JP2012233091A - Lubricating oil base oil for hydrocarbon refrigerant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricating oil base oil of excellent lubricity, reduced in abrasion of a cooling device using a hydrocarbon refrigerant.SOLUTION: The lubricating oil base oil for the refrigerant comprises substantially a 1-8C hydrocarbon compound, and comprises a polyoxypropylene glycol or polyoxypropylene triol having 300-3,200 of number-averaged molecular weight, or a mixture thereof. The lubricating oil base oil has excellent features in an abrasion wear of a cooling system, compatibility with the refrigerant, and volume resistivity.

Description

  The present invention relates to a lubricating base oil for hydrocarbon refrigerants, that is, a base oil for a lubricating oil for a cooling machine using a hydrocarbon refrigerant, and a lubricating oil composition containing the base oil. The present invention relates to a base oil composed of propylene glycol and / or polyoxypropylene triol and having an excellent lubricating function, and a lubricating oil composition containing the base oil.

  Conventionally, chlorofluorocarbons such as dichlorofluoromethane have been often used as refrigerants for compression refrigerators. However, since chlorofluorocarbons may destroy the ozone layer, hydrogen-containing chlorofluorocarbon compounds have been studied. However, hydrogen-containing chlorofluorocarbon compounds are concerned about the impact on global warming.

  Therefore, the use of hydrocarbon-based refrigerants that do not have such problems has been studied. However, when using a mineral oil or alkylbenzene, which is conventionally used as a lubricating oil when a hydrocarbon-based refrigerant is used, the hydrocarbon-based refrigerant dissolves completely in the lubricating oil, and the viscosity of the lubricating oil is reduced. There are problems that the performance deteriorates and the cooling capacity of the refrigerant decreases.

  Therefore, it is known to use a polyalkylene glycol derivative as a base oil in place of mineral oil or the like (for example, Patent Document 1). Furthermore, a polyalkylene glycol derivative that does not undergo phase separation in the temperature range in which the refrigerator is operated and has excellent compatibility with a refrigerant has been proposed (Patent Document 2).

Japanese Patent Laid-Open No. 10-158671 Republished WO2007 / 026647

  Conventionally, as described in Patent Document 2, it has been common technical knowledge that refrigerant and lubricating oil need to circulate in the system without phase separation within a wide temperature range from low temperature to high temperature. . The common sense is the same even for so-called natural refrigerants such as hydrocarbons, ammonia, carbon dioxide and the like that are attracting attention as refrigerants suitable for environmental protection, and it is necessary that the refrigerant and the lubricating oil should not be phase-separated. Has been. However, in a cooling system using hydrocarbon as a refrigerant, there is a problem that even if a lubricating oil having higher compatibility with the hydrocarbon is used, the wear of the cooler, particularly the compressor, cannot be reduced. Therefore, in order to solve the problem, various investigations were performed using lubricating oils having different compatibility. Surprisingly, the use of a base oil having low compatibility resulted in less wear of the device and excellent lubrication. It turns out that sex can be obtained.

That is, the present invention is a lubricating base oil for refrigerants substantially comprising a hydrocarbon compound having 1 to 8 carbon atoms, wherein the lubricating base oil has a number average molecular weight of 300 to 3200. A lubricating base oil comprising glycol, polyoxypropylene triol, or a mixture thereof.
Further, the present invention is a cooling system including a compressor, a condenser, an evaporator and an expansion valve, in which a refrigerant and a lubricating base oil are enclosed,
In the compatibility test with refrigerant / lubricant base oil (mass ratio) = 80/20 according to JIS K2211, the refrigerant is a hydrocarbon compound having 1 to 8 carbon atoms, and from 90 ° C. It is a cooling system that exhibits two-layer separation in the temperature range of −60 ° C.

  When the lubricating base oil of the present invention is used, the amount of metal powder discharged into the lubricating oil due to wear of the cooling system, mainly the compressor, is significantly reduced. This is contrary to conventional technical common sense. The reason for this is unclear, but as the refrigerant changes from fluorocarbon to hydrofluorocarbon and hydrocarbon, the polarity of the refrigerant changes, and the lubricity in the system caused by the cooling system with refrigerant and refrigerating machine oil changes. I think that. That is, it is considered necessary to reexamine the relationship between the compatibility of the refrigerating machine oil and the lubricity using a direct and clear index such as the wear amount of the apparatus used in the present invention according to the refrigerant.

It is a block diagram which shows an example of the cooling system which can use the lubricating base oil of this invention. It is sectional drawing which shows an example of the compressor which can use the lubricating base oil of this invention.

  The lubricating base oil of the present invention (hereinafter sometimes referred to as “base oil”) is polyoxypropylene glycol, polyoxypropylene triol, or a mixture thereof. However, a small amount of monol produced as a by-product in the polymerization process of propylene oxide may be included. Preferably polyoxypropylene glycol is used. In the case of using a mixture of polyoxypropylene glycol and polyoxypropylene triol, the triol is preferably 50% or less of the total mass with the glycol from the viewpoint of viscosity and heat stability.

  Polyoxypropylene glycol and / or triol, in the presence of a ring-opening addition polymerization catalyst, in the case of polyoxypropylene glycol, for example, ethylene glycol and propylene glycol as an initiator, in the case of polyoxypropylene triol, triol, For example, propylene oxide can be obtained by anionic ring-opening addition polymerization using glycerin or the like as an initiator, respectively. Examples of the ring-opening addition polymerization catalyst include alkali metal compound catalysts and double metal cyanide complex catalysts. Examples of the alkali metal compound catalyst 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; sodium hydroxide and hydroxide Examples thereof include hydroxides such as potassium and cesium hydroxide; carbonates such as sodium carbonate and potassium carbonate. Preferably, an alkali metal hydroxide such as potassium hydroxide is used.

  Examples of the initiator include divalent or trivalent alcohols, amines, phenols, and alkylene oxide adducts thereof. Examples of the dihydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, and 1,6-hexanediol. Examples of the trihydric alcohol include glycerin, trimethylolpropane, trimethylolethane, and hexane. And triols.

  Examples of amines include alkanolamines such as monoethanolamine, diethanolamine, triethanolamine and isopropanolamine; heterocyclic amines such as N- (2-aminoethyl) piperazine and N-aminomethylpiperazine; ethylenediamine and propylenediamine And aliphatic amines such as hexamethylenediamine; aromatic amines such as tolylenediamine and diaminodiphenylmethane.

  Examples of phenols include bisphenol A and resorcinol. An initiator may be used individually by 1 type and may use 2 or more types together. Of the above initiators, divalent or trivalent alcohols are preferable. Particularly, those obtained by ring-opening or addition polymerization of propylene oxide from the viewpoint of low viscosity and good thermal stability, such as propylene glycol Dipropylene glycol is preferred.

  The obtained base oil has a number average molecular weight of 300 to 3200, preferably 500 to 2000. Those having a number average molecular weight of not less than the lower limit can have appropriate compatibility with the refrigerant, and those having a number average molecular weight of not more than the upper limit have kinematic viscosity suitable as a base oil. The molecular weight range corresponds to about 5 to about 50 degrees of polymerization of oxypropylene units. The number average molecular weight can be measured by gel permeation chromatography (GPC) using polystyrene as a standard sample.

  The base oil exhibits two-layer separation in a temperature range of 90 ° C. to −60 ° C. in a compatibility test with refrigerant / lubricant base oil (mass ratio) = 80/20 according to JIS K2211. Lubricating base oils that are compatible with the refrigerant in all or part of this range have a large amount of wear on the device and do not have a sufficient lubricating effect. Accordingly, the present invention is a cooling system including a compressor, a condenser, an evaporator, and an expansion valve, in which a refrigerant and a lubricating base oil are enclosed, wherein the refrigerant is a hydrocarbon compound having 1 to 8 carbon atoms. As a lubricant base oil, a two-layer separation is exhibited in a temperature range of 90 ° C. to −60 ° C. in a compatibility test at 80/20 refrigerant / lubricant base oil (mass ratio) according to JIS K2211 A cooling system is also provided.

The base oil of the present invention preferably has a kinematic viscosity at 100 ° C. of ² to 200 mm ² / s. Those having a kinematic viscosity equal to or higher than the lower limit are excellent in sealing properties and have no danger of refrigerant leakage. In addition, those having the upper limit value or less have low viscosity resistance and excellent lubricity. Preferably, the kinematic viscosity at 100 ° C. is 5 to 100 mm ² / s. More preferably, it is about 10 mm ² / s when the mass ratio of refrigerant / base oil is 80/20.

Further, the base oil preferably has a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more, more preferably 6 × 10 ¹⁰ Ω · cm or more, and most preferably 1 × 10 ¹¹ Ω · cm or more. . A material having a volume resistivity of 1 × 10 ¹⁰ Ω · cm or more exhibits sufficient electrical insulation. On the other hand, in terms of preventing the generation of static electricity, the volume resistivity is preferably 1 × 10 ¹⁵ Ω · cm or less, and more preferably 1 × 10 ¹⁴ Ω · cm or less.

  The present invention also relates to a lubricating oil composition containing the above lubricating base oil and an antioxidant. The composition may contain the following other additives as required. Examples of the antioxidant include phenol-based and amine-based antioxidants, specifically, phenol-based dibutylhydroxytoluene (BHT) and the like, and amine-based dimethyl succinate-1- (2- Hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (trade name, manufactured by TINUVIN622 BASF) and the like. Other additives include extreme pressure agents such as phosphate esters such as tricresyl phosphate (TCP) or phosphites such as trisnonylphenyl phosphite; phenyl glycidyl ether, cyclohexene oxide, epoxidized soybean oil, etc. Stabilizers; Copper deactivators such as benzotriazole and its derivatives; Antifoaming agents such as silicone oils and fluorinated silicone oils; Load bearing additives, chlorine scavengers, detergent dispersants, viscosity index improvers, oiliness agents , Rust inhibitors, corrosion inhibitors, pour point depressants, and the like. As for the compounding quantity of antioxidant, 0.01-1 mass% is preferable with respect to the total mass with base oil. The compounding quantity of another additive is 0.5-10 mass% normally with respect to the total mass with a base oil and antioxidant.

  In the present invention, the refrigerant substantially consists of a hydrocarbon compound. Here, the term “substantially” means that it consists only of hydrocarbons, excluding impurities inevitably included. The hydrocarbon compound has 1 to 8 carbon atoms, preferably 1 to 5, and more preferably 3 to 5. Those having a carbon number within the above range are suitable for use as a refrigerant because of their boiling points. Examples of the hydrocarbon compound include methane, ethane, ethylene, propane, cyclopropane, propylene, n-butane, isobutane, n-pentane, and isopentane, and propylene or propane is preferable. These hydrocarbon compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The amount of the base oil or lubricating oil composition of the present invention can be widely varied in the range of 99/1 to 10/90 as the mass ratio of refrigerant / base oil or lubricating oil composition. / 50 is preferable.

  The base oil or lubricating oil composition of the present invention is used in various cooling systems such as car air conditioners, indoor air conditioners, refrigerators, freezers, vending machines or various hot water supply systems for showcases, refrigeration / heating systems, gas heat pump systems, etc. can do. In particular, it is preferably used in a compression cooling system including the compressor 1, the condenser 2, the expansion valve 3, and the evaporator 4 shown in FIG. 1, and imparts lubricity to the sliding portion of the compressor 1.

  FIG. 2 is a longitudinal sectional view of a hermetic rotary compressor that is an example of the compressor 1. In FIG. 2, a refrigerant such as propane is supplied from a supply pipe 13, compressed by a compression mechanism 12 driven by a motor mechanism 11, once discharged into a casing 10, and then sent from a discharge pipe 14 to a condenser. . Although the lubricating oil composition 15 reduces the friction of the sliding part in the compression mechanism 12, it is difficult to completely prevent the wear of parts, and metal powder generated by the wear accumulates in the lubricating oil composition 15. By measuring the amount of the metal powder, the lubricating performance of the lubricating oil can be directly evaluated. Needless to say, the lubricating oil composition 15 of the present invention can also be used in other types of compressors, for example, reciprocating compressors.

  Next, the present invention will be described in more detail using examples and comparative examples, but the present invention is not limited to these examples.

  Into a 5 L autoclave, 400 g of propylene glycol as an initiator and 12 g of potassium hydroxide (purity 95 mass%) as a catalyst are added, the temperature of the autoclave is raised to 110 ° C., and 3600 g of propylene oxide is introduced over 10 hours. did. After confirming that the pressure in the autoclave became constant and all the propylene oxide had reacted, the contents were extracted. Synthetic magnesium silicate (Kyowad 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added to the contents to adsorb the catalyst, and then insoluble matter was removed by filtration to obtain polyoxypropylene glycol. The number average molecular weight determined by GPC of the obtained polyoxypropylene glycol was 580. Details of GPC will be described later.

  A polyoxypropylene glycol was obtained in the same manner as in Example 1 except that the amount of propylene glycol was changed to 200 g.

  Polyoxypropylene glycol was obtained in the same manner as in Example 1 except that 400 g of propylene glycol was changed to 300 g of tripropylene glycol and the amount of propylene oxide was changed to 3500 g.

  Polyoxypropylene glycol was obtained in the same manner as in Example 1 except that propylene glycol was changed to polypropylene glycol and the amount of propylene oxide was changed to 3000 g.

<Comparative Example 1>
After adding 162 g of powdered sodium methoxide to a 5 L autoclave, the temperature was raised to 110 ° C., and 4350 g of propylene oxide was introduced over 10 hours. After introducing propylene oxide, the pressure became constant, and it was confirmed that all propylene oxide had reacted, and the contents were extracted. Thereafter, the catalyst was removed in the same manner as in Example 1 to obtain polyoxypropylene methyl ether having a number average molecular weight (Mn) of 1480.

<Comparative example 2>
222 g of n-butanol (manufactured by Kyowa Hakko Chemical Co., Ltd.) and 0.3 g of a complex metal cyanide complex having a tert-butyl alcohol ligand as a catalyst were added to a 5 L autoclave. Thereafter, at 130 ° C., 200 g of propylene oxide was introduced over 2 hours to cause initial activity, and after 3976 g of propylene oxide was introduced over 6 hours at 130 ° C., the pressure became constant and all propylene oxide reacted. As a result, the content was extracted to obtain polyoxypropylene butyl ether having a number average molecular weight (Mn) of 1470.

<Comparative Example 3>
520 g of 2-ethylhexyl alcohol (manufactured by Kyowa Hakko Chemical Co., Ltd.) and 14.8 g of potassium hydroxide (purity 95% by mass) as a catalyst are added to a 5 L autoclave and subjected to reduced pressure treatment at 100 ° C. for 1 hour to remove moisture. The alcoholate was converted. Subsequently, the temperature of the autoclave was raised to 110 ° C., and 4176 g of propylene oxide was introduced over 10 hours. After confirming that the pressure in the autoclave became constant and all the propylene oxide had reacted, the contents were extracted. Synthetic magnesium silicate (Kyowad 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added to the contents to adsorb the catalyst, and then insoluble matters were removed by filtration. The resulting polyoxypropylene-2-ethylhexyl ether had a number average molecular weight (Mn) of 1170.

<Comparative example 4>
Comparative Example 3 except that 540 g of octadecyl alcohol (Calcoal 8098, manufactured by Kao Corporation) was added, 9.8 g of potassium hydroxide was added, and after reduced pressure treatment at 120 ° C. for 1 hour, 2552 g of propylene oxide was added. Similarly, polyoxypropylene octadecyl ether having a number average molecular weight (Mn) of 1550 was obtained.

<Comparative Example 5>
To a 5 L autoclave, 304 g of propylene glycol and 12.3 g of potassium hydroxide (purity 95% by mass) were added as a catalyst. After the temperature was raised, 2552 g of propylene oxide and 1232 g of ethylene oxide were introduced at 110 ° C. over 10 hours. After confirming that the pressure became constant and all propylene oxide and ethylene oxide reacted, the contents were extracted. The catalyst was removed in the same manner as in Example 1 to obtain polyoxy (propylene / ethylene) glycol having a number average molecular weight (Mn) of 1022.

<Comparative Example 6>
500 g of a 28% sodium methoxide methanol solution was added to a 5 L autoclave, and after raising the temperature to 110 ° C., 2007 g of propylene oxide was introduced over 4 hours. After the pressure became constant, it was cooled to 80 ° C. and 460 g of pearl sodium hydroxide was added. A reduced pressure treatment was performed at 120 ° C. for 1 hour to form an alcoholate while removing moisture. Thereafter, 700 g of methyl chloride was introduced over 3 hours, and aging was performed for 3 hours. After aging, the mixture was cooled to 80 ° C. and neutralized by adding 800 g of phosphoric acid, and 500 g of distilled water was added to separate the neutralized salt. Next, synthetic magnesium silicate (Kyowad 600S, manufactured by Kyowa Chemical Industry Co., Ltd.) was added to adsorb the catalyst, and then insoluble matter was removed by filtration to obtain propylene glycol dimethyl ether having a number average molecular weight (Mn) of 191. .

<Comparative Example 7>
As the base oil, a commercially available mineral oil (SUNISO 5GS, manufactured by Nippon Sun Oil Co., Ltd.) was used.

<Comparative Example 8>
As a base oil, a commercially available polyol ester (Mobil EAL Arctic 68, manufactured by Exxon Mobil Co., Ltd.) was used.

Each base oil was evaluated by the following method. The results are shown in Tables 1 and 2. In these tables, PO represents propylene oxide, EO represents ethylene oxide, and the numerical value in parentheses is the average added mole number of the monomer calculated from the number average molecular weight.
<Molecular weight>
GPC measurement of the base oil was performed under the following conditions to determine the number average molecular weight (Mn).
[GPC measurement conditions]
Model used: HLC-8220GPC (manufactured by Tosoh Corporation)
Data processing device: SC-8020 (manufactured by Tosoh Corporation)
Column used: TSG gel G2500H (manufactured by Tosoh Corporation)
Column temperature: 40 ° C., detector: RI, solvent: tetrohydrofuran, flow rate 0.6 ml / min sample concentration: 0.25% by mass, injection volume: 10 μl
Standard sample for preparing a calibration curve: Polystyrene ([Easical] PS-2 [Polystyrene Standards], manufactured by Polymer Laboratories)

<Compatibility with refrigerant>
Based on JIS K2211 “Refrigerating machine oil” “Compatibility testing method with refrigerant”, a mixture of 20% by mass of base oil and 80% by mass of refrigerant (propane) was gradually added from room temperature to −60 ° C. in a constant temperature bath. The temperature at which the phase separation starts after cooling and the temperature at which the phase separation gradually starts from room temperature to + 90 ° C. were measured using an optical sensor. In the table, “partially compatible” means that partial phase separation was observed under this condition (from −60 ° C. to 90 ° C.), and “completely compatible” always dissolved. “Incompatible” means that the two layers were always separated.

<Kinematic viscosity>
According to JIS K2283-1983, the kinematic viscosity (mm < ² > / s) of the temperature of 40 degreeC and 100 degreeC was measured using the glass capillary-type viscometer.

<Abrasion amount>
Propane as a refrigerant and base oils of Examples and Comparative Examples are sealed in a compression cooling system having a compressor as shown in FIG. 2 at a ratio of propane / base oil = 80/20% by mass, and continuously for 100 hours. After the operation, the base oil in the compressor was recovered, and the solid content in the base oil was separated by filtration using a 300 mesh wire net and quantified. The solid content is a metal content deposited by wear of parts in the compressor, and the smaller the amount, the better the lubricity. In addition, since it was thought that the influence with respect to the abrasion loss of antioxidant was negligible, it did not add in this evaluation.

<Volume resistivity>
Based on “Volume Resistivity Test Method” of JIS C2101 “Electrical Insulating Oil”, the volume resistivity (Ω · cm) of the base oil was measured.

  As shown in Table 2, the base oils having high compatibility with the refrigerant (Comparative Examples 1 to 4 and 6 to 8) all had a larger amount of wear than the base oils of Examples shown in Table 1. . The one containing polyoxyethylene in the main chain (Comparative Example 5) had low compatibility and a small amount of wear, but was found to be unsuitable for hydrocarbon refrigerants because of low volumetric efficiency.

  The lubricating base oil of the present invention is useful as a lubricating oil by preventing wear of the apparatus in a cooling system using a hydrocarbon refrigerant.

DESCRIPTION OF SYMBOLS 1 Compressor 2 Condenser 3 Expansion valve 4 Evaporator 10 Casing 11 Motor mechanism 12 Compression mechanism 13 Supply pipe 14 Discharge pipe 15 Lubricating oil composition

Claims (9)

  A lubricating base oil for refrigerants substantially consisting of hydrocarbon compounds having 1 to 8 carbon atoms, wherein the lubricating base oil has a number average molecular weight of 300 to 3200, polyoxypropylene glycol, polyoxypropylene triol Or a lubricating base oil comprising a mixture of these. The lubricating base oil according to claim 1, wherein the kinematic viscosity at 100 ° C. is ² to 200 mm ² / s.   The lubricating base oil according to claim 1 or 2, wherein the refrigerant is propane.   The lubricating base oil according to claim 1 or 2, wherein the refrigerant is propylene.   A lubricating oil composition comprising the lubricating base oil according to any one of claims 1 to 4 and an antioxidant.   The lubricating oil composition according to claim 5, which is used for a car air conditioner, an indoor air conditioner, a refrigerator, a freezer, a vending machine or a hot water supply system for a showcase, a refrigeration / heating system, or a gas heat pump system. A cooling system including a compressor, a condenser, an evaporator, and an expansion valve, in which a refrigerant and a lubricating base oil are enclosed,
In the compatibility test with refrigerant / lubricant base oil (mass ratio) = 80/20 according to JIS K2211, the refrigerant is a hydrocarbon compound having 1 to 8 carbon atoms, and from 90 ° C. A cooling system that exhibits two-layer separation in the temperature range of -60 ° C.   The cooling system according to claim 7, wherein the lubricating base oil is composed of polyoxypropylene glycol, polyoxypropylene triol, or a mixture thereof having a number average molecular weight of 300 to 3200.   The cooling system according to claim 7 or 8, wherein the cooling system is a car air conditioner, an indoor air conditioner, a refrigerator, a freezer, a vending machine or a hot water supply system for a showcase, a refrigeration / heating system, or a gas heat pump system.

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