COMPOSITIONS USEFUL AS REFRIGERANTS

Abstract: A refrigerant composition comprising a mixture of difluoromethyl trifluoromethyl ether and at least one other fluorine containing compound selected from 1,1,1,2-tetrafluoroethane, fluoromethyl trifluoromethyl ether and bis(difluoromethyl) ether is claimed.

Description: COMPOSITIONS USEFUL AS REFRIGERANTS. * The present invention relates generally to 5 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) and the azeotropic mixture of 10 dichlorodifluoromethane with 1,1-difluoroethane (Refrigerant R-152a), the azeotrope being Refrigerant R-500. Mechanical refrigeration systems and related heat transfer devices such as heat pumps and 15 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 20 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 25 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 30 freedom from ob ectionable odour. Hitherto, heat transfer devices have tended to use fully and partially halogenated chlorofluorocarbon refrigerants such as dichlorodifluoromethane r (Refrigerant R-12) and chlorodifluoromethane 35 (Refrigerant R-22). 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 in place of Refrigerants R-12 and R-500, particularly the former. 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 difluoromethyl trifluoromethyl ether (CF3OCHF2) and at least one other fluorine containing compound selected from 1 , 1, 1 ,2-tetrafluoroethane (CF3CH2F), fluoromethyl trifluoromethyl ether (CF3OCH2F) and bis (difluoromethyl) ether (CHF2OCHF2) . Refrigerant compositions in accordance with the present invention typically contain from 5 to 952 by weight of difluoromethyl trifluoromethyl ether and from 95 to 52 by weight of at least one compound selected from 1 ,1,1,2-tetrafluoroethane , fluoromethyl trifluoromethyl ether and bis (difluoromethyl ) ether. Additionally, the refrigerant 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 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 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 preferred refrigerant compositions of the invention consist essentially of difluoromethyl trifluoromethyl ether and at least one other fluorine containing compound selected from 1,1 , 1 ,2-tetrafluoroethane , fluoromethyl trifluoromethyl ether and bis (difluoromethyl) ether. Although the refrigerant compositions of the invention may be zeotropic they are preferably azeotropic or azeotrope-like. The preferred compounds for use in admixture with the difluoromethyl trifluoromethyl ether are 1,1, 1,2-tetrafluoroethane and fluoromethyl trifluoromethyl ether, since the resulting refrigerant compositions may provide a particularly suitable replacement for Refrigerant R-12. Therefore, according to one preferred embodiment of the present invention there is provided a refrigerant composition comprising a mixture of difluoromethyl trifluoromethyl ether and 1,1,1,2-tetrafluoroethane . Such compositions may additionally comprise one or more further refrigerant compounds, such as fluoromethyl trifluoromethyl ether and/or bis (difluoromethyl ) ether and/or at least one other fluorinated ether containing residual hydrogen atoms and/or at least one other hydrofluoroalkane . However, refrigerant compositions which consist essentially of difluoromethyl trifluoromethyl ether and 1,1,1, 2-tetrafluoroethane are preferred. In the case of refrigerant compositions comprising difluoromethyl trifluoromethyl ether and 1,1,1,2-tetrafluoroethane as essential components, compositions comprising from 25 to 75 2 by weight of di luoromethyl trifluoromethyl ether and from 75 to 25 2 by weight of 1 ,1,1,2-tetrafluoroethane are preferred, with compositions comprising from 25 to 50 2 by weight of difluoromethyl trifluoromethyl ether and from 75 to 50 2 by weight of 1,1,1,2-tetrafluoroethane being especially preferred. Table 1 shows the results of analysing the performance of a number of refrigerant compositions of the invention in a refrigeration cycle to assess the suitability thereof as a replacement for R-12. All the compositions analysed comprised difluoromethyl trifluoromethyl ether (E-125 in the Table) and 1 ,1 , 1 ,2-tetrafluoroethane (R-134a in the Table) in varying amounts. The percentage by weight of each component in the refrigerant compositions analysed is" given in the second row of the Table. Thus, the results of analysing the performance of the following refrigerant compositions are given in Table 1: (1) A composition comprising 75 2 by weight of 1,1, 1 ,2-tetrafluoroethane and 25 2 by weight of difluoromethyl trifluoromethyl ether. (2) A composition comprising 50 2 by weight of 1,1,1,2-tetrafluoroethane and 50 2 by weight of difluoromethyl trifluoromethyl ether. (3) A composition comprising 25 2 by weight of 1 , 1 , 1,2-tetrafluoroethane and 75 2 by weight of difluoromethyl trifluoromethyl ether. The operating conditions which were used for the analysis are comparable to 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 Table 1, 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 under identical operating conditions is also shown in Table 1 by way of comparison. From Table 1, it is apparent that refrigerant compositions according to the invention comprising difluoromethyl trifluoromethyl ether and 1,1,1,2-tetrafluoroethane can exhibit a performance in a refrigeration system which is comparable to that of Refrigerant R-12. It is also apparent that refrigerant compositions containing from 25 to 50 2 by weight of difluoromethyl trifluoromethyl ether and from 75 to 50 2 by weight of 1,1,1,2-tetrafluoroethane offer a particularly suitable alternative to Refrigerant R-12. Furthermore, the glide in the evaporator for all the mixed refrigerant compositions tested was 0.8°C or less showing that such compositions are azeotrope like. According to another preferred embodiment of the present invention there is provided a refrigerant composition comprising a mixture of difluoromethyl trifluoromethyl ether and fluoromethyl trifluoromethyl ether. Such compositions may additionally comprise one or more further refrigerant compounds, such as 1 ,1, 1 ,2-tetrafluoroethane and/or bis (difluoromethyl ) ether and/or at least one other fluorinated ether containing residual hydrogen atoms and/or at least one other hydrofluoroalkane . However, refrigerant compositions which consist essentially of difluoromethyl trifluoromethyl ether and fluoromethyl trifluoromethyl ether are preferred. Compositions comprising difluoromethyl trifluoromethyl ether and fluoromethyl trifluoromethyl ether benefit from the high capacity (cooling duty per unit swept volume) of the former compound and high efficiency (coefficient of performance) of the latter compound. Such compositions preferably comprise from 25 to 75 2 by weight of difluoromethyl trifluoromethyl ether and from 75 to 25 2 by weight of fluoromethyl trifluoromethyl ether. Table 2 shows the results of analysing the performance of a number of refrigerant compositions of the invention in a refrigeration cycle to assess the suitability thereof as a replacement for R-12. All the compositions analysed comprised difluoromethyl trifluoromethyl ether (E-125 in the Table) and fluoromethyl trifluoromethyl ether (E-134a in the Table) in varying amounts. The percentage by weight of each component in the refrigerant compositions analysed is given in the second row of the Table. Thus, the results of analysing the performance of the following refrigerant compositions are given in Table 2: (1) A composition comprising 75 2 by weight of difluoromethyl trifluoromethyl ether and 25 2 by weight of fluoromethyl trifluoromethyl ether. (2) A composition comprising 50 2 by weight of difluoromethyl trifluoromethyl ether and 50 2 by weight of fluoromethyl trifluoromethyl ether. (3) A composition comprising 25 2 by weight of difluoromethyl trifluoromethyl ether and 75 2 by weight of fluoromethyl trifluoromethyl ether. The operating conditions which were used for the analysis are comparable to 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 KF Isentropic Compressor Efficiency: 75 2 The performance parameters of the- refrigerant compositions which appear in Table 2 have been described previously in connection with Table 1. The performance of Refrigerant R-12 under identical operating conditions is also shown in Table 2 by way of comparison. From Table 2, it is apparent that refrigerant compositions according to the invention comprising difluoromethyl trifluoromethyl ether 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 for all the mixed refrigerant compositions tested was 1.9°C or less 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 atmospheric lifetime, ozone depletion potential and efficiency. They are especially valuable for applications currently satisfied by R-12 such as domestic refrigeration. TABLE 1 REFRIGERANT R-12 R-134a/E-125 2 BY WEIGHT 100 75/25 50/50 25/75 CONDENSER PRESSURE (Bar) 9.60 10.87 11.56 12.29 EVAPORATOR PRESSURE (Bar) 1.23 1.21 1.36 1.54 DISCHARGE TEMPERATURE (°C) 120.8 106.0 99.5 93.8 RETURN GAS TEMPERATURE (°C) 20.0 20.3 20.3 20.3 VOLUMETRIC FLOW (M 3 /s x 10*) 0.140 0.145 0.138 0.133 COOLING DUTY PER UNIT SWEPT VOLUME ( W/m 3 ) 714 690 725 752 COEFFICIENT OF PERFORMANCE 1.90 1.82 1.76 1.67 BOILING BP* -29.8 -30.11 -33.21 -35.95 POINT (°C) DP** -29.8 -28.92 -31.66 -34.80 GLIDE IN EVAPORATOR (°C) 0 0.6 0.8 0.6 * BP - Bubble Point ** DP = Dew Point TABLE 2 REFRIGERANT R-12 E-125/E-134a 2 BY WEIGHT 100 75/25 50/50 25/75 CONDENSER PRESSURE (Bar) 9.60 10.85 9.07 7.73 EVAPORATOR PRESSURE (Bar) 1.23 1.38 1.14 0.96 DISCHARGE TEMPERATURE (°C) 120.8 90.2 91.4 92.0 RETURN GAS TEMPERATURE (°C) 20.0 20.7 20.8 20.5 VOLUMETRIC FLOW (M 3 /s x 10*) 0.140 0.149 0.173 0.200 COOLING DUTY PER UNIT SWEPT VOLUME (KW/m 3 ) 714 671 578 500 COEFFICIENT OF PERFORMANCE 1.90 1.70 1.76 1.78 BOILING BP* -29.8 -34.75 -30.60 -25.83 POINT (°C) DP** -29.8 -32.15 -27.37 -23.50 GLIDE IN EVAPORATOR (°C) 0 1.7 1.9 1.2 * BP = Bubble Point ** DP - Dew Point

Claims: Claims : 1. A refrigerant composition comprising a mixture of difluoromethyl trifluoromethyl ether and at least one other fluorine containing compound selected from 1,1,1,2-tetrafluoroethane, fluoromethyl trifluoromethyl ether and bis (difluoromethyl) ether. 2. A refrigerant composition as claimed in claim 1, characterised in that it comprises from 5 to 952 by weight of difluoromethyl trifluoromethyl ether and from 95 to 52 by weight of at least one compound selected from 1,1,1,2-tetrafluoroethane, fluoromethyl trifluoromethyl ether and bis(difluoromethyl) ether. 3. A refrigerant composition as claimed in claim 1 or claim 2, characterised in that it comprises difluoromethyl trifluoromethyl ether and 1,1,1,2-tetrafluoroethane . 4. A refrigerant composition as claimed in claim 3, characterised in that it consists essentially of difluoromethyl trifluoromethyl ether and 1,1,1,2-tetrafluoroethane. 5. A refrigerant composition as claimed in claim 3 or claim 4, characterised in that it comprises from 25 to 75 2 by weight of difluoromethyl trifluoromethyl ether and from 75 to 25 2 by weight of 1,1,1,2-tetrafluoroethane . 6. A refrigerant composition as claimed in claim 5, characterised in that it comprises from 25 to 50 2 by weight of difluoromethyl trifluoromethyl ether and from 75 to 50 2 by weight of 1, 1,1,2-tetrafluoroethane . 7. A refrigerant composition as claimed in claim 1 or claim 2, characterised in that it comprises difluoromethyl trifluoromethyl ether and fluoromethyl trifluoromethyl ether. 8. A refrigerant composition as claimed in claim 7, characterised in that it consists essentially of 5 difluoromethyl trifluoromethyl ether and fluoromethyl trifluoromethyl ether. 9. A refrigerant composition as claimed in claim 7 or claim 8, characterised in that it comprises from 25 to 75 2 by weight of difluoromethyl 10 trifluoromethyl ether and from 75 to 25 2 by weight of fluoromethyl trifluoromethyl ether. 10. A heat transfer device containing a refrigerant composition as claimed in any one of claims 1 to 9. 11. Use of a refrigerant composition as claimed in any one of claims 1 to 9 in a heat transfer device. 15 12. A method for providing cooling which comprises condensing the refrigerant composition claimed in any one of claims 1 to 9 and thereafter evaporating it in a heat exchange relationship with a body to be cooled. 13. A method for providing heating which comprises 20 condensing the refrigerant composition claimed in any one of claims 1 to 9 in a heat exchange relationship with a body to be heated and thereafter evaporating it. 25 30 35

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