FIELD OF THE INVENTION
The present invention relates to haat-transfer compositions based on 2,3,3,3-tetrafluoropropene which hava improved miscibility with lubricant oil.
TECHNICAL BACKGROUND
Fluids based on fluorocarbon compounds are widely used in vapor compression heat-transfer systams, especially air-conditioning, haat-pump, refrigeration or freezing devices. The common feature of these devices is that they ara based on a thermodynamic cycle comprising vaporization of the fluid at low pressure {in which the fluid absorbs heat); compression of the vaporized fluid up to a high pressure; condensation of the vaporized fluid to liquid at high pressure (in which the fluid expels heat); and dapressurization of the fluid to complete the cycle,
The choice of a heat-transfer fluid (which may be a pure compound or s
mixture of compounds) is diet a tad firstly by tha thermodynamic properties of the
fluid, and secondly by additional constraints. Thus, a particularly important
criterion is that of the environmental impact of the fluid under consideration. In
particular. chlorinated compounds (chlorofluorocarbons snd
hydrochlorofluorocarbons) have the drawback of damaging the ozone layer. N on-chlorinated compounds are therefore now generally preferred, such ss hydrofluorocarbons, fluoro ethers and fluoro olefins,
Another environmental constraint is thst of the global warming potential (GWP). It is thus essential to devalop heat-transfer compositions which have a GWP that is ss low as possible and good energy performance qualities.
Moreover, to lubricate the moving parts of the compressors) of a vapor compression system, a lubricant oil must be added to the heat-transfer fluid. The oil msy generally be mineral or synthetic.
The choice of lubricant oil is made as a function of tha type of compressor, and so as not to react with the heat-transfer fluid itsetf or with me other compounds present in the system.
For certain haat-transfer systems (especislly small ones), the lubricant oil is generally permitted to circulate throughout tha circuit, the pipework being designed such that the oil csn flow by gravity to the comprassor. In other hest-

transfer systems (especially large ones), an oil separator is provided immediately sfter the compressor, and aleo an oil level management device, which ensures return of the oil to the compressor^ Even when an oil separator is preaenth the pipework of the system must stilt be designed such that the oil can return by gravity to the oil separator or to the compressor.
Document WO 2004/037 913 describes compositions based on fluoro Olefins snd especially based on tetrafluoropropene or pentafluoropropene. Exsmpte2 reports the miscibility of 1h2,3,3h3-pentafluoropropene (HFO-l225ye) with various lubricant oils, snd also that of 1,3,3,3-tetrafluoropropene {HFO-I234ze) with various lubricant oils. Example 3 reports the competibility of HFO-1234ze and of 3,3,3-trifluoropropene (HFO-1243zf) with lubricant oils of the poly alky lene glycol type.
Document WO 2005/042 663 specificslly concerns the miscibility of mixtures of fluoro olefins snd of lubricant oils. The examples provided for these mixtures ere essentially the same as those in document WO 2004/037 913.
Document WO 2006/094 303 describes a Isrge number of hest-transfer compositions comprising fluoro olefins and additional compounds. Among the numerous compositions cited are mixtures besed on 2,3,3,3-tetrafluoropropene (HF0-I234yf) and 1,1,1,2-tetrsftuoroethane (HFC-I34a). Moreover, the document generslly teaches of combining the list of the numerous possible refrigerant mixtures with a list of lubricant oils,
When the heat-transfer com pound (a) have poor miscibility with the lubricant oil, said oil hes a tendency to be trapped in the evaporator and not return to the compressor, which does not ensble correct functioning of the system.
In this regard, there is still a need to develop low-GWP heat-transfer compositions (which hsve good energy performance), in which the hest-transfer compounds show good miscibility with the lubricant oil.
In particular, HFO-1234yf is a heat-transfer compound thet is particularly interesting especially due to its low GWP end its good energy performance. On the other hand, its miscibility with certain lubricant oils is imperfect and limits its application. It is thus desirable to improve the miscibility of compositions based onHFO-1234yf with the ususl lubricant oils.
SUMMARY OF THE INVENTION
The invention relates firstly to a composition comprising 2,3,3,3-tetrafluoropropene, 1,1,1.2-tetrafluoroethane and polyalkylene glycol,

According to one embodiment, 2,3,3,3-tetrafluoropropene, 1,1,1,2-tetrafluoroethene and the polysikylene glycol represent at least 95%, preferably at least 99% and more particularly preferably at least 99.9% of the composition.
According to one embodiment, the composition comprises from 1% to 99% of polyalkylene glycol, preferably from 5% to 50%, more particularly preferably from 10% to 40% and ideally from 15% to 35%.
According to one embodiment, the mass ratio between 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane is from 1/99 to 99/1, preferably from 25/75 to 95/5, more particularly preferably from 50/50 to 92/8 and id sally from 55/45 to 92/8.
According to one embodiment, the polyalkylene glycol has a viscosity from 1 to 1000 centistokes at 40°c, preferably from 10 to 200 centistokes at 40"C, more particularly preferably from 20 to 100 centistokes at 40°C and ideally from 40 to 50 centistokes at 40"C.
According to one embodiment, the composition also comprises: one or more sdditives chosen from heat-transfer compounds, lubricants, stabilizers, surfactants, tracers, fluoresces, odorant agents, aolubilizers, and mixtures thereof; preferably one or more additives chosen from stabilizers, surfactants. tracers, fluoresces, odorant agents and solubilizers, and mixtures thereof.
The invention also relates to the use of a polyalkylene glycol as a lubricant oil in a vapor compression circuit, in combination with a hest-transfer fluid comprising, and preferably consisting of, a mixture of 2,3,3.3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane.
According to one embodiment, the polyalkylene glycol is used in a proportion of from 1% to 99%, preferably from 5% to 50%, more particularly preferably from 10% to 40% and ideally from 15% to 35%, relative to the sum of the polyalkylene glycol and of the heat-transfer fluid.
According to one embodiment, the mass ratio between 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane in the heat-transfer fluid is from 1/99 to 99/1, preferably from 25/75 to 95/5, more parliculerly preferably from 50/50 to 92/8 and ideally from 55/45 to 92/8.
According to one embodiment, the mass ratio between 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrafluoroethane in the heat-transfer fluid is from 80/40 to 99.9/0,1, preferably from 68/32 to 99.9/0.1, more particularly preferably from 68/32 to 95/5.
According to one embodiment, the polyalkylene glycol has a viscosity from 1 to 1000 centistokes at 40*0, preferably from 10 to 200 centistokes at

40°C, more particularly preferably from 20 to 100 centistokes at AO"C end ideally from 40 to 50 centistokes at 4CTC.
The invention also relates to a heat-transfer installation comprising a vspor compression circuit containing a heat-transfer composition which is a composition as described above.
According to one embodiment, the installation ia chosen from mobile or stationary haat-pump heating, sir-conditioning, refrigeration, freezing snd Rsnkine-cycle installations, and espadally from motor vehicle air-conditioning installations,
Tha invention also relates to e process for heating or cooling a fluid or s body by mesns of a vapor compression circuit containing a heat-transfer fluid, said proceas successivaly comprising at least partial evaporation of the nest-transfer fluid, compression of the heat-transfer fluid, at leaat partial condensation of the heat-transfer fluid and dapressurization of the heat-transfer fluid, in which the hest-transfer fluid is combined with s lubricant oil to form a heat-transfer composition, said heat-transfer composition being s composition as described above,
The invention also relates to a process for reducing the environmental impact of a heat-transfer installation comprising a vspor compression circuit containing an initial heat-transfer fluid, said process comprising a step of replacing the initial heat-transfer fluid in the vapor compression circuit with s final heat-transfer fluid, tha final heat-transfar fluid having s lower GWP than the initial heat-transfar fluid, in which the final heat-transfer fluid is combined with a lubricant oil to form a heat-transfer composition, said heat-trsnsfer composition being a composition as dascribed above.
The invention also relates to the us© of 1,1,1,2-tetrafluoroethane for increasing the miscibility of 2,3,3,3-tetrafluoropropene with a lubricant oil,
According to one embodiment, the lubricant oil is s poly alky lane glycol, and preferably has a viscoaity from 1 to 1000 centistokes at 4G°C, more preferably from 10 to 200 centistokes at40°C, more particularly preferably from 20 to 100 centistokas st 40°C and ideally from 40 to 50 centistokes at 40*C.
According to one embodiment, the 1,1.1,2-tetrafluoroethane is used in a proportion of from 1% to g9%, preferably from 5% to 75%, more particularly preferably from 8% to 50% and ideally from 8% to 45%, relative to the sum of 1,1.1,2-tetrafluoroethane and 2,3,3,3-tetrafluoropropene,
The invention also relates to a kit comprising:

- s heat-transfer fluid comprising 2,3,3,3-tetrafluoropropene and
1,1,1,2-tetrafluoroathane, on the one hand;
- a lubricant oil comprising a polyalkylene glycol, on the other hand;
for use in a heat-transfer installation comprising a vapor compression
circuit
The present invention makes it possibly to satisfy the needs fett in the prior art. It more particularly provides low-GWP heat-transfer compositions, which have good energy performance, in which tha heat-transfer compounds show good miscibility with the lubricant oil.
In particular, the invantion provides heat-transfer compositions based on HFO-1234yf, which have improved miscibility with certain lubricant oils such es polyalkylene glycols.
This is accomplished by mixing HF0-I234yf with HFC-i34a. Thus, the present inventors have noted thet HFC-134a improves the miscibility properties of HFO-l234yf with polyalkylene glycols, beyond that which might be expected by a simple extrapolation of the miscibility proparties o1HFO-1234yf, on the one hand, and of HFC-1 34a, on the other hand, with the lubricant oil. There is thus e synergistic effect between HFO-1234yf and HFC-134afrom the point of view of the miscibility with the lubricant oit.
The oils of polyalkylene glycol type have good lubricant power, a low flow point, good fluidity at low temperatura, and good compatibility with the alastomers generally present (n a vapor compression circuit. They are moreover relatively less expensive than other lubricant oils and are oils whose use is currently very widespread in certain fields, and especially in the field of motor vehicle air-conditioning. It is therefore very advantageous to improve the miscibility of HFO-1234yf with a lubricant oil of the polyalkylene glycol type, so as to be able to use this haat-transfer compound to a wider extent in combination with this lubricant oil.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1 is a graph representing the miscibility of various mixtures of HFO-1234yf and HFC-I34a with a polyalkylane glycol ND8 oil. The proportion of HFC-134a relative to the mixture of HFO-1234yf and HFC-134a is indicated on the x-axis and ranges from 0 to 100%, and the temperature from which the mixture ceases to be miscible with tha oil ia indicated on the y-axis (in °C). The experimental data are represented by black circles. The abbreviations NM and M denote, respectively, tha non-miscibility zone and tha miscibility zone. All the

results sre obtained with s content of oil ND6 of 17% relative to the sum of the three compounds HFO-1234yf/HFC-134a and oil ND8. Reference will be msde to the example below for further details.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The invention is now described in greater detail and without limitation in the description that follows.
Unless otherwise mentioned, throughout the application The indicated proportions of compounds are given as mess percentages.
According to the present patent applicstion, the globsl wsrming potentisl (GWP) is defined relative to carbon dioxide snd relative to e duration of 100 yeers, according to the method indicated In "The scientific assessment of ozone depletion, 2002, a report of the World Mateoralogical Association's Global Ozone Research and Monitoring Project".
The term "heat-transfer compound" or, respectively, "heat-trsnsfer fluid" (or coolant fluid) means a compound or, respectively, a fluid thst is capable of absorbing heat by evaporating at low temperature and low pressure and of expelling heat by condensing at high temperature and high pressure, in a vapor compression circuit. In general, a heat-transfer fluid may comprise one, two. three or more then three heat-transfer compounds.
The term "heat-trsnsfer compoaition" means a composition comprising a heel-transfer fluid and optionally one or more additives that are not heaMransfer compounds for the intended application.
The invention is based on the use of two heat-transfer compounds, namely HFO-1234yf and HFC-134a, and of a lubricant oil, to form a heat-transfer composition.
The heat-transfer composition may be introduced in unmodified form into a vapor compression circuit. Alternatively, the heat-transfer fluid (namely HFO-1234yf and HFC-134a), on the one hand, and the lubricant oil, on the other hand, may be introduced separately into the circuit, at the same point or otherwise. The individual heat-transfer compounds (HFO-1234yf and HFC-134a) may also be introduced seperately.
The lubricant oil ia preferably of the polyalkylene glycol type.

In general, the polyalkylene glycol oil that is suitable for use in the context of the invention comprises from 5 to 50 rapeated oxyalkylene units, each containing from 1 to 5 carbon atoms.
The polyalkylene glycol may be linear or branch ad. It may be a homopolymer or a copolymer of 2, 3 or more than 3 groups chosen from oxyethylene, oxy propylene, oxybutylene and oxypentylene groups and combinations thereof.
Preferred polyalhylene glycols comprise at least 50% of oxypropylene groups. For the purposes of the invention, the polyalhylene glycol may comprise polyalkylene glycols of differant formulae as a mixture.
Suitable polyalkylene glycols are described in document US 4 971 712. Othar suitable polyalkylene glycols are polyalkylene glycols containing hydroxy! groups at each end, as described in document US 4 755 316. Other suitable polyalkylene glycols are polyalkylene glycols having a capped hydroxy! end. The hydroxy! group may be capped with an alkyl group containing from 1 to 10 carbon atoms (and optionally containing one or more heteroatoms such as nitrogen), or a fluoroalkyl group containing heteroatoms euch as nitrogen, or a fluoroalkyl group as described in document US 4 975 212, or other similar groups.
When the two hydroxy! ends of the polyalkylene glycol are capped, tha same end group or s combination of two different groups may be used,
The end hydroxy! groups may also be capped by forming an ester with a carboxylic acid, as is described in document US 5 008 028. The carboxylic acid may also be fluorinated.
When the two ends of the polyaEkyEene glycoE are capped, one or the other may be capped with an ester, or alternatively one end may be capped with an ester and the other end may be free or may be capped with one of the abovementioned aEkyE, hateroalkyl or fluoroalkyl groups.
Examples of commercially available lubricant oils of polyalkylene glycol type are the Goodwrench oils from General Motors and Mopar-56 from Daimler-Chrysler. Other suitable oils are manufactured by Dow Chemical and Denso,
The viscosity of the lubricant oil may be, for example, from 1 to 1000 centistokes at 40°C, preferably from 10 to 200 centistokas at 40°C, mora particularly preferably from 20 to 100 centistokes at 4Q°C and ideally from 40 to 50 cantistokes at 40°C.
The viscosity is determined according to the ISO viscosity grades, in accordance with standard ASTM D2422.

The oil sold by Den so under the name NDS, with a viscosity of 48 centistokes, is particularly suitable.
The proportion of lubhcant oil that needs to be used in combination with the heat-transfer fluid mainly depends on the type of installation concerned. Specifically, the total emount of lubricant oil in the installation depends mainly on the nature of the compressor, whereas the total amount of heat-transfer fluid in the installation depends mainly on tha exchangers and on the pipework.
In general, the proportion of lubricant oil in the heat-transfer composition, or, in other words, relative to the sum of tha lubricant oil and of the heat-transfer fluid, is from 1% to 99%, preferably from 5% to 50%h far example from 10% to 40% or from 15% to 35%,
According to one particular embodiment, the lubricant oil used consists of the polyalkylene glycol described above, with the exception of any other lubhcant compound.
According to an alternative embodiment, another lubricant oil is used in combination with the polyalkylene glycol. It may be chosen especially from oils of mineral origin, silicone oils, paraffins of natural ohgin, naphthenes, synthetic paraffins, alkylbenzenes, poly-o-olefins, polyol esters and/or polyvinyl ethers. Polyol esters and polyvinyl ethers are prefarred. When another lubricsnt ail is used in combination with the polyalkylene glycol it is prefersble for the miscibility of the HFO-1234yf and/or of the HFC-134a wtth this ail to be greater than the respective miscibility of HFD-I234yf and/or of HFC-i34a with the polyalkylene glycol. This is especially the case for at least some of the oils of polyol ester or paly vinyl ether typa.
Tha heet-transfer compounds mainly used in the context of the present invention are HFO-1234yf and HFC-134a,
However, the heat-transfer compositions according to the invention may optionally comprise one or mora additional heat-transfer compounds, besides HFO-1234yf and HFC-I34a. These additional heaMransfer compounds may be chosen especially from hydrocarbons, hydrofluorocarbons, ethers, hydrofluoro ethers and fluora olefins.
According to particular embodiments, the heat-transfer fluids according to the invention may be ternary compositions (consisting of three heat-trsnsfer compounds) or quaternary compositions (consisting of four heaMransfar compounds), in combination with the lubricant ail to form the heat-transfer compositions according to the invention.
Howaver, binary heat-transfer fluids ara preferred.

The term 'binary fluid11 means either a fluid consisting of a mixture of HFO-1234yf and HFC-134a; or a fluid consisting assentially of HFCM234yf and HFC-134a, but which may contain impurities to a proportion of leiss than 1%H preferably Jess than 0.5%, preferably less then 0.1%. preferably less than 0.05% and preferably less than 0.01%.
According to particular embodiments, the proportion of HFQ-1234yf in tha haat-transfer fluid may be: from 0,1 to 5%; or from 5 to 10%; or from 10 to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from 30 to 35%; or from 35 to 40%; or from 40 to 45%; or from 45 to 50%; or from 50 to 55%; or from 55 to 60%; or from 60 to 65%; or from 65 to 70%; or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 65 to 90%; or from 90 to 95%; or from 95 to 99.9%.
According to particular embodimentsH the proportion of HFC-134a in the heat-transfer fluid may be: from 0.1 to 5%; or from 5 to 10%; or from 10 to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from 30 to 35%: or from 35 to 40%; or from 40 to 45%; or from 45 to 50%; or from 50 to 55%: or from 55 to 60%; or from 60 to 65%; or from 65 to 70%; or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 85 to 90%; or from 90 to 95%; or from 95 to 99,9%.
The values given in tha three preceding paragraphs apply to the heat-transfer fluid without lubricant oil, and not to the heat-transfer composition which comprises the heat-transfer fluid, the lubricant Oil and optionally other additives.
Tha other additives that may be usad in the context of the invention may be chosen especially from stabilizers, surfactants, tracers, fluorescein, odorant agents and sotubilizers.
The stabilizer(s). whan they are present, preferably represent not more than 5% by mass in the heat-transfer composition. Among the stabili2ers, mention may be made espaciaily of nitromathsne, ascorbic acid, terephthalic acid, azoles such as tolutriazole or banzotriazole, phanolic compounds such as tocopherol, hydroquinone, t-butylhydroquinona, 2,6-di-tert-butyl-4-methylphenol, epoxides (optionally fluorinated or perfluorinated slkyl, or alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, ally! glycidyl ether or butylphanyl glycidyl etharH phosphites, phosphonates, thiols and lactonas.
As tracers (which can be dateded), mention may be made of deuteratad or non-deuterated hydrofluorocsrbons, deuterated hydrocarbons. perfluorocarbons, fluoro ethers, bromo compounds, iodo compounds, alcohols, aldehydes, Ketones, nitrous oxide and combinations thereof The tracer is

different from the heat-transfer compound(s) of which the heat-transfer fluid is composed.
Examples of solubilizers that may be mentioned include hydrocarbons, dimethyl ether, polyoxyalkylene ethers, amides, ketones, nitriles, chlorocarbons, esters, lactones, aryl ethers, fluoro ethers and 1,1,1-trifluoroaiksnes. The solubilizer is different from the heat-transfer compound(s) of which the heat-transfer fluid is composed.
Fluorescers thst may be mentioned include nsphthalimides, perylenes, coumahns, anthracenes, phenanthracenesr xanthenes. thioxanthenes, nsphthoxanthenes snd fluoresceins, snd derivatives snd combinations thereof
Odorant agents that may be mentioned include slkylacrylates. ally) aery lates, scry lie acids, scry lie esters, slkyl ethers, alkyl esters, alkynes. aldehydes, thiols, thio ethers, disulfides, sllylisothiocysnstes, alksnoic scids, smines, norbornenes, norbornene derivatives, cyclohexene, heterocyclic aromatic compounds, sscaridoie and o-methoxy(methyl)phenol, snd combinstions thereof.
The heat-transfer process according to the invention is bssed on the use of an installation comprising s vspor compression circuit which contains a heat-transfer composition (namely a heat-transfer fluid and at lesst onelubricsnt oil). The heat-transfer process may be a process for heating or cooling s fluid or a body.
The vspor compression circuit comprises at lesat one evaporator, a compressor, a condenser end a depressunzer, and siso lines for transporting the fluid between these components. The evsporator and the condenser comprise s heat exchanger for exchanging heat between the heat-transfer fluid snd another fluid or body.
As compressor, use may be made especislly of a single-stage or multi-stage centrifugal compressor or a centrifugsl mini-compressor Rotary, piston or screw compressors may also be used. The compressor may be driven by sn electric motor or by s gas turbine (for exsmple fed with the exhaust gsses of a vehicle, or mobile applications) or by gearing.
The installation may comprise an electricity-generating turbine (Ranking cycle).
The instellation may si so optionslly comprise st lesst one heat-exchange fluid circuit used for transmitting heat (with or without a chsnge of stste) between the heat-transfer fluid circuit and the fluid or body to be hested or cooled.

The installation may also optionally comprise two (or more) vapor compression circuits, containing identical or different heat-transfer fluids. For example, the vapor compression circuits may be coupled together.
The vapor compression circuit operates according to a standard vapor compression cycle. The cycle comprises the change of state of the heat-transfer fluid from a liquid phese (or liquid/vapor two-phase system) to a vepor phase at a relatively low pressure, followed by compression of the fluid in vapor phese up to a relatively high pressure, the change of state (condensation) of the heat-transfer fluid from the vapor phase to the liquid phase at e relatively high pressure, end reduction of the pressure to recommence the cycle.
In the case of a cooling process, heat derived from the fluid or body that is being cooled (directly or indirectly, via a heat-exchange fluid) is absorbed by the heat-transfer fluid, during the evaporation of the latter, this taking place et e relatively low temperature relative to the environment. The cooling processes comprise air-conditioning processes (with mobile installations, for example in vehicles, or stationery installations), refrigeration and freezing processes or cryogenic processes.
In the case of a heating process, heat is yielded (directly or indirectly, via a heat-exchange fluid) from the heat-trensfer fluid, during the condensation of the latter, to the fluid or body that is being haated, this taking place et a reletively high temperature relative to the environment. In this cese, the installation for transferring heat is known as a "heat pump'1.
It is possible to use any type of heet exchanger for the implementation of the heat-transfer fluids according to the invention, and especially co-current heat exchangers or, preferably, counter-current heat exchangers. It is also possible to use micro-channel exchengers.
The invention in particular makes it possible to use cooling processes at moderate temperature, i.e. thoae in which the temperature of the cooled fluid or body is from-15X to 15aC, preferably from-10X to 10DC and more particularly preferably from -5DC to 5X (ideally about 0°C).
The invention also makes it possible to use heating processes at moderate temperature, i.e. those in which the temperature of the heated fluid or body is from 30X to 80°C, preferably from 35°C to 55DC and more particularly preferably from 40DC to 50eC (ideally about 45DC).
In the processes of "cooling or heating at moderate temperature" mentioned above, the inlet temperature of the heat-transfer fluid into the evaporator is preferably from -20°C to 10flC, especially from -15QC to 5°C, mora

particularly prefarably from -10°C to 0°C, for example about -5°C; and the condensation start temperature of the heat-transfer fluid in the condenser is preferably from 25°C to 9{TCh especially from 30"C to 70°C, more particularly preferably from 35°C to 55X, for example about 50°C. These processes may be refrigeration, sir-conditioning or nesting processes.
The invention also makes it possibta to use cooling processes at low
temperature, iL©L those in which the temperature of the cooled fluid or body is
from -40DC to -10°C, prefarably from -35°C to -25°C and more particularly
preferably from -30eC to -20°C (ideally about -25°C),
i In the "low-temperature cooling" processes mentioned above, the inlet
temperature of the heet-transfer fluid into the evaporator is preferably from -45°C to -15'C, especially from -40°C to -20°C and more particularly preferably from -35°C to -25DCh for example about -3CTC; and the condensation start temperature of the heat-transfer fluid in the condenser is preferably from 25°C to 80°Ch especially from 3CTC to 60°C and more particularly preferably from 35X to 55X, for example about 40eC.
It should be noted that the addition of HFC-134a to a heat-transfer fluid consisting of HFO-1234yf (or comprising HFO-1234yf) improves the miscibility of the heat-transfer fluid with the lubricant oil, i.e. increaaes the threshold temperature for appearance of the non-miscibility zone (defined as being the temperature from which the compounds in the liquid phase form an emulsion), snd thus makes it possible to increase the possibilities of use of the heat-transfer fluid, for example by enabling use at a higher condensation temperature.
More generally, the invention enables the replacement of any heat-transfer fluid in all hest transfer applications, for example in motor vehicle air-conditioning. For example, the heat-trsnsfer fluids and heat-transfer compositions according to the invention may serve to replace:
- 1,1,1,2-tetrafluoroethsne {R134a);
- l,1-difluoroethane(R152a);
- 1h1,1,3.3-pentafluoroprooane(R245fa);
- mixtures of pentafluoroethane (R125), 1,1,1,2-tetrsfluoroethane (Rl34a) and isobutane (R600a), namely R422;
- chlorodifluoromethane (R22);
- the mixture of 512% thloropentafluoroethene and 48.8% chlorodifluoromethene (R22). namely R502;
- any hydrocarbon;

- the mixture of 2Q% difluoromethane (R32), 40% pentafluoroethane (R125) and 40% 1,1,1,2-tetrafluoroethane(Rl34a)r namely R407A;
- the mixture of 23% difluoromethane (R32)r 25% pentefluoroethane (R125) end 52% 1r1,1,2-tetrafluoraethane(R134a), namely R4D7C;
- the mixture of 30% difluoromethane (R32), 30% pentafluoroethene (R125) and 40% 1,1,1,2-tetrafluoroethene(Rl34a). nemely R407F:
- R1234yf(2,3r3r3-tetrafluoropropene);
- R1234ze (1,3,3.3-tetrafluoropropene).
EXAMPLE
The example that follows illustrates the invention without limiting it.
In this example, the miscibility of HFO-1234yf, HFC-134e and mixturee thereof with a lubricant oil of the type PAG ND6 is studied.
An autoclave is placed in a glass-panelled tank fed with a ;hermostatically maintained bath of water or of glycol-water depending on the est temperatures, from -3Q°C to +B0DC.
For each heat-transfer fluid tested (mixture of HF0-I234yf and HFC-134a in given proportions), the heat-transfer fluid is introduced into the autoclave. Next, e first amount of dafined lubricant oil is edded, and the mixture s stirred. The temperature in the autoclave is increased until an emulsion is obtained, indicating the non-miscibility of the mixture. The mixture is then pooled, an additional amount of oil is added thereto and this operation is performed fteratively.
This procedure makes it possible to produce, for each given HFO-l234yf/HFC-134a transfer fluid, a curve for visualization of the non-miscibility :oneofthe mixture with the oil PAGr as a function of the temperature.
Reciprocally, exploitation of the date makes it possible to determine, for e given lubricant oil concentration, the non-miscibility threshold temperature as a unction of the proportion of HFC~134a in the HFO-1234yf/HFC~134a mixture. This is shown in figure 1, for en amount of lubricant oil of 17%.
When the mixture does not contain any HFC-134a, the emulsion appears ^ a tempereture of 26°C. On the other hand, whan the mixture does not contain *ny HFO-1234yf, the emulsion appears ete temperature of 69"C. This makes it jossible to plot a theoretical dashed line, representing the expected emperature for the eppearance of an emulsion with a mixture of HFO-1234yf

and of HFC-134a, this being obtained by weighting of the respective miscibility temperatures.
Experimentally, it is noted, however, that the miscibility zone is larger than that theoretically expected. This means that there is a synergistic effect between HFO-1234yf and HFC-134a with regard to the miscibility with the lubricant oil,
A similar result is obtsined with an amount of lubricant oil of 30%, for example, instead of 17%. It is thus observed that the addition of 20% HFC-I34a to HFO-1234yf makes it possible to improve the miscibility zone by about 10 degrees relative to the expected value.

1. A composition comprising 2,3,3,3-tetrafluoropropene. 1,1,1,2-tetrsfluoroethane and polyalkylene glycol.
2. The composition as claimed in claim 1h in which 2.3,3,3-tetrafluoropropene, 1,1.1 ,2-tetrafluoroethane and the polyslkylene glycol represent at least 95%. preferably at least 99% and more particularly preferably at least 99.9% of the composition,
3. The composition as claimed in claim 1 or 2, comprising from 1% to 99% of polyalkylene glycol, preferably from 5% to 50%, more particularly preferably from 10% to 40% snd ideally from 15% to 35%.
4. The composition as claimed in one of claims 1 to 3, in which the mass ratio between 2,3,3,3-tetrafluoropropene and 1,1,1,2-tetrsfluoroethsne is from 1/99 to 99/1, preferably from 25/75 to 95/5, more particulsrly preferably from 50/50 to 92/8 and ideslly from 55/45 to 92/8.
5. The composition as claimed in one of claims 1 to 4, in which the polyalkylene glycol hss a viscosity from 1 to 1000 centistokes at 40°C, preferably from 10 to 200 centistokes et 40°C, more psrticularly preferably from 20 to 100 centistokes at 40°C and ideally from 40 to 50 centistokes et 40°C,
6. The composition as claimed in one of claims 1 to 5. also comprising: one or more additives chosen from haat-transfer compounds, lubricants, stabilizers. surfactants, tracers. fluoresces, odorant agants, solubihzers, and mixtures thereof; preferably one or more additives chosen from stabilizers, surfactants, tracers, fluorescers, odorant agents and solubilizera. and mixtures thereof.

7. The use of a polyalkylene gEycol as a lubricant oil in a vapor compression circuit, in combination with a heat-transfer fluid comprising, end preferably consisting of, a mixture of 2,3,3,3-tetrafluorapropene and 1,1,1,2-tetrafluoroethane^
8. The use es claimed in claim 7, in which the polyalkylene gEycol is used in a proportion of from 1% to 99%, preferably from 5% to 50%, more particularly preferably from 10% to 40% and ideally from 15% to 35%, relative to the sum of the polyalkylene glycol and of the heat-transfer fluid.
9. The use as claimed in claim 7 or 8, in which the mass ratio between 2,3,3.3-tetrafluorapropene and 1,1,1,2-tetrafluoroethane in the heat-transfer fluid is from 1/99 to 99/1, preferably from 25/75 to 95/5, more particularly preferably from 50/50 to 92/8 and ideally from 55745 to 92/6.
10. The use as claimed in one of claims 7 to 9, in which the polyalkylene glycol has a viscosity from 1 to 1000 centistokes at 40DC, preferably from 10 to 200 centistokes at 40*C, more particularly preferably from 20 to 100 centistokes at 40"C and ideally from 40 to 50 centistokes et 40'C.
11. A heat-transfer installation comprising a vapor compression circuit containing a heat-transfer composition which is a composition as claimed in one of claims 1 to 6.
12. The installation as claimed in daim 11. chosen from mobila or stationary heat-pump hesting, eir-conditioning, refrigeration, freezing and Rsnkine-cyde installations, and especially from motor vehicle air-conditioning installations,
13. A process for heating or cooling a fluid or a body by means of a vapor compreaaion drcuit containing a heat-transfer fluid, said proceas successively comprising at least partial evaporation of the heat-transfer fluid, compression of the heat-transfer transfer fluid,

at least partial condensation of the heat-transfer fluid and depressurization of the heat-transfer fluid, in which the heat-transfer fluid is combined with a lubricant oil to form a heat-transfer composition, said heat-transfer composition being a composition as daimad in on© of claims 1 to 6.
14. A process for raducing the environmental impact of a heat-transfer installation comprising a vapor compression circuit containing an initial heat-transfer fluid, said process comprising a step of replacing the initial heat-tranafer fluid in the vapor compression circuit with a final heat-transfer fluid, the final heat-transfer fluid having a Eowar GWP than the initial haat-transfer fluid, in which the final heat-transfer fluid is combined with a lubricant oil to form a heat-transfer composition, said heat-transfer composition baing a composition as claimed in one of claims 1 to 6,
15. The use of 1,1,1,2-tetrafluoroethene for increasing the miscibility of 2,3,3,3-tetrafluoropropene with a lubricant oil
16. The use as claimed in daim 15, in which the lubricant oil is a polyalkylene glycol, and preferably has a viscosity from 1 to 1000 centistokes at 40°C, more preferably from 10 to 200 centistokes at 40"C, more particularly preferably from 20 to 100 cantistokes at 40"C and ideally from 40 to 50 centistokea at 4Q"C.
17. The use as claimed in claim 15 or 16, in which the 1,1,1.2-tetrafluoroethane is used in a proportion of from 1% to 99%. preferably from 5% to 75%, more particularly preferably from 8% to 50% and ideally from 6% to 45%, relative to the sum of 1,1,1,2-tatrafluoroethane and 2,3,3,3-tetrafluoropropene.
16. A kit comprising:
- a heat-transfar fluid comprising 2.3,3,3-tetrafluoropropana and 1.1,1,2-tetrafluoroethane, on the one hand;
- e lubricant oil comprising a polyalkylene glycol, on the other hand;

for use in a heat-transfer installation comprising a vapor compression circuit