INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1952
The results may be explained qualitatively by the highly tentative hypotheses that extraction tends t o follow the transient film mechanism for all solvent droplets; t h a t when certain impurities are present they tend t o concentrate a t the water interface if the solvent is nonpolar, thus setting u p interfacial barriers t o transfer; and that numerous alcohols when added t o such nonpolar solvents tend t o displace or destroy any such interfacial barriers. NOMENCLATURE
c = concentration
Subscripts or Superscripts C = continuous phase D = dispersed phase or drops i = interfacial concentrations * = superscript indicating equilibrium concentration LITERATURE CITED
Beck, T. R., R.S. thesis, University of Washington, 1949. Chu, J. C.,Taylor, C. C . , and Levy, D. J., IND.ENQ.CHEM., 42, 1157 (1950).
of solute in either phase, gram moles per
ml.
D
631
= diffusivity of solute in either phase, square cm. per second
= correction factor in Equation 4 = effective mass transfer coefficient for either phase, cm. per second KD = over-all mass transfer coefficient based on drop concentrations, cm. per second m = appropriate slope of equilibrium curve defined by Equation 5 h r o D = over-all number of transfer units for a column based on drop concentrations ANOD=difference in NODbetween tall and short columns R = per cent extraction r = radius of drop considered as a sphere, cm. = time for a drop t o rise through the continuous phase, seconds At = difference in t between tall and short columns = life of a transient film. Usually taken as t h e time for a t, drop t o rise a distance equal t o i t s own diameter, seconds v = velocity of rise of drops, cm. per second 4 = parameter in Wilke’s (14) correlation for diffhsivities in liquids
fc
k
Farmer, W. S., “Controlling Variables in Liquid-Liquid Extraction from Single Drops,” Oak Ridge National Laboratories, Unclassified Rept. 635 (1950). Fetterly, L. C., Ph.D. thesis, University of Washington, 1950. Hermann, A. J., and Chong, A. T.,B.S. thesis, University of Washington, 1950. Higbie, R., Trans. Am. I n s t . Chem. Engrs., 31,365 (1935). Licht, W., Jr., and Conway, J. B., IND.ENG.CHEM.,42, 1151 (1950).
McGregor, D.X., B.S. thesis, University of Washington, 1949. Robinson, P. A., and Morgenthaler, A. C., Jr., B.S. thesis, University of Washington, 1948. Sherwood, T. K., Evans, J. E., and Longcor, J. V. A., IND.ENO. CHEM.,31, 1144 (1939). Thomas, L. E. K., B.S. thesis, University of Washington, 1950. Ward, A. F. H., Research (London), Suppl., Surface Chemistrv 1949,55.
West, F. B., Robinson, P. A., Morgenthaler, A. C., Jr., Beck, T. R., and McGregor, D. K., IND. ENG.CHEM.,43,234 (1951). Wilke, C.R.,Trans. Am. I n s t . Chem. Engrs., 45,218 (1949). RECEIVED for review January 30, 1951.
A C C E P T ~December D 20, 1951.
n gFnyrin g
Washing in Porous Media
Process
development
H. E. CROSIER1 AND L. E. BROWNELL UNIVERSITY OF MICHIGAN, ANN ARBOR, MICH.
THIS
research is part of a series of studies on the basic phenomena of filtration. Other investigations have been made on fluid flow through porous media ( 5 4 , on t h e drying of porous media ( I ) , and on t h e application of these theories t o filter design (2, 4). This research involves a study of the factors influencing the “washing” of filter cakes. Washing is t h e removal of t h e filtrate from the filter cake by means of a second liquid, called the wash. I n a majority of cases t h e flow is laminar as both the pori spaces in the filter cake and t h e pressure drop causing flow are relatively small. This investigation was limited t o the laminar washing of porous beds in the flooded condition in which the wash and filtrate follow the same channels. Different channels are usually used in filter-press washing. I n t h e experimental work the major portion of the data was obtained on uniformly sized fractions of glass spheres from 16 t o 200 mesh. The glass beads offered the advantages of having a known sphericity and porosity and of being unaffected by the filtrate or wash. T o determine the effects of sphericity and porosity, nickel saddles and angular Wausau quartz sand were used. Tests were made also on calcium carbonate, Filter-cel (diatomaceous earth), and Crystolon, a silicon carbide abrasive. T h e prop1
Present address, Colgate-Palmolive-Peet Co., Jersey City, N. J.
erties of these materials are listed in Table I. Figures 1 through 5 are photomicrographs of some of these materials. The liquids used as the filtrate and wash were aqueous glycerol solutions, aqueous solutions of glycerol containing 201, sodium chloride, distilled water, and dilute sodium chloride solutions. For each experimental run t h e concentration of filtrate in the exit streams was determined either continuously by t h e use of a conductivity bridge, or stepwise b y titration. At t h e end of each run the amount of filtrate left in the cake was found by destroying t h e cake and analyzing the remaining liquid. OF THE POROUS MEDIA TABLE I. PROPERT~ES Material Glass beads
Filter-cel
Diameter, Dp, Ft. 0.0174 0.0004 0.0005 9 . 0 x 10-6 3 3 x 10-6
