Magnetocaloric hydrogen liquefaction system with MOF based ortho-para conversion

Abstract

System (100, 200) for magnetocaloric hydrogen liquefaction comprising a hydrogen liquefaction unit (50) configured to receive a gaseous hydrogen (GH) stream to be liquefied and to discharge a liquified hydrogen (LH) stream, the hydrogen liquefaction unit (50) comprising: - at least one ortho-para conversion heat exchanger (10) comprising a metal organic framework (MOF) catalyst and configured to realize ortho to para spin-isomer conversion of the gaseous hydrogen (GH) stream, and - a magnetocaloric liquefaction unit (20) comprising a magnetic refrigerator and configured to perform a magnetocaloric liquefaction of the gaseous hydrogen (GH) stream.

Description

TITLEMagnetocaloric hydrogen liquefaction system with MOF based ortho-para conversionDESCRIPTIONTECHNICAL FIELD

[0001] The subject-matter disclosed herein relates to an innovative system for magnetocaloric hydrogen liquefaction with metal-organic framework (=MOF) catalyst for realizing ortho to para hydrogen conversion.BACKGROUND ART

[0002] As an alternative to fossil fuels, hydrogen applications are becoming more and more relevant in the energy transition.

[0003] Typically, the hydrogen is stored in gaseous form and is subsequentially compressed and fed to a liquefaction plant so to generate liquefied H2 to be used as a fuel.

[0004] It has been studied that a possible method to perform hydrogen liquefaction is magnetocaloric refrigeration.

[0005] At ambient conditions, hydrogen is at gaseous state and is composed at 75% of its ortho-isomer and at 25% of its para-isomer. However, if orthoisomers of hydrogen reach cryogenic conditions, there is the risk of boiling off phenomena and corresponding hazards, which would affect the liquefaction conversion rate and thus the process efficiency.

[0006] From document US 2022 / 099366 Al it is known a system comprising an active magnetic regenerative refrigerator apparatus that includes a highmagnetic field section in which a hydrogen heat transfer fluid can flow from a cold side to a hot side through at least one magnetized bed of at least one magnetic refrigerant, and a low magnetic field or demagnetized section in which the hydrogen heat transfer fluid can flow from a hot side to a cold side through the demagnetized bed.

[0007] From document CN 114353432 B it is known a hydrogen liquefaction device adopting magnetic refrigeration. The device comprises a hydrogen gas source, a pre-cooling system used for pre-cooling the hydrogen of the gas source, a magnetic refrigeration system using a multi-layer active magnetic regenerative process used for refrigerating the precooled hydrogen, an expansion element used for reducing the pressure of the cooled hydrogen.

[0008] Therefore, it would be desirable to have a hydrogen liquefaction system with higher process efficiency using efficient ortho para conversion system and efficient cooling through magnetocaloric effect; moreover, it would be desirable to have hydrogen liquefaction system able to liquefy hydrogen with reduced or no risk of boiling off phenomena.SUMMARY

[0009] According to an aspect, the subject-matter disclosed herein relates to a system for magnetocaloric hydrogen liquefaction comprising a hydrogen liquefaction unit configured to receive a gaseous hydrogen stream to be liquefied and to discharge a liquified hydrogen stream, the hydrogen liquefaction unit comprising: at least one ortho-para conversion heat exchanger comprising a metal organic framework (MOF) catalyst and configured to realize ortho to para spinisomer conversion of the gaseous hydrogen stream, and a magnetocaloric liquefaction unit comprising a magnetic refrigerator and configured to perform a magnetocaloric liquefaction of the gaseoushydrogen stream.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a schematic diagram of an embodiment of an innovative system for magnetocaloric hydrogen liquefaction with metal-organic framework,Fig. 2 shows a schematic diagram of the embodiment of Fig. 1 provided with an electrochemical compression unit.DETAILED DESCRIPTION OF EMBODIMENTS

[0011] According to an aspect, the subject-matter disclosed herein relates to an innovative system for producing liquified hydrogen with a higher efficiency due to the liquefaction of gaseous hydrogen by means of magnetocaloric effect and the conversion of gaseous hydrogen from ortho to para spin-isomer by using metal organic frameworks (=MOFs).

[0012] The liquefaction of gaseous hydrogen is performed by means of a magnetocaloric liquefaction unit in which repeatedly a magnetic material absorbs and rejects heat through a change in the magnetic field, originating the magnetocaloric effect and reaching very low temperatures. The magnetocaloric liquefaction unit adopts a reversed Carnot cycle consisting of four continuous steps: adiabatic magnetization, isothermal magnetization, adiabatic demagnetization and isothermal magnetization. The magnetocaloric liquefaction unit can reach approximately 50% of theoretical Carnot efficiency, while the typical compressed-gas refrigeration systems (for example systemsimplementing Claude cycle or Brayton cycle) can reach approximately 38% of theoretical Carnot efficiency.

[0013] The conversion of gaseous hydrogen from ortho to para spin-isomer is performed using metal organic framework (MOF) catalyst implemented in a suitable heat exchanger, so to convert all or most of the gaseous hydrogen to para spin-isomers in an efficient way.

[0014] The combination of these two processes allows to reach a higher hydrogen conversion efficiency from gaseous state to liquid state and to perform an overall energy demand reduction of the conversion.

[0015] Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. The examples and drawing figures are provided by way of explanation of the disclosure and should not be construed as a limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.

[0016] Fig. 1 shows, for example and without limitations, a schematic diagram of a first embodiment of an innovative system for magnetocaloric hydrogen liquefaction 100 (referred in the following as “system 100”) according to the present disclosure. The system 100 comprises a hydrogen liquefaction unit 50 configured to receive a gaseous hydrogen (=GH) stream to be liquefied and to discharge a liquified hydrogen (=LH) stream.

[0017] With non-limiting reference to Fig. 1, the hydrogen liquefaction unit 50 comprises at least one ortho-para conversion heat exchanger 10 configuredto realize ortho to para spin-isomer conversion of the gaseous hydrogen stream. As it will be better described in the following, the at least one ortho-para conversion heat exchanger 10 comprises a metal organic framework (=MOF) catalyst. The hydrogen liquefaction unit 50 comprises further a magnetocaloric liquefaction unit 20 comprising a magnetic refrigerator and configured to perform a magnetocaloric liquefaction of the gaseous hydrogen stream.

[0018] It is to be noted that the one or more ortho-para conversion heat exchanger 10 may be integrated with the magnetocaloric liquefaction unit 20 (i.e. the conversion performed by the at least one ortho-para conversion heat exchanger 10 and the magnetocaloric liquefaction performed by the magnetocaloric liquefaction unit 20 are substantially simultaneous) or the magnetocaloric liquefaction unit 20 may be subsequent to the one or more ortho-para conversion heat exchanger 10 (i.e. the magnetocaloric liquefaction unit 20 is be arranged downstream of the one or more ortho-para conversion heat exchanger 10 and the magnetocaloric liquefaction performed by the magnetocaloric liquefaction unit 20 is subsequent to the conversion performed by the at least one ortho-para conversion heat exchanger 10).

[0019] It is also to be noted that the system 100 may comprise a plurality of ortho-para conversion heat exchangers 10 arranged in series or in parallel between each other.

[0020] The ortho to para spin-isomer conversion of the gaseous hydrogen stream is an exothermic reaction, thus releasing heat H2 (see e.g. the big black arrow exiting from the ortho-para conversion heat exchanger 10 shown in Fig. 1). In particular, the exothermic heat of conversion of ortho to para hydrogen at 20K is about 254 calories per mole. However, as it will be better described below, the ortho-para conversion heat exchanger 10 advantageously periodically receives heat to restore the efficiency of the unit. It is to be noted that the term “periodically” is used in the present disclosure both to meanoccasionally and at regularly occurring intervals, based on the need to regenerate the catalytic bed.

[0021] In particular, the ortho-para conversion heat exchanger 10 comprises at least one reaction chamber filled with a catalytic bed comprising metal organic frameworks (MOFs) catalyst and encased by a shell apt to be traversed by a flow of a cooling fluid. The at least one reaction chamber is transversed by the gaseous hydrogen stream received by the hydrogen liquefaction unit 50 so to realize ortho to para spin-isomer conversion.

[0022] Advantageously, the ortho-para conversion heat exchanger 10 comprises a plurality of reaction chambers, each reaction chamber being filled with the catalytic bed comprising metal organic frameworks (MOFs) and being traversed by the gaseous hydrogen stream, while each shell is traversed by a flow of a cooling fluid.

[0023] Advantageously, the metal organic framework (MOF) catalyst is chosen among Zn-MOF-74, Mn-MOF-74(1), Cu-MOF-74, Ni-MOF-74, preferably is Ni-MOF-74. Even more advantageously, the metal organic framework (MOF) catalyst can be in the form of meta-MOFs, that is M2(m- dobdc), wherein M is a metal, a metal ion or a metal ion containing complex and m-5 dobdc is 4,6-dioxido-l,3-benzenedicarboxylate. In particular, M2(m- dobdc) can be synthesized with M chosen from Mg, Mn, Fe, Co, and preferably with M being Ni, to have a Mn2(m-dobdc), Fe2(m-dobdc), Co2(m-dobdc), and preferably Ni2(m-dobdc), also known as Ni-meta-MOF-74.

[0024] Advantageously, the metal organic framework (MOF) catalyst is in the form of solid granules. Even more advantageously, the solid granules are within the dimension range of 0.2 mm up to 2 mm, preferably within 0.5 mm and 1 mm. Specifically, the MOF catalyst, in the form of solid granules can be obtained through pellettization, granulation, extrusion and / or 3D printing of a MOF powder. Even more specifically, the MOF solid granules can be obtained by mixing a propercombination of MOF powder with binder (for example: Methyl Cellulose, HPMC, PVA, MRA, KH570, EC and PVP), solvent, carbon nanostructures (for example graphene), metallic powders (for example Al and Cu), inert porous materials, aerogels and / or geopolymers.

[0025] As already stated, the magnetocaloric liquefaction unit 20 comprises a magnetic refrigerator, in particular comprising several magnetic refrigerant modules, preferably arranged in series or cascade, which operate by exploiting the properties of a magnetocaloric material (for example Holmium and particularly poly crystalline Holmium) subject to the magnetic field generated by a magnetic field source (for example a permanent magnet or an electromagnetic magnet, driven by an electronic circuit to switch on and off the magnetic field and adjust the magnetic field generated).

[0026] The magnetocaloric materials show magnetocaloric effects (=MCE), which is the physical property whereby the material heats or cools when subject to an applied magnetic field or when a magnetic field changes. By the cycle based on magnetocaloric material, the gaseous hydrogen is cooled down to a target temperature, which in the case at issue is around -253°C, namely the hydrogen liquefaction temperature, so to discharge liquified hydrogen downstream of the hydrogen liquefaction unit 50. However, in other embodiments, the target temperature can be different.

[0027] Advantageously, the magnetocaloric liquefaction unit 20 comprises further a cooling system configured to circulate a cooling fluid, typically helium. The helium or the cooling fluid in general is configured to remove heat Hl generated from the liquefaction performed by the magnetocaloric liquefaction unit 20 so to cool it, in particular to cool it to the target temperature mentioned above.

[0028] Typically, a hydrogen liquefaction cycle includes the step of precooling hydrogen to temperatures of about 70-100 K before being liquified tocryogenic temperatures (which, according to the present disclosure, is performed through magnetocaloric liquefaction). Advantageously, the system 100 and 200 further comprises a precooling heat exchanger located upstream of or integrated in the at least one ortho-para conversion heat exchanger 10 and configured to remove heat from the gaseous hydrogen GH stream. In particular, the precooling heat exchanger may use a stream of liquid nitrogen or other refrigerant such as helium, neon, hydrogen, hydrocarbons or a stream of mixed refrigerants as a cooling fluid in order to cool down the gaseous hydrogen GH stream.

[0029] According to a possibility, the heat Hl (or part of the heat Hl) generated by the liquefaction performed by the magnetocaloric liquefaction unit 20 is periodically provided (by means of the cooling fluid mentioned above) to the ortho-para conversion heat exchanger 10 so to regenerate the ortho-para conversion heat exchanger 10, in particular to regenerate the catalytic bed comprising metal organic frameworks (MOFs).

[0030] According to a possibility, with non-limiting reference to Fig. 2, the system 200 further comprises an electrochemical compression unit 30 arranged upstream of the hydrogen liquefaction unit 50 and comprising at least one electrochemical compressor (possibly a plurality of electrochemical compressors, as better described in the following). In particular, the electrochemical compression unit 30 is configured to receive the gaseous hydrogen GH stream, in particular at a main inlet 31 of the electrochemical compression unit 30, and perform an electrochemical compression, so to discharge to the gaseous hydrogen GH stream at higher pressure and / or with a higher purity, in particular at a main outlet 32 of the electrochemical compression unit 30. It is to be noted that the gaseous hydrogen stream discharged at the main outlet 32of the electrochemical compression unit 30 has a higher pressure and / or a higher purity with respect to the gaseous hydrogenstream received at the main inlet 31 of the electrochemical compression unit 30.

[0031] In other words, the electrochemical compression unit 30, in particular the main outlet 32, is fluidly coupled to the hydrogen liquefaction unit 50, advantageously to the ortho-para conversion heat exchanger(s) 10, so to perform electrochemical compression of the gaseous hydrogen GH stream before it is received by the ortho-para conversion heat exchanger(s) 10. It is to be noted that, depending on the pressure at which the electrochemical compression is performed, the gaseous hydrogen GH stream may be purified from contaminants and / or its pressure may be increased.

[0032] According to a possibility, the electrochemical compression unit 30 may comprise for example two electrochemical compressors in series or cascade, the upstream compressor being configured to perform the electrochemical compression at a first pressure so to purify the gaseous hydrogen GH stream and the downstream compressor being configured to perform the electrochemical compression at a second pressure so to increase the pressure of the gaseous hydrogen GH stream.

[0033] Advantageously, the electrochemical compression unit 30 comprises further a cooling system configured to circulate a cooling fluid, for example water or a mixture of water and glycol or air, so to remove heat H3 generated from the compression performed by the electrochemical compression unit 30 and therefore to cool it.

[0034] Specifically, the heat H3 (or part of the heat H3) generated by the electrochemical compression unit 30 may be periodically provided to the ortho-para conversion heat exchanger 10 so to regenerate the ortho-para conversion heat exchanger 10, in particular to regenerate the catalytic bed comprising metal organic frameworks (MOFs).

[0035] Advantageously, the system 100 and 200 may further comprise a hydrogen storage unit (not shown in any figure) located upstream of the hydrogen liquefaction unit 50 and fluidly coupled to the hydrogen liquefaction unit 50 (as it will be better described below, if the system has also the electrochemical compression unit 30, the hydrogen storage unit may be arranged upstream of it or downstream of it). The hydrogen storage unit is configured to store gaseous hydrogen and to selectively provide the gaseous hydrogen stream to the hydrogen liquefaction unit 50 (or to the electrochemical compression unit 30 if present, in particular to the main inlet 31).

[0036] As already stated, the electrochemical compression unit 30 may be located upstream of the hydrogen storage unit, in particular if the gaseous hydrogen GH stream is supplied to the electrochemical compression unit 30 through a pipeline. According to this possibility, the electrochemical compression unit 30 may perform purification and / or compression of the gaseous hydrogen GH stream before being stored in the hydrogen storage unit; advantageously, the hydrogen storage unit may act as a “buffer” in order to stabilize, if necessary, the gaseous hydrogen GH flow rate supplied to the hydrogen liquefaction unit 50. According to another possibility, the electrochemical compression unit 30 may be located downstream of the hydrogen storage unit, so to purify and / or compress the gaseous hydrogen GH stream supplied by the hydrogen storage unit to the hydrogen liquefaction unit 50.

[0037] Advantageously, the system 100 and 200 may further comprise a thermoelectric device (not shown in any figure) thermally coupled to the magnetocaloric liquefaction unit 20 and configured to receive the heat Hl removed by the cooling fluid so to generate electric power. For example, the thermoelectric device may be a Peltier cell or in general a thermoelectric electricity generator. Advantageously, if the system further comprises the electrochemical compression unit 30, the heat H3 (or part of the heat H3)generated by the electrochemical compression unit 30 may also be provided to the thermoelectric device so to generate electric power.

[0038] Advantageously, the system 100 and 200 may further comprise an electrolyzer (not shown in any figure) located upstream of the hydrogen liquefaction unit 50 and that is fluidly coupled to the hydrogen liquefaction unit 50. In particular, the electrolyzer is configured to receive a water flow and electric power, advantageously electric power produced by a renewable energy plant, and to perform electrolysis of water so to generate the gaseous hydrogen GH stream to be provided to the electrochemical compression unit 30 (if any) and then to the hydrogen liquefaction unit 50.

[0039] Typically, mechanical compressors (centrifugal or reciprocating compressors) are used for downstream compression in green H2 production plants (i.e. plants which uses renewable energy for producing H2). However, mechanical compressors struggle to match with variable Renewable Energy Systems (=RES) load profile, resulting in working for a great part of their lifetime out of the optimal design point, thus leading to excessive energy consumption. The innovative system according to the present disclosure, thanks to the fact that it does not include any mechanical compressor, allows to follow any variable load profile with no issues of partial load or without any decrease in energy performances.

[0040] Advantageously, the system 100 and 200 may further comprise a Stirling cycle generation unit (not shown in any figure) thermally coupled to the magnetocaloric liquefaction unit 20. Advantageously, the Stirling cycle generation unit is configured to receive the heat Hl (or part of the heat Hl) generated by the magnetocaloric liquefaction unit 20 and removed by the cooling fluid so to generate electric power. Advantageously, if the system further comprises the electrochemical compression unit 30, the heat H3 (or part of the heat H3) generated by the electrochemical compression unit 30 may also be provided to the Stirling cycle generation unit so to generate electric power.

[0041] Advantageously, the system 100 and 200 may further comprise a solid- state hydrogen storage unit (not shown in any figure) configured to physically store hydrogen. Advantageously, the solid-state hydrogen storage unit comprises metal hydrides or metal organic framework (MOF) or one or more of various forms of ice.

[0042] Advantageously, the solid-state hydrogen storage unit is thermally coupled to the magnetocaloric liquefaction unit 20 and is configured to receive the heat Hl (or part of the heat Hl) removed by the cooling fluid of the magnetocaloric liquefaction unit 20 so to release stored hydrogen, in particular by performing a solid-gas state transition, and provide the gaseous hydrogen stream to the hydrogen liquefaction unit 50. Advantageously, if the system further comprises the electrochemical compression unit 30, the heat H3 (or part of the heat H3) generated by the electrochemical compression unit 30 may also be provided to the solid-state hydrogen storage unit so to release stored gaseous hydrogen.

Claims

CLAIMS1. A system (100, 200) for magnetocaloric hydrogen liquefaction comprising a hydrogen liquefaction unit (50) configured to receive a gaseous hydrogen (GH) stream to be liquefied and to discharge a liquified hydrogen (LH) stream, the hydrogen liquefaction unit (50) comprising: at least one ortho-para conversion heat exchanger (10) configured to realize ortho to para spin-isomer conversion of the gaseous hydrogen (GH) stream, and a magnetocaloric liquefaction unit (20) comprising a magnetic refrigerator, the magnetocaloric liquefaction unit (20) being configured to perform a magnetocaloric liquefaction of the gaseous hydrogen (GH) stream, wherein the ortho-para conversion heat exchanger (10) comprises a metal organic framework (MOF) catalyst.

2. The system (100, 200) of claim 1, wherein the ortho-para conversion heat exchanger (10) is integrated with the magnetocaloric liquefaction unit (20).

3. The system (100, 200) of claim 1, wherein the ortho-para conversion heat exchanger (10) comprises at least one reaction chamber encased by a shell apt to be traversed by a flow of a cooling fluid, wherein the at least one reaction chamber is filled with a catalytic bed comprising metal organic frameworks (MOFs) catalyst.

4. The system (100, 200) of claim 1, wherein the metal organic framework (MOF) catalyst is chosen among Zn-MOF-74, Mn-MOF-74(1), Cu- MOF-74, Ni-MOF-74, preferably is Ni-MOF-74.

5. The system (100, 200) of claim 1, wherein the metal organic framework (MOF) catalyst is a meta-MOF, that is M2(m-dobdc), wherein M is a metal, a metal ion or a metal ion containing complex, preferably chosenfrom Mg, Mn, Fe, Co and Ni, and m-dobdc is 4,6-dioxido-l,3- b enzenedi carb oxy 1 atex .

6. The system (100, 200) of claim 1, wherein the metal organic framework (MOF) catalyst is in the form of solid granules with dimension ranging from 0.2 mm up to 2 mm.

7. The system (100, 200) of claim 1, wherein the magnetocaloric liquefaction unit (20) comprises further a cooling system configured to circulate a cooling fluid, wherein the cooling fluid is configured to remove heat (Hl) generated from the liquefaction performed by the magnetocaloric liquefaction unit (20) so to cool it.

8. The system (100, 200) of claim 7, wherein the heat (Hl) generated by the liquefaction performed by the magnetocaloric liquefaction unit (20) is periodically provided to the ortho-para conversion heat exchanger (10) so to regenerate the ortho-para conversion heat exchanger (10).

9. The system (100, 200) of claim 1, further comprising a hydrogen storage unit located upstream of and fluidly coupled to the hydrogen liquefaction unit (50) and configured to store gaseous hydrogen, wherein the hydrogen storage unit is configured to selectively provide the gaseous hydrogen (GH) stream to the hydrogen liquefaction unit (50).

10. The system (100, 200) of claim 1, further comprising an electrochemical compression unit (30) arranged upstream of and fluidly coupled to the hydrogen liquefaction unit (50) and comprising at least one electrochemical compressor, the electrochemical compression unit (30) being configured to receive the gaseous hydrogen (GH) stream and perform an electrochemical compression, so to discharge the gaseous hydrogen (GH) stream at higher pressure and / or with a higher purity.

11. The system (100, 200) of claim 10, wherein the electrochemical compression unit (30) further comprises a cooling system configured to circulate a cooling fluid, wherein the cooling fluid is configured toremove heat (H3) generated from the compression performed by the electrochemical compression unit (30) so to cool it.

12. The system (100, 200) of claim 11, wherein the heat (H3) generated by the electrochemical compression unit (30) is periodically provided to the ortho-para conversion heat exchanger (10) so to regenerate the ortho-para conversion heat exchanger (10).

13. The system (100, 200) of claim 7, further comprising a thermoelectric device thermally coupled to the magnetocaloric liquefaction unit (20), wherein the thermoelectric device is configured to receive the heat (Hl) removed by the cooling fluid so to generate electric power.

14. The system (100, 200) of claim 1, further comprising a Stirling cycle generation unit thermally coupled to the magnetocaloric liquefaction unit (20), wherein the Stirling cycle generation unit is configured to receive the heat (Hl) removed by the cooling fluid so to generate electric power.

15. The system (100, 200) of claim 1, further comprising an electrolyzer located upstream of and fluidly coupled to the hydrogen liquefaction unit (50), wherein the electrolyzer is configured to receive a water flow and electric power, in particular electric power produced by a renewable energy plant, and to perform electrolysis of water so to generate the gaseous hydrogen (GH) stream to be provided to the hydrogen liquefaction unit (50).

16. The system (100, 200) of claim 1, further comprising a solid-state hydrogen storage unit configured to physically store hydrogen, wherein the solid-state hydrogen storage unit is thermally coupled to the magnetocaloric liquefaction unit (20), wherein the solid-state hydrogen storage unit is configured to receive the heat (Hl) removed by the cooling fluid of the magnetocaloric liquefaction unit (20) so to release stored hydrogen and provide the gaseous hydrogen (GH) stream to the hydrogen liquefaction unit (50).1517. The system (100, 200) of claim 16, wherein the solid-state hydrogen storage unit comprises metal hydrides or metal organic framework (MOF).

Images