NO813829L - TEXTILE FILTER FOR FILTERING OF A GAS CURRENT, INCLUDING ORGANIC FIBERS INSERTED WITH ACTIVE MONOMERS - 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

Textile filter for filtering a gas stream, comprising organic fibers grafted with active monomers.

The present invention relates to the filtration and purification of gas, and more particularly to filters which have chemical and physical retention capabilities.

When it comes to gas filtration, filters with a mechanical effect are very common, and the quality of the filters is mainly determined by ! the dimensions of the pores in the wall and the substrate to be filtered. The performance of the filters can be improved by using known techniques from wet filters with the disadvantages of conditioning and limited durability.

In order to achieve not only mechanical but also chemical retention of unwanted particles in a gas stream, it is proposed to use composite filters with retained active substances, which, in the same way as in dry filters, present major problems in retaining the active product, which usually can only be solved by optimizing the retention wall, many times at the expense of significant losses of charge and often with cancellation of the item.

Among these active products, it is also known that a number of monomers for various reasons have chemical affinity and retention properties for certain classes of harmful particles, which can be of interest in the filtration technique, but many times with the disadvantages mentioned above when it applies to the retention and retention of these active materials.

It is known from another area that fibres, and more particularly textile fibres, can be grafted with certain organic monomers to give them new properties, particularly when it comes to color affinity and the allocation of hydrophilic and flame retardant properties.

The purpose of the present invention is to propose a new class of dry filters with fibrous filtration substrate

i which have improved retention and fixation properties and i 'which can be easily modified, without presenting noticeable risks

during operation, while at the same time they have a greatly extended operating time.

Another object of the present invention is to propose filters with a simple design, low manufacturing costs which optimally and with great versatility combine improved mechanical retention properties and chemical retention properties for filtering and treating gas streams.

In order to achieve this according to the characteristic of the present invention, such a dry filter for filtering a gas stream which carries with it organic particles to be removed comprises a substrate of organic, natural or synthetic fibres, which is characterized by at least part of the fibers in the substrate is grafted with at least one organic monomer which can retain physically or chemically at least some of the said particles that are entrained in the said gas flow.

According to the invention, the grafting on the fibers of a filter substrate enables reactive monomers that have an affinity for certain classes of solid particles or liquids carried in

a gas stream, thus in a simple and particularly effective way to transfer its special advantages to the grafted agents and certainly to make the agents reactive, and to the mechanical filtering properties of the fiber carpet or layer that is grafted in this way by enabling a better distribution of the the chemical substances in the interior of the filtration substrate without the usual risks of entrainment not only of the retained particles, but also of the active substance and/or the particles fixed on the latter, while at the same time obtaining an optimized mechanical filtration system at the expense of a controllable, very low loss of charge.

Other properties and advantages of the present invention will be apparent from the following description of various embodiments, which shall illustrate the invention.

Various grafting techniques have been developed in recent years, particularly with the aim of modifying the physical properties of the elements to be grafted, especially textile fabrics, and these grafting techniques can be classified into three large groups: - Ionic grafting in a moist environment, by using initiators that e.g. cerium, permanganate or ferric ions in a mineral acid environment. In the particular case, the fibres, especially of cellulose or its derivatives, are impregnated with acidic solutions of initiators, they are then treated with monomers selected with specific conditions for each product, in vapor phase or azeotropically for acrylic derivatives, or in solvent phase. Grafting of quaternary ammonium salts, on the other hand, takes place without an initiator in the presence of a solution of a strong base, as particularly described in French patent 1,585,665. In all cases, the tissue is washed, rinsed after the reaction and then dried. For grafting in the solvent phase, the appearance of körbo cations on the products is promoted, comprising a double bond, ' especially in the presence of AlCl^ or ZnC^. The carbo-cations attach to the substances in suspension in the solvent, for example silicon dioxide, carbon black or aluminum oxides. - Grafting using UV irradiation. This irradiation has weak energy, and it is necessary to use photo-initiators for the reaction, which can be carbonyl groups, benzophenone or diacetyl vapor. This method has the advantage that it makes it possible to modify fibers that are known to be inert, such as e.g. polypropylene or polyester. - Inoculation using accelerated particles with high energy or gamma rays produced e.g. of a radioactive source such as cobalt 60. Under the influence of particles with high energy, free radicals are formed in the interior of the organic fibers by absorption of hydrogen atoms and these unstable radicals promote the initiation of grafting of the selected monomers. Thus, if F-CH-F symbolically represents the fibers and M the monomer to be grafted, it is achieved ; at the end of the reaction a grafted fiber F-C-F. The reaction is carried out either by irradiating the fibers alone in the presence or absence of water, or by irradiating the fibers which have been impregnated with the monomers.

Grafting by means of high-energy particles is preferably used in the production of the filters according to the invention, as can be seen below, because by a method with radicals it is possible to graft two or more different monomers onto the same fiber, whatever its nature, and each grafted homopolymer retains its various special properties from the reactive agent. In this way, it is possible to extend the field of application of the filter, to apply several different properties to one and the same fiber. Furthermore, the industrial application of such a radical reaction has advantages due to a low energy consumption compared to other methods, the reaction is carried out at ambient temperature, and therefore no heat input is required. The reaction can be carried out in countercurrent, on raw fibres, but also on woven or knitted fibres; for a dry weave, the preliminary operations such as wetting and wicking can thus be omitted.

In a first embodiment, a filter according to the invention is described which is intended for the retention of odors and grease in household exhaust fumes.

The production of fibers to obtain a textile carrier which forms at least part of the filtering substrate is carried out by the action of a stream of accelerated particles. As previously mentioned, this operation can take place on a fiber cloth or on a product that has been knitted in advance. The irradiation is momentary, and only acts as a force for acceleration' of the particles. A power that is usually used for this type of irradiation is between 20 and 50 kw, which enables an irradiation of 500 KeV to over 1 MeV, with a power of 600 KeV usually being sufficient. Increasing the radiation dose, and thereby increasing the number of reactive positions, can be achieved by passing the fiber material several times under the energy current, e.g. using a passing system called

"in port order".

The outgoing filtering substrate consisting of a loose composition of organic, natural or synthetic fibers, in peroxidized form or not, is brought into contact with the following families of monomers for successive grafting: a) Chlorinated monomers or ammonium salts, or preferably alkyl phosphonates which at the end of the chain especially has a vinyl group. These products transfer flame resistance to the fibers treated with them, and a degree of grafting for the fibers of the order of 20% is, for example, sufficient to make them self-extinguishing. b) Monomers of alkyl acrylates having 4.5 or 6 carbon atoms, or acrylonitrile, or isoprene, or especially butadiene-styrene copolymers. These compounds have a marked affinity for fat, the absorption of which takes place by the formation of a fat polymer solution in a first step, and then in a second step a chemical bridge building is carried out. -According to the invention, the substrate element which is produced in such a way prevents the retained, more precisely fixed fat from being carried away outside the filter by the air flow which is charged with water vapour, unlike in the existing active filters. c) Acrylonitrile, mercaptans, peracids, ethylacetoacetates, ethylacetamidomalonates, amine derivatives. These compounds give the fibers in the filtering substrate reactivity towards aldehydes or unsaturated derivatives, which in particular enable the chemical fixation of acrolein and thereby carrying out a splitting of fat.

It should be understood that such a filter according to the invention can also be obtained in the form of a variant by treating several fiber cloths separately with the compounds a) to c) and not connecting them again, weaving them or knitting them until after the copolymerization.

Ordinary filters retain the fat when deposited on the filtering substrate and cannot in any case retain more volatile substances, such as e.g. acrolein. Furthermore, as previously mentioned, when it comes to simple deposition, the grease is very quickly carried back by air which is saturated with water vapor to the drain pipes where it deposits again and thus poses a danger for the propagation of fire.

In contrast, the filters, according to the invention, not only retain grease and volatile products, but fix them in an efficient and permanent manner. A fiber substrate with a weight per m 2 of between 150 and 500 grams, typically 300 g/m 2 , and with a permeability to air of less than 20 mm of water, which is between 4000 and 15000 m 3 /m 2 /hour, preferably 8000

3 2 2

to 10,000 m /m /hour, holding back, per m : more than 100 g of fat in bound form;

more than 40 g of heavy hydrocarbons from the burning and splitting of fats; and over 90% of the acrolein that is formed, of which at least 50% is in bound form at a content of acrolein in the air to be filtered of less than 0.05 mg/m 3; which corresponds to the average number of exhaust gases released in a household kitchen over the course of 2 to 3 months in a family of 3 people.

In another embodiment, a textile carrier is described which is used for filtering and removing unwanted elements from air before it is introduced into a room or a workshop.

This embodiment is also equally used for the intake and/or introduction into a closed factory hall of air that is free of odors, dust and organic products, as a purification of the air at workplaces, especially in the paint and varnish industry.

According to the invention, it is possible to choose grafting monomers judiciously in relation to the particular products to be removed, e.g. unsaturated derivatives, aldehydes (as previously mentioned) or esters responsible for the smell, by grafting at least . a part of the filtering substrate fibers with compounds such as e.g. peracids, mercaptans or acrylonitrile, as in example 1. Incidentally, grafting on at least part of the filtering substrate fibers is made possible by amine derivatives, moreover, the weakly acidic vapors are chemically retained in the form of salts up to 50% by weight of the filter for a degree of grafting on 20% of the grafted fibers in the filtering substrate. Grafting with sulphonated derivatives or acrylic polyacids makes it possible to retain basic vapors up to 100% by weight of grafted fibers in the filter. It can i.a. organic, natural or synthetic fibers grafted with buradiene-styrene are introduced into the filtering substrate, typically with a degree of grafting of 20%, which makes it possible to retain in the filter up to 200% of its own weight of grafted fibers of benzene, toluene , hexane or acetone.

In a third embodiment, a filter according to the invention is described to make air polluted by tobacco cleaner, which is particularly suitable for public spaces, public means of transport, airplanes or also conference halls and waiting rooms.

The filtration devices in question are based on the principle that retention of solid particles and tar occurs with the help of

a mechanical filter which is usually connected to an electric filter. These devices, as mentioned in the introduction to the present application, do not allow an effective retention of visible particles due to the fact that they are simply deposited on the filtering substrate, in such a way that compounds such as hydrocyanic acid, carbon monoxide, tar, nicotine and also acrolein is not retained, only the dilution effect,

of the pollutants in the room makes it possible to achieve a very limited cleaning.

According to the invention, a filtering substrate is produced by

to irradiate organic fibers under a stream of accelerated particles, with a strength of approximately 30 kw, in such a way that the particles receive an energy of 600 KeV, with an irradiation time

which varies between 0.1 and a few seconds, depending on the desired percentage of free radicals, an irradiation time of one second being sufficient to achieve a desired degree of grafting of the order of 20%. During this irradiation process, part of the fibers that have been irradiated are then determined to constitute the filtering substrate, and are brought into contact with the epoxypropylammonium or epoxypropyltrimethylammonium mineral salts whereby 1, 2 or 3 hydrogen atoms can be replaced with methyl, ethyl - or propyl radicals. Unsaturated amine molecules can also be used instead of ammonium groups, as described in example 1. The molecules that have not reacted are removed by washing with solvent or with a mixture of water solvent in the presence of a strong base (e.g. soda in a concentration of 0.1 to 3 n).

Another part of the irradiated organic fibers is brought into contact with vapors or solvent solutions of acrylic acid in the presence of oxalic acid. Excess homopolymer formed is removed by washing with a mixture of water-organic solvent (alcohol, benzene or hexane).

A third part of the irradiated fibers is finally grafted in the same way in the presence of acrylonitrile or unsaturated compounds bearing an SH group with labile hydrogen, as described in the first example.

The filtering substrate is then obtained by mixing the three categories of grafted fibers well using commonly used means, - e.g. by carding, before knitting or weaving of the fibers which. must form a filtering substrate that is homogeneous.

The filtering substrate obtained in this way makes it possible to permanently retain:

nicotine,

100% hydrocyanic acid,

more than 90% acrolein, if the content of acrolein is below 0.05 mg/m 3 in the air to be filtered; and

over 50% carbon monoxide, the air to be returned after filtration has a CO content of less than 10 ppm.

These values are valid for the treatment of smoke from approximately 5000 cigarettes for a filtering substrate in a filter of

600 grams with a unit surface of 1 u 2. Such a filtering substrate can, for example, be used as a filtering cartridge in a device which can consist of a cylindrical part with a diameter of approx. 30 cm and a height of approx. 30 cm, as the cylinder is equipped at its lower and upper parts with openings that promote air passage. Forced air passage through the substrate preferably takes place with the help of a small electric ventilator with a weak power of the order of 50 - 100 watts.

In a fourth embodiment, a filtering substrate is described which is more specifically intended for use in hospitals and in common rooms.

It is well known that one of the causes of the spread of epidemics is the transmission of disease germs with the soil, especially with the air. One way to reduce the existing risks at the stage where the air is taken into the room is to treat it using compounds such as e.g. organic salts of copper, silver or heavy metals, certain peroxides such as benzoyl peroxide, acids with strong adhesion to protein materials such as e.g. acrylic polyacid, such as e.g. the salts of hydroxypropylammonium. It should be noted here that viruses cannot be effectively affected without the help of chlorine or iodine.

For the production of the filtering substrate according to the invention, the organic fibers are first irradiated, e.g. in the form of a cloth, as in the previous example, in the presence of air and moisture, which promotes the formation of peroxides, which are stable at ambient temperature.

The irradiated fiber mass is then separated into two parts to achieve distinct grafting: A first part is treated with epoxypropylammonium chloride or epoxypropyltrimethylammonium iodide at a temperature above 50°C and the homopolymer formed was not extracted.

The second part is treated with a mixture of acrylonitrile

and silver acrylate or acrylic acid and silver acrylate at a temperature e.g. above 50°C, and the homopolymer formed is extracted with water.

The two grafted parts with different monomers were well mixed and knitted to form a homogeneous filtering mass.

It goes without saying that such a filtering substrate can be obtained by placing sheets of the previously irradiated fibers next to each other after knitting and subjecting one to the first reaction and the other to the second reaction.

The filtering substrate obtained in this way clearly performs, according to the internal arrangement of this substrate, the mechanical removal of dust from the air, but also provides a marked sanitary effect in that it limits the spread of disease germs, inhibits them and destroys them. As with the other filters according to the invention, the inoculation attaches the monomers to the fibers that make up the filtering substrate with a real chemical bond that prevents the monomers and their mixtures with different germs from being reintroduced with the air to be cleaned, in contrast to the risk of that they could pass the filter if the similar active agents were simply deposited on a filtering mass.

Connections such as quaternary ammonium salts have very significant bacteriostatic effects, and their mode of action is based on the depolymerisation of the proteins, which cooperates in the destruction of the walls of the bacterial cells. At the same time, the aldehydes react strongly with the amine groups in the cell wall of the bacteria. Pseudomonas, the microbacteria and the spores are strongly affected by the aldehydes, the phenols, the quaternary ammonium salts and the salts of the heavy metals.

The use of such a filter not only has the purpose of sterilizing the surrounding air completely, regardless of which germs of disease are present, but aims to carry out an effective purification of this air before it is introduced into the premises or before it is returned to the atmosphere.

It is noted that the filtering substrate obtained in this way can be used with advantage when cleaning soil, as it is thus avoided that the presence of dust absorbed by moist cleaning compounds promotes the propagation of disease germs in situ.

The present invention is not limited to the examples described above in their preferred applications and can be subjected to modifications and variants which are self-evident to the person skilled in the art. When it comes to the area of dust removal in general, special attention should be paid to the filtering media of the present invention, whose grafted compounds can be net-formed and thus constitute a stable three-dimensional filtering material, especially for filtering substrates manufactured as non-woven. The methods in question have an appeal to latex resins or resins in solution in a solvent, which require a large expenditure of energy to evacuate solvents and carry out the polymerization. In the substrates according to the invention, on the other hand, the grafting is carried out by dry irradiation and, depending on the selected monomer, there is usually no removal of the homopolymer that is formed, as mentioned particularly in relation to the first part of the treated fibers in the embodiment else form as described last above.

Incidentally, at the level of purely mechanical filtration, it is possible to graft molecules onto the fibers which allow to reduce the spaces that occur in the network formed by the filtering substrate, e.g. by dosing the percentage content of the homopolymers formed, as this amount can be adjusted from 1 - 200 percent by weight in relation to the fibers to be treated. A new dimension can thus be obtained when it comes to dry filtration which, in addition to the properties of chemical fixation; which has already been mentioned provides properties for purely mechanical filtration that are greatly improved. Thus, an untreated, fibrous filter that retains from 98 to 99% of dust below 1 micron after seeding can retain up to over 99.95% of this dust.

Another important aspect consists in, in the case of purely mechanical filtration, made possible by grafting the fibers, an anti-sealing treatment of the filtering substrate. It is known that in order to facilitate the mechanical tapping in order to free a filtering substrate from the particles that are stuck and thus avoid tilting, silicones can be used in particular for application to the filtering substrate. Experience has shown many times that, by simply depositing these silicones on the filtering substrate material, removal of particles that stick to the filter along its length will also lead to a removal of the silicone coating, which leads to a very rapid clogging of the filter. According to the invention, the filtering substrate can be made permanently anti-adherent by grafting at least the fibers that make up the surface layer of the filtering substrate with monomeric perfluorine derivatives, e.g. ammonium-2,2,2-trifluoromethylmethacrylate in an environment of dimethylformamide or monochlorotrifluoroethylene in the presence of peroxides or halogenated silanes such as e.g. dimethyldichlorosilane. Depending on the method of fixation during grafting, this treatment resists wear and tear, which is not the case with the products that are simply deposited as previously mentioned. A grafting of the order of 10% is also sufficient to make ordinary fibers permanently hydrophobic and anti-adherent.

Claims (11)

1. Dry filter for mechanical filtration and chemical purification of a gas stream that carries with it particles to be removed, comprising a fibrous filtration substrate consisting of at least one fibrous tissue, comprising natural or synthetic organic fibers, characterized in that at least one part of said fibers in said filtration substrate is grafted with at least one organic monomer which can physically and chemically retain at least some of said particles that are entrained in said gas flow. 2. Filter according to claim 1, characterized in that said substrate consists of grafted fibers which are knitted or woven. 3. Filter according to claim 1 or 2, characterized in that said fibers are grafted by irradiation with high-energy particles. 4. Filter according to one of claims 1-3, characterized in that at least part of said fibers are grafted with compounds selected from the group consisting of peroxides, such as e.g. peracids, mercaptans, ethylacetoacetates and ethylacetamidomalonates. 5. Filter according to one of claims 1-4, characterized in that at least a part of said .fibres are grafted with quaternary ammonium salts. 6. Filter according to claim 5, characterized in that at least part of said fibers are grafted with ammonium epoxypropyl chloride or trimethylammonium epoxypropyl iodide and derivatives thereof. 7. Filter according to one of the preceding claims, characterized in that at least part of said fibers are grafted with monomers selected from the group consisting of acrylic acid, alkyl acrylate monomers with 4, 5 or 6 carbon atoms and acrylonitrile. 8. Filter according to one of the preceding claims, characterized in that at least part of said fibers are grafted with amine derivatives. 9. Filter according to one of the preceding claims, characterized in that at least part of said fibers are grafted with compounds selected from monomers with double bonds, isoprene, butadiene-styrene copolymers and polydlene. 10. Filter according to one of the preceding claims, characterized in that at least part of said fibers are grafted with silanes or fluorinated monomers. 11. Filter according to one of the preceding claims, characterized in that for each grafted fiber <p> the impregnation degree is greater than or equal to 20%.