Preparation of modified difunctional PDMS membranes and a comparative evaluation of their performance for the pervaporative recovery of p-cresol from aqueous solution

Cross-linked polydimethylsiloxane (PDMS) membranes modified by the sequential introduction of two different side-arm functional groups, (CH2)3OC2H5 and (CH2)3NMe2, have been prepared and evaluated for the pervaporative recovery of p-cresol from aqueous streams. The loading of the ether group was varied from 5 to 20% and that of the amino group from 5 to 15%. These loadings are expressed in terms of the mole percentages of Si atoms within the membrane containing the identified functional group. The performances of these difunctional membranes are compared with that of pure PDMS and with membranes modified with a single functional group. It was found that various combinations of ether and amino groups improved p-cresol flux while maintaining the high separation factor exhibited by PDMS modified by a high loading of the amino group. These new materials also facilitated the preparation of defect-free films. Membranes containing AEE (10%) +AMI (5%) gave a very similar performance to monofunctional membranes containing 20% amino, but unlike those membranes the new difunctional membranes possess good film forming properties. Another combination of note is the AEE (20%) + AMI (10%) membrane that produced both an excellent cresol flux (that was 30% higher than that achievable using either AEE or AMI modified membranes) and a high separation factor ca. 50.