JPH01288338A - Catalyst for catalytic reduction of nitrogen oxides - Google Patents

Abstract

PURPOSE:To obtain a catalyst prevented from a degradation due to heavy metal compound vapor in a flue gas by using a catalyst, which is composed of titanium oxide, one or more oxides of V, Cu, Fe or Mn and an oxide of Mo or W and which has few fine pores. CONSTITUTION:A catalyst for reduction of nitrogen oxide with ammonia as a reducing agent is composed of a titanium oxide, one or more oxides of V, Cu, Fe or Mn and an oxide of Mo of W. A summation of mole numbers of Mo or W oxide per unit specific surface area of this catalyst is specified to be 2X10<-6>-20X10<-6>mol/m<2>. Furthermore, a total pore volume of this catalyst is specified to the 0.2ml/g or larger and a volume of pores not larger than 30Angstrom in diameter is specified to the 25% or less of the total pore volume. As this catalyst has a reduced proportion of fine pores so as to prevent cloggings of pores, it is possible to keep a high denitration performance for a long time even in a flue gas containing a large amount of heavy metal compound vapor.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a catalyst for reducing nitrogen oxides using ammonia as a reducing agent, and in particular to a catalyst for reducing nitrogen oxides in exhaust gas containing a large amount of heavy metal oxides. Regarding reduction catalysts.

[Conventional technology]

Nitrogen oxides (NOx) emitted from various stationary sources are major air pollutants along with sulfur oxides (SOx). Although there are various methods for removing NOx, the mainstream method is to selectively reduce the NOx with ammonia added to the exhaust gas using a catalyst. This ammonia catalytic reduction denitrification catalyst must not be degraded by SOx or ash contained in the combustion exhaust gas of fossil fuels such as oil and coal. was invented and has already been widely put into practical use (Japanese Patent Application Laid-open No. 50-128681, JP-A No. 53-28148).

These catalysts are made by adding oxides of transition metal elements such as vanadium, molybdenum, tungsten, iron, and chromium to metatitanic acid or titanium oxide through kneading, impregnation, etc., and then firing them. As a denitrification catalyst, it has excellent activity and longevity.

[Problem to be solved by the invention]

However, when treating exhaust gas containing a large amount of heavy metal oxide vapor, such as low-quality coal combustion exhaust gas or exhaust gas from a boiler with ash circulation shown in Figure 1, which is frequently used in Europe, there is a possibility of a decrease in catalytic activity. was not taken into account.

In particular, as shown in Fig. 1, in the case of a combustion method in which the combustion ash collected by the electrostatic precipitator 7 is recirculated to the furnace 1 via the Tenryu ring road, it is made into molten slag in the furnace and taken out to the outside. , lead (Pb) and selenium (Se) contained in minerals in coal.
, arsenic (As), cadmium (Cd), zinc (Zn)
When the ash content is melted in the furnace and recovered as slag, metals such as metals are transferred into the exhaust gas as a single element or as oxide vapor, and in the upstream of the air preheater where the denitrification equipment is usually installed. It is known to exist as a highly concentrated vapor (H, Brumsack etaj2., En.
vironmentsl TecnoAogy Le
5.7 22 (1,982)). It has been found that denitrification catalysts are poisoned by these vapors and that countermeasures are required, but this point has not been taken into account in the above-mentioned practical catalysts.

The purpose of the present invention is to provide a catalyst that prevents deterioration of heavy metal compounds contained in exhaust gas due to steam, which has not been considered in the above-mentioned prior art, and which is difficult to achieve with conventional catalysts due to a significant decrease in activity. In addition, it is possible to denitrate exhaust gas containing a large amount of heavy metal compound vapor, such as the ash melting boiler with ash circulation shown in Figure 1, with the same amount of catalyst and simplicity as ordinary flue gas denitrification. It is in.

[Means to solve the problem]

The problem with the above-mentioned conventional technology is that it is composed of titanium oxide, an oxide of one or more elements among vanadium, copper, iron, and manganese, and an oxide of molybdenum or tungsten, and the number of moles of the oxide of molybdenum or tungsten is The sum is 2X10-6 to 20X1 per unit specific surface area of the catalyst.
0-''6 mol/d, with a total pore volume of 0.2
m 1 / g or more and the volume of pores with a diameter of 30 Å or less is 25% or less of the total pore volume, and is solved by a catalyst for catalytic reduction of nitrogen oxides using ammonia as a reducing agent. .

[Effect]

When a catalyst is brought into contact with a gas containing heavy metal compounds, the heavy metal compounds accumulate in the catalyst, reducing its activity.

Examining the change in pore distribution at this time, it was found that the number of pores with a diameter of 30 Å or less decreased significantly after contact with the heavy metal compound. From this, it is considered that pores with a diameter of 30 Å or less cause pore blockage in a short period of time, and this portion becomes inactive. In addition, the catalytic activity increases as the pore volume increases, so if all pores are reduced, the initial activity will drop (and become unusable). Reduce the following pores,
By preventing activity from being imposed on the pores of 30 Å or less, the activity is less likely to be lowered by heavy metal compounds.

〔Example〕

The catalyst of the present invention includes titanium oxide, Cu, FesM
It consists of one or more oxides among n and an oxide of Mo or W, and the volume of pores with a diameter of 30 Å or less is 25% or less of the total pore volume.

Specifically, this can be achieved by kneading or impregnating a catalyst powder or compact having the above composition with a sulfate such as aluminum sulfate or magnesium sulfate, or ethyl silicate or silica sol, followed by drying and firing. It can also be realized by supporting an active ingredient having the above composition on titanium oxide calcined at a high temperature or on a calcined product to which ethyl silicate, titania sol, silica sol, etc. are added. It is possible to realize the present invention in other ways as well, and this method is not taken.

When aluminum sulfate, ethyl silicate, etc. are added to a catalyst with a large pore volume, the surface of the catalyst is covered with these additives, and as a result, the small pores are closed and reduced.

At this time, the pore volume before addition is sufficiently large, so even if the total pore volume decreases slightly, it maintains a large value, and unlike heavy metal compounds, these additives have no poisoning effect, so there is almost no decrease in activity. do not have. In addition, by adding ethyl silicate, silica sol, or titania sol to titanium oxide, small pores can be reduced in the same way, or by sintering titanium oxide at high temperatures, small pores can be reduced by sintering. By supporting the active component, it is possible to effectively support the active component and a highly active catalyst can be obtained. In this way, the number of small pores is reduced, and since the catalyst is highly active, the activity will not be reduced even by heavy metal compounds.

Hereinafter, the present invention will be explained in detail with reference to specific examples.

Example 1 Metatitanic acid slurry 5 containing 3Qwt% titanium oxide
0kg, ammonium metavanadate (NH4VO3)
1.02 kg of ammonium molybdate and 3.81 kg of ammonium molybdate were added and heated and kneaded in a kneader to obtain a paste with a water content of 34%. The resulting paste was granulated using an extrusion granulator, dried using a fluidized bed dryer, baked at 400° C. for 2 hours, and then ground to 90% or more in a 100 mesh bath using a hammer mill. Add 4w of aluminum sulfate (Al1 (304)3) to this powder.
t%, water, and 15wt% of kaolin-based inorganic fibers to form a paste, and this paste was made into a 5U powder with a thickness of 0.3 nm.
After S304 steel strip was lath-processed into a wire mesh shape, aluminum oxide was thermally sprayed onto a metal substrate using a roller and applied under pressure. This was air-dried for 12 hours and then calcined at 500°C for 2 hours to obtain a plate-shaped catalyst.

Comparative Example 1 A plate-shaped catalyst was obtained in the same manner as in Example 1 except that aluminum sulfate was not added.

Example 2 The plate-shaped catalyst obtained in Comparative Example 1 was mixed with aluminum sulfate for 2
It was impregnated with an aqueous solution containing 0 wt%, air-dried, and calcined at 500° C. for 2 hours to obtain a catalyst.

Example 3 A catalyst was obtained in the same manner as in Example 2, except that the aqueous aluminum sulfate solution in Example 2 was replaced with 20 wt % of an aqueous magnesium sulfate solution (MgSO+).

Example 4 The aluminum sulfate aqueous solution of Example 2 was mixed with ethyl silicate (S
i (OC2H)4) and obtained a catalyst in the same manner.

Example 5 A metatitanic acid slurry containing 30 wt % titanium oxide was evaporated to dryness, dried at 150° C., and pulverized to obtain titanium oxide powder. After baking this powder at 500℃ for 2 hours, add 200g of ammonium metavanadate to 12.9g of ammonium metavanadate.
24.3 g of ammonium molybdate and 100 g of water
was added and evaporated to dryness while heating and kneading. This is 45
After calcining at 0°C for 2 hours, the mixture was pulverized and then pressure-molded into a size of 5φ×5 cranes to obtain a catalyst.

Example 6.7 A catalyst was obtained in the same manner as in Example 5 except that the firing temperature of the titanium oxide powder was changed to 300°C and 700°C.

Comparative Example 2 A catalyst was obtained in the same manner as in Example 5 except that the titanium oxide powder of Example 5 was only dried at 150° C. without being calcined.

Example 8 200g of titanium oxide powder dried at 150°C from Example 5
70 g of ethyl silicate was added to the mixture, heated and kneaded, evaporated to dryness, then calcined at 400° C. for 2 hours and pulverized to obtain a powder.

A plate-shaped catalyst was obtained using 200 g of this powder in the same manner as in Example 5, except for the same procedure as in Example 5.

Example 9 A catalyst was obtained in the same manner as in Example 5 except that ammonium paratungstate was dissolved in an aqueous hydrogen peroxide solution and an equimolar amount was added instead of ammonium molybdate in Example 5.

Examples 10 to 12 Catalysts were obtained in the same manner as in Example 5, except that in place of ammonium metavanadate, copper nitrate, iron nitrate, and manganese nitrate were added in equal moles.

In order to clarify the effects of the present invention, the pore volume of each catalyst in Examples and Comparative Examples was determined by the BET method using N2 adsorption at liquid N2 temperature for 100 Å or less, and by the mercury intrusion method for 100 Å or more. The total pore volume was taken as the total pore volume. In addition, a life test was conducted under the conditions shown in Table 1. These conditions simulate coal exhaust gas denitrification conditions by containing arsenic oxide (AS203) as a heavy metal compound in coal in the gas.

Table 1 and Table 2 also show the total pore volume of Examples 1 to 12 and Comparative Example 1.2, the ratio of pore volume of 30 Å or less to the total pore volume, and the results of the life test.

Table 2 below shows that the catalyst of the present invention exhibits little decrease in activity in the life test and has excellent durability.

〔Effect of the invention〕

According to the present invention, high denitrification performance can be maintained for a long period of time even with exhaust gas containing a large amount of vapor of heavy metal compounds, and a denitrification device with a small amount of catalyst can be realized. In particular, in the case of the Tenryu ring boiler shown in Figure 1, the heavy metal vapor concentration is extremely high.
In the conventional method using a catalyst, it is estimated that the amount of catalyst is required to be two to three times the normal amount, whereas in the present invention, there is almost no need to increase the amount of catalyst.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a boiler having a Tenryu ring, which is an example of the object of the present invention. 1... Furnace, 2... Energy saver, 6... Air preheater,
7...Electrostatic precipitator, 8...Chimney, 9...Tenryu Kanro. Agent Patent Attorney Takenaga Kawakita

Claims (1)

[Claims] (1) Consisting of titanium oxide, an oxide of one or more elements among vanadium, copper, iron, and manganese, and an oxide of molybdenum or tungsten, the unit of the catalyst is the sum of the moles of the oxides of molybdenum or tungsten. 2 x 10^-^6 to 20 x 10^-^6 mol/m per specific surface area
^2, the total pore volume is 0.2 ml/g or more, and the pore volume with a diameter of 30 Å or less is 2 of the total pore volume.
A catalyst for catalytic reduction of nitrogen oxides using ammonia as a reducing agent, which is adjusted to have a concentration of 5% or less.