GOST 11362 (ISO 6619)
Petroleum products and lubricants. Neutralization number. Potentiometric titration method
The essence of the method is that the test mass is dissolved in a specific solvent and titrated potentiometrically with an alcoholic solution of potassium hydroxide or hydrochloric acid using glass, calomel or silver chloride electrodes.
The meter readings are plotted manually or automatically against the respective volumes of titration solution. Take only clear inflection points on the titration curve. In the case where there is no clear inflection point on the curve, the end points are taken from the readings of the measuring device, corresponding to the readings for non-aqueous acidic and alkaline buffers.
The interstate standard GOST 11362 (ISO 6619) establishes a method for potentiometric titration. It is applicable to define:
- total acid number;
- acid number of strong acids;
- total base number;
- base number of strong alkalis in petroleum products and lubricants.
Also applicable for the determination of acids with a dissociation constant greater than 10-9; weak acids with a dissociation constant of less than 10-9 do not interfere with the determination.
In commercial and waste oils, acidic compounds include organic and mineral acids, esters, phenolic compounds, lactones, resins, heavy metal salts, ammonium salts and other weak bases, salts of polybasic acids, as well as inhibitors and detergents.
This method characterizes the relative change in oils during oxidation, independent of the color and other properties of the oils.
Commercial and waste petroleum products can contain acidic components present as additives or as decomposition products formed under operating conditions, for example, oxidation products. The relative amount of these substances can be determined by titration with alkalis.
The acid number allows you to estimate the amount of acidic components in the oil under test conditions. The acid number is used as a guide to control the quality of the lubricating oil.
Sometimes it is used as an assessment of the nature of the change in the lubricant during operation.
The content of the components should be determined empirically. Since many oxidation products cause an increase in acid number and organic acids have different corrosive properties, the presented method cannot be used to determine the corrosiveness of an oil under operating conditions. The relationship between the acid number and the corrosiveness of the oil in relation to metals has not been established.
The acid number can be determined in compounded engine oils.