Alternating fixed bed and fluidized bed reactor systems and methods

Abstract

The present disclosure relates to systems and methods for producing hydrogen among other products. In some embodiments, the method includes continuously performing a cracking step in a fixed bed mode and a flowing step in a fluidized bed mode. Such a continuous process may provide several advantages, including, for example, a step of regenerating a catalyst during the fluidized bed mode so that useful heat is generated for use in the endothermic cracking step.

Description

[Technical field]

[0001] The present disclosure relates to systems and methods for producing hydrogen and / or other products using alternating fixed and flow reactor systems and methods. [Background technology]

[0002] Hydrogen is one of the more important clean energy options of the future. Unfortunately, many existing methods and systems for producing hydrogen are not cost-effective and / or result in greenhouse gas emissions such as carbon dioxide. Solutions are needed to produce hydrogen in a cost-effective manner. It would be even more advantageous if such solutions were not energy intensive and / or did not produce substantial amounts of uncaptureable carbon dioxide. Summary of the Invention

[0003] Advantageously, the present application relates to new systems and methods that advantageously produce hydrogen in a cost-effective manner, that is not energy intensive, and / or that does not produce substantial amounts of uncaptureable carbon dioxide.

[0004] In one embodiment, the present application relates to a method for producing hydrogen and / or solid carbon. The method includes cracking a light hydrocarbon stream in a reactor in the presence of a catalyst under conditions suitable to produce at least (1) hydrogen and (2) carbon by-products deposited on the surface of the catalyst. The light hydrocarbon stream typically flows downward and the reactor is typically in a fixed bed reactor mode in the first stage of operation during cracking. When reacting continuously, the pressure drop across the reactor bed increases due to the accumulation of solid carbon by-products and the catalyst may also deactivate over time. When the conversion of the light hydrocarbons drops by more than 20%, or more than 30%, or more than 50%, and / or the pressure drop across the reactor increases by more than 5 psi, or more than 10 psi, or more than 20 psi, or more than 50 psi, the first stage of operation should be relatively completed and the second stage of operation may begin. In the second stage of operation, a light hydrocarbon gas, superheated steam, inert gas, or mixtures thereof are flowed upwardly through the reactor while the reactor is in a flow reactor mode and conditions are suitable to separate at least a portion up to all of the deposited carbon by-products from the surface of the catalyst. When the amount of solid carbon by-products being removed from the catalyst surface has substantially decreased or stopped, the second stage of operation shall be completed and a third stage of operation shall be initiated. In the third stage of operation, a mixture of air, oxygen, or a suitable oxidant is flowed upwardly through the reactor to regenerate the catalyst by reacting the oxidant with the carbon by-products.

[0005] In another embodiment, the present application relates to a method for producing hydrogen, comprising the steps of first cracking in a fixed bed mode in a first reactor, and then sequentially flowing in a fluidized bed mode. The cracking step comprises cracking a light hydrocarbon stream comprising methane in the reactor under conditions suitable for producing at least (1) hydrogen and (2) carbon by-products in the presence of a catalyst. The light hydrocarbon stream comprising methane is flowing downward and the reactor is in a fixed bed reactor mode. The carbon and catalyst separation step generally comprises flowing a light hydrocarbon gas comprising methane, superheated steam, an inert gas, or a mixture thereof upward through the reactor. The reactor is in a fluidized reactor mode and the superficial velocity of the flow is sufficient to separate at least a portion up to substantially all or all of the deposited carbon by-products from the surface of the catalyst. The catalyst regeneration process involves flowing an oxidant, such as air, oxygen, steam, or any other oxidant, to regenerate the catalyst by reacting the oxidant with the carbon by-products to generate heat for use in the cracking process.

[0006] In another embodiment, the present application relates to a reactor system including a reactor vessel containing a light hydrocarbon catalyst in a fixed bed configuration. The reactor vessel is configured to receive a downwardly flowing light hydrocarbon feed to produce hydrogen while depositing carbon by-products on the catalyst surface. The reactor vessel is configured to receive an upwardly flowing light hydrocarbon gas, superheated steam, or inert gas to fluidize the light hydrocarbon catalyst and then an oxidant to remove the deposited carbon by-products. The reactor system is configured to continuously alternate between a fixed bed reactor mode and a fluidized bed reactor mode.

[0007] These and other objects, features and advantages of the exemplary embodiments of the present disclosure will become apparent from the following detailed description of the exemplary embodiments of the present disclosure, taken in conjunction with the appended claims.

[0008] The various embodiments of the present disclosure, together with further objects and advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0009] [Figure 1] 1 illustrates an exemplary embodiment of a reactor system and / or method in which two reactors are connected in parallel.

[0010] [Diagram 2] 1 illustrates an exemplary embodiment of a reactor system and / or method having a separator and one or more heat exchangers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The following description of the embodiments provides non-limiting representative examples that refer to numbers to specifically illustrate the features and teachings of various aspects of the present invention. It should be recognized that the described embodiments can be realized separately or in combination with other embodiments of the description of the embodiments. Those skilled in the art who review the description of the embodiments should be able to learn and understand the described different aspects of the present invention. The description of the embodiments should facilitate the understanding of the present invention to the extent that other implementations that are not covered in detail but are within the knowledge of those skilled in the art who read the description of the embodiments are understood to be consistent with the application of the present invention.

[0012] The present application relates to methods and systems for producing hydrogen and / or solid carbon, among other potential products.

[0013] Cracking process The method generally involves cracking a light hydrocarbon stream in a reactor in the presence of a catalyst under suitable conditions to produce at least (1) hydrogen and (2) carbon by-products that deposit on the surface of the catalyst. The light hydrocarbons used are not particularly limited and may include, for example, C1-C6 or C1-C4 or C1-C2 alkanes such as methane, ethane, or natural gas, pure or in any suitable mixture with possible minor amounts of other components, for example, 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, inert gases such as nitrogen, or any mixtures thereof. That is, the light hydrocarbons or mixtures used may include any suitable composition such that the resulting product includes at least hydrogen and potentially carbon by-products that deposit on the surface of the catalyst. Particularly useful compositions may include light hydrocarbon streams that include methane or natural gas, for example, light hydrocarbon streams that include more than about 80%, or more than about 90%, or more than about 95%, or more than about 99% methane.

[0014] Suitable cracking catalysts and associated suitable conditions may vary depending on the system configuration, starting materials, desired products and other factors. In general, suitable light hydrocarbon cracking catalysts and associated suitable conditions include any catalyst and conditions that convert one or more heavier hydrocarbons into lighter hydrocarbons, carbon, or mixtures thereof. Suitable catalysts and reaction conditions may include, for example, activated carbon, iron ore, or metal pyrolysis catalysts such as nickel- or iron-based catalysts, metal-based catalysts with metals such as Ni, La, Fe, Mo, Co, Pd on supports such as alumina, TiO2, or SiO2, unsupported Fe, iron ore (waste), activated carbon, etc., with temperatures above about 500°C, or above about 600°C, or above about 700°C, or above about 1000°C according to the following reaction equation: [ka]

[0015] Typically, the reactor is in a fixed bed reactor mode during the cracking step. That is, the light hydrocarbon stream flows downwardly through the reactor while being heated and passes over a series of catalysts in fixed positions, such as on a series of trays, under the conditions described above, to form (1) hydrogen and (2) carbon by-products deposited on the surface of the catalyst. The hydrogen can be separated in any 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 recycled to the inlet of the reactor. Optionally, the unreacted light hydrocarbon stream can be treated prior to recycling to remove a substantial portion of impurities that may poison the catalyst. The hydrogen can be cooled and / or further purified for transportation, storage or use. Heat from the catalyst regenerating step can be used in the cracking step, as described further below. Rinse and recycle process After cracking in the fixed reactor mode, the reactor mode is switched to the flow reactor mode. Such alternation may be performed continuously, such that after the flow regeneration step, the reactor mode is switched back to the fixed reactor mode. In the flow reactor mode, a light hydrocarbon gas, steam, superheated steam, inert gas, or mixtures thereof is flowed upwardly through the reactor under conditions suitable for separating at least some to all of the accumulated carbon by-products from the surface of the catalyst. The catalyst is then regenerated by reacting an oxidant with the carbon by-products. In general, it may be desirable to remove a substantial portion of the solid carbon before it reacts to form CO2.

[0016] Conditions for separating the deposited carbon by-product and reacting the oxidant may vary depending on the particular reactor, reactants, desired products, etc. In some embodiments, suitable conditions for separating at least some to all of the deposited carbon by-product from the surface of the catalyst include using a suitable turbulence intensity to break up or shear the carbon deposits and separate them from the catalyst surface. Such turbulence may be generated in any convenient manner, for example, using an upflow superficial velocity of about 0.05 meters, about 0.1 meters, or about 0.5 meters, or about 1 meter up to about 5 meters or up to about 4 meters per second. If desired, the separated carbon by-product may be separated in any convenient manner.

[0017] The oxidant used to regenerate the catalyst is not particularly critical, so long as efficient catalyst regeneration is achieved. In some embodiments, air or pure oxygen may be introduced with the upwardly flowing stream of light hydrocarbon gas, steam, superheated steam, inert gas, or mixtures thereof, or may be added thereafter. The regeneration reaction is typically exothermic, and at least a portion of the heat generated may be used in the cracking process, if desired. At least a portion to all or nearly all of the carbon dioxide produced in the regeneration reaction may be separated or captured, for example, via a carbon dioxide capture and sequestration unit.

[0018] In some embodiments, a gas release zone can be used during the fluidized reactor mode. If present, such a gas release zone may comprise, for example, a vessel diameter configured to separate gas and solids while the reactor is fluidized, reduce catalyst, or both.

[0019] In some embodiments, the release zone may be configured to allow separation of the carbon products from the catalyst particles. At appropriate gas velocities, the catalyst particles may return to the fluidized bed zone, while the lighter carbon products are carried away by the gas stream. The solid carbon products may then be separated from the gas in a gas-solid separation process, if desired.

[0020] In some embodiments, one or more heat exchangers can be used. The type and location of the one or more heat exchangers can vary depending on the specific process conditions and equipment. In some embodiments, one or more heat exchangers can be placed between the low temperature light hydrocarbon feed and the high temperature cracking product to recover heat, thereby reducing the net energy requirement. Additionally or alternatively, one or more heat exchangers can be present between the low temperature light hydrocarbon feed and the high temperature catalyst regeneration product to recover heat, thereby reducing the net energy requirement.

[0021] Multiple Reactors In some embodiments, it may be desirable to have two or more reactors operating in parallel that carry out the above-described method. In this manner, a first reactor may operate in a production mode and a second reactor may operate in a regeneration mode, or vice versa. By operating two or more parallel reactors in opposite modes, heat can be shared, thereby making the process more efficient. For example, heat generated by a reactor operating in a regeneration mode can be transferred to a reactor operating in a production or cracking mode that requires heat. Heat exchangers or other mechanisms can be used to transfer heat between the reactors as needed.

[0022] Specific embodiments FIG. 1 shows two parallel reactors using an embodiment of the method described above. That is, natural gas is input to the top of the reactor and flows downward and is cracked over a fixed catalyst bed mode. Upflow in flow mode removes carbon deposits from the catalyst surface, and an air or oxygen purge regenerates the catalyst while producing heat. The modes of the two reactors alternate such that one is in production or cracking fixed mode while the other is in flow mode or regeneration mode. FIG. 2 shows additional potential embodiments that may be used, such as natural gas pretreatment and / or heating, membrane separators, natural gas recycle, heat recovery, hydrogen purification, carbon dioxide capture, and / or solid carbon separation.

[0023] In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will be apparent, however, that various modifications and changes may be made and additional embodiments may be realized without departing from the broader scope of the invention as set forth in the appended claims. The specification and drawings are therefore to be regarded in an illustrative rather than a restrictive sense.

Claims

1. 1. A method for producing hydrogen and solid carbon, comprising: cracking a light hydrocarbon stream in a reactor in the presence of a catalyst under conditions suitable to produce at least (1) hydrogen and (2) carbon by-products deposited on the surface of said catalyst, said light hydrocarbon stream flowing downward and said reactor being in a fixed bed reactor mode; flowing a light hydrocarbon gas, superheated steam, an inert gas, or a mixture thereof upwardly through the reactor, the reactor being in a flow reactor mode and the conditions being suitable for separating at least some, up to all, of the deposited carbon by-products from the surface of the catalyst; and regenerating the catalyst by reacting an oxidant with the carbon by-product. Including, The method further comprising utilizing at least a portion of the heat from the regenerating step in said cracking step.

2. The method of claim 1 , wherein the steps are performed continuously.

3. 10. The method of claim 1, wherein the conditions suitable for separating at least some, up to all, of the accumulated carbon by-products from the surface of the catalyst comprise a superficial velocity of about 0.05 to about 5 meters per second.

4. 10. The method of claim 1 further comprising the step of using a second reactor operating in parallel with the first reactor.

5. 5. The method of claim 4, wherein the first reactor operates in a production mode while the second reactor operates in a regeneration mode.

6. 5. The method of claim 4, wherein the first reactor operates in a regeneration mode while the second reactor operates in a production mode.

7. 10. The method of claim 1, further comprising using a second reactor and a third reactor, each reactor operating in parallel with the first reactor, and wherein at least one of the first reactor, the second reactor, and the third reactor operates in a regeneration mode while the remaining at least one of the first reactor, the second reactor, and the third reactor operates in a production mode.

8. The method of claim 1 wherein the inert gas is nitrogen.

9. 10. The method of claim 1, wherein the reactor alternates between a fixed bed reactor mode and a flow reactor mode.

10. 10. The method of claim 1, further comprising the step of separating the hydrogen from the unreacted light hydrocarbon gas, superheated steam, inert gas, or any mixture thereof.

11. separating hydrogen during said cracking step; separating the carbon by-product separated during said flowing step; and Separating or capturing at least a portion up to substantially all of any carbon dioxide formed in said regenerating step. The method of claim 1 further comprising:

12. 8. The method of claim 7, further comprising the step of recycling unreacted light hydrocarbon gas, superheated steam, inert gas, or any mixture thereof to the inlet of the reactor.

13. 10. The method of claim 1 further comprising capturing at least a portion of any carbon dioxide produced.

14. 13. The method of claim 12, further comprising operating a second reactor in parallel with the first reactor, wherein the second reactor performs the cracking step in a fixed bed mode while the first reactor performs the flowing step.

15. 14. The reactor system of claim 13, further comprising a second reactor operably connected in parallel.

16. 14. The reactor system of claim 13, wherein the reactor vessel comprises a gas release zone.

17. 15. The reactor system of claim 14, wherein the gas release zone comprises a vessel diameter configured to separate gas and solids while the reactor vessel is fluidized, reduce catalyst, or both.

18. 14. The reactor vessel of claim 13, further comprising a separator configured to separate hydrogen from light hydrocarbons, natural gas, or both.

19. 14. The reactor system of claim 13 further comprising a heat exchanger.

20. 14. The reactor system of claim 13, further comprising a second reactor and a third reactor operably connected in parallel.

21. 1. A method for producing hydrogen and solid carbon, comprising: cracking a light hydrocarbon stream in a reactor in the presence of a catalyst under conditions suitable to produce at least (1) hydrogen and (2) carbon by-products deposited on the surface of said catalyst, said light hydrocarbon stream flowing downward and said reactor being in a fixed bed reactor mode; flowing a light hydrocarbon gas, superheated steam, an inert gas, or a mixture thereof upwardly through the reactor, the reactor being in a flow reactor mode and the conditions being suitable for separating at least some, up to all, of the deposited carbon by-products from the surface of the catalyst; and regenerating the catalyst by reacting an oxidant with the carbon by-product. Including, The method further comprises the step of pretreating the unreacted light hydrocarbon gas to remove a substantial portion of catalyst-poisoning impurities.

22. The method of claim 21, further comprising using at least a portion of the heat from the regenerating step to crack light hydrocarbons.

23. 1. A method for producing hydrogen, comprising: (1) carrying out a cracking step in a fixed bed mode and a flowing step in a fluidized bed mode in a first reactor; the cracking step comprises cracking a light hydrocarbon stream comprising methane in a reactor in the presence of a catalyst under conditions suitable to produce at least (1) hydrogen and (2) carbon by-products deposited on the surface of the catalyst, the light hydrocarbon stream comprising methane flowing downward and the reactor being in a fixed bed reactor mode; performing said flowing step including flowing a light hydrocarbon gas including methane, superheated steam, an inert gas, or a mixture thereof upwardly through said reactor, said reactor being in a flow reactor mode, and wherein the superficial velocity of the flow is sufficient to separate at least some, up to all, of said deposited carbon by-products from the surface of said catalyst; and (2) regenerating the catalyst by reacting an oxidant with the carbon by-products during the flowing step to generate heat for use in the cracking step. A method comprising:

24. 1. A reactor system comprising: a reactor vessel containing a light hydrocarbon catalyst in a fixed bed configuration; the reactor vessel is configured to receive a downwardly flowing light hydrocarbon feed and produce hydrogen while depositing carbon by-products on a catalyst surface; the reactor vessel is configured to receive an upwardly flowing light hydrocarbon gas, superheated steam, or inert gas to fluidize the light hydrocarbon catalyst and thereafter receive an oxidant to remove accumulated carbon by-products; the reactor system is configured to sequentially alternate between a fixed bed reactor mode and a fluidized bed reactor mode; Reactor system.

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