CATALYTIC METHANE DECOMPOSITION AND CATALYST REGENERATION, METHODS AND USES THEREOF

Abstract

The present disclosure relates to a low temperature method for the production of pure hydrogen using a methane rich stream as raw material, and to perform in-situ catalyst regeneration. The process involves the decomposition of methane into COx-free hydrogen in an electrochemical/chemical membrane/chemical reactor or chemical fluidised reactor. As the methane decomposition reaction progresses, carbon structures (whiskers) are accumulated at the catalyst surface leading eventually to its deactivation. The catalyst regeneration is achieved using a small fraction of the produced hydrogen to react with carbon formed at the catalyst surface provoking the carbon detachment, thus regenerating the catalyst. This is achieved either by chemical/electrochemical methanation of carbon at the catalyst interface with hydrogen/protons or by rising the temperature of the catalyst, ideally keeping the reactor temperature constant. A single compact device is described, enabling the hydrogen production, hydrogen purification and catalyst regeneration.

Claims

1. A process for producing hydrogen comprising: feeding a methane rich stream to a chemical or electrochemical reactor, wherein the chemical reactor comprises a catalyst supported in a ceramic membrane or in a ceramic bed; contacting the methane rich stream with the catalyst at a selected temperature to produce hydrogen and solid carbon; and adding a regenerating stream to react at the catalyst interface with deposited carbon for catalyst regeneration.

2. The process of claim 1, wherein the chemical reactor is selected from the group consisting of: a membrane reactor, a packed bed reactor, and a fluidised bed reactor.

3. The process of claim 1, wherein the regenerating stream is a hydrogen pure stream.

4. (canceled)

5. The process of claim 3, wherein the molar ratio between the hydrogen pure stream and the produced hydrogen varies 5:95-15:85; 3:97-10:90.

6. The process of claim 1, further comprising a previous step of activating the catalyst by heating and reducing the catalyst at a selected temperature and atmosphere.

7. The process of claim 1, wherein the ceramic membrane comprises: porous ceramic membranes selected from the group consisting of: Al2O3, SiO2, TiO2 and ZrO2; or dense ceramic membranes selected from the group consisting of: BCY, BZY and BCZY; or porous or dense metallic membranes based on Pd or Pd alloys.

8. The process of claim 7, wherein the ceramic membrane further comprises coating layer comprising Ni, Fe, or mixtures thereof.

9. The process of claim 1, wherein the reactor further comprises a proton conducting cell for electrochemical separation of hydrogen from unreacted methane.

10. The process of claim 1, wherein the catalyst is activated with a hydrogen, methane or mixtures thereof; at a temperature between 350° C. and 750° C.

11. The process of claim 1, wherein the decomposition of the methane rich stream and carbon detachment is performed in a range of temperature of 500° C. and 750° C.

12. The process of claim 1, wherein the pressure is varied from 1 bar to 10 bar.

13. The process of claim 1, wherein the regeneration duration ranges from 15 min-2 h.

14. (canceled)

15. The process of claim 1, wherein the regenerating stream is pure hydrogen recovered from the reaction step.

16. The process of claim 1, wherein the regeneration stream comprises a downstream gas from the contacting step, comprising mostly of hydrogen and unconverted methane.

17. The process of claim 1, wherein the hydrogen consumed for carbon removal represents a small fraction (up to 5 vol. %) of the hydrogen produced during methane decomposition.

18. (canceled)

19. (canceled)

20. (canceled)

21. The process of claim 1, wherein the chemical reactor further comprises a separation membrane.

22. The process of claim 1, wherein the electrochemical reactor comprises an electrocatalyst, a proton conductor membrane and a counter-electrode and wherein the carbon detaching from a catalyst surface of a electrochemical reactor comprises contacting the catalyst with an inert gas flow and feeding the counter-electrode with a hydrogen pure stream for the catalyst regeneration.

23. The process of claim 1, further comprising the step of applying a potential difference between both electrodes to promote the permeation of the hydrogen from the regenerating gas through the membrane to react at the catalyst interface with deposited carbon for yielding methane and originating the carbon detachment from the catalyst surface.

24. The process of claim 1, wherein the regenerating gas is fed directly in the catalyst side above the atmospheric pressure, at a selected temperature, to react with formed carbon yielding methane.

25. The process of claim 1, wherein the catalyst comprises Ni, Fe, or Co particles, or a mixture thereof.

26. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of disclosure.

[0063] FIG. 1 illustrates a simplified schematic diagram of a device for the production of hydrogen and carbon, with catalyst regeneration: [0064] (1)—represents the electrochemical chemical reactor; [0065] (2)—represents the electrode that includes the catalyst; [0066] (3)—represents the proton conductor ceramic membrane; [0067] (4)—represents the counter-electrode; [0068] (5)—represents the inlet stream of the catalyst side; [0069] (6)—represents the downstream flow of the catalyst side; [0070] (7)—represents the inlet stream of the counter-electrode side; [0071] (8)—represents the downstream flow of the counter-electrode side; [0072] (9)—represents the heating system.

[0073] FIG. 2 illustrates a simplified schematic diagram of an alternative device for the production of hydrogen and carbon, with catalyst regeneration: [0074] (5)—represents the inlet stream of the catalyst side; [0075] (6)—represents the downstream flow of the catalyst side; [0076] (7)—represents the inlet stream of the permeate side of the membrane; [0077] (8)—represents the downstream flow of the permeate side of the membrane; [0078] (9)—represents the heating device; [0079] (10)—represents the chemical reactor; [0080] (11)—represents the catalyst; [0081] (12)—represents the hydrogen permselective membrane.

[0082] FIG. 3 illustrates a simplified schematic diagram of an alternative device for the production of hydrogen and carbon, with catalyst regeneration: [0083] (5)—represents the inlet stream of the catalyst side; [0084] (6)—represents the downstream flow of the catalyst side; [0085] (9)—represents the heating device; [0086] (10)—represents the chemical reactor; [0087] (11)—represents the catalyst.

[0088] FIG. 4 illustrates a simplified schematic diagram of an alternative device for the production of hydrogen and carbon, with catalyst regeneration: [0089] (5)—represents the inlet stream of the reactor; [0090] (6)—represents the downstream flow of the reactor; [0091] (9)—represents the heating system; [0092] (13)—represents the fluidised bed reactor; [0093] (14)—represents the catalyst pellets.

[0094] FIG. 5 is a graph of the hydrogen productivity and methane conversion versus time-on-stream during methane decomposition at 600° C.

DETAILED DESCRIPTION

[0095] The present disclosure is also further described, in particular, using embodiments of the disclosure. Therefore, the disclosure is not limited to the descriptions and illustrations provided. These are used so that the disclosure is sufficiently detailed and comprehensive. Moreover, the intention of the drawings is for illustrative purposes and not for the purpose of limitation.

[0096] It is disclosed a method for the production of pure hydrogen using methane as raw material (Equation 1), and to perform in-situ catalyst regeneration. The hydrogen is obtained by catalytic decomposition of methane according to the following equation:

CH.sub.4(g)⇄2H.sub.2(g)+C(s)ΔH°=75 kJ.Math.mol.sup.−1  (1)

[0097] According to Equation (1), solid carbon (coke) is also produced, which causes catalyst deactivation. In order to overcome this limitation, a catalyst regeneration step is required.

[0098] The present disclosure discloses a method for catalyst regeneration that uses hydrogen to remove coke at the catalyst interface, leading to the detachment of the carbon accumulated on the catalyst surface. Under the considered conditions mainly methane is produced, according to the next equation:

2H.sub.2(g)+C(s)⇄CH4(g)ΔH°=−75 kJ.Math.mol.sup.−1  (2)

[0099] The method can be performed in an electrochemical/chemical membrane/bed reactor. The reactor involves a Ni-based catalyst supported on a separation membrane or just a Ni-based supported catalyst, while the electrochemical reactor consists of a MEA (membrane electrode assembly) composed by a Ni-based cathode, a proton conductor membrane and a counter-electrode anode (e.g. Pt or cermet suitable for hydrogen oxidation). Methane is fed to the Ni side where it is decomposed to hydrogen and carbon.

[0100] The present application also describes a method for catalyst regeneration involving the hydrogenation of coke at the catalyst interface, leading to its detachment. During this step, mainly traces of methane are formed avoiding the contamination of hydrogen with undesired COx off-gases. The permeation of hydrogen towards Ni interface is achieved by electrochemical pumping. A potential difference is applied between Ni and the counter-electrode; protons permeate across the proton conductor membrane, reducing coke to methane at the Ni interface with electrons conducted by the external electrical circuit.

[0101] In an embodiment of the present application, catalyst regeneration is achieved supplying hydrogen to the Ni side. The Ni-based catalyst is supported in a membrane permeable to hydrogen or supported Ni-based catalyst pellets. Selective methanation of carbon takes place at the carbon-Ni interface, making carbon particles to detach. Moreover, selective heating up of the metal catalyst also promotes carbon detachment upon hydrogenation of the catalyst/carbon interface. The selective heating of the catalyst is achieved adding to it ceramic additives with very high relative permittivity such as calcium copper titanate (CaCu.sub.3Ti.sub.4O.sub.12), barium titanate (BaTiO.sub.3) or strontium titanates (SrTiO.sub.3 and Sr.sub.2TiO.sub.4). These materials absorb microwaves allowing the selective heating upon using a microwave source. The same effect can also be achieved by electrical heating the membrane or, more generally, the reactor; however, this is a less selective heating process besides being slower.

[0102] The terminology used in the present application is for the purpose of description and should not be regarded as limiting.

[0103] The terms “methane decomposition” and “decomposition” are used interchangeably herein when referring to the methane cracking leading to hydrogen and solid carbon, according to Equation (1).

[0104] The terms “carbon”, “solid carbon”, “carbon particles”, “carbon whiskers” and “coke” are used interchangeably herein when referring to the solid product of methane decomposition, according to Equation (1).

[0105] The terms “regeneration”, “carbon removal” and “hydrogenation” are used interchangeably herein when referring to the reaction between solid carbon and hydrogen to produce methane, according to Equation (2).

[0106] This present subject-matter discloses a method for methane decomposition and catalyst regeneration, in a single and compact device; the methane decomposition produces carbon that accumulates at the catalyst surface provoking its deactivation after a short time of operation, between 30 h and 120 h.

[0107] In a preferred embodiment, the methane decomposition is carried out in an electrochemical membrane reactor as illustrated in FIG. 1. This reactor (1) includes a MEA composed by a cermet cathode loaded with a Ni-based catalyst (2), a proton conductor ceramic membrane (3) and a counter-electrode (e.g. Pt or cermet suitable for hydrogen oxidation) (4). The cathode electrode (2) is then fed with methane (5) which is decomposed into hydrogen and carbon at the Ni-based catalyst. This reaction is performed in a range of temperature of 500° C. and 750° C., more preferably between 550° C. and 650° C. The reactor (1) is heated by means of a temperature-controlled heating device (9). In this embodiment, the catalyst regeneration is obtained by electrochemically pumping hydrogen from the anode (4) to the cathode (2) side, which is achieved applying a potential difference to the electrodes, where the negative side is the cathode. At the catalyst interface (2), hydrogen reacts selectively with the deposited carbon, producing mostly methane, allowing its detachment. In this embodiment, examples of said dense proton conductive membrane are BCY (yttrium-doped barium cerate), BZY (yttrium-doped barium zirconate) and BCZY (yttrium-doped barium cerate-zirconate) and the cathode layer is a cermet made of a composite of these materials and the Ni-based catalyst. The anode layer is made of a Pt catalyst or a cermet suitable for the hydrogen oxidation.

[0108] In another embodiment of the present application, methane decomposition is carried out in a chemical membrane reactor illustrated in FIG. 2. This reactor (10) includes a Ni-based catalyst (11) supported on a hydrogen and methane permeable membrane (12). In this embodiment, porous and dense ceramic or metallic membranes are applied. The membrane reactor (10) is fed with methane (5) which is decomposed into hydrogen and carbon on the Ni-based catalyst (11). This reaction is performed in a range of temperature of 500° C. and 750° C., more preferably between 550° C. and 650° C. The reactor (10) is heated by means of a temperature-controlled heating device (9). In this embodiment methane (7) is fed in the permeate side of the membrane (12) that sweeps hydrogen formed in the Ni catalyst (11) and supplies fresh methane to the reaction locus. This configuration allows methane conversion increase due to the reaction equilibrium shift. In this embodiment, examples porous ceramic membranes are Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2 and ZrO.sub.2. During the regeneration step, hydrogen (7) is fed to the permeate side and the Ni-based catalyst (11) is heated up when methane decomposition is interrupted. The regeneration of the catalyst can also be obtained using porous or dense membranes by increasing the hydrogen partial pressure or the temperature. This allows the hydrogenation of the carbon layer attached to the catalyst making the carbon particle to detach it. Carbon reduction at the catalyst interface can rely a chemical reaction with hydrogen or an electrochemical reaction with protons and electrons.

[0109] In a further embodiment of the present disclosure, methane decomposition can be carried out in a packed bed reactor as illustrated in FIG. 3. In the reactor (10) the Ni-based supported catalyst particles (11) contact with a methane inlet flow (5) which is decomposed into hydrogen and solid carbon. The decomposition reaction is performed in a range of temperature of 500° C. and 750° C., more preferably between 550° C. and 650° C. The carbon particles detachment from the metal catalyst can be achieved by increasing the hydrogen partial pressure and/or the temperature. However, this procedure is less selective to the hydrogenation of the interfacial carbon layer, originating a higher hydrogen consumption. After the detachment of the carbon particles, the bed is fluidised for carbon particles removal. The methane decomposition cycle is then resumed.

[0110] In a further embodiment of the present disclosure, methane decomposition can be carried out in a fluidised bed reactor illustrated in FIG. 4. In the reactor (13) the Ni-based supported catalyst particles (14) contact with a methane inlet flow (5) which is decomposed into hydrogen and solid carbon. The decomposition reaction is performed in a range of temperature of 500° C. and 750° C., more preferably between 550° C. and 650° C. The carbon particles detachment from the metal catalyst can be achieved by increasing the hydrogen partial pressure and/or the temperature. However, this procedure is less selective to the hydrogenation of the interfacial carbon layer, originating a higher hydrogen consumption.

[0111] Hydrogen can be selectively removed from the reactors using dense supported or unsupported metallic membranes based on Pd or Pd alloys, such as Pd—Ag alloy (77:23 wt. %). Additionally, a proton conducting cell (PCC) can separate hydrogen from unreacted methane electrochemically and running at the same temperature of the reactor. The separation can also be performed at a different temperature from the reaction medium. Carbon particles can be removed upon decantation, such as in the case of the membrane reactors, or using a cyclone, such as in the case of the fluidised reactor.

[0112] During this step, mainly methane is formed avoiding the contamination of hydrogen with undesired CO.sub.x, off-gases. The regeneration step is carried out using a small fraction (up to 5%) of the produced hydrogen. This feature allows to highly increase the efficiency and feasibility of the present disclosure.

[0113] In another embodiment of the application, methane from different sources such as biomass, natural gas, tail gases and livestock farming, can be used to produce hydrogen. In this embodiment, the hydrogen purity regarding final disclosure can be tailored based on the methane source.

[0114] The produced carbon particles can be reused for render back methane upon hydrogenation in a fluidised reactor operating at a pressure between 1 bar and 30 bar and temperature ranging between 500° C. and 750° C. This allows storing hydrogen, for example produced from renewable sources, which is difficult to store and to transport. The use of carbon as a hydrogen carrier is preferable to the use of CO.sub.2 (e.g., methanation of CO.sub.2), since the entropy of formation of carbon is much lower than the entropy of formation of CO.sub.2. This renders the thermodynamic round-trip efficiency of storing hydrogen using carbon carrier much higher compared with using CO.sub.2.

Example 1

[0115] The electrochemical reactor illustrated in FIG. 1 was assembled with a MEA made of a cathode electrode of BCY loaded with Ni catalyst particles (2), a BCY membrane (3) and a Pt anode counter-electrode (4). The assembly was placed in a temperature-controlled furnace (9) and heated up to 550° C. The cathode side (2) was then fed with pure CH.sub.4 (5) (5 ml.Math.min.sup.−1) and the decomposition conversion was assessed by analysing online the composition of the reactor outlet stream (6) by a CG equipped with TCD and FID detectors. At the same time the Pt anode (4) was fed with N.sub.2 (7) until the CH.sub.4 conversion reached a constant value. At this point the CH.sub.4 stream (5) from the Ni electrode (2) was replaced by N.sub.2 and the N.sub.2 stream (7) from the Pt electrode side (4) was replaced by H.sub.2. Two approaches were considered for the Ni catalyst regeneration.

[0116] In the first case, a potential difference of 0.4 V was applied between the electrodes to make the H.sub.2 to permeate through the BCY membrane (3) and react with the carbon at the Ni (2) interface, in the cathode side. In the second case, H.sub.2 was permeated to the Ni side (2) as a result of the partial pressure difference between both electrodes. In fact, at 550° C. the BCY membrane becomes permeable to H.sub.2 without needing of potential difference. In both approaches the outlet stream from the Ni side (6) was analysed by GC-TCD-FID and only H.sub.2 and CH.sub.4 were detected. During this test decomposition steps were alternated with catalyst regeneration steps and the catalyst stability was kept for at least for 500 h. On the other hand, the H.sub.2 supplied in the regeneration step represents a small fraction of the H.sub.2 produced (ca. 5%). FIG. 5 shows the evolution of the H.sub.2 productivity and CH.sub.4 conversion with time-on-stream (over 500 h) during methane decomposition

Example 2

[0117] In this example, CH.sub.4 decomposition and catalyst regeneration were carried out in a chemical reactor as illustrated in FIG. 2. The reactor (10) assembly as for the previous example but the CH.sub.4 decomposition was carried out at 750° C. During the regeneration step, Ni side was fed with H.sub.2 (5) and different temperature and pressure conditions were tested. On the other hand, the permeate side of the membrane was maintained under N.sub.2 atmosphere (7) during all these experiments.

[0118] Table 1 summarises the working conditions and main results for CH.sub.4 decomposition and catalyst regeneration steps. In this regeneration approach the H.sub.2 supplied in the regeneration step represents a small fraction of the H.sub.2 produced (ca. 5%).

TABLE-US-00001 TABLE 1 Methane conversion and fraction of removed coke under different working conditions. CH.sub.4 decomposition Catalyst regeneration T (° C.) P (bar) x.sub.CH.sub.4 (%) T (° C.) P (bar) m.sub.c (%) 750 1 76 550 3 20 550 6 20 650 3 40 650 6 40

Example 3

[0119] In this example, CH.sub.4 decomposition and catalyst regeneration were carried out in a chemical reactor as illustrated in FIG. 3. A packed bed reactor loaded with catalyst particles from breaking the cathode layer of Example 1 run the methane decomposition at 600° C. and room pressure, with cycles of 6 h. The regeneration step was achieved feeding pure hydrogen to the reactor at 6 bar for 2 h. FIG. 6 shows the evolution of the H.sub.2 productivity and CH.sub.4 conversion with time-on-stream (2 cycles of 6 h) during methane decomposition.

[0120] Furthermore, it is to be understood that the invention encompasses all variations, combinations, and permutations in which one or more limitations, elements, clauses, descriptive terms, etc., from one or more of the claims or from relevant portions of the description is introduced into another claim. For example, any claim that is dependent on another claim can be modified to include one or more limitations found in any other claim that is dependent on the same base claim.

[0121] Furthermore, where the claims recite a composition, it is to be understood that methods of using the composition for any of the purposes disclosed herein are included, and methods of making the composition according to any of the methods of making disclosed herein or other methods known in the art are included, unless otherwise indicated or unless it would be evident to one of ordinary skill in the art that a contradiction or inconsistency would arise.

[0122] Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value within the stated ranges in different embodiments of the invention, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. It is also to be understood that unless otherwise indicated or otherwise evident from the context and/or the understanding of one of ordinary skill in the art, values expressed as ranges can assume any subrange within the given range, wherein the endpoints of the subrange are expressed to the same degree of accuracy as the tenth of the unit of the lower limit of the range.

[0123] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0124] The above described embodiments are combinable.

[0125] The following claims further set out particular embodiments of the disclosure.

REFERENCES

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