(579e) In Situ Growth of ZIFs in Polybenzimidazole to Achieve Superior H2/CO2 Separation Performance | AIChE

(579e) In Situ Growth of ZIFs in Polybenzimidazole to Achieve Superior H2/CO2 Separation Performance


Hu, L. - Presenter, University At Buffalo
Lin, H., University of Buffalo, State University of New Yor
Bui, V., University at Buffalo
Polybenzimidazole (PBI) with a strong size-sieving ability and excellent thermal stability is a leading membrane material for H2/CO2 separation at elevated temperatures. For example, commercial m-PBI exhibited H2 permeability of 9.0 Barrer and H2/CO2 selectivity of 14 at 100 oC. Incorporating porous fillers in polymers to form mixed matrix materials (MMMs) is an effective way to improve their performance. However, most porous fillers have lower H2/CO2 selectivity than PBI, leading to higher H2 permeability but lower H2/CO2 selectivity in the MMMs. In this study, we demonstrate that ZIF nanoparticles (NPs) can be grown in-situ and grafted onto the PBI chains with excellent interfacial compatibility, which cross-links the polymer and increases simultaneously H2 permeability and H2/CO2 selectivity. Specifically, the precursors of 2-methyimdazole (2-MI) and Zn(NO3)2•6H2O for ZIF-8 are added to PBI/dimethylformamide solutions. The 2-MI and Zn2+ ions form ZIF-8 NPs, increasing gas permeability. Moreover, the imidazole rings on the PBI chains react with 2-MI and Zn2+ to form ZIF-7/8 structures, which cross-link PBI chains and enhance their size-sieving ability. The structures of MMMs were thoroughly characterized using FTIR, WXRD, TGA, and SEM. The ZIF-8 NPs have sizes of 0.7 - 1 μm, and ZIF-7/8 structures distribute evenly in the films. For example, an MMM containing 9.3 wt% ZIF-7/8 structures and 5.6 wt% ZIF-8 NPs exhibits H2 permeability of 12 Barrer and H2/CO2 selectivity of 29 at 100 oC, surpassing the Robeson upper bound. Moreover, this MMM shows stable H2/CO2 separation performance (H2 permeability of 11 Barrer and H2/CO2 selectivity of 21) when challenged with simulated syngas at 100 oC, indicating the great potential for practical application. This work presents a highly effective approach to prepare MMMs with great interfacial compatibility, high free volume, and strong size-sieving ability.