Diluent Tailored quaternary deep eutectic solvents for energy efficient carbon capture

Deep eutectic solvents (DESs) are recognized as promising environmentally friendly absorbents for carbon capture. While a considerable body of research has been dedicated to the development of ternary DESs, the energy performance of these systems, especially under low-dilution conditions, remains a relatively under-explored area. In this study, we developed a novel quaternary DES system by introducing water and ethylene glycol as diluents into the ternary DES [ChCl][MEA]-5% M. The impact of diluent incorporation was systematically evaluated through (1) simulated flue gas CO 2 capture experiments, (2) NMR and FTIR spectral analyses, and (3) CO 2 desorption experiments with regeneration heat evaluations. Energy efficiency assessments were subsequently conducted to quantify the overall performance enhancement. Key findings revealed that the formulated quaternary DES achieved a substantial viscosity reduction while maintaining 90.1 % of the baseline absorption capacity. The regeneration heat of [ChCl][MEA]-5%M−20 %H 2 O and [ChCl][MEA]-5%M−20 %EG was found to be reduced by 46.87 % and 46.62 %, respectively, in comparison with that of 30 wt% MEA. Remarkably, the diluted system exhibited 74.4 % lower heat exchanger capital cost and sensible heat loss compared to conventional ternary DESs, with normalized capacity of 4.07 mol CO 2 /kg. These results demonstrate that water/ethylene glycol-modified quaternary DESs present a technologically superior and economically viable alternative for industrial carbon capture applications, effectively balancing absorption efficiency, energy demand, and operational stability.