Comparison of dynamic oxygen electrode methods for the measurement of KLa



The dynamic oxygen electrode method for measuring KLa requires the use of a dynamic process model. Six models from the literature are described and compared with respect to their accuracy and ease of use. It is shown theoretically that for sufficient accuracy KLa should be less than the inverse electrode response time. Experimental measurements demonstrate their application to viscous and nonviscous systems. The liquid diffusion film is shown to cause an important measurement lag that can be accounted for by a first-order time delay. Investigation on the influence of the experimental starting conditions show the importance of the gas and hold-up dynamics. A new method is proposed to simplify the KLa calculation and to eliminate errors caused by starting conditions. This method, which accounts for gas, film, and electrode dynamical effects, requires only a simple semilog plot of the response data.