Chemistry: analytical and immunological testing – Lubricant – grease – mineral oil – hydrocarbon oil product – or... – Acidity – basicity or neutralization number
Reexamination Certificate
1999-01-05
2001-06-12
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Lubricant, grease, mineral oil, hydrocarbon oil product, or...
Acidity, basicity or neutralization number
C436S006000, C436S060000, C436S102000, C436S148000, C073S010000, C073S053050, C073S053060, C422S053000, C422S068100
Reexamination Certificate
active
06245571
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of characterizing the neutralization capacity of a lubricant comprising detergent additives including a reserve stock of basicity and to a device for the implementation of this method.
It finds its application in research and control laboratories of manufacturers of lubricants and in those of engine manufacturers.
STATE OF THE PRIOR ART
Diesel engines and more particularly large-size marine diesel engines generally use heavy fuel oils with a high sulphur content as fuels. During combustion, the sulphur can result in the formation of sulphuric acid under the effect of oxidation reactions or by combination with water.
This acid, which has a tendency to condense within the diesel engines, can result in corrosion of the metal parts and corrosive wear of major components, such as linings and sections.
In order to minimize these harmful effects, the lubricants used for these engines must exhibit a neutralization capacity.
For this reason, these lubricants are products of high basicity.
This basicity is usually contributed by overbased detergent additives which include a neutralizing species, for example calcium carbonate.
Use is commonly made, in measuring this basicity, of a method described in ASTM Standard D-2896, which makes it possible to determine a parameter, known as BN (Basic Number), which is expressed as mg of potassium hydroxide (KOH) per gram of lubricant.
This parameter is a macroscopic indicator which makes it possible to classify lubricants according to the potential necessary in order to ensure satisfactory and lasting protection of engines with respect to undesirable phenomena related to the presence of acids in general.
This parameter, representative of the basicity of the lubricant, does not take into account the true conditions of oxidation of the lubricants in diesel engines; it therefore cannot fully characterize their neutralization capacity.
Another method of characterizing the neutralization capacity of lubricants is described in the document Technical Papers Series, No. 872,158, entitled “Cylinder Wear Mechanism in an EGR-Equipped Diesel Engine and Wear Protection by the Engine Oil”, published by the Society of Automotive Engineers.
This method is targeted at measuring the rate of neutralization of the lubricant by sulphuric acid. It consists in introducing a 30 gram sample of lubricant into a leaktight tank equipped with a thermometer and a manometer and including a vent.
The tank being immersed in a water bath at a constant temperature and the lubricant sample being continually stirred by suitable means, 0.1 milliliter of concentrated sulphuric acid is introduced within the tank, when the temperature of the sample has stabilized, by means for a syringe through the open vent.
The vent is then immediately closed.
Starting at this moment, the pressure indicated by the manometer is recorded for 10 minutes.
The values of the recorded pressure are converted into the amount of carbon dioxide produced by the reaction of the sulphuric acid with the basic products present in the lubricant sample.
The rate of neutralization is characterized by the volume of carbon dioxide produced during the 4 minutes which follow the introduction of the acid; it is expressed as micromoles of carbon dioxide.
This method exhibits the disadvantage of employing a large volume of lubricant, whereas, on the other hand, in an operating engine, the neutralization phenomena occur at the surface of the lubricated components, such as the cylinders and pistons, and the amounts of lubricants involved are low.
With this method, the measurement of the rate of neutralization is very dependent on the stirring conditions of the lubricant in the tank inside which the reaction is carried out, which is unfavourable to the repeatability of the measurement and to the validity of the comparisons between measurements carried out with different lubricants.
Furthermore, it is representative only of slow phenomena, that is to say lasting several minutes.
ACCOUNT OF THE INVENTION
The object of the present invention is specifically to overcome these disadvantages and in particular to provide a process and a device for characterizing the neutralization capacity of lubricants which takes into account the true conditions of oxidation of lubricants in engines. This is because the results obtained by the method of the invention are representative of the neutralization phenomena which take place essentially at the surface of the lubricated components, which are characterized by low amounts of lubricants involved at any instant and high local concentrations of acid, which result from the phenomena of condensation and of solubilization of the acid in the lubricant.
It finds it application in the laboratories of the industries in which lubricants are manufactured and those of the constructors of engines for which these lubricants are intended.
To this end, the present invention provides a method of characterizing the neutralization capacity of a lubricant comprising detergent additives including a reserve stock of basicity, which consists in reacting, in a leaktight tank, at a constant temperature, the bases contributed by the additives present in a sample of known mass of lubricant with a predetermined amount of liquid acid at least equal to the stoichiometric amount, characterized in that it additionally consists:
in forming, within the leaktight tank, a film from the lubricant sample,
in depositing the predetermined amount of liquid acid at the surface of the film in a time of less than 0.5 second,
in recording, as a function of the time, the values of the pressure within the leaktight tank until the said pressure has stabilized;
in determining, from the recorded values of the pressure, at least one of the following three characterizing parameters: an initiation period for the reaction, a neutralization potential and a reaction rate.
According to a second characteristic of the method of the invention, the initiation period for the reaction is determined by the measurement of the time which passes between the beginning of the deposition of the liquid acid and the moment of passing through a minimum value of the recorded pressure.
According to another characteristic of the method of the invention, the amount of bases contributed by the detergent additives present in the lubricant sample being known and the recorded pressure reaching a stable value, the neutralization potential is determined by application of the following formula:
Ra
=
Δ
P
Pth
×
100
in which:
Ra represents the neutralization potential in %,
&Dgr;P represents the difference between the stabilized recorded pressure value and the minimum value of the recorded pressure,
Pth represents the theoretical pressure in the leaktight tank which would have been reached if the reaction had been complete.
According to another characteristic of the method, the reaction rate is equal to the maximum rate of increase in the recorded pressure.
According to another characteristic of the method of the invention, the lubricant film formed within the leaktight tank exhibits a thickness of between 20 and 150 microns.
According to another characteristic of the method of the invention, the liquid acid is preferably 95% sulphuric acid.
According to another characteristic of the method of the invention, the predetermined amount of 95% sulphuric acid corresponds to an excess of acid of between 0.5% and 200% and preferably equal to 96.7% with respect to the amount of bases contributed by the detergent additives.
Another subject-matter of the invention is a device for the characterization of the neutralization capacity of a lubricant comprising detergent additives including a reserve stock of basicity, comprising a leaktight tank equipped with means for maintaining at a constant temperature, in which the bases contributed by the additives present in a sample of known mass of lubricant are reacted with a predetermined amount of liquid acid at least equal to the stoichiometric amount, characterize
Blank Rome Comisky & McCauley LLP
Elf Antar France
Gakh Yelena
Warden Jill
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