JPH0510132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst for partially oxidizing hydrocarbons such as butane to hydrogen and carbon monoxide. In recent years, gas carburizing has been widely used as a surface hardening method for steel parts such as gears. In this surface hardening method, the steel product to be treated is placed in a carburizing furnace at approximately 900°C, and a carburizing gas containing hydrogen and carbon monoxide is introduced into the carburizing furnace. This method forms a hard layer of austenite containing carbon as a solid solution. The carburizing gas is generally produced by reacting a hydrocarbon such as butane or natural gas with air under a nickel catalyst. However, since this method is carried out at a high temperature of 1100 to 1200°C, the operation of the gas generator,
There is a problem with durability. Furthermore, since the temperature of the carburizing furnace is about 900° C. as mentioned above, the high-temperature gas generated at the above-mentioned high temperature must be cooled before use, which also poses a problem in terms of thermal energy. Furthermore, the reaction under the above-mentioned nickel catalyst was carried out at 900~
If the process is carried out at a low temperature of 1000°C, carbon may be deposited on the catalyst or the activity may be reduced, making it impossible to obtain the desired carburizing gas. The present invention was made to overcome these problems, and aims to provide a catalyst that can efficiently partially oxidize hydrocarbons even at low temperatures of 1000° C. or lower. That is, the catalyst for partial oxidation of hydrocarbons of the present invention is
A porous carrier consisting of alumina/magnesia spinel and 30 mol% or less of alumina and/or magnesia and having an average pore diameter of 0.01 to 2μ supports one or both of nickel and cobalt. This is a characteristic feature. According to the invention, natural gas, methane, ethane,
It is possible to provide a catalyst that can efficiently partially oxidize hydrocarbons such as propane and butane to hydrogen and carbon monoxide at a low temperature of 1000° C. or lower. Furthermore, even when this catalyst is used at such low temperatures, no carbon is deposited on the catalyst surface, and it has excellent durability. In addition, this catalyst can be used not only for producing carburizing gas as described above, but also for producing reducing atmosphere gas used in metal powder sintering, fuel gas for internal combustion engines, and the like. Furthermore, since the catalyst according to the present invention contains alumina/magnesia spinel as a carrier, it also has high mechanical strength. Furthermore, unlike in the case of general alumina carriers, the crystal structure of alumina does not change, and there is no decrease in surface area or strength due to such changes, and it exhibits an excellent effect on the durability of catalytic activity. In the present invention, the carrier is composed of an alumina-magnesia (MgAl ₂ O ₄ ) spinel and one or both of alumina (Al ₂ O ₃ ) and magnesia (MgO).
Therefore, MgAl ₂ O ₄ spinel in the carrier should account for 70 mol % or more, while one or both of Al ₂ O ₃ and MgO should be present in the carrier in an amount of 30 mol % or less. If the total amount of Al ₂ O ₃ and MgO exceeds 30 mol %, the above-mentioned effects due to the presence of spinel cannot be achieved, the catalyst activity decreases, and there is a risk that carbon may be deposited on the catalyst. Note that the above effect can be achieved even when almost no Al ₂ O ₃ and MgO are present. Further, the above-mentioned carrier is a porous material having an average pore diameter of 0.01 to 2μ. A porous body within this range can further improve the activity of the catalyst of the present invention. Incidentally, one or both of nickel and cobalt supported on the above-mentioned carrier functions as a catalyst component. Therefore, the total amount of catalyst components supported on the carrier is preferably in the range of 2 to 12% by weight (hereinafter referred to as wt%). If the supported amount is less than 2wt%, the purification activity will be low;
If the amount exceeds the amount supported, the activity cannot be improved commensurately with the amount supported. Next, a method for preparing the catalyst of the present invention will be explained. First, as a method for producing a porous body as a carrier as described above, there is a method of heating a molded body of a mixed powder of Al ₂ O ₃ powder and MgO powder to cause the two to react and sinter. In the above, the molded body of mixed powder is 1000 to 1600
Heat and bake in the range of ℃. At temperatures lower than 1000°C, the calcination is not sufficient, the amount of MgAl ₂ O ₄ spinel produced is small, and the strength of the carrier is weak. Furthermore, when the temperature is higher than 1600°C, MgAl ₂ O ₄ spinel particles grow too much and the pore volume decreases. In this case, when firing in the range of 1200 to 1600°C, a carrier having better heat resistance and strength can be obtained. The above spinel is produced by the reaction of equimolar amounts of Al ₂ O ₃ and MgO, so it is
By blending Al ₂ O ₃ or MgO in excess of equimolar amounts, Al ₂ O ₃ or MgO can remain in the carrier after heating and sintering. Also,
By leaving Al ₂ O ₃ and MgO unreacted, both Al ₂ O ₃ and MgO can be contained in the carrier. In addition, the equimolar amount of Al ₂ O ₃ and MgO is expressed as a weight ratio of Al ₂ O ₃ to MgO.
This corresponds to a case where the amount of (Al ₂ O ₃ /MgO) is 2.5 times the weight. To give a specific example regarding the above, carrier No. 1 in Table 1.
As shown in Figure 1, 42 mol% of α-Al ₂ O ₃ powder and MgO
By sintering a mixed powder of 58 mol% powder,
α-Al ₂ O ₃ completely reacts with MgO and excess MgO
remains in the carrier. However, in the carrier
_{MgAl2O4 spinel} accounts for 72 mol%, MgO28 mol%. Moreover, in order to obtain a porous body with an average pore size of 0.01 to 2μ, an Al ₂ O ₃ powder having an average particle size of 0.01 to 2μ is used. The term "particle size" used herein means the weight average particle size. In addition, the above Al ₂ O ₃ is not limited to α (alpha)-Al ₂ O ₃ , γ (gamma)-Al ₂ O ₃ , etc.
Al ₂ O ₃ can also be used. MgO powder mixed with Al ₂ O ₃ powder is mixed with Al ₂ O 3 powder in the sintered porous body.
It can be said to be the optimal binder for O ₃ powder, and its particle size is not particularly limited, but it mixes almost evenly with Al ₂ O ₃ powder, forms spinel with Al ₂ O ₃ , and improves the yield. In order to make the pore size of the carrier substantially uniform, it is preferable to use particles with a particle size of 0.1 to 500μ. Next, when firing the mixed powder, a small amount of organic glue such as dextrin is added to the mixed powder,
The mixture is then molded into a desired size using a tablet molding machine or the like, and then fired using an electric furnace or the like. The mixed powder is shaped into a desired shape such as granules, columns, or honeycombs. When supporting one or both of the catalyst components nickel and cobalt on the above-mentioned carrier, it is carried out in the same manner as in the case of supporting ordinary catalyst components, such as nickel nitrate, nickel sulfate, nickel chloride, cobalt nitrate, The support is immersed in a solution of raw materials for forming catalyst components such as cobalt sulfate and cobalt chloride, dried, and fired. Examples of the present invention will be described below. Example α-alumina (Al ₂ O ₃ ) powder with an average particle size of 1μ,
First, magnesia (MgO) powder with an average particle size of 1μ
The mixture was mixed in the proportions (mol %) shown in the table, a small amount of water was added thereto, the mixture was thoroughly mixed, and the mixture was molded into spherical pellets having a diameter of about 3 mm using a marmerizer (tablet molding machine). Next, the pellets were placed in an electric dryer and heated and sintered at 1350°C to produce porous bodies (carriers Nos. 1 to 6) as carriers. Also, for comparison, the total amount of Al ₂ O ₃ and MgO is
Comparative porous sintered bodies containing more than 30 mol % (carrier Nos. C1 and C2) were also produced in the same manner as above. Also, instead of the above α-Al ₂ O ₃ , the average pore diameter
A comparative porous sintered body (carrier No. C4) was produced in the same manner as above except that 100 Å of γ-Al ₂ O ₃ was used. Furthermore, α-Al ₂ O ₃ with the above average particle size of 1μ
Using α-Al ₂ O ₃ with an average particle size of 10μ instead of
A porous sintered body for comparison (carrier No. C5) was also produced in the same manner as above. Table 1 shows the properties of these supports, such as the ratio of MgAl ₂ O ₄ spinel to Al ₂ O ₃ and MgO, and also shows the properties of commercially available α-Al ₂ O ₃ for making comparative catalysts. Ta. In addition, in the same table, the pore volume is the pore volume (cm ³ ) per 1 g of carrier,
BET surface area refers to the surface area (m ² ) determined from the amount of nitrogen adsorbed per gram of carrier. Next, the above carrier is immersed in an aqueous solution of nickel nitrate, an aqueous solution of cobalt nitrate, or a mixed aqueous solution thereof at a predetermined concentration, and after drying, it is heated at 600°C in air for 30 minutes.
Catalysts according to the present invention (catalysts Nos. 1 to 15) were prepared by calcining for hours and supporting one or both of nickel and cobalt at the loading ratios shown in Table 2. For comparison, comparative carriers (carrier No. C1,
C2, C4, C5) and α-Al ₂ O ₃ carrier (Support No. C3)
Comparative catalysts (catalyst Nos. S1 to S8) were also prepared in the same manner as above, with the loading ratios shown in Table 2.

【table】

[Table] In these catalysts, the type of carrier and the amount of nickel and cobalt supported on the carrier (wt%) are
Shown in the table. Next, a catalyst activity evaluation test will be described.
In this test, in order to check the durability against carbon before evaluating the activity, carbon was first deposited on the catalyst, removed after heating, and then the original partial oxidation reaction test was performed. That is, the catalyst was previously held at 930° C. for 2 hours in a butane gas flow with a space velocity (SV) of 600 hr ⁻¹ to cause carbon precipitation. After cooling, it was held in air at 1100°C for 5 hours to remove carbonaceous matter. Thereafter, a quartz reaction tube was filled with the catalyst, an electric furnace was placed around it, and a partial oxidation reaction was carried out. For the reaction, a mixed gas of butane (C ₄ H ₁₀ ) gas and air was fed into the reaction tube at SV=12000 hr ^-1 . Here, the amount of air used was 1.025 times the amount (theoretical air amount) required to oxidize butane to carbon monoxide and hydrogen. Also, the reaction time is 930℃
And so. By gas chromatography, hydrogen (H ₂ ), carbon monoxide (CO), methane (CH ₄ ), carbon dioxide (CO ₂ ), oxygen (O ₂ ), nitrogen (N ₂ ) was measured. As a result, any of the above catalysts (catalyst Nos. 1 to 15,
S1 to S6), there is also H ₂ 29 in the generated gas.
~30% (capacity ratio), CO23~24%, _O2 0.39~0.41
%, _N2 contained 46-48%, _CH4 and _CO2
Different catalysts showed different values. In order to show the partial oxidation ability of each catalyst in the above reaction, Table 3 shows the amounts of CH ₄ and CO ₂ in the produced gas. Table 3 shows that the smaller the amount of CH ₄ and CO ₂ , the higher the partial oxidation ability of the catalyst. In other words, a catalyst with low activity capacity thermally decomposes butane, resulting in a large amount of CH ₄ and CO ₂ . As is clear from Table 3, the catalysts according to the present invention (catalyst Nos. 1 to 15) all produce extremely small amounts of CH ₄ and little CO ₂ , and have excellent activity. Recognize. Moreover, this catalyst was then subjected to the above reaction for several hours, but the above activity was almost negligible.

【table】

【table】

【table】

[Table] No change. Further, with the catalyst according to the present invention, no carbon deposition was observed on the catalyst even in the above-mentioned low temperature reaction. On the other hand, comparative catalysts using a carrier having more than 30 mol% of Al ₂ O ₃ , MgO, a carrier consisting only of α-Al ₂ O ₃ , or a carrier with an average pore diameter outside the range of 0.01 to 2 μ (Catalyst No.S1 to S8) are
It can be seen that the amount of CH ₄ and CO ₂ produced is large and the activity is low. Furthermore, in Table 3, when the catalyst of the present invention was used, the amount of CH ₄ by-product was extremely small. Since it is desired that the amount of CH ₄ in the carburizing gas described above be as small as possible, the catalyst of the present invention is found to be particularly excellent as a catalyst for producing carburizing gas. In addition, as another comparative example, mullite (Al ₄ Si ₂
A partial oxidation reaction was carried out under the same conditions as above using a conventional nickel catalyst in which 7.7% nickel was supported on an O ₁₃ ) carrier. As a result,
CH ₄ and CO ₂ were extremely high at 1.97% and 0.49%, and carbon was deposited on the catalyst surface, resulting in poor activity and durability.

Claims (1)

[Claims] 1 A porous carrier consisting of alumina/magnesia spinel and 30 mol% or less of alumina and/or magnesia and having an average pore diameter of 0.01 to 2μ, supporting one or both of nickel and cobalt. A catalyst for partial oxidation of hydrocarbons, characterized by: