β-Cyclodextrin containing Matrimid® sub-nanocomposite membranes for pervaporation application

Molecular-level mixed matrix membranes made of Matrimid (R)/beta-cyclodextrin (beta-CD) sub-nanocomposites for dehydrating isopropanol by pervaporation have been fabricated and studied. The separation efficiency of such membranes containing similar to 2 to 10 wt.% of beta-CD is superior over the neat Matrimid (R) membrane in terms of both flux and separation factor. However, phase separation due to beta-CD agglomeration occurs with an increase in beta-CD loading. Asymmetry in both morphology and surface property has also been observed. The separation properties depend upon the membrane mounting mode (i.e., using air-side or glass-side of the membrane against the feed during pervaporation tests). The flux and separation factor of both modes, nevertheless, display the same increase-and-decrease dependence on beta-CD loading. The unique characteristics of beta-CD such as hydrophilic exterior and interior cavity and the interactions between beta-CD molecules and the polymer matrix may create additional interface channels for water diffusion and provide size discrimination and chain rigidification for water/isopropanol selection. As a result, compared to mixed matrix membranes incorporated MgO or zeolite nanoparticles, embedding a low percentage of beta-CD into the Matrimid (R) leads to the enhanced and superior separation efficiency. On the other hand, a higher loading of beta-CD deteriorates separation performance due to the formation of a non-permeable beta-CD network. The proposed Matrimid (R)/beta-CD mixed matrix materials may open new perspective for the development of mixed-matrix hollow-fiber membranes because of the sub-nano-sized beta-CD and its unique molecular-level mixing characteristics. (C) 2008 Elsevier B.V. All rights reserved.