Analytical Considerations Related to Asphaltenes and Waxes in the Same Crudes

Increasingly waxy crudes containing significant quantities of asphaltenes require characterization, and established methods for separation of the waxes and asphaltenes are often not applicable. An analytical scheme is described employing only one solvent, methylethyl ketone, to separate asphaltenes and waxes, rather than an n-alkane and a ketone. The method consists of an asphaltenes fractionation by filtration at 50 °C, followed by wax recovery by cooling to a specified temperature (dependent upon the user's needs) and filtration. The carbon number distribution of the wax fraction may be determined by high-temperature gas chromatography, and the soluble oil (minus asphaltenes and wax) can be further characterized by liquid chromatography and mass spectrometry.