Experimental and DFT Approach on the Determination of Natural Gas Hydrate Equilibrium with the use of Excess N2 and Choline-Chloride Ionic Liquid as an Inhibitor

This work presents a thorough characterization of Hydrate-Liquid-Vapour-Equilibrium (HLVE) data for a Qatari natural gas type mixture, QNG-S1 obtained using two different experimental methods namely: a bench top reactor and a gas hydrate autoclave. The obtained experimental points were compared to each other and to the predicted curves using a commercial software package (HydraFLASH) and Katz gas gravity method. Another mixture where the QNG-S1 sample was diluted with nitrogen (N2) in a 1:1 ratio was also characterized for hydrate dissociation conditions using rocking cell apparatus only. It has been found out that the obtained HLVE results obtained for QNG-S1 from two experimental and two calculative methods deviate considerably. The possible reasons for these deviations are discussed in detail. They might be coming from uncertainties associated with the QNG-S1 mixture composition, precision of thermocouple associated with bench top reactor and limited prediction power of the software for a complex mixture like QNG-S1.The thermodynamic hydrate inhibition effect of a biocompatible ionic liquid, choline chloride (ChCl) has been tested for both QNG-S1 and QNG-S1+N2 at two concentrations (1 and 5 wt%) using rocking cell apparatus. It has been found that the ChCl is showing a typical classical thermodynamic inhibitor behavior for both the tested mixtures QNG-S1 and QNG-S1+N2 by shifting the hydrate equilibrium towards lower temperature and higher pressure. Likewise, the interaction between ChCl and model hydrate cages was analyzed using Density Functional Theory for characterizing the ionic liquid inhibition mechanism at nanoscopic level.