高通量、耐污染、超疏水的膜蒸馏用膜的制备及应用研究

发布时间：2018-06-04 22:31

本文选题：膜蒸馏 + 等离子体改性　；参考：《郑州大学》2015年硕士论文

【摘要】：膜蒸馏(Membrane Distillation,MD)是一种以多孔疏水膜为分离介质,以膜两侧蒸气压差为推动力的分离过程。MD过程结合了传统蒸馏方法和膜分离技术的优势,对非挥发性组分截留率高达100%,并且可以利用低级热能,是一种高效节能、环境友好的新型分离技术。然而膜蒸馏经历了近半个世纪的发展仍然未得到工业化应用,主要原因之一是缺少MD专用膜,因此制备专用的膜蒸馏膜成为MD过程工业化首先要解决的问题。膜材料的导热系数、疏水性以及膜的内部结构等参数都是影响MD性能的关键因素。本文首先以聚砜(PSf)和亲水性高分子聚乙烯吡咯烷酮(PVP)为高分子材料,使用双凝胶浴相转化法,以溶剂N-甲基吡咯烷酮(NMP)和水的混合溶液作为第一步凝胶浴,制备了表面开孔亲水性平板膜,然后使用CF4等离子体改性将膜疏水化后用于MD。结果显示使用双凝胶浴法能有效增大膜孔径,使膜表面变得疏松开孔。使用纯溶剂作为第一步凝胶浴时制备的膜性能最为优异,疏水改性后接触角能达到144o,DCMD通量能达到53.33 kg/m2·h(原料进口温度为70.3 oC),比商业疏水PVDF膜的高了将近80%。最后使用热质传递模型对膜的曲折因子进行模拟计算。结果表明基于亲水基底PSf膜的曲折因子接近1,而疏水PVDF膜的曲折因子则接近2.5,证明使用亲水材料作为主体材料制备膜能有效提高孔内连通性,降低传质阻力进而增大通量。针对FO-MD联合工艺中使用MD对FO过程驱动液浓缩,使用超疏水改性前后PVDF膜进行实验,研究在处理高盐浓度溶液时超疏水膜的优势。实验结果表明,超疏水PVDF膜比疏水膜具有更高的通量和截留率。更进一步地,超疏水膜表面由于浓缩导致的结晶量显著低于一般疏水膜,验证了超疏水表面在MD过程中存在抗润湿和抗粘附等优良性能。另外,在使用两种膜进行循环浓缩实验时发现超疏水膜的可重复使用性较好,具有良好的稳定性。最后,将超疏水改性前后的PVDF膜用于乳化油溶液的处理,结果表明使用疏水膜进行实验时膜很容易被润湿,导致通量和截留率逐渐下降。而使用超疏水膜时,只有长期运行才会出现截留率下降的情况,再一次证明了超疏水膜的优良性能。本文针对膜蒸馏过程目前存在的缺乏高性能膜材料等问题,制备了高开孔的亲水基膜,通过简单的等离子体表面改性,将不能直接用于MD过程的亲水膜疏水化,并且将疏水性不足、MD效率不高的普通疏水膜进行超疏水化,制备了通量高、稳定性良好且耐污染能力强的MD用膜。使用等离子体表面改性法制备MD膜,拓宽了MD膜材料的取材范围,提高了MD效率,具有良好的工业化应用前景,对新型高性能MD膜的制备具有重要的指导意义。
[Abstract]:Membrane DistillationMembrane Distillation (MDM) is a kind of separation process with porous hydrophobic membrane as the separation medium and steam pressure difference on both sides of the membrane as the driving force. The MD process combines the advantages of the traditional distillation method and the membrane separation technology. The rejection rate of nonvolatile components is as high as 100, and it can utilize low thermal energy. It is a new separation technology with high efficiency, energy saving and environmental friendliness. However, the development of membrane distillation has not been applied to industry for nearly half a century. One of the main reasons is the lack of special membrane for MD, so the preparation of special membrane is the first problem to be solved in the industrialization of MD process. The thermal conductivity, hydrophobicity and internal structure of the membrane are the key factors affecting the performance of MD. In this paper, polysulfone (PSF) and hydrophilic polymer polyvinylpyrrolidone (PVP) were first used as polymer materials, and the mixed solution of solvent N-methylpyrrolidone (NMP) and water was used as the first step gel bath. The surface hydrophilic membrane was prepared, and then modified by CF4 plasma, the hydrophobic membrane was used for MDD. The results show that the double gel bath method can effectively increase the pore size of the membrane and make the membrane surface porous. The membrane prepared by using pure solvent as the first step gel bath has the best performance. The contact angle of the hydrophobic modified membrane is up to 144oDMD flux of 53.33 kg/m2 / h (the inlet temperature of the raw material is 70.3oC ~ (-1), which is nearly 80% higher than that of the commercial hydrophobic PVDF membrane. Finally, the heat and mass transfer model is used to simulate the zigzag factor of the membrane. The results show that the zigzag factor of PSF membrane based on hydrophilic substrate is close to 1, while the zigzag factor of hydrophobic PVDF membrane is close to 2.5. It is proved that using hydrophilic material as the main material to prepare membrane can effectively improve the intrapore connectivity, reduce the mass transfer resistance and then increase the flux. In view of FO-MD combined process using MD to concentrate the driving fluid of FO process and using superhydrophobic modification of PVDF membrane before and after modification, the advantages of super hydrophobic film in the treatment of high salt concentration solution were studied. The experimental results show that the superhydrophobic PVDF membrane has higher flux and rejection than hydrophobic PVDF membrane. Furthermore, the crystallization amount of superhydrophobic surface due to concentration is significantly lower than that of general hydrophobic film, which verifies the excellent properties of superhydrophobic surface such as anti-wetting and anti-adhesion in MD process. In addition, it is found that the superhydrophobic membrane has good reusability and good stability. Finally, the PVDF membrane before and after superhydrophobic modification was used to treat emulsified oil solution. The results showed that the membrane was easy to be wetted when the hydrophobic membrane was used in the experiment, which resulted in the decrease of flux and retention rate. However, when the superhydrophobic film is used, the rejection rate will decrease only in the long run, which proves the excellent performance of the superhydrophobic film again. In order to solve the problem of the lack of high performance membrane materials in membrane distillation process, a hydrophilic membrane with high opening was prepared in this paper. The hydrophilic membrane could not be directly used in MD process by simple plasma surface modification. The ordinary hydrophobic membrane with low hydrophobicity and low MD efficiency was superhydrophobically prepared. The MD membrane with high flux, good stability and strong resistance to pollution was prepared. The preparation of MD membrane by plasma surface modification method broadens the range of materials and improves the efficiency of MD film. It has a good prospect of industrial application and has an important guiding significance for the preparation of new high performance MD film.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.893

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