Solubility and Characterization of CO₂ in 40 mass % <i>N</i>‑Ethylmonoethanolamine Solutions: Explorations for an Efficient Nonaqueous Solution

Abstract

The CO₂ solubility in <i>N</i>-ethylmonoethanolamine (EMEA) solutions was investigated using the vapor–liquid equilibrium (VLE) and the absorption–desorption apparatus. A tertiary amine, <i>N</i>,<i>N</i>-diethylethanolamine (DEEA), was used as a novel solvent, and other nonaqueous solvents, diethylene glycol, triethylene glycol, benzyl alcohol, <i>n</i>-butyl alcohol and polyethylene glycol-200, were used for comparison. The EMEA + DEEA solution displayed a much higher CO₂ solubility than other nonaqueous solutions though lower than the EMEA + H₂O solution in the VLE experiment. However, the EMEA + DEEA solution exhibited a higher cyclic absorption capacity than EMEA + H₂O solution in the cyclic absorption–desorption experiment. The reaction mechanism of EMEA + DEEA + CO₂ was investigated by ¹³C NMR spectroscopy, which indicated that the nonaqueous solvent of DEEA participated in the chemical absorption of CO₂, and thus improved the CO₂ solubility. The tertiary amine DEEA used as a nonaqueous solvent shows more excellent performance than alcohols and glycols