NL7904502A - METHOD FOR PREPARING A PLATE-SHAPED DENITERATOR CATALYST - Google Patents

Description

-1- 20734 / JD / tj * ---%

Applicant: Hitachi Shipbuilding & Engineering Co. Ltd., Osaka, Japan.

Short designation: Process for preparing a plate-shaped denitrant catalyst.

The invention relates to a method for preparing a plate-shaped denitrating catalyst.

These catalysts are used in a reaction where nitrogen oxides (Ν0χ) in exhaust gases are selectively catalytically reduced with nh3.

10 Since photochemical smog is due to Ν0χ from power plants, sinter or incinerators, various chemical factories, engines etc.,. it is desirable to have a method of effectively treating such contaminants. Of the methods hitherto proposed for denitrating exhaust gases, the method of catalytically reducing NO with NH- used as reducing agent X j is considered advantageous where the process can be carried out with a

relatively small amount of reducing agent because NH_ is selective with NO

j X

responds even when the exhaust gas is more than 1 full. % oxygen.

The previously known catalysts for use in this process include a support such as activated alumina, 3-alumina-alumina or zeolite and a heavy metal compound supported on the support. Such catalysts are usually granular and are mainly used in the form of a fixed bed which has the disadvantage of becoming clogged with dust contained in the exhaust gases or causing a large pressure drop, thus necessitating a booster with a large capacity. These problems can be overcome somewhat by using a catalyst with a larger particle or grain size, but the cores of the catalyst particles will then act less effectively, resulting in a reduced efficiency. In view of the problems described, it seems advantageous to use catalysts with a honeycomb structure to avoid clogging the catalyst layer with dust or to increase the pressure drop.

Power plants and sinter or incinerators usually produce large amounts of exhaust gases that require correspondingly large amounts of catalysts 7904502, r Λ -2- 20734 / JD / tj for treatment. Accordingly, the honeycomb structure catalysts, if useful for this purpose, must be of great shape and sufficient strength to be placed in the treatment device without any damage. Honeycomb-5 catalysts have previously been proposed which comprise a honeycomb support of metal, ceramic or a similar refractory and an active catalytic component placed on the support. Indeed, a metal, if used for the honeycomb structure, must be rendered porous on a surface by a difficult procedure in which the active component must be effectively applied thereto, while also the ceramic structures must have a greater wall thickness and sufficient hardness at a high I must be baked to maintain the desired strength. Therefore, the catalysts of this type require a great deal of work to prepare the honeycomb structure which serves as a support for the active catalytic component and thereby inevitably become expensive.

The present invention provides a process for preparing a plate-shaped deniter catalyst, characterized in that it consists of preparing a suspension of hydrated titanium oxide and a sol selected from the group consisting of silica sol, alumina sol and titanium oxide sol, baking the suspension for obtaining a porous substance, pulverizing the porous substance into a powder, treating a metal network for carrying the powder with a binder, forming a plate-like piece with the metal network as a core, drying or baking the piece to obtain a porous support and depositing a catalytically active component on the support.

Thus, the present invention provides a plate-shaped denitrating catalyst with a small thickness, high strength and a large surface area and is therefore suitable for processing into a honeycomb structure.

Furthermore, the present invention provides a plate-shaped de-nitriding catalyst with an active component supported by a high strength support.

Also, the present invention provides a plate-shaped denitrating catalyst which can be prepared without having to be baked for 7904502% by weight 20734 / JD / tj firming purposes. thereby retains high porosity resulting in increased activity.

The present invention provides a thin plate denitrant catalyst which has a high efficiency.

These and other features of the present invention are more likely to be given in the following detailed description by way of examples with respect to the accompanying drawings in which: Fig. 1 is a perspective view showing a flat sheet catalyst ; Fig. 2 is a perspective view showing a folded metal mesh 1; Fig. 3 is a perspective view showing a honeycomb structure catalyst.

Examples of hydrated titanium oxides useful for the preparation of the suspension of the present invention are orthotitanoic acid and metatitanoic acid. The ratio of the sol to the hydrated titanium oxide, which depends on the water content of the sol, is 1:10 to 10: 1, for example, when the sol is silicon oxide sol containing 20ί SiO ^ 20, aluminum oxide sol containing 1058 or titanium oxide sol containing 2058 Contains TiOg.

It is desirable to dry the suspension before it is baked. The suspension is preferably dried at 70-120 ° C for 0.5-2 hours. By firing, the sol is subjected to a dehydration condensation, the sol comprising the titanium oxide and forming a three dimensional reticulated structure which gives improved strength to the catalyst. While the titanium oxide serves as a carrier, the dehydration condensation products of silica sol, alumina sol and titanium oxide sol themselves are also the carriers of the active component. Such condensation products have a reticulated structure and will not interfere with the support function of the titanium oxide.

The powder step is performed in an ordinary manner. The particle size of the obtained powder is preferably -100 mesh (150 µm) or smaller, although this need not be limiting.

The sheet metal piece with a metal mesh is usually used to prepare a slurry from the powder and a binder, and the metal mesh covered with the slurry.

Binders commonly used are suitable for this purpose. Examples of suitable binders are alumina sol, silica sol, titanium oxide sol, phosphoric acid, boric acid and the like which, when dried or baked, undergo dehydration condensation and form a tough three-dimensional reticulated structure. The most suitable of these examples are alumina sol, silica sol and titanium oxide sol which act as carriers. Preferably, the binder contains a substance, such as an organic solvent, a polymer emulsion or carbon fibers, which evaporates, decomposes or burns away on drying or baking. Such a substance is effective in quickly drying the suspension of the powder and in which a greater porosity of the plate-shaped piece can be obtained. The amount of binder depends on the desired strength of the plate-shaped piece. When silica or alumina is used as the binder, the sol is preferably used in an amount, calculated as solids, of 10-20% of the powder.

The metal networks useful in this invention can be made from any carbon steel, stainless steel, copper, bronze, etc. The. wires forming the network may have a diameter such that the resulting structure formed into the desired shape will not be deformed during the preparation of catalysts or during the use of the resulting catalysts. The network may preferably have small openings, although this is not necessary. Satisfactory results can be obtained with openings usually about 10-100 mesh 2000-150 µm in size. The network may be in the form of a single flat network, a collection of superimposed flat networks, a wave-like, a zig-zag, a pleated or otherwise formed network formed by bending or folding a flat mesh, or a honeycomb structure composed of flat meshes and such curved or folded meshes in combination therewith. Honeycomb structure catalysts may be manufactured by the combination of a catalyst formed by a bent or folded metal network and another catalyst formed by a flat metal network: 7904502 _5- 20734 / JD / t: n honeycomb shapes can be triangular, square, rectangular, hexagonal or otherwise shaped according to the size of the dust particles in exhaust gases etc. Preferably, the plate-shaped piece has a small thickness usually 0.5-2.0 mm .

The plate-shaped piece is dried or baked under the same conditions as when drying or baking the initial slurry.

v

Examples of useful catalytic active components to be placed on the support are V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Sn, Sb, 10 Bi, W, Pt, Rh, Pd and similar metal compounds. These compounds are used alone, or some of them are useful in combinations.

Furthermore, these compounds can be used together with a P-compound, B-compound, alkaline earth metal compound or the like. Examples of the above compounds are oxides, acidic oxide salts, nitrates, sulfates, halides, hydroxides, organic acid salts, organic acid esters, alcoholates, etc. The type and amount of active ingredient carried by the carrier are in accordance with determine the temperature, composition and the like of the exhaust gas to be treated. The wearer must wear the active component in the same manner as when immersed.

The process of the present invention comprising the foregoing steps provides catalysts of the desired size and shape with a honeycomb structure. Since the titanium oxide particles are retained on the metal network by the tough three-dimensional structure resulting from the dehydration condensation of sol, a catalyst can be prepared with satisfactory strength without the need to bake a piece under pressure before strengthen.

This allows the catalyst to maintain an increased porosity resulting in increased activity. The thickness of the catalyst 30 is suitably variable by adjusting the amount of dense slurry of the pulverulent porous substance that is applied to the metal network so that an efficient catalyst of a reduced thickness can be prepared. As a result, the expensive active component can be used very advantageously at a low cost price.

The examples of the present invention are given below.

7904502 -6- 20734 / JD / tj F *%

Example I

Commercial titanium sulfate (100 parts by weight) was slowly added to 1000 parts by weight. parts of hot water at 80 ° C with stirring, and the meta-titanic acid formed by the hydrolysis of titanium sulfate was separated from the mixture 5, washed with water and dried at 100 ° C. A portion (100 parts by weight) of the dried product was kneaded thoroughly with 100 parts by weight. parts of commercial silica (containing 20% SiOg) to prepare a slurry which was dried at 100 ° C for 1 hour and then baked at 400 ° C for 3 hours. The baked product was powdered to a powder with a particle size up to 88 µL. Equal amounts of a powder and the silica sol, the same as previous x used and serving as a binder, were mixed together to obtain a powder containing dense suspension. The slurry was applied to both sides of a metal mesh as shown in Figure 1 and made of steel wires (SUS 304) with a diameter of 0.25 mm, the mesh having openings of 18 mesh and dimensions of 33 mm x 50 mm. The coated network was dried at 100 ° C for 1 hour and then baked at 400 ° C for 3 hours. In this way, a plate-shaped support which was 0.8 mm thick and which had the metal network 20 as its core was obtained. Then, the support was immersed in a 2N oxalic acid solution of NH 4 VO 2 (1.0 mol / liter) at room temperature for 30 minutes, then taken out of the solution and then dried at 100 ° C for 1 hour, leaving a plate-shaped catalyst A with incorporated V was obtained.

Catalysts B and C were prepared in the same manner as described above, except that 80 wt. parts and 60 wt. parts of the silica sol were mixed with the dried product of metatitanoic acid per 100 wt. parts of the latter.

Example II

Catalysts D, E and F were prepared in the same manner as in Example I.

except commercial alumina sol (containing 10% Al 2 O 3) was used in place of the silica sol mixed with the dried product of metatitanoic acid, the alumina sol being added in 200 wt. parts, 160 wt. parts and 120 wt. parts, respectively, 35 per 100 wt. parts of dried product.

7904502 -7- 20734 / JD / tj

Example III

Catalysts G, H and I were prepared in the same manner as in Example I except that commercial titanium oxide sol (containing 20% TiO2) was used instead of silica sol mixed with the dried product metatitanoic acid, the titanium oxide sol being added in 100 wt.

parts, 80 wt. parts and 60 wt. parts per 100 wt. parts of dried product.

.Comparative example

The dried product of metatitanoic acid obtained in Example 10 was baked at 400 ° C for 3 hours without mixing with silicon oxide desol. The same procedure as in Example I was then followed. for preparing a catalyst J.

Activity test

A flow type reactor tube was prepared which had a 50 mm high rectangular parallelepiped with 5 mm x 35 mm openings at its opposite ends. Catalyst A was placed in the parallel piped, and a test exhaust gas of the composition shown in Table A was passed through the reactor tube at a temperature of 250 ° C and at a flow rate of 1 liter / minute (in standard rate).

Table A

component of gas amount (vol.%) NO 0.05 NH3 0.05 25 CO2 13.0 h2o 10.0 02 3.6 SO2 0.025

Ng remainder 30

The deniter yield of the catalyst was calculated from the difference between the NO concentration at the inlet of the reactor tube and that at the outlet. Likewise, the catalyst was tested for the deniter yield at the reaction temperatures 250 ° C, 300 ° C, and 350 ° C.

In the same manner as above, the catalysts B-J were tested 7904502 'κ-8- 20734 / JD / tj for the deniter yield at the same temperatures. The results are given in Table B, which shows that all catalysts have excellent activity at temperatures of 250 ° C and above.

Strength Test 5 A polyvinyl chloride tape was attached to the peripheral portion of Catalyst A to secure this portion. The catalyst was then attached to the bottom of a cylindrical sieve 250 mm in diameter and 50 mm in height and made of a 6-mesh network. 100 ml of 5 mm diameter alumina balls were placed in the sieve. The sieve was placed on an automatic sieve device (amplitude 30 mm, frequency 290 / min) and oscillated for 1 hour. The weight reduction of the catalyst A was measured to determine the amount of wear. The same procedure as above was repeated for the catalysts B-J. The results are given in Table B, which reveals that Catalysts A-I of Examples I-III have greater wear resistance and greater strength than Catalyst J of Comparative Example.

Example IV

Seven metal meshes (50 mm x 100 mm), of the same type as used in Example 1, were folded in a zig-zag shape as shown in Fig. 2. The pieces of the catalyst in the form of a folded plate were prepared from the networks in the same manner as in Example 1. Also seven flat pieces of the catalyst were prepared in the same manner as in Example I using flat metal networks (50 mm x 50 mm) of the same type as used in example I. The folded catalyst pieces and catalyst flat pieces thus formed were alternately placed together to prepare a 50 mm cubic honeycomb structure catalyst for each side as shown in Fig. 3.

Activity test

In the same manner as above, the honeycomb catalyst was tested for deniter efficiency using a flow type reactor tube with a catalyst take-up portion. The 3 2 35 test exhaust gas was passed through the tube at a speed of 15.5 m / m per geometric unit area of the catalyst (in standard condition).

The results are tabulated in Table C.

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Table C

reaction deniter temperature efficiency (%) 250 78.0 5 300 89.5 350 97.3

Table C indicates that the honeycomb catalyst has excellent denitrating activity.

10 - CONCLUSIONS - 7904502

Claims (10)

A process for preparing a plate-shaped denitrating catalyst, characterized in that it consists of preparing a 5 'suspension of hydrated titanium oxide and a sol selected from the group consisting of silica sol, alumina sol and titanium oxide sol, baking the suspension for obtaining a porous substance, pulverizing the porous substance into a powder, treating a metal network for carrying the powder with a binder, whereby a plate-shaped piece is formed with the metal network as core, drying or baking the piece to obtain a porous support and depositing a catalytically active component on the support. 2. Process according to claim 1, characterized in that the binder is selected from d® <* ro®p consisting of aluminum oxide sol, silicon oxide sol, titanium oxide sol, phosphoric acid and boric acid. A method according to claim 1, characterized in that the binder contains an organic solvent, polymer emulsion or carbon fibers. Method according to claim 1, characterized in that the metal network is bent or folded in a wave-like or zig-zag shape. Method according to claim 1, characterized in that the metal network has a honeycomb structure. 6. Method according to claim 1, characterized in that the plate-like piece is formed by covering the metal network with a suspension of the powder and the binder. A method according to claim 1, characterized in that the active component is a compound of a metal selected from the group consisting of V, Cr, Ito, Fe, Co, Ni, Cu, Zn, Mo, Sn, Sb, Bi, W, Pt, Rh and Pd. Process according to claim 7, characterized in that the compound 30 is selected from the group consisting of oxides, salts of acid oxides, nitrates, sulfates, halides, hydroxides, salts of organic acids, esters of organic acids and alcoholates. Process according to claim 1, characterized in that the plate-shaped catalyst has a thickness of 0.5-2.0 mm. 35 10. Catalyst prepared according to the method of any one of the preceding claims. 7904502