US20170341025A1 - Aldehyde decomposition catalyst, exhaust gas treatment apparatus, and exhaust gas treatment method - Google Patents

Aldehyde decomposition catalyst, exhaust gas treatment apparatus, and exhaust gas treatment method Download PDF

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US20170341025A1
US20170341025A1 US15/526,626 US201515526626A US2017341025A1 US 20170341025 A1 US20170341025 A1 US 20170341025A1 US 201515526626 A US201515526626 A US 201515526626A US 2017341025 A1 US2017341025 A1 US 2017341025A1
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exhaust gas
catalyst
aldehyde
denitration
aldehyde decomposition
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Tsugumi Nishi
Susumu Hikazudani
Emi Shono
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Hitachi Zosen Corp
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Hitachi Zosen Corp
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    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/76—Iron group metals or copper
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    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8668—Removing organic compounds not provided for in B01D53/8603 - B01D53/8665
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
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    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
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    • B01D53/90—Injecting reactants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
    • B01J29/20—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type containing iron group metals, noble metals or copper
    • B01J29/24—Iron group metals or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/76—Iron group metals or copper
    • B01J29/763—CHA-type, e.g. Chabazite, LZ-218
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/21—Organic compounds not provided for in groups B01D2251/206 or B01D2251/208
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20761—Copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/708—Volatile organic compounds V.O.C.'s
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/45—Gas separation or purification devices adapted for specific applications
    • B01D2259/4566—Gas separation or purification devices adapted for specific applications for use in transportation means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas

Definitions

  • the present invention relates to a catalyst for decomposing aldehydes such as formaldehyde in combustion exhaust gas, and an exhaust gas treatment apparatus and an exhaust gas treatment method using the aldehyde decomposition catalyst.
  • Nitrogen oxides may be included in various combustion exhaust gases from internal combustion engines such as diesel engines and gas engines and combustion facilities such as waste-incineration plants, boilers, and gas turbines and exhaust gases from industrial facilities.
  • Some known methods for removing nitrogen oxides from combustion exhaust gases use alcohols as a reducing agent (e.g., Patent Literature 1).
  • Aldehydes are harmful to many organisms, and among them, formaldehyde is highly toxic and causes irritation of the respiratory system, eyes, throat, skin and the like.
  • Patent Literatures 2 and 3 are disclosed in Patent Literatures 2 and 3.
  • the catalyst disclosed in Patent Literature 2 is made of a zeolite selected from ZSM-5, faujasite, or mordenite, wherein the zeolite carries Pt.
  • Use of this catalyst is costly because the carrier carries a noble metal Pt.
  • the catalyst has to be used in a large amount to achieve sufficient aldehyde decomposition performance.
  • the catalyst disclosed in Patent Literature 3 is made of a zeolite selected from mordenite, ferrierite, ZSM-5, ⁇ -zeolite, Ga-silicate, Ti-silicate, Fe-silicate, or Mn-silicate, wherein the zeolite carries a noble metal selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, or Au. Among them, those including Pd or Ag as a noble metal achieve a relatively high formaldehyde decomposition rate. However, as with the catalyst disclosed in Patent Literature 2, use of a noble metal increases the cost. In addition, a large amount of the catalyst is required to decompose aldehydes.
  • Patent Literature 4 discloses a catalyst made of TiO 2 carrying an oxide of a metal selected from W, Mo, or V.
  • the catalyst disclosed in Patent Literature 4 achieves high performance in decomposing formaldehyde at around 500° C. (the conversion rate is slightly less than 90%), the catalyst achieves insufficient decomposition performance below 500° C. After various combustion exhaust gases and exhaust gases from industrial facilities are freed of nitrogen oxides using an alcohol as a reducing agent, the exhaust gases commonly have a temperature below 500° C. In such cases, the catalyst disclosed in Patent Literature 4 cannot be used.
  • Patent Literatures 2 and 3 made of particular zeolites as a carrier achieve high performance in decomposing formaldehyde at a relatively low application temperature up to around 300° C., and can be used for treating aldehydes in exhaust gases described above.
  • the present invention addresses the above problems, and one object of the present invention is to provide a useful aldehyde decomposition catalyst, and an exhaust gas treatment apparatus and an exhaust gas treatment method using the aldehyde decomposition catalyst, which substitute relatively inexpensive metals for expensive noble metals to lower the cost, and achieve sufficient aldehyde decomposition performance with a small amount of catalyst.
  • an aldehyde decomposition catalyst of the present invention is made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • the combustion exhaust gases contain aldehydes such as formaldehyde.
  • an aldehyde decomposition catalyst made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu, oxidation occurs and the aldehydes can be converted into a harmless gas.
  • the aldehyde decomposition catalyst of the present invention can decompose any kind of aldehydes. Among them, it is particularly desirable to decompose formaldehyde having a high toxicity.
  • the zeolite may be caused to carry Cu by any method, for example, the ion exchange method or impregnation method.
  • the temperature range of the combustion exhaust gas to which the present invention is applicable is not particularly limited but is advantageously from 200 to 600° C., and more advantageously from 200 to 400° C.
  • the decomposition performance is higher as the reaction temperature is higher, but the temperature of the combustion exhaust gas is suitably up to 600° C., or more suitably up to 400° C. in consideration of the limit temperature of the combustion exhaust gas, the cost, and the like.
  • the aldehyde decomposition catalyst of the present invention described above may have any form as long as it can decompose aldehydes.
  • it may be in the form of pellet or honeycomb.
  • the aldehyde decomposition catalyst of the present invention is made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu, and can decompose aldehydes such as formaldehyde in a combustion exhaust gas into a harmless gas.
  • the aldehyde decomposition catalyst of the present invention described above has sufficient aldehyde decomposition performance in a temperature range of 200° C. and higher. Therefore, it can be applied to decomposition of aldehydes in a combustion exhaust gas having a relatively low temperature. In addition, even a small amount of this catalyst can decompose aldehydes.
  • the above aldehyde decomposition catalyst can be applied to exhaust gas treatment apparatus for exhaust gases discharged from internal combustion engines such as diesel engines and gas engines and combustion facilities such as waste-incineration plants, boilers, and gas turbines, so as to efficiently decompose aldehydes contained in the combustion exhaust gases and prevent, for example, formaldehyde, which is harmful and highly toxic to organisms, from being released.
  • FIG. 1 is a flow chart showing a test apparatus used for catalyst performance tests of catalysts of Examples.
  • FIG. 2 is a block diagram showing an exhaust gas treatment apparatus of a marine diesel engine using an aldehyde decomposition catalyst.
  • FIG. 3 is a block diagram showing a variation of the exhaust gas treatment apparatus.
  • the aldehyde decomposition catalyst of the present invention will be hereinafter described in detail.
  • the aldehyde decomposition catalyst of the present invention is made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu, and catalysts included in the present invention will be hereinafter described as Examples.
  • NH 4 -CHA zeolite ZD12002AC from Zeolyst International with a SiO 2 /Al 2 O 3 molar ratio of more than 30
  • ZD12002AC Zeolyst International with a SiO 2 /Al 2 O 3 molar ratio of more than 30
  • Comparative Examples 2 to 4 the catalysts were prepared using the same zeolite species and aqueous metal solutions by the same method as disclosed in Japanese Unexamined Patent Application Publication No. Hei 10-309443.
  • the method of preparing the catalysts of Comparative Examples 2 to 4 was slightly different from the method of preparing the catalysts of Examples 1 to 2 and Comparative Example 1, but these two methods were essentially the same. Therefore, the results of the performance test of Examples 1 to 2 and Comparative Example 1 will now be compared with the results of the test disclosed in Japanese Unexamined Patent Application Publication No. Hei 10-309443.
  • Catalyst performance test was performed on the catalysts of Examples 1 to 2 and Comparative Example 1.
  • the catalysts of Examples 1 to 2 and Comparative Example 1 were press-molded and then ground to mesh sizes 28 to 14.
  • FIG. 1 is a flow chart of a test apparatus used for catalyst performance tests.
  • the catalyst obtained as described above was filled into a stainless reactor ( 1 ) having an inner diameter of 10.6 mm.
  • the reactor ( 1 ) filled with the catalyst receives a test gas at an upper portion thereof through a line ( 2 ) and discharges the gas treated with the aldehyde decomposition catalyst at a lower portion thereof through a line ( 3 ).
  • the test gas received by the reactor ( 1 ) through the line ( 2 ) is prepared by mixing the air from a line ( 4 ) with N 2 gas from a line ( 5 ).
  • the line ( 4 ) and the line ( 5 ) are provided with a valve ( 6 ) and a valve ( 7 ), respectively.
  • the degree of opening of the valve ( 6 ) and the valve ( 7 ) can be adjusted to control the flow rate of respective gases, thereby to control the gas flow rate and the mixture ratio.
  • the mixed gas is introduced into an upper portion of a heater ( 9 ) through a line ( 8 ), and the gas is heated to a predetermined temperature and fed from a lower portion of the heater ( 9 ) to the reactor ( 1 ) through the line ( 2 ).
  • an aldehyde solution (a formaldehyde solution for this embodiment, hereinafter referred to as “the formaldehyde solution”) is fed to the upper portion of the reactor ( 1 ) through a line ( 10 ).
  • the formaldehyde solution to be introduced into the reactor ( 1 ) is pumped up from a formaldehyde solution tank ( 11 ) by a liquid metering pump ( 12 ) and then merged from the line ( 10 ) into the line ( 2 ).
  • the treated gas discharged from the reactor ( 1 ) is discharged out through the line ( 3 ), while partially fed to gas analysis through a line ( 13 ).
  • Table 1 shows the test conditions applied to the test performed with the test apparatus of FIG. 1 .
  • the term “Balance” indicates that N 2 is added such that the total gas composition is 100%, that is, the gas composition other than O 2 , formaldehyde, and moisture is occupied by N 2 .
  • the space velocity (SV) is a value equal to the amount of gas (m 3 /h) to be treated flowing into the reactor divided by the volume (m 3 ) occupied by the reactor containing the catalyst. As this value is larger, the catalyst is contacted more efficiently.
  • the gas analysis was performed by measuring the outlet formaldehyde concentration with a gas detector tube. Based on the measurements by the gas detector tube, the decomposition rate indicating the formaldehyde decomposition performance of the catalyst was calculated from Formula (1) below.
  • formaldehyde (in) refers to the concentration of formaldehyde in the gas before introduction into the reactor ( 1 )
  • formaldehyde (out) refers to the concentration of formaldehyde in the gas discharged from the reactor ( 1 ).
  • the space value SV is set at 120,000/h.
  • Table 3 shows the results of Examples 1 to 2 and Comparative Example 1.
  • Example 1 achieved excellent decomposition rates of 70.4% and 85.3% under the temperature conditions of 200° C. and 250° C., respectively, and Example 2 achieved excellent decomposition rates of 65.5% and 75.6% under the temperature conditions of 200° C. and 250° C., respectively.
  • the catalyst of Comparative Example 1 achieved the decomposition rates exceeding 50% under the temperature conditions of both 200° C. and 250° C., but these decomposition rates did not largely exceed the value of 50% which constitutes a measure of decomposition rates and were about the same as those of the conventional catalysts.
  • the aldehyde decomposition catalyst of the present invention contains Cu, which is a relatively inexpensive metal, instead of expensive metals such as Pt. A small amount of this catalyst achieves better formaldehyde decomposition performance.
  • the combustion exhaust gas thereof contains a sulfur oxide in addition to a nitrogen oxide.
  • the combustion exhaust gas discharged from the diesel engine has a temperature of about 350° C. It is then discharged via a turbocharger and its temperature is reduced to about 200 to 300° C.
  • the sulfur oxide reacts with ammonia to generate ammonium sulfate that may deposit in an exhaust path to block the heat exchanger.
  • Embodiment 2 covers an exhaust gas treatment apparatus and an exhaust gas treatment method that use a small amount of catalyst to sufficiently decompose aldehydes, which is by-produced in denitration by denitration catalyst using alcohol as a reducing agent and contained in an exhaust gas having a low temperature of 200 to 300° C.
  • an exhaust gas having a temperature of about 350° C. is discharged from combustion chambers of a diesel engine ( 21 ) and is delivered from an exhaust pipe ( 22 ) to the turbine side of a turbocharger ( 24 ) via an exhaust reservoir tank ( 23 ).
  • the exhaust gas discharged from the turbocharger ( 24 ) via the exhaust gas path ( 28 ) has a reduced temperature of about 200 to 300° C., and is delivered to a denitration unit ( 25 ) including a denitration catalyst made of a prescribed zeolite carrying a prescribed metal.
  • the pressurized air delivered from a compressor of the turbocharger ( 24 ) is fed to combustion chambers of the diesel engine ( 21 ) via an air-supply reservoir tank ( 26 ).
  • an alcohol serving as a reducing agent is injected into the exhaust gas from an injection nozzle ( 25 b ) provided at an exhaust gas inlet, and the exhaust gas is contacted with a denitration catalyst ( 25 a ), such that oxidation of the alcohol occurs along with the denitration reaction so as to generate aldehydes.
  • the exhaust gas discharged from the denitration unit ( 25 ) is delivered to an aldehyde decomposition unit ( 27 ) serving as an aldehyde decomposition means.
  • the exhaust gas is contacted with the aldehyde decomposition catalyst ( 27 a ) of Embodiment 1, that is, the aldehyde decomposition catalyst ( 27 a ) made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • the aldehydes contained in the exhaust gas is effectively decomposed, and then the exhaust gas is discharged through an exhaust air chimney ( 29 ).
  • Embodiment 2 covers an exhaust gas treatment apparatus in which a combustion exhaust gas is discharged from the diesel engine ( 21 ) and introduced into a denitration unit ( 25 ) via a turbocharger ( 24 ), the combustion exhaust gas has a low temperature of 200 to 300° C., an alcohol serving as a reducing agent is fed to the combustion exhaust gas, and the combustion exhaust gas is contacted with a denitration catalyst for denitration, and the exhaust gas treatment apparatus further includes an aldehyde decomposition unit ( 27 ) serving as an aldehyde decomposition means having an aldehyde decomposition catalyst for decomposing aldehydes contained in the combustion exhaust gas discharged from the denitration unit ( 25 ), and the aldehyde decomposition catalyst is made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • a combustion exhaust gas is discharged from the diesel engine ( 21 ) and introduced into a denitration unit ( 25 ) via
  • Embodiment 2 covers an exhaust gas treatment method in which a combustion exhaust gas is discharged from the diesel engine ( 21 ) and introduced into a denitration unit ( 25 ) via a turbocharger ( 24 ), the combustion exhaust gas has a low temperature of 200 to 300° C., an alcohol serving as a reducing agent is fed to the combustion exhaust gas, and the combustion exhaust gas is contacted with a denitration catalyst for denitration, and the combustion exhaust gas discharged from the denitration unit ( 25 ) is contacted with an aldehyde decomposition catalyst to decompose aldehydes contained in the combustion exhaust gas, and the aldehyde decomposition catalyst is made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • Embodiment 2 covers a method including feeding an alcohol serving as a reducing agent to an exhaust gas discharged from a turbocharger ( 24 ) and having a low temperature of about 200 to 300° C.
  • the exhaust gas is contacted with a denitration catalyst to cause an oxidation reaction of the alcohol that generates aldehydes, in addition to the denitration reaction.
  • the aldehydes is effectively decomposed by an aldehyde decomposition catalyst made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • an aldehyde decomposition catalyst made of a zeolite in a cation form NH 4 having a structure of CHA or MOR and carrying Cu.
  • the aldehyde decomposition catalyst of the present invention used for decomposing aldehydes has sufficient aldehyde decomposition performance in a temperature range of 200° C. and higher. Therefore, it can be applied to decomposition of aldehydes in a combustion exhaust gas having a relatively low temperature. In addition, even a small amount of this catalyst can decompose aldehydes.
  • Use of Cu can reduce the cost since it is inexpensive as compared to expensive noble metals.
  • the denitration unit ( 25 ) arranged upstream in the exhaust gas path and the aldehyde decomposition unit ( 27 ) arranged downstream in the same are independent from each other. It may also be possible to arrange the denitration catalyst ( 32 ) upstream in an integrated container ( 31 ) and arrange the aldehyde decomposition catalyst ( 33 ), serving as an aldehyde decomposition means, downstream in the same, as shown in FIG. 3 .
  • the reference numeral ( 30 ) denotes an injection nozzle for alcohol.
  • the aldehyde decomposition catalyst ( 27 a ), ( 33 ) used in Embodiment 2 may be in any appropriate form such as powder, particle, granule (including spherical ones), pellet (cylindrical or annular ones), tablet, or honeycomb (monolithic body).
  • combustion exhaust gas treatment apparatuses having essentially the same structure as the above-described treatment apparatuses can be used on land as treatment apparatuses for a combustion exhaust gas discharged from, for example, diesel engines installed in a power plant.
  • combustion exhaust gas treatment apparatuses can be suitably applied to internal combustion engines such as dual fuel engines (DF engines) and gas engines.
  • DF engines dual fuel engines
  • gas engines For the DF engines and the gas engines, it is possible to denitrate exhaust gas discharged from, for example, a compressor of a turbocharger and having a temperature of about 200 to 300° C.
  • the combustion exhaust gas treatment apparatuses can be used for denitrating the combustion exhaust gas discharged from combustion facilities such as waste-incineration plants, boilers, and gas turbines.

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