JP2526403B2 - Method for producing A-type zeolite - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing zeolite, particularly A-type zeolite, from fly ash as a raw material.

[0002]

Zeolite is a crystalline aluminosilicate in which SiO ₂ tetrahedron and AlO ₂ tetrahedron are bonded in a three-dimensional network, and by utilizing its compositional and structural characteristics, a molecular sieve, Widely used as an ion exchanger, detergent builder, desiccant, catalyst, etc. In this zeolite,
There are natural zeolites and synthetic zeolites, but there are many kinds of each due to the difference in composition and crystal structure. For example, as synthetic zeolites, P-type zeolite, A-type zeolite, ZK-4 type zeolite, NA
-Type zeolite, X-type zeolite, Y-type zeolite, L-type zeolite, ZMS-5 type zeolite, etc. are known and used properly according to the purpose of use.

This synthetic zeolite is produced by hydrothermal reaction using sodium aluminate, aluminum hydroxide or the like as an alumina source and silica gel, silica sol, powdery silica glass or the like as a silica source, respectively. Since the fly ash generated upon combustion of the above contains silica and alumina, many methods using this as a raw material have been developed.

[0004] for example, a particular relationship between the content of the γ-Al ₂ O ₃ and mullite in Al ₂ O _3, and fly the content of alkali metal oxides is within a specific range A method of hydrothermally reacting a mixed slurry of ash and an aqueous solution of sodium hydroxide (Japanese Patent Laid-Open No. 22114/1990), a method of adding silicate ions to a mixed slurry of fly ash and an aqueous solution of sodium hydroxide to carry out a hydrothermal reaction ( JP-A-2
No. 229709), high-concentration sodium hydroxide and non-quality Al ₂ O ₃ are added to fly ash, and the mixture is kneaded and granulated for curing (Japanese Patent Application Laid-Open No. 3-40915).

However, the zeolites obtained by these methods are mainly those of the filibsite type, and although a small amount of the A-type zeolite may be by-produced depending on the production conditions, the A-type zeolite is the main component. Cannot be obtained in high yield.

[0006] As described above, when the fly ash is used as a raw material, the A-type zeolite is not produced, because the reactivity of the fly ash to the sodium hydroxide aqueous solution is insufficient.

[0007]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of providing a method for obtaining a high-yield A-type zeolite, which is useful as a molecular sieve and a drying agent, from fly ash as a raw material.

[0008]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies in order to develop a method for improving the reactivity of fly ash with an aqueous sodium hydroxide solution to selectively produce A-type zeolite. As a result, when solid sodium hydroxide was added to fly ash and the mixture was heat-treated at a temperature of 90 to 180 ° C. for at least 60 minutes, it was found that the reactivity of the fly ash with the aqueous sodium hydroxide solution was significantly improved. The present invention has been completed based on the above.

Up to now, in order to improve the reactivity of fly ash, it has been mixed with solid sodium hydroxide at 200 ° C.
Since it was considered necessary to heat at the above-mentioned high temperature, that is, 300 to 400 ° C. for a long time, it is totally expected that heating at such a relatively low temperature would improve the reactivity with the sodium hydroxide aqueous solution. It was outside.

That is, according to the present invention, a mixture of fly ash and solid sodium hydroxide is added in an amount of 90-18.
A heat treatment was carried out at a temperature of 0 ° C. for at least 60 minutes, and then the treated product thus obtained was slurried by adding sodium hydroxide and water and hydrothermally treated to obtain A.
-Type zeolite can be produced in high yield.

As the fly ash used as the raw material of the present invention, it is possible to use, as it is, dust collected during combustion of coal, which is collected by a dust collector. This fly ash generally contains SiO ₂ and Al ₂ O ₃ as main components, and further contains CaO, Na ₂ O, K ₂ O, Fe and the like.

In the present invention, 15% by weight of Al ₂ O ₃ is used.
Above, fly ash containing 50% by weight or more of SiO ₂ ,
For example, Al ₂ O ₃ 15 to 25% by weight, SiO ₂ 50 to 75
% By weight, CaO 0.1 to 6.0% by weight, Na ₂ O 0.1
~ 4.5 wt%, K ₂ O 0.1-4.5 wt% and Fe ₂
O ₃ is preferred to use one having a composition of 0 to 4.5 wt%.

The mixing ratio of this fly ash and solid sodium hydroxide is selected in the range of 5: 1 to 1: 2, preferably 2: 1 to 2: 3 by weight. If the amount of solid sodium hydroxide is less than this, sufficient improvement in reactivity cannot be achieved, and if the amount of solid sodium hydroxide is more than this, the alkali content becomes excessive and hydrothermal The yield of A-type zeolite due to the reaction decreases.

The mixture of fly ash and solid sodium hydroxide in the present invention is heated at 90 to 180 ° C.
It is preferably carried out at a temperature of 100 to 150 ° C. for at least 60 minutes, preferably 5 to 20 hours. In this case, if a low temperature is used, it is necessary to lengthen the heating time, and if it is intended to shorten the heating time, it is necessary to use a high temperature. Although it is possible to use a temperature higher than 180 ° C. or a time longer than 20 hours, it consumes a large amount of heat energy, which is economically disadvantageous. 9
At a temperature lower than 0 ° C and a treatment time of less than 60 minutes, the reactivity is not sufficiently improved.

The treated product thus obtained is composed of a mixture mainly composed of sodium silicate, which is easily soluble in water, and is mixed with an aqueous solution of sodium hydroxide to form a slurry to produce a usual A-type zeolite. A type zeolite can be easily produced by hydrothermal treatment under the conditions.

In order to suitably carry out the hydrothermal treatment in the present invention, the above-mentioned treated product, sodium hydroxide, water and, if necessary, an aluminum compound such as sodium aluminate or aluminum hydroxide are added to SiO ₂ / Al ₂ O. ₃ molar ratio about 1, Na ₂ O / SiO ₂ molar ratio 1.5-4 and H ₂
The mixture is mixed so that the O / Na ₂ O molar ratio is 20 to 100, and this mixture is preferably in the presence of a seed crystal, for example, a ground slurry of type A zeolite, at a temperature in the range of 70 to 100 ° C. for 1 to 10 hours. About hydrothermal treatment. After that, the solid content is taken out from the hydrothermally treated product by a known means such as filtration, washed sufficiently with water, and dried to obtain the desired A-type zeolite.

[0017]

According to the conventional method, it was difficult to produce the A-type zeolite directly from the fly ash, but according to the method of the present invention, the fly ash and the solid sodium hydroxide are heated to react with each other. The type zeolite can be efficiently produced. In addition, since the above-mentioned treated product can be obtained at a relatively low temperature, it is possible to utilize the waste heat of a thermal power plant, which is economically advantageous.

[0018]

Next, the present invention will be described in more detail with reference to examples. In addition, as the fly ash, SiO ₂ 5
9.13% by weight, Al ₂ O ₃ 18.03% by weight, Fe ₂
O ₃ 7.27% by weight, CaO 5.92% by weight, Na ₂
O 3.04% by weight, K ₂ O 1.98% by weight, SO ³
0.86% by weight and ignition loss 3.77% by weight
I used the one.

Example 5g of fly ash obtained by burning coal was mixed with 7g of solid sodium hydroxide, and the mixture was heated to 90 ° C.
It heat-processed at 100 degreeC, 110 degreeC, 120 degreeC, and 130 degreeC for 20 hours. The reaction rate in this case was determined and is shown in Table 1. The reaction rate was obtained from the dissolution rate when the treated product was treated with a heated hydrochloric acid solution.

[0020]

[Table 1]

As can be seen from Table 1, the higher the treatment temperature, the higher the reaction rate.

Next, 5 g of the fly ash and 7 g of solid sodium hydroxide were mixed, and this mixture was heated at 120 ° C.
Then, heat treatment was performed for 2 hours, 5 hours, 10 hours, and 20 hours, and the reaction rate was determined in the same manner as above. Table 2 shows the results
Shown in

[0023]

[Table 2]

Next, 5 g of the treated product thus obtained
2g sodium aluminate, 1g sodium hydroxide
50 g of water and 50 g of water were added and mixed, and 0.5 ml of a slurried slurry of A-type zeolite as seed crystals (0.05 g of A-type zeolite) was added.
After heat treatment for a period of time, the solid content was filtered, washed with water and dried to produce an A-type zeolite. Table 3 shows the reaction rate of the treated product and the formation rate of the A-type zeolite used in this case.

[0025]

[Table 3]

From Table 3, it can be seen that the higher the reaction rate of the treated product, the higher the production rate of A-type zeolite.

An X-ray diffraction pattern of an example of the A-type zeolite thus obtained is shown in FIG.

Comparative Example 5 g of fly ash used in the examples, 5 g of sodium aluminate, 10 g of sodium hydroxide and 45 g of water were mixed, and this mixture was heat treated at 90 ° C. for 20 hours as in the examples. As a result, the obtained zeolite was only hydroxysodalite, and almost no A-type zeolite was formed.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of an example of A-type zeolite obtained by the method of the present invention.

Claims (4)

(57) [Claims] 1. A mixture of fly ash and solid sodium hydroxide at a temperature of 90-180 ° C. for at least 6 parts.
A method for producing an A-type zeolite, which comprises performing a heat treatment for 0 minutes, and then adding sodium hydroxide and water to the thus-obtained treated product to form a slurry, followed by hydrothermal treatment. 2. The method for producing an A-type zeolite according to claim 1, wherein the mixing ratio of fly ash and solid sodium hydroxide is in the range of 5: 1 to 1: 2 by weight. 3. Al ₂ O ₃ content of 15% by weight or more, SiO
_{2. The} method for producing an A-type zeolite according to claim 1, wherein fly ash having a ₂ content of 50% by weight or more is used. 4. The method for producing an A-type zeolite according to claim 1, 2 or 3, wherein a mixture of fly ash and solid sodium hydroxide is heat-treated at a temperature of 100 to 150 ° C. for 5 to 20 hours.