The ionic liquid [EMIM]OAc as a solvent to fabricate stable polybenzimidazole membranes for organic solvent nanofiltration

Abstract

We have provided two feasible methods to prepare stable organic solvent nanofiltration (OSN) membranes by chemically cross-linking the polybenzimidazole (PBI) membranes fabricated from environmentally benign ionic liquids for the first time. A glutaraldehyde (GA)–water solution and a 1,2,7,8-diepoxyoctane (DEO)–n-heptane solution were employed to cross-link PBI membranes. The effects of these cross-linking agents on membrane stability and separation performance toward various solvents, including polar aprotic solvents, have been carefully examined. The GA cross-linking method, with little consumption of traditional organic solvents and energy, yielded a PBI membrane with a high and steady ethanol flux [3.69 L (m² bar h)⁻¹] and ethyl acetate flux [5.21 L (m² bar h)⁻¹]. Although PBI membranes cross-linked by DEO showed lower ethanol and ethyl acetate fluxes, they displayed impressive stability in aggressive solvents such as dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc). Overall, PBI membranes cross-linked by both agents exhibited reasonable rejections which varied slightly from solvent to solvent due to different solute–solvent–membrane interactions. This study not only offers a new range of membrane materials and fabrication approaches for OSN, but will also enhance membrane-based green technology for the recovery of organic solvents.