JPH0583304B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a carbon monoxide conversion catalyst, particularly an iron-based carbon monoxide conversion catalyst having excellent activity, strength and durability. (Prior art) The carbon monoxide conversion reaction is shown by the following equation, and iron-based catalysts, especially catalysts made of iron oxide and chromium oxide structures formed into appropriate shapes, have been widely used industrially for a long time. . CO + H ₂ OH ₂ + CO ₂ The catalyst is normally used in a temperature range of 300 to 400°C, but the strength of the molded catalyst decreases with time of use, sometimes causing powdering, resulting in pressure loss in the reactor. There was a serious drawback in that the amount increased, making it difficult to continue operation and forcing the catalyst to be replaced. For this reason, improving the durability of iron-based carbon monoxide catalysts has been a long-standing challenge in the industry, and many improvements have been made. In other words, in Special Publication No. 28-2471, iron, copper,
Salts such as zinc, nickel, manganese, aluminum, and magnesium are added, and in Special Publication No. 1571 (1971), iron powder was added to an iron-based precipitation catalyst to improve its strength. Further, in Japanese Patent Publication No. 42-17194, activity and durability were improved by greatly increasing the chromium oxide content in the iron-chromium catalyst. (Problems to be Solved by the Invention) The present invention solves the above-mentioned drawbacks, and has an activity and strength that is at least as good as or better than conventional catalysts.
Furthermore, the present invention provides an iron-based carbon monoxide conversion catalyst such as iron oxide-chromium oxide that has excellent durability. (Means for Solving the Problems) In order to solve the above-mentioned drawbacks, the inventors of the present invention conducted extensive research into improving iron-chromium catalysts, and found that iron present in the form of Fe ₃ O ₄ in the catalyst The inventors have discovered that reducing the catalytic strength greatly contributes to maintaining the catalyst strength, that is, durability, and that the catalytic activity is improved rather than impaired, and the present invention was achieved based on these findings. The raw materials for producing the catalyst of the present invention are those that can be used for producing ordinary iron-based carbon monoxide conversion catalysts, including water-soluble iron salts such as iron sulfate, iron chloride, and iron nitrate, and dichromate. Chromium compounds such as salts, chromates, chromium nitrate, and chromic anhydride can be used.
As a source of iron, ferrous sulfate is a suitable raw material because it is inexpensive, but the contamination of ferric salts must be avoided as much as possible since it attracts the formation of Fe ₃ O ₄ . The precipitation of iron or iron-chromium is carried out by a neutralization reaction using a suitable alkaline substance. At this time, all precipitation methods such as coprecipitation method, positive neutralization method, reverse neutralization method, continuous method, and batch method can be employed as long as consideration is given to preventing Fe ₃ O ₄ formation. The conditions for Fe ₃ O ₄ production are described in detail in Masao Kiyama's ``Chemistry of iron hydroxide () ()'' (Powder and Powder Metallurgy Vol. 23, No. ₃ ). ₄ Measures to prevent generation can be easily taken. For example, methods for reducing Fe ₃ O ₄ include: (a) reducing the iron content in the reaction solution; (b) increasing the pH to a value greater than or equal to 9 to 10; and (c) lowering the reaction temperature to a relatively low level of 50°C or lower. (2) Increase the amount of air blown to improve its dispersion, etc., and combine these conditions appropriately. The precipitate thus obtained is usually dried, crushed, molded,
The finished product is obtained through processes such as drying, but the present inventors believe that before and/or after molding, especially before molding, the iron hydroxide can be fired until the crystal water contained in the iron hydroxide is substantially completely dehydrated. It has been found that it is extremely effective in imparting durability. The firing temperature for this purpose is approximately 300 to 700℃, preferably 400 to 600℃.
Temperatures in the range of °C are required. It can be confirmed that the crystal water has been removed sufficiently by measuring the loss on ignition, but it is desirable that the loss on ignition of the fired product is 2% by weight or less. The increase in the amount of Fe ₃ O ₄ due to this firing operation is substantially zero.
Therefore, Fe ₃ O ₄ after firing or Fe ₃ in the finished product
The O ₄ content is considered to be equal to or higher than Fe ₃ O ₄ contained in the precipitate before firing. Incidentally, quantitative analysis of Fe ₃ O ₄ contained in Fe ₂ O ₃ is particularly difficult due to the presence of chromium oxide (CrO ₃ ) in carbon monoxide conversion catalysts, and at present no reliable quantitative analysis method has been established. It has not been. Therefore, Fe ₂ O ₃ by X-ray diffraction
The amount of Fe ₃ O ₄ can also be determined by comparing the intensity of the and Fe ₃ O ₄ diffraction lines. Molding methods include tableting,
Any conventional molding method such as extrusion or spheroidization can be used. (Function) The carbon monoxide conversion catalyst of the present invention has higher activity and strength than ordinary iron oxide-chromium oxide catalysts, so it can be used under the same conditions as conventional high-temperature conversion catalysts. However, the decrease in strength and activity under all normally conceivable reaction conditions is extremely small, making stable operation possible for long periods of time. (Example) The present invention will now be described in more detail with reference to Examples. Parts in the examples indicate parts by weight unless otherwise specified. In addition, the Fe ₃ O ₄ /Fe ₂ O ₃ ratio is the Fe ₃ O ₄ between each catalyst.
It is a value that indicates the relative size of a quantity, not an absolute value. Example 1 A mixed aqueous solution obtained by dissolving 675 parts of ferrous sulfate FeSO _{4.7H 2} O and ₃₃ parts of sodium dichromate Na ₂ Cr ₂ O 7.H ₂ O in 1370 parts of water was prepared by dissolving 195 parts of caustic soda. twenty five
% caustic soda aqueous solution. Fe ₃ O ₄ contained in the produced precipitate can be removed by stirring while blowing in a sufficient amount of air during and after the neutralization reaction.
I tried to minimize it. The precipitate thus obtained was analyzed using a popular X-ray diffraction device Miniflex No. 2005 manufactured by Rigaku Denki Co., Ltd. (the target was
(Cu, filter is graphite single crystal for monochrome, voltage 40KV, current 35mA) However, Fe ₃ O ₄ and
The ratio of the diffraction intensities (peak heights) of Fe ₂ O ₃ was 0.1. Furthermore, the Fe ₃ O ₄ /Fe ₂ O ₃ molar ratio obtained by quantitative analysis after washing away CrO ₃ with hot water was 0.0015. These values are small compared to the analytical values of other catalysts shown in Table 2.
The Fe ₃ O ₄ content was extremely low. This precipitate is filtered, dried, calcined at 400℃, and then crushed to form granules using a tablet machine.
It was molded into a 9.5 mmφ x 6.4 mmL tablet. Finally, this molded article was calcined at 250°C to obtain catalyst A. Further, Catalyst B was obtained by the same procedure as Catalyst A except that the calcination at 400° C. before molding was omitted. The loss on ignition of these catalysts A and B was 1.2% and 10.5% by weight, respectively. Ignition loss of catalyst B
Most of the 10.5% by weight corresponds to water of crystallization of iron hydroxide. Next, using Catalysts A and B, a catalyst durability test was conducted under the following test conditions. Reaction conditions Reactor: Stainless steel tubular reactor with inner diameter of 50 mm Catalyst loading: 100 ml Supply gas composition: 75% by volume of _H2 , 5% by volume of CO2 Space velocity: 5000 ₁ /hour (dry gas standard) Reaction temperature: 400℃ Test Time: 720 hours (30 days) After the test, the catalyst was taken out from the reactor and its strength (crushing strength in the diametrical direction of the catalyst particles) was measured. The results are shown in Table 1 below.

[Table] Catalyst A, which was calcined at 400°C to eliminate the crystallization water of iron hydroxide and had a loss on ignition of 1.2% by weight, showed almost no decrease in strength even after a long test, and did not turn into powder. I couldn't see it at all. Catalyst B, which was not calcined at a temperature exceeding 300°C and left crystal water, showed some decrease in strength after the test, but no powdering occurred and maintained sufficient strength. . Example 2 Four types of catalysts were prepared in exactly the same manner as catalyst A, but by changing the reaction temperature, amount of blown air, etc., catalysts C, D, and D with different Fe ₃ O ₄ contents were prepared.
E and F were obtained. For these catalysts and commercially available catalysts, the amount of Fe ₃ O ₄ was measured by X-ray diffraction and quantitative analysis. The results are shown in Table 2 below. Further, tests similar to those in Example 1 were conducted on these catalysts. The results are also shown in Table 2.

[Table] Catalysts C and D with a low amount of Fe ₃ O ₄ both showed little decrease in strength, no powdering was observed, and maintained sufficient strength. Catalysts E and F with a slightly higher amount of Fe ₃ O ₄
Although some decrease in strength was observed, there was almost no powdering and still sufficient strength was maintained. Commercially available catalysts containing several times more Fe ₃ O ₄ than these catalysts showed significant strength loss, some flaking, and were quite brittle. From these test results, it was found that the lower the Fe ₃ O ₄ content, the smaller the decrease in strength. Although various analytical methods were adopted in this test, this is because the presence of chromium in the catalyst makes it difficult to establish a quantitative analysis method, and the relative Fe ₃
For O ₄ amount, RAD-B manufactured by Rigaku Denki Co., Ltd.

Claims (1)

[Claims] 1. An iron-chromium catalyst for a carbon monoxide conversion reaction that produces hydrogen and carbon dioxide from carbon monoxide and water vapor, which contains iron oxide and chromium oxide as main components, and contains Fe ₃ O in the catalyst. A carbon monoxide conversion catalyst characterized in that the Fe ₃ O ₄ content is as low as 1500 or less expressed as a peak integral value of Fe 3 O ₄ by X-ray diffraction. 2 The iron content as a catalyst component is Fe ₂ O ₃ · nH ₂ O and/or FeOOH with low Fe ₃ O ₄ · nH ₂ O content.
The carbon monoxide conversion catalyst according to claim 1, which is obtained by calcining a precipitate. 3. The carbon monoxide conversion catalyst according to claim 2, wherein the iron content is obtained by calcining a precipitate at 300 to 700°C. 4. The carbon monoxide conversion catalyst according to claim 2 or 3, wherein the iron content is obtained by sintering a precipitate until the weight loss on ignition is 2% by weight or less.