JPH02258066A - Catalyst for preparing ammonia - Google Patents

Abstract

PURPOSE:To obtain a highly active catalyst by removing the poisoning of the catalyst due to chlorine by impregnating a hardly reducible oxide carrier with a ruthenium metal component using a ruthenium compound containing no chlorine. CONSTITUTION:A ruthenium compound containing no chlorine such as a ruthenium carbonyl complex or ruthenium nitrate is supported by hardly reducible oxide such as alumina or magnesia and reduced under vacuum and/or a hydrogen gas stream to obtain a metalloid ruthenium catalyst. Subsequently, an alkali metal compound such as a rubidium compound or a cesium compound is supported by said catalyst. By this method, catalyst poisoning action due to chlorine can be excluded and, when magnesia is used as the catalyst carrier, the catalyst accelerates reaction and becomes highly active.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst suitable for synthesizing ammonia from nitrogen and hydrogen.

(Conventional technology) Conventionally, an iron-based catalyst containing iron as a main component and supplemented with alumina, potassium oxide, etc. as a co-catalyst has been used to synthesize ammonia, but the ammonia synthesis activity of this catalyst is not exhibited at low temperatures. Therefore, the operational reaction temperature in industrial equipment is 400 to 50
Therefore, in the existing ammonia production method, it is necessary to increase the recirculation ratio of the reaction gas and increase the space velocity, and the power, heat transfer, etc. The increase in operating costs is significant.

The present inventors have previously provided a catalyst for ammonia production in which one of the Group I transition metals consisting of iron, ruthenium, osmium, and cobalt and an alkali metal are supported on activated carbon or porous carbon (Japanese Patent Publication No. 54 -3759
Publication No. 2). This catalyst for producing ammonia is prepared by adding an alkali metal to a group (1) metal catalyst supported on activated carbon, and is capable of synthesizing ammonia even at a low temperature of 200°C.

Subsequently, an ammonia production method using an alkali metal salt instead of an alkali metal for this catalyst system and using graphite-containing carbon having a specific surface area as a catalyst carrier was reported (Japanese Patent Publication No. 5916816 f4ri1 and the present invention They also reported a catalyst for producing ammonia with less poisoning effect by carbon oxide and water by supporting ruthenium chloride and an alkali metal salt on an alumina carrier (JOURN).
AL 0FCATALYSTS, Record, P, P, 29
6-304 (1985), 305-311 (1985)
5) l.

[Problem to be solved by the invention]

However, the present inventors have found that when ruthenium is supported on a carrier and is used in the form of chloride, the ammonia yield decreases due to catalyst poisoning.

The present invention further improves the catalyst for ammonia production by the present inventors, and provides a catalyst for ammonia production that does not have the poisoning effect of chlorine ions and uses an oxide carrier such as alumina or magnesia as a catalyst carrier. Take it as a challenge.

Furthermore, it is an object of the present invention to provide a catalyst in which an alkali metal compound has a promoting effect even in the absence of chloride ions.

[Means to solve the problem]

In the catalyst for producing ammonia in the present invention, a ruthenium compound that does not contain chlorine is supported on a refractory oxide, a metallic ruthenium catalyst is prepared by vacuum evacuation and/or reduction under a hydrogen stream, and then an alkali metal compound is supported. It is characterized by being manufactured by

As the ruthenium compound, compounds that do not contain chlorine can be used, such as ruthenium carbonyl complex, ruthenium acetylacetonate, ruthenium potassium cyanate, potassium ruthenate, ruthenium oxide, ruthenium nitrate, ruthenium red, etc. It is preferable to impregnate the refractory oxide by dissolving it in a polar organic solvent such as acetone, tetrahydrofuran, or water, and the ruthenium metal component is 0.1% to 20% by weight based on the refractory oxide catalyst carrier. , preferably 2
It is preferable to impregnate the resin in an amount of 5% to 5% by weight.

To prepare a ruthenium metal catalyst, first, after impregnating a catalyst carrier with a ruthenium compound solution,
Preferably evacuation at 150°C to 400°C, followed by 100°C to 700°C, preferably 300°C under a hydrogen stream.
It is preferable to carry out hydrogen reduction at ~500°C, but since ammonia production is carried out in a hydrogen atmosphere, the hydrogen reduction treatment may be omitted when preparing the catalyst and preparation may be carried out only by vacuum evacuation means, or vice versa. It is also possible to obtain metallic ruthenium by hydrogen reduction treatment, and the vacuum evacuation treatment may be omitted.

Next, the alkali metal compounds can be lithium, sodium, potassium, cesium, and rubidium compounds, with rubidium, cesium, and potassium compounds being particularly preferred; and the alkali metal compounds include nitrates, acetates, carbonates, and cyanates. It is preferable to impregnate the above ruthenium metal catalyst with a salt, hydroxide, etc. in the form of an aqueous solution.The alkali metal is added in an amount of 0.1 to 100 (mole ratio), preferably 5 to 20 (mole ratio) to the ruthenium metal. It's good to do that.

Note that instead of the alkali metal compound, an alkaline earth metal compound such as calcium, magnesium, or barium, which has a certain reaction promoting function as disclosed in the above-mentioned prior art, may be used.

In the catalyst carrier of the present invention, magnesia in particular has a reaction promoting function like an alkali metal oxide, so it has a certain level of ammonia synthesis activity even without the addition of an alkali metal oxide. However, even when magnesia is used as a catalyst carrier, the reaction can be further promoted by adding an alkali metal.

As the catalyst carrier, it is best to use a refractory oxide, such as alumina, magnesia, calcium oxide, zirconia, or the composite material cordierite. Since alumina is used as a catalyst carrier, it is best to use it as a single body. The catalyst carrier may be used in powder form, but it is better to use a pellet shape.Also, when loading it onto a car, the catalyst carrier may be formed into a honeycomb shape by known means and then impregnated with an active metal component. good.

The raw material gas for ammonia synthesis to which the catalyst of the present invention is applied is:
Although conventional ammonia synthesis gas does not require special purification, the catalyst of the present invention can be easily regenerated even if it is poisoned by carbon monoxide. It is also useful as a catalyst for ammonia production when using hydrogen produced by catalytic cracking reaction of light oil etc. in No. 63-142401).

The reaction temperature and reaction pressure in the ammonia synthesis reaction are preferably low temperature and high pressure in terms of equilibrium theory, but the catalyst of the present invention
~500°C, preferably 150°C to 350°C,
The catalyst of the present invention, which is carried out at a pressure of 1 to 300 atm, is active at a low temperature, so that ammonia can be obtained in a high concentration, making it easy to liquefy and separate it.

[Effect]

The catalyst for ammonia production of the present invention is prepared by impregnating a ruthenium metal component into a refractory oxide carrier using a ruthenium compound that does not contain chlorine, and is similar to the case where conventional ruthenium chloride is used as a raw material. It can eliminate the catalyst poisoning effect caused by chlorine ions and exhibits high ammonia synthesis activity. In addition, an alkali metal compound as a reaction promoter can be easily supported on a catalyst carrier in the form of an aqueous solution, and especially when magnesia is used as a catalyst carrier, it has a reaction promoting function in addition to its function as a catalyst carrier. The reaction activity can be further increased. Furthermore, in general, alumina and magnesia supports have extremely good affinity with ruthenium carbonyl complexes and alkali metal salts. Components can be easily and uniformly deposited, and a catalyst with a large amount of active metal components supported can be obtained.

The present invention will be described below with reference to Examples and Reference Examples, but the present invention is not limited thereto.

As a matter common to the Examples, in producing ammonia, a glass tube with an inner diameter of 18-1 is filled with a catalyst containing 1 g of the catalyst of the present invention, and while the catalyst layer is heated from the outside, carbon oxide is mixed. is the mixing ratio of nitrogen and hydrogen 1:
3. A raw material gas with a total pressure of 1 atm was caused to flow at a flow rate of 3.51/hr to react, and the amount of ammonia in the produced gas was measured by condensing it with liquid nitrogen.

[Example 1] FIG. 1 is a diagram showing the influence of the amount of cesium used on the ammonia yield in the ruthenium-cesium/alumina catalyst of the present invention.

Ruthenium carbonyl was dissolved in 40 tal of tetrahydrofuran, and this solution was pre-calcined in air at 500°C for 6 hours. 3.3 g of T-alumina (Catalysis Society Reference Catalyst, JRC-ALO-4) body
was impregnated with 2% by weight of ruthenium. Next, after removing the solvent at a low temperature, the reactor was evacuated at 350° C. to prepare a ruthenium metal catalyst.

This ruthenium metal catalyst was impregnated with an aqueous cesium nitrate solution at a cesium/ruthenium molar ratio of 1, 3, 5, 7, and 10, and dried overnight at 90°C to prepare a catalyst of the present invention.

Immediately before using the catalyst for ammonia production, the catalyst was heated to 350°C or 400°C and subjected to reduction treatment in a hydrogen stream for 4 hours.

Using these catalysts, ammonia synthesis was carried out at a reaction temperature of 400°C. The results are shown in FIG.

In Figure 1, the 0 mark is the one immediately after the catalyst was manufactured, and the Q mark is the 10
Shows the activity after hours of operation. The unit of the reaction product amount is μ-〇1g-1h, which indicates the amount of product generated per 1g of catalyst and 1 hour.
-1 (the same applies hereinafter) According to this, it can be seen that as the addition ratio of cesium increases, the reaction activity increases and a high ammonia synthesis activity is exhibited.

[Example 2] FIG. 2 is a diagram showing the influence of the amount of rubidium or potassium used on the ammonia yield in the ruthenium-rubidium or potassium/alumina catalyst of the present invention.

In Example 1, rubidium nitrate and potassium nitrate were impregnated in place of cesium, a catalyst was prepared at a reduction temperature of 350°C, and ammonia synthesis was performed at a reaction temperature of 350°C.

The results are shown in FIG.

In the figure, the 0 mark indicates the case of rubidium nitrate, and the 0 mark indicates the case of potassium nitrate. According to this, the yield of the product impregnated with rubidium nitrate and potassium nitrate is lower than that of the product impregnated with cesium in Figure 1. It can be seen that they have similar reaction activities.

Next, FIG. 3 is a diagram showing the life of the catalyst of the present invention.

The amount of each alkali metal added to ruthenium was set at a molar ratio of 10, hydrogen reduction was carried out at 350°C, and the reaction was carried out at 350°C.
Ammonia synthesis was carried out in the same manner as in Example 1 above, except that the procedure was carried out in Example 1 above. The results are shown in FIG.

As can be seen from Figure 3, the catalyst of the present invention maintains reaction activity for a long time with a constant reaction yield after an extremely short induction time, and the catalyst of the present invention maintains reaction activity for a long time with a constant reaction yield.
It can be seen that the reaction activity is highest in order of potassium.

Further, FIG. 4 is a diagram showing the influence of the reduction temperature of the catalyst on the reaction yield.

A ruthenium-cesium/alumina catalyst with a Cs/Ru molar ratio of 10 was prepared in the same manner as in each of the above examples except that the reduction temperature was changed, and the influence on the reaction yield was observed. is 400℃, 0 mark is 350℃, Δ mark is 31
The case where the reaction was carried out at 5°C is shown.

According to this, it can be seen that the reaction yield is high when the preparation temperature of the catalyst layer and the reaction temperature are high, but the catalyst of the present invention can obtain a high reaction yield by lowering the reduction temperature of the catalyst as much as possible.

For comparison, FIG. 4 shows the same catalyst as in Example 1 but with no cesium added.
The reaction results at 0°C are indicated by marks.

This shows that the activation effect is extremely low unless cesium is added.

Also, for comparison, the same amount of ruthenium as in Example 1,
and 400% impregnated into alumina using ruthenium chloride as a ruthenium compound to contain cesium.
Prepare a catalyst treated with cesium nitrate after reduction treatment at °C,
When used for ammonia synthesis at 400℃, the yield was 2.
00 μmol g-Ih-1. It can be seen that the catalyst of the present invention, which is indicated by the x mark in FIG. 4, has significantly higher reaction activity than a catalyst derived from ruthenium chloride prepared under similar reduction conditions.

[Example 3] FIG. 5 is a diagram showing the reduction temperature dependence of ammonia synthesis activity when a magnesia carrier is used and no alkali metal compound is contained.

In Example 1, a catalyst was prepared by using magnesia instead of the alumina carrier and carrying out hydrogen reduction without adding a cesium salt. FIG. 5 shows the results of changing the reduction temperature during catalyst preparation and changing the reaction temperature for ammonia synthesis by changing the reaction temperature to 350° C. and 400° C.

This shows that when magnesia is used as a carrier, it has a considerably high reaction activity even without the addition of cesium. Furthermore, the catalyst of the present invention is subjected to exhaust treatment at 350° C. before reduction, and it can be seen that the characteristics of the catalyst are mainly determined at this stage and are not greatly influenced by the subsequent reduction temperature.

[Example 4] A ruthenium metal catalyst was prepared in the same manner as in Example 1 using a magnesia support instead of the alumina support, and the ruthenium metal catalyst had an alkali metal/ruthenium molar ratio of 1.0. The catalyst of the present invention was prepared by impregnating it with an aqueous cesium nitrate solution.

Immediately before using the catalyst thus prepared for ammonia production, it was reduced at 350°C for 4 hours in a hydrogen stream,
Ammonia synthesis was performed by changing the reaction temperature. The results are shown in the table below. It can be seen that the amount of metal used is smaller than in the case of an alumina support.Also, in the case of potassium, rubidium, and cesium-doped ruthenium catalysts, the activity remained even though the reaction temperature rose from 315℃ to 330℃. The reason why is not increasing seems to be that the reaction has already proceeded to near equilibrium due to the high activity of these catalysts.

[Example 5] The ruthenium metal catalyst prepared in Example 1 (however, the ruthenium was prepared to be 5% by weight instead of 2% by weight) had a cesium/ruthenium molar ratio of 3.76.
Impregnated with cesium nitrate aqueous solution so that
The catalyst of the present invention was prepared by drying overnight.

This catalyst was reduced in the same manner as in Example 1, and the reaction temperature was 400.
℃, under atmospheric pressure, the raw material gas composition was 20% by volume, 60% hydrogen, and 20% diluent gas (helium) -xl-carbon oxide
Ammonia synthesis was carried out as follows. Changes in the amount of ammonia produced were measured by changing the proportion (mole fraction) of carbon monoxide in the raw material gas, and the results are shown in the table below. The unit of ammonia yield is μmo1 g-'h-' (hereinafter Margin) This shows that the catalyst of the present invention is not significantly affected by the poisoning effect of carbon monoxide.

Furthermore, in this experiment, when the inflow of carbon monoxide was stopped and the reaction was continued, the activity of the catalyst of the present invention returned to its original value, indicating that the CO poisoning was temporary.

[Reference example]

FIG. 6 is a diagram showing the reaction yield when ruthenium chloride is used as the ruthenium source.

A catalyst was prepared by impregnating magnesia in a ruthenium chloride aqueous solution so that the ruthenium content was 2% by weight relative to magnesia, and impregnating it with a potassium nitrate aqueous solution so that the molar ratio to ruthenium was the number on the horizontal axis. The mark indicates that the sample was subjected to hydrogen reduction treatment at 600° C. after being impregnated with ruthenium, and the 0 mark indicates that no hydrogen reduction treatment was performed.

The results of ammonia synthesis using this catalyst are shown in Figure 6.It shows that since the catalyst that is not subjected to hydrogen reduction contains chlorine, ammonia cannot be synthesized unless potassium is contained above a certain ratio to ruthenium. It can be seen that the activity is extremely low.

Furthermore, it can be seen that even in the case where the hydrogen reduction treatment was performed at 600° C., the activity was further increased by the addition of potassium salt.

〔Effect of the invention〕

The catalyst for ammonia production of the present invention can eliminate the catalyst poisoning effect caused by chlorine in conventional catalysts derived from ruthenium chloride, and when magnesia is used as a catalyst carrier, it has a reaction promoting function in addition to its function as a catalyst carrier. It can be used as a catalyst with even higher reaction activity. Furthermore, in the catalyst of the present invention, the ruthenium carbonyl complex and the alkali metal salt have extremely good affinity with the catalyst carrier, so that the ruthenium metal component and the alkali metal component can be easily and uniformly deposited within the pores of the catalyst carrier. As a result, a large amount of active metal components can be supported. Moreover, since it is resistant to the poisoning effect of carbon oxide, it is a useful catalyst even when the reaction gas contains carbon monoxide.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the effect of the amount of cesium used on the ammonia yield in the ruthenium-cesium-alumina catalyst of the present invention, and FIG. 2 is a diagram showing the effect of rubidium or potassium in the ruthenium-rubidium or potassium-alumina catalyst of the present invention. Figure 3 is a graph showing the effect of the amount of use of the catalyst on the ammonia yield, Figure 3 is a graph showing the life of the catalyst of the present invention, Figure 4 is a graph showing the effect of the reduction temperature of the catalyst on the reaction yield, and Figure 5 is a graph showing the effect of the reduction temperature of the catalyst on the reaction yield. FIG. 6 is a diagram showing the reduction temperature dependence of the ammonia synthesis activity when ruthenium chloride is used as the ruthenium source and no alkali metal compound is used. FIG. 6 is a diagram showing the reaction yield when ruthenium chloride is used as the ruthenium source. Applicant: New Combustion System Research Institute Co., Ltd. Agent Patent Attorney (1) Nobuhiko (5 others) Procedure (Method) % Formula % 1, Incident Indication 1999 Patent Application No. 245429 2, Title of invention: Catalyst for producing ammonia 3. Relationship with the person making the amendment Patent applicant name: New Combustion System Research Institute Co., Ltd. Representative: Takashi Suzuki 4゜Representative: 5 Date of amendment order: Sent on December 120, 1999 December 26, 1999 6. Drawing subject to amendment (Fig. 5) 7. Details of amendment

Claims (2)

[Claims] (1) Produced by supporting a chlorine-free ruthenium compound on a refractory oxide, preparing a metallic ruthenium catalyst by reducing in vacuum and/or under a hydrogen stream, and then supporting an alkali metal compound. A catalyst for ammonia production characterized by: (2) Claim 1, wherein the chlorine-free ruthenium compound is a ruthenium carbonyl complex or ruthenium nitrate, the refractory oxide is alumina or magnesia, and the alkali metal compound is a nitrate of rubidium, cesium, or potassium. Catalyst for producing ammonia as described.