Transient Characteristics of Oxygen Electrode and Determination of Volumetric Oxygen Transfer Coefficient in a Bubble Column

We investigated the transient characteristics of an oxygen electrode with a 50 μm PTFE membrane, which was employed to determine the liquid-phase volumetric oxygen transfer coefficient kLa' in a bubble column with air-water and a 65 vol. % glycerol solution system. The transient response curve of the probe in this case was represented by the semi-empirical equations proposed in this work. These equations have three parameters, i.e., kLa', the response time lag τ and the inverse first-order time constant k of the probe. These parameters were estimated by the nonlinear curve fitting of the experimental response data. The τ value was independent of superficial gas velocity and decreased with the rise in temperature of the liquid. The k value increased with increasing superficial gas velocity. It was found that the first-order delay of the response curve depended on the k/kLa' value and increased rapidly below k/kLa'= 5. The k/kLa' values of water and 65 vol.% glycerol solution were in the range of about 2 to 6. The kLa' value determined from the slope of the strait line portion of the semi-logarithmic plot of the experimental response data was about 80 to 95% of that determined by the nonlinear curve fitting at k/kLa'= 2.