WO2014072713A1

WO2014072713A1 - Heat transfer compositions

Info

Publication number: WO2014072713A1
Application number: PCT/GB2013/052914
Authority: WO
Inventors: Robert E. Low
Original assignee: Mexichem Amanco Holding S.A. De C.V.; Mexichem Uk Limited
Priority date: 2012-11-06
Filing date: 2013-11-06
Publication date: 2014-05-15
Also published as: GB201219962D0

Abstract

The invention provides a heat transfer composition comprising from about 61 to about 69 % by weight frans-1,3,3,3-tetrafluoropropene (R-1234ze(E)) and from about 31 to about 39 % by weight 1,1,1,2-tetrafluoroethane (R-134a).

Description

HEAT TRANSFER COMPOSITIONS

The invention relates to heat transfer compositions, and in particular to heat transfer compositions which may be suitable as replacements for existing refrigerants such as R- 134a, R-152a, R-1234yf, R-22, R-410A, R-407A, R-407B, R-407C, R507 and R-404a.

The listing or discussion of a prior-published document or any background in the specification should not necessarily be taken as an acknowledgement that a document or background is part of the state of the art or is common general knowledge.

Mechanical refrigeration systems and related heat transfer devices such as heat pumps and air-conditioning systems are well known. In such systems, a refrigerant liquid evaporates at low pressure taking heat from the surrounding zone. The resulting vapour is then compressed and passed to a condenser where it condenses and gives off heat to a second zone, the condensate being returned through an expansion valve to the evaporator, so completing the cycle. Mechanical energy required for compressing the vapour and pumping the liquid is provided by, for example, an electric motor or an internal combustion engine. In addition to having a suitable boiling point and a high latent heat of vaporisation, the properties preferred in a refrigerant include low toxicity, non-flammability, non-corrosivity, high stability and freedom from objectionable odour. Other desirable properties are ready compressibility at pressures below 25 bars, low discharge temperature on compression, high refrigeration capacity, high efficiency (high coefficient of performance) and an evaporator pressure in excess of 1 bar at the desired evaporation temperature.

Dichlorodifluoromethane (refrigerant R-12) possesses a suitable combination of properties and was for many years the most widely used refrigerant. Due to international concern that fully and partially halogenated chlorofluorocarbons were damaging the earth's protective ozone layer, there was general agreement that their manufacture and use should be severely restricted and eventually phased out completely. The use of dichlorodifluoromethane was phased out in the 1990's.

Chlorodifluoromethane (R-22) was introduced as a replacement for R-12 because of its lower ozone depletion potential. Following concerns that R-22 is a potent greenhouse gas, its use is also being phased out. Whilst heat transfer devices of the type to which the present invention relates are essentially closed systems, loss of refrigerant to the atmosphere can occur due to leakage during operation of the equipment or during maintenance procedures. It is important, therefore, to replace fully and partially halogenated chlorofluorocarbon refrigerants by materials having zero ozone depletion potentials.

In addition to the possibility of ozone depletion, it has been suggested that significant concentrations of halocarbon refrigerants in the atmosphere might contribute to global warming (the so-called greenhouse effect). It is desirable, therefore, to use refrigerants which have relatively short atmospheric lifetimes as a result of their ability to react with other atmospheric constituents such as hydroxyl radicals, or as a result of ready degradation through photolytic processes. R-410A and R-407 refrigerants (including R-407A, R-407B and R-407C) have been introduced as a replacement refrigerant for R-22. However, R-22, R-410A and the R-407 refrigerants all have a high global warming potential (GWP, also known as greenhouse warming potential). 1 ,1 ,1 ,2-tetrafluoroethane (refrigerant R-134a) was introduced as a replacement refrigerant for R-12. R-134a is an energy efficient refrigerant, used currently for automotive air conditioning. However it is a greenhouse gas with a GWP of 1430 relative to CO₂ (GWP of CO2 is 1 by definition). The proportion of the overall environmental impact of automotive air conditioning systems using this gas, which may be attributed to the direct emission of the refrigerant, is typically in the range 10-20%. Legislation has been passed in the European Union to rule out use of refrigerants having GWP of greater than 50 for new models of car. The car industry operates global technology platforms, and in any event emission of greenhouse gas has global impact, thus there is a need to find fluids having reduced environmental impact (e.g. reduced GWP) compared to HFC-134a.

R-152a (1 ,1-difluoroethane) has been identified as an alternative to R-134a. It is somewhat more efficient than R-134a and has a greenhouse warming potential of 120. However the flammability of R-152a is judged too high, for example to permit its safe use in mobile air conditioning systems. In particular it is believed that its lower flammable limit in air is too low, its flame speeds are too high, and its ignition energy is too low. Thus there is a need to provide alternative refrigerants having improved properties such as low flammability. Fluorocarbon combustion chemistry is complex and unpredictable. It is not always the case that mixing a non-flammable fluorocarbon with a flammable fluorocarbon reduces the flammability of the fluid or reduces the range of flammable compositions in air. For example, the inventors have found that if non-flammable R-134a is mixed with flammable R-152a, the lower flammable limit of the mixture alters in a manner which is not predictable. The situation is rendered even more complex and less predictable if ternary or quaternary compositions are considered.

Particular problems in relation to flammability may exist where the refrigerant is a blend. The exact flammability properties of a blend comprising a relatively flammable refrigerant and a relatively non-flammable refrigerant may not be predictable. When a refrigerant blend is stored in a vessel, if that vessel develops a leak, the refrigerant will often leak from the vessel at different proportionate rates, meaning that as the refrigerant escapes, the composition of the blend remaining in the vessel may change. The differential leakage rates can also vary with temperature. This change in composition can lead to the refrigerant contained in the vessel changing from a non-flammable composition to a flammable composition as a proportion of it leaks. It would be advantageous to obtain blended refrigerant compositions which were still considered non-flammable even if the vessel in which the blend is stored leaked.

There is also a need to provide alternative refrigerants that may be used in existing devices such as refrigeration devices with little or no modification.

R-1234yf (2,3,3,3-tetrafluoropropene) has been identified as a candidate alternative refrigerant to replace R-134a in certain applications, notably the mobile air conditioning or heat pumping applications. Its GWP is about 4. R-1234yf is flammable and its flammability characteristics are regarded in some quarters as not being acceptable for certain applications such as mobile air conditioning.

The environmental impact of operating an air conditioning or refrigeration system, in terms of the emissions of greenhouse gases, should be considered with reference not only to the so-called "direct" GWP of the refrigerant, but also with reference to the so- called "indirect" emissions, meaning those emissions of carbon dioxide resulting from consumption of electricity or fuel to operate the system. Several metrics of this total GWP impact have been developed, including those known as Total Equivalent Warming Impact (TEWI) analysis, or Life-Cycle Carbon Production (LCCP) analysis. Both of these measures include estimation of the effect of refrigerant GWP and energy efficiency on overall warming impact. Emissions of carbon dioxide associated with manufacture of the refrigerant and system equipment should also be considered.

The energy efficiency and refrigeration capacity of R-1234yf have been found to be significantly lower than those of R-134a and in addition the fluid has been found to exhibit increased pressure drop in system pipework and heat exchangers. A consequence of this is that to use R-1234yf and achieve energy efficiency and cooling performance equivalent to R-134a, increased complexity of equipment and increased size of pipework is required, leading to an increase in indirect emissions associated with equipment. Furthermore, the production of R-1234yf is thought to be more complex and less efficient in its use of raw materials (fluorinated and chlorinated) than R-134a. Current projections of long term pricing for R-1234yf is in the range 10-20 times greater than R-134a. This price differential and the need for extra expenditure on hardware will limit the rate at which refrigerants are changed and hence limit the rate at which the overall environmental impact of refrigeration or air conditioning may be reduced. In summary, the adoption of R-1234yf to replace R-134a will consume more raw materials and result in more indirect emissions of greenhouse gases than does R-134a.

A principal object of the present invention is therefore to provide a heat transfer composition which is usable in its own right or suitable as a replacement for existing refrigeration usages which should have a reduced GWP, yet have a capacity and energy efficiency (which may be conveniently expressed as the "Coefficient of Performance") ideally within 10% of the values, for example of those attained using existing refrigerants (e.g. R-134a, R-152a, R-1234yf, R-22, R-410A, R-407A, R-407B, R-407C, R507 and R- 404a), and preferably within less than 10% (e.g. about 5%) of these values. It is known in the art that differences of this order between fluids are usually resolvable by redesign of equipment and system operational features. The composition should also ideally have reduced toxicity and acceptable flammability.

The subject invention addresses the above deficiencies by the provision of a heat transfer composition comprising from about 61 to about 69 % by weight trans- ,3,3,3- tetrafluoropropene (R-1234ze(E)), and from about 31 to about 39 % by weight 1 ,1 ,1 ,2- tetrafluoroethane (R-134a).

All of the chemicals herein described are commercially available. For example, the fluorochemicals may be obtained from Apollo Scientific (UK).

As used herein, all % amounts mentioned in compositions herein, including in the claims, are by weight based on the total weight of the compositions, unless otherwise stated. By the term "about", as used in connection with numerical values of amounts of components in % by weight, we include the meaning of ± 0.5 % by weight.

In an embodiment, the compositions of the invention comprise from about 62 to about 68 % by weight R-1234ze(E) and from about 32 to about 38 % by weight R-134a.

Preferably, the compositions of the invention comprise from about 63 to about 67 % by weight R-1234ze(E) and from about 33 to about 37 % by weight R-134a.

In one aspect, the compositions of the invention comprise from about 64 to about 66 % by weight R-1234ze(E) and from about 34 to about 36 % by weight R-134a.

However in a further aspect, conveniently the compositions of the invention comprise from about 61 % to about 65% by weight R-1234ze(E) and from about 35 to about 39% by weight R-134a.

For the avoidance of doubt, it is to be understood that the stated upper and lower values for ranges of amounts of components in the compositions of the invention described herein may be interchanged in any way, provided that the resulting ranges fall within the broadest scope of the invention.

For example, in the following embodiments, the compositions of the invention comprise: from about 62 to about 67 % by weight R-1234ze(E) and from about 33 to about 38 % by weight R-134a;

from about 63 to about 68 % by weight R-1234ze(E) and from about 32 to about 37 % by weight R- 34a; from about 62 to about 66 % by weight R-1234ze(E) and from about 34 to about 38 % by weight R-134a;

from about 64 to about 68 % by weight R-1234ze(E) and from about 32 to about 36 % by weight R-134a; or

from about 61 to about 65% by weight R-1234ze(E) and from about 35 to about 39% by weight R-134a.

In a preferred embodiment, the compositions of the invention are substantially free of any other component that has heat transfer properties.

In one aspect, the compositions of the invention are substantially free of (i) any other hydrofluorocarbon compound (other than R-1234ze(E) and R-134a), and/or (ii) carbon dioxide, and/or (iii) any hydrocarbon. Any of the compositions of the invention described herein, including those with specifically defined amounts of R-1234ze(E) and R-134a, may consist essentially of (or consist of) the amounts of R-1234ze(E) and R-134a defined in those compositions.

By the term "consist essentially of, we include the meaning that the compositions of the invention contain substantially no other components, particularly no further hydrofluorocarbon compounds known to be used in heat transfer compositions (e.g. hydrofluoroalkanes or hydrofluoroalkenes, hydrocarbons and carbon dioxide). We include the term "consist of within the meaning of "consist essentially of. Compositions according to the invention conveniently comprise substantially no R-1225 (pentafluoropropene), for example conveniently substantially no R-1225ye (1 ,2,3,3,3- pentafluoropropene) or R-1225zc (1 ,1 ,3,3,3-pentafluoropropene), which compounds may have associated toxicity issues. By "substantially no" and "substantially free of, we include the meaning that the compositions of the invention contain 0.5% by weight or less of the stated component, preferably 0.1% or less, based on the total weight of the composition.

Certain compositions of the invention may contain substantially no:

(i) 2,3,3,3-tetrafluoropropene (R-1234yf),

(ii) c s-1 ,3,3,3-tetrafluoropropene (R-1234ze(Z)), (iii) carbon dioxide;

(iv) difluoromethane (R-32);

(v) 1 ,1-difluoroethane (R-152a);

(vi) pentafluoroethance (R125);and/or

(vii) 3,3,3-trifluoropropene (R-1243zf).

The compositions of the invention have zero ozone depletion potential.

R-134a has a GWP of 1430 according to the IPCC (Intergovernmental Panel on Climate Change) "AR4" assessment and R-1234ze(E) has a GWP of about 6. Accordingly, the compositions of the invention have a GWP between 435 and 575, typically from about 440 to about 570. In one embodiment, the compositions of the invention have a GWP of from about 450 to about 550, for example from about 460 to about 540. Preferably, compositions of the invention are non-flammable at a test temperature of 60°C using the ASHRAE-34 methodology. Advantageously, the mixtures of vapour that exist in equilibrium with the compositions of the invention at any temperature between about -20°C and 60°C are also non-flammable. In an embodiment, the compositions are of reduced flammability hazard when compared to R-1234ze(E) alone, R-1234yf alone, or a binary mixture of R-134a and R-1234yf that possesses the same proportion of R-134a as the compositions of the invention.

Flammability may be determined in accordance with ASHRAE Standard 34 incorporating the ASTM Standard E-681 with test methodology as per Addendum 34p dated 2004, the entire content of which is incorporated herein by reference.

In one aspect, the compositions have one or more of (a) a higher lower flammable limit; (b) a higher ignition energy; or (c) a lower flame velocity compared to R-1234ze(E) or R- 1234yf alone, or a corresponding binary mixture of R-134a and R-1234yf. In a preferred embodiment, the compositions of the invention are non-flammable. Advantageously, the mixtures of vapour that exist in equilibrium with the compositions of the invention at any temperature between about -20°C and 60°C are also non-flammable. Preferably, the compositions of the invention are less flammable compared to R- 1234ze(E), R-1234yf or an equivalent binary mixture of R-134a/R-1234yf in one or more of the following respects: lower flammable limit at 23°C; lower flammable limit at 60°C; breadth of flammable range at 23°C or 60°C; auto-ignition temperature (thermal decomposition temperature); minimum ignition energy in dry air or flame speed. The flammable limits being determined according to the methods specified in ASHRAE-34 and the auto-ignition temperature being determined in a 500ml glass flask by the method of ASTM E659-78.

In some applications it may not be necessary for the formulation to be classed as nonflammable by the ASHRAE-34 methodology; it is possible to develop fluids whose flammability limits will be sufficiently reduced in air to render them safe for use in the application, for example if it is physically not possible to make a flammable mixture by leaking the refrigeration equipment charge into the surrounds.

It is believed that the compositions of the invention exhibit a completely unexpected combination of low-/non-flammability, low GWP and improved refrigeration performance properties. Some of these refrigeration performance properties are explained in more detail below.

Advantageously, the volumetric refrigeration capacity of the compositions of the invention is at least 80% of the existing refrigerant fluid it is replacing, preferably at least 85%, 90% or even at least 95%.

The compositions of the invention typically have a volumetric refrigeration capacity that is at least 90% of that of R-1234yf. Preferably, the compositions of the invention have a volumetric refrigeration capacity that is at least 95% of that of R-1234yf, for example from about 95% to about 120% of that of R-1234yf.

In one embodiment, the cycle efficiency (Coefficient of Performance, COP) of the compositions of the invention is within about 5% or even better than the existing refrigerant fluid it is replacing

Conveniently, the compressor discharge temperature of the compositions of the invention is within about 15K of the existing refrigerant fluid it is replacing, preferably about 10K or even about 5K. The compositions of the invention preferably have energy efficiency at least 95% (preferably at least 98%) of R-134a under equivalent conditions, while having reduced or equivalent pressure drop characteristics and cooling capacity at 95% or higher of R-134a values. Advantageously the compositions have higher energy efficiency and lower pressure drop characteristics than R-134a under equivalent conditions. The compositions also advantageously have better energy efficiency and pressure drop characteristics than R-1234yf alone.

The heat transfer compositions of the invention are suitable for use in existing designs of equipment, and are compatible with all classes of lubricant currently used with established HFC refrigerants. They may be optionally stabilized or compatibilized with mineral oils by the use of appropriate additives.

Preferably, when used in heat transfer equipment, the composition of the invention is combined with a lubricant.

Conveniently, the lubricant is selected from the group consisting of mineral oil, silicone oil, polyalkyl benzenes (PABs), polyol esters (POEs), polyalkylene glycols (PAGs), polyalkylene glycol esters (PAG esters), polyvinyl ethers (PVEs), poly (alpha-olefins) and combinations thereof. PAGs and POEs are currently preferred lubricants for the compositions of the invention.

Advantageously, the lubricant further comprises a stabiliser. Preferably, the stabiliser is selected from the group consisting of diene-based compounds, phosphates, phenol compounds and epoxides, and mixtures thereof.

Conveniently, the composition of the invention may be combined with a flame retardant. Advantageously, the flame retardant is selected from the group consisting of tri-(2- chloroethyl)-phosphate, (chloropropyl) phosphate, tri-(2,3-dibromopropyl)-phosphate, tri- (1 ,3-dichloropropyl)-phosphate, diammonium phosphate, various halogenated aromatic compounds, antimony oxide, aluminium trihydrate, polyvinyl chloride, a fluorinated iodocarbon, a fluorinated bromocarbon, trifluoro iodomethane, perfluoroalkyl amines, bromo-fluoroalkyl amines and mixtures thereof. Preferably, the heat transfer composition is a refrigerant composition.

In one embodiment, the invention provides a heat transfer device comprising a composition of the invention.

Preferably, the heat transfer device is a refrigeration device.

Conveniently, the heat transfer device is selected from the group consisting of automotive air conditioning systems, residential air conditioning systems, commercial air conditioning systems, residential refrigerator systems, residential freezer systems, commercial refrigerator systems, commercial freezer systems, chiller air conditioning systems, chiller refrigeration systems, and commercial or residential heat pump systems. Preferably, the heat transfer device is a refrigeration device or an air-conditioning system.

The compositions of the invention are particularly suitable for use in mobile air- conditioning applications, such as automotive air-conditioning systems (e.g. heat pump cycle for automotive air-conditioning). Advantageously, the heat transfer device contains a centrifugal-type compressor.

The invention also provides the use of a composition of the invention in a heat transfer device as herein described. According to a further aspect of the invention, there is provided a blowing agent comprising a composition of the invention.

According to another aspect of the invention, there is provided a foamable composition comprising one or more components capable of forming foam and a composition of the invention.

Preferably, the one or more components capable of forming foam are selected from polyurethanes, thermoplastic polymers and resins, such as polystyrene, and epoxy resins. According to a further aspect of the invention, there is provided a foam obtainable from the foamable composition of the invention.

Preferably the foam comprises a composition of the invention.

According to another aspect of the invention, there is provided a sprayable composition comprising a material to be sprayed and a propellant comprising a composition of the invention. According to a further aspect of the invention, there is provided a method for cooling an article which comprises condensing a composition of the invention and thereafter evaporating said composition in the vicinity of the article to be cooled.

According to another aspect of the invention, there is provided a method for heating an article which comprises condensing a composition of the invention in the vicinity of the article to be heated and thereafter evaporating said composition.

According to a further aspect of the invention, there is provided a method for extracting a substance from biomass comprising contacting the biomass with a solvent comprising a composition of the invention, and separating the substance from the solvent.

According to another aspect of the invention, there is provided a method of cleaning an article comprising contacting the article with a solvent comprising a composition of the invention.

According to a further aspect of the invention, there is provided a method for extracting a material from an aqueous solution comprising contacting the aqueous solution with a solvent comprising a composition of the invention, and separating the material from the solvent.

According to another aspect of the invention, there is provided a method for extracting a material from a particulate solid matrix comprising contacting the particulate solid matrix with a solvent comprising a composition of the invention, and separating the material from the solvent. According to a further aspect of the invention, there is provided a mechanical power generation device containing a composition of the invention.

Preferably, the mechanical power generation device is adapted to use a Rankine Cycle or modification thereof to generate work from heat.

According to another aspect of the invention, there is provided a method of retrofitting a heat transfer device comprising the step of removing an existing heat transfer fluid, and introducing a composition of the invention. Preferably, the heat transfer device is a refrigeration device or (a static) air conditioning system. Advantageously, the method further comprises the step of obtaining an allocation of greenhouse gas (e.g. carbon dioxide) emission credit.

In accordance with the retrofitting method described above, an existing heat transfer fluid can be fully removed from the heat transfer device before introducing a composition of the invention. An existing heat transfer fluid can also be partially removed from a heat transfer device, followed by introducing a composition of the invention.

In another embodiment wherein the existing heat transfer fluid is R-134a, and and optional components such as a lubricant, a stabiliser and/or flame retardant, R- 1234ze(E) can be added to the R-134a in the heat transfer device, thereby forming the compositions of the invention, and the heat transfer device of the invention, in situ. Some of the existing R-134a may be removed from the heat transfer device prior to adding the R-1234ze(E) to facilitate providing the components of the compositions of the invention in the desired proportions.

Thus, the invention provides a method for preparing a composition and/or heat transfer device of the invention comprising introducing R-1234ze(E) and optional components such as a lubricant, a stabiliser and/or flame retardant, into a heat transfer device containing an existing heat transfer fluid which is R-134a. Optionally, at least some of the R-134a is removed from the heat transfer device before introducing the R-1234ze(E).

Of course, the compositions of the invention may also be prepared simply by mixing the R-1234ze(E) and R-134a (and optional components such as a lubricant, a stabiliser or an additional flame retardant) in the desired proportions. The compositions can then be added to a heat transfer device (or used in any other way as defined herein) that does not contain R-134a or any other existing heat transfer fluid, such as a device from which R-134a or any other existing heat transfer fluid have been removed.

In a further aspect of the invention, there is provided a method for reducing the environmental impact arising from operation of a product comprising an existing compound or composition, the method comprising replacing at least partially the existing compound or composition with a composition of the invention. Preferably, this method comprises the step of obtaining an allocation of greenhouse gas emission credit. By environmental impact we include the generation and emission of greenhouse warming gases through operation of the product.

As mentioned above, this environmental impact can be considered as including not only those emissions of compounds or compositions having a significant environmental impact from leakage or other losses, but also including the emission of carbon dioxide arising from the energy consumed by the device over its working life. Such environmental impact may be quantified by the measure known as Total Equivalent Warming Impact (TEWI). This measure has been used in quantification of the environmental impact of certain stationary refrigeration and air conditioning equipment, including for example supermarket refrigeration systems (see, for example, http://en.wikipedia.org/wiki/Total equivalent warming impact).

The environmental impact may further be considered as including the emissions of greenhouse gases arising from the synthesis and manufacture of the compounds or compositions. In this case the manufacturing emissions are added to the energy consumption and direct loss effects to yield the measure known as Life-Cycle Carbon Production (LCCP, see for example http://www.sae.org/events/aars/presentations/2007papasavva.pdf). The use of LCCP is common in assessing environmental impact of automotive air conditioning systems.

Emission credit(s) are awarded for reducing pollutant emissions that contribute to global warming and may, for example, be banked, traded or sold. They are conventionally expressed in the equivalent amount of carbon dioxide. Thus if the emission of 1 kg of R- 134a is avoided then an emission credit of 1x1300 = 1300 kg CO2 equivalent may be awarded. In another embodiment of the invention, there is provided a method for generating greenhouse gas emission credit(s) comprising (i) replacing an existing compound or composition with a composition of the invention, wherein the composition of the invention has a lower GWP than the existing compound or composition; and (ii) obtaining greenhouse gas emission credit for said replacing step.

In a preferred embodiment, the use of the composition of the invention results in the equipment having a lower Total Equivalent Warming Impact, and/or a lower Life-Cycle Carbon Production than that which would be attained by use of the existing compound or composition.

These methods may be carried out on any suitable product, for example in the fields of air-conditioning, refrigeration (e.g. low and medium temperature refrigeration), heat transfer, blowing agents, aerosols or sprayable propellants, gaseous dielectrics, cryosurgery, veterinary procedures, dental procedures, fire extinguishing, flame suppression, solvents (e.g. carriers for flavorings and fragrances), cleaners, air horns, pellet guns, topical anesthetics, and expansion applications. Preferably, the field is air- conditioning or refrigeration. Examples of suitable products include heat transfer devices, blowing agents, foamable compositions, sprayable compositions, solvents and mechanical power generation devices. In a preferred embodiment, the product is a heat transfer device, such as a refrigeration device or an air-conditioning unit. The existing compound or composition has an environmental impact as measured by GWP and/or TEWI and/or LCCP that is higher than the composition of the invention which replaces it. The existing compound or composition may comprise a fluorocarbon compound, such as a perfluoro-, hydrofluoro-, chlorofluoro- or hydrochlorofluoro-carbon compound or it may comprise a fluorinated olefin.

Preferably, the existing compound or composition is a heat transfer compound or composition such as a refrigerant. Examples of refrigerants that may be replaced include R-134a, R-152a, R-1234yf, R-410A, R-407A, R-407B, R-407C, R507, R-22 and R-404A. The compositions of the invention are particularly suited as replacements for R- 134a, R-152a or R-1234yf, especially R-134a or R-1234yf. Any amount of the existing compound or composition may be replaced so as to reduce the environmental impact. This may depend on the environmental impact of the existing compound or composition being replaced and the environmental impact of the replacement composition of the invention. Preferably, the existing compound or composition in the product is fully replaced by the composition of the invention.

The invention is illustrated by the following non-limiting examples.

Examples

Generation of accurate physical property model

The physical properties of R-1234ze(E) required to model refrigeration cycle performance, namely critical point, vapour pressure, liquid and vapour enthalpy, liquid and vapour density and heat capacities of vapour and liquid were accurately determined by experimental methods over the pressure range 0-200bar and temperature range -40 to 200°C, and the resulting data used to generate Heimholtz free energy equation of state models of the Span-Wagner type for the fluid in the NIST REFPROP Version 8.0 software, which is more fully described in the user guide www.nist.gov/srd/PDFfiles/REFPROP8.PDF, and is incorporated herein by reference. The variation of ideal gas enthalpy of the fluid with temperature was estimated using molecular modelling software Hyperchem v7.5 (which is incorporated herein by reference) and the resulting ideal gas enthalpy function was used in the regression of the equation of state for these fluids. The predictions of this model for R1234ze(E) were compared to the predictions yielded by use of the standard files for R1234ze(E) included in REFPROP Version 9.0 (incorporated herein by reference). It was found that close agreement was obtained for the fluid's thermodynamic properties.

The vapour liquid equilibrium behaviour of R-1234ze(E) was studied R-134a over the temperature range—40 to +60°C, which encompasses the practical operating range of most refrigeration and air conditioning systems. The composition was varied over the full compositional space in the experimental programme. Mixture parameters for the binary pair were regressed to the experimentally obtained data and the parameters were also incorporated into the REFPROP software model. The resulting software model was used to compare the performance of selected fluids of the invention with R-134a in an air conditioning cycle application.

Example 1

Air conditioning cycle comparison

In a first comparison the behaviour of the fluids was assessed for a simple vapour compression cycle with evaporation and condensing conditions typical of automotive heat pumping duty. In this comparison pressure drop effects were ignored. The comparison was made on the basis of equal compressor displacement for the reference fluid (R-134a) and for the mixed fluids of the invention. Comparison was made assuming equivalent mean evaporating and condensing temperatures and equal degrees of subcool, evaporator superheat and compressor return temperature for all fluids Table 1 : Cycle conditions

The generated performance data for selected compositions of the invention is set out in the following Tables. The tables show key parameters of the air conditioning cycle, including operating pressures, volumetric cooling capacity, energy efficiency (expressed as coefficient of performance for cooling COP) compressor discharge temperature and pressure drops in pipework. The volumetric cooling capacity of a refrigerant is a measure of the amount of cooling which can be obtained for a given size of compressor operating at fixed speed. The coefficient of performance (COP) is the ratio of the amount of heat energy removed in the evaporator of the heat pump cycle to the amount of work consumed by the compressor. Table 2: Theoretical Performance Data of R-134a/R-1234ze(E) blends

The performance of R-134a is taken as the reference point for comparison of cooling capacity, energy efficiency and pressure drop. This fluid is used as a reference for comparison of the ability of the fluids of the invention to be used in air conditioning. It should be noted in passing that the utility of fluids of the invention is not limited to automotive systems. Indeed these fluids can be used in so-called stationary (residential or commercial) equipment.

It is evident that fluids of the invention can provide improved energy efficiency compared to R-134a.

The compositions are especially attractive since they have non-flammable liquid and vapour phases at 23°C, and selected compositions are also wholly non-flammable at 60°C and/or exhibit significantly higher auto-ignition temperature than that of R- 1234ze(E) or R-1234yf.

Example 2

Binary compositions of R-134a and R-1234ze(E) were tested for flammable limit determination using test apparatus and protocol as described in ASHRAE Std 34-2007. The apparatus consisted of a 12 litre glass flask with agitator and electric arc ignition, temperature controlled to 60°C internal temperature and fed with gas samples to give the desired composition of refrigerant. The humidity in the flask was controlled to 50%RH at 25°C as required by the standard.

It was found that a mixture of 10% w/w R-134a in R-1234ze(E) exhibited flammability at 60°C (defined as producing a flame which reaches to the top of the flask and shows a cone angle of more than 90°). It was then found that a mixture of 15% w/w R-134a in R-1234ze(E) passed this test, and was therefore considered to be non-flammable by this test.

Binary compositions of R-134a/R-1234ze(E) were then assessed for fractionation using the NIST REFLEAK4.0 software, which is permissible for performing such analysis by ASHRAE Std34.

The software was used with input parameters for modelling R-1234ze(E) and the vapour liquid equilibrium of R-134a and R-1234ze(E). The input parameters for R-1234ze(E) were derived by performing measurements of vapour and liquid density, vapour pressure and vapour and liquid heat capacity to allow correlation of the thermophysical properties of the fluid to a Helmholtz energy equation of state as implemented in the NIST REFPROP and REFLEAK software packages. The phase equilibrium between R-134a and R-1234ze(E) was studied at a range of temperatures between -40°C and +60°C using a static-dynamic equilibrium cell apparatus to measure vapour pressure and phase compositions. The measured data were then used to fit the binary interaction parameters used in the IST software packages to best present the experimental data.

The REFLEAK software was then used to model vapour and liquid removal from a cylinder at a range of initial fill conditions and test temperatures as described in ASHRAE Std.34-2007. A vapour leak from an initially 90% liquid filled cylinder at 54.4°C was explored for a range of starting compositions of R-134a in R-1234ze(E). In this scenario the remaining liquid composition in the cylinder after the leak is the Worst Case Formulation for Flammability (WCFF) required to be tested under ASHRAE-34 for flammability classification of a blended refrigerant.

It was found that in this scenario an initial composition of at least 28% w/w R-134a was required to result in a final liquid composition of 15% or more R-134a remaining. Hence to achieve a WCFF in this fractionation test that is non-flammable, at 60°C at least 28% is required as a starting composition. In this scenario, the claimed compositions are clearly suitable.

The binary mixture was then assessed for vapour leakage at ambient temperature (23°C) and it was found that an initial composition of R-134a of 35% or higher was needed to ensure a final liquid composition of 15% w/w.

Consequently R-134a levels in the claimed range of 31 to 39% may be beneficial in ensuring that even if a refrigerant blend is stored in a leaking vessel, the ensuring blend is still non-flammable. However values towards the higher end of this range (i.e. conveniently about 35 to about 39% by weight R-134a, conveniently about 36 to about 39% by weight R-134a, the balance of the refrigerant blend being R1234ze(E)) may be preferable depending on the storage temperature of the vessel.

In summary, the invention provides new compositions that exhibit a surprising combination of advantageous properties including good refrigeration performance, low flammability, low GWP, and/or miscibility with lubricants compared to existing refrigerants such as R-134a and the proposed refrigerant R-1234yf.

The invention is defined by the following claims.

Claims

1. A heat transfer composition comprising from about 61 to about 69 % by weight fraA?s-1 ,3,3,3-tetrafluoropropene (R-1234ze(E)) and from about 31 to about 39 % by weight 1,1 ,1 ,2-tetrafluoroethane (R-134a).

2. A composition according to claim 1 comprising from about 61 to about 65% by weight R-1234ze(E) and from about 35 to about 39% by weight R-134a.

3. A composition according to claim 1 comprising from about 62 to about 68 % by weight R-1234ze(E) and from about 32 to about 38 % by weight R-134a.

4. A composition according to claim 3 comprising from about 63 to about 67 % by weight R-1234ze(E) and from about 33 to about 37 % by weight R-134a.

5. A composition according to claim 4 comprising from about 64 to about 66 % by weight R-1234ze(E) and from about 34 to about 36 % by weight R-134a.

6. A composition according to any of the preceding claims wherein the composition is substantially free of (i) any other hydrofluorocarbon compound, and/or (ii) carbon dioxide, and/or (iii) any hydrocarbon.

7. A composition according to any of the preceding claims wherein the composition is substantially free of any other component that has heat transfer properties.

8. A composition according to any of the preceding claims consisting essentially of R-1234ze(E) and R-134a.

9. A composition according to any of the preceding claims, wherein the composition is less flammable than R-1234ze(E) alone, R-1234yf alone, or a corresponding binary mixture of R-1234yf and R134a.

10. A composition according to claim 9 wherein the composition has:

(a) a higher flammable limit;

(b) a higher ignition energy; and/or

(c) a lower flame velocity compared to R-1234ze(E) alone, R-1234yf alone, or a corresponding binary mixture of R-1234yf and R134a.

11. A composition according to any of the preceding claims which is non-flammable.

12. A composition comprising a lubricant and a composition according to any of the preceding claims.

13. A composition according to claim 12, wherein the lubricant is selected from mineral oil, silicone oil, polyalkyl benzenes (PABs), polyol esters (POEs), polyalkylene glycols (PAGs), polyalkylene glycol esters (PAG esters), polyvinyl ethers (PVEs), poly (alpha-olefins) and combinations thereof, preferably wherein the lubricant is selected from PAGs or POEs.

14. A composition comprising a stabiliser and a composition according to any of the preceding claims.

15. A composition according to claim 14, wherein the stabiliser is selected from diene-based compounds, phosphates, phenol compounds and epoxides, and mixtures thereof.

16. A composition comprising a flame retardant and a composition according to any of the preceding claims.

17. A composition according to claim 16, wherein the flame retardant is selected from the group consisting of tri-(2-chloroethyl)-phosphate, (chloropropyl) phosphate, tri- (2,3-dibromopropyl)-phosphate, tri-(1 ,3-dichloropropyl)-phosphate, diammonium phosphate, various halogenated aromatic compounds, antimony oxide, aluminium trihydrate, polyvinyl chloride, a fluorinated iodocarbon, a fluorinated bromocarbon, trifluoro iodomethane, perfluoroalkyi amines, bromo-fluoroalkyl amines and mixtures thereof.

18. A composition according to any of the preceding claims which is a refrigerant composition.

19. A heat transfer device containing a composition as defined in any one of claims 1 to 17.

20. Use of a composition defined in any of claims 1 to 17 in a heat transfer device.

21. A heat transfer device according to claim 19 or a use according to claim 19 wherein the heat transfer device is a refrigeration device.

22. A heat transfer device or use according to claims 19 to 21 wherein the heat transfer device is selected from group consisting of automotive air conditioning systems, residential air conditioning systems, commercial air conditioning systems, residential refrigerator systems, residential freezer systems, commercial refrigerator systems, commercial freezer systems, chiller air conditioning systems, chiller refrigeration systems, and commercial or residential heat pump systems, preferably wherein the heat transfer device is an automobile air-conditioning system.

23. A heat transfer device or use according to claims 19 to 22 wherein the heat transfer device contains a compressor.

24. A blowing agent comprising a composition as defined in any of claims 1 to 17.

25. A foamable composition comprising one or more components capable of forming foam and a composition as defined in any of claims 1 to 17, wherein the one or more components capable of forming foam are selected from polyurethanes, thermoplastic polymers and resins, such as polystyrene, and epoxy resins, and mixtures thereof.

26. A foam obtainable from the foamable composition as defined in claim 25.

27. A foam comprising a composition as defined in any of claims 1 to 17.

28. A sprayable composition comprising material to be sprayed and a propellant comprising a composition as defined in any of claims 1 to 17.

29. A method for cooling an article which comprises condensing a composition defined in any of claims 1 to 17 and thereafter evaporating the composition in the vicinity of the article to be cooled.

30. A method for heating an article which comprises condensing a composition as defined in any one of claims 1 to 17 in the vicinity of the article to be heated and thereafter evaporating the composition.

31. A method for extracting a substance from biomass comprising contacting biomass with a solvent comprising a composition as defined in any of claims 1 to 17, and separating the substance from the solvent.

32. A method of cleaning an article comprising contacting the article with a solvent comprising a composition as defined in any of claims 1 to 17.

33. A method of extracting a material from an aqueous solution or from a particulate solid matrix comprising contacting the aqueous solution or the particulate solid matrix with a solvent comprising a composition as defined in any of claims 1 to 17, and separating the material from the solvent.

34. A mechanical power generation device containing a composition as defined in any of claims 1 to 17.

35. A mechanical power generating device according to claim 34 which is adapted to use a Rankine Cycle or modification thereof to generate work from heat.

36. A method of retrofitting a heat transfer device comprising the step of removing an existing heat transfer composition, and introducing a composition as defined in any one of claims 1 to 17.

37. A method of claim 36 wherein the heat transfer device is a refrigeration device.

38. A method according to claim 37 wherein the heat transfer device is an air conditioning system, preferably an automobile air conditioning system.

39. A method for reducing the environmental impact arising from the operation of a product comprising an existing compound or composition, the method comprising replacing at least partially the existing compound or composition with a composition as defined in any one of claims 1 to 17.

40. A method for preparing a composition as defined in any of claims 1 to 17, and/or a heat transfer device as defined in any of claims 19 or 21 to 23, which composition or heat transfer device contains R-134a, the method comprising introducing R-1234ze(E), and optionally a lubricant, a stabiliser and/or a flame retardant, into a heat transfer device containing an existing heat transfer fluid which is R-134a.

41. A method according to claim 40 comprising the step of removing at least some of the existing R-134a from the heat transfer device before introducing the R-1234ze(E), and optionally the lubricant, the stabiliser and/or the flame retardant.

42. A method for generating greenhouse gas emission credit comprising (i) replacing an existing compound or composition with a composition as defined in any one of claims 1 to 17, wherein the composition as defined in any one of claims 1 to 17 has a lower GWP than the existing compound or composition; and (ii) obtaining greenhouse gas emission credit for said replacing step.

43. A method of claim 42 wherein the use of the composition of the invention results in a lower Total Equivalent Warming Impact, and/or a lower Life-Cycle Carbon Production than is attained by use of the existing compound or composition.

44. A method of claim 42 or 43 carried out on a product from the fields of air- conditioning, refrigeration, heat transfer, blowing agents, aerosols or sprayable propellants, gaseous dielectrics, cryosurgery, veterinary procedures, dental procedures, fire extinguishing, flame suppression, solvents, cleaners, air horns, pellet guns, topical anesthetics, and expansion applications.

45. A method according to claim 39 or 44 wherein the product is selected from a heat transfer device, a blowing agent, a foamable composition, a sprayable composition, a solvent or a mechanical power generation device, preferably a heat transfer device.

46. A method according to claim 45 wherein the product is a heat transfer device.

47. A method according to any of claims 39 to 46 wherein the existing compound or composition is a heat transfer composition, preferably wherein the heat transfer composition is a refrigerant selected from R-134a, R-1234yf, R-152a, R-404A, R-410A, R-507, R-407A, R-407B, R-407D, R-407E and R-407F.

48. Any novel heat transfer composition substantially as hereinbefore described, optionally with reference to the examples.