Exhaust gas abatement system

Abstract

A system for removing a methane oxidation catalyst (MOC) poison from an exhaust gas includes a methane abatement device that can receive an exhaust gas having methane (CH4) and the MOC poison. The methane abatement device includes a guard bed that can remove the MOC poison from the exhaust gas and can produce an intermediate exhaust gas having CH4 and free of the MOC poison. The guard bed includes a MOC poison capture component having a first transition metal oxide, an alumina (AI2O3) support material, and a support material derived from dolomite. The methane abatement device further includes a MOC bed that is fluidly connected to and downstream of the guard bed. The MOC bed includes a MOC and can remove CH4 from the intermediate exhaust gas to produce a treated exhaust gas having less than about 200 parts per million by volume (ppmv) CH4.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 044,002, filed June 25, 2020, entitled “EXHAUST GAS EMISSIONS ABATEMENT SYSTEM”, which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates generally to the field of reducing exhaust emissions, and more specifically to reducing methane emissions from natural gas-fueled engines. More specifically, this disclosure relates to a dual-bed methane emission reduction system having a protective bed for converting, capturing, or otherwise removing methane oxidation catalyst poisons from exhaust gases produced by natural gas-fueled engines, and a methane oxidation catalyst (MOC) bed for converting and reducing methane emissions from the exhaust gases. Background Technology

[0004] Natural gas is an abundant and economical alternative to petroleum-derived fuels such as gasoline, kerosene, and diesel. Therefore, manufacturers of engines used in stationary and transportation applications / services are shifting their attention and efforts from petroleum-derived fuels to compressed natural gas (CNG) or liquefied natural gas (LNG) as fuel. Both CNG and LNG are cheaper and cleaner to burn than petroleum-derived fuels. For example, CNG and LNG emit approximately 75% fewer greenhouse gases, such as carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxides (NOx), when burned compared to some petroleum-derived fuels. x Furthermore, CNG and LNG produce significantly fewer particulates compared to petroleum-derived fuels. CNG and LNG are primarily (>90%) composed of methane (CH4). CH4 is a more potent greenhouse gas than CO2. Therefore, while using CNG and LNG reduces total emissions compared to petroleum-derived fuels, incomplete combustion of CNG and LNG can lead to undesirable CH4 emissions, i.e., high CO2 equivalents. Therefore, there is currently a need to treat engine exhaust gases generated from the combustion of CNG or LNG fuels to remove or reduce undesirable CH4 emissions before releasing them from the system. Summary of the Invention

[0005] In a first embodiment, the system for removing methane oxidation catalyst (MOC) poisons from exhaust gas includes a methane reduction unit that receives exhaust gas containing methane (CH4) and MOC poisons. The methane reduction unit includes a guard bed that removes the MOC poisons from the exhaust gas and generates an intermediate exhaust gas containing CH4 but free of the MOC poisons. The guard bed includes an MOC poison trapping component having a first transition metal oxide, an alumina (Al2O3) support material, and a dolomite-derived support material. The methane reduction unit also includes an MOC bed fluidly connected to and located downstream of the guard bed. The MOC bed includes MOCs and removes CH4 from the intermediate exhaust gas to generate treated exhaust gas having less than approximately 200 parts per million parts per volume (ppmv) of CH4.

[0006] In another embodiment, a method for removing methane oxidation catalyst (MOC) poisons from exhaust gas includes: feeding exhaust gas containing methane (CH4) and MOC poisons into a methane reduction unit, the methane reduction unit including a guard bed and an MOC bed fluidly connected to and located downstream of the guard bed; and contacting the exhaust gas with an MOC poison trapping component disposed within the guard bed. The MOC poison trapping component includes a first transition metal oxide, an alumina (Al2O3) support material, and a support material derived from dolomite. The method further includes removing the MOC poisons from the exhaust gas to produce an intermediate exhaust gas containing CH4 and free of MOC poisons.

[0007] In another embodiment, the methane oxidation catalyst (MOC) poison trapping component for removing MOC poisons from exhaust gas includes an alumina (Al2O3) support material having a first porosity, a dolomite-derived support material having a second porosity less than the first porosity, and a first transition metal oxide supported on the Al2O3 support material, the dolomite-derived support material, or both. The concentration of the first transition metal oxide is between about 1% by weight and 25% by weight, and the MOC poison trapping component removes sulfur dioxide (SO2), phosphorus (P), calcium (Ca), zinc (Zn), silicon (Si), and ash.

[0008] Additional features and advantages of the exemplary embodiments of this disclosure will be set forth in the following description and will be apparent in part from that description, or may be learned by practice of such exemplary embodiments. The features and advantages of such embodiments can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more apparent from the following description and the appended claims, or may be learned by practice of such exemplary embodiments set forth below. Attached Figure Description

[0009] The advantages of this disclosure will become apparent from the following detailed description and with reference to the accompanying drawings, wherein:

[0010] Figure 1 This is a block diagram of a system according to an embodiment of the present disclosure, the system including a natural gas-fueled engine that generates exhaust gases and an exhaust gas reduction system having a dual-bed methane reduction device having a methane oxidation catalyst (MOC) poison capture component;

[0011] Figure 2 It is compatible with the implementation scheme of this disclosure. Figure 1 A block diagram of a dual-bed methane emission reduction device used in conjunction with the system, the dual-bed methane emission reduction device including a protective bed with MOC poison-capturing components located upstream of the MOC bed;

[0012] Figure 3 It is applicable to the implementation scheme of this disclosure. Figure 2 A block diagram of a multi-layer protective bed in a dual-bed methane emission reduction device, wherein the multi-layer protective bed includes a first layer having a first MOC poison-capturing component and a second layer having a second MOC poison-capturing component;

[0013] Figure 4 This is a block diagram of a single-layer protective bed according to an embodiment of the present disclosure, the single-layer protective bed comprising at least one MOC toxicant capture component and being usable for... Figure 2 In a dual-bed methane emission reduction unit;

[0014] Figure 5 According to the implementation scheme of this disclosure, for Figure 1 An exemplary graph showing the percentage of CH4 conversion as a function of run time (TOS) for the guard bed (GB) and MOC systems;

[0015] Figure 6 This is an exemplary graph showing the distribution of MOC catalyst poison concentration as a function of the length of the protective bed, according to an embodiment of this disclosure.

[0016] Figure 7 This is an exemplary graph showing the distribution of MOC catalyst poison concentration as a function of MOC bulk length, according to an embodiment of this disclosure.

[0017] Figure 8 This is an exemplary graph showing the percentage of methane conversion as a function of run time for various guard bed formulations located upstream of the MOC at a temperature of 425°C, according to an embodiment of this disclosure.

[0018] Figure 9This is an exemplary graph showing the percentage of methane conversion as a function of run time, obtained at 470°C for various guard bed formulations located upstream of the MOC, according to one embodiment of this disclosure; and

[0019] Figure 10 It is based on the implementation scheme of this disclosure, using Figure 1 The flowchart shows a method for systemically treating exhaust gases containing methane and MOC poisons produced by natural gas-fueled engines. Detailed Implementation

[0020] One or more specific embodiments of this disclosure will now be described. These described embodiments are examples of the currently disclosed technology, including systems, protective beds, and methods for using the system to treat exhaust gases generated by the system to reduce methane emissions from natural gas-fueled engines. Additionally, for the purpose of providing a concise description of these embodiments, not all features of an actual embodiment can be described in the specification. It should be understood that in the development of any such actual embodiment, as in any engineering or design project, many implementation-specific decisions will be made to achieve the developer's specific objectives, such as compliance with system-related and business-related constraints, which may vary from implementation to implementation. Furthermore, it should be understood that such development efforts may be complex and time-consuming, but remain routine tasks of design, production, and manufacturing for those skilled in the art who benefit from this disclosure.

[0021] When describing elements of various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may exist in addition to those listed. Furthermore, it should be understood that references to “an embodiment” or “an embodiment” of this disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the described features.

[0022] As used herein, the terms “approximately,” “about,” and “substantially” refer to quantities that are close to a specified amount but still perform the required function or achieve the desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to quantities less than 10%, less than 5%, less than 1%, less than 0.1%, and less than 0.01% of the value.

[0023] Natural gas contains approximately 70% to approximately 95% methane (CH4). Natural gas in the form of compressed natural gas (CNG) and / or liquefied natural gas (LNG) is increasingly being used as a fuel to replace petroleum-derived fuels (e.g., gasoline, coal, etc.) or in combination with petroleum-derived fuels in engines used in stationary (electricity, drilling, etc.) and transportation (marine, rail, and other road transport) applications. For example, internal combustion engines can burn natural gas (e.g., CNG and LNG) to produce energy-containing combustion gases, which are extracted by engine components (e.g., pistons, turbines, etc.) to power the system. The combustion gases may contain unburned methane, oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), and nitrogen oxides (NOx). x Combustion gases from natural gas engines contain trace amounts of sulfur dioxide (SO2), water (H2O), nitrogen (N2), and other gases that exit the system as exhaust gases. SO2 in combustion gases originates from trace amounts (approximately 0.1 to approximately 8 parts per million parts (ppm)) of sulfur present in natural gas, as well as in diesel igniters (e.g., used in dual-fuel engines) and lubricating oils. For example, for spark-ignition natural gas engines, the SO2 level in combustion gases depends on the S levels in the natural gas fuel and the oil, as well as the fuel and oil consumption rates. In addition to SO2, combustion gases from natural gas engines also contain trace amounts (approximately less than 3000 ppm) of other chemical substances, such as those containing phosphorus (P), zinc (Zn), calcium (Ca), and silicon (Si). These latter substances are typically present in oil additives. Therefore, their presence and concentration in combustion gases can be attributed to oil consumption and the oil consumption rate, respectively. The amounts of residual non-methane hydrocarbons (NMHC), particulate matter (ash), CO2, and other emissions present in the exhaust gases from natural gas combustion are significantly lower than those present in the exhaust gases from petroleum-derived fuel combustion. Therefore, using natural gas for power generation reduces these specific emissions compared to petroleum-derived fuels.

[0024] However, under certain operating conditions, natural gas-fueled engines may not completely burn CH4. Therefore, unburned CH4 may slip into the exhaust gas and be released from the system. For example, a natural gas engine operating in a lean fuel (e.g., oxygen-enriched fuel) configuration can produce exhaust gas with approximately 200 parts per million parts per volume (ppmv) to approximately 3000 ppmv of CH4. It has been recognized that CH4 is a more efficient greenhouse gas than CO2 (e.g., 1 mole of CH4 ≥ 25 molar equivalents of CO2). Therefore, it is desirable to develop and deploy an exhaust gas emission reduction system that can remove or reduce CH4 escape by bringing the CH4 level in the exhaust gas at or below prescribed emission levels (e.g., below approximately 150 ppmv to 200 ppmv).

[0025] One technique for reducing CH4 involves oxidizing methane in the presence of a methane oxidation catalyst (MOC). In methane oxidation technology, hot CH4-containing waste gas is contacted with the MOC, which catalytically converts CH4 into CO2 and H2O in the presence of O2. MOCs typically used for CH4 reduction include at least one active metal oxide supported on a porous inorganic oxide carrier. As a non-limiting example, MOCs that can be used to oxidize or reduce CH4 may include noble metal oxides such as platinum (Pt), palladium (Pd), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), osmium (Os), and gold (Au), base metals (e.g., barium (Ba), cesium (Cs), etc.), and rare earth elements (cerium (Ce), yttrium (Y), lanthanum (La), neodymium (Nd), etc.). In some embodiments, the MOC may include other elements as dopants or promoters. Furthermore, MOCs can contain various porous inorganic oxides as supports (e.g., alumina (Al₂O₃), titanium dioxide (TiO₂), zirconium oxide (ZrO₂), etc.) and mixtures thereof. As understood by those skilled in the art, Pd-based MOCs (in the form of PdO) exhibit the highest activity in methane oxidation, i.e., the ability to advantageously convert and reduce methane emissions at reaction temperatures >300°C. However, noble metal oxide catalysts, particularly PdO-based MOCs, are highly sensitive to chemicals commonly present in exhaust gases such as SO₂, P, Zn, Ca, and Si. Therefore, the methane oxidation performance of MOCs is adversely affected by some of these chemicals. Hereinafter, the chemicals SO₂, P, Zn, Ca, and Si are referred to as MOC poisons. These poisons adversely affect the methane oxidation activity of MOCs, i.e., the ability of MOCs to convert / reduce CH₄, as well as their performance stability and lifetime. Catalyst poisons adversely affect MOCs by chemically reacting with, physically covering, or adsorbing onto the active sites of the MOC, thereby preventing the MOC from fully exerting its methane oxidation activity. The main active sites on PdO-based MOCs are the oxygen vacancies on PdO. The methane oxidation reaction proceeds through intermediate complexes formed between these oxygen vacancies and CH4 molecules in the exhaust gas. The aforementioned catalyst poisons either chemically react with the oxygen vacancies on PdO or physically cover the active sites. Therefore, the catalyst poisons effectively prevent methane from approaching and reacting with the active sites, thus deactivating them for methane oxidation.

[0026] For example, at optimal methane oxidation exhaust gas temperatures (e.g., between approximately 300°C and 600°C, more specifically between 400°C and 530°C), oxygen vacancies in PdO react with SO2 or its oxidized form SO3 present in the exhaust gas to form stable palladium sulfate (PdSO4). Palladium sulfate is inactive for CH4 oxidation. Furthermore, PdSO4 cannot decompose under typical CH4 oxidation conditions and at optimal methane oxidation exhaust gas temperatures. Therefore, in the presence of SO2 in the exhaust gas, the catalytic activity and overall catalyst performance stability / lifetime of PdO-based MOCs are adversely affected by PdSO4 formation. Other catalyst poisons such as P, Zn, Ca, Si, and ash can also react with or physically cover active sites in the MOC, further contributing to an overall reduction and deactivation of the MOC's methane oxidation activity. Therefore, it may be desirable to develop and deploy sulfur and other catalyst poison capture devices and technologies in conjunction with natural gas engines to remove catalyst poisons and allow the catalytic performance of MOCs placed downstream of such devices to be maintained at their peak levels.

[0027] This disclosure provides embodiments of an exhaust gas emission reduction system and its usage method, wherein the exhaust gas emission reduction system includes a dual-bed methane emission reduction device with a guard bed and an MOC (Metal Oxide Catalyst), which effectively removes MOC catalyst poisons and reduces CH4 emissions from natural gas-fueled engines. Furthermore, this disclosure provides embodiments of an improved guard bed formulation for removing MOC catalyst poisons. As discussed in further detail below, the guard bed is located upstream of the MOC bed and may include one or more layers of one or more components that substantially convert, capture, or remove MOC catalyst poisons from the exhaust gas. Thus, catalyst poisons in the exhaust gas are removed before it is fed to the MOC. This allows the MOC catalyst to fully utilize its peak activity and performance in methane oxidation / reduction, thus paving the way for commercially viable exhaust gas emission reduction systems to reduce methane emissions from natural gas engines in stationary or transport services.

[0028] In view of the above, Figure 1This is a block diagram of one embodiment of a power generation system 10 according to the present disclosure, which may include an exhaust gas reduction system. In operation, system 10 receives and consumes natural gas to generate electricity and exhaust gas as a byproduct. As discussed in further detail below, the exhaust gas reduction system treats the exhaust gas in a methane reduction unit to produce treated exhaust gas. In the illustrated embodiment, system 10 includes a natural gas engine 12 and an exhaust gas reduction system 14 downstream of the natural gas engine 12. The natural gas engine 12 may be a spark-ignition engine or a dual-fuel engine. For example, the natural gas engine 12 may be a heavy-duty engine used in stationary applications (e.g., compressors, drilling, and power generation) or a heavy-duty engine used in transportation applications (e.g., road transport, mining, maritime transport, and rail transport).

[0029] During operation, the natural gas engine 12 receives natural gas fuel 18 and air 20, and combusts the air-fuel mixture to produce power 24 and exhaust gas 28. In a spark-ignition natural gas engine, the air-fuel mixture is compressed in the cylinder and then ignited by means of a spark plug to provide combustion of the mixture. In a dual-fuel engine, in addition to natural gas fuel 18, the natural gas engine 12 may receive a second fuel (e.g., diesel). The amount of the second fuel (diesel) is significantly less than the amount of natural gas fuel (typically between approximately 5% and 10% of the total fuel). In this particular case, the second fuel (diesel) serves as an igniter to ignite the primary natural gas fuel.

[0030] The natural gas engine 12 can operate in either lean combustion mode or rich combustion mode. In lean combustion mode, the natural gas engine 12 burns fuel 18 with excess air 20 (e.g., oxygen). For example, air 20 and fuel 18 can be supplied to the natural gas engine 12 in different ratios. The type of engine operation is defined as stoichiometric, lean (or lean), or rich (or rich) depending on whether the amount of oxygen in the air (and the total amount of air) is sufficient, greater than, or less than the amount required for complete combustion of the fuel. Typically, the combustion type is defined by the air-to-fuel (AFR) ratio. The AFR ratio can be expressed as the mass of air present in the engine relative to the mass of fuel. The AFR value for stoichiometric combustion of natural gas is approximately 17.2:1. This means that 17.2 parts air and 1 part fuel are required for stoichiometric combustion. Therefore, AFR < 17.2 corresponds to rich combustion, while AFR > 17.2 corresponds to lean combustion.

[0031] By operating the natural gas engine 12 in a lean combustion mode, at least a portion of the oxygen (O2) in the air-fuel mixture 20 remains unreacted and exits the natural gas engine 12 along with the exhaust gas 28. The unreacted O2 in the exhaust gas 28 can be used by the MOC to oxidize the unburned CH4 present in the exhaust gas 28.

[0032] According to this disclosure, fuel 18 is natural gas in the form of compressed natural gas (CNG), liquefied natural gas (LNG), or both. In some embodiments, fuel 18 may be a mixture of natural gas and one or more hydrocarbon fuels, such as, but not limited to, gasoline, kerosene, diesel, or gas oil. As used herein, "natural gas" is intended to refer to a mixture of hydrocarbons (C1-C6 hydrocarbons) with a carbon number in the range of 1 to 6, containing more C1 hydrocarbons (e.g., methane (CH4)) than the total amount of C2-C6 hydrocarbons. Hydrocarbons with a carbon number in the range of 1 to 6 include, but are not limited to, CH4, ethane (C2H6), propane (C3H8), and butane (C4H6). 10 ), pentane (C5H) 12 ) and hexane (C6H 14 According to embodiments of the invention, natural gas may have approximately 50% by volume to approximately 95% by volume or more of CH4. For example, natural gas may have at least 70% by volume, at least 90% by volume, or at least 95% by volume of CH4.

[0033] After combustion, the natural gas engine 12 directs exhaust gas 28 to the exhaust gas reduction system 14. The exhaust gas reduction system 14 includes a methane reduction device 30, which treats the exhaust gas 28 before it is released from the system 10 to convert, capture, and largely remove unwanted chemicals such as various catalyst poisons (SO2, P, Zn, Ca, Si, etc.) and CH4, NO. x Other combustion byproducts. For example, as mentioned above, exhaust gas 28 may include unburned CH4, oxygen (O2), and other undesirable gases such as nitrogen oxides (NOx). xThe exhaust gas 28 contains carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), nitrous oxide (N2O), and other combustion byproducts that may need to be removed before being released from system 10. In some embodiments, exhaust gas 28 may contain approximately 100 parts per million parts per volume (ppmv) to approximately 5000 ppmv of CH4, more specifically 200 ppmv to 3500 ppmv, and even more specifically 400 ppmv to 2500 ppmv of CH4. However, it has now been recognized that there is a need to reduce methane emission levels (typically by 70%–90%) to meet certain operating standards. For example, it is desirable for the CH4 level in the exhaust gas released from a natural gas operating system to be less than approximately 150 ppmv to 200 ppmv. Therefore, exhaust gas 28 must be treated in exhaust gas reduction system 14 to reduce and substantially remove unburned CH4 and other combustion byproducts from exhaust gas 28 before it is released from system 10. For example, in operation, the exhaust gas reduction system 14 disclosed herein first treats exhaust gas 28 in a guard bed 36 to convert, capture, and substantially remove MOC catalyst poisons (e.g., SO2, Zn, P, Ca, Si, ash, etc.), thereby producing treated intermediate exhaust gas 42. After removing the catalyst poisons, the treated intermediate exhaust gas 42 is fed into an MOC bed 40, which oxidizes and significantly reduces the CH4 level in exhaust gases 28 and 42, before the exhaust gas is released from system 10.

[0034] As described above, one technique for removing CH4 from exhaust gas 28 is the catalytic oxidation of CH4 on an MOC. The MOC, in the presence and participation of O2, converts CH4 into CO2 and water (H2O) through oxidation. The composition of the MOC typically includes at least one noble metal oxide supported on a porous inorganic oxide carrier. More specifically, the chemical composition of the MOC may include: (i) noble metal oxides of platinum (Pt), palladium (Pd), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), osmium (Os), and gold (Au), and combinations thereof; (ii) some base metals (Ba, Cs, etc.); (iii) rare earth elements (Ce, Y, La, Nd, etc.); (iv) small amounts of other elements as dopants or promoters; and (v) various porous inorganic oxides as carriers (e.g., alumina, titanium oxide, zirconium oxide, cobalt oxide, rare earth oxides, etc.) and mixtures thereof.

[0035] The catalytic activity and overall catalyst lifetime of MOCs based on Pd and other precious metals are adversely affected by various chemicals present in the exhaust gas 28. For example, chemicals such as SO2, P, Zn, Ca, Si, ash, etc., adversely affect the catalytic activity of MOCs in methane oxidation and their lifetime for methane oxidation / emission reduction. Therefore, these substances are used as catalyst poisons for MOCs. The sources and levels of catalyst poisons in exhaust gases from natural gas engines depend on: (i) their levels in the engine fuel source, i.e., their levels in natural gas fuel or natural gas and diesel fuel, lubricating oil, and (ii) the fuel and lubricating oil consumption rate. Some catalyst poisons (e.g., S) are present in one or more fuels 18, and other catalyst poisons (e.g., P, Zn, Ca, etc., other than S) are present in lubricating oil. Regarding sulfur, the total sulfur level in LNG gas is typically very low (e.g., less than about 1 ppmv), and in CNG and piped NG, the total sulfur level is typically less than about 5 ppmv. When sulfur level regulations are met, the sulfur level in diesel igniters is approximately 0.1% to 0.5% by weight. The sulfur level in lubricating oil ranges from approximately 0.2% by weight to approximately 2% by weight. Therefore, the main sources of sulfur in exhaust gases (such as exhaust gas 28) are fuel and lubricating oil from CNG-fueled engines and lubricating oil from LNG-fueled engines.

[0036] To mitigate the effects of catalyst poisoning on the MOC, the exhaust gas reduction system 14 includes a dual-bed methane reduction unit 30 with a catalyst poison trapping guard bed 36, hereinafter referred to as the "guard bed," located upstream of the MOC bed 40. In the illustrated embodiment, the guard bed 36 and the MOC bed 40 are housed in a single methane reduction unit. However, in some embodiments, the guard bed 36 and the MOC bed 40 may be in separate housings. The guard bed 36 and the MOC bed 40 are connected by suitable hardware (e.g., pipes, valves, flanges) that guides and feeds the intermediate exhaust gas 42 from the guard bed 36 to the MOC bed 40. Depending on the direction of the exhaust gas 28 flow, the guard bed 36 may be located at the top or bottom of the MOC bed 40 within the methane reduction unit 30. For example, in an embodiment where exhaust gas 28 flows from top to bottom of the methane emission reduction unit 30, the guard bed 36 is positioned above the MOC bed 40 such that exhaust gas 28 flows through the guard bed 36 before flowing through the MOC bed 40. In an embodiment where exhaust gas 28 flows from bottom to top of the methane emission reduction unit 30, the guard bed 36 is positioned below the MOC bed 40. In other embodiments, the guard bed 36 is horizontally positioned adjacent to the MOC bed 40. The methane emission reduction unit 30 can also be retrofitted into existing systems.

[0037] The guard bed 36 includes one or more layers of one or more MOC poison capture components 46 that convert, capture, and remove catalyst poisons from exhaust gas 28, and in the process generate intermediate exhaust gas 42 having substantially eliminated or significantly reduced amounts of catalyst poisons compared to exhaust gas 28 (e.g., untreated exhaust gas). According to embodiments of this disclosure, the guard bed 36 can remove approximately 50% to approximately 100% of the catalyst poisons from exhaust gas 28. For example, the guard bed 36 can remove 50%, 60%, 70%, 75%, 80%, 90%, or 100% of the catalyst poisons. One or more layers and components 46 may be used to capture and remove catalyst poisons from exhaust gas 28, including but not limited to transition metal (e.g., manganese (Mn), vanadium (V), copper (Cu)) oxides supported on or co-mixed with various high (e.g., greater than about 0.2 cc / g) or low (e.g., less than about 0.2 cc / g) porosities of inorganic oxides, such as alumina, titanium oxide, cerium oxide, and calcium or magnesium carbonates or oxides, or mixtures of oxide and carbonate materials. One or more components 46 of the guard bed 36 may catalytically react with at least a portion of the catalyst poisons in exhaust gas 28 and convert them into a more reactive substance, which reacts and is captured by other components of the guard bed 36, or be converted into a chemical substance that does not significantly harm the MOC and its catalytic performance, thereby generating intermediate exhaust gas 42. Intermediate exhaust gas 42 then exits guard bed 36 and flows into MOC bed 40, where it undergoes MOC in methane reduction unit 30. In some embodiments, one or more layers of the guard bed 36 and component 46 may chemically react with catalyst poisons in the exhaust gas 28 to produce stable chemicals retained on the surface of the guard bed 36. In another embodiment, one or more components 46 of the guard bed 36 may physically adsorb catalyst poisons in the exhaust gas 28, thereby trapping them in the guard bed 36. Intermediate exhaust gas 42 exiting from the guard bed 36 is fed into the MOC bed 40, where CH4 in the intermediate exhaust gas stream 42 is oxidized, i.e., converted into CO2 and H2O, to produce treated exhaust gas 48 having CH4 concentrations of less than approximately 150 ppmv to 500 ppmv. In this way, the exhaust gas emission reduction system 14 disclosed herein produces treated exhaust gas that meets emission regulations and is suitable for release from system 10.

[0038] As described above, the protective bed 36 removes catalyst poisons from the exhaust gas 28 to mitigate MOC poisoning in the MOC bed 40. The protective bed 36 may comprise one or more components 46 in a single layer or multiple components 46 in multiple layers. The single or multiple components 46 in each layer convert or capture one or more catalyst poisons present in the exhaust gas.

[0039] Figure 2This is a block diagram of a methane emission reduction device 30 according to an embodiment of the present disclosure, which has a multi-layer protective bed 50 located upstream of an MOC bed 40. In an illustrated embodiment, the multi-layer protective bed 50 includes a first layer 54 having a first catalyst poison conversion and / or capture component 56 (MOC poison capture component) and a second layer 58 having a second catalyst poison conversion and / or capture component 60 (MOC poison capture component) downstream of the first layer 54. The catalyst poison conversion and / or capture components 56, 60 in each respective layer 54, 58 may include one or more chemical substances (elements, metal hydroxides, or oxides) selected and configured to convert and / or capture / scavenger and at least partially remove catalyst poisons from exhaust gas 28. The layers 54, 58 are arranged in a sequential or stacked configuration. It should be noted that some embodiments of the present disclosure include

[0040] A single-layer protective bed instead of a multi-layer protective bed 50. The single-layer protective bed includes component 56, component 60, or a mixture of both.

[0041] As described above, components 56 and 60 remove catalyst poisons from exhaust gas 28. For example, components 56 and 60 may include chemicals that readily react with SO2 to oxidize SO2 in the exhaust gas (in the presence of oxygen) to form SO3. By converting SO2 to SO3, sulfur substances become more reactive with the surfaces of components 56 and 60. Therefore, compared to systems without components 56 and 60, the ability / degree by which components 56 and 60 remove sulfur substances from exhaust gas (e.g., exhaust gas 28) is improved. For example, components 56 and 60 promote the formation of stable and inert metal sulfates, such as manganese sulfate (MnSO4), aluminum sulfate (Al2(SO4)3), calcium sulfate (CaSO4), magnesium sulfate (MgSO4), etc. These sulfates are stable and, once formed, remain in the protective bed 50. Therefore, the active sites on the noble metal oxide phase, and more specifically, the oxygen vacancies within this phase of the MOC in MOC bed 36, remain unaffected by sulfur substances. Therefore, oxygen vacancies within the noble metal oxide phase of the MOC can be used to catalytically oxidize CH4 in the waste gas 28. In addition to chemicals that convert SO2 into SO3 and sulfates, components 56 and 60 also include other chemicals that react with, adsorb, and / or form stable complexes with other catalyst poisons in the waste gas 28, such as Zn, Ca, Mg, P, and ash. That is, components 56 and 60 react with and convert or adsorb and substantially trap these other catalyst poisons within the protective bed 50, preventing the catalyst poisons from leaving the protective bed 50 with the intermediate waste gas 42.

[0042] According to this disclosure, catalyst poisoning capture components that can be used to remove catalyst poisons from exhaust gases (e.g., exhaust gas 28) include, but are not limited to, transition metal oxides (manganese (Mn), vanadium (V), copper (Cu), etc.), lime (CaO), calcium magnesium oxides (CaMgO2), dolomite (CaMg(CO3)2) or mixtures thereof, metal oxides (e.g., magnesium oxide (MgO), aluminum oxide (Al2O3)), and combinations thereof. Some transition metal oxide sites react with SO2 and O2 in exhaust gas 28 to generate SO3. The resulting SO3 and residual O2 also react with the remaining available transition metal oxide sites to generate the corresponding transition metal sulfates. Furthermore, SO3 can readily react with porous inorganic oxides such as aluminum oxide and / or materials derived from dolomite in a protective bed to form stable aluminum and calcium or calcium and / or magnesium sulfates. These stable sulfates are inert and are retained within layers 54, 58 and components 56, 60 of the protective bed 50. Therefore, in this way, the sulfur present in exhaust gas 28 is converted into stable sulfates and can no longer exert undesirable effects on the active sites on the noble metal oxide phase of the MOC. Thus, during the operation of system 10, the active sites on the noble metal oxide phase of the MOC remain fully available for methane oxidation.

[0043] High-porosity materials such as Al2O3 and other inorganic oxide components of the protective bed 50 can also react with or adsorb other catalyst poisons present in the exhaust gas, such as P, Zn, Ca, Mg, Si, and ash, and substantially remove them. These other catalyst poisons cannot be removed by low-porosity materials (water pore volume less than about 0.2 cubic centimeters / gram (cc / g)) such as materials derived from dolomite. Porous materials can react with and bind or adsorb the aforementioned catalyst poisons, thereby trapping them in the protective bed and removing them from the exhaust gas. In some embodiments, component 56 in the first layer 54 of the protective bed 50 is a transition metal oxide or any other suitable metal oxide deposited on or mixed with a high-porosity material (water pore volume greater than about 0.2 cc / g) such as Al2O3, and component 60 in the second layer 58 of the protective bed 50 is a transition metal oxide or other suitable oxide deposited on or mixed with a relatively low-porosity material (water pore volume less than about 0.2 cc / g) derived from dolomite. The first layer 54 of the protective bed 50 may be a section that converts and / or captures a portion of the catalyst poisons in the exhaust gas 28 before the exhaust gas flows into the second layer 58 of the protective bed 50 for final capture of the remaining poisons. For example, the first layer 54 may remove approximately 5% to 90% or 30% to 70% of the catalyst poisons in the exhaust gas 28. In some embodiments, the first layer 54 is selective for certain catalyst poisons, and the second layer 58 is selective for other catalyst poisons. Specifically, component 56 in the first layer 54 may be selective for the oxidation of SO2 to SO3 and for certain elements and ash, and component 60 in the second layer 58 may complete the oxidation of SO2 to SO3 and is more selective for binding these sulfur substances and forming sulfates. According to embodiments of this disclosure, components 56 and 60 may include transition metal (e.g., Mn, V, Cu) oxides deposited on or mixed with high-porosity (water pore volume greater than about 0.2 cc / g) metal oxides and relatively low-porosity (water pore volume less than about 0.2 cc / g) dolomite-derived materials. Furthermore, the level of transition metals in the respective components 56 and 60 is from about 1% by weight (wt%) to 25% by weight, more specifically from about 5% by weight to 15% by weight.

[0044] Figure 3 An embodiment of a multi-layer protective bed 50 according to this disclosure is shown, which can be used to capture and remove catalyst poisons from exhaust gas 28. For example... Figure 3As shown, the multi-layer protective bed 50 has a total length 62 extending from the upstream end 64 to the downstream end 68, a width 70 (i.e., thickness) substantially perpendicular to the length 62 and extending between the first side 72 and the second side 74 of the protective bed 36, and a height 78 substantially perpendicular to the length 62 and the width 70 and extending between the top side 80 and the bottom side 82 of the multi-layer protective bed 50. The length 62, width 70, and height 78 define the volume 86 (e.g., the total protective bed volume) of the multi-layer protective bed 50. Although the multi-layer protective bed 50 has a rectangular shape in the illustrated embodiment, the multi-bed protective bed 50 may have any other geometry (e.g., square, cylindrical, elliptical, etc.). As should be understood, the layers 54, 58 and components 56, 60 in the multi-layer protective bed 50 may be arranged as fixed beds, movable beds, or removable beds. The latter allows for the replacement or replenishment of layers 54, 58 saturated with toxic substances without interrupting engine and exhaust emission reduction system operation.

[0045] like Figure 3 As shown, volume 86 is divided into a first layer 54 and a second layer 58. Volume 86 within the first layer 54 includes a first poison-capturing component 56, and the second layer 58 includes a second poison-capturing component 60. The first layer 54 extends along a first portion 90 of length 62, such that the first layer 54 occupies approximately 1% to approximately 99% of the total protective bed volume 86. Similarly, the second layer 58 extends along a second portion 92 of length 62, such that the second layer 58 occupies approximately 1% to approximately 99% of volume 86. The portions 90, 92 may be the same or different in size. For example, layers 54, 58 may be evenly distributed along the length 62 of the multi-layer protective bed 50. Thus, each portion 90, 92 of the respective layers 54, 58 is approximately 50% of the total length 62 of the multi-layer protective bed 50, and the respective poison-capturing components 56, 60 occupy approximately 50% of the total protective bed volume 86. In other embodiments, the size of portion 90 of the first layer 54 may be larger or smaller than the size of portion 92 of the second layer 58. Therefore, the first poison-capturing component 56 occupies more or less volume 86 than the second poison-capturing component 60. For example, the first poison-capturing component 56 may occupy about 1% to about 49% of volume 86, and the second poison-capturing component 60 may occupy about 51% to about 99% of volume 86, and vice versa.

[0046] In some embodiments, the first poison-capturing component 56 in the first layer 54 can partially oxidize SO2 to SO3 and partially react to capture SO3 in the form of sulfate, while reacting with non-sulfur catalyst poisons to adsorb, capture, and remove them. The second poison-capturing component 60 in the second layer 58 can primarily oxidize and capture the remaining unconverted SO3 in the first layer 54 (i.e., remove the remaining sulfur poisons), while also capturing and removing any remaining non-sulfur poisons that may have passed through the first layer 54. For example, in Figure 3 In the illustrated embodiment, the first poison-capturing component 56 is selected such that SO2 is partially oxidized to SO3 and captured as sulfate. Layer 54 also primarily reacts with non-sulfur catalyst poisons such as Zn, P, Ca, Mg, Si, ash, etc., adsorbing or capturing these non-sulfur catalyst poisons. The second poison-capturing component 60 in the second protective bed 58 is selected in such a manner that it completes the conversion of any SO2 that may have passed through the first bed 58 to SO3 and causes it (i.e., all remaining sulfur poisons) to react as sulfate and capture it, while simultaneously capturing some remaining non-sulfur poisons that may have passed through the first protective bed 54.

[0047] Therefore, to remove sulfur and catalyst poisons in the manner described above, the first poison capture component 56 may comprise at least one transition metal oxide deposited on or co-mixed with at least one preferably highly porous (water pore volume greater than about 0.2 mL / g) inorganic oxide material, such as, but not limited to, alumina (Al₂O₃), crystalline or amorphous aluminosilicates, titanium oxide, cobalt oxide, magnesium oxide, or any other suitable highly porous material or mixture thereof that can react, transform, adsorb, or otherwise bind with sulfur and non-sulfur catalyst poisons in the exhaust gas passing through the first layer 54. In this particular case, the transition metal oxide function provides the oxidation of SO₂ to SO₃ and its partial capture as sulfate, while the highly porous inorganic oxide material provides the necessary high surface area and chemical functionality required for binding, adsorbing, and / or capturing sulfur and non-sulfur poisons. The second poison capture component 60 comprises at least one transition metal oxide deposited on or mixed with a material having relatively low porosity (water pore volume less than about 0.2 mL / g) but high sulfur absorption capacity, selected from, but not limited to, calcium oxide (lime), calcium magnesium oxide, calcium carbonate, calcium magnesium carbonate (dolomite), and combinations thereof. For the second poison capture component 60, the transition metal oxide also functions to convert any remaining SO2 in the exhaust gas into SO3 and partially bind SO3 in the form of transition metal sulfates. The relatively low porosity material (e.g., <0.2 mL / g, derived from dolomite) accomplishes SO3 capture by forming sulfates, while simultaneously contributing to the removal of remaining non-sulfur poisons.

[0048] In one embodiment, component 56 and / or component 60 can be prepared by impregnating high-porosity (e.g., Al2O3) and low-porosity (e.g., dolomite-derived) inorganic materials with a suitable transition metal precursor to achieve a final transition metal concentration of approximately 1% to 25% in the respective poison-capturing components 58 and 60. More preferably, impregnation can be performed to achieve a transition metal concentration of approximately 5% to 20% by weight in the total poison-capturing components 58 and 60. By impregnating the high- and low-porosity materials of components 56 and 60 with transition metal precursors, the efficiency of poison-capturing components 56 and 60 for oxidation and SO2 removal is improved compared to materials / components not impregnated with transition metal precursors. In other embodiments, the transition metal precursor can be added during the synthesis stage of the high-porosity or relatively low-porosity materials in components 56 and 60, or co-mixed with components 56 and 60 during preparation via co-milling (physical mixing), which can subsequently shape components 56 and 60. Transition metals (M) can be transition metal precursors (e.g., M). x (NO3) y M x Cl y etc.), transition metal hydroxides (M(OH) x ) or transition metal oxides (M x O y The form of ) is added in the above steps. In all cases, the transition metal in the final poison-capturing components 56 and 60 is in the form of transition metal oxides.

[0049] In some embodiments, the volume 86 of the protective bed may be a single layer rather than multiple layers, such as in a multi-layer protective bed 50. For example, a single-layer protective bed may include a physical mixture comprising a first poison-capturing component 56 and a second poison-capturing component 60. Figure 4 An embodiment of a single-layer protective bed 96 for use in a methane emission reduction unit 30 to remove catalyst poisons from exhaust gas 28 is shown. In the illustrated embodiment, the volume 86 of the single-layer protective bed 96 is uniformly filled with a trapping material 98, which is a physical mixture of poison trapping components 56 and 60. The ratio of components 56 and 60 in the trapping material 98 can be 1:1, 1:2, 1:3, 1:4, 2:3, 2:1, 3:1, 4:1, 3:2, or any other suitable ratio. In some embodiments, the mixture 98 comprises separate pellets of the first poison trapping component 56 and separate pellets of the second poison trapping component 60. In other embodiments, the trapping material 98 comprises shaped particles (e.g., granules) of the trapping components formed by co-extruding the physical mixture of the two components 56 and 60.

[0050] By incorporating protective beds 50 and 96 into the methane emission reduction unit 30, the catalytic performance and MOC lifespan in methane oxidation can be significantly improved / extended. For example, returning to... Figure 2 During operation, the methane emission reduction unit 30 receives exhaust gas 28 from a natural gas engine (e.g., natural gas engine 12). While in the methane emission reduction unit 30, exhaust gas 28 flows into guard beds 50, 96 and comes into direct contact with poison capture components 56, 60, 98. Components 56, 60, 98 capture catalyst poisons through reaction, conversion, adsorption, or other means, and remove catalyst poisons from exhaust gas 28 during the generation of intermediate exhaust gas 42. After the generation of intermediate exhaust gas 42, guard beds 50, 96 guide intermediate exhaust gas 42 to MOC bed 40, which includes a methane oxidation catalyst (MOC) 94.

[0051] As described above, MOC 94 can be any noble metal oxide catalyst. For example, MOC 94 can be a PdO-based catalyst on a support containing inorganic oxides (e.g., zirconium oxide). In MOC bed 40, intermediate waste gas 42 is directly contacted with MOC 94. MOC 94 comprises at least one active noble metal oxide phase, which reacts with CH4 in intermediate waste gas 42 and oxidizes CH4 to form CO2 and H2O, partly due to the presence of oxygen in the waste gas. Because guard beds 50, 96 remove catalyst poisons from waste gas 28, the active noble metal oxide phase of MOC 94 is not adversely affected by the poisons and can therefore be fully utilized for the oxidation / reduction of CH4 in intermediate gas 42. Compared to MOCs without guard beds 50, 96, the above situation allows MOC 94 to fully exert its methane oxidation activity and maintain it for a considerable period of time (e.g., tens of thousands of hours of operation). Therefore, the CH4 level in the treated waste gas 48 produced by methane emission reduction unit 30 can be approximately 150 ppmv-200 ppmv. CH4 levels of approximately 150 ppmv-200 ppmv are at or below permissible CH4 emission levels.

[0052] Example

[0053] The following describes experiments illustrating the performance of the protective beds disclosed herein. Each experiment below is typically conducted using various powder protective bed formulations that were intentionally poisoned with SO2 or aged upstream of the MOC bed. The MOC formulation used throughout the experiments is as follows: (Pd (4 wt%) Pt (0.5 wt%) Rh (0.125 wt%) on a zirconium (ZrO2) support). Each powder protective bed was prepared using any suitable technique known in the art to produce the desired chemical composition as shown in Table 1. For reference, the performance of the MOC was tested without a protective bed (Examples 1 and 15).

[0054] The experiments were conducted in a high-throughput powder catalyst test apparatus. Each reactor in the high-throughput powder catalyst test apparatus was loaded such that the ratio of guard bed to MOC was 50 / 50% by volume. The ability of the powder guard bed to remove catalyst poison in each corresponding powder guard bed / MOC sample was evaluated by comparing the performance (or capacity) of the MOC oxidation or conversion model (e.g., simulation) of methane present in the exhaust gas feed composition downstream of each corresponding powder guard bed. To compare the catalytic activity of the various powder guard bed / MOC samples, the temperature (T50) required to achieve 50% methane conversion during performance testing was determined. CH4 (See Table 1). Performance testing was conducted in two phases in all cases except Example 1. In the first phase (Examples 2-17), the powder guard bed / MOC samples were placed in a high-throughput SO2 aging test bench and fed with a gas containing 5 parts per million parts (ppm) SO2, 500 ppm CH4, and 10 vol% H2O for 10,000 h. -1 SO2 aging was performed for 24 hours at a gas hourly space velocity (GHSV) and an inlet gas temperature of 470°C, where GHSV was calculated by dividing the gas volumetric flow rate (L / hr) by the catalyst volume (L). After SO2 aging, the powder guard bed / MOC sample was removed from the SO2 test bench and reloaded into a “clean” high-throughput test bench, and tested using a simulated feed containing 2000 ppm CH4, 1000 ppm CO, 7.5 vol% CO2, 6 vol% O2, 150 ppm NO, and 15% H2O. As used herein, a “clean” high-throughput test bench is intended to represent a sulfur-free high-throughput test bench. In the second phase of testing, performance was tested without adding SO2 to the gas feed. The powder guard bed / MOC sample of Example 1 was not subjected to SO2 aging but was directly subjected to the second phase (clean, SO2-free feed) test.

[0055] surface methane oxidation activity (T50) CH4 )

[0056]

[0057] The numbers in parentheses represent the weight % concentration of the corresponding element in the final protective bed formulation.

[0058] Analysis of the data in Table 1 shows that, after SO2 aging, powder protective bed / MOC samples (e.g., Examples 2-6) containing calcium-magnesium (i.e., dolomite) derived and calcium oxide (lime) based protective bed formulations exhibited the lowest T50. CH4Value (392℃-395℃). T50 observed in Examples 2-6 CH4 The values ​​are at the desired levels, indicating that the dolomite-derived and lime-based protective bed formulations have the best methane oxidation activity compared to other powder-protected bed / MOC combinations tested. Furthermore, some SO2-aged powder-protected bed / MOC samples from Examples 2-6 provided catalytic activity very similar to the un-SO2-aged reference / control MOCs (i.e., T50). CH4 (value) (T50) CH4 =391℃). It should be noted that the MOC sample (Example 15) aged with SO2 without a protective bed exhibited significantly lower methane oxidation activity, which is due to its T50 at 458℃. CH4 The value demonstrates that this value is 67°C higher than that of the MOC without SO2 aging (Example 1). Therefore, as determined from the data in Table 1, the powder guard bed with a calcium-magnesium or calcium formulation effectively removes SO2 MOC catalyst poisons that would otherwise adversely affect and significantly reduce the catalytic activity and activity stability of the MOC. It should be noted that, compared to other powder guard bed / MOC samples tested, the guard bed formulation with transition metal oxides deposited on a support containing calcium-magnesium oxides (e.g., CaMgO2) along with Al2O3 (e.g., Example 2) provided the best SO2 capture performance. This is achieved by the lowest T50. CH4 The value (392°C) demonstrates that, relative to all tested SO2-aged powder-protected bed / MOC samples, this protective bed formulation (Example 2) exhibits the highest methane oxidation activity. Notably, after SO2 aging, the specific transition metal oxidation and CaMgO2 and Al2O3 powder-protected bed formulation of Example 2 provided substantially the same T50 as the reference MOC sample (Example 1). CH4 Value (i.e., methane oxidation activity), this reference MOC sample was not aged with SO2 and was tested without a protective bed (the most active sample, T50). CH4 =391℃).

[0059] In the presence of oxygen, the transition metal (Mn or Cu) oxides in the guard bed formulation provide rapid oxidation of SO2 to SO3. The calcium-magnesium-based support in the guard bed formulation primarily reacts with and captures SO3 in sulfate form, while Al2O3 primarily provides a higher surface area and chemical functionality, which is beneficial for adsorbing, reacting with, or capturing some other non-sulfur poisons that may be present in the exhaust gas. Furthermore, Al2O3 can at least partially contribute to the further removal of sulfur-containing poisons by reacting them and converting them to aluminum sulfate. Examples 2-6 and their corresponding data clearly illustrate the beneficial effects of containing transition metal oxides, calcium, magnesium, and aluminum oxide in the guard bed formulation disclosed herein upstream of the MOC bed. For example, the disclosed transition metal oxide, calcium, magnesium, and aluminum oxide guard bed formulation is effective in removing S-containing catalyst poisons from exhaust gases originating from natural gas combustion engines, thus allowing the MOC catalyst placed downstream to fully utilize and maintain its methane oxidation activity and performance stability. Therefore, the transition metal oxide, calcium, magnesium and alumina protective bed formulations disclosed herein are suitable for methane emission reduction systems to reduce unburned methane from natural gas-fueled engines in stationary and transport services.

[0060] Double-layer protective bed

[0061] As described above, the protective bed of this disclosure can have multiple layers with different protective bed formulations. A bilayer protective bed formulation was prepared, and the removal of sulfur and other catalyst poisons was tested (Example 18). The first layer of the bilayer protective bed comprises transition metal oxides and Al2O3 components. The second layer of the bilayer protective bed comprises transition metal oxides and calcium magnesium carbonate (dolomite) derived components. These two layers and components are arranged in a stacked configuration (one after the other) and are located upstream of the MOC bed.

[0062] The first layer of the protective bed - Preparation of Al2O3 components :

[0063] The first layer of the double-layer protective bed can be prepared by impregnating (extruded) alumina aggregates (e.g., alumina granules) formed with an aqueous solution of a transition metal precursor. The transition metal precursor can be added to the alumina aggregate formulation before or after extrusion. For example, the transition metal precursor can be added to the extrusion mixture used to prepare the alumina granules. The extrusion mixture is prepared by mixing alumina (or aluminum hydroxide) powder and a peptizing agent. Alternatively, an aqueous solution of the transition metal precursor can be added to the prepared alumina granules (e.g., extrudate) by any impregnation method known in the art. For example, the alumina granules can be impregnated by volume impregnation or by circulating an impregnation solution. The alumina granules can be of any suitable geometry. As a non-limiting example, the alumina granules can be cylindrical, multi-lobed (e.g., trilobed), spherical, annular, or sheet-like. The size range of the alumina granules is approximately 1.2 mm to 10 mm in diameter and approximately 4 mm to 10 mm in length.

[0064] The Al2O3 component / carrier used in Example 18 was prepared according to the method described in U.S. Patent 4,579,729. In short, the extrusion mixture (for the carrier) was prepared by placing 654 g of wide-pore alumina powder (LOI = 23.5 wt%) in a mill mixing bowl, and while running the mill mixing bowl, a solution of nitric acid gelling agent was added to form an alumina / gelling agent solution mixture. The alumina / gelling agent solution mixture was milled in a mill for approximately 15 minutes to allow the gelling agent to react with the wide-pore alumina powder. Alternatively, an inorganic hydroxide sol binder (e.g., aluminum hydroxide sol) may be mixed with the wide-pore alumina powder for approximately 10 to 30 minutes to allow for the gelation or bonding of the wide-pore alumina powder. Extrusion aids (e.g., citric acid, Superfloc, and / or Methocell, etc.) may also be added to the alumina / gelling agent mixture to improve extrusion ease and, if necessary, partially generate additional porosity.

[0065] After adding one or more extrusion aids, add approximately 130g of DI water to the mill and restart the mill. Once the DI water addition is complete, mill the extrusion mixture for approximately 15 minutes, transfer it to a stainless steel pan, and extrude it using a stencil into trefoil (TL) pellets with a diameter of approximately 2.5mm. Collect the TL pellets and transfer them to a drying convection oven, where they are dried overnight at 120°C. After drying, crush and sieve the TL pellets to obtain TL pellets with a length of approximately 4mm to 6mm. Calcine the dried and graded TL pellets to 600°C at a heating rate of 2°C / min in a drying air stream of 40L / hr and maintain at 600°C for 6 hours.

[0066] After calcination, TL granules are impregnated using a pore volume impregnation method to achieve a 10% Mn concentration on the TL granules. An impregnation solution is prepared by dissolving approximately 6460 g of Mn(NO3)2·4.85H2O in 6914 mL of DI water to produce a manganese nitrate (Mn(NO3)2·4H2O) solution containing approximately 25% to approximately 75% by weight of Mn(NO3)2. The volume of the prepared impregnation solution is then replenished with additional DI water to adjust the total volume to meet the pore volume requirements for the amount of extrudate to be impregnated (8680 mL). For example, in the pore volume impregnation method, the volume of the impregnation solution used is substantially the same as that of the pore volume TL granules. In this particular embodiment, the total water pore volume of the Al2O3 TL granules is 0.868 mL / g. Therefore, the volume of the Mn(NO3)2 impregnation solution was adjusted to 8680 mL and used to impregnate 10 kg of Al2O3 TL granules in a rotary impregnation vessel. While the vessel was rotating, a portion of the Mn(NO3)2 impregnation solution was added to the TL granules in a small flow pattern. The TL granules and the Mn(NO3)2 impregnation solution were homogenized for several minutes. After homogenizing the TL granules and a portion of the Mn(NO3)2 impregnation solution, the remaining Mn(NO3)2 impregnation solution was slowly added to the rotary impregnation vessel to form impregnated granules.

[0067] The impregnated granules were tumbled in a rotary impregnator for approximately 10 minutes, then transferred to a tray and air-dried overnight, followed by drying at 120°C for 12 hours in a dry air stream of 40 L / hr. The dried impregnated granules were then calcined to 600°C using a heating rate of 2°C / min and held at 600°C for 6 hours.

[0068] The second layer of the protective bed - Preparation of the second component:

[0069] The second layer of the bilayer protective bed can be prepared in a manner similar to the first layer. As described above, in the bilayer protective bed, the second layer is located downstream of the first layer. The second layer comprises transition metal oxides and dolomite-derived components prepared by mixing 25 kg of dolomite (CaMg(CO3)2) powder particles with an average particle size of approximately 5 micrometers (µm) to approximately 15 µm in a mixing mill with 6476.5 g of LUDOX AS-40 silica sol binder having a silica solids content of 40 wt% in a mixing mill to form an extrusion mixture. LUDOX AS-40 silica sol is used as a binder to bond the individual dolomite powder particles together and helps to shape the dolomite particles into shaped aggregates (e.g., granules, spheres, rings, flakes, etc.) of the desired diameter by extrusion.

[0070] The extrusion mixture was milled in a mixing mill for approximately 10 minutes. While in the mixing mill, approximately 294 g of Methocel was added to the extrusion mixture after approximately 2 minutes, followed by approximately 126.5 g of Superfloc after approximately 6 minutes of milling. The extrusion mixture was milled for another 10 minutes, and the resulting mixture was extruded into TL extrudate strips with a diameter of 2.5 mm. The TL extrudate strips were air-dried overnight at ambient temperature, followed by overnight drying at 100°C in a convection drying oven. The dried TL extrudate strips were crushed to form pellets with a length of approximately 4 mm to approximately 8 mm, and calcined to 600°C at a heating rate of 2°C / min in a drying air stream of 40 L / hr and held at 600°C for 6 hours to form calcined dolomite-derived TL extrudate. The calcined dolomite-derived TL extrudate was impregnated with a transition metal precursor to form Mn-impregnated dolomite-derived TL pellets (e.g., a second component) with a double-layer protective bed. The calcined dolomite-derived TL extrudate was impregnated with the Mn(NO3)2 impregnation solution described above for the Al2O3 component of the first layer of the double-layer protective bed. The target final concentration of Mn in the dolomite-derived component was 8% by weight. The Mn-impregnated dolomite-derived TL pellets were air-dried overnight, followed by drying in a convection oven at approximately 120°C for at least 2 hours. After drying, the impregnated dolomite-derived TL pellets were subjected to a drying air stream of 40 L / hr, heated at a heating rate of 2°C / min, and calcined at 600°C for approximately 6 hours.

[0071] Example 19—Double-layer protective bed

[0072] To illustrate the ability of the dual-layer guard bed described in Example 18 to capture sulfur-containing and other catalyst poisons from the exhaust gases generated and output by an engine operating on LNG as fuel, the dual-layer guard bed was located upstream of the MOC bed, and the CH4-reducing activity of the MOC in the MOC bed was evaluated. For example, the methane conversion rate measured during this test was used as a measure of the effectiveness of the guard bed in capturing poisons from the exhaust gases. The test was conducted using a 12L six-cylinder spark-ignition engine operating under lean fuel conditions. The test was carried out at approximately 50,000 h⁻¹ of GHSV. The fuel used to operate the natural gas engine was LNG with approximately 98 vol% CH4, 2 vol% C²⁺, and less than 0.1 ppm S. The exhaust gas produced by the natural gas engine consisted of 1600 ppmv CH4, 450 ppm CO, 7.3 vol% CO2, 8.4 vol% O2, 140 ppmv NO, 12.5 vol% H2O, and 0.15 ppm SO2, and the temperature of the exhaust gas in the natural gas engine was approximately 470°C. A double-layer protective bed was used, with a first (upstream) layer containing 1.03 kg of 2.5 mm diameter TL pellets of 10% Mn / Al2O3 (Example 18) and 3.6 kg of 2.5 mm TL pellets of 8 wt% Mn / dolomite (Example 18). MOC was prepared by coating a slurry containing MOC catalyst components onto a 4.16-inch diameter × 3.5-inch length ceramic monolithic substrate with a repaired substrate surface having 400 cpsi (pore channels per square inch). The MOC catalyst coated on the repair substrate consists of 4 wt% Pd, 0.5 wt% Pt, and 0.125 wt% Rh on ZrO2.

[0073] The above test results of the double-layer protective bed formulation in Example 18 show that Figure 5 middle. Figure 5 This is graph 100 showing the percentage of CH4 conversion as a function of time in hours. As shown in the figure, data 102 clearly demonstrates that the dual-layer guard bed / MOC system of this disclosure maintained 100% CH4 conversion during the test. Therefore, the dual-layer guard bed formulation of Example 18 used for this test effectively converts, adsorbs, or captures S and other poisons present in engine exhaust gas, thereby allowing the PdO-based MOC to fully exert its methane oxidation / reduction activity during the duration of the test.

[0074] Figure 6 and Figure 7 Figures 130 and 132 show the distribution curves of catalyst poisons / concentration as a percentage of weight (wt%) with the length of the guard bed and the length of the MOC bed, respectively. Figure 6 and Figure 7The toxic substance distribution curves shown were obtained by chemical composition analysis of the protective bed and MOC bulk samples used in the aforementioned engine tests using inductively coupled plasma (ICP) technology. The used protective bed and MOC bulk samples were taken from different sections along the length of the respective protective bed layers. Figure 6 ) and different sections along the length of the MOC (Material of Combustion) Figure 7 As described above, the double-layer protective bed and the MOC bed are subjected to exhaust gas flow for 1000 hours. Therefore, the MOC in the double-layer protective bed formulation and the MOC bed are exposed to catalyst poisons originating from LNG fuel and lubricating oil used to operate the natural gas engine. Figure 6 As shown, the Mn / Al2O3 component in the first protective bed effectively captured and reduced the concentrations of sulfur (S), silicon (Si), and phosphorus (P) catalyst poisons in the exhaust gas, while the Mn / dolomite-derived component in the second protective bed captured and reduced the residual concentrations of S and P in the exhaust gas. It should be noted that since the dolomite-derived granules were extruded together with the silica sol acting as a binder, the Si concentration in the second protective bed was not measured. Therefore, the Si concentration in the second protective bed will not represent the amount of Si removed from the exhaust gas through the second protective bed. Zn was not detected along the length of the double protective bed because Zn is distributed over a large surface area of ​​the protective bed, so the amount of Zn is relatively small (below the detection limit).

[0075] like Figure 7 As shown, the catalyst poison concentration along the length of the MOC monolithic bed is very low (<0.05 wt%). Specifically, the data show that the S concentration is as low as 0.025 wt%, decreasing to approximately 0.01 wt% along the length of the MOC. Furthermore, the P level on the used MOC is below detectable levels throughout the entire length of the MOC bed. The Si concentration was not determined due to the presence of silica in the MOC monolithic support material. The above catalyst poison distribution curves and catalyst performance data demonstrate that the dual-layer guard bed disclosed herein effectively removes both S-containing and S-free MOC poisons from exhaust gas. Therefore, compared to systems without the disclosed guard bed, the MOC catalyst can fully utilize its CH4 oxidation / conversion and CH4 emission reduction activities (see [link to relevant documentation]). Figure 8 and Figure 9 ).

[0076] Single-layer protective bed

[0077] In addition to the bilayer protective bed test, the CH4 conversion activity of MOCs was also tested using a single-layer protective bed. The layer of a single-layer protective bed comprises a single component, such as a transition metal (M) / Al2O3 or M / dolomite-derived material. However, in some embodiments, the layer of a single-layer protective bed comprises a physical mixture of two or more components, as discussed in further detail below. The single component of a single-layer protective bed can be prepared by physically mixing appropriately sized Al2O3 and Mn / dolomite powder particles, adding a solvent or binder to prepare an extrusion or molding mixture with the desired forming consistency, and extruding or otherwise shaping this mixture of particles to produce a homogeneous mixture of Al2O3 and dolomite-derived aggregates (e.g., pellets, flakes, spheres, or rings). In this particular embodiment, the Al2O3 and dolomite-derived particles are chemically bonded. The addition of the transition metal M (e.g., Mn) can be accomplished by adding a transition metal precursor during the preparation of the extrusion mixture or during the pre-forming stage of the mixture. In other embodiments, the transition metal M can be incorporated into the Al2O3 and dolomite-derived aggregates by impregnation with a transition metal precursor. In all cases, the extrusion mixture must be gelled with a carefully selected peptizing solvent, or a binder needs to be added.

[0078] Adding additives (such as pectin or binders) to the forming mixture provides proper bonding of the particles and ensures sufficient structural integrity of the calcined granules, flakes, rings, or spheres. Pectin modifies the surface of particles (e.g., Al2O3 or materials derived from dolomite) by making them more reactive, which facilitates bonding of the particles with other particle surfaces. Some pectin can be large enough or bulky enough (e.g., having a large molecular size, such as citric acid-C6H8O7) to not only improve the surface reactivity of the particles (i.e., the sensitivity to bonding) but also increase the final pore size and porosity of the calcined aggregates. The increase in pore size can be significant compared to particles treated with pectin of smaller size (e.g., nitric acid HNO3). These increases in pore size or total porosity of the single-component forming and calcining aggregates allow for better access to and reaction with catalyst poisons on their surfaces and / or allow for the containment of larger amounts of catalyst poisons. As a non-limiting example, pectin includes nitric acid, acetic acid, citric acid, or any other suitable pectin. In addition to adhesives, other extrusion aids (such as Methocel, Superfloc, etc.) can be added to the molding or extrusion mixture to improve the molding process. These can also impart additional pore size changes and an increase in total porosity.

[0079] In other embodiments, the layer of the monolayer protective bed is a physical mixture of two components. For example, the layer may be a physical mixture of M / Al2O3 and M / dolomite-derived components, such as those discussed above with respect to Example 18. The physical mixture can be produced by mixing pre-formed Al2O3 particles (as granules, flakes, rings, or spheres) with pre-formed dolomite-derived particles (as granules, flakes, rings, or spheres). In some embodiments, the pre-formed Al2O3 and dolomite-derived particles are mixed before impregnation with the M precursor. In other embodiments, the pre-formed Al2O3 and dolomite-derived particles are mixed after impregnation with the M precursor. In the physical mixture of Al2O3 and dolomite-derived particles, there is no chemical bond between the Al2O3 component and the dolomite-derived component.

[0080] Examples 20 and 21—Single-layer protective bed

[0081] The single component used in Examples 20 and 21 was prepared as follows: 654 g of wide-pore alumina (LOI = 23.5 w%) was added to the mixing bowl of a grinder, the grinder was started, and a solution of nitric acid (Example 20) or acetic acid (Example 21) gelling agent was added to the grinder. The corresponding gelling agent solution was prepared by adding 10.8 g of 69.4 wt% nitric acid to 687 g of DI water or by adding 10.8 g of glacial acetic acid (100%) to 724 g of (DI) water. The alumina / gelling agent solution mixture was ground for 15 minutes to allow the gelling agent to react with the alumina powder. After the alumina powder was gelled, the grinder was stopped, and a mixture of 500 g dolomite, 10 g Superfloc, 6 g Methocell, and 130 g of 40 wt% solid Ludox AS-40 silica sol binder (Example 20) or 130 g of DI water (Example 21) was added to the grinder, and the grinder was restarted. The resulting extrusion mixture of 50 wt% Al2O3 and 50 wt% dolomite was ground for 15 minutes, and then extruded using a template into long Al2O3-dolomite TL granular strips with a diameter of 2.5 mm. The Al2O3-dolomite TL granular strips were dried overnight at 120 °C in a convection oven. After drying, the Al2O3-dolomite TL granular strips were crushed and sieved to obtain Al2O3-dolomite TL granular strips with a size of approximately 4 mm-6 mm in length. The Al2O3-dolomite TL granular strips of a certain size were calcined to 600 °C in a drying air stream of 40 L / hr at a heating rate of 2 °C / min and held at 600 °C for 6 hours.

[0082] After calcination, the Al2O3-dolomite TL granules were impregnated using the pore volume impregnation method described above with reference to Example 18. In summary, the total pore volumes of the calcined Al2O3-dolomite TL granules in Example 20 (nitric acid gel solution) and Example 21 (acetic acid gel solution) were 0.50 mL / g and 0.55 mL / g, respectively. To impregnate the Al2O3-dolomite TL granules from Example 21, a transition metal impregnation solution was prepared by dissolving 397.3 g of Mn(NO3)2·4H2O in 60%-70% total DI water (330 mL) to saturate the total pore volume of the extrudate to be impregnated. The volume of the impregnation solution was adjusted with additional DI water to achieve the total volume required to meet the pore volume of the extrudate to be impregnated (550 mL). Approximately 1 kg of the calcined Al2O3-dolomite TL granules from Example 21 was placed in a rotating impregnation vessel. While rotating the container, approximately half of the Mn(NO3)2 impregnation solution was added to the Al2O3-dolomite TL granules in a small-flow mode. After homogenizing the mixture, the remaining impregnation solution was slowly added to the rotating extruder. After adding the impregnation solution, the impregnated granules were tumbled in the rotating impregnation container for approximately 10 minutes. The resulting wet-impregnated Al2O3-dolomite TL granules were air-dried overnight, then dried at 120°C for 12 hours in a dry air stream of 40 L / hr, and calcined to 600°C at a heating rate of 2°C / min, and held at 600°C for 6 hours.

[0083] Figure 8Figure 140 shows the percentage of methane conversion as a function of run time (hours) at 425 °C for different guard bed materials placed in front of the MOC. Data 142 was obtained by testing powder (315µm-500µm fraction) guard bed / MOC samples in a high-throughput test bench with 16 reactors. For each guard bed / MOC run, a total of 2 mL of guard bed / MOC sample was loaded into each reactor in the test bench. The weight ratio of guard bed powder to MOC powder loaded into the respective reactors was maintained at approximately 1.9:1. The guard bed powder and MOC powder were diluted with inert silicon carbide (SiC) particles of the 315µm-500µm fraction to bring the volume of each corresponding guard bed and MOC powder to 1 mL. Table 2 below lists the guard bed formulations used for each corresponding run. The following operating conditions were used: GSHV = 100,000 h⁻¹, reactor temperature (RxT) = 425 °C. The exhaust gas feed composition was as follows: 2000 ppm CH4, 350 ppm CO, 4.5% CO2, 10.5% O2, 150 ppm NO, 12 vol% H2O, and the remaining balance N2 to bring the total to 100%. The MOC used was a MOC catalyst coated on a ZrO2 substrate with a repair substrate of 4 wt% Pd, 0.5 wt% Pt, and 0.125 wt% Rh. SO2 was added to the exhaust gas feed starting after 25 hours of operation and maintained throughout the test duration.

[0084] Table 2. Reactor test bench protective bed operation at 425℃ 1-7

[0085]

[0086] like Figure 8As shown, data 142 indicates that all samples exhibited approximately 92%–97% CH4 conversion before the addition of SO2 (1.5 ppm). Notably, the CH4 conversion / oxidation activity of all samples was stable before the addition of SO2. After 25 hours of operation with the addition of SO2, the CH4 conversion / oxidation activity of MOC decreased rapidly without a guard bed (Run 1). For example, within 5 hours after the addition of SO2, the CH4 conversion / oxidation activity of MOC was below 20% of the CH4 conversion. In contrast, in test runs with the disclosed guard bed, MOC maintained its CH4 conversion for a longer period than in Run 1 without a guard bed. For example, the CH4 conversion of MOC was improved when using guard beds with low porosity 8 wt% Mn / dolomite-derived guard beds (Run 2) and high porosity 8 wt% Mn / Al2O3 guard beds (Run 3). As shown in data 142, the high-porosity 8 wt% Mn / Al2O3 protective bed composition is superior in improving the CH4 conversion / methane oxidation activity of the MOC compared to the low-porosity 8 wt% Mn / dolomite-derived protective bed formulation. Without being bound by theory, the improved CH4 methane conversion / oxidation activity of the MOC can be attributed to the conversion and capture of SO2 by the active MnO2 centers and the Al2O3 or dolomite support surface of the disclosed protective bed formulation. Furthermore, as... Figure 8 As shown, MOCs used in combination with Al2O3-based protective beds exhibit better CH4 conversion / oxidation activity compared to protective beds based on dolomite. This may be partly due to the higher SO2 uptake capacity of the Al2O3-based protective bed compared to the lower pore volume (e.g., 0.17 mL / g) of the dolomite-based protective bed. For example, the higher porosity (e.g., pore volume) of the Al2O3-based protective bed provides greater MnO2 dispersion and accessibility, and therefore greater SO2 / SO3 deposition and reactivity with Al2O3 (in the form of Al2(SO4)3) and retention therein, compared to the lower porosity of the dolomite-based protective bed.

[0087] When a physical mixture of high-porosity Al2O3 pellets and low-porosity dolomite-derived pellets is used, as in Run 4, the SO2 capture capacity of the guard bed is improved compared to runs using only high-porosity Al2O3 pellets (Run 3) and dolomite-derived pellets (Run 2) in the guard bed, and the CH4 conversion / methane oxidation activity of the MOC is maintained for a longer time. However, in runs where co-extruded high-porosity Al2O3 and dolomite-derived pellets are used in the guard bed (e.g., Runs 5-7), the MOC unexpectedly exhibits significantly higher CH4 conversion / methane oxidation stability compared to runs with discrete pellets having Mn / Al2O3 components (Run 3), runs with discrete pellets having Mn / dolomite-derived components (Run 2), or runs with discrete pellets having a physical mixture of Mn / Al2O3 and Mn / dolomite-derived components (Run 4). For example, as shown in data 142, MOCs (runs 5-7) used in combination with a protective bed of co-extruded Al2O3 and dolomite-derived pellets maintained CH4 conversion / oxidation activity for over 40 hours after the addition of SO2. Unbound by theory, the unexpected CH4 conversion / oxidation of MOCs when used in combination with co-extruded Al2O3 / dolomite-derived pellets can be partly attributed to the fact that the co-extrusion of small Al2O3 and dolomite-derived particles and the subsequent chemical bonding between them impart the desired chemical functions (catalytic poison removal site activity of Al2O3 and dolomite), higher porosity than dolomite particles alone (0.50 mL / g to 0.55 mL / g water pore volume for nitric acid and acetic acid, respectively), and the accessibility of the relatively low porosity (0.17 cc / g water pore volume) of the dolomite-derived particles promotes reactivity with SO2 and other exhaust gas poison molecules. It should be noted that in run 7, the MOC used in combination with a protective bed of co-extruded Al2O3 with 8 wt% acetic acid sol and particles derived from dolomite exhibited significantly better CH4 conversion / oxidation activity stability compared to its nitric acid sol analogue (runs 5 and 6). This may be partly due to the stronger pore-forming ability of the larger acetic acid molecules compared to nitric acid molecules.

[0088] In addition to testing the protective bed formulation disclosed herein at 425°C, the ability of the protective bed formulation to remove MOC toxins from exhaust gas at higher temperatures (e.g., 470°C) was also tested. Figure 10 This is Figure 146, showing the percentage of methane conversion as a function of operating time (hours) at 470°C for different guard bed materials placed in front of the MOC. Similar to the reference above. Figure 8For the samples described, each reactor on the test bench was loaded with a total of 2 mL of guard bed / MOC. The weight ratio of guard bed powder to MOC powder loaded in each corresponding reactor was approximately 1.9:1. Inert SiC was used to dilute the guard bed powder and MOC powder to a volume of 1 mL for each powder. Table 3 below lists the guard bed formulations used for each corresponding run. The operating conditions were as follows: GSHV = 100,000 h -1 And RxT = 470℃. The exhaust gas feed composition is as follows: 2000ppm CH4, 350ppm CO, 4.5% CO2, 10.5% O2, 150ppm NO, 12 vol% H2O, and the balance N2. The MOC used is a MOC catalyst coated on a ZrO2 substrate with a repair substrate of 4 wt% Pd, 0.5 wt% Pt, and 0.125 wt% Rh. 1.5ppm SO2 was added to the exhaust gas feed after 25 hours of operation and maintained throughout the test duration.

[0089] Table 3. Protective bed operation of reactor test bench at 470℃ 8-11

[0090]

[0091] like Figure 9 As shown in Data 148, all samples achieved approximately 99%–100% CH4 conversion before the addition of SO2. However, after 25 hours of operation, the CH4 conversion / oxidation activity of the control MOC sample (run 8) without a guard bed rapidly decreased. Conversely, test runs (runs 9–11) with the disclosed guard bed component located in front of the MOC bed enabled the MOC to maintain the desired CH4 conversion / oxidation activity for more than 10 hours after the addition of SO2. Similar to… Figure 8 Data 142, and data 148, of samples containing both high-porosity Al2O3 powder and low-porosity dolomite-derived powder, showed improved CH4 conversion / oxidation activity of the MOC. However, unexpectedly, at a higher operating temperature of 470°C, the 8 wt% Mn / nitric acid sol-extruded Al2O3 and dolomite guard bed (run 11) exhibited significantly higher CH4 conversion / oxidation activity compared to the control MOC sample and other guard bed formulations. Therefore, Figures 5 to 9 The performance data shown clearly demonstrate the substantial benefits and performance advantages of the protective bed formulation disclosed herein for effectively removing SO2 and other MOC poisons from exhaust gases produced by natural gas-fueled engines.

[0092] This technology also includes methods for reducing methane emissions in exhaust gases produced in engine systems operating on natural gas. Figure 10This is a flowchart of an embodiment of method 200, by which an exhaust gas reduction system (e.g., exhaust gas reduction system 14 described above) can treat exhaust gas (e.g., exhaust gas 28) containing methane and a methane oxidation catalyst (MOC) poison. Method 200 includes feeding (box 204) the exhaust gas (e.g., exhaust gas 28) containing CH4 and a catalyst poison into an exhaust gas reduction system (e.g., exhaust gas reduction system 14) having guard beds (e.g., guard beds 36, 50, 96), as referenced above. Figures 1 to 4 Method 200 further includes passing the exhaust gas through a protective bed (e.g., protective beds 36, 50, 96) (box 206). As described above, the protective bed may have a single or multiple MOC poison-capturing components. Additionally, the MOC poison-capturing components may be single-component or multi-component materials having transition metal oxides supported on an Al2O3 carrier material, a carrier material derived from dolomite, or both.

[0093] Method 200 also includes removing catalyst poisons from the exhaust gas (box 208) to produce an intermediate exhaust gas (e.g., intermediate exhaust gas 42). For example, as described above, a protective bed containing transition metal oxides as well as Al2O3 and materials derived from dolomite can react, transform, adsorb, and capture catalyst poisons, preventing them from passing through the protective bed and adversely affecting the performance and catalyst lifetime of the MOC. The intermediate exhaust gas leaving the protective bed is substantially free of catalyst poisons that could adversely affect the catalytic performance / activity and overall lifetime of the MOC.

[0094] Method 200 further includes passing the intermediate waste gas through (box 210) a bed of MOC (e.g., MOC bed 40) and oxidizing and reducing (box 212) the methane in the intermediate waste gas to produce a treated waste gas (e.g., treated waste gas 50) with less than about 150 ppmv-200 ppmv of methane. By removing catalyst poisons upstream of the MOC bed, the guard bed of this disclosure allows the MOC to fully exert its methane oxidation activity. That is, the MOC can efficiently and effectively convert more than about 80% of the methane in the intermediate waste gas. Therefore, the guard bed / MOC system disclosed herein results in the treated waste gas released from the system having methane emission levels at or below the desired or regulated emission levels.

[0095] As described above, certain embodiments of the systems and methods disclosed herein may include a catalyst poison capture guard bed located upstream of a methane oxidation catalyst (MOC) bed. This guard bed comprises one or more components that react, transform, adsorb, and thereby remove and / or capture catalyst poisons such as sulfur dioxide (SO2), phosphorus (P), zinc (Zn), calcium (Ca), silicon (Si), etc., which would otherwise poison the MOC in a methane reduction unit and adversely affect its performance. The guard bed may comprise a single layer or multiple layers having a single MOC poison capture component or multiple MOC poison capture components arranged in a continuous or mixed configuration. The MOC poison capture component in the guard bed may include transition metals (in oxide form), alumina (Al2O3), materials derived from dolomite, or both. By employing the exhaust gas reduction system of this disclosure, methane present in the exhaust gas generated in a lean-burn natural gas engine can be removed efficiently and effectively via a methane oxidation catalyst. Therefore, exhaust gas released from a natural gas engine equipped with an exhaust gas emission reduction system having the methane emission reduction device disclosed herein may have methane emission levels at or below the desired or regulated emission levels.

[0096] This disclosure may be embodied in other specific forms without departing from its substance or essential characteristics. The described embodiments should be considered in all respects as illustrative rather than restrictive. Therefore, the scope of this disclosure is indicated by the appended claims rather than by the foregoing description. All changes falling within the equivalent meaning and scope of the claims are to be included within the scope of the claims.

Claims

1. A system for removing a methane oxidation catalyst (MOC) poison from an off-gas, the system comprising: a methane abatement device configured to receive the off-gas comprising methane (CH4) and the MOC poison, wherein the methane abatement device comprises: a guard bed configured to remove the MOC poison from the off-gas and produce an intermediate off-gas comprising the CH4 and free of the MOC poison, wherein the guard bed comprises a MOC poison capture component comprising a first transition metal oxide, an alumina (AI2O3) support material, and a dolomite-derived support material, and wherein the MOC poison capture component is a co-extrudate of the first transition metal oxide, the AI2O3 support material, and the dolomite-derived support material, such that the MOC poison capture component is a single component; and a MOC bed fluidically connected to and downstream of the guard bed, wherein the MOC bed comprises a MOC and is configured to remove CH4 from the intermediate off-gas to produce a treated off-gas having less than 200 parts per million by volume (ppmv) CH4.

2. The system of claim 1, wherein the guard bed is a single bed.

3. The system of claim 1, wherein the first transition metal oxide in the MOC poison capture component is at a concentration of 3 wt% to 20 wt%.

4. The system of claim 1, wherein the dolomite-derived support material is a mixture of dolomite (CaMg(C03)2), calcium magnesium oxide (CaMg02), quicklime (CaO), and MgO, or combinations thereof.

5. The system of claim 1, wherein the first transition metal oxide is an oxide of manganese (Mn), vanadium (V), copper (Cu), and combinations thereof.

6. A method for removing a methane oxidation catalyst (MOC) poison from an off-gas, the method comprising: feeding the off-gas comprising methane (CH4) and the MOC poison to a methane abatement device comprising a guard bed and a MOC bed fluidically connected to and downstream of the guard bed; contacting the off-gas with a MOC poison capture component disposed within the guard bed, wherein the MOC poison capture component comprises a first transition metal oxide, an alumina (AI2O3) support material, and a dolomite-derived support material, and wherein the MOC poison capture component is a co-extrudate of the first transition metal oxide, the AI2O3 support material, and the dolomite-derived support material, such that the MOC poison capture component is a single component; and removing the MOC poison from the off-gas to produce an intermediate off-gas free of MOC poison and comprising CH4.

7. The method of claim 6, wherein the step of "contacting the off-gas with a MOC poison capture component disposed within the guard bed" comprises passing the off-gas through a single bed of the MOC poison capture component.

8. The method of claim 6, comprising feeding the intermediate off-gas to the MOC bed having MOC and removing the CH4 from the intermediate off-gas to produce a treated off-gas having less than 200 parts per million by volume (ppmv) of CH4.

9. A methane oxidation catalyst (MOC) poison capture component for removing MOC poisons from off-gas, the MOC poison capture component comprising: an alumina (AI2O3) support material having a first porosity; a dolomite-derived support material having a second porosity that is less than the first porosity; a first transition metal oxide, wherein the first transition metal oxide is at a concentration of 1 weight percent to 25 weight percent (wt%), and wherein the MOC poison capture component is a co-extrudate of the first transition metal oxide, the AI2O3 support material, and the dolomite-derived support material, such that the MOC poison capture component is a single component; and wherein the MOC poison capture component removes sulfur dioxide (SO2), phosphorous (P), calcium (Ca), zinc (Zn), silicon (Si), and ash.

10. The MOC poison capture component of claim 9, wherein the dolomite-derived support material is a mixture of dolomite (CaMg(CO3)2), calcium magnesium oxide (CaMgO2), quicklime (CaO), and MgO, or combinations thereof.

11. The MOC poison capture component of claim 9, wherein the transition metal oxide is an oxide of manganese (Mn), vanadium (V), copper (Cu), and combinations thereof.

12. The MOC poison capture component of claim 9, wherein the first porosity is greater than 2.0 milliliters (mL) per gram (g).

13. The MOC poison capture component of claim 9, wherein the second porosity is less than 0.2 mL / g.

14. A system for removing methane oxidation catalyst (MOC) poisons from off-gas, the system comprising: a methane abatement device configured to receive the off-gas comprising methane (CH4) and the MOC poisons, wherein the methane abatement device comprises: a guard bed configured to remove the MOC poisons from the off-gas and produce an intermediate off-gas comprising the CH4 and free of the MOC poisons, wherein the guard bed comprises a MOC poison capture component comprising a first layer and a second layer, the first layer comprising a first transition metal oxide and an alumina (AI2O3) support material, the second layer comprising a second transition metal oxide and a dolomite-derived support material, and wherein the second transition metal is the same or different than the first transition metal; and a MOC bed in fluid connection with the guard bed and downstream of the guard bed, wherein the MOC bed comprises a MOC and is configured to remove CH4 from the intermediate off-gas to produce a treated off-gas having less than 200 parts per million by volume (ppmv) of CH4.

15. The system of claim 14, wherein the guard bed is a single bed.

16. The system of claim 14, wherein the first transition metal oxide in the MOC poisons capture component is at a concentration of 3 wt% to 20 wt%.

17. The system of claim 14, wherein the dolomite-derived support material is a mixture of dolomite (CaMg(C03)2), calcium magnesium oxide (CaMg02), quicklime (CaO), and MgO, or combinations thereof.

18. The system of claim 14, wherein the first transition metal oxide is an oxide of manganese (Mn), vanadium (V), copper (Cu), and combinations thereof.

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