Process for preparing alkenylhalosilanes and reactor suitable therefor

Abstract

Described is a method for producing alkenyl halosilanes by reacting alkenyl halide selected from the group comprising vinyl halide, vinylidene halide, and allyl halide with halosilane selected from the group comprising monohalosilane, dihalosilane, and trihalosilane in the gas phase in a reactor comprising a reaction tube (1) that has an inlet (2) at one end and an outlet (3) at the other end, said reactor further comprising an annular-gap nozzle (4) that is mounted on the inlet (2), extends into the reaction tube (1), and has a central supply duct (5) for one reactant (7) and a supply duct (6), which surrounds the central supply duct (5), for the other reactant (8). In order to carry out said method, alkenyl halide is injected into the reaction tube (1) through the central supply duct (5), halosilane is injected thereinto through the surrounding supply duct (6), and both substances flow through the reaction tube (1) in the direction of the outlet (3). The described method allows alkenyl halosilanes to be produced at a high yield and with great selectivity. The amount of soot formed is significantly lower than in conventional reactors. The invention also relates to a reactor for carrying out gas-phase reactions, said reactor being characterized by at least the following elements: A) a reaction tube (1) that has B) an inlet (2) at one end, C) an outlet (3) at the other end, and D) an annular-gap nozzle (4) which includes a central supply duct (5) for one reactant (7) and a supply duct (6), which surrounds the central supply duct (5), for another reactant (8), said nozzle being mounted on the inlet (2) and extending into the reaction tube (1).

Claims

1. A reactor suitable for gas phase reactions, comprising: a reaction tube comprising an inlet at one side of the tube, an outlet at the other side of the tube, the outlet opening to a reservoir vessel suitable to contain a cooled product of the gas phase reaction, an annular gap nozzle comprising a central feed for one reactant and a feed surrounding the central feed for another reactant, which is mounted at the inlet and opens into the reaction tube, wherein the feed surrounding the central feed has a side wall angled towards the central feed of the annular gap nozzle a preheating zone connected to the inlet in such a way so as to heat reactants for the gas phase reaction to a reaction temperature, and a line connected from the reservoir to near the outlet, the line configured to recycle the cooled product in the reaction mixture.

2. The reactor according to claim 1, further comprising a means to vary the flow rate of the reactant(s) in the annular gap nozzle positioned at the central feed and/or at the feed surrounding the central feed.

3. A process for preparing alkenylhalosilanes by reacting alkenyl halide selected from the group consisting of vinyl halide, vinylidene halide and allyl halide with halosilane selected from the group consisting of mono-, di- and trihalosilane in the gas phase in the reactor according to claim 1 wherein the alkenyl halide is injected into the reaction tube through the central feed and halosilane through the surrounding feed, and they flow through the reaction tube in the direction of outlet (3).

4. The process according to claim 1, wherein the alkenyl halide is vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene bromide, allyl chloride or allyl bromide, and the halosilane is di- or trichlorosilane or di- or tribromosilane.

5. The process according to claim 1, wherein the alkenyl halide is vinyl chloride or allyl chloride, and the halosilane is trichlorosilane.

6. The process according to claim 1, characterized in that the annular gap nozzle is a two-phase nozzle.

7. The process according to claim 1, wherein the reactor further comprises a device to vary the flow rate of the reactant(s) positioned at the central feed and/or at the feed surrounding the central feed.

8. The process according to claim 1, wherein the mono-, di- or trihalosilane to alkenyl halide is in a ratio of 1.0 to 10 mol:mol.

9. The process according to claim 1, wherein a hot reaction mixture is quenched with a liquid crude product at the product end of the reaction tube.

10. The process according to claim 1, wherein the temperature in the interior of the reaction tube is between 400 and 700° C.

11. The process according to claim 1, wherein the pressure in the interior of the reaction tube is from 1.0 to 2.0 bar abs.

12. The process according to claim 1, wherein the flow rate of the alkenyl halide in central feed is controlled by a closed-loop temperature control circuit.

13. The process according to claim 1, wherein the residence time of the reaction mixture in the reactor from opening of the annular nozzle to the outlet is 0.5 to 10 sec.

Description

(1) FIG. 1 describes the process according to the invention and the reactor according to the invention. This shows the reaction tube (1) equipped on the left-hand side with an inlet (2) for the reactants (7, 8), for example for vinyl chloride and for trichlorosilane. In a preheating zone (9) connected to the inlet (2), the reactants (7, 8) are heated to the required reaction temperature. An annular gap nozzle (4) having a central feed (5) for alkenyl halide (7) and a feed (6) surrounding the latter for halosilane opens into the reaction tube (1). The annular gap nozzle (4) opens into the reaction tube (1) such that the alkenyl halide and a mist of halosilane surrounding the latter can be injected into the reaction tube. The reaction tube (1) ends on the right-hand side with an outlet (3) for the reaction mixture. This outlet (3) opens into a reservoir vessel (10) for the cooled product (11). A portion of the product (11) is recycled via a line (12), under the action of the pump (13), close to the outlet (3) and is injected into the reaction mixture present at that point. This results in shock cooling of the reaction mixture and formation of the cooled product (9). This is then passed via outlet (3) into the reservoir vessel (10).

(2) The example below describes the invention in specific detail, without any intention of limitation thereby.

(3) Vinyl chloride was reacted with trichlorosilane in a nozzle reactor (diameter 200 mm, length 6000 mm) to give vinyltrichlorosilane. The trichlorosilane and vinyl chloride reactants were preheated here to 400° C. in a preheating zone. At the top of the reactor was a two-phase nozzle in which the two reactants were fed in separately. Vinyl chloride was injected in the middle of the axis, while trichlorosilane was fed in in an annular gap around the vinyl chloride feed. On exit of the vinyl chloride from the nozzle, the reaction to give vinyltrichlorosilane then ensued in the ensheathing trichlorosilane stream. The reaction zone was kept away from the reactor wall here by the ensheathing trichlorosilane fed in in excess. The result was a pure gas phase reaction between trichlorosilane and vinyl chloride. The yield-reducing wall reactions which lead to the formation of soot, for example, were prevented.

(4) The reaction proceeds continuously in the tubular reactor connected to the annular gap nozzle (4). At the end of the reactor, there was a quench of the hot reaction gas with liquid crude product, which very substantially suppressed further reaction to give silicon tetrachloride.

(5) In the example, 100 kg/h of gaseous vinyl chloride (centre of tube) and 650 kg/h of trichlorosilane (via an annular gap around the vinyl chloride feed) were fed in at 450° C. at the reactor inlet. In the first part of the reactor, the reactant mixture stream was heated further to about 500° C. Then the reaction began to proceed noticeably, and a reaction zone formed, which had its highest temperatures at about 625° C. At the position in the reactor where the gas stream reached the temperature of 630° C., the hot reaction gas was quenched with liquid crude product to about 40° C. The vinyl chloride conversion was 83%; the selectivity was 92%.

(6) The reactor used had a diameter of 200 mm and a length of 6000 mm. The following mass flow rates of the reaction mixture at the reactor outlet were found:

(7) TABLE-US-00003 vinyl chloride = 17.0 kg/h trichlorosilane = 457.1 kg/h vinyltrichlorosilane = 197.3 kg/h hydrogen chloride = 44.5 kg/h silicon tetrachloride = 20.6 kg/h high boilers/further secondary components = 13.5 kg/h

(8) Thus, this reactor had a monthly production output of 142 t of vinyltrichlorosilane and a space-time yield of 1046 kg/(m.sup.3*h). A higher space-time yield was achieved than in the above-described comparative examples with prior art reactors, and the vinyltrichlorosilane selectivity of the nozzle reactor used, at 92%, was likewise higher than in the comparative examples. The higher vinyltrichlorosilane selectivity was achieved by virtue of a lower incidence of silicon tetrachloride by-product and of high boilers or further secondary components.

(9) The construction of the nozzle was such that the vinyl chloride was introduced in the centre of the tube via an exit orifice of 25 mm. Around the vinyl chloride feed was an annular gap with s=2 mm and Da=35 mm for the trichlorosilane feed.

(10) Advantages of the process according to the invention and of the reactor of the “nozzle reactor” type according to the invention are found to be the enhanced selectivity and the enhanced space-time yield based on the vinyltrichlorosilane target product, because wall reactions are selectively prevented through the ensheathing with a trichlorosilane stream. Moreover, the reactor can be described as having low backmixing, as a result of which a lower level of by-products, for example silicon tetrachloride, soot and 1,2-bis(trichlorosilyl)ethane, is formed in the reaction system in question.

(11) By virtue of the wall reaction being very substantially prevented through the flanking with trichlorosilane, the formation of soot is minimized and the intervals for the cleaning operations of the reactor are extended.

(12) The nozzle reactor used in accordance with the invention can be operated with a distinctly increased vinyl chloride conversion, because it works with low backmixing. This increases the space-time yield of vinyltrichlorosilane compared to the reactants used conventionally.