Thermodynamic and kinetic study of methane hydrate formation in surfactant solutions: From macroscale to microscale

This work investigated the thermodynamics and kinetics of methane hydrate formation in the presence of cetyltrimethylammonium bromide (CTAB) solutions at both micro and macro scales. The cage occupancy and hydration number of methane hydrates for different CTAB solutions were determined using Raman spectra and thermodynamic calculations. The obtained results indicated that the cage occupancy ranged between 3.1 and 3.6 while the hydration number ranged between 5.9 and 6.1. Additionally, the equilibrium conditions of methane hydrate were experimentally determined in both pure water and CTAB solutions, and the results revealed that CTAB had no impact on the phase equilibria of methane hydrate. Thirdly, the kinetic rate constants of methane hydrate were determined through microscopic experiments, and the values for deionized water, 0.001 mol/L CTAB, and 0.003 mol/L CTAB were determined to be 5.80 × 10–6, 6.30 × 10–6, and 6.50 × 10–6 (mol/(m2·s·MPa)), respectively. Moreover, large-scale reactor experiments demonstrated the ability of CTAB to promote the hydrates formation. Specifically, gas consumption rates increased by 26.2% and 13.6% with the addition of 0.001 mol/L CTAB and 0.003 mol/L CTAB, respectively, in comparison to pure water.