Fractionation of Asphaltene by Complex Formation with <i>p</i>-Nitrophenol. A Method for Structural Studies and Stability of Asphaltene Colloids

Abstract

Cumene solutions of asphaltenes (8 g/L) were treated with p-nitrophenol (PNP) and a precipitated solid was collected after 3 days. For the asphaltene samples examined, between 48 and 70% of the sample could be precipitated by this treatment. PNP, known to form charge-transfer complexes with aromatic compounds, probably forms this type of compounds with asphaltenes, leading to precipitation. The sample precipitated was dissolved in chloroform, and the PNP was removed by extraction with aqueous sodium hydroxide. Although the initial asphaltene sample has the usual high solubility in toluene (higher than 50 g/L, room temperature), the precipitated asphaltene sample obtained in this way (A1), has a very low solubility in toluene (≈90 mg/L, room temperature). These results show that asphaltenes are a mixture of compounds with vast differences in solubility and suggest that their solutions in aromatic solvents are constituted by a colloidal phase, formed by the low-soluble fraction A1 dispersed by a soluble asphaltene fraction A2.