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Gas Transport Properties in Cross-Linked and Vacuum Annealed Poly(oxyindole biphenylylene) Membranes
- Ortiz-Espinoza, Jesús, Ruiz-Treviño, F. Alberto, Hernández-Martínez, Hugo, Aguilar-Vega, Manuel J., Zolotukhin, Mikhail G.
- Industrial & engineering chemistry process design and development 2018 v.57 no.37 pp. 12511-12518
- Fourier transform infrared spectroscopy, carbon dioxide, crosslinking, gases, gels, hydrogen, methane, moieties, nitrogen, permeability, process design, solvents, temperature, wide-angle X-ray scattering
- This work studies useful routes to produce cross-linked poly(oxyindole biphenylylene) bearing a cross-linkable propargyl group, PNPr. Thus, the effect of cross-linking temperature and time on gas permeability and ideal selectivity for a non-cross-linked PNPr membrane to produce a cross-linked PNPr membrane is studied in detail in order to learn how more productive membranes, in terms of permeability–selectivity combinations, and membranes resistant to solvent swelling and CO₂ plasticization may be produced. Systematic studies on structure/processing/property relationship assessed by Fourier transform infrared attenuated total reflectance (FTIR-ATR), gel content (GC [%]), swelling degree (SD [%]), specific volume, wide-angle X-ray diffraction (WAXD), and gas permeability measurements reveal that PNPr membranes cross-linked under vacuum (1 mmHg) at 190 °C for 24 h, and further vacuum-annealed for 1584 h, at 35 °C and 10–³ mmHg, produce membranes that overcome the typical trade-off between permeability and selectivity. In effect, the thermally cross-linked membranes annealed under vacuum for 1584 h, as compared to the non-cross-linked membranes, possess P(H₂) and P(CO₂) that increase by 2.4 and 2.1 factors while selectivity increases from 25 to 45 for the H₂/CH₄ pair and from 25 to 39 for the CO₂/CH₄ pair, whereas P(O₂) increases by a 2.4 factor with an associated increase in selectivity from 4.4 to 9.6 for O₂/N₂ which situates this membrane above Robeson’s 2008 upper-bound limit, at least for this pair of gases. The cross-linked membranes are resistant to solvent selling, since their SD [%] in NMP is on the order of 1–3%, and also to CO₂ plasticization since the plasticization pressure was not observed at least up to the 18 bar upstream pressure studied here.