JPS6114089B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention mainly relates to a method for producing an alkali-containing silicate from silica sand and a caustic alkali, and provides a method for producing a granular alkali-containing silicate that has good fluidity and is particularly suitable as a raw material for glass production. . As a method for producing alkali-containing silicates,
Methods are known in which silica sand and caustic alkali are reacted in a fluidized bed at high temperatures. For example, a method in which silica sand and caustic soda are reacted at a temperature of 320 to 450°C in a fluidized bed formed by supplying hot gas from the lower part of a reaction vessel (Special Publication No. 45-2310), and also a method in which silica sand and an aqueous sodium hydroxide solution are sprayed. about 480
A method of reacting at a temperature of ~620℃
28647). In the former case, granules made of silicic anhydride coated in whole or in part with sodium metasilicate are obtained, and in the latter case, an alkali-containing silicate, which is a granular product in a mixed state of sodium metasilicate and finely divided silica sand, is obtained. However, when the alkali-containing silicate obtained by the above method etc. is melted, the reaction between the silica sand and other components is insufficient, and when the silicate is in a melting furnace, bubbles such as air accompanying the silicate are The drawback is that it cannot be removed sufficiently from the glass, resulting in unreacted substances and fine bubbles remaining in the glass product. The present inventors have conducted intensive research on a method for producing alkali-containing silicates, which are particularly suitable for manufacturing glass products, mainly from silica sand and caustic alkali. The inventors have discovered that the desired alkali-containing silicate can be obtained by carbonating 50% by weight, and have thus come to provide the present invention. That is, the present invention supplies a powder raw material containing at least silica sand into a reaction vessel, forms a fluidized bed in which a heated gas containing 3% by volume or more of carbon dioxide gas is blown into the reaction vessel from below, and An alkali-containing silicate, characterized in that an aqueous solution of caustic alkali is sprayed from the upper part of a reaction vessel and the temperature of the fluidized bed is maintained at 150 to 310°C to convert 50% by weight or more of the caustic alkali into alkali carbonate. This is a manufacturing method. The alkali-containing silicate obtained by the present invention is almost independent granules, has good fluidity, and is easy to handle. In addition, since the particle surface of the alkali-containing silicate of the present invention is mostly coated with alkali carbonate, the alkali carbonate foams when melted in the melting kiln, resulting in sufficient convection and mixing, resulting in good glass products. can get. That is, when melted, the reaction between the silica sand of the alkali-containing silicate and other components takes place sufficiently, and the air bubbles in the melt are also efficiently removed, so that almost all fine unreacted substances and air bubbles are removed. You can get glassware that does not contain. The powder raw material used in the present invention contains at least silica sand, and when the final product is an alkali silicate, silica sand may be used alone. In addition, when the final product is glass, silica sand and other glass raw materials such as feldspar, dolomite, alkali carbonate, alkali sulfate, carbon, boric acid, lithium, alkali sulfite, arsenite, etc. are appropriately mixed. The content of silica sand in the glass raw material mixture is preferably 60% by weight or more. Note that raw material powder having a particle size of 20 to 500 μm is preferably used. On the other hand, the caustic alkali in the present invention is generally caustic soda or caustic potassium, and an aqueous solution of the alkali with a concentration of 10 to 60% by weight is preferably used from the viewpoint of use and reactivity. In addition,
As the aqueous solution of caustic alkali, alkali-containing industrial wastewater, for example, wastewater obtained by wet dust collection of exhaust gas from a melting kiln in glass manufacturing, may be used. On the other hand, the reaction vessel used in the present invention generally has a dispersion plate for supplying heated gas from the lower part to form a uniform fluidized bed, a nozzle for spraying the caustic aqueous solution from the upper part, and a supply port for powder raw materials. There is no particular restriction as long as the structure has an outlet for taking out the generated alkali-containing silicate particles. For example, the supply port for the powder raw material is located on the side wall of the reaction vessel above the distribution plate, and the outlet for the alkali-containing silicate is located on the side wall of the reaction vessel facing the supply port for the powder raw material at approximately the same height as the distribution plate. It is preferable to let In the present invention, it is extremely important to convert at least 50% by weight or especially at least 80% by weight of the caustic alkali sprayed together with the raw material into alkali carbonate in order to obtain an alkali-containing silicate suitable as a raw material for glass manufacturing. It is. In other words, when an alkali-containing silicate in which the conversion of caustic alkali to alkali carbonate is less than 50% by weight is melted, convection and mixing due to uniform and sufficient foaming cannot be achieved, and as a result, fine unreacted particles are formed in glass products. This results in particles and bubbles remaining. Therefore, in the present invention, in order to produce an alkali-containing silicate in which 50% by weight or more of the caustic alkali is converted into alkali carbonate, the powder raw material containing mainly silica sand must be heated at a temperature of 200°C or less, generally from 100 to 200°C. It is necessary to feed the reaction vessel at That is, when the powder raw material is supplied to the reaction vessel at a temperature of 200°C or higher, the proportion of alkali metasilicate produced by the reaction between silica sand and caustic alkali increases, and more than 50% by weight of the caustic alkali becomes alkali carbonate. Cannot be converted. In addition, in the present invention, heating gas containing 3% by volume or more of carbon dioxide gas is blown into the reaction vessel.
The above is necessary for converting to alkali carbonate. That is, if the carbon dioxide concentration of the heating gas is less than 3% by volume, the caustic alkali may not be carbonated sufficiently and may adhere to the raw material powder, or even if the temperature of the fluidized bed is increased, the caustic alkali may react with the silica sand. Since it produces alkali metasilicate, it is difficult to convert it to more than 50% by weight alkali carbonate. Increasing the carbon dioxide concentration of the heated gas by 3% or more by volume has the advantage of lowering the temperature of the fluidized bed. It is preferable to use gas or the like with a carbon dioxide content of 3 to 25% by volume. By blowing heated gas containing carbon dioxide gas into the reaction vessel from the bottom, a fluidized bed is formed on the dispersion plate of the reaction vessel, and the supplied powder raw material is fluidized. On the other hand, the aqueous caustic alkali solution sprayed from the lower part of the reaction vessel adheres to the surface of the fluidized powder raw material, reacts with carbon dioxide gas in the heated gas, and is converted into alkali carbonate. Of course, a portion (50% by weight or less) of the caustic alkali remains attached to the powder raw material, or reacts with the powder raw material to produce metasilicate. In addition, in the present invention, the temperature of the fluidized bed is set to 150~
The temperature is maintained at 310° C., which is lower than in conventional methods, and the temperature can be adjusted by adjusting the temperature of the heated gas blown into the reaction vessel. If the temperature of the fluidized bed is below 150° C., water in the sprayed aqueous caustic solution will not be sufficiently distilled, making it impossible to obtain an alkali-containing silicate with good fluidity. Furthermore, if the temperature of the fluidized bed is 310° C. or higher, the reactivity between the caustic alkali and the powder raw material increases, making it difficult to carbonate more than 50% by weight of the caustic alkali. In order to convert 50% by weight or more of caustic alkali into alkali carbonate, the present invention produces a desired alkali-containing silicate by simultaneously satisfying each of the above operational requirements. That is, as mentioned above, the alkali-containing silicate obtained by the present invention has better reactivity as a raw material for glass production than the conventional alkali-containing silicate obtained by mixing alkali carbonate and silica sand, and can be used in a melting kiln. Reduction is also possible. Example 1 A fluidized bed reaction vessel made of stainless steel with an inner diameter of 0.6 m and a height of 2.0 m and provided with an air distribution plate inside was used.
Raw materials: SiO ₂ 98.5%, Al ₂ O ₃ 1%, Fe ₂ O ₃
Silica sand with an average particle size of 200μ containing 0.1%, CaO, and trace amounts of MgO was continuously supplied to the reaction vessel at a rate of 330g/min, and heavy oil combustion gas (containing 10% by volume carbon dioxide gas) was blown from the bottom of the reaction vessel to flow it. formed the floor. Meanwhile, at the same time as heating, a 50% (by weight) aqueous solution of caustic soda was continuously added at a rate of 130 g/min (in terms of solids) from a spray nozzle attached to the upper part of the reaction vessel. The heated gas was adjusted so that the temperature of the fluidized bed was 300°C, and the average residence time in the fluidized bed was about 30 minutes to obtain a spherical reaction product that was an alkali-containing silicate intermediate product. Ta. The reaction products were obtained by carrying out the same procedure under the above conditions except that the raw material silica sand was maintained at each predetermined preheating temperature shown in Table 1. Table 1 also shows the results of a separate analysis of the alkaline components of each reaction product.

【table】

[Table] In Table 1, Nos. 6 and 7 correspond to comparative examples, and when the moisture content of raw silica sand was 12%, the dispersion plate was clogged and continuous operation was not possible. Example 2 A heat exchange device was provided inside a heavy oil combustion device, and heated gas containing carbon dioxide gas and air adjusted to a predetermined mixing ratio was used in the same reaction vessel as in Example 1. The experiment was carried out under the same conditions as in Example 1 except that the temperature at which the raw material silica sand was supplied was 120°C. The results are shown in Table 2.

[Table] In Table 2, Nos. 1 and 2 correspond to comparative examples. Example 3 The reaction temperature was varied as shown in Table 2 by changing the temperature of the heated gas supplied from below the container. The experiment was carried out under the same conditions as in Example 1 except that the powder raw material (silica sand) was supplied to the reaction vessel at 120°C. The results are shown in Table 3. From this, when the reaction temperature is 150 to 310℃, a granular product with good fluidity can be obtained, and 50wt% of the supplied caustic soda can be obtained.
It can be seen that the above is converted to soda carbonate.

[Table] Note that Nos. 1, 2, 6, and 8 in Table 3 correspond to comparative examples. Example 4 Example 2 No. 1, 3, Example 3 No. 3, Example 1 No. 2, Example 3 No. 4 and products separately prepared by the method of the invention The carbonated soda content of
200g of each sample of 90wt% and 94wt% was taken and melted in an electric furnace at 1400°C for 2 hours. After cooling, 20 g test pieces were prepared, and the number of batches and seeds were measured. The batch number represents the number of unreacted raw material particles in the test piece, and the seed number represents the number of bubbles remaining in the test piece. The results are shown in Table 4. When the sodium carbonate content of the product was 50 wt% or more, the number of seeds and batches decreased significantly, and good glass products were obtained. In addition, No. 1 in Table 4
corresponds to a comparative example.

[Table] Example 5 Silica sand 75wt%, feldspar 5wt%, dolomite 19wt%,
The reaction was carried out under the same reaction conditions and operations as in the example except that the powder raw material was supplied to the reaction vessel at 120°C using a powder raw material containing 1 wt% of saltpeter and an average particle size of 250 μm. A reactant was obtained because it was a silicate-containing intermediate product. The analysis result of the alkaline component of the generated reaction product was 85wt% soda carbonate.
The sodium silicate content was 8wt% and the caustic soda content was 7wt%. In addition, test pieces were made from the above product in the same manner as in Example 4, and the number of batches and seeds were measured. As a result, the number of batches was 2 and the number of seeds was 5.

Claims (1)

[Claims] 1. A powder raw material containing at least silica sand is supplied into a reaction vessel, and a heated gas containing 3% by volume or more of carbon dioxide gas is blown into the reaction vessel from the lower part to form a fluidized bed, and the upper part of the reaction vessel is The temperature of the fluidized bed is increased by spraying an aqueous solution of a more caustic alkali.
50% by weight of the caustic alkali maintained at 150-310℃
A method for producing an alkali-containing silicate, which comprises converting the above into an alkali carbonate.