WO2010046676A1 - Precious metal gauze assembly - Google Patents
Precious metal gauze assembly Download PDFInfo
- Publication number
- WO2010046676A1 WO2010046676A1 PCT/GB2009/051206 GB2009051206W WO2010046676A1 WO 2010046676 A1 WO2010046676 A1 WO 2010046676A1 GB 2009051206 W GB2009051206 W GB 2009051206W WO 2010046676 A1 WO2010046676 A1 WO 2010046676A1
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- WO
- WIPO (PCT)
- Prior art keywords
- precious metal
- gauze
- catalyst
- gauzes
- tube
- Prior art date
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- 239000010970 precious metal Substances 0.000 title claims abstract description 98
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 100
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 50
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 46
- 230000003647 oxidation Effects 0.000 claims abstract description 43
- 239000007789 gas Substances 0.000 claims abstract description 37
- 238000000034 method Methods 0.000 claims abstract description 21
- 239000003054 catalyst Substances 0.000 claims description 57
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 47
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 38
- 229910052763 palladium Inorganic materials 0.000 claims description 23
- 229910052697 platinum Inorganic materials 0.000 claims description 21
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 16
- 229910000831 Steel Inorganic materials 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- 239000010959 steel Substances 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 4
- 239000001301 oxygen Substances 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 4
- 238000009420 retrofitting Methods 0.000 claims description 2
- 239000010948 rhodium Substances 0.000 description 15
- 229910052703 rhodium Inorganic materials 0.000 description 12
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- LELOWRISYMNNSU-UHFFFAOYSA-N hydrogen cyanide Chemical compound N#C LELOWRISYMNNSU-UHFFFAOYSA-N 0.000 description 6
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 4
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical compound [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 3
- 229910001260 Pt alloy Inorganic materials 0.000 description 3
- 238000009940 knitting Methods 0.000 description 3
- 229910017604 nitric acid Inorganic materials 0.000 description 3
- 238000009941 weaving Methods 0.000 description 3
- 238000006189 Andrussov oxidation reaction Methods 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910017052 cobalt Inorganic materials 0.000 description 2
- 239000010941 cobalt Substances 0.000 description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 239000001272 nitrous oxide Substances 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 229910001252 Pd alloy Inorganic materials 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- XKUTVNLXHINPAP-UHFFFAOYSA-N azane platinum Chemical compound N.[Pt] XKUTVNLXHINPAP-UHFFFAOYSA-N 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
- C01B21/24—Nitric oxide (NO)
- C01B21/26—Preparation by catalytic or non-catalytic oxidation of ammonia
- C01B21/267—Means for preventing deterioration or loss of catalyst or for recovering lost catalyst
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0053—Details of the reactor
- B01J19/006—Baffles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/24—Stationary reactors without moving elements inside
- B01J19/248—Reactors comprising multiple separated flow channels
- B01J19/2495—Net-type reactors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/32—Packing elements in the form of grids or built-up elements for forming a unit or module inside the apparatus for mass or heat transfer
- B01J19/325—Attachment devices therefor, e.g. hooks, consoles, brackets
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/42—Platinum
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/44—Palladium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
- B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/0605—Binary compounds of nitrogen with carbon
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
- C01B21/24—Nitric oxide (NO)
- C01B21/26—Preparation by catalytic or non-catalytic oxidation of ammonia
- C01B21/28—Apparatus
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C3/00—Cyanogen; Compounds thereof
- C01C3/02—Preparation, separation or purification of hydrogen cyanide
- C01C3/0208—Preparation in gaseous phase
- C01C3/0212—Preparation in gaseous phase from hydrocarbons and ammonia in the presence of oxygen, e.g. the Andrussow-process
- C01C3/0216—Preparation in gaseous phase from hydrocarbons and ammonia in the presence of oxygen, e.g. the Andrussow-process characterised by the catalyst used
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C3/00—Cyanogen; Compounds thereof
- C01C3/02—Preparation, separation or purification of hydrogen cyanide
- C01C3/0208—Preparation in gaseous phase
- C01C3/0212—Preparation in gaseous phase from hydrocarbons and ammonia in the presence of oxygen, e.g. the Andrussow-process
- C01C3/022—Apparatus therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/32—Details relating to packing elements in the form of grids or built-up elements for forming a unit of module inside the apparatus for mass or heat transfer
- B01J2219/324—Composition or microstructure of the elements
- B01J2219/32466—Composition or microstructure of the elements comprising catalytically active material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/32—Details relating to packing elements in the form of grids or built-up elements for forming a unit of module inside the apparatus for mass or heat transfer
- B01J2219/324—Composition or microstructure of the elements
- B01J2219/32491—Woven or knitted materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/32—Details relating to packing elements in the form of grids or built-up elements for forming a unit of module inside the apparatus for mass or heat transfer
- B01J2219/33—Details relating to the packing elements in general
- B01J2219/3306—Dimensions or size aspects
Definitions
- This invention relates to apparatus for supporting precious metal gauzes, particularly catalyst and catchment gauzes used in ammonia oxidation vessels, and processes using such apparatus.
- Ammonia oxidation is carried out industrially with air to generate nitric oxide, which used to make nitric acid (the Ostwald Process) or with air and methane to generate hydrogen cyanide (the Andrussow Process).
- the reactant gases are mixed and passed at elevated temperature and pressure through a reaction vessel in which is placed a pack of platinum/rhodium gauzes that catalyse the oxidation reactions.
- the gauzes are typically circular and are supported on a frame or basket that holds them perpindicular to the flow of gases through the reactor.
- the catalyst pack may also comprise one or more palladium-rich gauzes, known as "catchment gauzes" that act to capture volatilised platinum.
- the gauze pack can give rise to unacceptable pressure drop thereby increasing compression costs. There is also the possibility of enhanced side reactions due to increased contact time with the catalyst structure. Furthermore there is a desire to increase the amount of catchment gauze used in order to more effectively capture the volatilised platinum, but this is limited by the increased pressure drop this would cause.
- the invention provides a precious metal gauze assembly, suitable for use in an ammonia oxidation vessel, comprising a precious metal gauze in the form of a tube mounted between process fluid-impermeable end members, wherein one end member provides a closed end to the tube and the other end member extends radially from the tube thereby providing an open end through which gases may enter or exit the assembly, and suspending means attached to one or both end members by which the assembly may be secured within a reactor.
- the precious metal gauze assembly therefore provides a means for passing gases radially through the precious metal gauze.
- Radial flow reactors are known, however, to our knowledge none comprise a precious metal gauze assembly wherein an end member serves as suspending means by which the unit is secured within a reactor.
- radial flow catalyst structures have not heretofore been used in ammonia oxidation vessels.
- the radial flow arrangement allows for a reduced pressure drop for the same gauze volume or an increase in the amount of gauze for the same pressure drop, thus offering the operator increased operational flexibility and reduced compression costs.
- the precious metal gauze to be formed into a tube may comprise one or more platinum catalyst gauzes and/or one or more palladium catchment gauzes.
- Precious metal gauzes may be formed by weaving or knitting or otherwise forming precious metal filaments into a gauze-like structure.
- Such catalyst gauzes are well established and may consist of platinum or platinum alloy filaments of thickness from 0.02 to 0.15 mm woven to provide rectangular interstices, knitted to provide a regular looped structure or simply agglomerated to provide a non-woven irregular structure.
- 'filament ' is meant to include wires that have a substantially circular cross-section and also wires that are flattened or otherwise shaped and thereby have a non-circular cross section.
- Knitted gauzes are well established and typically comprise 0.076 mm diameter wire, woven to provide 1024 apertures per square centimetre and prepared to a specific weight per unit area dependant upon the wire composition. Knitted gauzes offer a number of advantages in terms of catalyst physical properties, catalyst activity and lifetime. Knitted gauzes comprise a regular looped structure and may be formed using wire with diameters in the same range as woven materials, in a variety of shapes and thicknesses using variety of stitches such as tricot, jacquard, satin stitch (smooth sunk loops) and raschel.
- EP-B-0364153, page 3, line 5 to line 56 describes knitted gauzes of particular use in the present invention. Non-woven gauzes are described for example in GB 2064975 and GB 2096484.
- the precious metal ammonia oxidation catalyst is preferably platinum (Pt) or a platinum alloy, such as an alloy of platinum with rhodium (Rh) and/or palladium (Pd) containing >85% preferably >90% Pt by weight. Alloys used in ammonia oxidation in the production of nitric acid or hydrogen cyanide include 10% Rh 90% Pt, 8% Rh 92% Pt, 5% Pd 5% Rh 90% Pt and 5% Rh 95% Pt. Alloys containing upto about 5% of iridium (Ir) may also be used in the present invention.
- the precious metal catalyst may desirably be formulated to reduce nitrous oxide by-product formation, and may thus have an increased rhodium (Rh) content, or may contain other components such as cobalt (Co).
- Catchment gauzes based on palladium are desirably used in ammonia oxidation plants to act as so-called “getters” or collectors of 'vaporised' platinum lost by chemical action, evaporation or mechanical losses from the precious metal catalyst.
- Such catchment gauzes may be in the form of woven or knitted gauzes or agglomerated non-woven gauzes akin to those described above for the precious metal catalysts. Any palladium present in a gauze will be able to catch vapourised platinum passing over it, hence the palladium content of the catchment gauze may be from 10 to > 95% wt, preferably >40%, more preferably >70%.
- One or more palladium based catchment gauzes may be used.
- the catchment gauzes may be knitted, e.g. according to the aforesaid EP-B-0364153.
- the palladium-based guard material may be woven or knitted into a precious metal ammonia oxidation catalyst gauze by using it as a filament in the weaving or knitting process.
- Palladium-based guard materials suitable for weaving or knitting into gauze structures are palladium or palladium alloys with nickel (Ni), cobalt (Co) or gold (Au).
- a catchment gauze may be fabricated from a 95:5% wt Pd:Ni alloy.
- the palladium-based guard material may desirably be formulated to reduce nitrous oxide by-product formation, and may thus preferably contain a small amount, e.g. ⁇ 5% rhodium (Rh).
- palladium gauzes containing amounts of platinum and rhodium may be used. Such gauzes may comprise, for example >92% wt palladium, 2-4% wt rhodium and the remainder platinum, or alternatively comprise 82-83% wt palladium, 2.5-3.5% wt rhodium and the remainder platinum.
- Ceramic fibres comprising an inert refractory material, such as alumina, zirconia or the like, may also be woven or knitted into catchment gauzes in addition to the palladium-based materials.
- catalyst and catchment gauzes are combined it is desirable that they are arranged in the tube wall so that the gases contact first with the catalyst gauzes and then catchment gauzes.
- the number of gauzes employed depends on the pressure at which the process is operated. For example in a plant operating at low pressure, e.g. up to about 5 bar abs., typically ⁇ 10, often 3 to 6 gauzes may be employed, while at higher pressures, e.g. up to 20 bar abs., a greater number of gauzes, typically >20, often 35-45, may be employed. If adjacent woven gauzes are present, to facilitate replacement, they are preferably arranged so that their warps or wefts are at an angle of 45° to each other. Angular displacement, suitably at 90°, may also be used between adjacent woven gauzes to reduce opportunities for gas channelling.
- the tube may further comprises a steel mesh.
- steel we mean suitable high-temperature stable alloys, including non-Fe-based alloys such as Ni-based materials.
- the cross section of the tube may be circular, oval, or polygonal, e.g. having between 3 and 50 sides.
- Tubular arrangements have the advantage over conventional circular-cut gauzes in that that the gauze may be formed into a tube from the square or rectangular form in which it was woven or knitted, thereby reducing waste during fabrication.
- Cylindrical tubes are preferred. Where the precious metal gauze tube is cylindrical, the closed end member may be circular with a diameter at least that of the tube, and the open end member may be ring shaped with a central hole of diameter at most equal to that of the tube.
- the end members are suitably fabricated from steel sheet.
- the suspending means may be attached to one or both end members. Preferably the suspending means are provided by extending the end member forming the open end of the assembly.
- the end members When the assembly is placed in a reactor, the end members may also be inclined to direct the flow of gases through the gauze in the desired manner.
- baffles may also be provided on the assembly to direct the flow of gases radially through the gauze. For example a conical baffle may be placed on the closed end member.
- the flow of gases through the assembly may be radially inwards, i.e. from the periphery of the unit towards its centre, or may be radially outwards, i.e. from the central region outwards to wards the periphery.
- outward radial flow is preferred.
- the flow through the vessel may be upflow or downflow.
- the precious metal gauze assembly may be placed in a reaction vessel as a standalone unit, it is possible that the assembly may be used in combination with a conventional circular precious metal ammonia oxidation catalyst. Accordingly, the invention further provides a catalyst combination comprising a circular precious metal ammonia oxidation catalyst gauze on a supporting framework and a tubular precious metal catalyst gauze in the assembly of the present invention.
- One or more catchment gauzes may also be provided under the circular precious metal catalyst gauzes but this is less preferred where the tubular gauze assembly comprises catchment gauzes.
- the circular precious metal catalyst and catchment gauzes may be the same or different from the tubular precious metal catalyst and catchment gauzes disposed in the precious metal gauze assembly.
- the supporting framework for the circular gauzes may be any currently in use and includes simple girder support arrangements that extend across the ammonia oxidation vessel and so- called “baskets" in which the circular precious metal gauzes are supported on the base of a cylindrical unit suspended within the ammonia oxidation vessel.
- the tubular precious metal gauze assembly may be separate from the supporting framework for the circular precious metal gauzes, but in a preferred embodiment, the tubular precious metal gauze assembly is suspended from the circular precious metal catalyst-supporting framework using the suspending means. In a particularly preferred arrangement, the tubular precious metal gauze assembly is suspended from a precious metal catalyst basket.
- the precious metal gauze assembly according to the present invention may be installed in any ammonia oxidation vessel having a suitable space to accommodate it. Alternatively, the vessel may be adapted to make a suitable space available. Ammonia oxidation vessels vary in size but are typically domed cylindrical vessels with internal diameters in the range 0.5-6 metres. The precious metal gauze assembly may be fabricated to fit within these reactors. For example, in a 1.5 m diameter vessel, the wall thickness of the tube may be 180 mm by 700-750 mm in height.
- the precious metal gauze assembly may be placed below the circular precious metal gauzes so that the gases enter the ammonia oxidation vessel through an inlet in the top, then pass vertically (i.e. axially) downwards through the precious metal catalyst layer, enter the open end of the precious metal gauze assembly then pass radially through the precious metal gauze walls of the tube and then out of the base of the unit and exit the ammonia oxidation vessel via an outlet in the base.
- the arrangement may be reversed in an upflow vessel.
- the invention further provides a method of retrofitting an ammonia oxidation vessel comprising suspending a precious metal gauze assembly beneath the circular precious metal catalyst. This is desirably accomplished by fixing a precious metal gauze assembly to the existing precious metal catalyst gauze support frame.
- the invention further provides an ammonia oxidation process comprising the step of passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a tubular precious metal catalyst gauze catalyst disposed in the precious metal gauze assembly.
- the process comprises passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a circular precious metal catalyst gauze on a supporting framework and a tubular precious metal gauze catalyst disposed in the precious metal gauze assembly.
- the oxidation process may be operated at temperatures of 750-1000 0 C, particularly 850-950 0 C, pressures of 1 (low pressure) to 15 (high pressure) bar abs., with ammonia in air concentrations of 7-13%, often about 10%, by volume.
- the operating conditions are similar.
- the present invention is particularly suited to processes and ammonia oxidation reactors operated at pressures in the range 6-15 bar abs, particularly 7-15 bar g (so-called high pressure plants) because the tubular precious metal gauze assembly may readily be placed in the vessel without having to move or adjust heat recovery means commonly found just below the gauzes n medium pressure and atmospheric plants.
- the catalyst assembly of the present invention may comprise 2-10 platinum oxidation gauzes and 2-5 palladium catchment gauzes formed into a tube, optionally with one or more steel meshes to act as a strengthening material.
- a catalyst combination may be used comprising 1 or 2 circular precious metal ammonia oxidation catalyst gauzes followed by one or more gauzes of palladium catchment in a conventional arrangement, followed by a radial flow arrangement of tubular precious metal ammonia oxidation catalyst and/or further catchment gauzes.
- the catalyst assembly may comprise between 2 and 10 circular platinum catalyst gauzes without catchment and the precious metal gauze assembly used only for catchment gauzes.
- Figure 1 is a cut-away side elevation of a precious metal gauze assembly according to a first embodiment with the end members arranged to provide outwards radial flow,
- Figure 2 is a cut-away side elevation of a precious metal gauze assembly according to a second embodiment with the end members arranged to provide inwards radial flow
- Figure 3 is a cut-away side elevation of an ammonia oxidation vessel containing a precious metal gauze assembly arranged to provide outwards radial flow
- Figure 4 is a cut-away side elevation of an ammonia oxidation vessel containing a catalyst combination comprising a precious metal gauze supported in a basket and precious metal gauze assembly suspended from said basket with the end members arranged to provide outwards radial flow.
- the precious metal gauze assembly comprises a vertical tube 10 formed from one or more precious metal gauzes, mounted on a circular steel sheet 12 that extends horizontally across the width of the tube 10, thereby forming a closed end.
- a conical baffle 14 that acts to direct gas radially through the gauzes.
- a ring-shaped steel end member 16 having a central hole corresponding to the internal diameter of the tube 10 is mounted on the other end of the gauzes, thereby forming an open end.
- the end member 16 is angled upwards from the tube at about 45 degrees.
- Suspending arm 18 is formed by vertically extending the edge of the ring member 16.
- the suspending arm 18 has a flange 20 at its extremity to permit installation of the assembly into a reactor. In use, gases enter the assembly via the central hole in the ring-shaped end member 16, pass through meshes 10, and then out of the assembly.
- the precious metal gauze assembly comprises a vertical tube 30 mounted on a ring-shaped steel end member 32, having a central hole corresponding to the internal diameter of the tube, thereby forming an open end.
- the assembly has a circular steel sheet end member 34 mounted horizontally on the tube and extending across its width thereby providing a closed end.
- a conical baffle 36 On the upper surface of sheet 34 and extending across its width is a conical baffle 36.
- Suspending arm 36 is formed by extending the sides of the ring end member 32 horizontally then vertically from the tube to above the end member 34.
- the suspending arm 36 has a flange 40 at its extremity to permit installation of the assembly into a reactor.
- gases enter the assembly via the annular void 38, pass through the walls of tube 30, and then out of the assembly via the central hole in ring end member 32.
- a cylindrical ammonia oxidation vessel comprises a domed upper portion 50 with inlet 52 and a domed lower portion 54 with outlet 56.
- a flanged joint 58 joins the upper and lower portions.
- a catalyst containment unit Suspended from this joint 58 within the vessel is a catalyst containment unit as depicted in Figure 1 in which the walls of tube 10 are fabricated from multiple layers of platinum ammonia oxidation gauze with one or more layers of palladium catchment gauze on the outer (vessel wall-facing) surface.
- a mixture of ammonia and air, optionally containing methane is passed at elevated temperature and pressure through the inlet 52, passes downwards and is deflected by member 16 to pass through the open end of the precious metal gauze assembly.
- the gases then pass radially, with the assistance of baffle 20, through the catalyst and catchment gauzes where the ammonia oxidation reaction takes place.
- the reacted gases then exit the unit and are deflected downwards to the lower portion 54 of the vessel and then out of the vessel via outlet 56.
- a cylindrical ammonia oxidation vessel comprises a domed upper portion 60 with inlet 62 and a domed lower portion 64 with outlet 66.
- a flanged joint 68 joins the upper and lower portions.
- a precious metal gauze- support 70 Suspended from this joint 68 within the vessel is a precious metal gauze- support 70 in the form of a steel-frame basket containing a circular precious metal gauze pack 72 made up of a plurality of platinum/rhodium ammonia oxidation gauzes and optionally one or more palladium catchment gauzes.
- a precious metal gauze assembly as depicted in Figure 1 in which the tube is made up of a plurality of palladium catchment gauzes and the flange 20 on the suspending means 18 is attached to limbs 74 extending from the underside of basket 70.
- a mixture of ammonia and air, optionally containing methane, is passed at elevated temperature and pressure through the inlet 62 and distributed over the surface of the catalyst gauze pack 72 by means of distribution means (not shown).
- the gases pass downwards (axially) through the gauze pack where the ammonia oxidation reactions take place.
- the hot gas mixture then passes downwards and is deflected by member 16 to pass through the open end of the precious metal gauze assembly.
- the gases then pass radially, with the assistance of baffle 20, through the catchment gauzes where volatilised platinum is captured.
- the reacted gases then exit the assembly and are deflected downwards to the lower portion 64 of the vessel and then out of the vessel via outlet 66.
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Abstract
A precious metal gauze assembly, suitable for use in an ammonia oxidation vessel is described, comprising a precious metal gauze in the form of a tube mounted between process fluid-impermeable end members, wherein one end member provides a closed end to the tube and the other end member extends radially from the tube thereby providing an open end through which gases may enter or exit theunit, and suspending means attached to one or both end members by which the assembly may be secured within a reactor. The assembly may be suspended below a conventional precious metal ammonia oxidation gauze pack.
Description
Precious metal gauze assembly
This invention relates to apparatus for supporting precious metal gauzes, particularly catalyst and catchment gauzes used in ammonia oxidation vessels, and processes using such apparatus.
Ammonia oxidation is carried out industrially with air to generate nitric oxide, which used to make nitric acid (the Ostwald Process) or with air and methane to generate hydrogen cyanide (the Andrussow Process). In both processes, the reactant gases are mixed and passed at elevated temperature and pressure through a reaction vessel in which is placed a pack of platinum/rhodium gauzes that catalyse the oxidation reactions. The gauzes are typically circular and are supported on a frame or basket that holds them perpindicular to the flow of gases through the reactor. The catalyst pack may also comprise one or more palladium-rich gauzes, known as "catchment gauzes" that act to capture volatilised platinum.
In conventional arrangements the gauze pack can give rise to unacceptable pressure drop thereby increasing compression costs. There is also the possibility of enhanced side reactions due to increased contact time with the catalyst structure. Furthermore there is a desire to increase the amount of catchment gauze used in order to more effectively capture the volatilised platinum, but this is limited by the increased pressure drop this would cause.
Therefore there is a need to provide a catalyst arrangement that overcomes these problems.
Accordingly the invention provides a precious metal gauze assembly, suitable for use in an ammonia oxidation vessel, comprising a precious metal gauze in the form of a tube mounted between process fluid-impermeable end members, wherein one end member provides a closed end to the tube and the other end member extends radially from the tube thereby providing an open end through which gases may enter or exit the assembly, and suspending means attached to one or both end members by which the assembly may be secured within a reactor.
The precious metal gauze assembly therefore provides a means for passing gases radially through the precious metal gauze. Radial flow reactors are known, however, to our knowledge none comprise a precious metal gauze assembly wherein an end member serves as suspending means by which the unit is secured within a reactor. Moreover, to our knowledge, radial flow catalyst structures have not heretofore been used in ammonia oxidation vessels. The radial flow arrangement allows for a reduced pressure drop for the same gauze volume or an increase in the amount of gauze for the same pressure drop, thus offering the operator increased operational flexibility and reduced compression costs.
In the present invention, the precious metal gauze to be formed into a tube may comprise one or more platinum catalyst gauzes and/or one or more palladium catchment gauzes.
Precious metal gauzes may be formed by weaving or knitting or otherwise forming precious metal filaments into a gauze-like structure. Such catalyst gauzes are well established and may consist of platinum or platinum alloy filaments of thickness from 0.02 to 0.15 mm woven to provide rectangular interstices, knitted to provide a regular looped structure or simply agglomerated to provide a non-woven irregular structure. Herein the term 'filament ' is meant to include wires that have a substantially circular cross-section and also wires that are flattened or otherwise shaped and thereby have a non-circular cross section. Woven gauzes are well established and typically comprise 0.076 mm diameter wire, woven to provide 1024 apertures per square centimetre and prepared to a specific weight per unit area dependant upon the wire composition. Knitted gauzes offer a number of advantages in terms of catalyst physical properties, catalyst activity and lifetime. Knitted gauzes comprise a regular looped structure and may be formed using wire with diameters in the same range as woven materials, in a variety of shapes and thicknesses using variety of stitches such as tricot, jacquard, satin stitch (smooth sunk loops) and raschel. EP-B-0364153, page 3, line 5 to line 56 describes knitted gauzes of particular use in the present invention. Non-woven gauzes are described for example in GB 2064975 and GB 2096484.
The precious metal ammonia oxidation catalyst is preferably platinum (Pt) or a platinum alloy, such as an alloy of platinum with rhodium (Rh) and/or palladium (Pd) containing >85% preferably >90% Pt by weight. Alloys used in ammonia oxidation in the production of nitric acid or hydrogen cyanide include 10% Rh 90% Pt, 8% Rh 92% Pt, 5% Pd 5% Rh 90% Pt and 5% Rh 95% Pt. Alloys containing upto about 5% of iridium (Ir) may also be used in the present invention. The precious metal catalyst may desirably be formulated to reduce nitrous oxide by-product formation, and may thus have an increased rhodium (Rh) content, or may contain other components such as cobalt (Co).
Catchment gauzes based on palladium are desirably used in ammonia oxidation plants to act as so-called "getters" or collectors of 'vaporised' platinum lost by chemical action, evaporation or mechanical losses from the precious metal catalyst. Such catchment gauzes may be in the form of woven or knitted gauzes or agglomerated non-woven gauzes akin to those described above for the precious metal catalysts. Any palladium present in a gauze will be able to catch vapourised platinum passing over it, hence the palladium content of the catchment gauze may be from 10 to > 95% wt, preferably >40%, more preferably >70%. One or more palladium based catchment gauzes may be used. The catchment gauzes may be knitted, e.g. according to the aforesaid EP-B-0364153. Alternatively the palladium-based guard material may be woven or knitted into a precious metal ammonia oxidation catalyst gauze by using it as a
filament in the weaving or knitting process. Palladium-based guard materials suitable for weaving or knitting into gauze structures are palladium or palladium alloys with nickel (Ni), cobalt (Co) or gold (Au). For example a catchment gauze may be fabricated from a 95:5% wt Pd:Ni alloy. In addition the palladium-based guard material may desirably be formulated to reduce nitrous oxide by-product formation, and may thus preferably contain a small amount, e.g. <5% rhodium (Rh). In particular, palladium gauzes containing amounts of platinum and rhodium may be used. Such gauzes may comprise, for example >92% wt palladium, 2-4% wt rhodium and the remainder platinum, or alternatively comprise 82-83% wt palladium, 2.5-3.5% wt rhodium and the remainder platinum. Ceramic fibres comprising an inert refractory material, such as alumina, zirconia or the like, may also be woven or knitted into catchment gauzes in addition to the palladium-based materials.
Where catalyst and catchment gauzes are combined it is desirable that they are arranged in the tube wall so that the gases contact first with the catalyst gauzes and then catchment gauzes.
The number of gauzes employed depends on the pressure at which the process is operated. For example in a plant operating at low pressure, e.g. up to about 5 bar abs., typically <10, often 3 to 6 gauzes may be employed, while at higher pressures, e.g. up to 20 bar abs., a greater number of gauzes, typically >20, often 35-45, may be employed. If adjacent woven gauzes are present, to facilitate replacement, they are preferably arranged so that their warps or wefts are at an angle of 45° to each other. Angular displacement, suitably at 90°, may also be used between adjacent woven gauzes to reduce opportunities for gas channelling.
In order to increase the strength of the assembly, the tube may further comprises a steel mesh. By the term "steel" we mean suitable high-temperature stable alloys, including non-Fe-based alloys such as Ni-based materials.
The cross section of the tube may be circular, oval, or polygonal, e.g. having between 3 and 50 sides. Tubular arrangements have the advantage over conventional circular-cut gauzes in that that the gauze may be formed into a tube from the square or rectangular form in which it was woven or knitted, thereby reducing waste during fabrication.
Cylindrical tubes are preferred. Where the precious metal gauze tube is cylindrical, the closed end member may be circular with a diameter at least that of the tube, and the open end member may be ring shaped with a central hole of diameter at most equal to that of the tube. The end members are suitably fabricated from steel sheet.
The suspending means may be attached to one or both end members. Preferably the suspending means are provided by extending the end member forming the open end of the assembly. When the assembly is placed in a reactor, the end members may also be inclined to direct the flow of gases through the gauze in the desired manner. Additionally, baffles may also be provided on the assembly to direct the flow of gases radially through the gauze. For example a conical baffle may be placed on the closed end member.
The flow of gases through the assembly may be radially inwards, i.e. from the periphery of the unit towards its centre, or may be radially outwards, i.e. from the central region outwards to wards the periphery. For simplicity of design, outward radial flow is preferred. In this case it may be desirable to include a baffle that acts as a heat shield and prevents the hot gases exiting the assembly from contacting directly with the inside wall of the ammonia oxidation vessel.
The flow through the vessel may be upflow or downflow.
Whereas the precious metal gauze assembly may be placed in a reaction vessel as a standalone unit, it is possible that the assembly may be used in combination with a conventional circular precious metal ammonia oxidation catalyst. Accordingly, the invention further provides a catalyst combination comprising a circular precious metal ammonia oxidation catalyst gauze on a supporting framework and a tubular precious metal catalyst gauze in the assembly of the present invention.
One or more catchment gauzes may also be provided under the circular precious metal catalyst gauzes but this is less preferred where the tubular gauze assembly comprises catchment gauzes.
The circular precious metal catalyst and catchment gauzes may be the same or different from the tubular precious metal catalyst and catchment gauzes disposed in the precious metal gauze assembly.
The supporting framework for the circular gauzes may be any currently in use and includes simple girder support arrangements that extend across the ammonia oxidation vessel and so- called "baskets" in which the circular precious metal gauzes are supported on the base of a cylindrical unit suspended within the ammonia oxidation vessel.
The tubular precious metal gauze assembly may be separate from the supporting framework for the circular precious metal gauzes, but in a preferred embodiment, the tubular precious metal gauze assembly is suspended from the circular precious metal catalyst-supporting
framework using the suspending means. In a particularly preferred arrangement, the tubular precious metal gauze assembly is suspended from a precious metal catalyst basket. The precious metal gauze assembly according to the present invention may be installed in any ammonia oxidation vessel having a suitable space to accommodate it. Alternatively, the vessel may be adapted to make a suitable space available. Ammonia oxidation vessels vary in size but are typically domed cylindrical vessels with internal diameters in the range 0.5-6 metres. The precious metal gauze assembly may be fabricated to fit within these reactors. For example, in a 1.5 m diameter vessel, the wall thickness of the tube may be 180 mm by 700-750 mm in height.
The precious metal gauze assembly may be placed below the circular precious metal gauzes so that the gases enter the ammonia oxidation vessel through an inlet in the top, then pass vertically (i.e. axially) downwards through the precious metal catalyst layer, enter the open end of the precious metal gauze assembly then pass radially through the precious metal gauze walls of the tube and then out of the base of the unit and exit the ammonia oxidation vessel via an outlet in the base. The arrangement may be reversed in an upflow vessel.
In cases where a combination of circular precious metal gauze and tubular precious metal catalyst is used, the invention further provides a method of retrofitting an ammonia oxidation vessel comprising suspending a precious metal gauze assembly beneath the circular precious metal catalyst. This is desirably accomplished by fixing a precious metal gauze assembly to the existing precious metal catalyst gauze support frame.
The invention further provides an ammonia oxidation process comprising the step of passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a tubular precious metal catalyst gauze catalyst disposed in the precious metal gauze assembly.
In one embodiment, the process comprises passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a circular precious metal catalyst gauze on a supporting framework and a tubular precious metal gauze catalyst disposed in the precious metal gauze assembly.
In the oxidation of ammonia to nitric oxide for the manufacture of nitric acid, the oxidation process may be operated at temperatures of 750-10000C, particularly 850-9500C, pressures of 1 (low pressure) to 15 (high pressure) bar abs., with ammonia in air concentrations of 7-13%, often about 10%, by volume. In the oxidation of ammonia with air in the presence of methane for the manufacture of hydrogen cyanide, the Andrussow Process, the operating conditions are similar. The present invention is particularly suited to processes and ammonia oxidation
reactors operated at pressures in the range 6-15 bar abs, particularly 7-15 bar g (so-called high pressure plants) because the tubular precious metal gauze assembly may readily be placed in the vessel without having to move or adjust heat recovery means commonly found just below the gauzes n medium pressure and atmospheric plants.
Hence for a low-pressure ammonia oxidation process, the catalyst assembly of the present invention may comprise 2-10 platinum oxidation gauzes and 2-5 palladium catchment gauzes formed into a tube, optionally with one or more steel meshes to act as a strengthening material. Alternatively a catalyst combination may be used comprising 1 or 2 circular precious metal ammonia oxidation catalyst gauzes followed by one or more gauzes of palladium catchment in a conventional arrangement, followed by a radial flow arrangement of tubular precious metal ammonia oxidation catalyst and/or further catchment gauzes. Alternatively the catalyst assembly may comprise between 2 and 10 circular platinum catalyst gauzes without catchment and the precious metal gauze assembly used only for catchment gauzes. Likewise in a high- pressure plant, there may be less than 15, e.g. 10 precious metal ammonia oxidation catalyst gauzes followed by the tubular catchment gauzes.
The invention is further illustrated by reference to the drawings in which:
Figure 1 is a cut-away side elevation of a precious metal gauze assembly according to a first embodiment with the end members arranged to provide outwards radial flow,
Figure 2 is a cut-away side elevation of a precious metal gauze assembly according to a second embodiment with the end members arranged to provide inwards radial flow, Figure 3 is a cut-away side elevation of an ammonia oxidation vessel containing a precious metal gauze assembly arranged to provide outwards radial flow, and Figure 4 is a cut-away side elevation of an ammonia oxidation vessel containing a catalyst combination comprising a precious metal gauze supported in a basket and precious metal gauze assembly suspended from said basket with the end members arranged to provide outwards radial flow.
In Figure 1 the precious metal gauze assembly comprises a vertical tube 10 formed from one or more precious metal gauzes, mounted on a circular steel sheet 12 that extends horizontally across the width of the tube 10, thereby forming a closed end. On the upper surface of sheet 12 and within the tube 10 is placed a conical baffle 14 that acts to direct gas radially through the gauzes. A ring-shaped steel end member 16 having a central hole corresponding to the internal diameter of the tube 10 is mounted on the other end of the gauzes, thereby forming an open end. The end member 16 is angled upwards from the tube at about 45 degrees. Suspending arm 18 is formed by vertically extending the edge of the ring member 16. The suspending arm 18 has a flange 20 at its extremity to permit installation of the assembly into a reactor.
In use, gases enter the assembly via the central hole in the ring-shaped end member 16, pass through meshes 10, and then out of the assembly.
In Figure 2, the precious metal gauze assembly comprises a vertical tube 30 mounted on a ring-shaped steel end member 32, having a central hole corresponding to the internal diameter of the tube, thereby forming an open end. At the other end of the tube 30, the assembly has a circular steel sheet end member 34 mounted horizontally on the tube and extending across its width thereby providing a closed end. On the upper surface of sheet 34 and extending across its width is a conical baffle 36. Suspending arm 36 is formed by extending the sides of the ring end member 32 horizontally then vertically from the tube to above the end member 34.
Providing the suspending means in this manner provides a peripheral annular void 38 through which gases may flow to the precious metal gauzes. The suspending arm 36 has a flange 40 at its extremity to permit installation of the assembly into a reactor.
In use, gases enter the assembly via the annular void 38, pass through the walls of tube 30, and then out of the assembly via the central hole in ring end member 32.
In Figure 3, a cylindrical ammonia oxidation vessel comprises a domed upper portion 50 with inlet 52 and a domed lower portion 54 with outlet 56. A flanged joint 58 joins the upper and lower portions. Suspended from this joint 58 within the vessel is a catalyst containment unit as depicted in Figure 1 in which the walls of tube 10 are fabricated from multiple layers of platinum ammonia oxidation gauze with one or more layers of palladium catchment gauze on the outer (vessel wall-facing) surface.
In use, a mixture of ammonia and air, optionally containing methane, is passed at elevated temperature and pressure through the inlet 52, passes downwards and is deflected by member 16 to pass through the open end of the precious metal gauze assembly. The gases then pass radially, with the assistance of baffle 20, through the catalyst and catchment gauzes where the ammonia oxidation reaction takes place. The reacted gases then exit the unit and are deflected downwards to the lower portion 54 of the vessel and then out of the vessel via outlet 56.
In Figure 4, a cylindrical ammonia oxidation vessel comprises a domed upper portion 60 with inlet 62 and a domed lower portion 64 with outlet 66. A flanged joint 68 joins the upper and lower portions. Suspended from this joint 68 within the vessel is a precious metal gauze- support 70 in the form of a steel-frame basket containing a circular precious metal gauze pack 72 made up of a plurality of platinum/rhodium ammonia oxidation gauzes and optionally one or more palladium catchment gauzes. Suspended from basket 70 is a precious metal gauze assembly as depicted in Figure 1 in which the tube is made up of a plurality of palladium
catchment gauzes and the flange 20 on the suspending means 18 is attached to limbs 74 extending from the underside of basket 70.
In use, a mixture of ammonia and air, optionally containing methane, is passed at elevated temperature and pressure through the inlet 62 and distributed over the surface of the catalyst gauze pack 72 by means of distribution means (not shown). The gases pass downwards (axially) through the gauze pack where the ammonia oxidation reactions take place. The hot gas mixture then passes downwards and is deflected by member 16 to pass through the open end of the precious metal gauze assembly. The gases then pass radially, with the assistance of baffle 20, through the catchment gauzes where volatilised platinum is captured. The reacted gases then exit the assembly and are deflected downwards to the lower portion 64 of the vessel and then out of the vessel via outlet 66.
Claims
1. A precious metal gauze assembly, suitable for use in an ammonia oxidation vessel, comprising a precious metal gauze in the form of a tube mounted between process fluid-impermeable end members, wherein one end member provides a closed end to the tube and the other end member extends radially from the tube thereby providing an open end through which gases may enter or exit the unit, and suspending means attached to one or both end members by which the unit may be secured within a reactor.
2. A precious metal gauze assembly according to claim 1 wherein the precious metal gauze comprises one or more platinum catalyst gauzes and/or one or more palladium catchment gauzes.
3. A precious metal gauze assembly according to claim 1 or claim 2 wherein the tube further comprises a steel mesh.
4. A precious metal gauze assembly according to any one of claims 1 to 3 wherein the cross section of the tube is circular, oval, or polygonal.
5. A precious metal gauze assembly according to any one of claims 1 to 4 wherein the tube is cylindrical, the closed end member is circular with a diameter at least that of the tube, and the open end member is ring shaped with a central hole of diameter at most equal to that of the tube.
6. A precious metal gauze assembly according to any one of claims 1 to 5 wherein the suspending means are provided by extending the end member forming the open end of the unit.
7. A precious metal gauze assembly according to any one of claims 1 to 6 wherein baffles are provided on the unit to direct the flow of gases radially through the assembly.
8. A catalyst combination comprising a circular precious metal ammonia oxidation catalyst gauze on a supporting framework and a precious metal catalyst disposed in the precious metal gauze assembly according to any one of claims 1 to 7.
9. A catalyst combination according to claim 8 wherein a palladium catchment gauze is provided underneath the circular precious metal catalyst.
10. A catalyst combination according to claim 8 or claim 9 wherein the supporting framework for the circular gauzes comprises a girder support arrangement or is a basket in which the precious metal gauzes are supported on the base of a cylindrical support structure.
11. A catalyst combination according to any one of claims 8 to 10 wherein the precious metal gauze assembly is separate from the supporting framework for the circular precious metal gauzes, or is fixed to the supporting framework for the circular precious metal gauzes.
12. An ammonia oxidation process comprising the step of passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a tubular precious metal catalyst disposed in the precious metal gauze assembly according to any one of claims 1 to 8.
13. An ammonia oxidation process according to claim 12 wherein the gas mixture is passed through a catalyst combination according to any one of claims 9 to 11.
14. An ammonia oxidation process according to claim 12 or claim 13 comprising passing a gas mixture comprising ammonia, an oxygen containing gas such as air and optionally a methane containing gas through a circular precious metal catalyst gauze on a supporting framework and then through a tubular precious metal catalyst disposed in the precious metal gauze assembly.
15. An ammonia oxidation process according to any one of claims 12 to 14 operated at temperatures of 750-10000C, pressures of 1 to 15 bar abs., with ammonia in air concentrations of 7-13% by volume.
16. A process according to any one of claims 12 to 15 operated at pressures in the range 6-15 bar abs.
17. A method of retrofitting an ammonia oxidation vessel comprising suspending a precious metal gauze assembly according to any one of claims 1 to 8 beneath an existing precious metal catalyst gauze support frame.
18. A method according to claim 17 comprising fixing a precious metal gauze assembly according to any one of claims 1 to 8 to the existing precious metal catalyst gauze support frame.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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GB0819096.9 | 2008-10-20 | ||
GBGB0819096.9A GB0819096D0 (en) | 2008-10-20 | 2008-10-20 | Pressure metal gauze assembly |
Publications (1)
Publication Number | Publication Date |
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WO2010046676A1 true WO2010046676A1 (en) | 2010-04-29 |
Family
ID=40097622
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/GB2009/051206 WO2010046676A1 (en) | 2008-10-20 | 2009-09-17 | Precious metal gauze assembly |
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WO (1) | WO2010046676A1 (en) |
Cited By (4)
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EP3056267A1 (en) * | 2015-02-12 | 2016-08-17 | Umicore AG & Co. KG | Catalyst gauze and installation for the catalytic oxidation of ammunia |
US9663366B2 (en) | 2012-03-05 | 2017-05-30 | Basf Se | Ammonia oxidation reactor with internal filter element |
WO2020234584A1 (en) * | 2019-05-22 | 2020-11-26 | Johnson Matthey Public Limited Company | Catalyst gauze |
RU2776371C1 (en) * | 2019-05-22 | 2022-07-19 | Джонсон Мэттей Паблик Лимитед Компани | Catalyst grid |
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9663366B2 (en) | 2012-03-05 | 2017-05-30 | Basf Se | Ammonia oxidation reactor with internal filter element |
EP3056267A1 (en) * | 2015-02-12 | 2016-08-17 | Umicore AG & Co. KG | Catalyst gauze and installation for the catalytic oxidation of ammunia |
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RU2678681C1 (en) * | 2015-02-12 | 2019-01-30 | ЮМИКОР АГ энд КО.КГ | Catalyst grid and installation for catalytic oxidation of ammonia |
US10258966B2 (en) | 2015-02-12 | 2019-04-16 | Umicore Ag & Co. Kg | Catalyst gauze and installation for the catalytic oxidation of ammonia |
WO2020234584A1 (en) * | 2019-05-22 | 2020-11-26 | Johnson Matthey Public Limited Company | Catalyst gauze |
RU2776371C1 (en) * | 2019-05-22 | 2022-07-19 | Джонсон Мэттей Паблик Лимитед Компани | Catalyst grid |
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