Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/122—Incoherent waves
  • B01J19/127—Sunlight; Visible light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/24—Stationary reactors without moving elements inside
  • B01J19/2475—Membrane reactors
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
  • C01B13/02—Preparation of oxygen
  • C01B13/0229—Purification or separation processes
  • C01B13/0248—Physical processing only
  • C01B13/0251—Physical processing only by making use of membranes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
  • C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
  • C01B3/042—Decomposition of water
  • C01B3/045—Decomposition of water in gaseous phase
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
  • C01B3/501—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by diffusion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S20/00—Solar heat collectors specially adapted for particular uses or environments
  • F24S20/20—Solar heat collectors for receiving concentrated solar energy, e.g. receivers for solar power plants
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/0873—Materials to be treated
  • B01J2219/0877—Liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/0873—Materials to be treated
  • B01J2219/0892—Materials to be treated involving catalytically active material
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0405—Purification by membrane separation
  • C01B2203/041—In-situ membrane purification during hydrogen production
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0465—Composition of the impurity
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2210/00—Purification or separation of specific gases
  • C01B2210/0043—Impurity removed
  • C01B2210/0046—Nitrogen
• • 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
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/40—Solar thermal energy, e.g. solar towers
• • 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
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• • 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
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency
  • Y02P20/133—Renewable energy sources, e.g. sunlight

Definitions

• the invention relates to a method and equipment for producing hydrogen by dissociation of water vapor by means of concentrated solar energy. It applies more particularly but not exclusively, for applications in many areas:
• hydrogen and oxygen can be used as a means of storing energy.
• the water on board such a station will circulate in a closed loop in a chain of user devices and can thus be used for several successive uses.
• This loop will necessarily include hydrogen and oxygen storage equipment as well as a fuel cell. The latter will have the function of producing electrical energy and regenerating the water circulating in the loop.
• hydrogen can be used as fuel. Indeed, in sunny countries around the globe, there is growing interest in large-scale hydrogen production using solar energy in order to have a non-polluting, renewable energy vector that can be used in the condition or as an additive to natural gas.
• hydrogen is an interesting fuel. Indeed, the automotive industry is preparing new generations of vehicles running on hydrogen using an engine thermal or fuel cell. In both cases, the hydrogen fuel distribution infrastructure will include means for producing hydrogen. In sunny countries around the world, solar hydrogen production will provide a sustainable supply of green fuel.
• thermochemical Approach to the problem shows in particular the possibility of dissociating the molecule of water by means of two-step cycles carried out in two reaction chambers: (1) in one, oxidation of a metal (Fe 1 Zn ...) at a temperature high (400 0 C) with release and discharging hydrogen and (2) in the other, reduction of the metal oxide at very high temperatures (> 2000 ° C) with release and removal of the oxygen.
• thermochemical cycle The circulation of the Zn metal and the ZnO oxide from one chamber to the other makes it possible to carry out in a steady state a cycle intended to dissociate the water in order to produce hydrogen and oxygen.
• a disadvantage of such a thermochemical cycle is to require the implementation of two reaction chambers between which it is necessary to ensure a transfer of material as well as heat exchanges suitable for bringing the reagents to the optimum temperature. The resulting process is therefore complex and subject to irreversibilities that degrade the energy efficiency.
• the subject of the invention is a novel process for producing hydrogen by dissociation of water vapor by means of concentrated solar radiation, in which the thermal energy of said radiation is no longer the main driving force of this dissociation. .
• the invention relates to a novel process for producing hydrogen and oxygen by dissociation of water vapor by means of concentrated solar radiation.
• the invention relates to a new process for producing hydrogen and oxygen by dissociation of water vapor, wherein this dissociation is significantly increased by different complementary actions.
• the subject of the invention is new equipment for implementing this new process for producing hydrogen.
• the method may further include in situ selective extraction of oxygen produced by at least one selective oxygen extraction membrane.
• the temperature of the treatment chamber will be adapted for the operation of extraction membranes.
• the surface-to-volume ratios of the at least one membrane that is selective for hydrogen and / or oxygen may be high. Indeed, it should be taken into account that the flow of hydrogen and / or produced oxygen is proportional to the surface of the membrane and that said surface is housed in a determined volume. Therefore, to obtain a flow of hydrogen and / or oxygen at least sufficient, it is interesting to have the largest possible area in the determined volume.
• said ratios may be defined so as to obtain an ion current density of at least 1A / cm 2 .
• a direct deposition of the photo-catalytic target on said at least one selective extraction membrane with hydrogen and / or oxygen may be carried out.
• Said at least one membrane that is selective for hydrogen and / or oxygen may constitute electrolytic cells, ie cells with virtually zero electronic conduction ( ⁇ e ⁇ 0),
• Said at least one membrane that is selective for hydrogen and / or oxygen may constitute cells with mixed conduction, ionic ( ⁇ j) and electronic ( ⁇ e ). . ⁇ -
• the process may include continuous introduction of the appropriate pressure water vapor.
• the pressure range for the dissociation reaction may be typically 3 to 15 bars and that of the temperatures of 300 to 1000 ° C.
• the concentration rate of solar radiation may be between 500 and 3000.
• the concentration level may be not only equal to the known concentrations used but also lower, thus reducing the amount of solar energy required.
• the dissociation rate can be increased, by ionization of the water vapor of the boundary layer, by means of a cold plasma.
• the rate of dissociation of the water vapor can be considerably increased, in particular by the formation of excited molecules or active ions such as H + , H 2+ , OH “ , 0 “ , O 2 " etc.
• the plasma will act as a source of available electrons to prime dissociation reaction chains by the dissociative attachment process mentioned below.
• the dissociation rate may be increased by the application of an electric field between the permeable membranes respectively selective for oxygen and hydrogen, when they are installed together in the reaction chamber, in order to better separate the negative and positive ions produced and facilitate their respective migrations to the appropriate extraction membranes.
• ⁇ G is the free energy variation of Gibbs
• T. ⁇ S is the quantity of heat to be supplied
• T the temperature
• ⁇ S the variation of the entropy.
• the ⁇ G energy which is comparable to a work, can be provided in mechanical, electrical or photonic form.
• the only contribution likely to intervene in this term ⁇ G corresponds to the photons directly absorbed by photo-catalytic reactions contributing to the direct dissociation of the water vapor.
• the radiation absorbed and converted into heat it must, of course, be accounted for in the term T. ⁇ S and not in the term ⁇ G.
• the total energy absorbed remains substantially constant, when the temperature of this vapor increases from 100 to 1000 ° C., while the Gibbs energy ⁇ G and the thermal energy T. ⁇ S, which are its components, respectively active and passive , vary almost linearly in opposite directions from each other. Under these conditions, for example between 100 and 75O 0 C, the average temperature in the reaction chamber, that is to say the fraction of photon energy converted into heat from 5 to 20%.
• the photo-catalytic water dissociation reactions occur mainly in the boundary layers in direct contact with the surfaces of the photo-catalytic targets, under the influence of the incident concentrated solar radiation.
• One of the photo-catalytic mechanisms of water vapor dissociation results from oxidation-reduction properties produced by some semiconductors exposed to solar radiation.
• a semiconductor is TiO 2 titanium dioxide, which is generally in the form of a layer of fine grains, applied by sintering on the surface of a support.
• titanium dioxide TiO2 is the seat of an ionization mechanism resulting from the creation of electron-hole pairs that diffuse towards the surface of the grains.
• the semiconductor materials other than UO 2 presented above are also capable of carrying out the photo-catalytic dissociation reaction of the water molecules according to a mechanism similar to that described.
• a chain dissociation mechanism can be established when a water molecule encounters an electron on the surface of a suitable semi-coupler.
• An example of such a mechanism is written:
• MPO highly selective oxygen permeable membranes
• the material generally used is a perovskite ceramic having a high ionic conductivity at high temperature for O 2 - ions.
• MPO CM mixed-conduction membranes
• MPO PEC electrochemical pump
• the O 2 - ions diffuse from one side to the other of the membrane under the effect of the oxygen partial pressure gradient
• the material has a high ionic conductivity for O ions 2 ' and a high electronic conductivity, so that an ionic current and an electronic current of opposite direction are established in the volume of the membrane, one compensating the other, the resulting electric current being zero.
• the MPO CM membranes operating without an electric generator is the oxygen partial pressure gradient and therefore the chemical potential difference which is the driving force of the oxygen transfer, which implies that the oxygen partial pressure in upstream of the membrane is greater than that downstream: P02I> Po * 2. This assumes that the rate of dissociation of the water vapor in the boundary layer upstream of the membrane is sufficiently high.
• MPO CM membranes can operate at high temperature, typically 800 to 1000 D C. Indeed, it is now known to build such membranes, either perovskite ceramic or a ceramic-metal alloy, said cermet A technology of these membranes selectively permeable to oxygen is developed at the Dutch ECN Laboratory by JF Vente, WGHaije and ZSRack, particularly for applications in the chemical industry or the manufacture of solid electrolytes for high temperature fuel cells of the SOFC type (acronym for Solid Fuel Oxide CeII). This technique is described in a data sheet, titled “Mixed conduct membranes with an oxygen flux greater than 10 ml / cm 2 / min", which gives a list of the many materials used for their manufacture.
• the ceramics concerned are generally oxides of La-Sr-Fe-Co, Sr-Fe-Co, La-Sr-Ga-Fe etc. These ceramics are known for their excellent selective permeability to oxygen at temperatures below 1000 g C.
• the permeation of oxygen is through the membrane by an ionic conduction mechanism.
• the oxygen molecules dissociate at the simple contact of this surface and form negative ions O 2 " .
• These ions migrate towards the downstream face, pushed by the difference of chemical potential due to the difference of Oxygen pressure and they are neutralized at their output on the downstream face, giving up four electrons that cross the membrane against the current.
• MPH 1 The highly selective hydrogen permeable membranes (hereinafter referred to as MPH) 1 are of several types: (1) mixed conduction perovskite ceramic membranes (MPH CM), (2) perovskite ceramic membranes operating as an electrochemical pump (MPH) PEC) 1 (3) dense composite metal membranes (MMC) and (4) Knuds ⁇ n diffusion membranes (MPH DK). The procedures of these first two types of membranes are shown in Figures 1c and 1d attached.
• MPH CM mixed conduction perovskite ceramic membranes
• MPH PEC electrochemical pump
• MMC dense composite metal membranes
• MPH DK Knuds ⁇ n diffusion membranes
• the material used has, at elevated temperature, a high ionic conductivity for H + ions as well as a high electronic conductivity.
• the positive ions H * diffuse from one side to the other of the membrane under the effect of the hydrogen partial pressure gradient.
• a ionic current and an electronic current of opposite signs are established in the volume of the membrane, the resulting electric current is then zero.
• MPH CM membranes therefore operate without an electrical generator, the transfer motor is the partial pressure gradient and therefore the chemical potential difference of hydrogen between the upstream and downstream of the membrane. This operation implies that the hydrogen partial pressure upstream of the membrane is greater than that downstream: Pt "1> PH22.
• the material constituting this type of membrane is a ceramic with high temperature properties of mixed electronic and protonic conduction.
• the principle of such membranes differs from that described above for the oxygen extraction membranes, in that the ionic conduction of the O 2 - ions has been replaced by that of the H + protons Complex materials making it possible to produce such membranes are presented in the article by EA Payzant et al, "Pyrochlore-Perovskite Protons Transfer Membranes", published in Oak Ridge's FY 2004 Progress Report.
• the H + ions move from one side to the other of the membrane under the effect of an electric field produced by an electric potential difference applied by means of electrodes, the anode being disposed on the upstream face of the membrane and the cathode on the downstream face.
• a particular material having a high ionic conductivity for H + ions and zero electronic conductivity is described in an article of
• the mode of operation of these membranes can be likened to a high temperature electrolysis mechanism.
• An advantage of this mode of operation is to allow the passage of hydrogen through a membrane even when the upstream partial pressure much lower than that downstream: PMI ⁇ PHZ2.
• microporous membranes based on the Knudsen diffusion mechanism MPH DK
• the microporous material is generally a ceramic, in particular alumina.
• These membranes generally have poor selectivity.
• the principle of operation of these membranes implies that the hydrogen partial pressure upstream of the membrane is greater than that downstream: PH1> PH22.
• Porous ceramic membranes operating according to the Knudsen diffusion principle are commercially available. They have certain advantages: good stability at high temperature, high value of their gas permeability and low cost. Nevertheless, they are very selective.
• a convergent optical device adapted to focus at best on the incident solar radiation
• At least one membrane that is selectively permeable to hydrogen disposed in the vicinity of said at least one photo-catalytic target and connected to the outside to extract the hydrogen,
• the necessary optical concentration it will be between 500 and 3000. It is defined by the ratio between the intensity of the light radiation incident on the optical system and the intensity of the concentrated light radiation in the focal spot.
• the convergent optical device or optical concentrator may be an orientable Fresnel mirror, consisting of reflective facets, or a heliostat field, similar to that of the Themis solar power plant built in France, or still a double reflection system, consisting of a fixed parabola and rotatable heliostats, made in France by the CNRS for the solar ovens of Mont-Louis and Odeillo.
• Said treatment chamber may further comprise at least one selectively oxygen permeable membrane connected to the outside.
• the membranes selectively permeable to oxygen and / or hydrogen installed in the treatment chamber may be in the form of glove fingers and / or radial lamellae and / or honeycombs.
• the equipment may further include at least one of the following:
• a heat exchanger for each membrane that is selectively permeable to hydrogen and / or oxygen, a heat exchanger whose inlet of the hollow active element is connected to said membrane that is selectively permeable to hydrogen and / or oxygen, the outlet of this hollow element opening respectively to a device for exploiting hydrogen and / or oxygen,
• a water tank and a suitable pump supplying water to the envelopes of active hollow element (s) and a pipe connecting the outlet (s) of elements to the chamber; treatment to supply water vapor.
• equipment for producing hydrogen for implementing the method according to the invention may comprise:
• a convergent optical device adapted to focus at best on the incident solar radiation
• said extraction chamber comprising at least one membrane selectively permeable to one of the two gases, hydrogen and oxygen, connected to the outside.
• said equipment may further comprise at least one of the following elements:
• the hollow active elements of these at least two exchangers being arranged in series and respectively fed by the hydrogen and oxygen streams leaving the extraction chambers and reaction and the envelopes of these active elements being supplied with water for example by said reservoir and said pump, - a conduit for evacuation of the residual steam from the extraction chamber connecting the outlet of this chamber to a trunk at the other end of which the outlet of the heat exchanger casing ends, the outlet of this horn being connected by a tubing to the steam inlet mouth of the reaction chamber.
• the reaction chamber is exposed to concentrated solar radiation.
• This chamber contains water vapor delivered by a suitable feeder.
• the concentrated solar radiation penetrates through an access window such as a transparent window, for example made of quartz, and strikes at least one photocatalytic target deposited in the vicinity of at least one membrane. 'extraction.
• Upstream of said at least one membrane remains a residue (retentate) composed of gases other than the extracted gas.
• this residue (retentate) composed of water vapor mixed with hydrogen or oxygen, is then conveyed to the reactor.
• second chamber in which is disposed at least one membrane which extracts hydrogen or oxygen.
• the residue (retentate) of this second selection operation is mainly steam which is recycled by mixing it with the steam injected into the reaction chamber.
• Table II there are also three configurations characterized by the fact that the apparatus comprises only the reaction chamber.
• the hydrogen and oxygen extraction membranes if any, are arranged side by side in this chamber. It should be noted that in this case, the circulation of the residue is simplified: the water vapor remains in the reaction chamber, the water vapor provided just compensating for the dissociated fraction and converted into oxygen and hydrogen.
• FIGS. 2b and 2d two types of membranes operate according to an electrochemical pumping mode and the process for producing hydrogen according to the invention is in both cases a method of electrolysis of high temperature water vapor. .
• the electric field required for this purpose is maintained by an electric potential difference applied between the two electrodes of the membrane. This implies that an electric generator supplies the energy consumed by the membrane concerned. The electrical energy consumed will be even lower than the difference in the partial pressures of the pumped gas will be lower between the upstream and downstream of the membrane.
• the H + ions that passed through the electrolytic membrane form hydrogen by recombining with the electrons driven by the external electrical circuit.
• the potential difference to be applied between the electrodes is directly related to the difference in chemical potential on either side of the electrolytic membrane.
• this mechanism of dissociation of the water vapor, in a boundary layer in contact with the grains of an illuminated photocatalytic target and in the vicinity of a membrane that is selective for one of the gases produced is very different and much more efficient than the decomposition of water vapor in a homogeneous medium, in thermodynamic equilibrium.
• Said at least one membrane located in the first chamber when it is directly exposed to solar radiation, will have a high active surface radiation. For this reason it should have forms allowing a high surface area ratio and have, for example, tubular, lamellar or alveolar shapes.
• the membrane In the case of electrochemical pumping membranes used for high temperature electrolysis, the membrane is a solid electrolyte and has a high ionic conductivity in the considered temperature range and an almost zero electronic conductivity, as shown in FIGS. 1b, 1d, 2b and 2d.
• the electrodes are disposed on both sides of the solid electrolyte membrane.
• the direct absorption of the concentrated radiation, by photochemical reagents which participate in the dissociation of the water reduces the potential difference between the electrodes of the electrolysis cell and hence the electrical energy consumed.
• the generated electric current can be relatively high. Since the current density per unit area must remain compatible with the limit imposed by the material used, it may be necessary to arrange the membranes in series and increase the potential difference applied to all, to decrease accordingly the amplitude of the current generated.
• the membranes used are mixed conduction membranes, that is to say having a conductivity that is both ionic and electronic
• the reactions on either side of the membrane are the same as those indicated above. high. Nevertheless, in this case, the transfer of oxygen or hydrogen through the membrane can only take place if the partial pressure of C ⁇ gas is stronger upstream than downstream. This assumes that the rate of dissociation of the water vapor in the boundary layer upstream of the membrane is sufficiently high.
• the Gibbs free energy ⁇ G is entirely supplied by the fraction of solar radiation absorbed by the photochemical reactions leading to the dissociation of the water vapor. In this case there is no need for electrical energy and the concentrated solar radiation alone is sufficient.
• FIGS 1 and 2 are illustrations of the selective membranes discussed above;
• FIG. 3 is a diagrammatic representation of an equipment for producing hydrogen using solar energy according to the invention.
• FIG. 4 is a schematic representation of a two-chamber steam dissociation apparatus implementing the method according to the invention.
• Figure 5 shows a schematic section of two electrolytic membranes in the form of glove fingers.
• a hydrogen production equipment comprises a mirror 10, in the form of a parabola of revolution, mounted on a foot 11 and orientable towards the sun, and a device for dissociating water vapor 12 disposed at the focus of said mirror and carried by an arm 13 secured to this mirror.
• the opening surface of the mirror 10 may be 50 m 2 , the focal area of 5 dm 2 and the volume of the apparatus 12, 20 dm 3 approximately.
• the water vapor dissociation apparatus 12 is a suitably thick-walled bell-shaped chamber 14 defining a treatment chamber, which encloses a reaction chamber 16 disposed at the front ( lower part) and an extraction chamber
• suitable metal is meant a metal chemically chemically relative to the reactants and products at the temperature used such as stainless steel.
• the reaction chamber 16 is closed by a concave quartz port 20, mounted fixed and sealed between annular jaws 21, integral with the wall of the bell 14.
• This porthole is transparent to solar radiation, stable at high temperature and able to withstand the high internal pressure of the chamber 16.
• this bell 14 is insulated by a thick layer 22 of thermal insulation, silica wool for example.
• a first group 24 of membranes 26 selectively permeable to oxygen one of the MPO CM or MPO PEC types defined above.
• These membranes 26 may have the form represented by rigid glove fingers and they are each coated with a layer, for example sintered of a photocatalytic semiconductor, such as TiO 2 titanium dioxide.
• the group 24 comprises a large number (from ten to twenty, for example) of membranes 26, regularly arranged and sealingly attached to the bottom 28 of a round collector housing 30, of a suitable material (ceramic or metal) connected to a duct 32 for evacuating the product oxygen.
• the diameter of the window 20 is substantially equal to the diameter of the circle in which the group 24 of the membranes 26 is installed. If the membranes 26 are of the MPO PEC type, the internal and external electrodes of two neighboring membranes will be connected in series by means of, for example, for example, isolated bushings installed in the metal base 28 of the collector box 30.
• the membranes 26 may have the form of radial lamellae or any other form ensuring them a surface to volume ratio as high as possible.
• the bottom 34 of the reaction chamber 16 is pierced by an opening 35, on which is connected the inlet mouth of a hollow active element 36 and high surface area ratio, (the serpentine shown, for example) , belonging to a heat exchanger 38, for confined fluids, comprising a casing 40 enclosing this element 36.
• the outlet mouth 37 of this element 36 leads to the inlet of the extraction chamber 18.
• a demineralised water tank 42 provided with a feed pump 44, at high pressure and variable flow rate, and a distribution duct 46, is arranged in the vicinity of the apparatus 12.
• Two exchangers. 48 and 50, connected to the exchanger 38, are installed along the duct 46, outside the apparatus 12.
• the envelopes 52 and 54 of the exchangers 48-50 are arranged one after the other, in series with the duct 46 and the outlet of the casing 54 is connected to the inlet of the casing 40 of the exchanger 38 installed in the apparatus 12.
• the active hollow elements 56 ⁇ t 58 internal envelopes 52 and 54 are respectively arranged in series with the hydrogen extractor conduits 60 and oxygen 32.
• the various fluids concerned circulate against the current in the hollow active elements and in the envelopes of these heat exchangers.
• the inlet of the casing 40 of the exchanger 38 is connected by a duct 39 to the outlet of the casing 54 and the outlet of the casing 40 is connected by a duct 62 to the first inlet of a trunk 64
• the second inlet of this horn 64 is connected by a duct 66 to the outlet of the extraction chamber 18 and its outlet, connected by a pipe 68 to the inlet of the reaction chamber 16.
• the active elements 36, 56 and 58 heat exchangers 38, 48 and
• heat exchange active elements are described in the European patent application of the Japanese company EBARA, published under the number EP 1 122505 in August 2001.
• the extraction chamber 18 contains a stack 70 of pallet-permeable membranes 72, highly selective for hydrogen, of one of the MPH CM, MPH PEC or MPH MMC types defined above.
• each puck may comprise a deposited thin metallic layer r
• Such a membrane 72 comprises a fine gas extraction pipe 74 pierced in said ring and joining the substrate. These crowns are approximately 10 cm in internal diameter and 5 mm in thickness.
• the membranes 72 are stacked with spacer pads 76, in the form of rings, thus creating separation spaces of the same thickness.
• the number of membranes 72 in the stack 70 is from ten to twenty and their extraction ducts 74 are connected to a common manifold 78, ensuring the evacuation of the hydrogen produced, connected to the outlet pipe 60 of the chamber 18. If the membranes 72 of the extraction chamber 18, are of the MPH PEC type, they will preferably keep their shape in pallets and remain superimposed in the stack 70. In this case, the anode and the cathode two contiguous membranes will be directly connected to each other.
• perovskite ceramics conducting O 2 ' ions will be used.
• S. Herring describes the composition of such a high temperature electrolysis cell.
• the dense electrolytic membrane is made of zirconia stabilized with yttrium.
• the cathode is a porous layer made of a strontium-doped lanthanum-manganese mixture and the anode, a strontium doped, sintered lean-manganese-lanthanum layer. All of these layers constitute a sandwich structure which can be easily transposed to the glove finger geometries, shown in FIG. 5 described below, of the membranes that can be used in the reaction and extraction chambers of the device. dissociation of water vapor, object of the invention. It is the same for the diaphragm membranes of the extraction chamber 18.
• the locations of the membranes 26 and 72 respectively permeable to oxygen and hydrogen can be reversed, the membranes installed in the reaction chamber 16 retaining their shape in glove fingers and those installed in the extraction chamber 18, their form palettes.
• the hydrogen-permeable membranes installed in the reaction chamber are of one of the MPH CM or MPH PEC types, these membranes will again have the form of glove fingers or radial lamellae.
• membranes of the MPH MMC type can not be installed in the reaction chamber 16 since their maximum operating temperature can not exceed 650 ° C. and the temperature in this chamber is approximately 750 ° C.
• the oxygen-permeable membranes will preferably be installed in the reaction chamber, since their optimum temperature operating temperature is from 800 to 900 ° C.
• the membranes installed in the reaction chamber will be of two kinds, one permeable to oxygen and the other permeable to hydrogen, but all will have a high surface-to-volume ratio and will be adapted to function properly at the same time. relatively high temperatures (800 to 90 ° C).
• These two kinds of membranes will be associated with two kinds of individual collectors, respectively assigned to oxygen and hydrogen and connected to two common collectors.
• the membranes of the first group will, for example, be gathered in the center of the collector box and those of the second group installed around it.
• the collector box will comprise two cells provided with extraction ducts, one round in the center and the other in a ring around it.
• the other subsets of the water vapor dissociation apparatus 12, described in FIG. 4, remain unchanged.
• the glove finger membranes 80 and 81 each comprise a tubular layer 82 and 83 constituted by the solid electrolyte. These two layers are integral with a plane support 84 constituting a wall of the collector housing 30 and the whole forms a gas-permeable sintered assembly made of perovskite ceramics of ion-conductive type.
• the inner and outer walls of the two substrates 82 and 83 are coated with gas-permeable sintered electrodes, namely an anode 86-87 on their inner faces and a cathode 88-89 on their outer faces.
• the anode 86 is connected to the cathode 89 by a conductor 90 which passes through the support 84.
• a conductor 90 which passes through the support 84.
• On the cathodes 88-89 are deposited gas-permeable photocatalytic layers 92-93 and an identical layer 94 on the exposed parts. of support 84,
• the solar radiation concentrated by the parabolic mirror of revolution 10, enters the reaction chamber 12 speaks concave window 20 and illuminates all the photocatalytic coatings of the membranes in glove fingers 26.
• a large part of the photonic energy of this concentrated radiation is directly converted into chemical energy, the latter resulting from the dissociation of the water vapor present in the reaction chamber into oxygen and hydrogen.
• the re-emitted infrared radiation increases the temperature of the dissociated water vapor boundary layer in contact with it. coating and, as a result, improves the dissociation rate.
• the water vapor present in the reaction chamber 16 is there with a pressure of 5 to 15 bars and a temperature of up to 800 ° C. in said boundary layer. The means to obtain this state of affairs will be presented and commented on later.
• this gas selectively passes through the membranes 26, to be collected in the collector housing 30.
• the oxygen extraction conduit 32 causes this gas, thus filtered and collected, to penetrate into the hollow active element 58 This stream of oxygen is cooled there and then comes out for proper storage.
• the hot mixture 800 p C
• This mixture then enters the hollow active element 36 of the heat exchanger 38 and cools it to exit at about 450 û C then enter the extraction chamber 18.
• the hydrogen present is filtered by the membranes 72, in the form of pallets stacked with the appropriate separation spaces 76, then collected by the manifold 78 and discharged through the extraction duct 60, This duct 60 causes the stream of hydrogen thus produced to enter into the active hollow element 56 of the heat exchanger 48. This stream is cooled there and then comes out for proper storage.
• a demineralized water stream at the ambient temperature of the tank 42, is injected in the liquid state into the casing 52 of the first exchanger.
• thermal 48 of the equipment Due to the high temperature (400 ⁇ C) of the hydrogen which circulates in the hollow active element 56, the liquid water which penetrates, counter-current to the previous one, into the envelope of this element is vaporized and the steam produced at a temperature of about 300 ° C.
• this water vapor passes through the casing 54 of the heat exchanger 50 whose hollow active element 58 is crossed by the very hot oxygen stream (800 0 C) coming out of the collector box 38.
• the stream of water vapor which comes out at a temperature of about 500 0 C, enters the envelope 40 of the third heat exchanger 38 of equipment.
• the temperature of this stream of water vapor increases under the action of the very hot steam and hydrogen mixture stream (800 ° C.) which passes through the hollow active element 36.
• hot which leaves by the conduit 62, penetrates into the trunk 64 which leads the conduit 66 which ensures the evacuation of water vapor at approximately 400 ⁇ C remaining in the extraction chamber 18 after filtering and evacuation of hydrogen.
• the resulting stream of water vapor is injected into the reaction chamber 16, where there is a high pressure, under the action of the pump 44, and a high temperature under the action of concentrated solar radiation which enters through the porthole 20.
• a plasma is said to be cold when the ionic and molecular temperatures in the ionized zone remain very cold compared to that of the electronic population.
• electronic collisions are able to create active radicals that participate in the chemical reactions of dissociation of water vapor.
• the cooling of the electrons takes place partly by conversion to heat and partly by the chemical reactions thus produced. In this way, it is possible to selectively increase the latter with a small amount of electrical energy.
• a thermal plasma hot plasma
• pulsed discharges make it possible to create a cold plasma having the desired properties, for example pulsed periodic crown discharges, or pulsed barrier discharges.
• a pulsed barrier discharge can be used a composite device in the form of pencil.
• a filiform metal electrode On the axis of the rod is disposed a filiform metal electrode. The latter is coated with an insulating ceramic sheath.
• This device is inserted into the water vapor and the central electrode is connected to a generator of very short high voltage pulses (pulse duration one to a few microseconds, one millisecond recurrence time, pulse voltage 15 kilovolts) . It is formed R
• steerable parabolic mirror 10 may be replaced by any other form of optical concentrator, in particular those indicated above: a set of reflecting facets constituting a steerable Fresnel mirror, a heliostatic field or a double system including a fixed parabolic mirror and adjustable flat mirrors.

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