PROCESS FOR PREPARING TRIMETHYLCHLOROSILANE

Abstract

A process for preparing trimethylchlorosilane (M3) and methyltrichlorosilane (M1) by disproportionation of dimethyldichlorosilane (M2) in the presence of an Al.sub.2O.sub.3 catalyst is described herein. The dimethyldichlorosilane used is in the form of a silane mixture that includes 80-100% by weight of dimethyldichlorosilane (M2). The difference in content from 100% by weight includes M1 and M3.

Claims

10. Process for preparing trimethylchlorosilane (M3) and methyltrichlorosilane (M1) by disproportionation of dimethyldichlorosilane (M2) in the presence of an A1203 catalyst, the dimethyldichlorosilane being used in the form of a silane mixture that comprises 80-100% by weight of dimethyldichlorosilane (M2), and wherein the difference in content from 100% by weight comprises M1 and M3.

11. The process according to claim 10, wherein the catalyst is activated prior to the disproportionation by passing (i) SiCl.sub.4, or (ii) HCl gas; or (iii) a mixture of HCl gas and at least one chlorosilane of the formula (II)
R.sub.xSiCl.sub.4-x   (II), where the radicals R are independently selected from the group consisting of (i) hydrogen and (ii) C.sub.1-C.sub.5 alkyl radical, and the index x has the values 0, 1, 2 or 3, over the catalyst at a temperature within a range from 330° C. to 550° C.

12. The process according to claim 11, wherein the chlorosilane is M2 or SiCl.sub.4.

13. The process according to claim 11, wherein the catalyst is activated prior to the disproportionation by passing HC1 gas over the catalyst.

14. The process according to claim 10, wherein an Al.sub.2O.sub.3 catalyst having a BET surface area within a range of 100-200 m.sup.2/g is used.

15. The process according to claim 10, wherein an Al.sub.2O.sub.3 catalyst having a pore volume within a range of 0.1-1 cm.sup.3/g is used.

16. The process according to claim 10, wherein a γ-Al.sub.2O.sub.3 catalyst is used.

17. The process according to claim 10, wherein the silane mixture comprises 98-100% by weight of M2.

18. The process according to claim 10, wherein the process is executed continuously.

Description

EXAMPLES

[0047] The experiments were carried out in a tubular reactor filled with Al.sub.2O.sub.3 (Al 3438 T ⅛″ pellets, BASF). The reactor was heated with a heating jacket; the heating zone filled with catalyst had a height of approx. 30 cm and a diameter of 5 cm. The M2 was first vaporized and preheated before it was able to come into contact with the catalyst. The product mixture was condensed and collected by means of a reflux condenser.

[0048] GC measurements were performed using an Agilent 6890N (WLD detector; columns: HP5 from Agilent: length: 30 m/diameter: 0.32 mm/film thickness: 0.25 μm; RTX-200 from Restek: length: 60 m/diameter: 0.32 mm/film thickness: 1 μm). Retention times were compared with the commercially available substances, all chemicals were used as purchased. All values are in percent by weight.

Example 1

[0049] The catalyst was activated with vaporized SiCl.sub.4 at 450° C. (internal measurement in the centre of the bed). 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 378° C. and with a contact time in the reactor of ˜20 s, and the condensed product mixture was analysed.

[0050] The product mixture consisted of 76.9% by weight of M2, 13.3% by weight of M1 and 9.6% by weight of M3. Small amounts of unidentified by-products were present.

Example 2

[0051] With the same catalyst load as in example 1, 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 377° C. and with a contact time in the reactor of ˜30 s, and the condensed product mixture was analysed.

[0052] The product mixture consisted of 74.1% by weight of M2, 15.4% by weight of M1 and 10.2% by weight of M3. Small amounts of unidentified by-products were present.

Example 3:

[0053] With the same catalyst load as in example 1, 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 485° C. and with a contact time in the reactor of ˜7 s, and the condensed product mixture was analysed.

[0054] The product mixture consisted of 75.1% by weight of M2, 14.2% by weight of M1 and 10.7% by weight of M3. Small amounts of unidentified by-products were present.

Example 4

[0055] The catalyst was activated with HCl gas at 450° C. (internal measurement in the centre of the bed). 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 390° C. and with a contact time in the reactor of ˜25 s, and the condensed product mixture was analysed.

[0056] The product mixture consisted of 77.9% by weight of M2, 12.8% by weight of M1 and 9.3% of M3. Small amounts of unidentified by-products were present.

Example 5

[0057] The catalyst was activated with a mixture of HCl gas and vaporized SiCl.sub.4 at 450° C. (internal measurement in the centre of the bed). 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 400° C. and with a contact time in the reactor of ˜18 s, and the condensed product mixture was analysed. The product mixture consisted of 78.0% by weight of M2, 12.6% by weight of M1 and 9.4% by weight of M3. Small amounts of unidentified by-products were present.

Example 6

[0058] 20 g of catalyst (activated beforehand with HCl) and 150 mL of M2 were heated to 350° C. for 3 hours in a closed autoclave. After cooling, the autoclave was opened and the contents analysed.

[0059] The product mixture consisted of 76.8% by weight of M2, 14.1% by weight of M1 and 9.1% by weight of M3. Small amounts of unidentified by-products were present.

Comparative Example 1

[0060] With an unactivated catalyst load, 150 mL of vaporized M2 was pumped through the catalyst bed at a reactor internal temperature of 350° C. and with a contact time in the reactor of ˜60 s, and the condensed product mixture was analysed.

[0061] The product mixture consisted of 68.3% by weight of M2, 14.4% by weight of M1 and 7.7% by weight of M3. Also present was a further 8.4% by weight of partially chlorinated methylated disiloxanes that cannot be used further.

[0062] The examples show that both the yield of M3 and the amount of M1 formed are much better than the values achieved in the prior art. They also correspond to the thermodynamic equilibrium cited in EP0219718.