RU2119491C1 - Method of isolation of trimethylchlorosilane from its mixture with silicon tetrachloride - Google Patents

Abstract

FIELD: organosilicon compounds. SUBSTANCE: invention relates to organosilicon compounds employed in producing various-type polymer silicon-containing compounds and consists in treating trimethylchlorosilane-silicon tetrachloride mixture with reagents I or II in presence of acid catalyst followed by isolation of trimethylchlorosilane by rectification. Reagent I has general formula R¹Si(OP)_4-n, where n=0-2, R is C₁-C₄-alkyl, and RO[Si(OR)₂O]_nH, methyl, ethyl or phenyl. Reagent II has general formula C₁-C₄ where n=1-10 and R (C₁-C₄) alkyl. EFFECT: simplified procedure. 2 cl, 5 ex

Description

 The invention relates to the chemistry of organosilicon compounds used to produce polymer silicon-containing products of various classes.

In the technology of organosilicon synthesis, there are a number of processes characterized by the formation of a mixture of trimethylchlorosilane and silicon tetrachloride. The mixture itself is not a commercial product, but its components, especially trimethylchlorosilane (which is a scarce product), are of considerable value. In this regard, the problem of the separation of trimethylchlorosilane from its mixture with silicon tetrachloride is quite relevant, although it is associated with certain difficulties. These difficulties are exacerbated when the molar ratio of the components is close to unity, because the mixture is azeotropic with a boiling point of 54.6 ^o C.

 Of particular interest is the separation of trimethylchlorosilane from an azeotropic mixture is of direct synthesis technology for trimethylchlorosilanes (MCS). World production of MHS currently reaches 900 thousand tons per year. Upon rectification of the products of direct synthesis of MHS, an azeotropic mixture of trimethylchlorosilane with silicon tetrachloride is formed in an amount of 10-40 kg per ton of commodity monomers. The separation of the azeotropic mixture was solved in various ways. Most studies on the separation of trimethylchlorosilane from the azeotrope are aimed at finding methods of bonding only silicon tetrachloride or converting it into compounds with a higher boiling point and subsequent isolation of commercial trimethylchlorosilane (metal halide adsorption (US Pat. Japan 74 (1953)); complex formation with pyridine, dimethylformamide ( US Pat. No. 2,752,379 (1956)); azeotropic distillation with acetonitrile (US Pat. No. 3,114,678 (1963)); ethoxylation (US Pat. No. 2,945,873 (1960)). However, these methods are complex and are accompanied by a large amount of unused waste. Another possible way is the conversion of both components of the azeotropic mixture to obtain compounds such as hexamethyldisiloxane and others (alcohol and alkaline hydrolysis (US Pat. England 735101 (1955)); interaction with fluorine compounds (US Pat. US. 1142364 (1963)). Due to the complexity of the processes taking place in this case, these methods also did not find application in industry.

 At present, in plants of the organosilicon complex, the azeotropic mixture is subjected to hydrolysis with water, neutralized wastewater, and solid hydrolysis products are stored at the landfill.

 Closest to the proposed method is a method for the separation of trimethylchlorosilane from a mixture with silicon tetrachloride, according to which the mixture is reacted in the liquid phase in the presence of an acid catalyst with a reagent such as trimethylethoxysilane, as a result of which silicon tetrachloride is converted into silanes containing ethoxy groups (US Pat. England 647181 (1950) (analog)).

 The disadvantage of this method is that trimethylchlorosilane used as a reagent is itself a scarce product that is not produced in industry, and its preparation is fraught with a number of difficulties (multi-stage, corrosion, evolution and the need to capture gaseous HCl, etc.).

 An object of the present invention is to simplify the method.

The technical result is achieved due to the fact that the method of separation of trimethylchlorosilane from its mixture with silicon tetrachloride involves processing the mixture in the presence of an acid catalyst with organoalkoxysilane of the general formula
R $\genfrac{}{}{0ex}{}{\text{1}}{\text{n}}$ Si (OR) _4-n ,
Where
n is 0-2;
R = alkyl (C ₁ -C ₄ );
R ¹ = CH ₃ , C ₂ H ₅ or C ₆ H ₅ ,
or oligoalkoxysiloxane of the general formula
RO [Si (OR) ₂ O] _n H,
Where
n is 1-10;
R = alkyl (C ₁ -C ₄ ).

 Used oligoalkoxysiloxanes can be either linear or branched structure.

Of the vast number of such compounds, the most used and available, in our opinion, are di-, tri- or tetraethoxysilane, or the corresponding silicon methoxy derivatives containing methyl, ethyl or phenyl radicals at the silicon atom and silicon tetraethoxy or methoxy derivatives. It is even more effective to use oligoalkoxysiloxanes for treating the azeotropic mixture, since they themselves (and the corresponding organochloroalkoxy derivatives of silicon) already have a boiling point well above 57 ^o C. As such compounds, readily available ethyl silicates (e.g. ethyl silicate-32, ethyl silicate-40 or ethyl silicate-50). In addition, as such a reagent, a source of alkoxy groups, it is possible to use waste products of ethyl silicate production - bottoms. The bottoms of ethyl silicate production contain both linear and cyclic oligoalkoxysiloxanes. These compounds, unlike trimethylethoxysilane, are readily available since produced in industrial volumes.

Compounds such as HCl, H ₂ SO ₄ and ZnCl ₂ can be used as a catalyst for this reaction. For example, a catalyst such as HCl can be added either in the form of an aqueous concentrated solution of hydrochloric acid, or by bubbling dry gaseous hydrogen chloride, or it is formed directly in the reaction volume as a result of the interaction of silicon tetrachloride with alcohol, which is almost always present in the corresponding alkoxysiloxane .

Silicon chloroesters remaining after the isolation of trimethylchlorosilane can be sent to the corresponding organoxylation process to obtain the initial
R $\genfrac{}{}{0ex}{}{\text{1}}{\text{n}}$ Si (OR) _4-n ,
Where
n is 0-2;
R is alkyl (C ₁ -C ₄ );
R ¹ = CH ₃ , C ₂ H ₅ or C ₆ H ₅ ,
or
RO [Si (OR) ₂ O] _n H,
Where
n is 1-10;
R = alkyl (C ₁ -C ₄ ).

 This allows you to implement a virtually waste-free process for the separation of trimethylchlorosilane from its mixture with silicon tetrachloride.

The reaction was carried out in a flask under reflux at the boiling temperature of the mixture. Depending on the amount of OR radicals in the reagent molecule, the molar ratio between it and silicon tetrachloride (in the initial azeotrope) varies from 2: 1 to 1: 1. The duration of boiling was determined by the rate of passage of the reaction and was 2-10 hours. The content of silicon tetrachloride in the reaction mixture was monitored chromatographically. After completion of the reaction (the absence of silicon tetrachloride in the reaction mixture or, if the reaction did not complete, the presence of it in the minimum quantities for this mixture of reagents), trimethylchlorosilane was distilled off at a reflux temperature of 56-60 ^o C.

Example 1. A mixture of silicon tetrachloride and trimethylchlorosilane (51 and 32.5 g, respectively) was charged into a flask under reflux, 79 g of CH ₃ Si (OC ₂ H ₅ ) ₃ was added and refluxed at 65 ^° C for 2.5 hours After distillation, 99.1% of trimethylchlorosilane from the charged was obtained.

Example 2. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 and 54.3 g, respectively) was loaded, 133 g of (CH ₃ ) ₂ Si (OC ₂ H ₅ ) ₂ was added and boiled at 70 ^° C for 2, 5 hours. After distillation, 98.6% of trimethylchlorosilane from the charged was obtained.

Example 3. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 and 54.3 g, respectively) was loaded, 104 g of Si (OC ₂ H ₅ ) ₄ was added and boiled at a temperature of 70 ^° C for 2.5 hours. After distillation 99.8% of trimethylchlorosilane from the charged was obtained.

Example 4. According to claim 1, 100 g of an industrial azeotrope fraction was loaded containing 34 g of silicon tetrachloride and 57 g of trimethylchlorosilane, 41.6 g of Si (OC ₂ H ₅ ) ₄ was added and boiled at a temperature of 70 ^° C. for 2.5 hours After distillation, 81% of trimethylchlorosilane from the charged was obtained.

Example 5. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 and 54.3 g, respectively) was loaded, 204 g (CH ₃ ) ₂ Si (OC ₄ H ₉ ) _{3 was} added and heated under reflux for 3.5 h After distillation, 97.9% of trimethylchlorosilane from the charged was obtained.

Example 6. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 g and 54.3, respectively) was loaded, 128 g of C ₂ H ₅ Si (OC ₂ H ₅ ) _{3 was} added and heated under reflux for 2.5 hours. After distillation, 98.9% of trimethylchlorosilane from the charged was obtained.

Example 7. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 g and 54.3, respectively) was loaded, 132 g of C ₂ H ₅ Si (OCH ₃ ) ₃ were added and heated under reflux for 2.5 hours. After distillation 96.9% trimethylchlorosilane of the charged was obtained.

Example 8. According to claim 1, a mixture of silicon tetrachloride and trimethylchlorosilane (85 g and 54.3, respectively) was loaded, 139 g of bottoms from the production of ethyl silicate RO [Si (OR) ₂ O] _n H were added and heated under reflux for 4 hours After distillation, 91.9% of trimethylchlorosilane from the charged was obtained.

 With an increase in the temperature of processing the reaction mixture, the reaction rate increases, so it is advisable to carry out the process at elevated temperatures. The upper temperature limit of the process is usually determined by the boiling point of the highest boiling component of the reaction mixture.

 You can carry out the process at elevated pressure, because in this case, the processing temperature can be increased significantly above the boiling point of the individual components of the mixture.

 Thus, the proposed solution to the process of separation of trimethylchlorosilane from a mixture of it with silicon tetrachloride in comparison with the prototype can significantly simplify the process while maintaining a high degree of extraction of trimethylchlorosilane.

 The authors are not aware of the use of organoalkoxysilanes or oligoalkoxysiloxanes to isolate trimethylchlorosilane from a mixture with silicon tetrachloride. Therefore, the proposed solution, in our opinion, satisfies the criterion of "inventive step".

Claims (2)

1. The method of separation of trimethylchlorosilane from a mixture of trimethylchlorosilane with silicon tetrachloride by treating it with a reagent in the presence of an acid catalyst followed by separation of trimethylchlorosilane by distillation, characterized in that organoalkoxysilanes of the general formula are taken as a reagent for treating the mixture
R $\genfrac{}{}{0ex}{}{\text{1}}{\text{n}}$ Si (OR) _4-n ,
where n = 0 - 2;
R is alkil (C ₁ - C ₄ );
R ¹ is CH ₃ , C ₂ H ₅ or C ₆ H ₅ ,
or oligoalkoxysiloxanes of the general formula
RO [Si (OR) ₂ O] _n H,
where n = 1 to 10;
R is alkil (C ₁ - C ₄ ).  2. The method according to claim 1, characterized in that as the reagent take distillation residues from the production of ethyl silicate.