NO753816L - - Google Patents

Description

Holding device for electrodes and membrane in an electrolysis cell.

The present invention relates to a holding device for use

in the construction of electrolysis cells and assembly of such cells.<*>More specifically, the invention applies to a cell frame cast in synthetic organic polymer material with cast-in parts and channels for retaining cell elements., supply and removal of cell fluids as well as setting up and joining together of

cell frames in assemblies.

For the production of chlorine, sodium hydroxide and hydrogen from aqueous solutions of sodium chloride, electrolysis cells of either the membrane or mercury type have previously been used. In recent years, however, merabran cells have become increasingly important due to the increasing price of mercury and pollution problems in connection with the use of mercury cells. Most membrane cells have previously been made of concrete, but the use of liners made of different polymer materials, including polyvinyl chloride and polypropylene, has been proposed.

By developing dimensionally stable anodes and efficient permselective membranes, it has now become possible to increase the production capacity for batteries of membrane cells. Owing to the now available possibility of using flat electrodes with a thin separating membrane between the electrode, high assemblies of thin cells have become possible. Thus, massive cell wall constructions are "no longer necessary or desirable, and efforts have been made to develop construction materials that are satisfactory for

production of electrolytic cells and which can easily be produced in thin sheets and are able to withstand the current ones

surroundings, reactants and manufactured products during the electrolysis. Attempts have been made to produce cells and cell frames from . synthetic organic polymer materials', but this has often proved to be expensive and the manufactured products have not been sufficiently durable under the current operating conditions,

possibly due to stress states produced in the plastic material during tool processing or due to material weakening produced by this process. Tool processing of filled polymer materials exposes surfaces of the filling material, and

this can be unfavorable for long-term use under electrolysis conditions, particularly in the presence of electrolyte and the manufactured cell products at higher temperatures or when the temperature varies within a range that is large enough to produce significant expansions and contractions that can lead to impairments in the surfaces of filled polymer material where the filling material is exposed.

Polypropylene has been used as an acid-resistant and hydroxide-resistant construction material and has been filled with various high-temperature-resistant materials, such as talc, mica and asbestos, but have not previously been used for the production of cast frames of the present type for joining to form batteries of electrolysis cells. Such products are relatively easy to manufacture, assemble and use and have a long service life

as the respective frames or holding devices have proven to be very resistant to mechanical stresses, sleeve loads, expansions, contractions, shrinkage and other deformations during electrolysis

of aqueous solutions of sodium chloride. The holder frame according to the invention consists of a synthetic organic frame of polymer material for enclosing the anode and cathode as well as supporting

of a membrane, and whose special features according to the invention consist of 1

that it in combination with a corresponding other holding device in such a way that the electrodes located closest to each other in the two. devices have opposite polarity, form an electrolysis cell with anode, anode and an intermediate membrane, each holding device'. :-\ : includes inlets and outlets for electrolytic fluids to anolyte and catholyte chambers, so that the cell formed by two composite

holding devices have at least one inlet to and outlet from the anolyte chamber as well as at least one inlet to and one outlet from the catholyte chamber, under which

each inlet and outlet is connected to an outlet that is part of the holding device in question.

In preferred embodiments of the device of the invention, synthetic resin and organic polymer are made of polypropylene containing a filler material such as asbestos, mica, calcium silicate, talc or mixtures of these materials, - the holding device being injection-molded into a frame in which there are seats for setting and fastening means for correct assembly of a number of holding frames for a ceilefoatery, as well as being equipped with cast-in mounting means for holding different cell parts in the desired position. The invention also includes methods for electrolysis by

use of electrolysis cells which comprise existing holding devices, methods for manufacturing such holding devices as well as intermediate mounting means or electrode frame to hold these in the desired position in the present holding devices.

The invention will be better understood from the following description with reference to the attached drawings, on which: Fig. 1 is a perspective sketch of a cell assembly comprising a number of holding devices according to the present invention, Fig. 2 shows a vertical section through a pair holding frames according to the present invention and with "ice cut away parts, as well as parts of further, adjacent holding devices, as two complete such devices must be combined to form an electrolysis cell", Fig. 3 shows a section along plane 3 - 3 in Fig. 2 , with certain parts being cut away, and Fig. 4 is a partial section through the T-shaped rectangular "picture frame" which is used as a spacer for connecting an electrode to the holder frame of polymer material according to the present invention.

The assembly 11 of electrolysis cells in fig. 1 comprises a foundation 13, individual cell frames 15 mounted together with intermediate gaskets (not shown) for tight suspension purposes, front and rear in clamping plates, respectively. 17 and 19, horizontal supporting side bars 21 and 23 which are firmly connected to the foundation 13 and held in

svstand above this by means of vertical parts 25, 27, 29 and 31, as well as rods 33, 35, 37, 39 and 41 which are each threaded at both ends and provided with tightening nuts for pressing the end plates against each other to thereby hold the frames together in lfluid-tight interconnection, usually by means of intermediate gaskets. The threaded ends 43 and 45 and the tightening nuts 47 and 49 on the rod 41 are shown, and it will be obvious to those

other rods are equipped with similar threaded ends and fcil^fchecking nuts. A roller which serves as a bearing to facilitate the sliding movement of the plate 17 is denoted by the reference number 51. The plates 17 and 19 are equipped with through passages to hold the clamping bars in position and transfer the holding forces to the plates. The Eolder frames 15, the construction of which will be discussed in more detail in connection with fig. 2 and 3, comprises outer setting means 53, which are equipped with outer pieces in fixed connection with the frames and the mold (at 53) for adaptation to and resting against the support rod 23 to facilitate mutual assembly of the main frames, as will be described later in connection with fig. 2 and 3.

Iffig 2,, where the assembly of holding frames for the formation of electrolysis cells is shown without the outer parts of the frames, apart from electrical connections, being the upper inlet and outlet passages. Because connections are not shown (shown according to 3), the frames 15 are held together with intermediate gaskets 61 for a fluid-tight installation, so that an electrolysis cell is formed when electrodes and intermediate membranes are placed in place. Frame 5 has walls 16 which delimit the cell created by assembling the frames and prevent leakage into the nearest adjacent cells, 65 and 67. The cell 69 formed by assembling the frames 15 includes an anode

71, a cathode 73 and a membrane 75, which is shown here held by the inner, passive surface of the anode 71. The anode 71 is electrically and mechanically (by welding) connected to the conductor 77> and the cathode 73 is similarly connected to the conductor 79 .Both of these conductors are arranged mainly vertically and have their upper ends led out

through openings, respectively 81 and 83, in the frames and for contact with outer conductors 85 and 87, for the supply of electricity to the cell 69

from the cathode conductor in the cell 67 and. current transfer from cell 69

to the anode conductor in the cell 65. Sealing means &9 and 91 are arranged to ensure a fluid tight connection to prevent gas or liquid loss. As shown for the outgoing anode conductor from the cell 65, the seal comprises a number of compliant neoprene washers or p-rings 63 which are compressed against a spring<p>rin<g>95 by tightening a threaded cap<£e97 in a threaded collar " 99 against a power-transmitting rigid disc 101. The discs or O-rings or possibly fastening devices of another appropriate type, such as wedges, are thus pressed against the anode conductor and hold this tightly in place in order to

prevent fluid loss from the cell.

The conductors 77 and 79, and with them also the electrodes 71 and 73, are held in place by means of support brackets 103 and 105, which by means of screws 107 and 109 are attached to cast projections 111 and 113. The conductors may be welded or otherwise mostly associated with

the brake pads for additional support.

As shown, the cathode 73 fits into a specially arranged opening in the holding frame at the cathode end and is further held in place by contact pressure from the attached gasket when the holding frames are pressed together. In order to improve the anode's rigidity, it is mounted on an angle holder or a series of angle brackets 115, which are held in position 1 relative to the holder frame 15 by means of appropriate means, e.g. screws, binders, press gaskets 61, etc. Use of the angle brackets 115 or intermediate roontering means in the form of a T-shaped "picture frame<*> of the type shown in Fig. 4. and which can be exchanged with the available angle pieces, serves

to provide additional strength and prevent unwanted exfoliation of the anode material.

Membrane 75, which in the embodiment shown is held against the anode 71, is maintained in position by tight fitting in place between the angle pieces 115, the frame parts 117, 119 and 121 and also inserted in suitable channels or grooves such as those which hold the pieces 127 and 129 at 123 and 125, and is held in place in the frame 15 by means of screws. It will be noted that the membrane is not shown completely vertical throughout its extent, but is pressed against the anode to better hold it in place. It is important that the distance between! the electrodes are kept constant to achieve the best possible electrolytic effect, and it is also important that the membrane is kept close to the anode to prevent chlorine gas produced on the anode's active side,

facing away from the membrane, can penetrate between anode and membrane. In a similar way, the distance between membrane and cathode should be kept constant in order not to prevent the removal of the produced hydrogen gas and allow free flow of electrolyte* It will be obvious that in other embodiments according to the invention, in which the membrane is held in position between the two electrodes with clearance between the membrane and the electrodes, it may be desirable for the active side of the anode to face the membrane or for both anode sides to be active. In designs where the membrane is to be placed against the cathode, the cell construction must be modified accordingly.

An important feature of the present invention is the embedding of various organs for supplying and removing fluid from the manufactured electrolysis cells, so that it will not be necessary to drill out such passages in the holder frame. In fig. 2, the only such passage shown is arranged for supplies to the anolyte and catholyte compartment as well as for the anolyte connection or branch. Other connections for inlet and outlet are shown in fig. 3. The anolyte connection 131, which is molded into the holding frame 15, stands through eh passage 133 in connection with the anolyte space 135 in the cell $9. At the end of the passage 133 which opens into the anolyte space, a sealing plug 139 is screwed into place by means of precast threads in the frame 15, or fixed in some other way in the frame, thereby narrowing the passage to the opening which is shown at 139. In the same way path year one adds seal branch 134

(fig. 3) for catholyte in connection through the passage 141 with the catholyte space 143, and is narrowed to the opening 45.

The use of such narrowed openings, which can be replaced by others of different sizes^: allows regulation of the rate of flow into the cell...

In fig. 3, the holding frame 15 and the cell 69 comprise a further, optionally connected supply branch 147, an open branch

151 for chlorine, an outlet branch 149 for hydrogen, outlet connection 153 for sodium hydroxide solution and outlet connection 155 for

diluted anolyte. It will be noted that the overflow passages 157 and 159 lead a respective overflow from the anolyte 161 and the catholyte 163 (behind the membrane) to the outlets for the respective catholyte and anolyte.

The holding device 15 is also equipped with an additional anolyte intake 167 and an additional catholyte intake 165, both of which can be

connected by channels or passages, not shown, to that of the cell

inner. Such passages may be drilled in the frame if that

want to use supplies from the top of the cell, and can be embedded in advance and plugged back in when they are not in use.

If, in a similar way, it is not desired to use bottom feeds, the passages 133 and 141 can be plugged again. The branch 147 can be

useful when it is desired to use several membranes for the formation of

a buffer room, which must be supplied with liquid. As mentioned in connection with

the other additional connections, any passage can be opened or re-plugged depending on the desired application.

Although that. is not particularly shown, it is within the scope of the invention to use "labyrinth-passage" for inlet and outlet strifts,

thereby increasing the resistance in any flow through which current leakage can occur* In the case of liquid supplies through narrowed openings, the resistance will thus be greater and the current leakage reduced, due to greater resistance through the smaller flow cross-section. This will be particularly effective in connection with upper flow supplies, when sufficiently small openings are used to produce

discontinuous liquid supply in the form of drops that fall through chlorine and hydrogen phases over the electrolyte 1 or anode and

the cathode compartment. Such discontinuous liquid supplies naturally constitute very high resistance to current leakage. Such interrupted flows can likewise be produced by withdrawn overflow, with cell fluid and diluted anolyte dripping from the cell electrolyte levels to lower levels to produce discontinuous "flows". The electrolytes can of course also be interrupted by wood

removal from the cell walls to prevent electrical leakage through them.

In this regard, the polymeric construction material for the cell's holding devices is advantageous because it is not electrically conductive.

In fig. 4 shows part of a T-shaped "picture frame" which constitutes

a mounting device in the form of a spacer for holding an electrode, such as e.g. the pulled-out mesh anode 71 in fig. 2 and 3 i

the holding frame; 15. In fig. 2, the framework 115 is shown as an angle piece, while in fig. 4 consists of a T-shape 169 with a horizontal section 171 and an upper vertical top section 173

and eh corresponding lower section 175. The upper part of the T-shaped top section 173 is held in a massive part of the holding frame 15 méns

the lower section retains the extracted hood anode 177.

As shown, one clearance is created between the anode 177 and the membrane 179 which is retained between the upper part of the T-shape and the gasket

181. In the case of varying conditions and locations, the whole thing can of course be arranged so that the clearance becomes larger, smaller or ceases.

By modifying the construction shown, a monopolar cell type can be easily produced simply by changing the electrical connections in such a way that each cell is charged independently with an electrolysis voltage. In a similar way, electrical interconnection between bipolar cells can be done internally instead

on the outside of the cells. Instead of such electrical connections being made on the upper side of the cell, they can also be made along one or the other side wall of the cells. The cell's main separators, which are shown as middle vertical construction parts of the frames, can be replaced with several such parts, which are then preferably made with less thickness to save plastic material. These partition walls can be moved to one or the other side of the holding frame, but it is preferred that they are mainly located in the middle area of the holding frame, as shown in the figures, to divide the relevant cells into roughly equal spaces and to achieve greater strength and dimensional stability for

the cast piastre stem. Instead of using neoprene washers, which are pressed tightly against the electrode conductors by compression of a packing nut, other sealing types can be used, for example individual O-rings, cylinders, hollow conical wedges etc... Such components can be made of neoprene or other suitable polymer materials, e.g.

polytetrafluoroethylene and other fluorine-containing polymers. Instead of using rigidly held members for fixing the membrane and/or the electrodes in place, these members can be elastic, such as e.g. neoptoo tape, which presses the gasket or other parts against the frame during assembly assembly, and which possibly fits into recesses in the frame. Such temporary bodies can be used until the various holding frames are tightly compressed during construction of the cell battery. Instead of using such

means, a cement, such as e.g. neoprene cement, is used to hold the electrodes and membranes temporarily in place. Such a cement should be sufficiently strong to hold the different parts together in correct mutual relation until they are brought into permanent assembly by compression of the different holding frames. During disassembly, the cement will not bind the various parts to such a degree that they cannot be removed without permanent damage.

In certain cases, it may be possible to refrain from using gaskets and instead use mutually adapted parts of polypropylene

the frames which are held together so tightly by means of the compression devices used that the various assembled parts are kept in the desired permanent relation to each other without the need for softer packing material to prevent leaks. In those cases where the neoprene gaskets are omitted, the polypropylene frame's yield strength can be increased by mixing in rubber or other elastomeric materials in the casting mixtures, e.g. 5 to 25% ethylene propylene elastomer.

The cells shown in fig. 2 and 3 form a middle part of a cell assembly. It will be obvious that the end frames of the cell battery must be of a different design, as they each consist of half a cell frame with the outer ends omitted. It is believed that it will not be necessary to describe such a construction in more detail in this connection, as it is believed to be self-evident.

The only construction material for the present holding devices that has been found to be satisfactory in use and can be easily injection molded is polypropylene and more specifically polypropylene Sfrlt with a suitable filler material, such as e.g. can be chosen from the material group consisting of asbestos, raica, calcium silicate, fcalcum and mixtures of these materials. The filler material can be made up of mixtures of two, three or four components, and it is considered particularly advantageous to include both calcium silicate and mica in such mixtures.

In certain cases, certain other recognized equivalent filling materials can also be used. If only one of the aforementioned filling materials is used, the use of calcium silicate is preferable, as this material has the fiber form that is considered most suitable. The polypropylene material referred to can be made of a common resin material intended for injection molding, such as e.g. the unmodified inert-filled or impact-resistant (rubber-modified) polypropylene mateTria.le>T* SV knnnl vmerf unp snui •Fr/r-o-r f 41 -nT-z-i/JitVt-csi» maA Aa anon ole a r\ atr

as listed in the 1973 - 74 Modem Plastics Encyclopedia on p

552. When such resin materials are injection molded in accordance with

the methods described on pages 338 - 410 of the just-mentioned publication, it will thus be possible to produce appropriate gold frames suitable for use in assembling electrolysis cells of the "filter press" type and consisting of 10 - 60 such frames, for the electrolysis of aqueous sodium chloride - solutions.

The frames just described will be able to withstand the influence of the electrolyte and the produced electrolysis products, and will be satisfactorily dimensionally stable during electrolysis processes even with temperature variations between 40 and 95°C and pH variations from 3 to 14. Although it will be possible to use polypropylene resin that contains neither copolymer nor rubber, provided that the desired content of filler water improves the dimensional stability, heat resistance, etc. to a sufficient degree to make the material suitable for chlorine cells in commercial operation, will

usually a mixture of homopolymer and copolymer is preferred, in such a mixture the ratio between these components will normally be from 10 to 40% copolymer, for example of the type marketed by Shell Chemical Company as Shell 7525, and 10 to 40% homopolymer, whereby the total content of these components should be 40 to 90% in the final product. Instead of the homopolymer material, copolymer of this material with other materials can be used, e.g. propylene/acrylic acid copolymers such as Exxon D-561. The proportions of s.lagmodlf ice and rubber can be from 0 - to 20%, as it is preferred that such material is present in any case in a certain small percentage, normally from 3 to 15% of the total product. , When the term "polypropylene" is used here in a general sense, it includes copolymer and copolymers of homopolymer and binders such as lower unsaturated organic acids, e.g. acrylic acid, methacrylic acid as well as other monoalkeno acids with 3 to 6 carbon atoms and equivalent acids, as well as homopolymers.

The filler material, which can consist of talc, asbestos, calcium silicate, mica or a mixture of these materials, preferably comprises calcium silicate fibres, such as e.g. Wollastonite fibers or synthetic calcium silicate fibers, and may preferably also contain mica flakes or small discs. These fibers of calcium-

silicate, whether natural or synthetic, asbestos and talc can come in a large number of commercially available diameters, e.g. from 180 Å for chrysotile asbestos to as much as 1 mm, although the fiber diameters will usually be less than 0.1 mm,

e.g. 0.001 to 0.05 mm. The fiber lengths will normally be in the range of 10 to 1 million times the diameter, preferably

20 to 1000 times, and will usually be in the length range

1 mm to 2 cm. The mica material used will usually be sufficiently finely divided to be able to pass through a sieve with mesh number 40, and preferably through a sieve with mesh number 200 (standard sieve series for OSA). Although these sizes are indicated as clues, it will be obvious that in certain cases it may be desirable to use other material dimensions to achieve special effects.

The proportion of the described inorganic filler material in the present injection molded holder frames is from 10 to 60%, preferably 15 to 50% and preferably 20 to 40%. 50 to 100% of the filling material is made up of calcium silicate fibres. - In certain embodiments of the invention, however, 10 to 30% asbestos will be used together with 90 to 70% polypropylene homopolymer or 5 to 20% mica flakes, 10 to 30% asbestos fiber, 15 to 50% polypropylene homopolymer and 20 to 60% polypropylene copolymer, and such compositions will produce

satisfactory products. Instead of a certain proportion of the calcium silicate, a corresponding proportion of talcum powder can be added,

which can make up 10 to 50% of the first-mentioned material. The calcium silicate and/or talc used can also be treated with silanes or silicones to modify the silanol and siloxane groups of these materials as well as to vary the properties for

the molded polypropylene. Various impact modifier rubber materials of a known type can be used for obvious purposes. The rubber species used may be of any type normally considered applicable for the present purpose within the polymer technique, and mixtures of these materials may also be used, but elastomeric materials based on ethylene or polypropylene are preferred, as materials based on both of these polymers.

Various other additives may be present in small proportions, usually not more than 10% and preferably not more than 5%, in the present molded products, and may e.g. consists of coloring agents, agents to release the mold, and fire-retardant chemicals. Description of such materials and of the polymers, fillers and rubber materials used for the composition of the injection-mouldable polypropylene resin used in accordance with

to the present invention, is described in more detail in the 1973 - 1974 Modern Plastics Encyclopedia as well as in the 1972 - 1973 edition of this encyclopedia, and will therefore not be described in more detail here.

The injection molding of the holding frames takes place in accordance with known processes for casting large objects (the frame dimensions will be about 1.1 m x 1.1 m x 1.1 m x 9 cm, and the distance between anode and cathode in each cell formed by assembling two frames will normally be about 1 cm). A description of such molding can be found in the article entitled: Giant, Thick-Sectioned Plastic Parts Achieved by Nevj Method, in the May 1972 issue of Product Engineering magazine and in an article entitled: Unusual Technique Makes Impossible Parts, in the September issue of Modern Plastics 1971. Appropriate molding methods are detailed in the aforementioned articles: The molded frame produced, although made of thermoplastic materials, will not soften at the present electrolysis cells operating temperature, which can be as high as 95°C. These

cells are in continuous operation for long periods of time, e.g. 6 months, without the appearance of distortions, cracks, material shrinkage, stiffening or other harmful effects on lack of dimensional stability. Without the reinforcing inorganic fillers, the results are not as satisfactory, but the cast retainers are still usable. It is believed that the molding process will tend to cover all fibrous material near the surfaces of the molded article, thus preventing any

exposing such reinforcement material to influence the contents of the electrolytic cell, which contributes to the stabilization of the injection-molded frames. Such products are considered to be superior compared to similar items produced by machining reinforced polypropylene stock materials.

The construction materials for the various components in the available cells have been selected based on requirements for resistance to the special substances present in the environment. The anode, which is preferably made of extruded titanium mesh, although other valve metals can also be used, e.g. tantalum, and which can be coated on its active surface with a noble metal or a noble metal oxide, e.g. ruthenium oxide, will be resistant to chlorine and acidic salt solution in the anolyte compartment. The conductor rods used in such a room are preferably made of copper to achieve good conductivity, and are coated with titanium for resistance to the electrolyte. The mesh portion of the anode has openings of 2 to 700 mm 2 in preferably 100 to 600 mm 2 , and the ratio between the openings and

the nominal one main surface of the anode lies in areas around

25 to 70%, preferably 40 to 70%. The mesh has normal

a thickness from 0.2 to 2.5 mm, preferably 1 to 2 mm, and its strand or snip width is from 0.7 to 2.5 mm; preferably 1 to 2 mm. The anode is preferably activated with ruthenium oxide on its back/namely the side facing away from the membrane.

The cathodes used can be of any electrical type

conductive material which is capable of resisting attack by the cell fluid present, which has a relatively high sodium hydroxide content. Appropriate cathodes are made of steel mesh and connected to a copper conductor, but other cathode materials and conductor materials can also be used, including iron, graphite, lead dioxide on graphite, lead dioxide on titanium and precious metals,

, such as platinum, iridium, ruthenium and rhodium. The precious metals can be applied as surface coatings on conductive substrates, such as e.g. can be made of copper, silver, aluminium, steel or iron. The cathodes used are preferably in the form of a screen or drawn metal mesh, and, like the anodes, will be of a flat or other appropriate design, so that the distance between the electrodes will be approximately the same over the entire active electrode surfaces.

The openings in the cathode screen or mesh will normally make up at least 25% of the surface area on one cathode side, and preferably 30 to 80% of this surface, and preferably around 45 to 65% of the surface.

The opening surface is usually 0.5 to 1000 mm 2 , and preferably 2 to 100 mm<2>When a mesh screen is used, the mesh strands will preferably have a diameter of 0.5 to 3 mm. Both electrodes will

f

normally be held in a completely or mainly vertical position^Cwith a deviation usually no more than 10° from the vertical direction and preferably no more than 5°. The presently preferred cation permselective membrane is of a hydrolyzed copolymer of perfluorinated hydrocarbon and a fluorosulfonated perfluorovinyl ether. The perfluorinated hydrocarbon is preferably tetrafluoroethylene, although other perfluorinated and saturated or unsaturated hydrocarbons with 2 to 5 carbon atoms are also used, of which monoolefin hydrocarbons are preferred, especially those with two to four carbon atoms and most preferably those with two to three carbon atoms, e.g. tetrafluoroethylene, hexafluoropropylene. The sulfonated perfluorovinyl ether most useful is that having the formula FS02CF?CF2OCF(CF3)-CF2QCF=CF2. Such a material, which is designated perfluoro-2-(2-fluorosulfonyletoxy)-propyl-vinyl-ether, will be referred to as PSEPVE in the following and can be modified into equivalent monomers, such as e.g. by modifying the inner perflDorosulfonyletoxy component to the corresponding propoxy component as well as by changing propyl to ethyl or butyl, plus conversion of the substitution positions for sulfonyl,

respectively use of isomers of perfluoro-lower alkyl groups.

However, it is preferable to use PSEPVE.

The method for producing the hydrolyzed copolymer is described in example XVII in US patent no. 3,282,865, while an alternative method is mentioned in Canadian patent no. 849,670, which also describes the use of the finished membrane

in fuel cells, which in this document are designated as electrochemical

cells. Briefly, the aforementioned copolymer can be produced by reaction ay PSEPVE or equivalent material with tetrafluoroethylene or equivalent in Desired volume fractions in water at elevated temperature and pressure for more than 1 hour, after which the mixture is cooled It will then separate into a lower perfluoroether layer and an upper layer of aqueous medium with dispersed content ay the desired polymer. The molecular weight is undeterminable, but the equivalent weight is about 900 to 1600, preferably from 1100 to 1400, and the percentage of PSEPVE or similar compound is about 10 to 30%, preferably 15 to 20% and preferably about 17%. The unhydrolysed copolymer can be compression molded at high temperature and high pressure to produce plate-reel membranes that can vary in thickness

from.0.02 to 0.5 mm. These are then further processed to hydrolyze the present -SO2F groups to -SO3H groups,

by treatment with 10 per cent sulfuric acid or by the methods specified in the above-mentioned patents. Presence,

of -SbjH groups can be determined by titration, as described; in the said Canadian patent document. Further details of the different percentage steps are described in Canadian Patent No. 752,427 and in US Patent No. 3,041,317.

Improved versions of the above described copolymers can

achieved by chemical surface treatment of these, such as e.g. by treatments with the aim of modifying the -S03~ group in the surface.

. The sulfone group can e.g. is changed on the membrane to produce a concentration gradient or can be partially replaced by a phosphorus or phosphonic group. Such changes can be made during the manufacturing process or after the membrane's manufacture. Carried out as a subsequent surface treatment of membKanér, the treatment depth will usually be from 0.001 to 0.01 ram. In certain cases, it may be desirable to convert the sulfonyl or sulfonic acid group on one side of the membrane (such as the anode side) to sulfonamide, which is more hydrophilic, which can be carried out in the manner described in US patent document no. 3,784,399. The membrane can also be in laminated form, which is preferable, as the laminates are of a thickness in the range of 0.07 to 0.17 mm on the anode side and OO. 01 to 0.07 mm on the cathode side, as the respective laminates resp. have equivalent weights in the ranges 1000 to 1200 and 1350 to 1600. A preferred thickness for the laminate on the anode side is in the range 0.07 to 0.12 mm and is preferably around 0.1 mm, while. the preferred thickness of the laminate on the cathode side is 0.02 to 0.07 mm, and preferably about 0.05 mm. Preferred and most preferred equivalent weights are respectively 1050 to 1150 and 1100 .as well as 1450 to 1550 and 1500. The higher the equivalent weight for the individual laminate, the smaller the preferred thickness used, within the given ranges.

In addition to the previously mentioned copolymers and the aforementioned r-^j:: modifications thereof, it has been found that. another type of membrane material is also significantly better than known membrane types for use in connection with the present processes. Although it may appear that tetrafluoroethylene (TFE) polymers which are sequentially styrenated and sulfonated cannot be used for the production of satisfactory cation-active permselective resins for

application in the current electrolysis processes, it has nevertheless been established that perfluorinated ethylene/propylene polymer (FEP).

which are styrenated and sulfonated form a usable membrane. Sulfostyrenated:FEP is surprisingly resistant to hardening and other failure when used under the current operating conditions.

Examples of suitable membranes produced by the described

process are products of RAI Research Corporation, New York,

with designations 18ST12S and 16ST13S, the former being styrenated to 18% and having 2/3 of the phenyl group monosulfonated,

and the latter is styrenated to .16% and has .13/16 of the phenyl groups monosulfonated. To obtain 18% styrene, a simple solution of 17% styrene in methyl chloride is used, and to obtain 16%

styrene ring, a solution of 16% styrene in methylene chloride is used.

The membrane walls will usually have a thickness of 0.02 to 0.5 mm,

preferably about 0.07 to 0.4 mm, and most preferably 0.1 to 0.2 mm. The thickness ranges for the various parts of the previously mentioned laminated membranes have already been indicated. Mounted on a suitable network of polytetrafluoroethylene asbestos, titanium or other suitable network for support, the threads or fibers of the network will usually have a thickness of 0.01 to 0.5 mm, preferably 0.05 to 0.15 mm, which corresponds to a thickness up to the membrane thickness. It will often be preferable that the wire thickness is less than half the membrane thickness, but wire thicknesses greater than the membrane thickness can also be used, e.g. 1.1 to 5

times the membrane thickness. The relevant network, screen or cloth will have an opening ratio of around 8 to 80%, preferably 10 to 70% and most preferably 30 to 70%. The cross-section of the wires will usually be circular, but other shapes, such as e.g. ellipse shape, kszadrat and rectangle shapes can also be used. The supporting network is preferably made up of a screen or a cloth, and even that

can be adhered to," the membrane is preferably fused at high temperature and high pressure prior to hydrolysis of the copolymer in question. The assembly of membrane and network can be clamped or otherwise secured in place in a holder or carrier. For

to maintain the desired distance between the membrane and one or the other, or possibly both electrodes, gaskets and/or vertical wires or strips of suitable plastic material are used, e.g. polytetrafluoroethylene. The cell width will usually be from 0.3 to 1 cm, while the distance from the anode to the membrane will be from 1.5 to 6 mm, but may also be 0 mm. Similar distance specifications also apply to the cathode/membrane distances.

After injection molding of the holding frames at an elevated temperature

and pressure, the frames for cells and cell batteries are assembled, as shown in fig. 1.- 4, When the T-shaped frame or "picture frame" at right angles is used for holding the electrodes and possibly also the membrane, this frame will fooe in a material that is able to resist attack by the surrounding electrolyte. The frame on the anode side will thus often be made of titanium or titanium-coated metal, while the frame on the cathode side will usually be made of mild steel. Similar rules' apply to different casting devices, support brackets etc.

After assembly of the frames into cells and clamping

of these to cell batteries, as shown in fig. 1, the cylinder is filled with electrolyte liquid and the electrolysis process can be initiated. The anode compartment is filled with an almost saturated salt solution with a sodium chloride content of about 25%, and the cathode compartment is filled

with water, which initially contains a small amount of salt

to improve water conductivity. The electrolysis current is switched on,

and the chlorine and hydrogen that are produced in the cells are removed continuously, as chlorine and anolyte - in certain cell structures are separated after removal from the cell count than before this process. Sodium hydroxide is preferably removed continuously during the electrolysis process, but can also be removed after an electrolysis period has been completed. Diluted anolyte is passed through a saturation step,

in which the sodium chloride content. is increased again, after which the liquid is returned to the anode compartment. The sodium chloride content in the withdrawn anolyte is around 22% by weight, while the corresponding percentage in the returned anolyte from the saturation step is around 25%. The anolyte can be given increased acidity and preferably has a pH value in the range 1 to 6, preferably

1 to 5, and most preferably around 3 to 4.5, e.g. 3.9 to 4.3. The catholyte's pH value is naturally around 14 due to

the high sodium hydroxide content. The electrolyte temperature will be kept at less than 105°C, preferably in the range 20 to 95°C and most preferably around 80 to 95°C. The electrolyte temperatures can be regulated by recirculation of

parts of the electrolytes, by regulating supply parts

to the different zones as well as by changing the temperatures of the added liquids. Cooling and other cooling agents can also be used.

The voltage applied per cell will usually be from 2.3

to 5 or 6 volts, and is preferably in the range 3.3 to 4.3 volts. In a preferred method, the voltage can sometimes be as high as 4.5 volts. Ideally, however, the voltage should lie between 3.3 and 4.1 volts. The current density will usually be from 0.2 to 0.5 amperes/cm 2 and preferably around 0.3 amperes/cm 2 The withdrawal of sodium hydroxide from the catholyte compartment takes place at such a rate that the manufactured product is at a concentration of 5 to 45%, preferably 5 to 25% and most preferably around 8 to 12%.

The following embodiment examples will illustrate, but are in no way intended to limit the invention to these embodiments.

If nothing else is stated, all proportions will be stated in parts by weight and all temperatures in °Ci

EXAMPLE 1

A holding frame of the type shown in fig. 2 and 3 are injection molded using the so-called "Eimco Envirotech" method for injection molding large plastic articles at normal elevated molding temperatures and pressures.

The mold is constructed so that passageways, protrusions, ledges, ribs, branches, setting and fastening devices are molded into the manufactured frame. When this is important, threaded or partially threaded holes are also cast to remain available for receiving threaded opening plugs or other parts of the holding frame. The frames are made from a blend of "25% calcium silicate fibres, 10% impact-modifying EP gurami,

37.5% Exxon D-561 propylene-acrylic acid polymer and 27.5% Shell 7525 polypropylene copolymer, after which the manufactured products are examined and tested. It has been found that the frames' surface material is resin-enriched in relation to the other parts of the frame material, so that few or no fibers

of inorganic material is uncovered on the surfaces. When tested in a representative aqueous electrolyte solution suitable for use in one electrolysis cell for the production of chlorine and sodium hydroxide from sodium chloride solutions, the frame will therefore not show any significant weakening, possibly because there are no inward-rattling cracks or points where calcium silicate is exposed. In tests to determine dimensional stability at temperatures within the range of 40 to 95°C, as such temperatures usually occur, during normal electrolysis in this cell type, the holding frames are also found to be stable without faults, cracks, cracks or other irregularities.

The fabricated holder frames are assembled into cells using neoprene gaskets, intermediate titanium "picture frame" holders for the anodes and similar steel holders for the cathodes, nylon screws and polypropylene rectangular nring2 pieces being used to retain the membrane in the frame and' in close contact with the anode. The anode used consists of an extended titanium mesh, while the cathode consists of a steel screen. The anode conductor is made of titanium-coated copper while the cathode conductor is made of copper. The extracted mesh anode is of a thickness of approx. 2.0 mm,

and the string thickness of the netting is approx. 2mm; The mesh openings have a rhombus shape with the longest axis:; in the horizontal direction and makes up approximately 50% of the mesh surface. The distances across the rhombus openings are respectively 0.75 and 1.25 cm. On the side facing away from the membrane, the anode is coated with an active coating of ruthenium oxide of a thickness of 0.07 mm, which is applied in accordance with known standard methods for producing dimensionally stable anodes. The cathode is made of mild steel mesh and has an equivalent diameter of 2.0 mm, as well as an opening proportion of around 50%. ■.■

The membrane consists of hydrolyzed PSEPVE. of the previously described type, and consists of a laminate with a thickness of 0.17 mm, and : of which .2/3 has an equivalent weight of about 1100 and 1/3 has an equivalent weight of about 1500.. The membrane side. with the highest molecular weight

weight faces the cathode, while the side made up of the flatter and thicker layer with low molecular weight is tightly pressed against the anode and stiffened with a support mesh of polytetrafluoroethylene wire with a diameter of about 0.3 mm and which is woven into a screen or cloth with an opening share of around 22%.

The holding frames and cell walls have an extent of about 1.1.x 1.1 m, and the cells have a thickness of about 11 cm. ' The cell walls and other plastic parts in the cell, such as e.g. Fences, walls that form facilities, connections and passages, as well as ledges and channels usually have a thickness of 1 to 3 cm.

Between the cathode and the membrane is arranged a number of spacer cylinders with a diameter of 2.5 ram, and which are used as vertical spacers for every 15 cm along the gap between the membrane and the cathode, the spacers together with the gasket, which is of such a thickness that a gap of about 2.5 mm between cathode and. membrane, keeps the membrane at a fixed distance from the cathode and in close contact with the anode.

When assembling the cell, the different frames are placed

on the temporary staging bodies or stakes, after which

the electrodes are inserted and the membranes are temporarily held in place with the help of adhesive (Velcro or other suitable temporary or permanent seals can also be used) and later with the help of the sealing gaskets. Before tightly joining the different holding frames to each other, the membrane is normally placed in position in the frame by using an appropriate solvent, e.g. glycerol, which prevents drying out of the membrane during assembly of the cell and is of particular use when a large number of cells (35), as in the present case, are to be joined to a cell battery. After assembling the cells in the desired position, namely in a filter press arranger, the cells are pulled together so tightly that liquid leaks are prevented. Fig. 1 shows an assembled cell battery. The cells are connected

then sources for the supply of fluids and electrical power as well as.to:

outlet pipe.

The anode compartments are then filled with an almost saturated acidic salt solution

with a degree of concentration of around 25% and. a pH value of around 4.1, while the cathode spaces are filled with water, to which a small amount of sodium hydroxide is initially added to increase the conductivity of the solution. The electrolysis current is switched on and a current density of 0.3 amperes/cm is created. The voltage drop across each cell is noted during preparation in equilibrium of aqueous sodium hydroxide solutiong, chlorine and hydrogen. Under such conditions, the voltage drop across the cell will be about 4 volts, the current load will be about 3 kijioamps and the total voltage about 12.0 volts direct current. At an operating temperature of around 50°C and other temperatures in the range 85 to 95°C, the cell battery will produce around 3 tonnes of chlorine per day with a chlorine efficiency of around 96% with the addition of acid"]; - Hien's sodium hydroxide efficiency is around 90 % at a concentration of 80 to 100 g/1. The chlorine efficiency without acid addition will be of the order of 90%. After € months of operation under the conditions described above, the cell battery and electrodes? membrane, holding frames, gaskets and fasteners are opened The electrodes and diaphragm were still operable, and the frame showed no sign of significant weakening or deformation, despite the fact that the temperature during normal cell operation, including certain shutdowns, varied in the range of 40 to .95°C. The neoprene cement used

as a binder could still be easily removed from the membrane and frame walls, so that the membrane can be used again. In a modification of the present test, whereby Velcro- •

fasteners were used to hold the membranes in position, •" ;

the membranes could be easily separated and removed without membrane damage.

In an embodiment variant of this test, the used filled polypropylene resin was produced from a resin mixture of 30% of the previously mentioned calcium-silicate fibres. 10% impact-modifying EP gurnmi, 45% Exxon D--561 propylene/acrylic acid copolymer blend

as well as 15% polypropylene copolymer of the type Shell 7525. The results obtained in these cases were almost as good as with the previously mentioned material forms, except that it was noted that the frames were somewhat more susceptible to cracking during

extreme conditions. In a further embodiment, 20% asbestos and 80% polypropylene homopolymer were used. Although the holder frame produced in this way will be very usable, it has in no way proven to be as good as the design described at the outset. An improvement of this construction material, as carried out and tested in the same way as described above, is, however, a mixture of 20% asbestos, 10% mica, 40% homopolymer and 30% copolymer.

EXAMPLE 2

The specified production process in example .1 is repeated for use. of 30% calcium silicate fibres, 10% impact-modifying EP rubber,

45% Exxon D-561 propylene/acrylic acid copolymer resin and 15% polypropylene copolymer of the type Shell 7525, while the membrane material used was unlaminated PSEPVE hydrolyzed copolymer with a thickness of about 0.2 mm in connection with the same type of reinforcing polytetrafluoroethylene screen . In a similar way, the membranes in question were also replaced by membrane types - with the designations 18ST12S and 163T13s with "equivalent thicknesses from RAI Research Corporation.. When using a current density of 0.3 ampere/cm under all these conditions, satisfactory operation of the cells was achieved without damage to the frame material neither from the acidic anolyte nor from the alkaline catholyte. When modifying the cells, the coating of ruthenium oxide on the titanium anodes was extended into an active coating on all anode surfaces, while the distance between cathode and membrane was reduced to 2 mm. conditions, efficient electrolysis was carried out without damage to the frame material. When the electrodes were held in place by means of T-shaped, intermediate head pieces, they were also found to have less tendency to sign than when held only by gaskets, although angle frames will also have satisfactory stiffness.

The cells according to this design example also proved to work satisfactorily when the membranes were fixed against the cathodes or were placed halfway between anode and cathode, as well as fixed

in the desired position using Teflon spacers with a diameter of 1.5 mm.

EXAMPLE 3

Holder frames are produced by the method described in example 1, from the construction material consisting of 35% polypropylene homopolymer, 35% polypropylene copolymer and the rest of the material (without impact modifiers) in the form of mica flakes (mesh size 200), calcium silicate fibers (Wollastonite),

calcium silicate fibers (synthetic), talc or asbestos (chrysotile).

Unmodified homopolymer, copolymer as well as homopolymer and copolymer

in a mixture ratio of 50:50 was also used. Holder frames were

cast in each of these materials. When tested under practical conditions in electrolytes or during electrolysis processes, it was found that the use of calcium silicate fibers in a homopolymer/copolymer mixture gives the best results, and that filled polymers give clearly better physical properties, especially with regard to dimensional stability and heat resistance, than the unfilled ones materials. Although this difference in quality is significant, it will be possible to use all the composite polypropylene frames in commercial operation, and

the non-composite frames will also be practically usable, although of poorer quality.

Frames made of other polymers, such as, for example, polyvinyl-3<bride, polytetrafluoroethylene and polyethylene, will, although they are not normally commercially usable for longer periods of operation, be operable for a shorter time in electrolysis cells,<p>g will be appropriate when, by ordinary injection molding technology, they are made with the various connections etc., passageways, openings, setting,

mounting and fixing devices firmly embedded.

The combination of polypropylene frame and cation-active permselective

membrane of the type designated Dupont Nafion X R-, '. : . the best alternative in terms of dimensional stability, chemical resistance and longevity, especially when the membrane is fixed directly in the frame without intermediate gaskets.

EXAMPLE 4

The manufacturing processes indicated in example 1 are repeated,

but the temperatures, voltages and pH values during the various electrolysis processes are varied within the specified ranges, namely from 20 to 95°C, from 3.3 to 4.3 volts, from 3 to 4.5

anolytic pH value and from 0.2 to 0.4 amperes/• cm 2. The design and placement of the electrodes is also varied over the previously stated areas for open mesh surfaces and opening conditions as well as distances between the electrodes. Under all conditions, satisfactory electrolysis was achieved and the frames proved to be sufficiently stable for commercial operation. No significant problems occurred during the operation of these cells, and the manufacturing costs for the holding frames were reduced to a significant extent due to the easy manufacture of the frames by injection molding. Due to the pre-molded projections, ledges, channels, etc. in the holding frames, the assembly of the components is further facilitated, which can also be carried out in less time and consequently less assembly costs. Electrolysis cells of the present embodiment according to the invention thus represent a significant advance in connection with the electrolysis of aqueous halide solutions.

The invention has been described with reference to special constructions and illustrative examples, but is in no way limited to these, as it will be obvious to those skilled in the field that a large number of similar constructions and processes can be carried out within the scope of the invention.

Claims (12)

1. Coil device made of synthetic organic polymer for enclosing anode and cathode as well as supporting a membrane in an electrolysis cell, characterized in that it is combined with a corresponding other holding device in such a way that the electrodes furthest from each other in the two devices have opposite polarity , forms one electrolysis cell with anode, cathode and an intermediate membrane, each holding device comprising an inlet and outlet for electrolysis fluid in connection with the anolyte and catholyte chamber, so that the cell formed by td composite holding devices has at least one inlet to and one outlet from the anolyte chamber as well as at least one inlet to and outlet from the catholyte chamber, each inlet and outlet being in connection with an outlet that is included in the relevant holding device. 2. Holding device as stated in claim 1, for use during electrolysis of aqueous halide solutions, characterized in that said synthetic organic polymer is polypropylene filled with a number material selected from a material group consisting of asbestos, mica, calcium silicate, talc and mixtures of these materials. 3. Holding device as specified in claim 2, characterized in that it is of such a molded design that the surfaces of the holder have a larger proportion of polymer than the inner areas, thereby improving the device's resistance to the adjacent electrolyte. 4. Holding device as stated in claim 3, characterized in that the construction material contains 15 to 50% calcium silicate fibres, mica flakes or a mixture of these components, and is resistant to deformation during use in an electrolysis cell for the production of chlorine and sodium hydroxide f^ ca aqueous sodium hydroxide solution. 5. Holding device as stated in claim 3, characterized in that it comprises a frame with cast-in outer setting and fixing organs for placing a holding rod which is used for holding a plurality of holding devices assembled into a cell battery of filter press type. 6. Holding device as stated in claim 5, characterized in that further setting devices separate from said setting and fastening means are arranged to support the devices on a number of horizontally extending supports during assembly.. 7. Holding device as stated in claim 3, characterized in that it includes embedded electrodes in the desired position, and which includes mounting pieces for retaining a preliminary mounting component for an electrode.. 8. Holding device as stated in claim 7 <,> characterized by . that the display component has a T shape and is of a rectangular "picture frame" type with the upper part of the T shape arranged horizontally and the vertical leg on top of this, in that a section of the horizontal part is arranged to be attached to the holding device and another part is arranged to be attached to the electrode, whereby the electrode is supported by the T-frame and thereby held in the desired position. 9. Rectangular frame for an electrode in an electrolysis cell for the production of chlorine, sodium hydroxide and hydrogen from aqueous sodium chloride solutions, characterized in that it is designed for attachment to part of the cell's holding device as well as to the electrode to support this, the frame having T -shaped cross section with the T-shaped cross section arranged horizontally and the vertical leg on top of this. 10. Procedure for electrolysis of aqueous sodium chloride solution which is carried out for an electrolysis voltage of 2.3 to 6 volts between an anode and a cathode at a temperature of about 80 to 95°C in a membrane cell, characterized in that the walls of the cell are made of molded polypropylene filled with a filling material selected from a material group consisting of asbestos, mica, calcium silicate, talc and mixtures of these materials. 11. Method as stated in claim 10, characterized in that the surface of the cell walls has a greater proportion of polypropylene than the interior of the walls, thereby improving the resistance of the wall rafts to adjacent electrolyte, in that the filled polypropylene comprises 15 to 50% calcium silicate fibres, mica flakes or a mixture of these materials and is resistant to deformation during operation. 12. Method for producing a holding frame for electrolysis cells for electrolysis of aqueous sodium chloride solutions, characterized in that the holding frame is injection molded from a mixture of polypropylene and filler material selected from a material group consisting of asbestos, raica, calcium silicate, talc, and mixtures of these materials, in the form of molded cell parts for two different cells, each holding device being made for joining with another holding device of the same type to form a complete cell, said holding devices and formed cells being provided with cast-in inlet and outlet passages as well as mounting devices for retention of cell parts.