FR2832417A1 - Synthetic oil compositions containing a synergistic combination of arylamine type antioxidants as additives, useful in gas turbine oils based on synthetic esters of polyols - Google Patents

Abstract

Oil composition for turbines with a resistance to depositiion and improved oxidation stability comprises a major proportion of a synthetic ester as base oil and a small proportion of an additive formulation comprising a diphenylamine(DPA) a phenyl-alpha-naphthalene(PANA) and an oligomer formed by reaction of a DPA with a PANA . Oil composition for turbines with a resistance to deposition and improved oxidation stability comprises a major proportion of a synthetic ester as base oil and a small proportion of an additive formulation comprising a diphenylamine(DPA) a phenyl-alpha-naphthalene(PANA) and an oligomer formed by reaction of a DPA with a PANA . The diphenylamine constituent of the anti-oxidant composition is of the formula (I): R = 4-12C alkyl; The phenyl-alpha-naphthalene is of the formula (II): R<1> = H, 4-12C alkyl or 7-12C alkaryl. The oligomer is formed by reaction of a DPA compound with a PANA compound in the presence of an organic peroxide at a high temperature. An Independent claim is also included for a process for increasing the oxidation stability and resistance to deposition of a synthetic ester.

Description

<Desc / Clms Page number 1>

The present invention relates generally to turbine oils, based on esters, in particular based on diesters and esters of polyols, which exhibit higher antioxidant power and reduced tendency to form deposits. It relates more particularly to oils for turbines, comprising esters of pentaerythritol with fatty acids as base oils, further comprising a synergistic combination of antioxidants consisting of arylamines.

Organic compositions, such as mineral oils and lubricating compositions, are susceptible to oxidative deterioration and in particular are subject to such deterioration at elevated temperatures in the presence of air. This deterioration often leads to a build-up of insoluble deposits that can foul engine parts, reduce performance and increase maintenance. This is especially the case for lubricating oils used in jet airplanes where wide temperature ranges and extreme operating conditions can be encountered. Proper lubrication of aircraft gas turbines, for example, requires the ability to operate at bulk oil temperatures as low as -55 C and up to 2300-2600C. Ester-based lubricating oil compositions prepared from pentaerythritol and a mixture of fatty acids and containing selected additive combinations are well known. These lubricants are functional over a wide temperature range and exhibit good thermal and oxidative stability.

However, the need for an even more effective and long-lasting ester-based lubricant composition is a primary goal for lubricant manufacturers. The present invention addresses this continuing need.

The present invention relates to an oil composition for turbines, exhibiting a power

<Desc / Clms Page number 2>

increased antioxidant and resistance to deposit formation, as well as a method of achieving this in turbine oils.

The lubricating oil for gas turbines, of the present invention, comprises a major proportion of a base oil based on esters of synthetic polyols, comprising diesters and esters of polyols, preferably of a base oil. based on polyol esters, and a small proportion of a three component antioxidant / deposit limiting additive of the arylamine type. More specifically, the three components are (1) a substituted diphenylamine (DPA), (2) a phenyl-α-naphthylamine (PANA) and (3) an oligomeric antioxidant prepared by reacting a DPA and a PANA. Other conventional additives such as extreme pressure additives, reducing flow weight, providing oxidation stability, antifoaming, providing hydrolysis stability, providing improved viscosity index performance, antiwear and corrosion inhibitors, among others, can also be used. Further, the three component arylamine antioxidant formulation of the present invention can also be used in conjunction with other known antioxidant additives.

Synthetic polyol ester base oil constitutes the dominant proportion of the fully formulated synthetic ester lubricating oil composition. In general, the ester-based fluid is present at concentrations of about 90 to 99% by weight of the composition.

It should be noted that the term "comprising" is used frequently throughout the description of the present invention and also in the appended claims. The term "comprising", as used in the present description and the appended claims, means "specifying the presence of features.

<Desc / Clms Page number 3>

d'une ou plusieurs autres de leurs étapes, constituants ou groupes. Le terme"comprenant"est différent de l'expression Il consistant en", qui exclut la présence ou l'addition d'une ou plusieurs autres de leurs étapes, constituants ou groupes. indicated, of integers, steps or constituents mentioned, but without excluding the presence or addition

one or more of their steps, constituents or groups. The term "comprising" is different from the term II consisting of ", which excludes the presence or addition of one or more of their steps, constituents or groups.

A turbine oil having surprisingly superior performance on deposits comprises a major proportion of a synthetic ester type base oil and a small proportion of a three component arylamine type antioxidant additive. Synthetic esters include diesters and esters of polyols. The three component antioxidant additives are formed from (1) a substituted diphenylamine (DPA), (2) a phenyl-a-naphthylamine (PANA) which can be substituted or alkylated, and (3) an oligomeric antioxidant prepared by reacting DPA with PANA.

The diesters which can be used for the improved anti-deposit oil for turbines of the present invention are formed by esterification of linear or branched C6 to C15 aliphatic alcohols with one of the diacids such as adipic acid, sebacic acid. and azelaic acid. Examples of diesters are di-2-ethylhexyl sebacate and dioctyl adipate.

Synthetic polyol ester base oil is formed by esterifying an aliphatic polyol with a carboxylic acid. The aliphatic polyol contains 4 to 15 carbon atoms and has 2 to 8 esterifiable hydroxyl groups. Examples of polyols are trimethylolpropane, pentaerythritol, dipentaerythritol, neopentylglycol, tripentaerythritol, and mixtures thereof.

The carboxylic acid reactant used to produce the synthetic polyol ester base oil is selected from a monocarboxylic acid

<Desc / Clms Page number 4>

aliphatic and a mixture of an aliphatic monocarboxylic acid and an aliphatic dicarboxylic acid.

Carboxylic acid contains 4 to 12 carbon atoms and includes straight chain and branched chain aliphatic acids. Mixtures of monocarboxylic acids can be used.

The preferred polyol ester base oil is an oil prepared from technical pentaerythritol and a mixture of C4 to C12 carboxylic acids. Technical pentaerythritol is a mixture which comprises about 85 to 92% by weight of monopentaerythritol and 8 to 15% by weight of dipentaerythritol. A conventional commercial technical pentaerythritol contains about 88% by weight monopentaerythritol of formula 1 and about 12% by weight of dipentaerythritol of formula 2 Formula 1.

Formula 2.

Technical pentaerythritol may also contain some amount of tri- and tetrapentaerythritol which are usually formed as byproducts during the production of technical pentaerythritol.

<Desc / Clms Page number 5>

The preparation of esters from alcohols and carboxylic acids can be carried out using conventional methods and techniques known to, and familiar to those skilled in the art, and are not in themselves part of the art. the present invention. In general, technical pentaerythritol is heated with the desired mixture of carboxylic acids, optionally in the presence of a catalyst. Usually, a slight excess of acid is used to force the reaction to complete. Water is removed during the reaction and any excess acid is then removed from the reaction mixture by stripping. Technical pentaerythritol esters can be used without further purification or can be further purified using conventional techniques such as distillation.

For the purposes of the present description and the appended claims, it is understood that the expression "technical pentaerythritol ester" means the base oil of the polyol ester type prepared from a technical pentaerythritol and a mixture of. C4 to Ciz carboxylic acids.

As previously indicated, a small proportion of the three component arylamine anti-deposit and oxidation inhibitor additive is added to the polyol ester base oil. This three component additive is usually used in an amount selected to represent about 0.5 to 10% by weight of the fully formulated lubricating oil composition. Each of the three essential components of the three component additive is described in detail below.

The diphenylamine (DPA) component of the additive formulation is represented by Formula 3.

<Desc / Clms Page number 6>

Formula 3

In formula 3, R represents an alkyl group having from about 4 to about 12 carbon atoms. Suitable alkylamines include dioctyldiphenylamine, didecyldiphenylamine, didodecyldiphenylamine, dihexyldiphenylamine, and the like. Dioctyldiphenylamine (DODPA) is the preferred compound and the preferred concentration is from about 0.2 to about 5.0% by weight of the fully formulated lubricating oil composition. These DPA compounds are commercially available.

The phenyl-a-naphthylamine (PANA) component of the additive formulation is represented by formula 4: Formula 4

In formula 4, R 1 may represent H or an alkyl group containing about 4 to 12 carbon atoms or an alkaryl group containing 7 to 12 carbon atoms. The alkyl group can be a straight or branched chain alkyl group, the tertiary alkyl structure being preferred, or it can be an alkylaryl group.

Specific effective compounds in this class include phenyl-α-naphthylamine, N- (para-tertio-octylphenyl) alpha-naphthylamine, N- (4cumylphenyl) alpha-naphthylamine and para-tertio-

<Desc / Clms Page number 7>

corresponding dodecylphenyl- and para-tertio-butylphenyl-alpha-naphthylamines. Preferred naphthylamines are those in which R 1 represents a tertiary alkyl group comprising 6 to 10 carbon atoms. The preferred concentration of each component is in the range of from about 0.2 to about 5.0% by weight of the fully formulated lubricating oil composition. These PANA compounds are commercially available.

The third component of the three component arylamine antioxidant additive formulation is an oligomer formed by reaction of a DPA component and a PANA component. More specifically, the oligomer is produced by reacting a DPA with a PANA in the presence of one or more organic peroxides at an elevated temperature. The reaction products are a homooligomer of DPA and cross oligomers of DPA and PANA. The DPA oligomer formed covers a wide range of degrees of oligomerization. Usually, under the conditions described above, about 75% by weight of the oligomer consists of dimers, trimers, tetramers and pentamers. The DPA having been defined by formula 3 above and PANA having been defined by formula 4 above, the reaction can be simplified and generalized as illustrated by reaction 1 below REACTION 1 (x + y) DPA + z PANA ====> (DPA) x + (DPA) y (PANA) z
It is hypothesized that the bond between DPA and PANA can occur between two nitrogen atoms, between a nitrogen atom in one PANA or DPA and a carbon atom in another PANA or DPA, or between carbon atoms in two different aryl rings from naphthyl or phenyl groups. It is believed that most of the bonds between DPA and PANA molecules are bonds between a nitrogen atom in a DPA or PANA and a carbon atom in naphthyl or aryl substituents of another DPA or PANA. For those who want

<Desc / Clms Page number 8>

More detailed information, the possible linkages are described in detail in US Pat. No. 3,509,214. However, Reaction 1 above is not intended to imply only that the crossed oligomers are block copolymers. . The oligomers are considered to be very random with regard to the order of incorporation of DPA and PANA. The indices y and z are intended only to indicate the number of DPA or PANA molecules in the cross oligomer.

In order to achieve a high conversion of DPA and PANA to the desired oligomers, it is desirable that the DPA: PANA molar ratio be in the range of about 1: 1 to 10: 1, usually about 1.2: 1 to about 5: 1, more typically about 1.5: 1 to about 4: 1, more preferably about 1.75: 1 to about 2.5: 1 or 3: 1; and is preferably equal to about 2: 1.

The oligomerization reaction can be carried out in bulk or in solution by heating a mixture of DPA, PANA and organic peroxide at temperatures advantageously in the range of about 700C to 2000C for a time of about 1 hour at 10 a.m. The various constituents can be added in any order, in increments, or else can be introduced in a metered manner into other constituents. The reaction can be carried out in vacuo to remove volatiles from the decomposition of organic peroxides, if desired. DPA and PANA can be dissolved in suitable organic solvents such as aliphatic hydrocarbons or lubricants consisting of synthetic esters, which have extractable hydrogen atoms. The reaction can also be carried out in the presence of lubricants consisting of synthetic esters produced by condensation of monohydric alcohols and / or polyhydric alcohols with monocarboxylic or polycarboxylic acids, as described above. Other solvents useful for

<Desc / Clms Page number 9>

Reaction of DPA, PANA and organic peroxides are the solvents consisting of alkanes having 6 to 16 carbon atoms in a linear, branched or cyclic structure. These solvents are easily removed by volatilization.

After the reaction of DPA, PANA and organic peroxides, it is desirable to raise the temperature of the reaction mixture to completely decompose the organic peroxides. Under the optimized conditions indicated above, most of the desired reactions which form homo-oligomers and cross-oligomers have occurred before the step of decomposing the residual peroxide. The peroxide decomposition step is carried out at temperatures in the range of from about 1400C to about 2000C for a period of time in the range of from about 5 min to about 2 h and preferably at low temperatures. pressures below atmospheric pressure.

Reaction under the conditions described above results in the presence of greater than 70 mole% of DPA and PANA in oligomeric forms consisting of dimers or higher oligomers. Any residual proportion of DPA and PANA is predominantly in monomeric form and is present with DPA and PANA which are also part of the three component additive.

Any organic peroxide which has a half-life of about 1 hour at temperatures in the range of about 700C to about 2000C can be used as a source of free radicals. This group includes acyl peroxide, peresters, peroxyketals and alkyl peroxides, all of which are commercially available. The amount of peroxide used is usually in the range of about 0.5 to 3.0 moles / mole of diarylamines.

<Desc / Clms Page number 10>

A detailed description and full characterization of these oligomers can be found in EPO Patent No. EP 734,432 B.

The preferred concentration of this oligomeric component is in the range of from about 0.2 to about 5.0% by weight of the fully formulated lubricating oil composition.

Preparation of the oligomer
DODPA (783 g, 2 moles), Irganox Lot (331.5 g, 1 mole) and technical pentaerythritol ester (1114.5 g) were introduced into a 5 L flask with three necks equipped with a thermometer, a stopcock and a distillation column. Irganox LO-6® is an octylated PANA having the molecular formula C24H29N in which the octyl group consists of highly branched 1, 1,3, 3tetramethylbutane. The Irganox Lot is available from CIBA-GEIGY. The reaction mixture was heated to 1400C under a nitrogen atmosphere. Ditertiobutyl peroxide (526.3 g, 3.6 moles) was added in portions over 45 min. The reaction was continued for 3 h, during which time the tert-butyl alcohol was collected through the distillation column at a head temperature of 80-85 ° C. The color changed from fluorescent bluish to brown. The reaction temperature was then raised to 1700C over 1 hour and was maintained at 1700C for 40 min. An additional amount of tert-butyl alcohol was collected. Then a vacuum was carried out slowly to speed up the distillation until a pressure of 200 kPa was reached. The reaction mixture was kept under these conditions for 20 min to remove all of the residual alcohol. The vacuum was released under a nitrogen atmosphere and the mixture was cooled. The reaction product was then collected as a 50% by weight formulation of active ingredient in lubricant.

<Desc / Clms Page number 11>

Examples 1 to 4
For Examples 1-4, the turbine base oil formulation used in all cases was a technical grade pentaerythritol ester further containing an antiwear additive consisting of tricresyl phosphate, corrosion inhibitors consisting of tolutriazole. and sebacic acid, and bulking additives consisting of thiodipropionic acid and an amine phosphate. The DPA component used in Examples 1, 2 and 4 was dioctyldiphenylamine (DODPA). The PANA component used in Examples 1, 2 and 3 consisted of Irganox Law which is an octylated PANA having the molecular formula C24H29N in which the octyl group is a highly branched group (e.g. 1,1,3,3- tetramethylbutyl). The Irganox Lot is available from CIBA-GEIGY. The oligomeric component, used in Examples 1, 3 and 4, was prepared as described above.

For Example 1, all three components were added to the base oil so as to achieve a total amount of 3.0% by weight of the oil of the fully formulated lubricating oil composition. For Example 2, only the components DPA and PANA were added to the base oil so as to achieve a total amount of 3.0% by weight of the fully formulated lubricating oil composition. For Example 3, only the oligomer and PANA components were added to the base oil so as to achieve a total amount of 3.0% by weight of the fully formulated lubricating oil composition. For Example 4, only the oligomer and DPA components were added to the base oil so as to achieve a total amount of 3.0% by weight of the fully formulated lubricating oil composition. Thus, for Examples 1 to 4, the total amount of additives consisting of arylamines remained

<Desc / Clms Page number 12>

constant at 3.0% by weight of the fully formulated lubricating oil composition.

274 à 316 C. Les essais sur les exemples 1 à 4 ont été effectués à 288 C. Dans l'essai, l'huile passe d'un réservoir à travers un filtre et une pompe jusqu'à une unité de cokéfaction. L'huile pénètre dans la section de cokéfaction à 1490C et est exposée à un tube chauffé par résistance dans lequel l'huile est soumise à un gradient de température de 288 C dans la section inférieure du tube jusqu'à approximativement 371 C. Après une période d'attente de 48 h, l'appareil est démonté, le dépôt dans le tube est pesé et évalué et la viscosité de l'huile usagée (testée) et l'indice d'acide total (IAT) sont mesurés. Les résultats obtenus pour les exemples 1 à 4 sont résumés sur le tableau 1 ci-dessous. The formulations of Examples 1-4 were subjected to the ALCOR high temperature test. The ALCOR high temperature test is a classic deposition test for synthetic engine oils and is part of the General Electric D50TF1 standard. The test can be carried out at temperatures in the range of

274 to 316 C. The tests on Examples 1 to 4 were carried out at 288 C. In the test, the oil passes from a reservoir through a filter and a pump to a coking unit. The oil enters the coking section at 1490C and is exposed to a resistance heated tube in which the oil is subjected to a temperature gradient of 288 C in the lower section of the tube to approximately 371 C. After 48 h waiting period, the apparatus is disassembled, the deposit in the tube is weighed and evaluated and the viscosity of the used oil (tested) and the total acid number (TAI) are measured. The results obtained for Examples 1 to 4 are summarized in Table 1 below.

Table 1

<tb>
<tb> Number <SEP> of <SEP> example <SEP> 1 <SEP> (a) <SEP> l <SEP> (b) <SEP> 2 <SEP> 3 <SEP> 4
<tb> Constituent <SEP> oligomer <SEP> (% <SEP> in <SEP> weight) <SEP> 1,4 <SEP> 1, <SEP> 4--1, <SEP> 4 <SEP> 1, 4
<tb> Constituent <SEP> DPA <SEP> (% <SEP> in <SEP> weight) <SEP> 1,1 <SEP> 1, <SEP> 1 <SEP> 1, <SEP> 7--1, <SEP> 6
<tb> Component <SEP> PANA <SEP> (% <SEP> in <SEP> weight) <SEP> 0.5 <SEP> 0.5 <SEP> 1.3 <SEP> 1, <SEP> 6
<tb> Total <SEP> of <SEP> 3 <SEP> constituents <SEP> (% <SEP> in <SEP> weight) <SEP> 3.0 <SEP> 3.0 <SEP> 3, <SEP> 0 <SEP> 3.0 <SEP> 3.0
<tb> Weight <SEP> of <SEP> deposit <SEP> in <SEP> test <SEP> ALCOR <SEP> (g) <SEP> 7 <SEP> 6 <SEP> 10 <SEP> 9 <SEP > 5
<tb> Evaluation <SEP> of <SEP> deposit <SEP> in <SEP> test <SEP> ALCOR <SEP> 1 <SEP> 1 <SEP> 7 <SEP> 5, <SEP> 5 <SEP> 1, <SEP> 8
<tb> Delta <SEP> viscosity <SEP> in <SEP> test <SEP> ALCOR <SEP> 15, <SEP> 7 <SEP> 13.4 <SEP> 26.6 <SEP> 22.1 <MS> 22.1
<tb> Delta <SEP> IAT <SEP> in <SEP> test <SEP> ALCOR0-0, <SEP> 2 <SEP> 0-0, <SEP> 12 <SEP> 0, <SEP> 35
<tb>

Examples 1 (a) and 1 (b), which are mixtures of all three antioxidant constituents, show the best overall test performance. Examples 2 and 3 did not show the same performances of low amount of deposit or limitation of

<Desc / Clms Page number 13>

the increase in viscosity. Example 4 gave a slightly lower weight of deposit in the tube but a proportionately poorer rating and did not exhibit the same degree of IAT viscosity control as the formulation using all three antioxidant components. It is evident from these results that a synergistic combination of an oligomeric component, a DPA component and a PANA component confers better thermal and oxidation stability than combinations of two oligomeric components / DPA, oligomer / PANA or DPA / PANA.

Reasonable variations and modifications may be made within the scope of the preceding description and of the claims appended to the present invention, the nature of which is to obtain superior performance with an antioxidant additive of the three-component arylamine type for a turbine oil, with respect to all possible permutations of two-component arylamine antioxidant additives for turbine oil.

Claims (19)

A turbine oil composition exhibiting increased resistance to deposition and improved oxidation stability, characterized in that it comprises a major proportion of a synthetic ester base oil and a small proportion of synthetic ester base oil. 'an additive formulation comprising a DPA (diphenylamine) component represented by the formula

wherein R represents an alkyl group having from about 4 to about 12 carbon atoms; a PANA (phenyl-a-naphthylamine) component represented by the formula

wherein R1 is selected from the group consisting of H, an alkyl group containing about 4 to 12 carbon atoms and an alkaryl group containing 7 to 12 carbon atoms; and an oligomer formed by reacting a DPA component and a PANA component in the presence of at least one organic peroxide at an elevated temperature. 2. Composition according to claim 1, characterized in that the synthetic ester base oil is the esterification product of an aliphatic polyol containing 4 to 15 carbon atoms and 2 to 8 esterifiable hydroxyl groups brought to react with a carboxylic acid containing 4 to 12 carbon atoms. 3. Composition according to claim 1, characterized in that the ester-based base oil <Desc / Clms Page number 15> Synthetic is the esterification product of technical pentaerythritol and a mixture of C4-Ciz carboxylic acids.

4. Turbine oil composition according to claim 1, characterized in that the total weight of the DPA, PANA and oligomer additives represents about 0.5 to about 10% by weight of the fully formulated lubricating oil composition. 5. Turbine oil composition according to claim 1, characterized in that the DPA component represents about 0.2 to about 5% by weight of the fully formulated lubricating oil composition. 6. A turbine oil composition according to claim 1, characterized in that the PANA component represents from about 0.2 to about 5% by weight of the fully formulated lubricating oil composition. 7. A turbine oil composition according to claim 1, characterized in that the oligomeric component represents about 0.2 to about 5% by weight of the fully formulated lubricating oil composition. 8. A turbine oil composition according to claim 1, characterized in that the DPA component comprises a dioctyldiphenylamine. 9. Turbine oil composition according to claim 1, characterized in that R1 represents a branched alkyl group having 8 carbon atoms. 10. Turbine oil composition according to claim 9, characterized in that R1 represents a 1,1, 3,3-tetramethylbutyl group. 11. Turbine oil composition according to claim 1, characterized in that the oligomeric component is formed by reacting a dioctyldiphenylamine and an octylated PANA in the presence of at least one organic peroxide at an elevated temperature. 12. Turbine oil composition according to claim 1, characterized in that the reaction of <Desc / Clms Page number 16> Formation of oligomers involves using a DPA: PANA molar ratio ranging from about 1: 1 to about 10: 1. 13. A turbine oil composition according to claim 1, characterized in that the oligomer formation reaction comprises the use of a DPA: PANA molar ratio ranging from about 1.2: 1 to about 5: 1. 14. Turbine oil composition according to claim 1, characterized in that the organic peroxide comprises ditertiobutyl peroxide. 15. Turbine oil composition according to claim 1, characterized in that the elevated reaction temperature is in the range of about 700C to 2000C. 16. A method of increasing the resistance to deposition and improving the oxidative stability of a synthetic ester base oil, characterized by adding to said turbine oil an additive comprising a DPA component represented by. the formula

wherein R represents an alkyl group having from about 4 to about 12 carbon atoms; a PANA constituent represented by the formula

<Desc / Clms Page number 17> wherein R1 is selected from the group consisting of H, an alkyl group containing about 4 to 12 carbon atoms and an alkaryl group containing 7 to 12 carbon atoms; and an oligomer formed by reacting a DPA component and a PANA component in the presence of at least one organic peroxide at an elevated temperature. 17. The method of claim 16, characterized in that the synthetic ester base oil is the esterification product of an aliphatic polyol containing 4 to 15 carbon atoms and 2 to 8 esterifiable hydroxyl groups brought to react with a carboxylic acid containing 4 to 12 carbon atoms. 18. The method of claim 16, characterized in that the synthetic ester base oil is the esterification product of technical pentaerythritol and a mixture of C4 to C18 carboxylic acids. 19. The method of claim 16, characterized in that the total weight of the DPA, PANA and oligomer additives represents about 0.5 to about 10% by weight of the fully formulated lubricating oil composition.