Experimental measurement and thermodynamic modeling of hydrate stability conditions in the methane + cyclopentane + tetra-n‑butyl ammonium chloride (TBAC) aqueous solution system

Abstract

The present study investigates hydrate dissociation conditions in methane + cyclopentane (CP) and tetra-n‑butyl ammonium chloride (TBAC) aqueous solution. The experimental work was done using an isochoric vessel with varying compositions of the promoters in the pressure and temperature ranges of (1.42 to 4.90) MPa and (291.2 to 298.9) K, respectively. The methane hydrate dissociation pressure was predicted by the Gibbs minimization method. The findings denote that adding CP to the TBAC-containing system shifts the hydrate dissociation temperature of methane to higher values. The results also show an average increase of 12, 9, 5, and 3 K in hydrate dissociation temperature for 5, 10, 20, and 30 wt% TBAC in aqueous solution within the pressures. These results can be caused by the existence of more dodecahedral cages that are inhabited by methane. Thus, it makes hydrates more stable and increases the temperature of hydrate dissociation. On the other hand, adding TBAC to CP containing system has an inhibitor effect. The methane hydrate dissociation temperature was not changed sensibly when a 5 wt% TBAC was added to CP containing system. When the addition of the TBAC weight percentage to CP containing system is increased to 10, the average hydrate dissociation temperature decreases by 1 K within the pressures. When adding 20 and 30 wt% TBAC to CP containing system an average decrease of 2 K and 3 K in the hydrate dissociation temperature is resulted, respectively, within the pressures. The reduction in the hydrate dissociation temperatures can be attributed to salting-out and ion clustering. The experimental data and modeling results for the hydrate dissociation pressures exhibit an AARD of 2.4 %.