Catalyst for oxidation of ammonia to oxides of nitrogen

 

(57) Abstract:

The essence of the invention: catalyst for the oxidation of ammonia to nitrogen oxides, including oxides of base metals as the main catalytically active component supported on a carrier monolithic structure made of heat-resistant material. While the media has channels with a hydraulic diameter 0,8 - 30 mm and volume of voids 60 - 80%. 5 C.p. f-crystals, 2 tab.

The invention relates to the industrial production of nitric acid, and more particularly to a catalyst for the oxidation of ammonia to oxides of nitrogen based on the oxides of base metals.

Known catalyst for the oxidation of ammonia to oxides of nitrogen, including as a catalytically active component oxides of base metals, for example, oxides of cobalt supported on a carrier monolithic structure made of heat-resistant material, for example, silicon dioxide, zirconium, magnesium [1].

A disadvantage of the known catalysts are unsatisfactory performance properties, caused by rapid loss of selectivity. It is assumed that the loss of selectivity is exclusively the result of reducing the current is and the catalyst surface, as evidenced by the results of research S. P. S. Andrew, and G. C. Chinchen [2].

The objective of the invention is to develop a catalyst for the oxidation of ammonia to oxides of nitrogen, which has the best selectivity.

The problem is solved, we offer a catalyst for the oxidation of ammonia to oxides of nitrogen, comprising as the main catalytically active component oxides of base metals supported on a carrier monolithic structure made of heat-resistant material, due to the fact that the catalyst contains media having channels with a hydraulic diameter 0,8 - 30 mm and volume of voids 60-85%, when the content of the catalytically active component is 5 to 60% by weight of the catalyst.

The monolithic carrier structure may be an extruded body with made it through channels, that is, a body like satam, or body, made of corrugated sheets of metal or ceramic material, folded with the formation of the monolith with through channels. The above description of the media provides a large ratio of surface to volume, so the tendency to accumulation of dust on the catalytic surface is the displacement, and thus the catalytic activity is retained significantly longer than known catalysts of oxides of base metals.

Suitable heat-resistant material to perform media monolithic structures are, for example, titanium dioxide, zirconium and silicon, oxides of aluminum, cerium, magnesium, alkaline earth metals, lanthanum, mullite, kaolin clay, silicates, thin foil of an alloy based on iron, for example, Nickel - chromium stainless steel.

The monolithic carrier structure is preferably made from sheets of fibrous silicate paper, fibers which have an average diameter of 2 to 50 μm and an average length of 2 to 60 mm Fiber sheets are grooving on the appropriate standard car, while the carrier is formed by folding corrugated sheet or corrugated sheets.

A catalytically active component supported on a carrier impregnated with a solution containing at least one soluble salt of the desired metal, with subsequent processing to convert the salts into oxides. But preferably a catalytically active component supported on a carrier by buttering suspension of metal oxides or by immersing wear is on the media, you can apply one or more layers of binder based on refractory oxides, such as, for example, silicon dioxide, titanium dioxide, oxides of aluminum, cerium, lanthanum or mixtures thereof. These layers can be applied to the media by spreading or dipping.

So, for example, a typical manufacturing process, the proposed catalyst for the oxidation of ammonia includes the following stages: corrugation of the sheets of heat-resistant material, which may be provided with a coating binder, forming corrugated sheets in the monolithic body, the calcination of the body at 400 - 800oC, drawing on the body of the catalytically active component or its precursor, for example, by spreading or dipping, followed by drying and calcining at 400 - 700oC.

A binder can also be added to the suspension or solution of the catalytically active component before application to corrugated sheet. The proposed catalyst includes any oxides of base metals, which are selective in regard to the oxidation of ammonia to oxides of nitrogen. As examples of the oxides of cobalt, iron, bismuth, chromium, manganese and mixtures thereof, which may have additive cerium, zinc, cadmium, or lithium in small quantities. Preferably the catalytically active component to provide the obsession supported on a carrier catalytically active component is about 5-60%, preferably 15-25% by weight of the catalyst.

Operation of the proposed catalyst is carried out typically in the following conditions. The catalyst is placed in a cylindrical reactor in which the process is performed under a pressure from about atmospheric to 10 bar. Containing approximately 0.5-11% of ammonia, the air is pre-heated to a temperature of approximately 300oC and fed into the reactor. After a short contact time with the catalyst temperature in the reactor is raised to approximately 800oC in the air oxidation of ammonia to oxides of nitrogen. The output from the reactor gas flow turn to nitric acid known method of absorption in water.

Example 1. The preparation of the catalyst of cobalt oxide (II, III) deposited on a monolithic carrier structure.

Sheet size 500 mm x 500 mm trading, rich silicates heat-resistant paper with a thickness of 0.25 mm, consisting of fibers of silicon dioxide with an average diameter of about 6 mm and an average length of 20 mm (the product of the foreign firm crane & company, Inc., USA) were grooving to a height of about 2.5 mm on the standard car. The obtained corrugated sheet supply a top layer of the same material as the corrugated sheet, and roll with obrazovatelny media put the suspension, containing cobalt as the catalytically active material and a binder. The suspension is prepared by mixing 1200 grams of CO (NO3)26H2O with 250 g of demineralized water and 845 g stabilised with ammonia binder of silica (trade product "Syton T40" the foreign firm Monsanto company, UK). The suspension is stirred in a ball mill at room temperature for 12 hours, after which the suspension is ready for application to the media. The process of applying is carried out by re-immersing the carrier in the slurry, followed by drying at room temperature to a final load of nitrate of cobalt in the amount of 25% by weight of the carrier. After the end of the application process with nitrate of cobalt media is subjected to activation by calcination in an air stream at 450oC for about 2 hours While the cobalt nitrate is decomposed to a catalytically active oxide - oxide of cobalt (CO3O4). The ultimate load of nitrous oxide of cobalt is about 19% by weight of the carrier.

Example 2. The preparation of the catalyst of cobalt oxide (II, III) caused by the impregnation of the carrier monolithic structure.

The media is prepared in the same manner as in example 1. the najednou mixer capacity 2.3 l of demineralized water, 450 g of powder of aluminum oxide (trade product "Versal" the foreign firm Kaiser Chemicals, USA), 775 g of the same powder of aluminum oxide, pre-calcined at 350oC for 1 h in air flow, 45 g of 62% by weight of nitric acid, 154 g of binder based on polyethylene glycol with mol. 20 000 (commercial product "PEG 20 000" foreign companies Hoechst, Germany) and 4 g of surfactant (trade product "Surfynol 104 E of the foreign firm er products & Chemical Inc., The Netherlands). The resulting mixture is treated in a ball mill at room temperature for about 12 h of the Layer of binder is applied to the media by re-immersion in a binder on the basis of aluminum oxide, followed by drying to achieve 30 - 40 g of a binder on m2the surface of the carrier. After coating, the carrier is subjected to a calcination at 600oC for 2 hours in air flow. In conclusion, the media coverage is impregnated with the molten nitrate of cobalt in the form of uranyl at a temperature of approximately 80oC to achieve load about 19 wt.% oxides of cobalt (II, III) on the target monolithic catalyst after calcined in air stream at 450oC for about 2 h

Example 3. Activity monolithic catameran of 3.8 mm and a length of 500 mm. Experiments are performed in isothermal conditions by placing the reactor in a furnace with thermostat.

In the first experiment was charged to the reactor 1.7 g of the catalyst in the form of parts with obtaining the thickness of the catalyst layer 453 mm Through the catalyst layer through the mix ammonia and air with increasing concentration of ammonia at 500 and 600oC, respectively, and with a speed of 14 700 nl/kg Katalizator. The achieved output of oxides of nitrogen (NOx) are given in table. 1, in which the output is expressed in volume.% NOxin terms of the amount of ammonia in the original mixture.

In the second experiment was charged to the reactor 0.6 g parts catalyst to obtain a catalyst layer with a thickness of 160 mm Through this layer duct of a mixture of ammonia and air with increasing concentration of ammonia is passed with the speed of 41,600 nl/kg catalyst hour at 500 and 650oC, respectively. The resulting output of oxides of nitrogen are given in table. 2.

1. Catalyst for oxidation of ammonia to oxides of nitrogen, comprising as the main catalytically active component oxides of base metals supported on a carrier monolithic structure made of heat-resistant material, characterized in that italiani catalytically active component 5 - 60% by weight of the catalyst.

2. The catalyst p. 1, characterized in that the heat-resistant material selected from the group including titanium dioxide, zirconium and silicon, oxides of aluminum, cerium, magnesium, alkaline earth metals, lanthanum, mullite, kaolin clay, silicates and a thin foil of an alloy based on iron.

3. The catalyst p. 2, characterized in that the heat-resistant material made of silica fibers having an average diameter of 2 to 50 μm and an average length of 2 to 60 mm

4. The catalyst p. 1, characterized in that the catalytically active component selected from the group comprising the oxides of cobalt, iron, bismuth, chromium, manganese and mixtures thereof, which may have additive from the group comprising zinc, cerium, cadmium, and lithium.

5. The catalyst p. 1, characterized in that the catalytically active component contains a cobalt oxide (II, III) and/or iron oxide (II, III).

6. The catalyst p. 1, characterized in that the content of catalytically active component supported on a carrier is 15 to 25% by weight of the catalyst.

 

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FIELD: chemical industry.

SUBSTANCE: the invention is pertinent to the field of chemical industry, in particular to production of a catalysts and processes of oxidation of ammonia in production of a weak nitric acid. The invention offers an ammonia conversion catalyst on the basis of the mixture of oxides of unitized structure and a method oxidation of ammonia in production of weak nitric acid. The catalyst represents a mixture of oxides of the over-all formula (AxByO3Z)k (MmOn)f, (NwPgvOv)r where: A - cation of Ca, Sr, Ba, Mg, Be, Ln or their mixtures; B - cations of Mn, Fe, Ni, Co, Cr, Cu, V, A1 or their mixtures; x=0-2, y=1-2, z=0.8-l.7; M - A1, Si, Zr, Cr, Ln, Mn, Fe, Co, Cu, V, Ca, Sr, Ba, Mg, Be or their mixtures; m=l-3, n=l-2; N - Ti, Al, Si, Zr, Ca, Mg, Ln, W, Mo or their mixtures, P - phosphorus, O - oxygen; w=0-2, g=0-2, v=l-3; k, f and r - mass %, at a ratio (k+f)/r=0-l, f/r=0-l, k/f = 0-100. The catalyst is intended for use in a composition of a two-stage catalytic system generated by different methods, also in a set with the trapping platinoid screens and-or inert nozzles. The technical result ensures activity, selectivity and stability of the catalyst to thermocycles at its use in two-stage catalytic system with a decreased loading of platinoid screens.

EFFECT: the invention ensures high activity, selectivity and stability of the catalyst to thermocycles at its use in two-stage catalytic system with a decreased loading of platinoid screens.

8 cl, 1 tbl, 5 ex

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