Beyond polyimide: Crosslinked polybenzimidazole membranes for organic solvent nanofiltration (OSN) in harsh environments

In this work, we report a new class of organic solvent nanofiltration (OSN) membranes fabricated from polybenzimidazole (PBI) which exhibit superior chemical stability compared to other well-known polymeric membranes such as polyimide. Integrally skinned asymmetric PBI membranes were prepared and crosslinked using either an aliphatic or an aromatic bifunctional crosslinker. Three batches of membranes with the same composition were prepared and crosslinked with each crosslinker. The membrane performance showed excellent reproducibility in organic solvents and water in terms of flux and retention profile. Also, both membranes showed good tolerance towards extreme pH conditions. To critically assess their chemical stability the membranes were tested in realistic chemical process conditions that employ different types of acids and bases, e.g. concentrated dichloroacetic acid in acetonitrile, piperidine in N,N-dimethylformamide (DMF) and monoethanolamine in water. The membranes modified with aliphatic crosslinker could not retain their properties when DMF was used as the organic solvent. This was found to be due to dissolution of PBI in DMF rather than degradation due to pH exposure. On the other hand, it was shown that the membrane modified with the aromatic crosslinker exhibits superior stability and higher permeances in comparison to the membrane crosslinked with the aliphatic crosslinker. The results obtained show that membranes fabricated from crosslinked PBI were stable and have the potential for applications in chemically harsh conditions found in processes ranging from pharmaceutical to petrochemical industries.