Abstract
The Danckwerts’ plot method is a commonly used graphical technique to independently determine the interfacial area and mass-transfer coefficient in gas–liquid contactors. The method was derived in 1963 when computational capabilities were limited and intensified process equipment did not exist. A numerical analysis of the underlying assumptions of the method in this paper has shown a bias in the technique, especially for situations where mass-transfer rates are intensified, or where there is limited liquid holdup in the bulk compared to the film layers. In fact, systematic errors of up to 50% in the interfacial area, and as high as 90% in the mass-transfer coefficients, can be expected for modern, intensified gas–liquid contactors, even within the commonly accepted validity limits of a pseudo-first-order reaction and Hatta numbers in the range of 0.3 < Ha < 3. Given the current computational capabilities and the intensified mass-transfer rates in modern gas–liquid contactors, it is therefore imperative that the equations for reaction and diffusion in the liquid films are numerically solved and subsequently used to fit the interfacial area and mass-transfer coefficient to experimental data, which would traditionally be used in the graphical Danckwerts’ method.
Highlights
Novel types of process equipment have recently been developed in which the mixing and hydrodynamics of gasses and liquids directly lead to better gas–liquid mass-transfer performance [1,2,3,4,5].By reducing limitations in heat and mass transfer, chemical processes can be performed at their intrinsic kinetic conditions
Accurate measurements of the interfacial area for gas–liquid mass transfer, and of the gasand liquid-phase mass-transfer coefficients, are required in order to understand the effect of different design and operating parameters on the mass-transfer performance of gas–liquid contactors and reactors
(kL ) using the Danckwerts’ plot in the intermediate reaction regime for the different equipment. These results show that the Danckwerts’ plot method leads to acceptable estimations of the. These results show that the Danckwerts’ plot method leads to acceptable estimations of the interfacial area but estimates of the mass-transfer coefficient are subject to a systematic error
Summary
Novel types of process equipment have recently been developed in which the mixing and hydrodynamics of gasses and liquids directly lead to better gas–liquid mass-transfer performance [1,2,3,4,5]. By reducing limitations in heat and mass transfer, chemical processes can be performed at their intrinsic kinetic conditions. These intensified processes will help meet the societal demand for safer, more efficient, and economical production of chemicals. Accurate measurements of the interfacial area for gas–liquid mass transfer (aGL ), and of the gasand liquid-phase mass-transfer coefficients (kG and kL , respectively), are required in order to understand the effect of different design and operating parameters on the mass-transfer performance of gas–liquid contactors and reactors
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