JPH01151940A - Catalyst for removal of nitrogen oxides - Google Patents

Abstract

PURPOSE:To remove nitrogen oxides in a flue gas at a high efficiency even in case that mole ratio of NO/NO2 is unbalanced by making a catalyst composed of titanium oxide, vanadium oxide and tungsten oxide support a composite oxide of copper oxide and chromium oxide. CONSTITUTION:As a catalyst for ammonia catalytic reduction process of nitrogen oxides in a combustion gas such as boiler flue gas, titanium oxide constitutes the first component and vanadium oxide and tungsten oxide the second component. A composite oxide of copper oxide and chromium oxide is made to support by the aforementioned catalyst as the third component. The catalyst thus obtained removes nitrogen oxides in the flue gas at a high remove rate even in case that mole ratio of NO/NO2 is deviated particularly to <=1.0.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a catalyst for removing nitrogen oxides contained in combustion exhaust gas such as boiler exhaust gas.

[Conventional technology]

Heavy oil and coal-fired boilers, combustion furnaces attached to various chemical equipment,
Methods for detoxifying nitrogen oxides (hereinafter referred to as Box) in exhaust gas from steel plants, nitric acid plants, and internal combustion engines such as diesel engines and turbines include adsorption methods,
Oxidation absorption methods, solidification collection methods, catalytic reduction methods, etc. are known.

Among these, the catalytic reduction method, which does not require post-treatment, is economically and technically superior.

Among the catalytic reduction methods, the selective catalytic reduction method, which is not affected by the presence or absence of oxygen in the exhaust gas, facilitates the denitrification operation and is technically superior. One method is to add ammonia and perform catalytic reduction to decompose NOx in exhaust gas into harmless nitrogen and water, which has been industrialized as the most economical and effective method, and is currently in use. Nine plants are in operation.

Catalysts used in this method include tungsten oxide, vanadium oxide, molybdenum oxide, iron oxide, etc. supported on titanium oxide as the 9 catalyst (Japanese Patent Publication No. 57-36012), and cerium oxide supported on titanium oxide as the 9 catalyst (Japanese Patent Publication No. 57-36012). i35
59) etc. are known. In addition to catalysts using titanium oxide as a carrier, there is also a catalyst in which vanadium oxide is supported on aluminum oxide with a high specific surface area (Japanese Patent Publication No. 56-44778), but it is suitable for the treatment of exhaust gas containing sulfur oxides such as heavy oil and coal combustion exhaust gas. Specifically, a catalyst using titanium oxide as a carrier is superior in terms of resistance to poisoning by sulfur oxides.

Among these, the titanium oxide-vanadium oxide-tungsten oxide catalyst has high activity and excellent durability, so it is used as a catalyst for removing nitrogen oxides in many actual plants.

[Problems to be Solved by the Invention] In an actual plant using a titanium oxide-vanadium oxide-tungsten oxide catalyst, a phenomenon has been observed in which the IJOX removal efficiency changes in response to changes in the operating conditions of the exhaust gas generation source. No about NOx in this slick exhaust gas.
When we measured the concentration of J4110x by separating it into ``HMO'' and ``Not'' in a steady state, we found that most of J4110x existed in the form of HAMO, and although a high removal efficiency was obtained, in an unsteady state, t'! It became clear that most of the NOX was present at 1 dol and only a low removal efficiency could be obtained.

In order to investigate this phenomenon in more detail in the laboratory, the present inventors investigated the reaction of titanium oxide-vanadium oxide-tungsten oxide catalyst between NO and NH, the reaction of a mixed gas of no and Not with As a result of conducting experiments on the reaction with [1], it was found that the reduction reaction by Box OMHz proceeds according to the following equations (1) to (3), and that the NOx removal efficiency changes significantly depending on the abundance ratio of No and No. understood.

410 + 4MB, + o, → 4
N, + 6H, O---(1) No + NO1
+ 2 MH, → 2N, +311. O・・
・ (2) 6Mo, +ann, →
7N. It was found that when the molar ratio of no/so is below to, dNo/No gradually decreases as the ratio becomes smaller, and when 13of shown in equation (3) is used alone, it decreases markedly. FIG. 1 shows a graph of the NOx removal efficiency of this No-No1 mixed system.

As described above, when using the conventional titanium oxide-vanadium oxide-tungsten oxide catalyst, there is a drawback that the NOx removal efficiency is significantly reduced when the N07M01 molar ratio is less than 0 or when HOI is used alone.

The present invention solves the drawbacks of the conventional method for removing Nag from exhaust gas, and especially No/! 3o, it is an object of the present invention to provide a catalyst for removing nitrogen oxides from exhaust gas that can maintain a high removal rate even when the molar ratio is biased to 1.0 or less.

[Means for solving problems]

The present inventors discovered that NOx in exhaust gas (No in D, is NO/
When the IJO1 molar ratio is biased to 1.0 or less, N
As a result of extensive research into improving conventional catalysts that reduce Ox removal efficiency, we have developed a catalyst in which steel oxide and chromium oxide are supported in the form of a composite oxide on the conventional titanium oxide-vanadium oxide tungsten oxide catalyst. It was discovered that the present invention is not affected by changes in the concentration of No in exhaust gas, and the present invention was completed.

That is, the catalyst for removing nitrogen oxides of the present invention contains titanium oxide as the first component, vanadium oxide and tungsten oxide as the second component, and a composite oxide of copper oxide and chromium oxide as the third component. That's what happens.

In order to prepare the above-mentioned titanium oxide-vanadium oxide-tungsten oxide-steel oxide/chromium oxide composite oxide-containing catalyst, the titanium sources must first be inorganic titanium compounds such as titanium chloride and titanium sulfate, titanium oxalate, and tetraalcohol. You can choose from organic titanium compounds such as cutitan. As a vanadium source, vanadium oxide,
Among vanadyl sulfate, vanadyl oxalate, ammonium metavanadate, etc., ammonium haharatungstate, ammonium metatungstate, etc. can be selected as the tungsten source. Next, the copper source can be selected from copper sulfate, steel nitrate, etc., and the chromium source can be selected from chromium sulfate, chromium nitrate, chromic acid, ammonium dichromate, etc. Furthermore, in order to improve the formability and strength of the catalyst, clay-based inorganic substances such as montmorillonite, acid clay, bentonite, kaolin, halloysite, and sericite, glass wool, glass fiber, rock wool, etc.
A carrier may also be used by adding an inorganic fibrous material such as Kao wool. However, from the point of view of catalytic activity, it is preferable that these additives be added in an amount of 50 wt% or less based on the main component of the carrier.10 Generally, vanadium oxide and tungsten oxide are used in proportions of 1 to 1 titanium oxide, respectively. α001~α1, α01~
α2. In order to obtain good catalytic activity, the compounding ratio of the composite oxide of a copper compound and a chromium compound added as the third component should be 1 to 1 of titanium oxide (LOO2~
IIL2, preferably in the range of 101 to α1. By selecting the shape of the catalyst of the present invention, a fixed bed,
Although either a moving bed or a fluidized bed reactor can be used, the reaction temperature is usually 200 to 600°C, preferably 250 to 450°C. The reaction time is 2000 to 101011LOO per cubic meter of catalyst]
The ON range is selected. The reaction pressure is not particularly limited as it can be carried out at atmospheric pressure, reduced pressure or increased pressure.

This will be explained in detail below using Examples.

<Example 1> 12.9 F of ammonium metavanadate and 1 aOf of ammonium paratungstate dissolved in water were added to 625 t (Tie, 2 oor) of metatitanic acid slurry, and the resulting slurry solution was evaporated to dryness.

It produces nine solids.

Additionally, ammonium dichromate ((NH*)tCrm
Nitric acid steel Ccu was added to a solution in which O,]44f was dissolved in 100-water and further ammonia water (28-chi solution 46-) was added.
A solution prepared by dissolving OO) m-3H@o]42t in 100-g water was slowly added dropwise, and after the addition was completed, stirring was continued for 60 minutes. During this time, a small amount of ammonia water is added dropwise to maintain the pH of the solution at &7. A slurry solution 1F is produced.

Next, thoroughly knead the cake containing the solid mixture and slurry solution B using a kneader. After mixing, extrude into a rod shape with a diameter of 3 cm, 12
After drying at 0°C for 6 hours, it was fired at 450°C for 5 hours. The obtained catalyst had a weight ratio of Ti01:V2O5:WOI
: (OuO"0rlO1) -1:α05:108:
(Has a composition of LO2.

For comparison, a catalyst was prepared in the same manner as above by adding water only to the solid mass. The obtained catalyst has a weight ratio of Tie
,: vlog: WQ, = 1: (LO5:(LO8
(hereinafter referred to as the catalyst of Comparative Example 1).

1 + 226t solid chromium oxide and 2 chromium oxide? and 2 tons of copper oxide were added to prepare a catalyst in the same manner as in the following examples.

The weight ratio of Ti01 to the obtained catalyst was 710@
: WOI : auo :
Qr, Q, = x 1: (LO5:
It has a composition of 108=101:101 (hereinafter referred to as the catalyst of Comparative Example 2).

(2) Nitrogen oxide removal test The catalysts of the present invention and comparative series prepared as described above were directly tested at @3
, a cylindrical shape with a length of 5 to 5 cm, and this was filled into a small quartz reactor with an inner diameter of 24 mm, and S'V 2 (LO00 hr
A denitrification activity test was carried out using the following gas composition.

(Gas composition 1) (Gas composition 2) No: 1
90ppm No: 10ppmNo
l: 10ppm No.: 190p
pmNHs: 200ppm NHB:
200ppmOR: 5% 0. :5% Co! :12 Yu CO: 12%H! O:
9% H, O: 9% N,: remainder
! ! Heavy: The NOx level at the inlet and outlet of the remaining reactor was measured using a chemiluminescence Box analyzer. The results are shown in Table 1.

As is clear from Table 1, the catalyst according to the present invention has a gas composition of 1
Both show good activity (mow removal rate) for gas composition 1 and 2, but the comparative catalyst shows high activity for gas composition 1, but low activity for gas composition 2, especially at 25 cc and reaction temperature. is noticeable when the temperature is relatively low.

Examples 2 to 6 In the same manner as in Example 1, five types of catalysts of the present invention were prepared by varying the addition TFT of ammonium dichromate and steel nitrate.

Using these catalysts and gas having gas composition 2, the relationship between reaction temperature and nitrogen oxide removal rate was determined in the same manner as in Example 1. The results obtained are shown in Table 2.

As is clear from Table 2, implementation rows 2 to 6, i.e. Ti0
1: V cooperation 0@: WOB: 0u
OOrlO1= 1: a-mouth 5: (LO8:
(High i activity was obtained within the range of LOO2~(L2).

[Effects of the Invention] By using the catalyst of the present invention, it is possible to remove nitrogen oxides in the exhaust gas, in which most of the nitrogen oxides are contained as nitrogen dioxide, with a high removal rate similar to that of nitrogen monoxide. .

[Brief explanation of the drawing]

FIG. 1 is a chart showing the effects of the catalyst of the present invention.

Claims (1)

[Claims] In a catalyst that catalytically reduces nitrogen oxides in exhaust gas in the presence of ammonia, the first component is titanium oxide, the second component is vanadium oxide and tungsten oxide, and the third component is copper oxide and chromium. A catalyst for removing nitrogen oxides from exhaust gas, characterized by containing a composite oxide of oxides.