Process for preparing vinyl chlorosilanes

Details Process for preparing vinyl chlorosilanes Process for preparing vinyl chlorosilanes

2000-04-24

2001-09-18

Shaver, Paul F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

C422S186220, C422S198000, C422S198000, C423S342000

Reexamination Certificate

active

06291698

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing vinyl chlorosilanes by non-catalyzed, thermal reaction of chlorosilanes with vinyl chloride using a reactor combination of a ring-gap reactor equipped with an optionally rotating displacement body and a downstream reactor.
2. Discussion of the Background
Vinyltrichlorosilane is a valuable intermediate which, owing to its four reactive groups, is suitable for many applications. For example, it is used in the sizing of glass fibers and in the manufacture of cable materials.
DE-C 936 445, DE-A 22 10 189 and, in particular, DE-C 20 02 258 disclose that upon passing vinyl chloride/chlorosilane mixtures such as, for example, vinyl chloride/trichlorosilane mixtures, through appropriately-heated, empty ceramic, glass or iron tubes, industrially acceptable yields of vinyl chlorosilanes are achieved. The reaction proceeds purely thermally, i.e., without a catalyst. In the reaction of trichlorosilane with vinyl chloride, the following main reaction proceeds:
Main reaction:
C
2
H
3
Cl+SiHCl
3
&rlarr2;C
2
H
3
SiCl
3
+HCl
In addition to the main equilibrium reaction, there are the following side reactions and secondary reactions:
 C
2
H
3
Cl+SiHCl
3
→SiCl
4
+C
2
H
4
4 SiHCl
3
→3 SiCl
4
+Si+2 H
2
C
2
H
3
Cl→C
2
H
2
+HCl
C
2
H
2
→2 C+H
2
C
2
H
4
+SiHCl
3
—→C
2
H
5
SiCl
3
C
2
H
4
+SiHCl
3
—→C
2
H
3
SiCl
3
+H
2
C
2
H
3
SiCl
3
+SiHCl
3
→Cl
3
SiC
2
H
4
SiCl
3
Despite these side reactions and secondary reactions, according to DE 40 01 820 A1, the selectivity for vinyltrichlorosilane, based on the vinyl chloride used in deficient amounts, depending on the ratio of the starting materials and the degree of conversion, is from 50 to 98% in the case of tubes 122 to 150 cm in length and 25 to 35 mm in diameter, residence times from 0.2 to 20 seconds, reaction temperatures from 400 to 750° C. and pressures from 1 to 3 bar. However, the reactor output (or capacity) of the reactors in this case is only from 0.8 to 3.2 metric tons of vinyltrichlorosilane/month. Selectivity and degree of conversion are inversely proportional to one another; the reactor output passes through a maximum as a function of the degree of conversion. A high selectivity is therefore accompanied with an unsatisfactory and economically unacceptable reactor output at a low degree of conversion. According to DE-A 20 02 258, although increasing the tube diameter up to 50 mm produces an increase in reactor output in proportion to the greater reactor volume, at still greater diameters, the specific reactor output, based on the reactor volume, decreases. It is therefore impossible to increase the space-time yield of vinyltrichlorosilane, or even only maintain it, by increasing the reactor tube diameter to above 50 mm.
An improved process for preparing vinyl chlorosilanes by reacting is chlorosilanes with vinyl chloride is, according to DE 40 01 820 A1, carried out in a ring-gap reactor which has a heatable reaction tube having an internal diameter d
1
and in the interior of which is situated a displacement body having an outer diameter d
2
, and which extends over the entire length of the reaction tube, is axially and symmetrically disposed within the reaction tube and which may optionally rotate. The relationship d
1
=d
2
+2a applies here, where a is generally at least 1 cm and is always <5 cm. If the displacement body is substantially shorter than the reaction tube, the yield is decreased. This finding corresponds to the teaching of the three abovementioned publications, according to which, in the case of empty tube reactors, the yield falls if the tube diameter exceeds 5 cm. According to DE 40 16 021 A1, the capacity of the reactor and the space-time yield of the process using a ring-gap reactor can be further increased if the reaction components are preheated to 120 to 400° C. prior to entering the reactor. However, even using this measure, much of the reactor volume is still lost in that the reaction components are heated to approximately 550° C., in order that they react adiabatically in the remaining reactor volume.
SUMMARY OF THE INVENTION
One object of the invention is to increase the space-time yield of vinyl chlorosilane.
Another object of the invention is to maintain a high selectivity for the desired vinylchlorosilane at a high degree of conversion.
Another object of the invention is to maintain an economically acceptable high reactor output at a high degree of conversion.
Another object of the invention is to provide a process in which secondary or minor reactions are suppressed.
Another object of the invention is to provide a process in which the deposition of soot and/or elemental silicon is suppressed.
Another object of the invention is to provide a process in which the formation of undesirable high-boilers is suppressed.
These and other objects have been attained by the present invention, the first embodiment of which provides a process for preparing vinyl chlorosilanes, that includes:
thermally and non-catalytically reacting chlorosilane with vinyl chloride at a temperature of 550 to 700° C. by flowing said chlorosilane and vinyl chloride through a ring-gap space in a ring-gap reactor to produce reaction gas; the ring-gap space having a cross-sectional area and a volume; and
after the flowing, further reacting, adiabatically, the reaction gas in a second zone;
wherein the second zone has a cross-sectional area that is greater than the cross-sectional area of the ring-gap space; and wherein the second zone has a volume that is in a ratio to the volume of the ring-gap space of 0.15:1 to 1.5:1.
Another embodiment of the invention relates to an apparatus for carrying out the above process, which includes a combination of a ring-gap reactor and a second reactor which is downstream from the ring-gap reactor in a flow direction; wherein the ring-gap reactor includes a ring-gap space having a volume and a cross-sectional area; wherein the second reactor has a cross-sectional area that is greater than the cross-sectional area of the ring-gap space; and wherein the second reactor has a volume that is in a ratio to the volume of the ring-gap space of 0.5:1 to 1.25:1.


REFERENCES:
patent: 3666782 (1972-05-01), Mui et al.
patent: 5075480 (1991-12-01), Hange et al.
patent: 5344950 (1994-09-01), Hange et al.
patent: 5808128 (1998-09-01), Fiolitakis
patent: 936 445 (1955-12-01), None
patent: 20 02 258 (1971-08-01), None
patent: 2 210 189 (1973-09-01), None
patent: 40 01 820 A1 (1991-07-01), None
patent: 40 16 021 A1 (1991-11-01), None

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