Preparation Of Poly (Vinylidene Fluoride) Hollow Fiber Microfil Tration Membrane And Experimental Study Of Membrane Fouling Characteristics

In this paper, preparation of poly (vinylidene fluoride) hollow fiber microfiltrationmembrane and experimental study of membrane fouling characteristics were investigated. By controlling such membrane prepariation conditions as polymer concentration in casting solution, coagulation bath composition and temperature, inner bore fluid composition and temperature, air gap and kinds of solvents, PVDF hollow fiber membrane with excellent performance was prepared by thermal induced phase separation(TIPS) method in permeability, porosity, membrane pore structure. By atomic force microscope (AFM),scanning electron microscope (SEM) and other tests. The performance of different hollow fiber membranes as permeability，membrane pore structure and the membrane antifouling trends under the same operating conditions were characterized and compared. Inaddition, the adhesive force of membrane-foulant and foulant-foulant during different water quality conditions (pH, ionic strength, calcium ion concentration and the presence or absence of kaolinite) were studied. The main conclusions are as follows:(1) The hollow fiber membrane TIPS1with excellent performance was prepared bythermal induced phase separation (TIPS) method. When the composition of casting solution20wt%PVDF/40wt%DCAc/40wt%TEP, mixing temperature393k, inner bore liquid as40wt%EG/60wt%DMAc, air gap of10mm, coagulation bath as60wt%TEP/40wt%water, hollow fiber membrane with excellent comprehensive performance were prepared. The pure water flux under0.1Mpa pressure is3600L/m2h, the mechanical strength, porosity and the average pore diameter is3.6Mpa,85.7%,0.124μm, respectively.(2) Compared with hollow fiber membrane TIPS2prepared by single solvent, TIPS1membrane has better permeability, greater mechanical strength, higher retainment rate and more narrow distribution, and the surface of TIPS1membrane is relatively more smooth. In addition, under the same pressure or the same initial flux, compared with TIPS2membrane, TIPS1membrane with smaller pore size is more vulnerable to membrane fouling.(3) When the pH value increases, the adhesion force of membrane-HA, HA-HA decrease; As the ionic strength increases, the adhesion force of membrane-HA,HA-HA increases; When calcium ion concentration increases, due to the effect of "salt bridge" of the calcium ion, both the membrane-HA adhesion force and HA-HA adhesion force showthe change trend of first increases and then decreases.Under various conditions, the membrane flux decline extent as well as to the retainment rate of HA has a certain correlation between the adhesion force of membrane-HA and HA-HA.(4) As pH4.7for BSA isoelectric point, there was a transition from increase to decrease for the adhesion forces of membrane-HA and HA-HA as pH value increased; When the ionic strength increases, the adhesion force of membrane-HA and HA-HA showeda trend of increase; there was a transition from increase to decrease for the adhesion forces of membrane-HA and HA-HA as the pH value increased Under various conditions, the membrane flux decline extent and the retainment rate of BSA have a certain correlation between the adhesion force of membrane-BSA and BSA-BSA(5) With the increase of pH, membrane-SA adhesion force decreased while there was a transition from increase to decrease for the adhesion forces of SA-SA; With the increase of ionic strength, there was a transition from increase to decrease for the adhesion forces of membrane-SA while the adhesive force between SA-SA showed a trend of increase. As the doses of calcium ions increased, both of the membrane-SA and SA-SA adhesion force showed a transition from increase to decrease Under different conditions,the retainment rate of SA and membrane flux decline rate does not have a good correlation with the adhesion forces.(6) Kaolinite particles aggravated the permeate flux decline extent of HA-fouled membrane but mitigated the permeate flux decline extent of BSA、SA-fouled membrane in the initial filtration stage,while the flux decline extent in the later filtration stage had no relationship with kaolinite particles for each type of foulant used. In the presence of the kaolinite particles, the flux recovery rate of HA-fouled membrane declined but the rec overy rate of BSA、SA-fouled membrane increased. Moreover, contrary to BSA and SA,both the membrane-HA adhesion force and HA aggregations increased because of thepresence of kaolinite particlese.