EP0130215B1

EP0130215B1 - Monopolar, bipolar and/or hybrid membrane cell

Info

Publication number: EP0130215B1
Application number: EP84900568A
Authority: EP
Inventors: Donald W. Abrahamson; Marilyn J. Harney; Andrew J. Niksa; James J. Stewart; Elvin M. Vauss, Jr.
Original assignee: Eltech Systems Corp
Current assignee: Eltech Systems Corp
Priority date: 1982-12-27
Filing date: 1983-12-20
Publication date: 1989-04-26
Also published as: WO1984002537A1; NO163575B; DE3379737D1; AU2438884A; NO843391L; FI77270B; IL70543A0; BR8307663A; GR79738B; FI843345A0; DK406684D0; ATE42580T1; AU565760B2; EP0130215A1; PT77900A; IT8349571A0; IT1197764B; FI843345A; ES8706216A1; FI77270C

Abstract

Monopolar, bipolar, and highbrid filter press electrolytic cells for electrolytic processes utilizing a novel method of introducing and removing electrical energy. The invention contemplates a novel low pressure, high surface contact area connecting means for joining the anode element and cathod element of electrode assemblies. The invention also contemplates a low pressure, high surface contact area contact of the current distributor member to the back plate.

Description

Membrane-type electrolyzers are generally of two distinct types, the monopolar type in which the electrodes of each cell are directly connected to a source a power supply, or the bipolar type in which adjoining cells in a cell bank have a common electrode assembly therebetween, said electrode assembly being cathodic on one side and anodic on the other.
In the past these two designs have been so different that few parts have been interchangeable. Thus, each type of cell has required substantially different components. Further, even when components have been similar they have generally required separate manufacturing tools and processes.
Several designs of both monopolar and bipolar membrane cells incorporate a pair of formed metal pan structures which define the anode and cathode compartment when similar pans are assembled in a facing relationship with a membrane interposed therebetween. Cells of this type are described in U.S. Patents 4,017,375 and 4,108,752, for example.
Because of the rigorous corrosive conditions existing in the electrolytes of both the anode and cathode chambers, it has been necessary to form the anode and cathode pan out of material which is resistant to the respective electrolyte. In most cases, anode pans were formed from titanium or other valve metals or their alloys in sheet form. Similarly, cathode pans were formed from ferrous metals such as steel, stainless steel, or nickel. An example of such pans in a monopolar cell is described in U.S. Patent 4,244,802. However, this patent requires expensive lamination of the highly conductive metal outer layer to the pan.
In a bipolar electrolyzer the electrical connections between the anode/cathode parts of a bipolar element have provided serious design problems. Due to the different corrosive environments of the anode and cathode the parts are made of different materials. Electrically connecting these materials has been done in several ways, each with some inherent disadvantages. For example, the use of titanium/stud bonded plates has had the problem of hydrogen diffusing through the stud plate and hydriding the titanium and thereby destroying the bond. Trimetal (titanium/copper/steel) plates have overcome the hydriding problem, but at high cost. Other forms of mechanical connections have been difficult because of the requirements of internal bolts or fasteners to apply the joint pressure required to make these mechanical connections viable.
In a monopolar electrolyzer in addition to the necessity of corrosion resistance, there is the necessity of conducting current from the external power source into, and out of, the monopolar elements and evenly distributing the current across the active electrode surfaces. In order to carry and distribute this current with low ohmic losses (especially in large area electrodes) a low resistance conductor must be used. This conductor may be made of a large cross section of the corrosion-resistant metal or of a smaller cross section of a metal such as copper or aluminum, for example, which has a specific resistance 5 to 50 times lower than the corrosion-resistant metals. Obviously, these low resistance metals must be protected from corrosion by the electrolytes.
One method used in the past in monopolar membrane electrolyzers has been to use a copper conductor bar with a suitable corrosion-resistant metal bonded or clad to the copper. The disadvantages of this approach are high manufacturing costs, limited shape and size availability, difficult welding, chamber width limited by the width of the conductor bar, interference with electrolyte flow, longer current paths necessary due to conductor spacing causing uneven current distribution to the membrane, problems of sealing the cells where the conductor bars pass through the cell structure, high cost dictating a higher current density and therefore high structural IR losses and the requirement of removal of conductor bars before electrodes can be recoated. (IR is an abbreviation from the Ohm's Law equation, V = IR, which means voltage equals current multiplied by resistance. Thus, by IR, we intend voltage.)
A second approach was to eliminate the copper and carry the current in the corrosion-resistant metal electrode structure. Since the electrical resistance of the corrosion resistant metal (e.g., titanium, nickel, stainless steel) is high compared to copper and aluminum, the voltage loss is increased and the length of the current path must be kept as short as possible (i.e., small electrode dimension parallel to the current path). This then limits the size of an electrode active area, increases the sealing perimeter to active area ratio, and requires many smaller components to create the same total active area. Thus, a larger active area to sealing perimeter would also - provide the additional benefit of a more efficient use of the membrane area (i.e., active area/purchased area ratio is higher). Current distribution and connection to external buswork is also difficult with this approach.
Therefore, this invention aims to reduce the ohmic loss in monopolar or bipolar electrolyzer structures, by reducing the electrical resistance due to structural components and mechanical connection problems, to improve current distribution, to allowfor greater electrode active areas and to decrease the sealing perimeter to active area ratio.
The invention relates to a filter press electrolyzer comprising bulkheads, at least one electrolytic cell having an anode electrode assembly and a cathode electrode assembly and an ion-exchange membrane resiliently engaged therebetween, said electrode assemblies having electrode active areas and back plates of electrically conductive material forming at least a portion of an electrolyte compartment, said cell including sealing means and means for introducing and removing fluids and electrical energy.
A bipolar electrolyzer of this general type is described in US Patent 4 389 289, the teaching of which is acknowledged as prior art by virtue of the laying open to public inspection of its Italian counterpart. This known bipolar electrolyzer comprises frames of inert plastic material provided with means to introduce and remove anolyte and catholyte and the electrolyzer is assembled under pressure in such a way that resilient mats are elastically compressed between the electrode bipolar elements. Hydraulic sealing is provided by 0-rings in each joint of the plastic frames receiving a membrane or a bipolar element. The plates forming the bipolar elements are located inside the plastic frame and hence inside the electrolyzer.
In the filter press electrolyzer according to the invention;

(a) the back plates of the electrode assemblies are formed integrally with pans of electrically conductive material, each of these pans also incorporating peripheral sealing means and, as the means for introducing and removing fluids, integral electrically conductive manifolds,
(b) the electrical energy is passed between two adjacent back plates of the pans of adjacent cells and between the back plate of an end cell and a bulkhead via a current distributor member through mechanical contact joints involving only a pressure connection at a pressure between 0.034 and 6.89 bar, these contact joints being at least substantially as large as the dimensions of the electrode active areas and being separated from cell electrolyte by the back plates of the pans and being located outside the adjacent cells, and
(c) at least some of the electrode assemblies include spring compression members extending between the back plates and the active electrode areas.

This invention provides a structure for membrane electrolyzers which requires little or no retrofitting. As newer and better electrode elements are developed they may be retrofitted without loss of the novel current distributor member and/or the novel monopolar, bipolar, or hybrid cell to cell low pressure contact feature.
This invention also contemplates a cathode assembly design and anode assembly design, usable with a single current distributor member design for both bipolar and monopolar membrane electrolyzers without modification allowing a single production of items to be used in both types of electrolyzers by simply changing the assembly sequence. Because of this unique ability another electrolyzer configuration is contemplated which is a hybrid or combination monopolar and bipolar arrangement of cells within one electrolyzer. The hybrid electrolyzer may comprise a number of sections electrically arranged in a series (i.e. bipolar) fashion or a number of sections electrically arranged in parallel (i.e. monopolar) fashion or any combination of bipolar and monopolar. The advantages are ability to select electrolyzer current to match a convenient or existing rectifier capacity, avoid the shortcomings of bipolar design (such as current leakage, single current path through electrolyzer, high voltage circuits), avoid the shortcomings of monopolar design (reduction in amount of buswork required, lower current circuits). Other advantages and configurations of a hybrid design will be readily apparent to those skilled in the art.
Additional advantages of the invention include the ability to change current distributor members without changing other components, the ability to change cell elements without changing other components, the ability to allow for current density changes optimizing power cost versus capital costs, and the ability to obviate any need for conductor bars.
The present invention also provides for use of the electrolyzer as set out above to produce caustic and halogen from brine.
The monopolar embodiment of the present invention contemplates having current distributor members situated between adjacent cathode assemblies and between adjacent anode assemblies thereby allowing current to be brought into and removed from said anode and cathode assemblies within said cells via a low pressure, low current density, high area connection.
The invention also relates to an electrolyzer having a bipolar filter press electrolytic cell. Cells of this type generally contain bipolar electrode assemblies, and membranes, and are contained within bulkheads connected by tie rods which may or may not be spring loaded. The bipolar embodiment of the present invention contemplates the current distributor member situated between each end plate and a bipolar electrode assembly, with an anode side facing one end plate and a cathode side facing the other end plate, thereby allowing current to be brought into and removed from said cells via the novel low pressure, low current density, high area connection. Further, conducting electrical current from cell to cell is accomplished via a novel low pressure, high surface contact area, low current density mechanical connections between the back plates of the anode and cathode elements of the bipolar electrode assemblies, with an interposed current distributor member.
Also, the invention relates to an electrolyzer having a hybrid combination monopolar and bipolar cells arranged within one electrolyzer. Electrolyzers of this type may be made up of a number of bipolar sections arranged in a monopolar fashion, that is each bipolar section electrically connected in parallel within the end walls of one electrolyzer; or it may be made up of a number of monopolar sections arranged in a bipolar fashion, that is each monopolar section electrically connected in series within the end walls of one electrolyzer; the electrical connections to the electrodes using the low pressure high area, connection between the current distributor members and the back plates of the electrode assemblies. Also, the hybrid embodiment of the present invention contemplates any arrangement of monopoIar and bipolar assemblies within one electrolyzer. The hybrid embodiment contemplates use of the low pressure, high area, low current density connection, with the contact area for said connection substantially the same dimensions of the active area of said electrodes.
Anodes suitable for use in the instant invention comprise an anode back plate (integral with the pan) and an active anode surface area.
In a preferred embodiment, the active anode surface area comprises a foraminous anode of the type comprising a valve metal substrate having an electrocatalytic coating applied thereto of precious metals and/or oxides thereof, transition metal oxides and mixtures of these materials. The anode member is generally planar in form and may be constructed of any foraminous material such as expanded metal mesh, perforated plate or wire screen. This foraminous material has a high surface area and large number of points of contact with the membrane brought about by having a large number of small perforations, for example it may be expanded metal mesh having what is known as "micromesh size" pores. This active anode area is mechanically and electrically attached to the anode back plate preferably by welding, e.g. by resistance welding. Further, the active anode area is preferably attached to the back plate via springs. Thus, the anode may be spring loaded against the membrane to help provide a large number of points of contact. These springs may take many forms and be of various metals, preferably the same metal as used to form the active anode area.
Cathodes for use in the invention comprise a cathode back plate and an active cathode surface area. The cathode back plate is integral with a cathode pan preferably stamped from a planar sheet of nickel, iron, steel, stainless steel, or other similar alloy. The active cathode surface area is likewise made of a material such as iron, steel, stainless steel, or other similar alloy. The cathode active surface area is foraminous in nature and may be a reticulate metal member. It is understood, however, that nickel mesh, steel mesh, etc., and spring loaded systems similar to those described hereinabove in relation to anodes are also suitable. Also, other known types of cathodes for use in zero gap and/or finite gap cells are suitable for use in the invention.
The cathode active surface area is electrically and mechanically attached to the cathode pans. In the case of cathodes fabricated from metal mesh analogous to the mesh anodes described hereinabove welding is the preferred method of attachment. In the case of reticulated cathodes the preferred method of attachment is plating, most preferably galvanic plating; this contact can however be realized solely by mechanical pressure if so desired.
Finally, while the anodes and cathodes have been described in their relationship to the preferred embodiment of the instant invention, namely a membrane gap cell (zero gap cell), whether or not the cell has a finite gap between membrane and electrode is not critical to the present invention. Thus, the present invention is also suitable for use in finite gap cells.
The electrodes of the present invention preferably utilize pans with a single back plate configuration. Thus pans for the anode assemblies and pans for the cathode assemblies are both formed on similar dies and are substantially identical in size and shape, the differences being: the manifolding arrangement used which allows the proper fluids to enter and exit the particular area, i.e., cathode area or anode area; the materials of the pans, the anode pan generally being made of a valve metal preferably titanium or'a a titanium alloy or other metal resistant to corrosive conditions of the anode chamber, and the cathode pan being made of nickel, steel, stainless steel or alloys thereof or other metal resistant to corrosive conditions of the cathode chamber; and the location of the sealing means or groove to contain the sealing means.
The pans are formed to create an integral frame attached to the back plate which forms a chamber for containing electrolytes and electrode active areas. The back plate is generally planar and preferably flexible to allow it to conform to a current distributor member to provide a good electrical connection. The frames are fabricated integral with the pans of solid corrosion resistant metals (anode: titanium or alloys, cathode: steel, nickel, stainless steel, etc.) fabrication being by pressing, drawing, roll forming, welding, extruding, forging, etc. or a combination. The gasketing may be "0" rings, flat gaskets, extruded gaskets or other well known means (U.S. #4,344,633). The frame of the pan may contain an area which may be rigidified by applying a grouting or filler material and also has a face area which may be sealed by flat gaskets, O-rings or other gasket shapes when pans are arranged in facing relation with a membrane therebetween.
One purpose of rigidifying the pans with a grout or filler material is to provide a reinforcement of thin pan metal enabling it to withstand a compressive gasket force without collapse thus allowing economic use of the expensive corrosion resistant metals through the use of thin material, i.e., sheet metal on the order of 0.015 to 0.10 inch (0.038 to 0.254 cm) thick. Other purposes include making handling of the electrodes easier and increasing the internal pressure holding capacity.
Suitable for use as grouting or filler materials are, for example, thermoplastics, elastomers, resins, urethanes, formed metal shapes, and various polyfluorinated materials. Presently preferred are epoxy group and fiberglass reinforced polyester or vinyl esters. The grout or filler materials may be "cast in place" or prefabricated and subsequently placed and/or bonded in place. In either case, it is advantageous to be able to remove these materials relatively easily for electrode recoating processes.
Membranes suitable for use in the invention are generally fluorinated polymeric materials which have surface modifications necessary to perform the ion-exchange function. One presently preferred material is a perfluorinated copolymer having pendant cation exchange functional groups. These perfluorocarbons are a copolymer of at least two monomers with one monomer selected from a group including vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoro(alkylvinyl ether), tetrafluoroethylene and mixtures thereof.
The second monomer often is selected from a group of monomers usually containing an S0₂F or sulfonyl fluoride pendant group. Examples of such second monomers can be generically represented by the formula CF₂= CFR_lS0₂F. R1 in the generic formula is a bifunctional perfluorinated radical comprising generally 1 to 8 carbon atoms but upon occasion as many as 25. One restraint upon the generic formula is a general requirement for the presence of at least one fluorine atom on the carbon atom adjacent the -S0₂F group, particularly where the functional group exists as the -(-S0₂NH)mQ form. In this form, Q can be hydrogen or an alkali or alkaline earth metal cation and m is the valence of Q. The R₁ generic formula portion can be of any suitable or conventional configuration, but preferably the vinyl radical comonomer joins the R₁ group through an ether linkage.
Such perfluorocarbons are available commercially such as through E.I. duPont under the Trademark NAFION. Perfluorocarbon copolymers containing perfluoro (3,6-dioxa-4-methyl-7- octenesulfonyl fluoride) comonomer have found particular acceptance in C1₂ cells. Where sodium chloride brine is utilized for making chloralkali products from an electrochemical cell, it has been found advantageous to employ membranes having their preponderant bulk comprised of perfluorocarbon copolymer having pendant sulfonyl fluoride derived functional groups, and a relatively thin layer of perfluorocarbon copolymer having carbonyl fluoride derived functional groups adjacent one membrane surface. It is presently preferred to have these membranes further modified with inorganic surface treatments which impregnate the surface of said membranes with metallic materials such as, i.e. Zr0₂, and Ti0₂ to help prevent gas bubble buildup along the membrane electrode interface. By removing this problem the cell is able to operate more efficiently. A more detailed description of this type of membrane modification can be found in U.S. Patent No. 4 421 579.
The present invention utilizes a novel current distributor member for introducing current into or removing it from the cells. It is used in monopolar cells, in bipolar cells and in hybrid cells to connect to external power sources or other sections of the electrolyzer. This results in the ability evenly and with lower IR losses to introduce and to distribute current into and out of the cell without constriction of cell size due to the IR loss of the anodes and cathodes. This is possible by utilizing current distributor members having dimensions of electrical contact that are substantially the same as the dimensions of the electrode assemblies. It is clear that the current distributor members may be dimensionally greater in, size than the electrode assemblies. However, since this would not increase the contact area it would provide no advantage in relation to lowering to IR loss. Since copper and aluminum are far better conductors of current than valve metals and certain stainless steel alloys, cells may be greater in size while maintaining an acceptably low IR loss level. It is to be understood, however, that while copper and aluminum are preferred because of the weight and cost savings and lower volume of metal needed, any conductive metal will work if enough volume is provided to carry the necessary current with acceptable IR losses. In addition, this novel current distributor member allows for higher current densities to be used within the cell and therefore allows for greater caustic and chlorine production from a cell that must be run at a lower current density per unit area.
The current distributor member is generally a solid copper planar sheet but may also be any suitable conductor having sufficient cross sectional area to carry the required current with low IR loss and good current distribution. Suitable examples of these other conductive metals include, for example, nickel, iron, steel, as well as alloys of these metals and alloys of copper and aluminum.
In monopolar electrolyzers and monopolar cell assemblies in hybrid electrolyzers the current distributor members are placed between adjacent anode pans with the back side of each pan facing the current distributor member to form a single monopolar anode element. Likewise, current distributor members are placed between adjacent cathode pans with the back side of each pan facing the current distributor member to form a single monopolar cathode element.
In bipolar electrolyzers and in bipolar sections of hybrid electrolyzers there is a current distributor member between adjacent cell back plates of the bipolar electrode assembly, an anode side of the current distributor facing one back plate and a cathode side facing the other back plate.
The current distributor members protrude past the side of the electrolyzer on one side only. For example, in monopolar electrolyzer the members between adjacent anode assemblies extend on one side while the members between adjacent cathode assemblies extend on the opposite side. This extension is then used to connect via a bus system, to the power source or other sections of the electrolyzer.
In addition to being the preferred planar sheets, which may be metal clad planar sheets said current distributor members may also be sheets having calendered, dimpled, corrugated or serrated surfaces or having an interface material attached to, or inserted between, said surfaces as well as having conductive compounds, i.e., greases containing particles of conductive metals distributed therein on their surfaces. The reason for these surface modifications, if used, is to improve the electrical contact between the current distributor members and the anodes and/or cathodes by ensuring that the highest amount of mechanical surface contact is maintained and contact resistance is minimized between the current distributor members and anodes or cathodes. Further, it is contemplated that the thickness of the current distributor members may vary across the length of the member based on the current and voltage requirements, to reduce cost. It is understood that if tapered members are used the taper of the anode members and the taper of the cathode members are reversed so as to provide a parallel stack of cells to be compressed between the bulkheads. Finally, the current distributor member may also be used to provide structural support for the cell.
For monopolar, bipolar and hybrid configurations, the current distributor member is held in mechanical contact with an electrode assembly back plate over a substantial portion of the total area by hydraulic or static pressure of the electrolytes in the pans, by the spring pressure of the anode and/or cathode structures and by being compressed in the filter press arrangement by the bulkhead-tie rod assemblies. The electrical connection is made outside the cell so that it is separated from the electrolyte via the back plates of the pans. The back plate restrains the electrolyte so that the electrolyte does not contact the electrical connection. The pressure applied is in the range of from about 0.5 to 100 psi, (0.034 to 6.89 bar), preferably in the range of from about 1 to 20 psi (0.069 to 1.376 bar). Increased pressure reduces contact resistance. Normally for known mechanical connections of electrical joints (i.e., bus work) a low area, high pressure (i.e., 500-5000 psi) (34.48 to 344.8 bar) joint is used to get a low specific joint resistance and current densities across the joint are high (i.e., 200-2000 asi) (31-310 amps/cm²) with the joint contact voltage loss equal to the product of specific resistance times current density. Also, other factors such as "current streamline" effects enter into the total voltage loss across this type of mechanical joint. In the case of the contact of the current distributor to the back plate of the present invention, the joint pressure is lower (1-20 psi) (0.069 to 1.376 bar) yielding a higher specific resistance, but the joint area is very large yielding a low current density (i.e., 0.5 to 10 asi) (0.0775 to 1.55 amps/cm²) and thus a low ohmic loss across the joint. For example, a copper to titanium joint, as might be used on the anode, operating at 3 asi (0.465 amps/ cm²) with a pressure of 5 psi (0.3448 bar) (specific resistance of 3.5 x 10-³ ohm-in²) (22.58 x 10-³ ohms/cm²) would have a voltage loss of 1.05 x 10-² volts, and a copper to nickel joint, as might be used on the cathode, operating at 3 asi (0.465 amps/cm²) with a pressure of 5 psi (0.3448 bar) (specific resistance 7.7 x 10-⁵ ohm-in^z) (49.68 x 10-⁵ ohms/cm²) would have a voltage loss of 2.33 x 10-⁴ volts. The difference between copper to titanium and copper to nickel is due to differences in contact resistance due to different materials and different surface preparations, oxides, etc. Modifications to the metal surfaces or the use of interface materials to take advantage of lower contact resistance of various metals is further discussed hereinbelow.
A thin pan is preferred because it is flexible and conforms to the current distributor member in a connection creating a large contact area. Additionally, materials such as conductive reticulates (sponge metal), Multilam (Trademark), conductive wools and the like may be used as an interface in contact with the current distributor member or back plates to increase the contact area. Because contact resistance is also dependent upon the materials in contact, the distributor member and/or the pan may be coated with a material as an interface to make the contact resistance lower. Suitable examples include coatings and plating of metals such as silver, gold, platinum, nickel and copper by methods such as plasma spraying, painting, flame spraying, sputtering, vapor deposition and combinations of the above.
In addition, sealing means such as a gasket may be placed between the distributor member and pan. This sealing means is located so as to _'be around the perimeter of the current distributor member and anode assembly or cathode assembly pan to prevent entrance of corrosive elements which could oxidize the contact and thereby increase resistance. The sealing means may also employ a conductive and/or anti-oxidation material.
The key to the success of the use of these connections is the fact that the low current densities required, i.e., approximately 0.5 to 10 asi (0.0775 to 1.55 amps/cm²), with pressures at the joint of approximately less than 1 to about 100 psi (0.069 to 6.89 bar) results in low IR losses at a high resistance junction (joint).
The bulkheads, tie rods and associated equipment used to hold the cells in place in the electrolyzer and seal the cells are those generally well known in the art. They are generally the same size as the cells to be pressed between said bulkheads and generally are constructed of heavy gauge steel. The bulkheads and tie rods may or may not be electrically isolated from the cells as is preferable in each particular use.
Introduction of brine, caustic, water and removal of hydrogen, chlorine, caustic, anolyte and catholyte is accomplished by integral manifolding. The integral manifolding is constructed of titanium metal or nickel metal as the case warrants for particular inputs and outputs, inlets and outlets, and said integral manifolding is electrically isolated from the individual cells preferably by being physically spaced so as not to be in contact with the cells of polarity not desired in that particular manifold line.
The bipolar filter press zero gap electrolyzers of the present invention, for example, are configured such that an anode assembly pan back plate is in back-to-back facing relationship with a cathode assembly pan back plate. Between the back plates is a current distributor member. On either exposed, opposite active electrode face of said anode assemblies and said cathode assemblies is a membrane which is in physical contact with said exposed active electrode faces. On either side of the exposed surfaces of said membranes are opposite polarity active electrode faces.
The monopolar filter press zero gap electrolyzers of the present invention are configured such that two anode pan back plates are in back-to-back facing relationship and are separated by a current distributor member. On each exposed, opposite active anode face of said anodes is a membrane which is in physical contact with the active anode face. On the other side of the membranes are cathode assemblies in pairs back-to-back with current distributor members in between each pair. This stack assembly is repeated until the desired number of cells is reached.
Bulkheads are provided for either the monopolar or bipolar electrolyzer on either end with connecting tie rods and associated paraphernalia to contain the so-produced cells. Sealing of the stack is provided by either gaskets or O-rings, the appropriate face or channeling necessary for gaskets and/or O-rings being provided in the respective anode and cathode assembly pans.
The present invention is more fully described by reference to the appended drawings and the discussion hereinbelow. In the drawings:

Figure 1 is an exploded view of a monopolar filter press electrolyzer of the invention; .
Figure 2 is an exploded view of another monopolar electrolyzer;
Figure 3 is a plan view in partial cross section of the assembled monopolar filter press electrolyzer of the invention;
Figure 4 is a cross sectional view of an integral manifold;
Figure 5 is a side elevational and top view of a monopolar cathode assembly;
Figure 6 is a side elevational and top view of a monopolar anode assembly;
Figure 7 is an exploded partial cross sectional view of an integral manifold assembly;
Figure 8 is an exploded view of a bipolar filter press electrolyzer of the invention;
Figure 9 is an exploded view of one version of a hybrid filter press electrolyzer of the invention;
Figure 10 is an elevational view in partial cross section of a bipolar section of a filter press electrolyzer of the invention;
Figure 11 is an elevational view in partial cross section of a monopolar section of a filter press hybrid electrolyzer of the invention;
Figure 12 is a plan view in partial cross section of one version of a hybrid filter press electrolyzer of the invention;
Figure 13 is a side elevational view of a cathode pan; and
Figure 14 is a side elevational view of an anode pan.

Figures 1 and 3-7 relate to a monopolar embodiment of the present invention. Figure 1 shows a monopolar electrolyzer (1) consisting of a plurality of vertical anode assemblies (4) and cathode assemblies (5) in physical contact with permselective membranes (6) (zero gap). Also shown are integral discharge and inlet manifolds (100). Additionally bulkheads (2) and tie rods (3) are illustrated.
Figure 2 shows an exploded view of another filter press electrolyzer as used in Example 1 and Example 2. As in Figure 1 the electrolyser (1) comprises bulkheads (2), tie rods (3), anode assembly (4), cathode assembly (5) and membrane (6).
Figure 3 shows a partial cross sectional plan view of the electrolyzer of Figure 1 in its assembled condition. This view shows anode pans (10) located on either side of current distributor member (30). Likewise cathode pans (20) are located on either side of current distributor members (30). The anode pans (10) have active anode areas (11) attached to said pans via springs (12) and also incorporate a sealing means (13). Similarly the cathode pans (20) have active cathode areas (21) attached to them, in this particular case reticulate bodies without springs, and also utilize a sealing means (23). These anode and cathode assemblies are alternated and are in contact with and separated by membranes (6). Spacers (40) are utilized as necessary to maintain proper cell dimensions. Finally, grouting material (50) for making the pans more rigid is shown.
Figure 4 is a cross sectional view of one embodiment of integral manifolding showing the position of the integral manifold (100) with relation to membranes (6), spacers (40), cathode assemblies (5) and anode assemblies (4). Integral manifold (100) is comprised of spacer (101), sealing means (103), manifold sealing means (106) and manifold sections (107).
Figure 5 shows a monopolar cathode assembly (5) in greater detail. Shown are two cathode pans (20) (see the top view), active cathode area (21), peripheral sealing means (23), current distributor member (30) and integral manifolds (100). Similarly, Figure 6 illustrates a monopolar anode assembly (4) comprising two anode pans (10) (see the top view), active anode area (11), peripheral sealing means (13), current distributor member (30) and integral manifolds (100).
Figure 7 represents a detailed view of an integral manifolding embodiment showing an anode assembly (4), a cathode assembly (5) and an integral manifold (100). Specifically, the integral manifold (100) is shown as comprising spacer section (101), sealing means (103), coupler (104) and manifold sections (107). Also shown are current distributor member (30) and spacer (40). Obviously, the manifold sections (107) and spacer sections (101) of the cathode manifolding are reversed for the anode manifolding.
Figure 8 shows a bipolar electrolyzer (32) consisting of a plurality of vertical anode pan assemblies (35) and cathode pan assemblies (36) which in the assembled condition are in physical contact with permselective membranes (37) (zero gap). A single terminal current distributor member (61) is located on each end of the electrolyzer and further current distributor members, referred to as interface materials (38), are located between and in contact with the backs of adjacent anode and cathode pan assemblies. Also shown are integral discharge and inlet ports (131). Additionally bulkheads (33) and tie rods (34) are illustrated.
Figure 9 shows a preferred embodiment of one version of a hybrid electrolyzer of the present invention. As in Figure 8 the electrolyzer (32) comprises bulkheads (33), tie rods (34), anode assemblies (35), cathode assemblies (36), membranes (37), intermediate current distributors referred to as interface material (38), terminal current distributors (61) and integral discharge and inlet ports (131).
Figure 10 shows a partial cross sectional elevation view of Figure 8. This view shows anode pans (35) and cathode pans (36). Located on either end of the electrolyzer is a single terminal current distributor member (61). The anode pans have active anode areas (42) attached to said pans via springs (43) and also incorporate a sealing means (44). Similarly the cathode pans (36) have active cathode areas (52) attached to them, in this particular case reticulate bodies without springs, and also utilize a sealing means (54). These anode and cathode assemblies are alternated and are in contact with and separated by membranes (37). Intermediate current distributors referred to as interface materials (38) are,utilized to help maintain proper electrical contact. Finally, grouting material (81) for making the pans more rigid is shown. It is understood that as many cells as desired may be placed between the bulkheads, in a variety of monopolar and/or bipolar sections arranged and connected together in an electrolyzer.
Figure 11 shows a partial cross sectional elevation view of a monopolar electrolyzer or a monopolar section of a hybrid electrolyzer. This view shows anode pans (35) located on either side of current distributor member (61). Likewise cathode pans (36) are located on either side of current distributor members (61). The anode pans have active anode areas (42) attached to said pans via springs (43) and also incorporate a sealing means (44). Similarly the cathode pans (36) have active cathode areas (52) attached to them, in this particular case reticulate bodies without springs, and also utilize a sealing means (54). These anode and cathode assemblies are alternated and are in contact with and separated by membranes (37). Spacers (71) are utilized as necessary to maintain proper cell dimensions. Finally, grouting material (81) for making the pans more rigid and insulators (91) are shown.
Figure 12 shows a partial cross sectional plan view of the electrolyzer of Figure 9 in the assembled condition. This view shows anode pans (35), and cathode pans (36) as well as membranes (37), interface materials (38), current distributor members (61), insulators (91), grouting material (81), cathode active area (52), cathode sealing means (54), anode sealing means (44), anode active areas (42) and anode springs (43).
Figure 13 shows a detailed view of a cathode pan assembly (36) with cathode pan (51), cathode active area (52), peripheral sealing means (54) and integral discharge and inlet ports (131). Figure 14 shows a detailed view of an anode pan assembly (35) with anode pan (41), anode active area (42), sealing means (44) and integral discharge and inlet ports (131).
The present invention is further illustrated by the examples which follow.

EXAMPLE 1

This example illustrates the contact resistance and low voltage drop between the current distributor member and the anode as well as between the current distributor and the cathode.
An electrolytic cell, as illustrated in Figure 2, having an active surface area of 10 inches (25.4 cm) by 30 inches (76.2 cm) was assembled utilizing a spring-loaded titanium DSAT^M anode and a reticulate nickel cathode. The cell also utilized a NAFION" membrane separator between the anode and cathode. The cell was run at zero-gap. There was a copper reticulate member positioned at the anode pan back surface and a copper current distribution member positioned against the copper reticulate. There was also a copper current distributor member positioned against the cathode pan back surface. Electrolube, a conductive grease, was utilized between the anode pan back and copper current distributor as well as between the cathode back pan and copper current distributor.
At 2 asi (0.31 amps/cm²), contact resistance between the current distributor member and the anode pan back surface was approximately 10 mV and approximately 3 mV between the current distributor member and the cathode pan back surface. These contact resistances were measured using a millivolt meter from the back of the pan to the current distributor member.

EXAMPLE 2

This example shows the usefulness of a reticulate interface material.
The 300 square inch (1935 cm²) monopolar cell was operated with a spring-loaded mesh DSA^TM coated anode and a reticulate nickel cathode with a NaCI electrolyte feed. The membrane was a NAFION^RTM ion exchange membrane. The cell was run both with and without a copper reticulate material, of substantially the same surface area as the active membrane area, placed between the back plate of the titanium anode pan and the copper metal current distributor member, also having a surface area substantially the same as the active membrane area. At a current density of 2 asi (0.31 amps/cm²), the contact resistance between the back plate of the anode pan and the current distributor member was 64 mV without the copper reticulate interface material and 12 mV when the copper reticulate interface material was utilized. The benefit of using this embodiment of the invention to reduce contact resistance is thus clearly demonstrated.

Claims

1. A filter press electrolyzer comprising bulkheads (2), at least one electrolytic cell (1, 32) having an anode electrode assembly (4, 35) and a cathode electrode assembly (5, 36) and an ion-exchange membrane (6, 37) resiliently engaged therebetween, said electrode assemblies having electrode active areas (11,21) and back plates (10, 20) of electrically conductive material forming at least a portion of an electrolyte compartment, said cell including sealing means and means for introducing and removing fluids and electrical energy, characterized in that:

(a) said back plates (10, 20) of the electrode assemblies are formed integrally with pans of electrically conductive material, each of said pans also incorporating peripheral sealing means (13, 23) and, as said means for introducing and removing fluids, integral electrically conductive manifolds (100),

(b) the electrical energy is passed between two adjacent back plates (10, 10; 20, 20; 10, 20) of the pans of adjacent cells and between the back plate of an end cell and a bulkhead (2) via a current distributor member (30, 61) through mechanical contact joints involving only a pressure connection at a pressure between 0.034 and 6.89 bar, said contact joints being substantially as large as the dimensions of the back plates (10, 20), and being separated from cell electrolyte by the back plates (10, 20) of the pans and being located outside the adjacent cells, and

(c) at least some of said electrode assemblies include spring compression members (12), extending between said back plates and the active electrode areas.

2. The electrolyzer according to claim 1, characterized in that said electrode assembly pan includes a portion rigidified by grouting (50) or a filler material.

3. The electrolyzer according to claim 1 or 2, characterized in that the electrical contact joint connects a cathode back plate (20) with an anode back plate (10).

4. The electrolyzer according to claim 1, 2 or 3, characterized in that said current distributor member (30, 61) is in the form of a solid planar metal sheet made from nickel, iron, steel, aluminum, copper or alloys thereof.

5. The electrolyzer according to claim 1, 2 or 3 characterized in that said current distributor member (30, 61) provides structural support for said cell (32).

6. The electrolyzer according to claim 5, characterized in that each current distributor member protrudes past the side of the cell on one side only.

7. The electrolyzer according to claim 4, 5 or 6, characterized in that said current distributor member (30, 61) has a coating of conductive material on sides which are in contact with said back plates.

8. The electrolyzer according to claim 4 or 5, characterized in that said current distributor member (30, 61) is a metal clad planar sheet.

9. The electrolyzer according to claim 4, 5, 6 or 7, characterized in that said current distributor member (30, 61) and said back plates have in contact with their surfaces an interface material selected from sponge metal, conductive wools, conductive metal sheets or combinations thereof.

10. The electrolyzer according to any preceding claim, characterized in that said electrode assemblies including spring compression members are anode assemblies comprising a valve metal back plate (10) and a valve metal electrode substrate having an electrocatalytic coating thereon (11).

11. The electrolyzer according to any one of claims 1 to 9, characterized in that said electrode assemblies including spring compression members are cathode assemblies comprising a back plate (20) and a cathode surface (21) made of nickel, iron, steel or stainless steel.

12. The electrolyzer according to any preceding claim, characterized in that said current distributor member (30, 61) conducts current to or from the electrodes from a source exterior to said electrolyzer or from another section of the electrolyzer through an external path.

13. The electrolyzer according to claim 12, characterized in that it comprises at least one monopolar electrolytic cell in which the current distributor members are positioned between back plates of adjacent electrode assemblies of the same polarity.

14. The electrolyzer according to claim 12, characterized in that it comprises at least one bipolar electrolytic cell in which said current distributor member (30, 61) is between the back plates of the anode (35) and cathode (36) assemblies of at least one bipolar assembly.

15. The electrolyzer according to any preceding claim, characterized in that it comprises, in combination, monopolar and bipolar cells arranged between said bulkheads.

16. The electrolyzer according to any preceding claim, characterized in that said integral manifolds contain a spacer (101), a sealing means (103), manifold sealing means (106) and manifold sections (107).

17. An anode assembly for use in a filter press electrolyzer according to any one of claims 1-16, wherein said anode assembly comprises a back plate (10) forming at least a portion of an anolyte compartment, said back plate being integral with a pan having peripheral sealing means (13) and integral electrically conductive manifolds (100) comprising discharge and inlet ports, an active anode area and resilient spring compression members (12) extending within said anolyte compartment between said back plate (10) and said active anode area (11), the anode assembly having a front face made up of the active anode area (11) and the peripheral sealing means (13) of the pan for facing a membrane (6, 37) and an opposed cathode assembly including an identical back plate integral with a pan to make up an electrolyte compartment, the rear face of the anode assembly back plate (10) external of the electrolyte compartment being adapted to form, with a current distributor member (30, 61), and with the rear face of another anode assembly or of a cathode assembly including an identical back plate integral with a pan or with a bulkhead, said mechanical contact joint involving only a pressure connection, said contact joint being substantially as large as the dimensions of the back plate (10).

18. The anode assembly of claim 17, wherein said back plate of the anode is made from a valve metal while said active anode area comprises a valve metal substrate having an electrocatalytic coating thereon.

19. A cathode assembly adapted for use in a filter press electrolyzer according to any one of claims 1-16, wherein said cathode assembly comprises a back plate (20) forming at least a portion of a catholyte compartment, said back plate being integral with a pan having peripheral sealing means (23) and integral electrically conductive manifolds (100) comprising discharge and inlet ports, an active cathode area and resilient spring compression members extending within said catholyte compartment between said back plate and said active cathode area, the cathode assembly having a front face made up of the active cathode area and the peripheral sealing means (23) of the pan for facing a membrane (6, 37) and an opposed anode assembly including an identical back plate integral with a pan to make up an electrolyte compartment, the rear face of the cathode assembly back plate (20) external of the electrolyte compartment being adapted to form, with a current distributor member (30, 61 and with the rear face of another cathode assembly or of an anode assembly including an identical back plate integral with a pan or with a bulkhead, said mechanical contact joint involving only a pressure connection, said contact joint being substantially as large as the dimensions of the back plate (20).

20. The cathode assembly of claim 19, wherein said active cathode area comprises a cathode surface made of nickel, iron, steel or stainless steel.

21. Use of the filter press electrolyzer according to any one of claims 1-16 for electrolysis of brine.