Liquid-Liquid Extraction Spray Columns

ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT

Liquid-Liquid Extraction Spray Columns Drop Formation and Interfacial Transfer Area FREDERICK W. KEITH, JR.~, AND A. NORMAN HIXSON Universifpof Pennsylvania, Philadelphia, Pa.

P

ASSAGE of droplets of a liquid through another part,ially or totally immiscible liquid due to a difference in density is a familiar phenomenon. The process is used in both industrial and laboratory spray columns for countercurrent liquid-liquid extraction. Design of such equipment requires a knowledge of flow rates, concentrations, and the rate of material t,ransfer for the system. The last factor depends on the diffusion and convection conditions of the system and on the interfacial area available for transfer; it is a t present necessary to determine these factors by scaling up 1aborat.ory data or by making a rough estimate on the basis of a very similar system operating on a large scale. Such approximations are moderately successful only for small differences in diffusional Characteristics (26). Few quantitative data are available to show the effect on transfer area of changes in flow rates, number and size of nozzles, and physical characteristics of the solvents and the solute. The ultimate effect of changing these physical variables is a change in average drop size of the dispersed phase. The transfer area depends on holdup, rate of drop formation, and the average surface area per drop. These factors, in t a n , are functions of drop size, rate of rise of drops, and the distortion and extent of coalescence of drops. It has also been shown t h a t transfer is dependent on convection as well as diffusional forces and that the proportion due to convection is affected by drop size (28, 40). Unusually large material transfer has been found a t the dispersed phase inlet (40) or outlet ( 1 4 ) ; these end effects are also partially dependent on drop size and number. Very little information is available on the formation of drops, their sizes and shapes, and the conditions associated with their mot,ion through the ambient fluid in a liquid-liquid system. As a basis for considering these data, it is necessary to outline the visible changes t h a t occur as the flow rate through a nozzle is increased. At low flows, drops form individually a t the nozzle tip and grow in size until the buoyance force overcomes interfacial tension and the drop is released. At increased flow rate, a point is reached where a very short continuous neck of liquid exists between the nozzle tip and the point of drop detachment; this velocity will be called the jetting point. Further increases rapidly lengthen the jet, which appears as a smooth column of liquid with occasional transient lumps. Finally, the jet takes on a ruffled appearance a t its outer end and the drops formed are less uniform than in the earlier stages; this occurs a t or near the maximum length of the jet and will be termed the critical velocity. Increasing the flow rate further decreases the jet length and increases drop nonuniformity until the jet breakup point retreats to the nozzle tip and a nonuniform spray of rather small drops results; this last point will be called the disruptive velocity. Most of the recorded work on jets has dealt wit,h factors affecting jet length ( 3 , 7 , 10, 11, 38,@) for liquid-into-air jets, both upward and downward. Smith and Moss ( 4 2 ) showed t h a t the critical velocity occurred when eddy turbulence overcame the restraining forces of interfacial tension. Merrington and Richardson (52) referred t’o the range of velocities between the 1

Present address, The Sharples Corp., Philadelphia, Pa.

258

jetting point and the critical velocity as the varicose region because of the occasional lumps in the jet; between the critical and disruptive velocities lay the sinuous region, as identified by irregular weaving of the jet. These characteristics are not always obvious in liquid-into-liquid jets, but the terms will be retained for identification. A number of investigators have studied drop size resulting from the breakup of liquid-into-air jets ( 1 1 , 2 2 ,52, S S , S 7 ) and gasinto-liquid jets (15, 27, $1) Some papers on extraction spray towers have made qualitatiye note of drop sizes ( 4 , 26,40). Hayworth and Treybal(20) studied drop size in liquid-liquid systems for a static continuous phase a t flow rates mostly below the jetting point. A correlation for drop diameter was developed for these systems The recommended range of rates for this correlation, however, is too low for practical application in most spray towers. Photographs of their flow range were presented and also some data for the largest drops at higher flow rates, but the results are too scattered to fix a peak condition. Several studies

t-L- Gapillary air leak

4 f * 6 -tc

T

t o vacuum

Capillary tubing: 7.39 mm. O.D. 2.1 mm. I.D.

Stopcock

6.5 cm. ~

?.

t-L- 14.835 cm3

L1.0mm. bore glass copillary glass vent tube

35cm.

~~/-Thin-walled I/z in. Tyg on tubing

End rough

‘4

6. 75 mm.

DETAIL OF DROPPING TIP

~

I%Dropping Figure 1 .

tip

Apparatus for measuring interfacial tension

INDUSTRIAL AND ENGINEERING CHEMISTRY

Vol. 47, No. 2

ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT

Table 1. Solvent Isoamyl alcohol Benzene %-Butylalcohol n-Butyl chloride Cyclohexane Diisopropyl ketone Ethyl acetate

Sources and Boiling Ranges of Solvents Source

Paragon Paragon Baker Paragon Paragon Eastman Phillips & Jacobs

Quality Purification Technical Distilled Thiophene-free None Analyzed None Reagent None Reagent None Practical Distilled Commercial Distilled

Baker Phillips & Jacobs

Commercial Technical Petroleum Practical Reagent Analyzed Commercial

ketone

Table II.

Distilled None Distilled Distilled None None Distilled

Boiling 9 n t Range, C. 131.3-132.3 80.1 116 -118 77 - 78 80.6- 80.9 123 -124.5 Azeotropic at 70.4 35 - 36.5 144.2-147.1 66.2- 69.2 114.9-116.0 67 - 69 110 -111 139.3-141.3

from laboratory extraction tower results and to permit more accurate estimation of the effect on transfer efficiency of various changes - in the Dhvsical characteristics of extraction columns and their flow systems. The investigation was limited to the use of organic solvents lighter than mater as the dispersed phase and water as the continuous phase. Solutes were used in mut,ually saturated systems only for their effect on the phy.sica1 properties and not for mass transfer area; this is similar to t h e a p p r o a c h of H a y w o r t h a n d Treybal (20). -

I

Physical Properties of Phases from Tower Runs Physical properties are determined for 12 water-organic solvent systems

Solvent Phase

Dynes/Cm.

Isoamyl alcohol %-Butylalcohol n-Butyl chloride Cyclohexane Diisopropyl ketone Ethyl acetate Ethyl ether Ethylhexanediol %-Hexane Methyl isobutyl ketone Isopropyl ether Toluene

5.1 1.8 24.2 40.7 16.4 4.5 10.5 4.1 40.6 10.7 18.3 35.6

p0

0.8242 0.8427 0.8784 0.7723 0.8031 0,8988 0.7103 0.9445 0.6746 0.8006 0.7225 0.8606

pW

0.9929 0.9865 0.9957 0.9968 0.9963 0,9922 0.9891 0.9967 0.9971 0.9950 0.9949 0.9969

fig

3.566 2.740 0.428 0,877 0.616 0.476 0.235 79.23 0.320 0.576 0.324 0.549

fiw

0.991 1.191 0.924 0.895 0,909 1.203 1.021 1.046 0.891 0.933 0.930 0.894

For solvents that are not available commercially in reasonably pure condition, a technical or commercial grade was used. I n order to avoid, as far as possible, the interference of any surface active impurities, these solvents were water-washed and then distilled t o remove low and high boiling cuts. I n no case was more than about 5% of the original solvent eliminated. For solvents that are commercially available in satisfactory purity a t a reasonable price, the reagent grade was generally used. Laboratory distilled water was used throughout the investigation. There were two exceptions to this procedure. Ethylhexanediol was not distilled although a techniral grade was used. To obtain the high value of interfacial tension desired, it was necessary to use a reagent grade cyclohexane. The solvents tested are listed in Table I with the source, grade, and boiling range. The physical properties of these solvents in mutually saturated water-solvent systems are listed in Table 11. The solutes used were C.P. 99.5% glacial acetic acid Baker analyzed, reagent benzoic acid (Mallinckrodt), sucrose (Paragon), and Alkaterge C (Commercial Solvents Corp). Solutions of Alkaterge C were prepared on an approximate volumetric basis ae the surface activity of such a material is probably not strictly reproducible. The physical properties of the toluene-water system containing solutes are shown in Table 111. The drop volume method wag used to measure interfacial tension because i t seemed comparable to other methods in accuracy when prolonged aging of the surface was not under study ( 1 , 8, 24, 36). The method of calculation and the table of correction factors of Harkins and Brown ( 1 7 )were used. The data of Addison on migration times ( 2 ) caused some concern since they indicated uncertainty as to the correct value of the interfacial tension that should be used when the jet varied in length with flow rate. These data, however, also showed that the time required to reach surface equilibrium for pure solvente was extremely small, so that static interfacial tension as determined by the drop volume method would seem to apply to jet

on extraction a t very low flow rates have determined drop sizes (13,50,40, 44). A number of theoretical and experimental results in liquidliquid systems are available for rates of drop rise and the corrections required for the usual laws of terminal velocity of particles (6, 8, 9, 10, 12, 15, SO, 44). The breakup of drops exceeding a critical size at a related critical rate of drop rise has also been treated experimentally ( 3 2 ) and theoretically ( 2 1 ) . Several investigators have noted the flattening effect on drops during motion (16, 21, do), while qualitative observations have also been made on coalescence in extraction towers ( 4 , 6 , 26). Farmer ( 1 9 ) made precise eccentricity measurements on a few drops, but the data are too limited for average results. Johnson and Bliss ( 2 6 ) found that spray tower efficiency was increased by avoiding nonuniform drop sizes in the dispersed phase. Plate-type distributors tend to give irregular drop sizes, as noted by Blanding and Elgin (6); a picture by Laddha and Smith ( 2 9 ) shows the nonuniformity of drop sizes from a hemispherical distributor a t low throughput. Sherwood, Evans, and Longcor (40) gave the first quantitative data on calculated interfacial areas and their effect on transfer coefficients for single drop transfer. They found that application of a calculated area term resulted in a coefficient showing an increase in transfer with drop size, as would be expected because of the increased internal convection. Other data (15) show little effect of drop size on the coefficient or show the Table 111. Physical Properties of Toluene-Water System with Solutes coefficient becoming constant above a certain drop size. Concentration, Interfacial Grams/c~. Density Viscosity, The investigation described in this Wt. % Tension CP. Solute Toluene Water Dynes/CA. po pw l"0 fiW paper was undertaken to determine _ Sucrose Negligible 40.4 34.2 0.8592 1.1784 0.547 5.55 quantitatively the factors affecting Sucrose Negligible 17.2 36.3 0.8594 1.0686 0.546 1,550 26" Negligible 9.2 0.8631 drop size in liquid-liquid systems and Alkaterge C 0.9971 0.555 0.918 Alkaterge C 6.5" Negligible 15.4 0.8620 0.9970 0.552 0.910 to obtain data on other factors contribAlkaterge C l.05 Negligible 25.3 0.8610 0.9970 0.550 0.902 Acetic acid 0.52 9.36 21.7 0.8614 1.0133 0.549 1.101 uting to the calculation of interfacial Benzoic acid 4.00 0.21 24.3 0.8689 0.9970 0.576 0.890 transfer area. The results can serve Benzoic acid 6.75 0.29 21.8 0.8760 0.9974 0.607 0.898

two purposes-to allow calculation of more fundamental transfer coefficients February 1955

Drops/IOO co. of toluene.


259

ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT breakup a t any length. The case for systems containing solutes is different and wiIl be treated in a subsequent paper. T h e interfacial tension apparatus was adapted from t h a t of Powney and Addison (36)and is shown in Figure 1. I n operation the stopper was inserted in a 250-cc. wide-mouthed extraction flask almost filled with equal quantities of t h e phases of t h e liquidliquid system being tested. T h e whole apparatus was immersed to the stopcock in a constant temperature bath. With the Tygon tubing acting as a water tight flexible bellows, the calibrated bulbs could be filled as often as necessary without removing the apparatus from t h e bath. A run consisted of counting the number of drops formed during emptying of a calibrated bulb. The rate of drainage was controlled by t h e size of the capillary air leak. The liquid preferentially wetting the glass tip should be used as the drop-forming phase.

Figure 2.

Apparafus

for drop size measurements

9 preliminary study on the benzene-water system showed that a drop formation time of 3 minutes minimum gave reproducible results t h a t checked well with t h e literature. For solvents of lower interfacial tension, 2 minutes was sufficient, while as long as 6 minutes was needed for higher tensions. Except for oc. . . , , casional check runs the smaller bulb was usea tnrougnout t h e study. The dropping tip was prepared to meet the requirements of Harlrins and Brown. They recommended a 9- to 11-mm. tip diameter for liquid-liquid systems, but a 6.375-mm. tip was used t o give a greater number of drops and thus reduce the error a t the start and finish of a run Values of interfacial tensions for unknown systems may frequently be estimated from the literature for systems without solutes ( 5 , 18, 26, 35, 39, 4 1 ) and with solutes ( I S , 19, $4). Viscosities n-ere measured in standard Ostwald-Cannon-Fenslre viscosimeters calibrated on water, acetone, carbon tetrachloride, benzene, and glycerol. Densities of the phases were determined in capped pycnometers. All measurements of physical properties .>

260

.

1,

1

.

1

.1

were made on mutually saturated phase mixtures, including solutes, at 25.0 i 0.1" C. I t is estimated t h a t the interfacial tensions were accurate to k 0 . 2 dyne per em., t h e densities to 10.0003 gram per cc., and the viscosities t o about 1 0 . 0 0 4 cp Drop size measurements are made on dispersed solvent phase from single nozzle

The layout and flow diagram for the apparatus used for the measurement of drop sizes is shown in Figure 2. The column itself, E, was a glass tube 3.75 cni. (1.44 inches) in inside diameter. For the majority of the runs the active distance between stoppers was 87.0 em. (20.2 inches) or 118.4 cm. (46.6 inches), but there was no apparent effect of column length on the drop measurements. The bottom was a neoprene stopper with the dispersed phase inlet a t its center and the continuous phase outlet to the side. The top was a cork stopper through which passed the dispersed phase overflow and the continuous phase inlet; the latter consisted of five 3/82-inchholes in 9-mm. glass tubing bent a t right angles t o provide horizontal motion of the inlet water phase. Starting 10 cm. above the longest nozzle, a 50-cm. length of column was marked off in IO-cm. lengths for use in counting drop frequency. Various nozzles were connected by short pieces of neoprene tubing to the solvent inlet above the bottom stopper; a wire spider near the end of the nozzle ensured centering of the jet. Neoprene tubing in contact vrith the solvents was extracted with acetone and benzene prior to use. Solvent, stored in a 2-liter flask, D, was fed to the column by controlled air pressure in the flask. A pinch clamp on a short piece of neoprene tubing provided a shutoff from the tower, but it was not used for flow control and was wide open during operation. Compressed air was metered to the system through a globe and a needle valve in series and passed through a trap, A . A 1-gallon bottle acted as a pressure reservoir and surge tank. The pressure to the feed flask, D ,was controlled by an adjustable leg of glass tubing in about a 2-foot column of acetylene tetrabromide; the lower end of the glass leg was drawn to a fine nozzle t o give a more even flow of air. The top of this pressure leg column was closed and a saran tube led the excess air to a scrubbing flask filled with the same solvent as the dispersed phase. From here it was led to the bottom of the 2-liter flask, K , used for colIecting the dispersed phase overflow. As the solvent level in the feed flask, D,was lowered during operation, the increasing head in flask K provided most of the necessary increase in back pressure to maintain a constant flow to the nozzle. This setup worked very well and gave constant flow rates with excellent control, A wide-mouthed half-gallon bottle, G, served as a reservoir for the continuous phase. Liquid was pumped, H , to the I-liter flask, J , which served as an adjustable-level constant head feed tank. The flow was from this tank to the top of the column, while the continuous phase was down through the column, through the interface level control, and bark to the reservoir, G . A cooling coil in the reservoir was adequate t o hold the temperature a t 25 f 2" C. A two-way 120" stopcock placed after the interface-level control permitted determination of the continuous phase flow rate. A short mercury manometer, F , open to the atmosphere, indicated the static pressure head a t the bottom of column E , A longer water manometer approximately indicated the pressure drop across the nozzle plus a small length of inlet tube (the latter was negligible). Photographs were taken of the tower during operation with an Eastman Kodak Model B. S , with portrait attachment So. 8, as shonn a t L. The camera was on a level with the center of the column and a t a distance of 33 inches. A strip of nonreflecting white paper pasted t o a board the length and width of the column and placed 1/4 inch behind the column was a satisfactory background. This could be adjusted with respect t o the lighte and camera t o give a dark crescent on both sides of each drop. Nozzles. The nozzles were made from pieces of capillary or thin-walled glass tubing. The tip was cut! a t right angles to the axis and ground, when necessary, to remove nicks and chips. The inlet end was sealed to a 1-inch length of 7-mm. thin-walled tubing to fit the standard neoprene connection a t the bottom stopper. For most of t h e runs the length of t h e main part of the nozzle was 3 inches. Nozzle A was also made in lengths of 2, 1, and 0.15 inches; nozzle G was also made in a 1-inch length. The

INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y

Vol. 47, No. 2

ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT diameters of the nozzles were measured with a calibrated microscope scale. D a t a on t h e nozzles are given in Table IV. Nozzles are referred t o by letter and length in inches-that is, a 3-inch length of 2.77-mm. (inside diameter) capillary is nozzle A-3.

Table IV. Nozzle Designation

A B C D F G

Measurements of Glass Nozzles Inside Diameter Inch

Mm. 2.77 2.12 1.15 0.71 4.33 6.66

Outside

Diameter, Mm.

0.109 0.0835 0.0453 0.0280 0.170 0.262

8.94 7.39 6.32 5.39 6.58

..

NOZZLE SIZE ON

.-

D w e r h e d Phose Flow

R o t e , Uy ( c m ' / s a e )

Figure 3

Experimental Procedure. Prior to use, solvent and water were kept in mutual contact with frequent shaking a t or near 25" C. for about 48 hours. The only preparation required for the column was t o insert the proper nozzle. I n starting up, the aqueous continuous phase was circulated, the rate adjusted, and the temperature regulated at 25 f 2' C.by t h e coil in t h e reservoir. The dispersed solvent phase was quickly passed through the tower once to bring it to t h e temperature of t h e continuous phase; it was then returned to the feed flask and the run waa started. The first run of a series was made a t the jetting point, the second below the maximum jet length, t h e third near or a t the maximum, the fourth above t h e maximum, and the fifth a t a very high rate. When the jet length was set and the interface had reached equilibrium just below the continuous phase inlet, the flow rates were checked, a picture was taken, t h e jet length was checked, and the uniformity of drop size was noted. The rate of drop rise for 5 t o 20 drops of representative sizes was determined over a 40or 50-om. length of column and t h e temperatures were checked. The photographic film was developed but not printed as it was found that i t was easier t o count the drops by transmitted light. For most runs the number of drops over a 40- or 50-cm. length of column was counted directly from the negative with the aid of a jeweler's eyeglass. For more complete data the negative was projected on a screen; horizontal and vertical diameters of all the drops in a representative section of column were measured and an enlargement factor was calculated from a marked length of column on the screen. The results of the projected counts agreed well with the direct counts and the error of this measurement was probably about 3% The average drop volume was calculated from the average rate of drop rise, the number of drops, and the dispersed phase flow rate. By assuming a spherical drop, the drop diameter, drop surface area, surface area per unit time, and surface area per unit volume of dispersed phase could be calculated. The full results of the 570 runs made are on file with A. N. Hixson at the University of Pennsylvania. February 1955

Each system exhibits maximum interfacial transfer area at a particular flow rate of dispersed phase

The most easily observed effect of increasing the flow rate through a nozzle was t h e varying length of the jet. It was very small at the jetting point, increased to a maximum, and then became shorter. The length of the jet was also affected by the flow rate of t h e continuous phase; it was longest with no flow and became shorter with increases in rate. This pattern was found for all t h e liquids tried and for all nozzle sizes. Results for a range of nozzle sizes for the toluene-water system are shown in Figure 3 for a continuous phase flow rate of about 100 cc per minute. The almost linear variation below the maximum and the rather sharp maximum seemed t o be characteristic of t h e phenomenon except for the largest nozzle. The average drop volume passed through a rather sharp minimum when plotted against the dispersed phase flow rate. T h e form of this curve was nearly a V, as shown by thorough tests a t the start of the investigation. I n later runs where the number of tests was not so large, i t often occurred that t h e flow rate giving the exact minimum was bracketed but not hit. I n this case the minimurn was readily determined with only a small uncertainty by graphical interpolation of t h e available data. Corresponding to this minimum drop volume was a minimum drop diameter based on the assumption of a spherical drop. These two minima did not correspond in any regular manner with flow rate maximum jet length but generally occurred near the latter.

' --y/\ -'- I I

d

EFFECT OF NOZZLE SIZE ON

l -

The surface area per unit volume of dispersed phase flow, A s , depends only on average drop size; thus, by the geometry of a sphere, A s = ~ / D D .Therefore, t h e interfacial contact area per unit volume of flow, assumed to be t h e same as transfer area, depends only on drop diameter in an inverse ratio. Consequently, when the drop diameter went through a minimum, the transfer area went through a maximum a t the same flow rate. Transfer area plotted against dispersed flow rate, UT,gave an inverted-V type of curve with varying degrees of flatness; this type of plot allowed determination of an interrun maximum point, as was the case with minimum drop volume. Such plots are shown in Figure 4 for the toluene-water system with several nozzle sizes. The only data available in the literature for comparison with these area results are calculated values from the correlation of Hayworth and Treybal (20). This correlation applies strictly only for nozzle velocities below 10 em. per second; for rates of 10 t o 30 cm. per second the equation correlates only the largest drops observed, and a t higher rates the data were considered too erratic for correlation. Nozzle rates in the present study were greater than 10 em. per second for the common solvents except in the largest nozzle and many of the maximum area values occurred a t rates greater than 30 em. per second. I n Figure 4


261

ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT are shown the area curves for toluene in water for nozzles C, A, and F as computed from the Hayworth and Treybal correlation. Nozzle velocities and drop sizes for these curves are as follows:

Uv cc./sec. UN: cm./sec.

Do (by correlation of HayTq-orth and Treybal, ZO), cm. DO (observed), om.

C 0.28- 0 . 4 3 2 7 . 0 -41.4

Nozzle A 0.90- 1.80 14.9 - 2 9 . 9

0.34- 0 . 2 5 0.37- 0 . 3 3

0 67- 0 . 5 1 0.74- 0 . 5 5

F 170- 4.0 1 1 . 5 -27.2 0.90- 0 . 6 8 0 82- 0 . 7 7

Agreement is reasonably good considering t h a t all the values are beyond the recommended range of the correlation where the latter shows an ever-decreasing drop size and that the correlation is based on a static continuous phase The rate of formation of new transfer area is given by AT as square em. per second and is found from the product of A s and Uv. The maximum value of As and its corresponding UV and their product, A T , reprebent the optimum operating conditions for the dispersion nozzles of a spray tower and, therefore, are the basis for most of the correlations obtained in this investigation These three functions are defignated by the additional subscript M ; thus A ~ . w U , V M ,and AT.M indicate values corresponding to the peak data of A s while B s , Uv and AT are used for any other point. Correlations are based on peak values that represent optimum operating conditions

I

I n view of the importance of A m and its corresponding data, since every solvent tested shoned such a maximum, the values found for these peak data are given in Table V. Some of the solvents of higher viscosity and lower interfacial tension would not form individual drops from the larger nozzles. When the dispersed phase flop rate was reduced below the point of a medium length jet, the jet collapsed and retreated back inside the nozzle. For isoamyl alcohol, n-but3 1 alcohol, and ethylhexanediol, the flow giving 4831 v a s the loaest flow that could be run; this was considerably below maximum jet length. It is obvious that operation of a tower a t such a n unstable point nTould not be feasible, but these data were considered t o be peak data in order to be consistent with the other results Inasmuch as peak values depend on a number of factors, including a graphical interpolation, their reproducibilitv was tested. This is shown in Table VI for repeat runs from Table V with the same nozzles for the toluene-water and diisopropyl ketone-water systems. These check runs weie interspersed with other runs both in operation and in calculation so a s to avoid “wishful” control a s much as possible. The reproducibility for A S Mand UVMis good. Both show an average mean deviation of about 2.6% and a maximum of about 470 The results of repeat iuns in Table Tr also indicate that the velocity of a moving continuous phase has no effect. Apparently, drop formation and the method of jet breakup are independent of the increased turbulence of the higher flow rates. Since the length of the jet is affected by the continuous phase flow rate, it is apparent that diop formation is not a function of jet length. It should be noted, however, that a static continuous phase gives somewhat different results for the peak data than does a phase moving in the range of 15 to 81 cubic feet per (hour) (square foot). The static values for A ~ . vand UVMare generally higher than the moving phase values. The differences, hoxTever, are sufficiently small that the data of Tables V and VI are probably good for continuous phase flow rates well below the tested minimum of 15 cubic feet per (hour) (square foot). The peak values of the dispersed phase flow late, UVM,are plotted against nozzle diameter, DN,in Figure 5. For some solvents this curve appears to be smooth, but for others the line for nozzles G, P, and A seems to show a break with the curve for nozzles B, C, and D. The effect of nozzle length on peak data wm not sufficiently tested to tell its exact nature and magnitude. One set of toluene 262

Table V. Nozzle Size

Maximum Surface Area and Related Data for Solvents and Water Av. LV 4sx, U v .w , ATM, Cc,/&,

Sq. cm./Cc.

Cc./Sec.

Sq. Cm./Sec.

-4-3 F-3

c-3

162 144 135

Isoamyl Alcohol 21.0 16.7 18.1

c-3 B-3 ‘4-3 F-3 G-3

98 107 114 171 103

%-Butyl Alcohol 25.9 29.2 17.7 20.6 26.0b

0,050 0.08 0 . 38Qa 0.549 1.0b

1.30 2.37 6.89 11.3 26.0

c-3 B-3 A-3 F-3 G-3

130 112 125 120 120

n-Butyl Chloride 21.4 11.4 13.2 9.47 5.23

0.313 0,932 1,524 2.25 4.02

6.68 10.62 16.4 21.4 20.2

D-3 c-3 B-3 .4-3 F-3 G-3

112 138 141 173 I57 112

Cyclohexane 32.6 18.3 14.4 11.8 7.20 6.89

0.350 0.820 2.00 2.04 4.13 5.97

11.4 15.0 28.8 24.1 29.7 41.2

c-3 B-3 B-3 -4-3 A-3 A- 1 F-3 F-3 G-3

82 113

103 106 95 120 100 117

c-3 A-3 F-3

141 121 153

E t h y l Acetate 24.0 12.0 10.5

0.153 0.545 0.680

3.67 6.54 7.11

c-3 A-3 F-3

178 119 118

Ethyl E t h e r 25.5 18.8 17.6

0.510 0.527 0.551

13.0 9.91 9.68

c-3 4-3 F-3

95 110 165

Ethylhexanediol 20.6 17.1 19.2

0.0595

1.23 1.54 1.94

c-3 B-3 A-3 F-3 G-3

128 110 152 119 120

n-Hexane 21.4 15.2 8.90 8.10 7.63

C-3 B-3 A-3 F-3 G-3

99

105 140 167 102

D-3 c-3 B-3 A-3 F-3 G-3

91 141 88 108 105 104

111

0.235 0,2025 0 , 235a

4.94 3.38 4.25

Diisopropyl Ketone 22.0 0 . 408 15.6 0,860 16.9 0.855 14.1 1.08 15.2 1.08 14.3 1.17 11.8 1.50 11.7 1.63 11.1 2.45

0 . 0Q03a

0.101a 0.515

1.30 1.76 2.80 9.16

Methyl Isobutyl Ketone 25.3 0.262 18.4 0.548 14.7 0.655 10.8 1.03 13.8 1.50 Isopropyl E t h e r 35.6 25.3 14.1 12.9 10.9 9.92

0.150 0.265 0.620 0,840 1.25

1,63

Toluene 23.6 0.490 269 c-3 24.1 0.488 89 c-3 22.0 0.490 133 c-3 22.8 0.466 457 c-3 15.5 1,28 111 B-3 14.7 1.18 128 B-3 12.3 1.R5 96 A-3 1 2 . 8 1.39 133 A-3 12.3 1.56 253 A-3 12.4 1.57 417 A-3 12.3 1.47 130 A-2 12.3 1.32 137 A- 1 12.4 1.23 125 A-0.15 8.35 2.95 86 B-3 8.67 2.73 121 F-3 8.10 2.92 247 F-3 7.97 2.70 436 F-3 6.63 5.60 94 G-3 a Showed peak at lowest dispersed rate attainable. b Estimated; too m a n y drops in column for good count.

INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y

8.99 13.5 14.4 15.3

16.5 16.7 17.6

19,1

27.3

11.0 19,5

15.7 22.7 69.9 6.63 10.1 9.62 11.1

20.7

5.33 6.70 8.74 10.8 13.6 16.1 11.5

11.8

10.8 10.6 19.7 17.3 19.1 17.7 19.2 19.5 18.1

16.2 15.2 24.7 23.7 23.6 21.6 37.2

Vol. 41,No. 2


,26 Nozzle G-3

2.0

-

.IO

- A-3 -

.00

= e-3

.06

-

e= .I2

.oe -

,

I

I

l

02

,

1

1

I

1

I

.IO

U"M

I

1

,

(cs.hsc.)

1

1

1

1.0

Figure 5

data shows a deviation of UVMgreater than would be expected from the average error and also shows a small but distinct increase in velocity, b u t not area, with nozzle length. A set of data for diisobutyl ketone indicates the opposite trend with velocity but again no effect on area. It would appear, then, that ABMis independent of nozzle length and that UVMis either independent or shows only a very slight increase with increasing nozzle length. The length of the shortest nozzle, 0.15 inch, approximates thickness of a heavy plate distributor, indicating that the correlations of this investigation might be used for plate distributors or sieve plates operating with the appropriate flows and no surface agglomeration.

water system. The only reason for. selecting this system was that the relative refractive indices of toluene and water produced a very sharp outline of the drops so that measurements were facilitated. It was necessary to obtain an equivalent spherical diameter from the horizontal and vertical diameters measured from the projected photograph. From a consideration of the limited accuracy of the measurements and the large number of drops involved, it was decided that an arbitrary diameter calculated as the mean of the two measured diameters was satisfactory. Size distribution on a percentage basis was plotted on arithmetic-probability paper against the mean equivalent diameter, D'D, as measured directly from the projections since all the latter had the same enlargement factor. Typical results for these counts are shown in Figure 6 for nozzle F-3. The lowest flow rate, IO 1.50 cc. per second, was just above the jetting point and shows good uniformity of drop size. The next flow rate, 2.54 cc. per second, was a little below the critical velocity and shows only a slight decrease in uniformity but a marked decrease in drop size, as would be expected when UVMis approached. The next flow rate, 3.10 cc. per second, was above UVMand shows the effect of a number of large drops. The highest flow rate indicates a corresponding increase in the propor-

Uniformity of drops i s related to flow rate regions defined for jet length

I n general, the uniformity of the drop sizes obtained on jet breakup could be related to the flow rate regions as defined for jet length. Below the jetting point the drops formed were very uniform, and in the varicose region they showed almost as much uniformity. In the region of the critical flow, a decrease in uniformity was noted and in the sinuous region a n increasingly wide range of drop sizes was obtained. As the disruptive stage was reached, the sizes became somewhat more uniform and usually tended to be fairly small. When operation was extended into the spray region, which occurred a t a fairly low velocity for the larger nozzles, the drops remained small and sometimes decreased further in size. Drop size distribution was studied thoroughly for the toluene-

c E

., .Pa

Percanlage of Tolel Drape Smaller

Table VI.

Reproducibility of Peak Data for Solvent-Water Systems Surface Area (Cm.a/Cm.a) AY. deviation,

Nozzle Size

Av. A B M

e-3 B-3 A-3 F-3

23.1 15.1 12.4 8.27

B-3 A-3 F-3

16.3 14.6 11.7

February 1955

%

Toluene 3.12 2.65 1.40 2.90

Flow Rate, Cc./Seo. A v . deviation,

AY. U V M

%

0.483 1.23 1.52 2.82

1.82 4.06 4.15 3.90

Diisopropyl Ketone 3.84 0.86 3.76 , 1.08 1.56 0.21

0.30 0.00 4.15

in

S i r e Than

%

Figure 6

tion of large drops with a decrease in uniformity. It is the sudden appearance of larger drops near the critical velocity that terminates the constant increase of surface area found in the varicose region. As the flow rate is increased further, the frequency of occurrence of these large drops increases a t a faster rate and thereby accounts for the sudden drop in surface area beyond the maximum value. The results of a uniformity analysis, as measured by the standard deviation for a normal probability curve, are given in Figure 7 for a number of operating conditions. Uniformity is definitely


263

ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT 8 6

a function of the flow rate for all the nozzles. Uniformity is better for smaller nozzles but is also good for lower flow rates with larger nozzles. Uniformity starts to decrease as UVM is approached and it falls off very sharply for flows only somewhat larger than UVM,which is indicated by the arrow8 (Figure 7 ) . A decrease in nozzle length, as for nozzle A-I, decreases uniformity in the lower flow range when compared to a longer nozzle such as nozzle A-3. It seems that a decrease in interfacial tension alone, as shown by the nozzle F-3 runs containing Alkaterge C, is insufficient t o cause a change in the uniformity. Rates of drop rise are lower than predicted by Newton’s law or drag coefficient for spheres

Both qualitative and quantitative data were obtained o n drop behavior during free rise in the column after formation. Rates of droT rise, relative to the continuous phase, were measured approximately in determining drop volumes. All but the smallest drops encountered were in the Reynolds number range covered by Newton’s law. Figure 8 shovs this law for toluene drops in water and also shows the rates predicted by the drag coefficient for rigid spheres. The expelimental points for drops over 0.4 cm. in diameter fall well below both curves. These results are in line with the observation of Hinze ( 6 1 ) that the deformation and vibration of liquid drops in a fluid will increase the resistance to flow appreciably above that for rigid globules. Hughes and Gilliland ( d 3 ) studied the factors affecting deformation of liquid drops in air and gave relations for predicting the distortion based on terminal velocity. However, application of their results to liquid-liquid drop systems is uncertain because of the continuous oscillation and fluttering tendency of such systems. Qualitatively, however, in agreement with the results of Bond and Newton (8, 9), it appears that the drag coefficient for drops may be less than that for solid spheres in the smaller drop sizes primarily because of the finite viscosity of the drop liquid; a t larger drop sizes, distortion should increase with a resultant increase in the drag coefficient to a value greater than that for spheres. The transition diameter toluene drops in water should lie in the range of 0.15 to 1.5 cm. as appears to be the case in Figure 8. Farmer ( 1 3 ) and West and coworkers (44) reported drop rise curves showing similar deviations. It seems, therefore, that experimental rates of rise are necessary for extraction area calculations. Figure 9 shows the observed rates for all the pure solvents tested and Figure 10 s h o m the results for the toluene-water system with solutes. These curves represent the best lines through the data and have an average error between 2 and 3% for each of the solvents. Drop measurements in sufficient numbers to give flattening 264

data were available for only a feff solvents; these diameters were corrected for the knovm enlargement of the projections. In addition, the horizontal diameters were divided by an experimentally determined factor of 1 2 5 to correct for magnification in the round column. The vertical diameter was corrected for drop rise during the */ip-second camera exposure. The best curves for these corrected data are shown in Figure 11; the average deviation of the points is 5 to 10%. A comparison of the graph with the physical properties of the systems indicates that flattening is proportional to drop size and density difference and inversely proportional t9 interfacial tension. I t should be noted that the drop shapes were constantly varying and that the data of Figure 11 therefore represent the mean shape based on measurements of a large number of drops for each system Using photographs of several individual drops of carbon tetrachloride in water, Farmer ( 1 3 ) found eccentricities of 1.10 to 1.86 for drops with equivalent spherical diameters of 0.26 to 0.52 cm., respectively. These data fall along the curve for ethyl acetate, a s expected, since these systems have almost identical ratios of density difference to interfacial tension. The flattening of a drop of any given volume has an effect on surface area. I f it is assumed that the flattened shape is that of a n oblate spheroid, the mag4tude of the effect is readily calculated from the equations for the volume and surface area of a sphere and of a spheroid. For drops of the same volume, eccentricities of 1.2, 1.6, and 2.0 increase the surface area of the sphere by 0.6, 4.1,and 9.6%, respectively. Observations on coalescence in the column were based entirely on watching drops rise the full height of the tower and recording whether any of these drops coalesced with any others. A distinction was made between coalescence of a few or of most of the drops. These results are recorded in Table YII.

RATE OF DROP RISE

I

RELATIVE TO CONTINUOUS

-

>

---

-.I5

.2

.4

.3

~

1 j

Observed rate Newton’s law f o r spheres

Drag coefficient for

.5

.6

.7 .S .9 1.0

DD (em.)

Figure 8

Some of the solvents used seemed t o form drops no larger than a certain size. This was particularly true of ethyl acetate and n-butyl alcohol which coalesced readily to form largc drops that immediately split into two or more smaller drops. Other solvents showing some coalescence also shoa-ed a distinct upper limit to the size of drops found among the larger nozzles. For toluene, several nozzles larger than nozzle G were tested for single drop formation, and during the course of this m-ork a few


Vol. 41, No. 2

ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT The peak data obtained with these solutes' Comparison of these results with those for pure toluene shows little effect for the Alkaterge C but a marked change for the other solutes. These results will be discussed more fully in a subsequent paper dealing with correlation of the data.

in toluene-water are given in Table IX.

limits of suitable operating range for dispersion nozzles are defined by jetting point and onset of nonuniformity

RATE OF DROP RISE RELATIVE TO CONTINUOUS PHASE 01

2

3

5

4

7

6

Volumetric

Drop Dlameler,

8

9

10

I1

Do (cm.)

Figure 9

of the largest drops broke up while rising. As a result of these observations, approximate estimates of critical drop size may be made for a few solvents. These data are shown in Table VIIT as ranges within which the critical drop size probably falls. These sizes are probably sensitive to any marked difference in the turbulence conditions found in the column.

As a result of the observations on jets, it is possible to define a most suitable range of operation for the dispersion nozzles of liquidI2 13 liquid spray towers. The lower end of the range is set by the jetting point velocity since this combines the lowest economical flow rate with high uniformity. This velocity for the common solvents is 50 to 80% of UVM. The upper limit of the suitable range is determined by the onset of appreciable nonuniformity of drop sizes because this factor gives rise to a reduction of transfer area, loss of fine droplets by entrainment, and excessive coalescence. The rate a t this point is frequently only a few per cent higher than UVM,seldom more than 20y0. --

Third components differ markedly in effect on peak data

Table VIII.

The number of solutes tested was not large, but their physical characteristics varied widely a s a means of high-spotting the effects of solutes on tower operation. All solutes were used in the toluene-water system so t h a t comparison of results would be facilitated. Alkaterge C was a strongly surface active material soluble in toluene but negligibly so in water; it markedly changed the interfacial tension but, had almost no effect on the other physical properties. On the other hand, sucrose was soluble in the water phase, but negligibly so in the toluene phase; it markedly changed the density and viscosity of the water but had no effect on the toluene phase and little effect on interfacial tension. Acetic acid and benzoic acid changed the physical properties of both phases. but the former favored the water phase and the latter the toluene phase, both by roughly 20 to 1 on a weight percentage basis.

Table VII. Solvent Phase Toluene

Dispersed Phase Toluene Ethyl acetate Isopropyl ether Diisopropyl ketone Methyl isobutyl ketone n-Butyl alcohol

Table IX.

l.On l.Oa 6.5a 6.5" 265 26a

Solute Concn., Solute

%

...

sucrose' ' 40.4 Sucrose 17.2 Acetic acid 0.52 Benzoic acid 4.00 Benzoic acid 6.75 Alkaterge C 1.0" Alkaterge C 6.5a Alkaterge C 2 P

D

..

.. .. .. .. .. ......

C NC NC

NC NC NC NC NC NC NC NC

Nozzle Size B A F G NC NC N C N C .. N C N C . . NC . . . . NC . . . . . . N C .. NC . . . . NC . . . . . . NC . . . . NC . . NC N C NC NC SC MC MC .. MC MC MC MC

..

... . . . . .

..... ..... ..... .....

... .*. ... ... ... ...

.. .. .. ..

..

.. ..

a

negl negl. negl. negl. negl. negl.

Nozzle Size

A8M. . UVM, Sq. Cm./ Cc./

cc.

.Set.

ATM Sq. Cm./

Sec.

C-3 F-3 C-3 F-3 C-3 F-3

0.545 2.69 0.520 3.06 0.412 2.97

12.6 23.7 11.7 27.0 9.85 26.2

Acetic Acid 118 21.5 112 11.5

0.375 1.65

8.06 18.9

Benzoic Acid 111 22.2 118 10.1 128 22.5 125 10.5

0.370 1.96 0.326 1.78

8.21 19.7 7.32 18.7

1.22 0.360 1.02 1.65

16.5 7.87 15.4 20.7

9.36 9.36

C-3 F-3

4.00 4.00 6.75 6.75

0.21 0.21 0.29 0.29

C-3

17.2 40.4 40.4 40.4

L17,

Cc / Min.

Alkaterge C 128 23.2 122 8.80 107 22.5 116 8.84 125 23.9 123 8.80

0.52 0.52

negl. negl. negl. negl.

Cm. 1 . 3 (approx.) 0.7-0.8 0.7-0,s 0.7-0.8 0,6-0.7 0.3-0.4

Maximum Surface Area and Related Data for Toluene-Water with Solutes

Concentration, Wt. % Toluene Water

Coalescence of Solvent Phase Drops

Cyclohexane ..... ... n-Butyl alcohol ..... ... n-Butyl chloride ..... ... .. SC Diisopropyl ketone ..... NC NC N C N C ..... ... ,. NC , . SC MC Ethyl acetate Methyl isobutyl ketone NC N C SC MC ..... ... .. NC . . N C N C Isoamyl alcohol . . NC N C N C Ethylhexanediol Ethyl ether sc MC MC ..... n-Hexane NC NC N C N C Isopropyl ether N C SC SC N C MC Drops/100 ml. toluene. N C = no coalescenoe SC = some coalescence MC = much coalescence

:February 1955

Estimated Critical Drop Sizes for Solvent-Water Systems Solvent Phase as Critical Dn,

F-3 C-3 F-3

A-3 C-3 A-3 F-3

Sucrose 102 113 123 123

13.5 21.8 15.1 12.6

Drops of Alkaterge C/100 ml. of toluene.

MC

..

SC

.. ..

..

NC MC

Within the range defined above lies the flow rate, UVM,as determined by the point of maximum transfer area. Such a critical point has not previously been reported and is important in a spray extraction column. The maximum of the area is sharp with a rapid decrease in area on either side of the peak. For almost all of the solvents and nozzles tested, this maximum area in terms of the area per unit volume of dispersed phase flow, A ~ M , is 10 to 25% greater than t h a t at the jetting point and is 3 to


265


Table X.

DX, Inch

UN,

Cm./Sec. 12 -87

0,120 0.095 0.042 0.250

I ,

I

,

.3

.4

.5

I

,

6

.l

I

.6

V ~ l u r n e t iCrop ~ ~ Oiomeler,

.B 1.0 D g (crn.)

II

IZ

13

Figure 10 Concn., W t . Solute Acetic ocid Benzoic acid Benzoic acid Alkaterge C Alkaterge C Alkoterge C Sucrose Sucrose

Toluene 0.52

4.00

% Water

9.36 0.21

6.75

0.29

0.01 0.065 0.26

Negligible Negligible Negligible 17.2

Negligible Negligible

40.4

Alkaterge C conc. i n drops/cc. of toluene; phases mutually saturated with respect to all components

15y0higher than t h a t a t the nonuniformity flow rate. The peak measurements appear to be reproducible with less than 5% error. For the best operation of a sprag tower, several factors appear to be important. Flow of the dispersed phase must be even and steady; each of the dispersion nozzles must receive an equal portion of the total feed; and the nozzle length should be 2 inches or greater. A dispersion head of the type used by Sherwood, Evans, and Longcor (40)seems particularly suitable. The experimental data are insufficient to show conclusively whether or not there is a real discontinuity in the curve of UVM versus nozzle diameter in the region of a 0.1-inch nozzle. Cyclohexane and the alcohols show a break well beyond the average error of the measurements; most of the solvents not indicating a break between nozzles B and A do show a marked curvature. The exact cause of the change in behavior in this nozzle range is not known, but it is suggested that the effect may mark the region where the jet begins t o taper after leaving the nozzle so that D N is not strictly equal to DJ. This tapering was very marked in the high viscosity solvents but wa8 also apparent with most solvents in the larger nozzles. Data on one toluene jet from nozzle A-3 showed a 22% reduction in diameter from the nozzle to the breakup point. No particular value of the dimensionless correlation groups seemed to be involved in the transition from nozzles B t o il. I n view of the observation by Johnson and Bliss ( 2 6 )that poor results with spray towers for high rates of flow might be due to excessive nonuniformity, it is interesting t o compare the suitable operating range, a s defined above, with the rates actually used by several investigators. This is done in Table X for methyl isobutyl ketone using the linear nozzle velocity, U N . Sherwood and coworkers ( 4 0 ) operated at very high velocities and the nonuniformity of drops may well have been responsible for the decrease found in the mass transfer coefficient a t higher rates. Johnson and Bliss ( 2 6 ) changed the number of nozzles in their distributor so that their flow rates probably remained in the range shown; their maximum rate agrees well with that found in the present work and it is of interest. that their capacity coeffi266

Nozzle Velocities Used Phase

for Methyl Isobutyl Ketone Suitable Range, Cm./Sec. Jet Nonpoint L 7 ~ . % 4 uniformity

Reference (40) ($6) (6)

4.5-21 38 (rnax.) 61 (max.)

7

9 12

i)

..

(6)

15 20 38 4

.. ..

, .

cients did not show a maximum with dispersed flow rate. Blanding and Elgin ( 6 ) apparently s p t their maximum rates to avoid the disruptive range but, for the larger nozzle, were well into the nonuniform region. The results of several investigators ( I S , SO, 40, 44) show up to 40% of the extraction in a tower occurring a t the dispersed phase inlet. All of these tests were made below the jetting point; with a jet there is no expansion time and a very short formation time, EO that no extra transfer would be expected a t this point for a tower under normal operating conditions, as reported by Geankoplis and Hixson (14). A study of the solvents shocr-ing appreciable coalescence, a s listed in Table VII, indicates several strong trends. Coalescence is promoted by low interfacial tension and by increasing nozzle size and therefore by increasing drop size; the last also generally implies a n increase with higher rates of drop rise. These trends are opposite to those noted by Appel and Elgin ( 4 ) The conditions found to accompany coalescence in the present investigation seem reasonable because increasing drop size and decreasing interfacial tension both promote oscillation and vibration of the drops and thus increase the chances of contact between drops

t

0

I 71

.2

.4

/~

'

.8

.6

I RISE IN COLUMN I 1

10

1.2

Drop Diameter f o r Sphere of Same Volume os Spheroid, 0,

Figure

1.4

(cm)

11

One criticism of large spray towers is that in long columns the drops of the dispersed phase may coalesce so much that transfer area is greatly reduced. It is noteworthy that the solvent characteristics promoting coalescence are apparently the same ones, in general, that lead to a relatively small critical drop size a t the velocities achieved in a liquid-liquid system. Table VI11 shows that the critical drop sixes for the lower interfacial tension systems are often smaller, even in large nozzles, than the drop sizes attained in medium nozzles with higher tension system?. For strongly coalescing solvents in long towers, the transfer area should be based on the critical drop size and not on the initial drop size.


Vol. 47, No. 2

ENGINEERING. DESIGN, AND PROCESS DEVELOPMENT Inasmuch as a point of maximum area was found for each of the nozzles and solvents tested, these peak values were considered to be unique functions for each system. An applicable equation was developed by dimensional analysis and correlations were obtained for both maximum area and its corresponding velocity. These results permit calculation of the interfacial area per unit volume of extractor and will be presented in a subsequent paper. Nomenclature

The metric system of measurement was used throughout this investigation, except ae noted on graphs. The units given are, therefore, the ones in which the factors were measured or calculated. If a factor was not measured or calculated, no units are indicated.

As = surface area per unit volume of dispersed phase flowing, sq. cm./cc.

AT = surface area formed per unit time, sq. cm./sec. DD =i diameter of spherical drop, cm. D‘D = ( D E DE')/^ = equivalent drop diameter from pro-

+

jected photographs, mm. = horizontal diameter 01 flattened drop, mm. = vertical diameter of flattened drop, mm. = diameter of jet a t breakup point = inside diameter of nozzle, cm. = DE/DE‘ = eccentricity of flattened drop = length of jet to breakup point, cm. = volumetric flow rate of continuous phase, cc./min. = linear flow rate of dispersed phase in nozzle, cm./sec. = velocity of drop rise relative to continuous phase, cm./sec. UT. = volumetric flow rate of dispersed phase, cc./sec. T’D = average drop volume of dispersed phase, cc. U , viscosity, cp. p = density, grams/cc. u p = standard deviation of normal probability distribution, cm. =i

Subscripts C refers to continuous phase

D refers to dispersed phase M refers to peak values corresponding to maximum area

0 refers t o organic phase W refers to aqueous phase literature Cited (1) Adam, N. K., “Physics and Chemistry of Surfaces,” 3rd ed., pp. 387-8, 424, Oxford Univ. Press, New York, 1941. (2) Addison, C. C., J . Chem. SOC.,1943, p. 535; 1944, pp. 252, 477;

1945, p. 98, 354; 1946, p. 579; 1948, p. 963. (3) Addison, C. C., Phil. Mag., 36, 73 (1945). (4) Appel, F. J., and Elgin, J. C., IND. ENG.CHEM.,29, 451 (1937). (5) Bartell, F. E., Case, L. O., and Brown, H., J . Am. Chem. Soc., 55, 2419 (1933). ( 6 ) Blanding, F. H., and Elgin, J. C., Trans. Am. Inst. Chem. Engrs., 38, 305 (1942). (7) Bohr, N., Trans. Roy. SOC.(London), 209A, 281 (1909). (8) Bond, W. N., Phil. Mag., Ser. 7, 4, 899 (1927). (9) Bond, W. N., and Newton, D. A., Ibid., 5, 794 (1928).

February 1955

.

(10) Chemical Engineers Handbook (J. H. Perry, editor), 3rd ed.,

Section 11 (1950). (11) De Juhasz, K. J., Zahn, 0. F., and Schweitzer, P. H., Penna.

State College, Bull. No. 40, 24 (1932). (12) Elgin, J. C., and Browning, F. M., Trans. A m . Inst. Chem. Engrs., 31, 639 (1935); 32, 105 (1936). (13) Farmer, W. S., Oak Ridge Natl. Laboratories, Unclassified Rept. 635, 1950. ENG.CHEM.,42, 1141 (14) Geankoplis, C. J., and Hixson, A. N., IND. (1950). (15) Guyer, A., and Peterhans, E., Helv, Chim. Acta, 26, 1107 (1943). (16) Hadamard, J., Compt. rend., 152, 1735 (1911). (17) Harkins, W. D., and Brown, F. E., J . Am. Chem. SOC.,41, 499 (1919). (18) Harkins, W. D., and Cheng, Y . C., Ibid., 43, 35 (1921). (19) Harkins, W. D., and Humphrey, E. C., Ibid., 38, 228 (1916). ENGI. CHEM.,42,1174 (20) Hayworth, C. B., and Treybal, R. E., IND. (1950). (21) Hinze, J. O., Appl. Sci. Research, A-I, 263, 273 (1949). (22) Holroyd, H. B., J. Franklin Inst., 215, 93 (1933). (23) Hughes, R. R., and Gilliland, E. R., Chem. Eng. Progr., 48, 497 (1952). (24) Hutchinson, E., J. Colloid Sci., 3, 219, 235 (1948). (25) International Critical Tables, IV, 435-7; ,McGraw-HilI, New York, 1930. (26) Johnson, H. F., Jr., and Bliss, H., Trans. Am. Inst. Chem. Engrs., 42, 331 (1946). (27) Krevelen, D. W. van, and Hoftijzer, P. J., Cliem. Eng. Progr., 46, 29 (1950). (28) Kronig, R., and Brink, J. C., A p p l . Sci. Research, A2, 142 (1950). (29) Laddha, G. S., and Smith, J. XI., Chem. Eng. Progr., 46, 195 (1950). (30) Licht, W., Jr., and Conway, J. B., IND. ENG.CHEM.,42, 1151 (1950). (31) Maier, C. G., and Ralston, 0. C., U. S. Bur. Mines, Bull. 260, 1927. (32) Merrington, A. C., and Richardson, E. G., Proc. Phys. SOC. (London), 59, 1 (1947). (33) Neumann, H., and Seeliger, R., 2. Physik, 114, 571 (1939). (34) Ohnesorge, Q., 2. angew. math. Mech., 16, 355 (1936). (35) Pound, J. R., J . Phys. Chem., 30, 791 (1926). (36) Powney, J., and Addison, C. C., Trans. Faraday SOC.,33, 1243 (1937). (37) Prausnitz, P. H., Kolloid-Z., 76, 227 (1936). (38) Rayleigh, Proc. Roy. SOC.(London), 29, 71 (1879); 34, 130 (1882). (39) Satterly, J., and Collingswood, L. H., Trans. Roy. SOC.Can., 111,25, 205 (1931). (40) Sherwood, T. K., Evans, J. E., and Longcor, J. V., IND.ENQ. CHEM.,31, 1144 (1939). (41) Silbereisen, X., 2. physik. Chem., 143A, 157 (1929). (42) Smith, S. W. J., and Moss, H., Proc. Roy. Soc. (London), A93, 373 (1917). (43) Tyler, E., and Watkin, F., Phil. Mag., 14, 849 (1932). (44) West, F. B., Robinson, A. P., Morgenthaler, A. C., Jr., Beck, T. R., and McGregor, D. K., IND. ENG.CHEM.,43,234 (1951). R ~ C E I V Efor D review April 2, 1952.


ACCEPTED September 9, 1954.

267

Liquid-Liquid Extraction Spray Columns

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