Patent Application
20240059560
This invention relates to methods and systems for producing hydrogen from hydrocarbons.
Hydrogen is typically produced by steam methane reforming or electrolysis. In steam methane reforming, natural gas is reacted with water at high temperature and pressure to yield hydrogen and carbon monoxide. Additional hydrogen can be obtained by reacting the carbon monoxide with water to yield hydrogen and carbon dioxide. In electrolysis, an electrochemical reaction is used to split water into hydrogen and oxygen. Steam methane reforming, used to produce over 95% of all hydrogen, requires large amounts of water and also produces millions of metric tons of carbon dioxide per year. Electrolysis is less cost efficient than steam methane reforming, requiring large amounts of water as well as large amounts of electrical power.
This disclosure generally relates to systems and methods for hydrogen production from hydrocarbons. Embodiments include systems and methods for reduction of a gas phase metal halide with a gas phase hydrocarbon to yield elemental carbon, a hydrogen halide and the metal, and re-oxidation of the metal with the hydrogen halide to yield hydrogen gas and the metal halide. The reduced metal halide and carbon catalyze the pyrolysis of gas phase hydrocarbons to yield additional elemental carbon and hydrogen gas.
Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.
In addition to the embodiments of the attached claims and the embodiments described above, the following numbered embodiments are also innovative.
Systems and methods described herein are advantageously more energy efficient than steam methane reforming and much more energy efficient than electrolysis. These systems and methods can be powered using electricity, do not include water as a reactant, do not produce carbon dioxide as a product, and produce a highly pure carbon by-product. In addition, these systems and methods produce a free-flowing elemental carbon powder, without the buildup of carbon tar products on hot pyrolysis reactor surfaces.
The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.
In reaction 102, the metal salt is sublimed to yield a gas phase metal salt. The metal salt is typically a metal halide in the form of an anhydrous powder. Reaction 102 is endothermic and occurs under temperature and pressure conditions selected to sublimate the metal salt. In reaction 104, the gas phase metal salt reacts with a gas phase hydrocarbon to yield the metal in elemental form, carbon in elemental form, and a gas phase hydrogen halide. In some cases, reaction 102 is initiated by blowing the metal salt toward a heated reaction zone in a reactor with the gas phase hydrocarbon. Metal chloride reduction in reaction 104 is exothermic and occurs in the absence of a catalyst under temperature and pressure conditions selected such that contacting the gas phase metal salt with the gas phase hydrocarbon reduces the metal in the metal salt and decomposes the hydrocarbon. In some implementations, reaction 102 occurs before reaction 104. In some implementations, reaction 102 and reaction 104 occur concurrently. In some implementations, reaction 106 occurs concurrently with reactions 102 and 104. In reaction 106, which in one implementation occurs in the absence of the metal salt (i.e., after the metal salt has been consumed in reaction 104, with excess hydrocarbon present), the hydrocarbon is decomposed to yield elemental carbon and hydrogen gas. Reaction 106 by itself is endothermic and occurs under temperature and pressure conditions selected to pyrolyze the hydrocarbon in the presence of the metal and carbon in elemental form, which can serve as a catalyst. Reaction 106 will proceed until the reactants have cooled to a temperature such that pyrolysis is kinetically stopped, typically around 850° C.
By way of example, as depicted in
For the example depicted in
In reaction scheme 500, the metal and carbon solids from reactions 104 and carbon solids from reaction 106, if present, are combined with a mixture including a solvent and the hydrogen halide from reaction 104. In some implementations, the products of reaction 104 and 106 are cooled (e.g., to a temperature in a range between about 25° C. and about 200° C.) before contacting the hydrogen halide and solvent at a corresponding appropriate pressure (e.g., a pressure in a range between about 0.1 bar and about 20 bar) to initiate reaction 502. In one implementation, the metal and carbon solids are provided to a heated mixture including the solvent and the hydrogen halide. The hydrogen halide and the metal react to yield hydrogen gas and the metal salt dissolved in the solvent, which can be substantially depleted of hydrogen halide upon completion of the reaction. Generally, carbon does not react with hydrogen halide acids, and can be filtered off and removed in reaction zone 504. In some implementations, the metal salt can be recovered from the solvent by precipitation, which occurs when re-acidifying the solution in zone 506 with the gaseous products of reaction 104. The precipitated metal salt is removed from the solvent by filtration in zone 508. The metal salt, which is typically solvated, can be contacted with gases from reactions 104 and 106 to yield the anhydrous metal salt, gas phase hydrogen halide, and vaporized water, along with hydrogen. The anhydrous metal salt can be provided as a reactant for reaction 102 in reaction scheme 100, and the gases can be provided to reaction zone 506. Hydrogen gas can be collected from reaction 502 and from reaction 106 (through zone 506).
In the example depicted in
In 602, a hydrocarbon is pyrolyzed in the presence of Mn+Xn (g) to yield a gaseous product and a solid product. A molar ratio of hydrocarbon to metal halide is typically in a range of about 0.5 to about 25, and residence time is typically in a range of about 0.1 seconds to about 20 seconds. The pyrolysis typically occurs in a reactor at a temperature in a range of about 1000° C. to about 1200° C. The gaseous product is a mixture including hydrogen gas (H2) and hydrogen halide (HX), with H2 typically in a range of about 92 mol % to about 96 mol % and HCl typically in a range of about 4% to about 8%. The solid product is a mixture including the metal (M) and carbon (C) in elemental form.
In 604, the gaseous product and the solid product are separated. In some embodiments, the products from 602 are cooled before separation in 604. In one example, the products are provided to a heat exchanger (e.g., a recuperative heat exchanger), where heat from the products is transferred to another stream (e.g., HX) in process 600.
In 606, the solid product from 604 is reacted with HX (e.g., recycled from and/or heated by other streams in process 600, as discussed with respect to 604) to yield a product mixture. A molar ratio of HX to M is typically in a range of about 1:1 to about 100:1. The reactor can be an adiabatic reactor. The reaction typically occurs in a reactor at a temperature in a range between about 900° C. and about 1200° C. In some cases, the HX includes a small amount of H2 (e.g., less than about 5 mol %, or less than about 3 mol %), such that the product includes H2+HX+Mn+Xn (g)+C, with the total amount of H2+HX including up to 4 mol % H2 and at least 95 mol % HX. In certain cases, the small amount of H2 is stripped from the HX, such that the HX is substantially pure (>99 mol % or >99.9 mol % pure) before the solid product from 604 is reacted with the HX.
In 608, the product mixture from 606 is cooled to yield a solid product including a mixture of Mn+Xn (s)+C and a gaseous product including a mixture of H2+HX, with the total amount of H2+HX including up to 4% H2 and at least 95 mol % HX. The cooling can be achieved in a flash cooler in which the gas stream is injected into a vessel at lower pressure, decreasing its temperature. Cooling can also be achieved using a heat exchanger. In some cases, the solid product is separated in 608 to yield a stream of Mn+Xn (s) and a stream of C. That is, further downstream processing (e.g., in 612-616) is not needed to separate Mn+Xn and C. In 610, the solid and gaseous products from 608 are separated. In one embodiment, separation is achieved with a ceramic candle filter.
In 612, the solid product from 610 is heated in a furnace to evaporate Mn+Xn (s), thereby yielding a mixture including Mn+Xn (g)+C. In 614, C is removed from the mixture of 612. In 616, Mn+Xn (g) from the mixture of 612 is recycled to 602.
In 618, HX and H2 from 610 are separated to yield a HX stream and a H2 product stream. In one example, HX and H2 are separated by contacting the gaseous mixture with aqueous HX to capture the HX, leaving substantially pure H2 (e.g., >99% or >99.9% pure) as the primary hydrogen product stream. In 620, the HX stream from 618 is provided to 606. In 622, the H2 product stream from 618 exits process 600 as substantially pure hydrogen (e.g., >99 mol % or >99.9 mol % pure).
In 624, HX and H2 from 604 are separated to yield a HX stream and a H2 product stream. In 626, HX from 624 is provided to 606. In 628, the H2 product from 624 exits process 600.
In some embodiments, operations can be added to or omitted from process 600. In some embodiments, the order of operations in process 600 can be altered. In one example, the solid product is separated in 608 or 610 to yield a stream of Mn+Xn (s) and a stream of C. That is, further downstream processing (e.g., in 612-616) is not needed to separate Mn+Xn and C, and Mn+Xn and C are separated as solids before Mn+Xn is evaporated.
Stream 710 (CH4) is provided to heater 712 to yield stream 714 (CH4). Stream 716 (NiCl2 (s)) is provided to heater 718 to yield stream 720 (NiCl2 (g)). Streams 714 (CH4) and 720 (NiCl2 (s)) are provided to reactor 722 at a CH4:NiCl2 molar ratio in a range of about 10:1 to about 20:1 (e.g., about 13:1 to about 17:1 or about 14:1 to about 16:1). Gas phase exothermic reduction of Ni′ and endothermic pyrolysis of CH4, as shown in Equations 1 and 2, occur in reactor 722.
CH4+2NiCl2 (g)→2Ni+C+4HCl ΔH°=−147 kJ/mol CH4 (1)
CH4→C+2H2 ΔH°=75 kJ/mol CH4 (2)
Table 1 lists CH4:NiCl2 molar ratio and CH4 conversion to carbon according to Equations 1 and 2 for Examples 1-19. The CH4:NiCl2 molar ratios range from about 1 to about 20, with CH4 conversion in a range from about 10% to about 100% for residence times ranging from about 5 seconds to about 20 seconds. The residence time for Example 19 (95 mol % conversion, 6.08 CH4:NiCl2 mol ratio) was about 16 seconds. The residence time for Example 13 (88% conversion, 15.43 CH4:NiCl2 mol ratio) was about 8 seconds.
From reactor 722, stream 724 (H2+HCl+Ni+C) is provided to heat exchange zone 704, where stream 724 is cooled by stream 726 (recycled HCl) in heat exchanger 728. Heat exchanger 728 can be a recuperative heat exchanger. In heat exchanger 728, stream 726 cools stream 724 to a temperature in a range between about 150° C. and about 250° C. (e.g., about 200° C.). In one example, heat exchanger 728 is a shell and tube exchanger, and stream 724 is provided to the tube side. Stream 730 (C+Ha+HCl+Ni) is provided to filter 732, where the gaseous products (H2+HCl) are separated from the solid products (C+Ni). In one example, filter 732 is a candle filter.
Stream 734 (H2+HCl) is provided to separator 736 in H2 separation zone 706 to yield stream 738 (H2) and stream 740 (HCl). In one example, separator 736 operates by spraying stream 734 with aqueous HCl (e.g., 20 wt % HCl at 25° C.) to capture the HCl from stream 734. Stream 738 (substantially pure H2) exits system 700 from separator 736. Stream 740 (aqueous HCl) can be distilled (e.g., by pressure swing distillation) to produce anhydrous HCl. Stream 738 (>99.9 mol % pure) is the primary hydrogen product stream. Stream 740 (HCl) is returned to heat exchanger 728 in stream 726.
From filter 732, stream 742 (Ni+C) is provided to reactor 744 in metal halide reclamation zone 708. Reactor 744 can be an adiabatic reactor or a heated reactor. The Ni and C solids typically have a particle diameter in a range of about 0.1 μm to about 1 μm (e.g., about 0.1 μm to about 0.5 μm, or about 0.2 μm to about 0.4 μm). From heat exchanger 728, stream 746 (HCl) is provided to heater 748. Stream 746 can include a small amount (e.g., less than about 5%) of H2. From heater 748, stream 750 (HCl) is provided to reactor 744 with a molar ratio of HCl:Ni in a range of about 5:1 to about 50:1. In reactor 744, Ni reacts with HCl to yield NiCl2 (g), as shown in Equation 3.
Ni+2HCl→NiCl2 (g)+H2 ΔH°=110 kJ/mol Ni (3)
The HCl in stream 750 heats the solids from stream 742 in reactor 744 to a temperature in a range between about 1000° C. and about 1200° C. thereby driving the formation of NiCl2 (g) in reactor 744. In one example, reactor 744 has a downflow design and is co-fed with HCl and Ni+C solids (e.g., concurrent gas-solid flow in an adiabatic reactor with hot HCl gas). A residence time in reactor 744 is typically in a range of about 5 seconds to about 30 seconds (e.g., about 10 seconds).
In some cases, stream 746 (and thus stream 750) includes a small amount (e.g., less than about 5%) of H2. An equivalent molar quantity of chlorine gas is added to stream 750 via stream 756. The chlorine gas reacts with H2 in stream 750 to form excess HCl gas. This excess HCl gas is removed via stream 750′, leaving 750 as a stream of pure HCl (e.g., >99 mol % pure or >99.9 mol % pure). Stream 750′ is provided to separator 752 in H2 separation zone 706′. In some embodiments, separator 752 is a chlor-alkali electrolyzer, which produces pure hydrogen (stream 754) and chlorine (stream 756) from a stream of HCl (stream 750′). Stream 754 (>99.9 mol % H2) exits system 700 and can be combined with primary hydrogen product stream 738 (>99.9 mol % H2).
From reactor 744, stream 758 (H2+HCl+NiCl2 (g)+C) enters cooler 760, where NiCl2 (g) is condensed to yield NiCl2 (s). Heat from cooler 760 can be used to generate steam to power H2 separation in one or both of H2 separation zones 706, 706′. Stream 762 (H2+HCl+NiCl2 (s)+C) enters filter 764, where the solid products are separated from the gaseous products. In one example, filter 764 is a ceramic candle filter. Stream 766 (H2+HCl) is combined with stream 740 (HCl) and recycled to heat exchanger 728 in stream 726 (HCl). Stream 768 (NiCl2 (s)+C) is recycled to heater 718 in hydrocarbon decomposition zone 702, where NiCl2 (s) is evaporated to yield NiCl2 (g). Stream 770 (C) exits heater 718 as carbon solids. In some cases, heat from stream 770 is provided to heater 712 to heat stream 710, and stream 772 (C) exits system 700 as cooled carbon solids.
In some implementations, components in system 700 (e.g., heaters, heat exchangers, filters) and be repositioned or removed. Other components may be added. One or more streams in system 700 can combined, removed rerouted. Operating parameters may be altered to achieve desired results, such as percentage conversion to hydrogen, purity of streams, and the like.
Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.
Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.
Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.
This application claims the benefit of U.S. Patent Application No. 63/134,796 entitled “PRODUCTION OF HYDROGEN FROM HYDROCARBONS” and filed on Jan. 7, 2021, which is incorporated herein by reference in its entirety.
This invention was made with government support under contract DE-AR00001019 awarded by the Advanced Research Projects Administration—Energy, part of the U.S. Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/011691 | 1/7/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63134796 | Jan 2021 | US |
