Phase Equilibria Data and Thermodynamic Analysis for Liquid-Hydrate-Vapor (LHV) with High Ethanol Concentrations

Significant portions of the oil reserves in Brazil are located in deep or ultradeep waters. Oil production from these reservoirs implies a constant awareness of gas hydrate formation. The petroleum industry uses thermodynamic inhibitors to reduce the temperature and increase the pressure of hydrate formation in order to ensure hydrate-free production. Because ethanol is abundant in Brazil and it also works as a hydrate thermodynamic inhibitor, its use is more common. However, experimental data of hydrate phase equilibria (HPE) at high ethanol concentrations are scarce, and there is a limited characterization of the existing data. This study reports LHV equilibrium data for C2H6 and a mixture of CH4/C2H6 at high ethanol concentrations and compiles the equilibrium data with ethanol from the literature to evaluate their consistency as hydrate-inhibited systems as well as to present a comparison between predictive approaches for hydrates with ethanol. We apply a consistency test with three criteria to characterize all HPE data with ethanol in the literature data. The experimental data were measured for up to 45 wt % of ethanol. The CH4, CO2, and C2H6 hydrate data deviated from the average behavior established by the criteria for 5 and 15, 2 and 5, and 5 wt %, respectively. The C3H8 hydrate data from the literature obeys the average behavior of the test criteria as well as the C2H6 and CH4/C2H6 data measured. All predictions were in general agreement with the experimental data for ethanol concentrations of up to 15 wt %.