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Corrosion is an omnipresent disruption factor in refinery processes, and one that can result in high production costs. Crude oils containing high levels of naphthenic acid or sulfur pose a high risk of corrosion. The acid number, also known as total acid number (TAN), is used to assess the corrosion potential of crude oil and refined petroleum products, and it directly affects their price.

However, determining the acid number in crude oils, bitumen, and high-wax samples can be challenging using test methods such as potentiometric titration (ASTM D664) or color-indicator titration (ASTM D974). This is why ASTM D8045 was established, which specifies the use of thermometric titration.

Thermometric titration monitors the enthalpy change of the reaction rather than the potential. Oil samples are dissolved in a solvent mixture of xylene and isopropanol and then titrated with potassium hydroxide in isopropanol.

The endpoint of the titration is indicated by an inflection in the titration curve. In cases where the enthalpy change is small (e.g., weak acids neutralized by strong bases), a catalytic indicator is used to make the titration endpoint visible.

Thermometric titration is much faster, requires less reagents, and minimal sensor maintenance compared to the procedures in ASTM D664 or ASTM D974. This makes thermometric titration a much more cost-effective choice.

Download the Application Bulletin to learn more about the analysis. The document contains detailed instructions and troubleshooting tips for the analysis.

Watch the video to learn more about this titration method:


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