著者

Nitta Junya Terasaka Koichi Fukuda Hisashi Iwahashi Misa

出版者

公益社団法人 化学工学会

雑誌

アジア・太平洋化学工学会議発表論文要旨集

巻号頁・発行日

vol.2004, pp.969, 2004

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To produce xanthan gum which is a valuable bio-product as food, cosmetic and pharmaceutical, the stirred tank bioreactors are usually used in industry. Due to the yield stress of xanthan solution, however, local stagnant zone is appeared far from the impeller. In the stagnant zone, the oxygen feed to microorganism is limited so that the productivity of xanthan is also limited. On the other hand, the bubble column has little stagnant zone in viscous xanthan solutions under slug flow regime. Therefore, the performance of oxygen transfer into xanthan solutions in bubble column bioreactor is investigated. At first, gas holdups and volumetric oxygen transfer coefficients were measured in several concentrations of xanthan aqueous solutions in four standard bubble columns whose diameters are 0.03, 0.06, 0.1 and 0.2 m. In entire operating range and in all bubble columns, the slug bubble flow was observed. The experimental gas holdups were well estimated by the semi-theoretical Nicklin's equation modified to apply for non-Newtonian liquids having yield stress by Terasaka et al. Although the gas holdup increased with decreasing column diameter and increasing superficial gas velocity under slug bubble flow range, it was hardly influenced by the concentration or apparent viscosity of xanthan solutions. On the other hand, the volumetric oxygen transfer coefficient increased with decreasing yield stress of liquid, increasing diffusion coefficient, decreasing column diameter and increasing gas holdup in the experimental conditions. By correlation of all experimental results, an empirical equation was proposed. Secondly, to design more efficient bioreactors and to scale up, the standard bubble columns were improved with inserting partitioning perforated plates into the standard columns. The gas holdup and volumetric oxygen transfer coefficient were measured in the partitioned bubble columns as well as 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 even for large column diameter. Therefore, the partitioned bubble column bioreactors were developed for more suitable production of xanthan gum in this study.