CS232120B1 - Preparation method of dispersed siliceous hydroxide - Google Patents

Description

The present invention relates to a process for the preparation of dispersed silica hydrooxide.

The smallest, submicrometer silica particles are prepared most often by high temperature controlled hydrolysis of silica [R. Iller: The chemistry of silica, Willey-Imterscience, New York, (1979)].

The disadvantage of these processes is that they require expensive starting materials and are technically demanding. In many applications, however, particles in the range of 1 to 50 µm may be sufficient. These can be prepared by utilizing sol-gel transition in growth, i. j. small sol particles are dispersed in the gaseous medium and the silicic acid is dopolymerized at (higher temperatures during the drop of the particles to the bottom of the reactor. The preparation of microparticles in hover is relatively complex and thus suffers from its reprocessability.

The crushing and grinding processes are in turn very energy intensive. It is often necessary to separate the obtained material and remove coarser fractions.

The above disadvantages are substantially eliminated by the process of preparing dispersed silica hydrooxide having a primary particle size of 2 to 40 ₍ am according to the invention, which consists in making aqueous solutions of amides with a total concentration of 0.5 to 75% and substituted amides alone or in the presence mineral or organic acids and the controlled polymerization of silicic acid presented in the form of aqueous solutions of sodium or potassium silicates with a concentration of 3 to 35% of S1O2 in solution. Free ammonia, which is released from the amides in the reaction under the alkali environment The viscous alkali metal salt results in the formation of silica hydrooxide in a very fine flocculent form under defined end conditions The polymerization can be carried out at normal laboratory temperatures, i.e. about 20-25 ° C, where the precipitation of the hydrooxide proceeds slowly, or It is possible to accelerate the reaction by heating the mixture up to the boiling point, the SiO ₂ to amide ratio being equal to 0.7 to 5.

The primary particle dimensions of the fumed silica hydride are a function of the polymerization process conduction, in particular the concentration of the starting components.

The advantage is that by suitable chosen reaction conditions we prepare discrete microparticles which retain their dimensions during the whole preparation process, i. j. the product obtained is composed of primary finely dispersed silica hydrooxide particles, wherein the secondary, easily disintegrating adhesives formed during drying can be spread with a slight pressure. The formation of adhesives, granules, in most applications is desirable in practice, since the amount of unwanted dust drift is reduced during manufacturing processing.

The examples below illustrate the mode of operation without limiting the invention in any way.

EXAMPLE

To 40 L of water in the reactor was added 30 L of aqueous sodium silicate solution (water glass) with a density of 1.359, and 5 L of formamide was added with vigorous stirring. After stirring, the mixture is left to stand for 48 hours, whereupon the precipitate formed is filtered off, washed with water until neutral and dried.

The dispersed silica hydrooxide is in the form of easily disintegrating lumps with primary particles of 2 to 20, having a specific surface area of 342 m ² . g ¹ .

Example 2

To 10 l of sodium silicate solution with a density of 1.359 is added 15 l of water and 12.5 l of an aqueous solution in which 2.5 kg of acetamide is dissolved. The mixture is stirred occasionally and after 72 h the precipitate formed is filtered, washed neutral with water and dried. The specific surface of the material thus obtained is 120 m ² . g ^_1 with primary particles from 3 to 40 μιη.

Example 3

10 l of a potassium silicate solution having a density of 1.32 and 10 l of water are introduced into an open vessel and a mixture of 3 kg of dimethylformamide and 3 l of water is added with stirring. The mixture is stirred occasionally and after 100 h the suspension is filtered, washed neutral with water and dried. The lumpy material obtained contains primary particles of 2 to 25 μ’ΐη.

Example 4

The reactor was charged with 15 L of an aqueous solution containing 1 kg of formamide and 2 kg of dimethylformamide. While stirring, a solution containing 10 l of sodium silicate (water glass) with a density of 1.359, diluted with 10 l of water, is added. The mixture is stirred occasionally and after 7 days the suspension obtained is filtered off and the filter cake is washed with water until neutral and dried. The product is a dispersed silica hydride having a primary particle size of 2 to 30 µm and a specific surface area of 200 m ² . g ^-1 .

Example 1 and d 5

The reactor was charged with 10 L of freshly prepared aqueous solution containing

232

250 ml of 98% sulfuric acid and 1 l of formamide. While stirring, a solution containing 10 L of water and 10 L of sodium silicate solution having a density of 1.359 is added. The polymerization is carried out with occasional stirring of the mixture for 72 hours, after which time the product is filtered off, washed with water until neutral and dried. The primary particles of the product obtained had diameters of 10 to 40 μπι and a specific surface area of 70 m ² . g ' ¹ .

Example 6

The procedure is the same as in Example 5, except that 1000 milliliters of 1-glacial acetic acid is used instead of sulfuric acid and the polymerization proceeds for 100 hours. The primary particles of the product obtained have diameters of 5 to 40 µm and a specific surface area of 110 m ² . g ^-1 .

Claims (1)

SUBJECT A process for the preparation of a dispersed silica hydrooxide having a primary particle size of 2 to 40 ₍ m 2 aqueous solutions of sodium and potassium silicates), characterized in that aqueous solutions of sodium or potassium silicates having a concentration of 3 to 35% such as formamide, acetamide or dimethylformamide, either ^one alone, or -S přídavkům acids such as sulfuric acid and chlorovodí20 Example 7 The procedure is as in Example 5 except that the reaction mixture is heated to the boiling point of the mixture after the addition of the silicate and is maintained at boiling for 30 minutes, after which the precipitated hydrooxide 9 is filtered, washed and dried. The product obtained contains particles having a particle size of 8 to 40 μπι. The microparticle-shaped silica of less than 40 microns has utility as a filler in polymers, as an adjuvant in the cosmetics industry, in the pharmaceutical industry, and the like. According to the particular application, various values of the physical parameters of the material, such as particle size, pore size and volume, specific surface area and the like are required. Or with an addition of organic acids such as acetic acid and formic acid, the amides or mixtures thereof with acids being used in the form of their aqueous solutions with a total concentration of 0.5 to 7.5%, the total weight of silica in the solution being The total weight of the amide after mutual mixing is from 0.7 to 5, after which the resulting suspension is freed from the mother liquors by washing and dried.