Thermodynamic modeling CO2 absorption in semi-aqueous monoethanolamine with N-methyl-2-pyrrolidone using electrolyte NRTL model

Partially replacing water with N-methyl-2-pyrrolidone (NMP) in aqueous monoethanolamine (MEA) solutions has been shown to reduce the energy demand of CO₂ capture. However, the absence of rigorous thermodynamic models for semi-aqueous MEA-NMP solvents hinders process design and optimization. This study develops a thermodynamic model for CO₂ absorption in NMP–H₂O–MEA–CO₂ mixtures using the electrolyte NRTL framework. The model extends the established H₂O–MEA–CO₂ system by incorporating NMP-specific parameters while preserving accuracy in the aqueous regime. A sequential regression approach is applied to correlate key properties relevant to CO₂ capture, including CO₂ solubility, excess enthalpy, heat of absorption, and liquid heat capacity across binary to quaternary systems. Viscosity and density are also modeled to support mass transfer calculations. To improve model accuracy, new CO₂ solubility data are measured for NMP–H₂O–MEA–CO₂ mixtures at 313–393 K. The model accurately represents CO₂ solubility across a wide range of CO₂ loadings, temperatures, and NMP contents, revealing a decrease in solubility and a 10–25 kJ/mol CO₂ increase in heat of absorption with NMP addition. The developed model enables rigorous process simulation and facilitates the design of energy-efficient CO₂ capture using semi-aqueous MEA-NMP solvents.