Kinetics of Asphaltene Precipitation in a Heptane-Toluene Mixture

The enlargement of asphaltene particles precipitated in a heptane-toluene mixture (Heptol) was mechanistically modeled using mass and population balance equations. The kinetic parameters used in the model equations were optimized through fitting of the model predictions to the experimental data. The significance of this study is the investigation of growth mechanism of asphaltene particles based on supersaturation not reported in the literature. Agglomeration and growth mechanisms of asphaltene precipitation were quantitatively related to the supersaturation as a driving force in the form of rate equations. Using a fractal dimension for asphaltene particles found in the literature resulted in a better consistency between the model predictions and experimental data. Size analysis was carried out using a Horiba LB-550 nanoparticle size analyzer, which uses a dynamic laser scattering technique to measure the size of the asphaltene particles in the range of 1 nm to 6 mu m. The concentration of asphaltene in the liquid mixture during the development of flocs was measured using the spectrophotometry technique. Particle enlargement from about 8 nm to 2 mu m lasted about 2 h in a mixture of asphaltene toluene containing 115.3 mg of asphaltene/kg of toluene when 0.79 kg of n-heptane/kg of toluene was added as an antisolvent.