Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Application of Peng-Robinson equation of state for modelling the multiphase equilibrium properties in Athabasca bitumen/ethane mixtures Ting Sun a , Ali Takbiri-Borujeni b, ⁎ , Hossein Nourozieh c , Ming Gu b a China University of Petroleum, Beijing, China b West Virginia University, United States c Computer Modelling Group Ltd, Canada ARTICLE INFO Keywords: Phase behavior Bitumen Peng-Robinson equation of state Solvent ABSTRACT Phase behavior of (bitumen + solvent) mixtures and their properties are essential for surface upgrading methods and enhanced oil recovery applications. The objective for this work is to systematically model the phase par- titioning and component distribution in the (bitumen + solvent) mixtures. To perform equation of state mod- elling, compositional analysis of bitumen is utilized to characterize the bitumen sample and its components up to C 100 . The full range of components is utilized in Peng-Robinson equation of state (PR-EOS) to predict the equilibrium phase properties, such as composition and density, in vapor-liquid and liquid-liquid regions. Based on the results, PR-EOS accurately captures the composition of phases, component distribution in each phase, and phase densities. Thereafter, an algorithm is proposed to lump the components on the basis of two-phase envelope generation. The results indicate that Athabasca bitumen and its phase behavior in (bitumen + solvent) mixtures can be well represented in multi-phase regions by four pseudo-components. 1. Introduction Determining phase behavior and estimating the thermodynamic properties for complex fluid systems or ill-defined fluids, such as (bi- tumen + solvent) mixtures, present significant challenges. Despite the importance of phase behavior data for production, pipeline transpor- tation, upgrading, and refining of such fluids, limited experimental data for bitumen-containing mixtures have been reported in the literature. This is due to the fact that experimental measurements for these sys- tems are usually expensive and time-consuming. This issue is even more pronounced when multiple phases form at equilibrium conditions. Modelling is a credible alternative for studying the phase behavior and the interaction of (bitumen + solvent) systems. The thermodynamic modelling of (bitumen + solvent) systems is limited compared to simple hydrocarbon systems and conventional oil. This might be due to complex nature and lack of a known character- ization method for heavy oil and bitumen. Although different char- acterization schemes, as stated by Kumar and Okuno [1], have been proposed for different reservoir fluids [2–6]; for example, gas con- densates [7–10], volatile oils [11,12], near-critical fluids [13–16], the methods for heavy oil and bitumen characterizations are limited [1,17–18]. This led to variety of models in literature for pseudo-com- ponent determination in the phase behavior study of (bitumen + solvent) mixtures. Mehrotra et al. [19] utilized Bishnoi et al. [20] characterization method to develop five pseudo-component in order to study the phase behavior and solubility of carbon dioxide and ethane in Athabasca and Peace River bitumens using Peng-Robinson equation of state (PR-EOS). The critical properties calculated from Kesler and Lee [21] correlation provided a good agreement with the experimental solubility data. Fu and Puttagunta [22] and Fu et al. [23] considered a pseudo-component in the vapour-liquid equilibrium calculations of (bitumen + solvent) systems for the sake of simplicity. They developed a temperature-de- pendent correlation for binary interaction parameters to represent the vapour-liquid data. Mehrotra and Svrcek [24,25] and Mehrotra et al. [26] utilized PR-EOS along with Kesler and Lee [21] correlation for calculating critical properties to estimate the nitrogen, carbon mon- oxide, methane, carbon dioxide, and ethane solubility in Athabasca, Cold Lake, and Wabasca bitumen at the temperatures up to 110 °C and at the pressures up to 10 MPa. The bitumen was characterized using three pseudo-components which represent distillable maltene, un- distillable maltene, and asphaltene that could adequately match the experimental data. Frauenfeld et al. [27] estimated the methane, ethane, propane, and carbon dioxide solubility in Lloydminster Aber- feldy oil and a blended Cold Lake/Lloydminster oil using PR-EOS. The binary interaction parameters were adjusted to tune the model. https://doi.org/10.1016/j.fuel.2019.04.106 Received 28 February 2019; Received in revised form 11 April 2019; Accepted 16 April 2019 ⁎ Corresponding author. E-mail address: Altakbiri@mail.wvu.edu (A. Takbiri-Borujeni). Fuel 252 (2019) 439–447 0016-2361/ © 2019 Elsevier Ltd. All rights reserved. T