JPH0480852B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field The present invention is a method of forming a compound with the general formula Si _o H _2o+2 by reacting an alloy containing silicon and magnesium with an acid.
The present invention relates to a method for producing silicon hydride represented by (n is a positive integer). BACKGROUND ART In recent years, with the development of the electronics industry, the demand for silicon for semiconductors such as polycrystalline silicon or amorphous silicon has increased rapidly. Silicon hydride, Si _o H _2o+2 , has recently gained importance as a raw material for the production of silicon for semiconductors.
In particular, demand for silane (SiH ₄ ) and disilane (Si ₂ H ₆ ) is expected to increase significantly in the future as raw materials for semiconductors for solar cells. Conventionally, several methods as illustrated below are known as methods for producing silicon hydride. Mg Si+4+HClag.→2MgCl ₂ +1/nSi _o H _2o+2 +(1
−1/n) H ₂ Mg ₂ Si+4NH ₄ Br−33℃ ―――――――→ in lig.NH ₃ 2MgBr ₂ +4NH ₃ +1/nSi _o H _2o+2 +(1−1/
n) H ₂ SiCl ₄ +LiAlH ₄ ――――――――→ in etharLiCl+AlCl ₃ +SiH ₄ Si+SiCl ₄ +2N ₂ →SiHCl ₃ +SiH ₃ Cl 2SiHCl ₃ →SiCl ₄ +SiH ₂ Cl ₂ 2SiH ₂ Cl→SiHCl ₃ +SiH ₃ Cl 2SiH _{3 Cl} →SiH ₄ +SiH ₂ Cl 2Problems with the prior art Among these conventionally known methods, the method of reacting a silicon alloy such as magnesium silicide with an acid in an aqueous solution, for example, This method does not require an expensive reducing agent, nor does the reaction need to be carried out at low temperatures _or under _pressure , as in other reactions. This is basically the easiest method to implement since it does not have the disadvantages of using hexachlorodisilane (Si ₂ Cl ₆ ). However, the fatal drawback of this method is that the conversion rate (hereinafter referred to as yield) of silicon in silicon alloys to monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), and other highly useful silicon hydrides is low. (Z.Anorg, Allgem.Chem., 303, 283
(1960), JACS, 57, 1349 (1935)). As a result of our earnest efforts to solve the problems in the above-mentioned method, the present inventors have discovered that the yield of useful SiH ₄ and Si ₂ H ₆ can be significantly improved by developing various technologies such as those proposed above. did it. For example, in the method described above, by coexisting an organic solvent such as a hydrocarbon, ether, or organosilicon compound in the reaction system (Japanese Patent Application No. 58-245773, 58-245772, 59-
119380), and by-product higher silicon compounds (represented by the general formula SixHyOz, where x is a positive integer of 3 or more, and y and z are each 2x
+2, a positive integer not exceeding 2x, and one of which is not 0) is converted into SiH ₄ , Si ₂ H ₆ using a base catalyst.
By decomposing and lowering the grade of
110703, 59−113194, 59−106461, 59−175663,
59-141331), the yields of SiH ₄ and Si ₂ H ₆ could be significantly improved. In one method, it is usually preferable to use a large excess of acid in terms of the yield of silicon hydride, and therefore, if the unreacted acid after the reaction is to be discarded, it is preferable to use a large excess of acid. Not economical. Therefore, it is desirable from the economic point of view of the process to use a large excess of acid in the reaction and to circulate and reuse the unreacted acid in the reaction residue. Basic idea In order to solve the problem of low yield in the method described above, the present inventors have conducted intensive studies and found that magnesium salts are produced as by-products in the reaction system by the reaction of maznesium alloy and acid. (For example, if hydrochloric acid is used as the acid, magnesium chloride,
When using sulfuric acid, it is magnesium sulfate)
The extremely surprising fact has been discovered that there is a very strong correlation between the yield (conversion rate) of silicon hydride and the yield (conversion rate) of silicon hydride produced. The present invention was completed based on the basic idea that by controlling the amount of the by-product magnesium salt in the reaction system to a specific concentration or less, the yield of these substances could be greatly improved. This is what we have reached. DETAILED DISCLOSURE OF THE INVENTION The silicon alloy used in the method of the present invention contains silicon and magnesium as essential components, and may also contain a third component metal.
The atomic ratio of magnesium to silicon (Mg/Si) is preferably in the range of 1/3 to 3/1.
Specific examples include Mg ₂ Si, Mg ₂ SiNi, Mg ₂ SiAl,
Mg ₂ SiBa, Mg ₂ Si ₂ Ce, Mg ₆ Si ₁₇ Cu ₁₆ ,
Examples include Mg ₃ Si ₆ Al ₈ Fe, and Mg ₂ Si is particularly preferred. These can also be used as a mixture of two or more. The particle size of the silicon alloy is preferably as small as possible, specifically 1000 μm or less, preferably
It is 100 μm or less, more preferably 10 μm or less.
A conventional pulverization method can be used to subdivide the silicon alloy, and the purpose can be achieved using a pulverizer such as a ball mill, rod mill, or jet mill. The acids used are hydrochloric acid, hydrobromic acid,
Examples include inorganic acids such as hydrofluoric acid, sulfuric acid, and phosphoric acid, and organic acids such as formic acid, oxalic acid, and propionic acid. Among these, hydrochloric acid and sulfuric acid are particularly preferred. The acid concentration in the solution is not particularly limited in the present invention, but the acid concentration is 1 to 50 wt%.
The range is preferably from the viewpoint of yield of silicon hydride. Note that organic solvents such as ether compounds, hydrocarbons, halogenated hydrocarbons, silicon hydrides, and organosilicon compounds can also be present in these acid aqueous solutions. The ratio of these used is 0.001 to 1000 times the volume of the acidic aqueous solution, preferably 0.01 to 1000 times the volume of the acidic aqueous solution.
It has 10 times the capacity. In the reaction between the silicon alloy and the acid mentioned above, it is economically desirable to use the silicon alloy and the acid in the reaction molar equivalent ratio, but in reality, the yield of silicon hydride is reduced if the amount of acid used is excessive. It is preferable.
For example, the ratio of Mg ₂ Si and acid used is at least the reaction molar equivalent ((H ⁺ /Mg ₂ Si) molar ratio = 4.0), preferably (H ⁺ /Mg ₂ Si) molar ratio = 4.4 or more, more preferably 8.0 or higher. Reaction molar equivalent ((H ⁺ /
When reacting at Mg ₂ Si) molar ratio = 4.0),
Unreacted silicon alloy particles often remain in the reactor, which not only results in an extremely low yield of silicon hydride, but also accumulates alloy particles in the reaction system, which is unfavorable for operation. On the other hand, when a large excess of acid is used, it is necessary to circulate and reuse the unreacted acid in the reaction residual liquid from the economical point of view of the process. In this case, one possible method is to add the amount of acid consumed by the reaction with the alloy to the reaction residual liquid and re-supply it to the reactor. The concentration of the by-product magnesium salt is quite high, and the reaction must always proceed in a state close to saturated solubility. The present invention defines the concentration of magnesium salt in the acidic aqueous solution fed to the reactor. According to the findings of the present inventors, the concentration of by-product magnesium salt and silicon hydride, especially SiH ₄ and Si ₂ H ₆
As shown in the examples below, the relationship between the yield and the magnesium salt is not a linear relationship, but when the concentration of the magnesium salt exceeds a certain value, the yield decreases rapidly. Therefore, by allowing the reaction to proceed while paying close attention to control so that the concentration is always kept below a certain value.
They found that the yields of SiH ₄ and Si ₂ H ₆ were significantly improved. In the present invention, the concentration range of the magnesium salt in the reaction solution in the reactor or in the acid aqueous solution supplied to the reactor depends on the type of salt such as magnesium chloride, magnesium sulfate, magnesium phosphate, magnesium nitrate, etc. Although it varies somewhat, it is 10wt% or less, preferably 5wt% or less. As will be described later, when the concentration increases by 10 wt%, the yield of silicon hydride decreases significantly. However, in the present invention, the concentration of the magnesium salt in the acidic aqueous solution and the concentration of the acid are, respectively, weight of acid component/weight of acid component + weight of _H2O x 100 weight of magnesium salt/weight of magnesium salt + _H2
The weight of O x 100. The detailed reason and exact mechanism as to why there is a strong correlation between the concentration of magnesium and the yield of silicon hydride are currently unknown, but the reaction between acids and alloys is microscopic. As you can see, it is a heterophasic reaction in which the surface of the alloy particle is the reaction zone, but depending on its concentration, the produced magnesium salt does not leave the reaction zone and accumulates on the particle surface, covering most of the surface, causing the reaction to fail. We estimate that this will effectively halt further progress. Perhaps, as defined in the present invention, by maintaining the concentration of magnesium salt in the reaction system below the above value, the solubility or detachability of the magnesium salt generated on the surface of the silicon alloy particles during the reaction can be maintained well. As a result, the reaction on the silicon alloy surface is always effectively promoted, and as a result, the yield to silicon hydride is considered to be increased. Next, a specific reaction pattern when carrying out the method of the present invention will be described. The method of reaction between the silicon alloy and the acid is not particularly limited in the present invention, but for example, a method of charging the silicon alloy into a reactor containing an acidic aqueous solution, a method of charging the silicon alloy with the reactor containing the acidic aqueous solution, and a method of charging the acidic aqueous solution and the silicon alloy into the reactor at predetermined rates, respectively. Methods include charging the (The ratio of the silicon alloy to the acid used is such that the acid is at least 4.4 times the molar equivalent, preferably at least 8 times the molar equivalent, per 1 mole of silicon in the silicon alloy. Generally, the larger the amount of acid used, the more silicon hydride The reaction temperature is preferably lower, and is in the range of -90 to 100°C, preferably -50 to 50°C. The reaction between a silicon alloy and an acid is extremely fast, and the reaction is usually completed within a few minutes of contact time. Although the atmospheric gas is not necessarily required, hydrogen, helium, argon, nitrogen, etc., which do not react with the silicon hydride produced, may be used if necessary. Various methods can be employed to maintain the concentration of magnesium salt in the acidic aqueous solution supplied to the reactor below a certain level, particularly below 10%. For example, when using a volatile acid such as hydrochloric acid,
A method in which unreacted acid is recovered and recycled as hydrogen chloride gas by heating and distilling the reaction residual liquid, and a method that utilizes the solubility difference of magnesium salt depending on temperature, that is, a method in which the magnesium salt is removed by cooling the reaction residual liquid. A method in which a part of the reaction residue is separated and removed as a solid substance. A method in which a part of the water in the reaction residue is separated by heating and distillation, and a part of the magnesium salt is precipitated and separated. Examples include a method of discarding a portion as is (that is, so-called purge), and a method of solvent extraction of dissolved magnesium salts. It goes without saying that the present invention is not limited to the above method. Separation and purification of the produced gas can be easily carried out by conventional cryogenic separation, adsorption, etc., respectively. Hereinafter, preferred embodiments of the present invention will be illustrated by Examples. Examples Hereinafter, the present invention will be specifically explained using examples. Examples 1 to 6 Into a separable flask with a capacity of 1 charged with 650 g of an aqueous hydrochloric acid solution with a concentration of 20 wt%, 0 g, 20 g, 50 g, 70 g, and 70 g of anhydrous magnesium chloride were added in advance, respectively.
100g and 140g were dissolved, and then 6.0g of magnesium silicide (Mg ₂ Si) (particle size
100 to 200 meshes (78.2 mmol-Si) were continuously added at a constant rate of 0.15 g/min for 40 minutes with stirring. During this time, the reaction temperature was maintained at 0° C. by cooling the reaction solution with a refrigerant. After the reaction was completed (after the addition of the silicon alloy was completed), the temperature of the reaction solution was further increased in a hydrogen gas atmosphere, and the reaction solution was kept under reflux (approximately 106 to 109° C.) for 30 minutes. The gas generated during the reaction and heat treatment is collected in a trap cooled at the temperature of liquid nitrogen, and after the heat treatment is completed, the SiH ₄ , Si ₂ H ₆ , and Si ₃ H ₈ in the gas are removed. The amount was analyzed and determined by gas chromatography. The results are shown in Table 1 and Figure 1. As described above, it can be seen that when the concentration of magnesium chloride is changed in the range of 0 to 20% by adding the reagent magnesium chloride, the yield decreases rapidly after reaching 10%. Examples 7 to 12 In Examples 1 to 6 above, 710 g of sulfuric acid aqueous solution with a concentration of 20 wt% was used instead of hydrochloric acid, and 0 g, 20 g, and 40 g of magnesium sulfate were added in advance to this, respectively.
Experiments were conducted in the same manner as in Examples 1 to 6, except that magnesium silicide was added after dissolving 100 g, 60 g, 80 g, and 100 g. The results are shown in Table 1 and Figure 2. As described above, it can be seen that when the concentration of magnesium sulfate is varied in the range of 0 to 20% by adding the reagent magnesium sulfate, the yield decreases rapidly after reaching 10%. Example 13 A continuous reaction was actually carried out according to the flow shown in FIG. In FIG. 3, 1 is a reactor, 2 is a distillation device in this case, and 3 is a hydrochloric acid concentration adjustment tank. In a hydrogen gas atmosphere, a hydrochloric acid aqueous solution with a concentration of 25 wt% was added at 13.34 g/min to a reactor with a capacity of 200 ml equipped with a condenser set at -17°C.
g/min and magnesium silicide 0.55g/min
Continuous addition was continued for 8 hours at a constant rate of min. In this case, the ratio of magnesium silicide and acid used was (H ⁺ /Mg ₂ Si) molar ratio = 12.8. The reaction was carried out while refluxing diethyl ether (approximately 35°C). During the continuous reaction, a portion of the reaction solution was withdrawn in an overflow manner to maintain a nearly constant amount of the reaction solution in the reactor (approximately 70 ml). The reaction residue extracted from the reactor was separated into an aqueous layer and a diethyl ale layer. During the continuous reaction, the concentration of hydrochloric acid in this aqueous layer is approximately 20 wt% (HCl weight / (HCl weight + H ₂ O weight) × 100), and the magnesium chloride concentration is approximately 12 wt % (MgCl ₂ weight / (MgCl ₂ weight + H ₂ O Weight) x 100)
It was hot. Next, this water layer is distilled into distillation device 2 with approximately 105
After heating and distilling at ℃ to recover hydrochloric acid as hydrogen chloride gas (hydrochloric acid recovery rate approximately 90%), and absorbing the gas with water,
The hydrochloric acid concentration was adjusted to 25wt% by adding a predetermined amount of hydrochloric acid and water in the hydrochloric acid concentration adjustment tank, and the reactor 1 was
supplied. In addition, when hydrogen chloride was recovered, the entire amount of magnesium chloride was deposited as a residue in the can and discarded. That is, the salt concentration in the acid aqueous solution supplied to the reactor was 0. The gas generated during the reaction was first collected in a trap containing diethyl ether cooled to -70°C (Trap ()) and then in a trap (Trap ()) cooled at the temperature of liquid nitrogen. After the reaction was completed, the amounts of SiH ₄ , Si ₂ H ₆ and Si ₃ H ₈ in the diethyl ether layer, trap () and trap () were analyzed and quantified by gas chromatography. The results are shown in Table 1. Example 14 In Example 1, after layer separation of the reaction residual liquid,
Discard 2/3 of the aqueous layer, and add approximately 7.2 g/h of agricultural hydrochloric acid to the remaining 1/3 reaction residue in hydrochloric acid concentration adjustment tank 3.
The experiment was conducted in the same manner as in Example 1, except that water was added at a rate of about 2.1 g/min, and the hydrochloric acid concentration was 25 wt% and fed to the reactor at a constant rate of 14.02 g/min. Concentration of magnesium chloride in the acidic aqueous solution supplied to the reactor in this case (MgCl ₂ weight/(MgCl ₂ weight + H ₂
O weight x 100) was approximately 6.4 wt%. The results are shown in Table 1. Comparative Example 1 In Example 13, the magnesium chloride concentration was 12wt.
% of the aqueous layer of the reaction residual liquid was directly transferred to the hydrochloric acid concentration adjustment tank 3.
At the same time, concentrated hydrochloric acid and water were added to make the hydrochloric acid concentration 25 wt%, and the solution was supplied to the reactor at a constant rate of 15.77 g/min. Magnesium chloride precipitated during the reaction was taken out of the system as a solid, neutralized with alkali, and then discarded. In this case, the concentration of magnesium chloride in the acidic aqueous solution supplied to the reactor is
It was 20wt%. The results are shown in Table 1. Example 15 In Example 13, a 30 wt% sulfuric acid aqueous solution was supplied instead of a 25 wt% aqueous hydrochloric acid solution. A portion of the water was distilled off by heating and distilling the aqueous layer of the reaction residual liquid in distillation device 2. At the same time, the precipitated magnesium sulfate is separated and removed as a solid, and the remaining sulfuric acid aqueous solution containing magnesium sulfate is further added with a predetermined amount of concentrated sulfuric acid and water in the sulfuric acid concentration adjustment tank 3, so that the sulfuric acid concentration in the sulfuric acid aqueous solution is reduced to 30wt%. and supplied to the reactor at a constant rate of 15.14 g/min. In this case, the concentration of magnesium sulfate in the sulfuric acid aqueous solution was 7.8 wt%. The results are shown in Table 1. Example 16 In Example 15, the aqueous layer of the reaction residue was cooled to -5°C, the precipitated magnesium sulfate was separated and removed as a solid, and the remaining sulfuric acid aqueous solution containing magnesium sulfate was further added to the sulfuric acid concentration adjustment tank 3. By adding a predetermined amount of concentrated sulfuric acid and water, the sulfuric acid concentration in the sulfuric acid aqueous solution was adjusted to 30 wt%, and the solution was supplied to the reactor at a constant rate of 15.21 g/min. In this case, the concentration of magnesium sulfate in the sulfuric acid aqueous solution is 8.5wt%
It was hot. The results are shown in Table 1. Comparative Example 2 In Example 15, the aqueous layer of the reaction residue was directly placed in the sulfuric acid concentration adjustment tank 3, and the sulfuric acid concentration was adjusted to 30 wt% by adding concentrated sulfuric acid and water, and the sulfuric acid concentration was adjusted to 15.67 g/min.
was fed into the reactor at a constant rate of . In this case, the concentration of magnesium sulfate in the sulfuric acid aqueous solution is
It was 12.7wt%. The results are shown in Table 1. Comparative Examples 3 and 4 In Examples 13 and 15, the supply rates of hydrochloric acid and sulfuric acid were 4.29 g/min and 4.80 g/min, respectively.
The experiment was conducted in the same manner as in Example 1, except that the reaction residual liquid was discarded without being reused. In this case, the ratio of magnesium silicide and acid used was (H ⁺ /Mg ₂ Si) molar ratio = 4.1. The results are shown in Table 1.

[Table] Effects of the Invention As described above, the present invention provides a method for producing silicon hydride by reacting an alloy containing silicon and magnesium with an acidic aqueous solution, in which part or all of the acid component remaining in the reaction residue is removed. It is characterized by recycling magnesium salt and maintaining the concentration of magnesium salt in the acidic aqueous solution supplied to the reactor at 10 wt% or less.
In the process according to the present invention, it is possible to react a silicon alloy with an acid in a large excess of acidic aqueous solution, and it is also possible to react silicon hydride by suppressing the concentration of magnesium salt in the circulating reaction residue below a certain level. Yields are increased and process economics are significantly improved.

[Brief explanation of the drawing]

1 and 2 are graphs showing the results of Examples, and FIG. 3 is a flow sheet diagram for implementing the present invention.

Claims (1)

[Claims] 1. An alloy containing silicon and magnesium, hydrochloric acid,
In a method for producing silicon hydride represented by the general formula Si _o H _2o+2 (n is a positive integer) by reacting with an acid aqueous solution of sulfuric acid, phosphoric acid, nitric acid, or a mixed acid thereof, the produced silicon hydride is The acid component remaining in the reaction residue after separation is recycled to the reactor as at least a part of the acid aqueous solution, and the concentration of the entrained magnesium salt in the acid aqueous solution supplied to the reactor is controlled. A method for producing silicon hydride, characterized in that the content is maintained at 10wt% or less. 2. The method according to claim 1, wherein the alloy containing silicon and magnesium is magnesium silicide. 3. Claim 1, characterized in that after all or a part of the magnesium salt dissolved in the reaction residual liquid is separated and removed, the acid component in the reaction residual liquid is recycled and reused. The method described in.