## Abstract

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.

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 language | English |
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Publication status | Published - Jun 2016 |

Event | 17th International Conference on Petroleum Phase Behavior and Fouling - Elsinore, Denmark Duration: 19 Jun 2016 → 23 Jun 2016 |

### Conference

Conference | 17th International Conference on Petroleum Phase Behavior and Fouling |
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Abbreviated title | PetroPhase 2016 |

Country/Territory | Denmark |

City | Elsinore |

Period | 19/06/16 → 23/06/16 |