Crystal structure of asphaltene under mechanical stress of ball milling

Abstract

This work aims to investigate the structural behaviour of asphaltene under mechanical stress using ball milling. Asphaltene samples were collected and separated from Kuwait export crude using n-heptane and subsequently ball milled for up to 24 h. X-ray diffraction was used to provide an insight into asphaltene macrostructure properties, which subsequently utilised to determine crystallite parameters. The results showed that the mechanical stress has a great influence on these structural parameters, with an increase of the aromatic sheet's inter-layer distance from 3.6 $\AA$ to 3.9 $\AA$. While the height of stacked aromatic sheets per cluster and the number of stacked aromatic sheets per cluster decreased from 24.6 $\AA$ to 9.3 $\AA$ and 8 to 3.2, respectively. A significant increment in the aromaticity value was also observed after the ball milling experimentations, indicating mechanical stress induces cyclisation and aromatisation. The XRD profiles of the higher milling time samples reveals a high background intensity. This suggests a formation and/or increasing the proportion of highly disordered materials. In addition, the effects magnitude on asphaltene crystal parameters between the mechanical stress against heat stress was compared. The results showed core structural parameters are more sensitive to mechanical stress over heat stress.