WO2020221598A1 - Process for photocatalytic decontamination of a gaseous medium in the presence of an external electric field - Google Patents

Process for photocatalytic decontamination of a gaseous medium in the presence of an external electric field Download PDF

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WO2020221598A1
WO2020221598A1 PCT/EP2020/060747 EP2020060747W WO2020221598A1 WO 2020221598 A1 WO2020221598 A1 WO 2020221598A1 EP 2020060747 W EP2020060747 W EP 2020060747W WO 2020221598 A1 WO2020221598 A1 WO 2020221598A1
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photocatalyst
elements
groups
electric field
organic compounds
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French (fr)
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Antoine Fecant
Céline PAGIS
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IFP Energies Nouvelles
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/68—Halogens or halogen compounds
    • B01D53/70—Organic halogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20707—Titanium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20792—Zinc
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/70—Non-metallic catalysts, additives or dopants
    • B01D2255/702—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/80—Type of catalytic reaction
    • B01D2255/802—Photocatalytic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/20—Halogens or halogen compounds
    • B01D2257/206—Organic halogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B01D2257/7027—Aromatic hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/708—Volatile organic compounds V.O.C.'s
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

  • the field of the invention is that of the decontamination of a gaseous medium comprising volatile organic compounds by means of a photocatalytic process.
  • a first method consists in bringing the gaseous medium into contact with an adsorbent (also called here a capture mass) consisting mainly of activated carbon.
  • an adsorbent also called here a capture mass
  • VOCs volatile organic compounds
  • Photocatalysis is based on the principle of activating a semiconductor or a set of semiconductors such as a photocatalyst, using the energy provided by the irradiation.
  • Photocatalysis can be defined as the absorption of a photon, the energy of which is greater than the forbidden bandwidth or "bandgap" according to English terminology between the valence band and the conduction band, which induces the formation of an electron-hole pair in the case of a semiconductor.
  • bandgap forbidden bandwidth
  • a semiconductor is characterized by its forbidden band or “bandgap”, ie the energy difference between its conduction band and its valence band, is specific to it. Any photon with energy greater than its forbidden band can be absorbed by the semiconductor. Any photon with energy below its forbidden band cannot be absorbed by the semiconductor.
  • Z. Jiang et al. (Chemosphere, 56, p. 503-508, 2004) carried out the photocatalytic degradation under electric field of the red organic pigment X-3B by a TiO2-based semiconductor deposited on an aluminum conductive plate electrically connected to one of the two electrodes.
  • This implementation allows a deposition rate of 0.3 to 4 gTiO2 / m2 depending on the number of deposits made, which corresponds to a loading rate relative to the total electrode area of less than 2 g / m2.
  • C.M. Tank et al. (Solid State Science, 13, p. 1500-1504, 201 1) implemented the photocatalytic degradation under electric field of methylene blue by a semiconductor based on TiO2 deposited on porous silicon serving as an electrode. This implementation has low photocatalyst loading rates relative to the total electrode area.
  • US 2018/0185785 describes an air purification process comprising the use of an electric field prior to the photocatalytic reaction to cause the precipitation of pollutants.
  • the method further claims the coupled use of a photocatalytic material and an absorbent material.
  • the photocatalytic material is brought into contact with at least one of the two electrodes generating the electric field.
  • the known implementations of the prior art reveal that the photocatalyst is in electrical contact with at least one of the electrodes generating the electric field, this implementation involves the consumption of at least part of the electrons supplied by the electric generator by reagents, and thus additional energy consumption due to the passage of an electric current.
  • the object of the invention is to provide a new and more efficient way of photocatalytic decontamination of a gaseous medium using an external electric field, using a photocatalyst.
  • the photocatalytic decontamination process according to the invention makes it possible to achieve improved performance, in particular with better mineralization of VOCs.
  • the state of the art relating to photocatalytic processes in the presence of an electric field differs from the invention in that there is an electrical contact of the active photocatalytic species with at least one of the electrodes used to generate the. electric field, this induces a consumption of electric current between the electrodes.
  • this implementation does not allow a high charging rate per unit of electrode area, which has the particular drawback of having to use very large electrode areas to improve the efficiency of the systems, and therefore represents a cost and a large footprint of the systems.
  • the method according to the invention allows a higher loading rate per unit electrode area than the methods known from the state of the art.
  • the presence of an external electric field allows a better separation of the electron-hole pairs generated after the absorption of photons by the photocatalyst.
  • the invention describes a photocatalytic process for the treatment of a gaseous charge containing one or more volatile organic compounds and dioxygen, said process comprising the following steps: a) a gaseous charge containing one or more organic compounds is brought into contact.
  • the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field, c) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength absorbable by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.
  • group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IU PAC classification.
  • the total pore volume and the pore distribution are determined by nitrogen porosimetry as described in the book "Adsorption by powders and porous solids. Principles, methodology and applications ”written by F. Rouquérol, J. Rouquérol and K. Sing, internationale Press, 1999.
  • specific surface area means the BET specific surface area (SBET in m2 / g) determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established using the BRUNAUER-EMMETT-TELLER method described in the periodical " The Journal of American Society ", 1938, 60, 309.
  • the maximum absorbable wavelength by a semiconductor is calculated using the following equation:
  • external electric field is meant a voltage applied to an electrical system, without current generation and therefore without circulation of electrons from the anode to the cathode.
  • the applied voltage causes the creation of a potential, by the localized accumulation of medium electrons on the anode and the localized defect of medium electrons on the cathode, without current flow between the two electrodes.
  • Ohmic losses, intrinsic to any system, are not considered to be an electric current.
  • reaction medium is understood to mean the mixture formed by the feedstock containing one or more volatile organic compounds (VOCs) and dioxygen.
  • volatile organic compounds means, according to Directive 1999/13 / EC of the European Council, any compound containing at least the element carbon and one or more of the following elements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon or nitrogen, except carbon dioxide, and having a vapor pressure of 0.01 kPa or more at a temperature of 273.15 K.
  • the invention describes a photocatalytic process for treating a gaseous feed containing one or more volatile organic compounds and oxygen, said process comprising the following steps: a) a gaseous charge containing one or more volatile organic compounds and dioxygen is brought into contact with a photocatalyst, b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generators of said electric field, c) the photocatalyst is irradiated by at least one irradiation source producing at least one wavelength that can be absorbed by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.
  • a photocatalyst is brought into contact with a gaseous feed containing one or more volatile organic compounds and oxygen.
  • the feed treated according to the process is in gaseous form, and contains volatile organic compounds, as well as oxygen.
  • the feed treated according to the process is air, preferably air containing up to 10,000 ppm of volatile organic compounds.
  • the volatile organic compounds are chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes and ketones, alone or as a mixture.
  • a gaseous diluent fluid may be present in the reaction medium.
  • the presence of a diluting fluid is not required for carrying out the invention, however it may be useful to add it to the feed to ensure the dispersion of the feed in the reaction medium, to control the adsorption. reagents / products on the photocatalyst, dilution of the products to limit their recombination and other side reactions of the same order.
  • the presence of a gaseous diluent fluid also makes it possible to control the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalysed reaction.
  • the nature of the diluting fluid is chosen such that its influence is neutral on the environment reaction or that its possible reaction does not interfere with carrying out the desired reaction of degradation of the volatile organic compounds.
  • the gaseous diluent fluid is chosen from N2, 02, or air.
  • the photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors.
  • the wavelengths of the photons absorbable by said photocatalysts are between 310 nm and 1000 nm (ie a bandgap for inorganic, organic or organic-inorganic hybrid semiconductors generally between 1, 24 and 4 eV).
  • the semiconductor is chosen from inorganic semiconductors.
  • the inorganic semiconductors can be chosen from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium. They can also be composed of elements of groups NIA and VA, such as GaP, GaN, InP and InGaAs, or elements of groups II B and VIA, such as CdS, ZnO and ZnS, or of elements of groups IB and VI IA, such as CuCI and AgBr, or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi2Te3 and Bi203, or elements groups II B and VA, such as Cd3P2, Zn3P2 and Zn3As2, or elements of groups IB and VIA, such as CuO, Cu20 and Ag2S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe203 and Ni
  • the semiconductor is chosen from TiO2, Bi203, CdO, Ce203, Ce02, CeAI03, CuO, Fe203, FeTi03, ZnFe203, V205, ZnS, ZnO, W03 and ZnFe204, alone or as a mixture.
  • the semiconductor is chosen from organic semiconductors. Said organic semiconductors can be tetracene, anthracene, polythiophene, polystyrenesulfonate, phosphyrenes, fullerenes and carbon nitrides.
  • the semiconductor is chosen from organic-inorganic semiconductors.
  • organic-inorganic semiconductors mention may be made of crystallized solids of MOF type (for Metal Organic Frameworks according to the English terminology).
  • MOFs are made up of inorganic subunits (transition metals, lanthanides, etc.) and interconnected by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining hybrid crystallized networks, sometimes porous.
  • the photocatalyst is composed of one or more inorganic semiconductors.
  • the semiconductors of said photocatalyst can optionally be doped with one or more ions chosen from metal ions, such as for example ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, non-metallic ions, such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic ions.
  • metal ions such as for example ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti
  • non-metallic ions such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic ions.
  • the semiconductors constituting said photocatalyst may contain particles comprising one or more element (s) in the metallic state chosen from an element of groups IVB, VB, VIB, VI IB, VIIIB, IB, II B, 11 IA, IVA and VA of the Periodic Table of the Elements.
  • Said particles comprising one or more element (s) in the metallic state are in direct contact with said semiconductor.
  • Said particles may be composed of a single element in the metallic state or of several elements in the metallic state capable of forming an alloy.
  • the expression “element in the metallic state” (not to be confused with “metallic element”) is understood to mean an element belonging to the family of metals, said element being at zero oxidation degree (and therefore in the form of metal).
  • the element (s) in the metallic state are chosen from a metallic element of groups VI IB, VIIIB, IB and MB of the Periodic Table of the Elements, and particularly preferably from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium.
  • Said particles comprising one or more element (s) in the metallic state are preferably present in the form of particles with sizes between 0.5 nm and 1000 nm, very preferably between 0.5 nm, and 100 nm and even more preferably between 1 and 20 nm.
  • the semiconductors constituting said photocatalyst can be sensitized at the surface with any organic molecules capable of absorbing photons.
  • the process for preparing the photocatalyst can be any preparation process known to those skilled in the art and suitable for the desired photocatalyst.
  • the photocatalyst used in the process according to the invention can be in different forms (nanometric powder, nanoobjects with or without cavities, ...) or shaped (films, monolith, micrometric or millimeter size beads, ... ).
  • the photocatalyst is advantageously in the form of a nanometric powder.
  • the contacting of the gaseous charge containing one or more volatile organic compounds and dioxygen with said photocatalyst can be done by any means known to those skilled in the art.
  • the contacting of the gaseous charge containing one or more volatile organic compounds and dioxygen with said photocatalyst can be carried out in a crossed fixed bed or in a licking fixed bed.
  • the photocatalyst can also be deposited directly on optical fibers.
  • said photocatalyst is preferably fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen, is sent through the photocatalytic bed.
  • said photocatalyst When the contact is in a fixed licking bed, said photocatalyst is preferentially fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen, is sent to the photocatalytic bed.
  • the photocatalyst can also be deposited directly on optical fibers.
  • step b) of the method according to the invention the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating the field.
  • the photocatalyst is not in electrical contact, nor in physical contact with the electrodes generating said field.
  • the device for generating the electric field can be placed within the reaction medium or outside.
  • the location of the device will be adapted to the implementation of the process (fixed bed, licking bed, etc.).
  • the shape and size of the electrodes generating the electric field can be of any kind, adapted to the device and to the implementation of the method.
  • Electrodes generating the electric field include at least one conductive compound, such as steel, copper.
  • the device for generating the electric field is such that the photocatalyst is subjected to an electric field of between 10 V / m and 100 kV / m, preferably, the electric field is between 100 V / m and 10 kV / m.
  • step c) is carried out before step b).
  • the photocatalyst is irradiated by at least one irradiation source producing at least one wavelength that can be absorbed by the photocatalyst (ie less than the forbidden bandwidth of the semiconductor constituting said photocatalyst according to the variant where the photocatalyst is composed of at least one semiconductor) so as to degrade the volatile organic compounds into carbon dioxide by photocatalysis.
  • a photocatalyst composed of one or more semiconductors can be activated by the absorption of at least one photon.
  • the absorbable photons are those whose energy is greater than the forbidden bandwidth, at the "bandgap".
  • the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the widths of the forbidden band of the semiconductors constituting the photocatalyst or of a shorter wavelength.
  • any irradiation source emitting at least one wavelength suitable for the activation of said photocatalyst, that is to say absorbable by the photocatalyst, can be used according to the invention.
  • the irradiation source can be both natural by solar irradiation or by artificial irradiation of laser, Hg, incandescent lamp, fluorescent tube, plasma or light-emitting diode (LED, or LED in English for Light-Emitting Diode).
  • the source of irradiation is natural by solar irradiation.
  • the irradiation source produces radiation of which at least part of the wavelengths is less than the maximum absorbable wavelength (Amax) by the constituent semiconductors of the photocatalyst according to the invention.
  • the source of irradiation is solar irradiation, it generally emits in the ultra-violet, visible and infrared spectrum, that is, it emits a wavelength range of 280 nm to 2500 nm approximately (according to ASTM G173-03).
  • the source emits at at least one wavelength range greater than 280 nm, very preferably between 315 nm and 800 nm, which includes the UV spectrum and / or the visible spectrum.
  • the irradiation source provides a flow of photons which irradiates the reaction medium containing the photocatalyst.
  • the interface between the reaction medium and the light source varies depending on the applications and the nature of the light source.
  • the source of irradiation is an artificial or natural source of irradiation.
  • the irradiation source is located outside the reactor and the interface between the two can be an optical window made of pyrex, quartz, organic glass or any other interface allowing the photons absorbable by the photocatalyst according to the invention to diffuse from the external medium within the reactor.
  • the performance of said process is conditioned by the absorption capacity of said photocatalyst as well as by the supply of photons suitable for the photocatalytic system for the reaction envisaged, and therefore is not limited to a range of pressure or of specific temperatures apart from those ensuring the stability of the product (s).
  • the temperature range employed for the photocatalytic production of hydrogen is generally -10 ° C to + 200 ° C, preferably 0 to 150 ° C, and very preferably 0 and 50 ° C.
  • the pressure range used for the process is generally from 0.01 MPa to 70 MPa (0.1 to 700 bar), preferably from 0.1 MPa to 5 MPa (1 to 50 bar), and even more preferably from 0.1 MPa to 2 MPa (1 to 20 bar).
  • the process according to the invention can be carried out with a dry or wet gas up to 100% relative humidity, preferably the gas to be treated contains 0 to 60% relative humidity.
  • Material A is a commercial material consisting of TiO 2 nanoparticles supported by quartz fibers sold under the name Quartzel TM by the company Saint Gobain®. QuartzelTM is known to those skilled in the art for its excellent photocatalytic properties in air purification.
  • Photocatalyst B is a commercial TiO2-based semiconductor (Aeroxide® P25, Aldrich TM, purity> 99.5%).
  • the particle size of the photocatalyst is 21 nm and the specific surface area measured by the BET method is equal to 52 m2 / g.
  • H2PtCl6.6H20 (37.5% by mass of metal) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double-jacketed glass reactor. 3 ml of methanol then 250 mg of TiO 2 (Aeroxide® P25, Aldrich TM, purity> 99.5%) are then added with stirring to form a suspension.
  • the mixture is then left with stirring and under UV radiation for two hours.
  • the lamp used to provide the UV radiation is an HPK TM mercury vapor lamp of
  • the mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid.
  • Two water washes are then carried out, each of the washes being followed by centrifugation.
  • the powder recovered is finally placed in an oven at 70 ° C. for 24 hours.
  • the C Pt / TiO 2 photocatalyst is then obtained.
  • the Pt element content is measured by plasma source atomic emission spectrometry (or inductively coupled plasma atomic emission spectroscopy "ICP-AES" according to English terminology) at 0.93% by mass.
  • Photocatalyst D is a semiconductor based on commercial ZnO (Lotus Synthesis TM).
  • the specific surface measured by the BET method is equal to 50 m2 / g.
  • the mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid.
  • Two water washes are then performed, each of the washes being followed by centrifugation.
  • the powder recovered is finally placed in an oven at 100 ° C. for 12 hours.
  • the solid recovered then undergoes a calcination treatment in air at a flow rate of 1 L / g / h at 150 ° C. for 1 hour then at 450 ° C. for 2 hours with a temperature rise of 5 ° C./min.
  • the photocatalysts A, B, C, D and E are subjected to a test for photooxidation of toluene in the gas phase in a continuous through-bed reactor provided with a quartz optical window with a surface area of 5.3.10-4 m2 and of a frit facing the optical window on which the material is deposited.
  • Two copper electrodes shaped to suit the reactor and spaced an average of 2.4 cm apart are located inside the device.
  • the electrodes are surrounded by a Teflon ® film such that the photocatalyst is not in direct contact, and connected to a generator (Keysight, E36106A) so as to apply an electric field in the area where the photocatalyst is located.
  • the UV-Visible irradiation source is provided by an Xe-Hg lamp (Asahi TM, MAX302 TM).
  • the irradiation power is always maintained at 30 W / m2 measured for a wavelength range between 315 and 400nm.
  • the overall duration of each test is approximately 100 hours. The tests are carried out in two stages: a first stage of equilibrium without irradiation, a second stage of photooxidation under irradiation which makes it possible to estimate the photocatalytic performance.
  • the toluene mineralization rate values are markedly higher for an implementation according to the invention regardless of the photocatalysts used.

Abstract

The invention relates to a photocatalytic process for treating a gas feed comprising volatile organic compounds (VOCs) and dioxygen, using a photocatalyst in the presence of an external electric field, with the proviso that the photocatalyst is not in electric contact with the field-generating electrodes. Said method is carried out by bringing said feed containing the VOCs and the dioxygen into contact with said photocatalyst, and then by subjecting the photocatalyst to an external electric field and by irradiating the photocatalyst.

Description

PROCEDE DE DECONTAMINATION PHOTOCATALYTIQUE D’UN MILIEU GAZEUX EN PRESENCE D’UN CHAMP ELECTRIQUE EXTERNE PHOTOCATALYTIC DECONTAMINATION PROCESS OF A GASEOUS MEDIUM IN THE PRESENCE OF AN EXTERNAL ELECTRIC FIELD
Domaine technique Technical area
Le domaine de l'invention est celui de la décontamination d’un milieu gazeux comprenant des composés organiques volatiles au moyen d’un processus photocatalytique. The field of the invention is that of the decontamination of a gaseous medium comprising volatile organic compounds by means of a photocatalytic process.
Art antérieur Prior art
Actuellement, il existe de nombreux procédés permettant la décontamination d’un milieu gazeux, en particulier de l’air, susceptible de contenir des composés organiques volatiles. Currently, there are many processes for decontaminating a gaseous medium, in particular air, which may contain volatile organic compounds.
Une première voie consiste à mettre en contact le milieu gazeux avec un adsorbant (appelé aussi ici masse de captation) constitué principalement de charbon actif. Cependant, l’inconvénient de ce type d’adsorbant est qu’il doit être remplacé périodiquement pour assurer l’efficacité du système. Une autre voie proposée pour éliminer les composés organiques volatiles (COV) dans un milieu gazeux, notamment l’air, consiste en la dégradation photocatalytique de ces composés. Aujourd’hui, les dispositifs utilisés, comprenant principalement du dioxyde de titane (Ti02) en tant que phase active, présentent l’inconvénient de ne pas minéraliser totalement ces composés organiques volatiles, ce qui peut conduire à un relargage de ces composés potentiellement nocifs dans le milieu gazeux. A first method consists in bringing the gaseous medium into contact with an adsorbent (also called here a capture mass) consisting mainly of activated carbon. However, the downside to this type of adsorbent is that it must be replaced periodically to keep the system working. Another route proposed for removing volatile organic compounds (VOCs) in a gaseous medium, in particular air, consists of the photocatalytic degradation of these compounds. Today, the devices used, mainly comprising titanium dioxide (TiO 2) as active phase, have the drawback of not completely mineralizing these volatile organic compounds, which can lead to a release of these potentially harmful compounds in the gaseous medium.
La photocatalyse repose sur le principe d'activation d'un semi-conducteur ou d’un ensemble de semi-conducteurs tel qu’un photocatalyseur, à l'aide de l'énergie apportée par l'irradiation. La photocatalyse peut être définie comme l'absorption d'un photon, dont l'énergie est supérieure à la largeur de bande interdite ou "bandgap" selon la terminologie anglo-saxonne entre la bande de valence et la bande de conduction, qui induit la formation d'une paire électron-trou dans le cas d’un semi-conducteur. On a donc l'excitation d'un électron au niveau de la bande de conduction et la formation d'un trou sur la bande de valence. Cette paire électron-trou va permettre la formation de radicaux libres qui vont soit réagir avec des composés présents dans le milieu, afin d’initier des réactions d’oxydo-réduction, ou alors se recombiner suivant divers mécanismes. Un semi-conducteur est caractérisé par sa bande interdite ou « bandgap », i.e. la différence d'énergie entre sa bande de conduction et sa bande de valence, lui est propre. Tout photon d’énergie supérieure à sa bande interdite peut être absorbé par le semi-conducteur. Tout photon d’énergie inférieure à sa bande interdite ne peut pas être absorbé par le semi-conducteur. Photocatalysis is based on the principle of activating a semiconductor or a set of semiconductors such as a photocatalyst, using the energy provided by the irradiation. Photocatalysis can be defined as the absorption of a photon, the energy of which is greater than the forbidden bandwidth or "bandgap" according to English terminology between the valence band and the conduction band, which induces the formation of an electron-hole pair in the case of a semiconductor. We therefore have the excitation of an electron at the level of the conduction band and the formation of a hole on the valence band. This electron-hole pair will allow the formation of free radicals which will either react with compounds present in the medium, in order to initiate oxidation-reduction reactions, or else recombine according to various mechanisms. A semiconductor is characterized by its forbidden band or “bandgap”, ie the energy difference between its conduction band and its valence band, is specific to it. Any photon with energy greater than its forbidden band can be absorbed by the semiconductor. Any photon with energy below its forbidden band cannot be absorbed by the semiconductor.
Des procédés de décontamination photocatalytique d’un milieu gazeux sont connus dans l’état de l’art, notamment dans les publications de Y. Boyjoo et al., Chemical Engineering Journal, 310, p. 537-559, 2017; W.X. Zou et al., Chemosphere, 218, p. 845-859, 2019. Processes for the photocatalytic decontamination of a gaseous medium are known in the state of the art, in particular in the publications by Y. Boyjoo et al., Chemical Engineering Journal, 310, p. 537-559, 2017; W.X. Zou et al., Chemosphere, 218, p. 845-859, 2019.
Des procédés photocatalytiques en présence d’un champ électrique sont également connus dans l’état de l’art. Photocatalytic processes in the presence of an electric field are also known in the state of the art.
Z. Jiang et al. (Chemosphere, 56, p. 503-508, 2004) ont mis en œuvre la dégradation photocatalytique sous champ électrique du pigment organique rouge X-3B par un semi- conducteur à base de Ti02 déposé sur une plaque conductrice d’aluminium connectée électriquement à une des deux électrodes. Cette mise en œuvre permet un taux de déposition de 0,3 à 4 gTi02/m2 suivant le nombre de dépôts effectués ce qui correspond à un taux de chargement par rapport à la surface totale d’électrode inférieur à 2 g/m2. Z. Jiang et al. (Chemosphere, 56, p. 503-508, 2004) carried out the photocatalytic degradation under electric field of the red organic pigment X-3B by a TiO2-based semiconductor deposited on an aluminum conductive plate electrically connected to one of the two electrodes. This implementation allows a deposition rate of 0.3 to 4 gTiO2 / m2 depending on the number of deposits made, which corresponds to a loading rate relative to the total electrode area of less than 2 g / m2.
C.M. Tank et al. (Solid State Science, 13, p. 1500-1504, 201 1) ont mis en œuvre la dégradation photocatalytique sous champ électrique du bleu de méthylène par un semi- conducteur à base de Ti02 déposé sur du silicium poreux servant d’électrode. Cette mise en œuvre présente des taux faibles de chargement en photocatalyseur par rapport à la surface totale d’électrode. C.M. Tank et al. (Solid State Science, 13, p. 1500-1504, 201 1) implemented the photocatalytic degradation under electric field of methylene blue by a semiconductor based on TiO2 deposited on porous silicon serving as an electrode. This implementation has low photocatalyst loading rates relative to the total electrode area.
S.C. Xu et al. (ACS Sustainable Chem. Eng., 4, p. 6887-6893) ont mis en œuvre la réduction du Chrome VI contenu dans une eau contaminée en chrome III par photocatalyse sous champ électrique sous l’action d’un semi-conducteur à base de Ti02 déposé sur une grille de titane servant d’électrode. L’utilisation d’une grille à fine maille permet d’atteindre des taux de chargement en photocatalyseur par rapport à la surface totale d’électrode allant jusqu’à 250 g/m2. S.C. Xu et al. (ACS Sustainable Chem. Eng., 4, p. 6887-6893) implemented the reduction of Chromium VI contained in water contaminated with Chromium III by photocatalysis under an electric field under the action of a semiconductor based of Ti02 deposited on a titanium grid serving as an electrode. The use of a fine mesh grid achieves photocatalyst loading rates relative to the total electrode area of up to 250 g / m2.
Aussi, US 2018/0185785 décrit un procédé de purification de l’air comprenant l’utilisation d’un champ électrique au préalable de la réaction photocatalytique pour provoquer la précipitation des polluants. Le procédé revendique par ailleurs l’utilisation couplée d’un matériau photocatalytique et d’un matériau absorbant. Le matériau photocatalytique est mis en contact avec au moins une des deux électrodes génératrices du champ électrique. Les mises en œuvre connues de l’art antérieur révèlent que le photocatalyseur est en contact électrique avec au moins une des électrodes génératrice du champ électrique, cette mise en œuvre implique la consommation d’au moins une partie des électrons fournis par le générateur électrique par les réactifs, et ainsi une consommation énergétique supplémentaire due au passage d’un courant électrique. Also, US 2018/0185785 describes an air purification process comprising the use of an electric field prior to the photocatalytic reaction to cause the precipitation of pollutants. The method further claims the coupled use of a photocatalytic material and an absorbent material. The photocatalytic material is brought into contact with at least one of the two electrodes generating the electric field. The known implementations of the prior art reveal that the photocatalyst is in electrical contact with at least one of the electrodes generating the electric field, this implementation involves the consumption of at least part of the electrons supplied by the electric generator by reagents, and thus additional energy consumption due to the passage of an electric current.
Objet de l’invention Object of the invention
L’objet de l’invention est de proposer une voie nouvelle et plus performante de décontamination photocatalytique d’un milieu gazeux à l’aide d’un champ électrique externe, mettant en œuvre un photocatalyseur. Le procédé de décontamination photocatalytique selon l’invention permet d’atteindre des performances améliorées, notamment avec une meilleure minéralisation des COV. The object of the invention is to provide a new and more efficient way of photocatalytic decontamination of a gaseous medium using an external electric field, using a photocatalyst. The photocatalytic decontamination process according to the invention makes it possible to achieve improved performance, in particular with better mineralization of VOCs.
L’état de l’art concernant les procédés photocatalytiques en présence d’un champ électrique diffère de l’invention par le fait qu’il y a un contact électrique de l’espèce active photocatalytique avec au moins une des électrodes utilisées pour générer le champ électrique, ceci induit une consommation de courant électrique entre les électrodes. De plus, cette mise en œuvre ne permet pas un taux de chargement par unité de surface d’électrode élevé ce qui a notamment pour inconvénient de devoir utiliser des surfaces d’électrodes très importantes pour améliorer l’efficacité des systèmes, et représente donc un coût et un encombrement important des systèmes. Le procédé selon l’invention permet un taux de chargement par unité de surface d’électrode plus élevé que les procédés connus de l’état de l’art. The state of the art relating to photocatalytic processes in the presence of an electric field differs from the invention in that there is an electrical contact of the active photocatalytic species with at least one of the electrodes used to generate the. electric field, this induces a consumption of electric current between the electrodes. In addition, this implementation does not allow a high charging rate per unit of electrode area, which has the particular drawback of having to use very large electrode areas to improve the efficiency of the systems, and therefore represents a cost and a large footprint of the systems. The method according to the invention allows a higher loading rate per unit electrode area than the methods known from the state of the art.
Sans être lié à aucune théorie, la présence d’un champ électrique externe permet une meilleure séparation des paires électrons-trous générées après l’absorption de photons par le photocatalyseur. Without being bound by any theory, the presence of an external electric field allows a better separation of the electron-hole pairs generated after the absorption of photons by the photocatalyst.
D’autre part, aucun des documents de l’art antérieur ne divulgue un procédé de décontamination photocatalytique d’un milieu gazeux sous irradiation, mettant en œuvre un photocatalyseur en présence d’un champ électrique externe et dans lequel l’espèce active photocatalytique n’est pas en contact électrique avec les électrodes génératrices du champ électrique. Plus particulièrement, l’invention décrit un procédé photocatalytique de traitement d’une charge gazeuse contenant un ou plusieurs composés organique volatiles et du dioxygène, ledit procédé comprenant les étapes suivantes : a) on met en contact une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec un photocatalyseur, b) on soumet le photocatalyseur à un champ électrique externe, étant entendu que le photocatalyseur n’est pas en contact électrique avec les électrodes génératrices dudit champ électrique, c) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde absorbable par ledit photocatalyseur de manière à dégrader les composés organiques volatiles en dioxyde de carbone. On the other hand, none of the documents of the prior art discloses a process for the photocatalytic decontamination of a gaseous medium under irradiation, using a photocatalyst in the presence of an external electric field and in which the photocatalytic active species n is not in electrical contact with the electrodes generating the electric field. More particularly, the invention describes a photocatalytic process for the treatment of a gaseous charge containing one or more volatile organic compounds and dioxygen, said process comprising the following steps: a) a gaseous charge containing one or more organic compounds is brought into contact. volatiles and dioxygen with a photocatalyst, b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field, c) the photocatalyst is irradiated with at least one irradiation source producing at least one wavelength absorbable by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.
Définitions et abréviations Definitions and abbreviations
Les termes suivants sont définis dans le cadre de la présente invention pour une meilleure compréhension : The following terms are defined within the scope of the present invention for a better understanding:
Dans la suite, les groupes d'éléments chimiques sont donnés selon la classification CAS (CRC Handbook of Chemistry and Physics, éditeur CRC press, rédacteur en chef D.R. Lide, 81ème édition, 2000-2001). Par exemple, le groupe VIII selon la classification CAS correspond aux métaux des colonnes 8, 9 et 10 selon la nouvelle classification IU PAC. In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, editor CRC press, editor in chief D.R. Lide, 81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IU PAC classification.
Les propriétés texturales et structurales des photocatalyseurs décrits ci-après sont déterminées par les méthodes de caractérisation connues de l'homme du métier. The textural and structural properties of the photocatalysts described below are determined by the characterization methods known to those skilled in the art.
Le volume poreux total et la distribution poreuse sont déterminés par porosimétrie à l’azote tel que décrit dans l'ouvrage « Adsorption by powders and porous solids. Principles, methodology and applications » écrit par F. Rouquérol, J. Rouquérol et K. Sing, Academie Press, 1999. The total pore volume and the pore distribution are determined by nitrogen porosimetry as described in the book "Adsorption by powders and porous solids. Principles, methodology and applications ”written by F. Rouquérol, J. Rouquérol and K. Sing, Academie Press, 1999.
On entend par « surface spécifique », la surface spécifique BET (SBET en m2/g) déterminée par adsorption d’azote conformément à la norme ASTM D 3663-78 établie à partir de la méthode BRUNAUER-EMMETT-TELLER décrite dans le périodique "The Journal of American Society", 1938, 60, 309. On calcule la longueur d'onde maximale absorbable par un semiconducteur à l'aide de l'équation suivante :
Figure imgf000006_0001
The term “specific surface area” means the BET specific surface area (SBET in m2 / g) determined by nitrogen adsorption in accordance with the ASTM D 3663-78 standard established using the BRUNAUER-EMMETT-TELLER method described in the periodical " The Journal of American Society ", 1938, 60, 309. The maximum absorbable wavelength by a semiconductor is calculated using the following equation:
Figure imgf000006_0001
Avec Amax la longueur l'onde maximale absorbable par un semiconducteur (en m), h la constante de Planck (4,13433559.10-15 eV.s), c la vitesse de la lumière dans le vide (299 792 458 m.s-1) et Eg la largeur de bande interdite ou "bandgap" du semiconducteur (en eV). With Amax the maximum wavelength absorbable by a semiconductor (in m), h the Planck constant (4,13433559.10-15 eV.s), c the speed of light in vacuum (299,792,458 ms-1) and Eg the forbidden bandwidth or “bandgap” of the semiconductor (in eV).
On entend par « champ électrique externe », une tension appliquée à un système électrique, sans génération de courant et donc sans circulation d’électrons de l’anode à la cathode. La tension appliquée entraîne la création d’un potentiel, par l’accumulation localisée d’électrons du milieu sur l’anode et le défaut localisé d’électrons du milieu sur la cathode, sans passage de courant entre les deux électrodes. Les pertes ohmiques, intrinsèques à tout système, ne sont pas considérées comme un courant électrique. By "external electric field" is meant a voltage applied to an electrical system, without current generation and therefore without circulation of electrons from the anode to the cathode. The applied voltage causes the creation of a potential, by the localized accumulation of medium electrons on the anode and the localized defect of medium electrons on the cathode, without current flow between the two electrodes. Ohmic losses, intrinsic to any system, are not considered to be an electric current.
On entend par « milieu réactionnel », le mélange formé par la charge contenant un ou plusieurs composés organiques volatiles (COV) et du dioxygène. The term “reaction medium” is understood to mean the mixture formed by the feedstock containing one or more volatile organic compounds (VOCs) and dioxygen.
On entend par « composés organiques volatiles (COV) », selon la directive 1999/13/CE du conseil européen, tout composé contenant au moins l’élément carbone et un ou plusieurs éléments suivants : hydrogène, halogène, oxygène, soufre, phosphore, silicium ou azote, à l’exception du dioxyde de carbone, et ayant une pression de vapeur de 0,01 kPa ou plus à une température de 273,15 K. The term “volatile organic compounds (VOCs)” means, according to Directive 1999/13 / EC of the European Council, any compound containing at least the element carbon and one or more of the following elements: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon or nitrogen, except carbon dioxide, and having a vapor pressure of 0.01 kPa or more at a temperature of 273.15 K.
Description détaillée de l’invention Detailed description of the invention
Dans le sens de la présente invention, les différents modes de réalisation présentés peuvent être utilisés seuls ou en combinaison les uns avec les autres, sans limitation de combinaison. In the sense of the present invention, the various embodiments presented can be used alone or in combination with each other, without limitation of combination.
L’invention décrit un procédé photocatalytique de traitement d’une charge gazeuse contenant un ou plusieurs composés organique volatiles et du dioxygène, ledit procédé comprenant les étapes suivantes : a) on met en contact une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec un photocatalyseur, b) on soumet le photocatalyseur à un champ électrique externe, étant entendu que le photocatalyseur n’est pas en contact électrique avec les électrodes génératrices dudit champ électrique, c) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde absorbable par ledit photocatalyseur de manière à dégrader les composés organiques volatiles en dioxyde de carbone. The invention describes a photocatalytic process for treating a gaseous feed containing one or more volatile organic compounds and oxygen, said process comprising the following steps: a) a gaseous charge containing one or more volatile organic compounds and dioxygen is brought into contact with a photocatalyst, b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generators of said electric field, c) the photocatalyst is irradiated by at least one irradiation source producing at least one wavelength that can be absorbed by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.
Etape a) de mise en contact d’une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec un photocatalyseur Step a) of bringing a gas charge containing one or more volatile organic compounds and oxygen into contact with a photocatalyst
Selon l’étape a) du procédé selon l’invention, on met en contact un photocatalyseur avec une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène. According to step a) of the process according to the invention, a photocatalyst is brought into contact with a gaseous feed containing one or more volatile organic compounds and oxygen.
La charge Load
La charge traitée selon le procédé se présente sous forme gazeuse, et contient des composés organiques volatiles, ainsi que du dioxygène. De manière préférée, la charge traitée selon le procédé est de l’air, préférentiellement de l’air contenant jusqu’à 10 000 ppm de composés organiques volatiles. The feed treated according to the process is in gaseous form, and contains volatile organic compounds, as well as oxygen. Preferably, the feed treated according to the process is air, preferably air containing up to 10,000 ppm of volatile organic compounds.
Les composés organiques volatiles sont choisis parmi les hydrocarbures halogénés, les hydrocarbures aromatiques, les alcanes, les alcènes, les alcynes, les aldéhydes, les cétones, seuls ou en mélange. The volatile organic compounds are chosen from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes and ketones, alone or as a mixture.
Un fluide diluant gazeux peut être présent dans le milieu réactionnel. La présence d'un fluide diluant n'est pas requis pour la réalisation de l'invention, cependant il peut être utile d'en adjoindre à la charge pour assurer la dispersion de la charge dans le milieu réactionnel, le contrôle de l'adsorption des réactifs/produits sur le photocatalyseur, la dilution des produits pour limiter leur recombinaison et autres réactions parasites du même ordre. La présence d’un fluide diluant gazeux permet aussi le contrôle de la température du milieu réactionnel pouvant ainsi compenser l'éventuelle exo/endo-thermicité de la réaction photocatalysée. La nature du fluide diluant est choisie de telle façon que son influence soit neutre sur le milieu réactionnel ou que son éventuelle réaction ne nuise pas à la réalisation de la réaction souhaitée de dégradation des composés organiques volatiles. Avantageusement, le fluide diluant gazeux est choisi parmi le N2, 02, ou l’air. A gaseous diluent fluid may be present in the reaction medium. The presence of a diluting fluid is not required for carrying out the invention, however it may be useful to add it to the feed to ensure the dispersion of the feed in the reaction medium, to control the adsorption. reagents / products on the photocatalyst, dilution of the products to limit their recombination and other side reactions of the same order. The presence of a gaseous diluent fluid also makes it possible to control the temperature of the reaction medium, thus being able to compensate for the possible exo / endothermicity of the photocatalysed reaction. The nature of the diluting fluid is chosen such that its influence is neutral on the environment reaction or that its possible reaction does not interfere with carrying out the desired reaction of degradation of the volatile organic compounds. Advantageously, the gaseous diluent fluid is chosen from N2, 02, or air.
Le photocatalyseur The photocatalyst
Le photocatalyseur est composé d’un ou de plusieurs semi-conducteurs inorganiques, organiques ou organiques-inorganiques. Les longueurs d’onde des photons absorbables par lesdits photocatalyseurs sont comprises entre 310 nm et 1000 nm (soit une largeur de bande interdite pour les semi-conducteurs inorganiques, organiques ou hybrides organiques- inorganiques généralement comprise entre 1 ,24 et 4 eV). The photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors. The wavelengths of the photons absorbable by said photocatalysts are between 310 nm and 1000 nm (ie a bandgap for inorganic, organic or organic-inorganic hybrid semiconductors generally between 1, 24 and 4 eV).
- Selon une première variante, le semi-conducteur est choisi parmi les semi-conducteurs inorganiques. Les semi-conducteurs inorganiques peuvent être choisis parmi un ou plusieurs éléments du groupe IVA, tels que le silicium, le germanium, le carbure de silicium ou le silicium-germanium. Ils peuvent être également composés d'éléments des groupes NIA et VA, tels que GaP, GaN, InP et InGaAs, ou d'éléments des groupes II B et VIA, tels que CdS, ZnO et ZnS, ou d'éléments des groupes IB et VI IA, tels que CuCI et AgBr, ou d'éléments des groupes IVA et VIA, tels que PbS, PbO, SnS et PbSnTe, ou d'éléments des groupes VA et VIA, tels que Bi2Te3 et Bi203, ou d'éléments des groupes II B et VA, tels que Cd3P2, Zn3P2 et Zn3As2, ou d'éléments des groupes IB et VIA, tels que CuO, Cu20 et Ag2S, ou d'éléments des groupes VIIIB et VIA, tels que CoO, PdO, Fe203 et NiO, ou d'éléments des groupes VI B et VIA, tels que MoS2 et W03, ou d'éléments des groupes VB et VIA, tels que V205 et Nb205, ou d'éléments des groupes IVB et VIA, tels que Ti02 et HfS2, ou d'éléments des groupes NIA et VIA, tels que In203 et ln2S3, ou d'éléments des groupes VIA et des lanthanides, tels que Ce203, Pr203, Sm2S3, Tb2S3 et La2S3, ou d'éléments des groupes VIA et des actinides, tels que U02 et U03. De manière préférée, le semi- conducteur est choisi parmi le Ti02, le Bi203, le CdO, le Ce203, le Ce02, le CeAI03, le CuO, le Fe203, le FeTi03, le ZnFe203, le V205, le ZnS, le ZnO, le W03 et le ZnFe204, seuls ou en mélange. - Selon une autre variante, le semi-conducteur est choisi parmi les semi-conducteurs organiques. Lesdits semi-conducteurs organiques peuvent être le tétracène, l'anthracène, le polythiophène, le polystyrènesulfonate, les phosphyrènes, les fullerènes et les nitrures de carbone. - According to a first variant, the semiconductor is chosen from inorganic semiconductors. The inorganic semiconductors can be chosen from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium. They can also be composed of elements of groups NIA and VA, such as GaP, GaN, InP and InGaAs, or elements of groups II B and VIA, such as CdS, ZnO and ZnS, or of elements of groups IB and VI IA, such as CuCI and AgBr, or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi2Te3 and Bi203, or elements groups II B and VA, such as Cd3P2, Zn3P2 and Zn3As2, or elements of groups IB and VIA, such as CuO, Cu20 and Ag2S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe203 and NiO, or elements of groups VI B and VIA, such as MoS2 and W03, or elements of groups VB and VIA, such as V205 and Nb205, or elements of groups IVB and VIA, such as Ti02 and HfS2, or elements of groups NIA and VIA, such as In203 and ln2S3, or elements of VIA groups and lanthanides, such as Ce203, Pr203, Sm2S3, Tb2S3 and La2S3, or elements of groups VIA and actinides, such as U02 and U03. Preferably, the semiconductor is chosen from TiO2, Bi203, CdO, Ce203, Ce02, CeAI03, CuO, Fe203, FeTi03, ZnFe203, V205, ZnS, ZnO, W03 and ZnFe204, alone or as a mixture. - According to another variant, the semiconductor is chosen from organic semiconductors. Said organic semiconductors can be tetracene, anthracene, polythiophene, polystyrenesulfonate, phosphyrenes, fullerenes and carbon nitrides.
- Selon une autre variante, le semi-conducteur est choisi parmi les semi-conducteurs organiques-inorganiques. Parmi les semi-conducteurs organiques-inorganiques, on peut citer les solides cristallisés de type MOF (pour Métal Organic Frameworks selon la terminologie anglo-saxonne). Les MOFs sont constitués de sous-unités inorganiques (métaux de transition, lanthanides...) et connectées entre elles par des ligands organiques (carboxylates, phosphonates, imidazolates...), définissant ainsi des réseaux hybrides cristallisés, parfois poreux. - According to another variant, the semiconductor is chosen from organic-inorganic semiconductors. Among the organic-inorganic semiconductors, mention may be made of crystallized solids of MOF type (for Metal Organic Frameworks according to the English terminology). MOFs are made up of inorganic subunits (transition metals, lanthanides, etc.) and interconnected by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining hybrid crystallized networks, sometimes porous.
De manière préférée, le photocatalyseur est composé d’un ou de plusieurs semi-conducteurs inorganiques. Preferably, the photocatalyst is composed of one or more inorganic semiconductors.
Les semi-conducteurs dudit photocatalyseur peuvent éventuellement être dopés avec un ou plusieurs ions choisis parmi des ions métalliques, tels que par exemple des ions de V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, des ions non-métalliques, tels que par exemple C, N, S, F, P, ou par un mélange d’ions métalliques et non-métalliques. The semiconductors of said photocatalyst can optionally be doped with one or more ions chosen from metal ions, such as for example ions of V, Ni, Cr, Mo, Fe, Sn, Mn, Co, Re, Nb, Sb, La, Ce, Ta, Ti, non-metallic ions, such as for example C, N, S, F, P, or by a mixture of metallic and non-metallic ions.
Les semi-conducteurs constitutifs dudit photocatalyseur peuvent contenir des particules comportant un ou plusieurs élément(s) à l’état métallique choisis parmi un élément des groupes IVB, VB, VIB, VI I B, VIIIB, IB, Il B, 11 IA, IVA et VA de la classification périodique des éléments. Lesdites particules comportant un ou plusieurs élément(s) à l’état métallique sont en contact direct avec ledit semi-conducteur. Lesdites particules peuvent être composées d’un seul élément à l’état métallique ou de plusieurs éléments à l’état métallique pouvant former un alliage. On entend par « élément à l’état métallique » (à ne pas confondre avec « élément métallique ») un élément appartenant à la famille des métaux, ledit élément étant au degré d’oxydation zéro (et donc sous forme de métal). De préférence, le ou les éléments à l’état métallique sont choisis parmi un élément métallique des groupes VI I B, VIIIB, IB et MB de la classification périodique des éléments, et de manière particulièrement préférée, parmi le platine, le palladium, l'or, le nickel, le cobalt, le ruthénium, l’argent, le cuivre, le rhénium ou le rhodium. Lesdites particules comportant un ou plusieurs élément(s) à l’état métallique se présentent préférentiellement sous la forme de particules de tailles comprises entre 0,5 nm et 1000 nm, de manière très préférée entre 0,5 nm, et 100 nm et encore plus préférentiellement entre 1 et 20 nm. The semiconductors constituting said photocatalyst may contain particles comprising one or more element (s) in the metallic state chosen from an element of groups IVB, VB, VIB, VI IB, VIIIB, IB, II B, 11 IA, IVA and VA of the Periodic Table of the Elements. Said particles comprising one or more element (s) in the metallic state are in direct contact with said semiconductor. Said particles may be composed of a single element in the metallic state or of several elements in the metallic state capable of forming an alloy. The expression “element in the metallic state” (not to be confused with “metallic element”) is understood to mean an element belonging to the family of metals, said element being at zero oxidation degree (and therefore in the form of metal). Preferably, the element (s) in the metallic state are chosen from a metallic element of groups VI IB, VIIIB, IB and MB of the Periodic Table of the Elements, and particularly preferably from platinum, palladium, gold, nickel, cobalt, ruthenium, silver, copper, rhenium or rhodium. Said particles comprising one or more element (s) in the metallic state are preferably present in the form of particles with sizes between 0.5 nm and 1000 nm, very preferably between 0.5 nm, and 100 nm and even more preferably between 1 and 20 nm.
Les semi-conducteurs constitutifs dudit photocatalyseur peuvent être sensibilisés en surface avec toutes molécules organiques susceptibles d'absorber des photons. The semiconductors constituting said photocatalyst can be sensitized at the surface with any organic molecules capable of absorbing photons.
Le procédé de préparation du photocatalyseur peut être n'importe quel procédé de préparation connu de l'homme du métier et adapté au photocatalyseur souhaité. The process for preparing the photocatalyst can be any preparation process known to those skilled in the art and suitable for the desired photocatalyst.
Le photocatalyseur utilisé dans le procédé selon l’invention peut se présenter sous différentes formes (poudre nanométrique, nanoobjets comportant ou non des cavités,...) ou mises en formes (films, monolithe, billes de taille micrométrique ou millimétrique,...). Le photocatalyseur se présente avantageusement sous forme de poudre nanométrique. The photocatalyst used in the process according to the invention can be in different forms (nanometric powder, nanoobjects with or without cavities, ...) or shaped (films, monolith, micrometric or millimeter size beads, ... ). The photocatalyst is advantageously in the form of a nanometric powder.
La mise en contact Getting in touch
La mise en contact de la charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec ledit photocatalyseur, peut se faire par tout moyen connu de l'homme du métier. De manière préférée, la mise en contact de la charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec ledit photocatalyseur, peut se faire en lit fixe traversé ou en lit fixe léchant. Le photocatalyseur peut également être déposé directement sur des fibres optiques. The contacting of the gaseous charge containing one or more volatile organic compounds and dioxygen with said photocatalyst can be done by any means known to those skilled in the art. Preferably, the contacting of the gaseous charge containing one or more volatile organic compounds and dioxygen with said photocatalyst, can be carried out in a crossed fixed bed or in a licking fixed bed. The photocatalyst can also be deposited directly on optical fibers.
Lorsque la mise en contact est en lit fixe traversé, ledit photocatalyseur est préférentiellement fixé au sein du réacteur, et la charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène, est envoyée à travers le lit photocatalytique. When the contacting is in a fixed bed crossed, said photocatalyst is preferably fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen, is sent through the photocatalytic bed.
Lorsque la mise en contact est en lit fixe léchant, ledit photocatalyseur est préférentiellement fixé au sein du réacteur, et la charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène, est envoyée sur le lit photocatalytique. Le photocatalyseur peut également être déposé directement sur des fibres optiques. When the contact is in a fixed licking bed, said photocatalyst is preferentially fixed within the reactor, and the gaseous charge containing one or more volatile organic compounds and oxygen, is sent to the photocatalytic bed. The photocatalyst can also be deposited directly on optical fibers.
Lorsque que la mise en contact est en lit fixe ou en lit léchant, la mise en œuvre peut se faire en continu ou dans un réacteur fermé. Etape b) de soumission du photocatalyseur à un champ électrique externe When the bringing into contact is in a fixed bed or in a licking bed, the implementation can be carried out continuously or in a closed reactor. Step b) of subjecting the photocatalyst to an external electric field
Selon l’étape b) du procédé selon l’invention, on soumet le photocatalyseur à un champ électrique externe, étant entendu que le photocatalyseur n’est pas en contact électrique avec les électrodes génératrices du champ. According to step b) of the method according to the invention, the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating the field.
Selon un mode de réalisation préférentiel, le photocatalyseur n’est pas en contact électrique, ni en contact physique avec les électrodes génératrices dudit champ. According to a preferred embodiment, the photocatalyst is not in electrical contact, nor in physical contact with the electrodes generating said field.
Le dispositif de génération du champ électrique peut être disposé au sein du milieu réactionnel ou à l’extérieur. La localisation du dispositif sera adaptée à la mise en œuvre du procédé (lit fixe, lit léchant, ...). The device for generating the electric field can be placed within the reaction medium or outside. The location of the device will be adapted to the implementation of the process (fixed bed, licking bed, etc.).
La forme et la taille des électrodes génératrices du champ électrique peuvent être de toute sorte, adaptées au dispositif et à la mise en œuvre du procédé. The shape and size of the electrodes generating the electric field can be of any kind, adapted to the device and to the implementation of the method.
Les électrodes génératrices du champ électrique comprennent au moins un composé conducteur, tel que l’acier, le cuivre. Electrodes generating the electric field include at least one conductive compound, such as steel, copper.
Le dispositif de génération du champ électrique est tel que le photocatalyseur est soumis à un champ électrique compris entre 10 V/m et 100 kV/m, de manière préférée, le champ électrique est compris entre 100 V/m et 10 kV/m. The device for generating the electric field is such that the photocatalyst is subjected to an electric field of between 10 V / m and 100 kV / m, preferably, the electric field is between 100 V / m and 10 kV / m.
Selon une variante, on réalise l’étape c) avant l’étape b). Alternatively, step c) is carried out before step b).
Etape c) d’irradiation du photocatalyseur Step c) irradiation of the photocatalyst
Selon l’étape c) du procédé selon l’invention, on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde absorbable par le photocatalyseur (soit inférieure à la largeur de bande interdite du semi-conducteur constitutif dudit photocatalyseur selon la variante où le photocatalyseur est composé d’au moins un semi-conducteur) de manière à dégrader les composés organiques volatiles en dioxyde de carbone par photocatalyse. According to step c) of the method according to the invention, the photocatalyst is irradiated by at least one irradiation source producing at least one wavelength that can be absorbed by the photocatalyst (ie less than the forbidden bandwidth of the semiconductor constituting said photocatalyst according to the variant where the photocatalyst is composed of at least one semiconductor) so as to degrade the volatile organic compounds into carbon dioxide by photocatalysis.
Un photocatalyseur composé d’un ou plusieurs semi-conducteurs peut être activé par l'absorption d'au moins un photon. Dans le cas des semi-conducteurs, les photons absorbables sont ceux dont l'énergie est supérieure à la largeur de bande interdite, au "bandgap". Autrement dit, les photocatalyseurs sont activables par au moins un photon d'une longueur d'onde correspondant à l'énergie associée aux largeurs de bande interdite des semi-conducteurs constituant le photocatalyseur ou d'une longueur d'onde inférieure. A photocatalyst composed of one or more semiconductors can be activated by the absorption of at least one photon. In the case of semiconductors, the absorbable photons are those whose energy is greater than the forbidden bandwidth, at the "bandgap". In other words, the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the widths of the forbidden band of the semiconductors constituting the photocatalyst or of a shorter wavelength.
Toute source d'irradiation émettant au moins une longueur d'onde adaptée à l'activation dudit photocatalyseur c'est-à-dire absorbable par le photocatalyseur peut être utilisée selon l'invention. La source d’irradiation peut être aussi bien naturelle par irradiation solaire qu’artificielle de type laser, Hg, lampe à incandescence, tube fluorescent, plasma ou diode électroluminescente (DEL, ou LED en anglais pour Light-Emitting Diode). De manière préférée, la source d'irradiation est naturelle par irradiation solaire. Any irradiation source emitting at least one wavelength suitable for the activation of said photocatalyst, that is to say absorbable by the photocatalyst, can be used according to the invention. The irradiation source can be both natural by solar irradiation or by artificial irradiation of laser, Hg, incandescent lamp, fluorescent tube, plasma or light-emitting diode (LED, or LED in English for Light-Emitting Diode). Preferably, the source of irradiation is natural by solar irradiation.
La source d'irradiation produit un rayonnement dont au moins une partie des longueurs d'onde est inférieure à la longueur d'onde maximale absorbable (Amax) par les semi- conducteurs constitutifs du photocatalyseur selon l’invention. Lorsque la source d’irradiation est l’irradiation solaire, elle émet généralement dans le spectre ultra-violet, visible et infra rouge, c'est-à-dire elle émet une gamme de longueur d'onde de 280 nm à 2500 nm environ (selon la norme ASTM G173-03). De préférence, la source émet à au moins une gamme de longueur d'onde supérieure à 280 nm, de manière très préférée comprise entre 315 nm et 800 nm, ce qui inclut le spectre UV et/ou le spectre visible. The irradiation source produces radiation of which at least part of the wavelengths is less than the maximum absorbable wavelength (Amax) by the constituent semiconductors of the photocatalyst according to the invention. When the source of irradiation is solar irradiation, it generally emits in the ultra-violet, visible and infrared spectrum, that is, it emits a wavelength range of 280 nm to 2500 nm approximately (according to ASTM G173-03). Preferably, the source emits at at least one wavelength range greater than 280 nm, very preferably between 315 nm and 800 nm, which includes the UV spectrum and / or the visible spectrum.
La source d'irradiation fournit un flux de photons qui irradie le milieu réactionnel contenant le photocatalyseur. L'interface entre le milieu réactionnel et la source lumineuse varie en fonction des applications et de la nature de la source lumineuse. The irradiation source provides a flow of photons which irradiates the reaction medium containing the photocatalyst. The interface between the reaction medium and the light source varies depending on the applications and the nature of the light source.
La source d’irradiation est une source d’irradiation artificielle ou naturelle. Dans un mode préféré lorsqu’il s’agit d’irradiation artificielle, la source d'irradiation est localisée à l'extérieur du réacteur et l’interface entre les deux peut être une fenêtre optique en pyrex, en quartz, en verre organique ou toute autre interface permettant aux photons absorbables par le photocatalyseur selon l’invention de diffuser du milieu extérieur au sein du réacteur. The source of irradiation is an artificial or natural source of irradiation. In a preferred embodiment when it comes to artificial irradiation, the irradiation source is located outside the reactor and the interface between the two can be an optical window made of pyrex, quartz, organic glass or any other interface allowing the photons absorbable by the photocatalyst according to the invention to diffuse from the external medium within the reactor.
La réalisation dudit procédé est conditionnée par la capacité d’absorption dudit photocatalyseur ainsi que par la fourniture de photons adaptés au système photocatalytique pour la réaction envisagée, et de ce fait n’est pas limitée à une gamme de pression ou de température spécifiques en dehors de celles permettant d’assurer la stabilité du produit ou des produit(s). La gamme de température employée pour la production photocatalytique de dihydrogène est généralement de -10°C à + 200°C, de manière préférée de 0 à 150°C, et de manière très préférée de 0 et 50 °C. La gamme de pression employée pour le procédé est généralement de 0,01 MPa à 70 MPa (0,1 à 700 bar), de manière préférée de 0,1 MPa à 5 MPa (1 à 50 bar), et encore plus préférentiellement de 0,1 MPa à 2 MPa (1 à 20 bar). The performance of said process is conditioned by the absorption capacity of said photocatalyst as well as by the supply of photons suitable for the photocatalytic system for the reaction envisaged, and therefore is not limited to a range of pressure or of specific temperatures apart from those ensuring the stability of the product (s). The temperature range employed for the photocatalytic production of hydrogen is generally -10 ° C to + 200 ° C, preferably 0 to 150 ° C, and very preferably 0 and 50 ° C. The pressure range used for the process is generally from 0.01 MPa to 70 MPa (0.1 to 700 bar), preferably from 0.1 MPa to 5 MPa (1 to 50 bar), and even more preferably from 0.1 MPa to 2 MPa (1 to 20 bar).
Le procédé selon l’invention peut être réalisé avec un gaz sec ou humide jusqu’à 100% d’humidité relative, de manière préférée le gaz à traiter contient de 0 à 60% d’humidité relative. The process according to the invention can be carried out with a dry or wet gas up to 100% relative humidity, preferably the gas to be treated contains 0 to 60% relative humidity.
Les exemples suivants illustrent l'invention sans en limiter la portée. The following examples illustrate the invention without limiting its scope.
EXEMPLES EXAMPLES
Exemple 1 : Photocatalyseur A - Quartzel ® Example 1: Photocatalyst A - Quartzel ®
Le matériau A est un matériau commercial constitué de nanoparticules de Ti02 supportées par des fibres de quartz vendu sous la dénomination QuartzelTM par la société Saint Gobain®. Le QuartzelTM est connu par l’homme du métier pour ses excellentes propriétés photocatalytiques en purification de l’air. Material A is a commercial material consisting of TiO 2 nanoparticles supported by quartz fibers sold under the name Quartzel ™ by the company Saint Gobain®. QuartzelTM is known to those skilled in the art for its excellent photocatalytic properties in air purification.
Exemple 2 : Photocatalyseur B - Ti02 Example 2: Photocatalyst B - Ti02
Le photocatalyseur B est un semi-conducteur à base de Ti02 commercial (Aeroxide® P25, Aldrich™, pureté > 99,5%). La granulométrie du photocatalyseur est de 21 nm et la surface spécifique mesurée par méthode BET est égale à 52 m2/g. Photocatalyst B is a commercial TiO2-based semiconductor (Aeroxide® P25, Aldrich ™, purity> 99.5%). The particle size of the photocatalyst is 21 nm and the specific surface area measured by the BET method is equal to 52 m2 / g.
Exemple 3 : Photocatalyseur C - Pt/Ti02 Example 3: Photocatalyst C - Pt / Ti02
0,0712 g de H2PtCI6,6H20 (37,5% en masse de métal) est inséré dans 500 ml d'eau distillée. 50 ml de cette solution sont prélevés et insérés dans un réacteur double enveloppe en verre. 3 ml de méthanol puis 250 mg de Ti02 (Aeroxide® P25, Aldrich™, pureté > 99,5%) sont alors ajoutés sous agitation pour former une suspension. 0.0712 g of H2PtCl6.6H20 (37.5% by mass of metal) is inserted into 500 ml of distilled water. 50 ml of this solution are taken and inserted into a double-jacketed glass reactor. 3 ml of methanol then 250 mg of TiO 2 (Aeroxide® P25, Aldrich ™, purity> 99.5%) are then added with stirring to form a suspension.
Le mélange est alors laissé sous agitation et sous rayonnement UV pendant deux heures. La lampe utilisée pour fournir le rayonnement UV est une lampe HPK™ à vapeur de mercure de Le mélange est ensuite centrifugé pendant 10 minutes à 3000 tours par minute afin de récupérer le solide. Deux lavages à l’eau sont ensuite effectués, chacun des lavages étant suivi d'une centrifugation. La poudre récupérée est enfin placée dans une étuve à 70°C pendant 24 heures. The mixture is then left with stirring and under UV radiation for two hours. The lamp used to provide the UV radiation is an HPK ™ mercury vapor lamp of The mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid. Two water washes are then carried out, each of the washes being followed by centrifugation. The powder recovered is finally placed in an oven at 70 ° C. for 24 hours.
On obtient alors le photocatalseur C Pt/Ti02. La teneur en élément Pt est mesurée par spectrométrie d'émission atomique à source plasma (ou inductively coupled plasma atomic émission spectroscopy "ICP-AES " selon la terminologie anglo-saxonne) à 0,93 % en masse. The C Pt / TiO 2 photocatalyst is then obtained. The Pt element content is measured by plasma source atomic emission spectrometry (or inductively coupled plasma atomic emission spectroscopy "ICP-AES" according to English terminology) at 0.93% by mass.
Exemple 4 : Photocatalyseur D - ZnO Example 4: Photocatalyst D - ZnO
Le photocatalyseur D est un semi-conducteur à base de ZnO commercial (Lotus Synthesis™). La surface spécifique mesurée par méthode BET est égale à 50 m2/g. Photocatalyst D is a semiconductor based on commercial ZnO (Lotus Synthesis ™). The specific surface measured by the BET method is equal to 50 m2 / g.
Exemple 5 : Photocatalyseur E - Ce02 Example 5: Photocatalyst E - Ce02
30,04 g de Ce(N03)3 (Aldrich ®, 98%), sont dissous dans 150 mL d’eau distillée sous agitation. Une solution à 1 M d’ammoniaque est préparée à partir d’une solution mère d’hydroxyde d’ammonium (Aldrich ®, 28-30%). La solution à 1 M d’ammoniaque est ajoutée sous agitation dans la solution contenant Ce(N03)3 jusqu’à atteindre un pH environ égal à 10. L’agitation est maintenue 3 heures. 30.04 g of Ce (NO3) 3 (Aldrich®, 98%) are dissolved in 150 mL of distilled water with stirring. A 1 M solution of ammonia is prepared from a stock solution of ammonium hydroxide (Aldrich ®, 28-30%). The 1 M ammonia solution is added with stirring to the solution containing Ce (NO3) 3 until a pH of approximately equal to 10. Stirring is continued for 3 hours.
Le mélange est ensuite centrifugé pendant 10 minutes à 3000 tours par minute afin de récupérer le solide. Deux lavages à l’eau sont ensuite effectués, chacun des lavages étant suivi d'une centrifugation. La poudre récupérée est enfin placée dans une étuve à 100°C pendant 12 heures. Le solide récupéré subi ensuite un traitement de calcination sous air à un débit de 1 L/g/h à 150°C pendant 1 heure puis à 450°C pendant 2 heure avec une montée en température de 5°C/min. The mixture is then centrifuged for 10 minutes at 3000 revolutions per minute in order to recover the solid. Two water washes are then performed, each of the washes being followed by centrifugation. The powder recovered is finally placed in an oven at 100 ° C. for 12 hours. The solid recovered then undergoes a calcination treatment in air at a flow rate of 1 L / g / h at 150 ° C. for 1 hour then at 450 ° C. for 2 hours with a temperature rise of 5 ° C./min.
On obtient alors le photocatalyseur E Ce02. Une analyse par diffraction des rayons X montre la présence de phase Ce02 de manière majoritaire. Par microscopie électronique à transmission, la taille moyenne des particules est évaluée à 8 nm. Exemple 6 : Mise en œuvre des photocatalyseurs en adsorption et photo oxydation du toluène The E CeO2 photocatalyst is then obtained. An X-ray diffraction analysis shows the presence of the CeO 2 phase in the majority. By transmission electron microscopy, the average particle size is evaluated at 8 nm. Example 6: Use of photocatalysts in adsorption and photo oxidation of toluene
Les photocatalyseurs A, B, C, D et E sont soumis à un test de photooxydation du toluène en phase gazeuse dans un réacteur continu à lit traversé muni d’une fenêtre optique en quartz d’une surface de 5,3.10-4 m2 et d’un fritté en face de la fenêtre optique sur lequel est déposé le matériau. The photocatalysts A, B, C, D and E are subjected to a test for photooxidation of toluene in the gas phase in a continuous through-bed reactor provided with a quartz optical window with a surface area of 5.3.10-4 m2 and of a frit facing the optical window on which the material is deposited.
Deux électrodes en cuivre de forme adaptée au réacteur et espacées en moyenne de 2,4 cm sont disposées à l’intérieur du dispositif. Les électrodes sont entourées d’un film Teflon ® tel que le photocatalyseur ne soit pas en contact direct, et reliées à un générateur (Keysight, E36106A) de manière à appliquer un champ électrique dans la zone où se situe le photocatalyseur. Two copper electrodes shaped to suit the reactor and spaced an average of 2.4 cm apart are located inside the device. The electrodes are surrounded by a Teflon ® film such that the photocatalyst is not in direct contact, and connected to a generator (Keysight, E36106A) so as to apply an electric field in the area where the photocatalyst is located.
Environ 100 mg de photocatalyseur sont déposés sur le fritté. Avant chaque essai, les photocatalyseurs ont été conditionnés par thermodésorption à 115°C pendant 12 heures. Les tests sont réalisés à température ambiante sous pression atmosphérique en faisant passer un air sec contenant 70 ppmV de toluène à un débit de 60mL/min. On suit la teneur résiduelle en toluène et la production de gaz dioxyde de carbone produit issu de la photooxydation du toluène par une analyse de l’effluent toutes les 7 minutes par chromatographie en phase gazeuse (GC FID / méthaniseur FID). La source d'irradiation UV- Visible est fournie par une lampe Xe-Hg (Asahi™ , MAX302™ ). La puissance d’irradiation est toujours maintenue à 30 W/m2 mesurée pour une gamme de longueur d’onde comprise entre 315 et 400nm. La durée globale de chaque essai est d’environ 100 heures. Les tests se déroulent en deux étapes : une première étape de mise à l’équilibre sans irradiation, une deuxième étape de photooxydation sous irradiation qui permet d’estimer les performances photocatalytiques. About 100 mg of photocatalyst are deposited on the frit. Before each test, the photocatalysts were conditioned by thermodesorption at 115 ° C. for 12 hours. The tests are carried out at room temperature under atmospheric pressure by passing dry air containing 70 ppmV of toluene at a flow rate of 60mL / min. The residual toluene content and the production of carbon dioxide gas produced from the photooxidation of toluene are monitored by analyzing the effluent every 7 minutes by gas chromatography (GC FID / methanizer FID). The UV-Visible irradiation source is provided by an Xe-Hg lamp (Asahi ™, MAX302 ™). The irradiation power is always maintained at 30 W / m2 measured for a wavelength range between 315 and 400nm. The overall duration of each test is approximately 100 hours. The tests are carried out in two stages: a first stage of equilibrium without irradiation, a second stage of photooxidation under irradiation which makes it possible to estimate the photocatalytic performance.
Les taux de minéralisation calculés comme le pourcentage de C02 mesuré rapporté à la quantité théorique de C02 issu de la photooxydation du toluène sont donnés au tableau 1 ci- dessous (une valeur de 100% indiquera qu’aucun produit carboné autre que C02 n’est formé lors de la réaction).
Figure imgf000016_0001
The mineralization rates calculated as the percentage of C02 measured relative to the theoretical quantity of C02 resulting from the photooxidation of toluene are given in Table 1 below (a value of 100% will indicate that no carbon product other than C02 is formed during the reaction).
Figure imgf000016_0001
Tableau 1 - Résultats du taux de minéralisation du toluène pour les différents photocatalyseurs en fonction du champ électrique appliqué Table 1 - Results of the toluene mineralization rate for the different photocatalysts as a function of the applied electric field
Les valeurs de taux de minéralisation du toluène sont nettement supérieures pour une mise en œuvre selon l’invention quelles que soient les photocatalyseurs mis en œuvre. The toluene mineralization rate values are markedly higher for an implementation according to the invention regardless of the photocatalysts used.

Claims

REVENDICATIONS
1. Procédé photocatalytique de traitement d’une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène, ledit procédé comprenant les étapes suivantes : a) on met en contact une charge gazeuse contenant un ou plusieurs composés organiques volatiles et du dioxygène avec un photocatalyseur, b) on soumet le photocatalyseur à un champ électrique externe, étant entendu que le photocatalyseur n’est pas en contact électrique avec les électrodes génératrices dudit champ électrique, c) on irradie le photocatalyseur par au moins une source d'irradiation produisant au moins une longueur d'onde absorbable par ledit photocatalyseur de manière à dégrader les composés organiques volatiles en dioxyde de carbone. 1. Photocatalytic process for the treatment of a gaseous charge containing one or more volatile organic compounds and dioxygen, said process comprising the following steps: a) a gaseous charge containing one or more volatile organic compounds and dioxygen is brought into contact with a photocatalyst, b) the photocatalyst is subjected to an external electric field, it being understood that the photocatalyst is not in electrical contact with the electrodes generating said electric field, c) the photocatalyst is irradiated by at least one source of irradiation producing at at least one wavelength absorbable by said photocatalyst so as to degrade the volatile organic compounds into carbon dioxide.
2. Procédé selon la revendication 1 , dans lequel la charge traitée est de l’air, préférentiellement de l’air contenant jusqu’à 10 000 ppm de composés organiques volatiles. 2. The method of claim 1, wherein the treated feed is air, preferably air containing up to 10,000 ppm of volatile organic compounds.
3. Procédé selon l’une quelconque des revendications précédentes, dans lequel les composés organiques volatiles sont choisis parmi les hydrocarbures halogénés, les hydrocarbures aromatiques, les alcanes, les alcènes, les alcynes, les aldéhydes, les cétones, seuls ou en mélange. 3. Method according to any one of the preceding claims, wherein the volatile organic compounds are selected from halogenated hydrocarbons, aromatic hydrocarbons, alkanes, alkenes, alkynes, aldehydes, ketones, alone or as a mixture.
4. Procédé selon l’une quelconque des revendications précédentes, dans lequel un fluide diluant gazeux est présent dans le milieu réactionnel. 4. A method according to any preceding claim, wherein a gaseous diluent fluid is present in the reaction medium.
5. Procédé selon l’une quelconque des revendications précédentes, dans lequel le photocatalyseur est composé d’un ou de plusieurs semi-conducteurs inorganiques, organiques ou organiques-inorganiques. 5. A method according to any preceding claim, wherein the photocatalyst is composed of one or more inorganic, organic or organic-inorganic semiconductors.
6. Procédé selon la revendication 5, dans lequel dans lequel le photocatalyseur est un semi-conducteur inorganique choisi parmi un ou plusieurs éléments du groupe IVA, tels que le silicium, le germanium, le carbure de silicium ou le silicium-germanium, les composés d'éléments des groupes NIA et VA, tels que GaP, GaN, InP et InGaAs, ou d'éléments des groupes MB et VIA, tels que CdS, ZnO et ZnS, ou d'éléments des groupes IB et VII A, tels que CuCI et AgBr, ou d'éléments des groupes IVA et VIA, tels que PbS, PbO, SnS et PbSnTe, ou d'éléments des groupes VA et VIA, tels que Bi2Te3 et Bi203, ou d'éléments des groupes NB et VA, tels que Cd3P2, Zn3P2 et Zn3As2, ou d'éléments des groupes IB et VIA, tels que CuO, Cu20 et Ag2S, ou d'éléments des groupes VIIIB et VIA, tels que CoO, PdO, Fe203 et NiO, ou d'éléments des groupes VIB et VIA, tels que MoS2 et W03, ou d'éléments des groupes VB et VIA, tels que V205 et Nb205, ou d'éléments des groupes IVB et VIA, tels que Ti02 et HfS2, ou d'éléments des groupes NIA et VIA, tels que In203 et ln2S3, ou d'éléments des groupes VIA et des lanthanides, tels que Ce203, Pr203, Sm2S3, Tb2S3 et La2S3, ou d'éléments des groupes VIA et des actinides, tels que U02 et U03. De manière préférée, le semi- conducteur est choisi parmi le Ti02, le Bi203, le CdO, le Ce203, le Ce02, le CeAI03, le CuO, le Fe203, le FeTi03, le ZnFe203, le V205, le ZnS, le ZnO, le W03 et le ZnFe204, seuls ou en mélange. 6. The method of claim 5, wherein the photocatalyst is an inorganic semiconductor selected from one or more elements of group IVA, such as silicon, germanium, silicon carbide or silicon-germanium, composed of elements of groups NIA and VA, such as GaP, GaN, InP and InGaAs, or elements of groups MB and VIA, such as CdS, ZnO and ZnS, or elements of groups IB and VII A, such as CuCI and AgBr, or elements of groups IVA and VIA, such as PbS, PbO, SnS and PbSnTe, or elements of groups VA and VIA, such as Bi2Te3 and Bi203, or elements of groups NB and VA , such as Cd3P2, Zn3P2 and Zn3As2, or elements of groups IB and VIA, such as CuO, Cu20 and Ag2S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe203 and NiO, or d ' elements of groups VIB and VIA, such as MoS2 and W03, or elements of groups VB and VIA, such as V205 and Nb205, or elements of groups IVB and VIA, such as Ti02 and HfS2, or elements of NIA and VIA groups, such as In203 and ln2S3, or elements of VIA groups and lanthanides, such as Ce203, Pr203, Sm2S3, Tb2S3 and La2S3, or elements of VIA groups and actinides, such as U02 and U03 . Preferably, the semiconductor is chosen from TiO2, Bi203, CdO, Ce203, Ce02, CeAI03, CuO, Fe203, FeTi03, ZnFe203, V205, ZnS, ZnO, W03 and ZnFe204, alone or as a mixture.
7. Procédé selon la revendication 5, dans lequel dans lequel le photocatalyseur est un semi-conducteur organique choisi parmi le tétracène, l'anthracène, le polythiophène, le polystyrènesulfonate, les phosphyrènes, les fullerènes et les nitrures de carbone. 7. The method of claim 5, wherein the photocatalyst is an organic semiconductor selected from tetracene, anthracene, polythiophene, polystyrenesulfonate, phosphyrenes, fullerenes and carbon nitrides.
8. Procédé selon la revendication 5, dans lequel le photocatalyseur est un semi-conducteur organique-inorganique choisi parmi les solides cristallisés de type MOF. 8. The method of claim 5, wherein the photocatalyst is an organic-inorganic semiconductor chosen from crystalline solids of MOF type.
9. Procédé selon l’une quelconque des revendications précédentes, dans lequel le photocatalyseur est soumis à un champ électrique compris entre 10 V/m et 100 kV/m. 9. A method according to any preceding claim, wherein the photocatalyst is subjected to an electric field between 10 V / m and 100 kV / m.
10. Procédé selon l’une quelconque des revendications précédentes, dans lequel le procédé est réalisé avec un gaz sec ou humide jusqu’à 100% d’humidité relative, de manière préférée le gaz à traiter contient de 0 à 60% d’humidité relative. 10. Process according to any one of the preceding claims, in which the process is carried out with a dry or wet gas up to 100% relative humidity, preferably the gas to be treated contains from 0 to 60% humidity. relative.
11. Procédé selon l’une quelconque des revendications précédentes, dans lequel on réalise l’étape c) avant l’étape b). 11. Method according to any one of the preceding claims, in which step c) is carried out before step b).
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