FI70150B - TORRFILTER - Google Patents

Abstract

The filter comprises a filtering substrate including organic, natural or synthetic fibers, of which at least part are grafted with at least one organic monomer capable of retaining physically and chemically some of the particles to be eliminated which are conveyed by the gas stream. The fibers are grafted by irradiation at room temperature and woven or needled, the fibers comprising advantageously multi grafted fibers or a set of fibers grafted differently. A grafting with fluorinated monomers further improves the qualities of the mechanical filtering of the filter.

Description

DRY FILTER - TORRFILTER

This invention relates to a dry filter for filtering and purifying gas, in particular to a dry filter which physically and chemically retains impurities.

In the filtration of gases, the use of mechanically operated filters is quite widespread. The properties of such a filter are primarily determined by the dimensions of the pores in the walls to be filtered and in the filter medium. The efficiency of these filters can be improved by using the so-called wet filter technology, which is overshadowed by the deterioration of the filter over time.

German patent publication DE-A-27 37 070 discloses a method for purifying gases containing mineral acids using a filter structure containing absorbents, in which the absorption is based on ion exchange. This method is suitable for mineral products that are chemically decomposed into ions in water so that they can be recycled through the resin regeneration step.

In order to trap the harmful particles in the gas mass, not only mechanically but also chemically, combination filters using bound active substances have also been proposed. However, even in dry filters, this causes considerable binding problems, which are usually solved only by optimizing the retaining walls, which in turn causes considerable and often excessive filter resistances.

Among these active substances, numerous monomers are known to have chemical aggregation and binding tendencies towards certain groups of harmful particles at different concentrations, which may be useful in filtration techniques but which nevertheless involve the above-mentioned disadvantages of retaining harmful particles.

It is also known in the art that fibers, especially textile fibers, can be incorporated into certain organic monomers 2 701 50 to provide them with new properties such as color affinity and hydrophilicity or non-combustibility.

In the magazine TAPPI Vol. 55 No. 6, 1972, pp. 858-867 in R.B. In Phillips et al., "Modification of Pulp and Paper by Graft Copolymerization", it is known to graft monomers into paper filters to improve their physical, especially mechanical, properties.

It is an object of the present invention to provide a new type of dry filter with a filter material made of fibers, the retention and attachment properties of which are considerably improved and easily modified, and which does not present a significant risk of removal, while its service life is considerably improved.

Another object of the invention is to provide simple filters with low production costs which combine, in the best possible way and with the greatest possible possibilities of variation, improved mechanical and chemical retention properties for filtering and treating gas streams.

The invention which achieves the above objects comprises a dry filter for mechanical filtration and chemical purification of a gas stream containing removable particles, comprising a filter part consisting of at least a fibrous felt containing organic synthetic or natural fibers and in which at least one of the fibers of the filter part is grafted capable of physically and chemically trapping at least some of the particles carried by the gas stream. The dry filter according to the invention is characterized in that at least some of the fibers are grafted with compounds selected from the group consisting of peracids, mercaptans, ethyl acetoacetates and ethyl acetamido malonates.

According to the present invention, by grafting reactive monomers onto the fibers of a filter medium which tend to associate with certain solid or liquid groups of particles carried by the gas stream, the advantages of grafted substances as reactants and conventional release hazard, not only with respect to retained particles but also with respect to the active agent and / or particles attached thereto, while providing optimized mechanical filtration with controlled low filter resistances.

Other features and advantages of the present invention will become apparent from the following descriptions of embodiments, which are given by way of illustration but not by way of limitation.

In recent years, various grafting methods have been developed with the intention of changing the physical properties of the elements to be grafted, in particular textile fibers. These grafting methods can be classified into three main groups: ionic grafting by a wet method using initiators such as seriura, permanganate and Ferri ions used in an acidic mineral medium. in the gas or azeotropic stage for acrylic derivatives, or in the solvent stage. Grafting of 4-component ammonium salts instead takes place without initiator in a concentrated base solution, e.g. French Patent No. 1,585,665 describes. In each case, the fabric is washed and rinsed after the reaction and then dried. Grafting in the solvent step promotes the appearance of carbon cations in double-bonded products, especially if AlCl 3 or ZnCl 2 is involved. Carbon cations adhere to substances in suspension in the solvent, e.g.

/ - Grafting by ultraviolet radiation. Due to the low energy of this radiation, it is necessary to use a photocatalyst, which may contain carbonyl groups, benzophenone or diacetyl vapors. The advantage of this method is that it can be used to convert fibers which are considered unreacted, such as polypropylene or polyester.

Grafting by means of high-force accelerated particles or gamma rays produced, for example, by radioactive cobalt 60. The effect of such particles on the organic fiber is to form free radicals as hydrogen atoms are released as these unstable radicals promote the onset of grafting of selected monomers. Thus, if F-CH-F symbolically represents a fiber and M a graft monomer, a grafted fiber F-C-F is obtained at the end of the reaction. The reaction takes place either radially \

M

by burning the fiber alone under the influence of moisture or not, or by irradiating the fiber impregnated with monomers.

The filters of this invention are preferably made using high energy particle grafting because, as will be seen below, the radical scavenging process makes it possible to graft two or more different monomers into the same fiber, each grafted homopolymer of any kind retaining its characteristic reagents. In order to expand the range of use of the filter, it is thus possible to provide the same fiber with several different properties. Moreover, in industry, such a radical reaction consumes less energy compared to other methods because the reaction takes place at room temperature and does not require additional heat. The reaction can take place upstream (in the production line) in crude fibers, but also in woven or camouflaged fibers; in the dry fabric, no preliminary soaking and wetting steps are required.

In a first embodiment, a filter according to the present invention is described for filtering odors and fats in cooker hoods.

The production of fibers to obtain a Textile which forms at least a part of the material to be filtered takes place under the influence of accelerated particle flux. As referred to above, 70150 this operation can be performed on fibrous gauze or already anesthetized product. Irradiation occurs in an instant and depends only on the power of the particle accelerator. The power generally considered suitable for this type of irradiation is 20-50 kW, which gives an irradiation value of 500 KeV - more than 1 MeV, with a power of 600 KeV generally being sufficient. The degree of irradiation and thus the number of reaction sites can be increased by using the fibrous material several times in the radiation stream, for example "folded".

The original filterable material, consisting of loosely attached organic natural or synthetic fibers, whether or not oxidized to peroxide compounds, is placed next to each other for the following grafts in connection with the following groups of monomers: (a) chlorinated monomers or ammonium salts or preferably alkyl phosphonates. a vinyl group at the end of the chain. These products make the treated fibers refractory, for example a grafting ratio of the fibers of the order of about 20 ° / o is sufficient to make them self-extinguishing.

(b) alkyl acrylate monomers comprising A, 5 or 6 carbon atoms, or acrylonitrile or isoprene or in particular butadiene-styrene copolymers. These compounds have a considerable tendency to associate with fats, which are first absorbed in the form of a fat-polymer solution, followed by the formation of a chemical bridging bond. The filter thus implemented in accordance with the present invention prevents trapped or rather attached fats from migrating outside the filter with the water vapor-containing air stream, unlike existing active filters; (c) acrylonitrile or mercaptans or peracids or ethyl acetoacetates, ethyl acetoamidomalonates and amine derivatives. These compounds impart reactivity to the fibers of the filter medium with respect to aldehydes or unsaturated derivatives, which allows them to chemically bind acrolein, in particular as a result of the decomposition of fats.

It is clear that according to the invention such a filter can alternatively be made by separately treating several fibrous layers with the compounds mentioned in (a) to (c) and joining the layers by weaving or flocking only after copolymerization.

Conventional filters trap fats as they settle on the filter cloth and are in no way able to filter more volatile substances such as acrolein. In addition, as previously referred to, when the fats alone precipitate, they soon pass with the water vapor-saturated air into the exhaust ducts, where they re-precipitate and thus pose a risk of fire spreading.

Instead, the filter of the present invention not only traps fats and volatiles, but also traps them effectively and permanently. With a fiber filter weighing 150-500 grams per square meter - usually 300 g / m2 - and having an air permeability of less than 4000-15,000 m3 / m2 / hour under a 20 mm thick layer of water - preferably 8000-10,000 m2 / m3 / h - can be retained per square meter: more than 100 grams of fat in bound form; more than 40 grams of heavy hydrocarbons from the combustion and decomposition of fats; and more than 90% of the acrolein formed, of which at least 50% in bound form, with an acrolein content of less than 0.05 mg / m 3 of filterable air; which is equivalent to an average of 3 steam from a family kitchen in 2-3 months.

Another embodiment describes a textile filter used to filter and purify air of undesirable substances before it is allowed into a room or workroom.

This embodiment is as suitable for removing and / or blowing air cleaned of odors, dust and organic substances within the factory as for cleaning air in workplaces, especially in the paint and varnish industry.

According to the present invention, it is possible to select graft monomers on a case-by-case basis so as to create a particularly strong tendency for the filter material to coalesce with the substances to be eliminated, for example unsaturated derivatives, aldehydes (as previously described) or odor-causing esters. compounds such as peracids, mercaptans or acrylonitrile as in Example 1. In addition, grafting amino derivatives onto at least some of the fibers of the filter medium also makes it possible to retain chemically weak acid vapors in the form of salts up to 50% by weight of the filter when the filter contains 20% grafted fibers. Grafting with sulfonated or unsulfonated derivatives of polyacrylic acids, on the other hand, allows the retention of base vapors up to 100% by weight of the fibers grafted to the filter. In addition, natural or synthetic organic fibers grafted with butadiene-styrene, usually 20%, can be added to the filter medium, allowing the filter to retain up to 200% of its own weight of grafted fibers of benzene, toluene, hexane or acetone.

A third embodiment describes a filter according to the present invention for the purification of tobacco smoke-contaminated air, which is particularly well suited for public spaces, public transport vehicles, airplanes or even meeting rooms and waiting rooms.

Current filter equipment is based on the filtration of solid particles and tar by means of a mechanical filter, to which an electrostatic precipitator is usually attached. These devices, as mentioned in the preamble of this application, do not effectively trap visible particles due to the fact that they are simply deposited on the filter cloths, so compounds such as hydrocyanic acid, carbon monoxide, tars, nicotine or acrolein are not filtered and only by the dilution effect. quite limited cleaning is achieved in the room.

According to the present invention, the material to be filtered is prepared by irradiating organic fibers in an accelerated particle flux with an output of about 30 kW with an energy of 600 KeV, with an irradiation time ranging from 0.1 seconds to a few seconds 70150 a depending on the desired percentage of free radicals. to obtain a grafting rate of the order of 20%. In this irradiation process, some of the fibers thus irradiated, which are intended to form a filter material, are then contacted with mineral salts of epoxypropylammonium or epoxypropyltrimethylammonium, in which 1,2 or up to 3 hydrogen atoms can be replaced by methyl, ethyl or propyl radicals. Unsaturated amino molecules can also be used instead of ammonium groups, as described in Example 1. Unreacted molecules are removed by washing in a solvent or solvent-water mixture with a strong base (for example, soda at ordinary concentration, i.e. 0.1-3N).

Another portion of the irradiated organic fibers is contacted with vapors or solutions that dissolve acrylic acid in conjunction with oxalic acid. Excess homopolymers are removed by washing with an organic water-solvent mixture (alcohol, benzene or hexane).

Finally, a third of the irradiated fibers are grafted in the same manner in the presence of acrylonitrile or unsaturated derivatives containing the SH group with free hydrogen, as described in the first example.

The filter material is then obtained by thoroughly mixing the three groups of grafted fibers by a commonly used means, for example by carding, before these fibers are formed into a relatively homogeneous filter material by fluffing or weaving.

With the filter material thus obtained, the following can be permanently retained: nicotine; 100% hydrocyanic acid; - more than 90% of acrolein when the air to be filtered has an acrolein content of less than 0,05 mg / m 2; and more than 50% of carbon monoxide, after filtration with a CO content of less than 10 ppm in the blown air.

9 70150 These values are valid for treating the smoke of approximately 5,000 cigarettes with a 600 gram felt filter with a uniform surface area of 1 m2. Such a filter can be used, for example, as a filter cartridge in a device which can consist of a cylinder about 30 cm in diameter and height, with openings at the top and bottom through which air can pass. The air is forced to pass through the filter, preferably with a small, low-power electric fan of about 50-100 watts.

A fourth embodiment describes a filter specifically for use in hospitals and residential communities.

It is well known that one of the major causes of the spread of epidemics is the spread of microorganisms on the ground but especially in the air. One way to avoid these risks is that when air enters these premises, it is treated with compounds such as organic salts of copper, silver or heavy metals, certain peroxides such as benzoyl peroxide, acids that adhere tightly to proteins such as polyacrylic acid, as well as hydroxypropyl. It should be mentioned in this context that only chlorine or iodine can be effective against viruses.

To prepare the filter material according to the present invention, the organic fibers are irradiated, for example, in the form of gauze, most firstly, as in the previous example, under the influence of air and moisture, which causes the formation of permanent peroxides at room temperature. Next, the irradiated pulp is separated into two parts for separate grafts:

The first part is treated with epoxypropylammonium chloride or epoxypropyltrimethylammonium iodide at a temperature above 50 ° C, without removing the homopolymer formed.

10 70150

The second part is treated with a mixture of acrylonitrile and silver acrylate or acrylic acids and silver acrylates, for example at a temperature above 50 ° C, whereby the formed homopolymer is removed with water.

These two groups grafted with different monomers are mixed thoroughly and fluffed to obtain a homogeneous filterable mass. It is self-evident that such a filter material can be obtained by superimposing, after fluffing, the pre-irradiated fibrous layers, one of which has undergone the first and the other of the latter reaction.

The filter material thus made, of course, in accordance with the internal order of the substance, mechanically cleans the air of dust, but it also has a significant healing effect in that it restricts, prevents and destroys the growth of microorganisms. As with the other filters of this invention, grafting, which attaches the monomers to the fibers forming the filter media by a true chemical bond, prevents these monomers and their various microorganism mixtures from re-migrating with the air to be purified, contrary to what might occur if the corresponding active ingredients would simply be layered on top of the mass to be filtered.

Compounds such as quaternary ammonium salts have very significant bacteriostatic effects. Their mode of action is based on the depolymerization of proteins, thus promoting the destruction of bacterial cell walls. Similarly, aldehydes react strongly with the amino groups on the bacterial cell wall. Aldehydes, phenols, quaternary ammonium salts and salts of heavy metals, in turn, have a strong effect on Pseudomonas bacilli, micro-bacteria and spores.

1 1 70150 The express purpose of the use of such a filter is not to completely sterilize the room air, whatever pathogens it contains, but to achieve effective remediation of the air before it is released into the room or blown into the outside air.

It should be mentioned in passing that the filter material thus obtained can be used for cleaning floors and thus prevent the dust absorbed by the moist material used in the cleaning from spreading microorganisms on site.

The present invention is not limited to the examples of their preferred applications described above, and may be modified and varied to those skilled in the art. Thus, in the field of mechanical dust removal in general, special attention must be paid to the filter materials of this invention, the grafted compounds of which may crosslink and thus form a stable three-dimensional filter material, especially for nonwoven fiber filters. Current methods use resins as latex or as a solution in solvents, which requires considerable energy consumption to separate the solvents and effect polymerization. Instead, in the materials of the present invention, the irradiation takes place dry, and depending on the monomer selected, the homopolymer formed generally does not need to be removed, as mentioned e.g. in the case of the fibers first treated in the last embodiment.

In addition, at a purely mechanical filtration level, it is possible to graft into the molecules molecules which reduce the interstices in the network formed by the filter material, for example by regulating the percentages of homopolymers formed which can be adjusted to 1-200% by weight of the fibers to be treated. Thus, a new dimension can be reached in dry filtration by ensuring, in addition to the chemical fixing properties already mentioned, a considerably improved mechanical filtration ability. Thus, an untreated fiber filter, 12,70150 that retains 98-99 ° / ° normalized silica dust containing 2% less than 1 micron of dust, can retain up to more than 99.95% of this dust after grafting.

Another important aspect in the field of purely mechanical filtration, made possible by the grafting of the fibers, is the anti-condensation treatment of the filter material. It is known that in order to facilitate the mechanical vibration removing particles adhering to the filter and to prevent sludge, e.g. silicones added to the filter aid. However, experience has shown that when these silicones are simply deposited on the filter cloth, the removal of particles adhering to the filter also gradually results in the disappearance of the silicone coating, which results in rapid condensation of the filter. According to the present invention, the filter medium is permanently immobilized by grafting at least the monomers of perfluorinated derivatives into the fibers forming the surface layer, for example 2,2,2-trifluoromethylmethanammonium acrylate in dimethylformamide medium or monochlorotrifluoroethylene with peroxides or halogenated methanes such as di-halogenated silanes. By grafting, this treatment lasts in use unlike in the case where the products are merely added, as mentioned earlier.

Indeed, a grafting of about 10% is sufficient to make ordinary fibers permanently water-repellent and non-sticky.

Claims (8)

A dry filter for the mechanical filtration and chemical purification of a gas stream containing removable particles, comprising a filter section consisting of at least an organic synthetic or natural fiber fibrous felt and at least a portion of the fibers of the filter section grafted with at least one organic monomer capable of chemically retaining some of the particles carried by the gas stream, characterized in that at least some of the fibers are grafted with compounds selected from the group consisting of peracids, mercaptans, ethylacetoacetates and ethylacetamidomalonates. Filter according to Claim 1, characterized in that at least some of the fibers are grafted with ammonium derivatives of your quaternary 11. Filter according to Claim 2, characterized in that at least some of the fibers are grafted with epoxypropylammonium chloride or epoxypropyltrimethylammonium iodide or derivatives thereof. Filter according to one of the preceding claims, characterized in that at least some of the fibers are grafted with monomers selected from the group consisting of acrylic acid, alkyl acrylate monomers having 4, 5 or 6 carbon atoms and acrylonitrile. Filter according to one of the preceding claims, characterized in that at least some of the fibers are grafted with amine derivatives. Filter according to one of the preceding claims, characterized in that at least some of the fibers are grafted with compounds selected from double-bonded monomers, isoprene, butadiene-styrene copolymers and polyenes. 701 50 Filter according to one of the preceding claims, characterized in that at least some of the fibers are grafted with silanes or fluorinated monomers. Filter according to one of the preceding claims, characterized in that the degree of grafting of each grafted fiber is 20% or more. PATENTKRAV 70150