Influence of oxygen adsorption on the dynamic K_La measurement in three‐phase slurry reactors

To check for possible mass transfer limitations of oxygen and/or carbon dioxide in kinetic experiments on microbial desulphurization of coal, it is important to properly measure the volumetric mass transfer coefficient (k_La) especially at high slurry densities. Volumetric mass transfer coefficients of oxygen, at different solid hold‐up values (ε_s = 0 to 0.28) of coal slurries (d_par < 100 * 10⁻⁶ m), were measured in a lab scale fermentor and in a lab scale pachuca tank, using the dynamic gas–liquid absorption method. It was shown that serious errors could occur due to oxygen adsorption at the coal surface. Using the data of an independently measured adsorption isotherm, the real k_La could be calculated from the measured apparent k_La. The results show a k_La decrease of 40% to 50% at a volumetric solid hold‐up of 28%. Estimation of the oxygen and carbon dioxide transfer rates, from the measured mass transfer coefficients, indicates that the stirred fermentor is suitable for kinetic experiments at high slurry densities, whereas the pachuca tank and shake flask are not. © 1992 John Wiley & Sons, Inc.