PROCESS FOR PRODUCING TRICHLOROSILANE WITH STRUCTURE-OPTIMISED SILICON PARTICLES

Abstract

A process for for producing or preparing chlorosilanes. The process includes providing chlorosilanes having the general formula H.sub.nSiCl.sub.4-n wherein n is from 1 to 3. Once provided, the chlorosilanes are placed into a fluidized bed reactor where a hydrogen and silicon tetrachloride-containing reaction gas is reacted with a particulate contact mass containing silicon at temperatures of 350° C. to 800° C. The operating granulation is understood as meaning the granulation or granulation mixture introduced into the fluidized bed reactor contains at least 1% by mass of silicon-containing particles S described by a structural parameter S. Where the S has a value of at least 0 and is calculated as follows S=(φ.sub.S−0.70).Math.ρ.sub.SD/ρ.sub.F where φ.sub.S is a symmetry-weighted sphericity factor; the ρ.sub.SD is a poured density [g/cm.sup.3], and the ρ.sub.F is an average particle solids density [g/cm.sup.3].

Claims

1-7. (canceled)

8. A process for producing chlorosilanes, comprising: providing a chlorosilane of general formula 1
H.sub.nSiCl.sub.4-n  (1), wherein n is from 1 to 3; placing the chlorosilane in a fluidized bed reactor, wherein a hydrogen and silicon tetrachloride-containing reaction gas is reacted with a particulate contact mass containing silicon at temperatures of 350° C. to 800° C., wherein the operating granulation, understood as meaning the granulation or granulation mixture introduced into the fluidized bed reactor, contains at least 1% by mass of silicon-containing particles S described by a structural parameter S, wherein S has a value of at least 0 and is calculated as follows: $\begin{array}{cc}S=\left({\phi }_s-0.70\right).Math.\frac{{\rho }_{SD}}{{\rho }_F},& \mathrm{equation}\left(1\right)\end{array}$ wherein φ.sub.S is a symmetry-weighted sphericity factor; wherein ρ.sub.SD is a poured density [g/cm.sup.3]; and wherein ρ.sub.F is an average particle solids density [g/cm.sup.3].

9. The process of claim 8, wherein the symmetry-weighted sphericity factor Ys of the particles S is from 0.70 to 1 and wherein the sphericity of the particles describes the ratio between a surface area of a particle image and a circumference of the particles.

10. The process of claim 8, wherein the average particle solids density ρ.sub.F of the particles having a structural parameter S≥0 is from 2.20 to 2.70 g/cm.sup.3 and wherein the determination is carried out according to DIN 66137-2:2019-03.

11. The process of claim 8, wherein the operating granulation has a particle size parameter d.sub.50 of 70 to 1500 μm and wherein the particle size parameter is determined according to DIN ISO 9276-2.

12. The process of claim 8, wherein before entry into the reactor the reaction gas preferably comprises at least 10% by volume of hydrogen and silicon tetrachloride.

13. The process of claim 8, wherein the molar ratio of hydrogen and silicon tetrachloride is from 1:1 to 10:1.

14. The process of claim 8, wherein the produced chlorosilane of general formula 1 is trichlorosilane (TCS).

Description

[0070] FIG. 1 shows by way of example a fluidized bed reactor 1 for performing the process according to the invention. The reaction gas 2 is preferably blown into the contact mass from below and optionally from the side (for example tangentially or orthogonally to the gas stream from below), thus fluidizing the particles of the contact mass to form a fluidized bed 3. To start the reaction the fluidized bed 3 is generally heated using a heating apparatus arranged externally to the reactor (not shown). Heating is typically not required during continuous operation. A portion of the particles is transported out of the fluidized bed 3 into the void 4 above the fluidized bed 3 with the gas flow. The void 4 is characterized by a very low solids density which decreases in the direction of the reactor outlet 5.

EXAMPLES

[0071] All examples employed silicon of the same type in terms of purity, quality and content of secondary elements and impurities. The grain fractions employed in the operating granulations were produced by crushing chunk Si.sub.mg (98.9% by mass Si) and subsequent milling or by atomization techniques known to those skilled in the art to produce particulate Si.sub.mg (98.9% by mass Si). Said fractions were optionally classified by sieving/sifting. Grain fractions having certain values for structural parameter S were thus produced in targeted fashion. Contact masses having defined mass fractions of silicon-containing particles having a structural parameter S of not less than 0 were subsequently blended by combining and mixing these grain fractions. The remainder of the grain fractions comprised silicon-containing particles having a structural parameter S of less than 0. The grain fractions together summed to 100% by mass. The granulations employed in the experiments had particle size parameters d.sub.50 between 330 and 350 μm. To ensure the greatest possible comparability between the individual experiments no additional catalysts or promoters were added.

[0072] The following process was employed in all examples. During the experiments the operating temperature of the fluidized bed reactor was about 520° C. This temperature was kept approximately constant over the entire experimental duration using a heating means and a heat exchanger. The reaction gas composed of H.sub.2 and STC (molar ratio 2.3:1) and the operating granulation were both added in such a way that the height of the fluidized bed remained substantially constant over the entire experimental duration. The reactor was operated at 1.5 MPa of positive pressure over the entire experimental duration. Both a liquid sample and a gas sample were respectively taken at run times of 48 h and 49 h. The condensable proportions of the product gas stream (chlorosilane gas stream) were condensed at −40° C. using a cold trap and analyzed by gas chromatography (GC) before TCS selectivity and [% by mass] were determined therefrom. Detection was via a thermal conductivity detector. In addition, the TCS selectivity-weighted productivity [kg/(kg*h)], i.e. the amount of produced chlorosilanes per hour [kg/h] based on the amount of operating granulation [kg] employed in the reactor weighted with the TCS selectivity, was used as a basis. The obtained values after 48 and 49 h were averaged in each case. After each run the reactor was emptied completely and refilled with operating granulation.

[0073] The employed contact masses and the results of the experiments are summarized in table 1. ms is the mass fraction of particles having a structural parameter S>0.

TABLE-US-00001 TABLE 1 mS ≥ 0 TCS TCS selectivity- [% selectivity weighted productivity Experiment S by mass] [% by mass] [kg/(kg*h)] VB1* 0.005 0.02 19 0.21 VB2* 0.005 0.2 20 0.22 VB3* 0.005 0.5 20 0.22 AB1 0.005 1 22 0.28 AB2 0.005 5 22 0.30 AB3 0.005 10 23 0.31 AB4 0.005 20 24 0.31 AB5 0.005 50 24 0.33 AB6 0.005 75 24 0.33 AB7 0.005 95 24 0.34 AB8 0.050 20 25 0.31 AB9 0.053 20 24 0.32 AB10 0.040 20 23 0.33 *not inventive