WO2001074977A2

WO2001074977A2 - Lubricant and flushing compositions

Info

Publication number: WO2001074977A2
Application number: PCT/US2001/010152
Authority: WO
Inventors: Gregg M. Millman
Original assignee: Ici Americas Inc.
Priority date: 2000-03-31
Filing date: 2001-03-29
Publication date: 2001-10-11
Also published as: WO2001074977A3; AU2001251111A1

Abstract

A lubricant composition comprises an ester derivable from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms. The composition has a low viscosity and is suitable for use in refrigerant systems with HFC gases. The composition is also used as a flushing fluid for a refrigerant system.

Description

LUBRICANT AND FLUSHING COMPOSITIONS

This invention relates to lubricant and flushing compositions comprising an ester of an aromatic carboxylic acid and, in particular, the use of such compositions in refrigeration systems. Historically mineral oils were used in lubricant compositions for chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerant gases. In recent years, environmental pressures have dictated a move away from such traditional refrigerant gases to hydrofluorocarbon gases (HFC). HFC gases have proved less damaging to the environment. This change in refrigerant gas has necessitated a change in lubricant composition away from mineral oils which are not compatible with these new HFC gases. More polar, HFC-compatible synthetic lubricant compositions are used. Examples of suitable synthetic lubricants are polyalkylene glycols, polyol esters, polyvinyl ethers and alkylbenzenes. EP461435B discloses the use of esters of phthalic acid, isophthalic acid or terephthalic acid with straight chain or branched primary monovalent alcohols having 4 to 20 carbon atoms as lubricants for refrigerant compressors utilising chlorine-free hydrocarbons as refrigerants. These lubricants have good miscibility with the chlorine-free hydrocarbon refrigerants and have viscosities ranging from 10 to 150cSt at 40°C.

Surprisingly it has now been found that a different class of esters of aromatic carboxylic acids, having low viscosity levels, is suitable for use in lubricant and flushing compositions.

According to a first aspect of the present invention, a lubricant composition comprises an ester derivable from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms.

For the aromatic monocarboxylic acid, preferably the aromaticity is in the form of a single benzene ring. The benzene ring may be substituted. Suitable substituents include alkyl, halogen, alkoxy, and haloalkyl. The monocarboxylic acid is preferably directly attached to the benzene ring. The monovalent aliphatic alcohol may be branched or straight chained and it may be saturated or unsaturated. Preferably it has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms.

The ester has the general formula R¹-A - COOR² wherein R¹ is the optional substituent on the aromatic carboxylic acid residue A-CO and R²O is derived from the monovalent aliphatic alcohol wherein R² is a branched or straight chained, saturated or unsaturated hydrocarbon containing from 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms and more preferably 1 to 8 carbon atoms. (A is the aromatic hydrocarbon.) Examples of suitable esters are 2-ethyl hexyl benzoate, hexyl benzoate, butyl benzoate, isopropyl benzoate, and ethyl benzoate.

The lubricant composition has a viscosity at 40°C from 1 to 15 cSt. The lubricant composition may also comprise one or more lubricant additives at levels between 0.0001 and 10 %. Suitable additives include antioxidants, antiwear additives, extreme pressure agents, acid scavengers, stabilisers, surfactants, viscosity index improvers, corrosion inhibitors, metal deactivators or passivators, lubricity improvers or oiliness agents, friction modifiers.

The lubricant composition may also comprise one or more lubricant base fluids at levels between 5% and 95%. Such base fluids may or may not themselves be miscible with hydrofluorocarbon refrigerant gases. Examples of such base fluids include organic esters, polyalkylene glycols, polyvinyl ethers, carbonate esters, cyclic acetals and ketals, phosphate esters, mineral oils, polyalphaolelϊns and alkyl benzenes. According to a second aspect of the present invention, the use of a lubricant composition in a refrigeration system wherein the lubricant composition comprises an ester derived from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms.

The refrigerant in the refrigerant system suitably comprises a HCFC, a HFC or a blend of refrigerants containing at least one HFC, HCFC or both. Preferably the refrigerant does not contain any chlorine atoms. Suitable HFC gases include R134a (1,1,1 ,2-tetrafluoroethane), R-32 (difluoromethane), R-125 (1,1,1, 2,2-pentafluoroethane), R-152a (1 ,1-difluoroethane) and R-143a (1,1 ,1- trifluoroethane). There may be other components in the refrigerant blend, for example hydrocarbons, preferably with 1 to 6 carbon atoms, fluorinated hydrocarbons and other refrigerants, for example carbon dioxide and ammonia. There are generally two types of refrigeration system. Firstly there are systems in which the lubricant and refrigerant are present as a mixture and circulate around the refrigeration system as such. An example of such a refrigeration system is an automotive refrigeration system. Secondly there are systems in which the refrigerant circulates in the system and the lubricant composition is in a sump in the compressor. Examples of such systems are open and closed hermetic refrigerators and industrial and commercial refrigerators. Preferably the refrigeration system according to the invention is the second type of refrigeration system defined above.

A range of different materials is used in the construction of the components of a refrigeration system including metals and plastic materials. Other materials such as oils may be used in the assembly of the hardware of such systems and the components of the refrigerant working fluid especially additives may be susceptible to thermal or hydrolytic decomposition. During use and through wear, some of these materials may be present in the refrigeration loop and be carried around the system by the flow of refrigerant as unwanted residues. Other unwanted residues may also be introduced through servicing or the repair of refrigeration systems or in retrofilling new refrigerant or lubricant to the system once it has been used. In particular plastic materials, paraffinic materials, polyalpha-olefins, silicone oils and carbonaceous materials especially high molecular weight and non-polar materials may be found as unwanted residues in the refrigeration loop. Such materials may be deposited in the refrigeration system especially in areas of constriction, and cause blockages and trap additional materials, for example particulate matter. Deterioration in performance and in extreme cases, system failure may occur due to such blockages. In retrofilling processes, it is known to remove the old refrigerant and lubricant from the system and then to flush the empty system with a flushing agent. In known flushing compositions, the material employed to flush the refrigeration system, may not have a beneficial lubricating effect. In these circumstances, residual-flushing material left in the system may act to impair the lubrication of the compressor during subsequent performance.

According to a third aspect of the present invention, a flushing composition which comprises an ester derived from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms.

According to a fourth aspect of the invention, the use of a flushing composition which comprises an ester derived from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms in a refrigeration system for the removal of deposits in the refrigeration system.

The flushing composition may also comprise one or more additives at levels between 0.0001 and 10 %. Suitable additives include surfactants, wetting agents, detergents, dispersants, surface-tension reducing agents and the like, as well as conventional lubricant additives such as antioxidants, antiwear additives, extreme pressure agents, acid scavengers, stabilisers, surfactants, viscosity index improvers, corrosion inhibitors, metal deactivators or passivators, lubricity improvers or oiliness agents, friction modifiers.

The flushing composition may also comprise.one or more base fluids at levels between 5% and 95%. Such base fluids may or may not themselves be miscible with hydrofluorocarbon refrigerant gases. Examples of such base fluids include organic esters, polyalkylene glycols, polyvinyl ethers, carbonate esters, cyclic acetals and ketals, phosphate esters, mineral oils, polyalphaolefins and alkyl benzenes. The invention also provides a method of removing deposits from a refrigeration system which comprises charging a flushing composition, comprising an ester derived from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms, circulating the flushing composition through the refrigeration system for a period of time sufficient to remove at least some deposits and removing the flushing composition containing at least some deposits from the refrigeration system. In a preferred embodiment, the method of removing deposits (flushing process) further comprises the steps of removing the old refrigerant and lubricant contained in a refrigeration system prior to charging the flushing composition to the refrigeration system and charging the refrigeration system with a new refrigerant and lubricant and optionally other components after the flushing composition has been removed from the refrigeration system. The flushing composition may be charged to the refrigeration system while the system is charged with old refrigerant and lubricant and the system operated for a period of time, for example 1 or more days, so the flushing composition acts to reduce or remove unwanted residues during refrigeration use. Under such circumstances, the refrigeration system may be retrofilled or serviced with a new refrigerant and lubricant without conducting a separate flushing procedure between operation with the old refrigerant/lubricant and the new refrigerant/lubricant although a separate flushing procedure may be conducted if desired. Flushing the refrigeration system during use is especially preferred where the scale of the system is large such as in commercial or industrial applications, for example supermarket refrigeration and air-conditioning units.

The flushing composition is suitably employed at a level of 1 to 15, preferably 2 to 10 litres per tonne of refrigerant capacity of the refrigeration system. Suitably, the flushing composition is present in the refrigeration system for at least 10 minutes and preferably at least 20 minutes when used to flush a system during retrofilling.

The old refrigerant and/or lubricant may be expelled from the system using a pressurised gas for example air or nitrogen. Similarly, if desired, the flushing composition may be removed from the system using a pressurised gas. The old refrigerant and lubricant may typically comprise a CFC refrigerant and a mineral oil lubricant although the method of removing deposits is also applicable to refrigeration systems in which the old refrigerant was a HFC and/or a HCFC refrigerant and the old lubricant was a synthetic material, for example a polyalkylene glycol lubricant, an alkyl benzene, a polyvinyl ether and an organic ester.

The refrigerant which is charged to the system after the flushing process is suitably a HCFC refrigerant, a HFC refrigerant, or a blend of refrigerants containing at least one HFC, HCFC or both. Suitably the refrigerant does not contain chlorine atoms, thus the refrigerant is preferably consists essentially of only HFC refrigerant. Other known refrigerant gases including carbon dioxide, hydrocarbons, for example pentane and isobutane, and ammonia may also be employed as the refrigerant gas.

The lubricant composition that is charged to the system after the flushing process is preferably a synthetic lubricant chosen from a polyalkylene glycol, an alkyl benzene, a polyvinyl ether and an organic ester, said organic ester to include the flushing composition itself.

The present invention is further illustrated with reference to the following non-limiting examples.

Example 1

Table 1 illustrates the physical properties of a lubricant composition comprising 2- ethylhexyl benzoate

Table 1

R134a is 1 ,1,1 ,2-tetrafluoroethane available ex Ineos Fluor

The 2-ethylhexyl benzoate ester has good low temperature properties and a low viscosity.

Example 2

A lubricant composition comprising 2-ethylhexyl benzoate was evaluated using a Falex pin and Vee block wear tester and a Four Ball wear tester. Conditions for the Falex pin and Vee wear test were those of standard test method ASTM D2670-88, but using Aluminium Vee blocks, under an atmosphere of R143a (1,1,1-trifluoroethane available ex Ineos Fluor) refrigerant. The test was run for 5 hours at a load of 200 lbs., and the wear determined as the number of gear teeth of the ratchet mechanism advanced to maintain load constant during the test period.

Conditions for the Four Ball wear test were those of standard method ASTM

D4172-94, using a test duration of 1 hour, and a load of 40 kg. The wear was determined by the average of the diameter, in mm, of the scars worn on the lower balls.

The performance of the test composition was compared with other synthetic lubricant compositions of comparable viscosities. The results are shown in Table

2.

Table 2

Emkarate RLδHplus is a polyol ester available ex Uniqema (an ICI Business) with a viscosity of about 5.7 cSt at 40°C.

Zerol 55 is an alkylbenzene available ex Chevron with a viscosity of about 7 cSt at 40°C

The ester according to the present invention has superior wear performance with respect to the alkylbenzene.

Example 3 The efficiency of 2-ethylhexylbenzoate and isopropyl benzoate as flushing fluids was evaluated for the removal of mineral oil deposits. Approximately 3g of mineral oil (Suniso 4GS) were baked at 175 °C for 71 hours in an aluminium tray. The relevant ester was added dropwise to the baked mineral oil sample in the tray suspended at an angle of 45° and its effectiveness as a flushing fluid visually monitored. The performance of each ester was visually compared with other synthetic lubricant compositions tested under the same conditions.

PAO6 is a polyalphaolefin, Durasyn 166 ex BP Amoco

Emkarox VG 33 W is a polyalkylene glycol ex Uniqema (a Business of ICI).

Claims

1. A lubricant composition comprising an ester derivable from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms.

2. A lubricant composition according to claim 1 wherein the monovalent aliphatic alcohol has 1 to 8 carbon atoms.

3. A lubricant composition according to either claim 1 or 2 having a viscosity at 40 °C from 1 to 15 cSt.

4. A lubricant composition according to any of claims 1 to 3 wherein the ester is selected from 2-ethylhexyl benzoate, hexyl benzoate, butyl benzoate, isopropyl benzoate and ethyl benzoate.

5. A lubricant composition according to any of claims 1 to 4 further comprising 0.0001 to 10% of one or more lubricant additives.

6. A lubricant composition according to any of claims 1 to 5 further comprising 5 to 95% of one or more lubricant base fluids.

7. Use of a lubricant composition according to any of claims 1 to 6 in a refrigeration system.

8. A flushing composition which comprises an ester derived from the reaction of an aromatic monocarboxylic acid with a monovalent aliphatic alcohol having 1 to 15 carbon atoms.

9. A flushing composition according to claim 8 wherein the monovalent aliphatic alcohol has 1 to 8 carbon atoms.

10. A flushing composition according to either claim 8 or 9 having a viscosity at 40 °C from 1 to 15 cSt.

11. A flushing composition according to any of claims 8 to 10 wherein the ester is selected from 2-ethylhexyl benzoate, hexyl benzoate, butyl benzoate, isopropyl benzoate and ethyl benzoate.

12. A flushing composition according to any of claims 8 to 11 further comprising 0.0001 to 10% of one or more lubricant additives.

13. A flushing composition according to any of claims 8 to 12 further comprising 5 to 95% of one or more lubricant base fluids.

14. Use of a flushing composition according to any of claims 8 to 13 in a refrigeration system for the removal of deposits in the refrigeration system.

15. A method of removing deposits from a refrigeration system which comprises charging a flushing composition, according to any of claims 8 to 13, circulating the flushing composition through the refrigeration system for a period of time sufficient to remove at least some deposits and removing the flushing composition containing at least some deposits from the refrigeration system.

16. A method according to claim 15 which further comprises the steps of removing the old refrigerant and lubricant contained in a refrigeration system prior to charging the flushing composition to the refrigeration system and charging the refrigeration system with a new refrigerant and lubricant after the flushing composition has been removed from the refrigeration system.

17. A method according to either of claims 16 or 17 wherein the flushing composition is employed at a level of 1 to 15 litres per tonne of refrigerant capacity of the refrigeration system.

18. The use of an ester as a lubricant wherein the ester has the formula: R¹-A - COOR² wherein R¹ is an optional substituent on an aromatic carboxylic acid residue A-CO,

R²O is derived from the monovalent aliphatic alcohol wherein R²is a branched or straight chained, saturated or unsaturated hydrocarbon containing from 1 to 15 carbon atoms, and

A is an aromatic hydrocarbon.

19. The use of an ester as a flushing agent wherein the ester has the formula:

R¹-A- COOR² wherein R¹ is an optional substituent on an aromatic carboxylic acid residue A-CO,

A is an aromatic hydrocarbon.