DE3029948A1 - METHOD FOR REMOVING OZONE FROM A GAS MIXTURE CONTAINING OZONE - Google Patents

Description

description

The invention relates to the decomposition of ozone and in particular to the catalytic decomposition of ozone.

Ozone is thermodynamically unstable and would slowly decompose at 250 C in the absence of a catalyst. The smell of ozone is perceptible to living things in the air at a concentration of less than 1 ppm. Concentrations Above 2 ppm ozone causes irritation in living beings in the respiratory tract, and occurs at higher concentrations Damage to the cell tissue. The presence of ozone in the area is not even in lower concentrations desirable.

Ozone can be removed from a gas stream by a number of methods such as gas scrubbing, thermal decomposition and gas adsorption. An apparatus for scrubbing gas or gas adsorption requires maintenance and is not always applicable when space requirements and weight play a special role.

Ozone is often produced as an undesirable by-product in photocopiers and similar equipment, which leads to the oxidation of Metal compounds can result. It can also be in

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such a concentration that the well-being of those working in the vicinity is impaired can be. Ozone is sometimes used in wastewater treatment, and some of it could end up remain after processing. As a gas, ozone can also be used near arc lamps, welding work, and power sources occur with high voltage.

Ozone occurs in the air at altitudes above 25,000 feet. At altitudes of 25,000 to 30,000 feet, the concentration can between 0 and 20 ppm and at 30,000 to 55,000 feet between 20 and 20,000 ppm. Air for the passenger cabin airliners normally use the primary air compressor provided by one or more aircraft engines, flows through the passenger cabin and arrives via a valve into the open. This regulates the air pressure in the cabin, which should normally be around 63 cm Hg, which is what Corresponds to atmospheric pressure at an altitude of 5,000 feet. Since a number of aircraft at an altitude of 25,000 to The passengers and the aircraft crew fly 30,000 feet and a relatively large amount of air is conveyed through the cabin exposed to high average ozone concentrations.

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It is an object of the present invention to remove at least a portion of the ozone from a gas stream to be able to.

In accordance with the present invention includes a method for removing ozone from an ozone-containing gas mixture passing the gas mixture over a catalyst, so that at least part of the ozone is a catalytic Is subject to decomposition to oxygen, said catalyst containing catalytic material, the one or contains several members of the group consisting of Pt, Ru, Rh, Pd, Ir, Os, Fe, Co, Ni, Ag, Mn and Sn as well as from alloys, Mixtures and compounds containing one or more of these metals exists.

The catalytic material can be mounted on a ceramic or metallic support, and between the catalytic material and the support, an intermediate layer of refractory metal oxide may be provided.

The layer of refractory metal oxide can be applied as a so-called slurry ("washcoat") and one or more of the oxides of B, Al, Ba, Sr, Ca, Mg, Be, Si, Ti, Zr, Sc, Y and the rare earths. Preferably

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3, the slipping load should be between 0.2 g / in and 2 g / lie in the support, and one is particularly preferred

3 3

Load of between 0.4 g / in and 1 g / in. The catalyst loading of the platinum group metals is preferably in of the order of 20 to 200 grams per cubic foot, whereas the charge of the remaining catalytic mentioned above Metal relative to the weight of the support with the slurry is preferably on the order of 50 to 1,000 grams per cubic foot.

The support, which can include channels extending from one end to the opposite end, can be made of ceramic Material such as cordierite, or made from a base metal or a platinum group metal. Preferably If the support is made of an oxidation-resistant metal or alloy, and Kanthai D is preferred or an iron alloy containing chromium and aluminum and Fecralloy (registered trademark). The composition of Kanthai D is in% by weight: chromium 23%, cobalt 0.5-2%, aluminum 0.7% and the remainder iron.

The cell density of the support, i.e. the number of cells or channels above the end face of the support, is preferably at 200 cells / in and above and one prefers 350 cells /

in and above.

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The preferred catalytic material is selected from the group consisting of Pt, Pd, Fe, Ag and Mn, and of these metals, in turn, are particularly preferred for Pt, Ag and Mn.

The catalytic material can be an integral part of the support or can be associated with the support. If the If support contains one or more metals of the platinum group, these can, for example, form the catalytic material. Similarly, iron compounds formed on the surface of the support by corrosion of the metal can act as catalytic Material work when the column is made of an iron-containing alloy.

In order to observe the parameters related to the catalytic decomposition of ozone, a Series of catalysts tested in a tubular reactor. The catalyst samples showed a catalytic Material on a metal support of Fecrylloy with the composition of 15 wt.% Chromium, 4.5 to 4.8 wt.% Aluminum, 0.4 to 0.5 wt.% Yttrium and the remainder iron, a length of 1 in and a diameter of 2 in was attached with the support an alumina slurry wore. The slurry charge was 0.7 g / in. One happened in the tubular reactor ozone-containing gas flow the catalyst. With the intention of,

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to do that, a gas stream containing a mixture of nitrogen and oxygen passed first an electric heater, to allow the temperature of the gases to be set before ozone is released when a high voltage was produced, the gas flow was supplied. The concentration of that present in the gas stream Ozone was essentially 1.5 ppm. This concentration was determined using a Dasibi, Model 1003 ozone analyzer and measured after the catalyst. The space velocity was 325,000 hr ~ and the gas pressure was 15 psig (29.7 psia).

A number of tests were performed on samples of the catalyst containing various catalytic materials.

The cell density of the supports used was 400 cells / in and the temperature of the gas was 150 ° C.

The results are shown in graphical form in Figures 1 through 22 of the accompanying drawings. Details of the Test results according to the drawing are shown in Tables 1, 2 and 3 below.

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Table 1

Catalytic material, charge of the catalytic Fig.

that on the support with material of the support

the slurry with the slurry is attached / ft ^

platinum

platinum

5.5% Rh, 94.5% Pt 35% Rh, 65% Pt platinum and silver palladium

33 1/3 Pd 66 2/3 Pt silver

Manganese dioxide (MnO ") Manganese trioxide (Mn ₃ O ₃ )

Triiron tetraoxide (Fe ₃ O ₄ )

120 1 120 2 120 3 120 4th Pt 120 + Ag 500 5 120 6th 120 7th 500 8th 500 9 250 10 375 11

Table 2 below refers to a series of tests performed with platinum as the catalytic material on one charge of 120 g / ft were run on a series of supports with different cell densities. The temperature was on Maintained 150 ° C.

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Table 2

ο
Cell density in cells / in Fig,

180 12

400 1

550 13

1200 1 4

These results are summarized in Figure 15, which is a graph of ozone conversion as a function of cell density.

Other series of tests were performed with platinum as the catalytic material at a load of 120 g / ft on supports

2 carried out at a cell density of 400 cells / in. the Gas stream temperatures were varied as shown in Table 3.

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Table 3

Temperature of the gas flow ⁰ C Fig.

20 16

50 17

80 18

125 19

150 1

200 20

250 21

Finally, these results are summarized in Figure 22 which is a graph of ozone conversion as a function of temperature.

In all of the previous tests, the maximum back pressure of the support was 8 mm Hg. This low back pressure is one the benefits of using metal supports. A further advantage of these supports is, inter alia, that they come with

Cell densities over 500 cells each can be manufactured in lighter than ceramic supports.

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In summary, the invention relates to decomposition of ozone. In particular, the invention relates to a method for removing ozone from an ozone-containing one Gas mixture, the gas mixture being passed over a catalyst so that at least part of the Ozone is subject to catalytic decomposition into oxygen, the aforementioned catalyst being catalytic material contains, which contains one or more members of the group consisting of Pt, Ru, Rh, Pd, Ir, Os, Fe, Co, Ni, Ag, Mn and Sn as well as from alloys, mixtures and compounds that contain one or more of these metals, consists.

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Claims (1)

Applicant : JOHNSON, MATTHEY & CO., LIMITED, 43, Hatton Garden, London, EC1N 8EE, England Title : Method of Removing Ozone From One Ozone-containing gas mixture Claims 1. Procedure for removing ozone from one Ozone-containing gas mixture, characterized in that the gas mixture is passed over a catalyst is to catalytically decompose at least part of the ozone into oxygen, the catalyst as catalytic material of one or more members of the group consisting of Pt, Ru, Rh, Pd, Ir, Os, Fe, Co, Ni, Ag, Mn and Sn as well as alloys, mixtures and compounds comprising one or more of these Contains metals. 2. The method according to claim 1, characterized in that the catalytic material on a ceramic or metallic support is attached. 3. The method according to claim 2, characterized in that the support has a first layer of refractory Carries metal oxide on which a second layer of the catalytic material is attached. 6/8/80 - 2 - 130009/0876 BATH ORIGINAL 4. The method according to claim 3, characterized in that that the refractory metal oxide layer is one or more of the oxides of B, Al, Ba, Sr, Ca, Mg, Be, Contains Si, Ti, Zr, Sc, Y and the rare earths. 5. The method according to claim 3, characterized in that the charge of the first layer of refractory Metal oxide is on the order of 0.2 g / in and 2 g / in in the support. 6. The method according to claim 5, characterized in that the charge of the first layer of refractory Metal oxide is on the order of 0.4 g / in and 1 g / in in the support. 7. The method according to any one of claims 2 to 6, characterized in that the catalyst loading relative to the total weight of the support and the first layer in the order of 20 to 200 g / ft for Pt, Ru, Rh, Pd, Ir and Os and in on the order of 50 to 1000 g / ft ³ for Fe, Co, Ni, Ag, Mn and Sn. 8. The method according to any one of claims 1 to 7, characterized characterized in that the substrate consists of an oxidation J 21 P 254 6/8/80 - 3 - 130009/0876 solid alloy is produced, which apart from impurities 23 wt.% chromium, 0.5 - 20 wt.% Contains cobalt, 0.7% by weight aluminum and the remainder iron. 9. The method according to any one of claims 1 to 8, characterized in that the substrate consists of an oxidation-resistant Alloy is produced which, apart from impurities, 15% by weight of chromium, 4.5 to 4.8% by weight Contains aluminum, 0.4 to 0.5% by weight yttrium and the remainder iron. 10. The method according to claim 8 or claim 9, characterized characterized in that the catalyst support is a cell density of at least 200 cells per inch. J 21 P 254 6/8/80 - 4 - 130009/0876