GB2454931A - Use of clathrates in gas storage - Google Patents

Abstract

A gas, for example hydrogen, methane or carbon dioxide, is enclathrated, and/or dissociated from a clathrate, for example clathrate hydrate, in the presence of an emulsion-templated porous support, for example polyHiPE. The emulsion-templated porous support enhances the practical applicability of gas storage by clathrates.

Description

Clathrates for gas storage This invention relates to the use of clathrates as gas storage materials, for example in the storage of hydrogen, methane, carbon dioxide or other gases.

Hydrogen is a useful material, and technology based on the use of hydrogen, tbr example in fuel cells, is likely to he of greater value in the future. Cost-effective hydrogen-based applications require effective means of storing hydrogen. At room temperature and pressure hydrogen is a gas which is difficult to handle because of its large volume and reactivity.

Liquefaction requires expensive and costly apparatus and liquid hydrogen can he difficult and dangerous to handle. Known methods for producing hydrogen from chemical compounds in si/il are generally unsatisfactory for many industrial uses.

Clathrate hydrates have been studied as media for the storage of hydrogen (see for example Struzhkin. V. V.; Militzer, B.; Mao, W. L.: Mao, U. k.; Hemley, R. J. (7iem. Rev. 2007, 107 No. 10, 4133). Clathrate hydrates comprise "host" cages of H20 assemblies, in which are bound "guest" materials. Clathrate hydrates have the potential to provide a safe and environmentally friendly solution to the need for hydrogen storage. However, the incorporation of hydrogen into clathratc hydrates can take an extremely long time (days or weeks) and furthermore the timescale of "freezing" the H2-l-120 clathrate structures can be unpredictable. Enhancement of hydrogen enelathration kinetics together with good rechargeability is still a challenge for developing clathrate hydrates as a feasible hydrogen sto rage material.

In principle a wide range of gases --not just hydrogen -may be stored within clathrates and the clathrates need not necessarily he clathrate hydrates hut can comprise any suitable host not just H20. Numerous other hosts are possible. such as for example those listed in US patent application publication US 2004/0230084 (Yagi).

There is no particular limitation of the type of gas that may he stored as guest in a clathrate beyond the requirement that the host and guest must he sufficiently compatible to form a stable clathrate structure, optionally in the presence of stabilizing agents. Known clathrates include those comprising (as guest) H2. 02, N2, CH4, C0,, air, H9S, Ar, Kr, Xe, He and Ne, amongst others (see for example international patent application publication no. WO 2006/13 1738 (Hcriot-Watt University) and Lokshin, K. A. Ct a!., Physical Rcviet Letters 2004. /93. No. 12, 125503). The stored gas may also comprise a mixture -for example, natural gas.

Whilst improvements in the storage of gases in general would he desirable. there are particular needs to enhance the technology ft)r storing some particular gases from a technological and environmental viewpoint. The importance of hydrogen storage and the possibility of cnclathration of hydrogen have been mentioned above. Gas remediation solutions are required to trap undesirable gases. Climate change and in particular global warming has prompted a search fir better means of sequestration of certain gases, for example C02. Methane and natural gas also act as valuable fuels and therefore their storage is also important. These gases can all be stored in clathrates. In some eases the host may be a useful commodity as well as the guest; for example a elathrate of H2 within CH4 or octane can act as a dual fuel.

However, to date the feasibility of clathrates as gas storage means has been severely limited by the poor speed, reliability and cyclablity of enclathration and dissociation.

From a first aspect the present invention provides a method comprising the enclathration of a gas, in the presence ot an emulsion-templated porous support.

Consistent with conventional meanings in the art, the term cluthratc" also includes semi-clathrate". As known in the art, a scmi-clathratc is an association comprising a host and a guest wherein the guest forms part of the clathrate framework: tir example the guest. or one of the guests if there is more than one. may both he physically bonded to the host cage structure. and occupy some of the cavities.

Emulsion-templated porous supports are known in the art (see for example Cameron, N. R. Polvnwr 2005. 46. 1439) and are formed by the curing or solidification of a continuous (non-droplet) phase around a template of internal (droplet) phase, followed by the removal of the internal (droplet) phase.

As exemplified below, the use of an emulsion-templated porous support increases the speed S of gas clathrate tbrnrntion. Thus the present invention allows gas to be incorporated into clathratc cages more quickly than has previously been possible. This results in easier and lc.pcnsive gas charging, whether in a specialized gas charging plant, or in situ.

The choice of the type of Support is significant because other supports, such as powdered I 0 activated carbon, have been thund to have no significant effect on the enclathration kinetics, even when used in large amounts.

The present invention also allows the gas to be released from the clathratc structures more quickly. This allows ease of use at the point where gas is required, for example in fuel cells.

1 5 and this advantage is particularly relevant where the storage is within a self-contained, remote or mobile unit, such as a vehicle.

Transitions between liquid and solid phases can be unpredictable; for example a laboratory chemist may find crystallization of a chemical compound to be difficult in practice, and may try various techniques to initiate the seeding of crystals. Similar unpredictability has hitherto been seen in the fbrmation of clathrate structures and is a significant barrier to industrial applicability. One of the commercial advantages of the present invention is that it allows enclathration and dissociation to occur predictably and reliably.

The present invention allows multiple storage/release cycles. Cyclability of gas enclathration means that gas storage units can he Used repeatedly, thereby reducing the down-time, costs and practical difficulties associated with maintenance, conditioning or replacement. Data presented below show the reproducibility of gas enclathration when the same emulsion-templated porous support is Used on consecutive runs.

The present invention also allows gas uptake to occur rapidly and reproducibly in the absence of any agitation or mechanical mixing. This is an advantage since the incorporation of mixing devices adds complexity to the apparatus as well as introducing additional system weight and energy requirements.

Without wishing to be hound by theory, it is believed that the emulsion-templated porous support results in advantages because o its particular porous and interconnected nature. A thin film is believed to form on the surface of the support thereby greatly increasing the interthcial area for gas mass diffusion.

Ernulsion-templated porous supports are relatively inexpensive and can be produced as moulded monoliths, for example thr use as fuel tanks.

Preferably the clathrate is a clathrate hydrate. i.e. the host comprises H20. Thus, gas molecules, for example H2 molecules are stored within H20 cages. Clathrate hydrates are particularly advantageous because the host is merely water, is extremely easy and cost-effective to obtain, store, and dispose of and is particularly environmentally friendly.

Regardless of the type of host, the present invention is of particular utility in the storage of hydrogen, hydrocarbon gas (e.g. methane) or carbon dioxide. It is particularly preferred to store these gases in clathrate hydrates, i.e. in H20 hosts.

Hydrocarbon gas includes up to C4 hydrocarbon compounds which may be saturated or unsaturated, for example methane, ethanc and propane.

The present invention is also applicable to different gases, such as for example 02. N2, air, HS, Ar, Kr. Xe, He and Ne. or mixtures of such gases.

It is known that "stabilizer" (also known in the art as "promoter") materials may be used to aid the formation of clathrates. and such materials arc thereibre optionally present (along with the gas to he stored) in the clathratc structures according to the present invention.

Examples of stabilizers include tetrahydrofuran (TH F) and tetra-n-butylamrnonium bromide (TBAB) amongst others. These examples arc particularly useful when the clathrate is a clathrate hydrate. for example when the gas to he stored is hydrogen.

Other examples of stabilizers include cyclic ethers (for example ethyleneoxide (EO), 1,3-dioxolane, I,3-and I,4-dioxane, and trimethyleneoxide), per alkyl-onium salts. alkylamines (for example tert-butylamine), diamines, diols, crown ethers and their complexes.

methylcyclohexane and methyl-tert-butyl ether (MTBE). These stabilizers may for example he used when the clathrate is a clathrate hydrate.

Stabilizers are believed to enhance the stability of certain types of clathrate structure. For example H2 and THF can both be contained as guests within the so-called sit structural framework of clathrate hydrate such that THF sits within some larger cavities thereof The use of a suitable stabilizer enhances the gas storage capacity of certain clathrates and allows lower gas enclathration pressures.

Stabilizers act as guests in the sense that they may be contained within the host (in a clathrate) or may form a cage together with the host (in a semi-clathrate).

Semi-clathratcs share many of the physical and structural properties of true clathrates. The principal difference between the two groups is that, in true clathrates. guest molecules are not physically bonded to the host lattice: rather, they are held within and lend stability to cavities through van der Waals interactions. In contrast, in scmi-clathrates, guest molecules both physically bond with the water structure and OCCUPY cavities. For example, in the quaternary (or peralkyl) ammonium salt semi-clathrate hydrates, the quatemary ammonium salt (QAS) hydrophobic cation takes a cage filling role, while the negatively charged anion is hydrogen bonded with the water lattice-work.

The emulsion of the emulsion-tempJatcd porous support may be a high internal phase emulsion (HIPE) as detined in Cameron. N. R. Polymer 2005. 46. 1439. As stated in this document and generally accepted in the art. a HIPE has an internal (droplet) phase volume ratio of 0.74 or greater.

The support may he a polymer. For example the support may be a polyHiPE. which is an eniulsion-templated polymer wherein the template is a high internal phase emulsion (HIPE).

The support preferably has abundant interconnected macropores and low bulk density, and optionally has micropores or mesopores. Thus the support can enhance gas storage without being of prohibitive weight for practical use. The support allows gas uptake kinetics to be accelerated by factors of more than 100 with good recyclability.

The emulsion used to make the emulsion-templated support usually comprises two liquid phases, with droplets of one phase within the other. Typically one phase is aqueous and the other organic, though any two immisciblc phases can he used. For example, the emulsion can contain aqueous droplets within an organic continuous phase, the latter being I 0 polyrnerized into tile base material of the support. Alternatively, the emulsion can contain organic droplets (e.g. a solvent) within an aqueous continuous phase which contains polymerizable monomers, the latter being polymerized into the base material of the support.

Such water-in-oil (w/o) or oil-in-water (o/w) emulsions allow the preparation of a wide variety of porous polymers and other materials. For example, the polymer may comprise 1 5 polystyrene, in which case the starting materials in the continuous phase comprise styrene monomer(s) and other optional materials such as a crosslinker (e.g. divinyl benzene [DVB]). Other examples of suitable polymers prepared in an organic phase include tlloSe prepared from acrylates or methacrylates. Polymers can he prepared by polymerization of components in an aqueous phase, such as for example acrylamide or iV- 2() isopropylacrylamide. Supercritical (02-ill-water (c/w) emulsions can also be used to prepare polyacrylamide and poly(2-hydroxyethyi acrylate) materials, amongst others.

Alternatively, inorganic materials niay be prepared, for example by the sol-gel polycondensation of tctraethylorthosilicate (TEOS) in the aqueous phase of an 0/w emulsion.

Tile support is prepared by mixing the two phases, curing or otherwise solidifying the continuous phase and removing tile droplet phase as known in the art.

To the support is added the material which will form the host. [or example. if the clatllrate is a clathrate hydrate, then water. which may he in the form ol a stock solution with optional other components (such as for example a stabilizer, in which case an appropriate amount of stabilizer is present bused on known effective H'O:stabilizcr ratios), is mixed with the host. ()

The clathrate may be formed in apparatus known in the art, such as for example a high pressure stainless steel cell.

Thus, it is believed that a clathrate thin film formS on the surface of the support.

Preferably the emulsion-templated porous support comprises relatively large voids, which may for example he approximately spherical. Preferably there are interconnecting windows between voids. Typically the windows are smaller than the voids. Additionally, iii some cases smaller pores may be present within the walls of certain emulsion-templated porous supports; these smaller pores may be micropores or mesopores, i.e. these smaller pores may preferably he no greater than 50, no greater than 30, no greater than 20. no greater than 10 or no greater than 2 nrn.

1 5 Preferred void diameters fall within the ranges 1-100 micro-rn, 5-50 micro-rn and most preferably 15-25 micro-rn. Preferably the average void diameter falls within the ranges 1-micro-rn, 5-50 micro-rn and most preferably 15-25 micro-rn.

Preferred window diameters fall within the ranges 0.05-50 micro-rn, 0.1-20 micro-rn and most preferably 0.5-10 micro-rn. Preferably the average window size falls within the ranges 0.05-50 micro-rn, 0. 1-20 micro-rn and most preferably 0.5-10 micro-rn.

Most prelrahly the support has voids of diameter 1 5-25 micro-rn and windows of size 0.5-micro-rn.

Preftrably no more than 20%. more prefirahly no more than I 5%. more preferably no more than 10%, more preferably no more than 5%, most preferably flO more than 1%. weight-fbi--weight. of support is used, relative to the amount of host (or relative to the combined amount of' host and stabilizer, if a stabilizer is used).

Preferably the pore volume of the support is at least 74%. more preferably at least 80%, more preferably at least 90%, more preferably at least 95°/u, most preferably at least 99%.

For the avoidance of doubt, the pore volume is the percentage volume of voids, windows, pores and any other non-solid parts.

Preferably the bulk density of the support is no greater than I g/ cm3, more preferably no greater than 0.1 g/ cm3, more preferably no greater than 0.05 g/ cm3. more preferably no greater than 0.01 g/ cm3. For the avoidance of doubt, the bulk density is the overall density of the material.

Preferably the absolute density of the Support IS no greater than 5 g/ cm3, more preferably no greater than 2 g/ cm3, more preferably no greater than I g/ cm3, more preferably no greater than 0.1 gi cm3. For the avoidance of doubt, the absolute density is the density of the solid part of the material. i.e. the density not including the voids, windows, and pores.

From a further aspect the present invention provides the use of an emulsion-templated porous support in enhancing the enclathration of a gas, and/or the dissociation of a gas from a clathrate.

From a further aspect the present invention provides a composition in the form of a clathrate or suitable fbr fbrming a clathrate, comprising a clathrate-forming host and an emulsion- 2() templated porous support, and optionally a gas.

From a further aspect the present invention provides a composition comprising a gas clathratc and an emulsion-templated porous support.

From a further aspect the present invention provides a composition comprising a clathrate and an emulsion-templated Porous support. and optionally a gas.

From a yet further aspect the present invention provides an apparatus comprising an emulsion-templated porous support. optionally a clathrate-forming host and optionally a gas. wherein said apparatus is selected from one of the following devices or a component thereof: a fuel cell, an energy storage device, a gas storage device for example a modified gas tank, a gas separation device fi)r example an in-line gas separation cartridge, a gas sequestration device tbr example an in-line gas sequestration cartridge, a gas transportation device for example a modified gas tank, and a vehicle for example an automobile.

The preferred features specified above in relation to the method of the invention apply niutatis inutandis to the uses, compositions and apparatus of the invention.

Thus the present invention allows improvements in gas storage, gas transportation/distribution. use of fuels, gas sequestration, and waste gas trapping. The present invention also brings about improvements in the separation of one or more gases from a mixture: thr example by the preferential enclathration of methane over hydrogen, ethane or propane; carbon dioxide over methane or nitrogen; or hydrofluorocarbons from gas mixtures.

The present invention will now be described further by way of non-limiting example with IS reference to the following drawings in which:-Figure 1 is a schematic illustration of clathrate hydrate dispersed on an crnulsion-tcmplated porous support; Figure 2 is an electron micrograph of an emulsion-templated OOUS SUppOrt Figure 3 shows the pore size distribution of an emulsion-templated porous support; Figure 4 is a schematic diagram of experimental apparatus used to prepare the supported clathrate hydrate; Figure 5 shows cooling/heating curs es thr a clathrate-firming solution containing TI-I F stabilizer with and without a support: Figure 6 shows kinetic plots of hydrogen enclathration in the presence of THF stabilizer with and without a support: Figure 7 shows temperature vs. time plots ot a THF-l-120 system in the presence and absence of H. and with and without a SUpport.

Figure 8 shows a kinetic plot of hydrogen cnclathration in bulk THF-H20 clathrate hydrate.

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Figure 9 shows kinetic plots of hydrogen enclathration in the presence of Ti-IF stabilizer at higher pressures than in Figure 6, without a support, with an activated carbon support, and with an emulsion templated support; Figures 10 to 13 are analogous to Figures 5 to 8 respectively except that they relate to expcrirnents wherein TBAB is used as stabilizer in place of THF; Figure 14 shows a pressure vs. temperature plot of enclathration within scmi-clathrate hydrate in the presence of TBAB and subsequent dissociation under heating; and Figures 15 and 16 arc analogous to Figures 5 and 6 respectively except that they relate to experiments wherein the guest is methane in place of hydrogen in the absence of any stabilizers; and Figure 17 shows a pressure vs. temperature plot of cnclathration of methane within clathratc hydrate in the absence of any stabilizers and subsequent dissociation under heating.

Example I -Preparation and characterization of polyHiPE poler SUPPQ Typically the organic phase 10 mL was comprised of 5 ml Divinylbcnzene (DVB. Aldrich 8() vol% m-and p-divinylhenzenc, the remainder m-and p-ethylstyrenc. purilied by passing through a column of basic alumina to remove the inhibitor) and 5 ml porogen(s) (chlorobenzcne -2-chloroethvlhenzene I: I ratio by volume. Aldrich) Ibilowed by adding 2 ml sorbitan monooleate (Aldrich, Span 80. HLB=4.3) (20 vol% to monomer porogen mixture). The aqueous phase (90 ml) contained 0.2 g potassium persulfate (Aldrich) and 1.0 g calcium chloride (Alclrich). The separate organic and aqueous phases were purged with nitrogen for 15 mm, and then the aqueous phase was added dropwise to the organic under nitrogen with constant mechanical stirring. Full details of the procedure for preparing PoIyHIPE materials can be found elsewhere (Hainey. P.; Huxharn, 1. M.; Rowatt, B.; Sherrington, D. C.; Tetley, L. Macminolecules 1991, 24. 117; and Cameron, N. R.: Barhctta, A. Journal of. Materials Chemistry 2000, im'), 2466). The morphology ol polyl-IIPE was observed using a Hitachi S-4800 cold Field Emission Scanning Electron Microscope (FE-SEM). The dry polymers samples were prepared on 15 mm Hitachi M4 aluminium stubs using either silver dag or an adhesive high purity carbon spectrO tab. The samples were then coated with a 2 nm layer of gold using an Emitech K550X automated sputter coater. The FE-SEM measurement scale bar was first calibrated using certified SIRA calibration standards. The Brunauer-Emrnett-Teller (BET) surface area (P/P() 0.05 -0.20) was measured with nitrogen adsorption at 77.3 K using an ASAP242O volumetric adsorption analyzer (Micromeritics). Samples were degassed at 90 °C fbr IS h under vacuum before analysis. The pore size distribution analysis was conducted using Macropore intrusion volumes, bulk densities, and macropore size distributions were recorded by mercury intrusion porosimetry using a Autopore Mercury Porosimeter IV 9500 (Micromeritics) over a pressure range of 0.10 -60000 psia. Intrusion volumes were calculated by subtracting the intrusion arising from mercury interpenetration between beads (pore size >150 tm) from the total intrusion.

Figure 2 shows the SEM image of polyHIPE polymer. It can be clearly seen that the macroporous polyH IPE polymer is built with open cells (voids) containing a large number of interconnected pore windows. The pore size distribution of the windows, derived using a mercury porosimetrv method in Figure 3 exhibits a narrow peak centered at 9.1 im and a shoulder ieak at around 6.7 pm. Its hulk density is 0.056 g/cm3. Its BET surface area obtained from nitrogen adsorption is around 230 m/g, consistent with a previous report (Hainey. P.; Huxham, I. M.; Rowatt, B.; Sherrington. D. C.; Tetley, L. Macromnolt'cules 1991. 24. 117). The macroporous structure of polyl I IPE can be efficiently tuned by control over synthesis conditions (Hainey. P.: 1-luxharn. I. M.: Rowatt, B.; Sherrington. D. C.: 3() Tetley. L. Macromolecules 1991. 24. 117: and Cameron. N.. R.; Barbetta. A. .Jownal of /tki/eria/s Chcnzisirr 2000. /0, 2466).

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Example 2 -. Formation of clatbratc hydrates A stock solution of tetrahydrofuran (THF. Aldrich). 5.56 mol% TI-IF in deionized water (THF* I 7H20) was prepared gravimetrically for stoichiornetric experiments (with all the large cages of s/I occupied by THF) (Hester, K. C.: Strobe!, T. A.; Sloan, E. D.; Koh, C. A.; Huq, A.; Schultz. A. J. J. Phi's. C7,cm. /3 2006, /10, 14024, and Strobel, T. A.; Taylor, C. J.; Hester, K. C.; Dcc, S. F.: Koh. C. A.; Miller, K. T.: Sloan, E. D. .1 P/zvs. C/win. B 2006, 1/0, 1712 1). Similarly. 2.56 mol% solution of tctra-n-hutylammoniurn bromide (TBAB, Fisher) with a stoichiometric composition of TBAB*38H20 was prepared (Chapoy, A.; Anderson, R.: Tohidi, B. .1. Am. (hen,. Soc. 2007, /29, 746). A 20.0 g THF or TBAB stock solution together with a given amount of polyl-IIPE polymer SUpport was loaded in a 60-cm3 high pressure stainless steel cell (New Ways of Analytics, Lörrach, Germany) for the formation and dissociation of clathrate hydrates and fbr hydrogen enclathration under continuous cooling or heating. For methane clathrate experiment, the pure water with a mount of 20.0 g in the absence of any stabilizers was used. The temperature of coolant in the circulator was controlled by a programmable thermal circulator (HAAKE Phoenix 11 P2, Thermo Electron Corporation). The temperature of compositions in the cell was measured using a Type K Thermocouple (Cole-Parmer, -250 -400 °C). The pressure was monitored using a High-Accuracy Gauge Pressure Transmitter (Cole-Parmer, 0 -3000 psia). Both thermocouple and transmitter are connected to a Digital Universal Input Panel Meter (Cole-Parmer). which communicate with a computer. Prior to experiments, the cell was slowly purged with hydrogen (UHP 99.999%. BOC Gases, Manchester, UK) or methane (UHP 999990/, BOC Gases, Manchester, UK) three times, and then pressurized to the desired pressure at a designated temperature. The temperature (T, K) and pressure (P. psia) with time (t, miii) of compositions within the cell were automatically interval-logged into a computer by MetcrVicw 3.0 software (Cole-Parmer). The experimental apparatus is shown in Figure 4.

Assuming that the true density of' polyHiPE and clathrate hydrates is around 1.0 g'cm'. the free space volume of the cell can he obtained by subtracting the sum volume of clatlirate and support. The hydrogen or methane enclathration capacity is approximately evaluated using Idea Gas Law with a pressure drop _IP and temperature. In addition, GASPAK 3.4l software (Horizon Technologies, USA) was employed to calculate the hydrogen enclathration capacity for comparison.

Example 3 -H/THF/H2O systems Figure 5 Figure 5 shows P-T plots of cooling and heating for the H2-THF-H20 ternary system under hydrogen pressure (temperature ramp: 2.5 K/h): (A) without polyHiPE (for clarity, the curve was vertically shifted by 60 psi); (B) with macroporous polyHlPE Support (20.Og T1-IF-H20 solution mixed with 3.() g polyl-IIPE).

It can be seen that for curve A -Tl-IF-H20 without support -there is a linear trend during continuous cooling and heating, indicating the pressure-temperature (P-I) relations of hydrogen in the system obey the idea gas law (PIT constant). There is no evidence for the formation and dissociation of hydrogen clathrate. By contrast, for curve B with added polyHlPE support. there is clear evidence for the formation and dissociation of hydrogen clathrate with a dramatic pressure drop on cooling and rapid rise on heating. During cooling, the clathrate formation was accompanied by a significant pressure reduction at 277.1 -275.2 K associated with an exothermal peak. The pressure drop recovered to a linear trend after 275.2 K. indicating the cessation of hydrogen clathrate formation from the liquid phase to solid clathrate. During the warming process, the rapid pressure rise suggests the release of enclathrated hydrogen and the dissociation of the clathrate starting approximately at 275.2 K and ending at around 282.3 K. The result may be attributed to the use of the polyHIPE support, whose large internal surface can homogeneously disperse the TUF-l120 clathrate and accelerate the formation of hydrogen clathrate hydrate. The gravimctric hydrogen enclathration capacity derived from this pressure drop, _IP (158 psi) at 270.0 K is evaluated as approximately 0. 18 wt% (THF clathrate) using the ideal gas law and around 0.15 wt% using GasPak 3.4l software based on the initial point (289.1 K. 1843 psi) and tinal point (268.4 K. 1553 psi) considering the non-ideality of the hydrogen gas at a high pressure.

Figure 6 Figurc 6 shows the kinetic plots of hydrogen encapsulation in THF-H20 clathrate hydrate with and without polvHlPE at 270.0 K with different mass ratios (THF-H20 solution: support): (a) 23- cm3 glass beads (baseline): (h) 20:() THF-H:O:polyHlPE (that is, without Suppoil) (c) 20:1 Tl-IF-H20:polyHlPE: (d) 20:3 (1st run); (e) 20:3 (2): (t) 20:3 (3rd). (g) 20:3 (4th). (li) 20:3 (5th) 1 0 The small pressure drop originating from the temperature change of hydrogen gas from cylinder to the cell was calibrated with 23 cm3 glass heads as a baseline shown in curve (a).

There is no distinct pressure drop observed at 270.0 K even after 1200 mm, suggesting no gas leakage occurred in the setup used here. It can be seen that without polyHIPE, the curve (b) shows a small pressure drop after 1200 mm, indicating an extremely slow hydrogen encapsulation in bulk THF-H20 clathrate hydrate. After adding polyHiPE support, a large pressure drop can be observed in curves (c -h). In the cases of the ratio for 20:3, the difference in pressure drop for first three runs (d, e, and f) could be related to the wettahility of polyl-IIPE support. Curve (0 shows a large pressure drop and after 200 mm there is flO further discernable pressure drop. indicating the completion of hydrogen enclathration. The similar profile thr three runs in curves (f g, and Ii) suggests the good cyclability of hydrogen encapsulation process using polyHiPE support. The maximum pressure drop (JP11) derived from the hydrogen enclathration at 270.0 K is around 150 psi tbr last three runs (at 1200 miii), consistent with the observation in Figure 5.

Figure 7 Figure 7 compares the 7'-/ plots of cooling and heating (2.5 K/h) thr the THF-H20 binary system under different conditions: (a) Processing at atmospheric pressure without polyHIPE and hydrogen (For clarity, the curve was backwardly shifted by 50 mm.): (b) Processing at atmospheric pressure without hydrogen hut with polvHlPE support: (c) Processing athigh hydrogen pressure with polyHiPE support (see Figure SB) (For clarity, the curve was horizontally forwarded by 100 miii.) It can be seen that in plot (a), there is no evidence of clathrate formation when the THF-H20 system is cooled at atmospheric pressure in the absence of hydrogen within the timescale of the present experiment. By contrast, after adding support, plot (b) shows an exotherm at 274.2 K during cooling and a disturbance at around 276.8 K during heating, suggesting the tbniiation and dissociation of THF-H20 binary clathrate hydrate in the absence of hydrogen gas. in the presence of high pressure hydrogen (around 1660 psi) plot (c), a similar cnclathration and dissociation profile was observed. The simultaneous enclathration of small hydrogen molecules and lai-ger THF molecules within the clathrate cages possibly I 0 contributes to the higher temperatures and greater exotherm for formation and dissociation of THF-H20 clathrate hydrate.

Figui-e 8 1 5 Figure $ shows the kinetic plot of hydrogen encapsulation in bulk THF-H20 clathrate hydrate at 270.0 K (corresponding to experiment [h] in Figure 6) and the linear-fitted line in the period of 2000-4300 mm. The linear equation is: P = 0.0074*t + 1640. At 1 60 mm for curve (h) in Figure 6 using support, Pg is around 1 526 psi (90% of hydrogen enclathration capacity), and thus for curve (b) in Figure 6 without support, ta is calculated to be around 1 5405 miii (I I days) using the above linear equation, showing an increase in gas uptake kinetics by a factor of' 257. Similarly, at t0 200 mm, Pg is around 151 7 psi (97% of hydrogen enclathration capacity), and thus 1,, is around I 6621 miii (12 days), suggesting an increase of 83 times in kinetics. Furthermore. the enhancement in kinetics is also effective at a higher gas pressure (Figure 9).

nc,7l1,.(' 9 Figure 9 shows the efficacy of the present invention at higher pressures and also a comparison between different kinds of support.

Figure 9 shows the kinetic plots of hYdrogen encapsulation in THF-H20 ciathrate hydrate at high pressure and 270.0 K: (a) 23_cm glass beads (baseline): (h) THF-H20 (20.0 g); (c) THF-H20 (20.0 g) + activated carbon powder (l0.Og); (d) THF-H20 (20.0 g) -f poJyHIPE (3.0 g).

(urve (a) shows the baseline obtained with 23-cm3 glass beads at higher pressure. Curves S (b) and (d) show a similar trend as in Figure 6, indicating that kinetic enhancement can occur at a higher pressure. The maximum pressure drop derived from the hydrogen enclathration at 270.0 K is around 1 78 psi tbr curve (d), slightly higher than that at low pressure in Figure 5 and 6.

It can be seen that the use of powdered activated carbon in curve (c) has flO obvious effect on the enclathration kinetics even though a large amount of carbon support (10.0 g) is used.

Thus, using macroporous polyHiPE polymer as a support with a homogeneous, highly porous, open-cell structure and low apparent density properties is significant.

Example 4 -H,'TBAB/HO syste We have also tested the applicability of using a polyHiPE support in the fbrmation of a serni-clathrate hydrate with tetra-n-butylamrnonium bromide (TBAB) as a stabilizer. A similar accelerated formation of hydrogen clathratc hydrate was observed.

bigure J') Figure 10 shows the P-i' plots of cooling and heating for H2-TBAB-I-120 ternary system (semi-clathratc hydrate) under hydrogen pressure (temperature ramp: 2.0 K/h): (A) 1'BAB-HO solution (20.0 g) without polyl-ILPE support: (B) TBAB-H20 solution (20.0 g) mixed with poIyHIPE support (3.4 g). It can be seen that the pressure drop (JP1 23 psi) of semi-elathrate hydrate without using poIyHIPE support (A) is much less than that using the support (B) (..JP2--= 34 psi). indicating the enhancement of hydrogen encapsulation in TBAB-E-1O semi-clathratc hydrate when using polyHlI'E as a support.

Figure 11 Kinetic enhancement can be found at different hydrogen enclathration temperatures (273.2 and 278.2 K).

Figure II shows the kinetic plots of hydrogen enclathration in TBAB-H20 semi-clathrate hydrate conducted under different conditions: (a) 23-cm3 glass beads (baseline) at 273.2 K: (b) TBAB-HO solution (23.0 g) without polyHiPE at 278.2 K; (c) TBAB-H20 solution (23.0 g) without polyHiPE at 273.2 K; (d) TBAB-H20 solution (20.0 g) with poJyHIPE Support (3.4 g) at 278.2 K; (e) TBAB-HO solution (20.0 g) with polyHiPE SUpport (3.4 g) at 273.2 K (1st run); (I) TBAB-H20 solution (20.0 g) with polyHiPE support (3.4 g) at 273.2 K (2 run). The maximum pressure drop (JP,,,1) derived from the hydrogen enclathration at 273.2 K is around 78 psi for curve (e) or (t).

1 5 Figure /2 Figure 12 shows the T-t plots of cooling and heating for TBAB-H20 system (2.5 KJh): (a) Processing at atmospheric pressure without polyHIPE and hydrogen (for clarity, the cui.ve was backwardly shifted by 100 miii.); (h) Processing at atmospheric pressure without hydrogen but with polyHlPE support; (c) Processing with polyHiPE support and high pressure hydrogen (see Figure lOB) (for clarity, the curve was forward shifted by 100 mm).

It can be seen that there is a similar pattern of temperature disturbance observed for all curves. Plots (a) and (b) suggest the formation and dissociation of TBAB-H20 semi-clathrate hydrate with or without support in the absence hydrogen gas. Plot (c) shows a similar pattern of clathrate formation in the presence of hydrogen under pressure.

Figure 13 We calculate that, to reach 90% ol' hydrogen enclathration capacity, 32222 miii (22 days) would be needed in the absence of support. but only 300 miii in the presence of support.

indicating a large increase in gas uptake kinetics by a factor of 107.

Figure 13 shows the kinetic plot of hydrogen encapsulation in bulk TBAB-H20 clathratc hydrate 273.2 K and the linear-fitted line in the period of 1000 4000 mm. The linear equation is P _0.0018*, + 1473. At a time of 300 miii for Figure 11(c) using support, the pressure is around 1415 psi near to equilibrium, and thus without support in Figure 11(b), the time needed to the same pressure is calculated to be 32222 mm (22 days) using the above linear equation, showing an increase in kinetic behaviour by a factor of 107 when using polyHIPE as support.

Figure /4 1 0 Figure 14 shows the P-T plot of enclathration and subsequent dissociation for the H2-TBAB-H10 ternary system under hydrogen pressure with 20.0 g TBAB-H20 solution and 3.4 g polyHIPE support: a-*h. enclathration conducting at 273.2 K (bath temperature) (see Figure 11(e)) : b-c---*d--e. heating PFOCCSS with a temperature ramp ol' 4.0 K/h. The pressure drop during the enclathration process (a-b) is consistent with the pressure jump during the dissociation process (b---*c-d-e), implying hydrogen incorporation into the TBAB-H20 semi-clathrate hydrate at around 273.2 K (a-ph).

Example 5 -CH4/HO systems Figure /5 Figure 15 shows P-T plots for cooling and heating for a CH4-H20 system under CH4 pressure (temperature ramp: 2.0 K,li): (A) H20 (20.Og) without polyHIPE support: (B) H20 (20.() g) with polyHIPE support (3.0 g).

The CH4-H20 system is consistent with the above observations obtained for the THF-H20- 112 svsteni in Figure 5. There is no clear evidence for the fomiation and dissociation of the CFI4-H20 clathrate in the absence of the polyHIPE support under these unmixed conditions (curve A). By contrast, in the presence of the support (curve B). there is evidence fir the lormation and dissociation of methane clathrate with a dramatic pressure drop upon coolmg and a rapid rise upon heating, indicating the enhancement of methane encapsulation in the 1120 clathratc hydrate when using polyHiPE as a support.

Figure /6 Figure 16 shows the kinetic plots of CH4 enclathration in H20 clathrate hydrate at 27 1.0 K; (a) H20 without sUppOlt (h) 1120 (20.0 g) with polyHIPE (3.0 g).

The very small pressure drop after I 200 mm in curve (a) is consistent with very slow methane cnclathration kinetics in the absence of mixing when no polyHiPE support is used.

By contrast, a relatively large and rapid pressure reduction is observed in the presence of the polyH IPE support, curve (h). The methane enclathration capacity derived from the pressure drop in curve (b) at 271.0 K after 1200 mm (JP 290 psi) was estimated to he approximately 2.6 wt % (H4 (37 v/v STP) based on the mass of water added using the ideal gas law and around 3.4 wt % as calculated using GasPak v3.4l software which takes account of the non-ideality of the gas. These calculations were based on the initial pressure (0 mm, 271.0 K, 1330 psi) and the final pressure (1200 mm, 271.0 K, 1037 psi) assuming that the free space volume in the cell is constant (37 cm3). The data demonstrate the greatly enhanced kinetics fbr methane enclathration in the presence of the support.

Figure 17 Figure 17 shows a P-7 plot of enclathration and dissociation fbr the CH4-H20 system under CH4 pressure with 1120 (20.0 g) and polyHIPE support (3.0 g): a-tb. enclathration conducting at 271.0 K (see Figure 16(h)); b-'c--d-e. heating process with a temperature ramp of 2.0 K/li. Thus Figure 1 7 shows methane enclathration within 1120 clathrate hydrate at 271.0 K (bath temperature) and subsequent dissociation under continued heating (2.0 K/h) in the presence of the polyl-IIPE support. The pressure drop during the enclathration process (a-b) is consistent with the pressure jump during the dissociation process (b-c-�d--.e). implying that the methane as incorporated into the clathrate hydrate at around 271.1) K (a-ph).

In summary, the present invention provides a method to improve gas enclathration kinetics and cyclability in clathratcs using emulsion-templated supports. The work is of particular significance in promoting hydrogen clathrate hydrates as practical means of gas storage.

Claims (16)

1. I. A method comprising the enclathration of a gas. and/or the dissociation of a gas from a clathrate, in the presence of an ernulsion-templated porous support.
2. 2. The use of an cmulsion-templated porous support in enhancing the enclathration of a gas, andor the dissociation of a gas from a clathrate.
3. 3. A composition in the fbi-rn of a clathrate or suitable for forming a clathrate, comprising a clathrate-forming host and an ernulsion-templated porous support, and optionally a gas.
4. 4. A composition comprising a gas clathrate and an ernulsion-templated porous support.
5. 5. A composition comprising a clathrate and an ernulsion-templated POOUS support, and optionally a gas.
6. 6. An apparatus comprising an emulsion-templated porous Support. optionally a clathrate-forming host and optionally a gas, wherein said apparatus is selected from one of the following devices or a component thereot a fuel cell, an energy storage device, a gas storage device for example a modified gas tank, a gas separation device for example an in-line gas separation cartridge, a gas sequestration device for example an in-line gas sequestration cartridge, a gas transportation device tbr example a modified gas tank, and a vehicle ibr example an automobile.
7. 7. A method, use. composition or apparatus, as claimed in any preceding claim, wherein the clathrate comprises clathrate hydrate.
8. 8. A method. use, composition or apparatus, as claimed in any preceding claim, wherein the gas comprises hydrogen.
9. 9. A method. use. composition or apparatus. as claimed iii ally preceding claim, wherein the gas comprises methane.
10. 10. A method, use, composition or apparatus, as claimed in any preceding claim, wherein the gas comprises carbon dioxide.
11. I I. A method, use, composition or apparatus. as claimed in any preceding claim, wherein the gas comprises hydrocarbon gas.
12. 12. A method, usc, composition or apparatus. as claimed in any preceding claim, wherein the clathratc comprises a stabilizer.
13. 13. A method, use, composition or apparatus, as claimed claim 12, wherein the stabilizer comprises THF or TBAB, preferably THF.
14. 14. A method, use, composition or apparatus, as claimed in any preceding claim, wherein the ernulsion-templated porous Support comprises voids �f diameter 5-50 micro-rn and smaller interconnecting windows of diameter 0.1-20 micro-rn.
15. 15. A method, use, composition or apparatus, as claimed in any preceding claim, wherein the emulsion comi;rises a HIPE (high internal phase emulsion).
16. 16. A method, use. composition or apparatus, as claimed in any preceding claim, wherein the support comprises a polymer.

    1 7. A method, use. composition or apparatus, as claimed in claim 1 6. wherein the polymer COf1SCS a vinyl polyiiici'.

    1 8. A method, use. composition or apparatus. as claimed in claim 1 7, wherein the polymer compnses polystyrene or a derivative thereoll 1 9. A method. use. composition or apparatus. as claimed in any preceding claim, wherein the cmulsion-teniplated porous support comprises polyH IPE.