What is the neutralisation number for oil?

The neutralisation number is an index which indicates the content of acids or bases in lubricating oils. It is specified for industrial lubricants such as gear oils, hydraulic oils or chain oils. It is the quantity of potassium hydroxide (KOH) in mg equivalent to the free acid or alkaline components contained in 1g of an oil. It therefore provides information about the level of acidic or alkaline components in fresh oil or used oil.

The neutralisation number is often equated with the TBN (Total Base Number) for engine oils. However, the TBN is determined by other test methods and applies to engine oils.

How is the neutralisation number determined?

The neutralisation number is determined by a colour indicator using the titration method. The measuring method is carried out according to DIN 51558 and the result is an amount of KOH in mg per 1g of the oil sample.

Titrator for determination of the neutralisation number

The photo shows a titrator with two oil samples. The left oil sample (orange) is coloured with the colour indicator, but has not yet reached the limit. The oil sample on the right (green) has already changed colour. The basic components have used up the acidic components and the pH value is tilted. As soon as the colour changes to green, the neutralization number is determined.


Heiko Stephan

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