Measurement of gas—liquid parameters in a mechanically agitated contactor

The volumetric mass transfer coefficient k_La for a mechanically agitated gas—liquid contactor was measured by employing the dynamic method developed recently by Panja and Phaneswara Rao (Trans. Inst. Chem. Eng., 69 (1991) 302), which consists of bubbling pure CO₂ into an aqueous solution and following the concentration of the bicarbonate ion continuously with the help of an electrical conductivity probe. A mathematical model was used which enabled the value of k_La to be determined by a non-linear least-squares method. In the present work the above method has been extended to study the effect of process variables such as temperature, solids concentration, viscosity and interfacial tension on k_La in a tank of diameter 16.4 cm with the standard tank configuration. The value of k_La was found to increase (1) with increasing temperature of the liquid, (2) with increasing amount of dissolved isopropanol and amyl alcohol, which cause a reduction in surface tension, (3) with increasing solids concentration in the range 0–6 wt.% and (4) with increasing ion concentration. However, the value of k_La was found to decrease (1) with increasing viscosity and (2) with increasing solids concentration above 6 wt.%. A new correlation for k_L was obtained from the values of K_L calculated from the present k_La data by knowing the value of interfacial area from the equation of Calderbank (Chem. Eng., 45 (1967) CE-209). The effect of the presence of an alcoholic compound (amyl alcohol) under miscible and immiscible conditions on gas holdup was also investigated experimentally. The gas holdup was found to first decrease and then increase in the miscible range of amyl alcohol, again decrease and finally increase at a higher volume fraction of amyl alcohol, when an immiscible phase of amyl alcohol also formed.