EP0205995B1 - Lubricant and its use - Google Patents

Abstract

Base oils can be substantially improved with respect to their oxidation stability and heat stability by the addition of additive combinations consisting of organic phosphates and organic phosphites as well as, if appropriate, silicones. <??>These lubricants are particularly suitable for refrigeration machines, heat pumps and similar installations, such as air-conditioning units. They can also be used as compressor oils and hydraulic oils.

Description

• (a) Dialkylbenzole oder Gemischen von Mono- und Dialkylbenzolen handelt, die gerade oder verzweigtkettige Alkylgruppen mit jeweils 1 bis 20 Kohlenstoffatomen aufweisen, und/oder
• (b) Poly-α-olefine handelt, und Additiven.

The invention relates to lubricants consisting of base oils based on mineral oils or mixtures of mineral oils with synthetic lubricants or exclusively of base oils based on synthetic lubricants, which are synthetic lubricants

• (a) Dialkylbenzenes or mixtures of mono- and dialkylbenzenes which have straight or branched chain alkyl groups each having 1 to 20 carbon atoms, and / or
• (b) Poly-α-olefins, and additives.

These lubricants are particularly suitable for refrigeration machines, heat pumps and related systems such as air conditioning systems. They can also be used as compressor and hydraulic oils.

Lubricants for refrigerating machine oils are still predominantly made up of highly refined mineral oils, which are dewaxed to improve the flow properties in the cold beyond what is customary for lubricating oils.

Pour points customary for chillers are in a range from -50 ^o C to -25 ^o C, depending on viscosity, and the cold pour points according to DIN 51568 are in a range between -16 ^o C and -38 ^o C.

The temperature at which flocculation of paraffin crystals occurs - important for the proper functioning of the lubricant - is also reduced by the additional dewaxing.

The mineral oils suitable for the production of refrigerating machine oils are obtained according to the known methods by distilling crude oils with subsequent refining (Ullmanns Encyklopadie der Technische Chemie, 4th edition, volume 20, pages 484 ff.). Depending on the origin of the crude oil, so-called paraffin-based or naphthenic-based lubricating oils are obtained.

Paraffin-based lubricating oils mainly contain paraffinic molecules, naphthenic-based predominantly naphthenic or cycloparaffinic molecules.

Because of their better properties in the cold, naphthenic oils are preferred for the production of refrigeration oils.

Refrigeration oils based on mineral oils usually contain no additives. Although attempts have often been made to improve the properties of the oils with the aid of additives, the success has so far been poor (ASHRAE Guide and Data Book 1969, section 23, page 281).

Recently, synthetic hydrocarbons such as alkylbenzenes and poly-α-olefins have been used increasingly as refrigeration oils. Compared to mineral oils, they primarily offer the advantage of better cold behavior both in terms of their flow behavior and because they naturally do not excrete paraffins. Most of these oils also contain no additives. Extensive treatises on refrigerating machine oils can be found in the ASHRAE Guide and Data Book 1969, Section 25 and Section 23, page 281 and ASHRAE Systems Handbook 1980, Section 32. Another treatise is from Hans O. Spauschus, Evaluation of Lubricants for Refrigeration and Air Conditioning Compressors, ASHRAE, Kansas City, 1984.

The alkylbenzenes used come from the known syntheses according to Friedel-Crafts by alkylation of benzene with alkyl chlorides or olefins (Ullmann, 4th edition, volume 14, pages 672 ff.). Α-Olefins which are produced by ethylene oligomerization or by cracking paraffins according to different processes serve as raw material for the production of polymer oils (Ullmann, 4th edition, volume 14, pages 664 ff.). In the next step, these α-olefins are polymerized and hydrogenated ("Synthetic Poly-α-olefin Lubricants Today and Tomorrow", M.Campen, DFKendrick, ADMarkin, and Ullmann, 4th edition, volume 20, pages 505 ff.) .

Technical progress in the field of refrigeration technology has led to a continuous increase in the requirements for the lubricant in terms of both cold behavior and thermal stability in recent years.

In particular, higher operating temperatures meant that conventional refrigerating machine oils tired prematurely without additional protection against aging and therefore had to be replaced early.

The higher efficiency of modern refrigeration units also places higher demands on the lubricating properties of a refrigeration machine oil to protect machine parts that are in frictional contact against wear.

In this case, attempts have been made to help each other by adding wear-reducing additives. Phosphate esters are described as additives (US Pat. No. 4,199,461). However, the addition of phosphate ester results in a reduction in the thermal stability of the lubricating oil. According to Dupont's brochure, FREON Product Information RT-56E, tricresyl phosphate (TCP) is recommended as a lubricant improver for alkylbenzene lubricating oil, but it should be noted that this additive affects the stability of the system.

The negative effect of the addition of organic phosphates on the thermal stability of the lubricants is not only mentioned in the Dupont brochure, but also by Hans O. Spauschus, Evaluation of Lubricants for Refrigeration and Air Conditioning Compressors, ASHRAE, Kansas City, 1984, Page 9).

The invention has for its object to provide lubricating oils with increased lubricating properties with improved low-temperature behavior and improved thermal stability and low foaming tendency.

• (1) einem oder mehreren organischen Phosphaten der allgemeinen Formel I
  
  worin R₁, R₂ und R₃ Alkyl-, Aryl- und Alkylarylgruppen bedeuten, die gleich oder verschieden sein können und jeweils 1 bis 15 Kohlenstoffatome aufweisen, in einer Menge von 0,01 bis 10 %, bezogen auf das Gesamtgewicht des Schmiermittels,und
• (2) einem oder mehreren organischen Phosphiten der allgemeinen Formel II
  
  worin R₁, R₂ und R₃ Alkyl-, Aryl- und Alkylarylgruppen bedeuten, die gleich oder verschieden sein können und jeweils 1 bis 15 Kohlenstoffatome aufweisen, in einer Menge von 0,001 bis 1 %, bezogen auf das Gesamtgewicht des Schmiermittels,

enthalten.The object is achieved in that the lubricating oils consist of an additive mixture

• (1) one or more organic phosphates of the general formula I.
  
  wherein R₁, R₂ and R₃ are alkyl, aryl and alkylaryl groups, which may be the same or different and each have 1 to 15 carbon atoms, in an amount of 0.01 to 10%, based on the total weight of the lubricant, and
• (2) one or more organic phosphites of the general formula II
  
  wherein R₁, R₂ and R₃ represent alkyl, aryl and alkylaryl groups, which may be the same or different and each have 1 to 15 carbon atoms, in an amount of 0.001 to 1%, based on the total weight of the lubricant,

contain.

It was thus found that a further addition in addition to the phosphate ester, namely the addition of an organic phosphite, leads to a significant qualitative improvement in the refrigerator oils.

The combination with phosphate esters improves the oxidation and heat stability of the lubricants and also improves wear protection.

The use of a special organic phosphite compound or a combination of organic phosphites with organic tin compounds and alkylphenols to improve the stability of the lubricants for refrigeration compressors is described in US Pat. Nos. 3,458,443 and 3,459,660.

Surprisingly, it has now been found that the combination of organic phosphites and phosphates improves the thermal and oxidative stability of the lubricants beyond that of the base oils. This is the subject of the present invention.

• 1.1 einem Grundöl auf Basis von Mineralölen
• 1.2 einem Grundöl auf Basis von Alkylaromaten
• 1.3 einem Grundöl auf Basis von Poly-α-olefinen und
• 1.4 einem Grundölgemisch aus Mineralöl und Alkylaromaten oder Poly-α-olefinen, und

einer Kombination von Additiven mit verbesserter thermischer und oxidativer Stabilität sowie verschleißmindernden Eigenschaften erhalten werden können, wenn als Additive insbesondere eingesetzt werden:

• 2.1 mindestens ein organisches substituiertes Phosphat der allgemeinen Formel I in einer Menge von 0,5 bis 5 %, vorzugsweise 1 bis 2 %, bezogen auf das Gesamtgewicht des Schmiermittels,
• 2.2 mindestens ein organisches substituiertes Phosphit der allgemeinen Formel II in einer Menge von 0,05 bis 0.5 %, vorzugsweise 0,1 bis 0,2 %, bezogen auf das Gesamtgewicht des Schmiermittels, und
• 2.3 mindestens ein organisches oder halogen- und insbesondere ein fluororganisches Silicon, in einer Menge von 1 bis 50 mg, insbesondere 3 bis 10 mg/kg Gesamtschmiermittel.

It has been found that lubricants, preferably for refrigeration compressors, heat pumps and related applications, consist of

• 1.1 a base oil based on mineral oils
• 1.2 a base oil based on alkyl aromatics
• 1.3 a base oil based on poly-α-olefins and
• 1.4 a base oil mixture of mineral oil and alkyl aromatics or poly-α-olefins, and

a combination of additives with improved thermal and oxidative stability and wear-reducing properties can be obtained if the following additives are used in particular:

• 2.1 at least one organic substituted phosphate of the general formula I in an amount of 0.5 to 5%, preferably 1 to 2%, based on the total weight of the lubricant,
• 2.2 at least one organic substituted phosphite of the general formula II in an amount of 0.05 to 0.5%, preferably 0.1 to 0.2%, based on the total weight of the lubricant, and
• 2.3 at least one organic or halogen and in particular an organofluorine silicone, in an amount of 1 to 50 mg, in particular 3 to 10 mg / kg of total lubricant.

In the combination of additives according to the invention, the substituted phosphite can be, for example, a trinonylphenyl phosphite, triphenyl phosphite, dodecyl diphenyl phosphite, dioctylphenyl phosphite, tridodecyl phosphite, didecylphenyl phosphite. The phosphites of medium molecular size such as dodecyl diphenyl phosphite, didodecylphenyl phosphite or triphenyl phosphite or mixtures thereof are preferably used.

Examples of the organic phosphates used here are triphenyl, diphenyl cresyl and / or tricresyl phosphate and other alkyl, aryl or alkylaryl derivatives of cresyl phosphate. Trialkylaryl phosphates such as triisopropylphenyl phosphate or trialkyl cresyl phosphate are preferably used. Isopropylated triphenyl phosphate is particularly preferred, in particular with an average content of 1 to 2 mol isopropyl per triphenyl phosphate.

The additive combination according to the invention can moreover contain one or more silicones in an amount of 1 to 100 mg, and preferably in an amount of 1 to 50 mg and in particular 3 to 10 mg, based on 1 kg total weight of the lubricant.

A methyl silicone is preferred as the silicone. It only serves to reduce foaming.

• H.M. Elsey, L.C. Flowers, J.B. Kelley
  "A Method of Evaluating Refrigerator Oils"
  Refrigerating Engineering, Juli 1952, Seiten 737 bis 743 und 782
• H.O. Spauschus, G.G. Doderer
  "Reaction of Refrigerant 12 with Petroleum Oils"
  ASHRAE Journal, Februar 1961, Seiten 65 bis 69;
• ASHRAE Standard 97 P
  "Method for Chemical Stability Testing of Merials Using Sealed Glass Tubes",
  Entwurf 9. Juli 1982.

To demonstrate the improved properties of the lubricants according to the invention, mixtures were subjected to an aging test which was developed by Elsey and Spauschus for refrigerating machine oils and is explained in the following documents:

• HM Elsey, LC Flowers, JB Kelley
  "A Method of Evaluating Refrigerator Oils"
  Refrigerating Engineering, July 1952, pages 737 to 743 and 782
• HO Spauschus, GG Doderer
  "Reaction of Refrigerant 12 with Petroleum Oils"
  ASHRAE Journal, February 1961, pages 65 to 69;
• ASHRAE Standard 97 P
  "Method for Chemical Stability Testing of Merials Using Sealed Glass Tubes",
  Draft July 9, 1982.

The tests were carried out in the following way:
Appropriately prepared - cleaned and acidified - glass tubes with a length of 200 mm and an inner diameter of 5 to 7 mm were welded at one end and tapered to a length of approx. 5 cm to 1.5 mm at the other end.

A coil of 0.1 mm copper wire and an approximately 15 mm long steel wire - 1.6 DIN 177-D5-1 - were inserted into glasses prepared in this way, 0.3 to 0.4 g of lubricant were weighed in and in a special device under vacuum and freezing added about the same amount of Freon refrigerant. Before the latter step, all gases were removed from the weighed oil by means of a vacuum. With the addition of nitrogen, the glasses were welded after the addition of the refrigerant. The glasses were then heated to the test temperature in a drying cabinet for a predetermined period. The test temperature was 175 ^o C or 200 ^o C, the test duration between 336 and 1008 hours (2 to 6 weeks).

In the course of the test, the samples were visually checked for color changes. At the end of the test, the glasses were blown up, collecting the gas and oil for inspection.

To demonstrate the improved properties, 4 glasses were filled with the same lubricant. Three glasses were subjected to the aging test. The fourth glass was kept as a comparison for the color change and the condition of the metals after the experiment.

The glasses of the experiment given in each case with a comparative example and an example with the same numbering were subjected to the aging procedure at the same time and for the same length of time. The results are shown in the tables following the experiments.

A

Prüfdauer in Stunden

B

Prüftemperatur, °C

C

Viskosität des Schmiermittels bei 40°C (mm²/s)

D

Farbe des Schmiermittels (Original)

E

Farbe des Schmiermittels nach Prüfung - visuelle Beurteilung

F

Umwandlung des Kältemittels Frigen (R12) in Frigen (R22) in %

G

Ölzustand (Untersuchung mittels IR-Spektrum)/ Metalle - visuelle Beurteilung

In the tables mean:

A

Test duration in hours

B

Test temperature, ° C

C.

Lubricant viscosity at 40 ° C (mm² / s)

D

Color of the lubricant (original)

E

Color of the lubricant after inspection - visual assessment

F

Conversion of the refrigerant Frigen (R12) to Frigen (R22) in%

G

Oil condition (examination by means of IR spectrum) / metals - visual assessment

Comparative Example 1

Tabelle I A B C D E F G Vergl.-Beisp.1 1008 175 68 3 10 >1,0 X/T Beispiel 1 1008 175 68 3 5 0,05 Z/V An alkylbenzene / mineral oil mixture (ratio 1: 1) was used as the base oil, viscosity class ISO 32, the alkylbenzene containing straight-chain C₁₀-C₁₂-alkyls and the mineral oil component consisting of highly refined naphthenic oil. 1% of an isopropylated triphenyl phosphate with an average isopropyl content of 1.5 moles per mole of triphenyl phosphate and 0.005% methyl silicone was added.

Table I A B C. D E F G Comp. Ex. 1 1008 175 68 3rd 10th > 1.0 X / T example 1 1008 175 68 3rd 5 0.05 Z / V

Comparative Example 2

Tabelle II A B C D E F G Vergl.-Beisp.2 1008 175 47 1 10 2,85 X/U Beispiel 2 1008 175 47 1 7 0,05 Z/V Base oil from alkylbenzene with branched alkyl groups (made from the reaction of benzene with tetrapropylene), viscosity class ISO 32, with the addition of 1% triisopropylphenyl phosphate and 0.005% methyl silicone.

Table II A B C. D E F G Comp. Ex. 2 1008 175 47 1 10th 2.85 X / U Example 2 1008 175 47 1 7 0.05 Z / V

Comparative Example 3

Tabelle III A B C D E F G Vergl.-Beisp. 3 744 175 67 4 10 0,1 Z/T Beispiel 3 1008 175 67 4 6 <0,05 Z/V Base oil from alkylbenzene with straight-chain alkyl groups, viscosity class ISO 68, with the addition of 1% triisopropylphenyl phosphate and 0.005% methyl silicone.

Table III A B C. D E F G Comp. Ex. 3rd 744 175 67 4th 10th 0.1 Z / T Example 3 1008 175 67 4th 6 <0.05 Z / V

Comparative Example 4

Tabelle IV A B C D E F G Vergl.-Beisp.4 1008 200 65 0 5 1,95 Z/U Beispiel 4 1008 200 65 0 3 0,3 Z/V Base oil from a mixture of poly-α-olefins, viscosity class ISO 68, with the addition of 1% triisopropylphenyl phosphate and 0.005% methyl silicone.

Table IV A B C. D E F G Comp. Ex. 4 1008 200 65 0 5 1.95 TO Example 4 1008 200 65 0 3rd 0.3 Z / V

Comparative Example 5

Tabelle V A B C D E F G Vergl.-Beisp.5 336 175 32 2 9 0,6 Y/T Beispiel 5 336 175 32 2 3 <0,05 Z/V Base oil made from highly refined naphthenic mineral oil, viscosity class ISO 46, with the addition of 1% triisopropylphenyl phosphate and 0.005% methyl silicone.

Table V A B C. D E F G Comp. Ex. 5 336 175 32 2nd 9 0.6 Y / T Example 5 336 175 32 2nd 3rd <0.05 Z / V

The examples show a clear qualitative improvement in the refrigerating machine oils of the lubricants according to the invention with regard to oxidation and heat stability compared to the comparative examples.

Claims (9)

1. Lubricants consisting of base oils derived from mineral oils or blends of mineral oils with synthetic lubricant liquids or consisting exclusively of base oils derived from synthetic lubricant liquids, said synthetic lubricant liquids being

   (a) dialkylbenzenes or mixtures of mono- and dialkylbenzenes including straight-chain or branched-chain alkyl groups each having 1 to 20 carbon atoms, and/or

   (b) poly-α-olefins,

   and additives,
   characterised in that they contain a mixture of additives consisting of:

   (1) one or more organic phosphates with the general formula I:

   

   in which R₁, R₂ and R₃ denote the alkyl, aryl and alkylaryl groups which may be the same or different and which each have 1 to 15 carbon atoms, in an amount of from 0.01 to 10%, based on the total weight of lubricant, and

   (2) one or more organic phosphites with the general formula II

   

   in which R₁, R₂ and R₃ denote the alkyl, aryl and alkylaryl groups which may be the same or different and which each have 1 to 15 carbon atoms, in an amount of from 0.001 to 1%, based on the total weight of lubricant.
2. Lubricant according to claim 1, characterised in that the phosphates are contained in an amount of from 0.5 to 5%, preferably from 1 to 2%, based on the total weight of lubricant.
3. Lubricant according to claim 1 or claim 2, characterised in that the phosphites are contained in an amount of from 0.05 to 0.5%, preferably from 0.1 to 0.2%, based on the total weight of lubricant.
4. Lubricant according to any one of the preceding claims, characterised in that it contains triphenyl, diphenyl cresyl and/or tricresyl phosphate.
5. Lubricant according to claim 4, characterised in that it contains triphenyl phosphate isopropyl, preferably with an average content of from 1 to 2 moles of isopropyl per mole of triphenyl phosphate.
6. Lubricant according to any one of the preceding claims, characterised in that it contains didodecylphenyl phosphite, triphenyl phosphite and especially dodecyldiphenyl phosphite and mixtures thereof.
7. Lubricant according to any one of the preceding claims, characterised in that it contains one or more silicones in an amount of from 1 to 100 mg, preferably from 1 to 50 mg and especially from 3 to 10 mg, based on 1 kg of the total weight of the lubricant.
8. Lubricant according to claim 7, characterised in that it contains a methyl silicone.
9. Use of the lubricant according to claims 1 to 8 for refrigerating machines.