Pervaporation dehydration of ethylene glycol through polybenzimidazole (PBI)-based membranes. 1. Membrane fabrication

Ethylene glycol is an important commodity in chemical industries and dewatering is a critical process in the production and recycle of ethylene glycol. In this work, we have developed dual-layer polybenzimidazole/polyetherimide (PBI/PEI) hollow fiber membranes for ethylene glycol dehydration via pervaporation. Three types of membranes have been prepared; namely, (1) PBI flat dense membranes; (2) PBI single-layer hollow fiber membranes; and (3) PBI/PEI dual-layer hollow fiber membranes. PBI flat dense membranes have the lowest separation performance due to severe swelling. PBI single-layer hollow fiber membranes show better separation performance in terms of permeation flux and separation factor but have very low tensile strains. The dual-layer PBI/PEI hollow fiber membranes have the best separation performance due to (1) unique combination of the superior physicochemical properties of the PBI selective layer and the less swelling characteristics of the PEI supporting layer, and (2) synergistic effects of molecularly designed membrane morphology via dual-layer co-extrusion. The effects of spinning parameters of PBI single-layer and PBI/PEI dual-layer hollow fiber membranes on pervaporation performance have been investigated. A thermal treatment of PBI/PEI dual-layer hollow fiber membranes at 75°C can significantly enhance the separation performance. Compared with other polymeric membranes, the newly developed PBI/PEI dual-layer hollow fiber membranes have much better separation factors and slightly lower fluxes for the ethylene glycol dehydration. It is believed that the science and engineering of designing PBI/PEI dual-layer hollow fiber membranes with an ultra-thin functional separation layer and a synergic supporting layer may open new perspective for the development of next-generation high-performance multilayer membranes for liquid separations.