Electrodes/electrolyte assembly, reactor and method for direct amination of hydrocarbons

Abstract

An electrodes/electrolyte assembly and a method for the direct amination of hydrocarbons, and a method for the preparation of said electrodes/electrolyte assembly is disclosed. The presented Solution allows the increase of conversion of said amination to above 60%, even at low temperatures. The electrodes/electrolyte assembly for direct amination of hydrocarbons has: an anode, electrons and protons conductor, that includes a composite porous matrix, containing a ceramic fraction and a catalyst for the amination at temperatures lower than 450 C.; a porous cathode, electrons and protons conductor, and electrocatalyst; an electrolyte, protons or ions conductor and electrically insulating, located between the anode and the cathode, made of a composite ceramic impermeable to reagents and products of the amination.

Claims

1. A method for obtaining an electrodes/electrolyte assembly for direct amination of aromatic hydrocarbons, the electrodes/electrolyte assembly comprising a simultaneously electron and proton conductive anode comprising a composite porous matrix, the composite porous matrix comprising a proton conductive ceramic fraction, wherein the ceramic fraction is barium cerate doped with nanoparticulated yttrium, and a metal catalyst for said direct amination of aromatic hydrocarbons at temperatures lower than 450 C., wherein the metal catalyst comprises nickel, nickel oxide or mixtures thereof, and wherein the porosity of the anode ranges between 10-40%; an electrocatalyst porous cathode having protonic and electronic conductivity comprising an electrocatalyst; a proton or ion conductive and electrically insulated electrolyte located between the anode and the cathode, made of a composite ceramic impermeable to reagents and to the products of said direct amination of aromatic hydrocarbon, wherein the anode and the cathode are electrically connected, and wherein the anode comprises a catalytic area higher than a catalytic area of the electrolyte and the cathode combined, wherein the method comprises the following steps obtaining the anode by mixing the metal catalyst with the proton conductive ceramic, and an organic additive, wherein a proportion of the nickel oxide on the proton conductive ceramic ranges from 30% (w/w) to 70% (w/w), and a concentration of the organic additive ranges from 5% (w/w) to 30% (w/w) in the presence or absence of a solvent to obtain a mixture; conforming the resulting mixture in a mould and pressing to obtain the anode; depositing the proton or ion conductive and electrically insulated electrolyte on the anode, and sintering at a temperature between 1300 C. and 1600 C. for 5 h to 24 h, with a heating rate of between 1 C..Math.min.sup.1 and 5 C..Math.min.sup.1 in an oxidising atmosphere to obtain the simultaneously electron and proton conductive anode; depositing the electrocatalyst porous cathode on the anode by co-pressing, co-sintering, spraying wet powder or directly applying commercial pastes; and sintering the cathode at a temperature ranging from 900 C. to 1100 C., with a rate of heating that varies from 1 C..Math.min.sup.1 to 5 C..Math.min.sup.1, in an oxidising atmosphere.

2. The method according to claim 1, wherein the organic additive is starch or polyvinyl alcohol.

3. The method according to claim 1, wherein additional layers of cathode are deposited and sintered after the deposition of a new layer, till reaching the desired electron conductivity and thickness.

4. The method according to claim 1, wherein the porosity of the anode ranges between 20-30%.

5. The method according to claim 1, wherein the electrodes/electrolyte assembly comprises a planar or tubular configuration.

6. The method according to claim 1, wherein the metal catalyst of the anode is a doped metal with at least one metal selected from the group consisting of aluminum, cobalt, copper, chromium, tin, strontium, iron, gadolinium, indium, iridium, yttrium, lanthanum, lithium, manganese, molybdenum, niobium, gold, palladium, platinum, silver, praseodymium, ruthenium, titanium, zinc, and mixtures thereof.

7. The method according to claim 1, wherein the barium cerate doped with yttrium is further doped with zirconium.

8. The method according to claim 1, wherein the barium cerate doped with yttrium ranged from 70% (w/w) to 30% (w/w).

9. The method according to claim 1, wherein the electrolyte comprises at least one element selected from the group consisting of aluminum, barium, calcium, cerium, copper, strontium, gadolinium, yttrium, indium, lanthanum, niobium, neodymium, praseodymium, samarium, titanium, zirconium or mixtures thereof.

10. The method according to claim 1, wherein the cathode comprises at least one metal selected from the group consisting of aluminum, cobalt, copper, chromium, tin, strontium, iron, indium, iridium, yttrium, lithium, manganese, molybdenum, niobium, gold, palladium, platinum, silver, ruthenium, titanium and zinc.

11. The method according to claim 1, wherein the electrocatalyst of the cathode comprises nanoparticulate platinum or nanoparticulate platinum and barium cerate doped with yttrium.

12. The method according to claim 1, wherein the cathode further comprises at least one oxide selected from the group consisting of aluminum, barium, calcium, cerium, copper, strontium, gadolinium, yttrium, lanthanum, niobium, neodymium, praseodymium, samarium, titanium and zirconium oxides.

13. The method according to claim 1, wherein the thickness of the electrolyte ranges between 10 m and 400 m.

14. The method according to claim 1, wherein the cathode is platinum, and the electrolyte is barium cerate doped with yttrium.

15. The method according to claim 1, wherein the cathode is platinum, the anode is nickel and barium cerate doped with yttrium and zirconium, and the electrolyte is barium cerate doped with yttrium and zirconium.

16. The method according to claim 1, wherein the hydrocarbon is benzene and the amination product is aniline.

17. The method according to claim 1, wherein the organic additive is starch or polyvinyl alcohol.

18. The method according to claim 1, wherein the sintering the cathode at the temperature ranging from 900 C. to 1100 C., is carried out between 1 h to 5 h.

Description

DETAILED DESCRIPTION

Brief Description of the Figures

(1) For easier comprehension of the invention the attached figures are annexed, which represent preferred embodiments of the invention that however are not intended to limit the present invention.

(2) FIG. 1Is a schematic representation of the cell or electrodes/electrolyte assembly (MEA): (1)Represents the electrode in contact with the reaction mediumanode; (2)Represents the electrolyte; (3)Represents the electrodecathode.

(3) FIG. 2Is a schematic representation of the cell or electrodes/electrolyte assembly and of the reaction scheme: (1)Represents the electrode in contact with the reaction mediumanode; (2)Represents the electrolyte; (3)Represents the electrodecathode.

(4) In a preferred embodiment of the invention, the direct amination of benzene to aniline is observed, where the benzene molecules and ammonia reagents are illustrated interacting with the anode where, upon the catalyst, takes place the activation of the reagents, the removal of one hydrogen atom from each reactant molecule, the oxidation of the hydrogen atoms at the surface of the catalyst, and the reaction of ammonium and benzene radicals to produce aniline. In this illustration it can be verified that there is no forming of molecular hydrogen.

(5) FIG. 3Photographs of scanning electronic microscopy (SEM) of the electrodes/electrolyte assembly (MEA), where the electrolyte layer (BCY), the electro anode (Ni+BCY), and the electro cathode (Pt) are visible. a) overall image, b) detailed image of the interface electro anode/electrolyte, c) detailed image of the interface electro cathode/electrolyte.

(6) The present invention describes a cell or electrodes/electrolyte assembly, and an electrochemical reactor, that comprises the electrodes/electrolyte assembly (MEA) for the direct amination of hydrocarbons, namely in the amination of benzene to aniline.

(7) The electrodes/electrolyte assembly (MEA) is comprised by a ceramic electrolyte of solid oxide, and two porous layers positioned on each of its faces and constituting the anode and the cathode.

(8) The anode (1) has the function of catalysing the chemical reaction of direct amination, catalysing the hydrogen oxidation reaction (both atomic or molecular), conducting the protons till the electrolyte and the electrons to the external electric circuit and promoting electrochemically a direct amination reaction.

(9) For its part, the cathode (3) shall promote a reduction reaction of the permeate protons with the electrons from the external circuit, or a reaction of the protons with the oxygen fed to the cathode, and the electrons from the external circuit.

(10) The electrolyte (2) has the function of permeating the protons and imposing a barrier to the permeation of reagents and reaction products and of the conduction of electrons.

(11) This application describes the preparation of electrodes/electrolyte cells or assemblies (MEA) for use in electrochemical reactors, employed for direct amination of hydrocarbons, namely of benzene. The reaction of direct amination of benzene to aniline is described by the following equation:

(12) $\begin{array}{cc}\underset{\underset{\mathrm{ammonium}}{}}{{\mathrm{NH}}_3}+\underset{\underset{\mathrm{benzene}}{}}{C_6{H}_6}\underset{\underset{\mathrm{aniline}}{}}{C_6{H}_5{\mathrm{NH}}_2}+\underset{\underset{\mathrm{hydrogen}}{}}{H_2}{H}_{298K}=-41,4J.Math.{\mathrm{mol}}^{-1}& \left(1\right)\end{array}$

(13) This reaction is strongly limited by the thermodynamic equilibrium. The production of aniline via direct amination is only economically feasible if it is possible to significantly increase the conversion of the reaction (1). This conversion can be improved by the removal of formed hydrogen. The most efficient way to conduct this removal is using an electrochemical pumping reactor of hydrogen. However, the efficient removal of hydrogen from the reaction medium is not sufficient by itself to obtain industrially attractive conversions, that is, conversions typically above 20%, and desirably above 50%.

(14) Thus, the present invention discloses the preparation of MEAs that, insert into a membrane electrochemical reactor, allow not only the electrochemical pumping of atomic hydrogen resulting from de amination reaction, but also the electrochemical promotion of the amination reaction, by improving the conversion and the selectivity of the reaction to values above 60%.

(15) The cell or electrodes/electrolyte assembly (Membrane Electrode AssemblyMEA) comprises the following elements: A ceramic electrolyte of solid oxides (2) (protons or ions conductive) located between two porous layers composing the anode and the cathode. The electrolyte (2) must be non-porous, i.e., impermeable to reagents and reaction products; The porous layer of the anode (1), preferably comprised of a metal oxide (e.g., nickel oxideNiO), which after being reduced to the metallic form promotes the reaction of direct amination of benzene, the electrochemical promotion of the amination reaction and an electro oxidation of the produced atomic or molecular hydrogen. The metallic oxide is supported on a solid oxideCeramicprotons conductive (e.g., barium cerate doped with yttriumBCY), that promotes a conduction of protons resulting from the reaction to the electrolyte, comprised by the protons conductor, preferably solely constituted by this one; Finally, the cathode (3) comprises a proton and electron thin conductive layer, and an electro catalyst which promotes the reduction of permeate protons. The protons reduction can be made by direct reaction with the electrons from the external circuit or with the oxygen, if available on the cathode side. Typically, the cathode is a thin layer of platinum nanoparticles applied directly to the electrolyte (2) and connected thereto after sintering. Another configuration uses a thin layer of a mixture of nanoparticulated platinum and BCY, applied on the electrolyte, and connected thereto after sintering.

(16) A ceramic/metallic MEA shall be inserted in an electrochemical reactor, which shall comprise one or more electrochemical cells. Each electrochemical cell may comprise the above described electrodes/electrolyte assembly (MEA), which may be planar or tubular, an anode chamber, where the amination reaction takes place, and a cathode chamber, where the reduction of protons occurs. In an electrochemical cell, which has a very similar configuration to the solid oxide fuel cellSOFC, the anode is electrically connected with the cathode through an external electric circuit. Once that it is pretended to promote the electrochemical pumping of hydrogen, atomic or molecular, and the electrochemical promotion of the amination reaction, it is necessary to feed electric power to the cell. The necessary difference of potential, that shall be supplied to the electrochemical cell, is limited above by the potential of electro oxidation of the benzene to products other than aniline and the lower level by the over voltages associated with the oxidation and reduction of hydrogen, electrochemical promotion of amination and ohmic resistance of the protons transport. On the other hand, the applied difference of potential must be selected depending on the temperature of the amination reaction and in a way to avoid deep dehydrogenation of benzene and subsequent formation of coke. The difference of potential to be applied may be higher than 0.2 V and lower than 1.5 V, preferably between 0.5 V and 1 V. So the cathode gives an output stream of molecular hydrogen.

(17) In the case of being supplied to the cathode a gas stream containing oxygen, the protons, when reacting with oxygen and electrons from the external circuit, do origin a difference of potential that is enough for the electrochemical pumping of hydrogen and the promotion of electrochemical amination, being in this case unnecessary to feed electric power to the reactor. The product of this reaction is in this case water vapour. As mentioned before, this concrete embodiment is only possible if for the observed voltage a deep dehydrogenation of the reagents doesn't occur.

(18) The reactor could operate at the maximum possible temperature, in the case of direct amination from benzene to aniline, lower than the temperature of decomposition of benzene and of aniline (about 400 C., in the case of use of a nickel containing catalyst). The protonic conductivity of the electrolyte increases with temperature as well as the kinetics of amination. Temperatures below 400 C. are also privileged, as there are low cost and high performance materials industrially available for the construction of electrochemical cells, particularly in what regards sealing. The operation temperature of the amination reactor may range between 250 C. and 450 C., preferably between 350 C. and 400 C.

(19) Since the conversion of the reaction per unit volume of reactor increases with the pressure of the reaction medium (anode), the pressure of the anode could be the highest allowed for the materials of the electrochemical reactor and by its compression costs. This operating pressure shall range between atmospheric pressure and 300 bar, more preferably between 7 bar and 30 bar.

(20) Electrolyte

(21) The electrolyte layer (2) shall be non-porous, i.e., its porosity shall be such that does not allow the permeation of reagents and products between the anode and the cathode. The electrolyte (2) has, as its main function, the physical separation of the reagents fed to the anode side (1) and to the cathode side (3); to ensure electrical isolation between the two electrodes, forcing the electrons formed at the anode (1) to circulate through an external circuit to the cathode (3); allow the transport of protons formed during the electro oxidation of hydrogen (atomic or molecular) in the amination reaction, from the anode (1) to the cathode (3).

(22) The ceramic oxides electrolyte (2) shall present high protons conduction, and this conductivity can be greater than 50 S.Math.cm.sup.1 at operation temperatures; it shall present a high degree of densification, i.e, shall present a negligible porosity, such that it is impermeable to the reagents and products of the amination reaction; being impermeable, in the case of the direct amination of benzene to aniline: to benzene, ammonia, aniline, to the atomic or molecular hydrogen, to oxygen and to nitrogen; it shall further have high mechanical and thermal resistance and present a thermal expansion compatible with the electrodes; it shall have chemical compatibility with chemical reagents and reaction products and have electrochemical stability when subjected to the applied difference of potential.

(23) The materials used in the preparation of the electrodes/electrolyte assembly have optimal protons conductivity inside the range of temperatures from 300 C. to 600 C. It was found that ceramic oxides of barium cerate doped yttrium (BCY) type have very high protons conductivity and are compatible with the direct amination reaction.

(24) Anode

(25) The electro anode or anode (1) contacts the reagents of the amination reaction (i.e., the reaction medium) and the electrolyte. The electro anode (1) is a composite layer located on one side of the electrolyte to promote the reaction of direct amination of benzene, oxidation of hydrogen (atomic or molecular), the conduction of protons to the electrolyte and of the electrons to the external electric circuit. The electro anode is porous, with metallic catalyst nanodispersed, in order to ensure a wide area where the amination reaction can occur, increasing synergistically the reaction yield at low temperatures.

(26) The anode (1) shall thus be simultaneously electrons and protons conductive. In a preferential embodiment, the composite matrix that comprises the anode, is usually formed by a metallic oxide (e.g., nickel oxideNiO), later reduced to its metallic form, and supported on a solid oxide proton conductor. This is the typical configuration of a cermet comprised of a metal and a ceramic protons conductor. The electrochemical reaction of oxidizing hydrogen (atomic or molecular) occurs inside the triple phase boundaries, preferably catalyzed by the nickel catalyst which is simultaneously catalyst of the chemical reaction of direct amination of benzene. Nickel is also a chemical and electrochemical catalyst that allows a promotion of direct amination reaction of benzene, the oxidation of hydrogen atoms as they are removed from de reagents, in order to originate the intermediate species which will react to produce the aniline, and its transportation to out of the reaction region under the action of the applied electric field. The removed hydrogen atoms, in form of protons, are conducted through the ceramic phase of the anode, to the electrolyte and from this to the cathode, where they are reduced to molecular hydrogen, or made to react with oxygen to form water. The directing force for an electrochemical reaction is the difference of potential imposed between the anode and the cathode, or the difference of potential generated by the electrochemical reaction of protons permeated with the oxygen available in the cathode and the electrons from the external electric circuit.

(27) The electrons conductivity of the anode (1) is related with the percolation through the nanoparticles of the metallic catalyst, preferably Ni, and therefore dependent on the concentration of the metal and on the protons conductor. For example, below the percolation threshold of Ni (about 30% (v/v) to 40% (v/v)), the cermet has essentially protons conductivity. On the other hand, above the threshold of percolation, the conductivity of the cermet is mostly for electrons, promoting the conduction of the electrons formed to the external circuit.

(28) The porosity of the anode layer (1) measures the fraction of volume occupied by pores (which diffuse reagents and reaction products) in relation to the total volume of the anode (1). The determination of the porosity can be experimentally effected by methods usually accepted as, for example, by the mercury porosimetry method [3]. Usually porosimetry is attained by reducing metal oxide to metallic form. However, the simple reduction of metallic oxide can be insufficient to originate an increased porosity for the diffusion of the reagents, preferably ranging from 10% to 40% inclusively. The additional porosity can be obtained through the addition of eliminated substances during a calcination of the MEA. These substances are additives that have the double function of facilitate the mixing of the proton and electronic conductive phases and the catalyst and formation of the electrode, function of binder/dispersant, and that of imparting porosity. In general these additives are starches various cereal or synthetic polymers, i.e. organic additives, preferably polymers which evaporate without leaving a trace at temperatures up to 900 C., such as PVA (polyvinyl alcohol). Corn starch is generally preferred as pore forming compound in that it presents a geometric shape similar to that of the anode and electrolyte precursor powders, is easily removed at temperatures well below the sintering temperatures and simultaneously functions as binder for the ceramic powders. Furthermore, it's an abundant and low cost raw material.

(29) Cathode

(30) The cathode or electro-cathode (3) shall promote a conduction of electrons from external circuit to the interface, where a reduction reaction of protons or their reaction with oxygen for the production of water vapour, occurs. As the electro-anode (1), the electro-cathode (2) shall present a porous structure and have mixed conductivity (ionic and electronic). In a preferred embodiment, the cathode (3) comprises a metal catalyst that promotes the reduction of protons to molecular hydrogen or the recombination of these protons with oxygen and electrons to form water vapour (e.g., platinum) supported on a proton conductor (e.g., BCY).

(31) Fabrication of MEA

(32) In a preferred embodiment, the anode (1) shall have a thickness above that of the electrolyte (2), and of the cathode (3), in order to provide a high catalytic area; on the other hand, the anode porosity allows for an efficient mass transfer to the reagents and amination reaction products. In a preferred embodiment, the electrodes/electrolyte assembly shall be as thin as possible in order to have high proton conductivity and thus allow installing electrochemical cells with high efficiency and lower ohmic losses in the direct amination of hydrocarbons, preferably in the production of aniline.

(33) The thickness of the electrodes/electrolyte assembly shall be, in a preferred embodiment, limited only by its mechanical strength and by its barrier effect against the reagents and reaction products, preferably with thicknesses between 100 m and 2000 m, more preferably between 300 m and 400 m inclusively. The planar configuration of a MEA is usually preferred, allowing the use of cheaper manufacturing methods. From the more used methods stands out the method of uniaxial pressing powders of metal oxides or ceramic oxides and the method of wet powder spraying, due to their practical and economic viability.

(34) In a preferred embodiment, the method to obtain the above described electrodes/electrolyte assembly comprises the following steps: mixing of the anode precursor powders: metallic oxide (e.g., NiO, with a medium diameter of 50 nm) and protons conductor (e.g., BCY, with a medium diameter of 400 nm), and an organic additive (e.g. corn starch). The proportion of metal oxide on the ions conductor varies from about 30% (w/w) to 70% (w/w) and the concentration of corn starch powder in the mixture varies between 5% (w/w) and 30% (w/w). The powders can be mechanically mixed in a ball mill or manually in a mortar. Grinding can be conducted in the presence of a solvent (e.g., isopropanol). The resulting mixture is then formed in a mould and pressed on a uniaxial press, cold or with heated plates, at a temperature between about 85 C. and 150 C., preferably about 90 C., so as to evaporate the solvent. The pressure applied on the disk varies between 550 bar and 1100 bar for 5 min to 15 min. The deposition of dry powder protonic conductor is then carried out (e.g., BCY, with a medium diameter of 400 nm) on the layer of the anode and pressing of the disc on the double-layer. The pressure applied to the double-layer varies between 1100 bar and 1500 bar. The double layer is finally co-sintered at a temperature ranging from 1300 C. to 1600 C., during 5 h to 24 h, with a heating rate varying from 1 C..Math.min.sup.1 to 5 C..Math.min.sup.1, in an oxidising atmosphere. The deposition of the electro-cathode (3), preferably platinum, on the double-layer of anode/electrolyte can also be effected by the method of co-pressing and co-sintering. However, in configurations of the electrolyte type (2) supported on the anode, the deposition of the porous cathode can be achieved by the method of wet powder spraying. The method consists in the preparation of a Pt/BCY suspension in an alcoholic solution of PVB (polyvinyl butyral) and its deposition on the electrolyte, using a manual aerograph, followed by a drying step. For the same configuration, the cathode layer can be obtained by manual application of a commercial platinum paste (nanodispersed platinum in a solvent and binders, for example Heraeus CL115349). For both deposition alternatives of the cathode, the electrodes/electrolyte assembly is finally sintered at a temperature that varies between 900 C. and 1100 C., preferably for 2 h and at a heating rate of between 1 C. min.sup.1, and 5 C. min.sup.1 in the presence of oxygen. The number of layers applied to the cathode (3), preferably platinum, is made in accordance with the desired thickness and conductivity. The application of each layer is followed by a sintering step. After the sintering step, the electrodes/electrolyte assembly can be placed directly in the electrochemical reactor, feeding H.sub.2 at a temperature that varies from 400 C. to 1000 C.
Reaction of Direct Amination of Benzene

(35) In other embodiments, the global reaction for production of aniline by direct amination of benzene with ammonia is represented by the equation (1). However, the reactional scheme involves several steps that consist in the activation (breakage) of the simultaneous bonds CH and NH, respectively from benzene and from ammonia. The activation of those bonds is allowed by the use of transition metal catalysts (e.g., Ni, Pd and Pt). The CH bond activation occurs when the benzene undergoes a process of physical adsorption at the surface of the metal catalyst, followed by chemical adsorption on the same catalyst, yielding a highly reactive compound, the phenyl radical (.C.sub.6H.sub.5). Activation of the ammonia NH bond is harder than the former, once that it is a stronger bond (107 kcal.Math.mol.sup.1). In a first stage the NH.sub.3 suffers also an adsorption on the catalyst surface, leading to breakage of one bond NH. The electrophilic attack is performed by the ammonia adsorbed on metallic catalyst, which loses its nucleophilic character (due to the unpaired pair of electrons of the nitrogen atom); .NH.sub.2 radical reacts with the phenyl radical to give a molecule of aniline. The formed aniline is then removed from the reaction medium through the porosity of the electro anode. Other reaction schemes are possible although having in common the formation of intermediate reaction species after losing the atomic hydrogen in form of radicals. The hydrogen radicals are formed in the adsorbed phase on the surface of the metallic catalyst.

(36) The formed pair of hydrogen radicals (.H) is electro oxidised and the resulting protons are transported through the ceramic phase of the electro anode to the electrolyte, and the electrons are transported through the metallic phase of the electro anode to the external circuit. In case that the radical pair .H forms molecular hydrogen, this one is adsorbed on the metal phase of the electro anode, oxidizing to protons that are conducted through the ceramic phase to the electrolyte. The directing force of the electrochemical reaction is the difference of electric potential imposed to the electrodes or resulting from the reaction of the permeated protons current with the oxygen in the electro cathode.

(37) The formation of radicals is electrochemically promoted by the electric field established between the anode and the cathode, which results in the modification of the surface of the catalyst [4]. The process herein disclosed for direct amination only exceptionally will allow the formation of molecular hydrogen. In other former preferred embodiments, and taking advantage in that the chemical catalyst for the amination reaction is the same as the electrocatalyst for the oxidation of hydrogen, preferably nickel, adsorbed hydrogen radicals, when being formed, are immediately oxidized to protons and transported through the electro anode to the electrolyte and from this to the electro cathode, where they undergo reduction or react with oxygen, as described before. Finally, if there is formation of molecular hydrogen, it is easily oxidized to protons and thus removed from the reaction medium. As mentioned above, with the present invention an increase of conversion of the direct amination reaction of benzene is verified, based on the uptake of hydrogen radicals formed during the reaction of benzene with ammonia and protons and its electro oxidation to protons and consequent prompt removal from the reaction medium. In a preferred embodiment, the reaction temperature of the amination of benzene on nickel shall be as high as possible, to allow fast reaction kinetics and also high protons conductivity. However, in a preferred embodiment, this temperature should not exceed 400 C., since at this temperature the occurrence of CHx-fragments begins and afterwards the formation of coke, resulting from the decomposition of benzene. Above 350 C. it begins to be observed the appearance of benzonitrile and compounds resulting from complete decomposition of the NH.sub.3. Thus, the preferred reaction temperature is between 200 C. and 450 C., more preferably between 300 C. and 400 C.

(38) On the other hand, in a preferred embodiment the difference of potential imposed shall be the highest possible, in order to be obtained a high protons transportation. This difference of potential shall be limited by the costs of energy and by the electrochemical dehydrogenation of benzene. The preferred difference of potential is thus between 0.2 V and 1.5 V.

(39) In a preferred embodiment, the electrodes/electrolyte assembly (MEA) is prepared by the co-pressing and co-sintering method. The anode layer is prepared with a mixture of NiO (Alfa Aesar, Ref. 45094, green, Ni 78.5%) and BCY (TYK Co.) for a final composition of 40% (w/w) of Ni. 10% (w/w) of corn starch are further added to the dry powder mixture. This mixture is grinded in an agate mortar, and finally cold formed in a metal mould with the aid of an uniaxial press at 1100 bar. The electrolyte layer is obtained by means of the deposition of dry powder of BCY (TYK Co.) on a layer, which constitutes the anode. The double layer is compressed at 1500 bar and sintered at 1400 C. for 5 h. Finally the cathode is deposited on the other face of the electrolyte through the application of a commercial platinum pastePt (Heraeus CL115349), and sintered at 900 C. for 2 h. The MEA is then introduced into the electrochemical reactor, where NiO undergoes reduction to Ni in presence of H.sub.2 at 400 C. The protons conductivity of BCY, obtained at 400 C., is 4.60 mS.Math.cm.sup.1. To the cathode side a nitrogen current is fed and a difference of potential of 1.2 V is imposed to the cell, corresponding to a H.sub.2 permeate flow rate of 2.25 mol.Math.s.sup.1.

(40) In a preferred embodiment, the electrodes/electrolyte assembly (MEA) is prepared by the above described co-pressing and co-sintering method, and set into the electrochemical reactor. The temperature of the reactor is set to 400 C. After reduction of NiO to Ni in presence of H.sub.2, an equimolar current of C.sub.6H.sub.6 and NH.sub.3 is fed to the anode side. The reaction temperature is 400 C., and the products are condensed at the exit of the anode chamber. To the cathode side a current of nitrogen is fed in order to maintain the pressure of both chambers substantially equivalent. The observed conversion of benzene to aniline is 0.5%. After imposition of a difference of potential of 1.2 V to the electrochemical cell, a rate of conversion of 60% is obtained from the reaction of benzene to aniline.

REFERENCES

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(42) The present invention is not, of course, restricted in any way to the embodiments described herein and a person with ordinary skill in the area can provide plenty of changes without departing from the general idea of the invention, as defined by the claims.

(43) The above described preferred embodiments are obviously combinable with each other. Additionally, the following claims define preferred embodiments of present invention.