부산대학교 도서관

This study elucidates the discrepancy in gas permeability between bulk films and asymmetric membranes of semi-crystalline cellulose acetates (CAs) from perspectives of thickness-confinement and crystallization suppression. CAs are the workhorse membrane materials for industrial CO 2 /CH 4 separation. Bulk films of CAs often exhibit CO 2 permeability values of 1.8–6.6 Barrers at 35 oC, which correspond to permeance values of 36–132 GPU for asymmetric membranes with assumed selective layers of 50 nm. However, commercial CA membranes can have CO 2 permeance values as high as 200 GPU with a CO 2 /CH 4 selectivity comparable to the bulk polymers. We hypothesize that as the CA films become thinner, the thickness confinement inhibits crystallization and thus increases gas permeability while retaining gas selectivity. To validate this hypothesis, freestanding cellulose diacetate (CDA) films with thicknesses ranging from 218 nm to 120 μm were prepared, and their crystallinity was determined using Differential Scanning Calorimetry and Wide-angle X-ray Diffraction analysis. Gas solubility and permeability can be satisfactorily correlated with the crystallinity using the empirical equations available in the literature. We demonstrate that the micro- or nano-confinement and dynamics in thin-film polymers are instrumental in understanding gas transport properties of industrial asymmetric membranes. Image 1 • Asymmetric cellulose acetate membranes show higher CO 2 permeability than expected. • Decreasing cellulose diacetate (CDA) film thickness suppresses crystallization. • Gas permeability and solubility in CDA thin films can be correlated with crystallinity. [ABSTRACT FROM AUTHOR]