Effects of gas depletion on gas-liquid reaction systems

Abstract

The gas holdup and, consequently, the interfacial area for absorption vary inversely with the rate of interfacial mass transfer in a gas-liquid reactor. This is the principal basis for the bounding influence of the gas phase on the rate of absorption when the gaseous feed contains only the reactant and the reaction does not have any gaseous products. A model of a nonisothermal gas-liquid CSTR is formulated that shows the effect of the gas phase on the steady-state temperatures and the steady-state multiplicity. The bounding influence of the gas phase becomes paramount when the gaseous feed is not in excess and the gas solubility and the reaction rate are large. The exothermic reaction between CO₂ and aqueous NaOH solution is studied experimentally in a CSTR. The results show that for this fast reaction system the depletion of both the gaseous and liquid reactants determines the steady state. For such a system, as predicted by the theory, the reactor performance does not depend on the reaction rate, the enhancement factor, the mass-transfer coefficient and the interfacial area, as long as the reaction remains fast.