Patent Application
20150166913
Embodiments of the invention relate to catalytic reforming of a mixture of a methane-containing fuel and internal combustion engine exhaust gas. In particular, embodiments of the invention relate to catalytic reforming of such engine exhaust gas recycle that contains an amount of methane and higher molecular weight organics sufficient to sustain the formation of H2 and CO (and/or CO2) in the reformer.
Conventional internal combustion engine designs can typically include a single fuel for combustion within the engine cylinders. This can require careful selection of an appropriate fuel, so that the fuel has appropriate combustion properties, such as a suitable Research Octane Number or a suitable flame speed. This can limit the selection of fuels, as some compositions that may be suitable from an energy content standpoint can lack appropriate combustion properties.
In addition to naphtha boiling range (gasoline) and distillate boiling range (kerosene or diesel) fuels, some alternative types of fuels are available for use in internal combustion engines. For example, an engine can be configured for use with natural gas as a fuel.
In one aspect, a method for reforming a fuel in an internal combustion engine is provided, said method including: (a) providing an exhaust gas-containing mixture to an exhaust gas recycle reformer, the exhaust gas recycle reformer comprising a reformer inlet, a reformer outlet, and a hydrocarbon-reforming catalyst composition, the exhaust gas-containing mixture comprising engine exhaust gas and a first hydrocarbon-containing fuel, the hydrocarbon-containing fuel comprising at least about 50 mol % methane, and (b) converting under reforming conditions at least a portion of the exhaust gas-containing mixture in the presence of a hydrocarbon-reforming catalyst composition comprising at least about 0.1 wt % of a hydrocarbon-reforming metal catalyst supported on a mixed metal oxide support, the mixed metal oxide support comprising at least about 20 wt % of a mixture of lanthanum oxide and aluminum oxide and at least about 10 wt % of a mixture of cerium oxide and zirconium oxide, the aluminum oxide optionally being γ-aluminum oxide. Optionally, the mixed metal oxide support can consist essentially of the mixture of lanthanum oxide and aluminum oxide and the mixture of cerium oxide and zirconium oxide.
In another aspect, a method for reforming a fuel in an internal combustion engine is provided, said method including: (a) providing an exhaust gas-containing mixture to an exhaust gas recycle reformer comprising a reformer inlet, a reformer outlet, and a hydrocarbon-reforming catalyst composition, the exhaust gas-containing mixture comprising engine exhaust gas and a first hydrocarbon-containing fuel, the hydrocarbon-containing fuel comprising at least about 50 mol % methane and a weighted carbon mole percentage of carbons in C2+ compounds of at least about 5%, and (b) converting under reforming conditions at least a portion of the exhaust gas-containing mixture in the presence of the hydrocarbon-reforming catalyst composition, the reforming conditions including a reformer outlet temperature of about 435° C. to about 500° C. Optionally, the reformer inlet temperature can be about 525° C. to about 650° C., or about 535° C. to about 625° C., or about 550° C. to about 600° C.
In the following description, all numbers disclosed herein are approximate values, regardless whether the word “about” or “approximate” is used in connection therewith. They may vary by 1%, 2%, 5%, and sometimes, 10 to 20%. Whenever a numerical range with a lower limit, RL and an upper limit, RU, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are expressly disclosed: R=RL+k*(RU−RL), wherein k is a variable ranging from 1% to 100% with a 1% increment, i.e., k can be 1%, 2%, 3%, 4%, 5%, . . . , 50%, 51%, 52%, . . . , 95%, 96%, 97%, 98%, 99%, or 100%. Moreover, any numerical range defined by two R numbers as defined in the above is also expressly disclosed. It is noted that for listings of RL or RU that begin with “about, e.g.,” the presence of about prior to each number is expressly included, but the term about is provided only once in the interest of clarity.
As used herein the terms “substantially free of an oxygen-containing gas” or “does not substantially include providing an oxygen containing gas” mean that an oxygen-containing gas other than the exhaust gas of the internal combustion engine is not purposely provided to the catalytic reforming unit. Additionally or alternatively, these terms can mean that not more than about 0.5 mol % (e.g., not more than about 0.2 mol %, not more than about 0.1 mol %, not more than about 0.05 mol %, or not more than about 0.01 mol %) of the total amount of gas supplied to the reforming unit is an oxygen-containing gas other than the exhaust gas of the internal combustion engine.
Octane ratings described herein generally refer to the Research Octane Number (RON), unless otherwise specified. RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
One potential alternative to traditional naphtha boiling range fuels for internal combustion engines can be to use natural gas. Natural gas can pose some alternative engineering challenges for use in a vehicle, such as storing the natural gas as a compressed gas to allow for additional fuel storage, but the abundant availability of natural gas can make such a trade-off worthwhile.
Methane is typically the primary component of a natural gas feed. The octane rating of methane is 129, but the flame speed of a primarily methane-containing feed can be low. One option for improving the flame speed for the overall fuel can be to reform at least a portion of the feed to make hydrogen. This can provide an at least partially reformed fuel with improved characteristics for operating an engine.
An option for reforming at least a portion of the feed can be to reform at least a portion of the methane in a feed. Steam reforming of methane in the presence of a catalyst can be implemented in a reaction zone within a powertrain in the engine. However, methane steam reforming is a reversible reaction, so achieving a desired level of reforming can be dependent on operating the reforming reaction at a desired temperature, as well as other selected conditions, so that a net amount of desired hydrogen is produced. Such a temperature can be lower than a conventional steam reforming temperature. Thus, using a reforming catalyst that is effective at the desired temperature can also be beneficial.
An alternate strategy for reforming a portion of a natural gas feed can be to focus on reforming the C2+ compounds within the feed, such as C2-C5 compounds or C2-C4 compounds. A typical natural gas feed can include about 3 vol % to about 10 vol % of C2+ compounds, such as ethane and propane. Conversion of such compounds is typically less endothermic than reforming of methane on a per carbon basis. While reforming of methane is reversible, reforming of C2+ compounds is essentially irreversible at temperatures above 400° C. under typical reforming conditions as described in this invention. Therefore, it can be desirable to select conditions that allow for conversion of C2+ compounds while reducing or minimizing the reactivity for methane formation from hydrogen and CO.
In various embodiments, the invention is based in part on discovery of a catalyst composition that can effectively convert an internal combustion engine exhaust stream containing a hydrocarbon-containing fuel to a mixture comprising H2, CO2, CO, H2O, N2, and a relatively large amount of methane, CH4. The methane can correspond to methane present in the hydrocarbon-containing fuel as well as methane formed under the conversion conditions via the methanation reaction. The conversion conditions can be selected to favor reforming of methane, to favor reforming of C2+ compounds with reduced or minimized methanation, or reforming of both methane and C2+ compounds.
A reformer operating in a powertrain environment can be viewed as a reformer operating under adiabatic conditions. During adiabatic operation of a reformer, the converter bed temperature can decrease because of the endothermic nature of the steam reforming reaction. As a result, the temperature across the reformer can decrease between the reformer inlet and the reformer outlet. Since methane reforming is reversible, the conversion of methane to syngas diminishes as the temperature at the converter (reformer) outlet decreases below a critical temperature, because the back reaction of syngas to methane becomes thermodynamically favored. Due in part to this reverse reaction, methane conversion and therefore the extent of heat recovery in the on-board reforming process are thermodynamically limited.
This thermodynamic limitation can be overcome at least in part by stopping the reforming process before the temperature in the converter decreases below a critical value. The critical temperature is a function of the converter inlet temperature and gas composition. In some aspects, for on-board reforming operating conditions, e.g., inlet temperatures of about 500° C. to about 650° C., such as about 600° C. or less, pressures of about 1 barg (˜100 kPag) to about 4 barg (˜400 kPag), and steam/carbon ratios of about 0.3:1, the converter outlet temperature can be limited to at least about 450° C. This can be achieved, for example, by controlling the amount of fuel provided to the reformer, limiting the amount of available catalyst in the reformer, limiting the activity of the reforming catalyst, or a combination thereof. Maintaining a converter outlet temperature of at least about 450° C. can reduce or minimize the amount of conversion of H2 and CO to form methane via the methanation reaction.
The invention further relates to a reforming catalyst that is able to function at lower temperatures and steam/carbon ratios than typically encountered in industrial steam reforming applications. The converter outlet temperature in the on-board methane reformer can be at least about 450° C. and the molecular ratio of steam contained in the EGR to carbon atoms contained in the fuel can be <1. Under these conditions, catalyst coking is known to be a potential issue. This invention can use a modified steam reforming catalyst that reduces or minimizes formation of coke and allows operation in the low temperature regime.
The invention further relates to increasing the fuel efficiency of an internal combustion engine in natural gas vehicles (NGV). The concept can be to selectively reform the C2+ hydrocarbons or other compounds contained in natural gas into syngas using the steam and waste heat contained in the exhaust. In addition to the heat recovery, the efficiency of the combustion process can be enhanced by the formation of H2.
In such aspects, a fuel that includes both methane and C2+ components can be injected into a reformer catalyst inserted into an exhaust gas recirculation (EGR) loop. In the reformer, the fuel can be partially converted into CO and H2 by steam reforming using the heat, water, and CO2 contained in the exhaust. The fuel reforming is described for the example of the reforming reaction with water (steam) in reaction equations 1) for methane reforming, 2) for ethane reforming, and 3) for propane reforming. Ethane and propane make up the main constituents of the C2+ fuel components.
CH4+H2O═CO+3H2 ΔH500° C.=221 kJ/mol fuel ° C. 1)
C2H6+2H2O—>2 CO+5H2 ΔH500° C.=186 kJ/mol fuel ° C. 2)
C3H8+3H2O—>3CO+7H2 ΔH500° C.=177 kJ/mol fuel ° C. 3)
Steam and CO2 reforming of hydrocarbons to syngas is endothermic. The endothermicity per fuel carbon decreases for paraffins with increasing carbon number. Under certain of the conditions of the present invention, e.g., in the temperature range between about 550° C. and about 400° C., and pressure range between about 1 barg (˜100 kPag) to about 5 barg (˜510 kPag) and low H2O/C ratios, the methane reforming is reversible, while reforming of C2+ hydrocarbons (including functionalized hydrocarbons such as alcohols), having lower temperature equilibrium limits, can continue to reform as temperature drops in an adiabatic operation beyond the point that methane would be reformed. Consequently the fuel conversion in the C1/C2+ combined reforming process could be potentially higher than it would be for methane fuel itself under kinetic limitation conditions.
This invention, in one embodiment, relates to identifying a suitable catalyst and process conditions that allow for conversion of C2+ hydrocarbons in a fuel (such as a natural gas feed) into syngas while reducing or minimizing the back reaction of syngas to methane. It has been unexpectedly determined that selective conversion of C2+ compounds can be performed if the conversion of C2+ compounds is conducted at a temperature where the reaction of syngas to methane is kinetically limited. This can allow reforming of C2+ compounds to be performed at the higher temperatures near the front of a reactor in an adiabatic operation while reducing or minimizing the amount of conversion of H2 and CO to methane (i.e., the methanation reaction) that would form as the temperature drops at the tail end of the reactor.
In a fuel reforming process for selective reforming of C2+ compounds, the converter inlet temperatures can be between about 500° C. to 650° C. while the outlet can be below about 500° C., such as about 400° C. to about 500° C., or about 400° C. to about 475° C., or about 400° C. to about 450° C. Additionally or alternately, the molar ratio of water contained in the exhaust gas recycle to carbon contained in the fuel can be <1. Under these conditions catalyst coking is known to be a potential issue. This invention can use a modified steam reforming catalyst that reduces or minimizes formation of coke and allows operation in the low temperature regime in which conversion of C2+ fuel components are thermodynamically favored while methane reforming and/or methanation are kinetically limited. A preferred catalyst can be based on rhodium supported on a mixed metal oxide comprising alumina, lanthana, ceria, and zirconia.
This invention further relates to optimizing the composition of a natural gas feed as transportation fuel. In order to take advantage of the C2+ reforming it could be beneficial to set the specification of the natural gas composition to contain a minimum amount of C2+ content. In regions with dry natural gas resources, the C2+ content may be elevated by blending liquefied propane gas, ethanol, or other C2+ molecules with natural gas to obtain a fuel that meets a desired compositional specification.
In some embodiments, the fuel used for a combustion engine can be a fuel containing at least about 50 mol % of methane, such as a fuel based on a natural gas feed (optionally modified by addition of other fuel sources containing additional C2+ compounds). In such aspects, the reformer can be operated to reform methane, or the reformer can be operated to selectively reform the C2+ compounds in the fuel.
In some embodiments, the reforming of methane can be performed in the presence of a reduced or minimized amount of water. During conventional reforming of methane, the ratio of the amount of water in the reaction environment to the number of carbon atoms in the feed for reforming can be at least about 3:1. It has been determined that by performing the reforming in the presence of a suitable catalyst, the ratio of water to carbon atoms in the feed can be from about 0.3:1 to about 1.0:1, or about 0.5:1 to about 1.0:1, or about 0.3:1 to about 0.9:1. Operating the reforming with a reduced amount of water can be beneficial, as this amount of water can be provided by an exhaust gas recycle stream.
In various embodiments, a hydrocarbon-containing fuel can be a fuel that contains at least about 50 mol % methane, or at least about 70 mol %, or at least about 80 mol %, or at least about 90 mol %. Natural gas is an example of a potential hydrocarbon-containing fuel that contains substantial amounts of methane. The hydrocarbon-methane containing fuel can also contain C2-C5 compounds, such as alkanes and/or functionalized hydrocarbons such as alcohols. The alkanes can include n-alkanes (ethane, propane, butane) and/or branched alkanes. Similarly, the alcohols or other functionalized hydrocarbons can include linear and/or branched compounds. In addition (or alternatively) to alcohols, other examples of functional groups in the functionalized hydrocarbons can include alkenes, ketones, aldehydes, carboxylic acids, alkynes, glycols, ethers, esters, and combinations thereof. A typical natural gas feed may contain only a few mole percent of C2-C5 alkanes (or more generally a few mole percent of C2-C5 compounds). For example, the total amount of C2+ alkanes and/or C2+ compounds in a natural gas feed can be about 0.5 mol % to about 10 mol % of the feed. In some embodiments, such as where C2-C5 alkanes and/or C2-C5 compounds are selectively reformed, it can be beneficial to use a fuel containing at least a minimum amount of C2+ alkanes and/or C2+ compounds, or alternatively a minimum amount of C2-C5 alkanes and/or C2-C5 compounds, or alternatively a minimum amount of C2-C4 alkanes and/or C2-C4 compounds. In such embodiments, the lower limit on the amount of C2+ alkanes and/or C2+ compounds can be at least about 5 mol % of the fuel, or at least about 6 mol %, or at least about 7 mol %, or at least about 8 mol % or at least about 9 mol % or at least about 10 mol %, or at least about 15 mol %, or at least about 20 mol %, or at least about 25 mol %, while the upper limit can be about 50 mol % or less, or about 40 mol % or less, or about 30 mol % or less, or about 25 mol % or less, or about 20 mol % or less, or about 15 mol % or less, or about 10 mol % or less. It is noted that each of the lower limits and upper limits recited above for the amount of C2+ alkanes and/or C2+ compounds in a fuel are expressly contemplated in conjunction with each other.
Additionally or alternatively, the lower limit on the amount of C2-C5 alkanes and/or C2-C5 compounds can be at least about 5 mol % of the fuel, or at least about 6 mol %, or at least about 7 mol %, or at least about 8 mol % or at least about 9 mol % or at least about 10 mol %, or at least about 15 mol %, or at least about 20 mol %, or at least about 25 mol %, while the upper limit can be about 50 mol % or less, or about 40 mol % or less, or about 30 mol % or less, or about 25 mol % or less, or about 20 mol % or less, or about 15 mol % or less, or about 10 mol % or less. It is noted that each of the lower limits and upper limits recited above for the amount of C2-C5 alkanes and/or C2-C5 compounds in a fuel are expressly contemplated in conjunction with each other.
Further additionally or alternatively, the lower limit on the amount of C2-C4 alkanes and/or C2-C4 compounds can be at least about 1 mol % of the fuel, or at least about 3 mol %, or at least about 5 mol %, or at least about 6 mol %, or at least about 7 mol %, or at least about 8 mol % or at least about 9 mol % or at least about 10 mol %, or at least about 15 mol %, or at least about 20 mol %, or at least about 25 mol %, while the upper limit can be about 50 mol % or less, or about 40 mol % or less, or about 30 mol % or less, or about 25 mol % or less, or about 20 mol % or less, or about 15 mol % or less, or about 10 mol % or less. It is noted that each of the lower limits and upper limits recited above for the amount of C2-C4 alkanes and/or C2-C4 compounds in a fuel are expressly contemplated in conjunction with each other.
Still further additionally or alternatively, the amount of C2+ compounds in a fuel, such as the amount of C2-C5 alkanes and/or C2-C5 compounds, can be described using a weighted average based on the relative amounts of carbon that are present in the fuel. In a fuel, an alkane containing 2 carbons such as ethane can be reformed to generate a larger number of hydrogens than a 1 carbon compound (methane). Similarly, compounds containing still larger numbers of carbon atoms can generally be reformed to generate larger amounts of hydrogen. As a result, the amount of reformable C2+ fuel in a fuel containing 1 mol % of ethane is not as large as the amount of reformable C2+ fuel in a fuel that contains 1 mol % of butane. One option for characterizing this can be to describe the mole percentage of carbon atoms in a fuel that are present in C2+ compounds (or alternatively in C2-C5 compounds or in C2-C5 alkanes) relative to the total number of carbon atoms in the fuel. As an example, a fuel containing ˜90 mol % CH4 and ˜10 mol % C2H6 will have a weighted carbon mole percentage of ˜81% carbons in CH4 and ˜19% carbons in C2H6. Based on weighted carbon mole percentage, the number of carbons present in a fuel as C2+ compounds (or alternatively in C2-C5 compounds or in C2-C5 alkanes) can be a weighted carbon mole percentage corresponding to a lower limit of at least about 5%, or at least about 6%, or at least about 7%, or at least about 8% or at least about 9% or at least about 10%, or at least about 15%, or at least about 20%, or at least about 25%, while the upper limit can be about 50% or less, or about 40% or less, or about 30% or less, or about 25% or less, or about 20% or less, or about 15% or less, or about 10% or less. It is noted that each of the lower limits and upper limits recited above for the weighted carbon mole percentage of carbon atoms in C2+ compounds and/or C2-C5 alkanes and/or C2-C5 compounds in a fuel are expressly contemplated in conjunction with each other.
In order to generate a fuel containing a desired amount of C2+ alkanes and/or C2+ compounds, a natural gas feed can optionally be combined with another source of C2+ alkanes and/or C2+ compounds prior to entering the reformer or within a reformer. Examples of other sources of C2+ alkanes and/or C2+ compounds include (but are not limited to) liquefied petroleum gas, liquefied propane, and alcohols such as methanol and/or ethanol.
If selective reforming of C2+ compounds is desired, the inlet and outlet temperatures of the reformer can be controlled to allow for improved reforming of C2+ compounds while reducing or minimizing the amount of methanation (e.g., the reverse of methane reforming). This can be achieved in part by using a lower outlet temperature for the reformer. Conventionally, a lower outlet temperature for a reformer can pose difficulties, as the thermodynamic equilibrium for methane reforming versus methane formation tends to favor methane formation at lower temperatures. However, these reactions are also kinetically limited at lower temperatures, while substantially complete reforming of C2+ compounds can be achieved. This can allow for reforming of the C2+ compounds without reaching the equilibrium value for the methane reforming/conversion reaction. In aspects where selective reforming of C2+ compounds is desired, the outlet temperature of the reformer can be at least about 435° C., or at least about 450° C., or at least about 465° C., or at least about 475° C. The inlet temperature can additionally or alternately be about 650° C. or less, or about 600° C. or less, or about 585° C. or less, or about 575° C. or less, or about 560° C. or less, or about 550° C. or less. Maintaining a desired temperature for the reformer inlet can allow for an effective amount of reforming while still maintaining a desired reformer outlet temperature under adiabatic operation.
If selective reforming of C2+ compounds is desired, both the fuel and the reformer temperatures can be controlled to allow for improved reforming while reducing or minimizing the amount of methanation. It is noted that selective reforming of C2+ compounds can still correspond to reforming more methane than C2+ compounds, since the overall fuel contains at least about 50 mol % methane. For example, selective reforming of C2+ compounds can correspond to having at least 15% of the carbons converted (reformed) in the reformer correspond to carbons from C2+ compounds, or at least about 20%, or at least about 22%, or at least about 25%, or at least about 27%. Of course, the percentage of carbon atoms corresponding to C2+ compounds can typically be less than 100% in a real feed containing at least about 50 mol % methane.
For a fuel containing at least about 50 mol % methane, or at least about 70 mol %, or at least about 80 mol %, one option for increasing the percentage C2+ carbons that are converted (reformed) relative to the total number of carbons converted can be to increase the mol % of C2+ compounds. In some aspects, a fuel can contain at least about 5 mol % of an individual C2+ component, such as at least about 5 mol % of C2 compounds, or at least about 5 mol % of C3 compounds, or at least about 5 mol % of C4 compounds, or at least about 5 mol % of ethane, or at least about 5 mol % of ethanol, or at least about 5 mol % of propane and/or a propane isomer, or at least about 5 mol % of butane and/or a butane isomer. Additionally or alternately, a fuel can contain at least about 10 mol % of C2+ compounds, or at least about 12 mol % of C2+ compounds, or at least 15 mol % of C2+ compounds, or at least about 17 mol % of C2+ compounds, or at least 20 mol % of C2+ compounds.
In some cases hydrogen can be added to the natural gas feed supplementing the amount of hydrogen produced by the reforming reactions. After any optional supplementing of the hydrogen content of a fuel, the hydrogen content of the fuel can be about 20 mol % or less, or about 15 mol % or less, or about 10 mol % or less, or about 5 mol % or less, or about 2 mol % or less, or about 1 mol % or less, or about 0.1 mol % or less (meaning the fuel is substantially free of H2). Alternately the H2 content of the feed to the reformer can be increased by forming H2 in a dedicated cylinder from which the EGR is drawn. This can be accomplished by running the cylinder under rich combustion conditions or by feeding fuel into this cylinder during the expansion stroke to form cracked products along with H2 from the C2+ components.
In various embodiments, the catalyst composition can include at least a metal catalyst (or metal-containing catalyst) suitable for reforming of hydrocarbons or hydrocarbon-like compounds. Often the catalyst composition can further include one or more metal oxide components that act as a support for at least a portion of the metal catalyst. The catalyst composition can optionally further include one or more molecular sieves, such as medium pore or large pore molecular sieves with cracking activity. Optionally, at least a portion of the metal catalyst (or metal-containing catalyst) can be supported on the one or more molecular sieves with cracking activity and/or supported on the small pore molecular sieve.
The one or more metal oxide components may be selected from any suitable metal oxide(s). Exemplary metal oxides can include, but are not necessarily limited to, aluminum oxides, silicon oxides, rare-earth metal oxides, Group IV metal oxides (e.g., Al2O3, including θ-Al2O3 and/or γ-Al2O3), SiO2, Y2O3, Sc2O3, La2O3, CeO2, Pr2O3 Sm2O3 Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, TiO2, ZrO2, HfO2, and mixtures thereof. For example, embodiments of a metal oxide mixture suitable for use in the catalyst compositions herein may include from about 1.0 wt % to about 99.0 wt %, based on the total weight of the catalyst composition, of a first metal oxide. The lower limit on the range of first metal oxide content may be about, e.g., 1.0 wt %, 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, or 97.5 wt %. The upper limit on the range of first metal oxide content may be about, e.g., 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, 97.5 wt %, or 99.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 2.5 wt % to about 95.0 wt %, from about 5.0 wt % to about 80.0 wt %, from about 10.0 wt % to about 55.0 wt %, from about 20.0 wt % to about 40.0 wt %, etc. A second metal oxide may optionally be present in an amount from about 1.0 wt % to about 99.0 wt %. The lower limit on the range of second metal oxide content may be about, e.g., 1.0 wt %, 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, or 97.5 wt %. The upper limit on the range of second metal oxide content may be about, e.g., 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, 97.5 wt %, or 99.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 97.5 wt % to about 5.0 wt %, from about 95.0 wt % to about 20.0 wt %, from about 90.0 wt % to about 45.0 wt %, from about 80.0 wt % to about 60.0 wt %, etc.
In particular embodiments, the first metal oxide may itself be a mixture of oxides disclosed herein. For example, in an embodiment, the first metal oxide is a mixture of La2O3 and γ-Al2O3. For a mixture of La2O3 and γ-Al2O3, or more generally for a mixture of La2O3 and Al2O3, the La2O3 can correspond to about 0.4 wt % to about 20 wt % of the combined weight of La2O3 and Al2O3. For example, the La2O3 can correspond to at least about 0.4 wt % of the combined weight of La2O3 and γ-Al2O3, or at least about 1.0 wt %, or at least about 2.0 wt %, or at least about 5.0 wt %, or at least about 10.0 wt %, and/or about 20.0 wt % or less, or about 15.0 wt % or less, or about 10.0 wt % or less, or about 5.0 wt % or less, or about 2.0 wt % or less. It is noted that all combinations for the upper and lower limit of the amount of La2O3 relative to the combined amount of La2O3 and Al2O3 are expressly contemplated herein. The amount of the La2O3 and γ-Al2O3 together may be, for example, from about 20.0 wt % to about 90.0 wt %, such as from about 30.0 wt % to about 50.0 wt % or from about 32.5 wt % to about 37.5 wt %, based on the total weight of the catalyst composition. Optionally, in such embodiments, the second metal oxide may itself also be a mixture of oxides disclosed herein. For example, the second metal oxide may comprise CeO2 and ZrO2. The amount of the CeO2 and ZrO2 together may be, for example, from about 10.0 wt % to about 80.0 wt %, such as from about 15.0 wt % to about 70.0 wt % or from about 20.0 wt % to about 65.0 wt %, or from about 30.0 wt % to about 60.0 wt %, or from about 40.0 wt % to about 80.0 wt %, based on the total weight of the catalyst composition. The Ce:Zr atomic ratio may be about, e.g., 10:0.5, 7.5:0.5, 5.0:1.0, 4.0:1.0, 3.0:1.0, 2.0:1.0, 1.0:1.0, or the like, or anywhere therewithin.
The at least one metal or metal-containing hydrocarbon reforming catalyst may be selected from the group consisting of Co, Ru, Rh, Pt, Pd, Fe, Ni, Ir, Zn, Re, and mixtures thereof. In some optional but preferred embodiments, the hydrocarbon reforming catalyst can be Rh or a mixture of metal/metal-containing catalysts that includes Rh. It will be understood that reference to the presence of such metals envisions their presence in elemental/and or compound form. Thus, amounts of such compounds refer to the total amount of metal, in the form or metal or in compound form, based on the total weight of the catalyst composition. The amount of metal-containing hydrocarbon reforming catalyst may range from about 1.0 wt % to about 50 wt %. The lower limit on the range of hydrocarbon reforming catalyst may be about, e.g., 1.0 wt %, 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, or 50.0 wt %. The upper limit on the range of metal-containing hydrocarbon reforming catalyst content may be about, e.g., 1.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 1.0 wt % to about 20.0 wt %, from about 2.5 wt % to about 17.5 wt %, from about 5.0 wt % to about 15.0 wt %, from about 7.5 wt % to about 10.0 wt %, from about 1.0 wt % to about 10.0 wt %, from about 2.0 wt % to about 9.5 wt %, from about 2.5 wt % to about 9.0 wt %, from about 3.0 wt % to about 8.0 wt %, from about 4.0 wt % to about 7.7 wt %, etc., based on the total weight of the catalyst composition.
Exemplary embodiments of suitable hydrocarbon reforming catalysts of the catalyst compositions herein may include two or more such hydrocarbon reforming catalysts. For example, the catalyst composition may include a non-zero amount up to 20 wt %, based on the total weight of the catalyst composition, of a first hydrocarbon reforming catalyst. The lower limit on the range of first hydrocarbon reforming catalyst content may be about, e.g., 0.25 wt %, 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. The upper limit on the range of first hydrocarbon reforming catalyst content may be about, e.g., 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 0.5 wt % to about 15.0 wt %, from about 1.0 wt % to about 10.0 wt %, from about 2.0 wt % to about 7.5 wt %, from about 2.5 wt % to about 5.0 wt %, etc. A second hydrocarbon reforming catalyst also may be present in an amount of >0 to about 20.0 wt %, based on the total weight of the catalyst composition. The lower limit on the range of second hydrocarbon reforming catalyst content may be about, e.g., 0.25 wt %, 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. The upper limit on the range of second hydrocarbon reforming catalyst content may be about, e.g., 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 0.5 wt % to about 15.0 wt %, from about 1.0 wt % to about 10.0 wt %, from about 2.0 wt % to about 7.5 wt %, from about 2.5 wt % to about 5.0 wt %, from about 0.75 wt % to about 2.0 wt %, etc. In exemplary hydrocarbon reforming catalysts, the first hydrocarbon reforming catalyst can include or be Rh and the second hydrocarbon reforming catalyst can include or be Pt, e.g., such that the hydrocarbon reforming catalyst comprises from about 1.0 wt % to about 6.0 wt % Rh, from about 1.5 wt % to about 5.0 wt %, from about 2.0 wt % to about 4.5 wt %, from about 2.5 wt % to about 4.0 wt % Rh and from about 0.5 wt % to about 5.0 wt % Pt, from about 0.75 wt % to about 3.0 wt %, or from about 1.0 to about 2.0 wt % Pt, based on the total weight of the catalyst composition.
In some embodiments, the catalyst composition comprising the support (e.g., metal oxide(s)) and hydrocarbon reforming catalyst(s), and optionally any molecular sieves, can comprise >˜80.0 wt % (e.g., >˜82.5 wt %, >˜85.0 wt %, >˜87.5 wt %, >˜90.0 wt %, >˜92.5 wt %, >˜95.0 wt %, from about 82.5 wt % to about 100.0 wt %, from about 85.0 wt % to about 99.0 wt %, from about 87.5 wt % to about 95.0 wt %) of particles having a size of 20-100 mesh (U.S.) (e.g., 25-90 mesh, 30-85 mesh, or 35-80 mesh). A more particular description for indicating particle size distribution using mesh size can be to use + and − designations. A “+” before the sieve mesh indicates the particles are retained by the sieve, while a “−” before the sieve mesh indicates the particles pass through the sieve. This means that typically ˜90% or more (e.g., ˜95% or more, ˜96% or more, ˜97% or more, ˜98% or more, ˜99% or more, ˜99.5% or more, or ˜99.9% or more) of the particles will have mesh sizes between the two values. For instance, if the particle size of a material is described as −80/+170, then ˜90% or more of the material will pass through an 80 mesh sieve and be retained by a 170 mesh sieve. Thus, in some embodiments, the catalyst composition may have a particle size distribution of −20/+100 mesh, e.g., −25/+90 mesh, −30/+85 mesh, or −35/+80 mesh. It should be noted that the particle size range specified above pertains to the particular test reactor that was utilized for some of the catalytic test of catalysts described herein. The preferred particle size range can change for different reactors and/or converter embodiments used in a vehicle application.
An additional or alternative optional way of describing particle size distribution refers to respective percentiles of log normal particle size distribution determined by means of a Malvern™ particle size analyzer using a hexane diluent. Thus, particles having a D50 of, for example, 0.5 mm have a median particle size of ˜0.5 mm. A D90 of 0.5 mm indicates that ˜90% of the particles have a particle size of less than ˜0.5 mm, and a D10 of 0.5 mm indicates that ˜10% of the particles have a particle size of less than ˜0.5 mm. The width or narrowness of a particle size distribution can be given by its span. The span is defined as (D90−D10)/(D50) and is therefore dimensionless. In some embodiments, the catalyst composition may be characterized as having a D50 from ˜0.15 mm to ˜1.0 mm (e.g., from ˜0.85 mm to 0. ˜16 mm, from ˜0.60 mm to ˜0.17 mm, or from ˜0.50 mm to ˜0.20 mm) and/or as having a span from about ˜0.5 to about ˜10, e.g., from ˜1.0 to ˜6.0, from ˜2.0 to ˜5.0, or from ˜3.0 to ˜4.0.
In certain embodiments, reforming and/or cracking catalysts as described herein can be provided in a reformer (or other reaction environment) in the form of a washcoated monolithic converter. This type of catalyst embodiment for providing a supported catalyst is commonly used for automotive converters. In such an embodiment, the catalyst composition can deposited on or otherwise supported on a flow through substrate with parallel or tortuous channels. The reactive gases can enter a plurality of channels at the front end of the converter and exit the same channels at the rear end of the converter. In another embodiment used, for example, for particulate filtration on diesel engines, half of the channels of the monolith can be plugged on the inlet side of the monolith and the alternate half of the channels can be plugged on the outlet side of the substrate. In this so-called wall flow substrate, the exhaust enters the portion of the channel system that is open on the inlet side. At least a portion of the exhaust then passes through the walls of the porous substrate and exits the substrate through the other half of the channel system. The monolith substrate can be made of, for example, ceramic or metal. Ceramic substrate materials include cordierite, SiC, alumina, titania and other oxides or mixtures of oxides. The catalyst is typically supported on the substrate in the form of a washcoat. An example of the preparation and application washcoats for monolithic catalysts is described in the literature “Catalytic Air Pollution” by Ronald M. Heck and Robert J. Farrauto published by Van Nostrand Reinhold, 1995. The preparation of a monolith substrate typically includes the preparation of a slurry containing the catalyst powder and typically a binder material suspended in a liquid phase. The catalyst containing slurry can then be washcoated onto the substrate. The washcoated substrate can then be subsequently dried and calcined in air or annealed in specified gas environments.
In some embodiments, the catalyst composition can further include one or more molecular sieves, such as one or more zeolites that provide cracking activity for conversion of the C2+ components in the feed. Any convenient molecular sieve with cracking activity can be used. For example, a molecular sieve with cracking activity such as ZSM-5 can be beneficial in some catalyst compositions. Other suitable molecular sieves can include medium pore and/or large pore molecular sieves. In some alternative aspects, instead of including a aluminosilicate type molecular sieve to provide cracking activity, a silicoaluminophosphate molecular sieve or an aluminophosphate molecular sieve can be included in the catalyst composition.
For molecular sieve(s) with cracking activity, the molecular sieve(s) can correspond to from about 1.0 wt % to about 99.75 wt %, based on the total weight of the catalyst composition. The lower limit on the range of the one or more molecular sieves added to the catalyst composition may be about, e.g., 1.0 wt %, 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, or 97.5 wt %. The upper limit on the range of the one or more molecular sieves added to the catalyst composition may be about, e.g., 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, 97.5 wt %, or 99.0 wt %, or 99.5 wt %, or 99.75 wt %. Combinations of such lower and upper limits may be selected and are expressly considered herein, e.g., from about 2.5 wt % to about 95.0 wt %, from about 5.0 wt % to about 80.0 wt %, from about 10.0 wt % to about 55.0 wt %, from about 20.0 wt % to about 40.0 wt %, etc.
In some embodiments, the one or more molecular sieve(s) can correspond to at least one medium pore aluminosilicate zeolite having a Constraint Index of 1-12 (as defined in U.S. Pat. No. 4,016,218). Suitable zeolites include zeolites having an MFI or MEL framework, such as ZSM-5 or ZSM-11. ZSM-5 is described in detail in U.S. Pat. Nos. 3,702,886 and RE 29,948. ZSM-11 is described in detail in U.S. Pat. No. 3,709,979. Preferably, the zeolite is ZSM-5. Another suitable zeolite can be MCM-68, which is described in detail in U.S. Published Patent Application 2014/0140921. Other useful medium pore molecular sieves can include ZSM-12 (U.S. Pat. No. 3,832,449); ZSM-22 (U.S. Pat. No. 4,556,477); ZSM-23 (U.S. Pat. No. 4,076,842); ZSM-34 (U.S. Pat. No. 4,086,186) ZSM-35 (U.S. Pat. No. 4,016,245); ZSM-48 (U.S. Pat. No. 4,397,827); and ZSM-57 (U.S. Pat. No. 4,873,067). Non-limiting examples of SAPO and AlPO molecular sieves include one or a combination of SAPO-11, SAPO-31, SAPO-41, AlPO-11, AlPO-31, AlPO-41 and PST-6. The molecular sieve(s) can also be at least one large pore aluminosilicate, aluminophosphate, or silicoaluminophosphate zeolite containing 12-ring pores. Suitable large pore molecular sieves can include those having AFI, AFS, ATO, ATS, *BEA, BEC, BOG, BPH, CAN, CON, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, -*ITN, IWR, IWW, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, OFF, OKO, OSI, SAF, SAO, SEW, SFE, SFO, SSF, SSY, and USI frameworks, as well as combinations thereof.
Another additional or alternative option for characterizing a zeolite (or other molecular sieve) is based on the nature of the ring channels in the zeolite. The ring channels in a zeolite can be defined based on the number of tetrahedral framework atoms included in the ring structure that forms the channel. In some embodiments, a zeolite can include at least one ring channel based on a 10-member ring. In such embodiments, the zeolite preferably does not have any ring channels based on a ring larger than a 10-member ring. Examples of suitable framework structures having a 10-member ring channel but not having a larger size ring channel can include EUO, FER, HEU, IFW, ITH, IMF, LAU, MEL, MFI, MFS, MTT, MVY, MWW, NES, PCR, PON, RRO, SFF, SFG, *SFV, STF, -SVR, STI, SZR, TON, TUN, and MRE, as well as combinations thereof.
Generally, a zeolite having the desired activity can have a silicon to aluminum molar ratio of about 2 to about 300, such as about 5 to about 100 or about 20 to about 40. For example, the silicon to aluminum ratio can be at least about 2, such as at least about 5, or at least about 10, or at least about 40, or at least about 50, or at least about 60. Additionally or alternately, the silicon to aluminum ratio can be about 300 or less, such as about 200 or less, or about 100 or less, or about 80 or less, or about 60 or less, or about 50 or less.
Additionally or alternately, the one or more molecular sieves in the catalyst composition can also include and/or be enhanced by a transition metal. The transition metal can be incorporated into the zeolite by any convenient method, such as by impregnation or by ion exchange. If the transition metal is added to the molecular sieve(s) prior to incorporating the molecular sieve(s) into the catalyst composition, the amount of transition metal can be expressed as a weight percentage of the one or more molecular sieves, such as having at least about 0.1 wt % of transition metal, or at least about 0.25 wt %, or at least about 0.5 wt %, or at least about 0.75 wt %, or at least about 1.0 wt %. Additionally or alternately, the amount of transition metal can be about 20 wt % or less, such as about 10 wt % or less, or about 5 wt % or less, or about 2.0 wt % or less, or about 1.5 wt % or less, or about 1.2 wt % or less, or about 1.1 wt % or less, or about 1.0 wt % or less. It is noted that the amount of transition metal is in addition to the weight of metal or metal-containing reforming catalyst in the catalyst composition.
Further additionally or alternately, the one or more molecular sieves can include non-framework phosphorus and/or be enhanced by phosphorus treatment. Including phosphorus in the additional molecular sieve can potentially provide increased stability for the molecular sieve(s) in the reaction conditions present during reforming and/or methanation as described herein. The weight of the phosphorus can be about 0.1 wt % to about 10.0 wt % based on the weight of the additional molecular sieve. Thus, the upper limit on the range of the phosphorus added to the one or more molecular sieves may be 10.0 wt %, 9.0 wt %, 8.0 wt %, 7.0 wt %, 6.0 wt %, 5.0 wt %, 4.0 wt %, 3.0 wt %, 2.0 wt %, 1.0 wt %, or 0.1 wt %; and the lower limit on the range added to the additional molecular sieve may be 10.0 wt %, 9.0 wt %, 8.0 wt %, 7.0 wt %, 6.0 wt %, 5.0 wt %, 4.0 wt %, 3.0 wt %, 2.0 wt %, 1.0 wt %, or 0.1 wt %. Ranges expressly disclosed include combinations of any of the above-enumerated upper and lower limits; e.g., 0.1 to 10.0 wt %, 0.1 to 8.0 wt %, 0.1 to 6.0 wt %, 0.1 to 5.0 wt %, 0.1 to 4.0 wt %, 0.1 to 3.0 wt %, 0.1 to 2.0 wt %, 0.1 to 1.0 wt %, 1.0 to 10.0 wt %, 1.0 to 9.0 wt %, 1.0 to 8.0 wt %, 1.0 to 7.0 wt %, 1.0 to 6.0 wt %, 1.0 to 5.0 wt %, 1.0 to 4.0 wt %, 1.0 to 3.0 wt %, etc. Of course, these total weights of the phosphorus shall be understood to exclude any phosphorus in the molecular sieve framework.
In embodiments where one or more molecular sieves are included in the catalyst composition, at least a portion of the metal catalyst(s) for reforming can be supported on the molecular sieve(s), or all of the metal catalyst(s) for reforming can be supported on the metal oxides.
Additionally or alternately, a small pore molecular sieve can be beneficial in the catalyst composition, such as a zeolite having the CHA framework type. In such additional or alternative embodiments, at least a portion of the metal or metal-containing catalyst can be supported on the small pore molecular sieve. In some aspects, the metal or metal-containing catalyst supported on the small pore molecular sieve can be rhodium. Supporting at least a portion of the (reforming) metal or metal-containing catalyst on the small pore molecular sieve can enhance the reforming reactivity for both methane and lower molecular weight C2+ components.
In this discussion, unless specifically noted otherwise, references to CHA framework type zeolites are understood to generally refer to any zeolite (or other molecular sieve) having the chabazite framework type. The chabazite framework type is designated as framework type code CHA in the International Zeolite Association database of zeolite structures. Other zeolites having the CHA framework type can include AlPO-34, MCM-2, MeAPO-44, MeAPO-47, SAPO-34, SAPO-47, SSZ-13, SSZ-62, and ZK-14, as well as combinations thereof. Chabazite can refer to a naturally occurring or a synthetic form of chabazite. Unless otherwise specified, a reference to chabazite, should be understood to generally refer to the zeolite chabazite (natural or synthetic), optionally containing any of the potential various counter ions and/or additional metals that can be present.
While rhodium supported on CHA framework type molecular sieve of the present invention can effectively enhance the formation of methane, additional rhodium supported multi-dimensional small pore molecular sieves can also be effective. Suitable small pore molecular sieves can include those having the AEI, AFT, AFX, ATT, DDR, EAB, EPI, ERI, KFI, LEV, LTA, MER, MON, MTF, PAU, PHI, RHO, and/or SFW framework types.
An additional or alternative option for characterizing small pore molecular sieves can be based on the ring structures in the molecular sieves. Some suitable small pore molecular sieves can include molecular sieves having an 8-member ring channel as the largest pore size for the molecular sieve.
Another additional or alternative option for characterizing small pore molecular sieves can be based on the effective size of the pore channels. In some embodiments, a suitable small pore molecular sieve can include a largest pore channel that has a maximum dimension of about 4.8 Angstroms or less, e.g., about 4.7 Angstroms or less, about 4.6 Angstroms or less, about 4.5 Angstroms or less, about 4.4 Angstroms or less, or about 4.3 Angstroms or less. In such a molecular sieve, the largest pore channel may also have a minimum dimension of at least about 3.5 Angstroms, or at least about 3.6 Angstroms, or at least about 3.7 Angstroms. In this discussion, the maximum and minimum dimensions of a pore channel for a molecular sieve refer to the size of a sphere that can diffuse through such a pore channel, as reported in the Database of Zeolite Structures that is maintained by the International Zeolite Association.
In various embodiments, the weight of the CHA framework type molecular sieve (or small pore molecular sieve) in the catalyst composition, and/or the weight of chabazite in the catalyst composition, can be from 1.0 wt % to 99.75 wt %, based on the total weight of the catalyst composition. The lower limit on the range of CHA framework type molecular sieve (or small pore molecular sieve) content, and/or the lower limit on the chabazite content, may be about, e.g., 1.0 wt %, 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, or 97.5 wt %. The upper limit on the range of CHA framework type molecular sieve (or small pore molecular sieve) content, and/or the lower limit on the chabazite content, may be about, e.g., 2.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, 20.0 wt %, 22.5 wt %, 25.0 wt %, 27.5 wt %, 30.0 wt %, 32.5 wt %, 35.0 wt %, 37.5 wt %, 40.0 wt %, 42.5 wt %, 45.0 wt %, 47.5 wt %, 50.0 wt %, 52.5 wt %, 55.0 wt %, 57.5 wt %, 60.0 wt %, 62.5 wt %, 65.0 wt %, 67.5 wt %, 70.0 wt %, 72.5 wt %, 75.0 wt %, 77.5 wt %, 80.0 wt %, 82.5 wt %, 85.0 wt %, 90.0 wt %, 92.5 wt %, 95.0 wt %, 97.5 wt %, or 99.0 wt %, or 99.5 wt %, or 99.75 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 2.5 wt % to about 95.0 wt %, from about 5.0 wt % to about 80.0 wt %, from about 10.0 wt % to about 55.0 wt %, from about 20.0 wt % to about 40.0 wt %, etc.
In embodiments where the catalyst composition also includes one or more metal oxides, the catalyst composition can include at least a minimum amount of chabazite (and/or a CHA framework type zeolite or other small pore molecular sieve) such as any of the lower limit amounts described above.
In some embodiments, the metal or metal-containing catalyst in a catalyst composition including a small pore molecular sieve can be any of the metal or metal-containing catalysts described above in the amounts as described above. This can include aspects where the metal or metal-containing catalyst is Rh or includes Rh. Alternatively, a first metal or metal-containing catalyst can be supported on the metal oxide support portion of the catalyst composition while a second metal or metal-containing catalyst, preferably Rh, can be supported on the small pore molecular sieve. In such embodiments, if any medium or large pore molecular sieves are also included in the catalyst composition, the medium or large pore molecular sieves can support no metal or metal-containing catalyst, or support a portion of the metal or metal-containing catalyst present on the metal oxide support, or support a portion of the metal or metal-containing catalyst present on the small pore molecular sieve, or a combination thereof.
In embodiments where different metal or metal-containing catalysts are supported on the metal oxide portion and the small pore molecular sieve portion of a catalyst composition, the total amount of metals in the catalyst composition can correspond to any convenient combination of an amount of metal or metal-containing catalyst supported on the small pore molecular sieve and an amount of metal or metal-containing catalyst supported on the metal oxide support. As an example, a catalyst composition may include Rh as a reforming metal catalyst on the small pore molecular sieve portion of the catalyst composition while including Ru on the metal oxide support portion of the catalyst composition. For example, the catalyst composition may include a non-zero amount up to about 20 wt %, based on the total weight of the catalyst composition, of a first metal or metal-containing compound(s) such as Rh and/or an Rh-containing compound (or other metal selected from Co, Ru, Rh, Pt, Pd, Fe, Ni, Ir, and combinations thereof that is supported on the small pore molecular sieve). The lower limit on the range of the first metal content may be about, e.g., 0.05 wt %, 0.10 wt %, 0.25 wt %, 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. The upper limit on the range of the first metal content may be about, e.g., 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 0.5 wt % to about 15.0 wt %, from about 1.0 wt % to about 10.0 wt %, from about 2.0 wt % to about 7.5 wt %, from about 2.5 wt % to about 5.0 wt %, etc. The catalyst supported on the metal oxide support portion of the catalyst composition may also may be present in an amount of >0 to about 20.0 wt %, based on the total weight of the catalyst composition. The lower limit on the range of catalyst supported on the metal oxide support may be about, e.g., 0.05 wt %, 0.10 wt %, 0.25 wt %, 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. The upper limit on the range of catalyst supported on the metal oxide support may be about, e.g., 0.50 wt %, 0.75 wt %, 1.0 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 4.0 wt %, 5.0 wt %, 7.5 wt %, 10.0 wt %, 12.5 wt %, 15.0 wt %, 17.5 wt %, or 20.0 wt %. Combinations of such lower and upper limits may be selected, e.g., from about 0.5 to about 15.0 wt %, from about 1.0 to about 10.0 wt %, from about 2.0 to about 7.5 wt %, from about 2.5 to about 5.0 wt %, from about 0.75 to about 2.0 wt %, etc. For example, an Rh or an Rh-containing compound may be supported on a small pore molecular sieve portion of the catalyst composition while Ru or an Ru-containing compound may be supported on the metal oxide portion of the catalyst composition, e.g., such that the catalyst composition comprises from about 1.0 to about 6.0 wt % Rh, from about 1.5 to about 5.0 wt %, from about 2.0 to about 4.5 wt %, or from about 2.5 to about 4.0 wt % Rh and from about 0.5 to about 5.0 wt % Ru, from about 0.75 to about 3.0 wt %, or from about 1.0 to about 2.0 wt % Ru, based on the total weight of the catalyst composition.
In various embodiments, the average reformer temperature can be maintained at or above about 450° C., e.g., above about 500° C., above about 550° C., above about 600° C., above about 650° C., from about 450° C. to about 650° C., from about 500° C. to about 650° C., from about 550° C. to about 600° C., from about 450° C. to about 550° C., or from about 475° C. to about 525° C.
One option for maintaining and/or increasing the temperature of a reforming reactor can be to use pre-combustion of a portion of the fuel as a source of heat for the reforming reactor. Pre-combustion can allow the inlet temperature for the reforming reactor to be varied without having to vary some other temperature within the engine. Conventionally, pre-combustion of fuel to provide heat for a reformer in an engine is not preferred, as any fuel burned to heat the reformer represents fuel that cannot be used to drive the powertrain. However, due to the thermodynamic limitation and potential kinetic limitations on the reforming reactions, using pre-combustion can allow increasing the amount of conversion before the thermodynamically limited or kinetically limited temperature is reached. For example, pre-combustion can allow the inlet temperature of the reformer to be increased to a temperature of about 525° C. to about 650° C., or about 525° C. to about 625° C., or about 525° C. to about 600° C., or about 550° C. to about 650° C., or about 550° C. to about 625° C., or about 550° C. to about 600° C. The resulting increase in enthalpy of the product mix due to the reforming reaction can raise the heat of combustion, which can essentially offset the loss in efficiency due to the pre-combustion. This can be desirable up to a point where raising the feed temperature by pre-combustion would lead to significant heat losses to the surrounding; e.g., a temperature over about 650° C.
In some embodiments, the invention can include a reformer for use in an exhaust gas recycle portion of an internal combustion engine powertrain, said reformer comprising at least one catalyst composition described herein. Such a reformer may be used in a method of operating an internal combustion engine. This may be accomplished, e.g., by providing an exhaust gas-containing mixture to an exhaust gas recycle reformer. The exhaust gas-containing mixture can typically comprise engine exhaust gas and a first hydrocarbon-containing fuel. At least a portion of the exhaust gas-containing mixture can be passed to the reformer and converted by the catalyst composition in the presence of heat to a reformed gaseous mixture (product) having an increased content of H2 relative to the mixture of exhaust gas and first hydrocarbon-containing fuel. The reformed gaseous mixture and a second hydrocarbon-containing fuel may be provided to the engine for combustion. Typically, the second hydrocarbon-containing fuel can be the same as the first hydrocarbon-containing fuel (i.e., it can be convenient to draw both the first and second hydrocarbon-containing fuels from a common source or tank, in some embodiments), although this need not always be the case. Where desired, the second hydrocarbon-containing fuel may be different from the first hydrocarbon-containing fuel. The reformed gaseous mixture and second hydrocarbon-containing fuel can then be combusted in the engine to form an exhaust gas. The net exhaust gas vented from the engine can be passed through a first heat exchanger to extract heat therefrom. The heat can be transferred to the reformer feed to aid in sustaining the reforming reactions therein.
An important direction in future gasoline engines can be use of exhaust gas recycle (EGR). In some aspects, use of recycled exhaust gas as part of the input fuel mixture to the engine can lower the temperature for combustion. This can allow the engine to run at a higher compression ratio without causing knocking, which can provide increased efficiency. However, the compression ratio and amount of exhaust gas recycle are limited conventionally by practical concerns. Increasing the amount of exhaust gas recycle in a conventional engine can cause the fuel delivered to the engine to become too dilute, leading to problems with the fuel flame speed. Additionally, the compression ratio can be limited by the fuel octane rating, or resistance of a fuel to combustion prior to spark ignition.
In various embodiments, use of exhaust gas recycle with reforming of fuel prior to combustion can allow for increased use of the exhaust gas recycle. For example, use of EGR can provide a medium with H2O and CO2 as reactants for reforming of natural gas to produce H2 rich gas to raise flame speed and potentially octane by reforming of lower octane C2+ components to H2 and CO. Typical ranges for EGR that can be used for the engine in conjunction with reforming can include about 20 vol % to 50 vol % of the engine air/EGR mix. For example, the amount of EGR can be at least about 20 vol % of the combined air and exhaust gas delivered to the engine, or at least about 25 vol %, or at least about 30 vol %, or at least about 35 vol %, and/or about 50 vol % or less, or about 45 vol % or less, or about 40 vol % or less, or about 35 vol % or less. It is noted that each of the lower limits and upper limits for the amount of exhaust gas recycle are explicitly contemplated in combination with each other. All or a portion of this EGR can be fed in conjunction with the natural gas fuel (or other fuel) from tankage to the reformer. The desired amount of EGR relative to feed to the reformer can depend on fuel input, engine design and engine load points. A high level of EGR can increase the amount of H2O and CO2 available for reforming, which can potentially mitigate the extent of temperature drop in the reformer. Alternatively, lowering EGR can raise the fuel concentration and thereby can enhance the kinetics for conversion.
The use of the catalyst compositions herein can serve to provide an increase in the flame speed of an internal combustion engine exhaust gas hydrocarbon mixture stream, consisting of natural gas and natural gas plus C2+ additions as described herein. An exhaust gas-containing mixture may be provided to an exhaust gas recycle reformer including a catalyst as described herein. The exhaust gas-containing mixture can typically comprise engine exhaust gas and a first hydrocarbon-containing fuel.
In various embodiments, a hydrocarbon-containing fuel can have a laminar flame speed at stoichiometric air to fuel ratio as measured at 25° C. and 1 atm of about 30 cm/sec to about 70 cm/sec. Addition of exhaust gas (such as by combining the hydrocarbon-containing fuel with an exhaust gas recycle stream) can reduce this laminar flame speed to a less than about 10 cm/sec, or less than about 5 cm/sec. Reforming of the mixture of hydrocarbon-containing fuel and exhaust gas can be used to produce a reformed mixture having a flame speed that is increased relative to the mixture prior to reforming. Thus, the reformed mixture can have a laminar flame speed of greater than about 5 cm/sec, or greater than about 7.5 about cm/sec, or greater than about 10 cm/sec, or greater than about 15 cm/sec.
The reformer may also be incorporated into an internal combustion engine powertrain. Many different variations of such power trains are known. One such powertrain envisioned can include an internal combustion engine having an exhaust manifold and a fuel intake manifold. A reformer comprising a catalyst composition as described herein can fluidly connect the exhaust manifold and the fuel intake manifold. The reformer and catalyst composition can be specifically configured to convert an exhaust gas-containing mixture form the exhaust manifold gas and a first hydrocarbon-containing fuel to a reformed gaseous mixture comprising H2, CO, and CH4, along with one or more exhaust gas constituents—typically including N2, H2O, CO2, trace quantities of minor species such as NOx and SOx, and the like. Conversion of a hydrocarbon feed should be understood to be calculated solely by the ratio of the difference between the mass (or number of moles) of hydrocarbon component of the feed entering the inlet of the reforming zone and the mass (or number of moles) of hydrocarbon component exiting the outlet of the reforming zone, divided by the mass (or number of moles) of hydrocarbon component of the feed entering the inlet of the reforming zone. Typically, the intake manifold can be configured to provide a reformed fuel mixture from the exhaust gas recycle unit and a second hydrocarbon-containing fuel to the internal combustion engine for combustion. As described above, the first and second hydrocarbon-containing fuels may be the same or different.
Referring now to
Hydrocarbon-containing fuel can be supplied to the powertrain in
Additionally or alternatively to situations where the fuel(s) correspond to a methane-containing fuel as described above, the hydrocarbon-containing fuel can be a conventional fuel, such as gasoline, and may optionally be the primary fuel supplied to the engine by direct injection into the engine. In such situations, other fuels can be used instead of or in combination with the conventional fuel (gasoline). Other such fuels can include, but are not necessarily limited to, LPG (liquefied petroleum gas), light ends, C2-C12 paraffins, naphtha, kerosene, diesel, FCC off-gas, oxygenated hydrocarbons (e.g., dialkyl ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, and the like, and combinations thereof; C1-C12 alcohols such as methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, a pentanol, a hexanol, and the like, and combinations thereof; fatty acid alkyl esters, for instance from mono-, di-, and/or tri-glyceride reaction with a C1-C4 alcohol, such as represented by FAME, FAEE, and the like, and combinations thereof; and the like; and combinations thereof), hydrocarbon-rich gas overhead from a refinery process, hydrocarbon-rich off-gas from a chemical process, or the like, or combinations thereof.
Whatever fuel is used as a feed in the methods described herein, it can advantageously have one, two, or all of the following characteristics: a relatively high paraffin content, no more than a modest aromatics content, and a relatively small content of polynuclear aromatics (PNAs, meaning compounds having two or more aromatic rings in its structure, typically two or more aromatic rings connected to each other, e.g., sharing two carbon atoms between them). The overall aromatics content of the hydrocarbon-containing fuel to be fed into the reforming zone can advantageously be no more than about 35 wt % (e.g., no more than about 30 wt %, no more than about 25 wt %, no more than about 20 wt %, no more than about 15 wt %, or no more than about 10 wt %), based on the weight of the hydrocarbon-containing fuel (optionally, the fuel can additionally have some aromatics content, e.g., at least about 0.1 wt %, at least about 0.5 wt %, at least about 1 wt %, at least about 2 wt %, at least about 3 wt %, at least about 4 wt %, at least about 5 wt %, at least about 7 wt %, at least about 10 wt %, or at least about 15 wt %, based on the weight of the hydrocarbon-containing fuel). Additionally or alternately, the PNA content of the hydrocarbon-containing fuel to be fed into the reforming zone can advantageously be no more than about 3 wt % (e.g., no more than about 2 wt %, no more than about 1 wt %, no more than about 0.5 wt %, or no more than about 0.1 wt %), based on the weight of the hydrocarbon-containing fuel (though PNAs can typically be undesirable for relatively high conversion in reforming, the fuel may nonetheless optionally have some PNA content, e.g., at least about 0.001 wt %, at least about 0.005 wt %, at least about 0.01 wt %, at least about 0.03 wt %, at least about 0.05 wt %, at least about 0.07 wt %, at least about 0.1 wt %, at least about 0.2 wt %, at least about 0.3 wt %, or at least about 0.5 wt %, based on the weight of the hydrocarbon-containing fuel). Further additionally or alternately, the paraffin content of the hydrocarbon-containing fuel to be fed into the reforming zone can advantageously be greater than about 50 wt % (e.g., at least about 55 wt %, at least about 60 wt %, at least about 65 wt %, at least about 70 wt %, at least about 75 wt %, at least about 80 wt %, at least about 85 wt %, at least about 90 wt %, at least about 95 wt %, at least about 96 wt %, at least about 97 wt %, at least about 98 wt %, or at least about 99 wt %), based on the weight of the hydrocarbon-containing fuel (though paraffinic hydrocarbons can typically be very desirable for relatively high conversion in reforming, the fuel may nonetheless optionally have some upper limit on paraffin content, e.g., up to about 99.9 wt %, up to about 99.5 wt %, up to about 99 wt %, up to about 98 wt %, up to about 97 wt %, up to about 96 wt %, up to about 95 wt %, up to about 90 wt %, up to about 85 wt %, up to about 80 wt %, up to about 75 wt %, up to about 70 wt %, up to about 65 wt %, or up to about 60 wt %, based on the weight of the hydrocarbon-containing fuel).
In
In one embodiment, the generation of hydrogen in the powertrain of
Referring now to
A method for reforming a fuel in an internal combustion engine, said method comprising: (a) providing an exhaust gas-containing mixture to an exhaust gas recycle reformer, the exhaust gas recycle reformer comprising a reformer inlet, a reformer outlet, and a hydrocarbon-reforming catalyst composition, the exhaust gas-containing mixture comprising engine exhaust gas and a first hydrocarbon-containing fuel, the hydrocarbon-containing fuel comprising at least about 50 mol % methane, and (b) converting under reforming conditions at least a portion of the exhaust gas-containing mixture in the presence of a hydrocarbon-reforming catalyst composition comprising at least about 0.1 wt % of a hydrocarbon-reforming metal catalyst supported on a mixed metal oxide support, the mixed metal oxide support comprising at least about 20 wt % of a mixture of lanthanum oxide and aluminum oxide and at least about 10 wt % of a mixture of cerium oxide and zirconium oxide, the aluminum oxide optionally being γ-aluminum oxide.
The method of Embodiment 1, wherein the mixed metal oxide support consists essentially of the mixture of lanthanum oxide and aluminum oxide and the mixture of cerium oxide and zirconium oxide.
The method of Embodiments 1 or 2, wherein the mixture of lanthanum oxide and aluminum oxide comprises about 0.4 wt % to about 15 wt % of lanthanum oxide based on the combined weight of lanthanum oxide and aluminum oxide.
A method for reforming a fuel in an internal combustion engine, said method comprising: (a) providing an exhaust gas-containing mixture to an exhaust gas recycle reformer comprising a reformer inlet, a reformer outlet, and a hydrocarbon-reforming catalyst composition, the exhaust gas-containing mixture comprising engine exhaust gas and a first hydrocarbon-containing fuel, the hydrocarbon-containing fuel comprising at least about 50 mol % methane and a weighted carbon mole percentage of carbons in C2+ compounds of at least about 5%, and (b) converting under reforming conditions at least a portion of the exhaust gas-containing mixture in the presence of the hydrocarbon-reforming catalyst composition, the reforming conditions including a reformer outlet temperature of about 435° C. to about 500° C.
The method of Embodiment 4, wherein the reformer inlet temperature is about 525° C. to about 650° C., or about 535° C. to about 625° C., or about 550° C. to about 600° C.
The method of any of the above embodiments, wherein the hydrocarbon-containing fuel comprises at least about 70 mol % methane, or at least about 80 mol % methane, or at least about 90 mol % methane.
The method of any of the above embodiments, wherein the hydrocarbon-containing fuel comprises at least about 5 mol %, or at least about 10 mol %, of ethane, ethanol, propane, propane isomers, butane, butane isomers, C2 compounds, C3 compounds, C4 compounds, or combinations thereof.
The method of any of the above embodiments, wherein the hydrocarbon-containing fuel comprises at least about 10 mol % (or at least about 15 mol %) of C2+ compounds, or at least about 10 mol % (or at least about 15 mol %) of C2 to C5 compounds, or at least about 10 mol % (or at least about 15 mol %) of C2 to C4 compounds.
The method of any of the above embodiments, wherein the hydrocarbon-containing fuel comprises a weighted carbon mole percentage of carbons in C2+ compounds of at least about 5%, or at least about 10%, or a weighted carbon mole percentage of carbons in C2 to C5 compounds of at least about 5%, or at least about 10%, or a weighted carbon mole percentage of carbons in C2 to C5 alkanes of at least about 5%, or at least about 10%.
The method of any of the above embodiments, wherein the hydrocarbon-containing fuel comprises about 5 mol % or less of H2 prior to converting at least a portion of the exhaust gas mixture under reforming conditions, wherein converting the at least a portion of the exhaust gas-containing mixture generates a reformed gas product comprising about 5 mol % to about 20 mol % H2, or a combination thereof.
The method of any of the above embodiments, wherein the hydrocarbon-reforming catalyst composition comprises a hydrocarbon-reforming metal catalyst loading from 0.5 wt % to 10.0 wt %, based on the total weight of the catalyst composition.
The method of any of the above embodiments, wherein the hydrocarbon-reforming metal catalyst is selected from the group consisting of Co, Ru, Rh, Pt, Pd, Ni, Ir, Zn, Re, and mixtures thereof, the hydrocarbon-reforming metal catalyst optionally comprising Rh.
The method of any of the above embodiments, wherein the hydrocarbon-reforming catalyst composition further comprises at least one medium pore molecular sieve or large pore molecular sieve, the at least one medium pore molecular sieve or large pore molecular sieve optionally comprising ZSM-5, phosphorus-modified ZSM-5, MCM-68, or a combination thereof.
The method of any of the above embodiments, wherein the hydrocarbon-reforming catalyst composition further comprises at least one small pore molecular sieve, the at least one small pore molecular sieve optionally comprising chabazite, a CHA framework molecular sieve, or a combination thereof.
The method of any of the above embodiments, wherein providing an exhaust gas-containing mixture to an exhaust gas recycle reformer comprises: passing at least a portion of the first hydrocarbon-containing fuel into a cylinder of the internal combustion engine after the combusting of the reformed gaseous mixture and second hydrocarbon-containing fuel to form a portion of the exhaust gas; cracking the at least a portion of the first hydrocarbon-containing fuel in the cylinder to form a cracked hydrocarbon-containing fuel; and providing the portion of the exhaust gas and the cracked hydrocarbon-containing fuel to the exhaust gas recycle reformer.
The method of Embodiment 15, further including prior to introducing the reformed gaseous mixture into the internal combustion engine, cooling the gaseous mixture by passing the gaseous mixture through the first heat exchanger or a second heat exchanger.
The method of any of the above embodiments, further comprising combusting a portion of the exhaust gas mixture prior to converting the at least a portion of the exhaust gas mixture under reforming conditions.
A series of tests was performed using a reforming catalyst composition in a plug flow reactor to simulate the reaction conditions that may be expected in a reforming reactor in an engine or powertrain environment. The reforming catalyst composition used in the tests (Catalyst A) included ˜3.5 wt % Rh supported on a mixed metal oxide comprising La2O3-γ-Al2O3 (˜35 wt % of total) and CeO2—ZrO2 (˜60 wt % of total). The La2O3—Al2O3 support was prepared separately by impregnation of an aqueous La(NO3)3 solution onto γ-Al2O3 followed by drying and calcination at ˜600° C. CeO2—ZrO2 was co-precipitated from an aqueous Ce(NO3)4 and Zr(NO3)4 solution onto the La2O3—Al2O3 support using urea as base. The Ce:Zr atomic ratio was ˜4:1. The La-γ-Al2O3—CeO2—ZrO2 support was calcined at ˜600° C. prior to incipient wetness impregnation with an aqueous solution containing Rh(NO3)3. After the precious metal impregnation the catalyst was calcined for ˜6 hours in air at ˜600° C.
In the tests, ˜0.01 g of catalyst powder (Catalyst A) sized to ˜25-40 mesh was diluted with ˜1.88 g of silica. The diluted catalyst was loaded into a vertically mounted cylindrical quartz plugged flow reactor (˜6 mm idט15 mm long) which was heated by a furnace. The temperature was measured in the front catalyst bed (˜¼ inch from catalyst inlet) and in the rear catalyst bed (˜¼ inch from the catalyst outlet). The average catalyst bed temperature was defined as the arithmetic average between the catalyst front bed and rear bed temperatures. A feed gas comprising ˜16.1 mol % methane, ˜15.3 mol % H2O, and ˜8.13 mol % CO2 in N2 (balance of feed gas) was fed over the catalyst to achieve a gas hourly space velocity of ˜26 khr−1 at ˜1.3 barg (˜130 kPag). This corresponded to a fuel delivery rate of ˜2.76 g methane/g Rh/s. The concentration of hydrocarbons was monitored by GC/FID (gas chromatography-flame ionization detection), while the concentration of reaction products carbon monoxide and hydrogen was detected by GC/TCD analyzers (gas chromatography-thermal conductivity detector). Data were collected for ˜6 hours time on stream at each temperature. The reforming reaction was investigated at different temperatures using the same catalyst. After completing the test at each temperature, the catalyst in the reactor was subjected to a stream containing ˜5% O2 at ˜550° C. for ˜10 min to remove any carbonaceous deposits that may have formed on the catalyst during the NG reforming step.
Table 1 below shows furnace set temperatures and the measured temperatures for the front and back of the catalyst bed at each furnace set temperature. It was noted that the catalyst bed temperatures tended to be slightly higher than the furnace set temperatures. This was because the heat flux from the furnace to the catalyst bed was larger than the heat consumed by the endothermic methane steam reforming reaction. The average of the front bed and back bed temperatures is shown as the temperature in
It was noted that the results in
Table 2 shows an example for a fuel composition of natural gas fuel containing methane and C2+ components comprising ethane, propane, iso-butane, n-butane, and iso-pentane. As shown in Table 2, an example of a potential natural gas composition was substantially composed of methane (more than 90 mol %), with less than 5 mol % each of propane and ethane.
The example of a natural gas composition shown in Table 2 was used as the basis for performing simulations for reforming of natural gas. The reforming was simulated at a ˜600° C. and a ˜500° C. inlet temperature at ˜1 barg (˜100 kPag) of pressure. A Gibbs adiabatic reactor model was used to simulate the product composition produced from steam reforming of the natural gas composition when combined with ˜30% exhaust gas recycle with equilibrium being reached.
One feature of the simulation results shown in
Propane steam reforming was performed using three different types of catalyst compositions including Rh as a reforming catalyst. It was noted that Catalyst A corresponded to a catalyst composition made using a mixture of the oxide supports used for Catalyst B and Catalyst C.
Catalyst A included ˜3.5 wt % Rh supported on a mixed metal oxide comprising La2O3-γ-Al2O3 (˜35 wt % of total) and CeO2—ZrO2 (˜60 wt % of total). The La2O3—Al2O3 support was prepared separately by impregnation of an aqueous La(NO3)3 solution onto γ-Al2O3, followed by drying and calcination at ˜600° C. CeO2—ZrO2 was co-precipitated from an aqueous Ce(NO3)4 and Zr(NO3)4 solution onto the La2O3—Al2O3 support using urea as base. The Ce:Zr atomic ratio was ˜4:1. The La-γ-Al2O3—CeO2—ZrO2 support was calcined at ˜600° C. prior to incipient wetness impregnation with an aqueous solution containing Rh(NO3)3. After the precious metal impregnation the catalyst was calcined for ˜6 hours in air at ˜600° C.
Catalyst B included ˜3.5 wt % Rh supported on a La2O3-γ-Al2O3 mixed metal oxide. The La2O3-γ-Al2O3 support was prepared separately by impregnation of an aqueous La(NO3)3 solution onto γ-Al2O3, followed by drying and calcination at ˜600° C. An aqueous solution of Rh(NO3)3 was impregnated onto the La2O3-γ-Al2O3 support by incipient wetness impregnation as described for catalyst A, followed by drying and calcination for ˜6 hours in air at ˜600° C.
Catalyst C included ˜3.5 wt % Rh supported on a CeO2—ZrO2 mixed metal oxide. CeO2—ZrO2 was prepared by co-precipitation from an aqueous Ce(NO3)4 and Zr(NO3)4 solution using urea as base. The Ce:Zr atomic ratio was ˜4:1. The CeO2—ZrO2 support was calcined at ˜600° C. prior to incipient wetness impregnation with an aqueous solution containing Rh(NO3)3. After the precious metal impregnation the catalyst was calcined for ˜6 hours in air at ˜600° C.
Using Catalysts A-C, a series of propane reforming tests were conducted in order to test the catalysts activity for reforming one of the C2+ components. The sequence consisted of four steps denoted as test protocols II (step 1), III (step 2), IV (step 3), and V (repeat of step 1). Each protocol is described below.
Test Protocol II (Propane Reforming, No Syngas Components Added)—
For the propane reforming test in test protocol II, ˜0.088 g of catalyst powders A, B, and C were each sized to ˜25-40 mesh and diluted with silica at a ratio ˜1:15. The diluted catalyst was loaded into a vertically mounted cylindrical quartz plugged flow reactor (˜6 mm idט15 mm long) which was heated by a furnace. The temperature was measured in the front catalyst bed (˜¼ inch from catalyst inlet) and in rear catalyst bed (˜¼ inch from the catalyst outlet). The average catalyst bed temperature was calculated from the catalyst bed temperatures at the inlet and outlet. A feed gas comprising ˜13.3 mol % propane, ˜27.4 mol % H2O, and ˜26.6 mol % CO2 in N2 (balance of gas composition) was fed over the catalyst to achieve a gas hourly space velocity of ˜26 khr−1 at a furnace set temperature of ˜400° C. The conversion of propane and the concentration of the reaction product methane were monitored by FID, while the concentration of reaction products carbon monoxide and hydrogen were detected by GC/TCD analyzers. Prior to the reforming test, catalysts were reduced for ˜20 minutes in a stream containing ˜20% hydrogen balance N2 followed by a N2 sweep for ˜20 minutes at ˜400° C. After ˜3 hours of reforming test II, catalysts were subjected to a stream containing ˜5% O2 (balance N2) for ˜5 minutes at ˜400° C. furnace set temperature in order to remove carbonaceous deposits that were formed during the reforming test II. The oxidation step was followed by a N2 sweep for ˜15 minutes at ˜400° C.
Test Protocol III (Propane Reforming, Addition of H2—
After completing test protocol II, including the oxidation and reduction steps at the end of the protocol, test protocol III was applied. In test protocol III, a feed similar to the propane-containing feed in test protocol II was used, except that ˜17% of the feed N2 was replaced with H2 in order to study the effect of hydrogen on the reforming of propane. After ˜3 hours of reforming test III, catalysts were subjected to a stream containing ˜5% O2 (balance N2) for ˜5 minutes at ˜400° C. in order to remove carbonaceous deposits that were formed during the reforming test III. The oxidation step was followed by a N2 sweep for ˜15 minutes at ˜400° C.
Test Protocol IV (Propane Reforming, Addition of H2 and CO)—
After completing test protocol III, including the oxidation and reduction steps at the end of the protocol, test protocol IV was applied. In test protocol IV, a feed similar to the propane-containing feed in test protocol II was used, except that ˜23% of the feed N2 was replaced with ˜17% H2 and ˜6% CO in order to study the effect of hydrogen and CO on the reforming of propane. After the reforming test IV, catalysts were subjected to a stream containing ˜5% O2 (balance N2) for ˜5 minutes at ˜400° C. in order to remove carbonaceous deposits that were formed during the reforming test IV. The oxidation step was followed by a N2 sweep for ˜15 minutes at ˜400° C.
Test Protocol V (Repeat of Test Protocol II)—
After completing test protocol IV, including the oxidation and reduction steps at the end of the protocol, test protocol V was applied. Test protocol V was a repeat of the conditions from test protocol II.
The results from applying test protocols II, III, IV, and V to Catalysts A, B, and C are shown in
Based on the results shown in
Additional characterization of Catalyst A was performed by using Catalyst A for steam reforming of a natural gas feed. During reforming of the natural gas feed, ˜0.1 g of catalyst powder A sized to ˜25-40 mesh was diluted with ˜1.8 g of silica. The diluted catalyst was loaded into a vertically mounted cylindrical quartz plugged flow reactor (˜6 mm idט15 mm long), which was heated by a furnace. The temperature was measured in the front catalyst bed (˜¼ inch from catalyst inlet) and in the rear catalyst bed (˜¼ inch from the catalyst outlet). The average catalyst bed temperature was defined as the arithmetic average between the catalyst front bed and rear bed temperatures. A feed gas comprising ˜16.1 mol % methane, ˜0.30 mol % ethane, 0.74 mol % propane, ˜15.3 mol % H2O, and ˜8.1 mol % CO2 in N2 balance was fed over the catalyst to achieve gas hourly space velocities of ˜10 khr−1 and ˜20 khr−1 at ˜1.3 barg (˜130 kPag). The total fueling rate was ˜0.26 g fuel/g Rh/s. The concentration of hydrocarbons was monitored by GC/FID, while the concentration of reaction products carbon monoxide and hydrogen was detected by GC/TCD analyzers. Data were collected for ˜6 hours time on stream at each temperature and average conversions between ˜1 hour and ˜6 hours time on stream were reported. After each temperature step, the catalyst was subjected to a stream containing ˜5% O2 at ˜550° C. for ˜10 minutes to remove any carbonaceous deposits that may have formed on the catalyst during the NG reforming step.
Tables 3 and 4 show the furnace set temperatures, the catalyst bed temperatures at the top and bottom, and the average catalyst bed temperatures measured for tests using the natural gas reforming test protocol over catalyst A for space velocities of ˜10 khr−1 and ˜20 khr−1, respectively.
Calculations were also performed to determine how the reaction product concentrations from the tests corresponding to Table 4 related to expected equilibrium concentrations based on thermodynamics. The approach to equilibrium for the tests shown in Table 4 was characterized using the following formula:
where PCH4, PH2O, PCO, and PH2 represented the respective partial pressures of methane, water, carbon monoxide, and hydrogen at the reactor outlet, and Keq represented the equilibrium constant for the methanation reaction.
Table 5 lists the values for η and the fraction of C2+ conversion relative to the total fuel conversion in the natural gas reforming tests at ˜20 khr−1 for the temperatures in Table 4. In Table 5, the fraction of C2+ conversion refers to the amount of carbons from C2+ compounds that were reformed relative to the total number of fuel carbons that were reformed.
As shown in Table 5, at temperatures of about 500° C. or less, the composition produced by selectively reforming the C2+ components started to diverge more substantially from the equilibrium composition. This was believed to be due to kinetic differences between conversion (reforming) of C2+ compounds versus conversion of methane. At temperatures of about 500° C. or less, reforming of C2+ compounds (such as C2 to C5 compounds) to form typical syngas components can have sufficiently favorable kinetics to allow for substantially complete reforming of C2+ compounds under the reforming conditions. By contrast, the reactions for reforming of methane and/or the reverse reaction for methane formation can be kinetically limited under the reforming conditions. As a result, at temperatures between about 435° C. to about 500° C., the output composition from reforming of a fuel mixture containing both methane and C2+ compounds can exit the reformer with product mixtures increasingly far from the thermodynamic equilibrium concentrations, as shown by the increasing value of η in Table 5. Due to such kinetic limitations, for a given input fuel composition, an increasing percentage of the hydrogen in the reformer output can correspond to hydrogen derived from reforming of C2+ compounds.
All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted. Should the disclosure of any of the patents and/or publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence.
As is apparent from the foregoing general description and the specific embodiments, while forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited thereby. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such variations are within the full intended scope of the appended claims. Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art
This application claims the benefit of provisional U.S. Application No. 61/915,555, filed on Dec. 13, 2013, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61915555 | Dec 2013 | US |
