(257ak) Molecular Thermodynamic Modeling of a Two-Step Asphaltene Precipitation Process

Asphaltene precipitation has attracted significant concern from petrochemical industry due to its extensive adverse effect over exploitation, transportation through downstream refining and cracking. As a complex process involving thousands of chemical compounds, it has been extensively correlated with empirical equations rather than being illustrated from a thermodynamics perspective. This paper aims to describe the precipitation process by taking into account the asphaltene molecular structure and interactions between different molecules. A hierarchical structure [Oliver C. Mullins, The Modified Yen Model, Energy & Fuels, 24 (2010), 2179-207] of asphaltene has been proposed recently to be composed of three different forms, i.e. individual molecules, nanoaggregates, and clusters. Based on this hierarchical structure, this paper presents a molecular thermodynamic framework for predicting the two phase transition points at critical nanoaggregate concentration (CNAC) and critical clustering concentration (CCC). To be more specific, a two-step phase equilibrium based on aggregation thermodynamics is proposed, and an activity coefficient model is used to account for nonideality of asphaltene solutions. The predicted results for asphaltene mixed with pure solvents can well represent experimental data.