A fundamental study of organofunctionalised PDMS membranes for the pervaporative recovery of phenolic compounds from aqueous streams

Modified polydimethylsiloxane (PDMS) composite membranes in which a known m ol% of the SiMe groups were replaced by a short methylene spacer group term inated by one of the four side-arm functional groups, acetate, -CO2Me; ethy lether, OEt; dimethylamino, -NMe2; and pyridyl, -py; were fabricated and te sted in short term trials for the pervaporative recovery of cresols from aq ueous solution. The influences of functional group type, functional group l oading, pH, temperature and purity of the feed solution were investigated. Three commercially available hydrophobic membranes were also examined for c omparison. It was found that significant performance enhancements, compared with an unfunctionalised PDMS membrane, were realised for all functionalis ed PDMS membranes, with dimethylamino and ethylether functionalities provin g the most effective. A functional group loading level close to 20% was fou nd to be optimal for this application, The influence of feed pH in the rang e of 5-8.5 was small on total flux but significant on selectivity for amine loaded membranes. By contrast, the effect of feed temperature was signific ant on total flux but negligible on selectivity. Low levels of phenolic imp urities in a p-cresol feed solution were found to have negligible effect on the separation. Compared with commercially available zeolite filled PDMS a nd PEBA membranes, the functionalised PDMS membranes showed a better overal l performance. The PV performance of all new membranes followed the trend: o-cresol > p-cresol > phenol. (C) 2001 Elsevier Science B.V. All rights res erved.