EP4168153A1

EP4168153A1 - Use of a sintered porous ceramic part for treating air

Info

Publication number: EP4168153A1
Application number: EP21733121.4A
Authority: EP
Inventors: Nicolas Raffin; Adrien Vincent; Yves Boussant-Roux; Laurent Pierrot; Vincent Gleize; Stéphane RAFFY
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2020-06-17
Filing date: 2021-06-17
Publication date: 2023-04-26
Also published as: FR3111568A1; WO2021255185A1

Abstract

Disclosed is an apparatus for treating air, at room temperature, of an enclosed inhabitable space, the apparatus comprising: - a sintered ceramic part (2) having a total porosity higher than 40%, the pores of a size larger than 300 µm representing less than 10% by volume of the porosity, - an air circulator (3) configured to generate a flow of air to be treated through the ceramic part, the ceramic part being a ceramic foam having a plurality of interlocking cells, delimited by ceramic walls and connected to each other by interconnection windows, the walls defining the cells being formed by agglomeration of grains, this agglomeration leaving gaps between the grains.

Description

Title: Use of a porous sintered ceramic part for air treatment

Technical area

The present invention relates to the use of a sintered porous ceramic part, in particular of a sintered ceramic foam, for treating, and in particular decontaminating, air, in particular the air of closed living spaces (homes, offices , vehicle interiors, ...).

Prior art

Air quality is an important subject in the field of public health.

In particular, the air can contain human pathogens transmissible by the respiratory route, or "pathogens". These pathogens can cause pathology in a human being, in particular in the respiratory tract.

In particular viruses, bacteria and fungi are known which can be transmitted by air. Mention may be made of the Influenza viruses and the coronaviruses, in particular SARS, SARS-CoV-2. These pathogens can be attached to suspended particles which, depending on their size, can enter gas exchange regions of the lungs, or even pass through the lungs to affect other organs.

Filtration with a fiber filter is widely used to retain particles in suspension because such a filter generally presents a good compromise between filtration efficiency and energy consumption. Collective or individual protection systems or industrial dust collectors are composed of non-woven fibrous media, that is to say of a veil or sheet of fibers oriented directly or at random and linked by friction, cohesion or adhesion. . These systems must be regularly renewed.

In addition, personal protective equipment conventionally uses paper or fabric filters. However, these filters are for single use only. They therefore generate waste in large quantities. They also require an uninterrupted manufacturing and distribution process to avoid shortage.

The air can also contain pollutants.

In particular, human activities, such as the combustion of fossil fuels in vehicles and various industrial processes, generate significant amounts of particulate matter. harmful. Typical air pollutants in homes and workplaces can include, for example, particulate matter, nitrogen oxides (NOx) or sulfur oxides (SOx), organic compounds including formaldehyde and volatile organic compounds similar (VOCs).

Activated carbon is widely used for the treatment of molecules by adsorption. Its mechanical resistance is limited. In addition, it needs to be replaced regularly.

Fiber filter filtration is also widely used to separate airborne pollutant particles.

US10188975 finally describes the use of "honeycomb" type cordierite filters to remove particulate pollutants, optionally coated with a sorbent and / or a catalyst to remove VOCs. Tests have shown that “honeycomb” type filters cause a high pressure drop.

Due to their very good chemical and mechanical resistance and their ability to work at high temperature, ceramic membranes can also be used as filters to clean up hot polluted gases.

There is therefore a need for new solutions for decontamination and / or pollution control of the air, and in particular of the air intended to be inhaled.

An aim of the invention is to meet, at least partially, this need.

Disclosure of the invention

The invention relates to an air treatment apparatus, in particular air at ambient temperature (20 ° C), the treatment apparatus comprising a sintered ceramic part having a total porosity greater than 40%, preferably greater than 50. %, preferably greater than 55%, or even greater than 60%, or even greater than 70% and preferably less than 90%, or even less than 85%, or even less than 80%, preferably between 55% and 85%.

Preferably, at least part of the surface defined by the porous network is coated with a coating for inactivating one or more pathogenic agents, and / or a catalytic coating suitable for a reaction of at least one pollutant. atmospheric.

The ceramic part also has the advantage of being able to be cleaned and / or purified in order to be reused. It therefore generates little waste. Preferably, the treatment apparatus comprises a pressure drop detector and an electronic unit, programmed to trigger or inform on the need for a cleaning and / or purification operation as a function of information received from the loss detector. dump. More preferably, it comprises a cleaning and / or purification tool, preferably controlled by the electronic unit as a function of the information received from the pressure drop detector. Maintenance is considerably simplified.

In one embodiment, the processing apparatus comprises a computer memory in which is recorded information relating to the ceramic part, preferably an identifier of the ceramic part and / or at least one photo representing, at least partially, the part. ceramic at a determined time, preferably before the first use of the ceramic part.

Preferably, the ceramic part also has one or more of the following characteristics:

- the median size of the pores is between 1 and 400 μm; as will be seen in more detail in the remainder of the description, such a total porosity offers a micro structure perfectly suited to the treatment of pathogens and pollutants;

- the ceramic part consists, for more than 90%, more than 95%, more than 99%, preferably substantially 100% of its mass, of a ceramic material, preferably of silicon carbide, preferably of silicon carbide recrystallized;

the ceramic part comprises more than 80% by mass of recrystallized silicon carbide, the intergranular porosity preferably being greater than or equal to 5% and less than 25%, preferably greater than or equal to 10% and less than 20%;

- the median size of the pores (D50 by volume, measured by mercury porosimetry) is greater than 1 μm, or even greater than 5 μm, greater than 7 μm, or even greater than 10 μm, or even greater than 20 μm, or even greater than 30 μm , or even greater than 40 μm, or even greater than 50 μm, preferably greater than 60 μm, preferably greater than 70 μm and / or less than 400 μm, or even less than 300 μm, or even less than 200 μm, or even less than 160 μm pm, or even less than 150 pm, or even less than 145 pm, less than 140 pm, less than 130 pm, preferably less than 120 pm;

the D90 percentile by volume on the cumulative distribution curve of the pore sizes classified in ascending order, measured by mercury porosimetry, is less than 250 μm, preferably less than 220 μm, preferably less than 200 μm, preferably less than 180 mih, and / or greater than 50 μm, preferably greater than 60 μm, preferably greater than 70 μm, preferably greater than 80 μm;

the pores of size greater than 300 μm represent less than 10% by volume, or even less than 5% by volume, of the total porosity;

the Dio percentile by volume on the cumulative distribution curve of the pore sizes classified in increasing order, measured by mercury porosimetry, is preferably greater than 5 μm, preferably greater than 8 μm;

- Preferably, the difference D90-D10 is less than 250 μm, or even less than 200 μm, or even less than 180 μm and / or greater than 40 μm, or even greater than 50 μm;

- the (D90 - Dio) / Dso ratio is preferably less than 2, preferably less than 1.8, preferably less than 1.7, preferably less than 1.6, preferably less than 1.5, and / or greater than 0.8, preferably greater than 0.9, preferably greater than 1.0;

- the tortuosity is greater than 1, or even greater than 1.1, or even greater than 1.2, or even greater than 1.3, or even greater than l, 4 and less than 2, or even less than 1.9, or even less than 1 , 8, or even less than 1.7, or even less than 1.6, preferably less than 1.5 and greater than 1;

the ceramic part comprises a surface layer having a total porosity less than 0.95 times the porosity at the center of the ceramic part, the pores of the surface layer preferably having a median size greater than 1 μm and less than 20 μm, the pores of the surface layer preferably having a median size greater than 1 μm and less than 20 μm, the total porosity of the surface layer preferably being greater than 30% and less than 70%, the thickness of the surface layer preferably being between 5 and 500 μm;

- the ceramic part is formed by an agglomeration of grains, all the grains preferably having an average aspect ratio, on average over all the grains, less than 2, preferably less than 1.5, the aspect ratio conventionally being the ratio L / l where L designates the length of the grain, i.e. its largest dimension, and 1 designates the width of the grain, i.e. its largest dimension in a transverse plane any perpendicular to the length direction.

The treatment apparatus may be an apparatus which actively filters the air, for example an air conditioner or an air-blowing heater, in particular an electrical apparatus. It then comprises an air circulator configured to generate an air flow to be treated through the ceramic part. The treatment apparatus can be used in particular for filtering the air of confined habitable spaces such as homes, offices or vehicle interiors, or public places, in particular public transport stations.

The treatment device can also be passive, and in particular be

- personal protective equipment such as a mask or even a cartridge suitable for use in personal protective equipment such as a mask or

- a device placed in a place where it is subjected to a flow of air in a natural state, for example placed in public places, in particular public transport stations.

In a first main embodiment, more than 95%, more than 97%, more than 98%, more than 99% of the total porosity of the ceramic part is open.

Preferably, the ceramic part is a ceramic foam having a plurality of nested cells, delimited by ceramic walls and connected to each other by interconnection windows.

A cell on the surface of the ceramic foam also generally has one or more openings to the outside. The pores are therefore generally accessible to the air outside the ceramic foam. The microstructure is then well suited to retain particles suspended in the air, and in particular particles carrying pathogens and polluting particles.

Preferably, the walls delimiting the cells are formed by agglomeration of grains, this agglomeration leaving interstices or “intergranular pores” between the grains. An example of ceramic foam is described in EP 1 778 601.

Preferably, the pore size distribution is bimodal. More specifically, the porosity distribution, measured with a mercury porosimeter, exhibits a first main peak centered on a first pore size and a second main peak centered on a second pore size.

The first pore size is considered to be the median size of the intergranular pores, and is representative of a so-called “intergranular” porosity. It is preferably less than 25 μm, even less than 20 μm and greater than 4 μm, preferably greater than 7 μm, preferably greater than 10 μm, preferably greater than 13 μm. Preferably, the intergranular porosity is at least 5%, preferably at least 8%, more preferably at least 10% and / or less than 25%, or even less than 20%.

The second pore size is considered the median cell pore size and is representative of a so-called "interconnect" porosity, constituting substantially the 100% complement of the intergranular porosity. It is preferably less than 400 μm, or even less than 300 μm, or even less than 200 μm, or even less than 180 μm, or even less than 160 μm, preferably less than 150 μm, or even less than 140 μm, preferably less than 130. μm, and preferably greater than 40 μm, or even greater than 50 μm, or even greater than 80 μm.

Preferably, the total porosity is greater than 55%, or even greater than 60%, or even greater than 70%.

A ceramic foam advantageously makes it possible to filter particles whose size is up to 30 times smaller than the median pore size, which makes it possible to limit the pressure drop. A ceramic foam advantageously presents an excellent compromise between the pressure drop and the filtration capacity.

In a second main embodiment, at least a portion of the ceramic part is coated with a coating for activating one or more pathogens.

This coating can cover the outer surface of the porous ceramic part, or even the entire surface available in the porosity network. The micro structure of the ceramic foams described above then offers a large contact surface which promotes the chemical inactivation of pathogens.

In a third main embodiment, at least part of the ceramic part is coated with a catalytic coating catalyzing a reaction of at least one atmospheric pollutant, preferably chosen from nitrogen oxides (NOx), nitrogen oxides. sulfur (SOx) and similar volatile organic compounds (VOCs).

This coating can cover the exterior surface of the porous ceramic part, or even the entire surface available in the porosity network. The micro structure of the ceramic foams described above then offers a large contact surface which favors the elimination of atmospheric pollutants. Of course, the characteristics of the various main embodiments can be combined.

The invention also relates to an air treatment method, and in particular to an air decontamination method, by means of an air treatment apparatus according to the invention, the method comprising contacting the air. air with the ceramic part of the air handling unit.

Preferably, the method comprises, after said bringing into contact, an operation of cleaning and / or purification of the ceramic part. This operation can in particular be mechanical, for example by washing, chemical or thermal.

Preferably, the method comprises the following steps: a) treating a first quantity of air by means of the air treatment apparatus according to the invention; b) cleaning and / or purification of the ceramic part of said air treatment device, then resumption of step a) to treat a second quantity of air.

The treated air is preferably extracted from a home, office or passenger compartment of a vehicle, for example a car, train, aircraft, truck or vehicle. 'a boat, or a closed public place.

Definitions

By "decontaminate" is meant to deactivate, preferably eliminate, one or more human pathogens transmissible by the respiratory route and contained in the air.

Any non-metallic and non-organic material is referred to as “ceramic”.

The term “catalytic coating” means a coating comprising or consisting of a catalyst material capable of catalyzing a chemical reaction.

The term “sintering” is conventionally called the consolidation by heat treatment at more than 1100 ° C, of a preform, possibly with a partial or total melting of some of its constituents (but not all of its constituents, so that the preform is not transformed into a liquid mass).

By “recrystallized silicon carbide” is meant recrystallized silicon carbide by high temperature treatment of the ceramic part, and in particular of the foam. ceramic. Recrystallization is a well-known phenomenon corresponding to a consolidation by sublimation of the smallest grains of silicon carbide then condensation to form the bond with the larger grains.

Unless otherwise specified, the term "pores" refers to all pores.

The pore size can, for example, be determined using a mercury porosimeter.

Applying Washburn's law mentioned in ISO 15901-1.2005 part 1, a mercury porosimeter is used to establish a pore size distribution by volume.

The pore size can alternatively be determined by tomography.

A bimodal pore size distribution has two main peaks, i.e. which have the highest peaks.

In a ceramic foam manufactured according to EP 1 778 601, an analysis using a mercury porosimeter makes it possible to demonstrate a bimodal pore size distribution, that is to say having first and second peaks. main distinct. These peaks are representative of the two families of pores, namely the intergranular pores and the interconnecting pores, and the median pore size of each of the families is considered to be given by the pore size corresponding to the top of each peak.

The pore size distribution can also be shown cumulatively, with the pore sizes listed in ascending order. Each pore size is thus associated with a percentile which corresponds, on the cumulative distribution curve, to the percentage of the volume of the porosity which consists of pores having a size smaller than said size.

The 50 percentile, or D50, is therefore the median size of a population of pores. This size divides, by volume, said population into two groups: a group representing 50% of the pore volume and whose pores have a size less than the median size and another group representing 50% of the pore volume and whose pores have a size greater than or equal to said median size.

The D10 and D90 percentiles of the pore population are therefore the pore sizes corresponding respectively to the percentages of 10% and 90% on the cumulative distribution curve of pore size distribution classified in ascending order. The total porosity, in percentage, is conventionally equal to 100 x (1 - the ratio of the geometric density divided by the absolute density).

The geometric density is measured according to standard ISO 5016: 1997 or EN 1094-4 and expressed in g / cm ³ . It is conventionally equal to the ratio of the mass of the sample divided by the apparent volume.

The absolute density value, expressed in g / cm ³ , is conventionally measured by dividing the mass of a sample by the volume of this ground sample so as to substantially eliminate the porosity.

We call "open porosity" the porosity attributable to all the accessible pores. Open porosity can be measured according to ISO15901-1.

Tortuosity is measured by nanotomography. The images have a resolution suitable for binarization. The use of software such as iMorph © makes it possible to obtain a three-dimensional geometric characterization and to calculate the tortuosity. Tortuosity is defined as the ratio between the length of the shortest path making it possible to cross the sample in the direction of its thickness, within its porosity, and the length of the line segment joining the starting point and the point of 'finish corresponding to this route, that is to say the distance between these points.

"Understand", "include" and "present" should be interpreted broadly and without limitation, unless otherwise indicated.

Brief description of the figures

Other features and advantages of the invention will become apparent on examination of the drawing, provided by way of illustration and not by way of limitation, in which:

- [Lig 1] FIG. 1 shows, at a first magnification, an image obtained with a Scanning Electron Microscope on samples taken at 10 to 20 mm from the surface of a ceramic foam of a treatment apparatus according to the invention ;

- [Lig 2] FIG. 2 shows, at a second magnification, an image obtained with a Scanning Electron Microscope on samples taken at 10 to 20 mm from the surface of a ceramic foam of a treatment apparatus according to the invention ; - [Fig 3] FIG. 3 shows, at a third magnification, an image obtained with a Scanning Electron Microscope on samples taken at 10 to 20 mm from the surface of a ceramic foam of a treatment apparatus according to the invention ;

- [Fig 4] Figure 4 shows schematically a ceramic part with variable porosity;

- [Fig 5] Figure 5 shows schematically an example of an air treatment device according to the invention.

In the various figures, identical references are used to designate identical or similar objects.

detailed description

An air treatment apparatus according to the invention may be intended for the decontamination of ambient air intended to be inhaled by a person. The air is typically at a temperature between 0 ° and 30 ° C, generally between 15 ° C and 25 ° C. Its pressure is atmospheric pressure.

The treatment apparatus comprises a ceramic part whose shape is suitable for the intended application. The forming processes by band casting, in English "tape casting", or by foaming are particularly suited to the production of preforms of complex shapes, which makes it possible to avoid / limit the machining steps.

In particular in one embodiment corresponding to the individual protections, the ceramic part may have the shape of a flat part, for example of a pellet, preferably having, seen from the front, a surface greater than 5 cm ² and / or less. to 100 cm ² , preferably less than 50 cm ² .

Preferably, the ceramic part according to the invention has, in particular in this embodiment:

- a thickness between 1 and 20 mm, preferably greater than 2 mm, or even greater than 3 mm and / or less than 15 mm, 10 mm, or 8 mm, and / or

- a length and / or a width greater than 1 cm or 3 cm and / or less than 10 cm, 8 cm, or 5 cm.

In another embodiment, the ceramic part may in particular have the shape of a flat or tubular part. Preferably, the ceramic part according to the invention has, in particular in this embodiment:

- a thickness between 2 mm and 100 mm, preferably greater than 5 mm, or even greater than 10 mm and / or less than 90 mm, 80 mm, 70 mm, and / or

- a length and / or a width greater than 1 cm, 5 cm, 10 cm and / or less than 100 cm, 80 cm, 50 cm, 30 cm.

The ceramic part is preferably removable from the treatment apparatus, in particular with a view to its cleaning and / or its purification.

The ceramic part is made of a sintered material.

All the processes for making a sintered part are possible, provided that the porosity is adapted. This adaptation can in particular consist of adding a pore-forming agent to the starting charge.

The ceramic part may in particular consist of silicon carbide or cordierite or titanium oxide T1O2 or of suboxides T1O2- _X where x is greater than 1 and less than 2, preferably between 1.4 and 1 , 9, preferably between 1.5 and 1.9, or of aluminum or zirconia or alumina or mullite or silica titanate or mixtures thereof.

According to one variant, the ceramic part comprises more than 80% by mass of silicon carbide (SiC), or even more than 90% of silicon carbide, or even more than 95% of silicon carbide, or even consists essentially of silicon carbide. . According to one possible embodiment, the silicon carbide can be doped with one or more elements chosen from nitrogen (N), gallium (Ga), phosphorus (P), boron (B), l aluminum (Al), beryllium (Be) and mixtures thereof.

According to a preferred variant, the silicon carbide is recrystallized silicon carbide, in particular in alpha form.

According to another variant, the ceramic part consists, in percentage by mass on the basis of the crystallized phases, from 25 to 55% of mullite (3AI ₂ O ₃ -2S1O ₂ ), 20 to 65% of corundum (Al ₂ O ₃ under alpha crystalline form), 10 to 40% zirconia (Z1Ό2), mullite, corundum and zirconia together representing more than 80%, preferably more than 90%, preferably more than 95%, preferably more than 98% of the mass of the crystallized phases. The following description is given with reference to an application to an electrical appliance of the air conditioner type. This application is not, however, limiting. In particular, the device can be personal protective equipment such as a mask.

First main embodiment: filtration

Preferably, as shown in FIG. 5, the treatment apparatus 1 comprises a ceramic part 2 and a circulator 3 making it possible to circulate contaminated and / or polluted air A, preferably at a temperature below 30 ° C. , at 25 ° C and / or above 10 ° C, preferably above 15 ° C, through the ceramic part 2.

The apparatus may also optionally include a heat exchanger, not shown, to change the air temperature, and / or a humidifier, not shown, to change the humidity of the air.

Conventionally, the circulator can include, for example, a pump and a set of pipes. It is optional. For example, for a breathing mask, no circulator is needed, the circulation resulting from inspiration by the wearer of the mask.

The ceramic part has a high total porosity in order to allow passage of the filter with a reduced pressure drop. The porosity must however be fine enough to provide a filtration function suitable for the particles targeted. But the ceramic part should not clog up too quickly.

Preferably, more than 95%, more than 97%, more than 99% of the total porosity of the product is open.

Porous ceramic foams, which have a low density (5 to 50% of the theoretical density), have proved to be remarkably well suited.

They can be made from the vast majority of ceramic powders, in particular alumina or silicon carbide.

The ceramic foams based on recrystallized silicon carbide described in EP 1 778 601 have particularly high available surfaces or, for an equivalent available surface area, a lower density. Recrystallized silicon carbide is particularly advantageous because it makes it possible to obtain parts having a specific microstructure. Figures 1 to 3 illustrate the specific micro structure of a recrystallized silicon carbide foam.

The walls of recrystallized silicon carbide delimiting the cells 10 are formed by agglomeration of grains 18, this agglomeration leaving interstices 20, or “intergranular pores” between the grains 18.

The walls thus have a so-called “intergranular” porosity. The intergranular porosity is therefore made up of the interstitial spaces that the agglomeration of these grains necessarily creates between the grains.

The cells 10 are interconnected by interconnection windows 12. Surface cells open out through openings 16 to the outside. Interconnecting porosity is created by "cell pores", namely the interconnecting windows 12 between cells 10 and openings 16 to the exterior of surface cells.

In the particular case of recrystallized silicon carbide foams, the intergranular porosity thus coexists with the interconnection porosity.

In the example shown in Figures 1 to 3, we observe the presence of cell pores and smaller intergranular pores.

The intergranular porosity is a function of the grain size of the ceramic powder, in particular of silicon carbide, used.

The interconnection porosity is a function of the foaming agent used, in particular its quantity in the starting charge which is shaped to constitute the preform.

The presence of intergranular porosity in fact confers both a very large available surface area and a low density.

Intergranular porosity foams are therefore effective for filtration and / or as a support for an inactivating coating of one or more pathogens, and / or as a catalyst support, while being lightweight.

Preferably: the median size of intergranular pores is 10 to 100 times smaller than that of cellular pores; and / or the intergranular porosity is at least 5%, preferably at least 8%, more preferably at least 10% and / or less than 25%, or even less than 20%; and / or the median size of the cellular pores is less than 400 μm, or even less than 300 μm, or even less than 200 μm, or even less than 180 μm, or even less than 160 μm and greater than 40 μm, or even greater than 50 μm, or even greater than 80 μm; and / or the median size of the intergranular pores is less than 25 μm, or even less than 20 μm and greater than 4 μm, or even greater than 7 μm; and / or the pore size distribution is bimodal; and / or the total porosity is greater than 55%, or even greater than 60%, or even greater than 70%.

Such foams can in particular be manufactured according to the following successive steps: a) preparation of a mixture M containing a ceramic powder in suspension, at least one gelling agent and at least one foaming agent, at a mixing temperature above the temperature of gelation of said gelling agent, b) shearing of said mixture M at a foaming temperature above said gelation temperature, until an intermediate foam is obtained, c) gelation of said intermediate foam by cooling said intermediate foam to a lower temperature at the gelling temperature of said gelling agent, d) drying of said gelled foam so as to obtain a preform whose humidity after drying is preferably less than 1%, e) curing by high temperature treatment of said preform so as to obtain a porous ceramic foam.

EP 1 778 601 provides further details on steps a) to e).

For an application to an air treatment, the inventors have however improved these steps with the following preferred characteristics: In step b), the shearing time is preferably greater than 25 min, so as to incorporate sufficient air to achieve the desired percentage of porosity.

In step a), a stabilizer can be added, as described in EP 1 778 601, but the presence of a stabilizer is optional. Preferably, the mixture M does not contain a stabilizing agent and the gelation and drying conditions are suitable to allow structural stabilization of the foam:

In step c), the gelation is preferably carried out at a temperature, in ° C, at least 2 times, even at least 3 times or even at least five times lower than the gelation temperature of the gelling agent, in ° C. More preferably, the intermediate foam obtained at the end of step b) is suddenly cooled (quenching) to this temperature, preferably at a cooling rate greater than 20 ° C / minute, preferably greater than 30 ° C / minute. Preferably, the intermediate foam is cooled immediately after the end of step b), preferably less than 5 minutes after the end of step b). For this purpose, the intermediate foam is preferably installed in a climatic oven.

In step d), the intermediate foam is preferably dried in two successive operations.

The first drying operation is to gradually increase the temperature while keeping it below the gelation temperature, preferably in a climatic oven, preferably in the climatic oven used for gelation. In a climatic oven, temperature and humidity are regulated, preferably until the interior of the oven is saturated with humidity, and forced ventilation allows the water to be extracted. The temperature is preferably increased as the residual moisture of the gel foam decreases, without exceeding the gel temperature. The temperature is preferably increased for a period greater than 1 hour, preferably greater than 24 h, 48 h, 72 h, 96 h, 120 h, and / or less than 1 week. It can be increased step by step or gradually, preferably step by step.

This first drying operation is preferably continued until the residual humidity of the gelled foam reaches an intermediate value, preferably greater than 70% of the initial humidity and / or less than 95%, preferably less than 90% of the initial humidity. Preferably, the first drying operation is continued until that the residual humidity of the gelled foam is less than 10%, preferably less than 5%, and / or greater than 2%, preferably greater than 3% or 4%.

The second drying operation preferably comprises drying at a temperature above 40 ° C, at 50 ° C, at 60 ° C, at 80 ° C or at 100 ° C, preferably until the residual humidity is reduced to less than 1%.

These preferred conditions advantageously make it possible to set the structure of the foam, even in the absence of a stabilizing agent, which facilitates the control of this structure and makes it possible in particular to limit the size of the pores, in particular so that the pores of size greater than 300 μm represent less than 10% by volume of the porosity. They also have the advantage of being easy to implement, even industrially.

Finally, they prevent sagging of the foam, even in the absence of a stabilizing agent, which makes it possible to manufacture a ceramic foam having a great thickness, for example greater than 60 mm or greater than 80 mm.

The invention thus relates to a process for manufacturing a ceramic foam comprising steps a) to e), in which step d) comprises a so-called first drying operation, preferably in a climatic oven.

Generally, one skilled in the art knows how to modify the pore size distribution, in particular by modifying the rheology and the shear.

In particular, he knows how to increase the total porosity, and in particular the cell porosity, by increasing the quantity of air in the foam, for example by increasing the duration and / or the speed of shearing.

He also knows that the intergranular porosity can be increased by increasing the particle size of the ceramic powder.

According to a particular embodiment, the ceramic part, and in particular the ceramic foam, has a lower total porosity on the side of the air to be decontaminated.

In particular, as shown in Figure 4, it may include a porous body 25 and one or more surface layers 26-27 superimposed from the surface of the porous body, the total porosity and / or the median pore size of the surface layers. being different, preferably less than the total porosity at the barycenter C of the porous body. In a particularly advantageous embodiment, the total porosity of the surface layer is less than 0.95, 0.90 or 0.8 times the total porosity at the barycenter of the porous body.

Preferably, the total porosity of the surface layer is greater than 30%, or even greater than 35% and preferably less than 70%, or even less than 60%, or even less than 50%.

Preferably, the pores of the surface layer have a median size greater than 1 μm, or even greater than 2 μm, or even greater than 3 μm and less than 20 μm, or even less than 10 μm, or even less than 5 μm.

The thickness of the surface layer is preferably between 5 and 500 μm, preferably greater than 10 μm and / or less than 400 μm, or even less than 200 μm, or even less than 100 μm.

In one embodiment, the ceramic part has a plurality of said superimposed surface layers from the surface of the porous body, the superimposed superficial ceramic layers having respective total porosities and / or different median pore sizes.

According to one variant, the surface layer (s) can be spaced from the porous body.

In one embodiment, the total porosity and / or the median size of the pores is all the lower the further the surface layer is from the porous body 25. There is thus a gradient of total porosity, the total porosity and the median size. of the layer defining the inlet face 30 of the air to be filtered being lower than those of the other layer (s).

Preferably, the total porosity of a surface layer, preferably of each surface layer, is greater than 30%, or even greater than 35% and preferably less than 70%, or even less than 60%, or even less than 50%.

Preferably, the pores of a surface layer, preferably of each surface layer have a median size greater than 1 μm, or even greater than 2 μm, or even greater than 3 μm and less than 20 μm, or even less than 10 μm, or even less than 5 pm. The thickness of a surface layer, preferably of all the surface layers is preferably between 5 and 500 μm, preferably greater than 10 μm and / or less than 400 μm, or even less than 200 μm, or even less at 100 pm.

The different layers can result from the juxtaposition of different individual ceramic pieces or from the projection of an adherent coating on the surface of the porous body or from the impregnation of a part of the porous body in order to locally modify the porosity. .

In particular when the ceramic part is a ceramic foam of recrystallized silicon carbide, a said surface layer can be obtained by impregnating part of the thickness of the preform with a slip based on silicon carbide. The slip may optionally include pore-forming agents such as a foaming agent. The slip then at least partially fills the pores. After sintering, it thus leads to a so-called surface layer.

Preferably, the impregnated portion extends from the inlet face 30 of the air to be filtered.

Variable porosity depending on the depth advantageously makes it possible to mechanically trap particles of different sizes, and therefore to broaden the spectrum of possible applications.

According to an advantageous variant, whatever the type of ceramic part, the ceramic part is devoid of a coating. It then acts as a pure filter.

Second main embodiment: decontamination

In one embodiment, at least a portion of the exterior surface and / or the porous network-defined surface of the ceramic part is coated with a coating for inactivating one or more pathogens.

The inactivation coating is suitable for the pathogens to be inactivated.

In particular, the inactivation coating can be a coating eliminating one or more pathogens, for example bactericidal and / or virucidal. The inactivation coating may in particular consist of nanoparticles, in particular based on silver and / or copper.

The inactivation coating can be deposited by impregnation directly into the porous structure. In particular, in the case of a ceramic foam, the coating inactivation can be deposited by impregnation directly on the walls of the porous network of the foam.

An inactivating coating is particularly useful if the micro structure of the ceramic part is not sufficient to prevent pathogens from passing through the ceramic part. Simple tests can verify if this situation occurs.

The very porous microstructure, and in particular the micro structure of a ceramic foam, advantageously offers a very large exchange surface with the inactivation coating.

Third main embodiment: pollution control

In one embodiment, at least part of the surface defined by the porous network is coated with a catalytic coating suitable for removing at least one atmospheric pollutant chosen from nitrogen oxides (NOx), oxides sulfur (SOx), similar volatile organic compounds (VOCs).

All coatings used in gas abatement applications can be used for the ceramic part. The ceramic part can in particular be provided with a catalytic coating allowing the elimination of nitrogen oxides and / or sulfur oxides. The coating can in particular be based on platinum.

The coating can be deposited on one of the outer faces of the ceramic part, preferably the air inlet face to be filtered.

The very porous microstructure, and in particular the micro structure of a ceramic foam, advantageously offers a very large exchange surface with the catalytic coating.

Cleaning, purification

Whatever the embodiment, the ceramic part offers excellent mechanical resistance to compression and allows a wide variety of shapes.

Advantageously, the ceramic part can be cleaned and / or purified in order to be reused. Cleaning involves removing unwanted material that has accumulated in the pores. Purification consists of inactivating pathogens accumulated in the pores.

The refractoriness, chemical stability and mechanical strength of ceramic materials, in particular silicon carbide, make it possible in particular to subject the ceramic part, or even the air treatment apparatus according to the invention, to a continuous heat treatment. or punctual (especially when it comes to personal protective equipment such as a mask), to eliminate pathogens, and in particular viruses and bacteria, sensitive to heat.

The duration of the heat treatment is adapted to the pathogens and the temperature applied.

Heat treatments at higher temperatures can also be used to burn off the filtered particles and thus clean the filter.

Cleaning and / or purification can also result from a chemical action, for example bactericidal or virucidal. For example, the ceramic part can be immersed in a bactericidal or virucidal bath.

Cleaning or purification can also result from a mechanical action, for example by washing the ceramic part, for example by putting it in the dishwasher.

The treatment apparatus may optionally include a pressure drop detector 32 and an electronic unit 34 for controlling the pressure drop detector 32.

The pressure drop detector 32 may for example be a Pitot tube, with a capillary integrated into the glass or metal capsule.

The pressure drop detector 32 and the electronic unit make it possible to assess the level of contamination continuously or on an ad hoc basis and to inform an operator accordingly, for example by means of a screen.

Preferably, the treatment apparatus further comprises a cleaning and / or purification tool 36. In a preferred embodiment, the ceramic part is disassembled and subjected to this tool.

Preferably, this tool, for example a heating resistor, is integrated into the treatment apparatus, for example fixed in contact with the ceramic part. Preferably, it is controlled by the electronic unit 34, preferably as a function of information received from the pressure drop detector. The electronic unit 34 can thus trigger an operation for cleaning or purifying the ceramic part at regular time intervals and / or according to the information supplied by the pressure drop detector 32. The processing apparatus may optionally comprise a computer memory 38 in which is recorded information relating to the ceramic part, for example an identifier or a photo showing its state at a time.

Such a memory, for example of the RFID chip type, advantageously makes it possible to facilitate traceability.

Functioning

The operation follows directly from the above description.

Initially, a photo of the microstructure of the ceramic part is taken and saved in computer memory 38.

The circulator 3, supplied with energy for example by the electrical network, sucks in polluted and / or contaminated A air and circulates it through the ceramic part 2. The contaminated particles and the polluting particles are retained by the porous sintered microstructure .

The variation in porosity per layer, and in particular the presence of surface layers 26 and 27, advantageously allows filtration of a wide range of particles.

Particles, but also polluting gases in the air, also come into contact with the activation coating and with the catalytic coating. Contact with the inactivating coating causes inactivation, and preferably destruction of pathogens. Contact with the catalytic coating causes a chemical reaction to destroy certain polluting gases. Filtration helps ensure prolonged air contact with the coatings. The action of destroying pathogens and / or pathogens is therefore very effective.

The treated air T exits the treatment unit under the effect of the pressure exerted by the circulator.

After a certain period of use, or on the instruction of an operator, or following the detection of a clogging by the pressure drop detector 32, the electronic unit 34 controls the heating resistor 36 so as to destroy the agents. pathogens and / or remove accumulated material.

Destruction of pathogens can thus result from contact with the inactivating coating and / or heating. In some applications, the inactivation coating is therefore optional. After cleaning and / or purification, the ceramic part 2 can be reused.

At any time, the micro structure of the ceramic part can be compared to the photo recorded in the computer memory 38.

Examples of realization

The following examples are provided for illustrative purposes only. They are not limiting and make it possible to better understand the technical advantages associated with the implementation of the present invention.

The proportions of the silicon carbide powders and the additives used to make the foamy mixtures are provided in Table 1 below. SiCi, S1C2, and SiC 3 denote the mass percentages of the three silicon carbide powders used, on the basis of the mineral material. The percentages of the additives are given on the basis of the mass of the mineral material (SiC).

The ceramic foam of Example 1 was made from the teaching of WO2006018536A1, in particular from Examples 21 to 23.

In this example, the aqueous premix B comprising gelatin, foaming agent, glycerin and hardener diluted in 58% deionized water was heated in a water bath at 55 ° C.

The aqueous phase slip A comprising the mineral SiC powders, the mass load of which is 80% and the pH of which has been adjusted by adding sodium hydroxide to 10.5 was added to the premix B.

After constant mechanical stirring for 28 minutes (step b)), the intermediate foam obtained was poured, at room temperature (20 ° C), into a mold making it possible to manufacture a preform of dimensions 600mm x 400mm x 65mm.

After casting, the mold was placed in a climatic oven under forced ventilation.

The temperature in the oven was lowered to 5 ° C to gel the intermediate foam (step c)).

Then the gelled foam obtained was dried (step d)), in the climatic oven, according to the following cycle (first drying operation):

5 ° C for 24 h without humidity regulation; 15 ° C for 72 h at 80% humidity;

20 ° C for 24 hours at 80% humidity;

25 ° C at 80% humidity until at least 90% humidity loss is reached.

The mold was then placed in a drying oven according to the following cycle (second drying operation): rise at 25 ° C / h up to 100 ° C; hold for 4 h at 100 ° C; free descent up to 20 ° C.

After demoulding, the preform resulting from drying was baked at 2240 ° C for 3 hours under Argon to obtain a sheet of recrystallized silicon carbide foam (step e))

The ceramic foam of Example 2 was made by the same process as the foam of Example 1, but mechanical agitation during the foaming step was carried out for 20 minutes. The foam of Example 2 therefore incorporates less air.

The ceramic foam of Example 3 was made according to the same process as the foam of Example 2 but, after pouring the foamy mixture, the mold was placed in a study at 15 ° C without ventilation. The foam temperature of approximately 15 ° C was reached between 12 and 24 hours.

Foams exhibit the classic cellular or "honeycomb" structure of foams. In particular, they exhibit a structure in which the cells are dispersed substantially randomly in the three dimensions of space.

In addition, the diameter of the cells is in the order of a hundred micrometers. These cells are therefore quite different from the canals of honeycomb structures, which typically have a cross section whose equivalent diameter reaches several millimeters.

Typically, foams finally exhibit high macropore connectivity and high specific surface area, which leads to high permeability.

The cells each define a volume of generally spherical shape because they are formed by the agglomeration of ceramic grains around air bubbles.

The foam of each example was characterized as follows: The volume and the pore size were measured according to the ISO 15901-1.2005 standard using an Autopore IV porosimeter 9500 series Micromeritics, by intrusion of Mercury, up to

2 bar, in a sample of about 1 cm ³ taken from the heart of the foam plate.

The pore size distribution curve shows two main peaks centered on the first and second pore sizes, shown in Table 1. The area of the ^1st peak corresponds to the volume of intergranular pores of the walls delimiting the cells of the foam. .

The pressure drop was measured at a temperature of 20 ° C and under a dry air flow of 60 liters / minute, on average on 5 pellets 36 mm in diameter and 4 mm in height taken from the heart of each plate. mousse. The lower the pressure drop, the better the performance.

The equibiaxial flexural strength was measured according to standard ASTM C 14992009, on average on 5 pellets 36 mm in diameter and 4 mm in height taken from the heart of each foam plate. The higher the mechanical strength, the better the performance. The filtration efficiency was evaluated with regard to standard NF-EN 14683. A test with an aerosol of water inoculated with bacteria (Staphylococcus aureus), the average size of which is

3 µm has been used in accordance with practice for surgical masks. The higher the filtration rate, the better the performance.

Table 1

D5 _O = median size

An example is considered to be particularly well suited to the intended application if it presents

- a pressure drop of less than 10 mbar;

- an equibiaxial flexural strength greater than 6 MPa; and

- filtration efficiency greater than 95%.

The results indicate that Examples 1 and 2 are particularly suitable for the intended application. In particular, they exhibit very good filtration efficiency and mechanical strength. Example 1 also shows a very low pressure drop. Example 3 is not preferred due to a high pressure drop.

Without being limited by this theory, the inventors explain the remarkable performance of ceramic foams according to the invention, by the very specific structure of the foam. The interconnection windows between the cells make it possible to create tortuous channels through the foam. These tortuous channels reduce the pressure drop and yet are effective at filtering out particles much smaller than their cross sections. Filtration does not therefore necessarily result from a blockage of the particles when they are pushed by the air flow through pores of smaller dimensions, as in the filters of conventional sintered material used, for example, to filter gases. exhaust. The shape of the tortuous channels would explain the efficiency of the filtration.

Surprisingly, and without being able to explain it in a theoretical way, the excellent performances of Examples 1 and 2 are also associated with a specific pore size distribution, and in particular with:

a limited number of large cells, and in particular at a D90 of less than 250 μm, preferably less than 200 μm;

a low (D9O-DIO) / DSO, or “span” ratio, preferably less than 1.5; - a low median size D50, less than 150 mhi.

The sintered ceramic foams according to the invention thus offer both remarkable filtration efficiency, but also a very low pressure drop. This compromise makes it possible to limit the energy required to circulate the air through the ceramic part, and therefore to limit the consumption of the circulator. It also allows the ceramic part to be used in applications where air circulation results from a simple inhalation, for example in a personal breathing mask.

As is now clear, the invention makes it possible to optimize air treatment, in particular the air in confined living spaces such as homes, offices and vehicle interiors.

In particular, a treatment apparatus according to the invention allows both the filtration of particles efficiently and with a low pressure drop, the activation of pathogens and the elimination of polluting organic substances. The ceramic part used is advantageously reusable, even imperishable, and recyclable. Of course, the invention is not, however, limited to the embodiments described, provided for illustrative purposes only.

In particular, any treatment device, whether or not comprising a circulator, is envisaged. A passive treatment device, that is to say not powered by a power source, for example a personal breathing mask filtering the air inhaled by a person is considered to be a treatment device.

Claims

1. Device for treating air, at room temperature, in a confined living space, said device comprising:

- a sintered ceramic part (2) having a total porosity greater than 40%, the pores of size greater than 300 μm representing less than 10% by volume of said porosity,

- an air circulator (3) configured to generate an air flow to be treated through the ceramic part, the ceramic part being a ceramic foam having a plurality of nested cells, delimited by ceramic walls and connected to one another by means of interconnection windows, the walls delimiting the cells being formed by agglomeration of grains, this agglomeration leaving interstices between the grains.

2. Apparatus according to the preceding claim, wherein the pores of the ceramic part having a size greater than 300 μm represent less than 5% by volume of said porosity.

3. Apparatus according to any preceding claim, wherein the median pore size is less than 150 µm.

Apparatus according to any preceding claim, wherein the ceramic piece has a pore size distribution, measured with a mercury porosimeter, which is bimodal and which has first and second major peaks centered on first and second major peaks. second pore sizes between 4 and 25 µm and between 40 and 180 µm, respectively, the intergranular porosity, represented by the first peak, being greater than or equal to 5% and less than 25%.

5. Apparatus according to the immediately preceding claim, wherein:

- said second pore size is greater than 50 μm and / or less than 160 μm, and / or

- Said first pore size is greater than 7 μm and less than 20 μm.

6. Apparatus according to any preceding claim, wherein the ceramic part has a tortuosity greater than 1 and less than 2.

7. Apparatus according to any preceding claim, wherein, on the cumulative distribution curve of pore sizes, ranked in ascending order,

- the D90 percentile by volume is less than 250 pm, and / or

- the D50 percentile by volume is greater than 40 pm and / or less than 140 pm.

8. Apparatus according to the immediately preceding claim, wherein

- the D90 percentile by volume is less than 200 pm, and / or

- the D50 percentile by volume is less than 130 pm.

9. Apparatus according to any preceding claim, wherein the sintered ceramic part (2) has a total porosity greater than 55% and less than 80%.

10. Apparatus according to any preceding claim, wherein the ceramic part consists of silicon carbide or cordierite or aluminum titanate or zirconia or alumina or mullite or silica or mixtures thereof.

11. Apparatus according to any preceding claim, wherein the ceramic part has:

- more than 80% by mass of recrystallized silicon carbide, and / or

- an open porosity which represents more than 98% of the total porosity, and / or

- an intergranular porosity greater than or equal to 10% and less than 20%.

12. Apparatus according to any preceding claim, wherein the ceramic part comprises a surface layer whose pores have a median size greater than 1 µm and less than 20 µm, the total porosity of the surface layer being greater than 30%. and less than 70%, the thickness of the surface layer being between 5 and 500 μm.

13. Apparatus according to the immediately preceding claim, wherein the ceramic part comprises several said surface layers having different respective total porosities.

14. Apparatus according to any preceding claim, wherein

- at least part of the outer surface of the ceramic part and / or of the surface of the porous network of the ceramic part is coated with a coating for inactivating one or more pathogens, and / or at least part of the outer surface of the ceramic part and / or of the surface of the porous network of the ceramic part is coated with a catalytic coating suitable for a reaction of at least one atmospheric pollutant.

15. Apparatus according to any one of the preceding claims, comprising a pressure drop detector (32) and an electronic unit (34) programmed to trigger or inform on the need for a cleaning and / or purification operation depending on the device. information received from the pressure drop detector.

16. Apparatus according to the preceding claim, comprising a cleaning and / or purification tool (36) controlled by the electronic unit as a function of information received from the pressure drop detector.

17. Apparatus according to any preceding claim, comprising a computer memory (38) in which is recorded information relating to the ceramic part.

18. An air treatment method comprising the following steps: a) treatment of a first quantity of air by means of an air treatment apparatus according to any one of the preceding claims; b) cleaning and / or purification of the ceramic part of said air treatment device, then resumption of step a) to treat a second quantity of air, the air being extracted from a dwelling, an office , of a passenger compartment of a vehicle chosen from among a car, a train, an aircraft, a truck and a boat, or of a closed public place.

19. A method of manufacturing an apparatus according to any one of claims 1 to 17, wherein the ceramic foam is produced according to the following successive steps: a) preparation of a mixture M containing a ceramic powder in suspension, at least a gelling agent and at least one foaming agent, the preparation being carried out at a mixing temperature above the gelation temperature of said gelling agent, b) shearing of said mixture M at a foaming temperature above said gelation temperature, up to obtaining an intermediate foam, c) gelation of said intermediate foam by cooling said intermediate foam to a temperature below the gelation temperature of said gelling agent, d) drying of said gelled foam so as to obtain a preform, e) curing by high temperature treatment of said preform so as to obtain a porous ceramic foam, process in which,

- in step a), no stabilizer is added to the mixture M; and or

- in step c), the gelation is carried out at a temperature, in ° C, at least twice lower than the gelation temperature of the gelling agent, in ° C, and / or

- step d) comprises a first drying operation in a climatic oven, without exceeding the gel temperature.