No abstract

Gas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schiigerl et al. (1977) are presented. Data for cocurrent and batch systems are qualitatively explained using Zuber and Findlay's theory (1965) and bubble structure, and quantified further using a dynamic gas disengagement technique. Unified empirical correlations for the gas holdup and axial dispersion coefficients are presented.Applications of bubble columns as bioreactors and for the process of coal liquefaction are relatively recent. Characteristics of the liquid-phase media in these two reactors can be fairly well represented by dilute alcohol solutions. The only work reported on this subject is by Schugerl et al. (1977) for relatively lower gas and liquid throughputs. They propose an empirical correlation for gas holdup involving the bubble diameter which is more difficult to estimate than the gas holdup. They do not propose any correlation for determining the axial dispersion coefficient.The experimental studies were carried out in two different diameter columns using cocurrent and batch systems. Five aliphatic alcohols (methanol, ethanol, n-propanol, i-propanol, and butanol) were investigated with concentration varying from 0.5 wt % to 2.4 wt %. The gas holdup was measured using a hydrostatic head technique. The axial dispersion coefficient was measured using heat as a tracer, and was based on the dispersion model. A dynamic gas disengagement method is applied to quantify the bubble-size distribution and bubble-rise velocities. This method involves a measurement of a decline in liquid height as a function of time, after gas flow is suddenly stopped. The experimental data are explained both qualitatively and quantitatively. Empirical correlations for gas holdup and the axial dispersion coefficient, applicable over a wide range of gas and liquid throughputs are presented.This infers that the dispersion coefficient and the gas holdup are interrelated.