GAS-PHASE BACKMIXING IN BUBBLE-COLUMN REACTORS

Gas-phase backmixing and holdup for the air-water system were measured in 0.15-and 0.25-m-dia. bubble columns. Novel experimental and analytical techniques were used to analyze the gas-phase residence time distribution. A Levenberg-Marquardt-type optimization scheme was used to obtain the two reactor model parameters: Peclet and Stanton numbers. Operating variables included the column diameter and the superficial gas- and liquid-phase velocities. A two-bubble-class hydrodynamic model has been proposed to predict the gas-phase backmixing in bubble column reactors. The model assumes a bimodal distribution of the gas phase with large bubbles flowing in a plug-flow manner and the small bubbles partially backmixed. The model only needs easily measurable parameters and has been validated by comparing experimental as well as literature data on gas-phase backmixing with the model predictions. The model is more realistic than the conventional single-bubble-class model and provides a rational approach to predict the gas-phase backmixing in scaling-up bubble-column reactors.