Molecular-thermodynamic framework for asphaltene-oil equilibria

摘要

Asphaltene precipitation is a perennial problem in production and refinery of crude oils. To avoid precipitation, it is useful to predict the solubility of asphaltenes in petroleum liquids as a function of temperature, pressure and liquid-phase composition. In the molecular-thermodynamic model presented here, both asphaltenes and resins are represented by pseudo-pure components, and all other components in the solution are represented by a continuous medium which affects interactions among asphaltene and resin particles. The effect of the medium on asphaltene-asphaltene, resin-asphaltene, resin-resin pair interactions is taken into account through its density and molecular-dispersion properties. To obtain expressions for the chemical potential of asphaltene and for the osmotic pressure of an asphaltene-containing solution, the authors use the integral theory of fluids coupled with the SAFT model to allow for asphaltene aggregation and for adsorption of resin on asphaltene particles. With these expressions, a variety of experimental observations can be explained including the effects of temperature, pressure and composition on the phase behavior of asphaltene-containing fluids. For engineering application, the molecular parameters in this model must be correlated to some macroproperties of oil such as density and molecular weight. When such correlations are established, it will be possible to calculate asphaltene-precipitation equilibria at a variety of conditions for realistic systems.