【作者】 魏平；

【导师】 高从堦；

【作者基本信息】 浙江大学 ， 化学工程， 2013， 博士

【摘要】 渗透汽化技术以其能耗低,易与发酵耦合等优点在低浓度乙醇浓缩和高浓度乙醇脱水方面有着重要的应用前景。然而高选择性透醇膜材料的缺乏制约了在低浓度乙醇浓缩方向的工业化进程。另外,对于高浓度乙醇脱水,无机-有机杂化膜表现出了优异的分离性能,是近年来的研究热点方向,但该类膜存在着无机颗粒与聚合物基质相容性差及无机颗粒分散性差的问题。针对低浓度乙醇浓缩,本文重点研究了根据不同的膜材料选择原则,筛选了醇溶性和疏水性两种材料,制备透醇膜并考察其分离性能,建立传递模型分析膜的分离特性。对于杂化透水膜,采用硅烷偶联剂对分子筛进行改性,利用端氨基静电效应提高纳米分子筛的分散性以及与聚合物的相容性；考察常规超声分散技术对聚合物膜结构和性能的影响。1.根据溶解度参数原则,选取和考察了醇溶性材料用于低浓度乙醇浓缩的可行性。由于其他醇溶性材料成膜性较差,重点研究了聚乙烯醇缩丁醛(PVB)的渗透汽化性能。结果表明PVB与其良好的醇溶性相反,呈现出优先透水性能。利用和频光谱仪表征了PVB膜材料在空气、以及和乙醇水溶液接触后表面性质的变化。结果发现PVB膜材料表面的基团发生翻转使得PVB膜疏水性下降,通过比较醇接触前后PVB膜接触角变化验证了膜表面疏水性的改变,接触角从83.4°降到70.40,因此,根据溶解扩散机理,表面疏水性下降使得PVB膜对乙醇的优先吸附选择性下降。2.针对醇溶性PVB膜材料渗透汽化选择性异常现象,基于UNIFAC-FV模型分析了乙醇和水在PVB膜中的溶解性质,利用Fujita’s自由体积理论模型分析了乙醇和水在PVB膜内的扩散行为。将两个模型相关联,发现虽然在局部范围内由于PVB和乙醇的亲和力大于水,其溶解选择性大于1,但是乙醇浓度增加带来的溶胀作用以及温度提高使得膜自由体积增大,会造成水扩散系数远远大于乙醇,因此扩散选择性小于1,在这两个相反因素的共同作用下使得PVB膜表现为优先透水性质。另外分析了计算与实验结果间的误差可知,模型整体趋势与实验结果吻合,说明该模型能够很好地描述乙醇和水在PVB膜内的渗透汽化行为。3.根据极性相似原则筛选了聚偏氟乙烯(PVDF)作为膜材料,制备表面有分离选择层的非对称膜。考察了PVDF分子量、刮膜液厚度、挥发温度、溶解温度、凝胶浴组成和温度等对膜结构和膜性能的影响,以渗透汽化性能为指标确定了本实验条件下的最优制膜参数：溶解温度为40。C,蒸发温度为60℃,蒸发时间为20min,凝胶浴温度为25℃,凝胶浴为纯水。该条件下所得膜的分离因子为7.20,通量为2.95 kg.m-2.h-1(真空度：200Pa,温度40℃)。4.针对疏水性表面膜具有醇优先透过的特性,为了进一步提高膜的选择性,通过加入氨水改变相转化过程的方法制备疏水性更好的PVDF非对称膜,并考察了氨水对膜表面性质和性能的影响。接触角测试结果表明氨水的加入提高了膜的疏水性,膜的分离选择性也得到了相应地提高,当铸膜液中氨水浓度为5.88mM时,膜的分离因子由不添加氨水的7.20提高到9.23。其次尝试利用添加氨水的超疏水PVDF改性PDMS膜,发现虽然复合膜的疏水性得到了提高,但是由于表层的PVDF为多孔层未能很好将水排斥到膜的外侧减少与PDMS接触的机会,因此PDMS膜的分离因子提高幅度不大,由5.03提高到5.80。5.高浓度乙醇脱水渗透汽化膜的研究：以强亲水的NaA型分子筛作为添加剂,聚丙烯酸钠(PAAs)为膜基质,采用含端氨基的APTES改性NaA分子筛,利用端氨基自身的静电排斥效应和氨基与羧酸基团的离子对作用提高分子筛分散性以及和PAAs的相容性；考察了超声分散对膜结构和性能的影响。经过APTES改性后的分子筛在PAAs中的分散性得到明显的改善,同时与PAAs的相容性得到了提高,无选择性空穴明显减少。与未改性的杂化膜相比,改性的杂化膜的分离性能得到了提高。超声技术是提高杂化膜中无机颗粒分散性的常规方法,本文发现超声对杂化膜的结构产生了明显的影响：随着超声时间的增加,铸膜液的黏度降低,膜内出现了结晶,当超声时间达到2.5h时,发展成片层结构从而影响膜的渗透通量。综上所述,本文通过对不同原则筛选优先透醇膜材料性能以及过程机理研究,为将来研制优先透醇膜材料提供了思路。同时探明了硅烷偶联剂改性分子筛改善相容性和分散性的机理,以及超声技术对膜结构和膜性能的影响,为制备性能良好的杂化膜提供了新方法。更多还原

【Abstract】 Pervaporation (PV) has become one of the most promising separation process for low concentration ethanol aqueous solution due to low-cost and achieve continuous product coupled with fermentation. However the materials with good ethanol-permselective properties are few and restrict industrialization process. In addition, inorganic-organic matrix mixed membranes show excellent separation performance for ethanol dehydration. However, inorganic materials are hard to well disperse and incompatibility with polymer matrix. This study focuses on the membrane material selection based on different principles. Alcohol-soluble and hydrophobic materials were chosen to separation low concentration ethanol solution and investigated the pervaporation performance. Moreover, transport model was built to analyze the membrane separation properties. For mixed matrix dehydration membrane, the zeolite was modified using 3-aminopropyl-triethoxysilane to improve the dispersibility and compatibility. And the effect of ultrasonic treatment on membrane structure and performance were investigated.1. Base on solubility parameter principle, the feasibility of concentrated ethanol by alcohol-soluble materials was first investigated. This study focused on PVB membrane performance due to the poor film-forming of other material. However, the pervaporation results showed the PVB membranes were more perm-selective to water than to ethanol. Sum frequency generation (SFG) was employed to analyze property of membrane surface in different environment. It was found that the hydrophobicity of PVB membrane decreased due to the change of surface states. The water contact angel of PVB membrane confirmed this result. The contact angel decreased from 83.4° to 70.4°。Therefore, the preferential adsorption selectivity to ethanol of PVB membrane will decrease according to solution-diffusion mechanism.2. Adopted UNIFAC-FV model and Fujita free volume theory to study the solubility and diffusivity of ethanol and water in the PVB membranes. It was found that the sorption selectivity was more than 1 in certain range due to the affinity of PVB and ethanol is greater than the water. However, the diffusion selectivity was far less thanl due to the membrane swelling and free volume increase caused by ethanol concentration and temperature increase. Finally, the combination of sorption and diffusion induced PVB membrane was water perm-selective. Moreover, the comparison between theoretical and experimental results and error analysis showed the model can accurately reflect the sorption and diffusion behavior of water and ethanol in the PVB membranes.3. Selection and preparation of PVDF asymmetric membranes base on similar polarity principle. The effects of molecular weight, thickness of casting blade, evaporation temperature, dissolve temperature, composition and temperature of coagulation bath on the morphology and separation performance of membranes were first investigated. From the sing-factor experiment results, the optimum condition was the material was 6020, evaporation, dissolve temperature and coagulation bath temperature,60℃,40℃,25℃ respectively and composition of coagulation bath was water (separation factor and flux was 7.20 and 2.95 Kg·m-2-h-1).4. In view of the hydrophobic surface membrane has good ethanol-permselective performance. More hydrophobic PVDF asymmetric membranes were prepared by adding ammonia in casting solution in order to improve the selectivity. And the effect of ammonia on the membrane surface properties and performance were investigated. The result of water contact angel demonstrated the hydrophobicity of PVDF asymmetric membranes increased after adding ammonia. As a result, the pervaporation performance was improved that the separation factor increased to 9.23 when the concentration of ammonia was 5.88mM compared to 7.20 without ammonia.Second, try to modified PDMS membranes by super-hydrophobic PVDF and found that although the hydrophoicity of membranes increased, the results of pervaporation showed the performance of PVDF/PDMS was not improved. The separation factor just increased from 5.03 to 5.80. The results were due to porous PVDF surface membrane failed to reduce the chance of water in contact with the PDMS membrane.5. The study on mixed matrix membranes pervaporation dehydration of ethanol. Polyacrylic acid sodium (PAAs) was chosen as the bulk polymer and NaA zeolite was employed as the inorganic filler due to its hydrophilic nature. To improve the dispersion and compatibility of NaA zeolite with PAAs membranes, NaA zeolite surface was modified with amino functional silane-coupling agents. Compared to unmodified zeolite, the dispersibility and compatibility of modified zeolite was improved obviously and non-selective voids eliminated due to the electrostatic repulsion effect and ion-ion interaction between-NH3+group on surface-modified NaA and COO- group on PAAs. Furthermore, the effect of ultrasonic dispersion on the membrane structure and performance were investigated. With increasing ultrasonication time, the viscosity of the casting solution decreased as the chain entanglements decreased and crystallization occurred. When the ultrasonic time exceeded 2.5 h, the relative separation factor decreased due to the appearand & of a lamellar structure.In summary, the study on performance of ethanol perm-selective membrane choose by different selection principles and process mechanism which provides a new idea for ethanol perm-selective membranes development. Silane coupling agent proved to be a good method to improve the compatibility and dispersion of mixed matrix membranes through electrostatic repulsion effect and ion-ion interaction. The high performance mixed matrix membranes can be prepared by this method.更多还原