conditions 1) and 3) but are out of the range of the condition (2),
It can be understood that the same applies to the case of 1% by weight and 18% by weight with respect to the raw material powder.

[Effects of the Invention] Powdered sodium acid metaphosphate having a high P ₂ O ₅ content has a drawback that it has a strong hygroscopic property, and thus the surface of the particles becomes sticky and adhered lumps are formed to quickly lose fluidity. However, according to the present invention, as described above in detail, the sodium acid metaphosphate does not lose its original characteristics, has a low hygroscopic property, and is a powder. It is possible to obtain a modified product having good flowability and solubility as a result, and as a result, it becomes easy to handle the powdery sodium acid metaphosphate having a high P ₂ O ₅ content, and the trouble in use is significantly reduced. As a result, the usefulness is improved.

Claims (1)

(57) [Claims] 1. A powdered sodium acid metaphosphate having a P ₂ O ₅ content of 72 to 77% and a fluidizing gas having a water content of 20 g / m ³ or less and 2 to 15% by weight of the raw material powder as a binder. Granulated by the fluidized granulation method using the water of the
A method for modifying powdery sodium acid metaphosphate having a high P ₂ O ₅ content, characterized in that