Green Preparation of Thin Films of Polybenzimidazole on Flat and Hollow Fiber Supports: Application to Hydrogen Separation

Abstract This work shows the preparation of thin films, with thickness from 70 nm to 1 μm, of meta ‐polybenzimidazole (m‐PBI) on polyimide P84 supports. Ethanolic solutions of m‐PBI were used to coat flat and hollow fiber supports of asymmetric P84 with m‐PBI in a process where the coating and drying was performed at room temperature. A solution of NaOH in EtOH allowed the dissolution of the m‐PBI powder, providing the perfect coating solution to build thin films of m‐PBI without damaging the polymeric support. It also meant a green alternative, avoiding the use of toxic solvents, such as dimethylacetamide. The resulting membranes have been tested for the separation of H 2 mixtures at high temperature at different setups to allow checking their reproducibility. With 100 nm thickness the membranes showed their best gas separation performance. For flat membranes at 180 °C and 3 bar feed pressure a H 2 permeance of 48.5 GPU was obtained, with respective H 2 /CO 2 and H 2 /N 2 selectivities of 33.3 and 55.8. Besides, the hollow fibers under a feed pressure of 6 bar and tested at the same temperature showed near 90 GPU of H 2 with a H 2 /CO 2 selectivity of 13.5 in the one‐fiber module and over 39 GPU of H 2 with a H 2 /CO 2 selectivity of 20.2 in the five‐fiber module. Finally, the stability of the membranes was proved for 22 days at 180 °C.