WO2012010761A1

WO2012010761A1 - Chevrel phase wall for the selective electrolytic transfer of cations through the wall, and associated manufacturing method and transfer method

Info

Publication number: WO2012010761A1
Application number: PCT/FR2011/051403
Authority: WO
Inventors: Sakina Seghir; Jean-Marie Lecuire; Sébastien DILIBERTO; Valérie BOUQUET; Maryline Guilloux-Viry; Michel Potel; Clotilde Boulanger
Original assignee: Université Paul Verlaine Metz; Centre National De La Recherche Scientifique (Cnrs); Université De Rennes 1
Priority date: 2010-07-23
Filing date: 2011-06-20
Publication date: 2012-01-26
Also published as: FR2963027B1; FR2963027A1

Abstract

The invention relates to an electrolyte separation wall, comprising an active layer (22) made of a sulfide Chevrel phase material (Mo_nS_n+2 or M_xMo_nS_n+2) for the selective transfer of cations through the wall, and a porous substrate (21) made of a porous material and serving as a carrier for the active layer (22). A process for selectively transferring cations uses such a transfer wall (2). According to a method for manufacturing such a transfer wall (2), the surface of a tablet of porous material is coated with a solution of polymer precursors containing molybdenum, and the solution is sulfided and reduced by heat.

Description

Cheyrel phase wall for the selective electrolytic transfer of cations through the wall, manufacturing process and transfer process.

FIELD OF THE INVENTION

The present invention relates to a Chevrel phase wall for the selective transfer of cations through the wall by an electrolytic process, a method of manufacturing said wall and a method of selectively transferring cations through said wall. The invention further relates to an electrolytic type process for transporting cations, through a suitable wall, from a first electrolyte solution containing one or more classes of ions of the same charge or charge, to a second electrolytic solution.

PRIOR ART

A process of this type is already known using, as separation wall, a wall formed of molybdenum cluster chalcogenides, in particular the ΜθβΧβ phases known as Chevrel phases, described in international patent application WO 2009/007598. This process has also been the subject of the following publications:

Electrochemical reactions of reversible intercalation in Chevrel compounds for cationic transfer - Principle and application on Co ²⁺ ion; S. Seghir, C. Boulanger, S. Diliberto, JM Lecuire, M. Potel, 0. Merdrignac-Conanec; in Electrochemis try Communications, 10, 2008, 1505-1508.

Selective transfer of cations between two electrolytes using the intercalation properties of Chevrel phases; S. Seghir, C. Boulanger, S. Diliberto, M. Potel, JM. Cook it ; in Electrochimica Acta, 55, 2010, 1097-1106. These documents explain that cations can be transported through the wall of material of formula Mo ₅ X _s (with X = S, Se, Te) called Phases de Chevrel where reversible redox systems of the type occur:

Mo ₆ Xg + xM ^{n +} + xn e ^" M _x Mo ₆ X ₈

These systems are diversified by the nature of the cation M ^{n +} , chalcogen X and stoichiometry x ternary.

In an experimental setup implementing the selective transfer method, the transfer wall is placed between two compartments respectively comprising a platinum-plated electrode that operates in anode and a stainless steel electrode that operates as a cathode. The first compartment contains a first electrolyte which contains different cations of an effluent to be treated. The second compartment contains a second electrolyte for receiving the transferred cations.

A continuous electric current is established between the anode and the cathode. In the overall electrochemical operation of all the two compartments, intercalation of the cation occurs at the interface M _x Mo ₆ Ss / first electrolyte (effluent to be treated, mixture of cations M ^{n +} , M ' ^{n +} , M' ^{, n +} for example), according to:

Mo ₆ X ₈ + xM ^{n +} + xn e- => M _x Mo ₆ X ₈

The deintercalation of this same cation M ^{n +} at the interface M _x o ₆ S ₈ / second electrolyte (recovery solution of M ^{n +} for example) is carried out reciprocally according to

M _x Mo ₆ X ₈ = Mo ₆ X ₈ + x ⁿ e ^" + xM ^{n +}

The mobility of the metal cation in the Chevrel phase thus makes it possible to transfer the desolvated M ^{n +} cation from one medium to another without transferring any other chemical species from one or the other of the compartments. A transfer wall in pellet form is obtained by hot sintering a mixture of powder composition adapted to the stoichiometry of the desired material. This produces discs of active material with a thickness of 2 to 5 millimeters.

The tests with walls composed of selenated and sulphurized phases have shown that in particular the cations of the following metals can be transferred from one electrolyte to another: iron, manganese, cobalt, nickel chromium, copper, zinc, cadmium. The limits of current densities obtained are between 10 and 20 A / m ² , with faradic yields greater than 90%, or even greater than 98%, and with very good selectivity.

The tests also showed that the transfer rate had a limit, but that it was possible to push back this limit by decreasing the thickness of the wall, which allows higher current densities. However, the necessary mechanical strength of the wall limits the decrease in its thickness.

OBJECTIVES OF THE INVENTION

The object of the invention is therefore to provide a Chevrel phase selective transfer wall enabling a good transfer speed.

STATEMENT OF THE INVENTION

With these objectives in view, the subject of the invention is an electrolyte separation wall comprising an active layer made of sulphurous Chevrel phase material for the selective transfer of cations through the wall, characterized in that it comprises a support porous material made of a porous material serving as a support for the active layer.

The inventors have succeeded in producing a wall with a porous support which provides the mechanical strength and an active layer whose thickness can be very small. They found that the porous support was not obstacle to the electrochemical reactions that occur at the level of the active layer. By reducing the thickness of the active layer, the transfer speed reached is much greater than the speed limit according to the prior art, which is one of the objectives of the invention.

The porous material is chosen for example from mullite, silica, fiberglass, quartz or a ceramic. These materials have the necessary qualities to fulfill the role of the wall, namely the mechanical strength, the resistance to the products contained in the electrolytes and the porosity. They also resist the temperature necessary for the synthesis of the active layer.

The porosity of the porous material is, for example, between 0.4 and 0.6. This value expresses the material ratio in relation to the volume occupied. It constitutes a good compromise between the volume of the electrolyte present in the porous support and the mechanical strength of said support.

According to a method of manufacturing the transfer wall, a solution of polymeric precursors containing molybdenum and another metal in the form of cations is prepared, the solution is spread on the porous support and a sulphurization and a hot reduction of the solution. The polymer precursor solution makes it possible to form a support for molybdenum and the metal cation. Because of its consistency, the polymer precursor solution is distributed regularly and in a controlled manner, which makes it possible to control the cationic composition, and consequently the final composition of Μ _χ Μθ6 8 8, and the quantity of the final active layer. Sulfurization followed by a hot reduction of the precursor layer deposited, which provides sulfur in a controlled manner and form the Chevrel phase.

The other metal M of the phase M _x Mo6S ₈ is for example selected from copper, nickel, cobalt or zinc. Any metal leading to a ternary Chevrel phase may be suitable, particularly if the cation has an ionic radius less than 0.1 nm.

In particular, the sulfurization step is preceded by a step of calcining the organic compounds. The organic compounds that form the polymer precursors are no longer necessary for the future, and they can be eliminated. Calcination does this by leaving the molybdenum and the metal in place.

For example, the sulphurization step is carried out under a stream of a mixture of hydrogen (H ₂ ) and hydrogen sulphide (H ₂ S). It is found that the sulfur combines with the molybdenum and the metal to form a mixture of compounds of formula M0S ₂ , CU ₂ S and optionally M _x MoS ₂ .

In a complementary manner, the sulphurization step is followed by a reduction step under hydrogen flow (H ₂ ). At the end of this step, a compound of formula M _x Mo ₆ S ₈ is formed.

By way of example, the solution comprises a soluble salt of molybdenum hexavalent, which leads to an oxide by thermal degradation, such as tetrahydrated ammonium heptamolybdate (NH ₄ ) ₆ o ₇ 0 ₂₄ , 4H ₂ 0 for bring molybdenum, and a soluble salt of the other metal such as nitrate or acetate. This latter soluble salt is, for example, copper nitrate hydrate (Cu (NO ₃ ) ₂ , 2.5H ₂ O) to provide copper.

In a final step, the electrochemical or chemical deintercalation of the other metal M is carried out. Depending on the cation that it is desired to transfer, the presence of the other metal M is undesirable. It can then be easily removed in this step. The active wall is then composed of MoeSs. The chemical deintercalation is carried out for example by an attack with hydrochloric acid.

The solution is distributed for example by centrifugation. The support is rotated about an axis perpendicular to one of its surfaces and the solution is deposited on said surface at the center of rotation. It is distributed evenly over the entire surface.

In particular, the viscosity of the solution is between 20 and 60 cP. By adjusting the viscosity, it is possible to control the thickness of the film formed by the solution deposited on the porous support.

The subject of the invention is also a process for the selective extraction of cations by electrochemical transfer, characterized in that a transfer wall as described above is used as the electrolyte separation wall, and cation transfer is ensured through said electrolyte transfer wall. transfer wall by generating a potential difference between firstly the first electrolyte, and secondly the second electrolyte or said transfer wall, so as to cause intercalation of the cations in the transfer wall on the side of the first electrolyte , diffusion of the cations in it, and their deintercalation in the second electrolyte.

According to other characteristics:

at least one of the electrolytes is non-aqueous. The electrolytes may be different between the compartments, in particular by differentiation of the nature of the base salts, by the level of acidity, by the presence of complexing agents, by the nature of the solvents, in particular organic or inorganic non-aqueous solvents such as for example DMSO, DMF, ionic liquids, solid electrolytes, etc.

the transfer wall is electrically connected to a device for measuring the potential between said wall and reference electrodes located respectively in each electrolyte and the potential applied between said electrolytes is adjusted accordingly. the potential difference is generated between the first electrolyte and the transfer wall, and the deintercalation of the cations on the side of the second electrolyte is a chemical deintercalation by a chemical oxidant in the second electrolyte.

a succession of transfers of cations is ensured through transfer walls arranged successively between end electrolytes, and with one or more electrolytes intermediate between the different transfer walls.

the transferred metal is electrodeposited on a cathode.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and other features and advantages will appear on reading the description which follows, the description referring to the appended drawings among which:

Figure 1 is a sectional view of a transfer wall according to the invention;

FIG. 2 is an X-ray diffraction analysis graph of the porous material for the manufacture of a wall according to FIG. 1;

Figures 3 and 4 are schematic views of a test fixture for checking the porosity or tightness of the wall of Figure 1;

Figure 5 is a block diagram of the device for implementing the selective transfer method; Figure 6 illustrates an arrangement using a plurality of compartments and serial transfer walls.

DETAILED DESCRIPTION

A transfer wall in the form of a tablet 2 according to the invention is formed of a porous support 21 on which a thin active layer 22 is deposited. The manufacture of sealed pellets is carried out in a first phase of manufacture of the porous support 21, and a second phase of application of the active layer 22 on the support 21.

Elaboration of the porous support

The porous support 21 may be commercially available in mullite, quartz or ceramic. By way of example, an embodiment is detailed below, which is derived from the protocol given by the article by Garcia-Gabaldon et al. on the production of ceramic membranes based on kaolin and alumina developing a modular porosity for their application as separation membrane in electrochemistry: Effect of porosity on the effective electrical conductivity of different ceramic membranes used as separators in electrochemical reactors, Journal of Membranes Sciences 280 (2006) 536-544.

The protocol is as follows: initially a mixture provided for 5 g of material consists of: - 2.52 g of Kaolin (hydrated aluminum silicate Al ₂ Si ₂ O ₅ (OH) ₄ ,

3.80 g Alumina A1 ₂ 0 ₃

1 g of commercial potato starch.

The mixture of the powders is homogenized in a porcelain mortar and then wetted with a minimum volume of acetone to avoid the formation of aggregates. This mixture is dried in the open air for 14 hours. The powder obtained is then regrinded manually with the mortar for 10 minutes and then by fraction of about 1 g, it is shaped into a pellet by pressing into a matrix of 25 mm diameter at a pressure of 2 tons for 5 min. The compacted pellets form a disc 1 mm thick. The samples are subjected to two successive heat treatments.

A first heating at 300 ° C allows the oxidation to the air of potato starch. This organic binder is removed in 1 hour and thus creates porosity. An additional treatment at 1100 ° C for 8 to 24 hours ensures satisfactory mechanical strength. After this heat treatment, discs 24 mm in diameter and 1 mm in thickness are obtained. The surface is 4.5 cm ² .

X-ray diffraction analysis was performed on the porous pellet (Figure 2). The recorded spectrum shows the absence of impurities as well as the formation of an alumina phase and a mullite phase.

The evaluation of the porosity of the pellet was tested using pH paper and nitric acid HNO3 in the following manner represented in the diagram of FIG. 3: the turning of the pH paper made it possible to confirm a good porosity of the pellet. The porosity controls give average values of 0.553 by volume for initial contents of 10% of starch and 0.501 for contents of 5%.

The second phase of the manufacture of the pellet consists of coating this porous support with an active layer according to the method which is described below. Elaboration of the active layer

A deposition solution is prepared by a polymer precursor method, based on the Pechini process. Hydrated copper nitrate and tetrahydrated ammonium heptamolybdate are mixed with monohydrated citric acid in an aqueous medium, and the mixture is stirred at a temperature between 80 and 90 ° C. Ethylene glycol is then added. The viscosity of the solution is adjusted between 20 and 60 cP, either by heating to increase it or by adding distilled water to reduce it. This solution is then spread on a flat disk-shaped surface of the porous support 21. For this, the porous support 21 is placed in rotation around the axis of the disk, and the necessary quantity of the solution is deposited in the center of the disk. using a micropipette. The rotation speed is 1000 rpm for a few seconds, then 4000 to 5000 rpm for 10 to 20 seconds to homogenize the distribution of the solution on the disc.

The wall is placed in an oven and undergoes:

a calcination step at a temperature between 400 and 450 ° C to remove organic compounds;

a sulphurization step with a mixture of hydrogen and hydrogen sulphide at a temperature of between 500 and 650 ° C; and

a reduction step with hydrogen at a temperature of between 500 and 650 ° C.

An active layer 22 of Chevrel phase Cu _x Mo ₆ S ₈ is thus synthesized. The variation of the viscosity makes it possible to vary the thickness of the active layer thus produced. The thickness obtained is typically between a few microns and 25 microns.

A sealed edge is then placed at the periphery of the wall and the tightness of the active layer 22 is checked with the assembly of FIG. 4: the pH paper does not turn, which means that the active layer 22 is sealed.

For the final synthesis of the binary phase MO _Ô SS, a chemical deintercalation of the copper is carried out electrochemically or chemically after the completion of the coating.

Selective transfer process

The diagram of FIG. 5 shows a device for implementing a selective transfer method using transfer walls according to the invention. The device comprises a tank 1 having two compartments 11 and 12, adapted to receive an electrolyte and separated by a partition wall 13 in which is placed a transfer wall 2 consisting of a disc-shaped pellet 2, mounted in the partition 13 tightly.

The device also comprises an anode A1 placed in the first compartment 11 and a cathode C2 placed in the second compartment 12. A potential difference ΔΕ can be applied between the anode A1 and the cathode C2 by means known per se, in order to impose and control a current i between electrolytes E1 and E2.

The active layer 22 is placed on the side of the first compartment 11, even if the system also functions when it is on the side of the second compartment 12. A spring loaded contact system 44 provides an electrical connection with the contour of the covered chip 2 graphite lacquer, and makes it possible to connect it to a control apparatus, adapted in particular for measuring the interface potential Eil, Ei2 of the wafer with respect to reference electrodes 33, 34 respectively arranged in each compartment 11, 12 of the tank 1, as illustrated in FIG.

The implementation of the device is typically carried out as follows:

The compartments 11 and 12 are filled with the desired electrolyte, for example, and in no way limiting, 100 ml Na ₂ S0 ₄ 0 5 M + M ₍ i) SO ₄ as the first electrolyte E1 in the first compartment 11, and 100 ml Na ₂ SO ₄ 0.5 M as the second electrolyte E 2 in the second compartment 12, with M _(i) being one or more metal cations which it is desired to separate. The anode A1 is placed in the first compartment 11 and the cathode C2 in the second compartment 12, and the contact 44 of the pellet with potentiometric control means, connected to the reference electrodes 33, 34 immersed in electrolytes E1 and E2. It is thus possible to control the interface potentials and to adjust accordingly the global potential ΔΕ applied between the anode A1 and the cathode C2, so as to obtain a current density relative to the operational surface of the transfer wall 2, or of the set of transfer walls arranged in parallel, for example between 2 and 200 A / m ² .

An overall intensiostatic regime is established between the anode A1 and the cathode C2. In the overall electrochemical operation of all two compartments, the electrolyte E1 being an original solution to be treated comprising a mixture of the cations of different metals and identical or different charges, M ^{n +} , M ' ^{n +} , M' ^{, n '+} for example, and the electrolyte E2 being a recovery solution of the metal M, it occurs:

the intercalation of the cation M ^{n +} at the interface of the active layer 22 with the electrolyte El, according to:

Mo ₆ S ₈ + x M ^{n +} + x ⁿ e ^" => M _x Mo ₆ S ₈

the deintercalation of this same cation at the interface of the active layer 22 with the electrolyte E2 (recovery solution of M ^{n +} for example), which is carried out reciprocally according to

M _x Mo ₆ S ₈ => Mo ₆ S ₈ + x ⁿ e ^" + x M ^{n +}

The mobility of the metal cation in the Chevrel phase thus makes it possible to transfer the desolvated M ^{n +} cation from one medium to another without transferring any other chemical species from one or the other of the compartments.

It will also generally be noted that the electrolytes placed in the two compartments 11, 12 comprising the anode A1 and the cathode C2 may be different, in particular by the nature of the base salts, by the level of acidity, by the presence of complexing, by the nature of the solvents, in particular organic or inorganic non-aqueous solvents (DMSO, DMF, ionic liquids, solid electrolytes, etc.). It is thus possible, for example, to carry out ionic transfer of a sulphate medium to a chloride medium without diffusion of said medium.

In the variant of Figure 6, the vessel has three compartments. The two end compartments 11 ', 12' are equivalent to the compartments 11 and 12 of the example shown in FIG. 1. An additional compartment 15 containing an electrolyte E3 is situated between the two compartments 11 'and 12' and separated therefrom. by partition walls 13 ', 13 "each having one or two transfer walls 2', 2" according to the invention. These transfer walls 2 ', 2 "may be of the same type, simply to increase the selectivity of the transfer from the compartment 11' to the compartment 12 ', They can be managed differently by a specific control of the potentials applied between the various compartments by For example, two types of cations can be transferred from compartment 11 'to compartment 15, and only one from compartment 15 to compartment 12'.

In the case of the variant of FIG. 6, the intermediate electrolyte (s) E3 may also be identical or different from one or both electrolytes E1 or E2.

Example 1

A porous pellet 21 coated with an active layer 22 based on sulphurous Chevrel phase is used as transfer wall 2, as described above, in an arrangement according to FIG. 5. The transfer of cations between the first compartment 11 containing the first electrolyte El (cation solution T 0.1 M in medium Na ₂ S0 ₄ 0, 1 M, H ₂ S0 ₄ 0, 1 M) and the second compartment 12 containing the second electrolyte E2 recovery at 0.1 M Na ₂ S0 ₄ , and 0 , 1 M H ₂ S0 ₄ was studied for the wall made as previously described based on Mo ₆ S ₈ , and at different current densities. The study focused on verifying for various cations M ^{n +} the faradic yields of transfers, determining the boundary conditions and evaluating the transfer rate limit. The transfer process is based on preconditioning with an amount of intercalated cation estimated from the mass Mo6S ₈ deposited for a stoichiometry of M _{y /} 2Mo ₆ S ₈ . Table 1 shows the results obtained at a current density of 90 A / m ^2.

Table 1.

Faradic yields are found to be interesting by being greater than 94% and a transfer rate very much higher than the speed limit of the prior art, which was of the order of 0.29 mol / h / m ² .

selectivity

In the selective cation transfer process, the first electrolyte E1 contains a mixture of cations of which only one type is transferred through the wall. The selectivity results from the fact that during the electrolysis operation, the voltage applied between the two faces of the active layer 22 allows the intercalation and the deintercalation of only one type of cation. To transfer the other cations, it would be necessary to apply a higher potential, which is not the purpose of the process. The type of cation that is transferred has a minimum intercalation potential and a maximum deintercalation potential that is expressed relative to the reference potential given by a saturated calomel electrode (SCE).

Transfer experiments were performed for synthetic mixtures of cations such as Cd / Zn and Co / Ni, made from mixtures of two equimolar cations (0.1 M). The selectivity of the transfer is expressed by a transfer selectivity rate of the cation M ^{n +} represented by the ratio M _t ^{n +} / Σ Mj _. ^{n +} of the quantity of cations transferred M _t ^{n +} to the sum of the cations transferred in compartment 2, for example Co _t / (Cot + Nit) for the mixture Co ²⁺ + Ni ²⁺ .

This ratio is therefore even closer to 100% that the selectivity is large and takes a value of 50% if no selectivity develops.

Table 2 summarizes the selectivity levels obtained for the different mixtures. The values indicated correspond to the average of the selectivity levels obtained every hour during the electrolysis of 1 to 7 hours.

Table 2.

It is found that despite the small thickness of the active layer 22, the selectivity is not affected. On the other hand, the transfer rate is greatly improved, from 0.29 to 1.7 mol / h / m ² approximately.

Claims

An electrolyte separation wall having an active layer (22) of sulfurous Chevrel phase material (Mo _n S _{n + 2} or M _x Mo _n S _{n + 2} ) for the selective transfer of cations through the wall, characterized in that it comprises a porous support (21) made of a porous material serving as a support for the active layer (22).

2. Wall according to claim 1, wherein the porous material (21) is selected from mullite, silica, fiberglass, quartz or a ceramic.

3. Wall according to claim 1, wherein the porosity of the porous material (21) is between 0.4 and 0.6.

4. A method of manufacturing a wall according to one of claims 1 to 3, wherein a solution is prepared of polymeric precursors containing molybdenum and another metal in the form of cations, the solution is extended on the porous support (21). ) and the solution is sulphurized and heat reduced to form an active layer (22) on the porous support (21).

5. The method of claim 4, wherein the sulfurization step is preceded by a step of calcining the organic compounds.

6. Process according to claim 4, wherein the sulphurization step is carried out under a stream of a mixture of hydrogen (H ₂ ) and hydrogen sulphide (H ₂ S).

7. The method of claim 4, wherein the sulfurization step is followed by a reduction step under hydrogen flow (H ₂ ).

The process according to claim 4, wherein the solution comprises molybdenum in the form of a soluble hexavalent molybdenum salt such as tetrahydrated ammonium heptamolybdate (NH ₄ ) 6MO ₇ O ₂ , 4H ₂ O.

9. The method of claim 4, wherein the other metal is selected from copper, nickel, cobalt or zinc.

The method of claim 9, wherein the solution comprises the other metal in the form of a soluble salt such as nitrate or acetate.

11. The method of claim 10, wherein one carries out the electrochemical or chemical deintercalation of the other metal in the last step.

12. The method of claim 4, wherein the solution is distributed for example by centrifugation.

13. The method of claim 4, wherein the viscosity of the solution is between 20 and 60 cP.

14. A process for the selective extraction of cations by electrochemical transfer, characterized in that a transfer wall (2) according to one of claims 1 to 3 is used as the electrolyte separation wall, and the transfer is ensured. cations through said transfer wall (2) by generating a potential difference (ΔΕ) between first electrolyte (El) and second electrolyte (E2) or transfer wall (2). ), so as to cause intercalation of the cations in the transfer wall (2) on the side of the first electrolyte, diffusion of the cations therein, and their deintercalation in the second electrolyte (E2).

15. The method of claim 14, wherein at least one of the electrolytes (E1, E2) is non-aqueous.

16. The method of claim 14, wherein the transfer wall (2) is electrically connected to a device for measuring the potential between said wall and reference electrodes (33, 34) located respectively in each electrolyte (E1, E2). ) and the potential applied between said electrolytes (E1, E2) is adjusted accordingly.

17. The method of claim 14, wherein the potential difference (ΔΕ) is generated between the first electrolyte (El) and the transfer wall (2), and the deintercalation of the cations on the side of the second electrolyte (E2) is a chemical deintercalation by a chemical oxidant in the second electrolyte.

18. The method of claim 14, wherein the transferred metal is electrodeposited on a cathode.