CO_2捕集炭膜的前驱体结构设计及性能

Precursors Structural Design and Property of Carbon Membrane for CO_2 Capture

从分子结构设计出发,合成了一系列新型刚性、高自由体积的聚酰亚胺炭膜前驱体,并制备了炭膜.采用热重分析(TGA)、傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)研究了不同聚酰亚胺前驱体的热分解特性及在热解炭化过程中化学结构、微结构的变化规律;测试了所制备炭膜的气体分离性能.结果表明,前驱体的自由体积分数显著影响炭膜的气体分离性能;聚合物结构越具刚性,自由体积越大,所得炭膜结构越疏松,极微孔道尺寸越大,越有利于气体分子在炭膜极微孔道中的渗透、扩散与传输.其中,刚性大体积基团芴基、酚酞cardo基团和六氟异丙基的引入能有效破坏分子链间的堆积,提高聚合物的自由体积,所形成炭膜的结构较疏松,均表现出优异的气体渗透性和分离选择性,超越了Robeson上限,解决了传统炭膜气体渗透性能低的问题.特别是采用羟基官能化聚酰亚胺前驱体制备的炭膜在保持较高气体分离选择性的同时,CO_2气体的渗透性高达24770 Barrer(1 Barrer≈7.5×10-18m2·s-1·Pa-1),可实现对CO_2的有效分离和捕集,展现出良好的商业化应用前景.

A series of novel polyimide precursors with rigidity and high free volume was designed and synthesized for the preparation of carbon membranes. The pyrolytic characteristics of polyimides and chemical structures and microstructures of derived carbon membranes were characterized by means of thermogravimetric analysis（ TG）,Fourier transform infrared spectroscopy（ FTIR）,X-ray diffraction（ XRD） and high-resolution transmission electron microscopy（ HRTEM）. The gas separation performance of carbon membranes was evaluated using pure gases H_2,O_2,N_2,CO_2 and CH_4. The results indicated that space configuration and free volume of polyimide precursors significantly affected the microstructures and gas separation performance of derived carbon membranes. The higher the structure rigidity of polyimide was,the higher its fractional free volume（ FFV） was,the microstructure of prepared carbon membrane became looser and ultramicropore size became larger,resulting in the higher gas permeability of carbon membrane. Wherein,introduction of rigid groups such as fluorene,phthalide,hexafluoroisopropyl in polyimides could effectively disrupt the packing between the molecular chains and enhance the FFV of polyimides. The derived carbon membranes with looser microstructures exhibited excellent gas separation performance which surpassed the Robeson upper bond.Especially,the carbon membrane prepared from ortho-hydroxyl functionalized polyimide exhibited the highest gas permeability among the seven carbon membranes,that was 24770 Barrer（ 1 Barrer≈7. 5×10-18m2·s-1·Pa-1） for CO_2,showing an attractive application prospect for the CO_2 separation and capture.