A thermodynamic approach to selection of suitable hydrate formers for seawater desalination

An integrated thermodynamic approach for selecting a suitable hydrate former for desalination prior to process design is presented. From amongst the various formers reported in literature, methane, carbon dioxide (CO2), ethane, propane and iso-butane were chosen for this investigation. Simulation studies related to formation of hydrates in pure and saline water (2-8 wt% salt) for the 5 chosen formers have been conducted to predict phase equilibria along with gas solubility in the aqueous phase. A commercial software HydraFLASH was used for this purpose. In addition, the hydration number and phase change enthalpy associated with hydrate formation/dissociation has been calculated, the latter determined using the Clapeyron equation. Simulation results wherever appropriate were validated with experimental data and good agreement was observed. The implications of the thermodynamic data obtained on desalination process design have been discussed to arrive at a suitable choice of former. The results favor propane and ethane as preferred candidates for hydrate based desalination.