In this work, acids have been extracted from eight crude oils by ion-exchange extraction and liquid−liquid
extraction, and the two methods have been compared. The acid distribution as a function of increasing acid
strength is obtained for the different extracts using a recently developed high-performance liquid chromatography
(HPLC) procedure based on normal phase separation on a cyanopropyl stationary phase. The fractions are
characterized with regard to molecular weights by gel permeation chromatography, functional groups by Fourier
transform infrared spectroscopy, and quantitative distributions by HPLC. The results show that the different
extraction methods give different yields and compositions. The acid profiles are not necessarily different for
biodegraded and non-biodegraded oils, but the yields are much higher in biodegraded oils, as expected from
bulk acid determinations like total acid number. The profiles can to some degree be correlated with surface
activity of the acidic compounds.
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