NEW ORGANIC LIQUIDS CARRYING HYDROGEN AND NITROGEN, THEIR USES FOR THE TRANSPORT AND STORAGE OF HYDROGEN, AND THE PROCESSES FOR GENERATION OF HYDROGEN USING THEM

Abstract

The present invention relates to novel nitrogen-containing organic hydrogen-carrying liquids (OHCLs), as well as the corresponding OHCL / dehydrogenated OHCL pairs. The invention also relates to their uses for hydrogen transport and storage, and to hydrogen generation processes using them.

Description

Title of the invention: NEW ORGANIC LIQUIDS CARRYING NITROGEN, THEIR USES FOR THE TRANSPORT AND STORAGE OF HYDROGEN, AND PROCESSES FOR GENERATION OF HYDROGEN USING THEM

[0001] The present invention relates to novel nitrogenated organic hydrogen-carrying liquids (OHCLs), as well as the corresponding OHCL / dehydrogenated OHCL pairs. The invention also relates to their uses for hydrogen transport and storage, and to hydrogen generation processes using them.

[0002] After more than a century of intensive use of fossil fuels as the predominant energy source, these natural resources are being depleted, and it is increasingly necessary to develop alternative energy sources to replace traditional ones. These must be inexpensive, safe, non-polluting, and easy to implement.

[0003] For these reasons, stable organic fluids have been developed in particular that are capable of safely and efficiently storing and releasing an energy fluid, for example a fuel, through a catalytic reaction.

[0004] Containing the highest energy density per unit mass and producing only water upon combustion or oxidation in a hydrogen-oxygen fuel cell, hydrogen is considered one of the most efficient and environmentally friendly candidates as a future fuel. Hydrogen is a highly energetic compound compared to conventional fossil fuels and burns in air at widely varying concentrations (including 5% to 75%).

[0005] The concept of using hydrogen as a significant energy carrier was suggested as early as the 1970s. However, the transport and storage of hydrogen are key to achieving the promising "hydrogen era." Therefore, a major challenge is finding suitable hydrogen carriers. For decades, scientists have been searching for suitable materials for hydrogen storage.

[0006] Recently, organic compounds, such as formic acid, methanol-water mixtures, formaldehyde-water mixtures, and carbohydrates, have been intensively studied as potential hydrogen storage materials. Among them are organic hydrogen-carrying liquids (OHCLs), which can be dehydrogenated and hydrogenated by involving large quantities of hydrogen and could be used for land transport applications, are of particular interest.

[0007] In principle, hydrogen is fixed to the hydrogen-deficient organic liquid (dehydrogenated LOHC) by means of a hydrogenation reaction to produce a hydrogen-rich organic liquid (hydrogenated LOHC), which must be a stable liquid under ambient conditions and therefore transportable and storable. The hydrogen-rich organic liquid is then dehydrogenated in a second reaction to regenerate the hydrogen and the hydrogen-deficient organic liquid. Advantageously, these LOHCs are thus capable of being reversibly hydrogenated and dehydrogenated in the presence of a catalyst. Furthermore, thanks to their high volumetric density (50-100 g of hydrogen per liter of hydrogenated LOHC) and mass content (typically 5-10% by mass of hydrogen in hydrogenated LOHC) and their stability under ambient conditions, it is possible to transport and store them in simple tanks, cisterns, or pipelines.The most frequently cited LOHCs are aromatic hydrocarbons and heteroaromatic compounds from the carbazole family. Aromatic hydrocarbons include, in particular, benzene, toluene, naphthalene, biphenyl derivatives, and benzyltoluenes, including dibenzyltoluenes (DBT). In their hydrogenated form, they form cyclic alkanes. These compounds have the advantage of a wide temperature range for their use in liquid form, for example, from -40°C to over 300°C for the dibenzyltoluene / perhydrodibenzyltoluene pair. Furthermore, these aromatic compounds, as well as their cyclic alkanes, exhibit high stability. Finally, some aromatic compounds, such as toluene, are produced globally on a significant scale (25 Mt / year for toluene), making the rapid development of this type of hydrogen transport feasible.Their hydrogenation is carried out at high pressure and moderate temperature (example of DBT: 40-80 bar, 180°C, -71 kJ / molH2) while dehydrogenation is carried out at atmospheric pressure and higher temperature (example of DBT: 1 bar, 300°C, 71 kJ / molH2). Regarding heteroaromatic compounds of the carbazole family, the most frequent compounds are N-ethylcarbazole (NEC) and furan, pyrrole, and indole derivatives. In this case, the hydrogenation reaction leads to cyclic amines or cyclic ethers.

[0008] Amines address the problems raised by previous LOHC solutions. In particular, primary amines are very interesting for energy storage using H2 as a carrier because they offer a maximum mass storage equivalent to 8 or even 13%, well beyond the mass storage values ​​reported in the literature.

[0009] However, there is still currently a strong demand for LOHCs enabling ever more mass storage of hydrogen, while being able to be obtained at least partially from renewable resources.

[0010] The invention therefore aims to provide new hydrogenated organic liquids capable of generating by catalytic dehydrogenation mass and volume contents of hydrogen higher than those generated by conventional LOHCs, of which at least one of the compounds of the dehydrogenated LOHC / hydrogenated LOHC pair is synthesizable from a bio-based, renewable resource, such as wood lignin.

[0011] Another object of the invention is to propose hydrogenated LOHCs whose dehydrogenated counterparts have the capacity to catalytically and reversibly hydrogenate, as well as dehydrogenated LOHCs having the capacity to catalytically and reversibly hydrogenate into these hydrogenated LOHCs.

[0012] Yet another object of the invention is to propose a dehydrogenation process for these new hydrogenated organic liquids which is efficient, high conversion, and selective (to avoid any degradation of the LOHC).

[0013] Thus, according to a first aspect, the invention relates to a hydrogen-bearing organic liquid (HOLC) of the following formula (I):

[0014] [Chem.l] ' n m,

[0015] in which:

[0016] n is 0, 1, 2, 3 or 4;

[0017] at least one of the carbons of

[0018] [Chem.2] .. RR. -R n R

[0019] being optionally substituted by an Rh group independently selected from linear or branched alkyls at C4 to C4 and Y groups;

[0020] X and Y are independently a perhydrogenated aryl group or a perhydrogenated heteroaryl group, said group being optionally substituted by at least one R2 group, independently selected from linear or branched C1 to C4 alkyl groups, linear or branched C1 to C4 O-alkyl groups, -NRaRb groups, with Ra and Rb independently selected from linear or branched C1 to C4 alkyl groups.

[0021] The compounds of formula (I) preferably have a volumetric density of hydrogen ranging from 35 g / L to 70 g / L and / or a mass content of hydrogen ranging from 6% to 13%.

[0022] The volumetric density is calculated for 1 liter of hydrogenated vector by formula (1):

[0023] [Math.l] mass H2 released by hydrogenated LOHC (g) . . Volumetric density H2 (-) =-------------—--------— „—--- (1 ) Total volume of hydrogenated LOHC (L)

[0024] The mass content of hydrogen is determined by formula (2):

[0025] [Math.2] . mass H2 released by hydrogenated LOHC (Gj) . mass content of H2 (%) = 100 x ---------------:----:-------------——— (2) total mass at LOHC hydrogen(g)

[0026] According to a particular embodiment, none of the carbons of

[0027] [Chem.3] X n

[0028] is not substituted by a group Rp

[0029] According to a particular embodiment, at least one of the carbons of

[0030] [Chem.4]

[0031] is optionally substituted by an Rp group independently selected from linear or branched alkyls at C4 to C4 and Y groups.

[0032] According to a particular embodiment, X is a perhydrogenated aryl group, X being in particular a cyclohexyl group.

[0033] According to another particular embodiment, X is a perhydrogenated heteroaryl group, X being in particular selected from the piperidinyl, piperazinyl, hexahydropyrimidinyl, and hexahydropyridazinyl groups.

[0034] According to a particular embodiment, n is 0, 1 or 2.

[0035] According to a particular embodiment, the invention relates to an organic liquid hydrogen carrier in which: - X is a perhydrogenated aryl group or a perhydrogenated heteroaryl group, said group being substituted by at least one R2 group, independently selected from linear or branched C1- to C4-alkyl groups, linear or branched C1- to C4-alkyl O-alkyl groups, and -NRaRb groups, with Ra and Rb independently selected from linear or branched alkyl groups at C1 to C4; and / or - n is 1, 2, 3 or 4.

[0036] According to a particular embodiment, the hydrogen-carrying organic liquid according to the invention is chosen from cyclohexylmethanamine, 2-cyclohexylethanamine, cyclohexanepropanamine, 4-methylcyclohexylmethanamine, 1-(2-methylcyclohexyl)methanamine, and 1-(3-methylcyclohexyl)methanamine.

[0037] According to a particular embodiment, the organic hydrogen-carrying liquid according to the invention is chosen from compounds of the following formula:

[0038] [Chem.5]

[0039] [Chem.6] NH2

[0040] [Chem.7]

[0041] [Chem. 8]

[0042] [Chem.9]

[0043] [Chem. 10]

[0044]

[0045] According to another aspect, the invention also relates to the use of at least one compound of the following formula (I), as an organic hydrogen-carrying liquid (OHCL): [Chem. 11]

[0046] in which:

[0047] n is 0, 1, 2, 3 or 4;

[0048] at least one of the carbons of

[0049] [Chem. 12]

[0050] being optionally substituted by an Rh group independently selected from linear or branched C4-Ci alkyls and Y groups; X and Y are independently a perhydrogenated aryl group or a perhydrogenated heteroaryl group, said group being optionally substituted by at least one R2 group, independently selected from linear or branched C4-Ci alkyl groups, linear or branched C4-Ci O-alkyl groups, -NRaRb groups, with Ra and Rb independently selected from linear or branched C4-Ci alkyl groups.

[0051] All embodiments mentioned above with respect to compounds of formula (I) can also be applied here, alone or in combination.

[0052] According to a particular embodiment, the invention relates to the use of at least one compound of formula (I), as LOHC for the transport and storage of hydrogen.

[0053] According to another aspect, the invention also relates to a pair of a hydrogenated organic hydrogen-bearing liquid (HOLC) and a dehydrogenated HOLC, the hydrogenated HOLC having the following formula (I), and the dehydrogenated HOLC having the following formula (II):

[0054] [Chem. 13]

[0055] [Chem. 14] n "N (II),

[0056] in which:

[0057] n is 0, 1, 2, 3 or 4;

[0058] X is the perhydrogenated counterpart of the aryl or heteroaryl group X', optionally substituted by at least one R2 group, independently selected from linear or branched C1 to C4 alkyl groups, linear or branched C1 to C4 O-alkyl groups, -NRaRb groups, with Ra and Rb independently selected from linear or branched C1 to C4 alkyl groups;

[0059] A is -CH2- and n' is n, or A is -CH=CH- and n' is 1 or 2,

[0060] at least one of the carbons of group A being optionally substituted by an Rb group independently chosen from linear or branched alkyls at C4 to C4 and Y' groups,

[0061] X' and Y' are independently an aryl or heteroaryl group, said group being optionally substituted by at least one R2 group, independently selected from linear or branched C1 to C4 alkyl groups, linear or branched C1 to C4 O-alkyl groups, -NRaRb groups, with Ra and Rb independently selected from linear or branched C1 to C4 alkyl groups.

[0062] Thus, a compound of formula (II) with n'=1 corresponds to a compound (I) with n=2, and a compound of formula (II) with n'=2 corresponds to a compound (I) with n=4.

[0063] An example of a compound couple of formula (I) / compound of formula (II) with A being -CH=CH- can be the 3-cyclohexylpropanamine / cinnamonitrile couple.

[0064] All embodiments mentioned above with respect to compounds of formula (I) can also be applied here, alone or in combination.

[0065] The hydrogenated compounds of formula (I) are suitable for dehydrogenation to produce, in addition to the corresponding compounds of formula (II), hydrogen.

[0066] The dehydrogenated compounds of formula (II) are in turn capable of regenerating by catalytic hydrogenation the corresponding compounds of formula (I) according to the invention.

[0067] According to another aspect, the invention also relates to a hydrogen generation process comprising at least one catalytic dehydrogenation step of an organic hydrogen-carrying liquid (OHCL) of formula (I) as defined above.

[0068] According to a particular embodiment, at least one dehydrogenation step is carried out in the presence of one or more catalysts based on a metal chosen from among the metals of group VIII, and their alloys, the metal being in particular chosen from among Ru, Os, Fe, Co, Rh, Ni, Pt, Pd, Au, Ir, and their alloys.

[0069] According to a more particular embodiment, the at least one dehydrogenation step is a single dehydrogenation step carried out in the presence of one or more catalysts based on a metal chosen from Ru, Pt, Pd, Ir, Rh, and / or Ni.

[0070] According to a particular embodiment, at least one dehydrogenation step is carried out in a reactor, in particular in a reactor comprising the catalyst in a fixed bed.

[0071] According to a particular embodiment, at least one dehydrogenation step is carried out in a batch, semi-batch or continuous type reactor.

[0072] Generally, the compound (I) according to the invention is preheated to the reaction temperature, and in particular injected into a reactor. At the reactor outlet, the liquids produced are separated from the hydrogen by gas / liquid separation.

[0073] According to a particular embodiment, at least one dehydrogenation step is carried out at a temperature of 80 to 320°C, and / or at a pressure of 0.8 to 2 bar.

[0074] According to a particular embodiment, the process according to the present invention comprises a first dehydrogenation step in the presence of one or more catalysts based on a metal chosen from the metals of group VIII, and their alloys, the metal being in particular chosen from Ru, Os, Fe, Co, Rh, Ni, Pt, Pd, and Au, and then a second dehydrogenation step in the presence of one or more catalysts based on platinum, palladium, iridium, rhodium, and / or nickel.

[0075] According to a particular embodiment, the process according to the present invention comprises a first dehydrogenation step in the presence of one or more catalysts based on a metal chosen from the metals of group VIII, and their alloys, the metal being in particular chosen from Ru, Os, Fe, Co, and Rh, then a second dehydrogenation step in the presence of one or more catalysts based on platinum, palladium, iridium, rhodium, and / or nickel.

[0076] These are successive steps, carried out in particular in the order indicated above.

[0077] The metal can be pure or in the form of an alloy, and / or in the form of powder, granules, or in contact with a high surface area substrate.

[0078] According to a further particular embodiment, said first dehydrogenation step is carried out in the presence of one or more catalysts chosen from among catalysts based on ruthenium, cobalt, nickel, ruthenium oxide (in particular IV), cobalt oxide (II), cobalt oxide (III), iron oxide (II), iron oxide (III), nickel oxide, or a mixture thereof.

[0079] Suitable metallic or metal oxide-based catalysts are commercially available. Metal oxide-based catalysts can also be manufactured using techniques well known to those skilled in the art. For example, by wet impregnation, pyrolysis, the "electroless" method, using polyols, or from metal powder using a microwave heating process. Once the operation is complete, the sample is, for example, ground and used without further treatment.

[0080] These catalysts generally contain a small amount of active components dispersed on supports with a high specific surface area. Various types of high specific surface area supports can be used for the preparation of catalysts, including silica, activated carbon, gamma-alumina, organometallic structures, and other support materials. Gamma-alumina (γ-alumina) is commonly used as a support material for dehydrogenation catalysts because of its high specific surface area and its ability to maintain high metal dispersions even at high temperatures. Thus, γ-alumina can be used as a support for the metal and metal oxide catalysts used in the context of the present invention.

[0081] Metal-organic frameworks (MOFs) can also be used for the stabilization and support of metal catalysts and often offer very good catalytic efficiency, due to the considerably increased internal surface area and well-defined pore structures provided by MOFs. MOFs are microporous materials synthesized by the assembly of metal ions with organic ligands. MOF-supported catalysts can be prepared by incorporating unsupported catalysts into the cavities of the MOFs. Alternatively, metal catalysts can be first stabilized, notably with certain surfactants, and then encapsulated by MOFs.

[0082] According to a more particular embodiment, said first dehydrogenation step in the presence of one or more catalysts chosen from among the Ru-based catalysts, for example the Ru / Al2O3, Ru / C, Pt / Al2O3, and Pt / C catalysts.

[0083] Alternatively, the first dehydrogenation step can be carried out electrochemically, in particular by electro-oxidation in a basic medium with nickel-based catalysts. This first electrochemical dehydrogenation step can be carried out by techniques well known to those skilled in the art, in particular using a NiSe anode, as described for example by Huang et al. (Angew. Chem. Int. Ed. 2018, 57, 13163-13166).

[0084] According to a more particular embodiment, said second dehydrogenation step in the presence of one or more catalysts chosen from platinum, palladium, or nickel-based catalysts, for example Pt / Al2O3, Pd / Al2O3, Pt / C, Pt / CeO2, Pt / MgO, Pt / ZrO2, Pd / C, Pt / hBN, Ni / Al2O3 catalysts.

[0085] A possible purification between the two steps is possible.

[0086] According to another aspect, the invention also relates to a process for regenerating a compound of formula (I) from a compound of formula (II) as defined above, the process comprising a step of catalytic hydrogenation of said compound of formula (II).

[0087] This step can be carried out in the presence of a Raney type catalyst, for example Raney nickel or Raney cobalt, possibly doped.

[0088] The processes can be operated in batch or semi-batch reactors or even continuously in "slurry", "tricle bed", fluidized bed or fixed bed type reactors.

[0089] Generally speaking, the hydrogenation reaction is carried out at a temperature of 100 to 200°C, for example from 100 to 130°C.

[0090] The pressure can vary from 10 to 280 bar (or 1 to 28 MPa).

[0091] Of course, the pressure / temperature combination can be adjusted according to the nature of the dehydrogenated LOHC / hydrogenated LOHC couple. The choice of catalyst is generally made taking into account the nature of the dehydrogenated LOHC / hydrogenated LOHC couple under consideration.

[0092] This step can also be carried out electrochemically, by techniques well known to those skilled in the art, in particular by electrocatalytic hydrogenation in an alcoholic-alkaline medium using ferromagnetic catalysts that can be prepared by leaching Ni-Al and Co-Al alloys, as for example described by Tusupbekova et al. (Pharmaceutical Chemistry Journal volume 19, pages 134-136(1985)).

[0093] According to another aspect, the invention relates to a method for transporting and / or storing hydrogen characterized in that it employs at least one compound of formula (I) as defined above.

[0094] The compounds of formula (I) according to the invention can be used in particular in electrochemical or combustion energy conversion devices or in hydrogenation processes as a renewable source of hydrogen or as a fuel.

[0095] According to another aspect of it, the present invention relates to the use, in particular in electrochemical or combustion energy conversion devices, of at least one compound of formula (I) according to the invention.

[0096] All the compounds considered according to the invention are known organic liquids already used as solvents in fine chemicals. Thus, the infrastructure for transporting them already exists.

[0097] Moreover, these are stable compounds under normal temperature and pressure conditions, which makes it possible to consider their transport in standard containers or tanks which can be loaded onto ships, trains or trucks depending on the context.

[0098] The direct applications of a compound of formula (I) according to the invention are the transport and storage of hydrogen.

[0099] The compound of formula (I), can be transported and stored to the place of use of hydrogen, then transformed by dehydrogenation into a compound of formula (II) and into hydrogen.

[0100] The hydrogen produced can then be used as a reagent in an industrial process (hydrodesulfurization, hydrogenation of various compounds, valorization of CO2 in gaseous or liquid fuels ... ).

[0101] The hydrogen produced can also be used as a decarbonized energy carrier either by combustion or by powering an electrochemical energy conversion device.

[0102] Moreover, the liquid properties of these organic compounds make them good candidates for use as fuels for heat engines or electrochemical energy conversion devices.

[0103] They are compatible with storage in a vehicle's tank where dehydrogenation can be carried out to produce hydrogen to power the vehicle. Once dehydrogenated, the LOHC can be stored for later unloading in exchange for hydrogenated LOHC according to the invention.

[0104] Definitions

[0105] As understood here, value ranges in the form of "xy" or "from x to y" or "between x and y" include the bounds x and y as well as the integers between these bounds. For example, "1-5" or "from 1 to 5" or "between 1 and 5" denotes the integers 1, 2, 3, 4, and 5. Preferred embodiments include each integer taken individually in the value range, as well as any subcombination of these integers. For example, preferred values ​​for "1-5" may include the integers 1, 2, 3, 4, 5, 1-2, 1-3, 1-4, 1-5, 2-3, 2-4, 2-5, etc.

[0106] As used herein, the term "alkyl" refers to a linear or branched alkyl group, particularly a linear one, having the number of carbon atoms indicated before the term, in particular 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, etc. Thus, an expression such as "C1-C4 alkyl" refers to an alkyl radical containing 1 to 4 carbon atoms. The same applies to the term "alkane".

[0107] As used herein, the term "arene" refers to a mono- or bicyclic, substituted or unsubstituted, hydrocarbon aromatic cyclic system having 6 to 10 carbon atoms in the ring. Examples include benzene and naphthalene. Preferred arenes include unsubstituted and substituted benzene and naphthalene. The definition of "arene" includes condensed cyclic systems, including, for example, cyclic systems in which an aromatic ring is condensed to a cycloalkyl ring. Examples of such condensed cyclic systems include, for example, indane, indene, and tetrahydronaphthalene.

[0108] As used herein, the term "heteroarene" refers to a cyclic aromatic system containing 5 to 10 carbon atoms in which one or more ring carbon atoms are replaced by at least one heteroatom such as -O-, -N- or -S-, in particular -N- and / or -O-. Examples of heteroarenes include pyrrole, furan, thiophene, pyrazole, imidazole, thiazole, isothiazole, isoxazole, oxazole, oxathiol, oxadiazole, triazole, oxatriazole, furazane, tetrazole, pyridine, pyrazine, pyrimidine, pyridazine, triazine, indole, isoindole, indazole, benzofuran, isobenzofuran, purine, quinazoline, quinoline, isoquinoline, benzoimidazole, benzothiazole, benzothiophene, thianaphthene, benzoxazole, benzisoxazole, cinnoline, phthalazine, naphthyridine and quinoxaline. Included in the definition of "heteroarene" are condensed cyclic systems, including, for example, cyclic systems in which an aromatic ring is condensed to a heterocycloalkyl ring.Examples of such fused cyclic systems include, for example, phthalamide, phthalic anhydride, indoline, isoindoline, tetrahydroisoquinoline, chromane, isochromane, chromene and isochromene.

[0109] EXAMPLES

[0110] Example 1: Two-step dehydrogenation of a compound of formula (I) according to the invention

[0111] The two-step dehydrogenation is carried out as follows:

[0112] [Chem. 15]

[0113] Cyclohexylmethanamine is first selectively converted to cyanocyclohexane via a 5% Ru / Al12O3 catalyst, then cyanocyclohexane is converted to benzonitrile via a Pt / Al12O3 catalyst.

[0114] Step 1: Cyclohexylmethanamine Cyanocyclohexane

[0115] The reaction conditions are grouped in the following table:

[0116] [Tables 1] Starting product Final product Catalyst Temperature (°C) Time (h) Cyclohexylmethanamine Cyanocyclohexane 5% Ru / Al₂O₃ 190 4

[0117] Cyclohexylmethanamine is thus converted into cyanocyclohexane.

[0118] Step 2: Cyanocyclohexane Benzonitrile

[0119] The reaction conditions are grouped in the following table:

[0120] [Tables2] Starting product Final product Catalyst Temperature (°C) Time (h) Cyanocyclohexane Benzonitrile 5% Pt / Al₂O₃ 220 18

[0121] The two-step approach ensures the selectivity of the reaction during the dehydrogenation of the aromatic ring.

Claims

Demands

1. Pair of a hydrogenated organic hydrogen-bearing liquid (HOLC) and a dehydrogenated HOLC, the hydrogenated HOLC having the following formula (I), and the dehydrogenated HOLC having the following formula (II): [Chem. 16] A n / n [Chem. 17] in which: n is 0, 1, 2, 3 or 4; at least one of the carbons of [Chem. 18] S 4 V ' n V being optionally substituted by an Rh group independently chosen from linear or branched Ci to C4 alkyls and Y groups; X and Y are independently the perhydrogenated corresponding of the aryl or heteroaryl group X', optionally substituted by at least one R2 group, independently selected from linear or branched C1-to-C4 alkyl groups, linear or branched C1-to-C4 O-alkyl groups, -NRaRb groups, with Ra and Rb independently selected from linear or branched C1-to-C4 alkyl groups; A is -CH2- and n' is n, or A is -CH=CH- and n' is 1 or 2, at least one of the carbons of group A being optionally substituted by an RB group independently chosen from linear or branched alkyls at C1 to C4, and groups Y', X' and Y' are independently an aryl or heteroaryl group, said group being optionally substituted by at least one R2 group, independently chosen from linear or branched alkyl groups. branched at C4 Ci, linear O-alkyl groups or branched at C4 Ci, -NRaRb groups, with Ra and Rb independently chosen from linear alkyl groups or branched at C4 Ci.

2. Couple according to claim 1, wherein: - X is a perhydrogenated aryl group, X being in particular a cyclol group - X is a perhydrogenated heteroaryl group, X being in particular selected pari ridinyl, piperazinyl, hexahydropyrimidinyl, and hexahydropyridazinyl.

3. Couple according to any one of the preceding claims, in which n is 0, 1 or 2.

4. Couple according to claim 1, wherein the hydrogenated LOHC of formula (I) is selected from cyclohexylmethanamine, 2-cyclohexylethanamine, cyclohexanepropanamine, 4-methylcyclohexylmethanamine, 1-(2-methylcyclohexyl)methanamine, and 1-(3-methylcyclohexyl)methanamine.

5. A method for generating hydrogen comprising at least one catalytic dehydrogenation step of the hydrogenated organic hydrogen-bearing liquid (OHL) of formula (I) of a couple according to claim 1, forming, in addition to hydrogen, the dehydrogenated OHL of formula (II) of said couple according to claim 1.

6. A process according to claim 5, wherein at least one dehydrogenation step is carried out in the presence of one or more catalysts based on a metal selected from the metals of group VIII, and their alloys, the metal being in particular selected from Ru, Os, Fe, Co, Rh, Ni, Pt, Pd, Au, Ir, and their alloys.

7. A process according to any one of claims 5 to 6, wherein at least one dehydrogenation step is carried out in a reactor, in particular in a reactor comprising the catalyst in a fixed bed and / or in a batch, semi-batch or continuous type reactor.

8. A process according to any one of claims 5 to 7, wherein at least one dehydrogenation step is carried out at a temperature of 80 to 320°C, and / or at a pressure of 0.8 to 2 bar.

9. A process according to any one of claims 5 to 8, comprising a first dehydrogenation step in the presence of one or more catalysts based on a metal selected from the metals of Group VIII and their alloys, the metal being in particular selected from Ru, Os, Fe, Co, Rh, Ni, Pt, Pd, and Au, and then a second step dehydrogenation in the presence of one or more platinum, palladium, iridium, rhodium, and / or nickel-based catalysts.