JPS5911340B2 - Improved shaped catalyst for nitrogen oxide purification - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a shaped catalyst for removing nitrogen oxides (nitrogen monoxide, nitrogen dioxide, etc., hereinafter referred to as NOx) from exhaust gas.

Specifically, the present invention reduces NOx in exhaust gas containing a large amount of dust, such as exhaust gas from heavy oil-fired or coal-fired boilers, cement factory or sintering furnace exhaust gas, to harmless nitrogen using a reducing agent such as ammonia. This invention relates to improvements in dust-free molded catalysts.

More specifically, the present invention provides the above-mentioned NOx purification catalyst by welding and carrying a molten substance having catalytic activity on the end face facing the gas flow direction of the catalyst gas inlet side contact part, so that wear and tear due to dust is prevented. NOx that becomes minor
This invention relates to improvements in shaped catalysts for purification.

Exhaust gas from heavy oil-fired or coal-fired boilers, cement factories, or sintering furnaces contains a large amount of dust, and countermeasures against this dust are a priority issue in order to purify the NOx contained in these exhaust gases. be.

In particular, after removing as much dust as possible from the exhaust gas, NO
Since purification of x incurs various economic disadvantages, in recent years, a process in which dust-containing exhaust gas is directly passed through a catalyst layer and subjected to a NOx purification reaction has become dominant.

A suitable catalytic process for this purpose is to increase the particle size to increase the space inside the catalyst packed bed and allow dust to pass through, or to move the dust to the catalyst surface. Methods that have been proposed include blowing or sieving off the dust, and switching the flow direction of the exhaust gas to remove the dust adhering to the catalyst in reverse flow, but both methods are complicated in terms of process, but they can achieve the desired effect. Many of them are insufficient.

Various attempts have therefore been made to change the shape of the catalyst to facilitate the passage of dust and reduce the amount of dust adhering to the surface of the catalyst.

For example, a rod-shaped catalyst with a representative diameter of 5 to 40 mm and a length of 200 to 2000 mm, a cylindrical catalyst with an inner diameter of 5 to 30 Nn, an outer diameter of 10 to 40 mm, and a length of 200 to 2,000 mm, and an equivalent diameter of 3 to 2 mm.
0rrvn, the thickness of the partition wall separating the communication holes is 0.5 to 4
rran-, a honeycomb-shaped catalyst with an aperture ratio of 30 to 90 inches in cross section, a length in the gas flow direction of 200 to 2.000 rrrIrL, a square or rectangular catalyst with a side length of 200 to 2.000 Tran1 and a thickness of 3 to 10 mm. Catalysts are molded into various shapes such as plate-shaped catalysts, and these molded catalysts are shaped into rod-shaped catalysts, the outer peripheral surface of cylindrical catalysts, the partition wall surface of honeycomb catalysts, and the plate surface of plate-shaped catalysts. This is a process in which high deNOx (denitrification) performance can be obtained by arranging the gases in parallel with the gas flow direction at appropriate filling pitches without clogging with dust.

In the case of dust-free catalysts used in such processes, substrates with the above shapes are pre-molded using ceramic materials such as cordierite, mullite, silicon carbide, α-alumina, and γ-alumina. A method of coating or impregnating the catalyst material on the substrate is considered, but there are fundamental drawbacks such as differences in the coefficient of thermal expansion between the substrate and the catalyst material and weak mutual strength of the catalyst material on the substrate. Therefore, as a method that does not withstand long-term use and causes the least problems, a method has been considered that involves mixing the catalyst material or, in some cases, the carrier substrate raw material and the catalyst material to form the above-mentioned shape.

In general, catalytic activity is proportional to the surface area and pore volume of the catalyst, and in order to obtain a molded catalyst with high activity at low temperatures, it can be molded by extruding it without applying too high pressure or by pouring it into a pre-prepared mold. However, a method of increasing the pore volume of the catalyst is preferred.

Therefore, when trying to obtain a highly active catalyst that exhibits high performance even at low temperatures and high space velocities, the strength of the shaped catalyst is weak;
In particular, the disadvantage of being susceptible to wear cannot be avoided.

Therefore, 25 to 30? When processing coal-fired boiler exhaust gas that contains a large amount of dust such as /rrl, a large amount of dust collides with the end face facing the gas flow direction of the gas inlet side contact part of the catalyst at a high flow velocity of 2 to 30 meters/second. As a result, the catalyst wears out extremely severely, and during long-term reactions, the catalyst is severely worn out, resulting in a situation where economical operation becomes impossible.

This abrasion phenomenon does not necessarily occur uniformly on the catalyst end surface, but may occur due to slight differences in the extrusion pressure, etc. due to unevenness in the strength of the matrix of the catalyst molded body. In practical terms, there remained a serious problem in that the wear progressed and caused a huge amount of wear in a much shorter time than if the wear progressed uniformly.

In order to solve these problems, the present inventors have developed metal components used as denitrification catalyst active components, such as VX.
W, Mo XCu, Fe, Cr, Mn, Cei Sn,
Zn, Pb1Ti, Ni, CosNb, TaXpX B
X Bi The present invention was completed based on the finding that an outstanding effect on the above-mentioned problems can be obtained by increasing the strength of the catalyst base material in that part.

When supporting the molten body of the catalyst substance on the catalyst end face,
The shaped catalyst may be supported after being molded by a predetermined method and fired, or the molded product may be supported after drying and before being fired.

Melting can be easily carried out using a conventional method, such as an electric furnace or a heavy oil burner heating furnace.

Although it is possible to mechanically impregnate and support the catalyst molded material in this melt, it is also possible to use a thermal spraying method.

In the thermal spraying method, compound powder or metal powder is continuously supplied to a thermal spraying device, placed in a flame, melted and ejected at the same time, and is deposited on the end of the molded body by thermal spraying.

As equipment for general thermal spraying, powder type gas spraying equipment (e.g.
thermo spray) and plasma flame spraying equipment (e.g. plasma jet type).

In the previous device, when using acetylene-oxygen flame, approximately 3.10
Powder can be melted and ejected at temperatures as high as 0°C and approximately 2,700°C when using a hydrogen-oxygen flame.

In the rear device, a plasma flame is created using argon, nitrogen, etc., and the compound can be melted at a high temperature of 5,000°C or higher.

Both devices are of course capable of spraying metals, and metal spraying is already practiced on an industrial scale.

In the present invention, the components involved in melting include metals, oxides, carbides, nitrides, sulfates, sulfides, nitrates, chlorides,
Any of phosphates, carbonates, organic acid salts, etc. may be used, or a mixture of two or more thereof may be used.Example 1 A composite phase of titanium oxide and silicon monoxide (Ti02-Si0
2) was prepared by the method described below.

Water 80tVfC tetrachloride fta/(T i C 14
) 1 1.4 kg was gradually added dropwise while stirring under water cooling, and then 4.5 kg of Snowtex 10 (containing 20 to 21 weight coefficient as silica sol sio2 manufactured by Nissan Chemical) was added.

While maintaining the temperature at about 30°C, aqueous ammonia was gradually added dropwise while stirring well until the pH reached 7.
Furthermore, it was left to mature for 2 hours.

The thus obtained Ti02-Si02 gel was filtered, washed with water, dried at 120°C for 10 hours, further washed with water, and then dried at 500°C.
It was baked at ℃ for 3 hours.

The composition of the obtained powder was Ti02/Si0 as an oxide.
2=4 (molar ratio), BET surface area is 220rr? /?
Met.

The powder obtained here is hereinafter referred to as 1-TSj.

140 fI of oxalic acid was dissolved in 60 mm of water, and 7 1.5 r of ammonium metavanadate was added thereto. The above TS 500 f was added to the solution, mixed well, and kneaded well with a kneader.

After kneading while adding an appropriate amount of water, the outer diameter is 30rIrr.
rL1 was molded into a cylindrical shape with an inner diameter of 20 cm and a length of 500 wn using an extruder, dried at 120°C for 6 hours, and then calcined in air at 400°C for 5 hours.

The composition of the obtained cylindrical catalyst was TS:V205=90=10 in weight percentage as oxide.

Next, ammonium metavanadate placed in a porcelain crucible was heated to 750° C. in an electric furnace to melt it, and the end face of the cylindrical catalyst was impregnated into the melt and allowed to hold.

The part on which metal vanadium was supported was 5 cm deep in the center from the end face of the catalyst.

A desktop activity test was conducted on the obtained catalyst using the following method.

One cylindrical catalyst was immersed in a molten salt bath with an inner diameter of 38.87 mm.
The stainless steel reaction tube of 1Ell1 was filled, and NH3 was added to the synthesis gas having the composition shown below, which is similar to boiler exhaust gas, at a flow rate of 14.7t/min (SV3,000).
hr") into the catalyst layer, and the relationship between reaction temperature and NOx reduction rate (Q) was determined (NOx analysis was carried out using a Chemilumi 2 CLD/S model manufactured by Yanagimoto Co., Ltd.).

NO 200ppm So 2 80 0p pQl02
4 volumetric CO2 10 tt H20 10 〃 N2 Remaining NH3 200 ppm The obtained NOx reduction rate is 70% at 200℃, 250℃
76% at 300℃, 83% at 350℃, 84% at 350℃
, 86% at 400° C., and no difference was observed depending on whether molten vanadium oxide was supported or not.

The hardness of the catalyst was tested by a pencil scratch tester (JI
S-K-5400).

The hardness of the end face portion of the catalyst not supporting molten vanadium oxide was 2H, and the hardness of the end face portion of the catalyst supporting molten vanadium oxide was 9H or more.

Example 2 Titanium phosphate was prepared by the method described below.

Add 300v of 98q6 sulfuric acid to 6t of water and add 76t of titanium tetrachloride.
0g was gradually dissolved under ice cooling and stirring.

After keeping this at a temperature of 8.0℃, diluted with 3.5 tons of water.
Add 46 1fI of 5% orthophosphoric acid dropwise and leave it at 80%
It was aged for 5 hours at ℃.

After filtering the thus obtained titanium phosphate gel and washing with water,
It was dried at 0°C, washed with water, and then fired at 570°C for 3 hours.

The composition of the obtained powder is T i 02 /P as an oxide.
2 05 = 2 (molar ratio), bulk specific gravity is 0.1 5 5
f/C. C. , the pore volume is 4.14C. C. /7,
The surface area is 6 3.37? It was Z2/S'.

Note that the result of X-ray diffraction analysis was that the shape was amorphous.

On the other hand, oxalic acid 6001 was dissolved in 260 rnl of water, and ammonium metavanadate 276S' was added to the dissolved solution.The above titanium phosphate 5001 was added, mixed well, and kneaded well with a kneader.

After kneading while adding an appropriate amount of water, the outer shell is 80 mm square,
Pitch 7. 7 mm, cell wall thickness i. 7 mm (
It was molded into a honeycomb shape with an outer wall 2-3rrrIrL) using an extruder, dried at 120°C for 6 hours, and then fired in air at 400°C for 5 hours.

The composition of the obtained nicum-like catalyst was titanium phosphate:v205=70:30 in weight percentage as an oxide.

Plasma spraying of CuO powder was applied to the end face of the honeycomb-shaped catalyst described above.

The CuO powder to be thermally sprayed is 100 to 300 mesh, and the plasma gas is argon too (SCPH).
The ratio (volume) of hydrogen 4 (SCPH) to 60V
, 400 A of direct current was used.

Metallic copper was supported up to a depth of 5 mm in the sprayed area.

Regarding the obtained catalyst, a catalyst NOx reduction performance test was conducted according to Example 1, and as a result, no difference was observed depending on whether CuO was supported or not.

In addition, the hardness of the catalyst was tested according to Example 1, and as a result, C
The hardness of the end surface of the catalyst that does not support uO is 2H, and CuO
The hardness of the end face portion of the catalyst supporting the was 9H or more.

Example 3 Aqueous solution containing ammonium metavanadate 7 5.6 f% copper nitrate 8 9.3 f 60 mA! The same TS500f as used in Example 1 was added to the mixture, mixed well, and kneaded well using a kneader.

After kneading while adding an appropriate amount of water, the thickness is 5 rran.
, molded into a plate shape with a width of 160 mm and a length of 450 mm using an extruder,
Put the molded product into a mold and make it 60K4/cr! After pressing at a pressure of 100° C. and drying at 120° C. for 6 hours, it was fired in air at 400° C. for 5 hours.

The composition of the obtained plate-shaped catalyst was TS:V205:CuO=85:10:5 in weight percentage as an oxide.

Next, plasma spraying of Cu powder was applied to the end face of the plate-shaped catalyst.

The Cu powder to be thermally sprayed had a size of 100 to 300 mesh, and the plasma spraying conditions and supporting depth were the same as in Example 2.

Regarding the obtained catalyst, a catalyst NOx reduction performance test was conducted according to Example 1, and as a result, no difference was observed depending on whether Cu was supported or not.

In addition, the hardness of the catalyst was tested according to Example 1, and as a result, C
The hardness of the end face portion of the catalyst not supporting U was 3H, and the hardness of the end face portion of the catalyst supporting Cu was 9H or more.

Example 4 Oxalic acid acidic aqueous solution 6 containing 75.6f of ammonium metavanadate and 33.11f of ammonium tungstate
TS 50 02 used in Example 1 was added to 0-, mixed well, and kneaded well with a kneader.

After kneading the mixture while adding an appropriate amount of water, a cylindrical catalyst was prepared according to Example 1.

The composition of the obtained cylindrical catalyst was TS:V205:WO3285:10:5 in weight percentage as oxide.

Next, manganese dioxide was supported on the end surface of the cylindrical catalyst by a gas spraying method.

The flame is an acetylene-oxygen flame (acetylene: 13 PSI,
Oxygen: 20 PSI) was used.

The loading depth of manganese was approximately 50 mm.

Regarding the obtained catalyst, a catalyst NOx reduction performance test was conducted according to Example 1, and as a result, no difference was observed depending on whether MnO2 was supported or not.

In addition, as a result of testing the hardness of the catalyst according to Example 1, M
The hardness of the end surface of the catalyst that does not support nO2 is P2H, and M
The hardness of the end face portion of the catalyst supporting n 0 2 was 9H or more.

Example 5 A catalyst was prepared in the same manner as in Example 1 except that metallic aluminum was used instead of molten vanadium pentoxide.

There was no difference in the NOx reduction performance of the catalyst between unsupported and supported catalysts.The hardness of the unsupported catalyst was 2H.
The supported catalyst was 9H or higher.

Example 6 A honeycomb-shaped catalyst was prepared from the catalyst material of Example 1 according to Example 2.

Molten vanadium pentoxide was supported on the end face of the obtained catalyst in accordance with Example 1.

The loading depth of vanadium was approximately 58 mm.

Regarding the obtained catalyst, a catalyst NOx reduction performance test was performed according to Example 1, and as a result, no difference was observed depending on whether V205 was supported or not.

In addition, the hardness of the catalyst was tested according to Example 1, and the results showed that v
The hardness of the end surface of the catalyst that does not support 205 is 2H, v2
The hardness of the end face portion of the catalyst supporting 05 was 9H or more.

Example 7 The catalysts obtained in Example 1 and Example 4 were subjected to a durability test using actual gas.

196 cylindrical catalysts were fixed in a box-shaped reactor with a width of 210 wm, a length of 210 wm, and a length of 2000 mm in parallel with the gas flow.

NOx was removed by adding NH3 to the exhaust gas of a boiler that uses coal as fuel in this reactor.

Exhaust gas composition is NOx250-300ppm1SOx
800~1,200p'prn
3 to 4 volumes of N oxygen, 10 to 12 volumes of carbon dioxide, 10 to 14 volumes of water vapor, and the remainder nitrogen, to which NH3 is added so that NH3/NO x = 1 (molar ratio) The soot and dust contained in the exhaust gas is 25~
30S'/Nrr? It is.

The above exhaust gas is heated in advance to bring the reactor inlet temperature to 33℃.
It was set at 0° C. and supplied at 441 Ni/hr (the linear velocity corresponds to 4.9 m/sec based on the empty cylinder).

). Table 1 shows the results of the catalyst durability test.

After the 3000 hour durability test, when we took out the catalyst, we found that
A significant difference was observed between the unsupported and supported catalysts.

That is, in the case of the unsupported catalyst, the end face of the gas inlet contacting part of the catalyst layer was catalytically worn, whereas in the case of the supported catalyst, there was almost no wear.

Claims (1)

[Claims] 1. In a catalyst molded into a shape that allows dust to blow through to purify nitrogen oxides in dust-containing exhaust gas, a molten material exhibiting catalytic activity is welded and supported on the end face facing the gas flow direction of the catalyst gas inlet side contact part. An improved molded catalyst for purifying nitrogen oxides, which is characterized in that it at least prevents wear and tear of the end face of the catalyst due to dust.