Classifications

• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/8671—Removing components of defined structure not provided for in B01D53/8603 - B01D53/8668
  • B01D53/8675—Ozone
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/88—Handling or mounting catalysts
  • B01D53/885—Devices in general for catalytic purification of waste gases
• • 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
  • B01J15/00—Chemical processes in general for reacting gaseous media with non-particulate solids, e.g. sheet material; Apparatus specially adapted therefor
  • B01J15/005—Chemical processes in general for reacting gaseous media with non-particulate solids, e.g. sheet material; Apparatus specially adapted therefor in the presence of catalytically active bodies, e.g. porous plates
• • 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
  • B01J23/48—Silver or gold
  • B01J23/50—Silver
• • 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
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
  • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/8953—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with zinc, cadmium or mercury
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
  • B64D13/00—Arrangements or adaptations of air-treatment apparatus for aircraft crew or passengers, or freight space, or structural parts of the aircraft
  • B64D13/06—Arrangements or adaptations of air-treatment apparatus for aircraft crew or passengers, or freight space, or structural parts of the aircraft the air being conditioned
  • B64D2013/0603—Environmental Control Systems
  • B64D2013/0685—Environmental Control Systems with ozone control

Definitions

• the present invention relates generally to catalytic reactors, and more particularly, to a catalytic reactor for the decomposition of ozone in air.
• the application of the catalytic reactor of the present invention includes, but is not limited to, the decomposition of ozone present in the conditioned air supplied to aircraft cabins.
• Aircraft environmental control systems supply pressurized and conditioned air to the aircraft cabin.
• the temperature, pressure and relative humidity must be controlled to provide for the comfort of the flight crew and passengers within the aircraft.
• Modern commercial jet aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more above sea level where the ozone content of the air is relatively high Accordingly, dunng operation at high altitudes the air supplied to the aircraft cabin from the environmental control system may contain ozone at a level of 1 - 3 ppmv
• the presence of ozone in the air within the aircraft cabin can cause lung and eye irritation, headaches, fatigue and/or breathing discomfort
• present Federal Aviation Agency (FAA) regulations limit ozone concentrations on commercial flights to 0 1 ppmv dunng a three hour time pe ⁇ od and 0 25 ppmv maximum at any time.
• FAA Federal Aviation Agency
• catalytic converters to reduce or eliminate undesirable ozone in the air supplied to aircraft cabins, in situations where relatively high ozone levels are expected, is known in the art
• An example of a commonly known type of catalytic converter is illustrated in U S Patent 4,405,507 which discloses a ceramic (cordie ⁇ te) monolithic support structure having a high surface area washcoat applied to the monolithic support, with the washcoat being used to carry the catalyst (in this case a platinum group metal and a non-precious Group VLTI metal oxide or aluminate)
• the washcoat is subject to att ⁇ tion when exposed to continued vibration and thermal cycling, such as that which may be expenenced when a converter is used in an aircraft application
• the washcoat and the catalyst carried by the washcoat may be washed off of the ceramic monolithic support structure during routine maintenance cleaning
• catalytic reactors of this type typically include
• Patent Applications 08/271,922 and 08/494,656 each disclose improved catalytic ozone converters of compact size and lightweight construction.
• Each of the co-pending applications discloses an aluminum or aluminum alloy support structure which comprises one or more plate-fin elements disposed within a converter housing.
• Each of the plate-fin elements includes a plurality of fins ananged in an axial succession of off-set fin rows between the inlet and outlet ends of the housing.
• the configuration of the plate-fin elements results in a relatively high mass transfer between the ozone-containing air and the ozone carried by the plate-fin elements for purposes of ozone decomposition
• the plate-fin elements have an integral anodized surface layer at least two microns thick, with the cataiyst disposed on and within the anodized surface layer.
• one or more Group VIII noble metals and optionally base metals from Groups VII, Ilia, and VTIa are disposed on and within the anodized surface layer of the plate-fin elements.
• the anodizing steps required in each disclosure are relatively expensive
• the catalysts which are disposed on and in the surface layer may be at least pamallv removed dunng routine maintenance cleaning
• the catalytic reactor compnses a core structure constructed from a catalytically-active metal alloy
• the core support structure has an inlet end effective for receiving a flow of ozone-containing air and an outlet end effective for discharging the ozone-containing air therefrom
• the catalytically-active metal alloy is effective for decomposing at least a portion of the ozone present m the ozone-containing air as the ozone-containing air flows between the inlet and outlet ends of the core structure
• the catalytically-active metal alloy compnses a silver- containing metal alloy, and may have a composition including silver and copper
• the catalytically-active metal alloy may have a composition comp ⁇ sing, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel
• the catalytically-active metal alloy may be
• the core support structure is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and outlet ends of the core structure so that the flow of the ozone-containing air is substantially turbulent between the inlet and outlet ends.
• the core structure may comp ⁇ se at least one plate-fin element, with each of the plate-fin elements having a plurality of fins which are ananged in an axial succession of rows of the fins between the inlet and the outlet ends of the core structure
• Each of the rows of fins defines a plurality of flow channels, and the fins of each of the rows are laterally off-set relative to the fins of axially adjacent ones of the rows so as to define the plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet and the outlet ends of the core structure
• Each of the fins may have a generally rectangular cross- section
• an alternative to p ⁇ or catalytic reactors is accomplished by providing a method for decomposing ozone in air
• the method compnses the steps of constructing a core structure from a single, catalytically-active metal alloy, with the core structure having an inlet end and an outlet end.
• the method may further comp ⁇ se the step of thermally activating the catalytically-active metal alloy, with the activating step comp ⁇ sing the step of heating the catalytically-active metal alloy to a temperature ranging from about 300°F to about 420°F for a period of time rangmg from about 30 minutes to about 60 minutes
• the heating step comprises the step of calcining the alloy to the stated temperature for the stated period of time
• the method may also comp ⁇ se the step of configu ⁇ ng the core structure so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air between the inlet end and the outlet end of the core structure
• the catalytically-active metal alloy may be as desc ⁇ bed with respect to the first aspect of the invention
• a mam advantage of the apparatus and method of the present invention is the provision of a light, compact and cost efficient catalytic converter for the decomposition of ozone in air, with the reactor bemg substantially mass-transfer limited
• Fig 1 is a fragmentary isometnc view illustrating a po ⁇ ion of a core structure, comp ⁇ sing a plate-fin element, which may be incorporated in the catalytic converter of the present invention
• Fig 2 is an elevational view taken along line 2-2 in Fig 1
• Fig. 3 is an ozone destruction curve for the catalytically-active alloy of the present invention and illustrates the effects of thermally activating the alloy
• Fig. 4 is a se ⁇ es of graphs illustrating the effect of temperature on the surface composition of the catalytically-active metal alloy of the present invention
• Fig 5 is photo micro-graph of the surface of the catalytically-active metal alloy of the present invention in an as-received condition.
• Fig 6 ts a photo micro-graph of the surface of the catalytically-active metal alloy of the present invention after thermal activation
• Fig. 7 is an ozone destruction graph illustrating the ability of the catalytically- active metal alloy of the present invention to recover after temporary exposure to a sulfur dioxide contaminated, ozone-contatmng feed air.
• Fig. 1 is a fragmentary isometric view illustrating a portion of a core structure 10 of a catalytic reactor for the decomposition of ozone in air. according to a prefened embodiment of the present invention
• the core structure 10 includes at least one plate-fin element 12, with a portion of one of the plate-fin elements 12 being illustrated in Figs. 1 and 2.
• the core structure 10 comprises a plurality of the plate-fin elements 12 mounted within a generally cylindrical housing (not shown), with the plate-fin elements ananged in a tightly packed cylindrical configuration, as a plurality of generally concentric annular rings
• the center of the cylindrical space defined by the housing may be occupied by a small diameter support tube containing a short plate-fin element strip.
• the core structure 12 includes an inlet end 14 which is effective for receiving a flow of ozone-containing air, indicated by flow anows 16, and an outlet end 18 effective for discharging the ozone-containing air 16 from the core structure 10
• the catalytic reactor of the present invention provides a relatively lightweight and compact device for reducing the ozone content within the ozone-containing air 16, which may be supplied to an environmental control system for aircraft cabin pressurization and/or conditioning. When used in such an aircraft application, the catalytic reactor of the present invention may be mounted inside a conduit in se ⁇ es flow relationship with the aircraft environmental control system.
• the ozone-containing air 16 may be supplied to the catalytic reactor from a compressor stage of a gas turbine engine of the aircraft, or alternatively may be provided from other sources such as ram air and/or a combination of engine compressor bleed and ram air In typical aircraft applications, the temperature of the ozone-containing air 16 may range from about 300°F ( 149°C) to about 420°F (216°C).
• each of the plate-fin elements 12 compnses a plurality of fins 20 which are ananged in an axial succession of rows 22 of the fins 20 between the inlet end 14 and the outlet end 18 of the core structure 10
• Three of the rows 22 of fins 20 are illustrated in Fig. 1 and designated as 22 A, 22B, and 22C Rows 22 A and 22B are further illustrated in the elevation view shown in Fig.
• Each of the rows 22 includes a plurality of the fins 20 and defines a plurality of flow channels 24
• the fins 20 of each of the rows 22 are laterally off-set by a distance x (Fig. 2) relative to the fins 20 of axially adjacent ones of the rows 22
• the fins 20 of row 22B are laterally off-set with respect to the fins 20 of rows 22A and 22C Consequently, each plate-fin element 12 of the core structure 10 is configured so as to define a plurality of tortuous flowpaths for the flow of the ozone-containing air 16 between the inlet end 14 and the outlet end 18 of core structure 10
• This results m a substantially turbulent flow of the ozone-containmg air 16 between the inlet end 14 and the outlet end 18 of core structure 10 which in turn results in a relatively high mass transfer between the ozone-contammg air 16 and the subsequently described catalyst, from which each plate-fin element 12 is constructed
• Fig. 2 Each of the rows 22 includes a pluralit
• each of the fins 20 has a generally rectangular cross-section in a prefened embodiment, as seen in an axial view, and includes a height H, a thickness t, a pair of flats F, and an axial depth
• Each fin 48 approximates a full sine-wave shape as illustrated in brackets in Fig.
• each fin row 22 has a lateral fin density which may also be va ⁇ ed with application
• each fin 20 may alternatively have other geomet ⁇ c shapes such as a generally t ⁇ angular cross-section, or a generally trapezoidal cross-section
• Each of the plate-fin elements 12 is constructed, or fabricated from a catalytically-active metal alloy which comprises a central feature of the present invention
• the catalytically-active metal alloy may be shaped by conventional means such as stamping so as to form the plurality of fins 20
• the catalytically-active metal alloy compnses a silver-containing metal alloy and, in a prefened embodiment, has a composition including silver and copper as p ⁇ nciple constituents
• An example of an alloy which the inventors have determined to be acceptable for use in the present invention has a composition comprising, on a weight basis, about 55% silver, about 39% copper, about 5% zmc and about 1% nickel.
• composition conesponds to the following atomic ratios- Ag.Cu.Zn:Ni -*30:36 4 5 1
• the catalytically-active metal alloy of the present invention must comp ⁇ se a silver-containing metal alloy
• the alloy is extremely active for ozone decomposition, providing mass-transfer- limited performance at temperatures as low as 212°F ( 100°C) Accordingly, for low temperature applications, i e temperatures in which the ozone-contaming air 16 is less than about 300°F ( 149°C) the silver-containing metal alloy must be activated by calcining, or heating the alloy in au ⁇ to a temperature ranging from about 300°F (149°C) to about 420°F (216°C) for a penod of time ranging from about 30 minutes to about 60 minutes For higher temperature applications, i e. those in which the ozone-containing air 16 is at least 300°F (149°C) the thermal activation step may be omitted
• thermodynamic analysis of the surface composition of the plate-fin element 12 as a function of temperature was performed Again, the composition of the silver- containing metal alloy conesponded to atomic ratios of: 30 36 4 5 1
• the results of the thermodynamic analysis illustrated graphically in Fig. 4, show that the surface composition of the silver-containing metal alloy (which is exposed to air) varies with temperature At ambient temperature, the equilibrium surface composition is a mixture of CuO, Ag 2 O, ZnO and NiO As shown in Fig.
• a laboratory-scale reactor was assembled to include a section of a plate-fin element having 2 rows of fins, with each row of fins including 8 fins.
• Measured fin dimensions were approximately as follows fin height (H in Fig 2) was 181 in. (4 60 mm), fin thickness was 0.0036 in ( 091 mm), and fin axial depth was 177 in. (4 50 mm)
• the lateral fin density in each row was 16 fins/in
• the plate- fin section was constructed from a silver-containing metal alloy having a composition comprising about 55% Ag, about 39% Cu, about 5% Zn and about 1% Ni.
• the section of the plate-fin element was mounted in the laboratory-scale reactor and air containing 2 3 ppm by volume ozone was flowed through the plate-fin element, so as to contact multiple surfaces of the silver-containing metal alloy, at 1 x 10 ⁇ GHSV at STP and at the following five temperatures.
• Table 1 provides a reference value for compa ⁇ son with the actual conversion as measured expe ⁇ mentally
• the calculation assumes that the catalyst is able to convert any ozone which reaches it, that is, the chemical reaction is not limiting. The calculation then is based on the reaction rate which should be observed if mass transfer of the reactants and products to and from the catalyst is limiting (L Hegedus,
• the "as-received" surface of the silver-containing metal alloy had a "white- copper” sheen.
• the "as-received” metal alloy surface was relatively smooth in appearance with sub-micron size surface striations (possibly due to milling of the alloy during manufacture).
• the activated silver-containing metal alloy surface had a dull gray appearance which was observed immediately after thermal activation.
• the surface of the activated silver-containing metal alloy is roughened with particles which are about 1-10 microns in diameter.
• Further analysis of both the "as-received” and activated fin samples using EDX confirmed that the "particles" observed on the surface of the activated silver- containing metal alloy contained high concentrations of silver. In contrast, copper and oxygen were found in extremely low concentrations. This result supported the thermodynamic analysis discussed previously in conjunction with Fig. 4, verifying that silver metal is the active site for ozone decomposition.
• a laboratory reactor was assembled to a test section of a plate-fin element, having the same number of rows and fins, and made from the same alloy, as that described in Example 1. Durability testing was conducted to determine the ability of the silver-containing metal alloy to recover from a temporary poisoning with SO 2l as follows.
• a "clean" feed air containing 2.3 ppm by volume of ozone was flowed through the plate-fin element at 1 x IO 6 GHSV at STP and at the following temperatures: 212°F, 302°F, 392°F, 482°F (100°C, 150°C, 200°C and 250°C)
• 1 ppm by volume SO 2 was added to the ozone-containing air for a pe ⁇ od of 5 hours, after which the aforementioned "clean" feed was used for an additional 75 hours, at each temperature.
• the ozone conversion was measured after 1 hour. 5 hours.
• Catalyst poisoning by surface adso ⁇ tion of SO 2 can be reversible depending on the strength of the cataiyst-adsorbate bond.
• the rapid recovery in catalyst performance after SO 2 removal shown in Table 2 and Fig. 7 demonstrates that this poisoning was reversible over the temperature range tested Accordingly, the temporary performance attenuation observed was due to "masking" of the catalyst sites by SO 2
• the present reactor is cost reduced relative to prior reactors since it is not necessary to apply a washcoat to, or anodize, a metallic substrate. Additionally, since the alloy itself comprises the active catalyst, the catalyst will not be removed during routine maintenance cleaning.
• the use of the silver-containing metal alloy of the present invention in conjunction with the prefened embodiment inco ⁇ orating the plate-fin elements, provides relatively high mass transfer between the ozone and the silver catalyst, and accordingly permits the use of a compact, lightweight reactor While the foregoing description has set forth the prefened embodiments of the invention in particular detail, it must be understood that numerous modifications, substitutions and changes can be undertaken without departing from the true spirit and scope of the present invention as defined by the ensuing claims.
• the catalytic reactor of the present invention has been illustrated to include at least one plate-fin element in a prefened embodiment, other turbulent-producing structures may also be used, provided that the structure is made from the silver-containing alloy of the present invention.
• the use of a turbulent-producing structure is prefened, the silver-containing metal alloy of the present invention may be advantageously utilized for ozone decomposition in structures which experience laminar flow conditions. The invention is therefore not limited to specific prefened embodiments as described, but is only limited as defined by the following claims.

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• 1997
  • 1997-05-09 WO PCT/US1997/007841 patent/WO1997041948A1/en not_active Application Discontinuation
  • 1997-05-09 EP EP97924632A patent/EP0906147A1/de not_active Withdrawn
  • 1997-05-09 JP JP09540222A patent/JP2000510039A/ja active Pending

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