Thin film composite membranes comprising of polyamide and polydopamine for dehydration of ethylene glycol by pervaporation

Thin film composite membranes comprising of a polyamide (PA) and polydopamine (PD) were prepared and studied for dehydration of ethylene glycol. The chemical composition, surface hydrophilicity and sorption uptake of permeant in the active skin layer of the membranes were characterized, and the effects of the number and sequence of the PD and PA sublayers in the membrane skin on the pervaporation performance were studied. It was shown that using 1 or 2 PD sublayers as a surface layer (i.e., on top of PA) or a transition layer between PA and the substrate would increase both permeation flux and selectivity for dehydration of ethylene glycol. Since inorganic salts are often present in spent glycol solutions in practical applications, the influence of inorganic salt in the feed on ethylene glycol dehydration was also studied using NaCl as a representative salt. The presence of NaCl in the feed solution enhanced the separation factor, while the permeation flux was reduced. Unlike pervaporative separation of binary water/ethylene glycol solutions where the separation factor was reduced at a higher temperature, the separation factor increased with an increase in temperature when NaCl was present in the feed.