EP3393648A1

EP3393648A1 - Spiral-shaped photoreactor

Info

Publication number: EP3393648A1
Application number: EP16794572.4A
Authority: EP
Inventors: Elena Sanz; Sebastien Gonnard; Antoine Fecant; Florent Guillou; Cyprien CHARRA
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2015-12-21
Filing date: 2016-11-08
Publication date: 2018-10-31
Also published as: WO2017108248A1; FR3045410A1; FR3045410B1

Abstract

The invention relates to a spiral-shaped photoreactor (10) comprising at least one plate (40) wound in a spiral shape about a central axis (x) and forming at least one spiral-shaped flow channel (30), wherein said flow channel (30) is connected to at least one pipe for the intake of a reaction mixture and to at least one pipe (35) for the discharge of said reaction mixture; characterised in that said flow channel (30) is delimited on one side by one face of the plate, which comprises a layer (41) of at least one photocatalyst, and on the other side by the other face of said plate, which comprises a means (51) for emitting photons at a wavelength suitable for activating said photocatalyst in the presence of the reaction medium in the flow channel (30).

Description

SPIRAL PHOTOREACTEUR

Technical field of the invention

The present invention relates to a photoreactor and more particularly to a spiral geometry photoreactor that can be used in a wide variety of industrial applications, and especially for the treatment (depollution) of air, water, the photocatalytic conversion of a fuel into to increase its octane number, the dehydrogenation of compounds containing an alcohol function, photocatalytic dissociation of water, photochemical cleavage reactions, photocatalytic reduction of carbon dioxide.

State of the art

Photocatalysis allows interesting chemical reactions stimulated by light in the presence of a photocatalyst. One of the problems with this approach is the design of the reactor, which must allow a large exchange surface between the reaction medium and the catalyst, a high light transmission, and a low pressure drop in the case of continuous reactors. A problem is to have a large illuminated exchange surface between the photocatalyst and the reaction medium.

Two types of photoreactor configurations can be distinguished in the prior art: suspended photocatalyst reactors and immobile photocatalyst reactors.

With respect to the first photoreactor configuration category, the finely divided photocatalyst is suspended in the charge to be treated. Depending on the regime and the concentration of particles we can speak of bubble column type reactor (or "slurry bubble column" according to English terminology, or "slurry" in a simplified expression). Compared to fixed bed reactors, this type of reactor allows a larger contact area between the photocatalyst and the charge but also a better penetration of light within the catalytic bed with respect to a stack of photocatalyst grains (Lim and al., Chemosphere 54, 2004, 305-312: "tricholoroethylene degradation by photocatalysis in annular flow and annulus fluidized bed photoreactors"). However, the disadvantage of this type of reactor is the need for a step of separation of the photocatalyst downstream of the reactor, which can be made difficult because of the nature of the photocatalyst, in the form of a nanometric powder . Indeed, the separation of nanoscale particles of photocatalyst is a difficult step and very expensive, said particles also tend to form agglomerates. On the other hand, the so-called shielding effect of the particles in suspension considerably reduces the irradiation of the photocatalyst suspended in the charge. With respect to the second photoreactor configuration category, the photocatalyst is fixed on a support. Typically, the photocatalyst is coated on a wall of the reactor, or on internals of the reactor. In this type of configuration, the material transfer limitations are greater and the photocatalytic surface ratio on the reactor volume is generally lower.

An object of the present invention is to design a reactor, of photoreactor type, which is compact, adjustable according to the type of reaction envisaged in said photoreactor, while comprising a large exchange surface between the reaction medium and the catalyst, and a good light transmission (and therefore better energy efficiency) ..

Objects of the invention

The present invention relates to a spiral-shaped photoreactor comprising at least one plate wound spirally about a central axis (x) and forming at least one spiral-shaped flow channel, wherein said flow channel is connected at least one inlet pipe of a reaction mixture and at least one outlet pipe of said reaction mixture;

characterized in that said flow channel is delimited on the one hand by a face of said plate which comprises a layer of at least one photocatalyst, and on the other hand by the other side of said plate which comprises a medium of emission of photons of wavelength adapted to the activation of said photocatalyst in the presence of said reaction medium in said flow channel.

Preferably, the width of said flow channel is between 0.1 and 500 mm.

In an embodiment according to the invention, the photoreactor comprises a first spirally wound plate and a second plate spirally wound around a central axis (x), forming at least two spiral-shaped flow channels, substantially parallel to each other.

Advantageously, said first spirally wound plate comprises on at least one of its two faces a layer of at least one photocatalyst, and said second spirally wound plate comprises on at least one of its two faces opposite the photocatalyst layer means for emitting photons of wavelength suitable for activating said photocatalyst of said first spirally wound plate in the presence of said reaction medium in said flow channel.

Preferably, said first spirally wound plate comprises on both sides a layer of at least one photocatalyst and said second spirally wound plate comprises on both sides a photon emission means of suitable wavelength. activating said photocatalyst of said first spirally wound plate in the presence of said reaction medium in said flow channel.

Advantageously, the distance "D" between said first spirally wound plate and said second spirally wound plate is between 0.1 and 500 mm.

Preferably, the thickness of the first spirally wound plate is between 0.01 and 100 mm.

Advantageously, the photocatalyst is selected from TiO ₂ , CdO, Ce ₂ O ₃ , CoO, Cu ₂ O, Bi ₂ O ₃ , Fe ₂ O ₃ , CuO, PdO, FeTiO ₃ , Nn ₂ 0 ₃ , NiO, PbO, ZnO, Ag ₂ S, CdS, MoS ₂ , Ce ₂ S ₃ , SnS, Cu ₂ S, CulnS ₂ , In ₂ S ₃ , ZnS and ZrS ₂ .

Advantageously, the photocatalyst is doped with one or more ions selected from metal ions, non-metallic ions, or a mixture of metal and non-metallic ions.

Preferably, the photocatalyst further comprises at least one co-catalyst selected from a metal, a metal oxide or a metal sulphide.

Advantageously, said photon emission means emits in the ultraviolet and / or visible spectrum.

Preferably, said photon emitting means emits at a nominal wavelength at maximum 50 nm less than the maximum wavelength absorbable by the photocatalyst and produces an irradiation such that at least 50% by number of photons are absorbable by the photocatalyst.

Advantageously, the light power density produced by said second spirally wound plate is greater than or equal to 5 kW / m ² .

Description of figures

FIG. 1 is a radial sectional view of the spiral-shaped photoreactor 10 according to a first embodiment according to the invention, the photoreactor comprising a spirally wound plate 40 comprising on one of its two faces a layer 41 of photocatalyst and on the other of its two faces a photon emission means 51. The arrows in black represent the direction of flow of the reaction mixture in the flow channel 30. In this figure, the flow of the reaction mixture is carried out in the tangential direction relative to the central axis (x) of the photoreactor 10, ie from the center of the photoreactor to its periphery.

FIG. 2 is a radial sectional view of the spiral-shaped photoreactor 10 according to another embodiment of the invention, the photoreactor comprising a first spirally wound plate 40 comprising a photocatalyst layer 41 on its two faces and a second spirally wound plate 50 comprising a photon emission means 51 vis-à-vis the photocatalyst layer 41. For the sake of clarity, the layer The black arrows represent the flow direction of the reaction mixture in the flow channels 30 and 31. In this figure, the photocatalyst and the photon emission means are not shown in FIG. flow of the reaction mixture is carried out in the tangential direction relative to the central axis (x) of the photoreactor 10.

FIG. 3 is an enlarged view in radial section of the photoreactor 10 according to FIG. 2 in which the flow channels 30 and 31 are shown, as well as the spiral plates 40 and 50 (two-plate configuration). The plate 40 comprises on each of its two faces a photocatalyst layer and the plates 50 comprise on each of its two faces a photon emission means 51. The arrows in black represent the direction of flow of the reaction mixture in the channels in this figure, the flow of the reaction mixture is made in the tangential direction relative to the central axis (x) of the photoreactor 10.

Detailed description of the invention

Referring to FIG. 1, schematically illustrating a first embodiment of the photoreactor according to the invention, the spiral-shaped photoreactor 10 here comprises a single plate wound in a spiral 40 about a central axis (x) and forming a spiral-shaped flow channel. The flow channel 30 is bounded on the one hand by a surface comprising a photocatalyst layer 41, and on the other by a surface comprising a photon emission means 51 emitting at least one wavelength adapted to the photocatalyst. activating said photocatalyst in the presence of said reaction medium in said flow channel 30. In this embodiment, the spiral wound plate 40 comprises on one of its two faces said photocatalyst layer 41 (described in detail below), and the other of its two faces the photon emission means 51 (described in detail below).

The flow channel 30 allows the flow of the reaction medium into the photoreactor. The flow channel 30 is connected to at least one inlet pipe and at least one outlet pipe 35 of the reaction medium. The inlet pipe may be located in an axial or radial position or tangential with respect to the central axis (x) of the photoreactor 10. Similarly, the outlet pipe 35 may be located in an axial or radial or tangential position relative to to the central axis (x) of the photoreactor 10.

Moreover, the dimensions of the openings of the inlet and outlet ducts connected to the flow channel 30 may be chosen such that the flow of the reaction medium in the photoreactor 10 is carried out either in the axial direction or in the direction tangential to the central axis (x) of the photoreactor 10. In the embodiment illustrated in FIG. 1, the direction of flow of the reaction mixture is tangential to relative to the central axis (x) of the photoreactor 10; the flow channel 30 is connected to an inlet duct (not shown in FIG. 1) opening into the center of the photoreactor 10, and is connected to an outlet duct 35 situated at the periphery of the photoreactor 10. In the embodiment according to which the photoreactor 10 comprises a single spirally wound plate 40, the width of the flow channel 30 is between 0.1 and 500 mm, preferably between 1 and 100 mm and even more preferably between 2 and 20 mm .

In the embodiment according to which the photoreactor 10 comprises a single spirally wound plate 40, said spirally wound plate 40 comprises on one of its two faces a layer 41 of photocatalyst, and on the other of its two faces the photon emission means 51. The spirally wound plate 40 may be made of any material capable of being wound, such as, for example, polymeric materials. However, the plate may also consist of any rigid material that can withstand the reaction medium to which said plate is subjected, in terms of pressure, temperature, corrosion and abrasion. By way of non-limiting example, the spiral wound plate 40 may be formed from the following materials: steel, rigid polymers (such as polypropylene or high density polyethylene), iron, cast iron, fiber special alloys (such as 316L ™ stainless steel and AW-3003 ™ aluminum alloy).

Advantageously, the surface of the spirally wound plate 40 on which the photocatalyst layer 41 is deposited can be textured before making said deposition of the photocatalyst layer 41. Obtaining a textured surface of the spirally wound plate 40 makes it easier to grip and / or support the photocatalyst. The texturing of the surface of said spirally wound plate 40 may be carried out by any method known to those skilled in the art, and for example by the plaster technique (for example "mineral washcoat") or by the addition of texturing elements in the form of a texturizing layer (for example felt, foam, textile, etc.) on the surface of the spirally wound plate 40, or by the introduction of a loose packing or structured in the channels of flows 30 or 31.

The photocatalyst layer 41 may be deposited either directly on said spirally wound plate 40 or on the textured surface of the spiral wound plate 40, as previously described, by any method known to those skilled in the art, and for example by :

dip-coating ("dip coating" according to the English terminology); - spin coating ("spin coating" according to the English terminology);

spray ("spray coating" according to the English terminology).

The surface of the layer 41 of photocatalyst deposited on the spirally wound plate 40 may be perfectly smooth, be rough or may have reliefs, for example of the chevron type, adapted so as to promote the mixing of the reaction medium and to increase transferring the reactants from said reaction medium to the surface of the spirally wound plate 40 comprising the photocatalyst layer 41 The thickness of the photocatalyst layer 41 can be between 1 nm and 10 mm, preferably between 1 μηι and 1 mm , and even more preferably between 10 and 500 μηι.

The total thickness of the spirally wound plate 40 comprising the photocatalyst layer 41 is between 0.01 and 100 mm, preferably 0.01 and 20 mm, and more preferably between 0.1 and 5 mm.

According to the invention, the photocatalyst layer 41 comprises at least one inorganic, organic or hybrid organic-inorganic semiconductor, supported or not on a non-semiconductor matrix. The band gap width of inorganic, organic or hybrid organic-inorganic semiconductor is generally between 0.1 and 4 eV.

According to a first variant, the photocatalyst layer 41 comprises at least one inorganic semiconductor. The inorganic semiconductor may be one or more selected from one or more Group IVA elements, such as silicon, germanium, silicon carbide or silicon-germanium. It may also be 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 VIIA, such as CuCl 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 Bi ₂ Te ₃ and Bi ₂ 0 ₃ , or elements of groups MB and VA, such as Cd ₃ P ₂ , Zn ₃ P ₂ and Zn ₃ As ₂ , or elements of groups IB and VIA, such as CuO, Cu ₂ 0 and Ag ₂ S, or elements of groups VIIIB and VIA, such as CoO, PdO, Fe ₂ O ₃ and NiO, or elements of groups VIB and VIA, such as MoS ₂ and WO ₃ , or elements of groups VB and VIA, such as V ₂ 0 ₅ and Nb ₂ 0 ₅ , or elements of groups IVB and VIA, such as Ti0 ₂ and HfS ₂ , or elements of groups NIA and VIA, such as In ₂ 0 ₃ and In ₂ S ₃ , or elements of groups VIA and lanthanides, such as Ce ₂ 0 ₃ , Pr ₂ 0 ₃ , Sm ₂ S ₃ , Tb ₂ S ₃ and La ₂ S ₃ , o u of elements of groups VIA and actinides, such as U0 ₂ and U0 ₃ .

Preferably, the photocatalyst is selected from TiO ₂ , CdO, Ce ₂ O ₃ , CoO, Cu ₂ O, Bi ₂ O ₃ , Fe ₂ O ₃ , CuO, PdO, FeTiO ₃ , In ₂ 0 ₃ , NiO, PbO, ZnO, Ag ₂ S, CdS, MoS ₂ , Ce ₂ S ₃ , SnS, Cu ₂ S, CulnS ₂ , In ₂ S ₃ , ZnS and ZrS ₂ . According to another variant, the photocatalyst layer 41 comprises at least one organic semiconductor. Among the organic semiconductors, mention may be made of tetracene, anthracene, polythiophene, polystyrene sulphonate and fullerenes.

According to another variant, the photocatalyst layer 41 comprises at least one hybrid organic-inorganic semiconductor. Among the organic-inorganic hybrid semiconductors, mention may be made of crystalline solids of the MOF type (for Metal Organic Frameworks according to the English terminology). The MOFs consist of inorganic subunits (transition metals, lanthanides, etc.) connected to each other by organic ligands (carboxylates, phosphonates, imidazolates, etc.), thus defining crystallized hybrid networks, sometimes porous.

The photocatalyst may optionally be doped with one or more ions selected 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.

Optionally, the photocatalyst may contain in addition to the semiconductor at least one co-catalyst. The cocatalyst can be any metal, metal oxide or metal sulfide. The cocatalyst is preferably in contact with at least one constituent semiconductor of the photocatalyst. Among the metals, mention may be made, for example, of Pt, Au, Pd, Ag, Cu, Ni, Rh and Nr. Among the metal oxides, mention may be made, for example, of Cr ₂ O ₃ , NiO, Pt0 ₂ , Ru0 ₂ , Ir0 ₂ , CuO, Mn ₂ 0 ₃ . Among the metal sulphides, mention may be made, for example, of MoS ₂ , ZnS, Ag ₂ S, PtS ₂ , RuS ₂ and PbS.

In a variant, the photocatalyst can be deposited on a non-activatable support by close UV irradiation (wavelength irradiation up to 280 nm). This support is either an electrical insulator, such as for example Al ₂ 0 ₃ , Si0 ₂ and Zr0 ₂ , or an electrical conductor such as for example carbon black, carbon nanotubes and graphite.

The mode of synthesis of the photocatalyst may be any synthesis mode known to those skilled in the art and adapted to the desired photocatalyst. The mode of adding possible cocatalysts can be done by any method known to those skilled in the art. Preferably, the cocatalyst is introduced by dry impregnation, excess impregnation or by photo-deposition.

The photocatalyst layer 41 is activated by the direct or indirect radiation of a photon emission means. Photocatalysis is based on the principle of activation of a semiconductor, or photocatalyst, using the energy provided by the irradiation. Photocatalysis can be defined as the absorption of a photon whose energy is greater than the forbidden bandgap or "bandgap" according to the English terminology between the valence band and the conduction band, which induces the forming an electron-hole pair in the 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 that will either react with compounds present in the medium or then recombine according to various mechanisms. Each photocatalyst has a difference in energy between its conduction band and its valence band, or "bandgap", which is its own.

A photocatalyst can be activated by the absorption of at least one photon. Absorbable photons are those whose energy is greater than the bandgap, the photocatalyst. In other words, the photocatalysts can be activated by at least one photon of a wavelength corresponding to the energy associated with the bandgap width of the photocatalyst or of a lower wavelength. The maximum wavelength absorbable by the photocatalyst is calculated using the following equation:

, h x c

A max =,!

E

*

With A _max the length the maximum wave absorbable by the photocatalyst (in m), h the Planck constant (4,13433559.10 ^"15 eV.s), c the speed of light in a vacuum (299,792,458 m. ^"1 ) and Eg the bandgap or" bandgap "of the photocatalyst (in eV). In the first embodiment according to the invention, the spiral-shaped plate 40 comprises on the other of its two faces a photon emission means 51. The photon emitting means 51 emits at least one wavelength suitable for activating said photocatalyst, that is to say absorbable by the photocatalyst. The photon emission means may for example use a natural irradiation source such as natural solar radiation or an artificial irradiation source such as laser, Hg, incandescent lamp, fluorescent tube, plasma or light emitting diode (LED , or LED in English for Light-Emitting Diode). Preferably, the photon emission means uses an artificial irradiation source. The photon emitting means emits radiation of which at least a portion of the wavelengths is less than the maximum absorbable wavelength (A _max ) by the photocatalyst. The photon emitting means generally emits in the ultraviolet and / or visible spectrum, i.e. it emits a wavelength range greater than 280 nm, preferably 315 to 800 nm.

According to a first variant, the photon emission means uses a monochromatic irradiation source. By monochromatic irradiation source is meant a source producing photons at a given wavelength, also called the nominal wavelength. In this case, the irradiation source is preferably of the laser type. According to a second variant, the photon emission means uses an irradiation source producing photons in a wavelength range of plus or minus 50 nm, preferably of plus or minus 20 nm, with respect to the nominal wavelength. In this case, the photon emission means is preferably of the light emitting diode type (LED, or LED in English for Light-Emitting Diode).

One or more photon emission means can be used. According to a first variant, the photon emission means can be centralized, as in the case of a single laser. According to another variant, the photon emission means may be dispersed, as in the case of a multitude of light-emitting diodes.

The photon emission means 51 emits a photon flux 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.

According to a first variant, the irradiation source used by the photon emission means can thus be located outside the reactor, the interface between the two is then made by means of an optical waveguide as for example optical fiber. This variant is particularly indicated in the case of a laser source and this especially as the power of the source is large.

According to a second variant, the irradiation source used by the emission means is located in the reactor, preferably near the photocatalyst to limit losses. This implementation is for example adapted to the use of LEDs.

Whether for one or the other of the variants, the arrangement of the sources or waveguides will generally be preferred so as to maximize the surface of the interface between the photon emission means and the reaction medium per unit volume of photoreactor.

The power of the source is such that it is greater than the objective of conversion of the load in terms of the reaction energy affected by the electrical efficiency of the source, namely the ratio of the irradiation power emitted by the source on the electric power required to generate it, the quantum efficiency, namely the ratio between the catalytic acts induced by photocatalysis and the number of photons absorbed by the photocatalyst affected stoichiometric coefficients of the photocatalyzed reaction and an optical yield taking into account the dispersion of the irradiation between the source and the photocatalyst, for example due to the absorbing nature of the solvent and the optical interfaces or when conducting the irradiation in a waveguide.

The energy efficiency of the light source is defined by the following equation: luminous flow

irra diatio n p

electric

with fiow light the power of the irradiation of the light source in watts and _Pe electric power consumed by the light source. The energy efficiency of the photon emission means is preferably greater than 20%, more preferably greater than 30%.

In order to optimize the overall energy efficiency of the method according to the invention, the photon emission means 51 preferably emits radiation whose wavelength is adapted to the activation of the photocatalyst. According to a preferred variant of the process according to the invention, a photon emission means is used which emits at a nominal wavelength at a maximum of 50 nm less, preferably at most 20 nm below, at the maximum wavelength. absorbable by the photocatalyst (and therefore greater than the energy corresponding to the band gap) and which produces an irradiation such that at least 50% by number of photons are absorbable by the photocatalyst. By way of example, in the case of a Ti0 ₂ photocatalyst having a band gap of 3.2 eV (ie a maximum absorbable wavelength of 390 nm), the photon emission means emits preferably irradiation between 370 and 390 nm.

Preferably, the irradiation generated is such that at least 50% by number of photons, preferably at least 80%, preferably at least 90%, very preferably at least 95% by number of photons are absorbable. by the photocatalyst. In other words, at least 50% of the photons, preferably at least 80%, preferably at least 90%, very preferably at least 95% of the photons have an energy greater than or equal to the forbidden band width of said photocatalyst. Preferably, the light power density is greater than or equal to 5 kW / m ² , preferably greater than or equal to 15 kW / m ² .

Referring to Figures 2 and 3, schematically illustrating a second embodiment in which the spiral-shaped photoreactor 10 comprises two parallel spiral-wound plates 40 and 50, ie about the same central axis (x). The first spiral wound plate 40 and the second spiral wound plate 50 thus form two spiral-shaped flow channels 30 and 31 substantially parallel to one another. In this particular embodiment, the first spiral wound plate 40 comprises on its surface (ie on both sides) a layer 41 of photocatalyst, and the second spiral wound plate 50 comprises on its surface (ie on both sides) a photon emitting means 51 emitting at least one wavelength adapted to activating said photocatalyst of said first spirally wound plate 40 in the presence of the reaction mixture in the flow channels 30 and 31. In this embodiment according to the invention, the nature and function of the photocatalyst deposited in layer 41 on the first spiral wound plate 40 and the nature and function of the photon emitting means 51 deposited on the second spiral wound plate 50 are identical to those mentioned in the context of the first embodiment according to the invention.

In an alternative of the second embodiment (not shown in the figures), the first spiral wound plate 40 may comprise on at least one of its two faces a layer 41 of photocatalyst and on the other side a means of emission of photons 51, and alternatively the second spirally wound plate 50 may comprise on one of its two faces on its surface a photon emission means 51 and on the other of its two faces a layer 41 of photocatalyst, it being understood that each flow channel is delimited on the one hand by a surface comprising a layer 41 of at least one photocatalyst, and on the other hand by a surface comprising a photon emission means 51.

The flow channels 30 and 31 allow the flow of the reaction medium in the photoreactor 10. The flow channels 30 and 31 are connected to at least one inlet line and at least one outlet line to the reaction medium. The inlet and outlet ducts of the flow channels 30 and 31 may be identical, ie a single inlet duct may feed the flow channels 30 and 31 of the photoreactor 10 of a reaction mixture and a single duct of outlet 35 can recover the reaction mixture from the flow channels 30 and 31 of the photoreactor 10.

The inlet and outlet ducts may be located in an axial or radial position or tangential to the central axis (x) of the photoreactor 10. Furthermore, the dimensions of the openings of said inlet and outlet ducts connected to the flow channels 30 and 31 may be chosen such that the flow of the reaction medium in the photoreactor 10 is carried out either in the axial direction or in the direction tangential with respect to the central axis (x) of the photoreactor 10. In the embodiment illustrated in FIG. 3, the flow channels 30 and 31 are connected to an inlet duct (not shown in FIG. 2) opening into the center of the photoreactor 10, and are connected to an outlet duct. 35 located at the periphery of the photoreactor 10.

The distance "D" between the first spiral wound plate 40 and the second spiral wound plate 50 depends on several parameters, namely the type of photocatalytic reaction, the nature of the flowing reaction medium and the flow rate of said reaction medium. Advantageously, the distance "D" between the first plate wound in spiral 40 and the second spirally wound plate 50 is between 0.1 and 500 mm, preferably between 1 and 100 mm and even more preferably between 2 and 20 mm.

Advantageously, a spacer can be used to maintain a constant and sufficient distance "D" between the plates 40 and 50, particularly in the case where the spiral shape of the photoreactor is obtained by winding the plates. The spacer may be of alveolar structure to allow the passage of the reaction medium between the plates 40 and 50. The spacer may consist of a continuous material such as a textured pattern (for example a grid). The thickness of the second spiral wound plate 50 is between 0.01 and 100 mm, preferably between 0.05 and 20 mm and even more preferably between 0.5 and 10 mm.

The second spiral wound plate 50 may further comprise a waveguide combined with a photon emission means locatable in the center of said second spiral wound plate 50. In the embodiment where the second coil plate spiral 50 comprises a waveguide, it may also be to introduce into the photoreactor 10 the radiation of an external radiation source, which may be natural as the sun, or artificial as a laser.

The photoreactor according to the invention can be used for producing a photocatalytic reaction for which the residence time of the reaction medium in the photoreactor can be between 0.0001 and 5 hours, preferably between 0.001 and 1 hour, and even more preferably between 0.1 minutes and 15 minutes.

The use of a photoreactor 10 according to the invention makes it possible to overcome a certain number of limitations encountered in most of the photoreactors known from the state of the art (as described above in the state of the art), and allows in particular:

to obtain a luminous power per unit area very high, greater than or equal to 5 kW / m ² , preferably greater than or equal to 15 kW / m ² , and even more preferably greater than or equal to 18 kw / m ² , comparison with conventional UV lamps (of the order of 1 kW / m ² );

to obtain a radiant surface per unit of very high reaction volume, thanks to the radiant arrangement of the reactor, in comparison with an annular configuration;

to obtain a very good luminous efficiency, because very little irradiation is lost by reflection / diffraction, thanks to the radial and close arrangement of the emitting and photocatalytic plates; to adapt the size of the reactor to each particular configuration by virtue of the modularity of the photoreactor according to the invention, and thus to make the residence time correspond to the kinetics of the reaction by modifying the number of turns in the photoreactor;

to perform a wide variety of photocatalytic reactions and in many situations.

Furthermore, the photoreactor according to the invention can be used for any type of photocatalytic reaction, regardless of the number of phases of the reaction medium circulating in the flow channel or channels, and whatever the direction of the flow of the reaction medium. the phase (s) of the reaction medium (for example upward and / or downward flow).

In another variant embodiment, the photoreactor according to the invention can be used for the implementation of any photochemical reaction. In a photochemical reaction, at least one of the constitutive reagents of the reaction medium absorbs irradiation and is selectively carried in a metastable excited state. The deactivation processes of this state induce intra and intermolecular rearrangements leading to the products of the reaction. By way of example for the photochemical reactions, mention may be made of photo-oxidation or photo-reduction reactions, photo-isomerization of maleic acid, halogenation of hydrogen carbon compounds (such as the bromination of cyclohexane), photolysis of water, photo-polymerization, photo-crosslinking.

Example

By way of nonlimiting example, the photoreactor according to the invention can be used in a step of the process for extracting sulfur compounds from a gasoline type hydrocarbon fraction or from liquefied petroleum gas (LPG) by liquid extraction. liquid with a soda solution, known method of the state of the art. When the majority of the sulfur species are mercaptans, or thiols, a known method consists in carrying out an extraction of the sulfur species using a soda solution circulating in a recycling loop, as described in US 4,081, 354. The sulfur species of mercaptan type dissociate in sodium thiolates in contact with sodium hydroxide. After the extraction step, the sodium thiolate loaded sodium hydroxide is oxidized in an oxidation reactor in the presence of a dissolved catalyst, for example based on cobalt phthalocyanine. Thus, sodium thiolate species are converted to disulfides. The soda solution rich in disulfide-type species is brought into contact with a hydrocarbon phase which makes it possible to extract the disulfide-type species and thereby regenerate the soda solution, which can then be reused in the liquid-phase extraction step. liquid. This method however has several disadvantages because the oxidation catalyst circulates together with the aqueous phase of soda throughout the steps of extraction and regeneration of the process, which can pose significant technical and efficiency problems. The use of a photoreactor according to the invention (see Example 1 below) overcomes the drawbacks mentioned above, while being more compact than conventional photoreactors (see Example 2 below). .

In the following examples, the efficiency of a photoreactor according to the invention (example 1) and a conventional photoreactor (example 2) are compared. By way of nonlimiting example, the two reactor configurations are used for a process for regenerating sodium hydroxide from sodium thiolates, according to a photocatalytic oxidation reaction producing sodium hydroxide on the one hand and disulphides of sodium hydroxide. somewhere else. The reactions involved in the reactor are as follows:

a) Adsorption by the photocatalyst of two photons and generation of two electron pairs (e, reducing species) / hole (h ⁺ , oxidizing species)

2 hrs -> 2h ⁺ + 2nd ^"

b) Oxidation of thiolates (RS) to disulfides

2 RS ^" + 2 h ⁺ ^ RS-SR

c) Regeneration of HO ions ^" in the presence of oxygen

½ 0 ₂ + H ₂ 0 + 2 e → 2 OH ^"

Let the following equation-balance:

2HS

2 RS + ½ 0 ₂ + H ₂ 0 * RSSR + 2 HO

In the context of the present invention, it is necessary to distinguish:

the electrical power of the photon emission means (for example of a lamp) corresponding to its nominal power (in W); and

the luminous power (in W also) corresponding to the fraction of the electric power which is effectively transformed into light.

The yield of this transformation is considered here of the order of 30%.

In what follows, only the light power (in W) or the light power density (expressed in W / m ² ) is referred to.

The process according to the examples requires the conversion in the presence of air of the thiolate type compounds contained in a soda stream. The total flow rate is 5 m ³ / h, the thiolate flow rate to be converted is 0.07 mol / s, with a desired conversion of 97%. The residence time of the reaction medium in the photoreactor must be 5 minutes and 30 seconds. Thus, it is necessary to produce one mole of photon to convert one mole of thiolate, or 0.07 moles of photons per second. Considering that 30% of the photons emitted are useful with a photocatalyst based on rhodium nanoparticles deposited on titanium dioxide (as described in the scientific publication published in Journal of the Chemical Society, Faraday Trans. I, 1985, 81, 1237), that is to say that they lead to electron / hole pairs performing redox reactions of thiolates oxidation and OH ^" regeneration, the necessary light output is 1, 36.10 ²³ photons / s. Using a wavelength of 365 nm (corresponding to the emission in the ultraviolet range necessary for the activation of the photocatalyst Rh / Ti0 ₂ ), the necessary light output is 74.2 kW.

Moreover, in order to make comparable the efficiency of the two configurations of photoreactors (ie according to the invention and according to the state of the art), Ray et al (Catalysis today, 40, (1998) 73-83: "Development of a new photocatalytic reactor for water purification ") define a parameter" k "equal to the ratio between the irradiated specific surface area (S _cat irradiated), representing the total surface of irradiated catalyst, in contact with the reaction medium within the photoreactor, by reactor unit volume (V _reac tor) or k = S _ca ta irradiated / V _reac tor (m ² / m ^3). Another important parameter is defined herein as the specific radiant surface "k '" is the total radiating surface in contact with the reaction medium within the photoreactor, by volume of the reactor unit, or k' = Séante / V _reac tor (in m ² / m ³ ). The light power necessary for the radiation determines a minimum radiant surface in the reactor, which is more compact as the coefficient k 'will be large.

EXAMPLE 1 Extraction of sulfur compounds in a photoreactor according to the present invention

In this example, the flow of the reaction mixture in the photoreactor 1 0 is made in the direction tangential to the central axis (x) of the photoreactor 1 0, i.e. from the center of the photoreactor to its periphery.

A spiral photoreactor 10 is used according to the second particular embodiment according to the invention in which the photoreactor comprises a first spirally wound plate 40 comprising a layer 41 of photocatalyst based on rhodium nanoparticles deposited on titanium dioxide. and a second spiral wound plate 50 having on its surface a photon emitting means 51 in the form of a set of light-emitting diodes.

Each wound spiral plate 40 and 50 has a width of 3.0 m in an effective area of 6.0 m ² / mi _ined area (both sides of each plate wound spiral 40 and 50 are used). The spiral wound plate 50 comprising photon emission means 51 has a thickness of 1.0 cm; the spiral wound plate 40 comprising the photocatalyst layer 41 has a thickness of 0.5 cm. The distance "D" between the two spirally wound plates 40 and 50 is 1.0 cm in order to allow a good diffusion of the light from the photon emission means through the reaction medium to the layer 41 of photocatalyst, while maintaining a useful volume sufficient for the residence time of the reagents. The process according to Example 1 requires converting in the presence of air the thiolate-type compounds contained in a stream of sodium hydroxide. The total flow rate is 5 m ³ / h, the thiolate flow rate to be converted is 0.07 mol / s, with a desired conversion of 97%. The residence time of the reaction medium in the photoreactor must be 5 minutes and 30 seconds. To obtain such a residence time, the photoreactor according to example 1 must then comprise (by calculation) 46 m ² of useful area for each spirally wound plate 40 and 50, which corresponds to a photoreactor comprising a winding of 10 turns .

The total reactor volume (V _reac tor) is then 0.88 m ^3.

The light power (in W) emitted by the light-emitting diodes 51 is here is of the order of 1.6 kW / m ² . The total area occupied by the light-emitting diodes being 46.0 m ² , the resulting luminous power is 74.9 kW.

Finally, the coefficient k '(ie the specific radiant surface) is calculated to be 51.9 m ² / m ³ . Thus, the light output provided by the photoreactor according to the invention (74.9 kW) is greater than the necessary light output (74.2 kW).

Example 2: Regeneration step of a sodium-type solvent loaded with sulfur-containing products in an annular classic photoreactor (example not in accordance with the invention)

By comparison with the photoreactor according to Example 1, a photoreactor known from the state of the art, with an annular arrangement comprising an internal illumination is used. The reactor is composed of two concentric tubes, an outer tube and an inner tube. The outer tube, 4.2 cm internal diameter, is coated photocatalyst on its inner surface. The inner tube, 2.2 cm in diameter, is made from a UV-transparent material. The reaction medium circulates in the space formed between the two tubes. A lamp of 2.0 cm diameter and the same power area as in Example 1 (ie 1.6 kW / m ² ) is placed in the center of the inner tube. As in the case of Example 1 according to the invention, the expected total light output is 74.2 kW.

For the annular reactor of Example 2, in order to reach the light power required for the reaction, it is necessary to have either a cylindrical reactor 730 m long or a reactor 10 m long but composed of 73 tubes, ie a total reactor volume (reactor) 1, 9 m ³ reactor. The residence time of the reaction medium in the reactor is 9.4 min.

The coefficient k '(specific radiant surface) is calculated as 24.4 m ² / m ³ .

The photocatalytic reactor according to the invention (example 1) is thus more than twice as compact as a conventional tubular reactor example 2). Moreover, the radiant surface of the reactor according to the invention is more than two times greater than that of the tubular reactor.

Claims

1. A spiral-shaped photoreactor (10) comprising at least one spirally wound plate (40) about a central axis (x) and forming at least one spiral-shaped flow channel (30), wherein said channel is flow (30) is connected to at least one inlet line of a reaction mixture and at least one outlet line (35) of said reaction mixture;

characterized in that said flow channel (30) is delimited on the one hand by a face of said plate which comprises a layer (41) of at least one photocatalyst, and on the other hand by the other side of said plate which comprises a wavelength photon emission means (51) adapted to activate said photocatalyst in the presence of said reaction medium in said flow channel (30).

2. photoreactor according to claim 1, characterized in that the width of said flow channel (30) is between 0.1 and 500 mm.

3. photoreactor according to claim 1 or 2, characterized in that it comprises a first spirally wound plate (40) and a second spirally wound plate (50) about a central axis (x), forming at least two spirally-shaped flow channels (30,31) substantially parallel to one another.

4. Photoreactor according to claim 3, characterized in that said first spirally wound plate (40) comprises on at least one of its two faces a layer (41) of at least one photocatalyst, and said second plate wound in a spiral ( 50) comprises on at least one of its two faces facing the photocatalyst layer (41) a photon emission means (51) of wavelength suitable for activating said photocatalyst of said first photocatalyst spirally wound plate (40) in the presence of said reaction medium in said flow channel (30).

Photoreactor according to claim 4, characterized in that said first spirally wound plate (40) comprises on both sides a layer (41) of at least one photocatalyst and said second spirally wound plate (50) comprises on its two sides a layer (41) of at least one photocatalyst and two faces a photon emission means (51) of wavelength adapted to activate said photocatalyst of said first spiral wound plate (40) in the presence of said reaction medium in said flow channel (30).

The photoreactor according to claim 4 or 5, characterized in that the distance "D" between said first spiral wound plate (40) and said second spiral wound plate (50) is between 0.1 and 500 mm.

7. photoreactor according to any one of claims 3 to 6, characterized in that the thickness of the first spirally wound plate (40) is between 0.01 and 100 mm.

8. photoreactor according to any one of claims 1 to 7, characterized in that the photocatalyst is selected from Ti0 ₂ , CdO, Ce ₂ 0 ₃ , CoO, Cu ₂ 0, Bi ₂ 0 ₃ , Fe ₂ O ₃ , CuO, PdO, FeTiO ₃ , Nn ₂ O ₃ , NiO, PbO, ZnO, Ag ₂ S, CdS, MoS ₂ , Ce ₂ S ₃ , SnS, Cu ₂ S, CulnS ₂ , In ₂ S ₃ , ZnS and ZrS ₂ .

9. Photoreactor according to any one of claims 1 to 8, wherein the photocatalyst is doped with one or more ions selected from metal ions, non-metallic ions, or a mixture of metal ions and non-metal.

The photoreactor according to any one of claims 1 to 9, wherein the photocatalyst further comprises at least one co-catalyst selected from a metal, a metal oxide or a metal sulfide.

1 1. A photoreactor according to any one of claims 1 to 10, wherein said photon emitting means emits in the ultraviolet and / or visible spectrum.

The photoreactor according to any one of claims 1 to 11, wherein said photon emitting means emits at a nominal wavelength at maximum 50 nm less than the maximum wavelength absorbable by the photocatalyst and produced irradiation such that at least 50% in number of photons are absorbable by the photocatalyst.

13. Photoreactor according to any one of claims 4 to 12, characterized in that the light power density produced by said second spiral wound plate (50) is greater than or equal to 5 kW / m ² .