A generalized regular solution model for asphaltene precipitation from n-alkane diluted heavy oils and bitumens

Abstract

Regular solution theory with a liquid–liquid equilibrium was used to model asphaltene precipitation from heavy oils and bitumens diluted with n-alkanes at a range of temperatures and pressures. The input parameters for the model are the mole fraction, molar volume and solubility parameters for each component. Bitumens were divided into four main pseudo-components corresponding to SARA fractions: saturates, aromatics, resins, and asphaltenes. Asphaltenes were divided into fractions of different molar mass based on the gamma molar mass distribution. The molar volumes and solubility parameters of the pseudo-components were calculated using solubility, density, and molar mass measurements. The effects of temperature and pressure are accounted for with temperature-dependent solubility parameters and pressure-dependent diluent densities, respectively. Model fits and predictions are compared with the measured onset and amount of precipitation for seven heavy oil and bitumen samples from around the globe. The overall percent average absolute deviations (%AAD) of the predicted yields were less than 1.6% for the diluted heavy oils. A generalized algorithm for characterizing heavy oils and predicting asphaltene precipitation from n-alkane diluted heavy oils at various conditions is proposed.