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In this work, a comprehensive model is developed for the absorption of carbon dioxide into aqueous mixtures of primary or secondary alkanolamines with tertiary alkanolamines. The model, which is based on penetration theory, incorporates an extensive set of important reversible reactions and takes into account the coupling between chemical equilibrium, mass transfer, and chemical kinetics. The reaction between CO 2 and the primary or secondary amine is modeled according to the zwitterion mechanism. The key physicochemical properties that are needed for the model are the CO 2 physical solubility, the CO 2 and amine diffusion coefficients, and the reaction rate coefficients and equilibrium constants. Data for carbon dioxide absorption into aqueous mixtures of diethanolamine and methyldiethanolamine are compared to model predictions.

A wetted-sphere absorption apparatus was used to measure the liquid-phase diffusion coefficients for hydrogen sulfide, carbon dioxide, and nitrous oxide over the temperature range 293-368 K. The experimental results obtained in this work are compared with values in the literature and with predictions from the Wilke-Chang equation. The data presented here extend the temperature range of reported diffusivities for these gases in water.

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The kinetics of the reaction between CO2 and aqueous diethanolamine (DEA) were estimated over the temperature range of 293−343 K from absorption data obtained in a laminar-liquid jet absorber. The absorption data were obtained over a wide range of DEA concentrations and for CO2 partial pressures near atmospheric. A rigorous numerical mass-transfer model based on penetration theory in which all chemical reactions are considered to be reversible was developed and used to estimate kinetic rate coefficients from the experimental absorption data. The kinetic data were found to be consistent with the zwitterion mechanism. The scarce zwitterion rate coefficient estimates reported in the literature are in fair agreement with the results of this work.