A Study On The Enhancement Of PVDF Ultrafiltraiton Membrane Preparation And Exploration For Highly Efficient Additive

Nowadays, the worsening condition of water shortage and pollution together with the advancing drinking water quality standard make people pay more attention to the ultrafiltration technology, which is characterized with high efficiency, low energy consumption, simple treatment process and free of additive addition, however, membrane fouling and some other related problems restrain its application in water treatment engineering, and there are many solutions but the improvement of membrane itself is a critical one to resolve the problems.In the present research, a quite stable polymer PVDF was employed as membrane material. First, membranes were prepared with PVP and LiCl as additive respectively via a dry/wet phase inversion method, effect of membrane formation factors on the permeability, separation performance, pore structure, hydrophilicity and mechanical strength of the membranes were investigated for the two types of casting solution system, and the corresponding mechanisms were analyzed, in this way, the dry/wet phase inversion method for PVDF ultrafiltration membrane preparation was enhanced. The results indicated that the type of additive is the most influencing factor, and the enhanced membrane preparation conditions are as follows: PVDF 16～18wt%, additive content 2～4 wt%, evaporation time 10～30s, indoor temperature 15～25℃, relative humidity 60-90%, coagulation temperature(distilled water) 20～30℃, solvent DMAc. Under the enhanced membrane formation process, this research made a try to seek highly effective additives, the results demonstrated that Fe-DS-S, glycerol-S1, citric acid-S2 and several other chemicals could remarkably improve the membrane permeability while its separation performance would not be decreased substantially, and the general performance of them are comparable to the commonly used lithium chloride or even better than it. Further research found that the introduction of Fe-DS-S in the casting solution could increase the pure water flux of membrane for three times while its rejection of pepsin(35K) is still higher than 75.6%, moreover, this type of membrane exhibits good compaction resistant behavior. Water purification performance of the Fe-DS-S PVDF membranes displayed the powerful effectiveness on the control of turbidity, color, and bacterial in effluent after membrane filtration. The presence of FeOOH on membrane surface would enhance the hydrophilicity of the membrane, thus would relieve the membrane fouling caused by adsorption of hydrophobic organics, this is of great significance for the application of membrane separation technology in water treatment engineering.Basing on above analysis, effect of composite additive was studied, it was found that it is practical to adjust the performance of membrane according to the combination of different excellent additives, and the proper combination of nanomaterial and general additive could double the pure water flux while the the separation performance was maintained, and sometimes it is even possible to increase the permeability and rentention capability simultaneously, the combination of SiO₂ (MO-1) and Fe-DS-S set an good example for this.