Fractionation of asphaltene by complex formation with p-nitrophenol. A method for structural studies and stability of asphaltene colloids

Cumene solutions of asphaltenes (8 g/L) were treated with p-nitrophenol (PN P) and a; precipitated solid was collected after 3 days. For the asphaltene samples examined, between 48 and 70% of the sample could be precipitated b y this treatment. PNP, known to form charge transfer complexes with aromati c compounds, probably forms this type of compounds with asphaltenes, leadin g to precipitation. The sample precipitated was dissolved in chloroform, an d the PNP was removed by extraction with aqueous sodium hydroxide. Although the initial asphaltene sample has the usual high solubility in toluene (hi gher than 50 g/L, room temperature), the precipitated asphaltene sample obt ained in this way (A(1)), has a very low solubility in toluene (approximate to 90 mg/L, room temperature). These results show that asphaltenes are a m ixture of compounds with vast differences in solubility and suggest that th eir solutions in aromatic solvents are constituted by a colloidal phase, fo rmed by the low-soluble fraction Al;dispersed by a soluble asphaltene fract ion A(2).