WO2008142560A2 - Method for the production of binary clathrate hydrates of hydrogen - Google Patents

Abstract

A method for the effective production of binary clathrate hydrates of hydrogen and a co-former is provided, said method comprising the formation of water-in-oil nanoemulsions, such as, e.g., surfactant reverse micelles in an organic solvent, and the formation of clathrate hydrate nanocrystals from the water droplets thus obtained.

Description

"METHOD FOR THE PRODUCTION OF BINARY CLATHRATE HYDRATES OF HYDROGEN"

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Field of the invention The present invention relates to a method for the production of binary clathrate hydrates of hydrogen and to the products thereof. More particularly, the present invention relates to an effective method for the production of binary clathrate hydrates of a hydrate former (e.g., hydrogen) and a co-former (e.g., tetrahydrofuran) based on the formation of water-in-oil emulsions (e.g., nanoemulsions) and to the products thus obtained.

Hydrogen storage is one of the most important and challenging problems that researchers both in the industry and the academy are facing toward the development of a hydrogen-based economy. To date, the main methods employed to store hydrogen are: 1) under high pressure as a gas, 2) in liquid form, and 3) adsorbing hydrogen in the form of a hydride in hydride-forming metals and other inorganic and organic compounds. All the above mentioned methods have severe drawbacks.

Storing hydrogen as a gas requires heavy-duty containers, and the pressures required to obtain an economically viable mass ratio are inherently hazardous, no matter how technologically advanced the container is. Composite materials for high- pressure containers are currently being developed, but their cost is high. Storing hydrogen as a liquid also poses safety problems; moreover, a large fraction of the stored energy is lost when converting hydrogen gas to the liquid phase, and by keeping it as a liquid at extreme temperatures (a few Kelvins). Inorganic and organic supports (metals, intermetallic compounds, carbon nanotubes, etc.) can adsorb reversibly variable amounts of hydrogen at ambient temperature and pressure but desorption therefrom requires a high energy input and usually takes place at elevated temperatures. Background of the invention

Dyadin et al. "Clathrate hydrates of hydrogen and neon", Mendeleev Commun, 5, 209-210 (1999); and Dyadin, Y. A. et al., "Clathrate formation in water-noble gas (hydrogen) systems at high pressures", J. Struct. Chem. 40, 790-795 (1999) disclosed that hydrogen forms clathrate hydrates under very high pressure/low temperature conditions.

A clathrate is a supramolecular compound in which the guest species are enclosed within cages formed by the host species. Clathrate hydrates are clathrates, with the host framework made up of hydrogen-bonded H₂O molecules, and guest molecules trapped inside the water cages.

In 2002, Mao et al. found that hydrogen hydrate crystallizes in structures labeled as structure-ll (sll) clathrates; see, Mao, W. L., et al., "Hydrogen Clusters in Clathrate Hydrate", Science 297, 2247-2249 (2002). U.S. Pat. No. 6,735,960, "Composition and Method for Hydrogen Storage", issued May 18, 2004 disclosed that the synthesis of hydrogen clathrate hydrate can be performed using liquid water and hydrogen gas as the starting materials, directly from water and hydrogen gas by cooling them down under a pressure of 1-6 kbar, and the hydrate formed below 250 K. WO 2005/113424 relates to storing hydrogen in clathrate hydrate form, wherein the clathrate is formed starting from a composition consisting of water and a promoter in the presence of pressurized hydrogen, the promoter having the role of reducing the pressure and/or increasing the temperature needed to form a clathrate hydrate of hydrogen. The promoter is in fact a co-former, in the sense that it occupies a portion of the sites of the clathrate, replacing the hydrogen and thus lowering the hydrogen storage capacity. The co-former is disclosed to be THF (water soluble) or water insoluble compounds that form a two phases system.

Z. Sun et al., International Journal of Energy Research, vol. 27, 2003, pp. 747-756, reports the production of gas hydrates of methane or synthetic natural gas (92.5% methane) by using surfactants and liquid hydrocarbons as adjuvants. Sun et al. refer to oil-in-water (O/W) emulsions, i.e., wherein the bulk phase is water and the dispersed phase is an organic solvent and oil droplets are in contact with the hydrocarbon chain of surfactant molecules. Moreover, in the suggested quiescent condition a two phases system is obtained. The hydrophilic head groups of the same surfactant molecules are in contact with the bulk water phase. The surfactants disclosed are for example, SDS surfactant i.e. a surfactants specific for O/W dispersions. Notwithstanding the fact that methane forms si hydrates easily, contrary to hydrogen si I structures, the reaction times are very long, even in the presence of a promoter (table II). Moreover, this article actually suggests to avoid the presence of liquid hydrocarbons (promoters) to retain the storage capacity. US 2006/0009664 describes a method for hydrogen clathrate hydrate synthesis, in which ice and hydrogen gas are firstly supplied to a container at a first temperature and pressure, and then the container is pressurized with hydrogen gas to a second, higher pressure, where hydrogen clathrate hydrates are formed in the process.

The above methods using a co-former are a significant progress towards the use of clathrate hydrates as a means for the storage and transportation, but they suffer of some drawbacks. First, there is a problem with the choice of the coformer: a water insoluble coformer will provide a contact surface too small to give an acceptable speed of clathrate formation; on the other side, when using water soluble coformers (e.g. THF) the hydrate of pure coformer will be in competition with the hydrogen/coformer hydrate in terms of the kinetics of formation: this reduces too much the efficiency of the process of hydrogen hydrate formation, as discussed in above cited WO2005/113424.

To solve the above hydrogen clathrates forming problems, Lee et al. (Nature, vol. 434 (2005), pp. 743-746) experimentally probed the feasibility of obtaining high- content binary hydrates of THF and hydrogen (up to 4.03 wt% hydrogen at 120 bar), - A -

but their process takes weeks to complete. On the other hand, a similar hydrogen storage ratio, but with a much faster uptake, is achieved when adsorbing the water phase onto silica; however, the authors recognize that in the latter case (water adsorbed on silica), the additional silica weight takes the material out of the required range as a practical hydrogen storage material.

To this regard, WO2006/131738 (Heriot-Watt University) proposes to replace the coformer with ammonium salts and similar semi-clathrate hydrate forming compounds; however, such semi-clathrates contain very little amounts of hydrogen (well below 1 wt%), and many "onium" compounds which are used to stabilize the semi-clathrates are toxic and/or expensive, and therefore not suitable for storage and transportation purposes.

Also, the previous methods usually deal with solid or semi-solid systems, which makes it difficult to carry out a continuous production process. Another drawback is that the dimensions of the early clathrate crystallites obtained with the known methods are too large and will make processing of the reaction mixture difficult an expensive.

Therefore, there is the need for a different and more effective approach that could provide a method that solves the above mentioned problems and that allows to, among other things, reduce the amount of coformer and increase the amount of hydrogen included into the clathrate hydrate structures and to increase by several orders of magnitude the surface/volume ratio of hydrate-forming water systems. Summary of the invention

The above need is met by the present invention that provides a process for the production of binary clathrate hydrates of a hydrogen and a co-former, said process comprising the steps of forming a dispersion of water droplets having dimensions of 1 micron or less in a dispersing phase, in the presence of said co-former, and forming clathrate hydrate crystals from the water microdroplets thus obtained. In a preferred embodiment the dispersion is a nanodispersion, the water droplets having dimensions within the range of 2 to 300 nm, and the hydrate crystals are nanocrystals.

According to an embodiment of the invention, the dispersing phase is selected from one or more of organic solvents, hydrocarbons, fluorocarbons, ionic liquids, supercritical fluids, alkylcarbonates, etc.

According to the invention, the nanodispersion is a dispersion of surfactant reverse micelles in a dispersing medium.

In a further embodiment of the invention, hydrogen is replaced by another gas, e.g. fluorine, chlorine dioxide, difficult to transport and suitable to form binary clathrates with a coformer.

Preferred surfactants are disclosed in claim 13 and 14. The surfactants of claim 14 are a further object of the invention.

A further object of the invention are the binary clathrates hydrates as obtainable according to the above method. These hydrates are new and inventive because they can contain more than 1% (wt) and at least up to 4,1% (wt) of hydrogen. The hydrogen binary clathrate hydrates are available in si I and sH form.

The present invention allows to obtain many advantages, as described below and provides an excellent solution to the standing problems of hydrogen clathrate hydrates production. In the following, the terms "hydrate former" is used to denote hydrogen or a compound of interest whose storage in hydrate form is desired and important, while

"co-former" is used to denote a compound which helps in the formation of the clathrate of the hydrate former.

As illustrated in the following, the present method is inventive over the prior art in that it provides the following unforeseeable advantages.

The presence of an organic solvent allows a much broader choice of co-former: the presence of a bulk, dispersing phase formed by e.g. an organic solvent allows to employ also water-insoluble co-formers, such as cyclobutane, cyclopentane, cyclohexane, etc., and the bulk organic phase serves as a reservoir of the co-former which is kept ready for hydrate formation when the latter begins. Ideally, if needed, the dispersing phase may be entirely composed by the organic, water insoluble, co- former itself. On the other hand, the bulk dispersing phase acts as a "partition buffer" to limit the concentration of very water-soluble molecules (e.g., THF) into the water droplets, thus promoting the amount of hydrogen in the clathrate. The amount of co-former in the water droplets can be controlled through the amount of co-former in the dispersing phase. The nanometric size of water particles of less than 1 micron, in the form of an emulsion, results in a dramatic increase of the reaction speed. In fact, the average reaction time is within the range of 5 to 50 minutes, but with suitable stirring means it can be as low as 2-3 minutes. With the prior art methods, only water-miscible co- formers (e.g., tetrahydrofuran) could be used effectively, because water-insoluble molecules tend to form macroscopic interfaces that dramatically limit the mass transfer during the process of hydrate formation.

It is particularly surprising that this reduction of the reaction speed is obtained at the same time of a reduced presence of the co-former in the clathrate structures: in fact, the amount of hydrogen in the clathrate can be up to 4.1% (w/w) of the hydrate, compared with a theoretical maximum of 5% without co-former (see WO 2005/113424, page 4).

The reaction system can be kept under homogeneous conditions avoiding clogging of the reactor, due to agglomeration of hydrate fine particles. Indeed, hydrate nanocrystals which form from the nanoemulsion's water pools precipitate to the bottom of the reactor in form of a slurry which is free flowing and does not tend to clog, e.g., a discharge pipeline. This is different from the prior art methods, and proved helpful in the design of a continuous process. The present process can be made continuous by simply adding water and co- former, because the surfactant is not trapped into the forming hydrate but, instead, remains mostly into the liquid phase. Therefore, addition of fresh water/co-former mixture when the hydrate forms substantially replenishes the shrinking, surfactant- coated water pools, leading to a continuous production of hydrogen hydrate. The continuous addition of water and co-former under the appropriate pressure can be carried out with a liquid feeding means in a simple way by employing an isobaric process and apparatus as described in WO/2007/122647.

B. Bonso, in EP-A-1 652 906, reports a clathrate hydrate formation process which is made continuous by continuously restoring water in a reactor in order to supplement the water amount consumed in hydrate formation. This document, however, teaches that in order to separate ice from hydrate, proper pressure and temperature conditions should be applied in order to dissociate selectively the ice, and keeping the hydrate as a solid. This can be made only by working in a narrow range of thermodynamic [PfT) conditions. The invention method, instead, allows for a complete and positive compartimentalization of non-converted water into reverse- micelle water pools, thus giving a hydrate which is free of ice and/or interstitial water. Moreover, water retained in that way remains liquid also below the ice melting point, due to the ionic strenght into reverse-micelle water pool. This allows for water addition also below the ice point, with no ice formation. For the above mentioned reasons, application of the present process instead of that reported in EP-A-1 652 906 easily overcomes the problem of separation of the formed hydrate from water and/or ice, avoids the formation of ice in a wider temperature range and also below O⁰C, thus avoiding formation of ice plugs or incrustations that can block the system. Finally, hydrate produced in the invention process results in a finely divided (i.e. in a slurry) form and ready for usual pumping devices, avoiding any processes of further hydrate milling or grinding.

Further advantages are that the presence of a bulk organic phase enhances the concentration of hydrate former in the liquid phase and that the slurry obtained by the present invention is free of interstitial or non-converted water, due to an enhanced rate of water conversion in hydrate; the unconverted water is retained into the reverse-micellar phase; in fact, while the formed hydrate precipitates to the bottom, the liquid water is retained in the organic phase trapped into the reverse micelles, thus being amenable to recycling and reuse.

Still a further advantage resides in that, by exploiting the ionic stress of the water pool, non-reacted water can be kept at the liquid state even below the water freezing point, allowing for the exploitation of a wider range of formation conditions, possibly with a stronger subcooling in order to enhance hydrate formation. Moreover, by keeping the water in its liquid state allows for an easier recovery of the formed hydrate that precipitates down the reactor bottom.

The invention will now be disclosed in greater details with reference to the following description, examples and figures, where: Brief description of the drawings Figure 1 is a graph showing the temperature, pressure and gas flow profiles for a typical hydrogen hydrate formation;

Figure 2 summarizes the results of two experiments on formation of THF hydrate vs THF-H₂ hydrate; Figure 3 summarizes the results of an experiment, where THF is not added to the system;

Figure 4 shows the results of an experiment that rules out the possibility of pure THF hydrate formation instead of the binary system H₂-THF hydrate; Figure 5 shows the results of Dynamic Light Scattering measurements carried out on three samples of hydrates formed from a nanoemulsion according to the invention;

Figure 6 shows the dissociation temperature trend by varying the THF amount in the reaction mixture;

Figure 7 shows the tuning effect of the addition of tetrahydrothiophene (as a coformer) to a nanoemulsion system, both in the absence (triangles) and presence (squares) of hydrogen.

Figure 8 shows the P, T and gas flow profiles for the formation of a binary cyclopentane/hydrogen hydrate. Figure 9 shows the use of H₂-THF hydrate prepared according to the invention as a hydrogen-storage material for a PEM fuel cell; and Figure 9A is a scheme of the apparatus shown in fig. 7.

According to the invention, the water is dispersed in the form of minute elements, or droplets, in a dispersing medium that is water insoluble and ensures the presence of the co-former within the water "elements".

The water dispersion is most preferably in the form of a "water-in-oil" nanoemulsion system, i.e. a system comprising water, "oil" (the dispersing medium) and an amphiphile, that is a single optically isotropic and thermodynamically stable liquid solution, and that is characterized by a finely dispersed water phase into a dispersing medium. The water droplets are stabilized on their surfaces by a film of an amphiphilic substance (e.g. a surfactant), which is mainly composed by a hydrocarbon tail and a polar and/or charged head group. One of the most peculiar properties of nanoemulsions is the very low interfacial tension between the oil and water phases, γ_o/w- A major role of the surfactant molecules adsorbing at the water droplet surface is to reduce γ_o/w sufficiently for the system to be thermodynamically stable. Water droplet sizes typically range from a few nanometers to tens of nm, evolving from nearly spheres to bicontinuous systems when the amount of added water is increased. Thus, for the present application the wording nanoemulsions is intended to refer to water "elements", i.e. pools or droplets, having dimensions within the range of 1 nm to several μm, preferably 1nm to 1 micron and most preferably 2 nm to 300 nm.. The internal contents of a nanoemulsion droplet exchange on a millisecond timescale and the system tends to remain dispersed and transparent (kinetically and/or thermodinamically stable) for months. Also, as for macroscopic phases, solutes are subject to a partition between the water (droplet) and dispersing phases according to a partition coefficient.

Information on nanoemulsions is obtainable from Fletcher, P. D. I.; Howe, A. M.; Robinson, B. H. J. Chem. Soc. Faraday Trans. 1 1987, 83, 985; Fletcher, P. D. I.; Clarke, S.; Ye, X. Langmuir 1990, 6, 1301; Biais, J.; Bothorel, P.; Clin, B.; Lalanne, P. J. Colloid Interface Sci. 1981 , 80, 136; Friberg, S.; Mandell, L.; Larson, M. J. Colloid Interface Sci. 1969, 29, 155. Irvin et al. ("Control of Gas Hydrate Formation Using Surfactant Systems", Ann. N. Y. Acad. Sci, 2000 912: 515-526) disclose the use of reverse micelles to encapsulate water, which can then be converted to gas hydrates where the gas is selected from methane and ethylene. No mention or suggestion is made of hydrogen and the specific application of nanoemulsions in binary clathrate hydrate production such as sll, sH and poly-hydrates. Moreover no mention or hint is made of the above discussed dramatic advantages obtainable by this technique of hydrate production as applied to binary hydrogen clathrate production for hydrogen storage, slurry production, rapid production etc. One exemplary embodiment of the invention process is characterized by the steps of:

1) preparing a liquid mixture of water, a co-former compound, a surfactant and a water insoluble organic solvent into a reactor, thus forming a nanoemulsion;

2) bringing the contents of the reactor under the appropriate pressure and temperature conditions for hydrate formation, wherein the pressure is provided by the hydrate-forming gas;

3) forming the binary clathrate hydrate; and 4) recovering and storing the produced hydrate.

Another exemplary embodiment of this process is characterized by the steps of:

1) preparing a liquid mixture of water, a co-former compound, a surfactant and awater insoluble organic solvent into a reactor, thus forming a nanoemulsion; 2) bringing the contents of the reactor under the appropriate pressure and temperature conditions for hydrate formation, wherein the pressure is provided by the hydrate-forming gas;

3) forming the binary clathrate hydrate, where water is continuously added at a suitable rate to restore the water content consumed by hydrate formation; and

4) removing the produced hydrogen hydrate from the reactor; wherein, in step 3) above, the continuous addition of water for restoring the predetermined amount can be effectively carried out by using an isobaric process and apparatus as described in WO/2007/122647. It is apparent to those skilled in the art that various other combinations of steps, which are different from the embodiments outlined above, can be used to the same end without departing from the scope of the present invention. In the following, each component of the hydrate forming nanoemulsion of the present invention will be described in detail. WATER

It is an advantage of the invention that water to be used for the invention method does not have to be de-mineralized water or other kinds of particularly-treated water. For example, sea water or tap water can be used. This is an additional and clear advantage when considering the application of the inventive process to e.g. the storage in sea water hydrate of hydrogen produced as a means of saving surplus energy from, e.g., a wind generator or a gas turbine. Moreover, due to the water retention feature into reverse micelles, the invention allows for a complete conversion of water thus optimizing its consumption and minimizing the amount of interstitial water. DISPERSING PHASES

Organic solvents suitable for use as dispersing phase (or dispersing medium) are acyclic and cyclic hydrocarbons, such as iso-octane, decane, cyclopentane, cyclohexane, decalin, etc., and fluorinated and perfluorinated derivatives thereof; halogenated hydrocarbons, such as chloroform, methylene chloride, and the like; aromatic hydrocarbon compounds, halogenated aromatic hydrocarbon compounds; water-insoluble cyclic ethers; alkylcarbonates, such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate derivatives; γ-butyrolactone, 2-methyltetrahydrofuran, nitromethane, alkyl formates, alkyl acetates, alkyl propionates, alkyl butyrates, phosphoric triesters, ethyl ether, etc.

Another class of dispersing media is that of supercritical fluids known to be applicable to reverse micelle production, such as, e.g., supercritical carbon dioxide, supercritical hydrocarbons such as ethane, ethene, propane, propene and so on. The above mentioned water dispersing media may be used either individually or in a combination of two or more thereof.

An example of a preferred dispersing medium is the class of the alkanes, such as iso-octane, cyclohexane, cyclopentane, etc. In a preferred embodiment, the organic solvent is acting as both the dispersing medium and as the clathrate co-former. This is useful when the hydrogen hydrate process is very fast, and the supply of co-former from the organic solvent dispersing medium would not take place at a sufficient rate for making the reaction continuous. When the co-former is also the organic solvent, there is plenty of it to be supplied into the hydrate-forming water pools or droplets, even if the formation rate is high. The amount of water in the dispersing phase is not critical for the formation reaction, provided the water is sufficiently dispersed in the dispersing phase. However, the minimum water amount for having a reasonable formation rate is ca 0.1 wt%. HYDRATE CO-FORMER A co-former in binary hydrates is a hydrate-former by itself, but its role is generally to stabilize the (larger) hydrate cages, thus allowing hydrogen to remain entrapped into the smaller cages. The presence of a co-former such as, e.g., tetrahydrofuran (THF), allows to obtain hydrogen hydrates at much milder P and T conditions than without THF.

Suitable molecules that can be advantageously used as hydrate co-formers are: cyclic ethers, such as tetrahydrofuran, 1 ,3-dioxolane, 2,5-dihydrofuran, tetrahydropyran, sulfolane, etc.; cyclic hydrocarbons, such as cyclobutane, cyclopentane, cyclohexane, which may be substituted by one or more methyl or ethyl groups; cyclic thioethers, such as tetrahydrothiophene etc. The above mentioned co-formers may be used either individually or in a combination of two or more thereof. The amount of co-former in the dispersing medium is within the range of 0 to 100% by weight of the dispersing phase, 100% being the case where the coformer has also the function of dispersing phase as above discussed. With respect to the water phase, the amount of co-former is within the range of 0.05% (w/w) to the stoichiometric amount. The content of coformer in the final hydrate can be at least reduced to 0.1% (w/w). As previously mentioned, by means of the claimed method, it is possible to produce hydrogen hydrates with up to 4-5% (wt) (ca. 400 normal-volumes) of H₂ in a safe, economic and continuous manner.

Generally, the pressure in the reactor is obtained by means of the pressure of the hydrogen itself; the pressure values are within the range of 5 to 200 bar and preferably of 10 to 120 bar. The reaction temperature is within the range of -30⁰C to +22°C, preferably -20⁰C to 10⁰C and most preferably is such as to avoid water freezing but such as to allow hydrates formation, e.g. within the range of +0.1 to +6°C. The trapped hydrogen is released from said hydrates by melting said hydrates at a temperature within the range of 253-283 K and at a pressure within the range of 0.1-50 MPa. As also shown by the experimental use of example 8 and fig. 7 and 7A, the obtained product is so stable that it can be manually removed from the reactor and stored at room temperature and ambient pressure to gradually release hydrogen for use e.g. to feed a fuel cell. SURFACE STABILIZERS (SURFACTANTS)

Preferred amphiphilic substances for stabilizing the surface of the water droplets are surfactants. These surfactant molecules are characterized by: i) its head group (non ionic, anionic, cationic, zwitterionic), and ii) number and type of lipophilic chains (single chain, twin-chain, gemini, etc.). Anionic surfactants suitable to be used in the invention process are selected from:

(1) single chain: Sodium dodecyl sulfate (SDS), ammonium lauryl sulfate, and other alkyl sulfate salts; Sodium laureth sulfate, also known as sodium lauryl ether sulfate (SLES); Alkyl benzene sulfonates; Soaps, or fatty acid salts; sodium p-alkyloxybenzenesulfonates; etc.

(2) twin-chain: Aerosol OT (Bis(2-ethylhexyl) sulfosuccinate sodium salt) and its derivatives, such as described in various papers by J. Eastoe et al. ("What Is So Special about Aerosol-OT?", Part 1 , Langmuir 2000, 16, 8733-8740; Part 2, Langmuir 2000, 16, 8741-8748; Part 3, Langmuir 2002, 18, 1505-1510; Part

4, Langmuir 2005, 21, 10021-10027; etc. and mixtures thereof. Suitable cationic surfactants are selected from:

(1) single chain: cetyl trimethylammonium bromide (CTAB), and other alkyltrimethylammonium salts; cetyl trialkylammonium bromides (alkyl = ethyl, propyl, butyl), Cetylpyridinium chloride (CPC); polyethoxylated tallow amine (POEA); Benzalkonium chloride (BAC); Benzethonium chloride (BZT); p- alkyloxybenzyl trialkylammonium halides and derivatives thereof; etc.

(2) twin-chain surfactants, such as those described below. (3) "gemini" surfactants, such as those described below.

(4) 1 ,4-piperazine derivatives, such as those described below. Zwitterionic surfactants that are suitable for the invention are selected from those which are known in the art and commercially available, such as dodecyl betaine, dodecyl dimethylamine oxide, cocamidopropyl betaine, coco ampho glycinate; and those which are novel and prepared as illustrated below in the Synthesis section. Suitable nonionic surfactants are selected from alkyl poly(ethylene oxides), alkyl polyglucosides (e.g., octyl glucoside, decyl maltoside, etc.), and Triton X-100 and analogues; fatty alcohols, such as cetyl alcohol, oleyl alcohol. Cocamide MEA, cocamide DEA, cocamide TEA may also be used. An example of further commercial nonionics is the series of Shell's NEODOL.

Perfluorinated surfactants may also be used. Examples thereof may include anionic or cationic perfluorinated surfactants, such as the perfluorinated sulphonic acids having the general formula:

C_nF₂n+iSθ₃H where Cn denotes an aliphatic chain, straight or branched containing from 5 to 20 carbon atoms. Perfluorinated surfactants are commercially available from the 3M Company, Minneapolis, Minn. The perhalogenated surfactant is usually available in commerce in a mixed aqueous/organic solvent system and may be utilized in that form. A preferred emulsion product is Zonyl FSN, a fluorocarbon surfactant composition containing 1.0% active ingredient; E. I. DuPont DeNemours and Company, Wilmington, Del. The amount of surfactant used in the invention method is within the range of 0 to 50 mol%, preferably of 0.01 to 10 mol%, with respect to water. It should be noted, however, that the surfactant remains into the dispersing medium and is not enclosed into the formed hydrate; therefore, it can be recycled for further hydrate formation, and the addition amount thereof does not affect the percentage of hydrogen effectively stored into hydrate. Particularly preferred embodiments of the surfactants used in the present invention are described below. Gemini surfactants:

(I) (H) where n = 4-20, each R, R' and R" can be the same or different from the other R's and is an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in L. Brinchi, R. Germani, L. Goracci, G. Savelli, CA. Bunton, "Decarboxylation and Dephosphohlation in new Gemini Surfactants: Changes in Aggregate Structures", Langmuir 2002; 18, 7821-7825;

(III) where n = 1-8, each R, R' and R" can be the same or different from the other R's and is an alkyl group of 1-30 carbon atoms; these compounds are synthesized as reported in A. Cipiciani, M. C. Fracassini, R. Germani, G. Savelli, CA. Bunton, "Nucleophilic Aromatic Substitution in Solutions of Cationic Bolaform", J. Chem. Soc. Perkin Trans. II, 1987; 547-551. Cationic surfactants such as: R R

CH₂ (CH₂)n CH₃ (_IV) where n = 6-24, each R, R' can be the same or different from the other R's and is an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in L. Brinchi, R. Germani, G. Savelli, N. Spreti, "Decarboxylation of 6-nitrobenzisoxazole- 3-Carboxylate as Kinetic Probe for Piperazinium-based Cationic Micelles", J. Colloid Interface ScL, 2004; 274, 701-705;

where n = 6-24, each R, R' can be the same or different from the other R's and can be an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in A. Cipiciani, R. Germani, G. Savelli, CA. Bunton, M. Mhala, e J. R.

Moffatt, "The Effects of Single- and Twin-Tailed Ionic Surfactants upon Aromatic

Nucleophilic Substitution", J. Chem. Soc. Perkin Trans. II, 1987; 541-546; and in L.

Brinchi, P. Di Profio, R. Germani, L. Goracci, G. Savelli, N. D. Gillitt, CA. Bunton, "Premicellar Accelerated Decarboxylation of 6-Nitrobenzisoxazole-3-carboxylate Ion and its 5-Tetradecyloxy Derivative", Langmuir, 2007; 23, 436-442.

(VI) (VII) (VIII) (IX) where n = 1-24, each R, R', R" can be the same or different from the other R's and can be an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in R. Germani, P.P. Ponti, T. Romeo, G. Savelli, N. Spreti, G. Cerichelli, L. Luchetti, G. Mancini, CA. Bunton, "Decarboxylation of 6-Nitrobenzisoxazole-3- Caώoxylate Ion in Cationic Micelles: Effect of Head Group Size", J. Phys. Org. Chem., 1989; 2, 553-558; L. Brinchi, R. Germani, G. Savelli, L. Marte, "Decarboxylation of β-Nitrobenzisoxazole-S-carboxylate in Aqueous Cationic Micelles. Kinetic Evidence of Microinterface Property Changes", J. Colloid Interface ScL, 2003; 262, 290-293. Chelating surfactants such as:

(X) (XI) (XII) where n = 1-24, each R, R¹ can be the same or different from the other R's and can be an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in L. Brinchi, P. Di Profio, R Germani, G. Savelli, N. Spreti, "Structurally Simple Lipophilic Polyamines as Carriers of Cupric Ions in Bulk Liquid Membrane" Eur. J. Org. Chem., 2002; 930-937; L. Brinchi, R. Germani, M.V. Mancini, G. Savelli, N. Spreti, "A New Carrier for Selective Removal of Heavy Metal Ions from Aqueous Solution by Bulk Liquid Membranes", Eur. J. Org. Chem., 2004; 3865-3871 ; N. Spreti, L. Brinchi, R. Germani, M.V.Mancini, G. Savelli "Quantitative Removal of Mercury(ll) from Water Through Bulk Liquid Membranes by Lipophilic Polyamines", Eur. J. Org. Chem., 2006; 4379-4384.

which was synthesized according to the following synthetic scheme:

Cationic Alkyl alcanolammonium compounds, according to the general formula:

R X^"

R — N—CH₂-(CH₂)m-CH₂-OH CH₂ (CH₂)P

^CH3 (XIV) wherein X = Cl, Br, CH₃SO₃, and R, R' = Methyl, Ethyl, n-Propyl, n-Butyl; n = 10, 12, 14,16, 18; m = 0, 1 , 2, 3, 4; were synthesized according to the following reaction scheme:

R R

\ K₂CO₃ /

CH₃-(CH₂)Ii-CH₂-X + NH *► CH₃-(CH₂)Ii-CH₂ N

/ CH₃CN \

R ³ R

CH₃-(CH₂)n-CH₂

Twin-chain ethanolammonium compounds, according to the general formula:

wherein X = Cl, Br, CH₃SO₃, and R = Methyl, Ethyl, n-Propyl, n-Butyl; n = 10, 12, 14, 16, 18; were synthesized according to the following reaction scheme:

Benzyl-alcanolammonium compounds, according to the general formula:

wherein X = Cl, Br, CH₃SO₃, and R = Methyl, Ethyl, n-Propyl, n-Butyl; n = 10, 12, 14, 16, 18; m = O, 1 , 2, 3, 4; were synthesized according to the following reaction scheme:

CH₃-(CH₂)n-CH₂-X

CH₃-(CH₂Jn-CH₂ — N + OH-CH₂-(CH₂)m-CH₂-X

Amine oxides

(XVII) (XVIII) where n = 6-24, each R, R' can be the same or different from the other R's and can be an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in L. Brinchi, C. Dionigi, P. Di Profio, R. Germani, G. Savelli, CA. Bunton, "Effects of Amine Oxide Surfactants on Reactions of Bromide and Hydoxyde Ions with Methyl Naphtalene-2-Sulfonate", J. Colloid Interface Sci., 1999; 211, 179-184; L. Goracci, R. Germani, G. Savelli, D. Bassani "Hoechst 33258 as a pH Sensitive Probe to Study the Interaction of Amine Oxide Surfactants with DNA", ChemBiochem., 2005; 6, 197-203.

where n= 6-24 and m=2-6. The above surfactant was synthesized as reported in L. Goracci et al., Langmuir, 2007, 23, pp. 10525-10532. Sulfobetaines H₃C- (CH₂)n CH₂-

(XXI) (XXII) where m=2-6 n = 6-24, each R, R' can be the same or different from the other R's and can be an alkyl group of 1-6 carbon atoms; these compounds are synthesized as reported in N. Spreti, A. Bartoletti, P. Di Profio, R. Germani, G. Savelli, "Effects of Ionic and Zwitterionic Surfactants on the Stabilization of Bovine Catalase", Biotechnol. Prog. 1995; 11 , 107-111.

(XXIII) (XXIV) where each of R to R" can be the same or different from the others and can be an alkyl group of 1-30 carbon atoms; these compounds are synthesized as reported in L. Brinchi, R. Germani, G. Savelli, "Ionic Liquids as Reaction Media for Estehfication of Carboxylate Sodium Salts with Alkyl Halides", Tetrahedron Lett., 2003; 44, 2027- 2029; D. Biondini, L. Brinchi, R. Germani, G. Savelli, "An Effective Chemoselective Esteήfication of Hydroxybenzoic Acids in Ionic Liquid Promoted by KF', Lett. Organic Chem., 2006; 3, 207-211.

Compounds of the above formula (XXII) were synthesized according to the following scheme:

Toluene IX.

Other preferred surfactants are

(XXV)

(XXVI) wherein Ri and R₂ can be linear or branched chains with a variable length in the range of 4 to 16 carbon atoms, with terminations of methyl, iso-propyl, ter-butyl, phenyl, or various cyclo-alkyl systems or a combination thereof. The preferred, but not unique, branching sites in the Ri and R₂ chains are at the positions relative to the carbons C1 , C2, and C3 numerating the chain from the oxygen bond site. X represents the counter-ion that can be any metal, inorganic, organic or metal- organic, positive ion. Also, the sulfonate chemical moiety can be replaced by any organic or inorganic group with negative charge. Surfactants as represented by structures 1 and 2 are synthesized as described in, e.g., Nave, S.; Eastoe, J.; Penfold, J. Langmuir 2000, 16, 8733; Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I. Langmuir 2002, 16, 8741 ; and Nave, S.; Eastoe, J.; Heenan, R. K.; Steytler, D.; Grillo, I., Langmuir 2002, 18, 1505. The invention will be further disclosed with reference to the following non-limiting examples. EXAMPLES Preparation Example In order to prepare a nanoemulsion dispersion to be subjected to hydrogen hydrate formation, 200 ml of iso-octane as a disperding medium was taken, to obtain a final solution volume of ca. 200 ml. A proper amount of aerosol OT (AOT; Sigma-Alrdich) was weighted and dissolved in the solvent, so to obtain a concentration of 0.1 M AOT in iso-octane. Then water was added in such an amount to keep the system in the stability region of the nanoemulsion and avoiding phase separation. Finally the co-former (e.g., THF) is added, in an amount depending of its partition equilibrium between water and the organic solvent and also depending on the target amount of co-former in the final hydrate structure.

The mixing of water, dispersing phase and coformer is carried out by using a conventional mixing apparatus such as a magnetic stirrer, a homomixer, a mechanical stirrer, a magnetically-coupled mechanical stirrer etc. As relates to the present example of THF-H₂ hydrate formation by a water-AOT-iso- octane nanoemulsion, it is possible to synthesize THF-H₂ hydrate in a simpler way as compared to the known technology. In particular, due to the existence of the partition equilibrium of THF between water and iso-octane, the kinetics of pure THF hydrate formation, that is in competition with the THF-H2 hydrate, is suppressed in a predictable way through the total amount of THF added to the system. The use of iso-octane as disperding medium enhances the hydrogen mass transfer to the hydrate and causes a much higher solubility of hydrogen in iso-octane as compared to bulk water, thus speeding up the hydrate formation and reducing the induction time. The presence of surfactant that gives water nanodroplets dispersed in iso- octane (reverse micelles), maximizes the surface contact between water and hydrogen gas, and provides for the formation of the first hydrate crystals which are orders of magnitude smaller than those with the existing processes. Moreover, the presence of reversed micelles gives the ability of controlling non-converted water; in fact, hydrate obtained in this way is not swelled with non-converted water because the latter remains trapped in the reverse micelles and is available for further conversion into hydrate. The water retained into reversed micelles is kept at the liquid state due to the ionic stress of the surfactant head groups, allowing to work at higher subcooling rates, which enhance formation, minimizing ice formation. Moreover, the density of the liquid system remains, both before and after the formation, lower than the bulk density of the synthesized hydrate, thus causing a deposition of the hydrogen hydrate in a finely divided crystal form, which is easily separable and recoverable from the liquid system. All these factor play a key role in an efficient THF-H₂ Hydrate synthesis: by the present invention, all these factors are concerted into a single process which is more efficient, safer, faster, and cheaper than the prior art methods. Example 1 Kinetic of THF-H₂-Hydrate Formation:

In Figure 1 the temperature, pressure and gas flow profiles for a typical hydrogen hydrate formation are shown. Curve B is related to temperature values, and shows a first phase of three steps of cooling, to bring the system down to the chosen formation temperature, where, after a certain induction time a peak of temperature (B1) related to the heat of formation is apparent. After all parameters were stabilized at the target set-points, a sub-cooling phase (B2) starts to bring the system down to a temperature below the water freezing point, -12°C in this specific case. After further stabilization of parameters, a warming ramp starts in order to dissociate the synthesized hydrate, for detecting the dissociation temperature indicated in B3. Curve A shows the system pressure profile where a first loading ramp is shown up to the selected experimental pressure, and then the reactor is kept in constant pressure mode by the experimental device, which is as described in WO/2007/122647. After the hydrate formation, the device is switched into pressure- dropping mode, just when the sub-cooling ramp starts. Curve C shows the gas flow profile, with the first constant flow step (C1) corresponding to the pressure loading phase and an absorption peak related to the hydrogen trapping in the hydrate phase (C2).

Example 2: Evidence of THF-H₂ Hydrate formation vs THF Hydrate formation Figure 2 summarizes the results of an experiment in which, in the same system, formation of the sole THF hydrate was carried out and, successively, THF-H2 hydrate formation was induced by applying an appropriate pressure of hydrogen gas. The ordinate axes of the graph report values in arbitrary units which are linearly related to the reported parameters; e.g., in Fig. 2 the axis of Pressure has values related to the % of full-scale of the pressure transducer/meter used, and Gas Flow:Temperature relates to the % of full-scale for gas flow meter and thermometer, respectively. The use of such an arbitrary units was necessary in order to obtain a better comprehensive view of all parameters measured into a single graph. The same applies in the following examples. The curves reported are: A) pressure profile, B) temperature profile C) gas flow profile. Curve B reports a trend of temperatures that follow several loops of cooling and warming between the values of 15°C and -15°C.

In the first step, as indicated in B1, the temperature ramps show the typical breaks due to the heat involved in the formation and then dissociation of the clathrate hydrate of THF only because, as is apparent in curve A, in that stage no gas pressure is applied. Before the start of the second loop, pressure is applied by means of hydrogen gas loading (up to 80 Bar in the reported example) as is seen in the first stages of curves A and C. After reaching the set experimental pressure, the second cooling/warming loop starts and the pressure changes linearity until reaching the formation (or dissociation) of the THF-H₂ hydrate, which is detectable by the second temperature breaks indicated in B2. An evidence of THF-H₂ hydrate is that the temperature value of these second breaks in B2, which are higher than those in B1; moreover, corresponding to the temperature peak of curve C, a small peak of gas flow is apparent, which is due to gas absorption. The third and last cooling/warming loop operates between the same temperatures of the first two loops, but differs therefrom in that the cooling ramp is stopped at the temperature of -3°C, to carry out a constant-temperature stage where the formation of the THF-H₂ hydrate is expected after a certain induction time. As evident in the graph during the stage at -3°C, formation of THF-H₂ hydrate occurs with its typical temperature peak that reaches the same peak temperature of the preceding formation in B2 as indicated by the two lines B3. Corresponding to this latter peak of temperature, a peak of gas flow is also present, which is indicated in C2 similar to the corresponding one in C1. In this formation at constant temperature, it is worth noting the corresponding segment in the pressure curve A, where a net drop of pressure is well defined corresponding to the temperature peak. This drop due to the hydrogen absorbed during the hydrate formation is a solid proof of the THF-H₂ synthesized by means of the present invention.

Example 3: Comparison with Example 2 shows lack of evidence of hydrate formation without THF.

Figure 3 summarizes the results of an experiment, compared to Example 2, where THF is not added to the system. The axes of the graphics report values in arbitrary units as defined in Example 2. The curves reported are: A) pressure curve, B) temperature curve C) gas flow curve. In this experiment the parameters follow the same profiles and values of those in Example 2. From the curves reported in Figure 3, it is clear that no gas uptake is detectable in the absence of THF, which is a proof of lack of hydrate formation. The horizontal line that crosses all the three temperature loops exactly matches all the dissociation temperature breaks: B1 , B2 and B3, which is a clear evidence that presence or absence of hydrogen pressure are not affecting the behavior of the system. Moreover, the horizontal line corresponds exactly to 0⁰C, the freezing point of water; this was a further proof of the formation of ice instead of hydrate.

The slight lowering of the dissociation temperature in the breaks B2 and B3 in comparison with the exact match of the B1 break is due to the effect of mechanical pressure of hydrogen that induces a cryoscopic lowering of the water freezing point. Evidence of the formation of ice is obtainable following the pressure curve A, where corresponding to the temperature peak B2, due to the evolution of the heat of formation, is found a pressure peak A1 due to the expansion of formed ice. If this section is compared to the same A1-B1 section of Example 2 (Figure 2), in the latter an exactly opposite behavior is well defined, which is due to an effective gas absorption. In the same way, it is possible to explain and compare the pressure trend in A2 both in Examples 2 and 3: in Example 2 a drop of pressure, due to gas uptake, is apparent in A2 corresponding to the B3 formation, whereas in Example 3 a pressure increase is detectable, corresponding to the B3 formation and due to ice volume expansion.

Finally, the C curve (gas flow profile) shows that no absorption peaks are detectable in correspondence to the ice formation under pressure; on the other hand, in C1 it is possible to observe a break of the slight flow consequent to the cooling of the system, which is due to a back flow caused by an expansion related to ice formation.

Example 4: Formation of H₂-THF hydrate above the temperature of pure THF hydrate formation. Figure 4 reports the results of an experiment that rule out the possibility of pure THF hydrate formation instead of the binary system H₂-THF hydrate. The axes of the graph report values in arbitrary units to give a clearer view of the profiles, and the curves reported are: A) pressure curve, B) temperature curve, C) gas flow curve. The experimental system, which was prepared according to the present invention, as outlined, e.g., in the Preparation Example above, was placed in the reactor and pressurized up to 160 Bar. Then the system was brought to a temperature of +5°C, as is seen in the B curve. This temperature was chosen because it is sufficiently above the temperature of pure THF hydrate formation, as to rule out the possible formation of pure THF hydrate, for it is well know that pressure changes do not affect the temperature of formation. Therefore, under these conditions only the formation of the binary system H₂-THF hydrate is possible, which indeed occurs as indicated in B1 by the temperature peak of formation. Corresponding to the B1 formation, a pressure drop indicated in A1 due to the gas absorbed is apparent, as well as a peak of gas flow indicated in C1. Moreover, along the final cooling ramp that brings the system down to a temperature of -14°C, no further hydrate or ice formation is detectable, this suggesting that all the water and THF present in the reaction mixture were consumed in the formation shown at B1 and ascribable to the H₂-THF hydrate system. Example 5: Determination the THF partition rate in water-oil systems.

In order to estimate the partition equilibrium of THF or other co-formers between water droplets and organic dispersing media, the following experiment was carried out: In a separatory funnel was placed 5Og of water, 5Og of iso-octane and 5Og of THF. After a proper mixing, the water phase was separated from the organic phase and weighted; similarly, the organic phase was weighted after the separation. In the water phase, an additional weight of ca. 13g was detected, while ca. 37g was the weight increase of the organic phase. As is clearly shown, the weight increase of both phases is due to the partition of THF between water and iso-octane, in which THF is miscible in all proportions.

With this simple experiment we were able to estimate that ca. 26% of THF is dissolved into water droplets phase, the remaining 74% being dissolved in the iso- octane phase. This experiment indicates that it is possible to tune the exact amount of THF, or other types of co-formers, that are designed to take part in the binary hydrate formation.

Example 6: Demonstration of water retention after hydrate formation. In Figure 5 are shown the results of Dynamic Light Scattering measurements carried out on three samples. The experiment concerns hydrate formation in water-oil emulsions where the size of the water droplets is at the nanometer level; in other words, we have carried out the experiment on a reversed-micelle system. The samples were prepared according to the present invention with the proper amounts of THF, AOT, water and iso-octane. The three samples differ in the amount of water and THF added; specifically, water was added in order to obtain a value of W₀ (molar ratio of water to surfactant) of 25, 50, and 80 and, for each sample, a corresponding amount of THF was added, such as to keep a stechiometric molar ratio of THF hydrate (THF/H₂O 1/17). After preparation, the samples were subjected to Dynamic Light Scattering analysis to get information about the size of the nano- aggregates. Light scattering measurements were made by using ca. 1 mL of sample in 6 mm diameter Pyrex glass culture tubes, protected from dust by Parafilm caps. The cylindrical glass sample tube was fitted to the center of a toluene-filled fluorimeter cuvette to provide refractive index matching against stray light reflections. The cuvette was housed in a black-anodized aluminum cell block, whose temperature was regulated by a Peltier thermoelectric element. The light source was a Coherent Innova 70-3 argon-ion laser operating at 4880 A. Light scattered at 90° was collected from approximately one coherence area ad imaged onto the slit of a photomultiplier tube (Products for Research, Inc.). A 64-channel Nicomp Model 370 computing autocorrelator (PSS Nicomp, Santa Barbara, CA) was used to calculate and display the diffusion coefficient, D, and associated derived parameters from cumulants analysis fits to the intensity autocorrelation function. All measurements showed reasonable goodness-of-fit values. The hydrodynamic radii, Rh, can be estimated by applying the Stokes-Einstein relationship:

D = kT/6πηR_h where η is the viscosity of the solution, which can be approximated to that of the dispersion phase (i.e., iso-octane). The recorded data, as reported in Figure 5, were 13, 24 and 40 nm, as diameter of the micelles, respectively for the samples at W₀ of 25, 50, 80. Then the samples were subjected to the THF hydrate formation by simple cooling at a temperature lower than the THF hydrate equilibrium temperature. After hydrate formation, an aliquot of the remaining liquid phase was taken for each of the samples, which were again measured by Dynamic Light Scattering. The recorded data for all the three post-formation samples show a constant size of the aggregates, after THF hydrate formation, around a value of ca. 4.7 nm. As for these systems a well known linear relationship between W₀ and micelle size (D = diameter) exists, we can write it down as:

D = A x W₀.

Once this behavior is known, it is possible to determine (a) the value of parameter A, which is the slope of the D-W₀ line, in this case being of ca. 0.5, and (b) the W₀ value for the residual aggregates left after THF hydrate formation, which, as show in Figure 5, is of ca. 9 (intersection of the two linear fitting curves). In this way, by means of a simple Light Scattering investigation, it is possible to demonstrate that the unconverted water remain trapped into the reversed micelles while the formed hydrate, which is free of unconverted water, is separated as a solid phase.

Example 7: Hydrate dissociation temperature as a function of THF amount. Figure 6 shows the dissociation temperature trend by varying the THF amount in the reaction mixture. Data are obtained according to a loop of formation as described in Example 2. Profiles B1 relate to dissociation temperatures of pure THF hydrate as indicated by tag B1 in Figure 2; profiles B2 relate to dissociation temperatures of H₂- THF hydrate as indicated by tag B2 in Figure 2. The data reported in Figure 6 differ for different amounts of THF added to the reaction mixture. After selecting a certain amount of water, THF was then added in order to cover a range from below to above the stoichiometric ratio for pure THF hydrate (THF/H₂O 1/17). All experiments were carried out as described in the previous examples and the pressure for synthesizing H₂-THF hydrate was set at 80 bar. The abscissa in Figure 6 reports the percent of stoichiometric ratio after considering: (i) the amount of water, and (ii) the partition equilibrium discussed in Example 5 (e.g., a value of 100% on the abscissa corresponds to a ratio of 1/17). As clearly seen in the chart, both profiles B1 and B2 follow the same trend, this indicating that a variation in the amount of added THF affects both pure THF hydrate and H₂-THF hydrate in the same way. Therefore, when the THF amount is lower than stoichiometric value, a corresponding lowering of the dissociation temperature indicates the formation of non-stoichiometric THF or H₂-THF hydrates, obviously in terms of the THF/H₂O ratio. Whereas, when the THF amount is equal to, or higher than, the stoichiometric ratio, both profiles tend towards the theoretical value at ca. 4°C for profile B1 of the THF hydrate, and ca. 7°C for H₂-THF hydrate synthesized at 80 Bar. It should be clarified that the values for THF/H₂0 ratio reported on the abscissa are only indicative, in that derived by a general evaluation of THF partition in a water-oil system as described in Example 5. THF partition coefficient could be affected by temperature, pressure, and presence of emulsifying agents, therefore easy, case-specific investigations should be carried out for each particular system adopted.

Example 8: Binary tetrahydrothiophene/hydrogen hydrate Figure 7 relates to the formation of a binary hydrate of hydrogen and tetrahydrothiophene (THS) instead of THF as a co-former. As reported in Example 7 and Figure 6 for THF, also THS is capable to form binary hydrates and thus trap hydrogen. Profile B1 reports equilibrium temperatures when no hydrogen pressure is applied, thus where formation of pure THS hydrate is supposed. Note how after an increase around 30-40 ml of THS addition the temperature remain constant reaching a plateau at ca. -0.5⁰C indicating that a stable stoichiometric ratio of THS hydrate is probably obtained. Profile B2 is the equilibrium temperature when H₂ pressure of 100 bars is applied. In this case the temperature values are related to the system H₂-THS, and it can be seen how T increases by increasing the amount of THS added to the system, showing a tendency to reach a plateau at ca. 4.6°C. The temperature values of B2 profile, higher than the ice melting point and B1 profile, indicate that neither ice, that should shows a melting point depression under hydrogen pressure, nor pure THS hydrate are formed, because in this latter case, B1 and B2 profiles should be superimposed, or B2 shows slight lower values comparing with B1 due temperature depression caused by hydrogen pressure application, as reported in Example 3, Figure 3. Equilibrium temperature values reported in B1 and B2 profiles were collected as reported in Example 2, Figure 2 for THF.

Example 9: Binary cyclopentane/hydrogen hydrate

Figure 8 relates to the formation of a binary hydrate of hydrogen and cyclopentane instead of THF as a co-former. As already reported for THF, B1 and B2 of the temperature profile B, are respectively dissociation temperatures under room pressure and 100 bar hydrogen pressure. B3 indicate instead formation under constant pressure. Note how also in this case B2 and B3 values are of ca. 7.5°C / 8.0⁰C, and greater than B1 , which is ca. 4.3°C. At the dissociations of B2 and B3, pressure profile A shows an overpressure due to the release of trapped hydrogen as indicated respectively in A1 and A2. At the formation temperature peak B3, profile C of the hydrogen flow, shows the typical absorption peak due to hydrogen trapping and binary hydrate formation, as indicated by C1. In this case it is important to note how a co-former such as cyclopentane, completely immiscible with water, behaves in a very similar way when compared with a totally water-miscible co-former, e.g., THF.

Example 10: Application of H₂-THF hydrate to a PEM Fuel Cell H₂-THF hydrate prepared according to the present invention, as detailed in the foregoing description and Examples, was used as a hydrogen-storage material for use with a PEM fuel cell. Specifically, a sample of H₂-THF hydrate (ca. 25 g) was poured into a plastic bottle (a commonly available yoghurt bottle; Figure 9) made of PET, and the bottle was capped with a screw stopper having at its center a hole provided with a pipe fitting. The fitting was connected to a polyethylene tube, the other end of which ended into an aluminum inlet to a single-stack PEM fuel cell formed as a pair of 6 cm x 6 cm aluminum plates sandwiching a Nafion membrane and two electrodes (Figure 9). Oxygen (in the form of ambient-pressure air) was supplied to the fuel cell through another inlet to the cell. Positive and negative terminals of the fuel cell were connected to an electric motor. When the H₂-THF hydrate started to dissociate (i.e., melt) by simple warming at room temperature, hydrogen gas was steadily liberated from the hydrate mass, thus flowing through the plastic tubing to the fuel cell. Thus fueled with hydrate-derived hydrogen gas flow, the single-stack fuel cell developed a potential difference of ca. 1 V, and started to generate an electric current which drove the electric motor for ca. 1 hour. Figure 9A is a schematic view of the apparatus of Fig. 9, wherein the bottle 1 containing hydrogen clathrates hydrates 7 is connected to fuel cell 3 with a duct 2 through which hydrogen released by the melting clathrates flows. A duct 4 provides an oxygen (air) source for the fuel cell 7, that is connected with electric connectors 5 to electric motor 6. In Fig. 9 hydrogen leaving the bottle 1 is bubbled in the water contained in a vial to show that hydrogen is released.

Claims

1. A method for the production of binary clathrate hydrates of hydrogen and a co- former, characterised in comprising the steps of forming a dispersion of water droplets in a dispersing phase, in the presence of an amphiphilic compound for stabilizing the surfaces of said dispersed water and forming clathrate hydrate crystals from the water droplets thus obtained in the presence of said co-former.

2. A method according to claim 1, wherein said dispersed water droplets have dimensions within the range of 1 nm to 1 micron and preferably of 2 nm to 300 nm.

3. A method according to claim 2, wherein said amphiphilic substance is a surfactant suitable to form water-in-oil emulsions, comprising the steps of: i) preparing a nanoemulsion of water, a co-former compound, a surfactant into a water insoluble dispersing medium in a reactor; ii) bringing the contents of the reactor to the pressure and temperature conditions for hydrate formation, wherein the pressure is provided by hydrogen; iii) forming the binary clathrate hydrate; and iv) recovering the produced hydrate.

4. A method according to claim 3, wherein water is added to said reactor to restore the water content consumed by hydrate formation and said produced hydrate is removed from said reactor.

5. A method according to any previous claim, wherein said coformer and said dispersing phase are the same.

6. A method according to any previous claim, wherein the amount of coformer in the dispersing phase is greater than its amount in the dispersed water droplets.

7. A method according to any previous claim, wherein said hydrates are formed at a temperature within the range of 243-295 K and at a pressure within the range of 1-

100 MPa.

8. A method according to any previous claim, wherein said trapped hydrogen is released from said hydrates by melting said hydrates at a temperature within the range of 253-283 K and at a pressure within the range of 0.1-50 MPa and preferably at room temperature and ambient pressure.

9. A method according to any previous claims, wherein hydrogen gas is replaced by another binary hydrate forming gas.

10. A binary clathrate hydrate of hydrogen and a co-former as obtainable by means of a process according to any of claims 1 to 9.

11. A binary clathrate hydrates of hydrogen and a co-former according to claim 10, wherein the amount of coformer is less than its stoichiometric value.

12. A binary clathrate hydrate of hydrogen and a co-former as obtainable by means of a process according to any of claims 1 to 9, wherein the content of hydrogen is higher than 1 wt%.

13. A method according to any previous claim 1 to 9, wherein the surfactant used is selected among one or more of the following:

where X^" is chloride, bromide, fluoride, iodide, methanesulfonate, p- toluenesulfonate, perchlorate, acetate, nitrate, sulfate, an alkyl sulfate (where alkyl = linear or branched CM2 alkyl), hydroxy, formate, benzoate, phtalate, salicylate, propanoate, butyrate, n = 4-20, each R, R' and R" can be independently an alkyl group of 1-6 carbon atoms;

where X^" is as described hereinabove, n = 1-8, each R, R' and R" can be independently an alkyl group of 1-30 carbon atoms;

where X^" is as described hereinabove, n = 6-24, each R, R¹ can be independently an alkyl group of 1-6 carbon atoms;

where X^" is as described hereinabove, n = 6-24, each R, R' can be independently an alkyl group of 1-6 carbon atoms;

(VI) (VII) (vπi) (IX) where X^" is as described hereinabove, n = 1-24, each R, R¹ and R" can be independently an alkyl group of 1-6 carbon atoms;

(X) (XI) (XII) where n 1-24, each R, R' can be independently an alkyl group of 1-6 carbon atoms;

where n = 6-24; CH₂ (CH₂)n cm (XIX) where n = 6-24;

where n 6-24, each R, R' can be independently an alkyl group of 1-6 carbon atoms;

where n 6-24, each R, R' can be independently an alkyl group of 1-6 carbon atoms;

H₃C-(CH₂)Ii CH₂-

(XXI) (XXII) where m=2-6; n 6-24, each R, R¹ can be independently an alkyl group of 1-6 carbon atoms;

(XXIII) (XXIV) where each of R to R2 can be the same or different from the others and can be an alkyl group of 1-30 carbon atoms;

wherein Ri and R₂ can be linear or branched chains with a variable length in the range of 4 to 16 carbon atoms, with terminations of methyl, iso-propyl, tert-butyl, phenyl, or various cyclo-alkyl systems or a combination thereof, X represents the counter-ion that can be any metal, inorganic, organic or metal-organic, positive ion, and the sulfonate chemical moiety can be replaced by any organic or inorganic group with negative charge.

14. A surfactant compound selected from one of the following formulas:

where n = 6-24, and m = 2-6.