Experimental measurement and thermodynamic modelling of phase equilibria of semi-clathrate hydrates of (CO2 + tetra-n-butyl-ammonium bromide) aqueous solution

Abstract

Comprehensive studies on semi-clathrate hydrates phase equilibria are still required to better understand characteristics of this type of clathrates. In this communication, new experimental data on the dissociation conditions of semi-clathrate hydrates of {carbon dioxide+tetra-n-butyl-ammonium bromide (TBAB)} aqueous solution are first reported in a wide range of TBAB concentrations and at different pressures and temperatures. A thermodynamic model is then proposed to predict the dissociation conditions of the semi-clathrate hydrates for the latter system. The (hydrate+TBAB) aqueous solution (H+Lw) phase equilibrium prediction is considered based on Gibbs free energy minimization approach. A modified van der Waals–Platteeuw solid solution theory developed based on the (H+Lw) equilibrium information is employed to predict the dissociation conditions of semi-clathrate hydrates of carbon dioxide+TBAB. The properties of the aqueous solution are estimated using the AMSA-NRTL electrolyte model (considering the association and hydration of ions). The Peng–Robinson equation of state is used for estimating the gas/vapour phase properties. Results show that the proposed model satisfactorily predicts the experimental values with an average absolute relative deviation of approximately 13%.