Operating method of refrigerant circulation system

Abstract

A method for operating a refrigerant circulation system that comprises a compressor, a condenser, an expansion mechanism, and an evaporator connected by piping in the stated order, wherein a refrigerant containing trifluoroiodomethane is used as a refrigerant, a refrigerator oil containing a polyol ester as a base oil is used as a refrigerator oil, the polyol ester is synthesized from a polyhydric alcohol and fatty acids, the proportion of a fatty acid having 9 carbon atoms is 65 mol% or less of the fatty acids, and the temperature of the whole refrigerant circulation system is kept at 160ºC or less.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a refrigerant circulation system. [Background technology]

[0002] Refrigeration equipment such as refrigerators and air conditioners are equipped with a refrigerant circulation system that includes a compressor, condenser, expansion mechanism (expansion valve, capillary), evaporator, etc. Cooling is performed by the circulation of refrigerant within this refrigerant circulation system.

[0003] The compressor in the refrigeration circulation system is filled with refrigerant oil to lubricate the sliding parts. The refrigerant oil dissolves in the refrigerant and circulates with the refrigerant within the refrigeration circulation system. The refrigerant oil is used after optimizing its physical properties, including the composition of additives, according to desired characteristics such as lubricity and compatibility with the refrigerant.

[0004] On the other hand, in recent years, as a measure against global warming and for safety reasons, there has been consideration to using refrigerants with low global warming potential (GWP) and that are non-flammable as refrigerants circulating within refrigerant circulation systems. For example, Patent Document 1 below proposes a refrigerant containing methane trifluoride iodide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2015-514827 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when using a refrigerant containing methane trifluoride iodide as a refrigerant in a refrigerant circulation system for the purpose of combating global warming and ensuring safety, the stability of the refrigerant oil may be insufficient depending on the type of refrigerant oil used and the circulation conditions within the refrigerant circulation system.

[0007] The present invention aims to provide an operation method for a refrigerant circulation system that can maintain the stability of refrigerating machine oil at a high level even when a refrigerant containing methyl iodide trifluoride is used in a refrigerant circulation system filled with a refrigerant.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by optimizing the type of refrigerating machine oil and the operating conditions of the refrigerant circulation system, and have completed the present invention.

[0009] That is, the present invention is an operation method for a refrigerant circulation system in which a compressor, a condenser, an expansion mechanism, and an evaporator are connected by piping in this order, using a refrigerant containing methyl iodide trifluoride as the refrigerant, and using a refrigerating machine oil containing, as a base oil, a polyol ester synthesized from a polyhydric alcohol and a fatty acid, with the proportion of the fatty acid having 9 carbon atoms in the fatty acid being 65 mol% or less, and maintaining the temperature of the entire refrigerant circulation system at 160°C or lower.

[0010] In the above method, the refrigerating machine oil may further contain a hindered phenol compound.

[0011] Also, in the above method, the refrigerating machine oil may further contain an acid scavenger.

Effects of the Invention

[0012] According to the present invention, it is possible to provide an operation method for a refrigerant circulation system that can maintain the stability of refrigerating machine oil at a high level even when a refrigerant containing methyl iodide trifluoride is used in a refrigerant circulation system filled with a refrigerant.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram showing an embodiment of a refrigerator.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail.

[0015] FIG. 1 is a schematic diagram showing an embodiment of a refrigerator. As shown in FIG. 1, the refrigerator 10 includes at least a refrigerant circulation system 6 in which a compressor (refrigerant compressor) 1, a condenser (gas cooler) 2, an expansion mechanism (capillary, expansion valve, etc.) 3, and an evaporator (heat exchanger) 4 are sequentially connected by piping through a flow path 5. As the refrigerant, a refrigerant containing iodomethane trifluoride is used. As the refrigerator oil, a refrigerator oil containing a polyol ester synthesized from a polyhydric alcohol and a fatty acid and having a proportion of a fatty acid having 9 carbon atoms in the fatty acid of 65 mol% or less as a base oil is used. During the operation of the refrigerant circulation system 6, the temperature of the entire refrigerant circulation system 6 is maintained at 160° C. or lower.

[0016] In the refrigerant circulation system 6, first, the high-temperature refrigerant discharged from the compressor 1 into the flow path 5 becomes a high-density fluid (supercritical fluid, etc.) in the condenser 2. Subsequently, the refrigerant liquefies by passing through a narrow flow path having the expansion mechanism 3, and further vaporizes in the evaporator 4 to become low temperature. The cooling by the refrigerator 10 utilizes the phenomenon that the refrigerant takes heat from the surroundings when it vaporizes in the evaporator 4.

[0017] In the compressor 1, a small amount of refrigerant and a large amount of refrigerator oil coexist under high-temperature conditions. The refrigerant discharged from the compressor 1 into the flow path 5 is in a gaseous state and contains a small amount (usually 1 to 10% by volume) of refrigerator oil as mist, and a small amount of refrigerant is dissolved in this mist-like refrigerator oil (point a in FIG. 1).

[0018] In the condenser 2, the gaseous refrigerant becomes a high-density fluid compressed, and a large amount of refrigerant and a small amount of refrigerator oil coexist under relatively high-temperature conditions (point b in FIG. 1). Further, the mixture of a large amount of refrigerant and a small amount of refrigerator oil is sequentially sent to the expansion mechanism 3 and the evaporator 4 and rapidly becomes low temperature (points c and d in FIG. 1), and then returned to the compressor 1 again.

[0019] The refrigerant circulation system 6 has components made of, for example, organic polymer material. More specifically, components made of organic polymer material are used, for example, as insulating parts in the compressor 1 and as sealing materials to prevent leakage of refrigerant and refrigerant oil in the compressor 1.

[0020] The refrigerant circulation system 6 is filled with refrigerant. The refrigerant used is one that contains methane trifluoride iodide. Such refrigerant is not particularly limited as long as it contains methane trifluoride iodide, and may contain only methane trifluoride iodide, or it may further contain refrigerants other than methane trifluoride iodide. The content of methane trifluoride iodide is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of refrigerant. Furthermore, the content of methane trifluoride iodide is preferably 100% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, based on the total amount of refrigerant.

[0021] Examples of refrigerants other than methane trifluoride include saturated fluorinated hydrocarbon refrigerants, unsaturated fluorinated hydrocarbon refrigerants, hydrocarbon refrigerants, fluorine-containing ether refrigerants such as perfluoroethers, bis(trifluoromethyl) sulfide refrigerants, and naturally occurring refrigerants such as ammonia and carbon dioxide, as well as mixed refrigerants of two or more selected from these refrigerants.

[0022] Examples of saturated fluorinated hydrocarbon refrigerants include saturated fluorinated hydrocarbons having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms. Specifically, these include difluoromethane (R32), trifluoromethane (R23), pentafluoroethane (R125), 1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), 1,1-difluoroethane (R152a), fluoroethane (R161), 1,1,1,2,3, Examples include 3,3-heptafluoropropane (R227ea), 1,1,1,2,3,3-hexafluoropropane (R236ea), 1,1,1,3,3,3-hexafluoropropane (R236fa), 1,1,1,3,3-pentafluoropropane (R245fa), and 1,1,1,3,3-pentafluorobutane (R365mfc), or mixtures of two or more of these.

[0023] As saturated fluorinated hydrocarbon refrigerants, the above are selected appropriately according to the application and required performance, for example: R32 alone; R23 alone; R134a alone; R125 alone; a mixture of R134a / R32 = 60-80% by mass / 40-20% by mass; a mixture of R32 / R125 = 40-70% by mass / 60-30% by mass; R125 / R143a = 40-60% by mass / 6 Preferred examples include mixtures of 0-40 mass%, mixtures of R134a / R32 / R125 = 60 mass%, 30 mass%, and 10 mass%, mixtures of R134a / R32 / R125 = 40-70 mass%, 15-35 mass%, and 5-40 mass%, and mixtures of R125 / R134a / R143a = 35-55 mass%, 1-15 mass%, and 40-60 mass%. More specifically, mixtures such as R134a / R32 = 70 / 30 mass%; R32 / R125 = 60 / 40 mass%; R32 / R125 = 50 / 50 mass% (R410A); R32 / R125 = 45 / 55 mass% (R410B); R125 / R143a = 50 / 50 mass% (R507C); R32 / R125 / R134a = 30 / 10 / 60 mass%; R32 / R125 / R134a = 23 / 25 / 52 mass% (R407E); and R125 / R134a / R143a = 44 / 4 / 52 mass% (R404A) can be used.

[0024] As a mixed refrigerant of methane trifluoride iodide and the above-mentioned saturated fluorinated hydrocarbon refrigerant, preferred examples include R32 / R125 / methane trifluoride iodide mixed refrigerant and R32 / R410A / methane trifluoride iodide mixed refrigerant. The ratio of R32 to methane trifluoride iodide in such a mixed refrigerant is preferably 10-90:90-10, more preferably 30-70:70-30, even more preferably 40-60:60-40, and particularly preferably 50-60:50-40, from the viewpoint of compatibility with refrigeration oil, low GWP, and non-flammability. Similarly, the ratio of the mixed refrigerant of R32 and methane trifluoride iodide to R125 is preferably 10-95:90-5, more preferably 50-95:50-5, and even more preferably 80-95:20-5, from the viewpoint of low GWP.

[0025] The unsaturated fluorinated hydrocarbon (HFO) refrigerant is preferably fluoropropene, more preferably fluoropropene with 3 to 5 fluorine atoms. Specifically, the unsaturated fluorinated hydrocarbon refrigerant is preferably one or more of the following: 1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,3,3,3-tetrafluoropropene (HFO-1234ze), 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2,3,3-tetrafluoropropene (HFO-1234ye), and 3,3,3-trifluoropropene (HFO-1243zf). From the viewpoint of refrigerant properties, it is preferable to use one or more selected from HFO-1225ye, HFO-1234ze, and HFO-1234yf.

[0026] Hydrocarbon refrigerants are preferably hydrocarbons having 1 to 5 carbon atoms, more preferably hydrocarbons having 2 to 4 carbon atoms. Specific examples of hydrocarbons include methane, ethylene, ethane, propylene, propane (R290), cyclopropane, n-butane, isobutane, cyclobutane, methylcyclopropane, 2-methylbutane, n-pentane, or mixtures of two or more of these. Among these, those that are gaseous at 25°C and 1 atm are preferred, with propane, n-butane, isobutane, 2-methylbutane, or mixtures thereof being preferred.

[0027] The refrigerant circulation system 6 is filled with refrigerant and refrigerant oil (i.e., it is filled with a working fluid composition for the refrigeration system that contains both refrigerant and refrigerant oil). The refrigerant oil contains a polyol ester as its base oil.

[0028] Polyol esters are esters synthesized from polyhydric alcohols and fatty acids. Saturated fatty acids are preferably used as the fatty acids. The number of carbon atoms in the fatty acids is preferably 4 to 20, more preferably 4 to 18, even more preferably 4 to 9, particularly preferably 5 to 9, and most preferably 8 to 9. The polyol ester may be a partial ester in which some of the hydroxyl groups of the polyhydric alcohol remain as hydroxyl groups without esterification, or a complete ester in which all hydroxyl groups are esterified, or a mixture of a partial ester and a complete ester.

[0029] Among the fatty acids constituting polyol esters, examples of fatty acids having 4 to 20 carbon atoms include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, and eicosanic acid. These fatty acids may be linear or branched. The fatty acids are preferably fatty acids having branches at the α and / or β positions, and more preferably branched fatty acids having 4 to 9 carbon atoms, specifically selected from 2-methylpropanoic acid, 2-methylbutanoic acid, 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylheptanoic acid, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid, and 2-ethylhexadecanoic acid, and preferably selected from 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.

[0030] In this embodiment, the proportion of C9 fatty acids among the fatty acids constituting the polyol ester must be 65 mol% or less. When the proportion of C9 fatty acids is 65 mol% or less, the generation of C9 fatty acids due to the decomposition of the polyol ester is reduced in the presence of a refrigerant containing methane trifluoride, and the increase in acid value is suppressed. From this viewpoint, the proportion of C9 fatty acids among the fatty acids constituting the polyol ester is preferably 60 mol% or less, more preferably 55 mol% or less. Furthermore, from the viewpoint of maintaining kinematic viscosity and low-temperature characteristics, the proportion of C9 fatty acids is preferably 20 mol% or more, more preferably 40 mol% or more, and even more preferably 45 mol% or more.

[0031] Furthermore, the fatty acids may include fatty acids other than those with 4 to 20 carbon atoms as described above. These fatty acids other than those with 4 to 20 carbon atoms may be, for example, fatty acids with 21 to 24 carbon atoms. These fatty acids with 21 to 24 carbon atoms may be henicoic acid, docosanic acid, tricosanic acid, tetracosanic acid, etc., and may be linear or branched.

[0032] In this embodiment, it is preferable to use a polyol ester synthesized from a fatty acid having 8 carbon atoms and a fatty acid having 9 carbon atoms. When using a polyol ester synthesized from a fatty acid having 8 carbon atoms and a fatty acid having 9 carbon atoms, it is more preferable that the proportion of the fatty acid having 8 carbon atoms among the fatty acids constituting the polyol ester is 40 to 80 mol%, and the proportion of the fatty acid having 9 carbon atoms is 20 to 60 mol%.

[0033] The polyhydric alcohol constituting the polyol ester is preferably a polyhydric alcohol having 2 to 6 hydroxyl groups. The number of carbon atoms in the polyhydric alcohol is preferably 4 to 12, more preferably 5 to 10. The polyhydric alcohol is preferably a hindered alcohol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, or dipentaerythritol. Because it has particularly excellent compatibility with refrigerants and hydrolysis stability, pentaerythritol, dipentaerythritol, or a mixed alcohol of pentaerythritol and dipentaerythritol is preferred.

[0034] The refrigeration oil according to this embodiment may contain only the above-mentioned polyol ester as the lubricating oil base oil, or it may contain lubricating oil base oils other than the above-mentioned polyol ester. The content of the above-mentioned polyol ester in the lubricating oil base oil may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the lubricating oil base oil.

[0035] Such lubricating oil base oils can include hydrocarbon oils, oxygen-containing oils other than the polyol esters mentioned above, and the like. Examples of hydrocarbon oils include mineral oil-based hydrocarbon oils and synthetic hydrocarbon oils. Examples of oxygen-containing oils include esters other than polyol esters, ethers, carbonates, ketones, silicones, and polysiloxanes.

[0036] Mineral oil-based hydrocarbon oils can be obtained by distilling crude oils such as paraffinic and naphthenic oils at atmospheric pressure and under reduced pressure to obtain lubricating oil fractions, and then refining these fractions using methods such as solvent delamination, solvent refining, hydrorefining, hydrocracking, solvent dewaxing, hydrodewaxing, clay treatment, and sulfuric acid washing. These refining methods may be used individually or in combination of two or more.

[0037] Examples of the synthetic hydrocarbon oils include alkylbenzene, alkylnaphthalene, poly-α-olefin (PAO), polybutene, ethylene-α-olefin copolymer, and the like.

[0038] Examples of the esters other than the polyol esters include aromatic esters, dibasic acid esters, complex esters, carbonic esters, and mixtures thereof.

[0039] Examples of the ethers include polyvinyl ether, polyalkylene glycol, polyphenyl ether, perfluoroether, and mixtures thereof.

[0040] From the viewpoint of ensuring lubricity, the kinematic viscosity of the lubricant base oil at 40 °C is preferably 3 mm 2 / s or more, more preferably 4 mm 2 / s or more, still more preferably 5 mm 2 / s or more. From the viewpoint of suppressing the viscous resistance in the compressor, the kinematic viscosity of the lubricant base oil at 40 °C is preferably 100 mm 2 / s or less, more preferably 500 mm 2 / s or less, still more preferably 400 mm 2 / s or less. From the viewpoint of ensuring lubricity, the kinematic viscosity of the lubricant base oil at 100 °C is preferably 1 mm 2 / s or more, more preferably 2 mm 2 / s or more. From the viewpoint of suppressing the viscous resistance in the compressor, the kinematic viscosity of the lubricant base oil at 100 °C is preferably 100 mm 2 / s or less, more preferably 50 mm 2 / s or less.

[0041] The viscosity index of the lubricant base oil may be 70 or more and may be 200 or less.

[0042] Note that the kinematic viscosity and viscosity index in the present invention mean the kinematic viscosity and viscosity index measured in accordance with JIS K2283:2000.

[0043] The lubricating oil base oil content may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of refrigeration oil.

[0044] The refrigeration oil according to this embodiment may preferably further contain a hindered phenol compound. In this specification, a hindered phenol compound is a compound having a structure in which at least one hydroxyl group and at least one, preferably two, tert.-butyl groups are bonded adjacent to a benzene ring. Examples of hindered phenol compounds include 2,6-di-tert.-butyl-p-cresol (DBPC), 2,6-di-tert.-butyl-phenol, 4,4'-methylenebis(2,6-di-tert.-butyl-phenol), and compounds with similar structures, with DBPC being preferred. From the viewpoint of further improving the stability of the refrigeration oil, the content of the hindered phenol compound may preferably be 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the total amount of the refrigeration oil. There is no particular upper limit on the content of hindered phenol compounds, and it is usually 5% by mass or less based on the total amount of refrigerant oil. However, from the viewpoint of suppressing discoloration of the refrigerant oil when air is mixed in, it may be preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.2% by mass or less, based on the total amount of refrigerant oil.

[0045] The refrigeration oil according to this embodiment may preferably further contain an acid scavenger.

[0046] Examples of acid scavengers include epoxy compounds (epoxy acid scavengers). Examples of epoxy compounds include glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils. These acid scavengers can be used individually or in combination of two or more.

[0047] As the glycidyl ether type epoxy compound, for example, an aryl glycidyl ether type epoxy compound or an alkyl glycidyl ether type epoxy compound represented by the following formula (1) can be used.

[0048] [ka] [In formula (1), R a [This represents an aryl group or an alkyl group having 5 to 18 carbon atoms.]

[0049] Preferred glycidyl ether type epoxy compounds represented by formula (1) include phenylglycidyl ether, n-butylphenylglycidyl ether, i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether, tert-butylphenylglycidyl ether, pentylphenylglycidyl ether, hexylphenylglycidyl ether, heptylphenylglycidyl ether, octylphenylglycidyl ether, nonylphenylglycidyl ether, decylphenylglycidyl ether, decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, and 2-ethylhexylglycidyl ether.

[0050] R a When the alkyl group represented by has 5 or more carbon atoms, the stability of the epoxy compound is ensured, decomposition before reaction with water, fatty acids, or oxidative degradation products, or self-polymerization of epoxy compounds can be suppressed, and the function as an acid scavenger can be easily obtained. On the other hand, R a If the alkyl group represented by has 18 or fewer carbon atoms, good solubility with the refrigerant is maintained, making it less likely for it to precipitate in the refrigeration system and cause problems such as poor cooling (reduced heat exchange efficiency) or deterioration of the refrigerant oil performance.

[0051] In addition to the epoxy compound represented by formula (1), other glycidyl ether type epoxy compounds that can be used include neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, polyalkylene glycol monoglycidyl ether, and polyalkylene glycol diglycidyl ether.

[0052] As an example of a glycidyl ester type epoxy compound, one represented by the following formula (2) can be used.

[0053] [ka]

[0054] In formula (2), R b This represents an aryl group, an alkyl group having 5 to 18 carbon atoms, or an alkenyl group.

[0055] Preferred glycidyl ester type epoxy compounds represented by formula (2) include glycidyl benzoate, glycidyl neodecanoate, glycidyl-2,2-dimethyloctanoate, glycidyl acrylate, and glycidyl methacrylate.

[0056] R b When the alkyl group represented by has 5 or more carbon atoms, the stability of the epoxy compound is ensured, preventing decomposition before reacting with moisture, fatty acids, and oxidative degradation products, and suppressing self-polymerization where epoxy compounds polymerize with each other, making it easier to obtain the desired function. On the other hand, R b If the alkyl or alkenyl group represented by has 18 or fewer carbon atoms, good solubility with the refrigerant is maintained, making it less likely for it to precipitate in the refrigerator and cause problems such as poor cooling.

[0057] A alicyclic epoxy compound is a compound that has a substructure in which the carbon atoms constituting the epoxy group directly constitute an alicyclic ring, as represented by the general formula (3) below.

[0058] [ka]

[0059] Preferred alicyclic epoxy compounds include, for example, 1,2-epoxycyclohexane, 1,2-epoxycyclopentane, 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, exo-2,3-epoxynorbornane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 2-(7-oxabicyclo[4.1.0]hept-3-yl)-spiro(1,3-dioxane-5,3'-[7]oxabicyclo[4.1.0]heptane), 4-(1'-methylepoxyethyl)-1,2-epoxy-2-methylcyclohexane, and 4-epoxyethyl-1,2-epoxycyclohexane.

[0060] Examples of aryloxirane compounds include 1,2-epoxystyrene and alkyl-1,2-epoxystyrene.

[0061] Examples of alkyloxirane compounds include 1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, 1,2-epoxytridecane, 1,2-epoxytetradecane, 1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,1,2-epoxyoctadecane, 2-epoxynonadecane, and 1,2-epoxyicosane.

[0062] Examples of epoxidized fatty acid monoesters include esters of epoxidized fatty acids having 12 to 20 carbon atoms with alcohols, phenols, or alkylphenols having 1 to 8 carbon atoms. Preferably, butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, octyl, phenyl, and butylphenyl esters of epoxy stearate are used as epoxidized fatty acid monoesters.

[0063] Examples of epoxidized vegetable oils include epoxy compounds derived from vegetable oils such as soybean oil, linseed oil, and cottonseed oil.

[0064] The acid scavenger is preferably at least one selected from glycidyl ester type epoxy compounds and glycidyl ether type epoxy compounds, and from the viewpoint of excellent compatibility with the resin material used in the components inside the refrigerator, it is preferably at least one selected from glycidyl ester type epoxy compounds.

[0065] The acid scavenger content is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, based on the total amount of refrigerant oil. Furthermore, the acid scavenger content is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, based on the total amount of refrigerant oil.

[0066] The refrigeration oil according to this embodiment may further contain other additives. Examples of other additives include antioxidants such as amine-based antioxidants, extreme pressure agents, oiliness agents, defoaming agents, metal deactivators, anti-wear agents, viscosity index improvers, pour point depressants, and detergent dispersants. The content of these additives may be 10% by mass or less or 5% by mass or less based on the total amount of refrigeration oil.

[0067] From the viewpoint of ensuring lubrication, the kinematic viscosity of the refrigerant oil at 40°C is preferably 3 mm. 2 / s or more, more preferably 4 mm 2 / s or more, more preferably 5mm 2It may be 1 / s or more. The kinematic viscosity of the refrigerant oil at 40°C is preferably 500 mm from the viewpoint of suppressing viscous resistance in the compressor. 2 / s or less, more preferably 400mm 2 / s or less, more preferably 300mm 2 It may be less than or equal to / s. The kinematic viscosity of the refrigerant oil at 100°C is preferably 1 mm from the viewpoint of ensuring lubricity. 2 / s or more, more preferably 2mm 2 It may be 100 mm² or more. The kinematic viscosity of the refrigerant oil at 100°C is preferably 100 mm² from the viewpoint of suppressing viscous resistance in the compressor. 2 / s or less, more preferably 50mm 2 It can be less than or equal to / s.

[0068] The viscosity index of the refrigeration oil may be 70 or higher and 200 or lower.

[0069] The pour point of the refrigeration oil is preferably -10°C or lower, more preferably -20°C or lower. In this invention, the pour point refers to the pour point measured in accordance with JIS K2269:1987.

[0070] The volume resistivity of the refrigerant oil is preferably 1.0 × 10⁻⁶. 9 Ω·m or greater, more preferably 1.0 × 10 10 Ω·m or greater, more preferably 1.0 × 10⁻⁶ 11 It may be Ω·m or greater. In this invention, volume resistivity refers to the volume resistivity measured at 25°C in accordance with JIS C2101:1999.

[0071] The water content of the refrigeration oil is preferably 1200 ppm or less, more preferably 600 ppm or less, even more preferably 100 ppm or less, and most preferably 50 ppm or less, based on the total amount of refrigeration oil. When the water content of the refrigeration oil is within the above range, the rise in the acid value of the refrigeration oil is more effectively suppressed over a long period of time, and the effects of the present invention are more pronounced. In this invention, the water content refers to the water content measured in accordance with JIS K2275 (Karl Fischer titration method).

[0072] The acid value of the refrigeration oil is preferably 1.0 mgKOH / g or less, more preferably 0.1 mgKOH / g or less. When the acid value of the refrigeration oil is 1.0 mgKOH / g or less, chemical stability can be more reliably ensured. The hydroxyl value of the refrigeration oil is usually 0 to 100 mgKOH / g, preferably 50 mgKOH / g or less, more preferably 20 mgKOH / g or less, even more preferably 10 mgKOH / g or less, preferably 0.1 mgKOH / g or more, more preferably 0.5 mgKOH / g or more. When the hydroxyl value of the refrigeration oil is 100 mgKOH / g or less, the insulating performance of the refrigeration oil can be more reliably ensured, and when the hydroxyl value of the refrigeration oil is 0 mgKOH / g or more, solubility in the refrigerant can be more sufficiently ensured. In this invention, the acid value refers to the acid value measured in accordance with JIS K2501:2003, and the hydroxyl value refers to the hydroxyl value measured in accordance with JIS K0070.

[0073] The ash content of the refrigeration oil is preferably 100 ppm or less, more preferably 50 ppm or less. In this invention, ash content refers to ash content measured in accordance with JIS K2272:1998.

[0074] In the operation method of the refrigerant circulation system 6 according to this embodiment, it is necessary to maintain the temperature of the entire refrigerant circulation system 6 at 160°C or below. By maintaining the temperature of the entire refrigerant circulation system 6 at 160°C or below, it is possible to significantly suppress the deterioration of the refrigerant containing methane trifluoride iodide and the refrigeration oil used together with it. From this viewpoint, it is preferable that the temperature of the entire refrigerant circulation system 6 be 150°C or below. There is no particular lower limit to the temperature of the entire refrigerant circulation system 6, but it may be, for example, -100°C. Maintaining the temperature of the entire refrigerant circulation system 6 at 160°C or below means controlling the temperature of the working fluid composition for the refrigerator circulating in the refrigerant circulation system 6 to be 160°C or below. Even if there is localized heat generation in the refrigerator, it is sufficient as long as the temperature of the working fluid composition for the refrigerator is maintained at 160°C or below throughout the entire refrigerant circulation system 6.

[0075] As mentioned above, one way to maintain the temperature of the entire refrigerant circulation system 6 below 160°C is to keep the temperature of the compressor 1, which is the hottest component in the refrigerant circulation system 6, below 160°C.

[0076] Temperature control factors in compressor 1 include, for example, the amount of refrigerant charged (low amount leads to temperature rise), the amount of refrigerant flowing into the compressor (low amount leads to temperature rise), the amount of refrigerant discharged from the compressor (high amount leads to temperature rise), the amount of refrigerant oil charged (low amount leads to temperature rise), the hydraulic pressure in the compressor (high amount leads to temperature rise), the rotational speed of the compressor (high amount leads to temperature rise), and the presence of moisture or air in the compressor (high amount leads to temperature rise). By appropriately setting and managing these control factors according to the specifications of the refrigerant circulation system 6, the temperature can be kept below 160°C.

[0077] Examples of refrigerators 10 equipped with the refrigerant circulation system 6 according to this embodiment include automotive air conditioners, dehumidifiers, refrigerators, cold storage warehouses, vending machines, display cases, cooling devices in chemical plants, residential air conditioners, packaged air conditioners, and heat pumps for hot water supply. [Examples]

[0078] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0079] [Lubricant base oil] Base oil A: Polyol ester of pentaerythritol and a mixed fatty acid of 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid (molar ratio: 48 / 52) (kinematic viscosity at 40°C: 68 mm²) 2 We prepared a solution with a viscosity index of 88 ( / s). Base oil B: Polyol ester of pentaerythritol and a mixed fatty acid of 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid (molar ratio: 44 / 56) (kinematic viscosity at 40°C: 68 mm²) 2 We prepared a solution with a viscosity index of 90 ( / s). Base oil C: Polyol ester of pentaerythritol and a mixed fatty acid of 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid / n-hexanoic acid (molar ratio: 38 / 57 / 5) (kinematic viscosity at 40°C: 70 mm²) 2 We prepared a solution with a viscosity index of 90 ( / s).

[0080] [Refrigerating machine oil] To the above lubricating oil base oil, 0.3% by mass of hindered phenol (DBPC) and 0.7% by mass of an acid scavenger (glycidyl neodecanoate) were added based on the total amount of refrigeration oil to prepare refrigeration oil.

[0081] [Refrigerant] As a refrigerant containing methane trifluoride, difluoromethane (R32), a 50 / 50 mass% mixture of difluoromethane (R32) / pentafluoroethane (R125) (R410A), and methane trifluoride were mixed to prepare a mixed refrigerant containing R32, R125, and methane trifluoride (mixing ratio (mass ratio): R32 / R410A / methane trifluoride = 37.5 / 23 / 39.5) (R32 / R125 / methane trifluoride = 49.0 / 11.5 / 39.5). This mixed refrigerant composition was assigned a GWP of 733 and is classified as a non-flammable refrigerant (A1) by ASHRAE.

[0082] (Examples 1-9 and Comparative Examples 1-3) The following tests were conducted using the above-mentioned refrigerant oil and refrigerant.

[0083] In a 200 ml autoclave, 30 g of refrigerant oil (initial hue L0.5, initial acid value 0.01 mg KOH / g or less), each prepared to have a water content as shown in Tables 1 to 3 below, was placed along with 30 g of the refrigerant prepared above, and one each of 0.6 mmφ × 50 mm catalysts (copper, iron, and aluminum). The autoclave was heated to the temperatures shown in Table 1 and held for 168 hours. After 168 hours, the hue (ASTM D156) and acid value of the refrigerant oil were measured. The results are shown in Tables 1 to 3.

[0084] [Table 1]

[0085] [Table 2]

[0086] [Table 3] [Explanation of Symbols]

[0087] 1... Compressor, 2... Condenser, 3... Expansion mechanism, 4... Evaporator, 5... Flow path, 6... Refrigerant circulation system, 10... Refrigeration unit.

Claims

1. A method for operating a refrigerant circulation system in which a compressor, condenser, expansion mechanism, and evaporator are connected in this order via piping, The refrigerant used consists only of difluoromethane (R32), pentafluoroethane (R125), and methane trifluoride, with a mass ratio of R32 and methane trifluoride to R125 of 80-95:20-5, and a mass ratio of R32 to methane trifluoride of 30-70:70-30. As a refrigeration oil, a refrigeration oil is used that contains a polyol ester as a base oil, which is synthesized from a polyhydric alcohol and a fatty acid, and in which the proportion of a fatty acid with 9 carbon atoms in the fatty acid is 52 mol% or more and 65 mol% or less. A method for maintaining the temperature of the entire refrigerant circulation system below 150°C.

2. The method according to claim 1, wherein the refrigeration oil further comprises a hindered phenol compound.

3. The method according to claim 1 or 2, wherein the refrigeration oil further comprises an acid scavenger.

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