Metrohm has revealed how its 864 Robotic Balance Sample Processor allows for the fully automated determination of Tan/TBN in industrial samples according to ASTM standards D 664 and D2896.
As manifested by the numerous standard procedures used all over the world, the determination of the total acid number (Tan) and total base number (TBN) of petroleum products is crucial for quality control in the oil industry.
These parameters provide invaluable information regarding petroleum degradation (oil aging) as well as the corrosion-enhancement properties and alkaline buffer capacity of the material.
The standards ASTM D 664 and ASTM D 2896 describe two simple methods for the determination of Tan and TBN based on potentiometric titration of the acidic and basic constituents, respectively.
Despite being relatively simple, these procedures, if carried out annually, are time-consuming and labour-intensive.
Further drawbacks are the handling of toxic solvent mixtures and the tedious cleaning of oil-smeared beakers and electrodes.
The 864 Robotic Balance Sample Processor allows to circumvent these drawbacks.
The fully automated and computer-controlled Tan/TBN determinations include weighing, solvent addition, waiting times for complete dissolution and optimised electrode-conditioning procedures between samples, as well as convenient collection of all data in a sophisticated database.
Results are available within minutes and even very low Tan/TBN values can be determined with reproducibility better than 2 per cent.
Depending on age and storage conditions, petroleum products can contain acidic or basic constituents that are either present as additives or as oxidation products that formed by oil degradation during service.
The relative amount of these materials defines the oil quality and can be determined by titration with bases or acids.
The acid/base number is a measure of the amount of acidic/alkaline substances in the oil.
In quality control of lubricating oil formulations, Tan/TBN are determined as standard parameters.
While the acid number is the number of mg KOH required to neutralise a 1g sample, the base number is the amount of basic components, expressed as mg KOH, contained in a 1g sample.
Depending on the sample, the titration equipment needs a special cleaning and conditioning procedure between individual samples to get rid of sticky oil components.
A fully automated system guarantees that these steps are always carried out in the same way to ensure optimum accuracy and reproducibility.
This work describes the automated determination of Tan/TBN in industrial samples according to ASTM D 664 and ASTM D 2896.
Instrumentation: 864 Robotic Balance Sample Processor; 809 Titrando; 800 Dosino; Precisa XR 205 A (balance).
The 864 Robotic Balance Sample processor is a fully automated system for determining the total acid or base number in oils.
It performs both the preparation of the sample and the determination as such.
A small amount of sample is put onto a beaker and placed on the sample rack.
All relevant analysis data, such as pipetting volume, position and identification of the sample, is entered into a sample data table of the Tiamo software.
A 10-mL pipetting tip is used to aspirate the amount of sample given in the sample data table.
The titration beaker is set to tare and the sample is added, after which the used pipetting tip is discarded.
The weighed sample is transported to the second work station where 60 mL of solvent is added.
Using 809 Titrando and the Solvotrode the TAN resp TBN value is determined by titration with the appropriate titrant.
At the end of the titration the beakers are emptied and the titration cell equipment is cleaned fully automatically.
Depending on the sample, an additional cleaning set in the external washing station (option) can be carried out.
