JPS58183946A - Denitration catalyst and preparation thereof - Google Patents

Abstract

PURPOSE:To reduce SO2 oxidizing catacity without lowering denitration capacicy, in a TiO2.WO3.V2O5 denitration catalyst comprising a composition containing catalytic components in a specific ratio, by increasing the concn. of V2O5 only in the surface layer part of said catalyst. CONSTITUTION:This catalyst has such a composition that WO3 is 2-12wt% to TiO2, V2O5 is 0.1-3wt% to TiO2 and the remainder is TiO2 and the concn. of V2O5 is made high only in the surface layer part thereof. This catalyst is prepared by a method wherein a kneaded molded body consisting of TiO2 and WO3 is immersed in a V-containing solution and the impregnated molded body is rapidly dried to be baked. The obtained catalyst is adapted to an exhaust gas containing sulfur oxide easily converted to catalyst poison or soot other than nitrogen oxide and develops the function thereof in good efficiency without receiving influence of the above-mentioned poisoning component in removing nitrogen oxide in a harmless state by subjecting the same to catalytic reduction under a proper temp. by using ammonia as a reducing agent to convert the same to nitrogen and water and suppresses reaction oxidizing SO2 to SO3.

Description

[Detailed Description of the Invention] A combustion furnace attached to various chemical equipment including humidity. Nitrogen oxides (hereinafter referred to as NOx) are contained in exhaust gas from steel plants and internal combustion engines such as diesel engines and turbo engines.
The present invention relates to a method for preparing a denitrification catalyst that effectively and economically reduces and renders denitrification harmless. In particular, the present invention
In addition to Ox, sulfur * oxides (hereinafter referred to as SO
This method is commonly used for exhaust gases containing soot and soot, and catalytically reduces NOx at moderate temperatures using acinania NH as a reducing agent, converting it into nitrogen N, and water H and O, rendering it harmless. When removing it. The present invention provides a catalyst that efficiently performs its functions without being affected by the above-mentioned poisoning components and that suppresses the oxidation reaction of sulfite residue SO to sulfur trioxide SO.

The present inventor has previously recommended that it is good to add a small amount of 5um lunar pentoxide VIOs to the main ingredients of anatase-type titanium oxide TiO, and M-type titanium oxide WQ.
Other TIO, -M. Many patent applications have already been filed for catalyst compositions such as O, -V2O, etc.

In contrast, from the viewpoint of a catalyst preparation method, the inventors of the present invention have attempted to crystallize (maintain) denitrification performance with a hemi-cam-shaped catalyst that is frequently used as a catalyst for removing NOx from exhaust gas containing dust.
In addition, we have discovered a denitrification catalyst that suppresses SO and oxidation performance, and a method for preparing the same, in order to minimize corrosion and radical opening caused by acidic ammonium sulfate in downstream equipment of a denitrification device.

First, the denitrification reaction in the catalyst starts from the surface of the gas contact part.
A coating type catalyst in which catalyst components are adhered and supported on a gycovite honeycomb-like base material. This was confirmed by the test. (See Figure 1) Furthermore, the side reaction in which S02 is converted to SO in the presence of O2 in the exhaust gas is rate-limited by gas diffusion like the denitrification reaction (because the catalyst itself also suppresses the SO2 oxidation reaction). It was revealed through reaction analysis using a bracket-type catalyst that the reaction rate in the entire catalyst layer is rate-determining.

Therefore, if one or more analysis results are used for a solid type catalyst composed only of catalyst components.

Tie,, WO, is uniformly distributed in the catalyst formation layer,
Sensitive to SO6 oxidation reaction and excellent denitrification activity■20
It can be seen that it is best to distribute as much as possible within 200 μm from the surface in contact with the gas. Coal-fired boiler exhaust gas contains a large amount of dust, such as sand and dust, and the catalyst used for this must be highly resistant to corrosion, so solid-type catalysts are preferred over coat-type catalysts as mentioned above. is more commonly used because it has a thicker catalyst layer.

8 In the following, the present invention will be explained using a honeycomb-shaped solid catalyst, but the present invention can also be applied to catalysts such as one particle or one cylinder, and even coated catalysts can be used even closer to the surface layer.
Even lower SO by carrying VCVtOs! It is possible to increase the oxidizing ability.

Generally, catalysts are fired at 600 to 650°C II6@ to impart V resistance.
, O, in the coexistence state, v, 0. In order to transform the anatase type of Tie into the rutile type, in the present invention, Ttot#:
After the molded body or Tidy-WO3 kneaded body is fired at the same temperature, *VtOs is supported by an impregnation method.

and v, 0. By using the preparation method of the present invention when supporting ■, 0. This makes it possible to distribute a large amount of particles near the surface of the molded body.

One of the preparation methods is to calcinate a honeycomb molded body made of Tie, WO, in a heated solution of citric acid, vanadyl sulfate, a solution of citric acid, etc. ,0. By thoroughly immersing the molded body in a solution containing evaporated water and then drying it in as short a time as possible without causing cracks in the molded body, V, O, and O are molded together with the evaporated water. This can be achieved by utilizing a type of adhesive phenomenon that tends toward the surface of the body. At this time, methods for increasing the Vtoell degree of the surface layer include a method of immersing the molded body made of Tidy + Wow in the vanadium-containing liquid in a semi-dry state, and a method of instantly immersing the molded body in a dry state in the vanadium-containing liquid m.
! i! There is a method of crushing it to prevent it from entering the inside of the molded body.

Another method is 20. by chemical reaction inside the molded body. is densely supported near the surface layer of the molded body. That is, a molded body made of TiO2 and WO3 is treated with dilute acid, then part of the moisture near the surface layer is removed by air drying or a combination of hot air drying, and then immersed in a vanadium amici solution to carry out a neutralization reaction between acid and alkali. This is a method of supporting Vt as near the surface layer of the molded body by utilizing metavanadium y-a:
Jv: Nium is heated and dissolved in an amino alcohol such as diethanolamine or t-methylamic acid. The dilute acids used here include hydrochloric acid, sulfuric acid, iron acetate, and sychoic acid. In addition, as a method of utilizing the neutralization reaction inside the molded product, the molded product is treated with acetic acid water, left in a semi-dry state, and then treated with vanadyl oxalate or vanadyl sulfate. A method of immersing it in an acid powder solution containing vanadium is also considered, but ammonia tends to turn into a gas phase (1) In the normal V4 manufacturing method, it is sealed as ammonia inside the molded body (this is difficult to do, so it is difficult to put it into practical use). Not the point.

The inventors have already developed Tr02 r WOs l v10
! Honeycomb catalyst composition consisting of WO to Tidy K
2 to 10 wt% of l + 005 to 3 wt% of V, O,
It is proposed that it is preferable to obtain high denitrification performance and low SO2 oxidation performance. (Special application 1977-077
818) However, according to the present invention, ■, 0. Don't lower the denitrification performance just by increasing the mutual concentration.
So, it becomes possible to reduce the oxidation performance.

The present invention will be specifically described below with reference to Examples.

[Actual A'fli 1] Anatase-type T produced from titanyl sulfate as a raw material
A honeycomb molded body (hole shape: square, opening: 6.0mg++, wall thickness: 165mm) consisting of iO and WO5 was immersed in a vanadyl sicolate solution for 30 minutes, and then dried in a hot air dryer set at 110°C for 5 hours. The catalyst was dried and then calcined at 450° C. for 3 hours to obtain a honeycomb catalyst A containing 0.5 parts of V and O based on 290 parts of Ti and 310 parts of W. In addition, as a comparative catalyst, the above-mentioned honeycomb molded body was immersed in vanadyl sikolate bath iK and then air-dried at room temperature for 1 day.
Dry for 5 hours in a dryer heated at C/Mi11.

Further, catalyst B was prepared by calcining at 450°C for 3 hours.

In order to investigate the vanadium concentration distribution of catalysts A and H, ray analysis was performed using an X-ray microanalyzer, and as shown in Figure 2, it was found that ``■'' was distributed in high concentration near the surface layer of the honeycomb formed body. On the other hand, catalyst B is distributed almost uniformly throughout.

Furthermore, in order to investigate the activity of Catalysts A and H, IK poplar exhaust gas was used to perform all the denitrification and SOt conversion performance under the test conditions shown in Table 1. As shown in Table 2, Catalyst A was superior to Catalyst B. High activity and low SO, fI! It was found that it has the ability to

Table 2 C Example 2] In Example 1, the effect of reducing SO and oxidation performance was not significant, so it was not practical, but V, O, and Ti as a support layer were used.
e, 4 for a honeycomb formed body of 90 parts W0.10 parts
Catalyst C was prepared in the same manner as catalyst A in Example 1 in terms of wt%, and a catalyst C was prepared as a comparative catalyst in the same manner as catalyst B in Example 10, except that the catalyst violet shown in Table 1 was destroyed. When the catalyst performance was evaluated using the same method as in 1, catalyst C had a denitrification rate of 755%, SO and oxidation forces were 2.8%, and catalyst C had a denitrification rate of 4755 and a S false oxidation rate of 59%.

■、0. There is no difference in denitrification performance when the degree of fineness is as high as 4wt, but the SO7 oxidation performance is lower than that of the surface layer. The amount of Catalyst C with increased concentration was much smaller, clearly demonstrating the effectiveness of the present invention.

[Example 3] The Tie, r WOB molded body of Example 1 was immersed in a 1N dilute sulfuric acid solution, dried at 50C for 1 hour, and metapanaji:
/Acid acid [Nirimu is immersed in a bath solution heated with 7-ethanol acid. Then, the temperature was increased to 110°C by the usual method.
Catalyst E containing the same amount of catalyst components as in Example 1 was obtained by drying for 10 hours at 450C and calcining for 5 hours at 450C.
As a result of planning in the same manner as in Example 1, the denitrification rate was 9468%, S
O, #R became 404 chi.

As described above, according to the method of the present invention, by intentionally increasing the VzOs of the surface layer of the molded article by 11 degrees, it has higher bacterial activity and lower SO2 oxidation performance than the conventional TiO2-WOB-V, O8 catalyst. The ability of hJ to provide a denitrification catalyst with

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the catalyst layer thickness effective for the denitrification reaction, and FIGS. 2 and 6 are explanatory diagrams of the concentration distribution of W and ■ in catalysts A and B.

Claims (1)

[Claims] +1) WQ in the composition is 2 to 12W for Tie.
tchi. ■20. is 01-3wt for Ti 02, and the rest is T10. , and the concentration of VtO (high only in the surface layer) is a denitrification catalyst characterized in that it is used for catalytic reduction of nitrogen oxides in exhaust gas by acinanium. +21 Kneading of Tie and WO. A method for preparing a denitrification catalyst characterized by immersing a molded body in a vanadium-containing solution, rapidly drying it, and then firing it. A method for preparing a denitrification catalyst, which comprises firstly immersing it in an alkaline solution containing Luna-5U, drying it, and then firing it.