Petroleum Fluids, Asphaltenes, Waxes and Other Applications

2 Petroleum Fluids, Asphaltenes, Waxes and Other Applications 

Most applications concerning phase equilibria of the systems the title of this section includes are based on equations of state with both pseudo-component 

Vakili-Nezhaad et a/. applied continuous thermodynamics to the calculation of the vapour pressure of petroleum fluids improving a method reported by Kehlen and Ratzsch that used an analytical expression for the vapour pressure of a continuous ensemble starting with a continuous version of Raoult s law. Assuming a combination of Trouton s rule and the Clausius-Clapeyron equation for the vapour pressure of the pure species and a Gaussian distribution to represent the polydispersity of the system to solve the integral 

Vakili-Nezhaad et al found relatively good agreement between calculated and experimental data neglecting the intermolecular interactions. The agreement between the calculated and experimental vapour pressure was improved when the intermolecular interactions were taken into account by the introduction of the UNIFAC model. 

Nichita et al applied the pseudo-component method to the wax precipitation from hydrocarbon mixtures. To do so a general form of a two-parameter equation of state was used for vapour and liquid phases. The heavy components were assumed to precipitate in a single solid solution. Because lumping in pseudo-components often results in difficulties in solid-liquid equihbrium calculations the authors proposed a delumping procedure (mentioned in section 9.3.1). Lira-Galeana et al calculated wax precipitation in petroleum mixtures by assuming the wax consisted of several solid phases each described as a piue component or pseudo-component immiscible with other solid phases. 

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