JPS6156164B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing trichlorosilane, and particularly to a method for hydrogenating silicon tetrachloride to trichlorosilane. High-purity silicon for semiconductors is produced by growing polycrystalline silicon generated by hydrogen reduction of trichlorosilane (SiHCl ₃ ) on a high-purity silicon polycrystal rod, and then converting it into a single crystal. However, in the reaction of trichlorosilane to silicon, about 70% of unreacted trichlorosilane is converted to silicon tetrachloride, so this reaction ratio is metal silicon: trichlorosilane: silicon tetrachloride. =1:
The ratio is 5:10 (weight ratio), and in this case, a large amount of silicon tetrachloride is produced as a by-product. Therefore, a method of converting this silicon tetrachloride into trichlorosilane and recycling it using the following formula Si + 3SiCl ₄ + 2H ₂ → 4SiHCl ₃ was investigated, but since the above reaction has a slow reaction rate, Methods using cuprous chloride, cement copper, electrolytic copper, etc. as catalysts have also been proposed, but none of these methods have yet given industrially satisfactory results and have not been put into practical use. . The present invention relates to an improved method for converting silicon tetrachloride into trichlorosilane, which uses silicon metal powder with a hardened apparent density of 1.5 to 2.0 g/cc,
A fluidized bed reactor charged with a catalytic amount of stamped copper having a loose apparent density of 0.9 to 1.2 g/cc was heated under pressure at 450 m
It is characterized by maintaining the temperature at ~550°C and supplying hydrogen gas and silicon tetrachloride thereto to cause a fluid reaction. To explain this, the present inventors have conducted various studies on the modification reaction of silicon tetrachloride to trichlorosilane, and have found that this reaction exhibits a certain thermodynamic composition under certain conditions, for example, at 500°C. If this is reacted at a molar ratio of hydrogen gas/silicon tetrachloride = 2, a trichlorosilane thermodynamic composition of 27.4 mol% will be obtained under a pressure of 10 kg, but this reaction is unrealistic without a suitable catalyst. Since this requires a long residence time, when cuprous chloride was added as a catalyst, it was found that in this case, a residence time of 50 seconds or more was required to reach the thermodynamic equilibrium concentration, and that electrolysis It was found that copper did not have much of a catalytic effect. Therefore, we further investigated this catalyst and used stamped copper as the catalyst, and in this case, e.g.
Even in a 150mmφ x 4000mm reaction tube, it reaches 90% of its thermodynamic equilibrium concentration in 25 seconds, and even in a 25mmφ x 300mm reaction tube.
It was confirmed that the reaction reached a sufficient equilibrium in 15 seconds in the reaction tube, and further research was conducted on the reaction conditions, etc., and the present invention was completed. The method of the present invention first involves converting silicon tetrachloride to trichlorosilane in a fluidized bed reactor, but this is because a uniform temperature distribution cannot be obtained in the static bed, so Although the concentration of chlorosilane produced decreases, the temperature distribution in the reaction zone in the fluidized bed reactor becomes uniform, and the concentration of trichlorosilane produced can also be made uniform. This fluidized bed reactor is charged with metallic silicon as a reaction raw material and a catalytic amount of stamped copper, which are kept in a fluid state in this reactor by silicon tetrachloride and hydrogen gas as reaction gases. However, this metallic silicon may be ordinary industrial metallic silicon containing about 2% of iron, aluminum, calcium, etc. as impurities, and there is no need for it to contain particularly large amounts of these impurities as a catalyst component. do not have. The stamped copper used as a catalyst to be added to the metallic silicon is made by processing commercially available copper powder with a stamping machine to form a flat plate, and then activating the surface by impact treatment. In order to prevent the surface from oxidizing, it is preferable that an inert substance such as wax or stearic acid be added during stamping to coat the surface. However, if this stamped copper is too heavy, it will be classified during flow in the fluidized bed reactor, and good fluidization conditions may not be obtained.
~2.0g/cc, and the loose apparent specific gravity is 0.9~1.2g/cc.
It is preferable to use a relatively light material with a dynamic apparent specific gravity of 1.1 to 1.5 g/cc. The amount of stamp copper to be added to the silicon metal may be a catalytic amount, which is sufficient if the copper adheres uniformly to the surface of the silicon metal, thereby forming active points on the surface of the silicon metal. Usually, if the addition exceeds this amount, copper alone will form a fluidized bed, making it impossible to form a good fluidized bed, so the addition of copper is limited to 2 to 5% of the total amount of silicon retained in the reactor. It may be within the range of . The reaction conditions for this reaction are that the above-mentioned trichlorosilane production reaction is a volume reduction reaction, and the trichlorosilane concentration increases by pressurizing the reaction system, so this should be under a pressurized state of at least atmospheric pressure or higher. Since the critical pressure of hydrogen gas is 35 atm, it is preferably about 30 Kg/cm ² or less. Regarding the reaction temperature, if it is below 450°C, the reaction rate will be slow and an oversized reactor will have to be used, which is a disadvantage.On the other hand, if it is above 550°C, the material of the reactor will be a problem. So this is
The temperature is preferably in the range of 450 to 550°C. Silicon tetrachloride gasified by preheating as described above and hydrogen gas are supplied to this fluidized bed reactor, whereby the aforementioned metallic silicon and stamped copper as a catalyst are fluidized within the reactor. A reaction takes place, and as the mixing ratio of hydrogen gas and silicon tetrachloride (H ₂ /SiCl ₄ =X) is increased, the concentration of trichlorosilane produced increases. This will increase the cooling heat in the reactor and reduce the STY in the reactor, so for this X, change this to 1~
It is preferable to set it to 3. In addition, in this reaction, the metal silicon that forms the fluidized bed decreases as the reaction progresses, and the height of the fluidized bed changes, so in order to prevent this fluctuation, it is necessary to add additional metal silicon to the reaction system. It is good to do. In addition, although the reaction in the method of the present invention proceeds according to the above-mentioned formula, hydrogen chloride gas may also be added to this reaction system, which allows the above-mentioned reaction, which is an endothermic reaction, to become exothermic. Therefore, by changing the amount of hydrogen chloride gas supplied, the reactor can be made into an adiabatic system. Next, examples of the method of the present invention will be given. Example 1 150g of metal silicon powder and its solidified apparent specific gravity of 2% by weight were placed in a 25mmφ x 600mm stainless steel reaction tube.
Stamped copper with a loose apparent density of 1.06 g/cc and a dynamic apparent density of 1.36 g/cc is charged, the internal pressure is maintained at 10 Kg/cmG, the internal temperature is maintained at 400°C, and hydrogen gas is injected here. and silicon tetrachloride H ₂ /SiCl ₄ = 2
When a mixed gas of (molar ratio) was introduced at a superficial gas linear velocity of 2.1 cm/sec to cause a reaction while flowing metal silicon and stamped copper into the column, a good flow condition was observed in the system. The trichlorosilane concentration was kept at 7.2
A cryogenic collection liquid of mol % was obtained. In addition, under the same conditions, the temperature was changed to 450℃ and 500℃.
℃, 550℃, and 600℃, the first
The results shown in the table were obtained, and this reaction
It was confirmed that the thermodynamic equilibrium composition was reached at ℃.

[Table] Example 2 The reaction was carried out in the same manner as in the previous example when the molar ratio of H ₂ /SiCl ₄ in the previous example was set to 5 and the internal pressure was set to 5KG, and when this molar ratio was set to 7.9 and the internal pressure was set to 15KG. In this case as well, good flow was achieved and the results shown in Table 2 were obtained.

[Table] Example 3 Using the same reaction tube as in Example 1, 150 g of metal silicon powder and 2% by weight of the same stamped copper as used in Example 1 were charged, and the internal pressure was increased.
8KG, internal temperature kept at 500℃, hydrogen gas 4.30℃
When the reaction was started by supplying a mixed gas of 2.17 mol/hour of silicon tetrachloride and 2.17 mol/hour of silicon tetrachloride, the trichlorosilane concentration was 26.8 mol% of the theoretical equilibrium value after 1 hour.
arrived at. After that, when hydrogen chloride gas was supplied at a rate of 0.15 mol/hour, the output of the heater to maintain the reaction system at 500°C could be reduced to 2/3, and the resulting trichlorosilane concentration changed. was not observed, and the trichlorosilane concentration did not change even when the hydrogen chloride feed rate was increased to 0.52 mol/hour. Example 4 60 kg of metal silicon powder was placed in a stainless steel reaction tube of 152.4 mmφ x 4000 mm, with a hardened apparent density of 1.6 g/cc, a loose apparent density of 0.94 g/cc, and a dynamic apparent density of 1.2.
3 kg of stamped copper of 1.5 g/cc is charged, and the internal pressure inside this reactor is maintained at 9 kg and the internal temperature is maintained _{at 500} °C. The reaction was started by supplying a mixed gas (molar ratio) at a superficial velocity of 10 cm/sec, and continuous operation was performed for 25 days. During this time, metallic silicon consumed during the reaction was additionally supplied so that the height of the fluidized bed remained constant, but when the reaction was continued without additional supply of stamped copper, the obtained cryogenic collected liquid The trichlorosilane concentration in was 26.3 mol% to 27.7 mol%, and when the copper concentration in the reactor was measured after the reaction was stopped,
It amounted to 2.7% by weight. In this case, when the reaction was carried out under the same conditions with the stamped copper having a hardened apparent density of 2.58 g/cc, a loose apparent density of 1.51 g/cc, and a dynamic apparent density of 1.96 g/cc, the reaction was performed under the same conditions. Since the temperature distribution became non-uniform and a favorable fluidization state could not be obtained, the reaction was stopped.

Claims (1)

[Claims] 1 Metallic silicon powder and solidified apparent density 1.5 to 2.0 g/
cc, a catalytic amount of stamped copper with a loose apparent density of 0.9 to 1.2 g/cc was placed in a fluidized bed reactor under pressure.
A method for producing trichlorosilane, which comprises maintaining the temperature at 450 to 550°C, supplying hydrogen gas and silicon tetrachloride thereto, and causing a fluid reaction. 2. The method for producing trichlorosilane according to claim 1, characterized in that hydrogen chloride gas is supplied simultaneously with silicon tetrachloride and hydrogen gas.