Patent Description:
Ozone is a well-known terrestrial air pollutant, and is also a naturally occurring component of the Earth's atmosphere. Ozone levels in the Earth's atmosphere are known to vary with altitude and seasonally, and aircraft with pressurized cabins that rely on compressed outside air for replenishment of cabin air can experience undesirably high ozone levels in the cabin or other pressurized areas. Ozone concentrations at typical flight cruising altitudes can be significantly higher than the <NUM> ppmv limit set by the FAA for aircraft cabin air. Accordingly, aircraft environmental conditioning systems (ECS) are commonly equipped with equipment for removing ozone from the air.

One technique to remove ozone is to catalytically decompose the ozone molecules to form oxygen molecules according to the reaction represented by the formula:.

Catalytic decomposition of ozone can be effective, but the effectiveness can decrease over time. In some cases, the effectiveness of the catalyst can decrease to a level where the catalyst must be replaced. Various technologies have been proposed for catalytic ozone decomposition, such as optimizing the formulation of the catalyst composition; however, there continues to be a demand for new approaches for ozone removal. <CIT> discloses air treatment systems including an environmental control system, a mixer, an air distribution duct system, and one of more catalysts for treating the air in the aircraft cabin environment. <CIT> discloses an apparatus and method for abatement of ozone from air, particularly from aircraft cabin air.

According to the invention, a method is provided for removing ozone from a gas (for example in an aircraft cabin system). The method comprises introducing the gas from a compressor that receives and compresses outside air to an inlet of a first air treatment module, where said module comprises the inlet, an adsorbent comprising a metal organic framework, and an outlet, to form a treated gas. The treated gas is introduced to a second air treatment module, said module comprising an inlet, a noble metal catalyst and an outlet and catalytically decomposing ozone in the treated gas at a temperature of <NUM>-<NUM> to form an ozone-depleted treated gas. Heat is applied to the adsorbent from a heat source to regenerate the adsorbent.

According to the invention, an aircraft cabin air system comprises a compressor that receives and compresses outside air, a first air treatment module and a second air treatment module. The first air treatment module comprises an inlet in fluid communication with the compressor, an adsorbent (e.g. an absorbent as described herein) comprising a metal organic framework, and an outlet. The second air treatment module comprises an inlet in fluid communication with the first air treatment module outlet, a noble metal catalyst and an outlet that discharges ozone-depleted air wherein the noble metal catalyst is disposed in an air flow path between the inlet and outlet at a temperature of <NUM>-<NUM>, and a thermal connection between the adsorbent and a heat source for regenerating the adsorbent.

The thermal connection may comprise a thermal connection to waste heat from an on-board heat-generating component.

Subject matter of this disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification.

With reference now to the Figures, <FIG> schematically depicts an example embodiment of an ozone removal system <NUM>. As shown in <FIG>, a gas <NUM> to be treated is introduced to an adsorbent module <NUM>. The adsorbent module <NUM> includes an adsorbent that comprises a metal organic framework. The absorbent may further comprise a transition metal oxide. Transition metals for oxide adsorbents include manganese, copper, nickel, cobalt, magnesium, aluminum, titanium, chromium or molybdenum or combinations comprising any of the foregoing. Examples of transition metal oxide adsorbents include manganese oxide (e.g., MnO<NUM>), copper oxide (e.g., CuO), nickel oxide (e.g., NiO), cobalt oxide (e.g., Co<NUM>O<NUM>), magnesium oxide (e.g., MgO), and TiO<NUM> or mixed oxides comprising any of the foregoing (e.g., mixed copper-manganese oxide, mixed manganese-cerium oxide, mixed magnesium-aluminum oxide, mixed MnO<NUM>-CeO<NUM>, mixed MnO<NUM>-ZrO<NUM>). Many transition metal oxides having a physical configuration (e.g., surface area and porosity parameters) suitable for adsorption of molecular species such as catalyst poisons are commercially available. Transition metal oxides suitable for adsorption can be prepared, for example, by sol-gel techniques known to produce metal oxides having mesoporous (or micro or macroporous) structures that promote adsorptive functionality. In some embodiments, the transition metal oxide adsorbent can also provide catalytic activity for catalytic removal of catalyst poisons, or for catalytic decomposition of ozone itself. Examples of transition metal oxides having catalytic activity include MnO<NUM>, Co<NUM>O<NUM>, CuO, NiO and MgO. The transition metal oxide(s) can be supported (e.g., dispersed on a high surface area support such as γ-Al<NUM>O<NUM>, TiO<NUM>, SiO<NUM>, ceria, zirconia, zeolites or activated carbon). The adsorbent module <NUM> can further comprise a substrate structure such as a zeolite monolith, honeycomb, fibers or corrugated support structure), onto which the adsorbent can be applied (e.g., as a wash coat).

The adsorbent comprises a metal organic framework (MOF). Metal organic framework materials are well-known in the art, and comprise metal ions or clusters of metal ions coordinated to organic ligands to form one-, two- or three-dimensional structures. A metal-organic framework can be characterized as a coordination network with organic ligands containing voids. The coordination network can be characterized as a coordination compound extending, through repeating coordination entities, in one dimension, but with cross-links between two or more individual chains, loops, or spiro-links, or a coordination compound extending through repeating coordination entities in two or three dimensions. Coordination compounds can include coordination polymers with repeating coordination entities extending in one, two, or three dimensions. Examples of organic ligands include but are not limited to bidentate carboxylates (e.g., oxalic acid, succinic acid, phthalic acid isomers, etc.), tridentate carboxylates (e.g., citric acid, trimesic acid), azoles (e.g., <NUM>,<NUM>,<NUM>-triazole), as well as other known organic ligands. Metal organic frameworks are further described by <NPL>.

A wide variety of metals can be included in a metal organic framework. In some embodiments, the metal organic framework comprises a transition metal or a transition metal oxide, including but not limited to any of the transition metals described above with respect to transition metal oxide adsorbents. In some embodiments, the metal used in the metal organic framework has catalytic activity for removal of catalyst poisons or for decomposition of ozone (e.g., Mn, Cu). In some embodiments, the MOF can include specific basic sites or metal oxide sites known to react with SO<NUM>. Examples of specific metal organic framework materials include Zn<NUM>O<NUM>C<NUM>H<NUM>, CuO<NUM>C<NUM>H<NUM>, UiO-<NUM>-NH<NUM> ({Zr(bdc-NH<NUM>)<NUM>} with (bdc-NH<NUM>) = <NUM>-amino-<NUM>,<NUM>-benzenedicarboxylate)). MOF's can be synthesized by hydrothermal or solvothermal techniques, where crystals are slowly grown from a hot solution. Templating for the MOF structure can be provided by a secondary building unit (SBU) and the organic ligands. Alternate synthesis techniques are also available, such as chemical vapor deposition, in which metal oxide precursor layers are deposited followed by exposure of the precursor layers to sublimed ligand molecules to impart a phase transformation to the MOF crystal lattice. Other materials can also be included in the adsorbent material or adsorbent module, such as other (non-transition metal) adsorbents (e.g., activated carbon), which can be used as a support for the transition metal oxide, or can be incorporated as a stand-alone component or as part of a composite material along with the transition metal oxide.

Similar to the transition metal oxide adsorbents, MOF adsorbents can be disposed on a support such as a ceramic monolith or fibers. Both types of adsorbents can, in some embodiments, provide technical effects such as catalytic removal of ozone to supplement the functionality of the downstream noble metal catalyst. MOF adsorbents can also provide regeneration capability, and in some embodiments, the method includes regenerating the adsorbent by application of heat (e.g., temperatures of at least <NUM>) along with a purge gas flow through the adsorbent module <NUM> that bypasses the catalyst module <NUM>.

In some embodiments, the adsorbent material can have one or more physical parameters that promote adsorption of catalyst poisons, and optionally promote catalytic activity of the adsorbent material. In some embodiments, the adsorbent can have a BET surface area in a range having a lower endpoint of <NUM><NUM>/g, more specifically <NUM><NUM>/g, even more specifically <NUM><NUM>/g, and an upper even more specifically <NUM><NUM>/g, or an upper endpoint for MOF's of <NUM><NUM>/g, more specifically <NUM><NUM>/g, and even more specifically <NUM><NUM>/g, or an upper endpoint for transition metal oxides of <NUM><NUM>/g and more specifically <NUM><NUM>/g. Any of the above lower and upper range endpoints can be combined to disclose a variety of different ranges. In some embodiments, the adsorbent can have an average pore size in a range having a lower endpoint of <NUM> and an upper endpoint of <NUM>, and a pore volume of less than or equal to <NUM><NUM>/g.

With continued reference to <FIG>, a treated gas <NUM> exits the adsorbent module <NUM> and is directed to a catalyst module <NUM>. Catalyst module <NUM> catalytically decomposes ozone in the treated gas <NUM>, and discharges an ozone-depleted treated gas <NUM>.

Similarly, although <FIG> depicts fluid flow moving directly from the adsorbent module <NUM> to the catalyst module <NUM>, one or more fluid process devices or functionalities can be interposed between the adsorbent module <NUM> and the catalyst module <NUM>. The catalyst module <NUM> comprises a noble metal catalyst. As used herein, the term "noble metal" means a metal selected from ruthenium, rhodium, palladium, iridium, platinum, gold, or combinations comprising any of the foregoing. In some embodiments, the noble metal is selected from palladium or platinum and their alloys. The noble metal can be dispersed in an oxide support such as Al<NUM>O<NUM>, ZrO<NUM>, TiO<NUM> and SiO<NUM>, and the catalyst (noble metal and oxide support) can be disposed on a carbon or ceramic substrate such as a honeycomb, corrugated sheet, fiber or other monolith structure. Ceramics for substrates can include but are not limited to sillimanite, petalite, cordierite, mullite, Zircon, Zircon mullite, spodumene, alumina, alumina-titanate, etc. Non-noble metal materials such as nickel, manganese, cobalt, copper, etc. (or oxides thereof) can also be included in the catalyst module, for example to provide additional catalytic decomposition of ozone at moderate temperatures.

As mentioned above, a notable application for catalytic decomposition of ozone is treatment of cabin air for pressurized aircraft. An example embodiment of an aircraft cabin air ozone removal system is schematically depicted in <FIG>. As shown in <FIG>, aircraft cabin air system <NUM> receives outside ambient air <NUM> and directs it to a compressor <NUM>. The compressor <NUM> can be a compressor section of a turbo-compressor aircraft engine, or can be an electrically-powered compressor. The compressor <NUM> compresses the air to a pressure of at least <NUM> psia, and typically to a greater pressure, which is then reduced by an aircraft ECS. In some embodiments, a turbo-compressor aircraft engine can provide bleed flow at <NUM>-<NUM> psi, whereas an electrically-powered compressor on a bleedless or low-bleed aircraft architecture may provide compressed air at lower pressures (e.g., about <NUM> psi). The compressor <NUM> produces compressed air <NUM>, which is directed to an ECS pack <NUM>. As depicted in the example embodiment of <FIG>, the ECS pack <NUM> includes an integrated adsorbent module <NUM> and an integrated catalyst module <NUM>.

Claim 1:
A method of removing ozone from a gas comprising:
introducing the gas from a compressor that receives and compresses outside air to an inlet of a first air treatment module, said module comprising the inlet, an adsorbent comprising a metal organic framework, and an outlet, to form a treated gas;
introducing the treated gas to a second air treatment module, said module comprising an inlet, a noble metal catalyst, and an outlet and catalytically decomposing ozone in the treated gas at a temperature of <NUM>-<NUM> to form an ozone-depleted treated gas; and
applying heat to the adsorbent from a heat source to regenerate the adsorbent.