Influence of polybenzimidazole main chain structure on H2/CO2 separation at elevated temperatures

Four polybenzimidazole (PBI) derivatives were prepared to study the effects of main chain chemistry and structure on H-2/CO2 perm selectivity of cast films. These structural variations were designed to exhibit high localized mobility at elevated temperatures, contain rigid and bent configurations that frustrated close chain packing, or possess bulky side groups. The modified PBIs exhibited high molecular weights, slightly lower thermal stabilities, and higher organo-solubilities compared with commercial m-PBI. Dilute polymer solutions (< 3.0 wt%) were used to fabricate high quality thin films under carefully optimized film processing conditions. Gas permeation properties of these PBl films were evaluated aL elevated temperatures (up to 250 degrees C) and pressures (up to 50 psia). It was found that the main chain structural variations effectively disrupted the PBl chain packing resulting in much improved film H-2 permeability (up to 997.2 barrer) compared with m-PBI (76.81 barrer) at 250 degrees C and 50 psia. However, lower H-2/CO2 selectivities (5-7(modified PBIs) versus 23 (m-PBI) were also measured and reflected the general trade-off betvveen gas permeability and selectivity. When tested at 250 degrees C, PM -based materials exhibited gas separation performance higher than the Robeson upper bound prediction and are promising materials for high temperature H-2 separation horn syngas. (c) 2014 Elsevier B.V. All rights reserved.