Preparation And Superhydrophobic Modification Of PVDF Hollow Fiber Membranes For Membrane Distillation

Membrane distillation(MD) technique is a kind of novel membrane separation technology combines membrane technology with distillation process, which has broad prospects in the fields of chemical separation and enrichment, seawater desalination, industrial waste water treatment and other fields. However, the large scale application of MD has not been realized. One of the reasons for impedeing industrialization is the lack of excellent special membranes for MD.In this study, PVDF hollow fiber membranes were fabricated by thermally induced phase separation(TIPS) method. Superhydrophobic modification was carried out in order to improve membrane distillation flux and reduce membrane fouling. This research provides a basis for the further development and application of MD technology.On the basis of solubility parameter and dielectric constant, the substitution of DOS and DOA for DOP was explored. PVDF/γ-BL/DOP, PVDF/γ-BL/DOA and PVDF/γ-BL/DOS were employed as casting solutions to prepare PVDF flat membranes. The morphologies and properties were characterized. It was found that the interconnected structure was observed in the cross section of membrane which was prepared through PVDF/γ-BL/DOS casting solution. The tensile strength and porosity of this membrane are higher than the membranes prepared from the other two casting solutions.Take PVDF/γ-BL/DOS as casting solution, nitrogen as lumen fluid, water as cooling bath, PVDF hollow fiber membranes with good permeability and interconnected structure were prepared by TIPS method. Effect of spinning parameters on the morphologies and properties was discussed. The porosity and tensile strength of the membrane are 84.36% and 6.941 MPa respectively. The MD flux reaches 77.6kg/m2?h at the feed temperature of 90°C. The membrane exhibited excellent mechanical property and permeability.Take PVDF/DMAc/PG as coating solution, papillary coating layer was constructed on the outer surfaces of PVDF hollow fiber membranes by immersion method. Superhydrophobic PVDF hollow fiber membranes were obtained. Effect of modification parameters on the morphologies and properties were explored. The contact angle of modified membrane reaches 156.6°.Original membrane and modified membrane were adopted in MD process in order to compare the MD flux and properties. At the initial stage of operation, the MD flux of modified membrane is slightly lower than original membrane. However, it attenuated slowly with time. Furthermore, the modified membrane exhibited attractive wetting risistance, pollution risistance and stability.Moreover, in this study, MWCNT-(COOC16H31)n was taken as filler to prepare thermal conductive PVDF composite membranes. An alternating current electric field was introduced to membranes structure orientation. Effect of MWCNT-(COOC16H31)n concentration and electric field orientation on the structure and properties of membranes was explored. It provides a basis for the further application in heat exchangers and promotes the development of thermal conductive polymers.