IL35330A - A trough for carrying out the electrolysis of an alkali metal halide - Google Patents

Description

A TROUG-H FOB. CARRYING- OUT THE ELECTROLYSIS OF AN ALKALI METAL HALIDE The present invention relates to a diaphragm or membrane trough, which can, more particularly, be used for the electrolysis of aqueous solutions of alkali metal halides.

In conventional diaphragm or membrane electrolysis troughs, the anode assembly comprises anodes, generally made of graphite, the lower parts of which are surrounded by a layer of lead which keeps them in a fixed position and allows them to be supplied with current from copper strips which are generally also sealed into this layer of lead. The assembly thus made up is thereafter placed in a concrete trough in which the cathode assembly will subsequently rest. In order to ensure that the base of the anode is both protected and leak-proof, a layer of asphalt of sufficient thickness is subsequently cast into the concrete base to cover the lead and the lower part of the graphite anodes, this being done to avoid penetration of the very corrosive brines during electrolysis.

The cathode assembly, comprising a battery of cathode fingers made of metal foil or wire gauze, covered with a diaphragm or membrane, is thereafter placed on the concrete support.

The use of graphite anodes has always involved certain disadvantages resulting from the inherent wear of the anodes, which, firstly, causes an increase in the voltage required for the good functioning of the trough since the distance between the anode and cathode diaphragm or membrane since particles of graphite become entrained in it. T e overall yield of the cell is thus reduced and the anodes only have a limited working life.

Recently, these graphite anodes have tended to be replaced by metal anodes, the surface of which is covered with a precious metal coating, the whole thereafter being subjected to an activation treatment. These anodes have the advantage of having very good resistance to corrosion by the anolyte, and are dimensionally stable and do not suffer from the disadvantages quoted above. Consequently, the working life of the diaphragms or membranes deposited on the cathodes is markedly improved.

In addition to the advantages resulting from their chemical nature, the use of such anodes has made it possible to introduce interesting improvements and simplifications into the actual manufacture of the anode assembly. In effect, eliminating the graphite makes it possible to avoid the use of materials such as lead and asphalt which served to fix and electrically supply the graphite anode and to protect the latter against corrosion during electrolysis.

It has, firstly, been proposed to connect the anodes directly to . he current distributors, consisting of parallel strips of copper, aluminium or some other metal which is a good conductor of electricity, the strips being cast, welded or brazed inside a sleeve of titanium or similar metal. Onto each elementary conductor thus r d c d a for those of the cell, a number of anodes following their normal distribution in the cell is then attached. The attachment can be effected by direct welding onto the conductor or by first attaching flanges to this conductor and bolting the anodes to these flanges. The conductors are placed horizontally and parallel, and extend from one side of the electrolysis trough to the other; the anodes are arranged parallel to one another in a vertical plane. The elementary conductors pass through the wall of the trough and are thereafter grouped together for connection to a source of current input (see French Patent No. 1,4-98,250).

According to another technique, the anodes are attached to a piece of titanium in the form of a dish or pan by titanium bolts passing through the anode and attached to lugs suitably welded to the base of the pan. Alternatively, parallel grooves are produced in the pan, and the anodes are bolted directly to these grooves. The piece, in the form of a pan, made of a thin sheet of titanium or similar metal covers the entire surface of the trough and is fixed by any appropriate means to a relatively thick copper or aluminium base which acts as the current input and distributor, it being possible for this base to consist of a single plate or of parallel . ' strips corresponding to the position of the anodes · (see French Patent No. 1,512,683).

Finally, anodes have been bolted onto titanium plates in the form of an L. These plates are themselves rig-i angles to hose plates, copper st s which serve !to feed' in the current (see British Patent No. 1,125,4-93). ; All these, earlier embodiments propose the use of a sleeve or casing of titanium or similar metal over the copper or aluminium' current infeed strip or plate, with the need to use this sleeve or casing as a relay , for the passage of current between the current infeed strip or plate and the anodes- These embodiments arc valuable and constitute a: not insignificant technical advance, but they nevertheless suffer from considerable disadvantages which the present invention seeks- to remedy. · · ·;.'■ According to the invention, there is provided a trough suitable fo carrying out the electrolysis of an alkali, metal, halide ,'which comprises an anode and a cathode assembly, the anode assembly comprising an electrically conducting..input support plate encased in ■ a layer of a metal which is chemically resistant to the and the products of electrolysis; electrolyte ana a plurality of metal anodes connected at one end directly to' the input by bolts secured in the support plate, and at the other end to a common connector. , The support plate, which serves to feed in current may be made of copper, aluminium or any other . metal or alloy which is a good current conductor.

The external casing of this support plate, the fixing bolts for the anodes and the nuts for fixing alloy which is chemically resistant to the anode medium, such as titanium, tantalum or similar metals, or their alloys. The assembly is preferably made of one and the same metal, or one and the same alloy.

The anodes consist of a plate or foil of a metal which is resistant to corrosion such as titanium, tantalum or similar metals or their alloys, preferably convered with a coating based on precious metals of the platinum group, subsequently subjected to an activation treatment. These anodes show good resistance towards the anolyte and good dimensional stability with respect to time.

The bolts may be fixed in the support plate by any appropriate means, pass through the casing to which fhey are fixed by welding, and serve, in their visible part, as elements for fixing the anodes (with nuts). These bolds serve as conductors of the electrical current and allow the current intended for the anodes to be taken directly from the support plate. The anodes can rest on separate collars or 011a single plate perforated with holes to allow the bolts to pass through. These collars or this plate are placed on the casing of the support plate which feeds in current.

The external casing of the support plate serving to feed in current ensures that this plate is chemically protected from the anode medium. The connection of the bolts to the casing is made leak-proof by welding.

It should be noted that this arrangement differs materially from prior art arrangements, for example that described in British Specification No. 1,125,493, referred plate and the support and nut is tightened up on the other end. Thus the nut is positioned on the other side of the support from the anode plate. This arrangement involves a more complicated removal procedure than that involved in the arrangement of the present invention. Firstly it is much simpler to remove the retaining nut from the^assembly of the present invention since it is above the base plate.

Secondly on removal of this nut, the anode plate can be removed quite simply without altering the position of the bolt in any way since this latter remains embedded in the support plate. In contrast in the prior art arrangement the bolt has to be removed before the anode plate can be removed.

The fact that the current is directly taken by the bolts for fixing the anodes to the support plate which serves to feed in current, allows the disadvantages encountered in the earlier types of apparatus to be remedied.

In effect, in the earlier types the difference in expansion between the support plate and the casing serving to conduct the current presents the danger of a bad electrical contact between the plate and the support. This can cause harmful drops in voltage which cannot be controlled effectively.

Taking the current directly from the support plate by the bolts, in accordance with this invention, eliminates all these dangers because the drop in voltage between the plate which feeds in current and the base of the anode may be limited by applying a uniform and appropriate tightening of the nuts which fix the anodes to the bolts..

A special feature of the trough of this invention is that the anodes are connected to one another at their upper part by means of a connecting device, after the cathode has been put into place. The connecting device, which serves to position the anodes appropriately, can have any desired shape and can be made of various materials such as metals, alloys, plastics and ceramics. It has, however, been found particularly adva tageous to produce the said device from a material which is an electrical conductor and is chemically inert, so as to improve the uniformity of electrical distribution of the anode assembl and eliminate electrical imbalances which can arise "between the various anodes.

I The fact that the current is directly taken from the support plate, and the use of the connecting device joining the anodes at their upper part, separately constitutes a considerable ■ improvement but their conjoint use produces a much greater improvement; it is thus always of interest to use them conjointly.

The invention will now be illustrated, merely I by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a support plate with its casing, and bolts securring the anodes in accordance with one embodiment of the present invention; Figure 2 is a modification of Figure 1 using a different method of fixing the bolts; and Figure 3 is a cross-sectional view of an electrolysis cell according to this invention after placing the cathode in position on the anode bottom.

In Figures 1 and 2, the support plate 1 which serves to distribute current is fed by the anode current inputs 2, welded to the plate 1 at 16. Plate 1 is perforated with holes which are thereafter tapped to receive bolts equipped with a collar 9· Casing 3 of t upper part of the plate 1, which can be connected by Welding to a lower casing so as to allow the plate 1 to ' be completely sheathed, is also pierced with holes in which the collars 9 of the bolts 4- for fixing the anodes seat (as is the case in Figure 1). These collars 9 can The periphery of collar 9 is welded to the casing 3, without adding metal.

In the case of Figure 1, the weld 5 is cleaned up to obtain a plane surface between the collar 9 and the casing 3> so as to provide a good surface for the base of anodes 7 to rest against. When all the bolts ari properly positioned and welded, the anodes, previously perforated to the size of the bolts, are fixed onto these bolts 4- by nuts 6 made of a material of the same nature ai the bolts 4· and the casing 3. Sheets or washers 8 of a non-corroding metal or alloy allow direct contact between the nut 6 and the base of the anode 7 to be avoided. - In Figure 3, the anode base described above has been deposited in a cellular trough 10 of concrete or of polyester, when the trough is of concrete, leak-proof sealing 11 may be achieved by means of a polyester gasket which separates the anode assembly from the periphery of the support base 1 and from its casing 3 and thus protects the assembly from corrosion by the anolyte-. The cathode 14· is thereafter put into place; it comprises a battery of fingers 15 of a metal fabric or of a perforated metal sheet, on which a diaphragm has been deposited. The anodes 7j at the top of which orifices have been provided, are joined to one another by a threaded rod 12 equipped with nuts and lock-nuts 13.

The diaphragm or membrane trough of the present invention, displays numerous advantages, including one great saving in weight of the anode assembly because the use of lead and graphite is dispensed with.

The protection of the support plate which feeds in current, achieved by means of a casing which is resistant to the corrosive action of the anolyte, dispenses with the use of asphalt.

The metal anodes mounted in accordance with the present invention are easily dismantled and can thus be very easily regenerated after the active deposit has worn. It is not necessary to dismantle the entire assembly if one anode has to be replaced.

The anode base thus obtained is produced once and for all, in contrast to conventional anode bottoms with graphite anodes, which have to be remade entirely at the end of each anode working life.

The time for which the diaphragms or membranes last is considerably increased because of the absence of clogging resulting from the wear of the graphite anodes.

Claims (1)

1. insufficientOCRQuality