Effect of EMIM-BF4 Ionic Liquid on Dissociation Temperature of Methane Hydrate in the Presence of PVCap: Experimental and Modeling Studies

Most of the studies done on kinetic hydrate inhibitors (KHIs) are related to the effect of KHIs on hydrate formation, and there are a limited number of research works on hydrate dissociation conditions in the presence of KHIs. In the subject of hydrate remediation, knowing the effects of KHIs on hydrate dissociation conditions is necessary. In this work, first, the effect of the presence of poly vinyl caprolactam (PVCap) as a KHI on methane hydrate dissociation conditions has been studied and the results show that dissociation temperature of methane hydrate in the presence of PVCap is higher than the noninhibited system and increases hydrate stability conditions. Then, at the second stage, the effects of EMIM-BF4 as a synergist for PVCap on methane hydrate dissociation conditions have been investigated. Different concentrations of EMIM-BF4 and PVCap have been studied, and a thermodynamic model has been developed to predict hydrate dissociation temperature. The experiments reveal that adding EMIM-BF4 to an aqueous solution of PVCap does not have a significant effect on methane hydrate dissociation conditions. The model has been developed based on the fact that the presence of PVCap changes the large to small cavity ratios, L/S, from its theoretical value, i.e. 3/1. It has been assumed that the number of small cavities to water molecules for methane hydrates in the presence of PVCap depends on PVCap concentration. A correlation is proposed to indicate this dependence. Different activity coefficient models have been tested to calculate water activity in the presence of PVCap and IL. The agreement between the experimental data and model results is found to be satisfactory.