Chemical Affinity Modeling of Methane Hydrate Formation and Dissociation in the Presence of Surfactants

Methane hydrate formation and dissociation and its kinetics after addition of sodium dodecylbenzenesulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), and Tergitol in the aqueous phase were investigated experimentally along with its storage capacity. The experiments were carried out with surfactant concentrations varying between 0 and 10 000 ppm in the aqueous phase. The nucleation temperature, pressure, dissociation temperature and point, pressure drop, formation rate, and storage capacity were significantly changed by the addition of surfactants in the aqueous phase during hydrate formation and dissociation. Maximum subcooling was required for nucleation after addition of 5000 ppm SDBS. The hydrate formation rate and rate constants were found to increase with the addition of surfactants, while the same were reduced with time. The formation rate increased 443-fold after addition of 10 000 ppm SDBS in the aqueous phase. The maximum storage capacity was found at 1000 ppm SDBS in the aqueous phase, which then decreased with a further increase in concentration. The chemical affinity model was developed for hydrate formation and dissociation and was employed successfully. Chemical affinity, thermodynamic extent of reaction, and affinity decay rates were calculated using the pressure and temperature data from the hydrate formation and dissociation trace with time. Affinity decay rates were increased after addition of surfactants, and the maximum was observed after addition of 1000 ppm SDBS in the aqueous phase. These results suggested that the surfactants, SDBS, CTAB, and Tergitol, improved the hydrate formation and dissociation effectively. The chemical affinity model can be efficiently employed for a better understanding of the hydrate formation and dissociation kinetics along with thermodynamics.