Alternating fixed and fluidized bed reactor systems and processes

Abstract

The present disclosure describes a system and method for producing hydrogen among other products. In some embodiments, the method comprises sequentially performing a decomposition step in a fixed-bed mode and performing a fluidization step in a fluidized-bed mode. Such sequential processes can bring several advantages, including, for example, regenerating the catalyst in the fluidized-bed mode to generate beneficial heat for use in the endothermic decomposition step.

Description

Technology Field

[0001] The present disclosure relates to a system and method for producing hydrogen and / or other products using alternating fixed and fluidized reactor systems and processes. Background Technology

[0002] Hydrogen is one of the increasingly important options for future clean energy. Unfortunately, many existing methods and systems for producing hydrogen are either not cost-effective or result in the emission of greenhouse gases such as carbon dioxide. What is needed is a solution that produces hydrogen in a cost-effective manner. Such a solution would be even more advantageous if it were not energy-intensive and did not generate a significant amount of non-capturable carbon dioxide.

[0003] Advantageously, the present application relates to a new system and method that advantageously produces hydrogen in a cost-effective manner, is not energy-intensive, and / or does not produce a significant amount of non-capturable carbon dioxide.

[0004] In one embodiment, the present application relates to a process for producing hydrogen and / or solid carbon. The process comprises decomposing a light hydrocarbon stream in a reactor in the presence of a catalyst to produce at least (1) hydrogen and (2) carbon byproducts deposited on the catalyst surface under conditions suitable for production. The light hydrocarbon stream generally flows downward, and the reactor is generally in a fixed-bed reactor mode during the first stage of operation in the decomposition. As the reaction continues, the pressure drop across the entire reactor bed increases due to the accumulation of solid carbon byproducts, and the catalyst may also become deactivated over time. When the conversion rate of the light hydrocarbon decreases by more than 20%, or more than 30%, or more than 50%, or the pressure drop across the entire reactor increases by more than 5 psi, or more than 10 psi, or more than 20 psi, or more than 50 psi, the operation of the first stage is relatively completed and the operation of the second stage may begin. In the operation of the second stage, when the reactor is in flow reactor mode and conditions are suitable for separating at least some of the carbon byproducts deposited on the catalyst surface from all of them, a light hydrocarbon gas, superheated steam, an inert gas, or a mixture thereof flows upward through the reactor. When the amount of solid carbon byproducts removed from the catalyst surface is significantly reduced or stops, the operation of the second stage is completed and the operation of the third stage begins. In the third stage of operation, a mixture of air, oxygen, or a suitable oxidizing agent flows upward through the reactor to react the oxidizing agent with the carbon byproducts and regenerate the catalyst.

[0005] In another embodiment, the present application relates to a process for producing hydrogen, comprising first performing a decomposition step sequentially in a fixed-bed mode, and then performing a fluidization step in a fluidized-bed mode in a first reactor. The decomposition step generally comprises decomposing a light hydrocarbon stream containing methane in a reactor in the presence of a catalyst under conditions suitable for producing at least (1) hydrogen and (2) carbon byproducts. The light hydrocarbon stream containing methane flows downward, and the reactor is in a fixed-bed reactor mode. The carbon and catalyst separation step generally comprises flowing a light hydrocarbon gas containing methane, superheated steam, an inert gas, or a mixture thereof upward through the reactor. The reactor is in a fluidized-bed reactor mode, and the surface velocity of the flow is sufficient to separate substantially all or part of the carbon byproducts deposited on the catalyst surface. The catalyst regeneration step comprises regenerating the catalyst by flowing an oxidizing agent, such as air, oxygen, steam, or other oxidizing agent, to react the oxidizing agent with the carbon byproducts to generate heat for use in the decomposition step.

[0006] In another embodiment, the present application relates to a reactor system comprising a reactor vessel containing a light hydrocarbon catalyst of a fixed-bed configuration. The reactor vessel receives a light hydrocarbon feed flowing downward to produce hydrogen and to allow carbon byproducts to be deposited on the surface of the catalyst. The reactor vessel is configured to receive a light hydrocarbon gas, superheated steam, or inert gas flowing upward to fluidize the light hydrocarbon catalyst, and then to receive an oxidizing agent to remove the deposited carbon byproducts. The reactor system is configured to sequentially alternate between a fixed-bed reactor mode and a fluidized-bed reactor mode.

[0007] These and other objects, features, and advantages of embodiments of the present disclosure will become clear from reading the following detailed description of embodiments of the present disclosure when considered together with the appended claims. Brief explanation of the drawing

[0008] Various embodiments of the present disclosure are best understood by referring to the following description together with the accompanying drawings, along with additional purposes and benefits. FIG. 1 illustrates a representative embodiment of a reactor system and / or process having two reactors connected in parallel. FIG. 2 illustrates a representative embodiment of a reactor system and / or process having a separator and one or more heat exchangers. Specific details for implementing the invention

[0009] The following description of embodiments provides non-limiting representative examples by reference to numbers to specifically illustrate the features and teachings of various aspects of the invention. The described embodiments should be recognized as being capable of being implemented separately or in combination with other embodiments described in the description of embodiments. A person skilled in the art reviewing the description of embodiments should be able to learn and understand the various aspects of the invention described. The description of embodiments should facilitate understanding of the invention to the extent that other embodiments not specifically addressed but within the knowledge of a person skilled in the art reading the description of embodiments are understood to be consistent with the application of the invention.

[0010] This application relates to a process and system for producing hydrogen and / or solid carbon among other potential products.

[0011] Decomposition step

[0012] This process generally involves decomposing a light hydrocarbon stream in a reactor in the presence of a catalyst under conditions suitable for producing at least (1) hydrogen and (2) carbon byproducts deposited on the catalyst surface. The light hydrocarbons to be used are not particularly limited and may include, for example, C1-C6, C1-C4, or C1-C2 alkanes such as methane, ethane, or natural gas in their pure form or any suitable mixture potentially containing small amounts of other components such as carbon dioxide, sulfur compounds such as H2S, water, nitrogen, and mixtures thereof. In some embodiments, the light hydrocarbon stream may also include steam, superheated steam, an inert gas such as nitrogen, or any mixture thereof. That is, the light hydrocarbons or mixtures to be used may have any suitable composition such that the resulting product contains at least hydrogen and potentially carbon byproducts deposited on the catalyst surface. A particularly useful composition may include a light hydrocarbon stream containing methane or natural gas, for example, a light hydrocarbon stream containing about 80% or more, or about 90% or more, or about 95% or more, or about 99% or more of methane.

[0013] Suitable decomposition catalysts and associated suitable conditions may vary depending on the system configuration, starting materials, desired products, and other factors. Generally, suitable light hydrocarbon decomposition catalysts and associated suitable conditions include all catalysts and conditions for converting heavier hydrocarbons or hydrocarbons into lighter hydrocarbons, carbon, or mixtures thereof. Suitable catalysts and reaction conditions may include, for example, metal pyrolysis catalysts such as activated carbon, iron ore, or nickel-based or iron-based catalysts; metal-based catalysts having metals such as Ni, La, Fe, Mo, Co, or Pd on supports such as alumina, TiO2, or SiO2; materials such as unsupported Fe, iron ore (waste), activated carbon, etc., and have a temperature of about 500°C or higher, or about 600°C or higher, or about 700°C or higher, or about 1000°C or higher, depending on the reaction equation:

[0014]

[0015] Generally, the reactor is in fixed-bed reactor mode during the cracking step. That is, the light hydrocarbon stream flows down in the reactor while being heated and passes over a series of catalysts in fixed positions, such as a series of trays, under the conditions described above, to form (1) hydrogen and (2) carbon byproducts deposited on the catalyst surface. The hydrogen can be separated in a convenient manner. In one embodiment, a separator such as a membrane separator can be used to separate the product hydrogen from the unreacted light hydrocarbon stream. The unreacted light hydrocarbon stream can be recirculated to the inlet of the reactor. If necessary, the unreacted light hydrocarbon stream can be treated before recirculation to remove a significant amount of impurities that could contaminate the catalyst. The hydrogen can be cooled and / or further purified for transport, storage, or use. As described in more detail below, the heat generated from regenerating the catalyst can be used in the cracking step.

[0016] Flow and regeneration stages

[0017] After decomposition in fixed reactor mode, the reactor mode is alternately switched to fluidized reactor mode. This alternation can be performed sequentially so that the reactor mode can be switched back to fixed reactor mode after a fluidized regeneration step. In fluidized reactor mode, light hydrocarbon gas, steam, superheated steam, inert gas, or a mixture thereof flows upward through the reactor under conditions suitable for separating some or all of the carbon byproducts deposited on the catalyst surface. Subsequently, the catalyst is regenerated by reacting the oxidizing agent with the carbon byproducts. Generally, it may be desirable to remove a significant amount of solid carbon before reacting to form CO2.

[0018] The conditions for separating the deposited carbon byproducts and reacting the oxidizing agent may vary depending on the specific reactor, reactants, desired product, etc. In some embodiments, conditions suitable for separating all or more of the carbon byproducts deposited on the catalyst surface involve separating the carbon deposits from the catalyst surface by allowing breakage or shear using appropriate turbulence intensity. Such turbulence can be generated in a convenient manner, such as using surface velocities of upward flow of about 0.05, about 0.1, or about 0.5 per second, or from about 1 to about 5, or up to about 4 meters. If desired, the detached carbon byproducts can be separated in a convenient manner.

[0019] The oxidant used to regenerate the catalyst is not particularly important as long as efficient catalyst regeneration is achieved. In some embodiments, air or pure oxygen may be introduced along with an upward flow stream of light hydrocarbon gas, steam, superheated steam, inert gas, or a mixture thereof, or alternatively added later. The regeneration reaction is generally an exothermic reaction, and at least some of the heat generated may be used in the decomposition step if desired. All or almost all of at least some of the carbon dioxide generated in the regeneration reaction may be separated or captured, for example, through a carbon dioxide capture and sequestration device.

[0020] In some embodiments, a gas separation zone (disengagement zone) may be used while in fluidized reactor mode. If present, such gas separation zone may include a vessel diameter configured to separate gas and solid, reduce catalyst, or both, while the reactor is fluidized.

[0021] In some embodiments, the separation zone may be configured to separate the carbon product from the catalyst particles. At an appropriate gas velocity, the catalyst particles may fall back into the fluidized bed zone while the light carbon product is carried by the gas stream. Then, if desired, the solid carbon product can be separated from the gas in a gas-solid separation process.

[0022] In some embodiments, one or more heat exchangers may be used. The type and location of the one or more heat exchangers may vary depending on specific process conditions and equipment. In some embodiments, one or more heat exchangers may be positioned between a low-temperature light hydrocarbon feed and a high-temperature decomposition product to recover heat, thereby reducing the net energy requirement. Additionally or alternatively, one or more heat exchangers may be positioned between a low-temperature light hydrocarbon feed and a high-temperature catalyst regeneration product to recover heat, thereby reducing the net energy requirement.

[0023] multiple reactors

[0024] In some embodiments, it may be desirable to have two or three or more reactors operating in parallel to perform the method described above. In this way, the first reactor operates in production mode while the second reactor operates in regeneration mode, or vice versa. Operating two or more parallel reactors in opposite modes allows for heat sharing, making the process more efficient. For example, heat generated in a reactor operating in regeneration mode can be transferred to a reactor operating in production or decomposition mode where heat is required. Heat can be transferred between reactors using heat exchangers or other mechanisms as needed.

[0025] Specific implementation example

[0026] FIG. 1 shows two parallel reactors using an embodiment of the method described above. Specifically, natural gas is input from the top of the reactor, flows downward, and is decomposed in a fixed catalyst bed mode. When flowing upward in a flow mode, carbon deposits are removed from the catalyst surface, and the catalyst is regenerated while air or oxygen purification generates heat. The modes of the two reactors alternate, with one in a production or decomposition fixed mode while the other is in a flow or regeneration mode. FIG. 2 shows additional potential embodiments that can be used for natural gas pretreatment and / or heating, membrane separators, natural gas recirculation, heat recovery, hydrogen purification, carbon dioxide capture and / or solid carbon separation.

[0027] In the foregoing specification, various embodiments have been described with reference to the accompanying drawings. However, it will be apparent that various modifications and changes may be made, additional embodiments may be implemented, and thereafter there may be no departure from the broader scope of the invention specified in the following claims. Accordingly, the specification and drawings should be regarded as descriptive rather than restrictive.

Claims

Claim 1 A process for producing hydrogen and solid carbon, comprising: a step of decomposing a light hydrocarbon stream in a first reactor in the presence of a catalyst under conditions suitable for producing at least (1) hydrogen and (2) carbon byproducts deposited on a catalyst surface, wherein the light hydrocarbon stream flows downward and the first reactor is in a fixed-bed reactor mode; a flow step of causing a light hydrocarbon gas, superheated steam, an inert gas, or a mixture thereof to flow upward through the first reactor, wherein the first reactor is in a flow reactor mode and the conditions are suitable for separating at least some to all of the carbon byproducts deposited on a catalyst surface; and a step of regenerating the catalyst by reacting an oxidizing agent with the carbon byproducts, wherein the process further comprises a step of using at least some of the heat from the regeneration step in the decomposition step. Claim 2 A process in which the above steps are performed sequentially in claim 1. Claim 3 In claim 1, the conditions suitable for separating at least part to all of the carbon byproduct deposited from the catalyst surface include a process comprising a superficial velocity of 0.05 to 5 meters per second. Claim 4 A process according to claim 1, further comprising using a second reactor operating in parallel with the first reactor. Claim 5 A process according to paragraph 4, wherein the first reactor operates in production mode while the second reactor operates in regeneration mode. Claim 6 A process according to claim 1, further comprising using a second reactor and a third reactor, wherein each reactor operates in parallel with the first reactor, and at least one of the first, second, and third reactors operates in a regeneration mode while at least one of the remaining first, second, and third reactors operates in a production mode. Claim 7 A process according to claim 1 in which the first reactor alternately operates between a fixed-bed reactor mode and a flow reactor mode. Claim 8 A process according to claim 1, further comprising the step of separating hydrogen from unreacted light hydrocarbon gas, superheated steam, inert gas, or a mixture thereof. Claim 9 A process according to claim 1, further comprising: a step of separating hydrogen during the decomposition step; a step of separating carbon byproducts separated during the flow step; and a step of separating or capturing at least a portion to substantially all of any carbon dioxide formed in the regeneration step. Claim 10 A process according to claim 6, further comprising the step of recirculating unreacted light hydrocarbon gas, superheated steam, inert gas, or a mixture thereof to the inlet of the first reactor. Claim 11 A process according to claim 1, further comprising the step of capturing at least a portion of any generated carbon dioxide. Claim 12 A process for producing hydrogen and solid carbon, comprising: a step of decomposing a light hydrocarbon stream in a reactor in the presence of a catalyst under conditions suitable for producing at least (1) hydrogen and (2) carbon byproducts deposited on a catalyst surface, wherein the light hydrocarbon stream flows downward and the reactor is in a fixed-bed reactor mode; a flow step of causing a light hydrocarbon gas, superheated steam, an inert gas, or a mixture thereof to flow upward through the reactor, wherein the reactor is in a flow reactor mode and the conditions are suitable for separating at least some to all of the carbon byproducts deposited on a catalyst surface; and a step of regenerating the catalyst by reacting an oxidizing agent with the carbon byproducts, wherein the process further comprises a step of pretreating unreacted light hydrocarbon gas to remove a significant portion of catalyst-contaminating impurities. Claim 13 In paragraph 12, the process further comprises a step of using at least a portion of the heat from a regeneration step to decompose light hydrocarbons. Claim 14 A process for producing hydrogen, comprising: (1) a step of performing a decomposition step in a fixed-bed mode and a fluidization step in a fluidized-bed mode sequentially in a first reactor, wherein the decomposition step comprises decomposing a light hydrocarbon stream containing methane in a reactor under conditions suitable for producing at least (1) hydrogen and (2) carbon byproducts deposited on the surface of a catalyst in the presence of a catalyst, wherein the light hydrocarbon stream containing methane flows downward and the reactor is in a fixed-bed reactor mode; wherein the fluidization step comprises flowing a light hydrocarbon gas containing methane, superheated steam, an inert gas, or a mixture thereof upward through the reactor, wherein the reactor is in a fluidized-bed reactor mode, and the surface velocity of the flow is sufficient to separate at least some to all of the carbon byproducts deposited on the surface of a catalyst; and (2) a step of regenerating the catalyst by reacting an oxidizing agent with the carbon byproducts during the fluidization step to generate heat for use in the decomposition step. Claim 15 A reactor system comprising a reactor vessel containing a light hydrocarbon catalyst of a fixed bed configuration; wherein the reactor vessel is configured to receive a light hydrocarbon feed flowing downward to generate hydrogen while causing carbon byproducts to be deposited on the surface of the catalyst; wherein the reactor vessel is configured to receive a light hydrocarbon gas, superheated steam, or inert gas flowing upward to fluidize the light hydrocarbon catalyst, and then to receive an oxidizing agent to remove the deposited carbon byproducts; wherein the reactor system is configured to operate sequentially alternately between a fixed bed reactor mode and a fluidized bed reactor mode. Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 delete Claim 21 delete Claim 22 delete

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