芳香聚酰亚胺气体分离膜

The Aromatic Polyimide Membrane for Gas Separation

芳香聚酰亚胺一直在电子、复合材料及粘接剂等领域广泛地应用。最近,聚酰亚胺膜已用于气体的分离过程。这是因为芳香聚酰亚胺是具有高玻璃化温度的玻璃态聚合物,它对小分子比大分子有更大的选择透过性,高选择性是与玻璃态聚合物的僵硬主链,对不同尺寸的分子提供筛分作用相连系的。新开发的芳香聚酰亚胺膜是用联苯四甲酸二酐与芳香二胺缩聚制备的聚酰亚胺溶液制造的。这种中空纤维状的膜是由一个多孔结构支撑的一个很薄的外表面组成的。它可通过聚合物溶液采用干——湿法过程纺丝而成,经溶剂交换干燥,外层的致密部分由计算可知厚度低于0.1μm。它对H_2与CO、CH_4.N_2及其它气体的分离有高度的选择性。由于它具有聚酰亚胺特有的耐高温性能,所以可以在很广的气体加工条件下使用。这种膜对水蒸气有很高的透过性,因而也可用于有机蒸气的脱水,或空气干燥。此膜对水蒸气的透过速度为乙醇的100～200倍。30%的乙醇水溶液,经一次膜分离,浓度可提高到99%。空气干燥系统可产出达到-50℃露点的空气。

Aromatic polyimides which are currently being considered for electronic, composite and adhesive applications are glassy polymer with a high glass transition temperature. The polymer membranes have been used for various gas separation processes, becaues they have high permselectivity for small molecules compared to larger molecules, the high selectivity is associated with a rigid chain backbone of the glassy polymer, providing a sieving effect based on molecular size.The newly developed aromatic polyimide membranes have been manufactured from the polyimide solution prepared by condensation of biphenyltetracarboxylicdianhydride and aromatic diamines, The hollow fiber membrane which has a thin outer skin supported by a porous structure, was prepared by spinning from the polymer solution using the dry-wet process, and then dried by solvent exchange. The thickness of the outer thin dense layer was calculated to be less than 0.1μm. They have high selectivity for H_2permeation rejecting CO, CH_4, N_2 and others. They also enjoy notable durability to high temperature, characteristic to aromatic polyimide and are applicable to wide range of gas processing conditions. The polyimide membrane has high H_2O vapor permeability and can be applied to dehydration of organic vapors, or air drying. The water vapor permeates 100-200 times faster than the ethanol vapor. 30wt% ethanol was concentrated up to 99wt% through one time membrane separation. Air drying system attained up to -50℃ dew point.