Influence of asphaltene structural parameters on solubility

Abstract

This paper investigates the influence of asphaltene’s structural parameters on its solubility, including aromatic sheet diameter and aromaticity. Aromatic sheet diameter (La) was determined by integrating the D1 and G bands of Raman spectra. Aromaticity was determined by the ratio of the integrated Fourier Infrared peaks of aliphatic carbon relative to aromatic carbon. Asphaltenes were extracted from five dead crude oils. Two types of solubility tests were conducted, with asphaltenes dissolved in both nonpolar (aromatic hydrocarbons) and polar (cyclic ethers and aromatic amines) solvents and re-precipitated using pentane; in addition to a scenario where asphaltenes were dissolved in toluene and re-precipitated using nonpolar (alkanes) and polar titrants (esters). The largest La was estimated to be 7.34 nm, while the other asphaltenes have a La within the range of 1.52–2.35 nm. La increases monotonically with aromaticity, which was inversely proportional to the hydrogen bonding capability. In terms of dispersant polarity, π-π interactions dominated, evidenced by a better asphaltene stability, which increased with aromatic core size. A reverse trend was recorded with nonpolar precipitants due to hydrogen bonding. This study argues that to inhibit the aggregation of asphaltene with large La, polar inhibitors should be used.