JPH0664981A - Method for removing sodium from expandable porous ceramic form - Google Patents

Abstract

PURPOSE:To provide a method improved in removing efficiency and shortened in treatment time, so designed that, in the first leaching process, a specified proportion of an organic solvent is added to washing water to help penetrate the washing water into the ceramic form followed by raising temperature using a 1% washing aqueous solution of ammonium chloride. CONSTITUTION:Firstly, and expandable porous ceramic form is produced by casting in a mold a mixture of aluminate slurry and silicate slurry. The silicate slurry comprises sodium silicate, fine ceramic powder, ceramic fibers, silica fume, surfactant, aluminum powder and ion-exchanged water; while, the aluminate slurry comprises sodium aluminate, fine ceramic powder, ceramic fibers, ion-exchanged water, etc. In the first leaching process for the above ceramic form, 5-50wt.% of an organic solvent is added to the ion-exchanged water; and in the second leaching process, a 1% washing aqueous solution of ammonium chloride is used; in this case, the temperature is raised from room temperature up to 80 deg.C to further improve the leaching efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a sodium component from a foamed porous ceramics compact, and more particularly to a cleaning method for rapidly and efficiently removing a sodium component in a leaching process.

[0002]

2. Description of the Related Art A method for producing a foamable porous ceramic called "celcoform" is usually carried out by the procedure shown in FIG. Cercoform is characterized in that aggregates such as ceramic fine powder and ceramic fibers and a surfactant are added to the respective slurries of sodium silicate and sodium aluminate, and both slurries are mixed, stirred and cast. During casting, aluminum powder was added to the silicate slurry, and foaming by hydrogen gas generated from the reaction between sodium hydroxide and aluminum powder produced when the two slurries were mixed, and gel of silicate slurry and aluminate slurry The foaming type porous ceramics compact is formed by simultaneous solidification by the chemical reaction.

However, since a large amount of sodium is contained in the starting materials sodium silicate and sodium aluminate, if the molded body is baked as it is, the molded body becomes vitrified due to the presence of sodium. Therefore, it is necessary to remove sodium from the molded body.
This process is called a leaching process.

The leaching process is a first-stage leaching process for removing free sodium hydroxide remaining in the molded body with washing water, and Na ₂ O.Al ₂ O ₃ .2SiO contained in the gel.
_It consists of a second-stage leaching process in which sodium is removed by ion exchange with ₂ to 1% ammonium chloride washing water (Tokuhyo 2-502374).

This method usually takes about 3 days,
There is a problem that the required time is long. Further, when the time of the leaching step is shortened, the amount of remaining sodium component increases, and the heat resistance sharply decreases.

Therefore, an object of the present invention is to provide a method for removing sodium from a foaming type porous ceramics molded body which solves the above conventional problems.

[0007]

As a result of earnest research in view of the above object, the present inventor has found that the surface tension of the washing water is reduced by adding an organic solvent to the washing water in the first-stage leaching step. Since it is easy for wash water to penetrate into the body, sodium hydroxide can be removed efficiently.
Increasing the temperature of the wash water increases the diffusion rate of the wash water in the molded body, so that sodium can be removed more efficiently, and in the second stage leaching step,
The present invention was completed by discovering that by increasing the temperature of 1% ammonium chloride washing water, the diffusion rate of the washing water in the molded body is increased and the sodium removal rate is increased.

That is, the method for removing sodium in the leaching step of the foamed porous ceramics molded article of the present invention is the first leaching step of removing the sodium hydroxide remaining in the molded article, which is ion-exchanged water. The leaching efficiency is increased by adding 5 to 50% by weight of an organic solvent to the wash water. In addition, in the first-stage leaching step of the foamed porous ceramics molded body, the temperature of the washing water, which is ion-exchanged water, is kept at room temperature or above
It is preferable to raise the temperature to 0 ° C. or lower to increase the leaching efficiency. Further, in the second stage leaching step of the foamed porous ceramics molded body, it is preferable to raise the temperature of the 1% ammonium chloride washing water to a temperature of room temperature or higher and 80 ° C. or lower to enhance the leaching efficiency.

[0009]

The method of the present invention will be described in detail below.

(1) Foamed Porous Ceramics Molded Body (Celcoform) Silicate slurry containing sodium silicate, ceramic fine powder, ceramic fiber, silica fume, surfactant and aluminum powder as main components, sodium aluminate, ceramic By mixing fine powder, ceramic fiber, and an aluminate slurry containing a surfactant as a main component and casting in a mold, foaming and gelation occur at the same time, and a foaming type porous ceramics molded body is formed. The molded body, free sodium hydroxide in the foaming reaction was largely remained, and the gel moiety of the molded body is constituted by _{Na 2 O · Al 2 O 3} · 2SiO 2. As described above, the molded body contains a large amount of sodium.

(2) Leaching process The leaching process is a first-stage leaching process for removing free sodium hydroxide remaining in the molded body with washing water, and Na ₂ O.Al ₂ O ₃ contained in the gel.・ 1% from 2SiO ₂
It preferably comprises a second stage leaching step of removing sodium by ion exchange with ammonium chloride wash water. The conventional leaching process requires 72 hours, which is a bottleneck in manufacturing. Therefore, in order to improve productivity, it is necessary to significantly reduce the time required for the leaching process.

The first stage leaching step is a process in which sodium hydroxide in the molded body is dissolved in the washing water which is ion-exchanged water and moves out of the molded body. Kinetically, either the dissolution of sodium hydroxide in the wash water or the diffusion of the dissolved sodium hydroxide out of the molded body becomes the rate-determining factor, and determines the removal rate of sodium.

[0013] In the second stage leaching process is a gel component in the compact Na ₂ of _{O · Al 2 O 3 · 2SiO} 2 Na + and 1% NH ₄ of Cl wash water NH ₄ ⁺ ion exchange process ,
Either the diffusion process of Na ⁺ after the ion exchange to the outside of the molded body becomes the rate-determining process, and the removal rate of sodium is determined.

(3) Determination of rate-determining process FIG. 3 shows the relationship between the leaching time in the first stage leaching step and the sodium content in the compact. The arrow in the figure indicates the time when the wash water is newly replaced. As the result of FIG. 3 shows, the sodium content in the molded product showed a smooth parabolic decrease tendency. If the dissolution of sodium hydroxide in the wash water is rate-determining, the sodium content in the molded body should show a rapid decrease as shown in the schematic diagram of FIG. 4 every time the wash water is replaced. . Therefore, the result of FIG. 3 shows that the rate-determining process is diffusion of dissolved sodium hydroxide out of the molded body.

FIG. 5 shows the relationship between the leaching time in the second stage leaching process and the sodium content in the compact. The arrow in the figure indicates the time when the 1% ammonium chloride washing water was replaced. The sodium content in the compacts also showed a smooth parabolic decreasing trend, indicating that the rate-determining process was diffusion of Na ^{+ out} of the compacts. In order to make the leaching process efficient, it is necessary to increase the diffusion rate of the wash water in the molded body.

(4) Inference based on diffusion kinetics Diffusion generally follows Fick's law.

J = -D∂C / ∂x D = D ₀ exp (-ΔG / (RT)) J: Amount of substance passing per unit time per unit area D: Diffusion coefficient ∂C / ∂x: Concentration gradient D ₀ : Constant term ΔG: Activation energy in diffusion ─ T: Absolute temperature R: Avogadro's number

Letting the diffusion amount per unit time be Q: Q = JA where A is the contact surface area. From the above three equations, the diffusion amount per unit time is Q = −AD ₀ exp (−ΔG / (RT)). There are four possible ways to increase the diffusion rate per unit time from this equation.

(4a) A method of increasing the contact area (A). That is, the contact area between the sodium hydroxide solution and the washing water in the compact is increased. However, this method is outside the scope of the present invention. (4b) A method of reducing the activation energy (ΔG).
It means lowering the activation energy in the rate-determining process that determines the diffusion rate. (4c) A method of increasing the temperature (T). (4d) A method of increasing ∂C / ∂x. This is given by the concentration difference between the sodium concentration in the molded body and the sodium concentration in the wash water, but the sodium concentration in the molded body is constant, and the increase in the sodium concentration in the wash water means that the wash water is It doesn't grow so big because it is overwhelmingly large. Therefore, the ∂C / ∂x term has little influence on the diffusion rate.

According to the above examination, sodium hydroxide or
In order to increase the diffusion rate of the wash water containing Na ⁺ , it is considered effective to lower the potential of the obstacles to diffusion and to raise the temperature of the wash water itself.

(5) Addition of organic solvent in the first-stage leaching process Since the rate-determining process in the first-stage leaching process is diffusion of wash water in which sodium hydroxide is dissolved in the molded body,
As a method for reducing the transfer resistance of the wash water in the molded body, there is a reduction in the surface tension of the wash water by adding an organic solvent. As shown in FIG. 6, when ethanol was added as an organic solvent to the washing water, the surface tension was drastically reduced. As a result, the wash water easily passes through the molded body, and the diffusion speed increases. Ethanol, acetone, isopropyl alcohol and the like are preferable as the organic solvent. As is clear from FIG. 6, when the addition amount of the organic solvent is 5% by weight or less, the reduction amount of the surface tension is not sufficient, and when it is 50% by weight or more, the further reduction of the surface tension cannot be expected. The amount is preferably 5 to 50% by weight.

(6) Temperature control in the first-stage leaching process When the temperature of the wash water is increased, the diffusion coefficient of the wash water is increased and the diffusion rate of the wash water in which sodium hydroxide is dissolved can be increased. Since the temperature of the washing water needs to be lower than the boiling point of the washing water, it is preferably 100 ° C. or lower. Regarding the time of the first stage leaching step, since the diffusion of the washing water is a rate-determining process as shown in FIG. 3, the sodium concentration in the molded body shows a parabolic decreasing tendency, and when the time exceeds a certain time, The rate of decrease of sodium concentration becomes extremely small. Therefore, the time of the first stage leaching step is 30 hours or less.

[0023] (7) a second stage leaching temperature control the second stage in the process the leaching step is 1% in the green body with ammonium chloride washing water Na ₂ O · Al ₂ O ₃ of · 2SiO ₂ Na ⁺ and NH ₄
^Since it is a process of ion exchange with ⁺ , the method of adding the organic solvent used in the first leaching step is NH
_This is not suitable because it causes ions other than ₄ ⁺ to coexist. Inclusion of Na ⁺ by raising the temperature of wash water 1
An effective method is to increase the diffusion coefficient of the ammonium chloride solution. The washing water temperature is preferably 100 ° C. or lower. The upper limit of the second stage leaching process is 30 hours.

(8) Allowable range of sodium concentration in the molded body FIG. 2 shows the sodium concentration contained in the fired body and 1250.
The relationship with the shrinkage rate of the sintered body under the condition of ° C x 24 hours is shown. When the residual sodium concentration is 0.2% or more, shrinkage of the sintered body occurs. That is, when a fired body containing a residual sodium concentration of 0.2% or more is used at a temperature of about 1250 ° C., dimensional shrinkage occurs and a shape change occurs. Therefore, the sodium concentration must be less than 0.2% by weight to ensure long-term durability.

[0025]

The present invention will be described in more detail by the following examples.

Example 1 With the composition shown in Table 1 below, a silicate slurry and an aluminate slurry were mixed, respectively, put into a separate plastic pot together with 15 alumina balls (diameter 2 cm), and ball-milled for 14 hours. .

Table 1 Silicate aluminate raw material slurry (g ) Slurry (g) Sodium silicate 280-Sodium aluminate-400 Ion-exchanged water 193.4 73.4 Aluminosilicate fiber 13.3 13.3 Silica fume 20 20 Cordierite 373.6 373.3 Kyanite 414.7 413.6 Total 1295.0 1294.0

After the completion of mixing, in the silicate slurry,
2.6 g (0.2% by weight) of surfactant and 1.9 g (0.15% by weight) of aluminum powder were added and kneaded with a spoon.
On the other hand, 2.6 g (0.2 wt%) in aluminate slurry
The surfactant of was added and kneaded with a spoon. Weigh each slurry so that the weight ratio of aluminate slurry / silicate slurry is 1.2, and after mixing and stirring,
It was poured into a 60 mm × 50 mm plastic mold to form a foam-controlled porous ceramic, which was used as a leaching sample.

To demonstrate the effectiveness of the organic solvent in the first stage leaching process, 15 liters of deionized water and 15
A liter of organic solvent (acetone, isopropyl alcohol, ethanol) was placed in a tank and mixed to obtain washing water. The molded body was placed in this washing water and left for 30 hours. At this time, stirring was performed with a stirrer in order to make the washing water uniform. After leaching, samples were taken from the surface and the inside of the molded body, and the sodium was quantitatively analyzed by the atomic absorption method. The results are shown in Table 2.

Table 2 Composition of Washing Water Inside Molded Body on Surface of Molded Body Sodium (wt%) Sodium (wt%) Ion-exchanged water 2.55 2.75 50% Acetone 2.28 2.17 50% Ethanol 2.17 2.10 50% Isopropyl alcohol 2.60 2.24

As shown in Table 2, the residual concentration of sodium was lowered by adding the organic solvent to the ion-exchanged water. This is because the surface tension of the cleaning water was lowered, so that the cleaning water easily penetrated into the molded body.

Example 2 In order to demonstrate the effect of the wash water temperature in the first-stage leaching process, the leaching molded body sample prepared in Example 1 was used, and the ion-exchanged water was used as the wash water. Was changed and leaching was performed. Table 3 shows the sodium concentration in the molded product after leaching for 30 hours.

Table 3 Temperature of ion-exchanged water inside molded product on surface of molded product Sodium (wt%) Sodium (wt%) 20 ℃ 2.55 2.75 30 ℃ 2.25 2.65 60 ℃ 1.13 2.00 80 ℃ 1.10 1.95

As shown in Table 3, increasing the temperature of ion-exchanged water greatly improved the leaching efficiency. However, since the surface tension is large, the permeability into the molded body is poor, and as a result, the sodium concentration is high inside the molded body. Therefore, the efficiency of the first stage leaching step can be greatly increased by adding the organic solvent to the wash water and raising the temperature of the wash water.

Example 3 In order to demonstrate the effect of the temperature of the 1% ammonium chloride cleaning solution in the second stage leaching step, the washing water temperature was raised and leaching was performed for 30 hours, and then the sodium concentration in the molded body was measured. . Table 4 shows the relationship between the wash water temperature and the sodium concentration in the molded body.

Table 4 Temperature of cleaning water inside the molded product on the surface of 1% ammonium chloride molded product Sodium (wt%) Sodium (wt%) 20 ℃ 0.29 0.19 30 ℃ 0.25 0.18 60 ℃ 0.12 0.085 80 ℃ 0.10 0.070

As shown in Table 4, the residual sodium concentration was remarkably lowered by raising the temperature of the washing water, and when the washing water temperature was 80 ° C., the residual sodium concentration was within the allowable range.
Below 0.2% by weight, the effect of wash water temperature was demonstrated.

[0038]

As described in detail above, the method for removing sodium from a foamed porous ceramics molded article of the present invention exhibits excellent sodium removal efficiency and can shorten the treatment time, thereby increasing the efficiency of the leaching step. be able to.

[Brief description of drawings]

FIG. 1 is a flow chart showing a manufacturing process of a foaming type porous ceramics molded body (celcoform).

FIG. 2 is a graph showing a relationship between a sodium concentration in a fired body and a shrinkage rate when the fired body is held at 1250 ° C. for 24 hours.

FIG. 3 is a graph showing the relationship between the leaching time in the first stage leaching process and the sodium concentration in the molded body.

FIG. 4 is a schematic diagram showing the relationship between the leaching time and the sodium concentration in the molded body when the leaching process is dissolution-controlled.

FIG. 5 is a graph showing the relationship between the time in the second stage leaching process and the sodium concentration in the molded body.

FIG. 6 is a graph showing the relationship between the addition amount and the surface tension when ethanol is added to ion-exchanged water.

Claims (3)

[Claims] 1. Sodium silicate, ceramic fine powder,
Ceramic fiber, silica fume, surfactant,
Foam obtained by mixing silicate slurry consisting of aluminum powder and ion-exchanged water with aluminate slurry consisting of sodium aluminate, ceramic fine powder, ceramic fiber, surfactant and ion-exchanged water, and then casting in a mold In the leaching step of the porous porous ceramics molded body, in the first stage leaching step of removing the sodium hydroxide remaining in the molded body, 5 to 50% by weight of an organic solvent is added to the washing water which is ion-exchanged water. A method for removing sodium, characterized by increasing the leaching efficiency by 2. The method for removing sodium according to claim 1, wherein the temperature of the washing water, which is ion-exchanged water, is raised to a temperature of room temperature or higher and 80 ° C. or lower in the first stage leaching step to increase leaching efficiency. And sodium removal method. 3. The method for removing sodium according to claim 1, wherein 1% ammonium chloride washing water is used in the second stage leaching step, and the temperature is raised from room temperature to 80 ° C. to increase the leaching efficiency. Characteristic sodium removal method.