A cellulose acetate/multi-walled carbon nanotube mixed matrix membrane for CO₂/N₂ separation

Carbon dioxide (CO₂) emissions have been rising indiscriminately and are becoming a major contributor to Earth's greenhouse effect. One of the most promising means of separating the hazardous CO₂ gas is to develop a cost effective and high-performance CO₂ separation membrane. From the wide range of membrane materials available, mixed matrix membrane (MMM) technology has shown the most promising results. In this study, MMMs were synthesized from cellulose acetate (CA) with multi-walled carbon nanotubes (MWCNTs) using the wet phase inversion technique. The results shown that MMMs with functionalized MWCNTs (MWCNTs-F) demonstrated the enhance permeance and selectivity towards the separation of CO₂/nitrogen (N₂). Thus, different loadings of MWCNTs-F into MMM were further investigated to interpret the physical morphologies and functionalities of MMMs, which enable the separation of CO₂/N₂ in a specific manner. Gas permeation measurements showed excellent MMM performances in terms of permeance and selectivity at 0.1wt% loadings of MWCNTs-F. This superior performance was due to the homogeneous dispersion between the MWCNTs-F and the CA matrix, which increased the sufficient free volumes between the polymer chains and enlarged the polymer/nanofiller interface, as confirmed by the X-ray diffraction results.