GB2294696A - Marine lubricant composition - Google Patents

Abstract

The composition contains a synthetic ester base oil and an aromatic amine and/or a hindered phonol as a hydrolytic stabilising agent. The lubricant is especially used in equipment operating in a marine environment e.g. sliding machine parts or hydraulic systems. A typical composition contains ditridecyl adipate (base oil), dioctyldiphenyl amine and butylated hydroxytoluene plus corrosion, rust and foam inhibitors.

Description

IMPROVED MARINE LUBRICANT WITH ENVIRONMENTAL AND PERFORMANCE ADVANTAGES FTELD OF THE INVENTION This invention relates to a more environmentally responsible marine lubricant useful for equipment operating in marine environments.

DESCRIPTION OF THE RELATED ART Because of concerns over environmental issues, lubricants used in marine applications have come under increased scrutiny. Various non-mineral based vegetable and synthetic oils have been proposed as alternatives to conventional mineral base oils. Two environmental issues of concern to lubricants which may be released to the environment are ecotoxicity and biodegrability. S. J. Randles and M. Wright discuss these issues in a paper entitled "Environmentally Considerate Ester Lubricants for the Automotive and Engineering Industries", Technische Akademie Esslinger 8th International "Tribology 2000" Colloquium, Proceedings VI (1992).

Rapeseed and other vegetable oils are generally more biodegradable than mineral oils. On the other hand, they suffer thermal and oxidative stability problems. Synthetic oils such as polyalphaolefins are stable but are not as biodegradable. Polyols and diesters are more biodegradable but tend to be susceptible to hydrolysis, particularly in hot aqueous environments.

It would be desirable to have a more environmentally responsible lubricant which is also hydrolytically stable for use in aqueous environments, especially lubricants which are exposed to aqueous environments at elevated temperatures.

SUMMARY OF THE INVENTION The invention relates to a marine lubricant composition with improved stability in aqueous environments which comprises: (a) a synthetic ester base oil; (b) a hydrolytic stability agent, said agent containing from about 0.1 to about 3.0 wtO/o, based on lubricant composition, of at least one of an aromatic amine and a hindered phenol.

In another embodiment, there is provided a method of lubricating machine parts in an aqueous marine environment which comprises lubricating the machine parts with the marine lubricant according to the invention. Yet another embodiment relates to a method for stabilizing a marine lubricant containing a synthetic ester base oil against hydrolysis which comprises incorporating into the base oil at least one of an aromatic amine and a hindered phenol.

DETAILED DESCRIPTION OF THE INVENTION The term "marine lubricant" refers to lubricants used in a marine environment excluding lubricants for marine internal combustion engines, e.g., marine diesel engines and two-cycle engines. Lubricants for engines have different requirements from the present marine lubricants which are intended as lubricants for sliding machine parts and hydraulic systems which operate in an aqueous environment. Preferred marine lubricants are marine hydraulic fluids.

Synthetic ester base oils include esters of monocarboxylic and dicarboxylic acids, and esters prepared from C5 to C12 monocarboxylic acids and polyols. Suitable polyols include neopentylglycol, trimethylolpropane and pentaerythritol.

Preferred synthetic ester base oils are esters of monocarboxylic acids and dicarboxylic acids, especially esters of dicarboxylic acids Esters of monocarboxylic acids have the formula R1COOR where R is C1 to C10 alkyl and R1 is C8 to C20 alkyl or alkenyl. Esters of dicauboxylic acids have the formula

where R3 and R4 are each independently C6 to C20 alkyl, R5 is C1 to C4 alkyl or hydrogen and n is an integer from 1 to 10. Examples of preferred esters include ditridecyladipate, di-n-decylsebacate, di-2-ethylhexyladipate, di-2ethylhexyl-2,4-dimethyladipate, di-2-octylazelate and di-3,5,5-trimethylhexylsebacate.

Hydrolytic stability agents are at least one of an aromatic amine and a hindered phenol preferably hindered phenols. Preferred aromatic amines are those conventionally known in the art as antioxidants and include alkyl substituted diphenyl amines and phenyl naphthyl amines such as 4,4'-dioctyldiphenylamine, 4,4'-dodecyldiphenylamine, phenyl-alpha-naphthylamine, N,N' di-sec-butyl-p-phenylenediamine and the like.Preferred hindered phenols are those conventionally known in the alt as antioxidants and include sterically hindered monohydric and dihydric phenols such as 2,6-di-tert-butylphenol, 2,6di-tert-butyl-4-methylphenol, 4,4'-methylene bis(2,6-di -tert-butylphenol), and n octadecyl-3 ,5-di-tert-butyl-4-hydroxyhydrocinnamate. The preferred amounts of aromatic amine and/or hindered phenol is from 0.5 to 2.0 wtO/o, based on lubricant composition. The hydrolytic stability agents provide hydrolytic stability to the ester base oil especially under conditions favorable to hydrolysis such as high temperature and acidic!basic conditions.

The marine lubricant formulation preferably includes conventional corrosion inhibitors and iust inhibitors. Examples of corrosion inhibitors include thiazoles, triazoles, thiadiazoles, imidazolines, fatty acid amines, acid phosphates and their amine salts, amines and their salts, ethoxylated amines, phenols, and alcohols, dimer and trimer carboxylic acids, and the like. Examples of rust inhibitors include alkenyl succinic acids and anhydrides and their amino derivatives, sulfurized alkyl phenols, polyoxyalkylene polyols and the like. Corrosion and rust inhibitors are typically present in amounts of from 0.1 to 0.5 wtO/o, based on marine lubricant formulation.

If desired, the subject marine lubricant folmulation may contain other conventional additives such as antifoam agents, antiwear agents, antioxidants, extreme pressure agents, friction modifiers, other hydrolytic stabilizers and the like. The additives are disclosed, e.g., in "Lubricants and Related Products", by Dieter Klamann, Verlag Chemie, Deerfield Beach, Florida, 1984.

Two factors which should be considered when there is likelihood of lubricant entering the marine environment are biodegradability and ecotoxicity. It is known that synthetic esters according to the invention are more biodegradable than other types of synthetic oils such as polyalphaolefins and more biodegradable than mineral oils. However, additive packages can affect both biodegrability and ecotoxicity. The present marine lubricants do not contain metals or dispersants which can adversely affect biodegrability and ecotoxicity. Also, ecotoxicity data is now required by some countries for materials which may be released to the aquatic environment. An accepted standard for ecotoxicity is the acute mysid toxicity test in which the LC50 lethal concentration required to kill 50% of the mysid shrimp population after 96 hours is measured.A LC50 value of 100 ppm is generally accepted as a standard for ecotoxicity. The greater the LC50 value, the less toxic the material. It is preferred that the marine lubricant formulations of this invention have LC50 values of 100 or greater.

While it is known that certain classes of chemicals commonly used as lubricant additives are undesirable based on their impact on biodegradability and/or ecotoxicity, such effects are typically concentration dependent. Thus it is difficult to predict the effect of any given additive package on ecotoxicity, and it is desirable to test such additive packages against an accepted standard such as the LC50 test.

The marine lubricant compositions of this invention can be used in equipment which are in service in aquatic environments, e.g., steam catapults on aircraft carriers, loading cranes, or hydraulic application where lubricant may be discharged to the environment.

This invention will be further understood by reference to the following examples which include a preferred embodiment of the invention.

Example 1 A marine lubricant formulation was prepared blending the components shown in Table 1.

TABLE 1 Amount, % Component Function By Weight 1. ditridecyl adipate(a) base oil 97.75 2. dioctyldiphenyl amine(b) anti-oxidant 1.00 3. butylated hydroxytoluene(c) anti-oxidant 1.00 4. alkylated benzotriazole(d) corrosion inhibitor 0. 10 5. succinic anhydride amine(e) anti-rust 0.10 6. silicone polymer(f) anti-foam 0.05 (a) Vistone A30 available from Exxon Chemical Company.

(b) Vanlube 81 available from R. T. Vanderbilt Company.

(c) Navgard BHT available from Uniroyal Chemical Company.

(d) Reomet 39 available from Ciba-Geigy Company.

(e) Mobilad C-603 available from Mobil Chemical Company.

(f) PC-I 244 available from Monsanto Company.

This lubricant formulation is clear, leaves no sheen on water and has a low pour point of less than -50 C. Pour points of-24"C or lower are desirable for operations in cold environments.

LC50 values were evaluated using mysid shrimp, mysidopsis bahia. Nominal loading concentrations of lubricant for the test were 500 mg/l, 250 mg/l, 125 mg/l, 62.5 ml/l, 31.2 mdl with a natural sea water control. These samples were mixed in a mixing vessel for 24 hours followed by a one hour settling period.

The Water Accommodated Fraction (WAF) was drawn through the outlet at the bottom of the mixing vessel and distributed into two replicate chambers with a separate aliquot prepared for water quality measurements.

Water quality measurements (dissolved oxygen, pH, salinity and temperature) were performed on each treatment on Day 0 and at termination. Mysids were exposed for a 96-hour period.

The Lethal Concentration (LC50) value is the calculated nominal loading concentration that is lethal to 50% of a population of test organisms during a specified period. The 96-hour LCS0 value was 182.5 mg/l with 95% confidence intervals of 150.4 to 230.3 mg/l.

This value of 182.5 mg/l (182.5 ppm) compared to an accepted standard of 100 ppm demonstrates that the marine lubricant formulation has a low level of toxicity.

Example 2 This example demonstrates the capability of the oil of Example 1 to provide metal protection in a hot aqueous environment relative to the base oil alone or a commercial navy catapult oil using a bench test described as follows.

The bench test involves aluminum and copper composition beakers filled with 90% lubricant and 10% water stored at 1800F for 60 days. Following completion of the bench test, the metal coupons were died and evaluated visually for evidence of corrosion. The results are summarized in Table 2.

TABLE 2 SAMPLE COPPER ALUMINUM l(a) slight tarnish, light orange shiny metal appearance color similar to freshly similar to fresh aluminum polished sample sample 2(b) dark tarnish, transparent moderate tarnish, metal blank streaked with dark lines 3(c) graphite black tarnish, metal discolored (a) Lubricant of Example 1.

(b) Commercial oil used for Navy catapult systems.

(c) Base oil of Example 1.

These results demonstrate that in a hot aqueous environment, the lubricant oil according to the invention is stable and offers good metal protection relative to Samples 2 or 3, which showed substantial corrosion. A comparison of Samples 1 and 3 shows that base oil alone without additives according to the invention undergoes significant corrosion under test conditions. Tests on other synthetic esters with and without the presence of water (no additives) indicates that ester hydroysis is a significant factor in metal corrosion. The metal sample with water present showed substantial corrosion whereas the sample without water showed no corrosion (no tamish) under test condition noted above.

Claims (12)

CLAIMS:

1. A marine lubricant composition with improved stability in aqueous environments which comprises: (a) a synthetic ester base oil; (b) a hydrolytic stability agent, said agent containing from about 0.1 to about

3.0 Wt0/o, based on lubricant composition, of at least one of an aromatic amine and a hindered phenol.

2. The composition of claim I wherein the marine lubricant is a marine hydraulic oil.

3. The composition of claim 1 wherein the hydrolytic stability agent is a combination of aromatic amine and hindered phenol.

4. The composition of claim 1 wherein the aromatic amine is alkyl substituted diphenyl amine or phenyl naphthyl amine.

5. The composition of claim 1 wherein the hindered phenol is a sterically hindered monohydric or dihydric phenol.

6. The composition of claim 1 additionally comprising a corrosion inhibitor.

7. The composition of claim 1 additionally comprising a rust inhibitor.

8. The composition of claim 1 wherein the synthetic ester is an ester of a dicarboxylic acid.

9. The composition of claim 2 wherein the marine hydraulic oil is a catapult oil.

10. The composition of claim 1 wherein the LC50 value is at least 100 ppm.

11. A method for lubricating sliding machine parts in an aqueous environment which comprises lubricating the machine parts with the lubricant composition of claim 1.

12. A method for stabilizing a maine lubricant containing a synthetic ester base oil against hydrolysis which comprises adding to the base oil from about 0.1 to about 3.0 wt%, based on lubricant, of at least one of an aromatic amine and a hindered phenol.