摘要
随着近年来“温室效应”、大气污染等问题的日益凸显,气体的分离方法愈来愈受到全球性的关注。采用膜技术进行气体分离已经成为目前最有效的方法之一,其关键因素在于高效分离膜的研究与开发。本研究以金属有机框架材料为掺杂体,聚酰亚胺为母体材料,合成了复合中空纤维膜,并考察了多种气体的分离效果。
本文合成了金属有机框架材料Cu3(BTC)2,采用X-射线衍射(XRD)、扫描电镜(SEM)、投射电镜(TEM)等分析技术表征了其结构和形貌,用氮气吸附脱附等温曲线计算材料的比表面积和孔径分布和孔容大小,结果表明Cu3(BTC)2具有高比表面积(1396m2g-1),对CO2具有较强的吸附能力。
将Cu3(BTC)2混合掺杂于聚酰亚胺中,通过原了力显微镜(AFM)考察了其均匀分散、合成致密平板膜的条件。采用干/湿纺法成功制得PI-Cu3(BTC)2复合中空纤维膜。考察了纺丝液配比、Cu3(BTC)2颗粒度、纺丝温度、压力等条件、酰胺化程序控温等对中空纤维膜的影响。PI-Cu3(BTC)2复合中空纤维膜为非对称膜,其横截面的SEM图显示该膜由致密表面层、指状孔结构层和海绵状结构层构成。Cu3(BTC)2颗粒均匀地分散在致密表面层和指状孔结构中。
考察了不同纺丝工艺及不同后处理程序所得PI-Cu3(BTC)2复合中空纤维膜对气体通量及分离效率的影响,确定达到最佳分离效率的纺丝工艺及后处理程序。研究了PI-Cu3(BTC)2复合中空纤维膜对氢气、二氧化碳、氧气、氮气和甲烷气体的透过率,与气体的动力学直径大小顺序一致,气体通量为氢气>二氧化碳>氧气>氮气>甲烷。随着Cu3(BTC)2含量增加,氢气的渗透通量增加,而二氧化碳,氧气,氮气和甲烷渗透通量减少。因此对H2气体的选择性均随Cu3(BTC)2含量的增加而显著增加。在Cu3(BTC)26wt%的复合中空纤维膜中,H2渗透性比纯聚酰亚胺中空纤维膜增长了45%,而理论选择性增加了2-3倍。
A worldwide greenhouse effect and the serious problems of air pollution cause a global concerning. At present, the membrane technique is the one of the most promising gases separation strategies; the key point for the membrane technique is to design and fabricate new efficient membrane. In this study, a kind of metal organic framework material, Cu3(BTC)2 was chosen as inorganic additives, while Polyimide (PI) was chosen as the continuous polymer matrix, a series mixed matrix membrane (MMM) hollow fibers were synthesized, and the permeable performance of various gases were investigated.
MOF nanocrystal Cu3(BTC)2 was synthesized and characterized by XRD, SEM and TEM. The results of nitrogen adsorption-desorption showed that the products possessed a high surface area of 1396 m2/g, and contained highly ordered micropores. It had high CO2 adsorption capacity.
The images of AFM showed that Cu3(BTC)2 nanocrystals can be highly dispersed into PI matrix without voids. PI-Cu3(BTC)2 MMMs were successfully spun into hollow fiber by the dry/wet-spinning method. The ratio of inorganic additives, the particle size, the spin temperature and pressure, as well as the programmed-temperature imidation proves were investigated to optimize the spin conditions. PI-Cu3(BTC)2 MMM hollow fibers were a kind of in asymmetric membrane. SEM images of the cross-sections revealed the membrane was consisted by surface dense layer, finger-like voids near surface and sponge-like supporting layer. The Cu3(BTC)2 particles were highly dispersed in the surface dense layer and finger-like voids. There was significant plastic deformation of the polymer matrix owing to the strong affinity between the Cu3(BTC)2 and polyimide.
The gas permeance, as well as the selectivity of PI-Cu3(BTC)2 MMM hollow fibers were investigated. The separation permeance of various gases was in the sequence of H2> CO2> O2> N2>CH4 which was consisted with the gas molecular dynamic diameter sequence. The H2 permeance was remarkably enhanced as the Cu3(BTC)2 loading increased, while the permeance of other gases were decreased. Hence the selectivity of H2 to the other gases was significantly increased. When Cu3(BTC)2 loading was 6wt%, the permeation of the H2 increased 45% while the ideal selectivity increased 2-3 times compared to pure polyimide.
引文
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