JPS638207A - Hydrogenation of silicon tetrachloride - Google Patents

Abstract

PURPOSE:To moderate reaction condition of a hydrogenation reactor and improve the yield of dichlorosilane, by reacting silicon tetrachloride with metallic silicon at a specific temperature and simultaneously reducing the resultant reaction product with hydrogen gas. CONSTITUTION:Metallic silicon and silicon tetrachloride are respectively fed to a reaction column 1 and reacted at a temperature within the range of 1,100-1,300 deg.C. The resultant reaction product is then introduced into a hydrogenation column 5, quenched with hydrogen gas (from a hydrogen circulator 8) and cooled to a temperature within the range of 400-700 deg.C and simultaneously reduced with the hydrogen to form a mixed gas of dichlorosilane, trichlorosilane, silicon tetrachloride and hydrogen. The resultant mixed gas is then cooled (in a cooler 6) and separated into the hydrogen gas and liquefied dichlorosilane, trichlorosilane and silicon tetrachloride in a separator 7. The hydrogen gas, together with supplied hydrogen gas, is circulated through the hydrogen circulator 8 and fed into the hydrogenation column 5. On the other hand, the liquefied substances, e.g. silane, etc., are separated into the silicon tetrachloride, dichlorosilane and trichlorosilane in a distillation step and the silicon tetrachloride is circulated and fed to the reaction column 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for hydrogenating silicon tetrachloride. More specifically, the present invention relates to a hydrogenation method for converting silicon tetrachloride into lorsilane, which is suitable for producing amorphous silicon, as a raw material.

(Prior Art) Chlorosilanes such as trichlorosilane (s1acz3) and dichlorosilane (BIH2Qt2) are very useful as raw materials for producing high-purity silicone for semiconductors or as raw materials for producing amorphous silicon used in solar energy. To produce high-purity silicon for semiconductors, a mixed gas of chlorosilane and hydrogen is brought into contact with an electrically heated silicon rod to precipitate silicon crystals by reduction. 70
% and multi-iK by-products. In addition, for the latter H production of amorphous Noricon, the following disproportionation reaction is performed from chlorosilane 4 (
SiHCl2-*SiH4+-1-3Sict.

, 2 S i H2c L , 2-* S i H4
Z + Si c tr, t Silane (SiH4z
), which is converted into amorphous silicon by glow discharge. It can be seen that in this disproportionation reaction, silicon tetrachloride is produced several times as much as silane, as described above. This by-produced silicon tetrachloride is recycled to the reaction tower for reuse as a raw material, and is converted into chlorosilane through a hydrogenation reaction. Up to now, several methods have been proposed for converting silicon tetrachloride into chlorosilane through a hydrogenation reaction, but the method disclosed in Japanese Patent Application Laid-open No. 1/7/1973 No. 22 is particularly famous. . In this method, metallic silicon powder is introduced from the top of the hydrogenation reactor, and a mixed gas of hydrogen and silicon tetrachloride is supplied from the bottom, at a temperature of uro-r.
Chlorosilane is produced by the following reaction in a fluidized bed under the conditions of roC and pressure.

jsict + 2Hλ + Gi Nige S i Hc
t3gS i Q tp + -2E(,2+ 81 ;=
2 S i H2C12 Mainly produces trichlorosilane, but dichlorosilane is also produced as a by-product. The mixture of trichlorosilane, dichlorosilane, silicon tetrachloride, and hydrogen gas leaving the reactor is cooled and everything except hydrogen gas is condensed and liquefied, and then chlorosilane and unreacted silicon tetrachloride are separated by distillation. It is recycled and reused as a raw material in the hydrogenation reactor. When chlorosilane is used for producing amorphous silicon, it is converted into mono-7rane by the above-mentioned disproportionation reaction, and becomes a raw material for amorphous silicon. Silicon tetrachloride, which is produced as a by-product during the disproportionation reaction, is separated by distillation and recycled to the hydrogenation reactor and reused as a raw material. In the conventional method described above, the operating conditions of the hydrogenation reactor are harsh, with temperatures ranging from 0°C to 100°F and pressures ranging from 100°F to 300°F, making it difficult to manage the operation of the hydrogenation reactor. The corrosive environment of the reactor is severe.Furthermore, the concentration of trichlorosilane in the chlorosilane produced is high, which increases the amount of silicon tetrachloride produced as a by-product during the disproportionation reaction, resulting in a large circulating flow rate of silicon tetrachloride. There is a problem in that as the equipment capacity increases, the operating costs also increase.

(Problems to be Solved by the Invention) The present invention was achieved as a result of intensive studies to solve the above-mentioned problems of the conventional method. The present invention provides a method for hydrogenating silicon tetrachloride that requires less amount of silicon tetrachloride as a by-product and that increases the yield of dichlorosilane.

(Means for Solving the Problems) The gist of the present invention is to introduce and supply the reaction tower metal, silicon, and silicon tetrachloride, respectively.//QQ~13oo
The reaction product was then introduced into a hydrogenation tower and quenched with hydrogen gas to give a reaction temperature of 100 to 700 °C.
℃, and simultaneously reduce the reactant with hydrogen to produce a gas mixture of dichlorosilane/trichlorosilane, silicon tetrachloride, and hydrogen, and then cool the gas mixture to separate hydrogen gas and add it together with make-up hydrogen gas. The hydrogenation method for silicon tetrachloride is characterized in that silicon tetrachloride is recycled and supplied to the hydrogenation tower, and silicon tetrachloride is separated from dichlorosilane and trichlorosilane by a distillation operation and then recycled and supplied to the reaction tower.

The present inventor obtained the following findings as a result of studying the possibilities of various reactions. That is, silicon tetrachloride //QO~/30
When brought into contact with powdered metal 7 chloride in a high temperature range of 0° C., silicon dichloride and silicon trichloride can be produced in considerably high concentrations according to the following reaction formula.

5iCtp +Si□, 2Sict2 3sictg+Sl;=gS i et3Silicon dichloride and silicon trichloride obtained by this reaction are unstable, but when quenched (quenched) with hydrogen gas, they are simultaneously converted to dichlorosilane by hydrogenation reduction. It was found that it was stabilized in the form of (Sin et ) and trichlorosilane (SiHct3) and obtained in high yield.

In particular, the concentration of dichlorosilane is higher than in conventional hydrogenation methods, so when converting it to silane through a disproportionation reaction to produce amorphous silicon, there is an advantage that by-product silicon tetrachloride is reduced and the amount of circulation is also reduced. . Since pressure has little effect on the above reaction, normal pressure is employed. The raw material silicon metal may be silicon obtained through metallurgy.
The size of the powder particles is preferably 130 to 300 microns. When the reaction temperature is lower than 100°C, the conversion rate to silicon dichloride and silicon trichloride becomes low, and when it is higher than /300°C, it is disadvantageous in terms of reactor material and thermoeconomics. The temperature after quenching is preferably lOo to 700° C. If the temperature is lower than this, the reactivity is poor, and if the temperature is higher than this, silicon chloride may remain and metal silicon may be formed. The hydrogen column may be of a non-catalytic type or may be of a catalytic type depending on the case. A copper-based catalyst is suitable as the catalyst, and a fixed bed type is used, so that the gas after quenching passes through the catalyst bed.

The present invention will be further described in detail below based on part 70-/- of FIG. 1 showing an embodiment. 1 is a fluidized bed type reaction column, into which silicon tetrachloride to be recovered in the subsequent distillation step and disproportionation step is charged from the bottom. The temperature inside the reaction tower is 100θ
Since the temperature is higher than 0.degree. C., silicon tetrachloride is preheated to an appropriate temperature using a preheater before being charged. Reference numeral 2 denotes a hopper for metal silicon powder, and metal/licon powder is fed at a constant rate from the top of the reaction tower by a quantitative feeding device (not shown). The preferred type of reaction tower is a tray type or empty column type fluidized bed, and metallic silicon reacts with silicon tetrachloride rising while descending within the reaction tower to produce silicon dichloride and silicon trichloride. Since the reaction is at a high temperature of 1100 to 7300°C, a heating method using an electric heating coil 3 is adopted. The mixed gas of silicon dichloride, silicon trichloride, hydrogen, and silicon tetrachloride flowing out from the top of the reaction tower then enters the hydrogenation tower and is hydrogenated by hydrogen gas at room temperature and simultaneously quenched (quenched) to form silicon dichloride. is converted into dichlorosilane (51H2ct2) and silicon trichloride is converted into trichlorosilane (SiHct3). In order to increase the yield of dichlorosilane and trichlorosilane, it is necessary to rapidly cool the hydrogen gas to 4 to 700℃ at the same time as the hydrogenation, and for this reason, the amount of circulating hydrogen gas injected into the hydrogen column is reduced even if it is hot after cooling. It can be decided after consideration.

The mixed gas of hydrogen, dichlorosilane, trichlorosilane, and unreacted silicon tetrachloride exiting column J is cooled to -30 to -30°C by cooler B, and the components of dichlorosilane, trichlorosilane, and silicon tetrachloride are liquefied. Dichlorosilane and trichlorosilane are separated from hydrogen gas in a separator 7 and sent to a distillation process by a pump 7. Dichlorosilane and trichlorosilane are separated from silicon tetrachloride by a distillation device (not shown) and sent to a disproportionation process to be converted into silane. . The silicon tetrachloride recovered in the above-mentioned distillation step and disproportionation step is recycled and reused as a raw material for the reaction column. Since hydrogen gas is sent out of the system as a component of the product silane (SiH4+), it is necessary to replenish this amount as well.

(Example) A reaction tube made of Aruna (//) with an inner diameter of 2 mm was filled with high purity Riza and flathead metal silicon (//), and the outside of the reaction tube was heated with an electric heater (Kanthal wire) (/3). .2♂Heated to 0°C. When the temperature of the reaction tube reached a predetermined temperature, a certain amount of silicon tetrachloride gas (/ = t/min
) and passed through a high-temperature metal silicon packed bed to react. Inject hydrogen gas at room temperature into the reaction part log gas in parallel flow with the reaction part output log gas in an amount approximately equal to the amount of silicon tetrachloride gas (
/~! t/min) and keep the gas temperature after mixing at about 2
Set it so that the temperature is 00℃. This gas is transferred to a condenser (/j)
The condensate was collected and the heavy metal was measured and used as a sample for analysis.

An example of the experimental results is shown below) Experiment time: 60 minutes Noricone tetrachloride supply flow rate: Otsuj l/m i
nHydrogen gas supply flow rate: jjt/minMetal silicon packed bed temperature: /210℃ Temperature after hydrogen gas quenching: &75℃Condensate weight 2 3gAnalysis results after air condensationDichlororon y:srmot% trichloro7 run = 3j 〃4 Licon chloride = 3 (Effects of the invention) According to the present invention described above, the following effects can be obtained.

(1) The hydrogenation reaction tower can be operated at normal pressure, making it easier to manage the operation including the injection of metal silicon. (2) The hydrogenation reaction tower can be operated at normal pressure, which lowers the hydrogen partial pressure and lowers the hydrogen partial pressure of the reaction tower. (3) Due to the high yield of dichlor 7 run, the amount of silicon tetrachloride as a by-product when converted to disilane through the disproportionation reaction is small, reducing the circulation amount and increasing the equipment capacity. And the operating cost can be reduced.

[Brief explanation of drawings]

Figure 1 shows 70 sheets showing an example of the present invention, Figure 2 shows the experimental equipment of the present invention, /: reaction tower, 2: silicon hopper, 3: electric heating coil, ri: preheater, j: hydrogen, etc. tower, t: cooler, 7: separator, r
: hydrogen circulation machine, 2: pump, l/: reaction tube, /λ: metal silicon, 13: electric heater, /l: evaporator, lj: condenser.

Claims (1)

[Claims] Metallic silicon and silicon tetrachloride are charged and supplied to the reaction tower, respectively, and reacted at a temperature range of 1100 to 1300°C.The obtained reactants are then introduced into a hydrogenation tower, quenched with hydrogen gas, and reacted at a temperature of 400 to 700°C. At the same time as cooling to a temperature range, the reactant is reduced with hydrogen to generate a mixed gas of dichlorosilane, trichlorosilane, silicon tetrachloride, and hydrogen,
Next, the mixed gas is cooled, hydrogen gas is separated, and the hydrogen gas is recycled and supplied to the hydrogenation tower together with make-up hydrogen gas, and silicon tetrachloride is separated from dichlorosilane and trichlorosilane by a distillation operation and is recycled and supplied to the reaction tower. A method for hydrogenating silicon tetrachloride.