JP3212577B2 - Exhaust gas treatment catalyst, exhaust gas treatment method and treatment apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various incinerators such as municipal waste incinerators, industrial waste incinerators, sludge incinerators, etc.
Regarding technology for purifying exhaust gas discharged from pyrolysis furnaces, melting furnaces, etc., especially exhaust gas for individually or simultaneously detoxifying halogenated aromatic compounds such as nitrogen oxides and dioxins contained in the exhaust gas The present invention relates to a treatment catalyst, an exhaust gas treatment method, and a treatment device.

[0002]

2. Description of the Related Art Exhaust gas discharged from various incinerators such as municipal garbage incinerators, industrial waste incinerators, and sludge incinerators includes the types of incineration objects and incineration conditions. May contain harmful substances such as harmful halogenated aromatic compounds represented by dioxins and PCBs, and highly condensed aromatic hydrocarbons in addition to nitrogen oxides. It causes serious damage to the natural environment and has become a serious social problem.

Conventionally, to remove the above harmful substances contained in exhaust gas, titania (TiO ₂ ) has been used as a carrier as a denitration catalyst or a decomposition catalyst such as dioxins, and vanadium pentoxide (V ₂ O ₅ ) as an active ingredient. ), And at least one metal oxide such as tungsten trioxide (WO ₃ ) is supported.

[0004] An example of this conventional method for producing a catalyst will be described below. First, a solution of titanium sulfate or titanium chloride, which is a raw material of TiO ₂ as a catalyst carrier, is heated and hydrolyzed or neutralized with NH ₃ or the like to precipitate, and the obtained hydrous titanium oxide is subjected to 400 to 600. By performing heat treatment at about ° C, TiO _{2 serving} as a catalyst carrier is obtained. next,
A raw material solution such as an ammonium salt of V ₂ O ₅ or WO _{3 serving as} an active component is mixed with TiO ₂ , mixed, formed into a honeycomb shape or the like, and fired at 450 to 550 ° C.

[0005] The catalyst thus obtained has a small specific surface area of about 50 to 68 m ² / g, and its activity at a low temperature of 200 ° C or lower is remarkably reduced. At present, the decomposition treatment is performed at 200 ° C. or higher by heating the exhaust gas again.

[0006] Dioxins are thermally decomposed at a high temperature in an incinerator, but when they pass through a gas cooling device and are removed by a dust remover, they are regenerated in a low temperature range of 400 ° C or less. This may be a problem.

Conventionally, exhaust gas is once passed through a dust remover (eg, a bag filter), and then dioxins are removed. For this reason, after passing through the dust remover, the concentration of dioxins is low (0.2 to 0.3 ng / Nm ³ ), so that dioxins of low concentration are removed with high efficiency, for example, the Ministry of Health and Welfare It is necessary to secure the emission regulation value of 0.1 ng-TEQ / Nm ³ .

[0008] In view of the above problems, the present invention improves the denitration activity in a low temperature range of 200 ° C or lower and the activity of decomposing harmful substances such as dioxins and highly condensed aromatic hydrocarbons.
An object of the present invention is to provide an exhaust gas treatment catalyst, an exhaust gas treatment method, and a treatment apparatus that reliably remove harmful substances in exhaust gas and simultaneously remove dust and gaseous organic compounds from exhaust gas.

[0009]

Means for Solving the Problems The invention of claim 1 for solving the above problems is an exhaust gas treatment catalyst for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, and the like,
At least one member selected from the group consisting of a carrier composed of titanium oxide, vanadium, tungsten, molybdenum, niobium, tantalum, a mixture of two or more of these metal elements, and a solid solution of two or more of these metal elements; And acid component (H 2 _{O 2} )
5.6 ≦ H _O ≦ + 4.8 .

The invention of claim 2 is characterized in that, in claim 1, the specific surface area of the catalyst is 90 m ² / g or more.

[0011] The invention of claim 3 is characterized in that, in claim 1, the catalyst reaction temperature is 100 to 300 ° C.

[0012] The invention of claim 4 is the invention according to claim 1.
The titanium oxide carrier is titanyl sulfate or chloride
Characterized by firing at high temperature using titanium as a starting material
And

[0013] The invention of claim 5 is the invention according to claim 1.
The carrier made of titanium oxide is
Obtain tanoic acid precipitate or add ammonia or urea
To obtain a titanic acid precipitate by neutralization
It is characterized by the following.

[0014] The invention of claim 6 is the invention according to claim 1.
Therefore, a carrier made of titanium oxide is used as a starting material for magnesium oxide.
Addition of a compound containing a titanium element to obtain a titanate precipitate
I'm sorry.

The invention of claim 7 is the invention according to claim 1.
The carrier consisting of titanium oxide
Characterized by the addition of potassium or alkaline earth metal
I do.

The invention of claim 8 is characterized in that the harmful substances in the exhaust gas are brought into contact with the catalysts of claims 1 to 7 to decompose the harmful substances in the exhaust gas.

According to a ninth aspect of the present invention, in the eighth aspect , the harmful substance in the exhaust gas is selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols, and halogenated toluenes. It is characterized in that it is at least one halogenated aromatic compound. Here, the term “halogenation” refers to fluorination, chlorination, bromination, and iodination.

[0018] The invention of claim 10 is the invention according to claim 9, wherein the dioxins are polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polybrominated dibenzo-p-dioxins. (PBDDs), polybrominated dibenzofurans (PB
DFs), polyfluorinated dibenzo-p-dioxins (P
FDDs), polyfluorinated dibenzofurans (PFDF)
s), polyiodinated dibenzo-p-dioxins (PI
DDs), polyiodinated dibenzofurans (PIDFs)
It is characterized by being.

[0019] invention [Claim 11] The method of claim 8, in the presence of ammonia, characterized by decomposing nitrogen oxides selectively reduced to.

[0020] The invention of claim 12 is an exhaust gas treatment apparatus for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, etc., and a dust removal apparatus for removing dust in the exhaust gas, and the dust removal apparatus. A catalyst device having the exhaust gas treatment catalyst according to any one of claims 1 to 7 provided on the downstream side of the device.

According to a thirteenth aspect of the present invention, in the eighth aspect , a means for introducing a basic substance is provided in the catalyst device. "

The invention of claim 14 is the invention of claim 12 or
13, wherein the temperature of the exhaust gas introduced into the catalyst device is set to 100 to 300 ° C.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

The catalyst according to the present invention has a high specific surface area capable of catalytically reducing or decomposing harmful substances contained in exhaust gas to make it harmless, and has an acid strength of -5.6 ≦ H _O ≦ + 4. 8 and
It is the oxidation catalyst.

Here, harmful substances often contained in the exhaust gas include nitrogen oxides, dioxins, and the like.
Hazardous substances such as aromatic hydrocarbons with high condensation degree and gaseous organic compounds.

As the above-mentioned oxidation catalyst, a carrier composed of titanium oxide, vanadium, tungsten, molybdenum, niobium, tantalum, a mixture of two or more of these metal elements, and a solid solution of two or more of these metal elements are oxidized. And a catalyst component containing at least one selected from the group consisting of materials, and a range of acid strength (H 2 _O ).
This is a catalyst in which the range is -5.6 ≦ H _O ≦ + 4.8 . this is,
This is because, in the case of a catalyst having an acid strength higher than -5.6, the decomposition rate and the denitration rate of dioxins decrease as shown in Examples described later. Here, in the present invention, the acid strength refers to the ability of an acid point on the catalyst surface to give a proton to a base or the ability to receive an electron pair from a base, and the measuring method includes an indicator method and the like. Here, the acid strength of the catalyst is generally determined by the electronegativity of the substance, the binding energy, the polarity effect, the steric effect and the like.

The acid strength can be reduced by the following operation, but the present invention is not limited to this. The kind of the anion of the starting material at the time of preparing the catalyst is, for example, Cl ⁻ . Select the type of alkali at the time of neutralization precipitation. For example, urea has lower acid strength than ammonia. A complex oxide having a weak acid strength (such as an active ingredient containing Mg) is formed. A small amount (several percent or less) of alkali or alkaline earth metal is added to eliminate strong acid sites. The firing atmosphere is an oxidizing atmosphere (for example, firing in air) or a reducing atmosphere (for example, firing in a hydrogen atmosphere). Change the firing temperature.

As the catalyst component, for example, vanadium pentoxide (V ₂ O ₅ ), tungsten trioxide (WO ₃ ), molybdenum trioxide (MoO ₃ ), niobium pentoxide (Nb)
₂ O ₅ ) and tantalum pentoxide (Ta ₂ O ₅ ). Note that it is preferable to use tungsten trioxide rather than vanadium pentoxide from the viewpoint of high SOx resistance.

The above-mentioned metal oxides may be used alone or as a mixture of powders of a plurality of types of metal oxides. Also, a solution of at least one compound selected from the group consisting of compounds of vanadium, tungsten, molybdenum, niobium, and tantalum, and compounds containing two or more of these metal elements, for example, titanium, vanadium, tungsten, molybdenum, niobium, and tantalum Using solutions of sulfate, nitrate, ammonium salts, chlorides, hydroxides, alkoxides, alkylates, etc. of these, mix these solutions, evaporate the solvent, dry and bake to form oxides The powdery composition of the metal oxide obtained by the above can be preferably used.

It is natural that the catalyst used in the exhaust gas treatment preferably has a large contact area with the gas. However, depending on the degree of the packing density of the powder catalyst, the flow back pressure of the exhaust gas is preferably increased. Absent. As a countermeasure, for example, a honeycomb-shaped molded body obtained by compressing a powder to a predetermined density without excessively reducing its specific surface area is used.

When the above-mentioned oxidation catalyst is used as an exhaust gas treatment catalyst for treating exhaust gas from an incinerator, its specific surface area is 90 m ² / g or more, preferably 90 to ²⁰⁰ m ^2.
It is preferably ² / g. It has a specific surface area of 200
If m ² / g is exceeded, 200 when exhaust gas is treated
This is because, in the temperature range of ° C., the specific surface area decreases due to the growth of the particles, the thermal stability is poor and the activity is reduced, and it cannot be used stably for a long period of time. Also,
If the specific surface area is less than 90 m ² / g, the activity at 300 ° C. or lower is remarkably reduced as in the conventional case, which is not preferable.

The acid strength (H _O ) of the present invention is -5.6 ≦ H _O ≦
The oxidation catalyst with +4.8 has an exhaust gas treatment temperature of 100 to
The processing capacity is exhibited at 300 ° C, preferably 150 to 200 ° C.

The catalyst according to the present invention may use one of the above-mentioned various metal oxides, but a composition comprising a plurality of metal oxides is more preferably used as described above. The components and the composition ratio of the catalyst composition are not particularly limited. However, as a typical example, vanadium pentoxide is 1 to 10 parts by weight and 3 to 10 parts by weight of the catalyst component is 100 parts by weight of the titanium oxide carrier. A composition of 1 to 20 parts by weight of tungsten oxide, a composition of 1 to 10 parts by weight of vanadium pentoxide and 1 to 20 parts by weight of molybdenum trioxide, a composition of 1 to 10 parts by weight of vanadium pentoxide and 1 to 10 parts by weight of niobium pentoxide It is preferable that the composition be 1 to 10 parts by weight of vanadium pentoxide and 1 to 20 parts by weight of tantalum pentoxide. The metal oxide can be used alone, or an inorganic substance or the like can be added thereto, or can be used by being supported on a base material. As the carrier substrate, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia, titania (Ti
O ₂ ), silica alumina, zeolite and the like are suitably used, and particularly, titania (titanium oxide), and a compound or a mixture of titania and another element such as zirconia are preferable.

Here, the harmful substances in the exhaust gas to be decomposed by the catalyst of the present invention include, in addition to nitrogen oxides, harmful halogenated aromatics represented by dioxins and PXB (X represents halogen). The term refers to harmful substances such as aromatic compounds and aromatic hydrocarbons having a high degree of condensation, but is not limited to harmful substances (or environmental hormones) in exhaust gas that can be decomposed by the oxidation catalyst of the present invention.

The ash to be decomposed in the present invention and the aromatic halogen compounds contained in soil are not limited to harmful substances (eg, environmental hormones) represented by dioxins and PCBs. is not. Here, the dioxins are a general term for polyhalogenated dibenzo-p-dioxins (PXDDs) and polyhalogenated dibenzofurans (PXDFs) (X represents a halogen), and a halogen compound and a certain organic compound are used. It is said that a small amount is generated during the combustion of halogen compounds. Depending on the number of halogens, there are monohalides to octahalides, of which dibenzo-p-dioxin tetrachloride (T ₄ CDD) is known to have the highest toxicity. The harmful halogenated aromatic compounds include, in addition to dioxins, various organic halogen compounds which are precursors thereof (for example, aromatic compounds such as phenol and benzene (for example, halogenated benzenes,
Halogenated phenol and halogenated toluene, etc.) and halogenated alkyl compounds, etc.) and need to be removed from the ash. That is, dioxins represent not only chlorinated dioxins but also halogenated dioxins such as brominated dioxins. PXBs (polyhalogenated biphenyls) are a general term for compounds in which several halogen atoms are added to biphenyl, and there are isomers depending on the number and position of substitution of halogen, but in the case of PCB (polychlorinated biphenyl), , 2,6-dichlorobiphenyl, 2,2'-dichlorobiphenyl, 2,3,5-trichlorobiphenyl and the like are typical, are highly toxic and may generate dioxins when incinerated. It needs to be removed from the ash. Needless to say, the PXBs include the coplanar PXB.

[0036] Highly condensed aromatic hydrocarbons are a general term for polynuclear aromatic compounds, which may contain one or more OH groups, are recognized as carcinogenic substances, and need to be removed from exhaust gas. .

In many production processes, exhaust gas containing, for example, gaseous organic compounds such as formaldehyde, benzene or phenol in addition to dust may be generated. These organic compounds are also environmental pollutants and significantly impair human health and need to be removed from the exhaust gas.

The nitrogen oxide to be treated in the present invention usually means NO and NO ₂ , and a mixture thereof.
It is also called NOx. However, the NOx often contains various oxidation numbers and unstable nitrogen oxides in addition to the above. Accordingly, x is not particularly limited, but is usually a value of 1 to 2. It becomes nitric acid, nitrous acid, etc. in rainwater or NO, or NO is said to be one of the main causes of photochemical smog, and is a harmful compound to the human body.

By using the above-mentioned catalyst according to the present invention, the above-mentioned harmful substances such as nitrogen oxides, dioxins, highly condensed aromatic hydrocarbons and the like and gaseous organic compounds are reduced or decomposed catalytically. And can be detoxified. Here, the dioxins, dioxin precursors, halogenated aromatic compounds such as PXB, and highly condensed aromatic hydrocarbons in the exhaust gas of the above-mentioned harmful substances are the oxidation catalysts of the present invention which have a reduced acid strength. Detoxification treatment is performed by oxidative decomposition of.

As for nitrogen oxides, a basic substance (for example, ammonia or the like) is present on the upstream side of the apparatus filled with the catalyst of the present invention, and detoxification is performed by a reduction reaction.

FIG. 1 is a schematic diagram of an exhaust gas purifying apparatus using the above catalyst. As shown in FIG.
A dust removal device 12 for removing dust in exhaust gas 11 discharged from various incinerators such as a municipal waste incinerator, an industrial waste incinerator, and a sludge incinerator; a nitrogen oxide, a dioxin, and a highly condensed aromatic hydrocarbon And a catalyst device 13 having the above-mentioned exhaust gas treatment catalyst for removing harmful substances such as the above. The dust removing device 12 can collect dust and solid dioxins in the exhaust gas, thereby preventing the catalyst device 13 from being deteriorated and the catalyst from being clogged.

The following shows the concentrations of nitrogen oxides and chlorinated aromatic compounds as typical halogenated aromatic compounds in the exhaust gas. The concentration of nitrogen oxides in the exhaust gas is 200 to 5
0 ppm by volume. The concentration of chlorinated aromatic compounds such as dioxins in the exhaust gas ranges from several tens mg to several μg / Nm ^3.
It is. In the present invention, the contact condition between the exhaust gas 11 and the catalyst is preferably 20 to 2 Nm ³ / h / kg-catalyst. Further, the exhaust gas treatment temperature is 100 to 300 ° C,
Suitably, 100-200 degreeC is preferable. This is because in this exhaust gas treatment temperature range, dioxins are not generated by resynthesis of the precursor of dioxins, which is a preferable treatment temperature.

Also, a dust removing device (for example, a bag filter)
Even when the exhaust gas is cooled to a low temperature when the treatment is performed in step 12, if the temperature is around 200 to 150 ° C., it becomes possible to treat the harmful substances in the exhaust gas without reheating. It should be noted that, in order to perform efficient collection in the dust removing device 12, even if cooling is performed using a cooling device on the upstream side of the dust removing device 12, even if reheating is performed before entering the catalytic device. It is preferable to limit the temperature to 250 ° C. where the regeneration rate of dioxins is low.

In the apparatus for purifying exhaust gas from an incinerator according to the present invention, denitration and removal of dioxins are performed by one catalyst device 1.
3 can be performed at the same time. In that case, ammonia may be introduced into the catalyst device 13 through an injection nozzle 14 that injects, for example, ammonia as a basic substance.

As shown in FIG. 2, on the downstream side of the bag filter 22 as a dust removing device for removing dust in the exhaust gas 21, first, a denitration reaction device 24 having the above-mentioned catalyst equipped with an ammonia injection nozzle 23 is provided. After that, the dioxin decomposition catalyst device 25 having the above-described catalyst may be separately provided. The steam gas heater 26 may be provided on the upstream side of the denitration reaction device 24 if necessary.

As shown in FIG. 3, a dioxin decomposition catalyst device 33 is first provided after a bag filter 32 as a dust removing device for removing dust in the exhaust gas 31, and then an ammonia injection nozzle 34 is provided on the downstream side. A denitration reaction device 35 may be provided. In this case, since the denitration device 35 is provided on the downstream side of the exhaust gas catalytic reaction device 33, it is not affected by ammonia used for denitration. Furthermore, since dioxins are decomposed by the dioxin decomposition catalyst reaction device 33, there is no fear of resynthesis of dioxins even when heating for denitration. Note that a steam gas heater 36 may be provided upstream of the denitration reaction device 35 as necessary.

[0047]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. [Example 1] An aqueous solution of titanyl sulfate was hydrolyzed by heating to obtain a precipitate of metatitanic acid. The obtained metatitanic acid cake is filtered and washed with water. Next, the cake was dried at 100 ° C., and then baked at 500 ° C. for 5 hours to obtain a titanium oxide carrier. With respect to 100 parts by weight of this titanium oxide, ammonium paratungstate and ammonium metavanadate are dissolved in oxalic acid so that each becomes 14 parts by weight as WO ₃ and 4 parts by weight as V ₂ O ₅ , and are kneaded with titanium oxide. Then, after forming into a honeycomb shape and drying, 500
Calcination was performed at 5 ° C for 5 hours to obtain a catalyst (1).

Example 2 A catalyst (2) was obtained in the same manner as in Example 1, except that ammonium molybdate having a predetermined weight ratio was used instead of ammonium paratungstate. Was.

Example 3 The procedure of Example 1 was repeated, except that niobium chloride was dissolved in ethanol to give 5 parts by weight of Nb ₂ O ₅ instead of ammonium paratungstate. Catalyst (3) was obtained.

Example 4 The procedure of Example 1 was repeated, except that tantalum chloride was dissolved in ethanol to obtain 5 parts by weight of Ta ₂ O ₅ instead of ammonium paratungstate. Catalyst (4) was obtained.

Example 5 Aqueous ammonia was added to an aqueous solution of titanium chloride for neutralization and precipitation.
A catalyst (5) was obtained in the same manner as in Example 1 except that a precipitate of orthotitanic acid was obtained.

Example 6 An operation was performed in the same manner as in Example 1 except that a small amount of magnesium sulfate was added to an aqueous solution of titanyl sulfate, followed by neutralization and precipitation by adding aqueous ammonia to obtain a precipitate of orthotitanic acid. A catalyst (6) was obtained.

Example 7 An aqueous solution of titanyl sulfate was hydrolyzed by heating to obtain a precipitate of metatitanic acid. After filtering the obtained metatitanic acid cake, a dilute potassium hydroxide solution is added to the cake and kneaded. After drying the kneaded material at 100 ° C.,
A catalyst (7) was obtained in the same manner as in Example 1 except that calcination was performed at 00 ° C. for 5 hours to obtain a titanium oxide carrier.

FIG. 4 shows the NH ₃ TPD curve of the catalyst (7). NH ₃ TPD (temperature-programmed
The outline of the desorptopn) test is shown below. First, as a pretreatment, excess adsorbed substances on the catalyst sample surface are removed at 450 ° C. Then, after adsorbing NH ₃ sufficiently at 100 ° C., the temperature is raised at a constant rate, and the amount of desorbed NH ₃ is quantified with respect to time (temperature). <Test conditions> The sample amount was 0.1 g. First, as a pretreatment, a heating rate is set to 10 ° C./min under He flow, heating is performed to 450 ° C., and then heating is performed at the same temperature for 30 minutes. Next, the NH ₃ adsorption treatment is performed by heating at 20 torr and 100 ° C. for 15 minutes, and further heating in vacuum for 10 minutes.
Heated at 0 ° C. for 1 hour. Furthermore, He is used as a thermal desorption process.
The temperature was raised at a rate of 10 ° C./min under circulation, and the mixture was heated to 800 ° C. to measure the amount of desorbed NH ₃ . Analysis was by quadrupole mass spectrometry. Here, NH ₃ adsorbed to acid sites on the catalyst surface in the condition (base), detached from the NH ₃ adsorbed to weak acid sites by heating in order, NH ₃ adsorbed to strong acid acid strength If the temperature is not so high, it will not desorb. As a result,
A catalyst with a larger amount of NH ₃ desorbed in a high-temperature portion has a higher acid strength.

In FIG. 4, the horizontal axis represents the temperature (° C .: corresponding to the elapsed time after the start of the temperature rise), and the vertical axis represents the desorption rate (m mol).
/ Sec · g). That is, the amount of NH ₃ desorbed per unit time for 1 g of the catalyst is shown. From FIG.
This Example product (catalyst (7)) is comparative (described later comparing catalytic)
It was confirmed that the amount of NH ₃ desorbed in the high-temperature portion was smaller than that in the high-temperature portion, and the acid sites having strong acid strength disappeared by the addition of the alkali, and the acid strength was reduced.

Example 8 A catalyst (8) was obtained in the same manner as in Example 1, except that urea was added to the aqueous solution of titanyl sulfate for neutralization and precipitation to obtain a precipitate of orthotitanic acid. .

[0057] In Example 9 Example 5, except that the firing temperature was 300 ° C. The same procedure as in Example 5, to obtain a catalyst (9).

[0058] In Example 10 Example 6, except that the firing temperature was 300 ° C. Similarly operating as in Example 6, to obtain a catalyst (10).

[0059] In Example 11 Example 7, except that the firing temperature was 300 ° C. Similarly operating as in Example 7, to obtain a catalyst (11).

[0060] In Example 12 Example 8, except that the firing temperature was 300 ° C. The same procedure as in Example 8, to obtain a catalyst (12).

Comparative Example 1 A comparative catalyst (1) was obtained in the same manner as in Example 1, except that the metatitanic acid obtained by filtration was dried as it was.

The exhaust gas from the municipal garbage incinerator was used as a simulated gas composition as shown in Tables 1 and 2 and introduced into a catalytic reactor filled with a honeycomb catalyst to be treated. Dioxins (DX) at the outlet of the catalytic reactor
N) Concentration (total concentration of PCDDs, PCDFs, PCB)
(Ng-TEQ / m ³ N) and the decomposition rate were measured. The acid strength was determined by the indicator method. Table 1 shows the test conditions and test results. The decomposition rate was determined by the following equation (1).

Decomposition rate = (1-DXN concentration at outlet / DXN concentration at inlet) × 100 (1)

[0064]

[Table 1]

[0065]

[Table 2]

As is apparent from Tables 1 and 2,
It has been found that the use of the catalyst according to the present invention significantly improves the decomposition rate of dioxins, and can ensure a decomposition rate of 95% or more. As can be seen, the use of the catalyst according to the invention leads to a marked reduction in the concentration of dioxins, particularly for catalysts whose acid strength is less than -5.6. Further, it is noted that those having a high specific surface area (127 m ² / g) treated at a firing temperature of 300 ° C. can reduce the exhaust gas temperature to about 0.1 ng-TEQ / m ³ N at 150 ° C. As described above, by using the catalyst having an acid strength lower than -5.6 according to Examples 1 to 4, the harmful substances in the exhaust gas were more efficiently removed.

Next, a denitration test was performed using the same catalyst. The denitration test was performed at 150 ° C. and 200 ° C. using the gases shown in “Table 3” and “Table 4” as simulation gases. The denitration rate was determined by the following equation (2). The test conditions and test results are shown in Tables 3 and 4.

Denitration rate = (1−outlet NOx concentration / inlet NOx concentration) × 100 (2)

[0069]

[Table 3]

[0070]

[Table 4]

As is apparent from Tables 3 and 4,
It was found that the use of the catalyst according to the present invention significantly improved the denitration rate, and it was possible to secure a denitration rate of 97% or more. Even at 150 ° C, the denitration rate is 87%.
It is noteworthy to get more. Further, by using the catalyst having a high specific surface area according to Example 5, harmful substances of nitrogen compounds in the exhaust gas were also efficiently removed.

[0072]

As described above, according to the first aspect of the present invention, there is provided an exhaust gas treatment catalyst for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, etc. At least one member selected from the group consisting of a carrier made of titanium, and a mixture of vanadium, tungsten, molybdenum, niobium, tantalum, a mixture of two or more of these metal elements, and a solid solution of two or more of these metal elements And an acid strength (H _O ) of -5.6 ≦
Since H 2 _O ≦ + 4.8, the decomposition and denitration rates of dioxins are good even at low temperatures.

According to the second aspect of the present invention, since the specific surface area of the catalyst is as high as 90 m ² / g or more in the first aspect, it is possible to decompose dioxins and the like even at a low temperature of 100 ° C. The catalyst activity is maintained for a long period of time. .

According to the third aspect of the present invention, in the first aspect, since the catalyst can be treated at a low optimum activity temperature of 100 to 300 ° C., the dioxins are not regenerated and the dioxins are decomposed. Can be.

The unique product of [claim 4] to [claim 7]
According to the catalyst by the method, it has a specific range of acid strength
Therefore, harmful substances can be satisfactorily decomposed.

According to the invention of claim 8 , the harmful substances in the exhaust gas can be decomposed by contacting the harmful substances in the exhaust gas with the catalysts of the first to seventh aspects.

[0077] The invention of claim 9 is that the harmful substance in the exhaust gas is at least one kind selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols and halogenated toluene. The hydrogenated aromatic compound can be decomposed.

[0078] According to the invention of the claim 10, the dioxins, polychlorinated dibenzo -p- dioxins (PCDDs), polychlorinated dibenzofurans (PCDF
s), polybrominated dibenzo-p-dioxins (PBD
Ds), polybrominated dibenzofurans (PBDFs), polyfluorinated dibenzo-p-dioxins (PFDDs),
It can decompose harmful substances such as polyfluorinated dibenzofurans (PFDFs), polyiodinated dibenzo-p-dioxins (PIDDs), and polyiodinated dibenzofurans (PIDFs).

[0079] invention [Claim 11] according to claim 8, in the presence of ammonia, can be decomposed by further selective reduction of nitrogen oxides.

An invention according to claim 12 is an exhaust gas treatment apparatus for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, or the like, comprising: a dust removal apparatus for removing dust in the exhaust gas; The catalyst device having the exhaust gas treatment catalyst according to claim 1 provided on the downstream side of the device, so that the exhaust gas treatment catalyst having a high specific surface area is used to halogenate dioxins, dioxin precursors, PXB and the like in exhaust gas. Oxidative decomposition of aromatic compounds and aromatic hydrocarbons with a high degree of condensation becomes possible.

According to the invention of claim 13 , in claim 11 , since means for introducing a basic substance is provided in the catalyst device, denitration becomes possible by addition of a basic gas. Becomes possible.

The invention of claim 14 is the invention of claim 12 or
In 13 , since the temperature of the exhaust gas introduced into the catalyst device is set to 100 to 300 ° C., the decomposition treatment in the exhaust gas can be performed at a particularly low temperature.

Further, even if a catalyst device in which a catalyst for denitration and a catalyst for oxidative decomposition of a halogenated aromatic compound and a highly condensed aromatic hydrocarbon are separated is arranged in parallel, it is possible to decompose exhaust gas.

Further, by combining the catalyst device according to the present invention with a low-temperature dust removing device, it becomes possible to remove halogenated aromatic compounds such as dioxins and high-condensation degree aromatic hydrocarbons in exhaust gas and to remove denitration. Dust, H
It is possible to remove harmful substances such as Cl, SOx, and heavy metals at the same time.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an exhaust gas treatment device.

FIG. 2 is a schematic diagram illustrating an example of an exhaust gas treatment device.

FIG. 3 is a schematic diagram illustrating an example of an exhaust gas treatment device.

FIG. 4 is a graph of an NH ₃ TPD curve.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 Exhaust gas 12 Dust removal device (eg, bag filter) 13 Catalytic device 14 Ammonia injection nozzle 21 Exhaust gas 22 Bag filter 23 Ammonia injection nozzle 24 Denitration reaction device 25 Dioxin decomposition catalyst device 26 Steam gas heater 31 Exhaust gas 32 Bag filter 33 Dioxin decomposition catalyst Apparatus 34 Ammonia injection nozzle 35 Denitration reaction apparatus 36 Steam gas heater

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-164335 (JP, A) JP-A-9-103646 (JP, A) JP-A 10-235191 (JP, A) Hattori Ei et al. New Catalytic Chemistry ”(Showa 63-4-15) Sankyo Publishing Co., Ltd. p. 132 Table 7-3 (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53 / 86

Claims (14)

(57) [Claims] 1. An exhaust gas treatment catalyst for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, or the like, comprising a carrier made of titanium oxide, vanadium, tungsten, molybdenum, niobium, and tantalum. It is composed of a mixture of two or more metal elements and a catalyst component containing at least one selected from the group consisting of oxides of two or more solid solutions of these metal elements, and has an acid strength (H 2 _{O 2} ) of −
5.6 ≦ H _O ≦ + 4.8 exhaust gas treatment catalyst, characterized in that. 2. The exhaust gas treatment catalyst according to claim 1, wherein the specific surface area of the catalyst is 90 m ² / g or more. 3. The exhaust gas treatment catalyst according to claim 1, wherein the optimum activation temperature of the catalyst is 100 to 300 ° C. 4. The method according to claim 1, wherein the carrier comprising titanium oxide is titanyl sulfate or titanium chloride.
The starting material is fired at a high temperature.
Exhaust gas treatment catalyst. 5. The method according to claim 1, wherein the carrier comprising titanium oxide is prepared by heating and hydrolyzing titanium.
Obtain an acid precipitate or add ammonia or urea
To obtain titanic acid precipitate by neutralization
An exhaust gas treatment catalyst comprising: 6. The method according to claim 1, wherein the carrier comprising titanium oxide is used as a starting material in a magnesium source.
To obtain a titanate precipitate by adding a compound containing sulfur
An exhaust gas treatment catalyst, comprising: 7. The method according to claim 1, wherein the support made of titanium oxide is an alkali
Or characterized by adding an alkaline earth metal
Exhaust gas treatment catalyst. 8. contacting toxic substances in the exhaust gas to claims 1 to 7 for the catalyst, an exhaust gas processing method characterized by decomposing the harmful substances in the exhaust gas. 9. The method according to claim 8, wherein the harmful substance in the exhaust gas is at least one halogenated aromatic selected from dioxins, polyhalogenated biphenyls, halogenated benzenes, halogenated phenols and halogenated toluenes. An exhaust gas treatment method characterized by being a compound. 10. The method of claim 9, wherein the dioxins are polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polybrominated dibenzo-p-dioxins (PBDDs), polyodors. Dibenzofurans (PBD
Fs), polyfluorinated dibenzo-p-dioxins (PF
DDs), polyfluorinated dibenzofurans (PFDFs),
Polyiodinated dibenzo-p-dioxins (PIDD
s), an exhaust gas treatment method characterized by being polyiodinated dibenzofurans (PIDFs). 11. The exhaust gas treatment method according to claim 9, wherein nitrogen oxides are selectively reduced and decomposed in the presence of ammonia. 12. An exhaust gas treatment device for purifying exhaust gas discharged from an incinerator, a pyrolysis furnace, a melting furnace, or the like, comprising: a dust removal device for removing dust in the exhaust gas; and a dust removal device provided downstream of the dust removal device. An exhaust gas treatment device comprising the catalyst device having the exhaust gas treatment catalyst according to any one of claims 1 to 7 . 13. The exhaust gas treatment device according to claim 12, wherein a means for introducing a basic substance is provided in the catalyst device. 14. The temperature of the exhaust gas introduced into the catalyst device according to claim 12 or 13 ,
An exhaust gas treatment device characterized by a temperature of ° C.