Article ID: 12we164
The escapable gas holdups and volumetric oxygen transfer coefficients were measured in several concentrations of xanthan aqueous solutions in four standard bubble columns, in which slug bubble flow was observed. The experimental escapable gas holdups were well estimated by the semi-theoretical Nicklin's equation modified to apply for non-Newtonian xanthan aqueous solutions having yield stress. Although the escapable gas holdup increased with decreasing column diameter and increasing superficial gas velocity, it was hardly influenced by the concentration or apparent viscosity of 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 correlation of all experimental results, an empirical equation was proposed. To design a more efficient bioreactor, the partitioning perforated plate which is applicable for larger column than those of Terasaka a nd Shibata (2003a) was inserted into the standard bubble column. The gas holdup and volumetric oxygen transfer coefficient were measured in the partitioned bubble columns and 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 diameter. Therefore, the partitioned bubble column bioreactors were developed for more suitable production of xanthan gum in this study.
