Measurement of Overall Volumetric Mass Transfer Coefficients for Carbon Dioxide in a Well-Mixed Reactor Using a pH Probe

Carbon dioxide can serve as a source of carbon for photosynthetic cell cultures, but it must reside in the aqueous phase prior to uptake. Carbon dioxide is a gas at room temperature and pressure, and its solubility in water is very low. It resides in the aqueous phase as four different species, carbon dioxide, CO 2; carbonic acid, H 2 CO 3; bicarbonate ion, HCO 3 -; and carbonate ion, CO 3 =, whose equilibrium concentrations are pH dependent. With these factors taken into account, a model has been developed to allow the pH profile of an aqueous phase, undergoing a sudden application of bubbles containing carbon dioxide, to be used as a measure of the transient dissolved carbon dioxide concentration in a reactor. Experimentally measured carbon dioxide profiles were used to calculate the overall volumetric mass transfer coefficients for carbon dioxide into a well-mixed reactor as a function of temperature, stirring speed, and aeration rate. Finally, an empirical correlation is provided to predict the overall volumetric mass transfer coefficient of carbon dioxide as a function of these three operating variables.