EP1383941A1

EP1383941A1 - Modular electrochemical cell

Info

Publication number: EP1383941A1
Application number: EP02713991A
Authority: EP
Inventors: Werner Haenni; Cédric Faure; Philippe Rychen
Original assignee: CSEMCENTRE SUISSE D'ELECTRONIQUE ET DEMICROTECHNIQUE SA; Centre Suisse dElectronique et Microtechnique SA CSEM
Current assignee: Adamant Technologies SA
Priority date: 2001-05-01
Filing date: 2002-04-22
Publication date: 2004-01-28
Also published as: US20040146779A1; US7335284B2; EP1254972A1; WO2002088430A1; JP2004525765A

Abstract

The invention concerns a modular electrochemical cell comprising: two substantially identical assemblies (10, 12) including each in a mount (14) perforated by a cylindrical housing and an opening (36) passing through it in its portion located outside said housing and capable of being connected to a fluid supply or discharge conduit, and a disc-shaped electrode (22) arranged inside each housing, the two mounts being arranged such that their respective electrodes are opposite each other; inserted between said assemblies, interposed means (38) serving, at least, to ensure the circulation and distribution of said fluid between the electrodes; and members (44) for mutually assembling together said assemblies and said interposed means. Said cell is useful for depollution of waste water by oxidising contaminants contained therein.

Description

MODULAR ELECTROCHEMICAL CELL

The present invention relates to electrochemical cells. It relates, more particularly, to a modular electrochemical cell which uses disc-shaped electrodes, advantageously made of diamond, both in monopolar mode and in bipolar mode, with electrode spacings adjustable at will and in the most diverse configurations. allowing, in particular, to work with two or three different liquid flows.

Thanks to its modularity, the cell according to the invention can thus be used, in a very simple manner, both for research and development work as in pilot or industrial installations.

This type of electrochemical cell finds a particularly interesting application in the depollution of wastewater by oxidation of the contaminants that it contains.

More specifically, the modular electrochemical cell according to the invention is characterized in that it comprises:

- two substantially identical assemblies each comprising a frame pierced with a cylindrical housing and an opening passing through it in its portion located outside said housing and which can be connected to a conduit for supplying or discharging a fluid , and a disc-shaped electrode placed inside each housing, said frames being arranged so that their respective electrodes are opposite one another,

- inserted between said assemblies, intermediate means having, at least, the function of ensuring the circulation and distribution of said fluid between the electrodes, and

- Assembly members between them of said assemblies and of said intermediate means. Preferably, the electrodes comprise a conductive substrate and a conductive layer of diamond deposited on the substrate. Furthermore, each electrode is fixed to a conductive support disc which can be connected to a power source and whose axial position inside the housing is adjustable from the outside to be flush with the external face of the electrode and the edge of the frame. In addition, the housing advantageously contains a ring surrounding the support disc and whose axial position is adjustable from the outside to compress a seal between the electrode, the housing and the disc. In a first type of configuration, the two frames each have an opening which opens inwards by a groove in an arc of a circle and are arranged so that said grooves are diametrically opposite, the opening of a frame used to supply the fluid and the opening of the other frame for its evacuation. According to an embodiment using this first configuration, said intermediate means comprise an insulating washer pierced with orifices situated opposite said grooves, each of these orifices communicating with the internal portion of the washer by a radial channel.

According to another embodiment, said intermediate means comprise: - an insulating flat spacing ring pierced with orifices situated opposite said grooves, each of these orifices communicating with the internal portion of the ring by a radial channel, and

- two insulating washers arranged on either side of the ring and each pierced with a slot in an arc of a circle situated opposite one of the grooves.

According to yet another embodiment, said intermediate means comprise:

an insulating flat ring pierced by two slots in an arc of a circle situated opposite said grooves, a disc-shaped bipolar electrode disposed inside said ring, and

- Two insulating washers arranged on either side of the ring and each pierced with orifices located opposite one of the grooves, each of these orifices communicating with the internal portion of the washer by a radial channel.

In a second type of configuration, the frames each have two openings which open inwards through two grooves in an arc of diametrically opposite circles, said frames being arranged so that their respective grooves are facing each other, the openings of each frame used respectively for the supply and evacuation of a fluid.

According to an embodiment using this second configuration, said intermediate means comprise:

a permselective conductive membrane of the ion exchange type or a porous diaphragm, and

- Two insulating washers arranged on either side of the membrane or of the diaphragm and each pierced with orifices situated opposite said grooves, each of these orifices communicating with the internal portion of the washer by a radial channel. According to another embodiment, said intermediate means comprise:

- a central hollow ring which can be connected to a supply pipe and to a fluid discharge pipe,

- two insulating washers arranged on either side of the ring,

two permselective conductive membranes of the ion exchange type or two porous diaphragms disposed respectively on the other side of the two washers, and

- Two insulating washers disposed respectively on the other side of the two membranes or diaphragms and each pierced with orifices located opposite said grooves, each of these orifices communicating with the internal portion of the washer by a radial channel. Other characteristics of the invention will emerge from the description which follows, given with reference to the appended drawing in which:

FIGS. 1 and 2 show, respectively in axial section in exploded perspective, a first embodiment of a monopolar cell,

FIG. 3 represents, in exploded perspective, a second embodiment of a monopolar cell with a large inter-electrode space,

FIG. 4 represents, in exploded perspective, a third embodiment of a bipolar cell,

FIG. 5 represents, in exploded perspective, a fourth embodiment of a membrane cell, and

- Figure 6 shows, in exploded perspective, a fifth embodiment of a cell with two membranes. It will be noted that, in the present description, the elements common to the various embodiments of the invention are designated by the same reference numbers.

In Figures 1 and 2, there are shown in 10 and 12 two identical sets. Each is based on a frame 14, made of polypropylene, which has the shape of a disc having two truncated portions 16 diametrically opposite to form two flat faces serving as a stable base for the device.

The cage 14 is pierced with a central cylindrical housing inside which takes place a movable ring with L-shaped section 18, of aluminum or plastic, receiving, also in a mobile manner, a disc 20, of copper or nickel.

The outer face of the disc 20 receives, by tin welding or by bonding by means of a silver-based paste, an electrode 22 formed of a substrate which can be, for example, made of silicon, of carbide of silicon, titanium or zirconium, coated on its external face with a layer of doped diamond to be electrically conductive. This electrode can advantageously be produced according to the technique described in the document FR 99 02483.

The inner face of the disc 20 is fixed to the end of a central screw 24 passing through a tapped hole formed in the bottom of the cage 14 and the other end of which receives a locking nut 26.

The bottom of the cage 14 is pierced with six tapped holes, regularly distributed around its periphery, receiving a screw 28 actuable from the outside to act on the ring 18 by means of a coil spring 30.

Note that the edge of the ring 18 facing the electrode 22 has a bevelled face on the outside, which acts on an O-ring 32 trapped between the electrode, the housing wall and the disc.

Finally, the cage 14 is pierced on its edge, outside the perimeter occupied by the electrode, of a tapped hole into which a nozzle 34 is screwed intended for the connection of a pipe not shown. This nozzle opens, inside, in a groove 36 having the shape of an arc of a circle of approximately 90 °, of the same axis as the assembly. The figures show, in reality, two diametrically opposite grooves 36 because, in a configuration described below, the cell according to the invention needs them.

The cell also comprises, between the two assemblies 10 and 12, a supply washer 38 which is made of an elastomer as, for example, one of the products sold under the designations of Viton and EPDM. This washer has an external contour corresponding to that of the cages 14 and a circular internal contour of the same diameter as that of the electrodes 22.

The washer 38 is pierced with circular orifices 40 of diameter corresponding to the thickness of the groove 36 and forming a belt of the same radius as it. The orifices 40 are thus located opposite the groove 36. Each of these orifices communicates with the internal portion of the washer 38 by a radial channel 42.

The figures show that the orifices 40 cover the entire periphery of the washer 38, although only those which are located facing the groove 36. This arrangement, however, has the advantage of making the washer perfectly homogeneous. Of course, one could be satisfied with a series of orifices 40 only opposite the groove.

The two assemblies 10 and 12, with the washer 38 inserted between them and the end pieces 34 arranged in a diametrically opposite manner, are assembled by means of six bolts and nuts distributed at the periphery of the cell. In order not to clutter the drawing, only FIG. 2 shows the heads 44 of these bolts and the holes 46 made in the cages 14 and the washer 38 to allow their passage. Before assembling the cell which has just been described, it is necessary, for each of the assemblies 10 and 12, to be flush with the external face of the electrode 22 and the internal face of the cage 14. This is done by acting on the screw 24 then, once the outcrop has been made, blocking it by means of the nut 26. When the assembly has been carried out, using the six bolt-nuts, the six screws 28 are used, with using the springs 30, compress the seal 32 against the electrode 22.

In operation, the screws 24 are respectively connected to the terminals of an appropriate power source, while liquid supply and evacuation pipes are respectively connected to the end pieces 34. The liquid introduced into the cell by the one of the tips is, typically, polluted wastewater. The electrolysis process carried out in the cell will allow purified water to appear on the other end accompanied by gas resulting from the reaction.

Thanks to the structure of the cell, the liquid introduced under pressure, for example at the bottom of the left-hand assembly 10, opens into the lower groove 36 then into the orifices 40 of the washer 38 which are located opposite it, before being injected into the space separating the two electrodes 22 through the radial channels 42 associated with the orifices 40. The liquid is subjected, in this space, to the electrolysis process and is then introduced, at the top of the assembly on the right 12, in the upper groove 36 through the channels 42 and corresponding orifices 40 before being evacuated to the outside.

To fix the ideas, and purely for information, the electrodes 22 have a diameter of the order of 10 cm and a thickness of between 0.5 and 3 mm, while disc 20 has a thickness of 10 to 12 mm. The thickness of the washer 38 is also between 0.5 and 3 mm.

The cell which has just been described is suitable for fluids with relatively low conductivity. When working with high conductivity electrolytes, typically greater than 3 - 5 mS / cm, it is necessary to increase the space between the two electrodes. In this case, which constitutes the second embodiment of the cell according to the invention, the supply washer 38 is replaced, as shown in FIG. 3, by a spacer ring 48, made of polypropylene, and by two identical washers 50, arranged on either side of the ring 48, and produced, like the washer 38, in an elastomer. These three components have the same external and internal contours as the washer 38.

The spacer ring 48, the thickness of which can be up to 10 mm, has the same series of circular orifices 40 and the same radial channels 42 as the washer 38. The washers 50 only have, in addition to the holes 46 for the passage of the bolts, two slots 52 (of which only one is useful) of the same shape as the slots 36 and positioned so as to come to their gaze during assembly of the cell.

It can thus be seen that, in this embodiment, the distribution of the liquid in the space between the electrodes and then its collection are ensured by the central ring 48, the two washers 50 only serving to allow the transport of the liquid between the cages 14 and the ring 48.

The cell described above can also take a bipolar structure.

In this case, which constitutes the third embodiment of the invention, the supply washer 38 of the first embodiment is replaced, as shown in Figure 4, by a ring 54 of polypropylene, and by two identical washers 56, arranged on either side of the ring 54, and made of an elastomer. These three components have the same external and internal contours as the washer 38. The interior of the ring receives an electrode 58, of the same thickness and of the same diameter as the electrodes 22. It is formed of a conductive substrate coated on its two sides of a layer of diamond doped to be made electrically conductive. The electrode 58, as well as the two electrodes 22, can advantageously be produced according to the teaching of document EP 810147.9.

The ring 54 comprises, in addition to the holes for the passage of the bolts, two diametrically opposite slots 60, of the same shape as the grooves 36 and positioned so as to come to their gaze during assembly of the cell. The two washers 56 are identical to the washer 38. In this embodiment, they are the ones that distribute and collect the liquid.

Of course, the bipolar cell of FIG. 4 can comprise several intermediate electrodes 58 associated with a ring 54, in order to ensure, as for the cell of FIG. 3, a larger interelectrode space. In this case, additional washers 56 are inserted between the different rings 54.

According to a fourth embodiment of the invention, represented in FIG. 5, the assemblies 10 and 12 of FIG. 1 are replaced by assemblies 62 and 64 which are distinguished only by the fact that they comprise two end pieces 34 and necessarily two circular grooves 36, diametrically opposite, the liquid to be treated then being supplied by one of the end pieces and emerging through the other. This cell works with two electrolytes which do not mix and form respectively, according to a known process, an anolyte flow and a catholyte flow. In this case, the supply washer 38 of FIG. 1 is replaced by a stack, the central element of which is a membrane 66 made of an electrically conductive material and selectively permeable to certain ions, such as an ion exchange membrane. in Nafion. Alternatively, the membrane 66 may be replaced by a porous diaphragm. On either side of this element, there are, arranged symmetrically, two washers 68 made of elastomer, then two rings 70 made of polypropylene and, finally, two new washers 72 made of fluorinated elastomer. All these components have the same external contour as the washer 38 and have the six holes 46 for the passage of the assembly bolts. The washers 68 and 72 and the ring 70 also have the same circular interior contour as the washer 38.

The washers 68 have no other particular opening. The rings 70 are identical to the spacer ring 48 in FIG. 3, while the washers 72 have the same slots 60 as the ring 54 in FIG. 4. It will be noted that, in the embodiment of FIG. 5, the rings 70 serve only to increase the space between the electrodes, as is the case with the ring 48 in FIG. 3. When this cell has to work with liquids with low conductivity, it is therefore possible to eliminate the rings 70 thus as the washers 68 and 72 and replace them with the washers 38 in FIG. 1. Finally, FIG. 6 represents a fifth embodiment of the cell according to the invention. In this case, the supply washer 38 of FIG. 1 is replaced by a stack of elements having the same external contour as the washer 38 and having the six holes 46 for the passage of the assembly bolts. The central element is a hollow ring 74, made of polypropylene, provided with two diametrically opposite ends 76, intended to be connected respectively to a supply pipe and to a liquid discharge pipe.

The cell of FIG. 6 can work, according to a known process, with three separate flows, namely a flow of anolyte and a flow of catholyte, circulating respectively in the assemblies 62 and 64, and a flow of liquid to be treated circulating through the ring 74.

On either side of this ring, there are, arranged symmetrically, two washers 78 identical to the washers 68 of FIG. 5, then two membranes 80 identical to the membrane 66 of the same figure. The membranes 80 can also be replaced by porous diaphragms. The stacking continues, as in the cell of FIG. 5, by two washers 68, two rings 70 and two washers 72.

When this cell has to work with liquids with low conductivity, it is therefore possible, as for the cell in FIG. 5, to remove the rings 70 as well as the washers 68 and 72, and replace them with the washers 38 in FIG. 1.

In all the embodiments which have just been described, it may be advantageous to lengthen the path of the fluids between the electrodes, which improves the efficiency of the electrochemical processes. To obtain this effect, various elements of the cell, such as, for example, the washer 38 in FIG. 1, can be provided in their center with a grid 82 serving as a promoter of turbulence and a spacer between electrodes. This grid is advantageously made of an insulating and chemically stable material, such as polypropylene or polyethylene.

Thus, an electrochemical cell is proposed whose modular structure, linked to the use of interchangeable elements, allows it a wide variety of configurations meeting the various needs of users.

Claims

1. Modular electrochemical cell, characterized in that it comprises:

- two substantially identical assemblies (10, 12, 62, 64) each comprising a frame (14) pierced with a cylindrical housing and an opening passing through it in its portion located outside of said housing and which can be connected to a conduit for supplying or discharging a fluid, and a disc-shaped electrode (22) disposed inside each housing, the two frames being arranged so that their respective electrodes face the one of the other,

- Assembly members between them of said assemblies and of said intermediate means.

2. Cell according to claim 1, characterized in that said electrodes (22) comprise a conductive substrate and a conductive layer of diamond deposited on said substrate.

3. Cell according to claim 1, characterized in that each electrode (22) is fixed on a conductive support disc (20) which can be connected to a power source and whose axial position inside said housing is adjustable from the outside to be flush with the outside face of the electrode and the edge of the frame.

4. Cell according to claim 3, characterized in that said housing contains a ring (18) surrounding the support disc (20) and whose axial position is adjustable from the outside to compress a seal (32) between the electrode, the housing and the disc.

5. Cell according to claim 1, characterized in that the frames (14) each have an opening which opens inwardly by an arcuate groove (36) and are arranged so that said grooves are find diametrically opposite, the opening of a frame serving to bring the fluid and the opening of the other to its evacuation.

6. Cell according to claim 5, characterized in that said intermediate means comprise an insulating washer (38) pierced with orifices (40) located opposite said grooves, each of these orifices communicating with the internal portion of the washer by a channel radial (42).

7. Cell according to claim 5, characterized in that said intermediate means comprise:

an insulating flat spacing ring (48) pierced with orifices (40) situated opposite said grooves, each of these orifices communicating with the internal portion of the ring by a radial channel (42), and

- Two insulating washers (50) arranged on either side of the ring and each pierced with a slot in an arc (52) situated opposite one of the grooves.

8. Cell according to claim 5, characterized in that said intermediate means comprise:

- a flat insulating ring (54) pierced by two slots in an arc (60) situated opposite said grooves,

- a bipolar disc-shaped electrode (58) disposed inside said ring, and

- two insulating washers (56) arranged on either side of the ring and each pierced with orifices (40) located opposite one of the grooves, each of these orifices communicating with the internal portion of the washer by a radial channel (42).

9. Cell according to claim 1, characterized in that the frames (14) each have two openings which open inwardly through two diametrically opposite arc-shaped grooves (36), said frames being arranged so that that their respective grooves are facing each other, the openings of each frame serving respectively for the supply and evacuation of a fluid.

10. Cell according to claim 9, characterized in that said intermediate means comprise:

- a selectively permeable conductive membrane (66) or a porous diaphragm, and - two insulating washers (38) arranged on either side of the membrane or diaphragm and each pierced with orifices (40) located opposite said grooves, each of these orifices communicating with the internal portion of the washer by a radial channel (42).

11. Cell according to claim 9, characterized in that said intermediate means comprise:

- a central hollow ring (76) which can be connected to a supply pipe and to a fluid discharge pipe,

- two insulating washers (78) arranged on either side of the ring,

two conductive membranes which are selectively permeable (80) or two porous diaphragms disposed respectively on the other side of these two washers, and

- two insulating washers (38) respectively disposed on the other side of the two membranes or diaphragms and each pierced with orifices (40) located opposite said grooves, each of these orifices communicating with the internal portion of the washer by a radial channel (42).