Carbon dioxide solubility in mixtures of methyldiethanolamine with monoethylene glycol, monoethylene glycol–water, water and triethylene glycol

•Amine-glycol blends for combined acid gas/water removal in natural gas treatment.•Non-aqueous and aqueous methyldiethanolamine-ethylene glycol are promising solvents.•Carbon dioxide reacts chemically with both methyldiethanolamine and ethylene glycol.•Demonstrated by vapor-liquid equilibrium and nuclear magnetic resonance experiments.•Hypothesis of ethylene glycol autoprotolysis in the presence of the amine.