Specially designed internals were used in a novel two-stage internal-loop airlift reactor to effectively decrease liquid backmixing by analogy with the tanks-in-series concept.The effects of the inter-stage internal type

superficial gas and liquid velocities and gas-liquid separator on the gas holdup and liquid circulation velocity in each stage were experimentally studied.The results showed that superficial gas velocity had a significant effect on the difference between gas holdups in the riser and the downcomer and liquid circulation velocity in the second stage (the top stage)

but had a smaller effect on those in the first stage (the bottom stage).The gas holdups both in the riser and the downcomer slightly decreased with an increase in superficial liquid velocity.A mathematical model for predicting liquid circulation velocity was proposed based on the balance between driving and resistance forces

and a good agreement was obtained between the calculated and experimental data.