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 reversible two-step reactions in the liquid phase has been presented. This model has been used to determine mass transfer rates, enhancement factors and concentration profiles over a wide range of process conditions. Although results presented in this paper deal with reactions of unit stoichiometric and kinetic orders only, the model has been prepared for general orders. The effect of reversibility of each individual reaction along with their combined reversibility has been presented over a wide range of Hatta numbers. Influence of species diffusivity has also been considered. It has been shown that for low mobility of the gaseous species, the enhancement by reversible reactions can be higher than the corresponding enhancement obtained assuming the reactions to be irreversible. The presence of solute loading has been found to significantly affect the absorption characteristics of the system. An approximate method to determine infinite enhancement factors for reversible two-step reactions has been presented. The match between numerically predicted 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 agreement was observed for a wide range of gas?liquid contact times.

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