抄録
Escapable gas holdups and volumetric oxygen transfer coefficients were measured at several concentrations of xanthan aqueous solutions in four standard bubble columns in which a slug bubble flow was observed. The experimental escapable gas holdups were well estimated by the semi-theoretical Nicklin’s equation modified for non-Newtonian xanthan aqueous solutions having yield stress. Although the escapable gas holdups increased with decreasing column diameter and increasing superficial gas velocity, it was hardly influenced by the concentration or apparent viscosity of the xanthan aqueous solutions. The volumetric oxygen transfer coefficient increased with decreasing yield stress of the liquid, increasing diffusion coefficient, decreasing column diameter, and increasing gas holdup. By correlating all experimental results, an empirical equation was proposed. To design a more efficient bioreactor, the partitioning perforated plate which is used in columns larger than those used by Terasaka and Shibata, was inserted in the standard bubble columns. The gas holdup and volumetric oxygen transfer coefficient in the partitioned bubble columns were measured and were compared with those in the standard bubble columns. The volumetric oxygen transfer coefficients in the partitioned bubble columns became larger than those in the standard bubble columns at a fixed superficial gas velocity, even for large column diameters. Therefore, in this study, partitioned-bubble column-bioreactors were developed for more suitable production of xanthan gum.
