RU2486133C1 - Method of producing silica sols soluble in anhydrous organic solvents - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering for producing colloidal particles of silica, specifically sols thereof (silica sols), which are soluble in anhydrous organic solvents, and can be used in chemical industry to produce various nanostructured polymer composite materials, in synthesis of various adsorbents, various binding substances, catalyst supports etc. The silica sol synthesis reaction is carried out in conditions of ultrasonic vibrations which prevent aggregation of nanoparticles.

EFFECT: simple synthesis technique, low power consumption when producing the end product and low cost thereof.

5 ex, 2 dwg

Description

The invention relates to chemical technology for the production of colloidal particles of silica, namely its sols (silicasole), soluble in anhydrous organic solvents. The invention may find application in the chemical industry for the production of various nanostructured polymer composite materials, in the synthesis of various adsorbents, various binders, carriers for catalysts, etc.

There are various methods for preparing silicasols soluble in anhydrous organic solvents.

A known method of producing silicasol, in the form of a dispersion in a hydrophobic organic solvent. A method of producing silica sol soluble in organic solvents is the centrifugation of an aqueous dispersion of silica sol to precipitate silica particles contained therein. The resulting silica precipitate is dissolved and dispersed in a hydrophilic organic solvent. This is followed by mixing the obtained sol with an oleophilic agent to modify the surface of silica particles with oleophilic compounds, and re-isolating the silica particles in the form of a precipitate by centrifugation of silica sol. The final step in the preparation of silica sol in a hydrophobic solvent is the mixing and dispersion of the separated silica particles in a hydrophobic organic solvent [1].

The method of obtaining alcohol (C _1-3 at) dispersion of silica sol (silica sol) containing less than 1% (wt.) Water and up to 56% SiO ₂ . The method of producing silica sol soluble in organic solvents consists in processing an aqueous dispersion of silica sol with a concentration of SiO _{2 of} 50% (wt.) Strongly acidic cation exchange resin to reach pH = 4, followed by the addition of 0.6-2 times the amount of alcohol and removal of the azeotropic mixture alcohol and water. The following is the separation of particles of a solid cation exchange resin and concentration of the filtrate of the alcohol dispersion of silica sol [2].

A known method of producing silicasol with a specific surface of 25 to 550 m ² / g, not containing aggregated particles. The method of producing silica sol consists in mixing an aqueous sol of silica with propanol, followed by distillation of an azeotropic mixture of water with propanol to obtain a concentration of SiO _{2 of} 10-50% (wt.), Water 7.5% (wt.) And propanol> 90% (weight .). The operation of replacing water with propanol is repeated sequentially, several times, until a stable propanol dispersion of silica sol is obtained [3].

The above methods for producing silicasols soluble in anhydrous organic solvents are based on the conversion of a previously prepared aqueous dispersion of silica sol by substitution of a solvent. The disadvantages of these methods are their multi-stage and, as a consequence, increased energy consumption in the production of silicasols. In addition, it is difficult to directly control the size of the particles of silicasol in the process of their synthesis, which is due to the use of previously obtained aqueous silicasols.

The closest analogue of the proposed method for producing silicasoles soluble in anhydrous organic solvents is the production method described in [4]. The essence of the method consists in the formation of the molecular structure of individual silica particles forming the synthesized silica sol by hydrolysis of a hyperbranched polyethoxysiloxane in a solvating solvent medium followed by intramolecular cyclization of the obtained product by boiling and distillation of the resulting water. Hydrolysis is carried out in the presence of acid until the complete conversion of ethoxyl groups. The distillation of water is carried out together with the distillation of the organic solvent. This method of producing silicasols allows to obtain organosoluble silicasols directly as a result of their direct synthesis, and not by substitution of a solvent in the initial silicasols, as described in [1-3]. By changing the parameters of the process for producing silica sol, it is possible to control the particle sizes of silica and obtain sols with desired characteristics (particle size 3-60 nm).

The disadvantage of the method for producing silica sol described in [4] is the need for the preliminary stage of the synthesis of hyperbranched polyethoxysiloxane from tetraethoxysilane or other alkoxysilanes, as well as the relatively high duration of the very stage of silica sol production, which increases the amount of energy consumed for the implementation of technological processes associated with the production of silica sol, and increases the cost of the final product.

The technical result of the claimed invention is that the proposed method for producing silicasols soluble in anhydrous organic solvents allows their synthesis directly from alkoxysilanes, which simplifies the synthesis technology, reduces energy consumption for the production of the final product and, as a result, reduces its cost.

The technical result is achieved due to the fact that the synthesis of silicazole is carried out under continuous exposure to ultrasonic vibrations and the gradual continuous introduction of water, necessary for the complete hydrolysis of alkoxysilane or alkoxysiloxane in the reaction mixture, while continuously distilling low molecular weight hydrolysis products, and substances can be taken as alkoxysilane or alkoxysiloxane or products of their partial hydrolysis from the series: tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane, and as a solvating solvents, solvents from the series: ethyl acetate, butyl acetate, acetone, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxane, while the ratio of alkoxysilane or alkoxysiloxane with a solvating solvent is such that the content of silica in the synthesized hydrolysis is 0 at the moment 3% of the mass.

Figure 1 shows a typical particle size distribution of synthesized silicasole. Figure 2 shows the dependence of the characteristic particle sizes of the synthesized silicasol on the concentration of alkoxysilane or alkoxysiloxane in the initial reaction mixture (in terms of SiO ₂ ).

The synthesis of silicasol soluble in anhydrous organic solvents is as follows: in a mixture consisting of alkoxysilane or a product of its partial hydrolysis, alkoxysiloxane and a solvating solvent, water is gradually supplied under constant heating and exposure to ultrasonic vibrations. As a result of the hydrolysis of alkoxysilane or alkoxysiloxane, a low molecular weight product is formed - monohydric alcohol and silicon dioxide in the form of soluble nanosized particles that form a sol. The low molecular weight hydrolysis product is constantly removed from the reaction mixture along with excess solvent by distillation. At the end of the process, when all the alkoxysilane or alkoxysiloxane contained in the reaction mixture is completely hydrolyzed, distillation of the excess solvent is possible in order to obtain more concentrated silicasoles. In this case, at the initial stage of synthesis, the formation of primary particles of silicon oxide occurs, which is common for all types of processes for producing silicasoles. With the further introduction of water and the formation of an additional amount of silicon oxide as a result of hydrolysis of the remaining amount of alkoxysilane or alkoxysiloxane, the enlargement of primary particles occurs due to their growth, but not aggregation. The latter is due to the fact that particle aggregation is difficult as a result of powerful ultrasonic action on the reaction mixture. In addition, since the deposition of silicon oxide on existing primary particles is energetically advantageous, the formation of new particles practically does not occur. The above is confirmed by particle size data obtained by dynamic light scattering. Figure 1 shows a clear statistical distribution of nanosized particles of synthesized silicasole, mainly in the region of 12 nm. Figure 2 shows the dependence of the characteristic particle sizes of the finished silica sol on the concentration of alkoxysilane or alkoxysiloxane in the initial reaction mixture.

Based on the proposed solutions, a number of silicasoles were synthesized, with various concentrations of alkoxysilane or alkoxysiloxane in the initial reaction mixture, as well as various combinations of alkoxysilane or alkoxysiloxane with solvating solvents. At the same time, tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane were tested as alkoxysilane, and products of their partial hydrolysis were tested as alkoxysiloxane. The solvating solvent was selected from the series: ethyl acetate, butyl acetate, acetone, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxane. Regardless of the combination options for the types of solvating solvent and alkoxysilane or alkoxysiloxane, their ratio in the initial reaction mixture was chosen so that the silica content in the synthesized silicazole at the end of the hydrolysis process was 0-61.3 mass%. It was experimentally established that the particle size of silicasol does not depend on the combination of types of solvating solvent and alkoxysilane or alkoxysiloxane, but is determined by the concentration of alkoxysilane or alkoxysiloxane in the solvating solvent. The rate of introduction of water into the reaction mixture was determined experimentally in each tested synthesis variant. An excessively high rate of water supply to the reaction mixture led to the formation of silicasol with a wide statistical distribution of particle sizes, and an excessively low rate of water supply increased the synthesis time. The average synthesis time was no more than 2 hours, while the synthesis time of silica sol according to the prototype of the invention [4], including the stage of synthesis of hyperbranched polyethoxysiloxane, was about 80 hours. Below, as an example, are some typical of the tested options for the synthesis of silicasol according to the invention.

Example 1

The ratio in the initial reaction mixture

butyl acetate: tetraethoxysilane = 25: 1

Water - in the amount necessary for the complete hydrolysis of tetraethoxysilane

The synthesis time is 1.7 hours

The average particle size of silica sol is 3 nm

Example 2

The ratio in the initial reaction mixture

diethylene glycol dimethyl ether: tetrapropoxysilane = 9: 1

Water - in the amount necessary for the complete hydrolysis of tetraethoxysilane

Synthesis time - 1.4 hours

The average particle size of silicasol is 24 nm

Example 3

The ratio in the initial reaction mixture

tetrahydrofuran: tetrabutoxysilane = 8: 1

Water - in the amount necessary for the complete hydrolysis of tetraethoxysilane

Synthesis time - 1.6 hours

The average particle size of silica sol is 45 nm

Example 4

The ratio in the initial reaction mixture

acetone: ethyl silicate - 40 (product of partial hydrolysis of tetraethoxysilane) = 8: 1

Water - in the amount necessary for the complete hydrolysis of tetraethoxysilane

Synthesis time - 1.3 hours

The average particle size of silicasol is 64 nm

Example 5

The ratio in the initial reaction mixture

dioxane: tetraethoxysilane = 5: 1

Water - in the amount necessary for the complete hydrolysis of tetraethoxysilane

Synthesis time - 1.8 hours

The average particle size of silicasol is 84 nm

Thus, the above data confirm the reliability of the claimed technical result.

Sources of information taken into account when drawing up an application for an invention

1. Patent EP No. 372124 B ₁ , 1992

2. EP patent No. 812803 A ₁ , 1996

3. Patent EP No. 699626 A ₁ , 1996

4. RF patent No. 2140393 1999 (prototype).

Claims (1)

The method of producing silicasols soluble in anhydrous organic solvents, consisting in the hydrolysis of alkoxysilane or products of its partial hydrolysis - alkoxysiloxanes in the environment of a solvating solvent, followed by intramolecular cyclization of the obtained product and the joint distillation of water and an organic solvent, characterized in that the synthesis is carried out under continuous exposure to ultrasonic oscillations and gradual continuous introduction of water necessary for the complete hydrolysis of alkoxysilane or alkoxysilox in the reaction mixture, with continuous distillation of low molecular weight hydrolysis products, moreover, substances or products of their partial hydrolysis from the series: tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane can be taken as alkoxysilane or alkoxysiloxane, butyl acetate, butyl acetate, ethyl acetate as a solvating solvent acetone, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxane, wherein the ratio of alkoxysilane or alkoxysiloxane to solvate solvent is such that the silica content in the silica sol synthesized at the end of the hydrolysis process was 0-61,3 wt.%.

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