Photocatalytic composition

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 1 COMPOSITION PHOTOCATALYTI UE.

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

It also relates to a filter medium coated with this photocatalytic composition, as well as its manufacturing process and its use.

In the remainder of the description and in the claims, the term “photocatalyst agent” denotes an agent capable of destroying the various organic pollutants present in the air or in water, by photochemical reaction caused by the irradiation of ultra-rays. -purple (UV).

This chemical reaction is widely known under the term of photocatalysis and used for the treatment of air or water.

Schematically, the photocatalytic reaction is initiated by activating a solid semiconductor by UV radiation at a wavelength less than 380 nanometers, causing electronic changes within the semiconductor and leading, in the presence of air or water, to 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 the air or water, degrade the organic compounds until the carbon of the carbon chains is completely transformed into carbon dioxide (C02).

The photocatalytic reaction is capable of transforming, by the process described above, a large number of air pollutants, and in particular NO ,,, NH3, H2S, CO, 03, C2-C4 alkenes, chlorinated or not, the chloromethane, isooctane, benzene, toluene, xylene, isopropylbenzene, saturated aliphatic alcohols in Cl-C4, methylmercaptan, chlorophenol, nitrophenol, methyltertiobutylether, dimethoxymethane, aldehydes in C1-C4, acetone, formic acid, acetic acid, 2-methylpropanoic acid, dichloroacetyl chloride, dimethylformamide, trimethylamine, acetonitrile, and pyridine.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 2 In practice, as a solid semiconductor, that is to say as a photocatalyst, titanium dioxide Ti02 anatase is used which, activated by UV light, is electronically modified so as to lead to the formation of hydroxyl radicals OH 'and oxygen O' capable of attacking the organic compounds adsorbed on the Ti02 by degrading it until the organic carbon is completely transformed into carbon dioxide .

However, 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.

For 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 remainder of the description and in the claims, this association support-photocatalytic composition is designated by the term filtering medium.

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

It 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 and therefore degraded, so that the life of the composition was limited.

To solve this problem, various techniques have been proposed consisting in removing the carbon from the binder by calcination, in particular the technique of fixing the catalyst by Previously Made Titanium Powder (PMTP) or even Chemical Vapor Deposition (CVD), described in particular in the review CATALYSIS TODAY, flight; 39 No 3 pages 221 and 222.

However, 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, the calcination, carried out at temperatures of the order of 1700 ° C., results in the formation of powder which makes the composition difficult to use.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 3 To solve 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 polymer aluminosilicate of imogolite type.

The 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.

This gives a thixotropic gel transparent to solar radiation, requiring to be fluidized by stirring to allow regular coating on a support.

More precisely, to manufacture a filter medium, the gel obtained is applied to a support and then dried according to an unspecified technique.

The various tests show that a destruction of the pollutants of the order of only 12 or 26% is obtained depending on the light source used (see example 3).

Even 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 the preparation of the composition is very complicated but it also leads to insufficient results.

To 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 is made of a resin which may include, in some embodiments, from 5 to 40% by weight of colloidal silica.

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

One of the problems which the invention proposes to solve is that of providing a photocatalytic composition which is simple to prepare from constituents CA 02324909 2000-09-27 WO 99/51345 PCTIFR99 / 00748 4 which are commercially available, and capable of being coated directly on a support.

Another 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.

To solve the problem of providing a composition that is simple to use 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 an inorganic binding agent, characterized in that the inorganic binding agent comprises an aqueous colloidal dispersion of silica dioxide (SiO2), said aqueous colloidal dispersion of silica dioxide comprising silica particles capable of bonding together after having coated the photocatalyst agent.

The term “aqueous colloidal dispersion of silica dioxide (SiO 2)” denotes a dispersion of amorphous silica particles with a high specific surface area negatively charged in water.

In practice, the specific surface of the silica particles is greater than 80 m 2 / g, advantageously 100 m 2 / g for a particle size of between 25 and 30 nanometers.

Likewise, it is greater than 300 m2 / g, advantageously 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 electrical double layer, thus conferring self-adhesive properties on said particles.

As already stated, the silica particles are capable of bonding together after having coated the particles with photocatalyst agents.

To 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 (SiOZ).

It has indeed appeared quite surprisingly that the use of an aqueous colloidal dispersion of SiO 2 of the type described above makes it possible to greatly improve the rate of adsorption of polluting substances on the agent CA 02324909. 2000-09-27 WO 99/51345 PCT / FR99 / 00748 photocatalyst as well as the yield of the photocatalysis, this being probably due to the self-bonding properties of the SiO2 particles.

According to a first characteristic of the invention, the SiO 2 particles represent from 20 to 50% by weight of the colloidal aqueous dispersion, advantageously 48% by weight.

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

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

According 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.

Advantageously, titanium dioxide (TiO 2) anatase alone is used as the photocatalyst agent.

However, the photocatalyst agent can also result from a mixture of several agents such as TiO 2, cerium oxide etc ...

To improve photocatalytic efficiency, the titanium dioxide (TiO2) particles have a diameter between 10 and 30 nanometers.

Likewise, to obtain optimum adsorption efficiency, the photocatalytic composition comprises 10 to 60 parts (on a dry basis) of the aqueous colloidal dispersion of silica dioxide, the balance to 100 parts consisting of TiO 2 anatase.

Advantageously, the photocatalytic composition comprises 50 parts of the aqueous colloidal dispersion of silica dioxide and 50 parts of anatase titanium dioxide.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 6 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 further comprises zeolites modified with metal ions.

The term “zeolite” denotes a group of hydrated natural aluminosilicates of alkali or alkaline earth metals.

In 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% silver ions.

It has in fact been observed 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 modified zeolites those of the photocatalysis described above.

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

= 30 to 50%, advantageously 47% of SiO2 = 30 to 50%, advantageously 47% of TiO2 anatase = 2 to 10%, advantageously 6% of zeolite with 2% silver According to another embodiment of the invention, in order to adsorb the organic molecules present in the pollution peaks, the photocatalytic composition further comprises activated carbon.

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

In this way, the photocatalytic composition, including activated carbon, will act on the ambient air in two stages:

u first of all, adsorption of the pollutants present in the pollution peaks on the activated carbon;

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 7 u then, photocatalysis degrading the pollutant contained in the activated carbon, thus allowing the regeneration of said activated carbon.

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

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

u 10 to 40%, preferably 25% TiO2 anatase, u 10 to 40%, preferably 25% activated carbon, u 40 to 60%, preferably 50% SiO2.

The 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 silica suspension until 'to obtain a homogeneous suspension which can be applied directly to a support.

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

The invention also relates to a filter medium.

As already stated, the term “filtering medium” denotes the association of support - photocatalytic composition.

In a known manner, a filter medium can be composed of one or more treated supports.

Thus, the photocatalytic composition of the invention can be deposited on at least one of the faces of a support.

It has in fact been observed that, thanks to their self-bonding properties, the SiO2 particles not only bind together while coating the TiO2 particles, but also bind to the support.

In addition and above all, a strong increase in the yield of the photocatalysis is observed, this being probably due to the particular structure of the SiO 2 particles, which makes it possible to maintain a high porosity and a high specific surface area of ​​the layer after drying.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 8 Unlike the deposit of a composition transparent to UV rays described in document FR-A-2 749 777, the deposit made with the composition of the invention is opaque to UV rays while retaining optimum efficiency, a property which can be implemented in fields of application such as posters, banners, wall hangings.

Moreover, one can have recourse to several types of supports such as glass fibers, nonwoven support, and this, in a nonlimiting manner.

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

The term “acoustic panel” denotes in particular the constituent tiles of the double ceilings.

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

Natural convection produces a movement of cold air from the bottom of the room which, while heating, rises to the top of the room to thus come 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 the gases.

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

It has in fact been observed that the use of an aqueous colloidal dispersion of SiO 2 makes it possible to coat the organic fibers of the support, so that said support is not subjected to the photocatalysis reaction and therefore deteriorated over time.

The use of the colloidal dispersion of SiO 2 on this type of support therefore makes it possible to increase the life of the filter medium.

According to an advantageous embodiment of the invention, only one face of the support of the filter medium is coated with the photocatalytic composition of the invention, the other face being coated with a second composition capable of destroying odors comprising a derivative of undecylenic acid.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 9 Advantageously, the undecylenic acid derivative is sodium or methyl or ethyl undecylenate, and this in a nonlimiting manner.

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

It has in fact been observed that this type of composition makes it possible to combine and potentiate several different actions, namely:

= that of the derivative of undecylenic acid which ensures the destruction of odors, in particular of the amine type, sulfur derivatives, etc.

= that of dioctyl sulfosuccinate which acts by destroying the keratin of mites.

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

= from 80 to 98%, advantageously 96% of sodium undecylenate, = from 2 to 20%, advantageously 4% of dioctylsulfosuccinate In a variant, in addition to a support coated with the photocatalytic composition, the filter medium comprises a pre-filter in the form of a support coated with a composition capable of destroying odors and mite-type insects comprising a derivative of undecylenic acid and dioctyl sulfosuccinate.

The invention also relates to the process for 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 20 g / mZ of TiO 2.

For a value of less than 5 g / m2, the photocatalysis reaction is reduced given the insufficient thickness of the layer of the photocatalytic composition on the support.

For a value greater than 40 g / m2, no increase in the photocatalytic yield is observed.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 In the embodiment according to which the filter medium has a support face or a pre-filter coated with a composition based on undecylenic acid and on sulfosuccinate, this coating is carried out at a rate of 2 g / m 2.

In 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 method of impregnation or traditional coating, which makes the process very simple compared to the prior art.

In the case of wall hanging papers or else acoustic panels, the composition of the invention may be in the form of a paint to be applied directly to the support.

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

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

Example 1 The following experiment shows the improvement in the adsorption capacity and the photocatalytic yield of the photocatalytic composition of the invention by comparison with a filter medium of the prior art.

The test consists in 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 UV rays, part of the isopropyl alcohol is transformed into acetone and thus reveals the photocatalytic efficiency of titanium dioxide.

The disc consists of a fibrous support coated with a photocatalytic composition consisting of:

= 50 parts of binders = 50 parts of TiO2.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 11 Examples 1, 2, 3, 4 are carried out with various types of Ti02 coated on the disc with a surface area equal to 18 cm2, at a rate of 4.5 at 17 g / mZ.

The inorganic binder used is a colloidal dispersion of SiO 2 sold by NISSAN under the brand SNOWTEX 50.

Example 5 uses a filter medium marketed by MATRIX in which the binding of TiO 2 with the support is carried out by calcining the binding agent.

The analyzes are carried out by gas chromatography.

The results are shown in the following table:

TABLE1 Example 1 Example 2 Example 3 Example 4 Example 5 TiO2 DT51 'TiOZ REF22 TiO2 REF2 TiO2 P-253 Filter media 16 g / mZ 17 g / mZ 4.5 g / m2 12.5 g / m2 Prior art 4 2.88 g / m2 Quantity of acetone 46 69 50 71 26.5 formed / mol 1: DT 510: Ti02 sold by RHODIA 2: REF2: Ti02 with a specific surface area equal to 75 m2 / g 3: sold by DEGUSSA 4: marketed by MATRIX It is observed that the last disc causes the formation of a very small quantity of acetone compared to the photocatalytic composition of the invention.

It is also noted that a deposit of TiO 2 of between 4.5 g / m 2 and 12.5 g / m 2 (examples 3 and 4) makes it possible to obtain good photocatalytic efficiency.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 12 Example 2 The reaction yield of various compositions according to the invention coated on a support of the nonwoven type (reference 1045) manufactured by AHLSTROM LYSTIL and perforated was calculated. by the PERFOJET process so as to improve the through flow rates (low pressure drop).

The pollutant used is isobutane.

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

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

TABLE 2 Binder * / Ti02 Duration of irradiation Reaction yield in part in sec Surface cm2 h% average 64.5 REF 1 20/80 65.8 6 54.30 10 g / m2 65.8 6 67.4 REF 2 20 / 80 67.5 6 75.38 10 g / mZ 65.7 6 65.2 REF 2 20/80 65.4 6 75.50 20 g / m2 65.7 6 64.5 REF 1 50/50 64, 8 6 44.58 10 g / m, 68.2 6 67.8 REF 1 50/50 67.8 5 36.40 10 g / m2 67.8 5 REF2 50/50 65.1 6 88.52 10 g / m2 65.1 6 CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 13, REF 2 50/50 67.8 5 64.75 g / mZ 67.8 5 66.2 REF2 50/50 66.2 6 81.53 g / m2 66.4 6 67.2 REF 2 50/50 67, 2 6 84.03 10 g / mZ 67.2 6 66.9 6 REF2 50/50 64.8 6 2.95 10 g / m2 66.9 6 without C4H10 * Snowtex 50 sold by NISSAN.

It is observed that the best reaction yields are obtained with compositions of the invention containing 50 parts of the colloidal aqueous dispersion (SiO2) of silica and 50 parts of titanium dioxide REF 2.

It is also noted that deposits of 10 g / m2 of TiO 2 generate reaction yields greater than deposits of 20 g / m2, all other conditions being identical, which leads to a reduction in the cost of the filter media.

When the test is carried out without the organic pollutant isobutane, the photocatalytic efficiency 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 material.

The figures in the table are therefore significant to within 3%.

The appended FIG. 1 shows the reaction yield obtained for the photocatalytic compositions coated at a rate of 10 g / m2 of TiO2, ie Examples 1A, 1B, 2A, 2A ', 2B, 2B', 3B and 4B.

CA 02324909 2000-09-27 WO 99/51345 PCT / FR99 / 00748 14 Example 3 The effectiveness of the photocatalytic composition of the invention including activated carbon was evaluated in this example.

To 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.

The photocatalytic composition consists of:

u 25% of Ti02 with a specific surface area equal to 250 m2 / gv 25% of activated carbon with a specific surface area equal to 900 m2 / g and marketed by CECA u 50% by weight of Si02 (Snowtex 50).

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

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

We obtain :

u an amount of methanol equal to 22.3 micromoles per hour and per gram;

u an amount of carbon dioxide (CO2) equal to 8.65 micromoles per hour and per gram.

The percentage of mineralization, that is to say of transformation of the polluting agent into C02 is 30%.

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

The advantages of the invention emerge clearly from the description.

Note in particular the high adsorption capacity and the remarkable efficiency of TiO 2 when it is mixed with a colloidal aqueous dispersion of silica.

CA 02324909 2000-09-27 WO 99/51345 PCTIFR99 / 00748 Note also the simplification of the manufacturing process of the filter medium by making use in particular of impregnation or continuous coating techniques, in particular by Size-press.