Process for preparing chlorosilanes

Abstract

The present disclosure relates to a process for producing chlorosilanes in a fluidized bed reactor by reaction of a hydrogen and silicon tetrachloride-containing reaction gas with a particulate contact mass containing silicon and a catalyst. The chlorosilanes have the general formula H.sub.nSiCl.sub.4-n and/or H.sub.mCl.sub.6-mSi.sub.2. The reactor design is described by an index K1, the constitution of the contact mass is described by an index K2 and the reaction conditions are described by an index K3.

Claims

1. A process for producing chlorosilanes in a fluidized bed reactor, comprising: reacting a hydrogen and silicon tetrachloride-containing reaction gas with a particulate contact mass containing silicon and a catalyst, wherein the chlorosilanes have the general formula H.sub.nSiCl.sub.4-n and/or H.sub.mCl.sub.6-mSi.sub.2 where n=1-3 and m=0-4, and wherein the reactor design is described by an index $K1=.Math.\frac{V_{\mathrm{reactor},\mathrm{eff}}}{A_{\mathrm{tot},\mathrm{cooled}}.Math.d_{\mathrm{hyd}}};$ wherein is a fill level of the reactor; wherein V.sub.reactor, eff is an effective volume of the reactor [m.sup.3]; wherein A.sub.tot, cooled is a sum of cooled surface areas in the reactor [m.sup.2]; wherein d.sub.hyd is a hydraulic reactor diameter [m]; and wherein V.sub.reactor, eff is 1 to 300 m.sup.3; and wherein d.sub.hyd is 0.5 to 2.5 m; wherein the constitution of the contact mass is described by an index $K2=R_{Si}.Math.\frac{B_{AK}.Math.{}_{rel}}{d_{32}};$ wherein B.sub.AK is a breadth of the particle size distribution of the contact mass [m]; wherein d.sub.32 is a particle Sauter diameter [m]; wherein R.sub.Si is a purity of the silicon; wherein .sub.rel is a relative catalyst distribution in the contact mass; wherein .sub.rel is 0.001 to 7; wherein d.sub.32 is 10 to 2000 m; wherein B.sub.AK is 10 to 1500 m; and wherein R.sub.Si is 0.75 to 0.99999; wherein the reaction conditions are described by an index $K3=\frac{u_L}{v_F.Math.{10}^6}.Math.\frac{p_{\mathrm{diff}}}{g}.Math.\frac{1}{{}_F};$ wherein u.sub.L is a superficial gas velocity [m/s]; wherein v.sub.F is a kinematic viscosity of a gaseous reaction mixture within an interior of the reactor [m.sup.2/s]; wherein .sub.F is a fluid density [kg/m.sup.3]; wherein p.sub.diff is a pressure drop over fluidized bed [kg/m*s.sup.2]; wherein g is an acceleration due to gravity [m/s.sup.2]; wherein p.sub.diff is 10 000 to 200 000 kg/m*s.sup.2; wherein u.sub.L is 0.05 to 2 m/s; wherein .sub.F is 2 to 20 kg/m.sup.3; wherein v.sub.F is 3*10.sup.7 to 5.4*10.sup.6 m.sup.2/s; and wherein K1 has a value of 2 to 20, wherein K2 has a value of 0.001 to 200 and wherein K3 has a value of 0.5 to 10 000.

2. The process of claim 1, wherein K1 has a value of 3 to 18.

3. The process of claim 1, wherein K2 has a value of 0.005 to 100.

4. The process of claim 1, wherein K3 has a value of 0.5 to 10,000.

5. The process of claim 1, wherein the effective reactor volume V.sub.reactor, eff is 5 to 200 m.sup.3.

6. The process of claim 1, wherein the hydraulic plant diameter d.sub.hyd is 0.75 to 2 m.

7. The process of claim 1, wherein the pressure drop over the fluidized bed p.sub.diff is 30,000 to 150,000 kg/m*s.sup.2.

8. The process of claim 1, wherein the particle Sauter diameter d.sub.32 is 50 to 1500 m.

9. The process of claim 1, wherein the breadth of the particle size distribution of the contact mass B.sub.AK is 100 to 1000 m.

10. The process of claim 1, wherein the relative catalyst distribution in the contact mass .sub.rel is 0.005 to 5.

11. The process of claim 1, wherein the catalyst is selected from the group of Fe, Al, Ca, Ni, Mn, Cu, Zn, Sn, C, V, Ti, Cr, B, P, O, Cl and mixtures thereof.

12. The process of claim 1, wherein the superficial gas velocity u.sub.L is 0.1 to 1 m/s.

13. The process of claim 1, wherein the fluid density .sub.F is 5 to 15 kg/m.sup.3.

14. The process of claim 1, wherein the kinematic viscosity v.sub.F is 1.5*10.sup.6 to 5.4*10.sup.6 m.sup.2/s.

15. The process of claim 1, wherein the absolute pressure in the fluidized bed reactor is 0.5 to 5 MPa.

16. The process of claim 1, wherein the reaction is performed in a temperature range of 350 C. to 800 C.

17. The process of claim 1, wherein the reaction gas contains, before entering the reactor, at least 10 vol % of hydrogen and silicon tetrachloride.

18. The process of claim 1, wherein the fluidized bed reactor is integrated into an integrated system for production of polycrystalline silicon.

19. The process of claim 1, wherein wherein A.sub.tot, cooled is a sum of cooled surface areas as determined by laser measurements or 3D scans in the reactor [m.sup.2]; or wherein B.sub.AK is d.sub.90-d.sub.10; or wherein the catalyst at least contains Cu as a catalytically active element.

20. The process of claim 1, .sub.rel is calculated according to equation 6, $\begin{array}{cc}{}_{rel}=.Math.\frac{o_{\mathrm{spec},\mathrm{cat}}}{o_{\mathrm{spec},\mathrm{SiK}}};& \left(\mathrm{equation}6\right)\end{array}$ wherein is a mass ratio of catalyst/silicon granulation or catalyst loading; wherein O.sub.spec, cat is an average specific surface area of the catalyst [m.sup.2/kg]; wherein O.sub.spec, SiK is an average specific surface area of the silicon granulation [m.sup.2/kg]; and wherein the average specific area is determined by gas adsorption according to the BET method (ISO 9277).

Description

EXAMPLES

(1) In order to apply the findings and correlations to productivity in the production of chlorosilanes and to define the ranges for the indices K1, K2 and K3 (operating ranges) detailed investigations on continuously operated fluidized bed reactors of different sizes were performed.

(2) Various experiments V were performed (Table 1: V1 to V31), wherein varied in each case were the hydraulic plant diameter d.sub.hyd with values from 0.3 m to 3 m, the superficial gas velocity u.sub.L with values from 0.01 m/s to 4 m/s, the particle Sauter diameter d.sub.32 with values from 5 m to 2500 m, the breadth of the operating granulation B.sub.AK with values from 10 to 2000 m and the relative catalyst distribution over the contact mass .sub.rel with values of 0.0001 to 10, the purity of the silicon with values of 0.75 to 0.99999, the catalyst loading 2 with values of 0.00001 to 0.4 and the pressure drop over the fluidized bed p.sub.diff with values of 5000 to 400 000 kg/m*s.sup.2.

(3) The particle solids density .sub.P may in principle be considered to be approximately constant. The fluid density .sub.F is typically in a range from 2 to 20 kg/m.sup.3. The kinematic viscosity v.sub.F is typically in a range from 6.Math.10.sup.7 to 4.5.Math.10.sup.6 m.sup.2/s.

(4) The indices K1, (equation 1), K2 (equation 4) and K3 (equation 7) resulted from the chosen/prescribed parameters. The productivity [kg/(kg*h)], i.e. the produced amount of chlorosilanes per hour [kg/h] based on the amount of contact mass (operating granulation) employed in the reactor [kg], was used as a basis for evaluation of the selected combinations of K1, K2 and K3 and for definition of the optimal ranges. A productivity of >0.01 kg/(kg*h) is considered optimal/acceptable.

(5) TABLE-US-00002 TABLE 1 Productivity Experiment K1 K2 K3 [kg/(kg*h)] V1 1.37 2.81 155 <0.01 V2 1.97 2.72 149 <0.01 V3 2.94 2.93 153 0.088 V4 3.27 3.21 137 0.094 V5 4.96 3.04 144 0.169 V6 6.76 2.61 163 0.212 V7 8.39 2.88 159 0.337 V8 8.39 0.000006 154 <0.01 V9 8.39 0.0006 157 <0.01 V10 8.39 0.0011 156 0.045 V11 8.39 0.0073 156 0.079 V12 8.39 0.014 157 0.124 V13 8.39 0.027 160 0.180 V14 8.39 14.6 184 0.407 V15 8.39 19.2 188 0.320 V16 8.39 147 179 0.115 V17 8.39 221 193 <0.01 V18 8.39 2.87 10193 <0.01 V19 8.39 3.01 0.45 <0.01 V20 8.39 3.12 0.83 0.027 V21 8.39 3.17 3.77 0.098 V22 8.39 3.09 5.01 0.123 V23 8.39 3.84 14.1 0.241 V24 8.39 3.99 277 0.541 V25 8.39 3.74 608 0.184 V26 8.39 3.09 1058 0.133 V27 8.39 3.02 4115 0.094 V28 8.39 3.12 7684 0.048 V29 8.39 2.99 9056 0.025 V30 12.1 4.22 270 0.420 V31 13.1 4.08 283 0.393 V32 16.4 3.87 288 0.228 V33 19.7 3.74 269 0.018 V34 21.8 3.93 248 <0.01

(6) The experiments demonstrate that chlorosilanes are producible by using LTC with particularly high productivity when the process is performed in the optimal ranges of the indices K1, K2 and K3.