A fundamental mass transport model based on molecular insights for pervaporation desalination

Pervaporation (PV) desalination, a promising technology to produce clean water, lacks some fundamental understanding of the molecular transport mechanism. We perform molecular dynamic simulations to unravel the molecular transport mechanism in polyvinyl alcohol PV desalination membranes. It is revealed that the dispersion forms of confined water molecules transform from nano-sized clusters to single molecules as the concentration gradient decreases within the membrane. The diffusion modes of confined water molecules with various dispersion forms are distinguished. The solvation free energy analysis explains the compensation mechanism of ions in membranes. Based on the simulation results, an analytical expression is derived to describe the relationship between the transport diffusion coefficient and solubility of confined water molecules. Using this analytical expression, a solution-diffusion model is established to calculate the permeability of PV desalination, and is validated with experimental results. These findings pave an avenue for building a theoretical framework of PV desalination.