New and used petroleum products may contain acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products.
The relative amount of these materials can be determined by titrating with bases.
The acid number is a measure of this amount of acidic substance in the oil, always under the conditions of the test.
The acid number is used as a guide in the quality control of lubricating oil formulations.
It is also sometimes used as a measure of lubricant degradation in service.
The total acid number (TAN) or total base number (TBN) of petroleum products is an important parameter.
TAN is a property typically associated with industrial oils.
It is defined as the amount of acid and acid-like material in the oil.
Oxidation and nitration resins make up the majority of this material.
As the oil is used, acidic components build up in the lubricant causing the TAN number to increase.
A high TAN number represents the potential for accelerated rust, corrosion and oxidation and is a signal that the oil should be replaced.
Critical TAN numbers are dependant on oil type.
TBN is a property usually associated with engine oils.
It is defined as the oils' ability to neutralise acid.
The higher the TBN, the more acid it is able to neutralise.
This quality is also referred to as alkaline reserve and is directly proportional to the amount of active detergent contained in the oil.
New engine oils typically possess TBN's from 5.0 to 15.0, depending on manufacturer and intended service.
As the oil is used, it becomes contaminated with acids and the TBN drops.
Generally, TBN levels below 3.0 are considered too low and indicate that the oil should be changed.
One cause of TBN depletion relates to the use of low quality, high sulphur fuel.
During the combustion process, this sulphur turns to sulphuric acid and in turn, accelerates TBN depletion.
The importance of the TAN/TBN is manifested by the numerous standard procedures used the world over (ASTM, DIN, IP, ISO).
The sample is dissolved in a mixture of solvents and is titrated potentiometrically with an acid or base using a glass indicating electrode and a reference electrode or a combination electrode.
The meter readings are plotted manually or automatically against the respective volumes of titrating solution and the end points are taken only at well-defined inflections in the resulting curve.
When no definite inflections are obtained, end points can be taken at meter readings corresponding to those found for aqueous acidic and basic buffer solutions.
For many tests, the mixture of solvents can be hazardous and toxic in nature.
It is therefore important to use an automated system that allows the operator to alter these solvents and amounts in the future, should these mixtures be changed.
Such a future proof automated system is the 855 Robotic Titrosampler from Metrohm.
The 855 Robotic Titrosampler provides high-performance titration automation with a minimal footprint.
The 855 Robotic Titrosampler is an automated titrator that combines the highest quality standards in titration - based on the Titrando technology - automation.
Its features inlcude: 40 per cent less lab space; easy handling thanks to features like plug-and-play; user-friendly thanks to complete packages; and three-year warranty as standard.
This synthesis of automation and titration, processes series of up to 140 samples on a small footprint.
The 855 Robotic Titrosampler is an all-rounder with all the features of automation.
Modern automation means not just moving around samples - its key elements are sample preparation and sample processing.
Thorough rinsing and cleaning of the electrode and titration head assembly is of paramount importance for this difficult and often grimy application.
Sample racks offering different size beakers are also offered as standard, or customers can have sample racks designed to fit any type of beaker.
The packages include everything that is required to set up a ready-to-use system.
Data management and system control is performed by Tiamo titration software.
