Abstract
In the present work, PEGDME with different molecular weight (Mn ∼ 250 and 500 g/mol) was added into Nafion-based membranes as CO2-philic additive, aiming at improving their CO2 capture performance. The physical, chemical and morphological characteristics of the hybrid membranes were thoroughly investigated using different techniques, including TGA, XRD, SEM and FTIR. The gas transport properties were studied by means of mixed gas permeation tests at different relative humidity conditions. CO2 permeability is greatly enhanced upon the addition of the PEGDME. The addition of 40 wt% PEGDME 250 into the Nafion matrix shows a CO2 permeability of 57.4 Barrer at the dry state, which is 36 folds higher than the pristine Nafion. The presence of water vapor in the gaseous streams further enhances the CO2 permeability and CO2/N2 selectivity, reaching a value of 446 Barrer and 37, respectively, under fully saturated conditions. However, the further increase of the PEGDME content in the Nafion matrix leads to undesirable micro phase separation (defects were observed from the morphological analysis), causing serious loss of the selectivity. Finally, in order to improve the theoretical understanding of the transport mechanism, a modified Maxwell model was successfully applied to describe the separation performances of the resulted Nafion/PEGDME hybrid membrane. The model results suggest that an interconnected CO2-philic structure is obtained upon the addition of PEGMDE and water to the ionomer matrix, forming preferential pathways for gas permeation able to enhance the membrane performance.
Highlights
Gas separation membranes have been applied in different industrial separation processes for many decades, such as H2 purification, N2 production, natural gas purification and vapor recovery [1]
ionic liquids (ILs) have been employed as CO2-philic additives in different membranes, including supported ionic liquid membranes (SILMs), poly–ionic liquid (PIL–IL) composite membranes, polymer
Compared to Nafion, the pure PEG dimethyl ether (PEGDME) curve is relatively simple: there is only one single stage weight loss, which is attributed to the thermal decomposition of PEGDME typically observed at 170 °C and 320 °C for PEGDME 250 and PEGDME 500, respectively
Summary
Gas separation membranes have been applied in different industrial separation processes for many decades, such as H2 purification, N2 production, natural gas purification and vapor recovery [1]. In a more recent report from Shao et al [18], PEGDME was added into a UV cross-linked PEG matrix, where the addition of PEGDME significantly reduced the density of the resulted membranes and increased the free volume, greatly improved the CO2 permeability. PEGDME of two different molecular weight (i.e. 250 and 500) are selected to prepare hybrid membranes with Nafion for CO2 separation, as combining CO2-philic PEGDME with Nafion matrix should further promote the CO2 transport toward a higher value and reduce its dependence on RH. Mixed-gas permeability tests of CO2/N2 in Nafion/PEGDME membranes at 35 °C and various RH conditions were performed, and the effects of different types/amounts of PEG as well as the role of water vapor on the morphology and permeation properties of these hybrid membranes were discussed. The experimental data were interpreted by using a modified Maxwell model, pursuing the achievement of a more fundamental understanding on the effect of PEGMDE addition on the polymer structure and on the permeation mechanisms
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