An improved thermodynamic model for Wax precipitation using a UNIQUAC + PC-SAFT approach

• UNIQUAC to account for solid phase.
• PC-SAFT to calculate the fugacity of vapor and liquid phases.
• The model is evaluated for six North Sea oil samples.
• The PC-SAFT parameters for petroleum plus fractions are estimated using new correlations in literature.
• The comparison with Lira-Galeana et al. [1], Pedersen et al. [2] and Dalirsefat and Feyzi [3] models.

Wax precipitation is a serious challenge in the oil industry due to decrease in oil production and transmission efficiency. Wax precipitation modeling plays an important role to forecast the Wax appearance temperature (WAT) and the amount of precipitation. In this work, solid solution theory is used for Wax precipitation modeling. The perturbed hard chain statistical associating fluid theory (PC-SAFT) equation of state (EOS) is implemented in order to calculate the fugacity of vapor and liquid phases and their corresponding compressibility factors. UNIQUAC activity coefficient model is chosen to account for the non-ideality of solid phase. The resultant equilibrium ratios are included in the three phase equilibrium calculations and stability analysis. The proposed model is applied to calculate the amount of precipitates and WAT for six North Sea oil samples to evaluate the prediction accuracy. The crude oil samples contain several cuts and heavy fractions. The PC-SAFT EOS parameters for petroleum plus fractions are estimated using available correlations in literature. In addition, the modeling results are compared with the results of Lira-Galeana et al. [1], Pedersen et al. [2] and Dalirsefat and Feyzi [3] models. The results show improvements and demonstrate the proposed model as a comparable forecasting tool for Wax precipitation modeling in oil transmission and processing facilities.