JPH05154349A - Method and catalyst for removing nitrogen oxide in combustion exhaust gas - Google Patents

Abstract

PURPOSE:To decompose nitrogen oxide at relatively low temp. and to make a process compact by catalytically reacting nitrogen oxide in combustion exhaust gas with an iron silicate catalyst and a hydrocarbon reducing agent to decompose and remove the same. CONSTITUTION:Nitrogen oxide such as nitrogen monoxide or nitrogen dioxide, oxygen gas or sulfur dioxide is usually contained in the combustion gas of a gas turbine. At the time of the decomposition of this combustion gas, iron silicate used as a catalyst has a crystalline structure wherein an iron atom is substituted within a silicate skeleton in the form of a solid solution and the Si/Fe ratio thereof is 10-60. As a hydrocarbon reducing agent, propylene, ethylene, methane, ethane, propane, butane or the like are disignated. Combustion exhaust gas containing nitrogen oxide, oxygen and, if necessary, sulfur dioxide is catalytically reacted with the iron silicate catalyst and the hydrocarbon reducing agent to decompose and remove nitrogen oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing nitrogen oxides in combustion exhaust gas and an iron silicate catalyst used in the method.

[0002]

2. Description of the Related Art JP-A-63-10091
No. 9 discloses that the nitrogen oxide in the exhaust gas is removed by contacting the exhaust gas discharged from an internal combustion engine such as an automobile containing nitrogen oxide with a copper catalyst in the presence of hydrocarbons in an oxidizing atmosphere. A method of removing, and a catalyst obtained by supporting copper on zeolite etc. as a copper catalyst used in the method is disclosed, but also for applying to exhaust gas containing sulfurous acid gas and the effect in that case, There is no specific teaching about the effect when the copper catalyst is applied to the exhaust gas at a relatively low temperature around 300 ° C., or the use of the iron silicate catalyst in place of the copper catalyst.

In Japanese Patent Laid-Open No. 2-265649, a crystalline copper silicate catalyst is contacted with an oxidizing exhaust gas containing at least hydrocarbons and nitrogen oxides discharged from an internal combustion engine such as an automobile. Disclosed is a method for removing the nitrogen oxides and a crystalline copper silicate catalyst used in the method, but also for applying to an exhaust gas containing a sulfurous acid gas and the effect in that case,
There is no specific teaching about the use of an iron silicate catalyst in place of the copper silicate catalyst and its effect. When the copper silicate catalyst is used at a relatively low temperature of around 300 ° C, it is around 400 ° C. It is merely taught that the purification rate of NOx is remarkably lowered as compared with the case of using at a relatively high temperature.

"Catalyst" (Vol. 32 No. 6, 19)
(Published September 10, 1990, pages 430-433)
Describes a selective reduction reaction of NO by hydrocarbons and copper ion exchange ZSM-5 in the presence of O ₂ and SO _2, but using iron silicate in place of the copper ion exchange ZSM-5 and There is no teaching about its effect, and if a small amount of SO ₂ coexists,
It merely teaches that the conversion rate of NO decreases remarkably at a relatively low temperature around 0 ° C. and that the conversion rate of NO decreases when the concentration of coexisting O ₂ increases to about 10%. When the copper ion exchange ZSM-5 is used, there are drawbacks such as poor durability.

Conventionally, for example, in a gas turbine for cogeneration, ammonia is injected into the exhaust gas of the gas turbine, and ammonia and NOx are reacted on the catalyst to generate NO.
method for removing x and TiO ₂ − used in the method
V ₂ O ₅ -WO ₃ catalysts and zeolite catalysts are known, but they have drawbacks such as requiring dangerous ammonia and having to use expensive catalysts.

Conventionally, for example, a gasoline engine for automobiles,
Strict air-fuel ratio control for gas engines for cogeneration, etc.
A method of catalytically decomposing and removing Ox on a three-way catalyst composed of active ingredients such as platinum and rhodium and the three-way catalyst used in the method are known, but they cannot be applied in an oxygen atmosphere, and a strict air-fuel ratio is required. There are drawbacks such as the need for control and reduced efficiency.

The present invention is directed to the nitrogen oxidation in the combustion exhaust gas containing nitrogen oxides, oxygen gas and, if necessary, sulfur dioxide and hydrocarbons such as gas turbine exhaust gas, gas engine exhaust gas, gasoline engine exhaust gas and diesel engine exhaust gas. As a method of removing substances, the above-mentioned problems in the prior art are solved, and even when a small amount of sulfurous acid gas coexists in the exhaust gas, nitrogen oxidation is efficiently performed at a relatively low contact temperature of about 300 ° C. It is an object of the present invention to provide a method for decomposing and removing a substance and a catalyst used in the method, which is inexpensive, easy to produce, excellent in selectivity, and capable of maintaining stable and high activity for a long period of time.

[0008]

According to the present invention, a combustion exhaust gas containing nitrogen oxide, oxygen gas and optionally sulfurous acid gas is catalytically reacted in the presence of an iron silicate catalyst and a hydrocarbon reducing agent. The present invention provides a method for removing nitrogen oxides in combustion exhaust gas, characterized by decomposing and removing the nitrogen oxides, and an iron silicate catalyst used in the method.

The combustion exhaust gas in the present invention is usually 50 to 5000 pp of nitrogen oxides such as nitric oxide and nitrogen dioxide.
m, preferably 100 to 3000 ppm, oxygen gas of 0.
1 to 15%, preferably 0.1 to 10%, and in the case of a diesel engine or a gasoline engine, a sulfur dioxide gas of 0 to 600 ppm, preferably 0 to 300 ppm, and a combustion exhaust gas having a balance of nitrogen gas as necessary.

The iron silicate catalyst used in the present invention is a liquid A comprising iron chloride (FeCl ₃ .6H ₂ O), sulfuric acid, sodium chloride, tetrapropylammonium bromide [(C ₃ H ₇ ) ₄ NBr] and distilled water. And a solution B composed of water glass and distilled water and a solution C composed of saline solution, sulfuric acid, tetrapropylammonium bromide and sodium hydroxide were mixed, and then 1
It is heated and kept at around 90 ° C, and after washing it is baked at 540 ° C.
This fired body was manufactured by a method of immersing this fired body in NH ₄ NO ₃ , converted to an ammonium type, washed with water, dried and fired at 540 ° C. It is characterized by having a dissolved crystalline structure, and the Si / Fe ratio is usually in the range of 10 to 60, preferably 25 to 50.

Examples of the hydrocarbon reducing agent used in the present invention include propylene, ethylene, methane, ethane, propane, butane and the like, and propylene is preferable from the viewpoint of NOx removal rate. The amount used is usually 500-
4000 ppm, preferably 1000-2000 pp
The range is m. When the hydrocarbon reducing agent is present in the combustion exhaust gas, it can be used as it is as a reducing agent in the subsequent catalytic reaction.

The catalytic reaction in the present invention is usually 250 to
At a reaction temperature of 350 ° C, preferably 280-320 ° C,
It can be performed using a conventionally known device. When the reaction temperature is less than 250 ° C, the conversion rate of nitrogen oxides is too low, which is not preferable, and when the reaction temperature exceeds 350 ° C, the conversion rate of nitrogen oxides is decreased, which is not preferable.

[0013]

According to the present invention, firstly, without using a harmful substance such as liquid ammonia, an inexpensive catalyst is used and the temperature of about 300 ° C. is maintained even in the presence of oxygen gas and a slight amount of sulfurous acid gas. It is possible to decompose and remove nitrogen oxides in combustion exhaust gas such as gas turbine exhaust gas efficiently at a relatively low temperature.

According to the present invention, secondly, by strictly controlling the air-fuel ratio, it is not necessary to set the oxygen concentration in the exhaust gas to 0%,
Using an inexpensive catalyst, nitrogen oxides in combustion exhaust gas such as gas engine exhaust gas can be decomposed and removed efficiently at a relatively low temperature of around 300 ° C. even in the coexistence of oxygen gas and a slight amount of sulfurous acid gas. ..

According to the present invention, thirdly, gas-turbine exhaust gas, gas engine exhaust gas, and gasoline, which are inexpensive, easy to manufacture, excellent in selectivity, and capable of maintaining stable high activity for a long period of time. A catalyst suitable for removing nitrogen oxides in combustion exhaust gas such as engine exhaust gas and diesel engine exhaust gas is provided.

According to the present invention, fourthly, nitrogen oxides in combustion exhaust gas such as gas turbine exhaust gas, gas engine exhaust gas, gasoline engine exhaust gas, diesel engine exhaust gas can be decomposed and removed at a relatively low temperature of around 300 ° C. The advantages are that the process is compact and the cost is low.

[0017]

The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 5.39 g of iron chloride FeCl ₃ .6H ₂ O, 10.1 ml of sulfuric acid (purity 98%), sodium chloride NaCl 3
5.85 g, tetrapropylammonium bromide (C ₃ H ₇ ) ₄ NBr 17.25 g and distilled water 180
Solution A consisting of g, water glass (SiO ₂ : 28.93% by weight, Na ₂ O: 9.28% by weight) 207 g, and solution B consisting of 135 g of distilled water, and 16.3% by weight of saline 7
Three kinds of solutions were prepared: 45 g, sulfuric acid (purity 98%) 4.63 ml, tetrapropylammonium bromide 6.48 g, and sodium hydroxide 7.2 g. Add the solution C to a 1000 ml beaker and adjust the pH to 1 at room temperature.
The solution A and the solution B were added dropwise with vigorous stirring. After completion of dropping, the mixed solution was transferred to an autoclave, and was stirred at a temperature rising rate of 1.5 ° C./min for 1 hour.
The temperature was raised to 60 ° C and then to 210 ° C at a rate of 0.2 ° C / min. After cooling, the product is washed with water until no chlorine ions are detected, then 1
It was dried overnight at 10 ° C. Then, it was baked in air at 540 ° C. for 3.5 hours. Subsequently, the fired body was placed in a NH ₄ NO ₃ solution having a concentration of 1 mol, immersed at 80 ° C. for 1 hour and washed with water. This operation was repeated 3 times to convert to ammonium type. After that, after washing with water at room temperature, it is dried at 110 ° C for a whole day and night, and further baked in air at 540 ° C for 3.5 hours.
H-Fe-silicate (Si / Fe = 50) (hereinafter referred to as proton type iron silicate 50 or simply iron silicate 50
The catalyst was obtained. The iron silicate 50 catalyst thus obtained was charged into an atmospheric fixed bed flow reactor, and NO gas 1000 ppm, propylene 1000 ppm.
, 10% by volume of oxygen gas and a mixed gas of N ₂ balance on the catalyst under the conditions of a reaction temperature of 300 ° C. and W / F (catalyst weight / gas flow rate ratio) of 0.3 g · sec · cm ^−3. The reaction was carried out and the change with time of the conversion rate of NO gas was obtained. The analysis of the reaction gas was used chemiluminescent NO _X analyzers and gas chromatography. The obtained results are shown in FIG. Steady activity was obtained after about 1 hour.

Example 2 Example 1 was repeated except that the amount of iron chloride in the liquid A was changed to 10.8 g.
In the same manner as in H-Fe-silicate (Si / Fe = 2
5) The same experiment as in Example 1 was carried out except that a catalyst (hereinafter referred to as "proton-type iron silicate 25 or simply iron silicate 25") was used. The obtained results are shown in FIG. Steady activity was obtained after about 1 hour.

Comparative Example 1 Na-ZSM-5 type biolite (manufactured by Tosoh Corporation, Si / Al
= 25) 5g was put in a 1 molar NH ₄ NO ₃ solution and the temperature was 80 ° C.
It was soaked in water for 1 hour and washed with water. This operation was repeated 3 times, washed with water at room temperature, dried at 110 ° C for 24 hours, and then dried in air.
By the method of firing at 40 ° C. for 3.5 hours, H-ZSM-
5 (Si / Al = 25): A proton type ZSM-5 catalyst was obtained. Example 1 except that the H-ZSM-5 catalyst was used.
The same experiment was performed. The obtained results are shown in FIG.
When the deactivated catalyst was treated with oxygen at 500 ° C., CO ₂
Was generated and the catalytic activity was completely restored. From this,
The deactivation of the catalyst is considered to be due to carbon deposition.

Comparative Example 2 Boric acid (H ₃ BO ₃ ) 1.2 was used instead of iron chloride in the liquid A.
H-B- in the same manner as in Example 1 except that 32 g was used.
Silicate (Si / B = 50): A proton type boron silicate catalyst was obtained. The same experiment as in Example 1 was conducted except that the HB-silicate catalyst was used. The obtained results are shown in FIG.

Comparative Example 3 Instead of iron chloride in the liquid A, gallium sulfate [Ga ₂ (SO ₄ )
₃ ] · nH ₂ O was used in the same manner as in Example 1 except that 4.2 g of H-Ga-silicate (Si / Ga = 50): proton-type gallium silicate catalyst was obtained. The H-Ga-
The same experiment as in Example 1 was conducted except that a silicate catalyst was used. The obtained results are shown in FIG. The deactivation of the catalyst is considered to be due to carbon deposition as in Comparative Example 1.

Example 3 Using H-Fe-silicate-25 catalyst, reaction temperature and N
The same experiment as in Example 1 was conducted for the relationship with the O conversion rate, and the temperature dependence of the stationary activity is shown in FIG. Good steady activity was obtained at a relatively low temperature around 300 ° C. 300 ° C
The NO removal rate decreased as the reaction temperature exceeded the above range, but the NO removal activity was reproduced when measured again at a temperature lower than that after the activity test at 600 ° C. From this, it is clear that the decrease in activity at high temperature is not due to the deterioration of the catalyst.

Comparative Example 4 The same experiment as in Example 3 was conducted except that the H-ZSM-5 catalyst was used. The obtained results are shown in FIG. About 475 ° C
The above activity showed steady activity, but it was deactivated in the lower temperature range.

Example 4 A raw material gas consisting of 1000 ppm NO gas, 10% by volume oxygen gas and balanced N ₂ gas was used as propylene 1000 pp.
m and H-Fe-silicate (Si / Fe = 25) catalyst in the presence of a reaction temperature of 300 ° C. and W / F = 0.3 g
A catalytic decomposition reaction of NO gas with propylene is carried out under the condition of sec · cm ⁻³ , and propylene in the reaction is expressed by the formula: CO + CO ₂ yield (CO × yield) = ([CO] + [CO ₂ ] ) / ([C ₃ H ₆ ] × 3) × 100% (where [CO] is the amount of CO gas (mol) at the catalyst layer outlet, and [CO ₂ ] is the amount of CO ₂ gas (mol) at the catalyst layer outlet. ) And [C ₃ H ₆ ] represents the amount (mol) of propylene at the catalyst layer inlet), and the CO _x yield, that is, the carbon balance was determined. The obtained results are shown in FIG. Propylene is completely gasified and no carbon is formed, indicating that the catalyst is not poisoned by carbon.

Comparative Example 5 Na-ZSM-5 type zeolite (manufactured by Tosoh Corporation, Si / Al
= 25) 4 g was washed with water, immersed in a 0.1 mol / l copper acetate aqueous solution 400 cc, and then washed again with water. After performing this operation 3 times, Cu-ZSM-5 obtained by a method of drying at room temperature for one day and then calcining in air at 540 ° C. for 3.5 hours.
The same experiment as in Example 4 was performed except that a (Si / Al = 25) catalyst was used. The obtained results are shown in FIG. It is considered that a part of the added propylene produces carbon which causes a decrease in catalytic activity.

Comparative Example 6 The same experiment as in Example 4 was carried out except that H-ZSM-5 (Si / Al = 25) catalyst was used. The obtained results are shown in FIG. It is considered that most of the added propylene is producing carbon which causes a decrease in catalytic activity.

Comparative Example 7 Cu-ZSM-5 (S obtained by the same method as in Comparative Example 5
i / Al = 25): The same experiment as in Example 4 was performed except that a copper ion exchange ZSM-5 catalyst was used. The obtained results are shown in FIG. 4 together with the results of Example 4. At relatively low temperatures around 300 ° C., both showed almost the same NO conversion rate.

Example 5 The same experiment as in Example 4 was carried out except that 240 ppm of sulfurous acid gas was allowed to coexist. The obtained results are shown in FIG. The result is substantially the same as when sulfurous acid gas does not coexist,
Particularly, at a relatively low temperature around 300 ° C., a good NO conversion rate was shown.

Comparative Example 8 The same experiment as in Comparative Example 7 was conducted except that 240 ppm of sulfurous acid gas was allowed to coexist. The obtained results are shown in FIG. 40
It was found that the NO conversion was excellent at a relatively high temperature of about 0 ° C., but the NO conversion was remarkably reduced at a relatively low temperature of about 300 ° C., and it was found to be affected by the coexistence of sulfurous acid gas.

[Brief description of drawings]

FIG. 1 is a graph showing changes in NO conversion with time for various metallosilicate catalysts in Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the relationship between the NO conversion showing the steady activity of the catalyst and the reaction temperature in Examples and Comparative Examples of the present invention.

FIG. 3 is a graph showing changes with time in CO + CO ₂ yield with respect to added propylene for various catalysts in Examples and Comparative Examples of the present invention.

FIG. 4 is a graph showing the relationship between the NO conversion rate and the reaction temperature in the case where sulfurous acid gas does not coexist for the catalysts of Examples and Comparative Examples of the present invention.

FIG. 5 is a graph showing the relationship between the NO conversion rate and the reaction temperature when sulfurous acid gas coexists in the catalysts of Examples and Comparative Examples of the present invention.

Claims (5)

[Claims] 1. A method for catalytically removing combustion oxides containing nitrogen oxides, oxygen gas and sulfurous acid gas in the presence of an iron silicate catalyst and a hydrocarbon reducing agent to decompose and remove the nitrogen oxides. A method for removing nitrogen oxides in combustion exhaust gas, comprising: 2. A flue gas containing nitrogen oxides, oxygen gas and optionally sulfurous acid gas is reacted at a reaction temperature of 250 to 350 ° C. in the presence of an iron silicate catalyst and propylene to remove the nitrogen oxides. The method for removing nitrogen oxides from combustion exhaust gas according to claim 1, characterized in that the method is carried out by decomposition and removal. 3. The method for removing nitrogen oxides in combustion exhaust gas according to claim 2, wherein the reaction temperature is in the range of 280 to 320 ° C. 4. The nitrogen oxide in the combustion exhaust gas according to claim 1, wherein the iron silicate catalyst has a structure in which iron atoms are substituted and solid-solved in a silicate skeleton and has a Si / Fe ratio of 10 to 60. Removal method. 5. An iron silicate catalyst used in the method according to claim 1.