PT116729B - METHOD FOR TREATMENT OF NITROUS OXIDE AND FORMATION OF NITRIC OXIDE IN SIMULTANEOUS - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A METHOD FOR THE TREATMENT OF NITROUS OXIDE AND FORMATION OF NITRIC OXIDE, INCLUDING SUPPLYING A GAS CURRENT OF N2O TO THE REDUCTION CATALYST OF A MEMBRANE, SIMULTANEOUSLY WITH SUPPLYING A GAS CURRENT OF NH3 AO MEMBRANE OXIDATION CATALYST, WHERE BOTH MEMBRANE OXIDATION AND REDUCTION CATALYSTS ARE AT THE SAME REACTION TEMPERATURE. THIS IS A NEW N2O Abatement METHOD, WHICH CAN BE REINTEGRATED IN NITRIC ACID INSTALLATIONS TO TREAT N2O WHILE PRODUCING, IN A VALUABLE WAY, IN A VALUABLE PRODUCT IN THE FORMATION OF NITRIC ACID.

Description

DESCRIPTION

METHOD FOR TREATMENT OF NITROUS OXIDE

AND SIMULTANEOUS NITRIC OXIDE FORMATION

FIELD OF THE INVENTION

The present invention relates to a method for simultaneously treating nitrous oxide and nitric oxide formation, respectively, in the reduction and oxidation catalysts of a membrane, both oxidation and reduction catalysts of the membrane being at the same reaction temperature. . This is a new N2O abatement method which can be reintegrated into nitric acid plants to treat N2O while advantageously producing NO, a valuable product in the formation of nitric acid.

BACKGROUND OF THE INVENTION

The electrochemical formation of nitric oxide is a known process and has been covered in several literature documents, being particularly the focus of the following patent literature.

European patent application EP 0023813 relates to a method and apparatus for forming nitric oxide (NO) from ammonia. A gas containing ammonia is placed in contact with an oxidation catalyst deposited on a surface of a solid electrolyte while a gas containing oxygen is placed in contact with a second catalyst capable of dissociating gaseous oxygen into oxygen ion deposited on a second surface of the solid electrolyte. The oxygen ion is transported through the solid electrolyte to react with ammonia to form nitric oxide under simultaneous production of electrical energy. Thus, NO is formed by the electrochemical oxidation of ammonia (NH3) through an oxide ion conducting membrane.

International patent application WO 2006041300 relates to a catalytic membrane reactor for the oxidation of NH3 to NO during the manufacture of nitric acid, wherein the membrane reactor comprises a mixed electronic and ionic conductive membrane which is capable of transporting oxygen, comprising a multi-component oxide having a perovskite or perovskite-related structure represented by the formula ΑχΑ'χΈθ3-ζ, wherein A represents a lanthanide element or a mixture thereof, A' represents an alkaline earth metal or a mixture thereof, B represents a metal of transition or a mixture thereof, x and x' each represent numbers such that 0 X^l,l, O^x'^1,1 and 0,9 (x+x') 1,1, and z represents a number that makes the compound charge neutral. The invention also relates to a method for the oxidation of NH3 to NO. The product and method according to the invention lead to NO selectivities of up to 98% and no formation of N2O during the high temperature oxidation of NH3, resulting in a highly efficient and intensified process for the manufacture of nitric acid.

One of the disadvantages of current non-electrochemical nitric acid manufacturing processes is the emission of N2O. During the last few decades, the concentration of nitrous oxide (N2O) in the atmosphere has been increasing at a rate of 0.2-0.3% per year, leading to current levels that are 18% higher than those before the industrial revolution. This is of great concern due to the large contribution of N2O to global warming (with an impact 298 times greater than CO2), with serious negative impacts on ozone depletion and climate change.

manufacture of nitric acid is the largest single source of anthropogenic N2O emissions with 125xl0 ⁶ t CO2 equiv produced per year. For reference, for every tonne of HNO3 produced in a typical nitric acid plant, approximately twice that number of tonnes of CO2 equiv of N2O is produced, highlighting a serious environmental impact.

Typical processes for N2O abatement are those of thermal or catalytic decomposition. However, both of these methods convert ο N2O solely into heat and its reduction products, namely those of nitrogen and oxygen. For typical industrial processes, NO yields are generally 95-97%, with the remainder being approximately 1.5-2.5% N2O and 4-4.5% N2. It has been estimated that an increase in NO yield of 1% in a nitric acid plant would correspond approximately to an additional profit of ~500 k€ per year. Thus, although solving the environmental issue, typical processes for abatement of the N2O by-product through its reduction have major negative impacts on profit.

Considering the above, there is still a need to provide a method that provides less nitrous oxide emissions, while still forming the desired reaction products of the nitric acid manufacturing process.

SUMMARY OF THE INVENTION

Surprisingly, the problem mentioned above has been solved by the present invention.

The present invention provides a method for simultaneously treating nitrous oxide and forming nitric oxide, characterized in that it comprises feeding a gaseous stream of N2O to the reduction catalyst of a membrane, simultaneously feeding a gaseous stream of NH3 to the catalyst. of oxidation of said membrane, wherein both oxidation and reduction catalysts of the membrane are at the same reaction temperature.

In one embodiment, the method of the invention further comprises a step of pre-treating the membrane by flowing reducing gases onto the oxidation catalyst. Preferably, the reducing gases are selected from hydrogen and ammonia.

In another embodiment, the method of the invention further comprises a step of heating the membrane to the reaction temperature before feeding the oxidation and reduction catalysts to the membrane.

In one embodiment, the reaction temperature of the method of the invention ranges between 500-900 °C. In a preferred embodiment, the reaction temperature of the method of the invention ranges between 600-800°C and in a more preferred embodiment, the reaction temperature of the method of the invention ranges between 650-750°C.

In one embodiment of the invention, the reduction catalyst comprises a material of general formula (Αι-χΑ'χ) _a (B) bO _c , where A represents a rare earth element or a mixture thereof, A' represents an alkaline earth metal or a mixture thereof, B represents a transition metal or a mixture thereof, x, a and b represent numbers such that 0 x^1, 0.6 a ^1.4, 0.6 b 1.4, and c represents a number that makes the compound charge neutral. Preferably, the reduction catalyst comprises perovskite or perovskite-based material.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1A is a schematic representation of one embodiment of the method of the invention in a tubular fuel cell having a pure oxide ion conducting membrane: (1) It depicts an anode offering mixed conductivity of electrons and oxide ions and catalytic activity for the NH3 oxidation reaction; (2) represents a pure conductive electrolyte of oxide ions; (3) a cathode offering mixed conductivity of electrons and oxide ions and catalytic activity for the N2O reduction reaction; and (4) represents an electronically conductive interconnect material.

Figure 1B is a schematic representation of the plurality of tubular fuel cells of Figure 1A connected by an electronically conductive interconnecting material and thus assuming a tubular stack configuration.

Figure 2 is a schematic representation of one embodiment of the method of the invention in a planar fuel cell configuration having a pure oxide ion conductive membrane.

Figure 3 is a schematic representation of an embodiment of the method of the invention in a tubular mixed conductive membrane: (5) represents a material offering catalytic activity for the NH 3 oxidation reaction on the permeate side; (6) represents a mixed conductive membrane of electrons and oxide ions; and (7) represents a material on the feed side that offers mixed conductivity of electrons and oxide ions and catalytic activity for the N2O reduction reaction.

Figure 4 represents a comparison of the theoretical cell potential obtained (A) with the method of the invention using a pure conductive electrolyte membrane of oxide ions and (B) with the method known from the prior art (EP 0023813).

Figure 5 shows conductivity profiles in a preferred embodiment of the invention using La _x Sr0.9-xFeo.4Tio.603-6 perovskite anode compositions.

Figures 6 and 7 show the conductivity profiles in a preferred embodiment of the invention using peroveskite (LaSr)(Fe,Ti)03-δ cathode electrocatalyst compositions.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is a method for simultaneously treating nitrous oxide and forming nitric oxide, comprising feeding a gaseous stream of N2O to the reduction catalyst of a membrane, simultaneously feeding a gaseous stream of NH3 to the catalyst of oxidation of said membrane, wherein both oxidation and reduction catalysts of the membrane are at the same reaction temperature.

Surprisingly, the method of the invention simultaneously performs oxidation and reduction reactions respectively involved in nitric oxide formation and nitrous oxide treatment. This is due to the presence of a membrane having oxidation and reduction catalysts, both catalysts being at the same reaction temperature, thereby promoting the conversion of N2O to N2 electrochemically at the same temperature as ο NH3 oxidizes to NO, on the reverse side.

Considering the known methods for forming nitric oxide and nitric acid, one skilled in the art would not expect that using a single reaction temperature for both oxidation and reduction catalysts on a membrane would provide a viable method, as each oxidation and reduction reaction has specific requirements to be met for it to occur.

Furthermore, nitrous oxide, which is a polluting gas formed during the common manufacturing process of nitric acid, as an unwanted side product, is now reintegrated by the method of the present invention due to the feasible reaction temperature of both sides of the membrane. of catalyst. Thus, this recovery and reuse of nitrous oxide in the method of the invention clearly reduces (or even eliminates) its emission into the atmosphere as a noxious gas. Thus, it was not expected that nitrous oxide treatment and nitric oxide formation would successfully occur simultaneously.

Thus, the method of the present invention allows the once environmentally harmful chemical nitrous oxide to be efficiently and simultaneously converted into nitric oxide and nitrogen, the former being beneficial for various chemical processes such as nitric acid formation, while the latter can be released with safety for the atmosphere.

In addition to the above, the method of the present invention further removes the need to supply molecular oxygen to the reducing side of the membrane. The method of the invention produces the necessary oxide ions at the respective cathode or feed side of the electrochemical cell by the intrinsic decomposition of N2O directly into oxide ions at the cathode due to the presence of a suitable catalyst at the reduction side.

Furthermore, the method of the invention provides superior cellular potential compared to methods known from the prior art (Figure 4). This increases the driving force for oxide ion migration, improving its efficiency. The invention provides a new N2O abatement method which can be reintegrated into nitric acid plants to treat N2O while advantageously producing NO, a valuable product in the formation of nitric acid.

The method of the invention further comprises an additional step which is a pre-treatment of the membrane by flowing reducing gases into the oxidation catalyst, the reducing gases being selected from hydrogen and ammonia, to activate the oxidation catalyst.

Furthermore, the method may comprise a step of heating the membrane to the reaction temperature before feeding the gases into the membrane oxidation and reduction catalysts, preventing loss of these reaction precursors.

As already indicated, the reaction temperature is a critical parameter for carrying out the method of the invention. The reaction temperature ranges between 500-900°C, preferably 600-800°C, and more preferably 650-750°C.

The reduction catalyst used in the method of the invention must consist of a material that allows a high catalytic activity for the N2O reduction reaction. Said material has the general formula (Αι-χΑ'χ) _a (B) b0 _c , where A represents a rare earth element or a mixture thereof, A' represents an alkaline earth metal or a mixture thereof, B represents a metal of transition or a mixture thereof, x, a and b represent numbers such that 0 x^1, 0.6 to 1.4, 0.6 b 1.4, and c represents a number that makes the compound charge neutral. Preferably, the reduction catalyst comprises perovskite or perovskite-based material, such as (La, Sr) (Fe, Ti) δ-based electrocatalysts. The electrocatalysts made of these materials contain high levels of La and Fe, thus offering high catalytic activity and also high electronic and oxide ion conductivity in the oxidizing conditions of the cathode compartment to benefit the electrochemical reaction. The reduction catalyst used in the method of the same invention is designed to electrochemically convert N2O to nitrogen at the same reaction temperature as the NH3 oxidation catalysts on the reverse side.

In one embodiment, a tubular membrane comprising a mixed conductive anode of electrons and oxide ions, such as that of a perovskite or perovskite-based material, Lni-xAxMOs, where Ln is a rare earth element, A is an alkaline earth metal and M is a transition metal or mixture of transition metals, preferably containing Fe, is manufactured by green extrusion containing a pore former.

Figure 5 shows an example of anode composition selection in a perovskite system containing (La,Sr)(Fe,Ti)Os-6, in particular potential La _x Sr0.9-xFeo perovskite anode electrocatalyst compositions. 4Thio.603-6 where it is clearly seen that higher conductivities are obtained in materials containing higher La contents under the reducing conditions of the anode compartment (10 ^-12 Pa). Alternatively, in one embodiment for better performance, the anode may be formed from a composite mixture of an oxide ion-conducting ceramic oxide or a mixed electron-oxide ion-conducting ceramic oxide, where the second phase of the composite is that phase offering high electronic conductivity, such as a metal or mixture of metals, preferably those of Pt, Pd, Ni, Cu, or Co, or a ceramic phase offering high electronic conductivity in reducing atmospheres. On this extruded tube a thin layer of an oxide ion conducting electrolyte such as yttria-stabilized zirconia is formed by a suitable process such as dip coating. In order to reduce ohmic resistance potential losses, electrolyte layer thickness should be minimized, with thicknesses less than 20 pm being preferred for target working temperatures <600 °C. An additional layer is deposited over the electrolyte to form the cathode, of a single material or composite material, which offers mixed conductivity of electrons and oxide ions and catalytic activity for N ₂ 0 reduction and which is designed to be catalytically active for the N2O reduction reaction at the same temperature as the NH3 oxidation reaction on the opposite side of the cell. Examples such as perovskite or perovskite-based material such as LnixAxMOs, or LnlYkCU where Ln is a rare earth element, A is an alkaline earth metal and M is a transition metal or mixture of transition metals, preferably containing Fe, Co, ass or

Ni, or materials of the AB2O4 spinel structure, where A and B in the spinel structure may be divalent, trivalent, or tetravalent cations, preferably containing high concentrations of transition elements, such as Fe, Co, Cu, or Ni.

Figure 6 shows an example of cathode composition selection in a perovskite system containing (La, Sr) (Fe, Ti) 03-δ, where it is clearly observed that higher conductivities are obtained in materials containing lower and higher La contents. of Fe in the oxidizing conditions of the cathode compartment. These phases can be combined with oxide ion conductive phases, such as yttria-stabilized zirconia, to form the cathode's overall requirements of mixed conductivity of electrons and oxide ions and catalytic activity for N2O reduction. The anode-electrolyte and cathode combination forms an electrode-membrane unit (MEA), a repeating unit that can be combined in series to produce higher voltage, and/or in parallel to allow higher current where each unit is separated by an electronically conductive interconnecting material. The formation of the functional MEA can be formed by a single sintering step, involving the complete MEA, or in two steps, firstly where the anode and electrolyte are sintered at an elevated temperature, preferably in the range of 1300 -1600 °C, followed by a second sintering step at a lower temperature, preferably in the range of 1000-1300 °C, after cathode deposition. In the first option, it is beneficial to add a pore-forming agent to the cathode before its deposition. 0 NH3 is passed in the anode compartment and ο N2O is passed in the cathode compartment. The N2O is reduced on the cathode side producing nitrogen, thus converting this formerly polluting gas into the environmentally safe nitrogen product, while also providing dissociated oxide ions which are subsequently transported through the membrane to the anode. At the anode, these oxide ions lead to the oxidation of gaseous NH3 to NO. Electricity and heat are simultaneously provided by this embodiment. Typical working temperatures of this embodiment will be in the range 500-900°C. Furthermore, the thermodynamic information provided in Figure 4 highlights that this embodiment provides a method which is spontaneous and which can be used to generate electricity.

In a further embodiment, a planar MEA configuration comprising the same anode, electrolyte and cathode materials is formed. In this embodiment, the combination of planar anode, electrolyte, and cathode layers forms a planar membrane electrode unit (MEA), a repeating unit that can be combined in series to produce higher voltage, and/or in parallel to allow a higher current where each unit is separated by an electronically conductive interconnecting material. Gas leaks between each layer are managed using ceramic or glass seals. The operating conditions of this planar cell are those defined for the previous tubular configuration. In this embodiment, simultaneous conversion of N2O to the useful product NO, a precursor to industrial processes such as nitric acid synthesis, the environmentally harmless N2 as well as the production of heat and electricity, is provided. Furthermore, the thermodynamic information provided in Figure 4 highlights that this embodiment provides a method which is spontaneous and which can be used to generate electricity.

In one embodiment, a tubular membrane comprising a mixed conductive material of electrons and oxide ions, such as that of a perovskite or perovskite-based material, Lni-xAxMOs, where Ln is a rare earth element, A is an alkaline earth metal and M is a transition metal or transition metal mixture, preferably containing Fe, is manufactured by green extrusion. This extruded tube is densified by sintering at elevated temperature, high enough to remove all open porosity. On the feed side of this tube, a suitable electrocatalyst is also provided which is designed to be catalytically active for the N2O reduction reaction at the same temperature as the NH3 oxidation reaction on the opposite side of the cell. Examples of suitable catalyst materials are perovskite or perovskite-based materials, such as Lni- _x A _x M03, or LnM2O4 where Ln is a rare earth element, A is an alkaline earth metal and M is a transition metal or mixture of transition metals, preferably containing Fe, Co, Cu or Ni, or materials of the AB2O4 spinel structure, where A and B in the spinel structure may be divalent, trivalent, or tetravalent cations, preferably containing high concentrations of transition elements, such as Fe, Co, Cu or Ni. On the permeate side, catalysts may be employed to promote NH3 oxidation, such as perovskite or perovskite-based material, Lni- _x A _x M03, where Ln is a rare earth element, A is an alkaline earth metal, and M is a transition metal or mixture of transition metals, preferably containing Fe, or a composite mixture of an oxide ion-conducting ceramic oxide or a mixed electron-conductive ceramic oxide and oxide ions, where the second phase of the composite provides electronic conductivity high, such as a metal or mixture of metals offering catalytic performance, preferably those of Pt, Pd, Ag, Ni, Cu, or Co.

Figures 5, 6 and 7 show examples of composition selection in a perovskite system containing (La, Sr) (Fe,Ti)O3-6 adapted to operate at the same temperature for N2O reduction and NH3 oxidation simultaneously, so that so that these reactions provide N2O treatment while producing NO, which is a valuable product in the formation of nitric acid. 0 NH3 is passed in the permeate compartment and ο N2O is passed in the feed compartment. The N2O is reduced on the feed side producing nitrogen, thus converting this formerly polluting gas into the environmentally safe nitrogen product, while also providing dissociated oxide ions which are subsequently transported through the permeate side of the mixed conductive membrane. On the permeate side, these oxide ions lead to the oxidation of gaseous NH3 to NO. Heat is provided simultaneously. Typical working temperatures of this embodiment will be in the range 500-900°C. In this embodiment, the method simultaneously provides for the conversion of N2O to the useful product NO, a precursor to industrial processes such as nitric acid synthesis, the environmentally harmless N2 as well as heat production.

Furthermore, Figure 4 highlights that said embodiment offers a method that is spontaneous. Figure 4 reveals that the method of the invention provides complete conversion of N2O to N2 at the cathode and NH3 to NO at the anode when a pure oxide ion conductive electrolyte membrane is used, thereby generating a much greater driving force for ion migration. oxide. On the contrary, prior art methods describe the use of oxygen or an oxygen-containing gas on the cathode (feed) side (where oxygen is present instead in its molecular form) and where electrocatalytic decomposition of N2O. This figure demonstrates that, in addition to N2O abatement and production of useful NO product, a higher cellular potential is provided by the method of the present invention, thereby advantageously increasing the driving force for oxide ion migration, improving the efficiency of the process.

In a further embodiment, a planar electrochemical cell comprising the same materials as the components is formed. In this embodiment, the combination of these components forms a planar unit. Gas leaks are managed using ceramic or glass seals. The operating conditions of this planar device are those defined for the previous tubular configuration.

In a further embodiment, a gas mixture containing NO and the unwanted by-product N2O is passed along the cathode or feed side of the devices mentioned above. Here, the desired reduction method (that of N2O reduction) is preferred over that of NO reduction due to temperature control in the range of 500700°C and selection of the reduction catalyst. In this embodiment this selectivity for N2O reduction is intrinsically achieved by taking advantage of the slower kinetics of NO reduction compared to those of N2O reduction, in order to differentiate the compound that preferentially undergoes reduction. In this embodiment, the invention thus avoids the need for pre-separation of N2O from the NO-containing product of NH3 reduction, a highly attractive feature for its implementation by reintegration into the nitric acid process. This is possible due to an identical reaction temperature that is specifically selected to preferentially select N2O reduction over NO reduction.

Claims (8)

1. Method for simultaneously treating nitrous oxide and forming nitric oxide, characterized in that it comprises feeding a gaseous stream of N2O to the reduction catalyst of a membrane, simultaneously feeding a gaseous stream of NH3 to the oxidation catalyst of the membrane. said membrane, in which both the membrane oxidation and reduction catalysts are at the same reaction temperature and in which the reduction catalyst is constituted by a material of general formula (AixA'x) _a (B) bO _c , in which A represents a rare earth element or a mixture thereof, A' represents an alkaline earth metal or a mixture thereof, B represents a transition metal or a mixture thereof, x, a and b represent numbers such that 0 < x < 1, 0, 6 < ad 1.4, 0.6 < bd 1.4, and c represents a number that makes the compound charge neutral. Method according to claim 1, characterized in that it further comprises a step of pre-treating the membrane by flowing reducing gases into the oxidation catalyst. Method according to claim 2, characterized in that the reducing gases are selected from hydrogen and ammonia. Method according to claims 1 to 3, characterized in that it further comprises a step of heating the membrane to the reaction temperature before feeding the membrane oxidation and reduction catalysts. 5. Method according to any of claims 1 to 4, characterized in that the reaction temperature varies between 500900 °C. 6. Method according to claim 5, characterized in that the reaction temperature varies between 600-800°C. 7. Method according to claim 6, characterized in that the reaction temperature varies between 650-750°C. Method according to claim 1, characterized in that the reduction catalyst is constituted by perovskite or material based on perovskite.