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Absorption and desorption of CO2 and CO in alkanolamine systems Jamal, Aqil


Absorption and desorption of carbon dioxide (CO₂) and carbon monoxide (CO) in aqueous alkanolamine solutions are modeled and important kinetic and physical property data are obtained using novel experimental methods. The model is based on the principle of diffusional mass transfer accompanied with fast to very slow chemical reactions in the liquid phase. Fast reactions are represented by CO₂ absorption/desorption in aqueous alkanolamines and slow reactions are represented by CO absorption in aqueous diethanolamine (DEA). The experiments for CO₂ absorption and desorption were conducted in a novel hemispherical contactor designed and developed in this work. The absorption experiments were conducted at near atmospheric pressure using pure CO₂ saturated with water at 293 to 323 K with initially unloaded solutions. The desorption experiments were performed at 333 to 383 K for CO₂ loadings between 0.02 to 0.7 moles of CO₂ per mole of amine using humidified N₂ gas as a stripping medium. The experiments for CO absorption were carried out in a 660 mL batch autoclave reactor at 313 to 413 K with amine concentration between 5 to 50-wt% in distilled water. The partial pressure of CO in the reactor was varied from 800 to 1100 kPa. The data for CO₂ absorption and desorption in aqueous amine systems were analyzed using a new, rigorous mathematical model. The model predicts the experimental results well for all amine systems studied. The results indicate that the theory of absorption with reversible chemical reaction could be used to predict desorption rates. The kinetic data obtained show that desorption experiments could be used to determine both forward and backward rate constants accurately. The absorption experiments on the other hand could only be used to determine forward rate constants. The data for CO absorption in aqueous diethanolamine (DEA) solutions were analyzed using the model for mass transfer with extremely slow reactions. The data are consistent with a mechanism by which formyl-diethanolamine (DEAF) is predominantly formed by direct insertion of CO into DEA. The data also confirm that DEAF formation via the DEA-formate reaction is relatively slow and reversible.

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