Gas separation: apparatus – Solid sorbent apparatus – Plural solid sorbent beds
Patent
1993-09-16
1995-01-10
Spitzer, Robert
Gas separation: apparatus
Solid sorbent apparatus
Plural solid sorbent beds
96135, 96154, B01D 5304
Patent
active
053796810
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a passive filter including a self-regenerating composition of materials which has a capability to take up and keep gaseous, particularly smelling substances from the surrounding air and after that slowly emit these substances and/or their rest products destructed by oxidation or reduction. The invention is described based on gaseous, smelling substances, but does not exclude its application on gaseous substances generally whether these substances emit odour or not.
THE PRIOR ART
According to Swedish patent publication SE-C-387 681 it is known to prevent or reduce the appearance of condensate on a surface by coating the surface with a layer of a composition of materials including granules with heat-insulating and sorbating properties. By chance it was observed that the known coating also has a certain capability to remove odour from the air to which it is in contact by acting as a passive filter. However continued experiments showed a weakness in the smell removing properties of the known coating, namely that it was quickly saturated, at which its capability to take up odour ceased and the coating itself started smelling.
It has long been known that porous materials have a capability to take up odour. Porous materials are used as filters in ventilation equipment by which the smelling substances are sorbated when air, polluted by smelling substances, is forced through the filters by means of a mechanical ventilation. This use is known from a great number of patent publications, as e.g. SE-C-218 164, DE-A-2 129 795, DE-A-1 619 586 and U.S. Pat. No. 4,604,110.
A special case is described in patent publications DE-A-3 735 222 and DE-A-3 801 652. The purpose of the device described is to put a chemical sorbating layer combined with a diffusion-tight layer as a shielding between the contaminated building structure and habitable rooms.
Porous materials also are used to suck smelling substances in a liquid phase or dissolved in a liquid, e.g., to serve as a so-called cat litter or a sorbating material for sanitation works. The patent publications WO 82/04408 and GB-A-1 593 058 describe such materials.
Porous materials also are used in combination with hygroscopic additives for taking up moisture in packings and spaces for apparatuses. Such a material is known from the patent publication DE-B-1 260 441.
The above-described observation of the, in the patent publication SE-C-387 681 described materials capability to take up odour, opened the way to an up to now disregarded technic concerning removing of smelling substances or chemicals from the air in a room, namely to use the fact that smelling substances are volatile and that they only smell in a gaseous shape and that they follow the gas laws.
Smelling substances are more or less volatile and odour arises in that molecules or micro-particles evaporate from the surface of a smelling substance. The evaporation continues until the surrounding air is saturated. In this condition as many odour molecules will be taken up and evaporate at the surface of the smelling substance.
Smelling substances are characterized in that the perception of the odour arises at very low concentrations (as a rule some milligram per m.sup.3 air) and far before the point of saturation is reached. The concentration rate of the smelling substance in the air at which odour can be perceived is called the smell threshold value. In order to eliminate the odour, more odour molecules must be eliminated from the air than are emitted from the surface of the smelling substance. In that way that the rate of smelling substances will be below the smell threshold value.
Smelling substances have a gas pressure and their spreading in the room follow the gas laws. This is the reason why odour very quickly spreads in a closed room. As a result of the partial pressure, the odour molecules penetrate into porous materials where they move slower than in the air space. The porous surface therefore takes up more odour molecules than it emits. However, a state of equil
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