CHEMICAL LOOPING SYSTEMS FOR CONVERSION OF LOW- AND NO-CARBON FUELS TO HYDROGEN

Abstract

Disclosed herein are systems and methods for producing H2 from low carbon fuels (LCFs) using metal oxides in a chemical looping process.

Claims

1. A system for converting a carbon-neutral or low-carbon fuel, the system comprising: a first reactor comprising a plurality of particles in which a primary metal oxide is disposed on a support, and an inlet for providing a carbon-neutral or low-carbon fuel, wherein the first reactor is configured to reduce the primary metal oxide to produce a reduced metal or a reduced metal oxide; and a second reactor configured to oxidize at least a portion of the reduced metal or reduced metal oxide from the first reactor, to regenerate the primary metal oxide.

2. The system of claim 1, wherein the fuel is selected from the group consisting of ammonia, hydrazine, carbohydrazide, and hydrogen sulfide.

3. The system of claim 2, wherein the fuel is ammonia.

4. The system of claim 1, wherein the system is configured to operate at a temperature of between 50 C. and 2000 C.

5. The system of claim 1, wherein the system is configured to operate at a pressure of between 1 atm and 30 atm.

6. The system of claim 1, wherein the system is configured to operate at a GHSV of between 50 hr.sup.1 and 5000 hr.sup.1.

7. The system of claim 1, wherein the first reactor comprises a co-current moving bed reactor, a counter-current moving bed reactor, a fluidized bed reactor, or a fixed bed reactor.

8. The system of claim 1, wherein the second reactor comprises a co-current moving bed reactor, a counter-current moving bed reactor, a fluidized bed reactor, or a fixed bed reactor.

9. The system of claim 1, wherein the inlet for the fuel is situated at the top, in the middle, or at the bottom of the first reactor.

10. The system of claim 1, wherein the primary metal oxide is Fe.sub.3O.sub.4.

11. The system of claim 1, wherein the support is selected from the group consisting of oxides of Ti, Al, Co, Cu, Mg, Mn, and Zn, or any combination thereof.

12. The system of claim 1, wherein the support is MgAl.sub.2O.sub.4.

13. The system of claim 1, further comprising a hydrogen separation unit.

14. A method of converting a carbon-neutral or low-carbon fuel, the method comprising: reducing a primary metal oxide in a reduction reaction between the fuel and the primary metal oxide, to produce a reduced metal or a reduced metal oxide, in a first reactor, thereby producing hydrogen; and oxidizing at least a portion of the reduced metal or reduced metal oxide with an oxidant, in a second reactor, thereby regenerating the primary metal oxide.

15. The method of claim 13, wherein the fuel is selected from the group consisting of ammonia, hydrazine, carbohydrazide, and hydrogen sulfide.

16. The method of claim 14, wherein the fuel is ammonia.

17. The system of claim 13, comprising conducting the method at a temperature of between 50 C. and 5000 C.

18. The method of claim 13, comprising conducting the method at a pressure of between 1 atm and 30 atm.

19. The method of claim 13, wherein the first reactor comprises a co-current moving bed reactor, a counter-current moving bed reactor, a fluidized bed reactor, or a fixed bed reactor.

20. The method of claim 13, wherein the second reactor comprises a co-current moving bed reactor, a counter-current moving bed reactor, a fluidized bed reactor, or a fixed bed reactor.

21. The method of claim 13, comprising introducing the fuel at the top, in the middle or at the bottom of the first reactor.

22. The method of claim 13, wherein the primary metal oxide is Fe.sub.3O.sub.4.

23. The method of claim 13, wherein the support is selected from the group consisting of oxides of Ti, Al, Co, Cu, Mg, Mn, and Zn, or any combination thereof.

24. The method of claim 13, wherein the support is MgAl.sub.2O.sub.4.

25. The method of claim 13, further comprising a step of separating the hydrogen from any co-products.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows a process flow diagram of ATH technology for liquid fuel production.

[0014] FIG. 2 shows a phase diagram of the FeNH.sub.3O system at 450 C. and 1 atm.

[0015] FIG. 3 shows an operating line for the reducer reactor at 450 C. and 1 atm.

[0016] FIG. 4 shows a phase diagram of the FeOH.sub.2 system at 450 C. and 1 atm.

[0017] FIG. 5 shows the gas phase analysis of a fixed bed run with Fe.sub.3O.sub.4 and NH.sub.3 at 600 C. and 1 atm at a GHSV of 500 hr.sup.1.

[0018] FIG. 6 shows the gas phase analysis of a fixed bed run with Fe.sub.3O.sub.4 and NH.sub.3 at 600 C. and 1 atm at a GHSV of 150 hr.sup.1.

[0019] FIG. 7 shows the solid phase analysis of a fixed bed run with Fe.sub.3O.sub.4 and NH.sub.3 at 600 C. and 1 atm at a GHSV of 500 hr.sup.1.

[0020] FIG. 8 shows the solid phase analysis of a fixed bed run with Fe.sub.3O.sub.4 and NH.sub.3 at 600 C. and 1 atm at a GHSV of 150 hr.sup.1.

[0021] FIG. 9 shows the steady state composition of a simulated counter current moving bed with Fe.sub.3O.sub.4MgAl.sub.2O.sub.4 system at 600 C. and 1 atm at a GHSV of 150 hr.sup.1.

[0022] FIG. 10 shows the calculated equilibrium constant for experiments with different gas-solid contact pattern demonstrating controllability in reducer reactor performance

[0023] FIG. 11 shows the normalized rate of weight change of Fe.sub.3O.sub.4 on reduction with ammonia for 400 C. and 600 C.

[0024] FIG. 12 shows the normalized rate of weight change of Fe.sub.3O.sub.4MgAl.sub.2O.sub.4 on reduction with ammonia for 400 C. and 600 C.

DETAILED DESCRIPTION

[0025] A process is proposed for deriving H.sub.2 from low carbon fuels (LCF) with the use of metal oxide in a chemical looping system. This process employs the synergistic effect of utilizing thermodynamics while being able to harness the catalytic property of the metal oxide. The proposed process is flexible to several LCFs such as ammonia (NH.sub.3), hydrazine (N.sub.2H.sub.4), carbohydrazide (CH.sub.6N.sub.4O), hydrogen sulfide (H.sub.2S), etc., to utilize them as potential sources of H.sub.2 generation. This process can be easily integrated with upcoming concepts like H.sub.2 economy while reducing the carbon footprint for H.sub.2 generation.

Definitions

[0026] The terms comprise(s), include(s), having, has, can, contain(s), and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms a, and and the include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments comprising, consisting of and consisting essentially of, the embodiments or elements presented herein, whether explicitly set forth or not.

[0027] The conjunctive term or includes any and all combinations of one or more listed elements associated by the conjunctive term. For example, the phrase an apparatus comprising A or B may refer to an apparatus including A where B is not present, an apparatus including B where A is not present, or an apparatus where both A and B are present. The phrases at least one of A, B, . . . and N or at least one of A, B, . . . N, or combinations thereof are defined in the broadest sense to mean one or more elements selected from the group comprising A, B, . . . and N, that is to say, any combination of one or more of the elements A, B, . . . or N including any one element alone or in combination with one or more of the other elements which may also include, in combination, additional elements not listed.

[0028] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

The Disclosure

[0030] The following section describes in detail the various configurations, methods and design of specific operating conditions disclosed as a part of this write-up.

[0031] The metal-oxide composition consists of two components, namely primary and secondary. In embodiments, the primary metal-oxide is Fe.sub.3O.sub.4. The primary metal-oxide should be able to crack LCF selectively. The secondary metal-oxide can be a combination of oxides of metals selected from Ti, Al, Co, Cu, Mg, Mn, Zn, etc., or even a combination complex like MgAl.sub.2O.sub.4. The secondary metal-oxide serves to strengthen the primary metal-oxide and can enhance reactivity by forming complexes which have a better thermodynamic selectivity than iron-oxide alone. The oxygen-carrier metal-oxide may contain a combination of primary and secondary metal-oxides in varying weight percentages accompanied by dopants to increase the overall activity of the metal oxide. The metal-oxide can be prepared by methods including but not limited to extrusion, pelletizing, co-precipitation, wet-impregnation, and mechanical compression. Techniques, like sintering the synthesized metal-oxide or adding a binder, can be used to increase the strength of the metal-oxide.

[0032] A model metal-oxide composition consists of a primary metal-oxide of Fe.sub.3O.sub.4 supported on a secondary metal oxide of the formula MgAl.sub.2O.sub.4. This complex can be Fe.sub.3O.sub.4 rich, MgAl.sub.2O.sub.4 rich or even have an overall non-stoichiometric support composition. The feedstock for this application can be any LCF including but not limited to ammonia, hydrazine hydrate, carbohydrazide, and hydrogen sulfide. In some embodiments, the LCF is ammonia. FIG. 1 shows the conceptual schematic of the proposed configuration. The process configuration is described using ammonia as an example of LCF. As illustrated in FIG. 1, the proposed process employs a novel metal-oxide reaction with NH.sub.3 to produce a mixture of N.sub.2, H.sub.2, and H.sub.2O at an operating temperature of 450 C. (450 C. used as an example temperature) in the reducer. The reduced metal-oxide then performs water-splitting to generate pure H.sub.2 in the oxidizer resulting in a reduced energy penalty for separating N.sub.2 and H.sub.2 over the conventionally used thermal cracking of ammonia technology which forms one mixed stream of the cracked products. The net-combination of the reducer and combustor performance is such that the total H.sub.2 recovered from NH.sub.3 feed is >99.99%. The H.sub.2 can be further purified to fuel cell grade directly.

[0033] The proposed chemical looping reaction scheme can alleviate shortcomings in the conventional ammonia to hydrogen (ATH) process. Compared to the conventional technique, the ATH chemical looping process can increase the overall H.sub.2 production efficiency by >20% and the thermochemical efficiency by >12.7%. The process platform is based on a co-current moving bed reactor system design to maximize NH.sub.3 conversion to H.sub.2 while minimizing the capital cost associated with the chemical looping reactor size. As discussed earlier conventional catalytic cracking techniques are limited by kinetics at temperatures of 450 C. or lower, on the other hand, the co-current moving bed ATH process offers an effective control over the residence time of both the gas and solid phases and thus drives the reaction to thermodynamic equilibrium at 450 C. The temperature 450 C. is used to illustrate the process, this can be further extended to temperatures up to 2000 C. Further, at these low operating temperatures, mechanical conveying systems can be employed between the reducer and combustor which can minimize the energy penalty and particle attrition for transporting the metal-oxide solids.

[0034] FIG. 2 shows the thermodynamic phase diagram of the NH.sub.3FeO system at 450 C. and 1 atm. The y-axis is the solids conversion of the Fe.sub.2O.sub.3 phase, wherein a solids conversion of 100% denotes complete oxygen transfer from Fe.sub.2O.sub.3 to NH.sub.3. The NH.sub.3 conversion is displayed in terms of the amount of H.sub.2O production per mole of NH.sub.3, with a value of 100% conversion denoting the formation of 1.5 moles H.sub.2O per mole of NH.sub.3.

[0035] FIG. 3 shows the various operating conditions that can be obtained in the reducer reactor of the LCF to H.sub.2 system. The choice of an operating condition for the reducer reactor system shown in FIGS. 1, 2 and 3 is made based on FIG. 4, which shows the phase diagram of the H.sub.2OFe system.

[0036] FIG. 4 shows that the steam re-oxidation from Fe (corresponding to 100% solids conversion) yields Fe.sub.3O.sub.4 (corresponding to 11% solids conversion) as the highest thermodynamically feasible oxidation state. This led to the choice of Fe.sub.3O.sub.4 as the input for the reducer reactor as shown in FIG. 3. The operating line is chosen based on 11% solids conversion and yields a gas conversion of 13.4%, corresponding to an outlet gas composition of 0.201 moles H.sub.2O, 1.29 moles of H.sub.2, 1.5 moles N.sub.2 per mole of NH.sub.3. This performance is constant beyond a Fe.sub.3O.sub.4/NH.sub.3 ratio of 0.05. However, the operating condition depicted in Line A corresponds to a Fe.sub.3O.sub.4/NH.sub.3 ratio of 0.4 to have good heat balance conditions in the combined system. The oxygen lost as H.sub.2O is recovered in the oxidizer, yielding an H.sub.2 production efficiency of 99% (i.e. 1.495 moles of H.sub.2 per mole of NH.sub.3) based on FIG. 4. The flexibility to operate under a wide range of Fe.sub.3O.sub.4/NH.sub.3 ratios is important as the solids flowrate is used to transfer heat from the exothermic oxidizer reactor to the endothermic reducer reactor resulting in a near autothermal condition. This minimizes the thermal energy penalty for H.sub.2 production. The reducer and the oxidizer both are proposed to be operated as packed moving bed type system to minimize physical attrition to the oxygen carrier particles. The operation of a counter-current moving bed oxidizer has advantages in terms of reducing the net steam consumption while adjusting the gas and solid phase residence times for reaching thermodynamic equilibrium. In the configuration proposed in FIG. 1, a mechanical conveyor type system is proposed to transport the solids to the reducer reactor. The reducer and the oxidizer reactors can be operated as co-current and counter-current moving beds, fluidized beds or even fixed bed type systems. The temperature and pressure of operation for yielding a >99% H.sub.2 production efficiency can be between 400 C. to 800 C., and 1 bar to 30 bar respectively. It should be noted that lower temperatures and pressures are preferred for commercial modules.

[0037] FIG. 5 and FIG. 6 shows the results of proof-of-concept laboratory studies using the iron-based catalytic metal oxide (Fe.sub.3O.sub.4) performed in a fixed bed system. This fixed bed represents the reducer section in the looping system. In FIGS. 5 and 6, the gas analysis of the outlet of the fixed bed is depicted. Both the fixed beds represented by FIGS. 5 and 6 were run at 600 C. and 1 atm pressure with a GHSV of 500 hr.sup.1 and 150 hr.sup.1 respectively. Spherical particles of Fe.sub.3O.sub.4 were used in the fixed bed for this test. For the fixed bed tests, spherical particles were synthesized from chemical grade compounds. These particles were then calcined under inert conditions at a temperature of 950 C. The experiments with a GHSV of 500 hr.sup.1 and 150 hr.sup.1 have been referred to as Experiment A and B respectively.

[0038] Both the FIGS. 5 and 6 show a steady increase in the N.sub.2 and H.sub.2 concentration before reaching a steady state. The conversion for NH.sub.3 goes up to approximately 65% and 62% for 500 hr.sup.1 and 150 hr.sup.1 respectively. Unlike the conventional catalytic NH.sub.3 decomposition, H.sub.2O also is a product which is in significant quantities. This loss of H.sub.2 in the form of H.sub.2O from the reducer is balanced out by the re-oxidation reaction in the oxidizer.

[0039] FIGS. 7 and 8 represent the solid composition on the top of the fixed bed. This was calculated from the X-Ray Diffraction (XRD) analysis done on the samples from 500 hr.sup.1 and 150 hr.sup.1 GHSV for FIGS. 7 and 8 respectively. The particles form a core shell structure with respect to the reduced phases, as seen in FIGS. 7 and 8. The Fe layer is the dominant surface layer corresponding to a core-shell structure and the phase consistent with the calculated Equilibrium constant for both the GHSVs.

[0040] FIG. 9 depicts the gas phase data of a simulated counter-current bed with Fe.sub.3O.sub.4MgAl.sub.2O.sub.4 particles. These particles include 50% Fe.sub.3O.sub.4 and 50% MgAl.sub.2O.sub.4 by weight and are synthesized and sintered in the same way as the Fe.sub.3O.sub.4 particles. For a simulated counter-current moving bed, a solid profile of a counter-current moving bed was setup with 50% of the bed filled with reduced particles and 50% of them filled with the oxidized particles. The bed was setup in such a way that the reduced particles would meet the gas coming into the reactor and the gas exited the reactor with being in contact with the oxidized particles. For this Fe.sub.3O.sub.4MgAl.sub.2O.sub.4 particles were reduced under hydrogen to yield FeMgAl.sub.2O.sub.4 particles, which would act as reduced particles.

[0041] As seen from FIG. 9, an average ammonia conversion of 99.9% was achieved with the counter current moving bed configuration. The figure represents the mole fractions of the products and the unreacted ammonia during steady state run operation of the moving bed. This experiment has been referred to as Experiment C.

[0042] The steady state values for NH.sub.3 reaction with Fe.sub.3O.sub.4 for different residence times and gas-solid contact pattern are plotted in terms of a NH.sub.3 cracking equilibrium constant (K.sub.NH3=C.sub.NH3/(C.sub.NH3+C.sub.N2+C.sub.H2+C.sub.H2O). The experiments were carried out at 600 C. for demonstrating control over the equilibrium composition in terms of the equilibrium constant and different metal-oxide phases. FIG. 10 shows the K.sub.NH3 calculated for these experimental runs for different thermodynamic contact patterns. Experiment A and B show a calculated equilibrium constant that is consistent with the final solids contact stage being Fe. Experiment C shows a calculated equilibrium constant that is consistent with the final solids contact stage being Fe.sub.3O.sub.4. These experimental data points show that the system performance can be controlled using different gas-solid contact pattern and yield further experimental proof for the thermodynamic performance.

[0043] FIGS. 11 and 12 show the normalized rate of reaction of the metal oxide and ammonia at 400 C. and 600 C. FIG. 11 represents the normalized rate of reaction of pure Fe.sub.3O.sub.4 and FIG. 12 does the same for Fe.sub.3O.sub.4MgAl.sub.2O.sub.4. For both the metal oxides, ammonia reacts with the metal oxide, reducing it in the process which can be measured as a decrease in weight of the metal oxide in a thermogravimetric analyzer. As there is a reduction in weight the rate of weight change is a negative number, which has been considered in an absolute fashion in both FIGS. 11 and 12. These rates have been normalized with respect to the fresh active oxygen content. For the two FIGS. 11 and 12, the active oxygen that reacts with ammonia comes from Fe.sub.3O.sub.4.

[0044] Both FIGS. 11 and 12 are a proof of concept for ammonia decomposition at 400 C., as there is an appreciable reduction of the metal oxide. From a kinetics standpoint, both FIGS. 11 and 12 show a higher reduction rate at 600 C. than 400 C. The 400 C. graphs for both FIGS. 11 and 12 have a non-zero rate of reduction after the initial spike in the reaction. With a moving bed configuration, the residence time and the amount of metal oxide reduced can be very accurately controlled and thus a unit can be run within the bounds of the initial spike in the reaction ensuring efficient utilization of the kinetics of this system.

Embodiments

[0045] The following are embodiments of the disclosure.

[0046] (1) A system configuration is proposed, utilizing a low carbon fuel and an H.sub.2 production efficiency of >99% from these LCFs. The system configuration itself includes two primary reactors, a reducer and an oxidizer reactor each of which can be a co-current or a counter-current moving bed, fluidized bed or a fixed bed.

[0047] (2) A system configuration, in-conjunction with Embodiment 1, converts LCFs to H.sub.2, using an (Fe) to LCF (C) molar ratio which can vary from 0.01 to 5.0. In certain embodiments, the molar ratio is about 0.01, about 0.05, about 0.1, about 0,15, about 0.2, about 0.25, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 0.55, about 0.6, about 0.65, about 0.7, about 0.75, about 0.8, about 0.85, about 0.9, about 1, about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 4.5 or about 5 The temperature of operation can vary between 50 C. to 2000 C. In certain embodiments, the temperature may vary between 400 C. to 1190 C., The pressure of operation can vary between 1 atm and 30 atm. In certain embodiments, the pressure is about 1 atm, about 2 atm, about 3 atm, about 4 atm, about 5 atm, about 6 atm, about 7 atm, about 8 atm, about 9 atm, about 10 atm, about 11 atm, about 12 atm, about 13 atm, about 14 atm, about 15, atm, about 16 atm, about 17 atm, about 18 atm, about 19 atm, about 20 atm, about 21 atm, about 22 atm, about 23 atm, about 24 atm, about 25 atm, about 26 atm, about 27 atm, about 28 atm, about 29 atm, or about 30 atm.

[0048] (3) A reactor configuration is proposed, in conjunction with Embodiment 1, which has a flexible injection location for the LCF stream into the reactor system. The injection location can be situated on the top, middle or bottom section of the system, such that sufficient residence time for reaching thermodynamic equilibrium for the final adjusted gas composition is achieved.

[0049] (4) A system configuration of the co-current moving bed reducer reactor can handle a variety of low or no carbon feedstocks, including but not limited to ammonia, hydrazine hydrate, carbohydrazide, hydrogen sulfide when used in conjunction with design considerations being satisfied for Embodiments 1 and 2. The invention reduces the energy input to separate and purify hydrogen from the product streams compared to conventional catalytic cracking process.

[0050] It is understood that the foregoing detailed description and accompanying examples are merely illustrative and are not to be taken as limitations upon the scope of the disclosure. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications, including without limitation those relating to the chemical structures, substituents, derivatives, intermediates, syntheses, compositions, formulations, or methods of use of the invention, may be made without departing from the spirit and scope thereof.

REFERENCES

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[0053] (3) Yin S. F., et. al., A mini-review on ammonia decomposition catalysts for on-site generation of hydrogen for fuel cell applications, Applied Catalysis A: General, 2004, 277, 1-9

[0054] (4) T. E. Bell L. Torrente-Murciano, H.sub.2 Production via Ammonia Decomposition Using Non-Noble Metal Catalysts: A Review, Top Catal, 2016, 59, 1438-1457

[0055] (5) Makepeace J. et. al., Ammonia decomposition catalysis using non-stoichiometric lithium imide, Chem. Sci., 2015, 6, 3805.