Mass transfer with complex chemical reactions in gas-liquid systems: two-step reversible reactions with unit stoichiometric and kinetic orders

An absorption model to study gas-liquid mass transfer accompanied by revers ible two-step reactions in the liquid phase has been presented. This model has been used to determine mass transfer rates, enhancement factors and con centration profiles over a wide range of process conditions. Although resul ts presented in this paper deal with reactions of unit stoichiometric and k inetic orders only, the model has been prepared for general orders. The eff ect of reversibility of each individual reaction along with their combined reversibility has been presented over a wide range of Hatta numbers. Influe nce of species diffusivity has also been considered. It has been shown that for low mobility of the gaseous species, the enhancement by reversible rea ctions can be higher than the corresponding enhancement obtained assuming t he reactions to be irreversible. The presence of solute loading has been fo und to significantly affect the absorption characteristics of the system. A n approximate method to determine infinite enhancement factors for reversib le two-step reactions has been presented. The match between numerically pre dicted results and those obtained from the approximate technique was found to be within 0.05%. Finally, the present model has been validated against a practical system. The absorption of CO2 in NaOH and bicarbonate solutions in model contactors has been chosen for this purpose. An excellent agreemen t was observed for a wide range of gas-liquid contact times. (C) 2000 Elsev ier Science S.A. All rights reserved.