Concentration-Dependent Nanoscale Network Connectivity in Water-Lean CO 2 Capture Solvent Clusters Revealed by Structural Studies

Water-lean solvents for point source carbon dioxide capture generally reveal an increase in polarity and viscosity with higher CO 2 loadings. Among these, N -(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA) exhibits notable CO 2 capture properties due to its formation of CO 2 -dependent molecular tetramers. Wide-angle X-ray scattering (WAXS) was used to examine the evolution of nanoscale clusters at different CO 2 loadings ranging from 0 to 42 mol % CO 2 and from −17 to 90 °C. Computational and experimental data were used to estimate the solvent density, cluster size, and cluster–cluster correlations of various tetrameric species, enabling quantitative assessment of WAXS-derived structures. Particularly, the Teubner–Strey thermodynamical model was used to investigate the microphase separation of our system, while the molecular nearest-neighbor behavior was obtained through scattering- and molecular-dynamics-derived structure factor analysis. The experimentally derived correlation length (ξ) and periodicity ( d ) of the CO 2 -bound clusters of 2-EEMPA grow as the concentration of CO 2 increases, reaching ξ = 5.0 Å and d = 11.6 Å, in agreement with simulation results. Our findings capture the detailed structural changes that occur with CO 2 variation and compare them with chemical process simulations and physical properties measurements. The structural insights derived from this study provide crucial input to the modeling and design of the CO 2 capture solvents.