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首页> 外文期刊>Separation and Purification Technology >Membrane characterisation by SEM,TEM and ESEM:The implications of dry and wetted microstructure on mass transfer through integrally skinned polyimide nanoflltration membranes
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Membrane characterisation by SEM,TEM and ESEM:The implications of dry and wetted microstructure on mass transfer through integrally skinned polyimide nanoflltration membranes

机译：SEM，TEM和ESEM表征膜：干湿法微结构对通过整体蒙皮的聚酰亚胺纳米滤膜传质的影响

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Due to their excellent resistance to a range of solvents,integrally skinned polyimide membranes have been used to achieve selective separations in a range of solvent-based industrial and lab-scale chemical operations.These include:homogeneous catalyst recycle,petrochemical dewaxing,solvent exchange and chiral resolutions.However,despite the widening scope of use of these membranes,there is still little understanding of how the microstructure defines their separation performance.As a first step towards determining this,integrally skinned nanoflltration membranes were fabricated by phase inversion using Lenzing P84 polyimide.The microstructures of these membranes,dry and wetted in solvent,were investigated by SEM,TEM and ESEM(where appropriate).SEM and TEM imaging of dry membranes revealed that this type of polyimide membrane has three microstructurally distinct polyimide layers,not the two indicated in prior literature.Furthermore,TEM images reveal nano-sized pore-like features in the polyimide structure,which indicate that the transport mechanism is probably neither only solution-diffusion nor only pore flow.ESEM imaging showed that when saturated in ethanol at the working pressure of the ESEM(5.50 Torr),the microstructure of the membranes changes;it is wispy and thus quite different to the more solid polymer nodules and interconnected polymer network observed in the dry membranes.Thus,transport and separation mechanisms based on the structure of the dry membranes may not be accurate.Overall,these results indicate that the current theory used to describe polyimide membrane mass transfer and separation performance(where it is based on dry membrane microstructures),most likely needs to be rethought.
机译：由于其对多种溶剂的优异耐受性，整体蒙皮的聚酰亚胺膜已被用于在多种基于溶剂的工业和实验室规模的化学操作中实现选择性分离，包括：均相催化剂循环，石化脱蜡，溶剂交换和然而，尽管这些膜的使用范围不断扩大，但对微结构如何定义其分离性能的了解仍然很少。作为确定这一点的第一步，使用Lenzing P84聚酰亚胺通过相转化制备了整体蒙皮的纳米滤膜。通过适当的SEM，TEM和ESEM研究了这些膜在溶剂中干和湿的微观结构。干膜的SEM和TEM成像表明，这种类型的聚酰亚胺膜具有三个微结构不同的聚酰亚胺层，而不是两个此外，TEM图像显示了p中的纳米孔状特征Olyimide结构，表明其传输机理可能不仅是溶液扩散，而且不是孔流。ESEM图像显示，当乙醇在ESEM（5.50 Torr）的工作压力下饱和时，膜的微观结构发生变化;稀疏的，因此与在干膜中观察到的更固态的聚合物结节和相互连接的聚合物网络完全不同。因此，基于干膜结构的传输和分离机理可能不准确。总体而言，这些结果表明，目前使用的理论是为了描述聚酰亚胺膜的传质和分离性能（基于干膜的微观结构），最有必要重新考虑。

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