Functional groups in fractionated asphaltenes and the adsorption of amphiphilic molecules

Fractionated asphaltenes have been studied by X-ray photoelectron spectroscopy (XPS). Distinct differences in the content of certain functional groups were observed between two asphaltene sub-fractions. The sub-fraction that contained the smallest and least aromatic asphaltenes was found to contain a high concentration of carboxylic carbons, while the sub-fraction that consisted of the largest, most aromatic and highly unstable asphaltenes did not. The adsorption of amphiphilic molecules, containing various functional groups, to fractionated and unfractionated asphaltenes was also investigated. It was observed that amphiphilic molecules with acidic functional groups adsorbed to the asphaltenes from the unstable sub-fraction to a larger extent than did amphiphilic molecules with basic functional groups. The more acidic amphiphilic molecules were also observed to be the most effective ones in stabilizing asphaltenes. (C) 2003 Elsevier B.V. All rights reserved.