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Lab Methods

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Acid Number

  • Method ASTM D664
  • Repeatability None Established
  • Reproducibility None Established
  • Blending linear
  • Additive Correction No

The purpose of this test is to determine the amount of acidic components in Petroleum products, lubricants, and Biodiesel/Biodiesel blends (B5/B10/Etc). The product must be soluble or nearly soluble in the titration solvent (Isopropyl Alcohol/Toluene/Water) otherwise the method will not yield consistent results. This method is very similar to the D974 Acid Number. The major difference comes from the method of titration. This method uses an electronic titrator. This allows for acidity to be measured in dark products that a visual color change cannot be observed.

As stated in the D974 additives and degradation play a major role in the presence of acids in petroleum products.