Non-isothermal gas absorption with reversible chemical reaction

Abstract

A fundamental description of non-isothermal mass transfer accompanied by a single reversible chemical reaction has been presented. The description is based on the Higbie penetration theory. Arrhenius type dependence of solubility, reaction rates and diffusivities on temperature has been assumed. Special emphasis has been paid to bimolecular irreversible reactions where depletion of the liquid phase reactant occurs. In addition, the mass transfer behavior in the infinite enhancement regime has also been presented. It has been shown that the Shah criterion fails under conditions where depletion of the liquid phase reactant occurs. In the infinite enhancement regime, the non-isothermal enhancement factor is dependent on the ratio of the diffusivities of the reactants, the ratio of the initial stoichiometric reactant concentrations and the activation energies of solubility and reactant diffusivity. These characteristics of the infinite non-isothermal enhancement factor have been reported earlier by Asai et al. (1985, A.I.Ch.E. J.31, 1304–1312). Additionally, it has been shown that, for bimolecular irreversible reactions, the use of correlations for interfacial temperature rise that assume all heat to be released at the interface is not valid for systems with low Lewis numbers but also not for systems where depletion of the liquid phase reactant occurs. Further, the model has been used to study the effect of reversibility on bimolecular reactions. The effect of temperature dependence of the solubility of the gaseous component and diffusivities of the various species on the overall enhancement has been presented. Since the non-isothermal enhancement factor of bimolecular reversible reactions is dependent on various parameters, it is not possible to determine its value by analytical or via approximate techniques. One is forced to use numerical methods for this purpose instead.