Ozone Mass Transfer with Combined Effects of Ozone Decomposition and Reaction with Pollutants in a Semibatch Stirred Vessel

Abstract

The mathematical models for a semibatch stirred gas-liquid contactor proposed by Anselmi et al. (1984, 1985) are extended to described the mass transfer of ozone absorption, decomposition and reaction with pollutants in aqueous solution with the decomposition and reaction rate expressions of general reaction orders (not necessarily integers) taking into consideration the effects of ozone decomposition and reactions on absorption. Four system equations are employed to describe the ozone (A) concentrations in the bulk liquid (CALb), the hold-up gas (CAGi), and the outlet gas in the free volume above the liquid surface (CAGe), and the pollutant (B) concentration in the bulk liquid (CBTLb), respectively. The combined effects of ozone decomposition and reaction with pollutant on the mass transfer, which are reflected by the enhancement factor (Er) defined as the ratio of mass absorbed per unit area in time t with chemical reactions to that without chemical reactions or of the purely physical absorption, are considered in the refined model. Furthermore, the model also takes into account the variation of Er with CALb and CBTLb, which vary with time during the course of gas-liquid contacting. Comparison of the predicted values of concentrations of the proposed model in simplified from with the experimental data of Anselmi et al (1985) indicates good agreement. For ozonation systems with high reaction rates(for example, ozonation of o-cresol investigated by Beltran et al. (1990)), the enhancement factors are large and cause significant influence on the mass transfer of the ozone and pollutant.