Polar-solvent fractionation of asphaltenes from heavy oil and their characterization

In accordance with the asphaltene fractionation scheme proposed, an oil residue with a boiling point above 250°C is mixed with acetone (acetone/residue ratio of 3: 1) and divided into two parts containing mainly high-molecular-mass (resin-asphaltene concentrate) and low-molecular-mass (deasphalted oil) components. From each part, asphaltenes are isolated with n-heptane (1: 40 v/v) and then separated in a Soxhlet apparatus with a 1.85: 1 (v/v) n-heptane/toluene mixture into two subfractions, insoluble and soluble in this mixture, respectively. This procedure has allowed four asphaltene subfractions to be isolated, which have different compositions as shown by Fourier-transform IR spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry, and UV spectrophotometry.