Self-supported polymer monoliths for CO2 capture

Increasing CO2 concentration in the atmosphere due to anthropogenic activities has resulted in global warming and climate change. Carbon capture, utilization and storage play a pivotal role in reducing CO2 emissions while we simultaneously transition to other low-carbon energy sources. Post-combustion flue gas and ambient air are two important sources for capturing CO2. While aqueous amines are the most mature technology for CO2 capture, amine-functionalized solid sorbents form the state-of-the-art technology for CO2 capture from air. The degradation of amines in the presence of other acid gas impurities typically found in post-combustion flue gas and the dead weight and energy penalty associated with the presence of inorganic support on which the active amine species is usually impregnated or covalently tethered are among the key challenges in developing efficient sorbents for CO2 capture. This dissertation addresses these two challenges while improving the performance of the developed sorbents towards post-combustion flue gas and direct air capture. This dissertation explores the synthesis and performance of self-supported amine-functionalized polymer monoliths for CO2 capture via ice templating and inverse template 3D printing techniques. Three main objectives are addressed – i) understanding the effect of SO2, a model acid gas, on the CO2 capture performance of the self-supported polymer sorbent, ii) incorporating additives in the ice-templating process to tune the morphology of the developed contactor, and iii) synthesizing self-supported polymer monoliths with well-defined channel structures and densities, to study the feasibility of these monoliths in practical applications. Work on the first objective showed the following main results. SO2 binds irreversibly to specific amine sites in the self-supported polymer sorbent and deactivates them permanently. The mechanism of interaction between amines and SO2 was identified. The SO2 uptake for a given feed composition and flow rate depends on the adsorption cycle time. Hence, by varying the cycle time, it was demonstrated that the ideal CO2/SO2 selectivity could be improved by a factor of 10 simply by taking advantage of the transient kinetic selectivity of CO2. This emphasizes the need to optimize the process to go hand-in-hand with discovering new acid-gas-resistant materials. The second objective involved the modification of the sorbent morphology to cater to direct air capture. This was achieved by incorporating small amounts of alumina additive in the reaction mixture during ice-templating. This was found to reduce the pore size, and pore wall thickness of the self-supported polymer sorbent. As a result, the CO2 uptake of the sorbent was improved under ultra-dilute concentrations of CO2. This alumina incorporated self-supported polymer sorbent showed higher CO2 uptake than the traditional amine-impregnated alumina sorbent under humid CO2 conditions relevant to ambient air. The developed sorbents also formed weaker interactions with CO2 than the conventional sorbents, resulting in lower thermal energy requirements for sorbent regeneration. Lastly, in the third objective, self-supported polymer monoliths with well-defined channel dimensions and densities were synthesized using a combination of ice-templating and inverse-template 3D printing. The monoliths developed herein were found to have lower pressure drops than the fibers and monoliths compared. They were also found to have superior mechanical and oxidation stability than their traditional supported amine counterparts. However, they showed signs of internal mass transfer limitations, requiring additional strategies to modify the monolith's macropore structure and macroscopic form. Overall, this dissertation opens up new opportunities for the development of self-supported polymer monoliths for CO2 capture and provides fundamental insights into ice-templating and sorbent evaluation.

Date

2023-12-18

Resource Type

Text

Resource Subtype

Dissertation

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