Determination and Measurements
of Mass Transfer Kinetics of CO<sub>2</sub> in Concentrated Aqueous
Monoethanolamine Solutions by a Stirred Cell
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Abstract
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 CO<sub>2</sub> partial
pressure (3–4 kPa) was employed to satisfy the criterion for
a pseudo-first-order reaction. Very low inert gas pressures of N<sub>2</sub> 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 CO<sub>2</sub> at
298.15 K agrees with literature. The reaction activation energy (<i>E</i><sub>a</sub>) of aqueous MEA + CO<sub>2</sub> is 44.89
kJ mol<sup>–1</sup>, and the pre-exponential factor value is
4.14 × 10<sup>11</sup>. The enhanced mass transfer coefficient
in the liquid phase, <i>k</i><sub>L</sub><i>E</i>, initially increases with the concentration of MEA solutions but
decreases when the molarity of MEA is higher than 8 M