Asphaltenes Precipitated by a Two-Step Precipitation Procedure. 1. Interfacial Tension and Solvent Properties

Asphaltenes were precipitated into two fractions using a two-step precipitation procedure. The first fraction was obtained by mixing 3:1volumes of n-pentane/crude oil followed by filtration. In the following step the second fraction was precipitated out from the filtrate using 18:1 volumes of n-pentane/crude oil. Whole asphaltenes were precipitated using 40:1 pentane-to-crude oil ratio. Three crude oils were used and the asphaltene fractions obtained were characterized with regard to onset of precipitation, interfacial tension and radius of gyration. The second fraction was more soluble at increasing heptane-to-toluene ratios, more interfacially active and showed different organization properties at the interface between oil and water. Small angle neutron scattering showed that the second fraction formed aggregates with lower radius of gyration. The results show that asphaltenes consist of fractions with different solvent properties and indicates that asphaltenes should be looked at as more than one solubility class.