Carbon dioxide transport rate in a stirred and sparged tank: Stirring speed and gas flow rate influences

Abstract

Gas-liquid transport rate of CO₂ in a stirred and sparged tank reactor has been studied. The volumetric mass transfer coefficient k_La has been determined by a dynamic method of both CO₂ absorption and desorption. The k_La values obtained by both techniques, absorption and desorption, present small differences, although the data obtained by desorption are more reliable and less error. The influences of the stirring speed (values from 100 to 700 rpm) and the gas flow rate (value of 0.1, 0.5 and 1 L/min) have been analyzed. The measurements were carried out by controlling the pH value or by letting its value evolve with the CO₂ absorption. For the calculations of the volumetric carbon dioxide mass transfer coefficient, the concentrations of the different species formed when CO₂ is dissolved in water were taken into account. Experimental values of the volumetric mass transfer coefficient for CO₂ as a function of stirring speed and gas flow rate were fitted and an empirical equation for k_La prediction is proposed. Moreover, values of the volumetric mass transfer coefficient for O₂ have been determined in the same reactor under the identical conditions, obtaining also an empirical equation. The comparison of the volumetric mass transfer coefficients for both CO₂ and O₂ is discussed. In general, the results achieved are in agreement with the few data previously published.