JPS6245169B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a wet method for manufacturing sodium silicate, and more specifically, when manufacturing sodium silicate with a low impurity content and a relatively high silicate ratio by a wet method, conventionally unavoidable The present invention relates to a wet method for producing sodium silicate, which can substantially prevent the formation of scales, and therefore allows continuous operation to be used instead of batchwise operation. Sodium silicate, also called water glass, is produced mainly by the so-called dry method in which silica sand (quartz) and soda ash are heated and melted at a high temperature of 1,300 to 1,500°C to obtain anhydrous sodium silicate, which is then dissolved in water. Manufactured in
However, this dry method not only requires a large amount of thermal energy to carry out, but also requires expensive equipment, which requires a large amount of capital investment, and also has the disadvantage that maintenance management of the equipment is difficult. be. In addition, the dry method has the disadvantage that the quality of the raw material silica sand is limited in order to suppress impurities, particularly iron and aluminum, in the sodium silicate product to a very small amount. In contrast, the wet manufacturing method for sodium silicate uses highly reactive soluble amorphous silica as the silica source.
This method involves adding an aqueous solution of caustic soda to the solution and dissolving it at a relatively low temperature in a conventional autoclave. In this wet method, sodium silicate can be produced using an ordinary autoclave at a low temperature of 80 to 200°C, so there are no problems seen in the dry method described above. However, sodium silicate produced by the wet method generally has a disadvantage in that it contains more impurities than that produced by the dry method. That is, in the wet method, as the soluble amorphous silica that is the silica source, in addition to clay, diatomaceous earth, etc., silica dust, etc., which are by-produced during the production of ferrosolene, metallic solene, etc., are used.

[Table] Table 1 shows the typical composition (wet basis) of clay and silica dust, which are typical soluble amorphous silicas. Contains impurities. Therefore, in the wet method using soluble amorphous silica as the silica source, the impurity content of the sodium silicate product inevitably increases compared to the dry method. Therefore, in the conventional wet method, soluble amorphous silica is heated and dissolved in an aqueous solution of caustic soda at a relatively high temperature to suppress contamination of the product with impurities as much as possible. Performing the heat melting at a relatively high temperature is also advantageous in increasing the utilization rate of soluble amorphous silica and caustic soda. This is because the dissolution rate of soluble amorphous silica in a caustic soda aqueous solution of a constant concentration increases with temperature, so the higher the temperature, the less undissolved matter in the dissolution treatment solution, and as a result, it is filtered out from the dissolution treatment solution. This is because the amount of undissolved matter is reduced, and the amount of soda accompanying this is also reduced. However, the reality is that increasing the heating melting temperature in the wet method does not bring about good results. That is, in the conventional wet method, a mixture of soluble amorphous silica and caustic soda is heated in advance to a desired temperature using an appropriate heater and then supplied to an autoclave, or the autoclave itself is heated with a steam jacket or the like. A method is adopted in which a suitable heating means is provided and the mixture is heated to a desired temperature in an autoclave, but such heating methods inevitably cause scale to form on the inner wall (heat transfer surface) of the heater or autoclave. It's put away. This scale occurs when the impurity content of soluble amorphous silica, which is the silica source, is high, or when the molar ratio of SiO ₂ /Na ₂ O (silica ratio) in the mixture of soluble amorphous silica and caustic soda aqueous solution is high. This is particularly noticeable. The generation of scale inevitably leads to a decrease in the thermal efficiency of the heater, blockage of the heater piping, etc., and the inability to stir the processing liquid in the autoclave. If conventional wet methods were used for production, batch operations had to be adopted. The present invention aims to improve the above-mentioned wet method, and even when producing sodium silicate with a high silica ratio and few impurities, there is almost no scale formation, and therefore continuous operation is adopted. The present invention provides a new wet method for producing sodium silicate that enables the following. That is, when heating a mixture of soluble amorphous silica and an aqueous caustic soda solution, if the silica ratio of the mixture is low, scale may occur on the heat transfer surface even if the mixture is heated to a relatively high temperature. There is no. The present invention takes advantage of this property by preparing a first mixture with a relatively low silica ratio and a second mixture with a relatively high silica ratio, and heating the former to a relatively high temperature and the latter to a relatively low temperature. Afterwards, the two are mixed to produce sodium silicate without external heat supply. Accordingly, the wet method for producing sodium silicate according to the present invention is a wet method for producing sodium silicate in which soluble amorphous silica is heated and dissolved in an aqueous solution of caustic soda in an autoclave.(a) soluble amorphous silica and caustic soda A mixture with an aqueous solution, SiO ₂ /Na ₂ O
The first mixture having a molar ratio of 0.1 to 3 is heated to 80 to 250°C.
(b) heating a second mixture of soluble amorphous silica and an aqueous caustic soda solution with a SiO ₂ /Na ₂ O molar ratio of 0.5 to 6 to 50 to 200°C; ) The first and second mixtures, respectively heated, are mixed and the resulting mixture is processed in an autoclave without external heat supplementation. In the present invention, the soluble amorphous silica used as the silica source has an average particle size of 2.
It is preferably less than mm. The use of soluble amorphous silica with a particle size exceeding 2 mm is not preferable because there is a possibility that a portion with a high silica ratio may appear locally in the mixture. The first mixture and the second mixture of the present invention are prepared by mixing soluble amorphous silica and a caustic soda aqueous solution, respectively, and the silica ratio of the first mixture is 0.1 to 0.1.
3, the silica ratio of the second mixture is adjusted to 3.7-6, respectively. The first mixture, which has a relatively low silica ratio, is heated to 80 to 250°C, and the second mixture, which has a relatively high silica ratio, is heated to 80 to 250°C.
The mixture is heated to 50-200 °C. The first mixture and the second mixture, each heated to a predetermined temperature, are then mixed and this mixture is processed in an autoclave without supplementing it with heat.
According to the knowledge obtained by the present inventors, when the temperature of the mixture in the autoclave is 180° C. or higher, the amount of impurities contained in the product sodium silicate, especially the amount of iron, decreases as the temperature increases. Therefore, in order to obtain sodium silicate with few impurities, the temperature of the mixture inside the autoclave must be maintained at 180°C or higher. In the present invention, in order to prevent scale formation within the autoclave, an autoclave without heating means is used, so the heating temperature and supply amount of each of the first mixture and second mixture supplied to the autoclave are , selected such that the above temperature conditions are satisfied in the autoclave. The mixing ratio of the first mixture and the second mixture is determined by taking into consideration the silica ratio of the sodium silicate to be produced. By the way, when it is desired to produce sodium silicate with a silicate ratio of about 3, a first mixture with a silicate ratio of about 2.0 and a second mixture with a silicate ratio of about 3.7 are prepared at a weight ratio of about 1:1: Mixed in 2. The first mixture and the second mixture supplied into the autoclave are heated without external heat supplementation.
The autoclave is kept at a temperature of 180°C or higher for about 6 hours, whereby the soluble amorphous silica is dissolved in the caustic soda aqueous solution to the maximum extent and sodium silicate is produced. The mixture that has been processed in the autoclave contains the product sodium silicate, undissolved components such as impurities, and caustic soda.This mixture is processed using a procedure similar to the conventional wet method, and is first filtered using a filter press or the like. The product sodium silicate is recovered by means. The filter cake is washed with water and the washed filtrate can be concentrated to obtain the sodium silicate product or recycled and mixed with the first and/or second mixture of the present invention for reuse. One of the advantages of the wet method according to the present invention is that it does not involve the generation of scale, so that sodium silicate can be produced in a continuous operation, and this will be explained below with reference to the accompanying drawings. Soluble amorphous silica, which is a silica source preferably ground to an average particle size of 2 mm or less, and a caustic soda aqueous solution are supplied to stock solution supply tanks 11 and 21, and in supply tank 11, a first mixture having a silica ratio of 0.1 to 3 is supplied. In the tank 21, a second mixture having a silica ratio of 3.7 to 6 is prepared. The mixture in each supply tank is transferred to a heat exchanger 12
and 22, respectively, the primary melting tank 1
3 and 23 continuously. Next, a first mixture in which at least a portion of soluble amorphous silica is dissolved in a caustic soda aqueous solution is continuously taken out from the primary dissolution tank 13, and is heated to a temperature of 80 to 250 ml by heat exchange with steam in a heat exchanger 14. After being heated to .degree. C., it is continuously supplied to the autoclave 30.
On the other hand, a second mixture in which at least a part of soluble amorphous silica is dissolved in a caustic soda aqueous solution is continuously taken out from the primary dissolution tank 23, and is heat-exchanged with the autoclave effluent in a heat exchanger 24.
After being heated to 200°C, it is continuously introduced into an autoclave 30. The first mixture and the second mixture supplied to the autoclave 30 are combined and heated to 180°C.
Maintain the above temperature and stay at that temperature for about 6 hours. The autoclave effluent containing the product sodium silicate is continuously taken out into line 31, and after heat recovery in heat exchangers 24, 12 and 22, respectively, it is fed via pressure regulator 32 to filter press 33, where it is Product sodium silicate is recovered in line 34. The filter cake containing undissolved matter is washed with water, the undissolved residue is discharged from the system through line 35, and the washing filtrate, which is a dilute solution of sodium silicate, is sent through line 36 to stock solution supply tank 11 and/or 21.
will be forwarded to. As mentioned above, in the conventional wet sodium silicate manufacturing method, it is not possible to adopt continuous operation, so it is natural that the raw materials must be prepared and heated repeatedly for each batch, which reduces the productivity of the equipment. must necessarily be low. In addition, in the conventional method, it is necessary to remove scale that has grown on the heat transfer surface inside the autoclave and/or the heater, which requires periodic cleaning of the equipment with caustic soda.
This also reduces work efficiency and productivity of the equipment.
Furthermore, the conventional wet method has the disadvantage that the heat contained in the autoclave effluent can hardly be used effectively. Of course, even with conventional wet methods, for example, by installing a tubular heat exchanger in an autoclave,
Although it is not impossible to heat the stock solution with the heat contained in the autoclave effluent, it is impractical to perform such heat exchange in a batch operation. However, according to the present invention, continuous operation can be employed in the wet sodium silicate manufacturing method, so that workability and productivity of the apparatus are improved, and energy consumption can be significantly improved. By the way, in the dry method using silica sand as the silica source, the conventional batch wet method using white clay as the silica source, and the continuous wet method of the present invention, No. 3 sodium silicate (SiO ₂ concentration 29%, silica ratio) was used.
Table 2 shows the energy required to produce 1 ton of 3.1-3.3).

[Table] Example 1 Using clay having the composition shown in Table 1 as a silica source, sodium silicate was manufactured in a continuous operation according to the manufacturing process diagram shown in the attached drawings. White clay crushed to a particle size of 1 mm or less and a caustic soda aqueous solution are supplied to raw material supply tanks 11 and 21, and supply tank 1
In supply tank 1, the first mixture with a solid content concentration of 37% and a silica ratio of 2.0 was supplied, and in the supply tank 21, a solid content concentration of 37% and a silica ratio of 3.7 was supplied.
A second mixture was prepared. Next, each mixture was heated to 90° C. in heat exchangers 12 and 22 and supplied to heated primary dissolution tanks 13 and 23, respectively, each having an internal volume corresponding to an average residence time of 6 hours. Then, the first mixture flowing out from the primary dissolution tank 13 was continuously sent to the heat exchanger 14 using a high-pressure pump, where the mixture was heated to 225° C. and then supplied to the autoclave 30. On the other hand, the second mixture flowing out from the primary dissolution tank 23 was sent to the heat exchanger 24 using a high-pressure pump, where the mixture was heated to 185° C. and continuously supplied to the autoclave 30. As a result, the temperature of the mixture inside the autoclave was maintained at an average of 200°C. The average residence time in the autoclave was 3 hours, and the hydraulic pressure between the high pressure pump and the autoclave was 34 to 36 Kg/cm ² . A total of 600 hours of continuous operation was carried out under the above operating conditions, during which no operational troubles caused by scale formation occurred, with an average clay reaction rate of 90.5% and an average silica ratio of 3.01. The product sodium silicate was obtained. The amount of impurities in the product sodium silicate (converted value when the SiO ₂ concentration is 29%) is Fe ₂ O ₃ on average.
0.029wt%, and Al ₂ O ₃ was 0.20wt% on average. Furthermore, after the operation was completed, the walls of the heat exchanger and autoclave were observed, and almost no scale was observed, and it was concluded that continuous operation for an even longer period of time was possible. Example 2 In the same manner as in Example 1, white clay crushed to a particle size of 1 mm or less and a caustic soda aqueous solution were supplied to the stock solution supply tanks 11 and 21, and in the supply tank 11, the solid content concentration was 30%,
A first mixture with a silica ratio of 1.5 was prepared in the supply tank 21, and a second mixture with a solid content concentration of 37% and a silica ratio of 5.5 was prepared in the supply tank 21. Next, each mixture is transferred to heat exchangers 12 and 2.
Primary dissolution tank 1 heated to 95℃ in 2 and each having an internal volume corresponding to an average residence time of 6 hours.
3 and 23. Then, the first mixture flowing out from the primary dissolution tank 13 was continuously sent to the heat exchanger 14 using a high-pressure pump, where the mixture was heated to 160° C. and then supplied to the autoclave 30. On the other hand, the second mixture flowing out from the primary dissolution tank 23 is
This is sent to the heat exchanger 24 using a high pressure pump, where the mixture is heated to 120°C and placed in the autoclave 3.
0 was continuously supplied. As a result, the liquid temperature of the mixture inside the autoclave was maintained at an average of 150°C. Also, the average residence time in the autoclave is 3
The liquid pressure between the high pressure pump and the autoclave was 23 to 25 Kg/cm ² . A total of 500 hours of continuous operation was carried out under the above operating conditions, during which no operational troubles caused by scale formation occurred, with an average clay reaction rate of 83.0% and an average silica ratio of 3.01. The product sodium silicate was obtained. The amount of impurities in the product sodium silicate (converted value when the SiO ₂ concentration is 29%) is Fe ₂ O ₃ on average.
0.312wt%, and Al ₂ O ₃ was 0.53wt% on average. Furthermore, after the operation was completed, the walls of the heat exchanger and autoclave were observed, and almost no scale was observed, and it was concluded that continuous operation for an even longer period of time was possible. Example 3 In the same manner as in Example 1, white clay crushed to a particle size of 1 mm or less and a caustic soda aqueous solution were supplied to the stock solution supply tanks 11 and 21, and in the supply tank 11, the solid content concentration was 37%,
A first mixture with a silica ratio of 0.5 was prepared in the supply tank 21, and a second mixture with a solid content concentration of 37% and a silica ratio of 5.0 was prepared in the supply tank 21. Next, each mixture is transferred to heat exchangers 12 and 2.
Primary dissolution tank 1 heated to 95℃ in 2 and each having an internal volume corresponding to an average residence time of 6 hours.
3 and 23. Then, the first mixture flowing out from the primary dissolution tank 13 was continuously sent to the heat exchanger 14 using a high-pressure pump, where the mixture was heated to 200° C. and then supplied to the autoclave 30. On the other hand, the second mixture flowing out from the primary dissolution tank 23 is
This is sent to the heat exchanger 24 using a high pressure pump, where the mixture is heated to 150°C and placed in the autoclave 3.
0 was continuously supplied. As a result, the liquid temperature of the mixture inside the autoclave was maintained at an average of 190°C. Also, the average residence time in the autoclave is 3
The liquid pressure between the high pressure pump and the autoclave was 32 to 34 Kg/cm ² . A total of 600 hours of continuous operation was carried out under the above operating conditions, during which no operational troubles caused by scale formation occurred. The product sodium silicate was obtained. The amount of impurities in the product sodium silicate (converted value when the SiO ₂ concentration is 29%) is Fe ₂ O ₃ on average.
0.025wt%, and Al ₂ O ₃ was 0.23wt% on average. Furthermore, after the operation was completed, the walls of the heat exchanger and autoclave were inspected, and as a result, almost no scale was observed, and it was concluded that continuous operation for an even longer period of time was possible.

[Brief explanation of the drawing]

The drawings are process diagrams for carrying out the wet sodium silicate manufacturing method of the present invention in a continuous operation. 11, 21... Raw solution supply tank, 12, 22, 1
4, 24... Heat exchanger, 13, 23... Primary melting tank, 30... Autoclave, 32... Pressure regulator,
33...Filter press, P...High pressure pump.

Claims (1)

[Claims] 1. In a wet method for producing sodium silicate in which soluble amorphous silica is heated and dissolved in a caustic soda aqueous solution in an autoclave, (a) a mixture of soluble amorphous silica and a caustic soda aqueous solution, wherein SiO ₂ /Na ₂ O molar ratio is 0.1~
(b) a mixture of soluble amorphous silica and an aqueous caustic soda solution with a SiO ₂ /Na ₂ O molar ratio of 3.7 to 250°C;
(c) the heated first mixture and the second mixture, respectively;
A wet method for producing sodium silicate, characterized in that a mixture is mixed and the resulting mixture is processed in an autoclave without external heat supplementation.