Molecular-thermodynamic framework for asphaltene-oil equilibria

• Published in: AIChE journal 1998-05, Vol.44 (5), p.1188-1199
• Main Authors: Wu, Jianzhong, Prausnitz, John M., Firoozabadi, Abbas
• Format: Article
• Language: English
• Subjects: Applied sciences; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels
• ISSN: 0001-1541; 1547-5905
• DOI: 10.1002/aic.690440516

Asphaltene precipitation is a perennial problem in producing and refining crude oils. To avoid precipitation, it is useful to know the solubility of asphaltenes in petroleum liquids as a function of temperature, pressure and liquid‐phase composition. In the novel molecular‐thermodynamic framework presented here, both asphaltenes and resins are represented by pseudo‐pure components while all other components in the solution are represented by a continuous medium that affects interactions among asphaltene and resin particles. The effect of the medium on asphaltene‐asphaltent: resin‐asphaltene, resin‐resin pair interactions is taken into account through its density and dispersion‐force properties To obtain expressions for the chemical potential of asphaltene and for the osmotic pressure of an asphaltene‐containing solution, the SAFT model is used in the framework of McMillan‐Mayer theory, which considers hard‐sphere repulsive, association and dispersion‐force interactions. By assuming that asphaltene precipitation is a liquid‐liquid equilibrium process, a variety of experimental observations can be explained, including effects of temperature, pressure, and composition on the phase behavior of asphaltene‐containing fluids. For practical quantitative applications, the model outlined here requires molecular parameters that must be estimated from a few experimental data.