JPS5849296B2 - Highly active exhaust gas denitrification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst used in a reaction for selectively catalytically reducing nitrogen oxides in flue gas with ammonia.

Nitrogen oxides emitted from various chemical factories, automobiles, and other sources are considered to be the cause of photochemical smog, and there is a need for the development of effective treatment methods.

Several flue gas denitrification methods have been proposed in the past, but
Among them, the catalytic reduction method of nitrogen oxides using ammonia as a reducing agent can reduce the amount of oxygen even if more than 1% by volume of oxygen coexists in the exhaust gas.
Since ammonia selectively reacts with nitrogen oxides, it is considered to be an advantageous method in terms of utility as a reducing agent.

As a catalyst used in this method, one in which a heavy metal compound is supported on a suitable carrier is known.

Among them, there are catalysts in which oxides of copper, iron, and vanadium are supported on activated alumina, catalysts in which these are treated with sulfur dioxide gas, and catalysts in which sulfates of these metals are supported in activated alumina. , is known to have high catalytic activity even if the flue gas contains a considerable amount of sulfur compounds.

However, these catalysts have had the problem that when used for a long time in exhaust gas containing sulfur oxides, the activated alumina support is gradually sulfated, resulting in deterioration of catalytic activity.

In addition, catalysts obtained using carriers that are difficult to sulfate, such as silica, diatomite, and cordierite, had extremely low activity.

Recently, it has been discovered that a catalyst consisting of a certain type of metal sulfate supported on an activated silica/alumina carrier of a predetermined composition is effective as a catalyst to solve the above problem of catalyst deterioration. .

In other words, a catalyst in which copper sulfate, iron sulfate, or vanadyl sulfate is supported on an activated silica/alumina carrier containing 40 to 90% by weight of silica components does not contain high concentrations of sulfur oxides in flue gas. Catalytic activity can be maintained for a long time even when the catalyst is used.

However, this catalyst is also unsatisfactory in terms of activity and lifetime.

The present invention relates to improvement of the above catalyst, and aims to provide a catalyst for exhaust gas denitrification that can be used for exhaust gas containing sulfur oxides while maintaining high activity for a long period of time. .

The flue gas denitrification catalyst according to the present invention has a silica component of 40 to 40%
Copper sulfate and tungsten oxide are supported on an activated silica and alumina carrier containing 90% by weight.

Here, the carrier is so-called activated silica-alumina obtained by dehydrating a mixed human convex gel consisting of silica hydrogel and alumina hydrogel.

Note that a carrier made of a simple mixture of silica and alumina or a carrier made of ceramics fired at a high temperature are not preferable because the activity of the catalyst made by supporting a metal on them is low.

If the silica component is less than 40% by weight in this carrier, if the obtained catalyst is used for a long time in a reaction to treat flue gas containing sulfur oxides, the catalyst will deteriorate significantly and the silica component will be reduced. If the amount exceeds 90% by weight, the activity of the resulting catalyst, especially the initial activity, will be low, so either case is not preferred.

Sulfuric acid steel has catalytic activity in the catalytic reduction reaction of nitrogen oxides with ammonia by being supported on the above-mentioned carrier.

The tungsten oxide compound acts to further enhance the catalytic activity of the metal compound by being supported on the same carrier.

The supported amount of tungsten oxide is 0.12-0.22S'/
The carrier is 1 gram.

Below the lower limit of this range, the above-mentioned effect will not be sufficiently exhibited, and even if it exceeds the upper limit, the improvement in the above-mentioned effect will not be so significant.

These metal compounds may be supported on the carrier by any conventional method.

For example, in a method of impregnating and supporting by dipping, first, each of the metal compounds is dissolved in the same solvent.

This solvent is preferably one that does not damage the activated silica or alumina carrier and evaporates or decomposes even at relatively low temperatures; examples thereof include water, aqueous ammonia, monoethanolamine, and oxalic acid. Ru.

Next, the carrier is immersed in this solution.

Note that separate solutions may be prepared from copper sulfate and tungsten oxide, and the carrier may be immersed in these solutions one after another.

The compound impregnated with the metal compound in this way is finally fired at an appropriate temperature.

Since the flue gas denitrification catalyst according to the present invention is configured as described above, it can be used for a long period of time while maintaining high activity against flue gas containing sulfur oxides.

Therefore, if this catalyst is used, the desired denitrification rate can be achieved at low temperatures with a small amount of filling, the denitrification equipment can be made more compact, and the pressure loss in the catalyst layer can also be suppressed. You can get many benefits such as:

Next, examples of catalysts according to the present invention are shown together with comparative examples, and the composition and denitrification rate of each of these catalysts are shown in Table 1.

Comparative Example 1 Catalyst 1 A predetermined amount of water glass (JISB No.) was neutralized with sulfuric acid, left overnight at room temperature, and a predetermined amount of A 12 (SO4) was added to it.
3 Added aqueous solution.

Next, (NH3)CO3 was added to this liquid while stirring well to make the liquid alkaline.

The solid phase was washed with a solution containing NH4Cl, filtered once and
It was dried at 10°C.

This dried product has a diameter of 80mm. ,, The molded product was molded into a disk shape with a height of 6 mm, and the molded product was fired at 500° C. for 4 hours to obtain activated silica/alumina carriers with various compositions.

These carriers were each mixed with the same volume of approximately 20% by weight of CuS.
Silica was obtained by immersing it in an O4 aqueous solution for 2 hours at room temperature, dehydrating it by centrifugation, and drying it at 110°C for 4 hours.

Alumina=Cu-based catalyst 1 was prepared.

Comparative Example 2 Catalysts 2 to 13 The carrier in Comparative Example 1 was immersed in the same volume of an ammonia aqueous solution of WO2 at a predetermined concentration at room temperature for 2 hours, centrifugally dehydrated, and dried at 110°C for 4 hours.

This operation was repeated several times as necessary to prepare silica-alumina-W catalysts 2 to 13.

Example Catalysts 14 to 18 Catalysts 6 to 10 were immersed in a CuSO4 aqueous solution in Catalyst 1, and the following procedure was performed in the same manner as the preparation method for Catalyst 1 to prepare silica.
Alumina-W-(:u-based catalysts 14 to 18 were prepared.

Catalyst Activity As shown in Fig. 1, a fixed bed flow type reaction tube 1 consisting of seven compartments 1a is filled with about 1 liter of each catalyst, and NH3 in the same volume as NO is introduced into the reaction tube 1. Approximately 400
Boiler flue gas heated to °C (each composition is shown in Table 2).

) was flowed for about 3000 hours at a flow rate of 35 Nm3/h.

The activity of each catalyst before and after using the above catalyst was compared by the following method.

In a normal flow system, a cylindrical quartz reaction tube with a diameter of 30 mm is filled with 10 mL of catalyst crushed into 8 to 14 meshes, and the mixed gas shown in Table 3 is fed under temperature control at a space velocity of 10 mm.
The denitrification rate was determined by flowing at a time of 000 hours-1.

The test results are shown in Table 1. FIG. 2 is a graph showing the relationship between the amount of W supported and the denitrification rate (catalytic activity) in the catalyst of the example, assuming that the amount of W supported is W metal: C0,18(z)/support (1) or less: It can be seen that the catalytic activity increases as the amount increases.

As shown in Table 1, W alone has extremely low activity, so the fact that such a high activity can be obtained by co-supporting W and Cu means that the combination of these co-supported metals This shows that excellent synergistic effects can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a reaction tube, and FIG. 2 is a graph showing the relationship between the amount of metal supported and the denitrification rate in the catalyst of the example of the present invention.

Claims (1)

[Claims] It is a catalyst for the catalytic reduction of nitrogen oxides using monium and monia, and is a highly active exhaust catalyst in which W copper and tungsten oxide are supported on an activated silica/alumina carrier containing 40 to 90% by weight of silica component. Catalyst for smoke denitrification.