COMPOSITIONS USEFUL AS REFRIGERANTS

Abstract: A refrigerant composition comprising a mixture of 1,1,1,2-tetrafluoroethane and at least one fluorinated ether selected from trifluoromethyl methyl ether and fluoromethyl trifluoromethyl ether is claimed.

Description: COMPOSITIONS USEFUL AS REFRIGERANTS. The present invention relates generally to refrigerant compositions for cooling and heating applications and to the use of such compositions in heat transfer devices. More particularly, the present invention is concerned with refrigerant compositions which are designed to replace dichlorodifluoromethane (Refrigerant R-12). Mechanical refrigeration systems and related heat transfer devices such as heat pumps and air-conditioning systems are well known. In such devices, a refrigerant liquid of a suitable boiling point evaporates at low pressure taking heat from a 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. The mechanical energy required for compressing the vapour and pumping the liquid may be provided by 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 of a refrigerant include low toxicity, non- flammability , non-corrosivity, high stability and freedom from objectionable odour. Hitherto, heat transfer devices have tended to use fully and partially halogenated chlorofluorocarbon refrigerants. Particular mention may be made of dichlorodifluoromethane (Refrigerant R-12) which possesses a suitable combination of properties and has for many years been the most widely used refrigerant. In recent years, however, there has been increasing international concern that the fully and partially halogenated chlorofluorocarbons may be damaging the earth's protective ozone layer and there is general agreement that their manufacture and use should be severely restricted and eventually phased out completely. 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 substantially lower, preferably zero, ozone depletion potentials . In addition to the possibility of ozone depletion, it has been suggested that significant concentrations of chlorofluorocarbon 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 . The present invention provides a refrigerant composition which may be used as a replacement for Refrigerant R-12. The composition contains refrigerant compounds which have essentially zero ozone depletion potentials and comparatively low direct global warming potentials . Accordingly, the present invention provides a refrigerant composition comprising a mixture of 1,1,1,2-tetrafluoroethane (CF3CH2F) and at least one fluorinated ether selected from trifluoromethyl methyl ether (CF3OCH3) and fluoromethyl trifluoromethyl ether « 5 (CF3OCH2F) . Refrigerant compositions in accordance with the present invention typically contain from 5 to 952 by weight of 1,1,1,2-tetrafluoroethane and from 95 to 52 by weight of the ether. Additionally, the refrigerant 10 compositions of the invention may contain other refrigerant compounds which have low and preferably zero ozone depletion potentials, for example other hydrofluoroalkanes and/or other fluorinated ethers containing residual hydrogen atoms. Examples of other hydrofluoroalkanes which may be incorporated in the 15 refrigerant compositions of the invention include difluoromethane (R-32), 1 , 1 , 1-trifluoroethane (R-143a) , 1 , 1 , 2 , 2-tetrafluoroethane (R-134), pentafluoroethane (R-125) and 1 , 1-difluoroethane (R-152a) . Examples of other fluorinated ethers which may be included in the 20 refrigerant compositions of the invention are the fluorinated dimethyl ethers containing residual hydrogen atoms . Although the refrigerant compositions of the invention may comprise other refrigerant compounds, the 25 preferred refrigerant compositions of the invention consist essentially of 1,1,1,2-tetrafluoroethane and at least one fluorinated ether selected from trifluoromethyl methyl ether and fluoromethyl trifluoromethyl ether. 30 Although the refrigerant compositions of the invention may be zeotropic they are preferably azeotropic or azeotrope-like . In one embodiment of the present invention, the t refrigerant composition comprises a mixture of 35 1,1,1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether. A specific composition of this type is one which consists essentially of the stated components. Such compositions will typically comprise from 25 to 75 2 by weight of 1,1,1,2-tetrafluoroethane and from 75 to 25 2 by weight of fluoromethyl trifluoromethyl ether. Refrigerant compositions of the invention comprising 1,1,1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether as essential components may suitably replace Refrigerant R-12 in many applications. However, such compositions may be particularly useful as a replacement for R-12 in heat pumps and automotive air conditioners. Heat pumps and automotive air conditioners operate with high discharge temperatures, typically around 80 °C, which tends to result in fairly high pressures in the condenser. By using blends of 1,1,1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether as the working fluid in such systems, it is possible to achieve lower condenser pressures at these high discharge temperatures than is possible when Refrigerant R-12 or 1,1,1,2-tetrafluoroethane (the generally accepted replacement for Refrigerant R-12) are used. Our research indicates that at a discharge temperature of 80°C a condenser pressure of around 17.7 bar is attainable when using a refrigerant composition comprising 25 2 by weight of 1,1,1,2-tetrafluoroethane and 75 2 by weight of fluoromethyl trifluoromethyl ether. Table 1 shows the performance of a number of refrigerant compositions of the invention comprising 1,1,1,2-tetrafluoroethane (R-134a in the Table) and fluoromethyl trifluoromethyl ether (E-134a in the Table). The percentage by weight of each component in the refrigerant compositions evaluated is given in the second row of the Table. Thus, refrigerant compositions respectively comprising 75 2 by weight of 1,1,1,2-tetrafluoroethane and 25 2 by weight of fluoromethyl trifluoromethyl ether; 50 2 by weight of 1,1,1,2-tetrafluoroethane and 50 2 by weight of fluoromethyl trifluoromethyl ether; and 25 2 by weight of 1,1,1,2-tetrafluoroethane and 75 2 by weight of fluoromethyl trifluoromethyl ether were evaluated. The operating conditions which were selected for the evaluation are representative of those existing in a domestic refrigeration system. Specifically, these conditions were as follows: Evaporator Temperature: -25°C Condenser Temperature: 40°C Superheat: 45°C Subcooling: 10°C Cooling Duty: 1 KW Isentropic Compressor Efficiency: 75 2 The performance parameters of the refrigerant compositions which are presented in the Table, i.e. condenser pressure, evaporator pressure, discharge temperature, return gas temperature, volumetric flow, system efficiency (coefficient of performance, by which is meant the ratio of cooling duty achieved to mechanical energy supplied to the compressor) , refrigeration capacity (cooling duty per unit swept volume of the compressor), and the glide in the evaporator (the temperature range over which the refrigerant composition boils in the evaporator), are all art recognised parameters. The performance of Refrigerant R-12 and 1,1,1,2-tetrafluoroethane, which is the generally accepted replacement for Refrigerant R-12, under identical operating conditions are also shown in Table 1 by way of comparison. From Table 1, it is apparent that refrigerant compositions according to the invention comprising 1,1,1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether can exhibit a performance in a refrigeration system which is not too far removed from that of Refrigerant R-12. Furthermore, the glide in the evaporator was only 0.2°C for all the mixed refrigerant compositions evaluated showing that such compositions are azeotrope like. In a preferred embodiment of the present invention, the refrigerant composition comprises a mixture of 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether, optionally together with fluoromethyl trifluoromethyl ether and/or at least one other fluorinated ether containing residual hydrogen atoms and/or at least one other hydrofluoroalkane . Particularly preferred refrigerant compositions are mixtures consisting essentially of 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ethe . Refrigerant compositions comprising a mixture of 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether have been found to exhibit a similar performance to Refrigerant R-12 in a refrigeration cycle. In consequence, such compositions may be used in place of Refrigerant R-12 which is at present widely used as a working fluid in refrigeration systems and related heat transfer devices. Furthermore, compositions comprising 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether benefit from the particularly short atmospheric lifetime of trifluoromethyl methyl ether (ca 3.6 years) and, thus, can exhibit a low direct global warming potential . Preferred refrigerant compositions based on 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether comprise from 5 to 75 2 by weight of 1,1,1,2-tetrafluoroethane and from 95 to 25 2 by weight of trifluoromethyl methyl ether. Particularly preferred refrigerant compositions of this type comprise from 5 to 60 Z by weight of 1,1,1,2-tetrafluoroethane and from 95 to 40 2 by weight of trifluoromethyl methyl ether, with compositions comprising from 25 to 50 2 by weight of 1,1,1,2-tetrafluoroethane and from 75 to 50 2 by weight of trifluoromethyl methyl ether being especially preferred. The preferred compositions are therefore characterised by the presence of a substantial amount of trifluoromethyl methyl ether which confers on the composition a lower direct global warming potential. However, surprisingly such compositions also exhibit a performance in a refrigeration system which is comparable to Refrigerant R-12. Trifluoromethyl methyl ether is slightly flammable and our research suggests that mixed refrigerant compositions comprising in excess of 40 2 by weight of this ether and less than 60 2 by weight of 1,1,1,2-tetrafluoroethane may also be flammable. It is believed that the potential flammability of such refrigerant compositions may not be a problem in practice, bearing in mind that heat transfer devices are essentially closed systems and that certain devices, such as domestic refrigeration systems, only contain small quantities of the refrigerant. Moreover, the benefit of using a refrigerant composition comprising a large amount of trifluoromethyl methyl ether opposite reduced global warming potential may outweigh any possible disadvantage opposite flam ability. However, if flammability is a concern, then compositions containing from 70 to 95 2 by weight of 1,1,1,2-tetrafluoroethane and from 30 to 5 2 by weight of trifluoromethyl methyl ether are preferred, with compositions containing from 70 to 85 2 by weight of 1,1,1,2-tetrafluoroethane and from 30 to 15 2 by weight of trifluoromethyl methyl ether being particularly preferred, in view of their non-flammability. Table 2 shows the performance of a number of refrigerant compositions of the invention comprising 1,1,1,2-tetrafluoroethane (R-134a in the Table) and trifluoromethyl methyl ether (E-143a in the Table). The percentage by weight of each component in the refrigerant compositions evaluated is given in the second row of the Table. Thus, refrigerant compositions respectively comprising 75 2 by weight of 1,1,1,2-tetra luoroethane and 25 2 by weight of trifluoromethyl methyl ether; 50 2 by weight of 1,1,1,2-tetrafluoroethane and 50 2 by weight of trifluoromethyl methyl ether; and 25 2 by weight of 1,1,1,2-tetrafluoroethane and 75 2 by weight of trifluoromethyl methyl ether were evaluated. The operating conditions which were selected for the evaluation are representative of those existing in a domestic ref igeration system. Specifically, these conditions were as follows: Evaporator Temperature: •25°C Condenser Temperature: 40°C Superheat : 45°C Subcooling : 10°C Cooling Duty: 1 KW Isentropic Compressor Efficiency: 75 2 The performance parameters of the refrigerant compositions which are presented in the Table, i.e. condenser pressure, evaporator pressure, discharge temperature, return gas temperature, volumetric flow, system efficiency (coefficient of performance, by which is meant the ratio of cooling duty achieved to mechanical energy supplied to the compressor), refrigeration capacity (cooling duty per unit swept volume of the compressor), and the glide in the evaporator (the temperature range over which the refrigerant composition boils in the evaporator), are all art recognised parameters. The performance of Refrigerant R-12 and 1,1,1,2-tetrafluoroethane, which is the generally accepted replacement for Refrigerant R-12, under identical operating conditions are also shown in Table 2 by way of comparison. From Table 2, it is apparent that refrigerant compositions according to the invention comprising 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether can exhibit a performance in a refrigeration system which is comparable to that of Refrigerant R-12. Furthermore, the glide in the evaporator was essentially zero for all the mixed refrigerant compositions tested showing that such compositions are azeotrope like. The refrigerant compositions of the invention may be prepared by a simple mixing process. The compositions are useful in all types of compression cycle heat transfer devices. Thus, they may be used to provide cooling by a method involving condensing the refrigerant composition and thereafter evaporating it in a heat exchange relationship with a body to be cooled. They may also be used to provide heating by a method involving condensing the refrigerant composition in a heat exchange relationship with a body to be heated and thereafter evaporating it. The compositions of the invention provide a good compromise between capacity and efficiency combined with low atmospheric lifetime and essentially zero ozone depletion. They are especially suitable for applications currently satisfied by Refrigerant R-12, for example domestic refrigeration, automobile air-conditioning and refrigerated food transport. TABLE 1 * BP - Bubble Point ** DP = Dew Point TABLE 2 * BP = Bubble Point ** DP =• Dew Point

Claims: Claims : 1. A refrigerant composition comprising a mixture of 1,1,1,2-tetrafluoroethane and at least one fluorinated ether selected from trifluoromethyl methyl ether and fluoromethyl trifluoromethyl ether. 2. A refrigerant composition as claimed in claim 1, characterised in that it comprises from 5 to 95 2 by weight of 1,1,1,2-tetrafluoroethane and from 95 to 5 2 by weight of the ether component. 3. A refrigerant composition as claimed in claim 1 or claim 2, characterised in that it comprises a mixture of 1,1,1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether. 4. A refrigerant composition as claimed in claim 1 or claim 2, characterised in that it comprises a mixture of 1,1,1,2-tetrafluoroethane and trifluoromethyl methyl ether. 5. A refrigerant composition as claimed in claim 4, characterised in that it comprises from 5 to 75 2 by weight of 1,1,1,2-tetrafluoroethane and from 95 to 25 2 by weight of trifluoromethyl methyl ether. 6. A refrigerant composition as claimed in claim 5, characterised in that it comprises from 5 to 60 2 by weight of 1,1,1,2-tetrafluoroethane and from 95 to 40 2 by weight of trifluoromethyl methyl ether. 7. A refrigerant composition as claimed in claim 6, characterised in that it comprises from 25 to 50 2 by weight of 1,1,1,2-tetrafluoroethane and from 75 to 50 2 by weight of trifluoromethyl methyl ether. 8. A refrigerant composition as claimed in claim 4, characterised in that it comprises from 70 to 95 2 by weight of 1,1,1,2-tetrafluoroethane and from 30 to 5 2 by weight of trifluoromethyl methyl ether. 9. A refrigerant composition as claimed in claim 8, characterised in that it comprises from 70 to 85 2 by weight of 1,1,1,2-tetrafluoroethane and from 30 to 15 2 by weight of trifluoromethyl methyl ether. 10. A refrigerant composition as claimed in any one of the preceding claims which additionally comprises at least one other refrigerant compound having a low or zero ozone depletion potential selected from other hydrofluoroalkanes and other fluorinated ethers containing residual hydrogen atoms. 11. A heat transfer device containing a refrigerant composition as claimed in any one of claims 1 to 10. 12. Use of a refrigerant composition as claimed in any one of claims 1 to 10 in a heat transfer device. 13. A method for providing cooling which comprises condensing the refrigerant composition claimed in any one of claims 1 to 10 and thereafter evaporating it in a heat exchange relationship with a body to be cooled. 14. A method for providing heating which comprises condensing the refrigerant composition claimed in any one of claims 1 to 10 in a heat exchange relationship with a body to be heated and thereafter evaporating it.

Inventors: MORRISON JAMES DAVID, POWELL RICHARD LLEWELLYN, MORRISON, JAMES, DAVID, POWELL, RICHARD, LLEWELLYN
Applicants: ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1992
Main classification: C09K5
IPC codes: C07C19, C07C43, C09K5, F25B1