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Preparation of Defect-Free Asymmetric Membranes for Gas Separations

机译：制备用于气体分离的无缺陷不对称膜

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摘要

A technique was developed to prepare defect-free, asymmetric, polymer membranes for gas separation. The preparation method eliminates the need for coatings,which are usually required to render asymmetric,polymer based,membranes gas selective. In this method, a casting solution containing a polymer, solvent, and salt additive is given a desired shape and immersed in a coagulation bath containing a nonsolvent. The nonsolvent is selected to have a low affinity for both the solvent and salt additive. After the complete coagulation of the membrane, the additive salt is leached out in a second bath. This leads to the formation of an asymmetric membrane that has a well-interconnected porous network. The fine membrane structure is preserved by solvent exchange before it is finally dried. Polyetherimide (PEI) (Ultem 1000) membranes were prepared from casting solutions containing 23,25, and 26.5% (wt) PEI, various amounts of lithium nitrate and N-methyl-2-pyrrolidinone (NMP).Membrane performance was determined for the separation of oxygen from air. The effects of polymer concentration,additive salt concentration and the drying process on oxygen permeance, and the actual separation factor of the membrane are discussed.The addition of a small amount of solvent to the coagulation bath improved the leaching of the salt additive and produced membranes with a more open structure. A polymer concentration of 23% produced membranes with the highest performance.
机译：开发了一种技术来制备用于气体分离的无缺陷，不对称的聚合物膜。制备方法消除了对涂层的需要，而涂层通常是使不对称的，基于聚合物的膜气体选择性所必需的。在该方法中，使包含聚合物，溶剂和盐添加剂的浇铸溶液具有所需形状，并将其浸入包含非溶剂的凝固浴中。选择非溶剂对溶剂和盐添加剂都具有低亲和力。膜完全凝结后，在第二浴中浸出添加剂盐。这导致形成具有良好互连的多孔网络的不对称膜。在最终干燥之前，通过交换溶剂来保持微细的膜结构。聚醚酰亚胺（PEI）（Ultem 1000）膜是由含有23,25和26.5％（wt）PEI，各种量的硝酸锂和N-甲基-2-吡咯烷酮（NMP）的流延溶液制备的。从空气中分离氧气。讨论了聚合物浓度，添加剂盐浓度和干燥工艺对膜的透氧性以及膜的实际分离系数的影响。在凝固浴中添加少量溶剂可改善盐添加剂和膜的浸出具有更开放的结构。聚合物浓度为23％时，制成的膜性能最高。

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