Composition

Abstract

The present invention provides a composition comprising carbon dioxide (C02, R-744), difluoromethane (R-32) and trifluoroiodomethane (CF3I) and the use of such a composition as a working fluid in a heat transfer system, such as a refrigeration, heat pump or air conditioning system.

Description

[0001] The present invention relates to compositions suitable for use as working fluids in air conditioning and refrigeration applications. The compositions disclosed herein are particularly useful in heat pump water heaters, air conditioning systems for trains, buses, cars, and trucks, commercial refrigeration systems including supermarket display systems and cold storage rooms (such as walk-in refrigerators and freezers), and transport refrigeration systems.

[0002] Any prior art documents or background listed or discussed in this specification should not necessarily be regarded as an admission that the document or background is part of the prior art or common general knowledge.

[0003] Carbon dioxide (CO2, R-744), as a refrigerant with a low global warming potential (GWP), is favored in applications where non-flammability of the refrigerant is required. These applications include air conditioning systems for trains, buses, cars, and trucks; heat pump water heater systems; commercial refrigeration systems including supermarket display systems and cold storage rooms; and transport refrigeration systems incorporated into refrigerated shipping containers or trucks.

[0004] Compared with other fluorocarbon refrigerants used in the same applications, CO2 has two main drawbacks. First, it suffers from low energy efficiency at ambient temperatures above about 25 to 30 °C. Second, its operating pressure is much higher than that of traditional fluorocarbon-based systems.

[0005] Non-flammable refrigerant mixtures containing difluoromethane (R-32) and CO2 have been proposed (see Adams et al., (J. Chem. Eng. Data 16 (1971) 146-149) and US7238299, the contents of which are incorporated herein by reference in their entirety). Such non-flammable compositions can contain up to about 60 wt% of R-32.

[0006] However, although this binary refrigerant composition is formulated to be non-flammable, it will still be considered flammable according to ASHRAE Standard 34 (2019). This is because the mixture is non-azeotropic. ASHRAE Standard 34 requires consideration of the results of a series of vapor leaks in the temperature range of -40 °C to 60 °C to identify whether a leak can produce a more flammable composition than the "formulated" composition. When this is done for the non-flammable binary mixture of R-32 and CO2, the vapor leak at -40 °C will result in the formation of a flammable composition because the more volatile CO2 is preferentially removed from the system, leading to fractionation of the remaining material such that it contains more than 60% of R-32.

[0007] Accordingly, refrigerant compositions are desired that address these problems while preferably maintaining the non-flammability of pure CO2. Such compositions should also preferably have a low GWP. In particular, for certain applications such as air conditioning systems in passenger vehicles or stand-alone refrigeration systems, the EU fluorinated gas regulations will require a GWP of about 150 or less.

[0008] The present invention addresses the above and other deficiencies and the above needs by providing a composition comprising carbon dioxide (CO2, R-744), difluoromethane (R-32), trifluoroiodomethane (CF3I) and optionally 1,1-difluoroethylene (R-1132a). Such a composition will hereinafter be referred to as "the composition of the present invention".

[0009] The inventors have found that a relatively small amount of CF3I can be added to R-744 and R-32 to ensure that the resulting mixture does not fractionate into a flammable composition when analyzed according to ASHRAE Standard 34. In addition, a small amount of a flammable species (e.g., R-1132a) can be added to the mixture of the present invention without forming a flammable composition.

[0010] The composition of the present invention is considered to be particularly useful in heat transfer systems that utilize a transcritical refrigeration cycle (e.g., refrigeration, air conditioning and heat pump systems). The basic transcritical cycle consists of the following steps:

[0011] (a) Evaporating the liquid refrigerant at low pressure to remove heat from a low temperature source fluid such as air;

[0012] (b) Compressing the resulting refrigerant vapor in a compressor to obtain a hot high pressure gas;

[0013] (c) Cooling the high pressure gas by heat exchange with a sink at a higher temperature than the source to obtain a cooler dense refrigerant gas at high pressure. This gas is referred to as a "supercritical" fluid because it is above its critical temperature; and

[0014] (d) Expanding the supercritical fluid through an expansion valve or other restricting device to produce a two-phase mixture of liquid refrigerant and vaporized refrigerant vapor at low pressure; and then returning the mixture to the evaporator stage (a) to complete the cycle.

[0015] Optionally, in such a cycle, an internal heat exchange process occurs between the warm high pressure gas leaving the gas cooler and the cold vapor flowing from the evaporator to the compressor. This process occurs in an "internal heat exchanger" ("IHX") and has the effect of increasing the refrigeration capacity and cycle efficiency.

[0016] Conveniently, such a transcritical refrigeration cycle may include a receiver located after the evaporator (and before the IHX, if one is used). This is used to maintain an overcharge of refrigerant when the external ambient temperature causes the gas cooler pressure to decrease.

[0017] It has also been found that the compositions of the present invention are suitable for such cycles, whether or not combined with the features of an IHX or a receiver.

[0018] The compositions of the present invention will now be described in detail.

[0019] According to the present invention, there is provided a composition comprising CO2, R-32, and CF3I.

[0020] Typically, the compositions of the present invention comprise from about 50 to about 98% by weight, such as from about 52 or about 55 to about 95% by weight, for example from about 59 to about 92% by weight, preferably from about 65 or 70 to about 90% by weight, and optionally from about 75 to about 87% by weight of CO2.

[0021] Conveniently, the compositions of the present invention comprise from about 1 to about 30% by weight, such as from about 2 to about 25% by weight, for example from about 3 to about 21% by weight, and optionally from about 3 to about 15% by weight of R-32.

[0022] Advantageously, the compositions of the present invention comprise from about 1 or 2 to about 20% by weight, such as from about 3 to about 15 or about 13% by weight of CF3I.

[0023] Typically, the compositions of the present invention comprise from about 50 to about 98% by weight of CO2, from about 1 to about 30% by weight of R-32, and from about 1 to about 20% by weight of CF3I, such as from about 55 to about 90% by weight of CO2, from about 2 to about 28% by weight of R-32, and from about 2 to about 17% by weight of CF3I, for example from about 57 to about 85% by weight of CO2, from about 2 to about 26% by weight of R-32, and from about 3 to about 17% by weight of CF3I.

[0024] The compositions of the present invention may additionally comprise R-1132a.

[0025] When present, the compositions of the present invention typically comprise from about 1 or about 2 to about 20% by weight, such as from about 4 to about 17% by weight, for example from about 7 to about 16% by weight, and optionally from about 10 to about 15% by weight of R-1132a.

[0026] Advantageously, the amount of R-1132a is selected such that the compositions of the present invention comprise a combined amount of less than about 37% by weight, such as less than about 35% by weight, of R-32 and R-1132a.

[0027] Conveniently, the compositions of the present invention comprise a weight ratio of R-32 to CF3I of less than about 2:1, such as less than about 1.8:1 R-32 to CF3I.

[0028] The composition of the present invention may additionally comprise an additional component selected from 1,1,1,2-tetrafluoroethane (R-134a), trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)), 2,3,3,3-tetrafluoropropene (R-1234yf), 1,1,1,2,3,3,3-heptafluoropropane (R-227ea) and mixtures thereof.

[0029] Typically, the additional component is R-134a or R-134a and one or more of R-1234yf and R-1234ze(E). Alternatively, the composition may additionally comprise one or more of R-1234yf and R-1234ze(E) as an additional component.

[0030] Conveniently, the composition of the invention comprises from about 1 to about 15 wt %, such as from about 3 to about 12 wt %, for example from about 4 or about 5 to about 10 wt % of said additional component.

[0031] In one embodiment, the composition of the present invention may consist essentially of the components. By the term "consisting essentially of", it is included that the composition of the present invention is essentially free of other components, in particular free of other (hydrogen)(fluorine) compounds known for use in heat transfer compositions (e.g., (hydrogen)(fluorine) alkanes or (hydrogen)(fluorine) alkenes). The term "consisting of" is included within the meaning of "consisting essentially of".

[0032] In one embodiment, the compositions of the present invention are substantially free of any components having heat transfer properties (except for the components specified).For example, the compositions of the present invention may be substantially free of any other hydrofluorocarbons.

[0033] By "substantially free" and "substantially free", it is included the meaning that the composition of the present invention contains 0.5% or less of the component by weight, preferably 0.4%, 0.3%, 0.2% or 0.1% or less, based on the total weight of the composition.

[0034] As used herein, unless otherwise indicated, all % amounts referred to in compositions herein (including the claims) are by weight based on the total weight of the composition.

[0035] The term "about" as used in conjunction with a numerical value for the amount of a component in % by weight includes a meaning of ±0.5 wt%, for example ±0.2 wt%.

[0036] For the avoidance of doubt, it should be understood that the upper and lower limits of the ranges of the amounts of the components in the compositions of the invention described herein can be interchanged in any manner, provided that the resulting range falls within the broadest scope of the invention.

[0037] The compositions of the invention preferably have a zero ozone depletion potential value.

[0038] Typically, the compositions of the invention have a global warming potential (GWP) of less than 220, such as less than about 210 or less than about 200, for example, less than about 150, preferably less than about 140.

[0039] Conveniently, the compositions of the invention are non-flammable, as determined according to ASHRAE Standard 34:2019. For example, using the ASHRAE-34 method, the compositions of the invention are non-flammable at a test temperature of 60°C. Advantageously, the vapor mixture that is in equilibrium with the compositions of the invention at any temperature between about -20°C and 60°C is also non-flammable.

[0040] It is believed that when used in refrigeration systems, particularly air conditioning systems, the compositions of the invention exhibit low / non-flammability, low GWP, improved lubricant miscibility, and improved performance properties. Some of these properties are described in more detail below.

[0041] Typically, the compositions of the invention have a coefficient of performance (COP) greater than or approximately equal to that of CO2.

[0042] Conveniently, the compositions of the invention have a temperature glide in the condenser or evaporator of less than about 11 K, such as less than about 9 K, for example less than about 7 K.

[0043] Advantageously, the compositions of the invention have a volumetric refrigeration capacity within about 25% of that of CO2, such as within about 20% of that of CO2, for example within about 15% of that of CO2.

[0044] Typically, the compositions of the invention have an operating pressure in the condenser or evaporator that is lower than that of CO2.

[0045] Typically, the compositions of the invention are suitable for existing equipment designs and are believed to be compatible with all types of lubricants and are currently used with established HFC refrigerants. Optionally, they can be stabilized or solubilized with mineral oil by using suitable additives.

[0046] Preferably, the lubricant is selected from mineral oil, silicone oil, polyalkylbenzene (PAB), polyol ester (POE), polyalkylene glycol (PAG), polyalkylene glycol ester (PAG ester), polyvinyl ether (PVE), poly(α-olefin), and combinations thereof, preferably where the lubricant is selected from PAG, POE, and combinations thereof.

[0047] Conveniently, the stabilizer is selected from diene-based compounds, phosphates, phenolic compounds, and epoxides, and mixtures thereof.

[0048] In another aspect of the present invention, there is provided the use of the composition of the present invention as a working fluid in a heat transfer system.

[0049] Typically, the heat transfer system is a refrigeration, heat pump, or air conditioning system.

[0050] Preferably, the refrigeration system comprises a commercial refrigeration system (such as a supermarket display refrigeration system, a beverage cold storage refrigeration system, a warehouse refrigeration system, or a cold room refrigeration system) or a transport refrigeration system (e.g., a refrigeration system assembled to a refrigerated transport container or a refrigeration system assembled to a vehicle).

[0051] Conveniently, the heat pump system comprises a water heater heat pump system.

[0052] Preferably, the air conditioning system comprises a transport air conditioning system, such as a bus, car, train, or truck air conditioning system.

[0053] Advantageously, the heat transfer (e.g., refrigeration, heat pump, and / or air conditioning) system defined above operates as a transcritical heat transfer system for at least part of the year.

[0054] In some applications in the use of transcritical cycle technology, the vapor compression cycle used is a single compression cycle typical in mobile air conditioning applications. In other applications, the gas compression is carried out in two stages, which allows for efficient operation at a larger temperature difference between the heat source and the heat sink. It is believed that the composition of the present invention is suitable for both single and double compression stage cycles.

[0055] In one aspect of the present invention, there is provided the use of the composition of the present invention as a heat transfer device, such as a replacement for an existing working fluid in a new heat transfer device designed to meet the same application requirements.

[0056] Conveniently, the existing working fluid is R-410A. Alternatively, the existing working fluid can be R-407C.

[0057] In another aspect of the present invention, there is provided a heat transfer device comprising the composition of the present invention.

[0058] Preferably, the heat transfer device is a transcritical heat transfer device, such as a transcritical refrigeration, heat pump, or air conditioning device.

[0059] Optionally, the transcritical heat transfer device comprises an internal heat exchanger (IHX) system.

[0060] The transcritical heat transfer device may further comprise a receiver located after the evaporator, or, if an IHX is present, between the evaporator and the IHX.

[0061] According to another aspect of the present invention, there is provided a method of generating heat, which comprises condensing the composition of the present invention near a body to be heated.

[0062] According to another aspect of the present invention, there is provided a method of generating cooling, which comprises evaporating the composition of the present invention near a body to be cooled.

[0063] All chemicals described herein are commercially available. For example, the fluorinated compound can be obtained from Apollo Scientific (UK).

[0064] The composition of the present invention can be prepared by simply mixing CO2, R-32 and CF3I (and optional components such as R-1132a and / or lubricant) in desired proportions. The composition can then be added to a heat transfer device or used in any other manner defined herein.

[0065] The present invention is illustrated by the following non-limiting examples. Examples

[0066] The vapor-liquid equilibrium behavior of CO2 with CF3I and R-32 has been described in the academic literature, and the available data has been used to generate interaction parameters for use with the NIST REFPROP9.1 software. The experimental study of CF3I with R-32 and R-1132a and R-1132a with CO2 and R-32 was carried out using a constant volume equilibrium apparatus in the temperature range from -40 °C to 70 °C, and the resulting data was also used to fit the binary interaction parameters for each binary pair. The measurement principle of this experimental work was to determine the vapor pressure of a series of known compositions over a temperature range and then regress to a thermodynamic model to minimize the difference between the calculated and observed pressures on the data set.

[0067] The interaction parameters thus obtained were used with the NIST REFLEAK5.1 computer program to simulate the fractionation of ternary CO2 / R-32 / CF3I mixtures and quaternary R-744 / R-1132a / R-32 / CF3I mixtures at -40 °C. The compositions studied had 1-30% of R-32 and the quaternary compositions had up to 15 wt% of R-1132a. The initial charge compositions for these simulations were 90% of the maximum allowable liquid charge, where the allowable liquid was calculated according to the requirements of ASHRAE Standard 34 (2019). For each composition, the fractionation was run from the initial charge to 95% mass loss.

[0068] Modeling of a series of compositions led to the following observations.

[0069] · If the total amount of R-1132a + R-32 in the blend is less than about 35%, the initial vapor and liquid compositions are non-flammable.

[0070] · If the mass ratio of R-32 to CF3I in the composition is less than or equal to about 2:1, the final liquid and vapor compositions will be substantially free of CO2 and R-1132a and will contain less than 58 wt% of R-32, thus ensuring that it will be non-flammable.

[0071] Then, standard refrigeration cycle modeling techniques are used to estimate the performance of selected compositions of the present invention. The performance of R-744 is also calculated as a comparative example. In cases where the cycle conditions result in the high-pressure side of the cycle operating above the fluid critical temperature ("transcritical" cycle), the compressor discharge pressure is varied to optimize the cycle efficiency (coefficient of performance - COP). The modeled cycle is a transcritical cycle that uses an internal heat exchanger (IHX) to exchange heat between the gas leaving the gas cooler and the low-pressure vapor leaving the evaporator.

[0072] For modeling purposes, the following conditions are assumed:

[0073]

[0074] Table 1: Model input conditions

[0075] The performance data for selected compositions of the present invention are shown in Table 2 below.

[0076] From the performance data, it can be seen that the compositions of the present invention have excellent energy efficiency and reduced operating pressures compared to CO2. In addition, the GWP of the compositions is less than about 210.

[0077] From the performance data, it can be seen that including more than about 30 wt% of R-32 in these compositions is not desirable because the temperature glide in the evaporator becomes greater than 11K. An R-32 content of 21% or less ensures that the GWP of the composition will be below 150, which is required for some applications under the EU fluorinated gas regulations.

[0078] The compositions of the present invention can be further enhanced by adding R-1132a, for example, by replacing a portion of the R-744 content with R-1132a such that the R-1132a content is between 1% and 15 wt%, without generating a flammable composition during fractionation. Adding R-1132a reduces the compressor discharge temperature and reduces the temperature glide in the evaporator. Compared to R-744, such compositions also have higher energy efficiency and reduced operating pressures.

[0079]

Claims

1. A composition, comprising: (a) 70 to 98% by weight of carbon dioxide (CO2, R-744); (b) 1 to 25% by weight of difluoromethane (R-32); and (c) 1 to 20% by weight of trifluoroiodomethane (CF3I).

2. The composition according to claim 1, comprising 70 to 95% by weight of CO2.

3. The composition according to claim 2, comprising 70 to 92% by weight of CO2.

4. The composition according to claim 3, comprising 70 to 90% by weight of CO2.

5. The composition according to claim 4, comprising 75 to 87% by weight of CO2.

6. The composition according to claim 1, comprising 2 to 25% by weight of R-32.

7. The composition according to claim 6, comprising 3 to 21% by weight of R-32.

8. The composition according to claim 7, comprising 3 to 15% by weight of R-32.

9. The composition according to claim 1, comprising 2 to 20% by weight of CF3I.

10. The composition according to claim 9, comprising 3 to 15% by weight of CF3I.

11. The composition according to claim 10, comprising 3 to 13% by weight of CF3I.

12. The composition according to claim 1, wherein the composition additionally comprises 1,1-difluoroethylene (R-1132a).

13. The composition according to claim 12, comprising 1 to 20% by weight of R-1132a.

14. The composition according to claim 13, comprising 2 to 20% by weight of R-1132a.

15. The composition according to claim 14, comprising 4 to 17% by weight of R-1132a.

16. The composition according to claim 15, comprising 7 to 16% by weight of R-1132a.

17. The composition according to claim 16, comprising 10 to 15% by weight of R-1132a.

18. The composition according to claim 12, comprising a combined amount of less than 37% by weight of R-32 and R-1132a.

19. The composition according to claim 18, comprising a combined amount of less than 35% by weight of R-32 and R-1132a.

20. The composition according to claim 1, comprising R-32 and CF3I in a weight ratio of less than 2:1 of R-32 to CF3I.

21. The composition according to claim 20, comprising R-32 and CF3I in a weight ratio of less than 1.8:1 of R-32 to CF3I.

22. The composition according to claim 1, wherein the composition additionally comprises additional components selected from 1,1,1,2-tetrafluoroethane (R-134a), trans-1,3,3,3-tetrafluoropropene (R-1234ze(E)), 2,3,3,3-tetrafluoropropene (R-1234yf), 1,1,1,2,3,3,3-heptafluoropropane (R-227ea), and mixtures thereof.

23. The composition according to claim 22, wherein the additional component is one or more of R-1234yf and R-1234ze(E) and R-134a.

24. The composition according to claim 22, wherein the composition comprises 1 to 15% by weight of the additional component.

25. The composition according to claim 24, wherein the composition comprises 3 to 12% by weight of the additional component.

26. The composition according to claim 25, wherein the composition comprises 4 to 10% by weight of the additional component.

27. The composition according to claim 26, wherein the composition comprises 5 to 10% by weight of the additional component.

28. The composition according to claim 1, the composition consisting essentially of the components.

29. The composition according to claim 1, wherein the composition is non-flammable as determined by ASHRAE Standard 34:2019.

30. The composition according to claim 1, wherein the composition has a global warming potential (GWP) of less than 220.

31. The composition according to claim 30, wherein the composition has a GWP of less than 210.

32. The composition according to claim 31, wherein the composition has a GWP of less than 200.

33. The composition according to claim 32, wherein the composition has a GWP of less than 150.

34. The composition according to claim 33, wherein the composition has a GWP of less than 140.

35. A composition comprising a lubricant and the composition according to claim 1.

36. The composition according to claim 35, wherein the lubricant is selected from mineral oil, silicone oil, polyalkylbenzene (PAB), polyol ester (POE), polyalkylene glycol (PAG), polyalkylene glycol ester (PAG ester), polyvinyl ether (PVE), poly(α-olefin), and combinations thereof.

37. The composition according to claim 36, wherein the lubricant is selected from PAG, POE, and combinations thereof.

38. A composition comprising a stabilizer and the composition according to claim 1.

39. The composition according to claim 38, wherein the stabilizer is selected from diene-based compounds, phosphates, phenol compounds, and epoxides, and mixtures thereof.

40. The composition according to claim 1, which has a coefficient of performance (COP) greater than or equal to CO2.

41. The composition according to claim 1, which has a temperature slip in the evaporator of less than 11 K.

42. The composition according to claim 41, which has a temperature slip in the evaporator of less than 9 K.

43. The composition according to claim 42, which has a temperature slip in the evaporator of less than 7 K.

44. The composition according to claim 1, which has a volumetric refrigerating capacity within 25% of CO2.

45. The composition according to claim 44, which has a volumetric refrigerating capacity within 20% of CO2.

46. The composition according to claim 45, which has a volumetric refrigerating capacity within 15% of CO2.

47. The composition according to claim 1, wherein the composition has an operating pressure lower than that of CO2 in a condenser or a gas cooler.

48. Use of the composition according to any one of claims 1 to 47 as a working fluid in a heat transfer system.

49. The use according to claim 48, wherein the heat transfer system is a refrigeration system, a heat pump system or an air conditioning system.

50. The use according to claim 49, wherein the refrigeration system comprises a commercial refrigeration system.

51. The use according to claim 50, wherein the commercial refrigeration system is a supermarket display refrigeration system, a beverage cold storage refrigeration system, a warehouse refrigeration system or a cold room refrigeration system.

52. The use according to claim 49, wherein the refrigeration system comprises a transport refrigeration system.

53. The use according to claim 52, wherein the transport refrigeration system is a refrigeration system assembled to a refrigerated transport container or a refrigeration system assembled to a vehicle.

54. The use according to claim 49, wherein the heat pump system comprises a water heater heat pump system.

55. The use according to claim 49, wherein the air conditioning system comprises a transport air conditioning system.

56. The use according to claim 55, wherein the transport air conditioning system is a bus, car, train or truck air conditioning system.

57. The use according to claim 48, wherein the heat transfer system operates as a transcritical heat transfer system for at least part of a year.

58. Use of the composition according to any one of claims 1 to 47 as a replacement for an existing working fluid in a heat transfer device.

59. The use according to claim 58, wherein the existing working fluid is R-410A.

60. A heat transfer device comprising the composition defined in any one of claims 1 to 47.

61. The heat transfer device according to claim 60, wherein the heat transfer device is a transcritical heat transfer device.

62. The heat transfer device according to claim 61, wherein the transcritical heat transfer device is a transcritical refrigeration, heat pump or air conditioning device.

63. A method of generating heat, which comprises condensing the composition according to any one of claims 1 to 47 near a body to be heated.

64. A method of generating cooling, which comprises evaporating the composition according to any one of claims 1 to 47 near a body to be cooled.

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