WO2025169833A1 - Lubricant base oil, lubricant oil composition, and cooling system - Google Patents

Abstract

The present invention provides: a lubricant base oil which enables a refrigerant containing the lubricant base oil to have improved chemical stability when used over a long period; and a lubricant oil composition including the lubricant base oil.　This lubricant base oil is for mixing with a refrigerant, the refrigerant including a hydrocarbon compound having 1-8 carbon atoms. The lubricant base oil contains a compound represented by formula 1 and has a metal content of 10 ppm or less.　Formula 1: R¹\{(R²O)_mR³\}_n; R¹ is an initiator residue; the R² moieties are each independently a C2-C4 hydrocarbon group; the R³ moieties are each independently a hydrogen atom or a C1-C4 alkyl group, wherein at least one of the R³ moieties is a C1-C4 alkyl group; m is 1-200; and n is 1-8.

Description

Lubricating base oils, lubricating oil compositions and cooling systems

The present invention relates to lubricating base oils, lubricating oil compositions, and cooling systems.

Various lubricating base oils are used to ensure smooth circulation of the refrigerant in compression-type refrigerators. Compounds such as polyalkylene glycols, polyol esters, and polyvinyl ethers can be used as lubricating base oils depending on the type of refrigerant. For example, Patent Document 1 discloses in its working examples that a lubricating base oil containing an epoxy compound such as 1,2-epoxyhexadecane and a polyalkylene glycol is mixed with the refrigerant. Furthermore, because the refrigerant and lubricating base oil are sealed and used within the refrigerator for long periods of time, they must be stable enough to prevent the formation of precipitates even after long-term use.

Japanese Patent Application Publication No. 6-240278

However, when refrigerants blended with conventional lubricating base oils are used for an extended period of time, deposits can form. As such, there is room for improvement in the chemical stability of refrigerants blended with lubricating base oils when used for an extended period of time.

The present invention provides a lubricating base oil that improves the chemical stability of refrigerants blended with the lubricating base oil when used over an extended period of time, and a lubricating oil composition containing the lubricating base oil.

The present invention has the following aspects.
[1] A lubricating base oil that is mixed with a refrigerant,
the refrigerant contains a hydrocarbon compound having 1 to 8 carbon atoms;
The lubricating base oil comprises a compound represented by the following formula 1:
A lubricating base oil having a metal content of 10 ppm or less.
R ¹ {(R ² O) _m R ³ } _n ...Formula 1
In formula 1,
^R1 is an initiator residue;
^R2 is independently a hydrocarbon group having 2 to 4 carbon atoms,
^R3 's each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms;
At least one of the ^R3s is an alkyl group having 1 to 4 carbon atoms,
m is 1 to 200;
n is 1 to 8.
[2] The lubricating base oil according to [1], wherein at least one of ^R2 is a hydrocarbon group having 3 carbon atoms.
[3] The lubricating base oil according to [1] or [2], wherein at least one of ^R3 is a methyl group.
[4] The lubricating base oil according to any one of [1] to [3], wherein the hydrocarbon compound of the refrigerant comprises propane.
[5] The lubricating base oil according to any one of [1] to [4], wherein the hydrocarbon compound of the refrigerant contains propylene.
[6] The lubricating base oil according to any one of [1] to [5], wherein the number average molecular weight of the compound represented by formula 1 is 300 to 5000.
[7] A lubricating oil composition comprising the lubricating base oil according to any one of [1] to [6], and either or both of a refrigerant and an additive.
[8] The lubricating oil composition according to [7], wherein the refrigerant is propane.
[9] The lubricating oil composition according to [7] or [8], wherein the refrigerant is propylene.
[10] The lubricating oil composition according to any one of [7] to [9], which is used in a car air conditioner, an indoor air conditioner, a refrigerator, a freezer, a hot water supply system for a vending machine, a hot water supply system for a showcase, a refrigeration/heating system, or a gas heat pump system.
[11] A cooling system equipped with a compressor, a condenser, an evaporator, and an expansion valve, in which a refrigerant containing a hydrocarbon compound having 1 to 8 carbon atoms and the lubricating base oil according to any one of [1] to [6] are enclosed.
[12] The cooling system according to [11], which is for a hot water supply system, refrigeration/heating system, or gas heat pump system for a car air conditioner, an indoor air conditioner, a refrigerator, a freezer, a vending machine, or a showcase.

According to the present invention, the chemical stability of refrigerants blended with lubricating base oils is improved when used over long periods of time.

1 is a diagram illustrating a schematic configuration of a cooling system according to an embodiment.

The meanings of the terms are as follows:
"Active hydrogen" refers to a hydrogen atom derived from an active hydrogen-containing group and a hydrogen atom derived from a hydroxyl group of water.
The "active hydrogen-containing group" refers to at least one group selected from the group consisting of a hydroxyl group bonded to a carbon atom, a carboxyl group, an amino group, a monovalent functional group formed by removing one hydrogen atom from a primary amine, and a sulfanyl group.
The term "initiator residue" refers to a group obtained by removing one or more active hydrogens from an initiator.
"Unit" means an atomic group formed directly by polymerization of a monomer.
The "number average molecular weight" is a polystyrene-equivalent molecular weight obtained by GPC measurement.
The "metal content of the lubricating base oil" is the total amount of metal elements detected by elemental analysis using ICP atomic emission spectrometry. The unit of metal content, ppm, is based on mass.
The "kinematic viscosity" is a value measured at 100°C in accordance with JIS K2283:2000.
The "viscosity index" is a value calculated from the measured value of kinematic viscosity in accordance with JIS K2283:2000.
The "volume resistivity" is a value measured in accordance with the "volume resistivity test method" of JIS C2101:2010 "Electrical insulating oil."
The use of "to" to indicate a range of values means that the values before and after "to" are included as the lower and upper limits. The ranges of values disclosed in this specification can be combined in any way to create new ranges of values.

[Lubricant base oil]
The lubricating base oil of the present invention can impart lubricity to the sliding parts of a compressor in a compression-type refrigerator, for example, by mixing with a refrigerant.

(refrigerant)
The refrigerant to be mixed with the lubricating base oil of the present invention contains a hydrocarbon compound having 1 to 8 carbon atoms. In consideration of a boiling point suitable for use as a refrigerant, the hydrocarbon compound of the refrigerant preferably has 1 to 5 carbon atoms, more preferably 3 to 5 carbon atoms, even more preferably 3 or 4 carbon atoms, and most preferably 3 carbon atoms.

Examples of hydrocarbon compounds for the refrigerant include methane, ethane, ethylene, propane, cyclopropane, propylene, n-butane, isobutane, n-pentane, and isopentane. Of these, propane and propylene are preferred.
The hydrocarbon compounds of the refrigerant may be used singly or in combination of two or more kinds.

(Compound represented by formula 1)
The lubricating base oil of the present invention contains a compound represented by the following formula 1 (hereinafter referred to as "compound 1").
R ¹ {(R ² O) _m R ³ } _n ...Formula 1

In Formula 1, ^R1 is an initiator residue. The initiator is not particularly limited as long as it is a compound having an active hydrogen-containing group. The initiator may have one or more active hydrogen-containing groups. Examples of initiators include aliphatic monoalcohols, aliphatic diols, aliphatic alcohols having 3 to 8 hydroxyl groups, amines, phenols, salts thereof, and alkylene oxide adducts thereof. However, the initiator is not limited to these examples.
The initiators may be used alone or in combination of two or more.

The aliphatic monoalcohol may be a saturated aliphatic monool, an unsaturated aliphatic monool, or a cyclic aliphatic monool. Of these, saturated aliphatic monools are preferred. Examples of saturated aliphatic monools include methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, tert-butanol, n-hexanol, octyl alcohol, and 2-ethylhexanol. However, saturated aliphatic monools are not limited to these examples.

Examples of aliphatic diols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, and 1,6-hexanediol. However, aliphatic diols are not limited to these examples.

Examples of aliphatic alcohols having 3 to 8 hydroxyl groups include glycerin, trimethylolethane, trimethylolpropane, hexanetriol, pentaerythritol, dipentaerythritol, diglycerin, meso-erythritol, methyl glucoside, glucose, sucrose, trehalose, and sorbitol. However, aliphatic alcohols having 3 to 8 hydroxyl groups are not limited to these examples.

Examples of amines include alkanolamines, heterocyclic amines, aliphatic amines, and aromatic amines.
Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, and isopropanolamine.
Examples of heterocyclic amines include N-(2-aminoethyl)piperazine and N-aminomethylpiperazine.
Examples of the aliphatic amine include ethylenediamine, propylenediamine, and hexamethylenediamine.
Examples of aromatic amines include tolylenediamine and diaminodiphenylmethane.
However, the amines are not limited to these examples. One type of amine may be used alone, or two or more types may be used in combination.

Examples of phenols include bisphenol A and resorcinol.
However, the phenol is not limited to these examples. One type of phenol may be used alone, or two or more types may be used in combination.

As initiators, aliphatic monoalcohols, aliphatic diols, and aliphatic alcohols having 3 to 8 hydroxyl groups are preferred, with aliphatic diols and aliphatic alcohols having 3 to 8 hydroxyl groups being more preferred.

In Formula 1, the n (R ² O) _m R ^3s may be the same or different. In each (R ² O) _m , one type of R ² O may be present, or two or more types of R ² O may be present. When two or more types of R ² O are present, the bonding order of each R ² O is not limited. For example, when two types of R ² O are present, the two types of R ² O may be arranged randomly, alternately, or in blocks. (R ² O) _m may be a random copolymer or a block copolymer having units based on two or more types of alkylene oxide.

Each ^R2 is independently a hydrocarbon group having 2 to 4 carbon atoms. The hydrocarbon group of ^R2 preferably has 2 or 3 carbon atoms, and more preferably has 3 carbon atoms. Therefore, it is preferable that at least one of ^R2 is a hydrocarbon group having 3 carbon atoms, and it is more preferable that all of ^R2 are hydrocarbon groups having 3 carbon atoms.

The hydrocarbon group of ^R2 may be linear or branched. When ^R2 has a branched chain, the branching position and number of branches are not particularly limited.

Examples of ^R2 include _-CH2CH2- , -CH2CH2CH2-, -CH2CH2CH2CH2- _, -CH2CH2CH2CH2-, -CH( _{CH3 ) CH2-} , _{-CH2CH ( CH3 )} -, -CH( _CH3 ) _CH2CH2- , and _-CH2CH ( _CH3 ) _{CH2- . -CH2CH2- and -CH2CH} ( _{CH3 )} - are preferred, _{and -CH2CH ( CH3 )} - is more preferred.

In formula 1, ^R3 's are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The number of carbon atoms in the alkyl group of ^R3 is preferably 1 to 3, more preferably 1 or 2, and most preferably 1. In other words, ^R3 is most preferably a methyl group.

Among ^R3 , examples of alkyl groups having 1 to 4 carbon atoms include _-CH3 , _-CH2CH3 , _-CH2CH2CH3 , _{-CH2CH2CH2CH3} , _-CH ( _{CH3 ) CH3} , -CH _{( CH3 ) CH2CH3 , and -CH2CH} ( _CH3 ) _{CH3 .}

In Formula 1, at least one of the n R ^3s is an alkyl group having 1 to 4 carbon atoms. All of the n R ^3s may be alkyl groups having 1 to 4 carbon atoms. The n R ^3s may be the same as or different from one another. In other words, the R ^3s bonded to the ends of the n (R ² O) _m chains may be the same as or different from one another.

In formula 1, m is 1 to 200, preferably 5 to 100, more preferably 7 to 60, and even more preferably 8 to 50. When m is equal to or greater than the lower limit of the above numerical range, a lubricating base oil with a good viscosity index is likely to be obtained. When m is equal to or less than the upper limit of the above numerical range, a lubricating base oil with good low-temperature fluidity is likely to be obtained.

In formula 1, n is 1 to 8, preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. When n is equal to or greater than the lower limit of the above numerical range, a lubricating base oil with a good viscosity index is likely to be obtained. When n is equal to or less than the upper limit of the above numerical range, a lubricating base oil with a good volume resistivity is likely to be obtained.

The number average molecular weight of the compound represented by Formula 1 is preferably 300 to 5,000, more preferably 500 to 3,000, and even more preferably 700 to 2,000. When the number average molecular weight is equal to or greater than the lower limit of the above numerical range, it is easy to achieve adequate compatibility with the refrigerant. When the number average molecular weight is equal to or less than the upper limit of the above numerical range, it is easy to obtain a lubricating base oil with good kinematic viscosity.

(Physical properties of lubricating base oil)
The metal content of the lubricating base oil of the present invention is 10 ppm or less. Therefore, the chemical stability of a refrigerant blended with the lubricating base oil is improved when used for a long period of time. The metal content of the lubricating base oil is preferably 8 ppm or less, more preferably 5 ppm or less, and even more preferably 3 ppm or less. From the viewpoint of production efficiency, the lower limit of the metal content of the lubricating base oil is preferably 0.1 ppm or more.

There are no particular restrictions on the metal elements contained in the lubricating base oil. In the synthesis reaction of compound 1, alkylene oxide can be addition polymerized to an initiator in the presence of a catalyst. Metal elements derived from the catalyst used in this synthesis reaction may remain in the lubricating base oil. In order to keep the metal content of the lubricating base oil to 10 ppm or less, it is preferable to thoroughly remove the catalyst after the synthesis reaction of compound 1.

When measuring the metal content of a lubricating base oil, there is no particular limitation on the metal elements to be detected, and the detection targets are all metal elements that may be contained in a catalyst expected to be used in the production of the lubricating base oil.
Examples of residual metals derived from the catalyst include Na, K, Zn, Co, Fe, Ni, Al, Sr, Mn, Cr, Cu, Sn, Pb, Mo, W, and V. However, the metal elements that can be detected are not limited to these examples. Furthermore, the metal elements that can be detected may be one type or two or more types.

The kinematic viscosity of the lubricating base oil at 100°C is not particularly limited, but may be, for example, 2 to 200 mm ² /s, 5 to 100 mm ² /s, or 7 to 50 mm ² /s. When the kinematic viscosity is equal to or greater than the lower limit of the above-mentioned range, sealing performance is improved, making refrigerant leakage less likely. When the kinematic viscosity is equal to or less than the upper limit of the above-mentioned range, viscous resistance is small and lubricity is improved.

The viscosity index of the lubricating base oil is preferably 50 or higher, more preferably 80 or higher, and even more preferably 100 or higher, as this improves viscosity characteristics. The higher the upper limit of the viscosity index of the lubricating base oil, the better, and there are no particular limitations, but it may be, for example, 140, 160, 200, etc.

The volume resistivity of the lubricating base oil is not particularly limited, but may be, for example, 1×10 ¹⁰ to 1×10 ¹⁵ Ω·cm, 6×10 ¹⁰ to 1×10 ¹⁴ Ω·cm, or 1×10 ¹¹ to 1×10 ¹⁴ Ω·cm. When the volume resistivity is equal to or greater than the lower limit of the above-mentioned range, electrical insulation properties are improved. When the volume resistivity is equal to or less than the upper limit of the above-mentioned range, static electricity generation is easily prevented.

(Method for producing lubricating base oil)
The lubricating base oil is obtained by addition polymerizing an alkylene oxide to an initiator in the presence of a catalyst to elongate the oxyalkylene chain ((R ² O) _m ) to introduce an alkyl group having 1 to 4 carbon atoms at the end of the chain, thereby obtaining Compound 1, and then removing the catalyst from the reaction solution containing Compound 1. Details and preferred embodiments of the initiator are as described above.

Examples of the catalyst include alkali metal catalysts and double metal cyanide complex catalysts (hereinafter referred to as "DMC catalysts"), but the catalyst is not limited to these examples.
The catalyst may be used alone or in combination of two or more kinds.

Examples of alkali metal catalysts include alkali metals such as sodium and potassium; alkali metal alkoxides such as sodium methoxide, sodium ethoxide, sodium propoxide, potassium methoxide, potassium ethoxide, and potassium propoxide; hydroxides such as sodium hydroxide, potassium hydroxide, and cesium hydroxide; and carbonates such as sodium carbonate and potassium carbonate.
The alkali metal catalysts may be used alone or in combination of two or more.

The DMC catalyst is believed to have at least a metal element and an organic ligand.
Examples of metal elements of the DMC catalyst include Zn, Fe, Co, Ni, Al, Sr, Mn, Cr, Cu, Sn, Pb, Mo, W, and V. However, the metal elements of the DMC catalyst are not limited to these examples.
The DMC catalyst may contain one or more metal elements.

Examples of organic ligands for DMC catalysts include t-butyl alcohol (hereinafter referred to as "TBA"), n-butyl alcohol, iso-butyl alcohol, t-pentyl alcohol, iso-pentyl alcohol, N,N-dimethylacetamide, ethylene glycol mono-t-butyl ether, ethylene glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), iso-propyl alcohol, and dioxane. Dioxane may be 1,4-dioxane or 1,3-dioxane. However, the organic ligand is not limited to these examples.
The organic ligands may be used alone or in combination of two or more.

Examples of alkylene oxides include ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, methyl glycidyl ether, 2,3-epoxy-1-propanol, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, hexyl glycidyl ether, tetrahydrofuran, epichlorohydrin, styrene oxide, and cyclohexene oxide. Preferred alkylene oxides are ethylene oxide and propylene oxide, with propylene oxide being more preferred. However, alkylene oxides are not limited to these examples.

Alkylene oxides may be used singly or in combination of two or more. In other words, one type of alkylene oxide may be homopolymerized using an initiator, or two or more types of alkylene oxides may be copolymerized using an initiator. In the case of copolymerization, two or more types of alkylene oxides may be block copolymerized using an initiator, or random copolymerized.

The reaction temperature, reaction time, and reactor pressure for the ring-opening addition polymerization reaction are not particularly limited. The reaction temperature may be, for example, 80 to 150°C, or 90 to 140°C. The reaction time may be, for example, 3 to 30 hours, or 5 to 20 hours. The reactor pressure may be, for example, 0.01 to 0.9 MPaG, or 0.03 to 0.7 MPaG.

The method for introducing an alkyl group having 1 to 4 carbon atoms is not particularly limited, and examples thereof include the following Method 1 and Method 2.
Method 1: A method in which an alkyl halide having 1 to 4 carbon atoms is reacted with the hydroxyl group at the end of an oxyalkylene chain.
Method 2: A method in which a metal alkoxide having an alkyl group having 1 to 4 carbon atoms is reacted with the hydroxyl group at the end of an oxyalkylene chain.

Details and preferred embodiments of the alkyl group of the alkyl halide are the same as those explained for R ^3. Examples of halogen include, but are not limited to, fluorine, chlorine, bromine, and iodine.

The details and preferred embodiments of the alkyl group of the metal alkoxide are the same as those explained for R ^3. Examples of the metal of the metal alkoxide include, but are not limited to, Na and K.

The reaction temperature, reaction time, and reactor pressure for Method 1 and Method 2 are not particularly limited. The reaction temperature may be, for example, 30 to 150°C, or 40 to 140°C. The reaction time may be, for example, 1 to 20 hours, or 2 to 10 hours. The reactor pressure may be, for example, 0.01 to 5 MPaG, or 0.05 to 2 MPaG.

The conversion rate in the reaction for introducing an alkyl group having 1 to 4 carbon atoms into the terminal of the oxyalkylene chain ((R ² O) _m ) is not particularly limited, but may be, for example, 50 to 100%, 60 to 95%, or 70 to 90%. When the conversion rate in the reaction is equal to or greater than the lower limit of the above-mentioned range, at least one of the n R ^3s is likely to be an alkyl group having 1 to 4 carbon atoms. When the conversion rate in the reaction is equal to or less than the upper limit of the above-mentioned range, compound 1 is easily synthesized.

The method for removing the catalyst is not particularly limited, and examples thereof include the following methods 3, 4, and 5.
Method 3: A method in which the catalyst is adsorbed using an adsorbent, and then the adsorbent with the adsorbed catalyst is removed by filtration.
Method 4: Neutralizing the catalyst with a neutralizing agent and then removing the neutralized catalyst by filtration.
Method 5: A method of removing the catalyst during filtration using a charged filter.

In removing the catalyst, any of Method 3, Method 4, and Method 5 may be performed alone, or two or more of them may be combined as appropriate, or all of Methods 3, 4, and 5 may be performed. When two or more or all of Methods 3, 4, and 5 are performed, the order in which they are performed is not particularly limited. As a method for removing the catalyst, Methods 3 and 4 are preferred, with Method 3 being more preferred, from the viewpoint of further reducing the metal content.

Examples of adsorbents include synthetic silicates, ion exchange resins, activated clay, oxide salts, and acid clay. Examples of synthetic silicates include magnesium silicate, aluminum silicate, and hydrotalcite. Examples of oxide salts include magnesium oxide and aluminum oxide. However, the adsorbents are not limited to these examples.
The adsorbents may be used alone or in combination of two or more.

Examples of the neutralizing agent include amines, alkali metal hydroxides, organic acids, inorganic acids, and salts thereof. Examples of the inorganic acid include sulfuric acid, phosphoric acid, and hydrochloric acid. Examples of the organic acid include lactic acid. However, the neutralizing agent is not limited to these examples.
The neutralizing agents may be used alone or in combination of two or more.

Commercially available charged filters may be used. Examples of commercially available charged filters include the Zeta Plus Adsorption Depth Filter Cartridge EC Series (a product of 3M), RO Wind (a product of Organo Corporation), and SupraCap 200 (a product of Seitz AKSJ). However, charged filters are not limited to these examples.

[Lubricating oil composition]
The lubricating oil composition of the present invention comprises the above-described lubricating base oil and either or both of a refrigerant and an additive. In one example, the lubricating oil composition may comprise a lubricating base oil and a refrigerant, a lubricating base oil and an additive, or a lubricating base oil, a refrigerant, and an additive. The lubricating oil composition of the present invention can, for example, impart lubricity to the sliding parts of a compressor supplied with a refrigerant. The refrigerant is as described above.

Examples of additives include antioxidants, extreme pressure agents, stabilizers, copper deactivators, antifoaming agents, load-bearing additives, chlorine scavengers, oxygen scavengers, detergent-dispersants, viscosity index improvers, oiliness agents, rust inhibitors, corrosion inhibitors, and pour point depressants, but the additives are not limited to these examples.
The additives may be used alone or in combination of two or more.

Examples of the antioxidant include phenol-based antioxidants and amine-based antioxidants.
Examples of phenol-based antioxidants include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and 2,2'-methylenebis(4-methyl-6-tert-butylphenol).
Examples of the amine antioxidant include phenyl-α-naphthylamine and N,N'-diphenyl-p-phenylenediamine.
The antioxidants may be used alone or in combination of two or more.

Examples of extreme pressure agents include phosphorus-based extreme pressure agents such as phosphate esters, acid phosphate esters, phosphites, acid phosphites, and amine salts of these.

Examples of stabilizers include epoxy compounds such as phenyl glycidyl ether, alkyl glycidyl ether, alkylene glycol glycidyl ether, cyclohexene oxide, α-olefin oxide, and epoxidized soybean oil.

Examples of copper deactivators include benzotriazole and its derivatives, such as N-[N,N'-dialkyl (alkyl group having 3 to 12 carbon atoms) aminomethyl]triazole.

Examples of antifoaming agents include silicone oil and fluorinated silicone oil.

The proportion of the lubricating base oil may be 40 to 99.9 mass%, 45 to 90 mass%, or 50 to 80 mass% of the total amount of the lubricating oil composition. If the proportion of the lubricating base oil is equal to or greater than the lower limit of the above numerical range, chemical stability when mixed with a refrigerant is likely to be improved. If the proportion of the lubricating base oil is equal to or less than the upper limit of the above numerical range, compatibility with the refrigerant is preferred.

When a lubricating oil composition contains a refrigerant, the proportion of the refrigerant may be 0.1 to 80 mass%, 10 to 60 mass%, or 20 to 50 mass% of the total amount of the lubricating oil composition. A refrigerant proportion equal to or greater than the lower limit of the above numerical range is preferable in terms of compatibility with the lubricating base oil. A refrigerant proportion equal to or less than the upper limit of the above numerical range is likely to improve chemical stability when mixed with the lubricating base oil.

When the lubricating oil composition contains an additive, the proportion of the additive may be 0.1 to 60 mass%, 1 to 40 mass%, or 2 to 20 mass% of the total amount of the lubricating oil composition. If the proportion of the additive is equal to or greater than the lower limit of the above numerical range, the antioxidant properties of the base oil will be improved. If the proportion of the additive is equal to or less than the upper limit of the above numerical range, it is preferable in terms of compatibility with the refrigerant.

[Mechanism of action]
The metal content of the lubricating base oil of the present invention as described above is 10 ppm or less. Therefore, even when the refrigerant is used for a long period of time under severe conditions, deposits are unlikely to occur. Thus, the lubricating base oil of the present invention improves the chemical stability of the refrigerant blended with the lubricating base oil when used for a long period of time.

[Application]
The lubricating base oil and the lubricating oil composition can be used in various refrigeration systems such as car air conditioners, indoor air conditioners, refrigerators, freezers, vending machines, hot water supply systems for showcases, refrigeration/heating systems, gas heat pump systems, etc. The lubricating base oil and the lubricating oil composition are particularly preferably used in a compression-type refrigeration system equipped with a compressor 1, a condenser 2, an expansion valve 3, and an evaporator 4 as shown in FIG.
The compression refrigeration system shown in Figure 1 contains a refrigerant containing a hydrocarbon compound having 1 to 8 carbon atoms and a lubricating base oil. The lubricating base oil and lubricating oil composition circulate through a compressor 1, a condenser 2, an expansion valve 3, and an evaporator 4. The lubricating base oil provides lubricity to the sliding parts of the compressor 1.

The amounts of lubricating base oil and refrigerant used in this invention can be varied widely within the range of 99/1 to 10/90 in terms of the refrigerant/lubricating base oil mass ratio. The mass ratio is preferably within the range of 90/10 to 50/50.

The following examples will explain the embodiments in more detail. However, the present invention is not limited to the following description. Examples 1-7 are examples, and Examples 8-10 are comparative examples.

[Measurement and Evaluation]
(number average molecular weight)
The lubricating base oil was subjected to GPC measurement under the following conditions to determine the number average molecular weight (Mn).
GPC measurement conditions:
Model used: HLC-8220GPC (Tosoh Corporation)
Data processing device: SC-8020 (Tosoh Corporation product)
Column used: TSG gel G2500H (Tosoh Corporation)
Column temperature: 40°C, detector: RI, solvent: tetrahydrofuran, flow rate: 0.6 mL/min, sample concentration: 0.25% by mass, injection volume: 10 μL
Standard sample for creating a calibration curve: polystyrene ([Easycal] PS-2 [Polystyrene Standards], product of Polymer Laboratories)

(metal content)
20 g of lubricating base oil containing the compound represented by Formula 1 in each example was purified and then completely incinerated using a burner. The incinerated powder residue was mixed with 100 mL of aqueous hydrochloric acid solution to prepare a measurement sample. The contents of Na, K, Zn, and Co were measured using an ICP optical emission spectrometer (SII Nanotechnology (Hitachi High-Tech Science) "SPS3500"). The total amount of these detected metal elements was calculated as the metal content of the lubricating base oil.

(chemical stability)
The test for evaluating chemical stability was conducted in accordance with the sealed tube test described in JIS K2211-2009. More specifically, iron, copper, and aluminum were placed in a test tube as catalysts. Then, 0.7 mL of a lubricating base oil containing the compound represented by Formula 1 for each example and 0.7 mL of a refrigerant were placed in the test tube, and the opening of the test tube was sealed. The sealed test tube was heated at 175°C for 14 days, and the presence or absence of precipitates in the solution in the test tube was confirmed. Propane was used as the refrigerant.

[Example 1]
After adding 162 g of powdered sodium methoxide to a 5 L autoclave, the temperature was raised to 110° C., and 4,350 g of propylene oxide was introduced into the autoclave over 10 hours. After the propylene oxide was introduced, the pressure became constant, and after it was confirmed that all of the propylene oxide had reacted, the temperature inside the system was cooled to 100° C. Thereafter, 152 g of methyl chloride was introduced over 3 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 2000 g of the resulting compound was transferred to a 5 L separable flask. 2000 g of distilled water and 20 g of phosphoric acid were added, and the aqueous layer was removed by oil-water separation. 60 g of a magnesium silicate-based adsorbent (Kyowado 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added to the polyether compound in the oil layer as an adsorbent, and the mixture was stirred at 110 ° C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polyoxypropylene glycol dimethyl ether.
The amount of residual metal in the obtained polyoxypropylene glycol dimethyl ether was 0.6 ppm, and the number average molecular weight determined by GPC was 1,480.

[Example 2]
After adding 162 g of powdered sodium methoxide to a 5 L autoclave, the temperature was raised to 110°C, and a mixture of 3,000 g of propylene oxide and 1,350 g of ethylene oxide was introduced into the autoclave over 10 hours. The mixture of propylene oxide and ethylene oxide was introduced. After that, it was confirmed that the pressure had become constant and all of the propylene oxide and ethylene oxide had reacted, and the temperature in the system was cooled to 70°C. Thereafter, 152 g of methyl chloride was introduced over 5 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had become constant and that the methyl chloride had reacted, 2000 g of the resulting compound was transferred to a 5 L separable flask, to which 2000 g of distilled water and 10 g of sulfuric acid were added, and the aqueous layer was removed by oil-water separation.
To the polyether compound on the oil layer side, 100 g of an aluminum silicate-based adsorbent (Kyowad 700, manufactured by Kyowa Chemical Industry Co., Ltd.) and 20 g of acidic sodium pyrophosphate were added as adsorbents, and the mixture was stirred for 2 hours at 110° C. Thereafter, the catalyst was thoroughly removed by filtration of insoluble matter, yielding polyalkylene glycol dimethyl ether.
The amount of residual metal in the obtained polyalkylene glycol dimethyl ether was 1.8 ppm, and the number average molecular weight determined by GPC was 1,480.

[Example 3]
208 g of propylene glycol monoethyl ether and 12 g of potassium hydroxide (purity 95% by mass) as an addition polymerization catalyst were added to a 5 L autoclave, and the temperature was raised to 110°C. After that, the system was subjected to dehydration treatment under reduced pressure for 1 hour to reduce the water content, and then 2,200 g of propylene oxide was introduced into the autoclave over 10 hours. The propylene glycol monoethyl ether used as an initiator was an ethanol-propylene oxide adduct.
The pressure inside the autoclave became constant, and it was confirmed that all of the propylene oxide had reacted. After cooling to 50°C, 350 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C and a reduced pressure methanol removal treatment was carried out for 10 hours. Thereafter, the temperature inside the system was cooled to 100°C, and 101 g of methyl chloride was introduced over 2 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 2000 g of the resulting compound was transferred to a 5 L separable flask. 2000 g of distilled water and 40 g of 35% hydrochloric acid were added, and the aqueous layer was removed by oil-water separation. 60 g of a synthetic hydrotalcite adsorbent (Kyowado 1000, manufactured by Kyowa Chemical Industry Co., Ltd.) and 10 g of phosphoric acid were added to the polyether compound in the oil layer as adsorbents, and the mixture was stirred at 110 °C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polypropylene glycol ethyl methyl ether.
The amount of residual metal in the resulting polypropylene glycol ethyl methyl ether was 6.3 ppm, and the number average molecular weight determined by GPC was 1,100.

[Example 4]
74 g of n-butanol and 12 g of sodium hydroxide (purity 95% by mass) as a catalyst were added to a 5 L autoclave, and the temperature was raised to 100°C. 1,500 g of propylene oxide was then introduced into the autoclave over 12 hours. It was confirmed that the pressure inside the autoclave became constant and all of the propylene oxide had reacted. After cooling to 50°C, 140 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C and a reduced pressure methanol removal treatment was carried out for 10 hours. The temperature inside the system was then cooled to 80°C, and 51 g of methyl chloride was introduced over 4 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, the resulting compound was transferred to a 5 L separable flask. Then, 1500 g of distilled water was added, and the aqueous layer was removed by oil-water separation. To the polyether compound in the oil layer, 40 g of an aluminum silicate-based adsorbent (Kyowado 700, manufactured by Kyowa Chemical Industry Co., Ltd.) was added as an adsorbent, along with 20 g of phosphoric acid and 40 g of sodium acid pyrophosphate, and the mixture was stirred at 110 °C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polypropylene glycol butyl methyl ether.
The amount of residual metal in the resulting polypropylene glycol butyl methyl ether was 2.1 ppm, and the number average molecular weight determined by GPC was 1,500.

[Example 5]
74 g of n-butanol and 12 g of potassium hydroxide (purity 95% by mass) as a catalyst were added to a 5 L autoclave, and the temperature was then raised to 100°C. A mixture of 1,200 g of propylene oxide and 600 g of ethylene oxide was then introduced into the autoclave over 15 hours. It was confirmed that the pressure inside the autoclave became constant and all of the propylene oxide had reacted. After cooling to 50°C, 140 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C and a reduced pressure methanol removal treatment was carried out for 10 hours. The temperature inside the system was then cooled to 100°C, and 51 g of methyl chloride was introduced over 2 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 1800 g of the resulting compound was transferred to a 5 L separable flask. Then, 1800 g of distilled water and 40 g of sodium pyrophosphate were added, and the aqueous layer was removed by oil-water separation. 50 g of magnesium silicate adsorbent (Kyowado 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added as an adsorbent to the polyether compound on the oil layer side, and the mixture was stirred at 110 ° C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polyalkylene glycol butyl methyl ether.
The amount of residual metal in the resulting polyalkylene glycol butyl methyl ether was 8.2 ppm, and the number average molecular weight determined by GPC was 1,800.

[Example 6]
32 g of methanol and 13 g of potassium hydroxide (purity 95% by mass) as a catalyst were added to a 5 L autoclave, and the temperature was then raised to 100°C. Then, 1,180 g of propylene oxide was introduced into the autoclave over 10 hours. A mixture of 88 g of ethylene oxide was then introduced into the autoclave over 1 hour. The pressure inside the autoclave became constant, and it was confirmed that all the components had reacted. After cooling to 50°C, 180 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C, and a reduced pressure methanol removal treatment was carried out for 10 hours. The temperature inside the system was then cooled to 100°C, and 63 g of methyl chloride was introduced over 2 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 1300 g of the resulting compound was transferred to a 5 L separable flask. Then, 1300 g of distilled water and 40 g of sodium pyrophosphate were added, and the aqueous layer was removed by oil-water separation. 50 g of magnesium silicate adsorbent (Kyowado 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added as an adsorbent to the polyether compound on the oil layer side, and the mixture was stirred at 110 ° C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polyalkylene glycol butyl methyl ether.
The amount of residual metal in the resulting polyalkylene glycol butyl methyl ether was 1.0 ppm, and the number average molecular weight determined by GPC was 1,250.

[Example 7]
32 g of methanol and 13 g of potassium hydroxide (purity 95% by mass) as a catalyst were added to a 5 L autoclave, and the temperature was then raised to 100°C. Then, 1,268 g of propylene oxide was introduced into the autoclave over 12 hours. It was confirmed that the pressure inside the autoclave became constant and all the components had reacted. After cooling to 50°C, 180 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C and a reduced pressure methanol removal treatment was carried out for 10 hours. The temperature inside the system was then cooled to 100°C, and 63 g of methyl chloride was introduced over 2 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 1300 g of the resulting compound was transferred to a 5 L separable flask. Then, 1300 g of distilled water and 40 g of sodium pyrophosphate were added, and the aqueous layer was removed by oil-water separation. 50 g of magnesium silicate adsorbent (Kyowado 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added as an adsorbent to the polyether compound on the oil layer side, and the mixture was stirred at 110 ° C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polyalkylene glycol butyl methyl ether.
The amount of residual metal in the resulting polyalkylene glycol butyl methyl ether was 0.8 ppm, and the number average molecular weight determined by GPC was 1,250.

[Example 8]
After adding 162 g of powdered sodium methoxide to a 5 L autoclave, the temperature was raised to 110°C, and 4,350 g of propylene oxide was introduced into the autoclave over 10 hours. After introducing the propylene oxide, the pressure became constant, and it was confirmed that all of the propylene oxide had reacted. After cooling the temperature in the system to 100°C, 152 g of methyl chloride was introduced over 3 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had stabilized and that the methyl chloride had reacted, 2000 g of the resulting compound was transferred to a 5 L separable flask. 2000 g of distilled water was then added, and the aqueous layer was removed by oil-water separation. 15 g of a magnesium silicate-based adsorbent (Kyowado 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added to the polyether compound in the oil layer as an adsorbent, and the mixture was stirred at 110 ° C for 2 hours. The catalyst was then thoroughly removed by filtration of insoluble matter, yielding polypropylene glycol dimethyl ether.
The amount of residual metal in the resulting polypropylene glycol dimethyl ether was 15 ppm, and the number average molecular weight determined by GPC was 1,480.

[Example 9]
After adding 162 g of powdered sodium methoxide to a 5 L autoclave, the temperature was raised to 110°C, and a mixture of 3,000 g of propylene oxide and 1,350 g of ethylene oxide was introduced into the autoclave over 10 hours. After the introduction of the mixture of propylene oxide and ethylene oxide, the pressure became constant, and it was confirmed that all of the propylene oxide and ethylene oxide had reacted. After cooling the temperature in the system to 70°C, 152 g of methyl chloride was introduced over 5 hours to carry out terminal methylation.
After the introduction of methyl chloride, the pressure in the system became constant, and it was confirmed that the methyl chloride had reacted. After that, the obtained compound was filtered to remove insoluble matter, and polyalkylene glycol dimethyl ether was obtained.
The amount of residual metal in the obtained polyalkylene glycol dimethyl ether was 500 ppm, and the number average molecular weight determined by GPC was 1,480.

[Example 10]
74 g of n-butanol and 12 g of sodium hydroxide (purity 95% by mass) as a catalyst were added to a 5 L autoclave, and the temperature was raised to 100°C. 1,500 g of propylene oxide was then introduced into the autoclave over 12 hours. It was confirmed that the pressure inside the autoclave became constant and all of the propylene oxide had reacted. After cooling to 50°C, 140 g of a 28% sodium methoxide methanol solution was added. After the addition, the temperature was raised to 120°C and a reduced pressure methanol removal treatment was carried out for 10 hours. The temperature inside the system was then cooled to 80°C, and 51 g of methyl chloride was introduced over 4 hours to carry out terminal methylation.
After confirming that the pressure in the system after the introduction of methyl chloride had become constant and that the methyl chloride had reacted, the resulting compound was transferred to a 5 L separable flask, and 10 g of an aluminum silicate-based adsorbent (Kyowad 700, manufactured by Kyowa Chemical Industry Co., Ltd.) and 10 g of acidic sodium pyrophosphate were added as adsorbents, followed by stirring for 2 hours at 110° C. Thereafter, insoluble matter was filtered off to obtain polypropylene glycol butyl methyl ether.
The amount of residual metal in the resulting polypropylene glycol butyl methyl ether was 50 ppm, and the number average molecular weight determined by GPC was 1,500.

R ¹ , R ² O, R ³ , m, and n in formula 1 of the compounds obtained in each example are shown in Table 1. In Table 1, PO represents propylene oxide, and EO represents ethylene oxide.

In the refrigerants blended with each of the lubricating base oils of Examples 8-10, precipitates were formed after heating at 175° C. for 14 days.
In contrast, in Examples 1-7, the metal content was 10 ppm or less. In the refrigerants blended with each of these lubricating base oils, no precipitates were formed even after heating at 175°C for 14 days. Thus, in Examples 1-7, the chemical stability of the refrigerants blended with the lubricating base oils was improved when used for a long period of time.

According to the present invention, the chemical stability of refrigerants blended with lubricating base oils is improved when used over long periods of time.

This application claims priority from Japanese Patent Application No. 2024-16295, filed February 6, 2024, the entire contents of which are incorporated herein by reference.

1...Compressor, 2...Condenser, 3...Expansion valve, 4...Evaporator

Claims (12)

A lubricating base oil for mixing with a refrigerant,
the refrigerant contains a hydrocarbon compound having 1 to 8 carbon atoms;
The lubricating base oil comprises a compound represented by the following formula 1:
A lubricating base oil having a metal content of 10 ppm or less.
R ¹ {(R ² O) _m R ³ } _n ...Formula 1
In formula 1,
^R1 is an initiator residue;
^R2 is independently a hydrocarbon group having 2 to 4 carbon atoms,
^R3 's each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms;
At least one of the ^R3s is an alkyl group having 1 to 4 carbon atoms,
m is 1 to 200;
n is 1 to 8. 2. The lubricating base oil of claim 1, wherein at least one of ^R2 is a hydrocarbon group having 3 carbon atoms. 2. The lubricating base oil of claim 1, wherein at least one of ^R3 is a methyl group. The lubricant base oil of claim 1, wherein the hydrocarbon compound of the refrigerant comprises propane. The lubricant base oil of claim 1, wherein the hydrocarbon compound of the refrigerant comprises propylene. The lubricating base oil according to claim 1, wherein the number average molecular weight of the compound represented by formula 1 is 300 to 5,000. The lubricating base oil according to any one of claims 1 to 6,
a refrigerant and/or an additive;
1. A lubricating oil composition comprising: The lubricating oil composition according to claim 7, wherein the refrigerant is propane. The lubricating oil composition according to claim 7, wherein the refrigerant is propylene. The lubricating oil composition according to claim 7, which is used in car air conditioners, room air conditioners, refrigerators, freezers, hot water supply systems for vending machines, hot water supply systems for showcases, refrigeration/heating systems, or gas heat pump systems. a compressor, a condenser, an evaporator, and an expansion valve;
A cooling system in which a refrigerant containing a hydrocarbon compound having 1 to 8 carbon atoms and the lubricating base oil according to any one of claims 1 to 6 are sealed. The cooling system of claim 11, wherein the cooling system is for a car air conditioner, an interior air conditioner, a refrigerator, a freezer, a vending machine, a hot water supply system for a showcase, a refrigeration/heating system, or a gas heat pump system.