Abstract:
A modular electrochemical cell having two interchangeable assemblies each with a support structure defining a cylindrical recess and having a fitting for connecting a pipe to the assembly. A disc-shaped electrode is arranged inside each recess and the assemblies are arranged relative to each other so that their respective electrodes face each other. A modular insert is inserted between the assemblies to define an open space between the electrodes and to distribute fluid to a plurality of openings spaced from each other along an edge of this open space. Securing members secure together the two assemblies and the modular insert, and passages in the support structures convey fluid between the fittings and the modular insert.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     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 and in bipolar mode, with electrode separations which can be adjusted at will and in the most diverse configurations making it possible, in particular, to operate on two or three different liquid streams. 
     BRIEF SUMMARY OF THE INVENTION 
     Thanks to its modularity, the cell according to the invention can thus be used in a very simple way both for research and development work and in pilot or industrial-scale plants. 
     This type of electrochemical cell finds a particularly advantageous application in the decontamination of waste water by oxidizing the contaminants it contains. 
     More specifically, the modular electrochemical cell according to the invention is characterized in that it comprises:
         two roughly identical assemblies each comprising a support structure pierced with a cylindrical housing and with an opening passing through in its portion situated outside the said housing and able to be connected to a pipe for conveying or removing a fluid, and a disc-shaped electrode arranged inside each housing, the said support structures being arranged in such a way that their respective electrodes face each other,   inserted between the said assemblies, insert means having, at least, the function of circulating and distributing the said fluid between the electrodes, and   members for connecting the said assemblies and the said insert means together.       

     As a preference, the electrodes comprise a conducting substrate and a conducting layer of diamonds deposited on the substrate. Furthermore, each electrode is fixed on a conducting support disc which can be connected to a power source and whose axial position inside the housing is adjustable from the outside so as to lie flush with the outer face of the electrode and the edge of the support structure. In addition, the housing advantageously contains a ring surrounding the support disc and the axial position of which is adjustable from the outside so as to compress a seal between the electrode, the housing and the disc. 
     In a first type of configuration, the two support structures each have an opening which opens, towards the inside, via a groove in the shape of an arc of a circle, and are arranged in such a way that the said grooves are diametrically opposed, the opening of one support structure serving to convey fluid and the opening of the other serving to remove it. 
     According to one embodiment using this first configuration, the said insert means comprise an insulating washer pierced with orifices situated facing the said grooves, each of these orifices communicating with the internal portion of the washer via a radial duct. 
     According to another embodiment, the said insert means comprise:
         an insulating flat spacer annulus pierced with orifices situated facing the said grooves, each of these orifices communicating with the internal portion of the annulus via a radial duct, and   two insulating washers arranged one on each side of the annulus and each pierced with a slot in the shape of an arc of a circle situated facing one of the grooves.       

     According to yet another embodiment, the said insert means comprise:
         an insulating flat annulus pierced with two slots in the shape of arcs of a circle situated facing the said grooves,   a disc-shaped bipolar electrode arranged inside the said annulus, and   two insulating washers arranged one on each side of the annulus and each pierced with orifices situated facing one of the grooves, each of these orifices communicating with the internal portion of the washer via a radial duct.       

     In a second type of configuration, the support structures each have two openings which emerge, inwards, via two diametrically opposed grooves, in the form of arcs of a circle, the said support structures being arranged in such a way that their respective grooves face each other, the openings of each support structure being used one for conveying and the other for removing a fluid. 
     According to an embodiment using this second configuration, the said insert means comprise:
         a selectively permeable conducting membrane of the ion exchanger type or a porous diaphragm, and   two insulating washers arranged one on each side of the membrane or of the diaphragm and each pierced with orifices situated facing the said grooves, each of these orifices communicating with the internal portion of the washer via a radial duct.       

     According to another embodiment, the said insert means comprise:
         a central hollow annulus which can be connected to a pipe for conveying and to a pipe for removing fluid,   two insulating washers arranged one on each side of the annulus,   two selectively permeable conducting membranes of the ion exchanger type or two porous diaphragms arranged respectively on the other side of these two washers, and   two insulating washers arranged respectively on the other side of the two membranes or diaphragms and each pierced with orifices lying facing the said grooves, each of these orifices communicating with the internal portion of the washer via a radial duct.       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other features of the invention will become apparent from the description which will follow, given with reference to the attached drawing in which: 
         FIGS. 1 and 2  depict, in axial section an exploded perspective view, respectively, a first embodiment of a monopolar cell, 
         FIG. 3  depicts, in exploded perspective, a second embodiment of a monopolar cell with very well separated electrodes, 
         FIG. 4  depicts, in exploded perspective, a third embodiment of a bipolar cell, 
         FIG. 5  depicts, in exploded perspective, a fourth embodiment of a membrane cell, and 
         FIG. 6  depicts, in exploded perspective, a fifth embodiment of a cell with two membranes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be noted that, in this description, the elements common to the various embodiments of the invention are denoted by the same reference numerals. 
     In  FIGS. 1 and 2 ,  10  and  12  have been used to represent two identical assemblies. Each has, as its basis, a support structure  14 , made of polypropylene, which has the shape of a disc exhibiting two diametrically opposed truncated portions  16  to form two flat faces giving the device a stable base. 
     The cage  14  is pierced with a central cylindrical housing in which there sits a mobile ring with an L-shaped cross section,  18 , made of aluminum or plastic and receiving, also such that it can move, a disc  20  made of copper or of nickel. 
     The outer face of the disc  20  has, soldered or bonded to it using a silver-based paste, an electrode  22  formed of a substrate which may, for example, be made of silicon, silicon carbide, titanium or zirconium, coated on its outer face with a layer of doped diamond to make it electrically conductive. This electrode may advantageously be produced using the technique described in 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 end of the cage  14  and the other end of which takes a lock nut  26 . 
     The end of the cage  14  is pierced with six tapped holes distributed uniformly around its periphery, receiving a screw  28  that can be actuated from the outside to act on the ring  18  via a coil spring  30 . 
     It will be noted that the edge of the ring  18  facing the electrode  22  has a face that is chamfered on the outside and acts on an O-ring seal  32  trapped between the electrode, the wall of the housing and the disc. 
     Finally, the cage  14  is pierced on its edge, outside of the perimeter occupied by the electrode, with a tapped hole into which there is screwed a fitting  34  intended for the connection of a hose, not depicted. This fitting opens, on the inside, into a groove  36  in the shape of an arc of a circle subtending about 90°, with the same axis as the assembly. The figures in actual fact show two diametrically opposed grooves  36  because, in a configuration described later on, the cell according to the invention needs these. 
     The cell also comprises, between the two assemblies  10  and  12 , a supply washer  38  which is made of an elastomer such as, for example, one of the products marketed under the names of Viton and EPDM. This washer has an external contour corresponding to that of the cages  14  and a circular internal contour with the same diameter as the electrodes  22 . 
     The washer  38  is pierced with circular orifices  40  of the diameter corresponding to the thickness of the groove  36  and forming a belt with the same radius as this groove. The orifices  40  thus lie facing the groove  36 . Each of these orifices communicates with the internal portion of the washer  38  via a radial duct  42 . 
     The figures show that the orifices  40  cover the entire periphery of the washer  38  even though only those lying facing the groove  36  are of use. This arrangement, however, has the advantage of making the washer perfectly homogeneous. Of course, it would be possible to settle for a series of orifices  40  only facing the groove. 
     The two assemblies  10  and  12 , with the washer  38  inserted between them and the fittings  34  arranged diametrically opposed, are assembled using six bolts and nuts distributed around the periphery of the cell. In order not to clutter the drawing,  FIG. 2  depicts only the heads  44  of these bolts and the holes  46  made in cages  14  and the washer  38  that allows them to pass. 
     Before the cell which has just been described is assembled, it is necessary, for each of the assemblies  10  and  12 , to bring the outer face of the electrode  22  flush with the inner face of the cage  14 . This is done by action on the screw  24  and then, once the two items are flush with each other, by locking it using the nut  26 . When assembly has been performed, using the six nuts and bolts, the six screws  28 , with the aid of the springs  30 , serve to 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 piping for conveying and removing liquid is connected respectively to the fittings  34 . The liquid introduced into the cell via one of the fittings is typically a contaminated waste water. The electrolysis process performed in the cell will allow purified water to appear on the other fitting, accompanied by gas resulting from the reaction that has taken place. 
     Thanks to the structure of the cell, the liquid introduced under pressure for example in the bottom of the left-hand assembly  10 , opens into the lower groove  36  then into the orifices  40  of the washer  38  which lie facing it, before being injected into the space between the two electrodes  22  via the radial ducts  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 right-hand assembly  12 , into the upper groove  36  through the ducts  42  and the corresponding orifices  40  before being removed to the outside. 
     To set a concrete example, and purely by way of illustration, the electrodes  22  have a diameter of the order of 10 cm and a thickness of between 0.5 and 3 mm, while the 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 that has just been described is suitable for fluids with relatively low conductivity. When working with electrolytes that have a high conductivity, typically in excess of 3-5 mS/cm, it is necessary to increase the separation of the two electrodes. In this case, which is the second embodiment of the cell according to the invention, the supply washer  38  is replaced, as shown in  FIG. 3 , by a spacer annulus  48 , made of polypropylene, and by two identical washers  50  arranged one on each side of the annulus  48  and made, like washer  38 , of elastomer. These three components have the same internal and external contours of the washer  38 . 
     The spacer annulus  48 , the thickness of which may be as much as 10 mm, has the same series of circular orifices  40  and the same radial ducts  42  as the washer  38 . 
     The washers  50  simply comprise, in addition to the holes  46  for the passage of the bolts, two slots  52  (only one of which can be used) with the same shape as the slots  36  and positioned in such a way as to face them when the cell is assembled. 
     It can thus be seen that, in this embodiment, the distribution of liquid into the space between the electrodes followed by its collection are provided for by the central annulus  48 , the two washers  50  serving solely to allow the liquid to be transported between the cages  14  and the annulus  48 . 
     The cell described above may also adopt a bipolar structure. In this case, which is the third embodiment of the invention, the supply washer  38  of the first embodiment is replaced, as shown by  FIG. 4 , by an annulus  54  made of polypropylene and by two identical washers  56  arranged one on each side of the annulus  54  and made of elastomer. These three components have the same external and internal contours as the washer  38 . 
     The inside of the annulus takes an electrode  58 , the same thickness and same diameter as electrodes  22 . It is formed of a conducting substrate coated on both sides with a layer of doped diamonds to make it electrically conductive. The electrode  58 , just like the two electrodes  22 , may advantageously be produced according to the teachings of document EP 810147.9. 
     The annulus  54  comprises, in addition to the holes for the passage of the bolts, two diametrically opposed slots  60  with the same shape as the grooves  36  and positioned such that they face them when the cell is assembled. 
     The two washers  56  are identical to the washer  38 . In this embodiment, it is these which distribute and collect the liquid. 
     Of course, the bipolar cell of  FIG. 4  may have several intermediate electrodes  58  associated with an annulus  54 , in order, just as with the cell of  FIG. 3 , to provide a greater electrode separation. In this case, additional washers  56  are inserted between the various annuli  54 . 
     According to a fourth embodiment of the invention, depicted in  FIG. 5 , the assemblies  10  and  12  of  FIG. 1  are replaced by assemblies  62  and  64  which differ from the former only in that they have two fittings  34  and have to have two diametrically opposed circular grooves  36 , the liquid for treatment then being conveyed by one of the fittings and re-emerging via the other. This cell works with two electrolytes which do not mix and which, respectively, according to a known process, form an anolyte stream and a catholyte stream. 
     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 electrically conductive material selectively permeable to certain ions, such as an ion exchange membrane made of Nafion. As an alternative, the membrane  66  may be replaced by a porous diaphragm. On each side of this element there are, arranged symmetrically, two elastomer washers  66  then two polypropylene annuli  70  and finally two further washers  72  made of fluoroelastomer. 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 annulus  70  also have the same circular interior contour as the washer  38 . 
     The washers  38  have no other special openings. The annuli  70  are identical to the spacer annulus  48  of  FIG. 3 , while the washers  72  have the same slots  60  as the annulus  54  in  FIG. 4 . 
     It will be noted that, in the embodiment of  FIG. 5 , the annuli  70  serve only to increase the separation between the electrodes, as is the case of the annulus  48  in  FIG. 3 . When this cell has to operate on liquids that have a low conductivity, the annuli  70  and the washers  68  and  72  can therefore be omitted and replaced with the washers  38  of  FIG. 1 . 
     Finally,  FIG. 6  depicts a fifth embodiment of the cell according to the invention. In this case, the supply washer  38  in  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 annulus  74  made of polypropylene, fitted with two diametrically opposed fittings  76  intended to be connected respectively to a pipe for conveying and to a pipe for removing liquid. 
     The cell of  FIG. 6  can, according to a known process, operate with three separate streams, namely an anolyte stream and a catholyte stream circulating respectively in the assemblies  62  and  64 , and a stream of liquid for processing circulating through the annulus  74 . 
     On each side of this annulus there are, arranged symmetrically, two washers  78  identical to the washers  68  in  FIG. 5 , then two membranes  80  identical to the membrane  66  in the same figure. The membranes  80  can also be replaced by porous diaphragms. The stack continues, as in the cell of  FIG. 5 , with two washers  68 , two annuli  70  and two washers  72 . 
     When this cell has to operate on liquids with low conductivity it is possible, as with the cell of  FIG. 5 , to omit the annuli  70  and the washers  68  and  72  and replace them with the washers  38  of  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, thus improving the efficiency of the electrochemical processes. In order to achieve this effect, various elements of the cell such as, for example, the washer  38  in  FIG. 1 , can be provided at their centre with a grating  82  whose purpose is to encourage turbulence and to act as a spacer between the electrodes. This grating is advantageously made of an insulating chemically stable material such as polypropylene or polyethylene. 
     Thus an electrochemical cell whose modular structure, associated with the use of interchangeable elements allows it a wide variety of configurations meeting the various user requirements have been proposed.