DD293097A5 - METHOD FOR THE PRODUCTION OF FINE PARTICULAR AMORPHIC TANNING PEBBLE ACIDS - Google Patents

Abstract

The invention relates to a process for the preparation of highly structured finely divided precipitated silicas from aqueous alkali silicate solutions. Fine-particle precipitated silicas are used as active fillers in numerous fields of application. The highly structured, finely divided silicic acids according to the invention are prepared by reacting alkali metal silicate solutions with acids or acidic substances when mixed by simple stirring and by temporarily applying high shear forces, so that, before reaching an electrolyte concentration of 0.3 N, a mixture of cationic and nonionic surfactants in one Concentration must be added so that the coagulation takes place below the critical micelle concentration of the surfactants used and of the surfactant mixture {finely divided silicas; cationic and nonionic surfactants, critical micelle concentration}

Description

Field of application of the invention

The Eitindung relates to a process for the preparation of finely divided amorphous precipitated silicas from aqueous alkali metal silicate solutions and acids or acid-like substances.

Finely divided silicas are used as active fillers in the processing of polymers. They are also used in the thickening and thixotroping of various material systems, as flow agents for bulk solids, as extenders for emulsion paints and carriers of biologically active substances.

Characteristic of the known state of the art

The majority of finely divided synthetic silicic acids is obtained by precipitation by wet chemical methods.

Raw materials for the production of silicic acids by wet chemical means are alkali metal silicate solutions, mainly Sodium waterglass solutions from which, while stirring at elevated temperatures, by addition of acids or acids Gases silicic acids are precipitated, whereby the occurrence of a gel state is avoided. Most precipitation processes involve partial neutralization of an alkali silicate solution in the presence of a soluble one Salt, which causes the coagulation of the silica. Here are the following basic process steps

run through:

In the neutralization of alkali metal silicate solutions with acids or acidic gases formed by polycondensation

small-molecule silicic acid colloidal SiO ₂ particles, which depend on the pH and the temperature to a certain

Grow in size. The electrolytes released during neutralization weaken the electrochemical double layer of the Kieselsäuresolteilchen and cause so from a certain concentration, the coagulation of these particles to agglomerates. The extent of coagulation is determined by the pH and the alkali ion concentration. It can also be additional

other electrolytes such as alkali, ammonium, calcium or other polyvalent metal ions are used for coagulation.

The coagulation of the colloidal SiO ₂ particles into agglomerates which form a suspended precipitate is controllable over the

pH and the metal ion concentration.

The resulting agglomerate structures (coagulates) are replaced by those in the further simultaneous and separate addition

crosslinked and reinforced by alkali silicate solution and acid-releasing "active silicic acid", wherein growth of these reinforcing silica building blocks must be avoided .. Under "active silicic acid" is SiO ₂ with a low

Degree of polymerization understood. The properties of the final products (precipitated silicas) depend crucially on particle growth, coagulation and

the reinforcement of the agglomerates. By changing the temperature, the pH and the electrolyte concentration, the properties of the precipitated silicas can be varied widely.

The disadvantages of all known processes for the preparation of finely divided precipitated silicas consist in the difficulty of

separate and controlled flow of particle growth, coagulation and amplification products with identical

Properties, such as primary particle size and distribution, size and size distribution of the aggregates or agglomerates,

specific surface and "high structure" reproducible.

Methods are known which provide targeted coagulation of colloidal SiO 2 particles by using compounds with

reach quaternary ammonium groups or similar groups.

Thus, US Pat. No. 2,819,002 describes a process for preparing planar aggregated silicas by flocculation with cationic Substances such as cetylmethylethylammonium bromide or similar compounds of phosphorus, of sulfur and of Arsenic. The flocculation occurs above the critical micelle concentration. Also according to DE 1003195 and GB 805491 finely divided silicas are prepared in the quaternary Ammonium compounds can be added after the precipitation of the suspension. In these procedures, the Ammonium compound not in the responsible for the Eigt of the precipitated silica process stages, but

causes only by flocculation of the SiO ₂ aggregates easier filterability.

According to DD 0202679 improved production of finely divided silicas is possible, if one with a Electrolytes mixed silica sol solution at a pH of 1 to 6 and elevated temperature by adding a solution

a surface-active nonionic polymer, such as homologous or substituted polyethylene glycols, a precipitation, wherein the polyethylene glycols are used in or above their critical micelle concentration.

All known processes for the preparation of powdery (one-part amorphous silicas using surface-active substances are characterized either by high costs, or by the surface-active substances used only to improve the filterability of the silica suspension or to prevent premature sedimentation of the precipitated products, and a targeted influencing of the aggregation of the SiO ₂ primary particles is not achieved. '-

Object of the invention The trick of the invention is the economical production of finely divided amorphous precipitated silicas. Explanation of the essence of the invention The object of the invention is a process for the preparation of finely divided silicic acids by controlling the precipitation, According to the invention, highly structured, finely divided silicas are obtained by reacting alkali silicate solutions with acids or

acidic substances when mixed by simple stirring and by temporary action of high shear produced by the fact that prior to reaching an electrolyte concentration of 0.3 N solutions of mixtures of cationic and pichtionogener surfactants are added in a concentration that coagulation below the critical

Micelle concentration of the surfactants used and the surfactant mixture is carried out. As non-ionic surfactants homologous and substituted polyethylene glycols are used. As cationic surfactants

quaternary ammonium compounds of the type trialkyl benzyl ammonium used. These cationic surfactants have a critical micelle concentration of 10 ^-5 to 10 ^-3 mol / l.

The inventive method is carried out so that dilute sodium silicate solution with a SiCVNa ₂ O Ratio (r _w modulus) between 3.0 and 4.9 and a SiO ₂ content between 50 and 100 g / l with dilute hydrochloric acid Concentration between 25 and 350g / l are dosed into a pool of water, that a degree of neutralization of 0.8 and a Electrolyte concentration of 0.3 N should not be exceeded. The reaction takes place in a temperature range from 80 to 100 ^° C.,

wherein the reaction mixture is stirred. To this sol phase, an aqueous solution of a mixture of cationic nonionic surfactants is added in a concentration such that the critical micelle formation concentration used

Surfactants and the surfactant mixture at any time of the synthesis in the reaction mixture is achieved. The ratio of Amount of the surfactant mixture to the SiO ₂ amount is 1: 100 to 1:80 in the sol stage and 1: 500 to 1: 400 in the total precipitation. As a result, targeted aggregation of the SiO ₂ primary particles formed in the sol phase is initiated. It arises Teilchonverbändu of primary particles of uniform particle size.

For rapid adjustment of a balance of this aggregate formation, it is expedient to allow high shear forces in the meantime to be acted upon by technically customary process-engineering devices on the reaction mixture.

The flocculate suspensions resulting from the addition of the surfactant mixture are usually further processed,

wherein by further simultaneous and separate supply of water glass solution and acid, the loose aggregates of

Flocculation phase to be strengthened. The degree of amplification is chosen according to the desired application and is

between 0.1 and 0.25 (amount of SiO ₂ in the sol phase in relation to the final SiO ₂ concentration).

The process according to the invention can be carried out batchwise and continuously.

By the novel process highly structured finely divided silicic acids are obtained, the specific Surface of 20 to 180m ² / g, whose average primary particle size of 10 to 100nm, whose average aggregate or. Agglomerate size without additional milling of 2 to 20 pm and their Dibutylphthalatadsorption of 100 to 400 ml Dibutyl phthalate per 100g SiO ₂ can be varied. It is an advantage of the method according to the invention that by adhering to the concentration requirement, the used

Minimized amount of surfactant and thus the precipitation conditions are optimized.

It was surprising and unpredictable that the flocculation effect of cationic surfactants over colloidal SiO ₂

can be significantly increased if non-ionic surfactants are added. This is the otherwise necessary amount

Cationic surfactant lowered to a quarter. This effect occurs even in the presence of very small amounts of nonionic surfactants. embodiments example 1 43.31 of water and 20 l of water glass (R _w = 3.67, 10% by mass of SiO ₂ ) are placed in a 250 l stirred reactor and heated to 90 ° C. After reaching the temperature, HCl is metered in at a rate of 9.46 l / h (c _H ci = 56.08 g / l). After reaching a NeutralisationsgraouS of 80% and lowering the temperature to 80 ⁰ C are water glass solution with

80 l / h and hydrochloric acid with 47,28l / h simultaneously and separately added. The product is filtered and dried. The dry one

Silica has the following texture values:

- specific surface: 55 mVg,

- DBP adsorption: 169DBPZIOOgSiO ₂ .

Example 2 The procedure is as in Example 1. After reaching a neutralization degree of 80%, 6g

((CH 3) ₂ CH ₂ C _e H ₆ CH ₂ CONHAlkyl) N ⁺ Cr (Quartolan, product of the VEB Hydrierwerk Rodleben) and 0.1 g

Octylphenylpolyethylenglykol dissolved in 11 dissolved in water and the temperature lowered to 80 ° C. After that will be Water glass solution (401 / h) (R _w = 3.67, 10Ma .-% SiO ₂ ) and hydrochloric acid (23.64l / h) (c _H ci = 56.08 g / l) separated and simultaneously

added.

After 2 hours, the reaction product was filtered off, washed and dried. The silica has the following texture values:

- specific surface: 29mVg

DBP adsorption: 258 ml DBP / 100 g SiO ₂ ,

Proportion below 1 μΐπ = 3.6 Ma .-%, proportion above 10 pm = 8 Ma .-%.

Example 3

The procedure is as in Example 1. After reaching a degree of neutralization of 80%, ₆ g ((CH ₃ I ₂ CH ₂ CeH ₆ AIRyI) N ⁺ Cr (C ₄ -Conratrat, product of the VEB Chemiekombinat Leuna-Werke) and 0.1 g Octylphenylpolyethylenglykol be dissolved in 11 water are added and the temperature lowered to 8O ⁰ C. Thereafter, water glass solution (80 l / h) (R _w = 3.67, 10Ma .-% SiO ₂ ) and

Hydrochloric acid (c _H ci - 56.08 g / l) (47.28 l / h) separated and introduced simultaneously. After 1 hour, the reaction product is filtered off,

washed and dried.

The following texture data was determined:

- specific surface area: 38m * / g,

DBP adsorption: 235ml DBP / 100g SiO ₂ ,

- Share under 1 μητι = 2.1 Ma .-%, share of ΙΟμιτι = 6.2Ma .-%.

Claims (2)

1. A process for the preparation of hochstnikturierten finely divided silicic acids by reacting alkali metal silicate solutions with acids or acidic substances when mixed by simple stirring or by temporary action of high shear forces, characterized in that prior to reaching an electrolyte concentration of 0.3 N solutions of mixtures cationic and nonionic surfactants are added in a concentration such that coagulation occurs below the critical micelle concentration of the surfactants and surfactant mixture used. 2. The method according to claim 1, characterized in that the ratio of the mixture of cationic and nonionic to the amount of SiO ₂ present is 1: 100 to 1:80 in the sol stage and 1: 500 to 1: 400 in the total precipitation batch.