Photocatalytic composition

00011 PHOTOCATALYTIC COMPOSITION.

0002The invention relates to a new photocatalytic composition, its manufacturing process and its use.

0003It also relates to a filtering medium covered with this photocatalytic composition, as well as its manufacturing process and its use.

0004In the following description and in the claims, “photocatalyst agent” means an agent capable of destroying the various organic pollutants present in the air or in water, this by photochemical reaction caused by the irradiation of ultraviolet rays (UN). This chemical reaction is widely known under the term of photocatalysis and implemented for the treatment of air or water.

0005Schematically, the photocatalytic reaction is initiated by activating a semiconductor solid by UV radiation at a wavelength below 380 nanometers, causing electronic changes within the semiconductor and leading, in the presence of air or water, the creation of oxygen radicals on the surface of the semiconductor. These radicals attack the organic compounds adsorbed on the semiconductor, and, by succession of chemical reactions involving oxygen in air or water, degrade the organic compounds until the carbon in the carbon chains is completely transformed into carbon dioxide (C0₂).

0006The photocatalytic reaction is capable of transforming by the process described above a large number of air pollutants, and in particular the ΝO_x, NH₃, H₂S, CO, 0₃, alkenes in C₂-VS₄ chlorinated or not, chloromethane, iso-octane, benzene, toluene, xylene, isopropylbenzene, aliphatic alcohols saturated in C_rVS₄, methylmercaptan, chlorophenol, nitrophenol, methyltertiobutylether, dimethoxymethane, C aldehydes_rVS₄, acetone, formic acid, acetic acid, 2-methylpropanoic acid, dichloroacetyl chloride, dimethylformamide, trimethylamine, acetonitrile, and pyridine. 2 In practice, titanium dioxide Ti0 is used as semiconductor solid, that is to say as photocatalyst agent.₂ anatase which, activated by UV light, is modified electronically so as to lead to the formation of OH hydroxyl radicals^* and oxygen O^* able to attack organic compounds adsorbed on Ti0₂ by degrading it until the organic carbon is completely transformed into carbon dioxide.

0007However, it is possible to use other photocatalyst agents such as, for example, those chosen from the group of metal oxides, alkaline earth oxides, actinide oxides and rare earth oxides.

0008For the treatment of air and liquid effluents, it is necessary to fix the photocatalytic compositions by means of binding agents on supports, in particular fibrous supports or supports of glass fibers. In the following description and in the claims, this association “support-photocatalytic composition” is designated by the term “filtering medium”.

0009It has long been proposed as a binding agent, to use organic molecules of the polyvinyl acetate, polyvinyl alcohol, etc. type.

0010It was quickly found that this implementation could not be satisfactory insofar as the carbon chains of the binder were also subjected to the photocatalysis process, therefore degraded, so that the shelf life of the composition was limited.

0011To solve this problem, various techniques have been proposed which consist in removing the carbon from the binder by calcination, in particular the technique of fixing the catalyst by "Previously Made Titanium Powder (PMTP)"

0012"Chemical Vapor Deposition (CND)", described in particular in the review "CATALYSIS TODAY", vol; 39 Νo 3page 221 and 222.

0013However, this type of technique has a certain number of drawbacks, such as that of increasing the duration and the cost of preparing the composition. In addition and above all, calcination, carried out at temperatures of the order of 1700 ° C., results in the formation of powder which makes the composition difficult to use. 3 To resolve this problem, it has been proposed in document FR-A-2 749 777 to replace the organic binder with an inorganic binder consisting of an inorganic aluminosilicate polymer of imogolite type.

0014The photocatalytic composition described in this document is in the form of an aluminosilicate gel to which a colloidal solution of photocatalyst agent is added. The preparation time of the aluminosilicate gel is of the order of several days and requires a multitude of relatively complicated steps. A thixotropic gel transparent to solar radiation is obtained, which needs to be fluidized by stirring to allow regular coating on a support.

0015More specifically, to manufacture a filtering medium, the gel obtained is applied to a support and then dried according to an unspecified technique. The various tests show that destruction of the pollutants is obtained on the order of only 12 or 26% depending on the light source used (see example 3).

0016Even if the photocatalytic composition described in this document has the advantage of being able to be coated on a support in a single layer, not only is the preparation of the composition very complicated, but it also leads to insufficient results.

0017To solve this problem, it has been proposed in documents JP-A-09/171801 and WO-A-97/00134, to coat the photocatalytic composition as such on a support, by means of an adhesive layer. . The adhesive layer consists of a resin which can include, in certain embodiments,

00185 40% by weight of colloidal silica.

0019In other words, this solution has the drawback on the one hand, of increasing the number of steps necessary for the manufacture of a filtering medium (coating of two successive layers on the support), and on the other hand , to use resins, by organic definitions, capable of being consumed during the photocatalysis process.

0020One of the problems which the invention proposes to solve is that of providing a photocatalytic composition which is simple to prepare from constituents 4 available commercially, and which can be coated directly on a support.

0021Another problem which the invention proposes to solve is to improve the adsorption capacity and the photocatalytic efficiency, that is to say the yield of the photocatalyst agent.

0022To solve the problem of providing a composition that is simple to implement and capable of being applied to a support in a single layer, the invention provides a photocatalytic composition comprising at least one photocatalyst agent and one inorganic binding agent, characterized in that the inorganic binding agent comprises an aqueous colloidal dispersion of silica dioxide (Si0₂), said aqueous colloidal dispersion of silica dioxide comprising silica particles capable of binding together after having coated the photocatalyst agent.

0023By "aqueous colloidal dispersion of silica dioxide (Si0₂) ”Denotes a dispersion of amorphous silica particles, of high specific surface area negatively charged in water. In practice, the specific surface of the silica particles is greater than 80 m²/ g, preferably 100 m²/ g for a particle size of between 25 and 30 nanometers. Similarly, it is greater than 300 m²/ g, preferably 350 m²/ g for a particle size of between 4 and 6 nanometers. The silica particles have OH groups and OH ions on their surface^" which form an electric double layer thus conferring on said particles self-adhesive properties. As already said, the silica particles are capable of binding together after having coated the particles with photocatalysts.

0024To solve the problem of improving the adsorption capacity and the photocatalytic efficiency of the composition, the binding agent consists exclusively of an aqueous colloidal dispersion of silica dioxide (Si0₂).

0025It has indeed appeared quite surprisingly that the use of an aqueous colloidal dispersion of Si0₂ of the type described above makes it possible to greatly improve the rate of adsorption of polluting substances on the photocatalyst agent as well as the yield of the photocatalysis, this being probably due to the self-bonding properties of the Si0 particles₂.

0026According to a first characteristic of the invention, the particles of Si0₂ represent from 20 to 50% by weight of the colloidal aqueous dispersion, advantageously 48% by weight.

0027For a concentration of less than 20%, the photocatalyst agent is less resistant to friction and turns into powder.

0028For a concentration greater than 50%, the photocatalyst agent loses its activity.

0029According to another characteristic of the invention, the particles of silica dioxide forming the aqueous dispersion have a diameter of between 10 and 50 nanometers, advantageously between 20 and 30 nanometers.

0030Advantageously, use is made, as photocatalyst agent, of titanium dioxide (Ti0₂) anatase alone.

0031However, the photocatalyst agent can also result from a mixture of several agents such as Ti0₂, cerium oxide etc.

0032To improve photocatalytic efficiency, particles of titanium dioxide (Ti0₂) have a diameter between 10 and 30 nanometers.

0033Likewise, to obtain optimum adsorption efficiency, the photocatalytic composition comprises from 10 to 60 parts (dry) of the aqueous colloidal dispersion of silica dioxide, the complement to 100 parts consisting of Ti0₂ anatase.

0034Advantageously, the photocatalytic composition comprises 50 parts of the aqueous colloidal dispersion of silica dioxide and 50 parts of titanium dioxide anatase. According to another embodiment of the invention, in order to prevent the development of harmful microorganisms and molds contained in the ambient air, the photocatalytic composition also comprises zeolites modified with metal ions.

0035By "zeolite" is meant a group of hydrated natural aluminosilicates of alkali or alkaline earth metals.

0036In practice, the metal ions are chosen from the group comprising silver, copper and zinc and are used in an amount of 1 to 3%. Advantageously, the zeolite is modified with 1.5% of silver ions.

0037It has indeed been found that this type of composition makes it possible to accelerate the destruction of microorganisms and molds contained in the ambient air while destroying the organic pollutants at the origin of certain odors, by combining the properties of the modified zeolites. that of photocatalysis described above.

0038According to an advantageous embodiment of the invention, the photocatalytic composition consists of (by weight):

0039• 30 to 50% o, advantageously 47% of Si0

0040• 30 to 50%, advantageously 47% of Ti0₂ anatase

0041• 2 to 10% o advantageously 6%> of zeolite with 2% silver

0042According to another embodiment of the invention, in order to adsorb the organic molecules present in the pollution peaks, the photocatalytic composition also comprises active carbon.

0043In known manner, the activated carbon is in the form of fibers or grains having a high specific surface and thus making it possible to adsorb the organic molecules.

0044In this way, the photocatalytic composition, including activated carbon, will act on the ambient air in two stages: υ first, adsorption of the pollutants present in the peaks of pollution on the activated carbon; 7 υ then, photocatalysis degrading the pollutant contained in the activated carbon, thus allowing the regeneration of said activated carbon.

0045In other words, the life of this composition will be greatly increased compared to the life of the activated carbon alone.

0046According to an advantageous form of this embodiment, the photocatalytic composition consists of (by weight): υ 10 to 40%>, advantageously 25%> of Ti0₂ anatase, υ 10 to 40%>, advantageously 25% of activated carbon, υ 40 to 60%, advantageously 50% of Si0₂.

0047The invention also relates to the process for manufacturing the photocatalytic composition according to which, with stirring, the photocatalyst agent and, where appropriate, the zeolites modified with metal ions and / or activated carbon are introduced into the colloidal aqueous suspension of silica up to '' to obtain a homogeneous suspension which can be applied directly to a support.

0048The invention therefore also relates to the use of the photocatalytic composition in the form of paint.

0049The invention also relates to a filter medium. As already said, by “filtering medium”, we mean the association support - photocatalytic composition. In known manner, a filtering medium can be composed of one or more treated supports.

0050Thus, the photocatalytic composition of the invention can be deposited on at least one of the faces of a support. It has indeed been found that, thanks to their self-shining properties, the particles of Si0₂ not only bonded together while coating the Ti0 particles₂, but also linked to support. In addition and above all, a strong increase in the yield of photocatalysis is observed, this being probably due to the particular structure of the Si0 particles.₂, which allows to maintain a high porosity and a high specific surface of the layer after drying. Unlike the deposition of a composition which is transparent to the UN rays described in the document FR-A-2 749 777, the deposition carried out with the composition of the invention is opaque to the UN rays while retaining optimum efficiency, a property which can be applied. used in application areas such as posters, banners, wallpaper.

0051In addition, several types of support can be used, such as glass fibers, non-woven support, without limitation.

0052In another embodiment, the support is in the form of an acoustic panel.

0053The term “acoustic panel” denotes in particular the tiles constituting the double ceilings.

0054In practice, the slab is coated with the photocatalytic composition.

0055Natural convection produces a movement of cold air from the bottom of the room which, while heating up, rises to the top of the room, thus coming into contact with the constituent tiles of the ceilings which, under the action of incandescent light or of the day, trigger a photocatalytic reaction leading to the destruction of gases.

0056The support can also be an organic fibrous support of paper type.

0057It has indeed been found that the use of an aqueous colloidal dispersion of Si0₂ used to coat the organic fibers of the support, so that said support is not subjected to the photocatalysis reaction and therefore deteriorated over time.

0058The use of the colloidal dispersion of Si0₂ on this type of support therefore makes it possible to increase the life of the filtering medium.

0059According to an advantageous embodiment of the invention, only one side of the support for the filtering medium is coated with the photocatalytic composition of the invention, the other side being coated with a second composition capable of destroying odors comprising a derivative of undecylenic acid. Advantageously, the undecylenic acid derivative is sodium or methyl or ethyl undecylenate, and this in a nonlimiting manner.

0060In order to destroy the mite type insects, said second composition also comprises dioctyl sulfosuccinate.

0061It has indeed been found that this type of composition makes it possible to combine and potentiate several different actions, namely: ^• that of the undecylenic acid derivative which ensures the destruction of odors, in particular of the amines, sulfur derivatives type, etc.

0062^• that of dioctyl sulfosuccinate which acts by destroying the keratin of mites.

0063In practice, said second composition contains (by dry weight):

0064• from 80 to 98% o, advantageously 96%> of sodium undecylenate,. from 2 to 20% o, advantageously 4% of dioctylsulfosuccinate

0065In a variant, in addition to a support coated with the photocatalytic composition, the filtering medium comprises a prefilter in the form of a support coated with a composition capable of destroying odors and insects of the mite type comprising a derivative of undecylenic acid and of dioctyl sulfosuccinate.

0066The invention also relates to the method of manufacturing a filter medium comprising a support on which the photocatalytic composition of the invention is coated at a rate of 5 to 40 g / m², advantageously 20g / m² from Ti0₂.

0067For a value less than 5 g / m², the photocatalysis reaction is reduced taking into account the too small thickness of the layer of the photocatalytic composition on the support.

0068For a value greater than 40 g / m², there is no increase in the rendering "mmeenntt n phhnottnorc.aattaallvyttiirqmue. In the embodiment according to which the filtering medium has a support face or a prefilter coated with a composition based on undecylenic acid and on sulfosuccinate, this coating is carried out at a rate of 2 g / m².

0069In addition, the method of manufacturing the filter medium of the invention has the advantage of being able to be carried out continuously, the coating being able to be carried out in particular by size press, or any other impregnation or traditional coating method, this which makes the process very simple compared to the prior art.

0070In the case of drapery papers or acoustic panels, the composition of the invention can be in the form of a paint to be applied directly to the support.

0071These filter media can therefore be used for the treatment and purification of air, but also for the treatment of liquid effluents.

0072The invention and the advantages which result therefrom will emerge more clearly from the following exemplary embodiments in support of FIG. 1 appended, which represents the reaction yield of the photocatalytic composition, object of the invention.

0073Example 1

0074The following experiment shows the improvement of the adsorption capacity and the photocatalytic yield of the photocatalytic composition of the invention by comparison with a filtering medium of the prior art.

0075The test consists of immersing a support disc coated with a photocatalytic composition in a solution of isopropyl alcohol, then subjecting the disc to the action of ultraviolet rays of wavelength less than 380 nanometers, for 90 minutes. Under the effect of UN rays, part of the isopropyl alcohol is transformed into acetone and thus reveals the photocatalytic efficiency of titanium dioxide.

0076The disc consists of a fibrous support coated with a photocatalytic composition consisting of: • 50 parts of binders

0077• 50 parts of Ti0₂. 11

0078Examples 1, 2, 3, 4 are made with various types of Ti0₂ coated on the disc with an area equal to 18 cm²'' at a rate of 4.5 to 17 g / m². The inorganic binder used is a colloidal dispersion of Si0₂ marketed by NISSAN under the brand "SNOWTEX 50".

0079Example 5 uses a filtering medium marketed by MATRIX in which the binding of Ti0₂ with the support is produced by calcination of the binding agent. The analyzes are carried out by gas chromatography.

0080The results are shown in the following table:

TABLE 1

0082Example 1 Example 2 Example 3 Example 4 Example 5

0083Ti0₂ DT51 'Ti0₂ REF2² Ti0₂ REF2 Ti0₂ P-25³ Filter media

008416 g / m² 17 g / m² 4.5 g / m² 12.5 g / m² Prior art⁴ 2.88 g / m²

0085Amount of acetone 46 69 50 71 26.5 <img file="WO9951345A1_D0001.tif" /> formed / μmol

00861 : DT 51^® : Ti0₂ marketed by RHODIA

00872 : REF2: Ti0₂ of specific surface equal to 75 m²/ g

00883 : marketed by DEGUSSA

00894 : marketed by MATRIX

0090It is noted that the last disc generates the formation of a very small amount of acetone compared to the photocatalytic composition of the invention. We also note that a deposit of Ti0₂ between 4.5 g / m² and 12.5 g / m² (Examples 3 and 4), allows good photocatalytic efficiency to be obtained. 12

0091Example 2

0092The reaction yield was calculated for various compositions according to the invention coated on a support of the nonwoven type (reference 1045) manufactured by

0093AHLSTROM LYSTIL and perforated by the PERFOJET process so as to improve through flow rates (low pressure drop). The pollutant used is isobutane.

0094The composition contains two types of Ti0₂ different of specific surface respectively equal to 250 m²/ g (designated REF 1) and 75 m²/ g (REF 2).

0095The following table shows all the essential parameters, namely the proportions of each of the constituents, the irradiated surface, the irradiation time and the average reaction yield, and the deposit 10 or 20 g / m² from Ti0₂ (REF 1 or REF 2).

TABLE 2

0097Binder^e/ Tic ”;, Irradiation time Reaction yield partly dry Surface cm² h% average

1A 64.5 6

REF 1 20/80 65.8 6 54.30

010010 g / m² 65,8 6

1B 67.4 6

REF 2 20/80 67.5 6 75.38

010310 g / m² 65,7 6

1C 65.2 6

REF 2 20/80 65.4 6 75.50

010620 g / m² 65,7 6

2A 64, S 6

REF 1 50/50 64.8 6 44.58

010910 g / m² 68,2 6

2A '67.8

REF 1 50/50 67.8 5 36.40

011210 g / m² 67,8 5

01132Ë 66.2 6

REF 2 50/50 65.1 6 88.52

011510 g / m² 65,1 6 <img file="WO9951345A1_D0002.tif" /> 13

01162B ^! 67,8

REF 2 50/50 67.8 5 64.75

011810 g / m² 67,8 5

2C 66.2 6

REF 2 50/50 66.2 6 81.53

012120 g / m² 66,4 6

01225 67.2 b

REF 2 50/50 67.2 6 84.03

012410 g / m² 67,2 6

4B 66.9 6

REF 2 50/50 64.8 6 2.95

012710 g / m² 66.9 6 without C4H10 <img file="WO9951345A1_D0003.tif" />

0128* Snowtex 50 marketed by NISSAN.

0129It is found that the best reaction yields are obtained with compositions of the invention containing 50 parts of the colloidal aqueous dispersion (Si0₂) of silica and 50 parts of titanium dioxide REF 2.

0130We also note that deposits of 10g / m² from Ti0₂ generate reaction yields higher than 20 g / m deposits², all other conditions being identical, which leads to reducing the cost of filter media.

0131When the test is carried out without the organic pollutant isobutane, the photocatalytic yield is practically zero, which is logical. It can be estimated that the low value obtained in this case (2.95%>) corresponds to the decomposition of parasitic organic matter. The figures in the table are therefore significant to within 3%.

0132In the appended FIG. 1, the reaction yield obtained for the photocatalytic compositions coated at the rate of 10 g / m2 of Ti0 is shown.₂ , or examples 1 A, 1B, 2A, 2A \ 2B, 2B ', 3B and 4B. 14 Example 3

0133In this example, the efficacy of the photocatalytic composition of the invention including activated carbon was evaluated.

0134To do this, a photocatalytic composition is coated on a non-woven type support (reference 1045) manufactured by AHLSTROM LYSTIL, and perforated by the PERFOJET process.

0135The photocatalytic composition consists of: υ 25%> of Ti0₂ with a specific surface equal to 250 m2 / g υ 25%> of activated carbon with a specific surface equal to 900 m2 / g and marketed by CECA υ 50% by weight of Si0₂ (Snowtex 50).

0136The media is irradiated with methanol at a rate of 3.4 ml / min, the pollutant content being equal to 281 ppm, with or without saturation phase in the dark.

0137The results obtained at equilibrium under UN are identical whether the media has been saturated or not.

0138We obtain: υ an amount of methanol equal to 22.3 micromoles per hour and per gram; υ an amount of carbon dioxide (C0₂) equal to 8.65 micromoles per hour per gram.

0139The percentage of mineralization, i.e. transformation of the polluting agent into C0₂ is 30%>.

0140The carbon balance, resulting from the degradation of methanol into a volatile by-product, is equal to 56%.

0141The advantages of the invention appear clearly from the description. It will be noted in particular, the strong capacity of adsorption and the remarkable efficiency of Ti0₂ when mixed with a colloidal aqueous dispersion of silica. 15

0142Note also the simplification of the manufacturing process of the filtering medium by using in particular continuous impregnation or coating techniques, in particular by Size-press.