JPH0566883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for partially oxidizing hydrocarbons such as butane to produce a heat treatment gas containing hydrogen and carbon monoxide. [Prior Art] A heat treatment gas containing hydrogen and carbon monoxide is used as a carburizing gas in a gas carburizing method or as a reducing atmosphere gas used during metal powder sintering. An example of a method using this heat treatment gas is a gas carburizing method, which is a surface hardening method for steel parts such as gears. This method involves placing a steel product as the material to be treated in a carburizing furnace at 850 to 950°C, and
This is a method in which a carburizing gas containing hydrogen and carbon monoxide is introduced into the steel part to form a hard layer of austenite containing carbon as a solid solution on the surface of the steel part. The above carburizing gas is generally produced by introducing a hydrocarbon such as butane or natural gas and air into a gas conversion retort filled with a catalyst.
As the catalyst in the gas conversion retort, a catalyst made of a porous carrier supporting nickel, cobalt, etc. is used. Inside the above gas conversion retort,
Partial oxidation of hydrocarbons by oxygen in the air is promoted by the catalyst, producing carburizing gas containing carbon monoxide and hydrogen. However, since this method is carried out at a high temperature of 1100 to 1200°C, there are problems with the operation and durability of the gas conversion retort. Furthermore, as the temperature of the carburizing furnace is approximately 900°C as mentioned above, the high-temperature carburizing gas generated at the above-mentioned high temperature must be cooled before use, resulting in a loss in terms of thermal energy. . On the other hand, when carburizing gas is produced at low temperatures by the above method, impurities such as methane (CH ₄ ) and carbon dioxide (CO ₂ ) in the generated gas are likely to be produced as by-products. In particular, the carburizing gas is required to have a small amount of impurities such as CH ₄ and CO ₂ , and the conventional methods described above still have points to be improved. [Problems to be solved by the invention] The present invention was made in view of the conventional problems, and is capable of efficiently producing a heat treatment gas with few impurities at a low temperature of 850 to 1000°C. It is intended to provide a method. [Means for Solving the Problems] The present invention provides heat treatment that partially oxidizes hydrocarbons by introducing air and hydrocarbons into a gas conversion retort filled with a catalyst to contain carbon monoxide and hydrogen. In the method for producing gas for industrial use, the catalyst comprises cobalt supported on a carrier consisting of alumina/magnesia spinel and 30 mol% or less of alumina and/or magnesia, and the inner diameter of the gas conversion retort/the diameter of the catalyst It is a granular material having a particle size with a particle size ratio of 6 to 60,
The method for producing a heat treatment gas is characterized in that the temperature in the gas conversion retort is 850 to 1000°C, and the air and hydrocarbons introduced into the gas conversion retort have an air excess ratio of 1.01 to 1.10. In the present invention, the catalyst charged in the gas conversion retort is one that promotes the reaction between air and hydrocarbons, and the catalyst is a carrier consisting of alumina/magnesia spinel and one or both of alumina and magnesia, and cobalt. Use a device that supports In addition, the above-mentioned carrier is one in which alumina/magnesia (MgAl ₂ O ₄ ) spinel accounts for 70 mol % or more, while one or both of alumina (Al ₂ O ₃ ) and magnesia (MgO) is present in an amount of 30 mol % or less. It is. The catalyst with the above structure has extremely high activity and durability at low temperatures of 1000° C. or lower, and also has high mechanical strength. Note that even when almost no Al ₂ O ₃ and MgO are present in the catalyst carrier, the catalyst has the above characteristics. In addition, the above carrier has an average pore diameter of 0.01 to 2μ.
It is preferable that it is a porous body of m. A porous body within this range can further improve the activity of the catalyst. In addition, the amount of cobalt that is the catalyst component supported is 2 to 12% by weight based on the carrier.
(hereinafter referred to as wt%). If the supported amount is less than 2 wt%, the catalyst activity will be low, and if it exceeds 12 wt%, the activity will not improve commensurately with the supported amount. The shape of the catalyst used in the present invention is granular in order to avoid collapse of the catalyst due to thermal expansion (strain). Further, the particle size of the granular catalyst is such that the ratio between the inner diameter of the gas shift retort to be filled and the particle size of the catalyst (inner diameter of retort/particle diameter of catalyst) is in the range of 6 to 60. If the ratio is less than 6, there will be a large amount of gas leakage between air and hydrocarbon, making it difficult for the reaction to proceed (see Examples). Also, this ratio is 60
If it exceeds , the pressure loss within the retort will increase, which is unfavorable for operation. Next, an example of a method for preparing the above catalyst will be explained. First, to prepare the carrier, Al ₂ O ₃ powder and MgO
There is a method of heating and firing a molded body of a mixed powder with a powder to cause the two to react. In addition, in order to use the catalyst in the form of granules, it is desirable that the molded body of the above-mentioned mixed powder be made into granules. By heating and baking the above,
MgAl ₂ O ₄ spinel is produced. Since the spinel is produced by the reaction of equimolar amounts of Al ₂ O ₃ and MgO, it is necessary to mix Al ₂ O ₃ or MgO in excess of the equimolar amount in the mixed powder. This allows Al ₂ O ₃ or MgO to remain in the carrier after heating and sintering. Also, Al ₂ O ₃
By leaving MgO 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, as shown in Example 1, by sintering a mixed powder of 60 mol% γ-Al ₂ O ₃ powder and 40 mol % MgO powder, MgO is converted into γ-Al ₂ O ₃ The excess γ-Al ₂ O ₃ changes to α-Al ₂ O ₃ during sintering and remains in the carrier. Therefore, MgAl ₂ O ₄ spinel accounts for 80 mol % and α-Al ₂ O ₃ accounts for 20 mol % in the carrier. In addition, in order to obtain a carrier made of a porous material with an average pore diameter of 0.01 to 2 μm, 0.01 μm as Al ₂ O ₃ powder is required.
Use particles having an average particle size of ~2 μm. Also,
MgO powder can be said to be the optimal binder for Al ₂ O ₃ powder in the sintered porous body, and its particle size is not particularly limited, but it is necessary to make the pore size of the carrier almost uniform. It is desirable to use particles having an average particle size of 0.1 to 50 μm. The "average particle size" herein means the weight average particle size. In addition,
Any type of Al ₂ O ₃ such as α-Al ₂ O ₃ or γ-Al ₂ O ₃ may be used as Al ₂ O ₃ . In addition, the heating and firing of the molded body of the mixed powder is 1000
It is preferable to carry out the heating in the range of ~1600°C. Within the above range, a carrier having excellent heat resistance and strength can be obtained. Next, in order to support cobalt as a catalyst component on the above-mentioned carrier, it is carried out in the same manner as in the case of supporting a normal catalyst component. The above carrier is immersed in a raw material solution, dried,
Fire. When the introduction gases of air and hydrocarbons are introduced into the gas conversion retort filled with the above catalyst, the temperature inside the retort is set in the range of 850 to 1000°C. 1000℃
When the temperature is higher, it is necessary to cool the gas for subsequent heat treatment such as carburization, which is inefficient in terms of energy. Also, 850℃
At lower temperatures, the reaction between oxygen in the air and hydrocarbons is less likely to proceed. Further, the excess air ratio of the introduced gas consisting of air and hydrocarbons is set to 1.01 to 1.10. Here, the excess air ratio is the ratio of the amount of supplied air to the amount of air (theoretical air amount) required for the oxygen and hydrocarbons in the air to react and completely change into hydrogen and carbon monoxide ( (ratio of supplied air amount/theoretical air amount).
In the present invention, when the excess air ratio is less than 1.01, the amount of by-product methane (CH ₄ ) gas in the heat treatment gas increases, and on the other hand, when it exceeds 1.10, the amount of by-product carbon dioxide (CO ₂ ) gas increases. The amount of increases. Furthermore, the space velocity (SV) at which the introduction gas of air and hydrocarbons is introduced into the gas conversion retort is 1000.
It is desirable to set it in the range of ~20000hr ^-1 . SV is
If it is less than 1000 hr ^-1 , the time for the products produced by the reaction to stay in the catalyst layer is too long, which tends to cause carbon deposition on the catalyst. Furthermore, when the SV exceeds 20000 hr ^-1 , hydrocarbons cannot be completely partially oxidized. As described above, the heat treatment gas produced according to the present invention can be used as a carburizing gas, a reducing atmosphere gas used during metal powder sintering, and the like. In particular, it can work effectively when used for carburizing, which requires gas with low impurities such as CH ₄ and CO ₂ . For example, when the heat treatment gas produced according to the present invention is used as a carburizing gas in a gas carburizing method, the heat treatment gas is
It is preferable to introduce it into the carburizing furnace at ~12000 hr ^-1 . [Effect of the invention] According to the present invention, at a low temperature of 850 to 1000°C,
A heat treatment gas consisting of hydrogen and carbon monoxide can be produced. Therefore, when using the heat treatment gas produced according to the present invention as a carburizing gas, there is no need to cool it before use. Further, according to the present invention, it is possible to produce a gas for heat treatment with a small amount of by-products of methane and carbon dioxide. Therefore, the heat treatment gas according to the present invention is particularly excellent as a carburizing gas that is required to contain few impurities. Further, according to the present invention, air and hydrocarbons can be introduced into the gas conversion retort at a high space velocity, and a large amount of heat treatment gas can be produced with a small amount of catalyst. [Examples] Examples of the present invention will be described below. Example 1 γ-alumina (Al ₂ O ₃ ) powder with an average particle size of 1 μm and magnesia (MgO) powder with an average particle size of 50 μm were mixed at a ratio of 60:40 (mol%), and this was mixed with a particle size of approx. It was molded into spherical pellets with a diameter of 2 mm. Next, heat the above pellets at 1350℃. This was sintered to produce a porous carrier. The support was 80 mol% _MgAl2O4 spinel and 20 mol% alpha-alumina _. Next, the above-mentioned carrier was immersed in an aqueous solution of cobalt nitrate, dried, and then calcined in air at 1350°C for 10 hours to prepare a catalyst according to the present invention. The catalyst was a pellet with a particle size of 2 mm, and 6.5 wt% of cobalt was supported on the catalyst. Next, 10ml of the above catalyst was filled into a gas conversion retort with an inner diameter of 18mmφ, and heated in a heating furnace from the outside of the retort.
Heated to 930°C. Then, a mixed gas of butane and air having a predetermined composition ratio was supplied into the retort at a SV of 12000 hr ^-1 . By gas chromatography,
Hydrogen (H ₂ ), carbon monoxide (CO), methane (CH ₄ ), carbon dioxide (CO ₂ ), and carbon-hydrogen (NHC) other than methane in the generated gas were measured. The result is the first
As shown in the figure. Note that the excess air ratio on the horizontal axis in the figure indicates the ratio of the amount of supplied air to the amount of air (theoretical air amount) required to completely partially oxidize butane into carbon monoxide and hydrogen. As is clear from Figure 1, the excess air ratio is 1.01.
It can be seen that within the range of ~1.10, a heat treatment gas consisting of H ₂ and CO with a small amount of CH ₄ and CO ₂ by-products can be produced. For comparison, a heat treatment gas was produced in the same manner as above using a catalyst in which 7.7 wt% of nickel was supported on a mullite (3Al ₂ O ₃ .2SiO ₂ ) carrier having a particle size of 2 mmφ. The results are shown in FIG. In the comparative example, the amount of by-products CH ₄ and CO ₂ in the generated gas is large. Example 2 MgAl ₂ O ₄ spinel 82 mol%, α-alumina 18
A pellet-like catalyst having a particle size of 8 to 12 mmφ was prepared by supporting 6.0 wt % of cobalt on a carrier consisting of mol %.
The catalyst 30 was packed into a gas conversion retort with an inner diameter of 120 mmφ, and a mixed gas of butane and air was heated.
It was supplied into the above retort at SV6000hr ^-1 . At that time, the excess air ratio of the mixed gas and the heating temperature in the retort were varied. The amount of CO ₂ and CH ₄ by-products in the generated gas was measured, and the results are shown in Figure 3. As is clear from Figure 3, it is possible to produce a heat treatment gas with a small amount of CH ₄ and CO ₂ by-products when the air excess ratio of the mixed gas is in the range of 1.01 to 1.10 and the temperature is in the range of 850 to 1000°C. . Example 3 MgAl ₂ O ₄ spinel 80 mol%, α-alumina 20
A heat treatment gas was produced in the following manner using catalysts in which 7.7 wt % of cobalt was supported on a carrier consisting of mol % and having particle sizes of 2 to 3 mmφ, 8 to 12 mmφ, and 30 mmφ. That is, each of the above three types of catalysts was used at 2,
Fill the gas conversion retort and check the temperature inside the retort.
A mixed gas of butane and air with an excess air ratio of 1.07 was supplied into the retort at 930°C and SV5000hr ^-1 .
The composition of the generated gas is shown in the table. In addition, the table shows the inner diameter D of the retort, the particle diameter d of the catalyst, and the ratio (D/
d) is also shown. As is clear from the table, if the ratio (D/d) between the inner diameter D of the retort and the particle size d of the catalyst is within the range of the present invention, it can be used for heat treatment with very small amounts of CH ₄ and CO ₂ by-products. It turns out that gas can be produced. Note that a carburizing gas that contains very few impurities is required. Therefore, as is clear from the table, by setting D/d within the range of the present invention, the amount of by-products of CO ₂ and CH ₄ is small, and the method of the present invention is particularly suitable for producing carburizing gas. I know that there is. 【table】

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the composition of the heat treatment gas produced according to the present invention in Example 1 and the comparative example, respectively, and Figure 3 shows the composition of CH ₄ and CO in the heat treatment gas produced in Example 2. 2 is a diagram showing the amount of by-products with _{No. 2} .

Claims (1)

[Claims] 1. A method for producing a heat treatment gas containing carbon monoxide and hydrogen by partially oxidizing hydrocarbons by introducing air and hydrocarbons into a gas conversion retort filled with a catalyst. The catalyst has cobalt supported on a carrier consisting of alumina/magnesia spinel and 30 mol% or less of alumina and/or magnesia, and the ratio of the inner diameter of the gas conversion retort to the particle size of the catalyst is 6 to 6. The temperature inside the gas conversion retort is 850 to 1000°C, and the air and hydrocarbons introduced into the gas conversion retort have an air excess ratio of 1.01 to 1.10. A method for producing a heat treatment gas, characterized in that: 2. The method for producing a heat treatment gas according to claim 1, wherein the air and hydrocarbons are introduced into the gas conversion retort at a space velocity of 1,000 to 20,000 hr ^-1 .