EP2160352A2 - Procédé de production d'hydrates de clathrates binaires d'hydrogènes et produits associés - Google Patents

Procédé de production d'hydrates de clathrates binaires d'hydrogènes et produits associés

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Publication number
EP2160352A2
EP2160352A2 EP08762723A EP08762723A EP2160352A2 EP 2160352 A2 EP2160352 A2 EP 2160352A2 EP 08762723 A EP08762723 A EP 08762723A EP 08762723 A EP08762723 A EP 08762723A EP 2160352 A2 EP2160352 A2 EP 2160352A2
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European Patent Office
Prior art keywords
hydrate
hydrogen
water
thf
carbon atoms
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EP08762723A
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German (de)
English (en)
Inventor
Simone Arca
Pietro Di Profio
Raimondo Germani
Gianfranco Savelli
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Priority to EP08762723A priority Critical patent/EP2160352A2/fr
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/02—Preparation of oxygen
    • C01B13/0229—Purification or separation processes
    • C01B13/0248—Physical processing only
    • C01B13/0251—Physical processing only by making use of membranes
    • C01B13/0255—Physical processing only by making use of membranes characterised by the type of membrane
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
    • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
    • C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
    • C01B3/0015—Organic compounds; Solutions thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/32—Hydrogen storage

Definitions

  • 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.
  • a hydrate former e.g., hydrogen
  • a co-former e.g., tetrahydrofuran
  • 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.
  • 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 metal, intermetallic compounds, carbon nanotubes, etc.
  • 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 H 2 O molecules, and guest molecules trapped inside the water cages.
  • 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.
  • Sun et al. refers 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.
  • WO2006/131738 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.
  • the present invention 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.
  • the dispersion is a nanodispersion
  • the water droplets having dimensions within the range of 2 to 300 nm
  • the hydrate crystals are nanocrystals.
  • the dispersing phase is selected from one or more of organic solvents, hydrocarbons, fluorocarbons, ionic liquids, supercritical fluids, alkylcarbonates, etc.
  • the nanodispersion is a dispersion of surfactant reverse micelles in a dispersing medium.
  • hydrogen is replaced by another gas, e.g. fluorine, chlorine dioxide, difficult to transport and suitable to form binary clathrates with a coformer.
  • another gas e.g. fluorine, chlorine dioxide
  • 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.
  • 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.
  • the present method is inventive over the prior art in that it provides the following unforeseeable advantages.
  • 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.
  • the dispersing phase may be entirely composed by the organic, water insoluble, co- former itself.
  • 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.
  • 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.
  • 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.
  • 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-H 2 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 H 2 -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 H 2 -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.
  • 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.
  • an amphiphilic substance e.g. a surfactant
  • nanoemulsions One of the most peculiar properties of nanoemulsions is the very low interfacial tension between the oil and water phases, ⁇ o /w- A major role of the surfactant molecules adsorbing at the water droplet surface is to reduce ⁇ 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.
  • the wording nanoemulsions is intended to refer to water "elements", i.e.
  • water to be used for the invention method does not have to be de-mineralized water or other kinds of particularly-treated water.
  • 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.
  • the invention allows for a complete conversion of water thus optimizing its consumption and minimizing the amount of interstitial water.
  • Organic solvents suitable for use as dispersing phase 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; ⁇ -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.
  • supercritical fluids known to be applicable to reverse micelle production
  • 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.
  • a preferred dispersing medium is the class of the alkanes, such as iso-octane, cyclohexane, cyclopentane, etc.
  • 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.
  • 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.
  • a co-former such as, e.g., tetrahydrofuran (THF)
  • THF tetrahydrofuran
  • 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.
  • 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).
  • 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 -30 0 C to +22°C, preferably -20 0 C to 10 0 C 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.
  • 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.
  • 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:
  • 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.
  • Suitable cationic surfactants are selected from:
  • cetyl trimethylammonium bromide CTAB
  • cetylpyridinium chloride CPC
  • POEA polyethoxylated tallow amine
  • BAC Benzalkonium chloride
  • BZT Benzethonium chloride
  • twin-chain surfactants such as those described below.
  • "gemini” surfactants 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:
  • Cn F 2 n+iS ⁇ 3 H 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.
  • 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;
  • 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 R
  • 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;
  • 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.
  • 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- Ca ⁇ oxylate Ion in Cationic Micelles: Effect of Head Group Size", J. Phys. Org. Chem., 1989; 2, 553-558; L. Brinchi, R. Germani, G.
  • each R, R 1 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.
  • 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.
  • 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.
  • 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 Este ⁇ fication of Hydroxybenzoic Acids in Ionic Liquid Promoted by KF', Lett. Organic Chem., 2006; 3, 207-211.
  • Ri and R 2 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 R 2 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.
  • 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.
  • 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.
  • a conventional mixing apparatus such as a magnetic stirrer, a homomixer, a mechanical stirrer, a magnetically-coupled mechanical stirrer etc.
  • reverse micelles 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.
  • 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.
  • B1 peak of temperature
  • B2 sub-cooling phase
  • 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-H 2 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 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.
  • 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.
  • the second cooling/warming loop starts and the pressure changes linearity until reaching the formation (or dissociation) of the THF-H 2 hydrate, which is detectable by the second temperature breaks indicated in B2.
  • THF-H 2 hydrate An evidence of THF-H 2 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-H 2 hydrate is expected after a certain induction time. As evident in the graph during the stage at -3°C, formation of THF-H 2 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.
  • 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.
  • 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.
  • the horizontal line corresponds exactly to 0 0 C, the freezing point of water; this was a further proof of the formation of ice instead of hydrate.
  • Example 2 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.
  • Example 4 Formation of H 2 -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 H 2 -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 H 2 -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.
  • Example 5 Determination the THF partition rate in water-oil systems.
  • Example 6 Demonstration of water retention after hydrate formation.
  • 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 W 0 (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/H 2 O 1/17).
  • W 0 molar ratio of water to surfactant
  • THF stechiometric molar ratio of THF hydrate
  • 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.).
  • 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 H 2 - 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/H 2 O 1/17).
  • THF/H 2 0 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.
  • THS tetrahydrothiophene
  • 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. -0.5 0 C indicating that a stable stoichiometric ratio of THS hydrate is probably obtained.
  • Profile B2 is the equilibrium temperature when H 2 pressure of 100 bars is applied.
  • the temperature values are related to the system H 2 -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.
  • Figure 8 relates to the formation of a binary hydrate of hydrogen and cyclopentane instead of THF as a co-former.
  • 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.
  • B2 and B3 values are of ca. 7.5°C / 8.0 0 C, and greater than B1 , which is ca. 4.3°C.
  • pressure profile A shows an overpressure due to the release of trapped hydrogen as indicated respectively in A1 and A2.
  • profile C of the hydrogen flow shows the typical absorption peak due to hydrogen trapping and binary hydrate formation, as indicated by C1.
  • Example 10 Application of H 2 -THF hydrate to a PEM Fuel Cell H 2 -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 H 2 -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.
  • a plastic bottle a commonly available yoghurt bottle; Figure 9
  • 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
  • Positive and negative terminals of the fuel cell were connected to an electric motor.
  • H 2 -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.
  • the single-stack fuel cell developed a potential difference of ca.
  • FIG. 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.
  • hydrogen leaving the bottle 1 is bubbled in the water contained in a vial to show that hydrogen is released.

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Abstract

L'invention concerne un procédé pour la production efficace de clathrates hydrates binaires d'hydrogène et d'un co-formateur, ledit procédé consistant à former des nanoémulsions d'eau dans l'huile, telles que, par exemple, des micelles inverses de tensioactif dans un solvant organique, et à former des nanocristaux de clathrate hydrate à partir des gouttelettes d'eau ainsi obtenues.
EP08762723A 2007-05-24 2008-05-26 Procédé de production d'hydrates de clathrates binaires d'hydrogènes et produits associés Withdrawn EP2160352A2 (fr)

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PCT/IB2008/001324 WO2008142560A2 (fr) 2007-05-24 2008-05-26 Procédé pour la production de clathrates hydrates d'hydrogène binaires
EP08762723A EP2160352A2 (fr) 2007-05-24 2008-05-26 Procédé de production d'hydrates de clathrates binaires d'hydrogènes et produits associés

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WO2013032756A1 (fr) * 2011-08-26 2013-03-07 The Board Of Trustees Of The University Of Alabama Procédés et appareils de production d'hydrates de clathrate
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