Preparation and characterization of polyimide membranes modified by a task-specific ionic liquid based on Schiff base fo
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RESEARCH ARTICLE
Preparation and characterization of polyimide membranes modified by a task-specific ionic liquid based on Schiff base for CO2/N2 separation Pengzhi Bei 1 & Hongjing Liu 1 & Ying Zhang 1 & Yingjia Gao 1 & Zhiqiang Cai 1 & Yanming Chen 1 Received: 20 December 2019 / Accepted: 16 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In order to increase CO2/N2 selectivity of polyimide (PI) dense membranes, task-specific ionic liquid (TSIL), 1-aminoethyl-3buthylimidazolium hexafluorophosphate ([NH2ebim][PF6]), has been grafted to polymer chains as large side groups by forming the structure of Schiff base for the first time. The modified membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), dynamic thermomechanical analysis (DMA), and stress-strain testing. The results showed that TSIL had been successfully linked to PI chains by forming “C=N.” The modified membranes had more free volume, which was favorable to the improvement of CO2 permeability. The reduction of spin degree of freedom means the rigidity increment of polymer chains, which indicated that the selectivity of CO2/N2 can be enhanced. As a result, CO2 permeability of the modified membrane (TSIL-0.8 wt%) was increased from 5.28 to 10.2 Barrer, and CO2/N2 selectivity was increased from 21.9 to 92.8 at 30 °C and 0.1 MPa. Meanwhile, the effects of different feed pressures (0.1–0.6 MPa) and different operating temperatures (30–60 °C) on CO2/N2 transport properties were also investigated, and it was found that the separation performances of the modified membranes had already exceeded Robeson’s upper bound. Keywords Polyimide . Schiff base . [NH2ebim][PF6] . Rigidity . Selectivity
Introduction With the advance of human society, industrialization process has been accelerated dramatically. Massive emission of greenhouse gases, especially carbon dioxide (CO2), has exerted an adverse impact on the global environment (Julien and Heldebrant 2018). But at the same time, increasing importance has been attached to CO2 utilization such as manufacturing soda industry (Gajda et al. 2016), preparation for foaming agent in plastics industry (Tsivintzelis et al. 2016), shielding gas in welding process (Valensi et al. 2018), and supercritical
Responsible editor: Angeles Blanco * Hongjing Liu [email protected] * Yanming Chen [email protected] 1
School of Petrochemical Engineering, Shenyang University of Technology, Liaoyang 111003, People’s Republic of China
extraction technology (Fujii et al. 2018). Therefore, the recovery and utilization of CO2 play important roles in contemporary age. Gas separation membrane is progressively becoming a representative technology in separating CO2 from mixed gas. Lower energy consumption, lower investment costs, smaller footprint, and friendly environment offer numerous advantages for the application of membrane separation (Bian et al. 2017; Jhaveri and Murthy 2016). Nevertheless, the tra
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