ABSORBTION KINETICS OF CARBON DIOXIDE BY LITHIUM CARBONATE AQUEOUS SOLUTION

Abstract

The kinetics of absorption (chemisorption) of carbon dioxide by an aqueous solution of lithium carbonate at a temperature of 293 K and in the pressure range 8.0·103 – 3.2·104 Pa was studied. Lack of inhibition of the reaction by dissolving carbon dioxide, i.e. the occurrence of the reaction in the kinetic region was proven by conducting experiments to establish the dependence of the process rate on the intensity of stirring the solution. The voltage supplied to the stirrer motor was determined, starting from which the kinetic curves of CO2 absorption merged with each other, i.e. the rate of CO2 absorption ceased to depend on the intensity of mixing - the so-called maximum absorption rate. The effect of lithium carbonate concentration on the absorption rate was studied at a constant carbon dioxide pressure of 1.6·104 Pa. It was found that the initial reaction rate was practically independent on the initial concentration (zero order reaction). However, as the reaction product accumulated, it slowed down: the zero order of the reaction passed into the first. The dependence of the reaction rate on carbon dioxide pressure was determined at the same initial concentration of lithium carbonate solution 0.2027 M and different pressures. It was found that with increasing pressure the rate of the process increased linearly. First order on carbon dioxide concentration was observed. To explain the observed patterns, a diagram of the reaction mechanism is proposed, from which the kinetic equation was derived. The effective absorption rate constants were calculated. Based on the proposed reaction mechanism, the inhibition of absorption by the reaction product is explained. Its addition shifts the absorption-chemical equilibrium, thereby reducing the concentration of hydrogen ions. The resulting kinetic equation can serve as the basis for calculating and optimizing the operation of industrial carbon dioxide absorbers.