DIFFUSION-COEFFICIENTS SIGNIFICANT IN MODELING THE ABSORPTION RATE OFCARBON-DIOXIDE INTO AQUEOUS BLENDS OF N-METHYLDIETHANOLAMINE AND DIETHANOLAMINE AND OF HYDROGEN-SULFIDE INTO AQUEOUS N-METHYLDIETHANOLAMINE

Absorption rates of gaseous CO2 into aqueous blends of N-methyldiethan olamine (MDEA) and diethanolamine (DEA) and of gaseous H2S into aqueou s MDEA were measured in a quiescent, inverted-tube diffusiometer by mo nitoring the rate of pressure drop. A numerical model for absorption, diffusion, and reaction of CO2 and H2S in blends of MDEA, DEA, and wat er was developed. The model was used to regress diffusion coefficients of bicarbonate, carbamate, and MDEAH(2)CO(3) for the case of CO2 abso rption and of bisulfide ion for the case of H2S absorption from measur ed absorption rates. CO2 absorption rates and diffusion coefficients o f bicarbonate, carbamate, and MDEAH(2)CO(3) were obtained at 298.2 K a nd 318.2 K in aqueous solutions containing 50 mass % total amine at DE A:MDEA mole ratios of 1:20, 1:4, 1:3, and 2:3. H2S absorption rates an d 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.