The effects of chemical modifications on morphology and performance of 6FDA-ODA/NDA hollow fiber membranes for CO2/CH4 separation
Ren, J. Wang, R. Chung, T.-S. Li, D.F. Liu, Y.
Ren, J.
Wang, R.
Li, D.F.
Liu, Y.
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Abstract
We have studied the rheological characteristics, membrane formation and CO2-induced plasticization phenomenon of almost defect-free copoly(4,4′-diphenylene oxide/1,5-naphthalene-2,2′ -bis(3,4-dicarboxylphenyl) hexafluoropropane diimide) (6FDA-ODA/NDA) hollow fiber membranes. Experimental results indicate that the dope rheology changes from a Newtonian to non-Newtonian fluid with elasticity when increasing shear rate. The asymmetric 6FDA-ODA/NDA hollow fiber membranes exhibit plasticization if the feed pressure is greater than 75psi. Chemical cross-linking modifications with p-xylenediamine were conducted at ambient temperature in order to enhance anti-plasticization characteristics of 6FDA-ODA/NDA hollow fiber membranes. Chemical modified membranes show a significant reduction in CO2-induced plasticization at least up 550psi (37.4atm or 37.9×106Pa) if the immersion time is great 1.5min. However, deteriorations in permeance and permselectivity are clearly observed if the immerse time is greater than 5min. FTIR spectra confirm that the 6FDA-ODA/NDA polyimide can be chemically cross-linked with p-xylenediamine, while wide-angle X-ray diffraction (WAXD) spectra imply the d-space of 6FDA-ODA/NDA membranes slightly decreases with an increase in cross-linking time. SEM pictures show that the outer selective skin as well as substructure becomes denser and thicker after chemical modification. The slight decrease in d-space may account for the permselectivity increase for the cross-linked membranes if the immersion time is short. However, the benefit of d-space reduction is offset by a denser and more compact selective skin and substructure when the immersion is prolonged. © 2003 Elsevier B.V. All rights reserved.
Keywords
6FDA-ODA/NDA copolyimide, Anti-plasticization, Chemical cross-linking, CO2-induced plasticization, Gas separation
Source Title
Journal of Membrane Science
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Series/Report No.
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Date
2003-09-01
DOI
10.1016/S0376-7388(03)00266-7
Type
Article