Determination and Measurements of Mass Transfer Kinetics of CO₂ in Concentrated Aqueous Monoethanolamine Solutions by a Stirred Cell

The gas–liquid reaction rate was determined with a stirred cell from the fall in pressure and the reaction rate constant was determined by two data treatment methods, viz. a “differential” and an “integral” method. The liquid-side mass transfer coefficient without chemical reaction in the stirred cell reactor was determined via the pressure drop method. The kinetics of the reaction of carbon dioxide with aqueous monoethanolamine (MEA) solutions over a wide concentration range from 0.5 to 12 M at a temperature range from 298.15 to 323.15 K were studied using a stirred cell absorber with a plane gas–liquid interface. Low CO₂ partial pressure (3–4 kPa) was employed to satisfy the criterion for a pseudo-first-order reaction. Very low inert gas pressures of N₂ and solution vapor were kept, and the stirrer was sped up to reduce the gas-phase resistance. The results showed that the investigated reactions took place in the pseudo-first-order fast reaction regime. The reaction rate constant obtained for MEA with CO₂ at 298.15 K agrees with literature. The reaction activation energy (<i>E</i>_a) of aqueous MEA + CO₂ is 44.89 kJ mol^–1, and the pre-exponential factor value is 4.14 × 10¹¹. The enhanced mass transfer coefficient in the liquid phase, <i>k</i>_L<i>E</i>, initially increases with the concentration of MEA solutions but decreases when the molarity of MEA is higher than 8 M

Measurements and Correlations of Diffusivities of Nitrous Oxide and Carbon Dioxide in Monoethanolamine + Water by Laminar Liquid Jet

The molecular diffusivities of nitrous oxide (N₂O) with aqueous monoethanolamine (MEA) solutions up to 12 M were studied over a temperature range from 298.15 to 333.15 K under atmospheric pressure using a laminar liquid jet absorber. The diffusivities of CO₂ in aqueous MEA solutions were calculated by the “N₂O analogy” method. A simple and effective thermal control technique was used to control the temperatures of gas and liquid in the laminar liquid jet absorber. The rates of absorption were determined by measuring the flow of gas needed to replace the gas absorbed. The results showed that the diffusivities of both N₂O and CO₂ into aqueous MEA solution decrease with the increase of the concentration of MEA, and increase with an increase of the temperature of the solution. The relationship between the diffusivity and the viscosity of the solution roughly agrees with the modified Stokes–Einstein equation, but an exponent mathematical model was employed to simulate the diffusivity data and shows a better agreement between data and model for the diffusivity of N₂O and CO₂ in the monoethanolamine + water system