Characterization of acidic compounds in biodegraded oils

The aim of this study was to propose an experimental methodology for characterizing qualitatively and quantitatively the acidic compounds in biodegraded or immature oils. After liquid extraction with KOH and esterification, the recovered polar fraction is converted to hydrocarbons which are separated into aliphatic and aromatic fractions using liquid chromatography, in order to use specific mass spectrometry group type analysis. The aliphatic fraction is characterized in terms of acyclic compounds (n and iso paraffins) and cyclic (one to six rings) aliphatic hydrocarbons. The methodology was first tested on model compounds and then applied to eight oils covering a wide range of biodegradation levels. Three of the oils were genetically related. Results clearly show that the total amount of acids increases with extent of biological alteration. Furthermore, the acyclic/cyclic aliphatic acid ratio is directly correlated to the biodegradation level and to the total acidity (total acid number or TAN value) and can be used to predict the acidity risk at a regional scale.