PROCESS FOR PREPARING METHYLCHLOROSILANES WITH STRUCTURE-OPTIMISED SILICON PARTICLES

Abstract

A process for producing methylchlorosilanes of general formula 1, (CH.sub.3).sub.nH.sub.mSiCl.sub.4-n-m, in which n represents values from 1 to 3 and m represents values of 0 or 1 in a fluidized bed reactor is provided. A chloromethane-containing reaction gas is reacted with a particulate contact mass containing silicon in the presence of copper catalyst. An operating granulation contains at least 1% by mass of silicon-containing particles S described by a structural parameter S. S has a value of at least 0 and is calculated according to equation (1),

[00001]$S=\left({\phi }_s-0.70\right).Math.\frac{{\rho }_{\mathrm{SD}}}{{\rho }_F},$

wherein φ.sub.S is symmetry-weighted sphericity factor, ρ.sub.SD is poured density [g/cm.sup.3], and ρ.sub.F is average particle solids density [g/cm.sup.3].

Claims

1-9. (canceled)

10. A process for producing methylchlorosilanes of general formula 1
(CH.sub.3).sub.nH.sub.mSiCl.sub.4-n-m  (1), in which n represents values from 1 to 3 and m represents values of 0 or 1 in a fluidized bed reactor, wherein a chloromethane-containing reaction gas is reacted with a particulate contact mass containing silicon in the presence of copper catalyst, wherein an operating granulation, i.e. 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: $\begin{array}{cc}S=\left({\phi }_s-0.70\right).Math.\frac{{\rho }_{\mathrm{SD}}}{{\rho }_F},& \mathrm{equation}\left(1\right)\end{array}$ wherein φ.sub.S is symmetry-weighted sphericity factor ρ.sub.SD is poured density [g/cm.sup.3] ρ.sub.F is average particle solids density [g/cm.sup.3].

11. The process as claimed in claim 10, wherein the symmetry-weighted sphericity factor cps of the particles S is 0.70 to 1, wherein the sphericity of the particles S describes the ratio between the surface area of a particle image and the circumference.

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

13. The process as claimed in claim 10, wherein the operating granulation has a particle size parameter d.sub.50 of 70 to 1000 μm, wherein the particle size parameter is determined according to DIN ISO 9276-2.

14. The process as claimed in claim 10, wherein the silicon is a metallurgical silicon (Si.sub.mg) having a purity of 98% to 99.5% by mass silicon.

15. The process as claimed in claim 10, wherein the copper catalyst is selected from CuCl, CuCl.sub.2, CuO or mixtures thereof.

16. The process as claimed in claim 10, wherein the temperature is from 220° C. to 380° C.

17. The process as claimed in claim 10, wherein the reaction gas contains at least 50% by volume of MeCl before entry into the reactor.

18. The process as claimed in claim 10, wherein the produced methylchlorosilane of general formula 1 is dimethyldichlorosilane (DMDCS).

Description

[0078] 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 and forming a fluidized bed 3. To initiate the reaction the fluidized bed 3 is generally heated using a heating apparatus (not shown) arranged externally to the reactor. Heating is typically not necessary during continuous operation. A portion of the particles is transported by the gas flow from the fluidized bed 3 into the free space 4 above the fluidized bed 3. The free space 4 is characterized by a very low solids density which decreases in the direction of the reactor outlet 5.

EXAMPLES

[0079] 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. To ensure the greatest possible comparability between the individual experiments no additional catalysts or promoters were added.

[0080] The following process was employed in all examples. The granulations employed in the experiments had particle size parameters d.sub.50 between 320 and 340 μm. During the experiments the operating temperature of the fluidized bed reactor was about 340° C. This temperature was kept approximately constant over the entire experimental duration using a cooling means. The reaction gas, consisting of CH.sub.3Cl, and the operating granulation were added in such a way that the height of the fluidized bed remained substantially constant over the entire experimental duration and the granulation is fluidized over the entire reaction time. The reactor was operated at 0.05 Mpa of positive pressure over the entire experimental duration. Both a liquid sample and a gas sample were taken in each case after a run time of 3 h (constant productivity and selectivity achieved). 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 selectivity for dimethyldichlorosilane of general formula 1 (DMDCS selectivity) and [% by mass] were determined therefrom. Detection was via a thermal conductivity detector. In addition, the DMDCS selectivity and the productivity [kg/(kg*h)], i.e. the produced amount of methylchlorosilane of general formula 1 per hour [kg/h] based on the amount of contact mass (operating granulation) employed in the reactor [kg], weighted with the DMDCS selectivity, was used as a basis. After each run the reactor was emptied completely and refilled with contact mass.

[0081] The employed operating granulations and the results of the experiments are summarized in table 2. ms is the mass fraction of particles S having a structural parameter S>0.

TABLE-US-00002 TABLE 2 mS ≥ 0 DMDCS selectivity Productivity Experiment S [% by mass] [% by mass] [kg/(kg*h)] VB1* 0.005 0.02 82 0.10 VB2* 0.005 0.2 83 0.12 VB3* 0.005 0.5 83 0.14 AB1 0.005 1 86 0.16 AB2 0.005 5 86 0.23 AB3 0.005 10 90 0.31 AB4 0.005 20 91 0.31 AB5 0.005 50 92 0.33 AB6 0.005 75 94 0.30 AB7 0.005 95 95 0.30 AB8 0.050 20 92 0.33 AB9 0.053 20 93 0.34 AB10 0.040 20 92 0.33 *noninventive

[0082] The productivity [kg/(kg*h)], i.e. the produced amount of methylchlorosilanes of general formula 1 per hour [kg/h] based on the amount of contact mass (operating granulation) [kg] employed in the reactor, and the DMDCS selectivity were used as a basis for evaluation of the selected combinations of S and mS≥0 [% w] and definition of the optimal ranges. A productivity of >0.15 kg/(kg*h and a DMDCS selectivity≥86% based on the amount of methylchlorosilanes of general formula 1 are considered optimal and acceptable respectively. VB1 to VB5 and AB1 to AB10 are listed as representatives of a multiplicity of experiments performed for determining the optimal ranges. In experiments VB1 to VB5 the productivity and/or the DMDCS selectivity are inadequate. The optimal ranges for the parameters upon which the indices are based were determined from a multiplicity of such negative examples. The ranges recited at the outset in the example are therefore larger than the claimed ranges. The experiments verify that methylchlorosilanes, in particular DMDCS, may be produced by MRDS particularly productively and selectively when the process is performed in the optimal ranges of the indices S and mS≥0 [% w].