Mass transfer characteristics of a novel three-phase airlift contactor with a semipermeable membrane

The effects of hydrocarbon contaminants and solid loading on gas–liquid volumetric mass transfer coefficient, KLa, were studied in a three-phase 25 l concentric cylindrical airlift contactor with a semipermeable membrane. The porous membrane could retain a large volume of immobilized solid particles and enhanced mass transfer and mixing in the airlift contactor. A specific form of the continuity equation was combined with gas holdup values in order to set up an expression for the mass transfer coefficient calculation. Water with different hydrocarbon concentrations of 0–200 mg/l p-xylene and 0–25 mg/l naphthalene were used as liquid media, under varying solid loadings and superficial gas velocities. The results indicated that deviation of mass transfer coefficient could go either way when hydrocarbons were dissolved in water: the most significant reduction in KLa occurred at the concentration of 37 (mg/l) for p-xylene after which KLa recovered and increased slightly. A less severe depression of KLa was observed for naphthalene. Total solid loading in the airlift contactor was limited to the maximum amount of solid entrapped within the porous textile membrane. Higher superficial gas velocity resulted in the increase of the effect of solid loading on KLa.