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

Abstract The three-phase equilibrium curves of hydrate, aqueous, and gas phases in the ternary system of ethane (C 2 H 6 ), ammonium bromide (NH 4 Br), 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 C 2 H 6 hydrate and the one steeper than that of simple C 2 H 6 hydrate. The latter implies the incorporation of NH 4 Br into C 2 H 6 hydrate while the former indicates the thermodynamic inhibition effect of NH 4 Br. To investigate the incorporation of NH 4 Br, Raman spectra of the N–H stretching vibration of NH 4 + were analyzed. Raman spectra imply the existence of the motionally restricted NH 4 + in the formed hydrate. Both results from the phase behavior and Raman spectra imply the formation of C 2 H 6  + NH 4 Br semi-clathrate hydrates.