The Feasibility of Binary and Ternary Hydrate Mixtures of CH4, CO2 and C3H8 for Metals Removal

Abstract The selection of suitable hydrate formers and their respective gas composition for high hydrate formation driving force is critical to achieve high water recovery and metals removal efficiency in the hydrate-based desalination process. This study presents a feasibility analysis on the possible driving force and subcooling temperatures for the binary and ternary mixtures of methane, carbon dioxide, and propane for hydrates-based desalination process. The driving force and subcooling of the gas systems was evaluated by predicting their hydrate formation phase boundary conditions in 2 wt.% NaCl systems at pressures ranges from 2.0 - 4.0 MPa and temperatures of 1 – 4°C using Modified Peng-Robinson Equation of State in the PVTSim software package. The results suggested that the driving force of CH4-C3H8 and CO2+C3H8 binary systems are similar to their ternary. Thus, the use of binary systems is preferable and simpler than the ternary systems. For binary gas composition CO2+C3H8 (70:30) exhibited a higher subcooling temperature of 8.07 ºC and driving force of 1.49 MPa in presence of 2wt% salt. In case of ternary system (CH4-C3H8-CO2) composition of (10:80:10) provided a good subcooling temperature of 12.86 ºC for hydrate formation. The results favour CO2-C3H8 as preferred hydrate formers for hydrate- based desalination. This is attributed due to the formation of sII structure and as it constitutes 136 water molecules which signifies a huge potential of producing more quantity of treated water.