本文選題：膜蒸餾 + 等離子體改性��； 參考：《鄭州大學》2015年碩士論文

【摘要】：膜蒸餾(Membrane Distillation,MD)是一種以多孔疏水膜為分離介質,以膜兩側蒸氣壓差為推動力的分離過程。MD過程結合了傳統(tǒng)蒸餾方法和膜分離技術的優(yōu)勢,對非揮發(fā)性組分截留率高達100%,并且可以利用低級熱能,是一種高效節(jié)能、環(huán)境友好的新型分離技術。然而膜蒸餾經歷了近半個世紀的發(fā)展仍然未得到工業(yè)化應用,主要原因之一是缺少MD專用膜,因此制備專用的膜蒸餾膜成為MD過程工業(yè)化首先要解決的問題。膜材料的導熱系數(shù)、疏水性以及膜的內部結構等參數(shù)都是影響MD性能的關鍵因素。本文首先以聚砜(PSf)和親水性高分子聚乙烯吡咯烷酮(PVP)為高分子材料,使用雙凝膠浴相轉化法,以溶劑N-甲基吡咯烷酮(NMP)和水的混合溶液作為第一步凝膠浴,制備了表面開孔親水性平板膜,然后使用CF4等離子體改性將膜疏水化后用于MD。結果顯示使用雙凝膠浴法能有效增大膜孔徑,使膜表面變得疏松開孔。使用純溶劑作為第一步凝膠浴時制備的膜性能最為優(yōu)異,疏水改性后接觸角能達到144o,DCMD通量能達到53.33 kg/m2·h(原料進口溫度為70.3 oC),比商業(yè)疏水PVDF膜的高了將近80%。最后使用熱質傳遞模型對膜的曲折因子進行模擬計算。結果表明基于親水基底PSf膜的曲折因子接近1,而疏水PVDF膜的曲折因子則接近2.5,證明使用親水材料作為主體材料制備膜能有效提高孔內連通性,降低傳質阻力進而增大通量。針對FO-MD聯(lián)合工藝中使用MD對FO過程驅動液濃縮,使用超疏水改性前后PVDF膜進行實驗,研究在處理高鹽濃度溶液時超疏水膜的優(yōu)勢。實驗結果表明,超疏水PVDF膜比疏水膜具有更高的通量和截留率。更進一步地,超疏水膜表面由于濃縮導致的結晶量顯著低于一般疏水膜,驗證了超疏水表面在MD過程中存在抗?jié)櫇窈涂拐掣降葍?yōu)良性能。另外,在使用兩種膜進行循環(huán)濃縮實驗時發(fā)現(xiàn)超疏水膜的可重復使用性較好,具有良好的穩(wěn)定性。最后,將超疏水改性前后的PVDF膜用于乳化油溶液的處理,結果表明使用疏水膜進行實驗時膜很容易被潤濕,導致通量和截留率逐漸下降。而使用超疏水膜時,只有長期運行才會出現(xiàn)截留率下降的情況,再一次證明了超疏水膜的優(yōu)良性能。本文針對膜蒸餾過程目前存在的缺乏高性能膜材料等問題,制備了高開孔的親水基膜,通過簡單的等離子體表面改性,將不能直接用于MD過程的親水膜疏水化,并且將疏水性不足、MD效率不高的普通疏水膜進行超疏水化,制備了通量高、穩(wěn)定性良好且耐污染能力強的MD用膜。使用等離子體表面改性法制備MD膜,拓寬了MD膜材料的取材范圍,提高了MD效率,具有良好的工業(yè)化應用前景,對新型高性能MD膜的制備具有重要的指導意義。
[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.
【學位授予單位】：鄭州大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ051.893

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本文編號：1979106