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Axial dispersion of the continuous phase in liquid-liquid extraction spray columns and internal sampling techniques Lim, Choon Jim


An internal sampler, a plastic cup probe, was constructed to replace a funnel-probe for sampling the dispersed phase (methyl isobutyl ketone) in a liquid-liquid extraction spray column. The dispersed phase sample can be withdrawn from the column by the plastic cup probe without being contaminated with the continuous phase water. For runs in which the mass transfer is from the continuous phase to the dispersed phase, the plastic cup probe results agree with those obtained by the funnel-probe. On the other hand, for runs in which the direction of mass transfer is reversed, the plastic cup probe tends to give slightly lower dispersed phase concentrations than does the funnel-probe at the same sampling elevation. It is believed that both methods of measuring concentrations are correct within less than 2%. The effect of mass transfer on the axial dispersion coefficient of the continuous phase in a 1.5-in. I.D. liquid-liquid extraction spray column was studied for various superficial velocities of two phases, and for various partitionable solute (acetic acid) concentrations in the continuous phase fed to the column. Tracer solution (sodium chloride solution) was injected steadily into the continuous phase in the column. Axial concentration profiles of the tracer were measured upstream, with respect to the continuous phase, from the tracer distributor. The steady state form of the dispersion equation was used to calculate the axial dispersion coefficient of the continuous phase. The results obtained show that there is no effect of mass transfer on the axial dispersion coefficient within the range of the investigation. Drop size distribution and holdup of the dispersed phase in the column also were measured. The drop size distribution always shows two peaks. It was found that there is no effect of mass transfer on both the drop size distribution and on the dispersed phase holdups within the range of investigation.

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