| Ultrafiltration separation technology is developed as a new type efficient separation technology in recent years. Compared with the traditional separation method, it has obvious advantages. So ultrafiltration separation technology has been widely applied in many fields.However, there are two main problems in the application process of ultrafiltration technology:one is that the membrane is easily polluted, which leads to the sharp decline of flux; the other is the high cost of membrane material, which increases the cost of membrane preparation.In this study, the flat ultrafiltration membrane is proposed to develop a low cost anti-polluted ultrafiltration membrane, which is prepared by blending hydrophilic polymers and PVC (polyvinyl chloride, PVC). This flat ultrafiltration membrane takes cheap PVC based the material; polyvinylpyrrolidone (PVP) as the pore-forming agent; N-N dimethyl acetamide (DMAC) as the solvent; and respectively uses the twain-80 (Tween80),polyethylene glycol 300 (PEG300), polyethylene glycol 1000 (PEG1000) and polyethylene glycol 20000 (PEG20000) to improve the performance of membranous hydrophilic.Through characterizing the microstructure of membrane, it is found that the prepared membrane forms a typical asymmetric structure, with the upper layer of membrane as compact separation layer, the lower layer as the fingerlike-hole supported layer. The addition of modifier does not change the structure and the forming mechanism of membrane. It is found that above-mentioned additives can improve the material hydrophilic of PVC membrane in different degrees. When the contents of Tween80, PEG300, PEG1000 and PEG20000 in the membrane are 6wt%, 8wt%, 8wt% and 6wt% respectively, the superficial contact angles of membrane material will decline by 57%, 29%, 39% and 57% respectively. It is analyzed that the addition of polymer with hydrophilic group can increase the membranous surface energy, which improves the hydrophilic of membrane.In this study, the fracturing wastewater of Daqing oilfield is taken as filtrate, and the anti-fouling performance of PVC membrane is examined by before and after modification. It is found that the PEG1000/PVC membrane has good oil resistance, lower than the membranous fouling degree of pure PVC membrane. When PEG1000 content in the membrane is 6wt%, the recovery rate of flux can reach 63.2%. It is analyzed that the modified layer has the anti-fouling performance mainly because of hydrophilic groups' brush formed on membrane surface by the membranous hydrophilic groups; so the oil droplets can not be easy to adsorb on the membrane surface because of energy consumption and overcoming resistance.The study also found that the thickness of the membrane will influence the mechanical strength and the flux. When the membrane hydrophilic is improved, the membrane components are more likely lost in the water, therefore, the mechanical properties of membrane will be affected. It is very necessary to choose a kind of additive which can both improve the hydrophilic of membrane and not affect the membrane mechanical strength. In this study, the composite membrane layer supported by polyester fiber was also prepared.Compared with the flat membrane, the composite membrane has better mechanical strength and flux. Using the composite membrane for a long-term research of water purification efficiency, it is found that the flux of the modified membrane is 14% higher than the unmodified membrane, and the attenuation of flux is 23% lower. |
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