(706b) Semi-Interpenetrating Networks (s-IPN) of Polybenzimidazole-Based Membranes for High-Temperature Pre-Combustion CO2 Capture | AIChE

(706b) Semi-Interpenetrating Networks (s-IPN) of Polybenzimidazole-Based Membranes for High-Temperature Pre-Combustion CO2 Capture


Li, S., University of Notre Dame
Guo, R., University of Notre Dame
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Research Interests in H2/CO2 separation at high temperatrues that relates to pre-combustion CO2 capture from syngas after the water-gas shift reactions. Membrane-assisted separation technology is more favorable to save energy comsumption and capital costs compared to current technologies such as physical absorptions. Separating H2 from CO2 at high temperatures (e.g., 100-300 oC) demands polymer membranes with high thermal stability and strong size-sieving capability, which is challenging for most conventional polymer materials. Polybenzimidazoles (PBIs), e.g., commercial m-PBI, are the leading polymer membrane materials for high-temperature H2/CO2 separation due to outstanding thermal stability and good size-sieving capability imparted by densely packed chains. However, m-PBI also suffers from extremely low H2 permeability (i.e., <3 Barrer at 35 oC) due to strong hydrogen bonding and pi-pi stacking interactions, limiting its applications in industrial processes. To improve H2 permeability while maintaining good size-sieving capability at high temperatures, we developed a novel macromolecular design of semi-interpenetrating polymer network (s-IPN) structures, where linear m-PBI chains penetrate through and get interlocked with rigid unimodal crosslinked networks with precisely controlled and tailorable crosslink density. In s-IPN design, penetration of m-PBI chains through a rigid network scaffold disrupts the tight chain packing of m-PBI by breaking up pi-pi stacking and hydrogen bonds, enabling enhanced H2 permeability. Simultaneously, the interlocking of m-PBI chains with a rigid network helps retain size-sieving capability at high temperatures due to suppressed chain relaxation. More importantly, the separation performance of s-IPN films can be finely tailored by adjusting crosslinked structure and network content, allowing for realizing superior separation performance. We have demonstrated that m-PBI-based s-IPN films containing pentiptycene-based polybenzoxazole (PPBO) networks and linear m-PBI exhibited significantly improved H2 permeability (e.g., by ~9 times at 35 oC) and well-maintained H2/CO2 selectivity spanning a wide temperature range up to 180 oC. Through synergistic efforts in adjusting the crosslink density and network content, these s-IPN films outperformed the predicted H2/CO2 upper bound at 180 oC.

In our recent work, we furthered the structure-property relationship study of the m-PBI-based s-IPN by examining the effect of the nature of unimodal network components via architecting s-IPN structures using a variety of glassy polymer networks of different types, i.e., crosslinked Matrimid®-like polyimide and crosslinked PBIs. By comparing s-IPN films of the same crosslink density and network content but different network structures (i.e., PBO vs. polyimide vs. PBI), we demonstrated that the segmental rigidity and microporosity of the crosslinked networks play an important role in regulating the gas transport in the resulting s-IPN films. For example, the Matrimid®-like polyimide networks with more well-defined crosslinked structures and narrower interchain distance favor more efficient penetration and interlocking of m-PBI chains compared to PPBO-based networks, leading to simultaneous enhancement of H2 permeability and H2/CO2 selectivity at high temperatures and exceeding the H2/CO2 upper bound at 180 oC. The greatly enhanced H2 permeability, superior size-sieving capability, and highly tailorable free volume architecture in PBI-based s-IPN design exemplify their promising prospects of energy-efficient pre-combustion CO2 capture.