Vapour-liquid equilibria (VLE) and gas hydrate phase equilibria predictions using the cubic-plus association equation of state: CSMGem extension to association EoS model

Abstract

Inaccurate predictions of the vapour-liquid equilibria of polar gas hydrate formers and organic inhibitors can lead to erroneous hydrate phase equilibrium predictions for these associating components. In this work, parameters of the cubic plus association equation of state (CPA-EoS) were optimized for associating components by simultaneous minimization of absolute errors of saturated liquid densities and vapour pressures compared to experimental data. Model prediction accuracies were compared with experimental data after optimizing binary interaction parameters. The proposed association equation of state (based on CPA-EoS) was employed to predict vapour-liquid equilibria of water/N2/H2+non-associating hydrate formers. Water was modelled using a 4C association scheme, i.e., comprising two proton donor and acceptor sites on each water molecule, which has been used previously (Chapman, 1989; Hammerschmidt, 1934; Kontogeorgis, 2006a; Tsivintzelis, 2010; Tsivintzelis et al., 2014; Wichterle and Kobayashi, 1972; Williams and Katz, 1954). For model development and validation, phase envelopes were predicted and validated with experimental solubility data for several systems. Furthermore, the CPA-EoS was also coupled with the Colorado School of Mines Gibbs Energy Minimization (CSMGem) algorithm for hydrate phase equilibria predictions. The predictions were in close agreement with experimental hydrate phase equilibria measurements.