Towards improved membrane production: using low-toxicity solvents for the preparation of PEEK nanofiltration membranes

In this work it is shown that PEEK membranes are “green” from the production point of view when compared with commercial polyimide (PI) based organic solvent nanofiltration (OSN) membranes. Green metrics (E-factor and solvent intensity) and waste cost were used in order to assess the environmental burden of PEEK membranes: the solvent intensity of PEEK membranes is 8.3 vs. 35–224 for PI based membranes, and the waste cost for PEEK membranes is 46 £ kg−1 of polymer vs. 1019 £ kg−1 of polymer (bench scale) and 189 £ kg−1 of polymer (industrial scale) for PI based membranes. Scaling-up of PEEK membranes to spiral-wound modules was successfully achieved with permeances between 0.26 L h−1 m−2 bar−1 and 0.47 L h−1 m−2 bar−1 for THF, and molecular weight cut-offs (MWCO) of ∼300 g mol−1. As a final assessment, the solvent intensity and environmental burden associated with permeating a THF flow of 100 L h−1 using PEEK membranes was also assessed. The results showed a waste cost of 1.4 £ m−2 of membrane, significantly lower than PI based membranes.