Liquid-Phase Volumetric Mass Transfer Coefficient for Dilute Alcohol Solution in an External-Loop Airlift Reactor with a Porous Plate (effect of Pore Size of Porous Plate)

The aim of this work is to investigate the influence of the addition of alcohol on the behavior of an external-loop airlift reactor with a porous plate. The mass transfer parameter in dilute aqueous solutions of three aliphatic alcohols (methanol, ethanol and n-propanol) was examined using five kinds of porous plates. The results showed that dilute alcohol addition enhanced dramatically liquid-phase volumetric mass transfer coefficient, kLaR, in the riser, especially led to the remarkable enhancement of that for the porous plate having small pore diameter due to smaller bubble diameter than with water system. This behavior is enhanced by alcohols with long carbon chain lengths probably due to the inhibition of bubble-bubble coalescence at the porous plate and in the liquid. This surprising result might be explained by a strong increase in kL values in liquid-phase volumetric mass transfer coefficient due to the increasing amount of small bubbles leading to large partial pressure of transfer component within bubbles based on capillary pressure as explained previously [1]. Also, the results showed that the liquid-phase volumetric mass transfer coefficient increased with the concentration of alcohol, but led to reduction of the volumetric mass transfer coefficient over any critical concentration for each porous plate. Moreover, empirical equation for liquid-phase volumetric mass transfer coefficient is obtained.