Diffusion Coefficients Significant in Modeling the Absorption Rate of Carbon Dioxide into Aqueous Blends of N-Methyldiethanolamine and Diethanolamine and of Hydrogen Sulfide into Aqueous N-Methyldiethanolamine

Absorption rates of gaseous CO 2 into aqueous blends of N -methyldiethanolamine (MDEA) and diethanolamine (DEA) and of gaseous H 2 S into aqueous MDEA were measured in a quiescent, inverted-tube diffusiometer by monitoring the rate of pressure drop. A numerical model for absorption, diffusion, and reaction of CO 2 and H 2 S in blends of MDEA, DEA, and water was developed. The model was used to regress diffusion coefficients of bicarbonate, carbamate, and MDEAH 2 CO 3 for the case of CO 2 absorption and of bisulfide ion for the case of H 2 S absorption from measured absorption rates. CO 2 absorption rates and diffusion coefficients of bicarbonate, carbamate, and MDEAH 2 CO 3 were obtained at 298.2 K and 318.2 K in aqueous solutions containing 50 mass % total amine at DEA:MDEA mole ratios of 1:20, 1:4, 1:3, and 2:3. H 2 S absorption rates and diffusion coefficients of bisulfide ion were obtained at 298.2 K and 318.2 K in aqueous solutions containing 20, 35, and 50 mass % MDEA.