EP0359631A1 - New electrolysis cell and electrolysis unit for putting it in active operation - Google Patents

Abstract

The present invention relates to an electrolysis cell and to its use in an electrolysis unit. The electrolysis cell of the invention is characterised in that it consists of a chamber in which are located, face to face, two base electrodes which are electrically insulated from one another, the base cathode consisting of a solid plate of a conductive material (5) and the base anode being a bulky anode consisting of a solid plate of a conductive material (4) on which are located one or more grids of expanded metal (6), and in that in the said cell there is located, at each end thereof, on either side of the electrodes, a plate of insulating material which is pierced with orifices (13).

Description

The present invention relates to an electrolysis cell intended in particular for the implementation of a process coupling both an electrolysis of a chemical species in solution and simultaneous extraction of the chemical species produced, in an organic phase.

The invention relates more particularly to a cell intended for the electrochemical oxidation of cerium 3+ into cerium 4+ and simultaneous extraction of cerium 4+ in the organic phase.

There is described in FR-A 2 570 087 an electrolysis cell for electrochemically oxidizing cerium 3+ to cerium 4+. Said cell comprises two anode compartments, a cathode compartment located between the two aforementioned anode compartments, and two cationic membranes separating each of the two anode compartments from the cathode compartment.
In FR-A 2 570 087, there is also described a method of electrolytic oxidation of a chemical species involving the aforementioned cell, characterized in that said solution is treated in the first anode compartment of an electrolysis cell comprising a first anode compartment and a cathode compartment separated by a first cationic membrane, the solution from the first anode compartment is then treated in a second anode compartment of the above-mentioned electrolysis cell and separated from the above-mentioned cathode compartment by a second cationic membrane, recovers the solution from the second anode compartment which constitutes the production, an electrolyte is circulated in the aforementioned cathode compartment.

This type of apparatus makes it possible to obtain "Faraday" yields and a high transformation rate of cerium 3+.

However, its use is ill-suited when treating solutions with a very low concentration of cerium 3+ because, due to the low current density, the surface of the electrodes must be increased so that the size of the installation becomes important.

Furthermore, when using a conventional electrolysis cell without separator, a major drawback is the reduction tion possible at the cathode of the product formed at the anode.

In order not to use heavy technology using a separator electrolysis cell and to overcome the drawbacks of conventional electrolysis cells, it was proposed in French patent application No. 88/03021 to simultaneously perform the electrochemical oxidation of cerium 3+ to cerium 4+ in the aqueous phase and the extraction of the cerium 4+ formed in an organic phase extracting the cerium 4+ emulsified in the aqueous phase.

As a result, the trapping of cerium 4+ in the organic phase makes it possible to obtain a high conversion rate which would never have been possible in a conventional cell without a separator and also avoids secondary reactions at the cathode. .

Such a process, using an oil-in-water type emulsion, requires perfectly adapted apparatus preserving the coalescence and settling of the emulsion.

A first objective of the invention is to provide an electrolysis cell which makes it possible inter alia to implement a process involving the electrolysis of a chemical species in the aqueous phase and the extraction of the species produced in the emulsified organic phase in said aqueous phase.

Another objective of the invention is to propose an electrolysis cell which does not use heavy technology.

Another objective of the invention is to provide an electrolyte cell which can be used on an industrial scale and which can operate both continuously or discontinuously.

A final objective of the invention is to have an electrolysis cell having a great flexibility of adaptation as a function of the electrochemical operation to be carried out.

The electrolysis cell of the invention is characterized in that it consists of an enclosure in which are placed face to face two base electrodes electrically isolated from each other, the base cathode consisting of a solid plate of a conductive material and the base anode being a volume anode consisting of a plate full of a conductive material on which are placed one or more grids of expanded metal and that in said cell is placed at each end of that here, on either side of the electrodes, a plate of insulating material pierced with orifices.

A preferred variant of the invention consists in interposing between the two base electrodes, one or more electrode modules consisting, on the one hand, of a plate full of a conductive material working on a cathode face and on the 'other anode face and, on the other hand, one or more expanded metal grids placed on the anode face; the electrode module (s) being inserted so that the anode side of the plate faces the base cathode and optionally faces the cathode side of another module; the electrode module (s) being electrically isolated from the base electrodes and possibly from each other.

• - La figure 1 est une représentation schématique d'une cellule d'électrolyse selon l'invention qui correspond à une vue de profil.
• - La figure 2 est une représentation schématique d'une cellule d'électrolyse selon une autre variante préférentielle de l'invention qui correspond à une vue de face.

Other characteristics and advantages of the invention will be better understood on reading the description which follows, made with reference to the appended drawings in which:

• - Figure 1 is a schematic representation of an electrolysis cell according to the invention which corresponds to a side view.
• - Figure 2 is a schematic representation of an electrolysis cell according to another preferred variant of the invention which corresponds to a front view.

The electrolysis cell of the invention shown in FIG. 1 consists of an enclosure (1) having an externally parallelepeledic shape (preferably cubic or rectangular) made of insulating material, for example glass, conventional plastic material such as polyvinylidene difluoride, polyvinyl chloride, polypropylene, polymers of the methyl methacrylate type (PLEXIGLAS®).

It is desirable that said enclosure has a removable wall in order to facilitate the handling of the electrodes and the maintenance of the apparatus.

Opposite, there are provided an inlet (2) and an outlet (3) for the fluid.
Preferably, the fluid supplied at the bottom of the cell is discharged at the top of the latter.

In order to ensure good circulation of the fluid, it is preferable to give the ends of the cell, a flared shape (10) as illustrated in FIG. 2: the walls narrowing between the cell body and the entry or exit of fluids.

In this enclosure, a variable number of electrodes is stacked which depends on the configuration of the electrolysis cell.

One advantage of the electrolysis cell of the present invention is that it can have either a monopolar configuration or a bipolar configuration.

In a monopolar configuration, there is an anode (4) and a cathode (5) which are connected to a current supply. They consist of a plate full of conductive material.

As anodes, one or more grids (6) of expanded metal are added which increase the anodic surface and which, moreover, have a turbulence promoting effect which promotes the transfer of anodic material.

The grids are made of mesh, the largest opening of which can be placed parallel or perpendicular to the flow of the fluid. Preferably, one chooses to put a grid perpendicularly and in the case of several grids to perform a cross stacking, namely alternating grids with parallel meshes and perpendicular to the fluid.

The number of grids can vary between 1 and 5 and is preferably between 2 and 4.

It is thus possible to adapt the number of grids to the desired anode surface. It follows that the ratio between the anodic and cathodic surface can vary within wide limits from 1.0 to 10 but preferably it is chosen between 4.0 and 7.0.

A preferred embodiment of the electrolysis cell of the invention is the bipolar configuration which makes it possible to obtain specific surface areas of electrodes even higher.

In the bipolar configuration, there are two basic electrodes (4), (6) and (5) and at least one electrode module (7). Only the base electrodes are connected to a current supply.

The base cathode (5) consists of a solid plate, therefore of small surface, which favors the transfer of material. The anode consists of a solid plate (4) and one or more grids of expanded metal (6).

One or more electrode modules are interposed between the anode and the base cathode. By this expression is meant a set of electrodes consisting of a solid plate (8) one of the faces of which functions as an anode and the other face of which operates as cathode. On the anode face of said plate (8), one or more expanded metal grids (9) are placed.

The electrode module (s) are stacked so that the anode side faces the cathode side of another module or the base cathode (5).

According to the invention, it is possible to introduce a variable number of modules which has no critical character and which can range, for example, from 1 to 10.

The electrolysis cell of the invention has great flexibility of use, in particular for covering a wide range of electrode surfaces, owing to the fact that it is possible to act both on the number of grids of expanded metal and on the number of modules implemented.

If one does not operate in the maximum configuration of modules initially planned, the missing modules should be replaced by solid plates (11) made of insulating material (plastic) in order to fill the dead volume. Said plates are placed outside the anode and / or the base cathode.

As regards the characteristics of the electrodes, their chemical nature will be specified. They are made of a conductive material resistant to chemical and electrochemical oxidation.

The base anode (4), the base cathode (5) and the solid plate (8) playing both the cathode and anode roles can be more particularly made of graphite, titanium, titanium coated with '' a precious metal, for example platinum, palladium, irridium. Preferably, a solid metal plate is used.
As for the geometric shape of the solid electrodes, it depends on the shape of the enclosure.

The expanded metal grid (s) may also be made of titanium, optionally coated with a precious metal. It will not depart from the scope of the invention to use the expanded metal in the form of a canvas.

In the electrolysis cell of the invention, whether in monopolar or bipolar configuration, the electrodes are electrically isolated from each other. To this end, the electrodes can be separated by a spacer (12) made of insulating materials.

As insulating materials, the following plastics may be mentioned by way of examples:
- polyvinyl chloride,
- polyvinylidene difluoride
- polypropylene,
- polymethyl methacrylate (PLEXIGLAS®).

The spacer which is interposed between the base electrodes and any modules is preferably in the form of a frame which consists of an insulating plate having the dimensions of the cathode, hollowed out in its center and the width of said frame is minimized but sufficient to ensure mechanical stability of the electrode assembly.

The thickness of the spacer delimits the distance between the electrodes. It is desirable that it be as small as possible in order to reduce the dead volumes in the cell. Generally, the distance between the two electrodes varies between 1 mm and 5 mm and, preferably, is chosen around 2 mm.

The use of a spacer applied between the anode and the cathode forces the fluid to pass through the stack of grids. As a result, the transfer of material to the cathode is disadvantaged.

Another characteristic of the electrolysis cell of the invention is the presence of a plate (13) of insulating material pierced with orifices, located at each end of the cell and placed on either side of the electrodes.
Said plate can be produced, for example, from the aforementioned plastics.
Its shape matches that of the enclosure.

It is pierced with orifices having a diameter which can vary, for example, between 0.5 mm and 5.0 mm and of preparation between 1.0 and 2.0 mm.

In an electrolysis cell having the preferred bipolar configuration according to the invention, the presence of such a plate disadvantages the passage of the current lines in the dead volumes thus making it possible to obtain a higher Faraday yield.

A preferred variant of the invention illustrated in FIG. 2 consists in filling the space defined in the upper and lower part of the cell, by introducing obstacles to the circulation of the fluid such as for example grids or balls (14). made of insulating material. At the level of the arrival of the fluid (2), this avoids an excessive jet effect and the flow is uniform.

As for the operation of the cell, the arrival of the fluid takes place at the anode due to the presence of the spacer between anode and cathode. The fluid circulates in a longitudinal direction.
As for the electric current, it flows in a transverse direction.

The electrolysis cell which is the subject of the present invention therefore has the following advantages:
- high capacity electrolyser (due to high specific electrode areas).
- The fluid feeds are made at the level of the anodes so as to favor the transfer of material there and also to avoid the coalescence of the emulsion in the meshes of the expanded metal.
- Dead volumes are minimized so as to avoid coalescence and settling of the emulsion.

The electrolysis cell of the invention can be integrated into an electrolysis assembly making it possible to implement a method coupling both an electrolysis operation and an extraction operation.

As examples of a process that can be implemented in said cell, there may be mentioned an electrochemical oxidation process of cerium 3+ to cerium 4+ in emulsion which consists in simultaneously carrying out the electrochemical oxidation of cerium 3+ in cerium 4+ in the aqueous phase and the extraction of cerium 4+ 4+ formed in an organic phase extracting cerium 4 + emulsified in the aqueous phase which makes it possible to obtain, after separation of the phases, an organic phase loaded with cerium 4 +.

The aqueous phase consists of the cerium 3+ salt solution. Mention may be made, as salts, of cerium sulfate or nitrate III. Its maximum concentration depends on the solubility of the salt and can vary for example according to the solubility between 0.1 and 1.5 moles / liter. The minimum bound is not critical, but a lower concentration results in a lower current density.

A mineral acid, preferably sulfuric or nitric acid, is added in an amount such that the normality of the aqueous phase varies between 0.5 and 5 N and preferably between 1 and 2 N.

The aqueous phase defined above is brought into contact with an organic phase containing a water-insoluble cerium extracting agent 4+.

The extraction agent used in the process of the invention must be able to selectively extract the cerium 4+.

A cationic extraction agent and more particularly an organophosphorus acid can be used.

dans les formules (I) à (III) R₃ représente R₂ ou l'hydrogène et R₁ et R₂ sont des radicaux hydrocarbonés aliphatiques, cycloaliphatiques et/ou aromatiques.We can mention those that meet the following general formulas:

in formulas (I) to (III) R₃ represents R₂ or hydrogen and R₁ and R₂ are aliphatic, cycloaliphatic and / or aromatic hydrocarbon radicals.

Said radicals can contain from 1 to 18 carbon atoms and at least one of them comprises at least 4 carbon atoms.

It is preferred to use mono- or dialkylphosphoric, mono- or dialkylphosphonic, alkylphenylphosphonic, mono- or dialkylphosphinic acids.

Even more preferably, use is made of di (ethyl-2-hexyl) phosphoric acid and di (ethyl-2-hexyl) phosphonic acid.

All the extraction agents mentioned can of course be used alone or as a mixture.

The organic phase contains, where appropriate, an organic diluent inert with respect to the extracting agents in order to improve the hydrodynamic properties of the organic phase. Many organic solvents or their mixtures can be used as diluents. However, in the present case, a diluent must be chosen which cannot be oxidized by cerium 4+.

By way of examples, mention may be made of aliphatic or cycloaliphatic hydrocarbons and halogenated hydrocarbons or a mixture of them.

Preferably, an aliphatic hydrocarbon is used such as, for example, hexane, heptane, dodecane, petroleum fractions of the kerosene or isoparaffin type.

The proportion of extracting agent in the organic phase is not critical and can vary within wide limits. However, it is generally advantageous for it to be as high as possible. Thus, in the case of cationic extractants, a concentration of extractant of 0.5 to 2.0 moles per liter of organic phase leads to advantageous hydrodynamic separation conditions.

The aqueous phase and the organic phase are brought into contact by emulsifying the organic phase in the aqueous phase.

The proportion of the organic phase relative to the aqueous phase can vary within wide limits. The organic phase can represent from 5 to 66% of the volume of the two phases and, preferably, from 33 to 66%, and more preferably 50%.

The organic phase is emulsified in the aqueous phase by stirring.

The organic phase being emulsified in the aqueous phase, the aqueous solution of the cerous salt is electrolysed under the conditions given below.

The electrolysis is preferably carried out at room temperature: most often between 15 ° C and 25 ° C. It is possible to work at a higher temperature, which promotes the kinetics of the electrochemical reaction and the transfer of materials to the electrodes, but the choice of temperature depends on the solubility of the cerous salt.

The conditions of the electrolysis operation depend on the discontinuous or continuous mode of operation of the electrolysis cell and will be specified below.

At the end of the electrolysis, an organic phase highly charged with cerium 4+ is recovered which is separated from the aqueous phase by any appropriate means, in particular decantation.

The electrolysis cell of the invention is perfectly suited for the implementation of the process defined above.

It can therefore be used in an electrolysis assembly comprising at least the following means:
- a mixer intended to form and stabilize the emulsion,
- means for conveying the emulsion,
- the electrolysis cell previously described,
- Means intended to evacuate the gas produced at the cathode.

A continuously operating electrolysis unit further includes:
- means for supplying the aqueous phase,
- means for supplying the organic phase,
- Means for withdrawing the emulsion charged in this case produced electrochemically.

A more detailed description of the installation is given below with reference to FIG. 3 which is a schematic representation of an installation operating continuously according to a preferred variant of the invention.

The installation is supplied from the outside in aqueous phase (15) introduced into a storage tank (16) and in organic phase (17) introduced into a storage tank (18).

Two pumps (19) and (20) convey said fluids and food try in (21) and (22) the mixer (23).

At the outlet (26) of the mixer, the emulsion formed is conveyed via a pump (27) to the inlet (2) of the electrolysis cell (1), object of the present invention.

At the outlet (3) of the electrolysis cell, the charged emulsion passes through a degasser (28) then a refrigerant (29).

It is then recycled in the mixer (23) at (30) in the upper part of the mixer.

A part of the emulsion drawn off at (31) in the lower part of the mixer constitutes the production. It is then sent to a storage tank (33), optionally equipped with a withdrawal valve (34), by means of a pump (32).

It is possible to place on the fluid circulation circuits, means for controlling the flow rates, for example a volume flow meter with float (35).

More specifically, the mixer (23) is equipped with a central agitation (24) and possibly with a valve (25) for drawing off. It can be envisaged to use a static mixer of the KENICS® or SULZER® type. Preferably, a stirred tank is used.

The electrolysis cell (1) has been described in detail and is preferably a bipolar cell.

The degasser (28) is intended to remove the gas produced at the cathode. You can use a flat or coil degasser. Preferably, a flat degasser is used and it should preferably be given an elongated shape in order to avoid the formation of dead zones.

It is possible to provide cooling means placed at the outlet of the degasser to compensate for any heating of the emulsion. For this purpose, one can put a double jacket refrigerant (29) with water circulation.

With regard to the various pumps (19), (20) and (32), these are metering pumps. As for the pump (25) intended to convey the emulsion, it is possible to use a centrifugal or volumetric pump. A centrifugal pump is preferably used.

The operating conditions of the installation depend on the size of the various devices involved in the installation. By way of illustration, they are specified below for a concrete embodiment of the invention.

The electrolysis cell represented by FIGS. 1 and 2 and then used in the examples has the following characteristics.

It consists of an enclosure (1) made of PLEXIGLAS® having a volume of approximately 1 dm³. It comes in the form of a box with a lid.

In this enclosure, a variable number of electrodes having a square shape are stacked. The electrodes full plates or expanded metal grids are 13 cm side.

In a monopolar configuration, the cell has a base cathode which is a plate (5) of platinum titanium having a surface of 0.017 m² and a base anode which is a volume anode consisting of a plate (4) of platinum titanium having an area of 0.017 m² and a stack of 1 to 4 grids (6) of 2.5 micron platinized expanded titanium, of standard mesh N (10 x 5.8 x 1.1 mm) for which the effective area of electrode is 1.407 m² per m² of grid.

In the bipolar configuration, there is between the basic electrodes, from 1 to 4 additional electrode modules consisting, on the one hand, of a plate (8) in platinum titanium having a surface of 0.017 m², working on one side in cathode and on the other side in anode and, on the other hand, from 1 to 4 grids (9) of 2.5 μm platinum-expanded expanded titanium, of standard mesh, as described above.

The electrode module (s) are inserted so that the anode side of the plate faces the base cathode and possibly faces the cathode side of another module.

The following table specifies the anodic (A _ea ) and cathodic (A _ec ) surfaces likely to be obtained as well as the surface ratio A _ea / A _ec .

The surface area ratio A _ea / A _ec can vary between 2.4 and 6.6.

When not operating in the maximum configuration, the vacuum is filled by a set of full PLEXIGLAS® plates (13 cm x 13 cm).

The electrodes are electrically isolated from each other by a spacer (12) which is a plastic frame (P.V.C.) with a thickness of 2 mm.

In the cell, is placed at each end thereof, on either side of the electrodes, a plastic plate (P.V.C.) pierced with holes of 2 mm in diameter.

The ends of the cell have a flared shape (10) as illustrated in FIG. 2.

The space defined in the upper and lower part of the cell is filled by a stack of plastic grids (14).

The electrolysis cell described above is integrated into a main circuit containing a mixer (23), a pump (27), a degasser (28) and a refrigerant (29).

The mixer (23) is equipped with a central agitation (24) and the inlet (30) and the outlet (26) of the emulsion are placed opposite.

Its characteristics are as follows:
- cylindrical tank with a total volume of 3.06 liters = 250 mm in height and 125 mm in diameter,
- 50 mm diameter stirring device = double turbine with 4 straight blunt blades 50 mm in diameter,
- 4 counter blades of 12 x 12 x 250 mm.

The pump (27) intended to convey the emulsion at a flow rate specified in the examples is a conventional pump of the centrifugal type.

The degasser (28) is a flat degasser having a surface area of 9 dm².

The refrigerant (29) is a double jacket refrigerant, without specific characteristics.

In the case of continuous operation, the main circuit is coupled to a supply and withdrawal circuit comprising:
- a storage tank (16) for the aqueous phase and a metering pump (19),
- a storage tank (18) for the organic phase and a metering pump (20),
- a metering pump (32) and a storage and settling tank (33) of the emulsion equipped with a withdrawal valve (34).

As regards the operation of the electrolysis assembly, it varies depending on whether the electrolysis operation is carried out in a continuous or discontinuous mode.

However, in all cases, the operation for forming the emulsion is identical and carried out with relatively vigorous stirring between 1000 and 1500 revolutions / minute.

In discontinuous operation, a sufficient circulation speed is ensured which depends on the configuration of the electrolysis cell. As an indication for the cell described above, it can vary between 0.3 and 1.5 m³ / h depending on whether the configuration is monopolar or bipolar with up to 3 electrode modules. A potential is imposed which depends on the electrochemical operation to be carried out. For example, in the case of the electrochemical oxidation of cerium 3+ to cerium 4+, we place ourselves at the limit of the oxygen release potential. Generally, we place ourselves at less than 50 millivolts of said potential. It depends on the medium and the electrodes. In the case of platinum titanium electrodes, an anode potential of 1.7 to 1.8 volts is defined with respect to the normal hydrogen electrode.

The duration of the electrolysis can be continued until obtaining a balance that results in constant tension, intensity and concentration.

In continuous mode, an operating point is defined which corresponds to a desired conversion rate, which imposes, for a given electrode area, the intensity of the current in the cell and the supply and withdrawal rates.

The choice of operating mode depends on the electrochemical operation to be performed and on the desired conversion rate. To obtain high conversion rates, it is preferable to work batchwise. On the other hand, if one wishes lower conversion rates, for example, to achieve the depletion of a solution in a given chemical species, the continuous mode of operation can be preferred because of its adequacy with a mode of production on an industrial scale.

Examples of embodiment of the invention are given below, given by way of non-limiting indication.

EXAMPLE 1 :

In this example, the implementation of the electrolysis cell described above operating in bipolar mode and in continuous mode is described.

For the description of this example, reference is made to FIG. 3.

The aqueous phase (15) consists of a cerous sulphate solution containing 0.2 mole / liter of cerium 3+ and having a sulfuric acid normality of 1 N. It is introduced into the storage tank (16) and supplied with (21) the mixer (23) at a flow rate of 1.39 liters / hour.

The organic phase (17) is composed of di (2-ethylhexyl) phosphoric acid in solution in kerosene at a rate of 1 mole / liter. It is introduced into the storage tank (18) and feeds into (22) the mixer (23) at a flow rate of 1.39 liters / hour.

In the mixer (23), the organic phase is emulsified in the aqueous phase by stirring at 1100 rpm. The content of the emulsion in the organic phase is 50% by volume.

The emulsion leaves the mixer (23) at (26) and then circulates at a speed of 880 liters / hour in the main circuit comprising the electrolysis cell (1), the degasser (28) and the refrigerant (29).

The configuration of the cell shown more precisely in FIGS. 1 and 2 is as follows:
- base anode (4) and base cathode (5)
- 3 electrode modules
- anodic stack of 3 grids (6) and (9)
- total anodic area: 0.352 m²
- total cathodic surface: 0.068 m²

Electrochemical oxidation of cerium 3+ to cerium 4+ is carried out at room temperature.

The current intensity is 2.06 A.

The organic phase is loaded with cerium 4+.

The withdrawal is carried out at a flow rate of 2.78 liters / hour of the emulsion loaded in (31) which is transported to the storage tank (33).

After separation of the aqueous and organic phases by decantation, the following results are determined:
- [Ce ^{3 ·} ] in aqueous phase = 0.029 mole / l
- conversion rate: 85.3%
- [Ce ^{4 ·} ] in aqueous phase = 0.046 mole / l
- [Ce ^{4 ·} ] in organic phase = 0.166 mole / l
- fraction of cerium recovered in organic phase: 83%
- partition coefficient of Ce ^{4 ·} between the 2 phases: 36
- faradaic yield: 77%

EXAMPLE 2

Example 1 is reproduced except as regards the composition and the flow rate of the phases, the configuration of the installation remaining identical.

The aqueous phase (15) consists of a cerous sulphate solution containing 0.2 mole / liter of cerium 3+ and having a sulfuric acid normality of 2 N. It feeds into (21) the mixer (23) at a rate of 0.93 liter / hour.

The organic phase (17) is composed of di (2-ethylhexyl) phosphoric acid in solution in kerosene at the rate of 2 moles / liter. It feeds (22) the mixer (23) at a flow rate of 0.46 liters / hour.

In the mixer (23), the organic phase is emulsified in the aqueous phase by stirring at 1100 rpm. The content of the emulsion in the organic phase is 33%.

At the outlet (26) of the mixer (23), the emulsion circulates at a speed of 880 liters / hour.

Electrolysis is carried out in a manner identical to example 1. The intensity of the current is 1.6 A.

The charged emulsion at (31) is drawn off at a flow rate of 1.4 liters / hour.

The results obtained are as follows:
- [Ce ^{3 ·} ] in aqueous phase = 0.071 mole / l
- conversion rate: 64.3%
- [Ce ^{4 ·} ] in aqueous phase = 0.0047 mole / l
- [Ce ^{4 ·} ] in organic phase = 0.248 mole / l
- fraction of cerium recovered in organic phase: 62%
- partition coefficient of Ce ^{4 ·} between the 2 phases: 52
- current efficiency at equilibrium: 50%

EXAMPLE 3

In this example, the implementation of an electrolysis cell operating in bipolar mode and in discontinuous mode is described.

The installation includes only the main circuit shown in Figure 3, namely, the mixer (23), the pump (27), the electrolysis cell (1), the degasser (28) and the refrigerant (29) .

The aqueous phase consists of a cerous sulphate solution containing 0.2 mole / liter of cerium 3+ and having a sulfuric acid normality of 1 N. 3000 cm³ of said phase are introduced into the mixer (23).

The organic phase is composed of di (2-ethylhexyl) phosphoric acid in solution in kerosene at a rate of 1 mole / liter. 3000 cm³ of said phase are introduced into the mixer (23). In the mixer (23), the organic phase is emulsified in the aqueous phase by stirring at 1100 rpm. The content of the emulsion in the organic phase is 50% by volume.

The emulsion leaves the mixer (23) at (26) and then circulates at a speed of 880 liters / hour in the main circuit comprising the electrolysis cell (1).

The configuration of the cell shown more precisely in FIGS. 1 and 2 is as follows:
- base anode (4) and base cathode (5)
- 1 electrode module (7)
- anodic stack of 4 grids (6) and (9)
- total anodic area: 0.224 m²
- total cathodic surface: 0.034 m²

Electrochemical oxidation of cerium 3+ to cerium 4+ is carried out at room temperature, by imposing a potential on the anode of 2.49 volts / ENH.

The electrolysis lasts 4 hours.

The organic phase is loaded with cerium 4+.

After separation of the aqueous and organic phases by decantation, the following results are determined:
- [Ce ^{3 ·} ] in aqueous phase = 0.01 mole / l
- conversion rate: 95%
- [Ce ^{4 ·} ] in aqueous phase = 0.052 mole / l
- [Ce ^{4 ·} ] in organic phase = 0.184 mole / l
- fraction of cerium recovered in organic phase: 92%
- partition coefficient of Ce ^{4 ·} between the 2 phases: 36
- Faradic yield: 89.5%

EXAMPLE 4

Example 3 is reproduced but by modifying the configuration of the electrolysis cell which becomes the following:
- base anode (4) and base cathode (5)
- 2 electrode modules (7)
- anodic stack of 4 grids (6) and (9)
- total anodic surface: 0.336 m²
- total cathodic surface: 0.051 m².

Oxidation of cerium 3+ to cerium 4+ is carried out by imposing a potential on the anode of 3.18 volts / ENH.

The electrolysis lasts 4 hours 30 minutes.

The results obtained are as follows:
- [Ce ^{3 ·} ] in aqueous phase = 0.0068 mole / l
- conversion rate: 96.6%
- [Ce ^{4 ·} ] in aqueous phase = 0.0052 mole / l
- [Ce ^{4 ·} ] in organic phase = 0.188 mole / l
- fraction of cerium recovered in organic phase: 94%
- partition coefficient of Ce ^{4 ·} between the 2 phases: 36
- Faradic yield: 78%.

EXAMPLE 5

In this example, the implementation of an electrolysis cell operating in monopolar mode and in discontinuous mode is described.

The installation includes only the main circuit shown in Figure 3, namely, the mixer (23), the pump (27), the electrolysis cell (1), the degasser (28) and the refrigerant (29) .

The aqueous phase consists of a cerous sulphate solution containing 0.2 mole / liter of cerium 3+ and having a sulfuric acid normality of 1 N. 3000 cm³ of said phase are introduced into the mixer (23).

The organic phase is composed of di (2-ethylhexyl) phosphoric acid in solution in kerosene at a rate of 1 mole / liter. 3000 cm³ of said phase are introduced into the mixer (23). In the mixer (23), the organic phase is emulsified in the aqueous phase by stirring at 1100 rpm. The content of the emulsion in the organic phase is 50% by volume.

The emulsion leaves the mixer (23) at (26) and then circulates at a speed of 540 liters / hour in the main circuit comprising the electrolysis cell (1).

The configuration of the cell shown more precisely in FIGS. 1 and 2 is as follows:
- base anode (4) and bae cathode (5)
- anodic stack of 2 grids (6)
- total anodic area: 0.064 m²
- total cathodic surface: 0.017 m²

Electrochemical oxidation of cerium 3+ to cerium 4+ is carried out at room temperature, by imposing a potential on the anode of 1.63 volts / ENH.

The electrolysis lasts 14 hours.

The organic phase is loaded with cerium 4+.

After separation of the aqueous and organic phases by decantation, the following results are determined:
- [Ce ^{3 ·} ] in aqueous phase = 0.0102 mole / l
- conversion rate: 97.8%
- [Ce ^{4 ·} ] in aqueous phase = 0.048 mole / l
- [Ce ^{4 ·} ] in organic phase = 0.185 mole / l
- fraction of cerium recovered in organic phase: 95.6%
- partition coefficient of Ce ^{4 ·} between the 2 phases: 39
- Faradic yield: 83.1%

Claims (26)

1. Electrolysis cell characterized in that it consists of an enclosure in which are placed face to face two base electrodes electrically insulated from each other, the base cathode consisting of a plate full of a material conductor and the base anode being a volume anode consisting of a plate full of a conductive material on which are placed one or more grids of expanded metal and that in said cell, is placed at each end thereof, of on either side of the electrodes, a plate of insulating material pierced with orifices. 2. Electrolysis cell according to claim 1 characterized in that one or more electrode modules are interposed between the two base electrodes; the electrode module (s) being made up on the one hand of a plate full of a conductive material working on a cathode face and on the other anode face and, on the other hand, of one or more grids expanded metal placed on the anode side; the electrode module (s) being inserted so that the anode side of the plate faces the base cathode and optionally faces the cathode side of another module; the electrode module (s) being electrically isolated from the base electrodes and possibly from each other. 3. Electrolysis cell according to one of claims 1 and 2 characterized in that the enclosure has an inlet and an outlet, opposite. 4. Electrolysis cell according to one of claims 1 to 3 characterized in that its ends have a flared shape. 5. Electrolysis cell according to one of claims 1 to 4 characterized in that the volume anode comprises from 1 to 5 grids. 6. Electrolysis cell according to claim 5 characterized in that the volume anode comprises a grid placed perpendicular to the flow of the fluid. 7. Electrolysis cell according to one of claims 1 to 5 characterized in that the volume anode comprises several grids arranged in a cross stack with respect to the flow of the fluid. 8. Electrolysis cell according to one of claims 2 to 7 characterized in that it comprises from 1 to 10 electrode modules. 9. Electrolysis cell according to one of claims 1 to 8, characterized in that the ratio between the anodic and cathodic surface varies between 1.0 and 10. 10. Electrolysis cell according to one of claims 1 to 9 characterized in that the electrodes in the form of a solid plate are made of graphite, titanium or titanium coated with precious metal, that the grids of expanded metal are made of titanium or made of titanium coated with a precious metal. 11. Electrolysis cell according to one of claims 1 to 10 characterized in that the electrodes are electrically insulated from each other by a spacer made of insulating material. 12. Electrolysis cell according to one of claims 1 to 11 characterized in that the plate placed on either side of the electrodes is pierced with orifices having a diameter varying between 0.5 mm and 5.0 mm . 13. Electrolysis cell according to one of claims 1 to 12 characterized in that the space defined in the upper and lower part of the cell is filled by obstacles to the circulation of the fluid. 14. Electrolysis cell according to claim 13 characterized in that said obstacles are grids or balls of insulating material. 15. Use of the electrolysis cell described in one of claims 1 to 14 to the implementation of a process coupling the electrolysis of a chemical space in the aqueous phase and the simultaneous extraction of the species produced in an extractive organic phase thereof emulsified in the aqueous phase. 16. Use of the electrolysis cell according to claim 15 in the implementation of a process coupling the electrolysis of cerium 3+ to cerium 4+ and the extraction of cerium 4+ formed in an organic phase extracting cerium 4+ emulsified in the aqueous phase leading to the production of an organic phase loaded with cerium 4+. 17. Electrolysis assembly involving the electrolysis cell described in one of claims 1 to 14, for the implementation of a method coupling an electrolysis of a chemical species in the aqueous phase and the extraction of the 'species produced in organic phase characterized by the fact that it comprises:
- a mixer in which the emulsion is formed,
- means for conveying the emulsion,
- the electrolysis cell described in one of claims 1 to 14,
- Means intended to evacuate the gas produced at the cathode. 18. An electrolysis assembly according to claim 17 characterized in that it comprises means intended to cool the emulsion which follow the means intended to evacuate the gas produced at the cathode. 19. Electrolysis assembly according to one of claims 17 and 18 characterized in that it comprises:
- means for supplying the aqueous phase
- means to feed the organic phase
- Means for withdrawing the emulsion charged in this case produced electrochemically. 20. An electrolysis assembly according to one of claims 17 to 19 characterized in that the mixer is a stirred tank. 21. An electrolysis assembly according to one of claims 17 to 20 characterized in that the means for conveying the emulsion are a centrifugal or volumetric pump. 22. Electrolysis assembly according to one of claims 17 to 21 characterized in that the means intended to evacuate the gas produced at the cathode are a flat degasser. 23. Electrolysis assembly according to one of claims 17 to 22 characterized in that the means for cooling the emulsion are constituted by a coolant with circulation of cold water. 24. An electrolysis assembly according to claim 19 characterized in that the means for supplying and withdrawing fluids are constituted by a storage tank and a metering pump for fluids. 25. An electrolysis assembly according to one of claims 17 to 24 characterized in that it comprises a main circuit for circulating the emulsion comprising a mixer (23), a pump (27), the electrolysis cell described in one of claims 1 to 14 (1), a degasser (28), an optional refrigerant (29). 26. An electrolysis assembly according to claim 25 characterized in that it further comprises, a storage tank (16) of the aqueous phase, a storage tank (17) of the organic phase, a storage tank of the emulsion (33), pumps (19), (20), (32) for conveying said fluids.

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