PARTIAL DEHYDROGENATION of ORGANIC LIQUIDS

Abstract

PARTIAL DEHYDROGENATION OF ORGANIC LIQUIDS The present invention relates to a process for producing hydrogen by partial dehydrogenation of an organic liquid, said process comprising a step of supplying at least one organic liquid with a Degree of Hydrogenation DHplus, a step of partially dehydrogenating said liquid, a step of recovering partly hydrogen gas and partly said organic liquid with a Degree of Hydrogenation DHmoins, and wherein the DHplus / DHmoins ratio is between 1 and 25, excluding limits. The invention also relates to a hydrogenation / dehydrogenation cycle comprising at least the process for producing hydrogen by partial dehydrogenation of an organic liquid of the invention and at least one hydrogenation reaction of said organic liquid. Figure to be published with the abstract: None

Description

Title of the invention: DEHYDROGENATION PARTIAL ORGANIC LIQUIDS

[0001] The present invention relates to the transport of hydrogen by means of liquid organic compounds, in particular liquid organic compounds bearing aromatic rings, which can be hydrogenated in order to "transport" hydrogen molecules, and then dehydrogenated in order to release said hydrogen molecules.

[0002] The use of aromatic molecules has already been studied in the field of hydrogen transport and storage (technology known as "Liquid Organic Hydrogen Carrier" in English and also known by the acronym "LOHC").

[0003] The principle consists first of attaching hydrogen to a support molecule. This is the hydrogenation step. The support molecule is preferably liquid at room temperature. This hydrogenated support molecule can be easily transported and handled, and in particular more easily and safely than hydrogen in its gaseous or liquid state. The principle then consists of releasing the hydrogen present on the support molecule, advantageously near, and preferably in the immediate vicinity of, the point of consumption. This is the dehydrogenation step.

[0004] Among the molecules considered, the use of benzyltoluene and / or dibenzyltoluene is an interesting option which has been the subject of studies and publications in the scientific literature and in the patent literature.

[0005] Thus, patent EP2925669 describes the use of a mixture comprising isomers of benzyltoluene and / or dibenzyltoluene in catalytic processes for fixing and releasing hydrogen in or from the mixture. The work of A. Bulgarin et al. (“Int. Journal of Hydrogen Energy”, 45(1), (2020), 712-720) mentions the dehydrogenation of perhydrodibenzyltoluene in the presence of a platinum-on-alumina catalyst at a temperature of 280°C to 300°C.

[0006] Beyond the instantaneous performance of the hydrogenation and dehydrogenation steps, the sequencing of cycles and the maintenance of performance (hydrogen fixation / release yield) is a key parameter for the economic viability of this technology. Furthermore, in the case of dibenzyltoluene (DBT), the cycle is based on total hydrogenation to perhydrodibenzyltoluene (H18-DBT), but the total dehydrogenation to release 18 hydrogen atoms is carried out under severe operating conditions (280°C to 300°C), conditions that are close to the stability limit of DBT (330°C to 350°C). This has not only the disadvantage leading to a decrease in performance over the cycles, but also impacts the yield of the operation over time, not to mention the purity of the hydrogen produced which degrades during the cycles due to by-products formed by the support molecule.

[0007] The solutions proposed so far are therefore promising but not entirely satisfactory. Indeed, the hydrogen-carrying liquids as currently proposed undergo significant degradation during hydrogenation / dehydrogenation cycles, so that they need to be replaced relatively often.

[0008] There remains today a need for industrializable processes which could make it possible to fix and release hydrogen, said process being carried out under less severe conditions than those currently known in order to be able to consider a large scale development of this technology, by promoting a large number of hydrogen fixation / release cycles, while maintaining the performance of the carrier liquid and thus being able to have a technology economically compatible with the development of the transport, production and use of hydrogen on a large scale, in particular in hydrogen engines for transport, for example automobiles, trains, boats, to name only the main uses concerned.

[0009] The inventors have now discovered that it is possible to carry out many hydrogen fixation / release cycles (hydrogenation / dehydrogenation) using an organic carrier liquid, comprising at least one aromatic ring, by limiting the rate of degradation of said carrier liquid during cycles, and thus enabling the transport and supply of hydrogen in a more economically profitable manner, particularly in terms of the lifetime of the carrier liquid and the purity of hydrogen at the end of the dehydrogenation operations of said carrier liquid.

[0010] Other advantages will become apparent from the following description of the present invention.

[0011] Thus, and according to a first aspect, the present invention relates to a process for producing hydrogen by partial dehydrogenation of an organic liquid, said process comprising: - a step of supplying at least one organic liquid with a Degree of Hydrogenation DHpius, - a step of partial dehydrogenation of said liquid, - a recovery step, on the one hand, of gaseous hydrogen and on the other hand, of said organic liquid with a Degree of Hydrogenation DH less, - the DHpius / DHmoins ratio being between 1 and 25, excluding limits, preferably between 1.1 and 20 inclusive limits.

[0012] By "Degree of Hydrogenation" is meant the fraction, by number, of double bonds in the organic liquid that are hydrogenated, that is, saturated with hydrogen atoms, relative to the total number of double bonds capable of being hydrogenated. For example, the DiBenzylToluene (DBT) molecule has 3 aromatic rings and potentially 9 double bonds capable of being hydrogenated. DBT has a Degree of Hydrogenation of zero (0), and the fully hydrogenated DBT molecule has a Degree of Hydrogenation of one (1).

[0013] A DHpius / DHmoins ratio of 1 (not included in the present invention) indicates that there is no release of hydrogen during dehydrogenation. A DHpius / DHmoins ratio of 25 (not included in the present invention) corresponds to a residual Degree of Hydrogenation DHmoins of the organic liquid after the dehydrogenation step of 4%.

[0014] By "partial dehydrogenation" it is understood that a total dehydrogenation of the organic liquid is not achieved but only a partial dehydrogenation, leading to an organic liquid with a Degree of Hydrogenation DHminus strictly greater than 0.

[0015] The "partial" dehydrogenation reaction described above can be carried out as a classic dehydrogenation reaction, however without seeking to achieve a 100% yield of said dehydrogenation reaction, that is to say without seeking to supply all of the hydrogen molecules transported by the organic liquid.

[0016] Various means can be used to avoid achieving a 100% yield (corresponding to a dehydrogenation rate of 100% of the hydrogen atoms that can be dehydrogenated). Among these means, well known to those skilled in the art, one or more of the following may be cited, without limitation: - blocking the reaction before obtaining a 100% dehydrogenation yield, - reaction temperature lower than the temperature usually used for the dehydrogenation reaction, - reaction pressure lower than the pressure usually used for the dehydrogenation reaction, - a non-selective dehydrogenation catalyst, - as well as any other means of regulating the dehydrogenation reaction kinetics.

[0017] Controlling the dehydrogenation conditions thus makes it possible to conduct this reaction partially, contrary to the teaching given to man of the craft in the prior art. By operating a partial dehydrogenation step, that is, by not conducting the reaction until all the transported hydrogen atoms are released, it was surprisingly discovered that the energy expenditure is lower, while retaining a quite satisfactory quantity of transported hydrogen molecules.

[0018] Indeed, one of the problems associated with the hydrogenation and dehydrogenation cycles of organic liquids used in hydrogen transport is their stability when heated to temperatures close to their boiling point. It has been observed that these organic liquids can be modified by dimerization or rearrangement / reorganization, leading to the formation of various chemical species. These modifications result in a loss of purity of the initial organic liquid and a loss of yield over time. This loss is primarily linked to inherent changes in the characteristics of the organic liquid, including, but not limited to, a change in viscosity, which can be detrimental to the handling, storage, and use of the organic liquid for hydrogen transport.

[0019] Thus, the process according to the present invention allows an improvement in the stability of the organic liquid subjected to hydrogenation / dehydrogenation cycles and consequently less generation of degradation products of said organic liquid, and in particular of light degradation products (therefore volatile and therefore likely to contaminate the released hydrogen), and / or of heavy degradation products (therefore likely to increase the viscosity of the organic liquid and thus penalize subsequent cycles).

[0020] Other advantages resulting from the system of the present invention include, in particular, that when the hydrogenation or dehydrogenation temperature is lower than that encountered in the prior art for equivalent reactions carried out to yields of up to 100%, the thermal degradation of the support molecule is greatly reduced, and consequently the lifetime of said support molecule is improved. An increased lifetime of the support molecule also makes it possible to substantially increase the number of cycles.

[0021] The degree of advancement of the dehydrogenation reaction can be easily controlled by all means known to those skilled in the art, for example according to the indications provided by K. Millier et al. (“Experimental assessment of the degree of hydrogen loading for the dibenzyl toluene based LOHC System”, International Journal of Hydrogen Energy, 41, (2016), 22097-22103), and in particular by Raman spectrometry, by measurement of the refractive index, by measurement of the density, or by measurement of the quantity of hydrogen produced, and others.

[0022] In the process of the present invention, the organic liquid may be of any nature well known to those skilled in the art, capable of transporting hydrogen atoms, that is to say, capable of being at least partially hydrogenated and / or at least partially dehydrogenated. The organic liquid usable in the process according to the present invention may also be a mixture of two or more organic liquids that may have identical or different degrees of hydrogenation.

[0023] The organic liquid usable within the framework of the present invention most often and advantageously possesses at least one aromatic ring, possibly partially dehydrogenated.

[0024] More particularly, the organic liquid usable in the process of the present invention corresponds to the general formula (1): (AX)nB (1) in which: - A and B, identical or different, represent independently of each other, an aromatic ring possibly partially dehydrogenated, and possibly substituted by one or more hydrocarbon radicals, saturated or partially or totally unsaturated, comprising from 1 to 20 carbon atoms, preferably from 1 to 18 carbon atoms, preferably still from 1 to 12 carbon atoms, better from 1 to 10 carbon atoms, better still from 1 to 6 carbon atoms, typically from 1 to 3 carbon atoms, - X represents a spacer group, chosen from a single bond, an oxygen atom, a sulfur atom, the divalent radical -(CRR')m-, the divalent radical >C=CRR', and the divalent radical -NR”-, - R and R', identical or different, are chosen independently of each other, from hydrogen and a hydrocarbon radical, saturated or partially or totally unsaturated, comprising from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, - R” represents a hydrocarbon radical, saturated or partially or totally unsaturated, comprising from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, - m represents an integer between 1 and 4 inclusive, and - n can be equal to 0 or represents an integer equal to 1, 2 or 3, preferably equal to 1 or 2, with the restriction that when n is equal to 0, B is substituted by one or more hydrocarbon radicals, as defined previously.

[0025] By "#aromatic ring#", we mean aromatic hydrocarbon monocycles and aromatic hydrocarbon polycycles, comprising from 6 to 20 carbon atoms. By "#polycycle#", we mean fused or condensed rings.

[0026] When n equals 0, the organic liquid of formula #(l) defined above belongs to the alkylbenzene family, possibly partially dehydrogenated. When n equals 2 or 3, the (AX) groups may be identical or different.

[0027] According to a preferred embodiment of the present invention, in the organic liquid of general formula (1), n ​​is different from 0 and B is substituted by a hydrocarbon radical. Preferably, said hydrocarbon radical is an alkyl radical comprising from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, and preferably the alkyl radical is the methyl radical.

[0028] According to another preferred embodiment of the present invention, in the organic liquid of general formula (1), n ​​is equal to 0 and the organic liquid of formula (1) is generally selected from linear alkylbenzenes, optionally partially dehydrogenated, and branched alkylbenzenes, optionally partially dehydrogenated, such as, for example and without limitation, partially dehydrogenated alkylbenzenes and their homologs, in which the alkyl portion comprises from 10 to 20 carbon atoms. Such alkylbenzenes include, again without limitation, decylbenzene, dodecylbenzene, octadecylbenzene, and their at least partially dehydrogenated homologs, to name but a few.

[0029] As previously stated, organic liquids conforming to the general formula (1) above can be used alone or in mixtures of two or more of them in any proportion. According to a preferred embodiment of the invention, the organic liquid used in the process of the present invention may contain a compound bearing at least one aromatic radical, optionally partially dehydrogenated, or a mixture of two or more compounds bearing at least one aromatic radical, optionally partially dehydrogenated. According to a particularly preferred embodiment, the organic liquid used in the process of the invention is liquid at ambient temperature and ambient pressure.

[0030] According to yet another preferred embodiment of the present invention, the organic liquid is chosen from benzyltoluene (BT), dibenzyltoluene (DBT), their partially dehydrogenated homologues, as well as mixtures thereof in all proportions.

[0031] In a particularly preferred embodiment, the organic liquid is chosen from among the organic liquids sold by Arkema under the trade names of the Jarytherm® range.

[0032] Other organic liquids, and at least partially dehydrogenated analogues, suitable for the purposes of the present invention are, for example, those marketed by the company Eastman, and in particular under the trade name Marlotherm®.

[0033] As further examples of organic liquids suitable for the purposes of the present invention, we may cite #: - diphenylethane (DPE) and its isomers, in particular 1,1-DPE (CAS 612-00-0), 1,2-DPE (CAS 103-29-7) and their mixtures (notably CAS 38888-98-1), such organic liquids being commercially available or described in the literature, for example in document EP0098677, - ditolylether (DT) and its isomers, in particular those corresponding to CAS numbers 4731-34-4, CAS 28299-41-4 and their mixtures, these being notably available commercially from the company Lanxess, under the trade name DiphylDT, - phenylxylylethane (PXE) and its isomers, in particular those meeting CAS numbers 6196-95-8, CAS 76090-67-0 and their mixtures, notably available commercially from the company Changzhou Winschem, under the trade name PXE oil, - l,2,3,4-tetrahydro-(l-phenylethyl)naphthalene (CAS 63674-30-6), this product being commercially available notably from Dow under the reference Dowtherm™#RP, - diisopropylnaphthalene (CAS 38640-62-9), notably available from Indus Chemie Ltd under the trade name KMC 113, - monoisopropylbiphenyl and its isomers (CAS 25640-78-2), notably available under the trade name Wemcol, and - phenylethylphenylethane (PEPE) and its isomers (CAS 6196-94-7), notably available from Changzhou Winschem or Yantai Jinzheng, - as well as their at least partially dehydrogenated counterparts, - and mixtures of two or more of them, in all proportions, to mention only the main organic liquids known and usable within the framework of the present invention.

[0034] The organic liquid usable within the framework of the present invention may further contain one or more additives well known to those skilled in the art, and for example, but not limited to, selected from antioxidants, passivators, pour point depressants, decomposition inhibitors, and mixtures thereof. An organic liquid particularly preferred for the process of the present invention comprises at least one antioxidant.

[0035] Among the antioxidants that can be advantageously used in the organic liquid, phenolic antioxidants, such as dibutylhydroxytoluene, butylhydroxyanisole, may be cited by way of non-limiting examples. tocopherols, as well as the acetates of these phenolic antioxidants. We can also mention amine-type antioxidants, such as phenyl-a-naphthylamine, diamine-type antioxidants, such as N,N'-di-(2-naphthyl)-para-phenylenediamine, but also ascorbic acid and its salts, ascorbic acid esters, alone or in mixtures of two or more of them or with other components, such as green tea extracts, coffee extracts.

[0036] Generally, the organic liquid used in the partial dehydrogenation process according to the invention is a fully hydrogenated organic liquid or at least partially dehydrogenated. According to one embodiment of the invention, the organic liquid used in the partial dehydrogenation step has a Degree of Hydrogenation DHpius less than or equal to 1. The Degree of Hydrogenation DHpius is strictly greater than 0, preferably greater than or equal to 0.1, preferably even greater than or equal to 0.2, better still greater than or equal to 0.4, most preferably greater than or equal to 0.6, advantageously greater than 0.8.

[0037] In a particularly preferred embodiment of the process according to the present invention, the organic liquid used in the dehydrogenation step has a Degree of Hydrogenation DHpius that satisfies the following inequality: 0.6 < DHplus < 1.

[0038] At the end of the partial dehydrogenation step of the organic liquid, it is therefore partially dehydrogenated, and advantageously practically but not totally dehydrogenated. According to one embodiment of the invention, the organic liquid at the end of the partial dehydrogenation reaction has a Degree of Hydrogenation DHminus strictly less than 1, preferably less than or equal to 0.8, preferably even less than or equal to 0.6, better still less than or equal to 0.4.

[0039] In a particularly preferred embodiment of the process according to the present invention, the organic liquid at the end of the partial dehydrogenation step has a Degree of Hydrogenation DHmoins satisfying the following inequality: 0 < DHmoins < 0.6.

[0040] As previously stated, the ratio DHpius / DHmoins is different from 1 (no dehydrogenation reaction) and therefore DHpius cannot be equal to DHmoins.

[0041] The dehydrogenation reaction can be carried out according to any method known to a person skilled in the art, with the restriction that it is not conducted in such a way as to dehydrogenate all of the organic liquid used.

[0042] Among the operating conditions that can be implemented, the following may be cited as non-imitative examples: - the reaction temperature generally between 250°C and 350°C, and preferably between 280°C and 330°C, and most preferably between 280°C and 320°C, - the reaction pressure generally between 0.01 Pa and 3 Pa, and preferably between 0.1 Pa and 2 Pa, and preferably the reaction pressure is atmospheric pressure.

[0043] The reaction is most often and advantageously carried out in the presence of at least one dehydrogenation catalyst well known to those skilled in the art. Among the catalysts that can be used for said partial dehydrogenation reaction, heterogeneous catalysts containing at least one metal on a support may be cited by way of non-limiting examples. Said metal is chosen from among the metals of columns 3 to 12 of the IUPAC periodic table of elements, that is to say, from among the transition metals of said periodic table. In a preferred embodiment, the metal is chosen from among the metals of columns 5 to 11, more preferably from columns 5 to 10 of the IUPAC periodic table of elements.

[0044] The metals of these catalysts are most often chosen from iron, cobalt, copper, titanium, molybdenum, manganese, nickel, platinum and palladium and mixtures thereof. Preferably, the metals are chosen from copper, molybdenum, platinum, palladium, and mixtures of two or more of them in any proportion.

[0045] The catalyst support can be of any type well known to those skilled in the art and is advantageously chosen from porous supports, more advantageously from refractory porous supports. Non-limiting examples of supports include alumina, silica, zirconia, magnesia, beryllium oxide, chromium oxide, titanium oxide, thorium oxide, ceramics, carbon such as carbon black, graphite, and activated carbon, as well as combinations thereof. Specific and preferred examples of supports usable in the process of the present invention include amorphous silico-aluminates, crystalline silico-aluminates (zeolites), and supports based on titanium-silica oxide.

[0046] The process according to the present invention comprising a step of partial dehydrogenation of an organic liquid advantageously fits into one or more cycles, more advantageously several cycles, of hydrogenation / dehydrogenation thus allowing the storage and transport of hydrogen in said hydrogenated organic liquid.

[0047] The hydrogenation reaction can be carried out according to any method well known to those skilled in the art on an organic liquid as defined above, advantageously an organic liquid comprising at least one aromatic ring and preferably an organic liquid corresponding to the general formula (1) as defined above.

[0048] The hydrogenation reaction is generally carried out at a temperature between 120°C and 200°C, and preferably between 130°C and 180°C, and even more preferably between 140°C and 160°C. The pressure used for this reaction is generally between 0.1 MPa and 5 MPa, preferably between 0.5 MPa and 4 MPa, and even more preferably between 1 MPa and 3 MPa.

[0049] Most often, the hydrogenation reaction is carried out in the presence of a catalyst, and more particularly a hydrogenation catalyst well known to those skilled in the art, and advantageously chosen from among, by way of non-limiting example, heterogeneous catalysts containing metals on a support. Said metal is chosen from among the metals of columns 3 to 12 of the IUPAC periodic table of elements, that is to say, from among the transition metals of said periodic table. In a preferred embodiment, the metal is chosen from among the metals of columns 5 to 11, more preferably from columns 5 to 10 of the IUPAC periodic table of elements.

[0050] The metals of these hydrogenation catalysts are most often chosen from iron, cobalt, copper, titanium, molybdenum, manganese, nickel, platinum, and palladium, and mixtures thereof. Preferably, the metals are chosen from copper, molybdenum, platinum, palladium, and mixtures of two or more of them in any proportion.

[0051] The catalyst support can be of any type well known to those skilled in the art and is advantageously chosen from porous supports, more advantageously from refractory porous supports. Non-limiting examples of supports include alumina, silica, zirconia, magnesia, beryllium oxide, chromium oxide, titanium oxide, thorium oxide, ceramics, carbon such as carbon black, graphite, and activated carbon, as well as combinations thereof. Specific and preferred examples of supports usable in the process of the present invention include amorphous silico-aluminates, crystalline silico-aluminates (zeolites), and silica-titanium oxide-based supports.

[0052] According to a preferred embodiment, the hydrogenation reaction is carried out on a totally or partially dehydrogenated organic liquid, preferably partially dehydrogenated, in particular when said organic liquid is obtained from the partial dehydrogenation process as defined above.

[0053] The hydrogenation reaction can be partial or total, and preferably the hydrogenation reaction is total, that is to say that all the double bonds of the carrier liquid that can be hydrogenated are totally hydrogenated.

[0054] According to another aspect, the present invention relates to a hydrogenation / dehydrogenation cycle comprising at least the process as just defined of production of hydrogen by partial dehydrogenation of an organic liquid and at least one hydrogenation reaction of said organic liquid.

[0055] In the cycle of the present invention, it should be understood that the hydrogenation reaction of the organic liquid (the carrier molecule that will store the hydrogen) can be carried out once or repeated two or more times. Thus, a first partial or total hydrogenation can be performed, followed by one or more further partial or total hydrogenations directly on the organic liquid from the immediately preceding step.

[0056] Similarly, in the cycle of the present invention, it should be understood that the process of partial dehydrogenation of the organic liquid (support molecule which will release hydrogen) can be carried out once or repeated two or more times, provided that at least one, advantageously two, more advantageously several, and more preferably all the dehydrogenation processes are carried out in a partial manner, that is to say, without totally dehydrogenating the organic liquid, as indicated above.

[0057] In the cycle according to the invention, it may thus be envisaged to operate one or more dehydrogenation processes, of which at least one is a partial dehydrogenation process according to the invention, prior to and / or following one or more hydrogenation steps of an organic liquid capable of storing, transporting and releasing hydrogen.

[0058] The dehydrogenation and hydrogenation reaction(s) can be carried out with identical or different dehydrogenation and hydrogenation yields. It is thus possible to carry out at least one dehydrogenation reaction partially (including at least one partially), followed by another reaction to a higher, lower, or identical degree of dehydrogenation. Similarly, it is possible to carry out at least one hydrogenation reaction partially or completely, followed by another reaction to a higher, lower, or identical degree of dehydrogenation.

[0059] It has been observed that the cycle of the present invention allows storage in liquid form at ambient temperature and pressure, transport in liquid form at ambient temperature and pressure and the release of hydrogen in a safe manner and with quite acceptable economic yields, in particular due to limited and controlled aging (degradation) of the organic liquid, i.e. an organic liquid with improved stability, thanks to the partial dehydrogenation step of the process according to the present invention.

[0060] Improving the stability of the organic liquid results in less generation of light degradation products (therefore volatile and consequently susceptible to contaminate the released hydrogen), and heavy degradation products, therefore likely to increase the viscosity of the product and penalize subsequent cycles.

[0061] The cycle of the present invention thus represents an efficient and economically cost-effective system for transporting hydrogen, and this in a safe manner since it avoids transporting hydrogen in gaseous form. The cycle of the present invention allows the "transport" of hydrogen molecules, that is to say, fixing hydrogen onto an organic liquid and then releasing the hydrogen fixed onto said organic liquid, as already proposed in the prior art, with the difference that at least one dehydrogenation step of the cycle is not carried out completely but only partially, as described above.

[0062] The invention is now illustrated by means of the following examples which are provided as embodiments of the invention, without however imposing any limitation on the scope of protection as defined in the attached claims. EXAMPLES

[0063] The following examples correspond to partial dehydrogenation tests carried out on an organic liquid, which is DiBenzylToluene (DBT), from the company Arkema.

[0064] A 100 mL three-necked flask equipped with a condenser is loaded with 0.1 mole of DBT and 0.15 mol% of a catalyst, which is a platinum catalyst (0.5 wt%) on alumina. The assembly is purged with nitrogen to remove all traces of ambient air from the reactor. After calibrating the thermal conductivity analyzer (FTC200, version 1.05, Wagner) at room temperature, the mixture is heated to 300°C using a heating jacket. The released hydrogen is collected by the constant flow of nitrogen, and the amount of hydrogen produced is continuously monitored using the thermal conductivity analyzer (FTC200, version 1.05, Wagner).

[0065] The number of moles of hydrogen released can be correlated with the Degree of Hydrogenation DHminus at the end of the dehydrogenation step. For each trial, the molar percentage of DBT that has been degraded is determined (number of moles remaining / number of moles introduced).

[0066] The results are presented in the following Table 1: [Tables 1] % degradation DBT 0 5 0.15 1 0.33 0.01 0.67 0.008 1 0.002

[0067] The above results clearly show that total dehydrogenation (DHminus = 0) leads to a 5% degradation of DBT. With a partial dehydrogenation step (DHminus > 0), the degradation of DBT is considerably reduced, becoming negligible or almost negligible for a DHminus greater than 0.15.

[0068] It is thus possible, for example, to consider a succession of partial dehydrogenation reactions, each leading to the release of hydrogen and a small remaining fraction of DBT (undegraded DBT), even with a DH less than 0.33 (remaining DBT fraction of 0.99%). After n partial dehydrogenation reactions, and therefore n hydrogen release reactions, the degradation of DBT will be contained within quite reasonable limits, with the degradation equivalent to 0.99n at the end of the nth dehydrogenation reaction.

Claims

Claims

1. Method for storing and / or transporting hydrogen, said method comprising: - a step of providing at least one organic liquid with a Degree of Hydrogenation DHpius, - a step of partial dehydrogenation of said liquid, - a step of recovering on the one hand gaseous hydrogen and on the other hand said organic liquid with a Degree of Hydrogenation DHmoins, - the ratio DHpius / DHmoins being between 1 and 25, limits excluded, preferably between 1.1 and 20 limits inclusive.

2. Process according to claim 1, in which the partial dehydrogenation step is carried out by implementing one or more of the following means, taken alone or in combination of two or more of them: - blocking the reaction before obtaining a 100% dehydrogenation yield, - reaction temperature lower than the temperature usually used for the dehydrogenation reaction, - reaction pressure lower than the pressure usually used for the dehydrogenation reaction, - nature of the dehydrogenation catalyst which is not very selective, - as well as any other means making it possible to regulate the kinetics of the dehydrogenation reaction.

3. A method according to either of claims 1 or 2, wherein the organic liquid is liquid at room temperature and ambient pressure.

4. A method according to any preceding claim, wherein the organic liquid is a mixture of two or more organic liquids which may have the same or different Degrees of Hydrogenation.

5. A method according to any one of the preceding claims, wherein the organic liquid has at least one aromatic ring, optionally partially dehydrogenated.

6. A method according to any one of the preceding claims, wherein the organic liquid corresponds to the general formula (1): (AX)nB (1) in which: - A and B, identical or different, represent independently of one another, an aromatic cycle which is optionally partially dehydrogenated, and optionally substituted by one or more hydrocarbon radicals, saturated or partially or totally unsaturated, comprising from 1 to 20 carbon atoms, preferably from 1 to 18 carbon atoms, more preferably from 1 to 12 carbon atoms, better still from 1 to 10 carbon atoms, better still from 1 to 6 carbon atoms, typically from 1 to 3 carbon atoms, - X represents a spacer group, chosen from a single bond, an oxygen atom, a sulfur atom, the bivalent radical -(CRR')m-, the bivalent radical >C=CRR', and the bivalent radical -NR”- - R and R', identical or different, are chosen independently of one another, from hydrogen and a hydrocarbon radical, saturated or partially or totally unsaturated, comprising from 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms,- R' ' represents a saturated or partially or totally unsaturated hydrocarbon radical containing from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, - m represents an integer between 1 and 4 inclusive, and - n can be equal to 0 or represents an integer equal to 1, 2 or 3, preferably equal to 1 or 2, with the restriction that when n is equal to 0, B is substituted by one or more hydrocarbon radicals, as defined above.,

7. A method according to any one of the preceding claims, wherein the organic liquid is chosen from benzyltoluene (BT), dibenzyltoluene (DBT), their partially dehydrogenated homologues, as well as their mixtures in all proportions.

8. A method according to any preceding claim, wherein the organic liquid has a Degree of Hydrogenation DHpius satisfying the inequality 0.6 < DHpius < 1.

9. A method according to any preceding claim, wherein the organic liquid has a Degree of Hydrogenation DHminus satisfying the inequality 0 < DHminus < 0.

6.

10. Hydrogenation / dehydrogenation cycle comprising at least the process according to any one of claims 1 to 9 for producing hydrogen by partial dehydrogenation of a liquid 16 organic and at least one hydrogenation reaction of said organic liquid.

11. Cycle according to claim 10, comprising one or more dehydrogenation processes, at least one of which is a partial dehydrogenation process according to any one of claims 1 to 9, prior to and / or following one or more hydrogenation reactions of an organic liquid capable of storing, transporting and releasing hydrogen.