EP0479338B1

EP0479338B1 - Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine.

Info

Publication number: EP0479338B1
Application number: EP91121101A
Authority: EP
Inventors: Takashi c/o Kyodo Oil Technical Research Kaimai; Hisashi c/o Kyodo Oil Technical Research Yano
Original assignee: Japan Energy Corp
Current assignee: Eneos Corp
Priority date: 1989-07-05
Filing date: 1989-10-17
Publication date: 1997-08-27
Anticipated expiration: 2009-10-17
Also published as: KR0131016B1; EP0406479B1; SG49165A1; KR950005694B1; DE68928281T2; DE68928281D1; ES2099120T5; EP0406479A1; DE68914448T2; ES2051340T5; EP0536814A1; DE68927916T2; EP0479338A3; DE68925537D1; EP0479338A2; EP0480479A2; ES2104650T3; EP0406479B2; KR910003077A; DE68914448T3

Description

This invention relates to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine such as hydrofluorocarbon (HFC), preferably HFC-134a (1,1,1,2-tetrafluoroethane).
Heretofore, compounds containing fluorine and chlorine as a constituent element such as R-11 (trichloromonofluoromethane), R-12 (dichlorodifluoromethane) as a chlorofluorocarbon (CFC), R-22 (monochlorodifluoromethane) as a hydrochlorofluorocarbon (HCFC) have been used as a refrigerant for freezers, air conditioners and refrigerators; for instance. In connection with recent problem on breakage of ozone layer, new refrigerants containing no chlorine such as HFC-134a are proposed as a possible replacement for R-12, causing no breakage of ozone layer.
As a refrigeration lubricant, there are known many mineral-series and synthetic oils. However, it has been confirmed that these oils are very poor in the compatibility with HFC-134a and cannot be applied thereto. Therefore, it is important to take a countermeasure on this problem at the present. Furthermore, the lubricity, electric insulating property, energy saving property, anti-wear performance, sealability, thermal stability and prevention of sludge formation, for instance mentioned as performances required in the refrigeration lubricant, so that they are required to be considered in the development of the above countermeasure.
Incidentally, there have hitherto been known polyether series synthetic lubricants as a synthetic oil, which are reported in Journal of the Oil Chemistry, vol. 29, No. 9, pp 336-343 (1980) and Journal of the Petroleum Technology, vol. 8, No. 6, pp 562-566 (1985). Furthermore, Japanese Patent laid open No. 61-281199 describes a mixture of polyglycol represented by a general formula of R₁[O-(R₂O)_m-R₃]_n, an alkylbenzene and the like, and Japanese Patent laid open No. 57-63395 describes an oil obtained by mixing a polyether such as high molecular weight polyoxypropylene monobutyl ether with an epoxycycloalkyl compound, and Japanese Patent laid open No. 59-117590 describes a high viscosity mixed oil of a polyether compound and a paraffinic or naphthanic mineral oil.
However, the conventional synthetic lubricants as mentioned above cannot be a refrigeration lubricant using HFC-134a as a refrigerant from a viewpoint of compatibility, for instance.
In US Patent No. 4,755,316, polyoxyalkylene glycol (hereinafter abbreviated as PAG) having hydroxyl groups (-OH) at both terminals is reported as a refrigeration lubricant using HFC-134a. Further, it is described that PAG is dissolved in HFC-134a within a wide temperature range as compared with general PAG containing hydroxyl group and alkyl group at its terminals, whereby the recycle of the lubricant into a compressor is improved in the refrigeration system and the seizuring in the actuation of the compressor at high temperature is prevented. Moreover, the temperature range compatible with HFC-134a is described to be between -40°C and +50°C.
On the contrary, HFC-134a is a replacing refrigerant of R-12 and is mainly expected for use in a car air conditioner or a refrigerator, for instance. In case of the refrigerator, it is required to have a good compatibility between lubricant and refrigerant, and further the lubricant itself is necessary to have an electric insulating property because the motor is substantially existent in the refrigeration system. However, the conventional compounds examined as a lubricant for HFC-134a refrigerant inclusive of PAG disclosed in US Patent No. 4,755,316 are remarkably poor in the electric insulating property as compared with the conventional refrigeration mineral oil and high in the hygroscopicity.
EP-A-0 378 176 discloses a fluid composition for use in compression refrigeration comprising

(A) a refrigerant selected from hydrochlorofluorocarbons and hydrofluorocarbons and
(B) a lubricant comprising esters made from polyhydric alcohols with alkanoic acids, for instance trimethylolpropane triheptonate, and
(C) a specific polyether polyol.

Said document is a document in the sense of Art. 54 (3) EPC.
WO-A-90 12 849, which also forms state of the art in the sense of Art. 54 (3) EPC only, describes a liquid composition comprising a major amount (more than 50% by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50% by weight) of a lubricant comprising the carboxylic ester of a polyhydroxy compound.
It is an object of the invention to provide a refrigeration lubricant, which has an excellent compatibility with a new refrigerant such as HFC-134a within a wide temperature range, a high electric insulating property and a low hygroscopicity, for compressors using a hydrofluorocarbon refrigerant containing no chlorine.
At the present, a part of commercially available esters is used in systems using refrigerants such as R-12, R-22, but is incompatible with HFC-134a as a new refrigerant or is very narrow in the compatible range therewith. In this connection, the inventors have aimed at the fact that the ester has a high electric insulating property, a low hygroscopicity, a good lubricity and a high stability as compared with PAG and made various studies with respect to the molecule design of the ester showing a wide range of compatibility with HFC-134a, and found that only esters having a considerably restricted structure can be used in the HFC-134a refrigeration system, and as a result, the invention has been accomplished.
According to a first aspect, the present invention refers to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises an ester obtainable by reacting

a) trimethylol propane (TMP), with
b) 2-ethylhexanoic acid.

According to a second aspect, the present invention refers to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting

a) trimethylol propane (TMP), with
b) 2-ethylhexanoic acid
c) adipic acid

According to a third aspect, the present invention refers to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting

a) one or more polyvalent alcohols selected from
- trimethylol ethane (TME),
- trimethylol propane (TMP), and
- trimethylol butane (TMB), with
b) one or more straight-chain monovalent fatty acids having a carbon number of 3 to 10, and/or branched-chain monovalent fatty acids having a carbon number of 4 to 10,

i) said lubricant does not contain a polyether polyol in an amount of 5 to 95 weight percent according to the general formula

Z-[(CH₂-CH(R₁)-O-)_n-(CH₂-CH(CH₃)-O-)_m-R₂]_p

wherein
- Z is the residue of a compound having 1 to 8 active hydrogens,
- R₁ is hydrogen, ethyl or mixtures thereof
- n is 0 or a positive number,
- m is a positive number
- n+m is a number having a value which will give a polyether polyol with a number average molecular weight range from about 400 to about 5000,
- R₂ is hydrogen or an alkyl group of 1 to 6 carbon atoms,
- p is an integer having a value equal to the number of acLive hydrogens of Z,
- and
ii) said lubricant is not used in a liquid composition comprising a major amount (more than 50 % by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50 % by weight) of said lubricant.

According to a fourth aspect, the present invention refers to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting

a) one or more polyvalent alcohols selected from
- trimethylol ethane (TME),
- trimethylol propane (TMP), and
- trimethylol butane (TMB), with
b) one or more straight-chain monovalent fatty acids having a carbon number of 3 to 10, and/or branched-chain monovalent fatty acids having a carbon number of 4 to 10, and
c) one or more polybasic acids having a carbon number of 4 to 10,

Furthermore, according to a fifth aspect, the present invention refers to the use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting

a)- one or more polyvalent alcohols selected from
- trimethylol ethane (TME),
- trimethylol propane (TMP), and
- trimethylol butane (TMB), with
b) one or more branched-chain monovalent fatty acids having a carbon number of 4 to 10, and

i) said lubricant does not contain a polyether polyol in an amount of 5 to 95 weight percent according to the general formula

Z-[(CH₂-CH(R₁)-O-)_n-(CH₂-CH(CH₃)-O-)_m-R₂]_p

wherein
- Z is the residue of a compound having 1 to 8 active hydrogens,
- R₁ is hydrogen, ethyl or mixtures thereof
- n is 0 or a positive number,
- m is a positive number
- n+m is a number having a value which will give a polyether polyol with a number average molecular weight range from about 400 to about 5000,
- R₂ is hydrogen or an alkyl group of 1 to 6 carbon atoms,
- p is an integer having a value equal to the number of active hydrogens of Z,
- and
ii) said lubricant is not used in a liquid composition comprising a major amount (more than 50 % by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50 % by weight) of said lubricant.

In a preferred embodiment of the invention, the hydrofluorocarbon refrigerant is 1,1,1,2-tetrafluoroethane (HFC-134a).
As the polyvalent alcohol, trimethylol ethane, trimethylol propane and trimethylol butane, which are represented by the following general formula (II):
(in which R is an alkyl group having a carbon number of not more than 3) are used.
When the carbon number of R in the general formula (II) is not less than 4, the compatibility of the resulting ester with HFC-134a and the like is largely lowered.
Straight or branched-chain monovalent fatty acids having a carbon number of 3-10 or 4-10, resp., are used. As the monovalent fatty acid, mention may be made of propionic acid, butanoic acid, isobutanoic acid, pentanoic acid, isopentanoic acid, hexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, 2-ethyl hexanoic acid, nonanoic acid, isononanoic acid 3,5,5-trimethyl hexanoic acid and decanoic acid.
As to the polybasic acid, the polybasic acid having a carbon number of not more than 3 is a special product and is difficult to be cheaply available and is poor in the stability of the ester after the synthesis.
The carbon number of the polybasic acid is 4-10 for ensuring the compatibility with HFC-134a at a wide range. As the polybasic acid, mention may be made of adipic acid, azelaic acid and sebacic acid. Preferably, the monovalent fatty acid is 2-ethylhexanoic acid, and the polybasic acid is adipic acid.
Moreover, the reason why the amount of the polybasic acid added in the invention is limited to not more than 25 mol% per the total fatty acid is due to the fact that when it exceeds 25 mol%, the gelation may be caused and it is difficult to obtain desirable physical properties.
The ester compounds used in the invention can be obtained by the esterification reaction through dehydration reaction between the specified polyvalent alcohol and the specified fatty acid as mentioned above, or the general esterification reaction through an acid anhydride, an acid chloride or the like as a derivative of the fatty acid.
In any case, it is desirable that the ester does not contain carboxyl group.
When the acid value exceeds 3, there may be caused an unfavorable phenomenon that the metal soap is formed and precipitated by the reaction with a metal used inside the refrigerator, so that the acid value is preferably not more than 3. Furthermore, when the hydroxyl value exceeds 50, there may be caused an unfavorable phenomenon that the resulting ester becomes cloudy, so that the hydroxyl value is preferably not more than 50.
The esters used in the invention exhibit a good compatibility with the refrigerant HFC-134a and the like over a wide range of from low temperature to high temperature as a lubricant for use in a refrigerator using HFC-134a as a refrigerant, whereby the lubricity and thermal stability of the refrigeration lubricant can be considerably improved. Furthermore, they are high in the electric insulating property and small in the hygroscopicity as compared with PAG conventionally examined as a refrigeration lubricant for HFC-134a.
Therefore, by use of the refrigeration lubricants comprising the ester used in the invention as a main component the problems on the compatibility with HFC-134a and the hygroscopicity, which have never been solved in the conventional technique can be solved, and the electric insulating property, which comes into problem when HFC-134a is used in a compressor for a refrigerator, can be further enhanced.
Moreover, additives usually used in the lubricant such as antioxidant, anti-wear agent and epoxy compound, for instance; may properly be added to the refrigeration lubricant used in the invention.

Examples 1-8 , Comparative examples (B-1)-(B-3) and (C-1)-(C-2)

The performances as a refrigeration lubricant using HFC-134a as a refrigerant were evaluated with respect to eight esters A-1 - A-8 shown in the following Table 1 (all of which esters were not commercially available but were prepared according to the invention).
For the comparison, the same evaluation as mentioned above was made with respect to commercially available PAG (B-1 - B-3, made by Asahi Denka Co., Ltd.) and esters (C-1 - C-2, made by Nippon Oil and Fats Co. Ltd.) as a refrigeration lubricant shown in the following Table 2.
The lubricity, compatibility, thermal stability, electric insulating property and hygroscopicity as performances of the refrigeration lubricant for the compressor shown in Tables 1 and 2 were evaluated under the following conditions.

Lubricity

Seizuring load (Falex load-carrying capacity) was measured according to ASTM D-3233-73 under a controlled atmosphere of HFC-134a blown.

Compatibility

After 0.6 g of the test lubricant and 2.4 g of the refrigerant (HFC-134a) were sealed in a glass tube, the cooling at 1°C/min and the heating were carried out, during which a temperature causing two-phase separation was measured.

Thermal stability

After 1 g of the test lubricant, 1 g of the refrigerant (HFC-134a or R-12) and a catalyst (wire of iron, copper or aluminum) were sealed in a glass tube, the mixture was heated to 175°C, andthecolor of the lubricant after 10 days was judged by ASTM color system according to ANSI/ASHRAE 97-1983.

Electric insulating property

It was evaluated by a dielectric constant at 80°C according to JIS C-2101.

Hygroscopicity

Into a beaker of 100 mℓ there were charged 60 g of the test lubricant, which was left to stand at a temperature of 25°C and a humidity of 70% for 3 hours and then the water concentration was measured.

The evaluation results are shown in the following Table 3.

Table 2

	Type	Trade name	Color (ASTM)	Dynamic viscosity at 40°C (cSt) mm²/s
B-1	PAG 1	Adekapol M-30 1)	L 0.5	32.8
B-2	PAG 1	Adekapol M-110 2)	L 0.5	105.2
B-3	PAG 1	Adekapol MH-50 3)	L 0.5	54.6
C-1	ester	dioctyl sebacate	L 0.5	11.4
C-2	ester	Unistar MB-816 4)	L 0.5	8.1

1) polyoxypropylene glycol monoalkyl ether
2) polyoxypropylene glycol monoalkyl ether
3) polyoxyethylene propylene glycol monoalkyl ether
4) monoester of 2-ethylhexanol and palmitic acid

As seen from Table 3, when the esters used in the invention are compared with the conventional PGA (B-1 - B-3) used for comparison shown in Tables 2 and 3, the electric insulating property represented by the dielectric constant is 100,000 times or more and the two-phase separation at a high temperature is not caused. Furthermore, the seizuring load is excellent and the hygroscopicity is low. The thermal stability is equal in case of the HFC-134a system, but is considerably excellent in case of the R-12 system.
Recently, HFC-134a causing substantially no breakage of ozone layer is closed up instead of R-12 widely used as a refrigerant in order to cope with the breakage of ozone layer through chlorofluorocarbon and hydrochlorofluorocarbon being a greatest problem in world-wide scale, but is poor in the compatibility with the conventional refrigeration lubricant, which is a bar for the development of replacement system. However, the refrigeration lubricants used in the invention have a sufficient compatibility with HFC-134a as a refrigerant and a high electric insulating property and also are excellent in the total performances, so that they have an effect that the conventional systems can be used as they are even when HFC-134a is used instead of the conventional R-12 and R-22 as a refrigerant.

Claims

Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component an ester obtainable by reacting
a) trimethylol propane (TMP), with

b) 2-ethylhexanoic acid
Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting
a) trimethylol propane (TMP), with

b) 2-ethylhexanoic acid

c) adipic acid
wherein the amount of adipic acid is not more than 25 mol % per total fatty acid.
Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting
a) one or more polyvalent alcohols selected from
trimethylol ethane (TME),

trimethylol propane (TMP), and

trimethylol butane (TMB), with

b) one or more straight-chain monovalent fatty acids having a carbon number of 3 to 10, and/or branched-chain monovalent fatty acids having a carbon number of 4 to 10,
with the proviso that
i) said lubricant does not contain a polyether polyol in an amount of 5 to 95 weight percent according to the general formula

Z-[(CH₂-CH(R₁)-O-)_n-(CH₂-CH(CH₃)-O-)_m-R₂]_p

wherein
Z is the residue of a compound having 1 to 8 active hydrogens,

R₁ is hydrogen, ethyl or mixtures thereof

n is 0 or a positive number,

m is a positive number

n+m is a number having a value which will give a polyether polyol with a number average molecular weight range from about 400 to about 5000,

R₂ is hydrogen or an alkyl group of 1 to 6 carbon atoms,

p is an integer having a value equal to the number of active hydrogens of Z,

and

ii) said lubricant is not used in a liquid composition comprising a major amount (more than 50 % by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50 % by weight) of said lubricant.
Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting
a) one or more polyvalent alcohols selected from
trimethylol ethane (TME),

trimethylol propane (TMP), and

trimethylol butane (TMB), with

b) one or more straight-chain monovalent fatty acids having a carbon number of 3 to 10, and/or branched-chain monovalent fatty acids having a carbon number of 4 to 10, and

c) one or more polybasic acids having a carbon number of 4 to 10,
wherein the amount of the polybasic acid(s) is not more than 25 mol % per total fatty acid,
with the proviso that
i. said lubricant is not used in a liquid composition comprising a major amount (more than 50 % by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50 % by weight) of said lubricant.
Use of a lubricant for compressors using a hydrofluorocarbon refrigerant containing no chlorine, wherein said lubricant comprises as a main component one or more esters obtainable by reacting
a) one or more polyvalent alcohols selected from
trimethylol ethane (TME),

trimethylol propane (TMP), and

trimethylol butane (TMB), with

b) one or more branched-chain monovalent fatty acids having a carbon number of 4 to 10, and
with the proviso that
i) said lubricant does not contain a polyether polyol in an amount of 5 to 95 weight percent according to the general formula

Z-[(CH₂-CH(R₁)-O-)_n-(CH₂-CH(CH₃)-O-)_m-R₂]_p

wherein
Z is the residue of a compound having 1 to 8 active hydrogens,

R₁ is hydrogen, ethyl or mixtures thereof

n is 0 or a positive number,

m is a positive number

n+m is a number having a value which will give a polyether polyol with a number average molecular weight range from about 400 to about 5000,

R₂ is hydrogen or an alkyl group of 1 to 6 carbon atoms,

p is an integer having a value equal to the number of active hydrogens of Z,

and

ii) said lubricant is not used in a liquid composition comprising a major amount (more than 50 % by weight) of a fluorine containing hydrocarbon refrigerant and a minor amount of (less than 50 % by weight) of said lubricant.
Use of a lubricant according to any of claims 3 to 4, wherein said straight-chain monovalent fatty acid is selected from
propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid.
Use of a lubricant according to any of claims 3 to 5, wherein said branched-chain monovalent fatty acid is selected from
isopentanoic acid, isoheptanoic acid, 2-ethylhexanoic acid, isononanoic acid and 3,5,5-trimethylhexanoic acid.
Use of a lubricant according to claim 4, wherein said polybasic acid is selected from
adipic acid, azelaic acid, and sebacic acid.
Use of a lubricant according to any of claims 1 to 8, wherein said hydrofluorocarbon refrigerant is 1,1,1,2-tetrafluoroethane.