Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
1999-12-15
2001-02-20
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
C508S391000, C508S398000, C508S586000
Reexamination Certificate
active
06191081
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to medium and high ash engine oils of extended life as evidenced by a reduction in viscosity increase, oxidation and nitration, comprising a base oil of lubricating viscosity and a particular combination of detergents.
BAC.KGROUND OF THE INVENTION
Natural gas fired engines are large, having up to 16 cylinders, and often generating between 500-3000 HP. The engines are typically used in the Oil and Gas industry to compress natural gas at well heads and along pipelines. Due to the nature of this application, the engines often run continuously near full load conditions, shutting down only for maintenance such as for oil changes. This condition of running continuously near full load places severe demands on the lubricant. Indeed, since the lubricant is subjected to a high temperature environment, the life of the lubricant is often limited by oil oxidation processes. Additionally, since natural gas fired engines run with high emissions of oxides of nitrogen (NO
x
), the lubricant life may also be limited by oil nitration processes. Therefore, it is desirable for gas engine oils to have long life through enhanced resistance to oil oxidation and nitration.
The combustion of diesel fuel often results in a small amount of incomplete combustion (e.g., exhaust particulates). The incombustibles provide a small but critical degree of lubrication to the exhaust valve/seat interface, thereby ensuring the durability of both cylinder heads and valves. The combustion of natural gas is often very complete, with virtually no incombustible materials. Therefore, the durability of the cylinder head and valve is controlled by the properties of the lubricant and its consumption rate. For this reason, gas engine oils are classified according to their ash content, since it is the lubricant ash which acts as a solid lubricant to protect the valve/seat interface. The oil industry has accepted guidelines which classify gas engine oils according to their ash level. The classifications are:
Ash Designation
Ash Level (wt %. ASTM D874)
Ash less
Ash < 0.1%
Low Ash
0.1 < Ash < 0.6
Medium Ash
0.6 < Ash < 1.5
High Ash
Ash > 1.5
The ash level of the lubricant is often determined by its formulation components, with metal-containing detergents (e.g., barium, calcium) and metallic-containing antiwear additives contributing to the ash level of the lubricant. For correct engine operation, gas engine manufacturers define lubricant ash requirements as part of the lubricant specifications. For example, manufacturers of 2-cycle engines often require the gas engine oil to be Ashless in order to minimize the extent of harmful deposits which form on the piston and combustion chamber area Manufacturers of 4-cycle engines often require the gas engine oils to be Low, Medium or High Ash to provide the correct balance of engine cleanliness, and durability of the cylinder head and valves. Running the engine with too low an ash level will likely result in shortened life for the valves or cylinder head. Running the engine with too high an ash level will likely cause excessive deposits in the combustion chamber and upper piston area.
Gas engine oil of enhanced life as evidenced by an increase in the resistance of the oil to oxidation, nitration and deposit formation is the subject of U.S. Pat. No. 5,726,133. The gas engine oil of that patent is a low ash gas engine oil comprising a major amount of a base oil of lubricating viscosity and a minor amount of an additive mixture comprising a mixture of detergents comprising at least one alkali or alkaline earth metal salt having a Total Base Number (TBN) of about 250 and less and a second alkali or alkaline earth metal salt having a TBN lower than the aforesaid component. The TBN of this second alkali or alkaline earth metal salt will typically be about half or less that of the aforesaid component.
The fully formulated gas engine oil of U.S. Pat. No. 5,726,133 can also typically contain other standard additives known to those skilled in the art, including dispersants (about 0.5 to 8 vol %), phenolic or aminic anti-oxidants (about 0.05 to 1.5 vol %), metal deactivators such as triazoles, alkyl substituted dimercaptothiadiazoles (about 0.01 to 0.2 vol %), anti wear additives such as metal di thiophosphates, metal dithiocarbamates, metal xanthates or tricresylphosphates (about 0.05 to 1.5 vol %), pour point depressants such as poly (meth) acrylates or alkyl aromatic polymers (about 0.05-0.6 vol %), anti foamants such as silicone antifoaming agents (about 0.005 to 0.15 vol %), and viscosity index improvers, such as olefin copolymers, polymethacrylates, styrene-diene block copolmyers, and star copolymers (up to about 15 vol %, preferably up to about 10 vol %).
SUMMARY OF THE INVENTION
The present invention relates to a lubricating oil of extended life as evidenced by reductions in viscosity increase, oxidation and nitration, relative to current commercial and reference oils, which comprises a major amount of a base oil of lubricating viscosity and a minor amount of a mixture of metal salicylate detergent(s) and a metal sulfonate and/or metal phenate detergent(s). The present lubricating oil would be particularly useful as a medium ash or high ash gas engine oil.
DETAILED DESC.RIPTION OF THE INVENTION
A lubricating oil composition is described comprising a major amount of a base oil of lubricating viscosity and a minor amount of a mixture of one or more metal salicylate detergent(s), and one or more metal phenate(s) and/or metal sulfonate detergents. Also described is a method for extending the life of lubricating oils as evidenced by a reduction in viscosity increase, oxidation and nitration by adding to the oil an additive comprising a mixture of one or more metal salicylate detergent(s), and one or more metal sulfonate(s) and/or one or more metal phenate(s).
The lubricating oil base stock is any natural or synthetic lubricating base oil stock fraction typically having a kinematic viscosity at 100° C.. of about 5 to 20 cSt, more preferably about 7 to 16 cSt, most preferably about 9 to 13 cSt. In a preferred embodiment, the use of the viscosity index improver permits the omission of oil of viscosity about 20 cSt or more at 100° C.. from the lube base oil fraction used to make the present formulation. Therefore, a preferred base oil is one which contains little, if any, heavy fraction; e.g., little, if any, lube oil fraction of viscosity 20 cSt or higher at 100° C..
The lubricating oil basestock can be derived from natural lubricating oils, synthetic lubricating oils or mixtures thereof. Suitable lubricating oil basestocks include basestocks obtained by isomerization of synthetic wax and slack wax, as well as hydrocrackate basestocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude. Suitable basestocks include those in API categories I, II and III, where saturates level and Viscosity Index are:
Group I—less than 90% and 80-120, respectively;
Group II—greater than 90% and 80-120, respectively; and
Group III—greater than 90% and greater than 120, respectively.
Natural lubricating oils include animal oils, vegetable oils (e.g., rapeseed oils, castor oils and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale.
Synthetic oils include hydrocarbon oils and halo-substituted hydro-carbon oils such as polymerized and inter-polymerized olefins, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, allylated diphenyl sulfides, as well as their derivatives, analogues and homologues thereof, and the like. Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers and derivatives thereof wherein the terminal hydroxyl groups have been modified by esterification, etherification, etc. Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids with variety of alcohols. Esters useful as synthetic oils also include those made from C.
5
to C.
12
monocarboxylic acids and polyols and polyol ethers.
Cartwright Stanley James
Finch James Walter
Allocca Joseph J.
ExxonMobil Research and Engineering Company
Johnson Jerry D.
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