JP2013226543A - Method for purifying combustion exhaust gas, and denitration catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying a combustion exhaust gas and a denitration catalyst, allowing effective reduction of nitrogen oxides (NOx) from the combustion exhaust gas wherein the high-concentration nitrogen oxides and sulfur oxides (SOx) are present, wherein an exhaust gas temperature is as low as 300°C or below, and which is exhausted from an engine for a ship, for example.SOLUTION: In a method for purifying a combustion exhaust gas, the combustion exhaust gas added with an alcohol as a reducer is brought into contact with a denitration catalyst wherein hydrogen and cobalt are carried in sodium-type zeolite having an acid strength corresponding to a Hammett acidity function H≤-7 at a temperature of 180-300°C to remove nitrogen oxides in the exhaust gas. Preferably, the reducer is ethanol, methanol, or isopropyl alcohol. Preferably, the sodium-type zeolite is ZSM-5 (MFI) zeolite or mordenite (MOR) zeolite.

Description

  The present invention relates to a purification method for removing nitrogen oxides from combustion exhaust gas, and a denitration catalyst.

In general, the method of removing nitrogen oxides (NOx) contained in combustion exhaust gas is to contact a gas obtained by adding ammonia (NH ₃ ) as a reducing agent to exhaust gas and contacting a denitration catalyst mainly composed of vanadium or titania. The ammonia selective catalytic reduction (SCR) method, which is removed by this process, is the mainstream, and has been put into practical use as a denitration device for stationary power plants.

By the way, when fuel containing sulfur such as heavy oil is used, sulfur oxide (SOx) is present in the combustion exhaust gas together with nitrogen oxide (NOx). The operating temperature of the denitration facility when sulfur oxide is present must be equal to or higher than the precipitation temperature of ammonium sulfate from the viewpoint of preventing the precipitation of ammonium sulfate on the catalyst. The precipitation temperature of ammonium sulfate is related to the sulfur trioxide (SO ₃ ) concentration and ammonia (NH ₃ ) concentration in the exhaust gas. When the SO ₃ concentration and the NH ₃ concentration increase, the precipitation temperature of ammonium sulfate increases.

Since the exhaust gas discharged from the marine engine is C heavy oil, the SOx concentration in the exhaust gas is about 600 ppm and the NOx concentration is about 1000 ppm. The NH ₃ concentration used as the reducing agent is a maximum of 800 ppm. Accordingly, the precipitation temperature of ammonium sulfate at this time is about 280 ° C. On the other hand, the exhaust gas temperature for ships is 300 ° C. or lower, usually about 250 ° C., so that ammonium sulfate is precipitated under these conditions, and stable catalyst performance cannot be maintained.

Thus, in order to use a denitration catalyst by the ammonia SCR method in the purification treatment of exhaust gas discharged from a marine engine having a high concentration of SOx and NOx and having a low exhaust gas temperature, the precipitation temperature of ammonium sulfate is set to the exhaust gas temperature. Must be: The precipitation temperature of ammonium sulfate is determined by the SO ₃ concentration and the NH ₃ concentration. Since the NH ₃ concentration is determined by the NOx concentration in the exhaust gas and the target denitration rate, this value cannot be reduced. Therefore, in a marine engine whose exhaust gas temperature is lower than the precipitation temperature of ammonium sulfate, exhaust gas is reheated before blowing ammonia (NH ₃ ) used as a reducing agent, and the exhaust gas temperature is reheated to exceed the precipitation temperature of ammonium sulfate. By doing so, the denitration catalyst by the ammonia SCR method is used.

  In addition, as a denitration catalyst other than the ammonia SCR method, there is a direct decomposition method in which nitrogen oxide is decomposed into nitrogen and oxygen only by contacting with the catalyst.

In Patent Document 1 below, nitrogen oxides, particularly NO, contained in exhaust gas discharged from an internal combustion engine can be directly decomposed, and oxygen (O ₂ ) generated by the decomposition and coexist in the exhaust gas. As a nitrogen oxide purification catalyst with a very small reduction in catalytic activity due to oxygen (O ₂ ), a nitrogen oxide purification catalyst comprising a rare earth oxide or a rare earth composite oxide having a cubic C-type structure is disclosed. However, the exhaust gas purification method by the direct decomposition method using the nitrogen oxide purification catalyst described in Patent Document 1 has a problem that the reaction temperature for exhaust gas purification is as high as 600 ° C. or higher.

  Patent Document 2 below discloses an exhaust gas purification method using a catalyst having a denitration performance that removes nitrogen oxide (NOx) even in exhaust gas containing sulfur oxide, and iron, cobalt, silver as a denitration catalyst. NOx in the exhaust gas is reduced by contacting the exhaust gas with excess oxygen in the presence of ethanol and / or isopropyl alcohol as a reducing agent using β zeolite supporting molybdenum or tungsten. An exhaust gas purification method for reduction and removal is described.

  In Patent Document 3 below, proton type β zeolite is used as a catalyst, and in the presence of ethanol and / or isopropyl alcohol as a reducing agent, an oxygen-exhaust exhaust gas is contacted to oxidize nitrogen in the exhaust gas. An exhaust gas purification method for reducing and removing waste NOx is described.

In the following Patent Document 4, Na-ZSM-5 zeolite or H-ZSM-5 type zeolite having a SiO ₂ / Al ₂ O ₃ ratio of 27 or more and 100 or less is used as a catalyst carrier, and the catalyst carrier is a cobalt salt aqueous solution. ZSM-5 loaded with cobalt by immersing it in (cobalt nitrate, acetate, chloride, etc.), ion-exchange the Na (or H) portion of the catalyst support and Co at an ion exchange rate of 40 to 100%. An exhaust gas purification method is described in which type zeolite is used as a denitration catalyst and liquefied petroleum gas having a composition of propane and butane is used as the reducing agent.

  However, even in the exhaust gas purification methods using the reduction removal method using the denitration catalyst described in Patent Documents 2 to 4, there is a problem that the reaction temperature of the exhaust gas purification is about 300 ° C. to 500 ° C. and is still high. It was.

  In view of this, no catalyst having practical denitration catalyst performance has been found at present at a temperature of 300 ° C. or less, which is the exhaust gas temperature of marine engines.

JP 2007-229558 A JP 2004-358454 A JP 2004-261754 A JP-A-11-188238

  The object of the present invention is to solve the above-mentioned problems of the prior art, in which high concentrations of nitrogen oxides (NOx) and sulfur oxides (SOx) exist, and the exhaust gas temperature is as low as 300 ° C. or lower, for example, marine engines. An object of the present invention is to provide a method for purifying combustion exhaust gas and a denitration catalyst that can effectively reduce nitrogen oxides from the combustion exhaust gas discharged from the exhaust gas.

As a result of intensive studies in view of the above points, the inventors of the present invention have used combustion exhaust gas to which alcohol as a reducing agent is added, hydrogen and cobalt (Co) in a zeolite having a predetermined acid strength (H ₀ ). The present inventors have found that nitrogen oxides can be effectively reduced from combustion exhaust gas by contacting the supported denitration catalyst at a temperature of 300 ° C. or lower, and have completed the present invention.

In order to achieve the above object, a combustion exhaust gas purification method invention according to claim 1 is a combustion exhaust gas purification method, wherein the sodium type has an acid strength corresponding to Hammett's acidity function H ₀ of −7 or less. It is characterized by removing nitrogen oxides in exhaust gas by bringing combustion exhaust gas in which alcohol as a reducing agent is added to a denitration catalyst in which hydrogen and cobalt are supported on zeolite at a temperature of 180 to 300 ° C. It is said.

  The invention according to claim 2 is the method for purifying combustion exhaust gas according to claim 1, wherein the reducing agent is ethanol, methanol, or isopropyl alcohol.

  Invention of Claim 3 is the purification method of combustion exhaust gas of Claim 1 or 2, Comprising: A sodium type zeolite consists of a ZSM-5 (MFI) zeolite or a mordenite (MOR) zeolite, It is characterized by the above-mentioned. It is said.

  Invention of Claim 4 is the purification method of combustion exhaust gas as described in any one of Claims 1-3, Comprising: Combustion exhaust gas is exhaust gas which burned C heavy oil, It is characterized by the above-mentioned.

The invention according to claim 5 is a denitration catalyst used in the method for purifying combustion exhaust gas according to claim 1, wherein hydrogen is added to sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less. And cobalt, and is characterized by being used in contact with combustion exhaust gas to which alcohol is added as a reducing agent at a temperature of 180 to 300 ° C.

  According to the invention of the method for purifying combustion exhaust gas of the present invention, high concentrations of nitrogen oxides (NOx) and sulfur oxides (SOx) exist, and the exhaust gas temperature is as low as 300 ° C. or less, for example, marine engines, that is, marine vessels. This produces an effect that nitrogen oxides can be effectively and efficiently reduced from combustion exhaust gas discharged from large-scale diesel engines, large-scale boilers such as factories and power plants, and district heating and cooling.

  Moreover, according to the denitration catalyst used in the method for purifying combustion exhaust gas of the present invention, combustion with a low concentration of nitrogen oxide (NOx) and sulfur oxide (SOx) and an exhaust gas temperature as low as 300 ° C. or less is present. There is an effect that nitrogen oxides can be effectively and efficiently reduced from the exhaust gas.

It is a flowchart of the catalyst performance evaluation test apparatus used in the Example of this invention.

  Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

The method for purifying combustion exhaust gas according to the present invention is a method for purifying combustion exhaust gas, which is a denitration catalyst in which hydrogen and cobalt are supported on sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less. Further, it is characterized in that nitrogen oxides in the exhaust gas are removed by bringing the combustion exhaust gas to which alcohol as a reducing agent is added at a temperature of 180 to 300 ° C.

  The alcohol that is a reducing agent used in the present invention is not particularly limited, and ethanol, methanol, or isopropyl alcohol is generally preferable. The reason is that an alcohol with a small amount of carbon considered to be completely oxidized is preferable.

  On the other hand, the hydrocarbon which is the reducing agent used in the above-described embodiment of Patent Document 3 is effective only when the exhaust gas temperature is high. In addition, hydrocarbons are designated as flammable gases, and when a flammable gas is loaded on a ship, it is necessary to install a safety device or the like. is there.

The denitration catalyst used in the method for purifying combustion exhaust gas of the present invention has hydrogen (H) and cobalt (Co) supported on a sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less. Is.

Here, Hammett's acidity function H ₀ is defined by the ability of an acid point on the surface of a solid acid to give a proton to a base (Bronsted acidity) or the ability to receive an electron pair from a base (Lewis acidity), and is expressed by a pKa value. It can be measured by a known indicator method or gas base adsorption method. For example, by measuring the amount of heat when ammonia is adsorbed to the acid point, it can be measured using an ammonia adsorption heat method for measuring the acid strength distribution.

The acid strength H ₀ of the Hammett of zeolite varies depending on the composition ratio of the zeolite, the preparation method of the zeolite, and the structure of the zeolite.

The acid strength H ₀ of the Hammett of zeolite is determined by the structure of the zeolite such that mordenite (MOR) <ZSM-5 (MFI) <BEA (β) <Y.

  Therefore, in the denitration catalyst according to the present invention, the sodium-type zeolite is preferably composed of ZSM-5 (MFI) zeolite or mordenite (MOR) zeolite.

The catalyst in which Co is supported on the proton-type β zeolite described in Patent Document 3 described above has acid sites of H and Co on the catalyst surface. In the present invention, a catalyst in which Co is supported on a sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less has acid sites of Na and Co on the catalyst surface. The strength of the acid point is H>Co> Na, and it is considered that the stronger the acid point, the more easily the alcohol as the reducing agent reacts. Therefore, in the proton type, there is a possibility that a reaction between protons and alcohol unrelated to the denitration reaction occurs, and the alcohol is consumed excessively. By using sodium-type zeolite, excessive consumption of alcohol is suppressed and performance is improved.

  The denitration catalyst according to the present invention is brought into contact with combustion exhaust gas to which alcohol is added as a reducing agent at a temperature of 180 to 300 ° C.

Here, according to the catalyst of the present invention, excellent nitrogen oxide removal performance can be obtained even when the temperature of the exhaust gas is relatively low, such as about 180 to 300 ° C. When the exhaust gas temperature for ships reaches about 160 ° C in the flue, the sulfur oxide (SOx) contained in the exhaust gas for ships becomes anhydrous sulfuric acid, which combines with moisture and becomes sulfuric acid (H ₂ SO ₄ ). It is not preferable because the phenomenon of adhesion and corrosion of metal (problem of low temperature corrosion) occurs. Accordingly, the temperature of the exhaust gas for ships is usually not lowered to 180 ° C. or lower, and the denitration catalyst according to the present invention is preferably 180 ° C. or higher with respect to the combustion exhaust gas to which alcohol is added as a reducing agent.

  The manufacturing method of the denitration catalyst used for the purification method of combustion exhaust gas of the present invention is as follows.

First, sodium type ZSM-5 (MFI) zeolite or mordenite (MOR) zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less is placed in an aqueous solution of ammonium nitrate (NH ₄ NO ₃ ), Stir at 70-90 ° C. for 2-24 hours, then filter and wash. Next, the filtered washing product is dried at a temperature of 100 to 120 ° C. for 1 to 4 hours to obtain NH ₄ -MFI zeolite or NH ₄ -MOR zeolite.

Thereafter, NH ₄ -MFI zeolite or NH ₄ -MOR zeolite is converted into, for example, cobalt nitrate [Co (NO ₃ ) ₂ ], cobalt acetate [Co (C ₂ H ₃ O ₂ ) ₂ ], cobalt chloride [CoCl ₂ ], formic acid. cobalt placed in an aqueous solution of _{[CoC 4 H 14 O 8)} ] cobalt compounds such as, at a temperature 70 to 90 ° C., after stirring for 2-24 hours, washed by filtration. Next, the filtered and washed product is dried at a temperature of 100 to 120 ° C. for 1 to 4 hours, and further calcined at a temperature of 450 to 550 ° C. for 3 to 5 hours, whereby Co / H-MFI zeolite or Co / H-MOR is obtained. Zeolite is produced.

  In the denitration catalyst according to the present invention, the Co loading is preferably 1 to 4% by weight.

  Here, if the amount of cobalt ions supported is less than 1% by weight, the amount supported is small, that is, the number of active sites is too small, which is not preferable. On the other hand, if the amount of cobalt ions supported exceeds 4% by weight, the proportion of Co oxide on the surface that does not contribute to the denitration reaction increases, which is not preferable.

  The denitration catalyst used in the method for purifying combustion exhaust gas of the present invention can also be produced as a honeycomb type denitration catalyst, for example, by supporting sodium zeolite, hydrogen and cobalt on a honeycomb structure.

  First, a step of applying a slurry made of sodium-type zeolite, water, and silica sol to glass paper is performed to prepare a base material for manufacturing a honeycomb structure.

  Next, the step of obtaining a corrugated plate-like substrate by processing the sodium-type zeolite-supporting substrate into a corrugated shape, the step of obtaining the flat plate-like substrate by processing the above-mentioned substrate into a flat plate, and the corrugated shape A honeycomb structure is manufactured by carrying out a step of alternately laminating the substrate and the flat substrate.

  Further, a step of ion exchange of hydrogen and cobalt is performed on the sodium-type zeolite-supported honeycomb structure produced by the above method to produce a honeycomb-type denitration catalyst.

  Alternatively, the above-mentioned sodium-type zeolite-supporting base material is processed into a corrugated shape to obtain a corrugated plate-like base material, the above-mentioned base material is processed into a flat plate to obtain a flat base-like base material, A step of obtaining a corrugated catalyst by ion exchange of hydrogen and cobalt with respect to a base material; a step of obtaining a flat catalyst by ion exchange of hydrogen and cobalt with respect to the flat base material; and the corrugated catalyst; A step of alternately laminating the flat catalyst is carried out to produce a honeycomb type denitration catalyst.

  In this manner, a sodium-type zeolite is fixed to glass paper using an inorganic binder such as silica sol, and a desired shape such as a honeycomb structure can be obtained by molding this.

  In this case, since there is no possibility of clogging even when a high concentration slurry is used, a high concentration slurry can be used, and the operation of loading the sodium-type zeolite is sufficient. Also, unlike the method of generating sodium-type zeolite on the substrate, it does not require the high-temperature and high-pressure conditions required for sodium-type zeolite generation because it supports already prepared sodium-type zeolite. If there is, it can be sufficiently produced.

  Also, when the metal of the catalyst component is supported on the manufactured sodium-type zeolite supporting honeycomb, there is an advantage that solid-liquid separation can be easily performed because of the molded support.

  Here, the steps from the production of the base material for producing the honeycomb structure to the final production of the honeycomb type denitration catalyst will be specifically described as follows.

(Preparation of base material)
First, a sodium-type zeolite, water and silica sol are mixed to prepare a slurry.

  In the denitration catalyst according to the present invention, the sodium-type zeolite is preferably composed of ZSM-5 (MFI) zeolite or mordenite (MOR) zeolite.

  As the silica sol, an acidic type containing about 20% by weight of silica can be used.

  Moreover, when producing a slurry, the weight ratio of a sodium-type zeolite, water, and a silica sol is adjusted to 100: 100: 46, for example.

  Next, the slurry thus obtained is applied to glass paper. Silica sol contained in such a slurry functions as an inorganic binder, and when corrugated, it can retain the corrugated shape and is intended to produce a honeycomb structure that can be corrugated. The base material can be obtained.

  In applying a slurry obtained by mixing sodium-type zeolite, water and silica sol, any conventionally known method may be used. For example, a so-called soaking method, brush coating method, spray coating method, dropping coating method Etc.

  As described above, a flat substrate on which sodium-type zeolite is supported is obtained. Since the slurry is applied to the flat glass paper in this way, there is no possibility of clogging when the slurry concentration is high, and a high concentration slurry can be used for the application from the beginning, and a single carrying operation. A sodium-type zeolite-supporting substrate can be obtained.

(Base material molding)
The sodium-type zeolite supporting substrate as described above can be formed into a corrugated shape using a corrugator. On the other hand, an inorganic binder such as silica sol added by applying slurry serves as a binder for glass paper. As a result, the corrugation can be maintained after the glass paper is molded. Therefore, the sodium-type zeolite-supporting base material is a material suitable for producing a honeycomb structure.

  When producing a honeycomb structure using the above-mentioned sodium-type zeolite-supporting base material, various methods can be considered as processing for the sodium-type zeolite-supporting base material. As one method, the base material is corrugated. To form a corrugated base material, and alternately stack a plurality of corrugated base materials and a plurality of flat base materials having a flat surface shape that has not been subjected to molding processing. Thus, there is a method for forming a honeycomb structure.

  Various methods known in the art may be used for corrugating the sodium-type zeolite-supporting substrate. For example, the sodium-type zeolite is supported on a gear-shaped disk having a corrugated outer periphery. By rotating the substrate, it is possible to obtain a corrugated plate along the outer peripheral waveform of the disk. Alternatively, a metal panel having a groove having a predetermined shape is used, and the sodium-type zeolite-supporting substrate placed in the mold is pressed along the groove of the mold by a pressing jig. It is also possible to mold.

  Next, a drying process is performed on the corrugated substrate after molding. Although the conditions in that case are not specifically limited, For example, it is set | placed over the period of 1 hour-3 hours at the temperature of 110-300 degreeC by air atmosphere.

  The flat substrate and corrugated substrate obtained as described above are subjected to a firing step. Although the conditions in that case are not specifically limited, For example, it is put over 3 hours at the temperature of 500-550 degreeC by an air atmosphere.

  The disk that rotates and moves the flat plate base material after drying has a flat plate-like substrate and a corrugated plate-like substrate that are alternately arranged when the honeycomb structure is manufactured. It is convenient to place it side by side with the disk.

  A honeycomb structure can be obtained by alternately laminating the corrugated substrate and the flat substrate processed as described above. In this honeycomb structure, each flat plate-like substrate and corrugated plate-like substrate need only be kept in contact with each other. It is also possible to maintain the contact state by placing it in the box.

(Preparation of honeycomb type denitration catalyst)
A honeycomb type denitration catalyst can be obtained by supporting hydrogen and cobalt having catalytic activity on the honeycomb structure obtained as described above.

In the present invention, hydrogen and cobalt are supported on a sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less.

When performing ion exchange for supporting hydrogen and cobalt on zeolite as described above, a honeycomb structure supporting the above ZSM-5 (MFI) type zeolite or mordenite (MOR) type zeolite was converted to ammonium nitrate (NH ₄ It is put into an aqueous solution of NO ₃ ), immersed at a temperature of 70 to 90 ° C. for 2 to 24 hours, and then washed. Subsequently, the washed product is dried at a temperature of 100 to 120 ° C. for 1 to 4 hours to obtain NH ₄ -MFI zeolite or NH ₄ -MOR zeolite.

Thereafter, NH ₄ -MFI zeolite or NH ₄ -MOR zeolite is converted into, for example, cobalt nitrate [Co (NO ₃ ) ₂ ], cobalt acetate [Co (C ₂ H ₃ O ₂ ) ₂ ], cobalt chloride [CoCl ₂ ], formic acid. cobalt placed in an aqueous solution of _{[CoC 4 H 14 O 8)} ] cobalt compounds such as, at a temperature 70 to 90 ° C., after soaking for 2-24 hours, washed. Next, the washed product is dried at a temperature of 100 to 120 ° C. for 1 to 4 hours, and further calcined at a temperature of 450 to 550 ° C. for 3 to 5 hours, whereby a Co / H-MFI zeolite or a Co / H-MOR zeolite is obtained. And a honeycomb structure carrying the denitration catalyst of the present invention, that is, a honeycomb type denitration catalyst is obtained. The amount of Co supported by the denitration catalyst according to the present invention is preferably 1 to 4% by weight.

  Here, as described above, a step of applying a slurry made of sodium-type zeolite, water, and silica sol to glass paper is carried out to produce a substrate for producing a honeycomb structure, Processing the sodium-type zeolite-supporting base material into a corrugated shape to obtain a corrugated base material, processing the base material into a flat plate to obtain a flat base material, and the corrugated base material. A step of obtaining a corrugated catalyst by ion-exchange of hydrogen and cobalt, a step of obtaining a flat catalyst by ion-exchanging hydrogen and cobalt to the flat substrate, and the corrugated catalyst and the flat catalyst. A honeycomb type denitration catalyst may be manufactured by alternately stacking layers.

  According to the method for purifying combustion exhaust gas of the present invention, high concentrations of nitrogen oxides (NOx) and sulfur oxides (SOx) are present, and the exhaust gas temperature is as low as 300 ° C. or less, for example, marine engines, ie large marine vessels. Nitrogen oxides can be effectively reduced from combustion exhaust gas discharged from diesel engines, factories and power plants, large-scale boilers such as district heating and cooling.

  Moreover, according to the denitration catalyst used in the method for purifying combustion exhaust gas of the present invention, combustion with a low concentration of nitrogen oxide (NOx) and sulfur oxide (SOx) and an exhaust gas temperature as low as 300 ° C. or less is present. Nitrogen oxides can be effectively and efficiently reduced from exhaust gas.

  Next, examples of the present invention will be described together with comparative examples, but the present invention is not limited to these examples.

Example 1
As a denitration catalyst used in the method for purifying combustion exhaust gas of the present invention, hydrogen (H) and ZSM-5 (MFI) type zeolite, which is a sodium type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7, are used. A catalyst carrying cobalt (Co) was produced.

First, 10 g of a commercially available ZSM-5 (MFI) zeolite (trade name: Mizukashi-bus EX122, manufactured by Mizusawa Chemical Industry Co., Ltd .: acid strength -7) was added to a 0.1 mol (M) ammonium nitrate [NH ₄ NO ₃ ] aqueous solution. The solution was placed in 200 ml, stirred at a temperature of 80 ° C. for 24 hours, filtered and washed. Subsequently, the filtered washed product was dried at 110 ° C. for 3 hours to obtain NH ₄ -MFI zeolite. Furthermore, NH ₄ -MFI zeolite was put in 200 ml of 0.1 mol (M) cobalt nitrate [Co (NO ₃ ) ₂ ] aqueous solution, stirred at a temperature of 80 ° C. for 24 hours, and then filtered and washed. Next, the filtered and washed product is dried at 110 ° C. for 3 hours, and further calcined at 500 ° C. for 4 hours, whereby the hydrogen (H) / cobalt (Co) ion exchange ZSM-5 (MFI) zeolite of the present invention is obtained. Got. The amount of Co supported by this catalyst was 1.46% by weight.

  A denitration catalyst performance evaluation test corresponding to the combustion exhaust gas purification method of the present invention was conducted using the denitration catalyst of the present invention thus produced. FIG. 1 shows a flow chart of a denitration catalyst performance evaluation test apparatus.

First, the catalyst made of H / Co-ZSM-5 (MFI) -type zeolite obtained as described above is pulverized after press molding and sized to a mesh size of 28 to 14, and the denitration catalyst powder is obtained. Prepared. Next, in the test apparatus shown in the flow chart of FIG. 1, a denitration reactor consisting of a stainless steel reaction tube having an inner diameter of 10.6 mm is filled with denitration catalyst particles, and ethanol as a reducing agent is added at a concentration of 700 ppm. Using the exhaust gas having a NO concentration of 1000 ppm, a performance evaluation test was performed under the test conditions shown in Table 1 below.

  The gas analysis at the outlet of the denitration reactor measured the outlet NOx concentration using a nitrogen oxide (NOx) meter. From the measured value with the NOx meter, the NOx removal rate, which is the NOx removal performance of the catalyst, was calculated by the following mathematical formula (1).

Denitration rate (%) = (NOx _in −NOx _out ) / NOx _in × 100 (1)
The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 2 below.

(Example 2)
As in the case of Example 1, the denitration catalyst performance evaluation test corresponding to the combustion exhaust gas purification method of the present invention is performed under the test conditions shown in Table 1 above, but differs from the case of Example 1 above. Is that methanol is used as a reducing agent at a concentration of 4000 ppm. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 2 below.

(Comparative Example 1)
For comparison, a denitration catalyst performance evaluation test corresponding to the method for purifying combustion exhaust gas is carried out in the same manner as in the case of Example 1 above. However, the difference from the case of Example 1 is that This is the use of a catalyst in which cobalt (Co) is supported on BEA type zeolite, which is a sodium type zeolite having an acid strength corresponding to Hammett's acidity function H ₀ of 5.

This denitration catalyst was produced as follows. First, 10 g of commercially available BEA-type zeolite (trade name H-BEA-35, manufactured by Z-Demi-Catalyst Co., Ltd .: acid strength -5) is placed in 200 ml of 0.1 M Co (NO ₃ ) ₂ aqueous solution, After stirring at 80 ° C. for 24 hours, it was filtered and washed. The filtered and washed product was then dried at 110 ° C. for 3 hours and further calcined at 500 ° C. for 4 hours to obtain cobalt (Co) ion-exchanged zeolite. The amount of Co supported by this catalyst was 1.92% by weight.

  A denitration catalyst performance evaluation test corresponding to the method for purifying combustion exhaust gas was carried out in the same manner as in Example 1 above, using the denitration catalyst produced in Comparative Example 1 in this way. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 2 below.

(Comparative Example 2)
For comparison, a denitration catalyst performance evaluation test corresponding to a method for purifying combustion exhaust gas is performed in the same manner as in the case of Example 1. The difference from the case of Example 1 is that the method for purifying combustion exhaust gas As the denitration catalyst used in the above, a catalyst in which cobalt (Co) is supported on a Y-type zeolite which is a sodium-type zeolite having an acid strength corresponding to the Hammett acidity function H ₀ of −3 is used.

This denitration catalyst was produced as follows. First, 10 g of a commercially available Y-type zeolite (trade name Mizukashi-bus Y-420, manufactured by Mizusawa Chemical Industry Co., Ltd .: acid strength-3) is placed in 200 ml of 0.1 M Co (NO ₃ ) ₂ aqueous solution, and the temperature is 80. The mixture was stirred at 24 ° C. for 24 hours, and then filtered and washed. The filtered and washed product was then dried at 110 ° C. for 3 hours and further calcined at 500 ° C. for 4 hours to obtain cobalt (Co) ion-exchanged zeolite. The amount of Co supported by this catalyst was 10.33% by weight.

  A denitration catalyst performance evaluation test corresponding to a method for purifying combustion exhaust gas was carried out in the same manner as in Example 1 above, using the denitration catalyst produced in Comparative Example 2 in this manner. In Comparative Example 2, a reducing agent was used. Ethanol was used at a concentration of 700 ppm. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 2 below.

(Comparative Example 3)
For comparison, a denitration catalyst performance evaluation test corresponding to a method for purifying combustion exhaust gas is performed in the same manner as in the case of Example 1. The difference from the case of Example 1 is that the method for purifying combustion exhaust gas As a denitration catalyst used in the above, a catalyst in which cobalt (Co) is supported on ZSM-5 (MFI) zeolite, which is a sodium type zeolite having an acid strength corresponding to Hammett's acidity function H ₀ of −7, was used. is there.

This denitration catalyst was produced as follows. First, 10 g of commercially available ZSM-5 (MFI) zeolite (trade name: Mizukashi-bus EX122, manufactured by Mizusawa Chemical Industry Co., Ltd .: acid strength -7) was added to 0.1 mol (M) of cobalt nitrate [Co (NO ₃ ). ₂ ] The solution was placed in 200 ml of an aqueous solution, stirred at a temperature of 80 ° C. for 24 hours, and then washed by filtration. The filtered and washed product was then dried at 110 ° C. for 3 hours and further calcined at 500 ° C. for 4 hours to obtain cobalt (Co) ion-exchanged zeolite. The amount of Co supported by this catalyst was 2.6% by weight.

  A denitration catalyst performance evaluation test corresponding to a method for purifying combustion exhaust gas was carried out in the same manner as in Example 1 above, using the denitration catalyst produced in Comparative Example 3 in this way. Ethanol was used at a concentration of 700 ppm.

The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 2 below.

  As is clear from the results in Table 2 above, the denitration test of Example 1 according to the present invention shows a higher denitration rate than the denitration tests of Comparative Examples 1 and 2, and the denitration catalyst according to the present invention. However, it can be seen that the reaction temperature is 250 ° C. and the catalyst performance is high. In Comparative Example 3, the NOx removal rate is as high as that in Examples according to the present invention as compared with Comparative Examples 1 and 2, but as described later, sulfur oxide (SOx) as compared with Examples. The durability in the presence of is inferior.

Here, as an amount indicating the denitration performance, a reaction rate constant K when the denitration reaction is assumed to be a primary reaction of NOx was used as an index. That is, the reaction rate constant K is represented by the following formula. And in the denitration test of Example 1 by said this invention, and the denitration test of Comparative Examples 1-3, the reaction rate constant K was computed from the following formula, and the result of the obtained reaction rate constant K was shown in the following It is shown in Table 3.
K = −In (1-x) × SV
K: Reaction rate constant X: Reaction rate (denitration rate)
SV: Space velocity (l / h)

  As is apparent from the results in Table 3 above, in the denitration tests of Examples 1 and 2 according to the present invention, both of the reaction rate constants K were higher than in the denitration tests of Comparative Examples 1 and 2, and nitrogen oxides ( It can be seen that NOx) is efficiently reduced.

(Example 3)
Next, in order to confirm that the denitration catalyst can effectively reduce nitrogen oxides even in the presence of a high concentration of sulfur oxide (SOx), the denitration catalyst according to the present invention is treated with sulfur trioxide (SO _3). ).

Under the conditions shown in Table 4 below, a resistance test in which the denitration catalyst was exposed to a gas containing sulfur trioxide (SO ₃ ) for a certain period of time was performed, and the resistance of the denitration catalyst according to the present invention to sulfur oxide (SOx) was tested. .

In Example 3, the H / Co-ZSM-5 (MFI) type zeolite produced in Example 1 according to the present invention was converted into a gas containing sulfur trioxide (SO ₃ ) before performing the denitration catalyst performance evaluation test. It was exposed for 47 hours. In addition, sulfur trioxide (SO ₃ ) was sent to the evaporation pipe using a fixed liquid feed pump, gasified in the evaporator, and then flowed into the reaction pipe.

Next, using this denitration catalyst after the exposure to sulfur trioxide, a denitration catalyst performance evaluation test corresponding to the combustion exhaust gas purification method was conducted in the same manner as in Example 1 above. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 5 below.

Example 4
In the same manner as in Example 3, the denitration catalyst according to the present invention is tested for resistance to sulfur trioxide (SO ₃ ). The difference from Example 3 is that in Example 4, the present invention The H / Co-ZSM-5 (MFI) -type zeolite produced in Example 1 according to the present invention was exposed to a gas containing sulfur trioxide (SO ₃ ) for 110 hours before performing the denitration catalyst performance evaluation test. .

  Next, using this denitration catalyst after the exposure to sulfur trioxide, a denitration catalyst performance evaluation test corresponding to the combustion exhaust gas purification method was conducted in the same manner as in Example 1 above. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 5 below.

(Comparative Example 4)
For comparison, the denitration catalyst was tested for resistance to sulfur trioxide (SO ₃ ) in the same manner as in Example 3 above. The difference from Example 3 was that Comparative Example 4 The Co-ZSM-5 (MFI) zeolite produced in Comparative Example 3 is exposed to a gas containing sulfur trioxide (SO ₃ ) for 36 hours before the denitration catalyst performance evaluation test.

Next, using this denitration catalyst after the exposure to sulfur trioxide, a denitration catalyst performance evaluation test corresponding to the combustion exhaust gas purification method was conducted in the same manner as in Example 1 above. The results of the evaluation test of the obtained NOx removal catalyst performance are shown in Table 5 below.

  As is clear from the results in Table 5 above, the denitration test using the denitration catalyst after the exposure to sulfur trioxide in Examples 3 and 4 of the present invention was compared with the denitration test using the denitration after the exposure to sulfur trioxide in Comparative Example 4. All show high denitration rates, and it can be seen that the denitration catalyst according to the present invention has excellent resistance to sulfur oxides (SOx) contained in a large amount of exhaust gas discharged from marine engines, for example.

  As is apparent from this, according to the method for purifying combustion exhaust gas of the present invention, high concentrations of nitrogen oxides (NOx) and sulfur oxides (SOx) are present, and the exhaust gas temperature is 300 ° C. Nitrogen oxides can be effectively reduced from combustion exhaust gas discharged from ships engines, that is, large diesel engines for ships, large-scale boilers such as factories and power plants, and district heating and cooling. Is possible.

Claims (5)

A combustion exhaust gas purification method comprising a denitration catalyst in which hydrogen and cobalt are supported on sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of −7 or less, and an alcohol as a reducing agent added to the combustion exhaust gas Is removed at a temperature of 180 to 300 ° C. to remove nitrogen oxides in the exhaust gas.   The method for purifying combustion exhaust gas according to claim 1, wherein the reducing agent is ethanol, methanol, or isopropyl alcohol.   The method for purifying combustion exhaust gas according to claim 1 or 2, wherein the sodium-type zeolite comprises ZSM-5 (MFI) zeolite or mordenite (MOR) zeolite.   The method for purifying combustion exhaust gas according to any one of claims 1 to 3, wherein the combustion exhaust gas is exhaust gas obtained by burning C heavy oil. A denitration catalyst used in the method for purifying combustion exhaust gas according to claim 1, wherein hydrogen and cobalt are supported on a sodium-type zeolite having an acid strength corresponding to Hammett acidity function H ₀ of -7 or less. A denitration catalyst, wherein the catalyst is used in contact with combustion exhaust gas to which alcohol is added as a reducing agent at a temperature of 180 to 300 ° C.

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