of packed columns for liquid--liquid extraction. The input of pulsing energy increases transfer rates and promotes counterflow of the two phases. The wetting characteristics of the packing influence performance.The toluene-benzoic acid-water system was used to observe the performance of a 2-in. diam. column containing ceramic (hydrophilic) rings, polyethylene (hydrophobic) rings, or a sieve-plate cartridge. The packed columns showed lower flooding limits than the plate column, but polyethylene packing gave highest transfer rates and capacities. The pulsing energy input was much lower for the plastic packing to effect a higher transfer rate.Flooding limits for the pulsed, packed columns were lower than for packed columns which were not pulsed. Columns packed with rings so that the ratio of diameter to packing size was 4:l gave higher flooding limits and better Performance than a ratio of 8:l. Liquid-liquid extraction columns have been found particularly effective for the recovery of uranium from fission products. The input of pulsing energy increases the rate of mass transfer and permits a reduction in the height of the column required and in capital investment.In a sieve-plate column the dispersed and continuous phases pass through holes in the plates and result in intimate contact between the phases. The pulsing action is necessary for satisfactory counterflow of the phases which may not otherwise occur. The pulsed, plate column has been investigated in detail (13 among many) in reference to its performance and flooding characteristics.The packed column offers a simpler type of construction, especially for larger diameters. The proper use of pulsed, packed columns requires information about flooding limits and transfer rates. Wetting characteristics of the packing surfaces are of special significance in liquid-liquid systems. The work reported below was conducted to observe the effect of surface wetting characteristics on performance and to compare a packed column with a plate column for the same system and operating conditions.
SURFACE EFFECTSLittle information appears in the literature concerning the performance and flooding characteristics of pulsed, packed columns. Qualitative behavior can be inferred; if the continuous phase wets the packing, the dispersed phase will move through the column as small droplets; if the dispersed phase wets the packing, it will move up the column as a film on the packing surface. In the latter case holdup of the dispersed phase will increase, and flooding will D. B. Grove i s with United Technology Corporation, Sunnyvale, California.
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