WO2001087465A1

WO2001087465A1 - Method for n2o catalytic breakdown

Info

Publication number: WO2001087465A1
Application number: PCT/EP2001/005074
Authority: WO
Inventors: Helge Wessel; Michael Baier; Thomas Fetzer; Klaus Harth; Volker Schumacher; Herbert Wanjek; Bernhard Otto
Original assignee: Basf Aktiengesellschaft
Priority date: 2000-05-13
Filing date: 2001-05-04
Publication date: 2001-11-22
Also published as: DE10023538A1; AU7050601A

Abstract

The invention relates to a method for vapor phase catalytic heterogeneous breaking down of N2O, through arranging, upstream a fixed bed catalyst, a material inert with respect to N2O breakdown.

Description

Process for the catalytic decomposition of N0

description

The present invention relates to a process for heterogeneously catalyzed gas phase decomposition of NO by introducing a material which is inert with respect to NO decomposition upstream of the fixed bed catalyst.

N ₂ 0 arises as a by-product in many processes in which HN0 _{3 is used} as an oxidizing agent in the liquid phase. In particular when alcohols, aldehydes and ketones, for example cyclohexanol and cyclohexanone are converted to adipic acid, acetaldehyde to glyoxal or glyoxal to glyoxylic acid, considerable amounts of N ₂ O are released. Furthermore, N0 is formed in the production of nicotinic acid and hydroxyla in. In addition, N0 also forms as a by-product in the production of nitric acid by burning NH.

From Science, 251 (1991), page 932 it is known that N0 has a certain damage potential for the earth's atmosphere. N0 is considered an essential source of NO in the stratosphere, which in turn is said to have a significant impact on the depletion of ozone in the stratosphere. In addition, N0 is considered a greenhouse gas, although the global warming potential of N0 should be about 290 times greater than that of C0.

EP-A-687 499 describes a catalyst for the catalytic reduction of NO _x and / or for the oxidation of hydrocarbons in exhaust gases, which consists of a copper oxide-zinc oxide-aluminum oxide spinel of the chemical formula Cu _A ZncAl _D C> ₄ , where A + C + D = 3, A> 0, C> 0 and D <0. The ratio of Cu and Zn to AI is kept within wide limits in this publication.

WO-A-94/16798 describes a process for the catalytic decomposition of pure or N0 contained in gas mixtures. An M _x AlO ₄ ~ catalyst is used as the catalyst. This is obtained by mixing CuAl 0 ₄ with Sn, Pb, or an element of the 2nd main group or subgroup of the Periodic Table of the Elements as oxide or salt or in elemental form and subsequent calcination at a temperature of 300 to 1300 ° C and one Pressure from 0.1 to 200 bar.

WO-A-94/27709 describes zeolitic catalysts. WO-A-93/04774 discloses silver-containing supported catalysts with an Al 0 _{3 support} which has a BET surface area of 26 to 350 m ² / g.

In addition to silver-containing catalysts, N0 can also be decomposed on other catalysts containing precious metals. For this purpose, e.g. Pt, Pd or Rh on different supports [Chem. Abstracts 6 (1965) 1481]. Precious metal-containing catalysts have been e.g. also described as suitable for the decomposition of N0 in anesthetic gases. JP-OS 55-31 463 proposes catalysts containing Pt, Pd, Rh, Ir and / or Ru for this purpose. Another example of a Pd-containing catalyst is known from DE-OS 35 43 640.

All of these catalyst systems successfully decompose N0. However, the catalyst systems are not optimal in terms of their thermal stability at high temperatures (> 500 ° C). In many cases, the deactivation of the catalysts is problematic, which necessitates frequent replacement of the catalyst bed. Especially at temperatures above 500 ° C, which are advantageous for an almost complete decomposition of the N0 with an acceptable amount of catalyst, there is often a strong, irreversible deactivation. The required high reactor temperatures also generally require energy-intensive and costly preheating of the gas stream. Furthermore, a complex dilution of the exhaust gas with air or cycle gas is required to reduce the N0 concentration in the exhaust gas.

Precious metal-containing catalysts are decomposition-active at comparatively low temperatures, but have the disadvantage of high catalyst costs. In addition, precious metals show considerable loss of material through evaporation at the required decomposition temperatures. Furthermore, the processing of the used catalysts is associated with high costs, which is why a large-scale N ₂ 0 decomposition of noble metal-containing catalysts is extremely unattractive economically.

The catalyst systems described above also all have the disadvantage of catalyst deactivation by partial or complete catalyst poisoning by constituents contained in the gas containing NO. The N ₂ 0 -containing gas which is brought into contact with the catalyst systems can contain catalyst poisons such as, for example, foreign metals and / or metallic compounds, organic and / or organometallic compounds and / or inorganic elements and / or compounds which are present on the catalyst precipitate, block the active centers and / or with chemical reactions occur with the catalyst and / or with catalyst components, which leads to a rapid deactivation of the catalysts and to a significant reduction in the service life of the catalysts. In particular, sulfur levels and / or silicone levels and / or halogen levels and / or levels of carbon compounds and / or water levels in the N ₂ 0 -containing gas adversely affect the activity of the N ₂ 0 decomposition catalysts described in the prior art.

The object of the present invention was therefore to provide a process for heterogeneously catalyzed gas phase decomposition of N ₂ O which alleviates the disadvantages mentioned above.

Accordingly, a new and improved process for the heterogeneously catalyzed gas phase decomposition of N ₂ 0 has been found, which is characterized in that an inert material with respect to N0 decomposition is arranged in front of the fixed bed catalyst.

The material which is inert with respect to N0 decomposition according to the invention can e.g. consist of:

- inorganic materials, e.g. Oxides, sulfates, carbonates, nitrides, carbides, chlorides, fluorides, silicates or silicones,

- organic materials such as Resins, waxes, foams or plastics,

or their mixtures. Inorganic oxides such as A1 ₂ 0 ₃ or Si0 ₂ are preferably used.

This material serves to absorb catalyst-deactivating constituents and / or to retain them chemically and / or physically before the gas stream to be cleaned is brought into contact with the N ₂ O decomposition catalyst.

The material according to the invention which is inert with respect to N ₂ O decomposition can be used in various geometric shapes, preferably tablets, strands, trilobes, hollow strands, star strands, honeycombs or combinations thereof. The material inert with respect to N0 decomposition can be applied directly upstream of the N ₂ 0 decomposition catalyst or spatially separated therefrom. The material is preferably applied in the gas stream to be cleaned directly in front of the catalyst in the form of a bed. The proportion of the inert material with respect to the N ₂ 0 decomposition in the total bed is generally 0.05 to 75% by volume, preferably 1.5 to 50% by volume, particularly preferably 2.5 to 35% by volume.

The catalysts to be used according to the invention can be prepared by various methods which are generally known. Preference is given to using catalysts which, for example, are described in WO-A-94/16798 or in DE-A-198 48 595.

The process according to the invention for the catalytic decomposition of N ₂ 0 can be used in the case of pure N ₂ 0 or contained in gas mixtures.

The process according to the invention is preferably used for the decomposition of NO in exhaust gas streams containing NO, such as those used, for example, in processes for the production of adipic acid and longer-chain dicarboxylic acids, nitric acid, hydroxylamine derivatives, caprolactam, glyoxal, methylglyoxal, glyoxylic acid or in processes for the combustion of nitrogenous products Materials, e.g. Ammonia.

The process is particularly suitable for the decomposition of N ₂ O in exhaust gases from the production of adipic acid and nitric acid. Furthermore, the method according to the invention is suitable for cleaning process gases from ammonia combustion.

The N ₂ 0 can be removed from the nitric acid off-gases without further nitrogen oxides, N0χ, (valuable products) being decomposed in significant amounts. Other nitrogen oxides are nitrogen monoxide (NO), nitrous oxide (N ₂ 0 ₃ ), nitrogen dioxide (N0), nitrous oxide (N ₂ 0 ₄ ), nitrous oxide (N ₂ 0s), nitrogen peroxide (N0 ₃ ). The nitrogen oxide content, N0χ, can generally be 0 to 50% by volume, preferably 1 to 40% by volume, particularly preferably 10 to 30% by volume, based on the total gas.

The process according to the invention is suitable for purifying exhaust gases whose N ₂ O content is between 0.01 and 50% by volume, preferably between 0.01 and 30% by volume, particularly preferably between 0.01 and 20% by volume the total gas.

In addition to N ₂ 0 and other nitrogen oxides N0 _X , the exhaust gases can also contain, for example, N, 0, CO, C0, H0 and / or noble gases, without this having a significant effect on the activity of the catalysts. Slight inhibitions of the catalyst activity can be compensated for by increasing the catalyst volume or by reducing the load. In general, the process according to the invention can be carried out in a temperature range from 280 to 1100 ° C., preferably 330 to 1000 ° C., particularly preferably in a range from 380 to 920 ° C. The deactivation of the catalysts of the process is significantly less than that known from the prior art due to the attachment according to the invention with regard to the N0 decomposition of inert materials upstream of the N ₂ 0 decomposition catalyst.

Examples

10

example 1

Preparation of the catalyst

15 A mixture of 2169.3 g Puralox® SCF, 1185.93 g Pural® SB, 1090.1 g Cu (N0 ₃ ) ₂ x 6H ₂ 0, 370.74 g CuO, 1495.6 g Zn (N0 ₃ ) ₂ x 4H ₂ 0, 492 g ZnO, 2129.6 g Mg (N0 ₃ ) ₂ x 6H ₂ 0 were 30 min with the addition of 750 g of water. rolled, extruded into 3 mm strands, dried and calcined at 750 ° C for 4 h.

20

Experimental Procedure

An 800 mm long reaction tube made of Hasteloy C, divided into two, was used as the test apparatus for the adiabatic procedure

25 heating and reaction zone. The inside diameter was 18 mm. In order to be able to measure the temperature profile in the tube, an inner tube with an outside diameter of 3.17 mm was used, in which a thermocouple could easily be moved. The N0 decomposition was tested in a typical exhaust gas mixture of an adipic acid

30 would be with the following gas composition:

N ₂ 0: 20 vol. -%

N0 ₂ : 17 vol. -%

N ₂ : 47 vol. -%

35 0 ₂ : 7.5 vol. -%

H ₂ 0: 3 vol. -%

C0 ₂ : 2.5 vol. -%

Rest: other components

40

45

Claims

claims

1. A process for heterogeneously catalyzed gas phase decomposition of N0, characterized in that an inert material with respect to N ₂ 0 decomposition is arranged upstream of the fixed bed catalyst.

2. Process for heterogeneously catalyzed gas phase decomposition of

N ₂ 0 according to claim 1, characterized in that the inert material consists of inorganic oxides.

3. Process for heterogeneously catalyzed gas phase decomposition of

N0 according to one of claims 1 or 2, characterized in that the inert material consists of aluminum oxides, silicon oxides or other mixtures.

4. A process for heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to one of claims 1, 2 or 3, characterized in that the inert material in the decomposition reactor is attached directly upstream of the N ₂ 0 decomposition catalyst.

5. A process for heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to any one of claims 1, 2, 3 or 4, characterized in that the inert material is attached in the form of a bed in front of the catalyst.

6. A process for the heterogeneously catalyzed gas phase decomposition of NO according to one of claims 1, 2, 3, 4 and 5, characterized in that the proportion of the inert material in the entire bed is 0.05 to 75% by volume, preferably 1 , 5 to 50 vol .-%, particularly preferably 2.5 to 35 vol .-%.

, Process for the heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to one of Claims 1, 2, 3, 4, 5 and 6, characterized in that the decomposition is carried out at temperatures of 280 to 1100 ° C, preferably 330 to 1000 ° C, particularly preferably carried out at 380 to 920 ° C.

8. A process for heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to any one of claims 1, 2, 3, 4, 5, 6 and 7, characterized in that the decomposition in the presence of 0.01 to 50 vol .-% NO and / or N0 ₂ , based on the total gas. Process for the heterogeneously catalyzed gas phase decomposition of N0 according to one of Claims 1, 2, 3, 4, 5, 6, 7 and 8, characterized in that the gas mixture in addition to N ₂ 0 and NO is also N, 0, CO, C0, H0 and / or contains the noble gases.

Process for the heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to one of Claims 1, 2, 3, 4, 5, 6, 7, 8 and 9, characterized in that the N0 content of the gas mixture to be purified is generally from 0.01 to 50% by volume is preferably between 0.01 and 30% by volume, particularly preferably between 0.01 and 20% by volume.

Process for the heterogeneously catalyzed gas phase decomposition of N ₂ 0 according to one of Claims 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, characterized in that it is to be purified

Part or all of the exhaust gases are exhaust gases from the production of dicarboxylic acid, preferably the production of adipic acid with the use of nitric acid.

Process for the heterogeneously catalyzed gas phase decomposition of N0 according to one of Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11, characterized in that the waste gases to be cleaned are process gases of ammonia combustion.