JPS6048124A - Process for removing oxides of nitrogen - Google Patents

Abstract

PURPOSE:To prevent decrease of decomposing capacity for NOX even in the absence of SOX, by using catalyst supporting vanadium pentoxide on titanium dioxide carrier and contd. metal sulphate. CONSTITUTION:Catalyst prepd. by allowing to support vanadium pentoxide on titanium dioxide carrier and incorporating metal sulphate such as nickel sulphate, manganese sulphate, cobalt sulphate, etc. of further >= one kinds of tungsten trioxide and molybdenum trioxide, is preferred. Nickel sulphate is most preferred among metal sulphates. Suitable compsn. is 70-99wt% titanium dioxide, 0.1-10wt% vanadium pentoxide, 0-15wt% >= one kinds of tungsten oxide and molybdenum trioxide, and 0.1-5wt% metal sulphate. Metal sulphates are incorporated by kneading or impregnation, but is must be calcined in the final stage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing nitrogenous substances contained in industrial flue gas such as flue gas and nitric acid plant tail gas. More specifically, the present invention relates to a method for removing glLl oxygen substances from exhaust gas that does not contain SOx.

In recent years, many attempts have been made to eliminate nitrogen oxides from industrial exhaust gas as mentioned above. - When carbon oxide, hydrocarbons, hydrogen, etc. are used as reducing gases, they react with oxygen in the process gas, so not only do they require a large amount of reducing gas, but they also generate a large amount of heat and produce ammonia as a by-product. Since there are disadvantages such as the accompanying disadvantages, a method is generally attempted in which ammonia, which does not have these disadvantages, is used as a reducing gas and reacted selectively with nitrogen oxides.

The present invention provides an excellent mercury that uses ammonia as a reducing gas to reduce nitrogen oxides to water and nitrogen, rendering them harmless. Precious metals such as platinum are well known as catalysts used in shikihara genketsu, which uses ammonia as the reducing gas. (USP2.975.0
22) However, your catalyst is expensive, causes the phenomenon of by-products such as N20, and has disadvantages such as being poisoned by sulfur oxides in exhaust gas. In addition, various base metal catalysts have been proposed to overcome the drawbacks of rotten catalysts.

For example, vanadine oxide, molybdenum oxide, tungsten oxide CU, SP3.279. @84. ), manganese oxides, iron oxides, vanadium oxides and molybdenum oxides, iron and manganese oxides (GPL, 253
．． 685), copper oxide (USP 3.524.721),
Vanadine oxide and oxides of copper, tin, chromium, titanium, etc.
#A oxide and or sericum oxide (Tokumen 49-77881)
, chromium oxide and oxides of tin, titanium, etc.
-2668) etc.

These base metal oxides are usually used supported on a known carrier such as activated alumina.

However, the influence of water on the activity of these catalysts,
It has drawbacks in deterioration due to certain L/IVi sulfur oxides, selective reduction of ammonia, and decomposition characteristics of excess ammonia. Furthermore, it has been reported that the cause of catalyst deterioration is not only the deterioration of the base metal oxide itself, but also deterioration due to thermal deterioration of the carrier and sulfur dioxide gas. (October 1949 Environmental Pollution Seminar, Text, Okayama University, Kasaoka Ceremony Presentation) Therefore, in order to eliminate future drawbacks, various researches were carried out, and as a result, transition metal oxides were used as a carrier mainly composed of titanium oxide. Catalysts supporting one or more of these have been developed and put into practical use industrially.

However, depending on the type of exhaust gas, it is still far from perfect.
In particular, when removing NOx from exhaust gas that does not contain SOx, a catalyst in which titanium oxide is supported on oxidized (Nadicum) is currently used, but it has the following problems.

That is, the titanium oxide supports currently in practical use are
This serves as an active site for the reaction NO+NH8+70,1-N11+HIlO, and NOx is effectively decomposed.

However, in exhaust gas that does not contain SOx, the SO7 is scattered into the mechanical gas by the gas flow, resulting in a decrease in active sites and a drawback that the NOx resolution deteriorates over time. In addition, when treating exhaust gas containing SOx, the SOx in the exhaust gas, especially SOs, is the SOx contained in the catalyst. The above-mentioned decrease in activity is not observed due to the adsorption equilibrium relationship with NH.The phenomenon described above occurs in exhaust gas that does not contain SOx, especially at temperatures above 350°C, where oxidative decomposition of NH begins. It will be done.

As a result of various studies, the inventors of the present invention have found a method for removing NOx in which the NOx decomposition ability hardly decreases over time even when used with exhaust gas that does not contain SOx, and have completed the present invention.

The method according to the present invention uses a catalytic metal jtI sulfate, such as nickel sulfate, containing panadicum oxide supported on a titanium oxide carrier.
In this method, a catalyst containing manganese sulfate or copal sulfate, or a catalyst containing at least one of tungsten oxide and molybdenum oxide is used.

Among metal sulfates, nickel KM acid is particularly effective in this case.

The proportions of each component in the catalyst are preferably within the ranges shown below.

The carrier whose main component is titanium oxide is 70% in terms of titanium oxide.
~99% by weight, panadicum oxide 0.1-10% by weight,
One or more of tungsten oxide and molybdenum oxide is 0-1
5% by weight, and metal sulfates range from 1 to 5% by weight.

When the catalyst preparation method is (1) kneading method, the metal sulfate can be incorporated using a precursor such as panazicum oxide or monomonicum metavanadate, a precursor such as tungsten oxide, molybdenum oxide, ammonium tungstate, ammonium molybdate, etc. The body, metal sulfate, and titanium oxide are kneaded, formed into a predetermined shape by extrusion, granulation, etc., and fired.

(2) In the impregnation method, titanium oxide is formed into a predetermined shape by extrusion method, granulation method, etc., and the fired product is dissolved in the vanadium oxide, tungsten oxide, or molybdenum oxide precursor and metal sulfate. impregnated in a solution of
Dry and fire.

Although these are typical methods, it goes without saying that other general catalyst preparation methods can be applied.

Further, a method for removing NOx in exhaust gas using the catalyst according to the present invention is as follows.

This can be carried out by bringing exhaust gas containing nitrogen oxides into contact with the above catalyst at 150°C to 500°C in the coexistence of ammonia.

This will be explained in detail below using examples.

The performance test of the prepared catalyst was carried out in a Pyrex glass tube with an inner diameter of 50 mm (the outside is kept warm) with an apparent capacity of 8.
The reactor was filled with 6 me of catalyst and brought into contact with a mixed gas having the composition shown in Table 1 below at a space velocity of 15 tO00Hr-'' (room temperature equivalent) to measure the nitrogen oxide removal rate in the mixed gas.

Note that the nitrogen oxide removal rate m is expressed by the following formula.

Table 1 Example 1 The metatitanic acid cake obtained from the titanium oxide manufacturing process using the sulfuric acid method was recovered as titanium oxide by IFf, and baricum chloride (Ba C1B, 2Hg) was added to the metatitanic acid.
O) Add 42 f and stir thoroughly. After drying the kernel slurry at 100 tlZ, it was baked in the dark at 600°C for 3 hours.

The obtained fired product was pulverized using a temple mill and the particle size was adjusted to obtain about 11 molded titanium oxide products. This molded product was heated to 100°C.

The mixture was dried for 12 hours and then calcined at 500°C for 3 hours to obtain a titanium oxide spherical support IA'.

500 d of this carrier, 280 y of ammonium metatungstate aqueous solution (WO, containing 5o96), 10 y of vanadyl chefate aqueous solution (VBO, containing 2o96)
A catalyst was obtained in which Ti01 was 1:91 by making up 202 to 11 as 0p and nickel sulfate.

The denitrification rate is determined at reaction temperatures of 250°C, 300°C, and 350tE.
81.0515 93.7% 95.9 respectively in Ic
%Met.

Examples 2 to 6 Catalysts having the compositions shown in the table below were obtained in the same manner as in Example 1.

Example 7 As in Example 1, V, 05: WO,: MnSO4: Ti01 =
A catalyst having a ratio of 1:7:2:90 was obtained.
The denitrification rate was 74.5% at reaction temperatures of 2500°C, 300°C, and 350°C.

They were 89.4% and 927%.

Example 8 In the same manner as in Example 1, a catalyst was obtained in which V, θs: WOg: CoSO4:Ti01=1near:2:90. The denitrification rate is determined by the reaction temperature of 2.
501 75.2% each for 30CF and 35CF
.

It was 89.896.93.2%.

patent applicant

Claims (4)

[Claims] In order to remove nitrogen oxides from exhaust gas containing unoxidized substances (1), the exhaust gas is transferred to a catalyst in which panadicum oxide and metal sulfate are supported on a carrier mainly composed of titanium oxide in the coexistence of ammonia. A method of selectively removing nitrogen oxides by contacting at a temperature of 150°C or higher and 500°C or lower. (2) When removing nitrogen oxides from exhaust gas containing nitrogen oxides, the exhaust gas is transferred to a carrier containing titanium oxide as a main component in the coexistence of ammonia with #2 panadicum, metal sulfates, tungsten oxide, and molybdenum oxide. A method for selectively removing nitrogen oxides by contacting the catalyst at 150°C or higher with one or more supported catalysts. (3) The method according to Claims 11+1 and 2, wherein the metal sulfate is one or more of nickel sulfate, WLFI12 manganese, and cobalt sulfate. (4) The carrier mainly composed of titanium oxide is 70 to 99% by weight in terms of titanium oxide, and the amount of panadicum oxide is 0.1 to 10% by weight.
3. The method according to claim 1, wherein the content of one or more of tungsten oxide and molybutylene oxide is 0-15% by weight, and the metal sulfate is 0.1-5% by weight.