Base Number Determination in Motor Oil

In the present application note, color change at the equivalence point is detected using a phototrode and methyl orange as an indicator.

Background:

In case of engine oils, fuel combustion process is invariantly associated with oxidative side reaction. This oxidation leads to formation of acidic impurities in presence of sulfur

components in the oils. Presence of basic additives has significant role in neutralizing these acid formation and increasing shelf life of the oil. These basic additives are quantified by determining the base number of oil.

Base number (BN) is defined as the quantity of acid, expressed in terms of the equivalent

number of milligrams of potassium hydroxide that is required to neutralize all basic constituents present in 1 gram of sample. Determination of BN is essential for accessing the quality of oils to be used and also to monitor the depletion in case of used oils. BN is evaluated using titrimetric technique with phototrode where the samples are titrated with alcoholic hydrochloric acid and equivalence point can be evaluated by visual color change of the indicator as explained in ASTM D974.

Reaction:

BOH + HCl ----------> BCl + H2O

HCl is used as a titrant for Base number determination in motor oil. Its titer can be determined using photometric titration using M766 application method.

Download the application below for detailed method for base number determination using photometric titration.