JPS5824172B2 - Ammonia Osankabunkaisuruhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst that decomposes ammonia gas contained in exhaust gas into nitrogen gas and water.

Currently, a catalytic reduction method using ammonia has been developed as a method for removing nitrogen oxides (hereinafter abbreviated as NOx) from various exhaust gases.

In this case, it is common to add more than an equivalent amount of ammonia to maintain a high denitrification rate.

Therefore, even if NOx is removed, excess ammonia may flow out.

If this ammonia is emitted as it is, there is a risk that it will become a new source of pollution.

In addition, excess ammonia reacts with acidic gas in the exhaust gas to form ammonium salts, which adhere to the pipes at the rear of the denitrification tower and cause problems such as blockage.

Therefore, in the ammonia reduction denitrification method, it is important to decompose excess ammonia.

In addition, exhaust gases from various chemical plants that use ammonia often contain ammonia, but since ammonia is well absorbed by aqueous solutions, it has been relatively easy to remove ammonia.

However, when removing ammonia by absorption method,
When the processing gas temperature is high, the processing gas must be cooled, and problems also remain in the processing of the absorption liquid.

The best way to solve these problems is to decompose the ammonia in the exhaust gas and turn it into nitrogen and water, making it harmless.

Conventionally, Pt-based catalysts, Pt-Rh-based catalysts, and the like have been used industrially as catalysts for oxidizing ammonia to nitrogen monoxide at temperatures of 800° C. or higher.

However, since this catalyst does not reduce nitrogen oxides to nitrogen, the treated gas is still harmful to the human body.

Other catalysts for ammonia oxidation that have been reported so far include NiOCoO+Feze3+ CuO+ Bi.
There are oxide catalysts such as 2O3 and MnO2.

However, with these catalysts, in addition to nitrogen, N20. There is also a considerable amount of NOx produced.

Furthermore, the activity is not sufficient at the desired reaction temperature of 300 to 400°C.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to exhibit high activity over a wide temperature range, and to be able to use other gases such as SO2.
The object of the present invention is to provide a method for detoxifying ammonia into nitrogen and water using a catalyst with good selectivity even in the presence of , CO2, etc.

The feature of the present invention is that a gas containing ammonia and oxygen is brought into contact with each other, and the ammonia in the gas is oxidized and decomposed as shown in equation (1), and the ammonia is rendered harmless to nitrogen and water.
→2 N2 + 6 N20 Method (1) (for this, a catalyst containing at least one of titanium and copper as an active main component of molybdenum, tungsten, vanadium, cerium, and iron to promote the reaction) is used. It's about using it.

When ammonia is decomposed and removed using the catalyst of the present invention, the reaction temperature is 250 to 450°C, preferably 300 to 450°C.
NH3 can be decomposed efficiently over a wide temperature range of 400°C.

At a reaction temperature of 250° C. or lower, the reaction rate is low, and in order to obtain a high ammonia decomposition rate, it is necessary to lower the space velocity, which increases the size of the apparatus and makes it uneconomical.

Furthermore, when the reaction temperature is 450° C. or higher, the NOx production rate increases.

The reaction pressure is not particularly limited, but from atmospheric pressure to 10 kg/
cytt or higher.

When decomposing and removing ammonia in a gas using the catalyst of the present invention, as shown in equation (1), 374 moles of oxygen is required as much as the amount of ammonia stoichiometrically.

In an actual process, the amount of oxygen is preferably several times or more that of ammonia in order to sufficiently increase the reaction rate.

If the processing gas does not contain a sufficient amount of oxygen, this problem can be easily solved by mixing oxygen or air into the processing gas.

At this point, there is enough oxygen to decompose surplus ammonia after nitrogen oxides in the boiler exhaust gas are reduced to ammonia, so the reaction can be carried out as is.

Although the space velocity varies depending on the reaction temperature and other coexisting components in the gas, it is 1,000 to 100.0OOh=',
Preferably, ammonia can be decomposed efficiently within the range of 2,000 to 30,000 h-1.

The catalyst of the present invention has titanium as a first component, copper as a second component, and at least one selected from molybdenum, tungsten, vanadium, cerium, and iron as a third component.
At the end of catalyst preparation, the second component is added to the first component.
The atomic ratio of the components is 0.02-1, preferably 0.05-0.
5, and the atomic ratio of the third component to the first component is from 0.01 to 0.5, preferably from 0.02 to 0.5.

In addition, a catalyst can be prepared by supporting the above-mentioned active component on a refractory porous carrier or by mixing it with a phase component, but in this case, the sum of the weights of the above three catalyst components is When the amount is 3% or more, preferably 5% or more of the total weight of the catalyst, a highly active catalyst can be obtained.

For the preparation of the catalyst of the present invention, any of the precipitation methods, kneading methods, etc. that are commonly used in production can be used, and there are no particular limitations.

In addition, the final catalyst molding method is the usual tablet molding method.
Any method can be used depending on the purpose, such as an extrusion molding method or a transfer granulation method.

When preparing the catalyst of the present invention, titanium raw materials include various titanium oxides, titanic acid (T 102・nN20), which produces titanium oxide when heated, titanium tetrachloride, titanium sulfate, titanyl sulfate (T i O204
) etc. can be used.

Alternatively, a preferred method is to neutralize an aqueous solution of titanium tetrachloride, titanium sulfate, etc. with aqueous ammonia, aqueous alkali, alkali carbonate, urea, etc. to form a precipitate, and then thermally decompose the precipitate to obtain an oxide.

When the catalyst of the present invention is prepared using rutile-type or anatase-type titanium oxide calcined at high temperature, its activity is not sufficient, but by treating these titanium oxides with hot concentrated sulfuric acid, some of the titanium oxides can be recovered. Alternatively, a highly active catalyst of the present invention can be prepared by replacing the entire titanium sulfate with titanium sulfate and producing the above precipitate.

As a raw material for copper, copper oxide, or copper hydroxide, copper sulfate, copper nitrate, etc., which produce copper oxide by heating, can be used.

It is also a good method to obtain copper oxide by adding the above-mentioned alkaline precipitant to an aqueous solution of these various copper salts to form a copper hydroxide, and then thermally decomposing this.

Further, as a raw material for molybdenum, molybdenum oxide, molybdic acid, ammonium molybdate, etc. can be used.

As the iron raw material, any of various iron oxides, iron hydroxides, iron nitrates, iron sulfates, iron chlorides, iron acetates, etc. can be used.

As raw materials for vanadium, vanadium oxide, ammonium metavanadate, vanadyl sulfate, etc. can be used.

Cerium raw materials include cerium oxide, cerium nitrate,
Any of cerium sulfate, cerium chloride, cerium acetate, cerium carbonate, cerium oxalate, etc. can be used.

Further, as the tungsten raw material, tungsten oxide, tungstic acid, ammonium paratungstate, etc. are preferable.

Tungstic silicic acid and its salts containing silica as a carrier component are also preferred raw materials.

Hereinafter, the content of the present invention will be explained in more detail with reference to Examples.

Example-1 A catalyst used in the method of the present invention and a catalyst used as a comparative example were prepared as follows.

Example Catalyst 1 Take metatitanic acid slurry 5002 (150? as T i 02) and add copper nitrate (Cu Q'JO3) to it.
2 ・3 N20) 53.4 i1i′ and ammonium molybdate ((NH4)6MO7024・4
N20) Add 19.5F.

Furthermore, 500 ml of distilled water was added, and the mixture was sufficiently kneaded in a kneader.

After preliminarily firing the resulting paste mixture at 300°C for 5 hours, 3% by weight of graphite was added and the molding pressure was approximately 5%.
00 kg/cyyi, the tablet is compressed into a size of 6 mrrt in diameter and 6 mm in thickness.

The obtained molded product was fired at 500° C. for 4 hours.

The catalyst thus obtained has an atomic ratio of Ti:Cu:Mo=8
It has a composition of 5:10:5.

Comparative Example Catalyst 1 577 Il of hexachloroplatinic acid (N2PtC1e) aqueous solution (10rPt/100g solution) was diluted with distilled water to make a total volume of 70ml, and this was added to 100 pieces of activated alumina carrier pulverized into 10 to 20 meshes. Impregnated.

After drying at 120°C for 5 hours, drying at 450°C in a hydrogen stream for 3 hours.
Reduce baking time.

The catalyst is a 0.5% (wt) platinum catalyst on an alumina support.

The catalyst activity testing apparatus was of a normal atmospheric pressure fixed bed flow system, and the reaction tube was made of Pyrex glass with an inner diameter of 16 rnrn and had a thermocouple protection tube made of Pyrex glass with an outer diameter of 5 rnrn inside.

This reaction tube is heated in an electric furnace to set the reaction temperature.

Place 4 ml of catalyst in the center of the reaction tube (the example catalyst is 10 to 20
After sizing) into a mesh, a gas with the following composition is passed through the catalyst bed at a space velocity (hereinafter abbreviated as SV) of approximately 30,000h', and ammonia, NH,
The concentration of the remaining 3300 pp[1I 02 3% N2 was measured to determine the ammonia decomposition rate, the NOx concentration at the outlet of the catalyst layer was measured to determine the NOx production rate, and the N20 concentration was measured to determine the N20 production rate.

Note that ammonia analysis was performed using the indophenol method.

NOx was measured using a chemiluminescence NOx analyzer.

N20 was measured by infrared absorption method.

The ammonia decomposition rate, NOx generation rate, and N20 generation rate were determined from the following equations.

The activity of Example Catalyst 1 and the platinum catalyst given as a comparative example was measured under the above conditions, and the results shown in FIG. 1 were obtained.

As shown in this figure, the comparative example catalyst exhibits high activity comparable to that of the example catalyst.

However, in the comparative example catalyst, the oxidative decomposition products of ammonia include NOx +N20 in addition to nitrogen.

Therefore, it is unsuitable for the purpose of making ammonia harmless.

On the other hand, the example catalyst shows the same level of activity as the highly active Pt-based catalyst, and the NOx product is about 1% even at 450°C, and the N20 is also low at less than 10%, which is the lower limit of quantitative analysis. It showed very good performance.

Example-2 Using a catalyst prepared in the same manner as in Example-1 except for changing the composition ratio of titanium, copper, and molybdenum, a gas having the same composition as shown in Example-1 was heated at 5V-30, 000h
The activity test of the catalyst was carried out by distributing it in ', and the results shown in Table 1 were obtained.

Ti/Cu/Mo with molybdenum added compared to <Ti/Cu (90:10) catalyst as shown in Table 1.
(85:10:5) The ammonia decomposition activity of the catalyst has clearly increased.

Furthermore, the NOx production rate is lower and the selectivity is increased.

In addition, the Ti/Cu/Mo catalyst is a Ti/Mo catalyst that does not contain copper (
The improved low temperature activity compared to the 90:10) catalyst will also be evident.

In addition, in the range of 250 to 450° C., the amount of N20 produced was small and negligible at less than iop per biliter for all catalysts.

It is also characterized by a relatively low NOx production rate even at high temperatures.

Example-3 The same method as Example-1 was used except that instead of ammonium molybdate, iron hydroxide precipitate produced by dropping aqueous ammonia into a solution of ferrous sulfate was used, and molybdenum and iron were replaced. Ti:Cu of the prepared Ti/Cu/Fe catalyst
:The activity test was conducted under the same conditions as in Example 2 by changing the composition ratio of Fe, and the results shown in Table 2 were obtained.

As shown in Table 2, <Ti/Cu (90: 10)
Compared to the catalyst, T i/Cu//Fe with added iron
(80:10:10) The ammonia decomposition activity of the catalyst is clearly increased.

Furthermore, the NOx production rate is lower and the selectivity is increased.

In addition, the Ti/Cu/Fe catalyst is a Ti/'Fe catalyst that does not contain copper.
It will also be clear that the low temperature activity is improved compared to the (90:10) catalyst.

And it shows more sufficient activity at high temperatures.

Example-4 Ti/Cu/
The activity test was carried out under the same conditions as in Example 2 by changing the combined acid ratio of 'I'i:Cu:V of the V catalyst, and the results shown in Table 3 were obtained.

As shown in Table 3 <Ti/Cu (90:10)
Compared to the catalyst, vanadium-doped Ti/Cu/v (
85:10:5) The catalyst clearly has increased ammonia decomposition activity at low temperatures.

In addition, the Ti/Cu/V catalyst is Ti/V (90
: 10) It is also clear that the activity is significantly improved compared to the catalyst.

Example-5 It was prepared in the same manner as in Example-1 except that instead of ammonium molybdate, cerium hydroxide precipitate produced by dropping aqueous ammonia into a solution of cerium nitrate was used, and molybdenum and cerium were replaced. The Ti:Cu:Ce composition ratio of the Ti/Cu/Ce catalyst was changed and an activity test was conducted under the same conditions as in Example 2, and the results shown in Table 4 were obtained.

As shown in Table 4 <Ti/Cu (90: 10)
Ti/Cu with cerium compared to catalyst
/Ce (80:10:10) catalyst has clearly increased ammonia decomposition activity at low temperatures.

In addition, Ti/Cu/Ce catalyst is a Ti/Ce catalyst that does not contain copper (
It is also clear that the activity is significantly improved compared to the 90:10) catalyst.

There is also a tendency for the NOx generation rate to be low near 400°C.

Example-6 Ti/Cu prepared in the same manner as Example-1 except that ammonium tungstate was used instead of ammonium molybdate and molybdenum and tungsten were replaced.
An activity test was conducted under the same conditions as in Example 2 by changing the Ti:Cu:W composition ratio of the /W catalyst, and the results shown in Table 5 were obtained.

As shown in Table 5, compared to <Ti/Cu (90: 10) catalyst, Ti/Cu/ with tungsten added
The W (85:10:5) catalyst clearly has increased ammonia decomposition activity at low temperatures.

In addition, the Ti/Cu/W catalyst is Ti/W (9
It is also clear that the activity is significantly improved compared to the 0:10) catalyst.

Thus, as the amount increases, it tends to exhibit low temperature activity.

Example 7 In this example, the catalyst of Example 1 was used, and the reaction temperature was 35.
The results of investigating the relationship between Sv, NH3 decomposition rate, and NOx production rate under constant conditions of 0°C will be described.

Table 6 shows the results of the reaction conducted under the same conditions as in Example-1 except that Sv, that is, the gas flow rate, was changed.

From this result, the catalyst of the present invention has an Sv of 30.00.
Even when set to 0h', the catalyst shows sufficient catalytic activity for practical use.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the ammonia decomposition rate, NOx and NO production rate, and temperature of a catalyst according to an embodiment of the present invention.

Claims (1)

[Claims] 1. A gas containing ammonia and oxygen but not containing nitrogen oxides, (a) titanium oxide, (b) copper oxide, and (c) molybdenum oxide, tungsten oxide, vanadium oxide. , at least one of cerium oxide and iron oxide is an active main component, the atomic ratio of copper to titanium is in the range of 0.02 to 1 to titanium, and molybdenum, tungsten, vanadium, A catalyst in which the atomic ratio of at least one of cerium and iron to titanium is in the range of 0.01 to 0.5 (excluding those prepared using high-temperature calcined rutile or anatase titanium oxide). A method for oxidatively decomposing ammonia, which is characterized by converting ammonia in a gas into nitrogen and water.