GAS-LIQUID MASS-TRANSFER IN A BUBBLE COLUMN WITH ORGANIC LIQUIDS

Water, methanol, toluene and ligroin were aerated in a bubble column of 0.15 m I.D. and a height of 4.3 m. Using a gas disengagement technique, the holdups of large bubbles were found to be similar in all liquids whereas the holdups of small bubbles differed significantly. Oxygen mass transfer studies with a dynamic absorption method were impaired by height- and time-dependent oxygen depletion in the gas phase. Only at low dispersion heights, there was agreement with the results of a steady state method. Photographic determination of the small bubbles' diameters and knowledge of their holdup fraction allowed to estimate their potential contributions to the mass transfer rate at gas flow rates up to 0.2 m/s. These contributions were generally high and in ligroin the estimates even exceeded the observed total oxygen transfer rate. It is concluded that the finite rates of coalescence and break-up reduce the driving force for mass transfer from the small bubble fraction.