WO2010102592A1

WO2010102592A1 - A layered filtration material and device for purification of gaseous medium

Info

Publication number: WO2010102592A1
Application number: PCT/CZ2010/000026
Authority: WO
Inventors: Jiri Duchoslav; Lukas Rubacek
Original assignee: Elmarco S.R.O.
Priority date: 2009-03-10
Filing date: 2010-03-03
Publication date: 2010-09-16
Also published as: CZ2009152A3

Abstract

A layered filtration material containing a photocatalyzer from a group of metal oxides or semimetal oxides, especially TΪO₂, ZnO, ZrO₂ or SiO₂, in a form of inorganic nanofibres and/or nanoparticles, while the photocatalyzer is arranged between two inert filtration layers (1, 3), which are inert towards action of the photocatalyzer and action of UV radiation, and at least one of them is permeable for UV radiation, while from outer sides of both inert filtration layers (1, 3) there are arranged polymeric nanofibrous layers (4, 5). The invention also relates to a device for purification of gaseous medium, especially air, comprising the above mentioned layered filtration material.

Description

A layered filtration material and device for purification of gaseous medium

Technical field The invention relates to a layered filtration material containing a photocatalyzer from the group of metal oxides or semimetal oxides, especially TiC>₂, ZnO, ZrO₂ or Siθ2, in a form of inorganic nanofibres and/or nanoparticles.

The invention also relates to a device for purification of gaseous medium, especially of air, comprising the, above mentioned layered filtration material.

Background art

The known property of metal oxides and semimetal oxides, e.g. of TiO₂, ZnO, ZrO₂ or SiO₂ is their catalytic activity under the action of UV radiation, which causes oxidation and degradation of organic substances on their surface or in its vicinity. These oxides may be prepared in a form' of nanoparticles or nanofibres with high specific surface, ;while the specific surface is important parameter for the speed and efficiency of catalytic process, as with increasing specific surface also the speed and efficiency of catalytic process increases.

This is especially utilised in case of TiO₂ in crystallic modification of anatase in combination with UV radiation, for example in self-cleaning coatings, layers or textiles, which use for photo-catalysis the UV component of solar radiation.

When utilising the photocatalytic properties of metal oxides or semimetal oxides, especially of TiO₂ in a systems for purification of air, for example in air- conditioning devices, there is problem with incorporation of particles into the filtering medium, while silicate or other adhesives or binders are used, through which an active surface of oxide is expressively reduced and due to this the efficiency of catalytic process is slowed down and reduced. US 2007/0151921. Ai - discloses a self-cleaning filtration membrane comprising a plate or a mat containing fibres and photocatalytic nanoparticles in vicinity or on surface of the fibres, while the fibres may contain microfibres and/or nanofibres and the nanoparticles may comprise the nanoparticles of TiO₂. The description of the application Talso mentions layers of nanofibres produced from colloid solutions of inorganic materials such as TiO₂, ZrO₂ or SiO₂, while these nanofibres may be mixed with glass or inorganic microfibres to increase their mechanical strength. This document further describes a cleaning device with self- cleaning nanofibrous membrane fastened in a body of the device in vicinity of inlet of contaminated air or liquid, which are delivered through the device by means of a fan or a pump, while they pass through the nanofibrous membrane, in which the contaminants are adsorbed on the surface of nanofibres. Behind the nanofibrous membrane there is arranged . a source of UV radiation, which continually or in interrupted manner radiates the nanofibrous membrane in ordef to decompose the contaminants adsorbed on the, surface of nanofibres.

If the described self-cleaning filtration membrane contains polymeric microfibres and/or nanofibres,; on whose surface or inside the fibres in vicinity of their surface are photocatalytid nanoparticles, during the photo-catalysis and during irradiation by UV radiation, the^decomposition of polymer and overall destruction of such membrane occurs. At the same time there is a great danger of releasing the photocatalytic nanoparticles into the medium being purified.

The self-cleaning filtration membranes formed of nanofibres from inorganic materials such as TiO₂, ZrO₂ or SiO₂ are very fragile and therefore are not capable of permanent operation at industrial utilisation, and there occurs breaking of nanofibres during installation, maintenance and also due to vibrations during operation and subsequently flying off or flushing off of these fragments into the medium being purified. The fragility of the described inorganic nanofibres and their breaking is not eliminated even when they are mixed with inorganic or glass microfibres, which are of similar properties, and moreover they may be breaking during manipulation with the membrane or operation of the purification device. Moreover, the increasing quantity of microfibres deteriorates catalysing abilities of membrane.

US 2007/02844303 A1 discloses a nanofibrous structure or a membrane containing nanofibres of polymer insoluble in water, while the polymer fibres are enwrapped by TiO₂, ZnO, SnO₂. The nanofibrous structure or membrane is designed for filtration and it cannot be utilised at exposure to UV radiation even for photocatalysis, because in this case degradation of polymeric nanofibres and destruction of the whole nanofibrous structure or membrane occurs.

WO 2008/034190 describes a ceramic filter for purification of water, which contains ceramic nanofibres applied onto a ceramic porous substrate, while the filter may be used also as a photocatalytic one. The disadvantage of this solution are great pressure gradients, respectively very small flow rates of fluids through the filter due to small porosity of ceramic carrying substrate. The described flow rate is

800 l/m² per hour, which is flow rate suitable for water, but insufficient for filtration of air, where the flow rates higher by two to three orders are required. Further disadvantage for filtration of air is a necessity to have a planar arrangement of the filter.

Published patent application KR 1020080086066 A describes a photocatalytic filter using the nanofibres of metal oxide produced through electrostatic spinning and calcination process, production method of the photocatalytic filter and an air cleaner using the photocatalytic filter. The nanofibres of metal oxide are formed of ZnO nanofibres or TiO₂ nanofibres. The production method of photocatalytic .filter consists of following steps: creation of a first substrate in which a plurality of holes is performed; creation of nanofibres of metal oxide on the first substrate through electrostatic spinning; calcination of nanofibres of metal oxide created on the 'first substrate; and covering of calcinated nanofibres of metal oxide by a second substrate, in which a plurality of holes is performed. Simultaneously the step of creation of nanofibres from metal oxide on the first substrate by means of electrostatic spinning consists of: electrostatic spinning of first nanofibres of metal oxide arranged in lateral or longitudinal direction on the first substrate; and electrostatic spinning of second nanofibres of metal oxide on the first nanofibres of metal oxide so that the second nanofibres of metal oxide are arranged in perpendicular direction to the direction of arrangement of the first nanofibres of metal oxide. The disadvantage of this solution is complexity of production process and a very thin layer of nanofibres of metal oxide, which becomes after calcination even thinner. Maximum thickness of layer of nanofibres of metal oxide before calcination is 3 micrometers. It is not possible to create a thicker layer. During calcination there occurs contraction of nanofibres and considerable loss of adhesion towards the carrying substrate, which may lead to complete fall-off of the calcinated layer from the substrate. During calcination and the related contraction of fibrous layer the layer cracks and macroscopic flaws having dimensions of tenths of millimetres up to millimetres are created, what reduces homogeneity of the layer and its filtration characteristics.

During calcination of nanofibres of metal oxide applied on the first substrate the holes in the first substrate may be partially clogged, by which the permeability of the filter to the air is worsened. Besides this, due to fragility of nanofibres of metal oxide, at application -of the filter during air purification, fragments of nanofibres of metal oxide will be released and they will be carried away through holes in the first or in the second substrate in the direction of the air flow. The goal of the invention is to reduce or to totally remove shortcomings of the background art and to, create a layered filtration material containing photocatalyzer suitable for photocatalytic purification of gases, especially of air.

Principle of the invention The goal of the invention has been achieved by a layered filtration material containing a photocatalyzer according to the invention, whose principle consists in that the photocatalyzer is arranged between two inert filtration layers, which are inert towards action of the photocatalyzer and action of UV radiation, and at least one of them is permeable for UV radiation, while from outer sides of both inert filtration layers there are arranged polymeric nanofibrous layers. By arranging the photocatalyzer between two inert filtration layers a direct contact of nanoparticles and/or nanofibres of the photocatalyzer with the layer of polymeric nanofibres is prevented, and consequently also their degradation during photocatalysis. Polymeric nanofibrous layers serve only to prevent flying away of nanoparticles and/or nanofibres, possibly of parts of nanofibres of photocatalyzer outside the space of the layered filtration material delimited by polymeric nanofibrous layers.

To protect the polymeric nanofibrous layers, these layers are from the outer side provided by abrasion-resistant layers, while at least that abrasion-resistant layer, which is arranged on ^"the side of inert filtration layer permeable for UV radiation, is also permeable for UV radiation.

At the same time it is advantageous, if the inert filtration layer permeable for UV radiation is formed of textile formation made of glass fibres.

In case that one of the inert filtration layers is impermeable for UV radiation, it is formed of filtration paper for the purpose to reduce the costs for the layered filtration material.

The principle of the device for purification of gaseous medium, especially of air, containing the above mentioned layered filtration material consists in that, at least one side of the layered filtration material is subjected to action of UV radiation, while all layers' irradiated by UV radiation in front of the photocatalyzer are formed of materials permeable for UV radiation.

Further features of the ^device according to the invention are defined in dependent claims.

Description of the drawing

Exemplary embodiment of the layered filtration material according to the invention is schematically ^"represented on the drawings, where the Fig. 1 represents distribution of layers of filtration material, the Fig. 2 a view of non-woven textile of glass fibres when magnified 600 times, the-Fig. 3 a view of polymeric nanofibrous layer with 600 times magnification, the Fig. 4 a view of nanoparticles of photocatalyzer with 600 times magnification and the Fig. 5 a view of inorganic nanofibrous layer of photocatalyzer with 600 times magnification.

Examples of embodiment

The layered filtration material according to the example of embodiment represented in the Fig. 1 contains first inert filtration layer ±, formed e.g. of a filtration paper or textile formation of glass fibres or other material being resistant towards action of photocatalyzer and action of UV radiation, on which there is applied a layer 2 of photocatalyzer from the group of metals or semimetals especially TΪO2, ZnO, Zr₁O₂ ,or SiO₂, in a form of inorganic nanofibres and/or nanoparticles and/or particles, which is covered by second inert filtration layer 3, which is permeable to UV radiation and is formed for example of a textile formation of glass fibres. On outer side of the first inert filtration layer 1 there is applied first polymeric nanofibrous layer 4, which is from its outer side protected by first abrasion resistant layer 6. On outer side of the second filtration layer 3 there is applied second polymeric nanofibrous layer 5 permeable for UV radiation, which is from its outer side protected by second abrasion-resistant layer 7, which is permeable for UV radiation. The first and the second polymeric layers 4, 6 prevent flying away of nanoparticles of photocatalyzer from the layer 2 of photocatalyzer both during manipulation with layered filtration material and operation, and they may be made of any suitable polymer, for example of polyacrylonitrile (PAN) or of PA6. During production of the layered filtration material with photocatalyzer in the form of nanoparticles the nanoparticles are applied on the first inert filtration layer ± in a dry or wet state. Thickness of the layer 2 of photocatalyzer is chosen taking into account technological conditions, in which the filter with layered filtration material will be operated, especially the size of nanoparticles of photocatalyzer and their specific surface, flow rate.^'.^' of gas being purified, guantity of impurities, which should be removed from the gas being purified and possibilities of penetration of UV radiation through entire thickness of the layer 2 of photocatalyzer. The basis weight of the layer 2 of photocatalyzer varies usually from 20 g/m² to 60 g/m². After applying the layer 2 of photocatalyzer is overlaid by the second inert filtration layer 3 and consequently both inert filtration layers are from their outer side overlaid by polymeric nanofibrous Iayersi4, 5, which are from their outer side protected by abrasion-resistant layers 6, 7/ At the same time it is advantageous if the polymeric nanofibrous layers 4, 5 are applied on respective abrasion-resistant layers 6, 7 in device for production of nanofibres through electrostatic spinning, e.g. according to WO2005/024101, CZ ' patent 299527, WO2008/028428, eventually WO2009/010020 or through any known method.

During production 'of-iiyered filtration material with photocatalyzer in the form of nanofibres, the layer^;2^:όf photocatalyzer is formed of a layer of inorganic nanofibres formed of selected photocatalyzer from the group of metals or semimetals, especially Tidif-^'ZnO, Zrθ2 or SiC<2. At the same time it is advantageous, if these ' inorganic nanofibrous layers are produced through electrostatic spinning according to CZ PV 2008-277. In cases, when the first inert filtration layer Λ_ and/or the second inert filtration layer 3 is made of material which is resistant to calcination temperatures at production of inorganic nanofibres, e.g. of textile formation from glass^5lfibres, the layer 2 of photocatalyzer may be created through electrostatic spinning on this substrate and during assembly of the layered filtration material this two-layered textile may be used, on which the nanofibrous layer 2 of photocatalyzer is already to be found, as the first inert filtration layer ± or as the second inert filtratiόn^yer 3. If there is need to increase thickness of the layer 2 of photocatalyzer, two two-layered textiles with nanofibrous layer 2 of photocatalyzer may be ? us"ed^r: and assembled with nanofibrous layers 2 of photocatalyzer against each_fpther. In this position the textile layers of glass fibres are outside and they create tfoe first inert filtration layer Λ_ and the second inert filtration layer 3. In the particular-example for the first as well as for the second inert filtration layer 1, 3 non-woven textiles of glass fibres delivered to the market by the company Crane Nonwovens under the designation Craneglas or by the company Hexcel under the designation Hexcel were used. The same textiles were also used for the abrasion-resistant layers 6, 7. The layer of inorganic nanofibres formed of the selected photocatalyzer from the group of metals or semimetals, especially TiC^, ZnO, ZrO∑ or SiC>2, may be produced through electrostatic spinning also as separate layer In case, that such nanofibrous layer of photocatalyzer does not show sufficient consistency and strength, it is advantageous to break it into nanofibres and to apply them on the first or the second inert filtration layer 1 or 3 likewise above described nanoparticles of photocatalyzer.

For selection of material of inert filtration layers it is important to know, from

— r which side of the layered filtration material the UV radiation will be radiating, as the inert filtration layer on the side reversed from the source of UV radiation may be made of material impermeable or less permeable to UV radiation, e.g. of filtration paper or viscose, while the inert filtration layer from the side of radiating of UV radiation must be sufficiently permeable for UV radiation. Nevertheless in some cases it is advantageous, if UV radiation is radiating from both sides of the layered filtration material. In this case for both inert filtration layers it is necessary to use material sufficiently permeable for UV radiation. If such embodiment is used with one source of radiation, the installation of such layered filtration material into filtration device is simplified, as both inert filtration layers are equivalent and it therefore does not matter with which side it is positioned to the source of UV radiation. Similarly also the polymeric nanofibrous layers 4, 5 may be different, out of which the layer which is in the direction of passage of the purified air the front one may have lower basis weight, which usually lies within an interval of 0,05 to 0,8 g/m², while the rear polymeric nanofibrous layer usually has higher basis weight, which usually lies within an interval of 0,8 to 1 g/m². This prevents flying away of nanoparticles, especially if the layer 2 of photocatalyzer is created of nanoparticles. For the purpose of reinforcement a reinforcement grid may be inserted between the layers of layered filtration material.

The device for purification of gaseous medium, especially air of organic pollutants and other organic substances and/or microorganisms comprises the layered filtration material, which contains the photocatalyzer from group of metal oxides or semimetal oxides,' especially TΪO₂, ZnO, ZrO₂ or SiO₂ in the form of inorganic nanofibres and/or nanoparticles, and the source of UV radiation. The photocatalyzer is arranged in the layer 2 of photocatalyzer between two inert filtration layers 1, 3, which are inert towards action of photocatalyzer and action of UV radiation, and at least one of them is permeable for UV radiation, while from outer side of inert filtration layers 1, 3 there are arranged polymeric nanofibrous layers 4, 5 and the source of UV radiation is arranged in direction of passage of the purified gaseous medium before and/or behind the layered filtration material, while the source of UV radiation is directed towards the layered filtration material, whose irradiated side is made of, materials permeable for UV radiation up to the photocatalyzer. At the same . time the source of UV radiation may also be the daylight.

Industrial applicability The layered filtration material according to the invention is able to remove microorganisms, organic pollutants and other organic substances present in the air or from other suitable gas being purified, both in trace amount or industrial amount very well, and therefore is applicable in photocatalytic devices for purification of air or other gases, for example in the air-conditioning devices. From the purified gas, by means of photo-catalysis, it is possible to eliminate essentially any organic substance from the group of hydrocarbons, alcohols, aldehydes, ketones, organic acids, etc. The result of photocatalysis is CO₂ and H₂O.

Claims

1. A layered filtration material containing a photocatalyzer from a group of metal oxides or semimetal oxides, especially Tiθ₂, ZnO, Zrθ₂ or Siθ₂, in a form of inorganic nanofibres and/or nanoparticles, characterised in that, the photocatalyzer is arranged between two inert filtration layers (1, 3), which are inert towards action of the photocatalyzer and action of UV radiation and at least one of them is permeable for UV radiation, while from outer sides of both inert filtration layers (1 , 3) there are arranged polymeric nanofibrous layers (4, 5).

2. The layered filtration material according to the claim 1, characterised in that, from the outer side of the polymer nanofibrous layers (4, 5) there are arranged abrasion-resistant layers (6, 7), while at least that abrasion-resistant layer (6, 7), which is arranged on the side of inert filtration layer (1, 3) permeable for UV radiation is itself permeable for UV radiation. 3. The layered filtration material according to the claim 1 or 2, characterised in that, the inert filtration layer (1 ,

3) permeable for UV radiation is formed of a textile formation made of glass fibres.

4. The layered filtration .material according to any from the previous claims, characterised in that, one from the inert filtration layers (1, 3) is impermeable for UV radiation, and at the same time it is formed of filtration paper.

5. The layered filtration material according to any from the claims 2 to 4, characterised in that, the. abrasion-resistant layer (6, 7) permeable for UV radiation is formed of a textile formation of glass fibres.

6. A device for purification of gaseous medium, especially air, comprising the layered filtration material according to any of the previous claims characterised in that, at least one side of the layered filtration material is subjected to action of UV radiation, while all layers irradiated by UV radiation before the photocatalyzer are formed of materials permeable for UV radiation.

7. The device according to the claim 6, characterised in that, the UV radiation is formed of respective portion of the daylight spectrum in surrounding of the device.

8. The device according to the claim 6 or 7, characterised in that, the UV radiation is created by a source of UV radiation positioned in direction of passage of the purified gaseous medium in front of and/or behind the layered filtration material.