DE2026657A1 - Catalytic combustion of ammonia - to nitrogen and water , using excess oxygen over cobalt/copper oxide - Google Patents

Abstract

Combustion is carried out with excess O2 below 700 degrees C, using catalyst contg. 5-70 wt.% Co2O3 and/or CuO on inert carrier, pref. theta-alumina. Catalyst can also contain n-conducting semiconductor oxide, pref. MnO, in 1:10 wt. ratio to Co2O3 and/or CuO to ensure good reproducibility of catalytic activity. Complete combustion is achieved in single stage at relatively low temp. and without formation of nitrous gases. Catalyst is not poisoned by S cpds.

Description

Method for the catalytic combustion of ammonia The present invention relates to a method for the catalytic combustion of ammonia with oxygen to form nitrogen and water according to the reaction equation The technical ammonia combustion with air to nitrous gases according to the reaction equations has long been known and is widely used in practice as a preliminary stage for the production of nitric acid. This reaction according to the reaction equations II and III takes place above all on platinum contacts or on certain oxide catalysts at temperatures of 780-9400 C under normal or elevated pressure, a large excess of air or oxygen always being used. In contrast, the catalytic conversion according to reaction equation I has hitherto only been carried out with an oxygen deficit, for the following reasons: 1. So that the formation of nitrous gases, which is undesirable here, is avoided.

2. Because the so far used for the combustion of ammonia with oxygen to nitrogen and water applied catalysts containing the elements of group VIII of the periodic table in metallic or elemental form, only in reducing Atmosphere, i.e. if there is insufficient oxygen, are stable. This burn under However, the oxygen deficiency is incomplete, so that only a partial one Combustion, above all, is a decomposition of the ammonia to a substantial extent gas mixture consisting of nitrogen and hydrogen takes place.

For example, from the German Auslegeschriit 1 202 772 a Process for the destruction of the ammonia contained in coke or gasworks gases known in which initially the ammonia with an oxygen deficit of nickel catalysts au nitrogen and hydrogen is decomposed The resulting hydrogen must then in the second, downstream post-combustion stage under renewed Added air can be completely burned The aim of the invention On the other hand, the process is catalytic ammonia combustion according to the reaction equation I perform with excess oxygen in one go, without doing anything Form significant amounts of nitrogen oxides. The last-mentioned condition is at the same time the requirement to run the process at comparatively low temperatures to be carried out, since the formation of nitrogen oxides increases with increasing temperature. The requirements must be placed on the catalyst used the combustion of ammonia to nitrogen and in an oxidizing atmosphere To accelerate water so that the ammonia content of the end gas when used technically acceptable space velocities is below 500 ppm.

It should also be taken into account that in practice the feed gases in addition to ammonia, in many cases they also contain sulfur compounds that easily converted into SO2 and SO3 by the oxidizing atmosphere on the catalyst can be. However, these compounds act as so-called contact poisons, the reduce the activity of the catalyst used. This drop in activity it can be compensated by increasing the reaction temperature under certain circumstances. It should be noted, however, that the higher the reaction temperature, the higher the tendency wäcfigt to the undesired formation of nitrogen oxides here The searched The process should therefore also be useful when using sulfur-containing feed gases and in this case too, working at the lowest possible reaction temperatures (8000 o) allow; This task is solved by a method for catalytic Combustion of ammonia with oxygen to form nitrogen and water, which is characterized is that the combustion with excess oxygen at temperatures below 7000 to C on a quay; alysator is carried out, the cobalt-IIi-oxide (Co203) and / or Copper oxide (Cu0) in amounts of 5 - 70 wt. On an inert carrier.

This finding is all the more surprising as it has been unsuitable up to now prepared cobalt oxide catalysts at operating temperatures around 8000 C for technical Generation of nitrogen oxides were used. (Z.f. anorg. And general chemistry, volume 281 (1955), p. 241.) As an inert support material for the catalyst according to the invention Theta clay in particular has proven to be well suited. But it can also other ceramic carrier materials which are customary for catalysts Application.

For good reproducibility of the catalytic effectiveness it would be an advantage if a catalyst is used which, in addition to the cobalt-III-oxide and / or copper oxide, an addition of n-conducting semiconductor oxides, preferably Has manganese oxide. The weight ratio of cobalt III oxide and / or copper oxide to semiconductor oxide should be 10: 1.

The mode of operation of the method according to the invention is to be achieved by the the following examples are explained.

Example 1 relates to the use of a catalyst as follows Composition: 25% by weight Co2O3 75% by weight theta-alumina (Al2O3, # -modification) A corresponding amount of theta-alumina was used to prepare the catalyst an aqueous cobalt nitrate solution was added, followed by stirring evaporated and heated until the nitrogen oxide development ceases. Afterward this mass was granulated and dried in a muffle furnace at 450 ° C. for a further 20 hours. The cobalt is initially located in the catalyst, which has a grain size of 2-4 mm as Co-III oxide (Co203). However, this does not exclude that in the course of the Ammonia combustion as a result of the reaction temperatures lying above 5000 C. some conversion to Oo-IV oxide (CO3O4) takes place, the feed gas had the following composition; 61.8% by volume N2 10.9 "" air 25.3 "" water vapor 2.0 "" NH3 + 0.04-0.08 t II SO2 The oxygen excess of the feed gas was below Consideration of the given reaction equation (I) at 53.

The duration of the experiment was four days. The test results are in in Table 1 below.

Table 1 Run- room- S02-hous. max temp. Salary time Schwin- im A set gas catalyst layer NH3 NO TAG N1 / 1.h ppm in the end gas conversion rate ° C ppm pp 1. 5000 Q 540 6 504 99w98 2. 5000 400 698 16 506 99.94 3, 5000 400 695 0 506 100 4. 5000 800 695 20 396 99.92 The results in Table 2 relate to the second example that was carried out with a catalyst, cobalt oxide and Contains manganese oxide in a weight ratio of 10: 1 and consequently the following Composition comprises: 20% by weight 00203 2 "" Mn2O3 78 "" Theta-Alumina (Al2O3, @ -Modification) tie test duration was eight days this time. The feed gas and the The excess of oxygen was the same as in Example 1. The manganese oxide is included in the catalyst as Mn2O3. The catalyst was prepared in the same way In the same way as in example 1, of course using a corresponding amount of manganese nitrate became.

Table 2 Run- room- SO2-hous. max temp. Content of NH3 time in the end gas conversion rate feed gas catalyst layer NH3 NO day g N1 / 1.h ppm ° C ppm ppm% 1. 3000 0 467 3 194 99.99 2. 5000 0 510 2 180 99.99 3. 5000 400 470 16 256 99.94 4. 5000 400 642 16 216 99.94 5. 5000 400 670 13 396 99.95 6. 5000 400 648 13 216 99.95 7. 5000 400 698 18 360 99.94 8. 5000 800 690 262 360 99.9 As a result the extraordinary activity of this catalyst could initially affect the operating temperature still essential be kept lower than in Example 1, so that the NO formation is even lower.

Finally, the third example concerns the use of a catalytic converter following composition: 20 wt. CuO 80 "" theta-alumina (Al2O3, @ -modification) An appropriate amount of theta alumina was used to make this catalyst mixed with an aqueous solution of copper nitrate. This was followed by stirring Rusted down until the stiekoxydevelopment ended.

After the mass had been granulated (2-4 mm), it was placed in a muffle furnace heated to 450 ° C. for a further 24 hours.

The feed gas again had the same composition as in the Examples 1 and 2. It also contained 0.1% by volume of 502. In one over 4 days The ongoing experiment was the ammonia already at 620 C up to a final content of 33 ppm NH3 burned. The NO content of the end gas was 500 ppm. The velocity of space was 5000 Nl / l h.

Claims (2)

P a t e n t a n s p r ü c h e 1. Process for the catalytic combustion of ammonia with oxygen to nitrogen and water, characterized in that combustion with excess oxygen is carried out at temperatures below 700 ° C on a catalyst, the cobalt III oxide (CO2O3) and / or copper oxide (CUO) in quantities of 5 - 70% by weight on an inert Contains carrier. 2. The method according to claim 1, that preferably as an inert carrier Theta clay is used. 35 Process according to Claims 1 and 2, characterized in that that the catalyst in addition to the cobalt III oxide and / or copper oxide an addition of n-conductive lead oxides, preferably nangan oxide, in a weight ratio of Contains cobalt III oxide and / or copper oxide to semiconductor oxide of 10: 1.