Implementation of Exp-6 potential function in thermodynamic modeling of clathrate hydrates phase equilibria

Abstract

Accurate modeling of clathrate hydrates phase behaviors is of significant importance to petroleum industry. It is well known that accurate consideration of the cavity force field can lead to more accurate predictions of incipient conditions of clathrate hydrates. Intermolecular repulsive force is the dominant force in cavity space that is a determinative factor in taking the guest–host interactions into account. As the result, further modifications in potential function part of van der Waals and Platteeuw (vdWP) solid solution theory could improve the model accuracy. In this study, the influence of repulsive force between guest–host molecules in hydrate cavities was investigated through replacing Kihara potential function by Exp-6 potential function. The vdWP model equations were derived based on new potential function. The pair potential parameters were regressed using equilibrium dissociation conditions data of simple hydrates of natural gas constituents. The determination performances of Kihara and Exp-6 potential functions were compared in aspects of incipient hydrate dissociation conditions and hydrate composition of binary hydrate formers and mixtures of natural gas systems. The results show a promising improvement in vdWP model in case of binary hydrate systems, while the accuracy of the model does not change dramatically in case of natural gas hydrate system. This is due to cancellation of changes in Gibbs energy of occupation for different guest species and the natural gas composition.