(339f) Effect of SO2 on CO2 Capture Performance of Self-Supported Branched Poly(ethyleneimine) Scaffolds

The separation of CO₂ from post-combustion flue gas is a critical component in global carbon emission control and climate change mitigation. Structured contactors in the form of monoliths for CO₂ capture not only combat the high energy consumption and corrosion rate observed in traditionally used aqueous amines but also offer a low pressure drop in comparison to pellet or powder adsorbents.¹ Amine materials have shown improved sorption capacities in the presence of humidity, compared to other nanoporous materials such as metal organic frameworks (MOFs) and zeolites, which sometimes have reduced performance in the presence of humidity.^2,3 Two critical challenges in developing a cost-effective amine-based adsorbent for CO₂ capture from flue gas are the creation of a support material that contains the CO₂-philic functionality and the combatting presence of acid gas impurities such as SO₂ in the feed stream. In this work, we have synthesized a self-supported monolithic sorbent by crosslinking poly(ethyleneimine) (PEI) at sub-ambient temperatures using an ice templating method.⁴ Scanning electron microscopy (SEM) confirms the presence of templating-induced porosity, which is also a function of the temperature of crosslinking and concentration of PEI. Breakthrough experiments with simulated flue gas are performed to show the effect of pore morphology on the breakthrough behavior and sorbent capacity for CO₂ capture in the presence of humidity. The ratio of CO₂ adsorption capacity to SO₂ adsorption capacity for the synthesized PEI scaffolds was 1.5 for pseudo-equilibrium adsorption and increased to 16 when the cycle time was reduced. This in comparison to a ratio of 0.86 obtained for a powdered sorbent of PEI impregnated in an inorganic silica support.⁵ Since tertiary amines have a higher affinity for SO₂ than CO₂, and the temperature and degree of crosslinking affect the distribution and relative ratio of primary, secondary, and tertiary amines in the crosslinked PEI scaffolds respectively, these two parameters can be tuned to improve the selectivity for CO₂ by at least 57%. Additionally, with a sorbent lifetime of over 15 cycles in the presence of SO₂, the crosslinked PEI scaffolds are promising materials for CO₂ capture from flue gas with scope for improvement by optimizing the cycle time.

References:

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