Phase behavior of ethane hydrate system in the presence of ammonium bromide

The three-phase equilibrium curves of hydrate, aqueous, and gas phases in the ternary system of ethane (C2H6), ammonium bromide (NH4Br), and water were measured at pressures up to 3 MPa and temperatures of 278.45-283.76 K. The phase equilibrium curves exhibit two trends; the curve paralleled with that of simple C2H6 hydrate and the one steeper than that of simple C2H6 hydrate. The latter implies the incorporation of NH4Br into C2H6 hydrate while the former indicates the thermodynamic inhibition effect of NH4Br. To investigate the incorporation of NH4Br, Raman spectra of the N-H stretching vibration of NH4+ were analyzed. Raman spectra imply the existence of the motionally restricted NH4+ in the formed hydrate. Both results from the phase behavior and Raman spectra imply the formation of C2H6 + NH4Br semi-clathrate hydrates.