Fluid Phase Equilibria 301 (2011) 80–97 Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid A new formulation of the predictive NRTL-PR model in terms of k ij mixing rules. Extension of the group contributions for the modeling of hydrocarbons in the presence of associating compounds Joan Escandell a , Evelyne Neau a,∗ , Christophe Nicolas b a Laboratory M2P2, UMR 6181, University of Méditerranée, Faculty of Sciences of Luminy, 13288 Marseille, France b Laboratory LMGEM, UMR 6117, University of Méditerranée, Faculty of Sciences of Luminy, 13288 Marseille, France article info Article history: Received 7 July 2010 Received in revised form 5 November 2010 Accepted 15 November 2010 Available online 19 November 2010 Keywords: Equation of state Group contribution method Vapor–liquid and liquid–liquid equilibria Enthalpy of mixing abstract A generalized NRTL model was previously proposed for the modeling of non ideal systems and was extended to the prediction of phase equilibria under pressure according to the cubic NRTL-PR EoS. In this work, the model is reformulated with a predictive k ij temperature and composition dependent mixing rule and new interaction parameters are proposed between permanent gases, ethane and nitro- gen with hydrocarbons, ethane with water and ethylene glycol. Results obtained for excess enthalpies, liquid–vapor and liquid–liquid equilibria are compared with those provided by the literature models, such as VTPR, PPR78, CPA and SRKm. A wide variety of mixtures formed by very asymmetric compounds, such as hydrocarbons, water and ethylene glycols are considered and special attention is paid to the evolution of k ij with respect to mole fractions and temperature. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The description of phase equilibria occurring in complex sys- tems such as petroleum fluids with water or glycol has become more and more important with the exploitation of reservoirs in extreme conditions. Besides theoretical association models, such as SAFT (Statistical Associating Fluid Theory) [1,2] CPA (Cubic Plus Association) [3] or the predictive QC-GCEoS [4] equa- tions, simple models based on the cubic Redlich–Kwong or Peng–Robinson EoS still represent a great interest for industrial applications. In particular, petroleum industry currently describes phase equilibria by means of cubic EoS based on the EoS/G E approach; among them: the PPR78 (Predictive Peng–Robinson 1978) EoS [5] has gained an unquestionable success for the prediction of the binary interaction parameter k ij of nonpolar compounds, while the VTPR [6] (Volume Translated Peng–Robinson) model based on the UNIFAC group contribution model appears to be one of the most reliable simple model for the prediction of thermodynamic proper- ties for a wide series of mixtures, involving solids and electrolytes. Nevertheless, these models appear not to be appropriate for the ∗ Corresponding author at: Laboratoire de Chimie Physique, 163 Avenue de Luminy - Case 901, 13288 Marseille Cedex 09, France. Tel.: +33 491 82 9149; fax: +33 491 82 9152. E-mail address: evelyne.neau@univmed.fr (E. Neau). description of strong demixings occurring in mixtures containing water or glycols with hydrocarbons. Due to these limitations, the modeling of reservoir fluids in the presence of associating compounds is mainly performed with empirical composition dependent mixing rules, such as the SRKm (Soave–Redlich–Kwong modified) and SRK-KD equations, respec- tively, proposed by Panagiotopoulos and Reid [7] and Kabadi and Danner [8]. The main interest of this correlation relies on the exten- sive set of interaction parameters available in industrial simulators, in particular for water–hydrocarbon mixtures; however, no spe- cific parameters were developed for glycol–hydrocarbon systems, which are therefore modeled with standard values. In addition, the SRKm mixing rule suffers from the Michelsen–Kirstenmacher syn- drome [9] which might affect the representation of highly dilute mixtures. The NRTL-PR [10] equation of state was thus developed to pro- vide a simple cubic EoS allowing a full prediction of phase equilibria occurring in highly nonideal systems. The model is based on the EoS/G E approach, in which the Peng–Robinson equation of state is associated with a generalized version of the NRTL model [11]. In this work, the model is reformulated with predictive k ij temperature and composition dependent mixing rules and new interaction parameters are proposed between permanent gases, ethane and nitrogen with hydrocarbons, ethane with water and ethylene glycol. Results obtained for excess enthalpies, liquid–vapor and liquid–liquid equilibria with the NRTL-PR group contributions are compared with those provided by the literature 0378-3812/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2010.11.009