DD250536B5 - Process for the preparation of methylchlorosilanes - Google Patents

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to the preparation of methylchlorosilanes according to the principle of direct synthesis according to Müller-Rochow. Methylchlorosilanes are the precursors of a wide range of technically and economically important silicone products, such. As silicone coatings, oils, rubbers.

Characteristic of the known technical solutions

It is known to prepare methylchlorosilanes according to the principle of direct synthesis according to Mueller-Rochow (see W. Noil, Chemie und Technologie der Silicones, 1960, pp. 22ff.).

The results of the synthesis reaction, d. H. the activity of the mixture of powdered silicon and catalyst (hereinafter referred to as contact mass), the temporal stability of the activity, the selectivity of the reaction towards the preferred main product dimethyldichlorosilane (DDS) and the utilization of the raw materials are, except the reactor design, the reaction and The qualities of the starting materials chloromethane and silicon to a great extent dependent on the nature of the copper-containing catalyst used. So far, copper is the best catalyst for selective DDS synthesis. It has been used in the form of:

1. metallic copper, as:

a) cement copper, (DD-PS 21 380, DE-OS 2214611, GB-PS 1201 466)

b) electrolytic copper (DE-OS 2212218)

c) oxidic copper, produced by pyrometallurgical process from cement copper (DE-OS 3235943)

In DE-OS 3312775 it is proposed that such a partially oxidized copper preparations by the addition of amounts of copper (II) formiatzu modified with the aim to reduce the level of silicon products with boiling points above 7O ⁰ C. The disadvantage of this procedure is mainly in the complicated production of partially oxidized copper.

2. Copper compounds, as:

a) salts, for example CuCl (U.S. Patent No. 2,464,033), CuCl ₂ (U.S. Patent 2,464,033) Cu ₂ S (U.S. Patent No. 2,904,574), (Cu (O ₂ CH) ₂ Radosavljevice, inter alia, Khim. i Prakt. Primeninie Kremneorg Soedinenie, Trudy Konf. Leningrad 1958, No.6, p.37)

b) oxides / hydroxides (SU-PS 130882, Trambouze J. chim. phys. 1954, no. 51, p. 505)

c) Alloy Component (DE-PS 11 58976, US-PS 2380995, M.Dvorak, Technical Digest., Prague 1968, No. 10, p.310) In general, all these catalysts are in need of improvement in terms of activity, stability and selectivity. This was achieved by adding a variety of activators (often zinc, aluminum) or promoters (often antimony). In particular, the variants 2 a and 2 b for a large-scale implementation cumbersome and expensive, since the corresponding copper compounds must be prepared in advance. The production of copper alloys (2c) is complicated and alloying the copper catalyst in the entire amount of silicon unfavorable, since this leads in the continuously operating reactor to a constant unwanted copper enrichment and thus a reduction in the DDS yield. The preferred method is the use of mechanically comminuted electrolyte copper (1b), wherein the catalyst is generally modified by alloying with or admixing activators and promoters. To prepare the catalyst, molten electrolyte copper is sprayed in the air or inert gas stream and then ground in vibratory mills using grinding aids to form a copper powder suitable for direct synthesis. The production of cement copper (1 a)

or from copper oxide preparations prepared therefrom (1 c) is complicated, polluting and recommended only in the presence of an already developed copper wet metallurgy.

Object of the invention

The aim of the invention is an improved process for the direct synthesis of methylchlorosilanes, with which the degree of conversion of chloromethane and silicon and the yield of dimethyldichlorosilane can be made more effective.

Explanation of the essence of the invention

It was an object of the present invention to develop a catalyst system which combines the economy of production with an improvement in the activity, the temporal stability of the activity and the selectivity of the synthesis in the direction of the desired main product dimethyldichlorosilane (DDS).

Surprisingly, it has been found that this object is achieved by the use of a mixed catalyst, which is a mechanical mixture of copper powder and anhydrous copper salts of lower aliphatic, saturated mono- or dicarboxylic acids. Particularly suitable mono- or dicarboxylic acids are the first three members of the homologous series.

The catalyst contains 1 to 75% by weight of its total copper content in the form of anhydrous copper salts of a particle size of less than 300 μm, preferably smaller than μm. Copper (II) formate, as the copper salt of the lower monocarboxylic acids, is preferably used in amounts of from 30 to 50% by weight of copper, based on the total copper content of the catalyst. Of the lower dicarboxylic acids, copper (II) oxalate is particularly suitable, in amounts of from 10 to 50% by weight of copper, based on the total copper content of the catalyst.

The catalyst gives in admixture with silicon powder, the contact mass, which by simple mechanical mixing as

z. As stirring, shaking, vortexing in the gas stream, is obtained. The contact material is used with a total copper content of 1 to 30% by weight, preferably 2 to 10% by weight, of copper for the reaction with chloromethane in the direct synthesis. The copper is proportionally in the form of copper powder and in the form of copper salts in the contact mass.

The direct synthesis is in reactors, such as. B. fluidized bed, fluidized bed or Rührbettreaktionen, carried out at temperatures ranging from 250 to 400 ° C, wherein the resulting gaseous reaction products are removed from the reaction zone. The contact material may possibly further conventional known additives such. As activators (Zn, Al u.a.) And / or promoters (Sb and others) are added. When using copper salts of lower dicarboxylic acids, the use of activators is not mandatory, the reaction starts without their addition and achieves high activity. The catalyst according to the invention ensures a high proportion of DDS in the reaction product even in the lower range of the stated temperatures and when using small quantities of catalyst. Under these conditions, a selectivity-reducing, copper enrichment in continuous driving is prevented.

Advantages of the procedure according to invention are a high activity of the contact mass, a high temporal stability of the activity with at the same time high selectivity in direction DDS. In addition, the use of the catalyst of the invention leads to a shortening of the formation phase, d. H. the fresh contact mass, which is constantly added to the continuous reactor, already contributes to the reactor result after a short time.

embodiment

The results were determined on a rotating shaken, gradient-free reactor according to Baglaj (Baglaj, B.I. et al., Kin e Kat 1975, No. 16, p. 804) under the same standard reaction conditions.

Reaction conditions:

Shaking frequency of the reactor: 25 s " ¹

Contact mass

-Technical silicon grain б = 50μπι 9.5 g

Total catalyst copper content, based on the contact mass 5Ma .-%

Zinc dust 0.025 g chloromethane throughput 2.71 (NB) .h ^-1 reaction temperature 340.degree. C. The copper powder used was mechanically comminuted electrolytic copper.

The experimental evaluation was determined by gas chromatography as a function of time:

Activity: Ma .-% methylchlorosilanes in the reaction product (gas phase)

Selectivity: Ma .-% DDS in the methylchlorosilanes

After completion of the test, the degree of silicon conversion was determined by determining the silicon content in the reactor residue.

The total copper content is given as the copper content of the batch constituents in% by mass, based on the total copper content.

Result compilation

catalyst

Ex. Illustration copper Copper- Copper- Verse.- A S U powder formate oxalate duration Wt .-% Wt .-% Wt .-% Hrs. 1 1 + 2 100 6 41 43 44 2 1 + 2 50 50 - 6 64 66 68 3 1 + 2 - 100 - 2 29 48 10 4 3 + 4 100 - - 6 41 43 44 5 3 + 4 50 - 50 6 73 69 77 6 3 + 4 - - 100 2 41 30 14 7 75 - 25 6 67 66 75 8th 90 10 6 63 59 69

A: average activity in% by weight of MCS S: average selectivity in% by weight of DDS U: degree of conversion of silicon in% by mass

Claims (8)

Invention claim: 1. A process for the preparation of methylchlorosilanes by reaction of gaseous chloromethane with a contact mass containing powdered silicon and copper-containing catalyst and optionally other known additives, characterized in that the catalyst is a mechanical mixture of copper powder and anhydrous copper salts of lower aliphatic saturated mono- or dicarboxylic acids contained in the contact mass. 2. The method according to item 1, characterized in that the catalyst is contained in the contact mass with a total copper content of 1 to 30 wt .-%. 3. The method according to item 2, characterized in that the catalyst is contained with a total copper content of 2 to 10 wt .-% in the contact mass. 4. The method according to item 1, characterized in that the catalyst contains 1 to 75Ma .-% of its total copper content as the copper salt of lower aliphatic, saturated mono- or dicarboxylic acids. 5. The method according to item 4, characterized in that the catalyst contains copper (II) formate as the copper salt. 6. The method according to item 5, characterized in that the catalyst contains 30 to 50 wt .-% of its total copper content as copper (II) formate. 7. The method according to item 4, characterized in that the catalyst contains copper (II) oxalate as the copper salt. 8. The method according to item 7, characterized in that the catalyst contains 10 to 50Ma .-% of its total copper content as copper (II) oxalate.