NO135184B - - Google Patents

Description

The present invention relates to a lubricant composition for a gas turbine or jet engine. Gas turbine aircraft engines are operated under extreme environmental conditions. External atmospheric temperatures are usually in the region below 0 and internal engine temperatures are in the order of 204-260°C or above.

These operating conditions cause serious stress on the lubricating oil, so much so that the most advanced mineral lubricating oil compositions cannot be used in gas turbine engines. Synthetic ester-based lubricating oil compositions which essentially contain a precisely balanced mixture of additives are used for the lubrication of gas turbine engines. These ester-based oils can be used over wide temperature ranges and show good thermal stability, anti-wear, load-bearing and anti-oxidation properties.

With advanced, more powerful gas turbine engines, higher levels of thermal and oxidative stress are placed on lubrication. the oil composition. The present invention is directed towards an improved synthetic ester-based lubricating oil composition.

US Patent No. 3-330,763 describes a synthetic lubricating oil composition with improved loading properties and uses a penaerythritol ester-based oil, containing in combination an ammonium thiocyanate and a cyclic amine compound of the type represented by phenyl-o-naphthylamine.

US Patent No. 3,247,111 describes an ester-based lubricant which contains as essential additive ingredients: 1) an antioxidant such as diphenylamine or phenyl-ct-naphthylamine, 2) a salt of 1-salicylalaminoguanidine, and 3) a phosphorus compound or ester, e.g. triphenyl phosphate. These three ingredients are absolutely necessary for the lubricants of this patent. The synthetic lubricating oil composition according to the invention comprises a large proportion of an aliphatic ester base oil with lubricating properties, produced by reaction of pentaerythritol, a polypentaerythritol or trimethylolpropane and an organic monocarboxylic acid with 2-18 carbon atoms per molecule, and the invention is characterized in that said composition also contains (A) 0.01-2.5 wt-# of a substituted ammonium thiocyanate with the formula: where R is an alkyl or aminoalkyl group with from 1-30 carbon atoms, or a radical with the formula: where R"" is a radical of the formula "(C^^n- ^er n is 2, 3 or 4 and R', R" and R<1>" each means hydrogen or a hydrocarbon group having from 1-30 carbon atoms and ( B) 0.04-2% by weight of a polyhydroxy-substituted anthraquinone with the formula:

where X, Y and Z each represent hydrogen or a hydroxyl group, and where at least one of these is a hydroxyl group.

More particularly, a lubricating oil composition according to the invention will consist of an ester base, formed by reaction between a pentaerythritol or trimethylolpropane with an organic monocarboxylic acid, 0.01-2.5% by weight of the prescribed ammonium thiocyanate and 0.04-2.0% by weight of the prescribed polyhydroxy-substituted<*> anthraquinone.

The invention is based on the fact that an ester-based lubricating oil composition containing the aforementioned additive combination has superior loading properties. While special ester-based lubricating oil compositions containing ammonium thiocyanates in combination with cyclic amines have effective load properties as shown in the prior art, the discovery of a new and very specific additive combination in a special fluid formulation was very surprising "in order to produce an unexpected improvement in load properties .The importance of the structure of the hydroxyanthraquinone is confirmed by data showing the lack of effectiveness for many of these compounds.

The base fluid component of the lubricating oil according to the invention is an ester-based fluid, produced from a pentaerythritol or trimethylolpropane and a mixture of hydrocarbon monocarboxylic acids. It is clear that the pentaerythritol class includes the polypentaerythritols such as dipentaerythritol, tripentaerythritol and tetrapentaerythritol as suitable constituents for the ester base oil.

The hydrocarbon monocarboxylic acids used to form the ester-based fluid include the straight and branched chain aliphatic acids, cycloaliphatic acids and aromatic acids as well as mixtures of these acids. The acids used have

2-18 carbon atoms per molecule, and the preferred number is 5-10 carbon atoms. Examples of suitable acids are acetic acid, -propionic acid, butyl acid, valerian acid, isovaleric acid, caproic acid, decanoic acid, cyclohexanonic acid, naphthenic acid, benzoic acid, phenyl-. acetic acid, tertiary butyl acetic acid and 2-ethylhexanoic acid.

Usually these acids are reacted in proportions leading to a fully esterified pentaerythritol or trimethylolpropane, and the preferred ester bases are the pentaerythritol tetraesters. Examples of commercially available tetraesters include tetraerythritol-tetracaproate, which is prepared from purified pentaerythritol and impure caproic acid, containing other G₂—G₂₂ monobasic acids. Other suitable tetraesters are prepared from a technical grade of pentaerythritol and a mixture of acids, comprising 38% valeric acid, 13% 2-methylpentanoic acid, 32% octanoic acid and 13% pelargonic acid. Other active esters are the triester of trimethylolpropane, in which trimethylolpropane is esterified with a monobasic acid mixture, consisting of 2% valeric acid, 9% caproic acid, 13% heptanonic acid, 7% octanonic acid, 3% caprylic acid, 65% pelargonic acid and 1% capric acid. Trimethylol propane triheptanoate, trimethylol propane pentanoate and tri-methylol propane hexanoate are also suitable ester bases.

The ester base comprises the main part of the ready-formulated synthetic ester-based lubricating oil composition. The ester base usually makes up at least 90% of the lubricating oil composition and usually makes up 90-98% of the lubricant.

The ammonium thiocyanate component of lubricating oil compositions according to the invention is represented by the formula:

where R is an alkyl- or amino-substituted alkyl group with 1-30 carbon atoms or a radical of the formula: where R"" is a radical of the formula ~(CH2)n- where n is equal to 2, 3 or 4, and R<1> , R" and R'" each means hydrogen or a hydrocarbon group of 1-30 carbon atoms. In the preferred compounds, R is an aliphatic hydrocarbon radical of 8-22 carbon atoms and R', R" and R'" are hydrogen or an aliphatic hydrocarbon radical of 1-4 carbon atoms. Active ammonium thiocyanates include bis-(2-ethyl-hex<y>l )ammonium thiocyanate, tert. ~^ 2_ Q- 22 a^ y^ ammon^ um^^-' oc' yanat > sec . "Cjo-iij alkylammonium thiocyanate, tert. -octylammonium thiocyanate, endodecylammonium thiocyanate, tert.~^ i2- lH alkylammonium thiocyanate, nonylammonium thiocyanate, laurylammonium thiocyanate, stearylammonium thiocyanate, dimethyl-2-ethylhexylammonium thiocyanate, dibutyloctylammonium thiocyanate, N,N<1->di-( t-octyl)-1,2-ethanediammonium thiocyanate and N,N'-di-(t-C-^g_22 alkyl)-1,2-ethanediammonium thiocyanate. Ammonium thiocyanate is usually used in a concentration of 0.01-2.5% by weight, and the preferred range is 0.05-0.5$ The other essential component of the lubricating oil composition is a polyhydroxy substituted anthraquinone inhibitor represented by the formula:

where X, Y and Z each mean hydrogen or a hydroxyl group, and where at least one of these is a hydroxyl group. There are certain essential features of the structure of the polyhydroxy-substituted anthraquinone. This compound must have at least two hydroxyl groups and both of these must be connected to ring carbon atoms in the a position of the quinone ring, i.e. in positions 1, 4, 5 and 8. Additional hydroxyl groups can be present without changing the effect of the specified compounds. Compounds with only one hydroxyl group or compounds with more than one hydroxyl group, • but only with one in the 1, 4, 5 and 8 position are not effective according to the invention. The specific polyhydroxy substituted anthraquinones indicated above must be used with the prescribed ammonium thiocyanate to provide the improved lubricating oil composition of the invention.

Examples of effective polyhydroxy-substituted anthraquinones include 1,4-dihydroxyanthraquinone, 1,5}-dihydroxyanthraquinone, 1,2,4-trihydroxyanthraquinone and 1,2,5,8-tetrahydroxyanthraquinone.

The ineffective hydroxy-substituted hydroxyanthraquinones include 1-hydroxyanthraquinone, 5-hydroxyanthraquinone, 1,2-dihydroxyanthraquinone and 2,5-dihydroxyanthraquinone.

Generally, the effective polyhydroxy substituted anthraquinone inhibitor will be used in a concentration of between 0.04

and 2.0% by weight of the lubricating oil composition, and the preferred concentration is from 0.05-0.25% by weight. The lower concentration limit for the amount of inhibitor is significant as amounts of 0.035% by weight do not produce the improvements according to the invention.

Base fluid A in the lubricating oil compositions tested below was a technical grade pentaerythritol containing a minor amount of dipentaerythritol which was esterified with a mixture of fatty acids comprising (in mole %) about 38% valeric acid, 13% 2-methylpentanoic acid, 32% n-octanoic acid and 17% pelargonic acid where the average acid carbon chain length is around 6.5.

This base fluid had the following properties:

Base fluid B was a commercial pentaerythritol tetravalerate fluid.

The lubricating oil composition of the invention and comparative fluids were tested according to the "Ryder Gear Scuff Test" set forth in "Federal Test Method Standards 971", Test Method 6508. The results of this test are given in Table I below.

The aforementioned "Ryder Gear Test" shows the improved lubricating oil compositions according to the invention, based on the use of specific anthraquinones in correct concentrations when used in a synthetic ester-based oil with different ammonium thiocyanates. Experiment 6, where the inhibitor is quinizarin, shows that there are important features of the concentration of this component, as it is not effective at the experimental concentration. Experiment 5 shows an ineffective anthraquinone. Tests 7, 8 and 9 show the surprising improvement in the "Ryder Gear Scuff Load Test" produced by the lubricating oil compositions according to the invention.

The "Micros Failure Load Test" is carried out on a commercially available friction machine which simulates rolling and sliding wear on the surface of toothed gear wheels. The point of lubricant breakdown is indicated by the applied load in kg/cm 2 . The results of this test are given in Table II below.

Tests 2 and 3 in Table II show substantially unimproved fluids containing 1-hydroxyanthraquinone and 1,2-dihydroxyanthraquinone combined with the "Primen JMT" salt of thiocyanic acid. Experiments 4-6 show outstanding improvement in load characteristics for the fluid according to the invention, where the improvement extends from about 50% to 100% greater load carrying capacity than the base fluid (experiment 1) and the fluids with 1-hydroxyanthraquinone and alizarin (1,2-dihydroxyanthraquinone).

Claims (1)

Synthetic lubricating oil composition, comprising a major proportion of an aliphatic ester base oil with lubricating properties, produced by reaction of pentaerythritol, et'polypentaerythritol or trimethylolpropane and an organic monocarboxylic acid with 2-18 carbon atoms per molecule, characterized in that said composition also contains (A) 0.10-2.5% by weight of a substituted ammonium thiocyanate of the formula: where R is an alkyl or aminoalkyl group with 1-30 carbon atoms, or a radical with the formula: where R"" is a radical of the formula ~(^ 2^ n~ where n is ^e^--Ler and R', R" and R'" each means hydrogen or a hydrocarbon group with 1-30 carbon atoms; and (B ) 0.04-2% by weight of a polyhydroxy-substituted anthraquinone with the formula: where X, Y and Z each represent hydrogen or a hydroxyl group, and where at least one of these is a hydroxyl group.