EP0400712A1 - Frame for electrolyzer of the filter-press type and electrolyzers of the filter-press type - Google Patents

Abstract

Structural frame for an electrolyser of the filter-press type comprising a vertical metal sheet (1), a peripheral frame made up of two vertical uprights (2, 3) and of two horizontal lengthwise members (4, 5) and a metal sheeting (6) covering the sheet (1) and the two uprights (2, 3), the two lengthwise members (4, 5) being made of the same material as the sheeting (6), being inserted between the uprights (2, 3) and being integrally fastened to the sheeting (6). Electrolysers of the filter-press type comprising this structural frame. <IMAGE>

Description

The invention relates to electrolysers of the filter press type and more particularly to chassis used in the construction of these electrolysers.

Electrolysers of the filter press type are generally formed by a stack of vertical frames which delimit electrolysis chambers in which electrodes are arranged vertically. Selectively permeable membranes or electrolyte permeable diaphragms can be inserted between the frames to separate the electrolysis chambers.

In document US-A-4069129 (ASAHI GLASS COMPANY), electrolysers of the filter press type are described, in which the frames are frames formed from an assembly of tubes which are used for the circulation of electrolytes and of products of electrolysis. The electrodes are perforated metal plates, which are fixed to the frames, along their periphery. In these known electrolysers, the tubes forming the frames must be made of a material which withstands the chemical and thermal conditions prevailing in the electrolyser; they are generally made of titanium or nickel, depending on whether they are in an anode chamber or in a cathode chamber of a membrane cell used for the electrolysis of aqueous solutions of sodium chloride. Titanium and nickel have the disadvantage of having a high electrical resistivity, compared to materials such as steel, copper or aluminum, so that these electrolysers have poor energy yields.

In documents EP-A-185271 (ORONZIO from NORA) and WO 86/3787 (THE DOW CHEMICAL), electrolysers of the filter press type are described, in which the frames include a vertical sheet and a peripheral frame, the whole being lined with a stamped metal sheet. The sheet is used to convey the electric current to the electrodes and is therefore generally made of steel, copper or aluminum. The stamped sheet is used to isolate the sheet and the frame from the aggressive chemical medium present in the electrolyser; it is made of titanium or nickel, depending on whether it is in an anode chamber or in a cathode chamber of a membrane cell for the electrolysis of aqueous solutions of sodium chloride. In these known electrolysers, the chassis have a low resistance to the conduction of electric current, which constitutes an advantage. These frames have the disadvantage, however, that their frame is unusable for the circulation of electrolytes and electrolysis products, because it is entirely covered by the stamped metal sheet.

The invention aims to provide a chassis for an electrolyser of the filter press type, which combines the respective advantages of the known electrolysers described above, while avoiding their drawbacks. It more particularly aims to provide a chassis having a low overall resistance to the conduction of electric current, and in which a part of the frame can be used for the circulation of electrolytes and electrolysis products.

Consequently, the invention relates to a chassis for an electrolyser of the filter press type, comprising a vertical metal sheet jacketed with a metal sheet and a peripheral frame formed by two vertical uprights and two horizontal beams; according to the invention, the two uprights are secured to the sheet and are covered with the metal sheet, and the two side members are made of the same material as the sheet, are inserted between the uprights and are secured to the sheet.

In the chassis according to the invention, the frame has the function of delimiting an electrolysis chamber of the electrolyser, the latter having to contain a vertical electrode.

The sheet has the function of stiffening the chassis, support the frame and conduct the electric current through the electrolyser. The sheet metal material is not critical, provided it is electrically conductive. However, it is especially recommended to make it from a metal or metal alloy which is a good conductor of electricity; steel, copper and aluminum are preferred.

The material used for the side uprights of the frame is not critical.

The function of the metal sheet is to isolate the metal sheet and the uprights of the frame from the aggressive chemical medium present in the electrolyser. It must therefore be made of a material which is impermeable to the aggressive constituents of this medium and inert towards them. By way of example, in the case of membrane electrolysers intended for the production of chlorine and aqueous solutions of sodium hydroxide, it is possible to use a material selected from titanium, tantalum, niobium, zirconium, tungsten and the alloys of these metals, when the chassis is intended to form an anode chamber of the electrolyser; when the chassis is intended to form a cathode chamber of the electrolyser, the material of the metal sheet is advantageously chosen from nickel and nickel alloys. The metal sheet must also be shaped so that it rests on the sheet, between the uprights and overlaps the uprights. The profile to be given to the sheet therefore depends on the dimensions and the shape of the side members and can be obtained by a stamping or folding operation. The thickness of the sheet must be sufficient for it to withstand the mechanical stresses to which it is subjected during the operation of the electrolyser. Notwithstanding this condition, it is advantageous to use the thinnest possible sheet, so that its electrical resistance, transversely to its surface, is as low as possible. The optimum thickness can be easily determined as soon as its other dimensions have been fixed, the material constituting it and the operating conditions of the electrolyser.

The horizontal frame rails must be made in a material which resists the aggressive chemical medium present in the electrolyser. We prefer to make them in the same material as the metal foil. They must also be secured to the metal foil in a sufficiently watertight manner to isolate the sheet and the uprights of the chassis from the aggressive medium present in the electrolyser. The joining of the side members to the metal sheet is usually obtained by welding.

The chassis according to the invention is intended to be attached to similar chassis to form an electrolyser of the filter press type. In it, the chassis according to the invention serves to delimit an electrolysis chamber containing a vertical electrode. The electrode is generally made of metal and can be connected to the metal foil by means of electrically conductive junction elements. These can for example be studs or metal profiles welded to the electrode and to the metal sheet. It is recommended that the metal foil is welded to the sheet metal, under the joining elements, to reduce the electrical resistance of the assembly.

In accordance with a particular embodiment of the invention, the chassis comprises, on the one hand, a metal sheet and a peripheral frame on each face of the sheet and, on the other hand, two vertical electrodes arranged respectively on the side and on the 'other of the sheet and respectively connected to the metal sheets by electrically conductive junction elements. In the case of a frame intended for a monopolar electrolyser, the two electrodes are two anodes or two cathodes; the two metal sheets can then be made of the same material and the metal sheet must be extended by a metal strip extending outside the frame, to be connected to a source of electric current. In the case where the frame is intended for an electrolyser of the bipolar type, one electrode is an anode and the other electrode is a cathode, the metal sheet then serving for the transfer of the electric current from the cathode to the anode when the electrolyser is in operation.

In the chassis according to the invention, the uprights and the frame members may have any cross section compatible with the construction of the electrolyser. We prefer to give them a polygonal cross section, generally square, rectangular or trapezoidal.

In an advantageous embodiment of the chassis according to the invention, the longitudinal members are profiled so as to form, along the sheet, two longitudinal channels which are pierced with openings on their respective walls which face each other; one of the channels is also connected to an electrolyte intake conduit, the other channel being connected to a conduit for discharging the products of electrolysis. In this embodiment of the invention, the channels of the side members serve to distribute the electrolyte in the electrolysis chamber delimited by the frame and to evacuate the products thereof resulting from the electrolysis.

As explained above, the chassis according to the invention can be adapted to the construction of monopolar electrolysers or bipolar electrolysers.

The invention therefore also relates to monopolar electrolysers of the filter press type and bipolar electrolysers of the filter press type, formed from a stack of chassis in accordance with the invention, said chassis delimiting electrolysis chambers which contain electrodes. . The invention applies especially to electrolysers of this type, in which the electrolysis chambers are separated by separators which are permeable to ions. The separators are sheets interposed between the successive frames of the stack and made of a material capable of being traversed by an ion current during the operation of the electrolyser. They can be either diaphragms permeable to aqueous electrolytes or membranes with selective permeability.

Examples of diaphragms which can be used in electrolysers according to the invention are asbestos diaphragms, such as those described in patent US-A-1855497 (STUART) and in patents FR-A-2400569, EP-A-1644 and EP -A-18034 (SOLVAY & Cie) and diaphragms in organic polymers, such as those described in patents FR-A-2170247 (IMPERIAL CHEMICAL INDUSTRIES PLC) and in patents EP-A-7674 and EP-A-37140 (SOLVAY & Cie).

The term “membranes with selective permeability” is understood to mean thin, non-porous membranes comprising an ion-exchange material. The choice of the material constituting the membranes and of the ion exchange material will depend on the nature of the electrolytes subjected to the electrolysis and on the products which it is sought to obtain. As a general rule, the material of the membranes is chosen from those which are capable of withstanding the thermal and chemical conditions normally prevailing in the electrolyser during electrolysis, the ion-exchange material being chosen from anion-exchange materials or cation exchange materials, depending on the electrolysis operations for which the electrolyser is intended.

For example, in the case of electrolysers intended for the electrolysis of aqueous solutions of sodium chloride for the production of chlorine, hydrogen and aqueous solutions of sodium hydroxide, membranes which are well suited are cationic membranes in fluorinated polymer, preferably perfluorinated, containing cationic functional groups derived from sulfonic acids, carboxylic acids or phosphonic acids or mixtures of such functional groups. Examples of membranes of this type are those described in patents GB-A-1497748 and GB-A-1497749 (ASAHI KASEI KOGYO KK), GB-A-1518387, GB-A-1522877 and US-A-4126588 (ASAHI GLASS COMPANY LTD) and GB-A-1402920 (DIAMOND SHAMROCK CORP.). Membranes particularly suitable for this application of the cell according to the invention are those known under the names "NAFION" (DU PONT DE NEMORS & Co) and "FLEMION" (ASAHI GLASS COMPANY LTD).

The electrolysers according to the invention find a particularly advantageous application for the production of chlorine and aqueous solutions of sodium hydroxide by electrolysis of aqueous solutions of sodium chloride.

• La figure 1 est une vue en élévation, avec arrachement partiel, d'une forme de réalisation du châssis selon l'invention;
• La figure 2 est une vue en plan, avec arrachement partiel, du châssis de la figure 1;
• La figure 3 est une coupe verticale selon le plan III-III des figures 1 ou 2;
• La figure 4 montre une variante de réalisation d'un détail de la figure 3;
• La figure 5 est une vue en plan analogue à la figure 2, avec arrachement partiel, d'une autre forme de réalisation du châssis selon l'invention;
• La figure 6 est une coupe selon le plan VI-VI de la figure 5;
• La figure 7 montre, en section transversale, verticale, un électrolyseur monopolaire du type filtre-presse, conforme à l'invention;
• La figure 8 montre, en section transversale, verticale, un électrolyseur bipolaire du type filtre-presse, conforme à l'invention.

Special features and details of the invention will emerge from the description which follows, with reference to the accompanying drawings.

• Figure 1 is an elevational view, partially broken away, of an embodiment of the chassis according to the invention;
• Figure 2 is a plan view, partially broken away, of the frame of Figure 1;
• Figure 3 is a vertical section along the plane III-III of Figures 1 or 2;
• Figure 4 shows an alternative embodiment of a detail of Figure 3;
• Figure 5 is a plan view similar to Figure 2, partially broken away, of another embodiment of the frame according to the invention;
• Figure 6 is a section along the plane VI-VI of Figure 5;
• FIG. 7 shows, in vertical cross section, a monopolar electrolyser of the filter press type, according to the invention;
• FIG. 8 shows, in vertical cross section, a bipolar electrolyser of the filter press type, according to the invention.

In these figures, the same reference notations designate identical elements.

In the following description, the invention is specifically applied to electrolysers of the cationic membrane filter press type, for the production of chlorine and aqueous sodium hydroxide solutions by electrolysis of aqueous sodium chloride solutions.

The chassis according to the invention, shown in Figures 1 to 3, is designed to form two anode chambers paired with a monopolar electrolyser. It comprises a vertical sheet 1 of copper and two peripheral frames respectively disposed on either side of the sheet 1. The frames have a rectangular cross section. They each include two vertical uprights 2 and 3 of copper or steel, welded to the sheet 1 and two longitudinal members 4 and 5 of titanium. The sheet is lined in two titanium sheets 6 folded in the shape of an Ω, so that they are applied to the sheet 1 under the side members 4 and 5 and overlap the uprights 2 and 3. The titanium sheets 6 are welded to the side members 4 and 5 by means of continuous weld beads, so as to form a sealed assembly. Two vertical anodes 7 (visible in Figures 1 and 3) are disposed respectively inside the frames. Each of them consists of an openwork vertical titanium plate, carrying a conductive coating with low overvoltage for the electrochemical oxidation of chloride ions. Such coatings are well known in the art of electrolysis. Each plate 7 is fixed to the sheet 6 by means of vertical titanium profiles 8. The sheet 1 is extended outside the frames in the form of a marginal strip 9 intended to be connected to the positive terminal of a source direct current. The electrical connection between the current source (not shown) and the anode plates 7 is made via the marginal strip 9, the sheet 1, the titanium sheets 6 and the profiles 8. The electrical connection between the sheet 1 and the sheets 6 can be obtained under the action of the hydrostatic pressure of the electrolyte during the operation of the electrolyser; as a variant, it is possible to provide welding points for the sheets 6 to the sheet 1, under the profiles 8.

The tubular beams 4 and 5 are tubes of rectangular section thus delimiting four longitudinal channels 23. Their ends are hermetically welded to the sheets 6. They are moreover pierced with openings 10 regularly distributed on their walls which face each other. The lower tubular beams 5 are provided with a tube 11 for the admission into their respective channels 23, of an aqueous solution of sodium chloride to be electrolyzed; similarly, the upper beams 4 are provided with a tube 12 for the evacuation of the electrolysis products, in this case chlorine and a dilute solution of sodium chloride.

In the variant shown in FIG. 4, the side members 4 and 5 are each formed of a titanium plate folded in a U and welded to the titanium sheet 6 so as to delimit the channel 23.

In the case of a frame intended to form two chambers cathode twin of the electrolyser, the horizontal beams 4 and 5, the sheets 6, the profiles 8 and the plates 7 (forming cathodes) are made of nickel. The nickel plates 7 can advantageously carry a conductive coating with low overvoltage of electrochemical reduction of the protons; such coatings are well known in the art of electrolysis.

The chassis according to the invention, shown in Figures 5 and 6, is designed to form two twin chambers, respectively anode 13 and cathode 14, of a bipolar electrolyser. For this purpose, it has the same spatial configuration as the chassis of FIGS. 1 to 3 and it also comprises a vertical sheet 1 of copper and, on each face of the latter, two vertical uprights 2 and 3 of copper or steel, welded to the sheet 1. The anode chamber 13 is arranged like each of the twin anode chambers of the chassis of FIGS. 1 to 3. It includes a titanium sheet 6 covering the sheet 1 and the two uprights 2 and 3, two titanium beams 4 and 5 pierced with a row of openings on their opposite walls, facing the titanium sheet 6 and a titanium anode (carrying an active coating for the electrochemical oxidation of chloride ions) fixed to the sheet 6 by titanium profiles 8. In the cathode chamber 14, the sheet 1 and the two vertical uprights 2 and 3 are covered with a nickel sheet 6 ′. The two tubular beams 4 ′ and 5 ′ (pierced with a row of openings 10 ′ in their facing walls), the plate 7 ′ and the profiles 8 ′ are made of nickel. The nickel cathode plate 7 ′ is preferably provided with an active coating for the electrochemical reduction of the protons. The tubing 11 ′ is used for the admission of water or a dilute aqueous solution of sodium hydroxide into the channel 23 ′ defined by the lower beam 5 ′ and the tubing 12 ′ is used for the evacuation of the products of the electrolysis (in this case hydrogen and a concentrated aqueous solution of sodium hydroxide) outside the channel 23 ′ defined in the upper tubular beam 4 ′.

The electrolyser shown in FIG. 7 is of the monopolar type. It is made up of a stack of vertical frames, alternately anodic 15 and cathodic 15 ′. The anode frames 15 are similar to those described above, with reference to FIGS. 1 to 3. The cathode frames 15 ′ are analogous to the anode frames 15, in which the constituent elements in titanium have been replaced by similar elements in nickel. These nickel elements of chassis 15 ′ have the same reference numbers as their respective counterparts of chassis 15, but are assigned a prime index (′). At each end, the electrolyser is terminated by a 15 ′ cathode half-frame. The chassis 15 and 15 ′ are separated by cationic membranes 16, which thus delimit alternately anodic and cathodic electrolysis chambers. The stack of frames 15 and 15 ′ and membranes 16 is retained between end plates 17 and 18, connected by tie rods not shown. Sheets 24 of an electrically non-conductive material provide electrical insulation between the flanges 17 and 18 and the end half-frames 15 ′ of the electrolyser. The marginal bands 9 (FIG. 2) of the sheets 1 of the anode frames 15 are connected to a common bus bar, connected to the positive terminal of a direct current source, the marginal bands 9, the bus bar and the current source n 'not being visible in Figure 7. Similarly, the marginal strips of the sheets 1 of the cathode frames 15' are connected to a common bus bar, connected to the negative terminal of the DC source. Furthermore, the pipes 11 and 12 of the anode frames 15 open respectively into a common manifold 19 for admitting an aqueous solution of sodium chloride and into a manifold 20 serving for the evacuation of a chlorine emulsion in a solution. dilute aqueous sodium chloride. By analogy, the tubes 11 ′ and 12 ′ of the cathode frames 15 ′ open respectively into two general collectors 19 ′ and 20 ′, the manifold 19 ′ serving for the admission of water or a dilute solution of sodium hydroxide in the cathode chambers and the collector 20 ′ serving for the evacuation of the hydrogen produced during the electrolysis and of a concentrated solution of sodium hydroxide.

The electrolyser shown in FIG. 8 is of the bipolar type. It is formed by a stack of chassis conforming to that shown in FIGS. 5 and 6 and by cationic membranes 16, so as to delimit alternately anodic 13 and cathodic 14 electrolysis chambers. At its ends, the electrolyser is terminated by two half-frames, respectively anode 21 and cathode 22. The sheet 1 of the anode half 21 is connected to the positive terminal of a direct current source, not shown and the sheet 1 of the cathode half frame 22 is connected to the negative terminal of the current source.

Claims (10)

1 - Chassis for an electrolyser of the filter press type comprising a vertical metal sheet (1), lined with a metal sheet (6) and a peripheral frame formed by two vertical uprights (2, 3) and two horizontal beams ( 4, 5), characterized in that the two uprights (2, 3) are secured to the sheet (1) and are covered with the metal foil (6), and in that the two longitudinal members (4, 5) are produced in the same material as the sheet (6), are inserted between the uprights (2, 3) and are secured to the sheet (6). 2 - Chassis according to claim 1, characterized in that the longitudinal members (2, 3) are profiled so as to form, along the sheet (6) longitudinal channels (23) which are pierced with openings (10) on their respective walls which face each other, the channels (23) being in communication with conduits (11, 12) for the admission and for the evacuation of an electrolyte. 3- Chassis according to claim 2, characterized in that the beams (2, 3) are U-folded plates and welded to the sheet (6) to form therewith the channels (23). 4 - Chassis according to any one of claims 1 to 3, characterized in that the uprights (2, 3) and the side members (4, 5) have a square, rectangular or trapezoidal cross section. 5 - Chassis according to any one of claims 1 to 4, characterized in that the metal sheet (1) is made of a material selected from steel, copper and aluminum, and the metal sheet (6) is a material selected from titanium and nickel. 6 - Chassis according to any one of claims 1 to 5, characterized in that it comprises, on the one hand, a metal sheet (6, 6 ′) and a peripheral frame on each face of the sheet (1) and , on the other hand, two vertical electrodes (7, 7 ′) disposed respectively on either side of the sheet (1) and respectively connected to the sheets (6, 6 ′) by junction elements (8, 8 ′) conductors of electricity. 7 - Chassis according to claim 6, characterized in that the sheet (1) is extended outside the frame by a metal strip (9) forming a junction conductor to a current source. 8 - Electrolyser of the monopolar type, filter press, comprising a stack of chassis delimiting electrolysis chambers containing vertical electrodes, characterized in that it comprises chassis (15, 15 ′) according to claim 7. 9 - Bipolar type electrolyser, filter press, comprising a stack of chassis delimiting electrolysis chambers containing vertical electrodes, characterized in that it comprises chassis in accordance with claim 6. 10 - An electrolyser according to claim 8 or 9, characterized in that it comprises membranes (16) with selective permeability, alternating with the frames.

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