Classifications

• • 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
• • 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
  • B01D53/32—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 by electrical effects other than those provided for in group B01D61/00
  • B01D53/326—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 by electrical effects other than those provided for in group B01D61/00 in electrochemical cells
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2256/00—Main component in the product gas stream after treatment
  • B01D2256/16—Hydrogen
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/80—Water

Definitions

• the present invention relates to a device for the purification and electrochemical compression of hydrogen with several stages of compression.
• the subject of the invention is a device in which the constituent electrochemical cells have a smaller and smaller surface area in the direction of the hydrogen flow.
• Electrochemical compressors for hydrogen are devices based on the proton conductive properties of certain materials. They allow to pressurize hydrogen (potentially a few hundred bars) by a simple process in one step, using a low power supply.
• An MEA comprises a membrane consisting of a polymer proton conductor, for example a type ionomer PFSA (perfluorosulfonic acid) such as Nafion ®, separating two anode and cathode electrodes, respectively.
• the electrodes generally comprise platinum or a platinum alloy supported by carbon.
• the solvated protons that is to say the protons surrounded by water molecules, migrate through the ionomeric membrane under the effect of the electric field and are reduced to the cathode in the form of hydrogen according to the following half-equation : (3)
• the electrical voltage useful for extracting hydrogen from the gaseous mixture and recovering it at the cathode at the same pressure as at the anode corresponds to the voltage required for the purification of hydrogen.
• This voltage depends mainly on the resistance of the membrane, the electrocatalytic properties of the electrodes (charge transfer resistance) and the operating conditions.
• E p (V) the electric voltage of the electrochemical cell for the purification of uncompressed hydrogen
• An electrochemical cell used in this configuration is a proton pump that creates a flow of hydrogen between the anode and cathode compartments and promotes its storage under pressure.
• the electrochemical compressors operate in stationary conditions, at a constant temperature (advantageously corresponding to the optimum temperature of the membrane constituting the electrochemical cells) and at constant constant current.
• the electrochemical compressors with several compression stages are produced by a succession of electrochemical cells, or membrane-electrode assemblies (AME), of equivalent surfaces, and therefore operating at a constant current density.
• AME membrane-electrode assemblies
• the pressure at different stages of compression remains the only degree of freedom capable of influencing the operation of the compressor.
• n g corresponding to the ratio between the number of moles of water constituting the procession surrounding the protons and the number of moles of protons crossing the membrane, depends on the operating conditions of operation, that is to say the temperature (T), the current density (j) and the partial pressure of hydrogen (P H2 ).
• n g is illustrated by the following relation:
• the object of the present invention is to provide a device forming a multi-stage electrochemical compressor, able to pressurize hydrogen flowing through this device.
• This compressor comprises a plurality of membrane-electrode assemblies (AME) connected in series with each other, each membrane-electrode assembly forming an electrochemical cell.
• AME membrane-electrode assemblies
• the compressor is structured in such a way that the surface area of the electrochemical cells decreases according to the flow of hydrogen through the compressor.
• a device is capable of purifying and / or pressurizing hydrogen. It can therefore be used in connection with pure hydrogen or with a gaseous mixture containing hydrogen, especially from steam reforming.
• this device comprises a plurality of membrane-electrode assemblies (AME) connected in series with each other, each membrane-electrode assembly forming an electrochemical cell.
• AME membrane-electrode assemblies
• such a device is called multistage compressor. In other words, it comprises at least two AMEs, the cathode of the first MEA being arranged in series with the anode of the second MEA.
• the first MEA is the one arranged at the inlet of the gas stream which therefore arrives at the anode of the first MEA, while the second MEA is the one disposed at the outlet of the pressurized hydrogen, collected at the level of the cathode of the second MEA.
• the fact that the MEAs are connected in series thus makes it possible to ensure the passage of the gas flow and the flow of current along the compressor, from one electrochemical cell to the next.
• the device forming a multi-stage electrochemical compressor is able to pressurize hydrogen flowing through this device. He understands :
• ⁇ membrane-electrode assemblies where n is an integer equal to or greater than 2; each MEA forming an electrochemical cell; said MEAs being arranged to be traversed by a stream of hydrogen, and being electrically connected in series with each other; each of the MEAs comprising an active surface capable of providing oxy-reduction reactions of hydrogen; MEAs having active surfaces that are distinct from one another and decreasing in the direction of circulation of hydrogen.
• the MEAs are connected in series from the fluidic and electrical point of view.
• the successive gas compartments are perfectly gastight to each other and to the outside.
• the tightness between the compartments is ensured by the proton exchange membrane of each MEA, associated with one or more seals arranged at its periphery.
• the seal to the outside is ensured by the very design of the compartment.
• the MEAs are not arranged concentrically. They preferably have a flat surface. This flat configuration makes it possible to stack the MEAs according to the "filter-press" principle, which greatly facilitates the design of the system and the sealing system between each successive cell and to the outside.
• each of the MEAs is advantageously intended to be connected to an external source of single electrical current.
• the device according to the invention comprises n membrane / electrode assemblies (n ⁇ 2) which are necessarily electronically connected in series with each other. It is the use of a single source of electric power that imposes the electronic connection of the adjacent MEAs.
• the cathode (site of the evolution of hydrogen 2H + + 2 e-> H 2 ) and the anode (place of reduction of the hydrogen H 2 -> 2H + + 2 e-) of two successive AME are advantageously connected electrically between them by an electronic conductor to circulate the desired electronic current between these electrodes, with the lowest possible electrical resistance.
• the electrodes are brought into contact with a current-collecting material which does not impede the evolution of gas at the cathode and the access of the gases to the anode (metallic porous metal grid consisting of sintered particles, diffusion layer of carbon, etc.) and who can drive the electrons together.
• a current-collecting material which does not impede the evolution of gas at the cathode and the access of the gases to the anode (metallic porous metal grid consisting of sintered particles, diffusion layer of carbon, etc.) and who can drive the electrons together.
• each MEA may be connected to a separate source of electrical power. This embodiment corresponds to the case where the MEAs are electrically isolated from each other. It then requires control of the voltages and currents applied to each MEA independently of each other in order to optimize hydrogen transport and pressurization.
• the device comprises a single source of electric current, it is not necessary to control the voltage or the current of each AME.
• the device, and more precisely the electrodes of each AME automatically adapts the intensity of the current to the applied voltage and it is the same current that crosses the entirety of the AMEs put in series. This is all the more advantageous in the event of failure of one of the electrochemical cells.
• the current can no longer cross the system, there is no risk of accidental and excessive accumulation of gas in one of the compartments.
• the potential difference measured across the AMEs will increase in the opposite direction (1 / S).
• the voltage to be applied to the system will be the sum of the voltages of each cell.
• the cathode of the electrode n-1 and the anode of the electrode n are subjected to the same potential.
• the active surface of the electrochemical cells of the device decreases in the direction of circulation of the hydrogen.
• the AME of the n th electrochemical cell has an active surface area greater than that of the A ⁇ of the n + 1 electrochemical cell positioned downstream of the n th electrochemical cell.
• an MEA comprises a proton conductive membrane made of a material, advantageously requiring the presence of water for the transport of protons.
• the membrane consists of a type ionomer PFSA (perfluorosulfonic acid), such as Nafion ® or Aquivion ®.
• PFSA perfluorosulfonic acid
• other materials can be used for the manufacture of a proton exchange membrane.
• it can also be:
• sPEEKs sulfonated polyetherketones
• the transport of water molecules (electroosmosis coefficient) within the materials differs according to the nature of the materials used. It is generally determined experimentally and makes it possible to establish empirical laws of evolution as a function of the experimental parameters, in particular the temperature and the pressure.
• the membrane separates the two electrodes, the anode and the cathode respectively.
• the membrane is in direct contact with the electrodes.
• the membrane serves as a support for the electrodes and therefore has an area greater than or equal to that of the electrodes.
• the electrodes comprise a catalyst of the electrochemical reactions described above, preferably platinum or a platinum alloy, supported by carbon.
• the electrodes may also contain an ionomer, advantageously of the same nature as that constituting the membrane.
• the surface area of the electrochemical cells is defined as the area useful for the electrochemical reactions (active surface of the ⁇ ). Even more advantageously, it is the common surface of the two electrodes and the membrane. Said surface allows in particular the passage of the current and the gas flow. In other words, this area corresponds to that of the surface electrically connected and in contact with the gas flow (in particular hydrogen) at each electrochemical cell.
• the electrodes and the membrane have the same dimensions and therefore a surface of the same area, advantageously superimposed.
• the two anode and cathode electrodes have the same dimensions and therefore a surface of the same area, possibly less than that of the membrane.
• the first MEA has a surface area greater than that of the second MEA. More generally and considering a succession of AMEs arranged in series, the nth (n) AME has a surface area greater than that of the next AME (n + 1).
• the device object of the present invention makes it possible to avoid the accumulation of liquid water between each of the AMEs, the hydrogen circulating within the device can be humidified during its compression (pressurization), in particular in each of the compartments separating two adjacent MEAs.
• the humidification rate of the hydrogen is advantageously maintained or regulated to be between 50 and 100% relative humidity in each of these compartments.
• the spacing between adjacent electrochemical cells is constant according to the flow of hydrogen through the device. Due to the decrease in the area of the surface between two successive electrochemical cells, the volume of the compartment delimited by these two successive electrochemical cells is advantageously decreasing according to the flow of hydrogen through the device.
• the spacing between adjacent electrochemical cells of the device forming a multistage electrochemical compressor varies according to the flow of hydrogen through the compressor.
• the spacing between adjacent electrochemical cells of the device forming a multi-stage electrochemical compressor decreases according to the flow of hydrogen through the compressor. A decrease in the spacing between adjacent electrochemical cells makes it possible to benefit more from the gain in hydrogen pressure related solely to the geometry of the device.
• the area of the surface (S n ) of an n th electrochemical cell (n being an integer) in the compressor comprising a plurality of cells is determined by the following relation:
• (Si) and (S 2 ) represent the area of the surface of the first and second electrochemical cells respectively, and (j 1 ), (j 2 ) and (j n ) represent the respective current density respectively the first, the second and the n th electrochemical cell.
• the active surface of each electrochemical cell (S) is flat.
• said current density (j n ) is defined by the following relation:
• n g represents the ratio between the number of moles of water surrounding the protons and the number of moles of protons passing through the electrochemical cell and depends on the nature of the membrane used in the electrochemical cell;
• (T) represents the operating temperature of the device and is advantageously constant
• ⁇ represents the hydrogen partial pressure at the outlet of the n th cell
• the current density can be expressed as a function of the pressure of hydrogen, .
• a and b being independently of one another between 0.01 and 0.1.
• the areas of the surfaces of the electrochemical cells are chosen so as to guarantee a constant value of the magnitude n g along the device, and in this case along the compression stages.
• n g corresponds to the ratio between the number of moles m of water constituting the procession surrounding the protons on the one hand, and the number of moles n of protons crossing the membrane of an electrochemical cell on the other hand during oxidation-reduction reactions of hydrogen.
• the surface areas of the electrochemical cells are chosen so that the variations in current density compensate for the pressure variations along the compressor.
• the invention is directed to a method of electrochemically compressing hydrogen or a gas mixture containing hydrogen based on the use of a device comprising a plurality of membrane-electrode assemblies (MEAs). connected in series with each other, each membrane-electrode assembly forming an electrochemical cell, in particular a device as described above.
• MEAs membrane-electrode assemblies
• the current density is defined by the formula mentioned above.
• the ratio n g is advantageously constant throughout the device.
• the temperature is advantageously kept constant. Even more advantageously, it corresponds to the optimum temperature of the membrane used in the electrochemical cells.
• the present invention also relates to the use of the device for purifying hydrogen and / or compressing hydrogen.
• the invention and the advantages thereof will appear more clearly from the following figures and examples given to illustrate the invention and not in a limiting manner.
• Figure 1 shows the principle of purification and compression of hydrogen through an electrochemical cell.
• FIG. 2 represents a hydrogen compressor through a stack of electrochemical cells having surfaces of identical area
• FIG. 3 represents a device according to the invention, that is to say a staged stack of electrochemical cells having areas of decreasing area in the direction of the flow of hydrogen and water, each of the AME being connected to a separate source of electrical power.
• FIG. 4 represents a device according to the invention, that is to say a staged stack of electrochemical cells having areas of decreasing area in the direction of the flow of hydrogen and water, and comprising an external source; single electric current.
• FIG. 1 describes the operating principle of an electrochemical hydrogen compressor.
• the electrochemical cell consists of a membrane / electrode assembly, in which the and the are respectively the anode and cathode compartments; 2a and 2c are diffusion layers, generally made of porous carbonaceous material; 3a and 3c are respectively the anode and cathode electrodes; and, 4 is the resistance proton exchange membrane (Rm).
• Rm resistance proton exchange membrane
• Each of the electrodes is generally associated with a current collector which is not shown so as not to impair the clarity of the figures.
• a constant current (I) corresponds to a constant flux of the number of moles of protons H + , imposed by an electrical surge
• FIG. 2 illustrates a compressor comprising k electrochemical cells (AMEs) of surfaces of the same area.
• AMEs electrochemical cells
• the membrane / electrode assemblies have surfaces of the same area (S) whereas n g is only a function of the hydrogen pressure. It follows therefore that this function decreases with increasing pressure, therefore the parameter (m) corresponding to the number of moles of water passing through the protonic conductive membrane decreases along the stages.
• n g will depend on two parameters namely the pressure and the current density.
• the effect of the pressure on the quantity n g will be counterbalanced by that of the current density so as to maintain the magnitude n g constant along the compressor, which will prevent any accumulation of water between two consecutive stages.
• the invention proposes a reduction of the surface area of the electrochemical cells along the compressor which allows this constant current increase (FIGS. 3 and 4).
• the reduction ratio between the surfaces of two consecutive electrochemical cells depends on the desired optimal operating conditions.
• the spacing between electrochemical cells can be constant or decrease in the direction of circulation of hydrogen.
• the electrodes and the membrane of each MEA advantageously have a surface of the same area.
• FIG. 4 illustrates another embodiment in which the device according to the invention comprises a plurality of membrane assemblies. electrodes electronically connected in series to each other by means of the electronic conductor (5). This device relates to the case where each of the MEAs is connected to an external source of single electric current.
• the electronic conductor (5) provides the connection between two consecutive MEAs. It is made of an electronically conductive material and may especially be in the form of a grid, superimposed grids, foam, carbon fabric, porous (material comprising voids, pores) based on sintered conductive particles ...
• the material electronically conductor (5) may be of a material that will not degrade under the selected operating conditions.
• the electronically conductive material (5) is advantageously chosen from the group consisting essentially of titanium, carbon, but also certain metals or alloys (in particular steel) advantageously coated with a deposit less sensitive to corrosion (for example a coating of gold or based on chromium).
• it is not Ni, A1, Cu, or Zn.
• the electronic conductor (5) electronically connects a first electrode of a first MEA and a second electrode of a second MEA adjacent, these electrodes being of opposite signs. In view of their electronic connection, said first and second electrodes are at the same potential. In other words, an electrode of an AME is at the same potential as the electrode opposite the adjacent ⁇ .
• the electronic conductor (5) is made of a porous material. It can thus define the volume of the compartment separating two successive MEAs, especially when it is in the form of a foam, stack of grids or porous sintered particles of electronically conductive material.
• the present invention provides a means for calculating the surfaces of the electrochemical cells (S) constituting the multi-stage compressor.
• the expression of the quantity n g as a function of the parameters temperature (T), current density (j) and hydrogen pressure is given by the following relation:
• the objective is to maintain a constant flow of water along the electrochemical compressor at constant temperature and current, which makes it possible to obtain a dependence exclusively between the hydrogen pressure and the current density.
• the relationship can be rewritten as follows:
• n g is known or can be determined experimentally. It is therefore possible for each value n g given to establish the relation between the current density and the hydrogen pressure, namely the following relation:
• the spacing between the membrane electrode assemblies in the compressor makes it possible to adjust the hydrogen pressure between two adjacent electrochemical cells.
• the volume of the compartment delimited by two successive electrochemical cells decreases along the flow of hydrogen in the compressor. This gives a further increase in pressure without providing additional electrical energy.
• Electric surge necessary to prime electrochemical reactions is then written as a function of hydrogen pressures on stage I and at the stage I + 1 and the volumes V I and V I + 1 of the compartments delimited respectively by the cells I and 1 + 1 on the one hand and the cells I + 1 and I + 2 on the other hand, under the form:
• the second term represents a gain in electrical energy due to the decrease in the volume of the compartments delimited by the electrochemical cells I and 1 + 1 on the one hand and the cells I + 1 and I + 2 on the other hand .
• the electrochemical cells that make up the electrochemical compressor are subjected to the same mechanical stresses. Consequently, the same difference in hydrogen pressure is imposed on the different electrochemical cells. This pressure difference is chosen as a function of the thickness and the mechanical properties of the proton exchange membrane.
• the proton exchange membrane is composed of Nafion ®.
• the operating temperature of the compressor is chosen according to the optimum temperature of this material, equal to 80 ° C.
• the compressor runs at a constant temperature.
• the invention makes it possible to calculate the surfaces (S) of each electrochemical cell for a four-stage compressor composed of five electrochemical cells, the surface of the first cell being imposed.
• the surface of the two electrodes is equal to the surface of the membrane.
• this surface corresponds to the useful surface, that is to say to the surface on which the electrochemical reactions can take place (in contact with the gas flow, in particular hydrogen and the current).
• a constant current is imposed, in this case equal to 100A.
• the surface of the first membrane / electrode assembly (AME) S 0 is set at 100 cm 2 . Given the constant current (I) of 200 A imposed, this corresponds to a current density (j 0 ) equal to 2 A / cm 2 .
• the first membrane / electrode assembly (AME) So is subjected to a zero pressure difference and the hydrogen inlet pressure in the electrochemical compressor is the atmospheric pressure (1 bar).
• Each membrane / electrode assembly (AME) is subjected to a pressure difference of the order of 5 bars.

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• 2013
  • 2013-06-26 FR FR1356158A patent/FR3007669B1/fr active Active
• 2014
  • 2014-06-26 EP EP14739896.0A patent/EP3013738A1/de not_active Withdrawn
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