脱羧
膜
聚合物
傅里叶变换红外光谱
选择性
气体分离
高分子化学
化学工程
羧酸
膜结构
磁导率
吸附
材料科学
化学
分析化学(期刊)
色谱法
有机化学
催化作用
吸附
工程类
生物化学
作者
Raymond Thür,Vincent Lemmens,Daan Van Havere,Machiel van Essen,Kitty Nijmeijer,Ivo F.J. Vankelecom
标识
DOI:10.1016/j.memsci.2020.118195
摘要
Thermally induced decarboxylation cross-linking of carboxylic acid bearing polyimides has been recently introduced to create cross-linked polymer membranes with enhanced gas permeability. The main focus has been on the cross-linking of high permeability/low selectivity 6FDA copolymers with a relatively low amount of carboxylic acid groups. In contrast, decarboxylation cross-linking was applied in this work on a low permeability/high selectivity polymer with a large amount of –COOH groups (pure 6FDA-DABA). 6FDA-DABA membranes were thermally treated at different temperatures (100 °C, 180 °C, 250 °C, 350 °C and 400 °C and tested for CO2/CH4 and CO2/N2 separation and thoroughly characterized by ATR-FTIR, TGA-MS, DSC, EDX, XRD, density measurements, fluorescence spectroscopy and gas sorption measurements. Two counteracting mechanisms defined the overall performance of the cured membranes. Physical tightening of the membrane significantly enhanced the CO2/CH4 separation factor with increasing annealing temperature due to an improved polymer chain packing efficiency, which was confirmed by fluorescence spectroscopy and membrane density experiments. In contrast, cross-linking through decarboxylation occurred from 330 °C onward and induced a more open polymer structure for 6FDA-DABA-350 and 6FDA-DABA-400. Consequently, the more open polymer structure resulted in an increase in permeability of all gases. For 6FDA-DABA-350, a synergy was observed between the dilation effect of cross-linking and the tightening effect, causing a simultaneous, strong improvement of both separation factor (+100%) and permeability (+40%). As a result, the membrane performance crossed the 2018 mixed-gas upper bound and scored very close to the 2008 Robeson upper bound. Moreover, the cross-linked 6FDA-DABA-350 showed an increased resistance to CO2-induced plasticization thanks to covalent cross-linking.
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