(339f) Effect of SO2 on CO2 Capture Performance of Self-Supported Branched Poly(ethyleneimine) Scaffolds
AIChE Annual Meeting
Tuesday, November 15, 2022 - 1:42pm to 2:00pm
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.
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