Versatile separation layer for separation and purification of ethanol/cyclohexane mixtures by pervaporation process

Abstract

Quaternized cyclodextrin (CD) obtained by quaternization reaction of bromine-CD and N, N-Dimethylethylenediamine, are used for preparing PV membranes. Three different kinds of composite membranes are interfacially synthesized on the polyacrylonitrile substrate. The different sequences of piperazine and quaternized CD reacted with trimesoyl trichloride show a great difference in separation of polar/nonpolar mixture. The topmost layer of CD-based polyamide layer shows a higher separation factor, which can be inferred that quaternized CD played the major role during separation. Quaternized CD can integrate cavity size, polar and non-polar characteristics to achieve exceptional screening performance. PV performance of the optimal membrane at 25 °C is measured using the 5 wt% ethanol and cyclohexane mixture, exhibiting the separation factor of 66.7. PV performances of other different organic mixtures prove that nonpolar inner cavity of CD has a stronger inclusion of cyclohexane than other smaller nonpolar molecules, thus enhancing the repulsion of cyclohexane from the mixture. In summary, these outside polar quaternary ammonium salt structures of quaternized CD have a high selectivity for polar solvents. The nonpolar cavity of CD shows the inclusion ability of nonpolar solvents, especially the organic solvent with large molecular volume, which hinders their penetration and improves the separation factor.