Osmotically assisted solvent reverse osmosis membrane for dewatering of aqueous ethanol solution

Abstract

To meet the demand of ethanol, researchers are encouraged to develop sustainable membrane processes for solvent recovery. Osmotically assisted reverse osmosis (OARO) process, a new membrane technology, shows a promising alternative for desalination; but it has never been applied in solvent recovery because OARO membranes have relatively larger pore sizes than the molecular sizes of solvents. Therefore, the traditional RO membranes require further modification to separate water from ethanol. Two simple approaches are considered in this work: (1) heat treatment of commercial RO membrane to reduce the pore size of the selective polyamide layer and (2) deposition of tannic acid (TA)-polyethyleneimine (PEI) complex to boost the affinity of the membrane with water molecules. The modified RO membrane achieves over 95% rejection of ethanol, as well as highly efficient recovery of ethanol during osmotically assisted solvent reverse osmosis (OASRO). Furthermore, molecular dynamic simulation elucidated the underlying mechanisms of the effects of annealing and coating on membrane pore size and surface affinity to water/ethanol molecules, respectively. This work opens an opportunity for further development of a more efficient and effective solvent purification process.