EP0980416B1 - Polyalkylene glycols as lubricants for co 2?-based refrigerating machines - Google Patents

Abstract

Disclosed are fuel compounds containing lubricant based on polyalkylene-glycols, which are suitable for lubricating refrigerating machines, heat pumps and related equipment, for which the fuel required is carbon dioxide.

Description

The invention relates to equipment compositions containing lubricants based on polyalkylene glycols, which are used for the lubrication of refrigeration machines, Heat pumps and related equipment, such as air conditioners, using carbon dioxide are operated as refrigerants.

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 in 1881 using carbon dioxide as the refrigerant. Until the middle of this century, carbon dioxide was mainly used in ship refrigeration systems below its critical temperature (critical point T _k = 31.4 ° C / p _k = 72.9 bar). Glycerin was used as the lubricant. Later, with the introduction of CFC refrigerants, carbon dioxide was hardly used anymore.

The exit from environmentally harmful chlorofluorocarbons (CFCs) as a refrigeration machine resource has caused carbon dioxide as possible Consider refrigeration equipment again. Is carbon dioxide easily and cheaply available and has no harmful influence on the ozone layer out. Carbon dioxide continues to stand out as a refrigeration machine resource due to a higher isentropic and volumetric compared to CFC equipment Cooling efficiency.

Development work with the natural refrigerant CO ₂ was resumed only in the 1980s. Initial tests showed the technical possibilities of a transcritical, also called supercritical, carbon dioxide cycle with pressures of over 100 bar.

Various research centers have now taken up this concept and work on the implementation of suitable refrigeration systems. At the same time, however also on the further development of the conventional method in the subcritical Area worked.

Polypropylene glycols and polyalkylene glycol copolymers containing propylene oxide monomer units have long been known as lubricants.

EP 0 421 765-A1 describes their compatibility with R134a (1,1,1,2-tetrafluoroethane) described as refrigeration machine resources. R134a and carbon dioxide are fundamentally different resources. EP 0 421 765-A1 gives no indication of solubility / miscibility, compatibility, thermal and hydrolytic stability of equipment compositions containing polyalkylene glycols and carbon dioxide.

EP 0 017 172-A1 describes polyalkylene glycol-neopentyl polyol esters mixtures disclosed as a lubricant for compressors. EP 0 017 172-A1 gives none Reference to refrigeration machines or the use of lubricants in refrigeration machine resources.

EP 0 861 883-A2, WO 98/08912, EP 0 908 509-A1, EP 0 844 299-A1 and EP 0 959 121-A1 have an earlier seniority, but are only after the priority date of the present application published and thus as Article 54 (3) documents only to be evaluated in terms of novelty. These are very different Lubricants, etc. also polyalkylene glycols, in addition to very different refrigerants or refrigerant mixtures disclosed, among other things also called carbon dioxide is. However, the combination of a refrigerant, which is in the consists essentially of carbon dioxide, with polyalkyl ken glycols, which contain at least 40% propylene oxide monomer units.

For carbon dioxide as refrigeration machine resources are compared to conventional ones Refrigerants such as fluorine / chlorine or fluorine hydrocarbons have increased operating pressures and operating temperatures (or Δp 's and ΔT' s) required high demands on sealing materials, moving parts and lubricants put. This is especially true for refrigeration systems operating in a transcritical Cyclic process operated.

Polyalkylene glycols have already been used as lubricants for both processes proposed (see e.g. Lubricants for Carbon Dioxide; U. Hesse, H.O.Spauschus in Refrigeration Science and Technology, Proceedings, Aarhus Denmark 3-6 Sept. 1996, ISSN 0 151 163).

In a transcritical cycle, the compression cycle takes place Go through states in which the carbon dioxide as a refrigerant both in the subcritical (subcritical) as well as in supercritical (supercritical) Area.

CO ₂ behaves very differently with regard to the solubility properties. Subcritical CO ₂ is polar, while CO ₂ is non-polar in the supercritical range. The polyalkylene glycols according to the invention are soluble in CO ₂ for higher mass fractions of lubricants over the entire temperature range from the critical temperature T _k to below -55 ° C. With smaller proportions of lubricants, the polyalkylene glycols are no longer or only partially soluble in carbon dioxide.

• ausgezeichnete thermische und chemische Stabilität
• sehr gute hydrolytische Stabilität
• sehr gute Schmierungseigenschaften
• komplett mischbar in den für die Betriebsmaschinen notwendigen Mischungsverhältnissen
• eine geringe Hygroskopizität
• hohe Verträglichkeit mit Dichtmaterialien und
• gutes Viskositäts-Temperatur-Verhalten.

The invention is based on the problem of finding a selection of possible polyalkylene glycols which meet the following requirements for lubricants for CO ₂ refrigeration machines:

• excellent thermal and chemical stability
• very good hydrolytic stability
• very good lubrication properties
• completely miscible in the mixing ratios necessary for the operating machines
• low hygroscopicity
• high compatibility with sealing materials and
• good viscosity-temperature behavior.

This applies in particular to the difficult conditions of the transcritical Refrigeration cycle. Because of the higher pressures and increased efficiency refrigeration machines for the transcritical area are designed smaller and often have small diameters in the pipe systems. This requires one sufficient mobility of the lubricant in the corresponding temperature range.

(a) zu mindestens 40%, vorzugsweise 60 %, der Monomereinheiten aus Monomereinheiten des Typs -(-CH(CH₃)-CH₂-O-)- und/oder -(-CH₂-CH(CH₃)-O-)- und

(b) zum verbleibenden Rest im wesentlichen aus Monomereinheiten des Typs -(-R-O-)- , wobei R eine lineare oder verzweigte, gesättigte Alkylengruppe mit 2 bis 6 Kohlenstoffatomen ist, ggf. 1 bis 2 weitere Oxy-Gruppen (-O-) tragen kann und für jede Monomereinheit verschieden sein kann.

Surprisingly, it has proven to be suitable for solving these tasks: equipment compositions for refrigeration machines, heat pumps and related systems, such as air conditioning systems, containing carbon dioxide as the refrigerant, the refrigerant consisting exclusively of carbon dioxide, and polyalkylene glycols or their mixtures consisting of, each based on the polymer chain:

(a) at least 40%, preferably 60%, of the monomer units from monomer units of the type - (- CH (CH ₃ ) -CH ₂ -O -) - and / or - (- CH ₂ -CH (CH ₃ ) -O -)- and

(b) to the remainder essentially from monomer units of the type - (- RO -) -, where R is a linear or branched, saturated alkylene group with 2 to 6 carbon atoms, optionally 1 to 2 further oxy groups (-O-) can wear and can be different for each monomer unit.

The polyalkylene glycols have hydrogen, alkyl, aryl, alkylaryl, aryloxy, Alkoxy, alkylaryloxy and / or hydroxy end groups (c). The end groups of the alkyl or aryl type preferably have 1 to 8, particularly preferably 1 to 4, Carbon atoms. In the latter case, these are alkyl and / or alkoxy end groups.

Particularly good results are obtained for the polyalkylene glycols according to the invention regarding high density and good lubricating properties on the one hand and the above Properties achieved on the other hand achieved when the polyalkylene glycol as Main component, namely at least 60%, propylene oxide units (monomer units of type (a)) contains.

The polyalkylene glycols according to the invention are thus either homopolymers, namely polypropylene glycol (or polypropylene oxide), or copolymers, terpolymers etc. further containing monomer units of type (b). For this case the monomer units can have a statistical distribution or a block structure exhibit. In a further embodiment of the invention, the monomer units of type (b) contained at least 5% in the polymer chain. The monomer units of type (b) are preferably ethylene oxide and / or butylene oxide units.

The polyalkylene glycols according to the invention can be obtained by reacting alcohols, including the polyalcohols, as starter compounds with alkylene oxides such as ethylene oxide, propylene oxide and / or butylene oxide. This have only one free hydroxyl group as the end group after the reaction. Polyalkylene glycols with only one hydroxy group are compared to those with two preferred free hydroxyl groups.

Particularly preferred in terms of stability, hygroscopicity and compatibility are polyalkylene glycols, e.g. after a further etherification step none free hydroxyl groups have more.

With regard to the molecular weights, preference is given to those polyalkylene glycols which average molecular weights of 400 to 3000 g / mol, particularly preferably of Have 1000 to 2000 g / mol.

The polyalkylene glycols according to the invention are distinguished by densities of more than 940 kg / m ³ , and preferably even more than 1000 kg / m ³ , and moreover surprisingly also have the properties listed above, which are required for use as a refrigerating machine oil in combination with carbon dioxide as a refrigerant are.

Surprisingly, it was found that the return transport of the polyalkylene glycol lubricants to the compressor with less good solubility is particularly well ensured if their density is significantly higher than that of the liquid carbon dioxide in this temperature / pressure range. In such a case, an effective phase separation takes place even under the special conditions in CO ₂ refrigeration machines, in which the polyalkylene glycol according to the invention forms the lower phase according to its higher density, and carbon dioxide forms the upper phase. A backflow of the polyalkylene glycol to the compressor is thus guaranteed with the appropriate system design. This is important for the mixture ratios of CO ₂ refrigerant / polyalkylene glycol lubricant, for which the lubricant is no longer completely soluble in CO ₂ .

Polyalkylene glycols with a density of over 940 kg / m ³ are particularly suitable under these conditions. Practical tests have shown, however, that those with higher densities, above about 1000 kg / m ^{3, worked} even better. This can be explained by a faster settling of the polyalkylene glycols according to the invention when complete solubility in the carbon dioxide refrigerant is no longer ensured.

In addition, additives customary in the equipment compositions such as Wear improvers, anti-foaming agents, antioxidants such as alkylated phenolic Antioxidants such as especially Irganox® L101, viscosity index improver, Corrosion protection agents or high-pressure additives, such as in particular Phosphate esters may be included.

(1) einer Säurekomponente, wobei die Säurekomponente,

(a) bezogen auf die Gesamtcarbonsäuregruppenkonzentration, aus mindestens 40 mol% n-Pentansäure besteht und

(b) zu dem verbleibenden Rest aus linearen oder verzweigten C6- bis C10- Monocarbonsäuren und / oder verzweigten C5- Monocarbonsäuren besteht, und

(2) einer Alkoholkomponente mit 4 bis 8 Hydroxygruppen, einem, zwei oder drei quartären Kohlenstoffatomen und 5 bis 21 , vorzugsweise 5 bis 15, Kohlenstoffatomen, wobei die -OH-Gruppen des Polyhydroxyalkohols als Alkoholkomponente vorzugsweise mit solchen Kohlenstoffatomen verbunden sind, die ihrerseits lediglich quartäre Kohlenstoffatome in Nachbarstellung aufweisen. Der Polyhydroxyalkohol als Alkoholkomponente kann weiterhin 0 bis 4, bevorzugt 0 , 1 oder 2, Etherbrücken enthalten. Besonders bevorzugt ist die Alkoholkomponente: Pentaerythritol und / oder Dipentaerythritol und / oder Tripentaerythritol. In einer weiteren Ausgestaltung enthält die Betriebsmittelzusammensetzung einen Ester oder ein Estergemisch, dessen Alkoholkomponente bezogen auf die Gesamtalkoholgruppenkonzentration (der Ester) zu mindestens 50 mol% aus Dipentaerythritol und / oder Tripentaerythritol besteht. Ester mit diesen Alkoholgruppen haben sich insbesondere für Kältemaschienen, die im transkritischen Bereich betrieben werden, bewährt.

Furthermore, the polyalkylene glycols according to the invention can be used together with neopentyl polyol esters as lubricants. Such esters are disclosed, for example, in German patent application DE 197 19 132 of RWE-DEA Aktiengesellschaft für Mineralöl und Chemie, filed on May 7, 1997. This ester or the ester mixture preferably consists of neopentyl polyol esters of the following type:

(1) an acid component, the acid component,

(a) based on the total carboxylic acid group concentration, consists of at least 40 mol% of n-pentanoic acid and

(b) to the remaining residue consists of linear or branched C6 to C10 monocarboxylic acids and / or branched C5 monocarboxylic acids, and

(2) an alcohol component with 4 to 8 hydroxyl groups, one, two or three quaternary carbon atoms and 5 to 21, preferably 5 to 15, carbon atoms, the -OH groups of the polyhydroxy alcohol as the alcohol component preferably being linked to those carbon atoms which in turn are only have quaternary carbon atoms in the adjacent position. The polyhydroxy alcohol as the alcohol component can further contain 0 to 4, preferably 0, 1 or 2, ether bridges. The alcohol component is particularly preferred: pentaerythritol and / or dipentaerythritol and / or tripentaerythritol. In a further embodiment, the operating agent composition contains an ester or an ester mixture, the alcohol component of which, based on the total alcohol group concentration (the ester), consists of at least 50 mol% of dipentaerythritol and / or tripentaerythritol. Esters with these alcohol groups have proven particularly useful for refrigeration machines operating in the transcritical field.

With regard to the acid component, those esters or ester mixtures are also preferred, independently of one another, whose acid component according to (1) (a), based on the total carboxylic acid group concentration, consists of at least 60 mol% of n-pentanoic acid; whose acid component according to (1) (b) consists predominantly of branched monocarboxylic acids, particularly preferably of 5 to 40 mol% of branched monocarboxylic acids, based on the total carboxylic acid group concentration. In the latter case, the acid components remaining for the complete esterification of all hydroxyl groups consist of linear C5 to C10 monocarboxylic acids. Preferably, all the hydroxyl groups of the alcohol component are completely esterified in the ester or the ester mixture. The neopentyl glycol esters according to the invention preferably have densities above 940 kg / m ³ , generally even above 1000 kg / m ³ .

According to a further embodiment of the invention, the inventive Polyalkylene glycols used together with neopentyl polyol esters as lubricants which are predominantly, i.e. more than 90%, preferably about 100%, branched C5 to C10 acid groups, particularly preferably branched C8 to C10 acid groups. Regarding the definition of the preferred Alcohol groups of these neopentyl polyol esters will refer to the paragraph above taken.

The proportion of the polyalkylene glycols according to the invention is preferably at least 20% by weight, particularly preferably at least 40% by weight, based on the Lubricant content (i.e. the lubricants without refrigerants and additives) in the resource composition. The percentage of neopentyl polyol esters as Lubricants differ when using lubricant mixtures Compound classes preferably 20 to 60% by weight, particularly preferably 40 to 60% by weight, based in each case on the proportion of lubricant in the equipment composition.

Tests have demonstrated the effectiveness of the polyalkylene glycols according to the invention as lubricants in CO ₂ refrigeration machines. For example, FIG. 1 shows the viscosity / vapor pressure / temperature behavior of a mixture of carbon dioxide and the polyalkylene glycol Triton GL-220® from DEA Mineraloel AG (butanol-started polypropylene oxide).

Claims (15)

1. A working compositions for refrigeration machines, containing carbon dioxide as a refrigerant and polyalkylene glycols and/or mixtures thereof, where the polyalkylene glycols consist of the following, based on the polymer chain:

   (a) at least 40 %, preferably at least 60 %, of the monomer units of monomer units of the type -(-CH(CH₃)-CH₂-O-) - and/or -(-CH₂-CH(CH₃)-O-)- and

   (b) monomer units of the type -(-R-O-)- for the remainder, where R is a linear or branched, saturated alkyl group with two to six carbon atoms, optionally has one to two other oxy groups (-O-) and may be different for each monomer unit,

   (c) has terminal groups which are

   (i) hydrogen and/or hydroxyl terminal groups and/or

   (ii) alkyl, aryl, alkylaryl, aryloxy, alkoxy and/or alkylaryloxy terminal groups

   whereby the refrigerant consists exclusively of carbon dioxide.
2. The working composition according to Claim 1, characterized in that the working composition contains polyalkylene glycols and/or mixtures thereof,
   (c) having terminal groups which are

   (i) hydrogen and/or hydroxyl terminal groups and/or

   (ii) alkyl, aryl, alkylaryl, aryloxy, alkoxy and/or alkylaryloxy terminal groups having one to eight carbon atoms, preferably one or four carbon atoms.
3. The working composition according to one of the preceding claims, characterized in that the working composition contains polyalkylene glycols and/or the mixtures thereof, whose monomers of the type (b) constitute at least 5 % of the monomer units of the molecule.
4. The working composition according to one of the preceding claims, characterized in that the working composition contains polyalkylene glycols and/or the mixtures thereof, whose monomers of the type (b) are ethylene oxide units and/or butylene oxide units and/or are synthesized therefrom.
5. The working composition according to one of the preceding claims, characterized in that the working composition contains polyalkylene glycols and/or mixtures thereof, having only one free hydroxyl group per molecule.
6. The working composition according to one Claims 1 through 4, characterized in that the working composition contains polyalkylene glycols and/or mixtures thereof, which do not have any free hydroxyl groups per molecule.
7. The working composition according to one of the preceding claims, characterized in that the working composition contains polyalkylene glycols and/or mixtures thereof, having a molecular weight of 400 to 3000 g/mol, especially preferably 1000 to 2000 g/mol.
8. The working composition according to one of the preceding claims, characterized in that the working composition also contains esters or an ester mixture, where the esters are neopentylpolyol esters.
9. The working composition according to Claim 8, characterized in that the neopentylpolyol esters consist of

   (1) an acid component, whereby the acid component consists of

   (a) at least 40 mol % n-pentanoic acid, based on the total carboxylic acid group concentration,

   (b) linear or linear or branched C6- to C10-monocarboxylic acids and/or branched C5-monocarboxylic acids for the remainder, and

   (2) an alcohol component with four to eight hydroxyl groups, one, two or three quaternary carbon atoms, five to twenty-one carbon atoms and zero to four ether linkages.
10. The working composition according to Claim 8, characterized in that the neopentylpolyol esters consist of

    (1) a C5- to C10-acid component, whereby the acid component consists of at least 90 mol % branched carboxylic acids, based on the total carboxylic acid group concentration, and

    (2) an alcohol component with four to eight hydroxyl groups, one, two or three quaternary carbon atoms, five to twenty-one carbon atoms and zero to four ether linkages.
11. The working composition according to one of the preceding claims, characterized in that the working composition contains polyalkylene glycols or polyalkylene glycol ester mixtures, each according to one of the preceding claims, having a density of more than 940 kg/m³, preferably more than 1000 kg/m³.
12. The working composition according to one of the preceding claims, characterized in that the working composition contains only polyalkylene glycols according to one of Claims 1 through 7 or polyalkylene glycol ester mixtures according to one of Claims 8 through 11 as lubricants.
13. A use of the polyalkylene glycols or polyalkylene glycol-ester mixtures according to one of the preceding claims as a lubricant in refrigeration machines which are operated with carbon dioxide.
14. The use according to Claim 13, characterized in that the working is carried in a transcritical circulating process.
15. The use according to Claim 13, characterized in that the working is carried in a subcritical circulating process.

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