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膜蒸馏（membrane distillation，MD）是用多孔疏水膜作为分离介质，以膜两侧的蒸汽压差为传质驱动力的膜分离过程，能够同时实现热和质地传递，可以有效去除溶液中的易挥发组分，而对非挥发性组分理论上达100%地截留。然而，目前膜蒸馏技术尚未能实现大规模的工业化应用，膜通量不高、易被污染甚至润湿是其主要原因。本论文提出单一多巴胺涂覆改性方法，在商业化聚四氟乙烯（polytetrafluoroethylene，PTFE）微孔膜表面构建了一层超薄、多孔且空气中亲水/水下疏油的特殊表面，同时提高了原PTFE膜的真空膜蒸馏（Vacuum membrane distillation, VMD）通量和耐油污染能力。利用多巴胺在含氧和弱碱性条件下能够在任何材料表面氧化自聚的特性，制备出了多巴胺改性的亲/疏水复合膜并对制备过程进行了调控。在真空膜蒸馏测试中，与原PTFE膜的通量值28.8kg/m2·h相比，多巴胺改性膜（0.5DA@PTFE-4）通量值为89.6kg/m2·h，通量增幅达210%（进料液温度为70℃）。原膜和多巴胺改性膜在长达35小时的真空膜蒸馏长时间运行下，结果表明多巴胺改性膜具有较好的稳定性。最后，通过对膜孔是否浸润以及不同亲水材料改性膜的膜蒸馏性能测试研究，推测膜表面亲水化后引入的极性基团，能促进与极性水分子作用，加快蒸汽汽化速率从而提高多巴胺改性膜的通量。基于多巴胺改性膜在空气中亲水和水下疏油的特性，研究了原PTFE膜和多巴胺改性膜（0.5DA@PTFE-4）在真空膜蒸馏过程中处理含500mg/L的矿物油盐水乳液的分离性能。原膜由于表面疏水易与矿物油滴黏附从而使得膜污染严重甚至润湿，而亲水化后的改性膜则表现出了一定的抗油污染能力，在含油盐水乳液中可有效运行长达30小时;Membrane distillation (MD) is a membrane separation process using a porous hydrophobic membrane as a separation medium with a vapor pressure difference on both sides of the membrane as a mass transfer driving force. It can simultaneously achieved heat and mass transfer and can effectively remove the volatile components of the solution, while theoretically 100% cut off for non-volatile components. However, the membrane distillation technology has not yet been able to realize large-scale industrial applications, The main reasons are attributed to to the lower membrane flux, the membrane easy to be contaminated or even wetted. In this paper, a single dopamine coating modification method was proposed to construct a special surface which ultra-thin, porous and in-air hydrophilic/underwater oleophobic on the commercial polytetrafluoroethylene (PTFE) microporous membrane. The vacuum membrane distillation (VMD) flux and oil pollution resistance of the original PTFE membrane are simultaneously improved.Inspired by dopamine can be coated on the surface of any material under oxygen and weak alkaline conditions, the dopamine modified hydrophilic/hydrophobic membrane was prepared and the preparation process was be controlled. In the vacuum membrane distillation test, the flux value of the dopamine modified membrane (0.5DA@PTFE-4) was 89.6 kg/m2·h as compared with the flux value of the pristine PTFE membrane of 28.8 kg/m2·h, the flux increased by 210% (the feed temperature is 70℃). The pristine membrane and dopamine modified membrane were operated under vacuum membrane distillation for 35 hours, and the results showed that the dopamine modified membrane possessed better stability. Finally, through systematic studies on whether the membrane pores are wetted and the membrane distillation performance of different hydrophilic material modified membranes, we speculated that the introducing polar groups on the membrane surface can promote the membrane interact with polar water molecules and accelerate the vaporized rate. Then the flux of the dopamine modified membrane was improved.Based on the unique characteristic of dopamine modified membrane that is hydrophilic in air and oleophobic under water, the separation performance of the pristine membrane and the modified membrane in the vacuum membrane distillation for treating oily brine (3.5% NaCl brine contained 500mg/L mineral oil ) were studied. The pristine membrane was easily fouled and wetted due to its hydrophobic feature while the hydrophilic modified membrane exhibited a certain degree of resistance to oil pollution and has operated more than 30 hours in oily brine.
|孙位仕. 基于多巴胺改性的亲/疏水复合膜及其膜蒸馏性能[D]. 中国科学院大学,2018.|
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