Experimental study of the aqueous CO₂-NH₃ rate of reaction for temperatures from 15 °C to 35 °C, NH₃ concentrations from 5% to 15% and CO₂ loadings from 0.2 to 0.6

The absorption reaction between aqueous NH3 and CO2 was studied using the Wetted Wall Column. A total of 27 different cases are investigated in the region defined by temperatures from 15 °C to 35 °C, NH3 concentrations from 5% to 15%, which are the typical solvent conditions in absorption columns, and lastly CO2 loadings from 0.2 to 0.6.

The resulting overall mass transfer coefficient of absorption measured follows the trends described by the modelling of the reactor and the equations used to describe the rate of the absorption reactions. Moreover, the overall mass transfer coefficient of absorption is in agreement with data available in the literature, valid in smaller portions of the investigated region.

From the data analysis, the kinetics of the absorption reactions in the liquid phase is characterized. The equation proposed to fit the data is a power law equation which reproduces the experimental results measured at different CO2 loadings. This represents a novelty because in literature the kinetic model of the reaction is usually fitted only to data for unloaded solutions (CO2 loading equal to zero).

Hence, in this case there is an experimental evidence that the kinetic model holds true in every loading conditions. The kinetic model intercept the values found in literature in every range of concentration. Consequently, the model is valid in every conditions and the rate of the reaction between NH3 and CO2 in liquid phase is described with an Arrhenius constant with a pre-exponential factor of 1.41·108 [mol/(m3s)] and an activation energy of 60,680 [J/mol], a linear dependence on the CO2 concentration and a dependence on the NH3 with an exponent γ = 1.89.

The proposed equation is found to be appropriate for implementation into process simulation software.