Gas‐liquid kinetics: The absorption of carbon dioxide in diethanolamine

Abstract

Abstract The absorption of carbon dioxide in pure diethanolamine was studied in a gas‐liquid stirred reactor at 85°, 95°, and 105°F. Over forty runs were made but only nineteen were reported here since several were invalidated by difficulties with the stirring mechanism and reaction‐temperature control. The absorption was followed by pressure‐time measurements with the carbon dioxide pressure ranging between 30 and 4 cm. of mercury. Experimental data were consistent and reproducible. An equation describing the gas‐liquid absorption system was derived and then simplified by considering only the kinetic region. The experimental data were correlated with the simplified equation by both integral and differential methods and indicate that the reaction follows a third‐order rate equation: first order in carbon dioxide and second order in diethanolamine. A mechanism explaining the observed order is described. Justification for assuming kinetic control of the absorption was demonstrated by doubling and tripling the stirring speed which produced no significant change in the absorption rate. Also, the temperature dependence of the pseudo‐rate constants was out of the range of ordinary mass transfer control. This agrees with the results of a theoretical model reported previously (6).