The Preparation And Application Research Of Ultra-filtration Membrane In Coking Waste Water

Polyvinylidene fluoride (PVDF) is a kind of preparing membrane polymer whichhas good chemical stability, thermal stability, high mechanical strength and low price.This research aims to prepare a membrane applying to treat coking waste water withPVDF as raw material. The best condition of PVDF preparation is determined byorthogonal experiment, and the optimum dosage of additive agent is obtained bysingle factor experiment. The modified experiments of PVDF are managed in coatingmodification and blending modification.At first, the orthogonal experiment is used to determine the optimum condition.In the experiments, the additives are LiCl and polyvinylpyrrolidone (PVP) and thesolvent is N,N-dimethyl acetamide (DMAc). The results of experiment indicate thatthe15%PVDF/2.4%PVP/1.6%LiCl/81%DMAc reacts in75℃oil bath and thecoagulating bath is water in35℃. At the moment, the pure water flux of membraneis383.75L/m2·h, COD removal rate is77.3%, the porosity is84%, the contact angle is66.1degrees.Then the coating modification of PVDF chooses nomination TiO2as modifierand the concentration and time of modification are researched. The results indicatethat the best condition is0.5%concentration of TiO2and18h coating time. And thepure water flux is316.43L/m2·h, COD removal rate is80.62%, porosity is81.34%and contact angle is41.25degrees. The membrane has relatively high pure water fluxand the surface hydrophilicity is improved.Afterwards the blending modification of PVDF uses nomination TiO2andembellished nomination TiO2by polypethylene glycol (PEG). The results of TiO2blending modification experiment indicate that the membrane is the best when theTiO2concentration is0.4%. At this time the pure water flux of membrane is225.27L/m2·h, COD removal rate is71.54%, the porosity is83.50%, the contact angleis57.75degrees. The results of PEG-TiO2blending modification experiment indicatethat the membrane is the best when the PEG concentration is0.12%. At this time the pure water flux of membrane is308.48L/m2·h, COD removal rate is79.19%, theporosity is86.78%, the contact angle is54.20degrees. Thus it can be seen that thesurface hydrophilicity is improved and membrane antipollution is enhanced.At last, the modified membranes are used in COD desorption of high concentratecoking waste water. The results indicate that the PEG-TiO2membrane has high CODremoval rate and recovery rate of pure water flux. It can be further studied on the oilremoval process of the pretreatment of coking waste water. When it is used to treatcocking waste water with the COD value of5125.40mg/L,the pure water flux ofmembrane is308.48L/m2·h and the COD removal rate is82.86%, the waste water fluxstabilizes at151.94L/m2·h, the flux recovery is87.81%. It follows that the PEG-TiO2blending membrane can more effectively treat high concentration coking water andhas high antipollution and recycling rate.Combining the results of experiments, the PEG-TiO2modified membrane ismore suited to use to treat coking waste water. It can be further researched to use inindustrial process in coking waste water treatment.