Plasma treatment device for treating a gas phase and associated method

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

[0001] “Device for treating a gas phase by plasma and associated method”

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of devices for non-thermal plasma treatment of a gas phase. It finds particularly advantageous application in the field of air treatment, for example indoor air, and / or pollutant emissions, and / or olfactory nuisances.

[0004] STATE OF THE ART

[0005] Volatile organic compounds (VOCs) are known to have adverse health effects, including irritation of the eyes and mucous membranes, respiratory tract, heart and nervous system problems, headaches, and nausea. Some VOCs are even recognized as carcinogenic and / or toxic for reproduction or mutagenic (so-called "CMR" compounds for Carcinogenic-Mutagenic-Reprotoxic).

[0006] The risks posed by VOCs have led to numerous regulations, resulting in a complex set of measures to meet the standards. These standards aim to reduce VOCs, odors, and ensure satisfactory biological air quality.

[0007] Beyond VOCs, other harmful species can have adverse effects on health, the environment, or olfactory comfort. This is the case with microorganisms such as bacteria, viruses, fungi, and / or their spores.

[0008] There is therefore a need to develop a system for the depollution / decontamination of gaseous phases likely to include harmful species such as indoor air or pollutant 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 and decoration materials highlighting depolluting properties. There is no certification for indoor air purification devices, and some of them can lead to the formation of compounds potentially more harmful than the VOCs initially present.

[0009] Today, filtration is the most widely used technique in this field. HEPA filters trap suspended matter, including organic matter. However, organic matter, which is attached to the filters or has settled in the ducts of filtration systems, is a prime breeding ground for microorganisms. Furthermore, nano-sized viruses are not captured by these filters.

[0010] 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 processing 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 and also microorganisms. Indeed, cold plasma destroys the DNA of these microorganisms without distinction of size and is therefore effective on these pathogens. 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).

[0011] Conventional cold plasma treatments, for example those generated by dielectric barrier discharge (abbreviated DBD), are energy-intensive and generate harmful compounds such as ozone, by-products of the degradation of the treated pollutants.

[0012] US 2005 / 0118079 A1 describes a device for gas purification using surface electrodes comprising photocatalysts to improve the efficiency of a non-thermal plasma. However, ANSES (French National Agency for Food, Environmental and Occupational Health and Safety) in France advises against the use of physicochemical air treatments because their effectiveness, particularly against viruses, has not been proven. Following sometimes incomplete degradation of pollutants, they can also negatively impact indoor air quality by forming compounds that are potentially hazardous to health, including CMR chemical agents.

[0013] Document FR2918293 A1 describes a gas treatment unit comprising electrodes separated by layers of photocatalyst.

[0014] Document EP2762170 A1 describes a gas treatment device combining the activity of a photocatalyst and a cold surface plasma.

[0015] 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 provide 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 examining the following description and its accompanying drawings. It is understood that other advantages may be incorporated.

[0016] SUMMARY

[0017] 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 electrical voltage, a plasma is generated between the at least one injection electrode and the at least one electrode connected to the ground.

[0018] The separator material exhibits electrically insulating behavior when subjected to an electrical voltage lower than a threshold voltage, called the "breakthrough 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 breakthrough voltage.

[0019] The separator material thus provides access to two plasma generation regimes: a homogeneous regime (electrical discharges generated when the material behaves as an insulator) and an erratic regime, also called an energetic regime (electrical discharges generated when the material behaves as a conductor), which corresponds to an energetic multi-filament regime. These two regimes can appear simultaneously or successively.

[0020] The erratic regime does not exist in conventional DBD devices. This regime, in conjunction with the homogeneous regime, allows for the improvement of cold plasma treatment by improving the degradation of the treated compounds and limiting residual harmful degradation by-products. This also allows for the degradation of a wider range of pollutants than with a conventional DBD device.

[0021] The synergy between these two regimes allows for more efficient electrical discharges, which improves the efficiency and speed of gas phase treatment. The device can thus be made more compact and of simplified design.

[0022] The gas phase treatment 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 as well as its maintenance.

[0023] 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 the energy cost, of treating a gas phase is thus reduced. The safety of use of the device is also improved.

[0024] Another aspect relates to a method of treating a gas phase using the device according to the first aspect, and comprising:

[0025] - introducing the gas phase into the at least one electrode assembly, - 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.

[0026] The method has the effects and advantages described in relation to the device according to the first aspect.

[0027] Furthermore, because plasma discharges are more efficient, the gas phase treatment time can be reduced compared to treatment with a conventional DBD device. This is particularly advantageous for virus removal, which generally requires more energy (and more time) than VOC removal.

[0028] BRIEF DESCRIPTION OF THE FIGURES

[0029] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0030] Figure 1 represents an overview of the device and its operating principle, according to an exemplary embodiment.

[0031] Figure 2 represents a diagram of the electrical circuit for studying the electrical behavior of the separator material, according to an example.

[0032] Figure 3 schematically represents the electrical behavior of the separator material according to several exemplary embodiments, in comparison with an insulator of a DBD device.

[0033] Figures 4 to 6 represent different electrode geometries in an assembly, according to several exemplary embodiments.

[0034] Figures 7 to 9 represent different assembly arrangements, according to several exemplary embodiments.

[0035] Figures 10A and 10B represent two graphs showing the percentage of degradation of VOCs, respectively ethylene and isopropanol, as a function of the voltage applied to an assembly to generate the cold plasma, in comparison with two assemblies of DBD devices of the state of the art.

[0036] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily to the scale of practical applications. In particular, the relative dimensions between the VOCs, the electrodes and the device are not representative of reality.

[0037] DETAILED DESCRIPTION

[0038] Before commencing a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below.

[0039] According to one example, the breakdown 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 signal and for a tip / tip electrode geometry on the surface of the separator material, for a gap 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 semiconductive particles dispersed in a matrix. It must, however, have the dielectric properties with an insulator / conductor transition for the selected operating voltage range. The insulating phase also has the charge trapping / detrapping characteristics required to enable the energy regime.When the separator material is a composite material comprising conductive or semiconductive particles dispersed in a matrix, the separator material offers a variety of choices in the nature of the particles and the matrix 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, electrical properties. This is quite 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 implementing 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 for an erratic regime.

[0040] According to one example, the conductive or semiconductive particles are dispersed homogeneously in the matrix. They can be distributed substantially throughout the entire thickness of the matrix, and more particularly throughout substantially the entire volume of the matrix.

[0041] In one example, the matrix is ​​insulating. The separator material can therefore be a composite material comprising an insulating matrix and conductive or semiconducting inclusions. The separator material is thus globally semiconducting 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 (electrical discharges generated when the separator material behaves as an insulator) and the erratic regime, also referred to as the energetic regime (electrical discharges generated when the separator material behaves as an insulator). According to one example, the separator material being a composite material comprising conductive or semiconducting particles dispersed in an insulating matrix, the insulating matrix is ​​based on or made of a material selected from the group consisting of a polymer and a ceramic, and the conductive or semiconducting particles are based on or made of a material selected 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.

[0042] According to one example, the device does not include any means for treating a gas phase other than the plasma generated with the electrode assembly.

[0043] According to one example, the separator material has no 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, with pores being present on the external face of the material and therefore in contact with the medium surrounding the material. This porosity induces an adsorption effect of the gases on the separator material, which increases the efficiency of the device. A porosity range of 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 lifetime in erratic regime.

[0044] In one example, the material is a semiconductor ceramic, having a microstructure comprising:

[0045] - 5 to 40% by volume of a particulate conductive phase,

[0046] - 60 to 95% by volume of a particulate insulating phase, the particle size of the conductive phase being between 5 nm and 11 pm, 65 to 80% of the conductive particles having an average diameter of less than 1 pm and 20 to 35% of the conductive particles having an average diameter of between 1 and 11 pm;

[0047] - and the distance between two neighboring conductive phase particles being between 30 Angstroms and 5 pm.

[0048] According to one example, the material constituting the conductive phase is chosen from the group consisting of MoSi2, TiB2, TiN, NisSi, HfB2, ZrB2.

[0049] According to one example, the particle size of the insulating phase is between 0.3 and 3 μm. 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.

[0050] According to one example, the MoSi2 particle-based conductive phase further comprises between 0% and 2% by weight of carbon.

[0051] In one example, the surface of the semiconductor ceramic is vitrified.

[0052] According to one example, the MoSi2 particle-based conductive phase further comprises 1 wt% of an element selected from Al, Ta, Ti, Zr, Y and B.

[0053] 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 of less than 10 kV and preferably 6 kV.

[0054] According to one example, the injection electrode has, on at least a portion of the assembly, a tip configuration also referred to as a tip electrode. The tip 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.

[0055] 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 the plasma.

[0056] According to one example, the separator material has a cylindrical shape extending in a main extension direction of the assembly, and:

[0057] - 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,

[0058] - on a second portion of the assembly, distinct from the first portion, the electrode connected to the 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.

[0059] In the first portion, the plasma is generated in the homogeneous regime. In the second portion, the plasma is generated mainly in the erratic regime. The assembly thus has 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 successively treated by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

[0060] 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.

[0061] According to one example, the first portion and the second portion are separated by an intermediate portion, the assembly being configured such 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.

[0062] Depending on the volume constraint associated with the device, it is also possible to provide that the first and second portions are directly juxtaposed, in order to limit the size of the device.

[0063] According to one example, the separator material has a first face and a second face opposite the first face, the injection electrode and the grounded electrode are arranged on the first face of the separator material, the injection electrode and the grounded electrode 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 the two homogeneous and erratic regimes. These two regimes can coexist spatially. The assembly thus has a treatment zone in which the two regimes coexist and follow each other temporally. The gas phase thus passes through the treatment zone and is successively treated by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

[0064] According to one example, on the second face of the separator material, at least one injection electrode and at least one grounded electrode are further 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 by the electrodes. The compactness of the device is further improved.

[0065] In one example, the injection electrode and the grounded electrode each have a facing tip configuration between the injection electrode and the grounded electrode. This promotes surface rather than bulk discharge.

[0066] According to one example, the grounded electrode has a first face comprising at least one opening exposing the separator material, 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 grounded electrode. This geometry can be described as a "tip / surface plane". An advantage of this geometry is that it promotes the quantity of plasma generated.

[0067] In one example, the assembly is connected to a power module configured to power the assembly with a pulsed electrical voltage signal. The pulsed signal allows a pulsed voltage to be applied to generate the plasma. This type of current is compatible with all assembly geometries.

[0068] In one example, the assembly is connected to a power supply module configured to power the assembly with an alternating voltage signal. An alternating signal is less expensive and simpler to implement in use. The design of the device is therefore simplified and its cost reduced. For this, it is preferable for the electrodes to be arranged on the same face of the separator material.

[0069] In one example, the device includes a plurality of assemblies stacked in at least one direction perpendicular to a main extension direction of the assembly. The plurality of assemblies allows for increasing the amount of gas phase treated, while reducing the dead volume between the assemblies to increase the compactness of the device.

[0070] In 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.

[0071] According to one example, in the device, the gas phase is at atmospheric pressure.

[0072] In the remainder of the description, the term "on" does not necessarily mean "directly on". Thus, when it is indicated that a part or member A is supported "on" a part or member B, this does not mean that the parts or members A and B are necessarily in direct contact with each other. These parts or members A and B may be either in direct contact or be supported on each other by means of one or more other parts. The same applies to other expressions such as, for example, "A acts on B", which may mean that "A acts directly on B" or that "A acts on B by means of 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", "inner", "outer".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 concept of "longitudinal" corresponds to the main direction of extension of the assembly, a direction which is substantially parallel to the direction of circulation of the gas phase in the assembly.

[0073] We will also use a reference whose longitudinal or back / front direction corresponds to the x axis, the transverse or right / left direction corresponds to the y axis and the vertical or down / up direction corresponds to the z axis.

[0074] 11 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 has 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. It is therefore understood that the thickness of the material can be the smallest of the other dimensions of the material (compared to the length, the width or the radius for example).

[0075] The device 1 for treating a gas phase 2 is now described according to several exemplary embodiments with reference to the figures.

[0076] As illustrated in Figure 1, the device 1 is configured so that a gaseous phase 2 to be treated flows into the device 1. The gaseous phase 2 may comprise suspended species 20, and in particular polluting species, for 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 gaseous phase 2 circulates. For this, the device may comprise a suction module 14 for the gaseous 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.

[0077] 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.

[0078] 12 of the 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 electric voltage, a plasma is generated between the injection electrode 110 and the electrode connected to 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.

[0079] During its circulation in the device 1, the gaseous 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 gaseous 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 the species 20 are eliminated.

[0080] The injection electrode 110 and the grounded electrode 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 referred to as the trigger voltage Vo. When the separator material 112 is subjected to an electrical voltage greater than or equal to the trigger voltage Vo, it exhibits electrically conductive behavior allowing the passage of an electric current. This separator material 112 therefore exhibits a non-linear electrical resistance (the ratio U / l is not constant). Below the trigger voltage Vo, it exhibits a high impedance and therefore a very low leakage current, and preferably a zero leakage current.Above the breakdown voltage Vo, the material 112 has a lower impedance and allows the passage of a higher leakage current. In other words, beyond the breakdown voltage Vo, the impedance of the separator material 112 drops to allow electrical conduction in the form of a leakage current. When the voltage returns to a level below the breakdown voltage, the impedance increases again to return to its initial value. The transition can be abrupt when changing from insulating / conducting behaviors but also from insulating / low leakage current / conducting behaviors. The wider the transition zone (Le., voltage range), the more the weakly mixed homogeneous regime exists.

[0081] It is therefore understood that the separating material 112 can pass from one behavior to the other and vice versa depending on the applied voltage, unlike an insulator which is destroyed beyond its breakdown voltage and which can no longer regain insulating behavior when the voltage drops.

[0082] These electrical behaviors of the separator material 112 can be observed using the assembly 4 illustrated in FIG. 2, in which a power source 40 supplies an electrical circuit connected to the separator material 112. The electrical circuit comprises a voltmeter 41 connected in parallel to the separator material 112 and an ammeter 42 connected in series to the circuit. It is thus possible to measure the voltage across the separator material 112 and the intensity of the current flowing 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. FIG. 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.

[0083] At the breakdown voltage, the insulator 7 is destroyed and no longer exhibits insulating behavior. When they are subjected to a voltage greater than the breakdown voltage Vo, the separator materials 112a, 112b, 112c change 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 gradual as illustrated by the three curves 112a, 112b, 112c. The shape 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 called an energetic regime).

[0084] 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 access the two plasma generation regimes, particularly in combination with a 50 Hz AC signal, an electro-ceramic material and a surface geometry.

[0085] Generally speaking, the person skilled in the art will know how to adapt the value of the trigger voltage according to the nature of the signal, the nature of the material and the geometry for the intended application.

[0086] 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.

[0087] The skilled person will be able to adapt the variable parameters without any difficulty to obtain the desired effect. In particular, he will be able to adapt the nature of the signal (for example, for a pulsed 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 known as the inter-electrode "gap"). Naturally, the reactor will also be sized in relation to the desired end use in terms of flow rate.

[0088] 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 an energetic multi-filamentary volume regime by discharge in the conductive behavior, or even a mixed regime.

[0089] The energy regime is not accessible with insulators in conventional DBD devices. This regime allows, 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 a plasma in a homogeneous regime, such as sulfides, aromatic compounds, and halogenated VOCs. The treatment of VOCs in a plasma in a homogeneous regime can also generate ozone and / or harmful reaction byproducts.

[0090] During the development of the invention, it was observed that a complementary treatment to a homogeneous plasma 3 by a plasma 3 in an energetic regime makes it possible to limit, and preferably to eliminate, the residual ozone as well as the reaction by-products as well as to obtain a better selectivity in CO2. This complementary treatment also makes it possible to degrade molecules which would not have been degraded by a plasma 3 discharge in a homogeneous regime, too low in energy, and in particular ketones or even acids.

[0091] Furthermore, 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 a homogeneous regime and plasma discharges 3 in an energetic regime allows an aggregation of the particles possibly present in the 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 the device 1 are reduced, which limits the fouling of the assembly 11 and / or the risk of short circuit.

[0092] The device 1 can be used in a process for treating a gaseous phase 2. This gaseous phase 2 can be indoor air, for example inside a building, or an industrial waste gaseous phase.

[0093] The gaseous phase 2 can be introduced into the assembly 11, for example by suction through the suction module 14. The suction module is sized in relation to the treatment capacity of the device, which is itself sized according to the need for treatment of the gaseous phase. For example, for the treatment of the air in a room of 30 m 2 a flow rate of 250Nm 3 / h is desirable.

[0094] The electrical voltage can be applied to the assembly 11 to generate a plasma 3 between the injection electrode 110 and the grounded electrode 111 to treat the gas phase 2. The voltage applied to generate the plasma 3 can have a non-zero value of less than 10 kV, for example between 3 and 6 kV.

[0095] According to one example, the gas phase 2 is introduced continuously into the device 1. The plasma treatment 3 can also be carried out continuously. Alternatively, it can be provided that the plasma treatment is carried out discontinuously or non-constantly. For example, it can be provided that the activation of the treatment and / or its flow rate are controlled according to the pollution of the gas phase to be treated. For this, it is possible to provide sensors arranged to measure a parameter relating to the pollution or contamination of the gas phase. The control is a function of these measurements. Thus, according to this control, the volume of gas phase 2 sucked in can then be treated by successive volumes.

[0096] Specific examples of separating material

[0097] The separator material 112 is now described according to several exemplary embodiments.

[0098] The separator material 112 can be chosen from:

[0099] - a semiconductor material, for example a semiconductor ceramic, such as for example SiC, ZnO or GaN,

[0100] - a semiconducting polymer,

[0101] - a composite material comprising conductive or semi-conductive particles dispersed in an insulating matrix.

[0102] The composite material may, in one example, comprise conductive or semiconductive 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 semiconductive particles may be based on or made of a metal, a metal alloy or a ceramic. For example, the composite material may be a polymer / metal, polymer / ceramic, a 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%.

[0103] Porosity can also be predicted to be zero or low.

[0104] When a volume plasma is generated, for example with one electrode in contact with the separator material 112 (for example electrode connected to ground 111) and the other electrode (for example the injection electrode 110) not in contact with the material while 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 required to initiate the cold plasma. The lower this thickness, the more the erratic regime is thus favored since it will appear more quickly for lower initiation voltages. However, if this thickness is too thin, this limits the lifetime of the reactor by 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.

[0105] When generating a surface plasma, it was shown during the development of the invention that the thickness does not have a significant influence on the plasma. However, this thickness can impact the lifetime 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.

[0106] Note that these thicknesses are correlated with the dimensioning of the reactor and can therefore be adapted according to this dimensioning.

[0107] 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.

[0108] 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).

[0109] The composite ceramic is formed from a conductive phase included in an insulating matrix. This makes it possible to obtain a globally semiconducting material with a microstructure of the same type as Sialon and SiC-based semiconducting ceramics (grain boundaries, defects, etc.) and optimal thermomechanical properties.

[0110] 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 global approach.

[0111] In order for the injected charges not to be conducted through the volume of the ceramic, the implantation of the charges must be done at a speed higher 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 formation of a double Schottky barrier. The grain boundaries are in fact comparable to two back-to-back Schottky diodes. Trapping induces a space charge, there is therefore a field gradient then a relaxation of this space charge this relaxation depending on the carrier transit time and the thickness of the insulator. The greater the thickness of the insulator, the greater the relaxation time and the "breakdown" voltage (in fact conduction) is high.

[0112] Conduction in ceramics in this example is controlled by several mechanisms:

[0113] - first of all, at the ceramic interfaces: the Schottky emission (the increase in electronic emission when the applied electric field increases is due to the decrease in the extraction work), which determines the quality of the injection and which is strongly correlated with the quality of the contacts and the field emission;

[0114] - then, in the mass of the ceramic: the Poole-Frenkel effect (trapping / detrapping) and the hopping effect (conduction by jump).

[0115] The Fowler-Nordheim tunneling effect and space charge also participate in conduction both at interfaces and in the bulk.

[0116] The constraint is now carried by the material's ability to withstand severe environmental constraints.

[0117] The materials considered for the conductive phase can be GaN, MoSi2, HfB2, TiB2, ZrB2 or even TiN.

[0118] Properties of these materials are given in the following table.

[0119] Molybdenum disilicide (MoSi2) can be an advantageous material for the realization of the conductive phase due to its intrinsic qualities but also due to 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 a high resistance to oxidation up to 1600°C, that MoSi2 has a high thermal conductivity 50 WMK, and that MoSi2 is thermodynamically stable.

[0120] 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 as connections between capacitors whose dielectric is formed by TAI2O3.

[0121] Near the critical region, only a few percolating beam paths remain, making the role of capacitors very important. With a microstructure featuring large alumina "packets" that are the capacitors governing the conduction mechanism, and which are too large to allow the passage of charges by tunneling, the charges remain trapped in the alumina and conduction remains very limited.

[0122] Conversely, when the conductive particles are small and above all well dispersed, the percolation threshold is lowered and there is instantaneous conduction as soon as a voltage is applied, the inter-particle distance having been greatly reduced.

[0123] Two microstructures of the same compositions can thus present totally 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 that where none are in contact.

[0124] Therefore, the microstructure according to the invention is a homogeneous distribution of 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 tunnel effect, compensate for the tearing off of excessively large MoSi2 particles which would cause a break in the conduction process by distant percolation and to obtain satisfactory mechanical properties.

[0125] The presence of a "conductive particle size gradient" 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:

[0126] - “small particles”: average diameter less than 240 nm (19.5 to 24% of the particles in the conductive phase);

[0127] - “medium particles”: average diameter of 240 nm to 1 pm (45.5 to 56% of the particles in the conductive phase);

[0128] - “large particles”: average diameter of 1 pm to 11 pm (20 to 35% of the particles in the conductive phase).

[0129] 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.

[0130] The probability of transfer by tunnel effect decreases with the inter-particle distance; when we have large particles, it is preferable to compensate these distances by defects in the inter-particle zone or by the presence of small particles which ensure conduction always without contact but by tunnel effect made easier by the smallest inter-particle distances.

[0131] Medium particles are of "intermediate" use, ensuring conduction once it is established (and can play the role of either large or small particles depending on where they are located) and allowing the material to be homogenized.

[0132] The expected microstructure is therefore grains as well as agglomerates of MoSi2 grains (of controlled sizes) distributed uniformly in the matrix.

[0133] It should be noted that, when the alumina grain size is reduced, the number of grain boundaries is increased and thus the number of trapping regions is extended, with conduction increasing; therefore, the alumina grain size is also a factor to be controlled.

[0134] We therefore propose a semi-conductor ceramic comprising:

[0135] - 5 to 40% by volume of a particulate conductive phase, preferably based on MoSi2 particles;

[0136] - 60 to 95% by volume of a particulate insulating phase, the particle size of the conductive phase being between 5 nm and 10 pm, and the distance between two neighboring particles of conductive phase being between 0.1 and 10 pm.

[0137] Preferably, a semiconductor ceramic is proposed comprising:

[0138] - 10 to 30% by volume of a conductive phase based on MoSi2 particles,

[0139] - 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, the term "particle" means a grain or an aggregate / cluster of grains.

[0140] The measurement method used to measure the size of MoSi2 particles involves scanning electron microscopy observation of the fracture surface of broken samples. The images are then reprocessed using ESIVISION Analysis 3.2 software. The average diameter of the MoSi2 particle is obtained.

[0141] Advantageously, the semiconductor ceramic may comprise 15 to 25% by volume of MoSi2 and preferably 21 to 24% by volume of MoSi2.

[0142] According to the present invention, a "conductive phase based on MoSi2 particles" is understood to be essentially composed of these particles. It may however include other constituents such as carbon, boron or various metals.

[0143] 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 an alternative 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 of insulating phase + conductive phase) of a simple element (C, B, etc.) or of a rare earth. An advantage of the introduction of carbon (boron or rare earth) is to improve the mechanical properties of the conductive phase in MoSi2. The insulating phase can be made from AI2O3, SisN4, mullite (2 SiC>2, 3 AI2O3), or even ALON.

[0144] Properties of these materials are given in the following table.

[0145] In one embodiment of the ceramic according to the invention, the insulating phase of the ceramic is made from SisN4. Indeed, this material has greater hardness, greater thermal conductivity and greater resistivity than AhOs, mullite and ALON.

[0146] In another embodiment of the ceramic according to the invention, the insulating phase is made from ALCh.

[0147] Indeed, alumina (AI2O3) has high electrical resistivity, excellent creep resistance at temperatures above 1400°C and good resistance to chemical attack. 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 similar 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 pm.

[0148] The measurement method used to measure the particle size of the insulating phase involves scanning electron microscopy observation of the fracture surface of broken samples. The images are then reprocessed using ESIVISION Analysis 3.2 software. The average particle diameter of the insulating phase is obtained.

[0149] 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%. It is also possible to provide for the porosity to be zero or low.

[0150] This porosity value depends on the technique used to make the ceramic. For example, if natural sintering is used to make the ceramic, the average porosity is less than or equal to 10%. If hot press sintering (HP) is used, the average porosity of the ceramic is less than or equal to 2%. Finally, if current-assisted sintering (SPS) is used, the average porosity of the ceramic is less than or equal to 3%. All of these sintering techniques will be described in more detail below.

[0151] 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 lead to the disintegration of the semiconductor ceramic. Vitrification of the surface of the semiconductor ceramic therefore makes it possible to improve the strength 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 the invention can also comprise 0.1 to 0.9% by weight of lanthanide compound (for example La2Os, or La2Be). A lanthanide (La2O3, LaBe) is a material promoting electronic emission. Thus, its addition, in small quantities, to the semiconductor ceramic makes it possible to reinforce the thermo-emission of the semiconductor ceramic.

[0152] A method of manufacturing the semiconductor ceramic according to this example is now described.

[0153] To solve the long-term reliability problems of electrically conductive ceramics, it is important to develop a material under optimal conditions and control its microstructure in order to obtain the desired properties. The electrical characteristics depend on the volume percentage of the conductive phase and the type of microstructure developed after sintering.

[0154] The production process, whose most important parameters determine the microstructure and thus the physical characteristics of the sintered samples, is in fact the crucial phase. These parameters concern in particular:

[0155] - the nature of the powders,

[0156] - the proportions of the insulating and conductive phases,

[0157] - the quantity and composition of additives,

[0158] - deagglomeration processes,

[0159] - the shaping technique,

[0160] - the sintering conditions.

[0161] The manufacturing process of a semiconductor ceramic includes the following steps:

[0162] - 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,

[0163] - mixing 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),

[0164] - drying and sieving of the composition;

[0165] - sintering 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 conductive phase is between 30 Å and 5 pm.

[0166] As described above, the conductive phase may be selected from the group consisting of MoSi2, TiB2, TiN.

[0167] Furthermore, the insulating phase can be based on alumina AI2O3 or mullite, SisN4. To prepare the first slip, the conductive phase of MoSi2 is mixed with water with a pH between 8 and 10.

[0168] This improves 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 prevents the agglomeration of the alumina particles AI2O3 II and is advantageously introduced at a level of 0.1% by weight.

[0169] The two slips are then mixed to obtain a mixture of the two phases. The intimate mixing of the two slips is carried out using a jar turner or ball mill. The grinding time is between 5 and 24 hours.

[0170] 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 placed with glass beads (diameter 10 mm) in a 250 pm mesh sieve of an electric sieve, the powder passed to 250 pm is poured into a 100 pm mesh sieve containing alumina beads (diameter 3 mm).

[0171] The composite powder thus collected and roughly granulated is ready to be shaped and then sintered. The shaping step is optional. Its implementation depends on the sintering technology used. The shaping step transforms the material into a green product with controlled size, shape and surface area and specific density and microstructure. Careful control of the density and microstructure of a green ceramic is necessary to obtain the performance of the final product because the defects introduced by the shaping process are generally not eliminated by sintering.

[0172] A smooth and even surface is normally desirable and may be essential for some products. Strength must be sufficient to carry out the operations that follow forming. Product reproducibility is very important for industrial production. The size and density of the green part must be controlled to maintain a constant shrinkage factor between the green and sintered part. For the forming stage, so-called compaction or dry compaction technology can be used.

[0173] Compaction is a process of shaping powder or granulated material enclosed in a rigid or flexible mold.

[0174] Dry compaction is a widely used process due to its reproducibility and its ability to produce large-format parts of various shapes that do not shrink during drying. It preferably includes the following steps:

[0175] - (1) filling of the matrix;

[0176] - (2) compaction and shaping;

[0177] - (3) ejection of the part;

[0178] - (4) densification.

[0179] The composition is then sintered. Unlike ceramic firing, sintering does not, in principle, involve the bonding of particles by a glassy phase. The coherence and densification of the pressed powders occur as a result of transformations affecting the surface of the particles and leading to solid-solid interfaces called grain boundaries. The sintering conditions determine the microstructure and therefore the properties of the final material.

[0180] Advantageously, different technologies can be used for sintering the composition. For example, in one embodiment of the method, the sintering is natural sintering. In another embodiment, the sintering is hot press sintering. In yet another embodiment, the sintering is current-assisted sintering (SPS).

[0181] For the implementation of hot press sintering, the press furnace used is of the Goliath type (Stein Heurtey Physitherm) combining a press (maximum load 20 tonnes) and a graphite resistance furnace (maximum temperature 2200°C) the use of which requires an inert atmosphere or a high vacuum.

[0182] Temperature control is provided by a 5 / 26% tungsten / rhenium thermocouple placed near the resistor and by a bichromatic pyrometer (IRCON®) which measures the actual temperature at the surface of the tool. Hot press sintering (HP) produces 37 mm pellets. It does not require any pellet shaping.

[0183] 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 to obtain the best densification / microstructure compromise favorable to the expected electrical behavior is 1500°C.

[0184] For natural sintering, the same furnace is used as for hot pressing. However, in this case, the samples are placed in a graphite crucible after the shaping step and are not subjected to any load during sintering.

[0185] In order to limit gas exchange with the outside, the preformed pellets are placed in an alumina crucible for "bogue firing", i.e. the use of loose powder of the same nature as the pellets and coating them to avoid any contact with the furnace atmosphere. Spark Plasma Sintering (SPS) can also be carried out, as described above. Spark Plasma Sintering (SPS) allows materials to be densified while retaining the characteristics of the initial powders and densifying difficult materials.

[0186] Current-assisted sintering (SPS) is a process similar to conventional hot pressing. The precursors (metals, ceramics, polymers and their composites, etc.) are introduced into a chamber (made of graphite) allowing uniaxial pressure to be applied during sintering.

[0187] The main difference in this process is that the heat source is not external. An electric current (direct current - pulsed direct current - or alternating current) passes through the conductive pressing chamber and also, in appropriate cases, through the sample.

[0188] Thus, the enclosure itself acts as a heating source, which allows 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, above all, 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 existing materials.

[0189] Densification is increased by the use of a pulsed current or field.

[0190] Special examples of assemblies 11

[0191] The assembly 11 is now described in more detail according to several exemplary embodiments, with reference to figures 4 to 6.

[0192] Conventional assembly geometries 11 used in DBD devices can be used for device 1 with separator material 1 12.

[0193] Particular geometries have further been developed. According to one example, at least the injection electrode 110 has, on at least a portion of the assembly 11, a pointed configuration. An electrode with a "point configuration" is understood to mean a configuration in which the electrode forms one or more peak structures, the point-shaped or equivalently peak-shaped end of these structures being arranged opposite the other electrode, for example the grounded electrode 111. By "point" or "peak", it is not necessarily implied that the end is conical; it may be sharp and planar. For example, the electrode may have a brush structure, the ends of the brush being arranged opposite the other electrode, as illustrated in FIG. 4. According to another example, the electrode may extend in a main extension direction between two point-shaped ends, as illustrated in FIG. 5.In another example, the electrode may be in the form of a rod, the ends of the rod forming the pointed structures described above. The pointed configuration of an electrode promotes plasma discharges in the erratic regime, in synergy with the nature of the separator material 1 12.

[0194] A first geometry is described with reference to Figure 4, according to an exemplary embodiment. The assembly 11 extends in a main extension direction x substantially parallel to the flow direction of the gas phase 2 in the assembly 11. The separator material 112 may have a cylindrical shape centered on the main extension direction x, and separate the injection electrode 110 and the electrode connected to the ground 111. By "cylindrical", it is meant that the cross-section of the separator material 112 may have a substantially circular, elliptical or ovoid shape.

[0195] The assembly 11 may have a first portion 11 a and a second portion 11 b, these portions being distinct from one another. Preferably, the first portion 11 a is located upstream of the second portion 11 b in the direction of flow of the gas phase 2 in the assembly 11.

[0196] In the first portion 11 a, the grounded electrode 111 and the injection electrode 110 may together form a coaxial structure centered around the main extension direction x, on either side of the cylindrical separator material 112. Note that the injection electrode 110 may be arranged inside the cylinder formed by the separator material 112, the grounded electrode 111 then being arranged outside the cylinder, or vice versa. This first portion 11 a promotes plasma discharges 3 in the homogeneous regime.

[0197] In the second portion 11 b, the grounded electrode may extend coaxially to the main extension direction x around the separator material 112. The grounded electrode 111 is then preferably arranged outside the separator material 112. The separator material 112 may delimit an interior volume 1120. The injection electrode 110 may be arranged in this interior volume 1120. The injection electrode 110 has a tip configuration in this volume. For example, the injection electrode 110 may have a brush structure whose tip ends are arranged opposite the separator material 112 and the grounded electrode 111. Preferably, the tip ends are arranged radially opposite 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.

[0198] In the first and second portions 11 a, 11 b, the grounded electrode 111 may be in the form of a grid or a plate. In the first portion 11 a, the injection electrode 110 may be in the form of a spiral.

[0199] The two portions 11 a, 11 b being distinct, it is understood that two treatment zones are thus formed:

[0200] - a first zone in which plasma discharges 3 in homogeneous regime are favored,

[0201] - a second zone in which plasma discharges 3 in energy regime are favored.

[0202] 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 zones are spatially distinct. Preferably, gas phase 2 flows into the first zone and then into the second zone to be successively treated by a homogeneous plasma and then an energetic plasma.

[0203] As illustrated in Figure 4, the portions 11 a, 11 b may be separated by an intermediate portion 11 c. 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 may thus react with each other to continue their degradation before entering the second zone. In particular, the ozone may react with the reaction by-products or the species 20 that have not been degraded in the first zone for their degradation.

[0204] Naturally, the person 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.

[0205] 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 face 11a 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, 111 may be arranged on each of the faces of the separator material 112. Thus, the compactness of the device 1 is improved.

[0206] For example, the injection electrode 110 may have a pointed configuration opposite the grounded electrode 111. These geometries allow the generation of plasma discharges according to the two homogeneous and energetic regimes. These two regimes may in particular coexist spatially. The assembly thus has a treatment zone in which the two regimes coexist and follow each other temporally. In these two geometries, the plasma discharge energetic regime 3 may be predominant.

[0207] In the second geometry, the injection electrode 110 and the grounded electrode 111 each have a pointed configuration facing each other. For example, each electrode 110, 111 may extend in a main extension direction, for example the y direction, between two pointed ends. The electrodes 110, 111 are arranged such that at least one end of each injection electrode 110 faces one end of a grounded electrode 111.

[0208] The assembly 11 may comprise several injection electrodes 110 and several grounded electrodes 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 gas phase 2 in the assembly 11. The grounded electrodes 111 may 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 may be spaced a distance d from a row of grounded electrodes 111. The distance d may be chosen so as to favor a particular plasma discharge regime. This is particularly the case when the assembly 11 is powered by a pulsed signal, as described in more detail later. The distance d is for example between 3 and 25 mm, preferably between 10 and 15 mm.

[0209] In the third geometry, the separator material 112 may be at least partly covered by the grounded electrode 111. The grounded electrode 111 then has an upper face 111a comprising openings 1110 leaving the separator material 112 visible. The injection electrode 110 may 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 the latter. The injection electrode 110 may extend in an oblique direction, and preferably perpendicular, to the first face 111a of the grounded electrode 111.

[0210] According to one example, the grounded electrode 111 has several openings 1110, and an injection electrode 110 is arranged at each opening 1110.

[0211] The injection electrode 110 may 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 may be connected, preferably directly, to the power supply module 13.

[0212] In each of the described geometries, the injection electrode 110 may be connected directly or via another element, such as another injection electrode 110 or a conductive element, to the power supply module 13.

[0213] For each of the geometries described, the power supply module 13 configured to supply the assembly 11 can supply it with a pulsed electric current. This pulsed electric current comprises phases of application of the current interspersed with phases during which no current is applied. The electrical signal supplying the assembly 11 is therefore discontinuous. The voltage applied to the assembly is thus pulsed and may be positive or negative. A phase of application of the current, preferably each phase of application of the current, 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.

[0214] For the second and third geometries, the power supply module 13 can supply the assembly 11 with an alternating electric current (abbreviated AC). An AC power supply requires that the electrodes 110, 111 be arranged on the same face of the separator material 112. This type of power supply is less expensive 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 a 50 Hz alternating signal at only 3 kV (compared to 20 kV for conventional DBD devices), with an inter-electrode distance of 10 to 15 mm for the second geometry.

[0215] Note that it may be provided that the device 1 is configured so as to be supplied with both pulsed current and alternating current. This may in particular make it easier to spatially separate one or more plasma discharge zones in a homogeneous regime and one or more plasma discharge zones in an energetic regime. For this, the device 1 may comprise several assemblies 11, a portion of these assemblies 11 being supplied with pulsed current and the other portion being supplied with alternating current. Alternatively or in addition, for an assembly 11, and in particular for the second and third geometries, a portion of the injection electrodes 110 may be supplied with pulsed current and the other portion may 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 direction of extension 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 assemblies of planar geometry 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 illustrated in Figure 9, the assemblies of cylindrical geometry can be stacked in the y and z directions to form a compact stack.

[0216] The device 1 may comprise 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

[0217] As an example, the degradation of two VOCs was measured with an assembly 11 having a conventional tip / plane geometry, therefore in volume, with a distance between electrodes of 4 mm. The applied signal is a positive pulsed square signal. The separator material 1 12 is a semiconducting ceramic according to the particular example described previously. These measurements were compared with an assembly of a conventional DBD reactor 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, the gas phase 2 comprises ethylene at an initial concentration of 500 ppm. In Figure 10B, the gas phase 2 comprises isopropanol at an initial concentration of 500 ppm.In both cases, the VOCs are degraded at a lower voltage than that required to generate the plasma for conventional DBD device assemblies. Furthermore, higher degradation percentages are achieved for both VOCs for assembly 11 including the semiconductor ceramic.

[0218] Assembly 11 described above was tested on many 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.

[0219] In view of the above description, it appears clearly that the invention proposes a device improving the treatment of a gaseous phase by plasma, and in particular air.

[0220] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. The present invention is not limited to the examples previously described. Many other variant embodiments are possible, for example by combining previously described characteristics, without departing from the scope of the invention. In addition, the characteristics described in relation to one aspect of the invention may be combined with another aspect of the invention. In particular, the device may comprise any characteristic allowing the implementation of a step of the method and the method may comprise any step resulting from the implementation of a characteristic of the device.

Claims

Claims Device (1) for treating a gaseous 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 "separating 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 the ground (111), and in which the separator material (112) has an electrically insulating behavior when the separator material (112) is subjected to an electrical voltage lower than a threshold voltage, called "starting voltage", and an electrically conductive behavior allowing the passage of a current when the separator material (112) is subjected to an electrical voltage greater than or equal to the starting voltage,and characterized in that the separator material (112) is a composite material comprising conductive or semiconductive 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 semiconductive 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 separator material (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 the 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 tip configuration arranged 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 electrical 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 grounded electrode (111) are arranged on the first face (112a) of the separator material (112), the injection electrode (110) and the grounded electrode (111) being arranged at a distance from each other. Device (1) according to the preceding claim, wherein, on the second face (112b) of the separator material, at least one injection electrode (110) and at least one grounded electrode (111) are further arranged at a distance from each other. Device (1) according to either of the two preceding claims, wherein the injection electrode (110) and the grounded electrode (111) each have a facing tip configuration between the injection electrode (110) and the grounded electrode (111).Device (1) according to either of Claims 5 and 6, wherein the grounded electrode (111) has a first face (111 a) comprising at least one opening (1110) leaving the separator material (112) visible, 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 grounded electrode (111). Device (1) according to either of the preceding claims, wherein 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 either 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 direction of extension (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, • applying 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 of less than 10 kV and preferably 6 kV. Method according to either of the two preceding claims, in which, in the device (1), the gas phase (2) is at atmospheric pressure.

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