JPH0355408B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing trichlorosilane by dechlorination hydrogenation reaction of tetrachlorosilane. High-purity silicon is used in large quantities in the semiconductor industry, and in order to manufacture it, crude silicon is generally reacted with hydrogen chloride to create trichlorosilane, which is purified by distillation to create high-purity trichlorosilane. , produces high-purity silicon for semiconductors through hydrogen reduction and decomposition at high temperatures of 1,000 to 1,300 degrees Celsius. When the crude silicon is reacted with hydrogen chloride, a considerable amount of tetrachlorosilane is produced as a by-product. High-purity silicon can be produced by reducing tetrachlorosilane with hydrogen, but this method is rarely used industrially because the reaction rate is slow and the reaction rate is low. Additionally, the trichlorosilane form is more useful than tetrachlorosilane since trichlorosilane is widely used as a raw material in the silicone resin industry. From the above background, various methods of producing trichlorosilane from tetrachlorosilane have been attempted. (Prior art and its problems) As a previous technology for producing trichlorosilane from tetrachlorosilane, there is a technology for hydrogenating tetrachlorosilane to trichlorosilane in the presence of hydrogen using copper or copper chloride as a catalyst (Japanese Unexamined Patent Application Publication No. 1983-1998-
161915, JP-A-56-73617, JP-A-59-45919, etc.). In addition, using a catalyst containing a platinum group metal, tetrachlorosilane is added at a molar ratio of 1 to 1/40 to hydrogen in a hydrogen stream at a temperature range of 450 to 1100 C for a contact time of 1 to 1/40 with the catalyst. There is a technology (Japanese Patent Publication No. 55-10532) that produces trichlorosilane by passing it for 300 seconds. however,
Not only when copper chloride is used as a catalyst, but also when copper is used as a catalyst, copper chloride is generated during the reaction process, and since these copper chlorides are volatile under the reaction conditions, they may be mixed into trichlorosilane. Reactions using copper or copper chloride catalysts cannot be operated for long periods of time because they reduce product purity and consume the catalyst. On the other hand, in technologies that use catalysts containing platinum group metals, the platinum group metals are supported on activated carbon, alumina, or silica, but the carrier used there is porous activated carbon. In addition, γ-alumina is used as the alumina, and the silica appears to be porous silica gel, which is commonly used. Incidentally, in the case of this catalyst, although the platinum group metal as a catalyst component is not consumed like copper or the like, the carrier is consumed and the activity decreases, making it impossible to operate for a long period of time. (Means for solving the problem) In the case of industrial production, it is extremely important to continuously obtain products of constant quality over a long period of time. The present inventors have focused on the excellence of the production technology of trichlorosilane using platinum group metal as a catalyst, and from the viewpoint of industrialization, have spent many years researching and developing catalysts that can withstand long-term use and reaction conditions using them. However, using a catalyst in which at least one selected from the group consisting of platinum group metals and platinum group metal silicides is supported on a non-porous silica carrier,
A method for producing trichlorosilane continuously over a long period of time at a reaction temperature of 500 to 1100 DEG C. and a hydrogen/tetrachlorosilane molar ratio of 0.5 to 40 has been invented. (Function) Regarding catalysts used in reactions, the larger the surface area, the greater the catalytic activity. Therefore, it is common general technical knowledge to use a carrier with a large surface area, but the present invention is based on this common sense. However, in the dehalogenation hydrogenation reaction of tetrachlorosilane, when silica with a high surface area is used as a carrier, the silica is highly reactive and easily attacked, and it is significantly consumed and the supporting effect of the catalyst component is impaired. This is due to the discovery that the catalyst loses its activity in a short period of time due to insufficient catalytic activity. For example, when a reaction is carried out using palladium-supported silica gel with a surface area of 250 m ² /g as a catalyst, most of the catalyst reacts with tetrachlorosilane and hydrogen and disappears approximately 100 hours after the start of the reaction, resulting in loss of catalytic activity. be exposed. The reason for this is that since palladium is uniformly dispersed and supported in the form of fine particles on the silica surface, a large amount of the silica surface activated during dehalogenation and hydrogenation by the catalyst reacts in a short time. Therefore, in order to eliminate such drawbacks and create a long-life catalyst, it is necessary to reduce the surface area of the silica support.
For example, a silica carrier with a surface area of 1 to 10 m ² /g
When using silica bricks, there is almost no decrease in catalytic activity 100 hours after the reaction, but the silica used as a binder for the bricks disappears in the reaction, resulting in a decrease in strength and eventually turning into powder, making it unusable. . On the other hand, when the reaction is carried out using a non-porous silica carrier as in the present invention, there is almost no decrease in catalytic activity and the amount of silica lost in the reaction is virtually negligible, so the strength of the carrier is reduced. Since there is virtually no deterioration, long-term operation can be carried out. The non-porous silica used as the carrier for the catalyst used in the present invention has no pore structure in the bulk structure of the carrier, and "non-porous" means:
The BET surface area (N ₂ ) measured by a BET surface area measurement device is 1.0 m ² /g or less. An example of non-porous silica is a solidified glass-like fused silica, which has the advantage of increasing activity even under the above surface area conditions and within that range. It is better to increase the surface area within an allowable range in order to facilitate the support, and for this purpose it is preferable to use a silica carrier prepared by etching a glass-like solidified fused silica with hydrofluoric acid by at least 0.1μ or more. A silica carrier whose glass-like solidified fused silica surface has been polished by at least 0.1μ using an abrasive such as silicon carbide, or a glass-like solidified fused silica surface which has been treated by contacting high-temperature hydrogen with chlorosilanes. A silica support is used. In addition, the surface area is 150 to 300 m ² /g,
Preferably, a silica carrier obtained by crystallizing 180 to 250 m ² /g of silica gel at high temperature may be used. The method of treatment with hydrofluoric acid may be etching, and it is not necessarily necessary to etch more than 0.1μ, but it is preferable that the etching is 0.1μ or more, and there is no limitation on the degree of etching of 0.1μ or more. This can be carried out, for example, by immersing 1 part by weight of a silica carrier, which is a glassy solidified fused silica, in 0.5 parts by weight to 5 parts by weight of a 50% HF aqueous solution at room temperature for 1 to 10 hours. At this time, the weight of the silica carrier decreases by 5 to 36 wt%, the surface becomes uneven and the color becomes white. In addition, as for the method of polishing, it is sufficient to perform polishing, and it is not necessarily necessary to polish more than 0.1μ, but it is preferable to polish to 0.1μ or more, and there is no limitation on the degree of polishing of 0.1μ or more. For example, this can be done by blowing an abrasive such as carborundum, which is used in the production of ordinary frosted glass, with air at room temperature. At this time, the surface becomes white due to minute irregularities. Furthermore, when using high temperature hydrogen and chlorosilanes, for example, at 600 to 800°C, a mixed gas of hydrogen and tetrachlorosilane is applied to a silica carrier at least 100%
By contacting for more than a period of time, fine irregularities can be generated on the surface. In addition, when filling a reactor with a catalyst and solidified fused silica as a heat medium when performing a hydrogenation reaction of chlorosilanes,
If the solidified fused silica is taken out and used when one cycle of operation is completed, this solidified body is efficient as a silica carrier because it has been subjected to the above-mentioned surface treatment during the reaction. As the catalyst component, a platinum group metal and at least one type of platinum group metal are used. That is, platinum, palladium, ruthenium, rhodium, iridium, osmium and their silicides are used,
At least one member selected from the group consisting of palladium, ruthenium and silicides thereof is preferable in terms of high catalytic activity and low catalyst cost, and more preferably at least one member selected from the group consisting of palladium and palladium silicide. used. Here, as palladium silicide,
A material having a Pd ₂ Si crystal structure is preferably used. Moreover, these catalyst components may be used in combination of two or more types. For example, a combination of palladium and ruthenium. When palladium is used as a catalyst component, its supported amount is approximately 0.01 to 5.0 wt% based on the total weight of the catalyst.
It is preferably about 0.1 to 1.5 wt%. If the supported amount of palladium is less than about 0.01 wt%, the catalyst activity will not be sufficiently exhibited and a long contact time will be required, which is undesirable. If the supported amount exceeds about 5.0 wt%, not only will the cost increase, but the palladium Since the bonding force with the silica carrier becomes weak, the catalyst component may peel off during the reaction, which is not preferable. Furthermore, as mentioned above, the preferred supported amount of palladium is approximately 0.1 to 0.5 wt%, but when this amount is supported on a silica carrier, the size and degree of dispersion of the palladium particles are appropriate, and the catalytic activity is sufficiently exerted. Moreover, the bond between the palladium and silica surfaces becomes strong, resulting in a stable catalyst. If something other than palladium is used as a catalyst component, the supported amount will vary somewhat depending on the component, but it should be approximately the same amount as palladium. Further, when two or more catalyst components are used, the above supported amount may be satisfied for all catalyst components. The combination and the supported amount ratio may be appropriately selected depending on the reaction conditions and the like. When producing the catalyst used in the present invention, the following method is preferably used in order to uniformly support the catalyst components on the silica carrier. That is, after a silica carrier is impregnated with an aqueous solution of a platinum group metal chloride or nitrate or their ammonia complex salt at a predetermined concentration, the aqueous solution that is not retained on the carrier surface is removed, dried as it is, and then reduced. It must be done in a certain way. Although the excess aqueous solution may be removed by declination, methods such as vacuum filtration and centrifugal filtration are more preferably used. If you do not use this method and dry up the catalyst with an excess solution present on the surface, the supported metals will be unevenly supported, and there will be areas where the bonding strength of the metals etc. to the support is weak, which may cause problems during the reaction. That part peels off, which I don't like. For the reasons mentioned above, the amount of the catalyst component supported is determined by the concentration of the aqueous solution of the metal salt used for the support, and the concentration of the metal salt in the aqueous solution is selected depending on the desired amount of support. If the supported amount of the catalyst component exceeds about 5 wt%, it may cause peeling of the catalyst component during the reaction, which is not preferable. A catalyst carrying a silicide of a platinum group metal can be produced by contacting a catalyst carrying a platinum group metal with a silicon halide such as silicon tetrachloride and hydrogen at 400°C to 800°C. The reaction system for carrying out the method of the present invention can be carried out by a normal flow reaction system such as a solid bed by appropriately selecting the catalyst shape and the like.
Although the shape of the catalyst particles is not particularly limited,
For example, it is economical to use 3 to 30 mm fused silica or crushed quartz. Regarding the reaction conditions of the present invention, the reaction temperature is 500~
1100℃, preferably 700~900℃, hydrogen pressure 1~
20atm, preferably 1~10atm, contact time 0.01~
It is 20 seconds, preferably 0.1 to 3 seconds, and can also be carried out in 1 second or less. Further, the hydrogen/tetrachlorosilane molar ratio is preferably 0.5 to 40, preferably 2.0 to 10. When the reaction temperature is below 500℃, the yield of trichlorosilane is very low and inefficient;
If this is done above, trichlorosilane and tetrachlorosilane will be hydrogenolyzed and silicon will precipitate, making it impossible to achieve the purpose. The reaction under high pressure is disadvantageous because the yield of trichlorosilane production does not improve significantly by increasing the hydrogen pressure. However, since the reactor can be made compact by pressurizing, it is preferable to set the pressure to 1 to 20 atm. If the contact time is 0.01 seconds or less, the reaction rate to trichlorosilane will be insufficient, but since the reaction will be almost completed within 20 seconds, a contact time of 20 seconds or more will be industrially disadvantageous. A more advantageous contact time is
It is 0.1 to 3 seconds, more preferably 0.2 to 1 second. The molar ratio of hydrogen and tetrachlorosilane is 0.5
The above conditions are necessary to improve the reaction yield, but if it exceeds 40, the concentration of tetrachlorosilane and trichlorosilane produced becomes too dilute, which not only lowers the yield per reactor, but also reduces the cooling The decomposition efficiency of hydrogen, tetrachlorosilane, and trichlorosilane decreases, making it inefficient. As described above, the present invention makes it possible to industrially obtain trichlorosilane with good yield over a long period of time from tetrachlorosilane. In the present invention, the catalyst is not consumed during the reaction, so the reaction can be continued for a long period of time, and the reaction can be carried out efficiently by selecting appropriate reaction conditions. (Examples) Next, the present invention will be explained based on examples so that the content of the present invention can be understood more clearly, but the present invention is not limited to these examples. In addition, in the following Examples and Comparative Examples, the surface area is measured using the "Rapid Surface Measuring Device" manufactured by Shibata Scientific Instruments Co., Ltd.
SA-100". The surface areas of the carriers used in Examples 1 to 5 and Example 9 were all measured with the above device and were below the measurement limit. Below this measurement limit means below 0.2 m ² /g. Example 1 A crushed fused silica body whose composition is shown in Table 1 was
It was sieved so that the mesh size ranged from 4.76 to 9.52 mm. Palladium chloride was heated and dissolved under acidic conditions with hydrochloric acid to prepare an impregnating solution of an aqueous solution having a concentration of palladium chloride of 100 g. This impregnating liquid is impregnated into the sieved silica carrier, and the excess impregnating liquid that is not retained on the silica surface is removed by applying a gradient.
After drying, it was reduced by passing hydrogen at room temperature. At this time, the amount of palladium supported was determined by analysis to be 0.31 wt%. Catalyst A thus produced was packed into a quartz reaction tube to construct a fixed bed flow reactor and tested. Molar ratio of tetrachlorosilane and hydrogen 1:3
A mixed gas was passed through the reaction mixture at a reaction temperature of 800°C and a contact time of 0.3 seconds, and the reaction gas was analyzed by online gas chromatography. Gas analysis values at the beginning of the reaction were 23.0% tetrachlorosilane, 2.0% trichlorosilane, and 2.0% hydrogen chloride (this percentage is volume %, the same applies hereinafter), and the conversion rate from tetrachlorosilane to trichlorosilane was 8%. It was hot. The yield of trichlorosilane gradually increased over time, and after 100 hours, analytical values of 21.87% tetrachlorosilane, 3.13% trichlorosilane, and 3.13% hydrogen chloride were obtained, and the conversion rate was 12.5%. After that, the conversion rate remained almost constant, and even though the reaction continued for 4000 hours, the catalyst activity did not decrease and a constant conversion rate was obtained. In addition, when the used catalyst was extracted, there was virtually no decrease in catalyst strength.

[Table] Example 2 The fused silica crushed body whose composition is shown in Table 1 was
It was sieved so that the mesh size ranged from 4.76 to 9.52 mm. Etching was performed by immersing 1 part by weight of the sieved crushed fused silica in 2 parts by weight of a 50% hydrofluoric acid aqueous solution at room temperature for 4 hours. At this time, the weight reduction due to etching was 23%. After etching, the silica carrier was washed with a large amount of water and then dried. Next, palladium chloride was heated and dissolved under acidic conditions with hydrochloric acid to prepare an impregnating solution containing 100 g of palladium chloride/aqueous solution. The above silica carrier was impregnated with this impregnating liquid, and the excess impregnating liquid not retained on the silica surface was removed with a gradient, and after drying, it was reduced by passing hydrogen at room temperature. At this time, the amount of palladium supported was determined by analysis to be 0.42 wt%. Catalyst B thus prepared was packed into a quartz reaction tube and tested using a fixed bed flow reactor. Molar ratio of tetrachlorosilane and hydrogen 1:3
A mixed gas was passed through the mixture at a reaction temperature of 800°C and a contact time of 0.45 seconds, and the reaction gas was analyzed by online gas chromatography. Gas analysis values at the beginning of the reaction showed that tetrachlorosilane was 22.5%, trichlorosilane was 2.5%, and hydrogen chloride was 2.5%, and the conversion rate from tetrachlorosilane to trichlorosilane was 10%. The trichlorosilane yield gradually increased over time, and after 100 hours, the yield was 21.2% for tetrachlorosilane, 3.8% for trichlorosilane, and 3.8% for hydrogen chloride.
% analysis was obtained, and the conversion rate was 15%. After that, the conversion rate remained almost constant, and even though the reaction continued for 4000 hours, the catalyst activity did not decrease and the conversion rate remained constant. Furthermore, when the used catalyst was extracted, there was virtually no decrease in catalyst strength. Further, using 100 g of the above silica carrier, a catalyst having 6% palladium supported was prepared by impregnating 120 c.c. of an impregnating solution with a palladium chloride concentration of 100 g/diluted and heating and drying it. A reaction test was conducted using this catalyst under the same conditions as above. The conversion rate of tetrachlorosilane to trichlorosilane was 15%, but when the used catalyst was taken out, 90% of the palladium supported on the catalyst had peeled off, so this heating dry-up method was not suitable for catalyst production. is not very suitable. Example 3 A reaction test was conducted using Catalyst B, which was exactly the same as in Example 2. However, prior to the reaction, a mixed gas of trichlorosilane and hydrogen was passed at 700°C to convert the palladium supported on the catalyst into palladium silicide, and then the reaction was carried out under exactly the same conditions as in Example 2. From the beginning of the reaction, the conversion rate of tetrachlorosilane to trichlorosilane was 15%.
The reaction for 4000 hours showed a constant conversion rate.
When the spent catalyst was analyzed by X-ray diffraction,
A peak corresponding to palladium silicide with a Pd ₂ Si crystal structure was obtained. Example 4 A silica carrier was prepared by polishing a 4.76-9.52 mm fused silica crushed body by blowing carborundum with air. Next, an acidic aqueous solution of hydrochloric acid having a palladium chloride concentration of 65 g was prepared as an impregnating solution.
The above silica carrier was impregnated with this impregnating liquid, and the excess impregnating liquid not retained on the silica surface was removed by tilting the container, and after drying, it was reduced by passing hydrogen at room temperature. At this time, the amount of palladium supported was determined by analysis to be 0.33 wt%. Catalyst C thus obtained was tested using the same reactor as in Example 2. A mixture of tetrachlorosilane and hydrogen with a molar ratio of 1:5 was reacted at a reaction temperature of 700°C.
℃, contact time was 0.2 seconds. After reaching steady activity, the reaction gases were 14.7% tetrachlorosilane, 2.3% trichlorosilane, and 2.3% hydrogen chloride, the conversion rate was 13.8%, and continuous operation was possible for up to 4000 hours without a decrease in activity. . Example 5 A mixed gas of tetrachlorosilane and hydrogen was continuously applied to a fused silica crushed body of 4.76 to 9.52 mm at 800°C.
A silica support was prepared by surface treatment for 300 hours. This silica support was impregnated with an acidic impregnating solution of hydrochloric acid having a palladium chloride concentration of 100 g/min, the excess liquid not retained on the surface was removed, and after drying, the carrier was reduced by passing hydrogen at room temperature to prepare catalyst D. The amount of palladium supported was 1.0 wt%. This Catalyst D was tested using the same reactor as Example 2. Molar ratio of tetrachlorosilane and hydrogen 1:7, reaction temperature 600°C,
When the reaction was carried out for a contact time of 0.5 seconds, the composition of the reaction gas after steady activity was achieved was 11.1% tetrachlorosilane, 1.4% trichlorosilane, and 1.4% HCl, and the conversion rate was 11.2%. Even when Catalyst D was used, continuous operation for 4000 hours was possible without any decrease in activity. Comparative example 1 4.76 to 9.52 of quartz brick with physical properties shown in Table 2
Palladium chloride concentration is 50 using crushed body of mm as a carrier.
A 1% palladium-supported quartz brick catalyst (catalyst E) was prepared using an impregnating solution of 1% palladium (catalyst E). A reaction test was conducted under the same conditions as in Example 2. The conversion rate of tetrachlorosilane to trichlorosilane is initially
It was 15%, but gradually decreased as the reaction progressed, dropping to 13% after 50 hours and 12% after 100 hours. After 100 hours, the catalyst had completely lost its strength, and when trying to remove the catalyst, it turned into powder.

[Table] Comparative Example 2 A reaction test was conducted under the same conditions as in Example 2 using Catalyst F in which 1% palladium was supported on silica gel shown in Table 3. The conversion rate of tetrachlorosilane to trichlorosilane was initially 15%, but decreased as the reaction progressed, dropping to 8% after 30 hours, 6.5% after 50 hours, and 4% after 100 hours. did. When the catalyst was taken out after 100 hours, it was found that the catalyst did not retain its shape and was almost powdered, and 93.8 wt% of the catalyst weight had decreased and disappeared.

[Table] Example 6 When the silica gel shown in Table 4 was heat-treated at 950°C for 3 hours, the crystallized silica gel shown in Table 5 was obtained. Analysis by X-ray diffraction confirmed that the amorphous silica had become a mixture of crisbalite and tridymite. Using Catalyst G in which 1% palladium was supported on this crystallized silica gel, a dechlorination hydrogenation test of tetrachlorosilane was conducted using the same apparatus as in Example 2. When the molar ratio of H ₂ /tetrachlorosilane = 7.0, the reaction temperature was 800°C, and the contact time was 0.5 seconds, the conversion rate of tetrachlorosilane to trichlorosilane was 20%, and 1000
A continuous time test was conducted, but no decrease in conversion rate was observed.

【table】

[Table] Comparative Example 3 When the silica gel shown in Table 6 was heat-treated at 950°C for 3 hours, no crystallization occurred. When the silica gel shown in Table 7 was heat-treated at 950°C for 3 hours, no crystallization occurred.

【table】

[Table] Example 7 Catalyst H on which 0.4% ruthenium was supported was prepared using a silica carrier treated with hydrofluoric acid in the same manner as in Example 2. When Catalyst H was tested under exactly the same conditions as in Example 2, the conversion rate of tetrachlorosilane to trichlorosilane was 10%, and even though the test was conducted continuously for 1000 hours, no decrease in the conversion rate was observed. Example 8 A catalyst supporting 0.4% platinum was prepared using a silica carrier treated with hydrofluoric acid in the same manner as in Example 2. When the catalyst was tested under exactly the same conditions as in Example 2, the conversion rate of tetrachlorosilane to trichlorosilane was 4%, and no decrease in the conversion rate was observed after 1000 hours of continuous testing. Example 9 A fused silica crushed body of 4.76 to 9.52 mm was impregnated with a 1:1 mixed impregnating liquid of 100 g of palladium chloride and 100 g of ruthenium chloride, and after removing the excess impregnating liquid that was not retained on the silica surface, it was dried. 0.3 wt% palladium-0.3 wt% ruthenium supported catalyst J was prepared by hydrogen reduction.
Using this catalyst, a mixed gas of tetrachlorosilane and hydrogen at a molar ratio of 1:5 was passed at a reaction temperature of 750°C and a contact time of 0.25 seconds. After reaching steady activity, the reaction gas was 14.1% tetrachlorosilane, 2.6% trichlorosilane, and 2.6% hydrogen chloride, with a conversion rate of 15.6%, and no decrease in activity was observed after 1000 hours of continuous testing.

Claims (1)

[Claims] 1. A method for producing trichlorosilane by catalytic hydrogenation from a gas containing tetrachlorosilane and hydrogen, comprising: (a) non-porous silica containing a metal selected from the group consisting of a platinum group metal and a silicide of a platinum group metal; (b) reaction temperature 500 to 1100°C (c) hydrogen/tetrachlorosilane molar ratio 0.5 to
A method for producing trichlorosilane, characterized in that the reaction is carried out at 40 °C.