JP2506357B2 - Method for producing catalyst for removing nitrogen oxides in exhaust gas - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a catalyst for catalytic reduction removal of nitrogen oxides in exhaust gas with ammonia, and particularly to a catalyst poison substance contained in exhaust gas. The present invention relates to a method for producing a catalyst that is resistant to deterioration and has excellent moldability and mechanical strength.

(Prior Art) Nitrogen oxides contained in exhaust gas from various combustion furnaces are substances that are not only harmful to the human body themselves but also cause air pollution such as photochemical smog. In order to remove (denitrify) this nitrogen oxide, a catalytic reduction method (selective reduction) is currently widely used with ammonia. As a catalyst for this purpose, the catalyst currently in practical use is disclosed in JP-A-50-51.
No. 966 and Japanese Patent Laid-Open No. 52-122293, Titania (T
The catalyst is composed mainly of iO ₂ ) and vanadium (V), molybdenum (Mo), tungsten (W), etc. added thereto. These catalysts had high activity and little deterioration with respect to sulfur oxides in exhaust gas, and were excellent in terms of life. However, in the exhaust gas, arsenic (As), selenium (Se), tellurium (Te), etc. It has been found that the presence of volatile substances causes poisoning and activity deterioration.

The present inventors have found that a catalyst containing zeolite as a main component has excellent toxicity resistance against these volatile catalyst poisons, and in particular, a copper-loaded zeolite catalyst has a high activity and maintains a high activity for a long time. He found this and applied for Japanese Patent Application No. 61-157448.

(Problems to be Solved by the Invention) However, the above zeolite-based catalyst is insufficient in terms of moldability and mechanical strength, and it has been desired to obtain a catalyst molded body having sufficient strength.

(Means for Solving Problems) The present invention has been made to solve the above problems, and in a method for producing a catalyst by catalytic reduction removal of nitrogen oxides in exhaust gas with ammonia, an active metal component Add 10 to 90% by weight of titania to the copper-supported zeolite, and add water to the mixture to knead it.
23-43% by weight, and then 5-30% of the total amount of catalyst
It is intended to provide a method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises adding and mixing the mixture in an amount of% by weight, and then drying and firing after molding.

(Operation) According to the present invention, by mixing the inorganic fiber in the catalyst composition, the individual catalyst particles are cross-linked with each other, and the mechanical strength can be increased. Here, in order to sufficiently exert the effect of the inorganic fibers, it is important to appropriately cut the fibers, and this cutting degree is largely controlled by the softness of the catalyst kneaded product when the fibers are added and mixed. When the kneaded product is hard, the fibers are excessively cut, and the effect cannot be expected sufficiently. On the contrary, if it is too soft, the fibers are hardly cut and the fluidity of the kneaded product is lowered, so that the moldability is impaired. By adding and mixing fibers in a kneaded product having a softness defined by the water content limited in the present invention, not only it is possible to obtain practically sufficient mechanical strength without impairing moldability, but also kneading It has the effect of improving the particle size distribution of the product and further improving the moldability.

(Example) In the method for producing a catalyst according to the present invention, as the zeolite, any of mordenite, ferrierite, pentasil-type zeolite ZSM-5 manufactured by Mobil Oil Co., etc. can be adopted, but the SiO ₂ / Al ₂ O ₃ ratio is 10 or more, average pore size is 10Å
The following are preferable. As a method for supporting the active metal component, methods such as substitution, kneading, and impregnation using various metal salt aqueous solutions can be adopted. The carrying amount is 0.01
A range of 20 to 20% by weight can be adopted, but it is preferable to control the amount to be not more than the cation exchange capacity of zeolite. The titania may be any of metatitanic acid and chlorinated titania, but is preferably fine particles having a specific surface area of 20 m ² / g or less and an average particle diameter of 2 μm or less.

The mixing ratio of zeolite and titania may be 1/9 to 9/1 in terms of zeolite / titania weight ratio. If this ratio is too small, the catalytic performance of the zeolite is not utilized, and if the ratio is too large, the strength-imparting effect and particle size improving effect of titania are not significant, so the zeolite / titania weight ratio is 3/7 to 8 /. 2 is more preferable.

When the amount of the inorganic fiber added is too large, the catalyst activity, life and moldability are deteriorated, and when it is too small, the strength improving effect does not appear. Therefore, 5 to 30% by weight of the total amount of the catalyst is suitable.

The catalyst paste obtained by the present manufacturing method can be formed into a catalyst molded body by a method of extrusion molding into a cylinder, a cylinder, a honeycomb shape, or a method of coating and molding on a metal, ceramic woven cloth, or the like.

Zeolites have a pronounced dilatancy and the particles have very low mechanical strength. Dilatancy is
It develops when the particle sizes are relatively uniform. When strong and fine particles such as titania are added, the particle size distribution can be widened, dilatancy can be eliminated and moldability can be improved, and at the same time titania also functions as a matrix and is expected to improve mechanical strength. However, since the binding force between zeolite-titania, different or similar particles is not strong,
Binders etc. are required. Inorganic fibers are used for this purpose, but depending on the method of introduction at the stage of catalyst production, not only this effect is not fully exhibited but, on the contrary, it may adversely affect.

In the present invention, the inorganic fiber is mixed after the water content of the kneaded zeolite and titania is adjusted to 23 to 43% by weight. When the water content is out of this range, the kneaded product does not have an appropriate softness as described above, the degree of cutting of the inorganic fibers becomes insufficient, and a catalyst excellent in moldability and mechanical strength cannot be obtained.

When inorganic fibers are added during wet kneading, if the fibers are excessively cut, the cross-linking function between the particles by the fibers is reduced, and the effect of improving strength cannot be expected. On the other hand, if the fibers are not cut too much, the plasticity of the catalyst kneaded product is lowered and the formability is sacrificed. In particular, when the catalyst kneaded product is pressure-applied and molded on a metal mesh-shaped metal lath plate with a roller, the paste does not properly enter the mesh of the lath plate, and it becomes impossible to form a plate-shaped catalyst.

The present inventors have found that the degree of cutting of the inorganic fiber is largely controlled by the softness of the catalyst kneaded product when the fiber is added and mixed.

According to the method for producing the catalyst of the present invention, after the zeolite and the titania are sufficiently mixed and kneaded in advance, the inorganic fiber is added and mixed into the kneaded product having an appropriate softness, so that the fiber is appropriately cut and molded. It is possible to obtain a catalyst having excellent properties and mechanical strength. If zeolite and inorganic fibers are mixed and kneaded, and then titania is added and mixed, or zeolite, titania and inorganic fibers are mixed and kneaded at the same time, it is difficult to control the cutting degree of the fibers well.

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 1.2 kg of hydrogen-type synthetic mordenite powder having an SiO ₂ / Al ₂ O ₃ ratio of 23 and an average pore diameter of 7Å was added with copper acetate (Cu (CH ₃ COO) ₂ ).
1.7 l of Cu aqueous solution (Cu concentration: 2.1 g / l) was added, and the mixture was stirred, and copper was supported on the modenite by the substitution method, dried at 180 ° C., and then calcined at 500 ° C. for 2 hours. 500 g of the obtained copper-supported mordenite powder was wet-added with water using a kneader.
Kneaded for 30 minutes. Subsequently, 500 g of CR-50 (specific surface area 10.7 m ² / g), which is titania for pigment manufactured by Ishihara Sangyo, was added and kneaded for 1 hour. After appropriately adding water to adjust the water content of the kneaded product to 33.4%, 150 g of kaool was added as an inorganic fiber and kneaded for 40 minutes. Next, after adding 10 g of METOLOSE and kneading for 30 minutes, a catalyst paste was obtained. This paste was pressed onto a wire mesh lath plate made of stainless steel SUS304, which was obtained by spraying alumina in an oxygen atmosphere, by pressing with a roller to form a plate, which was air-dried at room temperature for about 8 hours and then at 500 ° C for 2 hours.
It was calcined for an hour to obtain a plate catalyst.

Examples 2 and 3 In Example 1, a plate-like catalyst was obtained under the same conditions except that the water content of the catalyst kneaded product when the inorganic fiber was added was 38.6% and 25.1%, respectively.

Comparative Examples 1 and 2 In Example 1, a plate-shaped catalyst was prepared under the same conditions except that the water content of the catalyst kneaded product when the inorganic fiber was added was 22.5% and 40.8%, respectively.

Comparative Examples 3 and 4 In Example 1, the amount of the inorganic fiber added was 1% by weight and 33% by weight of the total amount of the catalyst, respectively, and the other conditions were the same to prepare the catalyst.

Example 1 With respect to the catalysts of Examples 1 to 3 and Comparative Examples 1 to 4, 8 kg of a grid (MGH-70 manufactured by Howa Kogyo Co., Ltd.) was tilted at an angle of 45 ° from a height of 500 mm to 100 × 100 mm under constant temperature and humidity conditions. The catalyst (plate-shaped) test piece of No. 1 was dropped, and the amount of abrasion was measured.

Table 1 shows the amount of wear of each of the above catalysts. When the water content of the catalyst paste at the time of adding the inorganic fibers is around 23% by weight, the paste rapidly hardens, the fibers are severely cut, and the strength improving effect decreases, so that the wear amount rapidly increases. When the paste water content is 23 to 40, the paste maintains an appropriate softness, so that the wear amount can be suppressed to be small. 40% paste water content
When it exceeds, the paste is remarkably softened, the inorganic fibers can hardly be cut, the fibers in a long state remain, and it becomes impossible to form a plate-like catalyst.

Further, in Comparative Example 3, the amount of inorganic fibers added is too small, so that the effect of improving strength is small and the amount of wear is large. In Comparative Example 4, it was difficult to form a plate-like catalyst because the amount of inorganic fibers added was too large.

(Effects of the Invention) According to the present invention, it is possible to obtain a catalyst that is less deteriorated by a catalyst poisonous substance such as arsenic or sulfurous acid gas contained in exhaust gas, and sufficiently exert the effect of the inorganic fiber as a binder in the production of the catalyst. It is possible to obtain a zeolite-titanium-based catalyst which has good moldability and excellent mechanical strength.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiaki Matsuda 3-36 Takaracho, Kure-shi Babcock Hitachi Co., Ltd. Kure Research Institute (72) Inventor Nobue Teshima 3-36 Takaracho, Kure-shi Kure Research Institute Co., Ltd. 56) References JP 61-171539 (JP, A) JP 52-46385 (JP, A) JP 62-176546 (JP, A)

Claims (1)

(57) [Claims] 1. A method for producing a catalyst for catalytically reducing and removing nitrogen oxides in exhaust gas with ammonia, wherein titania is added to a zeolite carrying copper as an active metal component in an amount of 10 to 90.
Wt% is added, and water is added to this and kneaded, and the water content of this kneaded product is adjusted to 23 to 43% by weight, and then inorganic fibers are added and mixed by 5 to 30% by weight of the total amount of the catalyst, dried after molding, and fired. A method for producing a catalyst for removing nitrogen oxides in exhaust gas, comprising: