WO2009104784A1

WO2009104784A1 - A mixed refrigerant composition comprising hfc1234yf and hfc125, and a method for operating refrigerator using the same

Info

Publication number: WO2009104784A1
Application number: PCT/JP2009/053129
Authority: WO
Inventors: Takashi Shibanuma; Tatsumi Tsuchiya
Original assignee: Daikin Industries, Ltd.
Priority date: 2008-02-22
Filing date: 2009-02-17
Publication date: 2009-08-27

Abstract

The present invention provides a mixed refrigerant of tetrafluoropropene (CF₃CF=CH₂) and pentafluoroethane (CF₃CHF₂), which is free from the risk of ozone layer depletion, has little effect on global warming (i.e., having a low GWP) and is nonflammable; a flame-resistant or nonflammable refrigerant composition containing the mixed refrigerant, alternative refrigerants to R134a and R410A, which contain the flame-resistant or nonflammable refrigerant composition; and a method for operating the refrigerator containing the refrigerant. The flame-resistant or nonflammable refrigerant composition contains HFC1234yf and HFC125, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 95/5 to 75/25.

Description

DESCRIPTION

A MIXED REFRIGERANT COMPOSITION COMPRISING HFC1234YF AND HFC125, AND A METHOD FOR OPERATING REFRIGERATOR USING THE SAME

TECHNICAL FIELD

The present invention relates to a mixed refrigerant that contains tetrafluoropropene and pentafluoroethane; a flame- resistant or nonflammable refrigerant composition that contains the mixed refrigerant; the flame-resistant or nonflammable refrigerant composition-containing refrigerants that are used as alternatives to R134a and R410A; and a method for operating a refrigerator that uses the refrigerant.

BACKGROUND ART

Chlorofluorohydrocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used as a refrigerant in refrigerators, as a heating medium (refrigerant) in heat pumps, etc., singly, in the form of an azeotropic composition, or as a mixture thereof. These refrigerants have been collectively called chlorofluorocarbons .

However, in the 1980s, it was found that some types of chlorofluorocarbons, once released in the atmosphere, deplete the ozone layer of the stratosphere and eventually have seriously adverse effects on the earth's ecosystem, including humans. Therefore, the use of chlorofluorocarbons (CFCs) posing a high risk of ozone layer depletion is restricted under international agreements, and their use and production have already been prohibited in some advanced countries.

A fluorocarbon called a hydrofluorocarbon (HFC) is most commonly used as an alternative to such chlorofluorocarbons. Specifically, dichlorodifluoromethane (R12) has been used as a refrigerant for household refrigerators, car air conditioners, turbo-refrigerators, and refrigeration devices for cargo containers. However, because of the above-described agreements, dichlorodifluoromethane (R12) has been replaced by 1,1,1,2- tetrafluoroethane (HFC134a) . Furthermore, dichlorodifluoromethane (R22) is gradually being replaced by R410A, which is an HFC-mixed refrigerant composition.

However, -alternative HFCs have a high GWP, and therefore their use is allowed provided that they are not released to the outside.

Under such circumstances, two regulations (so-called F- gas regulations), i.e., "Regulation on certain fluorinated greenhouse gases" and "Directive relating to emissions of f-gas from air conditioning systems fitted to cars", were promulgated in the EU in June 2006. Specifically, mobile air conditioners (e.g., car air conditioners) incorporated in newly manufactured automobiles after 2011, and all automobiles from 2017, must use a refrigerant having a GWP no higher than 150. When this regulation comes into effect, the use of HFC134a, which is currently used as a refrigerant for mobile air conditioners and has a GWP of 1,300, will no longer be allowed. Instead of HFC134a, the use of carbon dioxide (CO₂) , whose GWP is as small as 1, is being proposed and studied. However, carbon dioxide has the following drawbacks. Since it must be highly pressurized, the refrigerator inevitably becomes large, and its refrigeration efficiency is low.

Under such circumstances, several HFC refrigerants having a low GWP have been newly proposed. Japanese Unexamined Patent Publication No. 1992-110388 discloses HFC propenes. Specific examples thereof include fluoropropene (HFC12βlyf; CH₃CF=CH₂) , trifluoropropene (HFCl243zf ; CF₃CH=CH₂, HFC1243yc; CH₃CF=CF₂) , and tetrafluoropropene (HFCl234ze; CF₃CH=CHF, HFC1234yf; CF₃CF=CH₂) . Japanese Unexamined Patent Publication No. 1992-110388 also discloses that these propenes may be mixed with a conventionally used HFC compound that contains HFC125.

WO2004/037913 discloses HFC propenes that may be combined and used as a refrigerant. Specific examples of propenes disclosed in WO2004/037913 include trifluoropropene (HFC1243zf; CF₃CH=CH₂), tetrafluoropropene (HFCl234ze; CF₃CH=CHF, HFC1234yf; CF₃CF=CH₂) , and pentafluoropropene (HFC1225ye; CF₃CF=CHF) .

US7279451 discloses HFC propenes such as HFC1234yf and HFC1225ye, and implies that the propenes may be used in combination with HFC125, etc.

US2007/0007488 discloses a mixture of HFC1234yf and HFC125, wherein the content of HFC125 is 50% to 95%, preferably 60% to 90%, and more preferably 70% to 90%.

WO2006/094303 discloses HFC propenes and various compositions containing such HFC propenes, including a mixture with HFCl234yf and HFC125, but its mixing ratio is not specifically disclosed.

These HFC propenes have a GWP of about 10 at the most, which is significantly lower than those of currently used refrigerants, such as HFC134a (GWP = 1,300) and R410A (GWP =

1,980) . Note that the GWP of known refrigerants are based on the Third Intergovernmental Panel on Climate Change Assessment Report (IPCC, 2001) .

However, HFC1234yf is flammable, although very slightly, having a flammability limit of 5.6 to 13.4 vol% in air.

DISCLOSURE OF THE INVENTION [PROBLEM TO BE SOLVED BY THE INVENTION]

One of the main objects of the present invention is to provide a mixed refrigerant of tetrafluoropropene (CF₃CF=CH₂) and pentafluoroethane (CF₃CHF₂) , which is free from the risk of ozone layer depletion, has little effect on global warming (i.e., has a low GWP) and is flame-retardant or nonflammable; a nonflammable refrigerant composition containing the mixed refrigerant; the flame-retardant or nonflammable refrigerant composition- containing refrigerants that are used as alternatives to R134a and R410A; and a method for operating a refrigerator containing the refrigerant.

[MEANS FOR SOLVING THE PROBLEM] The inventors of the present invention carried out extensive research in view of the above problems and found the following.

HFC1234yf has a low GWP, and therefore is attracting public attention as a potential material for an environmentally friendly refrigerant, but HFC1234yf itself is not a desirable refrigerant owing to its flammability. However, when HFC1234yf is used in combination with HFC125 at a specific constituent ratio, the mixture forms a flame- resistant or nonflammable refrigerant composition that retains the cooling ability of HFC1234yf while reducing the GWP compared to that of conventionally used HFC refrigerants .

The present invention provides the following flame- resistant or nonflammable refrigerant compositions that function as a refrigerant. The present invention also provides the following methods for operating a refrigerator using the refrigerant .

Item 1. A flame-resistant or nonflammable refrigerant composition comprising HFC1234yf and HFC125.

Item 2. The- refrigerant composition according to Item 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 95/5 to 75/25.

Item 3. The refrigerant composition according to Item 1, wherein the mass ratio of HFCl234yf/HFC125 in a liquid phase is in the range of from 93/7 to 75/25. Item 4. The refrigerant composition according to Item 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 93/7 to 80/20.

Item 5. The refrigerant composition according to Item 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 90/10 to 80/20.

Item 6. The refrigerant composition according to any one of Items 1 to 5, which further comprises a stabilizer.

Item 7. A method for operating a refrigerator using the refrigerant composition of any one of Items 1 to 6. Item 8. A method for producing a flame-resistant or nonflammable refrigerant composition comprising mixing HFCl234yf and HFC125 in a liquid phase with an HFCl234yf/HFC125 mass ratio in the range of from 95/5 to 75/25.

EFFECTS OF THE INVENTION

The mixed refrigerant composition of the present invention, which comprises tetrafluoropropene and pentafluoroethane, is free from the risk of ozone layer depletion, has little effect on global warming (i.e., has a low GWP), and is flame-resistant or nonflammable.

DETAILED EXPLANATION OF THE INVENTION The refrigerating capacity and coefficient of performance (COP) of the HFC1234yf (boiling point: -29°C) are compared with those of a conventional product HFC134a (boiling point: -26⁰C) . The refrigerating capacity and COP of the HFC1234yf are 98% and 81%, respectively based on those of the HFCl34a. This result revealed that HFC1234yf has almost no GWP, and has a satisfactory refrigerating capacity that can function as an alternative to HFC134a.

Because HFC1234yf is slightly flammable, CF₃I or a like nonflammable component is added to form a nonflammable refrigerant. However, CF₃I has drawbacks in its stability and ozone depleting potential (ODP) , and therefore such a mixture cannot function as an alternative.

The present inventors conducted extensive research on the relationship between the flammability and the mixing ratios of HFC1234yf, which has a flammable range, and nonflammable HFC125. As a result, they found that the refrigerant composition (hereinafter also referred to as "mixed refrigerant") containing HFCl234yf and HFC125 can be made nonflammable by containing about 20 mol% (21 mass%) or more HFC125 in the vapor phase (evaluated by ASHRAE method below) . Accordingly, by suitably mixing HFCl234yf with HFC125, it is possible to obtain a nonflammable refrigerant having a low GWP and excellent refrigerating capacity. The flarπmability is evaluated according to the ASHRAE method (a 12 L spherical glass flask, ignition by discharge, measured at 60°C) . The ASHRAE method is described in ASHRAE Standard 34-2001-ASTM Designation; E681. The results of the flammability measurement revealed that mixed gas of HFC1234yf and HFC125 (vapor phase) becomes nonflammable when it contains 21 mass% or more HFC125.

According to the ASHRAE method, flammability of the leaked gas mixture composition is evaluated. The leaked gas mixture composition is evaluated for combustion at a temperature selected from either -40°C or the temperature 10 K higher than the boiling point of the gas mixture, which is higher. Regarding the mixed refrigerant that contains HFC1234yf and HFC125, the leaked gas mixture composition is evaluated at a temperature 10 K higher than the boiling point of the gas mixture.

As mentioned above, the mixed refrigerant becomes nonflammable when its mixing ratio in the vapor phase is about HFCl234yf/HFC125 = 79/21 (mass% ratio or mass ratio) . The mixed refrigerant containing HFC1234yf and HFC125 comes to a vapor- liquid equilibrium at a temperature 10 K higher than the boiling point of the gas mixture. When the mixing ratio in the vapor phase is such that the gas mixture becomes nonflammable, the mixing ratio of HFC1234yf and HFC125 in the liquid phase is HFC1234yf/HFCl25=90.β/9.4 (mass ratio). The results revealed that an HFC1234yf/HFC125 mixture (liquid phase) containing about 10 mass% or more HFC125 is nonflammable.

In other words, the mixing ratio of HFC1234yf and HFC125 in the liquid phase of HFC1234yf/HFC125=90.6/9.4 (mass ratio) corresponds to HFC1234yf/HFC125 =79/21 (mass ratio) in the vapor phase wherein the mixed refrigerant becomes nonflammable and vapor-liquid equilibrium. Therefore, by adding HFC125 in an amount approximately meets that mixing ratio, the flammability of HFCl234yf is gradually lowered. Specifically, when the liquid phase mixing ratio of HFC 125 is about 5 mass% or more, the mixed refrigerant is flame-resistant, and when the liquid phase mixing ratio of HFC 125 is about 10 mass% or more, the resulting mixture becomes completely nonflammable.

Accordingly, the content of HFC125 is generally 5 mass% or more, preferably 7 mass% or more, and more preferably 10 mass% or more. The upper limit thereof is 25 mass% or less, and preferably 20 mass% or less. This is because when the content of HFC125 exceeds 25 mass%, the refrigerating ability of the mixed refrigerant is lowered to about 90% or less of the case where HFC123'4yf is used singly. Moreover, because HFC125 has a high GWP (3,400), the content thereof is preferably 25 mass% or less.

Specifically, the HFC1234yf/HFC125 mixing mass ratio in the liquid phase is generally 95/5-75/25, preferably 93/7-75/25, more preferably 93/7-80/20, and most preferably 90/10-80/20.

The refrigerant 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 stabilizer contains at least one type of compound selected from the above compounds (i) , and may optionally contain at least one type of compound selected from the above compounds

(ϋ).

The amount of stabilizer used may vary depending on the type of stabilizer used as long as it does not impair the performance of the nonflammable composition. The stabilizer is used in an amount of generally about 0.1 to about 10 parts by weight, and preferably about 0.1 to about 5 parts by weight, per 100 parts by weight of the mixture of HFC125 and HFC1234yf.

The following known compounds may be used as a polymerization inhibitor singly or in combination with the stabilizer. Examples of compounds usable as a polymerization inhibitor include 4-methoxy-l-naphthol, hydroquinone, hydroquinonemethyl ether, dimethyl-t-butyl phenol, 2,6-di-tert- butyl-p-cresol, benzotriazole, etc.

The amount of polymerization inhibitor is generally about 0.1 to about 5 parts by weight, and preferably about 0.3 to about 1 part by weight, per 100 parts by weight of the mixture of HFC125 and HFC1234yf .

It is preferable that the mixed refrigerant contain at least one component selected from the above-mentioned polymerization inhibitors and stabilizers mentioned above.

HFC125 has a GWP of 3,400, and the GWP of HFC1234yf is 10 or less. Therefore, if the content (mass%) of HFC125 in the mixed refrigerant composition becomes 1/10, the GWP of the mixed refrigerant composition also becomes 1/10 or less. HFC1234yf has a relatively high boiling point and low vapor pressure for use as a refrigerant in devices such as air conditioners and therefore a pipe having a large diameter becomes necessary. Such a drawback can be overcome by adding HFC125, which is a refrigerant that has a low boiling point, to lower the boiling point and raise the vapor pressure. The addition of

HFC125 allows making the diameter of the pipe small, simplifying the piping design compared to the case when HFC1234yf is used alone .

BEST MODE FOR CARRYING OUT THE INVENTION

[EXAMPLES]

The following Examples and Comparative Examples are provided to illustrate the present invention in further detail, but are not intended to limit the scope of the invention. Example 1

HFC1234yf/HFC125 gas mixtures with various ratios were placed in 12 L spherical glass flasks and maintained at 6O⁰C. According to ASHRAE STANDARD 34-2001 ASTM Designation E681, the mixed gases were ignited by discharge (1.5 kV) , and the flammability or nonflammability was determined by observing the -

- 9- spread of the flame at that time. As a result, it was confirmed that when the content of HFC125 in the mixed gases was not less than 20.8 mass%, the mixed gases were nonflammable.

According to the ASHRAE method, flammability of the leaked gas mixture composition is evaluated. In this case, flammability of the leaked gas mixture composition was evaluated at a temperature 10 K higher than the boiling point of the gas mixture .

The vapor-liquid equilibrium was therefore adjusted so that the vapor phase was achieved at the ratio of

HFC1234yf/HFCl25=79/21 (mass ratio) by varying the mixing ratio in the liquid phase at a temperature 10 K higher than the boiling point of the mixed refrigerant gas. Under this condition, such vapor phase was achieved when the mixing ratio of HFC1234yf and HFC125 in the liquid phase was HFC1234yf/HFC125=90.4/9.6 (mass ratio) .

Accordingly, -it became clear that when the HFC1234yf and HFC125 mixed refrigerant contained about 9.6 mass% or more HFC125 in the liquid phase, the mixed refrigerant in the vapor phase was nonflammable according to the ASHRAE method. Comparative Example 1

The refrigerating capacity and COP were measured by conducting an operation under the following conditions. HFCl234yf was used as the heating medium (refrigerant) , the evaporating temperature of the heating medium (refrigerant) in the evaporator was set at 15⁰C, the condensing temperature in the condenser was set at 45°C, the degree of superheat was 5°C, the degree of supercooling was 15⁰C, and the efficiency was 70%. As a result, the refrigerating capacity was 130 kJ/kg and the COP was 5.90. Example 2

The refrigerating capacity and COP were measured in the same manner as in Comparative Example 1, except that HFC1234yf/HFC125=90/10 (mass ratio) was used as the heating medium (refrigerant) . As a result, the refrigerating capacity was 124 kJ/kg and the COP was 5.89. These values correspond to 95.3% and 99.8% of the refrigerating capacity and COP, respectively, of the case when HFC1234yf was used alone. Example 3

The refrigerating capacity and COP were measured in the same manner as in Comparative Example 1, except that

HFC1234yf/HFC125=80/20 (mass ratio) was used as the heating medium (refrigerant) . As a result, the refrigerating capacity was 119 kJ/kg and the COP was 5.86. These values correspond to 91.5% and 99.3% of the refrigerating capacity and COP, respectively, of the case when HFC1234yf was used alone. Example 4

The refrigerating capacity and COP were measured in the same manner as in Comparative Example 1, except that HFC1234yf/HFC125=75/25 (mass ratio) was used as the heating medium (refrigerant) . As a result, the refrigerating capacity was 117 kJ/kg and the COP was 5.84. These values correspond to 90.0% and 98.9% of the refrigerating capacity and COP, respectively, of the case when HFC1234yf was used alone.

Accordingly, it can be concluded that when HFC125 is mixed with HFC1234yf in such a manner that the content of HFC125 in the mixed refrigerant becomes about 5 mass% to about 25 mass% and preferably about 7 mass% to about 20 mass%, the following effects can be achieved.

^■ The flammability of HFC1234yf, which is the drawback of HFC1234yf, can be controlled or reduced.

^■ The low pressure of HFC1234yf can be compensated and therefore design changes such as piping arrangements, etc., become easier.

^■ While maintaining the refrigerating capacity of HFCl234yf at about the same level or about 90%, the GWP can be reduced to 1/2 to 1/6, and 1/3 to 1/8 of a conventionally used refrigerant such as Rl34a or R410A respectively.

The above points allow the mixture of the present invention to be used as a practical nonflammable refrigerant that is environmentally friendly.

Claims

1. A flame-resistant or nonflammable refrigerant composition comprising HFC1234yf and HFC125.

2. The refrigerant composition according to claim 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 95/5 to 75/25.

3. The refrigerant composition according to claim 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 93/7 to 75/25.

4. The refrigerant composition according to claim 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 93/7 to 80/20.

5. The refrigerant composition according to claim 1, wherein the mass ratio of HFC1234yf/HFC125 in a liquid phase is in the range of from 90/10 to 80/20.

6. The refrigerant composition according to any one of claims 1 to 5, which further comprises a stabilizer.

7. A method for operating a refrigerator using the refrigerant composition of any one of claims 1 to 6.

8. A method for producing a flame-resistant or nonflammable refrigerant composition comprising mixing HFC1234yf and HFC125 in a liquid phase with an HFC1234yf/HFC125 mass ratio in the range of from 95/5 to 75/25.