Components for use in electrochemical cells and their use in oxygen separation

TECHNICAL AREA

The invention relates to the field of electrochemical reactors which facilitate the transfer of oxygen. More particularly, the invention relates to oxygen-semipermeable membranes, electrochemical reactor components comprising the oxygen-permeable membrane, electrochemical reactors and reactor components comprising oxygen-permeable membranes and a catalyst, and electrochemical processes comprising the oxygen-permeable membrane and the catalyst for facilitating electrochemical processes. which use the oxygen transport from an oxygen-containing gas to a gas that consumes oxygen.

TECHNICAL BACKGROUND

For example, sulfur and nitrogen oxides are known to be harmful contaminants in gas streams emanating from stationary and mobile sources, such as power plants, automobiles, ships, trains, and so forth. Sulfur oxides are known to combine with steam to produce highly corrosive vapor which causes irritation of the eyes and mucous membranes, damage to metal-containing structures, and environmental degradation of the vegetation due to acid rain. Nitrogen oxides are toxic irritants and also harm the environment. Carbonyl sulfide (COS) is another toxic pollution formed as the product of the reaction between sulfur-containing compound and carbon monoxide in a gas effluent. Regulations regarding the discharge of these pollutants to the atmosphere have become increasingly stringent. The present invention describes an electrocatalytic process and an electrochemical cell for removing sulfur and nitrogen oxides from gas streams utilizing the chemical motive power of a fuel gas.

BRIEF SUMMARY OF THE INVENTION

A solid multi-component membrane for use in the methods of the present invention is described. The solid multicomponent membrane generally comprises intimate, gas-impermeable multiphase mixtures of an electronically conductive phase and an oxygen ion-conducting phase and / or gas-impermeable "single-phase" mixed metal oxides having a perovskite structure and having both electron-conducting and oxygen-ion-conducting properties. Solid multicomponent membranes for use in electrochemical reactors are also described comprising the aforementioned multiphase mixtures and / or the aforementioned mixed metal oxides, provided that the mixed metal oxides are represented by the formula:

AsA'tBuB'vB "WOX

wherein A represents a lanthanide or Y represents a mixture thereof, A 'represents an alkaline earth metal or a mixture thereof, B represents Fe, B' represents Cr or Ti or a mixture thereof, and B "Mn, Co, V, Ni or Cu or a mixture of which and s, t, u, v, w and x each represent a number such that:

s / t is about 0.01 to about 100;

u is about 0.01 to about 1;

v is 0.01 to about 1;

w is 0 to about 1;

x is the number satisfying the valences of A, A ', B, B' and B "in the formula, and

0.9 <(s + t) / (u + v + w) <1.1.

An element for use in the method of the invention is provided with a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with an oxygen-consuming gas, an electron-conductive path between the first and second surfaces, and an oxygen-ion conductive path between first and second surfaces described. The element also includes (1) a porous substrate, (2) an electron-conductive metal, metal oxide or mixture thereof, and (3) a catalyst. The porous substrate (1); the conductive coating (2) and a catalyst (3) can be applied as separate materials; or the functions of the porous substrate (1), the conductive coating (2) and the catalyst (3) may be combined into one or two materials. Elements for use in an electrochemical reactor as defined above are described which element comprises (1) a catalyst such as a sulfur reducing catalyst on a surface thereof or (2) (A) a solid multi-component membrane characterized by (1) an intimate one . a gas impermeable polyphase mixture of an electronically conductive phase and an oxygen ion conductive phase or (2) a mixed metal oxide material having a perovskite structure and (B) a conductive coating, a catalyst or a conductive coating comprising a catalyst.

An electrochemical reactor cell for transporting oxygen from an oxygen-containing gas to any gas that consumes oxygen is also described, generally comprising the aforementioned elements having an entrance end and an exit end and a passageway therebetween for moving one or more gases includes the input end to the output end. In one embodiment, the passage between the inlet end and the outlet end comprises a catalyst such as a catalyst of individual particles or fibers filled in the passage between the inlet end and the outlet end of the reactor cell. This electrochemical reactor cell is placed in an environment comprising an oxygen-containing gas on one side and an oxygen-consuming gas on the other side under reaction conditions of appropriate temperature and percentage of the respective gases.

An electrochemical reactor for reacting an oxygen-consuming gas with an oxygen-containing gas is also described, comprising a shell having an inlet end, an outlet end and a passageway therebetween for moving one or more gases from the inlet end to the outlet end and at least one of the above Reactor cells arranged in the shell, so that the shell and the reactor cell together a first zone for the introduction, Converting and discharging a first gas or gas mixture and a second zone (ie, the above-mentioned reactor cell passage) in the reactor cell and separately from the first zone through the reactor cell for introduction, reaction and discharge of a second gas or gas mixture. In one embodiment, the first zone and optionally the second zone comprise a catalyst such as a single particle or fiber catalyst filled between the shell and the outer surface of the reactor cell or in the passageway within the reactor cell.

Another aspect of the present invention is an electrochemical process for the extraction of oxygen from an oxygen-containing gas comprising

(A) providing an electrochemical cell comprising a first zone and a second zone separate from the first zone by the above-defined element,

(B) passing an oxygen-containing gas in contact with the element into the first zone and

(C) passing a reactant gas in contact with the element into the second zone.

When the present invention is an electrochemical process for extracting oxygen from an oxygen-containing gas other than free oxygen, such as SO 2, SO 3, N 2 O, NO or NO 2, the electrochemical process comprises

(A) providing an electrochemical cell comprising a first zone and a second zone separate from the first zone by the above-defined element,

(B) passing a gas containing the oxygen-containing gas, wherein the oxygen is in a form other than free oxygen, in contact with the element in the first zone and

(C) passing a reactant gas in contact with the element of the first zone therethrough.

This process can be used in a gas purification process in which gas containing oxygen other than free oxygen is a combustion or exhaust gas.

When a desired product is obtained by the above-mentioned oxygen extraction methods, such as synthesis gas, unsaturated hydrocarbons, elemental sulfur, or oxygen-free gas, those methods may include recovering the desired product from the zone in which it is produced. Oxygen-free gas can be obtained, for example, from the first zone.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

Fig. 1 is a side view and a cross section of a first embodiment of an electrochemical reactor according to the invention.

Fig. 2 is a plan view and a cross section of a second embodiment of an electrochemical reactor according to the invention.

FIG. 3 is a side view and a cross section of the reactor shown in FIG. 2. FIG.

FIG. 4 is an electron photomicrograph back-scattered image of the surface of one embodiment of the multicomponent solid-state membrane of the present invention at 500x magnification and FIG

Fig. 5 is an electron photomicrograph of a cross section of the same multicomponent solid membrane as shown in Fig. 4 at 5000 magnification.

Fig. 6 is a plan view and a cross section of a third embodiment of an electrochemical reactor suitable for carrying out the methods of the invention.

FIG. 7 is a side view and a cross section of a reactor shown in FIG. 6. FIG.

Fig. 8 is a side view and a cross-section of an element suitable for carrying out the method according to the invention.

Fig. 9 is a plan view and a cross-section of another electrochemical reactor suitable for carrying out the methods of the invention.

FIG. 10 is a side view and a cross section of the reactor shown in FIG. 9. FIG.

Fig. 11 is a side view and a cross-section of another embodiment of the invention suitable for carrying out the methods of the invention.

Fig. 12 is a plan view and a cross-section of another electrochemical reactor suitable for carrying out the methods of the invention.

FIG. 13 is a side view and a cross section of a reactor shown in FIG. 12. FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides an electrochemical reactor for a continuous process for transporting oxygen from an oxygen-containing gas to a reactant gas that consumes oxygen. Processes that are carried out with the present invention are, for example, the combustion of hydrogen to produce water, the partial oxidation of methane or natural gas to produce synthesis gas, the partial oxidation of methane and saturated hydrocarbon-containing gases to produce unsaturated hydrocarbons, the partial oxidation of Ethane, the substitution of aromatic compounds, the extraction of oxygen from oxygen-containing gases (for example, extraction of oxygen from NO x ', where x' has a value of 0.5 to 2, SO y, where y has a value of 2 to 3, steam, CO 2, etc.), Ammoxidation of methane to hydrogen cyanide, etc.

An embodiment of the electrochemical reactor according to the invention can be represented schematically as shown in FIG. 1, the side view and the cross-section of the reactor 1 showing a first zone 2 separated from a second zone 3 by element 4. The outer circumference of the first zone is defined by reactor tube 5 and the outer circumference of the second zone is defined by reactor tube 6. Reactor tubes 5 and 6 form a gas-tight seal with element 4 due to glass seals 7 and 8, respectively. Feed tubes 9 and 10 direct oxygen-containing gas 11 and oxygen-consuming gas 12 into zones 2 and 3, respectively. Exit ports 13 and 14 allow reacted gases to pass through 15 and 16 to zones 2 and 3, respectively.

In the embodiment, an oxygen-containing gas or gas mixture, such as air, is passed into contact with the element in the first zone, and the oxygen-consuming gas or gas mixture, such as a reactant gas-containing feed gas, is passed into contact with the element in the second zone. Since the oxygen-containing gas or gas mixture contacts the element, oxygen is reduced to oxygen ions which are transported by the element 4 to the surface facing the second zone. At the second zone, oxygen ions react with the oxygen-consuming gas or gas mixture, whereby the oxygen-consuming gas is oxidized and releases electrons. The electrons return to the surface facing the first zone via element 4.

In one embodiment, the oxygen-consuming gas is methane, natural gas, or hydrogen, and the oxygen-containing gas is a combustion or exhaust gas containing NOx 'and / or SOy, where x' and y are as defined above. When the combustion gas contacts the element, oxygen is reduced from NOx 'and / or SOy to oxygen ions transported by the element to the second zone where the oxygen ions are combined with the oxygen consuming gas to produce carbon dioxide and water, synthesis gas or olefins Depending on reaction conditions react. In one embodiment, nitrogen gas and elemental sulfur are electrochemically generated from NOx 'and SOy, formed in the first zone.

In another embodiment of the invention, the oxygen-containing gas is a gas containing vapor (ie, H 2 O gas). When H 2 O contacts the element, the oxygen from the H 2 O is reduced to oxygen ions which are transported by the element to the second zone where the oxygen ions react with, for example, methane or natural gas. The H 2 O is reduced to hydrogen gas (H 2) in the first zone. The hydrogen gas may be recovered and used, for example, to hydrogenate unsaturated hydrocarbons to provide fuel to an electric power generating fuel cell, to provide fuel for heating the electrochemical cell of this invention, or to provide a reactant gas for the electrochemical process for extracting oxygen an oxygen-containing gas according to the present invention.

Materials that coexist may participate in the electrochemical reduction or oxidation that takes place on the element of the invention. For example, if there is methane with ammonia in the second zone and an oxygen-containing gas is in the first zone, hydrogen cyanide and water can be formed electrochemically in the second zone.

Other combinations of materials that are reactive with one another to produce a wide range of products are possible and are conceivable within the scope of the present invention.

As used herein, the terms "oxygen-consuming gas", "reactant gas" and "oxygen-containing gas" include materials that are not gases at temperatures below the temperature ranges of the subject process of the invention and may include materials that are liquid or solid at room temperature. An example of an oxygen-containing gas that is liquid at room temperature is steam.

Multi-component membrane, as mentioned above, the solid multi-component membrane used in the electrochemical reactor according to the invention, an intimate, gas-impermeable, multi-phase mixture of any electronically conductive material with any oxygen ion conductive material and / or a gas-impermeable "single phase" mixed metal oxide with perovskite structure and be both with electron-conducting and oxygen-ion conductive properties. The term "gas-impermeable" is used herein to mean "substantially gas-impermeable or gas-tight" in that the mixture does not pass a substantial amount of the above-described oxygen-consuming or oxygen-containing gas through the mixture as a gas (ie, the mixture is non-porous rather than porous with regard to the relevant gases). In some cases, a low level of permeability to gases may be acceptable or unavoidable, for example when hydrogen gas is present.

The term "mixtures" in the context of the solid multicomponent membrane includes materials comprised of two or more solid phases and single phase materials in which the atoms of the various elements are mixed in the same solid phase as in the yttria-stabilized zirconia, which will be mentioned below. Examples of the preferred metal-doped metal oxides are single-phase materials, whereas the term "multiphase mixture" refers to a composition which disperses two or more solid phases without forming a single-phase solution.

In other words, the multiphase mixture is a "multiple phase" because the electronically conductive material and the oxygen ion conductive material are at least two solid phases in the gas impermeable solid membrane such that the atoms of the various components of the multicomponent membrane are, for the most part, not solidified in the same Phase are mixed together.

(1) multiple phases

The multi-phase solid state membrane of the present invention is substantially different from the known "doped" materials. A typical doping process involves adding small amounts of an element or its oxide (ie, dopant) to a large amount of a composition (ie Host material) such that the atoms of the dopant are permanently mixed with the atoms of the host material during the doping process, whereby the materials form a single phase. The multiphase solid-state membrane of the present invention, on the other hand, comprises an oxygen ion conductive material and an electronically conductive material which are not in the above-described doping / host material relationship, but are in substantially distinct phases. Thus, instead of being a doped material, the solid state membrane of the present invention may be referred to as a two-phase, dual-conductor, multi-phase or multi-component membrane.

The multiphase membrane of the present invention can be distinguished from the doped materials by routine methods such as electron microscopy, X-ray diffraction analysis, X-ray adsorption mapping, electron diffraction analysis, infrared analysis, etc., which detect differences in composition over a multi-phase region of the membrane. An example of such physical detection of the multiphase composition are the electron photomicrographs shown in FIG. 4 and FIG. 5 are shown. A detailed description of Figs. 4 and 5 follows in Examples 1 to 5 given below.

In general, the oxygen ion-conductive materials or phases are solid solutions (ie solid "electrolytes") formed between oxides containing divalent and trivalent cations, such as calcium oxide, scandium oxide, yttrium oxide, lanthana, etc., with oxides containing tetravalent cations, such as zirconia, thoria and ceria, or the oxygen ion conductive materials or phases include an oxygen ion-conductive mixed metal oxide having a perovskite structure. Their higher ionic conductivity is probably due to the presence of oxygen ion defects. An oxygen ion vacancy occurs for each bivalent or two trivalent cations that are replaced by a tetravalent ion in the lattice. Any of a large number of oxides such as yttria, stabilized zirconia, doped ceria, thoria-based materials, or doped bismuth oxides can be used. Some of the known solid oxide transfer materials include Y 2 O 3 -stabilized ZrO 2, CaO-stabilized ZrO 2, Sc 2 O 3 -stabilized ZrO 2, Y 2 O 3 -stabilized Bi 2 O 3, Y 2 O 3 -stabilized CeO 2, CaO-stabilized CeO 2, ThO 2, Y 2 O 3 -stabilized ThO 2. or ThO & sub2 ;, ZrO & sub2 ;, Bi & sub2; O & sub3 ;, CeO & sub2; or HfO 2 stabilized by the addition of one of the lanthanide oxides or CaO. Many other oxides are known which have been shown to have oxygen ionic conductivity which could be used in the multiple mixtures and are included in the present concept.

Among these solid electrolytes, the Y 2 O 3 (yttrium) oxide and CaO (calcium) oxide stabilized ZrO 2 (zirconium) oxide materials are preferred. These two solid electrolytes are characterized by their high ionic conductivity, their oxygen ion conduction over wide temperature ranges and oxygen pressures and their relatively low cost.

In addition, the inventors have found that mixed metal oxides with perovskite structure (at operating temperatures) have a very good oxygen ion conductivity. The term "perovskites" refers to a class of material having a structure based on the structure of the mineral perovskite, CaTiO₃. In its idealized form, the perovskite structure has a cubic lattice in which a unit cell has metal ions at the corners of the cell, another metal ion at its center, and oxygen ions at the midpoints of the cube edges. This is referred to as the ABO 3 type structure where A and B are metal ions.

In general, perovskite structures require that the sum of the valences of A and B ions be 6 and that the ratio between the radii of the ions in an ABO 3 structure containing two metal ions can be expressed by the formula:

where rA, rB and r & sub0; the radii of the A ions are B ions and oxygen ions, respectively, and t is a "tolerance factor" which may be in the approximate range of 0.7 to 1.0. Generally, perovskite structure compounds have A ions with a radius of between about 1.0 to about 1.4 angstroms and B ions with a radius between about 0.45 and about 0.75 angstroms. The inventors have generally found that when mixed metal oxides contain A ions of a perovskite structure whose radii approach the lower end of the A ion radius range for a given B ion as determined by the formula above, then oxygen ion conductivities generally increase. However, this trend toward increased oxygen ion conductivity may be limited by greater instability of the perovskite structure at operating temperatures as the A ionic radii approach the lower end of the desired radii for the perovskites with a given B ion.

A wide variety of metals and oxides of metals can be used to prepare perovskites useful in the present invention. In general, any combination of metals that meet the needs of a perovskite can be used. Typical examples of such metals are lanthanides, the metals of group Ia and IIa, the transition metals, Al, Ga, Ge, etc. Examples of preferred metals include La, Co, Sr, Ca, Fe, Cu, Ni, Mn, Cr, Y, Ba, Ti, Ce, Al, Sm, Pr, Nd, V, Gd, Ru, Pb, Na, W , Sc, Hf, Zr, oxides thereof and mixtures thereof. Bi and / or Ce are generally not required in the preferred embodiments, but may be present if desired. In one embodiment, Bi and / or Ce are present in amounts of less than 13 mole percent.

Preferred examples of A metals in the ABO 3 type materials usable in the present invention include the lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er , Tm, Yb and Lu), yttrium and the alkaline earth metals, especially Mg, Ca, Sr and Ba.

Preferred B metals in the ABO 3 materials for the present invention include the first series of transition metals, namely Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. Among these metals are Co, Mn, Fe and Cr are particularly preferred.

The perovskite structure is tolerant over a wide variety of multiple cation substitutions at both the A and B sites, so that a variety of more complicated perovskite compounds containing a mixture of A metals and B metals are useful in this invention. Perovskite materials containing more than two metals besides oxygen are preferred.

Increased oxygen ion conductivity can be achieved by using a mixture of metals as A ions having such stable oxidation states which are different as, at the operating temperatures of the process using the membrane, some + ions in the +3 oxidation state are stable and others are stable in the +2 oxidation state. Although the inventors do not wish to be bound by theory, it is believed that the presence of metal ions in a less stable oxidation state under metal ions in a more stable oxidation state generates oxygen ion vacancies in the ionic lattice, facilitating the migration of oxygen ions through the perovskite material.

The inventors have also found that the presence of chromium and / or titanium in the B sites of the perovskite lattice can be used to increase the stability of the perovskite structure under the conditions of electrocatalytic processes, and with chromium they observe an increase in electron conductivity, such as further described below.

Preferred mixed metal oxides having a perovskite structure can be represented by the formula:

AsAr'tBuB'vB "wOx (II)

where A is a first A ion, A 'is a second A ion, B is a first B ion, B' is a second B ion, B "is a third B ion, and s, t, u, v, w and x each represent a number such that:

s / t is from about 0.01 to about 100, preferably from about 0.1 to about 20;

u is from 0.01 to about 1, preferably from about 0.5 to about 1;

v is from 0.01 to about 1, preferably from about 0.05 to about 0.5;

w is 0 to about 1, preferably about 0.01 to about 0.5;

x represents a number which satisfies the valences of the other elements present in formula II, and

0.9 <(s + t) / (u + v + w) <1.1, preferably 0.99 <(s + t) / (u + v + w) <1.01.

In one embodiment, A represents a lanthanide or Y or a mixture thereof; A 'represents an alkaline earth metal or a mixture thereof; B returns Fe; B 'represents Cr or Ti or a mixture thereof and / or B "represents Mn, Co, V, Ni or Cu or a mixture thereof, wherein u and optionally w are greater than zero. In a preferred embodiment, A represents La or Y or a mixture thereof; A 'represents Ca or Sr or a mixture thereof; B returns Fe; B 'represents Cr and / or B "represents Mn or Co or a mixture thereof Small amounts of other elements may be present as those present as impurities.

Examples of perovskite-type mixed metal oxides usable as the solid oxygen-ion conductive electrolyte in the present invention include lanthanum strontium cobaltite, lanthanum strontium ferrite, lanthanum strontium iron chromite, lanthanum strontium iron chromium cobaltite, lanthanum strontium iron chromium ganganite, lanthanum -Strontium manganite, lanthanum calcium colbatite, lanthanum calcium iron chromite, lanthanum calcium iron chromium cobaltite, lanthanum calcium iron chromium manganite, Lanthanum calcium manganite, yttrium strontium ferrite, yttrium strontium cobaltite, yttrium strontium iron chromite, yttrium strontium iron chromium cobaltite, yttrium strontium iron chromium ganganite, yttrium strontium manganite, strontium cobalt ferrite, strontium iron cobaltite, gadolinium strontium cobaltite, etc., and Mixtures thereof. Specific examples are LaaSrbCoOX, LaaSrbFeOx, LaaCabCoOx, SrCoaFebOX, GdaSrbCoOX, etc., where a, b and x are numbers, where the sum of a and b is 1 and x is as defined in formula II above. The molar ratio between the respective metals represented by a: b can cover a wide range. Typical doping ratios a: b are 4: 1, 3: 1, 1: 4, 1: 3, etc.

The electronically conductive material or the electronically conductive phase of the membrane may be any material that exhibits sufficient electronic conductivity under the reaction conditions. In general, the electronically conductive phase comprises one or more metals or metal oxides that exhibit appreciable electronic conductivity at reaction temperatures. Suitable metals include silver, gold, platinum, rhodium, ruthenium, palladium, nickel, cobalt, copper, etc., with palladium and platinum being preferred. Examples of suitable metal oxides include bismuth oxides, tin-indium oxide mixtures, praseodymium-indium oxide mixtures, cerium-lanthanum oxide mixtures, niobium-titanium oxide mixtures, electron-conductive mixed metal oxides with perovskite structure, etc., among which the metal-doped metal oxides such as praseodymium-doped indium oxides, tin-doped indium oxides, cerium-doped lanthanum oxides, niobium doped titanium oxide mixtures, electron-conductive mixed metal oxides with perovskite structure, including the electron-conductive perovskites described above in connection with perovskites suitable as an oxygen ion-conductive component, etc., are preferred. Among the metal-doped metal oxides, praseodymium-doped indium oxides and the mixed metal oxides are particularly preferred.

In many ABO 3 -type mixed metal oxide compounds, the actual structure is a continuum of a pseudo-symmetric variant derived from the perfectly symmetrical simple cubic structure by small displacements of the ions. In some cases, these shifts result in little distortion of the unit cell, the symmetry of which is thus reduced to tetragonal or orthorhombic, and in others the deformation is such that the neighboring cells are no longer exactly identical, so that the actual unit cell is more than one of lower units. The ferroelectric properties of many of these oxides are due to such deviations from the ideal structure.

Electron conductivity of mixed metal oxides with perovskite structure generally increases when the A ion is partially substituted or "doped" with a divalent metal cation such as Ba, Ca or Sr. This trend towards greater electron conductivity is often associated with higher instability at operating temperatures. Perovskites, which are partially decomposed to a different structure, may have electron conductivity substantially different from that of the original perovskite structure.

As mentioned above, the inventors have found that the presence of chromium and / or titanium at the B sites of the perovskite lattice enhances the stability of the perovskite structure and that the presence of chromium has an additional advantage in increasing the electronic conductivity, even if chromium is present in the tetravalent oxidation state is present.

Although the inventors do not wish to be bound by any particular theory as to why the presence of certain metal ions enhances electron conductivity, the inventors have found that the presence of metal ions changing from one oxidation state to another without requiring a high redox potential can, in general, increase the electron conductivity. Examples other than chromium include iron, cobalt and manganese.

Specific examples of mixed metal oxide materials include lanthanum strontium manganite, lanthanum strontium cobaltite, lanthanum strontium iron chromite, lanthanum strontium iron chromium cobaltite, lanthanum strontium iron chromium ganganite, lanthanum calcium iron chromite, lanthanum calcium iron chromium cobaltite, lanthanum -Calcium Iron Chromium Manganite, Lanthanum Magnesium Chromite, Lanthanum Chromium Ferrite, Lanthanum Cobaltite, Yttrium Strontium Iron Chromite, Yttrium Strontium Iron Chromium Cobaltite, Yttrium-strontium-iron-chromium-manganite, yttrium-barium-copper (for example, YBa₂Cu₃Ox, wherein x is defined as in the above formula (II), etc.) and mixtures thereof.

Suitable ABO 3 -type compounds and as prepared are described in PCT Application No. 89085506, published May 9, 1989, Publication no. WO, 89/01922, Dow Chemical Company; Muller and Roy, "The Major Ternary Structural Families," pp. 175-201 (1974); Lines, ME and Glass, AM, "Principles and Applications of Ferroelectrics and Related Materials"; Pages 280-92 and Appendix F, pages 620-33 (Clarendon Press), Oxford (1977); and Evans, R. D., "An Introduction to Crystal Chemistry", Cambridge Univ. Press., Cambridge, 2nd Edition (1964), pages 167-71. Each of these references is incorporated by this reference for its disclosure regarding perovskites.

These multiphase multicomponent membranes may contain from about 1 to about 75 parts by volume of an electron-conductive material and from about 25 to about 99 parts by volume of an oxygen-ion-conductive material. The elements Bi, Ce and Ti may be excluded individually or in total from the preferred embodiments.

The multiphase multicomponent membranes can be made by combining at least one of the electronically conductive materials with at least one of the oxygen ion-conductive materials and forming the combined materials to form a dense, gas-tight, multiphase solid-state membrane. In particular, the solid membrane can be made by a process comprising the steps

(A) forming an intimate mixture of at least one material that is electronically conductive and at least one oxygen ion conductive material

(B) shaping the mixture into a desired shape and

(C) heating the shaped mixture to a temperature of at least 500 ° C to form a dense and solid membrane.

The solid membrane may also be made of at least one metal oxide, the metal thereof being electronically conductive, by a process comprising the steps

(A) forming an intimate mixture of at least one metal oxide, the metal thereof being electronically conductive, and at least one oxygen ion-conductive material

(B) heating the mixture at an elevated temperature in a reducing atmosphere to reduce the metal oxide to metal,

(C) forming the reduced mixture into a desired shape and

(D) heating the shaped mixture to a temperature of at least about 500 ° C to produce a dense and solid membrane.

(2) single-phase mixed metal oxide

As noted above, the multicomponent solid membrane employed in the electrochemical reactor of the present invention may comprise, as an alternative to a multiphase multicomponent membrane or in addition to the multiphase material, a gas impermeable "single phase" of mixed metal oxides having a perovskite structure and having both electronically and oxygen ionically conductive properties. Many of the perovskite type materials described above are suitable for this aspect of the present invention. Specific examples of perovskite materials that are suitable include the following materials:

LaCoOx;

La0,6Sr0,4CoOx;

La0,2Sr0,8CoOx;

YCoOx;

YBa 2 Cu 3 O x,

wherein x is defined as in the above formula (II), etc., but is not limited thereto.

The mixed metal oxides represented by the formula AsA'tBuB'vB "wOx (Formula II) described above are suitable for use as the single phase mixed metal oxide membrane of the present invention because they have the advantage of stability under electrocatalytic conditions as well as electron and oxygen ion conductivity Formula I given above also applies to this aspect of the present invention.

Mixtures of perovskites with additional conductive metal or metal oxide are also useful in the preparation of the multicomponent membrane used in the present invention. The additional conductive metal or metal oxide may be the same or different from the elements present in the perovskite. It has been found that the additional conductive metal or metal oxide forms a distinct phase of the perovskite material after heating, with additional conductive materials being formed by the perovskite to form electronically conductive paths through the membrane. In a preferred embodiment, the multicomponent membrane comprises a mixture of perovskite, such as lanthanum cobaltite, lanthanum strontium cobaltite, and an excess of a conductive metal or metal oxide, such as an excess of cobalt metal in a cobalt-containing perovskite.

In a further embodiment, the multicomponent membrane comprises a mixture of two or more perovskites, each perovskite having advantages in electron conductivity or oxygen ion conductivity, and may additionally include conductive metal or metal oxide as discussed above.

A variety of powder preparation methods can be used to prepare a solid state membrane having electron conductive and oxygen ion conductive properties, such as the perovskites described above. Suitable processes include (a) preparation of oxides, (b) thermal decomposition of nitrates and / or acetates, and (c) the citric acid production process.

(a) Method of preparation from oxides

As an example, the solid state membrane can be prepared from the oxides by a process comprising the steps of:

(A) Preparation of Perovskite Powder Containing the A and B Metals Described Above

(B) molding a mixture into a desired shape and

(C) heating the shaped mixture to a temperature sufficient to form a dense and solid membrane having electron conductivity and oxygen ion conductivity properties. In general, the temperature for this step is at least about 500 ° C, and generally at least about 1000 ° C.

(b) Preparation by thermal decomposition of nitrates and / or acetates

The preparation of mixed metal oxide compositions by thermal decomposition of nitrates and / or acetates comprises the steps:

(A) dissolving nitrate and / or acetate salts of the desired elements in a polar solvent, such as water,

(B) heating the polar solvent removal solution obtained in step (A) until a solid powder is obtained,

(C) heating the dried solid to a temperature sufficient to decompose the nitrate and / or acetate salts,

(D) shaping the mixture into a desired shape and

(E) heating the shaped mixture to a temperature sufficient to produce a dense and solid membrane having electron-conductive and oxygen-ion conductive properties. In general, the temperature for steps (C) and (E) is at least about 500 ° C. Step (C) is generally carried out at a temperature of at least about 900 ° C and step (E) generally at a temperature of at least about 1000 ° C.

(c) Preparation by a citric acid preparation method

The preparation according to the citric acid preparation method comprises

(A) mixing nitrate and / or acetate salts of the desired elements in a polar solvent, such as water containing citric acid in solution,

(B) heating the mixture to an elevated temperature to form a solid powder,

(C) molding the mixture into a desired shape and

(D) heating the shaped mixture to a temperature sufficient to form a dense and solid membrane having electron-conductive and oxygen-ion conductive properties. Again, the temperature for this step is at least about 500 ° C, and generally at least about 1000 ° C.

In the above-mentioned methods for producing the multi-component membrane, a binder is generally added to the mixture before the last heating step to assist in bonding the metal and / or metal oxide particles to a desired shape. The agent is preferably a material which will not interfere with the formation of a dense and solid membrane in the final step of heating the shaped mixture to a temperature of at least 500 ° C and which may readily disperse in the mixture. Such a binder may be, for example, a wax or a paraffinic hydrocarbon dispersed or dissolved in a suitable solvent. A specific example of a binder is Carbowax's 20M ™ (Supelco) dissolved in sufficient chloroform to distribute a binding amount of wax onto the electronically conductive and oxygen-ion conductive particles.

The modification and / or additional formation of the perovskite structures may take place under reaction conditions in the reactor cell comprising the mixed metal oxides of perovskite structure.

The element

The above-mentioned "element" preferably comprises:

(A-1) a solid electrolyte having a first surface coated with metal, metal oxide or a mixture thereof capable of reducing oxygen to oxygen ions and a second surface coated with metal, metal oxide or mixtures thereof, the oxygen ions with an oxygen-consuming gas can implement, with the proviso, that both coatings are stable and electron conductive at operating temperature and are connected to an outer electron conductive circuit;

(A-2) a solid multi-component membrane having a first surface and a second surface and comprising an intimate, gas-impermeable, multiphase mixture of an electronically conductive phase and an oxygen ion-conductive phase.

Element (A-1) will be described in more detail below.

The solid electrolytes of (A-1) may be any material which is stable under operating conditions and capable of transferring oxygen ions, especially at temperatures above 300 ° C. Preferably, the solid electrolyte is selected from the oxygen ion conductive materials described above in connection with the multi-component membranes in the present invention. Preferably, the solid electrolyte is a substantially non-porous gas impermeable solid.

Preferred solid electrolytes are the Y 2 O 3 (yttrium) oxide and CaO (calcium) oxide stabilized ZrO 2 (zirconia) materials and perovskite structured electrolytes. These solid electrolytes are characterized by their high ionic conductivity, their oxygen ion conductivity over wide temperature and oxygen pressure ranges, and their relatively low cost.

The conductive coating on the cathode side may be any material that can facilitate the reduction of oxygen to oxygen ions by supplying electrons to the cathode surface and that is stable under the operating conditions. Examples of metals and metal oxides useful in the preparation of the cathode include silver, platinum, nickel, gold, bismuth, palladium, copper, cobalt, chromium, iron, niobium-titanium, lanthanum-manganese mixtures, indium-tin oxide. Mixtures, praseodymium-indium oxide mixtures, combinations of any of the two metals or metal oxides used to make the perovskites described above, electronically conductive perovskites and mixtures of the metals, Metal oxides and combinations used to prepare perovskites.

The conductive coating on the anode side may be any of a wide variety of conductive materials that can facilitate the reaction of oxygen ions with an oxygen-consuming gas, provided that the material is also stable under the operating conditions. Examples of metals and metal oxides useful in the preparation of the anode coating include the materials described above in the preparation of the cathode, but more particularly include silver, gold, nickel, bismuth, manganese, vanadium, platinum, rhodium, ruthenium, Palladium, copper, zinc, cobalt, chromium and ferrous metals and metal oxides, any mixtures of these metals and metal oxides and further mixtures, such as silver-bismuth oxide mixtures, Tin-indium oxide mixtures, praseodymium-indium oxide mixtures, cerium-lanthanum oxide mixtures, etc., and mixtures thereof. Among these, silver, gold and mixtures of silver and gold are preferred.

Each conductive coating may be in the form of a thin film and / or a porous conductive coating. The conductive coating is preferably porous. The porous conductive coating can provide benefits in increasing the contact area between the membrane or coated electrolyte, and the gas or gas to be treated or gas can thereby increase the rate of electrocatalysis. The electrochemical reaction rate can be accelerated by pressing the electrical potential on this outer circle to increase the electron current in the direction of the conductive surface upon contact with the oxygen-containing gas. If the conductive coating comprises a catalyst, the speed for the electrochemical process can be increased even more.

The element may further comprise a porous substrate (1). The porous substrate (1) is porous to the reactant or product gases and serves as a carrier for the solid electrolyte having conductive coatings (A-1) and / or the multicomponent solid membrane (A-2). It can be any material that achieves the desired goal as long as it does not interfere with the reaction process under the reaction conditions. Any of a variety of oxides including yttria-stabilized zirconia, doped ceria, thoria-based materials, or doped bismuth oxides described above as oxygen-conductive materials and various other metal oxides may be used. Examples include CaO stabilized ZrO 2; Y₂O₃-stabilized ZrO₂; Sc 2 O 3 -stabilized ZrO 2; Y₂O₃-stabilized Bi₂O₃; Y₂O₃-stabilized CeO₂; CaO-stabilized CeO 2; ThO 2 ;; Y₂O₃-stabilized ThO₂; ThO & sub2 ;, ZrO & sub2 ;, Bi & sub2; O & sub3 ;, CeO & sub2; or HfO 2 stabilized by the addition of one of the lanthanum oxides or CaO; Al 2 O 3; etc.

The solid electrolyte having conductive coatings (A-1) and multi-component membrane (A-2) may be applied to a support substrate by a method such as vapor deposition on a porous substrate, impregnation of a porous substrate, co-impregnation of a porous support substrate, or any other for the preparation of Ceramic usual method, are applied. Alternatively, such elements can be made by tape casting a slurry mixture, slip casting or other technique. Any method is the heat treatment of the formed coated solid electrolyte or the membrane precursor to form a stable structure or until it is gas-tight, and attaching the obtained coated solid electrolyte or membrane to a support structure and also heat treatment to the final supported coated solid electrolyte or membrane to obtain. Other methods are possible as long as the supporting substrate allows an oxygen-containing gas and an oxygen-consuming gas to come into contact with the coated solid electrolyte or membrane of the present invention.

The present invention may be further described with reference to Figs. 2 and 3, which illustrate one embodiment of the electrochemical reactor of the invention. Fig. 2 is a plan view of a chemical reactor of the present invention which differs from an electrochemical reactor shown in Fig. 1, and Fig. 3 is a side view and a cross section of the same reactor as shown in Fig. 2. In both FIG. 2 As well as 3, the electrochemical reactor comprises a shell 20 in which a circular solid cylindrical reactor cell or a core 21 comprising a solid multi-component membrane is arranged. As can be seen from the construction illustrated in Figs. 2 and 3, the reactor includes an inner passage 22 in the core 21 which traverses the entire length of the core 21 and an outer passage 23 between the outer surface and the core 21 and the inner surface the shell 20.

In practice, the methods of the present invention are performed with an apparatus as illustrated in FIGS. 2 and 3 by passing, for example, an oxygen-consuming gas, through the inner passage 22 and an oxygen-containing gas through the outer passage 23. The oxygen-containing gas, which comes into contact with the outer surface of the dual-conductor core 21, is converted to oxygen ions, which migrate through the solid core 21 to the inner surface of the core 21. At the inner surface of the core 21, the oxygen ions react with the oxygen-consuming gas contacting the inner surface. During this reaction, although the oxygen ions lose electrons traveling on the inner surface of the core 21 to the outer surface of the core 21.

Of course, the above process can be reversed by passing an oxygen-containing gas through the inner passage 22 and an oxygen-consuming gas through the outer passage 23. Oxygen ions then travel through the solid core 21 to the outer surface of the core 21 and electrons migrate to the inner surface.

In general, for a process in which a synthesis gas is produced, one or more light hydrocarbons will be present in the internal passageway 22 and, if the element comprises a porous support for the membrane of the solid core 21, the porous support will normally be at the Outer surface of the membrane. The decision as to which zone to use for the oxygen-consuming gas and the oxygen-containing gas and the arrangement of a porous support, if any, will depend on which arrangement is most suitable for the particular application of the present invention. The determination of the most suitable arrangement is clearly in the ability of the expert to make a determination without undue experimentation.

Perovskite and multiphase membranes of the element also have different degrees of stability with respect to the presence of a reducing gas and other reactive gas components. Since the method of the invention exposes the membrane surface to such reactive components, it may be desirable to increase the surface area of ​​the multi-component membrane by formulating the surface of the membrane or coating the membrane with metal, metal oxide or perovskite, the stability to the gas with which it is used Contact comes, exhibit, protect. The inventors have found that by making the last layer of a perovskite or multiphase multicomponent membrane into a layer containing, for example, a lanthanide and chromium, this would be one way of maintaining the stability of a reactive gas such as a reducing gas or corrosive gas containing oxides of sulfur or nitrogen would aid exposed surface.

In one embodiment, the element comprises a multi-component membrane coated on one or both sides with conductive metal, metal oxide or a mixture thereof (2). Each conductive coating may be in the form of a thin film and / or a porous coating as described above in connection with the element comprising (A-1). When such an element comprises a first surface coated with a conductive metal or metal oxide or mixture thereof which can facilitate the reduction of oxygen to oxygen ions and a second surface also coated with a conductive metal, metal oxide or mixture thereof, For example, the first and second conductive coatings may be connected to an optional outer circle as in (A-1) above to facilitate the transfer of electrons from the second conductive surface to the first conductive surface. The conductive coatings may comprise a catalyst and an electrical potential may be applied across this outer circle to increase the electrochemical reaction rate even more than in (A-1) above.

An element of the present invention is shown schematically in Fig. 8, wherein a core 41 comprising a multi-component membrane or a solid electrolyte, on a surface 42 with a material 43 which is suitable for the reduction of oxygen to oxygen ions. This coating provides the cathode side of the cell. On a second surface 44 of the core 41, a further coating of material 45 is attached. This coating is the anode. Optionally, the two coatings may be connected by an outer circle via wire leads 46 and 47. If the core does not comprise any electrically conductive material, the outer circle is required. An ammeter 48 may be included in the circuit. A battery for applying an electrical potential between the two conductive coatings (electrodes) must also be present in the circuit.

The present invention may be further illustrated by way of example with reference to Figs. Fig. 9 is a plan view of an electrochemical reactor according to the present invention; and Fig. 10 is a side view of the same reactor. Both in FIG. 9 As well as 10, the electrochemical reactor comprises a shell 50 in which is arranged a circular solid cylindrical electrochemical cell comprising a core 51 comprising a multi-component membrane or a solid electrolyte. The inner surface of core 51 is coated with an electrically conductive metal or metal oxide serving as anode 52. The outer surface of the core is coated with an electrically conductive material 53, which serves as a cathode. Optionally, a wireline 56 is connected to the inside of the coating 52 and a second wireline 57 is connected to the outer coating 53, and the two wirewires are connected via ammeter 58 to an outer circle. A battery can be connected in series with the ammeter. As is apparent from the embodiment shown in FIG. 9 10 and 10, the reactor includes an inner open space 54 through the center of the cell and an outer open space 55 between the outer coating 53 or the anode of the cell and the shell 50.

The element also comprises a catalyst (3) independently of the above. The catalyst may be dispersed as a film over the surface of the element, or mixed at the surface of the solid multi-component membrane (e.g., by doping the solid membrane surface), or dispersed or dispersed or mixed in a conductive coating. For example, the catalyst may be a sulfur reducing catalyst on the cathode side of the element, or may be a dehydrogenating or oxidizing coupling catalyst on the anode side, as discussed further below.

The porous substrate (1); conductive coating (2); and / or catalyst (3) may be used as separate materials or the functions of the porous substrate (1); the conductive coating (2) and / or the catalyst (3) can be combined in one or two materials.

Optionally, the electrochemical cell used in the methods of the invention may contain a catalyst adjacent to the element. For example, when the electrochemical cell is used for gas purification, the inventors have found that the presence of a catalyst facilitates the reduction of oxides of sulfur and nitrogen and / or facilitates the decomposition of carbonyl sulfide on the first conductive surface (ie, cathode) of the electrochemical cell.

The catalyst may be in the form of discrete particles or fibers adjacent to the surface of the cell membrane.

In an embodiment illustrated in Figs. 6 and 7, the electrochemical cell comprises a solid core 33 comprising a multicomponent solid membrane having a first surface 32 capable of reducing oxygen to oxygen ions. The core 33 has a second surface 34 that can react oxygen ions with an oxygen-consuming gas in a second passage 36. Adjacent to the second surface 34 is a second passage 36 containing the catalyst 35.

In practice, the processes of the invention, such as the production of unsaturated hydrocarbons or the production of substituted aromatic compounds, can be carried out with a device as illustrated in FIGS. 6 and 7, similar to the processes using the device of FIGS. 2 and 3 become. The catalyst 35 may be adjacent to the first surface 32 instead of the second surface 34 by placing the catalyst 35 in a first pass adjacent to the first surface 32 or by inverting the first surface 32 and the second surface 34 such that the second surface 32 and 34 first surface is to be arranged. These last two arrangements can be used, for example, in processes for the extraction of oxygen from oxygen-containing gases.

In one embodiment of an electrochemical reactor illustrated in FIG. 11, the electrochemical cell comprises a solid core 61 comprising a solid multicomponent membrane or solid electrolyte coated with a material 62 to form a first electronically conductive surface 63 that facilitates reduction from oxygen to oxygen ions. A passage 71 is adjacent to the first surface 63. A first electronically conductive surface 63 comprises the cathode of the cell. The solid core 61 is coated with a material 4 to form a second electron-conductive surface 65 which is capable of facilitating the reaction of oxygen ions with an oxygen-consuming gas. A catalyst 69 is present in the second passage 70 adjacent to the second surface 65. A second electronically conductive surface 65 comprises the anode. The reactor optionally has lead wires 66 and 67 forming an outer circle. An ammeter 68 may be included in the outer circle.

The present invention may be further explained with reference to FIGS. 12 and 13. In both Figs. 12 and 13, the reactor comprises a shell 80 in which is disposed a circular solid electrochemical cell comprising a core 81 comprising a multi-component membrane or a solid electrolyte. A surface of the solid core 81 is coated with an electrically conductive metal, metal oxide or mixture thereof to form the first conductive surface 82. The other surface of the solid core 81 is coated with an electrically conductive material to form the second conductive surface 83. An optional wireline 87 is bonded to the first surface 82 and an optional second wireline 88 is bonded to the second surface 83 and the two wirewires are connected to form an outer circle by an optional ammeter 89. A battery may be connected in series with the ammeter. As can be seen from the construction illustrated in FIGS. 12 and 13, the cell includes a first passage 86 adjacent to the first surface 82. A second passage 84 including a catalyst 85 is located between the second surface 83 and the shell 80.

The particular catalysts may be used in the processes of the present invention, as explained more fully in the following description of the process.

The preferred embodiments of the electrochemical process now follow.

Extraction of oxygen from oxygen-containing gas

The electrochemical method for extracting oxygen from oxygen-containing gas according to the present invention is carried out using the electrochemical cell of the present invention. The process is generally carried out at a temperature in the range of about 300 ° C to about 1400 ° C. In one embodiment, the process may be carried out in a range of about 500 ° C to about 1400 ° C. In another embodiment, the process is carried out in the range of about 700 ° C to about 1100 ° C. In a preferred embodiment, the process is carried out at a temperature of at least about 400 ° C, and is preferably not higher than about 1000 ° C, and more preferably not higher than about 900 ° C. The electrochemical cell may be heated to the desired temperature and the temperature maintained during the reaction using a hot combustion gas, external heating and / or use of reaction exotherm.

The oxygen-containing gas treated by the process of the invention may be any gas containing free oxygen and / or containing oxygen in other forms, such as N 2 O, NO, NO 2, SO 2, SO 3, H 2, and the like. O (g) (ie, water vapor), CO? or a mixture of oxygen-containing gases, such as combustion gas, etc.

The reactant gas includes any gas that is capable of reacting with oxygen or oxygen ions, including one or more hydrocarbons that are in the gas phase and that can react with oxygen or oxygen ions under the process conditions, such as saturated and unsaturated lower aliphatic hydrocarbons. such as methane, natural gas, ethane, ethene, acetylene, propane, propene, propyne, butane, butene, butyne, isobutane, isobutene etc., saturated and unsaturated cyclic lower hydrocarbons such as cyclopropane, cyclobutane, cyclobutene, etc., aromatic hydrocarbons such as benzene, naphthalene, etc., and mixtures thereof, natural gas, hydrogen, carbon monoxide, hydrogen sulfide, methanol, ammonia, etc., and mixtures thereof. The selection of one or more gases capable of reacting with oxygen or oxygen ions under the reaction conditions of the present invention is within the scope of those skilled in the art.

Preferred reactant gases or gas mixtures for use in this process are those which are inexpensive per unit volume, by-products of an industrial process, and / or form suitable products when reacted with oxygen or oxygen ions. A particularly preferred gas for use as a reactant gas is natural gas.

In one embodiment of the method according to the invention, at least one electrochemical cell is provided in the passage for combustion gas or exhaust gases for purifying, purifying and recycling fuel gas or exhaust emissions. The electrochemical cell in this process separates a combustion gas zone from a zone containing combustion or exhaust gas.

The gas containing oxides of sulfur and / or nitrogen which is passed in contact with the first surface or cathode may contain SO 2, SO 3, NO 2, NO, N 2 O, etc., in amounts of only about 0.001 mol. % to about 100 mole percent. Preferably, the amount of sulfur and / or nitrogen in the gas stream to be treated is in the range of about 0.005 to about 5 mole percent, and more preferably in the range of about 0.1 to about 1 mole percent, since typical combustion and exhaust streams are oxides of Sulfur and / or nitrogen contained in this more preferred range in operation.

In the embodiment, a gas mixture containing one or more oxides of sulfur and / or nitrogen is passed into contact with the first surface of the element (the cathode) and the reducing gas is passed into contact with the second surface of the element (anode) , When the contaminant-containing gas contacts the first surface, oxygen is reduced to oxygen ions that are transported through the anode-side member. At the anode side (second surface), the oxygen ions react with the reducing gas and electrons are released. The electrons return to the cathode side.

In one embodiment, the method of the invention is performed with a device as illustrated in FIGS. 9 and 10 by passing a reducing gas through the inner open surface 54 and an oxide of sulfur and / or nitrogen-containing gas stream through the outer open space 55. The oxides of sulfur and nitrogen contacting the outer surface of the conductive coating 53 are reduced to release oxygen ions that migrate through the core 51 toward the inside of the conductive coating 52. At the surface of the inside coating 52, the oxygen ions react with the reducing gas contacting the inside of the conductive coating 52. During this reaction, the oxygen ions lose two electrons that migrate from the inner conductive coating 52 to the outer surface coating 53 through core 51 and optionally through the circuit formed by lines 56 and 57 and ammeter / battery 58.

In another embodiment, the anode and cathode are also reversed. That is, the inner conductive coating 52 is the cathode and the outer conductive coating 53 is the anode. In this embodiment, the fuel gas is passed through the outer open space 55 and the gas and gas containing oxides of sulfur and / or nitrogen are passed through the inner or middle open space 54. Otherwise, the operation in this embodiment is the same as the embodiment discussed above.

In the last two embodiments of the invention, the rate of gas cleaning is improved by applying an electrical potential between the anode and cathode. In general, a potential of up to about 4 volts can be applied between the electrodes. The desired electrical potential may be applied using a battery formed in an outer circle formed by 56, 57 and 58 in FIG. 10.

The inventors have also found that a high rate of gas purification can be achieved by selecting a solid membrane or solid electrolyte having a small thickness between the first surface and the second surface relative to the exposed surface of the electrolyte (ie, a small volume of electrolyte per unit area ), which decreases by the distance that the average oxygen ion must travel through the electrolyte per unit area. For example, thin walled high density yttria stabilized zirconia tubes with increased wall thickness efficiency of 1 mm, for example, can be obtained from Zircoa Products, Solon, Ohio. This efficiency enhancement does not require the attachment of external direct current sources, which makes this a preferred approach for carrying out the process economically.

A method for producing thin gas-tight refractory oxide layers for use in the solid electrolyte of the electrolytic cell of the present invention is a "vapor deposition" method such as the electrochemical vapor deposition method disclosed by Westinghouse Electric Corporation of AO Isenberg, "Proceedings of the Electrochemical Society , Vol. 77, No. 6, pp. 572-583 (1977), incorporated herein by this reference.

Among the metals and metal oxides which may be present as a conductive metal, metal oxide or mixture thereof on the cathode, silver, platinum and gold are particularly preferred.

In addition to sulfur and / or nitrogen oxides, the gas stream to be purified may also contain other components, such as nitrogen gas, oxygen gas, argon, helium, carbon dioxide, water vapor, carbon monoxide, unburned fuel, etc. The presence of oxygen-containing gases, such as oxygen gas and carbon dioxide, may For example, consume some of the fuel gas used to convert oxides of sulfur and / or nitrogen. However, the inventors have found that the present invention is most economical in most fields when used with such gas streams, since the additionally used fuel gas is significantly less expensive than the electricity used in electrolytic processes, such as those disclosed in U.S. Patent 4,659,448 , in relation to the relevant costs of fuel gas compared to kilowatt hours of electricity.

Optionally, the electrochemical cell used in the method of the invention may contain a catalyst adjacent to or coated on the first conductive surface. The inventors have found that the presence of a catalyst can facilitate reduction of oxides of sulfur and nitrogen and / or facilitate the decomposition of carbon sulfide on the first conductive surface (ie, cathode) of the electrochemical cell. The catalyst may be present as a film over the first conductive surface of the solid electrolyte of the electrochemical cell, dispersed or mixed in the first conductive coating (e.g., by doping the electron-conductive coating), or in the form of discrete particles or fibers adjacent to the first conductive one Surface of the cell (cathode), present.

In practice, the process of the present invention is practiced with an electrochemical cell as in FIGS. 12 and 13 similar to the process using the electrochemical cell of FIGS. 9 and 10.

First-pass catalysts include oxides of lanthanum, oxides of lanthanum doped with europium (Eu), oxides of a mixture of lanthanum, strontium and cobalt, oxides or a mixture of zinc and iron, oxides of molybdenum and oxides of tungsten. Specific examples of catalysts for reducing oxides of sulfur include La 2 O 3, La 0.6 Sr 0.4 CoO 3. (a perovskite), ZnFe 2 O 4, ZnMoO 4, FeWO 4, ZnFe 2 O 4, ZnMoO & sub4; etc. These catalyst materials may optionally retain the molecular formula and / or structure set forth herein during the process of the present invention, as the sulfur atom is highly reactive with or may combine with certain elements in the catalyst examples. For example, lanthanum oxides that tend to form lanthanum oxysulfides, and perovskites, such as the lanthanum strontium cobalt perovskites mentioned above, often lose their perovskite structure when exposed, for example, to oxides of sulfur.

Methods of making and using these catalysts are known in the art. Examples of references describing these catalysts include Baglio, "Lanthanum Oxysulfide as a Catalyst for the Oxidation of CO and COS by SO2", Ind. Eng. Chem. Prod. Res. Dec. (1982) Vol. 21, pp. 38-41, and Hibbert et al., "Flue Gas Desulfurization: Catalytic Removal of Sulfur Dioxide by Carbon Monoxide on Sulphided La1-x Srx CoO3", Part II, Applied Catalysis (1988) Vol 289-299.

This process of the invention is generally carried out at a temperature of at least about 300 ° C, and preferably at a temperature of at least about 400 ° C. The process temperature is preferably not higher than about 1000 ° C, and more preferably not higher than about 900 ° C. The temperature for a particular electrochemical cell / feed gas composition system can be readily optimized by one skilled in the art by examining the conversion rates at different temperatures for the optimum turnover rate / temperature. The upper limit for the operating temperature is generally below the temperature at which the electrochemical cell components decompose to undesirable materials.

The step of heating the electrochemical cell may be partially or completely provided by the heat normally present in the combustion or exhaust gas, such as that produced by combustion of hydrocarbons, or may be heated by an external source. Methods of controlling temperature, including cooling by injection with a low temperature gas, or mixtures of gases into the reactant gas zone and / or the zone containing the combustion or exhaust gas, convective cooling, liquid cooling, etc., may be used if necessary to overheat of the electrochemical process, and may be accomplished by various means well known in the art. Such measures are conceivable within the scope of the invention.

In general, the process of the invention is carried out at a pressure of from 0.1 to 100 atmospheres, more preferably between 0.5 and 10 atmospheres, and most preferably about 1.0 atmospheres.

The flow rate of the gas stream containing sulfur and / or nitrogen oxide through the cell may optionally be varied as long as there is sufficient contact by the gas flow with the cathode to obtain the desired reduction of sulfur and nitrogen emissions. Contact times of 0.1 to 100 seconds can be used, although contact times of 1 to 20 seconds are generally sufficient.

The flow rate of the reducing gas may also be varied, if desired, as long as there is sufficient contact by the reducing gas with the anode to provide the desired reduction in sulfur and nitrogen oxide emissions.

In the examples below, oxygen consuming gases are treated in a laboratory reactor similar to the reactor illustrated in FIG.

Multicomponent membrane Dangerous Preparations examples

The multi-component membranes used in Examples A-1 to A-14 are prepared as follows.

Example A

The dual-conductor membrane used in Examples A-1 and A-2 below is fabricated by preparing a disk containing palladium metal as the electronically conductive phase and yttria-stabilized zirconia (hereinafter referred to as "YSZ") as the ionic conductive phase. A mixed powder of 50% each of palladium oxide and yttria (8 mol%) stabilized zirconia is first prepared. The powder is then heated in a mixture of hydrogen and nitrogen atmosphere at 400 ° C for 15 minutes to reduce palladium oxide to palladium metal. To 4.0 g of the mixture is added 0.4 g Carbowax 20M ™ (obtained from Supelco) dissolved in chloroform and the resulting mixture is dried at 85 ° C. The resulting Pd / yttria-stabilized zirconia / Carbowax 20M ™ powder is pressed into a disk using 60,000 psi of pressure. The disk is then sintered in air at 1500 ° C for 30 minutes. The resulting disc is tight and gas tight. The disk has a diameter of 1 inch and 0.03 inches (0.76 mm) in thickness.

Example B

The dual conductor membrane used in Example A-3 below is made by preparing a disk containing platinum metal as the electronically conductive phase and YSZ as the ionically conductive phase. 9.52 g of Engelhard Platinum Ink (a product of Engelhard Corporation: Catalog No. 6926) is mixed with 3 cc of alpha-terpineol and then 2.0 g of yttria (8 mol%) stabilized zirconia are mixed in the diluted ink , The mixture is evaporated to dryness and terpineol is incinerated in an oven at 100 ° C. The dried mass is then pulverized and 8.49 g of the dried powdered powder are added to 0.94 g of Carbowax 20M ™ dissolved in 20 cc of chloroform. The chloroform is evaporated and the remaining powder is dried in an oven at 85 ° C for about 30 minutes and the powder is ground slightly and sieved through a 120 mesh sieve. Then, 5.0 grams of the sieved Pd / yttria-stabilized zirconia / Carbowax 20M ™ powder is compressed into a 1 to 3/8 inch (3.50 cm) diameter disk using 60,000 psi of pressure. The disk is then heated to 1650 ° C at a rate of 1 to 1/2 ° C / minute, sintered in air at 1650 ° C for 2 hours and cooled at a rate of 4 ° / minute. The resulting disc is tight and gas tight.

Example C

The dual conductor membrane used in Example A-4 below is made by preparing a disk containing a combination of lanthanum, chromium and magnesium oxides as the electronically conductive phase and YSZ as the ionically conductive phase. A powder mixture of 0.25 g MgO, 5.52 g CrO and 10.00 g La 2 O 3. is first produced. The powder is then dried at 100 ° C and comminuted again. Then, 5.0 g of the obtained La (Cr 9 Mg) powder is added to a hot aqueous solution containing 0.5 g of B 2 O 3, and the resulting solution is then dried and crushed to a very fine powder. Then, 4.5 cc of B-MgLaCr powder is mixed with 4.5 cc of yttria (8 mol%) stabilized zirconia followed by 10 wt% Carbowax 20M ™ dissolved in chloroform. The resulting mixture is then dried and comminuted to a powder mixture. 4.0 g of the powder mixture is then pressed into a disk using 60,000 psi of pressure. The disk is fired at a rate of 1 ° C to 2 ° C / min. heated to 1400 ° C, sintered in air at 1400 ° C for a total of 45 minutes, and cooled at a rate of 3.9 ° C / minute. The resulting disc is tight and gas tight.

Example D

The dual-conductor membrane used in Example A-5 below is prepared by preparing a disk containing BMgLaCrOx as the electronically conductive phase and YSZ as the ionic conductive phase in Example C above, which after sintering on one side (anode side) is impregnated with praseodymium, yttrium and zirconium , manufactured. The BMgLaCrOx / XSZ disc is prepared by applying 0.1 cm3 of an aqueous solution containing 0.218 grams of Pr (NO3) 3 .5H2 O, 0.212 grams of Zr (NO3) 4 .6H2 O, and 0.0115 Grams of Y (NO3) 3 .6H2 O per cm3 of water on a surface of the disc, impregnated. The disk is then dried and heated in air to 1100 ° C.

Example E

The dual conductor membrane used in Examples A-6 and B-3 below is made by preparing a disk containing praseodymium, doped indium oxide as an electronically conductive phase, and YSZ as an ionically conductive phase. The powder mixture of 31.22 g of In2 O3 powder, 4.26 g Pr6 O11 powder, 29.70 g yttria (8 mol%) stabilized zirconia powder, 100 cc distilled water, 4 drops Darvan C (a dispersant, commercially available from RT Vanderbilt and Company, Inc., Norwalk, Connecticut) and zirconia milling media are ground in a ball mill for 17 hours. The mixture is then dried at 200 ° C, 10 wt% Carbowax 20M ™ in chloroform is mixed, and the entire mixture is again dried at 100 ° C to remove the chloroform. The powder mixture is then comminuted again and 4.0 g of the mixture is pressed into a disk using 60,000 psi of pressure. The disk is then heated to 1550 ° C at a rate of 0.5 ° C to 1.0 ° C / minute, sintered in air at 1550 ° C for 3 hours, and cooled at a rate of 1 ° C / minute. The resulting disc is dense and gas-tight and finally has a diameter of 3.12 cm.

An electron photomicrograph backscattered image surface of the dual-conductor membrane prepared in accordance with Example E above, at 500X, is shown in FIG. Two areas corresponding to the two phases of the membrane are clearly visible in the picture. The flatter, smoother regions include the oxide ion-conductive phase, predominantly yttria-stabilized zirconia, as confirmed by x-ray adsorption mapping. The thin, small-grained band that extends near the top to the bottom of the center of the micrograph is the electronically conductive phase, which primarily comprises indium oxide.

A second electronic photomicrograph of the same membrane of example E in a cross-section 5000 times enlarged is shown in FIG. The small white particles are the electronically conductive indium containing phase and the gray area is the ionically conductive phase, preferably yttria stabilized zirconia. The very dark areas are due to small voids created in the cross-sectional surface during sample preparation.

The following examples illustrate how to make the membranes comprising mixed metal oxide in perovskite structure. Examples F and G illustrate the above-described preparation from the oxides.

Example F

A solid state membrane is made on the basis of an ABO3 type material of the formula La0.2 Sr0.8 CoOx. A powder mix of 7.50 grams of La & sub2; O & sub3 ;, 18.47 grams of Co & sub3; O & sub4; and 19.08 grams of SrO are ball milled in ethyl alcohol using zirconia milling media for about 24 hours. The resulting slurry is evaporated to dryness at 90 ° C and ground to a dry powder. This powder is mixed with 10% by weight of Carbowax 20M ™ dissolved in chloroform. The resulting mixture is dried at room temperature and comminuted to a powder mixture and sieved through an 80-mesh sieve. 4 grams of the powder are compressed to a desired shape using 60,000 psi of pressure. The shaped mixture is then slowly heated to about 600 ° C and the carbowax binder burned out, heated at a rate of about 0.6 ° C / minute at 1200 ° C, held at 1200 ° C for about 5 hours and at about 105 ° C at a rate of about 0.9 ° C / Minute cooled. The resulting membrane is dense and gas tight.

Example G

A membrane is prepared according to the method of Example F with the deviation of an equivalent molar amount of CaO used in place of SrO to produce a composition of the formula La0.2 Ca0.8 CoOx.

The following Examples HL illustrate the preparation of solid membranes according to the method of thermal decomposition of nitrate and / or acetate salt described above.

Example H

About 20.0 grams of lanthanum acetate, about 49.35 grams of strontium nitrate, and about 72.61 grams of cobalt acetate are dissolved in water. The solution is evaporated to near dryness while stirring on a hot plate. The concentrated mixture is then heated at 450 ° C for one hour in the air. The resulting powder is crushed in acetone and then calcined at 1150 ° C in the air for 5 hours. The resulting powder is ball-milled in acetone containing 3 drops of a dispersant Darvan CTM using zirconia grinding media for 20 hours. The powder suspension is dried at 200 ° C, mixed with 10% by weight of Carbowax 20M ™ in chloroform, and then the whole mixture is slowly dried on a hot plate with stirring, followed by further drying at 90 ° C in an oven. The resulting powder is minced with a mortar and pestle and sifted through an 80 mesh sieve. Four grams of the resulting powder are compressed to a desired shape using a pressure of 60000 psi. The shaped mixture is then slowly heated to 600 ° C and the Carbowax ™ binder is then heated at 1200 ° C at a rate of about 0.6 ° C / minute and left at 1200 ° C for about 5 hours and allowed to cool. The obtained La0.2Sr0.8 CoOx-ABO3 type multi-component membrane is dense and gastight.

Example J

A solid-state membrane is prepared according to the method of Example H except that iron acetate is used in place of cobalt acetate at equivalent molar amounts of the metal ion. The formula representing the product can be expressed as La 0.2 Sr 0.8 FeO x.

Example K

A solid-state membrane is prepared according to the method of Example H, except that iron acetate and chromium acetate are used in place of cobalt acetate in such amounts that the molar ratio of iron to chromium is 4: 1 and the total molar ratio of iron and chromium is equivalent to the number of moles of Cobalt is. The product obtained can be expressed by the formula La0.2 Sr0.8 Fe0.8 Cr0.2 Ox.

Example L

A solid-state membrane is prepared according to the method of Example H except that gadolinium acetate is substituted for lanthanum acetate at equivalent mole levels for the metal ions. The products obtained can be expressed by the formula Gd0.2Sr0.8 CoOx.

Preparation of solid state membranes by the above-described citric acid production process is illustrated by Example M below.

Example M

An ABO 3 -type multi-component membrane La 0.2 Sr 0.8 Fe 0.8 Cr 0.1 Co 0.1 O x is prepared from the nitrates or acetates by mixing them in a citric acid solution. About 30.0 grams of lanthanum nitrate, 60.96 grams of strontium nitrate, 117.85 grams of iron nitrate, 14.59 grams of chromium nitrate, 10.61 grams of cobalt nitrate, and 138.71 grams of citric acid are dissolved in water. The solution is placed in a round glass flask and mixed on a rotary evaporator under vacuum at 80 ° C until the mixture thickened. The liquid is poured into an evaporating dish and dried in a vacuum oven at 110 ° C under a partial vacuum for 20 hours. The powder is crushed and then calcined in air at 200 ° C for one hour and then at 900 ° C for 24 hours. The powder is placed in a plastic jar and ground in acetone containing three drops of the dispersant Darvan CTM with zirconia grinding media for 24 hours. The powder suspension is dried at 90 ° C, mixed with 5% by weight of Carbowax 20M ™ in chloroform, and then the whole mixture is slowly dried on a hot plate with stirring, followed by further drying at 90 ° C in an oven. The resulting powder is crushed with a mortar and pestle and sifted through a 60 mesh sieve. Four grams of the resulting powder are compressed to a desired shape using 37,500 psi of pressure. The shaped mixture is slowly heated to 600 ° C to burn off the Carbowax ™ binder and then heated to 1200 ° C at a rate of about 0.6 ° C / minute and left at 1200 ° C for about 5 hours, followed by cooling. The resulting membrane is dense and gas tight.

Example N

According to the procedure of Example M, a La0.2Sr0.8 Fe 0.8 Mn 0.2 Ox ABO 3 type multicomponent membrane is prepared by replacing the nitrates (or corresponding acetates) of the metals of this membrane in the amounts required to achieve the relative molar amounts of the abovementioned ABO 3 ; -Type formula produced.

Sauerstofffluxergebnisse

Each dual-conductor disk of Examples AN above is bonded between 2 1-inch diameter YSZ or mullite tubes. One end of this assembly is equipped with a quartz lined stainless steel tube or mullite feed tube for introduction of the oxygen consuming gas and the other end of this assembly is equipped with a stainless steel tube, mullite or silicon carbide feed tube for introduction of the oxygen containing gas. In each of the examples below, the assembly is placed in a cracking furnace which can be heated to 1100 ° C. The rate of oxygen flux through the disks comprising mixed metal oxides, tested in Examples A-7 through A-14, is determined by feeding 60 cc / minute of a conventional fuel mixture on the fuel side of the disk, supplying 200 cc / minute of air to the air Opposite the disk, analyzing the gas composition leaving the fuel side of the disk, in terms of volume percent CO & sub2 ;, CO and N & sub2; with a gas chromatograph and measuring the volume percent of water in the effluent by collecting water with a dry ice-acetone trap from the gas exiting the fuel side of that disk. The formulas below summarize how to calculate the total oxygen flux and oxygen flux per unit area:

Total O 2 -flux = (O 2 in effluent) + (O 2 in effluent as H 2 O) - (O 2 in feed) - (O 2 leak)

O 2; in the effluent = (flow rate to the outside) · ((% CO 2) + 0.5 · (% CO)) / 100

O 2; in the effluent as H 2 O = (grams H 2 O collected / hour) x (1 mole H 2 O / 18 g H 2 O) x (1 mole O 2/2 moles H 2 O) x (24200 cc O 2 / Mole O 2) · (1 h / 60 min)

O 2; in the feed = (flow rate on) x (% CO 2 in the feed) / 100

O 2; Leak in effluent (based on% N 2) = (flow rate to the outside) · (21% O 2/79% N 2) · (% N 2) / 100

O 2 flux per unit area unit = total O 2 flux / surface area of ​​the membrane which is "mixed" with the fuel.

Unless otherwise indicated herein, all parts, percentages, ratios and the like are based on volume at standard temperature and pressure (STP, 25 ° C and 1 atmosphere). If the temperature or pressure is not specified herein, the temperature is room temperature (about 25 ° C) and the pressure is about 1 atmosphere.

Example A-1

The reactor assembly containing Pd / YSZ dual conductor membrane of Example A is heated to 1100 ° C with a nitrogen feed at a rate of about 60 cc per minute to the side intended for the oxygen consuming gas and air fed at 200 cc / Minute on the opposite side of the dual-conductor membrane intended for the oxygen-containing gas. The nitrogen stream is then replaced with a gas containing 90 parts of hydrogen and 10 parts of argon at a rate that gives 61.0 cc / minute of hydrogen gas at STP. The effluent is then passed through a dry ice-acetone trap (-78 ° C) to collect the water produced and then through a gas collector for gas chromatographic analysis. The hydrogen-argon gas mixture is fed to the reactor for 3 hours and 1.23 grams of water are collected during this reaction period.

Gas chromatographic analysis shows no nitrogen, indicating that there is no leak for air in the reactor and that all of the oxygen is being transported through the dual conductor disk.

The surface of the hydrogen-exposed disk is 2.2 cm 2 and the amount and oxygen transported through the disk is equivalent to a current density of 550 mA / cm 2.

Example A-2

The reaction process in this example is carried out in the same manner as in the foregoing Example A-1 except that the hydrogen-argon gas mixture is replaced by a gas mixture containing 17 parts of methane and 83 parts of nitrogen.

Gas chromatographic analysis of the effluent gas shows that 94% yield of carbon monoxide mixed with hydrogen in a molar ratio of 1: 2 is obtained. The mixture of oxygen transported through the disk is equivalent to a current density of 531 mA / cm².

The above result shows that almost quantitative conversion of a mixture of hydrocarbons to synthesis gas can be obtained without an external loop for the flow of electrons.

Example A-3

The reaction process of this example is carried out in the same manner as in the preceding Example A-1 except that the dual-conductor membrane is replaced by the Pd / YSZ membrane prepared in Example B and the hydrogen-argon gas mixture is fed at a rate which delivers 61.6 cc / minute of hydrogen gas at STP and the hydrogen-argon gas mixture is fed to the reactor for 2 hours and 30 minutes. The reactor produces 0.38 g of water.

The surface of the hydrogen-exposed disk is 1.0 cm 2 and the amount of oxygen transported through the disk is equivalent to a current density of 463 mA / cm 2.

Example A-4

The reaction process in this example is carried out in the same manner as in the preceding Example A-1 except that the dual-conductor membrane is replaced by the BMgLaCrOx / YSZ membrane prepared in Example C, the hydrogen-argon gas mixture to the reactor via a Is fed for one hour and 0.107 g of water are collected during the reaction period.

The surface of the hydrogen-exposed disk is 2.8 cm 2 and the amount of oxygen transported through the disk is equivalent to a maximum current density of 114 mA / cm 2.

Example A-5

The reaction procedure in this example is carried out in the same manner as in the preceding Example A-1 except that (a) the dual-conductor membrane is replaced by the PrYZr-BMgLaCrOx / YSZ membrane prepared according to Example D, positioned so that the praseodymium Yttrium- and zirconium-impregnated side comes into contact with the hydrogen-argon gas mixture, (b) the hydrogen-argon gas mixture is fed to the reactor for one hour and 30 minutes (Run A) and for a period of 2 hours (Run B), and (c) 0.16 grams and 0.22 grams of water during Attempt A and B are collected.

The surface area of ​​the hydrogen-exposed disk is 2.8 cm 2 so that the amount of oxygen transported through the disk is equivalent to a current density of 114 mA / cm 2 for Run A and 117 mA / cm 2 for Run B.

Example A-6

The reaction procedure in this example is carried out in the same manner as in the preceding Example A-1 except that the dual conductor membrane is replaced by the PrInOx / YSZ membrane prepared according to Example E, the hydrogen-argon gas mixture to the reactor for 2 Hours are fed and 0.90 grams of water are collected during the reaction period.

Gas chromatographic analysis indicates no nitrogen, indicating that there is no leakage of air in the reactor and that all of the oxygen is being transported through the dual conductor disk.

The surface of the hydrogen-exposed disk is 2.2 cm and the amount of oxygen transported through the disk is equivalent to a current density of 601 mA / cm².

Example A-7

The perovskite disk of Example F is placed on a stainless steel backing plate 330 in an oven. Ground Corning glass (# 1724) is mixed with water to form a paste. A thin layer of this paste is then applied to the edge of the disc and a zirconia or mullite tube is then placed on the disc so that the wet paste can form a seal. The tube and disc are then heated in the oven. At 925 ° C, the milled glass melts to form a leak-tight seal between the disc and tube. The reactor is then heated to the desired temperature, with nitrogen being charged to the closed side of the disc (tube side) and to air on the opposite side. When the disc has reached the desired temperature, the nitrogen supply is replaced by a fuel to measure the oxygen flux. The conditions for measurement are 1100 ° C, 60 cc / minute of fuel supplied on the sealed side of the disc. The disk is tested with a standard fuel "mixture" consisting of 57% H 2, 21.5% CO 2, 16.5% CH 4, 5.0% Ar.

Examples A-8 to A-14

The reaction procedure of Examples Nos. A-8 to A-14 is carried out in the same manner as the foregoing Example A-7 except that the solid-state membrane of Example A-7 is replaced with solid-state membranes of Examples GN. The reaction conditions in Examples Nos. A-8 to A-14 are the same as in Example A-7.

The oxygen flux data for Examples Nos. A-7 to A-14 are summarized in Table 1 below. Table I oxygen flux data

SA = surface exposed to the fuel Powder preparation process:

A = oxide preparation

B = Thermal decomposition of nitrates or acetates

C = citric acid preparation

Gas cleaning results

Examples E-1 to E-9 below illustrate the preparation of zirconia tubes which can be used in the electrochemical gas purification cell of the present invention similar to the reactor illustrated in Figs. 9 and 10. These examples are not to be construed as limiting the scope of the invention as generally disclosed in the specification.

EXAMPLE E-1

Production of an open-ended tube with PbO / Au cathode and PbO / Au anode.

A dense zirconia tube 12 mm in outside diameter (OD) and 1 mm in wall thickness, yttria stabilized, obtained from Zircoa Products, Solon, Ohio (hereinafter referred to as "YSZ tube 1"), is coated on both its inner and outer surfaces with a thin layer a slurry made from equal volumes of PbO and gold ink (Engelhard Part No. A 4650, Lot No. M-13966) dispersed in alpha-terpineol. The organic solvent is evaporated by drying the tube in air at 85 ° C for 15-30 minutes. The coated tube is hung in an Inconel 600 tube in an oven and heated to 850 ° C under flowing air. The temperature is maintained at 850 ° C overnight and the tube is then allowed to cool to room temperature.

EXAMPLE E-2

Production of an open-ended tube with Pt cathode and Pt anode:

A YSZ tube 1 is filled with a suspension of 5% by volume CoO, 60% by volume NiO and 35% by volume ZrO 2. treated in alpha-terpineol along the entire inside length of the pipe and along 40.6 cm of the 61.0 cm outside length. The tube is coated and air-dried at 120 ° C, the coating process is repeated twice more. The coated tube is heated at 1650 ° C for 2 hours and allowed to cool. The fired tube is treated by immersion in concentrated HCl and then rinsed with distilled water. This is repeated until the color of the HCl solution remains unchanged. The anode is deposited on the inner surface of the tube by treatment with a suspension of Pt ink (Engelhard) containing 3% by weight of Bi & sub2; O & sub3; in alpha-terpineol. The cathode is similarly prepared by applying the suspension to the appropriate outer surface. The tube is air dried at 120 ° C and fired at 1065 ° C for 15 minutes. Resistance measurements show that the electrodes are electrically conductive.

EXAMPLE E-3

Production of open-ended tube with Pt / K + K cathode and Pt anode:

Following the procedure of Example E-2, after the platinum electrodes for the anode and the cathode have been applied and before the tube is dried in air at 120 ° C, a dilute solution of potassium hydroxide in water is applied to the cathode. Resistance measurements show that the Pt / K + K cathode and the anode are electrically conductive.

EXAMPLE E-4

Production of tubes with closed end:

Closed-end pipes were made by a slip-casting technique from an aqueous slurry of 5 mole percent yttria-stabilized zirconia at pH 9. The tubes have an outer diameter of 9.52 mm (OD) and an inner diameter (ID) of 6.35 mm, are 26.7 cm long and closed at one end. The tubes are fired at 1000 ° C, removed and polished. After re-firing at 1100 ° C, the tubes (hereinafter called "YSZ tube 2") are ready for electrode application.

Platinum electrodes are made by coating the inner surface (anode) and the outer surface (cathode) of a YSZ tube 2 with platinum color (Engelhard) diluted with terpineol. The top of 1 inch on the outside surface is left uncoated. After pouring excess ink, the tube is fired at 1500 ° C. The electrode resistance is tested with a multimeter. If the resistance of either the inner or the outer coating measures more than 0.5 ohms, the process of coating and separating is repeated. The second and subsequent coatings are fired at 1000 ° C. In general, 7 to 9 coatings are required to obtain the desired resistance.

The following examples illustrate the preparation of catalyst-containing reactor tubes.

EXAMPLE E-5

Preparation of a closed-end tube with La 2 O 3 / Pt cathode and Pt anode:

1 Grams of La & sub2; O & sub3; is mixed with 5 ml of terpineol. The outer platinum surface of a closed-end YSZ tube 2 made according to Example E-4 is then coated with this slurry. Only 10% of the slurry is applied to the pipe covering the bottom and 4 inches of the pipe. The reactor is then carefully assembled while the catalyst coating is still wet. The YSZ tube 2 is inserted into a quartz lining with the coated area extending into the hot zone of the furnace and the appropriate connections are made. The reactor is then heated slowly to a reaction temperature over three to four hours. When the reactor is heated, the electrodes are purged with air to remove vaporized terpineol.

EXAMPLE E-6

Preparation of a closed-end tube with La0.6 Sr0.4 CoOx / Pt cathode and Pt anode:

The procedure of Example E-5 is followed except that 1 gram of La & sub2; O & sub3; is replaced with about 1 gram of La0.6 Sr0.4 CoOx perovskite during slurry preparation for the catalyst coating.

EXAMPLE E-7

Preparation of a closed-end tube with ZnMnO 4 / Pt cathode and Pt anode:

The procedure of Example E-5 is followed except that 1 gram of La & sub2; O & sub3; is replaced with about 1 gram of ZnMoO & sub4; during the slurry preparation for the catalyst coating.

EXAMPLE E-8

Making a closed ended tube with FeWO 4 / Au cathode and Pt anode:

Anode production:

A YSZ tube, obtained from Zircoa Products, is coated on the inner surface with platinum ink diluted with terpineol. The platinum ink (Engelhard) is diluted to about 20% with alcohol. One end of the YSZ tube is plugged before the platinum slurry is added. After the addition of the platinum ink, the tube is rolled, so that the inner surface is uniformly coated. Excess ink is poured out of the tube and retained for further coating. The terpineol is evaporated in a drying oven at 100 ° C for one hour. The platinum anode is fired at 1065 ° C for 15 minutes. Two additional platinum coatings are required to reduce the anode resistance to less than 1 ohm.

Cathode production:

The YSZ tube with platinum anode, prepared as above, is coated with a gold-iron-tungstate cathode. The cathode is made by mixing gold ink (Engelhard) with iron tungstate (about 10: 1 by weight). About 1 gram of starch is added to this mixture as a pore former. The mixture is then diluted with 5 ml of terpineol. The resulting mixture is applied to the outside of the tube covering the inner surface except for the top and the bottom 10.2 cm of the tube. Excess material is retained for subsequent coatings. The terpineol is evaporated in a drying oven at 100 ° C for one hour before firing at 850 ° C for 2 hours. An additional coating is done to reduce the cathode resistance.

EXAMPLE E-9

Preparation of a closed-ended tube with zinc ferrite (ZnFe 2 O 3) cathode and platinum anode.

The procedure of Example E-5 is followed except that 1 gram of La & sub2; O & sub3; is replaced by 1 gram of zinc ferrite.

Sulfur dioxide removal example:

The tubes prepared above are placed in a quartz tube and provided with ports to allow delivery of gas mixtures to the core and annular regions. This is done by connecting a section of the quartz tube with an outside diameter of 14 mm across the central region of the zirconia tube using SWAGELOKTM tube fittings and Teflon ™ ferrules. A SWAGE-LOKTM tube fitting is also attached to each end of the zirconia tube which opens into the quartz sleeve. The assembly is placed in a cracking furnace which can heat to 1100 ° C and the leads are connected via an ammeter and an adjustable current source via circuits that allow current flow with or without additional electrical potential for the voltage source.

The electrodes are conditioned as follows:

The apparatus is hung in a cracking furnace and heated to 800 ° C, leaving air through the annular area and nitrogen through the core area. When the reactor reaches 800 ° C, as indicated with a thermocouple in the oven, the nitrogen flow is replaced by hydrogen at 20 cc / minute and the air is bubbled with a flow of 100 ml / minute of 1% (volume) of SO 2. replaced by helium.

The flow rate of 1% sulfur dioxide and the temperature are set as indicated in the table below and the results of the Fourier Transform Infrared Analysis of the product gas are summarized.

The formulas used to calculate the percent reduction of sulfur dioxide in the effluent and the% sulfur net value removed from the effluent are as follows:

Unless otherwise indicated, all parts, percentages, ratios and the like are in moles (based on weight and / or volume measurements) and "ppm" represents parts per million by volume (which is approximately equivalent parts per million to number of moles , based on the known gas law for ideal gases PV = nRT).

The data obtained using these methods are given in Tables VII to XVI below. The numeric values ​​for each example in the tables are based on an average of at least two trials.

Sulfur was found in the cold area of ​​the tubes used. TABLE VII Cathode: PbO / Au and anode: PbO / Au according to Example C-1

Example 1-1 shows that SO & sub2; can be reduced by using hydrogen as fuel gas in a shorted electrochemical cell. Examples 1-2 to 1-6 show that SO & sub2; can be effectively removed by applying a potential and using hydrogen as a fuel in an electrochemical cell. Example 1-7 shows results obtained with this cell at 800 ° C.

The 1% sulfur dioxide stream is replaced by a stream containing only 98 ppm sulfur dioxide, and the experiments are repeated. The results are summarized in Table VIII below. TABLE VIII Cathode: PbO / Au and anode: PbO / Au according to Example C-1

The results of Table VIII show that sulfur dioxide levels can be significantly removed using hydrogen as the fuel in the absence of an applied potential. The results also show that sulfur dioxide can be reduced even in very dilute streams. TABLE IX Cathode: Pt and Anode: Pt according to Example C-2 Fuel gas: H 2, 20 ml / min

The results in Table IX show that the sulfur dioxide reduction can be carried out using Pt electrodes.

The reactor cell of Table IX is then conditioned at 1000 ° C by replacing the gas stream containing 1% SO 2 with air at 100 ml / min and feeding nitrogen gas to the anode side of the reactor cell over a period of about 18 hours. The results obtained using this conditioned reactor cell are shown in Table X below. TABLE X Cathode: Pt and Anode: Pt according to Example C-2 Fuel gas: H 2, 20 ml / min

The results in Table X show that the reduction of sulfur takes place even in the presence of air. The difference in percent SO 2 removal between Tables IX and X appears to be that some sintering of Pt occurs during the 18 hour conditioning at 1000 ° C. TABLE XI Cathode: Pt (K + K) and Anode: Pt According to Example C-3 Fuel Gas: H 2, 20 ml / min

The results in Table XI show that sulfur dioxide removal occurs in the cell when the loop is closed (Runs Nos. 5-1 to 5-3), but not when shorted (Comparative Example C / 1).

The reactor cell of Table XI is then conditioned at 1000 ° C by diluting the 1% SO & sub2; containing gas stream with 15 ml / min of air. This reactor cell is then; rinsed (cathode area) with 30 ml / min. of air and then charged to a 1% SO? switched gas stream containing switched. The results obtained using this conditioned reactor cell are shown in Table XII below. TABLE XII Cathode: Pt (K + K) and Anode: Pt According to Example C-3 Fuel Gas: H 2, 20 ml / min

The results in Table XII indicate that sintering of the platinum may have occurred during air treatment at 1000 ° C. The results also show that the alkali-doped cathode is effective in removing oxygen dioxide in the presence of air (Example No. 5A-2).

Examples of data obtained using the reactor cells coated with various catalytic materials are shown in Tables XIII to XVII below. TABLE XIII Cathode: La 2 O 3 / Pt and Anode: Pt according to Example C-5 Combustion gas: H 2, 20 ml / min

Examples 6-1, 6-2, 6-4 and Comparative Examples C / 2 and C / 3 show that the percentage of SO & sub2; decreased and net percent S from the 1% SO & sub2; with high efficiency (> 85%) when the reactor cell short circuit according to the present invention is complete (Examples 6-1, 6-2 and 6-4) as opposed to the less than 20% SO2 reduction and net % S removal due to the presence of the catalyst alone when the circuit is open (C / 2 and C / 3). Examples 6-3 and 6-5 to 6-8 show that sulfur dioxide can be removed with high efficiency and that the production of harmful COS (carbonyl sulfide) can be minimized without applying voltage to the reactor cell and when the reactor cell is charged with a mixture of SO & sub2 ;, O & sub2 ;, CO & sub2; and N & sub2; is fed, which simulates the composition of a combustion gas. Table XIV Cathode: La0.6 Sr0.4 CoO3 / Pt and anode: Pt according to Example C-6 Fuel gas: H2, 20 ml / min

Examples 7-1 to 7-27 show a series of examples wherein temperature, applied voltage, composition of the gas supply, and flow rate of the gas supply are varied for a given reactor cell. The effect of applied voltage on% SO 2 reduction and net removed% S is slightly greater at temperatures less than 525 ° C than at higher temperatures. TABLE XV Cathode: ZnMo 4 / Pt and Anode: Pt according to Example C-7 Fuel gas: H 2, 20 ml / mm

Examples 8-1 to 8-4 show that emission of SO & sub2; and COS in another reactor cell of the present invention can be significantly reduced without applying voltage to the cell. Catalytic and thermal activity alone is minimal in Comparative Example C / 4. TABLE XVI Cathode: FeWO 4 / Au and Anode: Pt according to Example C-8 Fuel gas: H 2, 20 ml / min

Table XVI shows that the present invention achieves substantially greater SO2 removal and COS reduction (Examples 9-1 to 9-4) than achieved with catalytic and thermal activity alone (Comparative Examples C / 5 and C / 6) , TABLE XVII Cathode: ZnFe 2 O 4 / Pt Anode: Pt according to Example C-9

Experiments 10-1 to 10-4 show that zinc ferrite is an effective electrocatalyst for SO₂ reduction. and that an increasing driving force (applied potential) increases the distance speed. Experiment 10-1 also shows that there is no potential for SO₂ reduction. is required.

Experiments 10-5 and 10-6 and Comparative Experiment C / 7 show that in the presence of oxygen, zinc ferrite is still a more efficient SO 2 reduction electrocatalyst and that there is no oxygen transport under open loop conditions of Comparative Experiment C / 7. not removed. In fact, previously adsorbed SO & sub2; to desorb.

Run 10-7 shows that higher concentrations of oxygen do not adversely affect the SO 2 reduction process and Comparative Example C / 8 shows that when the loop is opened to stop oxygen transport, SO 2 reduction ceases and SO 2 desorption commences , Comparative experiment C / 9 is carried out about 24 hours after comparative experiment C / 8 and shows that the SO 2 desorption process stops when all of the adsorbed SO 2 has been removed. is removed and the SOz concentration is almost equal to the supply.

Experiments 10-8 through 10-10 show that recovery of oxygen transport restores the SO₂ reduction process, ie, the process is reversible and associated with oxygen transport.

The combined results in Tables XIII-XVII show that when the electrochemical cell comprises a catalyst coating, not only is a high percentage of sulfur dioxide removed from the effluent, but also a high net percentage of sulfur from the effluent due to the small amounts of carbon oxysulfide, formed as a reduction product between sulfur dioxide and carbon dioxide, in the mixed feed, which are characteristic of waste gas and combustion gas effluent, Will get removed. Tables XIII-XVII also show that a wide variety of catalytic materials can be used to advantage in increasing the reactor cell efficiency and that the increased efficiency is linked to the oxygen-ion transport of the reactor cell element of the present invention.

While the invention has been described in terms of the preferred embodiments, it is to be understood that various modifications thereof will become readily apparent to those skilled in the art after a reading of the specification. It is therefore to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

In particular aspects there is described a solid state multicomponent membrane for use in an electrochemical reactor characterized by a mixed metal oxide material having a perovskite structure comprising (1) a lanthanide or Y or a combination of lanthanide and Y, (2) at least one alkaline earth metal, (3) Fe and ( 4) Cr or Ti or combinations of Cr and Ti, in particular a membrane, wherein the mixed metal oxide comprises (1) La or Y or a combination of La and Y, (2) Ca or Sr or a combination of Ca or Sr, (3) Fe, (4) Cr and (5) Mn or Co or a combination of Mn and Co or wherein the mixed metal oxide material La, Sr, Fe, Cr and Co includes.

Also provided is an element for use in an electrochemical reactor or reactor cell having a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with an oxygen-consuming gas, an electron conductive path between the first and second surfaces, and an oxygen ion conductive path between the first and second surfaces, characterized the element comprises (a) a mixed metal oxide material having a perovskite structure as defined above, and (b) a conductive coating or catalyst and a conductive coating comprising a catalyst and in particular a sulfur reducing catalyst.

Also described is an element for use in an electrochemical reactor or in a reactor cell comprising a gas tight solid electrolyte having a first surface coated with conductive metal, metal oxide or mixtures thereof which can facilitate the reduction of oxygen to oxygen ions and a second surface coated with conductive metal, Metal oxides or mixtures thereof and the two conductive coatings are connected to an outer circuit, both coatings being stable at operating temperature and the first conductive coating comprising a sulfur reducing catalyst.

In addition, an element for use in an electrochemical reactor or reactor cell having a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with oxygen consuming gas, an electron conductive path between the first and second surfaces, and an oxygen ion conductive one Provided between the first and second surfaces, characterized in that the element comprises (A) a solid multi-component membrane characterized by (1) a solid electrolyte, (2) an intimate gas-impermeable multiphase mixture of an electronically conductive phase and an oxygen-ion conductive phase, or (3) a mixed metal oxide material having a perovskite structure and (B) a conductive one Coating, a catalyst or a conductive coating comprising a catalyst, wherein (B) comprises (1) a conductive coating, comprising an alkali or alkaline earth metal or metal oxide in an amount ranging from about 1% to about 50% by weight of the conductive coating, or (2) an oxidatively coupling catalyst, with the proviso that when the element comprises the solid electrolyte (1 ), (B) comprises a conductive coating or a conductive coating comprising a catalyst on each of the conductive surfaces, and the conductive surfaces are connected to an outer circle.

The above-mentioned membranes and elements may be used in an electrochemical reactor cell for reacting oxygen-consuming gas with oxygen-containing gas in an environment containing either oxygen-consuming gas or oxygen-containing gas, characterized by a solid state multi-component membrane or element having an entrance end and an exit end and a passage therebetween for moving one or more gases from the entrance end to the exit end, the solid state membrane and the element being as defined above.

The above-defined reactor cell may be used in an electrochemical reactor for reacting oxygen-consuming gas with oxygen-containing gas, characterized by:

a bowl having an inlet end and an outlet end and a passageway therebetween for moving one or more gases from the inlet end to the outlet end and

at least one electrochemical reactor cell, as defined above, in the shell with an inlet end and an outlet end and a passageway therebetween for moving one or more gases from the inlet end to the outlet end such that the shell and the reactor together form a first zone for introduction, Forming and discharging a first gas or gas mixture forms and the passage through the reactor cell forms a second zone in the electrochemical reactor for the introduction, reaction and discharge of a second gas or gas mixture. Preferably, the electrochemical reactor comprises a catalyst on a carrier in the first or second zone. The reactor preferably comprises an oxidatively coupling catalyst on a support in the first zone.

The sulfur reducing catalyst element as defined above may also be used in an electrocatalytic gas purification process, comprising:

(A) providing an electrochemical reactor comprising an element as defined above, wherein the sulfur reducing catalyst is present on the first surface of the element,

(B) passing a gas containing N? O, NO, NO ?, SO ?, SO? or a mixture thereof, in contact with the first surface of the element and

(C) passing a gas that can be reacted with oxygen in contact with the second surface of the element.

Also described is an electrocatalytic process for gas purification, comprising

(A) providing an electrochemical cell comprising a gas tight solid electrolyte or a mixed metal oxide material having a perovskite structure, the electrochemical cell having a first surface coated with a conductive material, metal oxide or mixtures thereof, capable of facilitating the reduction of oxygen to oxygen ions m, and a second surface coated with conductive metal, metal oxide, or mixtures thereof, wherein the two conductive coatings are connected via an outer circuit, wherein both coatings are connected to an outer circuit, both coatings are stable at operating temperature and the first conductive coating comprises a sulfur reducing catalyst,

(B) passing a gas that can react with oxygen in contact with the second reductive coating.

In the gas purification process, the sulfur reducing catalyst preferably comprises a combination of Zn and Fe, especially ZnFe 2 O 3.