Measurement and Prediction of Axial Distribution of Immobilized Glucose Oxidase Gel Beads Suspended in Bubble Column

Abstract

The axial distribution of gel beads suspended completely in a bubble column was measured by sampling the three-phase dispersion through a vertical pipe located at any height of the column axis under various operating conditions of superficial gas velocity U_G, average gel beads holdup ε_S and unaerated slurry height H_D. The gel beads used were prepared by entrapping glucose oxidase as well as fine palladium particles within calcium alginate gel to catalyze the air oxidation of glucose for efficient production of calcium gluconate. The conventional sedimentation-diffusion model, which includes the gel beads dispersion coefficient E_P and their settling velocity v_P to describe the axial distribution, is found to give unreasonable E_P values being at least twice as high as than those predicted from the published correlations, and also twice as high as the estimated values of the liquid dispersion coefficient E_L in the three-phase bubble column. This was assumed to be ascribed to the reduced apparent values of v_P, since the intrinsic E_P value should be nearly equal to the E_L value. In view of the fact that the gel bead has almost the same density as the liquid phase and the size is comparable to the mean bubble size, the model was modified by introducing an additional parameter, the rise velocity of the gel beads swarm u_m representing an effect of rising air bubbles on settling gel beads. The values of u_m were determined from the observed axial distributions by assuming that the E_P values are given by the reported correlation of E_L in suspension of the inert calcium alginate gel beads, and empirically correlated with U_G and ε_S. The axial distributions calculated from the modified model well agreed with the observed ones for the different H_D.