FR3105742A1 - Powdered athermal catalyst - Google Patents

Abstract

Powdery athermal catalyst comprising, in percentage by mass relative to its total mass: Between 27% and 30% of photo-activated titanium dioxide TiO2 Between 11% and 17% of manganese oxide MnO, Between 55% and 59% of zeolite type A hydrophilic synthetic.

Description

Powdered athermal catalyst

The present invention falls within the field of decontamination. It relates more particularly to the decontamination and pollution control of a gaseous medium, in particular indoor air.

Several studies show that indoor air has two main families of pollutants that we seek to eliminate: "chemical pollutants" and biological pollutants ".

The first family of pollutants consists of pollutants known as “chemical pollutants” which are organic or inorganic in nature and among which we find in particular “volatile organic compounds” known as VOCs.

The term “volatile organic compound” known as VOC is understood to mean any compound containing at least the element carbon and one or more of the following elements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon or nitrogen, with the exception of carbon oxides and inorganic carbonates and bicarbonates. VOCs are also characterized by having a vapor pressure of 0.01 KPa or more, at a temperature of 293.15 K, or by a corresponding volatility under particular conditions of use. VOCs therefore represent a very large family of compounds. These evaporate easily when passing from a liquid to gaseous state, or they sublimate easily when passing from a solid to gaseous state.

For example, chemical pollutants include formaldehyde, carbon monoxide, nitrogen oxides such as nitrogen monoxide NO, radioactive gases such as radon.

The second family of "biological pollutants" consists of microorganisms or tiny organisms. These include bacteria, viruses, phages, fungi in the state of spores or in the state of biological mold, but also mites.

In order to remove, or at least reduce, pollutants in the air, several air treatment systems can be used. For example, air conditioning units fitted with pollutant filters can be used as an indoor air treatment system.

However, various studies have shown that under normal conditions of use with regulated airflow speed, temperature and humidity, microorganisms could disadvantageously survive on the pollutant filter.

By way of example, tests have shown that so-called “fragile” microorganisms, such as Staphylococcus. epidermidis , Escherichia. coli and revundimonasB. diminuta , can survive between 2 and 6 days on a pollutant filter, while so-called "resistant" microorganisms, such as Bacillus. atrophaeus , MS-2 coliphage, Aspergillus. brasiliensis , survive beyond 6 days. Additional tests have also shown that Bacillus. atrophaeus can withstand the pollutant filter, without any loss of viability, for 210 days.

However, disadvantageously, the proliferation of microorganisms on the pollutant filter causes a modification of its filtering properties. This is because the pollutant filter loses its efficiency in treating air pollutants, its filtration capacity decreases sharply in the event of contamination by microorganisms. Microbial contamination of the pollutant filter also generates a risk of creating additional pollutants, not initially present in the air. Indeed, the growth of microorganisms on the pollutant filter generates chemical reactions with the initial pollutants in the air, these reactions then lead to the formation of additional pollutants which are dangerous for the environment and the health of living beings. . As a result, standard filtration can generate indoor air biocontamination which is harmful to users of indoor air conditioning units.

In addition, it has been found that in air conditioning units fitted with pollutant filters, a loose filter mounting is conducive to redistribution of indoor air pollutants or additional pollutants into the environment.

In this case, the pollutant filter serves only as a passageway or as a route for transforming the initial pollutants into other pollutants, without fulfilling its role of cleaning up indoor air.

Thus, the phenomenon of growth of microorganisms, the tightness of the assembly of the filter, as well as the maintenance of the integrity of the filters over time, are all factors to be taken into account in indoor air conditioning units. that we want to be efficient in treating and cleaning up indoor air.

In this sense, there are several known technical solutions to overcome the problem of pollutant filters in use in air conditioning units. These include the use of cold plasma, ionization, ozonation or photocatalysis. The disadvantage of using cold plasma in an air handling unit is that it consumes a lot of energy. This is because the voltage required to ignite the electrodes in a cold plasma destruction method is so high that it could damage a vehicle battery. In general, it is necessary to have a high voltage, greater than 1000 volts AC or greater than 1500 volts DC, to ignite the electrodes in a cold plasma destruction method.

In addition to excessive energy consumption, cold plasma treatment transforms nitrogen oxides NO _x from the atmosphere into ozone O _{3 .} However, ozone O3 is recognized as a harmful pollutant, conducive to allergies.

In addition, in humid conditions, the treatment of air with cold plasma disadvantageously forms hydrogen peroxide H ₂ O ₂ which is a disinfectant substance not recommended because it is dangerous for human health.

It should also be noted that the cold plasma treatment is limited to an air speed which arrives on the electrodes of the order of 0.5 meters / second. This speed limit does not allow rapid processing of a large volume of air contained in a large room.

In addition, except for dust removal, cold plasma treatment forms ions whose reactivity and pollution control efficiency with respect to air pollutants has not been scientifically proven. However, in the context of air pollution control, it is essential to eliminate both chemical and biological pollutants, and not just dust.

As a result, an alternative solution to the cold plasma air pollution control method which is energy efficient, does not create new harmful pollutants, which quickly treats a large volume of air by eliminating at the same time chemical pollutants and biological pollutants.

Another known method of treating air is ionization. Ionization is the creation of a high electronegative voltage that sends electrons into the atmosphere. When in contact with oxygen atoms in the air, these electrons make negative ions. These negative ions will, by electrostatic attraction, attach themselves to the polluting particles in the air, which they are positively charged or neutral, so as to precipitate polluting particles on the ground. The air will thus be purified.

However, ionization does not remove pollutants from the air, but only precipitates them to the ground. Polluting particles are therefore not destroyed but only extracted from the air and then accumulated on the ground.

In addition, ionization also generates a risk of ozone O3 production which is harmful to human health.

In addition, ionization has a low pollutant removal efficiency. For example, on average, an atmospheric ionizer removes, in 1 to 2 hours, only between 80 and 90% of dust and polluting particles from the air. The ability to quickly remove a high proportion of air pollutants over a short period of time remains to be improved.

Disadvantageously, ionization is limited to the removal of chemical pollutants, biological pollutants not being removed from the air by the ionization technique.

Accordingly, an alternative solution should be found to the ionization air pollution control method which does not generate new harmful pollutants, which rapidly treats a large volume of air by removing both chemical pollutants and pollutants. biological.

To overcome the limitation of ionization to chemical pollutants, it is known to use the technique of ozonation. Ozonation removes both chemical pollutants and biological pollutants such as microorganisms from indoor air. The principle of ozonation consists in producing, by electric discharges in tubular generators, ozone. In general, an ozonator has two conductive electrodes between which the polluted air to be treated passes. When passing between these two electrodes, the dioxygen in the air to be treated is transformed into ozone O3. The O3 partly oxidizes the pollutants in the air to be treated.

However, ozonation treatment has the disadvantage of replacing air pollutants with other types of indoor pollutants, including creating ozone O3. Indeed, O3 is classified among the indoor pollutants responsible for several pathologies, including headaches.

Disadvantageously, ozonation does not control the fate of species of microorganisms or particles that react with ozone. However, in the field of pollution control and indoor air treatment, it is customary to identify the pollutants present, both those to be destroyed and those that will potentially be created, in order to qualify the decontamination capabilities of an indoor air conditioning unit.

Likewise, the use in air handling units of the principle of photocatalysis is not entirely satisfactory.

In the field of air pollution control, photocatalysis consists of the formation of oxidation and reduction reactions on the surface of a semiconductor material exposed to a light source, in particular of the UV type.

The principle of photocatalysis is based on the activation of a semiconductor material by the emission of light. This material will then generate, on the surface, reactive electrons which will be at the origin of the oxidation-reduction reactions. These oxidation-reduction reactions generate, from the O ₂ contained in the air to be treated, super-oxidizing entities. These super-oxidizing entities will be capable of degrading VOCs, in particular into CO ₂ and H ₂ O, or will be capable of degrading the cell membranes of certain microorganisms, in particular of the bacteria or virus type. It is known, in air handling units, based on photocatalysis, to use titanium oxide as a semiconductor material which is subjected to UV radiation in order to activate it. For example, TiO _{2 is used} subjected to a radius of wavelength less than 365 nm.

However, one of the problems with photocatalysis treatment is the energy consumption.

Indeed, the photocatalysis technology alone consumes energy, in particular by the obligation to put in place a light source of the UV lamp type.

However, on average, UV lamps only have an efficiency of use of the energy produced between 30% and 40% to activate the semiconductor material, the rest being lost in the form of dispersed heat. This heat can reach up to 90 ° C on the surface of the lamps. In other words, only 30% to 40% of the energy produced by UV lamps is used to activate the semiconductor material, the rest of the energy being produced at a loss.

Consequently, the use of photocatalysis is a suboptimal solution in terms of efficiency of use of the energy produced as well as of the energy present within the air handling unit.

Indeed, all of the light energy emitted is not used to activate the surface of the semiconductor material, more than half of this light energy is lost in the form of heat, that is to say that it is unprofitable. This is one of the reasons photocatalysis technology is expensive in the energy it takes to operate.

Accordingly, an alternative solution should be found to improve the efficiency of converting light energy into energy activating the semiconductor material in the case of an air handling unit using the principle of photocatalysis.

Thus, all of the known techniques have several drawbacks, in particular the drawbacks listed below:
- The formation of unwanted or even dangerous secondary products, which can be new pollutants, during the oxidation of air pollutants,
- A high cost in material, energy and production,
- A low efficiency of use of the energy produced, a loss of the energy produced which is not entirely consumed for the operation of the air treatment unit,
- Air treatment which is limited to the elimination of chemical pollutants, in particular VOCs, ineffective with respect to biological pollutants,
- A possibility of treating the air only when the concentration of pollutants has reached a given threshold, often high,
- A possibility of treating the indoor air only when the volume of air, its flow rate, its speed of arrival on the pollutant filter are sufficient.

This is why, in order to avoid the drawbacks of the aforementioned techniques, found in the air treatment and conditioning units of the prior art, it is necessary to find an alternative solution to the existing solutions. This alternative solution should make it possible to decontaminate and depollute a gaseous medium, in particular indoor air, without causing the aforementioned problems.

The invention relates to a powdered athermal catalyst advantageously intended to be used as a filter for cleaning indoor air.

Such a device will find particular application in a unit for processing indoor air pollutants using photocatalysis.

The object of the present invention is to overcome the drawbacks of the state of the art, by proposing a powdered athermal catalyst comprising, in percentage by mass relative to its total mass:

- Between 27% and 30% photo-activated _{titanium dioxide TiO 2}

- Between 11% and 17% manganese oxide MnO,

- Between 55% and 59% of synthetic hydrophilic type A zeolite.

In addition, according to another characteristic of the catalyst of the invention, the _{photo-activated titanium dioxide TiO 2} consists of titanium dioxide TiO ₂ subjected to light radiation with a wavelength of between 100 and 400 nm.

According to a first preferred embodiment of the invention, in the pulverulent athermal catalyst of the invention, the photoactivated titanium dioxide TiO ₂ consists of 100% of TiO ₂ in the crystalline anatase form.

According to another embodiment of the invention, in the pulverulent athermal catalyst, the photoactivated titanium dioxide TiO ₂ consists of a mixture of TiO ₂ of anatase crystalline form and of TiO ₂ of rutile crystalline form.

Preferably, in this case, the photo-activated titanium dioxide TiO2 consists of a mixture of TiO2 of crystalline anatase form and TiO2 of rutile crystalline form, with a proportion of anatase / rutile between 60/40 and 99/1 , preferably 80/20.

According to a preferred embodiment, the titanium dioxide TiO ₂ is doped with silver Ag ions and / or platinum Pt ions.

Advantageously, in the powdered athermal catalyst of the invention, the hydrophilic synthetic zeolite of type A has a crystalline structure of sodalite.

The present invention also relates to a process for manufacturing a pulverulent athermal catalyst comprising, as a percentage by mass relative to its total mass, between 27% and 30% of _{photo-activated titanium dioxide TiO 2} , between 11% and 17% d 'manganese oxide MnO and between 55% and 59% of hydrophilic synthetic zeolite of type A, characterized in that the following steps are carried out:
- Is synthesized, in powder form, independently of each other, photoactivated titanium dioxide TiO ₂ , manganese oxide MnO and hydrophilic synthetic zeolite type A;

- Mixing, in an alcohol / demineralized water solvent, between 5 and 10% of _{photo-activated titanium dioxide TiO 2} , between 2 and 6% of manganese oxide MnO and between 10 and 20% of hydrophilic synthetic zeolite of type A in percentage by mass relative to the total mass of said solvent;

- Heat until the solvent has completely evaporated and the powdered athermal catalyst is obtained.

According to a particular embodiment of the process for manufacturing a pulverulent athermal catalyst of the invention, titanium dioxide TiO ₂ is synthesized by the sol gel route. In this particular case, the titanium dioxide TiO ₂ is synthesized from a titanium precursor at calcination temperatures of between 300 and 600 ° C.

According to a preferred embodiment of the process for manufacturing a powdery athermal catalyst of the invention, manganese oxide MnO is synthesized from a manganese precursor at calcination temperatures below 300 ° C. In this particular case, the manganese precursor is chosen from manganese acetate, manganese nitrate or manganese sulfate or a mixture of these.

According to a preferred embodiment of the process for manufacturing a pulverulent athermal catalyst of the invention, said hydrophilic synthetic type A zeolite is synthesized by carrying out the following steps:
- Distilled water is mixed in a 110: 1 ratio with NaOH until a homogeneous sodium hydroxide solution NaOH is obtained,
- Said soda solution is separated into two equal volumes to obtain a first volume of soda and a second volume of soda,
- Mixing, volume by volume, for 10 to 20 min, crystallized sodium aluminate at 17% in the first volume of sodium hydroxide until a solution A is obtained,
- Is dissolved, volume by volume, crystallized sodium silicate Na ₂ SiO ₃ in distilled water at 57%, until a solution B is obtained,
- Mixing, in a ratio of 3.8 / 1000, said solution B with said second volume of sodium hydroxide, until a mixture C is obtained,
- Said mixture C is added to said solution A, until a mixture D is obtained,
- The mixture D is heated until total evaporation of the water contained in the mixture D,
- The mixture D is cooled by lowering the temperature until the appearance of a solid E,
- Said solid E is filtered and rinsed with deionized distilled water until a pH of 9 is reached for the rinsing water,
- Said solid E is dried for a period of between 8 and 15 h, preferably 12 h, at a temperature of between 100 and 120 ° C, preferably 110 ° C, in order to obtain the hydrophilic synthetic zeolite of type A,
- Said hydrophilic synthetic type A solid zeolite is ground in powder form.

The present invention also relates to a solution for decontaminating and depolluting a gaseous medium which comprises demineralized water and a powdered athermal catalyst of the invention.

The present invention also relates to a solution for decontamination and depollution of a gaseous medium, which comprises demineralized water and a pulverulent athermal catalyst obtained by implementing the process for manufacturing a pulverulent athermal catalyst of the invention. .

The present invention also relates to the use of a solution for decontamination and depollution of a gaseous medium which comprises demineralized water and a pulverulent athermal catalyst of the invention for the decontamination and depollution of a gaseous medium containing chemical pollutants and / or biological pollutants.

The invention also relates to the use of a solution for decontamination and depollution of a gaseous medium which comprises demineralized water and a pulverulent athermal catalyst obtained by the implementation of the process for manufacturing a pulverulent athermal catalyst. of the invention, for the decontamination and depollution of a gaseous medium containing chemical pollutants and / or biological pollutants.

Other characteristics and advantages of the invention will emerge from the detailed description which follows of the non-limiting embodiments of the invention.

The present invention relates to a powdered athermal catalyst. By the term "powdered athermal catalyst" is meant a material having the consistency of a powder, capable of catalyzing. A material "capable of catalyzing" makes it possible to increase the speed of a chemical reaction without appearing to participate in it, without absorption or release of heat, without being a conductor of heat and without being the seat of a heat exchange.

Said powdered athermal catalyst of the invention is intended for use in the field of air treatment, in particular in an air treatment unit.

Said powdered athermal catalyst, by virtue of its physicochemical properties, makes it possible to decontaminate the air of its chemical pollutants, in particular VOCs and of its biological pollutants, in particular microorganisms.

According to the invention, said powdered athermal catalyst comprises a photo catalyst activated by UV, a cold catalyst (called low temperature) coupled to an adsorbent.

More specifically, said UV activated photo catalyst consists of titanium dioxide TiO ₂ photo activated by the emission of UV rays, said cold catalyst consists of manganese oxide MnO and the adsorbent consists of zeolite synthetic hydrophilic type A.

Photo-activated TiO ₂ has the advantage of being a stable, inexpensive semiconductor capable of regenerating without degradation and which exhibits high efficiency on several pollutants including chemical pollutants, such as aqueous chemical pollutants, and including biological pollutants, such as microorganisms.

MnO, in crystalline or amorphous form, allows; in contact with oxygen O ₂ in the air; under conditions of temperature between 35 and 55 ° C and hygrometric degree (relative humidity) between 30 and 80%, preferably 50%; to create extremely reactive radical species. The latter will generate oxidation-reduction reactions leading to the breaking of the chemical bonds constituting the chemical and biological pollutants. Manganese oxide MnO thus makes it possible to treat and eliminate pollutants which have a size of the order of a micro or nanometer, including aldehydes and formaldehyde, but also microorganisms.

Type A hydrophilic synthetic zeolite has the advantage of being pure and uniform in structure, in particular because it is produced by chemical synthesis. Therefore, by virtue of its composition, said type A hydrophilic synthetic zeolite has a particular affinity for chemical and biological pollutants. For example, this zeolite advantageously has a specific affinity for the cell membranes of microorganisms. The latter will be adsorbed by electrostatic bonding to the surface of the hydrophilic synthetic zeolite of type A. that such, a toxic nature towards certain microorganisms.

Thus, the invention relates to a pulverulent athermal catalyst comprising, in percentage by mass relative to its total mass:
-Between 27 and 30% photo-activated _{titanium dioxide TiO 2,}
- Between 11 and 17% manganese oxide MnO,
-Between 55 and 59% of hydrophilic synthetic zeolite of type A.

According to a particular embodiment, said pulverulent athermal catalyst has, in percentage by mass relative to its total mass, 29% of _{photo-activated titanium dioxide TiO 2} , 12% of manganese oxide MnO and 59% of hydrophilic synthetic zeolite. type A.

According to another particular embodiment, said pulverulent athermal catalyst consists, in percentage by mass relative to its total mass:
- Between 27 and 30% photo-activated _{titanium dioxide TiO 2}
- Between 11 and 17% manganese oxide MnO,
- Between 55 and 59% of hydrophilic synthetic zeolite of type A, the sum of the percentages of each of the constituents being equal to 100.

Advantageously and in these proportions, a synergy of action and operation exists between TiO ₂ , MnO and the hydrophilic synthetic zeolite of type A. When using the catalyst of the invention, in particular as a filter pollutant in an air treatment unit by photocatalysis activatable by UV rays, this synergy of action allows:
- decontaminate a volume of air, both of its chemical pollutants and of its biological pollutants,
- avoid the proliferation of microorganisms on the surface of the filter and in its internal structural volume,
- avoid the formation of undesirable by-products, such as for example formaldehyde, or any other new pollutants such as for example O3, H ₂ N ₂ ,
- to increase the efficiency of use of the energy necessary for the operation of the athermal catalyst within the air treatment unit.

Consequently, the synergy of action between TiO ₂ , MnO and the hydrophilic synthetic zeolite of type A of the catalyst of the invention has the consequence of reducing the amount of energy produced by UV rays, dissipated in the form of heat. , which is not used, while optimizing its use as much as possible within an air handling unit. The reduction in energy losses produced by UV rays makes it possible to reduce as much as possible the costs of treating indoor air by a treatment unit containing the athermic catalyst of the invention as a pollutant filter.

Indeed, TiO ₂ is a catalyst photoactivated by the emission of light energy, in particular UV. Advantageously, unlike the devices of the prior art, with the pulverulent athermal catalyst of the invention, all of the light energy necessary for the activation of the TiO ₂ will be used. Indeed, part of the energy emitted by UV rays will activate TiO ₂ , while the rest of the energy which dissipates in the form of heat will be stored by the cold MnO catalyst.

Thus, with the pulverulent athermal catalyst of the invention, all of the energy emitted by UV rays is used, either to activate TiO ₂ or to activate MnO. More precisely, the dissipated heat originating from the UV rays advantageously places the MnO in performance conditions for its catalytic action, that is to say in an environment having a temperature between 40 and 50 ° C.

Under these conditions, the coupling of the operating mode of the photo-activated TiO ₂ catalyst with the operating mode of the low-temperature MnO catalyst makes it possible to increase their respective catalytic actions. More particularly, the use within an air treatment unit by photocatalysis of a pollutant filter consisting of the athermic catalyst of the invention makes it possible, through the coupling of TiO ₂ with MnO, to optimize its capacity to destroy the chemical and biological pollutants of the indoor air passing through said filter.

Specifically, this coupling of the operating mode of TiO ₂ with that of MnO, within the pulverulent athermal catalyst, is effective for destroying the pollutants of the indoor air, when said pulverulent athermal catalyst comprises, with respect to its total mass , between 27 and 30% by mass of _{photo-activated TiO 2} and between 11 and 17% by mass of MnO. In fact, in these proportions, the minimum quantity of energy resulting from UV rays, necessary to activate the surface of the TiO _{2 ,} releases and dissipates sufficient heat to increase the temperature of the environment of the MnO and also to activate it.

Consequently, the use, as a filter, of the pulverulent athermal catalyst of the invention, within an air treatment unit by photocatalysis, makes it possible to use the energy dissipated in the form of heat to activate MnO, unlike the known photocatalytic treatment units comprising a TiO ₂ filter alone subjected to UV rays. With the catalyst of the invention, to carry out the photocatalysis necessary for the pollution control of the indoor air, the loss of energy consumed is less compared to a conventional photocatalysis system based on the activation of TiO ₂ by UV rays. .

According to the invention, _{photo-activated titanium dioxide TiO 2} consists of titanium dioxide TiO ₂ subjected to UV radiation comprising wavelengths of between 100 and 400 nm.

According to the invention, any means or light sources making it possible to provide UV radiation to activate TiO ₂ can be envisaged, such as, for example, artificial UV lamps of the light-emitting diode (LEDs) or fluorescent lamp type.

Preferably, the _{photo-activated titanium dioxide TiO 2} consists of titanium dioxide TiO ₂ subjected to UV radiation between 100 and 365 nm, more preferably subjected to radiation in the UV-C range of between 100 and 280 nm, advantageously 254 nm.

In fact, in the case of the use of the pulverulent athermal catalyst of the invention in a unit for treating polluted indoor air, photo activation of TiO ₂ by the rays of the UV-C range makes it possible, in addition to photoactivation of TiO ₂ , to have a biocidal action on microorganisms, in particular by destruction or alteration of their DNA. In other words, the use of UV-C rays for photo-activated TiO ₂ generates a double phenomenon of destruction of pollutants, in particular biological pollutants of the microorganism type. Advantageously, the use of UV-C has a direct biocidal action, as such, on microorganisms, and also an indirect biocidal action by activation of TiO ₂ . The latter, after activation by UV-C, generates oxidation-reduction reactions on the surface of the catalyst of the invention, which destroy microorganisms. Consequently, the combination of the biocidal action of UV-C rays and the activation of TiO ₂ by said UV-C makes it possible to have effective destruction of biological and chemical pollutants at the surface of the catalyst.

According to a preferred embodiment of the invention, the photoactivated titanium dioxide TiO ₂ consists of 100% TiO ₂ in crystalline anatase form. Indeed, the anatase form has the advantage of being the crystalline form active in photocatalysis in the UV range. Thus, a catalyst of the invention, containing 100% of titanium dioxide TiO ₂ in anatase form, allows all of the TiO _{2 to} be active in photocatalysis and plays its role of removing chemical and biological pollutants from the air. .

It should be noted that the anatase form of TiO ₂ is obtained at calcination temperatures of between 300 and 600 ° C., in particular when the TiO _{2 is} synthesized by the sol gel route. Beyond these temperatures, the rutile crystalline form of TiO ₂ is formed.

According to another embodiment of the invention, the _{photo-activated titanium dioxide TiO 2} consists of a mixture of TiO ₂ of crystalline anatase form and TiO ₂ of rutile crystalline form with a proportion of anatase / rutile between 60 / 40 and 99/1. TiO ₂ in the form of a mixture makes it possible to increase the separation of electronic charges at the surface of the powdery athermal catalyst therefore to increase its catalytic efficiency, in particular the efficiency of the photo-activated TiO ₂ catalyst, in the phenomenon of destruction of pollutants chemical or biological by the production of oxidation-reduction reaction.

According to a preferred embodiment, the photoactivated titanium dioxide TiO ₂ consists of a mixture consisting of 80% of TiO ₂ in anatase crystalline form and of 20% of TiO ₂ in rutile crystalline form.

According to another embodiment of the invention, the titanium dioxide TiO ₂ is doped with silver Ag ions and / or platinum Pt ions. Doping of TIO ₂ makes it possible to further increase the biocidal effect on microorganisms. -organisms and further enhances the destruction of pollutant byproducts formed. In fact, doping with Ag and / or Pt ions promotes the formation of an oxidation-reduction reaction at the surface of the catalyst of the invention, because the Ag and / or Pt ions are very chemically reactive, the presence of these ions increases the number of redox reactions possible.

According to another advantageous characteristic of the invention, the powdered athermal catalyst also comprises between 55% and 59% of hydrophilic synthetic zeolite of type A which has a crystalline structure of sodalite.

Type A hydrophilic synthetic zeolite has no natural equivalent. Type A hydrophilic synthetic zeolite has a crystalline structure which is formed by an anionic aluminosilicate framework, neutralized by alkali or alkaline earth cations. This structure combines several elementary sodalite cages. This sodalite cage consists of several polyhedra with eight faces of hexagonal shape and six faces of square shape. The sodalite cages, forming the hydrophilic synthetic type A zeolite, are connected to each other by their square faces, themselves separated by double rings with four tetrahedra.

This particular connection between the sodalite cages gives the synthetic hydrophilic type A zeolite an open 3D structure with a void ratio of around 47% relative to the total volume that occupies the entire 3D structure. Thus, the specific open 3D structure of the hydrophilic synthetic zeolite of type A of the catalyst of the invention makes it possible to have, for a minimal volume, a maximum adhesion and absorption surface for chemical or biological pollutants. These pollutants will be able to fit into the vacuum zones of the open 3D structure of the hydrophilic synthetic zeolite of type A, in order to be able to be treated when using the catalyst of the invention as a filter for pollutants within of an air treatment unit by photocatalysis.

In addition, the structure of the synthetic hydrophilic type A zeolite being very open, it allows the storage of water. In addition, by its hydrophilic character, synthetic type A zeolite has a high water retention capacity. Water is an essential actor in triggering redox reactions which remove the pollutants stored by the pollutant filter formed by the catalyst of the invention. Consequently, the water retention by the zeolite of the catalyst of the invention is a phenomenon which advantageously contributes to destroying chemical or biological pollutants.

Thus, among the known zeolites, the hydrophilic type A synthetic zeolite is specifically chosen to form the powdered athermal catalyst of the invention. In particular, the synthetic hydrophilic type A zeolite is chosen for its role of adsorbing biological, chemical or water pollutants within its 3D structure. Thanks to its particular physicochemical characteristics, this type A hydrophilic synthetic zeolite actively participates in the decontamination process of indoor air pollutants which requires a step of trapping air pollutants.

It should be noted that an excess of water, at the surface of the catalyst, hinders the accessibility of pollutants to its adsorption sites, therefore decreases its potential for destroying pollutants. An excessive amount of hydrophilic synthetic zeolite of type A, relative to the amount of TiO ₂ and MnO, may be the cause of this excess water on the surface, in particular because of the hydrophilic properties of said type A zeolite. This is why in order to avoid an excess of water at the surface, the athermal catalyst comprises a proportion of hydrophilic synthetic zeolite of type A of between 55 and 59% relative to its total mass.

In fact, the Applicant has observed that a proportion of hydrophilic synthetic type A zeolite of between 55% and 59% has the effect of regulating the quantity of water at the surface of the athermic catalyst of the invention, in particular when it is used as a pollutant filter in an air treatment unit by photocatalysis. The quantity of water is regulated by the phenomenon of mass transfer on the photo-activated catalyst TiO ₂ and on the cold catalyst MnO. In the present invention, the term “mass transfer phenomenon” is understood to mean the fact that after destruction of the pollutants by TiO ₂ and MnO, the pollutants which are trapped in the three-dimensional structure of the hydrophilic synthetic zeolite of the type. A, are transferred to TiO ₂ and MnO. However, for the catalyst of the invention, it is important for the proportion of synthetic hydrophilic type A zeolite to be greater than the respective proportions of TiO ₂ and MnO. Indeed, a higher proportion of hydrophilic type A synthetic zeolite allows it, by its hydrophilic character, to capture, within its internal structure, the new pollutants coming into contact with the catalyst of the invention, this while TiO ₂ and MnO destroy the pollutants present on its surface. Once the surface pollutants have been destroyed by the action of TiO ₂ and MnO, the pollutants which are retained in said zeolite move to the surface, to be destroyed in turn thanks to the phenomenon of “mass transfer”. The specific proportions of type A hydrophilic synthetic zeolite, which are greater than those of TiO ₂ and MnO in the catalyst of the invention, thus prevent saturation of the action of TiO ₂ and MnO in the event of excessive pollutant concentration in indoor air, for example during a pollution peak.

Consequently, an amount of type A hydrophilic synthetic zeolite of between 55% and 59% by mass relative to the total mass of the pulverulent athermal catalyst makes said catalyst durable over time, regardless of the humidity conditions and the concentration of pollutants contained in the air to be treated.

Thus, including the hydrophilic synthetic zeolite of type A, within the catalyst of the invention, and in these specific proportions between 55% and 59% by mass, through the phenomenon of mass transfer of pollutants, makes it possible to obtain a synergy of action between the adsorption of pollutants by the zeolite and the catalysis action by TiO ₂ and MnO. This synergy of action, through mass transfer, avoids the risk of saturation of TiO ₂ and MnO, which has the consequence of regenerating the zeolite. In fact, when the zeolite is not intimately mixed with the TiO ₂ and the MnO, the regeneration of the zeolite is non-existent. Consequently, the pollutant treatment efficiency decreases over time due to the saturation of the internal structure of the zeolite with pollutants. With the catalyst of the invention and in the proportions indicated of TiO ₂ , MnO and hydrophilic synthetic zeolite of type A, there is no saturation of the adsorption capacities of the pollutants by the zeolite. The pollutants can therefore advantageously be treated continuously and permanently over time with the catalyst of the invention used as a pollutant filter.

The present invention also relates to a process for the manufacture of a pulverulent athermal catalyst, comprising, in percentage by mass relative to its total mass, between 27 and 30% of _{photo-activated titanium dioxide TiO 2} , between 11 and 17% of manganese oxide MnO and between 55 and 59% of hydrophilic synthetic zeolite of type A comprising the following steps:
- Step a) Are synthesized, in powder form, independently of each other, photoactivated titanium dioxide TiO ₂ , manganese oxide MnO and hydrophilic synthetic zeolite of type A;
- Step b) Are mixed, in a solvent containing 20% alcohol and 80% demineralized water, between 5 and 10% of photo-activated titanium dioxide TiO2, between 2 and 6% of manganese oxide MnO and between 10 and 20% of hydrophilic synthetic zeolite of type A by mass relative to the total mass of said solvent;
- Step c) Said mixture is heated until complete evaporation of the solvent and the pulverulent athermal catalyst is obtained.

To manufacture the powdered athermal catalyst of the invention, it is necessary for step a) to independently synthesize TiO ₂ , MnO and the hydrophilic synthetic zeolite of type A, because the synthesis temperatures and the precursors at the origin of these three components are not the same.

In fact, the synthesis of TiO ₂ takes place, for example by sol gel route, from a titanium precursor, such as for example titanium tetrachloride TiCl ₄ , at calcination temperatures of between 300 and 600 ° C. .

On the contrary, the synthesis of manganese oxide MnO takes place from a manganese precursor, for example chosen from manganese acetate, manganese nitrate or manganese sulphate or a mixture thereof, at calcination temperatures below 300 ° C. In fact, above 300 ° C, in the calcination temperature range for the synthesis of TiO ₂ , starting from a manganese precursor, manganese dioxide MnO 2 is formed mainly and not _{manganese dioxide MnO 2.} manganese MnO, this is why it is impossible to combine the synthesis of TiO ₂ with the synthesis of MnO to manufacture the powdered athermal catalyst of the invention. It should be noted that the catalytic action of manganese dioxide MnO ₂ is unsatisfactory for removing pollutants from indoor air, unlike the catalytic action of manganese oxide MnO.

The synthesis of TiO ₂ in powder form can also be done by any other methods known to those skilled in the art, such as for example using the thermal plasma technique, laser pyrolysis, by hydrothermal synthesis or by any electrochemical route. .

To manufacture a pulverulent athermal catalyst according to the process of the invention, the synthesis of TiO ₂ in powder form by the sol gel route from a precursor of titanium tetrachloride TiCl _{4 will be} favored. To do this, the TiCl ₄ is mixed with absolute ethanol in a ratio of between 0.5: 10 and 3:10, preferably a ratio of 1:10, for 4 h at room temperature. The sol formed is then placed in an ultrasonic bath for a period of between 20 and 40 min, preferably 30 min. Then the sol is dried at a temperature between 100 and 130 ° C, preferably 120 ° C; for a period of 1 to 24 hours, preferably 7 hours, so as to obtain a powder. This powder is gradually calcined at a temperature between 530 and 570 ° C, preferably 550 ° C; for 2 to 3 hours, preferably 2 hours; by increasing the temperature in steps of 10 to 12 ° C / minute. The _{pulverulent TiO 2} obtained can then be cleaned with deionized distilled water, then dried at a temperature between 90 and 110 ° C, preferably 100 ° C.

To manufacture a pulverulent athermal catalyst according to the process of the invention, preference will be given, for the synthesis of MnO in powder form, to the use of a manganese acetate precursor. To do this, this manganese acetate is mixed with a solution of potassium permanganate in a mol / L ratio of 1.8 / 1.2 for a minimum of 24 hours at room temperature between 21 and 25 ° C. Then it is filtered and rinsed with deionized distilled water. The recovered MnO powder is calcined for several hours, preferably 72 hours, with a rise in temperature in steps of 6 ° C / min until a temperature of between 280 and 300 ° C is reached, then it is ground, rinsed with water. water and dried at a temperature of approximately 100 ° C. until the pulverulent MnO used to manufacture the catalyst of the invention is obtained.

To manufacture a powdered athermal catalyst according to the process of the invention, it is necessary that at the end of step c) all of the solvent has evaporated.

According to a particular embodiment of the process of the invention, if one works at room temperature, of the order of 25 ° C., for step c) above-mentioned, said mixture is heated to a temperature of between 75 and 130 ° C, preferably 100 ° C for a period of between 24 and 120 hours, preferably 72 hours.

According to a specific embodiment of the process for manufacturing a pulverulent athermal catalyst of the invention, said hydrophilic synthetic type A zeolite is synthesized by carrying out the following steps:
- Step 1: Distilled water is mixed with NaOH in a 110: 1 ratio, for example with NaOH tablets, until a homogeneous sodium hydroxide solution NaOH is obtained,
- Step 2: Said sodium hydroxide solution NaOH is separated into two equal volumes to obtain a first volume of sodium hydroxide and a second volume of sodium hydroxide,
- Step 3: Mixing, volume by volume, for 10 to 20 min, sodium aluminate crystallized at 17% in the first volume of sodium hydroxide until a solution A is obtained,
- Step 4: Dissolve, volume by volume, crystallized sodium silicate Na ₂ SiO ₃ in distilled water at 57%, until a solution B is obtained,
- Step 5: Mixing, in a ratio of 3.8 / 1000, said solution B with said second volume of sodium hydroxide, until a mixture C is obtained, preferably a clear mixture C,
- Step 6: Said clear mixture C is added to said solution A, until a mixture D is obtained,
- Step 7: The mixture D is heated until total evaporation of the water contained in the mixture D,
- Step 8: The mixture D is cooled by lowering the temperature until the appearance of a solid E,
- Step 9: Said solid E is filtered and rinsed with deionized distilled water until a pH of between 8.5 and 9.5 is reached for the rinsing water,
- Step 10: Said solid E is dried for a period of between 8 and 15 h, preferably 12 h, at a temperature of between 100 and 120 ° C, preferably 110 ° C, in order to obtain the hydrophilic synthetic zeolite of type A ,
- Step 11: The said solid type A hydrophilic synthetic zeolite is ground in powder form.

According to a particular embodiment, for step 7) above, the mixture D is heated to a temperature between 75 ° C and 130 ° C, preferably 100 ° C for 3 to 4 hours. The goal is to evaporate all of the water contained in mixture D.

According to a preferred embodiment, for step 8) above, the mixture D is cooled by lowering the temperature to a temperature value which is lower than that of step 7) and which is higher than ambient temperature. This lowering in temperature makes it possible to prevent the crystals of solid E from sticking to the bottom of the container in which the mixture D is initially located. According to a particular embodiment, for step 8), the temperature is lowered to 30 °. C considering that the ambient temperature is between 20 and 25 ° C, so as to be able to easily recover the solid E without it sticking to the bottom of the container.

Usually, for step 9, the pH of the rinsing water is measured, for example, with a pH meter or any other measuring means known to those skilled in the art making it possible to measure the pH. The fact of measuring the pH of the rinsing water makes it possible to indirectly give the pH of the surface state of the solid E, which will constitute the hydrophilic synthetic zeolite of type A. For the pulverulent athermic catalyst of the invention, it is important that the hydrophilic synthetic zeolite of type A has a slightly basic surface state in order to promote the formation of Van der Walls bonds with TiO ₂ and MnO, which in turn have a slightly acidic surface state. This pH complementarity between the hydrophilic synthetic zeolite of type A and, both TiO ₂ and MnO, facilitates the manufacture of the athermic catalyst of the invention and makes it structurally homogeneous.

For step 10) above, the duration and the drying temperature of the solid E make it possible to gradually eliminate the water molecules retained on the surface of said zeolite. In fact, too rapid evacuation of the water molecules risks generating cracks on the surface of the zeolite. These cracks on said zeolite weaken its 3D structure, which is nevertheless necessary and important for its role of adsorbent within the powdered athermal catalyst of the invention. This is why, to avoid this cracking phenomenon, we choose a drying time between 8 and 15 hours coupled with a temperature between 100 and 120 ° C, in order to eliminate the water molecules gradually, without risking weakening the structure. zeolite.

For step 11) above, the hydrophilic synthetic type A zeolite is ground into a powder by any means known to those skilled in the art. According to a particular embodiment of the invention, the hydrophilic synthetic type A zeolite is ground so as to obtain a particle size of between 0.5 and 2.5 μm. Indeed, this particle size of hydrophilic synthetic type A zeolite increases the affinity of certain microorganisms towards the surface of said zeolite. For the catalyst of the invention, the use of a hydrophilic synthetic zeolite of type A of micrometric size is favored for its increased affinity towards microorganisms, that is to say the biological pollutants of the indoor air. .

The present invention also relates to a solution for decontamination and depollution of a gaseous medium comprising both demineralized water and:
- either said powdered athermal catalyst of the invention,
- Or a pulverulent athermal catalyst obtained by implementing the process for manufacturing a pulverulent athermal catalyst as mentioned above.

The present invention also relates to the use of the decontamination and depollution solution of a gaseous medium for the decontamination and depollution of a gaseous medium containing chemical pollutants and / or biological pollutants.

The powdery athermal catalyst of the invention, its use in solution, and its use as a pollutant filter in an air treatment unit by photocatalysis makes it possible to remove chemical and biological pollutants from the air. interior.

The specific combination of the photo-activated TiO ₂ catalyst, the cold MnO catalyst and a type A hydrophilic synthetic zeolite adsorbent, for example as a pollutant filter in an indoor air treatment unit by photocatalysis, allow:
- by effect of complementary functioning of the zeolite, TiO2 and MnO, to treat large loads of air pollutants ranging from a few parts per million (= ppm) to hundreds of ppm, whatever the flow rate and the air speed arriving within the air handling unit,
- avoid the formation of new, uncontrolled pollutants, which are not initially present in the indoor air to be treated,
- a more optimum use of the energy supplied to the processing unit, without loss of this energy by heat dissipation, part of the energy being used for the activation of TiO ₂ the other to generate an adequate environment in temperature for the activation of MnO,
- to treat both chemical pollutants and biological pollutants, in particular microorganisms.

In order to show the performance of the athermal catalyst of the invention, the Applicant has carried out the experiment described below for the following biological pollutants:
- bacterial spores of Bacillus subtilis at a concentration of between 10 ⁴ to 10 ⁶ Colony Forming Unit / m ³ of air;
- Legionella pneumophilia bacteria at a concentration between 10 ⁴ to 10 ⁶ Colony Forming Unit / m ³ of air, and
- T2 bacteriophages at a concentration between 10 ³ to 10 ⁴ range forming unit / m ³ .

Experimental protocol:

The tests are carried out within a 0.8 m ³ class A isolator which includes a reactor having a “sandwich” configuration. This reactor comprises two stages of athermal catalyst according to the invention, the latter are each deposited on an aluminum honeycomb between which is placed an 18W UV-C lamp.

Using an aerosol generator, an air stream is created within the insulator, containing only one of the aforementioned pollutants in the concentrations indicated. This "polluted" air stream will be treated within the reactor by filtration and passage between the two stages of athermal catalysts of the invention.

To demonstrate the treatment efficiency of the catalyst of the invention, an air sample is taken using a bio-collector, before and after starting the reactor, which will be counted and analyze by impacting it on a culture medium corresponding to the tested pollutant.

A sample of air before, and, a sample of air after starting the reactor, are inoculated in order to determine the concentration of pollutants, by counting on the appropriate culture medium.

The air samples initially polluted by Legionella pneumophilia bacteria are inoculated on a BCYE medium marketed by Biomérieux and containing agar for legionella-type microorganisms and L-cysteine.

The air samples initially polluted by the bacterial spores of Bacillus subtilis are inoculated on LB Luria Bertani medium.

The air samples initially polluted by T2 bacteriophages are inoculated on a medium in which bacteria of the E. coli BAM type have been cultured in order to analyze the number of lysis plaques formed by the still living viruses. In this protocol, the same amount of air sample is seeded on the appropriate growth medium.

Experimental results

The results indicate reductions of 2 log (99.45%) for Legionella bacteria. pneumophilia , 1 log (96.67%) for Bacillus spores. subtilis and 3 log for T2 bacteriophages (99.98%) for the air samples taken after starting the reactor and treatment with the athermic catalyst of the invention compared to the initial air samples before treatment with the catalyst of the invention.

Thus, through these experiments, it is proved that the use of the athermal catalyst of the invention as a filter for treating contaminated air is effective against biological pollutants, in particular Legionella. p neumophilia , bacterial spores of Bacillus subtilis and T2 bacteriophages.

Carrying out this protocol with other contaminants has also demonstrated a total reduction on strains of Aspergillus brasiliensis and Staphylococcus epidermidis.

Thus, in addition to allowing the removal of chemical pollutants from the air, the athermal catalyst of the invention, used as a pollution control filter, makes it possible to remove biological pollutants.

Claims (16)

Powdered athermal catalyst comprising, in percentage by mass relative to its total mass:

• Between 27% and 30% photo-activated _{titanium dioxide TiO 2}
• Between 11% and 17% manganese oxide MnO,
• Between 55% and 59% of synthetic hydrophilic type A zeolite.

Pulverulent athermal catalyst according to the preceding claim, characterized in that the _{photo-activated titanium dioxide TiO 2} consists of titanium dioxide TiO ₂ subjected to light radiation with a wavelength of between 100 and 400 nm. Pulverulent athermal catalyst according to any one of the preceding claims, characterized in that the photoactivated titanium dioxide TiO ₂ consists of 100% TiO ₂ in crystalline anatase form. Pulverulent athermal catalyst according to Claim 1 or according to Claim 2, characterized in that the _{photo-activated titanium dioxide TiO 2} consists of a mixture of TiO ₂ in the crystalline anatase form and TiO ₂ in the rutile crystalline form. Pulverulent athermal catalyst, according to the preceding claim, characterized in that the _{photo-activated titanium dioxide TiO 2} consists of a mixture of TiO ₂ of crystalline anatase form and TiO ₂ of rutile crystalline form, with a proportion of anatase / rutile between 60/40 and 99/1, preferably 80/20. Pulverulent athermal catalyst according to any one of the preceding claims, characterized in that the titanium dioxide TiO ₂ is doped with silver ions Ag and / or platinum ions Pt. Powdered athermal catalyst according to any one of the preceding claims, characterized in that the synthetic hydrophilic type A zeolite has a crystalline structure of sodalite. Process for the manufacture of a pulverulent athermal catalyst comprising, as a percentage by mass relative to its total mass, between 27% and 30% of titanium dioxide TiO₂photo-activated, between 11% and 17% manganese oxide MnO and between 55% and 59% hydrophilic synthetic zeolite type A, characterized in that the following steps are carried out:

• _{The photo-activated titanium dioxide TiO 2} , the manganese oxide MnO and the hydrophilic synthetic zeolite of type A are synthesized in powder form, independently of each other;
• Are mixed, in an alcohol / demineralized water solvent, between 5 and 10% of _{photo-activated titanium dioxide TiO 2} , between 2 and 6% of manganese oxide MnO and between 10 and 20% of hydrophilic synthetic zeolite of type A in percentage by mass relative to the total mass of said solvent;
• The mixture is heated until complete evaporation of the solvent and the pulverulent athermal catalyst is obtained.

Process for manufacturing a pulverulent athermal catalyst, according to the preceding claim, characterized in that the titanium dioxide TiO ₂ is synthesized by the sol gel route Process for manufacturing a pulverulent athermal catalyst according to the preceding claim, characterized in that the titanium dioxide TiO ₂ is synthesized from a titanium precursor at calcination temperatures of between 300 and 600 ° C. Process for manufacturing a powdered athermal catalyst, according to any one of process claims 8 to 10, characterized in that manganese oxide MnO is synthesized from a manganese precursor at lower calcination temperatures at 300 ° C. Process for the manufacture of a pulverulent athermal catalyst, according to the preceding claim, characterized in that the manganese precursor is chosen from manganese acetate, manganese nitrate or manganese sulphate or a mixture of the latter. A method of manufacturing a powdered athermal catalyst, according to any one of process claims 8 to 12, characterized in that said hydrophilic type A synthetic zeolite is synthesized by carrying out the following steps:

• Distilled water is mixed in a 110: 1 ratio with NaOH until a homogeneous sodium hydroxide solution NaOH is obtained,
• Said soda solution is separated into two equal volumes to obtain a first volume of soda and a second volume of soda,
• Sodium aluminate crystallized at 17% in the first volume of sodium hydroxide is mixed, volume by volume, for 10 to 20 min, until a solution A is obtained,
• _{The crystallized sodium silicate Na 2} SiO ₃ is dissolved, volume by volume, in distilled water at 57%, until a solution B is obtained,
• Said solution B is mixed, in a ratio of 3.8 / 1000, with said second volume of sodium hydroxide, until a mixture C is obtained,
• Said mixture C is added to said solution A, until a mixture D is obtained,
• The mixture D is heated until total evaporation of the water contained in the mixture D,
• The mixture D is cooled by lowering the temperature until the appearance of a solid E,
• Said solid E is filtered and rinsed with deionized distilled water until a pH of 9 is reached for the rinsing water,
• Said solid E is dried for a period of between 8 and 15 h, preferably 12 h, at a temperature of between 100 and 120 ° C, preferably 110 ° C, in order to obtain the hydrophilic synthetic zeolite of type A,
• Said solid hydrophilic synthetic type A zeolite is ground in powder form.

Solution for decontamination and depollution of a gaseous medium, characterized in that it comprises demineralized water and a powdered athermal catalyst according to any one of claims 1 to 7. Solution for decontamination and depollution of a gaseous medium, characterized in that it comprises demineralized water and a pulverulent athermal catalyst obtained by implementing the method as defined by any one of claims 8 to 13 . Use of a solution for decontamination and depollution of a gaseous medium, according to claim 14 or according to claim 15, for the decontamination and depollution of a gaseous medium containing chemical pollutants and / or biological pollutants.