Study On The Microporous Structures Manipulation And Membrane Distillation Nerformance Of PTFE Sheet Membrane

Membrane distillation (MD), originating from the combination of distillation and membraneseparation technologies, can be carried out under a mild condition, the products of which showextremely high purity. The hydrophobic microporous membrane permits the diffusion of gasmolecules and prohibits the liquid through the membrane using the transmembrane pressuredifference as a driving force, resulting in the separation purpose. The low permeate flux anddisappointing antifouling still challenge the application of MD. Therefore,polytetrafluoroethylene (PTFE) membrane with excellent hydrophobicity, stablephysicochemical properties and satisfactory antifouling property, has become a type of idealmembrane material.In view of this, PTFE sheet membrane prepared by an extrusion-stretching-heat settingwas applied in SGMD for desalination, in which effects of the technological parameters on themembrane characteristics and SGMD performance were investigated. In addition, the SGMDparameters were also studied.The results indicate that PTFE sheet membrane with a fibril-node structure can besuccessfully fabricated. The average pore size increases with increasing the longitudinalstretching ratio due to the fibrils elongation. However, the average pore size decreases withenhancing the transverse stretching ratio owing to the abruption of node and therefore the slantfibrils. Furthermore, improved hydrophobicity can be obtained by a heat setting process owing tothe reduction of crystallinity and therefore the low surface tension.In SGMD, the permeate flux increases with increasing the average pore size due to the moremass transfer channel. In addition, the feed temperature and flow rate are positive to thepermeate flux owing to the higher driving force and weaken temperature polarization,concentration polarization, respectively. The feed concentration is negative to the permeate fluxbecause of the saturated vapor pressure reduction and concentration polarization. Finally, the saltrejection rate of the PTFE membrane in SGMD maintains at99.95%, indicating an excellent desalination purpose.In a long-term SGMD, membrane fouling occurs due to the deposition of salt crystallization,leading to a permeate flux decay. Periodic cleaning recovery experiments show that membranefouling can be effectively remitted and the PTFE membrane after washing process show anextremely permeate flux recovery of95%.