Refrigeration oil and its working fluid composition

Abstract

To provide a refrigeration oil that can suppress the consumption of antioxidants. [Solution] One aspect of the present invention is a refrigeration oil containing, as a base oil, an ester of a trihydric alcohol and a fatty acid having 14 to 20 carbon atoms, and an antioxidant, wherein the peroxide value of the ester is 5 mg / kg or more.

Description

[Technical Field]

[0001] This invention relates to refrigeration oil and working fluid compositions. [Background technology]

[0002] Refrigeration equipment such as refrigerators, car air conditioners, room air conditioners, and vending machines are equipped with a compressor for circulating refrigerant within the refrigeration cycle. The compressor is filled with refrigerant oil to lubricate the sliding parts. Refrigerant oil generally contains a base oil and additives selected according to the desired properties.

[0003] As a base oil for refrigeration oils as described above, for example, esters of polyhydric alcohols and carboxylic acids are often used. For example, Patent Document 1 discloses a refrigeration oil using a base oil of an ester which is a specific polyhydric alcohol and carboxylic acid with a peroxide value of 1 meq / kg or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-25683 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, antioxidants are commonly used additives in refrigeration oil along with the base oil. However, our research has revealed that when certain esters are used as the base oil, the antioxidant may be easily depleted depending on the properties of the ester. When the antioxidant is easily depleted, the amount of antioxidant remaining in the refrigeration oil decreases, which may prevent the expected antioxidant function from being fully realized. Furthermore, especially when phenolic antioxidants are used, quinone compounds are generated as the antioxidant is depleted, which can cause discoloration.

[0006] Therefore, one aspect of the present invention aims to provide a refrigeration oil that can suppress the consumption of antioxidants. [Means for solving the problem]

[0007] As described in Patent Document 1, it was previously thought that a lower peroxide value for an ester was preferable. However, the present inventors have found that in esters of trihydric alcohols and fatty acids having 14 to 20 carbon atoms, if the peroxide value is too low, the antioxidant is easily depleted when the ester is used as a base oil and an antioxidant is used as an additive.

[0008] One aspect of the present invention is a refrigeration oil containing, as a base oil, an ester of a trihydric alcohol and a fatty acid having 14 to 20 carbon atoms, and an antioxidant, wherein the peroxide value of the ester is 5 mg / kg or more.

[0009] The peroxide value (mg / kg) × acid value (mgKOH / g) of the ester may be 100 or less. The peroxide value (mg / kg) × acid value (mgKOH / g) of the ester may be 5 or more. The fatty acid with 14 to 20 carbon atoms may include oleic acid. The antioxidant may include 2,6-di-tert-butyl-4-methylphenol.

[0010] Another aspect of the present invention is a working fluid composition containing the above-mentioned refrigerant oil and a refrigerant. The refrigerant may contain hydrocarbons. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide a refrigeration oil that can suppress the consumption of antioxidants. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. One embodiment of the present invention is a refrigeration oil containing, as a base oil, an ester of a trihydric alcohol and a fatty acid having 14 to 20 carbon atoms, and an antioxidant.

[0013] A trihydric alcohol is an alcohol having three hydroxyl groups. A trihydric alcohol may be an aliphatic alcohol. Examples of trihydric alcohols include trimethylolethane, trimethylolpropane, trimethylolbutane, glycerin, and 1,3,5-pentanetriol. Trimethylolpropane is preferred as the trihydric alcohol.

[0014] The fatty acids having 14 to 20 carbon atoms (hereinafter also referred to as "C14-C20 fatty acids") may be saturated or unsaturated fatty acids. The C14-C20 fatty acids preferably include unsaturated fatty acids, more preferably unsaturated fatty acids with 18 carbon atoms (C18 unsaturated fatty acids), and even more preferably oleic acid. The content of unsaturated fatty acids (preferably C18 unsaturated fatty acids, more preferably oleic acid) may be 70% or more by mass, 75% or more by mass, 80% or more by mass, or 85% or more by mass, and may be 95% or less by mass, 93% or less by mass, or 90% or less by mass, based on the total amount of C14-C20 fatty acids.

[0015] In one embodiment, the C14-C20 fatty acid further includes, in addition to oleic acid, saturated fatty acids having 14-20 carbon atoms (hereinafter also referred to as "C14-C20 saturated fatty acid"). Examples of C14-C20 saturated fatty acids include tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptahexadecanoic acid, octadecanoic acid, nonadecanoic acid, and eicosanoic acid. These C14-C20 saturated fatty acids may be linear or branched. The C14-C20 saturated fatty acid preferably includes at least one selected from the group consisting of linear C14-C20 saturated fatty acids, more preferably includes at least one selected from the group consisting of linear tetradecanoic acid (myristic acid), linear hexadecanoic acid (palmitic acid), and linear octadecanoic acid (stearic acid), and even more preferably includes linear tetradecanoic acid (myristic acid), linear hexadecanoic acid (palmitic acid), and linear octadecanoic acid (stearic acid).

[0016] In another embodiment, the C14-C20 fatty acids further include, in addition to oleic acid, unsaturated fatty acids having 14 to 20 carbon atoms other than oleic acid (hereinafter also referred to as "C14-C20 unsaturated fatty acids"). The C14-C20 unsaturated fatty acids other than oleic acid may have, for example, 1 to 4, 1 to 3, 1 to 2, or 1 carbon-carbon unsaturated bond. Examples of the C14-C20 unsaturated fatty acids other than oleic acid include physeteric acid, myristoleic acid, palmitoleic acid, heptadecenylic acid, petroselinic acid, elaidic acid, vaccenic acid, linoleic acid, linolenic acid, hirgoninic acid, linolenic acid, and arachidonic acid. The C14-C20 unsaturated fatty acids other than oleic acid preferably include at least one selected from the group consisting of unsaturated fatty acids having 16 to 18 carbon atoms, and more preferably include palmitoleic acid.

[0017] In another embodiment, the C14-C20 fatty acids further include both C14-C20 saturated fatty acids and C14-C20 unsaturated fatty acids other than oleic acid in addition to oleic acid. The C14-C20 saturated fatty acids preferably include at least one selected from the group consisting of linear C14-C20 saturated fatty acids and at least one selected from the group consisting of unsaturated fatty acids having 16 to 18 carbon atoms, more preferably include at least one selected from the group consisting of myristic acid, palmitic acid, and stearic acid and palmitoleic acid, and still more preferably include myristic acid, palmitic acid, stearic acid, and palmitoleic acid.

[0018] The content of the C14-C20 saturated fatty acids may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 15% by mass or less, 12% by mass or less, or 10% by mass or less based on the total amount of the C14-C20 fatty acids. The content of the C14-C20 unsaturated fatty acids other than oleic acid may be 1% by mass or more, 3% by mass or more, or 4% by mass or more, and may be 10% by mass or less, 8% by mass or less, or 6% by mass or less based on the total amount of the C14-C20 fatty acids.

[0019] The content of each of the above-described fatty acids is measured by the following procedure. The ester is dissolved in ethanol and subjected to alkaline hydrolysis, followed by trimethylsilyl (TMS) derivatization using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). The types of fatty acids constituting the ester are confirmed as TMS derivatized products by GC / MS analysis of the resulting fatty acid derivatized products. Next, each fatty acid is quantified by GC analysis under the following GC conditions. (GC conditions) • Column: DB-5, 50℃ → 320℃ (15℃ / min) Injection: 300℃, 1μL, split ratio 50:1 • Detector: FID, 320℃ • Standard samples for calibration curves: Palmitic acid (reagent) is used for C14 and C16 fatty acids, and stearic acid (reagent) is used for C18 fatty acids. In addition, fatty acid ethyl compounds may be generated during the TMS derivatization process. The amount of fatty acid TMS derivatized and the amount of fatty acid ethyl compound are added together to calculate the amount of the fatty acid in question.

[0020] The peroxide value of the ester of a trihydric alcohol and a C14-C20 fatty acid is 5 mg / kg or more, preferably 10 mg / kg or more, 15 mg / kg or more, 20 mg / kg or more, or 25 mg / kg or more, from the viewpoint of suppressing the consumption of antioxidants. The peroxide value of the ester may be 400 mg / kg or less, 350 mg / kg or less, or 320 mg / kg or less. In this specification, the peroxide value refers to the peroxide value measured in accordance with JPI-5S-72.

[0021] From the viewpoint of further effectively suppressing the consumption of antioxidants, it is preferable that the peroxide value of the ester is within the above range, while the acid value of the ester is also within an appropriate range. Specifically, from the viewpoint of further effectively suppressing the consumption of antioxidants, the value of peroxide value (mg / kg) × acid value (mgKOH / g) of the ester is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, 6 or more, 7 or more, or 8 or more, preferably 150 or less, more preferably 130 or less, even more preferably 100 or less, 90 or less, 80 or less, 70 or less, 60 or less, or 50 or less.

[0022] From the viewpoint of further suppressing the consumption of antioxidants, the acid value of the ester is preferably 1 mg KOH / g or less, more preferably 0.6 mg KOH / g or less, even more preferably 0.5 mg KOH / g or less, 0.4 mg KOH / g or less, or 0.35 mg KOH / g or less, preferably 0.03 mg KOH / g or more, more preferably 0.05 mg KOH / g or more, even more preferably 0.08 mg KOH / g or more, 0.1 mg KOH / g or more, or 0.12 mg KOH / g or more. The acid value in this specification refers to the acid value measured in accordance with JIS K2501:2003.

[0023] One method for adjusting the peroxide value and acid value of an ester to the above-mentioned range is to use a C14-C20 fatty acid with a biomass content of 50% or more, preferably a C14-C20 unsaturated fatty acid with a biomass content of 50% or more, as the C14-C20 fatty acid constituting the ester, to synthesize the ester to achieve the desired acid value, and then to expose it to air for a certain period of time to achieve the desired peroxide value. By synthesizing an ester using such fatty acids and exposing the ester to air (the longer the contact time between the ester and air), the peroxide value of the ester tends to be higher than that of an ester synthesized by conventional methods. Furthermore, compared to the synthesis of esters for conventional refrigeration oils, it is not necessary to perform excessive treatment to reduce the acid value or peroxide value after synthesizing the ester, and such treatment can be performed as appropriate under the necessary conditions.

[0024] In this specification, biomass degree conceptually represents the percentage of carbon derived from biomass resources (or renewable resources) in the total amount of organic carbon in a sample. For a biomass degree, a value of 100% is expected for a substrate made entirely from biomass resources, 0% for a substrate made entirely from petroleum resources, and a value corresponding to the proportion of biomass-derived carbon in a mixture of biomass-derived and petroleum-derived substrates. Furthermore, the biomass content of an unknown sample refers to the "Biobased Carbon Content" measured according to ASTM D6866-21 "Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis," and is calculated using the following formula. Biomass Carbon Content (%) = pMC / REF(pMC) Here, pMC is the % Modern Carbon value calculated as 14Aspl / 14Astd × 100, REF(pMC) is the pMC value according to the year of production, and 14Aspl is the sample 14 C / 12 C ratio, 14Astd is the standard substance. 14 C / 12 These terms represent the C ratio, and if the calculated biomass content exceeds 100%, it is considered 100% (see the above test methods for details).

[0025] The biomass content of the ester or refrigeration oil containing the ester may preferably be 50% or more, 70% or more, 80% or more, 85% or more, or 100%, and from an economic standpoint, it may preferably be 95% or less or 92% or less.

[0026] The content of esters between trihydric alcohols and C14-C20 fatty acids may be 50% or more by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, or 95% or more by mass, based on the total amount of refrigerant oil.

[0027] The refrigeration oil may further contain base oils other than esters of trihydric alcohols and C14-C20 fatty acids. The other base oils may be, for example, hydrocarbon oils or oxygen-containing oils. Examples of hydrocarbon oils include mineral oils, olefin polymers, naphthalene compounds, alkylbenzenes, etc. Examples of oxygen-containing oils include monoesters (esters of monoalcohols), polyol esters other than esters of trihydric alcohols and C14-C20 fatty acids (esters of polyols having two or more hydroxyl groups), complex esters, polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, perfluoroethers, and other ethers.

[0028] Antioxidants included in refrigeration oil include, for example, phenolic antioxidants and amine-based antioxidants. Examples of phenolic antioxidants include 2,6-di-tert.-butyl-p-cresol, 2,6-di-tert.-butyl-phenol, and 4,4'-methylenebis(2,6-di-tert.-butyl-phenol). Examples of amine-based antioxidants include alkyldiphenylamine and naphthylamine. The antioxidant preferably includes a phenolic antioxidant, and more preferably includes 2,6-di-tert.-butyl-4-methylphenol.

[0029] The antioxidant content may be 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, based on the total amount of refrigerant oil, and may be 3% by mass or less, 2% by mass or less, or 1% by mass or less.

[0030] The refrigerant oil may further contain additives other than antioxidants. Examples of additives other than antioxidants include acid scavengers, anti-wear agents, lubricity agents, defoamers, metal deactivators, and viscosity index improvers. The total content of additives other than antioxidants is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and may be 5% by mass or less, or 2% by mass or less, based on the total amount of the refrigerant oil.

[0031] The refrigeration oil preferably further contains an acid scavenger, more preferably an epoxy-based acid scavenger. Examples of the epoxy-based acid scavenger include glycidyl ester compounds, glycidyl ether compounds, and alicyclic epoxy compounds. The content of the acid scavenger may be 0.1% by mass or more and 3% by mass or less based on the total amount of the refrigeration oil.

[0032] The refrigeration oil preferably further contains an antiwear agent, more preferably a phosphorus-based antiwear agent. Examples of the phosphorus-based antiwear agent include orthophosphate ester compounds, phosphite ester compounds, and thiophosphate ester compounds. The phosphorus-based antiwear agent is preferably an orthophosphate ester compound, more preferably at least one selected from tricresyl phosphate, triphenyl phosphate, trialkyl phosphate, and tri(alkylphenyl) phosphate. The content of the antiwear agent may be 0.1% by mass or more and 3% by mass or less based on the total amount of the refrigeration oil.

[0033] The kinematic viscosity of the refrigeration oil at 40 °C is 10 mm 2 / s or more, 20 mm 2 / s or more, 30 mm 2 / s or more, or 40 mm 2 / s or more, and may be 400 mm 2 / s or less, 300 mm 2 / s or less, 200 mm 2 / s or less, 100 mm 2 / s or less, or 60 mm 2 / s or less.

[0034] The kinematic viscosity of the refrigeration oil at 100 °C is 4 mm 2 / s or more, and 6 mm 2 / s or more, 8 mm 2 / s or more, or 9 mm 2 / s or more, and may be 40 mm 2 / s or less, 25 mm 2 / s or less, 15 mm 2 / s or less, 12 mm 2 / s or less, or 10 mm 2It can be less than or equal to / s.

[0035] The viscosity index of the refrigeration oil may be 110 or higher, 140 or higher, 150 or higher, 160 or higher, or 170 or higher, and may be 300 or lower, 250 or lower, or 220 or lower.

[0036] In this specification, kinematic viscosity and viscosity index refer to kinematic viscosity and viscosity index measured in accordance with JIS K2283:2000.

[0037] Refrigerant oil is used together with a refrigerant. That is, another embodiment of the present invention is a working fluid composition containing refrigerant oil and a refrigerant.

[0038] The refrigerant preferably contains hydrocarbons. The hydrocarbons are preferably hydrocarbons having 2 to 4 carbon atoms. The hydrocarbons are, for example, at least one selected from the group consisting of ethylene, ethane, propane (R290), propylene, cyclopropane, n-butane, isobutane (R600a), cyclobutane, and methylcyclopropane, preferably propane (R290) or isobutane (R600a), and more preferably propane (R290).

[0039] The refrigerant may consist solely of hydrocarbons, or it may further contain other refrigerants in addition to hydrocarbons. The hydrocarbon content may be 50% or more by mass, 60% or more by mass, 70% or more by mass, 80% or more by mass, 90% or more by mass, or 95% or more by mass, based on the total amount of refrigerant. Examples of such other refrigerants include saturated fluorinated hydrocarbons (HFCs) such as R32, R134a, R125, R143a, and R152a; unsaturated fluorinated hydrocarbons (HFOs) such as R1234yf and R1234ze; fluorinated ethers such as perfluoroethers; bis(trifluoromethyl) sulfide; methane trifluoride iodide; ammonia (R717); carbon dioxide (R744); and the like.

[0040] The amount of refrigerant oil in the working fluid composition may be 1 part by mass or more, or 2 parts by mass or more, and may be 500 parts by mass or less, or 400 parts by mass or less, per 100 parts by mass of refrigerant. [Examples]

[0041] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0042] Five types of esters (with a biomass content of approximately 90%) were synthesized from trimethylolpropane and a mixture of C14-C20 fatty acids obtained from animal and vegetable oils with a biomass content of 100% (C14 saturated fatty acid (myristic acid): approximately 0.2-2% by mass, C16 unsaturated fatty acid (palmitoleic acid): approximately 0.1-6% by mass, C16 saturated fatty acid (palmitic acid): approximately 4-6% by mass, C18 unsaturated fatty acid (oleic acid): approximately 87-93% by mass, C18 saturated fatty acid (stearic acid): approximately 1-2% by mass), with an acid value of 0-0.5 mgKOH / g. Five types of esters were prepared by changing the peroxide value by varying the contact time with air, etc., and these esters were used as base oils 1-5. Table 1 shows the peroxide value (measured according to JPI-5S-72), acid value (measured according to JIS K2501:2003), and the values ​​of peroxide value (mg / kg) × acid value (mgKOH / g) for each ester.

[0043] (Evaluation of residual amount of antioxidant) For each of the base oils 1 to 5, 0.3% by mass of the antioxidant (2,6-di-tert-butyl-4-methylphenol), 0.7% by mass of the acid scavenger (glycidyl neodecanoate), and 1% by mass of the anti-wear agent (tricresyl phosphate) were added to the total amount of refrigerant oil to prepare the refrigerant oils for Examples 1 to 4 and Comparative Example 1. Stability tests were conducted on each of the obtained refrigerant oils in accordance with JIS K2211-09 (autoclave test). Specifically, 30g of each refrigerant oil, adjusted to a water content of 1000ppm, was weighed into an autoclave, and after sealing in catalysts (iron, copper, and aluminum wires, all with an outer diameter of 1.6mm and a length of 50mm) and R290 (30g) as a refrigerant, the autoclave was heated at 175°C for 168 hours to perform the stability test. The antioxidant content (by mass) C0 in each refrigerant oil before the stability test and the antioxidant content (by mass) C1 in each refrigerant oil after the stability test were quantified using HPLC or GC, respectively, and the residual amount of antioxidant was calculated using the following formula. The results are shown in Table 1. Residual amount of antioxidant (mass%) = C1 / C0 × 100

[0044] [Table 1]

Claims

1. As a base oil, an ester of a trihydric alcohol and a fatty acid having 14 to 20 carbon atoms, It contains antioxidants, A refrigeration oil having a peroxide value of 5 mg / kg or more of the ester.

2. The refrigerating oil according to claim 1, wherein the value of the peroxide value (mg / kg) × acid value (mgKOH / g) of the ester is 100 or less.

3. The refrigeration oil according to claim 1 or 2, wherein the peroxide value (mg / kg) × acid value (mgKOH / g) of the ester is 5 or more.

4. The refrigerating oil according to any one of claims 1 to 3, wherein the fatty acid having 14 to 20 carbon atoms includes oleic acid.

5. The refrigerant oil according to any one of claims 1 to 4, wherein the antioxidant comprises 2,6-di-tert-butyl-4-methylphenol.

6. A refrigerating oil according to any one of claims 1 to 5, Refrigerant and A working fluid composition containing the following:

7. The working fluid composition according to claim 6, wherein the refrigerant contains a hydrocarbon.

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