The total acid number (TAN) measures the acidic components in a substance, typically in petroleum products like engine oils or lubricants. The TAN value indicates the quantity of acid in milligrams of potassium hydroxide (KOH) which is required to neutralize one gram of the sample.
The TAN value is an important parameter for assessing the acidity of oils and fuels. Regular monitoring of total acidity is essential for many reasons. It helps ensure proper performance and longevity of lubricants or petroleum products.
Fresh, unused oils have a low TAN value, but a high TBN (total base number) value. Over the service life of the oil, the TAN value increases while the TBN value (a measure of the alkaline reserve to neutralize acids) decreases.
The total acid number is an important parameter to monitor in petroleum products because excessive acidity can lead to corrosion and impairment of equipment. This Application Note describes the determination of TAN in sliding track oil with conductometric titration.
Sliding track oil
The sample was titrated with potassium hydroxide in 2-propanol solution until after the first equivalence point. The 5-ring conductivity measuring cell was used for this analysis.
The determination of the TAN value (Table 1) gave accurate results. An example determination is shown in Figure 2.
Table 1. Results of the sliding track oil determination by conductometric titration.
| Sample | Result TAN | RSD in % |
|---|---|---|
| Sample (n=3) | 0.40 mg KOH/g | 1.1 |
This method does not require indicators or complicated instruments. Compared to other titration methods, it is extremely sensitive and delivers precise results. The measurement is easy to carry out. It can be used for a wide range of sample types, including solutions, suspensions, and slurries.
The robust design of the conductivity sensor allows for easy cleaning. In contrast to potentiometric sensors, it does not require any rehydration period between the measurements.
Conductivity titration can be used for highly diluted solutions, nonaqueous solutions, and titration of weak acids or bases. The endpoint of this titration method is sharp and precise compared to other titration methods.
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