Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic -co- compound
Reexamination Certificate
2001-10-04
2003-11-11
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic -co- compound
Reexamination Certificate
active
06645923
ABSTRACT:
This invention relates to gas-fuelled engine lubrication.
Gas-fuelled engines, sometimes referred to as gas-fired engines or merely gas engines, are known and may be used in the oil and gas industry, for example, to drive pumping stations of natural gas pipelines, blowers and generators in purification plants and on gas tankers, to compress natural gas at well heads and along pipe lines and to produce electric power in fit-for-purpose plants. Their design may be two- or four-stroke, spark-ignited or compression-ignited, though four-stroke compression-ignited designs constitute a large percentage. Natural gas constitutes a typical fuel.
Problems in their lubrication are firstly, that the lubricant is subjected to sustained high temperatures leading to its oxidation, and secondly, that the engines emit relatively high quantities of oxides of nitrogen, leading to nitration of the lubricant. These problems reduce the working life of the lubricant.
U.S. Pat. No. 5,726,133 describes a way of meeting the above problems by using, in a natural gas engine oil, an additive mixture comprising a mixture of detergents comprising at least one first alkali or alkaline earth metal salt or mixture thereof of TBN of 250 and less, and at least one second alkali or alkaline earth metal salt or mixture thereof which is more neutral than the first salt.
EP-A-0 860 495 describes a lubricating oil composition stated to be excellent for NOx oxidation resistance and thermal oxidation resistance and suitable as a long-life engine oil for gas engine heat pumps. The composition includes a metal salicylate having a TBN of from 100 to 195, and optionally includes a metal phenate having a TBN of from 100 to 300.
There is, however, a desire to further improve the lubricant performance in the above respects, for example to enable the interval between lubricant changes to be extended.
The present invention meets this desire, as evidenced by and in the examples hereof, by using, as a first detergent, a salicylate having a TBN of 95 or less and a second detergent having a TBN of greater than 250.
Accordingly, a first aspect of the present invention is a gas-fuelled engine lubricating oil composition having a TBN in the range of 2 to 20 comprising:
(A) an oil of lubricating viscosity, in a major amount; and added thereto, in respective minor amounts:
(B) one or more metal hydrocarbyl-substituted salicylate detergents having a TBN of 95 or less, preferably 85 or less, more preferably 75 or less;
(C) one or more metal detergents, preferably salicylate, phenate or complex detergents, having a TBN of greater than 250, preferably greater than 265, more preferably greater than 275;
(D) preferably one or more dispersants, such as an ashless dispersant; and
(E) preferably one or more anti-wear additives.
A second aspect of the present invention is a method of lubricating a gas-fuelled internal combustion engine, the method comprising operating the engine and lubricating it with the composition defined above according to the first aspect of the invention.
A third aspect of the present invention is a method for enhancing the resistance of a gas-fuelled lubricating oil composition to oxidation and nitration, the method comprising the step of adding additives (B) to (E) as defined in the first aspect of the invention to the gas-fuelled lubricating oil composition.
“Major amount” means in excess of 50 mass % of the composition.
“Minor amount” means less than 50 mass % of the composition, both in respect of the stated additive and in respect of the total mass % of all the additives present in composition, reckoned as active ingredient of the additive or additives.
“Comprises or comprising” or cognate words is taken to specify the presence of stated features, steps, integers or components, but does not preclude the presence or addition of one or more other features, steps, integer components or groups thereof.
“TBN” (Total Base Number) is as measured by ASTM D2896.
Unless otherwise started, all proportions are expressed as mass % active ingredient, i.e. as if solvent or diluent or other inert material were absent.
The features of the invention will now be discussed in more detail below.
Lubricating Oil Composition
Preferably, the TBN of the lubricant composition is in the range of from 2 to 20, such as from 2.5 to 20, preferably from 6.5 to 20, more preferably from 6.5 to 15.
(A) Oil of Lubricating Viscosity
The oil of lubricating viscosity (sometimes referred to as lubricating oil) may be any oil suitable for the lubrication of a gas-fuelled engine. The lubricating oil may suitably be an animal, a vegetable or a mineral oil. Suitably the lubricating oil is a petroleum-derived lubricating oil, such as a naphthenic base, paraffinic base or mixed base oil. Alternatively, the lubricating oil may be a synthetic lubricating oil. Suitable synthetic lubricating oils include synthetic ester lubricating oils, which oils include diesters such as di-octyl adipate, di-octyl sebacate and tridecyl adipate, or polymeric hydrocarbon lubricating oils, for example liquid polyisobutene and polyalpha olefins. Commonly, a mineral oil is employed. The lubricating oil may generally comprise greater than 60, typically greater than 70, mass % of the composition, and typically have a kinematic viscosity at 100° C. of from 2 to 40, for example for 3 to 15, mm
2
s
−1
and a viscosity index of from 80 to 100, for example from 90 to 95.
Another class of lubricating oils is hydrocracked oils, where the refining process further breaks down the middle and heavy distillate fractions in the presence of hydrogen at high temperatures and moderate pressures. Hydrocracked oils typically have a kinematic viscosity at 100° C. of from 2 to 40, for example from 3 to 15, mm
2
s
−1
and a viscosity index typically in the range of from 100 to 110, for example from 105 to 108.
The oil may include ‘brightstock’ which refers to base oils which are solvent-extracted, de-asphalted products from vacuum residuum generally having a kinematic viscosity at 100° C. of from 28 to 36 mm
2
s
−1
and are typically used in a proportion of less than 30, preferably less than 20, more preferably less than 15, most preferably less than 10, such as less than 5, mass %, based on the mass of the composition.
(B) Salicylate Detergent
A detergent is an additive that reduces formation of piston deposits, for example high-temperature varnish and lacquer deposits, in engines; it has acid-neutralising properties and is capable of keeping finely divided solids in suspension. It is based on metal “soaps”, that is metal salts of acidic organic compounds, sometimes referred to as surfactants, which, in respect of (B), is salicylic acid.
The detergent comprises a polar head with a long hydrophobic tail, the polar head comprises a metal salt of the salicylic acid. Large amounts of a metal base are included by reacting an excess of a metal compound, such as an oxide or hydroxide, with an acidic gas such as carbon dioxide to give an overbased detergent which comprises neutralised detergent as the outer layer of a metal base (e.g. carbonate) micelle.
The metal may be an alkali or alkaline earth metal, e.g., sodium, potassium, lithium, calcium, and magnesium. Calcium is preferred.
Surfactants for the surfactant system of the overbased metal detergents contain at least one hydrocarbyl group, for example, as a substituent on an aromatic ring. The term “hydrocarbyl” as used herein means that the group concerned is primarily composed of hydrogen and carbon atoms and is bonded to the remainder of the molecule via a carbon atom, but does not exclude the presence of other atoms or groups in a proportion insufficient to detract from the substantially hydrocarbon characteristics of the group. Advantageously, hydrocarbyl groups in surfactants for use in accordance with the invention are aliphatic groups, preferably alkyl or alkylene groups, especially alkyl groups, which may be linear or branched. The total number of carbon atoms in the surfactants should be at least sufficient to impact the desired oil-
Chambard Laurent
Dunn Adrian
Garner Terence
Howard Jacqueline V.
Infineum International Ltd.
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