BASE OILS
A new way to decode the solvency of base oils
Thomas Feischl, Director of Business Development, eralytics GmbH Daniel Abbenor, Specialist Product Quality, Nynas AB, Nynäshamn
The aniline point and its importance in the lubricant industry
The aniline point of mineral base oils is a crucial indicator when it comes to formulating lubricants, especially in high-performance or sensitive applications. It essentially reflects the solvency power of a base oil, how well it can dissolve additives or other components in a lubricant formulation. A lower aniline point means higher solvency, which is important for dissolving polar additives (like detergents, dispersants, or antioxidants). This is typical of Group I or naphthenic base stocks and can be beneficial for certain applications that demand high additive loading or where varnish and deposit control is a concern.
On the other hand, Group II and III base stocks often have higher aniline points, indicating lower solvency but better oxidation stability and higher viscosity index – ideal for more modern, thermally stable formulations.
For some industrial applications such as the plasticisation of rubber, the production of greases and metalworking fluids, high solvency is essential. In addition to the technical challenges, the global transition to more highly refined and therefore less soluble products poses major challenges for the industry.
Traditional determination of the aniline point Knowing the actual aniline point of base oils is crucial for product development and incoming product quality control. The value is given in °C and describes the lowest temperature at which the chemical substance aniline remains in solution under test conditions. The measurement is typically carried out according to the standard test method ASTM D611. Measuring devices for determining the aniline point are offered by various suppliers with different degrees of automation.
In all cases, the fundamental problem comes from the chemical substance aniline itself, which is toxic, can cause physical damage, is suspected of being carcinogenic and is also extremely bad for the environment. All in all, this is a substance that every operator tries to avoid. Depending on the method, one determination takes between 20 and 60 minutes, including sample preparation.
New approach for estimating the aniline point with FTIR infrared spectroscopy FTIR (Fourier Transform Infrared Spectroscopy) measurements are widely used in the lubricant industry because this method offers a fast, non-destructive, and detailed chemical analysis of lubricants, both fresh and used. The monitoring of
Continued on page 48 LUBE MAGAZINE NO.187 JUNE 2025 47
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