High flux membranes for organic solvent nanofiltration (OSN)—Interfacial polymerization with solvent activation

This paper describes the formation of a new generation of organic solvent nanofiltration (OSN) membranes: high flux thin film composite (TFC) membranes prepared via interfacial polymerization (IP) and solvent activation. These are the first reported TFC membranes which are stable in DMF. They exhibit significantly higher permeabilities for polar aprotic solvents, including DMF, acetone and THF, than commercial integrally skinned asymmetric OSN membranes; and yet have comparable rejections. Solvent stable crosslinked polyimide (PI) ultrafiltration (UF) membranes were used as supports for the formation of these TFC membranes. To increase solvent flux we employed two approaches. In the first approach, the UF support was impregnated with polyethylene glycol (PEG). Comparison of membranes formed using UF supports with and without PEG suggests that PEG impregnated in the support plays an important role in thin film formation and, consequently, in solvent permeation, resulting in increased fluxes. The second approach we employed was to treat the TFC membranes with an “activating solvent” after the IP reaction. This resulted in dramatically improved solvent fluxes without compromising rejection; for some solvents, there was a flux only after activation. Such TFC membranes prepared by interfacial polymerization and treated with an activating solvent may lead to the next generation of high performance OSN membranes.