(298g) Modified Amine-Based Sorbent with Thermal and Chemical Stability and Reduced Desorption Energy for Direct Air Capture

Direct air capture (DAC) technology has emerged as a promising approach to the mitigation of carbon dioxide (CO₂) emissions from distributed sources. This key approach involves the direct removal of CO₂ from the atmosphere, typically using appropriate sorbent materials that selectively capture CO₂ molecules. In this regard, amine-based solid sorbent materials drew a particular interest in DAC due to their capabilities to selectively capture ultradilute (~400 ppm) concentrations of CO₂ from ambient air through the chemisorption process. However, solid amine sorbents suffer from thermal and oxidative degradations and desorption energy requirement over the cycles.

In this context, modifying amine structure with epoxide chemicals is an effective strategy for enhancing the molecular structural stability and lowering the energy required for CO₂ desorption. Herein, we synthesized modified-PEI (polyethyleneimine) sorbent with mesoporous silica substrate and explored the role of the epoxide chemicals in terms of different levels of modification to PEI for DAC. The improved thermal and chemical stability of the modified PEI sorbents resulted in long lasting and stable performances over unmodified PEI sorbent. The stability was also validated through in-situ FT-IR analysis. The desorption energy requirements for the modified PEI sorbents were significantly lower than that for the unmodified PEI sorbent. The modification most likely benefits from lowering the basicity and increasing the steric hindrance of the amine center, leading to lowering binding energy between adsorbed CO₂ molecules and modified amine sites. The reduced bonding strengths could also result in fast CO₂ desorption kinetics and lower degradation kinetics validated from temperature programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses, respectively. The equilibrium adsorption data were also obtained under ambient and sub-ambient CO₂ concentrations for unmodified and modified amine-based sorbents and described using the Toth isotherm model. The isotherm data for modified amine sorbents showed a shift in equilibrium resulting from the amine modification, leading to a decrease in the heat of CO₂ adsorption.

This work provides insights into the pivotal role of modified amine support with silica sorbents for heat of desorption energy in DAC systems and offers perspectives on addressing key challenges to understand the full potential of this state-of-the-art approach for carbon capture and climate mitigation.