N₂o decomposition catalyst in ostwald process

FIELD: inorganic synthesis catalysts.

SUBSTANCE: decomposition if N₂O under Ostwald process conditions at 750-1000°C and pressure 0.9-15 bar is conducted on catalyst, which comprises (A) support composed of α-Al₂O₃, ZrO₂, SeO₂, or mixture thereof and (B) supported coating composed of rhodium or rhodium oxide, or mixed Pd-Rh catalyst. Apparatus wherein N₂O is decomposed under Ostwald process conditions on the above-defined catalyst is also described. Catalyst is disposed successively downstream of catalyst grids in direction of stream of NH₃ to be oxidized.

EFFECT: increased catalyst activity.

8 cl, 2 tbl, 3 ex

The object of the invention is a catalyst for the decomposition of N₂O formed as a by-product of the catalytic oxidation of ammonia according to the method of Ostwald.

Catalytic combustion of ammonia to produce nitric acid is known (the way of Ostwald). The combustion of ammonia for large-scale production of NO as the first product of the method is carried out at high temperature (typically between 800 and 950° (C) using, for example, PtRh - or PtRhPd-alloys as catalysts. These catalysts are usually placed in the reactor in the form of woven or knitted meshes in several layers one above the other. To manufacture these nets are usually used wire from PtRh or PtRhPd with a diameter of, for example, 76 microns.

Since the combustion of ammonia noble metal in the form of the oxide is carried away via the gas phase, typically the nets catalysts installing regeneration grids, which are part of the platinum is delayed. In exchange reactions with platinum instead of in the gas phase becomes easier and cheaper palladium.

When getting nitric acid NO formed first on the grids of the catalyst, is subjected to oxidation to NO₂. After cooling gas stream is sent to an absorption tower and nitrogen oxides absorb water. Then adding oxygen is prevremeni is with the formation of nitric acid.

As by-products of the combustion of ammonia to form nitrogen and N₂O. In contrast, NO and NO₂N₂O not enter into any further reaction and after passing all stages of the process is displayed in the atmosphere. When using conventional catalytic nets and regeneration grids in the environment derive from 500 to 3000 ppm of N₂O, if not conducting any subsequent removal of N₂On (EP 1076634 B1).

N₂O some time classified as harmful to the climate gas, as it had an adverse effect on the ozone layer and global warming. Because of its potential for global warming is about 300 times larger than that of CO₂already a relatively small emission of N₂O makes a significant contribution to global warming. As a consequence, try to reduce anthropogenic emissions of N₂O.

Thus, the content of N₂O in the gas products of the combustion of ammonia should be reduced. This can be achieved either by reducing the formation of N₂O, or its decomposition.

For the decomposition of laughing gas have already been proposed several kinds of catalysts. Use and requirements differ depending on whether it is about the purification of waste gases, the destruction of laughing gas from excess gotoblas the CSOs narcotic substances or the removal of ammonia from industrial gaseous wastes. The material of the carrier also has an impact. For example, rhodium (oxide) on gamma-Al₂About₃has no effect on the reduction of N₂O in the process of Ostwald. For catalysts gaseous waste, in contrast, is primarily and preferably use gamma-Al₂About₃.

For catalysts gaseous waste is known, for example, systems with Pt, Rh, Ru and/or Ir: for example, in Japan patent JP 06142509 for the removal of N₂O recommend 0.3 to 2 wt.% Rh on alpha-Al₂About₃at a temperature of from 300 to 500°C. Also as catalysts there named Ru and Ir. These metals, by contrast, does not act in the process of Ostwald.

In the application JP 6142517 A1 describes deposited on alpha-Al₂About₃catalyst Rh or Ru and at least one oxide of Ti, Zr, or Nb. It also has a value that EN is not suitable for the process of Ostwald. Next are unsuitable titanium and niobium oxide.

Ru or Pd on SiO₂or Al₂About₃according to the application JP 2002253967 A1 is used for the decomposition of laughing gas, which is in excess as gaseous drugs. The respective reactors are steel tubes that are filled with grains of Al₂About₃coated with a layer of noble metal, and operated at 150-550°With (application JP 55031463 A1). Here you should also consider according to CNAE requirements due to the fact, what Ru, and Pd did not show any effect in the process of Ostwald and SiO₂in the process of Ostwald is not chemically stable. Patent JP 06182203 for the media containing fluorides, for catalysts of noble metals.

According to the application DE 4020914 A1 ammonia burn almost without formation of laughing gas when brought into contact with Pt, Pd, Rh or Ir in combination with at least one oxide of Mo, V However, the described method is not suitable for large scale industrial combustion of ammonia, but only to remove small concentrations of NH₃of gaseous waste.

Pure laughing gas may well decompose according to patent DE 3543640 on Pd, caused, for example, corundum, alumina or silicic acid. But palladium is completely inactive to reduce the number of N₂In the process of Ostwald.

Specifically for use in the process of Ostwald known, for example, the following systems:

In the application DE 19819882 A1 describes a catalyst for the decomposition of N₂O, which is included after the grid of the catalyst and before the heat exchanger and is in the form of a stationary layer. In particular, we are talking about a combination of CuO·Al₂About₃with tin or lead.

From the application DE 4128629 A1 famous silver catalyst deposited on Al₂O₃.

According to patent DE 10016276 proposed to talesfore, containing CuO. On an industrial scale was tested, for example, a catalyst based on CuO-Al₂O₃. Achieved a reduction of 80-90% N₂O installing, operating at atmospheric pressure, and about 70% of N₂O installation medium pressure (5.5 bar) in Antwerp (G.Kuhn: Proceedings of the Krupp Uhde Technologies Users Group Meeting 2000, Vienna, 12-16 März 2000). NO loss was <0.5 percent. In the publication (Applied Catalysis B: Environmental 44(2003) S.117-151) refer to the fact that copper could be released from the catalyst. Since the decomposition of ammonium nitrate catalyzed by copper, there would be a serious security problem.

According to patent US 2004023796 was developed catalyst for the decomposition of N₂O when 250-1000°based spinel oxide With media GeO₂(Co₃-xMxO₄and M represents Fe or Al and x=0-2). NO loss was <0.2 percent. A similar system containing cobalt oxide, also themselves have already been recommended for the oxidation of ammonia (patent EP 0946290 B1).

Patent US 5478549 describes the use of ZrO₂as catalyst for the decomposition of N₂O. Accordingly this theory in WO 0051715 apply that to the granules ZrO₂when receiving can be blended with iron and optimally transition metals.

Mixed oxide catalyst (ZrO₂and Al₂O₃is the subject matter of the application WO 9964139. The catalyst impregn the computerized salt of zirconium, should partially transform N₂O (about 15%) NO. N₂O have in common to decompose until 78-99%. The required amount of catalyst, however, is very large and, as a rule, requires the reconstruction of the reactor Converter.

Most of these catalysts are characterized by deficiencies that may occur from the point of view of safety, as in the above-described catalyst based on CuO-Al₂About₃or when conditions in the reactor are insufficiently stable. This applies as catalytically active components, and reinforcing structures, which can have a stabilizing function in relation to the catalytically active.

Therefore there is a need for systems catalysts that effectively removes N₂About in the process of Ostwald.

While the catalysts must meet the following requirements.

- Should not kataliziruetsa decomposition of NO, because this would have reduced the effectiveness of the method.

- If we are talking about a stationary catalyst bed, he must have a very high activity and cause only very slight pressure drop at the height of the catalyst layer. Increased pressure loss can also lead to loss of efficiency in obtaining NHO₃in particular, if it is impossible far the increase of pressure with available technical devices.

The catalyst should not cause a recalculation of the parameters of the existing Converter.

According to the invention proposes a catalyst comprising rhodium or rhodium oxide, associated with a suitable carrier, which unexpectedly causes a full decomposition of laughing gas, and particularly suitable for so-called FTC-nets (cf DE 19543102 S1). These systems use a multi-layer system without extra grid for regeneration (Catchment traps). Especially preferably the catalyst is in the form of a stationary layer.

As required above, such a catalyst can reduce the number of first primary product of the process of Ostwald - NO. Ceramic materials, such as, for example, alpha-Al₂About₃that is already in use as mechanical reinforcing material for grids catalysts, as recommended in the patent US 5478549 oxide ZrO₂or SEO₂consider special reaction conditions are chemically stable. So they can be with advantage used as a carrier of catalysts for the catalyst according to the invention.

The role of rhodium in relation to the N₂O technical level assessed rather negatively: research firms OMG showed that the rhodium in the alloy with platinum combustion of ammonia rather induces higher education N₂O (Ntrogen & Metanol, No.265, Sept./Okt. 2003, Seiten 45-47).

However, it was unexpectedly found that rhodium or rhodium oxide, deposited on alpha-Al₂About₃and/or ZrO₂, characterized by high catalytic activity concerning decomposition of N₂O. in Addition, it was found that mixed palladium-rhodium catalysts can be extremely effectively used for the decomposition of N₂O in the process of Ostwald, despite the fact that pure palladium or mixed palladium and Nickel catalysts do not reduce the number of N₂O (application US 2003/0124046 A1).

Preferably, if N₂O, formed on the grids of the catalyst for combustion of ammonia in adverse reactions and decays through one downstream of the catalyst, and the gas stream is conducted through the catalyst bed located downstream of the flow. Thus the catalyst may be located directly after the nets catalyst or in the case of grids for the regeneration of platinum ("Catchment traps") after these regeneration grids, as described, for example, in patent US 5478549.

The desired operating temperature for the catalyst in the decomposition of N₂O, are determined by the operating temperature during the combustion of ammonia. This temperature is not lower than 750°and not more than 1000°for known types of reactors IU the DN 800 and 950° C. the Reactors operate depending on the type of device at a pressure between 1 and 15 bar. The conditions under which the catalytic reaction is the decomposition of N₂O, of course, determine very high demands on the material of the catalyst: in case of insufficient chemical resistance, for example, leaching of the catalyst over a long time can lead to the enrichment of the components of the catalyst of the final product (e.g., fertilizers). This could adversely affect their safety in use (risk of explosion by reducing the ignition temperature).

For known catalysts, these requirements are met only in part.

Particularly preferably, the catalyst according to the invention is used in connection with so-called FTC systems (DE 19543102 S1). The use of special alloys and microstructures makes possible a substantial reduction in quantities of expensive noble metals without reducing the efficiency of transformation and the period of validity of the catalyst. Already this has been clearly lower value of N₂O in the gas products of the combustion of ammonia compared to a standard catalyst/catcher - grid system. Through combination with a catalyst for the decomposition of N₂O according to the invention the value of N₂O can be even brennigan. Also significant is the advantage in cost of production FTC systems containing less expensive precious metal.

A very good catalyst was rhodium or rhodium oxide, deposited on alpha-Al₂About₃or ZrO₂. Also has the advantage of combination with palladium: palladium-rhodium on alpha-Al₂About₃when using as a catalyst N₂O in the process of Ostwald leads to a clear reduction of N₂O.

Rhodium in the reaction conditions in the reactor downstream of the grids, always oxidized to oxide of rhodium, so the result has a catalytically active component, a rhodium oxide.

Research in real process conditions showed that the material-carriers of alpha-Al₂About₃and ZrO₂coated with rhodium or rhodium oxide, also for a long time retain their catalytic activity. It is also about the media containing both oxide and CEO₂separately or together with the aforementioned substances or combinations.

In contrast, for example, rhodium deposited on a gamma-Al₂About₃located under the mesh catalyst, completely unsuitable for the reduction of N₂O. similarly, rhodium or rhodium oxide, deposited on TiO₂that proved to be unsuitable for the reduction of N₂O when specific conditions about the ECCA Ostwald.

The catalytic activity of rhodium or rhodium oxide, deposited on alpha-Al₂About₃or ZrO₂is so high that the height of the layer of granules of the catalyst reaches 3 cm in order to install medium pressure to reduce the content of N₂O below 200 ppm.

If instead of granules using conventional ring process and cover them, for example, a thin surface shell Rh/oxide ceramics, the pressure loss through the system catalysts remains unchanged. But there is a condition that the active membrane before coating Rh calcined at high temperature >900°C, to obtain a stable oxides. This variant of the method is hardly suitable catalysts for gaseous wastes. But in the process of Ostwald this reach unexpectedly high catalytic activity at extremely low pressure loss. This method can also be extended to other media of different geometric shapes.

Also acceptable other well-known media, such as ceramic foam or cellular structure. The next option is the coating of rhodium or a thin surface shell Rh/ZrO₂on the grid of the Cantal or megapir (Megapyr) (FeCrAl alloy), often used as a separation between grid nets-catchers. As a dividing grid, and additional the data grid, underneath nets-catchers, can be coated with rhodium or rhodium/active shell and cause an apparent decrease in the number of N₂O.

Particularly preferred use of the material according to the invention, if it is used in conjunction with the FTC system. Dividing the grid, which are located between the individual grids FTC can then optionally be equipped with a catalyst and cause an apparent decrease in N₂O.

The receipt of the catalyst according to the invention is that protopectin ring process (or grid of Cantal) cover the surface membrane gamma-Al₂About₃, fired at high temperature (950° (C)to carry out the transformation in alpha-Al₂About₃and then coated Rh or Pd-Rh or Rh_xO_y. Instead of gamma-Al₂About₃can also be used a mixture of ZrO₂and gamma-Al₂About₃the same processing as described above. Without this treatment, the catalytic activity is much lower.

The resulting material is suitable as a stationary catalyst layer according to the invention.

Example 1

Active membrane gamma-Al₂About₃put in a known manner on the ring process or a grid of Cantal, dried and calcined at 950°With up to a full transformation into alpha-Al₂Oz. Yesenia cover Rh or Rh ₂O₃or PdRh is also a known method.

Example 2

The extrudate zirconium oxide with a length between 4 and 6 mm and a diameter of about 3.5 mm and the granules of alpha-Al₂About₃(diameter about 5 mm) is covered by a known method Rh or Rh₂O₃or PdRh and Pd.

Example 3 (comparative)

The titanium oxide and pellets of gamma-Al₂About₃with a diameter of 3-5 mm is covered by a known method Rh or PdRh.

The catalysts indicated in examples 1 and 2, tested in the process of Ostwald. The catalysts were located below the grid for the oxidation of ammonia. As a reference system used a conventional system catalyst with a regeneration nets. The process conditions were as follows: temperature = 880°C, pressure = 5 bar abs., download ammonia = 14.5 t NH₃/m²/day, the concentration of ammonia = 10,6% vol. in the mixture of the air/ammonia.

The proof of the activity of the claimed catalysts based on noble metals.

1. 0.6% of the noble metal on ZrO₂noble metal = 1% Pd, 99% Rh

2. 0.6% of the noble metal on ZrO₂noble metal = 30% Pd, 70% Rh

3. 0.6% of the noble metal on ZrO₂noble metal = 70% Pd, 30% Rh

4. 0.6% of the noble metal on ZrO₂noble metal = 95% Pd, 5% Rh.

The results are given in table 1, 2.

1. A catalyst for the decomposition of N₂O in the process of Ostwald at 750-1000°and 0.9-15 bar, where the catalyst contains

And the media, which consists of alpha-Al₂About₃, ZrO₂SEO₂or mixtures thereof, and

In - deposited on the media coverage of rhodium or rhodium oxide, or mixed Pd-Rh catalyst.

2. The use according to claim 1, in which the mixed Pd-Rh catalyst contains from > 0 to 95% Pd.

3. The use according to claim 2, in which the mixed Pd-Rh catalyst contains 30-70% Pd.

4. The use according to claim 1, in which the mixed Pd-Rh catalyst is Pd-Rh alloy.

5. Use one of the preceding paragraphs, where the catalyst is a catalyst stationary layer.

6. Use according to one of claims 1 to 3, where the katal is the blockage is in the form of pellets, Raschig rings, foam or cellular structure.

7. The use according to claim 1, where a is the alpha-Al₂About₃or Zr₂O.

8. Device for the decomposition of N₂O in the process of Ostwald, which applies at least one catalyst according to one of claims 1 to 7, which is located sequentially after the grids of the catalyst in the flow direction for the oxidation of NH₃.