JPH0550339B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is a catalyst for purifying nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas discharged from fixed combustion equipment of various factories including boilers, thermal power plants, steel plants, etc. Concerning the manufacturing method. In particular, NOx and sulfur oxides (mainly sulfur dioxide, hereinafter SOx)
Ammonia is added as a reducing agent to the exhaust gas that simultaneously contains the following: NOx is efficiently decomposed into harmless nitrogen and water through a catalytic reaction.
The present invention relates to a method for producing a catalyst that substantially suppresses the oxidation reaction of sulfur dioxide (SO ₂ ) to sulfur trioxide (SO ₃ ) that occurs simultaneously with the NOx reduction and removal reaction, and has excellent durability. <Description of Prior Art> Methods for removing NOx from exhaust gas can be broadly classified into adsorption methods, absorption methods, and catalytic reduction methods, but the catalytic reduction method has a large amount of exhaust gas to be treated and does not require wastewater treatment. It is advantageous both physically and economically. Catalytic reduction methods include a non-selective reduction method using a hydrocarbon such as methane, LPG, hydrogen, or carbon monoxide as a reducing agent, and a selective reduction method using ammonia as a reducing agent. In the latter case, NOx can be selectively removed even from exhaust gas containing a high concentration of oxygen, and only a small amount of reducing agent is required, so it is economically advantageous and is currently the most widely used method. When processing exhaust gas that contains a large amount of dust, such as exhaust gas from heavy oil-fired boilers or coal-fired boilers, the dust may adhere to the catalyst or accumulate between the catalysts, resulting in a decrease in catalyst performance and a pressure loss in the catalyst layer. A problem arises in that this leads to an increase in the amount of water and impedes smooth operations. In order to solve these drawbacks, catalyst shapes that allow dust to easily pass through the catalyst layer have been proposed. That is, methods in which pipe-shaped, honeycomb-shaped, and plate-shaped catalysts are arranged parallel to the gas flow are widely used. In particular, the plate-shaped catalyst obtained by supporting a contact substance (metal oxide) on a metal base material has enough strength to withstand use even if the thickness of the metal base material is reduced.
This has the advantage that the surface area per unit volume of the catalyst can be increased and the denitrification device can be made more compact. Generally, the catalyst material and the metal base material have different coefficients of thermal expansion, so that the catalyst material may crack due to thermal strain, or the catalyst material layer may peel off due to vibration or impact. Therefore, various production methods and catalysts have been proposed with the aim of improving the adhesion between the metal base material and the catalyst substance. For example, a catalyst is prepared by forming an uneven surface such as needle-like protrusions on the surface of a metal base material by mechanical processing such as knurling, milling, rolling, pressing, or electrical discharge machining, and fixing a catalyst substance on the uneven surface. JP-A-53-149884), a method of thermally spraying a metal or non-metal onto the surface of a metal base material and supporting a catalyst substance on the sprayed surface (JP-A-54-15490, JP-A-54-79189) JP-A-57-19040 discloses a method in which a coating layer with a large surface roughness is formed on the surface of a metal substrate by composite plating and then a catalyst component is supported thereon. All of the above inventions aim to increase the mechanical bonding force between the catalyst substance and the metal surface by roughening the surface roughness of the metal base material, but this increases processing costs and catalyst costs. There are drawbacks. <Object of the Invention> In view of the above points, the present invention overcomes the drawbacks of the prior art, and provides a nitrogen gas that is inexpensive, has good adhesion of the catalyst substance to the metal substrate, and has excellent denitrification activity and durability. A method for producing an oxide cleaning catalyst is provided. <Structure of the Invention> The present inventors coated the surface of a metal base material with a mixture of an oxide of at least one element selected from the group consisting of titanium, silicon, zirconium, and aluminum and vanadium oxide, and then The coating layer is treated at a high temperature of 700 to 1000°C to melt vanadium oxide and form a porous coating layer on the metal substrate, and then an oxide containing titanium is added to the coating layer as a catalyst A component. , vanadium oxide is used as the catalyst component B, and an oxide of at least one element selected from the group consisting of molybdenum, tungsten, copper, chromium, tin, and cerium is used as the catalyst component C.
The present invention was completed by discovering that a catalyst obtained by supporting a catalyst component contained as a component achieves the above object. The present invention will be explained in detail below. Vanadium oxide, which is the vanadium component of the porous coating layer in the present invention, is melted by firing at a temperature of 700°C or higher, and strongly bonds with fine particles such as titania, silica, zirconia and alumina, and also envelops these fine particles. , a solid phase reaction occurs with the surface of the metal base material, and as a result, a porous coating layer that is firmly bonded to the metal base material can be formed. The coating has a rough surface and is porous with many pores and excellent water retention, so the catalyst of the present invention has a stronger adhesion of the catalytic material than the catalyst of the prior art. It can be said that it is a catalyst with extremely excellent physical strength, with no cracking or peeling of the catalyst material even when subjected to thermal shock. It is difficult to use vanadium metal instead of vanadium oxide as the vanadium component in the porous coating. Melting point of vanadium metal (m.
p.1726°C), an extremely high temperature is required to melt the vanadium, which is undesirable because it increases the manufacturing cost of the catalyst, including the selection of the metal base material. On the other hand, in the catalyst of the present invention, since the vanadium component of the porous coating is made of vanadium oxide having a relatively low melting point, the catalyst manufacturing process is simple.
In addition, it has the advantage of providing an inexpensive catalyst with excellent strength. The porous coating layer in the present invention is prepared by degreasing a metal base material, and then forming a composite oxide containing vanadium oxide as an essential component, or a single oxide of each of titanium, silicon, zirconium, aluminum, etc., or a composite oxide consisting of two or more elements. (For example, a binary oxide consisting of titanium and silicon) is mixed well and an appropriate amount of water is added to the resulting slurry or paste, which is applied by painting, dipping, spraying, etc., and then dried. It is obtained by firing at a temperature higher than the melting point of vanadium oxide, preferably at a temperature of 700 to 1000°C for 1 to 60 minutes. Regarding the particle size of titanium, silicon, zirconium, and aluminum oxides, if they are too large, the adhesion to the metal base material will be poor, so the particle size should be 100 μm or less.
In particular, it is preferably 50 μm or less. The thickness of the porous coating layer does not need to be particularly limited, and is sufficient as long as the adhesion strength of the catalyst substance is usable, but the thickness is 10 μm or more, preferably 20 to 500 μm.
A range of m gives preferable results. The vanadium oxide content constituting the porous coating layer is preferably in the range of 3 to 50% by weight. If the vanadium oxide content is less than 3% by weight, adhesion to the substrate will be insufficient, and if it exceeds 50% by weight, the surface of the porous coating layer will be smoothed and the water retention will be deteriorated, so that the adhesion to the substrate will be insufficient. This is not preferable because the adhesion to the porous coating layer decreases. Therefore, the vanadium oxide content is preferably within the above range. The catalyst of the present invention is coated with a slurry or paste of a catalytic material containing the active material specified above on the porous coating by coating, dipping, spraying, etc., and then dried at a temperature of 300 to 650°C, preferably.
It can be obtained by firing at 400 to 550°C for 1 to 10 hours, preferably 3 to 6 hours. The amount of catalyst material supported is 50% per unit surface area of the catalyst.
A range of ~300 g/ ^m2 is preferred. If it is less than 50 g/m ² , the denitrification activity will be poor, and if it exceeds 300 g/m ² , the denitrification activity will not improve further and will almost reach equilibrium, but the raw material cost for the catalyst will increase, so the above range will give preferable results. give. The catalyst material of the present invention has an oxide containing titanium as the catalyst A component, a vanadium oxide as the catalyst B component, and molybdenum, tungsten, copper, chromium,
It consists of a mixture of oxides in which the catalyst C component is an oxide of at least one element selected from the group consisting of tin and cerium, and the composition is such that the A component is 80 to 95
Weight%, B component is 0.5-20% by weight, C component is 0-20% by weight.
Preferably, the content is within the range of 20% by weight.
The catalyst A component may be an oxide containing titanium,
Titanium oxide, a binary oxide consisting of titanium and silicon, a ternary oxide consisting of titanium, silicon and zirconium, or titanium phosphate can also be applied. The material of the metal base material in the present invention is pure iron, pig iron, steel, iron-containing alloy, etc., and the shape is flat plate, corrugated plate, rod, wire, honeycomb, hollow cylinder, etc. A structure of any shape that is a combination of shapes can be applied. For example, by catalyzing a part of the air heater element by the method of the present invention, it is possible to provide an air heater that has both heat exchange and denitrification functions. EXAMPLES The present invention will be specifically described below using Examples, but the present invention is not limited to these Examples. Example 1 Anatase-type titanium oxide (specific surface area 50 m ² /g, average particle size 0.3 μm) was added to a solution of ammonium metavanadate dissolved in an oxalic acid aqueous solution, mixed, concentrated to dryness, and then heated at 400°C. After firing for 3 hours, a powder having a TiO ₂ :V ₂ O ₅ ratio of 85:15 (weight ratio) was obtained. Water was added to this powder and thoroughly stirred with a homodisper to form a slurry. A cold rolled steel plate (SPCC) measuring 50 mm x 30 mm x 0.6 mm was immersed in the powder, dried at 750°C,
It was fired in an air atmosphere for 10 minutes to form a porous coating layer on the surface of the steel plate. The average thickness of the resulting coating layer was 50 μm. Next, an aqueous solution containing monoethanolamine 12c.c.
Ammonium paratungstate 32.3g in 350c.c.
After dissolving ammonium metavanadate
35.7g was dissolved to form a homogeneous solution. Add 500% anatase titanium oxide (specific surface area 50m ² /g) to this solution.
After mixing well, dry and heat at 400℃ for 5 minutes.
After firing for a time, TiO ₂ :V ₂ O ₅ :WO ₃ =90:5:5
A catalyst powder having a composition of (weight ratio) was obtained. 800 c.c. of water was added to 500 g of this catalyst powder, and after stirring with a homodisper while adding an appropriate amount of water to make a uniform slurry liquid, a steel plate on which the porous coating layer was formed was prepared. Soak, then at 100℃ for 5 hours.
After drying, it was fired at 400°C for 5 hours. The amount of catalytically active substance supported was 120 g/m ² per unit surface area of the catalyst. Example 2 Porous steel sheets were formed on the surface of the steel sheet in the same manner as in Example 1, except that zirconium oxide (surface area 45 m ² /g, average particle size 0.3 μm) was used instead of titanium oxide constituting the porous coating layer. The thickness of the coating layer was 100 μm. Next, in Example 1, a binary system consisting of titanium and silicon was used instead of titanium oxide, which was used as one of the catalyst components. A catalyst was prepared in the same manner as in Example 1, except that the same weight of oxide (TiO ₂ /SiO ₂ =4 molar ratio, surface area 160 m ² /g, hereinafter referred to as TS) was used.The amount of catalytically active material supported was It was 140 g/m ² per unit surface area of the catalyst. Example 3 In Example 2, a binary oxide consisting of titanium and silicon (average particle size 20 μm) was used instead of zirconium oxide constituting the porous coating layer. , _TiO2 /
A catalyst was prepared in the same manner as in Example 2, except that SiO ₂ =4 molar ratio, surface area 160 m ² /g) was used. The thickness of the obtained porous coating layer was 40 μm, and the amount of catalytically active substance supported was 100 μm per unit surface area of the catalyst.
g/ ^m2 . Example 4 In Example 1, γ-alumina (average particle size
A porous coating layer was formed on the surface of the steel plate in the same manner as in Example 1 except that a porous coating layer (25 μm) was used. The thickness of the coating layer was 150 μm. Next, a catalyst was prepared in the same manner as in Example 1, except that ammonium molybdate was used instead of ammonium paratungstate, which was used as a starting material for tungsten oxide, one of the catalyst components in Example 1. . The amount of catalytically active material supported was 90 g/m ² per unit surface area of the catalyst. Example 5 In Example 1, silica sand (average particle size 40μ) was used instead of titanium oxide used in the porous coating layer.
m, containing 99% SiO ₂ ), silica sand: V ₂ O ₅ =
A porous coating layer having a composition of 60:40 (weight ratio) was formed on a steel plate in the same manner as in Example 1. The thickness of the resulting coating layer was 130 μm. Next, the same catalytically active material used in Example 1 was supported on the porous coating layer in the same manner as in Example 1 to prepare a catalyst. The amount of catalytically active material supported was 180 g/m ² per unit surface area of the catalyst. Comparative Example 1 The same cold-rolled steel used in Example 1 was immersed in a 1N sulfuric acid aqueous solution for 30 minutes, taken out, washed with water, and then fired at 400°C for 2 hours. The same catalyst material used in Example 1 was supported on the steel plate in the same manner as in Example 1 to prepare a catalyst. The amount of catalytically active substance supported was 120 g/m ² per unit surface area of the catalyst. Example 6 The denitrification rate and adhesive strength of each of the catalysts of Examples 1 to 5 and Comparative Example 1 were measured by the following methods. (1) Measurement of denitrification rate Height is 300mm, reaction gas contact cross section is 50mm x 10
A mm square rectangular stainless steel cassette was filled with catalyst plates (50 mm x 300 mm) parallel to the gas flow direction, and the reaction temperature was set at 380°C. The denitrification rate was measured by introducing the catalyst into the catalyst cassette at a flow rate of 0.375 Nm ³ /H (standard state) while adding the catalyst. Gas composition NO 200ppm SO ₂ 800ppm O ₂ 4% by volume CO ₂ 10% by volume H ₂ O 10% by volume N ₂ balance NH ₃ 200ppm The denitrification rate depends on the NO concentration at the catalyst inlet and outlet.
NO x meter (chemiluminescence type, ECL- manufactured by Yanagimoto Seisakusho)
7S) and calculated according to the following formula. Denitrification rate (%) = (inlet NO concentration)
−(Outlet NO concentration)/(Inlet NO concentration)×100 The obtained results are shown in Table 1. (2) Measurement of adhesive strength Attach double-sided adhesive tape to one side of a 20mm x 20mm aluminum plate, and use these two aluminum plates to form a 30mm x 50mm
After adhering both sides of a catalyst plate of mm size, the aluminum plate was stretched using an Instron to measure the tensile strength when the catalyst material adhered to the aluminum plate was peeled off from the steel plate. The results obtained are shown in Table 1. Examples 7 to 11 Catalytically active substances were supported on the porous coating layer prepared according to Example 1 with different components.
The catalyst was prepared in a similar manner. Vanadium is used as a raw material source for catalytically active substances, including ammonium salts, copper,
Nitrate was used for iron, chromium, manganese, and cerium, and sulfate was used for tin. In each catalyst, the thickness of the porous coating layer was 40 to 60 μm, and the amount of catalytically active substance supported was 110 to 130 g/m ² per unit surface area of the catalyst. The denitrification rate and adhesive strength of each of the obtained catalysts were measured according to Example 6, and the results are shown in Table 1.
Shown below.

[Table] From Table 1, it can be seen that the catalysts of Examples exhibit excellent denitrification activity, and the adhesive strength of the catalyst material is also better than that of the catalysts of Comparative Examples.

Claims (1)

[Claims] 1 The surface of a metal base material is coated with a mixture of an oxide of at least one element selected from the group consisting of titanium, silicon, zirconium, and aluminum and vanadium oxide, and then The coating layer
The vanadium oxide is melted by treatment at a high temperature of 700 to 1000°C to form a porous coating layer on the metal substrate, and an oxide containing titanium is further added to the porous coating layer as a catalyst A component. , vanadium oxide is used as the catalyst B component, and molybdenum, tungsten,
A method for producing a catalyst for nitrogen oxide purification, comprising supporting a catalytically active material containing an oxide of at least one element selected from the group consisting of copper, chromium, tin, and cerium as a catalyst C component. 2. The method according to claim 1, wherein the vanadium oxide content in the porous coating layer-forming mixture is in the range of 3 to 50% by weight.