Performance of PDMS and organofunctionalised PDMS membranes for the pervaporative recovery of organics from aqueous streams

Abstract

Modified polysiloxane membranes containing different organofunctional side chains were produced and tested for the recovery of various organic contaminants from aqueous sterams, using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone (MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. In each case significant performance enhancements, over that achieved with an unfunctionalised poly(dimethylsiloxane) membrane, were realise. Phenol transport is significantly facilitated by the incorporation of basic groups into the membrane structure. This is thought to be due to a weak acid-base interaction, increasing phenol sorption into the membrane. For pyridine, chloroform and MIBK separations from water, selectivity towards the organic component is greatly enhanced by the incorporation of long chain alkyl groups. A dual effect of the increased organic content of the membrane leading to increased organic component sorption and reduced water sorption is thought to be responsible. The effect of varying the three process parameters, feed concentration, membrane cross-linking density and membrane functional loading, were investigated. Some flux coupling effects were apparent, particularly affecting the transport of water with changing organic component concentration. Changing the cross-linking density of the membrane was found to have negligible effect across the range studied. An optimal functional loading generally close to 10% exists.