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 mol% of the SiMe groups were replaced by a short methylene spacer group terminated by one of the four side-arm functional groups, acetate, -CO2Me; ethylether, OEt; dimethylamino, -NMe2; and pyridyl, -py; were fabricated and tested in short term trials for the pervaporative recovery of cresols from aq. soln. The influences of functional group type, functional group loading, pH, temp. and purity of the feed soln. were investigated. Three com. available hydrophobic membranes were also examd. for comparison. It was found that significant performance enhancements, compared with an unfunctionalized PDMS membrane, were realized for all functionalized PDMS membranes, with dimethylamino and ethylether functionalities proving the most effective. A functional group loading level close to 20% was found to be optimal for this application, The influence of feed pH in the range of 5-8.5 was small on total flux but significant on selectivity for amine loaded membranes. By contrast, the effect of feed temp. was significant on total flux but negligible on selectivity. Low levels of phenolic impurities in a p-cresol feed soln. were found to have negligible effect on the sepn. Compared with com. available zeolite filled PDMS and PEBA membranes, the functionalized PDMS membranes showed a better overall performance. The PV performance of all new membranes followed the trend: o-cresol > p-cresol > phenol. [on SciFinder (R)]