Methods for the determination of mass‐transfer coefficients and effective interfacial areas in packed absorption columns are reviewed. For each parameter, the methods are grouped into categories on the basis of their physical principle; the chemical systems used, experimental protocol, and the advantages and inconveniences are discussed. The treatment of end effects, the influence of packed bed height, and the recent efforts in standardization of measurement methods are also treated. The aim of the review is to give a broad overview of the methods used in literature in the last eight decades, some of which might be reconsidered in the light of modern measurement techniques and to evaluate them in relation to precision, practicality and hazardousness thereby to facilitate the search for reliable, precise, and convenient experimental practices.

Absorption methods for the determination of mass transfer parameters of packing internals: A literature review

................................................................................................................................................................... xi Acknowledgements ........................................................................................................................................... xiii

Survey of gas-liquid mass transfer in bioreactors

Chapter 2 – Investigation of the main performance characteristics of packed bed columns

This chapter discusses the industrial packings for column apparatuses. It reviews some experimental data for their performance characteristics and equations for calculating these values. For each industrial apparatus, the flow rates of the gas and liquid phases are preliminary fixed. In the case of uniform distribution of phases over the cross-section of the column, these values determine the average concentration difference. The increase of the mass transfer coefficient is connected with the reduction of the average contact time on the interface. The time decreases with the increase of the flow velocity and with reduction of the length of liquid film. As per the mass transfer theory, the intensification of the packed bed column can be achieved in two ways: creating packings that allow operation at high gas and liquid superficial velocities at small hydraulic diameter of the packing and creating packings that promote frequent breaks of the liquid film and coalescence and break of the drops and jets in the packing free volume. This chapter concludes by focusing on the comparisons among various important packings.

Chapter 3 – Industrial packings

The main objectives of this work were, first to see whether an unsteady-state diffusion theory was applicable to mass transfer into a liquid film flowing over the surface of a packing piece such as a Raschig ring or a Berl saddle, and, second, to obtain a general correlation for liquid phase mass transfer coefficients of these packings.Absorption of pure carbon dioxide by three solvents, water, methanol and n-butanol, were carried out in a column, where single pieces of Raschig rings or Berl saddles were located as shown in Fig. 1. Figs. 2 and 3 show the values of HL for a Raschig ring in case θ is 45°. When the values of (HL/z)·(Ga1/6/Sc1/2) are calculated from these data and plotted against Re as shown in Figs. 4 and 5, the data points for all runs come on a single line as represented by Eq. (5). These results indicate that mass transfer into a liquid film flowing over the packing pieces closely follows predictions based on the unsteady-state diffusion theory. Figs. 6, 7 and 8, similar to Figs. 4 and 5, show the results given with a Raschig ring (θ=90°), with a short wetted-wall column corresponding to a Raschig ring (θ=0°) and with a Berl saddle (θ=45°), respectively. The best lines through the data in these figures are expressed by Eqs. (6), (7) and (8), respectively. Taking the variation of HL with θ into account, Eqs. (19) and (20), giving the average values of HL for single pieces of Raschig rings and Berl saddles, have been obtained.In order to determine the effect of Schmidt number on HL for packed columns, additional experiments on the absorption of pure solute gases, hydrogen, oxygen and carbon dioxide, by water were carried out in a 7.0cm column packed with 15mm Raschig rings. Experimental results indicate that the values of HL vary as the 1/2 power of the Schmidt number, in agreement with the unsteadystate diffusion theory.

H. Hikita

Papers

Mass Transfer into a Liquid Film Flowing over a Packing Piece