Fractionation and Characterization of Asphaltenic and Resinous Fractions of Natural Bitumen

Abstract

In order to identify the finger prints of some fractions in butimen and to study the changes that take place when heavy oil is upgraded, precipitation, fractionation, and characterization of asphaltenes and resins from natural bitumen were carried out using UV/vis and FTIR Spectroscopy. The sample was purified and the asphaltenes fraction precipitated with n-hexane, fractionated into fractions A and B based on solubility and polarity with hexane/toluene mixture at a fixed ratio while resins recovered from maltenes was fractionated into subfractions X, Y, Z by liquid adsorption chromatography on a silica/alumina adsorption column with dichloromethane/methanol mixed solvent in the ratio of 4:1, 3:2 and :2:3, respectively. The results showed that crude asphaltene and its subfractions absorbed light of longer wavelength (465 – 640 nm), indicating that they are made up of polynuclear aromatic compounds. The results also revealed the presence of alkyl side chains and major oxygenated groups in both crude asphaltene and its subfractions (A and B). The spectra of crude resin and its subfractions showed that they absorbed radiation of longer wavelength (490-580 nm), which are character of polynuclear aromatic compounds with the extended conjugated system. However, IR spectra revealed that all the fractions including the crude resin contained aromatic rings with alkyl side chains and oxygenated group.