WO2004005441A2

WO2004005441A2 - Refrigeration lubricant composition

Info

Publication number: WO2004005441A2
Application number: PCT/GB2003/002891
Authority: WO
Inventors: Steven James Randles; Stuart James Mctavish
Original assignee: Imperial Chemical Industries Plc
Priority date: 2002-07-08
Filing date: 2003-07-04
Publication date: 2004-01-15
Also published as: AU2003253108A8; WO2004005441A3; AU2003253108A1; GB0215704D0

Abstract

A lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination in a refrigeration system comprising hydrofluorocarbon refrigerant gas is described. The lubricant composition comprises a synthetic refrigerator oil and 0.01 to 0.8 % by weight of a specific polyalkylene glycol additive.

Description

Lubricant Composition

The present invention relates to lubricant compositions. In particular the invention relates to a lubricant composition comprising synthetic refrigerator oil and a polyalkylene glycol derived additive and a refrigeration system comprising said lubricant composition and a hydrofluorocarbon refrigerant gas.

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 in terms of ozone depletion. 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. For example, there is very low mutual solubility between the mineral oil and HFC gas. More polar, HFC-compatible synthetic refrigeration lubricant compositions are used. Examples of suitable synthetic refrigerator oils are polyalkylene glycols, polyol esters, diesters, polyvinyl ethers, polycarbonates and alkylbenzenes and mixtures thereof.

Conventional refrigeration systems typically have a compressor, a drier, a condenser, an expansion device and an evaporator linked to form a loop in which a refrigerant circulates and is successively condensed and evaporated so as to provide a refrigeration effect. Various types of compressor are employed in refrigeration systems including reciprocating, scroll, rotary vane, centrifugal and screw compressors and are selected according to the particular application. The compressor contains moving parts, which are lubricated during use. The expansion device in refrigeration systems generally contains an area of constricted flow of refrigerant and may be, for example, a capillary tube or a thermal expansion valve (TXV).

In general, there are two types of refrigeration system: first, systems in which the refrigerant oil and refrigerant gas are present as a mixture and circulate around the refrigeration system as such, for example in automotive refrigeration systems; and secondly, systems in which the refrigerant gas circulates in the system and the refrigerant oil is present in a sump in the compressor, typically closed hermetic compressors for the domestic appliance market sector, and compressors used in industrial and commercial refrigerators. In the second case the system is designed to avoid or at least minimise carry over of the refrigerant oil from the compressor sump into the refrigeration loop although, in practice, carry over does occur to some extent due to the entrainment of the refrigerant oil in the refrigerant gas. Once refrigerant oil is carried into the refrigeration loop it is necessary that it be transported around the system and deposited back in the sump otherwise reduced refrigeration effectiveness may result and problems due to a reduced level of refrigerant oil in the sump may be encountered.

It is well known that deposits have the potential to cause various problems in a refrigeration system leading to reduced long-term reliability. The coldest point in most conventional refrigeration systems is the expansion device. Therefore, materials that have a low solubility in the refrigerant gas-oil mixture will tend to precipitate out at that point. Such deposition can result in flow restriction through the expansion device leading to a reduction in system efficiency. This causes the compressor to run longer to achieve the same level of cooling which can result in potential compressor burn out and higher energy consumption, poor temperature control, and, in extreme cases, system failure. Capillary tube systems for use in domestic refrigeration and room air conditioning systems are typically hermetically sealed for the lifetime of the equipment and are also narrow bore copper tubes of less than 1.5 mm, typically 0.6 - 0.8 mm, diameter. Therefore, deposition in such systems is a major disadvantage.

Deposits can also lead to fouling of the heat transfer surfaces, for example the condenser and/or evaporator surfaces, in the refrigeration system. Deposition on such surfaces leads to deterioration in system efficiency.

Process chemicals are used in the production and assembly of compressors. Typical examples are low pour point paraffinic processing fluids and wire winding lubricants, metal working lubricants, for example fin stamping and copper extrusion, detergents, corrosion inhibitors and fluxes. In many hermetic systems, system components, for example the copper motor windings are immersed to some extent or continually showered with a refrigerator-oil- rich oil/gas mixture at elevated temperatures, i.e. greater than 60 °C. The paraffinic assembly fluids have a wide molecular weight distribution. The longer chain length, i.e. higher molecular weight, material is substantially insoluble in the polar refrigerant oil (chosen to be compatible with the HFC refrigerant) of the oil-rich oii/gas mixture, which is under low pressure compressor sump conditions. However, components of the paraffinic processing fluids having chain lengths up to about 30 carbon units are soluble in the oil-rich oil/gas mixture under these conditions. When a small portion of the refrigerant oil is transported out of the sump, the soluble components of the paraffinic processing fluids are carried into the refrigeration loop and will be transported to the expansion device. In the region of the expansion device, the refrigerant oil/gas mixture is now gas rich (typically greater than 98%) and at low temperature. The solubility of the majority of conventional process chemicals used, i.e. the paraffinic processing fluids, is lower in HFCs than in CFCs and HCFCs. Consequently, the part of the soluble component of the paraffinic processing fluids that are about a chain length of 20 to 30 carbon units tend to come out of solution and are deposited, where as part of the soluble component of the paraffinic processing fluids, i.e. of chain length below about 20 carbon units, is still soluble enough in the small amount of refrigerant oil in the refrigerant-gas-rich oil/gas mixture.

The synthetic refrigerator oils, which are compatible with HFCs, are polar in nature as compared to mineral oils used with CFCs and HCFCs. Consequently low molecular weight oligomers, processing additives, impact modifiers, fillers, softeners, anti-ageing additives, crosslinking additives and accelerators present in plastic and elastomeric components of the compressor, which are soluble in polar solvents, tend to be leached out of the components by the refrigerator oils. For example, long chain amides e.g. stearamide derivatives can be leached from polyethylene terephthalate electrical insulator inserts, which are used in domestic refrigeration and room air conditioning equipment. The stearamide material is transported and deposited in the expansion device in the same way as the paraffinic processing fluids.

Further materials present and circulating in the refrigeration system are readily trapped in the sticky primary deposits of process chemicals and, for example, stearamide, which exacerbates the problem. Examples of such further materials are particulate system debris such as silica fines, gasket materials, machining debris, flux and wear debris. Deposits on heat exchangers include process chemicals and mineral oils.

As discussed above, blockages in refrigeration loop capillary tube systems, as used in domestic refrigeration and room air-conditioning, cannot be readily cleared when the compressor is operational in the field. This is a major disadvantage.

Much research has been undertaken as to how to prevent or inhibit capillary tube blockage caused by a range of materials from different sources. The research has primarily been focussed on two main areas: changes to the refrigeration system and the inclusion of defined additives to the refrigerator lubricant composition to combat blockage by specific materials.

Kao, WO98/26024, discloses a polyalkylene glycol additive of formula R¹0(EO)_m (PO)_nR² where R¹ covers a broad range of hydrocarbon group with 1 to 36 carbon atoms, R² covers a broad chemistry range of hydrogen, hydrocarbon group with 1 to 36 carbon atoms, acyl group with 1 to 24 carbon atoms and m=n = 0 to 50 provided m+n is from 1 to 100. The additive is used at a level of 1-20 wt% in an ester refrigeration oil where the refrigerant is a hydrofluorocarbon. Comparative examples are disclosed in which the additive is present at less than 1 wt%. The additive is present to inhibit formation of adhered materials in capillary tubes, which originate from deterioration of refrigerating oil, process chemicals and their deterioration products.

Daikin, EP0952206 A1 , discloses a polyalkylene glycol additive of formula R¹(R²0)_n(R³0)_mR⁴, where R¹ covers a very broad chemistry range of alkyl, alkoxy or aryl; R², R³ are 2-4 carbon alkylene; R⁴ is hydrogen or alkyl and neither n nor m are defined. The additive is for use at 0.1 to 20 wt% in a polyvinyl ether or polyol ester refrigeration oil in a system where the ^"refrigerant is a hydrofluorocarbon. According to Figures 4 and 5 in the examples the reduction in flow rate due to the presence of capillary tube blockage reduces as the wt% of additive is increased indicative of preferred additive levels of up to 10 wt%. The additive is present to prevent choking caused by contaminants in capillary tubes and expansion valves.

Idemitsu, US6193906, discloses a polyalkylene glycol additive, having a number average molecular weight of 200 to 3000, of formula R¹(OR²)_m (OR³)_nR⁴, where R¹ = R⁴ which also covers a broad chemistry range of 1-30 carbon atom hydrocarbon or acyl or hydrogen; R² is 2-4C alkylene; R³ is 2-30 carbon alkylene and n can be zero. The additive is for use with a range of synthetic refrigeration oils in a system where there is a choice of a range of refrigerants, of which hydrofluorocarbon is preferred. The examples, in Idemitsu, encompass additive levels from 5 to 30 wt%. The additive is present to improve lubrication between aluminium and steel materials in order to suppress wear between these materials and to prevent capillary tube clogging.

Japan Energy, EP881278 A1, discloses a polyalkylene glycol additive of formula R¹(OR²)_nR³ where R¹ is an alkyl group of 1 to 8 carbon atoms; R²is a 1-4 carbon alkylene; R³ is hydrogen or an alkyl group of 1-8 carbon atoms and n is the degree of polymerisation corresponding to a molecular weight of 300 to 3000. The additive is for use at 0.5 to 4.5 wt%, preferably at least 1 wt%, in a polyol ester refrigeration oil in a system where the refrigerant is a hydrofluorocarbon. The additive is used to inhibit blockage of the system capillary tube by reaction products of sulphur or phosphorus extreme pressure agents present in metal working oil with either a polyol ester refrigeration oil or hydrofluorocarbon refrigerant.

Lubrizol, EP0913457 A, discloses a liquid refrigeration composition which comprises a hydrofluorocarbon, a polyol ester and a performance additive chosen from an alkoxylated alcohol/phenol or an alkoxylated glycol. The alkoxylated alcohol/phenol is of structure R²0[(CH2)_yCH (R³) 0]_XH where R² covers a broad chemistry range of 1 to 20 aliphatic carbon atoms or aromatic/substituted aromatic 6 to 24 carbon atoms, R³ is hydrogen, methyl or ethyl, y = 1 to 3 and x = 2 to 50. Exemplification is of an alkoxylated phenol additive ( commercial product Triton X-45). The additive is present to provide anti-wear benefits in polyol esters. Idemitsu, EP1085077, discloses a polyalkylene glycol alkyl ether additive of formula R¹0(EO)_m(PO)_nR² where R¹= R² which is hydrogen or 1 to 10 alkyl but both cannot be hydrogen, m and n are positive numbers that satisfy a molecular weight range of 500 to 3000, EO is ethylene oxide and PO is propylene oxide. The additive is used at 1 to 20 wt% in a refrigerator oil selected from polyol ester or polyvinyl ether and it is stated that the aim of the invention is not met if less than 1 wt% of additive is present. The additive is used to dissolve materials that clog the capillary tube owing to the use of additives such as anti-oxidant, extreme pressure agent and a defoamer in the refrigeration oil.

It is an object of the present invention to provide a polyalkylene glycol additive, present at low concentration in a synthetic refrigeration oil capable of dispersing specific contaminants in a hydrofluorocarbon refrigerant gas containing refrigeration system.

According to the present invention, a lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination in a refrigeration system comprising hydrofluorocarbon refrigerant gas comprises:- a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R² is hydrogen or C1- C4 alkyl. Examples of process chemicals used in the production and processing of refrigeration compressors are low pour point paraffinic processing fluids and wire winding lubricants, metal working lubricants, for example for fin stamping and copper extrusion, detergents, corrosion inhibitors and fluxes. Examples of extractables from non-metallic compressor components are oligomers, processing additives, impact modifiers, fillers, softeners, anti-ageing additives, crosslinking additives and accelerators which are present in plastic and elastomeric components of the compressor. The contamination that is dispersed is preferably about C20 to C30 fraction of paraffinic processing fluids having a pour point.of greater than -20 °C, preferably greater than -10 °C, and/or fatty acid amides, for example stearamide, leaching from polyethylene/ polybutylene terephthalate electrical insulator inserts or nitrile/hydrogenated nitrile butadiene gasket seals into the synthetic refrigerator oil. The concentration of contaminants that is to be dispersed is up to 10000 ppm (wt/wt), preferably up to 5000 ppm. Preferably the lower limit for contaminant concentration is 50ppm.

The synthetic refrigerator oil is selected from polyalkylene glycols, polyol esters, diesters, carbonate esters, polyvinyl ethers, poly alphaolefins and alkylbenzenes and mixtures thereof. Preferred oils are polyol esters, mixtures of polyol esters with alkyl benzenes, polyvinyl ethers and diesters.

Especially preferred oils are polyol esters or mixtures of polyol esters with alkyl benzenes. Polyol esters particularly suitable for use in the invention are made from polyhydric alcohols and monobasic carboxylic acids by standard direct esterification methods. They may also be made by transesterification routes. Both routes are described in "Synthetic lubricants and high-performance functional fluids, 2^nd edition, edited by L. R Rudnick and R. L Shubkin, pages 70-71. Particularly preferred are polymerisation routes that do not use a catalyst. Particularly preferred polyol esters are made from one or more alcohols selected from neopentylglycol, trimethyolpropane and pentaerythritol and dimers and trimers thereof and one or more acids selected from linear and/or branched C₅ to C₁₈ acids, particularly C₅ to C₁₃ acids and more particularly C₅ to C₉ acids.

Preferred polyol esters have a kinematic viscosity of at least 5 cSt but not more than 240 cSt at 40 °C and a kinematic viscosity of at least 1.5 cSt at 100 °C.

Preferred polyol esters have a pour point of less than -30 °C more preferably less than -40°C. Preferred polyol esters have an acid number of less than 0.04 mgKOH/g. Preferred polyol esters have water content of less than 50 ppm.

Preferred polyol esters have hydroxyl numbers less than 5 mgKOH/g. Examples of preferred polyol esters include the EMKARATE^® RL range of polyol esters available ex Uniqema Ltd, a Business of ICI, in particular RL 22H and RL 9HPIus grades of lubricant. Alkylbenzenes particularly suitable for use in the invention include mono- alkylbenzenes, di-alkylbenzenes, di-phenylalkanes and mixtures thereof. Preferably, the alkyl component of the alkylbenzene is branched and is derived from propylene oligomers. Preferred alkylbenzenes for use in the invention have a molecular distribution in which at least 80 %, and more especially, 100 % of the molecular weight fraction is greater than 200.

Preferred alkylbenzenes have a kinematic viscosity of at least 5 cSt, and more preferably at least 7 cSt, but not more than 100 cSt at 40 °C and a kinematic viscosity of at least 1 cSt, and more preferably at least 1.5 cSt, but not more than 10 cSt at 100 °C. Preferred alkylbenzenes have a pour point of less than -10 °C more preferably less than -20 °C and particularly less than -30 °C.

Preferred alkylbenzenes have water content of less than 50 ppm. For the mixtures of alkylbenzenes and polyol esters the refrigerant oil comprises at least 55 % by weight of alkylbenzene and at most 45 % by weight of a polyol ester; more preferably between 55 % and 75 % by weight of alkylbenzene and between 45 % and 25 % by weight of polyol ester.

The polyalkylene additive is preferably present at 0.02 to 0.5 % by weight of the synthetic refrigerator oil.

In the formula for the additive R¹ is preferably C16 to C20 alkyl, particularly C18 alkyl, especially C18 linear, saturated alkyl. R² is preferably methyl or hydrogen, particularly hydrogen. The molecular weight range of the additive is preferably from 550 to 1300, more preferably 600 to 1000.

The polyalkylene glycol additive has a kinematic viscosity range of 2 to 20 cSt at 100 °C, preferably 4 to 15 cSt, more particularly 6 to 10 cSt. The hydroxyl value of the additive ranges from 50 to 90 mgKOH/g, more preferably from 55 to 80 mgKOH/g. The pour point of the additive is less than 10°C, more preferably less than 5°C. The maximum acid value of the additive is 2.00 mgKOH/g, more preferably 0.5 mgKOH/g.

A particularly preferred polyalkylene glycol additive is EMKAROX DGLP 169 available from Uniqema Ltd, a Business of ICI. Preferred lubricant compositions have a pour point of less than -30 °C more preferably less than -40 °C. Preferred lubricant compositions have an acid number of less than 0.04 mgKOH/g. Preferred lubricant compositions have hydroxyl numbers less than 5 mgKOH/g. Preferred lubricant compositions are catalyst free. Preferred lubricant compositions have water content of less than 50 ppm. The lubricant composition may include other additives at levels between 0.0001 and

10 % by weight. 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, foaming and anti-foaming agents. According to a second aspect of the present invention, the use in a refrigeration system comprising hydrofluorocarbon refrigerant gas of a lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination said composition comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R²is hydrogen or C1- C4 alkyl.

Suitable hydrofluorocarbon refrigeration gases include R-134a (1,1,1,2-tetrafluoroethane), R-32 (difluoromethane), R-125 (1,1,1,2,2-pentafluoroethane), R-152a (1 ,1-difluoroethane), R-143a (1 ,1 ,1-trifluoroethane) and mixtures thereof and the R- 400 and R-500 series. Other components typically found in refrigerant blends may also be included in the refrigeration gas. These include hydrocarbons, especially hydrocarbons having from 1 to 6 carbon atoms for example propane, isobutane, butane, pentane and hexane, fluorinated hydrocarbons and other refrigerants, for example carbon dioxide.

According to a third aspect of the present invention, a refrigeration system comprising a compressor, a condenser, an expansion device and an evaporator linked to form a loop in which refrigerant gas comprising hydrofluorocarbon circulates and is successively condensed and evaporated so as to provide a refrigeration effect the system further comprising a lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R² is hydrogen or C1- C4 alkyl. Preferably the expansion device of the refrigeration system is a capillary tube.

Preferably the compressor is a reciprocating compressor. Preferably the refrigeration system further comprises a drier. Preferably the system further includes in the loop pentane or hexane at levels of 2 to 7 wt%, preferably 3 wt%. The inclusion of pentane or hexane is particularly useful when the expansion device is already partially blocked.

According to a fourth aspect of the present invention a method of inhibiting the deposition of process chemicals, extractables from non-metallic compressor components and mineral oil contamination in a refrigeration system which comprises operating a refrigeration system charged with a refrigerant gas which comprises hydrofluorocarbon and a lubricant composition comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 of formula R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R² is hydrogen or C1-

C4 alkyl. The lubricant composition of the invention is used for dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination in a refrigeration system comprising hydrofluorocarbon gas therefore inhibiting the deposition of such contamination in the expansion device or on heat transfer surfaces. Further, materials such as particulate system debris such as silica fines, machining debris, wear debris, which could be trapped in the expansion valve by the sticky contamination deposits are now free to circulate through the refrigeration system.

The presence of the polyalkylene glycol additive in the refrigeration system at the low levels prescribed by the invention means that it does not compromise any of the desired properties of the synthetic refrigerator oil or the refrigerant gas comprising hydrofluorocarbon. For example, the viscosity at both 40 and 100 °C, low temperature miscibility in refrigerant gas (10 % by wt), acid value, pour point and flash point of the lubricant composition are maintained substantially at the values of the neat oil values. The anti-wear capability of the synthetic refrigerator oil is not adversely affected by the polyalkylene glycol additive presence. Furthermore the presence of the polyalkylene glycol additive at the low levels of the invention does not introduce undesired properties i.e. foaming is not induced by the presence of the additive. Also the presence at low levels means there are less likely to be undesirable interactions with other additives that may be present in the synthetic refrigerator oil. If there are no contaminants present in the system to be dispersed the presence of the polyalkylene glycol at low levels does not have a deleterious effect on the system.

Preferred application areas are domestic refrigeration and room air conditioning systems.

The invention will now be described further by way of example only with reference to the accompanying drawings and the following Examples.

In the drawings: -

Figures 1 and 2 are graphical representations of the results obtained in Example 3; and

Figure 3 is a graphical representation of the results obtained in Example 4; and

Figure 4 is a graphical representation of the results obtained in Example 5; and

Figure 5 is a graphical representation of the results obtained in Example 7. Example 1

®

Table 1 illustrates the physical properties of a lubricant composition, EMKARATE

RL ΘHPIus with 0.2 wt% EMKAROX ^w DGLP 169 according to the invention and for the synthetic refrigerator oil, EMKARATE ® RL 9HPIus only. EMKARATE ^® RL 9HPIus is a polyol ester synthetic refrigeration oil available ex Uniqema Ltd.

Table 1

The "in-house" miscibility test was undertaken as follows. A sight glass was charged with a lubricant composition according to the invention (0.6 g, 10 wt%) and subsequently evacuated and cooled to -78 °C. R-134a (5.4 g, 90 wt%) was then added to the sight glass and allowed to warm to room temperature. The sight glass was then cooled in 1 °C intervals until the lubricant and refrigerant mixture was observed to separate into two phases, defined as the low temperature miscibility point.

The presence of the polyalkylene glycol additive in the lubricant composition has no material impact on the desired physical properties of the synthetic refrigerator oil.

Example 2 Thermal stability was measured using a sealed tube test, which is a modification of the

ASHRAE 97 sealed tube test. A lubricant composition according to the invention (60 g) was dried until it contained less than 50 ppm water. The acid value was measured and the dried lubricant composition added to a dry 300 ml stainless steel autoclave. Aluminium, copper and steel coupons were then immersed in the lubricant composition. The autoclave was then subsequently evacuated, charged with R-134a so as to obtain a pressure of 600 psig at 175 °C and heated to 175 ^CC for 14 days. The acid value of the lubricant sample was then remeasured.

®

Table 2 illustrates the sealed tube test results for a lubricant composition, EMKARATE R RLL 99HHPPIIuuss wwiitthh 00..22 wwtt%% EEMMKKAARROOXX ^®® DDGGLLPP 116699 aaccicording to the invention and for the synthetic refrigerator oil, EMKARATE ^® RL 9HPIus only.

Table 2

The data shows that addition of the polyalkylene glycol additive, at the low levels according to the invention, to the synthetic refrigerator oil has no material affect on the thermal stability of the synthetic refrigerator oil.

Example 3

The flow through a refrigeration system capillary tube was measured for a system dosed with paraffin wax contamination. A test rig was set up having a Zanussi compressor (model GL 80 AA) linked to a capillary tube (2.2m long, 0.65mm internal diameter) via a line passing through a close-coupled heat exchanger. A return line from the capillary tube, through the close- coupled heat exchanger and back to the compressor completed the loop for the circulating refrigerant composition. The average suction and discharge pressures were respectively 22 and 265 psig. The ambient temperature was around 20 °C. Three way valves were located in the line immediately before and after the capillary tube to facilitate flow measurement. Nitrogen was passed through the capillary tube at a pressure of 150 psig and the time taken for five litres of nitrogen to pass through the capillary tube was measured to equilibrium from which an average flow in litres per minute was recorded. The system was purged with R- 134a and then charged with R-134a to the vapour pressure of the refrigerant. As the synthetic refrigerator oil^" '300 ml of EMKARATE ^® RL 9HPIus polyol ester oil, to which 1500 ppm paraffin wax contaminant, of hydrocarbon chain lengths typically C25, was added, was charged to the compressor. The flow through the capillary tube was measured once per day. Table 3 and Figure 1 illustrate the reduction of % flow of oil/gas mixture through a capillary tube of a refrigeration system containing 1500 ppm paraffin wax contaminant, monitored over a 40 day period. Sample A (comparative sample) is of a synthetic refrigeration oil EMKARATE ^® RL 9HPIus. Sample B is a lubricant composition comprising EMKARATE ^R RL 9HPIus and 0.2 wt% of EMKAROX DGLP169 as according to the invention. Table 3

In Figure 1 the top line represents sample B and the lower line comparative sample A.

Table 4 and Figure 2 illustrate the reduction of % flow of sample B and comparative sample A through a capillary tube of a refrigeration system containing 3000 ppm (by weight) of the paraffin wax contamination.

Table 4

In Figure 2 the top line is Sample B and the lower line is comparative Sample A. It can be seen from Figures 1 and 2 that the presence of the polyalkylene glycol additive, as according to the invention, inhibits the deposition of the paraffin wax contaminant in the capillary tube. Example 4

Example 3 was repeated wherein the paraffin wax was replaced by 1500 ppm (by weight) stearamide wax contamination. Table 5 and Figure 3 illustrate the reduction of % flow of oil/gas mixture through a capillary tube for comparative Sample A and Sample B.

Table 5

In Figure 3 the top line is Sample B and the lower line is comparative Sample A. It can be seen from Figure 3 that the presence of the polyalkylene glycol additive, as according to the invention, inhibits the deposition of the stearamide wax in the capillary tube.

Example 5

The percentage reduction in capillary flow was measured using the test rig of Example 3 for a range of polyalkylene glycol concentrations added to EMKARATE ® RL 9HPIus. The system was doped with 3000ppm paraffin wax contamination.

Table 6 and Figure 4 illustrate the results.

Table 6

The data clearly illustrates that addition of the polyalkylene glycol additive inhibits the deposition of the paraffin wax contamination in the capillary tube. It also illustrates that additive levels of 1 wt% and above are not suitable for dispersion of such contamination.

Example 6

The dispersing capabilities of polyalkylene glycol additives according to the invention and comparative additive materials in R-134a refrigerant were measured in accordance with the following method. 9.9 g synthetic refrigeration oil (EMKARATE ® RL 32H, a polyol ester available ex Uniqema Ltd), 9.9g mineral oil (Suniso 3GS), 0.6mmol of additive and 20g R-134a were mixed together at a temperature to mimic the typical operating conditions of a refrigerant system i.e. at -20 °C. The mixture was shaken to form a "dispersed state" and the time for the mixture to separate was measured. The results are illustrated in Table 7.

Table 7

Triton X-45 is an octylphenoxypolyethoxyethanol available ex Dow of chemical formula

C₈H₁₇-Ph -0-(EO)₄.₅H

EMKAROX ® VG 58 is a butanol derived polyalkylene glycol ex Uniqema Ltd

The data illustrates that the importance in the choice of R in the chemical formula of the polyalkylene glycol additive of the invention. For example Triton X-45 has a substituted aromatic group and EMKAROX VG 58 has a short chain alkyl group - both of which lead to lower dispersing capabilities as compared to the polyalkylene glycol of the invention.

Example 7

The percentage reduction in capillary flow was measured using the test rig of Example 3 for EMKARATE ® RL 9HPIus with 0.2 wt% of EMKAROX ® DGLP 169 for a refrigeration system not doped with contaminants. The results of two 40 day experiments are illustrated in Table 8 and Figure 5.

Table 8

In Figure 5 the top line is Run 1 and the lower line is Run 2.

It can be seen from Figure 5 that the use of the polyalkylene glycol additive has no material affect on the system when there is no contamination present.

Claims

1. A lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination in a refrigeration system comprising hydrofluorocarbon refrigerant gas comprises: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R² is hydrogen or C1- C4 alkyl.

2. A lubricant composition as claimed in claim 1 wherein the synthetic refrigerator oil is selected from polyol esters, mixtures of polyol esters with alkylbenzenes, polyvinylethers and diesters.

3. A lubricant composition as claimed in either of claims 1 or 2 wherein 0.02 to 0.5 wt% of the polyalkylene glycol additive is present.

4. A lubricant composition as claimed in any of claims 1 to 3 wherein R is C16-C20 alkyl

5. A lubricant composition as claimed in any of claims 1 to 4 wherein R ϋ2 ; is methyl or hydrogen.

6. The use in a refrigerator system comprising hydrofluorocarbon refrigerant gas of a lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination said composition comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide or mixtures thereof and R² is hydrogen or C1- C4 alkyl.

7. A refrigeration system comprising a compressor, a condenser, an expansion device and an evaporator linked to form a loop in which a refrigerant gas comprising hydrofluorocarbon circulates and is successively condensed and evaporated so as to provide a refrigeration effect the system further comprising a lubricant composition capable of dispersing process chemicals, extractables from non-metallic compressor components and mineral oil contamination comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_nR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide and mixtures thereof and R² is hydrogen or C1- C4 alkyl.

8. A method of inhibiting the deposition of process chemicals, extractables from non- metallic compressor components and mineral oil contamination in a refrigeration system which comprises operating a refrigeration system charged with a refrigerant gas which comprises hydrofluorocarbon and a lubricant composition comprising: - a) a synthetic refrigerator oil and b) 0.01 to 0.8 wt% of a polyalkylene glycol additive having a molecular weight range of 500 to 1500 and a formula of R¹0(AO)_πR² where R¹ is C13-C30 alkyl, n is a positive number that satisfies the molecular weight range, AO is ethylene oxide, propylene oxide or butylene oxide and mixtures thereof and

R² is hydrogen or C1-C4 alkyl.