Mutual effects of paraffin waxes and clathrate hydrates: A multiphase integrated thermodynamic model and experimental measurements

This paper presents an extensive analysis of complex wax and hydrate forming systems employing an integrated wax-hydrate thermodynamic model. The developed model uses integration of the UNIQUAC activity coefficient model, CPA equation of state and van der Waals-Platteeuw model, for the description of waxes, fluids and hydrates, respectively. Our recently published multiphase "Gibbs energy minimization" flash algorithm [1] is extended here to identify waxy solid phase(s) and is shown to be robust in characterizing complex systems where several phases, i.e., solid wax, vapour, liquid hydrocarbon, liquid aqueous, ice and hydrate phases (structure sI and sII) may coexist. The accuracy of model predictions is first validated by calculating the wax amount and composition in water-free systems for which experimental data are available. It is then used to explore the mutual effects of hydrates and waxes starting from a simple binary system of methane + n-heptadecane in the presence of water. The model is then used to analyse four multicomponent mixtures and a recombined light oil. The analysis includes investigations into the impact of hydrate formation on wax phase boundary, amount and composition and vice versa, as well as a variety of secondary important effects including the influence of the amount of light end in the feed and impact of the free aqueous phase on the wax amount and phase boundary. (C) 2016 Elsevier B.V. All rights reserved.