JPH0520143B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a catalyst for dehalogenating metal halides in the presence of hydrogen. More specifically, silicon, niobium or vanadium chloride;
This invention relates to a catalyst for dehalogenating halides such as iodides and bromides in the presence of hydrogen. In the electronics industry, there is a high demand for various new metals with extremely high purity, including the above-mentioned elements. In other words, high-purity silicon is used in large quantities as a base for LSIs, high-purity niobium is used as a superconducting material, and high-purity molybdenum, tungsten, etc. are used as metal silicide targets for LSIs, and in the future there will be even more use of these materials. It is believed that the new metal's uses will expand. These high-purity new metals are usually produced by first halogenating low-purity raw materials and then distilling them.
It is highly purified and then thermally cracked or hydrogenolyzed again to produce a high-purity product. In this case, it is advantageous to use lower-order halides, since higher-order halides are more difficult to decompose, resulting in lower yields and reaction rates, and require higher temperatures. Further, when higher halides are produced as a by-product of the decomposition reaction of lower halides, it is advantageous to convert them into lower halides again and recycle them. To give a more specific example, in the production of high-purity silicon, it is better to hydrogenolyze trichlorosilane than tetrachlorosilane, and it is better to hydrogenolyze trichlorosilane using niobium tetrachloride or niobium octatrichloride than niobium pentachloride. It is advantageous to increase the reaction rate and reaction yield, and to make the reaction conditions mild. Furthermore, since corrosive halides are handled, it is extremely important to lower the reaction temperature to reduce corrosion. [Prior art and its problems] As a prior art for dehalogenating metal halides, 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 Publication No. 58-161915, 1977-
73617, JP-A-59-45919, etc.). There is also a technique (Japanese Patent Publication No. 10532/1983) in which a similar reaction is carried out using a catalyst containing a platinum group metal. 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. Copper or copper chloride catalysts cannot be used for long-term practical use because they reduce product purity and also consume the catalyst. On the other hand, catalysts containing platinum group metals are said to be used as catalysts in which platinum group metals are supported on activated carbon alumina or silica. It appears that the silica used is porous silica gel, which is commonly used. By the way, in the case of this catalyst, although the platinum group metal is not consumed like copper, the carrier is consumed and the activity is significantly reduced, so that it cannot be used 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 excellent technology of using platinum group metals as catalysts, and have been conducting research and development for many years on catalysts that can withstand long-term use from the viewpoint of industrialization. As a catalyst for dehalogenation in the presence of hydrogen, 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 has a long life. The present invention has been completed based on the discovery that the catalyst performance is significantly improved. [Function] Since the larger the surface area of a catalyst, the higher the catalytic activity, it is common general technical knowledge to use a carrier with a large surface area, but the present invention takes measures that go against this common sense. However, under the reaction conditions of the dehalogenation reaction of metal halides in the presence of hydrogen, when silica with a high surface area is used as a support, the silica is highly reactive and easily corroded, resulting in significant depletion. This is due to the discovery that the supporting effect of catalyst components becomes insufficient and the catalyst loses its activity in a short period of time. For example, to convert tetrachlorosilane to trichlorosilane in the presence of hydrogen, the surface area is 250 m ² /g.
When using palladium-supported silica gel as a catalyst, most of the catalyst reacts with halides and hydrogen and disappears approximately 50 hours after the start of the reaction.
Catalytic activity is lost. 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 by the catalyst reacts in a short time. 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, when a silica brick with a surface area of 1 to 10 m ² /g is used as a silica carrier, there is almost no decrease in catalytic activity 100 hours after the reaction, but the strength decreases because the silica used as a binder for the brick disappears in the reaction. It deteriorates and eventually turns into powder, making it unusable. On the other hand, when a non-porous silica support is used as in the present invention, there is almost no decrease in catalytic activity, and the loss of silica in the reaction is a virtually negligible amount, so there is virtually no decrease in support strength. This makes it an innovative catalyst that can withstand long-term use. The non-porous silica used as a support in the catalyst of the present invention has no pore structure in the bulk structure of the support. (N ₂ ) is 1.0 m ² /g or less. A specific example of non-porous silica is a solidified glass-like fused silica, but it also increases activity even under the above-mentioned surface area conditions and within that range, and also supports catalyst components. It is better to increase the surface area to the extent permitted for ease of use, and for this purpose preferably the glassy fused silica solidified body is treated with hydrofluoric acid at least 0.1 μm.
A silica support that has been etched as described above, a silica support that has the surface of a glass-like solidified fused silica polished by at least 0.1μ using an abrasive such as silicon carbide, or a silica support that has the surface of a glass-like solidified fused silica polished with high-temperature hydrogen and chlorosilane. A silica carrier treated by contacting with is used. Also, the surface area is 150-300
A silica support obtained by crystallizing silica gel of m ² /g, preferably 180 to 250 m ² /g 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 to etching more than 0.1μ, and there is no limitation on the degree of etching of more than 0.1μ. For example, this can be carried out 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 an aqueous solution of 50% HF for 1 to 10 hours at room temperature. 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 more than 0.1μ, and there is no limitation on the degree of polishing, such as This can be done by blowing an abrasive such as carborundum, which is used in the production of normal 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 fused silica solidified body is taken out and used when one cycle of operation is completed, this solidified body has been subjected to the above-mentioned surface treatment during the above reaction.
Efficient as a silica carrier. As the catalyst component, at least one of a platinum group metal and a platinum group metal silicide is used. That is, platinum, palladium, ruthenium, rhodium, osmium and their silicides are used,
At least one selected from the group consisting of palladium, ruthenium, and silicides thereof is preferably used, and more preferably at least one selected from the group consisting of palladium and palladium silicide is used in terms of high catalytic activity and low catalyst cost. It will be done. Here, palladium silicide having a crystal structure of Pd ₂ Si is preferably used. Further, two or more of these catalyst components may be used in combination. 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 not preferable, and the supported amount will be about 5.0 wt%.
Exceeding this value not only increases cost, but also weakens the binding force of palladium with the silica carrier, which may cause peeling of the catalyst component 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. When using something other than palladium as a catalyst component,
Although the amount supported varies somewhat depending on its components, it is sufficient to use approximately the same amount as palladium. or,
When two or more types of 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. Even when platinum group metals other than palladium and silicides of platinum group metals, such as platinum, ruthenium, rhodium, osmium, iridium, or silicides of these or palladium, are used as catalyst components, the catalyst component Effects similar to those obtained when palladium is used as a material can be obtained. Next, when producing the catalyst of the present invention, it is preferable to use the following method 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 metal will be unevenly supported, and there will be areas where the bonding strength of the metal to the support is weak, which may cause problems during the reaction. That part peels off, which is not desirable. 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 metal salt concentration of the aqueous solution is selected and used depending on the desired amount of support. If the supported amount of the catalyst component exceeds about 5 wt%, this is undesirable because it causes the catalyst component to peel off during the reaction. 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 using the catalyst of the present invention can be carried out in a conventional flow reaction system such as a fixed bed by appropriately selecting the shape of the catalyst. Although the shape of the catalyst particles is not particularly limited, it is economical to use, for example, 3 to 30 mm fused silica or crushed quartz. Regarding the reaction conditions for the dehalogenation reaction of halides using the catalyst of the present invention, the temperature is 200-200°C.
1000℃, preferably 550~850℃, hydrogen pressure 1~
20atm, contact time 0.01~100 seconds, preferably 0.1~
Although the contact time is 5 seconds, a contact time of 1 second or less can sufficiently achieve the purpose. Further, the molar ratio of hydrogen/halide is preferably 0.5 to 30, preferably 2.0 to 10. By using the catalyst of the present invention, operations for dechlorinating tetrachlorosilane to trichlorosilane can be carried out industrially for a long period of time without any problems. Moreover, it is applicable not only to tetrachlorosilane but also to dehalogenation of other silicon halides, or niobium or vanadium halides in the presence of hydrogen. [Examples] Next, the present invention will be explained based on examples so that the content of the present invention can be more clearly understood, 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 "Rapid Surface Measurement Device SA-" manufactured by Shibata Scientific Instruments Co., Ltd.
100". The surface areas of the carriers used in Examples 1 to 5 and 11 were measured with the above-mentioned apparatus and all showed below the measurement limit. Below the measurement limit of the above device 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 with the passage of 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 a life test of the catalyst was conducted continuously for 4,000 hours, but no decrease in catalyst activity was observed, indicating a constant activity. 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. This impregnating solution 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 0.42wt%.
It was hot. 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 reactor at a reaction temperature of 800°C for 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%. As time progresses, the trichlorosilane yield increases with removal, and after 100 hours, the yield is 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 a life test of the catalyst was conducted continuously for 4000 hours, but no decrease in catalyst activity was observed, and the catalyst showed a constant activity. Furthermore, when the used catalyst was extracted, there was virtually no decrease in catalyst strength. In addition, using 100 g of the above silica carrier, impregnating it with 120 c.c. of an impregnating solution with a palladium chloride concentration of 100 g/
A catalyst supporting 6% palladium was prepared by heating and dry-up. Using this catalyst, a Teft reaction was carried out under the same conditions as above. The conversion rate of tetrachlorosilane to trichlorosilane is 15
%, but when the used catalyst was taken out after 5 hours of reaction time, 90% of the palladium supported on the catalyst had peeled off, so this heated dry-up method is not very suitable for catalyst production. 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 catalyst maintained constant activity for 4000 hours. When the spent catalyst was analyzed by X-ray diffraction, it was found that Pd ₂
A peak corresponding to palladium silicide with a Si crystal structure was obtained. Example 4 A silica carrier was prepared by polishing a fused silica crushed body of 4.76 to 9.52 mm by blowing air with carboladam. 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 test equipment as in Example 2. A mixed gas 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. Catalyst D was prepared by impregnating this silica support with an acidic impregnating solution of hydrochloric acid having a palladium chloride concentration of 100 g/min, removing the excess liquid not retained on the surface, and reducing the carrier with dry hydrogen at room temperature. The amount of palladium supported is
It was 1.0wt%. This catalyst D was tested using the same test equipment as in Example 2. When the reaction was carried out at a molar ratio of tetrachlorosilane and hydrogen of 1:7, a reaction temperature of 600°C, and a contact time of 0.5 seconds, the composition of the reaction gas after reaching steady-state activity was tetrachlorosilane.
11.1%, trichlorosilane 1.4%, Hcl 1.4%, 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 the activity decreased even after 1000 hours of continuous testing. could not be seen at all.

【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 supporting 0.4 ruthenium using a silica carrier treated with hydrofluoric acid in the same manner as Example 2
was prepared. When Catalyst H was tested under exactly the same conditions as in Example 2, the conversion rate of tetrachlorosilane to trichlorosilane was 10%, and no decrease in activity was observed after 1000 hours of continuous testing. Example 8 Catalyst I carrying 0.4% platinum was prepared using a silica carrier treated with hydrofluoric acid in the same manner as in Example 2. When Catalyst I was tested under exactly the same conditions as in Example 2, the conversion rate of tetrachlorosilane to trichlorosilane was 4%, and no decrease in activity was observed even after 1000 hours of continuous testing. Example 9 Using the same catalyst B as in Example 2, the reaction temperature was 350°C.
When a mixed gas of niobium pentachloride and hydrogen at a molar ratio of 1:1 was passed through the catalyst for a catalyst time of 0.5 seconds, the conversion rate of niobium pentachloride to niobium tetrachloride was 34.1%, and the test was conducted continuously for 1000 hours. However, no decrease in activity was observed. Example 10 Using the same catalyst B as in Example 2, the reaction temperature was 500°C.
The molar ratio of vanadium tribromide to hydrogen is 1:
When the mixed gas of 3 was passed through for a contact time of 0.4 seconds,
The conversion rate of vanadium tribromide to vanadium dibromide was 18%, and a continuous test was conducted for 1000 hours.
No decrease in activity was observed. Example 11 A fused silica crushed body of 4.76 to 9.52 mm was impregnated with a 1:1 mixed impregnating solution 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)

[Scope of Claims] 1. A catalyst for dehalogenating silicon, niobium or vanadium halides in the presence of hydrogen, which comprises a group consisting of a platinum group metal and a platinum group metal silicide in non-porous silica. A catalyst characterized by supporting at least one selected from the following. 2. The catalyst according to claim 1, wherein the platinum group metal and the silicide of the platinum group metal are palladium and palladium silicide. 3. The catalyst according to claim 1, wherein the non-porous silica is amorphous silica in the form of a glassy solidified fused silica. 4. The catalyst according to claim 3, wherein the non-porous silica is amorphous silica obtained by etching the surface of a glassy solidified fused silica using hydrofluoric acid. 5. The catalyst according to claim 3, wherein the non-porous silica is amorphous silica obtained by polishing the surface of a glass-like solidified fused silica using an abrasive. 6. The catalyst according to claim 3, wherein the non-porous silica is amorphous silica obtained by treating the surface of a glass-like solidified fused silica by contacting it with high-temperature hydrogen and chlorosilane. 7. The catalyst according to claim 1, wherein the non-porous silica is crystallized silica obtained by crystallizing silica gel having a surface area of 150 to 300 m ² /g at high temperature.