Natural gas combined cycle (NGCC) power plants are more energy efficient than their coal counterparts, and NGCC can be combined with CO₂ capture to further reduce emissions. CO₂ capture materials tailored for NGCC flue gas will be necessary for the advancement and widespread utilization of the technology. Adsorbents are often used in structured contactors to increase productivity and reduce pressure drop compared to traditional packed beds. However, structured contactors typically contain inactive binders or polymeric materials in addition to the adsorbent, which can limit the amount of active material in the contactor. The development of polymers with high CO₂ affinities eliminates the need for a binder by enabling contactors composed entirely of the active material.
One promising class of materials for this purpose is polymers of intrinsic microporosity (PIMs) due to their high surface area, permanent interconnected microporosity, solubility in common organic solvents, and options for fine tuning through chemical and morphological modifications. However, PIM-1 can only weakly bind CO₂ through physisorption in the micropores, leading to low uptake in dilute CO₂ feeds. To resolve this, we chemically modified the PIM-1 backbone with guanidine, a Brønsted base, to create a novel polymeric CO₂ adsorbent.
Here, we present the synthesis and characterization of PIM-guanidine. The adsorbent was evaluated extensively for CO₂ capture from dry and humid streams, including isobar, breakthrough, and cycling experiments. Solid state (13CP MAS) NMR spectroscopy after ¹³CO₂ adsorption was used to further probe the sorption mechanism and distinguish between physisorbed and chemisorbed CO₂. The results reveal guanidine’s role in the CO₂ adsorption mechanism, the advantages of functionalizing PIM-1, and the effect of humidity on PIM-guanidine’s performance. Finally, the powder is transformed into polymeric contactors composed completely of the active material. Overall, these results advance our understanding of amine-CO₂ chemistry and demonstrate PIM-guanidine’s potential for scale-up and industrial application in NGCC processes.

Simon Weston

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