DE1767078C3 - Process for the production of silicon tetrahalides - Google Patents

Description

25th

The invention relates to a process for the production of silicon tetruhalides by reacting Silicon hydrogen compounds with hydrogen chloride or hydrogen bromide in the presence of a catalyst.

Halosilanes, particularly silicon tetrahalides, are manufactured on a large scale by industry and have found various uses. Silicon tetrachloride is technically very important or silicon tetrafluoride, which on a large scale z. B. for the production of pure, finely divided Silicon dioxide and elemental silicon can be used.

Silicon tetrachloride is synthesized, for example, in a known manner in direct synthesis by the action of chlorine manufactured on silicon or substances containing silicon. Also by exposure to hydrogen chloride Silicon or silicon-containing substances, such as. B. ferrosilicon, chlorosilanes are formed. Play depending on the reaction conditions in addition to the main reaction according to the gross equation:

Si -I- 4HCI - SiCl, I 2 H ₂ (1)

including the reactions according to the gross equations:

Si-I- 3 HCl, = HSiCl ₃
and

H ₂

(2)

Si-I 2 HCl = - H ₂ SiCl ₂

(3)

a role. In most cases, there are mixtures which contain, in addition to silicon telrachloride, also chlorosilanes with SiH bonds. The reaction between silicon and hydrogen chloride begins at around 300 C and produces a chlorosilane mixture with trichlorosilane and silicon tetrachloride as the main components. With ^fi "increasing temperature, the ratio of the reaction products SiCl. _1: HSiCl ₃ in favor of the SiCl, moved, but one obtains about 10 even at 700C reaction temperature in excess silicon in the reaction furnace until 30 weight percent of HSiCl _3. If the reaction furnace is operated adiabatically, a further increase in temperature has only a minor effect on a shift in the SiCl ₁ : HSiCl ₃ ratio in favor of SiCl ₁ ; it only favors the course of side reactions and the thermal decomposition of the chlorosilanes.

Under these conditions, an increase in the hydrogen chloride throughput in the reaction furnace, which contains a large excess of silicon, can only lead to an increase in conversion, but not to a shift in the SiCl.: HSiCl ₃ ratio in the reaction product in favor of SiCl ₁ .

It is also used for the production of Siliciu.atetrahalogeniden the action of hydrogen halides on silicon hydrogen compounds is known, with at a temperature of over 100 C and in the presence of aluminum halide as a catalyst the hydrogen atoms of the silicon compound can be exchanged in sequence for halogen atoms (Hollemann-Wi bere, textbook of inorganic chemistry 47th to 56th editions 1960, p. 320).

The reaction mixture formed in these known syntheses has to be worked up further. z. B. pure silicon tetrachloride is obtained by fractional distillation. Doing so will be right high demands on the distillation technology rock. because the boiling points of the individual reaction products are very close together and the purity requirements are generally very high.

On the basis of the above considerations, the invention was based on the task, a method for the production of silicon tetrahalides by reacting silicon hydrogen compounds with To indicate hydrogen chloride or hydrogen bromide in the presence of a catalyst by means of which the above Disadvantages can be avoided and an almost complete conversion to halosilanes can be achieved without SiH bonds.

The characteristic feature of the invention is to see / u that silicon hydride compounds of the general formula

H _n SiCl ₄ ",

in which // - 1 to 4 can be reacted with the hydrogen chloride or hydrogen bromide in the presence of activated carbon, finely divided aluminum oxide or silicon dioxide at temperatures in the range from 200 to 800 ^° C., preferably from 300 to 700 ° C., optionally in the presence of hydrogen .

The implementation takes place according to the gross equation:

H _n SiCl, η + «HX - X _n SiCl _4. ,, + / (H ₂ (4),

it being possible for different halogens to occur simultaneously in the reaction product in one molecule.

_{In the case of the SiCl, r} HSiCl ₃ -H ₂ SiCl ₂ -H ₂ mixture obtained from the above-described reaction of silicon with hydrogen chloride, the chlorosilanes with SiH bonds, here HSiCl, and H ₂ SiCl ₂ , in a downstream reaction chamber filled with the large-area substance, with the amount of HCl gas equimolar to these substances according to equation (4), convert _{almost completely to SiCl 1} and H _2. Of course, a chlorosilane mixture separated off, for example by condensation of hydrogen, can also be reacted with hydrogen chloride over the catalyst, as described.

The process also allows chlorosilane mixtures, which are rich in dichlorosilane, even if

■ ο

apart from this, they essentially only contain trichlorositane, the dichlorosilane with an amount of HCl gas which is just equimolar to this according to equation (4) to convert almost completely to SIiCl and H ₂ , without any substantial amounts of HSiCl _{3 being added} to the hydrogen chloride Equation (4) react. Its properties (sensitivity to impact in the presence of oxidizing agents such as atmospheric oxygen and others, increased sensitivity to moisture compared to trichlorosilane, high vapor pressure at room temperature) often make dichlorosilane, also and especially in mixtures with trichlorosilane, an undesirable product.

As substances with a large surface and a large catalytic In addition to activated carbon, finely divided aluminum oxide, silicon dioxide and others proved. The reactions can be or overpressure, but are preferably carried out at normal pressure.

example 1

After thoroughly purging the apparatus with dry nitrogen, a mixture of hydrogen, dichlorosilane, trichlorosilane and silicon telrachloride, which was produced by reacting silicon with hydrogen chloride at 700 C and in which the chlorosilanes H ₂ SiCl ₂ , HSiCl ₃ and SiCl ₄ are molar to one another, was produced like <0.1: 18.7: 81.3 and H ₂ to the sum of the chlorosilanes were like 1.5 to 2: 1, in gaseous form at a rate _{corresponding to about 1 l HSiCl 3} / h, together with 1 l Hydrogen chloride / h was passed through a bed of 106 g of dried, oxygen-free, granulated activated carbon, heated to 500 "C., which was located in a fused silica tube 30 cm in length and 3 cm in diameter. This treatment was initially used for 2 to 3 hours for adsorption Components through the activated carbon, their activation and the establishment of a steady equilibrium.When the reaction furnace was in operation, the molar ratio of the chlorosilanes was then up

H ₂ SiCl ₂ : HSiCl ₃ : SiCl ₁ - <0.1: 2.7: 97.3

humiliated. Based on HSiCI ₃ , this corresponds to a current conversion of 85.6% according to equation (4).

Example 2

Using otherwise the same procedure as in Example 1, a mixture of H _{2 SiCl 2} , HSiCl ₃ , SiCl ₁ (molar ratio 0.05: 18.0: 82.0) and H ₂ (volume ratio H ₂ to the sum of the chlorosilanes) was produced = 1.5 to 2: 1) in gaseous form through the activated carbon bed heated to 200 ° C. After the pass, the mole ratio of the chlorosilanes was

H ₂ SiCl ₂ : HSiCl ₃ : SiCl, - -0.05: 14.4: 85.6.

Example 3

A mixture of trichlorosilane and silicon tetrachloride (molar ratio 12.4: 87.6) was with a

ίο A speed of 50 ml liquid mixture / h added dropwise into a flask, there immediately completely evaporated and passed with a stream of hydrogen chloride (1.5 l / h; thus molar ratio HCl: HSiCl ₃ = about 1.2) through an activated charcoal bed heated to 400 C. Otherwise

> 5 the same procedure as in Example I contained after the condensed product trichloride and silicon tetrachloride in the molar ratio 1.9: 98.1.

Example 4

A mixture of dichlorosilane and trichlorosilane (molar ratio 10.8: 89.2) was added dropwise to a flask at a rate of 50 ml liquid mixture / h, where it was immediately completely evaporated and with a stream of hydrogen chloride (2.0 l / h; thus molar ratio HCl : H ₂ SiCl ₂ = about 2) passed through an activated carbon bed heated to 400 C. With otherwise the same procedure as in Example 1, the product condensed at -78 ° C. contained dichlorosilane after the passage. Trichlorosilane and silicon tetrachloride in a molar ratio of 0.7: 86.4: 12.9.

Example 5

A mixture of trichlorosilane and dry, bromine-free, hydrogen bromide produced from bromine + tetralin (molar ratio HSiCl ₃ : HBr - ■ - 1: 1) became gaseous at a rate of about 10 l / h together with 0.5 l dry nitrogen / h a bed, heated to 500 ¹ C, of 20 g of dried, oxygen-free granulated activated carbon, which was located in a tube made of quartz glass 20 cm in length and 1.3 cm in diameter, passed. The same procedure as in Example 1 was followed with regard to adsorption, activation and establishment of equilibrium. Thereafter, by continuing the experiment from a product of 68.5 g condensed at about 50 ° _{C., 35 g of a colorless fraction were obtained by distillation, which consisted of trichloromonobromosilane, SiCl 3} Br (boiling point 84 ° C.; weight ratio silicon: chlorine: bromine = 13.0: 47.4: 39.0 versus theory 13.1: 49.6: 37.3).

Claims (1)

Claim: Process for the preparation of silicon tetrahalides by reacting silicon water compounds with hydrogen chloride or hydrogen bromide in the presence of a Katalyasotrs, characterized in that silicon hydrogen compounds the general formula H _n SiCI ₁ ", where η can be from 1 to 4, in the presence of activated carbon, finely divided aluminum oxide or silicon dioxide at temperatures in the range from 200 to 800 ° C., preferably from 300 to 700 ° C., optionally in the presence of hydrogen.