Carbon Capture with Molten Carbonate Electrolysis Cell

This Non-Provisional Patent application claims priority to U.S. Provisional Patent Application No. 63/648,289, filed May 16, 2024, and titled “Carbon Capture With Molten Carbonate Electrolysis Cell”, the entire contents of which is incorporated herein by reference.

Systems and methods are provided for using molten carbonate electrolysis cells for carbon capture.

A molten carbonate fuel cell (MCFC) transfers COfrom a cathode to an anode while generating electricity. Hydrogen in the anode side of the fuel cell is combusted with oxygen, driving the reaction forward. The transport of COfrom cathode to anode allows for concentration of COin the anode output. This can facilitate further separation and sequester of the CO, thus allowing a MCFC to be used as part of a carbon capture system.

The process used in a molten carbonate fuel cell can also be run in reverse. When operating such a system in reverse (or when operating a system specifically designed to operate in the “reverse” direction), the system can be referred to as a molten carbonate electrolysis cell (MCEC). In the cathode, methane and steam can be reformed to generated hydrogen, CO, and CO. Water is split to oxygen and hydrogen, with the COcombining with the oxygen atom to form a carbonate anion (CO) which travels to the anode side of the cell. After transport, the carbonate is converted back to oxygen and CO.

Even though an MCEC runs in “reverse” relative to an MCFC, an MCEC still provides an opportunity to concentrate COin an output stream. Thus, an MCEC can be used as a carbon capture device. For example, U.S. Pat. No. 10,608,272 describes integration of an MCEC with a solid oxide fuel cell in order to generate power from the solid oxide fuel cell while also capturing the COgenerated by the solid oxide fuel cell. In a configuration shown in U.S. Pat. No. 10,608,272, a portion of the anode output from the solid oxide fuel cell, which contains combustible fuels such as H, CO, and or hydrocarbons, is used as fuel to combust the oxygen that is present in the CO-enriched output stream generated by the MCEC. It is noted that the MCEC in U.S. Pat. No. 10,608,272 is also referred to as a reformer-electrolyzer-purifier. It is further noted that the “cathode” and “anode” designations for the MCEC in U.S. Pat. No. 10,608,272 appear to be based on how the cathode and anode would be labeled for an MCFC. According to the conventional definition of a fuel cell, the cathode should correspond to the portion of the fuel cell where electrons are a reactant.

U.S. Pat. No. 11,043,864 provides another example of a configuration that uses an MCEC in a carbon capture application. In U.S. Pat. No. 11,043,864, both an MCFC and an MCEC are used for capture of COfrom a combustion flue gas, such as a flue gas from a boiler or a natural gas turbine.

U.S. Pat. No. 11,619,167 provides another example of integrating an MCEC with a combustion turbine as part of a power generation system.

A journal article by Lu et al. describes performance and durability of molten carbonate electrolysis cells. (“Performance and Durability of the Molten Carbonate Electrolysis Cell (MCEC) and the Reversible Molten Carbonate Fuel Cell (RMCFC),” J. Phys. Chem. C 2016, Vol. 120, No. 25, 13427-13433.)

U.S. Pat. Nos. 7,815,873 and 8,754,276 provide examples of using reverse flow reactors to perform various endothermic processes in a cyclic reaction environment. Reverse flow reactors are an example of a reactor type that is beneficial for use in processes with cyclic reaction conditions. For example, due to the endothermic nature of reforming reactions, additional heat needs to be introduced on a consistent basis into the reforming reaction environment. Reverse flow reactors can provide an efficient way to introduce heat into the reaction environment. After a portion of the reaction cycle used for reforming or another endothermic reaction, a second portion of the reaction cycle can be used for combustion or another exothermic reaction to add heat to the reaction environment in preparation for the next reforming step.

U.S. Pat. No. 11,851,328 describes using high heat capacity fluids, such as COand HO, as the diluent or carrier gas for heat transport during the regeneration step of a reverse flow reactor or other types of cyclic flow reactors.

In an embodiment, a method for operating a molten carbonate electrolysis cell is provided. The method includes passing a cathode input flow containing 3.0 vol % or more HO, and 3.0 vol % or more of CO, a reformable hydrocarbon, or a combination thereof, into a cathode of a molten carbonate electrolysis cell. The method further includes providing electric current to the cathode of the molten carbonate electrolysis cell. The method further includes operating the molten carbonate electrolysis cell to produce a cathode output flow comprising H, HO, and CO, and an anode output flow comprising COand O. The HO content of the cathode output flow can be lower than the HO content of the cathode input flow. The method further includes mixing at least a portion of the anode output flow with fuel. Additionally, the method includes reacting the at least a portion of the anode output flow and the fuel under at least one of combustion conditions and partial oxidation conditions to form a reaction effluent. Optionally, the COcontent of the cathode output flow can be lower than the COcontent of the cathode input flow. Optionally, the cathode input flow can contain 3.0 vol % or more of CO.

In another embodiment, a method for operating a molten carbonate electrolysis cell is provided. The method includes passing a cathode input flow comprising 5.0 vol % or more H, 3.0 vol % or more HO, and 3.0 vol % or more of CO, into a cathode of a molten carbonate electrolysis cell. The method further includes providing electric current to the cathode of the molten carbonate electrolysis cell. Additionally, the method includes operating the molten carbonate electrolysis cell to produce a cathode output flow comprising H, HO, and CO, and an anode output flow comprising COand O. The COcontent of the cathode output flow can be lower than the COcontent of the cathode input flow The HO content of the cathode output flow can be lower than the HO content of the cathode input flow.

In various embodiments, systems and methods are provided for integration of molten carbonate electrolysis cells in applications for hydrogen production and for operating turbines using oxycombustion. In some aspects, the unusual output flows from an MCEC (or more typically a plurality of MCECs) can be synergistically used in combination with reverse flow reactors and/or partial oxidation units to allow for hydrogen production while also performing carbon capture. In other embodiments, the anode output from an MCEC (or a plurality of MCECs) can be used as the oxygen-containing gas for a combustion turbine. This can allow the turbine to be operated under oxycombustion conditions, which can facilitate performing carbon capture on the resulting flue gas.

The structure of a molten carbonate electrolysis cell (MCEC) can be similar to a molten carbonate fuel cell (MCFC), but there are several differences in the operation of a MCFC and a MCEC. For example, an MCFC generates electrical power, while an MCEC requires electrical power as an input.

As another example, the composition of the CO-enriched streams produced by the two types of cells is different. During operation of an MCFC, the cathode requires an input flow of COand O. A portion of the COand Oare transported across the electrolyte to the anode (in the form of carbonate ions), resulting in a cathode exhaust stream that is depleted in both COand O. Typically the cathode exhaust does not contain fuel components, such as Hor hydrocarbons. In the MCFC anode, His provided to the anode in some manner. This can be in the form an H-containing stream, in the form of hydrocarbons that are then reformed in the anode, or a combination thereof. A portion of this hydrogen is then consumed by the carbonate ions transported across the membrane to form COand water. However, at least some hydrogen, and possibly some methane, are also present in the anode exhaust.

By contrast, during operation of an MCEC, COis transported in the opposite direction across the electrolyte. This means that the cathode in an MCEC receives both COand water. This is converted, by addition of electrons, into Hand carbonate ions. Thus, the cathode exhaust for the MCEC is depleted in COand water (relative to the cathode input flow) while being enriched in H. The resulting carbonate ions in an MCEC are transported across the membrane to the anode, where the carbonate ions are converted back into COand O. Thus, the anode exhaust corresponds to COand O. Due to the different type of operation, the anode exhaust for a MCEC does not contain hydrogen, while the cathode exhaust of a MCEC typically does contain hydrogen.

Because the anode exhaust does not contain hydrogen while being enriched in COand O, the anode exhaust from an MCEC can be used as an O-containing stream for combustion reactions. In some embodiments, the anode exhaust is mixed with air, to reduce or minimize the content of nitrogen in the resulting flue gas from combustion. In other embodiments, the anode exhaust is used as the entire CO-containing stream, and/or mixed with other streams having substantially no Ncontent, so that the combustion reaction can be performed under oxycombustion conditions. As a result, use of a MCEC can provide unexpected synergies when integrated with certain types of processes.

One type of integration is use of a MCEC as part of a system for producing hydrogen from hydrocarbons. Typically, conventional systems for producing hydrogen from hydrocarbons have to overcome several types of obstacles. First, performing a controlled reaction on hydrocarbons so that His produced instead of HO (the typical combustion product) requires operating at elevated temperatures. To provide the necessary heat, either some type of partial oxidation is performed on the hydrocarbons, or additional hydrocarbons are combusted to provide heat. Additionally, a source of Ois needed for the partial oxidation/combustion. If air is used, the resulting flue gas will contain a substantial amount of Nthat requires substantial effort to separate from the COin the flue gas. Air separation units are available, but this is a high cost process that requires even more fuel of some type to perform the separation. And, the resulting high purity Ostream typically does not correspond to a gas flow with enough thermal heat capacity to allow for heat management in a partial oxidation/combustion environment.

In various embodiments, an MCEC can be used to mitigate one or more of the above difficulties associated with hydrogen production from hydrocarbons. One type of integration is to use the anode output flow from an MCEC as an oxygen-containing gas for an oxidation or combustion reaction. A susbstantial portion of the anode output flow from an MCEC corresponds to Oand COthat is formed from carbonate that is transported across the electrolyte. Optionally, a sweep gas such as HO can be used to reduce the concentration of Oand COin the anode, thus further driving the reaction. This allows the anode output stream to correspond to O, CO, and HO (or optionally another sweep gas), while containing a reduced or minimized amount of N, such as having substantially no N(less than 0.05 vol %).

This type of anode output stream, which contains a reduced or minimized amount of N, can be used as an oxygen-containing gas for an oxidation or combustion reaction. As one example, this type of oxygen-containing gas can be used for the regeneration (combustion) step of a reforming cycle being performed in a reverse flow reactor. As another example, this type of oxygen-containing gas can be used for a partial oxidation reaction. Because the oxygen-containing gas contains a reduced or minimized content of N, the separations required for forming a high purity CO-containing stream can be simplified. During combustion or oxidation, the reaction products will be HO and CO. The water can be separated from the COby condensation. If CO is present, additional combustion can be performed to make additional CO. This is in contrast to the separations that would typically be needed to separate COfrom N.

In addition to use of the anode output flow, the cathode reaction of the MCEC can also be used to assist with improving the purity of the Hproduct and/or increase the molar ratio of Hto CO for a synthesis gas product. Conventionally, a water gas shift reaction can be used to form additional hydrogen by converting CO to CO, but this typically requires addition of substantial amounts of HO. By contrast, if the Hproduct/synthesis gas product is used as part of the cathode input flow for the MCEC, the cathode reaction in the MCEC can be used to reduce the CO(and HO) content of the product flow while also generating additional H.

In addition to integration with systems for hydrogen production, an MCEC can also be used to provide an O-containing stream for power generation applications, such as electrical power generation using a natural gas fired turbine. In addition to containing O, the MCEC anode output flow contains a reduced or minimized amount of N, while also containing CO(and optionally HO) that can facilitate heat transport within the combustion zone for the turbine. Thus, the anode output flow can be used as an O-containing stream for combustion or partial oxidation reactions, while avoiding introduction of substantial amounts of Ninto a reaction environment. This can allow for simplified capture and sequestration of COfrom the resulting flue gas.

In some embodiments, COcapture can be performed on at least a portion of the anode output flow. In such embodiments, the Opresent in the anode output flow can be combusted to simplify the process of separating the COfrom the remaining components in the anode output flow.

Reformable Fuel: Reformable fuel is defined as any compound that contains sufficient amounts of hydrogen atoms and carbon atoms so that the compound can be at least partially converted in Hand carbon oxides under conditions suitable for hydrocarbon reforming. Alcohols are an example of non-hydrocarbon compounds that can also be reformed to produce at least Hand carbon oxides.

Electrolysis cell and electrolysis cell stack definitions: In this discussion, an electrolysis cell can correspond to a single cell, with an anode and a cathode separated by an electrolyte. The anode and cathode can receive input gas flows to facilitate the respective anode and cathode reactions for receiving electricity and transporting charge across the electrolyte to allow for production of hydrogen. An electrolysis cell stack can represent a plurality of cells in an integrated unit. Although an electrolysis cell stack can include multiple electrolysis cells, the electrolysis cells can typically be connected in parallel and can function (approximately) as if they collectively represented a single electrolysis cell of a larger size. When an input flow is delivered to the anode or cathode of an electrolysis cell stack, the electrolysis cell stack can include flow channels for dividing the input flow between each of the cells in the stack and flow channels for combining the output flows from the individual cells. In this discussion, an electrolysis cell array can be used to refer to a plurality of electrolysis cells (such as a plurality of electrolysis cell stacks) that are arranged in series, in parallel, or in any other convenient manner (e.g., in a combination of series and parallel). An electrolysis cell array can include one or more stages of electrolysis cells and/or electrolysis cell stacks, where the anode/cathode output from a first stage may serve as the anode/cathode input for a second stage. It is noted that the anodes in an electrolysis cell array do not have to be connected in the same way as the cathodes in the array. For convenience, the input to the first anode stage of an electrolysis cell array may be referred to as the anode input for the array, and the input to the first cathode stage of the electrolysis cell array may be referred to as the cathode input to the array. Similarly, the output from the final anode/cathode stage may be referred to as the anode/cathode output from the array.

It should be understood that reference to use of a electrolysis cell herein typically denotes an “electrolysis cell stack” composed of individual electrolysis cells, and more generally refers to use of one or more electrolysis cell stacks in fluid communication. Individual electrolysis cell elements (plates) can typically be “stacked” together in a rectangular array called an “electrolysis cell stack”. This electrolysis cell stack can typically take a feed stream and distribute reactants among all of the individual electrolysis cell elements and can then collect the products from each of these elements. When viewed as a unit, the electrolysis cell stack in operation can be taken as a whole even though composed of many (often tens or hundreds) of individual electrolysis cell elements. If a sufficiently large volume electrolysis cell stack is available to process a given exhaust flow, the systems and methods described herein can be used with a single molten carbonate electrolysis cell stack. In other embodiments of the invention, a plurality of electrolysis cell stacks may be desirable or needed for a variety of reasons. For the purposes of this invention, unless otherwise specified, the term “electrolysis cell” should be understood to also refer to and/or is defined as including a reference to an electrolysis cell stack composed of set of one or more individual electrolysis cell elements for which there is a single input and output, as that is the manner in which electrolysis cells are typically employed in practice. Similarly, the term electrolysis cells (plural), unless otherwise specified, should be understood to also refer to and/or is defined as including a plurality of separate electrolysis cell stacks.

It is noted that volume percentages of gas flows can be reported either on a “wet” basis, where all components in the gas flow are used to calculate volume percentages, or on a “dry” basis, where any water present in the gas flow is not considered when calculating volume percentages. In this discussion, unless otherwise specified, all volume percentages for gas flows are on a “wet” basis. It is understood that for a gas flow with no water content, the “wet” basis and “dry” basis values are identical.

Generally, a MCEC can include typical elements for an electrolysis cell and/or a fuel cell. For a MCEC, the cell can include an anode and a cathode that are separated by an electrolyte matrix that contains an electrolyte. An anode collector provides electrical contact between the anode and the other anodes in the stack, while a cathode current collector provides similar electrical contact between the cathode and the other cathodes in the fuel cell stack. Additionally anode collector allows for introduction and exhaust of gases from the anode, while the cathode current collector allows for introduction and exhaust of gases from the cathode. In some embodiments, a structural mesh layer can be disposed between the anode and the anode current collector.

During operation, COand HO are passed into the cathode current collector, along with an input flow of electrons. The COand HO react at or near an anode interface region, where the cathode has an interface with the electrolyte matrix. The reaction results in formation of carbonate ions (CO) and H. The carbonate ions are transported across the electrolyte. After transport, the carbonate ions reach an anode interface region, where a portion of the electrolyte is present in pores of the anode. The carbonate ions react to form COand O. Optionally, a sweep gas (such as a water) can be introduced into the anode to facilitate removal of the COand Ofrom the anode as an anode exhaust. Optionally, additional reforming can be performed in the cathode, to allow for additional Hgeneration, thus increasing the Hcontent of the cathode exhaust while also providing additional COfor transfer across the electrolyte.

In various embodiments, the flow direction within the anode of a molten carbonate fuel cell can have any convenient orientation relative to the flow direction within a cathode. One option can be to use a co-current or counter-current flow configuration. Using co-current flow or counter-current flow can assist with providing higher uniformity in gas concentrations within a fuel cell. However, using co-current or counter-current flow can increase the complexity of the gas flow management. Another option can be to use a cross-flow configuration, so that the flow direction within the anode is roughly at a 90° angle relative to the flow direction within the cathode. This type of flow configuration can have practical benefits, as using a cross-flow configuration can allow the manifolds and/or piping for the anode inlets/outlets to be located on different sides of a fuel cell stack from the manifolds and/or piping for the cathode inlets/outlets.

In various embodiments, the cathode input stream for a MCEC can include COand HO, while the cathode output stream or cathode exhaust for a MCEC can include H, HO, and CO. Electricity is also added to the cathode to provide electrons for the cathode reaction. The hydrogen is a reaction product from the conversion of CO, HO, and electrons into carbonate ions. The HO and COin the cathode exhaust correspond to unreacted input components that typically need to be present in order to have efficient operation of the electrolysis cell. If either the COor the HO becomes depleted in the cathode, the cell reaction will stop and/or other side reactions will occur.

Examples of combustion sources that can provide a COstream include, but are not limited to, sources based on combustion of natural gas, combustion of coal, and/or combustion of other hydrocarbon-type fuels (including biologically derived fuels). Additional or alternate sources can include other types of boilers, fired heaters, furnaces, and/or other types of devices that burn carbon-containing fuels in order to heat another substance (such as water or air).

Still other types of CO-containing streams can correspond to streams from other types of reactors/process elements that are integrated with the MCEC. Examples of other types of combustion sources include the combustion step of a reverse flow reactor and the output flow from a partial oxidation reactor.

In some embodiments, the COcontent of the cathode input stream can be 3.0 vol % to 50 vol %, or 3.0 vol % to 30 vol %, or 3.0 vol % to 15 vol %, or 3.0 vol % to 10 vol %, or 10 vol % to 50 vol %, or 10 vol % to 30 vol %. In some embodiments, the HO content of the cathode input stream can be 3.0 vol % to 50 vol %, or 3.0 vol % to 30 vol %, or 3.0 vol % to 15 vol %, or 3.0 vol % to 10 vol %, or 10 vol % to 50 vol %, or 10 vol % to 30 vol %.

Additionally or alternately, in some embodiments, a portion of the cathode input flow can correspond to methane (and/or other reformable hydrocarbons). In such embodiments, the combined content of COand CHin the cathode input flow can be 3.0 vol % or more, or 5.0 vol % or more, or 10 vol % or more, or 15 vol % or more, such as up to 50 vol % or possibly still higher. This provides a way to further increase the hydrogen produced by electrolysis cell without requiring additional input of electrons. In this type of optional embodiment, excess hydrocarbons can also be present in the cathode exhaust. Examples of hydrocarbon (including hydrocarbon-like) fuel streams that can be used as a feed for performing additional reforming in the cathode include natural gas, streams containing C-Ccarbon compounds (such as methane or ethane), and streams containing heavier Chydrocarbons (including hydrocarbon-like compounds), as well as combinations thereof. Still other additional or alternate examples of potential fuel streams can include biogas-type streams, such as methane produced from natural (biological) decomposition of organic material.

Optionally, the cathode output stream could also have inert compounds if such inert compounds are present in the cathode input flow. For example, if the source of COfor the cathode is a combustion source that uses air as an oxidant, both Nand Ofrom the air can optionally be present in the cathode output flow. In some embodiments, the cathode output flow or exhaust can be substantially free of Nand/or O, such as having a content of Nand/or Oof 1.0 vol % or less, or 0.1 vol % or less, such as down to 0.01 vol % (or detection limit) for Nand/or O. It is noted that Oin the cathode input flow can potentially react with Hformed in the cathode to make additional water, so in some embodiments it is preferable to have a reduced or minimized content of Oin the cathode input flow. In such embodiments, the cathode input flow can contain 0.1 vol % or less of O, such as down to having no Ocontent. Optionally, combustion can be performed on the cathode input flow prior to introduction of the flow into the cathode, so that any oxygen in the cathode input flow is used in a combustion reaction to form carbon oxides and water prior to passing the cathode input flow into the cathode. In some embodiments, the cathode input flow can contain 10 vol % or less of N, or 1.0 vol % or less, such as down to 0.01 vol % (or detection limit) for N.

More generally, in such embodiments, the cathode input flow can contain 0 vol % to 5.0 vol % of N, or 0 vol % to 2.0 vol %, or 0.1 vol % to 5.0 vol %, or 0.1 vol % to 2.0 vol %. In some alternative embodiments, an MCEC can be used to form a higher purity COstream (anode exhaust) from a stream (cathode input flow) that contains both COand N. In such alternative embodiments, the cathode input flow can contain 5.0 vol % to 80 vol % N, or 5.0 vol % to 50 vol %, or 10 vol % to 80 vol %, or 10 vol % to 50 vol %, or 25 vol % to 80 vol %, or 25 vol % to 50 vol %.

The cathode input flow can also contain H. For example, if COis formed by reforming hydrocarbons prior to entering the MCEC, the input flow can also contain the Hformed by reforming. In some embodiments where His present in the input flow to the cathode, the cathode input flow can contain 2.0 vol % to 75 vol % H, or 2.0 vol % to 50 vol %, or 2.0 vol % to 25 vol %, or 2.0 vol % to 10 vol %, or 5.0 vol % to 75 vol %, or 5.0 vol % to 50 vol %, or 5.0 vol % to 25 vol %, or 10 vol % to 75 vol %, or 10 vol % to 50 vol % or 10 vol % to 25 vol %, or 25 vol % to 75 vol %, or 25 vol % to 50 vol %.

Based on the reaction in the cathode, the Hcontent of the cathode output flow or cathode exhaust can have a higher Hcontent than the cathode input flow and a lower COcontent than the cathode input flow. In various embodiments, the Hcontent of the cathode output flow can be greater than the Hcontent of the cathode input flow by 2.0 vol % or more, or 5.0 vol % or more, or 10 vol % or more, or 20 vol % or more, such as up to 50 vol %, or possibly still higher. Additionally or alternately, in various embodiments, the COcontent of the cathode output flow can be lower than the COcontent of the cathode input flow by 2.0 vol % or more, or 5.0 vol % or more, or 10 vol % or more, such as down to 25 vol % or possibly still lower. It is noted that due to the transfer of carbonate ions across the electrolyte, the total volume of the cathode input flow will typically be different the total volume of the cathode output flow. When comparing the volume percentages, the vol % of a component in the cathode input flow is calculated relative to the total cathode input flow, while the vol % of a component in the cathode output flow is calculated relative to the total cathode output flow.

The anode output flow or anode exhaust can include COand O. In some embodiments, if no sweep gas is used, the anode exhaust can correspond to just COand O, in a molar ratio of roughly 2:1 based on the stoichiometry of the reaction for converting carbonate ions into COand O. More typically, a sweep gas can be used to assist with removing COand Ofrom the anode. Any convenient molar ratio of sweep gas to COcan be used. In some embodiments, the Oconcentration in the anode exhaust can be 3.0 vol % to 35 vol %, or 6.0 vol % to 35 vol %, or 10 vol % to 35 vol %, or 20 vol % to 35 vol %, or 3.0 vol % to 25 vol %, or 6.0 vol % to 25 vol %, or 10 vol % to 25 vol %, or 3.0 vol % to 15 vol %, or 6.0 vol % to 15 vol %. Preferably, the anode output flow/anode exhaust can include a reduced or minimized content of N. One option is for the anode exhaust to contain no N, or substantially no N(0.1 vol % or less). More generally, in such embodiments, the anode exhaust can contain 0 vol % to 5.0 vol % of N, or 0 vol % to 2.0 vol %, or 0.1 vol % to 5.0 vol %, or 0.1 vol % to 2.0 vol %.

During operation of an MCEC, an anode input flow is not strictly necessary. After carbonate ions are transported across the electrolyte, the carbonate ions are converted in the cathode into COand O. No additional inputs are required for this reaction to occur. However, in order to avoid a buildup of COand Oin the anode, a sweep gas can be added as an anode input flow. For example, steam can be used as a sweep gas. HO can be readily separated from CO, so adding steam as a sweep gas still allows for recovery of a high purity COstream with relatively simple separation techniques (such as separating water by condensation).

A suitable temperature for operation of an MCEC can be from 450° C. to 750° C., or 500° C. to 750° C., or 550° C. to 750° C., or 600° C. to 750° C., or 450° C. to 650° C., or 500° C. to 650° C., or 550° C. to 650° C. These temperatures correspond to cathode outlet temperatures. The cathode outlet will typically be hotter than the cathode inlet, but in some embodiments, the cathode outlet temperature could be similar to or even lower than the cathode inlet temperature. An example of a cathode inlet temperature is roughly 550° C. with a cathode outlet temperature of roughly 625° C. In another example, both the cathode inlet and cathode outlet can be at roughly 550° C. or at roughly 625° C. Prior to entering the cathode, heat can be added to or removed from the cathode input stream, if desired, e.g., to provide heat for other processes, such as reforming additional fuel. For example, if the source for the cathode input stream is a combustion exhaust stream, the combustion exhaust stream may have a temperature greater than a desired temperature for the cathode inlet. In such an embodiment, heat can be removed from the combustion exhaust prior to use as the cathode input stream. Alternatively, the combustion exhaust could be at very low temperature, for example after a wet gas scrubber on a coal-fired boiler, in which case the combustion exhaust can be below about 100° C. Alternatively, the combustion exhaust could be from the exhaust of a gas turbine operated in combined cycle mode, in which the gas can be cooled by raising steam to run a steam turbine for additional power generation. In this case, the gas can be below about 50° C. Heat can be added to a combustion exhaust that is cooler than desired.

Reverse flow reactors can be used for reforming of hydrocarbons. Integrating MCECs with reverse flow reactors can provide a variety of advantages when reforming hydrocarbons to make hydrogen or synthesis gas in a reverse flow reactor. First, the reforming product from the reverse flow reactors can be used as an cathode input flow for the MCEC. This can reduce the COcontent of the reforming product while increasing the Hcontent. Optionally, additional hydrocarbons could be added to the cathode input flow in order to perform additional reforming. Thus, a substantial synergy can be achieved just by using a the reforming effluent from an RFR as at least a part of a cathode input flow for an MCEC.

The MCEC can also provide an input flow for the regeneration step of the RFR. The anode output from an MCEC is an oxygen-containing gas that contains also COwhile having substantially no Ncontent. By adding fuel (such as methane or hydrogen) to the anode output flow, all of the components necessary for combustion can be introduced into the regeneration step. Optionally, a portion of the regeneration flue gas can be recycled to provide additional diluent/working fluid for the regeneration input flow. This can allow the regeneration step in the RFR to be performed under conditions, where the diluent or working fluid in the combustion environment is COand/or HO, and substantially no Nis present. Steam (HO) can be used as a sweep gas for the anode, to assist with moving the COand Oout of the anode as an anode exhaust or anode output flow.

Depending on the embodiment, reforming of hydrocarbons can be performed under steam reforming conditions in the presence of HO, under dry reforming conditions in the presence of CO, or under conditions where both HO and COare present in the reaction environment. As a general overview of operation during reforming in a swing reactor, such as a reverse flow reactor, a regeneration step or portion of a reaction cycle can be used to provide heat for the reactor. Reforming can then occur within the reactor during a reforming step or portion of the cycle, with the reforming reaction consuming heat provided during the reactor regeneration step. During reactor regeneration, fuel and an oxidant are introduced into the reactor from a regeneration end of the reactor. The bed and/or monoliths in the regeneration portion of the reactor can absorb heat, but typically do not include a catalyst for reforming. As the fuel and oxidant pass through the regeneration section, heat is transferred from the regeneration section to the fuel and oxidant. Combustion does not occur immediately, but instead the location of combustion is controlled to occur in a middle portion of the reactor. The flow of the reactants continues during the regeneration step, leading to additional transfer of the heat generated from combustion into the reforming end of the reactor.

After a sufficient period of time, the combustion reaction is stopped. Any remaining combustion products and/or reactants can optionally be purged. The reforming step or portion of the reaction cycle can then start. The reactants for reforming can be introduced into the reforming end of the reactor, and thus flow in effectively the opposite direction relative to the flow during regeneration. The bed and/or monoliths in the reforming portion of the reactor can include a catalyst for reforming. In various embodiments, at least a portion of the catalyst can correspond to a catalyst formed from a ceramic composition as described herein. As reforming occurs, the heat introduced into the reforming zone during combustion can be consumed by the endothermic reforming reaction. After exiting the reforming zone, the reforming products (and unreacted reactants) are no longer exposed to a reforming catalyst. As the reforming products pass through the regeneration zone, heat can be transferred from the products to the regeneration zone. After a sufficient period of time, the reforming process can be stopped, remaining reforming products can optionally be collected or purged from the reactor, and the cycle can start again with a regeneration step.

The reforming reaction performed within the reactor can correspond reforming of methane and/or other hydrocarbons using steam reforming, in the presence of HO; using dry reforming, in the presence of CO, or using “bi” reforming in the presence of both HO and CO. Examples of stoichiometry for steam, dry, and “bi” reforming of methane are shown in equations (1)-(3).

Dry Reforming: CH+CO=2CO+2H  (1)

Steam Reforming: CH+HO=CO+3H  (2)

Bi Reforming: 3CH+2HO+CO=4CO+8H.  (3)