The catalyst for decomposing nitrous oxide and method of implementation processes, including the formation of nitrous oxide

 

The present invention relates to a catalyst containing 0.1-10 mol%. Co3MxAbout4where M represents Fe or Al and x=0,25-2, on the media, the cerium oxide for the decomposition of N2O contains NO gases. The invention further includes a method for making process, including the formation of N2O. Contains N2O gas is introduced into contact with a catalyst containing 0.1-10 mol%. Co3MxO4where M represents Fe or Al and x=0.25 to 2 on the media, the cerium oxide at a temperature of 250-1000C. the Method may include the stage at which ammonia is oxidized in the presence of the oxidation catalyst, and the resulting gas mixture is introduced into contact with a catalyst containing a cobalt component on the carrier of the cerium oxide, at a temperature of 500-1000C. Technical effect is the creation of multi-active and thermally stable catalyst for the decomposition of N2O. 2 N. and 7 C.p. f-crystals, 7 Il.

The invention relates to a catalyst for decomposing nitrous oxide (N2O) to nitrogen and oxygen at temperatures 250-1000aboutC. the Invention also includes a method of implementation processes, including the formation of nitrous oxide.

In recent years vesiculosa effect). N2O formed during the catalytic oxidation of ammonia in the formation of nitric acid and the oxidation of alcohols and ketones, such as adipic acid production. In addition, when using the N2O, such as anesthetic gas flowing stream of N2O must not be discharged into the atmosphere, and to decompose.

Although N2O decays uniformly to some extent at high temperatures, most of the processes involve the use of catalysts of various types for its decomposition. However, the catalyst, which can work well in a certain temperature range and/or the gas mixture containing the N2O, do not necessarily work well with other operating conditions. Great importance is also the selectivity of the catalyst, particularly if the catalyst used in the oxidation of ammonia before installing absorption at the factory for the production of nitric acid. In this case, the catalyst should not be disposed of in the main product, i.e. nitric oxide (NO).

There are many catalysts for the decomposition of N2O, and most of them are based on using as an active component of the oxides of various metals, such as cerium oxide, cobalt oxide, axillo on zeolite media, and zeolites with substitution of the transition metal.

The catalyst for the recovery of oxide of nitrogen compounds known from Japanese application JP 48089185. Although this application does not mention specifically nitrous oxide, its definition also includes nitric oxide. The catalyst contains as its major component oxides Co and Ce. In the example, a mixture of 249 parts of cobalt acetate and 315 parts of cerium acetate was dissolved in water. ZrO2impregnated with this solution and was subjected to pyrolysis at 900oC for 5 hours, obtaining a catalyst containing CeO2and Co3O4on the surface of the carrier ZrO2.

From the application WO 93/15824 known contacts containing N2O gas with a catalyst containing oxides of Nickel plus cobalt oxide on the substrate Zirconia, at 280oC. the Ratio of Nickel oxide to cobalt oxide is 0.5 to 1:3-1. This application can be processed gases, containing pure and diluted with N2O.

Further, from EP 207857 B1 is known a catalyst consisting of cerium dioxide and 1-20 wt.%. at least Al, Si, Zr, Th, or rare earth metals in the form of oxides. This composition, which consists mainly of cerium dioxide and preferably 1-5 wt.%. these metal oxides may be used in the synthesis of methanol over p is a, dispersed on a refractory oxide such as ceria, improves the oxidation of hydrocarbons and carbon monoxide. Stated further that the dispersion with the addition of platinum on a refractory oxide provides a catalyst suitable for catalytic reduction of nitrogen oxides with hydrocarbons and/or carbon monoxide. There is no indication on the catalytic decomposition of nitrogen oxides without reducing agents. No examples related to nitrous oxide.

Application WO 98/32524 describes an invention relating to a catalytic recovery of nitric oxide and catalyst for the recovery of nitrogen oxides and oxidation of carbon monoxide and hydrocarbons. The main ingredient is gold, which is connected in complex transition metal and attached to the oxide carrier. There is no indication on the catalytic decomposition of nitrogen oxides without reducing agents. No examples related to nitrous oxide.

In Catalysis B: Environmental 13 (1977) 69-79, R. S. Drago et al. describe the catalytic decomposition of N2O on metal oxide carriers. Studied the decomposition of N2O using metal oxides deposited on silicon dioxide, magnesium oxide, calcium oxide and media, such hydrotalcite. It was found that CoO is the most is hardly the silicon dioxide were prepared by filling the pores of the support of silicon dioxide nitrates of metals, drying at 180oC and the decomposition of the nitrates to oxides at 500oC.

When applying CoO on MgO was obtained much more active catalyst. However, the catalyst activity decreased as the calcination at 1000oC. the Catalysts calcined at 500oC, gave 99% conversion of N2O, whereas the catalysts calcined at 1000oC, gave a 50% conversion of N2O. also Described the connection is similar to hydrotalcite, Co3Mg5Al2(OH)2CCA3yH2O. This predecessor was progulivali at 500oC or 800oC. BET-analysis of the catalysts of Co2O/2MgO, calcined at 500oC and 1000oC, showed respectively the specific surface 118 m2/g and 4 m2/,

If the catalyst for the decomposition of N2O includes cobalt oxide, as reported in the Journal of Chem. Soc. Faraday Trans. 1, 74 (7), 1595-603, where he studied the structure and activity of solid solutions of spinel CoxMg1-xAl2O for use as catalysts in the decomposition of N2O, the catalyst activity usually increases when octahedrites centres patterns impose a greater amount of cobalt ions.

The main purpose of the present invention was to obtain a multi-purpose active and is the temperature of 800-1000oC.

Another goal was the catalyst must be stable and retain their activity for at least a normal cycle, i.e. the time interval between the replacement catalyst for the oxidation of ammonia.

The next objective is to obtain a catalyst that could be used at high space velocities and to have a high selectivity for the decomposition of N2O no NO decomposition.

The goal was also to develop a method of reducing the amount of nitrous oxide in the processes, including the formation of nitrous oxide, such as processes for the production of nitric acid, the production of adipic acid and combustion of hydrocarbons in vehicle engines.

Another goal was the destruction of nitrous oxide from the tail gas from the apparatus for the production of nitric acid and other exhaust gases.

Numerous well-known catalysts for the decomposition of N2O initially assessed in relation to their activity and thermal stability. From literature it is known that the cobalt oxide has a high activity, at least initially, for some gas mixtures and at relatively low temperatures. It was reported that the decomposition of N2O in the tail gas of nitric acid plants provide higher is their cobalt and weakly calcined, i.e. at 200-500oC. Therefore, the authors of the present invention began with further research catalyst of this type to obtain a catalyst for the process gas. The main requirement for the new catalyst was that he should be thermally stable at the operating conditions of the oxidation of ammonia. This means that the catalyst must be active, selective and stable at temperatures of 800-1000oC and in gas mixtures formed during the catalytic oxidation of ammonia.

Then, a few containing cobalt oxide precursors were prepared and calcined for at least 5 hours at temperatures of about 900oC. These catalysts were compared with other known catalysts in the initial experience in the decomposition of N2O in the case of gas containing 2932 hours/million N2O and 2574 hours/million NO, where the ratio of NO:N2O was 0.88, with an average hourly rate of gas supply, GHSV 280000 h-1. The rate constants for decomposition was determined at 700aboutC.

These experiments confirmed that Co is the main metal in the Co-Mg-Al (excitotoxicity). The oxides were tested at different GHSV most active oxide conversion, too high in order to give an accurate modirzadeh Co, Mg and Al, was carried out for 48 hours at about 900oC. Experiments were performed at GHSV 108440 h-1and when 2932 hours/million N2O and 2575 hours/million NO, the rest of the gas mixture was argon. For these types of catalysts for the conversion of N2O and its rate constant was decreased during the test period. The specific surface of the catalyst decreased from 9.3 to 1.3 m2/g for B. E. T. These results clearly showed that the stability of such catalysts doubtful.

Then, the inventors began to explore the catalysts on the basis of active components on the carrier, for example, metal oxides such as zirconium dioxide, aluminium oxide, cerium dioxide and their mixtures. One of the advantages of the catalysts of this type will reduce the cost of material, if possible to essentially reduce the number of active component in the decomposition of nitrous oxide.

First cobalt-aluminum system is systematically evaluated in experiments on laboratory reactor. The composition of Co3-xAlxO4varied from x=0 to x=2.

The results of laboratory data by activity are shown in figure 1. It was found that there is increased activity determined after approximately 90 hours, when the aluminum add barb. This was unexpected, because when increasing the aluminum content is a continuous increase in surface area. Therefore, from the point of view of the specific reaction rate, it seemed best to work with rich cobalt spinel, although such materials tend to have a low specific surface area.

Another oxide system, which is also carefully studied, was a system of Co3-xFexO4in which x can vary from 0 to 2. These materials were tested in a laboratory microreactor, and the results are shown in figure 2. The highest activity was shown CoFe2O4. This particular composition can be described as "stable cobalt magnetite".

Although these two types of spinel showed high activity, their practical application in the form of pure phases at facilities was not considered for the following three reasons: any catalyst containing a high concentration of cobalt will be unacceptably expensive, all of the above active phase except rich aluminum spinels have a low specific surface area, and they also are deactivated even at a relatively low temperature of 800aboutC.

Accordingly, these phases can be considered useful only if they can be is used for this application. Requires the following properties: bearer must be a refractory material, preferably with a melting point above 1800aboutWith, so he resisted the sintering and maintained a high specific surface area when the process conditions. Further, the carrier should not substantially interact with the active phase, leading to loss of activity and/or selectivity. Finally, the media should be easily available at a price significantly lower than the price of the active phase.

The selection of the appropriate media proved more difficult than expected, and was soon understood that the possible combinations of the active phase and the material of the media need to be carefully assessed. First tested material media was magnesium oxide (magnesia). Then an experiment was carried on the activity in the pilot unit with the phase of cobalt-aluminate spinel with a nominal composition of Co2AlO4. It was found that the initial activity of this catalyst was good. However, it was found that during further testing there is a continuous deterioration in characteristics over time. Detailed analysis of the catalyst after the pilot test showed that happened the transfer of cobalt active phase spinel in magnesium wear which is more than the low activity, than spinel Co2AlO4and this explains decontamination. This process will continue until such time as the chemical activity of cobalt spinel and magnesium media will not be the same. Based on these observations and experiments, magnesia was excluded as a carrier for the catalyst to be used in the cleaning process gas for discharge into the atmosphere.

Another commonly used material for the carrier is alumina. However, it was found that as magnesium carrier is transferred transition metal of the active phase in the aluminum oxide, leading to the formation of rich aluminum oxide spinels, which have a lower specific speed than the active phase rich in cobalt spinel or perovskite. Therefore, the aluminum oxide should be excluded from among the promising materials media. Similar arguments were made against the use of aluminosilicates and aluminasilicate media.

Zirconium dioxide, cerium dioxide and their mixtures were used as the materials of the carrier in some catalysts for oxidation of carbon monoxide and hydrocarbons (WO 96/14153), and an active catalyst is a noble metal and in the texts of methanol. This catalyst contains 1-20% of at least Al, Si, Zr or Th. Based on the physical properties of cerium dioxide, it was decided to further explore this material media. The solubility of cobalt and iron in the cerium dioxide is low, and it was reported that the rate of diffusion of these elements in ceria is very low, therefore, ceria remains a promising material. Ceria in most cases will be in the form of CeO2but can also be in the form Ce2O3. Performed laboratory experiments with Co3O4/CeO2and the activity and stability of catalyst were the most promising. Were then conducted additional laboratory experiments and experiments on a pilot plant in order to establish the optimal composition of the catalyst of this type.

Samples of pure cerium oxide component without the active phase was also tested for activity against the decomposition of N2O laboratory microreactors under standard test conditions. At a temperature of 890oC has reached a conversion of 70% compared with conversions above 95% for the best supported on a carrier spinel catalysts. These results show the additional benefit or synergistic use of the media, will contribute to the decomposition of nitrous oxide. It was found that in contrast to the cerium oxide other media materials, such as aluminum oxide and magnesium oxide, is completely inert to the decomposition of nitrous oxide.

Catalysts deposited on ceria, can be produced in various ways using conventional methods of making catalysts. Cobalt salts, cobalt-aluminum salt and a cobalt-iron salt can be precipitated powder of cerium oxide, or the powder may be impregnated by them, and the resulting slurry may be dried and calcined. Then the catalyst particles can be given the desired shape by pelletizing, extrusion, extrusion, etc., High specific surface area of cerium dioxide is favorable, and because it will fall during baking, use of cerium dioxide with high initial specific surface area. When the working temperature specific surface area of cerium dioxide must be greater than 10 m2/g, preferably more than 50 m2/,

The invention is additionally illustrated by the following experiments and the respective tables and drawings.

Figure 1 shows the conversion of N2O for the active phases of Co3-xAldifferent phases of Co3-xFexO4at 890aboutWith in a laboratory microreactor.

Figure 3 shows the conversion of N2O catalysts for Co3O4-SEO2in a laboratory microreactor.

Figure 4 shows the data of the pilot plant activity for the conversion of N2O for various catalysts at 5 bar, 900aboutC and GHSV = 66000 h-1.

Figure 5 shows data from laboratory microreactor for the conversion of N2O using a variety of catalysts according to the invention.

Figure 6 shows the influence of the composition of the catalyst and the loading on the conversion of N2O in a laboratory microreactor.

Figure 7 shows the effect on the conversion of N2O add ZrO2the catalyst of Co2AlO4/CeO2.

The catalyst according to the invention consists essentially of 0.1 to 10 mol%. Co3-xMxO4where M represents Fe or Al and x = 0-2, on the media of cerium oxide. The preferred catalyst also contains from 0.01 to 2 wt.%. ZrO2.

The catalyst on the carrier preferably contains 1-5 mol%. cobalt component.

The media of the cerium oxide used in the manufacture of the catalyst should preferably have a specific surface area of more than 10 m2/g, preferably more than 5th Co3O4, Co3-xAlxO4where x = 0,25-2, or Co3-xFexO4where x = 0.25 to 2.

The main distinctive feature of the method according to the invention for the execution of processes, including the formation of N2O, is that containing the N2O gas is introduced into contact with a catalyst containing 0.1-10 mol%. Co3-xMxO4where M represents Fe or Al and x = 0-2, on the media of cerium oxide at a temperature of 250-1000aboutC. it is Preferable to use a catalyst which contains from 0.01 to 2 wt.%. ZrO2.

When the method according to the invention used in the apparatus for the production of nitric acid, ammonia is oxidized in the presence of the oxidation catalyst, and then the resultant gas mixture is introduced into contact with a catalyst containing a cobalt component on a carrier cerium oxide, at a temperature of 500-1000aboutC.

The tail gas from the installation of absorption at the exit from the installation of the oxidation of ammonia can be introduced into contact with a catalyst for the decomposition of N2O containing 0.1-10 mol%. Co3-xMxO4where M represents Fe or Al and x = 0-2, medium, the cerium oxide at a temperature of 250-500aboutC.

Containing N2O gas mixture from the process of obtaining Alienware decomposition of N2O containing 0.1-10 mol%. Co3-xMxO4where M represents Fe or Al and x = 0-2, medium, the cerium oxide at a temperature of 500-800aboutC.

Example 1

This example shows the results of tests carried out in laboratory scale using catalysts having respectively the concentration of Co3About41,5 or 10 mol%. on the media the cerium oxide. Conversion of N2O (%) as function of time are shown in figure 3. The tests were carried out under a pressure of 3 bar, GHSV = the 560,000 h-1and the composition of the gas:

N2O = 1200 hours/million

NO 10000 hours/million

Oxygen 4%

H2About = 1,7%

The rest is Up to 100% nitrogen

Experiments were performed at 800aboutC and 890aboutC. the results of the experiments are shown in figure 3. These experiments showed that the conversion of N2O was very high, about 98%. The stability of the catalyst was also promising. The best results were obtained when the catalyst contained 5 mol%. cobalt component.

Example 2

Then the catalysts used in the experiments of example 1 was tested on the pilot plant, which had conditions oxidation of ammonia. Further experiments included studies of the free catalyst Co2AlO4and a catalyst comprising a Co2AlO4on the media MgO. The catalyst conveniece. Experiments were performed under the following standard conditions: a pressure of 5 bar, a temperature of 900aboutC, GHSV 55000 h-1-110000 h-1. The gas composition was as follows: N2O = 1200-1400 hours/million; NO = 10%; oxygen = 4%; N2About = 16%, and the rest of the gas is nitrogen (plus Ar, CO2, etc., from air).

The results of these experiments are presented in figure 4 and show that the best catalyst for the conversion of N2O was about 95% after 100 days of operation. The NO decomposition was much below 0.5%, which was considered an acceptable level.

Figure 4 additionally shows that the catalyst of Co2AlO4without the media and the same active phase on MgO lose most of their activity after a few days of work.

Example 3

This example shows the results of the experiments carried out for 90 hours in a laboratory microreactor. Operating conditions were the same as in example 1, and the experiments were performed at temperatures of 800aboutC and 890aboutC. the Results are shown in figure 5, which shows that the spinel cobalt cerium dioxide is a more active catalyst than cobalt oxide in the cerium dioxide.

Example 4

This example shows the effect of catalyst composition and loading on the conversion of N2O in the lab is C. For all of the catalysts according to the invention the best results were achieved when the catalyst loading of about 2 mol%, but for some high activity was achieved already at very low loads, as shown in figure 6. Conversion of N2O more than 95% can be obtained at very low catalyst loading and even when 10 mol%, but probably will not be able to achieve conversion with increasing loading of the catalyst is higher than 5 mol%. Therefore, catalyst loading will also depend on practical and economic evaluations.

Example 5

This example shows the impact of adding ZrO2on the characteristics of the catalyst for Co2AlO4/CeO2installed at the pilot plant oxidation of ammonia. The catalyst was prepared by mixing the ingredients as in the previous examples, plus the addition of 0.01% wt. - 2% wt. a fine powder of ZrO2(particle size of 1-3 microns). Experiments were performed under the same standard conditions as in example 2. The figure 7 presents the results to add to 0.22, 0.28 and 0,90% wt. ZrO2compared to catalysts without ZrO2. The optimal concentration in this case was 0.2 wt.%. Effect of addition of ZrO2was the drop in catalyst activity over time.

In the lyst decomposition of N2O. Catalysts according to the invention can be used in a wide temperature range and will also be stable under varying gas composition. It was found that the presence of water, which often poses a problem, for example, in connection with the catalyst for exhaust of automobile engines, is not a serious problem for such catalysts. Accordingly, the new catalysts can be used for the decomposition of N2O processes, including the formation of N2O. Catalysts are particularly useful in combination with nitric acid, since N2O can be decomposed in the process gas, formed after the oxidation of ammonia, without substantial destruction of NO and can also be used on the tail gas after subsequent installation of absorption.

Claims

1. The catalyst for the decomposition of N2O at temperatures 250-1000With containing compound of cobalt on the carrier, characterized in that the catalyst contains 0.1 to 10 mol.% Co3MxAbout4where M represents Fe or Al and x=0,25-2, on the media, the cerium oxide.

2. The catalyst p. 1, characterized in that applied to the carrier, the catalyst contains 1-5 mol.% is the production of the catalyst, has a specific surface area greater than 10 m2/g, preferably greater than 50 m2/g at operating temperature.

4. The catalyst p. 1, characterized in that the cobalt component is the Co3AlxAbout3where x=0.25 to 2.

5. The catalyst p. 1, characterized in that the cobalt component is the Co3FexO4where x=0.25 to 2.

6. The way the implementation process, which yields the N2O, using a catalyst containing cobalt oxide on a carrier, characterized in that the gas containing2O enter into contact with a catalyst containing 0.1-10 mol.% Co3MxO4where M represents Fe or Al and x=0-2, medium, the cerium oxide at 250-1000C.

7. The method according to p. 6, characterized in that ammonia is oxidized in the presence of the oxidation catalyst and the resulting gas mixture is introduced into contact with a catalyst containing a cobalt component on the carrier of the cerium oxide at a temperature of 500-1000C.

8. The method according to p. 6, wherein the tail gas from the installation of absorption at the exit from the installation of the oxidation of ammonia is introduced into contact with the catalyst in the decomposition of N2O containing 0.1-10 mol.% Co3MxO9. The method according to p. 6, characterized in that it contains N2O gas mixture from the process for producing adipic acid is introduced into contact with the catalyst in the decomposition of N2O containing 0.1-10 mol.% Co3MxO4where M represents Fe or Al and x=0-2, medium, the cerium oxide at a temperature of 500-800C.

 

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