EP0435385B1 - Electrolytic cell for gas production comprising a stack of vertical frames - Google Patents

Abstract

Electrolyser for the production of a gas, comprising a stack of vertical frames (1, 2) defining electrolysis chambers (4, 5), a degassing chamber (17) above the stack, a conduit for allowing electrolyte to enter (23) the degassing chamber, a vertical pipe (18) connecting the degassing chamber to the lower part of the electrolysis chambers and a nozzle (20) arranged around the pipe and connecting the degassing chamber to the upper part of the electrolysis chambers, the pipe (18) communicating with the degassing chamber (17) through a connecting conduit (19, 21) passing through the nozzle (20).

Description

The invention relates to an electrolyser of the filter press type, for the electrolytic production of a gas.

Electrolysers of the filter press type are generally formed by a stack of vertical frames which delimit alternately anodic and cathodic 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 these electrolysers, gas is generated at the electrodes and an emulsion of electrolyte in the gas is generally collected at the outlet of the electrolysis chambers. The emulsion must be treated in a degassing chamber, to separate the gas from the entrained electrolyte.

In the documents EP-A-0052880 and EP-A-0053807 (OLIN CORPORATION), electrolysers of the type defined above are described, in which two degassing chambers are arranged above the stacking of the frames. One of the degassing chambers communicates with the anodic electrolysis chambers, while the other degassing chamber communicates with the cathodic electrolysis chambers. The communication of the degassing chambers with the electrolysis chambers comprises, on the one hand, nozzles opening into the upper part of the electrolysis chambers and serving for the transfer of the emulsion from the electrolysis chambers to the degassing chamber and , on the other hand, a pipe opening into the lower part of the electrolysis chambers and used for recycling, therein, the electrolyte separated from gas. The degassing chambers are also in communication with a fresh electrolyte intake pipe.

In these known electrolysers, the presence of a separate nozzle and pipe between each electrolysis chamber and the degassing chambers results in a large footprint and complicates the construction of the electrolyser.

The invention overcomes this disadvantage of the known electrolysers described above, by providing an electrolyser of the filter press type equipped with at least one degassing chamber for the separation of the entrained electrolyte with the gas produced in the electrolysis chambers. , whose size is reduced and construction simplified.

The invention therefore relates to an electrolyser for producing a gas, comprising a stack of vertical frames delimiting individual juxtaposed electrolysis chambers which are alternately anodic and cathodic and which each contain at least one electrode, at least one degassing disposed above the stack and connected to each of the anodic (or cathodic) electrolysis chambers by a nozzle opening in the upper part of the electrolysis chamber and by a pipe opening in the lower part of the d chamber electrolysis, and an electrolyte intake pipe in the degassing chamber; according to the invention the nozzle is arranged around the pipe so that the upper end of the nozzle is above the upper end of the pipe, and the pipe communicates with the degassing chamber by means of a junction conduit crossing the side wall of the pipe and that of the nozzle.

In the electrolyser according to the invention, the frames form the side wall of the electrolysis chambers. They can have any profile compatible with the construction of an electrolyser of the filter press type. They can either have a circular or polygonal profile, for example square, trapezoidal or rectangular. They must be made of a material which chemically withstands the conditions of electrolysis.

The degassing chamber is connected to all the anode (or cathode) electrolysis chambers, in which a gas is generated at the electrode. Its function is to collect the gas produced at the electrodes, to separate the electrolyte entrained with the gas and to recycle this electrolyte in the electrolysis chambers. The degassing chamber is also connected to a fresh electrolyte intake pipe and thus serves as a transit chamber for supplying the electrolysis chambers with fresh electrolyte. In the case where a gas is generated in all the electrolysis chambers, the electrolyser may comprise two degassing chambers, one of these being in communication with the anodic electrolysis chambers, while the other is connected to the cathode electrolysis chambers.

The connection of the degassing chamber with the electrolysis chambers comprises nozzles which are in communication with the upper part of the electrolysis chambers and pipes which are in communication with the lower part of said chambers. The upper part of the electrolysis chamber is understood to mean the upper half of its height; by lower part of the electrolysis chamber is meant the lower half of its height. The nozzles are used for the passage of gas from the electrolysis chambers into the degassing chamber, while the pipes are used to supply the electrolysis chambers with fresh electrolyte and to recycle there the electrolyte separated from the gas in the degassing chamber.

According to the invention, for each electrolysis chamber which is connected to the degassing chamber, the nozzle is arranged around the pipe and its upper end or edge is situated at a level higher than that of the upper end of the pipe. A junction conduit crossing the wall of the nozzle and that of the pipe puts the latter in communication with the degassing chamber. During the operation of the electrolyser, the electrolyte is established at the aforementioned junction conduit so that the electrolysis chambers are completely filled with electrolyte. The gas leaving the electrolysis chambers enters the degassing chamber via the nozzles, the electrolyte which separates from the gas at the outlet of the nozzles falls back into the degassing chamber where it mixes with the fresh electrolyte coming from the pipe. intake, and the electrolyte mixture passes through each pipe via the aforementioned junction pipe and is thus introduced into the electrolysis chambers.

In a particular embodiment of the electrolyser according to the invention, the junction conduit between the pipe and the degassing chamber is obtained by joining a part of the wall of the pipe against a part of the wall of the nozzle and by drilling an opening through the joined walls. This embodiment of the invention facilitates the construction of the electrolyser.

In a particular embodiment of the electrolyser according to the invention, the degassing chamber contains a horizontal or oblique partition, which is crossed by the nozzles so as to form a baffle on the electrolyte circuit between the outlet of the nozzles and its entry into the pipe. In this embodiment of the invention, the baffle has the effect of lengthening the circuit of the electrolyte in the degassing chamber, which improves the homogeneity of the mixture of the electrolyte fractions leaving the nozzles.

In another embodiment of the electrolyser according to the invention, the nozzle opens into a channel delimited inside an upper horizontal beam of the frame of the electrolysis chamber, and the pipe opens into a channel delimited a lower horizontal beam of said frame, the two channels being in communication with the electrolysis chamber. In an interesting variant of this embodiment, the two channels are connected by vertical tubes, located in the electrolysis chamber. In this variant of the invention, the vertical tubes have a double function. On the one hand, they participate in the circulation of the electrolyte in the electrolysis chamber; on the other hand, they constitute spacers reinforcing the rigidity of the electrolysis chamber and of the electrode.

In the electrolyser according to the invention, the arrangement of the nozzle around the pipe considerably reduces the space requirement and makes it possible, in accordance with an advantageous embodiment of the invention, to produce the degassing chamber in the form of an enclosure tubular, arranged transversely to the frames.

The electrolyser according to the invention is suitable for all electrolysis processes in which a gas is generated in a at least part of the electrolysis chambers. The invention applies especially to electrolysers for the production of chlorine and aqueous solutions of sodium hydroxide, in which the anodic electrolysis chambers are separated from the cathodic electrolysis chambers by ionic separators. The ionic separators used in the electrolysers according to the invention are sheets interposed between the electrolysis chambers 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 that 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 membrane material 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 fluoropolymer, 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 which are particularly suitable for this application of the cell according to the invention are those known under the names "NAFION" (DU PONT DE NEMOURS & Co) and "FLEMION" (ASAHI GLASS COMPANY LTD).

• La figure 1 est une vue en élévation, avec arrachement, d'une forme de réalisation particulière de l'électrolyseur selon l'invention;
• La figure 2 est une coupe verticale selon le plan II-II de la figure 1;
• La figure 3 montre un détail de l'électrolyseur des figures 1 et 2, à grande échelle et en coupe selon le plan III-III des figures 1 et 2;
• La figure 4 est une vue similaire à la figure 2, d'un tronçon unitaire d'une autre forme de réalisation de l'électrolyseur selon 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, broken away, of a particular embodiment of the electrolyser according to the invention;
• Figure 2 is a vertical section along the plane II-II of Figure 1;
• Figure 3 shows a detail of the electrolyser of Figures 1 and 2, on a large scale and in section along the plane III-III of Figures 1 and 2;
• Figure 4 is a view similar to Figure 2, of a unitary section of another embodiment of the electrolyser according to the invention.

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

In the description which follows, the invention is specifically applied to monopolar electrolysers of the filter press type with cationic membranes, for the production of chlorine, hydrogen and aqueous solutions of sodium hydroxide by electrolysis of aqueous solutions of chloride of sodium.

The electrolyser shown in FIGS. 1 to 3 is formed by a stack of alternately anodic 1 and cathodic 2 vertical frames 2. Selectively permeable membranes 3 are interposed between frames 1 and 2 to delimit alternately anodic electrolysis chambers 4 and cathodic 5, containing electrodes.

Frames 1 and 2 have a rectangular cross section. They are formed by two vertical uprights 6 welded to two horizontal rails 7. In the case of anode frames 1, the uprights 6 and the rails 7 are made of titanium, while in the case of cathode frames 2, they are made of nickel.

The electrodes are of the type described in Belgian patent application 08900867 (SOLVAY & Cie). They each comprise a pair of vertical sheets 8 of expanded metal, arranged on either side of several horizontal metal bars 9. The sheets 8 are welded to vertical profiles 10 formed from metal strips folded in U or Ω. The profiles 10 are welded to the horizontal bars 9 and these are welded to the uprights 6 of the frames, which they pass through. They are fixed together to a junction bar 11, intended to be coupled to a current source. The bars 9 and the profiles 10 thus cooperate in the coupling of the sheets 8 to the current source and to the support of these sheets inside the electrolysis chamber.

The material of the sheets 8, the bars 9 and the vertical profiles 10 depends on the destination of the electrode. In the case of anodes, the sheets 8 are made of titanium and carry an electrically conductive coating, at low overvoltage for the electrochemical oxidation of chloride ions, the bars 9 comprise a copper core jacketed in a titanium envelope and the vertical sections 10 are made of titanium. In the case of cathodes, the sheets 8 are made of nickel, the bars 9 comprise a copper core lined in a nickel casing and the vertical sections 10 are made of nickel.

The stack of frames 1 and 2 and membranes 3 is retained between two end plates 12, connected by tie rods not shown, seals 13 ensuring the seal.

The side members 7 of the frames 1 and 2 are hollow, so as to delimit internal channels of square or rectangular section, respectively 14 in the case of the lower side member and 15 in the case of the upper side member. Channels 14 and 15 communicate with the electrolysis chambers 4 and 5, via openings 16 made in the wall of the side members. In each electrolysis chamber 4 or 5, the two channels 14 and 15 are also connected by vertical tubes 27, arranged inside the electrolysis chamber, between the two sheets 8 of the electrode.

A degassing chamber 17 is arranged above the stack. It has the form of a horizontal tubular enclosure, arranged transversely with respect to the frames 1 and 2. The degassing chamber 17 communicates with the lower channel 14 of each anode chamber 4 by means of a vertical pipe 18 closed at its upper end and pierced with a lateral opening 19. It also communicates with the upper channel 15 via a vertical nozzle 20. The nozzle 20 is arranged around the pipe 18, so that its upper edge is located at a level higher than that of the upper edge of the pipe 18.

Figure 3 shows, in horizontal cross section, the assembly of the pipe 18 and the nozzle 20. The pipe 18 and the nozzle 20 have a rectangular cross section and are obtained by folding a sheet of titanium. The nozzle 20 is applied against the face of the pipe 18, in which the opening 19 is pierced. An opening 21 is pierced through the wall of the nozzle 20, opposite the opening 19 of the pipe 18, so that the pipe 18 communicates with the degassing chamber via the two openings 19 and 21.

Inside the degassing chamber 17, the nozzles pass through a horizontal partition 22. Under the partition 22, is disposed a horizontal tube 23 pierced with openings 24. The tube 23 passes through the end wall of the degassing chamber , to be connected to an intake duct (not shown) of an aqueous solution of sodium chloride.

A tube 25 opens into the upper part of the degassing chamber. It is used to evacuate the chlorine produced during electrolysis.

The electrolyser may include a second degassing (not shown), similar to the degassing chamber 17 and connected to the cathode chambers 5 by pipes and nozzles similar to pipes 18 and nozzles 20.

During the operation of the electrolyser shown in FIGS. 1 to 3, an aqueous sodium chloride solution is introduced into the degassing chamber 17 via the tube 23. When the sodium chloride solution in the degassing chamber 17 reaches the level openings 19 and 21, it passes into the anode electrolysis chambers, via the pipes 18, the lower channels 14 and the openings 16 thereof. Chlorine is generated on the sheets 8 of the anodes and passes into the degassing chamber going up through the electrolyte in the chambers 4, the channels 15 and the nozzles 20. At the outlet of the nozzles 20, the electrolyte entrained with the chlorine separates from it and falls back into the degassing chamber, where it mixes with the fresh electrolyte coming from the tube 23. The partition 22 creates a baffle lengthening the path traveled by the electrolyte separated from the chlorine, which guarantees better homogeneity of the sodium chloride solution introduced into the anode electrolysis chambers 4. The chlorine separated from the electrolyte escapes from the degassing chamber through the orifice 25. By a tube 26 in communication with the channels 14, anode chambers 4 are drawn off, a fraction of electrolyte corresponding to the quantity introduced by the intake tube 23.

In parallel with the production of chlorine in the anode chambers 4, hydrogen is generated in the cathode chambers 5. To this end, water or a dilute aqueous solution of sodium hydroxide is introduced into the cathode chambers 5, and extracting from these, via the lower channels 14, a fraction of a concentrated solution of sodium hydroxide, corresponding to the amount of water or dilute solution introduced into the electrolysis chambers. In addition, a concentrated aqueous solution of sodium hydroxide is separated from the hydrogen in a degassing chamber similar to chamber 17 and is returned to the cathode chambers 5.

In the electrolyser, the vertical tubes 27 produce a double function. On the one hand, they serve to cause an internal circulation of electrolyte inside the electrolysis chambers; on the other hand, they constitute stiffeners between the sheets 8 of the electrodes, opposing a deformation of these sheets under the effect of the pressure prevailing in the electrolysis chambers. The vertical tubes 27 therefore make it possible to produce very large width electrolysis chambers, without fear of a deflection of the sheets 8 of the electrodes.

In an alternative embodiment, not shown, of the electrolyser of FIGS. 1 to 3, the degassing chamber is formed by a stack of juxtaposed tubular sections, compressed between two end flanges. In this variant of the invention, it is conceivable to secure each section of the degassing chamber to a frame 1 of the electrolyser, so as to produce a unitary assembly. Figure 4 shows such a unitary assembly. It includes an anode frame 1, a section 17 'of the degassing chamber 17, a section 22' of the partition 22, a pipe 18 and a nozzle 20. The cohesion of the unitary assembly is ensured by the nozzle 20 at which the frame 1 and the sections 17 ′ and 22 ′ are welded.

Claims (10)

1. Electrolyser for the production of a gas, comprising

   - a stack of vertical frames (1, 2) defining adjoining individual electrolysis chambers which are alternately anodic (4) and cathodic (5) and each of which contains at least one electrode (8),

   - at least one degassing chamber (17) arranged above the stack and connected to each of the anodic (4) (or cathodic) electrolysis chambers by a nozzle (20) which is in communication with the upper part of the electrolysis chamber and by a pipe (18) which is in communication with the lower part of the electrolysis chamber, and

   - a conduit for allowing electrolyte (23) to enter the degassing chamber (17),

   characterized in that the nozzle (20) is arranged around the pipe (18), so that the upper end of the nozzle (20) is above the upper end of the pipe (18), and the pipe (18) communicates with the degassing chamber (17) by means of a connecting conduit (19, 21) passing through the side wall of the pipe (18) and that of the nozzle (20).
2. Electrolyser according to Claim 1, characterized in that a part of the wall of the nozzle (20) adjoins a part of the wall of the pipe (18) the connecting conduit being made up of two openings (19, 21) provided through the adjoining parts of walls respectively.
3. Electrolyser according to Claim 1 or 2, characterized in that the degassing chamber (17) comprises a horizontal tubular enclosure arranged transversely relative to the frames (1, 2).
4. Electrolyser according to any one of Claims 1 to 3, characterized in that the degassing chamber (17) contains a chicane comprising a horizontal or oblique partition (22) through the which the nozzles (20) pass.
5. Electrolyser according to any one of Claims 1 to 4, characterized in that the conduit for allowing electrolyte to enter comprises a tube (23) with a perforated wall, arranged in the degassing chamber (17).
6. Electrolyser according to any one of Claims 1 to 5, characterized in that the nozzle (20) opens into a channel (15) defined inside an upper horizontal lengthwise girder (7) of the frame of the electrolysis chamber, and the pipe (18) opens into a channel (14) defined in a lower horizontal lengthwise girder (7) of the said frame, the two channels being in communication with the electrolysis chamber.
7. Electrolyser according to Claim 6, characterized in that the two channels (14, 15) are connected by tubes (27) situated inside the electrolysis chamber.
8. Electrolyser according to Claim 7, characterized in that the tubes (27) connecting the two channels (14, 15) are situated between at least one pair of vertical perforated metal sheets (8) arranged facing each other and forming at least a part of the electrode of the electrolysis chamber.
9. Electrolyser according to any one of Claims 1 to 8, characterized in that it comprises two degassing chambers, one of which is connected to the anodic electrolysis chambers (4) and the other of which is connected to the cathodic electrolysis chambers (5), ion separators (3) being inserted between the electrolysis chambers (4, 5).
10. Electrolyser according to any one of Claims 1 to 9, for the electrolysis of aqueous sodium chloride solutions.

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