DK145968B - PROCEDURE FOR THE REMOVAL OF NITROGEN OXIDES FROM EXHAUST GAS - Google Patents

Description

(19) DENMARK

| J | (12) PUBLICATION <n) 145968 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No 1071/76 (51) Lnt.CI.3 B 01 J 8/02 (22) Filing date 12th year. 1976 // B 01 D 53/36 (24) Race day 12. odd. 1976 (41) Aim. available 22. s ep. 1976 (44) Submitted May 2, 19 & 3 (86) International Application No. - (86) International Filing Day - (85) Continuation Day - (62) Master Application No. -

(30) Priority 21. weird. 1975, 2512409, BE

(71) Applicant BIBIER ENGINEERING GMBH, B-45 Essen, BE: BAYER AKTIENGESELL = SCHAFT, B-5O9O Leverkusen, BE.

(72) Inventor Rudolf Bivivier, BE: Gotthard Uckert, BE: Guenter

Erben, BE.

(74) International Patent Bureau.

(54) Process for removing nitrogen oxides from exhaust gases.

The invention relates to a process for the removal of nitrogen oxides (NO) from exhaust gases of high content of oxygen and / or oxygen compounds, e.g. nitrous oxide, especially waste gases from nitrating plants or plants using nitric acid as an oxidizing agent, such as e.g. adipinsyreanlæg.

The exhaust gas from adipic acid plants contains large amounts of 0 nitrogen oxides. Eg. concentrations up to 10,000 vppm are found.

φ Such exhaust gas must not be discharged into the ambient air, as it presents significant disadvantages to the outside world.

German Patent No. 1,259,298 discloses a process by which nitrogen oxides are reduced by ammonia. For this purpose, a catalyst consisting of iron oxides and chromium oxides is used. It is well known to those skilled in the art that this process is economically feasible only when there is little oxygen present in the exhaust gas which can lead to an oxidation which acts against the reduction.

At the said adipic acid plants, there is not only a large proportion of nitrogen oxides (Ν0χ) in the exhaust gas, but also a large proportion of oxygen and nitrous oxide. The values for this are always in the range from e.g. 16% by volume, so that it can not be expected that the application of the above method can lead to satisfactory results.

The present invention is intended to provide a process for the removal of nitrogen oxides which is also economically useful when, after its composition, the exhaust gas acts in the direction of oxidation.

The process of the invention for the removal of nitrogen oxides (χ0χ) from exhaust gases containing high oxygen and / or oxygen compounds, in particular waste gas from adipic acid plants, is of the known kind in which the nitrogen oxides are reduced by ammonia at a temperature of at least 260 ° C under the influence of an iron oxide / chromium oxide catalyst, and the process is characterized in that the exhaust gas with the high content of oxygen and / or oxygen compounds is passed through the catalyst divided into several bearings, one before each bed being allowed one relative to the bed. volume measured ammonia partial flow.

In this process, the exhaust gas with strong oxidizing effect of nitrogen oxides can be liberated from these up to a very low residual content, e.g. of 100 ppm or less, but in addition, the specific maximum load capacity of the catalyst is found to rise very unexpectedly. That is, the amount of catalyst volume to be used for a particular exhaust gas stream is smaller than one might have expected. This results in cost savings, which further means that for a specific production of exhaust gas, less catalyst volume must be used, and consequently the reactor can be built smaller.

The method according to the invention is further explained in the following example.

Example In an experimental plant, 5,000 normal liters / hour were passed through a reactor. The exhaust gas from the adipic acid system had the following composition: 145968 3 C> 2 - 16% by volume H2O - 2.4% by volume N2 - 67% by volume% NO2 - 0.24% by volume NO - 0.36% by volume CO2 - 0 , 3 volume% N2O -.16 volume%.

This corresponds to a nitric oxide concentration of a total of 6,000 vppm when not taking the completely harmless N2O into account. Striking is the large proportion of nitrogen and nitric oxide.

Before the feed to the reactor, the exhaust gas was heated to 265 ° C. Three catalyst beds of different thickness were placed in the reactor. Prior to each bearing, an ammonia partial flow was initiated, which was measured relative to the volume of the bearings.

The catalyst consisted of 85% Fe (III) oxide, 10% Cr (III) oxide, 2% Cr (VI) oxide and admixtures of silicic acid, alkali and alkaline earth.

At the reactor output, a content of NO, NO2 of 100 vppm was measured. A maximum specific catalyst load capacity of 3000 n.orma ^ - ~ m / hour was found ^ This value was surprisingly ^ high. Experience could expect a value of 1000.

Further experiments were carried out at which the exhaust gas had a content of NO, NO2 of up to 10000 vppm. The exhaust gases were heated to a temperature of 260 ° C-310 ° C. The NO, NO2 concentrations at the exit of the reactor were of the order of 200 vppm. The specific maximum catalyst loading capacity reached a value of 5000 normal ~ m / tiM0 · m

The increase in catalyst load capacity can be explained by the fact that oxygen and nitric oxide unexpectedly work together in a favorable direction for the reduction.