Polymeric membranes for nanofiltration in polar aprotic solvents

Solvent stable organic solvent nanofiltration membranes were prepared through the chemical crosslinking of integrally skinned Lenzing P84 polyimide membranes using aliphatic diamines. The resultant membranes had a spongy structure and were stable in many organic solvents including toluene, methanol, methylene chloride, tetrahydrofuran, dimethyl formamide and n-methyl pyrrolidone. Operation in dimethyl formamide and tetrahydrofuran for 120 h showed that the membranes have stable fluxes and good separation performances, with DMF permeability in the range of 1–8 × 10−5 L m−2 h−1 Pa−1 (1–8 L m−2 h−1 bar−1) and a MWCO between 250 and 400 g mol−1. Possible re-imidization and loss of crosslinking at elevated temperatures limits their range of application to temperatures <100 °C. Their ease of preparation makes the membranes easily scalable and opens up future possibilities for further applications in harsh solvent environments.