EP1461404A1

EP1461404A1 - Operating medium for carbon dioxide-cooling systems and air-conditioning systems

Info

Publication number: EP1461404A1
Application number: EP02795046A
Authority: EP
Inventors: Jörg Fahl; Jürgen BRAUN
Original assignee: Fuchs Petrolub SE
Current assignee: Fuchs SE
Priority date: 2001-12-29
Filing date: 2002-12-24
Publication date: 2004-09-29
Anticipated expiration: 2022-12-24
Also published as: US20050127320A1; US7303693B2; DE10164056A1; AU2002360924A1; KR100695190B1; DE10164056B4; ES2356123T3; JP2005514492A; ATE487780T1; KR20040075914A; EP1461404B1; DE50214767D1; DK1461404T3; WO2003057804A1

Abstract

The invention relates to resource operating medium compositions containing additivated lubricants based on polyalkylene glycols and/or neopentyl polyol esters, which are additivated with alkylated triaryl phosphate esters which are suitable for lubricating refrigerators, air-conditioning systems, heat pumps and similar systems which are operated using carbon dioxide as an operating medium.

Description

Operating resources for carbon dioxide refrigeration and air conditioning systems

The invention relates to equipment compositions containing additive

Lubricants based on polyalkylene glycols and / or neopentyl polyol esters, which are suitable for the lubrication of refrigeration machines, air conditioning systems, heat pumps and related systems that are operated with carbon dioxide as a refrigerant.

Carbon dioxide has been used as a refrigeration machine resource since the beginning of modern refrigeration technology. The Linde company built the first compression refrigeration machine using carbon dioxide as early as 1881

Refrigerant. Until the middle of this century, carbon dioxide was mainly used in ship refrigeration systems with subcritical process control. Glycerin was used as the lubricant. Later, with the introduction of the fluorine-chlorine-hydrocarbon refrigerant, carbon dioxide was hardly used.

Currently, the halogenated fluorocarbon R134a is mainly used in automotive air conditioning systems and refrigerant mixtures such as e.g. R404A used. The use of the well-known refrigerant carbon dioxide (R744) has been increasingly considered in recent years. Polyalkylene glycols (PAG) have already been proposed as lubricants for car air conditioning systems

(See, for example, "Polyalkylene ether lubricants for CO ₂ car air conditioning systems", J. Fahl, E. Weidner in Air and Refrigeration Technology 36 (2000) 10, pp. 478-481, ISSN 0945-0459) For the application Polyol esters have been proposed in CO ₂ deep-freeze systems (see, for example, “ester oils for CO ₂ cooling and air conditioning systems”, J. Fahl in Refrigeration and Air Conditioning 53 (2000) 11, pp. 38-45, ISSN 0343-2246).

The advantages of the natural working material carbon dioxide (CO ₂ ) can be used in a transcritical cycle, however, operating pressures that are considerably higher than the current state of the art. In such a cycle, the working medium is both in the subcritical and in the supercritical state and there is a previously unknown lubrication problem. On the one hand, there should be an almost complete miscibility between lubricating oil and CO ₂ even at temperatures below - 40 ° C; on the other hand, under the influence of CO ₂ at pressures up to 150 bar and temperatures up to 220 ° C, appropriate lubrication and stability properties must be guaranteed. In air conditioning systems in particular, the lubricating oil is subject to extreme mechanical see and thermal loads. Tribological difficulties arise with experimental compressors of various designs.

The main reason for the compressor failures is assumed to be the comparatively high CO ₂ solubility in the lubricating oil and the resulting dilution and degassing effects. Initial practical studies in subcritically operated reciprocating compressors have shown that despite the minimum required mixture viscosity due to the influence of CO _2, extreme signs of wear occur, which can be attributed to mixed friction and insufficient lubrication. In the first prototype compressors of transcritically operated passenger cars

- Air conditioning systems were observed with commercially available neopentyl polyol esters (POE) or polyalkylene glycol (PAG) oils lubrication problems.

Only oils of certain chemical compounds show the required properties, such as a correspondingly good cold flow behavior as well as a favorable solubility behavior with CO ₂ . Studies have shown that the physical properties and the interactions of different base oils with subcritical and supercritical CO depend to a large extent on their chemical structure. Mineral oils are almost immiscible with CO and have proven to be hardly suitable in view of the rather moderate high-temperature stability compared to synthetic oils. In particular due to their unfavorable phase behavior and the comparatively low density, both hydrocrack oils, alkyl aromatics and polyalphaelefms (PAO) are to be classified as unsuitable for use in systems with an accumulator on the suction pressure side.

Due to the comparatively high volumetric cooling capacity of CO ₂ and the increased efficiency, refrigeration compressors for carbon dioxide can be designed smaller. This requires a very good load bearing capacity of the lubricant in the corresponding temperature range.

Experience has shown that polyalkylene glycols have excellent friction properties. The good absorption on metal surfaces can be attributed to the polar character. Due to this high surface activity and the low viscosity pressure dependence, low friction coefficients are achieved. There are special conditions in the tribological contact areas that are influenced by CO ₂ . Particularly when starting up and switching off, there are strong solubility-related effects which hinder the formation of a sufficient lubricating film, so that the lubricating gap can be washed out as a result of dissolved refrigerant, which can be caused, among other things, by the pressure equalization that occurs and changes in the surface tension. However, wear measurements on prototype compressors of different designs showed that the described dilution and degassing effects can only be compensated for to a limited extent by using correspondingly high-viscosity oils. Sufficient oil return from the evaporator is not always guaranteed. In addition, the studies with subcritically operated reciprocating compressors indicate that, despite sufficient mixture viscosity, there is an unusually high load in the area of mixed friction. Since the various elementary wear mechanisms usually overlap in practical tribotechnical systems, wear behavior cannot be estimated theoretically, but can only be determined experimentally using appropriate wear tests.

From a purely tribological point of view, if possible, only a little CO _{2 should dissolve} in the oil. On the other hand, for oil return and

Heat transfer in the refrigeration cycle requires good miscibility.

The invention is therefore based on the problem of appropriately adding lubricants for carbon dioxide refrigerants so that the mixture of carbon dioxide and lubricants also meet the following requirements in addition to the above:

- very good lubrication properties and high load carrying capacity

- best emergency running properties under mixed friction conditions

- excellent thermal and chemical stability.

For the heavy load conditions in CO ₂ refrigeration compressors, this is an option

Those skilled in the art recommend the use of customary known wear protection additives and / or high pressure additives. The wear protection additives commonly used in the lubricant sector are based on organometallic compounds such as zinc / phosphorus or zinc / sulfur compounds such as zinc dithiophosphate (ZDTP). Common low-ash active ingredients, on the other hand, contain no metallic elements and are, for example, organic mono- and polysulfides, saturated and unsaturated Fatty acids, natural and synthetic fatty acid esters, as well as primary and secondary alcohols.

Surprisingly, certain additives and base oil combinations have proven to be suitable for solving the above tasks:

Containing equipment compositions for refrigeration machines, heat pumps and related systems, such as air conditioning systems

(A) carbon dioxide as the refrigerant, the refrigerant preferably consisting essentially exclusively of carbon dioxide,

(B) a polyalkylene glycol and / or a neopentyl polyol ester as a lubricant and

(C) as an additive a phosphate ester of the following structure

embedded image in which

R optionally represents the same or different for each of the three phenyl radicals and for each n represents H or one or more Cl to C6 hydrocarbon radicals and n possibly identically or differently for each of the three phenyl radicals, represents an integer from 1 to 5, preferably 1, 2 or 3, with the proviso that at least one, preferably at least two, of the three phenyl radicals, particularly preferably all three phenyl radicals,

R is a C2 to C6, preferably C3 or C4, hydrocarbon radical, in particular t-butyl (t = tert.) And / or isopropyl.

Preferred embodiments of the above equipment composition are the subject of the subclaims or are explained below.

additives

The phosphate ester tricresyl phosphate known as a lubricant additive is not the subject of the invention (see Tables 2 and 3, comparative example there). Trikre- sylphosphate is a mixture of ortho-, para- or meta- monomethyl-substituted phosphates on the phenyl ring.

The phosphate ester used according to the invention is preferably used in an amount of 0.1 to 3% by weight, particularly preferably in an amount of 0.3 to 1.5% by weight, based on the lubricant.

T-Butylated triphenylphosphates are usually produced by alkylation of phenols and reaction with phosphoric acid trichloride. According to a preferred variant, the phosphate esters used according to the invention have at least one phenyl radical alkylated in the ortho position.

Compared to sulfurized or chlorinated additives, the triaryl phosphates claimed are less reactive and offer the advantage that they do not cause corrosion or discoloration in most metals. Furthermore, these active ingredients which are readily soluble in the base oils claimed are distinguished by their extraordinarily high thermal and oxidative stability.

In contrast to sulfur and zinc-based wear protection additives, the phosphates used are significantly more stable under the influence of CO ₂ and allow high operating temperatures. In particular, t-butylated triphyl phosphates are characterized by high hydrolytic stability.

polyalkylene

The polyalkylene glycols (PAG) used according to the invention have alkylene oxide units with 1 to 6 carbon atoms (-R-O-) as monomer units.

The polyalkylene glycols have hydrogen, alkyl, aryl, alkylaryl, aryloxy, alkoxy, alkylaryloxy and / or hydroxyl end groups. Taking alkylaryloxy

Groups are also understood to mean arylalkyl (en) oxy groups and alkylaryl and arylalkyl (en) groups (eg aryl-CH ₂ CH ₂ -). The end groups of the alkyl type, including the alkoxy type, or aryl Types, including the alkylaryl type, aryloxy type and alkylaryloxy type, preferably have 6 to 24 carbon atoms based on the aryl types, particularly preferably 6 to 18 carbon atoms and preferably 1 to 12 carbon atoms based on the alkyl types. The polyalkylene glycols according to the invention are thus either homopolymers, namely polypropylene glycol (or polypropylene oxide), or copolymers, terpolymers, etc. For the latter cases, the monomer units can have a statistical distribution or a block structure. If the polyalkylene glycols are not homopolymers, preferably at least 20%, preferably at least 40%, of all monomer units can be produced from polypropylene oxide (PO), and furthermore preferably at least 20% of all monomer units of these polyalkylene glycols can be produced using ethylene oxide (EO) (PO / EO- copolymers).

According to a further embodiment, preferably at least 20%, preferably at least 40%, of all monomer units can be produced from butylene oxide (BO), and furthermore at least 20% of all monomer units of these polyalkylene glycols can preferably be produced using ethylene oxide (BO / EO copolymers).

The starting compound is incorporated into the polymer when using (poly) alcohols and is also referred to in the sense of the invention as the end group of the polymer chain. Suitable starting groups are compounds which contain active hydrogen, such as e.g. n-butanol, propylene glycol, ethylene glycol, neopentyl glycols such as pentaerythritol, ethylenediamine, phenol, cresol or other (Cl- to C16- (mono-, di- or tri-) alkyl) aromatics, (hydroxyalkyl) aromatics, hydroquinone, aminoethanolamines, Triethylene tetramines, polyamines, sorbitol or other sugars. However, other C-H-acidic compounds such as carboxylic acids or carboxylic anhydrides can also be used as starting compounds

The polyalkylene glycols preferably have aryl groups or corresponding heteroaromatic groups, for example incorporated into the polymer chain, as side groups or end groups; the groups can optionally be substituted by linear or branched alkyl or alkylene groups, the alkyl or alkylene groups in the Preferably have a total of 1 to 18 carbon atoms. Suitable polyalkylene glycols can be produced, for example, using appropriate starting alcohol compounds, for example of the following type:

in which x and y represent an integer from 0 to 6, x + y is less than 7, x + y is greater than 1 and either y is greater than 0 (preferably 1 to 3) or R ¹ carries one or more hydroxyl groups. It is also possible that y is greater than 0 and R ¹ carries one or more hydroxyl groups at the same time. Y is preferably an integer from 1 to 3. R ¹ stands for a linear or branched Cl to C18 hydrocarbon group which optionally carries one or more hydroxyl groups. The starting alcohol compound can also be constructed in the same way from a condensed aromatic, such as naphthalene, instead of from benzene.

Cyclic ether alcohols such as hydroxyfurfuryl or hydroxy-tetrahydrofuran, nitrogen or sulfur heterocycles can also be used as starting groups. Such polyalkylene glycols are disclosed in WO 01/57164, which is hereby also made the subject of this application.

The polyalkylene glycols according to the invention preferably have an average molecular weight (number average) of 200 to 3000 g / mol, particularly preferably of 400 to 2000 g / mol. The kinematic viscosity of the polyalkylene glycols is preferably 10 to 400 mm ² / s (cSt) at 40 ° C. measured in accordance with DIN 51562.

The polyalkylene glycols used according to the invention can be prepared by reacting alcohols, including polyalcohols, as starter compounds with oxiranes such as ethylene oxide, propylene oxide and / or butylene oxide. After the reaction, these only have a free hydroxyl group as the end group. Polyalkylene glycols with only one hydroxyl group are compared to those with two free ones

Hydroxy groups preferred. Particularly preferred in terms of stability, hygroscopicity and compatibility are polyalkylene glycols which, for example after a further etherification step, no longer have any free hydroxyl groups. The alkylation of terminal hydroxyl groups leads to an increase in thermal stability and an improvement in CO ₂ miscibility.

By selecting suitable end groups, the miscibility can also be set such that there is in the phase diagram T versus lubricant content in the CO ₂ areas of complete miscibility and those with little or no miscibility. Neopentyl polyol esters and lubricant mixtures

Furthermore, neopentyl polyol esters can optionally also be used together with the polyalkylene glycols described above in the equipment according to the invention.

Suitable neopentyl polyol esters are esters of neopentyl polyols, such as neopentyl glycol, pentaerythritol and trimethylol propane, with linear or branched C4 to C12 monocarboxylic acids, if appropriate with the addition of appropriate dicarboxylic acids. Pentaerythritol is usually available as technical pentaerythritol, which is a mixture of mono-, di- and tripentaerythritol. However, their condensation products, such as dipentaerythritol and / or tripentaerythritol, are also suitable as alcohol components.

Pentaerythritol or mixtures with dipentaerythritol and / or is particularly suitable

Tripentaerythritol, preferably mixtures which predominantly contain dipentaerythritol.

Complex esters can be prepared by partial esterification of polyhydric alcohols with monohydric and polyhydric acids, such as C ₄ to C ₁₂ dicarboxylic acids. This creates dimers and oligomers. Complex esters are preferred when using neopentyl glycol and / or and trimethylol propane as the alcohol group.

In the test bench test described in the experimental part, the phosphoric acid esters used according to the invention were found to be effective even when these neopentyl polyol esters were used, i.e. Without the use of polyalkylene glycols, surprisingly proven to be excellent additives for improving the lubricating effect of the neopentyl polyol esters when used together with carbon dioxide as refrigeration equipment. Because of their less good lubricating properties - compared to polyalkylene glycols - neopentyl polyol esters have hitherto been regarded as less suitable for use together with carbon dioxide as operating media in refrigeration machines.

Compounds which are obtainable from neopentyl polyols and carboxylic acids are referred to as neopentyl polyol esters. Polyols are used as neopentyl polyols denotes those which do not have any hydrogen atoms which are in the β-position to the hydroxy group. These are polyols with preferably 2 to 8 hydroxyl groups, one, two or three quaternary carbon atoms and 5 to 21, preferably 5 to 15, carbon atoms, the hydroxyl groups of the polyol as the alcohol component being connected only to those carbon atoms, which in turn are only have quaternary carbon atoms in the adjacent position.

Examples include neopentylpoylol (NPG), trimethylolpropane (TMP), pentaerythritol (PE). The neopentyl polyols as alcohol component can further contain 1 to 4 ether bridges. The alcohol component is particularly preferred: pentaerythritol and / or dipentaerythritol (DPE) and / or tripentaerythritol (TPE).

Preferred acid components are n-pentanoic acid, n-heptanoic acid, octanoic acid, decanoic acid, 2-ethylhexanoic acid, 3, 5, 5-trimethylhexanoic acid and 2-hexyldecanoic acid and other Guerbet acids, or mixtures thereof. Adipic and dodecanedioic acids are particularly suitable for the preparation of complex esters. It has proven to be advantageous to prepare the neopentyl polyol esters by reacting the corresponding alcohols with mixtures of the corresponding acids. Complete esterification of all the hydroxyl groups of the neopentyl polyols and acid groups of the dicarboxylic acids which may be used is preferred.

According to a further embodiment of the invention, the polyalkylene glycols used according to the invention can be used together with neopentyl polyol esters as lubricants. With regard to the definition of the preferred alcohol groups of these neopentyl polyol esters, reference is made to the above paragraphs.

Other additives

Particularly suitable as a further additive are di-phenylamine and

Di- (C1 to C16 alkyl) phenylamines, for example octylated / butylated di-phenylamine. Instead of substituted phenyls, unsubstituted or C1- to C16-alkyl-substituted naphthyl radicals can also be used.

Composition of resources

The operating agent composition generally contains between 1 and 25% by weight of lubricant - this size can, however, also be outside the specified range, depending on the type of refrigeration machine - preferably at least 40% by weight, preferably at least 80% by weight, of the additives for the operating medium are polyalkylene glycols and / or neopentyl polyols, based on all the constituents of the operating medium.

The proportion of the particularly preferred polyalkylene glycols with at least one aromatic group is preferably at least 20% by weight, particularly preferably at least 40% by weight, in particular at least 80% by weight, based on the

Lubricant content (i.e. the lubricants without refrigerants and additives) in the operating fluid composition.

The proportion of neopentyl polyol esters as lubricants is preferably 20 to 20 when using lubricant mixtures of different classes of compounds

60% by weight, particularly preferably 40 to 60% by weight, in each case based on the proportion of lubricant in the composition of the operating medium.

Miscibility:

In view of the overall efficiency, a favorable solubility behavior between oil and CO is desirable. CO behaves very differently with regard to the solubility properties.

The polyalkylene glycols used in the compositions according to the invention are preferably miscible (soluble) for higher mass fractions of lubricants in CO ₂ over the entire temperature range from the critical temperature Tk to below -40 ° C., in some cases also below -55 ° C. With smaller proportions of lubricants, these polyalkylene glycols are no longer miscible or only partially miscible with liquid carbon dioxide (soluble). Studies of CO2-operated climate cycles show that due to the good miscibility of polyol ester lubricants, such as pentaerythritol esters in particular, a correspondingly high solubility is achieved.

This can lead to a dramatic drop in viscosity in the area of the engine parts of the refrigerant compressor to be lubricated. Under the prevailing conditions show immiscible or less miscible lubricants, such as. B. mineral oils, polyolefms, alkylbenzenes or polyalkylene glycols, however, not the mentioned drop in viscosity. Due to the inadequate miscibility, however, problems arise with regard to oil return transport, particularly in the expansion valve and evaporator components and the suction line, especially at low flow velocities. On the one hand, the requirement in the compressor, i. H. To achieve a correspondingly high mixture viscosity in the lubrication gap, on the other hand, miscibility at low temperatures in the area of the evaporator and suction line components must be ensured in order to guarantee the oil return and to ensure good heat transfer and good controllability of the system.

A so-called partial miscibility, i.e. a mixture gap existing in a certain temperature range for certain mixing ratios is of great importance here

Interest. Due to the advantageous temperature / solubility behavior, chillers that work without oil sump or oil return can also be used for this case.

The lubricant according to the invention preferably has in the range between greater than 0 and 20% by weight, preferably greater than 0 and 5% by weight, concentration of the lubricant in the refrigerant at temperatures of 15 ° C. and below (to -40 ° C., preferably to -55 ° C) and in the range of 30 and 60% by weight concentration in the relevant temperature range from -40 ° C (or -55 ° C) to + 30 ° C fully miscible with the equipment. Outside of these areas, i.e. e.g. between greater than 5 and less than 30% by weight »greater than 20 and less than 30% by weight of lubricant in the refrigerant, there is preferably a mixture gap.

The above criterion is e.g. polyalkylene glycols from C1 to C4 alkyl end groups capped using

Starting alcohols which have aryl groups. Examples include cresols, p- Hexylphenol or (hydroxymethyl) benzene. Such polyalkylene glycols are defined in more detail in the subclaims.

Experimental

The methods that have been tried and tested to test the wear behavior and load-bearing capacity of refrigeration oils, such as Shell® "four-ball device" (VKA), the "Almen Wieland testing machine" and "Falex pin and vee block test" are only suitable to a limited extent, since the Influence of compressed CO ₂ cannot be simulated here.

Wear tests carried out with 1 bar CO ₂ do not give any direct evidence of a strong negative effect of CO ₂ on wear behavior. Investigations with the "block-on ring" testing machine at 10 bar CO ₂ , on the other hand, show a clear influence of the base oils and especially additives on this

Wear behavior (D.Drees; J.Fahl; J.Himichs; "Effects of CO ₂ on Lubricating Properties of Polyolesters and Polyalkylene Glycols"; Proc. 13 ^th Int. Colloq. Synth. Lubricants and Operational Fluids; Esslingen 2002, publication in preparation ).

In contrast to test runs with conventional refrigerating machine oils, the

Bearings after tests with the compositions according to the invention have an excellent wear pattern.

To assess the long-term lubrication properties under the influence of compressed CO ₂ , endurance tests were carried out in specially designed roller bearing test benches under practical conditions. Finally, several development products were tested in prototype compressors and pilot plants. In a endurance test rig, the service life actually achieved was possible under specific operating conditions under a CO ₂ atmosphere of axial cylindrical roller bearings at speeds of up to 8000 min ^"1 under a CO ₂ pressure of 50 bar, at a maximum temperature of 90 ° C. The axial load was 8 kN.

The calculation bases that are generally used for dimensioning bearings do not take into account the influence of different basic liquids or the effect of additives, but are mainly based on the mixture viscosity.

Important influencing factors such as the presence of gases, such as this one Special cases CO ₂ are not included in these calculations, although they play a very important role. In order to obtain knowledge in this regard, endurance tests under practical conditions are necessary.

The test parameters are selected so that they are optimal for the examination

Test time is reached. The test parameters are summarized in Table 1.

The axial load on the axial cylindrical roller bearings to be examined (geometry AXK 18 x 35 x 4.5) is carried out by means of disc spring assemblies and can be adjusted using spacers of different thicknesses. Testing continues until at least one bearing fails due to damage. The test parameters are as follows:

Table 1: Test parameters Parameter abbreviation [unit] value

Axial load Pa [N] 8000

Hertzian pressure (roll): Pmax [N / mm ² ] 1622

Speed n [min ^"1 ] 800

CO ₂ pressure P [bar] 50

Oil temperature T oil [° C] 90

The oils shown in Table 3 were examined. ND 8 is a commercial product of the Japanese compressor manufacturer NIPPONDENSO (manufactured by Idemitsu Kosan) with, among other things, approx. 1-2% by weight tricresyl phosphate and 0.5% by weight BHT (2,6-di-tert-butyl-4- methylphenol) added. SP10 and SP 20 are

Commercial products from the Japanese compressor manufacturer S ANDEN (also manufactured by Idemitzu Kosan) with a similar additive.

The preferred polyalkylene glycol lubricating oils show (P4) a lubrication behavior even without the addition of phosphoric acid esters that corresponds to the added terminally methylated polyalkylene glycol (see PAG oil ND 8). The results in Table 2 clearly show that the additive used in combination with the basic liquids used under the influence of compressed CO ₂ significantly extends the service life. This effect is particularly clear in connection with highly soluble neopentyl polyol esters. Axial piston machines are favored for CO ₂ applications in cars because of their compact design and uniform flow rates. In the course of the first endurance tests with prototype compressors, the lubrication of the extremely stressed roller bearings proved to be particularly problematic. The test runs with the commercially available polyol esters and polyalkylene glycol oils resulted in a much shorter service life. Due to the favorable solubility characteristics and the excellent load-bearing capacity under the influence of near-critical CO ₂ , the formulations claimed are suitable as high-performance lubricants for CO ₂ automotive air conditioning and heat pump systems.

In the case of the commercially readily available phosphate ester additives, a distinction is made between those with cresol (additive C in Table 3) or those with xylenol groups (rarely used). The invention relates to t-butylated (additive A in Table 3) and / or isopropylated (additive B in Table 3) triphenyl phosphates. Surprisingly, these proved to be much more suitable than conventional ones

Tricresyl phosphate or triphenyl phosphate.

Table 2: Base oils measured values with and without additive

Table 3: Additives

Claims

claims

1. Equipment composition containing (A) carbon dioxide as a refrigerant, (B) polyalkylene glycols and / or neopentyl polyol esters as a lubricant and

(C) a phosphate ester of the following structure

where ^~ 3

R may be the same or different for each of the three phenyl residues and may be the same or different for each n, H or one or more Cl to C6 hydrocarbon residues, and n may be the same or different for each of the three Phenyl radicals represents an integer from 1 to 5, with the proviso that at least for one of the three phenyl radicals, R is a C2 to C6 hydrocarbon, preferably t-butyl and / or isopropyl.

2. Operating agent composition according to claim 1, containing 0.1 to 3% by weight, based on the lubricant, of the phosphate ester.

3. Resource composition according to one of the preceding claims, characterized in that the polyalkylene glycols no free

Have hydroxyl groups.

4. Operating agent composition according to one of the preceding claims, characterized in that the operating agent composition polyalkylene glycols based on the polymer chain and the alkylene oxide used

Monomer units consist of

- essentially exclusively from monomer units of the type - (- CH (CH ₃ ) -CH ₂ -O -) - or - (- CH ₂ -CH (CH ₃ ) -O -) -,

- 20 to 80% monomer units of the type - (- CH (CH ₃ ) -CH ₂ -O -) - or - (- CH ₂ -CH (CH ₃ ) -O -) - and the remainder from monomer units of the type - (-CH ₂ -CH ₂ -O -) - or - 20 to 80% monomer units of the type - (- CH (CH ₂ CH ₃ ) -CH ₂ -O -) - or - (- CH ₂ -CH (CH ₂ CH ₃ ) -O -) - and to the rest Monomulti units of the type - (- CH ₂ -CH ₂ -O -) -.

5. Operating agent composition according to one of the preceding claims, characterized in that the operating agent composition contains polyalkylene glycols or mixtures thereof, which have an average molecular weight (number average) of 200 to 3000 g / mol, particularly preferably of 400 to 2000 g / mol.

6. Resource composition according to one of the preceding claims, characterized in that the polyalkylene glycols contain aryl groups or heteroaromatic groups, which can optionally be substituted with linear or branched alkyl or alkylene groups, the alkyl or alkylene groups in the Preferably have a total of 1 to 24 carbon atoms.

7. Resource composition according to one of the preceding claims, characterized in that the polyalkylene glycols have the following end groups - alkyl, aryl, alkylaryl, aryloxy, alkoxy and / or alkylaryloxy

End groups with 1 to 24 carbon atoms.

8. Equipment composition according to one of the preceding claims, characterized in that the equipment composition contains esters or an ester mixture, the esters being producible by reacting

Neopentyl polyols, particularly preferably pentaerythritol, dipentaerythritol and / or tripentaerythritol, with linear and / or branched C4 to C12 carboxylic acids, optionally with the addition of C4 to C12 dicarboxylic acids.

9. Operating agent composition according to one of the preceding claims, characterized in that the operating agent contains neopentyl polyol esters and polyalkylene glycols.

10. Operating fluid composition according to one of the preceding claims, characterized in that the operating fluid composition at least 10 wt.% Polyalkylene glycols and / neopentyl polyester according to one of the preceding claims, based on all ingredients of the equipment.

11. Operating fluid composition according to one of the preceding claims, characterized in that the operating medium consists, in addition to the phosphate esters and the refrigerant, predominantly, based on the weight fraction, preferably exclusively, of polyalkylene glycols and / neopentyl polyesters according to one of the preceding claims.

12. Operating agent composition according to one of the preceding claims, characterized in that the operating agent furthermore a di-phenylamine, a di- (C1- to C16-alkyl) phenylamine as antioxidant, or compounds in which one or both phenyl groups against Naphtyl groups are exchanged contains.

13. Operating agent composition according to one of the preceding claims, characterized in that the phosphate ester has at least one of the phenyl radicals, an R, which is tert-butyl and / or isopropyl.

14. Use of the equipment composition according to one of the preceding claims in refrigeration machines, preferably in motor vehicles.

15. Use of the operating agent composition according to one of claims 1 to 13 in freezers (evaporation temperatures of less than -30 ° C), lubricants containing more than 90% by weight of neopentyl polyol ester being used.

16. Use of the operating agent composition according to one of claims 1 to 13 in passenger car air conditioning systems, lubricants which contain more than 90% by weight of polyalkylene glycols being used.