Catalyst for reducing oxides of nitrogen in the fluid and method of its manufacture

 

(57) Abstract:

SCR catalyst based on titanium, molybdenum and vanadium differs in that its catalytic activity lies significantly below the catalytic activity of the catalyst containing tungsten. This disadvantage is still offset by a relatively high volume of catalyst. In contrast to the hitherto usual practice, the content of molybdenum oxide, about 10 to 12 wt. % the invention provides that in the catalyst, the proportion of molybdenum in the form of treatise molybdenum Mo3is from about 0.01 to less than 5 wt.%, preferably 1,5 -4 wt. % based on the weight of the catalyst mass. Thus, this containing molybdenum catalyst can be achieved catalytic activity, which is comparable to the activity of the catalyst containing tungsten. The invention is applicable for all catalysts for the reduction of oxides of nitrogen with simultaneous presence of a reducing agent, that is, in particular, also the plate and honeycomb catalysts. 2 S. and 6 C.p. f-crystals, 3 ill.

The invention relates to a catalyst for reducing oxides of nitrogen in the fluid, such as exhaust gas or flue gas, install the action of the impact of nitrogen oxides in the exhaust gas incinerators established technology with the aim of catalytic decomposition of nitrogen oxides. When this proved successful so-called method of selective catalytic reduction (SCR), in which nitrogen oxides together with a suitable reducing agent, in most cases with ammonia NO3, in contact with the so-called DeNOx-catalyst and catalytically converted into environmentally safe nitrogen and water.

In DE-PS 2458888 (= US-PS 4085193) revealed also DeNOx-catalysts, which along with titanium as the main component contain vanadium and molybdenum or tungsten. It turned out that containing molybdenum catalyst does not reach the catalytic activity of the catalyst containing tungsten. This lack of activity can currently be compensated only at the expense of a larger volume containing molybdenum catalyst.

Presented as especially important homogeneous (well mixed) mixture of catalyst components leads to the fact that the catalyst relatively quickly poisoned by heavy metals and compounds of heavy metals, which are contained in the cleaning from nitrogen waste gas. By "homogeneous mixture" chemically stable and/or pre-calcined titanium dioxide TiO2according to US-PS 4085193, cannot be reached sufficient catalytic activity (US-PS 4085193).

In US-PS 495248 disclosed a catalyst to reduce oxides of nitrogen, which contains as a first component an oxide of titanium, as a second component an oxide of molybdenum MoO3and/or tungsten oxide WO3and as a third component - oxide and/or sulfate vanadium. For the content of the second components as the lower boundary of the specified 3 at.%. When the molar weight 144 g for MoO3and 96 g TiO2share MoO3for the lower boundary lies at about 5 wt.%. At the present time is particularly advantageous for the content of molybdenum of this catalyst was the content of the order of 10 - 12 wt.%, calculated in MoO3. It turned out that the catalytic activity of the titanium-molybdenum-vanadium catalyst specified in US-PS 4952548 ratios of atoms lies, as before, the lower catalytic activity of the standard titanium-tungsten-vanadium catalyst.

From DE-OS 3531810-known catalyst material for reduction of NOx, which is produced due to the operation of the active grinding of titanium oxide in the calcined anatase modification while adding vanadium oxide and possibly oxide mistweet in the amount of less than 1 at.% based on the Titan. The catalytic activity is achieved not simply by mixing substances, and due to the refining process, which occurs catalytically active compound, which differs from a pure mixture.

From EP-PS 0313755 also known containing molybdenum and vanadium catalyst based on titanium dioxide for the removal of oxides of nitrogen. Obtained in the catalyst by impregnating the dissolved compound of molybdenum and tungsten content of molybdenum and vanadium, calculated as MoO3and V2O5is 5-15 wt.% or 0.1 to 3.0 wt.%.

For the manufacture of such Ti/Mo/V catalysts (EP-OS 0360548) it is necessary to mix the ammonium molybdate and ammonium metavanadate with metatitanate acid in water in a plastic mass, to pelletize this mass, drying, calcinate at a temperature of 550oC and grind into powder. Thus obtained powder processed with water into a slurry, in which are immersed the metal carrier to cover. In conclusion, make repeated calcination at 500oC.

In addition, in DE-OS 2846476 described that for the manufacture containing titanium dioxide sintered product for catalytic removal of hazardous substances must Nepoklonov the mixture is dried, crushed into powder and pre-calicivirus, and the preliminary calcination is used for deposition of molybdenum oxide in powdered titanium dioxide, to achieve good activity. Then pre-calcined material is again mixed with water and kneaded into a viscous mass. This mass is formed into desired patterns and finally calicivirus.

The basis of the invention lies in the task of creating a catalyst for reducing oxides of nitrogen in the fluid, which contains titanium, molybdenum and vanadium, and catalytic activity which reaches the catalytic activity comparable catalyst containing tungsten. Later in the basis of the invention lies in the task of creating a method for producing such a catalyst.

Regarding the catalyst for this task is solved according to the invention, due to the catalyst to reduce oxides of nitrogen in the fluid with the catalyst mass, which contains titanium, molybdenum and vanadium in the form of their oxides, and the share of treatise molybdenum MoO3is about 0.01 - 5.0 wt.%, preferably about 1.5 to 4.0 wt.% and the proportion of vanadium pentoxide V2O5about 0.01 - 5.0 wt.%, preferably 0.5 to what Ethan TiO2the anatase form.

On how this problem is solved according to the invention, due to the fact that titanium dioxide is mixed with a dispersant such as water, in a plastic mass, to the mass of the added water-soluble compounds of molybdenum and vanadium, and optionally other excipients, and the mass kneaded further into the catalyst mass, then cover bearing elements with a layer of catalyst mass or ekstragiruyut of the catalyst mass cell elements or granularit catalyst mass in grains of granulate or pellets, after that dried equipped with a floor bearing elements or cellular elements or grains of granulate or pellets and calicivirus at a temperature of 400 - 700oC, preferably 500 to 600oC for several hours, preferably 2 to 4 hours

Made thus containing molybdenum catalyst to reduce oxides of nitrogen has a particularly high catalytic activity. This is achieved, in particular due to the fact that the content of molybdenum is particularly small. Corresponding to the invention the catalyst with the same catalytic activity as containing tungsten catalyst on doctitle be used in installations of power plants after melting furnaces cameras. Under chemically stabilized titanium dioxide it is understood such titanium dioxide, in which a diffraction-x-ray analysis shows specific to the lattice of titanium dioxide x-ray reflection. Such stabilized titanium dioxide is obtained, for example, as the end product of sulfate way.

Regarding the surface structure mainly made on the basis of titanium dioxide catalyst is preferred if the proportion of titanium dioxide in the form of rutile is less than 5 wt.%, preferably less than 1 wt. percent, based on the total amount of titanium dioxide TiO2. With titanium dioxide of the anatase form of a simple way to achieve high specific surface area and high activity, while the titanium dioxide in the form of rutile due to the different crystal lattice, in contrast, has a smaller specific surface area.

The catalyst may possess one or more of the following named properties that make the catalyst is particularly stable with respect arsenic poisoning and oxygen compounds of arsenic. Can be provided to choose contamination of the titanium dioxide to sodium Na, potassium K, and iron Fe soutetsu2may be less than 0.5 wt.%, preferably less than 0.2 wt.%. In addition, the proportion of sulfur, calculated as sulfate SO4is titanium dioxide, 0 to 3 wt.%, preferably about 1 to 2 wt.%.

Best for catalytic conversion of nitrogen oxides, the surface structure is obtained if the specific surface area of titanium dioxide TiO240 - 180 m2/g, preferably 70 to 130 m2/,

In Fig.1 shows catalytic activity k catalyst mass, depending on the content of treatise molybdenum for different concentrations of vanadium pentoxide in Fig. 2 - installation for burning with recirculation piping ash; Fig. 3 is a block diagram of the manufacturing process of the catalyst.

In Fig. 1 presents specified in Nm/h (normal meters per hour) the catalytic activity of k catalyst mass, depending on the content of treatise molybdenum indicated in wt.% MoO3for different concentrations of vanadium pentoxide V2O5. It is seen that the maximum catalytic activity is achieved when the content of treatise molybdenum of about 2 wt.%, based on the weight of the catalyst mass. The catalytic activity of the catalyst mass while less Predela relatively smaller content of treatise molybdenum MoO3.

The catalyst to reduce oxides of nitrogen, which were raised for the measurements presented in Fig. 1 data were made mainly according to Fig. 3.

As the initial product for the operation method 2 choose chemically stabilized titanium dioxide anatase form, with the proportion of rutile is less than 5 wt.%, preferably less than 1 wt.%. Further, the proportion of impurities of sodium, in this case, the sodium oxide Na2O, pollution potassium, in this case, the oxide and potassium (K2O, and iron Fe lying respectively at 0.2 wt.% or less. The proportion of sulfur as sulfate (SO4is 0 to 3 wt.%, preferably about 1 to 2 wt.%.

The titanium dioxide during the operation of method 2 is supplemented with water to a plastic mass, which during the operation of method 4, depending on the desired concentration again complement of water-soluble compounds of molybdenum and vanadium, such as heptamolybdate ammonium and ammonium metavanadate to mass M. the mass M knead.

After establishing the desired water content of the mass M to the mass M to increase the mechanical strength add inorganic minerals, such as clay and/or fibrous mi method 6 can be added other additives, for example, film-forming agent, a dispersant, a thickener and the like. Thus obtained mass mesida further into the catalyst mass M'.

During the operations of method 8, 10, 12 and 13 of this catalyst mass M' roll on the bearing element, for example tanety metal, or respectively ekstragiruyut in the cell element 20 or, respectively, formed into granules 22 or pellets 24.

After forming the catalyst mass M' all forms of execution (plate, honeycomb, granules, pellets) is dried during common to all forms, the operation of method 14 in conclusion common to all forms of operation of the method 16 calicivirus at a temperature of about 500oC for several hours (approximately 2 - 4 hours). Due to this relatively low temperature calcination is constrained by the growth of the pores, so that formed the structure of the catalyst mass with a relatively high specific surface area.

Equipped with a floor bearing elements 26 embed, for example, is inserted in the element box 28, which is formed of plate catalyst 18.

Alternative to metal bearing elements and to the formation of a catalyst mass M' would be also the like suspended in water catalyst mass, consisting of water, titanium dioxide, heptamolybdate ammonium and metavanadate ammonium. Ammonium compound of molybdenum and vanadium by calcining into the oxide compounds, such as MoO3and V2O5.

In the form shown in Fig. 2 schematic diagram of the installation for incineration of 26 visible furnace boiler 28 is enabled by the steam generator 30. To the boiler 28 on the input side is connected to the supply line coal 32 and the return line ash 34. On the output side you can see the exhaust tube slag 36. Formed in the boiler 28 coal combustion flue gas pays most of its thermal energy in the steam generator 30, not shown here in more detail, the heat transfer medium, for example water, and then flows in DeNOxthe reactor 10. In this DeNOxthe reactor 38 are lamellar and/or cell catalysts 18 or 20 respectively with the above-described catalyst mass. Before the flue gas comes in contact with the plate and/or cell catalysts 18 or 20 respectively, it is necessary to bring selective reduction contained in the flue gas nitrogen oxides reducing agent, here the ammonia through the pipeline supply of ammonia 40. Due contactyou the eNOxreactor 10 substantially free from nitrogen oxides in flue gas flows through the air heater 42, the filter unit 44 and the chimney 46. Deposited in the filter unit 44 of the flue gas dust is returned through the return line ash 34 to the boiler 28.

Due to the envisaged here recirculation of ash and coal use as fuel, resulting combustion flue gas is also the fraction of volatile compounds of heavy metals, which cannot be neglected. This is mainly oxygen compounds of lead, selenium, arsenic, cadmium, and zinc. These compounds are deposited on the catalytically active surfaces of the catalyst 18, 20 in DeNOxthe reactor 38 and can poison and thereby deactivate the catalyst mass. Due to the aforementioned properties of the catalyst mass in this case is achieved especially slow de-activated and poisoning of catalysts 18, 20 in DeNOxthe reactor 38.

1. Catalyst for reducing oxides of nitrogen in the fluid with the catalyst mass, which contains titanium, molybdenum and vanadium in the form of their oxides, characterized in that the proportion of treatise molybdenum MoO3is 0.01 to less than 5 wt.%, suppose yet 0.01 to 5 wt.%, preferably 0.5 to 2.0 wt.%, and titanium contained in the form of chemically stabilized titanium dioxide TiO2the anatase form.

2. The catalyst p. 1, characterized in that the proportion of titanium dioxide of rutile is less than 5 wt.%, preferably less than 1 wt.%, in the calculation of the total amount of titanium dioxide.

3. The catalyst according to any one of paragraphs.1 and 2, characterized in that the contamination of the titanium dioxide sodium, potassium and iron, respectively, less than 500 ppm, preferably less than 100 ppm.

4. The catalyst according to any one of paragraphs.1 to 3, characterized in that the proportion of phosphorus in the titanium dioxide is less than 0.5 wt.%, preferably less than 0.2 wt.%.

5. The catalyst according to any one of paragraphs.1 to 4, characterized in that the proportion of sulfur, calculated as sulfate SO4is titanium dioxide not more than 3 wt.%, preferably between 1 and 2 wt.%.

6. The catalyst according to any one of paragraphs.1 to 5, characterized in that the remote surface of the titanium dioxide is 40 to 180 m2/g, preferably 70 to 130 m2/,

7. The catalyst according to any one of paragraphs.1 - 6, characterized in that it is made in the form provided with a coating of a bearing element, in the form of a cell element, granulate or respectively in the český stabilized titanium dioxide of the anatase form is complemented by a disperser, for example, water, to a plastic mass, (b) to the mass sum of water-soluble compounds of molybdenum and vanadium, as well as, optionally, other excipients, and the mass kneaded further into the catalyst mass, c) then cover bearing elements with a layer of catalyst mass, or ekstragiruyut cellular elements of the catalyst mass, or granularit catalyst weight in grains of the granulate, or okomkovaniya in pellets, d) equipped with a floor bearing elements, or cellular elements, or respectively the grain of the granules or pellets are dried and calicivirus at a temperature of 400 - 700oC, preferably 500 to 600oC, for several hours, preferably 2 to 4 hours

 

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