An EoS approach for modeling asphaltene precipitation.

摘要

Asphaltene precipitation can occur unintentionally during solvent-based production and transportation schemes for heavy oils and intentionally in modern bitumen processes. In both cases, it is necessary to predict the conditions where precipitation occurs and the amount of precipitate.; While there has been considerable success in applying regular solution theory to predict asphaltene precipitation, an equation of state (EoS) approach has not yet been applied successfully. An EoS approach is an attractive alternative because most commercial simulators provide an EoS as a standard part of the thermodynamic package. The purpose of this project is to determine if the Peng-Robinson EoS can be adapted for a predicting asphaltene precipitation.; A thermodynamic model was developed based on the PR-EOS and the group contribution method to predict asphaltene precipitation from both asphaltene/toluene/alkane and bitumen/alkane systems. A liquid-liquid equilibrium was assumed between a primary bulk liquid phase and a second dense asphaltene phase. Bitumen was characterized in terms of solubility fractions: saturates, aromatics, resins and asphaltenes. Critical properties of the saturates, aromatics, and resins were estimated from their physical properties and compared to experimentally developed correlations. Asphaltenes were divided into fractions of different molar masses using a molar mass distribution function. The EoS parameters for asphaltenes were determined by fitting precipitation data from mixtures of asphaltenes, toluene, and heptane. (Abstract shortened by UMI.)