Designing Polymer Nanocomposites for Membrane Gas Separation: an Integrated Experimental and Modeling Approach

Membrane technology is an energy-efficient approach for pre-combustion CO₂ capture and H₂ purification. Conventional membranes are based on rigid polymers with strong size sieving ability, such as poly[2,2’-(m-phenylene)-5,5’-bisbenzimidazole] (PBI) that provides high H₂/CO₂ diffusion selectivity. In this study, we demonstrate enhanced H₂ sorption and diffusion in PBI films with embedded palladium (Pd) nanoparticles, which have strong affinity towards H₂. Pd nanoparticles with uniform diameters of 6 - 8 nm are prepared via a hot-injection colloidal synthesis. The loading of Pd nanoparticles in PBI increases H₂ sorption by almost 1,000 times, and at high Pd loadings, the Pd nanoparticles may form fast channels allowing the H₂ molecules to jump from one particle to another and thus increasing the effective H₂ diffusivity. For example, adding 70 wt.% Pd in PBI increases H₂ permeability from 25 to 70 Barrers, and H₂/CO₂ selectivity from 13 to 29 at 150 °C. Such performance is above the Robeson’s upper bound for H₂/CO₂ separation, demonstrating the potential of these new materials for industrial H₂/CO₂ separation. The gas transport in these PBI-Pd nanocomposites is being modeled using computational fluid dynamics (CFD) to elucidate the mechanisms for the facilitated H₂ transport.