Methane oxidation system

Abstract

A system for oxidising methane in a gas stream comprises a catalyst article comprising a methane oxidation catalyst and an electrically conductive material. The catalyst has a light-off temperature for methane oxidation. The conductive material can be heated by supplying electrical energy to it, thereby also to heat the catalyst. The system includes a conduit to supply the gas stream to the catalyst article and a source of electricity that is electrically connected to the catalyst article to supply electrical energy to the conductive material. The system also includes a control system, configured to control the source of electricity to supply electrical energy to the conductive material to adjust a current catalyst temperature to a predetermined catalyst temperature at which contacting the catalyst with the gas stream at a feed temperature below the light-off temperature provides an operating temperature that is above the light-off temperature.

Description

[0001] METHANE OXIDATION SYSTEM

[0002] Field of the invention

[0003] This invention relates to catalytic methane oxidation, particularly in the context of emissions control. The invention provides a system for oxidising methane in a methane containing gas and a method of treating a methane containing gas to oxidise methane in the methane containing gas.

[0004] to the invention

[0005] Oxidation of methane (CH4) is instrumental in curbing methane emissions from a variety of sources, such as exhaust gases, industrial waste gases, and natural gas deposits, by converting environmentally harmful methane into less harmful products, most prominently carbon dioxide (CO2) and water (H2O) according to the following reaction:

[0006] CH4+ 2O2-> CO2 + 2H2O

[0007] The oxidation of methane in such applications is typically catalysed by platinum group metal catalysts, most prominently platinum (Pt), palladium (Pd), and rhodium (Rd) catalysts.

[0008] The activity of methane oxidation catalysts is temperature sensitive, in that such catalysts only oxidise methane efficiently above what is called a light-off temperature, which is a temperature, for a particular catalyst, above which methane oxidation occurs at an acceptable rate and to an acceptable extent, e.g. above 50%.

[0009] In certain circumstances, the temperatures of methane containing gases to be subjected to methane oxidation over a methane oxidation catalyst are below the light-off temperature of the catalyst, which creates challenges in treating such gases, specifically in initiating methane oxidation and / or in sustaining methane oxidation over the catalyst.

[0010] Challenges in sustaining methane oxidation occur, for example, when, in addition to having a temperature below the light-off temperature, methane containing gases to be treated have low methane concentrations which generates insufficient heat energy from an exothermic methaneoxidation reaction to maintain the operating temperature above the light-off temperature, even after assisted initiation of light-off.

[0011] The abovementioned challenges may arise in relation to both fresh catalysts and aged catalysts, e.g. sulphur aged catalysts or hydrothermal aged catalysts. Aged catalysts have significantly higher light-off temperatures than fresh catalysts (e.g. above 400°C, even up to 480°C, or more).

[0012] Sulphur aging, in particular, complicates the use of methane oxidation catalysts, due to the loss of catalytic activity that results from such aging. It has been reported that exhaust gas containing less than 1ppm SO2 can deactivate a Pd catalyst in less than a day. In fact, levels as low as 0.1 ppm have been shown to lead to almost complete loss of methane oxidation activity.

[0013] Efforts to address the abovementioned challenges that are associated with methane oxidation catalysts are ongoing.

[0014] For example, US 2022 / 0090528 A1 discloses a system for oxidising methane in a lean-burn engine exhaust gas that is at a temperature below the light-off temperature of the methane oxidation catalyst used for such oxidation. The system provides for a combustible gas to be added to the exhaust gas, which combustible gas is oxidised by the catalyst at the available temperature of the exhaust gas and thus raises the operating temperature to above the light-off temperature.

[0015] WO 2022 / 076335 A1 discloses a catalyst composition that comprises a catalytically active material and a ferrite-based magnetic material. The magnetic material can be inductively heated to above the relevant light-off temperature for methane oxidation by exposing the catalyst composition to an alternating magnetic field, thereby also to heat the catalytically active material.

[0016] In WO 2022 / 133287 A1, electric heating of an exhaust gas in an exhaust gas aftertreatment system upstream of a catalytic converter of the aftertreatment system, using one or more electric heaters, is optimised to achieve a required light-off temperature for subsequent catalytic conversion of undesired compounds comprised by the exhaust gas. Provision is specifically made for the conversion of NOx contained in the exhaust gas, using a selective catalytic reduction (SCR) system or a diesel oxidation catalyst (DOC).The present invention finds application in further addressing the abovementioned challenges that are associated with catalytic methane oxidation.

[0017] of the invention

[0018] According to the invention, there is provided a system for oxidising methane in a methane containing gas stream, comprising:

[0019] a catalyst article comprising a methane oxidation catalyst and an electrically conductive material, wherein the methane oxidation catalyst has a light-off temperature for methane oxidation and wherein the electrically conductive material can be electrically heated by supplying electrical energy to it, thereby also to heat the catalyst;

[0020] a conduit to supply a feed stream of methane containing gas to the catalyst article; a source of electricity that is electrically connected to the catalyst article to supply electrical energy to the electrically conductive material; and

[0021] a control system that is configured to control the source of electricity to supply electrical energy to the electrically conductive material to adjust a current catalyst temperature to a predetermined catalyst temperature at which contacting the catalyst with the methane containing gas at a feed temperature below the light-off temperature provides an operating temperature over the catalyst that is above the light-off temperature.

[0022] The operating temperature may be equal to the temperature of the methane oxidation catalyst once a methane oxidation reaction has reached an overall steady state reaction rate.

[0023] The light-off temperature (T50) of the methane oxidation catalyst may be a temperature above which at least 50% of the methane in the methane containing gas feed stream is oxidised in the presence of, e.g. over, the catalyst.

[0024] The predetermined catalyst temperature may be a temperature that is above the feed temperature of the methane containing gas. The predetermined catalyst temperature may be below the light-off temperature. Preferably, the predetermined catalyst temperature is at least at or above the light-off temperature. Even more preferably, the predetermined catalyst temperature is a temperature that is above the light-off temperature.

[0025] Adjusting the current catalyst temperature to the predetermined catalyst temperature may include, through the supply of electrical energy to the electrically conductive material,increasing the current catalyst temperature to the predetermined catalyst temperature or maintaining the current catalyst temperature at the predetermined catalyst temperature. By supplying electrical energy to the electrically conductive material, heat energy is generated which increases the temperature of the electrically conductive material. Heat energy is then transferred from the electrically conductive material to the catalyst, for example by way of conduction heat transfer, to adjust the catalyst temperature to the predetermined catalyst temperature or to maintain the current catalyst temperature at the predetermined catalyst temperature.

[0026] The supply of electrical energy to the electrically conductive material may therefore be sufficient to achieve such an increase in or maintenance of the current catalyst temperature.

[0027] The control system may be configured to perform the supply of electrical energy to the electrically conductive material, when:

[0028] the feed temperature is below the light-off temperature; and / or

[0029] the operating temperature is at or below the light-off temperature; and / or

[0030] the current catalyst temperature is below the predetermined catalyst temperature.

[0031] The control system may further be configured to discontinue the supply of electrical energy or not to perform the supply of electrical energy to the electrically conductive material, when at least one of:

[0032] the feed temperature;

[0033] the operating temperature; and

[0034] the current catalyst temperature,

[0035] is at or above the light-off temperature, provided that, if the feed temperature is below the light-off temperature, the operating temperature and / or the current catalyst temperature remains at or above a predetermined threshold value that is equal to or greater than the light-off temperature while the supply of electrical energy is discontinued.

[0036] In other words, while the feed temperature is below the light-off temperature, if the operating temperature and / or the current catalyst temperature does not remain at or above the predetermined threshold value, then the supply of electrical energy to the electrically conductive material would not be discontinued, or would commence, or would recommence to restore the predetermined catalyst temperature.This may, for example, be applicable in low methane concentration situations, in which the concentration of methane in the methane containing gas is too low to generate sufficient heat energy from an exothermic methane oxidation reaction to maintain the operating temperature and / or the current catalyst temperature at or above the light-off temperature.

[0037] The predetermined threshold value may typically be a value above the light-off temperature and below the predetermined catalyst temperature, provided that the predetermined catalyst temperature has a value at or above the light-off temperature.

[0038] It will be appreciated that, in effect, if the operating temperature and / or the current catalyst temperature reaches or drops below the predetermined threshold value, i.e. below light-off temperature, then a decrease in the operating temperature and / or the current catalyst temperature would have been observed, providing basis for a conclusion of decreased catalytic activity of the catalyst.

[0039] The control system may be configured to calculate or measure temperatures such as the catalyst temperature. The control system may include one or more temperature sensors to take temperature measurements. The control system may be configured to use the calculated or measured temperatures to control the source of electricity selectively to supply and discontinue the supply of electrical energy to the electrically conductive material.

[0040] The control system may be configured to determine the methane concentration in the feed stream and / or in an outlet of the system of the invention. The control system may be configured to control the source of electricity selectively to supply and discontinue the supply of electrical energy to the electrically conductive material based on the methane concentration in the feed stream and / or the outlet.

[0041] The control system may include a temperature sensor to measure the feed temperature.

[0042] The control system may be configured to measure or calculate the operating temperature. The control system may include a temperature sensor to measure the operating temperature.

[0043] The control system may be configured to measure the catalyst temperature. The control system may include a temperature sensor to measure the current catalyst temperature.The control system may include a sensor to measure the methane concentration in the feed and / or in the outlet.

[0044] In one embodiment of the invention, the catalyst article may comprise a substrate and at least one washcoat layer. Preferably, the catalyst article may comprise a layered configuration wherein the catalyst composite comprises a substrate and at least two washcoat layers. Preferably, a first washcoat layer, also referred to as the bottom layer, is deposited on the substrate, and a second washcoat layer, also referred to as the top or outer layer, is deposited, at least partially, on the first washcoat layer. Preferably, the top or outer layer substantially covers the bottom layer.

[0045] Preferably, the first washcoat layer and the second washcoat layer are discrete from each other.

[0046] In an alternative embodiment, the catalyst article may comprise a zoned configuration wherein the catalyst composite comprises a substrate and at least two washcoat layers. Preferably a first layer is provided upstream of a second layer in a zoned configuration, i.e. the second layer is deposited on the substrate downstream of the first layer. This permits the first layer to contact the exhaust gas before the second layer.

[0047] Preferably the substrate has an inlet end and an outlet end, optionally wherein the first layer extends from the inlet end along an axial length of the substrate and the second layer extends from the outlet end along an axial length of the substrate.

[0048] Preferably the first coating extends from 20 to 80%, preferably 40 to 60%, even more preferably about 50% of an axial length of the substrate and / or wherein the second coating extends from 20 to 80%, preferably 40 to 60%, even more preferably about 50% of an axial length of the substrate, and / or wherein the first coating and the second coating together substantially cover the substrate.

[0049] Preferably the first coating and the second zone overlap by at least 10% of an axial length of the substrate. Preferably the first coating and the second zone overlap by up to 25% of an axial length of the substrate.

[0050] Preferably, the first coating and the second coating are discrete from each other.The substrate of the layered or zoned catalyst composite may be any conventional methane oxidation catalyst substrate and may comprise a metal or ceramic honeycomb structure. An example of a conventional methane oxidation catalyst substrate is flow-through substrate, e.g. a monolithic substrate having a plurality of fine, parallel gas flow passages extending therethrough. The passages are defined by walls on which the washcoat layer / s are applied. The washcoat layers are arranged so that the gases flowing through the passages contact the catalytic material in the top washcoat layer, when present in a layered configuration, or the first washcoat layer, when present in a zoned configuration. Preferably the catalyst substrate is a ceramic substrate. The ceramic substrate may be made of any suitable refractory material, e.g. cordierite, silicon nitride, mullite, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicates, zircon, alumina, aluminosilicates and mixtures thereof.

[0051] The first washcoat layer which is deposited upon, i.e. coated upon and adhered to, the substrate may comprise the electrically conductive material. Preferably, the first washcoat layer is substantially free of the methane oxidation catalyst. The electrically conductive material may be one or a combination of any two or more of any suitable electrically conductive metal, an electrically conductive oxide, an electrically conductive boride, an electrically conductive silicide, an electrically conductive carbide and / or an electrically conductive borosilicate.

[0052] In one embodiment of the invention, the electrically conductive material comprises one or a combination of an electrically conductive silicon carbide, reduced electrically conductive titania (black titania), graphene, activated carbon, black carbon, and a carbon precursor such as biomass.

[0053] Preferably, the electrically conductive material is a material as described in Austrian patent no. AT 525295, the contents of which are herewith incorporated herein by reference.

[0054] The second washcoat layer may comprise the methane oxidation catalyst. When the catalyst article is in a layered configuration, the second washcoat layer is at least partially coated upon and adhered to the first washcoat layer. When the catalyst article is in a zoned configuration, the second washcoat layer extends from the outlet end of the substrate along an axial length thereof.

[0055] The methane oxidation catalyst may, in particular, comprise one or a combination of two or more platinum group metals (PGMs) deposited on a high surface area refractory metal oxide.Preferably the methane oxidation catalyst may include a PGM washcoat loading of at least 80 g / ft3, preferably at least 120 g / ft3, even more preferably at least 300 g / f3.

[0056] The PGM may be supported on a suitable catalyst support. The catalyst support may be a high surface area refractory metal oxide such as alumina or silica. The catalyst support may comprise a mixed oxide or a mixture of oxides or a molecular sieve comprising alumina, silica and / or zirconia. The term “mixed oxide” as used herein refers to a mixture of oxides in a single phase. For example, the mixed oxide material may be a silica-alumina mixed oxide or a zirconia-alumina mixed oxide. Alternatively, the support material may be an aluminosilicate molecular sieve (zeolite) comprising alumina, silica and / or zirconia, or clathrasil.

[0057] Typically, the methane oxidation catalyst is one or a combination of two or more of platinum, palladium, and rhodium.

[0058] Preferably, the methane oxidation catalyst is platinum and / or palladium, with a bimetallic platinum-palladium catalyst being most preferred. Preferably the methane oxidation catalyst comprises platinum at a loading of from 15 g / ft3to 35 g / ft3, preferably from 20 g / ft3to 27 g / ft3. Preferably the methane oxidation catalyst comprises palladium at a loading of from 50 g / ft3to 300 g / ft3, preferably from 100 g / ft3to 270 g / ft3. Preferably the methane oxidation catalyst comprises platinum and palladium at a ratio of platinum to palladium of from 1:5 to 1:10 by weight.

[0059] The catalyst article, and more specifically the methane oxidation catalyst, may be an aged catalyst article, or catalyst. Preferably, the catalyst article, or catalyst, may, in particular, be a sulphide aged catalyst article, or catalyst. The catalyst article may be a hydrothermal aged catalyst article, or catalyst.

[0060] The light-off temperature of the catalyst may be equal to or greater than 480°C.

[0061] In another embodiment, the catalyst article may be an extruded catalyst article that comprises an extruded electrically conductive substrate. Preferably, the electrically conductive substrate may be substantially free of a methane oxidation catalyst. In particular, the electrically conductive substrate may be substantially free of PGMs. The electrically conductive substrate may be the same as the electrically conductive substrate as described above with reference to the layered catalyst composite. Preferably the electrically conductive substrate may comprise any suitable electrically conductive metal, an electrically conductive oxide, anelectrically conductive boride, an electrically conductive silicide, an electrically conductive carbide and / or an electrically conductive borosilicate. The electrically conductive substrate may optionally comprise a suitable filler material, wherein the electrically conductive material and the filler material have been co-extruded. A suitable filler material may comprise cordierite.

[0062] The extruded catalyst article may comprise a catalytic washcoat layer deposited upon, i.e. coated upon and adhered to, the extruded substrate. The catalytic washcoat layer may comprise the methane oxidation catalyst. The catalytic washcoat composition may be similar to the second or top washcoat layer as described herein. Preferably, the catalytic washcoat layer is the same as the second or top washcoat layer described above with reference to the layered catalytic composite embodiment.

[0063] The catalyst article may comprise an electrical contact to which the source of electricity is electrically connected, to supply electrical energy to the catalyst article and, thus, to the electrically conductive material.

[0064] The gas feed stream may in one embodiment of the invention comprise exhaust gas from an engine. In such a case, the system may form part of an exhaust gas aftertreatment system of the engine.

[0065] The engine may, in particular, be a methane burning engine, such as a natural gas burning engine.

[0066] In another embodiment of the invention, the gas feed stream may comprise fugitive methane emissions from an industrial or mining operation.

[0067] In yet another embodiment of the invention, the gas feed stream comprises methane emissions from a solid oxide fuel cell system or from a solid oxide electrolysis cell system.

[0068] In a further embodiment of the invention, the gas feed stream comprises ventilation air methane.

[0069] In yet a further embodiment of the invention, the gas feed stream may comprise an exhaust gas from a livestock house.The catalyst article may be located in a catalyst housing, into which the conduit supplying the feed stream of methane containing gas leads.

[0070] The invention also provides, as an independent further aspect thereof, a method of treating a methane containing gas to oxidise methane in the methane containing gas, the method comprising:

[0071] supplying a feed stream of methane containing gas to a catalyst article comprising a methane oxidation catalyst and an electrically conductive material, wherein the methane oxidation catalyst has a light-off temperature for methane oxidation and wherein the electrically conductive material can be electrically heated by supplying electrical energy to it, thereby also to heat the catalyst; and

[0072] supplying electrical energy to the electrically conductive material to adjust a current catalyst temperature to a predetermined catalyst temperature at which contacting the catalyst with the methane containing gas at a feed temperature below the light-off temperature provides an operating temperature over the catalyst that is above the light-off temperature.

[0073] The method may be a method of operating the system of the invention, as described with reference to the system of the invention.

[0074] Accordingly, the methane containing gas, the feed stream of methane containing gas, the catalyst article, the methane oxidation catalyst, the electrically conductive material, the light-off temperature, the current catalyst temperature, the predetermined catalyst temperature, the feed temperature, and the operating temperature may all be as described with reference to the system of the invention.

[0075] Adjusting the current catalyst temperature to the predetermined catalyst temperature may, as described in relation to the system of the invention, comprise, through the supply of electrical energy to the electrically conductive material, increasing the current catalyst temperature to the or maintaining the current catalyst temperature at the predetermined catalyst temperature.

[0076] The method may therefore include supplying sufficient electrical energy to the electrically conductive material to achieve such increase in or maintenance of the current catalyst temperature.

[0077] The supply of electrical energy to the electrically conductive material may be performed when:

[0078] the feed temperature is below the light-off temperature; and / orthe operating temperature is below the light-off temperature; and / or

[0079] the current catalyst temperature is below the predetermined catalyst temperature.

[0080] The method may include discontinuing the supply of electrical energy or not performing the supply of electrical energy to the electrically conductive material, when at least one of:

[0081] the feed temperature;

[0082] the operating temperature; and

[0083] the current catalyst temperature,

[0084] is above the light-off temperature, provided that, if the feed temperature is below the light-off temperature, the operating temperature and / or the current catalyst temperature remains above a predetermined threshold value that is equal to or greater than the light-off temperature.

[0085] Thus, the method may provide for low methane concentration situations as discussed with reference to the system of the invention.

[0086] The predetermined threshold value for the operating temperature and / or the current catalyst temperature may be as described with reference to the system of the invention.

[0087] The method may also include measuring, calculating or otherwise determining, one or more temperatures or methane concentrations and using such measurements to control the source of electricity selectively to supply and discontinue the supply of electrical energy to the electrically conductive material.

[0088] More specifically, the method may include at least measuring the feed temperature.

[0089] The method may also include measuring or calculating the operating temperature.

[0090] The method may further include measuring or calculating the current catalyst temperature.

[0091] The method may include measuring or calculating the methane concentration in the feed steam and / or the methane concentration in the outlet of the system of the invention.

[0092]

[0093] of an embodiment of the inventionThe invention will now be described in more detail and by way of illustrative example only, with reference to one embodiment thereof that is diagrammatically illustrated in the accompanying drawing identified as Figure 1.

[0094] In Figure 1, reference numeral 10 generally shows an assembly of a system 12 for treating a methane containing gas by oxidising methane in the methane containing gas, according to the invention, and an internal combustion engine 14.

[0095] The internal combustion engine 14 is connected to the system 12 by an exhaust gas line 16, as hereinafter described in more detail.

[0096] The engine 14 is capable of being fed with a combustible fuel along feed line 18, from a source of the combustible fuel.

[0097] The combustible fuel is, in the illustrated embodiment, natural gas, and the engine 14 is therefore a natural gas burning engine and, as such, a source of a methane containing exhaust gas.

[0098] In accordance with the invention the engine 14 may, however, be substituted with any other source of a methane containing gas that needs to be treated from an emissions perspective by oxidation of methane.

[0099] The system 12 comprises a catalyst article 20.

[0100] The catalyst article 20 comprises a methane oxidation catalyst (not illustrated individually) and an electrically conductive material (not illustrated individually).

[0101] The catalyst is, furthermore, a sulphur aged catalyst, having been aged by sulphur deposits thereon through use thereof in oxidising methane. As a result, the catalyst has a light-off temperature, for methane oxidation, which is above 480°C.

[0102] In the catalyst article 20, the catalyst is a layered catalyst composite comprising a substrate and at least two washcoat layers (neither the substrate nor the washcoat layers are individually illustrated in Figure 1). A first washcoat layer is deposited on the substrate, and a second washcoat layer is deposited, at least partially, on the first washcoat layer. The first washcoat layer and the second washcoat layer are discrete from each other.The substrate of the layered catalyst composite may be any conventional methane oxidation catalyst substrate and may comprise a ceramic honeycomb structure. In catalyst article 20, the substrate is a monolithic ceramic substrate made from cordierite.

[0103] The first washcoat layer which is deposited upon the substrate comprises an electrically conductive material. In the catalyst article 20, the first washcoat layer is substantially free of the methane oxidation catalyst. In the catalyst article 20, the electrically conductive material comprises an electrically conductive boride and / or an electrically conductive silicide.

[0104] In catalyst article 20, the electrically conductive material is comprised by the catalyst article 20 such that the provision of electrical energy to the electrically conductive material and the resulting heating of the electrically conductive material also heats the catalyst.

[0105] In catalyst article 20, the second washcoat layer comprises the methane oxidation catalyst. The second washcoat layer is at least partially coated upon and adhered to the first washcoat layer in a layered configuration. The methane oxidation catalyst is a bimetallic platinumpalladium catalyst supported on an alumina catalyst support.

[0106] The catalyst article 20 has an electrical connection (not illustrated) to which a source of electricity 21 is electrically connected along electricity supply line 23, to supply electricity to the catalyst article 20 and, thus, also to the electrically conductive material, in operation.

[0107] The source of electricity 21 may be any suitable and available source of electricity, such as a battery and / or a motor-generator. A suitable motor-generator may for example be an alternator, which may conveniently be operated by operation of the engine 14.

[0108] The catalyst article 20 is located inside a catalyst housing 22, downstream of the engine 14.

[0109] In connecting the engine 14 to the system 12, the exhaust gas line 16 leads to the catalyst housing 22, to feed exhaust gas produced by the engine 14, along the exhaust gas line 16, into the catalyst housing 22, for such exhaust gas to contact the catalyst article 20 and, as a result, also contact the catalyst, for methane in the exhaust gas to be oxidised in the presence of the catalyst.The system 12 further comprises three temperature sensors 24, 26, 28 that form part of a control system of the system 12.

[0110] One temperature sensor 24 is located to measure a feed temperature of the exhaust gas feed stream at which the exhaust gas feed stream is fed to the catalyst housing 22, immediately upstream of the housing 22. Thus, the temperature sensor 24 is located on or inside the exhaust gas line 16.

[0111] Another temperature sensor 26 is located to measure an operating temperature inside of the catalyst housing 22. Thus, the temperature sensor 26 is located on or inside the catalyst housing 22.

[0112] The other temperature sensor 28 is located to measure a current temperature of the catalyst article 22. Thus, the temperature sensor 28 is located on or in close proximation to the catalyst article 20.

[0113] The temperature sensors 24, 26, 28 may each be any type of sensor suitable to measure the temperature of a gas or article. For example, each the temperature sensors 24, 26, 28 may be any of a thermocouple, a resistance temperature detector, a thermistor, etc.

[0114] The control system also comprises an electronic processing and control unit 30 which is in electronic communication, along respective signal communication lines 32, 34, 36, with the temperature sensors 24, 26, 28, to receive values of the feed temperature, the operating temperature, and the current catalyst temperature, respectively from the temperature sensors 24, 26, 28.

[0115] The control unit 30 is also in electronic communication, along signal communication line 38, with the source of electricity 21 and is configured to exercise control over the source of electricity 21 , to control a level of electrical energy that is supplied from the source of electricity 21 to the catalyst article 20.

[0116] The control unit 30 comprises a processing circuit that has a processor and a memory device, and a controller that has input circuitry, a control logic circuit, an output circuit, and a communications interface.The control logic circuit would typically comprise algorithms or traditional control logic and may use lookup tables stored in the memory device for the determination of control parameters, most prominently the light-off temperature of the catalyst, a predetermined catalyst temperature to which the methane oxidation catalyst must be heated by supply of electrical energy to the catalyst article 20 in the circumstances hereinafter described, and a predetermined threshold value for the operating temperature and the current catalyst temperature.

[0117] In operation, the control unit 30 uses temperature values communicated to it by the temperature sensors 24, 26, 28 to exercise control over the source of electricity 21, by controlling the level of electrical energy that is supplied to the catalyst article 20 from the source of electricity 21.

[0118] More specifically, when the control unit 30 determines that one or more of the temperatures measured by the temperature sensors 24, 26, 28 is / are below the light-off temperature, and in the case of the current catalyst temperature is below the predetermined catalyst temperature (which may be equal to or below the light-off temperature) the control unit 30 would exercise control over the source of electricity 21 to supply electrical energy to the catalyst article 20, and thus to the electrically conductive material. Most typically, such control would be exercised with reference to the operating and / or feed temperatures being below the light-off temperature.

[0119] Such supply of electrical energy to the catalyst article 20 would be sufficient to adjust the current catalyst temperature to the predetermined catalyst temperature, which as mentioned is either a temperature above the light-off temperature or a temperature below the light-off temperature but at which an exothermic reaction with the exhaust gas feed stream is sustained over the catalyst, thus producing sufficient heat to bring the catalyst to, and maintain the catalyst at, a temperature above the light-off temperature, as determined with reference to the temperatures measured by one or more of the temperature sensors 24, 26, 28.

[0120] Supply of such sufficient electrical energy to the catalyst article 20 from the source of electricity 21 would continue at least until it is determined by the control unit 30, with reference to temperature measurements received from one or more of the temperature sensors 24, 26, 28, that there is sufficient heat, other than that resulting from the supply of electrical energy from the source of electricity 21 to the catalyst article 20, to maintain an operating temperature in the catalyst housing 22, over the catalyst, that is above the light-off temperature.In accordance with the invention, such heat other than that which arises from the supply of electrical energy from the source of electricity 21 to the catalyst article 20, may arise from the feed temperature of the methane containing gas having increased to a temperature above the light-off temperature, as determined by temperature sensor 24, or from an exotherm at a temperature above the light-off temperature being sustained over the catalyst through continuous oxidation of methane, as determined by temperature sensor 26.

[0121] In some cases, such as cases of low methane concentration in the exhaust gas, and when the feed temperature remains below the light-off temperature, oxidation of methane over the catalyst may not be able to sustain the operating temperature and / or current catalyst temperature above the light-off temperature. The control unit 30 would determine this with reference to temperature values of the operating and / or current catalyst temperature, as measured by the temperature sensors 26, 28, not remaining above the abovementioned predetermined threshold value, e.g. after the supply of electrical energy to the catalyst article 20 has been discontinued. The control unit 30 would then recommence the supply of electrical energy to the catalyst article 20.

[0122] Through oxidation of methane by the methane oxidation catalyst of the catalyst article 20 in the catalyst housing 22, the system 12 produces a treated exhaust gas feed stream having a reduced methane concentration than the exhaust gas feed stream emanating from the engine 14, which treated exhaust gas feed stream is discharged from the catalyst housing 22 along discharge line 34.

[0123] Discussion

[0124] The inventors have found that by operating a system for oxidising methane using a catalyst article that comprises a methane oxidation catalyst and an electrically conductive material which can heat the catalyst when supplied with sufficient electrical energy, methane oxidation may advantageously be achieved at methane containing gas feed temperatures below the methane light-off temperature of the catalyst.

[0125] This was found to be particularly useful in relation to aged catalysts, such as sulphur aged catalysts or hydrothermal aged catalysts, which have a significantly increased light-off temperature compared to fresh catalysts, typically in the order of around 480°C or more.The advantages of the invention find wide application, including to enable catalytic methane combustion at temperatures below light-off or mitigating methane from sources such industrial operations, including mining, or in ventilation air. It may also find useful application in starting up processes that demand methane oxidation and have insufficient operating temperature at start-up for such oxidation to commence.

[0126] Having the catalyst at a predetermined catalyst temperature, e.g. above the light-off temperature, at start-up may be particularly useful where the methane containing gas comprises a relatively high concentration of methane but is below the light-off temperature, whether because of a start-up condition of an engine producing the gas or because of the source of the gas producing a stream of the gas at such a temperature. Thus, light-off of methane may be achieved at a feed gas temperature below the light-off temperature, and may thereafter be sustained by heat energy from an exothermic methane oxidation reaction to maintain the operating temperature above the light-off temperature.

[0127] In low methane concentration conditions, the ability to maintain the catalyst at the predetermined catalyst temperature, e.g. above the light-off temperature, may be particularly useful to oxidise the methane content of such gas continuously, considering that the concentration of methane may be too low to sustain oxidation independently of catalyst heating.

Claims

Claims1. A system for oxidising methane in a methane containing gas stream, comprising:a catalyst article comprising a methane oxidation catalyst and an electrically conductive material, wherein the methane oxidation catalyst has a light-off temperature for methane oxidation and wherein the electrically conductive material can be electrically heated by supplying electrical energy to it, thereby also to heat the catalyst;a conduit to supply a feed stream of methane containing gas to the catalyst article; a source of electricity that is electrically connected to the catalyst article to supply electrical energy to the electrically conductive material; anda control system that is configured to control the source of electricity to supply electrical energy to the electrically conductive material to adjust a current catalyst temperature to a predetermined catalyst temperature at which contacting the catalyst with the methane containing gas at a feed temperature below the light-off temperature provides an operating temperature over the catalyst that is above the light-off temperature.

2. The system according to claim 1, wherein the predetermined catalyst temperature is a temperature above the feed temperature, preferably also above the light-off temperature.

3. The system according to claim 1 or claim 2, wherein adjusting the current catalyst temperature to the predetermined catalyst temperature includes, through the supply of electrical energy to the electrically conductive material, increasing the current catalyst temperature to the predetermined catalyst temperature or maintaining the current catalyst temperature at the predetermined catalyst temperature.

4. The system according to any of claims 1 to 3, wherein the control system is configured to perform the supply of electrical energy to the electrically conductive material when:the feed temperature is below the light-off temperature; and / orthe operating temperature is at or below the light-off temperature; and / orthe current catalyst temperature is below the predetermined catalyst temperature.

5. The system according to any one of claims 1 to 4, wherein the control system is configured to discontinue the supply of electrical energy or not to perform the supply of electrical energy, when at least one of:the feed temperature;the operating temperature; andthe current catalyst temperature,is at or above the light-off temperature, provided that, if the feed temperature is below the light-off temperature, the operating temperature and / or the current catalyst temperature remains at or above a predetermined threshold value that is equal to or greater than the light-off temperature while the supply of electrical energy is discontinued.

6. The system according to any one of claims 1 to 5, wherein the catalyst article comprises a layered catalyst composite comprisinga substrate;a first washcoat layer deposited on the substrate, wherein the first washcoat layer comprises the electrically conductive material; anda second washcoat layer deposited, at least partially, on the first washcoat layer, wherein the second washcoat layer comprises the methane oxidation catalyst.

7. The system according to any one of claims 1 to 5, wherein the catalyst article comprises a zoned catalyst composite comprisinga substrate;a first washcoat layer deposited on the substrate, wherein the first washcoat layer comprises the electrically conductive material; anda second washcoat layer deposited on the substrate downstream of the first washcoat layer, wherein the second washcoat layer comprises the methane oxidation catalyst.

8. The system according to claim 6 or 7, wherein the first washcoat layer is substantially free of a methane oxidation catalyst.

9. The system according to any one of claims 1 to 5, wherein the catalyst article is an extruded catalyst article comprisingan extruded substrate comprising the electrically conductive material; anda catalytic washcoat layer deposited on the extruded substrate, wherein the catalytic washcoat layer comprises the methane oxidation catalyst.

10. The system according to claim 9, wherein the extruded substrate is substantially free of a methane oxidation catalyst.

11. The system according to any one of claims 1 to 10, wherein the methane oxidation catalyst comprises platinum and palladium, wherein the platinum to palladium is present in a ratio of from 1:5 to 1:10 by weight..

12. The system according to any one of claims 1 to 11, wherein the methane oxidation catalyst is an aged catalyst, preferably a sulphide aged catalyst article or a hydrothermal aged article.

13. The system according to any one of claims 1 to 12, wherein the light-off temperature is equal to or greater than 480°C.

14. The system according to any one of claims 1 to 13, wherein the gas feed stream comprises:exhaust gas from an engine;fugitive methane emissions from an industrial or mining operation;comprises methane emissions from a solid oxide fuel cell system or from a solid oxide electrolysis cell system;ventilation air methane; orexhaust gas from a livestock house.

15. A method of treating a methane containing gas to oxidise methane in the methane containing gas, the method comprising - supplying a feed stream of methane containing gas to a catalyst article comprising a methane oxidation catalyst and an electrically conductive material, wherein the methane oxidation catalyst has a light-off temperature for methane oxidation, and wherein the electrically conductive material can be electrically heated by supplying electrical energy to it, thereby also to heat the catalyst; andsupplying electrical energy to the electrically conductive material to adjust a current catalyst temperature to a predetermined catalyst temperature at which contacting the catalyst with the methane containing gas at a feed temperature below the light-off temperature provides an operating temperature over the catalyst that is above the light-off temperature.

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