Process for recuperating palladium from a gas stream

Abstract

The present invention relates to a process for the capture of palladium from a gas stream comprising said palladium and oxygen, said process comprising contacting, at a temperature of at least 700 °C, said gas stream with an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

Description

[0001] PROCESS FOR RECUPERATING PALLADIUM FROM A GAS STREAM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for the capture of palladium (Pd) from a gas stream comprising said palladium and oxygen, said process comprising contacting, at a temperature of at least 700 °C, said gas stream with an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals. The process of the invention is especially useful in relation to industrial processes like the Ostwald process (showing a highly exothermic reaction) where a catchment gauze containing palladium is used.

[0004] BACKGROUND OF THE INVENTION

[0005] Chemical processes on an industrial scale often rely on catalysts of noble metals. Two of the metals used in this way are platinum and rhodium, highly precious metals that are lost from the catalyst over time, especially if the process is proceeding at high temperatures and / or is highly exothermic. One of these industrial processes is the Ostwald process.

[0006] Nitrogen-based inorganic fertilizers are produced from nitric acid obtained in the Ostwald process. In the first step, ammonia is oxidized over a Pt-Rh (typically 95:5 wt%) catalytic gauze at high temperature and moderate pressure to produce nitric oxide (NO). Under industrial conditions the yields achieved with the catalytic gauzes are 95-97 % depending on pressure and temperature. The strong greenhouse gas nitrous oxide (N2O) is an unwanted byproduct. Due to the highly exothermic nature of the oxidation reaction, Pt and Rh are lost as PtO2and RhO2into the gas phase, with Pt being the dominating loss. Along with the cost of the ammonia feedstock, metal loss causes the largest costs in the production of nitric acid. Capturing and recycling of the precious metals is therefore a key problem that needs to be solved.

[0007] There are different Pt catchment systems that have been utilized industrially to reduce the Pt loss including glass wool filters, Raschig rings, marble chips and Pd-X alloys (X = Au, Cu, Co, Ni). The most common technology used today is woven Pd-Ni (95:5 wt%) catchment gauzes installed downstream of the Pt-Rh catalyst gauzes; capturing the formed gaseous PtO2and incorporating Pt into the Pd based alloy. Unfortunately, there are a few drawbacks with the Pd-Ni catchment system. Complete reconstruction of the Pd-Ni wire gives rise to swelling and significant blockage of the gauzes; which in turn creates an undesired pressure drop. In addition, Pd is lost into the gas phase, affecting the cost-benefit of the process.

[0008] It would thus be highly beneficial to develop routes for the capture of such palladium during high temperature industrial processes.

[0009] SUMMARY OF THE INVENTION:

[0010] This task is solved by the present invention.

[0011] In a first aspect, the invention relates to process for the capture of palladium from a gas stream comprising said palladium and oxygen, said process comprising contacting, at a temperature of at least 700 °C, said gas stream with an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0012] In a specific embodiment, the invention relates to a process which captures palladium which has been lost by volatilization from a catchment gauze comprising palladium to said gas stream during a high temperature gas reaction carried out at temperatures of at least 700°C and wherein said gas stream is subsequently contacted with said oxide component. In a second aspect, the invention relates to the use of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals, for the capture of palladium from a gas stream at temperatures of at least 700 °C.

[0013] In a further aspect, the invention relates to a device for the capture of palladium from a combustion furnace of the type having a palladium catchment gauze arranged across the furnace in a direction transverse to the flow of gas therethrough, said device comprising or consisting an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0014] In another aspect, the invention relates to a catchment device for the capture of palladium, in an ammonia oxidation reaction, comprising an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0015] The invention is based on the surprising effect that the oxides as herein defined are / is able to highly effectively capture palladium, in particular if the Pd is mobilized / volatilized from a catchment gauze in a high temperature gas reaction.

[0016] DETAILED DESCRIPTION OF THE INVENTION:

[0017] The invention relates to a process for the capture of palladium (Pd) from a gas stream comprising said Pd and oxygen, said process comprising contacting, at a temperature of at least 700 °C, said gas stream with an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0018] In a preferred embodiment, the gas stream is contacted with the oxide component at a temperature of at least 750 °C, preferably at least 800 °C, more preferably at least 850 °C, such as at least 900 °C. A typical upper limit for the temperature is 950 °C, thus example temperature ranges include, 700 to 950 °C, 750 to 950 °C, 800 to 950 °C, 850 to 950 °C or 900 to 950 °C.

[0019] Typically, the Pd is lost by volatilization from a catchment gauze during a high temperature gas reaction carried out at temperatures of at least 700 °C.

[0020] The process ideally comprises contacting a gas stream, after its contact with such catchment gauze, with an oxide component as herein defined. The oxide component comprises or consists of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals

[0021] The gas stream comprises oxygen and Pd. It will be appreciated that the Pd will be in the vapour phase (i.e. gas phase) as Pd or a Pd containing gas species, in said gas stream.

[0022] In addition to oxygen and the palladium, the gas stream may comprise further gases such as NH3, H2, HCN, NO, N2O, H2O (in the form of steam), N2or combinations thereof. The gas stream may also comprise other metals in the gas phase, such as platinum and / or rhodium.

[0023] As said above, the invention is based on the surprising effect that the oxides as described herein are / is highly effective in capturing palladium from a gas stream at temperature of at least 700 °C.

[0024] The oxide component comprises or consists of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of iron (Fe), rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0025] Optionally, one or more of A may be in the form of a solid solution.

[0026] Optionally, one or more of B may be in the form of a solid solution.

[0027] Optionally, one or more of D may be in the form of a solid solution.

[0028] It is within the ambit of the invention for the oxide component to comprise (or consist of) one oxide of formula A2O3or one oxide of formula ABO3or one oxide of formula DO, or a mixture thereof. Alternatively, the first oxide component may comprise (or consist of) two or more oxides of formula A2O3, two or more oxides of formula ABO3or two or more oxides of formula DO, or a mixture thereof.

[0029] In one preferred embodiment, the oxide of formula ABO3is not LaNiO3.

[0030] It is preferred if the oxide component comprises or consists of at least one oxide of formula A2O3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids and wherein D is selected from alkaline earth metals.

[0031] Preferably, the first oxide component consists of one oxide of formula A2O3or one oxide of formula DO.

[0032] In a preferred embodiment of the process according to the invention said oxide of formula A2O3is an oxide wherein A is selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu and Gd; or from the group consisting of La, Nd, Gd, Dy, Ho, Y Sm, and Eu; or La, Gd, Dy, Ho and Nd, more preferably Nd and Gd; especially wherein said oxide is selected from the group consisting of Nd2O3, La2O3, Dy2O3, HO2O3and Gd2O3, preferably from Nd2O3and Gd2O3; most preferably wherein said oxide is Nd2O3.

[0033] It is preferred if the at least one oxide of formula ABO3is an oxide where A is selected form La, Nd or Gd and B is Ni or Fe, especially wherein said oxide is selected from LaNiO3, NdNiO3or LaFeO3, most preferably wherein said oxide is NdNiO3. In one embodiment, however, the at least one oxide of formula ABO3is not LaNiO3.

[0034] The at least one oxide of formula ABO3may be in the form of a perovskite or its RP phases / An+iBnO3n+i (n = integer, preferably n = 1 or 3). It is preferred if the at least one oxide of formula DO is an oxide wherein D is selected from Ca, Mg, Ba or Sr, more preferably Ca, Mg or Sr.

[0035] It is a preferred embodiment of the process of the invention, if the process according to the invention serves for the capture of Pd lost by volatilization from a catchment gauze comprising Pd to a gas stream contacted therewith in a high temperature gas reaction carried out at temperatures of at least 700°C which comprises contacting such gas stream, after its contact with such gauze, which contains thus volatilized Pd while such volatilized Pd is still essentially in the vapor phase and at a temperature of at least 700 °C, with said oxide component.

[0036] In a preferred general embodiment of the process of the invention the gas stream after its contact with said gauze is contacted with said oxide component at a temperature at around or above 800°C (or at 750°C to 900°C or at 750°C to 850°C or at 800°C to 900°C), preferably at around or above 900 °C (or at 850°C to 950°C), preferably wherein said high temperature gas reaction is carried out at temperatures of at around or above 800°C, preferably at around 900°C or above.

[0037] In a preferred embodiment of the process of the invention the catalytic reaction of the high temperature gas reaction is a catalytic ammonia oxidation or catalytic ammonia combustion.

[0038] In another aspect, the invention relates to the use of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals, for the capture of palladium from a gas stream at a temperature of at least 700 °C.

[0039] In another different aspect, the invention relates to a device for the capture of palladium from a combustion furnace of the type having a palladium catchment gauze arranged across the furnace in a direction transverse to the flow of gas therethrough, said device comprising or consisting of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0040] In a further different aspect, the invention relates to a catchment device for the capture of palladium, in an ammonia oxidation reaction, comprising or consisting of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO ora combination thereof, wherein A is selected from the group consisting of, rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

[0041] Definitions:

[0042] In the context of the invention “lanthanoid” is to be understood as meaning a series of chemical elements of atomic numbers 57-71 , from lanthanum through lutetium. Preferably the “lanthanoids” in the context of the invention are selected from La, Dy, Ho, Nd and Gd.

[0043] In the context of the invention “transition metal” is to be understood as meaning a chemical element in d-block of the periodic table, including groups 3 to 12. Preferably the “transition metals” in the context of the invention are selected from Fe and Ni.

[0044] In the context of the invention “alkaline earth metal” is to be understood as meaning the chemical elements Mg, Ca, Sr and Ba from Group 2 of the periodic table.

[0045] In the context of the invention “capture” is to be understood as meaning the fixation of previously volatilized palladium on an oxide or oxide component.

[0046] In the context of this invention “decompose” and / or “convert” is to be understood as meaning the conversion / decomposition, especially of N2O, especially to NO, NOx, N2and / or O2. This happens upon contact with an oxide component (or the oxide comprised therein) and thus for example leads to an abatement of N2O.

[0047] In the context of the invention “volatilization” is to be understood as meaning the removal of the palladium from e.g. the solid metal structure of e.g. the gauze and putting this noble metal or any derivative in its “vapor phase” (i.e. gas phase), including taking it up in this vapor phase e.g. in a gas stream. This volatilization usually happens at “high temperatures”.

[0048] In the context of the invention “high temperature” is to be understood as meaning at a temperature of or above 700°C.

[0049] In the context of the invention “contact” is to be understood as meaning a physical contact or close contact e.g. coming within 1 cm or less, e.g. between the gas of a “high heated gas stream” or a volatilized noble metal (or a derivative, e.g. in said gas stream with an oxide component.

[0050] In the context of the invention “perovskite” is to be understood as meaning that a perovskite is a compound, ABX3, that belong to the class of compounds that take a perovskite type structure. When X = 0, the perovskite is an oxide AB03. In the ideal perovskite structure, the B-site cation is 6-coordinated to oxygen and A-site is 12- coordinated to oxygen. A site cation is generally from (alkali earth) alkaline earth and rare earth elements whereas B site cation is generally selected from 3-5d elements, p-block elements. The perovskite oxide can have lower symmetry, being distorted, and may have oxygen vacancies in random or ordered patterns.

[0051] In the context of the invention “RP-phase” is to be understood as meaning that an RP phase is a phase that is described by the so-called Ruddlesden-Poppertype structure. The general formula is An+iBn03n+i or (AB03)n(A0) whereof n is an integer. The atomic arrangement in AB03(part of the structure) is the same as in the perovskite whereas AO is a structure fragment corresponding to half a rock salt layer. A site cation is generally from alkaline earth and rare earth elements whereas B site cation is generally selected from 3-5d elements, p-block elements. A RP-phase is conveniently described by the parameter “n” in the formula An+iBn03n+i; for example RP1 is meaning an RP structure with n =1 and hence representing A2BO4.

[0052] In the context of the invention “in form of a solid solution” is to be understood as meaning that a solid solution is a uniform mixture of two crystalline solids that share a common crystal lattice. Solid solutions often consist of two or more types of atoms that occupy the same crystallographic site in the crystal structure in a random manner. In the context of the invention “in an ordered arrangement” is to be understood as meaning that an ordered arrangement occurs when two or more types of atoms are having the potential to occupy the same crystallographic site in a crystal structure, however, their distribution is not random in nature as for a solid solution, but rather systematically alternating in manner.

[0053] Accordingly, in the context of this invention “one or more elements on A position in form of a solid solution or in an ordered arrangement” is to be understood as meaning that the compound has two or more types of category A-atoms that occupy the same crystallographic site in the structure in a random manner (solid solution) or in a systematic manner (ordered arrangement).

[0054] In the context of the invention “rare earth” is to be understood as meaning a cation representing Sc, Y, La or the fourteen 4f-elements; i.e. elements with numbers 21 , 38, and 57 to 71 in the Periodic Table.

[0055] In the context of the invention “lanthanoids / rare earth elements” is to be understood as meaning that the respective “A” is selected from both the lanthanoids or rare earth elements as defined herein.

[0056] In the context of the invention “An+iBn03n+i(n = 1 , 3) - Ruddlesden Popper phases is to be understood as described in the explanation given above for “RP-Phase”.

[0057] In the context of the invention “3-5d elements” is to be understood as meaning that 3-5d elements refer to 3d, 4d and 5d elements in the periodic table, altogether 10, 10 and 10 elements, respectively

[0058] In the context of the invention “p-block elements” is to be understood as meaning that p-block elements refer to the elements in groups 13, 14 and 15, in the periodic table.

[0059] The present invention is illustrated below with the aid of examples. These illustrations are given solely by way of example and do not limit the general spirit of the present invention.

[0060] EXAMPLES:

[0061] Experiment run in pilot plant: Nd2O3, Gd2O3, SrO, LaNiO3, NdNiO3and CaO were exposed to the real process conditions based on the Ostwald process (T = 900 °C, P = 5 bar and gas mix of 10 % NOx, 15 % H2O, 5 % O2and 1300 ppm N2O in N2) for 21 days. Cylindrical pellets of the oxides were sewn into megapyr nets for easier handling. The samples were placed at the top of raching rings in the gas stream after the Pt-Rh catalyst (95:5 wt.%)+Pd-Ni catchment gauze and a N2O decomposing catalyst, Co2AIO4.

[0062] Analysis of each oxide was performed to determine which elements had been captured. The results are shown in Table 1 below.

[0063] Table 1

Claims

CLAIMS:1 . A process for the capture of palladium from a gas stream comprising said palladium and oxygen, said process comprising contacting, at a temperature of at least 700 °C, said gas stream with an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

2. The process according to claim 1 , wherein the gas stream is contacted with said oxide component at a temperature of at least 750 °C, preferably at least 800°C, more preferably at least 900 °C.

3. The process according to claim 1 or 2, wherein said at least one oxide of formula ABO3is not LaNiO3.

4. The process according to any of claims 1 to 3, wherein said at least one oxide is of formula A2O3, DO, or a combination thereof.

5. The process according to claim 1 or 2, wherein said oxide of formula ABO3is an oxide where A is selected from the group consisting of La, Nd or Gd and B is Ni or Fe; preferably wherein said oxide is selected from the group consisting of LaNiO3, NdNiO3or LaFeO3; most preferably wherein said oxide is NdNiO3.

6. The process according to any of claims 1 to 5, wherein said oxide of formula A2O3is an oxide wherein A is selected from the group consisting of La, Ce, Pr, Nd, Dy, Ho, Y, Sm, Eu and Gd; or from La, Nd, Gd, Dy, Ho, Y and Sm; or from La, Dy, Ho, Gd and Nd, more preferably from Gd and Nd; especially wherein said oxide is selected from the group consisting of Nd2O3, La2O3, Dy2O3, Ho2O3and Gd2O3, preferably from Nd2O3and Gd2O3;most preferably wherein said oxide is Nd2O3.

7. The process according to any of claims 1 to 6, wherein said oxide of formula DO is an oxide wherein D is selected from the group consisting of Ba, Ca, Mg, and Sr, preferably Ca, Mg and Sr.

8. The process according to any of claims 1 to 7, wherein said oxide component comprises, or consists of, an oxide of formula A2O3as defined in claim 1 or 6.

9. The process according to any of claims 1 to 8, wherein said oxide component comprises, or consists of, an oxide of formula DO as defined in claim 1 or 7.

10. The process according to any one of claims 1 to 9, wherein the process captures palladium which has been lost by volatilization from a catchment gauze comprising said palladium to a gas stream contacted with said gauze in a high temperature gas reaction carried out at temperatures of at least 700°C and wherein said gas stream is subsequently contacted with said oxide component.11 .The process according to claim 10, wherein the gas stream is contacted with said oxide component at a temperature at around or above 800°C, preferably at around 900 °C or above, preferably wherein said high temperature gas reaction is carried out at temperatures of at around or above 800°C, preferably at around 900°C or above.

12. The process of claim 10 or 11 , wherein the high temperature gas reaction is a catalytic ammonia oxidation or catalytic ammonia combustion.

13. Use of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3IDO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected fromalkaline earth metals, for the capture of palladium from a gas stream at a temperature of at least 700 °C.

14. A device for the capture of palladium from a combustion furnace of the type having a palladium catchment gauze arranged across the furnace in a direction transverse to the flow of gas therethrough, said device comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of, rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

15. A catchment device for the capture of palladium, in an ammonia oxidation reaction, comprising or consisting of an oxide component comprising or consisting of at least one oxide of formula A2O3, ABO3, DO or a combination thereof, wherein A is selected from the group consisting of rare earth elements and lanthanoids, B is selected from the group consisting of 3-5d elements and p-block elements and wherein D is selected from alkaline earth metals.

16. The use according to claim 13, the device according to claim 14 or catchment device according to claim 15, wherein said oxide is an oxide as defined in any of claims 5 to 7, preferably claim 6 or 7.

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