Modeling the molecular composition of vacuum residue from oil sand bitumen

Vacuum residue is the most diverse and structurally complex fraction of petroleum. In this work, we develop a representation of the molecular composition of this petroleum fraction. The underlying assumption is that vacuum residue is a continuum in molecular structure that can be described using probability distribution functions. The structural definition of SARA classes (saturates, aromatics, resins, and asphaltenes) is formulated in consistency with recent findings in petroleomics and the chemistry of thermal cracking or conversion. Island-and archipelago-type structures are considered in the representation of resins and asphaltenes. The systematic assembly of residue molecules is executed using stochastic algorithms. The model is implemented with good results in simulating a vacuum residue from oil sand bitumen. The simulation allows visualization of detailed molecular distributions in vacuum residue and its SARA fractions. The model also gives acceptable predictions for the properties of the maltene and asphaltene fractions of the residue sample.