compositions

Abstract

To provide refrigerant compositions which have a low GWP while retaining the non-flammability of pure CO2.SOLUTION: The invention provides a composition comprising carbon dioxide (CO2, 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.SELECTED DRAWING: None

Description

[Technical Field]

[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, automobiles, and trucks, commercial refrigeration systems including supermarket display systems and cold rooms (such as walk-in refrigerators and freezers), and transportation refrigeration systems. [Background technology]

[0002] The listing or discussion of a prior-published document or any background art in this specification should not necessarily be taken as an acknowledgement that the document or background art is part of the state of the art or is common general knowledge.

[0003] Carbon dioxide (CO2, R-744) is favored as a low global warming potential (GWP) refrigerant for applications requiring non-flammability of the refrigerant. These applications include air conditioning systems for trains, buses, automobiles, and trucks; heat pump water heating systems; commercial refrigeration systems, including supermarket display systems and cold rooms; and transportation refrigeration systems installed in refrigerated shipping containers or trucks.

[0004] CO2 has two main disadvantages compared to other fluorocarbon refrigerants for similar applications: First, it suffers from low energy efficiency at ambient temperatures above about 25-30°C, and second, its operating pressure is much higher than that of conventional 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 US 7,238,299, the contents of which are incorporated herein by reference in their entireties). Such non-flammable compositions can contain up to about 60% by weight of R-32.

[0006] However, such a binary refrigerant composition, while nonflammable as formulated, would still be considered flammable according to ASHRAE Standard 34 (2019). This is because the mixture is nonazeotropic. ASHRAE Standard 34 requires that the results of a series of vapor leak experiments at temperatures ranging from -40°C to 60°C be considered to identify whether a leak could produce a composition more flammable than the "as formulated" composition. If this were performed on a nonflammable binary mixture of R-32 and CO2, a vapor leak at -40°C would result in the production of a flammable composition because the more volatile CO2 would be preferentially removed from the system, causing the remaining material to fractionate to contain more than 60% R-32.

[0007] It would therefore be desirable to identify refrigerant compositions that address these issues, preferably while retaining the non-flammability of pure CO2. Such compositions should also preferably have a low GWP. In particular, a GWP of about 150 or less would be required under the European Union F-gas regulations for certain applications, such as air conditioning systems in passenger vehicles or self-contained refrigeration appliances. DISCLOSURE OF THE INVENTION

[0008] The present invention addresses these and other deficiencies, and needs, by providing compositions comprising carbon dioxide (CO, R-744), difluoromethane (R-32), trifluoroiodomethane (CF1), and, optionally, 1,1-difluoroethylene (R-1132a). Such compositions are hereinafter referred to as "compositions of the invention."

[0009] The inventors have discovered that relatively small amounts 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 protocol. Additionally, small amounts of flammable species (e.g., R-1132a) can also be added to the mixtures of the present invention without producing a flammable composition.

[0010] The compositions of the present invention are believed to be particularly useful in heat transfer systems (e.g., refrigeration, air conditioning, and heat pump systems) that utilize a transcritical refrigeration cycle. The basic transcritical cycle consists of the following steps: (a) The evaporation of a liquid refrigerant at low pressure, which removes heat from a cold source fluid (such as air), (b) compression of the resulting refrigerant vapor in a compressor to produce a high-temperature, high-pressure gas; (c) Cooling of a high-pressure gas by heat exchange with a sink fluid at a higher temperature than the source, producing a cooler, denser refrigerant gas at high pressure (this gas is said to be a "supercritical" fluid because it is above its critical temperature); and (d) Expansion of the supercritical fluid through an expansion valve or other restriction device resulting in a two-phase mixture of liquid refrigerant and evaporated refrigerant vapor at low pressure (this mixture is then returned to the evaporator stage (a) to complete the cycle).

[0011] 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 takes place in an "internal heat exchanger" ("IHX") and has the effect of increasing the refrigeration capacity and efficiency of the cycle.

[0012] Conveniently, such a transcritical refrigeration cycle may contain a liquid accumulator located after the evaporator (and before the IHX, if used), which serves to hold the excess charge of the refrigerant when the external ambient temperature is such that the gas cooler pressure is reduced.

[0013] The compositions of the present invention have also been found to be suitable for use in such cycles, whether or not they incorporate an IHX or accumulator function.

[0014] The compositions of the present invention will now be described in detail.

[0015] In accordance with the present invention, a composition is provided comprising CO2, R-32, and CF3I.

[0016] Typically, the compositions of the present invention may comprise about 50 to about 98% CO2 by weight, such as about 52 or about 55 to about 95% by weight, for example, about 59 to about 92% by weight, preferably about 65 or 70 to about 90% by weight, and optionally about 75 to about 87% by weight.

[0017] Conveniently, the compositions of the present invention comprise from about 2 to about 25 wt. % R-32, for example, from about 3 to about 21 wt. %, optionally from about 3 to about 15 wt. %, such as from about 1 to about 30 wt. % R-32.

[0018] Advantageously, the compositions of the present invention comprise from about 1 or 2 to about 20 wt. % CF3I, such as from about 3 to about 15 or about 13 wt.

[0019] Typically, the compositions of the present invention contain about 50 to about 98 wt. % CO2, about 1 to about 30 wt. % R-32, and about 1 to about 20 wt. % CF3I, such as about 55 to about 90 wt. % CO2, about 2 to about 28 wt. % R-32, and about 2 to about 17 wt. % CF3I, e.g., about 57 to about 85 wt. % CO2, about 2 to about 26 wt. % R-32, and about 3 to about 17 wt. % CF3I.

[0020] The compositions of the present invention may further comprise R-1132a.

[0021] When present, the compositions of the present invention typically comprise about 4 to about 17 wt. % R-1132a, e.g., about 7 to about 16 wt. %, optionally about 10 to about 15 wt. %, or about 1 or about 2 to about 20 wt. % R-1132a.

[0022] Advantageously, the amount of R-1132a is selected so that the compositions of the present invention contain R-32 and R-1132a in a combined amount of less than about 37% by weight, such as less than about 35% by weight.

[0023] Conveniently, the compositions of the present invention comprise R-32 and CF3I in a weight ratio of R-32 to CF3I of less than about 2:1, such as less than about 1.8:1.

[0024] The compositions of the present invention may further 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.

[0025] 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 further comprise one or more of R-1234yf and R-1234ze(E) as additional components.

[0026] Conveniently, the compositions of the present invention comprise from about 3 to about 12% by weight, for example from about 1 to about 15% by weight, such as from about 4 or from about 5 to about 10% by weight, of the additional component.

[0027] In one embodiment, the composition of the present invention consists essentially of the listed components. The term "consisting essentially of" means that the composition of the present invention is substantially free of other components, particularly additional (hydro)(fluoro) compounds (e.g., (hydro)(fluoro)alkanes or (hydro)(fluoro)alkenes) that are known to be used in heat transfer compositions. The term "consisting of" is included in the meaning of "consisting essentially of."

[0028] In one embodiment, the compositions of the present invention are substantially free of any components (other than those specified) that have heat transfer properties. For example, the compositions of the present invention may be substantially free of any other hydrofluorocarbon compounds.

[0029] "Substantially free" and "substantially free" include meaning that the compositions of the present invention contain 0.5% by weight or less of the recited component, based on the total weight of the composition, preferably 0.4%, 0.3%, 0.2%, or 0.1% or less.

[0030] As used herein, all percentage amounts referred to in the compositions herein, including the claims, are by weight based on the total weight of the composition, unless otherwise specified.

[0031] The term "about" when used in connection with numerical values ​​of component amounts in weight percent includes ±0.5 weight percent, for example ±0.2 weight percent.

[0032] For the avoidance of doubt, it is to be understood that the upper and lower limits set forth in the ranges of amounts of ingredients in the compositions of the invention described herein can be interchanged in any manner so long as the resulting range falls within the broadest scope of the invention.

[0033] The compositions of the present invention have an ozone depletion potential of zero.

[0034] Typically, the compositions of the present invention have a global warming potential (GWP) that is less than about 220, such as less than about 210 or less than about 200, for example, less than about 150, preferably less than about 140.

[0035] Conveniently, the compositions of the present invention are non-flammable as determined by ASHRAE Standard 34:2019. For example, the compositions of the present invention are non-flammable at a test temperature of 60°C using ASHRAE-34 methodology. Advantageously, vapor mixtures in equilibrium with the compositions of the present invention are also non-flammable at any temperature between about -20°C and 60°C.

[0036] The compositions of the present invention are believed to exhibit a completely unexpected combination of low flammability / non-flammability, low GWP, improved lubricant compatibility, and improved performance characteristics when used in refrigeration systems, particularly air conditioning systems, some of which are described in more detail below.

[0037] Typically, the compositions of the present invention have a coefficient of performance (COP) that is greater than or approximately equal to the COP of CO2.

[0038] Conveniently, the compositions of the present invention have a temperature gradient 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.

[0039] Advantageously, the compositions of the present invention have a volumetric refrigeration capacity that is within about 20%, eg, within about 25%, such as within about 15%, of the volumetric refrigeration capacity of CO2.

[0040] Typically, the compositions of the present invention have an operating pressure lower than the operating pressure in a CO2 condenser or evaporator.

[0041] The compositions of the present invention are typically suitable for use in existing designs of equipment and are considered compatible with all types of lubricants currently in use with established HFC refrigerants. They may optionally be stabilized or compatibilized with mineral oils by the use of appropriate additives.

[0042] 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(alpha-olefin), and combinations thereof, preferably, the lubricant is selected from PAG, POE, and combinations thereof.

[0043] Conveniently, the stabilizer is selected from diene compounds, phosphates, phenolic compounds, and epoxides, and mixtures thereof.

[0044] 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.

[0045] Typically, the heat transfer system is a refrigeration, heat pump, or air conditioning system.

[0046] Preferably, the refrigeration system comprises a commercial refrigeration system (such as a supermarket display refrigeration system, a beverage cooler refrigeration system, a warehouse refrigeration system, or a cold room refrigeration system), or a transport refrigeration system (e.g., a refrigeration system mounted in a refrigerated shipping container or a refrigeration system mounted in a vehicle).

[0047] Conveniently, the heat pump system comprises a water heater heat pump system.

[0048] Preferably, the air conditioning system comprises a transportation air conditioning system, such as a bus, car, train, or truck air conditioning system.

[0049] Advantageously, the heat transfer (eg, refrigeration, heat pump, and / or air conditioning) system defined above operates as a transcritical heat transfer system for at least part of the year.

[0050] In some applications of transcritical cycle technology, the vapor compression cycle used is a single compression cycle, as is typical in mobile air conditioning applications. In other applications, gas compression is carried out in two stages, allowing efficient operation over large temperature differences between the heat source and heat sink. The compositions of the present invention are believed to be suitable for use in single and dual compression stage cycles.

[0051] One aspect of the present invention provides for the use of the compositions of the present invention as a replacement for existing working fluids in heat transfer devices, such as new heat transfer devices designed to meet the same application requirements.

[0052] Conveniently, the existing working fluid is R-410A. Alternatively, the existing working fluid may be R-407C.

[0053] In another aspect of the present invention, a heat transfer device is provided comprising the composition of the present invention.

[0054] Preferably, the heat transfer device is a transcritical heat transfer device, such as a transcritical refrigeration, heat pump, or air conditioning device.

[0055] Optionally, the transcritical heat transfer device comprises an internal heat exchanger (IHX) system.

[0056] The transcritical heat transfer device may also include a liquid accumulator located after the evaporator or between the evaporator and the IHX if an IHX is present.

[0057] According to another aspect of the present invention, there is provided a method of producing heat comprising condensing a composition of the present invention in the vicinity of a body to be heated.

[0058] According to another aspect of the present invention, there is provided a method of producing cooling comprising evaporating a composition of the present invention in the vicinity of a body to be cooled.

[0059] All chemicals described herein are commercially available, for example, fluorochemicals can be purchased from Apollo Scientific (UK).

[0060] The compositions of the present invention can be prepared by simply mixing CO, R-32, and CF3I (and optional components, such as R-1132a and / or lubricants) in the desired ratios. The compositions can then be added to a heat transfer device or used in any other manner described herein.

[0061] The invention is illustrated by the following non-limiting examples. [Example]

[0062] The vapor-liquid equilibrium behavior of CO2 with CF3I and R-32 has been described in the academic literature, and available data was used to generate interaction parameters for use in NIST REFPROP9.1 software. The vapor-liquid equilibrium behavior of CF3I with R-32 and R-1132a, and of R-1132a with CO2 and R-32, was experimentally studied over the temperature range of -40°C to 70°C using a constant volume equilibrium apparatus. The resulting data were also used to fit binary interaction parameters for each binary pair. The measurement principle for this experimental work was the determination of vapor pressures of a series of known compositions over a range of temperatures, followed by regression to a thermodynamic model to minimize the difference between the calculated and observed pressures across the data set.

[0063] The interaction parameters thus obtained were used in the NIST REFLEAK5.1 computer program to simulate fractionation of ternary CO2 / R-32 / CF3I and quaternary R-744 / R-1132a / R-32 / CF3I mixtures at 40 °C. The compositions studied had 1-30% R-32, and the quaternary compositions had up to 15 wt% R-1132a. The initial fill composition for these simulations was considered to be 90% of the maximum allowable liquid fill, and the allowable liquid fill was calculated according to the requirements of ASHRAE Standard 34 (2019). Fractionation was performed from the initial fill until 95% mass loss of each composition.

[0064] Modeling a range of compositions led to the following observations. If the total amount of R-1132a+R-32 in the blend is less than about 35%, the initial vapor and liquid composition is non-flammable. When the mass ratio of R-32 to CF3I in the composition is about 2:1 or less, the final liquid and vapor compositions are substantially free of CO2 and R-1132a and contain less than 58% by weight of R-32, ensuring that they are non-flammable.

[0065] Standard refrigeration cycle modeling techniques were then used to estimate the performance of selected compositions of the present invention. As a comparative example, the performance of R-744 was also calculated. When cycle conditions resulted in the high pressure side of the cycle operating above the fluid critical temperature (a "transcritical" cycle), the compressor discharge pressure was changed to affect cycle efficiency (coefficient of performance - The modeled cycle was a transcritical cycle using an internal heat exchanger (IHX) to exchange heat between the gas exiting the gas cooler and the low-pressure vapor exiting the evaporator.

[0066] For modeling purposes, the following conditions were assumed: [Table 1]

[0067] Performance data for selected compositions of the present invention are shown in Table 2 below.

[0068] Performance data shows that the compositions of the present invention have superior energy efficiency and reduced operating pressure compared to CO. In addition, the GWP of the compositions is less than about 210.

[0069] Performance data indicates that it is undesirable to include more than about 30 wt.% R-32 in these compositions due to temperature gradients in the evaporator exceeding 11 K. An R-32 content of 21% or less ensures that the GWP of the composition is less than 150, which is required for some applications under EU F-gas regulations.

[0070] The compositions of the present invention can be further enhanced by the addition of R-1132a, for example, by replacing a portion of the R-744 content with R-1132a, so that the R-1132a content is 1% to 15% by weight without producing flammable compositions during fractionation. The addition of R-1132a reduces the compressor discharge temperature and reduces the temperature gradient in the evaporator. Such compositions also have higher energy efficiency and reduced operating pressure compared to R-744. [Table 2]

[0071] The present invention includes the following aspects. [Aspect 1] (a) Carbon dioxide (CO2, R-744) and (b) difluoromethane (R-32), (c) trifluoroiodomethane (CF3I). [Aspect 2] The composition of embodiment 1, comprising about 50 to about 98% CO2 by weight, such as about 52 or about 55 to about 95% by weight, e.g., about 59 to about 92% by weight, preferably about 65 or 70 to about 90% by weight, optionally about 75 to about 87% by weight. [Aspect 3] The composition of embodiment 1 or 2, comprising about 2 to about 25 wt. % R-32, e.g., about 3 to about 21 wt. %, optionally about 3 to about 15 wt. %, such as about 1 to about 30 wt. % R-32. [Aspect 4] Aspect 4. The composition of any one of aspects 1 to 3, comprising about 1 or about 2 to about 20 wt. % CF3I, such as about 3 to about 15 or about 13 wt. % CF3I. [Aspect 5] Aspect 5. The composition of any one of aspects 1-4, wherein the composition further comprises 1,1-difluoroethylene (R-1132a). [Aspect 6] The composition of embodiment 5, comprising about 4 to about 17 wt. % R-1132a, e.g., about 7 to about 16 wt. %, optionally about 10 to about 15 wt. %, or about 2 to about 20 wt. % R-1132a. [Aspect 7] 7. The composition of embodiment 5 or 6, comprising R-32 and R-1132a in a combined amount less than about 37% by weight, such as less than about 35% by weight. [Aspect 8]

[0023] The composition of any one of the preceding embodiments, comprising R-32 and CF3I in a weight ratio of R-32 to CF3I of less than about 2:1, such as less than about 1.8:1. [Aspect 9]

[0023] The composition of any one of the preceding aspects, wherein the composition further comprises 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; e.g., the additional component is R-134a and one or more of R-1234yf and R-1234ze(E). [Aspect 10] The composition of embodiment 9, wherein the composition comprises from about 3 to about 12 wt. %, such as from about 1 to about 15 wt. %, such as from about 4 or from about 5 to about 10 wt. %, of the additional component. [Aspect 11] 10. The composition of any one of the preceding aspects, consisting essentially of the recited components. [Aspect 12] 10. The composition of any one of the preceding aspects, wherein the composition is non-flammable as determined in accordance with ASHRAE Standard 34:2019. [Aspect 13]

[0023] The composition of any one of the preceding embodiments, wherein the composition has a global warming potential (GWP) of less than about 200, e.g., less than about 150, preferably less than about 140, such as less than about 220 or about 210. [Aspect 14] 10. A composition comprising a lubricant, and the composition of any one of the preceding aspects, 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(alpha-olefin), and combinations thereof; and wherein the lubricant is selected from PAG, POE, and combinations thereof. [Aspect 15] A composition comprising a stabilizer, and the composition of any one of the preceding aspects, wherein preferably the stabilizer is selected from diene-based compounds, phosphates, phenolic compounds, and epoxides, and mixtures thereof. [Aspect 16]

[0023] The composition of any one of the preceding embodiments, having a coefficient of performance (COP) greater than or about equal to the COP of CO. [Aspect 17]

[0023] The composition of any one of the preceding embodiments, having a temperature gradient in the evaporator of less than about 11 K, such as less than about 9 K, e.g., less than about 7 K. [Aspect 18]

[0023] The composition of any one of the preceding embodiments, having a volumetric refrigeration capacity that is within about 20%, e.g., within about 25%, such as within about 15%, of the volumetric refrigeration capacity of CO2. [Aspect 19] 10. The composition of any one of the preceding aspects, wherein the composition has an operating pressure lower than the operating pressure in a CO condenser or gas cooler. [Aspect 20] 10. Use of the composition according to any one of the preceding aspects as a working fluid in a heat transfer system, such as a refrigeration, heat pump, or air conditioning system. [Aspect 21] 21. The use of embodiment 20, wherein the refrigeration system comprises a commercial refrigeration system, such as a supermarket display refrigeration system, a beverage cooler refrigeration system, a warehouse refrigeration system, or a cold room refrigeration system. [Aspect 22] 21. The use of embodiment 20, wherein the refrigeration system comprises a transport refrigeration system, such as a refrigeration system mounted on a refrigerated transport container or a refrigeration system mounted on a vehicle. [Aspect 23] 21. The use of aspect 20, wherein the heat pump system comprises a water heater heat pump system. [Aspect 24] 21. The use according to embodiment 20, wherein the air conditioning system comprises a transportation air conditioning system, such as a bus, car, train, or truck air conditioning system. [Aspect 25] 25. The use of any one of aspects 20 to 24, wherein the heat transfer system operates as a transcritical heat transfer system for at least part of the year. [Aspect 26] Aspect 20. Use of the composition of any one of aspects 1-19 as a replacement for an existing working fluid in a heat transfer device, preferably wherein the existing working fluid is R-410A. [Aspect 27] A heat transfer device comprising the composition of any one of embodiments 1-19. [Aspect 28] 27. The heat transfer device of embodiment 26, wherein the heat transfer device is a transcritical heat transfer device, such as a transcritical refrigeration, heat pump, or air conditioner. [Aspect 29] A method of producing heat, comprising condensing the composition of any one of embodiments 1-19 near a body to be heated. [Aspect 30] A method for producing cooling, comprising evaporating the composition of any one of embodiments 1-19 in the vicinity of a body to be cooled.

Claims

[Claim 1] (a) Carbon dioxide (CO ２ , R-744) and (b) difluoromethane (R-32), (c) Trifluoroiodomethane (CF ３ I).

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