Abstract
Kinetics of carbon dioxide evolution was investigated in agitation system. Reaction steps of carbon dioxide evolution in submerged fermentations may consist of three steps; the first, hydration of carbon dioxide liberated from living cells, the second, dehydration of bicarbonate ions and the third, formation of carbon dioxide bubbles. Taking into account the equilibrium between hydration of carbon dioxide and dehydration of bicarbonate ions at physiological pH value, the followings may be rate-limiting steps in mass transfer of carbon dioxide in submerged fermentations, dehydration of bicarbonate ions and the bubble formation. The overall velocity constant of these two reaction steps was determined in the agitation vessel. This reaction obeyed good first-order kinetics and the term of κ'HCO3- was introduced as a velocity constant. This value was influenced by agitation speed, temperature, viscosity of the fluid and carbonic anhydrase. The value of carbon dioxide coefficient (Kd)CO2, was higher than the oxygen absorption coefficient Kd. The driving force of mass transfer for carbon dioxide, DCO2-pCO2, therefore, was lower than that for oxygen, PB-PL. The relationship between the overall coefficient of oxygen transfer across gas-liquid interface KLα and the overall velocity constant of carbon dioxide evolution κ'HCO3- was expressed in the formula κ'HCO3-=0.40(KLα).0.68
