Method for improving the flammability of working fluids, use of acid scavengers as flammability enhancers, and flammability enhancers

Abstract

This method is for improving the combustion resistance of a working fluid containing a refrigerator oil and a refrigerant in a refrigerator filled with the working fluid, wherein the refrigerator oil contains 0.1 mass% to 10 mass% of an acid scavenger with respect to the total amount of refrigerator oil.

Description

[Technical Field]

[0001] The present invention relates to a method for improving the flame resistance of a working fluid, the use of an acid scavenger as a flame resistance enhancer, and a flame resistance enhancer. [Background technology]

[0002] Room air conditioners and other refrigeration units are filled with refrigerant oil and refrigerant (compositions containing these are called working fluids). When servicing, relocating, or removing a refrigeration unit, a technique called "pump-down" is sometimes used to recover the refrigerant (see, for example, Patent Document 1 below). Pump-down involves operating the compressor to collect the refrigerant gas inside the unit, and is a safe technique when performed according to the proper procedures.

[0003] However, if the pump-down procedure described above is performed with the piping disconnected due to an error in valve operation or other procedures, the equipment may draw in a large amount of air, and if the compressor continues to operate in this state, the pressure and temperature inside the compressor may rise. In this case, the refrigerant oil and refrigerant filled in the refrigeration unit may burn, which may lead to an explosion (diesel explosion). This phenomenon requires particular attention in refrigeration units that use low-GWP flammable refrigerants, which have attracted attention in recent years. In response to this, Patent Document 2 discloses a method for improving the flammability of a working fluid composition for refrigeration units containing refrigerant oil and refrigerant by adding di-tert-butyl-p-cresol. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-035356 [Patent Document 2] Japanese Patent Publication No. 2020-90605 [Overview of the project] [Problems that the invention aims to solve]

[0005] During the pump-down of a chiller, it is desirable to minimize the possibility of the working fluid burning. Furthermore, even if ignition occurs, it is desirable to be able to control the spread of combustion, prevent an increase in combustion pressure, and reduce the degree of harm. Therefore, the present invention aims to reduce the risk of combustion of the working fluid even if air is accidentally mixed in during the pump-down of a chiller. [Means for solving the problem]

[0006] The inventors have found that by including an acid scavenger in the refrigeration oil, the flammability of the working fluid can be further improved compared to conventional methods (for example, the method described in Patent Document 2).

[0007] One aspect of the present invention is a method for improving the flammability of a working fluid in a refrigerator filled with a working fluid containing refrigerant oil and refrigerant, wherein the refrigerant oil contains an acid scavenger in an amount of 0.1% by mass or more and 10% by mass or less based on the total amount of the refrigerant oil.

[0008] In this method, the amount of acid scavenger to be added when filling the refrigeration oil into the refrigeration unit may be set so that 0.1% by mass or more of the acid scavenger remains in the refrigeration oil, and the acid scavenger may be added to the refrigeration oil that has been filled into the refrigeration unit so that 0.1% by mass or more of the acid scavenger remains in the refrigeration oil.

[0009] Another aspect of the present invention is the use of an acid scavenger as a flame resistance improver, which involves adding 0.1% to 10% by mass of the acid scavenger to the refrigerant oil based on the total amount of the refrigerant oil, thereby improving the flame resistance of the working fluid in a refrigerator filled with a working fluid containing refrigerant oil and refrigerant.

[0010] Another aspect of the present invention is a flame resistance enhancer that improves the flame resistance of a working fluid in a refrigerator filled with a working fluid containing refrigerant oil and refrigerant, the enhancer containing an acid scavenger.

[0011] In each of the above side surfaces, the refrigerant may contain a flammable refrigerant. The refrigerant may contain a highly flammable refrigerant. The refrigerant may contain a slightly flammable refrigerant.

Advantages of the Invention

[0012] According to the present invention, even when air is accidentally mixed during the pump-down of a refrigerator, the combustion risk of the working fluid can be reduced. More specifically, for the working fluid containing the refrigerator oil and the refrigerant filled in the refrigerator, the combustion range and its maximum pressure under the self-ignition and combustion conditions of high temperature and high pressure in the coexistence of air can be reduced. That is, since the combustion resistance of the working fluid can be improved, even when air is accidentally mixed during the pump-down of the refrigerator, the risk of accidents due to the combustion and explosion of the working fluid can be significantly reduced.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram showing an embodiment of a refrigerator. [Figure 2] It is a schematic diagram of a combustion test device. [Figure 3] It is a graph showing an example of the relationship between the refrigerant concentration and the maximum pressure in the compressor.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail. One embodiment of the present invention is a method for improving the combustion resistance of a working fluid in a refrigerator filled with a working fluid containing refrigerator oil and a refrigerant. Another embodiment of the present invention is the use (application) of an acid scavenger as a combustion resistance improver, which can also be said to be a use (application) for improving the combustion resistance of a working fluid in a refrigerator filled with a working fluid containing refrigerator oil and a refrigerant. Another embodiment of the present invention is a combustion resistance improver for improving the combustion resistance of a working fluid in a refrigerator filled with a working fluid containing refrigerator oil and a refrigerant, which contains an acid scavenger.

[0015] ​ The above method includes a step of adding an acid scavenger to the refrigeration oil in an amount of 0.1% by mass or more and 10% by mass or less based on the total amount of the refrigeration oil. In the above use, an acid scavenger is added to the refrigeration oil in an amount of 0.1% by mass or more and 10% by mass or less based on the total amount of the refrigeration oil. The above combustion resistance improver can be added to the refrigeration oil in an amount of 0.1% by mass or more and 10% by mass or less based on the total amount of the refrigeration oil. The above method, use, and combustion resistance improver are effective when the working fluid is exposed to high-temperature and high-pressure auto-ignition and combustion conditions in the presence of air, and are particularly effective during pump-down of the refrigerator.

[0016] <00(00099>In addition, the method for improving the combustion resistance of the above working fluid may be rephrased in other expressions, such as, for example, a method for improving the flame retardancy of the working fluid, a method for suppressing the combustion of the working fluid, a method for narrowing the combustion range of the working fluid, a method for reducing the maximum pressure (hazard level) caused by the combustion of the working fluid, a method for reducing the risk of accidents caused by the combustion and explosion of the working fluid, etc.

[0017] The above use (application) as a combustion resistance improver may be rephrased in other expressions, such as, for example, use (application) as an agent for improving the flame retardancy of the working fluid (flame retardancy improver), use (application) as an agent for suppressing the combustion of the working fluid (combustion suppressor), use as an agent for narrowing the combustion range of the working fluid, use (application) as an agent for reducing the maximum pressure (hazard level) caused by the combustion of the working fluid (maximum pressure reducer, hazard level reducer), use (application) as an agent for reducing the risk of accidents caused by the combustion and explosion of the working fluid (accident risk reducer), etc. <C

[0018] The above combustion resistance improver may be rephrased in other expressions, such as, for example, an agent for improving the flame retardancy of the working fluid (flame retardancy improver), an agent for suppressing the combustion of the working fluid (combustion suppressor), an agent for narrowing the combustion range of the working fluid, an agent for reducing the maximum pressure (hazard level) caused by the combustion of the working fluid (maximum pressure reducer, hazard level reducer), an agent for reducing the risk of accidents caused by the combustion and explosion of the working fluid (accident risk reducer), etc.

[0019] Furthermore, one embodiment of the present invention relates to a working fluid containing refrigerant oil and refrigerant, wherein the refrigerant oil contains 0.1% to 10% by mass of an acid scavenger based on the total amount of refrigerant oil, thereby improving its flammability (during pump-down). This working fluid is effective when exposed to self-ignition and combustion conditions of high temperature and high pressure in the presence of air, and is particularly effective during pump-down of a refrigeration system. This working fluid with improved flammability may be expressed in other terms, such as a working fluid with improved flame retardancy, a working fluid with a narrowed combustion range, a working fluid with reduced maximum pressure (harmfulness) due to combustion, or a working fluid with reduced risk of accidents due to combustion and explosion.

[0020] The embodiments of the present invention will be described in more detail below, but unless otherwise specified, the matters described below are common to all embodiments of the methods, uses, and flame resistance improvers described above.

[0021] Figure 1 is a schematic diagram showing one embodiment of a refrigerator. As shown in Figure 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 3 (capillary, expansion valve, etc.), and an evaporator (heat exchanger) 4 are sequentially connected by a flow path 5. The refrigerator 10 (refrigerant circulation system 6) is filled with a working fluid containing refrigerant oil and refrigerant. The refrigerant circulation system 6 may further include an accumulator 7 between the evaporator 4 and the compressor 1 (on the side of the compressor 1) to suppress and prevent liquid refrigerant from flowing directly into the compressor 1.

[0022] Examples of such refrigeration devices 10 include automotive air conditioners, dehumidifiers, refrigerators, cold storage warehouses, vending machines, display cases, cooling equipment in chemical plants, residential air conditioners, packaged air conditioners, and heat pumps for hot water supply.

[0023] In the refrigerant circulation system 6, first, the high-temperature (usually 70-120°C) 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 as it passes through the narrow flow path of the expansion mechanism 3, and then vaporizes in the evaporator 4, becoming low temperature (usually -40-0°C). The cooling by the refrigerator 10 utilizes the phenomenon that the refrigerant absorbs heat from its surroundings when it vaporizes in the evaporator 4.

[0024] Inside compressor 1, a small amount of refrigerant and a large amount of refrigerant oil coexist under high temperature conditions (typically 70-120°C). The refrigerant discharged from compressor 1 into flow path 5 is in gaseous form and contains a small amount (typically 1-10 volume%) of refrigerant oil as a mist, with a small amount of refrigerant dissolved in this mist-like refrigerant oil (point a in Figure 1).

[0025] Inside the condenser 2, the gaseous refrigerant is compressed into a high-density fluid, and under relatively high temperature conditions (usually 40-80°C), a large amount of refrigerant and a small amount of refrigerant oil coexist (point b in Figure 1). Furthermore, the mixture of the large amount of refrigerant and the small amount of refrigerant oil is sequentially sent to the expansion mechanism 3 and the evaporator 4, where it rapidly cools to a low temperature (usually -40-0°C) (points c and d in Figure 1), and is returned to the compressor 1.

[0026] Refrigeration oil contains a base oil. The base oil may contain at least one selected from mineral oil and synthetic oil.

[0027] The mineral oil may be a paraffinic or naphthenic mineral oil obtained by refining a lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of crude oil such as paraffinic or naphthenic mineral oil, 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 appropriate combinations of two or more.

[0028] The synthetic oil may be, for example, a synthetic hydrocarbon oil or an oxygenated oil, and is preferably an oxygenated oil. Examples of oxygenated oils include esters, polyvinyl ethers, polyalkylene glycols, carbonates, ketones, polyphenyl ethers, silicones, polysiloxanes, and perfluoroethers. The base oil preferably contains an ester.

[0029] Examples of esters include aromatic esters, dibasic acid esters, polyol esters, complex esters, carbonate esters, and mixtures thereof. The ester is preferably a polyol ester.

[0030] Polyol esters are esters of polyhydric alcohols and fatty acids. The fatty acids may be linear or branched. The fatty acids are preferably saturated fatty acids. The number of carbon atoms in the fatty acids is preferably 4 or more, more preferably 5 or more, preferably 20 or less, more preferably 18 or less, and even more preferably 9 or less. The fatty acids preferably include fatty acids having branching at the α and / or β positions, and more preferably include one or both of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.

[0031] 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 or more, more preferably 5 or more, preferably 12 or less, and more preferably 10 or less. The polyhydric alcohol is preferably a hindered alcohol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, or dipentaerythritol, and is more preferably pentaerythritol due to its excellent compatibility with refrigerants and hydrolysis stability.

[0032] The kinematic viscosity of the base oil at 40°C is preferably 1 mm². 2 / s or more, more preferably 2 mm 2 / s or more, 3mm2 / s or more, or 4 mm 2 / s or more, preferably 500 mm 2 / s or less, more preferably 400 mm 2 / s or less. The kinematic viscosity of the base oil at 100 °C is preferably 1 mm 2 / s or more, more preferably 2 mm 2 / s or more, preferably 50 mm 2 / s or less, more preferably 30 mm 2 / s or less. The viscosity index of the base oil may preferably be -50 or more, more preferably -40 or more, still more preferably -30 or more, and may preferably be 300 or less, more preferably 120 or less, still more preferably 115 or less, and particularly preferably 110 or less. The kinematic viscosity and viscosity index in this specification mean the values measured in accordance with JIS K2283:2000.

[0033] The content of the base oil is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more based on the total amount of the refrigerant oil.

[0034] In the refrigerant oil, in addition to the base oil, an acid scavenger is contained. Examples of the method of containing an acid scavenger in the refrigerant oil include a method of directly adding and dissolving or dispersing an acid scavenger in the refrigerant oil, a method of preparing a concentrated solution in advance by dissolving an acid scavenger in a solvent capable of dissolving the acid scavenger and adding the concentrated solution to the refrigerant oil, and the like.

[0035] Examples of the acid scavenger include epoxy-based acid scavengers (epoxy compounds), carbodiimide-based acid scavengers (carbodiimide compounds), and the like. Both epoxy compounds and carbodiimide compounds react with water, fatty acids, oxidation degradation products, etc., and have the effect of preventing these substances from causing problems such as promoting the degradation of the refrigerant and lubricating oil. Epoxy compounds react relatively slowly with water, fatty acids, or oxidation degradation products, and carbodiimide compounds react quickly with water, fatty acids, or oxidation degradation products.

[0036] Regarding epoxy compounds, it was experimentally confirmed that they react with active species (hydrocarbon radicals, peroxide radicals, carboxylic acids, refrigerant degradation products, etc.) generated in the very early stages of ignition and combustion of a mixture of refrigerant and refrigerant oil, rendering them harmless. Specifically, analysis of the recovered oil after combustion experiments of a mixture of refrigerant and refrigerant oil (properties analysis, elemental analysis, gas chromatography, NMR) confirmed the ring-opening compounds of epoxy and the reaction products between epoxy compounds and active species.

[0037] For carbodiimide compounds, the reactive species in the very early stages of ignition and combustion of the refrigerant and refrigerant oil mixture are rapidly neutralized by a reaction mechanism such as those shown in formulas (1), (2), or (3) below. [ka] This reaction mechanism differs from that of phenolic antioxidants, and under autoignition and combustion conditions of high temperature and high pressure in the presence of air, the acid scavenger is remarkably effective in reducing flammability and hazard. In other words, the acid scavenger can be used as a flame resistance enhancer under autoignition and combustion conditions of high temperature and high pressure in the presence of air. Therefore, it is expected that the elucidation of the mechanism by the present inventors will significantly reduce accidents during pump-down.

[0038] Furthermore, when epoxy compounds and carbodiimide compounds are used in combination, the above effects are obtained synergistically. In addition, when chain-terminating antioxidants (for example, phenolic antioxidants such as di-tert-butyl-p-cresol, or amine-based antioxidants) or various peroxide decomposing agents are added together with epoxy compounds and carbodiimide compounds, the above effects are enhanced, and the amount of each epoxy compound and carbodiimide compound added can be reduced.

[0039] Examples of epoxy acid scavengers include various compounds having an epoxy group structure, such as glycidyl ester type epoxy compounds, glycidyl ether type epoxy compounds, oxirane compounds, alkyloxirane compounds, alicyclic epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils.

[0040] As glycidyl ester type epoxy compounds, epoxy compounds having a hydrocarbon group (aryl group, alkyl group, or alkenyl group) with 5 to 18 carbon atoms are preferred, more specifically, glycidyl benzoate, glycidyl neodecanoate, glycidyl-2,2-dimethyloctanoate, glycidyl acrylate, or glycidyl methacrylate.

[0041] As glycidyl ether type epoxy compounds, epoxy compounds having a hydrocarbon group (aryl group or alkyl group) with 5 to 18 carbon atoms are preferred, more specifically n-butylphenyl glycidyl ether, i-butylphenyl glycidyl ether, sec-butylphenyl glycidyl ether, tert-butylphenyl glycidyl ether, pentylphenyl glycidyl ether, hexylphenyl glycidyl ether, heptylphenyl glycidyl ether, octylphenyl glycidyl ether, nonylphenyl glycidyl ether, decylphenyl glycidyl ether, decyl glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, tetradecyl glycidyl ether, or 2-ethylhexyl glycidyl ether are preferred. Furthermore, the glycidyl ether type epoxy compound may also be neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, polyalkylene glycol monoglycidyl ether, polyalkylene glycol diglycidyl ether, etc.

[0042] Examples of oxirane compounds include oxirane compounds having hydrocarbon groups with 2 to 60 carbon atoms, such as alkyloxirane compounds having linear or branched alkyl groups with 2 to 18 carbon atoms, and (alkyl)aryloxirane compounds with 6 to 60 carbon atoms. More specifically, 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, 1,2-epoxyoctadecane, 1,2-epoxynonadecane, and 1,2-epoxyicosane. More specifically, examples of (alkyl)aryloxirane compounds include styrene oxide and alkyl-styrene oxide.

[0043] Examples of alicyclic epoxy compounds include compounds having a substructure in which the carbon atoms constituting the epoxy group directly constitute an alicyclic ring. An alicyclic epoxy compound may have one such substructure, or it may have two or more. More specifically, examples of alicyclic epoxy compounds include 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.

[0044] Examples of carbodiimide compounds include mono- or dialkylcarbodiimides having linear or branched aliphatic hydrocarbon groups with 1 to 12 carbon atoms, and mono- or di((alkyl)aryl)carbodiimides having aromatic hydrocarbon groups with 6 to 18 carbon atoms. Dialkylcarbodiimides and dialkylphenylcarbodiimides having alkyl groups with 1 to 10 carbon atoms, preferably 2 to 4, are preferred. More specifically, diisopropylcarbodiimide, bis(isopropylphenyl)carbodiimide, bis(diisopropylphenyl)carbodiimide, and bis(triisopropylphenyl)carbodiimide are preferred examples.

[0045] The acid scavenger content may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more, and may be 10% by mass or less, 7% by mass or less, or 5% by mass or less, based on the total amount of refrigerant oil. This acid scavenger content may be the content of the acid scavenger at any point in time (for example, at the time when the refrigerant oil is filled into the refrigeration unit, at the time when the refrigeration unit is pumped down, or at the time when the acid scavenger is replenished to the refrigerant oil filled into the refrigeration unit).

[0046] The refrigeration oil may further contain additives other than acid scavengers. Examples of such additives include antioxidants, anti-wear agents, extreme pressure agents, lubricity agents, defoamers, metal deactivators, viscosity index improvers, pour point depressants, and detergent dispersants. These additives may be used individually or in combination of two or more.

[0047] The kinematic viscosity of the refrigerant oil at 40°C is preferably 1 mm². 2 / s or more, more preferably 2 mm 2 / s or more, 3mm 2 / s or more, or 4mm 2 It may be 1 / s or more, preferably 500 mm 2 / s or less, more preferably 400mm 2 It may be less than or equal to / s. The kinematic viscosity of the refrigerant oil at 100°C is preferably 1 mm 2 / s or more, more preferably 2mm 2 / s or more, preferably 50mm2 / s or less, more preferably 30mm 2 It may be less than or equal to / s. The viscosity index of the refrigeration oil may preferably be -50 or higher, more preferably -40 or higher, even more preferably -30 or higher, preferably 300 or lower, more preferably 120 or lower, even more preferably 115 or lower, and particularly preferably 110 or lower.

[0048] The refrigerant may include a flammable refrigerant or a non-flammable refrigerant. According to this embodiment, even if the refrigerant includes a flammable refrigerant, the flammability of the working fluid can be improved. The flammable refrigerant may be at least one selected from the group consisting of slightly flammable refrigerants, weakly flammable refrigerants, and strongly flammable refrigerants. Non-flammable refrigerants, slightly flammable refrigerants, weakly flammable refrigerants, and strongly flammable refrigerants refer to refrigerants included in the flammability classifications of Class 1 (non-flammable refrigerants), Class 2L (slightly flammable refrigerants), Class 2 (weakly flammable refrigerants), and Class 3 (strongly flammable refrigerants), respectively, in the refrigerant safety class criteria of ISO 817:2014.

[0049] Examples of non-flammable refrigerants include trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane (R22), 2,2-dichloro-1,1,1-trifluoroethane (R123), 1,1,1,2-tetrafluoroethane (R134a), an azeotropic mixture of difluoromethane and pentafluoroethane (R410a), 1,1,1,3,3-pentafluoropropane (R245fa), 1-chloro-3,3,3-trifluoropropene (R1233zd), a mixture of HFCs and HFOs (R513A), and carbon dioxide (CO2).

[0050] Examples of mildly flammable refrigerants include difluoromethane (R32), 2,3,3,3-tetrafluoropropene (R1234yf), 1,3,3,3-tetrafluoropropene (R1234ze), and ammonia (R717).

[0051] Examples of weakly flammable refrigerants include 1-chloro-1,1-difluoroethane (R142b) and 1,1-difluoroethane (R152a).

[0052] Examples of highly flammable refrigerants include propane (R290) and isobutane (R600a).

[0053] In the embodiments described above, when performing a pump-down in the refrigerator 10 to collect refrigerant gas by operating the compressor 1 for purposes such as refrigerant recovery, the flammability of the working fluid can be improved. The improvement in the flammability of the working fluid can be confirmed in the combustion test in the embodiments described later, where, under a mixed atmosphere of refrigerant oil, refrigerant, and air, the maximum pressure inside the compressor is low (low hazard), and the flammability range of the working fluid is narrow (low probability of combustion), as illustrated in Figure 3.

[0054] According to this embodiment, by incorporating an acid scavenger into the refrigeration oil, the flammability of the working fluid can be improved, and consequently, even if pump-down is performed due to an incorrect operation such as the mixing of air, the risk of explosion of the working fluid (diesel explosion) can be significantly reduced.

[0055] In one embodiment, the amount of acid scavenger to be added to the refrigeration oil when filling the refrigeration oil can be set so that 0.1% by mass or more (preferably 0.5% by mass or more, or 1% by mass or more) of the acid scavenger remains in the refrigeration oil at the time of pump-down. For example, if the lifespan of the refrigeration oil is assumed to be 10 years, an accelerated test simulating 10 years of operation can be conducted in advance to determine the amount of acid scavenger to be added so that the period until the acid scavenger is consumed and disappears to 0.1% by mass or less is 10 years or more, and the acid scavenger can be added to the refrigeration oil in advance. More specifically, if the amount of acid scavenger that disappears by the recommended replacement period of the refrigeration oil (10 to 20 years) is X% by mass (0.1 to 10% by mass), then the initial amount of acid scavenger added to the refrigeration oil should be set to 1.1X% by mass or more.

[0056] In one embodiment, an acid scavenger may be added to the refrigerant oil filled in the refrigerator so that 0.1% by mass or more (preferably 0.5% by mass or 1% by mass or more) of the acid scavenger remains in the refrigerant oil when pumped down. Alternatively, the additive composition (antioxidants, anti-wear agents, and other additives) may be adjusted to suppress the generation of acid due to deterioration of the refrigerant oil or working fluid so that the acid scavenger in the refrigerant oil or working fluid is less likely to disappear. [Examples]

[0057] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0058] The base oil is a polyol ester of pentaerythritol and 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid (molar ratio: 50 / 50) (kinematic viscosity at 40°C: 68 mm²). 2 kinematic viscosity at 100°C: 8.3 mm² / s 2 We prepared a solution with a viscosity index of 88 ( / s).

[0059] [Examples 1 and 2] In Examples 1 and 2, in addition to the base oil mentioned above, refrigerant oil was prepared by adding 1% by mass and 5% by mass of acid scavenger A (glycidyl 2,2-dimethyloctanoate) based on the total amount of refrigerant oil, respectively.

[0060] [Example 3] In Example 3, in addition to the base oil mentioned above, refrigerant oil was prepared by adding 1% by mass of acid scavenger B (3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate) based on the total amount of refrigerant oil.

[0061] [Comparative Example 1] In Comparative Example 1, a refrigeration oil consisting solely of the above-mentioned base oil (refrigeration oil without an acid scavenger) was prepared.

[0062] [Comparative Examples 2 and 3] In Comparative Examples 2 and 3, in addition to the base oil mentioned above, refrigerant oil was prepared by adding 1% by mass and 5% by mass of an antioxidant (di-tert-butyl-p-cresol) to the refrigerant oil, based on the total amount of the refrigerant oil, respectively.

[0063] <Combustion Test> Figure 2 is a schematic diagram of the combustion test apparatus used in the combustion test. As shown in Figure 2, the combustion test apparatus 21 reproduces the mixing of air into the refrigerant piping and compressor during pump-down, and the adiabatic compression of the refrigerant, air, and refrigerant oil mixture. The combustion test apparatus 21 mainly consists of a refrigerant supply unit 22, an air supply unit 23, an oil supply unit 24, a temperature control unit 25, and a compressor (model engine) 26.

[0064] The refrigerant is supplied from the refrigerant supply unit 22, and then its flow rate is controlled by a mass flow controller 27 (Fujikin; FCST1050LC-4F2-F50L-N2, accuracy ±2%FS) before being supplied to the temperature control unit 25. The air is supplied from the air supply unit 23, then dehumidified by a dehumidifier 28, and then its flow rate is controlled by a mass flow controller 29 (Kofloc; MODEL8550MC-0-1-1) before being supplied to the temperature control unit 25. The refrigerant and air mixed in the temperature control unit 25 are heated to a predetermined temperature (260°C) before being supplied to the compressor 26.

[0065] After being supplied from the oil supply unit 24, the refrigerant oil is pressurized to 150 MPa by the compressor 30 and sprayed onto the mixture of refrigerant and air just before the intake port of the compressor 26 by the oil spray system 31 (manufactured by FC Design; common rail oil spray system).

[0066] The mixture of refrigerant, air, and refrigerant oil obtained above is supplied to a compressor 36 (ENYA; R155-4C, 4-stroke engine, stroke volume 25.42cc, compression ratio 16.0) and compressed by a motor 32 connected to the compressor 36. The compressor pressure is measured using a pressure gauge (Kistler; 6045A, linearity ±0.4% FSO). The motor 32's rotational speed and crank angle can also be controlled by an encoder 33.

[0067] Using the refrigerant oils and refrigerants of the examples and comparative examples shown in Table 1, the compressor pressure was measured using the combustion test apparatus described above, while varying the refrigerant concentration (volume %) relative to the total amount of refrigerant and air, and the refrigerant oil equivalent ratio (equivalent ratio: the ratio of the actually supplied oil flow rate to the oil flow rate required for complete combustion). The refrigerants used were propane (R290), difluoromethane (R32), and 2,3,3,3-tetrafluoropropene (R1234yf). Based on the measurement results, the refrigerant concentration (volume %) was plotted on the horizontal axis and the maximum compressor pressure (dimensionless pressure obtained by dividing by the maximum compressor pressure in a blank test without refrigerant) was plotted on the vertical axis. As an example, the plots for Example 1, Comparative Example 1, and Comparative Example 2 using R290 are shown in Figure 3. From these plots, the combustion range (maximum refrigerant concentration at which an increase in compressor pressure is observed: volume %) and the maximum pressure (maximum pressure value within each plot: dimensionless) were read. The results are shown in Table 1.

[0068] [Table 1]

[0069] As shown in Table 1 and Figure 3, refrigeration oil containing an acid scavenger significantly reduced the flammability range (probability of combustion) and the maximum pressure in the compressor (generated pressure (hazard)) compared to refrigeration oil without an acid scavenger and refrigeration oil containing an antioxidant. The magnitude of this effect is clearly evident from the significantly narrower area enclosed by the plot in Figure 3. Therefore, refrigeration oil containing an acid scavenger can improve the flammability of the working fluid even if air is accidentally mixed in during the pump-down of the refrigeration unit, and consequently, significantly reduce the risk of combustion and explosion (diesel explosion) of the working fluid. [Explanation of symbols]

[0070] 1... Compressor, 2... Condenser, 3... Expansion mechanism, 4... Evaporator, 5... Flow path, 6... Refrigerant circulation system, 7... Accumulator, 10... Refrigerator, 21... Combustion test device, 22... Refrigerant supply unit, 23... Air supply unit, 24... Oil supply unit, 25... Temperature control unit, 26... Compressor (model engine), 27, 29... Mass flow controller, 28... Dehumidifier, 30... Compressor, 31... Oil spray system, 32... Motor, 33... Encoder.

Claims

1. A method for improving the flammability of a working fluid in a refrigerator filled with a working fluid containing refrigerant oil and refrigerant, A method comprising adding to the refrigeration oil an acid scavenger containing at least one selected from a glycidyl ester type epoxy compound, an alicyclic epoxy compound, and a carbodiimide compound, in an amount of 0.1% by mass or more and 10% by mass or less based on the total amount of the refrigeration oil.

2. The method according to claim 1, wherein the content of the acid scavenger when filling the refrigerator with refrigeration oil is set such that 0.1% by mass or more of the acid scavenger remains in the refrigeration oil.

3. The method according to claim 1, wherein the acid scavenger is replenished in the refrigeration oil filled in the refrigeration oil so that 0.1% by mass or more of the acid scavenger remains in the refrigeration oil.

4. The method according to any one of claims 1 to 3, wherein the refrigerant includes a flammable refrigerant.

5. The method according to any one of claims 1 to 3, wherein the refrigerant includes a highly flammable refrigerant.

6. The method according to any one of claims 1 to 3, wherein the refrigerant includes a mildly flammable refrigerant.

7. The use of acid scavengers as flame resistance enhancers, The acid scavenger comprises at least one selected from glycidyl ester type epoxy compounds, alicyclic epoxy compounds, and carbodiimide compounds. The method of improving the flammability of the working fluid in a refrigerator filled with the working fluid containing the refrigerant and refrigerant is to include the acid scavenger in the refrigerant oil at a concentration of 0.1% to 10% by mass based on the total amount of the refrigerant oil.

8. The use according to claim 7, wherein the refrigerant includes a flammable refrigerant.

9. The use according to claim 7, wherein the refrigerant includes a highly flammable refrigerant.

10. The use according to claim 7, wherein the refrigerant includes a mildly flammable refrigerant.

11. A flame resistance enhancer for improving the flame resistance of a working fluid in a refrigerator filled with a working fluid containing refrigerant oil and refrigerant, A flame resistance enhancer containing an acid scavenger comprising at least one selected from glycidyl ester type epoxy compounds, alicyclic epoxy compounds, and carbodiimide compounds.

12. The flame resistance improver according to claim 11, wherein the refrigerant includes a flammable refrigerant.

13. The flame resistance enhancer according to claim 11, wherein the refrigerant includes a highly flammable refrigerant.

14. The flame resistance enhancer according to claim 11, wherein the refrigerant includes a mildly flammable refrigerant.

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