MXPA99007975A - Separation of oxygen from a gas containing oxig - Google Patents

Abstract

An electrochemical device for separating oxygen from an oxygen-containing gas comprising a plurality of flat electrically conductive solid electrolyte plates and electrically conductive, gas-impermeable interconnects assembled in a multiple cell stack. The electrically conductive anode and cathode material is applied to opposite sides of each electrolyte plate. A gas-tight denode seal is joined between the anode side of each electrolyte plate and the anode side of the adjacent interconnection. A regulating electrode, applied to each anode side of each electrolyte plate between the anode seal and the anode edge, eliminates the denode seal failure by maintaining the anode seal power density of 24 hours below approximately 1.5æW / cm2. A gas-tight seal is applied between the cathode sides of each electrolyte plate and the adjacent interconnect so that the anode and cathode seals are radially offset on opposite sides of the plate. The combination of regulating electrodes and displaced seals is particularly effective in eliminating deo seal failure

Description

SEPARATION OF OXYGEN FROM A GAS CONTAINING BRIEF OXYGEN DESCRIPTION OF THE INVENTION The ion-conductive inorganic oxide ceramics of certain compositions transport or permeate ions at high temperatures and this phenomenon is the basis for practical applications in fuel cells, analysis and monitoring of gases and the separation of gas mixtures. In a number of such practical applications, oxygen ions migrate as current under a gradient of potential imposed through an electrolyte conducting oxygen ions from the cathode side, where the oxygen ions are generated by oxygen reduction or other gases, towards the anode or oxygen side, where the oxygen ions are consumed to form oxygen or other gases. The solid oxygen ion conducting electrolytes can be constructed in tubular, flat plate, and honeycomb or monolithic multi-cell configurations. The flat plate configuration, in which a plurality of flat electrolytic cells are stacked to operate in electric series, is favored in many applications by the ease of assembly and compact dimensions. The practical application of ion conducting systems for gas separation, regardless of the configuration of the design, requires that the cells operate under differential pressure and / or differential gas composition between the feed side (cathode) and the permeate side (anode). In the separation of oxygen from an oxygen-containing gas, for example, the gas composition and / or the pressure of the oxygen-containing feed gas and the spent oxygen discharge gas (also defined as non-permeate gas) may differ. of the pressure and / or gas composition of the oxygen produced at the anode (also defined as permeate gas), depending on the stacking design and the product requirements. The gas tight seals between the selected structural components of the system are therefore required to maintain the purity of the product gas, whether the product is a spent oxygen discharge gas or high purity oxygen produced at the anode. An oxygen ion conducting system having a disk or flat stacking configuration is described in US Patent 4,885,142 in which an oxygen-containing gas is introduced through the axial feed ports, flows radially through the disks electrolyte stacks and is discharged through an axial discharge port preferably centrally located. The oxygen product is withdrawn through a separate series of axial discharge ports. The feed and product gases are separated by interengaged portions of the disk assembly, which are described to form a substantially sealed relationship. Stacking operates without differential pressure through the fabrics and the use of sealants is not described. A similar system is described in the J.W. Suitor et al., Entitled "Oxygen Separation From Air Using Zirconia Solid Electrolyte Membranes" in Proceedings of the 23rd Intersociety Energy Conversion Conference, Vol. 2. ASME, New York, 1988, p. 273-277, and of D.J. Clark et al entitled "Separation of Oxygen by Using Zirconia Solid Electrolyte Membranes" in Gas Separation and Purification, 1992, Vol. 6, No. 4, p. 201-205. U.S. Patent 5,186,806 discloses a planar solid electrolyte cell configuration in which the alternating plates and the gas distribution support members are stacked in series. In one configuration the plates are made of non-porous ion conductive material and the support members are made of non-porous electrically conductive material. A series of ports and flanges in the support members coincide with ports in the electrolyte plates to produce a flow configuration in which the supply air flows radially through the cathode sides of the electrolyte plates in a direction toward in, and oxygen-free air is withdrawn axially through a centrally located conduit formed by congruent ports in the electrolyte plates and support members. The oxygen formed on the anode sides in the electrolyte plates flows radially outward and is withdrawn through a plurality of axial conduits formed by separate congruent ports in the electrolyte plates and the distribution members. The sealing between the oxygen side and the sides of the feed gas of the stacking components according to the description is achieved by direct contact between the electrolyte plates and the flat flanges on the support members, and also on the periphery Stacking by contact between the continuous flat raised rings on the supporting members and the flat electrolyte plates. Sealant is not disclosed in the seal regions formed by direct contact between the regions of the support members and the electrolyte plates. The seal regions formed by the flanges in contact with the anode side and the cathode side of each electrolyte plate are radially and circumferentially out of phase, although the corresponding peripheral seals are congruent or directly opposite. An ion conducting device having a plurality of electrolyte plates in a stacked configuration is described in U.S. Patent 5,298,138 in which the electrically conductive support interconnections are not used. The electrolyte plates are separated by alternating spacers made of electrolyte material that are bonded near the edges of the plates by glass sealant to allow cross-flow feeding. While this stacking design is simplified by eliminating the interconnections, the electrolyte plates are not supported in the central region, which allows operation only at very low pressure differentials between the anode and cathode sides of the cells . European Patent Application Publication No. 0 682 379 A1 discloses a flat electrochemical device in series for gas separation in which the alternate electrolyte plates and the electrically conductive interconnections are assembled in a stacking configuration. The anode and the cathode in electrical contact with the opposite sides of each electrolyte plate are radially coextensive, ie congruent. The interconnections contain certain channels designed so that the feed gas flows through the cathode side in the cross flow mode and the oxygen formed on the anode side is withdrawn in a crossflow mode in a direction of flow, perpendicular to the flow of feed gas. The interconnections and the electrolyte plates are connected by sealed glass areas parallel to the channels in the interconnections. The portions of the anode and cathode seals are directly opposite in each electrolyte plate. A technical report entitled "Stacking Oxygen Separation Cell" by CJ Morrissey in NASA Tech Brief, Vol. 15, No. 6, item # 25, June 1991 describes flat stacked electrolyte cells comprising alternate electrolyte plates and gas distribution interconnections The anode and the cathode on each electrolyte plate are directly opposite through the electrolyte plate, ie they are congruent.The glass seals are used between each electrolyte plate and the adjacent interconnections and the seals are directly opposite to each other. Through the electrolyte plate, that is, they are congruent.This design includes an electrically insulating non-porous layer located at the edge of the stack between the interconnections.The flat stacked electrolyte cells comprising alternate electrolyte plates and interconnections having passages of recorded gas are described in a technical report entitled "Thinner, More Efficient Oxygen Separation Cells "by CJ Morrissey in NASA Tech Brief, Vol. 17, No. 4, item # 100, April 1993. Air is introduced into the cells through multiple axials that pass through the stack that provide feed in radiated flow through the cathode sides of the cells Oxygen-free air is withdrawn through a centered axial manifold The oxygen product from the anode sides of the cells is removed through additional axial multiples which pass through the stack at circumferentially placed locations between the air feed manifolds.The anode and the cathode in each electrolytic layer appear to be directly opposite through the electrolyte plate, i.e. they are congruent. are not specifically described in the text, it is evident from the drawings that the seals between each electrolyte layer and the adjacent interconnections an opposed directly across the electrolyte plate, i.e., they are congruent. Therefore, the state of the art in the design of stacked ion conductive electrolyte cells teaches methods for sealing the anode and cathode sides of the cells to avoid cross-contamination of the feed and product gases. The seal has proven to be difficult, although at high temperatures and electrochemically active conditions it was found in those systems. The practical application of ion conducting systems for gas separation, regardless of the design configuration, requires that the cells operate under differential pressures and / or differential gas compositions between the feed and product sides of the cells, and this in turn requires resistant gas tight seals between the stacked components. This need is focused on the invention which is described in the following specification and is defined by the claims that follow. The invention pertains to an electrochemical device for the recovery of oxygen from an oxygen-containing gas, and in particular to an improved operating method for flat series electrolytic cells. The invention is a method for separating oxygen from an oxygen-containing gas comprising contacting the oxygen-containing gas with a first surface of a flat solid electrolyte capable of transporting oxygen ions, supplying electrons to the first surface of the electrolyte. solid by means of a cathode in electrical contact. with a portion of the first surface, and electrochemically reducing oxygen in the oxygen-containing gas by consuming electrons to produce oxygen ions. The resulting oxygen ions are transported as current through the solid electrolyte by imposing an electric potential through the flat solid electrolyte, and the oxygen gas is produced on a second surface of the solid electrolyte by consuming oxygen ions and producing electrons. The electrons conducted from the second surface by an anode in electrical contact with a portion of the second surface, and the electrons are conducted from the anode by an electrically conductive interconnection impervious to the gas that is in electrical contact with the anode. The oxygen gas is collected in a cavity joined at least in part by the second surface of the solid electrolyte, the electrically conductive interconnection impervious to the gas, and a gas-tight anode seal placed between a portion of the second surface of the solid electrolyte. and an opposite portion of the electrically conductive interconnection. The oxygen gas is withdrawn from the cavity and a gas without oxygen is removed from contact with the first surface of the flat solid electrolyte. The power density of the 24-hour anode seal is maintained below 1.5 μ / cm2, preferably by one or more regulating electrodes. At least one of the regulating electrodes may be an extended portion of the anode or alternatively it may be an electrode that is separated from the anode. Both types of regulating electrodes can be used concurrently. Preferably at least one of the regulating electrodes is positioned between the anode and the anode seal. Optionally at least one of the regulating electrodes is not placed between the anode and the anode seal.

The pressure of the oxygen gas generated in the second surface of the solid electrolyte can be different than the pressure of the oxygen-containing gas in the first surface of the solid electrolyte. In one embodiment, the oxygen-containing gas comprises air, and the oxygen gas is withdrawn as a pressurized product of high purity at a pressure of at least 6 kPa greater than the pressure of the oxygen-containing gas. Alternatively, the oxygen-containing gas contains less than 20.9% by volume of oxygen. In another embodiment, the oxygen-containing gas comprises argon and an oxygen-depleted argon product is removed after contacting the oxygen-containing gas with the first surface of the solid electrolyte and after the oxygen is removed by reduction (ionization) and transported through the solid electrolyte. The argon product can be obtained at a pressure equal to or greater than the pressure of the oxygen gas in the cavity formed by the anode sides of the electrolyte plate and the interconnection. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of the cathode side of an electrolyte plate of the present invention. Figure 2 is a plan view of the anode side of an electrolyte plate. Figure 3 is a plan view of the anode side of an alternative electrolyte plate.

Figure 4 is a plan view of the cathode side of an interconnection. Figure 5 is a plan view of the anode side of an interconnection. Figures 6A and 6B are exploded section views including individual electrolytic cells. Figures 7A and 7B are assembled section views of multiple electrolytic cells in series. Figure 8 is a section of a quarter through the insulating support, electrode and cathode seal of an assembled stack. Figure 9 is a complete section through the insulating support, electrode, and cathode seal of an assembled stack. Figure 10 is a schematic isometric view of a complete electrolyte stack. Figure 11 is a plot of the flow efficiency versus the operation time for Examples 2 and 3 in the Specification. Figure 12 is a plot of the flow efficiency versus stacking differential pressure for Examples 3 and 4 in the Specification. Figure 13 is a schematic drawing of a three-layer test cell as a representative portion of an anode seal for determining the anode seal current. Figure 14 is a graph of the power density of the anode seal of 24 hours versus the duration of the test period for Example 5. The separation devices based on solid electrolytes conducting oxygen ions have practical applications in the production of high purity oxygen ions from the air and in the removal of r-esidual oxygen from inert gases such as argon or nitrogen. In any application, the solid electrolyte is operated with a difference in gas pressure and / or gas composition between the feed side (cathode) and the product or permeate side (anode) of the electrolyte. The resistance of the components in such a separation device and the stability of the gas-tight seals required between those components must be sufficient to sustain the practical pressure and / or compositional spreads during the economic useful time of the device. The separation devices based on solid electrolytes conducting oxygen ions can be constructed in tubular, flat plate and honeycomb or monolith configurations. The flat plate configuration, in which a plurality of flat electrolyte cells are stacked to operate in electrical series, is favored in many applications by ease of assembly, cost effectiveness and compact dimensions. The flat plate configuration can be designed with the resistance of appropriate component and seal integrity to operate at a pressure differential and / or gas composition differential between the feed gas and product streams while maintaining the purity requirements of the product gas stream. The present invention utilizes a flat plate stacking design and the method of operation that meets those requirements. Past difficulties have been experienced in the maintenance of such seals as reported in the cited references of the prior art summarized above. Anode seal failure occurs easily in stacking designs in which the seals on the anode and cathode sides of the electrolyte plate are directly opposite. This failure was observed as laminating at the interface between the seal material and the anode side of the electrolyte plate. It is considered that this seal failure may be the result of the deviated or residual anodic current passing through the seal. In the present invention, several improvements in stacking design were identified that reduce or eliminate the anode seal failure. One such improvement is the use of one or more regulating electrodes in contact with each electrolyte plate that modifies the electrolyte potential in the seal region so that the flow of current through the seal is minimized. A regulating electrode may be an extension of the anode beyond the edge of the projected area of the cathode on the opposite side of the electrolyte plate. Alternatively, a separate regulating electrode or grounding strip can be placed on the electrolyte plate between the anode and the anode seal. An extended anode and a separate grounding strip can be used in combination if desired. The term "regulating electrode" as used herein is defined as any electrode material that is in electrical contact with the electrolytic plate, which is located in an area of the electrolytic plate so that the area has no cathode material on the side opposite of it and maintains the power density of the anode seal 24 hours below approximately 1.5 μ / cm2. This 24-hour anode seal power density is preferably maintained by establishing the electrical contact between the regulating electrode and the anode-side interconnection. The projection of an area on the anode side of the plate covered by a regulating electrode on the cathode side of the electrolyte plate will not contact or overlap the cathode material. Typically the regulating electrode or electrode is placed on the anode side of the electrolyte plate. If desired, a regulating electrode can be located on the cathode side of the electrolyte plate if such a regulating electrode (a) is not in electrical contact with the cathode, (b) it is not in electrical contact with the interconnection on the side of the cathode. cathode, and (c) is in electrical contact with the interconnection on the anode side. At least a portion of such a regulator electrode on the cathode side is preferably directly opposite the anode seal. Another improvement is the radial displacement of the anode and cathode seals so that the seals do not overlap on opposite sides of each electrolyte plate. This feature, defined herein as offset stamps, requires a specific cell design geometry as described below. It has been found that a combination of offset seals and regulating electrodes is particularly effective in reducing or eliminating the anode seal failure by controlling the anode seal power density of 24 hours below approximately 1.5 μW / cm2. The flat or smooth plate design of the present invention uses internal electrolyte plates and electrically conductive interconnections that define individual electrochemical cells that operate in electrical series and insulate the feed gases and product as described above. The key component of each electrochemical cell is the electrolyte plate and the associated electrodes that distribute the electrical potential and the flow of electrons on the surface of the plate. The electrolyte plates should be as thin as possible while maintaining sufficient strength to operate at the required pressure differentials. The electrolyte plates are flat and are stacked in the axial direction; The shape of the plates in the radial direction can be circular, square, rectangular, or any other flat geometric shape. The preferred electrolyte plate of the present invention is generally square with rounded corners as shown in the plan view in Figure 1, which is the feed or cathode side of the plate. The electrode material 1, which is a cathode material forming the cathode, is applied to the central region of the electrolyte plate so that the regions without continuous electrode 3 and 5 are maintained. The region without electrodes 5 surrounds the opening 7 extending through the plate. The term "electrodeless region" means any region of the electrolyte plate that has no electrode material applied thereto. The electrolytic material is a multiple component ionic conductive metal oxide comprising an oxygen of at least two different metals or a mixture of at least two different metal oxides wherein the multiple component metal oxide demonstrates the ionic conductivity at the temperatures of operation of the device, typically greater than about 500 ° C. Any solid oxygen ion conducting electrolyte known in the art can be used; representative electrolytes include zirconia stabilized with yttrium, ceria impurified with stroma, ceria doped with gadolinium, and vanadium oxide of bismuth. The cathode material is formed from an oxidation resistant metal, an alloy or a mixed component mixed oxide oxide. Particularly useful electrode material includes strontium lanthanum cobaltite (LSCO), LaxSr? _xCo? 3-z, where x varies from 0.2 to 1 and z is a number that becomes neutral from the charge of the compound. The LSCO can be used as an intermediate coating of the lactate strontium cobaltite and the silver or silver palladium alloy that is applied to the electrode surface. The coating can be applied as a paste, or it can be applied by screen printing or equivalent methods, by electronic deposition or by other well-known techniques. The thickness of the cathode is approximately 0.1 to 100 microns. The representative dimensions of the electrolyte plate are 5 to 20 cm in width or diameter, and 0.01 to 0.065 cm in thickness.

The anode side of the electrolyte plate is shown in plan view in Figure 2. The electrode material 9 is applied around the opening 7 and is surrounded by the region without continuous electrode 11 having a width of d2. The width d2 is smaller than the width di on the cathode side of Figure 1, and the additional width or extension of the electrode 9 on the anode side is a regulating electrode as previously defined. Typically the difference between di and d2 is from about 0.1 to 2.0 cm and defines an extended anode that serves as the regulating electrode. A further definition of the extended anode is a portion of the material that is contiguous with and in electrical contact with the anode, and is not congruent and is not coextensive with the cathode on the opposite side of the electrolyte plate. An alternative anode side of the electrolyte plate is given in the plan view in Figure 3. The electrode material 13 is applied to the electrolyte plate and has the same shape and at least the same peripheral dimensions as the material of electrode 1 of Figure 1. The separate regulating electrode 15 is applied between the electrode 13 and the outer portion of the region without electrode 11. The regulating electrode 15 is also known as a ground connection strip, which is defined as a regulating electrode that is not in direct contact with the anode. Optionally, the electrode 13 is slightly larger than the electrode 1 of Figure 1. The opening 7 corresponds to the opening 7 of Figure 1. The width d3 is similar to the width d2 of Figure 2, and the width d3 is less than the width di on the cathode side of Figure 1. The anode preferably uses electrically conductive material similar to that of the cathode described above and the regulating electrode described below, although the different electrically conductive material can be used for any of its three types of electrode. The distribution of gas through the cathode side of the electrolyte plate, the removal of oxygen from the anode side of the plate and the transport of electrons from the anode side of an electrolyte plate to the cathode side of a Adjacent electrolyte plate are promoted by flat interconnections that have external dimensions generally similar to those of electrolyte plates. The interconnections are made of a gas-impermeable, oxidation-resistant material that has a coefficient of thermal expansion comparable to that of the electrolyte, a high electronic conductivity and a low ionic conductivity. The material can be an electrically conductive multiple component metal oxide, a metal or metal alloy, or a mixture of the two. Suitable electronically conductive oxides include lanthanum chromium, lanthanum manganite, calcium lanthanum manganite, and lanthanum calcium chromite. The lanthanum strontium manganite (LSM), Lao.5Sro.5 n03, is a preferred material for interconnections. The cathode side of an interconnection is shown in plan view in Figure 4, wherein the interconnection has a continuous generally flat peripheral region 17 and an opening 19 to the opposite side of the interconnection. The interconnection generally has the same shape and size as the electrolyte plates of Figures 1-3. A generally flat continuous region 21 surrounds the opening 19. The opening 19 is typically of equal or similar diameter as the opening 7 in the electrolyte plates of Figures 1-3. A plurality of raised areas 23, characterized in this mode as trunco-conical flanges or as spherical segments with flattened tops, which can also be described as pins, are placed between the flat regions 17 and 21. The depressed areas continuous or not elevated between the raised areas together with an adjacent electrolyte plate form a cavity in flow communication with the flat peripheral region 17 as described below. Alternatives for elevated areas 23 can be used, such as ribs, raised rectangular or triangular areas or the like, which perform essentially the same function as the raised areas 23. The upper portions of the raised areas 23 and the flat region 21 are generally coplanar, and this plane is above the plane formed by the flat region 17. The opposite or anode side of the interconnection is shown in plan view in Figure 5. A generally continuous flat region 25 is positioned around the periphery of the interconnection and a plurality of raised areas 27, characterized in this embodiment as trunco-conical ridges or spherical segments with flattened tops, which can also be described as pins, are generally positioned between the flat region 25 and the aperture 19. The depressed areas are continuous or not elevated between the raised areas together with an adjacent electrolyte plate form an interconnected cavity or cavities in flow communication c on opening 19 as described below. Alternatives for the raised areas 27 can be used, such as ribs, channels and the like, which perform essentially the same function as the raised areas 27. The continuous grounding strip 28 encircles the raised areas and electrically contacts the regulating electrode as described below. The upper portions of the raised areas 27, the upper part of the grounding rib 28 and the flat region 25 are generally coplanar.

A simple electrolytic cell is formed by an electrolyte plate having an anode and a cathode, and the adjacent surfaces of the two interconnect together by the anode and cathode seals tight to the appropriate gas and electrical connections. An exploded section view of an individual electrolytic cell is given in Figure 6A and is not necessarily to scale. The partial electrolyte plate 29, corresponding to the section I-I of Figures 1 and 2, has the cathode portion 31 and the anode portion 33 applied to the cathode and anode sides respectively. The anode portion 33 further extends in a radially outward direction that the cathode portion 31 and this extended portion form the regulating electrode portion 34. The regulating electrode portion 34 is a part of the complete regulating electrode formed by the extension of the anode 9 of Figure 2 beyond cathode 1 of Figure 1 in a radial outward direction. This extension is defined so that the width d2 of Figure 2 is less than the width di of Figure 1. The grounding rib 42 makes electrical contact with the regulating electrode 34 when the stack is assembled. Preferably the ratio L / t is greater than about 10, where L is the width of the regulating electrode portion 34 of Figure 6A, ie, the difference between di and width d2 and t is the thickness of the electrolyte plate 29 The L / t ratio is selected such that the power density of the 24-hour anode seal (defined below) through the anode seal 39 is less than about 1.5 μW / cm2. The power density of the anode seal is defined as the product of the anode seal potential measured in volts and the current density of the anode seal measured in Ampers / cm2. The anode seal potential is measured during the stacking operation as described below. The anode seal current density is measured in a separate test cell arrangement as described below where the test cell is • operated on the stacking seal potential and the stacking operating temperature. The value of the anode seal power density measured approximately 24 hours from the anode seal current density test operation (described below) is defined herein as the 24-hour anode seal power density. . The anode seal potential is defined as the electrical differential power measured between an electrical contact of the interconnection that is adjacent to the electrolyte anode side and a reference electrode located in the electrolyte in the vicinity of the anode seal. Additional specifications that define the anode seal potential include the following. The reference electrode is located on the lateral surface of the cathode of the electrolyte plate directly opposite from the anode seal, where the area of the electrical contact does not extend beyond the region defined by a projection of the anode seal on the side of the cathode of the electrolyte plate. The electrical contact to the interconnection that is in direct contact with the anode seal is made on the lateral surface of the cathode directly opposite from the anode seal. This electrical contact area does not extend beyond the region defined by a projection of the anode seal on the cathode side of the interconnection. With reference to Figure 6A, for example, the potential of the anode seal would be measured between the location 46 on the electrolyte plate 29 and the location 44 on the interconnection 37. The difference electrode is of the same type (composition, morphology and processing method) than that of the anode. In addition, the absolute oxygen pressure of the gas in contact with the difference electrode differs from the absolute oxygen partial pressure of the gas in contact with the anode by not more than 5% of the absolute oxygen partial pressure of the gas in contact with the anode. The anode seal potential is measured under non-transient steady-state conditions at the normal cell operating temperature, typically between 600 ° C and 850 ° C, and with the normal operating current density flowing through the electrolyte from the anode to the cathode, typically 50-1500 mA / cm2. The positioning of the interconnecting contact and the reference electrode is such that the absolute value of the zero current seal potential is minimized, and the value reduced to the minimum is preferably less than about 0.1 mV. The zero current seal potential is defined as the potential measured between the interconnection contact and the reference electrode under the same conditions as the measurement of the seal potential, although with steady state current but flowing through the cell. Such a zero current potential is generated, for example, by temperature gradients in the electrolyte and therefore the zero current potential is minimized by placing the reference electrode as close as possible to the interconnecting contact. If the absolute value of the zero current seal potential is not reduced to at least about 0.1 mV by the reasoned placement of the reference electrode, the seal potential is corrected by subtracting the zero current seal potential from the seal potential and redefining the seal potential as this difference. The current density through the anode seal caused by the anode seal potential defined above is small compared to the density of. total current through a stack containing multiple electrolytic plates and is therefore more difficult to measure directly. In order to measure the anode seal current density, a representative portion of the seal must be extracted and isolated, and the current density through the seal measured under the same seal potential as the anode seal potential measured in the Stacking at the same temperature. For this purpose, a representative portion of the seal can be defined as a test cell comprising a fragment of the interconnect material bound with the seal material to an electrode fragment of an electrolyte plate as defined below with respect to Example 5 and Figure 13. The cell should have a uniform cross section along all axes perpendicular to the seal interface, and should provide a geometrically well defined and quantized seal area of at least 0.5 cm2. In order for the electrochemical characteristics of the seal to be as representative as possible, the preparation of the test cell must be closely duplicated of the materials and processes and the process history of a stack as much as possible.

To ensure this duplication, the interconnecting fragment must have the same thickness, composition and manufacturing history as the interconnection, and is preferably a piece of an interconnection from the region of the anode (ground) seal. The electrolyte fragment should have the same thickness, composition and processing history as an electrolyte plate, and should be covered on one side only with a test electrode having the same composition and manufacturing history as the cathode in a stack. The anode seal surface of the interconnecting fragment and the electrodeless side of the electrolyte fragment must be joined with the same sealant as it is in a stack, and they must have the same composition, thickness and manufacturing history as a stack. There are several conceivable ways to prepare such a test cell. One method would be to fabricate a stack with an additional portion of the cathode applied to the cathode side of the electrolyte plate opposite the anode side seal with an area of at least 0.5 cm2. Following fabrication, this stack would be cut using a ceramic abrasion saw to remove a portion of the seal region that meets the dimensional criteria described above. Another method would be to prepare a test cell from separate segments of the stacking components. An interconnect fragment having a uniform cross section and which meets the dimensional criteria of the test cell, would cut the seal region of an interconnection. A fragment of electrolyte plate, of the same lateral dimensions as the interconnecting fragment, would be manufactured in exactly the same way as other electrolyte plates and prepared with a cathode test electrode (only on one side) in exactly the same way than the other electrochemical cells. These fragments would be joined using the sealant under exactly the same conditions of manufacture of a stack. A third method would be to prepare a test cell from separate components as before, although to use a specially prepared pellet of the interconnection material, prepared in exactly the same manner as the interconnection. In this case the electrolyte, the electrode and the seal would be dimensioned accordingly and prepared as before. In all those test cell methods, it is very important to ensure that the seal area is well defined and that there are no alternating current paths. For example, drips of sealant should be removed around the edge of the test cell that connects the electrode directly to the interconnection. One way to avoid current deflection is to grind up any excess sealant that follows the preparation of the test cell. Another way is to make the electrolyte fragment of the test cell slightly larger in lateral dimension than the interconnecting fragment, while leaving the electrode of the same size as the interconnecting fragment. In all those test cell methods, the cross-sectional area of the test electrode, the cross-sectional area of the anode seal and the cross-sectional area of the interconnection must be approximately equal. The term "roughly equal" is used herein to mean that the cross-sectional areas of either of two components differ by no more than 20%. For example, the cross-sectional area of the test electrode and the cross-sectional area of the anode seal should differ by no more than about 20%. The current density of the anode seal is defined as the current of the anode seal determined before divided by the cross-sectional area of the anode seal in the test cell. The anode seal power density is calculated as the product of the anode seal potential measured in Volts and the density of anode seal current measured in Ampers / cm2. The current density test cell of the anode seal as shown in Figure 13 must be approved at the same temperature as the stacking operation by applying an essentially constant potential across the test cell so that the seal potential Test cell anode is equivalent to the anode seal potential previously measured in the stack. The current density is determined as a function of the operating time of the test cell and the value after approximately 24 hours of continuous test cell operation is used to calculate the anode seal power density of 24 hours. The interconnecting portions 35 and 37 of Figure 6A correspond to section III-III of Figures 4 and 5. The anode seal 39 is positioned between the region without continuous electrode 41 (which corresponds to the region without continuous electrode 11 of Figure 2) and the generally flat continuous region 43 (corresponding to the generally continuous region 25 of Figure 5). The cathode seal 45 is located between the region without continuous electrode 47 (which corresponds to the region without continuous electrode 5 of Figure 1) and the generally continuous flat region 49 (which corresponds to the generally continuous flat region 21 of Figure 4) ). A preferred material for seals 39 and 45 is a glass-ceramic derived from lithium aluminosilicate (LAS) which is a material known in the art for use in seals as described for example in the article by TJ Headly and RE Loehman entitled "Crystallization of a Glass-Cera ic by Epitaxial Growth" in Journal of the American -Ceramic Society, Vol. 67, pp. 620-625, 1984. The anode seal 39 and the cathode seal 45 form gas-tight seals between the respective areas of the electrolyte plate and the interconnection when the stack is assembled as described below. The gas-tight seals maintain the purity of the product gas and prevent the loss of product, and avoid or minimize the mixing of the feed and product streams. The seals prevent or minimize gas mixing during the pressure differential and / or gas composition differential between the permeate and non-permeate feed streams. The gas tight seals also serve to join the electrolyte plates and interconnect together in the stack as shown below. The seals can be co-lit and attached directly to the electrolyte plates and interconnections, or alternatively one or more additional co-lit materials can be used. Optionally an electrically insulating support is placed between the cathode side of the electrolyte plate 29 and the cathode side of the interconnect 35 and a portion of this support is denoted as support 51. This support eliminates the damaging stresses on the electrolyte plate when the gas pressure on the anode side of the electrolytic cell is greater than the gas pressure on the cathode side of the cell. The support 51 may or may not be gas tight and is not applied continuously as explained in greater detail below. An exploded sectional view of an alternative individual electrolytic cell is given in Figure 6B. The components of this alternative electrolytic cell are identical to those of Figure ßA except for the electrode material applied to the anode side of the electrolyte plate 52. The anode portion 53 has a smaller extension in the external radial direction than the portion of anode 33 of Figure 6A, and the separate regulating electrode portion 55 is applied to the anode side of the electrolyte plate 52. The regulating electrode portion 55 is a part of the regulating electrode 15 of Figure 3. The rib of ground connection 56 makes electrical contact with the regulating electrode portion 55 when the stack is assembled. This grounding rib is typically continuous and makes continuous contact with the regulating electrode, although optionally it can be discontinuous, i.e. formed as a series of raised areas placed in a circular pattern that is in electrical contact at the regulating electrode.

A plurality of elements described in Figure 6A are assembled by placing electrolyte plates and alternating interconnections in a stack, and the stack is fired to produce a plurality of electrolytic cells in series, three of which are shown in Figure 7A. In the assembly process of each cell, an electrically conductive material is applied to the surfaces of the raised areas of each interconnection as defined by elements 23 of Figure 4 and 27 of Figure 5. When the stack is turned on, this Conductive material is linked to the elevated areas of the interconnections and to the electrodes of each electrolyte plate. The conductive material is shown in Figure 7 as forming layers 57 positioned between the interconnecting portion 59 and the cathode on the electrolyte plate 61, and forming layers 63 positioned between the adjacent interconnecting portion 65 and the anode on the plate. Electrolyte 61. The forming layers provide electrical connections between the electrodes and adjacent interconnections, and also provide mechanical support for the electrolyte plate. The conductive material is preferably silver initially applied as an ink before ignition. In the alternative embodiment described above, such as a plurality of the elements described in Figure 6B are assembled in a stack and ignited to produce a plurality of electrolytic cells in series, three of which are shown in Figure 7B. The cells of Figure 7B are identical to that of Figure 7A except for different regulating electrodes. In Figure 7A, the regulating electrodes 67 are radial extensions of the anodes of the respective electrolyte plates wherein each anode extends radially beyond the edge of the cathode on the opposite side of the electrolyte plate. This was described above with respect to Figures 1 and 2 wherein the regulating electrode is the extension of the anode having a width equal to the difference between the width d and in width d2. In Figure 7B, the individual regulator electrode portions 69 are positioned between each electrolyte plate and the adjacent interconnections. The complete regulating electrode for this alternative is shown as the element 15 in Figure 3, where the width d3 is less than the width di in Figure 1. A preferred feature of this embodiment of the present invention is the use of regulating electrodes which reduce or eliminate the anode seal failure by maintaining the 24-hour anode seal power density at less than about 1.5 μW / cm2. The anode seal failure can occur by disunity or delamination at the interface between the anode seal material and the interconnection, or alternatively by disunity or delamination at the interface between the anode seal material and the electrolyte plate. A second feature is that the anode seal is completely out of phase on the electrolyte plate relative to the corresponding cathode seal. The term "offset seals" is defined as the geometric seal arrangement in which the projection of any anode seal area on the cathode side of the electrolyte plate does not contact or overlap any cathode seal. This is illustrated in Figure 6A where the anode seal portion 39 is positioned adjacent the outer periphery of the electrolyte plate considering that the cathode seal portion 45 is positioned adjacent the central opening in the plate. The combination of the regulating electrode and the offset seals as used in the present invention is particularly effective in the elimination of the anode seal failure. The operation of the flat electrolytic cells as described above may require that the oxygen product pressure be higher than the pressure of the oxygen-containing feed gas, so that the cells operate in an oxygen pumping mode. This operation can pose a significant mechanical stress on the external region of * the electrolyte plate. As described above, this problem is selected by using the electrically insulating support 51 positioned between the cathode side of the electrolyte plate 29 and the interconnection 35 (Figure 6A). This electrically insulating support reduces the potentially harmful voltages on the electrolyte plate 29 when the gas pressure on the side of the anode 1 of the electrolytic cell is greater than the gas pressure on the cathode side of the cell. The multiple supports are shown in Figure 7A as the supports 71 and in Figure 7B as the supports 73. The electrically insulating support material should have a coefficient of thermal expansion that is substantially equivalent to the coefficient of thermal expansion of the adjacent electrolyte material. or that of the adjacent interconnection material. Substantially equivalent means that the coefficients of thermal expansion of the insulating support and an adjacent material on the temperature scale from about 20 ° C to about 750 ° C differ by less than about 2 micrometers / (meter • ° C), preferably in less than 1 micrometer / (meter • ° C), and more preferably in less than about 0.5 micrometer / (meter • ° C). Insulating support material having lower values of Young's modulus can tolerate greater differences in the coefficient of thermal expansion compared to electrolyte and interconnect materials, while insulating support materials with higher Young's moduli can tolerate differences lower in the coefficient of thermal expansion. The insulating support is prepared using one or more electrically insulating ceramics as described below. An electrically insulating ceramic is defined herein as any electrically non-conductive ceramic that does not permit the passage of electrical current when placed in an electric field (see Modern Ceramic Engineering, D. Richerson, 2nd Edition, Marcel Deckker, Inc. New York, p 228). Mixtures of such ceramics are selected to have high electrical resistance and to have coefficients of thermal expansion similar to those of the electrolyte and the interconnection materials. Representative ceramics for use in the insulating support include but are not limited to the oxides of Mg, Al, Si, Yb, Ca, Be, Sr, Nd, Sm, Er, Eu, Se, La, Gd, Dy and Tm. The insulating support can be manufactured by several different methods. In the first of these methods, the insulating support has been made by preparing a mixture of inorganic oxide glass or glass / ceramic combined with one or more electrically insulating ceramics in an inorganic carrier or carrier to form an ink, applying the ink to an interconnection or to the electrolyte plate and igniting at about 500 C. The ignition temperature preferably approaches or reaches the melting temperature of the glass, which is on the temperature scale from about 800 ° C to about 1000 ° C. The preferred coefficient of thermal expansion of the support material after firing is about 9 and about 15 micrometers / (meter • ° C). A typical ink composition is 70% by weight of solids and 30% by weight of liquid organic carrier or carrier, although other compositions can be used as required. A preferred composition scale of the solids portion of the mixture before ignition (excluding the organic carrier or carrier) contains about 0.3 to about 27% by weight of a lithium aluminosilicate glass with the remainder being the insulating ceramic magnesia (MgO) and alumina (A1203). The weight ratio of magnesia to alumina in the sample before ignition is selected to be between about 0.2 and about 8 in order to produce the preferred coefficient of thermal expansion of the insulating support material. In addition, the quantity of glasses is selected so that the final assembled insulating support after the ignition is electrically insulating.

In another method, an electrically insulating ceramic mixture is formed in a desired and concreted pattern to form an electrically insulating support. This concreted electrically insulating support is bonded to the electrolyte and interconnected by placing inorganic oxide glass or glass / ceramic between the insulating support and the electrolyte, placing inorganic oxide glass or glass / ceramic between the insulating support and the interconnection, and igniting at a temperature enough to connect the insulating support to both the electrolyte and the interconnection. Preferably, the glass of inorganic oxide or glass-ceramic is a glass of lithium aluminosilicate. Alternatively, the concreted electrically insulating support can be attached to the electrolyte by co-igniting at a sufficient temperature to attach the insulating support directly to the electrolyte without the use of non-metallic inorganic gases. The insulating support is further described in Figure 8, which corresponds to section IV-IV of Figures 7A and 7B. The insulating support is applied discontinuously so that a portion 75 forms a continuous support and additional portions 77 form individual supports separated by open spaces 79. This is illustrated more clearly in Figure 9, which is an expansion of section IV -IV for a corresponding complete section of the complete stack in the same axial location. The insulating support portions 81 and 83 are continuous on opposite sides of the stack, while the support portions 85 and 87 are discontinuous on opposite sides of the stack. The openings 89 and 91 allow the cross-flow of feed gas through the stack, as described more fully below, so that the oxygen-containing gas flows through openings 89 while the oxygen-free gas leaves the stack through the openings 91. The section of Figure 9 also shows the cathode 93 and the cathode seal circulating the central opening 97. The general assembly and the operation of the electrolytic cell stack are illustrated by the schematic isometric view of the Figure 10, which is not to scale. The cell stack is formed by a series of alternating electrolyte plates 95 with appropriate anodes and cathodes (not shown), interconnects 97 and insulating support material 99, with negative end plates 101 and positive end plate 103. The electrical connections positive and negative provide direct current to the stack, which operates approximately 50 to 700 Mb per cell. The gas from the feed containing fluid oxygen within one side of the stack as shown, flows through the cathode sides of the cells in a cross flow mode, and the oxygen-free gas exits at the opposite end of the stack. The insulating supports on the opposite stacking sides direct the gas in a cross flow mode as described above. A section through the stack shows the radial flow of the oxygen product gas through the anode side of an interconnection to the central opening 109. The central openings through the electrolyte plates and the interconnects, together with the seal of the Cathode described above, form a central conduit in gas flow communication with the anode side of each cell: the central conduit connects with the oxygen removal conduit 111, which in turn is connected with a gas-tight seal (not shown) to the bottom or positive end plate 103. Alternatively, an oxygen removal conduit could be connected to the negative end plate 101 (not shown). If desired, the oxygen product can be withdrawn from both ends of the stack (not shown). Stacking can be operated in at least two alternative modes. In the first mode, the feed gas is air and a high purity oxygen product comprising at least 99.5% by volume of oxygen is withdrawn through line 111. The storage air is typically introduced at a pressure significantly prior to the atmospheric which is enough to maintain adequate air flow through the stack. Typically oxygen is continuously produced at a pressure of at least 5kPa above the feed pressure, which is made possible by the application of the displaced seals, the regulating electrodes and the insulating supports described above. The stack is operated at a temperature above 500 ° C. In a second mode of operation, the feed gas is an inert gas such as nitrogen or argon that contains a lower concentration of oxygen as an impurity. The electrolyte cell stack is operated to remove a major portion of the oxygen so that the oxygen-free gas flowing from the sides of the cells typically contains less than about 100 ppbv to less than about 10% the volume of oxygen. The oxygen flow from conduit 111, which will be of high purity but low volume, can also be a useful product. In this embodiment, it may be desirable to operate the stack so that the pressures of feed gas and products without oxygen are above the pressures of the oxygen product. In such a case, the use of the support material in the stacking would be optional since the electrolyte plates will receive sufficient mechanical support from the forming layers and the anode seals described above. At higher operating pressures, the stacking assembly may require final restrictions to maintain the integrity of the stack. These final constraints operate on end plates 101 and 103 to provide axial compressive force that compensates for the tendency of the stack to separate under such pressures. While the present invention is preferably used for the separation of air to recover oxygen at high purity and the purification of the inert gas to remove residual oxygen, the invention can be applied to any gas mixture containing oxygen for a desired purpose or product. final. The electrolyte cell stack of the present invention can; made by methods known in the ion conducting ceramic art, for example as described in European Patent Application Publication No. 0 682 379 Al cited above. The invention can be applied with any materials known in the art and generally used in ion conductor stacks for electrolyte plates, electrodes, interconnections and seals. Other stacking geometries that would be embodiments of the present invention can be projected in which the regulating electrodes and displaced seals are used to control the seal power density of 24 hours in at least about 1.5 μW / cirr. Regulating electrodes and displaced seals can be applied with alternative stacking configurations to introduce the feed gas into the stack, to remove oxygen-free gas from the sides of the cathodes of the cells and / or to remove oxygen from the sides of the cells. anodes of the cells. An alternative embodiment of the invention, the electrically insulating material is incorporated within the cathode seal and the regulating electrodes are used as described above. The insulating material is preferably prepared by concreting a mixture of magnesium oxide (MgO) and aluminum oxide (A1203) and the insulating material is sealed to the sides of the cathode of the electrolyte plate and interconnected with a glass-sealed ceramic, for example such as that derived from a lithium aluminosilicate glass (LAS). In the preparation of the insulating material, aluminum oxide is used to reduce the coefficient of thermal expansion of the magnesium oxide so that the coefficient of thermal expansion to the walking material equals that of the electrolyte and the interconnecting materials. Part of the spinel of magnesium oxide (MgAl204) can be formed in itself during the concretion of the material. Alternatively, the aluminum oxide and the magnesium oxide can be ignited at sufficiently high temperatures to form a MgO / MgAl2? 4 ceramic. Alternatively, the insulating material can be co-fired with the electrolyte at approximately 1550 ° C without the use of glass sealant. In this alternative mode that uses insulating material in the cathode seal, full displacement of the anode and cathode seals is not required, which allows for additional flexibility in the stacking design. This embodiment can be applied to any stacking design having anode and cathode seals directly opposite or partially opposed as long as the insulation geometry allows the inclusion of a regulating electrode. For example, the embodiment could be applied to the flat stacking design described in European Patent Application Publication No. 0 682 379A1 referred to above. The combination of an insulating cathode seal and the regulating electrode will allow control of the anode seal power density of 24 hours in less than approximately 1.5μW / cm ?. EXAMPLE 1 The insulating support between the cathode sides of the electrolyte plate and the interconnection as described above can be formed by first applying to the stacking assembly and igniting an ink containing precursor materials in a liquid carrier or carrier. An ink for the formation of the ignition insulating support material was prepared as follows, 59.3 grams of alumina (Alcoa, SG 16), 255.7 grams of magnesia (Martin-Marietta, MC10-325), and 35.0 grams of an aluminosilicate glass. of lithium (Specialty Glass, SP1484-A) were combined and mixed in a stainless steel bowl 72.0 grams of a-Terpineol (Kodak) and 78.0 grams of V-006 (Heraeus, Cermalloy Division) were mixed in a second steel bowl stainless. One third of the solid mixture was slowly added to the liquids and mixed together with a rubber spatula until all the powder diffused. This stage was repeated with the remaining powder until all the powder was incorporated. The mixture was then processed four times through a triple laminator to produce the final ink, using the grinding separation recorded below: EXAMPLE 2 A two-cell stack was constructed and operated to demonstrate the use of a stacking design incorporating offset seals and regulating electrodes. A round stack of A2 cells of 7.6 cm in diameter was constructed from two ceria electrolyte plates impregnated with 10% molar strontium (SCO) and three Lao.5Sro.sMn03 (LSM) interconnected plates placed in alternating layers. The electrolyte plates were 0.025 cm thick. Both interconnections and electrolyte plates have a central hole, and the holes aligned in the stack to form a central axial conduit that collected the oxygen generated electrochemically between each anode. Each interconnect has a 0.38cm wide circumferential sealing surface near the outer periphery of the anode side for a glass-ceramic seal. The sealing surface of the interconnection on the cathode side was located around the central hole and was also 0.38cm wide. The electrolyte plates had sealing surfaces without an electrode on the cathode and anode sides that were aligned with the corresponding interconnect seal surfaces. The electrolyte insulation and interconnection components were joined on the same sealing surface with a lithium-ceramic aluminosilicate (LAS) glass to form gas-tight seals.

The electrodes on the anode side and on the cathode side of lanthanum strontium cobaltite (LSCO), La.: Sr? _xCo03_2, where x varies from 0.2 to 1.0 and z is a number that returns to the neutral charge compound, were applied to the electrolyte plates. An overcoat of LSCO and silver-palladium alloy was applied to the electrodes. The electrodes were applied so that the anode was oversized relative to the cathode by 0.14 cm at the outer edge, so that the portion of the anode extending beyond the circumference of the cathode formed a regulating electrode as previously described. In addition, a separate external regulating electrode or grounding strip of the same electrode composition was applied outside the extended anode. The grounding strip regulating electrode was 0.18 cm wide, and was separated from the anode by a 0.13 cm wide space of the SCO electrolyte. The cathode area was 21 cm2 per plate. Therefore, the anode and the configuration of the regulating electrode was similar to those described in Figures 3, 6B and 7B. The insulating support of Figure 6B was not used. The electrodes were connected to rib 0.05 cm high (0.13 cm wide) on the interconnection, separated by 0.13 cm wide channels. The silver was applied as a conductive layer between the upper surface of the interconnecting ribs and the. electrode. The upper surface of the ribs formed a common plane with the seal surface for the glass-ceramic seal on both sides of the interconnection. The channels allowed oxygen to flow radially to the central collection port at the anode, and air flowed through the cathode in a cross-flow mode. One of the terminal interconnection plates or end plates was attached to a 0.48 cm outer diameter section of stainless steel tubing for oxygen removal. The central hole in the other terminal interconnection plate or end plate was closed with a 2-inch square LSM plate bonded with LAS. The air was supplied to the cathode side of the stack at approximately 2 standard liters per minute. A voltage of approximately 1 volt was applied between the two terminal LSM interconnection plates at 750 ° C, and the electric-stacking current and the resulting flow velocity of the electrochemically generated oxygen were measured. A digital mass flow meter attached to the SS446 pipeline was used to measure the flow. The anode side pressure was controlled by a manual valve attached to the SS446 pipe and monitored by a Bourdon tube pressure gauge. Seal integrity was determined by calculating the "flow efficiency as follows: lOOx flow velocity O? measure (ccstd / min) Flow efficiency (%) = - Theoretical O2 flow rate (100% efficient) lOOx flow rate 0 ¿measure (ccstd / min) measured current (amperes) x 3.75x N where N is the number of cells in the stack and 3.75 is a conversion factor that has units of (standard cubic centimeters per minute / amper). The flow in standard cubic centimeters / minute is defined at 21 ° C. The theoretical flow velocity is realized when all the current is fully utilized - to produce the collected oxygen product, that is when one molecule of oxygen is produced by every four electrons that flow through each cell, and all the oxygen collected in absence of seal leaks. The stack was maintained at a constant pressure or differential of 2 kPa (higher pressure next to anodes) for the first 1025 first hours of operation, and subsequently at a differential pressure of 10kPa (higher anode side pressure). The stacking operation was continuously monitored for 5000 hours and the oxygen flow measured was essentially 100% of the theoretical throughout the period. This indicates the integrity of the seal and the absence of detectable leakage. EXAMPLE 3 A 2-cell round 7.6 cm stack was constructed according to the procedure described in Example 2, except that the electrodes were coextensive at their outer edges on the electrolyte plates, ie the outer diameter of both electrodes was equivalent and there was no regulating electrode on the anode side. The cathode area was 31 cm ~ per plate. The stack was operated at 750 ° C in a manner similar to Example 2, except that a voltage of one volt was applied to the stack at a permanent differential pressure of 6.9 kPa (higher side pressure). Flow efficiency was monitored in-line for 480 hours in the same manner as described in Example 2. After operating the stack for 480 hours, the flow efficiency was measured on the differential pressure scale from 0 to 6.9 kPa ( pressure of the higher anode side). The stacking operation was completed after 505 hours due to a significant loss in flow efficiency. The loss in flow efficiency was found to be a result of the debonding of the interface between the LAS seal and the electrolyte on the anode side of the electrolyte plate. Stacking performance as a function of on-line operation time is shown in Figure 11 for comparison with the performance of Example 2. The comparison demonstrates that regulating electrodes are required in stacks using offset seals to provide an anode seal hermetic to the resistant gas. EXAMPLE 4 A 5-cell round stack of 7.6 cm in diameter was constructed according to the procedure described in Example # 2, except that five electrolyte plates and six interconnections were used. The anode was oversized relative to the cathode at 0.11 cm at the outer edge. The external ground connection strip electrode on the anode side was 0.19cm wide, and was separated from the anode by a 0.10cm wide space of the SCO electrolyte. The cathode area was 24 cm2 per plate. An insulating support was used similar to that described with reference to Figures 6B, 7B, 8 and 9 using material prepared according to Example 1. The insulating support material was attached to the periphery without electrode on the cathode side of the electrolyte and that flat area adjacent to the periphery of the interconnection. The spaces were periodically left in the insulating support layer to allow the flow of air through the cathodes and the removal of oxygen-free air from the cathodes similar to the flow configuration shown in Figure 10. The stack was operated at 750 ° C in a manner similar to Example 2, except at a voltage of 2 volts and a permanent difference pressure of about 35 kPa (higher anode side pressure). After operating the stack for 1680 hours, the flow efficiency was measured on the differential pressure scale 0 to 83 kPa (higher anode side pressure) and was essentially 100% as shown in Figure 12. This indicates the excellent seal integrity that was maintained by using regulating electrodes and complete the integrity of the electrolyte plate that was maintained by using the insulating support layer. Figure 12 also showing the operation data on the differential pressure scale of 0-6.9 kPa for the stack of Example 3, which had no regulating electrodes. It is noted that the flow efficiency for this stacking design decreased rapidly as the differential pressure increased. EXAMPLE 5 To determine the maximum anode seal power density which prevents delamination or failure of the anode seal, several test cells were prepared and operated at various voltages using similar procedures for the stocks described in Examples 2, 3 and 4 Each test cell comprises a pellet (LSM) of lanthanum strontium manganite of 2.5 cm in diameter (representative of a stacking interconnection) linked with LAS directly to a strontium-doped electrolyte disk with strontium of 2.6 cm in diameter, 0.038 cm thick. The electrolyte had a 4 cm lanthanum strontium cobaltite (LSCO) electrode with a single coating of LSCO, silver and silver-palladium alloy applied to the air side.The LSCO electrode and the overcoating constitute the electrode of A porous silver layer was applied over the test electrode to act as a current collector .. For each test cell, a voltage was applied across the LSM pellet and the current collector at 750 ° C, Thus, the test electrode was negatively charged, thus simulating the configuration of LAS and SCO in the anode seal of an insulation.Voltage and current were measured routinely, including after the initial 24-hour period of operation The 24-hour anode seal power density was defined as the power density determined after approximately 24 hours of operation.The cross-sectional area of the test electrodes was used to Calculate the power density of anode seals. The cross-sectional area of the test electrode approximates the cross-sectional area of the anode seal during 20%. A schematic drawing of the test cell is shown in Figure 13 (it is not to scale). The assembly of test cells 201 comprised a pellet or layer 203 of interconnecting material LSM attached to the electrolyte layer 205 by the anode seal LAS 206. The test electrode 207 was applied to the cathode side of the electrolyte layer 205. as described before. The porous paddle current collector 209 was applied to the other side of the test electrode LSCO 207. The test cell assembly 201 was mounted in a controlled temperature test oven (not shown) with the required electrical connections and the lines of gas suitable for bringing the air into contact with the cathode side of the test cell. Voltage was applied across the test cell by potentiostat 211 and the actual voltage measured by potentiometer 213. Cell current was measured by ammeter 215. At the end of a continuous operation period, each test cell was removed of the test and anode seal tested for delamination with a rake blade. The delamination of LAS to SCO from the electrolyte junction indicated the failure of an anode seal in an operational stack. The data from these tests were summarized in Table 1 for essentially constant values of the potential applied through the test cell. The term essentially constant means that the absolute difference between the initial voltage and the 24-hour voltage varied by no more than 18% of the initial voltage. The relationship between the total operating time, the anode seal power density after the initial 24 hour operating period, and the integrity of the anode seal is plotted in Figure 14. This example clearly demonstrates the need to operate the anode side seals at a density of 24-hour power of less than 1.5 μW / cm "in order to maintain the integrity of anode seal union and avoid delamination and seal failure.

Therefore the present invention comprises several improvements in the design of flat electrolytic cell stacks that eliminates the anode seal failure. One such improvement in the radial displacement of the cathode anode seals so that the seals do not overlap on opposite sides of the electrolyte plate. This requires a specific cell design geometry as described above. Another improvement is the use of a regulating electrode on the anode side in the electrolyte plate that modifies or regulates the electrolyte potential in the seal region so that the current flow through the anode seal is minimized. This regulating electrode may be an extension of the anode beyond the outer edge of the cathode on the opposite side of the electrolyte plate. Alternatively or additionally, a separate regulator electrode may be placed in the electrolyte plate preferably between the anode and the anode seal. It has been found that a combination of displacement seals and regulating electrodes is particularly effective in reducing or eliminating anode seal failure by controlling the 24-hour anode seal power density in at least about 1.5 μW / cm2. . Another feature of the invention is the insulating support placed between the sides of the cathode of the electrolyte and the interconnection which eliminates potentially damaging voltages on the electrolyte plate 29 when the gas pressure on the anode side in the electrolytic cell is greater than the gas pressure on the cathode side of the cell. The improvements of the present invention are not limited to the stacking geometries described herein. Regulating electrodes and displaced seals can be implemented with alternative stacking configurations having different methods for introducing the feed gas into the stack, for removing oxygen-free gas from the cathode sides of the cells, and / or removing oxygen from the cells. sides of the anode of the cells. In any application, the regulating electrodes and displaced seals can be used to control the anode seal power density of -24 hours in at least about 1.5 μm W / cm2. The essential features of the present invention are fully described in the foregoing description. One skilled in the art can understand the invention and make various modifications without departing from the basic spirit of the invention, and without deviating from the scope and equivalents of the claims that follow.

Claims (12)

1. CLAIMS 1. A method for separating oxygen from an oxygen-containing gas characterized in that it comprises: (a) contacting the oxygen-containing gas with a first surface of a flat solid electrolyte capable of transporting oxygen ions; (b) supplying electrons to the first surface of the flat solid electrolyte via a cathode in "electrical contact with a portion of the first surface; (c) electrochemically reducing oxygen in the oxygen-containing gas by consuming electrons to produce oxygen ions; (d) transporting the resulting oxygen ions as current through electrolyte solid by imposing an electric potential through the solid electrolyte (e) producing oxygen gas on a second surface of the solid electrolyte by consuming oxygen ions and producing electrons, (f) conducting the electrons of stage (e) from the second surface by an anode in electrical contact with a second portion of the second surface: (g) conducting the electrons of step (f) from the anode by an electrically conductive interconnection impervious to the gas that is in electrical contact with the anode; (h) collecting the oxygen gas in a cavity joined at least in part by the second surface of the solid electrolyte, the electrically conductive interconnection impervious to the gas, and a third gas-tight anode seal positioned between a portion of the second surface of the solid electrolyte and an opposite portion of the electrically conductive interconnection, (i) withdrawing the oxygen gas from the cavity; (j) removes an oxygen-free gas from contact with the first surface of the flat solid electrolyte; (k) maintain the anode seal power density of 24 hours below approximately 1.5 μW / cmA 2. The method in accordance with the claim 1, characterized in that ^ the anode seal power density is maintained at least about 1.5 μW / cm "'by one or more regulating electrodes 3. The method according to the claim 2, characterized in that at least one of the regulating electrodes is an extended portion of the anode. 4. The method of compliance with the claim 2, characterized in that at least one of the regulating electrodes is separated from the anode. 5. The method of compliance with the claim 3, characterized in that at least one of the regulating electrodes is separated from the anode. 6. The method according to claim 2, characterized in that at least one of the regulating electrodes is placed between the anode and the anode seal. The method according to claim 1, characterized in that the pressure of oxygen gas generated in the second surface of the solid electrolyte is greater than the pressure of the oxygen-containing gas in the first surface of the solid electrolyte. 8. The method according to claim 1, characterized in that the gas containing oxygen is air. The method according to claim 7, characterized in that the oxygen gas is withdrawn as a pressurized product of high purity at a pressure of at least 5 kPa greater than the pressure of gas containing oxygen 10. The method of compliance with the claim 1, characterized in that the oxygen-containing gas is a gas containing less than 20.9% by volume of oxygen. The method according to claim 10, characterized in that the oxygen-containing gas comprises argon and an argon product lacking oxygen which is removed after contacting the oxygen-containing gas with the first surface of the solid electrolyte and then that the oxygen is removed by reduction and transported through the electrolyte in steps (c) and (d) 12. The method according to claim 11, characterized in that the product of argon is obtained at a pressure equal to or greater than the pressure of the oxygen gas in the cavity of step (h).