Investigation of the performance of biocompatible gas hydrate inhibitors via combined experimental and DFT methods

Abstract

In this work, three ionic liquids (ILs) from the bio-compatible family of choline cations attached to anions of varying hydrophobicity namely: choline acetate (ChOAc), choline bistriflamide (ChNtf2), and choline chloride (ChCl), have been tested for their gas hydrate inhibition properties for methane and a multi-component Qatari natural gas type mixture (QNG-S1). A rocking-rig assembly (RC-5) has been used to obtain the pressure-temperature (P-T) loops for the studied systems in absence/presence of inhibitors. Two concentrations of 1 and 5 wt% for the choline IL-inhibitors have been chosen which shows distinct effectiveness towards studied single and multi-component hydrate systems. Hydrate suppression temperatures (ΔT) have been calculated from the obtained dissociation data for quantitative analysis of inhibition effect of ILs and its trends against pressure dependence were discussed. Further, to understand the mechanism of hydrate formation and dissociation, the imaging of a complete P-T loop for CH4 + 5 wt% ChNtf2 system has been performed using a borescope camera attached to gas hydrate autoclave (GHA) apparatus. Furthermore, the main features of the interaction mechanism between selected ionic liquids and hydrate structures were elucidated at the molecular level through quantum chemical calculations by using density functional theory (DFT) methods. The results on the effectiveness of bio-compatible ILs as hydrate inhibitors compared to their conventional counterparts have been proposed in the manuscript.