High-performance absorption and regeneration of water vapor by choline chloride-based hydrophilic deep eutectic solvents

Moisture removal is essential in natural gas processing to prevent hydrate formation, corrosion, and operational issues in pipelines. In this work, a series of deep eutectic solvents (DESs) were synthesized by combining choline chloride with various hydrogen-bond donors: ethylene glycol (EG), triethylene glycol (TEG), tetraethylene glycol (TTEG), glycerol, and urea. Using a bubble-column system, their water vapor absorption capacities were evaluated and compared to TEG under controlled laboratory conditions. All synthesized DESs reduced the relative humidity (RH) of the outlet gas stream. At a gas flow rate of 100 mL·min⁻¹, the outlet RH was reduced more than 90% to less than 3%, confirming their effective dehydration performance. Among the systems studied, the 1:2 molar ratio choline chloride-ethylene glycol DES (Ethaline) exhibited the highest water vapor absorption capacity. This superior performance was attributed to its low viscosity and high hydrophilicity. For the highly viscous choline chloride-urea DES, the addition of approximately 2 wt% water was found to substantially reduce its viscosity while maintaining effective moisture absorption. Thermal regeneration effectively removed absorbed water, with approximately 80% of the absorbed water desorbed after 2 h of heating. Furthermore, repeated absorption-regeneration cycles showed negligible loss in absorption capacity.