Prediction of phase equilibrium for gas hydrate in the presence of organic inhibitors and electrolytes by using an explicit pressure-dependent Langmuir adsorption constant in the van der Waals–Platteeuw model

Abstract

A new approach is developed for the prediction of the melting curve of gas hydrate with single or multiple additives, including organic inhibitors and electrolytes. This is made possible by combining a predictive equation of state for the fluid phase, the Peng–Robinson–Stryjek–Vera equation of state (PRSV EoS) combined with the COSMO-SAC activity coefficient model through the first order modified Huron–Vidal (MHV1) mixing rule, and a modified van der Waals–Platteeuw model for the hydrate phase. We have examined this method for the change of the melting condition of gas hydrate upon addition of single organic inhibitor, single electrolyte, and a mixture of organic and electrolyte. The absolute average relative deviation in temperature (AARD-T) for these three types of systems are 0.79% (695 data points, T from 230.2K to 294.0K, P from 0.10MPa to 33.9MPa), 0.16% (810 data points, T from 259.5K to 299.1K, P from 0.13MPa to 71.56MPa), and 1.56% (316 data points, T from 248.2K to 292.9K, P from 0.90MPa to 73.28MPa), respectively. We believe that the proposed model is useful for the exploitation of natural or synthetic gas hydrates with multiple additives.