Study On Performance Of PVDF Hollow Fiber Membrane Distillation

The hollow fiber membrane parameters and modules are the key factor that affects the membrane distillation function. By adjustment of membrane parameters and membrane modules, flux and calorific efficiency can be improved. But at present, the membrane distillation process research tends to the study of different apply process and process mechanism. Systematic experimental study of the membrane parameters and modules of membrane distillation is less. This paper adopts the hydrophobic PVDF hollow fiber membrane made by self and uses 3.5 wt% NaCl aqueous solution as the experiment testing liquid to do direct contact membrane distillation(DCMD) and vacuum membrane distillation(VMD) experiments. It emphasizes the impacts of membrane and modules parameters over MD process function.The results showed that: the permeate flux of DCMD process increased obviously with the enhancement of feed temperature and flowing velocity, but decreased with the increase of membrane thickness. As the inner diameter of the fibers increased, flux nearly has no obvious influent. The permeate flux decreased but the total water production increased as the length and the packing fraction of the modules increased. The module that diameter of 1.0 mm, 0.1 mm thickness of the membrane, and packing fraction of 10.8%, length of 21cm, at the feed temperature 70℃, cool side temperature 30℃, velocity 0.1 m/s, the flux can reached 19.8kg/(m~2 .h).With the increase of the vacuum degree of the cold side and feed temperature, the flux increased obviously, but decreased with the increase of membrane thickness. As the inner diameter of the fibers increased, flux nearly has no obvious influent. The permeate flux decreased but the total water production increased as the length and the packing fraction of the modules increased. The module that diameter of 1.0 mm, 0.1 mm thickness of the membrane, and packing fraction of 10.8%, length of 21cm, at the feed temperature 70℃, velocity 0.66m/s, vacuum degree 0.095MPa the flux can reached 21.8kg/(m~2 .h).The rejection for NaCl was stable and kept at 99.99%, and the conductance of the product water was kept lower than 4μS/cm in all the experiments.Immersed VMD method was proposed in this paper, the special PVDF hollow fiber membrane with good machinery intensity was made out by the optimal process of making membrane and recipe of solution. Experiments indicate that the special membrane has machinery intensity bigger than 0.12MPa, the membrane flux was 5.8kg/(m~2.h) and rejection was 99.99%.