RU2447020C1 - Method of obtaining fine silica - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemistry and the technology of inorganic silicon-oxygen compounds and can be used to produce fine silica from chlorosilane by-products from chemical-metallurgical chloride production of polysilicon and other metals and chemical production of organochlorosilanes. The method involves hydrolysis, subsequent condensation and deposition of particles in a solvent. The starting material used is chlorosilanes with functionality higher than 3, which, before hydrolysis, are alkoxylated with lower aliphatic alcohols C1-C3 in amount of 1.0-1.2 moles alcohol per 1 g-atom chlorine in chlorosilane. Further, the reaction mixture is diluted with a solution of alcohol with water in amount of 0.53-0.77 moles water per 1 g-atom alkoxy groups to until achieving concentration of deposited particles in the solvent of 14.0-25.2 wt %. The reaction mixture is boiled at 67-84°C for 2.5-3.5 hours.

EFFECT: simple technique of obtaining fine silica from high-functional chlorosilanes with output of 97,3-98,5 wt % of the load, improved quality and application properties of said silica, with simultaneous trapping of 89,4-96,7 wt % of the load of the formed gaseous hydrogen chloride.

3 cl 13 ex, 2 tbl

Description

The invention relates to the chemistry and technology of inorganic silicon-oxygen compounds and can be used to obtain finely divided silicas from associated chlorosilanes of chemical and metallurgical chloride production of polysilicon and other metals (titanium, zirconium, aluminum) and chemical-technological production of organochlorosilanes.

The invention can also be used to obtain organosiloxane polymer compounds with regular structures of macromolecules from organochlorosilanes.

The currently existing main industrial technologies for the production of powders of synthetic silicon dioxide ( a- SiO ₂ ) are based on:

- liquid-phase deposition of amorphous silicic acid from solutions of alkali metal silicates with acidic reagents (hydrochloric, sulfuric, carbonic acids) at a temperature of 70-90 ° C;

- gas-phase combustion of chlorosilanes in plasma or at a temperature of 1000-1100 ° in an atmosphere of hydrogen and / or methane with the simultaneous capture of the resulting hydrogen chloride (pyrogenic method);

- hydrolytic treatment of chlorosilanes with water or water vapor (airgel method), including when they are chemically grafted onto the surface of finely divided silica.

Known technologies for the synthesis of silicas are associated with significant production and technological difficulties and high energy costs. The resulting commercial products are heterogeneous in structure, have a high dispersion of polydispersity. When using such silicas, their additional modification is required, for example, hydrophobization or hydroxylation. In addition, the particles are contaminated with chemical impurities that limit their use in high-tech fields, for example, as reinforcing fillers in the production of high-voltage insulating composites, biosorbents, inert carriers of medical preparations, highly pure raw materials for producing synthetic quartz for optics or growing quartz crystals, etc. P.

Thus, the creation of a simplified method for producing dispersed silicas with low resource costs and modified fine powders of high purity based on them with functional properties for widespread use in high-tech fields is an important and urgent task.

The technical problem solved by the claimed method is to simplify the technology for producing finely dispersed modified silicas and gaseous hydrogen chloride from chlorosilanes, which are by-products of chemical and metallurgical chloride production of polysilicon and other metals (titanium, zirconium, aluminum) and chemical-technological production of organochlorosilanes.

A known method of producing modified dispersed silica by preliminary hydroxylation of dispersed silica in the presence of catalytic amounts of acid at 105-110 ° C for 1.5-2 hours, drying, surface activation with alkali metal carbonates or alkali, followed by chemical modification with organoelement compounds of the general formula R _n SiCl _4-n , where n = 1-3; R is H; C ₂ H ₅ ; ClCH ₂ ; With ₆ H ₅ in the ratio (16-100): 1, respectively, with mechanical mixing of the components (RF Patent No. 2152903, publ. 07.20.2000, MKI: C01B 33/18).

However, this method uses a complex and multi-stage technology for the modification of finely divided silicas. In this case, the chemical grafting of organoelement compounds on the surface is not controlled and the gaseous reaction products (hydrogen chloride) formed from the particle volume are ineffectively removed by blowing with an inert gas or air. The resulting silicas contain residual chlorine ions (pH = 5-6) from the initial chlorosilanes, which negatively affect the properties of powder materials and products from them.

A known method of producing synthetic silicon dioxide from organosilicon monomer and polymer compounds, including hydrolysis, subsequent drying, thermal oxidation at 400-1200 ° C, grinding and dispersing particles to 0.5-100 microns (Japanese Application No. 58-151318, publ. 08.09 .1983 MKI: C08L 101/00; C01B 33/18).

However, this method implements a complex and costly technology, the implementation of which is based on thermal oxidative degradation of the synthesized organosilicon compounds: organosilanes, polysiloxanes and polysilazanes. During their thermal degradation, the organic part of the raw material is burned and lost, which is economically disadvantageous. In this case, the resulting silica particles are contaminated with combustion products, which does not increase their quality, but leads to an increase in their polydispersity and an increase in cost. At the same time, environmental pollution of the atmosphere with volatile products of thermal oxidation occurs.

A known method of carrying out low-temperature hydrolysis of organotrichlorosilanes in order to obtain finely divided powdery products that can be used as hydrophobic additives in construction equipment, as fillers in the manufacture of rubber, etc. (Method for the hydrolysis of organotrichlorisilanes. Auth. St. USSR No. 267907, published July 10, 1970; MKI: C08G 77/06). The method adopted for the prototype.

However, the implementation of this hydrolysis method is complicated by the consumption of a significant amount of auxiliary reagents to obtain a unit of the target product (1.08-2.13 g-mol of toluene; 001-0.15 g-mol of the sodium salt of an alkyl ester of a mono- or dibasic fatty sulfonic acid and 0.78 -5.53 g-mole of water per 1 g-atom of Cl ^{- the} initial chlorosilanes), which at the end of the synthesis process with dissolved hydrogen chloride in the form of hydrochloric waste are sent for disposal. In this case, polydisperse powders are formed with a specific surface area varying from 2 to 300 m ² / g.

The technical result of the invention is to simplify the technology for the preparation of finely divided silicas from highly functional chlorosilanes with a yield of 97.3-98.5% wt. from loading, improving their quality and consumer properties while capturing 89.4-93.7% wt. from loading the resulting gaseous hydrogen chloride.

The technical result is achieved in that in a method for producing finely dispersed silicas from chlorosilanes, including hydrolysis, subsequent condensation and precipitation of particles in a solvent, characterized in that the starting materials use chlorosilanes with a functionality of more than three, which are alkoxylated with lower aliphatic alcohols C1-C3 before hydrolysis based on 1.0-1.2 mol of alcohol per 1 g-atom of chlorosilane chlorine, followed by dilution of the reaction mixture with a solution of alcohol with water, based on 0.53-0.77 mol of water per 1 g-atom alkoxy RUP to the concentration of precipitated particles in the solvent of 14.0-25.2% wt. and boiling the reaction mixture in the temperature range of 67-84 ° C for 2.5-3.5 hours.

The essence of the invention lies in the fact that the preliminary alkoxylation of chlorosilanes with an equimolar amount of alcohol leads to the complete substitution of silicon for alkoxy groups in silicon and the maximum removal of the resulting gaseous hydrogen chloride from the reaction zone without the formation of alkyl chlorides. Subsequent dilution of the reaction products with boiling alcohol and the gradual introduction of hydrolyzing water with it leads to a stepwise substitution of alkoxy groups under mild homogeneous conditions for silanol with their subsequent polycondensation in an acidic medium by the intramolecular mechanism. In this case, an effective cyclization of the formed siloxane bonds and the formation of homogeneous porous discrete particles of spherical shape without the content of residual silanol groups in the structure occur.

A simplification of the technology for producing finely divided silicas consists in reducing the molar consumption of organic solvents and water per 1 g chlorine atom of the chlorosilanes used and in performing stepwise hydrolytic polycondensation in a homogenized medium while the reaction mixture is boiling. Compared with the cooling of the reaction mixture, which is traditionally used in the known methods for the aqueous hydrolysis of chlorosilanes, boiling provides a uniform temperature distribution in the reaction volume and smoothes out the supercooling (endothermic effect) arising from the intense evaporation of the resulting gaseous hydrogen chloride, and local overheating of the reaction mixture when it interacts with injected water. In addition, boiling promotes the formation of homogeneous discrete particles and the intensive evolution of gaseous hydrogen chloride from the reaction mixture.

Quality improvement is achieved by forming porous homogeneous silica particles of spherical and oval shape with a size of 5-50 microns with a narrow variation in specific surface area (98-243 m ² / g) without inclusions of sorbed hydrogen chloride impurities.

Improving the consumer properties of silicas is achieved by obtaining particles of a spherical and oval shape without residual silanol groups in the structure or with a minimum (<0.5% wt.) Their content. In addition, consumer properties are improved due to the presence of modifying hydrocarbon substituents (-H; -CH ₃ ; -C ₂ H ₃ ; C ₆ H ₅ ) at the silicon atom, the content of which and the conditions of introduction are set at the synthesis stage.

Hydrogen chloride formed in the inventive method is almost completely trapped during freezing in a collection trap, and the water-alcohol mixture with residual impurity hydrogen chloride, separated from the precipitated silica suspension, is distilled and the acidic components obtained are reused in the processes for the esterification and hydrolysis of chlorosilanes .

Justification of the parameters.

Preliminary alkoxylation of chlorosilanes with lower aliphatic alcohols C1-C3 (methyl, ethyl, isopropyl) is carried out at the rate of 1.0-1.2 mol of alcohol per 1 g-atom of chlorosilane chlorine. The use of alcohol of less than 1.0 mol per 1 g of chlorine atom does not lead to complete alkoxylation of chlorosilanes and the subsequent introduction of water is accompanied by violent hydrolysis with intensive heating of the reaction mixture and uncontrolled condensation of silanol groups to form a gel, the processing of which does not allow to obtain a high-quality product. The use of alcohol greater than 1.2 mol per 1 g-chlorine atom leads to the formation of alkyl chloride and a decrease in the yield of gaseous hydrogen chloride. In addition, due to excess alcohol, the effective loading of the starting reagents per unit of reactor is reduced and the yield of final products is reduced, which is not justified both technologically and economically.

Dilution of the reaction mixture with alcohol to ensure a concentration of precipitated silica particles of 14.0-25.2% (wt.) Is due to mild hydrolysis and subsequent controlled polycondensation of the formed silanol groups and effective cyclization of siloxane bonds in a homogeneous medium.

When the concentration of silica particles precipitated in alcohol is less than 14% wt. the yield of the target products per unit reactor volume is reduced, which does not lead to a simplification of the synthesis technology and an increase in the quality of silica particles. Concentration of more than 25.2% wt. leads to harsh conditions for the subsequent hydrolysis of chlorosilanes, accompanied by intense heating of the reaction mixture and uncontrolled polycondensation of silanol groups and gelation of precipitated silicas.

The required amount of hydrolyzing water is 0.53-0.77 mol per 1 g-atom of alkoxy groups. Less than 0.53 mol of water per 1 g-atom of alkoxy groups leads to prolonged and incomplete hydrolysis, which negatively affects the processes of polycondensation and cyclization during the formation of discrete particles. The yield of high-quality silica particles decreases and the gel yield increases. The introduction of more than 0.77 mol of water per 1 g-atom of alkoxy groups leads to intense heating of the reaction mixture due to the exothermic effect upon contact with H ₂ O-HCl, which contributes to the uncontrolled process of hydrolytic polycondensation and to a decrease in the yield of the target products.

The temperature range of 67-84 ° C is due to the boiling modes of the reaction (azeotropic) mixtures. The lower limit of 67 ° C is achieved by using methyl (C1) alcohol in the reaction (T _bp = 64.6 ° C). The synthesis process below 67 ° C occurs with a significant dilution of the reaction mixture with methyl alcohol, which leads to a violation of the ratio of the reaction components, a decrease in the practical yield of the target products and a deterioration in their quality. The process above 83 ° C is possible only through the use of alkoxylating alcohol C> 3, for example, butyl (C4) alcohol (T _bp. = 117.7 ° C), iso-amyl (C5) alcohol (T _bp. = 132 ° C ) and others. With an increase in the boiling point of alcohols, their molecular weight increases and at the same time the adsorption capacity of hydrogen chloride increases, which does not allow it to be effectively desorbed from the reaction products. In addition, with an increase in the molecular weight of alcohols, their mutual solubility with water changes and the conditions of homogenization of the reaction medium are violated. The water-alcohol mixture becomes heterogeneous and the substitution of reactive groups during polycondensation leads to gelation.

The time required for the synthesis of discrete particles in the boiling mode of the reaction mixture is 1.0-2.0 hours, which is sufficient for the formation of spherical forms of silica particles and maximum desorption of hydrogen chloride.

Boiling less than 1.0 hours is insufficient to complete the stepwise process of hydrolytic polycondensation, which leads to poor-quality formation of silica particles and a low yield of hydrogen chloride.

Boiling the reaction mixture for more than 2.0 hours does not simplify the technology and does not improve the quality of the target products, but leads to increased energy costs and is not economically justified.

The method is illustrated by the following examples.

Example 1

182.6 ml (270.3 g) silicon tetrachloride (f = 4.00) and slowly from the metering funnel are poured into a 1000 ml round-bottomed four-necked flask with a heater equipped with a glass stirrer, a reflux condenser, a mercury thermometer and a loading hopper-dispenser dropwise while stirring (n = 500-800 rpm), 191.4 ml of methyl alcohol are calculated dropwise at a rate of 1.1 mol of alcohol per 1 g of chlorosilane chlorine atom. As the alcohol enters, gaseous hydrogen chloride is formed, which, having high volatility (T _boil. = -90 ° C), exits through the upper part of the refrigerated refrigerator. After spending all the alcohol, stirring is continued for one hour, followed by turning on the mantle heater and bringing the reaction mixture to boiling point. As the reaction mixture boils through a metering funnel, 253.9 ml of methyl alcohol are mixed with 53.7 ml of water (at the rate of 0.55 mol per 1 g-chlorine atom). After the introduction of the entire amount of a water-alcohol solution, the reaction mixture was continued to boil with stirring for one and a half hours. During stirring during boiling, solid silica particles precipitate from the reaction mixture at the bottom of the flask. At the end of the process, the obtained reaction products in the form of a suspension are separated from the water-methanol mixture, washed from traces of HCl with dilute (0.01 N) ammonia water on a Shot glass filter under vacuum. Then, the silica suspension is washed with water to pH = 7 (according to the universal indicator) and dried in an oven at 100 ° C to a powder state for 1 hour. At the end of the silica powder is packaged in a glass dish with a sealed lid.

The yield of fine silica powder was 79.7 g or 97.9% (wt.) From the load.

Characterization of finely divided silica:

- in aggregated form is a white powder;

- particles have spherical and oval shapes, 5–50 μm in size (determined using a Vega II XMU-Tescan scanning electron microscope (Tescan, Czech Republic) at a magnification of × 10,000);

- the specific surface of the particles is 236 m ² / g (determined by the known method of measuring the nitrogen adsorption isotherm - BET method, GOST 14922-77);

- the pH of the aqueous extract is equal to 7 (on the color scale of the universal indicator);

- mass fraction of moisture (moisture content) is 1.5% wt. (determined according to GOST 14922-77);

- bulk density (determined by the standard method for bulk materials, GOST 14922-77):

uncompressed - 50 g / l;

condensed - 130 g / l.

HCl gas after passing through the drying column is condensed in a measuring trap cooled at minus 100 ° C in a Dewar vessel and then the trap is weighed together with the HCl condensate. The yield of HCl condensate was 181.0 g, which corresponds to 91.3% wt. from loading. After weighing, the condensate is poured into a sealed container and sent for safekeeping. Breakthrough of traces of hydrogen chloride (not more than 0.05-0.1% wt.) Is captured in the trap-absorber with a slightly alkaline solution.

A methanol-water solution with a trace amount of HCl is subjected to distillation distillation, after which the separated acidic components are reused in the re-process during esterification and hydrolysis.

Examples 2 ÷ 7:

The synthesis procedure is similar to Example 1, the technological parameters and properties of the obtained silica powders are shown in Table 1 and Table 2.

Examples 8 ÷ 13: - embodiments of the method with technological modes of hydrolytic polycondensation, beyond the stated limits.

Thus, the claimed method allows you to:

- to simplify the technology for producing powders of modified finely dispersed silicas from associated chlorosilanes by minimizing the consumption of reagents and related components;

- to improve the quality of silica particles by eliminating sorption of hydrogen chloride from the pores by chemical means under the action of ammonia water, as well as by reducing the dispersion of their dispersion to 5-50 microns and specific surface to 98-243 m ² / g;

- to expand the range and improve the consumer properties of silica particles by introducing at the stage of synthesis modifying trichlorosilanes with hydrocarbon substituents at silicon atoms: -H; -CH ₃ ; -C ₂ H ₃ ; -C ₆ H ₅ and others.

- minimize the loss of hydrogen chloride;

- reuse acidic water-alcohol components after their separation in the processes of esterification and hydrolysis of chlorosilanes.

Claims (3)

1. A method of producing finely dispersed silicas from chlorosilanes, including hydrolysis, subsequent condensation and precipitation of particles in a solvent, characterized in that chlorosilanes with a functionality of more than three are used as feedstock, which are subjected to alkoxylation with lower aliphatic alcohols C1-C3, based on 1 , 0-1.2 moles of alcohol per 1 g of chlorosilane chlorine atom, followed by dilution of the reaction mixture with a solution of alcohol with water at the rate of 0.53-0.77 moles of water per 1 g of alkoxy atom to a precipitate concentration particles in the solvent of 14.0-25.2 wt.% and boiling the reaction mixture in the temperature range of 67-84 ° C for 2.5-3.5 hours 2. The method according to claim 1, characterized in that as a feedstock, associated chlorosilanes of chemical-metallurgical chloride production of metals and chemical-technological production of organochlorosilane are used. 3. The method according to claim 1, characterized in that methanol, ethanol and iso-propanol are used as aliphatic alcohols C1-C3.