JPS629523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing lithium silicate. It is well known that lithium silicate, unlike sodium silicate, can form a moisture-resistant film and is therefore suitable for protective coatings on various substrates. It is also used as a flame retardant.

Therefore, this lithium silicate aqueous solution can be used alone or in combination with other coating materials to provide a flame-retardant and moisture-resistant coating film to a substrate by methods such as impregnation, spraying, and brush coating.

Nevertheless, the market for lithium silicate is much more limited than for sodium silicate, primarily due to its high manufacturing costs.

Many methods for producing lithium silicate have been proposed in the past, including the following methods: (1) Method of reacting silica sol with lithium hydroxide (Japanese Patent Publication No. 38-20484, Japanese Patent Publication No. 45-4184,
(2) Method of reacting metallic silicon with lithium hydroxide as a raw material for SiO ₂ (Special Publication No. 15160, 1972, 4637 of 1972)
(3) Method of ion exchange using Li-type cation exchange resin and sodium silicate (Special Publication No. 15468, 1972) (4) Method of thermally reacting silica gel with a substance containing lithium hydroxide (Special Publication No. 15468, 1972) No. 13224, Japanese Patent Publication No. 57-4257).

Method (1) yields preferable lithium silicate, but it consumes a lot of energy for concentration, etc., including the silica sol production process, and high costs are unavoidable. I can't get it. Since the method (3) requires diluting the aqueous sodium silicate solution, it also requires a concentration operation and is not industrially viable as it cannot recover 100% of lithium.

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Furthermore, although method (4) is the most suitable method industrially, lithium silicate itself cannot be obtained because lithium hydroxide is used in combination with sodium hydroxide or sodium silicate. Further, since pressurization operation is required, there is a cost burden on equipment investment.

The present invention relates to improvement of method (4) among these methods, and in view of the above-mentioned drawbacks of the prior art, the present inventors conducted intensive research and found that the reaction between silica gel and lithium hydroxide The present invention was completed based on the finding that the process can be carried out satisfactorily at normal pressure.

That is, the gist of the present invention is that the molar ratio composition of silica gel and lithium hydroxide is SiO ₂ /
Li ₂ O2.0~10 and solid content concentration (SiO ₂ + Li ₂ O)
A water-containing mixture is prepared so that the concentration ranges from 15 to 35% by weight, and then the water-containing mixture is mixed and cured at a temperature of 60°C or less until it becomes a uniform translucent slurry, peptized, and then stirred under normal pressure. The present invention relates to a method for producing lithium silicate, which is characterized in that the lithium silicate is aged at a temperature higher than the above temperature, and then allowed to cool.

In the present invention, silica gel is not particularly limited as long as it is amorphous silica other than silica sol, and examples include ordinary silica gel, fine powder silicic acid obtained by a wet method such as white carbon, Examples include finely powdered silicic acid from a dry process called Aerosil, dust which is a by-product from the silicon or ferrosilicon manufacturing process, naturally occurring soft silica stone, silica, and the like.

Of the above, in the present invention, it is most advantageous not only in terms of product quality but also industrially to use the paste or slurry silica gel obtained by neutralizing the sodium silicate aqueous solution with acid as a continuation of the process. be.

On the other hand, as the lithium hydroxide, any industrially available lithium hydroxide-containing material may be used, but LiOH.H ₂ O powder or an aqueous solution is typically used. Note that sodium hydroxide may also be used in combination, if necessary in the application.

The reaction ratio of the above raw materials is determined by the molar ratio of SiO ₂ /Li ₂ O.
2.0 to 10, preferably 3 to 8, and solid content concentration (SiO ₂ + Li ₂ O) 15 to 35% by weight, preferably 15
A range of ~30% by weight is preferable. The reason for this is that the product targeted by the present invention cannot be advantageously produced outside this range. If the concentration is less than 15% by weight, it is not practical for storage and transportation, and a concentration operation is required afterwards, so there is no point in producing the high-concentration product of the present invention at a low cost, and if it is more than 35% by weight, it becomes highly viscous. Fluidity is lost and good quality products cannot be obtained.

The above formulation is in the form of a paste or slurry, which is mixed uniformly. The mixing means may be stirring, kneading, shear dispersion, etc., and the mixture may be uniformly mixed depending on the properties of the mixture. In this step, the temperature must be kept at a temperature below the gelation temperature range of the lithium silicate obtained for a sufficient time. It is necessary to do this over time. Note that the temperature below the gelation temperature generally ranges from room temperature to 60°C, although there may be some variation depending on the composition of the mixture.

By continuing the uniform mixing operation, the silica gel is peptized, reducing its initial viscosity and becoming completely liquid. However, at this stage, the reaction is insufficient and the unreacted silica is a cloudy, opaque liquid. The cloudy liquid is a dispersion of fine particles that cannot be separated by filtration or centrifugation.

The mixing operation to reach this state does not necessarily have to take a long time; after homogenization, the mixture is allowed to stand and cure, and this period is at most 48 hours, but it is usually carried out for 5 to 24 hours. good.

Thus, in the present invention, it is important to carry out the peptization treatment at a temperature below the gelling temperature range and for a sufficient period of time.

Without this treatment, a large amount of unreacted silica remains in the subsequent simple heating and aging treatment, resulting in a significantly poor yield, and therefore a colorless and transparent aqueous lithium silicate solution cannot be obtained.

Next, it is essential to quickly raise the temperature of the resulting cloudy liquid mixture and maintain it at a temperature higher than 60°C for ripening. In other words, the viscosity of this cloudy mixed liquid increases as the temperature rises, unlike general physical properties.
At temperatures higher than 60℃, it will gel and become unstirable.
Therefore, in this gelled state, the temperature is preferably 90℃~
Maturing is maintained at a temperature of 100°C for at most 24 hours.

When the reactant thus aged is then allowed to cool down to a temperature below the gelling temperature range, for example to room temperature, it is completely liquefied and a colorless and transparent aqueous lithium silicate solution is obtained.

Next, if necessary, if there are any impurities mixed in, obtain a highly pure lithium silicate aqueous solution by filtration.
I can do it.

Thus, according to the method of the present invention, high-concentration and high-purity lithium silicate can be industrially advantageously produced by a simple operation and process of heating and mixing at normal pressure using inexpensive silica raw materials without the need for a concentration step. can be manufactured.

Example 1 A paste made by blending 500 parts by weight of silica hydrogel containing 20% by weight as SiO ₂ and 32 parts by weight of LiOH·H ₂ O powder was mixed at a temperature of 40°C for 1 hour, and then the temperature state The mixture was allowed to stand for 16 hours to obtain a cloudy slurry. Note that this cloudy liquid could not be filtered, and the filtered liquid was also cloudy. Next, when the temperature of this cloudy liquid was rapidly raised while stirring, the viscosity increased due to gelation, and when the temperature reached 80°C, stirring was stopped, and after standing at 95°C for 12 hours, it was allowed to cool.

After cooling, the resulting liquid was filtered to remove trace amounts of impurities such as iron hydroxide.The mother liquor was colorless and transparent, and analysis revealed that the liquid composition was _SiO2 : 18.81% by weight, _Li2O : 2.08%. It was a lithium silicate aqueous solution with a weight percent (SiO ₂ /Li ₂ O4.49).

Example 2 Silica hydrogel 500 containing 20% by weight as SiO ₂
A sodium-containing lithium silicate aqueous solution ( _{SiO 2} 19.10% by weight, Li ₂ 1.68% by weight of O, 0.98% by weight of Na ₂ O, and 4.39% by weight of SiO ₂ /M _{2 O} ).

Example 3 78 parts by weight of commercially available white carbon (trade name: Carplex #80 manufactured by Shionogi Pharmaceutical Co., Ltd.), 234 parts by weight of water, and 20 parts by weight of LiOH/H ₂ O powder were mixed and allowed to stand at 40°C for 24 hours until cloudy. An opaque slurry was obtained.
Next, this was quickly heated to 95° C. while stirring to form a gel. Note that stirring was stopped at 75°C. This is 12
The solution that was left to cool for several hours was a clear liquid containing a small amount of precipitated coarse silica gel particles. The composition of the liquid from which impurities were removed by filtration is 19.30% by weight of SiO ₂ , 2.15% by weight of Li ₂ O, molar ratio (SiO ₂ /Li ₂ O)
It was 4.46.

Comparative example A paste mixture with the same composition as Example 1 was heated at 40℃.
When the solution was quickly heated to 95° C. without being maintained at 95° C. and left to cool after 15 hours of cooling, the solution was not a colorless and transparent liquid but a cloudy lithium silicate aqueous solution in which unreacted silica was dispersed. In addition, an attempt was made to collect a transparent liquid by filtering and separating this cloudy aqueous solution, but the filtration was not easy and a clear aqueous solution could not be obtained.

On the other hand, when the paste-like mixture was subjected to pressure hydrothermal treatment at 150° C. for 5 hours and allowed to cool, a colorless and transparent lithium silicate liquid was obtained. Thus, it was found that heating at normal pressure does not cause a complete reaction unless the material is cured at a temperature below the gelation temperature range of lithium silicate.

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Claims (1)

[Claims] 1 The molar ratio composition of silica gel and lithium hydroxide is SiO ₂ /Li ₂ O2.0 to 10 and the solid content concentration (SiO ₂ +
A water-containing mixture is prepared so that Li ₂ O) is in the range of 15 to 35% by weight, and then the water-containing mixture is mixed and cured at a temperature below 60°C until it becomes a uniform translucent slurry, and peptized. 1. A method for producing lithium silicate, which comprises aging the lithium silicate at a temperature higher than the above temperature under normal pressure, and then allowing it to cool.