CS266793B1 - Method of amorphous synthetic silicon dioxide production with specific surface at least 200 m2/g - Google Patents

Abstract

The present invention relates to a process for the production of amorphous of synthetic silica o specific surface area of at least 200 m / g. Diluted water glass is precipitated with an acid mixture hydrochloric acid and chloride solution calcium in such a ratio to pH in the precipitation mixture was 2 - 5 and the CaCl 2 ratio: SiO 2 was 1.5-2.3. ■

Description

The present invention relates to a process for producing amorphous synthetic silica having a specific surface area of 200 m 2 G or more.

Various technological processes are known for the production of amorphous synthetic silica, which can be divided into fumed and wet. .

The fumed process for the preparation of amorphous silica consists in the hydrolysis of silicon tetrachloride vapors in a hydrogen-oxygen flame. Wet processes are further divided into hydrothermal, silica gel, ion exchange and precipitation methods. The hydrothermal process is based on silica sand and lime and the reaction takes place in an autoclave. Calcium is removed from the reaction products with acid and the remaining silicic acid is dried and ground. The silica gel method is based on solutions of water-soluble alkali silicates, which are converted into an unstable silica hydrosol by the action of an acid. The reaction is usually carried out in the acidic pH range and the hydrogel formed is washed with salts after maturation. Finally, it is dried, ground and, in special cases, sorted. The process of preparation of amorphous silica by means of ion exchangers is mostly based on dilute solutions of water glasses. Sodium oxide is removed from the water glass on an ion exchanger to give a very pure silica salt, which is dried over amorphous silica, for example with hot air in a spray dryer. The most widely used wet process for the production of amorphous silica is precipitation. It is mostly based on water glass, which is precipitated by acid. The properties of the final product can be varied by the intensity of stirring, the temperature, the change in the concentrations of the reactants and the change in pH. Sulfuric acid is mostly used for precipitation. Precipitation does not follow maturation, filtration, washing and drying. A process according to Czechoslovak Patent No. 85674 is also known. The diluted water glass is precipitated with hydrochloric acid in the presence of a calcium chloride solution added to the hydrochloric acid before precipitation and the pH of the reaction mixture is maintained at 5 * 6 during the precipitation. The reaction mixture is allowed to mature, followed by filtration, washing and drying.

More preferred is a process for the production of amorphous silica with a specific surface area of 200 m 2 / g or more according to the invention, characterized in that a dilute solution of water glass containing 5-10% by weight. It precipitates silica with a mixture of hydrochloric acid and calcium chloride solution in such a ratio that the pH in the precipitating mixture is 2-5 and the ratio of calcium chloride to silica in the precipitating mixture is 1.5-2.3.

The proposed process can be implemented, for example, so that the raw materials, ie dilute water glass containing 5 - 10 wt. silica, hydrochloric acid and calcium chloride solution are metered in the prescribed proportions into the precipitator. Hydrochloric acid and calcium chloride solution are mixed in a mixer before entering the precipitator. The precipitated suspension of amorphous silica is pumped from the precipitator to maturation tanks and, after maturation, is pumped to a press, where it is filtered off and washed with water from excess chlorides. The filter cake is either directly dried in a vortex or jet drier, or is whipped with water in the activator to a suspension which is dried in a spray drier.

According to the process of the invention, amorphous synthetic silica with a specific surface area of 200 m 2 / g or more can be produced, while according to Czechoslovak patent 85674, a product with a specific surface area of only 80-120 m 2 / g is obtained. Increasing the specific surface area according to the invention results in an increase in the adsorption capacity of the product thus produced.

The amorphous synthetic silica produced by the process of the invention is particularly suitable as a carrier for vitamins, herbicides, fragrance compositions, as a filler in various mixtures of, for example, synthetic resins, toothpastes and the like.

'- 1 266793

Example 1

1090 ml of 10 wt. of CaCl ₂ solution with 70 ml of 31 wt. HCl and metered over one minute with vigorous stirring into 650 ml of dilute water glass with a concentration of 8.84% by weight. SiO ₂ and specific gravities 1089 kg / m 2. Diluted water glass is obtained by mixing 232 g of water sodium glass of density 38-40 ° Bé with 476 g of water. The precipitated suspension was then stirred for a further two hours and the pH was maintained at 4.5. The CaCl ₂ : SiO ₂ ratio during the precipitation was 1.9. The filter cake was dried at 240 ° C. Obtained 65g of product with the composition:

SiO _{2 content} 89.7% hm. bulk density 167 kg / m; specific weight 1 828 kg / m- pH 6 humidity 5.8% hm. whiteness 94.4% specific surface (BET) 200 m ² / g

Example 2

Sodium water glass with a density of 38 - 40 ° Bé mixed with sodium water glass with a density of 50 52 ° Bé in a ratio of 3: 2 and undiluted with water to a SiO ₂ content of 8.24% by weight.

Raw materials, ie dilute water glass, hydrochloric acid with a concentration of 31% by weight. and a calcium chloride solution having a concentration of 10% by weight. flowed continuously into the precipitator via hydrostatic flow meters, the HCl and the CaCl ₂ solution being mixed in the mixer before entering the precipitator. The raw materials flowed into the precipitator in such a ratio that the pH of the precipitating mixture was 4 and the CaCl 2 SiO 2 ratio was 1.9. The suspension from the precipitator is pumped by the pump into the maturation tanks and, after maturing for 90 minutes, is pumped into the press and filtered and washed with water. Cake and calolis with a dry matter content of 23.2% by weight. in the activator mixed with water to a suspension with a dry matter of 12.9% by weight. The suspension is dried in a spray dryer with hot flue gas. Obtained product with the composition:

SiC _{2 content} 90.5% hm. bulk density 122.0 kg / m ' PH 5.9 humidity 3% hm whiteness 90% specific surface (BET) 260 m ² / g

Example 3

The procedure was the same as in Example 2, but the pH was maintained at 2.3 during the precipitation and the CaCl ₂ : SiO ₂ ratio was 1.9.

Obtained product with the composition:

SiO _{2 content} 89.9% hm. bulk density 124.4 kg / m ' pH 6.0 humidity 5.18% hm. whiteness 89.3% specific surface (BET) 319 m ² / g

OBJECT OF THE INVENTION

Claims (1)

OBJECT OF THE INVENTION A process for the production of amorphous synthetic silica with a specific surface area of at least 2CO m 2 / g, characterized in that a dilute water glass solution containing 5-10% hit. precipitates silica with a mixture of hydrochloric acid and calcium chloride solution in such a ratio that the pH in the precipitating mixture is 2 - 5 and the ratio of calcium chloride to silica in the precipitating mixture is 1.5 "2.3.