A New Thermodynamic Model for Paraffin Precipitation in Highly Asymmetric Systems at High Pressure Conditions

Mohammadreza Ameri Mahabadian, Antonin Chapoy, Bahman Tohidi Kalorazi

Research output: Contribution to conferencePoster


The predictions of the crystallization temperature and the amount of precipitates at high pressure
conditions may be inaccurate using existing thermodynamic models. This is due to the lack of data on
the high pressure molar volume of solid paraffins. This inaccuracy is even more pronounced for
mixtures of high asymmetry. Owing to this, the present work provides a new robust modelling
approach for solid-fluid equilibrium conditions especially for highly asymmetric systems.
The conventional methods for high pressure solid-fluid equilibrium modelling use the
thermophysical properties of constituents defined in the reference state to evaluate the fugacity of the
solid phase in the reference pressure. These fugacities are then used, by using an estimate of the
Poynting molar volume integration term, to calculate the solid phase non-ideality at high pressures. In
contrast, with a completely different strategy to approach the problem, the present method exploits the
values of thermophysical properties of importance (here temperatures and enthalpies of fusion and
solid-solid transition) evaluated at the high pressure condition by applying a new insight to the wellknown Clausius-Clapeyron equation. These modified parameters are then used for evaluation of the
fugacity in the solid phase at higher pressure using the fugacity of pure liquid at the same pressure and
applying the well-established formulation of the Gibbs energy change during melting. Despite those
approaches in the literature which have used the Clausius-Clapeyron formulation to modify the
Poynting term, here, this equation is used to accurately estimate the high pressure enthalpies of fusion
and solid-solid transition. Compared to the most recent works, the current approach simplifies the
solid phase non-ideality model.
The devised approach coupled with the well tested UNIQAC activity coefficient model is used to
describe the non-ideality of the solid phase. For the fluid phases, the fugacities are obtained by SRK
EoS with binary interaction parameters evaluated by a group contribution scheme. The model is
applied on highly asymmetric systems with solid-fluid experimental data over a wide range of
pressures. It is first used to predict crystallization temperature in binary systems (e.g. Methane + nHeptadecane) at high pressures and proves to be highly accurate. The model is then verified by
applying it on multicomponent mixtures resembling intermediate oil and natural gas condensates. An
extensive comparison with the literature models has been performed which proves higher accuracy
and superiority of the developed model.
Original languageEnglish
Publication statusPublished - Jun 2016
Event17th International Conference on Petroleum Phase Behavior and Fouling - Elsinore, Denmark
Duration: 19 Jun 201623 Jun 2016


Conference17th International Conference on Petroleum Phase Behavior and Fouling
Abbreviated titlePetroPhase 2016


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