CO₂ absorption and thermophysical properties of monoethanolamine in choline chloride-ethylene glycol

Abstract

Integrating CO₂ capture with electrochemical conversion offers a promising pathway to reduce the energy penalty associated with conventional solvent regeneration. In this context, the development of suitable solvents is crucial. In this study, we develop a non-aqueous Monoethanolamine (MEA)-based solvent composed of Choline Chloride (ChCl) and Ethylene Glycol (EG), designed to function simultaneously as a CO₂ absorbent and an electrolyte in an electrolyzer, thereby eliminating the need for intermediate solvent regeneration steps. Vapor-liquid equilibrium (VLE) measurements were performed to quantify chemical CO₂ absorption, while N₂O was used as an analogue gas to assess the physical CO₂ absorption. Although conventional 30 wt.% aqueous MEA exhibited stronger CO₂ binding at low CO₂ partial pressures (≤1 kPa), our non-aqueous MEA solvent demonstrated markedly higher capacities at moderate to high CO₂ partial pressures (up to 500 kPa), reaching up to 1.2, 1.1, and 0.9 mol CO₂/mol MEA at 25, 40, and 65 °C, respectively, exceeding the theoretical equilibrium limit of aqueous MEA. FTIR spectroscopy identified a transition from predominant carbamate formation at low CO₂ partial pressures to increased carbonate formation derived from EG, together with enhanced physical dissolution at higher CO₂ concentrations, indicating distinct and pressure-dependent reaction pathways. Evaluation of key physical properties, including viscosity, electrical conductivity, and thermogravimetric analysis (TGA), highlighted the critical role of solvent formulation in enabling process integration. While incorporation of ChCl increased viscosity due to its ionic nature, it substantially enhanced thermal stability and provided intrinsic ionic conductivity required for electrochemical operation. Overall, this work demonstrates how solvent composition design in non-aqueous solvent systems enables high CO₂ capacity, tunable reaction chemistry, and electrochemical compatibility, offering a practical pathway toward integrated, energy-efficient carbon capture and utilization technologies.