EP0552262A1

EP0552262A1 - Lubricants

Info

Publication number: EP0552262A1
Application number: EP19910919265
Authority: EP
Inventors: Elizabeth Jane Goodwin; Allan Stewart; Steven James Randles; Robert Ian George Thompson
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1990-10-09
Filing date: 1991-10-08
Publication date: 1993-07-28
Also published as: GB9021921D0; WO1992006147A1; JPH06501972A; AU8660291A

Abstract

Une composition destinée à être utilisée dans un dispositif de transfert thermique du type à compression comprend, en tant que liquide de travail, de l'hydrofluoroalkane ou de l'hydrochlorofluoroalkane, et comme lubrifiant un produit de réaction ou un ester comprenant les résidus d'un alcool monofonctionnel et d'un alcool difonctionnel, et au moins un acide difonctionnel. Le lubrifiant est au moins partiellement soluble dans le liquide de travail et possède un bon indice de viscosité, de préférence supérieur à 130.A composition for use in a compression type thermal transfer device comprises, as a working liquid, hydrofluoroalkane or hydrochlorofluoroalkane, and as a lubricant a reaction product or an ester comprising the residues of a monofunctional alcohol and a difunctional alcohol, and at least one difunctional acid. The lubricant is at least partially soluble in the working liquid and has a good viscosity index, preferably greater than 130.

Description

Lubricants

This invention relates to lubricants and more particularly to their use in heat transfer devices.

Heat transfer devices of the mechanical recompression type, including refrigerators, heat pumps and air conditioning systems, are well known. In such devices, a working fluid of a suitable boiling point evaporates at a low pressure taking heat from the surrounding zone. The resulting vapour is then compressed and passed to a condenser where it condenses and gives off heat to a second zone. The condensate is then returned through an expansion valve to the evaporator, so completing the cycle. The mechanical energy required for compressing the vapour and pumping the fluid is provided by, for example, an electric motor or an internal combustion engine.

The working fluids used in these heat transfer devices include dichlorodifluoromethane (R-12) the production of which is likely to be severely limited by international agreement in order to protect the stratospheric ozone layer. As is the case with other mechanical equipment, it is necessary for the moving parts of the heat transfer devices to be adequately lubricated and the devices are generally designed to use lubricants which are iiscible with the working fluids, mineral oil being used in conjunction with dichlorodifluoromethane.

Unfortunately some of the compounds, for example 1,1,1,2-tetrafluoroethane (R-13 a) which have been proposed as working fluids to replace dichlorodifluoromethane are insufficiently soluble in mineral oils to allow the latter to be used as lubricants. Polyalkylene glycols having -OH and other terminal groups have been proposed as alternatives but they are not entirely satisfactory for a number of reasons. Thus, whilst they show reverse solubility such that the working fluid tends to separate from the lubricant at temperatures above about 40°C, they often attract water to an extent sufficient to cause corrosion in the equipment. Furthermore they often fail to wet metals sufficiently to provide efficient lubrication and have an adverse effect on aluminium commonly used for the construction of compressors.

It has been found that certain esters as hereinafter defined are at least partially soluble in the working fluid used and are thereby excellent lubricants for use with 1,1,1,2-tetrafluoroethane and some related hydrofluorocarbon working fluids such as 1,1,2,2-tetrafluoroethane, and hydrochlorofluorocarbons such as monochlorotetrafluoroethane and are free from the disadvantages associated with polyalkylene glycols or esters having other structures. Furthermore, by varying the composition of the ester as hereinafter defined the evaporation loss, viscosity index and miscibility with the working fluid exhibited by such an ester may be varied to accomodate the needs of a wide variety of refrigeration systems such as those found in domestic, industrial and automotive refrigeration systems.

Accordingly, the present invention provides a composition for use in a compression type heat transfer device comprising: a) a hydrofluoroalkane or hydrochlorofluoroalkane working fluid; and b) a sufficient amount to provide lubrication of a reaction product comprising a residue Z¹ obtained after removing the hydroxyl group from a monofunctional alcohol, a residue Z-- of a diacid, and a residue Z obtained after removing the hydroxyl groups from a difunctional alcohol, which reaction product has a viscosity index of at least 130 and is at least partially soluble in the working fluid.

In a further aspect, the present invention provides a composition for use in a compression type heat transfer device comprising: a) a hydrofluoroalkane or hydrochlorofluoroalkane working fluid; and b) a sufficient amount to provide lubrication of an ester of the formula

Z¹-(Z²-Z³)_n-Z²-Z¹ (1) wherein Z¹ represents the residue remaining after removing the hydroxyl group from a monofunctional alcohol, Z² represents the residue of a diacid, Z³ represents the residue after removing the hydroxyl groups from a difunctional alcohol and n is a positive integer having a value of at least 1.

In a further aspect, the present invention provides a composition for use in a compression type heat transfer device comprising: a) a hydrofluoroalkane or hydrochlorofluoroalkane • working fluid; and b) a sufficient amount to provide lubrication of an ester of the formula _zll_(_Z21__z31)_a__(Z22__z31)_b_(_Z23__Z31)_c__z24_-Zll (2) wherein Z¹**- represents the residue remaining after removing the hydroxyl group from a monofunctional alcohol, Z²*--, Z²², and Z²³ are all different but each is a residue of a diacid, Z³¹ represents the residue after removing the hydroxyl groups from a difunctional alcohol, Z²^ is one of the group Z²**-, Z²², and Z²³, and a, b, and c, are the same or different provided that at least two of a, b, and c, are non-zero.

The working fluid may be one or more selected from the group containing R-23, R-32, R-125, R-22, R-134a, R-152a, R-134, R-124, R-124a, R-142a, R-143, R-133, R-123, and R-123a. Compositions of the present invention preferably contain R-134a as the working fluid.

The residue Z**- and Z*--**- is the residue obtained after the hydroxyl group has been removed from a monofunctional alcohol or a mixture of such alcohols. The monofunctional alcohol is suitably a monofunctional aliphatic primary alcohol, which may be linear, branched or a mixture of such linear and/or branched alcohols. The residue Z¹ and Z¹-¹* preferably contains from 4 to 18 carbon atoms, and in particular contains from 6 to 13 carbon atoms. In general miscibility with the working fluid is improved with branching of the residue Z**- and Z**-**-, whereas high viscosity indices are provided by using a residue Z¹ and Z^ which is linear in configuration. Where the working fluid comprises R-134a. particularly good miscibility is obtained by using a residue Z¹ and Z¹¹ which contains no more than 10 carbon atoms. Particularly low volatility is obtained by using a residue Z¹ and Z-*--*- which contains as many carbon atoms as possible, and at least 8 carbon atoms. Specific monofunctional alcohols which may be sued to provide suitable residues include isoheptanol, isotridecylalcohol, isooctylalcohol, isononanol and isodecanol or mixtures thereof.

The residue Z², Z²**-, Z²², and Z²³ is derived from a diacid, i.e. a difunctional acid. The diacid is suitably a difunctional aliphatic acid, which may be linear, branched, or a mixture of such linear and/or branched diacids. Preferably, however, the diacid is a linear diacid. The residue Z², Z²¹, Z²², and Z²³ preferably contains from 3 to 18 carbon atoms, and in particular from 4 to 9 carbon atoms. In general low volatility may be achieved by increasing the number of carbon atoms as high as possible within the hereinbefore defined ranges, whereas miscibility with the working fluid, in particular R-134a, is improved by the use of a residue Z², Σ²¹, Z²², and Z²³ having no more than 6 carbon atoms. Specific diacids which may be used to provide suitable residues include adipic, azelaic, glutaric, sebacic and succinic acids or mixtures thereof, with adipic, glutaric and succinic acids being particularly preferred. The residue Z³ and Z³¹ is the residue obtained after the hydroxyl groups have been removed from a difunctional alcohol or a mixture of such alcohols. The difunctional alcohol is suitably a difunctional aliphatic primary alcohol, which may be linear, branched or a mixture of such linear and/or branched alcohols. Particularly suitable difunctional alcohols are those wherein the separation of the functional groups is from 2 to 6 carbon atoms and is particularly 3 carbon atoms. Specific difunctional alcohols which may be used to Drovide suitable residues include propane diol, butane diol, hexane diol and neopentylglycol or mixtures thereof.

The reaction product and ester used in the present invention usually has a viscosity index (VI) of at least 130, and more usually of at least 140, with an upper limit of about 200.

The degree of polymerisation within the reaction product and ester determines at least in part the viscosity characteristics of the reaction product and ester. In general, an optimal viscosity index may be achieved with a low degree of polymerisation. Usually, therefore the parameter n in formula (1) and, if non-zero, any one or more of the parameters a, b, and c in formula (2) may have a value from 1 to 20, from 1 to 10, from 1 to 5, from 1 to 3 or more usually from 5 to 15.

The composition of the present invention may comprise a working fluid and a single reaction product or ester. Alternatively a mixture of such reaction products or esters may be employed without adverse effects. This is particularly advantageous in that in the preparation of an ester of formula (1) or (2), it is usual to obtain an ester mixture comprising at least two esters having the formula (1) or (2) wherein the value of n for each ester is different. Within such an ester mixture there may then be a distribution of values for the parameters n, a, b and c, in such circumstances reference to a preferred value for a parameter is reference to the mean average value of the parameter in the distribution on a number or molar basis. Thus, for example, an ester comprising the residues of neopentyl glycol, adipic acid and isoheptylalcohol typically has a viscosity at 40°C of 94.4 cSt and at 100°C of 14.4 cSt, where the average value for n is between 6 and 7, and the maximum value of n is about 12, whereas an ester comprising the same residues and a typical viscosity at 40°C of about 200 cSt and at 100°C of about 20cSt has an average value for n of about 9 and a maximum value for n of about 20.

The reaction product and ester of formula (1) or formula (2) may be present in the composition to any level which provides adequate lubrication under a given set of conditions. Typically the reaction product or ester may be present at a level between 5 and 20Z w/w, and in particular between 10 and 20Z w/w.

Specific compositions which show adequate lubrication and compatibility comprise refrigerant R-134a with 152 w/w of an ester having the structure of formula (1) wherein Z¹ is derived from isoheptanol, Z² is from adipic acid and Z³ is from neopentylglycol. Other satisfactory compositions include those comprising refrigerant R-134a with 15Z w/w of an ester having the structure of formula (2) wherein Z¹¹ is derived from isodecanol,

Z²¹, Z²², and Z²³ are from adipic acid, glutaric acid and succinic acid and Z³¹ is from neopentyl glycol.

It is also possible to include in the composition of the present invention other additives, which include simple diesters, and polyol esters. Additionally, other additives, such as antioxidants, extreme pressure and antiwear agents, detergents, defoaming agents, and corrosion inhibitors, which are commonly incorporated in lubricating oils may also be present.

Examples of suitable antioxidants include sterically hindered phenols, e.g. 2,6-di-t-butyl-4-methylphenol and

4,4'-methylenebis(2,6-di-t-butylphenol; aromatic amines, e.g. p,p-dioctylphenylamine, monooctyldiphenyiamine, phenothiazine, 3,7-dioctylphenothiazine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthalamines and alkylphenyi-2-naphthalamines; and sulphur-containing compounds such as dithiophosphates, phosphites, sulphides, and dithio metal salts, e.g. benzothiazole, zinc dialkyl dithiophosphates and zinc diaryldithiophosphates.

Examples of suitable extreme pressure and antiwear agents include phosphates, phosphate esters, phosphites, thiophosphites, e.g. zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, tricresyl phosphate, dicresyl phosphate; chlorinated waxes; sulphurised fats and olefins, e.g. thiodipropionic esters, dialkyl sulphides, dibenzyl sulphides, dialkyl polysulphides, alkyl-mercaptans, dibenzothiophene and 2,2'-dithiobis(benzothiazole) ; organic lead compounds; fatty acids; molybdenum complexes, e.g. molybdenum disulphide; halogen substituted organosilicon compounds; borates; and halogen substituted phosphorus compounds.

Examples of suitable detergents include sulphonates; long-chain alkyl substituted aromatic sulphonic acids; phosphonates; thiophosphonates; phenolates; metal salts of alkyl phenols; and alkyl sulphides.

Examples of suitable defoaming agents include silicon oils, e.g. dimethylpolysiloxane; and organosilicates, e.g. diethyl silicate.

Examples of suitable corrosion inhibitors include organic acids, amines, phosphates, alcohols, sulphonates and phosphites.

The reaction products and esters for use in the present invention may be prepared by using standard techniques. Typically, the reactants, i.e. mono- and difunctional alcohols and diacid or derivatives thereof, in appropriate proportions and usually with excess monofunctional alcohol are heated in the presence of a suitable catalyst, e.g. a titanium or tin catalyst or sulphuric acid. The water or other condensate of reaction, e.g. methanol where the methyl ester of the diacid is used, is removed under reflux and the reaction continued until a low acid value is achieved, e.g. 0.4 mg KOH.g"¹. On completion of the reaction the product is neutralised and purified.

The invention is illustrated but not limited by the following examples.

The viscosities at 40°C, and 100°C of a number of reaction products and esters were determined, as was the viscosity index (VI). A NOACK evaporation loss on each reaction product and ester was also determined at 250°C. Furthermore, the low and high temperature (°C) miscibilities of the reaction products and esters were also determined at the 102 level with refrigerant R-134a in which they were all at least partially soluble.

The results are shown in Table 1, wherein the following abbreviations have been used: AA - Adipic Acid AzA - Azelaic acid SbA - Sebacic acid AGS - Mixture of Adipic, Succinic, Glutaric acids in the approximate molar proportions 20:20:60, derived from a mixture of the methyl esters sold under the trade name "Imsol R" by ICI PLC. NPG - Neopentylglycol IHA - Isoheptylalcohol IOA - Isooctylalcohol TDA - Isotridecylalcohol ,9 - a mixture of G₇ and Cg alcohols, sold under the trade name "LINEVOL" by Shell PLC. 2EH - 2-ethyl hexanol nC7 - n-heptanol 1.2PD - 1,2 Propane diol 1.3BD - 1,3 Butane diol 1.4BD - 1,4 Butane diol

Table 1

Claims

1. A composition for use in a compression type heat transfer device comprising: a) a hydrofluoroalkane or hydrochlorofluoroalkane working fluid; and b) a sufficient amount to provide lubrication of a reaction product comprising a residue Z¹ obtained after removing the hydroxyl group from a monofunctional alcohol, a residue Z² of a diacid, and a residue Z³ obtained after .removing the hydroxyl groups from a difunctional alcohol, which reaction product has a viscosity index of at least 130 and is at least partially soluble in the working fluid.

2. A composition for use in a compression type heat transfer device comprising; a) a hydrofluoroalkane or hydrochlorofluoroalkane working fluid; and b) a sufficient amount to provide lubrication of an ester of the formula

Zl-(Z²-Z³)_n-Z²-Zl (1) wherein Z¹ represents the residue remaining after removing the hydroxyl group from a monofunctional alcohol, Z² represents the residue of a diacid, Z³ represents the residue after removing the hydroxyl groups from a difunctional alcohol and n is a positive integer having a value of at least 1.

3. A composition for use in a compression type heat transfer device comprising: a) a hydrofluoroalkane or hydrochlorofluoroalkane working fluid; and b) a sufficient amount to provide lubrication of an ester of the formula

_Zll._(Z21._z31_)a__(Z22._Z31_)b._(Z23__z31_)c._z24__Zll ₍₂) wherein Z^ represents the residue remaining after removing the hydroxyl group from a monofunctional alcohol, Z²¹, Z²², and Z²³ are all different but each is a residue of a diacid, Z³*-- represents the residue after removing the hydroxyl groups from a difunctional alcohol, Z²* is one of the group Z²¹, Z²², and Z²³, and a, b, and c, are the same or different provided that at least two of a, b, and c, are non-zero.

4. A composition as claimed in any one of claims 1 to 3 wherein the residue of the monofunctional alcohol is the residue obtained after the hydroxyl group has been removed from at least one monofunctional aliphatic primary alcohol.

5. A composition as claimed in claim 4 wherein at least one monofunctional aliphatic alcohol is branched.

6. A composition as claimed in any one of claims 1 to 5 wherein the residue of the monofunctional alcohol contains from 4 to 18 carbon atoms.

7. A composition as claimed in any one of claims 1 to 6 wherein the residue of the monofunctional alcohol is obtained from at least one monofunctional alcohol selected from the group consisting of isoheptanol, isotridecylalcohol, isooctylalcohol, isononanol, and isodecanol.

8. A composition as claimed in any one of claims 1 to 7 wherein the residue of the difunctional alcohol is obtained from a difunctional alcohol wherein the hydroxyl groups are separated by 2 to 6 carbon atoms.

9. A composition as claimed in any one of claims 1 to 8 wherein the residue of the difunctional alcohol is obtained after the hydroxyl groups have been removed from a least one difunctional aliphatic primary alcohol.

10. A composition as claimed in claim 9 wherein at least one difunctional aliphatic primary alcohol is linear.

11. A composition as claimed in claim 9 wherein the residue of the difunctional alcohol is obtained from at least one difunctional alcohol selected from the group consisting of propane diol, butane diol, hexane diol and neopentyl glycol.

12. A composition as claimed in any one of claims 1 to 11 wherein the residue of the diacid contains from 3 to 18 carbon atoms.

13. A composition as claimed in any one of claims 1 to 11 wherein the residue of the diacid is obtained from a difunctional aliphatic acid.

14. A composition as claimed in any one of claims 1 to 13 wherein the diacid is linear.

15. A composition as claimed in any one of claims 1 to 14 wherein the residue of the diacid is obtained from a diacid selected from the group consisting of adipic acid, glutaric acid, sebacic acid and succinic acid.