Total Base Number (TBN):
Total Base Number (TBN) is the measure of the quantity of basic components in a petrochemical sample. TBN is determined in both new and used oils and is a value of the oil’s ability to neutralize the acids produced in the oils during normal use. The higher the TBN value of an oil sample is initially, the more acidic components can be produced during the use of the oil.
Oils used for different purposes have different ranges of TBN values, but typically all types of oils are considered to have been completely consumed when the TBN value of the oil sample drops below 2mg KOH/g of sample. An ideal TBN range for all types of equipment is set by the equipment manufacturer and for optimal performance, frequent monitoring of the oil is used to ensure it stays in the acceptable range. Automotive oils have the lowest initial TBN values, with a range of 7-10 mg KOH/g sample. Contrarily, marine oils have very high initial TBN values, around 70mg KOH/g sample. The very high initial TBN values extend the amount of time allowed between changing the oil in the ships or submarines.
Two of the most common methods used to determine the TBN value of a sample are by potentiometric titration analysis. Although both methods use the same principle, each method uses a different mixture of solvents to dissolve the samples and different titrants for the analysis. This means that although both tests produce a TBN value, the results are not directly comparable. Thus it is recommended that the same method be used to monitor the samples over time to ensure consistent results are obtained.
ASTM D2896 – Base Number of Petroleum Products by Potentiometric Perchloric Acid Titration
ASTM D4739 – Base Number Determination by Potentiometric Titration
The full range of analysers are available from Camlab in the UK Including analysers for Total Base number and Total Acid Number