Spatially Mapping the CO₂ Alkaline Sorbent Diffuse Microenvironment Using Operando Raman Spectroscopy

Area of Science:

• Chemical Engineering
• Spectroscopy
• Environmental Science

Background:

• The diffuse microenvironment, balancing transport and kinetics, is vital for chemical process performance but challenging to observe.
• Direct air capture (DAC) of carbon dioxide is a critical technology for climate change mitigation, requiring efficient solvent design.

Purpose of the Study:

• To develop and demonstrate a novel method for spatially mapping the diffuse microenvironment during alkali metal hydroxide DAC.
• To elucidate the interplay of ions and mass transport phenomena at the gas-liquid interface in DAC systems.

Main Methods:

• Utilized a custom-built operando gas-absorption flow cell integrated with confocal Raman spectroscopy.
• Performed two-dimensional spatial chemical mapping of the diffuse microenvironment.
• Employed continuum modeling to infer local hydroxide depletion.

Main Results:

• Successfully mapped the concentration boundary layer at the gas-liquid interface during CO2 capture.
• Elucidated the dynamic interplay between carbonate and bicarbonate ions within the boundary layer.
• Inferred local hydroxide depletion, providing critical data for solvent performance evaluation.

Conclusions:

• The demonstrated technique offers a new platform for studying interfacial diffuse microenvironments in DAC and other chemical processes.
• Provides essential metrics for comparing DAC solvent performance and optimizing air contactor design, such as boundary layer thickness.