Influence of Alcohol Addition on Liquid-Phase Volumetric Mass Transfer Coefficient in an External-Loop Airlift Reactor with a Porous Plate

In this work, the effect of alcohol addition on the liquid-phase volumetric mass transfer coefficient, k(L)a(R), is studied in an external-loop airlift reactor with a porous plate using an air-water system to which methanol, ethanol or propanol was added in concentrations ranging from 0.002 to 1 wt%. The experimental results show that the addition of small amounts of alcohol increases dramatically the liquid-phase volumetric mass transfer coefficient in the riser, due to smaller bubble diameter than with the water system. This behavior is enhanced by alcohols with long carbon chain lengths, which may be probably explained on the basis of the inhibition of bubble-bubble coalescence at the gas sparger plate and in the liquid. This surprising result can be explained by a strong increase in k(L) values in liquid-phase volumetric mass transfer coefficients due to the increasing amount of small bubbles leading to larger partial pressure of transfer component within bubbles based on capillary pressure. A remarkable effect of alcohol addition on liquid-phase volumetric mass transfer coefficient was not observed above the critical concentration of each alcohol.