Abstract:
The present invention provides a non-flammable refrigerant, which is excellent in handleability while retaining the refrigerating capacity. Specifically, the present invention relates to a refrigerant composition comprising 36 to 50 mass % of 1,1,1,2-tetrafluoroethane (HFC134a) and 50 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO1234yf).

Description:
This application claims the benefit of U.S. Provisional Application No. 61/129,500 filed Jul. 1, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a mixed refrigerant composition containing 1,1,1,2-tetrafluoroethane (HFC134a) and 2,3,3,3-tetrafluoropropene (HFO1234yf) for use in refrigeration and air-conditioning systems. 
     BACKGROUND ART 
     With global warming becoming an increasingly serious issue worldwide, the development of environmentally friendly refrigeration and air-conditioning systems has become increasingly important. Refrigerants have a great influence not only on global warming, but also on the performance of refrigeration and air-conditioning systems. Therefore, the selection of a refrigerant has an important role in reducing carbon dioxide emissions that contribute to global warming. 
     Recently, various partially-fluorinated propenes having a double bond in the molecule, with a lower global warming potential (GWP) than known chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), have been proposed. 
     2,3,3,3-Tetrafluoropropene (HFO1234yf) is one such propene (see, for example, Patent Literatures 1 and 2). This refrigerant is flammable, and ignites at a concentration of 6.5 to 12.5 vol. % in air at 21° C. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: WO2005/105947 
         PTL 2: WO2006/094303 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     When the refrigerant is flammable, the use of a highly safe material in the electrical system is required, and an upper limit is set on the amount of the refrigerant to be charged into an apparatus. An object of the present invention is to provide a non-flammable refrigerant, which is excellent in handleability and free from the above requirements, while retaining the refrigerating capacity. 
     Solution to Problem 
     The inventors of the present invention carried out extensive research in view of the above problems and found that the problems can be solved by using a refrigerant composition containing 36 to 50 mass % of 1,1,1,2-tetrafluoroethane (HFC134a) and 50 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO1234yf), and preferably 36 to 42 mass % of HFC134a and 58 to 64 mass % of HFO1234yf in an apparatus in which the refrigerant is circulated through a compressor to form a refrigeration cycle. The present invention has been accomplished based on the above finding. 
     Specifically, the present invention provides the following non-flammable refrigerant composition. 
     Item 1. A refrigerant composition comprising 36 to 50 mass % of 1,1,1,2-tetrafluoroethane (HFC134a) and 50 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO1234yf). 
     Item 2. The refrigerant composition according to Item 1 comprising 36 to 42 mass % of 1,1,1,2-tetrafluoroethane (HFC134a) and 58 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO1234yf). 
     Item 3. The refrigerant composition according to Item 1 or 2, which further comprises a polymerization inhibitor. 
     Item 4. The refrigerant composition according to any one of Items 1 to 3, which further comprises a drying agent. 
     Item 5. The refrigerant composition according to any one of Items 1 to 4, which further comprises a stabilizer. 
     Item 6. A method of operating a refrigerator comprising circulating the refrigerant composition according to any one of Items 1 to 5 through a compressor. 
     Item 7. A method of producing the refrigerant composition according to Item 1 comprising mixing 36 to 50 mass % of 1,1,1,2-tetrafluoroethane (HFC134a) with 50 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO1234yf). 
     Item 8. A refrigerator comprising the refrigerant composition according to any one of Items 1 to 5. 
     Advantageous Effects of Invention 
     The following effects can be achieved by the refrigerant composition of the present invention.
     (1) The refrigerant composition of the invention achieves the same or improved cycle performance compared to a newly proposed HFO1234yf when used as a refrigerant for a heat pump apparatus.   (2) The refrigerant composition of the invention is non-flammable. Therefore, modification of the apparatus specification, such as the use of a highly safe material, is unnecessary.   (3) The refrigerant composition of the invention has no ozone depletion potential (ODP); therefore, it does not contribute to ozone layer depletion, even when not completely collected after use.   

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration view of the apparatus used in a flammability test. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present inventors conducted extensive research on the relationship between the flammability and the mixing ratios of HFO1234yf with a flammable range and HFC134a without a flammable range. The flammability is evaluated in accordance with the method described in Test Example 2. 
     As a result, they found that the refrigerant composition containing 36 to 50 mass % of HFC134a and 50 to 64 mass % of HFO1234yf (the refrigerant composition containing HFC134a/HFO1234yf at a ratio of 36/64 to 50/50 mass %) is non-flammable while retaining refrigerating capacity. Further, the refrigerant composition containing 36 to 42 mass % of HFC134a and 58 to 64 mass % of HFO1234yf (the refrigerant composition containing HFC134a/HFO1234yf at a ratio of 36/64 to 42/58 mass %) achieves more excellent effects, and the refrigerant composition containing 38 to 42 mass % of HFC134a and 58 to 62 mass % of HFO1234yf (the refrigerant composition containing HFC134a/HFO1234yf at a ratio of 38/62 to 42/58 mass %) achieves most excellent effects. 
     HFC134a has a GWP (Integration Time Horizon; ITH=100 yr) of 1,430, while the GWP of HFO1234yf is 4. When the content of HFC134a in the mixed refrigerant becomes 36 to 50 mass, the mixed refrigerant has a GWP less than about half that of HFC134a alone. 
     The non-flammable composition of the invention has high stability. If necessary, stabilizers may be added to meet the requirement of high stability under severe conditions. 
     Examples of such stabilizers include (i) aliphatic nitro compounds such as nitromethane and nitroethane; and aromatic nitro compounds such as nitrobenzene and nitrostyrene; (ii) ethers such as 1,4-dioxane; and amines such as 2,2,3,3,3-pentafluoropropylamine and diphenylamine; butylhydroxyxylene, benzotriazole, etc. The stabilizers can be used singly or in a combination of two or more. 
     The amount of stabilizer may vary depending on the type of stabilizer as long as it does not impair the performance of the non-flammable composition. In general, the amount of stabilizer is preferably about 0.1 to about 10 parts by weight, and more preferably about 0.1 to about 5 parts by weight, per 100 parts by weight of the mixture of HFC134a and HFO1234yf. 
     The composition of the present invention may further contain a polymerization inhibitor. Examples thereof include 4-methoxy-1-naphthol, hydroquinone, hydroquinonemethyl ether, dimethyl-t-butyl phenol, 2,6-di-tert-butyl-p-cresol, benzotriazole, etc. 
     In general, the amount of polymerization inhibitor is preferably about 0.01 to about 5 parts by weight, and more preferably about 0.05 to about 2 parts by weight, per 100 parts by weight of the mixture of HFC134a and HFO1234yf. 
     The composition of the present invention may further contain a drying agent. 
     A refrigeration cycle can be formed by circulating the refrigerant composition of the present invention through a compressor. It is also possible to produce an apparatus for forming a refrigeration cycle in which the refrigerant composition of the present invention is circulated through a compressor. 
     Examples of refrigerating systems capable of using the refrigerant composition of the invention include, but are not limited to, car air-conditioners, refrigerating units for automatic vending machines, industrial/household air-conditioners, gas heat pumps (GHP)/electrical heat pumps (EHP), etc. 
     EXAMPLES 
     The present invention will be described in more detail below by way of Examples; however, the invention is not limited thereto. 
     Test Example 1 
     As refrigerants, HFC134a and HFO1234yf were used in the following ratio (HFC134a/HFO1234yf): 40/60 mass % in Example 1, and 50/50 mass % in Example 2. Using a heat pump apparatus with a rated cooling capacity of 4 kW, operation was conducted at an evaporating temperature of the refrigerant in the evaporator of 10° C., a condensing temperature of the refrigerant in the condenser of 45° C., and degrees of superheat and subcool of 0° C. For comparison, the heat pump apparatus was operated using HFO1234yf (Comparative Example 1) under the same conditions as above, except for setting the degree of superheat at 2.4° C. 
     Based on the above results, the coefficient of performance (COP) and refrigerating effect were obtained using the following formulae.
 
COP=cooling capacity/power consumption
 
Refrigerating effect=cooling capacity/refrigerant circulation quantity
 
     Table 1 shows the COP and refrigerating effect of the refrigerants used in Examples 1 and 2 relative to those of the refrigerant used in Comparative Example 1 (=100). 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Refrig- 
                 Evaporating 
                 Condensing 
               
               
                   
                 COP 
                 erating 
                 Pressure 
                 Pressure 
               
               
                   
                 Ratio 
                 Effect Ratio 
                 (MPa) 
                 (MPa) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 
                 HFC134a/ 
                 101 
                 110 
                 0.46 
                 1.22 
               
               
                 1 
                 HFO1234yf 
                   
                   
                   
                   
               
               
                   
                 (40/60 
                   
                   
                   
                   
               
               
                   
                 mass %) 
                   
                   
                   
                   
               
               
                 Example 
                 HFC134a/ 
                 101 
                 111 
                 0.46 
                 1.23 
               
               
                 2 
                 HFO1234yf 
                   
                   
                   
                   
               
               
                   
                 (50/50 
                   
                   
                   
                   
               
               
                   
                 mass %) 
                   
                   
                   
                   
               
               
                 Compar- 
                 HFO1234yf 
                 100 
                 100 
                 0.43 
                 1.23 
               
               
                 ative Ex- 
                   
                   
                   
                   
                   
               
               
                 ample 1 
               
               
                   
               
             
          
         
       
     
     Test Example 2 
     The flammability of the mixed refrigerants forming the present refrigerant was evaluated by measuring the flammable range using a measurement apparatus in accordance with ASTM E681-2001. See  FIG. 1 . 
     A 12 L spherical glass flask was used so that the combustion state can be visually observed and photographically recorded on video. During the generation of excessive pressure by combustion, gas was allowed to escape from an upper lid. Ignition was achieved by discharge from electrodes placed at one-third of the distance from the bottom. 
                                           Test vessel: 280 mm Φ spherical (Internal volume: 12 liters)                                Test temperature: 60° C.   ±3°   C.       Pressure: 101.3 kPa   ±0.7   kPa       Water: 0.0088 g per gram of dry air   ±0.0005   g       Mixing ratio of refrigerant/air: 1 vol. % increments   ±0.2   vol. %       Refrigerant mixture:   ±0.1   mass %       Ignition method: AC discharge               Electrode interval: 6.4 mm (¼ inch)               Spark: 0.4 sec.   ±0.05   sec.                    
Evaluation criteria: When a flame extends at an angle of 90° or more from the ignition point, it was evaluated as flammable (propagation).
 
     Table 2 shows the flammability evaluation results of the mixed HFC134a and HFO1234yf. The results reveal that the boundary between non-flammable and flammable is established when the ratio of HFC134a/HFO1234yf is 36/64 mass, and that the composition containing 36 mass % or more of HFC134a is non-flammable, even when mixed with air at any ratio. Therefore, it is relevant that the refrigerant of the present invention is non-flammable. 
     
       
         
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Concentration  
                   
               
               
                 of HFC134a 
                 Concentration of mixed gas in air 
               
             
          
           
               
                 in mixed gas 
                 7 vol. % 
                 8 vol. % 
                 9 vol. % 
                 10 vol. % 
                 11 vol. % 
               
               
                   
               
               
                 34 mass % 
                 Non- 
                 Non- 
                 Flammable 
                 Non- 
                 Non- 
               
               
                   
                 flammable 
                 flammable 
                   
                 flammable 
                 flammable 
               
               
                 35 mass % 
                 Non- 
                 Non- 
                 Flammable 
                 Non- 
                 Non- 
               
               
                   
                 flammable 
                 flammable 
                   
                 flammable 
                 flammable 
               
               
                 36 mass % 
                 Non- 
                 Non- 
                 Non- 
                 Non- 
                 Non- 
               
               
                   
                 flammable 
                 flammable 
                 flammable 
                 flammable 
                 flammable 
               
               
                   
               
             
          
         
       
     
     INDUSTRIAL APPLICABILITY 
     The mixed refrigerant composition of the present invention is effective as a refrigerant composition for refrigeration and air-conditioning systems. 
     REFERENCE SIGNS LIST 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 1 
                 Ignition source 
               
               
                 2 
                 Sample inlet 
               
               
                 3 
                 Springs 
               
               
                 4 
                 12-Liter glass flask 
               
               
                 5 
                 Electrodes 
               
               
                 6 
                 Stirrer 
               
               
                 7 
                 Insulated chamber