Solubility and structural parameters of asphaltene subfractions separated from bitumen via an improved method

Asphaltene is an important component of bitumen, and it is closely related to the performance of bitumen. Asphaltene is a complex mixture, and it is obviously not accurate to simply regard it as the heptane-insoluble part in bitumen. In this paper, an improved reduced pressure column precipitation device was developed to separate the asphaltene sub-fractions in 2 kinds of road petroleum bitumen which had the same Performance Grade (PG) and almost free of wax, but significantly different physical aging degree. The separation process is strictly based on the solubility of asphaltene subfractions in different polar solvents. Based on the extended Hansen solubility parameter (HSP) model, 6 kinds of isolated asphaltenes were tested by turbidimetric titration test to determine their structural stabilities in three solubility directions: dispersion interaction, polar interaction and hydrogen bonding. Furthermore, the structural characteristic parameters (aromatic sheet diameters and aromaticity) of 6 kinds of asphaltenes were obtained using Raman spectroscopy and Fourier-transform infrared spectroscopy. The research showed that asphaltenes exhibited lower dispersion and stronger hydrogen bonding with the increasing of polarity. The aromatic hydrocarbon size and aromaticity also increased with polarity. The research results can explain bitumen phase imbalance (such as thermoreversible aging) caused by the change of asphaltene components.

Automated summary

In this study, an improved reduced pressure column precipitation device was used to separate asphaltene subfractions in two types of road petroleum bitumen. The research showed that the solubility of asphaltene subfractions varied in different polar solvents, and as the polarity increased, the dispersion of asphaltenes decreased while hydrogen bonding and aromatic characteristics increased. These findings can explain the phase imbalance in bitumen caused by changes in asphaltene components.