GB2067912A - Catalysts for removal of ozone from the atmosphere - Google Patents

Abstract

Ozone, which is present in the atmosphere and may be an irritating factor, may be removed from air by utilizing a filter material comprising a combination of at least one catalytic metal or metal oxide, preferably selected from Group VIII of the Periodic Table, and a carbonaceous pyropolymer with a solid support such as an alumina.

Description

SPECIFICATION Removal of ozone from the atmosphere The present invention relates to a filter material for use in removing ozone from air.

Ozone, which is found in the atmosphere of the earth, may cause sensory irritation in humans even in low concentration levels in air such as 0.05 to 0.1 ppm whereas higher concentrations such as from 0.2 to 2 ppm may cause severe reactions such as impaired respiration, chest pains, extreme fatigue, as well as chronic coughing. Although natural levels of ozone in air may range from 0.01 to 0.03 ppm or are less than this, ozone is increasingly being found at higher concentrations in cases of air pollution. This is especially true in specific situations where air circulation is limited, for example near high voltage electrical equipment, near ultraviolet sources, during arc welding operations, and, in recent instances, where ozone sickness has occurred to passengers and crew members in aircraft which are flying at relatively high altitudes.

The aircraft, in normal situations, usually attempt to fly at relatively high altitudes in order to conserve fuel. However, the ozone layer which is normally present in the upper atmosphere has been found to be coming closer to the earth and, therefore, high ozone levels have been found in aircraft which are flying at elevations in excess of 35,000 feet. The ozone sickness which may occur in these aircraft is potentially dangerous inasmuch as the members of the crew who are flying the aircraft may be subjected to the reactions hereinbefore set forth, such as impaired respiration and chest pains.

Currently, activated charcoal is being used in the aircraft in an attempt to eliminate the ozone.

However, the amount of activated charcoal which is required is relatively large, i.e. 400 pounds or more, and it is therefore desirable to find some substitute material which will act as a filter to effectively remove the ozone from the atmosphere in the aircraft but which requires a substantially smaller weight of material to achieve the same effect.

In the past, various substances have been used to decompose ozone to molecular oxygen, for example charcoal, glass, plastics, wood, natural or synthetic rubber, or chemicals which are sacrificial agents and will form compounds with ozone such as carbon monoxide, carbon dioxide or the metal oxides of nickel, copper and iron.

One method of removing ozone from the air which is being breathed would be to utilize a face mask or air stream filter containing a refillable cartridge which contains a catalyst capable of decomposing the ozone. While natural latex, synthetic rubber or similar highly unsaturated organic materials could be used, they would become spent after the ozone had reacted with them and they would therefore have to be disposed of. In contradistinction to this, it would be advantageous to utilize a catalytic material which would not lose its efficiency and thus would be usable for a relatively long period of time.

Therefore, the criteria desired for a catalytic material to be used to decompose ozone are that it should have a long active life, be susceptible to reactivation and in addition should possess the ability to decompose the ozone passing through the filter without releasing any fine particulate matter or producing undesirable side reactions.

We have now found a new filter material which is effective in decomposing ozone without the release of particulate matter and which possesses a long period of activity without the need for reactivation.

According to the invention there is provided a filter material for the removal of ozone from air, which comprises a combination of at least one catalytic metal or metal oxide and a carbonaceous pyropolymer with a solid support.

In a specific embodiment, the features of which are preferred singly and in combination, the filter material comprises a combination of platinum, rhodium and carbonaceous pyropolymer composited on an alumina having a surface area of from 10 to 500 m2/g.

Preferably the catalytic metal or metal oxide consists of or comprises a metal selected from Group VIII of the Periodic Table and more particularly from the noble metals of Group VIII, namely platinum, palladium, ruthenium, rhodium, osmium, and iridium, and combinations thereof such as platinum-ruthenium, palladiumruthenium, platinum-rhodium, palladium-rhodium, or a corresponding oxide.

One or more of the aforesaid metals or metal oxides and a carbonaceous pyropolymer are composited on a solid support which preferably comprises a refractory inorganic oxide possessing a surface area ranging from 10 to 500 m2/g. One method of preparing this type of support is to impregnate a suitable refractory inorganic oxide.

Examples of such oxides are the various forms of alumina such as alpha-alumina, beta-alumina, gamma-alumina or eta-alumina, silica, magnesia, zirconia, titania, and mixtures thereof such as silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-zirconia, silica-alumina-magnesia and silica-alumina-titania, the preferred oxide or oxide mixture being one which possesses a relatively large surface area, for example gammaalumina or silica-alumina. The catalytic metal (or metal oxide) is usually present on the solid support in an amount of from 0.01 to 1% by weight of metal.

The catalytic filter material may be prepared according to any method known in the art. The solid support may be in any desired shape, e.g.

particles, spheres, beads, or monoliths. In one method of preparing the filter material the solid support is impregnated with a solution, preferably an aqueous solution, of a soluble compound of the catalytic component, the metal concentration in said solution being sufficient to ensure the presence of at least 0.01% of the metal component in the finished catalyst. Compounds of metals of the platinum group which may be utilized to impregnate the solid support include chloropalladic acid, chloroplatinic acid, ammonium chloropalladate, palladous chloride, palladic chloride, platinous chloride, platinic chloride and the corresponding ruthenium, rhodium, osmium and iridium compounds. The catalytic impregnation may be carried out, if so desired, in the presence of an additive component, for example thiomalic acid, which will aid the impregnation of the catalyst support.

The catalyst support may be in any form desired prior to impregnation of the catalytic component thereon and may be manufactured by any method known in the art. For example, spheroidal inorganic oxide particles may be manufactured by dispersing an inorganic oxide hydrosol in the form of droplets into a suitable gelling medium and immediately thereafter subjecting the resulting hydrogel spheres to a particular series of aging treatments in a basic medium. The gelling medium which is employed in this process may be any suitable waterimmiscible suspending liquid such as a light gas oil which is chosen principally for its high interfacial tension with respect to water. When utilizing an inorganic oxide such as alumina, it is preferred to utilize a weak base with specific properties such as hexamethylenetetramine in the gelation medium.

Another method of preparing the solid support for the catalytic component of the filter material is to form a paste or dough of the support followed by extrusion thereof utilizing a conventional screw-type extruder. The dough or paste is processed through this extruder following which the freshly extruded material may be collected in the form of strands of indefinite or random lengths which are then dried and subsequently broken into extrudate particles. Alternatively, the freshly extruded material may be cut into random or predetermined lengths and subsequently dried or, if so desired, the freshly extruded material may be formed into spheres, for example, by the process whereby the extrudate strands are collected in a spinning drum, the strands becoming segmented and spheroidized under the spinning influence of the drum.Following this, the extrudate is dried and calcined at elevated temperatures to produce the desired solid support.

This support preferably already or subsequently contains a carbonaceous pyropolymer which is a polymer obtained by pyrolysis of a carbonaceous compound and contains recurring carbon and hydrogen atoms. To provide such a pyropolymer the refractory inorganic oxide may be impregnated by admixing a solution containing a carbohydrate with it. The carbohydrates which are preferably employed are those which are soluble in certain solvents at reasonable temperatures, the preferred solvent comprising water, although it is also contemplated that other solvents, for example low molecular weight alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol or isopropyl alcohol or aqueous solutions of these lower molecular weight alcohols, may also be employed.One criterion of the solvent to be employed is that the boiling point of the solvent should be lower than the decomposition temperature of the carbohydrate which is to be pyrolyzed. The fact that the carbohydrate is soluble in the particular solvent to be employed will ensure penetration of a sufficient amount of the carbohydrate with the solution into discrete particles of the refractory oxide. The impregnation or mixing of the carbohydrate solution with the refractory inorganic oxide is usually effected at atmospheric pressure and ambient temperature for a period of time sufficient to permit complete impregnation, the residence time usually ranging from 0.1 up to 4 hours or more.

Appropriate precursors for the carbonaceous pyropolymers include a variety of carbohydrates, which may be monosaccharides, disaccharides or polysaccharides, some specific examples of these compounds being the monosaccharides erythrose, threose, ribose, arabinose, lyxose, xylose, altrose, mannose, galactose, gulose, allose, glucose (dextrose), ta lose, dose, fructose, tagatose, sorbose and rhamnose; the disaccharides sucrose and trehalose; the trisaccharides gentianose, raffinose and melezitose; and the polysaccharides glycogen, inulin, dextrin, starch, cellulose, other pectic materials and plant carbohydrate gums.

The refractory inorganic oxide which has been impregnated with the carbohydrate solution is then dried, suitably at a temperature in the range of from 1100 to 1 1 50C. for a period of time ranging from 2 to 10 hours or more in duration.

Following this, the dried, impregnated oxide is then pyrolyzed at an elevated temperature, usually in the range from 6000 to 1 2000C. at atmospheric pressure, and preferably in an inert atmosphere, which may be supplied by effecting the calcination in a dry nitrogen atmosphere. The calcination is suitably conducted for a period of time ranging from 0.5 up to 4 hours or more. The resulting material may then be impregnated with the catalytic metal or metal oxide in a manner similar to that hereinbefore set forth in order to obtain the desired filter material.

Another method of preparing the filter material of the present invention also involves using a refractory inorganic oxide containing at least a monolayer of a carbonaceous pyropolymer on the surface thereof, but one which has been prepared by subjecting the inorganic refractory oxide (which may be in any form such as loose dry powder, flats, cylinders, spheres, rods or pellets) to a pyrolysis process in which a carbonaceous pyropolymer precursor is passed over the surface of the inorganic refractory oxide at pyrolysis conditions from 6000 to 1 2000C or more.

Examples of organic substances which may be used as precursors in this way and pyrolyzed to form the carbonaceous pyropolymer on the surface of the refractory oxide include aliphatic hydrocarbons such as ethane, propane, butane or pentane; cyclo-aliphatic hydrocarbons such as cyclohexane or methylcyclopentane; aromatic hydrocarbons such as benzene, toluene, the isomeric xylenes or naphthalene; aliphatic halogen derivatives such as chloromethane, bromoethane, chloroethane, bromopropane, chlorobutane, carbon tetrachloride, chloroform or 1,2dichloroethane; aliphatic oxygen derivatives such as ethyl alcohol, n-propyl alcohol, isopropyl alcohol, glycol, glycerol or ethyl ether; aliphatic sulfur derivatives such as ethyl mercaptan, n-propyl mercaptan or butyl mercaptan; aliphatic nitrogen derivatives such as dimethylamine, diethylamine, acetamide, propionamide, nitroethane, 1 -nitrobutane, acetonitrile or propionitrile; and heterocyclic compounds such as furan, furfural or pyran. The solid support may be obtained by placing a charge of an inorganic refractory oxide, such as gamma-alumina or silicaalumina, in an appropriate vessel which is thereafter heated to the desired pyrolysis temperature. The pyropolymer precursor is charged to the vessel and passed over the surface of the refractory inorganic oxide and is deposited there in at least a monolayer of carbonaceous pyropolymer containing recurring carbon and hydrogen atoms. Following its recovery the support may then be treated in a manner similar to that set forth in order to deposit the catalytic metal on the surface thereof.

The filter materials hereinbefore described may be utilized as filters for home or industrial air conditioning systems or in portable face masks.

For example, when being utilized in portable face masks, the filter material may be enclosed in a container constructed of either porous material or screening so that the air which is to be breathed can readily pass through the container and over the surface of the catalytic filter material, thereby decomposing the ozone and permitting molecular oxygen to be inhaled by the person wearing the face mask rather than the ozone. It is to be realized that any particular configuration of the filter container which is known in the art may be used and that the amount of catalytic filter material may vary within a relatively wide range, the smallest amount of material appropriate in any particular device being that which is sufficient to decompose ozone for the predetermined period of time appropriate to the device in question. By utilizing the catalytic metal (or metal oxide) on a solid support of the type described it is possible to obtain a filter material which will effectively decompose the ozone without releasing any finely divided particulate material into the air.

Claims (13)

1. A filter material for the removal of ozone from air, which comprises a combination of at least one catalytic metal or metal oxide and a carbonaceous pyropolymer with a solid support.

2. A material as claimed in claim 1 wherein the metal is selected from Group VIII of the Periodic Table.

3. A material as claimed in claim 2 wherein the Group VIII metal is platinum.

4. A material as claimed in claim 2 wherein the Group VIII metal is palladium.

5. A material as claimed in claim 2 wherein the Group VIII metal is a combination of platinum and rhodium.

6. A material as claimed in any of claims 1 to 5 wherein the solid support is an inorganic oxide.

7. A material as claimed in any of claims 1 to 5 wherein the solid support is a high surface area refractory inorganic oxide and contains at least a monolayer of a carbonaceous pyropolymer on the surface thereof.

8. A material as claimed in claim 6 or 7 wherein the inorganic oxide is alumina having a surface area of from 10 to 500 m2/g.

9. A material as claimed in claim 8 wherein the alumina is gamma-alumina.

10. A material as claimed in any of claims 1 to 9 which contains 0.01 to 1% by weight of catalytic metal.

11. A material as claimed in any of claims 1 to 10 wherein the carbonaceous pyropolymer has been obtained by pyrolysis at 600 to 1 2000C of a carbohydrate impregnated into the solid support.

12. A filter material as claimed in claim 1 and substantially as hereinbefore described.

13. A portable face mask, or a home or industrial air conditioning system, containing a filter material as claimed in any of claims 1 to 12.