A Two-Component Solubility Model of the Onset of Asphaltene Flocculation in Crude Oils

Abstract

A new, two-component asphaltene solubility model (ASM) has been developed to predict the phase behavior of asphaltenes in crude oils. Previous asphaltene solubility models have relied for solution upon simplifying assumptions (e.g., nucleation of a pure asphaltene or pure solvent phase) and approximation methods for determining crude oil solubility parameters. No such simplifying assumptions or approximations are needed if a simple correlation between the solubility parameter and the refractive index of nonpolar species is used to characterize the oil. Compositional ranges over which asphaltenes are stable, metastable, or unstable to phase separation can be defined from calculations of changes in Gibbs free energy using the Flory−Huggins theory for mixtures of crude oil and known amounts of hydrocarbon solvents and precipitants. Coupled values of the asphaltene solubility parameter and molar volume represent the only adjustable parameters in the model. Predictions have been tested against an extensive set...