WO2024068668A1

WO2024068668A1 - Plasma treatment device for treating a gas phase and associated method

Info

Publication number: WO2024068668A1
Application number: PCT/EP2023/076601
Authority: WO
Inventors: Béatrice Drazenovic
Original assignee: Prodea Depolluting
Priority date: 2022-09-28
Filing date: 2023-09-26
Publication date: 2024-04-04
Also published as: FR3139997A1

Abstract

The invention relates to a device (1) for treating a gas phase (2), the device comprising an assembly (11) of electrodes comprising an injection electrode and an electrode connected to a ground (12) of the device (1), which electrodes are separated by a separator material, the assembly (11) being configured such that, when a voltage is applied, a plasma (3) is generated between the injection electrode and the electrode connected to the ground, the separator material acting as an electrical insulator when the separator material is subjected to a voltage lower than a threshold voltage, which voltage is referred to as the "priming voltage", and as an electrical conductor for receiving a current when the separator material is subjected to a voltage higher than or equal to the priming voltage. The invention also relates to providing access to two plasma generation modes in order to improve the treatment of the gas phase (2).

Description

“Device for treating a gas phase by plasma and associated process”

TECHNICAL AREA

The present invention relates to the field of devices for non-thermal plasma treatment of a gas phase. Its application is particularly advantageous in the field of air treatment, for example indoor air, and/or polluting emissions, and/or olfactory nuisances.

STATE OF THE ART

It is known that volatile organic compounds (abbreviated as VOCs) have harmful effects on health, for example with irritation of the eyes and mucous membranes, respiratory tract, cardiac and nervous system disorders, headaches, and nausea. Some VOCs are even recognized as carcinogenic and/or toxic for reproduction or mutagenic (compounds known as “CMR” for Carcinogenic-Mutagenic-Reprotoxic).

The risks posed by VOCs have led to numerous regulations, resulting in a complex set of measures to meet standards. These standards aim to reduce VOCs, odors, and ensure satisfactory biological air quality.

Beyond VOCs, other harmful species can have harmful effects on health, the environment or olfactory comfort. This is the case for micro-organisms such as bacteria, viruses, fungi and/or their spores.

There is therefore a need for the development of a system for depollution/decontamination of gas phases likely to include harmful species such as indoor air or polluting discharges from human activity, for example from industry. In recent years, the indoor air purification market has grown with the marketing of equipment displaying indoor air purification properties in the form of stand-alone devices, as well as construction materials and decoration highlighting depolluting properties. There is no certification of indoor air purification devices, and some of them can lead to the formation of compounds potentially more harmful than the VOCs initially present.

Today, for this field, filtration is the most used technique. HEPA filters stop suspended matter, including organic matter. These, fixed on the filters or having sedimented in the conduits of the filtration systems, are however a favored place for the growth of micro-organisms. In addition, nanometric-sized viruses are not captured by these filters.

Non-thermal plasma technology (so-called “cold” plasma) has many advantages: it is an electrical and non-chemical technology, without consumables, non-selective, compact and modular (capable of treating flow rates ranging from a few cm ³ /h to tens of thousands of m ³ /h). Cold plasma treatments are effective on a multitude of pollutants, VOCs but also microorganisms. In fact, cold plasma destroys the DNA of these microorganisms regardless of size and is therefore effective on these pathogenic elements. It should be noted that this technology is very suitable for highly diluted pollution (low concentrations of pollutants), which makes it a technology of choice for the treatment of odors (low concentrations but high nuisances).

Conventional cold plasma treatments, for example generated by dielectric barrier discharge (abbreviated DBD), are energy intensive and generate harmful compounds such as ozone, degradation by-products of the treated pollutants.

Document US 2005/0118079 A1 describes a device for gas purification using surface electrodes comprising photocatalysts in order to improve the efficiency of a non-thermal plasma. ANSES (National Agency for Food, Environmental and Occupational Health Safety) in France, however, advises against the use of physico-chemical air treatments because of their effectiveness, particularly with regard to viruses. , is not proven. Following sometimes incomplete degradation of pollutants, they can also negatively impact indoor air quality through the formation of compounds potentially dangerous to health, including CMR chemical agents.

Document FR2918293 A1 describes a gas treatment unit comprising electrodes separated by layers of photocatalyst.

Document EP2762170 A1 describes a gas treatment device combining the activity of a photocatalyst and a cold surface plasma.

Document US 2020/0398245 A1, a plasma reactor for the conversion of hydrogen sulfide, comprising an internal electrode, an external electrode, and a dielectric barrier between the electrodes. An object of the present invention is therefore to propose a device improving the treatment of a gas phase by plasma, in particular by cold plasma, and in particular that of air. The other objects, characteristics and advantages of the present invention will appear on examination of the following description and its accompanying drawings. It is understood that other benefits may be incorporated.

SUMMARY

To achieve this objective, according to one aspect, a device for treating a gas phase is provided comprising at least one assembly of electrodes comprising at least one so-called injection electrode and at least one other electrode connected to the ground of the device, separated by a material called “separator material”, the assembly being configured so that, under the application of an electric voltage, a plasma is generated between the at least one injection electrode and the at least one electrode connected to ground.

The separator material exhibits electrically insulating behavior when it is subjected to an electrical voltage lower than a threshold voltage, called "start-up voltage", and electrically conductive behavior allowing the passage of a current when the separator material is subjected to an electrical voltage greater than or equal to the ignition voltage.

The separator material thus allows access to two plasma generation regimes: a homogeneous regime (electric discharges generated when the material behaves like an insulator) and an erratic regime, also called energy regime (electric discharges generated when the behavior of the material is conductive), which corresponds to a multi-filamentary energetic regime. These two regimes can appear simultaneously or successively.

Erratic RPM does not exist in conventional DBD devices. This regime, in conjunction with the homogeneous regime, makes it possible to perfect the cold plasma treatment by improving the degradation of the treated compounds and limiting residual harmful degradation by-products. This also makes it possible to degrade a wider range of pollutants than with a conventional DBD device.

The synergy between these two regimes allows more efficient electrical discharges, which improves the efficiency and speed of treatment of the gas phase. The device can thus be made more compact and of simplified design.

The treatment of the gas phase is thus improved by the joint application of these two plasma regimes on the gas phase flowing in the device. In addition, the use of catalyst is avoided, which simplifies the device and its maintenance.

Furthermore, during the development of the invention, it was demonstrated that this type of separator material made it possible to lower the value of the electrical voltage to be applied to generate the plasma. The cost, particularly energy, of treating a gas phase is thus lowered. The safety of use of the device is also improved.

Another aspect concerns a process for treating a gas phase using the device according to the first aspect, and comprising:

- the introduction of the gas phase into the at least one assembly of electrodes, - applying an electrical voltage to the assembly so as to generate a plasma between the at least one injection electrode and the at least one electrode connected to ground to treat the gas phase.

The method has the effects and advantages described in relation to the device according to the first aspect.

In addition, since plasma discharges are more efficient, the treatment time of the gas phase can be reduced compared to treatment by a conventional DBD device. This is particularly advantageous for the removal of viruses which generally requires more energy (and more time) than that of VOCs.

BRIEF DESCRIPTION OF THE FIGURES

The aims, objects, as well as the characteristics and advantages of the invention will emerge better from the detailed description of an embodiment of the latter which is illustrated by the following accompanying drawings in which:

Figure 1 represents an overview of the device and its operating principle, according to an exemplary embodiment.

Figure 2 represents a diagram of the electrical circuit for studying the electrical behavior of the separator material, according to an example.

Figure 3 schematically represents the electrical behaviors of the separator material according to several exemplary embodiments, in comparison with an insulator of a DBD device.

Figures 4 to 6 represent different electrode geometries in an assembly, according to several embodiment examples.

Figures 7 to 9 represent different assembly arrangements, according to several embodiment examples.

Figures 10A and 10B represent two graphs showing the percentage of degradation of VOC, respectively ethylene and isopropanol, as a function of the voltage applied to an assembly to generate the cold plasma, in comparison to two assemblies of DBD devices of the state of the art.

The drawings are given as examples and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the relative dimensions between the VOCs, the electrodes and the device are not representative of reality.

DETAILED DESCRIPTION

Before beginning a detailed review of embodiments of the invention, optional characteristics are set out below which may possibly be used in combination or alternatively.

According to one example, the ignition voltage is between 1 kV and 10 kV, preferably between 3 kV and 6 kV. These breakdown voltage parameters are taken for a 50 Hz AC type signal and for a tip/tip electrode geometry on the surface of the separator material, for a gap of between 5 and 15 mm. According to one example, the separator material is chosen from the group consisting of: a semiconductor material, for example a semiconductor ceramic, a semiconductor polymer, a composite material comprising conductive or semiconductor particles dispersed in a matrix . It must, however, have dielectric properties with an insulator/conductor transition for the operating voltage range selected. The insulating phase also has the charge trapping/untrapping characteristics required to enable the energy regime. When the separator material is a composite material comprising conductive or semiconductor particles dispersed in a matrix, the separator material offers a variety of choices in the nature of the particles and the matrix making it possible to obtain the two plasma generation regimes. This gives more flexibility in the nature of the material compared to a homogeneous material, and in particular to modulate the thermal, mechanical and electrical properties. This is completely different from the materials of existing solutions, which on the one hand do not aim to achieve these two regimes, and on the other hand are homogeneous materials formed from a single phase or multilayer assemblies of homogeneous materials. In particular, this is quite different from solutions using a photo-catalytic layer of TiC>2 under UV irradiation. This type of coating has a high dielectric constant (typically greater than 6), and does not allow an erratic regime to be obtained.

According to one example, the conductive or semiconductor particles are dispersed homogeneously in the matrix. They can be distributed substantially throughout the thickness of the matrix, and more particularly throughout substantially the entire volume of the matrix.

According to one example, the matrix is insulating. The separator material can therefore be a composite material comprising an insulating matrix and conductive or semi-conductive inclusions. The separator material is thus generally semiconductor and has a microstructure. The plasma initiation process then no longer depends on the intrinsic properties of one of the constituents and the microstructure of the surface, but on the material as a whole. In the presence of conductive grains surrounded by insulating grain boundaries, the charges are trapped on the surface of the grains thus inducing a curvature of the valence and conduction bands with the formation of a double Schottky barrier. The material is thus particularly suitable for accessing the two plasma generation regimes: the homogeneous regime (electric discharges generated when the separator material behaves like an insulator) and the erratic regime, also called energy regime (electric discharges generated when the behavior of the separator material is conductive). According to one example, the separator material being a composite material comprising conductive or semiconductor particles dispersed in an insulating matrix, the insulating matrix is based on or made of a material chosen from the group consisting of a polymer and a ceramic, and the conductive or semiconductor particles are based on or made of a material chosen from the group consisting of a metal, an intermetallic, a metal alloy, a ceramic. According to one example, of the thickness of material separating the two electrodes, at least 90%, and preferably at least 95%, of this thickness is formed by the separator material. According to one example, the separator material has no additional coating.

According to one example, the device does not include any other means of treating a gas phase than the plasma generated with the assembly of electrodes.

According to one example, the separator material does not have porosity. According to an alternative embodiment, the separator material has a non-zero average porosity and preferably greater than or equal to 10%. Preferably this porosity is between 10% and 30%. This porosity in the material has the advantage of improving the performance of the device. This porosity is open, pores being present on the external face of the material and therefore in contact with the environment surrounding the material. This porosity induces a gas adsorption effect on the separator material, which increases the efficiency of the device. A porosity range between 10% and 30% is particularly advantageous for the homogeneous regime. According to one example, the separator material has an average porosity of between 3 and 10%. This range is more advantageous for increasing the lifespan in erratic conditions.

According to one example, the material is a semiconductor ceramic, comprising a microstructure comprising:

- 5 to 40% by volume of a particulate conductive phase,

- 60 to 95% by volume of a particulate insulating phase, the size of the particles of the conductive phase being between 5 nm and 11 pm, 65 to 80% of the conductive particles having an average diameter less than 1 pm and 20 to 35 % of conductive particles having an average diameter between 1 and 11 pm;

- and the distance between two neighboring particles of conductive phase being between 30 Angstroms and 5 pm.

According to one example, the material constituting the conductive phase is chosen from the group consisting of MoSi2, TiB2, TiN, NisSi, HfB2, ZrB2.

According to one example, the particle size of the insulating phase is between 0.3 and 3 pm. According to one example, the material constituting the insulating phase is chosen from AI2O3, mullite, SisN4. According to one example, the ceramic comprises 15 to 25% by volume of MoSi2, and preferably 21 to 24% by volume of MoSi2.

According to one example, the conductive phase based on MoSi2 particles also comprises between 0% and 2% by weight of carbon.

According to one example, the surface of the semiconductor ceramic is vitrified.

According to one example, the conductive phase based on MoSi2 particles further comprises 1% by weight of an element chosen from Al, Ta, Ti, Zr, Y and B.

According to one example, the ceramic further comprises 0.1 to 0.9% by weight of lanthanide compound. According to one example, the voltage applied to generate the plasma has a non-zero value less than 10 kV and preferably 6 kV.

According to one example, the injection electrode has, on at least a portion of the assembly, a pointed configuration also called a tip electrode. The cutting-edge configuration of the injection electrode promotes electrical discharges in the erratic regime, in synergy with the nature of the separator material as well as the electrical signal and the geometry of the electrodes

According to one example, the device is more particularly configured to make the homogeneous and erratic discharge regimes coexist temporally or spatially during the generation of plasma.

According to one example, the separator material has a cylindrical shape extending in a main direction of extension of the assembly, and:

- on a first portion of the assembly, the electrode connected to ground and the injection electrode together form a coaxial structure on either side of the separator material, around the main extension direction of the assembly,

- on a second portion of the assembly, distinct from the first portion, the electrode connected to ground extends coaxially to the main extension direction of the assembly around the separator material, and the injection electrode has a pointed configuration arranged in an interior volume defined by the separator material.

On the first portion, plasma is generated in the homogeneous regime. On the second portion, plasma is generated mainly in the erratic regime. The assembly thus presents two treatment zones in which the two regimes coexist and are spatially separated. The gas phase thus passes through the first portion and the second portion to be treated successively by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

According to one example, the first portion is arranged upstream of the second portion, according to the direction of circulation of the gas phase in the assembly.

According to one example, the first portion and the second portion are separated by an intermediate portion, the assembly being configured so that under the application of the electrical voltage, a plasma is generated only in the first and second portions. The intermediate portion makes it possible to increase the spatial separation between the first and second portions. Thus, the by-products generated by the plasma treatment in one of these portions, and preferably in the first portion, can react with each other before the treatment is finalized in the other portion, preferably the second portion.

Depending on the volume constraint associated with the device, it is also possible for the first and second portions to be directly juxtaposed, in order to limit the bulk of the device.

According to one example, the separator material has a first face and a second face opposite the first face, the injection electrode and the electrode connected to ground are arranged on the first face of the separator material, the injection electrode injection and the electrode connected to ground being arranged at a distance from each other. The assembly can thus have a planar geometry, the electrodes being arranged on the same face of the separator material. This geometry allows the generation of plasma discharges according to both homogeneous and erratic regimes. These two regimes can coexist spatially. The assembly thus presents a treatment zone in which the two regimes coexist and follow each other temporally. There The gas phase thus passes through the treatment zone and is treated successively by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

According to one example, on the second face of the separator material, at least one injection electrode and at least one electrode connected to ground are also arranged at a distance from each other. The planar geometry of the assembly thus makes it possible to functionalize the two faces of the separator material using the electrodes. The compactness of the device is further improved.

According to one example, the injection electrode and the electrode connected to ground each have a pointed configuration facing each other between the injection electrode and the electrode connected to ground. This allows for a discharge on the surface rather than in volume.

According to one example, the electrode connected to ground has a first face comprising at least one opening leaving the separator material visible, at least one injection electrode being arranged in the at least one opening and extending from the separator material in an oblique direction, preferably perpendicular, to the first face of the electrode connected to ground. This geometry can be described as “surface point/plane”. An advantage of this geometry is to favor the quantity of plasma generated.

According to one example, the assembly is connected to a power supply module configured to power the assembly with a pulsed electrical voltage signal. The pulse signal makes it possible to apply a pulsed voltage to generate the plasma. This type of current is compatible with all assembly geometries.

According to one example, the assembly is connected to a power module configured to power the assembly with an alternating electrical voltage signal. An alternative signal is cheaper and easier to implement and use. The design of the device is therefore simplified and its cost reduced. For this it is preferable that the electrodes are arranged on the same face of the separator material.

According to one example, the device comprises a plurality of assemblies stacked in at least one direction perpendicular to a main extension direction of the assembly. The plurality of assemblies makes it possible to increase the quantity of the gas phase treated, while reducing the dead volume between the assemblies to increase the compactness of the device.

According to one example, the voltage applied to generate the plasma has a non-zero value less than 10 kV, between 3 and 6 kV. The voltage applied to generate the plasma is thus reduced compared to that generally used in DBD devices, typically greater than or equal to 20 kV.

According to one example, in the device, the gas phase is at atmospheric pressure.

In the remainder of the description, the term “on” does not necessarily mean “directly on”. Thus, when we indicate that a part or an organ A is supported “on” a part or an organ B, this does not mean that the parts or organs A and B are necessarily in direct contact with each other. with the other. These parts or bodies A and B can either be in direct contact or be supported on one another via one or more other parts. It is the same for other expressions such as for example “A acts on B” which can mean that “A acts directly on B” or that “A acts on B through one or more other parts” . In the detailed description which follows, use may be made of terms such as “horizontal”, “vertical”, “longitudinal”, “transverse”, “upper”, “lower”, “top”, “bottom”, “front », “rear”, “inside”, “outside”. These terms must be interpreted relatively in relation to the normal position of use of the device, and more particularly the direction of circulation of the gas phase in the device and the assembly. For example, the notion of “longitudinal” corresponds to the direction of main extension of the assembly, a direction which is substantially parallel to the direction of circulation of the gas phase in the assembly.

We will also use a marker whose longitudinal or rear/front direction corresponds to the x axis, the transverse or right/left direction corresponds to the y axis and the vertical or bottom/top direction corresponds to the z axis.

It is specified that in the context of the present invention, the thickness of a material is measured in a direction perpendicular to the surface along which this material presents its main extension. The thickness of the separator material can in particular be taken in a direction perpendicular to the main faces of the separator material, at least one of these faces being in contact with at least one electrode of the device. We therefore understand that the thickness of the material can be the smallest of the other dimensions of the material (compared to the length, width or radius for example).

The device 1 for treating a gas phase 2 is now described according to several embodiments with reference to the figures.

As illustrated in Figure 1, the device 1 is configured so that a gas phase 2 to be treated flows into the device 1. The gas phase 2 can comprise species 20 in suspension, and in particular polluting species, for example example VOCs, and/or microorganisms such as bacteria, fungi and/or their spores, viruses, particles. In order to degrade these species 20, the device 1 comprises a body 10 through which the gas phase 2 circulates. For this, the device can comprise a suction module 14 for the gas phase 2, for example a fan. The device 1 therefore comprises an air circulation circuit from an inlet of the body 10 to an outlet of the body 10, not shown in the figures.

The device 1 comprises at least one assembly 11 of electrodes. Each assembly 11 comprises at least one injection electrode 110 and at least one electrode 111 connected to ground

12 of device 1 hereinafter designated electrode connected to ground 111, as illustrated by Figures 4 to 6 described in more detail later. The assembly 11 is configured so that, under the application of an electrical voltage, a plasma is generated between the injection electrode 110 and the electrode connected to the ground 111. This voltage can be more particularly applied by a power supply module 13 connected to the electrodes 110.1 11. The power supply module 13 can be configured to supply the device 1, and more particularly the assembly 11, with an electric current, allowing the application of this voltage.

During its circulation in the device 1, the gas phase 2 comprising the species 20 to be treated circulates in the assembly 11. The plasma 3 generated in the assembly acts on the species 20 causing their degradation. The gas phase 2' at the outlet of the device 1 can thus be considered as depolluted or decontaminated, that is to say the quantity of species 20 is at least reduced, preferably species 20 are eliminated.

The injection electrode 110 and the electrode connected to ground 111 are separated by a separator material 112. In conventional DBD devices, this separator material 112 is an electrical insulator. In the device 1, the separator material 112 exhibits electrically insulating behavior when it is subjected to a certain electrical voltage lower than a threshold voltage, hereinafter designated starting voltage Vo. When the separator material 112 is subjected to an electrical voltage greater than or equal to the ignition voltage Vo, it exhibits electrically conductive behavior allowing the passage of an electric current. This separator material 112 therefore has a non-linear electrical resistance (the U/l ratio is not constant). Below the ignition voltage Vo, it has a high impedance and therefore a very low leakage current, and preferably zero leakage current. Above the ignition voltage Vo, the material 112 has a lower impedance and allows the passage of a higher leakage current. In other words, beyond the ignition voltage Vo, the impedance of the separator material 1 12 drops to allow electrical conduction in the form of a leakage current. When the voltage returns to a level lower than the starting voltage, the impedance increases again to return to its initial value. The transition can be abrupt when switching from insulator/conductor behaviors but also from insulator/low leakage current/conductor behaviors. The wider the transition zone (Le., voltage range), the more the weakly mixed homogeneous regime exists.

We therefore understand that the separator material 112 can go from one behavior to another and vice versa depending on the applied voltage, unlike an insulator which is destroyed beyond its breakdown voltage and which can no longer find a insulating behavior when the voltage drops.

These electrical behaviors of the separator material 112 can be observed thanks to the assembly 4 illustrated in Figure 2, in which a power source 40 supplies an electrical circuit connected to the separator material 112. The electrical circuit comprises a voltmeter 41 mounted in bypass on the material separator 112 and an ammeter 42 mounted in series on the circuit. We can thus measure the voltage across the separator material 112 and the intensity of the current passing through it. In this assembly 4, the material 112 can be held between two electrodes (for example two solid brass discs) by a system of springs and coated with conductive paste for better electrical contact. Figure 3 is a graph representing the intensity (I) of the current 5 as a function of the voltage 6 (V) across the separator material, for an insulator 7 and for three examples of separator material 112a, 112b, 112c.

At the breakdown voltage, insulator 7 is destroyed and no longer exhibits insulating behavior. When they are subjected to a voltage greater than the ignition voltage Vo, the separator materials 112a, 112b, 112c go from an insulating behavior where the current I is very low, or even zero, to a more conductive behavior in which the current I increases with the voltage across the material, a leakage current then being measurable. This increase can be sudden or more or less progressive as illustrated by the three curves 112a, 112b, 112c. The pace of this increase can influence the nature of the different non-thermal plasma regimes generated during the use of the device 1, among a homogeneous regime, a mixed regime or an erratic regime (also referred to as energy regime).

The ignition voltage can be between 1 kV and 10 kV, preferably between 3 kV and 6 kV. This type of value allows efficient and controlled operation to thus access the two plasma generation regimes, and in particular in combination with a 50 Hz AC type signal, an electro-ceramic material and a surface type geometry.

Generally speaking, those skilled in the art will be able to adapt the value of the ignition voltage according to the nature of the signal, the nature of the material and the geometry for the intended application.

The geometry defines in particular the shape of the electrodes, the placement of the electrodes in relation to the separator material, the inter-electrode gap, the stacking or arrangement of the cells.

A person skilled in the art will be able to adapt the variable parameters without any difficulty to obtain the desired effect. It will in particular know how to adapt the nature of the signal (for example for an impulse signal: its shape, its rising edge, its duration, its value), its frequency, the geometry and the placement of the electrodes (in particular the distance also called "gap » inter-electrode. Naturally also, the reactor will be sized in relation to the desired end use in terms of flow rate.

Thanks to these electrical behaviors of the separator material 112, when an electrical voltage is applied to the assembly 11, a cold plasma can be obtained by charges according to two main regimes: the homogeneous surface regime by discharge in the insulating behavior or a multi-filamentary energetic regime of volume by discharge in the conductive behavior, or even a mixed regime.

The energy regime is not accessible with insulators in conventional DBD devices. This regime makes it possible, in synergy with the homogeneous regime, to improve the degradation of species 20 and to extend the number of species 20 that can be treated by plasma. For example, certain VOCs are more efficiently degraded by plasma in a homogeneous regime, such as sulfides, aromatic compounds, and halogenated VOCs. The treatment of VOCs in a homogeneous plasma can additionally generate ozone and/or harmful reaction by-products.

During the development of the invention, it was observed that a complementary treatment to a homogeneous plasma 3 by a plasma 3 in energy regime makes it possible to limit, and preferably eliminate, the residual ozone as well as the by-products. reaction as well as obtaining better selectivity in CO2 This complementary treatment also makes it possible to degrade molecules which would not have been degraded by a plasma discharge 3 in a homogeneous regime, too low in energy, and in particular ketones or even acids .

In addition, the minimum voltage to be applied to generate a plasma 3 is lowered compared to a conventional DBD device thanks to the separator material 112. The discharges are also more efficient, which makes it possible to reduce the degradation time of the species 20. Furthermore, the coexistence of plasma discharges 3 in homogeneous regime and plasma discharges 3 in energy regime allows an aggregation of particles possibly present in gas phase 2, in the manner of an electrostatic filter. It is therefore possible to trap the particles at the outlet of the device 1, for example by adding a filter. The deposits inside device 1 are reduced, which limits the clogging of the assembly 11 and/or the risk of short circuit.

The device 1 can be used in a process for treating a gas phase 2. This gas phase 2 can be indoor air, for example inside a building, or a gas phase from industrial waste.

The gas phase 2 can be introduced into the assembly 11, for example by suction by the suction module 14. The suction module is sized in relation to the processing capacity of the device, which is itself sized in depending on the need for treatment of the gas phase. For example, for the treatment of air in a room of 30 ^m2, a flow rate of ^250Nm3 /h is desirable.

The electrical voltage can be applied to the assembly 11 to generate a plasma 3 between the injection electrode 110 and the electrode connected to the ground 111 to treat the gas phase 2. The voltage applied to generate the plasma 3 can present a non-zero value less than 10 kV, for example between 3 and 6 kV.

According to one example, the gas phase 2 is introduced continuously into the device 1. Plasma treatment 3 can also be carried out continuously. Alternatively, the plasma treatment can be carried out discontinuously or non-constantly. For example, the activation of the treatment and/or its flow rate can be controlled depending on the pollution of the gas phase to be treated. For this, sensors can be provided arranged to measure a parameter relating to pollution or contamination of the gas phase. The control depends on these measures. Thus, depending on this control, the volume of gas phase 2 sucked in can then be treated in successive volumes.

Particular examples of separator material

The separator material 112 is now described according to several exemplary embodiments.

The separator material 112 can be chosen from:

- a semiconductor material, for example a semiconductor ceramic, such as for example SiC, ZnO or GaN,

- a semiconductor polymer,

- a composite material comprising conductive or semiconductor particles dispersed in an insulating matrix.

The composite material may, according to one example, comprise conductive or semi-conductive particles dispersed in an insulating matrix. The insulating matrix may be based on or made of a polymer or a ceramic, for example. The conductive or semiconductor particles may be based on or made of a metal, a metal alloy or a ceramic. For example, the composite material may be polymer/metal, polymer/ceramic, cermet (ceramic/metal) or ceramic/intermetallic. The separator material may have a certain porosity. This porosity in the material has the advantage of improving the performance of the device. This porosity is preferably greater than or equal to 10%. Preferably this porosity is between 10% and 30%.

We can also predict that the porosity is zero or low.

When a volume plasma is generated, for example with one electrode in contact with the separator material 1 12 (for example electrode connected to ground 111) and the other electrode (for example the injection electrode 110) not in contact with the material by being separated from this material 112 by a gas (air for example), the greater the thickness of the separator material 112, the greater the voltage necessary for igniting the cold plasma. The lower this thickness, the more the erratic regime is favored since it will appear more quickly for lower starting voltages. However, if this thickness is too thin, this limits the lifespan of the reactor due to excessively high stresses exerted on said material (erosion of the material or mechanical stresses for example). Preferably, the thickness of the separator material 112 is between 0.5 mm and 15 mm, preferably between 2 mm and 6 mm. This thickness may be greater than or equal to 1 mm, preferably 2 mm, for example substantially equal to 3 mm.

When a surface plasma is generated, it was shown during the development of the invention that the thickness has no significant influence on the plasma. However, this thickness can impact the lifespan of the reactor. Preferably, the thickness of the separator material 112 is greater than or equal to 1 mm, preferably between 2 mm and 6 mm. According to a particular example, this thickness is substantially equal to 5 mm.

Note that these thicknesses are correlated to the dimensioning of the reactor and can therefore be adapted according to this dimensioning.

In the following, a particular example is described without limitation, in which the separator material 112 is a composite semiconductor ceramic, composed of an insulating phase and a conductive phase.

The operating mechanism of current semiconductor ceramics based on Sialon and SiC is based on the intrinsic properties of one of the constituents of the ceramic (surface conduction of SiC added to open porosity).

The composite ceramic is formed of a conductive phase included in an insulating matrix. This makes it possible to obtain an overall semiconductor material with a microstructure of the same type as semiconductor ceramics based on Sialon and SiC (grain boundaries, defects, etc.) and optimal thermomechanical properties.

The priming process then no longer depends on the intrinsic properties of one of the constituents and the microstructure of the surface, but on the material in its overall approach.

So that the injected charges are not conducted through the volume of the ceramic, the implantation of the charges must be done at a speed greater than the conduction speed translated by the relaxation time which characterizes the return to equilibrium after interruption of the field. In the presence of conductive grains surrounded by insulating grain boundaries, the charges are trapped on the surface of the grains thus inducing a curvature of the valence and conduction bands with the formation of a double Schottky barrier. Grain boundaries can in fact be compared to two Schottky diodes back to back. Trapping induces a space charge, there is therefore a field gradient then a relaxation of this space charge, this relaxation depending on the transit time of the carriers and the thickness of the insulation. The greater the thickness of the insulation, the greater the relaxation time and the “breakdown” voltage (in fact conduction) is high.

Conduction in ceramic according to this example is controlled by several mechanisms:

- first of all, at the interfaces of the ceramic: the Schottky emission (the increase in electronic emission when the applied electric field increases is due to the reduction in the extraction work), which determines the quality of the injection and which is strongly correlated with the quality of contacts and field emission;

- then, in the mass of the ceramic: the Poole-Frenkel effect (trapping/untrapping) and the hopping effect (conduction by jump).

The Fowler-Nordheim tunnel effect and space charge also participate in conduction both at interfaces and in the mass.

The constraint is now carried by the ability of the material to withstand severe environmental constraints.

The possible materials for the conductive phase can be GaN, MoSi2, HfB2, TiB2, ZrB2 or even TiN.

Properties of these materials are given in the following table.

Molybdenum disilicide (MoSi2) can be an advantageous material for producing the conductive phase because of its intrinsic qualities but also because of its ability to resist oxidation. The advantages induced by the use of a MoSi2 base for the conductive phase are that MoSi2 has a high melting temperature (2030°C), that MoSi2 has high resistance to oxidation up to 1600°C. , that MoSi2 has a high thermal conductivity 50 WMK, and that MoSi2 is thermodynamically stable.

When two phases of different electrical conductivities are mixed, the resulting compound is likely to have a very wide range of conductivity values. The conductive grains of MoSi2 behave like connections between capacitors whose dielectric is formed by TAI2O3.

Near the critical region, only a few percolating beam paths remain, the role of capacitors thus becoming very important. With a microstructure presenting large “bundles” of alumina which are the capacitors governing the conduction mechanism, and which are too bulky to allow the passage of charges by tunnel effect, the charges remain trapped in the alumina and the conduction remains very limited.

Conversely, when the conductive particles are small and especially well dispersed, the percolation threshold is lowered and we have instantaneous conduction as soon as a voltage is applied, the inter-particle distance having been greatly reduced.

Two microstructures of the same compositions can thus exhibit completely different behaviors depending on the arrangement of the two phases and it is therefore necessary to have a compromise between the two extreme cases where the MoSi2 grains percolate and the one where none is in contact.

Therefore, the microstructure according to the invention is a homogeneous distribution of the MoSi2 particles in the alumina matrix (by particle we mean grain or cluster of grains from 15 nm to 5 pm), this in order to allow the passage of charges by tunneling effect, compensate for the removal of too large MoSi2 particles which would cause a break in the conduction process by distant percolation and to obtain satisfactory mechanical properties.

The presence of a “gradient of conductive particle sizes” within the insulating matrix makes it possible to obtain the expected overall electrical effect (totally insulating then conductive behavior of the material). The particle size distribution is done for example according to the following diagram:

- “small particles”: average diameter less than 240 nm (19.5 to 24% of particles in the conductive phase);

- “medium particles”: average diameter of 240 nm to 1 pm (45.5 to 56% of the particles of the conductive phase);

- “large particles”: average diameter of 1 pm to 11 pm (20 to 35% of particles in the conductive phase).

In order not to obtain a conductive material as soon as the voltage is applied, it is preferable, for the same conductor/insulator ratio, to limit the passage of charges (no contact, no uniformly small inter-particle distances); this is why this particle size gradient is important. In order to delay conduction, large particles are used, few in number and far from each other.

The probability of transfer by tunnel effect decreases with the interparticle distance; when we have large particles, it is preferable to compensate for these distances by defects in the inter-particle zone or by the presence of small particles which ensure conduction always without contact but by tunneling effect made easier by the inter-distances. - party had the smallest.

Medium particles are of “intermediate” use, they ensure conduction once it is established (and can play the role of either large or small particles depending on where they are located) and make it possible to homogenize the material.

The expected microstructure is therefore grains as well as agglomerates of MoSi2 grains (of controlled sizes) uniformly distributed in the matrix.

It will be noted that, when the size of alumina grains is reduced, the number of grain boundaries is increased and the number of trapping regions is thus extended, with the conduction increasing; the size of the alumina grains is therefore also a factor to control.

We therefore propose a semiconductor ceramic comprising:

- 5 to 40% by volume of a particulate conductive phase, preferably based on MoSi2 particles;

- 60 to 95% by volume of a particulate insulating phase, the size of the particles of the conductive phase being between 5 nm and 10 pm, and the distance between two neighboring particles of the conductive phase being between 0.1 and 10 pm .

Preferably, we propose a semiconductor ceramic comprising:

- 10 to 30% by volume of a conductive phase based on MoSi2 particles,

- 70 to 90% by volume of a particulate insulating phase, the size of the MoSi2 particles being between 15 nm and 5 pm, and the distance between two neighboring MoSi2 particles being between 0.1 and 6 pm. In the context of the present invention, “particle” means a grain or an aggregate/cluster of grains.

The measurement method used to measure the size of MoSi2 particles includes scanning electron microscope observation of the fracture facies of broken samples. The images are then reprocessed using ESIVISION Analysis 3.2 software. We obtain the average diameter of the MoSi2 particle.

Advantageously, the semiconductor ceramic can comprise 15 to 25% by volume of MoSi2 and preferably 21 to 24% by volume of MoSi2.

According to the present invention, a “conductive phase based on MoSi2 particles” is understood to be essentially made up of these particles. It may, however, include other constituents such as carbon, boron or different metals.

Preferably, the conductive phase according to the invention comprises more than 90% of MoSi2 particles, more preferably more than 95%, even more preferably more than 97% of MoSi2. In a variant embodiment of the ceramic according to the invention, the conductive phase in MoSi2 comprises between 0.1% and 3% by mass (of the total mass insulating phase + conductive phase) of a simple element (C, B, etc.) or a rare earth. An advantage of the introduction of carbon (boron or rare earth) is to improve the mechanical properties of the conductive MoSi2 phase. The insulating phase can be made from AI2O3, SisN4, mullite (2 SiC>2.3 AI2O3), or even ALON.

Properties of these materials are given in the following table.

In one embodiment of the ceramic according to the invention, the insulating phase of the ceramic is made based on SisN4. Indeed, this material has greater hardness, greater thermal conductivity and greater resistivity than AhOs, mullite and ALON.

In another embodiment of the ceramic according to the invention, the insulating phase is made based on ALCh.

Indeed, alumina (AI2O3) has high electrical resistivity, excellent creep resistance at temperatures above 1400°C and good resistance to chemical attacks. Furthermore, an advantage of a composite of MoSi2 and AI2O3 for the conductive and insulating phases of the ceramic is that these two materials have close expansion coefficients, so as to reduce the thermal stresses between these two materials. Advantageously, the particle size of the insulating phase can be between 0.3 and 3 μm.

The measurement method used to measure the particle size of the insulating phase includes observation under a scanning electron microscope of the fracture pattern of broken samples. The images are then reprocessed using ESIVISION Analysis 3.2 software. The average particle diameter of the insulating phase is obtained.

The separator material may have a certain porosity. This porosity is an open porosity, the pores being accessible from the external face of the material. This porosity in the material has the advantage of improving the performance of the device. This porosity is preferably greater than or equal to 10%. Preferably this porosity is between 10% and 30%. We can also predict that the porosity is zero or low.

This porosity value depends on the technique used to make the ceramic. For example, if natural sintering is used to manufacture ceramics, the average porosity is less than or equal to 10%. If we use hot press sintering (HP for “Hot Press” according to Anglo-Saxon terminology), the average porosity of the ceramic is less than or equal to 2%. Finally, if current-assisted sintering (SPS for “Spark Plasma Sintering” according to Anglo-Saxon terminology) is used, the average porosity of the ceramic is less than or equal to 3%. All these sintering techniques will be described in more detail below.

However, in the event that the ceramic comprises open porosities, the surface of the semiconductor ceramic can be vitrified. This makes it possible to minimize the so-called “Pest” phenomenon which can cause the disintegration of the semiconductor ceramic. Vitrification of the surface of the semiconductor ceramic therefore makes it possible to improve the solidity of the ceramic. According to a variant making it possible to minimize the Pest phenomenon, the conductive phase in MoSi2 can comprise 1% by weight of an element chosen from Al, Ta, Ti, Zr, Y and B. Advantageously, the semiconductor ceramic according to invention may also comprise 0.1 to 0.9% by weight of lanthanide compound (for example La2Os, or even La2Be). A lanthanide (La2O3, LaBe) is a material favoring electronic emission. Thus, its addition, in small quantities, in the semiconductor ceramic makes it possible to reinforce the thermal emission of the semiconductor ceramic.

A process for manufacturing semiconductor ceramic according to this example is now described.

In order to solve the problems of reliability over time of electroconductive ceramics, it is important to develop a material under optimal conditions, to control its microstructure in order to obtain the desired properties. The electrical characteristics depend on the volume percentage of conductive phase and the type of microstructure developed after sintering.

The production process, the most important parameters of which determine the microstructure and thus the physical characteristics of the sintered samples, is in fact the essential phase. These parameters concern in particular:

- the nature of the powders,

- the proportions of the insulating and conductive phases,

- the quantity and composition of the additives,

- deagglomeration processes,

- the shaping technique,

- the sintering conditions.

The process for manufacturing a semiconductor ceramic comprises the following steps:

- preparation of a homogeneous suspension of a conductive phase, for example based on MoSi2 particles, to obtain a first slip, - preparation of a homogeneous suspension of a particulate insulating phase to obtain a second slip,

- mixing of the first and second slips to obtain a mixture of the two phases in the desired proportions (i.e. the first slip representing 5 to 40% by volume of the mixture and the second slip representing 60 to 95% by volume of the mixture),

- drying and sieving the composition;

- sintering of the composition to obtain a ceramic in which the size of the particles of the conductive phase is between 5 nm and 10 pm, and the distance between two neighboring particles of the conductive phase is between 30 Å and 5 pm.

As described above, the conductive phase can be chosen from the group consisting of MoSi2, TiB2, TiN.

Furthermore, the insulating phase can be based on alumina AI2O3OU mullite, SisN4. To prepare the first slip, the conductive phase of MoSi2 is mixed with water with a pH between 8 and 10.

This makes it possible to improve the homogeneity of the microstructure. To prepare the second slip, the insulating phase is mixed with water of pH equal to 10 containing a dispersant, advantageously a surfactant polymer of the ammonium polymethacrylate type such as DARVAN® C marketed by VANDERBILT. This dispersant makes it possible to avoid agglomeration of the alumina particles AI2O3 II is advantageously introduced at a level of 0.1% by weight.

The two slips are then mixed to obtain a mixture of the two phases. The two slips are thoroughly mixed using a jar turner or ball mill. The grinding time is between 5 and 24 hours.

The mixture is then dried in an oven for 48 hours. In order to avoid differential sedimentation of the two types of particles, rapid drying by ROTOVAP can be considered. The powder thus obtained is ground in a mortar; then deposited with glass beads (diameter 10 mm) in a 250 μm mesh sieve of an electric sieve machine, the powder passed at 250 μm pours into a 100 μm mesh sieve containing alumina beads (diameter 3 mm ).

The composite powder thus collected and roughly granulated is ready to be shaped, then sintered. The formatting step is optional. Its implementation depends on the sintering technology used. The shaping step transforms the material into a raw product having the controlled size, shape and surface area and particular density and microstructure. Careful control of the density and microstructure of a raw ceramic is necessary to obtain the performance of the final product because the defects introduced by the shaping process are generally not removable by sintering.

A smooth, even surface is normally desirable and may be essential for some products. The resistance must be sufficient to carry out the operations following shaping. Product reproducibility is very important for industrial production. The size and density of the green part must be controlled in order to maintain a constant shrinkage factor between the green and sintered part. For the shaping stage, we can use the so-called compaction or dry compaction technology.

Compaction is a process of shaping powder or granulated material enclosed in a rigid or flexible mold.

Dry compaction is a widely used process due to its reproducibility and its ability to produce large format parts and different shapes that do not shrink during drying. It preferably includes the following steps:

- (1) matrix filling;

- (2) compaction and shaping;

- (3) ejection of the part;

- (4) densification.

The composition is then sintered. Unlike ceramic firing, sintering does not, in principle, involve a bonding of particles by a vitreous phase. The coherence and densification of pressed powders occurs as a result of transformations affecting the particle surface and leading to solid-solid interfaces called grain boundaries. The sintering conditions determine the microstructure and therefore the properties of the final material.

Advantageously, different technologies can be used for sintering the composition. For example, in one embodiment of the method, the sintering is a natural sintering. In another embodiment, the sintering is a hot press sintering. In yet another embodiment, the sintering is current assisted sintering (SPS).

For the implementation of sintering by hot press, the press oven used is of the Goliath type (Stein Heurtey Physitherm) combining a press (maximum load 20 tonnes) and a graphite resistance oven (maximum temperature 2200°C) the use of which requires an inert atmosphere or a high vacuum.

Temperature control is ensured by a 5/26% tungsten/rhenium thermocouple placed near the resistor as well as by a bichromatic pyrometer (IRCON®) which measures the actual temperature on the surface of the tool. Hot press (HP) sintering produces 37 mm pellets. It does not require any shaping of the pellets.

Optimal densification of the ceramic is obtained for a temperature between 1600°C and 1700°C (and preferably equal to 1650°C) and a load of 45 MPa. The temperature allowing the best densification/microstructure compromise favorable to the expected electrical behavior to be obtained is 1500°C.

To carry out natural sintering, the same oven is used as that used for hot pressing. Simply, in this case the samples are placed after the shaping step in a graphite crucible, and are not subjected to a load during sintering.

In order to limit gas exchange with the outside, the preformed pellets are placed in an alumina crucible for “bug cooking”, that is to say the use of loose powder of the same nature as the pellets and coating them to avoid any contact with the oven atmosphere. It is also possible to carry out current-assisted sintering (SPS, abbreviated from the English Spark Plasma Sintering), as described previously. Current-assisted sintering (SPS) makes it possible to densify materials while retaining the characteristics of the initial powders and to densify difficult materials.

Current-assisted sintering (SPS) is a process similar to conventional hot pressing. The precursors (metals, ceramics, polymers and their composites, etc.) are introduced into an enclosure (made of graphite) allowing uniaxial pressure to be applied during sintering.

The major difference in this process is that the heat source is not external. An electric current (direct - pulsed direct - or alternating) passes through the conductive pressing chamber and also in appropriate cases through the sample.

Thus, the enclosure itself acts as a heating source which makes it possible to obtain high heating rates (up to 600 °C/min and more) and good heat transfer to the sample. . Very compact sintered objects can be obtained for lower temperatures (a few hundred degrees lower) and especially significantly shorter sintering times (a few minutes) than for conventional methods. Current-assisted sintering (SPS) is an extremely promising technique for improving the shaping of already existing materials.

Densification is increased by the use of a pulsed current or field.

Special examples of assemblies 11

The assembly 11 is now described in more detail according to several exemplary embodiments, with reference to Figures 4 to 6.

The conventional geometries of assemblies 11 used in DBD devices can be used for the device 1 with the separator material 1 12.

Special geometries have also been developed. According to one example, at least the injection electrode 110 has, on at least one portion of the assembly 11, a pointed configuration. By an electrode with a “tip configuration” is meant a configuration in which the electrode forms one or more peak-shaped structures, the tip-shaped end or equivalently peak-shaped end of these structures being arranged facing the another electrode, for example the electrode connected to ground 111. By “point” or “peak” it is not necessarily implied that the end is conical, it can be sharp and flat. For example, the electrode may have a brush structure, the ends of the brush being arranged opposite the other electrode, as illustrated in Figure 4. According to another example, the electrode may be extend in a main direction of extension between two tip-shaped ends, as illustrated in Figure 5. According to another example, the electrode can be in the form of a rod, the ends of the rod forming the structures pointed described above. The tip configuration of an electrode promotes plasma discharges in the erratic regime, in synergy with the nature of the separator material 1 12.

A first geometry is described with reference to Figure 4, according to exemplary embodiment. The assembly 11 extends in a main extension direction x substantially parallel to the direction of flow of the gas phase 2 in the assembly 11. The separator material 112 can have a cylindrical shape centered on the main extension direction x, and separate the injection electrode 110 and the electrode connected to ground 111. By “cylindrical” is meant that the cross section of the separator material 112 can have a substantially circular, elliptical or ovoid shape.

The assembly 11 may have a first portion 11 a and a second portion 11 b, these portions being distinct from each other. Preferably, the first portion 11a is located upstream of the second portion 11b according to the direction of flow of the gas phase 2 in the assembly 11.

In the first portion 11 a, the electrode connected to ground 111 and the injection electrode 110 can together form a coaxial structure centered around the main extension direction x, on either side of the separator material 112 cylindrical. Note that the injection electrode 110 can be placed inside the cylinder formed by the separator material 112, electrode connected to ground 111 then being placed outside the cylinder, or vice versa. This first portion 11 a promotes plasma discharges 3 in the homogeneous regime.

In the second portion 11 b, the electrode connected to the ground can extend coaxially to the main extension direction x around the separator material 112. The electrode connected to the ground 111 is then preferably arranged outside of the separator material 112. The separator material 112 can delimit an interior volume 1120. The injection electrode 110 can be placed in this interior volume 1120. the injection electrode 110 has a pointed configuration in this volume. For example, the injection electrode 110 may have a brush structure whose pointed ends are arranged facing the separator material 112 and the electrode connected to the ground 111. Preferably, the pointed ends are arranged radially facing the separator material 112, around the main extension direction x. This second portion 11 b promotes the generation of plasma discharges in the energy regime.

In the first and second portions 11 a, 11 b, the electrode connected to ground 111 can be in the form of a grid or a plate. In the first portion 11a, the injection electrode 110 can be in the form of a spiral.

The two portions 11 a, 11 b being distinct, understand that two treatment zones are thus formed:

- a first zone in which plasma discharges 3 in homogeneous regime are favored,

- a second zone in which plasma discharges 3 in energy regime are favored.

This geometry is particularly suitable for the degradation of certain VOCs, such as sulfides, which are better degraded by a homogeneous plasma in the first zone. These areas are spatially distinct. Preferably, the gas phase 2 flows into the first zone then into the second zone to be successively treated by a homogeneous plasma then an energetic plasma.

As illustrated in Figure 4, portions 11a, 11b can be separated by an intermediate portion 11c. Preferably, no plasma is generated in the intermediate portion 11 c. This intermediate portion 11 c serves as a buffer between the plasma generation zones 3. The species generated in the first zone can thus react with each other to continue their degradation before entering the second zone. In particular, the ozone can react with the reaction by-products or the species which have not been degraded in the first zone for their degradation.

Naturally, those skilled in the art will know how to adapt the geometry and dimensions according to the final application, and in particular according to the contact time of the plasma with the targeted species, the nature of the targeted species, the flow rate or the volume, etc.

A second geometry and a third geometry are now described with reference to Figures 5 and 6 respectively. In these two geometries, the separator material 112 has a first facel a and a second face 112b. The electrodes 110, 111 are arranged on the same face of the separator material 112, at a distance from each other. Electrodes 110, 11 1 can be arranged on each of the faces of the separator material 112. Thus, the compactness of the device 1 is improved.

For example, the injection electrode 110 can have a pointed configuration facing the electrode connected to ground 111. These geometries allow the generation of plasma discharges according to the two homogeneous and energy regimes. These two regimes can notably coexist spatially. The assemblage thus presents a treatment zone in which the two regimes coexist and follow each other temporally. In these two geometries, the plasma discharge energy regime 3 can be preponderant.

In the second geometry, the injection electrode 110 and the electrode connected to ground 111 each have a pointed configuration facing each other. For example, each electrode 110, 111 can extend in a main extension direction, for example the y direction, between two tip-shaped ends. The electrodes 110 111 are arranged so that at least one end of each injection electrode 110 faces one end of an electrode connected to ground 11 1.

The assembly 11 may comprise several injection electrodes 110 and several electrodes connected to ground 111. The injection electrodes 110 may be arranged in one or more rows in a direction substantially parallel to the direction x of flow of the phase gas 2 in the assembly 11. The electrodes connected to the mass 111 can also be arranged in one or more rows in a direction substantially parallel to the direction x of flow of the gas phase 2 in the assembly 11. A row of injection electrodes 110 can be spaced a distance d from a row of electrodes connected to ground 111. The distance d can be chosen so as to favor a particular plasma discharge regime. This is particularly the case when the assembly 11 is powered by a pulse signal, as described in more detail later. The distance d is for example between 3 and 25 mm, preferably between 10 and 15 mm.

In the third geometry, the separator material 112 can be at least partly covered by the electrode connected to the ground 111. The electrode connected to ground 11 1 then has an upper face 111 a comprising openings 1110 leaving the separator material 112 visible. The injection electrode 110 can extend from the opening 1110. The injection electrode 110 preferably extends from a first face 112a of the separator material 112, being in contact with it. The injection electrode 110 can extend in an oblique direction, and preferably perpendicular, to the first face 111a of the electrode connected to the ground 111.

According to one example, the electrode connected to ground 111 has several openings 1110, and an injection electrode 110 is arranged at each opening 1110.

The injection electrode 110 can be in the form of a rod, a first end of which is mounted on, preferably directly on, the separator material 112. The second end of the injection electrode 110 can be connected, from preferably directly, to the power module 13.

In each of the geometries described, the injection electrode 110 can be connected directly or via another element, such as another injection electrode 110 or a conductive element, to the power module 13.

For each of the geometries described, the power supply module 13 configured to power assembly 11 can supply it with a pulsed electric current. This pulsed electric current includes current application phases interspersed with phases during which no current is applied. The electrical signal supplying assembly 11 is therefore discontinuous. The voltage applied to the assembly is thus pulsating and can be positive or negative. A current application phase, preferably each current application phase, may have a duration less than or equal to 1 ps, for example substantially equal to 500 ns. A pulsed electric current has the advantage of being able to more easily modulate the nature of the plasma discharge regime obtained.

For the second and third geometries, the power module 13 can power the assembly 11 with an alternating electric current (abbreviated AC). An AC power supply in fact requires that the electrodes 110, 1 11 be arranged on the same face of the separator material 112. This type of power supply is cheaper and simpler to implement, which simplifies the design of the device 1 and reduces its cost. An AC electrical signal also makes it possible to further lower the voltage to be applied to obtain a plasma discharge. For example, the AC electrical signal has a frequency of 50 Hz. As an example, a plasma was obtained with an AC signal of 50 Hz at only 3kV (compared to 20 kV for conventional DBD devices), with a inter-electrode distance of 10 to 15 mm for the second geometry.

Note that the device 1 can be configured so as to be supplied with both pulsed current and alternating current. This can make it possible in particular to more easily spatially separate one or more plasma discharge zones in a homogeneous regime and one or more plasma discharge zones in an energy regime. For this, the device 1 can comprise several assemblies 11, part of these assemblies 11 being supplied with pulse current and the other part being supplied with alternating current. Alternatively or in addition, for an assembly 11, and in particular for the second and third geometries, part of the injection electrodes 110 can be supplied with pulse current and the other part can be supplied with alternating current. The device 1 preferably comprises several assemblies 11. These assemblies can be stacked so as to maximize the number of assemblies 11 and reduce the total volume of the device 1, in order to minimize its bulk. For this, the assemblies 11 can be stacked in a direction perpendicular to their main extension direction x, for example the z direction or the y direction, or in two directions y, z perpendicular to the x direction. As illustrated in Figures 7, 8A and 8B, the planar geometry assemblies can be stacked for example in the z direction. The device 1 can thus have a rectangular shape as illustrated in Figure 7, or cylindrical as illustrated in Figures 8A and 8B. As shown in Figure 9, cylindrical geometry assemblies can be stacked in the y and z direction to form a compact stack.

The device 1 may include assemblies 11 of different geometries, depending on the size, the flow rate of gas phase 2 to be treated, and/or the type of pollution to be treated. Examples of VOC treatments

For example, the degradation of two VOCs was measured with an assembly 11 presenting a classic tip/plane geometry, therefore in volume, with a distance between electrodes of 4mm. The applied signal is a positive square pulse signal. The separator material 1 12 is a semiconductor ceramic according to the particular example described above. These measurements were compared with a conventional DBD reactor assembly comprising either an alumina separator material 7a or a glass separator material 7b. These graphs represent the percentage of destruction 8 of the VOC as a function of the voltage applied to generate the plasma (V in kV). In Figure 10A, gas phase 2 includes ethylene at an initial concentration of 500 ppm. In Figure 10B, gas phase 2 comprises isopropanol at an initial concentration of 500 ppm. In both cases, the VOCs are degraded at a lower voltage than needed to generate the plasma for conventional DBD device assemblies. In addition, higher percentages of degradation are achieved for these two VOCs for assembly 11 comprising the semiconductor ceramic.

Assembly 11 described above has been tested on numerous other VOCs, for example a gas phase containing 3000 ppm of a mixture of 32 sulfur compounds was treated, which represents a very high concentration. A total VOC degradation rate of 75% was achieved.

In view of the preceding description, it clearly appears that the invention proposes a device improving the treatment of a gas phase by plasma, and in particular of air.

The invention is not limited to the embodiments previously described and extends to all the embodiments covered by the invention. The present invention is not limited to the examples previously described. Many other alternative embodiments are possible, for example by combining characteristics previously described, without departing from the scope of the invention. Furthermore, the features described in relation to one aspect of the invention may be combined with another aspect of the invention. In particular, the device can include any characteristic allowing the implementation of a step of the method and the method may include any step resulting from the implementation of a characteristic of the device.

Claims

Claims Device (1) for treating a gas phase (2) comprising at least one assembly (11) of electrodes comprising at least one so-called injection electrode (110) and at least one electrode (111) connected to a ground (12) of the device (1), separated by a material called “separator material” (112), the assembly (11) being configured so that, under the application of an electrical voltage, a plasma (3) is generated between the at least one injection electrode (110) and the at least one electrode connected to ground (111), and in which the separator material (112) exhibits electrically insulating behavior when the separator material (112) is subjected to an electrical voltage lower than a threshold voltage, called “start-up voltage”, and an electrically conductive behavior authorizing the passage of a current when the separator material (112) is subjected to an electrical voltage greater than or equal to the ignition voltage, and characterized in that the separator material (112) is a composite material comprising conductive or semiconductor particles dispersed in an insulating matrix, the insulating matrix being based on or made of a material chosen from the group consisting of a polymer and a ceramic, and the conductive or semi-conductive particles being based on or made of a material chosen from the group consisting of a metal, an intermetallic, a metal alloy, a ceramic. Device (1) according to the preceding claim, in which the injection electrode (110) has, on at least a portion of the assembly (11), a pointed configuration. Device (1) according to the preceding claim, in which the separator material (112) has a cylindrical shape extending in a main extension direction (x) of the assembly (11), and:

• on a first portion (11 a) of the assembly (11), the electrode connected to ground (111) and the injection electrode (110) together form a coaxial structure on either side of the material separator (112), around the main extension direction (x) of the assembly (11),

• on a second portion (11 b) of the assembly (1 1), distinct from the first portion (11 a), the electrode connected to ground (11 1) extends coaxially to the main extension direction (x) of the assembly (11) around the separator material (112), and the injection electrode (110) has a pointed configuration disposed in an interior volume (1120) defined by the separator material (112). Device (1) according to the preceding claim, in which the first portion (11 a) and the second portion (11 b) are separated by an intermediate portion (11 c), the assembly (11) being configured so that under the Application of the electric voltage, a plasma (3) is generated only in the first (11 a) and second (11 b) portions. Device (1) according to claim 2, in which the separator material (112) has a first face (112a) and a second face (112b) opposite the first face (112a), the injection electrode (110) and the electrode connected to ground (111) are arranged on the first face (112a) of the separator material (112), the injection electrode (110) and the electrode connected to ground (111) being arranged at a distance from each other. Device (1) according to the preceding claim, in which, on the second face (112b) of the separator material, at least one injection electrode (110) and at least one electrode connected to ground (111) are further arranged at distance from each other. Device (1) according to any one of the two preceding claims, in which the injection electrode (110) and the electrode connected to ground (111) each have a pointed configuration facing between the electrode. injection (110) and the electrode connected to ground (111). Device (1) according to any one of the two claims 5 and 6, in which the electrode connected to ground (111) has a first face (111 a) comprising at least one opening (1110) leaving the separator material visible ( 112), at least one injection electrode (110) being arranged in the at least one opening (1110) and extending from the separator material (112) in a direction oblique to the first face (111 a) of the the electrode connected to ground (111). Device (1) according to any one of the preceding claims, in which the assembly (11) is connected to a power supply module (13) configured to power the assembly (11) with a pulsed electrical signal. Device (1) according to any one of claims 5 to 8, wherein the assembly (11) is connected to a power supply module (13) configured to power the assembly (11) with an alternating electrical signal. Device (1) according to any one of the preceding claims, in which the separator material (112) has a non-zero average porosity and preferably greater than or equal to 10%, and preferably between 10% and 30%. Device (1) according to any one of the preceding claims, comprising a plurality of assemblies (11) stacked in at least one direction perpendicular to a main extension direction (x) of the assembly (11). Method for treating a gas phase (2) using the device (1) according to any one of the preceding claims, and comprising:

• the introduction of the gas phase (2) into the at least one assembly (11) of electrodes,

• the application of an electrical voltage to the assembly (11) so as to generate a plasma between the at least one injection electrode (1 10) and the at least one electrode connected to ground (11 1 ) to treat the gas phase (2). Method according to the preceding claim, in which the voltage applied to generate the plasma has a non-zero value less than 10 kV and preferably 6 kV. Method according to any one of the two preceding claims, in which, in the device (1), the gas phase (2) is at atmospheric pressure.