Influence of alcohol addition on gas hold-up, liquid circulation velocity and mass transfer coefficient in a Packed Bed Split- Cylinder airlift bioreactor

The aim of this work is to investigate the effect of different alcohols on the hydrodynamics and oxygen mass transfer characteristics in a split-cylinder airlift reactor, both with and without packing. The hydrodynamic parameters and mass transfer coefficient in 1% (v/v) aqueous solutions of four aliphatic alcohols (CnH2n+1OH, n = 1–4) were examined. The experimental results showed that the addition of alcohols increase gas hold-up and volumetric gas–liquid mass transfer coefficient which is due to smaller bubble diameter, but lead to a significant decrease of liquid circulation velocity relative to the values determined for tap water system. This behavior is enhanced by alcohols with long carbon chain lengths, which has been explained on the basis of surface tension effects. Small amount of ceramic Pall Ring packing with78% porosity has been inserted in the riser section of airlift bioreactor .The packing installation increases the overall gas– liquid volumetric mass transfer coefficient, gas hold-up and decreases bubble size and liquid circulation velocity.