Vacuum Membrane Distillation

Effectiveness of Water Desalination by Membrane Distillation Process

“…Fresh water derived from sea water is produced by evaporation processes (e.g., multi-stage flash) or by membrane processes, such as reverse osmosis or electrodialysis. Water desalination can be also accomplished by membrane distillation (MD), which is an evaporation/condensation process of volatile components through a hydrophobic porous membrane [ 1 , 2 ]. The MD membranes are not selective and their pores are filled only by the gas phase.…”

“…The MD membranes are not selective and their pores are filled only by the gas phase. This creates a vapor gap between the feed and the produced distillate, which is usually in direct contact with the membrane [ 1 , 2 , 3 , 4 ]. This MD configuration is called Direct Contact Membrane Distillation (DCMD).…”

“…The hydrophobic nature of the membrane prevents liquid solutions from penetrating into the pores due to surface tension forces. Membranes having these properties are prepared from polymers with a low surface energy, such as polypropylene (PP), polytetrafluoroethylene (PTFE) or poly(vinylidene fluoride) (PVDF) [ 1 ].…”

“…When the temperature is decreased, at a certain temperature the polymer is no longer soluble, and phase separation is induced. After removing the solvent, the resulting pores giving the membrane its unique features [ 1 ]. Variation of membrane morphology and pore structure is possible by controlling the thermodynamic conditions of the process (concentration of the polymer) and the kinetics (temperature, residence and drawing-relaxation time).…”

“…Finger-like microvoids and a sponge-like pore network allow the holding of a large volume of air, which can reduce the heat lost by conduction through the membrane wall. It was found that the polymer dope composition was the most significant parameter controlling the morphology and permeation characteristic of PVDF membranes [ 1 , 5 ].…”