Process for converting silicon tetrachloride to trichlorosilane

Abstract

The invention relates to a process for converting silicon tetrachloride (STC) to trichlorosilane (TCS), by introducing reactant gas containing STC and hydrogen into a reaction zone of a reactor in which the temperature is 1000-1600° C., wherein the reaction zone is heated by a heater located outside the reaction zone and the product gas containing TCS which forms is then cooled, with the proviso that it is cooled to a temperature of 700-900° C. within 0.1-35 ms, wherein the reactant gas is heated by the product gas by means of a heat exchanger working in countercurrent, wherein reactor and heat exchanger form a single, gas-tight component, wherein the component includes one or more ceramic materials selected from the group consisting of silicon carbide, silicon nitride, graphite, SiC-coated graphite and quartz glass.

Claims

1. A process for converting silicon tetrachloride (STC) to trichlorosilane (TCS), said process comprising introducing reactant gas comprising STC and hydrogen into a reaction zone of a reactor in which a temperature is 1100-1600° C., wherein: (a) the reaction zone is heated by a heater located outside the reaction zone and a product gas comprising TCS which forms is then cooled, with the proviso that the product gas is cooled to a temperature of 700-900° C. within 0.1-35 ms, (b) the reactant gas is heated by the product gas by use of a heat exchanger working in countercurrent, (c) the reactor and the heat exchanger form a single, gas-tight component, (d) the component comprises at least one ceramic material selected from the group consisting of silicon carbide, silicon nitride, graphite, SiC-coated graphite and quartz glass, and (e) a hydrodynamic residence time of reactant gas in the reaction zone is 1 to 10 ms.

2. The process as claimed in claim 1, wherein a total residence time in the reactor and the heat exchanger is 10-400 ms.

3. The process as claimed in claim 1, wherein cooling of the product gas is effected without hold steps.

4. The process as claimed in claim 1, wherein the product gas, according to a pressure at a reactor outlet, is cooled in each case to 700° C. within 0.1-10 ms in the case of a gauge pressure of 0.1 bar at the reactor outlet, within 0.1-20 ms in the case of a gauge pressure of 5 bar at the reactor outlet, and within 0.1-35 ms in the case of a gauge pressure of 10 bar at the reactor outlet.

5. The process as claimed in claim 1, in which the single component formed from the reactor and the heat exchanger comprises channels, wherein only product gas or only reactant gas flows through some of the channels, wherein channel depth and a number of channels vary with a length of the single component, wherein channels are present in which a hydraulic diameter of the channels is 0.05-1mm.

6. The process as claimed in claim 1, wherein a length of the single component is not more than 1500 mm.

7. The process as claimed in claim 1, wherein the heat exchanger has a ratio of exchange area to gas volume of >500 m.sup.−1.

8. The process as claimed in claim 1, wherein the reactor is operated at a gauge pressure of the product gas at a reactor outlet of 0-10 bar.

9. The process as claimed in claim 1, wherein a plurality of single gas-tight components each formed by the reactor and the heat exchanger are connected to one another, with provision of common passages for reactant and product gas.

10. The process as claimed in claim 2, wherein cooling of the product gas is effected without hold steps.

11. The process as claimed in claim 10, wherein the product gas, according to a pressure at a reactor outlet, is cooled in each case to 700° C. within 0.1-10 ms in the case of a gauge pressure of 0.1 bar at the reactor outlet, within 0.1-20 ms in the case of a gauge pressure of 5 bar at the reactor outlet, and within 0.1-35 ms in the case of a gauge pressure of 10 bar at the reactor outlet.

12. The process as claimed in claim 11, in which the single component formed from the reactor and the heat exchanger comprises channels, wherein only product gas or only reactant gas flows through some of the channels, wherein channel depth and a number of channels vary with a length of the single component, wherein channels are present in which a hydraulic diameter of the channels is 0.05-1 mm.

13. The process as claimed in claim 12, wherein a length of the single component is not more than 1500 mm.

14. The process as claimed in claim 13, wherein the heat exchanger has a ratio of exchange area to gas volume of >500 m.sup.−1.

15. The process as claimed in claim 14, wherein the reactor is operated at a gauge pressure of the product gas at a reactor outlet of 0-10 bar.

16. The process as claimed in claim 15, wherein a plurality of single gas-tight components each formed by the reactor and the heat exchanger are connected to one another, with provision of common passages for reactant and product gas.

17. The process as claimed in claim 1, wherein there are no seals between the heat exchanger and reactor.

18. The process as claimed in claim 1, wherein the temperature in the reaction zone is 1200-1600° C.

Description

(1) FIG. 1 shows, in schematic form, how such a parallel connection of reactor units can be configured.

(2) 1 shows the passage for reactant gas.

(3) 2 shows the passage for product gas.

(4) 3 shows one of the connected reactor units (single, gas-tight component).

(5) 4 shows a seal between the reactor units.

(6) FIG. 2 shows, in schematic form, how a parallel connection is heated.

(7) FIG. 2 describes a preferable execution of the combination of the inventive components.

(8) 1 shows the passage for the reactant gas; 2 shows the passage for the product gas.

(9) 3 shows one of the connected reactor units (single, gas-tight component).

(10) These units can be combined, for example, by means of seals 4.

(11) In this case, the seals are preferably used in the cold region, namely in the unheated region. The temperature in the unheated region may, for example, be less than or equal to 500° C.

(12) The heating 5, in a preferred embodiment, is limited to the reaction region and heats it to 1000-1600° C. The heating may be from the bottom or from the top (from the bottom in FIG. 2).

(13) It is possible here to employ all methods of heating familiar to those skilled in the art, preferably but not restricted to electrical heating and heat transfer by means of radiation.

(14) Preference is given to heating only the reaction zone, while the rest of the component is thermally insulated, see region 6.

(15) The combination of the individual reactor units 3 should preferably be configured such that the components are connected in a gas-tight manner to one another; this can be effected by a method familiar to those skilled in the art (for example by means of seals with appropriate tensioning of the components).

(16) The above-elucidated embodiments of the apparatus also allow the operation thereof under elevated pressure.

(17) For instance, the reactor can be operated at a gauge pressure of the product gas at the reactor outlet of 0-10 bar, preferably of 2-6 bar and more preferably at 3-5 bar. This has the advantage that the mass throughput and hence the economic viability are increased further.

(18) The pressure which results at the reactor inlet accordingly depends on the throughput.

(19) In addition, as well as hydrogen and STC, further components may also be present in the reactant gas, especially HCl, hydrocarbons, hydrochlorosilanes, oligochlorosilanes, hydrogenated oligochlorosilanes, organochlorosilanes, and also siloxanes and organosiloxanes.

EXAMPLES

(20) The experiments were conducted in an apparatus which consisted completely of SiC.

(21) A mixture of 676 mL/h and 264 l (STP)/h(l(STP): standard liters) of hydrogen was fed in.

(22) The minimum hydrodynamic diameter was 0.4 mm.

(23) The reactor was electrically heated in an oven; the heat input at the high temperatures took place predominantly via radiation.

(24) The measurement of the reaction temperature was determined as the maximum surface temperature of the apparatus by means of pyrometric measurement.

(25) The data determined by pyrometry corresponded to the measurement from a type B thermocouple mounted directly adjacent to the reaction zone.

(26) The hydrodynamic residence times are calculated from the ratio of reactor volume to volume flow rate under the conditions determined (p,T).

(27) The residence time in the reaction zone was between 2.8 (1000° C.) and 1.6 (1500° C.) ms.

(28) Table 1 shows the results of five experiments.

(29) In each case, the mass flow rates of H2 and STC, and also temperatures, residence times (RT), pressures and conversion rates (C rate), are reported.

(30) Measurements were effected at 1000° C., 1100° C., 1200° C., 1400° C. and 1500° C.

(31) TABLE-US-00001 TABLE 1 RT [ms] Mass flow rates Temperatures [° C.] To Pressure H2 Sicl4 Furnace temp. [bar] C rate [% by vt.] Experiment [l (STP)/h] [mL/h] Furnace monitor Pyrameter <700° C. Difference 1 2 3 4 5 6 1 264 676 1500 1500 1494 4.3 3.9 25.3 25.8 25.6 25.8 2 264 676 1400 1392 1391 3.1 3.6 25.6 25.1 24.8 3 264 676 1200 1185 1204 2.8 3.1 23.6 23.6 23.2 23.2 23.1 23.5 4 264 676 1100 1073 1127 2.5 2.9 17.9 17.9 17.9 18.0 16.1 5 264 676 1000 971 1035 2.3 2.7 2.5 2.7 3.3 3.7 4.7 4.9