Non-flammable or weakly flammable cooling mixtures, characterised by low relative volatility for two-phase heat-exchange systems

Abstract

The present invention relates to a cooling mixture comprising a fluorinated compound and a non-fluorinated compound, wherein the fluorinated compound is a hydrofluoroether and the non-fluorinated compound includes a carbonyl function, which has a flash point no lower than 23 C. and which is characterised by having low relative volatility. The present invention likewise relates to the use of such a mixture as a coolant in a heat-exchange device.

Claims

1. A refrigerant mixture consisting of a fluorinated compound and a non-fluorinated compound, wherein the fluorinated compound is a hydrofluoroether selected from 1-methoxyperfluoropentane, 1-methoxyperfluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-2-trifluoromethylpentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and 1H,1H,2H,3H-decafluoro-dipropylether, and the non-fluorinated compound has a carbonyl function and is selected from butyl formate, tert-butyl acetate, propyl acetate, methyl ethyl carbonate, dimethyl carbonate and pentan-3-one, said mixture having a flash point of 23 C. or above and being characterized by a low relative volatility.

2. A heat-exchange device comprising a heat-transfer fluid, wherein the heat-transfer fluid is a refrigerant mixture according to claim 1.

3. The heat-exchange device according to claim 2, wherein the heat-exchange device is a capillary-pumped two-phase exchanger or a mechanically-pumped two-phase loop.

4. A method of cooling, comprising producing cold by evaporating a heat-transfer fluid, wherein the heat-transfer fluid consists of a mixture according to claim 1.

5. The method of cooling according to claim 4, wherein the heat-transfer fluid circulates through a heat exchanger.

6. The method of cooling according to claim 5, wherein the heat exchanger is a capillary-pumped two-phase exchanger or a mechanically-pumped two-phase loop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention further relates to a heat-exchange device comprising as heat-transfer fluid a mixture according to the invention.

(2) FIG. 1 shows the compositiontemperature diagram of the liquid-vapour equilibrium of the mixture consisting of 3M Novec 7100 HFE (0.35% 1-methoxyperfluorobutane, 0.65% 1-methoxynonafluoroisobutane by weight based on total weight) and methanol. The diagram also shows the flash point value of the mixture as a function of the HFE mass fraction, x(HFE).

(3) FIG. 2 shows the compositiontemperature diagram of the liquid-vapour equilibrium of the mixture consisting of 3M Novec 7100 HFE (0.35% 1-methoxyperfluorobutane, 0.65% 1-methoxynonafluoroisobutane by weight based on total weight) and hexafluoropropan-2-ol.

(4) FIGS. 3.a-3.c list the composition temperature binary diagrams of the liquid vapour equilibria of certain mixtures according to the invention, characterized by flattened families of dew-point and boiling-point curves. A given diagram also shows the flash point value of the corresponding mixture as a function of the fluorinated compound mass fraction, x(F). The original UNIFAC thermodynamic model was used to calculate the liquid-vapour binary equilibrium and to calculate the flash point using Le Chatelier's rule (Annals of Mines 19, 388-395. 1891) for binary mixtures with a non-flammable component (Liaw H-J et al., Fluid Phase Equilibria. 300. 70-82. 2011). The resulting mixture enthalpy of vaporization is calculated by linear interpolation as a function of the mass composition.

(5) FIG. 3.a corresponds to the binary diagram of the mixture: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and butyl formate.

(6) FIG. 3.b corresponds to the binary diagram of the mixture: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and dimethyl carbonate.

(7) FIG. 3.c corresponds to the binary diagram of the mixture: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and pentan-3-one.

(8) For the purposes of the present invention, FP or flash point means the minimum temperature expressed in degrees Celsius at which a combustible substance emits vapours in a concentration sufficient to form a gaseous mixture with ambient air that ignites upon contact with a flame or hot spot, but insufficient for combustion to propagate by itself in the absence of said pilot flame. According to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 Dec. 2008 on classification, labelling and packaging of substances and mixtures, a fluid with an FP such as 23 C.FP<60 C. belongs to the weakly flammable category 3, the non-flammable category 4 corresponding to an FP of 60 C. or above.

(9) Flame retardant means, for the purposes of the present invention, a substance whose function is to reduce the flash point of another compound.

(10) A hydrofluoroether or HFE, also called fluoroether in the literature, is, for the purposes of the present invention, an ether R.sub.1OR.sub.2 in which some or all of the hydrogen atoms of the hydrocarbon chains R.sub.1 and R.sub.2 are replaced by fluorine atoms.

(11) Similarly, fluoro-alcohol means, for the purposes of the present invention, an alcohol R.sub.3OH in which some or all of the hydrogen atoms in the hydrocarbon chain R.sub.3 are replaced by fluorine atoms.

(12) A fluoro-alkane is, for the purposes of the present invention, an alkane, i.e. a saturated hydrocarbon, in which some or all of the hydrogen atoms are replaced by fluorine atoms.

(13) For the purposes of the present invention, the global warming potential, or GWP, is a comparative index associated with a greenhouse gas, which quantifies its marginal contribution to global warming compared with that of carbon dioxide over a 100-year period.

(14) A mixture with a low relative volatility refers, for the purposes of the invention, to a mixture that has a relative volatility close to unity over a wide range of composition, which is reflected in a liquid-vapour equilibrium diagram by almost coincident boiling-point and dew-point curves, thus forming a flattened family of curves, as in FIGS. 3.a, 3.b and 3.c. It should be noted that the existence of an azeotropic point is a condition that is neither necessary nor sufficient for such a flattening to emerge.

(15) The present invention relates, first, to a refrigerant mixture comprising a fluorinated compound selected from a hydrofluoroether, a fluoro-alcohol and a fluoro-alkane, and a non-fluorinated compound having a carbonyl or alcohol function, which has a flash point of 23 C. or above and which is characterized by a low relative volatility, exclusive of a mixture consisting of a hydrofluoroether and a non-fluorinated compound having an alcohol function.

(16) Such a mixture may optionally have an azeotropic point. That being the case, it necessarily has a low relative volatility over the composition range of interest.

(17) Advantageously, a refrigerant mixture according to the invention may therefore comprise a non-fluorinated compound that has a carbonyl function, also called a carbonyl compound in the following description, such as an ester, a carbonate, a ketone or an aldehyde.

(18) Ester means, more particularly, a compound R.sub.4COOR.sub.5, wherein R.sub.4 and R.sub.5 are hydrocarbon chains which may, according to the invention, independently be linear or branched, and contain between 1 and 10 carbon atoms.

(19) Carbonate means, more particularly, a compound R.sub.6OCOOR.sub.7, wherein R.sub.6 and R.sub.7 are hydrocarbon chains which may, according to the invention, independently be linear or branched, and contain between 1 and 10 carbon atoms.

(20) Ketone means, more particularly, a compound R.sub.8COR.sub.9, wherein R.sub.8 and R.sub.9 are hydrocarbon chains which may, according to the invention, independently be linear or branched, and contain between 1 and 10 carbon atoms.

(21) Aldehyde means, more particularly, a compound R.sub.10COH, wherein R.sub.10 is a hydrocarbon chain which may, according to the invention, be linear or branched and contain between 1 and 10 carbon atoms.

(22) In particular, the carbonyl compound may be selected from butyl formate, tert-butyl acetate, propyl acetate, methyl ethyl carbonate, dimethyl carbonate and pentan-3-one.

(23) The non-fluorinated compound of a mixture according to the invention may, in another embodiment, have an alcohol function.

(24) Alcohol more particularly refers to a compound ROH, wherein R.sub.11 is a hydrocarbon chain which may, according to the invention, be linear or branched, and contain between 1 and 10 carbon atoms, preferentially between 2 and 6 carbon atoms.

(25) Advantageously, the alcohol is selected from ethanol, propanol and propan-2-ol.

(26) In addition to a non-fluorinated compound, a mixture according to the invention comprises a fluorinated compound.

(27) Advantageously, the fluorinated compound may be a hydrofluoroether.

(28) According to one embodiment, the hydrocarbon chains R.sub.1 and R.sub.2 of said hydrofluoroether may independently be linear or branched, advantageously saturated, and contain between 1 and 10 carbon atoms.

(29) Preferentially, the hydrofluoroether has at least 5 fluorine atoms, and preferably at least 8 fluorine atoms.

(30) In a particular embodiment, R.sub.1 is an alkyl group containing from 1 to 3 carbon atoms, and notably a methyl group.

(31) In another embodiment, R.sub.2 is a perfluorinated hydrocarbon chain, i.e. a hydrocarbon chain in which all the hydrogen atoms are replaced by fluorine atoms. R.sub.2 then preferably has at least 3 carbon atoms, and more preferably its number of carbon atoms is comprised between 5 and 8.

(32) In a variant embodiment, R.sub.1 is an alkyl group having 1 to 3 carbon atoms, such as methyl, and R.sub.2 is a perfluorinated hydrocarbon chain which preferably has a number of carbon atoms between 3 and 8, notably between 4 and 6, such as perfluorobutyl, perfluorohexyl and perfluoro-2-methylpentyl.

(33) Alternatively, R.sub.1 and R.sub.2 may each independently contain at least one hydrogen atom.

(34) According to one embodiment, R.sub.1 and R.sub.2 are partially fluorinated hydrocarbon chains having from 1 to 8 carbon atoms, more advantageously from 2 to 5 carbon atoms.

(35) Preferentially, R.sub.1 then corresponds to the group CH.sub.2CF.sub.2CF.sub.2H, and more advantageously R.sub.2 is selected from CF.sub.2CF.sub.2H and CF.sub.2CFHCF.sub.3.

(36) In particular, the hydrofluoroether may be selected from 1-methoxyperfluoropentane, 1-methoxyperfluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-2-trifluoromethylpentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and 1H,1H,2H,3H-decafluoro-dipropylether.

(37) The fluorinated compound may also be a fluoro-alcohol, that is to say for the purposes of the present invention an alcohol R.sub.3OH in which some or all of the hydrogen atoms of the hydrocarbon chain R.sub.3 are replaced by fluorine atoms.

(38) According to one embodiment, the hydrocarbon chain R.sub.3 may be linear or branched, advantageously saturated, and contain between 1 and 10 carbon atoms.

(39) Preferentially, the fluoro-alcohol has at least 3 fluorine atoms, and preferably at least 5 fluorine atoms.

(40) According to a variant embodiment, the carbon atom that carries the alcohol function is not substituted by a fluorine atom. Preferentially, said carbon atom is then bound to at least one hydrogen atom, and preferably to 2 hydrogen atoms, or alternatively a hydrogen atom and an alkyl group that has 1 to 3 carbon atoms, such as methyl.

(41) In particular, the fluoro-alcohol may be selected from pentafluoropropanol, heptafluorobutanol and heptafluoropentan-2-ol.

(42) According to another embodiment, the fluorinated compound may be a straight- or branched-chain fluoro-alkane having between 1 and 10 carbon atoms.

(43) Even more advantageously, a mixture according to the invention may comprise a hydrofluoroether and a carbonyl compound, which may be more particularly as defined above.

(44) Such mixtures are characterized by the existence of strong intermolecular hydrogen bonds: hydrofluoroether is, due to the strong electron-attracting effect of the fluorine atom, a hydrogen donor, while the carbonyl group is an acceptor. These strong electrostatic interactions promote the formation of an azeotrope with a maximum boiling point. This negative azeotropic deviation, which is not found in any refrigerant mixtures in the literature, is particularly attractive insofar as the flash point of a mixture tends to be higher the higher its boiling point, due to the intrinsic link between these two quantities. If the mixture does not have an azeotropic composition, the family cluster of dew-point and boiling-point curves is nevertheless also concave, which therefore has the same effects on the flash point.

(45) Preferentially, a refrigerant mixture according to the invention comprises a hydrofluoroether and a carbonyl compound, said hydrofluoroether being selected from 1-methoxyperfluoropentane, 1-methoxyperfluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-2-trifluoromethylpentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether and 1H,1H,2H,3H-decafluoro-dipropylether, and the carbonyl compound being selected from butyl formate, tert-butyl acetate, propyl acetate, methyl ethyl carbonate, dimethyl carbonate and pentan-3-one, said mixture having a flash point of 23 C. or above and being characterized by a low relative volatility.

(46) Table 3 lists the compositions and characteristics of certain mixtures according to the invention, which are particularly advantageous. When the mixture has an azeotropic point, it is specified.

(47) TABLE-US-00003 TABLE 3 Characteristics of HFE - carbonyl compound mixtures of the invention FP (in C.) none T.sub.b (in C.) 84.9 T.sub.f (in C.) 69 H.sub.vap (kJ/kg) 105 18 106 90 358 Category 3 mixture X.sub.HFE = 0.43 23 249 Category 4 mixture X.sub.HFE = 0.93 60 123 17 90 4 366 azeotrope X.sub.HFE = 0.64 28 96 200 Category 3 mixture X.sub.HFE = 0.5 23 96 235 Category 4 mixture X.sub.HFE = 0.92 60 90 126 FP (in C.) none T.sub.b (in C.) 108 T.sub.f (in C.) 88 H.sub.vap (kJ/kg) 95.4 18 106 90 358 azeotrope X.sub.HFE = 0.77 31 112 156 Category 3 mixture X.sub.HFE = 0.48 23 110 232 Category 4 mixture X.sub.HFE = 0.93 60 110 114 14 102 95 332 azeotrope X.sub.HFE = 0.89 41 109 122 Category 3 mixture X.sub.HFE = 0.65 23 178 Category 4 mixture X.sub.HFE = 0.96 60 105 23 107 53 352 azeotrope X.sub.HFE = 0.73 39 114 165 Category 3 mixture X.sub.HFE = 0 23 107 53 352 Category 4 mixture X.sub.HFE = 0.90 60 112 121 13 102 39 388 azeotrope X.sub.HFE = 0.87 37 109 134 Category 3 mixture X.sub.HFE = 0.7 23 184 Category 4 mixture X.sub.HFE = 0.96 60 108 FP (in C.) none T.sub.b (in C.) 98 T.sub.f (in C.) 38 H.sub.vap (kJ/kg) 89 0 18 106 90 358 azeotrope X.sub.HFE = 0.55 25 109 210 Category 3 mixture X.sub.HFE = 0.47 23 108 232 Category 4 mixture X.sub.HFE = 0.94 60 102 106 14 96 58 285 azeotrope X.sub.HFE = 0.88 36 99 112 Category 3 mixture X.sub.HFE = 0.67 23 153 Category 4 mixture X.sub.HFE = 0.96 60 97 23 107 53 352 azeotrope X.sub.HFE = 0.55 31 111 207 Category 3 mixture X.sub.HFE = 0 23 107 53 352 Category 4 mixture X.sub.HFE = 0.90 60 116 17 90 4 366 azeotrope X.sub.HFE = 0.84 41 101 133 Category 3 mixture X.sub.HFE = 0.8 23 144 Category 4 mixture X.sub.HFE = 0.93 60 110 13 102 39 388 azeotrope X.sub.HFE = 0.67 22 105 187 Category 3 mixture X.sub.HFE = 0.70 23 180 Category 4 mixture X.sub.HFE = 0.96 60 101 FP (in C.) none T.sub.b (in C.) 93 T.sub.f (in C.) 94 H.sub.vap (kJ/kg) 140 18 106 90 358 Category 3 mixture X.sub.HFE = 0.43 23 104 264 Category 4 mixture X.sub.HFE = 0.91 60 96 159 14 96 58 285 Category 3 mixture X.sub.HFE = 0.57 23 202 Category 4 mixture X.sub.HFE = 0.9 60 154 14 102 95 332 Category 3 mixture X.sub.HFE = 0.53 23 230 Category 4 mixture X.sub.HFE = 0.92 60 155 23 107 53 352 Category 3 mixture X.sub.HFE = 0 23 107 53 352 Category 4 mixture X.sub.HFE = 0.87 60 167 0 17 90 4 366 azeotrope X.sub.HFE = 0.73 35 96 201 Category 3 mixture X.sub.HFE = 0.45 23 94 264 Category 4 mixture X.sub.HFE = 0.91 60 95 160 13 102 39 388 Category 3 mixture X.sub.HFE = 0.8 23 189 Category 4 mixture X.sub.HFE = 0.96 60 150 FP (in C.) none T.sub.b (in C.) 105 T.sub.f (in C.) 11 H.sub.vap (kJ/kg) 131 18 106 90 358 azeotrope X.sub.HFE = 0.72 44 110 195 Category 3 mixture X.sub.HFE = 0.47 23 109 251 Category 4 mixture X.sub.HFE = 0.92 60 108.5 149 14 102 95 332 azeotrope X.sub.HFE = 0.93 50 107 145 Category 3 mixture X.sub.HFE = 0.65 23 202 Category 4 mixture X.sub.HFE = 0.95 60 141 23 107 53 352 azeotrope X.sub.HFE = 0.66 37 110 206 Category 3 mixture X.sub.HFE = 0 23 107 53 352 Category 4 mixture X.sub.HFE = 0.89 60 156 13 102 39 388 azeotrope X.sub.HFE = 0.84 35 108 172 Category 3 mixture X.sub.HFE = 0.65 23 221 Category 4 mixture X.sub.HFE = 0.95 60 144

(48) Advantageously, a mixture according to the invention may include a fluoro-alcohol and a carbonyl compound, the fluoro-alcohol and the carbonyl compound which may be more particularly as defined above.

(49) Advantageously, the fluoro-alcohol is selected from pentafluoropropanol, heptafluorobutanol and heptafluoropentan-2-ol, and the carbonyl compound is selected from butyl formate, tert-butyl acetate, methyl ethyl carbonate, dimethyl carbonate and pentan-3-one.

(50) The compositions and characteristics of some of these mixtures are shown in Table 4. When the mixture has an azeotropic point, it is specified.

(51) TABLE-US-00004 TABLE 4 Characteristics of fluoroalcohol - carbonyl compound mixtures of the invention FP (in C.) none T.sub.b (in C.) 80 T.sub.f (in C.) 3 H.sub.vap (kJ/kg) 206 17 90 4 366 Category 3 mixture X.sub.HFE = 0.36 23 308 Category 4 mixture X.sub.HFE = 0.89 60 223 FP (in C.) 91 T.sub.b (in C.) 96 T.sub.f (in C.) N.A. H.sub.vap (kJ/kg) 195 0 18 106 90 358 Category 3 mixture X.sub.HFE = 0.41 23 103 291 Category 4 mixture X.sub.HFE = 0.95 60 97 203 13 102 39 388 Category 3 mixture X.sub.HFE = 0.64 23 265 Category 4 mixture X.sub.HFE = 0.96 60 203 FP (in C.) none T.sub.b (in C.) 100 T.sub.f (in C.) N.A. H.sub.vap (kJ/kg) 188 18 106 90 358 Category 3 mixture X.sub.HFE = 0.41 23 103 288 Category 4 mixture X.sub.HFE = 0.92 60 202 23 107 53 352 azeotrope X.sub.HFE = 0.36 30 109 293 Category 3 mixture X.sub.HFE = 0 23 107 53 352 Category 4 mixture X.sub.HFE = 0.8 60 221 17 90 4 366 azeotrope X.sub.HFE = 0.85 36 101 215 Category 3 mixture X.sub.HFE = 0.42 23 291 Category 4 mixture X.sub.HFE = 0.9 60 206

(52) Another category of refrigerant mixtures according to the invention comprises a fluoro-alcohol and an alcohol, which may be more particularly as defined above.

(53) The hydrogen bonds in such mixtures are very weak, since both components are hydrogen donors. This favours the emergence of a positive azeotropic deviation.

(54) Preferentially, the fluoro-alcohol is selected from pentafluoropropan-1-ol, heptafluorobutanol and heptafluoropentan-2-ol, and the alcohol is selected from ethanol, propanol and propan-2-ol.

(55) Table 5 summarizes the compositions and characteristics of some of these mixtures. When the mixture has an azeotropic point, it is specified.

(56) TABLE-US-00005 TABLE 5 Characteristics of fluoroalcohol - alcohol mixtures of the invention FP (in C.) none T.sub.b (in C.) 80 T.sub.f (in C.) 3 H.sub.vap (kJ/kg) 313 ethanol 13 78 114 837 azeotrope X.sub.HFE = 0.71 19 77 465 Category 3 mixture X.sub.HFE = 0.77 23 78 433 Category 4 mixture X.sub.HFE = 0.98 60 324 Propan-2-ol 11 82 88 606 Azeotrope X.sub.HFE = 0.8 23 78 372 Category 3 mixture Category 4 mixture X.sub.HFE = 0.98 60 319 FP (in C.) 91 T.sub.b (in C.) 96 T.sub.f (in C.) N.A. H.sub.vap (kJ/kg) 195 propanol 25 97 124 690 azeotrope X.sub.HFE = 0.72 29 92 334 Category 4 mixture X.sub.HFE = 0.98 60 205 FP (in C.) none T.sub.b (in C.) 100 T.sub.f (in C.) N.A. H.sub.vap (kJ/kg) 188 propanol 25 97 124 690 azeotrope X.sub.HFE = 0.58 29 96 399 Category 4 mixture X.sub.HFE = 0.97 60 203

(57) The present invention further relates to the use of a mixture according to the invention as heat-transfer fluid, advantageously in a heat exchanger such as a two-phase exchanger.

(58) It may be a capillary-pumped two-phase heat exchanger, such as heat pipes, CPL, LHP and thermosyphons, well known to the skilled person, or a mechanically-pumped two-phase loop.

(59) More generally, the invention also concerns a heat-exchange device comprising as heat-transfer fluid a mixture according to the invention.

(60) Said heat-exchange device may notably consist of a capillary-pumped two-phase exchanger or a mechanically-pumped two-phase loop.