Thermophysical properties of blended absorbents for CO2 capture: NMDEA with alkanol (C1–C2) at 298.15 K to 318.15 K

• Measured ρ , η , u , and n D of N-methyl diethanolamine + alkanol mixtures at T = (298.15 – 318.15) K. • Evaluated V m E , Δ η , Δ u , κ s E , and Δ n D from the measured data. • The V m E , Δ η , and κ s E values were predicted by the Graph theoretical approach. • FT-IR spectroscopy confirmed hydrogen bonding and molecular interactions. • The η and u values were correlated with various correlations. The purpose of this study is to investigate the thermophysical properties and molecular interactions of binary mixtures of N‒methyl diethanolamine (1) with alkanol (C 1 ‒C 2 ) (2) at T = 298.15 K to 318.15 K and at 0.1 MPa pressure, to gain insight into their structural behavior and intermolecular interactions. These properties would be employed in future studies for CO 2 absorption. To achieve this, density ( ρ ), viscosity ( η ), speed of sound ( u ), and refractive index ( n D ), of the mixtures were experimentally measured. Measured data were used to calculate excess molar volume ( V m E ), deviation in viscosity ( Δ η ), deviation in the speed of sound ( Δ u ), excess isentropic compressibility ( κ s E ), and deviation in refractive index ( Δ n D ), correlated with the RK equation. Partial ( V ¯ i ) and excess partial ( V ¯ i E ) molar volumes were derived to assess molecular contributions. Additionally, theoretical predications of V m E , Δ η , and κ s E values were performed using a Graph theoretical approach (GTA), and FTIR spectral data were analyzed to validate GTA predications and identify intermolecular interactions. The results show that the mixtures are strongly influenced by H–bonding, dispersive, and cohesive forces, as well as molecular structure. Negative values of V m E , Δ η , and κ s E values indicate strong attractive interactions and efficient packing, whereas positive Δ u and Δ n D reflect enhanced structural ordering. Partial molar volume ( V ¯ i ) analysis confirms the predominance of heteromolecular interactions. GTA predictions align with experimental data, and FTIR spectra corroborate H-bonding.