TERNARY COMPOSITIONS FOR HIGH-CAPACITY REFRIGERATION
The present invention relates to compositions
containing 2,3,3,3-tetrafluoropropene and uses thereof
as heat-transfer fluids, blowing agents, solvents and
aerosols.
The problems posed by substances which delete the atmospheric ozone layer (ODP: ozone depletion potential) were addressed in Montreal, where the protocol imposing a reduction in the production and use of chlorofluorocarbons (CFCs) was signed. This protocol has been the subject of amendments which have required that CFCs be withdrawn and have extended regulatory control to other products, including hydrochloro-fluorocarbons (HCFCs).
The refrigeration and air-conditioning industry has invested a great deal in the replacement of these refrigerants, and as a result, hydrofluorocarbons (HFCs) have been marketed.
The (hydro)chlorofluorocarbons used as blowing agents or solvents have also been replaced with HFCs.
In the automotive industry, the air-conditioning systems for vehicles sold in many countries have changed from a chlorofluorocarbon (CFC-12) refrigerant to a hydrofluorocarbon (1,1,1,2-tetrafluoroethane: HFC-134a) refrigerant which is less harmful to the ozone layer. However, from the viewpoint of the objectives set by the Kyoto protocol, HFC-134a (GWP = 1300) is considered to have a high warming potential. The contribution to the greenhouse effect of a fluid is quantified by a criterion, the GWP (global warming potential) which indexes the warming potential by taking a reference value of 1 for carbon dioxide.

Since carbon dioxide is non-toxic and non-flammable and has a very low GWP, it has been proposed as a refrigerant in air-conditioning systems as a replacement for HFC-134a. However, the use of carbon dioxide has several drawbacks, in particular linked to the very high pressure at which it is used as a refrigerant in the existing apparatuses and technologies.
Document WO 2004/037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, in particular penta-fluoropropene and tetrafluoropropene, preferably having a GWP at most of 150, as heat-transfer fluids.
Document WO 2005/105947 teaches the addition to tetra-fluoropropene, preferably 1,3,3,3-tetrafluoropropene, of a blowing coagent such as difluoromethane, penta-fluoroethane, tetrafluoroethane, difluoroethane, hepta-fluoropropane, hexafluoropropane, pentafluoropropane, pentafluorobutane, water and carbon dioxide.
Document WO 2006/094303 discloses binary compositions of 2,3,3,3-tetrafluoropropene (HFO-12 34yf) with di-fluoromethane (HFC-32), and of 2,3,3,3-tetrafluoro¬propene with 1,1,1,2-tetrafluoroethane (HFC-134a).
Quaternary mixtures comprising 1,1,1,2,3-pentafluoro¬propene (HFO-1225ye) in combination with difluoro-methane, 2,3,3,3-tetrafluoropropene and HFC-134a were disclosed in this document. However, 1,1,1,2,3-penta-fluoropropene is toxic.
Quaternary mixtures comprising 2,3,3,3-tetrafluoro¬propene in combination with iodotrifluoromethane (CF3I), HFC-32 and HFC-134a have also been disclosed in document WO 2006/094303. However, CF3I has a non-zero ODP and poses stability and corrosion problems.

The applicant has now developed 2,3,3,3-tetrafluoropropene compositions which do not have the abovementioned drawbacks and have both a zero ODP and a GWP which is lower than that of the existing heat-transfer fluids such as R410A (binary mixture of pentafluoroethane (50% by weight) and HFC-32 (50% by weight)).
The compositions used as a heat-transfer fluid in the present invention have a critical temperature greater than 87°C (critical temperature of R410A is 70.5°C). These compositions can be used in heat pumps for providing heat at temperatures up to 6 5°C but also at higher temperatures up to 8 7°C (temperature range at which R410A cannot be used).
The compositions used as heat-transfer fluid in the present invention have temperatures at the compressor outlet equivalent to the values given by R-410A. The condenser pressures are lower than the pressures of R-410A and the compression ratios are also lower. These compositions can replace R-410A without changing compressor technology.
The compositions used as a heat-transfer fluid in the present invention have saturation vapor densities which are less than the saturated vapor density of R410A. The volumetric capacities given by these compositions are equivalent to the volumetric capacity of R410A (between 90 and 99%) . By virtue of these properties, these compositions can operate with smaller pipe diameters and therefore less pressure drop in the steam pipework, thereby increasing the performance levels of the equipment.
The compositions according to the present invention are characterized in that they essentially contain from 15

to 50% by weight of 2,3,3,3-tetrafluoropropene, from 5 to 4 0% by weight of HFC-134a and from 4 5 to 6 0% by weight, preferably from 45 to 50% by weight of HFC-32.
The compositions according to the present invention can be used as heat-transfer fluids, preferably in compression systems and advantageously with exchangers operating in counterflow mode or in cross-flow mode with counterflow tendency. They are particularly suitable for systems of high-capacity refrigeration per unit volume swept by the compressor.
In compression systems, the heat exchange between the refrigerant and the heat sources takes place by means of heat-transfer fluids. These heat-transfer fluids are in the gaseous state (the air in air-conditioning and direct expansion refrigeration), liquid state {the water in domestic heat pumps, glycolated water) or two-phase state.
There are various modes of transfer:
the two fluids are arranged in parallel and travel in the same direction: co-flow (antimethodic) mode ;
the two fluids are arranged in parallel but travel in the opposite direction: counterflow (methodic) mode ;
the two fluids are positioned perpendicularly: cross-flow mode. The cross-flow may be with co-flow or counterflow tendency,*
one of the two fluids makes a U-turn in a wider pipe, which the second fluid passes through. This configuration is comparable to a co-flow exchanger over half the length, and for the other half, to a counterflow exchanger: pinhead mode.

The compositions according to the present invention are advantageously used in stationary air conditioning, preferably as a replacement for R-410A.
The compositions according to the present invention can be stabilized. The stabilizer preferably represents at most 5% by weight relative to the total composition.
As stabilizers, mention may in particular be made of nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butyl hydroquinone or 2,6 -di-tert-butyl-4-methylphenol, epoxides (alkyl, optionally fluorinated or per-fluorinated, or alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether or butylphenyl glycidyl ether, phosphites, phosphates, phosphonates, thiols and lactones.
The compositions according to the present invention, as a heat-transfer agent, can be employed in the presence of lubricants such as mineral oil, alkylbenzene, polyalkylene glycol and polyvinyl ether.
The compositions according to the present invention can also be used as blowing agents, aerosols and solvents.
EXPERIMENTAL SECTION
Calculation tools
The RK-Soave equation is used for calculating the densities, enthalpies, entropies and liquid/vapor equilibrium data of the mixtures. The use of this equation requires knowledge of the properties of the pure bodies used in the mixtures in question and also the interaction coefficients for each binary mixture.

The data required for each pure body are: The boiling point/ the critical temperature and the critical pressure, the curve of pressure as a function of temperature starting from the boiling point up to the critical point, and the saturated liquid and saturated vapor densities as a function of temperature.
HFC-32, HFC-134a:
The data on these products aer published in the ASHRAE Handbook 2005 chapter 20, and are also available from Refrop (software developed by NIST for calculating the properties of refrigerants).
HFO-1234yf:
The data of the temperature-pressure curve for HFO-12 34yf are measured by the static method. The critical temperature and the critical pressure are measured using a C80 calorimeter sold by Setaram. The densities, at saturation as a function of temperature, are measured using the vibrating tube densitometer technology developed by the laboratories of the Ecole des Mines of Paris.
Interaction coefficient of the binary mixtures The RK-Soave equation uses binary interaction coefficients to represent the behavior of the products in mixtures. The coefficients are calculated as a function of the experimental liquid/vapor equilibrium data.
The technique used for the liquid/vapor equilibrium measurements is the static-cell analytical method. The equilibrium cell comprises a sapphire tube and is equipped with two electromagnetic ROLSITM samplers. It is immersed in a cryothermostat bath (HUBER HS40). A magnetic stirrer with a field drive rotating at varying speed is used to accelerate reaching the equilibria. The analysis of the samples is carried out by gas

chromatography (HP58 90 series II) using a katharometer (TCD).
HFC-32/HFO-12 34yf, HFC-134a/HFO-1234yf:
The liquid/vapor equilibrium measurements on the binary mixture HFC-32/HFO-1234yf are carried out for the following isotherms: -10°C, 30°C and 70°C. The liquid/vapor equilibrium measurements on the binary mixture HFC-134a/HFO-1234yf are carried out for the following isotherms: 20°C. HFC-32/HFO-134a:
The liquid/vapor equilibrium data for the binary mixture HFC-134a/HFC-32 are available from Refprop. Two isotherms (-20°C and 20°C) and one isobar (30 bar) are used to calculate the interaction coefficients for this binary mixture.
Compression system
A compression system equipped with a counterflow
condenser and evaporator, with a screw compressor and
with an expansion valve is considered.
The system operates with 15°C of overheat and 5°C of
undercooling. The minimum temperature difference
between the secondary fluid and the refrigerant is
considered to be about 5°C.
The isentropic efficiency of the compressors depends on
the compression ratio. This efficiency is calculated
according to the following equation:
r\lsen=a-b(z-cf-~ (1)
x-e
For a screw compressor, the constants a, b, c, d and e of the isentropic efficiency equation (1) are calculated according to the standard data published in the "Handbook of air conditioning and refrigeration, page 11.52".

The %CAP is the percentage of the ratio of the
volumetric capacity supplied by each product over the
capacity of R410A.
The coefficient of performance (COP) is defined as
being the useful power supplied by the system over the
power provided or consumed by the system.
The Lorenz coefficient of performance (COPLorenz) is a
reference coefficient of performance. It is a function
of temperatures and is used for comparing the COPs of
various fluids.
The Lorenz coefficient of performance is defined as
follows:
(The temperatures T are in K)
rpcondenser rpcondenser rpcondenser { O average inlet outlet » '
rpevaporator rpevaporator rpevaporator { "1 average outlet inlet » '
The Lorenz COP in the case of air-conditioning and refrigeration is:
rpevaporator
COPlorenz= ^^ (4)
rpcondenser rpevaporator *
average average
The Lorenz COP in the case of heating is:
rpcondenser
COPlorenz= j-^E (5)
rpcondenser rpevaporator
average average
For each composition, the coefficient of performance of
the Lorenz cycle is calculated as a function of the
corresponding temperatures.
The %COP/COPLorenz is the ratio of the COP of the
system relative to the COP of the corresponding Lorenz
cycle.

Heating mode results
In heating mode, the compression system operates between a temperature for inlet of the refrigerant into the evaporator of -5°C and a temperature for inlet of the refrigerant into the condenser of 50°C. The system supplies heat at 45°C.
The performance levels of the compositions according to the invention under the heating mode operating conditions are given in table 1. The values of the constituents (HFO-12 34yf, HFC-32, HFC-134a) for each composition are given as percentage by weight.

Cooling or air-conditioning mode results
In cooling mode, the compression system operates between a temperature for inlet of the refrigerant into the evaporator of -5°C and a temperature for inlet of the refrigerant into the condenser of 50°C. The system supplies refrigeration at 0°C.
The performance levels of the compositions according to the invention under the cooling mode operating conditions are given in table 2. The values of the constituents (HFO-1234yf, HFC-32, HFC-134a) for each composition are given as percentage by weight.

CLAIMS
1. A composition essentially containing from 15 to 50% by weight of 2, 3 , 3 , 3-tetrafluoropropene, from 5 to 40% by weight of HFC-134a and from 45 to 60% by weight of HFC-32, preferably from 45 to 50% by weight of HFC-32.
2. The composition as claimed in claim 1, characterized in that it is stabilized.
3. A heat-transfer fluid comprising the composition as claimed in claim 1 or 2.
4. The heat-transfer fluid as claimed in claim 3, characterized in that it is used in compression refrigeration systems, preferably with exchangers operating in counterflow mode.
5. The heat-transfer fluid as claimed in claim 3 or 4, characterized in that it is used as a replacement for R-410A.
6. The heat-transfer fluid as claimed in any one of claims 3 to 5, characterized in that it is employed in the presence of a lubricant.
7. Blowing agents comprising the compositions as claimed in claim 1 or 2.
8. Solvents comprising the compositions as claimed in claim 1 or 2.
9. Aerosols comprising the compositions as claimed in claim 1 or 2.