What is aniline point and how to test the aniline point

The aniline point is a measure of the solubility properties of light petroleum products. Aniline is often used as a solvent in the petroleum industry to determine the solubility of petrochemical products or certain hydrocarbons in aniline. When aniline and test oil are mixed at a lower temperature (room temperature), they are divided into two layers. After heating, the test oil is in aniline. The solubility of the mixture increases, continue to heat until the two phases just reach complete mutual solubility, then the interface disappears, and the temperature of the mixed solution at this time is the aniline point (also known as the critical solution temperature).

Since the polarities of the various hydrocarbons that make up the oil are different, according to the theory of similar compatibility, the solubility of various hydrocarbons in aniline is different. The more similar the structure (polarity) of the hydrocarbon molecule is to the molecular structure (polarity) of aniline, the greater the solubility of this hydrocarbon in aniline and the lower the aniline point, in other words, the molecular structure of hydrocarbons is similar to the molecular structure of aniline The more similar, the lower the temperature required for dissolution (mutual solubility, reaching the critical dissolution temperature), and the lower the aniline point. Conversely, the more dissimilar the molecular structure of hydrocarbons is to that of aniline, the higher the temperature required for dissolution and the higher the aniline point.

For different oils, due to different compositions, their aniline points are different. Even if two oils with the same boiling range come from different crude oils, the aniline points will be different. Studies have shown that this is mainly related to the chemical composition of the oil. In addition, it is also related to the ratio of agent to oil and the purity of aniline and operating conditions.