JPH0520144B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) 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 aforementioned elements. That is,
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 and tungsten are used as metal silicide targets for LSIs. It is thought that the uses of metal will expand. These high-purity metals are usually produced by first halogenating a low-purity crude raw material, then distilling it to make it highly purified, and then thermally decomposing or hydrogenolyzing it again to produce a high-purity product. At that time, higher-order halides are more difficult to decompose, resulting in lower yields and reaction rates.
Due to the high temperatures required, it is advantageous to use lower order halides. 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 to hydrogenolyze niobium tetrachloride or niobium octatrichloride rather than niobium pentachloride due to the reaction rate.
This is advantageous in order to increase the reaction yield and to keep the reaction conditions mild. Furthermore, since corrosive halides are handled, it is extremely important to lower the reaction temperature to reduce corrosivity. For this purpose, higher-order halides are once changed into lower-order halides, and these reactions are collectively called dehalogenation reactions. (Prior art and its problems) As a prior art for dehalogenating metal halides, there is a technology for dehalogenating and 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.).
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, when copper chloride is used as a catalyst, of course
Even 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 mix with trichlorosilane, reducing product purity, and the catalyst is also consumed. Therefore, copper or copper chloride catalysts cannot be used in long-term practical use. 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, but porous activated carbon is used as the carrier, and γ- using alumina,
The silica also appears to be a commonly used porous silica gel. By the way, in the case of this catalyst, platinum group metals are not consumed like copper, but
Since the carrier is consumed and the activity is significantly reduced, it cannot be put into practical use 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 superiority of technology that uses platinum group metals as catalysts, and have been researching and developing catalysts that can withstand long-term use from the viewpoint of industrialization. As a catalyst for dehalogenating 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 corrosion-resistant ceramics or graphite has a long life. The present invention was completed based on the discovery that the catalyst performance was significantly improved. (Function) Since the larger the surface area of a catalyst, the greater the catalytic activity, it is common general knowledge to use a carrier with a larger surface area. Porous activated carbon, silica gel, γ-alumina, etc. are used as carriers in this dehalogenation reaction. is depleted and its activity decreases significantly. When using a catalyst having a corrosion-resistant ceramic or graphite carrier according to the present invention, the carrier is not consumed during the reaction and a long service life can be obtained. The corrosion-resistant ceramics herein are so-called new ceramics, and specifically, nitrides such as silicon nitride and boron nitride, and carbides such as silicon carbide are used. This is because the carrier in the present invention has extremely high corrosion resistance against high-temperature hydrogen and halogen atmospheres. Silicon nitride and other materials used for this carrier are difficult to manufacture and porous, making it difficult to support catalyst components, and conventionally used in semiconductor crucibles and structural materials. However, it is rarely used as a catalyst carrier; it was used for the first time in the dehalogenation reaction of halides, and there has been no example of its use in this reaction. The physical properties of the corrosion-resistant ceramic and graphite supports in the present invention are not limited in any way, but in order to support the active catalyst component and exhibit high activity, they are preferably porous bodies, with a porosity of 3 to 3. Preferably it is 50%, more preferably
It is 10-40%. Any silicon nitride, silicon carbide, or polon nitride obtained by conventional manufacturing methods can be used, but it is preferable to use a sintering method to make it porous. Further, as for the graphite, conventional porous graphite is preferably used. At least one of a platinum group metal and a platinum group metal silicide is used as the catalyst component. Namely, platinum, palladium, ruthenium, rhodium,
Iridium, osmium, and silicides thereof are used, but preferably at least one selected from the group consisting of palladium, ruthenium, and silicides thereof, and more preferably At least one selected from the group consisting of palladium and palladium silicide is used. Here, palladium silicide having a crystal structure of Pd ₂ Si is preferably used. Further, two or more types 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 10.0 wt% based on the total weight of the catalyst.
Preferably about 0.1 to 5.0 wt%, more preferably about 0.3
~2.0wt%. Palladium loading amount is approximately 0.01wt
If the supported amount is less than 10.0 wt%, the catalyst activity will not be sufficiently exhibited and a long contact time will be required, and if the supported amount exceeds about 10.0 wt%, the activity will not increase even if the supported amount is increased, resulting in high cost. This is not desirable. Furthermore, as mentioned above, the preferred amount of palladium supported is 0.3 to 2.0 wt%, but when supporting this amount on the carrier, the size of the palladium particles,
The degree of dispersion is appropriate and catalytic activity is fully exhibited. When using something other than palladium as a catalyst component, the supported amount will vary somewhat depending on the component, but it may be used in an amount that is approximately the same as that of palladium. In addition, when two or more types of catalyst components are used,
The above-mentioned 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 same effect as when using palladium can be obtained. Next, the catalyst of the present invention can be produced by any known method, but the following method is preferred in order to uniformly support the catalyst components. That is, after a carrier such as silicon nitride is impregnated with an aqueous solution of a platinum group metal chloride, nitrate, or their ammonia complex salt at a predetermined concentration, the aqueous solution that is not retained on the carrier surface is removed and then dried as is. It is better to do so and then return it. A catalyst supporting a silicide of a platinum group metal is prepared by heating a catalyst supporting a platinum group metal to a silicon halide such as silicon tetrachloride and hydrogen at 400℃ to 800℃.
It can be produced by contacting at ℃. The reaction system using the catalyst of the present invention can be carried out in a normal 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, spheres, cylinders, and crushed bodies of 3 to 30 mm. 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 and zirconium halides in the presence of hydrogen. (Examples) Next, the present invention will be described 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 "Rapid Surface Area Measuring Device SA" manufactured by Shibata Scientific Instruments Co., Ltd.
-100'' BET surface area was measured using nitrogen.
The surface areas of the carriers used in Examples 1 to 5 were all measured with the above device and were below the measurement limit. Below the measurement limit of the above device means below 0.2 m ² /g. Example 1 Palladium chloride was heated and dissolved under acidic conditions with hydrochloric acid to prepare an impregnating solution of an aqueous solution of palladium chloride. Table -
Silicon carbide (SiC) having a particle size of 4 mmφ shown in 1 was impregnated with the impregnating liquid, and the excess impregnating liquid that was not retained on the carrier 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 1 wt%. Catalyst A 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 0.21 seconds, and the reaction gas was analyzed by online gas chromatography. Gas analysis values at the beginning of the reaction were 23.5% tetrachlorosilane, 1.4% trichlorosilane, and 1.5% hydrogen chloride, and the conversion rate from tetrachlorosilane to trichlorosilane was 5.6%.
It was %. The trichlorosilane yield gradually increased over time, and after 100 hours, analytical values of 21.5% tetrachlorosilane, 3.5% trichlorosilane, and 3.5% hydrogen chloride were obtained, and the conversion rate was 14.0%. After that, the conversion rate is almost constant;
A lifetime test of the catalyst was conducted continuously for 4,000 hours, but no decrease in catalyst activity was observed, and a certain level of activity was observed.

[Table] Example 2 A reaction test was conducted using Catalyst A, which was exactly the same as in Example 1. 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 1. From the beginning of the reaction, the conversion rate of tetrachlorosilane to trichlorosilane is
14.0%, and the catalyst maintained constant activity for 4000 hours. When the spent catalyst was analyzed by X-ray diffraction, a peak corresponding to palladium silicide having a Pb ₂ Si crystal structure was obtained. Example 3 An acidic aqueous solution of palladium chloride in hydrochloric acid was prepared as an impregnation liquid. Approximately 3 to 6 mm of crushed silicon nitride (Si ₃ N ₄ ) shown in Table 2 is impregnated with the impregnating liquid, the excess impregnating liquid that is not retained on the supporting surface is removed by tilting the container, and then dried. Afterwards, it was reduced by passing hydrogen at room temperature. At this time, the amount of palladium supported was determined by analysis to be 1.1 wt%. Catalyst B thus obtained was tested using the same test equipment as in Example 1. A mixed gas of tetrachlorosilane and hydrogen with a molar ratio of 1:5 was reacted at a reaction temperature of 700°C.
℃ and a contact time of 0.15 seconds. After reaching steady activity, the reaction gases were 14.4% tetrachlorosilane, 2.2% trichlorosilane, and 2.2% hydrogen chloride, the conversion rate was 13.3%, and continuous operation was possible for up to 4000 hours without a decrease in activity. .

[Table] Example 4 A hydrochloric acid acidic impregnation solution of palladium chloride was prepared with a particle size of approximately 6
mmφ, bulk specific gravity 2.11 boron nitride (BN)
Catalyst C was prepared by impregnating a carrier, removing excess liquid not retained on the surface, drying, and reducing with hydrogen at room temperature. The amount of palladium supported was 0.5 wt%.
This Catalyst C was tested using the same test equipment as in Example 1. When the reaction was carried out at a molar ratio of tetrachlorosilane and hydrogen of 1:7, a reaction temperature of 720°C, and a contact time of 0.4 seconds, the composition of the reaction gas after reaching steady-state activity was 10.4% tetrachlorosilane and 2.1% trichlorosilane. , hydrogen chloride is 2.1%, and the conversion rate is
It was 16.8%. Even when Catalyst C was used, continuous operation for 1000 hours was possible without any decrease in activity. Example 5 A hydrochloric acid acidic impregnation solution of palladium chloride was prepared from approx.
Catalyst D was prepared by impregnating a graphite carrier with a bulk specific gravity of 1.77 using a 6 mm crushed body, removing excess liquid not retained on the surface, drying, and reducing with hydrogen at room temperature. The amount of palladium supported was 0.7 wt%.
This catalyst D was tested using the same test equipment as in Example 1. When the molar ratio of tetrachlorosilane and hydrogen was 1:7, the reaction temperature was 790°C, and the contact time was 0.15 seconds, the conversion rate of tetrachlorosilane to trichlorosilane was 19.6%. No decrease was observed at all. Comparative Example 1 4.76 to 9.52 of quartz brick with physical properties shown in Table 3
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 A reaction test was conducted under the same conditions as in Example 1. 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 1 using Catalyst F in which 1% palladium was supported on silica gel shown in Table 2. 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 Catalyst G supporting 0.4 wt% ruthenium was prepared in the same manner as in Example 1 using a silicon carbide carrier. When Catalyst G was tested under exactly the same conditions as in Example 1, the conversion rate of tetrachlorosilane to trichlorosilane was 9.4%, and no decrease in activity was observed even after 1000 hours of continuous testing. Example 7 Catalyst H supporting 0.4 wt% platinum was prepared in the same manner as in Example 1 using a silicon carbide carrier.
When Catalyst H was tested under exactly the same conditions as in Example 1, the conversion rate of tetrachlorosilane to trichlorosilane was 3.4%, and no decrease in activity was observed even after 1000 hours of continuous testing. Example 8 Using the same catalyst C as in Example 4, the reaction temperature was 350°C.
When a mixed gas of niobium pentachloride and hydrogen in a molar ratio of 1:1 was passed through for a contact time of 0.4 seconds, the conversion rate from niobium pentachloride to niobium tetrachloride was 36.2%, and the test was conducted continuously for 1000 hours. However, no decrease in activity was observed. Example 9 Using the same catalyst C as in Example 4, 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 0.3 seconds,
The conversion rate of vanadium tribromide to vanadium dibromide is
It was 16.2%, and after 1000 hours of continuous testing,
No decrease in activity was observed. Example 10 1:1 of palladium chloride and ruthenium chloride on a silicon nitride support of approximately 4-8 mm crushed bodies
0.3 wt% palladium - 0.3 wt% by impregnating with a mixed impregnating solution, removing excess impregnating solution not retained on the carrier, drying, and hydrogen reduction. Ruthenium supported catalyst I was prepared. 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 0.22 seconds. After the reaction gas becomes steady active, it becomes 14.1% tetrachlorosilane, 2.5% trichlorosilane, and 2.5% hydrogen chloride, and the conversion rate is 15.1%.
A continuous time test was conducted, but no decrease in activity was observed. (Effects of the Invention) The catalyst of the present invention has a very long life and high activity. Corrosion-resistant ceramics or graphite used as a carrier are highly corrosion resistant, but these have sufficient corrosion resistance in dehalogenation reactions at high temperatures in an atmosphere containing highly corrosive hydrogen chloride. It was previously unknown. In addition, since materials with high corrosion resistance usually have low surface activity and poor supporting ability, they are thought not to promote catalytic action and have never been used as catalyst carriers. Nevertheless, the catalyst of the present invention in which a platinum group metal or the like is supported on silicon carbide or the like has a long life and sufficiently high activity, and a high conversion rate can be obtained over a long period of time. .

Claims (1)

[Claims] 1 A catalyst for dehalogenating silicon, niobium or vandium halides in the presence of hydrogen, which comprises at least one selected from the group consisting of platinum group metals and platinum group metal silicides on corrosion-resistant ceramics or graphite. A catalyst characterized by supporting one of the following.