JPH0873876A - Ester-based lubricating oil - Google Patents

Abstract

PURPOSE: To obtain a lubricating oil, containing a mixture of a specific ester compound with a fatty acid isomer as a base oil, having excellent hydrolytic resistance and thermal stability, available in a short time at a low temperature and suitable as a refrigerator oil. CONSTITUTION: This ester-based lubricating oil contains a mixture of an ester compound having plural branched fatty acid residues of formula I (R<1> is a 1-10C straight-chain alkyl; R<2> is a 1-20C straight-chain alkyl; R<3> is H or a 1-10C straight-chain alkyl) with a fatty acid isomer as a base oil. Furthermore, the lubricating oil is preferably obtained by reacting (C) a mixture of a branched fatty acid fluoride of formula II with the fatty acid isomer (e.g. a fatty acid fluoride of 2,2-dimethylpentanoic acid) synthesized by reacting (A) an olefin (e.g. hexene) with (B) carbon monoxide and (C) hydrogen fluoride with (D) a polyhydric alcohol [e.g. 0.7-1.5mol based on 1mol component (A)].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ester-based lubricating oil, and more particularly to an ester-based lubricating oil excellent in hydrolysis resistance and thermal stability, which is preferably used as a refrigerating machine oil.

[0002]

2. Description of the Related Art Chlorine-containing chlorofluoroalkanes and hydrochlorofluoroalkanes have been widely used as a refrigerant CFC used in refrigerators. However, recently, due to chlorine contained in CFCs destroying the ozone layer in the stratosphere, restrictions on the use of CFCs are becoming strict worldwide. Therefore, the use of chlorine-free hydrofluoroalkanes as new refrigerants is becoming more prominent.

On the other hand, the mineral oil-based and alkylbenzene-based refrigerating machine oils that have been used so far cannot be used because of their poor compatibility with the above-mentioned new refrigerants. Therefore, a polyol ester-based refrigerating machine oil having good compatibility with a new refrigerant has been studied as an alternative refrigerating machine oil, and as an alternative refrigerating machine oil excellent in hydrolysis resistance and thermal stability, JP-A-4-31
4793, JP-A-5-1291, and JP-A-5-177.
87, JP-A-5-17789 and JP-A-5-20.
No. 9171 discloses a refrigerating machine oil using an ester obtained from a carboxylic acid in which the α-position carbon of a carbonyl group is branched in a secondary or tertiary manner and an acid derivative thereof.

[0004]

The polyol ester type refrigerating machine oil as described above has a good compatibility with the hydrofluoroalkanes which are a new refrigerant, but the esters are hydrolyzed by the presence of water. The development of esters with good hydrolysis resistance is urgent. Further, further improvement in thermal stability is required. An object of the present invention is to provide a polyol ester-based lubricating oil having excellent hydrolysis resistance and thermal stability, which is particularly suitable for refrigerators.

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a polyol ester type lubricating oil having the above-mentioned problems, and as a result, synthesized a branched fatty acid fluoride from olefin, carbon monoxide and hydrogen fluoride, and Polyol ester lubricating oil obtained by reacting a fatty acid fluoride with a polyhydric alcohol, that is, the α-position carbon of the carbonyl group is branched to secondary or tertiary, and each alkyl group attached to the α-position carbon of this carbonyl group is The present inventors have found that an isomer mixture of ester compounds having a plurality of all linear ester groups has extremely excellent hydrolysis resistance and thermal stability, and arrived at the present invention. In the above-mentioned prior art references, esters obtained from a carboxylic acid in which the α-position carbon of the carbonyl group is secondary or tertiary branched and an acid derivative thereof are described, for example, 2-ethyl-2,3 As in the case of 1,3-trimethylbutanoic acid and 2,2,4,4-tetramethylpentanoic acid (Japanese Patent Laid-Open Nos. 5-1291 and 5-209171), the carbonyl group α is actually used. Many of the alkyl groups attached to the position carbons include branched alkyl groups, which are different from the fatty acid isomer mixture of the present application.

That is, the present invention is an ester-based lubricating oil characterized by using a fatty acid isomer mixture of an ester compound having a plurality of branched fatty acid residues represented by the general formula (I) as a base oil.

Embedded image (R ¹ is a linear alkyl group having 1 to 10 carbon atoms, R ² is a linear alkyl group having 1 to 20 carbon atoms, and R ³ is hydrogen or a linear alkyl group having 1 to 10 carbon atoms).

As described above, the lubricating oil of the present invention is obtained by synthesizing a branched fatty acid fluoride from olefin, carbon monoxide and hydrogen fluoride and reacting the branched fatty acid fluoride with a polyhydric alcohol. The reaction formula is expressed as follows.

[Chemical 3] In addition, R ⁰¹ , R ⁰² , and R ⁰³ in the above reaction formula are R ¹ ,
These are alkyl groups or hydrogen groups corresponding to R ² and R ³ , but they do not necessarily coincide because an isomerization reaction also occurs in the carbonylation step. R is a hydrocarbon residue or an oxygen-containing hydrocarbon residue of an n-valent alcohol, and n is an integer of 2 or more.

In the general formula (I), R ¹ has ¹ carbon atom.
-10 alkyl group, R ² is an alkyl group having 1 to 20 carbon atoms, R ³ is hydrogen or an alkyl group having 1 to 10 carbon atoms, and preferably R ¹ is an alkyl group having 1 to 3 carbon atoms. , R ² is an alkyl group having 2 to 8 carbon atoms, and R ³ is hydrogen or an alkyl group having 1 to 3 carbon atoms. Examples of the olefin used as a raw material in the above carbonylation step include butylene, pentene, hexene and octene. For example, when hexene is used as a raw material, fatty acid fluorides of four isomers of 2,2-dimethylpentanoic acid, 2-ethyl-2-methylbutanoic acid, 2-ethylpentanoic acid and 2-methylhexanoic acid are obtained. By reacting this with alcohol, a fatty acid isomer mixture of the corresponding ester compound is obtained.

As alcohols used in the esterification step, hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, ditrimethylolethane, ditrimethylolpropane and dipentaerythritol, ethylene glycol, propylene. Examples thereof include polyhydric alcohols such as glycol and glycerol. The supply amount of alcohol is 2 molar equivalents or less per 1 mole of olefin (based on the number of moles of OH groups of alcohol), and preferably 0.7 to 1.5 moles. If the amount of alcohol used is too large, the hydroxyl value of the ester will be high and it will be susceptible to hydrolysis, which is not preferable.

The branched fatty acid fluoride obtained in the carbonylation step is synthesized from olefin, carbon monoxide and hydrogen fluoride. The α-position carbon of the carbonyl group is branched to secondary or tertiary due to the acid catalytic effect of hydrogen fluoride. However, it becomes a mixture of fatty acid fluorides composed of various fatty acid isomers. Further, an ester can be obtained by reacting the branched fatty acid fluoride with a polyhydric alcohol. In the present invention, in particular, the alkyl group attached to the α-position carbon of the carbonyl group is linear, and as described above, Since a mixture of fatty acid fluorides of fatty acid isomers and alcohol are reacted to obtain a mixture of various fatty acid isomer ester compounds, an ester excellent in hydrolysis resistance and thermal stability can be obtained.

The mixture of ester compounds obtained by the above reaction (hereinafter, also simply referred to as ester) can be purified by a general method such as alkali washing, distillation purification, adsorption treatment, hydrogenation treatment after the esterification reaction. . When the ester-based lubricating oil of the present invention is used as a refrigerator, additives such as an antioxidant, an antiwear agent, and an epoxy compound which are conventionally used in refrigerators are added to a mixture of the ester compounds as needed. can do. Further, the ester-based lubricating oil according to the present invention can be adjusted in kinematic viscosity by the reaction conditions in the above carbonylation step, and is also adjusted to a required kinematic viscosity by mixing the obtained several isomer mixtures. You can also do it.

According to the present invention, when an ester is produced by the above-mentioned method using olefin as a raw material, an ester mixture having excellent hydrolysis resistance and thermal stability can be obtained. That is, if the ester contains an acid residue of a primary fatty acid or the carbonyl group has a branched alkyl group at the α-position carbon, the hydrolysis resistance and thermal stability are adversely affected and the performance is reduced. Easy to do. Further, it is considered that a mixture of various fatty acid isomers of the ester compound can obtain excellent hydrolysis resistance and thermal stability in relation to each other.

[0013]

EXAMPLES The present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples. The hydrolysis resistance test of ethesul obtained in each Example and Comparative Example was conducted by the following method, and the results are shown in Table 1. In Table 1, the acid value before the test is the acid value of ethesul immediately after production, and the acid value after the test is the acid value of the ethesul after heating for 14 days. Note that the hydrolysis resistance test method is 1
This result also indicates thermal stability, since heating is carried out at 75 ° C. for a long period of time.

(Hydrolysis resistance test method) A test ester made of glass and iron, copper, and aluminum as catalysts were put in a glass test tube, and 10 g of lubricating oil adjusted to a water content of 1000 ppm and a refrigerant (R-134a, manufactured by Daikin Industries) After injecting 2 g, the mixture was sealed and the acid value after heating the sealed glass tube at 175 ° C. for 14 days was measured.

Example 1 An ester was produced using a stainless steel autoclave equipped with a Nak-drive type stirrer, three inlet nozzles at the top and one outlet nozzle at the bottom, and the internal temperature can be controlled by a jacket. First, the inside of the autoclave was replaced with carbon monoxide, and then hydrogen fluoride was introduced at a temperature of -20
It was cooled to ° C and pressurized with carbon monoxide to 20 kg / cm ² .
The reaction temperature was adjusted to -20 ° C and the reaction pressure was 20 kg / cm.
While supplying carbon monoxide so as to keep it at ² , 1-octene was supplied from the gas phase part of the autoclave to synthesize fatty acid fluoride. After the end of the 1-octene supply, the stirring was continued for about 20 minutes until the absorption of carbon monoxide was no longer observed. After the temperature inside the autoclave was set to -10 ° C and the pressure was reduced to normal pressure, neopentyl glycol in an equimolar amount (based on the number of moles of hydroxyl groups) with carbon monoxide absorbed in the reaction was supplied to the autoclave for 2 hours. It was made to react. The reaction solution was drained into ice water, washed with alkali, and the oil layer and the water layer were separated. The oil layer was purified by distillation to obtain diester. As a result of analyzing this with a gas chromatograph-mass spectrometer (GC-MS), it was confirmed to be a mixture of diesters of six fatty acid isomers.

Example 2 A fatty acid fluoride was synthesized at a temperature of −5 ° C., and an ester was synthesized in the same manner as in Example 1 except that trimethylolpropane was used instead of neopentyl glycol to obtain a triester. As a result of GC-MS analysis, it was confirmed to be a mixture of triesters of six fatty acid isomers.

Example 3 An ester was synthesized in the same manner as in Example 2 except that pentaerythritol was used instead of trimethylolpropane to obtain a tetraester. This is GC-
As a result of MS analysis, it was confirmed to be a mixture of tetraesters of 6 types of fatty acid isomers.

Example 4 An ester was synthesized in the same manner as in Example 1 except that 1-hexene was used instead of 1-octene and trimethylolpropane was used instead of neopentyl glycol to obtain a triester. . As a result of analysis by GC-MS, it was confirmed to be a mixture of triesters of four fatty acid isomers.

Example 5 An ester was synthesized in the same manner as in Example 4 except that 1-butene was used instead of 1-hexene to obtain a triester. As a result of analysis by GC-MS, it was confirmed to be a mixture of triesters of two fatty acid isomers.

Comparative Example 1 2-ethylhexanoic acid and neopentyl glycol were equimolar in molar ratio to a 4-necked flask equipped with a stirrer, a nitrogen gas blowing tube, a thermometer and a condenser (neopentyl glycol is the number of moles of hydroxyl group). Then, the esterification reaction was carried out while distilling out the water produced at 230 ° C. for 8 hours under a nitrogen stream to the outside of the system. Subsequently, the pressure was reduced (2 to 3 torr) and the reaction was carried out at the same temperature for 2 hours to obtain a diester. This ester is a diester composed of a branched fatty acid residue having a linear alkyl group on the α carbon, but it is not a mixture containing isomers of fatty acids.

Comparative Example 2 In the same 4-necked flask as in Comparative Example 1, 2,2-dimethylbutanoic acid, 2,2-dimethylpentanoic acid and 3,5,5-trimethylhexanoic acid were mixed in a molar ratio of 2: 2: 1. In terms of the ratio, the molar ratio of trimethylolpropane to the hydroxyl group and the carboxyl group is 1.0:
It was charged so as to be 1.5, and P-toluenesulfonic acid was added as an esterification catalyst so as to be 0.3% with respect to the weight of fatty acid and trimethylolpropane, and 200 ° C.
And reacted for 20 hours. The reaction solution is washed with alkali and
After dehydration at 20 ° C. and 20 torr for 2 hours, a triester was obtained. This ester is a triester composed of branched alkyl group fatty acid residues and is not a mixture containing isomers of fatty acids.

Comparative Example 3 2,2-Dimethylbutanoic acid was placed in a 4-necked flask equipped with a stirrer, a thermometer, a cooling tube, and a dropping funnel, and phosphorus trichloride was added.
The mixture was uniformly added dropwise from the dropping funnel over 1 hour at 40 ° C. so that the molar amount was 1,35 times that of 2,2-dimethylbutanoic acid, and the mixture was reacted at 40 ° C. for 3 hours. After allowing the reaction product to stand for 1 hour, the upper layer was separated and a fatty acid chloride was obtained by distillation. Charge the obtained fatty acid chloride into the same four-necked flask as above, and add 0.77 times the molar amount of trimethylolpropane based on the hydroxyl group to the fatty acid chloride at 70 ° C. over 1 hour, and allow to react at the same temperature for 3 hours. It was
After the reaction, it was washed with alkali and dehydrated at 90 ° C. and 20 torr to obtain a triester. This ester is a triester composed of a branched fatty acid residue having a linear alkyl group on the α carbon, but it is not a mixture containing isomers of fatty acids.

[0023]

Table 1 Acid value before test Acid value after test Example 1 0.01 0.01 Example 2 0.01 0.01 Example 3 0.01 0.01 Example 4 0.01 0.01 Example 5 0.01 0.01 Comparative Example 1 0.01 0.03 Comparative Example 2 0.01 0.17 Comparative Example 3 0.01 0.08

[0024]

As is apparent from the examples, the lubricating oil of the present invention shows no increase in acid value even in a long-term test at high temperature, and has extremely excellent hydrolysis resistance and thermal stability. There is. In addition, conventional ester-based lubricating oils are obtained by esterification reaction of various organic carboxylic acids and alcohols and require long-term reaction at high temperature.
Since it can be obtained at a low temperature in a short time by a reaction with an olefin, carbon monoxide, hydrogen fluoride and an alcohol, it can be obtained extremely industrially.

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[Procedure amendment]

[Submission date] December 22, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

As described above, the lubricating oil of the present invention is obtained by synthesizing a branched fatty acid fluoride from olefin, carbon monoxide and hydrogen fluoride and reacting the branched fatty acid fluoride with a polyhydric alcohol. The reaction formula is expressed as follows.

[Chemical 3] In addition, R ⁰¹ , R ⁰² , and R ⁰³ in the above reaction formula are R ¹ ,
These are alkyl groups or hydrogen groups corresponding to R ² and R ³ , but they do not necessarily coincide because an isomerization reaction also occurs in the carbonylation step. R is a hydrocarbon residue or an oxygen-containing hydrocarbon residue of an n-valent alcohol, and n is an integer of 2 or more.

Claims (2)

[Claims] 1. An ester-based lubricating oil comprising a mixture of fatty acid isomers of an ester compound having a plurality of branched fatty acid residues represented by the general formula (I) as a base oil, wherein: (R ¹ is a linear alkyl group having 1 to 10 carbon atoms, R ² is a linear alkyl group having 1 to 20 carbon atoms, and R ³ is hydrogen or a linear alkyl group having 1 to 10 carbon atoms). 2. The ester lubricating oil according to claim 1, which is obtained by reacting a fatty acid isomer mixture of branched fatty acid fluoride synthesized from olefin, carbon monoxide and hydrogen fluoride with a polyhydric alcohol.