Preparation Of Tubular Composite Micro-filtration Membrane And Its Performance

In recent years, membrane separation technology has been widely applied in water treatment industry. But, hollow fiber membrane、flat membrane and spiral-wound membrane module were chosen more frequently in the water treatment industries at present, tubular membrane’s utilization rate was low. Although tubular membrane had some disadvantages, such as less available membrane area and higher price, the high mechanical strength and strong stain resistance of tubular membrane made it have obvious preponderance in the treatment and reuse of industry wastewater. This paper is aimed to prepara a PVDF-PE composite tubular membrane which has well hydrophilia, using the PE blank tubular membrane as the basal tubular membrane, via the immersion precipitation phase inversion method, utilized blending and in-situ polymerization to enhance the hydrophilic performance of membranes, reslove the problem of the hydrophilic modification and pore size controlling of the PVDF-PE tubular membrane.At first, we prepared PEG400/PVDF blending flat membranes via PEG400 solutions with different concentration, to compare their morphology and structure、crystallazation、filtering performance, in order to analyse the influence of different concentration. The results of the experiments showed that the improvement of PVDF concentration in the casting solution couldn’t enhance the reject rate of the tubular membrane. When the concentration of PEG400 was lower than 5%, the membrane surface porosity was increased with the PEG400 content; when the concentration of PEG400 was higher than 5%, the membrane surface porosity was decreased with the PEG400 content. The membrane surface structure could influence the membrane cross section morphology, dense membrane surface was easy to get the finger holes cross section, and porous membrane surface was easy to get sponge-like internal structure. When the PEG400 content was 3wt%, PVDF flat sheet membrane could achieve a larger membrane flux relatively, while the concentration of PEG400 had no obivious influence for the hydrophilicity and pollution resistance.Next, we studied the influence of different ration of MMA/PVDF to PMMA/PVDF blending membranes’ morphology 、 crystallization and hydrophilicity by in-situ polymerication, then investigated the filtering and antifouling performance of the membranes. The PMMA which obtained by in-situ polymerication reduced the crystallization of PVDF, changed the morphology. The membrane reject rate had been improved after adding MMA in the membrane, but it didn’t increase with the concentration of MMA. However, the membrane flux correlated positively with the concentration of MMA, when the MMA’s concentration was 12.5wt%, membrane flux reached the maximum——2861L/(m2·h). The hydrophilic performance of PVDF blending membrane have improved with the increasing of MMA content, when MMA/PVDF=50%, the membrane flux decline rate declined from 15-20% to 0-6%.At last, based on the experiments of the first two chapters, we prepared PVDF/PE tubular membrane with 3%PEG400 blending or 12.5%MMA by in-situ polymerication, then compared the filtration and antifouling performance of self-restraint and commercial tubular membrane. In the PMMA/PVDF-PE tubular membrane, PMMA which polymerized by MMA and PVDF mixture could fill in the blank PE basement tubular membrane evenly, but the membrane surface was relatively rough, easy to be fouled. The porosity of the PMMA/PVDF-PE tubular membrane was larger than the others; it also possessed excellent hydrophilic performance, so its pure water flux was five times than the commercial tubular membrane. While in the filter pressure of 1MPa, the PMMA/PVDF-PE tubular membrane showed excellent flux and wonderful reject performance. The PMMA/PVDF-PE tubular membrane could be blocked by insoluble particle like nano Ca CO3, but it owned a certain ability to resist protein pollution.