Modelling phase equilibria for acid gas mixtures using the CPA equation of state. Part V: Multicomponent mixtures containing CO2 and alcohols

• CPA EoS was applied to predict the phase behaviour of CO2 containing mixtures.
• Multicomponent mixtures of CO2 with alcohols, water and alkanes were investigated.
• Results are presented using various modelling approaches/association schemes.
• CPA satisfactorily predicts multiphase multicomponent phase equilibria.
• Best results are obtained assuming cross association of CO2 with water and alcohols.

The Cubic plus association (CPA) equation of state has been previously applied to a variety of binary systems containing CO2 with alkanes, water, alcohols and glycols as well as a few multicomponent mixtures (with triethylene glycol, water and methane). In this study, we evaluate the performance of CPA for ternary and multicomponent CO2 mixtures containing alcohols (methanol, ethanol or propanol) water and hydrocarbons. This work belongs to a series of studies aiming to arrive in a single “engineering approach” for applying CPA to acid gas mixtures, without introducing significant changes to the model. In this direction, CPA results were obtained using various approaches, i.e. different association schemes for pure CO2 (assuming that it is a non-associating compound, or that it is a self-associating fluid with two, three or four association sites) and different possibilities for modelling mixtures of CO2 with water and alcohols (only use of one interaction parameter kij or assuming cross-association interactions and obtaining the relevant parameters either via a combining rule or using an experimental value for the cross-association energy). It is concluded that CPA is a powerful model that can be used for predictions of multicomponent mixture properties using no adjustable parameters fitted to the multicomponent system data. The results are satisfactory and rather similar with most investigated approaches. However, an overall assessment, also based on the obtained results of this series of studies [Tsivintzelis et al. Fluid Phase Equilib. 306 (2011) 38–56, J. Chem. Eng. Data 59 (2014) 2955–2972, Fluid Phase Equilib. 397 (2015) 1–17], reveals that the best approaches are those where the cross-association (solvation) of CO2 with alcohols and water is explicitly accounted for or alternatively when CO2 is considered to be a self-associating molecule (with three or four sites). Furthermore, it is recommended to use the experimental values of the cross-association energy for CO2–water and CO2–alcohols.

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