Mass transfer analysis of the isochoric–isotherm hydrate-based water desalination from CO2/C3H8 gas mixtures

The purpose of this study is to investigate the composition of the gas, liquid and hydrate phases during gas hydrate formation. The kinetics of gas hydrate formation from a CO₂/C₃H₈ gas mixture (initial molar ratio 80/20) under isochoric and isothermal (2, 4 and 6 °C) conditions from pure and saline water has been investigated. Experimental measurement of gas composition was performed by gas chromatography and that of the liquid phase by conductivity analysis. The main and novel finding of the present study is that at early times, the gas hydrate is supersaturated with CO₂, following an equilibrium concentration of CO₂ and C₃H₈ molecules at later times. Initially, the occupancy of the 5¹²6⁴ cages of the SII structure by the CO₂ molecules exceeds the equilibrium plateau. A gradual egress of CO₂ to the liquid/gas phase occurs afterward, eventually resulting in the decrease in CO₂ and increase in C₃H₈ apparent mass transfer coefficients.