Mesoscopic Structure Facilitates Rapid CO

Area of Science:

• Chemical Engineering
• Materials Science
• Environmental Science

Background:

• Aqueous amine solutions are traditional CO2 capture solvents, but water-lean organic solvents exhibit anomalously high mass transfer coefficients.
• The molecular and nanoscale structure of these concentrated organic solvents is key to understanding their enhanced CO2 capture performance.

Purpose of the Study:

• To investigate the molecular and nanoscale structure of a representative water-lean solvent, 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (IPADM-2-BOL).
• To correlate the solvent's structure with its CO2 mass transfer properties.

Main Methods:

• In situ liquid time-of-flight secondary ionization mass spectroscopy (TOF-SIMS) was used for chemical mapping.
• Two-dimensional (2D) and three-dimensional (3D) chemical mapping provided insights into the solvent's heterogeneity.
• Molecular dynamics simulations were employed to complement experimental findings.

Main Results:

• IPADM-2-BOL displayed a heterogeneous molecular structure with distinct regions of CO2-free solvent and zwitterionic carbonate ion clusters.
• Chemical mapping revealed CO2 diffusion through pockets and channels within the unreacted solvent.
• These mesoscopic structures were found to enhance CO2 diffusion and reactivity.

Conclusions:

• The heterogeneous nanoscale structure of water-lean solvents significantly enhances CO2 mass transfer and reactivity.
• Controlling the size, shape, and orientation of these structural domains offers a pathway to developing more efficient CO2 capture solvents.
• This understanding is applicable to a broader range of water-lean solvents for improved carbon capture kinetics.