NOVEL PHASE CHANGE MATERIAL AND METHODS OF USE

Abstract

The invention relates to a phase change material including one or more salts of low vapour pressure and low flammability and an energy storage system, method and device comprising the phase change material.

Claims

1. A phase change material including one or more salts of low vapour pressure and low flammability, wherein the salt comprises: (i) a conjugate base chosen from the group comprising benzoate, dihydrogen borate, bromide, tetra-phenylborate, ethanesulphonate, methanesulfonate, phosphonate, phosphate, diphenylphosphate, tosylate, triflate and salicylate; and (ii) a conjugate acid chosen from the group comprising pyrazolium, triazolium, dimethylethanolammonium, diethylenediammonium diethylammonium, ethylenediammonium, N,N-dimethylethylenediamine, diethylenetriamine, tetraphenylphosphonium, 1-alkyl-3-methylimidazolium, dipropylammonium, tris(2-aminoethyl)ammonium, imidazolium, caffeinium, 5-phenyl-1H tetrazolium, sodium, and guanadinium.

2. The phase change material of claim 1, wherein the one or more salts of low vapour pressure and low flammability are chosen from the group comprising pyrrazolium methanesulfonate, dimethylethanolammonium methansulfonate, dipropylammonium phosphonate, tris(2-aminoethyl) ammonium triflate, diethylammonium phosphonate, imidazolium diphenyl phosphate and caffeineium triflate.

3. The phase change material of claim 1, wherein the one or more salts of low vapour pressure and low flammability are chosen from the group comprising pyrazolium salicylate, pyrazolium ethanesulphonate, pyrazolium triflate, triazolium benzoate, triazolium borate, triazolium ethanesulphonate, triazolium salicylate, triazolium tosylate, triazolium triflate, imidazolium ethanesulphonate, imidazolium tosylate, imidazolium triflate, imidazolium ethanesulphonate, imidazolium tosylate, imidazolium triflate, imidazolium diphenylphosphate, dimethylethanolammonium methanesulphonate, tris(2-aminoethyl)ammonium triflate, caffeinium triflate, ethylenediammonium tosylate, diethylenediammonium(tosylate).sub.2, diethylenediammonium(ethanesulphonate).sub.2, and 5-phenyl-1H tetrazolium methanesulphonate.

4. The phase change material of claim 1, wherein the one or more salts of low vapour pressure and low flammability are chosen from the group comprising pyrazolium triflate, triazolium benzoate, triazolium borate, triazolium ethanesulphonate, triazolium salicylate, triazolium tosylate, triazolium triflate, imidazolium ethanesulphonate, imidazolium tosylate, imidazolium diphenylphosphate, dimethylethanolammonium methanesulphonate, tris(2-aminoethyl)ammonium triflate, caffenium triflate, ethylenediammonium tosylate, diethylenediammonium (tosylate).sub.2, diethylenediammonium(ethanesulphonate).sub.2, 5-phenyl-1H-tetrazolium methansulphonate, triazolium methanesulphonate, N,N-dimethylethylenediamine (methansulphonate).sub.2, diethylenetriamine(methanesulphonate).sub.3, diethylenetriamine(methanesulphonate).sub.2, tetraphenylphosphonium methanesulphonate, tetraphenylphosphonium bromide, tetraphenylphosphonium [tetra-phenylborate, C.sub.4mim tetra-phenylborate, C.sub.1mim tetra-phenylborate], and guanadinium methansulphonate.

5. The phase change material of claim 1 further comprising one or more nucleating agents.

6. The phase change material of claim 5, wherein the proportion of salt to nucleating agent is 0.005 to 5 wt %, preferably 0.01 to 1 wt %.

7. The phase change material of claim 6 wherein the nucleating agent is chosen from the group comprising inert inorganic compounds and carbon.

8. An energy storage system comprising: (a) a thermal energy source, (b) a thermal energy storage device including a phase change material according to claim 1 for absorbing and temporarily storing thermal energy provided by the energy source, and (c) a thermal energy conversion device which is operatively connected to the thermal energy storage device and which is capable of converting thermal energy into electric energy.

9. A method of energy storage comprising the steps of: providing thermal energy from an energy source to a phase change composition according to claim 1 for releasable storage of energy, releasing at least some of the stored thermal energy from the phase change composition to a heat extraction element in response to an energy need, and transferring the released thermal energy to an energy conversion device for conversion into electrical energy.

10. An energy storage device for temporarily storing and releasing thermal energy, the storage unit comprising: a reservoir for containment of the phase change composition of claim 1, and at least one heat transfer means in association with the reservoir.

Description

DETAILED DESCRIPTION

[0050] Preferred salts for use in the PCMs according to the present invention are listed in Table 1:

TABLE-US-00001 TABLE 1 Thermodynamic characteristics of novel organic salts suitable as phase change materials. T.sub.m H.sub.f H.sub.f.sup.v Material ( C. 2 C.) (J/g 5%) (J/cm.sup.3 5%) [Pyrazolium][Methansulphonate] 164 145 204 [Dimethylethanolammonium] 109 134 186 [Methansulphonate] [Dipropylammonium][Phosphonate] 138 135 171 [Tris(2-aminoethyl)ammonium][Tritiate] 123 112 168 [Diethylammonium][Phosphonate] 125 107 137 [Imidazolium][Diphenylphosphate] 102 93 130 [Caffenium][Triflate] 207 76 117 [Pyrazolium][Salicylate] 89 131 [Pyrazolium][Ethanesulphonate] 115 109 [Pyrazolium][Triflate] 60, 93, 129* 13, 17, 13 [Triazolium][Methanesulphonate] 135 133 [Triazolium][Benzoate] 66 143 [Triazolium][dihydrogen Borate] 120 55 [Triazolium][Ethanesulphonate] 89 98 [Triazolium][Salicylate] 67, 93* 55, 37* [Triazolium][Tosylate] 200 112 [Triazolium][Triflate] 168 129 [Imidazolium][Ethanesulphonate] 77, 128, 152* 14, 24, 86* [Imidazolium][Tosylate] 70, 111* 7, 35 [Imidazolium][Triflate] 32, 104, 161, 190* 26, 4, 5, 31* [Ethylenediammonium][Tosylate] 120 93 [Diethylenediammonium][Tosylate].sub.2 134 21 [Diethylenediammonium] 128 66 [Ethanesulphonate].sub.2 [5-phenyl-1H-tetrazolium] 115 50 [Methansulphonate] [N,N-Dimethylethylenediamine] 87 67 [Methansulphonate].sub.2 [Diethylenetriamine][Methanesulphonate].sub.3 182 90 [Diethylenetriamine][Methanesulphonate].sub.2 102 77 [Tetraphenylphosphonium] 313 97 [Methanesulphonate].sup.a [Tetraphenylphosphonium][Bromide].sup.a 149 100 [Tetraphenylphosphonium][tetra-Phenylborate].sup.a 201 66 [C4 mim][tetra-Phenylborate].sup.a 128 61 [C1 mim][tetra-Phenylborate].sup.a 257 116 [Sodium][methanesulphonate] & 187 76 [Guanidinium][methansulphonate] [Pyrazolium][Methanesulphonate] & 132 69 [Guanadinium][Methanesulphonate] Cn mim = 1-alkyl-3-methylimidazolium (where n = 1 (methyl), 4 (butyl)) .sup.a= aprotic salt *represents compounds that possess multiple solid-solid transition temperatures and a single melt (in column 2) along with the respective enthalpy of transitions and enthalpy of melt (column 3). For instance, in the case of [Imidazolium][Ethanesulphonate], there are two solid-solid transition temperatures (77 C., 128 C.) before the actual melting occurs at 152 C. The respective enthalpies of transitions are given as 14 and 24 J/g while the enthalpy of melting is 86 J/g. The other compounds in this category should be interpreted in the aforedescribed manner.

[0051] This can be compared with typical salts of the prior art such as those listed in the prior art such as Vijayraghavan et al, Energy Tech. 2013, 1 609-612.

[0052] It is noted that some of the compounds listed in Table 1 have been disclosed in the prior art but have not hitherto been recognised as a phase change material. These include for example, tetraphenylphosphonium bromide, tetraphenylphosphonium tetra-phenylborate, C4-mim tetra-phenylborate, C1-mim tetra-phenylborate and imidazolium triflate. The remaining compounds listed in Table 1 have not hitherto been described or recognised as a PCM.

[0053] The salts as exemplified in Table 1 are pure salts or pure zwitterions. By virtue of their molecular structure these salts absorb large amounts of heat as they melt and release this heat when the subsequently freeze again during cooling. H.sub.f is the latent heat of fusion, which expresses the quantity of energy that can be absorbed by the material per unit of PCM.

[0054] The salts of the present invention may be used as a pure compound or as a mixture with each other, or with other compounds such that the mixture exhibits a latent heat of fusion (H.sub.f) of 70-350 J/cm.sup.3/unit of volume, and a melting point of 25-250 C., more preferably 85-200 C., or even more preferably 85-140 C. For example, sodium methanesulphonate does not melt before decomposition (320 C.) and is therefore of no use on its own as a PCM. However, a successful PCM according to the present invention can be created when sodium methanesulphonate is mixed with a compound such as guanidinium methanesuphonate.

[0055] Certain advantages may be associated with using a mixture of PCMs, the advantages including the latitude to alter the heat release temperature range to ensure a best match with the intended use of the stored energy. For example, it is possible that two or more PCMs having melting temperatures above the desired temperature range can form a mixture that has a lower melting point, (or liquidus point). Certain combinations of PCMs can melt sharply at what is known as the eutectic temperature.

[0056] Additives may also be included in the pure PCM or mixture of PCMs. For example, to avoid supercooling of the PCM liquid before heat release, a non-dissolving component may be added to provide a nucleating function to the mixture. The nucleation agent may be a minor component and could be nano-particulate in form to avoid any separation tendency.

[0057] The materials described here can also usefully store energy in solid-solid phase transitions below the melting point where these exist. Either or both phase transition can be of utility as a means of storing thermal energy.

EXAMPLES

[0058] PCMs according to the present invention will be further described with reference to the following non-limiting examples:

PCMs

Example 1: Pyrazolium Methanesulphonate

[0059] One mole of pyrazole was dissolved in water, neutralised with one mole of methanesulfonic acid and the contents were stirred and kept in an ice bath. The resultant mixture was rotary evaporated at 70 C. (under reduced pressures) to remove water. The compound was then dried under vacuum to remove any residual moisture. The thermal and phase change behaviour of the pyrazolium methanesulfonate formed was studied by differential scanning calorimetry, revealing a melting point at 164 C. with an integrated enthalpy of fusion of 204 J/cm.sup.3. This compound was shown to have a very high enthalpy of fusion in the temperature region around 164 C.

Example 2: Dimethylethanolammonium Methansulfonate

[0060] An aqueous solution of 1 mole of 2-dimethylaminoethanol was neutralised with 1 mole of aqueous solution of methanesulfonic acid in an ice bath and the contents were stirred. The water in the mixture was distilled at 70 C. under reduced pressure and the resulting compound was further dried in a vacuum oven to remove traces of moisture. The phase change behaviour of the dimethylethanolammonium methanesulfonate formed was studied by differential scanning calorimetry and obtained a melting point of 109 C. with an integrated enthalpy of fusion of around 186 J/cm.sup.3.

Example 3: Dipropylammonium Phosphonate

[0061] One mole of aqueous solution of phosphorous acid was slowly added with stirring to 1 mole of aqueous solution of dipropylamine in an ice bath. The water in the mixture was evaporated to dryness at 70 C. under reduced pressure. The resulting dipropylammonium phosphate was further dried in a vacuum oven and the melting point was determined to be 138 C. with an integrated enthalpy of fusion of around 171 J/cm.sup.3.

Example 4: Tris(2-aminoethyl)ammonium triflate

[0062] Tris(2-aminoethyl)ammonium triflate was prepared by neutralising 1 mole of aqueous tris(2-aminoethyl)amine with one mole of aqueous trifluoromethanesulfonic acid in an ice bath. The water in the mixture was removed by distillation at 70 C. under reduced pressures. The resulting tris(2-aminoethyl)ammonium triflate was further dried in a vacuum oven to remove traces of water. The thermal and phase change behaviour was studied by differential scanning calorimetry, revealing a melting point of 123 C. and an integrated enthalpy of fusion of approximately 168 J/cm.sup.3.

Example 5: Diethylammonium Phosphonate

[0063] Diethylammonium phosphonate was made by neutralizing 1 mole of aqueous solution of phosphorous acid with 1 mole of aqueous solution of diethylamine in an ice bath. The water in the mixture was removed by distillation at 70 C. under reduced pressure. The diethylammonium phosphonate formed was further dried in a vacuum oven and thermal characterization was carried out by differential scanning calorimetry. The melting point was found to be 125 C. and an integrated enthalpy of fusion to be around 137 J/cm.sup.3.

Example 6: Imidazolium Diphenyl Phosphate

[0064] Imidazolium diphenyl phosphate was prepared by melt mixing technique. One mole of imidazole was mixed with one mole of diphenyl phosphate and the mixture was allowed to melt at 100 C. in an oil bath. The homogenous liquid was allowed to cool to room temperature. The solid imidazolium diphenyl phosphate obtained after cooling was analysed by differential scanning calorimetry to investigate the phase change behaviour. The compound begins to crystallise at 36 C., melts at 102 C. and exhibits an integrated enthalpy of fusion of approximately 130 J/cm.sup.3.

Example 7: Caffeineium Triflate

[0065] One mole of caffeine was dissolved in hot water, neutralised with one mole of trifluoromethanesulfonic acid and resultant mixture was evaporated to dryness at 70 C. under reduced pressure. The caffeineium triflate formed was further dried in a vacuum oven to remove any residual water. The thermal and phase change behaviour was studied by differential scanning calorimetry, produced a melting point of 207 C. with an integrated enthalpy of fusion of around 117 J/cm.sup.3.

Example 8: Ethylenediammonium Tosylate

[0066] The ethylenediammonium tosylate was synthesised by mixing the aqueous solutions of 1 mole of ethylenediamine (EDA) with 1 mole of p-toluenesulfonic acid and distilling off water at 60 C. under reduced pressure using rotatory evaporator. The compound was further dried in a vacuum desiccator at room temperature and analysed by differential scanning calorimetry to investigate the phase change behaviour. The compound melted at around 120 C. and produced an enthalpy of fusion of 93 J/g.

Example 9: Synthesis of Diethylenediammonium Ditosylate

[0067] The diethylenediammonium ditosylate was synthesised using the similar method described above except 2 moles of p-toluenesulfonic acid was used in place of 1 mole of the corresponding acid for making ([EDAH][OTs]. The dried compound was analysed by differential scanning calorimetry and it was found that it melted around 134 C. and exhibited an enthalpy of fusion of 21 J/g.

Example 10: N,N-Dmethyethylenediammonium dimesylate

[0068] The synthesis involve 1 mole of N,N-Dimethylethlenediamine and 2 moles of methanesulfonic acid and the rest of the procedure is the same as described above. The results of differential scanning calorimetry indicate that the compound melted at 87 C. and possessed an enthalpy of fusion of around 67 J/g.

Example 11: Synthesis of Diethylenetriammonium Dimesylate

[0069] The synthesis involves reaction of 1 mole of diethylenetriammonium and 2 moles of methanesulfonic acid and the rest of the procedure is the same as described above. The results of differential scanning calorimetry indicate that the compound melted at 102 C. and possessed an enthalpy of fusion of around 77 J/g.

Example 12: Diethylenetriammonium Trimesylate

[0070] Since this amine is a triamine it was fully protonated by reacting with 3 moles of methanesulfonic acid with 1 mole of the amine and method of synthesis is still the same as described above. The differential scanning calorimetry showed the melting at 182 C. and an enthalpy of fusion of around 90 J/g.

Example 13: Synthesis of Tetraphenylphosphonium Bromide

[0071] Nickel bromide (0.032 moles, 6.9 g), bromobenze (0.064 moles, 10 g) and triphenylphosphine (0.092 moles, 25 g) were mixed in benzonitrile (50 mL). The reaction was refluxed under N.sub.2 for 24 h and then cooled to room temperature. A solution of KBr (10% wt./wt., 150 mL) was added and the organic layer was extracted from dichloromethane (375 ml), dried with MgSO.sub.4 and conc. in vacuo to give an off-white solid. Further precipitation of by-product was induced by adding hexane (230 mL). The precipitate was filtered and the filtrate was conc. in vacuo to give a white solid (yield: 92%). The differential scanning calorimetry showed the melting at 149 C. and an enthalpy of fusion of 100 J/g.

Example 14: Tetraphenylphosphonium Tetraphenylborate

[0072] Sodium tetraphenylborate (0.005 moles, 1.8 g) and tetraphenylphosphonium bromide (0.0047 moles, 2.0 g) were dissolved in acetone (30 mL) and stirred for 6 h at room temperature. The mixture was then filtered over celite (545), and conc. in vacuo to give white solid (yield: 80%). The differential scanning calorimetry showed the melting at 201 C. and an enthalpy of fusion of around 66 J/g.

[0073] The above methods were used to synthesise [C4mim][tetra-Phenylborate] (m.p 128 C., 61 J/g) and [C1mim][tetra-Phenylborate] (m.p 257 C., 116 J/g) where the starting material [C4mim][Br] and [C1mim][Br] were used respectively.

Example 15: MixtureSodium Methanesulfonate & Guanadinium Methanesulfonate

[0074] As mentioned previously the PCM of the present invention may comprise a mixture of salts.

[0075] In this example a mixture of sodium methanesulfonate and guanadinium methanesulfonate was prepared at 1:1 by mass. The mixture was observed to melt sharply between 187 C. with enthalpy of 75.6 J/g and freeze very sharply at 180 C. The result of mixing has been to lower the melting point usefully, as suitable for lower input temperature applications.

[0076] It is noted that sodium methanesulphonate does not melt before decomposition (320 C.) and is therefore of no use on its own as a PCM. However, a successful PCM according to the present invention can be created when sodium methanesulphonate is mixed with guanidinium methanesuphonate.

Example 16: MixturePyrazolium Methanesulphonate & Guanadinium Methanesulphonate

[0077] In this example a mixture of pyrazolium methanesulphonate and guanadinium methanesulphonate was prepared at 1:1 by mass. The mixture produced a broad melting feature consisting of the eutectic melting and a liquidus, between 120 and 160 C. with total enthalpy of melting of 120 J/g. The eutectic melted at 132 C. and had individual enthalpy of fusion of 69 J/g. The eutectic froze very rapidly at 120 C.

Device

[0078] In another aspect of the present invention there is provided an energy storage device for temporarily storing and releasing thermal energy, the storage unit comprising: [0079] a reservoir for containment of the phase change material of the present invention, and [0080] at least one heat transfer means in association with the reservoir.

[0081] In one embodiment the heat transfer means is a heat input element and supplies thermal energy to the phase change material. In another embodiment the heat transfer means is a heat extraction element and withdraws thermal energy from the phase change material.

[0082] The heat transfer means may be a single device capable of alternatively supplying and extracting thermal energy. Alternatively, two or more separate heat transfer devices may be used. Typically, the supply and extraction of heat is achieved by use of a heat transfer fluid that circulates between the heat transfer means and externally attached components of the device.

System

[0083] The composition of the present invention can be used in any suitable system. For example, in one aspect of the invention there is provided an energy storage system comprising: [0084] (a) a thermal energy source, for example a solar thermal energy source, [0085] (b) a thermal energy storage device including a phase change material according to the present invention for absorbing and temporarily storing the thermal energy, which has been provided by the energy source, and [0086] (c) a thermal energy conversion device which is operatively connected to the thermal energy storage device and which is capable of converting thermal energy into electric energy.

[0087] The thermal energy source may for example include one or more of: [0088] a solar thermal collector [0089] an electrical heating element

[0090] Thermal energy conversion devices may for example, include one or more of: [0091] an organic Rankine cycle engine which is capable of converting thermal energy into electric energy; [0092] a hot water tank; or [0093] an absorption refrigeration or air conditioning device.

[0094] The system is based on the storage and later extraction of thermal energy. The stored thermal energy can be released on demand as needed from the PCM to the energy conversion device for converting the released thermal energy into other forms of energy.

[0095] The energy source may be of any convenient type including, solar thermal, geothermal, wind, tidal, photovoltaic or conventional coal power.

[0096] The heat extraction element may for example be connected to a heat engine configured for converting thermal energy into mechanical energy. The heat engine may also provide mechanical energy to an electrical generator for conversion into electrical energy. The electrical energy may be supplied to a utility grid.

[0097] Typically, the reservoir would comprise a tank such as a steel vessel.

Method

[0098] The present invention also provides a method of energy storage comprising the steps of: [0099] providing thermal energy from an energy source to the phase change composition of the present invention for releasable storage of energy, [0100] releasing at least some of the stored thermal energy from the phase change composition to a heat extraction element in response to an energy need, and [0101] transferring the released thermal energy to an energy conversion device for conversion into electrical energy.

[0102] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[0103] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

[0104] Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures.

[0105] Comprises/comprising and includes/including when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, includes, including and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to.