Process for preparing vinylchlorosilanes

Details Process for preparing vinylchlorosilanes Process for preparing vinylchlorosilanes

2000-04-24

2001-04-24

Shaver, Paul F. (Department: 1621)

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

Organic compounds

Silicon containing

Reexamination Certificate

active

06222056

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing vinylchlorosilanes by non-catalyzed, thermal reaction of chlorosilanes with vinyl chloride using a ring-gap reactor having an, if appropriate, rotating displacement body.
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 and especially vinyl chloride/trichlorosilane mixtures through appropriately heated empty tubes made of ceramic, glass or iron, industrially acceptable yields of vinylchlorosilanes are achieved. The reaction proceeds purely thermally, i.e., without a catalyst. In the reaction of trichlorosilane with vinyl chloride, the following reactions proceed.
Main reaction:
C
2
H
3
Cl+SiHCl
3
&rlarr2;C
2
H
3
SiCl
3
+HCl
In addition to the above 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 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%, with tubes of from 122 to 150 cm in length and diameters of from 25 to 35 mm, residence times of from 0.2 to 20 seconds, reaction temperatures of from 400 to 750° C. and pressures of from 1 to 3 bar. However, the 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 thus accompanied by an unsatisfactory and economically unacceptable reactor output at a low degree of conversion. According to DE-A 20 02 258, although increasing the size of the tube diameter to 50 mm increases the reactor output in proportion to the greater reactor volume, with 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 diameter of the reactor tube to above 50 mm.
An improved process for preparing vinylchlorosilanes by reacting chlorosilanes with vinyl chloride is, according to DE 40 01 820 A1, carried out in a ring-gap reactor which has a treatable reaction tube having an internal diameter d
1
in the interior of which is situated an, if appropriate, rotatable cylindrical displacement body which extends over the entire length of the reaction tube, is arranged axially symmetrically and has an outer diameter d
2
. In this case the relationship d
1
=d
2
+2a applies, 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, or the space-time yield of the process, can be further increased using a ring-gap reactor if the reaction components are preheated to from 120 to 400° C. prior to entry into the reactor. However, much reactor volume is still lost with this measure, in that the reaction components are heated to approximately 550° C. in order to react further adiabatically in the remaining reactor volume.
SUMMARY OF THE INVENTION
One object of the invention is to increase the space-time yield of vinylchlorosilane.
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 that allows specific temperature profiles and monitoring of the exiting reaction mixture from the ring-gap reactor.
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, which provides a process for preparing vinylchlorosilanes, that includes:
thermally and non-catalytically reacting chlorosilane with vinyl chloride at a temperature of 550 to 700° C. in a ring-gap reactor to produce a hot reaction gas that comprises vinylchlorosilane, the ring-gap reactor including a ring-gap space; and
after the hot reaction gas has flowed through the ring-gap space, rapidly cooling the hot reaction gas by quenching the hot reaction gas with a quenching liquid.
In the novel process, even at high degrees of conversion, a high selectivity for the desired vinylchlorosilane is associated with an economically acceptable high reactor output. This advantageous result is due, inter allay, to the fact that the process enables specific temperature profile and monitoring after exit of the reaction mixture from the ring-gap reactor. Secondary or minor reactions which, inter alla, can lead to deposition of soot and/or elemental silicon and to the formation of high-boilers are accordingly suppressed.
According to the invention, vinylchiorosilanes and especially vinyltrichlorosilane may be advantageously prepared from trichlorosilane and vinyl chloride. Other suitable chlorosilanes having a substitutable hydrogen atom are, for example, methylhydrogendichlorosilane and ethylhydrogen-dichlorosilane.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various other objects, features and attendant advantages of the present invention will become more appreciated as the same becomes better understood from the following detailed description.
Preferably, the chlorosilane and vinyl chloride are advantageously used without a diluting liquid or gaseous inert medium and are preferably used in a molar ratio of from 1:1 to 5:1, more preferably from 2:1 to 4:1. The reaction components can be preferably introduced at ambient temperature or, as described in DE 40 16 021 A1, the entire contents of which are hereby incorporated by reference, preheated to from 120 to 400° C., more preferably to from 220 to 400° C., into the ring-gap reactor, where they are further heated. At about 450° C., the exothermic substitution reaction begins which, at about 550° C., achieves a rate such that no further heat supply is necessary; the reaction can therefore essentially proceed adiabatically in the direction toward equilibrium. The zone of the ring-gap reactor in which the adiabatic reaction takes place is therefore not heated. Preferably, the temperatures in this zone are generally in the range from 550 to 700° C., more preferably from 550 to 650° C. Each of the above ranges includes all values and subranges therebetween.
The process according to the invention is preferably carried out at pressures of from 1.1 to 2.0 bar, more preferably from 1.1 to 1.4 bar. The residence times are preferably from 0.2 to 20 seconds, more preferably from 1.0 to 10 seconds. These ranges include all values and subranges therebetween.
As a preferred ring-gap reactor, the reactor described in DE 40 01 820

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