Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration.
Get more information about the standard at ASTM D664-24.
ASTM D664 is a standardized test method for determining the acid number of petroleum products, lubricants, biodiesel, and biodiesel blends through potentiometric titration. The acid number quantifies the number of acidic constituents in these substances, which is crucial for assessing product quality, performance, and potential corrosive behavior.
Details
The test method involves dissolving a sample in a solvent mixture, typically toluene and propan-2-ol, and titrating it with a base, such as potassium hydroxide (KOH), while continuously measuring the solution’s potential using a glass electrode. The endpoint of the titration is determined potentiometrically, indicating the amount of acidic substances present.
ASTM D664 includes two procedures:
•Test Method A: Designed for petroleum products and lubricants that are soluble or nearly soluble in the solvent mixture. It is applicable for acids with dissociation constants larger than 10⁻⁹.
•Test Method B: Specifically developed for biodiesel and biodiesel blends with low acidity and different solubility characteristics. This method requires an automatic titrator with endpoint-seeking capability.
By providing a reliable method for measuring acidic constituents, ASTM D664 plays a crucial role in maintaining product quality, optimizing performance, and preventing corrosion-related issues across these industries.
Industries & Applications
ASTM D664 is widely applied across various industries:
Petroleum: Used for quality control of crude oils, refined products, and lubricants to ensure they meet specified acid number limits, preventing potential equipment corrosion and ensuring product stability
Lubricant manufacturing: Assists in formulating lubricants by monitoring acid numbers to maintain product performance and longevity
Biodiesel production: Ensures biodiesel and its blends have acceptable acid numbers, indicating proper processing and storage conditions, which is essential for engine compatibility and performance
Automotive and machinery maintenance: Monitoring the acid number of in-service lubricants helps detect oil degradation and oxidation, allowing for timely oil changes and maintenance to prevent machinery wear and failure