Fractionation of Crude Oil Acids by HPLC and Characterization of Their Properties and Effects on Gas Hydrate Surfaces

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.